Use of Degraded Water Sources as Cooling Water in Power Plants, Notas de estudo de Engenharia de Produção

Baixe Use of Degraded Water Sources as Cooling Water in Power Plants e outras Notas de estudo em PDF para Engenharia de Produção, somente na Docsity! California Energy Commission October 2003 P500-03-110 C o n su lt an t R ep o rt Use of Degraded Water Sources as Cooling Water in Power Plants Gray Davis, Governor CALIFORNIA ENERGY COMMISSION Prepared By: Electric Power Research Institute Prepared For: California Energy Commission Public Interest Energy Research Program Marwan Masri Deputy Director Technology Systems Division Robert Therkelsen Executive Director iii CITATIONS This report was prepared by MND Consulting 2803 Woolsey Street Berkeley, CA 94705 Principal Investigator M. DiFilippo Maulbetsch Consulting 90 Lloyden Drive Atherton, CA 94027 Principal Investigator J. Maulbetsch This report was prepared for EPRI 3412 Hillview Avenue Palo Alto, California 94304 and Public Interest Energy Research Program (PIER) California Energy Commission 1516 Ninth Street Sacramento, CA 95814 This report describes research jointly sponsored by EPRI and the California Energy Commission. The report is a corporate document that should be cited in the literature in the following manner: Use of Degraded Water Sources as Cooling Water in Power Plants, EPRI, Palo Alto, CA, and California Energy Commission, Sacramento, CA: 2003. 1005359. v PRODUCT DESCRIPTION In electricity production, nearly all thermal power plants reject heat either to a large body of water (once-through cooling) or to the atmosphere via wet cooling towers—the predominant form of cooling in California. These towers, however, use considerable quantities of water. Competing state demands for freshwater have forced California thermal power plants to consider alternative cooling water supplies, though the availability of such supplies and data on their use and impact is limited. In fact, other than treated municipal effluent, few (if any) alternative sources of degraded water have been developed for cooling needs. EPRI and the California Energy Commission (CEC) cosponsored this project to provide basic tools and guidelines to public and private parties involved in source water evaluations for California power projects. Results & Findings Alternative water supplies—involving use of degraded or nonpotable water—offer significant opportunities for power plants to limit their use of freshwater. Potential sources of degraded water include contaminated groundwater, treated municipal effluent, industrial process water or wastewater, irrigation return water, brackish water, and other types of water impacted by humans or naturally-occurring minerals. This report investigates technological and environmental issues associated with the use of degraded water for cooling, by focusing on the following key areas: Water quality requirements—This discussion of water quality criteria includes a six-step framework for evaluating source water chemistry, chemical criteria for cooling towers, cooling system design and operating impacts, source water screening, treatment requirements, and disposal issues. It focuses on necessary water criteria to minimize operating problems with cooling tower systems such as loss of heat transfer, fouling, and corrosion. Technical feasibility—This section evaluates the technical feasibility and economics of using degraded water for cooling towers, with emphasis on three hypothetical case studies involving process wastewater, agricultural return water, and reclaimed municipal effluent. Environmental Impacts—This evaluation of environmental impacts associated with degraded water in wet cooling towers focuses on all streams leaving the cooling system, including cooling tower blowdown, drift, water loss to evaporation (as well as chemical constituents), and sludge generated from cooling tower treatment and/or maintenance. Commercially Available Treatment—This description of treatment technologies required in order to use degraded water for power plant cooling focuses on three areas of treatment: pretreatment (cooling tower makeup), sidestream (treating a portion of the recirculating water), and post-treatment (blowdown). ix ACKNOWLEDGMENTS The performance of this study was greatly aided by the contributions of many people. John Maulbetsch prepared Section 2.4, Rules and Regulations. Review comments provided by Kent Zammit and Kevin Shields of EPRI, Joe O’Hagan of the California Energy Commission and John Veil of Argonne National Laboratory. These acknowledgments should not be interpreted as meaning that all of the participants are in accordance with or endorse the conclusions of this study. The final report reflects the opinions and points of view of the author. xiii 6. Evaluate disposal issues. The methodology is utilized throughout the report in various formats to assess water sources, assess case studies and identify and discuss appropriate treatment options. Four actual sources of degraded water and freshwater are screened and compared. The produced water, agricultural return water and freshwater sources are located in the Central Valley of California and the reclaimed water source in the Bay Area. Each source was evaluated based on the chemical criteria found outlined in the report. The screening analysis shows that cycles of concentration may be significantly limited by one or more constituents for each degraded water source. For source waters that are impacted by scale, corrosion or environmental factors, there are commercially available treatment technologies that can be employed. Treatment generally falls into three categories, and depending on site-specific requirements, one, two or all three of the categories could be employed for a degraded water source. Each category is discussed generally in this section, and in greater detail, later in the report. Pre-treatment can be utilized to remove contaminants, adjust pH, soften (remove calcium and magnesium), reduce silica or reduce TSS. Side-stream can be used to soften, reduce silica or reduce TSS. Lastly, Post treatment is utilized to reduce blowdown volume (e.g. zero discharge) or meet discharge requirements. Lastly, the regulatory framework and specific rules, which apply to steam-electric power plant cooling in California, are also reviewed in this section. The discussion is confined to wet evaporative cooling with particular emphasis on those elements which would be most affected by the use of degraded water for cooling tower make-up. Environmental issues related to new power projects are numerous and complex. The information is presented in a generalized manner and is intended to identify issues of concern rather than specific regulatory requirements. Technical Feasibility Technical feasibility and economics of using degraded water for cooling towers is evaluated in this section. Three hypothetical case studies of power plants using degraded water for cooling are discussed and evaluated in detail. The case studies include process wastewater, agricultural return water and reclaimed municipal effluent. Water consumption, water treatment equipment, chemicals requirements, cooling tower blowdown, solid-waste generation, operating costs and order-of-magnitude capital costs are identified for each case study. All case studies are evaluated against freshwater for comparative purposes and to benchmark the cost analysis. The degraded water scenarios that are evaluated in the report are admittedly “difficult” from a freshwater treatment perspective, but as illustrated by the case studies, they are usable with appropriate treatment. Three degraded water case studies are evaluated in this section of the report: • Produced water - saline process wastewater generated by oil production xiv • Agricultural return water - saline water generated by flood irrigation • Reclaimed water - treated municipal effluent generated in urban areas Operating data, treatment equipment requirements, chemical and power consumption, sludge production, dedicated labor and operating and capital costs developed for all the scenarios are summarized in detail. The rationale for waste treatment selection is discussed in the applicable sections of this report. The daily operating cost which includes consumables, labor and amortization is also determined. The summary shows that water costs associated with degraded water are at least 1.5 to 2.5 times the costs associated with fresh water at inland plants and 1.1 to 1.2 times that of fresh water at coastal plants (based on assumed water chemistries, Table 3-1, and the evaluation basis, Table 3-2). These ranges could be broader/narrower depending on the quality of the water source. Generally speaking, the greater the TDS, hardness and silica of the degraded source water, the greater the ratio. Environmental Impacts Environmental impacts can originate from a variety of cooling tower streams and activities associated with the cooling circuit: • Evaporation • Drift • Blowdown • Waste streams from treatment processes associated with the cooling circuit • Sludge generated from cooling system maintenance All of these streams have the potential of transporting chemical constituents of concern and producing environmental impacts. When degraded water is employed for make-up, cooling tower evaporation can contain gaseous contaminants in addition to water vapor, e.g. trace levels of volatile organic compounds. Depending on the source water, constituents of concern, such as trace levels of heavy metals and organic compounds, could also be found in the circulating cooling water. Since drift and blowdown are component streams of circulating water, they contain all of its chemical constituents. Biological pathogens such as Legionella pneumophilia, which can thrive in cooling water systems and are transported via drift, pose a potential human health concern. Treatment processes, such as side-stream filtration and softening, evaporators and crystalizers, generate liquid, sludge and solid waste streams which are comprised of circulating water and its constituents - chemical compounds, particulate matter, biological material and treatment chemical byproducts. Lastly, sludge from cooling tower maintenance contains inorganic, organic and biological sediments generated by day-to-day operation. This section of the report discusses potential environmental impacts related to airborne and waterborne contaminants, water quality issues related to the disposal of blowdown and treatment process wastes, and safety as it relates to working in and around cooling towers. xv Legionella pneumophilia, which is the bacterium responsible for the well-documented outbreak of “Legionnaires’ Disease” in 1976, is discussed in some detail. Legionella can originate from a number of industrial and commercial sources including cooling towers and evaporative condensers. In the case of cooling towers, the pathway is drift - fine droplets or mist in the aerosol-size range carrying viable Legionella bacteria. OSHA estimates over 25,000 cases of the illness occur every year in the United States. More than 4,000 deaths are believed to occur, but only a fraction are reported. About 1,400 cases of Legionellosis are reported to the Center for Disease Control (CDC) annually and about 500 are confirmed. Legionella is transmitted by breathing aerosol-sized droplets of water that contain the bacteria. It is estimated that Legionelosis is fatal to 10 to 20 percent of those who contract it and much higher for at-risk individuals. Drift droplets from cooling towers containing Legionella bacteria must survive ambient conditions and not evaporate to be a threat to human health. Ambient air conditions that include low relative humidity will likely evaporate aerosol-sized drift droplets shortly after they exit the cooling tower. Larger drops exposed to air with low relative humidity could evaporate and shrink sufficiently to enter the alveoli. Conversely, under high-humidity conditions, drift aerosols could be carried for some distance, thus posing a potential health risk in urban areas or commercial/industrial parks. Drift poses more of a threat to individuals who work in the immediate vicinity of a cooling tower. Hyperlink addresses to the full texts of Legionella guidelines and position papers prepared by the Cooling Technology Institute (CTI) and American Society of Heating, Refrigerating and Air- Conditioning Engineers (ASHRAE) are found in Appendix A. Worker safety issues, which are also touched upon, can arise when working in and around cooling towers and related treatment equipment such as make-up and side-stream process treatment. Worker safety issues include (but are not limited to): • Legionellosis • Exposure to untreated degraded water containing volatile compounds, pesticides, heavy metals, hydrogen sulfide, etc. • Biological control chemicals such as chlorine and bromine compounds • Specialty chemicals used for scale and corrosion control • Chemicals (as well as waste streams) generated by water treatment equipment such as sulfuric acid, sodium hydroxide, hydrated lime, etc. • Maintenance wastes such as biological sediments Tools are available to assess Legionellosis and workplace hazards. In addition to the CTI guidelines and ASHRAE position paper, OSHA has an entire section of its technical manual dedicated to Legionnaire’s Disease, Section III, Chapter 7. There is also a section on assessing and documenting Legionellosis cases, OSHA Appendix III:7-5, Water Treatment Protocols for Facilities That Have Experienced a Legionnaires’ Outbreak. xix CONTENTS 1 INTRODUCTION....................................................................................................... 1-1 1.1 Objective of the Report ..................................................................................... 1-1 1.2 Report Scope of Work....................................................................................... 1-2 1.2.1 Water Quality Requirements for Cooling Systems..................................... 1-2 1.2.2 Technical Feasibility .................................................................................. 1-3 1.2.3 Environmental Impacts .............................................................................. 1-3 1.2.4 Commercially Available Treatment ............................................................ 1-3 1.2.5 Emerging Technologies ............................................................................. 1-4 2 WATER QUALITY REQUIREMENTS FOR COOLING SYSTEMS .......................... 2-1 2.1 Introduction ....................................................................................................... 2-1 2.1.1 Source Water Evaluation Methodology...................................................... 2-1 2.1.2 Cooling Tower Chemistry Criteria .............................................................. 2-3 2.1.3 Environmental Constituents of Concern .................................................... 2-5 2.2 Cooling Tower Operating Issues and Concerns................................................ 2-8 2.2.1 Cooling Tower Function and Operation ..................................................... 2-8 2.2.2 Operating Issues........................................................................................ 2-9 2.2.3 Cooling Tower Emissions ........................................................................ 2-10 2.3 Chemical Constituents of Concern in Cooling Water ...................................... 2-11 2.3.1 Types of Degraded Water........................................................................ 2-11 2.3.2 Chemical Species Typically Found in Degraded Water ........................... 2-12 2.3.3 Impacts of Chemical Constituents on Water Consumption, Source Selection and Waste Generation ....................................................................... 2-13 2.3.3.a Cycles of Concentration ................................................................... 2-13 2.3.3.b Water Quality Criteria Prediction Software ....................................... 2-16 2.3.3.c Water Supply Screening ................................................................... 2-17 xx 2.3.3.d Treatment Requirements for Degraded Water ................................. 2-21 2.3.3.e Post-Treatment Requirements for Degraded Water ......................... 2-24 2.4 Rules and Regulations.................................................................................... 2-25 2.4.1 Regulatory Background and Approach .................................................... 2-25 2.4.2 Statutory Basis for Regulations................................................................ 2-26 2.4.3 Regulated Discharges and Impacts ......................................................... 2-26 2.4.3.1 Water Consumption.......................................................................... 2-27 2.4.3.2 Wastewater Discharges.................................................................... 2-29 2.4.3.2.a Federal Regulations .................................................................. 2-29 2.4.3.2.b California Regulations ................................................................ 2-30 2.4.3.3 Air Quality Regulations ..................................................................... 2-32 2.4.3.3.a Federal Regulations .................................................................. 2-33 2.4.3.3.b California Regulations ............................................................... 2-33 3 TECHNICAL FEASIBILITY....................................................................................... 3-1 3.1 Introduction ....................................................................................................... 3-1 3.2 Case Studies..................................................................................................... 3-2 3.3 Evaluation Basis ............................................................................................... 3-4 3.4 Case Study 1 - the Central Valley - Produced Water ........................................ 3-4 3.5 Case Study 2 - the Desert - Agricultural Return Water.................................... 3-12 3.6 Case Study 3 - a Coastal Plant - Reclaimed Water ........................................ 3-18 3.7 Base Case - Fresh Water................................................................................ 3-22 3.7.1 Base Case - Fresh Water - Inland Plant .................................................. 3-23 3.7.1.a Central Valley Plant - Disposal Costs ............................................... 3-26 3.7.1.b Desert Plant - Disposal Costs........................................................... 3-27 3.7.2 Base Case - Fresh Water - Coastal Plant ................................................ 3-28 3.8 Degraded and Fresh Water Comparisons....................................................... 3-30 4 ENVIRONMENTAL IMPACTS.................................................................................. 4-1 4.1 Introduction ....................................................................................................... 4-1 4.2 Airborne and Waterborne Contaminants........................................................... 4-2 4.2.1 Airborne ..................................................................................................... 4-2 4.2.2 Cooling Tower Drift .................................................................................... 4-3 xxiii LIST OF FIGURES Figure 2-1 Source Water Evaluation Methodology .................................................................. 2-1 Figure 2-2 Cooling Tower Mass Balance................................................................................. 2-9 Figure 2-3 Cooling Tower Issues of Concern .........................................................................2-10 Figure 2-4 Make-up and Blowdown vs Cycles of Consentration.............................................2-15 Figure 2-5 Cooling Water Treatment ......................................................................................2-22 Figure 3-1 Make-Up Softening, SIde-Stream Softening, Make-Up and Side-Stream Softening......................................................................................................................... 3-8 Figure 3-2 SS Softener Capacity vs Precip’d Mg..................................................................... 3-9 Figure 5-1 Air Stripper............................................................................................................. 5-3 Figure 5-2 GAC Vapor-Phase Adsorber.................................................................................. 5-4 Figure 5-3 Catalytic Thermal Oxidizer ..................................................................................... 5-5 Figure 5-4 Vertical Pressure GAC, Media Filter....................................................................... 5-6 Figure 5-5 BIOFOR Aerobic Biological Filter ........................................................................... 5-8 Figure 5-6 Ion Exchange........................................................................................................5-10 Figure 5-7 Precipitation, Co-Precipitation...............................................................................5-13 Figure 5-8 Reactor Clarifier ....................................................................................................5-15 Figure 5-9 Evaporator ............................................................................................................5-21 Figure 5-10 Crystallizer ..........................................................................................................5-22 Figure 5-11 Final Silica vs Mg Precipitation (Temp 60-80°F, pH = 10.4) ................................5-24 Figure 5-12 Final Silica vs Mg Precipitation(Temp 104°F, pH = 10.4) ....................................5-24 Figure 5-13 Installed Cost vs Capacity...................................................................................5-25 Figure 5-14 Operating Cost vs Total Hardness ......................................................................5-25 Figure 5-15 Sludge Generation vs Total Hardness.................................................................5-26 xxv LIST OF TABLES Table 2-1 Cooling Tower - Water Quality Parameters ............................................................. 2-4 Table 2-2 Degraded Water Categories.................................................................................... 2-6 Table 2-3 Cooling Tower - Basic Water Quality Parameters...................................................2-18 Table 2-4 Maximum Cooling Tower Calcium with PO4 Present ..............................................2-19 Table 2-5 Source Water Screening ........................................................................................2-20 Table 2-6 Pre-, Side-Stream Treatment for Cooling Towers...................................................2-23 Table 2-7 Pre-Treatment of Contaminated Water for Cooling Tower Make-Up.......................2-24 Table 2-8 Power Plant Cooling Systems - Requirements for Approval ...................................2-28 Table 2-9 Steam Electric Power Generating Point Source Category, CFR Title 40, Chapter 1, part 423, BAT, NSPS, PSNS and PSES .......................................................2-30 Table 3-1 Source Water and Limiting Water Quality Criteria ................................................... 3-3 Table 3-2 Evaluation Basis...................................................................................................... 3-5 Table 3-3 Cooling Water Chemistry - Case Study 1 ................................................................ 3-7 Table 3-4 Case Study 1 - Produced Water - Treatment Cost Summary .................................3-11 Table 3-5 Case Study 1 - Produced Water - Disposal Cost Summary....................................3-13 Table 3-6 Cooling Water Chemistry - Case Study 2 ...............................................................3-15 Table 3-7 Case Study 2 - Agriculture Return Water - Treatment Cost Summary....................3-17 Table 3-8 Case Study 2 - Agricultural Return Water - Disposal Cost Summary......................3-18 Table 3-9 Cooling Water Chemistry - Case Study 3 ...............................................................3-20 Table 3-10 Case Study 3 - Reclaimed Water - Treatment Cost Summary..............................3-22 Table 3-11 Cooling Water Chemistry - Fresh Water Case......................................................3-24 Table 3-12 Base Case - Fresh Water - Inland Plant - Treatment Cost Summary....................3-25 Table 3-13 Base Case - Fresh Water - Central Valley Inland Plant - Disposal Cost Summary........................................................................................................................3-27 Table 3-14 Base Case - Fresh Water - Desert Inland Plant - Disposal Cost Summary...........3-28 Table 3-15 Cooling Water Chemistry - Fresh Water Case......................................................3-29 Table 3-16 Base Case - Fresh Water - Coastal Plant - Treatment Cost Summary .................3-30 Table 3-17 Comparison Summary - Degraded Water and Frrsh Water (1).............................3-31 Table B-1 Langelier, Ryznar and Puckorious Indices - Simplified Calculation ........................ B-2 Table B-2 Formulas - Maximum Allowable Cycles of Consentration....................................... B-3 Table B-3 Concentration Conversion Factors......................................................................... B-4 Introduction 1-2 • Identify potential types of degraded water, the pollutants specific to these types of water and the water quality requirements necessary for cooling water • Investigate the technical feasibility and environmental impacts of using degraded water for power plant cooling • Identify commercial and emerging treatment technologies to treat degraded or reclaimed water 1.2 Report Scope of Work In the production of electricity, almost all thermal power plants reject heat either to a large body of water (e.g. once-through cooling) or the atmosphere via wet cooling towers. Evaporative or wet cooling towers, which are the predominant form of cooling in California, use considerable quantities of water. For example, a 500 MW combined cycle plant (with approximately 33 percent of its power originating from steam generation) evaporates 2,500,000 gallons of water to the atmosphere per day. The competitive pressures associated with using freshwater for power generation are growing and many projects, which are now in the planning stages, are seriously considering dry cooling. Currently, there are three operating dry cooling systems in California (a total of approximately 800 MW of power), one project planning to use dry cooling is on hold, and a number of new projects are reviewing this alternative. In addition to dry cooling, one project is planning to install a wet/dry hybrid cooling tower. Alternative water supplies offer significant opportunities for power plants to limit their use of freshwater. However, there are uncertainties within the power community regarding the costs and environmental impacts of using degraded water for cooling. Note that degraded water is defined in this document as surface water, groundwater, treated municipal effluent or industrial process water/wastewater which is not suitable for potable use because of natural or manmade contamination. Additionally, the availability and quality of degraded water supplies have not been assessed or characterized in California. Potential sources of degraded water include: contaminated groundwater, treated municipal effluent, industrial process water or wastewater, irrigation return water, brackish water, etc. The report is organized into the following sections. 1.2.1 Water Quality Requirements for Cooling Systems Water quality criteria, which have evolved over the past 40 to 50 years, are utilized by the power industry and others to minimize operating problems with cooling tower systems such as loss of heat transfer, fouling and corrosion. Prior to discussing water quality requirements for cooling systems, this section of the report introduces a Source Water Evaluation Methodology to assess degraded and freshwater sources water for cooling tower make-up. The methodology is a six-step evaluation of source water chemistry, chemical criteria for cooling towers, cooling system design and operating impacts, source water screening, treatment requirements and disposal issues. The methodology provides a stepwise framework for the systematic evaluation of degraded water for cooling tower make-up. Elements of the methodology are utilized throughout the report. Introduction 1-3 Water quality criteria for cooling towers are presented. The cooling system is defined and associated operating issues and concerns are discussed, e.g. scaling, corrosion and biological fouling. To evaluate degraded water for cooling, it is first categorized into types, e.g. contaminated groundwater, reclaimed water, agricultural return water, etc. Pollutant types commonly found in degraded water are identified by category, e.g. volatile organic compounds, heavy metals, high levels of background salt, etc. The concept of cooling water cycles of concentration is introduced - this parameter is central to all source water evaluations. The determination of cycles of concentration is presented and its impact on water consumption and wastewater generation is discussed. Water quality criteria are then utilized to screen and evaluate several degraded water sources. Water quality requirements are also applied to freshwater to enable freshwater versus degraded water comparative analysis. Cooling water treatment requirements and waste disposal issues are briefly discussed in this section. Environmental rules and regulations are identified for each applicable cooling tower stream (e.g. blowdown, evaporation, etc.) and generally discussed. 1.2.2 Technical Feasibility The technical feasibility and economics of using degraded water for cooling towers is evaluated in this section. Three hypothetical case studies of power plants using degraded water for cooling are discussed and evaluated in detail. The case studies include process wastewater, agricultural return water and reclaimed municipal effluent. Water consumption, water treatment requirements, cooling tower blowdown, disposal requirements, operating cost and order-of- magnitude capital cost. All case studies are then evaluated against freshwater for comparative purposes and to benchmark the cost analysis. 1.2.3 Environmental Impacts Environmental impacts associated with degraded water in wet cooling towers are identified. These include an evaluation of all streams leaving the cooling system, i.e. cooling tower blowdown, drift, water loss to evaporation (as well as chemical constituents) and sludge generated from cooling tower treatment and/or maintenance. The rules and regulations discussed in Section 2, Water Quality Requirements for Cooling Systems, frame each area of environmental impact. Impacts such as surface and groundwater contamination, salt deposition from drift, Legionnaires Disease, vapor emissions from volatile organic chemicals, trihalomethane (THM), etc. are discussed. Occupational safety is discussed as it relates to the daily exposure of working in and around cooling towers. 1.2.4 Commercially Available Treatment Treatment technologies that are required in order to utilize degraded water for power plant cooling are identified in this section. Three areas of treatment are investigated: pre-treatment (cooling tower make-up), side-stream (treating a portion of the recirculating water) and post- treatment (blowdown). The technologies comply with the following criteria: generate minimal Introduction 1-4 environmental impact (hazardous process chemicals, waste, noise, etc.) and are commercially- available off-the-shelf technology. Technologies are also sorted into two areas: those required to remediate specific environmental problems and those required to maintain plant performance. 1.2.5 Emerging Technologies Emerging treatment technologies and processes that may make it possible to use degraded and reclaimed water are identified. The technologies in this section primarily focus on environmental issues - metals removal, pesticide removal and organic compound removal. One technology covers de-ionization (salinity reduction). Most of the technologies are in initial phases of research and development but show promise. Water Quality Requirements for Cooling Systems 2-3 2.1.2 Cooling Tower Chemistry Criteria Each chemical constituent (in some cases, constituent pair) that can effect cooling system performance must be evaluated separately to determine its maximum allowable concentration in the cooling system. Table 2-1 shows an evolution of published cooling water criteria over the past 23 years (Kunz, 1977, EPRI, 1982, EPRI, 1998, Eble, 1993). The criteria in the first three columns are applicable to power plants and the last column for oil refineries. These criteria are shown because they differ significantly from most power plant cooling parameters. Cooling systems in refineries are typically smaller and are usually not tied to overall plant efficiency. Therefore, they have higher limits and “push“ their cooling systems harder. Cooling systems at power plants can significantly effect steam cycle performance so operating criteria are more conservative. Also, the criteria for refineries include constituents not typically found in traditional cooling tower criteria for power plants, but are found in degraded water, e.g. BOD and COD (the cited reference includes numerous other criteria). The criteria found in column three of Table 2-1, which were developed by EPRI in 1998, are the most recent and should be used in cooling tower evaluations. Table 2-1 is also discussed in 2.3.3 Impacts of Chemical Constituents on Water Consumption, Source Selection and Waste Generation. One or more constituents will usually define the concentration limit for the cooling system. The limit pertains to solubility, e.g. a calcium limit can refer to the calcium sulfate solubility threshold. If the limit is exceeded, calcium sulfate will likely precipitate. Understanding the variability of water source(s) chemistry, as discussed in Step 1 above, is crucial in identifying all the possible solubility limitations. Water Quality Requirements for Cooling Systems 2-4 Table 2-1 Cooling Tower - Water Quality Parameters RefineryCurrentDegraded Water TC CoolingEPRI (13) System (13)StandardsEPRI (13)Kunz (13) 1993 (9)199819821977UnitsParameter 1,500 (max)(Note 6)900 (max)300mg/lCaCO3Ca (Note 10)500,000 (5)-----500,000(mg/l)2Ca x SO4 -----35,000 (5)75,000 (3)35,000 (2)-----mg/lCaCO3 x mg/l SiO2Mg x SiO 2 -----(Note 6)200-250 (3)30-50 (2)-----mg/lCaCO3M Alkalinity 5,000 (max)(Note 6)----------mg/lSO4 300 (max)150 (5)150150mg/lSiO2 50 (max)(Note 6)(Note 4)<5-----mg/lPO4 10 (max)<0.5 (5)-----0.5mg/lFe (Total) 1<0.5-----0.5mg/lMn 0.5<0.1-----0.08mg/lCu 1<1-----1mg/lAl 105-----5mg/lS 40 (max)<2 (12)----------mg/lNH3 7-9(Note 6)7.8-8.4 (3)6.8-7.2 (2)8.0 (max)pH ----------70,0002,500mg/lTDS 200<100 (7) - <300 (8)-----100-150mg/lTSS 200 (max)---------------mg/lBOD 200 (max)---------------mg/lCOD -----<0-----+1.5 (max)Langelier SI (11) ----->6-----+7.5 (max)Rysnar SI (11) ----->6----------Puckorius SI (11) Notes..... M Alkalinity = HCO 3 + CO3, expressed as mg/l CaCO3.1. Without scale inhibitor.2. With scale inhibitor.3. No recommendation given because of insufficient data.4. Conservative value - reference is made to EPRI's SEQUIL RS for predicting case-specific limits.5. SEQUIL RS takes into account parameters such as ionic associations, ionic strength (measure of background salt and ionic charge), pH and temperature to predict the solubility of certain salts. No value given - reference is made to EPRI's SEQUIL RS for predicting case-specific limits.6. <100 mg/l TSS with film fill.7. <300 mg/l TSS with open fill.8. Water quality parameters were prepared by Betz for refinery cooling towers accepting in-plant 9. wastewater as a means of conserving water. Refineries typically experience more severe operating conditions than power plants, e.g. higher temperatures, organic contamination, heavy metals, etc. No inference was made by the authors to the product of the Ca and SO 4 maximum operating values10. to be used to set a Ca x SO 4 limit (reference Kunz and EPRI values). Refer to Appendix B for a discussion of the Langelier, Ryznar and Puckorius calcium carbonate11. stauration indices. <2 mg/l NH3 applies when copper bearing alloys are present in the cooling system. This does not12. apply to 70-30 or 90-10 copper nickel. Refer to citations 4, 5, 6 and 7 found in Appendix A.13. For each constituent of concern found in Table 2-1, calculate the maximum cycles of concentration (N). N is a universal measure that not only defines the maximum concentration for a limiting chemical constituent but is also used to determine critical cooling tower operating conditions - make-up and blowdown rates. Water Quality Requirements for Cooling Systems 2-5 N C C Limit MU i = , (1) Where: N Cycles of concentration CLimit,i Water quality limit for constituent i CMU,i Concentration of constituent i in the make-up water For ion pair limits such as magnesium and silica, calculate the maximum cycles of concentration as follows: N C C C Limit ij MU i MU j = , , , (2) Where: CLimit,ij Water quality limit for constituents i and j CMU,i Concentration of constituent i in source water CMU,j Concentration of constituent j in source water After this calculation has been completed for each of the constituents of concern, the constituent or constituent pair with the lowest calculated N value will be the limiting parameter for that source of water or blend of source waters. This value of N will be the maximum cycles of concentration achievable without some form of pretreatment or side-stream treatment or specialty chemical addition (e.g. scale inhibition). 2.1.3 Environmental Constituents of Concern For degraded water, environmental concerns could include volatile organic solvents, pesticides, heavy metals, etc. Refer to Table 2-2. This table categorizes types of degraded water and the chemical constituents likely found in those waters. As stated previously, the availability and quality of degraded water supplies have not been assessed or characterized in California. This table is also discussed in more detail in 2.3.3. Many of the compounds found in degraded water (e.g. volatile organic compounds) have no measurable effect on cooling tower performance, but they are strictly regulated for environmental reasons. Therefore, it is likely that many of these regulated compounds will have to be removed from the feedwater prior to use in the cooling tower. Lastly, the cycles-of-concentration calculation outlined above should be applied to all degraded water constituents. Water Quality Requirements for Cooling Systems 2-8 characteristics define the extent of the disposal issue. All of the evaluations prior to this step impact disposal issues. The lower the cycles of concentration, the greater the volume of waste. As stated previously, large waste volumes pose significant problems for plants with no convenient or environmentally-acceptable means of liquid disposal. Also, Water Quality Objectives set forth by the local RWQCB may preclude any type of disposal (discussed later in this section). Conversely, a high cycles of concentration waste stream with elevated concentrations of source-water constituents may also pose disposal problems. For example, many municipal wastewater plants will not accept high-TDS wastewater, because it impacts their allowable discharge limit of dissolved salts and possibly their water recycling programs. 2.2 Cooling Tower Operating Issues and Concerns Interestingly, cooling tower water quality requirements have not changed much during the past fifteen years. In the mid-1980's the Electric Power Research Institute (EPRI) evaluated water quality requirements for cooling systems among other related topics. During that time, a shift in the manner of treating cooling towers was occurring. There was significant pressure from regulators to eliminate chromate (Cr+6) from industrial cooling towers (refer to Section 2.4.3.3.a, Federal Regulations) because of its carcinogenicity. Substitute metal-based corrosion inhibitors were being evaluated as well as non-metal inhibitors. Scale from mineral precipitation was typically not a problem since most cooling towers were operated at relatively low pH (6.5 to 7.5). With the move towards non-chromate treatment, pH control levels shifted upward (7.5 to 8.5) and new treatment approaches were being developed, e.g. molybdate and organic corrosion inhibitors and organic scale inhibitors. The shift from chromate control was driving specialty chemical providers to meet the changing demands for scale, corrosion and biological control. 2.2.1 Cooling Tower Function and Operation Make-up water is fed to the cooling tower to compensate for losses from evaporation, drift (sometimes known as windage) and blowdown. See Figure 2-2. Open recirculating cooling towers reject heat mostly from the evaporation of circulating water (approximately 1,000 BTUs of heat are released per pound of water evaporated). As air is forced through the body of the tower, it passes through a shower of droplets and across films of circulating water. As the relatively dry air contacts the water, it is humidified by accepting a small amount of water. The humidified air comprises cooling tower evaporation. As circulating water is evaporated, the mineral content remains (this also applies to TSS, non-volatile organic compounds, etc.) and the concentration of salts in the circulating water increases. Blowdown is used to bleed salt from the cooling tower to prevent excess mineral accumulation and deposition. If the concentration of certain salts exceeds solubility, precipitation will occur. The blowdown rate of the cooling tower is regulated to release an equivalent amount of salt that is added via make-up water (at a much lower concentration). Drift consists of droplets of circulating water that are entrained in the cooling air. Water Quality Requirements for Cooling Systems 2-9 Cooling Tower Evaporation Make-up Drift Blowdown Figure 2-2 Cooling Tower Mass Balance A simplified mass balance follows: Salts added by make-up = Salts lost to blowdown + Salts lost to drift The amount of water lost to drift is controlled via drift eliminators. Cooling tower manufacturers claim to achieve a drift rate of 0.002 to 0.004 percent of circulating rate. Actual drift rate may be higher in older or poorly maintained cooling towers. For a 500 MW combined cycle plant with a circulating rate of 240,000 gpm, the drift rate would be 5 to 10 gpm. The make-up rate is set to compensate for the water losses from the cooling tower. A simplified water balance follows: Make-up = Evaporation + Blowdown + Drift The cooling system is defined as the cooling tower, circulating water piping, main condenser(s), circulating water pumps and the cooling tower basin. In other words, all the components of cooling loop are included in the definition of cooling system. Circulating water may also serve auxiliary heat exchangers for lube oil cooling, bearing cooling water, etc. 2.2.2 Operating Issues The objectives of water quality criteria for cooling towers are based on practical considerations: • Minimize mineral scaling and biological fouling of heat transfer surfaces • Minimize corrosion of heat transfer and structural metal • Minimize fouling loads on cooling tower fill Water Quality Requirements for Cooling Systems 2-10 The term “minimize” is purposefully used because none of these phenomena can be completely prevented. Four areas of water quality concern are identified in Figure 2-3: scale, suspended solids, biological fouling and corrosion. Each area generates operating problems (alone and in combination) in cooling systems, such as loss of heat transfer, fouled cooling tower fill, structural failures and tube leaks. (Lisin, 1994) For example, certain mineral scales can form on the main condenser tubes in the presence of microbiological activity resulting in a loss of heat transfer and under-deposit corrosion. Microbiologically induced corrosion (MIC) occurs at the interface of a biological film and the metal surface. (EPRI, 1987) Generally, metabolic byproducts of biological activity react with the metal surface and can initiate a number of corrosion mechanisms. Biological Fouling Fouled Film Fill Loss of Heat Transfer Structural Failure Corrosion Structural Failure Tube Leaks Scale Loss of Heat Transfer Settleable Solids Fouled Film Fill Loss of Heat Transfer Figure 2-3 Cooling Tower Issues of Concern 2.2.3 Cooling Tower Emissions Cooling towers emissions leave the tower in four streams: evaporation, drift, blowdown and solid waste. Evaporation is the vapor stream from the cooling tower and it predominantly contains air and water. If volatile compounds (from degraded water) are present in the make-up water, they will also be found in the cooling tower evaporation stream. Under certain conditions, fogging can occur on cold days with partial condensation of the water-vapor stream occurring just above the cooling tower. Evaporation also contains trace levels of the chemical constituents found in circulating water from evaporated drift. Depending on ambient conditions, drift should completely evaporate shortly after it exits the cooling tower. Drift is considered as contributory to PM10 (mean droplet diameter of 10 microns or less) by many air quality districts. After the Water Quality Requirements for Cooling Systems 2-13 • Cooling tower packing/film, heat-exchanger surfaces and silt/debris provide surfaces to establish colonies • Airborne and waterborne nutrients • Degraded water constituents such as BOD, ammonia and organic compounds • Wet/dry interface in film fill 2.3.3 Impacts of Chemical Constituents on Water Consumption, Source Selection and Waste Generation Refer again to Figure 2-1, Source Water Evaluation methodology. In assessing proposed water sources, constituents of concern must be evaluated. Any one constituent could eliminate a possible source or require the imposition of significant treatment. Cooling tower chemistry criteria are used to evaluate constituents of concern. Refer to Table 2-1 for a list of constituents of concern. Note, that some of the criteria in Table 2-1 can be considered key parameters for degraded water, i.e. PO4 (total phosphate) , Cu (copper), Al (aluminum), S (sulfide), NH3 (ammonia), BOD (biological oxygen demand) and COD (chemical oxygen demand). There also may be other chemical constituents that are specific to degraded water that have not been identified yet. The last criteria cited in Table 2-1 are the Langelier Saturation (LSI), Ryznar Stability (RSI) and Puckorius Scaling Indices (PSI). The LSI was developed over 60 years ago to predict scaling and corrosion tendencies in water distribution systems. Later these indices were adopted to evaluate cooling water. The LSI evaluates key variables (calcium hardness, alkalinity, temperature and TDS) and determines pHs - the pH of CaCO3 saturation. If the difference between the actual pH of the source water and pHs (pH-pHs) is positive, the water has a scaling tendency, i.e. calcium carbonate is above its saturation level and will likely precipitate. A negative difference predicts no calcium carbonate scaling and the water will likely create a corrosive condition for mild steel pipe (in the absence of saturation, the pipe surface has no protective layer of CaCO3 and is directly exposed to corrosive agents such as oxygen). An ideal range for LSI is 0 to 1. The RSI (a variation on the LSI calculation) was developed to more closely predict calcium carbonate scaling and corrosion. RSI was developed by correlating empirical data based on actual municipal water systems. If RSI is greater than 7, corrosion is likely, and if it less than 6, scaling in likely. An ideal range for RSI is 6 to 7. The PSI modifies the Ryznar Index by calculating the system pH instead of using actual pH. The calculated pH relfects the actual alkalinity of the water and more accurately predicts scaling tendencies, especially in low-alkalinity waters. Note, these indices only predict tendencies of the bulk fluid in a cooling system and should only be limited to this level of analysis. Refer to Table B-1 in Appendix B for LSI, RSI and PSI calculation procedures. 2.3.3.a Cycles of Concentration Cycles of concentration, N, as described earlier, refers to the multiple of the concentration of a chemical constituent as a result of cooling tower evaporation (as water evaporates the salts stay Water Quality Requirements for Cooling Systems 2-14 behind and concentrate). The “cycled” concentration of a given constituent can be calculated by multiplying make-up concentration by N. Cooling tower blowdown, the wastewater stream from the cooling tower, is utilized to control concentration. Blowdown is usually withdrawn from the hot-water return to the cooling tower. However, depending on the particular configuration of the cooling loop, blowdown can be withdrawn from a number of points in the system (hot or cold side). The make-up or feed rate to the cooling tower is adjusted to compensate for losses from evaporation, drift (usually a very small volume of cooling water) and blowdown. N is calculated by the following flow and mass balances: MU = E + BD +D (flow balance) (3) where: MU make-up rate, gpm E Evaporation rate, gpm BD Blowdown rate, gpm D Drift rate, gpm MU x CMU,i = E x CE,i + BD x CBD,i + D x CD,i (mass balance) (4) where: CBD,i Concentration of chemical constituent “i” in the circulating water CE,i = 0 (evaporation only consists of water vapor) (5) CD,i = CBD,i, (drift is comprised of circulating water) (6) Substituting (5) and (6) into (4) yields: MU x CMU,i = CBD,i x (BD + D) (7) N C Ci BD i MU i = , , (8) where: Ni Cycles of concentration of constituent “i” Substituting (8) into (2) and (7) and solving for BD yields: BD E N D= − − 1 (9) For each chemical constituent of concern in a degraded water source, there will be a maximum allowable cycles of concentration. Calculating N is critical, since it not only establishes operating concentrations of key constituents, it also establishes flow conditions for the cooling system. Staying below that value will minimize scale and/or corrosion in the cooling loop. After the proposed water sources have been fully characterized on a flow capability and chemical basis, cooling tower chemistry criteria found in Table 2-1 should be imposed to evaluate the Water Quality Requirements for Cooling Systems 2-15 maximum N value for each constituent of concern. Regulatory criteria may also apply, e.g. the RWQCB may impose a limit on certain constituents such as copper or ammonia to meet their Water Qality Objectives for the point of discharge (discussed later in Section 2.4, Environmental Rules and Regulations). The output of this analysis will be the maximum cycles of concentration - chemistry-driven or regulatory-driven - achievable without treatment for each source of water. Note again, the smallest value of N for the suite of chemicals of concern defines the design cycles of concentration for a given source of water. Blowdown is calculated based on cycles of concentration (Equation 9 above) - the smaller the value of N, the larger the blowdown rate. Refer to Figure 2-4. Note that below 4.5 to 5.5 cycles of concentration, blowdown rates increase dramatically. Depending on water availability and discharge limitations, large volumes of blowdown may not be feasible regardless of source water quality. This is especially true for projects sited in desert or Central Valley locations where all wastewater is typically “contained” via discharge to lined evaporation ponds. Many projects in these locations are forced to evaluate treatment options (for freshwater as well as degraded water) that allow high cycles of concentration. Figure 2-4 Make-up and Blowdown vs Cycles of Consentration Water Quality Requirements for Cooling Systems 2-18 Table 2-3 Cooling Tower - Basic Water Quality Parameters Basic ParametersUnitsParameter 900 (max)(5)mg/lCaCO3Ca 500,000(mg/l)2Ca x SO 4 (Refer to Table 2-3b)mg/lCaCO3Ca with PO4 present 75,000 (3)35,000 (2)mg/lCaCO3 x mg/l SiO2Mg x SiO 2 200-250 (3)30-50 (2)mg/lCaCO3HCO3 + CO3 (Note 5)mg/lSO4 150mg/lSiO2 <0.5mg/lFe (Total) <0.5mg/lMn <0.1mg/lCu <1mg/lAl 5mg/lS <2 (9)mg/lNH3 7.8-8.4 (3)6.8-7.2 (2)pH 7.0-7.5 (4)pH with PO4 present 70,000mg/lTDS <100 (6) - <300 (7)mg/lTSS <100 (4)mg/lBOD <100 (4)mg/lCOD <0Langelier SI (8) >6Rysnar SI (8) Notes..... Cooling tower circulating water concentrations. PO 4 refers to total phosphate1. concentration. Refer to Table 3-1 and for detailed calculation pocedures. Without scale inhibitor.2. Assumes scale inhibitor is present.3. Consult with specialty chemical provider before finalizing control parameters.4. Refer to the CaSO4 limit.5. <100 mg/l TSS with film fill.6. <300 mg/l TSS with open fill.7. Refer to Appendix A for a discussion of the Langelier and Ryznar Saturation8. Indices for calcium carbonate. <2 mg/l NH 3 applies when copper bearing alloys are present in the cooling system. 9. This does not apply to 70-30 or 90-10 copper nickel. Water Quality Requirements for Cooling Systems 2-19 Table 2-4 Maximum Cooling Tower Calcium with PO4 Present Max Ca, mg/l CaCO3 @ Cooling Tower TDS, mg/lPO4 20,00010,0005,0002,500500mg/lpH 28525020016011057.00 1901651301007057.25 12510585654057.50 18016012510070107.00 120105806545107.25 8065504025107.50 140120957555157.00 9080605035157.25 6050403020157.50 Notes..... Cooling tower circulating water concentrations. PO 4 refers to total phosphate1. concentration. Refer to Table 3-1 and for detailed calculation pocedures. Assumes scale inhibitor is present.2. Consult with specialty chemical provider before finalizing control parameters.3. Water Quality Requirements for Cooling Systems 2-20 Table 2-5 Source Water Screening FreshReclaimedAg ReturnProduced WaterWaterWaterWater mg/lmg/lmg/lmg/l 41762,182982Na (by difference) 0.725622K 187655440Ca 0.764327013Mg 923962391,100HCO3 221021,480920Cl 31684,730110SO4 NDNR48NR (6)NO3 ND62NRTotal PO4 NDNRNR6S 161737120SiO2 0.1731421B (5) ND5NR5NH3 2978699,7233,879TDS <1811<1TSS NA8330BOD NA53280COD Operating Cooling Tower Assumptions..... 2005050200Cooling Tower Alkalinity, mg/l CaCO3 7.97.07.07.9Calculated pH (8) Screening-Level Cycles of Concentration - N - without Pre-Treatment (Refer to Tables 2-3a and 3b for control criteria and Table B-2 for calculation procedures) 20.04.7<19.0Ca 16.44.2<13.6Ca x SO 4 (7) 38.75.01.33.4Mg x SiO 2 9.48.84.11.3SiO2 NA1.3<1NACa (in presence of PO 4) 23580718TDS Notes..... Produced water from oil production in the Central Valley.1. Agricultural return water from the San Luis Drain.2. Secondary-treated reclaimed water from the Bay Area. t-PO 4, B, NH3 and COD were estimated.3. West Kern water. Silica concentration was modified for this analysis.4. B exists as H 3BO3 (non-dissociated boric acid) in water at this pH.5. NR = not reported, ND = non-detectable and NA = not applicable.6. H2SO4 used for pH control is accounted for when calculating the impact of additional SO 4 7. on CaSO4 solubility. Assume pH = 7.0 when PO 4 present.8. Reclaimed water would have been limited to 4.4 cycles of concentration based upon calcium sulfate criteria, however, the phosphate concentration is very high. In addition, produced water and agricultural return water had problems with calcium, calcium sulfate, magnesium/silica and silica. Note that phosphate posed problems for both agricultural return water and reclaimed water. Unless treated, these criteria severely limit the achievable cycles of concentration rendering the water unusable. Water Quality Requirements for Cooling Systems 2-23 Agricultural return water is severely limited by calcium, calcium sulfate, magnesium/silica and calcium phosphate. All constituents are treatable with softening. Side-stream lime/soda softening will be required to remove silica effectively. Bicarbonate alkalinity is very high and a significant amount of sulfuric acid will be required to reduce feedwater alkalinity for pH control. Calcium, magnesium and phosphate will also be reduced by this type of softening. Reclaimed water is limited by calcium, calcium sulfate and calcium phosphate - 4.4 to 4.7 cycles of concentration. All of these limitations could be controlled with calcium removal via make-up or side-stream softening. Note, ammonia levels are very high, and as with produced water, will necessitate the use of non-copper bearing alloys in the cooling system. Bromine will also be required in lieu of chlorine to avoid chloramine formation (again, discussed Section 4). Refer to Table 2-7 to review treatment requirements to treat a variety of environmental contaminants typically found in groundwater and surface water. These are common treatment technologies employed to remediate contamination. Treated water chemistry, chemical requirements, treatment technology and overall economics are discussed in detail in Sections 3 and 5. Table 2-6 Pre-, Side-Stream Treatment for Cooling Towers Side-Stream TreatmentPre-Treatment Warm Lime orLime orCooling Tower Lime/SodaLime/SodapHChemical Criteria SofteningFiltrationSofteningAdjustment(Note 3) PriPriCa Pri via CaPri via CaCa x SO4 PriPri via MgMg x SiO 2 SecSecPriM Alkalinity Pri via CaPri via CaSO4 Pri(Note 5)SiO2 SecSecPO4 PripH SecPriSecTSS Notes..... Pri = primary means of reduction - intention of process.1. Sec = secondary means - incidental reduction in process.2. Chemical criteria found in Table 2-1.3. Refer to Table 2-6 for removal of contaminants from degraded water for cooling4. tower make-up. There is some removal of SiO 2.5. Water Quality Requirements for Cooling Systems 2-24 Table 2-7 Pre-Treatment of Contaminated Water for Cooling Tower Make-Up Air StrippingAir Stripping StrongBiologicalLiquidVapor-PhaseVapor-Phase PrecipitationChelatingBaseTreatmentPhaseThermalGACChemical Parameter Co-PrecipIXIX(Note 4)GACOxidation(Note 3)(Note 5) SecPriPriPri - VolatilePri - VolatileOrganic Compounds SecPri (8)PriPesticides PriPriCationic Heavy Metals (12) Pri (11)PriPri (14)Anionic Heavy Metals (13) Pri (10)Pri - NO 3,ClO4NO3, ClO 4, F (9) SecPriSec (7)Biological (6) Notes..... Pri = primary means of reduction - intention of process1. Sec = secondary means - incidental reduction in process2. GAC is granular activated carbon.3. There are a variety of biological processes, e.g. constructed wetlands, trickling filter, fixed-film aerobic, etc.4. Refer to Table 2-2 for chemical parameters of contaminated groundwater and surface water treatment.5. Biological waste components include BOD, COD, NH 3, PO 4, etc. Typically found in reclaimed water6. as well as pharmaceutical, biotech, livestock/dairy and food processing waste streams. There will be some incidental removal of BOD and COD.7. Pesticides could be detrimental to biological processes because of its toxicity.8. Anaerobic biological treatment is required for NO 3 and ClO 4. Anaerobic treatment is still considered9. experimental for ClO 4. Depending on treatment conditions NO 3 removal may not be completely achievable.10. Applies to AsO 4 and SeO 3.11. Cationic heavy metals include Cu, Ni, Cd, Cr (+3) , etc.12. Anionic heavy metals include AsO 4, CrO 4, SeO 4, SeO 3, etc.13. Anaerobic biologic treatment is still somewhat experimental for anionic heavy metals.14. 2.3.3.e Post-Treatment Requirements for Degraded Water Most planned and many existing inland power plants in California will be designed as “zero discharge”, i.e. all wastewater is contained. Depending on the water source and the achievable cycles of concentration, wastewater generation in the form of cooling tower blowdown can be quite high (usually the largest waste stream at the plant). Wastewater in desert settings is often routed to imperviously-lined evaporation ponds for final on-site disposal. The focus of post treatment is to treat blowdown to reduce wastewater generation. Also note, in zero discharge plants, many waste streams are routed to the cooling tower, e.g. HRSG blowdown, plant washdown, ion exchange low-conductivity rinse water, etc. Sanitary wastewater is usually handled separately. Volume reduction is costly and almost always requires a combination of softening, evaporation or crystallization. A benefit of wastewater treatment via evaporative processes is a significant amount of high quality water is generated which can be reused in the plant, e.g. HRSG feedwater, inlet air cooling for the gas turbine, NOX control, etc. These technologies will be discussed in Sections 3 and 5. Water Quality Requirements for Cooling Systems 2-25 2.4 Rules and Regulations The environmental impacts of a variety of cooling systems (once through, wet cooling, etc.) have been the object of legislative and regulatory attention at both the Federal and State level. The regulatory framework and specific rules, which apply to steam-electric power plant cooling in California, will be reviewed in the following section. The discussion will be confined to wet evaporative cooling with particular emphasis on those elements which would be most affected by the use of degraded water for cooling tower make-up. Environmental issues related to new power projects are numerous and complex. The following information is presented in a generalized manner and is intended to identify issues of concern rather than specific regulatory requirements. 2.4.1 Regulatory Background and Approach Cooling system impacts may involve all the environmental media (air, water and land) and potential impacts to public health. Therefore, they are are governed by many parts of environmental laws and regulations. At the Federal level, these include the Clean Air Act, the Clean Water Act, the Resource Conservation and Recovery Act, and resultant regulations promulgated under NPDES, National Emissions Standards for Hazardous Air Pollutants (NESHAPS) and others. At the state level, relevant rules are found in the California Code of Regulations, especially Titles 17, 20, 23, 26 and 27 (Public Health, Public Utilities and Energy, Waters, Toxics and Environmental Protection respectively) and policies established by the State and Regional Water Quality Control Boards. Refer to Appendix A.1.1, Referenced Citations - Chapters 1 and 2 (citations 11 through 23) for a comprehensive list of related statutes discussed in this section. In past years in the federal framework, the regulatory philosophy was based on the requirement that responsible facilities mitigate environmental impacts with the most effective control technology applicable to their particular situation. Hence for steam-electric power generation, Clean Water Act Technology-based limits are categorized (generally based on the age of the plant) as follows: • BPT - Best Practical Control Technology Currently Available - note, since the early 1980s, the only aspect of BPT that applies to any current or future discharges is pH limits of 6.0 - 9.0. Other BPT controls are superceded by BAT. • BAT - Best Available Technology Economically Achievable • NSPS - New Source Performance Standards (for new power plants) • PSES- Pretreatment Standards for Existing Sources - pretreatment standards for discharge to sanitary sewer. • PSNS - Pretreatment Standards for New Sources - pretreatment standards for discharge to sanitary sewer. Water Quality Requirements for Cooling Systems 2-28 Table 2-8 Power Plant Cooling Systems - Requirements for Approval systems.... supply, pollution control General description of....water of----cooling systems Design, construction, operation impacts, water and---- consideration given to env. How selection made and 75-58 Section 25540.6(b)/Policy Public Resources Code, merits and economic/environmental Discussion of other choices visible plumes Assessment of impact of Determination of Compliance control district to complete Info necessary for air pollution Section 25294.8 Health and Safety Code, Safety Code, Section 25531. et seq. Also, Health and Cal. Code, title 22, §66261.20 et seq. Cal. Code, title 22, §66261.20 1702 (q) and (v) Cal. Code, title 20, Sects. 75-58 Requirements; NPDES; Policy Waste Discharge surrounding soil-vegetation Effect of emissions on California Code of Regulations, Title 20, Div. 2, Chap. 5---§2012, App. B RelevantSubsection Code/RegulationRequirementSubject(of App. B) None citedExecutive Summary(a)(1)(A) None citedProject Description(b)(1)(C) None citedSite/Facility Selection(b)(1)(D) Alternatives(f)(1)&(2) None citedNoise(g)(4) None citedVisual Resources(g)(6)(F) None citedAir Quality(g)(8)(A) Pubic Health(g)(9) Hazardous Materials(g)(10) Handling Waste Management(g)(12) Biological Resources(g)(13) Water Resources(g)(14) None citedAgriculture and Soils(g)(15) Water Quality Requirements for Cooling Systems 2-29 Cooling tower blowdown volume could be significant with the use of untreated degraded water because chemical constituents found in the water will likely limit cycles of concentration. Therefore, environmental rules will impact water usage and treatment and pre-, in-process or post treatment may be required to minimize discharge volumes (or treat to remove specific chemical compounds). Disposal issues usually revolve around cooling tower blowdown and treatment waste streams. The volume of the waste stream(s) and chemical characteristics define the extent of the disposal issue. The lower the cycles of concentration, the greater the volume of waste. As stated previously, large waste volumes pose significant problem for plants with no convenient or environmentally-acceptable means of liquid disposal. Also, Water Quality Objectives set forth by the local RWQCB may preclude any type of disposal (discussed later in this section). Conversely, a high cycles of concentration waste stream with elevated concentrations of source- water constituents may also pose disposal problems. As part of the analysis required to determine the appropriateness of water use at any site, a range of reasonable alternatives sites, including a “no project” alternative must be considered in accordance with California Public Resources Code section 25540.6(b). This must include a discussion of site selection criteria, any alternative sites and reasons for choosing the proposed site. In the context of considering water use for power plant cooling, these are important elements in establishing whether alternatives to inland fresh water use are “environmentally undesirable” or “economically unsound.” 2.4.3.2 Wastewater Discharges The information requirements for the Regional Water Quality Control Board (identified in Table 2-7, Section (g)(14), Water Resources) include a National Pollutant Discharge Elimination System (NPDES) permit and a Waste Discharge Requirements permit. 2.4.3.2.a Federal Regulations The basis for regulation of wastewater discharges promulgated at the federal level comes primarily from the Clean Water Act (Federal Water Pollution Control Act Amendments of 1972, as amended by Clean Water Act of 1977). Permitting authority is delegated to the states under the National Pollutant Discharge Elimination System (NPDES). The U.S. Environmental Protection Agency sets discharge limits which the states must meet at a minimum (although they may set more stringent limits at their discretion). These limits are set for individual categories of dischargers on the basis of existing treatment technologies, their costs and their applicability to the particular category. The following limits are for the Steam Electric Power Generating Point Source Category in CFR Title 40, Chapter 1, Part 423; 7-1-99 Edition. Refer to Table 2-9. Note that NSPS, PSNS, PSES and BAT waste discharge limitations are very similar and are described jointly in Table 2-9. An additional category, designated as Best Conventional Pollutant Control Technology (BCT), is “reserved” but currently undefined. Water Quality Requirements for Cooling Systems 2-30 2.4.3.2.b California Regulations In addition, the regulatory philosophy of many jurisdictions, including California, has shifted from technology-based discharge limits for particular categories to case-by-case determination of allowable limits based on the achievement of water quality objectives for particular receiving waters. These are reviewed briefly for the California situation below. The basis of wastewater discharge regulations promulgated by state regulatory authorities is the California Water Code and specifically, the Porter-Cologne Water Quality Control Act. Authority is given to the State Water Quality Control Board and nine Regional Water Quality Control Boards to “formulate and adopt water quality control plans” which include: • “establish[ing] such water quality objectives....[to] ensure the reasonable protection of beneficial uses and the prevention of nuisance • specify[ing] certain conditions or areas where the discharge of waste....will not be permitted” • prescrib[ing] requirements as to the nature of any proposed discharge”. It is under these Regional Board Plans, referred to a “basin plans”, that the operative rules for waste and wastewater discharge to both surface and groundwater are set which eventually determine whether power plant cooling systems are “environmentally undesirable or economically unsound”. Table 2-9 Steam Electric Power Generating Point Source Category, CFR Title 40, Chapter 1, part 423, BAT, NSPS, PSNS and PSES tower maintenance) (contained in chemicals required for cooling BAT Effluent LimitationPollutant or Pollutant Property 6 to 9pH 0.5 mg/l, maximum concentrationFree Available Chlorine (FAC) 0.2 mg/l, average concentration Average of daily values for 30 consecutive daysOne Day Maximum (mg/l)(mg/l) No detectable amountNo detectable amount126 priority pollutants (Table B) 0.20.2Chromium, total 1.01.0Zinc, total Water Quality Requirements for Cooling Systems 2-33 2.4.3.3.a Federal Regulations Air-borne emissions from cooling towers are regulated under the Clean Air Act, specifically the provisions of NESHAPS. Listed pollutants under NESHAPS with relevance to wet cooling towers include asbestos (in the case of older towers using cement-asbestos [CAB] fill), chromium, zinc and zinc oxide, and the tri-halomethanes. Also, Title 40 (Chapter1, Part 63, NESHAPS for Source Categories, Subpart Q, NESHAPS for Industrial Process Cooling Towers (IPCT), Section 63.402) states: “No owner....shall use chromium-based water treatment chemicals in any affected IPCT.” 2.4.3.3.b California Regulations Title 17 (Public Health, Division 3, Air Resources, Chapter 1, Air Resources Board, Subchapter 7.5, Airborne Toxic Control Measures; §93103, Regulation for Chromate Treated Cooling Towers) bans the use of hexavalent chromium containing compounds in cooling tower circulating water. For existing towers, especially wood towers, which have used such compounds in the past, a period of time is permitted to allow the chemicals to desorb from the tower and be eliminated so long as the level in the circulating water does not go above 0.15 mg/l (8 mg/l for wood towers) and tests show a continuous decrease over time. 3-1 3 TECHNICAL FEASIBILITY 3.1 Introduction The technical feasibility and economics of using degraded water for cooling towers is evaluated in this section. Three hypothetical case studies of power plants using degraded water for cooling are discussed and evaluated in detail. The case studies include process wastewater, agricultural return water and reclaimed municipal effluent. Water consumption, water treatment equipment, chemicals requirements, cooling tower blowdown, solid-waste generation, operating costs and order-of-magnitude capital costs are identified for each case study. All case studies are evaluated against freshwater for comparative purposes and to benchmark the cost analysis. Water, which would otherwise be usable for domestic or industrial purposes such as contaminated groundwater, is not evaluated in this section. After routine pre-treatment, e.g. air stripping, it was assumed that this type of water likely would not present any significant technological barriers for use as cooling tower make-up. There are also types of contamination that are currently not fully understood with respect to health hazards, e.g. trace levels of manmade or natural complex organic compounds found in groundwater or surface water. Scenarios involving these possible forms of contamination are not evaluated in this report because there are no existing regulatory standards nor are there water quality criteria for use in cooling (or general industrial use). Therefore, treatment approaches for these types of contamination cannot be evaluated. Other than a few examples of treated municipal effluent being used for cooling tower make-up (refer to Section 1, Introduction), degraded water is not typically used for power plant cooling in California. “Difficult” waters containing high levels of hardness, alkalinity, silica, salinity, etc. are commonly considered unusable when water source options are being evaluated for a power plant, especially when fresh water is available. Fresh water is typically selected for cooling, because special water treatment equipment is usually not required (e.g. softening, silica removal, etc.), specialty chemical treatment is usually straightforward, cooling system materials of construction are less costly (e.g. condenser metallurgy) and overall cooling system operation is more forgiving when water quality control problems are encountered. Three case studies of power plants using degraded water for cooling are discussed and evaluated in detail in this section. The case studies include process wastewater from oil production, agricultural return water and reclaimed municipal effluent. The degraded water scenarios are admittedly “difficult” from a freshwater treatment perspective, but as illustrated by the case studies, they are usable with appropriate treatment. Technical Feasibility 3-4 3.3 Evaluation Basis The parameters described in the evaluation basis were used for the three hypothetical case studies. Refer to Table 3-2 for a summary of evaluation parameters used throughout this section. Refer again to Table 3-1 for a summary of chemical analyses of the degraded water and fresh water sources evaluated. The table also includes a screening summary of critical water quality parameters (used to select treatment alternatives for each source water). 3.4 Case Study 1 - the Central Valley - Produced Water Produced water is a byproduct of oil production. Low-quality steam is injected into a producing reservoir where it is utilized to loosen and fluidize oil from oil-bearing rock or sand. Oil and water return to the surface where they are separated. The water is de-oiled, filtered, softened and re-injected as steam. Many reservoirs produce excess water which must be disposed of (some fields generate significant volumes of wastewater). Excess produced water is disposed of in salt sinks via percolation where groundwater is markedly saline or it is injected into non-producing zones. Salt sinks could also be considered a source of degraded water. Refer to Table 3-1 for a chemical analysis of produced water. Depending on the reservoir, hardness, silica and salinity can be significantly higher than shown in the table. One example of variability is TDS which is a measure of total salt content. Depending on location, produced water TDS can range from 500 mg/l to 15,000 mg/l in the Central valley. General Concerns Based on the screening analysis located at the bottom of Table 3-1, if the produced water is untreated, it is limited by calcium sulfate solubility (CaSO4) to 3.6 cycles of concentration in the cooling tower, magnesium/silica solubility product (Mg x SiO2) to 3.4 cycles, and silica solubility (SiO2) to 1.3 cycles. Refer to Table B-2 in Appendix B for the formulas used to calculate maximum allowable cycles of concentration. Note, these formulas are considered conservative and detailed analysis (involving common ion effects, solubility temperature adjustments, ionic strength adjustments), as discussed in Section 2.3.3.b, Water Quality Prediction Software, would yield less restrictive criteria. Calcium and magnesium concentrations are relatively low in this specific water, but the silica concentration is exceedingly high (high silica is typical for produced water). Although the sulfate in the source water is relatively low, a significant amount of sulfuric acid must be added to the cooling tower make-up to reduce the very high level of alkalinity (for calcium carbonate scale control in the cooling tower). This requirement significantly increases the sulfate concentration to the cooling tower. Also, ammonia poses a problem at 5 mg/l in the source water as it relates to wetted-surface metallurgy selection and biological control. Lastly, sulfide, BOD and COD are present and may effect the consumption of biological control chemicals. Technical Feasibility 3-5 Table 3-2 Evaluation Basis 500 MW Gas-Fired Combined Cycle1. Cooling System2. Cross-Flow Mechanical Draft TowerS 128,000Cooling Water Recirculation Rate, gpmS 25,000,000Air Flow, SCFMS 1,750Evaporation Rate, gpmS (1)0.002%Drift Rating, Pct of Recirculation RateS 2.6Drift Rate, gpmS Ambient Evaporation Data (for evaporation pond sizing)3. 80Central Valley, Class A Pan, inches/yearS (2)40Central Valley, Adjusted Pan, inches/yearS 120Desert, Class A Pan, inches/yearS (2)60Desert, Adjusted Pan, inches/yearS Chemical Costs (3)4. $15590% Lime (CaO), $/tonS $32098% Soda Ash (Na 2CO3), $/tonS $18098% Sulfuric Acid (H 2SO4), $/tonS $260100% Magnesium Chloride (MgCl 2), $/tonS $3.00Coag Aide (cationic polymer), $/poundS (4)$1.00Chlorine Dioxide (ClO2), $/poundS (4)$0.35Sodium Hypochlorite (NaOCl), $/poundS (4,6)$0.35Specialty Chemical Formulation, $/poundS $0.08Power, $/kwh5. Sludge Disposal6. $20Transportation, $/cubic yardS $50Disposal, $/tonS $35Operator Labor Costs, $/hour (fully burdened)7. Water Costs8. $50Produced, Agricultural Return Water, $/acrefootS $250Reclaimed Water, $/acrefootS $500Fresh Water, $/acrefootS (5)$2.10Demineralized Water Credit, $/1000 gallonsS Amortization @ 7% for 30 years.9. Notes..... Percent of cooling tower recirculation rate (manufacturer's rating).1. Adjusted pan data accounts for losses in evaporation efficiency as2. a result of evaporation pond depth, increased salinity over time, etc. Estimated delivered costs.3. Dry basis.4. Assumes treatment with RO and MB bottles - operating costs and5. capitalization ($0.60/1,000 gal) plus cost of fresh water ($1.50/1,000 gal). Formulation blend of corrosion inhibitor, scale inhibitor and dispersant.6. Technical Feasibility 3-6 Treatment Make-up softening was not considered because of the relatively low hardness of the source water. Side-stream softening was selected to benefit from the higher levels of hardness in the cooling water, i.e. magnesium precipitation is required for silica removal. Refer to Table 3-3 for a summary of operating chemistry (as well as water quality criteria, chemical feed requirements, flow rates, etc.). Side-stream softening is applied to a small portion of condenser return water to take advantage of the temperature of the water which should be at 105 to 115OF. Silica reduction is dramatically improved at higher temperatures. Refer to Figure 3-1 (middle figure, Side- Stream Softening) for a schematic representation of the process as it relates to the cooling system (this figure will be used for all case studies). Also, refer to Section 5.3, Pre-, Side-Stream and Post-Treatment Technologies for a discussion of the side-stream reactor clarifier process and Appendix C for operating and performance parameters of this treatment technology (i.e. expected effluent chemistry and chemical requirements). At a TDS limit of 35,000 mg/l (which is analogous to seawater salinity) for the cooling system, 10.3 cycles of concentration are achievable. This limit was set because there is a significant amount of metallurgical experience at this concentration, and at 10.3 cycles of concentration, the resulting blowdown rate is relatively low, 185 gpm. Recall, minimizing blowdown is critical to inland plants to reduce costly wastewater treatment and storage in evaporation ponds. The TDS limit could have been set at 70,000 mg/l for a blowdown rate of 93 gpm, but this would have forced metallurgical requirements to their practical limits, e.g. titanium heat exchanger metallurgy, non-metallic materials of construction for wetted surfaces wherever possible, etc. The side-stream softener was sized at 3,008 gpm based on a parametric analysis conducted using the silica removal data presented in Figure 5-12, Final Silica vs Mg Precipitation. Using the data in Figure 5-12, it was determined that a magnesium precipitation level of 175 mg/lCaCO3 yielded the most efficiently sized softener (design point is the “knee” of the capacity curve). Refer to Figure 3-2. Also, because there is an insignificant amount of magnesium in the feedwater, magnesium chloride (MgCl2) must be added to supplement magnesium floc formation. Technical Feasibility 3-9 Figure 3-2 SS Softener Capacity vs Precip’d Mg Cooling System Issues Based on the cooling tower chemistry presented in Table 3-3, silica is the limiting water quality parameter for the cooling tower. Calcium sulfate solubility and the magnesium/silica solubility product are well below saturation levels. Because ammonia is present at fairly high levels, 90-10 copper-nickel is recommended for the cooling system metallurgy. Copper alloys (yellow metal) such as admiralty brass should be avoided. Chlorine dioxide (ClO2) should be used for biological control because it does not react with ammonia. Bromination should not be considered for microbiological control because of the possibility of forming brominated organic compounds (bromine reacts with ammonia but the product is unstable and reverts to OBr-). It should be noted that biological control will be critical because of the favorable nutrient characteristics of ammonia. Cooling tower pH was purposely adjusted to 7.5 (120 mg/lCaCO3 alkalinity) to allow sulfides to associate to their volatile form (25 percent as H2S) in the circulating water. This should allow the air flow in the cooling tower to remove most of the sulfides and minimize oxidation by ClO2 (sulfides readily react with oxidizing biocides). There will be a substantial dilution effect of the air stream which should render H2S concentrations to non-detectable levels. Also a significant amount of sulfide will be lost in the vicinity of sulfuric acid addition where feedwater pH drops to 5.8. BOD and COD concentrations will be difficult to predict in the cooling tower, because some COD and BOD will be “consumed” by the cooling tower (oxidation via air flow and through biological activity). COD, however, may present a problem for chlorine dioxide consumption, but as stated previously, some of the COD will be consumed. Typically organic carbon in produced water is a mostly a mixture of aliphatic compounds (open chain). Since chlorine dioxide does not oxidize these compounds, this should not be a source of unnecessary ClO2 consumption. A residual of a 1-mg/l equivalent of free available chlorine should be maintained twice per day for at least two hours per application. This should keep biological growth within control. Lastly, because of the potential for biological Technical Feasibility 3-10 growth, a wide-spaced film fill (low surface area to volume ratio) or traditional packing should be utilized in the cooling tower. The specialty chemical program should focus on corrosion control because of high circulating water salinity and relatively low calcium hardness, alkalinity and pH. A biodispersant should be considered to prevent biological masses from adhering to cooling tower fill. Operating Costs Based on the chemical consumption rates presented in Table 3-3, side-stream softening should cost $3,976 per day to operate. The reactor clarifier will generate 19.0 tons per day of sludge (45 percent solids by weight). Equipment amortization costs for the side-stream softener should amount to $412 per day (equipment installation costs are discussed next). Cooling tower chemicals and produced water will cost $3,293 per day. Estimates of chlorine dioxide demand should be tripled to account for COD demand and vigorous biological growth. To maintain a residual of 1.3 mg/l of chlorine dioxide (1-mg/l equivalent of OCl-1) in 128,000 gpm of recirculating water for a total of four hours per day requires 1,001 pounds per day (triple calculated demand). Refer to Table 3-4 for an operating cost summary for Case Study 1. The side-stream softener must receive at least 2 to 3 hours of attention per shift to ensure adequate operation. Likewise, cooling system chemistry should be checked twice per shift to ensure that water quality parameters are within specification. Cooling tower blowdown should be automated (controlled continuously) based on circulating water conductivity (salinity). Specialty chemical usage was estimated on a formulation basis - a combination of corrosion inhibitor, scale inhibitor and dispersant (assumed for all cases including the base case). Since individualized treatment programs are site specific, it was felt that a generalized approach was more appropriate for this analysis. Also, specialty chemicals are consumed by the side-stream softening and lost to blowdown. The cost of specialty chemicals in this case study is significant, $1,724 per day, because of the size of the side-stream softener. Lastly, even though it is saline and considered wastewater, the cost assigned to produced water (as well as agricultural return water) assumes it has “intrinsic value” as a necessary commodity for power generation, and therefore, has commercial value. Technical Feasibility 3-11 Table 3-4 Case Study 1 - Produced Water - Treatment Cost Summary 90% Lime, $/day $275 98% Soda Ash, $/day $1,482 100% Magnesium Chloride, $/day $659 Coagulant Aide, $/day $325 Specialty Chemical Formulation, $/day $1,724 Sludge Disposal, $/day $1,235 Water Treating Chemicals, $/day $5,700 Softener Amortization Cost, $/day $353 Produced Water Cost, $/day $426 98% Sulfuric Acid, $/day $1,866 Chlorine Dioxide, $/day $1,001 Total Cooling Tower (basic chemicals) $3,293 Total Treating Costs, $/day $9,346 +8993$ 8,99$$8 ,993 ($3.39/1000 gallons) Equipment Costs Refer to Figure 5-13, Installed Cost vs Capacity, to estimate the cost of the 3,008 gpm side- stream softener (reactor clarifier). The softener should cost approximately $1,600,000 installed (includes peripheral equipment - chemical silos and feeders and sludge handling and dewatering). Three waste disposal alternatives were evaluated for this case study: • Evaporation ponds only • Evaporator with evaporation ponds • Evaporator and crystallizer with no evaporation ponds Assuming the plant is operated on a water conservation basis, many streams will be routed to the cooling tower, e.g. boiler blowdown, plant wash down ,etc. If we assume that an additional 5 percent of wastewater will be generated that cannot be routed to the cooling tower because of water quality concerns, then plant wastewater generation will be approximately 194 gpm. Based on the adjusted pan data for evaporation of 40 inches per year for the Central Valley, 0.49 acres are required for every gallon per minute of wastewater disposed to the evaporation pond. Therefore, 95 acres of ponds are required to contain and evaporate the plant wastewater. Note, Technical Feasibility 3-14 Treatment Make-up softening is utilized because of the high hardness of the source water. Even when blended with low hardness fresh water, the return water hardness exceeds 1,270 mg/lCaCO3. Refer to Table 3-6 for a summary of operating chemistry (as well as water quality criteria, chemical feed requirements, flow rates, etc.). Side-stream softening was also selected to further reduce hardness to satisfy calcium sulfate solubility limitations (as discussed previously, these limits are conservative). Note, calcium sulfate solubility is at 240 percent of maximum (this excess can be controlled with crystal modifiers and scale dispersants). If an excess of 600 to 700 percent of calcium sulfate could be tolerated (with crystal modifiers and scale dispersants), the side-stream soften could be eliminated. Refer to Figure 3-1 (bottom figure, Make-up & Side-Stream Softening) for a schematic representation of the process as it relates to the cooling system. Also, refer to Section 5.3, Pre-, Side-Stream and Post-Treatment Technologies for a discussion of the make-up and side-stream reactor clarifier processes and Appendix C for operating parameters and performance of this technology (i.e. expected effluent chemistry and chemical requirements). An operating TDS of 50,000 mg/l was selected for the cooling system. This will allow 10.3 cycles of concentration. This limit was set because blowdown has a significant impact on disposal and post-treatment costs as presented in Case Study 1 (if the TDS limit were set at 35,000 mg/l, blowdown would increase by 30 percent). At 50,000 mg/l salinity, titanium heat exchanger metallurgy and non-metallic materials of construction will be required wherever possible. Cooling System Issues Based on the cooling tower chemistry presented in Table 3-6, calcium sulfate is the limiting water quality parameter for the cooling tower. Calcium phosphate would have been a concern but make-up softening removes phosphate to non-detectable or very low levels. Any phosphate that may be generated by the degradation of organo-phosphates, which could be used for scale inhibition, should be removed by the side-stream softener. The magnesium/silica solubility product and silica are well below saturation levels. Sodium hypochlorite (NaOCl) should be utilized for biological control. Unlike produced water in Case 1, there are no concerns with ammonia (recall, every mg/l of ammonia consumes 10 mg/l of NaOCl). BOD and COD concentrations will be difficult to predict in the cooling tower, because some COD and BOD will be “consumed” by the cooling tower (oxidation via air flow and through biological activity). COD, however, may present a problem for chlorine consumption, but as stated previously, some of the COD will be consumed. A residual of a 1-mg/l equivalent of free available chlorine should be maintained twice per day for at least two hours per application. This should keep biological growth within control. Lastly, because of the potential for biological growth (BOD could provide some nutrient stimulation), a wide-spaced film fill (low surface area to volume ratio) or traditional packing should be used utilized in the cooling tower. Technical Feasibility 3-15 Table 3-6 Cooling Water Chemistry - Case Study 2 (Note 4) 10.28Cycles of Concentration =Agricultural Return Water/Fresh Water Blend Side-StreamSoftened50%50% SoftenerCoolingAcidifiedBlendedBlendedFreshAg Return EffluentWaterMake-upMake-upMake-upMake-upMake-upUnits 36,41436,2133,4843,4842,412894,735mg/lCaCO3Na by Diff 444444418mg/lCaCO3K 351233535715451,385mg/lCaCO3Ca 80281808055831,112mg/lCaCO3Mg 013649013675196mg/lCaCO3HCO3 450045000mg/lCaCO3CO3 4004000mg/lCaCO3OH 10,88210,8821,0591,0591,059312,087mg/lCaCO3Cl 25,44325,4432,4762,4762,476324,919mg/lCaCO3SO4 199199191919NA39mg/lCaCO3NO3 NDNDNDND1NA2mg/lPO4t-PO4 NANANANANANANAmg/lSS 3391313271637mg/lSiO2SiO2 73737770.1714mg/lBB NANANANANANANAmg/lNNH3 10.07.67.210.07.37.27.5pH 49,72649,8914,9114,8804,9252229,628mg/lTDS <310-20<3<36<111mg/lTSS 1.51.51.5NA3mg/lBOD 161616NA32mg/lCOD Pct of Limit..... 240%CaxSO4 15%MgxSiO2 26%SiO2 NAKSPCa3(PO4)2 Saturation 0.18LSI - Target Range = -1 to +1 7.27RSI - Target Range = +6 to +7 General Plant Data..... 1,928Make-up, gpm 185Blowdown, gpm 506Side-Stream Softener Feed, gpm TotalSide-StreamMake-up 55.05.349.745% Sludge, tons/day Chemical Feed Requirement..... 14.070.6613.41Na2CO3, tons/day (1) 5.110.664.44Ca(OH)2, tons/day (1) 0.000.000.00MgCl2, tons/day (2) 0.00NA0.00H2SO4, tons/day 881869Coagulant Aide, pounds/day (15 mg/l in cooling tower)124Specialty Chemical, pounds/day Notes..... Refer to Appendix B, softener performance calculations - US Filter Technical Data Book,1. Section 57, Class 1(Case 2) and Class 2. Must add an equivalent amount of lime & soda ash for MgCl 2 usage.2. ND = non detectable.3. BOD and COD not quantifiable in the cooling tower.4. Technical Feasibility 3-16 The specialty chemical program should focus on corrosion control because of very high circulating water salinity and relatively low calcium hardness, alkalinity and pH. Also, a crystal modifier/dispersant should be used to control calcium sulfate scale formation. A biodispersant should be considered to prevent biological masses from adhering to cooling tower fill. Operating Costs Based on the chemical consumption rates presented in Table 3-6, make-up softening should cost $8,417 per day to operate. Side-stream softening should cost $712 per day to operate. The reactor clarifiers will generate 55.0 tons per day of sludge (45 percent solids by weight). Equipment amortization costs for the side-stream softener should amount to $335 per day for the make-up softener and $155 for the side-stream softener (equipment installation costs discussed next). Note, because the make-up and side-stream softeners removes essentially all of the alkalinity entering the cooling tower, sulfuric acid is not required to adjust cooling tower alkalinity (nonetheless, a sulfuric acid addition system should be installed). Cooling tower chemicals, freshwater and return water should cost $2,734 per day. Estimates of chlorine dioxide demand should be tripled to account for COD demand and vigorous biological growth. To maintain a residual of 1 mg/l of free available chlorine (OCl-1) in 128,000 gpm of recirculating water for a total of four hours per day requires 1,117 pounds (dry basis) per day of sodium hypochlorite (triple calculated demand) Refer to Table 3-7 for an operating cost summary for Case Study 2. The side-stream softener must receive at least 2 to 3 hours of attention per shift to ensure adequate operation. Likewise, the cooling system chemistry should be checked twice per shift to ensure that water quality parameters are within specification. Cooling tower blowdown should be automated (controlled continuously) based on circulating water conductivity (salinity). Equipment Costs Refer to Figure 5-13, Installed Cost vs Capacity, to estimate the costs of the 1,928 gpm make-up softener and 506 gpm side-stream softener (reactor clarifier). The make-up softener should cost approximately $1,300,000 installed and the side-stream about $600,000 (includes peripheral equipment - chemical silos and feeders and sludge handling and dewatering). Three waste disposal alternatives were evaluated for this case study: • Evaporation ponds only • Evaporator with evaporation ponds • Evaporator and crystallizer with no evaporation ponds Assuming the plant is operated on a water conservation basis, many streams will be routed to the cooling tower, e.g. boiler blowdown, plant wash down ,etc. If we assume that an additional 5 percent of wastewater will be generated that cannot be routed to the cooling tower because of water quality concerns, then plant wastewater generation will be approximately 194 gpm. Technical Feasibility 3-19 General Concerns Based on the screening analysis located at the bottom of Table 3-1, if the agricultural return water is untreated, it is limited by calcium sulfate solubility (CaSO4) to 4.2 cycles of concentration in the cooling tower, magnesium/silica solubility product (Mg x SiO2) to 5.0 cycles and calcium phosphate solubility to 1.1 cycles. Refer to Table B-2 in Appendix B for the formulas used to calculate maximum allowable cycles of concentration. Since the setting for this plant is the California coast, high cycles of concentration in the cooling tower (resulting in less blowdown) are not an issue of concern. Therefore, a target of six cycles of concentration was set for the cooling tower. Note that power plants are required to obtain an NPDES permit if they discharge to state waters and must meet some very restrictive discharge requirements depending on the discharge location, e.g. Santa Monica Bay or San Francisco Bay. Many plants make an effort to route their wastewater (blowdown is usually the largest component of the waste stream) to a municipal treatment plant. For the purpose of this analysis, it was assumed that phosphate and ammonia are not removed before the water is delivered to the power plant. Municipal treatment plants are capable of removing these constituents, but it requires additional treatment processes and/or process modifications which the majority of treatment plants do not employ. General mineral parameters such as hardness, sulfate, silica, etc. are not effected by the treatment processes utilized by municipal effluent plants. Treatment Make-up softening is utilized to remove phosphate from the feedwater to the cooling tower. Without softening phosphate levels are 40 times saturation at a pH of 7.0. Even with specialty chemicals, this type of barrier cannot be overcome. Softening removes phosphate from cooling tower make-up, thus eliminating it as an issue of concern. Other parameters, such as calcium, magnesium, sulfate and silica, are moderately low and do not pose scaling problems at six cycles of concentration. Refer to Table 3-9 for a summary of operating chemistry (as well as water quality criteria, chemical feed requirements, flow rates, etc.). Refer to Figure 3-1 (top figure, Make-up Softening) for a schematic representation of the process as it relates to the cooling system. Also, refer to Section 5.3, Pre-, Side-Stream and Post-Treatment Technologies for a discussion of the make-up reactor clarifier process and Appendix C for operating parameters and expected performance of this technology (i.e. effluent chemistry and chemical requirements). Technical Feasibility 3-20 Table 3-9 Cooling Water Chemistry - Case Study 3 (Note 4) 6.01Cycles of Concentration =Reclaimed Water CoolingAcidifiedSoftened WaterMake-upMake-upMake-upUnits 991165165165mg/lCaCO3Na by Diff 38666mg/lCaCO3K 2103535190mg/lCaCO3Ca 5238787177mg/lCaCO3Mg 200330325mg/lCaCO3HCO3 00790mg/lCaCO3CO3 0000mg/lCaCO3OH 864144144144mg/lCaCO3Cl 7001167171mg/lCaCO3SO4 NDNDNDNDmg/lCaCO3NO3 NDNDND6mg/lPO4t-PO4 NDNDNDNDmg/lSS 72121217mg/lSiO2SiO2 18333mg/lBB 30555mg/lNNH3 7.95.89.47.5pH 2,402400363806mg/lTDS 10-20<3<38mg/lTSS 888mg/lBOD 555mg/lCOD Pct of Limit..... 11%CaxSO4 50%MgxSiO 2 48%SiO2 NAKSPCa3(PO4)2 Saturation 0.86LSI - Target Range = -1 to +1 6.15RSI - Target Range = +6 to +7 General Plant Data..... 2,088Make-up, gpm 345Blowdown, gpm 16.345% Sludge, tons/day Chemical Feed Requirement..... 0.00Na2CO3, tons/day (1) 2.90Ca(OH)2, tons/day (1) 0.00MgCl2, tons/day (2) 0.57H2SO4, tons/day 75Coagulant Aide, pounds/day (15 mg/l in cooling tower)62Specialty Chemical, pounds/day Notes..... Refer to Appendix B, softener performance calculations - US Filter Technical1. Data Book, Section 56. Must add an equivalent amount of lime & soda ash for MgCl 2 usage.2. ND = non detectable.3. BOD and COD not quantifiable in the cooling tower.4. Technical Feasibility 3-21 Cooling System Issues Based on the cooling tower chemistry presented in Table 3-9, ammonia is the only water quality parameter of concern in the cooling system. Calcium sulfate and magnesium/silica are well below saturation levels. At six cycles of concentration, the operating TDS of the cooling tower will be 2,400 mg/l. However, because of the presence of ammonia, 90-10 copper nickel should be employed for heat transfer surfaces. Carbon steel can be used for all other components in the cooling system. Copper alloys such as admiralty and brass should be avoided. Chlorine dioxide (ClO2) should be utilized for biological control because it does not react with ammonia (bromination could also be used in the presence of ammonia). Biological control will be critical because of the favorable nutrient characteristics of ammonia. BOD and COD concentrations will be difficult to predict in the cooling tower, because some COD and BOD will be “consumed” by the cooling tower (oxidation via air flow and through biological activity). COD, however, may present a problem for chlorine dioxide consumption, and as stated previously, some of the COD will be consumed. A residual of a 1-mg/l equivalent of free available chlorine should be maintained twice per day for at least two hours per application. This should keep biological growth within control. If blowdown is discharged to state waters, de-chlorination must be employed to remove residual ClO2. Lastly, because of the potential for biological growth, a wide-spaced film fill (low surface area to volume ratio) or traditional packing should be used utilized in the cooling tower. The specialty chemical program should focus on corrosion control to protect carbon steel components. A biodispersant should be considered to prevent biological masses from adhering to cooling tower fill. Operating Costs Based on the chemical consumption rates presented in Table 3-5a, make-up softening should cost $1,735 per day to operate. The reactor clarifiers will generate 16.3 tons per day of sludge (45 percent solids by weight). Equipment amortization costs for the make-up softener should amount to $335 per day (equipment installation costs discussed next). Cooling tower chemicals and reclaimed water should cost $3,411 per day. Because the make-up softener removes a significant amount of the alkalinity entering the cooling tower, sulfuric acid consumption is minimal. Estimates of chlorine dioxide demand should be tripled to account for COD demand and vigorous biological growth. To maintain a residual of 1 mg/l of free available chlorine (OCl-1) in 128,000 gpm of recirculating water for a total of four hours per day requires 1,001 pounds (dry basis) per day of sodium hypochlorite (triple calculated demand). Refer to Table 3- 5b for an operating cost summary for Case Study 3. The make-up softener must receive at least 2 to 3 hours of attention per shift to ensure adequate operation. Technical Feasibility 3-24 Table 3-11 Cooling Water Chemistry - Fresh Water Case (Note 4) 29.73Cycles of Concentration =Inland Plant Side-Stream SoftenerCoolingAcidified EffluentWaterMake-upMake-upUnits 4,8434,5918989mg/lCaCO3Na by Diff 272711mg/lCaCO3K 352604545mg/lCaCO3Ca 808233mg/lCaCO3Mg 0200775mg/lCaCO3HCO3 45000mg/lCaCO3CO3 4000mg/lCaCO3OH 1,9351,7603131mg/lCaCO3Cl 3,0013,00110132mg/lCaCO3SO4 NDNDNDNDmg/lCaCO3NO3 NDNDNDNDmg/lPO4t-PO4 NDNDNDNDmg/lSS 821501616mg/lSiO2SiO2 00NDNDmg/lBB 00NDNDmg/lNNH3 10.07.96.27pH 6,6556,789204221mg/lTDS <310-20<3<3mg/lTSS NDNDmg/lBOD NDNDmg/lCOD Pct of Limit..... 60%CaxSO4 16%MgxSiO 2 100%SiO2 NAKSPCa3(PO4)2 Saturation 0.92LSI - Target Range = -1 to +1 6.02RSI - Target Range = +6 to +7 General Plant Data..... 1,801Make-up, gpm 58Blowdown, gpm 290Side-Stream Softener Feed, gpm 1.745% Sludge, tons/day Chemical Feed Requirement..... 0.47Na2CO3, tons/day (1) 0.41Ca(OH)2, tons/day (1) 0.29MgCl2, tons/day (2) 0.74H2SO4, tons/day 10Coagulant Aide, pounds/day (15 mg/l in cooling tower)63Specialty Chemical, pounds/day Notes..... Refer to Appendix B: Softener performance calculations - US Filter Technical1. Data Book, Section 56. Must add an equivalent amount of lime & soda ash for MgCl 2 usage.2. ND = non detectable.3. BOD and COD not quantifiable in the cooling tower.4. Technical Feasibility 3-25 Operating Costs Based on the chemical consumption rates presented in Table 3-11, side-stream softening should cost $432 per day to operate. Also, refer to Table 3-12 for an operating cost summary. Table 3-12 Base Case - Fresh Water - Inland Plant - Treatment Cost Summary 90% Lime, $/day $64 98% Soda Ash, $/day $151 100% Magnesium Chloride, $/day $75 Coagulant Aide, $/day $31 Specialty Chemical Formulation, $/day $188 Sludge Disposal, $/day $111 Water Treating Chemicals, $/day $620 Softener Amortization Costs, $/day $88 Fresh Water, $/day $3,980 98% Sulfuric Acid, $/day $134 Sodium Hypochlorite, $/day $196 Total Cooling Tower (basic chemicals) $4,310 Total Treating Costs, $/day $5,018 ($193/1000 gallons) The reactor clarifier will generate 1.7 tons per day of sludge (45 percent solids by weight). Equipment amortization costs for the side-stream softener should amount to $103 per day (equipment installation costs discussed next). Cooling tower chemicals and freshwater should cost $4,310 per day. To maintain a residual of 1 mg/l of free available chlorine (OCl-1) in 128,000 gpm of recirculating water for a total of four hours per day requires 559 pounds (dry basis) per day of sodium hypochlorite (1.5 times the calculated demand). The side-stream softener must receive at least 2 to 3 hours of attention per shift to ensure adequate operation. Likewise, the cooling system chemistry should be checked twice per shift to ensure that water quality parameters are within specification. Cooling tower blowdown should be automated (controlled continuously) based on circulating water conductivity (salinity). Equipment Costs Refer to Figure 5-13, Installed Cost vs Capacity, to estimate the costs of the 290 gpm side-stream softener. The softener should cost approximately $400,000 (includes peripheral equipment - chemical silos and feeders and sludge handling and dewatering). Disposal cost scenarios for Central Valley and desert plants follow. Technical Feasibility 3-26 3.7.1.a Central Valley Plant - Disposal Costs Assuming the plant is operated on a water conservation basis, many streams will be routed to the cooling tower, e.g. boiler blowdown, plant wash down ,etc. If we assume that an additional 5 percent of wastewater will be generated that cannot be routed to the cooling tower because of water quality concerns, then plant wastewater generation will be approximately 61 gpm. Based on the adjusted pan data for evaporation of 40 inches per year for the Central Valley (0.49 acres are required for every qpm of wastewater). Therefore, 30 acres of ponds are required to contain and evaporate the plant wastewater. At $350,000 per acre, evaporation ponds would cost $15,500,000. An evaporator will reduce the plant wastewater stream by 90 percent to 6.1 gpm. Also, 54.9 gpm of high-quality distillate would be produced (less 2 mg/l TDS) and could be used for boiler feedwater (a credit of $2.10 per 1,000 gallons of distillate is applied in the cost summary). The evaporator will cost approximately $2,300,000 installed. Refer to Figure 5-13, Installed Cost vs Capacity, to estimate the cost of the evaporator. Power consumption would amount to 7,120 kwh per day (at 90 kwh per 1,000 gallons of product water) for a connected load of 300 kw. Power would cost $576 per day ($6.56 per 1,000 gallons of evaporator feedwater). A 3 acre evaporation pond would be required for evaporator concentrate at a cost of $1,050,000. A crystallizer would eliminate the need for an evaporation pond. A 6.1 gpm crystallizer would cost approximately $600,000 installed. At 200 kwh per 1,000 gallons of product water, power consumption for the crystallizer would be 1,757 kwh per day (75 kw connected load) for a cost of $140 per day ($15.94 per 1,000 gallons of crystallizer feedwater). Summarizing the results of evaluating waste disposal options (refer to Table 3-13), it is clear that an evaporator/evaporation pond or an evaporator/crystallizer will reduce disposal costs. Note, there is practically no cost difference between the evaporator disposal options, so the simpler of the two alternatives was selected. Three-shift operation should be assigned to monitor cooling system chemistry, the side-stream softener, evaporator and crystallizer (if installed as a result of further analysis). A dedicated crew of five operators would be required to oversee the water systems for a daily cost of $997 per day. Technical Feasibility 3-29 Table 3-15 Cooling Water Chemistry - Fresh Water Case (Note 3) 9.38Cycles of Concentration =Coastal Plant CoolingAcidified WaterMake-upMake-upUnits 8358989mg/lCaCO3Na by Diff 911mg/lCaCO3K 4224545mg/lCaCO3Ca 2933mg/lCaCO3Mg 2002175mg/lCaCO3HCO3 000mg/lCaCO3CO3 000mg/lCaCO3OH 2913131mg/lCaCO3Cl 8108632mg/lCaCO3SO4 NDNDNDmg/lCaCO3NO3 NDNDNDmg/lPO4t-PO4 NDNDNDmg/lSS 1501616mg/lSiO2SiO2 0NDNDmg/lBB 0NDNDmg/lNNH3 7.96.67pH 1,947207222mg/lTDS 10-20<1<1mg/lTSS NDNDmg/lBOD NDNDmg/lCOD Pct of Limit..... 26%CaxSO4 6%MgxSiO 2 100%SiO2 NAKSPCa3(PO4)2 Saturation 1.16LSI - Target Range = -1 to +1 5.55RSI - Target Range = +6 to +7 General Plant Data..... 1,948Make-up, gpm 205Blowdown, gpm NA45% Sludge, tons/day Chemical Feed Requirement..... NANa2CO3, tons/day (1) NACa(OH)2, tons/day (1) NAMgCl2, tons/day (2) 0.63H2SO4, tons/day NACoagulant Aide, pounds/day (10 mg/l in cooling tower)25Specialty Chemical, pounds/day Notes..... Refer to Appendix B: Softener performance calculations - US Filter Technical1. Data Book, Section 56. ND = non detectable.2. BOD and COD not quantifiable in the cooling tower.3. Technical Feasibility 3-30 Operating Costs Cooling tower chemicals and freshwater should cost $4,615 per day. To maintain a residual of 1 mg/l of free available chlorine (OCl-1) in 128,000 gpm of recirculating water for a total of four hours per day requires 559 pounds (dry basis) per day of sodium hypochlorite (1.5 times the calculated demand). Refer to Table 3-16 for an operating cost summary. Cooling system chemistry should be checked twice per shift to ensure that water quality parameters are within specification. Cooling tower blowdown should be automated (controlled continuously) based on circulating water conductivity (salinity). Table 3-16 Base Case - Fresh Water - Coastal Plant - Treatment Cost Summary Fresh Water, $/day $4,305 98% Sulfuric Acid, $/day $114 Specialty Chemical Formulation, $/day $74 Sodium Hypochlorite, $/day $196 Total Cooling Tower (basic chemicals) $4,689 ($1.67/1000 gallons) There is no water treatment equipment associated with this scenario. 3.8 Degraded and Fresh Water Comparisons Operating data, treatment equipment requirements, chemical and power consumption, sludge production, dedicated labor and operating and capital costs developed for all the scenarios are summarized in Table 3-17. The rationale for waste treatment selection is discussed in the applicable sections of this report. At the bottom of the table is the daily operating cost which includes consumables, labor and amortization. The unit cost is the daily operating cost divided by cooling tower make-up. The last line of the table is the ratio of daily unit cost for degraded water to fresh water for same scenario, i.e. inland and coastal plants. The summary shows that water costs associated with degraded water are at least 1.5 to 2.5 times the costs associated with fresh water at inland plants and 1.1 to 1.2 times that of fresh water at coastal plants (based on assumed water chemistries, Table 3-1, and the evaluation basis, Table 3-2). These ranges could be broader/narrower depending on the quality of the water source. Generally speaking, the greater the TDS, hardness and silica of the degraded source water, the greater the ratio. Lastly, the higher the TDS, the more sophisticated the materials of construction, e.g. 90-10 copper-nickel at TDS of 35,000 mg/l and titanium at TDS greater than 35,000 mg/l for the main condenser. Also, the presence of ammonia requires copper-nickel metallurgy and non-copper alloys (e.g. no admiralty brass). No costs were identified for these “metallurgical impacts”. As stated previously, only a few reclamation plants are nitrifying their effluent to remove ammonia. Technical Feasibility 3-31 Table 3-17 Comparison Summary - Degraded Water and Frrsh Water (1) Fresh WaterDegraded Water BaseBaseBaseCaseCaseCase Case 3Case 2Case 1Study 3Study 2Study 1 ReclaimedAgricultureProduced WaterReturnWater CoastDesertCentral ValleyCoastDesertCentral Valley Operating Data..... 9.429.729.76.010.310.3Cycles of Concentraton NANANA2,0889641,928Degraded Water, gpm 1,9481,8011,801NA964NAFresh Water, gpm 2055858345185185Blowdown, gpm Copper AlloyCopper AlloyCopper Alloy90-10 Cu NiTitanium90-10 Cu NiHeat Exchanger Metal Treatment Equipment..... NANANA2,0881,928NAMake-up Softener, gpm NA290290NA5063,008Side-Stream Softener, gpm NA6161NA195194Evaporator, gpm NANANANANA19.5Crystallizer, gpm NA2.03.0NA6.4NAEvaporation Pond, acres Chemical Consumption..... NA0.470.47014.074.6398% Soda Ash, tons/day NA0.410.412.905.111.7790% Lime, tons/day NA0.290.29002.54Magnesium Chloride, tons/day (2) NA10107588108Coagulant Aide, pounds/day 0.630.740.740.57010.3798% Sulfuric Acid, tons/day NANANA1,001NA1,001Chlorine Dioxide, pounds/day (2) 559559559NA1,117NASodium Hypochlorite, pounds/day (2) 25636362124575Specialty Chemicals, pounds/day (2) Other Operating Variables..... NA1.71.716.355.019.0Sludge, tons/day (Note 5)7,2007,200(Note 5)22,56028,200Power, kwh/day (Note 5)300300(Note 5)9401,175Connected Load, kw Operating Costs..... NANANA$2,307$213$426Degraded Water, $/day $4,305$3,980$3,980NA$2,130NAFresh Water, $/day $310$950$950$3,025$9,181$8,567Treatment Chemicals, $/day (5) (Note 4)$576$576(Note 4)$1,804$2,258Power, $/day NA-$168-$168NA-$528-$587Demineralized Water Credit, $/day NA$997$997NA$997$997Dedicated labor, $/day $4,615$6,335$6,335$5,332$13,797$11,661Total Operating Cost, $/day Equipment Cost..... NA$400,000$400,000$1,300,000$1,900,000$1,600,000Water Treating Equipment NA$3,000,000$3,400,000NA$6,700,000$5,600,000Disposal Equipment NA$3,400,000$3,800,000$1,300,000$8,600,000$7,200,000Total Equipment NA$751$839$287$1,899$1,590Amortization, $/day $4,615$7,086$7,174$5,619$15,696$13,251Total Daily Cost $1.65$2.73$2.77$1.87$5.65$4.77Daily Unit Cost, $/1,000 gallons (6) 1.142.071.73Cost Ratio - Degraded:Fresh Notes..... 500 MW combined cycle plant.1. 100% basis.2. Refer to Table 3-2 for unit cost assumptions.3. Minimal power requirement for water treatment and disposal - not calculated.4. Includes sludge disposal.5. Daily unit cost - operating cost per 1000 gallons of cooling tower make-up.6.