### i Arnold Schwarzenegger Governor 

# Performance, Cost and Environmental Effects of Salt Water Cooling Towers

Prepared For: 

## California Energy Commission Public Interest Energy Research Program

Prepared By: John S. Maulbetsch, Consultant Michael N. DiFilippo, ConsultantPIERFINALPROJECTREPORT

June, 2007 CEC-500-2007-XXX

### ii

### iii 

## Table of Contents

Preface ii Abstract v Executive Summary 1 1. Introduction 1.1 Motivation 1.2 Objective and scope 1.3 Organization of report 2. Cooling System Basics 2.1 Closed-cycle wet cooling systems 2.2 Mass and heat balances 2.2.1 Evaporation rate 2.2.2 Blowdown rate 2.3 Effect of water properties 3. Cooling Tower Performance 3.1 Effect of salinity on cooling tower performance 3.2 Seawater correction factor 3.3 Rules of thumb 3.4 Calculated capability with saline water make-up 4. Experience with Salt Water Towers 4.1 High salinity operation 4.2 Existing installations 4.3 Environmental effects 4.3.1 Blowdown 4.3.2 Drift 4.3.3 Baseline determinations 4.3.4 Cooling tower emissions impacts 4.3.5 Environmental studies 4.4 Operating experience 5. Salt Water Cooling System Costs 5.1 General cost factors 5.2 Case study 6. Summary and Conclusions 6.1 Effect on cooling tower thermal performance 6.2 Effect on cooling system cost 6.3 Effect on environmental impact 6.4 Effect on operation and maintenance Appendices

### iv

A Properties of Sea Water B Derivation of Cooling Tower Performance Characteristics C Site Visit Reports

### v 

## List of Figures 2-1 Schematic of closed-cycle wet cooling system 2-2 Closed-cycle wet cooling system mass and heat balance 3-1 Salt water correction factor 3-2 Effect of salinity on correction curves



## List of Tables 3-1 Base (fresh water) case study results 3-2 Comparative performance---fresh vs. salt water make-up 4-1 Salt water tower installations 5-1 Tower design configurations 5-2 Cost impact of thermal performance variation 5-3 Tower cost comparisons 5-4 Cooling system component cost comparisons

### vi 

## Abstract

This report contains information on the design, use, cost, operation and environmental effects of salt and brackish water cooling towers in comparison to fresh water towers as theya re used for power plant cooling. The topics covered are



### − a listing of salt water tower installations in the US and abroad

− an analysis of performance and cost differences between fresh and salt water towers

− a review of operating and maintenance experience on a few operating salt water towers at US power plants

− 

### a review of environmental effects at sites with operating salt water towers. The use of high salinity make-up water typically imposes a 4 to 8% performance penalty and a 35 to 50% cost penalty in comparison to fresh water towers of comparable cooling capability. Environmental effects of particular pertinence to salt /brackish water tower are primarily related to drift emissions and there largely confined to the near-field effects on plant buildings and equipment. Keywords: Salt water cooling towers Brackish water cooling towers Recirculating wet cooling Cooling tower drift Cooling tower performance Environmental effects of cooling towers

### 7 

## Executive Summary

### 8 

# 1
Introduction

1.1 Motivation The California Energy Commission (CEC) is increasingly interested in the use of high salinity water as make-up to power plant cooling towers for two reasons. First, the growing demands for both electricity and water in the State have created pressure to consider the use of non-fresh water for power plant cooling at new and existing plants designed for and operating with closed-cycle cooling. Second, there is beginning to be discussion of requiring some coastal plants, currently operating with once-through cooling using ocean water, to convert to closed-cycle cooling, presumably using ocean water as make-up. Potential issues associated with the choice of saline make-up include effects on tower thermal performance and on the choice of materials of construction, both of which may affect the cost of the tower. In addition, operating and maintenance (O&M) problems may arise as well as potentially exacerbated environmental problems particularly from the salinity of the drift. In light of this, the CEC wishes to obtain a better understanding of the effects on cost, performance, O&M requirements and environmental impacts encountered in the use of salt water cooling towers for power plant cooling. 1.2 Objective and Scope The objective of this study is provide information on the design, use, and operation of salt water cooling towers which will assist the CEC in evaluating alternative cooling systems for power projects in California. The study consists of five tasks.

− A survey of salt water tower installations in the US and abroad

− An analysis of performance and cost differences between fresh and salt water towers

− A review of operating and maintenance experience on a few existing salt water towers at US power plants

− A review of environmental effects at sites with operating salt water towers

− The preparation of a summary report on the results of the study

### 9

1.3 Organization of Report The remaining sections of the report are organized as follows. Section 2 provides a brief review of cooling tower design, operation and nomenclature for convenience of reference. Section 3 analyzes performance differences between cooling towers using high salinity make-up water and those using fresh water. Some simple rules of thumb from the existing literature are presented and evaluated. Some example calculations are presented for conditions relevant to California. Section 4 provides a list of seawater and brackish water cooling towers in operation in the US and abroad and summarizes the experience that some power plants have had with salt water cooling towers both in operation and maintenance and in environmental effects. Section 5 presents the effect of using high salinity water in cooling tower on cooling system cost. Finally, Section 6 summarizes the conclusions of the study. Three appendices contain properties of seawater (Appendix A), a derivation of the performance characteristics for wet cooling towers (Appendix B) and detailed reports on site visits and interviews with plants at which seawater or brackish water towers are currently in operation. A brief Executive Summary is provided at the beginning of the report.

### 10 

# 2 Cooling System Basics

2.1 Closed-cycle Wet Cooling System Closed-cycle, or re-circulated, wet cooling systems are usually the cooling system of choice for modern thermal power plants. The system, as shown schematically in Figure2-1, consists of two major components. These are the steam condenser, usually a shelland-tube surface condenser and a wet cooling tower, usually a mechanical-draft tower (recently more commonly of the counter-flow type, although the schematic shows a cross-flow configuration).

Figure 2-1: Closed-cycle wet cooling system (Mitchell, Robert D., 1989)



### Steam from the low pressure turbine exhaust flows into the condenser, where it is condensed on the outer surface of tubes with cooling water running through them. The condensed liquid is returned to the boiler to complete the power cycle.

### 11

The warmed cooling water leaving the condenser is sent to the cooling tower where it iscooled by heat rejection to the atmosphere, primarily by evaporation, and then recirculated to the condenser inlet. Figure 2-2 identifies the quantities involved in the cooling and water use processes and defines the important nomenclature.



## Figure 2-2: Closed-cycle cooling system mass and heat balance

The hot water from the condenser is introduced at the top of the tower and flows down through a “fill” section where it is brought into intimate contact with ambient air flowing counter to the direction of the falling water flow. Both sensible and latent heat transfer to the air cools the bulk of the water, which is then collected in a basin and returned to the condenser. The air leaves the tower, heated and humidified as an essentially saturated exhaust plume. The cooling is achieved by the evaporation of a small fraction (1 to 2%) of the recirculating water flow. Therefore, once the system is filled, the only water withdrawn from the environment is makeup water in amounts sufficient to replace that lost to evaporation, blowdown, 1 

### and drift. 2

1 Blowdown is water discharged from the cooling system in order to control the buildup of dissolved and suspended materials that concentrate in the system as a result of the evaporation. CONDENSER WET COOLING TOWER W circ
. (lbm/hr)

Condensate return Steam
W st (lbm/hr) Hot water temp T h (oF)

Cold water temp T c (oF) Make-up

w m u (lbm/hr) Blowdown w bd (lbm/hr) Inlet air w air (lbm/hr) T w b (oF) Plume w evap (lbm/hr)

w drift (lbm/hr)

p b (in Hg a ) T cond (oF)

### 12

2.2 Mass and Heat Balances The elements of complete mass and heat balances are shown in Figure 2-2. The water balance on the cooling tower is given by
w mu

### = w evap

### + wbd 

### + w d 

### (Eq. 2.1) The drift rate, w d 

### , is typically less than 0.002% of the circulating water rate (now usually specified at 0.0005% or less) as compared to the evaporation rate of 1 to 2% and the blowdown rate of 0.1 to 1%. Therefore, the drift rate is neglected in the following calculations. 2.2.1 Evaporation Rate The rate of evaporation of water from the tower is related to the heat load on the tower, Q tower 

### , which is equal to the heat load on the condenser, Q cond 

### , given by Q tower 

### = Q cond 

### = w circ *

### c p *

### (T h



### – T c 

### ) (Eq. 2.2) with the evaporation rate given by

w evap

### = Q tower *

### f

latent 

### /h fg 

### (Eq. 2.3) where h fg 

### = latent heat of vaporization (Btu/lbm); ~1000 Btu/lbm f latent 

### = fraction of total heat rejected by latent heat transfer (0.9 is used here. It can be lower depending on ambient conditions and design choice) For an older steam plant, as might be considered for retro-fit to closed-cycle cooling, a typical plant efficiency might be 35%. Of the 65% waste heat, perhaps 15% would be dissipated in the stack gases and 50% in the condenser cooling water. The heat duty for the cooling system would be approximately 5,000,000 Btu/hour per MW of electricpower generated. The values would differ slightly for the steam portion of combinedcycle plants, but these will be used for illustrative purposes. Therefore, the cooling system heat duty per MW Q tower 

### = 5 x 10 6 

### Btu/hr per MW (Eq. 2-4)

w evap

### = 5 x 10 6 

### x 0.9/1000 = 4,500 lbm/hr per MW or (Eq.2-4a)

w evap

### ~ 10 gpm/MW (Eq.2-4b)

2.2.2 Blowdown Rate Blowdown rates are set to control scaling, fouling, and corrosion by limiting the buildup of impurities in the circulating water. This criterion is normally expressed in terms of maximum allowable cycles of concentration (n), defined as the ratio of the concentration of conserved species in the circulating water (C i circ 

### ) to that in the makeup water (C i mu 

### ):

2 Drift refers to liquid water droplets entrained in the tower exit plume and released to the atmosphere.

### 13 n = C i circ

### /C i mu



### (Eq. 2-5) The mass balance of species i in the tower requires that

w mu 

### × C i mu 

### = wbd 

### × C i circ 

### (Eq. 2-6)

w bd 

### = (w evap 

### + wbd 

### ) × (C i mu 

### /C i circ 

### ) = (w evap 

### + wbd 

### ) x 1/n (Eq. 2-7) Therefore,
w bd

### = w evap

### / (n

± 1) (Eq. 2-8) Typical allowable cycles of concentration are from 3 to 6 (DiFilippo, M., 2003). For n = 5 as a typical value, the required blowdown is

w bd

### = [1/(5

±

1)] × wevap

### = 2.5 gpm/MWe (Eq. 2-9) and the required make-up is
w mu

### = w evap

### + wbd

### = 12.5 gpm/MWe (Eq. 2-10) Additionally, typical, consistent values of tower operating conditions are Circulating water flow rate, w circ 

### : ~ 500 gpm/MWe Condenser terminal temperature difference (TTD), T cond 

### – T h 

### : 6 to 8oF Tower range, T h 

### – T c 

### : 20 to 24oF Tower approach, T c

### - T amb. wet bulb 

### : 8 to 12oF Therefore, the achievable steam condensing temperature is given by

T cond 

### = T amb. wet bulb 

### + Approach + Range + TTD (Eq. 2-11) For an ambient wet bulb temperature of 70oF, values in the typical ranges of TTD = 7oF, Range = 22 oF, and Approach = 10 oF would provide a condensing temperature of 109oF, corresponding to a turbine back pressure of 2.5 in. Hga. Tower approach temperature depends on design ambient conditions as well as many other factors including tower type, size, fill choice, and air flow. In general, warmer, more humid conditions lead to lower approach temperatures, as in the southeastern U.S. and cooler, drier climates lead to higher ones, as in the northern and western regions. 2.3 Effect of water properties The properties of high salinity water differ from those of fresh water and those differences lead to slightly altered cooling tower perforamnce. For purposes of this report, high salinity water refers to seawater, concentrated sea water and to lower salinity or brackish waters found in bays or estuaries or as groundwater. The chemical composition of “normal seawater” is given in Table A-1 of Appendix A. Other tables in the Appendix provide values of several thermo-physical properties important to the performance of cooling towers for seawater of doubled concentration and of fresh water. (Office of Saline Water, 1959)

### 14

The derivation in Appendix B provides an fundamental discussion to aid in the understanding of the effect of these property differences on tower performance. The effects of specific properties are summarized here. 

# Vapor pressure The presence of salts in water reduces the vapor pressure at any given temperature as seen in Figure A-2a and A-2b in Appendix A. This reduces the driving force for evaporation and, in effect, lowers the “enthalpy of saturated air at the local water temperature” which lowers the driving force. Therefore, a higher KaV/L will be required to transfer the same amount of heat. 

# Surface tension The surface tension for seawater is somewhat higher than for fresh water. (Figure A-3; Appendix A) This tends to facilitate the breakup of the film, create smaller droplets and slightly increase the interfacial area per unit of fill volume, a. This would slightly enhance the performance with seawater compared to fresh water. The performance of drift eliminators is also dependent on surface tension. In general, a reduced surface tension will degrade the performance of drift eliminators. 

# Dynamic viscosity The dynamic viscosity of seawater is slightly higher than for freshwater (Figure A-4; Appendix A). This may result in slightly thicker films on the fill and a minor reduction in performance compared to fresh water. 

# Thermal conductivity

The thermal conductivity of seawater is lower than that of fresh water for the temperature range of relevance to cooling tower operation (Figure A-5 Appendix A). This may result in a lightly higher temperature drop through the liquid films which has been assumed to be zero in the Merkel analysis. Therefore, a slight decrease in performance might result. 

# Density and specific heat At a given temperature, the density of seawater is about 2 to 3% greater than fresh water, while the specific heat is about 4% less. (Figures A-6 and A-7; Appendix A). Therefore, a given volume of seawater has slightly less cooling capacity than fresh water. For a given heat load, either the water flow or the range must be increased somewhat for a salt water tower. These effects are all minor compared to the effect of vapor pressure.

### 15

Section 3 will provide the results of some tests, analyses and resulting rules of thumb for adjusting the rating of freshwater cooling towers to account for the use of salt water as the cooling medium.

Reference List 1. DiFilippo, M., Use of Degraded Water Sources as Cooling Water in Power Plants, EPRI and California Energy Commission, 1005359; 2003 2. Mitchell, Robert D., Survey of Water-Conserving Heat Rejection Systems, EPRI, EPRI GS-6252; 1989 3. Office of Saline Water, "Normal" Seawater Chemistry, U. S. Department of the Interior, 1959

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# 3 Cooling Tower Performance
Effect of salinity on cooling tower performance The thermal performance of a cooling tower on salt or brackish water will differ from that of an identical tower under identical conditions cooling fresh water. As was discussed in detail in Section 2, this results from variations in the thermodynamic and transport properties of salt water as a function of salinity. Of these, the most important is vapor pressure. The following paragraphs review several approaches to accounting for the effect of salinity on cooling tower performance. These include a simple correction factor and some simple “rules of thumb” for adjusting the design specifications. 

# Seawater correction factor A thorough discussion of the effect of salt water on cooling tower performance was presented in a 1991 Marley publication. (Ting, Bing-Yuan and D. M. Suptic, 1991) The approach recommended is to rate the cooling tower as if it were on fresh water and then to apply a correction factor. Figure 6 of that reference is reproduced here as Figure 3-1 (with an estimated curve for a salinity of 50,000 ppm added) The correction factor is plotted against L/G for a water salinity of level of two times seawater. The factor varies from 7% at an L/G = 1 to just under 2.5% at an L/G = 5.5. The reason for the decrease in the effect of salinity with increasing L/G can be seen by reference to Figure B-4 in Appendix B. Towers for a given range and wet bulb temperature designed for high L/G’s have much lower KaV/L and operate at much higher approach temperatures. The magnitude of the driving force, (h sat @ Tw 

### – h air 

### ), is correspondingly larger and the effect of a given decrease on the vapor pressure at the water surface, h sat @ Tw, 

### is also correspondingly less. 

# Rules of thumb Some rules of thumb have been put forward by the industry to estimate the reduction in cooling tower capability (or alternatively, the increased tower size required to meet the same heating load) incurred with salt water operation.

### 17

The simplest of these (Aull, R., 2005) suggests a 5% capability reduction for a salinity of 50,000 TDS. Similar estimates (Eftekharzadeh, S., M. Baasiri, and P. Lindahl, 2003) suggest a performance loss of 5.4% at a salinity of 50,000 TDS. Reference is made in that publication to a Fluor (Fluor R/D Division, 1957) paper which recommends increasing the design wet bulb by 0.055 C (~ 0.1 F) for each 4,000 ppm of dissolved solids. For sea water operating at 1.2 to 2. cycles of concentration, this corresponds to an increase in the design wet bulb of 0.55 to 1.1 C ( ~ 1. to 2. F).

Figure 3-1: Salt Water Correction Factor (from (Ting, Bing-Yuan and D. M. Suptic, 1991) 

### Figure 3-1 gives the recommended correction for a 2x seawater salinity or approximately 70,000 ppm. Assuming a linear correction factor adjustment with salinity, the corresponding line for 50,000 ppm would give a correction factor between 1.05 and 1.054 at approximately an L/G = 1 which seems appropriate for the conditions of interest to the study. (Eftekharzadeh, S., M. Baasiri, and P. Lindahl, 2003) Finally, using the rule of thumb suggested in the Fluor reference (Fluor R/D Division, 1957) of increasing the wet bulb temperature by 0.1 F for each 4,000 ppm of dissolved solids, assume a 1.25 F increase for a TDS of 50,000 ppm. 

# Calculated capability with saline water make-up Salt Water Correction Factor (from Ting and Suptic)

CF = 0.0016(L/G) 2 - 0.021(L/G) + 1.0894

1.020 1.030 1.040 1.050 1.060 1.070 1.080

0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 L/GCorrection Factor 2x Seawater

### 18

The CTI Workbook (CTI, 2005) was used to calculate the capability correction implied by the recommendation to increase the wet bulb temperature by 0.1 F for each 4,000 ppm increase in circulating water salinity. The calculation proceeds as follows. For a base (fresh water) case with design specifications of Wet Bulb Temperature: 75 F

Cold Water Temperature: 90 F Hot Water Temperature: 120 F

the CTI Workbook, gives the following KaV/L’s and the corresponding fill coefficient, C, for a range of L/G, as displayed in Table 3.1.

L/G KaV/L C

(n = -.7) 0.6 1.005 0.703 0.8 1.079 0.923 1 1.168 1.168 1.5 1.500 1.992 2 2.233 3.628 Table 3-1: Base (fresh water) case results


### The fill is assumed to have a characteristic of KaV/L = C * (L/G) -0.7 

### (Eq. 3-1) The same computation is the performed for § an assumed wet bulb temperature of 76.25 F (increased by 1.25 F per recommendation) § the same fill characteristics. The L/G at which the same cold water temperature can be obtained is determined and compared to the fresh water values in Table 3-1. The ratio of {(L/G) salt 

### /(L/G) fresh 

### } is the corresponding capability correction factor. This approach neglects the minor affects of variation in all thermo-physical properties with salinity and attempts to simulate the effect of the reduced vapor pressure with an increased wet bulb temperature. The results are tabulated in Table 3-2 and plotted on the same coordinates as Figure 3-1 for comparison to the published correction factor and show reasonable agreement. This suggests that for the usual range of circulating water salinities, operating temperature ranges and design points, the correction curve and the recommended elevation of the wet bulb temperature are consistent.

### 19 L/G (Fresh) C L/G (Saline) Ratio L/G 0.6 0.671 0.57 1.053 0.8 0.88 0.7625 1.049 1 1.11025 0.955 1.047 1.5 1.8725 1.442 1.040 2 3.32 1.936 1.033 

## Table 3-2: Comparative performance---fresh vs. salt water make-up

Figure 3-2: Effect of salinity on correction curve

Therefore, on the bases of literature recommendations and a simple computational correction, a capability reduction of approximately 5% appears to be reasonable for typical conditions. This additional capability can be provided in a variety of ways including § increased cell plan area (width or length) § additional cell or cells § increased air flow (fan power) the effect on design, materials selection and cost will be presented in Section 5. 

### Reference List 1. Aull, R., Personal Communication, 2005 Salt Water Correction Factor

1.010 1.020 1.030 1.040 1.050 1.060 1.070 1.080

0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 L/GCorrection Factor 2x Seawater 50,000 ppm CTI Calculations for 50,000 ppm

from Ting and Suptic

Linear correction from 2x seawater curve

### 20

2. CTI, CTI ToolKit, Version 3.0b, Cooling Technology Institute, 2005 3. Eftekharzadeh, S., M. Baasiri, and P. Lindahl, Feasibility of Seawater Cooling Towers for Large-Scale Petrochemical Development, Cooling Technology Institute, TP03-17; 2003 4. Fluor R/D Division, Impact of Salinity on Corrosion, Fluor Corporation, 1957 5. Ting, Bing-Yuan and D. M. Suptic, The Use of Cooling Towers for Salt Water Heat Rejection, The Marley Cooling Tower Company, 1991

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# 4 Experience with Salt Water Towers

4.1 High salinity operation The use of cooling towers on high salinity make-up water is not new. There are may such installations in the U.S. and abroad, at both power plants and industrial facilities. The make-up waters range from seawater with a nominal salinity of around 35,000 ppm (mg/kg) (See Table A-1 in Appendix A) to brackish waters with salinities ranging from a few hundred (or a few thousand) ppm in the case of groundwater or from a few thousand ppm to nearly full seawater concentration in the case of bays or estuaries. Here the salinity can vary significantly on a time-scale ranging from seasonal to hourly under the influence of rainfall, storms and tides. The salinity of the circulating water in the cooling system is that of the make-up water times the cycles of concentration, which is controlled by the rate of blowdown from the system. (See Eq. 2-5) Typically towers with high salinity make-up (approaching seawater salt content) are operated at low cycles of concentration in the range of x 1.5 to x 2. In the case of seawater this results in a circulating water concentration of 50,000 to 70,000 ppm. While there have been some examples of operating a tower at 100,000 ppm, this is rare. Some inland towers, operating on limited supplies of brackish groundwater or reclaimed water of perhaps 500 to 2,000 ppm at 5 to 10 cycles of concentration to conserve water and reduce the cost of evaporation or crystallization of the blowdown results in circulating water concentrations of 25,000 to 50,000 ppm. 4.2 Existing installations The following table (Table 4-1) gives examples of existing towers operating on salt or brackish water. The list is not complete but is based on information from two major tower vendors (GEA and SPX-Marley) plus a variety of other sources and personal contacts. The table attempts to provide information on tower size, operating point, materials of construction and source water. In many instances, this information was not available or easily obtained. The essential message from the accumulated information, however, is that towers of a wide range of size, application, materials of construction and make-up water quality have designed, installed and operated for several decades.

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Table 4-1: Salt Water Tower Installations

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Table 4-1: Salt Water Tower Installations (cont.)

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Table 4-1: Salt Water Tower Installations (cont.)

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4.3 Environmental Effects All closed cycle wet cooling systems with cooling towers have some environmental effects. Those normally considered are § Blowdown § Drift § Noise § Visible plumes Of these, noise and visible plumes from salt/brackish water towers are no different from those from fresh water towers. As such, they will not be discussed further in this study. The effects from blowdown and drift differ from those from fresh water towers to the extent that the salinity of the circulating water is higher. 4.3.1 Blowdown The environmental issues related to the discharge or treatment of blowdown from salt or brackish water cooling towers appears to differ little from those for fresh water towers. However, it should be noted that discharge options are limited.

i. High salinity (50,000 to 70,000 ppm) cannot be discharge to municipal water treatment facilities. ii. Treatment, volume reduction or on-site disposal of the blowdown steam would be prohibitively expensive. For towers operating on seawater make-up at 2 cycles of concentration, the blowdown rates are very high on the order of 10 gpm per MW or 5,000 gpm for a 500 MW steam plant. The cost of evaporation ponds, even if the plant were located in an area with a high net annual evaporation rate, would be extremely high of the order of a few hundred million dollars. The cost of evaporator/crystallizer systems, frequently used on zero-discharge plants but at far lower input rates, would be equally unacceptable. iii. For plants discharging to the Nation’s waterways under an NPDES permit, the stringency of the rules can vary from state to state and from site to site. For ocean discharges, at least under the California Ocean Plan, the increased levels of dissolved solids do not appear to be regulated with the exception of those specified toxic species of arsenic, copper, mercury, silver and zinc. For power plants (and other high volume discharges) limitations on both effluent concentrations and total mass discharges are imposed according to procedures and formulas documented in the Plan. A comparison with ocean desalination plants may be illuminating. Typical values for desalination plant capacity range from 20 to 112,000 acre-feet per year and “recovery” (defined as gallons of fresh water per gallon of seawater) from 15 to 50% depending on the technology used. Assuming a plant size of 100,000 acre-feet per year (~90 million gallons per day) and a recovery rate of 50%, the desalination plant would have a discharge stream with a salt concentration of 70,000 ppm and a flow rate of about 620,000 gpm. (California Coastal Commission, 1993)This would be roughly equivalent to the blowdown from seawater cooling towers operating at two cycles of concentration at twelve 500 MW power plants operating at 2 cycles of concentration. 4.3.2 Drift Elevated salinity in the circulating water could effect drift emissions and their subsequent environmental effects in two ways. First, if the modified properties of the water affected the performance of the drift eliminators themselves, the amount of drift emitted could change. However, inquiries with a manufacturer of drift eliminators

### 26

revealed that “there should be no difference in the efficiency of drift eliminators, since the drift capture efficiency of a drift eliminator section is a function of droplet size, air velocity and workmanship of installation”.....” as long as the salt water concentration does not lower the water's surface tension significantly”. Reference to Appendix A-5 indicates that the surface tension is slightly higher than for fresh water, so for the same drift eliminators and the same quality of installation workmanship, the drift emissions should be unchanged. Second, the drift droplets have a higher salinity so the mass emission of salt increases while the emission of the drift itself remains unchanged. This introduces two concerns. First, the amount of fine particulate matter (PM 10and PM 2.5 ) 3 released into the atmosphere as the drift droplets evaporate will increase. Second, the mass deposition of salt on neighboring soils, vegetation, buildings, vehicles and equipment will be higher than for fresh water towers. The effect of near-field salt drift on equipment on the plant site will be discussed in the following section. 4.3.2.1 PM 10 emissions Cooling tower drift is often discussed in the context of PM 10 emissions. National ambient air quality standards (NAAQS) limit PM 10 concentrations to an annual arithmetic mean of 50 ȝ g/m 3 (or 150 ȝ g/m 3 in any 24 hour period). (Environmental Protection Agency, 2006) In order to maintain these levels emissions limits are placed on point sources; in this case, 100 tons per year. The agency has defined an “emissions factor” for cooling tower drift emissions of 1.7 lb/10 3 gallons of recirculating water flow. This is based on the assumption that cooling tower drift eliminators limit drift to 0.02% of the recirculating water flow rate. It is further assumed that all of the drift evaporates in the atmosphere and that allthe dissolved and suspended matter in the drift is released as PM 10 . The simple application of this factor and that assumption to a wet cooling tower with seawater make-up operating at 1.5 cycles of concentration (drift salinity of 52,500 ppm) and a circulating water flow of 250,000 gpm (typical for a 500 MW steam plant) gives an emission rate for PM 10 of approximately 4,700 tons per year for an 80% capacity factor. However, these assumptions have been challenged as unrealistically conservative in several analyses. (Micheletti, Wayne, 2006;Reisman, J. and G. Frisbie, 2002)Even the EPA has characterized them as “conservatively high”. (USEPA, 1995) Specifically,

i. Modern drift eliminators have drift rates of 0.002% to 0.0005%, a factor of x10 to x40 lower than the 0.002% assumed in the Agency’s “emission factor”; ii. Calculations based on accepted drift drop size spectrum data (as for example in Figure 4-1) and plausible assumptions about the density and shape of the particles remaining following evaporation of the drift droplets suggest that only a small fraction (less than 15%) of the residual particles will have an aerodynamic diameter of less than 10 ȝ . (Micheletti, Wayne, 2006)

3 Particles with a mean aerodynamic diameter less than or equal to 10 (or 2.5) microns

### 27

Figure 4-1: Drift droplet size spectrum (from (Micheletti, Wayne, 2006))
Using a value of 0.002% and a 15% PM 10fraction, the calculated PM 10 emission rate for the 250,000 gpm seawater tower is reduced to 70 tons per year. It should be recognized that these assumptions and resulting calculations are uncertain. Drift rates are a function of the quality of installation and state of repair of drift eliminators and can be higher in practice than they are under ideal conditions. In addition, the drop size spectrum can change with different drift eliminator designs and with age and condition. Additionally, some fraction of the drift will inevitably hit the ground or surrounding structures and the dissolved material in those drops will not be released into the atmosphere. Only careful on-site measurements can give a credible estimate of the PM 10emission rates from any cooling tower. 4.3.2.2 Salt deposition The assessment of the impact of emissions from evaporative cooling systems must be done with an understanding of the background conditions which exist at the site. For instance, in the case of a coastal power plant, while cooling tower drift emissions will contribute to the ambient salt levels (i.e. deposition and concentration), there is already natural salt in the atmosphere. It is also likely that native vegetation has adapted to this environment and is more salt tolerant than natural species which are further inland. Further, the presence of sea salt in the air may already be having some local effects on the surrounding community, in the form of generalized corrosion or other effects. Studies of ambient or baseline conditions associated with prospective cooling system operation and impacts have been conducted in a number of situations. Some of these are cited in the table below.

### 28 Utility Site Proposed Cooling System Atlantic City Electric B. L. England – Coal-Fired, NJ (Wilber, K. R., 1975) Natural Draft - Brackish Water General Public Utilities Forked River Nuclear, NJ (Shofner, F. M. et al. , 1973) Natural Draft – Brackish Water Potomac Electric Chalk Point – Coal-Fired, MD (Davis, E. A., 1979) Natural Draft – Brackish Water Pacific Gas & Electric Geysers Geothermal, CA (PG&E, 1979) Mechanical Draft – Boron and Salts Oak Ridge National Laboratories K-25 Gaseous Diffusion Plant, TN Mechanical Draft - Chromates Pacific Gas & Electric Pittsburg – Oil Fired, CA Mechanical Draft – Brackish Water Florida Power Corp. Turkey Point Nuclear, FL Spray Systems, Mechanical Draft – Sea Water Table 4-??: Example Cooling Tower Environmental Impact Assessments Beyond, cooling-system specific studies, a number of atmospheric or background assessments have been conducted for the purpose of better understanding issues such as formation and role of condensation nuclei, impacts on visibility, assessment of corrosion issues, etc. (Porter, et al. , 2000; Wilber, K. R., 1974; Woodcock, A. H., 1952; Woodcock, A. H., 1953; Boyce, S. G., 1954;Rossnecht, G. F. et al. , 1973) Many, but not all of the studies have focused on coastal environments, where naturally occurring salt is produced from wind and wave action. 4.3.2.3 Cooling Tower Emissions Impacts Given these levels of naturally-occurring salts in coastal environments, it is important to document, on a site-specific basis, these background levels and contrast them against expected contributions from cooling systems. Background characterization would include:

§ ambient concentration and deposition of salts that are expected in the cooling tower circulating waters, § concurrent wind speed, wind direction and humidity history (Note that humidity is important relative to the size and fate of hydroscopic aerosols like sea salts and resultant condensation nuclei.) Cooling tower operating profiles (continuous, intermittent, etc.) and cooling tower emissions (droplet size, drift emissions rate, etc.) determined from source term measurements can be made. Published studies indicate that background salt concentrations vary considerably from, for example, 100 μg/m 3 with horizontal mass fluxes ranging from 500-1000 μg m -2 sec -1 in the Hawaiian Islands (Porter, et al. , 2000)to ambient salt concentration in near coastal environments in the southeastern United States of 2- 50 μg/m 3 [5]. Those measurements were conducted under lighter winds (2-4 m/s) and shorter fetches than typically occur around the Hawaii Islands These values are contrasted against vertical fluxes (i.e. deposition rates) of salts modeled from mechanical draft cooling towers of 50-500 μg m -2 sec -1 within 100 meters of the source. (Wilber, K. R. and R. O. Webb, 1983) Therefore, it is seen that drift from cooling systems can be more or less significant depending on background circumstances. 4.3.2.4 Environmental effects A number of environmental effects studies have been conducted by comparing deposition rates on surrounding land before and after the installation and operation of salt or brackish water cooling towers.

### 29

Appendix B-1, which documents the site visit to St. Johns River Power Park, contains a brief description of the results of pre- and post-operation field monitoring of deposition and uptake at plots in the vicinity of the towers. The conclusions, summarized there, are repeated here. ” The conclusions, documented in detail in permitting reports are summarized as follows :

− Some increased NaCl concentration was found in deposition samples after Unit #2 began operation.

− No significant increases were seen in soil or vegetation samples.

− Vegetation at the site with highest deposition was apparently unaffected.



### − No injury symptoms related to NaCl were observed on pasture grass or other vegetation on or in the vicinity of the Power Park.” These results are consistent with those reported elsewhere in numerous studies. The most extensive study was the Chalk Point Cooling Tower Project conducted in the late 1070’s by the Maryland Power Plant Research Program. (Davis, E. A., 1979)The results, summarized in both (EPA, 2000) and (Eftekharzadeh, S., M. Baasiri, and P. Lindahl, 2003), found “no measurable increase in soil salts concentration in the tobacco fields near the facility” and no instances [including Chalk Point] where cooling tower operation has resulted in measurable productivity losses in agricultural crops or measurable damage to ornamental vegetation.”

4.4 Operating Experience Information on performance and on operating and maintenance experience was solicited through visits and telephone interviews with the staff of plants equipped with seawater or brackish water towers. These included: Plants visited § St. Johns River Power Park, Jacksonville, FL § Plant Smith, Lynn Haven, FL § Plant Crist, Pensacola, FL § Plant Watson, Gulfport, MS Telephone interviews

§ Pittsburg Power Plant, Pittsburg, CA § Palo Verde Nuclear Generating Station, Palo Verde, AZ § GEA Integrated Cooling Technologies, Lakewood, CO Complete visit and interview reports are found in Appendix B. The major conclusions are summarized below. 1. Recent installations of mechanical cooling towers have used fiberglass reinforced plastic (FRP) structure, PVC fill and corrosion-resistant fittings (high grade stainless steel, silicon bronze (coated), titanium). Operating experience has been excellent but long term (> 15 years) is lacking. 2. Nearly all plants with high salinity cooling towers, both natural and mechanical draft, have encountered accelerated corrosion on unprotected metal surfaces on buildings and equipment on the plant site near the towers. 3. Both mechanical and natural-draft tower structures and basins constructed of concrete have experienced varying degrees of deterioration from exposure to salt

### 30 water. In some cases, very extensive repairs have been required. Chloride resistant concrete and rebar is recommended for high salinity applications. 4. In some cases, the high salinity water was also high in suspended solid at certain times. This often led to plugging of high efficiency full and deteriorated performance. This effect is unrelated to the salinity levels. 5. It must be recognized that some high TDS waters may result from operation with moderate TDS make-up and high cycles of concentration. This usually results in water chemistry that is very different from sea or brackish waters and may be high is scaling constituents. In these cases, more elaborate water treatments such as scale inhibition or softening maybe required.



### Reference List 1. Boyce, S. G., The Salt Spray Community, 1954 2. California Coastal Commission, Seawater Desalination in California--Key Desalination Facts, 1993 3. Davis, E. A., Environmental Assessment of Chalk Point Cooling Tower Drift and Vapor Emissions, Johns Hopkins University, PPSP-CCCTP-28; 1979 4. Eftekharzadeh, S., M. Baasiri, and P. Lindahl, Feasibility of Seawater Cooling Towers for Large-Scale Petrochemical Development, Cooling Technology Institute, TP03-17; 2003 5. Environmental Protection Agency, National Ambient Air Quality Standards (NAAQS), 2006 6. EPA, 316(b) Phase II Technical Devlopment Document, Chapter 6, Environemtal Protection Agency, 2000 7. Micheletti, Wayne, Atmospheric Emissions from Power Plant Cooling Towers, 2006 8. PG&E, Assessment of vegetation stress and damage near the Geysers Goethermal Power Plant Units, Pacific Gas & Electric Co., 1979 9. Porter, et al. , Vertical and Horizontal Aerosol Scattering Fields over Bellows Beach, Oahu during SEAS Experiment, School of Ocean and Earth Science, Universtity of Hawaii, 2000 10. Reisman, J. and G. Frisbie, Calculating Realistic PM10 Emissions from Cooling Towers, 2002 11. Rossnecht, G. F. et al. , The Size Distribution and Inland Penetration of Sea Salt Particles, 1973

### 31

12. Shofner, F. M. et al. , Ambient Sea Salt Measurements in the Forked River, NJ Environs, 1973 13. USEPA, Compilation of Air Pollutant Emission Factors (AP-42; Section 13.4 --Wet Cooling Towers), Environmental Protection Agency, 1995 14. Wilber, K. R., An Experimental Approach to the Evaluation of the Collection Efficiencies of Meshes Using the Mechanism of Inertial Impaction, University of Tennessee, 1974 15. Wilber, K. R., Ambient salt concentration study for Atlantic City Electric Company, B. L. England Station, 1975 16. Wilber, K. R. and R. O. Webb, Environmental Effects of Cooling Towers, Atomic Industrial Forum, 1983 17. Woodcock, A. H., Atmospheric Salt Particles and Raindrops, 1952 18. Woodcock, A. H., Salt Nuclei in the Marine Air as a Function of Altitude and Wind Force, 1953

# 5 Salt Water Cooling System Costs

In comparison to cooling systems designed to operate on fresh water, salt or brackish water systems are more expensive. This is the result of several factors.

§ The properties of sea water lead to reduced thermal capability for a given tower. § The higher levels of dissolved and suspended solids in salt or brackish water sources may require the use of lower efficiency, “low-clog” fill. § The aggressive nature of the higher salinity water normally requires the use of more corrosion resistant, and more expensive, materials for cooling system components and hardware. § Under some circumstances, deterioration of tower or basin materials may occur resulting in costly maintenance or repair. § The effects of salt drift deposition may result in higher costs for cleaning, protection or repair of equipment, structures and surfaces in the vicinity of the tower. Many of these costs are highly variable, site-specific and hence difficult to generalize. The following sections will briefly review some available information on the relative cost of fresh vs. saline water cooling systems. 5.1 General cost factors In late 2001, Washington Group International conducted a brief study (WGI, 2001) to estimate the cost of retrofitting plants with once-through cooling to closed-cycle cooling with mechanical draft cooling towers. Both fresh and saline water installations were considered. The cost estimates developed in this study included the entire cooling system with the exception of the condenser which was assumed to be retained in the retrofit. The system components for which a cost differential was identified were

§ Cooling tower § Circulating water pumps § Make-up water pump § Make-up “system” As noted above, the use of saline make-up results in a larger tower, made more so by the use of low clog fill, which is also constructed of more costly materials. In the WGI study, the precise composition of the saline make-up water was not specified. However, it was stated that the saline water towers were operated at 2 cycles of concentration (as opposed to 5 cycles of concentration for the fresh water towers). Assuming standard sea water as make-up, this gives a circulating water salinity of approximately 70,000 mgl. The analysis began by setting the freshwater tower conditions at WBT = 80, a 1 F recirculation allowance giving an inlet wet bulb of 81 F, an approach of 7 F, a range of 12 F and a condenser terminal temperature difference of 8 F. This corresponds to a condensing temperature of 108 F and a turbine exhaust pressure of 2.5 in Hga. It was not specified how the size and cost of the baseline freshwater tower designed to meet this performance was determined other than to say that− “structure costs assume a fiberglass mechanical draft tower with standard noise and drift abatement and no plume abatement” and

− “costs were estimated by scaling cooling tower costs provided by cooling tower vendors for fresh water make-up cooling towers”. It was not stated whether the baseline costs were consistent with “low first cost” designs or “total evaluated cost” designs. However, as will be seen in the case study discussed below the cost ratio is essentially identical for both assumptions. The salt water tower costs were adjusted in two ways: first, by adjusting the size of the tower to account for the performance reduction caused by the circulating water properties using the saltwater correction factor discussed in Section 3 (Figure 3.1); second, by increasing the cost of the tower to account for the more costly materials of construction The adjustment in tower size was set at 1.07 which, for seawater at 2 cycles of concentration, is consistent with the “2x seawater” curve in Figure 3-2 for an L/G = 1. Although WGI did not specify the L/G, this would be in a reasonable design range as discussed in Chapter 2. The adjustment in tower materials cost was set at x 1.4. This gives an overall cost ratio between saline and fresh water towers of x 1.5 (~ 1.07 x 1.4). (NB: It should be noted that while this procedure and the values used were clearly described in the text of (WGI, 2001), there was an apparent error in the report tables which caused the reported costs to differ in some cases from those that this procedure would yield.) Case study As part of the analysis for this study, former and current representatives of a cooling tower vendor (Wilber, K., 2004) were asked to estimate cooling tower costs for a given set of design specifications. These were: § Water flow rate, L: 100,000 gpm § Hot water temperature, T h : 120 F § Cold water temperature, T c : 90 F § Wet bulb temperature, T wb : 75 F This corresponds approximately to the heat load of a 200 MW steam plant. A comparison was provided between a fresh water tower and a tower operating with seawater as make-up and at 1.5 cycles of concentration, resulting in a circulating water salinity of 54,000 ppm. The two cases considered were a “low first cost tower” and an “evaluated tower”. The evaluated tower is larger with a higher capital cost but uses less pump and fan power. The capital costs and the operating costs are balanced to arrive at an optimized lifetime cost. In this example, the current value of power was set at $100/HP for the pump and fan power. Table 4-1 shows the design configuration for towers of both low first cost and evaluated cost designs sized to account for the performance difference between fresh and brackish water at 54,000 ppm.Table 5-1: Tower Design Configurations

Again, the cost increase consisted of two parts---an adjustment to account for the reduced thermal performance and another for the more costly materials of construction. Table 5.2 shows the cost differentials attributable to the reduced performance.

Low First Cost Evaluated Cost Make-up Water Cost ($1,000) Impact (%) Cost ($1,000) Impact (%) Fresh water 1,100 Base 1,400 Base Brackish (54,000 ppm) 1,149.5 4.5% 1,498 7.0% Table 5-2: Cost Impact of Thermal Performance Reduction Reference to Figure 3-2 indicates that a correction factor of 1.045 would be consistent with the Marley estimates for L/G’s in the range of 1. to 1.5. The higher correction factor for the evaluated cost tower suggests that larger plan area per cell and an additional cell (in the case of the evaluated cost, brackish water tower) resulted in a higher air flow and hence a lower L/G in spite of the presumably lower fan/pump power for the evaluated cost design. While this cannot be confirmed with the information provided, a correction factor of 1.07 is consistent with an L/G of 0.5 or less. The additional cost for the more costly materials to provide the corrosion resistance required for salt water operation is shown in Table 4-3. The comparison is between a “conventional” fresh water tower constructed of Douglas fir with galvanized fittings and an FRP tower with silicon bronze hardware and epoxy coating. Low First Cost Evaluated Cost Item Douglas Fir FRP Douglas Fir FRP “Base Tower” 1,100 1,287 1,400 1638 Increase for salinity -- 58

-- 115 Silicon Bronze fittings -- 112

-- 120 Epoxy coatings

-- 28

-- 30 Total 1,100 1,485 1,903 % increase

-- 35% 36% Table 5-3: Tower Cost Comparisons Several points are noteworthy. 1. The case study and the generalized cost factor analysis are roughly consistent and suggest a range of 35% to 50% increase in cost for salt or brackish water towers compared to fresh water towers. 2. The difference in the two estimates is primarily in the differential costs of materials rather than the cost differences attributable to performance reduction. This may be due, in part, to the fact that No. of Cells Cell Width Cell Length Fill Depth Inlet Air Height Fan HP Fan Dia # ft. ft. ft. ft. HP ft.

No. of Cells Cell Width Cell Length Fill Depth Inlet Air Height Fan HP Fan Dia # ft. ft. ft. ft. HP ft.

4 13 200 30 Brackish Water Tower, 54000 ppm 9 42 54 5.5 9 100 28 Fresh Water Tower Douglas fir, galvanized hardware 8 42 54 12 200 28
8 42 42 4 13 200 28 8 36 42 5 Fresh Water Tower Douglas fir, galvanized hardware Brackish Water Tower, 54000 ppm Low Cost Design

Evaluated Cost Designthe two estimates were done at different times; 2001, in the case of the WGI report and 2004 for the case study. Significant variations in the costs of lumber, plastics, and high grade metal parts have occurred over the past few years which may have altered the cost ratios. In any case, the determination of a 35% to 50% range is considered adequate for a general survey of this type. 3. The cost analyses discussed above included only the cooling tower itself. Other components of wet recirculating systems are also affected by make-up water salinity as noted in Section 5.1. Table 5-4 lists the cost ratios for other major components used in the WGI study. While the cooing tower is typically the largest cost component of the system, these differences can be sizable for large installations.

Table 5-4: Cooling System Component Cost Comparisons (from (WGI, 2001))



### Reference List 1. WGI, Estimated Cost of Compliance with EPA Proposed Rule 316(b), Washington Group International, Project 25258; 2001 2. Wilber, K., Personal Communication, 2004

Item Fresh water Salt water Cost ratio Cooling tower $24/TU $33.6/TU 1.4 Circ. water pump $130 - $260/BHP $210 - $416/BHP 1.6 Make-up water pump $337/BHP $539/BHP 1.6 Make-up system $150/gpm $200/gpm 1.3

# 6 Summary and Conclusions
The use of seawater, brackish estuarine or ground water or high salinity reclaimed water for cooling tower make-up is an attractive alternative to the use of fresh water in some locations. Table 2-1 lists over 50 seawater or brackish water towers currently installed inthe United States and over 90 worldwide. This report reviews the effect of using nonfresh water as cooling tower make-up on thermal performance, cost, environmental impact and operation and maintenance. 6.1 Effect on thermal performance Several of the thermo-physical properties of high salinity water differ from those of fresh water. These include

- density

- specific heat

- surface tension

- thermal conductivity

- vapor pressure

- viscosity
. Of these the most important in its effect on cooling tower performance is vapor pressure. The volumetric heat capacity (the product of density times specific heat) can affect the optimum design and operating point. Thermal conductivity, viscosity and surface tension play minor roles in the thermal performance of cooling towers; surface tension can affect the effectiveness of drift eliminators. The presence of salts in water reduces the vapor pressure at any given temperature as seen in Figure A.2 in Appendix A. This reduces the driving force for evaporation and the accompanying latent heat transport. Therefore, a higher fill volume or fill transfer coefficient will be required to transfer the same amount of heat, requiring a larger and more costly cooling tower. Alternatively, a tower of the same size and fill configuration will cool less water to the desired cold water temperature or deliver a higher cold water temperature. For circulating water salinities, given by the salinity of the make-up water multiplied by the tower cycles of concentration, of x 1.5 to x 2 that of seawater (~50,000 to 70,000 ppm) the thermal capability of a high salinity tower will be reduced by 4 to 8% below that of a fresh water tower at the same operating conditions. A recommended rule-of-

### thumb for specifying towers is to increase the design ambient wet bulb temperature by

0.055 C (0.1 F) for each 4,000 ppm of circulating water salinity. 6.2 Effect on cooling system cost In comparison to cooling systems designed to operate on fresh water, salt or brackish water systems are more expensive. This is the result of several factors. § The properties of sea water lead to reduced thermal capability requiring a larger and more expensive tower. § The higher levels of dissolved and suspended solids in salt or brackish water sources may require the use of lower efficiency, “low-clog” fill again requiring a larger tower. § The aggressive nature of the higher salinity water normally requires the use of more corrosion resistant, and more expensive, materials for cooling system components and hardware. § Under some circumstances, deterioration of tower or basin materials may occur resulting in costly maintenance or repair. § The effects of salt drift deposition may result in higher costs for cleaning, protection or repair of equipment, structures and surfaces in the vicinity of the tower. Cost estimates were obtained from a study by an experienced A&E firm using generalized cost adjustment factors and from a case study for a particular set of design specifications. 4. The case study and the generalized cost factor analysis are roughly consistent and suggest a range of 35% to 50% increase in cost for salt or brackish water towers compared to fresh water towers. 5. The difference in the two estimates is primarily in the differential costs of materials rather than the cost differences attributable to performance reduction. This may be due, in part, to the fact that the two estimates were done at different times nearly three years apart. 6. The differential cost estimates apply only to the cooling tower itself. Other components of wet recirculating systems are also affected by make-up water salinity.

6.3 Effect on environmental impact 

### A number of environmental effects studies have been conducted by comparing deposition rates on surrounding land before and after the installation and operation of salt or brackish water cooling towers. All studies reach essentially similar conclusions that no significant increase in salt concentrations in soils or vegetation nor any symptoms of environmental injury were observed in the vicinity of the plants.

### 6.4 Effect on operation and maintenance

Plant visits were made to four plants and telephone interviews were held with two additional plants and one cooling tower vendor. The major conclusions obtained from these visits and interviews are:

1. Recent installations of mechanical-draft cooling towers operating on high salinity make-up water using fiberglass reinforced plastic (FRP) structure, PVC fill and corrosion-resistant fittings (high grade stainless steel, silicon bronze (coated), titanium) have operated satisfactorily with no extraordinary O&M problems. 2. Operating experience has been excellent but long term (> 15 years) is lacking. 3. Nearly all plants with high salinity cooling towers, both natural and mechanical draft, have encountered accelerated corrosion on unprotected metal surfaces on buildings and equipment on the plant site near the towers. 4. Both mechanical and natural-draft tower structures and basins constructed of concrete have experienced varying degrees of deterioration from exposure to salt water.

# Appendix A Properties of Sea Water

A-1: Composition 

## A-2: Vapor Pressure A-3: Density A-4: Specific Heat A-5: Surface Tension A-6: Viscosity A-7: Thermal Conductivity

### Table A-1: Composition of “Normal“ Seawater Na 10,556 mg/kg (2) K 380 mg/kg Ca 400 mg/kg Mg 1,272 mg/kg HCO 3 140 mg/kg Cl 18,980 mg/kg Br 65 mg/kg SO 4 2,649 mg/kg SiO 2 <10 mg/kg Other 31 mg/kg Total 34,483 mg/kg
Notes..... 1. Only major ions shown. 2. These are true "ppm" units and are approximately the same as mg/l.



### "Normal" Seawater Chemistry (1) US Department of Interior, Office of Saline Water, July 1959

### Vapor Pressure

Correlating Equations for Vapor Pressure

Fresh water p = 8.0439E-09T 4 

### – 6.5750E-07T 3 

### + 8.5848E-05T 2 

### – 1.0248E-03T + 4.6622E-02 Seawater (TDS ~ 35,000) p = 1.0511E-08 T 4

### – 1.7569E-06 T 3 

### + 2.3539E-04 T 2 

### – 9.1406E-03T + 1.9585E-01
2x Seawater (TDS ~ 70,000) p = 3.9773E-09 T 4

### – 2.1465E-08 T 3 

### + 6.6345E-05 T 2 

### – 2.1540E-03T + 8.8876E-02Figure A-2a: Vapor pressure (80 to 100 F) 

## Vapor Pressure Comparison - 80F to 100F

0.4 0.45 0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.85 0.9 0.95

80 90 100 Temperature, deg FVapor Pressure, psi

Fresh water Seawater 2x SeawaterFigure A-2b: Vapor pressure (100 to 140 F)



### Surface Tension 

## Vapor Pressure Comparison - 100F to 140F

0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 2.8 3

100 110 120 130 140 Temperature, deg FVapor Pressure, psi

Fresh Water Seawater 2x Seawater

### Correlating Equations for Surface Tension

Fresh water
ı= -6.2500E-05T 2

### - 7.7607E-02T + 7.8297E+01 Seawater (TDS ~ 35,000)

ı= -8.0357E-05T 2

### - 7.4107E-02T + 7.8914E+01
2x Seawater (TDS ~ 70,000)

ı= -4.4643E-05T 2

### - 8.0679E-02T + 7.9991E+01


## Surface Tension - 40F to 140F

64.00 66.00 68.00 70.00 72.00 74.00 76.00 78.00

20 40 60 80 100 120 140 160 Temperature, FSurface Tension, dynes/cm

Pure Water 1x Seaw ater 2x Seaw ater

Figure A-3: Surface tension (40 to 140 F)

### Viscosity

Correlating Equations for Viscosity

Fresh water ȝ= 1.3063E-04T 2

### - 4.4363E-02T + 4.7808 Seawater (TDS ~ 35,000)

ȝ= 1.3688E-04 T 2 

### - 4.6918E-02T + 5.1116
2x Seawater (TDS ~ 70,000)

ȝ= 1.4313E-04 T 2 

### - 4.9283E-02T + 5.4285

Figure A-4: Dynamic viscosity (40 to 140 F) 

## Viscosity - 40F to 140F

1.00 1.50 2.00 2.50 3.00 3.50 4.00

20 40 60 80 100 120 140 160 Temperature, FViscosity, lb/ft-hr

Pure Water 1X Seaw ater 2X Seaw ater

### Thermal ConductivityFigure A-5: Thermal conductivity

### Density

Correlating Equations for Density

Fresh water ȡ = -2.1661E-08T 3 

### - 7.7583E-06T 2 

### + 6.7946E-04T + 8.3283 Seawater (TDS ~ 35,000)

ȡ = -4.4870E-08 T 3 

### + 1.1936E-06 T 2

### - 4.8336E-04T + 8.5780
2x Seawater (TDS ~ 70,000)

ȡ = -4.6417E-08 T 3 

### + 3.9388E-06 T 2

### - 1.1106E-03T + 8.8145



## Density - 40F to 140F

8.10 8.20 8.30 8.40 8.50 8.60 8.70 8.80 8.90

20 40 60 80 100 120 140 160 Temperature, FDensity, #/gal Pure Water 1x Seawater 2x Seawater

Figure A-6: Density (40 to 140F)

# Specific Heat

Correlating Equations for Specific Heat

Fresh water

c p

### = 1.6927E-10T 4

### - 7.2627E-08T 3 

### + 1.2276E-05T 2 

### - 9.5425E-04T + 1.0269 Seawater (TDS ~ 35,000)

c p

### = 1.3021E-11 T4 

### - 4.5718E-09 T 3 

### + 6.5104E-07T 2 

### + 1.5847E-05T + 9.5287E-01
2x Seawater (TDS ~ 70,000)

c p

### = 3.7037E-09 T 3 

### - 1.4196E-06 T 2 

### + 2.7834E-04T + 9.0270E-01

## Heat Capacity - 40F to 140F

0.90 0.92 0.94 0.96 0.98 1.00 1.02

20 40 60 80 100 120 140 160 Temperature, FHeat Capacity, BTU/#-F Pure Water 1x Seawater 2x Seawater



### Figure A-7: Comparison of Specific Heat (from Perry ¶ s [ ??? ]

# Appendix B

Derivation of Cooling Tower Performance

Characteristics

### Tower Performance Characteristics

The cooling of the water is achieved through the combined processes of heat and mass transfer from the hot water to the air as they pass through the tower fill. A brief description of the process will assist in understanding how the properties of the water, and in particular how the differences between the thermo-physical properties of salt or brackish water and those of fresh water affect cooling tower performance. As indicated in Figure B-1, the hot water enters the tower at the top and falls under gravity down through the tower fill and into the cold water basin. The air is drawn into the tower at the bottom and flows upward, counter to the downflow of the water, and exits through the fan to the atmosphere.

Figure B-1: Closed-cycle cooling system mass and heat balance
The purpose of the fill is both to slow the water as it descends through the fill and to create a large interfacial area between the water and the air, providing more time and a larger area for the transfer processes to take place. Fills are of two general types; film fill and splash fill. The film fills cause the water to flow in narrow films on the fill surfaces. The fill geometry is designed to and by geometric disrupt and mix the films by causing them to turn or reform as they flow downwards. Splash fills create small droplets as the falling water impacts the fill surfaces creating fresh surface for heat and mass transfer. The determination of the tower performance characteristics required for a given cooling load proceeds as follows: The heat load which must be rejected by the cooling tower to cool a given water flow, L, from the hot water temperature, T h 

### , to the desired cold water temperature, T c 

### , is given by CONDENSER WET COOLING TOWER W circ
. (lbm/hr)

Condensate return Steam
W st (lbm/hr) Hot water temp T h (oF)

Cold water temp T c (oF) Make-up

w m u (lbm/hr) Blowdown w bd (lbm/hr) Inlet air w air (lbm/hr) T w b (oF) Plume w evap (lbm/hr)

w drift (lbm/hr)

p b (in Hg a ) T cond (oF)

### Q w

### = L * c p

### * (T h 

### - T c 

### ) (Eq. B-1)

The heat transferred to the air equals that from the water and is given by Q a

### = G * (h airex

### – h airamb 

### ) (Eq. B-2) where G = air flow rate (lb/hr)

h = enthalpy of air stream per lb of dry air (Btu/lb) The transfer of heat from the water to the air stream at each point on the air-water interface within the tower is made up of i) a sensible heat component, driven by the difference between the local water surface temperature and the local free stream air temperature and ii) a latent heat component, carried by a mass transfer of evaporating water driven by the difference between the vapor pressure of water at the local water temperature and the vapor pressure of the water vapor in the air stream. Several critical assumptions simplify the analysis. These include 1. the water film is well mixed so the water surface temperature is the same as the bulk water temperature 2. the air at the surface of the film is saturated at the water temperature 3. The physics of the heat and mass diffusion processes are essentially the same; i.e., the Lewis number is equal to 1. With these assumptions the total heat transfer per unit interfacial area can be accurately represented with a combined transfer coefficient, K, and the difference between the enthalpy of air saturated at the local water temperature and the enthalpy of the bulk air stream.

Figure B-2: Incremental Heat Transfer Analysis

T w 

### h air 

### + dh air



### dQ L G dV

Tw - dTw h air

### From Eq. (B-1) and Figure B-2, KadV(h sat @ Tw 

### – h air 

### ) = LdT w

### (Eq. B-3) Integrating across the fill volume from 0 to V, yields KaV/L = 

# ∫

− h

c w T
T air

T sat w 

### h h dT

@ 

### (Eq. B-4)
The integration can be understood graphically in Figure B-3.

Figure B-3: Cooling tower operating curves The driving force for the combined heat transfer is the distance from the line A-B which represents the water operating line between T h 

### and T c 

### and also the enthalpy of saturated moist air. The line C-D represents the air operating line running from an inlet enthalpy consistent with the ambient wet bulb temperature and increasing linearly with a slope of L/G to an exit enthalpy consistent with the overall heat balance. Since the enthalpy of moist air is essentially a function only of the wet bulb temperature independent of relative humidity, it is not possible from the foregoing analysis to determine the exit state of the air. A further assumption by Merkel (Ref. ??) states that the exit air is saturated at the prescribed exit enthalpy and corresponds to some temperature intermediate between the water hot and cold temperatures. h ex

### = hamb 

### + L/G * (T h 

### – T c 

### ) Eq. (B-5) E

n
t h

Temperature

### This suffices to specify the complete state of the exit air and to determine the evaporation

rate from the cooling tower from

w evap

### = G * (Wex

### – Wamb 

### ) Eq. (B-6) where W = specific humidity in lb moisture/lb of dry air

Based on the foregoing analysis, knowing the ambient wet bulb, the inlet and outlet water temperature, determines the required tower characteristic (KaV/L). This value is readily generated by programs such as the CTI Workbook. (Ref. ???) A sample set of curves for a given wet bulb and a given range is shown in Figure B-4 for a number of approach temperatures as KaV/L vs. L/G. The performance characteristics of many fills can be approximated by a polynomial expression of the form

KaV/L = C * (L/G) n 

### (Eq. B-7) Figure B-4 shows such a fill characteristic with nominal values of n = -0.7 and C = 1.5 superimposed on the performance curves of a tower with a 32.4 F range at an 80 F wet bulb. The intersections of the characteristic line with the performance curves gives the approach temperature which can be obtained for the given range and wet bulb temperature for any L/G.

### Figure B-4: Example Performance Curves and Fill Characteristic (from CTI Workbook

for specified range and wet bulb temperature)