# American Petroleum Institute
Characterizing Cooling Water Systems in Petroleum Refineries
Briefing ReportPage i TA BLE OF CONTENTS Page Executive Summary

................................ ................................ ............................ v I. Introduction

................................ ................................ ................................ .......... 1 II. Cooling W ater Use Description

................................ ................................ ............ 3 II.1 Wh at drives the need for cooling in petroleum refineries?

................................ . 3 II.2 Wh at types of equipment require cooling?

................................ ........................ 5 II.3 Wh at are the types of cooling water systems?

................................ .................. 7 II.4 Are there specific requirements/limitations associated with cooling water usage?

................................ ................................ ................................ .............. 9 II.5 How are these cooling needs and requirements/limitations met?

.................... 11 II .6 Wh at dictates which cooling approach is used?

................................ .............. 12 II.7 Wh at volumes of cooling water are required for various approaches?

........... 14 III. Recirculated Cooling W at er Technology

................................ ............................ 17 III.1 Wh at are the components of a Recirculated cooling tower system?

............... 17 III.2 Wh at are the limitations of using recirculated systems?

................................ .. 18 III.3 Wh at must be considered when increasing cycles of conc entration in cooling towers? ?

................................ ................................ ............................ 19 III.4 Wh at quality/quantity of make
- up water is required and how is it determined?

................................ ................................ ................................ .... 22 III.5 Effects of brackish vs. fresh water?

................................ ................................ 24 III.6 Blowdown flows, handling, treatment?

................................ ............................ 25 III.7 Factors affecting drift and evaporation losses?

................................ ............... 26 III.8 Factors affecting chemical usage and concentrations?

................................ ... 27 IV. Converiti ng from Once
-through to Cooling Towers

................................ ............ 28Page ii

IV.1 Wh at would be involved in changing from once
- through cooling to cooling towers?

................................ ................................ ................................ ........... 28 IV.2 Effects on wastewater discharge volumes and quality?

................................ .. 30 IV.3 Effects on metallurgy in piping and exchangers?

................................ ............ 31 IV.4 Effects on refinery piping configurations?

................................ ....................... 32 IV.5 Effects on heat exchanger capacity?

................................ .............................. 33 IV .6 Additional space requirements?

................................ ................................ ...... 35 IV.7 Changes in water treatment requirements?

................................ .................... 36 IV.8 Changes in water pressure requirements?

................................ ..................... 37 V. Changing to Dry Cooling

................................ ................................ .................... 38 V.1 Wh at would be involved in changing to dry cooling?

................................ ....... 38 VI. Cooling W ater Recycle and Reuse

................................ ................................ .... 39 VI.1 Wh at are the options for recycle/reuse of cooling water? Practicality?

........... 39 VII. Cooling W ater Intake Structures

................................ ................................ ........ 40 VII.1 Wh at types of intake structures are used at refineries

................................ ..... 40 VII.2 Wh at is involved in retrofitting refinery intake structures (e.g. , moving screens)?

................................ ................................ ................................ ........ 41 VII.3 Other information on cost
- effectiveness of intake structure controls?

............. 42 VIII. Cost Implications

................................ ................................ ............................... 43 VIII.1 Cursory review of the EPA’s “Draft I nitial Cost Estimates”
-- May 17, 2001?

.. 43 VIII.2 Estimate the cost of installing a 17,400 gpm cooling tower

............................. 46 IX. References

................................ ................................ ................................ ........ 51 Appendix A EPA Draft Initial Cost Estima te Appendix B Quote for Cooling Tower Appendix C Quote for PumpsPage iii

Appendix D Quote for Clarifier Appendix E Quote for Traveling W ater ScreenPage iv LIST OF FIGURES Page Figure 1 Typical Distillation System

................................ ................................ ............. 4 Figure 2 Once Through Cooling System

................................ ................................ ...... 7 Figure 3 Clo sed Loop Cooling System

................................ ................................ ......... 7 Figure 4 Evaporative Cooling System

................................ ................................ .......... 8 Figure 5 Makeup & Blowdown vs. Cycles of Concentration

................................ ........ 23 Figure 6 Cooling Tower System for Estimate

................................ ............................. 46Page v Executive Summary Section 316(b) of the Clean W ater Act requires EPA to ensure that t he location, design, construction and capacity of cooling water intake structures reflect the best technology available for minimizing adverse environmental impact. EPA is developing national standards in three phases: Phase I for new facilities, Phase I I for existing electric generating plants that use large amounts of cooling water, and Phase III for manufacturing plants and for electric generating plants using smaller amounts of cooling water. By June 2003, EPA must propose the Phase III regulations a ddressing existing manufacturing facilities (which would apply to existing petroleum refineries) and EPA must issue final Phase III regulations by December 2004. The proposed Phase II regulations include a requirement to limit cooling water intake flow to that commensurate with closed loop recirculation of cooling water. This requirement is an option EPA may consider for the Phase III regulations, as well as an option to require air cooling in some cases as a means to limit cooling water intake flow. This report details the significant technical issues and costs associated with implementing either closed
- loop flow reduction or air cooling at petroleum refineries. The environmental benefit realized by either of these options would not justify the high cost to the industry. EPA should take the information presented in this report into account when drafting its Phase III rule, and should not require the petroleum industry to install air cooling or reduce intake flows to that commensurate with closed loop rec irculation. EPA should instead provide the petroleum industry the option of minimizing adverse environmental impact through the installation, operation, and monitoring of control technologies effective at reducing impingement and entrainment at the coolin g water intake. Depending on site
specific conditions and the particular technology selected, control technologies have been shown to be up to 90
- 100 percent effective at reducing impingement and entrainment. Technical and Economic Feasibility of Closed - Loop Recirculation and Air Cooling EPA may believe that the choice of cooling medium, and the switch from once
-through cooling to complete recirculation of cooling water with the installation of cooling towers, is readily achieved at manufacturing facilities, with little effect on process operations. In practice, however, the choice of once
-through cooling vs. recirculation is a complex decision based on numerous site
- specific considerations. In the refining industry, a requirement mandating a pa rticular cooling medium (water vs. air) or configuration (once
through vs. recirculation) will have significant technical and cost implications to process operations. EPA needs to understand the complex nature of cooling operations at refineries and the s ignificant potential impacts to the refining industry associated with these regulations. EPA should take the following implications to the refining industry into account when considering Phase III regulations that mandate cooling water recirculation, cool ing tower installation, and/or air cooling:Page vi

 A recirculation system cannot provide cooling water at temperatures as low as a once - through system, which provides cooling water at the temperature of the water source. This has significant process implication s at refineries. For example, a key factor to refinery profitability is to cut as deeply into the vacuum tower residue as possible. This is achieved by pulling as much of a vacuum as possible in the vacuum column, but this vacuum requires low condensing temperatures, which in turn requires cooler water.

 The recirculation temperature affects the design, sizing, and cost of all water
- cooled heat exchange equipment within the refinery; the higher cooling temperature will require larger and more costly hea t exchange equipment to achieve the same cooling duty as a once
-through system. Depending on specific space and pressure drop limitations, it may not be possible to add incremental heat exchange; wholesale replacement may be required.

 Installation of a cooling tower and related equipment (sumps, pumps, piping, etc.) is dictated by the unit operations being conducted at the particular refinery and by the space available. W hile it might be optimal to install one large cooling tower to replace an existin g once -through system, space and logistics will likely require building multiple cooling towers. This invariably leads to increased costs and operational complexity.

 Recirculation systems depend on evaporation to remove heat and thereby increase the concentration of hardness and dissolved solids in the cooling water system. If the dissolved solids content of the water is high it will limit the recirculation rate. Unless the quality of the intake water is very high, intake water pretreatment will be need ed to avoid scaling or corrosion in the recirculation system. Such pretreatment may entail precipitation, water softening, pH adjustment, and suspended solids removal.

 It is necessary to treat recirculating cooling water with a variety of chemicals to control scaling, deposition, biological growth and corrosion. Sulfuric acid is most of ten used to control pH. Corrosion inhibiters must be added to prevent corrosion. Slimicides are used to control biological growth.

 Facilities will typically treat the blowdown from cooling tower systems in the existing wastewater treatment plant and the extra loadings may drive the need for increased capacity. Cooling tower blowdown contains high dissolved solids as well as those chemicals added to prevent corrosion, scale, and biological growth. The need toPage vii

treat blowdown can significantly reduce residence time and therefore overall efficiency in the treatment system.

 Direct air cooling used in refineries is dictated by the dry bulb temperature at that site and cond itions of the process streams such as inlet temperature and required outlet temperature. Air cooling can be used in refineries only for specific applications. Many process requirements will still require the installation of cooling water exchangers downs tream of the air coolers. Air
- cooled exchangers tend to be large, require significant plot space, and can be a source of noise.

 Replacement of once through cooling with air
- cooled heat exchangers would demand an economically infeasible number of changes to the existing process equipment. Furthermore, whereas cooling water shell
- and
- tube exchangers can be stacked vertically in process units, air coolers cannot be stacked (because lower units would send heated air to higher units) and so it may be physica lly difficult or impossible due to space constraints to replace water
- cooled exchangers with air
cooled exchangers.

 We re conversion of a once
- through cooling water system a refinery even feasible, API’s estimate of the cost of such a conversion is much hi gher than that estimated by EPA. For a 17,400 gallon/minute system at a refinery, API estimates an installed cost of $ 9

. 2 million, with an annual operation and maintenance cost of $ 334 , 6 00. EPA estimated an installed cost of $1.34 million and an operatio n and maintenance cost of $179,000 for such a facility. This cost is an extremely burdensome cost to achieve a limited environmental benefit.Page viiiPage 1 of 50 I. Introduction Section 316(b) of the Clean W ater Act requires EPA to ensure that the location, design, construction and capacity of cooling water intake structures reflect the best technology available for minimizing adverse environmental impact. For many years, this provision has been implemented without federal standards in place, on a resource i ntensive, site
- by
- site basis. EPA is developing national standards in three phases: Phase I for new facilities, Phase II for existing electric generating plants that use large amounts of cooling water, and Phase III for manufacturing plants and for electric generating plants using smaller amounts of cooling water. EPA issued the Phase I regulations for new utilities and manufacturing facilities on December 18, 2001. In March 2002, EPA plans to issue the Phase II proposed rules for existing utilities, wi th the goal for making them final by August 2002. By June 2003, EPA must propose the Phase III regulations addressing existing manufacturing facilities (which would apply to existing petroleum refineries) and EPA must issue final Phase III regulations by December 2004. API expects the provision for the existing utilities (Phase II) will be the basis for developing the Phase III rules. Consequently, the Phase II regulations can have significant cost impacts on petroleum refineries. Some of the potential costs range from costs for studies and restoration projects for offsetting perceived adverse environmental impacts, to adding or retrofitting impingement reduction equipment to the intake structure, relocating the entire intake structure, reducing volumes by changing cooling tower operations (e.g., increasing cycles), reducing volumes from one
-through cooling systems by converting to recycle cooling towers, reducing volumes by reuse or recycle of cooling water for process uses, reducing volumes by installing dry cooling technology, and/or any combination of these options. EPA needs some additional information to better understand the nature of cooling operations at refineries and to understand the significant potential impacts to the refining industry associated with these regulations. EPA has invited API to meet and discuss these topics. This report will be the basis for the discussions at that meeting. AP I Project Objectives API senses EPA may have incorrect assumptions and/or incomplete understanding abou t petroleum refinery cooling operations, including how and why cooling water moves through a refinery, practical vs. theoretical options for recycle/reuse, implications of increasing cycles in existing cooling towers, the process consequences (e.g., thermo dynamic effects, effects in stream composition, material and equipmentPage 2 of 50

requirements, etc.) in changing from once through cooling to cooling towers, and feasibility vs. practicality of dry cooling. API commissioned the preparation of a briefing paper to add ress various issues associated with changing from a once through cooling system to a recirculating cooling tower system. This briefing paper provides answers to basic questions about refinery cooling operations and clarifies the significant technical is sues and extreme costs associated with implementing either closed
- loop flow reduction or air cooling at petroleum refineries. The environmental benefit realized by either of these options would not justify the extremely high cost to the industry.Page 3 of 50 II. Cool ing Water Use Description II.1 What drives the need for cooling in petroleum refineries? In petroleum refineries crude and refined oils are separated and subdivided into various fractions based on boiling point. This is accomplished by fractional distillation. The distillation is carried out in distillation column where the oil is heated up and vaporized in a fuel
- (fuel oil, natural gas or refinery fuel gas) fired heater. Various fractions are separated by condensing and cooling products that are withdrawn from the tower. From an overall heat balance point of view, the heat that is put into the system by burning fuel and/or the introduction of steam has to be removed or “rejected”. This is accomplished in various ways such as:

 Heat exchange with boiler feed water to generate steam
 Heat exchange with other process streams
 Rejection of heat using air coolers
 Rejection of heat to cooling water Figure 1 depicts a typical distillation system in a refinery. In this system three types of heat rejection systems are shown. The crude oil is preheated by exchanging with another process stream and fed to a fired heater. The partially vaporized products are sent to the distillation tower where different side streams are withdrawn based on the boiling point range of the product. The side streams are sent to strippers (a type of distillation column) where the boiling point range of the product is adjusted further by the addition of steam. The bottoms product from these strippers is cooled and sent to storage tanks or on to further processing. The vapors from these side strippers are sent back to the main tower. The overhead vapors from the main tower are condensed using an air
- cooled exchanger and then further cooled using a cooling water heat exchanger. Three types of heat exchangers are shown in this system:

 Type 1 heat exchangers such as steam generators and process stream heat exchangers
 Type 2 heat exchangers which use cooling water
 Air coolersPage 4 of 50 Feed P-42-- Water

Steam Gas To Recovery

P-36--

Light Cut

Steam Steam

Towe Bottoms Medium Cut

Heavy Cut Distillation Tower

Side Stripper Side Stripper

Type 2

Fired Heater Ai r Cooler

Type 1 Type 1 Type 1

Type 1 Type 1 - Heat Exchanger where the stream is heated/cooled against another Process stream Type 2 - Heat Exchanger where heat is rejected to cooling water Figure 1 Ty pical Distillation SystemPage 5 of 50

II.2 What types of equipment requir e cooling? Various types of heat exchangers in the refinery constitute the largest requirement for cooling. These are listed below: Distillate Condensers: These are used to cool and condense the overhead vapors from distillation towers. Since this service involves condensation of vapors, the heat duty of these exchanges tends to be relatively large; and due to the fact that there are numerous distillation towers in a refinery, distillate condensers represent the largest use of cooling water in a refinery. It is not uncommon to find scores of distillate condensers in a refinery. Steam Condensers: In these exchanges steam is condensed against cooling water, and the heat duty of these exchangers also tends to be relatively large since the service involves th e condensation. Refinery distillation towers that run under vacuum conditions typically use steam ejectors to generate the required vacuum. The steam needs to be condensed, and this is accomplished using cooling water exchangers. Product Coolers: Variou s refinery products need to be cooled before they are sent to storage tanks. This cooling is accomplished using cooling water exchangers, because of the low product outlet temperature requirements. It is not uncommon to find scores of product coolers in a refinery. Additionally, various process streams (liquid and vapor) are transported by rotating equipment: Compressors: Compressors fall into three general categories: centrifugal, rotary and reciprocating. Compressors are usually equipped with oil lubri cation systems to dissipate some to the heat of compression. The heat that is picked up by the lubricating oil is rejected from the system using air coolers or cooling water depending on the amount of heat rejection required and the temperature requiremen ts of the circulating oil. In addition, when multistage compressors are used, the process stream is cooled between stages using intercoolers and after coolers. Vacuum Pumps: Vacuum that is required in distillation processes is generated by using vacuum p umps, steam ejectors or using a combination of the two. W hen vacuum pumps are used, the cooling requirements are similar to compressors in that the heat picked up by the lubricating system needs to be rejected using air coolers or cooling water exchangers . W hen ejectors are used to create the vacuum, all the steam that is added needs to be condensed and cooled. This is typically done with cooling water exchangers.Page 6 of 50

Pumps: Pumps that are used in liquid service fall into two general categories: reciprocatin g and centrifugal. Pumps are also equipped with lubricating system and can require cooling, depending on the operating efficiency of the pump.Page 7 of 50

II.3 What are the types of cooling water systems? There are three types of cooling water systems:
a. Once Through Cooling Water System : In this type of system where the cooling capacity of the water is used only once without contacting the fluid or vapor being cooled. These systems use of water withdrawn from a surface water source such as a lake, river or estuary an d typically are returned to the same source. Figure 2 shows a typical once
- through cooling water system. Figure 2 Once Through Cooling Water System

b. Closed Loop Cooling Water System: In this system water is circulated in a closed loop piping system an d is subject to cooling and heating without evaporation or air contact. Heat that is absorbed by the water in a closed loop system is normally rejected using a heat exchanger to a once through cooling system. Figure 3 shows and example of a closed loop system. Figure 3 Closed Loop Cooling Water System Warm W ater Discharge

Cold W ater Intake Process Heat Exchanger Process Heat Exchanger

Process Heat Exchanger Process Heat Exchnager Cooler

Surge Tank Cold Water Intake Warm Water ReturnPage 8 of 50

Closed loop cooling water systems in U.S. refineries are rare. Since closed loop systems are not typical, they are not discussed further in this report. Evaporative Recirculating Cooling Water System: In this type of system, the heat that is picked up by the recirculating cooling water is rejected in a cooling tower by evaporation. In the cooling tower the hot water is sprayed against a rising stream of atmospheric air. The heat in the cooling water is re moved by heating the air as well as by evaporation. An example of an evaporative recirculating cooling tower system is shown in Figure 4. Figure 4

Evaporative Recirculation Cooling Water System

Blowdown Process Heat Exchanger Process Heat Exchanger Makeup W ater Intake Cooling Tower EvaporationPage 9 of 50

II.4 Are there specific requirements/limitations associated w ith cooling water usage? Cooling water must be of a quality that allows for control over scaling, deposition of suspended solids and corrosion in the equipment through which the cooling water passes. Scale formation limits heat transfer and is destructive to heat exchangers and other plant equipment; therefore, scale prevention chemistry is extremely important in recirculated cooling water system design. Scale can be controlled by optimization of chemical concentrations, pH and water temperature. In a rec irculated cooling water systems as shown in Figure 4, water is evaporated which concentrates the dissolved solids contained in the feed water. Make
- up water is added to the cooling water system to replace the water that is evaporated. The maximum cycles of concentration allowable and still minimize scale formation is a function of water chemistry. Impurities that form scale will determine the maximum cycles of concentration. Silica and Calcium concentrations are typically used to determine the cycles of co ncentration. Typical allowable concentrations of impurities in open recirculated cooling water are as follows: ppm

Total Dissolved Solids 3,000 Total Suspended Solids 200 Oil and Grease 10 pH Range 6.8 to 8.0 Aluminum (as Al) 1 Iron (as Fe) 1 Am monia (as NH 3 ) 10 Calcium (as CaCO 3 ) 1000 Copper (as Cu) 0.2 Chlorides (as Cl) 1000 Silica (as SiO 2 ) 150 The quality of the intake water is an important factor in the design of cooling water systems. In open recirculated systems, the intake water can be pretreated to lower thePage 10 of 50

concentration of specific ions in order to achieve an optimized number of cycles of concentration. There can be limitations on the maximum return water temperature in both closed loop and open recirculated systems. In once
-th rough systems there is usually a limitation on the return temperature depending on environmental considerations of the source of the water. In open recirculated water systems, the return temperature is often dictated by the need to limit corrosion in the cooling water piping in the refinery. Cooling water return temperatures of 100 o F to 110 o F are typical. Corrosion in the cooling water piping and heat exchanges is caused by the dissolved oxygen contained in the recirculating water, dissolved salt concentration and the temperature of the cooing water return. This is controlled by limiting the temperature of the return cooling water, and by the addition of corrosion inhibitors.Page 11 of 50

II.5 How are these cooling needs and requirements/limitations met? In once
- through cooling water systems, the intake water can be clarified to remove suspended solids and any limitation on the return water temperature can be met by increasing the flow of water. Makeup water to recirculated cooling water systems may be clarified to remove suspended solids and/or softened prior to being used as cooling water make
- up. Frequently a surface water or well water source is found that does meet minimum quality specifications without prior treatment. The circulating cooling water is treated with a variety of chemicals to control scaling, deposition, biological growth and corrosion. Sulfuric acid is most often used to control pH. Softening and other methods of removing dissolved solids prior to using the water for cooling tower makeup are usually n ot cost effective because of the relatively large volume and low concentration of solids. Dissolved solids removal from a cooling tower with sidestream softening is usually more cost effective because the impurities are more concentrated.Page 12 of 50

II.6 What dictates which cooling approach is used? Wh en cooling systems are designed for use in refineries a series of evaluations and decisions are made. The following flowchart illustrates such a decision tree.

No Yes

Yes

No

No Yes Yes

No Determine temperature to which process stream needs to be cooled

Is stream hot enough for steam generation

Is stream hot enough for heat recovery Design steam generator and determine process outlet temperature

Is air cooling feasible

Use cooling water exchanger Design heat exchange with other process streams

Design air cooler and determine outlet temperature

Is further cooling required

DonePage 13 of 50

In general, lower process outlet temperatures can be achi eved using water coolers than using air coolers. This is because the dry bulb temperature of the ambient air determines the lowest achievable temperature in air coolers and the wet bulb temperature of ambient air is the controlling factor for cooling wate r exchangers

. After going through the analysis as shown in the chart above, the heat load that needs to be rejected to cooling water is determined. Then an evaluation of once through cooling versus recirculating cooling water is carried out. The factors t hat go into this evaluation include:

 Location of the refinery with respect to the water source. In some cases local regulations might preclude the use of once through cooling water.
 The required cooling water supply temperature based on the cooling needs in the refinery.
 Plot space considerations within the refinery.
 The quality of the fresh water with respected to contaminants such as total dissolved solids, chlorides etc. needs to be evaluated. If the dissolved solids content of the water is high it wil l lower the number of cycles of concentration in the cooling tower. Consequently, the makeup water and blowdown treatment requirements will be higher.Page 14 of 50

II.7 What volumes of cooling water are required for various approaches? Once -through cooling system: In a o nce through system the volumetric flow of the water required is dictated by the amount of heat that needs to be rejected (Btu/hr) and the maximum allowable discharge temperature. For example, if a refinery needs to reject 130,500,000 Btu/hr with an intake temperature of 85 o F and a maximum discharge temperature of 100 o F, the flowrate of water is calculated as follows:


### 500 ) 85 100 ( 000 , 500 , 130 ) ( 

  gpm Flowrate = 17,400 gpm Even though this circulation rate is small compared to a mid sized refinery, it is used for illustratio n purposes because EPA used this size in the EPA study. The next higher EPA case was 104,000 gpm, which was considered too high to use as a representative case. Open Evaporative cooling system: The cooling water required in this type of system is the wate r required to makeup the losses due to:

 Evaporation
 Drift (entrainment)
 Blowdown (% of the makeup rate to prevent buildup of ions in the system)

Blowdown (B) Evaporation (E) Drift (D)

Cooling Tower Process Cooler
Makeup (M)Page 15 of 50

Makeup Requirement The make up water rate (M) is the sum of the evaporative losses (E), drift losses (D) and the blowdown (B). 

## B D E M    (1) The evaporative loss is a function of the heat rejected by the cooling tower and the drift loss is a function the circulation rate. The amount of dissolved solids (TDS) coming into the system with the make up water has to go out of the system with the blowdown stream to prevent TDS buildup in the circulating cooling water. Cycles of concentration (n) is calculated by:

n = TDS concentration in circulating water (y) TDS concentration in makeup water (x) 

## ) ( ) ( x n y   (2) and since the TDS concentration of the blowdown is the same as the circulating water 

### ) )( ( ) ( y

D B x M   (3) Combining equations (2) and (3) 

## ) )( ( ) ( nx

D B x M   (4) Therefore 

## ) ( D B n M   (5) Combining equations (1) and (3) 

## 1 ) 1 (

    n D n E B (6) and 

## ) 1 ( ) (

  n E n M (7) Wh ere: M = amount of makeup water E = amount of evaporated water D = amount of water loss by drift (specified by tower manufacturer) B = amount of blowdown n = number of cycles of concentration x = mass fraction of TDS in the makeup waterPage 16 of 50

The same equations apply when considering blowdown constituents other than TDS (e.g, silica, hardness, etc.)The following example illustrates the calculation of these parameters Assumed Cooling Tower Circulation rate 17,400 gpm Assumed Temperature Difference 15 o F Calculated duty (circ rate x temp. diff) 131 MM Btu/hr Heat of Vaporization (HV) 1037 Btu/lb Evaporation ( 

### 500

 HV Duty ) 252 gpm Dr ift (assumed to 0.1% of circulation) 17 gpm Assumed cycles of concentration 5 Blowdown (by equation 4) 46 gpm Makeup (by equation 3) 315 gpmPage 17 of 50 III. Recirculated Cooling Water Technology III.1 What are the components of a recirculated cooling tower system? Recircu lated cooling tower systems can be divided into three parts:

 Intake structure including the intake screens, pumps and piping

 Cooling Tower and cooling water circulation pumps, including any pretreatment systems

 Recirculation piping and heat exchangers a) Int ake Structure: Consists of the piping from the intake source including screens to remove suspended solids and marine organisms, intake pumps (number of pumps depends on the size and includes operating and spare pumps), and the piping from the intake pumps to the refinery. b) Cooling Tower : The cooling tower consists of basin capable of providing about 10 minutes of holdup based on the circulation rate of the system, a tower equipped with fill (wood or fiberglass), cooling tower sump, distribution piping and n ozzles to maximize air/water contact, fans to force atmospheric air through the tower and circulating pumps. c) Pretreatment : Depending on the quality of the intake water, a clarifier is used to remove suspended solids. If the dissolved solids content of t he intake water is too high, other pretreatment methods such as lime softening, ion exchange and reverse osmosis are included to increase the cycles of concentration allowable in the cooling tower. Pumps are required to transfer the water from the clarifie r to the cooling tower and the recirculating cooling water. d) Cooling Water Treatment : Chemical treatment of the recirculating water requires that chemical feed systems be installed. This includes tanks and pumps for each of the chemicals required. e) Recircu lation piping: This consists of the cooling water supply and return piping to the various process units in the refinery. Also includes all the sub
- headers in the refinery to carry the cooling water to heat exchangers. f) Blowdown Treatment: The blowdown fro m the cooling tower system is typically sent to the wastewater treatment plant. This stream would contain high dissolved solids and would contain hydrocarbons if heat exchanger leaks have occurred.Page 18 of 50

III.2 What are the limitations of using recirculated systems? The makeup water to a cooling tower may come from wells, reservoirs, lakes, rivers, and even treated wastewater. The impurities in these makeup water sources may cause a number of water related problems in the cooling system. Corrosion, scale, biological fouling, sludge formation, and chemical attack on the cooling tower components may be experienced when the chemistry of the cooling water is not properly controlled. The quality of the makeup water determines the amount and type of internal chemical treat ment required. Chemicals are added to protect the metal surfaces from the following problems:

 Corrosion.
 Scale deposits.
 Biological fouling. In a cooling tower, the recirculating water is saturated with atmospheric air as it passes through the tower. Thi s condition, combined with warm water temperatures and increasing dissolved salt concentration, results in water that is very corrosive to carbon steel. Corrosion inhibitors are required for all recirculated cooling tower systems. Selection of the optimu m inhibitor and dosage is based on the analysis of the water, materials of construction, environmental regulations, and other factors including cost of chemicals. Typical inhibitors are phosphates, molybdates, zinc and polyphosphates. Several corrosion in hibitor chemical treatment programs have been developed in the past fifteen (15) years. The most successful of these programs have been the stabilized phosphate and zinc phosphate treatments, which incorporate the use of copolymer dispersants. Scale is an adherent insoluble deposit laid down on surfaces of the cooling water system during operation, causing impaired heat transfer. Calcium carbonate is the principal scale formed when calcium bicarbonate breaks down and becomes even more insoluble as the te mperature rises (reverse solubility). Scale control can be accomplished through limiting the cycles of concentration. Refinery cooling towers also require continuous chlorination for control of microbiological activity and usually acid for pH control, wh ich prevents calcium carbonate scaling .Page 19 of 50

III.3 What must be considered when increasing cycles of concentration in cooling towers? Cycles of concentration are limited by makeup water quality, the design of the cooling tower itself, the design of the cooling sys tem piping, heat exchangers and by the type of pretreatment available for the makeup water. Variability of the makeup water quality must be considered: changes in total suspended solids, iron, calcium to magnesium ratio, alkalinity, sodium, silica, sulfate and chloride can lead to control problems, corrosion and deposition. Blowdown rates are difficult to control with variable quality makeup water, since the blowdown rate is set or adjusted based on laboratory tests. Variations in makeup water quality mak e setting this rate difficult without either exceeding chemistry limitations or wasting water. The only solution to this problem is on
- line analysis of some components of the circulating water quality, such as conductivity, pH and phosphate. These contin uous analyses are used to drive automatic blowdown valves, treatment chemical pumps and sulfuric acid pumps via a PLC controller. The cost for such automation is about $100,000 installed for a 17,400 gpm system. The level of reliability is questionable a s the various probes become fouled with deposits, requiring a preventative maintenance program to operate dependably. Similarly, chemical dosages are set based on makeup water characteristics and the cycled up components in the circulating water. Variable quality makeup water makes it difficult to control dosages without either overshooting or undershooting the proper dosage. As stated above, the use of automated systems is the only means of addressing the situation, adding both equipment and labor costs to the operation of the cooling system. Commonly used values (based on industry practice) exist for each of the potential contaminants that may be found in the makeup water stream. These values are set for cycled up (concentrated) cooling tower water and therefore directly limit the maximum cycles of concentration that can be achieved before equipment fouling, equipment scaling or equipment corrosion problems are encountered. The various limits are set based on many years of industry experience as well as extensive testing by various suppliers of treatment products and by the end users themselves. Industrial water treatment has been practiced extensively at least since the 1950’s so there is a large body of knowledge on the subject. Calcium carbonate depo sition is controlled by limiting the calcium level, generally no higher than 1,000 parts per million, by the addition of sulfuric acid to control pH within a range of 6.8 to 8.0 and by the addition of dispersants specific to calcium carbonate. The genera l limit of 1,000 ppm calcium as CaCO3 assumes the use of such dispersants.Page 20 of 50

Magnesium silicate limits are set to control scaling of surfaces contacted by the recirculated cooling water. The magnesium silicate limit is an empirical value (product of the mag nesium concentration x silica concentration) set at 100,000 ppm, and can only be controlled by limiting the levels of magnesium and silica in the recirculating water via blowdown. Because carbon dioxide is stripped from the water as it passes through a coo ling tower, the rise in pH (alkalinity) is controlled via the use of sulfuric acid and/or blowdown. Sodium and sodium chloride are limiting factors because of potential damage to the wooden structures of cooling towers and due to the corrosive potential fo r steel and stainless steel equipment components in the cooling water system. The general limit for chlorides is 1,000 ppm. Silica itself must be limited to no more than 200 ppm as SiO2 to avoid scaling. Sulfates must be limited in cooling systems having concrete components, such as the cooling tower basin, to avoid leaching of calcium from the concrete matrix. The general limit for water containing sulfates in contact with concrete systems is 3,000 ppm as SO4. Copper and iron in the makeup water can caus e severe deposition and corrosion problems at quite low levels. Copper levels above 0.2 ppm and iron levels above 1 ppm are unacceptable in the recirculated cooling tower water. Suspended solids in excess of 200 ppm in the cooling tower water are generall y not tolerated due to fouling and plugging problems. Typical design flow velocities for refinery heat exchangers range from 3 to 5 feet per second. Older systems may have flow velocities as low as 1 to 2 feet per second. A calcium limit of 1,000 ppm as CaCO3 would be acceptable for the higher velocities; however, a limit of 500 ppm as CaCO3 would be required for the lower flow velocities. Examples of makeup water quality affecting cycles of concentration would be as follows. Given adequate flow velocit ies, one could assume an upper calcium limit of 1,000 ppm as CaCO3. A makeup water containing 100 ppm of calcium could theoretically be cycled 10 times, 200 ppm of calcium in the makeup would limit cycles to 5 times, 300 ppm would limit cycles to 3.3 time s, and so forth. Clarification is often used as a pretreatment of makeup water. Clarification of the makeup water can control the levels of suspended solids in the makeup water; however, it will have no effect on the concentration of dissolved solids cont ained in the cooling water.Page 21 of 50

Cold lime softening of cooling tower makeup can be used to lower the calcium and silica levels of the makeup water. Effective cold lime softening can only reduce calcium levels to the 30 to 50 ppm range while silica can general ly be reduced to the 2 to 5 ppm range. Cost for cold lime softening is in the range of $50 per million gallons of water treated. In addition, the use of cold lime softening produces 200 to 300 pounds of sludge for each million gallons of water treated. Sludge disposal adds additional costs to the process.Page 22 of 50

III.4 What quality/quantity of make- up water is required and how is it determined? As illustrated in section II.7 makeup water is a function of the evaporation rate and the number of cycles of concentration. Eq uation (6) and (7) in section II.7 are used to calculate the blowdown and makeup rates 

## 1 ) 1 (

    n D n E B ) 1 ( ) (

  n E n M
where B is the blowdown rate D is the drift rate M is the makeup water rate E is the evaporation rate
n is the numb er of cycles of concentration In the example illustrated in section II.7 the makeup and blowdown rates are as follow: Makeup water

– 315 gpm Blowdown rate

– 46 gpm Using the equations shown above the following chart illustrates the makeup and blowdown as a function of number of cycles of concentration.Page 23 of 50 Figure 5 Makeup & Blowdown vs. Cycles of Concentration

As can be seen from the chart, the rate of change of both makeup and blowdown rates decreases rapidly until the cycles of concentration reaches about 7 after which the rate of decline is small. This is the reason most cooling towers are designed with a cycle of concentration of between 4 and 7. Another consideration is the TDS content of the makeup water and the allowable TDS content of the circulatin g water.

- 200 400 600 800

0.0 5.0 10.0 15.0 Number of CyclesMakeup/Blowdown Water Rate, GPM

Makeup Water Rate

Blowdown RatePage 24 of 50

III.5 Effects of brackish vs. fresh water? Brackish water contains higher dissolved solids such as chlorides than fresh water. The chloride content of the brackish water could be as high as 10,000 ppm. This will impact on the following:

 Cycles of co ncentration

– The cycles of concentration could be reduced to as low as 1.5 to 2 depending on the chloride content of the makeup water. This will require a larger volume of makeup water and also result in a larger blowdown flow.
 Cooling tower

– Due to the higher chloride content of brackish water, the cooling tower will be subject to greater corrosion and could require an upgrade in materials of construction, resulting in higher capital costs.
 Treatment Chemicals

– Depending on the TDS define content of th e circulating water, more treatment chemicals could be required to control corrosion and biological growth. This will result in higher operating costs.
 Circulation Pumps and Piping

– Due to the higher chloride concentration, the material of construction of the pumps and the distribution piping will require an upgrade to corrosion
- resistant alloy material, which will result in significant capital expenditure.
 Heat Exchangers

– The material of construction of the heat exchangers will require an upgrade to al loy materials and result in significant capital costs. These costs could be minimized somewhat by passing the cooling water on the tubeside of the exchanger.Page 25 of 50

III.6 Blowdown flows, handling, treatment? In a cooling tower system, part of the circulating water is removed as blowdown to prevent the buildup of TDS in the system. The example shown in section II.7 illustrates in detail the calculation method. In that example, the blowdown is calculated to be 46 gpm. This is for system in which the cooling tower makeu p water has a calcium concentration of ppm as CaCO3 and is operated with five cycles of concentration. Cooling tower blowdown is typically sent to wastewater treatment in refineries via the sewer. This is because in many cases the pressure on the process side of heat exchangers is higher than the cooling water pressure and any leaks in a heat exchanger would result in the contamination of the cooling water with hydrocarbons. This will impose a hydraulic load on the existing wastewater treatment. The ful l impact on wastewater treatment needs to be evaluated on a case
- by
- case basis.Page 26 of 50

III.7 Factors affecting drift and evaporation losses? In order to obtain efficient heat transfer in a cooling tower, the return cooling water (hot) is sprayed on to the packing to increase heat and mass transfer efficiency. This results in small droplets of water distributed throughout the tower. The high flow of atmospheric air passing through the tower results in the entrainment of some of these droplets, which are released to t he atmosphere and is referred to as drift. Cooling tower manufacturers have developed various methods such as baffling, packing etc. to minimize drift. The manufacturers often consider these design methods and know
- how proprietary. The manufacturers usu ally provide a guarantee on the maximum expected drift from cooling towers. Typical quantity of drift is <0.1% of the circulation rate of the cooling tower. The cooling tower operates on the principle of evaporative cooling by a combination of heat and ma ss transfer. Circulating water is cooled when some of it evaporates, removing the heat of vaporization. The evaporation loss in a cooling tower is a function of the total heat duty that needs to be rejected. The evaporation loss calculated by dividing th e heat duty by the latent heat of vaporization of water. In the example illustrated in section II.7, the evaporation is 252 gpm for a heat duty of 131 MM Btu/hr.Page 27 of 50

III.8 Factors affecting chemical usage and concentrations? The factors affecting treatment chemical usage and concentration are complex and inter
related. Most cooling tower vendors will utilize a modeling program such as WaterCycle to determine the exact requirements and limitations for a given makeup water. In general, the higher the concentration of a scaling or fouling component, the greater the treatment requirement. In almost every instance, the use of sulfuric acid will be required in a recirculating cooling system in order to control the pH of the water. The dosage is dependent upon makeup water alkalinity where the acid requirement is based on alkalinity in the cooling tower; so as number of cycles increases, and consequently the alkalinity increases, the sulfuric acid requirement also rises. Dispersants to control calcium carbonate, magnes ium silicate and silica are dosed based on the levels of magnesium and/or silica contaminant in the cooling water. For example: 200 ppm of calcium would generally require 20 ppm of dispersant while 1,000 ppm of calcium would require 100 ppm of dispersant. Use of chlorine or bleach to control microbiological growth and fouling is higher in cooling towers than in once through systems. Continuous chlorination is generally required for adequate control in refinery cooling towers with the dosage in the range of 2 to 5 pounds per 1,000 gallons of recirculation capacity. Some operators of cooling towers find that intermittent additions of chlorine are more effective. Corrosion inhibitors are not generally required in once through systems while recirculating syste ms will require inhibitors to control corrosion of copper alloys and carbon steel piping and heat exchangers. Again, the higher the cycles of concentration, the higher the requirement for corrosion inhibitors.Page 28 of 50 IV. Converting from Once -through to Cooling Towe rs IV.1 What would be involved in changing from once- through cooling to cooling towers? The typical petroleum refinery is complex system of process components that evolved over decades. Designers provided heat removal systems based upon the needs of the indivi dual components and the available cooling utilities. Plot siting issues are major design problems at refineries. Changing once
- through cooling systems to recirculating systems will involve site
- specific piping and equipment location issues that may not b e apparent to those more familiar with power plants. Each refinery component may have several different heat transfer needs, ranging from pump cooling to steam eduction
- generated vacuum. If the cooling tower can provide similar cooling capacity, then the p rocess heat exchangers will not need replacement. The problem is that the temperature difference provided by once
- through cooling is not readily replicated with cooling tower
- based systems. Consequently, the complex nature of a petroleum refinery will de mand site
- specific cooling system designs having multiple cooling towers (possibly placed far away from the process unit), the replacement of pumps, and/or the replacement of process heat exchangers (and possible associated piping, depending upon system hydraulics). There are practical aspects that need to be taken in account if changing from a once
through system to a recirculating system is being considered, such as:

 A key factor to refinery profitability is to cut as deeply into the vacuum tower residue as possible. This in turn means pulling as low a vacuum as possible in the vacuum column. Vacuum is generated using steam jet ejectors, and lower column vacuum requires more steam. Lower vacuum results in lower condensing temperatures, wh ich in turn requi res cooler water.
 Installation of a cooling tower in an existing refinery is dictated to a large extent by the space available and not by optimum location to minimize pipe runs, access to utilities etc. W hile it might be optimum to install one cooling tower to replace the existing once through system, space and logistics might require building multiple cooling towers. This invariably leads to increased costs. A cooling tower requires a sump or basin for collection and storage of the water recirculated over the tower and through the system. Hydraulic and pumping requirements set a minimum volume for the sump. Generally, the sump is sized to provide for at least 10 minutes of holdup based on the recirculating rate.Page 29 of 50

New recirculation pumps with enough he ad to overcome the hydraulic losses of the supply piping, heat exchangers and return piping plus the static head of the cooling tower will also be required. New cooling water supply and return piping to and from the cooling tower would need to be installed

. Since the flow of makeup water in the case of recirculation system is significantly smaller than a once through system, 315 gpm versus 17,400 gpm, (for the case illustrated in section II.7) new intake structure, supply pumps and lines to the refinery ma y be required. The thermal rating of heat exchangers in the refinery will need to be reviewed to account for any differences in the cooling water supply and return temperatures. This could be a very significant cost issue. The example shown in section IV .5 illustrates a case where more than 20% more heat exchanger area would be required.Page 30 of 50

IV.2 Effects on wastewater discharge volumes and quality? In a once through cooling water system there are no discharges of wastewater from the system. In an evaporative coo ling water system, the blowdown, which is a function of evaporative and drift losses and the number of cycles of concentration (shown in the example in section II.7 to be 46 gpm) is usually sent to wastewater treatment. The contaminant in the blowdown is high dissolved solids, and possibly hydrocarbons, if leaks from heat exchangers occur. Cooling tower blowdown is considered a process wastewater and is subject to refinery effluent guidelines.Page 31 of 50

IV.3 Effects on metallurgy in piping and exchangers? In refineries that use fresh water as the source of once through cooling water, the piping and heat exchangers (cooling water side) are usually designed with of carbon steel but in some cases corrosion resistant material are used. If the system is changed to a recircu lated cooling water system the TDS content of the circulating water can be higher that the once through water. If the TDS is kept within reasonable limits (< 3000 ppm), carbon steel would be an acceptable material of construction. If brackish water is use d for the cooling tower makeup, higher alloys such as admiralty, copper nickel alloys etc. would need to be considered and would result in higher capital costs. As mentioned before, if the pumps, distribution piping and exchangers in the refinery need to b e upgraded, it would require significant capital expenditures as well as result in significant costs in order to reduce impacts on refinery production capability. In refineries that use salt water as the source of once through cooling water, the piping and heat exchangers would most likely be made of alloy material. In these cases, changing to a recirculating cooling water system would not require changes provided the dissolved solid concentration in the recirculating water are kept within reasonable limits (described previously in this report).Page 32 of 50

IV.4 Effects on refinery piping configurations? If the temperature difference between the cooling water supply and return is the same for both once through and evaporative cooling water systems, resulting in the same ci rculation flow, the impact on piping configuration in the refinery should be minimal. If the temperature difference is substantially different resulting in different circulation flows, the piping inside the refinery will need to be evaluated to ensure th at the flows are within the allowable pressure drop and velocity limits. Typical limits are as follows:

Pressure drop psi/100ft Ma ximum velocity (ft/s) 1.0

– 2.0 10 The pressure drop limits are usually imposed in order to keep the hydraulic losses in th e system within reasonable limits. Lower pressure drops will result in lower velocities and could result in excessive scaling and corrosion. Higher pressure drops will require the circulating pump differential head to be higher resulting in increased cap ital and operating costs.Page 33 of 50

IV.5 Effects on heat exchanger capacity? In once through cooling water systems the supply temperature is the bulk temperature of the water source. Any seasonal variations in the cooling water supply temperature are also taken into a ccount in the design of heat exchangers in the refinery. In evaporative cooling towers the local wet bulb temperature (1) determines the cooling water supply temperature. Typically, a 10 o F approach (2) between the wet bulb temperature and the cooling wate r supply temperature is taken in the design of cooling towers
– i.e., the cooling water supply temperature is 10 o F above the design wet bulb temperature. Consequently, the cooling water supply temperature from the cooling tower in a recirculating system i s typically warmer than the supply temperature for once through system. This will lower the log mean temperature difference (3) in heat exchangers in the refinery and in certain cases require significantly more heat exchanger area. For example:
Units On ce Through Cooling

Tow er Heat Exchanger duty MM Btu/hr 1.0 1.0 Process Inlet Temperature o F 180 180 Required Process Outlet Temperature o F 120 120 Cooling W ater Inlet Temperature o F 80 90 Cooling W ater Outlet Temperature o F 95 105 Log Mean Temperature Difference (LMTD) o F 60 49 Heat Transfer Coefficient (U) Btu/hr
-ft2 125 125 Required Heat Exchanger Area ( 

### U LMTD Duty  ) ft2 133 163 As illustrated by this example, 22% extra heat exchanger area would be required if the system is cha nged from a once through to a cooling tower system. For the case illustrated in section II.7 this would mean that an additional 3,900 ft2 of heat exchanger would be needed. But for practical reasons, in some cases, new heat exchangers would need to be installed instead of installing only the additional area required. This would lead to significant capital costs. A detailed analysis of all the exchangers in the refinery should be carried out in order to understand the impact on the whole refinery. (1) Wet Bulb Temperature : The wet bulb temperature is a measure of the amount of moisture, in the form of invisible water vapor contained in the air. As the name implies it is measured by a standard thermometer whose bulb is covered by a muslin sleeve and that has been moistened by pure water.Page 34 of 50 The principle of the wet bulb thermometer is as follows; Water evaporates from the muslin cover passing into the air in the form of invisible water vapor. This is accomplished by absorbing heat from the thermometer bulb and t he mercury it contains. The thermometer therefore indicates a lower temperature than that of the dry bulb thermometer. (4) The difference between the readings of the dry and the wet thermometers is called the depression of the wet bulb. If the air contains nearly all the moisture it can possibly hold, evaporation from the muslin will be slight and the depression of the wet bulb will be small. However, if the air is very dry, containing little moisture, evaporation will be quite rapid and the depression of th e wet bulb will be quite large. In hot dry desert climates wet bulb depressions of over 45°F have been observed, but at sea the depression is seldom more than 10°F. If the air contains all the moisture it can possibly hold, there is no evaporation from th e muslin, and the dry and wet bulb thermometers will read the same. When this condition exists the air is said to be saturated. (2)Approach Temperature: The lowest possible temperature to which water can be cooled in a cooling tower corresponds to a wet bulb temperature of the air. This is not practical because at the wet bulb temperature, the partial pressure of the water in the air is equal to the vapor pressure of water resulting in a zero driving force. The difference between the water outlet temperature and the wet bulb temperature is called the approach temperature in a cooling tower. This is typically about 10 o F. (3) LM TD: Logarithmic Mean Temperature Difference (LMTD) is a measure of the difference in temperature between the hot side and cold side o f a heat exchanger. It is defined as          

  

2

1 2 1 T T Ln T T LMTD

Where, T1 and T2 are the difference in temperature between hot and cold side fluid at two ends of the exchanger. LMTD is an indication of the driving force available for heat exchange. (4) Dry Bulb Temperature : The dry bulb temperature is the atmospheric temperature of air at a specific location and at a specific time. It is measured by exposing a thermometer to the atmosphere. The temperature reported by the meteorological stations is the dry b ulb temperature.Page 35 of 50

IV.6 Additional space requirements? Installing a new cooling tower will require additional plot space in the refinery. For the cooling tower example used in this study (17,400 gpm circulation rate), the plot space required for the cooling tower is 100 feet x 60 feet. This includes the space required for the ancillary equipment such as the circulation pumps, chemical feed systems etc. In an existing refinery, the location of the cooling tower is often dictated by the space available and not b y optimum location to minimize pipe runs, access to utilities etc. Wh ile it might be optimal to install one cooling tower to replace an existing once
-through system, space constraints and logistics might dictate the use of multiple cooling towers resultin g in increased capital expenditures. Other considerations include impact of cooling tower drift on roads, houses and process units. The routing of the interconnecting piping between the cooling tower system and the existing cooling water distribution syst em needs to be considered. The cooling water intake structure for recirculation systems is significantly smaller that a once through system (315 gpm vs. 17,400 gpm in the example illustrated in section II.7) and, therefore, the space required for the new i ntake structure would be significantly smaller.Page 36 of 50

IV.7 Changes in water treatment requirements? Once through cooling systems are in general not chemically treated. There may be a need to chlorinate the once through cooling system intermittently to control mic robiological activity and fouling. Some once through systems use low levels of dispersant, 1 to 5 ppm, to control calcium carbonate scaling and suspended solids fouling. The change to cooling towers would require the feed of several different types of ch emicals for adequate control and protection of the cooling system. a) Sulfuric acid would be required to control alkalinity. b) Chlorination would be required to control microbiological fouling. c) The continuous feed of polymeric dispersants would be required to control calcium carbonate scaling, magnesium silicate scaling and suspended solids fouling. d) The continuous feed of corrosion inhibitors would be required to control the corrosion of copper alloys and carbon steel components of the system. Corrosion is an electrochemical process; the higher the TDS of the cooling water, the higher the rate of electrochemical reaction and the greater the concern with corrosion issues for cooling towers over once through systems. e) There may be a requirement for clarificatio n, to remove suspended solids to produce makeup water suitable for cooling tower use. f) There may be a requirement for cold lime softening, to produce makeup water with a calcium concentration suitable for cooling tower use. The following table lists the qua ntities of chemicals required for treatment for a 17,400 gpm cooling tower. As calculated in section II.7 the blowdown for this cooling tower would be 46 gpm and makeup water would be 315 gpm.
Chemical Concentration(ppm) in Circulating Water Usage (lbs/yr)* Dispersant 100 27,600 Corrosion Inhibitor 20 5,520 Sulfuric Acid 150 41,400 Chlorine 150 41,400 *assumes operation 24 hours per day, 365 days per yearPage 37 of 50

IV.8 Changes in water pressure requirements? The typical arrangement in a once through cooling system is to provide enough pressure in the supply pumps to overcome the hydraulic losses in the cooling water supply piping, heat exchangers and cooling water return piping in the refinery. As discussed, the volumetric capacity of once through cooling wate r pumps is significantly lower for cooling tower systems. Therefore, new pumps and supply piping will need to be installed to provide makeup water for the evaporative cooling system. New cooling water circulating pumps need to be installed inside the refinery to carry the cooling water to all the exchangers and return it to the cooling tower. The table below gives a comparison of the typical pressure requirement of the circulating pumps in a once through system and a recirculating cooling water system.

Component Differential Pressure A llowance (psi) Recirculating Cooling Water System Once Through Cooling Water System Cooling W ater Supply Main Header 15 15 Cooling W aster Supply Branches 5 5 Cooling Tower Static head (~45 ft.) 20 0 Cooling W ater Return Branches 5 5 Cooling W ater Return Main Header 15 15 Differential Head Required 60 40 Differential Head Required 140 ft 93 ftPage 38 of 50 V. Changing to Dry

Cooling V.1 What would be involved in changing to dry cooling? There are two types of dry cooling systems: direct dry cooling and indirect dry cooling. Direct dry cooling systems utilize air to directly condense or cool the process stream wh ile indirect dry cooling systems utilize a closed cycle water cooling system to cool the process stream and the heated water is then air cooled. Indirect air cooling is used in power plants while direct cooling is used for certain applications in refineries depending on process outlet temperature and plot space considerations. Indirect air cooling is not used in refineries because the lowest achievable cooling water supply temperature would be about 10 o F higher than the dry bulb temperature for that location. Frequently, process streams in refineries need to be cooled to a temperature lower than the dry bulb temperature and, therefore, indirect dry cooling is not technically feasible. Direct air cooling used in refineries is dictated by the dry bulb temperature at that site and conditions of the process streams such as inlet temperature and required outlet temperature. As previously discussed, air cooling can be used in refineries only for specific applications and even in these applications cooling water exchangers are installed downstream of the air coolers in order to meet the process re quirements. Additionally, since the heat transfer coefficient for air coolers is relatively low, air cooled exchangers tend to be large, require significant plot space, and can be a source of noise. Replacement of once through cooling with air
- cooled heat exchangers would demand an economically infeasible number of changes to the existing process equipment. Furthermore, whereas cooling water shell
- and
- tube exchangers can be stacked vertically in process units, air coolers cannot be stacked (because lower units would send heated air to higher units) and so it may be physically difficult or impossible due to space constraints to replace water
- cooled exchangers with air
- cooled exchangers.Page 39 of 50 VI. Cooling Water Recycle and Reuse VI.1 What are the options for recycle/reus e of cooling water? Practicality? Petroleum refineries in the U.S. practice water recycling where possible. For example, steam condensate is recycled back to the to system since it has a low dissolved solids content. Condensate that has been in contact with process fluids is also recycled, such as distillation overhead condensate and stripped sour water recycled to the desalter. In general, water needs to have a low dissolved solids content in order to be considered as a candidate for recycle in a petrol eum refinery. Cooling tower blowdown usually has a high dissolved solids content and is sent to wastewater treatment.Page 40 of 50 VII. Cooling Water Intake Structures VII.1 What types of intake structures are used at refineries Refinery water intake structures were built to accommodate design flow rates and to screen out trash, aquatic life, and debris that could damage pumps and heat exchange equipment. An intake structure typically consists of a pipe submerged in the waterway or a concrete channel at the shore, each with b ar screens or trash racks. More sophisticated designs can include traveling screens, fixed screens, perforated pipe, and velocity caps; however, it is believed that most facilities use simple intake structure designs.Page 41 of 50

VII.2 What is involved in retrofitting ref inery intake structures (e.g., moving screens)? Upgrading refinery intake structures involves a variety of considerations, and will depend on the type of upgrade being implemented.

 Permitting. Any construction at the shore of a waterway will require permi ts from the Army Corps of Engineers under Section 404 of the Clean Water Act. Such permits can involve significant studies to evaluate the impact of new construction on the waterway. In some cases, certain technologies (e.g., velocity caps) may be difficu lt to permit because of potential interference with navigation.
 Redesign of intake structure to reduce intake velocity . Meeting potential maximum intake velocity requirements could mean extensive redesign of the structure to make the intake area larger or to replace pipes with intake channels.
 Redesign to accommodate new technology . Retrofit of new technology would likely require substantial disruption of the existing operation. For example, installation of traveling screens will likely require increas ed intake channel width and depth. If the existing intake is a pipe, installation of traveling screens could require shutdown of the cooling water flow for days to weeks.
 Fish return system. For traveling screens, a fish return system would be needed to return fish and other aquatic life to the waterway. Such a system would require adequate distance from the intake to insure that the organisms are not re
- entrained.
 Utility

Access. Traveling screens and some other technologies would require electrical service to operate pumps, motors, lighting, etc. In many cases, the intake can be remotely located, and installation of electrical service can be prohibitive. For passive screens, an air supply would be required to provide periodic pulse
- cleaning capabi lities.
 Tie - in/refinery

dow n time. Installation of new intake structures would likely require that the cooling water flow be curtailed or stopped completely while the tie
- in is made. Depending on the nature of the tie
- in, the activity could take days or even weeks to complete. Since the refinery would not be able to operate at capacity during this time, the cost of lost production can be substantial.
 Land availability . In some cases, access to land at the water body may be limited, and installation of larger equipment and associated utilities may require the purchase of additional property.Page 42 of 50

VII.3 Other information on cost - effectiveness of intake structure controls? The cost
- effectiveness of intake controls can be highly variable for the population of refinery intakes. In some cases, intake controls can be very cost
- effective; that is, the technology provides a significant reduction in adverse environmental impact (e.g., ambient fish population increases through reduced impingement and entrainment) of the coo ling water intake. On the other hand, in some cases, even the best controls will have little impact on the populations of aquatic species in the water body. Therefore, evaluation of cost
- effectiveness of controls should be done on a site
- specific basis. Some of the factors that will impact cost
- effectiveness include ambient species that would be potentially affected, water body size/flow/tidal exchange, prevailing currents, ambient water quality for supporting aquatic life, and seasonal variations in all these factors. In the Technical Development Document (EPA
- 821
- R
- 01
- 036, November 2001) for the 316(b) regulations for new facilities, EPA has provided documentation of entrainment and impingement performance of various control technologies at power plants . The table below summarizes the performance information for some of the technologies that may be applicable to refinery intakes. However, the TDD notes that, although these technologies are promising, the performance is subject to site
- specific considerations, and that there are relatively few successful examples of full
- scale installations. Therefore, information on qualitative costs and technical feasibility considerations has been included in this table to provide further insights on technology selection. Technology Effectiveness Relative cost Technical Feasibility Impingement Entrainment Diversion/behavior al devices Highly variable,

depending on species No effect Low Generally feasible Fabric Screen 100% >90% Low Subject to damage under severe conditions Velocity cap Species dependent, up

to 90% reported No effect Moderate For offshore intakes We dge
-wire screen Reported to be very

effective ("no impingement") Variable, depending on slot size Moderate Prone to plugging, biofouling; adequate amb ient water current needed. Traveling fine
mesh screen Up to 90% Variable, depending on mesh size, over 90% reduction reported for certain species Moderate Prone to plugging, biofouling. Little operating experience. Traveling screen with modified fish ret urn system 70
- 80% reduction over

conventional traveling screens Generally not effective, depends on mesh size Moderate Generally feasiblePage 43 of 50 VIII. Cost Implications VIII.1 Cursory review of the EPA’s “Draft Initial Cost Estimates” -- May 17, 2001? Section 316(b) of th e Clean W ater Act requires EPA to ensure that the location, design, construction and capacity of cooling water intake structures reflect the best technology available for minimizing adverse environmental impact. EPA prepared a draft report dated May 17, 20 01, that contains the preliminary analyses to estimate the cost of cooling water intake structures and cooling system technologies that are in place at existing facilities. The draft document was reviewed and we offer the following comments: Chemical Addit ion Systems: Chemical addition system costs are not addressed in the draft report. Typically, once through cooling systems in refineries do not have chemical addition systems other than intermittent chlorination. The chemical use is cooling tower system s contribute significantly to operating costs Salvage Credit : In the EPA report, credit is taken for the salvage value of equipment when changing over from once through to recirculating cooling water system. Credit for old equipment in the case of refiner ies is location specific and depends to a large extent on the condition of the old equipment. Our experience shows that salvage credit for equipment in good condition is no more than 10 cents on the dollar. The analysis of costs should be based on no cre dit for salvage on old equipment and piping. Installed Costs : An installation factor of 30% on equipment costs has been used to determine installed costs. Our experience with refineries, supported by the literature, indicate that this factor should be 300 to 600% of equipment costs  depending on the location of the refinery and the general standards (for piping and equipment) that are typically applied to equipment and piping in refineries. Dry Cooling : The costs associated with the Dry Cooling option are incomplete. They do not include the costs of replacement of turbines, which would represent significant capital costs.

 Installed cost should reflect the total fixed capital investment, including not only equipment installation, but costs of piping, utilities, instrumentation, yard improvements, service facilities, buildings, contractor’s fees, and contingenc y. Fixed capital investment typically ranges from 371% to 501% of the purchased equipment cost; or up 566% under inflationary economic conditions. From Plant Design and Economics for Chemical Engineers, Second Edition, Peters, Max S. and Klaus D. Timmerhaus, McGraw
- Hill, New York, 1968, p.105.Page 44 of 50

Switching entirely to dry cooling for refineries is not a viable option since, as discussed earlier in this report, the cooling needs frequently require the process streams to be subcooled and it is not possible to achieve this using air coolers. Economic & Engineering Analysis of Proposed 316(b) New Facility Rule, August 2000 The EPA draft report stated that with certain exceptions, EPA developed all of the draft initial cost estimates using the cost data presented in the Economic and Engineering Analysis of Proposed 316(b) New Facility Rule, August 2000 (EEA). After review of the EEA, taking into account the referenced exceptions, it ap pears that the cost estimates presented to convert once through cooling to a recirculating system are based on a number of assumptions that are not representative of conditions at petroleum refineries and do not recognize the inherent differences between refinery and power plant cooling systems. If these assumptions were changed and the differences were recognized, the cost for conversion of once through to recirculating systems (cooling towers) at refineries would be significantly higher. Examples of these assumptions and factors are briefly described below along with the reference in the EEA. a) Differences between Refinery and Power Plant Cooling Systems : The cost for conversion of once through cooling to cooling towers at refineries would be significantly h igher than for power plants. This is due to the inherent differences between petroleum refineries and power plants. Based on the greater number of refinery sources that require cooling water and the typical geographic layouts of these various refinery sources, petroleum refineries would tend to end up with more cooling towers, of smaller size, than power plants. For equal intake cooling tower flows, the cost for conversion at petroleum refineries would therefore be significantly greater than for power plants. The reference that discusses the cost of switching to a recirculation system is found on page 6
-4 of the EEA. b) Differences in Refinery Cooling Tower Intake Flows : The average cooling tower intake flow is presented for the category of "petroleum and coal products", Appendix A, Table A
- 2. The number presented is 320 gpm, for 3,509 facilities. There are only approximately 150 refineries operating in the United States, so this sample base of 3,509 facilities is not representative of refineries. A limited survey of five refineries using once through water shows the average intake flow to be twenty times higher than the EPA estimate. Consequently, the actual average intake flow rate for refineries is significantly greater than used in the EEA. This suggests that the cost curves that were developed and included in Appendix A, which correlates capital cost and flow may be inaccurate.Page 45 of 50

c) Effect of Additional Refinery Heat Exchanger Capacity . As described in the response to question II
- 13, use of cooling tower water in stead of once through cooling water will result in a 22% increase in heat exchanger area. Considering that refineries are more likely to have significantly more sources that require cooling than power plants, the costs for additional heat exchanger capacity, for the same cooling water intake flow, will be greater at refineries than for power plants. This factor is not included in the discussion on page 6
-4 of the EEA on switching to a recirculating system.Page 46 of 50

VIII.2 Estimate the cost of installing a 17,400 gpm cooli ng tower Capital Costs: For comparison purposes, the cost estimate for a 17,400 gpm (circulation flow) cooling tower was developed. Even though this circulation rate is small compared to a mid sized refinery, it is used for illustration purposes because EPA used this size in the EPA study. The next higher EPA case was 104,000 gpm, which was considered too high to use as a representative case. The cost estimate includes the cost of the raw water intake system, a clarifier for suspended solids removal, induced draft cooling tower, circulating pumps and interconnecting piping. The costs do not include any changes that might be required to the heat exchangers in the refinery due to the change from once through to a recirculating system. The costs also do not include demolition costs and does not take any credit for salvage of old equipment and piping. Figure 6 shows a schematic of the system that illustrates the systems included in the cost estimate. Typically, a travelling screen would not be installed for a small intake flow (315 gpm) as is the case for this tower system. However, since the purpose of the cost estimate is to compare it to the estimate in the EPA draft document, a travelling screen has been included in the estimate. The costs are based on ven dor written and oral quotes for major equipment and ENSR’s database for other items. Basis: Cooling W ater Circulation (gpm) 17,400 Design Temperature Difference ( o F) 15 Design Dry Bulb Temperature ( o F) 91 Design Wet Bulb temperature ( o F) 80 Cooling W ater Supply Temperature ( o F) 90Page 47 of 50 Figure 6 Cooling Tower System for Estimate

CW to Process

Intake Pumps Capacity: 400 GPM Head: 120 Ft Clarifier Cooling Tower

Feed Pumps Capacity: 400 GPM Head: 30 Ft Circulating Pumps Capacity: 20,000 GPM Head: 160 Ft Makeup Water CWR from Process

200' 3000' 500'River Cooling Tower Battery Limit 500'Page 48 of 50

a) The following table provides a summary of the cost estimate. 1 Process Equipment Items (Note 1) Quantity Unit Cost Total Cost 2 Intake System 3 Travelling W ater Screens 2 70,000 $140,000 4 Intake Pump (315 gpm x 1.25 (SF) = 400 gpm, 120 Ft) 2 10,700 $21,400 5 Clarifier Mechanism (40' Diameter and 16') 1 180,000 $180,000 6 Clarifier Tank (40' D; 16' L Field Erected) 1 235,000 $235,000 7 Feed Pump (315 gpm x 1.25 (SF ) = 400 gpm, 30 Ft) 2 8,200 $16,400 8 Cooling Tower 9 Circulation Pump (20,000 gpm, 160 ft) 2 279,000 $558,000 10 Basin (36' x 72') 3 100,000 $300,000 11 Treatment System 12 Dispersant Tank
- 2000 gallon 1 3,000 $3,000 13 Feed Pu mpand Controls 2 2,000 $4,000 14 Corrosion Inhibitor Tank
- 500 gallon 1 1,000 $1,000 15 Feed Pumps and Controls 2 2,000 $4,000 16 Sulfuric Acid Tank
- 2000 gallon 1 7,000 $7,000 17 Feed Pump and Controls 2 19,000 $38,000 18 Bleach Tank
- 5000 gallon 1 8,000 $8,000 19 Feed Pumps and Controls 2 19,000 $38,000 20 Total Process Equipment (T.P.E.) $1,553,800 21 Piping & Mechanical [20]T.P.E. x 0.80 $1,243,000 22 Civil

– Site Wo rk, Structures, Foundations & Eart hwork [20] T.P.E. x 0.90 $1,398,000 23 Electrical [20] T.P.E. x 0.30 $466,000 24 Instrumentation [20] T.P.E. x 0.15 $233,000 25 Fire Protection [20] T.P.E. x 0.01 $16,000 26 Insulation [20] T.P.E. x 0.02 $31,000 27 Painting [20] T.P.E. x 0.1 $ 155,000 28 Sub Total (Equipment and Installation T.E & I.C) $5,096,000 29 Project Management & Engineering 30 Home Office Engineering [28] x 0.15 $764,000 31 Construction Management [28] x 0.05 $255,000 32 Line Item (Note 1) 3 $1,034,000 33 Cooling Tower (9000 gpm 2 operating, one spare) $3,102,000 34 (Field erected, marked up for engineering and civil works) 35 Total Installed Cost (T.I.C.) $9,217,000 36 Rounded up Cost $9,200,000Page 49 of 50

b) Cooling tower cost obtained from vendor has bee n marked up:
 20% for engineering
 90% for civil, sitework and foundation c) Process Equipment Cost: Costs of all process equipment are based on vendor quotes and ENSR database. It does not include the cost of any spare parts, taxes, freight and future escalati on. It also does not include buyer's indirect costs. d) Cost estimate is based on using ANSI pumps. If API pumps are required the cost of the pumps will increase by a factor of three. e) Piping & Mechanical: The cost of installing pipes interconnecting the process equipment. It includes all the valves, fittings and installation. f) Civil, Site W ork, Structures, Foundation and Earthwork: Includes the concrete pad for installation of process equipment. It does not include construction of any buildings. Does not incl ude demolition and removal of any equipment. It also does not include installation of any sewer system. g) Electrical: Includes the cost of connecting the new equipment to existing motor control centers. Does not include the cost of upgrade of the MCC. Doe s not include the cost of bringing additional power or upgrade of transformers. h) Instrumentation: Connecting all the necessary process equipment into a new control loop and connecting it to an existing control room. i) Fire Protection: Installation of fire protection. j) Insulation: The cost of installing insulation on pipes and equipment. It does not include any heat tracing of pipes and equipment. k) Painting: The cost of painting process equipment. l) Home Office and Engineering: Includes process engineering and deta iled engineering for the cooling tower systems. The following is the list of items that are not included in the cost estimate. This list is not intended to be a comprehensive list of exclusions but highlights important items: 1. Does not include the cost of any spare parts, taxes, freight and future escalation. It also does not include buyer's indirect costs. 2. Cost estimate is based on using ANSI pumps. If API pumps are required the cost of the pumps will increase by a factor of three. 3. Does not include construction of any buildings. Does not include demolition and removal of any equipment. It also does not include installation of any sewer system. 4. Does not include the cost of upgrade of the MCC if required. 5. Does not include the cost of bringing additiona l power to the site or upgrade of transformers.Page 50 of 50

6. Does not include the cost of engineering analysis to upgrade heat exchangers in the refinery. 7. Does not include the cost of replacing the heat exchangers in the refinery. 8. Does not include the cost of handling and treatment of sludge from the makeup water system. 9. Does not include the cost of handling and treatment of the blowdown stream. 10. Does not include the cost land acquisition (if necessary). 11. Operating Costs The following table defines the operating and maint enance costs for the cooling tower system. The operating costs are based on 8,000 hrs/yr of operation. Category Cooling Tower ($/yr) Once Through

($/yr) Net Costs

($/yr) Pumps and Blowers (@ 8,000 hrs/yr, 0.07 $/kwh) Cooling Tower Fan 156,700 156,7 00 Intake Pump 6,800 6,800 Feed Pump 2,300 2,300 Recirculating Pump 452,600 452,600

_ Chemical Addition Pumps 2,800 2,800 Chemicals (@ 8,000 hrs/yr)

Dispersant 42,000 42,000 Corrosion Inhibitor 9,600 9,600 Sulfuric Acid 5,000 5,000 Chlori ne 27,600 27,600 Spare Parts (2%of Total Purchased equipment -$ 2,963,800 ) 59,300 59,300 Labor (Operating and Maintenance ( 1 @ $30 ea, 8760 hrs ) 262,800 262,800

_ Total Operating Cost per Year (rounded) 1,050,000 715,400 334,600 Cost Comparison The following table compares the costs included in the EPA May 17 2001, draft document to the costs developed by ENSR for refineries: 17,400 gpm CT w/travelling screen ENSR estimate EPA estimate Capital Costs (installed) $ 9 , 2 00,000 $ 1,340,000 Incremental Operating Costs $ 334,600 $ 179,000Page 51 of 50 IX. References 1. Gary, James H., & Handwerk, Glenn E., Petroleum Refining Technology and Economics , Marcel Decker Inc, New York, 1975 2. Kern, Donald Q., Process Heat Transfer , M cGraw
- Hill Book Company, 1950 3. Rase, Howard F., & Barrow, M.H., Project Engineering for Process Plants , John Wi ley & Sons Inc., 1957 4. Evans, Frank L., Equipment Design Handbook for Refineries and Chemical Plants , Gulf Publishing, 1974 5. Nelson, W .L., Petroleum Refinery Engineering , McGraw Hill Company, 1958 6. Perry, John H., Chemical Engineers Handbook, Fourth Edition , M cGraw Hill Book Company 1963 7. Peters, Max S. and Klaus D. Timmerhaus, Plant Design and Economics for Chemical Engineers, Second Edition , M cGraw
- Hill, New York, 1968.