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2100 General Information

AbstractThis section discusses types of cooling water systems, types of cooling towers cooling tower components and provides a list of contacts and references for moinformation on cooling water systems.

The Cooling Tower Institute (CTI) has developed the industry standards for cootowers. The commonly used standards are referenced in Specification EXH-MS1317, included in this manual. Copies of the CTI manual or the CTI specificatiocan be obtained from:

Cooling Tower InstituteP.O. Box 73383Houston, TX 77273(713) 583-4087

Contents Page

2110 Cooling Water vs. Air Coolers 2100-3

2120 Types of Cooling Water Systems 2100-3

2121 Open Recirculating Cooling Water System

2122 Closed Loop Cooling Water System

2123 Tempered Cooling Water System

2130 Types of Cooling Towers 2100-5

2131 Natural Draft Towers

2132 Forced Draft Towers

2133 Induced, Mechanical Draft Cooling Towers

2140 Cooling Tower Components 2100-8

2141 Fills

2142 Drift Eliminators

2143 Cooling Tower Basin

2150 Contacts and References for Cooling Towers 2100-1

2151 Contacts: Cooling Tower Manufacturers and Specialists

Chevron Corporation 2100-1 December 1989

2100 General Information Heat Exchanger and Cooling Tower Manual

2152 References

December 1989 2100-2 Chevron Corporation

Heat Exchanger and Cooling Tower Manual 2100 General Information

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Note Figures 2100-6 through 2100-10 are 11 × 17 foldouts at the end of the section.

2110 Cooling Water vs. Air CoolersTypically, Chevron uses an open, recirculating cooling water system in order to cool fluids in the plant to temperatures lower than can be attained with air cooleWhen environmental concerns and water resource limitations do not control, cooling water can also be more attractive than air cooling for many other reaso

Section 100 of this manual contains more detailed information comparing waterair coolers.

2120 Types of Cooling Water SystemsLike steam, power, and instrument air, cooling water is a critical “utility.” It is required for all operating conditions, including startups, shutdowns, and upset conditions. Cooling towers are typically large wooden structures that use circu-lating ambient air to cool warm water. In a cooling tower, normally referred to asjust the “tower,” the hot water is cooled by exchange of its sensible and latent hwith relatively cool air.

About 80% of the cooling occurs from evaporation of a small portion of the wateas the air flowing through the tower contacts water cascading from the top to thbottom of the tower. Most of the Company’s cooling towers use a recirculating water system to conserve water resources and minimize operating costs.

There are three types of cooling water systems.

1. Open, recirculating cooling water system

2. Closed loop cooling water system

3. Tempered cooling water system

2121 Open Recirculating Cooling Water SystemFigure 2100-6 shows a typical open recirculating cooling water system using a cooling tower.

During normal operation of a cooling tower, all available cells should be used. Efan in the cell normally contains two-speed motor drivers. The cooling tower baand pump forebay serve as system storage and are sized for a minimum of 15 minutes of water storage at the normal circulating rate. Makeup water is based the concentration in the circulating water. The cooling tower blowdown can ideabe flow controlled by a conductivity analyzer.

The system circulating pumps are usually horizontal, centrifugal, double-suctionand single-stage. Pump discharge pressure is in the range of 55 to 65 psig. Theare normally three or four pumps, with at least two of them being turbine-driven



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assure 100% water circulation rate during a power failure. Under normal circumstances, the electric motor-driven pump and one turbine-driven pump operate while the other remaining turbine-driven pumps are on automatic standThe pumps take suction from the forebay and discharge to a common header. Acommon minimum flow recirculation line, directly back to the tower, is provided the pump discharges for pump protection and initial prestartup conditioning.

Chemicals are used to control scaling, corrosion, and fouling. The most importachemical is the corrosion inhibitor. Chemicals and components of the water treapackage are discussed in Section 2400.

Typical Process Cooling Water SystemCooling water circulation is controlled by starting and stopping the standby coowater circulation pumps based on pressure in the discharge header. There is nor temperature control on the circulating stream. A bypass recycles water to thecooling tower basin for low flow pump protection. Makeup to the cooling tower ion level control. Temperature, flow, and pressure of the cooling water to the plaand other users is monitored, frequently, in the control room. Return cooling waat the cooling tower inlet is sampled and analyzed for conductivity, chlorine, pHand corrosion inhibitor. Output from the conductivity analyzer resets a flow controller on the cooling tower blowdown line. Blowdown flow is also used to relate the addition of dispersant and corrosion inhibitor to the system. Output fromthe other analyzers regulates the addition of chlorine, acid or caustic, and corroinhibitor.

2122 Closed Loop Cooling Water SystemFigure 2100-7 is a process flow diagram for a typical closed loop cooling water system.

“Open” systems, as described in the previous section, typically cool 100°F to 12hot returning water to about 5°F to 10°F above the ambient wet bulb temperatuthe site. A “closed” system supplies a flow of high purity, inhibited cooling wateraround 100°F. Its function is to cool bearings, jackets, etc., of rotating equipmenthe plant, where the quality of the “open” cooling water is unacceptable for the service. The heat from a closed system is removed by heat exchangers using topen cooling water system. This system typically uses demineralized water for initial fill and subsequent makeup. It has its own pumping, minimum flow recircution line, surge tanks, and chemical feed systems. Pump discharge pressure isnormally about the same as in an open cooling water circulating system, 55 to 6psig. Corrosion inhibitor is added to the system upstream of the circulating watepumps.

Closed loop systems should include two surge tanks, each sized for 5 minutes water storage at total system design flow. They should be nitrogen blanketed tominimize the oxygen content in the water. Changes in fluid volume, temperatureand chemical balance should be monitored at the tanks. Under normal conditioboth tanks should be online, but either tank can be isolated for maintenance.



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2123 Tempered Cooling Water SystemFigure 2100-8 is a process flow diagram for a typical tempered cooling water system.

A tempered cooling water system is another closed loop system circulating highpurity inhibited cooling water, normally at a minimum of 140°F to process heat exchangers that cool streams with high pour points. Pump discharge pressuresabout 100 to 115 psig for these systems. This system also includes two surge tcirculating pumps, and a common minimum flow recirculating line. The system should use demineralized or high quality water for initial fill and subsequent makeup. Corrosion inhibitor is added intermittently to the system upstream of thcirculating pumps. Since the water is only cooled to 140°F, induced draft air cooheat exchangers remove process heat from the system. The temperature is matained by bypassing hot return water around the air coolers.

2130 Types of Cooling TowersThe oldest means of cooling and storing circulating water was to discharge the water into a pond of sufficient area so that the water was cooled by the air passover the surface of the pond. Spraying the heated water into the air over the poincreased the rate of cooling and reduced the area to around 5% of that requirewithout sprays. Because of this large space requirement and the windage lossewith spray ponds, the cooling tower was developed. A modern mechanical drafcooling tower requires about 2% of the area of a spray pond, and less than 0.01the area for a cooling pond or reservoir. Cooling towers come in all sizes. Somesmall enough to be portable. Others take up more plot space than one of the plthey serve, with capacities of 100,000 GPM and duties of up to 1 billion Btu/hr.

For industry, cooling towers are normally rectangular, wood, or metal structuresThe hot water is delivered to the top and falls through baffling-type fill into the basin below. Air enters at the bottom or side of the tower, cooling the water by convection and partial evaporation. The circulation of the air through the tower mbe either by natural draft, or by a forced or induced draft fan.

2131 Natural Draft TowersChevron still has a few natural draft towers in our producing and pipeline centerThe air circulates through a natural draft cooling tower because of the temperadifference between the air inside and outside of the tower. Natural draft towers been very popular with utilities, who can allow much longer payouts and frequeuse the natural draft principle in their large hyperbolic towers. Hyperbolic towersare not used by the oil industry and therefore are not discussed in this manual.

2132 Forced Draft TowersChevron also has a few forced-draft cooling towers. Forced-draft towers are ussmaller than induced-draft towers and have either centrifugal fans located at the



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base of the tower (which is constructed as a plenum to provide positive pressurairflow through the fill material) or axial fans on the side of the tower.

For the past 30 years, induced-draft cooling towers have been purchased insteforced draft cooling towers (for capacities greater than 2,000 GPM/cell). Forceddraft cooling towers have the following problems:

1. High air velocities through the fill and difficulty with promoting good air distrbution across the tower.

2. Greater difficulty with recirculation.

3. Lower efficiency and more plot plan space.

As a result of these problems, the Company normally purchases induced-draft cooling towers.

2133 Induced, Mechanical Draft Cooling TowersInduced-draft towers pull air into the tower. The induced draft is provided by a propeller-type axial fan located in the stack at the top of the tower.

Counterflow DesignSee Figure 2100-1. The induced-draft fan pulls the air into the inlet louvers at thbottom of the tower and up through the tower. In the counterflow tower, the returning hot water is piped to a distribution system of headers and lateral pipinconnected to pressure flow nozzles, which are located below the top of the towjust below the mist eliminators. The nozzles spray the water as droplets that thefall across the fill which acts as baffles to allow surface contact between the drolets and the rising air. The primary advantage of the counterflow tower is its efficiency. The coldest water contacts the driest air, and the warmest water contacmoist humid air.

Crossflow DesignSee Figure 2100-2. The induced-draft fan pulls the air into the inlet louvers placalong the tower’s sides, spanning its entire length and height. Air is introduced perpendicular to the falling water. The crossflow tower uses risers to pipe the returning hot water to the top of the tower where it is discharged to open gravitydistribution decks adjacent to the shroud protecting the fan. The floor of this decontains gravity flow nozzles, and the water level in the deck controls the rate owater flow onto the fill.

The water falls through orifices in the nozzles, and as it flows it is distributed acthe fill. The fill acts as baffles to allow surface contact between the droplets andcrossflowing air. Mist eliminators, forming a “V” at the center of the tower, mini-mize drift and windage losses as the air is pulled up to the fans in the center oftower.

Since the early 1970s, counterflow towers have used a lower pressure spray sycoupled with large plenum areas. In most cases, this feature has made counter



Fig. 2100-1 Counterflow Induced-Draft Tower

Fig. 2100-2 Crossflow Induced-Draft Cooling Tower



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towers preferable to crossflow towers because they are less expensive to instaloperate than crossflow towers. Crossflow towers are often specified when a lowflow rate or potentially contaminated air atmosphere is involved.

2140 Cooling Tower ComponentsTo become familiar with the components of cooling towers, refer to the followingfigures for details of the standard components for the two main types of coolingtowers that most petroleum plants use:

1. Figure 2100-9, Counterflow Cooling Tower: Perspective—Typical Parts andFraming

2. Figure 2100-10, Crossflow Cooling Tower: Transverse Elevation—Typical Parts and Framing

See Appendix I for a glossary of commonly used terms (CTI Bulletin 109).

2141 FillsThe two most significant decisions when purchasing a new cooling tower are:

1. Should we buy counterflow or crossflow?

2. Should we buy “splash” fill or “film” fill?

Section 2130 above compares the relative merits of counterflow and crossflow towers. This section discusses splash fill and film fill.

If there is no plugging problem (i.e., good water treating) and no serious hydro-carbon attack, the counterflow tower with polyvinyl chloride (PVC) film fill usuallwill have the lowest overall cost (installed cost + fan power cost + pumping costMost large crossflow towers use splash fill (normally a PVC material). Howeversome companies have small crossflow towers which stack thin sheets of plasticon very close centers and can be considered film fill.

Figures 2100-3 and 2100-4 illustrate the two basic types of cooling tower fill. Fimaterial is used to maintain an even distribution of water across the horizontal plane of the tower and to create as much water surface area as practical to enhevaporation and sensible heat exchange. The water/air interface ratio can be improved by creating either a large number of droplets or many thin vertical sheof water. Fill materials are commercially manufactured from wood, PVC, polystyrene, cellulose, and before environmental constraints, from asbestos cement bo

Splash FillFor years splash fill was the standard fill for cooling towers. Splash fill is constructed of successive layers of staggered impact surfaces. Small droplets aformed as the warm water falls through the fill and splashes off each layer.

Typical splash fill consists of redwood battens in thicknesses of 3/8 inch to 1 incand 1.5-inch to 2-inches deep, installed vertically on the narrow edge. These ba



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are on 0.25-inch to 2.5-inch centerline and form a deck that is usually installed zontally in the cooling tower on from 12- to 24-inch vertical centers. Each row inelevation is rotated 90 degrees to the row above it. The battens are 6 feet long.decks formed are 3 feet by 6 feet and two of them fill the 6-foot cross-sectional between the columns in the tower. Typically, there are about 20 decks in a towe

Where conditions permit, these splash decks are also made in egg-crate type intion molded polypropylene and PVC. They have the following advantages over fill discussed below:

1. There is no plugging as the spacing is far more open than in a film fill.

2. Inspection of every component of the tower is greatly simplified by moving sections of the deck out a piece at a time, and by being able to move easilydown the inside of the tower.

Film FillFilm fill came into use in cooling towers about 15 years ago (see Figure 2100-4has a honeycomb configuration and is usually a PVC material. This fill spreadswater droplets into thin sections throughout the cells of the fill, thereby cooling alarge surface area for the same energy. If the water is always clean, it behaves predicted. As film fill is more efficient than splash fill, it takes up much less volumin the tower. Two to 3 feet of film will provide the equivalent surface of 20 to 30 feet of wood splash fill, making the return header and the elevation of the towermuch lower. This results in lower head required and lower pumping costs.

Cooling tower support posts are normally on 6-foot centers. Typical film fill is manufactured in 3-foot by 6-foot cross-sectional areas with layer thicknesses o12, and 18 inches. Total depth in the tower typically ranges from 1 foot to 6 feetan example, where icing could be a problem, a 6-foot thickness could have a 1clear elevation at each 2-foot interval to allow for extra heavy supports under ea

Fig. 2100-3 Splash Fill



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feet of fill. Film fill is manufactured with various size flutes (openings) and sheethicknesses.

Film fill is most commonly used in counterflow towers and is normally installed just above the intake louver opening. In a retrofit it is usually installed just belowthe existing water distribution system. Good water distribution is very importantwith film fill. The use of film fill is not recommended where there is potential for hydrocarbon leakage into the fill, particularly waxy or heavy hydrocarbon. A towhas collapsed due to hydrocarbon contaminating the middle 12 inches of a 30-ifill. The “mushy” condition in the middle could not be observed from the top or bottom. Biofouling is another serious consideration for film fill. Bacterial growth most rapid at 98.6°F. For many of our towers, this is about half way through thefilm fill. Bacteria thrive on hydrocarbon, ammonia, nitrates, sulfates, etc. See Section 2440 for more information on biological fouling and control.

2142 Drift EliminatorsDrift is water droplets which are entrained in the air stream as it passes througtower. These water droplets contain dissolved and suspended solids in proportitheir concentration in the circulating water. Drift eliminators are baffles that causthe hot air with entrained water droplets to change direction a number of times.This process causes the droplets to hit the eliminator surface at every change odirection and fall back into the tower. The efficiency of a drift eliminator is a function of its design. Figure 2100-5 shows a sketch of the three major drift eliminatdesigns:

1. Herringbone, the least efficient.

2. Waveform, of intermediate efficiency.

3. Cellular, the most efficient.

Fig. 2100-4 Film Fill



For e drift

Drift eliminators are constructed of wood, PVC, polystyrene, or cellulose. PVC now dominates this group for the following reasons:

1. The returning water does not pass through them.

2. There is no sunlight to develop bacteria.

The drift eliminators fit as a series inside 3-foot wide sections with end flanges.a counterflow cooling tower, the drift eliminators are located 2 to 4 feet below thfan deck across the entire cross-section of the tower. For a crossflow tower, theeliminators are located in the middle one-third section of the tower. See Figures 2100-1 and 2100-2.

Fig. 2100-5 Different Types of Drift Eliminators



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2143 Cooling Tower BasinThe cooling tower basin should, as a minimum, be designed to provide:

1. Sufficient volume to allow 3 to 5 hours of operation if makeup water is lost.

2. A specific volume of fire water in case the regular water system fails.

3. A volume of cold water to allow a short period of operation below a specifietemperature in case of power failure. For example, the basin may allow 10 minutes operation before tower outlet temperature rises above 95°F, assumno convection effect.

4. The necessary head for proper operation of the cooling water circulating pumps.

Cooling tower forebay design is covered in more detail in Section 2240.

2150 Contacts and References for Cooling Towers

2151 Contacts: Cooling Tower Manufacturers and SpecialistsIncluded in this section is a list of cooling tower manufacturers, specialists, andresources for maintenance and repair.

Cooling Tower Manufacturers

MarleyP. O. Box 2912Mission, Kansas, 66201913/362-1818

Custodis-EcodyneP. O. Box 1267Santa Rosa, Ca., 94502707/544-5833

Hamon245 US Highway 22 WestBridgewater, N. J., 08807201/725-3311

BAC PritchardP. O. Box 7322Baltimore, Maryland, 21227301/799-6312

Contact the Utility Systems and Energy Management Section, ETD, for information and recommended contacts and specialists in these areas: (1) cooling towe(2) water treating, (3) upgrades and repairs



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2152 ReferencesIndustry Specifications:

Cooling Tower Institute, Inc.P. O. Box 73383Houston, Texas 77273(713) 583-4087

Company Documents:

Johnsen, C. W., “FCC Cooling Tower Electronic Vibration Switches,” 1/31/89. IMRichmond Refinery.

Outside Documents:

1. Hydraulic Institute Standards for Centrifugal, Rotary & Reciprocating Pump, 14th Edition, Hydraulic Institute, 1983.

2. Nystrom, James B., et al., “Modeling Flow Characteristics of Reactor SumpJournal of the Energy Division, ASCE, Vol. 108, No. EY3, November 1982.

3. Padmanabhan, M., and G. E. Hecker, “Scale Effects on Pump Sump ModeJournal of Hydraulic Engineering, ASCE, Vol. 110, No. 11, November 1984.

4. Prosser, M. J., The Hydraulic Design of Pump Sumps and Intakes, British Hydromechanics Research Association/Construction Industry Research anInformation Association, 1980.

5. Sweeney, Charles E., et al., “Pump Sump Design Experience: Summary,” Journal of the Hydraulics Division, ASCE, Vol. 108, No. HY3, March 1982.



December 1989

Heat Exchanger and Cooling Tower Manual

Chevron Corporation 2100-15

Fig. 2100-6 Typical Conventional Process Cooling Water System


December 1989



Fig. 2100-7 Typical Closed Loop Cooling Water System


December 1989



Fig. 2100-8 Typical Tempered Cooling Water System


December 1989



Fig. 2100-9 Counterflow Cooling Tower: Perspective—Typical Parts and Framing (Courtesy of Custodis-Ecodyne, Santa Rosa, CA)


December 1989



Fig. 2100-10 Crossflow Cooling Tower: Transverse Elevation—Typical Parts and Framing (Courtesy of Custodis-Ecodyne, Santa Rosa, CA)

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