WATER COOLING TOWER, TECHNOLOGY, THE AIR/WATER/HEAT REJECTION MACHINE
BY ROBERT BURGER
ROBERT BURGER ASSOCIATES, INC.
NEW YORK, N.Y.
PRESENTED TO THE
THIRD NATIONAL CONFERENCE ON COMPLETE WATEREUSE
SPONSORED BY
ENVIRONMENTAL DIVISION OF AIChE
AND THE ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO
JUNE 27TH,1976
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COOLING TOWER. MONEY MAKING SUPERSTAR
The following three cooling towers earned approximately $160,000.00 a year over
the previous years' operation. Fig. 1 saved General Foods Corporation in Tarry-
town, New York, close to $60,000.00. Fig. 2 earned the U.S. Government at the
General Accounting Office Building in Washington D.C. $30,000.00. Fig. 3 saved
a large Eastern Chemical Plant $20,500.00.
How was this accomplished? isy producing COLDER WATER.
At least 175,000 kilowatt hours have been saved by having these towers produce
more work for the same electrical energy input.
Of course, in this life nothing is free. To affect these savings the Owners had
to spend money. However, the amount of money spent will rapidly return itself.
In the case of cooling towers, small trickles of waste and inefficiency become
torrents when one is unaware of the loss. Consider that many towers operate 16
hours a day for nine months of the year and others like CF Chemical in Bartow,
Florida producing phosphates for fertilizers run 2k hours a day, 7 days a week
for 11 months of the year.
Most operating Personnel pay an absolute minimum of attention to the cooling
tower being aware only that it is that "i3ox in the back" where we send the hot
water to and it comes back cold.
Eiis discussion of cooling towers is aimed at only one end result.....COLD
MATER, the lack thereof, and methods of obtaining colder water.
The criteria of cooling tower performance is outlined in the Designed Conditions,
Fig. U specified when the cooling tower is purchased and/or rebuilt to mean the
cooling of a specific quantity of circulating water from entering the tower at
a particular temperature and leaving at a definite value. The difference bet-
ween these two temperatures is called "The Range" or Delta "T". This cooling
of the specific amount of water is also to be performed at a wet bulb tempera-
ture that is noted in the specifications. The difference between the cold dis-
charged water and wet bulb is called "The APPROACH to the wet bulb".
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FIG. 3. CHEMICAL PLANT REBUILT TOWER SAVED
PRODUCTION PLANNING $20,500.00
FIG. 2. GENERAL ACCOUNTING OFFICE SAVED $80,000.00
PER YEAR AFTER REBUILDING.
A. CELLULAR FILL
B. DRIFT ELIMINATORS
, rFRAMIc NON-CLOG NON-CORRODING LARGE ORIFICE C. PVC PIPING
(OTTO l£'' DIAMETER) OPENING. D. CERAMIC NOZZLES
FIG. 8.
WATER VAPOR DISCHARGE EQUAL TO APPROXIMATELY
1000 BTU PER POUND
FIG. 17. PVC PIPE ASSEMBLY WEIGHS APPROXIMATELY 75% OF
IRON WATER DISTRIBUTION SYSTEM
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According to Allied Chemical Corporation's Enthalpy charts for Genetron 12 refrig-
erant, Pig. 5, 1°F colder water returned to the condensors and compressors calcul-
ates to a three percent savings in electrical energy input to these machines.
Therefore a little more than three degrees colder water off the tower can save 10%
of the electrical energy and resulting charges thereof at any given time. A 2,000
ton refrigeration system (6,000 GPM of circulating water) could use $350,000.00
in electrical power a year. A 10% savings of $35>000.00 obtained by sending colder
water to the machinery, could be significant.
At the General Poods Plant in Tarrytown, New York, Fig. 1, the total water on the
tower was 3,750 GFM for two cells. Design Conditions were to cool the 3*750 GPM
from entering at 95° leaving at 85°F at 78°F wet bulb. Oily one cell at a time
could be converted since continuous plant operation is required.
The first indication that engineering calculations and predictions would be ex-
ceeded occurred when the total gallonage was put on the newly converted cell while
the old cell was being rebuilt. With 50% of the tower in operation and the same
electrical input to the Uo horse power motor, the one cell cooled the water to
Design with a 10° range, and 7° approach.
When both cells were operated with maximum water available, (3,750 GPM) the tem-
peratures were returned almost k° colder.
Records kept by the Chief Engineer indicated that there was a direct fuel oil
savings of approximately $300.00 a day since, in generating their own steam for
the turbines, the 6,000 gallons a day oil requirement was cut down to 5,700
gallons - a savings of 300 gallons a day. Further, the turbines were running
at 350 RPM less and head pressures were four to five pounds per square inch lower
than previous records indicated. These small increments add up to approximately
a $60,000.00 a year savings at today's costs. With escallation of 1 sorts pre-
valent, this figure should also escalate.
The ultimate savings however is that there is a 50% plant expansion contemplated,
and calculations Indicate that with the addition of 12" of cellular fill and piping
changes to larger diameters for the water distribution system, the existing cooling
tower with two 40 horse power motors and 16 foot diameter fan would be more than
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I
fig.
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FIG. 5. ENTHALPY CHART FOR GENETRON 12. CALCULATIONS
INDICATE 1°F COLDER WATER EQUAI£ 3% LESS
ELECTRIC ENERGY TO OPERATE COMPRESSOR.
FIG. 1. GENERAL FOODS SAVED $60,000.00 IN FIRST YEAR'S
OPERATION AFTER REBUILDING.
LA G N CONDITIONS
¦/Kv
riOM tNTIUIMO ' l°S* r
TOWER AT T,
TO HAVIKiO
rOWIK AT T,
AT SPCCIFIID WIT BULB TIMPCRATURE 7«*r
RANOf ¦ AT • T, - T, • 20* F
APPROACH « T, - T.b • T* f
FIG 4 DESIGN CONDITIONS SETS CRITERIA FOR TOWER, i.e.
* TO COOL 6000 GFM FROM ENTERING AT 105°F TO 85°F
AT 78°F WET BULB.
CELLULAR FILL COOLS GREATER PERCENT OF WATER
AT LESS STATIC PRESSURE.
FIG. 9. MANUFACTURERS HEAT TRANSFER PERFORMANCE CURVES
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adequate to take care of the new requirements. This should result in an economy
of approximately $40,000.00 which is the cost between new OEM equipment and addi-
tional rebuilding work.
Fig. 2 involves a large Government Office Building counterflow tower where original
design conditions were marginally met and G.S.A. required a 25^6 increase in per-
formance from 12,000 to 15,000 GFM due to higher loads. The successful bid was
$12^,000.00 less than an 004 Proposal to install a new facility. Since the cooling
tower was built using the vertical Building columns as the main tower supports,
cost of demolition and installation, including reconstructing the Building around
the new equipment dictated that the prudent way, would be to rebuild the existing
tower.
One of the keys to improvement is the ceramic nozzle Pig. 6 costing $10.00 each
which replaces a dozen or more bronze units $6.00 to $8.00 each plus the cost re-
duction for using PVC piping at $14.00 per foot installed for 12" diameter vs
$22.00 installed for galvanized steel. The weight differential is VCflo plus in
saving labor during installation.
The elements of rebuilding the tower are illustrated by Fig. 7.
A. 30" of cellular fill replaced 144" of wood splash bars.
B. Efficient fireproof drift eliminators which can be walked onJprovides
mist protection and also acts as a fireproof barrier.
C. A tremendous aid in upgrading this structure was the replacement of
old style gravity trough water distribution to PVC low pressure piping.
D. In conjunction with the PVC piping Ceramic non-clogging, nan-corroding
large orifice nozzles were installed.
This type of rebuilding is an open ended funnel. Additional capacity may be obtained
by pumping more water over the fill, increasing the depth of fill, increasing the
airflow, or any combination of these events will add up to more work for less invest-
ment. In this case the savings in dollars was generated by the fact that the four
60 horse power motors, after conversion, produced an additional 3,000 GFM of cooling.
If the 4 cell tower was not rebuilt and an additional cell installed - then 300
horse power vould have been required to produce the same amount of work that the
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presently rebuilt installation is doing using only 2k0 horse power. Multiplying
the current Washington DC power rates by the tower utilization result, in a KWH
reduction of 1,575 and a $11,91^.15 savings per year.
The third example is of a Chemical Plant Fig. 3, where the cooling tower was
designed originally to cool 800 GPM of water from entering the tower at 111°
leaving at 90° at a 75° wet bulb illustrates how a change in the wet decking heat
transfer surfaces alone produced startling results.
The water was not being returned cold enough to do the work properly and the
Production Planning Unit budgeted $30,000.00 to install another cooling tower to
make up the deficiency plus the capability for a 50* Plant expansion contemplated
in the future.
Thermal calculations indicated that with the present water distribution system
2k» of cellular fill would more than adequately return the 800 GPM back to the
process equipment at 90°. After conversion this actually occurred.
Further calculations indicate that with the additional of another 12", or total
of 36" thick cellular fill, together with a new water distribution system consist-
ing of PVC piping and ceramic square spray nozzles would be sufficient to expand
the water cooling capability of the tower by 50't.
Since the cost of this conversion is $9,500.00, we can calculate an actual sav-
ings of $20,500.00 plus at least $6,300.00 in not having to operate an additional
25 horse power motor for the now non-existent "new" tower in one year's operation.
COOLING TOWER FUNDAMENTALS
Before proceeding further, let us get a little into the fundamentals of cooling
tower technology. The basic principle of the cooling tower operation is that of
evaporative condensation and exchange of sensible heat. The air and water mixture
releases latent heat of vaporization which has a cooling effect on water by turning
a certain amount of liquid into its gaseous state thereby releasing the latent heat
of vaporization.
This is more effectively demonstrated by wetting the back of your hand with your
tongue and blowing on it. This effect is What happens inside the cooling tower.
The airstream releases latent heat of vaporization thereby dropping the temperature
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of the water on your skin. The liquid changing to it* vaporous state consumes heat
which is taken from the water remaining, thus lowering its temperature.
There is a penalty involved, and that is loss of water which goes up to the cooling
tower and is discharged into the atmosphere as hot moist water vapor. Fig. 8. Under
normal operating conditions this amounts to approximately one and two tenths percent
(1.2%) for each ten degrees of cooling range.
Sensible heat that changes temperature is also responsible for part of the cooling
tower's operation. When water is warmer than the air, there is a tendency for the
air to cool the water. The air then gets hotter as it gains the sensible heat of
the water and the water is cooled as its sensible heat is transferred to the air.
Approximately 25% of the sensible heat transfer occurs in the tower while the balance
of the 75% cooling is due to the evaporative effect of latent heat of vaporization.
The cooling tower, like any other device, process, or operation on this earth does
not escape the unchangeable law of the indestructability of matter, A cooling tower
is merely a machine that takes a mass of heat from one area and moves it to another
area. In more technical terms, it is referred to as "The heat rejection solution
of the chemical process" or "Correction of the heat penalty generation of compres-
sion equipment". However, to repeat, the cooling tower merely moves heat from
point "A" to point "B" and ultimately discharges this heat into the atmosphere which
Thermal Engineers euphemistically call a "Heat Sink".
To upgrade the performance of an existing cooling tower,the three major areas to
investigate are:
1. Wet decking fill.
2. Water distribution system.
3 Drift eliminators.
WET DECKING FILL
Generally the most significant improvements can be made simply by changing the fill.
This however is not done capriciously. The heat transfer must be investigated from
a Thermal Engineering point of view in conjunction with the fill characteristics as
determined by the manufacturers charts Fig. 9, which were developed very painstakingly
by trial, error and experimentation and is expressed as KAV or heat transfer charact-
L
eristics. It is quite obvious that this wood fill Pig. io, is extremely inefficient
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FIG. 15. CROSS-FLOW SPLASH BAR FILL
FIG. 16. CROSS-FLOW CELLULAR FILL CONVERSION
FIG. 11. CELLULAR FILL TURKS DROPLETS INTO THIH
WAiJiK JPILM.
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compared to the cellular fill, Fig. 11,coupled with the fact that the cellular fill
has a lower static pressure of the operation which further enhances the heat trans-
fer by more efficient utilization of the existing air. In wood slat splash bars,
Fig. 12, droplets of water bounce from one layer of wood to the other and the rising
air cools the outside surface of each sphere of the water droplets. Cellular fill takes
the saae droplet of water and spreads it out in a very thin molecular film where the
air can now effect the entire surface of the film. Fig. 13. Considerably more surf-
ace is then available to the flowing air for vaporization and sensible heat exchange
to take place. The film pack contains more surface area than splash bars and since
the design of cellular fill permits air to go through it with less static pressure,
it is extremely efficient compared to the old fashioned splash bar mixture system.
WATER DISTRIBUTION SYSTEM
For optimum performance, the water distribution system, must provide a uniform pat-
tern over the fill. The older type trough Fig. Ik, has a very uneven splash dist-
ribution based upon columns of water falling vertically and hitting cups which, when
accurately placed, distribute the water throughout the fill. Over the years this
delicate balance is destroyed as the tower deteriorates and the end result is a ver-
tical column of water, in many places, dropping three or four feet through the fill
before it is broken up, losing entire areas of efficiency. When a nozzle is clogged,
it leaves a dry spot on the fill and the air being lazy follows a path of least re-
sistance rushing up this dry spot wasting a tremendous amount of energy and cooling
potential.
difference between counterflow towers as illustrated above and crossflows des-
cribed below is that the air in counterflow moves vertically through the fill while
the crossflow tower, air flows horizontally through the fill. In both cases the
water drops vertically through the fill.
Crossflow cooling towers Jig. 15, also have a rebuilding capability to improve the
performance by changing the wood splash bars to cellular fill, installing redist-
ribution sections of predetermined levels, and adjusting the flow rate through the
hot water distribution basin to provide proper water 1ng through the fill.
Here again wood splash bars are replaced by the more efficient cellular fill sections
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Fig. 16, thereby reducing static operating pressure through the tower, providing a
more effective use of the input energy, and obtaining colder water from the tower.
Whether it be crossflow or counterflow, UNIFORMITY IS THE KEY TO SUCCESS.
Uniformity of water distribution, Uniformity of static pressure, Uniformity of fill
configuration, and Uniformity of air velocity, even though in a crossflow tower, the
pressure differential will vary with the height.
When replacement water distribution piping is necessary, Polyvinylchloride (PVC)
should be strongly considered for many reasons
a. The material is non-corroding, providing low maintenance cost.
b. This is extremely light in weight for its strength compared to
galvanized iron pipes.
c. Installed cost is at least 60% less than iron pipes. One man,
Fig. 17, can lift a 12' section of PVC piping, which if fabric-
ated from galvanized steel, would require four men plus an "A
Frame" with block and tackle.
In conjunction with PVC piping, the ceramic non-clogging, non-corroding nozzles,
Fig. 6 should be vised which greatly assists keeping the maintenance budget down.
Fig. 18 is of a counterflow cooling tower having 188 small orifices 1/8" diameter
nozzles with 32 1" spray arms. Constant inspection and man hours must be util-
ized in unplugging these small orifices as they clog with rust and debris, thereby
creating "hot spots" in the tower. The same tower Fig. 19» after being converted
to a PVC main header and ceramic nozzles only 12 large orifice (approximately 1"
diameter) to handle the same GPM of water.
nnTTTT ELIMINATION
The need for an efficient mechanical system to retain the water is obvious since
the spray or water distribution system turns the heavy stream of condensor or
process water into light droplets preparatory to being cooled by the airstream.
Fig. 20. Drift is defined as water droplets which are entrained in the air-
stream as they pass through the tower and are thrown out of the hot air discharge
plenum or fan stack. A baffling called "Drift Eliminators" is placed between the
water distribution system and the air discharge point to minimize dispersal of
entrained water droplets into the surrounding atmosphere.
Since cooling tower performance, i.e. heat removal, is a balance between waterflow
and air volume, drift eliminatoxs are normally designed to be efficient through a
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FIG. 18. PACKAGE TOWER WITH 188 SMALL NOZZLES OH 32 1"
DIAMETER SPRAY ARMS BEFORE CONVERSION.
FIG. 19. PACKAGE TOWER UPGRADED TO 12 CERAMIC NOZZLES
AND PVC PIPING.
FIG. 21. ACTUAL TWO PASS INEFFICIENT ELIMINATORS.
THREE PASS SLAT-TYPE DRIFT ELIMINATORS
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calculated range of airflow. Too great an air speed can result in excessive drift-
ing of water from the tower, while poorly designed eliminators will increase static
pressure through the tower, slowing the air and lowering the cooling capabilities
and efficiency of the unit.
The evaporative cooling is generated by the mixture of air and water, plus loss of
sensible heat. As the air moves counter or cross to the water, it will pick up a
lot of the mist and droplets, and carry them with the air flow out of the tower.
An actual section of a two pass eliminator is seen in Fig. 21, while the schematic
operation of a three pass drift eliminator is shown on Fig. 22. A newer more eff-
icient drift eliminator fabricated from Asbestos and impregnated with Chlorinated
Rubber has been developed, which causes the air to gently change its direction
approximately six times thereby obtaining greater surface contact to release water
droplets. Fig. 23 is a photograph of an actual section of cellular drift elimin-
ator while Fig. 2J+ illustrates the schematic mechanics of the six pass cellular unit.
fte curves Fig. 25 are pressure drop in water gauge plotted against air velocity
obtained from two Manufacturer's elimination systems comparing pressure drop of con-
ventional three pass wood against the baffling of cellular sections. This easily
translates into less power consumption for more work that is done. Calculating
actual Dollars and Cents figures is difficult, but it is obvious that a freer flow
of air will do considerably more cooling at less cost on a straight line relation-
ship. The pressure drop curves indicate the new efficient cellular drift elimin-
ators have about a 7% more efficient profile than three pass wood.
One key to the rebuilding and upgrading procedure is that the considerably lower
static pressure resistance of the cellular drift eliminators permit the available
air a higher velocity at no additional cost. The versatility of cellular drift
eliminator design can be seen in its applications to varying conditions. 100* drift
elimination is possible in theory, but impractical in application. Acceptable level
generally satisfactory is "not in excess of .2 of 1*".
Crossflow tower are often susceptible to drift probleos, because of a tendancy to-
wards higher air flow velocities designed into 'tills type of tower. Since the drift
requirements are more stringent, a different type of eliminator system is used
which has a very delicate balance desifQ and performance. If one or two of the
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eliminator blades are out of position, drift will occur quite readily. This is
illustrated in Fig. 26. In this case the fan was speeded up to deliver more air
and cellular fill was added to the job. Several Manufacturers have developed
cellular eliminators to overcome this problem. Here again the lower resistance of
these new type eliminators plus their drift elimination effectiveness make them a
desirable oonversion over the less efficient wood and more work can be produced
from the cooling tower with the same horse power expenditure. Many cross flow
towers were originally constructed with a single or double pass herring bone baffle
at the fan side of the unit. Fig. 27, illustrates this old style which is respon-
sible for the staining of many buildings due to excessive drift losses carrying
the chemical water treatment with it. A cellular drift elimination installation
Fig, 28 adds to the efficiency of the operation by stopping the air from making
heavy turns around the herring bone and also collects any droplets which may be
pulled towards the center by the fan.
There are many packaged cooling towers which use a zig-zag galvanized steel Fig. 29,
assembly for drift elimination. Besides being restrictive to air flow, excessive
drift develops as the water works its way up along the metal surface of the elim-
inator blades. Sulphuric fumes, prevalent in most City atmospheres, are drawn in-
side the cooling tower and turn to sulphuric acid which eats galvanizing resulting
in rusted blades which deteriorate. Fig. 30 clearly illustrate the deterioration
process. Fig. 31 shows this package being rebuilt completely with new drift elim-
inator blades, new PVC piping, ceramic spray nozzles and cellular fill. An additional
bonus of using Neoprene Asbestos material for wet decking fill and drift eliminators
is that it provides a fireproof barrier whereby a match, lighted cigarette, or
burning rag from an incinerator, landing on top of the drift eliminators when the
tower is not in operation,will preclude a fire since the heat source will extinguish
itself on the Asbestos before reaching the flammable wood fill below. Fig. 32 .
CONCLUSION: A blanket statement cannot and should not be made that "Old cooling
towers can be rebuilt to save large quantities of money, power, or can return water
colder by a significant amount". Each installation must be treated on an individual
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FIG. 26. CELLULAR ELIMINATORS IN COMBINATION WITH WOOD.
I 1— 1 1 1 1 i
300 400 500 600 700 800
VELOCITY FEET/MIN.
FIG. 25. PRESSURE DROP CURVES SHOWING Tf, LESS
STATIC OPERATING PRESSURE.
3-R4SS
SLAT TYPE
D/E
G-PASS
CELLULAR
D/E
FIG. 29. DETERIORATED STEEL ELIMINATOR SECTION.
FIG. 31- COMPLETE REBUILDING ADD6 NEW LIFE TO TOWER,
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basis with thermal, hydraulic, and. aerodynamic calculations studied of existing
conditions to see where areas of improvement can be largely anticipated. Since
significant sums of money can be spent on larger size cooling towers, it is strongly
recommended that a testing requirement be made part of the contract. The Cooling
Tower Institute has formulated ATP-105 which contains rigid testing procedures for
determining whether or not a cooling tower will produce what the Customer haa been
promised and is expected to pay for. The CTI will contract to have testing done
for a Customer for a fee, or a qualified Cooling Tower Rebuilding Firm could conduct
a test under strict supervision of the Owners Representative with proper maintenance
and application of sound modern engineering principals, a cooling tower can be given
a new lease on life and produce colder water which will assist in putting money in
the Bank for the Owner.
FIG. j2. CELLULAR FILL AND ELIMINATORS HAVE ADDED
BONUS OF BEING 100% FIREPROOF.
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