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EDC/yEGM COOLING TOWERS
ve Ord?r Court
Often times the cooling towers seem a trivial part of plant operations, and due to the seldom need for attention, the aforementioned is somewhat justified. But in reality, the cooling tower system is a vital necessity in the chemical process. The loss of cooling water to process condensers can cause extremely high pressures on distillation columns resulting in environmental releases, out of spec product, or worse, injury. Therefore, careful attention to haein levels, pump and fan operation, and water temperature are an extremely important part of the operators daily rounds.
OPERATION.
Cooling tower water is pumped through process condenser via a total of eight (8) pumps. The basins of nos. 1,2 & 3 towers are equalized through a common suction line and have six (6) pumps associated with it (of which there are normally only 4-5 pumps in service at any one time [a minimum of 4 pumps should be used to insure sufficient water flow to the condensers]). Number four (4) cooling tower has a separate suction and return line from nos. 1,2 & 3, and has two (2) pumps on it's suction (of which only 1 pump at a time is needed for normal operation). There is a suction and a discharge tie-in between the two sets of towers which can be used to optimise tower performances when the heat load is unbalanced.
Towers one, two, and three supply water to the process condensers in the two EDC plants, TCE section, and the D.H. still. Number four tower supplies water to the VDC Reactor, VDC Still, old no.3 EDC plant, and the TCE Stripper product exchangers. Due to the small heat load assigned to number four cooling tower, the basin temperature is noticeably lower than that of nos.1,2 & 3. Therefore it is advantageous to distribute some of number four tower's water to the processes that are cooled by the other three towers. This is done by the suction/discharge tie-ins mentioned earlier, and also by a tie-in by which number four cooling tower water (that has passed through the VDC Reactor and VDC Still condensers) is routed through a booster pump and discharged to the supply line of the other towers. This tie-in is located in the VDCM area.
HOIK : Due to the high amperage draw on nos. 7 & 8 and the booster pump, you should not attempt to run more than two (2) of these three pumps at any one time. Number four 480V bus cannot handle the load and will trip off. The normal amperage draw on pumps 1 through 6 is approximately 75 amps, nos. 7,8 and the booster pump average approximately 175 amps.
If an amperage draw of less than fifty (50) amps is
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noticed on pumps 1 through 6, or less than 150 on 7,8 & the booster pump, then the pump is not operating at it's capacity and should be attended to. If the pump cannot be primed due to a malfunction, it should be isolated and reported to the unit foreman for repairs, and another pump should be put in service if needed. For priming purposes, an aspirator line (which is driven by well water) is hooked to the bowls of each pump. This aspirator line is not to be put in service until it is needed due to the fact that the well water used is discharged to the cooling tower basin and is not a suitable make-up water except in an emergency.
The level in the cooling towers is maintained by two level control valves (one on tower no.2, and one on tower no. 4 tower) which supply treated Sabine River water to the towers for level control. There are high and low level alarms located on the EDC panel board for towers number three and four. As stated earlier, loss of cooling water is critical, therefore a low level alarm on the towers should be attended to without delay. If for some reason adequate Sabine water is not available for make-up, well water can be used. In case of emergency a fire hose or sprinkler system can be used to restore tower level to normal operation. Another source of make-up water is the return water from no.1 and no.2 EDC freon condensers. These condensers have the capability of using either Sabine or cooling tower water. When on Sabine water their returns are extra make-up and may need to be diverted to the ditch if tower levels exceed the high alarm point.
NOTE: When these freon condensers are on cooling tower water diversion to the ditch is in effect blowdown.
There are screens located at the suction pits of each tower which are used to filter the water and not allow trash or debris to enter pump suctions. When the screens become dirty a "waterfall" is created and screens must be cleaned. If screens go unattended, a vortex may form and allow air to be sucked into the pumps resulting in cavitation and loss of cooling on process condensers. On the other hand, a high level alarm is not critical, but can be costly if towers are allowed to overflow (due to loss of expensive chemicals which are added to treat cooling water [see TREATMENT]).
C/3 Each tower has two (2) cells in which the return water is cooled for recirculation. The water is returned to the top of the tower via the return risers and allowed to freefall to the basin. There are numerous slats positioned so that the falling water is broken into droplets which allows the heat to be removed much easier than trying cool a solid stream of water. The cooling is provided by an updraft of air created by the fan located atop the tower cells; air is pulled in through the open section at the tower bottom and
010802
Subject , to, protecti ve Order1'1 of 14th Judicial district Cobrt'
No.' 91-1.14 5 "
discharged through the fan exhaust. Each fan is equipped with a vibration switch which will cut the fan's power if vibration becomes too great, this is a safety feature which ic dfcmignfcd t prolong- ths lifs of th* fan and aaaooiated parts.
NOTE: In winter months, it is not unusual for ice to form on the slats inside the tower even though the return water temperature may be as high as 100-110 degrees F. If ice is noticed, the fan should be shut down on that cell as the tower structure is not designed to withstand the added weight of ice.
TREATMENT!.
1) CHLORINE- Chlorine is used to minimise algae inside the tower itself. Chlorine is fed via a one-ton chlorine cylinder and an aspirator system. The controlling range for chlorine is 0.1-0.4 ppm
2) BETZ 25K- Bets 25K is a mixture of BETZ 20K (which is an inhibitor used to prevent the formation of galvanic cells (corrosion) and provide a protective coating on the steel inside the exchangers) and BETZ 2020 which is a dispersant (used to remove the unusable phosphates found in the make-up water). The controlling range for filtered phosphates is 1520 ppm and the indication for 2020 level is the difference between filtered and unfilterd phosphates. If the difference becomes greater than 3 ppm, there is inadequate dispersant in the system to remove the unusable phosphates and can lead to fouling of the exchanger.
3) CALCIUM- Calcium levels of less than 120 ppm are desirable to minimize the fouling potential in the exchangers. The calcium level is controlled by blowing down the return water to the ditch via an automatic blowdown system. However, leaving the automatic valve wide open and throttling the manual block valve allows for easier control of calcium and less upsets in tower levels. Also, cycles (which is the ppm of calcium in the basin divided by the ppm of calcium in the make-up water) are used to assure that the proper amount of retention time of the chemicals in the exchangers is achieved. Cycles of 6-8 are optimum.
4) PH- The controlling range for PH is 7.2-7.8 and is controlled by adding soda ash to low PH water, and adding Sulfuric acid to high PH water. High PH's can lead to dissolved compounds losing their solubility and dropping out of suspension, thus becoming scale forming and may lead to exchanger fouling. Low PH's can erode the protective film on the metal and may erode the metal itself. Therefore, the PH must remain in the desired range to assure maximum protection from corrosion and fouling.
SL 010803
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APPROVED BY: DATE: 4/2/90
_____________________________________ ! LOW LEVEL IN COOLING TOWER !
OPERATOR ' S NAMEDATE:
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1. VERIFY LOW LEVEL ALARM IN COOLING TOWER BY VISUALLY CHECKING LEVEL.
2. IF LEVEL IS LOW, CHECK THE CONDITION OF ALL OTHER BASINS AND OBSERVE THE SABINE WATER MAKE UP VALVE AND ENSURE IT IS MAKING UP WATER AT A RATE TO CONTROL BASIN LEVEL. ADJUST THE LEVEL CONTROLLER TO INCREASE MAKEUP IF NECESSARY. KEEP LEAD OPERATOR INFORMED OF YOU ACTIONS AND CONDITION OF COOLING TOWER.
3. ADJUST COOLING TOWER RETURN WATER TO ENSURE EQUAL HEAT DISTRIBUTION.
4. IF LEVEL IN COOLING TOWER BASINS CONTINUES TO DECREASE, THEN ADDITIONAL WATER CAN BE ADDED FROM SEVERAL SOURCES DEPENDING ON OPERATING CONDITIONS. A. BLOCK OFF ANY BLOW DOWN B. SWITCH ANY WATER GOING TO THE CLEAN WATER DITCH TO THE BASINS. C. USE LEVEL CONTROLLER BYPASS D. IF LOW LEVEL IS IN #1, 2, OR 3 BASINS, RAISE LEVEL IN #4 TO INCREASE OVERFLOW. E. USE WELL WATER MAKE AS ANOTHER SOURCE OF MAKEUP F. TRIP SPRINKLER SYSTEM TO COOLING TOWER IN FIRE HOUSE.
---------- 5.
KEEP YOUR OPERATOR AND LEAD OPERATOR INFORMED OF COOLING TOWER BASIN LEVELS AND OF ALL YOU ACTIONS TO CONTROL THE LEVEL. LOSS OF COOLING TOWER WATER TO THE UNITS IS A CRITICAL SITUATION.
6. SEVERAL THINGS CAN CAUSE A LOW LEVEL IN THE COOLING . X;OWEHT.;-'BUT-,.W HAVE SEVERAL SAFE GUARDS TO KEEP US 'INFORMED. .7 ' A. LOW AND frifefirtLJSVEL ALARMS B*. AMP METERS ON; AL^_ PUMPS WITH DEVIATION ALARMS IF
THE AMPS DROP BELOW THE RED LINE SET POINT. C. CHECK VALVES ON PUMP DISCHARGE. D. SEVERAL SOURCES OF MAKE-UP WATER E. MEANS OF CROSS CONNECTING COOLING TOWER BASINS.
SL 010804
CODLING TOMER SAC NUMBERS
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CODLING TOWER PUMPS (55) AND MOTORS (50)
1
55-539
50-1558
2.
55-540
50-1559
3.
55-813
50-5648
4.
55-1623
50-1552
5.
55-984
50-1900
6.
55-1143
50-2266
7.
55-1511
50-2866
8.
55-1512
50--2867
TOWER
FANS (57)
FAN MOTORS (50)
1-1 (WEST)
1 1-2 (EAST)
57-263 57-264
50-1948 50-2822
GEAR BOXES (5: 52-121 52-122
2-1 (S) 2
2-2 (N)
3-1 (S) 3
3-2 (N)
57-296 57-314
57-361 57-436
50-1489 50-1534
50-6517 50-2267
52-142 52-151
52-172 52-260
4-1 (S) 4
4-2 (N)
57-265 57-266
50-2844 50-2845
52-336 52-555
SL 010805
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EDC/VDCM COOLING WATER DISTRIBUTION 5/1 I /SO
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VOC RX BTM5 COOLER 71--2!S3
rrp hfavy s~h.l cnm l--| # 1 71-1467
TCE HEAVY STILL CONO. #2 71-640 VOC OH STILL CONO. t--i 71-1601
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TEE PRODUCT COOLER !
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VOC STILL CONO. 71-1204
VDC REACTOR CONDENSER 7I-IB4B
CONDENSATE COOLER!
71-1203
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#1 RX CAS SEP 71-731
fl RX COND. j 71-730
EOC BTMS REC CDND 71-2522
EOC BTU REC CONO 71-2437
STRIPPER CONDENSER 71-MBS
12 RX CAS SEP 71-4B7
12 RX CONDENSER 71*466
SL 010809
N STILL CONO 71-RES
<I PROOUCT COOLER
7I-BR3
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#2 PROOUCT COOLER
71-RBI
STRIPPER CONOENER 71-BSD
RX GAS SEP COND 71-BOR
II RX C0NDEN5ER 7I-BB2
12 RX CONDENSER 71 "MB