Operation & Maintenance of Cooling Tower 1
Contents Basic of Cooling Towers Types of Cooling Tower Preparation for Startup Startup Cooling Tower Caution During Operation Water Quality Maintenance & Control Troubleshooting 2
What is Cooling Tower? A cooling tower is an equipment used to reduce the temperature of a water stream by extracting heat from water and emitting it to the atmosphere 3
Types of Cooling Towers 1. Natural Draft Cooling Towers 2. Mechanical draft Cooling Tower a) Forced Draft Cooling tower b) Induced Draft cooling Tower Natural Draft Cooling Tower Hot air moves through tower where Fresh cool air is drawn into the tower from bottom No fan is required Concrete tower <200 m Used for large heat duties 4
Mechanical Draft Cooling Tower Large fans to force air through circulated water Water falls over fill surfaces: maximum heat transfer Cooling rates depend on many parameters Large range of capacities can be grouped Mechanical draft Cooling tower is of three types Forced draft Induced draft cross flow Induced draft counter flow 5
Types of Cooling Towers Forced Draft Cooling Towers Air blown through tower by centrifugal fan at air inlet Advantages: suited for high air resistance & fans are relatively quiet Disadvantages: recirculation due to high air-entry and low air-exit velocities 6
Types of Cooling Towers Induced Draft Cooling Towers Two types Cross flow Counter flow Advantage: less recirculation than forced draft towers Disadvantage: fans and motor drive mechanism require weather-proofing 7
Types of Cooling Towers Induced Draft Counter Flow CT Hot water enters at the top Air enters at bottom and exits at top Uses forced and induced draft fans
Types of Cooling Towers Induced Draft Cross Flow CT Water enters top and passes over fill Air enters on one side or opposite sides Induced draft fan draws air across fill 9
Induced draft counter flow Cooling Tower Open type Counter Flow Closed Circuit Counter Flow 10
Main components of counter flow cooling Tower 1. Tower Casing 2. Tower support framework 3. Motor support framework 4. Air inlet Screen/louver 5. Fill media 6. Sprinkler head 7. Sprinkler pipes 8. Fan blades 9. Fan blade hub 10. Motor 11. Drift eliminator 12. Motor Control 13. Water basin 14. Pan strainer 15. Bleed Valve 16. Float Valve 11
Components of a cooling tower Frame and casing: support exterior enclosures Fill: facilitate heat transfer by maximizing water / air contact Cold water basin: receives water at bottom of tower 12
Components of a cooling tower CT Fan Fan Hub Fan Motor Sprinkler Head Sprinkler Pipe 13
Components of a cooling tower Float Valve Fill Media 14
Important terms for Cooling tower assessment 1. Range 2. Approach 3. 3.Cooling capacity 4. Evaporation loss 5. Cycles of concentration 6. Blow down losses 15
Selection of Cooling Tower 1. Range Difference between cooling water inlet and outlet temperature: Range ( C) = CW inlet temp CW outlet temp High range = good performance Range Approach Hot Water Temperature (In) (In) to the Tower (Out) from the Tower Cold Water Temperature (Out) Wet Bulb Temperature (Ambient) 16
Selection of Cooling Tower Approach Difference between cooling tower outlet cold water temperature and ambient wet bulb temperature: Approach ( C) = CW outlet temp Wet bulb temp Low approach = good performance Range Approach Hot Water Temperature (In) (In) to the Tower (Out) from the Tower Cold Water Temperature (Out) Wet Bulb Temperature (Ambient) 17
Selection of Cooling Tower Cooling Capacity Heat rejected in kcal/hr or tons of refrigeration (TR) = mass flow rate of water X specific heat X temperature difference High cooling capacity = good performance Range Approach Hot Water Temperature (In) (In) to the Tower (Out) from the Tower Cold Water Temperature (Out) Wet Bulb Temperature (Ambient) 18
Selection of Cooling Tower Evaporation Loss Water quantity (m3/hr) evaporated for cooling duty = theoretically, 1.8 m3 for e= every 10,000,000 kcal heat rejected Range Hot Water Temperature (In) (In) to the Tower (Out) from the Tower = 0.00085 x 1.8 x circulation rate (m3/hr) x (T1-T2) T1-T2 = Temp. difference between inlet and outlet water Approach Cold Water Temperature (Out) Wet Bulb Temperature (Ambient) 19
Selection of Cooling Tower 6. Cycles of concentration (C.O.C.) Ratio of dissolved solids in circulating water to the dissolved solids in make up water 7. Cycles of concentration (C.O.C.) Depend on cycles of concentration and the evaporation losses Blow Down = Evaporation Loss / (C.O.C. 1) 20
Cooling Tower Water Quality Parameter Unit Standard Value Ph 7.0-8.8 TSS PPM Less than 25 TDS PPM Les than 5000 Conductivity PPM Less than 2400 Alkalinity,CacO3 PPM 75-400 Chlorine PPM Less than 300 Silica PPM Less than 150 Total Bacteria CFU/ml Less than 10000 21
Startup & Operation Preparation for Start-up Cleaning Ensure that the water basin is free of dirt & other foreign material..open the drain and flush the water basin with clean water. Trial Circulation of Water Slowly rotate the sprinkler by hand to verify smooth operation. Start the circulating pump& run long enough to clean out the interior of thee tower and water pipes. Examine the Tower Be sure to lock out fan motor disconnect before servicing any portion of fan assembly. After the trial circulation of water check for foreign material and dirt within the tower and at the outlets of the sprinkler pipes.check the discharge screen for debris. 22
Preparation for Start-up Check for smooth operation and minimal clearance between blades & tower. Check the power supply for correct voltage. All electrical connections must be in accordance with all applicable electrical codes. Operate the tower fan for two to three hours. If abnormal vibration or sound develops,correct it & try same process. 23
Cooling Tower Start-up Pump Check rotation of tower pumps by starting pump momentarily. Once the proper rotation is established the flow to the tower by adjusting the pump discharge valve. After steady water flow is established ensure that the sprinkler head is rotating smoothly and that the proper RPM has been achieved. Fan Clear the intake & discharge areas of any foreign material. Set the fan thermostat for the desired temperature and check for proper operation. When fan is running measure the amperage draw and verify that it falls within nameplate rating. 24
Caution during operation Water Flow Cooling tower performance is affected by the volume flow rate of water. Proper attention should be given In order to maintain required flow rate during operation. Water Treatment The interior of the tower must be kept clean to ensure trouble freee operation.water treatment system is recommended for the area with critical water quality. Gear Reducer Oil level. The oil level in the gear reducer must be maintained at the proper level Overall Operation Periodic attention should be given to vibration,noise,temperature of the cooling water and electric current. If any changes are noticed corrective action should be taken. 25
Maintenance Cooling Tower Daily Checklist Description Overall visualization Water level Float valve Overflow Water leaking Vibration/Sound Comment Complete overall visual inspection to be sure all equipment is operating and that safety systems are in place.& water is flowing in the tower. Check water level in the water sump & make sure it is at the required level Check that the float valve is in place & working well Water must not overflow the tower sump Check if there is any leakage anywhere in the tower & record it for corrective action. Check either any abnormal sound or vibration from fan motor Blow-down Blow down the sump as per COC 26
Preventive Maintenance Plan-Weekly SN Activity Description 1 Fan motor condition Check the condition of the fan motor through temperature or vibration analysis and compare to baseline values 2 Clean suction screen Physically clean screen of all debris 3 Test water sample Test for proper concentrations of all dissolved solids,tds & Ph.Adjust blow down and chemicals as necessary. 4 Make-up water float switch Operate switch manually to ensure proper operation 5 Vibration Check for excessive vibration in motors, fans and pumps 27
Maintenance Plan-Monthly 7 Pan Strainer Clean the pan strainer 8 Bleed-off valve Check bleed-off valve to make sure it is operative 9 Float Valve Check operating level in pan and adjust float valve assembly 10 Water Distributor Check water distributor system and spray pattern 11 Drift elliminator Check drift eliminator either it is in proper position 12 Belt tension Check belt tension and adjust Inlet 13 screen/fan Look for proper positioning & scale build up & clean screen 14 Clean tower Remove all dust, scale & algae from tower basin, fill & spray nozzles 28
Preventive Maintenance Plan-Quaterly & Yearly 15 Fan blades 16 Check Bearing 17 Motor condition 17 Fill Media Check the fan blades,for crack,missing allignments & vibration Inspect bearings & drive belts for wear, adjust,repair or replace as necessary Check the condition of the fan motor through temperature or vibration analysis and compare to ensure long life Yearly Take out the fill media from the necessary Cooling Tower,clean, dry & set up again. Change if necessary 29
Cooling Tower Troubleshooting Table 1.Typical Problems & Trouble Shooting for Cooling Towers Problem/Difficulty 1.Voltage reduction Possible Causes Remedies/Rectifying Action Check the voltage 2a).Incorrect angle of axial fan blades Adjust the blade angle Excessive absorbed current/electrical load 2b).Loose belts on centrifugal fans (or speed reducers) Check belt tightness 3.Overloading owing to excessive air Regulate the water flow by flow-fill has minimum water loading per means of the valve square meter of tower section 4.Low ambient air temperature The motor is cooled proportionately and hence delivers more than name plate power 30
Table 1.Typical Problems & Trouble Shooting for Cooling Towers 1.Uneven operation of spray nozzles Adjust the nozzle orientation and eliminate any dirt Drift /carryover of water outside the unit 2.Blockage of the fill pack 3.Defetive or displaced droplet eliminators Eliminate any dirt in the top of the fill Replace or realign the eliminators 4.Excessive circulating water flow (possiblyowing to too high pumping head Adjust the water flow rate by means of the regulating valves. Check for absence of damage to the fill. 31
Table 1.Typical Problems & Trouble Shooting for Cooling Towers 1.Float valve not at correct level Adjust the make-up valve Loss of water from basins /pans 2.Lack of equalizing connections Equalize the basin of tower operating in parallel 32
Table 1.Typical Problems & Trouble Shooting for Cooling Towers 1.Water flow below the design value Regulated the flow by means of the valves 2.Irregular air flow or lack of air Check the direction of the rotation of the fans and/or belt tension(broken belt possible) Lack of cooling & hence increase in temperature owing to increased temperature range 3.a.Recycling or humid discharge Check the air descent velocity air 3b.Intake of hot air from older Install deflectors sources 4a.Blocked spray nozzles(or Clean the nozzles and/or the even blocked spraytubes tubes 4b.Scaling of joints wash or replace the item Clean or replace the material(washing with 5.Scaling of the fill pack inhibited aqueous. Sulfuric acid is possible but long, complex & expensive) 33
THANK YOU FOR YOUR ATTENTION Prepared by Tanul Islam, CE-PRAN-PIP 34