All about chemical engineering Cooling process Cooling towers Knowledge. Basic terminology

1. Cooling Tower & Water
CONTENTS:
▪ Cooling Tower – Definition, Basics
▪ Cooling Tower - Accessories
▪ Important Terms
▪ Basic Calculations
▪ Factors affecting Cooling Towers Performance
▪ Cooling Water’s - IS Standard Parameters & Performance Impact
▪ Learning & Concerns - Way forward
▪ Benefits to Organisation

2. Why Cooling Tower required..?
1. To remove Heat from a reaction – Process heat generated by chemical reaction
2. To remove Heat of Compression – Air compressors, DG Sets etc
3. To remove heat from Condensation – Chillers, vent condensers, etc
- Cooling towers are a very important part of many
chemical/ industrial plants.
- The primary task of a cooling tower is to rejectheat into
the atmosphere.
- They represent a relatively inexpensive and dependable
means of removing low-grade heat from cooling water.
- The make-up water source is used to replenishwater
lost to evaporation.
PURE BASICS OF CT OR DEFINITION..!!! :
Which Utility Equipment is easy to maintain - Water Chiller,
Brine Chiller, Air Compressor, Cooling Tower……?

3. Types of Cooling Towers:
1. Natural Draft.:
Typically works for very high flow rate of
45000 m3.hr and above
2. Mechanical Draft:
- Mechanical draft towers utilize large fans
to force or suck air through circulated water
- The water falls downward over fill surfaces,
which help increase the contact time
between the water and the air - this helps
maximize heat transfer between the two
- Cooling rates of Mechanical draft towers
depend upon their fan diameter and speed
of operation.
Important Factor to Note:
- Wet Bulb Temperature is fixed for a particular
time & date and location
- Natural draft dependent on Natural
conditions, where as, Mechanical Draft
dependent on contact time & air flow

4. Terms Importance of requirement…
Drift eliminators Water droplets that are carried out of the cooling tower
with the exhaust air, to trap them. Avoiding Water Loss
Fill Inside the tower, fills are added to increase contact
surface as well as contact time between air and water.
Thus they provide better heat transfer.
Plume The stream of saturated exhaust air leaving the cooling
tower.
Blow out Water droplets are blown out of the cooling tower by wind,
generally at the air inlet openings.
Louvers The purpose of louvers is to equalize air flow into the fill.
Nozzles Uniform water distribution at the top of the fill is essential
to achieve proper wetting of the entire fill surface
Fans To remove the hot air from cooling tower
COC represent the accumulation of dissolved minerals in the
recirculating cooling water.
Cooling Tower Accessories and brief descriptive :

5. Terms Importance
Blowdown The portion of the circulating water
that is removed in order to maintain
the number of dissolved solids and
other impurities at an acceptable
level.
Dry Bulb refers basically to the ambient air
temperature.
It is called “Dry Bulb” because the
sensing tips of the thermometer not
affected by the moisture of the air.
Wet Bulb is the temperature of adiabatic
saturation indicated by a moistened
thermometer bulb exposed to the
airflow.
Approach is the difference between the cooling
tower outlet cold water temperature
and Wet bulb temperature.
Range is the temperature difference
between the water inlet and the
water exit. ( Delta T)
Important Basic Terms and brief descriptive:
The below pic.represents,quite easily
understandable & easy to remember,for
a CT Performance:
Which is better indicator of Cooling
Tower performance, Range or
Approach…..?
Approach

6. Cooling Tower Performance indicators:
Cooling Tower Effectiveness:
is the ratio of range, to the ideal range, i.e., difference
between cooling water inlet temperature and ambient wet
bulb temperature.
CTE (%) = Range / (Range + Approach).
Cooling Tower Capacity:
is the heat rejected in kCal/hr or TR, given as product of mass
flow rate of water, specific heat and temperature difference.
CTR = M x CP x (T1-T2) /3024
Evaporation Loss:
is the water quantity evaporated for cooling duty
(Thumb Rule:10 LKCal heat reject requires 1.8 M3 water OR
0.8 % of pump Circulation Rate)
EL (m3/hr) = Circulation Rate (m3/hr) * Delta T (oC)/ 675
Blowdown Loss:
depend upon COC (cycles of concentration)
BL (m3 / hr)=Evaporation Loss (M3/hr)/ (COC–1)
COC is the ratio of dissolved
solids in circulating water to
the dissolved solids in make
up water.
COC = TDS in PPM of CTW
TDS in Makeup Water

7. Cooling Tower Performance indicators (contd.):
HTI (Holding Time Index):
is a calculated figure that indicates the time required to
reduce the chemical or makeup water added to a system to
50% of its original concentration.
HTI = 0.693 x HC/ BD
HC: Holding capacity in m3 & BD Blow down rate in m3/Hr
(Expressed in the Time units used for blowdown). NMT 200Hr
Time per Cycle:
The time per cycle is defined as the time it takes all the water
in a system to make one trip (from the discharge side of the
recirculationpump back to the suction side of the pump)
Time per Cycle = HC / R
R is Recirculation Rate M3/hr
Liquid /Gas Ratio (L/G):
is the ratio between the water and the air mass flow rates.
Against design values, seasonal variations require adjustment
and tuning of water and air flow rates to get the best cooling
tower effectiveness through measures like water flow rate and
blade angle adjustments.

8. the closer the approach to the
wet bulb, the more expensive the
cooling tower due to increased
size.
- (Thumb Rule: Usually a 2.8oC
approach to the design wet bulb
by Manufacturer)
Cooling Tower Design basis, Factors affect CT Size:
The heat load imposed on a
cooling tower is determined by the
process being served ( Ex. DG Sets
required small CT)
Range is a function of the heat
load and the flow circulated
through the system
Wet Bulb is controlling factor
from the aspect of minimum cold
water temperature to which water
can be cooled by the evaporative
method.

9. Drift Loss
Nozzles:
Louvers:
Circulation Water:
Make Up Water:
Fan Blade Angle:
Fills:
Factors affecting of Cooling Tower Performance:
Drift Eliminators must be in good Condition.
(ND – 2 % and MD – 0.2% loss of water)
Letus discussMitigationPlans:
Regularly check & Clean Nozzles
Blow Down Regular
1. Monitor TDS & TH Level and ACT
2. just like, how we do for “Boilers” to control
“Salts Concentration” (Humans: !!!)
- Additional to the above, there are 13 main
parameters, which are those….??? In Next slide
- Important to maintain the make up water
parameters and its impact……In Next Slide
Conclusion CHECK LIST : Monthly OR Quarterly.
Misplace of Louvers, leads to increase in Heat
Load and reduced efficiency
Vibration and increase in heat load and reduced
efficiency
Channeling, less heat transfer, loss in
performance, delay in process, safety. Regular
cleaning and replace damaged ones

10. Cooling Tower Make up Water quality Parameters:
Water Parameters Industry Standards
pH 6 to 8
Total dissolved Salts, ppm <1500
Residual Chlorine, ppm 0.2 to 0.5
Total Hardness, ppm as CaCO3 <300
Chloride hardness ( Permanent hardness), ppm as
CaCO3
<100
Temporary Hardness (Alkalinity), ppm as CaCO3 <200
Iron + Manganese < Nil
C O D < 150 ppm
Sulphate as SO4 < 500
Silica as SiO2 <40
Total Bacterial Count ( TBC) < 150 us/cm
Chloride, ppm <250
Turbidity, NTU <5

11. Water Parameters
IS 8188
Standards
Impacton Equipment's/Accessories
pH 7.7 to 8.2
Low pH < 7.7- Corrosion
High pH > 8.2 Scaling
Turbidity, NTU 20 Physical fouling, increasing scaling
Residual Chlorine, ppm 0.2 to 0.5 Biofouling affecting heat transfer and under deposit corrosion
Total Hardness, ppm as CaCO3 <1000 Scaling
Temporary Hardness (Alkalinity),
ppm as CaCO3
<250 Scaling
Iron + Manganese < 3 Iron fouling, High Manganese results in black color water
KMnO4 No (MgO3 Absorbed) Not applicable NA
C O D < 150 ppm Biofouling – Slime formation and corrosion in heat exchanger
Total dissolved Salts <5000 Scaling and Corrosion
Carbon dioxide Not applicable NA
Sulphate as SO4 < 3000 Corrosion
Silica as SiO2 150 Magnesium Silicate scaling
Total Bacterial Count ( TBC) < 10 ^ 5 cfu/ml Biofouling- Poor heat transfer and corrosion
Mild Steel Corrosionrate mils/year < 3 Pipeline and heat exchanger corrosion
Circulation Cooling Water Quality Parameters (IS 8188) and its
Impact on Equipment's & Accessories

12. Equipment
Type of
coupon
Period
(Days)
Corrosion
rate in
(MPY)
Standard
Corrosion limit
in MPY
CT 1
MS 65 21.908 <5
SS 65 0 <1
Copper 65 1.080 <1
CT 2
MS 53 13.851 <5
SS 53 0 <1
Copper 53 0 <1
Note:
Implementation of corrosion coupon rack and continuous monitoring periodically,
failure assessment and planning to mitigate avoid premature failures
Corrosion Coupons : Why it is required….
Installed the Corrosion Coupon Rack
in main Utility Cooling Tower to
monitor the corrosion level in the
Utility cooling circulation water to
monitor the corrosion level by
W/W method and results as attached
with action plan.
Picture case reference only

13. MGF ( Multi Grade Filter): Benefits
Multi Grade Filters for the Induced Draft Cooling Tower
(Case Study for reference purpose only)
Sl.
No.
Type of
Document
UOM
Standard
Parameters
Parameters
Before
Afteroperationof
one month
1 Turbidity NTU <20 54 10.2
2 TSS ppm <10 14 6
3 TDS ppm <2000 2000 1980
4 Ph --- 7.7 to 8.5 8.3 8.4
5 Hardness ppm <200 112 154
Note:
Improvement observed for the cooling tower parameters after installation of the same and now
Turbidity & TSS parameters are in green zone.
Installed Multigrade filter to the induced draft
cooling tower to remove the dead algae,
slime, Suspended particles, fouling present
in circulating cooling water. Performance
monitoredandfound improved
Picture case reference only

14. Benefits - Cooling Tower Performance to Organisation:
Variation in Make up Water
Parameters from Industry standards
Higher TDS in Circulation Water / COC
is higher
pH in the desired range in circulation
water ( Desired range 7.6 to 8.2)
Lesser Delta T (against designed)
Corrosion rate not monitoring
- Lower pH leads to corrosion
- Higher pH leads to scaling
Less Heat transfer, More Blow downs,
More chemical consumptions
More water consumptions, chocking of
nozzles, fast biological growth
No- Make up & Circulation Water
Parameters analysis
Not able to cool the Equipments
/Systems in given time, leads to loss of
Energy
Surprise leaks of systems and longer
breakdown
Leads to surprise breakdowns,
increased OPEX expenses, Business
loss

15. Opportunities for Improvement:
Value Deliverable
KeyPerformance
Indicator
Unit ofMeasurement Methodology Impact
Water Parametersleading to
Impact
Safety
Product Stewardship,
Product safe for use in
PharmaIndustry
Safe working manhours
Tracking safety releated
incidents, Continuous
improvementprojects towards
safety.
1) LessExposure to the chemicals
1)Microbial Organisms - can cause
health hazards.
Asset
Integrity
To Extend the Life of
equipment through
lower corrosion rate
1)MS<3 MPY
2)Cu< 0.5MPY
3)SRB - 100/100ml
4)TBC <10^ 5
1)Online Corrosion Monitor
2)Corrosion Coupon testing
1) Damaged Pipelines
2) Replacement Cost due to metal
loss
3) Associated downtime
4) Reduced Heat transfer efficiency
1)pH
2)TDS
3)Chlorides
4)Microbial Organisms
Water Saving
To reduce theintake of
make-up waterto the
cooling tower
KL or Cubic Meters
1)Increased COC
2)Reduced makeup water
consumption
1) Reduced Blowdown Qty
2) Increasing COCwithour
impacting cost ofchemical
treatment
1)TDS
2)Deposition causing minerals
Energy Saving
Improved energy
savings through
maintenance ofdeposit
freeheat transfer
surfaces
DegreesCentigrade
1)By maintaining the
approach temperatureofthe
Chillers
2)By reducing thefrequency
ofCondenser De-scaling
1) Approach Temp.
2) Increased Power Consumption
3) De-scaling Frequency
4) Associated Downtime
1)pH
2)TDS
3)Hardness
4)Microbial Organisms
Total Cost of
Operation
Reduced TCO to the
best extent possible
Monetary (Rupees)
1)Tracking theefficiency of
the chillers
2)Operational efficiency ofthe
CW systems.
1) Increased cleaning frequency
2) Reduced CTEfficiency
3) Cost ofDe-scaling
4) Cost ofManpower for cleaning
-

16. Key Takeaway’s:
Which Utility Equipment / system is
difficult to maintain…?
Critical Factors affecting in Cooling
Tower performance……!
Important parameter to monitor……!
Which is most critical factor in CT
System and decides CT ‘s
performance
What we need to do to maintain
Cooling Towers to give better
results…!
Drift, Nozzles, Fills, Blades &
etc
Approach and Heat Load
Chiller, Air Compressor…or Cooling
Tower
Quality - Make Up Water &
Circulation Water’s Parameters and
fills and nozzles
Monitor all the Parameters regularly
& Act accordingly