Pavan Kumar
Chemical
- Aug 27, 2019
- 366
Hi All,
I want to confirm my Blowdown and And Make up water calculations that I did for the Cooling Tower in our plant. Attached please find the sketch for the cooling tower with the IN and OUT streams ( please excuse me if it is shabby.) The cooling tower is supplied with Make Up water, M gpm. The evaporation and drift losses are E and D gpm respectively. The circulation water rate is C gpm. The Cooling tower supplies F gpm of cooling water to another tower which does not have its own Make Up water source ( This may sound strange but that's how it is and I am going to correct this situation. First I got to do the mass balance and hence this post.)
Also due to excess Make up water being supplied there is an over flow to the sewer at B gpm.
As per the guidance by Mr. Milton Beychok in the link below, I did the mass balance calculations and need confirmation.
Mass Balance:
Make Up water = M gpm
Evaporation Losses = E gpm
Drift Losses = D gpm
Overflow (Blowdown) = B gpm
Water to second tower = F gpm
Circulation water = C gpm
Temperature of water return to Cooling Tower = T1 Deg F
Temperature of water Out of Cooling Tower = T2 Deg F
Salt Concentration in Circulation Water = Xc
Salt Concentration in Make Up Water = Xm
M = E + D + B + F
Evaporation Rate, E = 0.00085 * C * ( T1-T2) gpm
Drift Loss , D = 0.2% of Circulation Rate = 0.002 *C gpm
Dissolved Salt Balance:
Xm * M = ( Xc * D) + ( Xc * B ) + ( Xc * F ) = Xc * ( D + B + F)
Cycles = Xc/ Xm = M / (D + B + F) = ( E + D + B + F ) / ( D + B + F) = [ 1 + E / (D=B+F) ]
From this B = [ E / ( Cycles -1 ) ] - ( D + B)
Now with my project Numbers:
C = 4025.55 gpm
T1 = 25.36 Deg C = 77.648 Deg F
T2 = 22.72 Deg C = 72.896 Deg F
E = 0.00085*C*(T1-T2) = 0.00085 * 4025.55 * (77.648-72.896) = 16.26 gpm
D = 0.002 * 4025.55 = 8.0511 gpm
F = 18.45 gpm ( as measured by our flow meter )
Xc = 428 Micro siemens / cm ( Concentration directly proportional to conductivity)
Xm = 319 Micro siemens / cm
Cycles = Xc / Xm = 428 / 319 = 1.34
B = [ E / ( Cycles - 1 ) ] - ( D + F )
= [ 16.26 / ( 1.34 -1) ] - ( 8.0511 + 18.45 )
= 47.8 - 26.5011 = 21.29 gpm
Make Up = E + D + B + F
M = 16.26 + 8.0511 + 21.29 + 18.45
= 64.05 gpm
Thanks and Regards,
Pavan Kumar
I want to confirm my Blowdown and And Make up water calculations that I did for the Cooling Tower in our plant. Attached please find the sketch for the cooling tower with the IN and OUT streams ( please excuse me if it is shabby.) The cooling tower is supplied with Make Up water, M gpm. The evaporation and drift losses are E and D gpm respectively. The circulation water rate is C gpm. The Cooling tower supplies F gpm of cooling water to another tower which does not have its own Make Up water source ( This may sound strange but that's how it is and I am going to correct this situation. First I got to do the mass balance and hence this post.)
Also due to excess Make up water being supplied there is an over flow to the sewer at B gpm.
As per the guidance by Mr. Milton Beychok in the link below, I did the mass balance calculations and need confirmation.
Mass Balance:
Make Up water = M gpm
Evaporation Losses = E gpm
Drift Losses = D gpm
Overflow (Blowdown) = B gpm
Water to second tower = F gpm
Circulation water = C gpm
Temperature of water return to Cooling Tower = T1 Deg F
Temperature of water Out of Cooling Tower = T2 Deg F
Salt Concentration in Circulation Water = Xc
Salt Concentration in Make Up Water = Xm
M = E + D + B + F
Evaporation Rate, E = 0.00085 * C * ( T1-T2) gpm
Drift Loss , D = 0.2% of Circulation Rate = 0.002 *C gpm
Dissolved Salt Balance:
Xm * M = ( Xc * D) + ( Xc * B ) + ( Xc * F ) = Xc * ( D + B + F)
Cycles = Xc/ Xm = M / (D + B + F) = ( E + D + B + F ) / ( D + B + F) = [ 1 + E / (D=B+F) ]
From this B = [ E / ( Cycles -1 ) ] - ( D + B)
Now with my project Numbers:
C = 4025.55 gpm
T1 = 25.36 Deg C = 77.648 Deg F
T2 = 22.72 Deg C = 72.896 Deg F
E = 0.00085*C*(T1-T2) = 0.00085 * 4025.55 * (77.648-72.896) = 16.26 gpm
D = 0.002 * 4025.55 = 8.0511 gpm
F = 18.45 gpm ( as measured by our flow meter )
Xc = 428 Micro siemens / cm ( Concentration directly proportional to conductivity)
Xm = 319 Micro siemens / cm
Cycles = Xc / Xm = 428 / 319 = 1.34
B = [ E / ( Cycles - 1 ) ] - ( D + F )
= [ 16.26 / ( 1.34 -1) ] - ( 8.0511 + 18.45 )
= 47.8 - 26.5011 = 21.29 gpm
Make Up = E + D + B + F
M = 16.26 + 8.0511 + 21.29 + 18.45
= 64.05 gpm
Thanks and Regards,
Pavan Kumar
