Question

The 600MW power plant has an efficiency of 36% with 15% of the waste heat being released to the atmosphere as stack heat and another 85% taken away in the cooling water. Instead of drawing water from the river, heating it, and returning it to the river, this plant uses an evaporative cooling tower wherein heat is released to the atmosphere as cooling water vaporized. At what rate must 15ºC makeup water be provided from the river to offset the water lost in the cooling tower?

Answer 1

rate of makeup water added is 367.75 kg/s

Step-by-step explanation:

given data

output power = 600 MW

efficiency = 36 %

waste heat = 15%

heat taken away in cooling tower = 85%

to find out

At what rate must 15ºC makeup water be provided from the river to offset the water lost in the cooling tower

solution

input power =
`(power)/(efficiency)`

input power =
`(600)/(0.36)`

input power = 1666.67 MW

total heat = input - output

total heat = 1666.67 - 600

total heat = 1066.67 MW

and we know

15% of waste heat is released to atmosphere

so Q atm = 0.15 × 1066.667

Q atm = 160 MW

and

and 85% of heat is taken away in the cooling water so

Q cooling tower = 0.85 × 1066.667

Q cooling tower = 906.66 MW

so

we know at 15ºC from saturated water tables hfg will be

hfg = 2465.4 kJ/kg

so rate of water lost in cooling tower added by means of make up water that is

Q cooling tower = m × hfg

906.66 × 1000 = m × 2465.4

m = 367.75 kg/s

so rate of makeup water added is 367.75 kg/s