At a steam power plant, steam engines work in pairs, the heat output of the firs

Question

At a steam power plant, steam engines work in pairs, the heat output of the first one being the approximate heat input of the second. The operating temperatures of the first are 730 C and 460 C, and the second 435 C and 260 C.

Part a) If the heat of combustion of coal is 2.8*10^7 J/kg, at what rate must coal be burned if the plant is to put out 860 MW of power. Assume the efficiency of the engines is 65% of the ideal (Carnot) efficiency.

Part b) Water is used to cool the power plant. If the water temperature is allowed to increase by no more than 4.5 C, estimate how much water must pass through the plant per hour.

I was able to find part a to be 100 kg/s but I cannot find part b.

Explanation / Answer

The extra heat produced is 35% of the amount whose 65% is 850MW.

Hence 463.08MW energy is to be removed.

Now, change in temperature of water is 4 deg C

So by the heat equation, we have, 463.08= m x 4186 x 4

m= 27656 kg per hour

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