Problem $1\mathrm{.}29($modified$),$ Masters and Ela, Introduction to Environmental Engineering and

Science, $3$rd Ed$.$:

A $950-M{W}_e$ power plant has an efficiency of $39$ percent with $20$ percent of the waste heat

being released to the atmosphere as exhaust stack heat and the other $80$ percent taken away in

the cooling water. Consider two cases for power plant cooling.

a$.$ Cooling water is drawn from a river with an upstream flow of $110\frac{m^3}{s}$ and a temperature

of $15C$ and is returned to the river after cooling the power plant.

i$.$ Is the system an open system or closed system?

ii$.$ Construct an energy balance for the system.

iii. If the cooling water is only allowed to rise in temperature by $13C,$ what flow rate

from the river would be required?

b$.$ If instead of drawing water from a river, heating it$,$ and returning it to the river, the plant

could use an evaporative cooling tower wherein heat is released to the atmosphere as

cooling water is vaporized into steam.

i$.$ Is the system an open system or closed system?

ii$.$ Construct an energy balance for the system

iii. At what flow rate must $15C$ makeup water be provided from the river to offset the

water lost in the cooling tower?