A coal-fired electric generating station produces 1500 MWe of electrical power.
ID: 3161681 • Letter: A
Question
A coal-fired electric generating station produces 1500 MWe of electrical power. Its steam temperature is 450°C, and its actual efficiency is 35%. It takes its cooling water from a very large neighbouring lake, whose temperature is 7°C.
a) What is the theoretical maximum value for the efficiency from the Laws of Thermodynamics?
b) What is the waste heat power that is transferred to the cooling water?
c) If regulations demand that the rise in temperature of the lake water must not exceed 10°C, what is the volume of cooling water that is required per second?
d) What would be the theoretical value for the efficiency if the cooling water would be heated up to 50°C? Discuss briefly 3 examples how one could use the 50°C warm water in a meaningful way.
e) If the sulfur content of the coal used in this plant is 1.75% by mass, what is the mass of SO2 produced per year?
Explanation / Answer
(a) Theoritical efficiency=(450-7)/(450+273)=0.6127 or 61.27 %
(b) waste heat power=total heat-work
total heat=(100/35)*1500=4285.7 MWe
waste heat=2785.7 MW
(c)let the volume is V m^3
mass per unit second=V*1000 kg
power=mass per unit second*4200*(10-7)=4285.7*10^6
we got V=340.13 m^3 per second
(d) if lower temp=50 C
efficiency=(450-50)/(450+273)=0.5532 or 55.32%
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