Part A At a steam power plant, steam engines work in pairs, the output of heat f

Question

Part A At a steam power plant, steam engines work in pairs, the output of heat from one being the approximate heat input of the second. The operating temperatures of the first are 670°C and 460 °C, and of the second 450 °C and 290'C. If the heat of combustion of coal is 2.8 x 10'J/kg, at what rate must coal be burned if the plant is to put out 1500 MW of power? Assume the efficiency of the engines is 60% of the ideal (Carnot) efficiency. Express your answer using two significant figures. I AZO O ? kg/s At Submit Request Answer

Explanation / Answer

Efficiencies of the engine are

for first n1 = (1-(460+273)/(670+273))*0.6 = 0.1336 and for second n2= (1-(290+273)/(450+273))*0.6 = 0.1328

So, when 1J heat is supplied to this engine, the output is 1*0.1336*0.1328 = 0.0177J

So, for 1500MW output, heat to be provided is 1500*10^6 / 0.0177 = 84557*10^6 J/s

So, burning rate of coal = 84557*10^6 J/s / 2.8*10^7 J/kg = 3019.9 kg/s

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