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Heat engines

  1. Oct 29, 2007 #1
    1. The problem statement, all variables and given/known data

    At a steam power plant, steam engines work in pairs, the output of the first contributing to the heat input of the second. Let the operating temperature of the first be 670.0 degrees C and 440.0 degees C, and of the second be 430.0 degrees C and 290.0 degrees C. If the heat of combustion of coal is 2.80 x 107 J/kg, at what rate (in kg/s) must coal be burned if the efficiency of the engines is only 60.0% of the ideal (Carnot) efficiency if the plant is to output 1000.0MW of power?

    2. Relevant equations

    e=W/Q(high) = 1- Q(low)/Q(high)

    3. The attempt at a solution

    I converted the temperatures from C to K.

    I am unsure how to connect the heat of the engines to the heat of combustion of coal and the rate it burns and the end power. I have tried working with the units to reach an answer with units kg/s:

    W= eQ(high) W=(.6)(943 K)= 565.8 J/s

    To reach units kg/s, (565.8 J/s) / (2.8 x 10^7 J/kg) = 1.6 x 10^10 kg/s, which is an outrageous answer and I did not base my work on any physics knowledge...

    So if someone could give me a starting point I would be very grateful,
  2. jcsd
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