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Homework Help: Finding Fuel Consumption

  1. Nov 29, 2015 #1
    • Member warned about posting with no effort shown
    1. The problem statement, all variables and given/known data
    A boiler is to produce 6250 kg/h of steam superheated by 40 oC at a pressure of 2.1 MN/m2. The temperature of the feedwater is 50 oC. If the thermal efficiency of the boiler is 70%, how much fuel oil will be consumed in one hour? The calorific value of the fuel oil used is 45000 kJ/kg, cp of superheated steam is 2.093 kJ/kg K.
    for pressure 2.1 Mn/m2
    hfg = 1880 kJ/kg
    hf = 920 kj/KG
    sat temp - 214.9

    2. Relevant equations
    in my notes i have efficiency as [generated steam * hfg] / [fuel consumed * CV ]

    3. The attempt at a solution
    my attempt gave me the answer of 373 which i found to be to small of a value
  2. jcsd
  3. Nov 29, 2015 #2


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    Staff: Mentor

    Show your work.
  4. Nov 29, 2015 #3
    i used efficiency = [generated steam * hfg] / [fuel consumed * CV ]
    for efficiency i used 0.70, for generated steam 6250, hfg 1880, CV as 45000
    and i found for the fuel consumed
  5. Nov 29, 2015 #4


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    Staff Emeritus
    Science Advisor
    Homework Helper

    I don't know about the formula in your notes.

    Remember, hfg is the difference in the amount of heat contained in saturated vapor and saturated liquid.

    What about the extra amount of heat which is contained in the superheated vapor? Where does that come from?
    What about the heat which is brought into the boiler from the feedwater at 50° C? How is that accounted for?
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