7-11
7-29 A coal-burning power plant produces 300 MW of power. The amount of coal consumed during a oneday period and the rate of air flowing through the furnace are to be determined.
Assumptions 1 The power plant operates steadily. 2 The kinetic and potential energy changes are zero.
Properties The heating value of the coal is given to be 28,000 kJ/kg.
Analysis (a) The rate and the amount of heat inputs to the power plant are
Q in
Qin
W net,out
300 MW
0.32
K th
Q in 't
937.5 MW
(937.5 MJ/s)(24 u 3600 s) 8.1 u 10 7 MJ
The amount and rate of coal consumed during this period are
mcoal
Qin
qHV
m coal
mcoal
't
8.1 u 107 MJ
28 MJ/kg
2.893 u 106 kg
24 u 3600 s
2.893 u 106 kg
33.48 kg/s
(b) Noting that the air-fuel ratio is 12, the rate of air flowing through the furnace is
m air
(AF)m coal
(12 kg air/kg fuel)(33.48 kg/s)
401.8 kg/s
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