Environmental Engineering Reference
In-Depth Information
Problem 10.8
This plant substitutes NG (formula CH
4
) instead of coal, with a heating value of 50 MJ/kg, in a
combined cycle mode having a thermal efficiency of 45%. (a) How much NG (m
3
/y at STP) is
consumed? (b) How much CO
2
(t/y) is emitted?
Problem 10.9
In order to ameliorate the CO
2
caused greenhouse effect, a power plant is built that enables the
capture of CO
2
from the flue gas. The plant runs on pure methane and oxygen, so the flue gas
consists only of CO
2
and H
2
O:
CH
4
+
2O
2
→
CO
2
+
2H
2
O
−
0
.
244 kWh(th)/mole CH
4
where the minus sign means that the process is exothermic; that is, energy is evolved. The plant must
produce its own O
2
. From oxygen suppliers we know that the energy requirement for air separation
is 250 kWh (electric) per metric ton of O
2
. An equal amount of electric energy is required for
liquefaction of 1 metric ton of CO
2
. The plant has a gross thermal efficiency
45 (that
is, thermal efficiency calculated before electricity is syphoned off for O
2
production and CO
2
liquefaction). (a) What percentage of the plant's electricity output is available for dispatch into the
grid? (b) What is the net thermal efficiency (electricity output per heat input after O
2
production
and CO
2
liquefaction)?
η
gross
=
0
.
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