Environmental Engineering Reference
In-Depth Information
Problem 5.1
A coal-fired power plant (PP) has a rated power of 1000 MW(el). It works at 100% capacity (base-
loaded) at a thermal efficiency of 35%. It burns coal having a heating value of 30 MJ/kg and a
sulfur content of 2% by weight, a nitrogen content of 1% by weight, and a mineral (ash) content
of 10% by weight.
(a) How much electricity does the power plant produce per year (kWh/y)?
(b) How much coal does the PP consume per year (metric tons per year, ton/y)?
(c) How much SO
2
does the PP emit per year (ton/y)? (Note that SO
2
has double the molecular
weight of S.)
(d) How much NO
2
does the PP emit per year (ton/y), assuming “thermal” NO
2
formation
doubles the rate of “fuel” NO
2
emissions? (Note that NO
2
has 3.28 times the molecular
weight of N.)
(e) How much fly ash does the PP emit per year (ton/y)? Assume all mineral content is emitted
as fly ash.
Tabulate the results of (a), (b), (c), (d), and (e).
Problem 5.2
Using the sulfur and nitrogen content of coal as in the previous problem, calculate the emission rate
of SO
2
and NO
2
per unit heat input (lb SO
2
/MBtu and lb NO
2
/MBtu), assuming again that total
NO
2
emissions are twice the fuel NO
2
emissions. Compare these values to the 1970 U.S. emission
standards for coal-fired large boilers: 1.2 lb SO
2
/MBtu and 0.7 lb NO
2
/MBtu.
Problem 5.3
A 1000-MW(el) power plant, of 35% thermal efficiency and 90% average capacity factor, uses
coal with a heating value of 30 MJ/kg. The combustible part of coal has the chemical formula CH.
The coal is burned with 20% excess air. Calculate the volumetric flow rate of the flue gas Q in
m
3
s
−
1
at STP.
Problem 5.4
How much air (m
3
/s at 1 atm) needs to be pumped through the boiler of the plant in Problem 5.3
in order to burn the coal (chemical formula CH) with 20% excess air?
Problem 5.5
The coal in the power plant of Problem 5.3 also contains 10% by weight mineral matter that
is converted in the boiler to fly ash. Calculate the mass concentration of the fly ash in the flue
gas (g/m
3
).
