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# Coal plant emissions calculations

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3. A coal-fired power plant produces a net electrical output of 500 MW. The composition of the coal burned is C = 72%, H = 5%, S = 2%, O = 8%, N = 1%, and ash = 12% by weight. Its higher heating value (HV) is 30,940 kJ/kg. The net thermal efficiency is 33 percent.
a) How much coal (in metric tons) does this plant consume in one day running at full capacity?
b) Assume that 75 percent of the ash in coal is entrained in the flue gas stream as flyash and the remainder is collected in the boiler as bottom ash. How many tons per day of flyash would be emitted from this plant in the absence of any particulate controls?
c) How many tons/day of SO2 are emitted if 97 percent of the sulfur in coal is converted to SO2?
d) How many tons/day of NOX emission rate is 300 ng/J (0.7 lbs/106 Btu)?
e) Carbon dioxide (CO2) is not presently a regulated air pollutant, although it is of growing concern because of its role as a greenhouse gas. For the power plant, calculate
i. The annual mass of CO2 emissions in metric tons/yr.
ii. The CO2 emission rate in ng/kJ of energy input to the plant.
iii. The CO2 emission rate in g/kW-hr of electricity generated.
Which of these measures seems most appropriate to you as a basis for comparing CO2 emissions from different fuels or technologies used for power generation? Explain your reasoning.

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#### Solution Preview

3. A coal-fired power plant produces a net electrical output of 500 MW. The composition of the coal burned is C = 72%, H = 5%, S = 2%, O = 8%, N = 1%, and ash = 12% by weight. Its higher heating value (HV) is 30,940 kJ/kg. The net thermal efficiency is 33 percent.

a) How much coal (in metric tons) does this plant consume in one day running at full capacity?

We know we are only getting 33% of that energy out of the coal. The plant generates 500 MW, but 67% of the energy is lost. We find the true energy of the value of the coal consumed as:

500MW /.33 = 1515.15 MW, which we can convert to joules per day using the conversion factor 1 megawatt = 86,400,000,000 joules / day.

1515.15 * 86,400,000,000 = 1.31 x10^14 j/ day

Now, we need to know how much coal it would take to produce this many joules. We are given coal's energy production as 30,940 kJ/kg, so the mass of coal needed is:
1.31 x10^11 / 30,940 = 4231063.05 kg
Since 1 metric ton= 1000 kg, this becomes 4231 tons per day.

b) Assume that 75 percent of the ash in coal is entrained in the flue gas stream as flyash and the remainder is collected in the boiler as bottom ash. How many tons per day of ...

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