Question

A small power plant produces 500MW of electricity through combustion of coal that has the following composition on a dry basis: 76.2 wt% carbon, 5.6% hydrogen, 3.5% sulfur, 7.5% oxygen, and the remainder ash. The coal contains 4.0 wt% water. The feed rate of coal is 183 tons/h, and it is burned with 15% excess air at 1 atm, 80°F, and 30.0% relative humidity.

(a) Estimate the volumetric flow rate ft3/min of air drawn into the furnace. (b) Effluent gases are discharged from the furnace at 625°F and 1 atm. Estimate the molar (lb-mole/
min) and volumetric ft3/min flow rates of gas leaving the furnace. (c) Injectionofdrylimestone(CaCO3)intothefurnaceisbeingconsideredasameansofreducingthe
SO2 emitted from the plant. The technology calls for SO2 to react with limestone: CaCO3 SO2 12O2 !CaSO4 CO2
Unfortunately, the process is expected to remove only 75% of the SO2 in the effluent gases, even though the limestone is fed at a rate 2.5 times the stoichiometric amount. What is the required feed rate of limestone? Since some of the SO2 is removed from the furnace effluent [in contrast to Part (b)], recalculate the molar flow rate and composition of the effluent from the furnace.
(d) The gas leaving the furnace passes through an electrostatic precipitator, where particulates from ash and limestone are removed, and then enters a stack (chimney) for release to the atmosphere. What is the gas velocity at a point in the stack where the stack diameter is 25 ft and the temperature is 300°F? Does the gas discharged from the stack meet the new Environmental Protection Agency standard that emissions from such power plants contain less than 75 parts of SO2 per billion?

Answer 1