Page 28 - Handbook of Energy Engineering Calculations

reduce greenhouse gases and the ensuing pollution when such gases are
emitted into the atmosphere. Thus, in the midwestern United States,
combustion of coal in steam power plants produces some 210 lb (95.3 kg) of
CO per million Btu (1.055 MJ) of coal used in a steam boiler. Contrast this
2
with 120 lb (54.4 kg) of CO produced per million Btu (1.055 MJ) of natural
2
gas used in a steam boiler.
On the basis of power generated, 1.9 lb (0.86 kg) of CO is produced per
2
kWh generated by a coal-fired boiler and turbine. With natural-gas firing of a

steam boiler, 1.25 lb (0.57 kg) of CO is produced per kWh generated. These
2
statistics indicate that more efficient combustion of fossil fuels reduces

greenhouse gases and operating costs. Hence design and operating engineers
are making strenuous efforts to improve combustion efficiency to comply
with ever stricter regulations while reducing plant operating costs.
As indicated later in this section of the handbook, some states and
countries are considering banning coal-fired power plants unless they meet

much more stringent emission requirements. At this writing, the
Environmental Protection Agency seeks to establish ozone levels of 0.060 to
0.070 ppm.

COAL FUEL COMBUSTION IN A FURNACE

A coal fuel has the following ultimate analysis (or percent by weight): C =
0.8339; H = 0.0456; O = 0.0505; N = 0.0103; S = 0.0064; ash = 0.0533;
2
2
2
total = 1.000 lb (0.45 kg). This coal is burned in a steam-boiler furnace.
Determine the weight of air required for theoretically perfect combustion, the

weight of gas formed per pound (kilogram) of coal burned, and the volume of
flue gas, at the boiler exit temperature of 600°F (316°C) per pound
(kilogram) of coal burned; air required with 20 percent excess air, and the
volume of gas formed with this excess; the CO percentage in the flue gas on
2
a dry and wet basis.

Calculation Procedure:

1. Compute the weight of oxygen required per pound (kilogram) of coal