Page 45 - Handbook of Energy Engineering Calculations
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contain a small amount of ash—usually less than 1 percent. This was ignored
in this calculation procedure because it does not take part in the combustion.
Industry is making greater use of discarded process waste to generate
electricity and steam by burning the waste in a steam boiler. An excellent
example is that of Agrilectric Power Partners Ltd., Lake Charles, LA. This
plant burns rice hulls from its own process and buys other producers’ surplus
rice hulls for continuous operation. Their plant is reported as the first small-
power-production facility to operate on rice hulls.
By burning the waste rice hulls, Agrilectric is confronting, and solving, an
environmental nuisance often associated with rice processing. When rice
hulls are disposed of by being spread on land adjacent to the mill, they often
smolder, creating continuous, uncontrolled burning. Installation of its rice-
hull burning, electric-generating plant has helped Agrilectric avoid the costs
associated with landfilling and disposal, as well as potential environmental
problems.
The boiler supplies steam for a turbine-generator with an output ranging
from 11.2 to 11.8 MW. Excess power that cannot be used in the plant is sold
to the local utility at a negotiated price. Thus, the combustion of an industrial
waste is producing useful power while eliminating the environmental impact
of the waste. The advent of PURPA (Public Utility Regulatory Policies Act)
requiring local utilities to purchase power from such plants has been a major
factor in the design, development, and construction of many plants by food
processors to utilize waste materials for combustion and power production.
COMBUSTION ANALYSIS BY THE MOLAL METHOD
A coal fuel has this ultimate analysis: C = 0.8339; H = 0.0456; O = 0.0505;
2
2
N = 0.0103; S = 0.0064; ash = 0.0533; total = 1.000. This coal is completely
2
burned in a boiler furnace. Using the molal method, determine the weight of
air required per lb (kg) of coal with complete combustion. How much air is
needed with 25 percent excess air? What is the weight of the combustion
products with 25 percent excess air? The combustion air contains 0.013 lb of
moisture per lb (0.006 kg/kg) of air.
Calculation Procedure:
