Page 190 - Handbook of Energy Engineering Calculations

Related Calculations. Cogeneration, in which I-C engines are finding greater
use throughout the world every year, is defined by Michael P. Polsky,
President, Indeck Energy Services, Inc., as “the simultaneous production of
useful thermal energy and electric power from a fuel source or some variant
thereof. It is more efficient to produce electric power and steam or hot water

together than electric power alone, as utilities do, or thermal energy alone,
which is common in industrial, commercial, and institutional plants.” Figures
1 and 2 in this procedure are from the firm of which Mr. Polsky is president.

With the increased emphasis on reducing environmental pollution,
conserving fuel use, and operating at lower overall cost, cogeneration—
especially with diesel engines—is finding wider acceptance throughout the
world. Design engineers should consider cogeneration whenever there is a
concurrent demand for electricity and heat. Such demand is probably most

common in industry but is also met in commercial (hotels, apartment houses,
stores) and institutional (hospital, prison, nursing-home) installations. Often,
the economic decision is not over whether cogeneration should be used, but

what type of prime mover should be chosen.
Three types of prime movers are usually considered for cogeneration—
steam turbines, gas turbines, or internal-combustion engines. Steam and/or
gas turbines are usually chosen for large-scale utility and industrial plants.
For smaller plants the diesel engine is probably the most popular choice

today. Where natural gas is available, reciprocating internal-combustion
engines are a favorite choice, especially with frequent startups and
shutdowns.

Recently, vertical modular steam engines have been introduced for use in
cogeneration. Modules can be grouped to increase the desired power output.
These high-efficiency units promise to compete with I-C engines in the
growing cogeneration market.
Guidelines used in estimating heat recovery from I-C engines, after all heat

loses, include these: (1) Exhaust-gas heat recovery = 28 percent of heat in
fuel; (2) Jacket-water heat recovery = 27 percent of heat in fuel; (3) Lube-oil
heat recovery = 9 percent of heat in fuel. The Diesel Engine Manufacturers

Association (DEMA) gives these values for heat disposition in a diesel
engine at three-quarters to full load: (1) Fuel consumption = 7366 Btu/bhp · h
(2.89 kW/kW); (2) Useful work = 2544 Btu/bhp · h (0.999 kW/kW); (3) Loss
in radiation, etc. = 370 Btu/bhp · h (0.145 kW/kW); (4) To cooling water =