Page 186 - Handbook of Energy Engineering Calculations

of the fuel at the average engine load can be recovered from the diesel-engine
liquid (usually water) cooling system.
Large stationary diesel engines in electric generating service are normally
operated at 80 percent of their maximum rated rpm. This allows a 20 to 25
percent overload capacity in the event it is needed in the generating station.

Diesel engines are often chosen for sites where there is a scarcity of
cooling water for steam condensers used in steam-power plants. A diesel
engine requires minimum amounts of cooling water for makeup purposes.

And diesel engines are often used in existing steam plants to handle peak
loads and provide a better overall heat balance for the plant. There are no
standby losses with a diesel engine because when it is shut down its fuel use
is zero. By comparison, a steam plant uses fuel when it is on standby.
Studies by the ASME Oil Engine Power Subcommittee show that diesel

engines produce about 9 kWh per gallon of fuel (2.3 kWh per liter of fuel) at
30 to 40 percent load factor, and 12 to 13 kWh per gallon of fuel (3.2 to 3.4
kWh per liter of fuel) at 80 to 90 percent load factor. Further, diesel engines

have a relatively small footprint and can often be installed in existing
structures with no need for any major alteration of the building. Fuel
consumption of diesels is relatively flat over the range of loads they handle.
The fuel consumption of industrial-use diesel engines is 5 to 6 gal/h (18.9 to

22.7 L/h) per 100 rated horsepower (74.6 kW) of the engine. *

COGENERATION ENERGY ECONOMICS USING I-C

ENGINES

Determine if an internal-combustion (I-C) engine cogeneration facility will
be economically attractive if the required electrical power and steam services

can be served by a cycle such as that in Fig. 1 and the specific load
requirements are those shown in Fig. 2. Frequent startups and shutdowns are
anticipated for this system.