MIL-HDBK-1003/11
Table 6
Summary Heat Balance: Cogeneration Using
Diesel-Engine Generators
Without Cogeneration
With Cogeneration
(Percent of Fuel Input)
Item
Useful
Useful
Heat
Work
Losses
Work
Recovered
Losses
Diesel Engine/Generator
33
33
Set
Jacket and Lubricant
Cooling Waters
30
15
15
Exhaust Gas
30
12
18
Radiation Losses
7
7
Totals
33
67
33
27
40
Overall Efficiency
33
60
4.3.2 Design Priority. The first responsibility of the jacket and
lubricant cooling system design shall be to cool the engine; heat recovery
equipment is of secondary importance. Silencing the engine is also of
secondary importance unless the engine is located outside the building close
to a quiet zone, e.g., sleeping quarters. All heat recovery installations
should provide alternate, conventional systems to reject heat from jacket
and lubricating oil cooling media (see Figure 2).
4.3.3
Heat Recovery from Jacket and Lubricant Cooling Systems.
4.3.3.1 Hot Water Systems. Recovery of waste heat from jacket coolant is
the preferred method of heat recovery. Heat recovery from the lower
temperature and flow of lubricant coolant may also prove economically
justified. Heat is recovered via heat exchangers to secondary loops (see
Figure 2). The engine coolant loop must be a closed system. Recovery of
heat from lubricant oil coolers is accomplished in the same fashion. These
hot water systems can be combined with an exhaust gas heat recovery boiler
into an integrated system.
4.3.3.2 Steam Systems. Jacket coolant leaving the engine is piped to a
heat recovery boiler. The reduced pressure in the boiler and in piping to
the boiler allow jacket coolant to flash to low pressure steam. Steam is
returned from process uses to the engine coolant inlet as condensate.
Pressures must be controlled and engine cooling system must be carefully
designed to prevent boiling or flashing within the engine. A static head
and controlled steam pressure system is preferred over a pressure-reducing
valve or an orifice at the boiler inlet.
17
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