Handbook of air conditioning and refrigeration / Shan K

When the engine jacket water is routed through the heat recovery muffler where additional heat
is extracted from the exhaust gas, an engine jacket heat recovery system is then combined with the
exhaust gas heat recovery system. At least a water circulating pump is required to circulate the hot
water flowing through the engine jacket and the heat recovery muffler as soon as the engine is operating.
To avoid excessive thermal stress, the temperature difference between the cooling water entering
and leaving the engine jacket should not exceed 15°F (8.3°C).
Steam can be produced at the top part of the heat recovery muffler with a steam separator and is
distributed to various process loads. Hot water from the bottom of the heat recovery muffler is then
mixed with the condensate returned from the remote steam loads. The mixture is forced through the
engine jacket and the heat recovery muffler by the circulating pump.
Sometimes, the engine coolant circuit in a heat recovery loop is separated from the process
loads by heat exchangers and forms a primary and secondary loop. A primary-secondary loop
isolates and protects the engine coolant circuit from process loads, leaks, and failures in the distribution
systems. A primary-secondary loop is especially useful for a multiple-engine installation.
A cooling tower can be connected to a heat recovery loop through a heat exchanger for the sake
of maintaining a required entering temperature of the engine jacket coolant at system part-load
operation. A coolant heater can be installed to preheat the coolant during start-up.
For space heating, hot water from the heat recovery muffler can be supplied directly to the
heaters in the conditioned space. For space cooling, an absorption chiller using recovered steam or
hot water should be installed to provide cooling for the conditioned space.
Cogeneration Using a Gas Turbine
REFERENCES
HEAT PUMPS, HEAT RECOVERY, GAS COOLING, AND COGENERATION SYSTEMS 12.29
Many cogeneration plants use a combustion gas turbine instead of a gas engine as the prime mover.
A gas turbine usually consists of a compressor section to raise the air pressure, a fuel/air mixing
and combustion chamber, and an expanding turbine section. The compressor and turbine are joined
by the same shaft. Capacity may vary from several hundred brakehorsepower (bhp) to more than
100,000 bhp (75,000 kW). Gas turbines are often connected to induction generators to produce
electric power through gear trains.
Steam boilers are often used as heat recovery units to produce steam at a pressure typically 15
psig (103 kPag) from the gas-turbine exhaust gas. Recovered heat can often be used as process heat
to operate an absorption chiller.
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