184.108.40.206 Supplemental Firing. Supplemental firing is not recommended for
most diesel engine exhaust gas heat recovery systems. Supplemental firing a
heat recovery boiler is more often considered in combustion
turbine/generator applications. Supplementary boilers may be considered to
accommodate thermal demands in excess of heat recovery boiler capacity.
Thermal storage should also be considered.
220.127.116.11 Combined Cycle Applications. Combined cycle cogeneration using a
back-pressure steam turbine-generator is shown in Figure 4 and includes the
a) Steam product from the heat recovery boiler is expanded through
a back-pressure steam turbine to generate additional power. The
back-pressure turbine exhaust is used for heating, ventilating and air
conditioning applications or for other uses of low pressure steam.
b) Condensing steam turbines may be used to generate larger
amounts of power than are available from back-pressure turbines.
c) A technology that appears promising or combined cycle
applications is the organic Rankine cycle. Relatively low temperature
exhausts from diesel-engines limit combined cycle applications of steam
turbine-generators. Substitution of an organic liquid, e.g., toluene, in
place of water for the working fluid allows a bottoming cycle of higher
efficiency than a similar steam system to be employed.
4.3.5 Thermal Storage. The need for supplemental boilers may be obviated
by using thermal storage systems. Engine and heat recovery equipment are
sized to meet thermal loads somewhere between the minimum and peak demands.
Hot water, and/or chilled water are pumped into separate storage tanks
during periods of low thermal demand. During periods of higher demand, hot
and chilled water are pumped from storage. The engine-generator set is run
at a constant load. The utility grid operates as a sink for electric
generation in excess of facility demand. Several utility companies in the
United States now offer funding assistance for installing thermal storage
systems. Refer to NAVFAC DM-3.16, Thermal Storage, for design guidance on
Uses for Recovered Heat.
18.104.22.168 Hot Water. Hot water is produced in the range of 190deg. F (88deg.
C) to 250deg. F (121deg. C) in jacket and lubricant cooling systems. Higher
temperature water is attainable from exhaust gas heat recovery boilers. End
uses of this hot water may include:
hot water for space heating applications,
domestic hot water heating,
commercial (dinging facility, laundry, etc.) hot water heating,
fuel oil preheating,