Page 199 - Sustainable On-Site CHP Systems Design, Construction, and Operations

172 De s i g n

installations presently use natural gas (NG) as their primary fuel source, with fuel oil
accounting for approximately 3 percent of installations and waste combustion accounting
for another approximately 3 percent of the CHP system installations. The use of biofuels
(solids, liquids, and gases) is growing, and, at this time, research is extensive into their
use, and it is expected that in the future the use of biofuels will be more extensive. In
fact, biofuels will likely have a major role in further enhancing CHP’s sustainability as
the fuel source will be essentially carbon neutral.
Typical CTG NG fuel systems components include: utility metering, pressure
reducing stations, moisture separators, fuel filters, and fuel flow-control valves. As
noted, CTGs often require higher-pressure natural gas (e.g., above 200 psig) than is
available from the local gas supply main. Therefore, natural gas compressors are required
to boost the gas pressure from the available NG system pressure to the pressure required
by the CTG. If the NG compressors are installed indoors, they must be installed in a
separate room with explosion-proof devices and leak detection and alarm. A backup
compressor should be provided, so that the CHP system can still operate with the loss
of one compressor.
The CHP system may require multiple NG pressure systems such as a high- and
low-pressure NG system, one for the CTG and one for the duct burners (e.g., 250 psig
and 30 psig), as well as a 5-psig system for any fired boilers and or fired absorption
chillers. All of the metering and reducing stations should be located in a common pro-
tected area, usually just outside of the plant away from any air intakes.
Except for the fuel gas compressor and the required higher pressure, a NG fuel
system for an IC engine is similar to a CTG NG system. Typical IC engine NG fuel system
components include utility metering, pressure reducing stations, fuel filters, and fuel
flow-control valves. An 8- to 10-ft-long surge pipe (a large diameter section of pipe)
can be provided near the engine gas inlet to account for gas pressure drop upon initial
start-up.
When fuel oil systems are used, either as a primary fuel source or as an alternate
fuel source, or as an on-site backup fuel in case of NG curtailment, fuel oil storage systems
are required. Any type of fuel storage must meet all of the codes, standards, and safety
requirements for its location and installation. Some regions/municipalities limit the
type and quantity of fuel stored as well the fuel storage tank locations with respect to
property lines and adjacent occupancies. For aboveground tanks, spill prevention is
often required to hold the leaking liquid fuel in the event of a tank rupture, and plans
may need to be submitted to the authorities that outline what to do in the unlikely event
of such a tank rupture. If storage tanks are located underground, double-wall tanks
with leak detection may be required. In any case, it is important for all to minimize any
release of raw fuel into the environment, whether the release is accidentally into the
sewer or into a pristine waterway, or into the ground where fuel contamination can
spread due to groundwater flows. Remediation after a spill is costly and time consuming.

Combustion Air
Proper combustion air system design is a critical component of sustainable CHP systems
that use a combustion turbine generator as their prime mover. As discussed in Chap. 3,
the power output of a combustion turbine decreases by approximately 0.5 percent for
each inch of water pressure loss across the combustion air-inlet system. The combustion
air system can include an outside air (OSA) louver (if the CHP system is located in a
building), inlet-air filter, inlet-air duct silencer, ductwork, and combustion-turbine-inlet