Page 29 - Sustainable On-Site CHP Systems Design, Construction, and Operations

8 CHP B a s i c s

sources (typically coal at that time) to minimize fuel transportation costs, but away
from customers who could benefit from the waste heat. Many engineers, including
Evan’s grandson, wrote papers showing how CHP consumed much less fuel compared
against even the most efficient condensing steam power plant, but to little avail.
While CHP declined in the United States in the mid-twentieth century, there were
exceptions, both with utility plants that provided heat to adjacent facilities, and facility
CHP systems that used the heat internally. An important milestone in CHP develop-
ment was the commercialization of combustion turbine generators (an air compressor
coupled to a gas turbine coupled to an electric generator with fuel injected into the
combustion chamber, see Chap. 3) in the late 1930s, and several methods were developed
to use the waste heat, including heat recovery steam generators (HRSG). Note that com-
bustion turbine generators (CTG) are often called gas turbines, which technically are
just a portion of the CTG.
In the 1960s, interest in CHP systems began slowly to reemerge in the United States,
and the first CTG CHP plant was installed to provide power, heating, and cooling to the
Park Plaza Shopping Center in Little Rock, Arkansas. However, even though engineers
showed interest and knew the value of CHP systems, one report stated that CHP
systems accounted for 15 percent of total U.S. power production in 1950, but only for
5 percent by the mid-1970s.
For those customers who wanted to install their own CHP systems, utility compa-
nies, not unexpectedly, resisted the loss of kilowatthour (kWh) sales and did not want
to interconnect with those facilities that installed their own CHP system. In 1978, in the
United States, due in part to the energy crisis being experienced by world industrial
economies at the time, and in the interest of improving energy efficiency, the U.S. Con-
gress as part of the National Energy Act passed the Public Utility Regulatory Policies
Act (PURPA). The law provided for a nonutility power market and mandated that util-
ity companies purchase electric power from CHP facilities which met the minimum
efficiency requirements. PURPA is regulated by the U.S. Federal Energy Regulatory
Commission (FERC).
Today, as energy prices remain volatile and the consequences of global warming loom,
there is a renewed appreciation and interest in CHP systems for the reasons highlighted
earlier, including the prospect of lower energy costs, improved reliability, lower prime
fuel usage, and helping to limit global warming by reducing overall carbon emissions.

CHP Basics
CHP systems use a variety of prime movers [e.g., reciprocating engines (CTGs)] to gen-
erate power. Further, CHP systems, importantly, recover useful thermal energy from
engines and/or exhaust gas for beneficial use in facilities and industries for space heat-
ing, space cooling, domestic hot water production, dehumidification, and even for
2
additional power production (combined cycle) as shown in Fig. 1-2. Efficient, sustainable
CHP systems maximize all available opportunities to utilize fuel energy that the prime
mover is unable to convert into shaft energy. If waste heat cannot be utilized effectively,
the resulting CHP plant efficiency, in effect, defaults to the limit of the prime mover
efficiency. Smaller prime movers cannot match the comparable performance of utility-
size prime movers. Where facility thermal energy requirements can utilize the waste
heat available from the prime mover, on-site equipment and energy requirements are
reduced and overall plant efficiency is increased.