Reciprocating internal
combustion engines are a well-established and widely used technology.
Worldwide production for
reciprocating internal combustion engines is over 200 million units per year. Reciprocating
engines include both diesel and spark-ignition configurations. They are
important for both transportation and for stationary uses. Their sizes range
from fractional horsepower engines to 5-story tall marine propulsion systems weighing
over 5 million pounds and producing over 80 megawatts (MW) of power. The long
history of technical development and high production levels have contributed to
making reciprocating engines a rugged, reliable, and economic choice as a prime
mover for CHP applications.
Reciprocating engine
technology has improved dramatically over the past three decades, driven by economic
and environmental pressures for power density improvements (more output per
unit of engine displacement), increased fuel efficiency, and reduced emissions.
Electronic Power Control
Modules (PCMs) have made
possible more precise control and diagnostic monitoring of the engine process.
Stationary engine manufacturers and worldwide engine R&D firms continue to
drive advanced engine technology, including accelerating the diffusion of
innovative technology and concepts from the automotive market to the stationary
market.
The features that have
made reciprocating engines a leading prime mover for CHP and other distributed generation
applications are summarized in Table 2-1.
2.2 Applications
Reciprocating engines
are well suited to a variety of distributed generation applications, and are
used throughout industrial, commercial, and institutional facilities for power
generation and CHP.
Reciprocating engines
start quickly, follow load well, have good part load efficiencies, and
generally have high reliabilities. In many cases, having multiple reciprocating
engine units further increases overall plant capacity and availability.
Reciprocating engines have higher electrical efficiencies than gas turbines of
comparable size, and thus lower fuel-related operating costs. In addition, the upfront
costs of reciprocating engine gensets are generally lower than gas turbine
gensets in sizes below 20 MW.
Reciprocating engine
maintenance costs are generally higher than comparable gas turbines, but the maintenance
can often be handled by in-house staff or provided by local service
organizations.
2.2.1
Combined Heat and Power
There are over 2,000
active reciprocating engine combined heat and power (CHP) installations in the U.S.
providing nearly 2.3 gigawatts (GW) of power capacity. These systems are
predominantly spark ignition engines fueled by natural gas and other gaseous
fuels (biogas, landfill gas). Natural gas is lower in cost than petroleum based
fuels and emissions control is generally more effective using gaseous fuels.
Reciprocating engine CHP
systems are commonly used in universities, hospitals, water treatment facilities,
industrial facilities, and commercial and residential buildings. Facility
capacities range from 30 kW to 30 MW, with many larger facilities comprised of
multiple units. Spark ignited engines fueled by natural gas or other gaseous
fuels represent 84 percent of the installed reciprocating engine CHP capacity.
Thermal loads most
amenable to engine-driven CHP systems in commercial/institutional buildings are
space heating and hot water requirements. The simplest thermal load to supply
is hot water. The primary applications for CHP in the commercial/institutional
and residential sectors are those building types with relatively high and
coincident electric and hot water demand such as colleges and universities,
hospitals and nursing homes, multifamily residential buildings, and lodging. If
space heating needs are incorporated, office buildings, and certain warehousing
and mercantile/service applications can be economical applications for CHP.
Technology development efforts targeted at heat activated cooling/refrigeration
and thermally regenerated desiccants expand the application of engine-driven
CHP by increasing the thermal energy loads in certain building types. Use of
CHP thermal output for absorption cooling and/or desiccant dehumidification
could increase the size and improve the economics of CHP systems in already
strong CHP markets such as schools, multifamily residential buildings, lodging,
nursing homes and hospitals. Use of these advanced technologies in other
sectors such as restaurants, supermarkets and refrigerated warehouses provides
a base thermal load that opens these sectors to CHP application.
Reciprocating engine CHP
systems usually meet customer thermal and electric needs as in the two hypothetical
examples below:
• A typical commercial
application for reciprocating engine CHP is a hospital or health care facility with
a 1 MW CHP system comprised of multiple 200 to 300 kW natural gas engine
gensets. The system is designed to
satisfy the baseload electric needs of the facility. Approximately 1.6 MW of
thermal energy (MWth), in the form of hot water, is recovered from engine
exhaust and engine cooling systems to provide space heating and domestic hot
water to the facility as well as to drive absorption chillers for space
conditioning during summer months. Overall efficiency of this type of CHP
system can exceed 70 percent.
• A typical industrial
application for engine CHP would be a food processing plant with a 2 MW natural
gas engine-driven CHP system comprised of multiple 500 to 800 kW engine
gensets. The system provides baseload power to the facility and approximately
2.2 MWth low pressure steam for process heating and washdown. Overall
efficiency for a CHP system of this type approaches 75 percent.
2.2.2
Emergency/Standby Generators
Reciprocating engine
emergency/standby generators are used in a wide variety of settings from residential
homes to hospitals, scientific laboratories, data centers, telecommunication
equipment, and modern naval ships. Residential systems include portable gasoline
fueled spark-ignition engines or permanent installations fueled by natural gas
or propane. Commercial and industrial systems more typically use diesel
engines. The advantages of diesel engines in standby applications include low upfront
cost, ability to store on-site fuel if required for emergency applications, and
rapid start-up and ramping to full load. Because of their relatively high
emissions of air pollutants, such diesel systems are generally limited in the
number of hours they can operate. These systems may also be restricted by permit
from providing any other services such as peak-shaving.
2.2.3
Peak Shaving
Engine generators can
supply power during utility peak load periods thereby providing benefits to
both the end user and the local utility company. The facility can save on peak
power charges and the utility can optimize operations and minimize investments
in generation, transmission, and distribution that are used only 0-200
hours/year. In a typical utility peak shaving program, a utility will ask a
facility to run its on-site generator during the utility’s peak load period,
and in exchange, the utility will provide the facility with monthly payments.
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