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Electric Generation Technologies for District Energy
The configuration at the University of Arizona is typical of many district
energy systems: A
central plant generates electricity, recycles the thermal
energy for cooling (or heating), and
distributes all the outputs to other
buildings in the network. (Photo courtesy of GLHN)
Not all district energy systems include electricity generation - some are
just heating, just cooling, or a combination of heating and cooling. But
quite frequently, district energy systems do include an electricity
component - especially all newer systems. The efficiency of the entire
system yields very attractive electricity costs for all buildings connected
to the system.
The prime movers for electric generation are similar
to those used for combined
heat and power (CHP). The main distinguishing factor
is size - district energy systems can be quite large
sine they supply a number of buildings. The most common
prime movers for district energy are gas turbines, steam
turbines, and large reciprocating engines. While fuels
cells and microturbines could be used, their smaller
size means they would need to have many units banded
together, or be used in combination with one of the
above larger technologies.
Courtesy: Princeton University Via Idea
Combustion or gas turbines are an established power
generation technology available in sizes from several
hundred kW to more than 100 MW. Gas turbines produce
high-quality heat that can be used to generate steam for
onsite use or for additional power generation (combined
cycle). Gas turbines can be set up to burn natural gas,
a variety of petroleum fuels, landfill or biogas, or can
have dual-fuel capability. Gas turbines are well suited
for CHP because their high-temperature exhaust can be
used to generate process steam at conditions as high as
1,200 pounds per square inch gauge (psig) and 900
degrees Fahrenheit. Much of the current US gas turbine-based CHP capacity
consists of large combined-cycle CHP systems that
maximize power production for sale to the grid while
supplying steam to large industrial or commercial users.
Simple-cycle CHP applications are common in smaller
installations, typically less than 40 MW.
Appropriate for: District Energy; Medium and
Large CHP
Further information:
-
Gas Turbines chapter from the Catalogue of CHP
Technologies (EPA CHP Partnership, PDF, 26 pgs)
- View a list of turbine manufacturers and project developers on our Resources page.
Courtesy: Siemens
Steam turbines generate electricity from the heat
(steam) produced in a boiler, converting steam energy
into shaft power. Steam turbines are one of the most
versatile and oldest prime mover technologies used to
drive a generator or mechanical machinery. The energy
produced in the boiler is transferred to the turbine
through high-pressure steam that in turn powers the
turbine and generator. This separation of functions
enables steam turbines to operate with a variety of
fuels, including natural gas, solid waste, coal, wood,
wood waste, and agricultural by-products. The capacity
of commercially available steam turbines ranges from 50
kW to more than 250 MW. Ideal applications of steam
turbine-based CHP systems include medium- and
large-scale industrial or institutional facilities with
high thermal loads, and where solid or waste fuels are
readily available for boiler use.
Appropriate for: District Energy; Large CHP;
Large Waste Heat Recovery
Further information:
-
Steam Turbines chapter from the Catalogue of CHP
Technologies (EPA CHP Partnership, PDF, 21 pgs)
- View a list of turbine manufacturers and project developers on our Resources page.
Courtesy: Cummins
Reciprocating internal combustion engines are the
most widespread technology for power generation,
commonly for small, portable generators to large
industrial engines that power generators of several
megawatts. Spark ignition engines for power generation
generally use natural gas, though they can be set up to
run on propane or landfill and biogas, and are available
in sizes up to 5 MW. Reciprocating engines start
quickly, follow load well, have good part-load
efficiencies, and generally are highly reliable. In many
instances, multiple reciprocating engine units can
enhance plant capacity and availability. Reciprocating
engines are well suited for applications that require
hot water or low-pressure steam.
Appropriate for: Small District Energy; CHP
Further information:
-
Reciprocating Engines chapter from the Catalogue
of CHP Technologies (EPA CHP Partnership, PDF, 28
pgs)
- View a list of engine manufacturers and project developers on our Resources page.
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