Waste Heat to Power Systems Page: 2 of 9
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energy consumed domestically.3 Roughly one-third of the energy consumed by industry is discharged as thermal
losses directly to the atmosphere or to cooling systems.4 These discharges are the result of process inefficiencies
and the inability of the existing process to recover and use the excess energy streams. Most of this waste energy,
however, is of low quality (i.e., available in waste streams with temperatures below 300 F or dissipated as
radiation heat loss) and is typically not practical or economical to recover with current technology.
The efficiency of generating power from waste heat recovery is heavily dependent on the temperature of the
waste heat source. In general, economically feasible power generation from waste heat has been limited primarily
to medium- to high-temperature waste heat sources (i.e., > 500 F). Emerging technologies, such as organic
Rankine cycles, are beginning to lower this limit, and further advances in alternative power cycles will enable
economic feasibility of generation at even lower temperatures over time.
Estimates of the amount of industrial waste heat available at a temperature high enough for power generation
with today's technologies (i.e., >500 F) are in the range of 0.6 to 0.8 Quads (or 6,000 to 8,000 megawatts [MW] of
electric generating capacity)5 on a national basis .'''8 Nonindustrial applications, such as exhaust from natural gas
pipeline compressor drives and landfill gas engines, represent an additional 1,000 to 2,000 MW of power
capacity,9 for a total of seven to ten gigawatts.
At the project level, a number of factors in addition to the temperature of the waste heat must be considered to
determine the economic feasibility of power generation from waste heat sources:
" Is the waste heat source a gas or a liquid stream?1o
" What is the availability of the waste heat-is it continuous, cyclic, or intermittent?
" What is the load factor of the waste heat source-are the annual operating hours sufficient to amortize
the capital costs of the WHP system?
" Does the temperature of the waste stream vary over time?
" What is the flow rate of the waste stream, and does it vary?
" Is the waste stream at a positive or negative pressure, and does this vary?
" What is the composition of the waste stream?
" Are there contaminants that may corrode or erode the heat recovery equipment?
The answers to these questions will determine system design and, ultimately, the economic viability of a WHP
project. Many high-temperature waste heat sources are straightforward to capture and use with existing
technologies. Other sources must be cleaned prior to use. The cleaning process is typically expensive, and
3 1Quad = 1015 Btu
4 Engineering Scoping Study of Thermoelectric Generator Systems for Industrial Waste Heat Recovery, Terry Hendricks, Pacific
Northwest National Laboratory, William Choate, BCS Incorporated, Report to U.S. DOE Industrial Technologies Program,
s Based on a range of net generation efficiencies of 20 to 30 percent and annual load factors of 50 to 85 percent.
6 Hendricks, Op cit.
Waste Heat Recovery in Industrial Facilities: Opportunities for Combined Heat and Power and Industrial Heat Pumps. EPRI,
Palo Alto, CA: 2010.
8 Waste Heat Recovery: Technology and Opportunities in the United States, Report for U.S. DOE, BCS, Incorporated, March
9 Estimate prepared by ICF International, Inc., 2011.
1o WHP systems operating with a liquid waste heat source can be designed around lower temperatures than one based on a
gaseous heat source, such as industrial process flue gases. The minimum liquid waste temperature for economically feasible
operation is 200 OF compared to 500 OF for gaseous waste streams.
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United States. Environmental Protection Agency. Combined Heat and Power Partnership. Waste Heat to Power Systems, text, May 30, 2012; Washington, D. C.. (digital.library.unt.edu/ark:/67531/metadc949408/m1/2/: accessed July 20, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.