Waste Heat to Power Systems
Waste heat to power (WHP) is the process
of capturing heat discarded by an existing
industrial process and using that heat to
generate power (see Figure 1). Energy-
intensive industrial processes—such as
those occurring at refineries, steel mills,
glass furnaces, and cement kilns—all
release hot exhaust gases and waste
streams that can be harnessed with well-
established technologies to generate
electricity (see Appendix). The recovery of
industrial waste heat for power is a largely
untapped type of combined heat and
power (CHP), which is the use of a single
fuel source to generate both thermal
energy (heating or cooling) and electricity.
CHP generally consists of a prime mover, a generator, a heat recovery system, and electrical interconnection
equipment configured into an integrated system. CHP is a form of distributed generation, which, unlike central
station generation, is located at or near the energy-consuming facility. CHP's inherent higher efficiency and its
ability to avoid transmission losses in the delivery of electricity from the central station power plant to the user
result in reduced primary energy use and lower greenhouse gas (GHG) emissions.
The most common CHP configuration is known as a topping cycle, where fuel is first used in a heat engine to
generate power, and the waste heat from the power generation equipment is then recovered to provide useful
thermal energy. As an example, a gas turbine or reciprocating engine generates electricity by burning fuel and
then uses a heat recovery unit to capture useful thermal energy from the prime mover's exhaust stream and
cooling system. Alternatively, steam turbines generate electricity using high-pressure steam from a fired boiler
before sending lower pressure steam to an industrial process or district heating system.
Waste heat streams can be used to generate power in what is called bottoming cycle CHP—another term for
WHP.1 In this configuration, fuel is first used to provide thermal energy in an industrial process, such as a furnace,
and the waste heat from that process is then used to generate power. The key advantage of WHP systems is that
they utilize heat from existing thermal processes, which would otherwise be wasted, to produce electricity or
mechanical power, as opposed to directly consuming additional fuel for this purpose.
The Opportunity for WHP
Industrial energy use represents the largest potential source of WHP generation.2 In 2009, the industrial sector
used the largest share of energy in the United States, accounting for more than 28 Quads, or 30 percent of all
Heat Exchanger
Waste Heat
Fuel is combusted
as part of an
industrial process
V	 -
Figure 1: Waste Heat to Power Diagram
1	Title 18: Conservation of Power and Water Resources; Part 292—Regulations under Sections 201 and 210 of the Public Utility
Regulatory Policies Act of 1978; Subpart A - General Provisions, 292.101 Definitions.
2	Waste heat streams in other segments are generally either too low in temperature (power generation) or too small in
volume (commercial and residential) to represent viable WHP sources.

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 may 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.6,7,8,9 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,10 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?11
•	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?
31 Quad = 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,
November 2006.
5	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.
I	Waste Heat Recovery in Industrial Facilities: Opportunities for Combined Heat and Power and Industrial Heat Pumps. EPRI,
Palo Alto, CA: 2010.
Waste Heat Recovery: Technology and Opportunities in the United States, Report for U.S. DOE, BCS, Incorporated, March
9	An Inventory of Industrial Waste Heat and Opportunities for Thermally Activated Technologies, Report for Oak Ridge
National Laboratory, United Technologies Research Center, 2004.
10	Estimate prepared by ICF International, Inc., 2011.
II	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 °F compared to 500°F for gaseous waste streams.

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
removing the contaminants often removes the heat at the same time. Other waste heat sources are difficult to
recover because of equipment configuration or operational issues.
Applicable Technologies
Steam Rankine Cycle (SRC) - The most
commonly used system for power
generation from waste heat involves using
the heat to generate steam in a waste hea
boiler, which then drives a steam turbine.
Steam turbines are one of the oldest and
most versatile prime mover technologies.
Heat recovery boiler/steam turbine
systems operate thermodynamically as a
Rankine Cycle, as shown in Figure 2. In the
steam Rankine cycle, the working fluid-
water—is first pumped to elevated
pressure before entering a heat recovery
boiler. The pressurized water is vaporized
by the hot exhaust and then expanded to
lower temperature and pressure in a
turbine, generating mechanical power
that can drive an electric generator. The
low-pressure steam is then exhausted to a condenser at vacuum conditions, where heat is removed by
condensing the vapor back into a liquid. The condensate from the condenser is then returned to the pump and
the cycle continues.
Organic Rankine Cycles (ORC) - Other working fluids, with better efficiencies at lower heat source temperatures,
are used in ORC heat engines. ORCs use an organic working fluid that has a lower boiling point, higher vapor
pressure, higher molecular mass, and higher mass flow compared to water. Together, these features enable
higher turbine efficiencies than in an SRC. ORC systems can be utilized for waste heat sources as low as 300 °F,
whereas steam systems are limited to heat sources greater than 500 °F. ORCs have commonly been used to
generate power in geothermal power plants, and more recently, in pipeline compressor heat recovery
The Kalina Cycle is another Rankine cycle, using a mixture of water and ammonia as the working fluid, which
allows for a more efficient energy extraction from the heat source. The Kalina cycle has an operating temperature
range that can accept waste heat at temperatures of 200 °F to 1,000 °F and is 15 to 25 percent more efficient than
ORCs at the same temperature level. Kalina cycle systems are becoming increasingly popular overseas in
geothermal power plants, where the hot fluid is very often below 300°F.12
The three types of Rankine power cycles discussed above overlap to a certain degree. There are advantages to
each, however:
Working Fluid
Heat In
Heat Out
Figure 2: Rankine Cycle Heat Engine
12 A Rankine cycle operating with a liquid waste heat source can be designed around lower temperatures than for one based
on a gaseous heat source, such as industrial process flue gases. The minimum liquid waste temperature for economically
feasible operation is 200 °F.

•	SRCs are the most familiar to industry and are generally economically preferable where the source heat
temperature exceeds 800 °F.
•	For lower temperatures, ORG or Kalina cycle systems are used. They can be applied at temperatures lower
than for steam turbines, and they are more efficient in moderate temperature ranges.
•	Kalina systems have the highest theoretical efficiencies. Their complexity makes them generally suitable
for large power systems of several megawatts or greater.
•	ORC systems can be economically sized in small, sub-megawatt packages, and they are also well suited for
using air-cooled condensers, making them appropriate for applications such as pipeline compressor
stations that do not have access to water.
In addition to Rankine cycle systems, there are a number of advanced technologies in the research and
development stage that can generate electricity directly from heat, and that could in the future provide additional
options for power generation from waste heat sources. These technologies include thermoelectric, piezoelectric,
thermionic, and thermo-photovoltaic (thermo-PV) devices. Several of these have undergone prototype testing in
automotive applications and are under development for industrial heat recovery.13
Economically feasible WHP applications are
generally based on recovering waste heat from
combustion exhaust streams with temperatures
above 500 °F. Industrial processes that produce
these temperatures include calcining operations
(cement, lime, alumina, and petroleum coke), metal
melting, glass melting, petroleum fluid heaters,
thermal oxidizers, and exothermic synthesis
processes. Key WHP opportunities within these
operations are provided below:
1. Primary Metals - Primary metals manufacturing
involves a large number of high-temperature
processes from which waste heat can be
recovered. Steel mills, for example, have various
high-temperature heat- recovery opportunities.
In integrated mills, waste heat can be recovered
from coke ovens, blast furnaces for iron
production, and basic oxygen furnaces for steel
production. There are also opportunities to
recover waste heat from electric arc furnaces. In
the aluminum industry there is energy recovery
potential from the exhaust of the Hall Heroult"
cells and secondary melting processes. Metal
foundries have a variety of waste heat sources,
such as melting furnace exhaust, ladle pre-
11 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,
November 2006.
14 The Hail-Heroult process is used for the production of aluminum.
Port Arthur Steam Energy
WHP from Petroleum Coke Plant
A heat recovery boiler/steam turbine WHP project at a
petroleum coke plant in Port Arthur, Texas, recovers
energy from 2,000 °F exhaust from three petroleum-
coke calcining kilns. The project produces 450,000 Ib/hr
of steam for process use at an adjacent refinery and 5
MW of power. The project creates an estimated
159,000 tons per year of C02 emissions savings.
Waste Heat Boiler, Unit 4

heating, core baking, pouring, shot-blasting,
castings cooling, heat treating, and quenching.
2.	Nonmetailic Mineral Product Manufacturing -
There are a number of strong opportunities for
WHP in this sector. Calcining in rotary kilns is a
high-temperature process that is used in the
manufacture of cement, gypsum, alumina, soda
ash, lime, and kaolin clay. The glass industry uses
raw material melting furnaces, annealing ovens,
and tempering furnaces, all operated at high
3.	Petroleum Refining - Basic processes used in
petroleum refineries include distillation
(fractionation), thermal cracking, catalytic, and
treatment. These processes use large amounts of
energy, and many involve exothermic reactions
that also produce heat. Modern refineries are
highly integrated systems that recover heat from
one process to use in other processes. However,
many operations still release high-quality waste
heat that could be recovered for power production. An example is the exhaust from petroleum coke calciners.
Petroleum coke is heated to 2,400 °F, and the exhaust is typically 900 to 1,000 °F leaving the calciner.
4.	Chemical Industry-There are several major segments of the industry, including petrochemicals, industrial
gases, alkalies and chlorine, cyclic crudes and intermediates (e.g., ethylene, propylene, and benzene/
toluene/xylene), plastics materials, synthetic rubber, synthetic organic fibers, and agricultural chemicals
(fertilizers and pesticides), in which high-temperature exhaust is released that could be recovered for power
generation. There are five CHP systems in U.S. ethanol plants operating on waste heat produced by thermal
oxidizers (which are operated for volatile organic compound destruction). These five plants have a combined
capacity of 17 MW.
5.	Fabricated Metals - Processes generating waste heat include metal pre-heating, heat treatment, cleaning,
drying, and furnace heating.
6.	Natural Gas Compressor Stations - There are more than 20 ORC power generation systems installed at
natural gas compressor stations in North America. These systems have a total electric capacity of 105 MW
using the exhaust heat from 668,000 horsepower of gas turbine-driven compressors.
7.	Landfill Gas Energy Systems - Landfills that use reciprocating internal combustion engines or turbines to
produce power could generate additional power with ORC systems using exhaust gases. Other landfills could
install ORC systems to generate power from the waste heat from flaring.
8.	Oil and Gas Production - There are a number of flared energy sources in oil and gas production that could
utilize WHP.
TransGas Pipeline Compressor Drive
A Pratt & Whitney ORC system is generating 865 kW
of net power from the exhaust of a Solar Centaur 40
gas turbine driving a natural gas pipeline compressor
on a TransGas Pipeline in Saskatchewan, Canada. The
installation is one of over 20 ORC WHP systems on
natural gas pipeline compressors in North America.

The total cost to install WHP systems include the costs	Table 1 - Waste Heat to Power Cost
associated with the waste heat recovery equipment (boiler or	Comparison
evaporator), the power generation equipment (steam, ORC,
or Kalina cycle), power conditioning and interconnection
equipment. It would also include the soft costs associated
with designing, permitting and constructing the system. The
installed costs of Rankine cycle power systems (steam, ORC or
Kalina) are fairly similar, differing more as a function of
project size and the complexity of site integration than type
of system. A first-cut estimate of the cost of producing power
from WHP systems is presented in Table 1. Representative
costs are shown that represent a range of project sizes (<400
kW to > 5 MW) and site complexity. Capital costs are
amortized over a 10 year period based on a cost of capital of
15 percent15 and 7,500 annual operating hours. Operation
and maintenance (O&M) cost estimates can vary widely. Rankine cycle power systems themselves have relatively
low maintenance costs. However, maintenance requirements of the heat recovery boilers and balance of plant
must also be included and these can vary by technology and by site conditions. As an example, steam systems
may require on-site boiler operators while ORCs can often run unattended. O&M costs of $0,005 - $0.020/kWh
were used for this comparison to reflect the wide range of maintenance requirements that might be experienced.
There are no fuel costs for true waste heat to power projects (i.e., no supplemental fuel use).
Current Market Status
Current market penetration of WHP projects in the
United States is limited compared to other types of
CHP. There are currently 34 WHP projects in place
totaling 557 MW of power generation capacity in
the United States, as shown in Table 2. Most of the
existing industrial WHP systems use a heat recovery
boiler, steam turbine, and generator, which are
limited to waste streams with relatively high
temperatures (> 500 °F).
Other options are entering the market that can be
used at lower temperatures and smaller sizes,
including ORCs, ammonia-water systems (e.g.,
Kalina cycles), and thermo-electric generators (still
in development) that use solid state systems that require no moving parts and sit directly in the waste stream.
Utilizing liquid streams below 200 °F and gas streams below 500 °F typically remains economically impractical with
today's technologies, however. Conversion to electricity is less efficient with all these technologies compared to
traditional electric generators, and project costs currently run high for a variety of reasons, including the cost of
the equipment and the cost of integrating the waste heat recovery system with the waste heat source. WHP is
generally considered only when the waste heat cannot be used directly within the process, or other recovery
methods are not practical within the facility. While the costs of these systems currently remain high, and
commercial demonstration is limited, the technologies continue to evolve rapidly.
Cost Component

Installed Costs, $/kW
$2,000 - $4,000
WHP Generating Costs
Amortized Capital, $/kWh
$0,055 - $0,125
O&M Costs, $/kWh
$0,005 - $0,020
Total Power Cost, $/kWh
Source: ICF International estimates, 2012
Table 2: Existing WHP Projects in the United States
by Application
Petroleum Refining
Non-metallic Mineral Industries
Primary Metals
Landfill Gas Power
Natural Gas Compressor Stations
Source: CHP Installation Database, DOE/ORNL, 2012
15 The relatively high cost of capital of 15 percent reflects current perceptions of technology and market risks.

Market Barriers
Technical Barriers. The principal hurdle for WHP systems is the heat recovery itself. While the power generation
equipment is commercially established and relatively standardized, each heat recovery situation presents unique
challenges. Some of the project-specific technical issues that affect project economics include:
•	The waste heat sources at a plant are dispersed and difficult to reach or consolidate, or are from non-
continuous or batch processes.
•	Seasonal operations and low-volume operations reduce the economic benefits of WHP.
•	Waste heat sources often contain chemical and/or mechanical contaminants that impact the complexity, cost,
and efficiency of the heat recovery process
•	There may be added cost and complexity for integrating the WHP system controls with existing process
•	Space limitations and equipment configurations make WHP systems difficult or impossible to site
Business Barriers. As industry recovers from the 2008 economic downturn, most businesses are reluctant to make
investments that do not increase production and ensure their economic survival. They are especially reluctant to
take on projects with perceived risks, such as energy recovery projects that are outside of their core business.
These concerns often lead to unrealistically high project hurdle rates for capital-intensive WHP projects. Small
projects (less than $5 million) can be particularly difficult to develop because the returns are often reduced by the
costs of due diligence, permitting, and siting. The economic downturn has exacerbated the inherent risk of
financing projects with long paybacks, especially projects dependent on uncertain future fuel prices and variable
electricity rates.
Securing financing from banks for WHP projects is a challenge because the systems can be technically
complicated, and they combine the risk associated with power generation with the risk inherent in the primary
business itself (i.e., there is no heat to recover if the plant shuts down).
There is also a general lack of end-user awareness of WHP technologies and how to implement them. Few
technology demonstrations or case studies currently exist, and most projects are very site- and process-specific.
There is resistance to accept new, unproven technology that could potentially jeopardize existing production
processes, despite significant potential benefits.
Regulatory Barriers. Economic issues related to equipment costs and forecasted energy savings may be the
greatest determinant of a successful WHP project; however, regulations and policies can have a substantial
impact on project economics. For example, if the power cannot be used on site, projects will require a power
purchase agreement with the utility. This is the case with WHP systems on natural gas pipeline compressor
stations. While 20 ORC-based systems have been installed in North America since 1999, all projects to date are in
states or provinces with renewable portfolio standards (RPS) or environmental credit systems that recognize
waste heat as a renewable or "renewable equivalent" resource. Prices offered for export power are usually
extremely low in the absence of some sort of emissions credit system. Because power from WHP systems
produces no additional GHG emissions if supplemental fuel firing is not used, industry advocates believe the
technology warrants incentives similar to those enjoyed by other clean energy technologies. To date, these
incentives are in place only in certain states. Currently, nine of 29 states with binding RPS16 include WHP as a
qualifying source (i.e., Colorado, Connecticut, Hawaii, Michigan, Nevada, North Carolina, Ohio, Pennsylvania, and
West Virginia), while six states with nonbinding renewable energy goals include WHP in some fashion (i.e.,
Indiana, Louisiana [pilot program], Oklahoma, North Dakota, South Dakota, and Utah). The more critical issue
16 http://www.ferc.gov/market-oversight/othr-mkts/renew/othr-rnw-rps.pdf

from the industry viewpoint may be that WHP projects do not currently qualify for the 10-percent federal
investment tax credit for CHP.
Resources and Additional Information
The U.S. Environmental Protection Agency CHP Partnership is a voluntary program that seeks to reduce the
environmental impact of power generation by promoting the use of cost-effective CHP. The Partnership works
closely with energy users, the CHP industry, state and local governments, and other clean energy stakeholders to
facilitate the development of new projects and to promote their environmental and economic benefits. . See
The U.S. Department of Energy's (U.S. DOE) eight regional Clean Energy Application Centers formerly called the
Combined Heat and Power (CHP) Regional Application Centers (RACs), promote and assist in transforming the
market for CHP, waste heat recovery, and district energy technologies and concepts throughout the United States.
See http://wwwl.eere.energy.gov/manufacturing/distributedenergy/ceacs.html
The U.S. Clean Heat and Power Association (UCHPA) is a trade association that brings together diverse market
interests to promote the growth of clean, efficient local energy generation in the United States. USCHPA's mission
is to increase deployment of combined heat and power and waste energy recovery systems to benefit the
environment and the economy. See www.uschpa.org.
Heat is Power is a trade association that works to educate decision-makers and the public about the
characteristics of waste heat as a resource for emission-free electricity and the development of WHP as an
economic driver and boost to U.S. global competitiveness. See www.heatispower.org.
The Database of State Incentives for Renewable Energy (DSIRE) website provides information about renewable
energy and energy efficiency incentives and policies in the United States. Relevant incentives and policies
established by the federal government, state governments, local governments, utilities and non-profit
organizations are included. DSIRE is funded by U.S. DOE. See www.dsireusa.org.
Waste Heat Recovery: Technology and Opportunities in U.S. Industry, BCS Incorporated, Report to U.S. DOE
Industrial Technologies Program, March 2008. Available at:
http://wwwl.eere.energy.gov/manufacturing/intensiveprocesses/pdfs/waste heat recoverv.pdf.

Appendix: Waste Heat Streams Classified by Temperature
Waste Heat Source
Commercial Waste Heat to

Power Technologies
• Furnaces
• High quality heat
• Waste heat boilers and
(>1,200 °F)
-Steel electric arc
-Steel heating
-	Basic oxygen
-Aluminum reverberatory
-	Copper reverberatory
-	Nickel refining
-Copper refining
-Glass melting
•	Iron cupolas
•	Coke ovens
•	Fume incinerators
•	Hydrogen plants
•	High heat transfer
•	High power-generation
•	Chemical and mechanical
steam turbines
• Prime mover exhaust streams
• Medium power-generation
• Waste heat boilers and
(500 -1,200 °F)
-Gas turbine
steam turbines (>500°F)

- Reciprocal engine
• Chemical and mechanical
• Organic Rankine cycle

• Heat-treating furnaces
contaminants (some streams
(<800 °F)

• Ovens
such as cement kilns)
• Kalina cycle (<1,000°F)

- Drying

- Baking


• Cement kilns

• Boilers
• Energy contained in numerous
• Organic Rankine cycle
(< 500 °F)
• Ethylene furnaces
small sources
(>300°F gaseous streams,

• Steam condensate
• Low power-generation
>175 °F liquid streams)

• Cooling Water
• Kalina cycle (>200°F)

- Furnace doors
• Recovery of combustion streams

-Annealing furnaces
limited due to acid concentration

-Air compressors
if temperatures reduced below

- IC engines
250 °F

- Refrigeration condensers

• Low-temperature ovens

• Hot process liquids or solids

For more information, contact:
Neeharika Naik-Dhungel	¦
U.S. Environmental Protection Agency	?	^
Phone: 202-343-9553	P,
power partners#1	e-mail: na/K-onunge/.nt'enjnAatSt'p^.gov	%r.
Last Updated: May 18, 2012