High-lift chemical heat pump technologies for industrial processes Page: 3 of 8
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Many industrial processes and manufacturing operations necessarily require heating and
cooling to produce a product. The attendant emissions from conventional process heating devices
involves the air emissions and thermal discharge into the environment. Likewise, process cooling
systems may use working fluids that are ozone depleting and are now being phased out.
Process industries in the United States consume approximately 23 x 1015 Btu (23 quads) or
24.3 x 1015 kJ of energy annually at a cost of almost $80 billion. Approximately 5 quads (5.3 x 1015
kJ) is embodied in energy feedstocks with the remainder used directly as heat (about 9.4 quads or
9.9 x 10"5 kJ including combustion losses) or to produce electricity. A significant portion, almost 7
quads (7.4 x 105 kJ), of this energy input is eventually discarded as waste heat (heat discarded in an
effluent stream and serves of no value to the process) (U.S. Department of Energy 1991).
Concern for protection of the environment has driven a number of legislative and regulatory
actions that increasingly restrict emissions of pollutants. Fossil fuels supply almost all of industry's
process heat and power. The 23 quads (24.3 x 1015 kJ) of fossil fuel burned by industry annually
results in emissions of about 12 million tons of combined nitrogen oxides and sulfur dioxides, and
almost 1.5 billion tons of carbon dioxide, a major greenhouse gas (U.S. Department of Energy 1991).
By recouping the energy from waste heat streams, industry can reduce the amount of fossil fuels that
must be combusted to meet energy needs, subsequently reducing combustion emissions. Alternately,
industry can expand production capacity without an attendant increase in the amount of fossil fuel
burned. Further, recovering waste heat energy can help defray the costs of pollution abatement and
control technologies needed to meet new environmental standards for fossil fuel emissions.
Capture and reuse of industrial waste heat resource represents an opportunity for industry
to conserve energy and reduce energy costs of production. Industrial heat pumps (IHPs) offer the
opportunity to capture the waste heat, upgrade it to useable temperatures, and reuse it in the
industrial process. It has been estimated that by using IHPs to recycle energy normally discharged as
waste heat, U.S. industry could reduce primary energy consumption by as much as 1.4 quads (1.5 x
1015 kJ) annually. This reduction in fossil fuel consumption results in the annual emission reductions
of CO2, NO, and SO, (U.S. Department of Energy 1992).
Heat pumps are required for process cooling/refrigeration applications particularly in the food
processing industry. Currently, the industrial/commercial market has approximately 42,000 installed
units with a total capacity of nearly 42 million refrigeration tons (RT). Approximately 85% of the
process cooling demand in this application is met using vapor compression equipment with
chlorofluorocarbon-based fluids (CFC's, HFC's or HCFC's) used as the working fluid. Replacement
technology will be needed in the near term due to the banning of these working fluids.
In an industrial setting, heat pumps are used to recycle heat from a lower temperature process
stream to one at a higher temperature that is useful to the industrial process, supplying heat that a
boiler or fired heater would otherwise supply. Many industrial heat pumps are used throughout the
world but are often referred to by other names. For example, a mechanical vapor recompressor
(MVR) used on a multiple effect evaporator is commonly known as a vapor compressor (Scheihing
1989). Also, 2000 dehumidification lumber dry kilns in the United States, and a like number in
Europe, use heat pumps to supply heat to dry lumber and cooling to remove water from the drying
lumber. IHP's are also found in petroleum refineries, chemical plants, and pulp and paper mills. They
can be closed, open, or semiopen cycles; mechanical or chemical; and electric or heat (steam) driven.
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Olszewski, M. & Zaltash, A. High-lift chemical heat pump technologies for industrial processes, article, March 1995; Tennessee. (digital.library.unt.edu/ark:/67531/metadc625661/m1/3/: accessed December 14, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.