Industrial Heat Pumps Improve Plant Efficiency and Recover Wasted Energy Resources

Advances in Industrial Energy-Efficiency Technologies

Prepared for:
U.S. Department of Energy
Office of Industrial Technologies
Washington, DC 20585

Produced by:
National Renewable Energy Laboratory
Golden, Colorado 80401-3393

In conjunction with:
Energetics, Inc.
Columbia, Maryland 21046

DOE/CH10093-144
DE92001236
February 1993

Process heat and power account for 70% of industryūs energy use

From steelmaking to milk production, virtually all industrial processes require both heating and cooling of the various process streams. One key to good energy efficiency is exchanging heat in the most effective way between components within the system, thereby cutting the need for additional heating or cooling. Finding the optimal configuration for heat exchange equipment within a given process is not a simple task, however. Using process integration techniques, engineers can determine how best to supply and remove heat from the many process streams by adding or moving heat exchangers or adding other equipment such as industrial heat pumps. By implementing the conclusions of process integration studies, plant managers can reduce net fuel use and waste discharge, while improving productivity.

Process heat integration identifies heat pump opportunities

The U.S. Department of Energyūs Office of Industrial Technologies (OIT) has been working with industry for several years to help implement process integration techniques and identify opportunities for installing industrial heat pumps. Using heat pumps for home heating is a familiar application. However, in industrial settings, heat pumps are slightly different because they recycle heat from a lower temperature process to a higher temperature process, supplying heat that would otherwise come from burning additional fuel. Although many industrial heat pump installations exist, they are far outnumbered by the opportunities not yet realized.

Since 1988, OIT has cosponsored with the Electric Power Research Institute (EPRI) several process integration studies that used the "pinch" analysis technique to locate good opportunities for new heat pump installations. Pinch analysis enables process engineers to study an industrial process as a whole to maximize energy efficiency. The technique can be used to track energy flows throughout a process, revealing where heat is being lost or wasted and identifying the areas where energy can be conserved for the least amount of money.

The consulting firms of Tensa Services and Linnhoff March performed the studies. Several electric utilities also participated, including Duke Power, Gulf States Utilities, Oklahoma Gas and Electric, and Utah Power and Light. These utilities hoped to gain information that would help their industrial customers.

Photo: Using heat pumps to recycle waste heat could save 1.6 exajoules (1.5 quadrillion Btu) of fuel normally burned in boilers and fired process heaters, saving more than $4 billion annually. [provided in source document]

The studies were conducted for 28 industrial host sites (14 were selected by OIT, 14 by EPRI). The sites are scattered across the United States and include petroleum refineries, chemical processing plants, pulp and paper mills, food processing plants, and a textile plant. Of the 14 OIT sites evaluated, managers of eight decided to proceed with the design of industrial heat pump systems for their plants.

Fuel savings worth at least $5.6 million per year were projected to result from modifications of the eight plants. About one-third of these savings would come from improved use of heat exchangers within the processes; the remaining two-thirds would result from adding heat pump systems. The economic payback periods for the eight sites range from 8 months to 2 years, short periods even at today's relatively low fuel prices. There would be other benefits as well-reduction in emissions of pollutants such as nitrogen oxides (NOx) and sulfur oxides (SOx), plant expansion at lower capital costs, and reductions in energy-related operation and maintenance costs (e.g., shutting down a boiler or cooling tower).

Photo: A thermal vapor recompressor was installed on American Fructose's evaporation system. The system saves the company $3000,000 annually in energy costs. (Photo courtesy of American Fructose, Inc.) [provided in source document]

Photo: The process integration study for this American Synthetic Rubber Company plant concluded that mechanical vapor recompression heat pumps, along with other charges, could save 60% of the energy consumed in one of the plantūs processes. (Photo courtesy of American Synthetic Rubber Company) [provided in source document]

Installed heat pump systems are saving energy

One of the OIT-sponsored process integration studies took place at the American Fructose, Inc. wet-corn milling plant in Decatur, Alabama. The plant uses large numbers of industrial dryers and evaporators to mill, cook, and convert corn starch to high-fructose corn syrup. In 1991, managers of the plant installed a new heat pump recommended by the study. The new heat pump saves the company $300,000 in energy costs (coal and natural gas) annually. Further energy and capital cost savings will be realized if this plant is expanded. The economic payback period for the heat pump installation is short-slightly more than 1 year. The increase in plant efficiency resulting from the changes has enabled plant management to shut down an existing heater and to circumvent the need for a new cooling tower. The associated environmental benefits include a reduction in NOx emissions by 42 metric tons per year.

The American Synthetic Rubber Company facility in Louisville, Kentucky, was the subject of another OIT process integration study. This study concluded that the facilityūs only process-to-process heat exchanger should be relocated and that two new heat pumps and seven new heat exchangers should be added. One of the new heat pumps could be used to produce medium-pressure process and the other to heat boiler feedwater. The recommended modifications could reduce the net fuel use (primarily coal) by almost 60%, saving more than $1 million per year in fuel costs. The majority of these savings would come from adding the heat pumps, which would have a combined payback period of 1.2 years. The facility would also reduce its annual emissions of NOx and SOx by 331 metric tons and 680 metric tons, respectively.

Photo: A mechanical vapor recompressor designed for Bowater's pulping mill should save more than $1 million annually in energy costs. (Photo courtesy of Bowater Incorporated) [provided in source document]

Photo: A mechanical vapor recompression heat pump designed for Kerr-McGee Refining's naphtha splitter operation would have a 2-year payback. (Photo courtesy of Kerr-McGee Refining) [provided in source document]

Major products of the Bowater, Inc. integrated pulp and paper mill located in Catawba, South Carolina, include market pulp, newsprint, and coated paper. The process integration study performed on this facility focused on the plantūs pulping operations and pulping-chemical recovery processes. Although the plantūs heating and cooling flows were found to be well integrated, the study showed that the boiler feed water could be heated by dirty, low-pressure steam rather than by clean, higher pressure steam. This redesign eliminates releasing the dirty steam to the atmosphere and leaves the clean steam available for other heat transfer applications. The addition of a new heat pump to accomplish these changes would increase the plantūs electricity use by less than 1% but reduce natural gas consumption for the processes analyzed by 10%-15%. The value of the anticipated savings would exceed $1 million annually. These savings, combined with the current estimated capital cost for the heat pump system, yield a payback period of slightly more than 6 months. The installed cost of the equipment is currently being reexamined; even if it rises, the economics of the new system would still be very favorable. The environment benefits of the system would include a decrease in NOx emissions of 91 metric tons per year.

Kerr-McGee Refining operates a petroleum refinery in Wynnewood, Oklahoma, that converts crude oil to a variety of refined products. OIT's process integration study showed that the facilityūs energy efficiency could be improved by modifying two existing heat exchangers and adding four new heat exchangers and two heat pumps. The redesigned process would eliminate one existing gas-fired heater and would reduce the net fuel consumption of the process steps analyzed by more than 40%, saving the company more than $600,000 annually in fuel costs (primarily natural gas). The economic payback for the project is predicted to be 2 years for the new heat pumps and 1 year for the heat exchanger modifications.

The final facility for which a heat pump design has been completed is the South Hampton Refining Company in Silsbee, Texas, a producer of specialty chemicals. The proposed heat pump system will be used to recompress the overhead vapors of a distillation tower to recover the energy contained in these vapors. The system is expected to reduce the plant's natural gas costs by $100,000 per year. In addition to save energy, the heat pump will allow increased plant throughput and higher productivity by removing a plant "bottleneck." The new system will make use of an existing company that is currently underutilized; running this compressor more closely to its rated load may result in even more energy savings. The heat pump system has an estimated payback period of approximately 1 year and could be installed as early as the summer of 1993.

Future efforts focus on design and demonstration

These five examples are typical of the energy, cost, and environmental benefits that can be achieved by implementing the measures recommended by analyses based on process integration techniques. OIT plans to work with the companies mentioned in these examples to implement the recommended designs, quantify the necessary capital investment, and demonstrate the achievable savings. Through demonstration projects such as these, OIT and industry are finding that improving the process itself and looking for opportunities for heat pumps will have significant long-term benefits for the efficiency, productivity, and economics of industrial plants. The large energy-efficiency improvements possible with these systems will be economical even with very low energy prices, and the development of even more efficient heat pumps will further broaden the opportunities for industrial heat pumps.

Plant managers interested in applying process integration techniques can consult a variety of published materials and organizations for help. Information on process integration and industrial heat pumps can be obtained from the U.S. Department of Energy.

For More Information:

Industrial Heat Pump Program
CE-221
Office of Industrial Technologies
U.S. Department of Energy
1000 Independence Ave., SW
Washington, DC 20585
(202) 586-7234


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Last Updated: February 13, 1996