Industrial Heat Pumps For Low-Temperature Heat Recovery
Industrial heat pumps can significantly reduce fossil fuel consumption and greenhouse gas emissions in drying, washing, evaporation and distillation processes in a variety of applications. They can also be used to produce steam and to provide process water heating and cooling. Industries that can benefit from this technology include food and beverage processing, forest products, textiles, and chemicals, industrial heat pumps are used in heat recovery to transfer heat from a relatively low-temperature source and “upgrade” it to a higher temperature, and to recover from high-humidity streams. Heat ex-changers and Recovery Systems in contrast are used to transfer heat from a warm stream to a cooler one.
What are the basic steps in the installation for a heat-pumps in your project?
As with any heat-recovery project, once a heat-pump opportunity is identified, the project needs to undergo a feasibility study and a detailed engineering design. However, a few areas warrant special attention:
Sizing: It is better to have a small, base-loaded installation with high operating hours than a unit that works at part load, part time.
Back-up: A process operation must still be able to run should the heat pump break down address the need for a back-up.
Alternates: A heat-pump installation will usually be more expensive than a passive-heat recovery project because heat has to be transferred twice (in and out of the heat pump), and a piece of rotating equipment may be needed.
A thorough heat-pump evaluation includes confirmation that a better alternative project has not been overlooked. Use of heat integration methods such as Pinch Technology, are useful for this type of evaluation. Pinch Technology, in particular, provides a set of systematic analytical methods and tools that help identify both heat-recovery project opportunities and heat-pumping opportunities. When heat pumps are used in drying, evaporation and distillation processes, heat is recycled within the process. For space heating, heating of process streams and steam production, heat pumps utilize (waste) heat sources between 20ºC and 100ºC.The most common waste heat streams in industry are cooling water, effluent, condensate, moisture, and condenser heat from refrigeration plants. Because of the fluctuation in waste heat supply, it can be necessary to use large storage tanks for accumulation to ensure stable operation of the heat pump.
Types of Heating and Drying
Space heatingHeat pumps can utilize conventional heat sources for heating of greenhouses and industrial buildings, or they can recover industrial waste heat that could not be used directly, and provide a low- to medium temperature heat that can be utilized internally or externally for space heating. Mainly electric closed-cycle compression heat pumps are used.
Process water heating and cooling
Many industries need warm process water in the temperature range from 40-90ºC, and often have a significant hot water demand in the same temperature range for washing, sanitation and cleaning purposes. This can be met by heat pumps. Heat pumps can also be a part of an integrated system that provides both cooling and heating. Mainly electric scanair compression heat pumps are installed.
Scanair Heat pumps are used extensively in industrial dehumidification and drying processes at low and moderate temperatures (maximum 80ºC). The main applications are drying of pulp and paper, various food products wood and lumber. Drying of temperature-sensitive products is also interesting. Heat pump dryers generally have high performance (COP 5-7), and often improve the quality of the dried products as compared with traditional drying methods. Because the drying is executed in a closed system, odors from the drying of food products etc. are reduced. Both closed-cycle compression heat pumps and cascade systems are used.
Evaporation and distillation processes
Evaporation and distillation are energy-intensive processes, and most heat pumps are installed in these processes in the chemical and food industries. In evaporation processes the residue is the main product, while the vapors distillate is the main product in distillation processes. Most systems are open or semi-open MVRs, but closed-cycle compression heat pumps are also applied. Small temperature lifts result in high performance with COPs ranging from 6 to 30. Scanair heat recovery systems absorb the wasted heat from refrigeration and air conditioning systems and converts it to free hot water by super heating the discharge vapour before the condenser. You can save money and the environment.