|Large scale - long term|
|Large scale - short term|
|2006 IPCC Sector categorization|
|Pulp and Paper Industry|
|Food and Beverages Industry|
|Industrial subsectors other|
|Industry: energy consumption, industrial processes, and product use|
Industrial heat pumps can work in a variety of ways. This description discusses industrial heat pumps in general and additionally focuses on the most common applications: Mechanical Vapour Recompression, Thermal Vapour Recompression, Absorption, and mechanical compression.
Mechanical vapour recompression is an open cycle process that increases the pressure of low-pressure waste gases, which increases the temperature of that gas, in order to reuse the heat. Reusing the heat reduces energy use and costs. This technology is especially applicable in industries that use thermal separation processes, such as evaporation and distillation. Main fields of application of this type of industrial heat pump are industries such as the food and beverages industry (HPTCJ, 2010), chemical industry, salt works and environmental technology (GEA, no date). The most common vapor used for recompression is steam. The potential energy savings are significant, but capital investment in the larger units can be high (IEA, 2010).
Thermal Vapour Recompression is a process that uses energy in high-pressure motive steam to increase the pressure of low-pressure waste vapor using a jet-ejector device. This type of industrial heat pump is typically used in evaporaters and the working fluid is steam. As with the mechanical vapour recompression pump, this is an open cycle pump system (ITP, 2003).
Absorption use a two-component working fluid and the principles of boiling-point elevation and heat of absorption to achieve temperature lift and to deliver heat at higher temperatures. The operating principle is the same as that used in steam-heated absorption chillers that use a Lithium Bromide/water mixture as their working fluid. Key features of absorption systems are that they can deliver a much higher temperature lift than the other systems, their energy performance does not decline steeply at higher temperature lift, and they can be customized for combined heating and cooling applications. (ITP, 2003).
Mechanical compression pumps use mechanically provided compression of a working fluid to achieve temperature lift. The working fluid is typically a common refrigerant. Commonly used in wood drying, this is a closed cycle system.
Industrial heat pumps
Industrial heat pumps are defined as active heat-recovery equipment that increases the temperature of a waste-heat stream to a higher and more useful temperature (ITP, 2003). The heat can then be used to replace purchased energy and therefore reduce energy costs. In other words, the technology is used to provide heat and increase industrial efficiency.
The increase in temperature is not without cost: an industrial heat pump requires an external source of energy. This can be either in the form of mechanical energy or thermal energy. Industrial heat pumps are effective when the benefits of using the heat-pumped waste heat exceed the costs of the external source of energy. Different types of industrial heat pump exist: mechanical vapour recompression, thermal vapour recompression, mechanical compression, and absorption heat pumps. Next to other characteristics, these systems differ in the external energy source used.
All heat pumps perform the same three basic functions (ITP, 2003):
a) Receipt of heat from a waste stream
b) Increase of the waste heat temperature
c) Delivery of the useful heat.
Mechanical vapour recompression
This type of heat pump mechanically compresses waste vapor which increases the pressure of the vapor. Because the heat pump uses a process stream as working fluid it is considered to be open cycle (ITP, 2003). In other words, after compression of the vapor and subsequent condensation of the heating steam, the condensate leaves the cycle. Mechanical drivers susch as electric motors, steam turbines, combusion engines and combustion turbines can be used to deliver the mechanical force.
Main fields of application of this type of industrial heat pump are industries such as the food and beverages industry, chemical industry, salt works and environmental technology (GEA, no date). The most common vapor used for recompression is steam. Figure 1 illustrates the functioning of an industrial heat pump using mechanical vapour recompression.
Thermal vapour recompression
This method works in a similar fashion as mechanical vapour recompression. The difference is that thermal vapour compression uses thermal energy as the external energy source to compress vapor instead of mechanical energy (ITP, 2003). Common applications of this method are evaporation processes,illustrated in Figure 2, and paper drying.
Absorption heat pump
The main advantages of the absorption heat pump is that they can deliver a much higher temperature lift, their energy performance does not decline steeply at higher temperature lift, and they can be customized for combined heating and cooling applications (ITP, 2003).
The main components of an absorption heat pump are the evaporator, condenser, generator and absorber,as illustrated in Figure 3 (ITP, 2003). An absorption heat pump uses high temperature prime energy into the desorber, which produces high pressure vapor. The high-pressure vapor is condensed in the condensor where the heat is recovered into a process stream. Subsequently, the high-pressure condensate from the condenser is throttled to a lower pressure in the evaporator, where the waste heat is recovered to vaporize the low-pressure condensate. Concentrated working fluid from the desorber contacts the low-pressure vapor from the evaporator in the absorber. This creates heat that is recovered into a process stream. The working fluid is then returned to the desorber to complete the cycle.
In a typical absorption heat-pumping application, waste heat at low temperature is delivered to the evaporator, and prime heat at high temperature is delivered to the generator. An amount of heat equivalent to the sum of the high- and low-temperature heat inputs can be recovered at an intermediate temperature via the condenser and absorber. This is analogous to the thermocompression heat pump, in which high-pressure steam is used to increase or lift low-pressure waste vapor to a higher pressure and temperature. However, in the case of the high-lift absorption heat pump, the temperature lift can be 200 to 300° F, rather than the 20 to 50° F of the thermocompression system. However, absorption pumps also have a higher first cost than the other types.
An alternate configuration for an absorption heat pump allows a medium-temperature waste-heat stream to split into one higher-temperature stream and one lower-temperature stream. Adjusting the operating pressures and working-fluid concentrations accomplishes this reconfiguration.
Mechanical compression heat pump
The most common application of industrial heat pumps is dehumidification drying of lumber (ITP, 2003). For this application, the mechanical compression heat pump is used. The technical characteristics of lumber drying using this method is illustrated in Figure 4. The heat pump compresses a working fluid, typically a common refrigerant, to increase its temperature. The working fluid is then exposed to the gas that needs to be heated, during which the working fluid cools and expands. The working fluid is subsequently guided back to the compressor to be heated again.
Industrial heat pumps work more effectively under certain circumstances. Table 1 illustrates the features that are favourable to the use of industrial heat pumps. Clearly, favourable circumstances are mainly associated with temperature lift required and overall costs.
|Feature favourable for industrial heat pump application||Reason|
|The process involves evaporation||Opportunity for highly effective heat pump|
|There are streams in an intermediate temperature range (160 to 200 oF)||Heat in this temperature range does not require too much lift|
Water, air or other process streams are heated from ambient to 150 to 250° F with steam or fuel
Heat pumps can easily supply heat in this temperature range
|Low pressure steam is vented or condensed|
Condensing steam is a convenient heat source that a heat pump can easily use
|The process involves distillation with a small temperature range between the reboiler and condenser|
Opportunity for highly effective heat pump because of low heat-pump temperature lift
|The amount of recoverable waste heat is large enough|
The potential savings have to be large enough to generate interest. Economies of scale favor large installations
The heat source is a clean liquid or condensing fluid
|Heat capture in the heat pump is simple|
The process entails continuous operation with a high number of operating hours
Project generates more annual savings
Electricity is cheap relative to fuel. For example the ratio of electricity cost to fuel cost on a Btu basis is < 3.
Reduces the effective cost of heat delivered by the heat
Both fuel and power prices are high (this is negative in general but is a benefit in conservation efforts)
Higher energy prices increase the value of cost savings relative to capital costs; this improves pay-back of the system
While Table 1 illustrates the general circumstances favourable for industrial heat pumps, Table 2 shows when it is recommended to use which industrial heat pump type.
|Temperature lift||Heat Source Type||Heat Sink Type||Suggested heat pump type |
with priority numbering
|<100 oF||Sensible cooling of liquid||Sensible heating of |
gas or liquid
|1. Closed cycle mechanical compression|
|<100 oF||Partial Condensation of liquid from vapor stream||Sensible heating of |
gas or liquid
|1. Closed cycle mechanical compression|
|<100 oF||Condensing steam||Evaporation of water||1. MVR|
|<100 oF||Condensing vapor (steam or other)||Sensible heating of |
gas or liquid
|>100 oF||All heat sources (except steam)||All heat sinks (except steam)||1. Absorption|
2. Multi-stage mechanical compression
|>100 oF||Low pressure steam||High pressure steam header||1. MVR|
3. Multi-stage mechanical compression
Overall, the heat pump technology is in a mature stage. Recent years have shown strong growth in the heat pump market. For instance, Figure 5 illustrates the overall heat pump market growth, thus including residential and other applications, in Austria, Finland, France, Italy, Germany, Norway, Sweden, Switzerland, and the UK. In these countries, since 2005 over 2 million heat pumps have been installed (EHPAa, 2010).
However, the specific industrial heat pump market is smaller since the focus for heat pumps has been the residential market (EHPAb, 2010). The potential of industrial heat pumps is large. For instance, Figure 6 shows the potential for large scalel heat pumps in Germany. From the figure it can be seen that large scale heat pumps have the possibility to provide around 19 % of German total energy consumption in 2005 (EHPAb, 2010). Of these large scale heat pumps, a large potential is in the chemical, paper and pulp and food industries. This shows that industrial heat pumps have a considerable potential.
A survey study into the potential of industrial heat pump technology in the food and beverage sector found that a total CO2 reduction effect of 40 million tonne of CO2/year can be expected from the eleven countries covered by the survey (HPTCJ, 2010). This effect comes from the substitution of steam boilers for heat pumps among applications at a use end temperature below 100 degrees Celsius. Especially, China (15 million tonne CO2/year) and the United States (14 million tonnes CO2/year) are identified by the survey to have a significant CO2 reduction potential (HPTCJ, 2010).
Energy market support occurs through the use of industrial heat pumps. Due to the increased industrial efficiency, less energy is required. This reduces the strain on the grid, and reduces the need for additional power plants. In addition, it reduces the use of resources, such as fossil fuels. Moreover, industrial heat pumps can offer several important non-economic benefits such as the effective increase in steam plant capacity (IEA, 1995) which support the energy market.
Industrial heat pumps are mainly used for waste heat utilization and, as such, increase industrial efficiency. A higher industrial efficiency leads to several environmental benefits. The greatest environmental benefits from the use of industrial heat pumps can be found in processes that rely most heavily on oil and coal for process heating (IEA, 1995). Main examples are the paper and pulp industry, iron and steel, and petroleum refining. In 1995, it was determined that industrial heat pumps offer the largest average environmental benefits, especially in terms of SOx and NOx, when they replace process heat that is heavily based on coal (IEA, 1995).
Industrial heat pumps lower the emissions associated with the use of fossil fuels, due to the increased efficiency of the system. There are no pollution emissions at the heat pump, although the generation of the electricity needed for the pump could cause CO2 emissions (depending on whether the generation takes place with or without fossil fuels), and the heat produced will reduce the need to produce heat by burning fossil fuels, which will reduce CO2 emissions. Heat pumps by reducing the need for fossil fuelled generating plants can consequently improve local and regional air quality.
A study into the performance of an industrial high temperature heat pump for wood drying clearly shows the potential climate and environment related benefits of the technology. It was found that annual oil consumption was reduced by at least 50 % compared to the conventional oil fired wood dryer (IEA, 2007, p. 17). The study calculated that approximately 300 000 liters per year in oil consumption was reduced, which is equivalent to 887 760 kg of CO2 (IEA, 2007,p. 17). At the same time, electrical energy consumption increased by 944 500 kWh/year due to the use of the heat pump's compressor, blowers and dryer fans, which is equivalent to 1 153 kg of CO2 (IEA, 2007, p. 17). However, it needs to be noted that the installation was located in Quebec, Canada which is heavily dependent on hydropower as the electricity source. Consequently, the emission factor of the grid is a 0.00122 kg of CO2-equivalent per kWh reduction (IEA< 2007, p.18). Therefore, under different circumstances the CO2 savings might differ considerably. The study found that about 886 607 kg of CO2 annually was reduced through the implementation of the industrial heat pump.
Another study into the food and beverage industry found that a significant potential for CO2 reduction exist within this industry, as illustrated in Figure 7 (HTPCJ, 2010). The study found that a total CO2 reduction effect of 40 million tonne of CO2/year can be expected from the eleven countries covered by the survey (HPTCJ, 2010). This effect comes from the substitution of steam boilers for heat pumps among applications at a use end temperature below 100 degrees Celsius. Especially, China (15 million tonne CO2/year) and the United States (14 million tonnes CO2/year) are identified by the survey to have a significant CO2 reduction potential (HPTCJ, 2010).
The main advantage of industrial heat pumps is the low operational costs of the system compared to conventional systems. However, the capital costs involved with heat pumps are larger compared to conventional systems. Consequently, the financial aspects differ between cases, and applications. Applicability of industrial heat pumps should therefore be assessed on a site-specific basis. It is possible, however, to provide a general framework of the financial requirements and costs involved with the implementation of an industrial heat pump.
Due to the cost savings while in operation, industrial heat pump economics are highly sensitive to the annual utilization rate (IEA, 1995). It is therefore important to determine the correct size of the system required and not to oversize the system. Payback of the high capital costs is faster when the utilization rate is as high as possible. It is better to have a small, base load system with high operating hours. SInce most industrial heat pumps are custom designed (ITP, 2003), there is no predictable relationship between size and unit cost. Typical payback time for industrial heat pump applications is between 2 and 5 years (ITP, 2003).
The operating costs are determines by two key parameters: the temperature lift required and the cost of the power source to run the compressor. Figure 8 illustrates these two key parameters and their influence on operating costs.
The study into the performance of an application of a industrial heat pump installation to dry wood found that the performance of that installation represented a 39 % to 43 % reduction in total annual energy costs (IEA, 2007, p. 17).
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