- Also called:
- waste-heat recovery
thermal-heat recovery
-
What is thermal-heat recovery?
Thermal-heat recovery involves capturing and reusing heat energy emitted from industrial processes that would typically dissipate unused into the environment. It has broad applications in energy systems like household heating and cooling and electricity generation, reducing fossil fuel consumption.
The feasibility of heat recovery depends on the waste heat's temperature and quantity. Heat exchangers are commonly used to transfer heat between fluid streams and include recuperators, regenerators, and evaporative-heat exchangers. Recovered heat can preheat materials, dry items, generate steam, and provide space and water heating. Generating electricity from waste heat is often more valuable due to electricity's versatility and efficient transport.
1 Britannica SourceCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
Why is it important to reuse heat energy?
Reusing heat energy, known as thermal-heat recovery, is important because it can reduce fossil-fuel consumption. Thermal-heat recovery has a wide area of potential applications, especially in household heating and cooling systems and in electricity generation.
Waste heat can be recovered through electromagnetic radiation, convection, and conduction. Heat exchangers are a widely used technology that enables the transfer of heat energy between hot and cold fluid streams. Geothermal heat pumps also gained popularity as a greener alternative to traditional boilers because they use 25–50 percent less electricity than conventional heating and cooling systems, and they produce less pollution.
2 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
How does a thermal-heat recovery system work?
Thermal-heat recovery systems capture and reuse heat energy from industrial processes that would typically be wasted, reducing fossil fuel consumption. These systems are applicable to household heating, cooling, and electricity generation.
Heat exchangers are a common technology used in thermal-heat recovery. They transfer heat between hot and cold fluid streams and come in three main types: recuperators, regenerators, and evaporative-heat exchangers. Other technologies include heat pumps, which transfer low-temperature heat to a higher-temperature sink, and heat pipes, which enable heat transfer over moderate distances with minimal heat loss. Recovered heat can be used to preheat materials, for drying, to make steam, and in space and water heating.
2 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
Where are thermal-heat recovery systems commonly used?
Thermal-heat recovery systems are commonly used across a wide area of potential applications to reduce fossil-fuel consumption. Heat exchangers, a widely used technology for thermal-heat recovery, are found extensively in fossil-fuel and nuclear power plants, gas turbines, the chemical industry, and in heating, air-conditioning, and refrigeration units. Recovered heat may be used directly for preheating raw materials, in drying operations, for making steam, and in space and water heating. Heat pumps are used in industry to pump low-temperature waste heat into a higher-temperature environment, and in the domestic sector to upgrade ambient sources of heat to temperatures suitable for domestic heating.
1 Britannica SourceCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
What are some benefits of using thermal-heat recovery in buildings or factories?
Thermal-heat recovery reuses heat energy from industrial processes that would otherwise go to waste, with applications ranging from household heating to electricity generation.
Benefits:
* It can reduce fossil-fuel consumption.
* Recovered heat may be used directly for preheating raw materials, in drying operations, for making steam, and in space and water heating.
* Generating electricity from waste heat is often more favourable than directly using recovered heat because of the versatility and relatively high value of electricity compared with heat.
* Heat pipes enable the transfer of heat over moderate distances with a very low heat loss and without the need for mechanical pumping.1 Britannica SourceCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
How does thermal-heat recovery help save energy and reduce pollution?
Thermal-heat recovery utilizes heat energy emitted from industrial processes that would otherwise be lost, reducing fossil fuel consumption. Though waste heat sources are common, their suitability for recovery depends on factors like temperature and quantity.
Heat exchangers, heat pumps, and heat pipes are technologies used in thermal-heat recovery. Heat exchangers transfer heat between fluid streams, heat pumps move low-temperature heat to a higher-temperature sink, and heat pipes efficiently transfer heat over moderate distances. Recovered heat can be used to preheat materials, generate steam, and for heating. Electricity generation from waste heat is often preferred due to electricity's versatility and ease of transport.
1 Britannica SourceCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
thermal-heat recovery, use of heat energy that is released from some industrial processes and that would otherwise dissipate into the immediate environment unused. Given the prevalence of heat-generating processes in energy systems, such as those found in household heating and cooling systems and in electricity generation, thermal-heat recovery has a wide area of potential applications and can reduce fossil-fuel consumption. However, although sources of waste heat are ubiquitous, not all waste heat is suitable for thermal-heat recovery, and economic or technical constraints sometimes preclude the use of available recovery technologies.
In many heat- and electricity-generating processes, after the heat demand of the process has been met, any excess or waste heat is released as exhaust. Since the laws of thermodynamics indicate that heat is transferred from higher to lower temperatures, the temperature of a process’s waste heat is thus inevitably lower than the temperature of the process itself. In determining the feasibility for heat recovery, the two most-crucial factors are the temperature of the waste heat and the quantity of heat produced. The heat-flux density (the rate of heat flow per cross-sectional area), the nature of the environment, the temperature of the heat, and process-specific considerations—such as the rate of cooling, which must be controllable in some industrial processes such as glass manufacture—also affect the suitability of waste heat for recovery. Generally speaking, the higher the temperature is, the more suitable the heat is for generating electricity (as opposed to being used directly).
Heat loss from a process occurs through three main mechanisms: electromagnetic radiation; convection, which is the transmission of energy through thermal currents in fluids; and conduction, which is the direct transmission of heat through a substance. Thermal-heat-recovery technologies employ one or a combination of those mechanisms in order to recover waste heat.
" height="20" alt="HEW Logo">
Heat exchangers are a widely used technology that enables the transfer of heat energy between hot and cold fluid streams and can be classified into three main types: recuperators, regenerators, and evaporative-heat exchangers. Recuperators operate continuously and transfer heat between fluids on either side of a dividing wall. Regenerators allow the transfer of heat to and from an absorbent medium, such as heat-conducting bricks. Regenerators operate periodically and feature a loading phase during which hot fluid charges the device and an unloading phase during which the heat is transferred to a cooler fluid. Evaporative-heat exchangers are frequently used in power-station cooling towers and use evaporation to cool a liquid in the same space as the coolant.
Heat exchangers are used extensively in fossil-fuel and nuclear power plants, gas turbines, and the chemical industry as well as in heating, air-conditioning, and refrigeration units. Recovered heat may be used directly for preheating raw materials, in drying operations, for making steam, and in space and water heating. Generating electricity from waste heat is often more favourable than directly using recovered heat because of the versatility and relatively high value of electricity compared with heat. Electricity can be used for power as well as heat applications, and it can be transported more efficiently than heat. Although high-temperature sources of waste heat are necessary to generate electricity at conventional power plants, it is possible to produce electricity at lower temperatures with nonconventional cycles such as the organic Rankine cycle. That cycle uses an organic working fluid with a low boiling point so that the evaporation occurs at a much lower temperature. The cooler waste heat is thus still able to produce a vapour to drive a turbine and generate electricity.
Other technologies relevant to thermal-heat recovery include heat pumps and heat pipes. Heat pumps are simple thermodynamic machines in which low-temperature heat from a source is transferred to a higher-temperature sink, using mechanical or high-temperature heat energy. In industry, there are several applications in which it is desirable to pump low-temperature waste heat into a higher-temperature environment. In the domestic sector, ground or air source heat pumps upgrade ambient sources of heat to temperatures suitable for domestic heating. Heat pipes enable the transfer of heat over moderate distances with a very low heat loss and without the need for mechanical pumping. Those may be used in combination with combined heat and power systems in order to transport the heat to district heating schemes or adjacent industrial facilities.
In practice, the application of thermal-heat-recovery technologies requires a use for the recovered energy, which often entails significant investment in electricity-generation capabilities if the heat cannot be used directly. Additionally, some heat exchangers need regular maintenance because of the corrosive gases in exhaust streams or require specialized materials to withstand the high temperatures, which can be costly and render the plant uneconomic.
The trusted destination for professionals, college students, and lifelong learners.
SUBSCRIBE
