Energy recovery
Encyclopedia
Energy recovery includes any technique or method of minimizing the input of energy
to an overall system
by the exchange of energy from one sub-system of the overall system with another. The energy can be in any form in either subsystem, but most energy recovery systems exchange thermal energy
in either sensible
or latent
form.
esous or liquid
) may be transferred to the make-up or input material flow. This input mass
flow often comes from the system's surroundings, which, being at ambient conditions, are at a lower temperature than the waste stream. This temperature differential allows heat transfer
and thus energy transfer, or in this case, recovery. Thermal energy is often recovered from liquid or gaseous waste streams to fresh make-up air and water
intakes in buildings, such as for the HVAC
systems, or process systems.
An energy recovery system will close this energy cycle to prevent the input power from being released back to nature and rather be used in other forms of desired work.
it should be possible to dramatically reduce the world energy consumption. The effect of this will then be:
In 2008 Tom Casten
, chairman of Recycled Energy Development
, said that "We think we could make about 19 to 20 percent of U.S. electricity with heat that is currently thrown away by industry."
A 2007 Department of Energy study found the potential for 135,000 megawatts of combined heat and power
(which uses energy recovery) in the U.S., and a Lawrence Berkley National Laboratory study identified about 64,000 megawatts that could be obtained from industrial waste energy, not counting CHP. These studies suggest about 200,000 megawatts—or 20% -- of total power capacity that could come from energy recycling
in the U.S. Widespread use of energy recycling
could therefore reduce global warming emissions by an estimated 20 percent. Indeed, as of 2005, about 42 percent of U.S. greenhouse gas pollution came from the production of electricity and 27 percent from the production of heat.
It is, however, difficult to quantify the environmental impact of a global energy recovery implementation in some sectors. The main impediments are
Energy
In physics, energy is an indirectly observed quantity. It is often understood as the ability a physical system has to do work on other physical systems...
to an overall system
System
System is a set of interacting or interdependent components forming an integrated whole....
by the exchange of energy from one sub-system of the overall system with another. The energy can be in any form in either subsystem, but most energy recovery systems exchange thermal energy
Thermal energy
Thermal energy is the part of the total internal energy of a thermodynamic system or sample of matter that results in the system's temperature....
in either sensible
Sensible heat
Sensible heat is the energy exchanged by a thermodynamic system that has as its sole effect a change of temperature.The term is used in contrast to a latent heat, which is the amount of energy exchanged that is hidden, meaning it cannot be observed as a change of temperature...
or latent
Latent heat
Latent heat is the heat released or absorbed by a chemical substance or a thermodynamic system during a process that occurs without a change in temperature. A typical example is a change of state of matter, meaning a phase transition such as the melting of ice or the boiling of water. The term was...
form.
Principle
A common utilization of this principle is in systems which have an exhaust stream or waste stream which is transferred from the system to its surroundings. Some of the energy in that flow of material (often gasGas
Gas is one of the three classical states of matter . Near absolute zero, a substance exists as a solid. As heat is added to this substance it melts into a liquid at its melting point , boils into a gas at its boiling point, and if heated high enough would enter a plasma state in which the electrons...
esous or liquid
Liquid
Liquid is one of the three classical states of matter . Like a gas, a liquid is able to flow and take the shape of a container. Some liquids resist compression, while others can be compressed. Unlike a gas, a liquid does not disperse to fill every space of a container, and maintains a fairly...
) may be transferred to the make-up or input material flow. This input mass
Mass
Mass can be defined as a quantitive measure of the resistance an object has to change in its velocity.In physics, mass commonly refers to any of the following three properties of matter, which have been shown experimentally to be equivalent:...
flow often comes from the system's surroundings, which, being at ambient conditions, are at a lower temperature than the waste stream. This temperature differential allows heat transfer
Heat transfer
Heat transfer is a discipline of thermal engineering that concerns the exchange of thermal energy from one physical system to another. Heat transfer is classified into various mechanisms, such as heat conduction, convection, thermal radiation, and phase-change transfer...
and thus energy transfer, or in this case, recovery. Thermal energy is often recovered from liquid or gaseous waste streams to fresh make-up air and water
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
intakes in buildings, such as for the HVAC
HVAC
HVAC refers to technology of indoor or automotive environmental comfort. HVAC system design is a major subdiscipline of mechanical engineering, based on the principles of thermodynamics, fluid mechanics, and heat transfer...
systems, or process systems.
System approach
Energy consumption is a key part of most human activities. This consumption involves converting one energy system to another, for example: The conversion of mechanical energy to electrical energy, which can then power computers, light, motors etc. The input energy propels the work and is mostly converted to heat or follows the product in the process as output energy. Energy recovery systems harvest the output power and providing this as input power to the same or another process.An energy recovery system will close this energy cycle to prevent the input power from being released back to nature and rather be used in other forms of desired work.
Examples of energy recovery
- Heat recovery is implemented in heat sources like e.g. a steel mill. Heated cooling water from the process is sold for heating of homes, shops and offices in the surrounding area.
- Regenerative brakeRegenerative brakeA regenerative brake is an energy recovery mechanism which slows a vehicle or object down by converting its kinetic energy into another form, which can be either used immediately or stored until needed...
is used in electric cars, trains, heavy cranes etc where the energy consumed when elevating the potential is returned to the electric supplier when released. - Active pressure reduction systems where the differentioal pressure in a preassurized fluid flow is recovered rather than converted to heat in a pressure reduction valve and released.
- Energy recovery ventilation
- Energy recyclingEnergy recyclingEnergy recycling is the energy recovery process of utilizing energy that would normally be wasted, usually by converting it into electricity or thermal energy. Undertaken at manufacturing facilities, power plants, and large institutions such as hospitals and universities, it significantly...
- Water heat recycling
- Heat recovery ventilationHeat recovery ventilationHeat recovery ventilation, also known as HRV, mechanical ventilation heat recovery, or MVHR, is an energy recovery ventilation system using equipment known as a heat recovery ventilator, heat exchanger, air exchanger, or air-to-air heat exchanger which employs a counter-flow heat exchanger between...
- Heat recovery steam generator
- Heat Regenerative Cyclone Engine
- Hydrogen turboexpander-generatorHydrogen turboexpander-generatorA hydrogen turboexpander-generator or generator loaded expander for hydrogen gas is an axial flow turbine or radial expander for energy recovery through which a high pressure hydrogen gas is expanded to produce work that is used to drive a electrical generator...
- Thermal diodeThermal diodeThe term thermal diode is sometimes used for a device which causes heat to flow preferentially in one direction. Or, the term may be used to describe an electrical diode in reference to a thermal effect or function...
- Thermal oxidizerThermal oxidizerA thermal oxidizer is a process unit for air pollution control in many chemical plants that decomposes hazardous gases at a high temperature and releases them into the atmosphere.-Principle:...
- Thermoelectric Modules
- Waste heat recovery units
Environmental impact
There is a large potential for energy recovery in compact systems like large industries and utilities. Together with Energy conservationEnergy conservation
Energy conservation refers to efforts made to reduce energy consumption. Energy conservation can be achieved through increased efficient energy use, in conjunction with decreased energy consumption and/or reduced consumption from conventional energy sources...
it should be possible to dramatically reduce the world energy consumption. The effect of this will then be:
- Reduced number of coal fired power plants
- Reduced airborne particles, NOxNOxNOx is a generic term for the mono-nitrogen oxides NO and NO2 . They are produced from the reaction of nitrogen and oxygen gases in the air during combustion, especially at high temperatures...
and CO2 - improved air quality - Slowing or reducing climate changeClimate changeClimate change is a significant and lasting change in the statistical distribution of weather patterns over periods ranging from decades to millions of years. It may be a change in average weather conditions or the distribution of events around that average...
- Lower fuel bills on transport
- Longer availability of crude oil
- Change of industries and economies not fully researched
In 2008 Tom Casten
Tom Casten
Thomas R. Casten, known as Tom Casten, is an American businessman, author, and activist known for his work on industrial energy recycling. Since 1977, Casten has founded and managed numerous companies and organizations associated with combined heat and power , decentralized energy, and waste...
, chairman of Recycled Energy Development
Recycled Energy Development
Recycled Energy Development, LLC aims to profitably reduce greenhouse gas emissions by capturing and recycling waste energy, especially through cogeneration and waste heat recovery.-Overview:RED develops, owns, and manages energy recycling facilities...
, said that "We think we could make about 19 to 20 percent of U.S. electricity with heat that is currently thrown away by industry."
A 2007 Department of Energy study found the potential for 135,000 megawatts of combined heat and power
Combined Heat and Power
Combined Heat and Power may refer to:* Cogeneration* Combined Heat and Power Solar...
(which uses energy recovery) in the U.S., and a Lawrence Berkley National Laboratory study identified about 64,000 megawatts that could be obtained from industrial waste energy, not counting CHP. These studies suggest about 200,000 megawatts—or 20% -- of total power capacity that could come from energy recycling
Energy recycling
Energy recycling is the energy recovery process of utilizing energy that would normally be wasted, usually by converting it into electricity or thermal energy. Undertaken at manufacturing facilities, power plants, and large institutions such as hospitals and universities, it significantly...
in the U.S. Widespread use of energy recycling
Energy recycling
Energy recycling is the energy recovery process of utilizing energy that would normally be wasted, usually by converting it into electricity or thermal energy. Undertaken at manufacturing facilities, power plants, and large institutions such as hospitals and universities, it significantly...
could therefore reduce global warming emissions by an estimated 20 percent. Indeed, as of 2005, about 42 percent of U.S. greenhouse gas pollution came from the production of electricity and 27 percent from the production of heat.
It is, however, difficult to quantify the environmental impact of a global energy recovery implementation in some sectors. The main impediments are
- Lack of efficient technologies for private homes. Heat recovery systems in private homes can have an efficiency as low as 30% or less. It may be more realistic to use energy conservation like insulation or improved buildings. Many areas are more dependant on forced cooling and a system for extracting heat from dwellings to be used for other uses are not widely available.
- Ineffective infrastructure. Heat recovery in particular need a short distance from producer to consumer to be viable. A solution may be to move a large consumer to the vicinity of the producer. This may have other complications.
- Transport sector not ready. With the transport sector using about 20% of the energy supply, most of the energy is spent on overcoming gravity and friction. Electric cars seems with regenerative breaking seems to be the best candidate for energy recovery. Wind systems on ships is under development. Very little work on the airline industry is known in this field.