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Combined Heat and Power (CHP), also known as cogeneration, is the method of recycling energy that would otherwise be wasted in order to produce electricity and supply heat from a single heat source simultaneously.
How does CHP work? The system utilizes what is called 'cascade energy', which describes the transfer of energy from electricity generation at the top, to thermal output at the bottom. A significant amount of energy is lost as energy 'descends' in this manner, and CHP aims to recover that lost energy and use it to meet on-site thermal energy needs - for example, district heating, steam and hot water supply, process heating, etc. In a conventional thermal plant, this part of heat energy would otherwise be wasted.
CHP works well with facilities plants that generate biomass (i.e., living or recently dead plant matter such as trees, wood chips, chemicals, animal waste), like food processing facilities and pulp and paper mills. It takes a lot of energy to properly burn and thereby dispose of biomass at these sites, and CHP captures the heat energy that is a byproduct of these energy-intensive processes. CHP also works in places that have their own on-site thermal load, often required to heat water and produce steam.
Not only does CHP capture what would otherwise be wasted energy; it also avoids transmission and distribution losses associated with conventional thermal plants that transport energy from long distances. This is because CHP systems are designed to meet the local energy demand (with energy captured from local processes), thereby alleviating the need to transmit energy across long distances. With energy transmission and distribution losses significantly reduced thanks to the CHP process, the overall efficiency of the CHP system can reach up to 90 percent, compared with 50 percent for the best conventional thermal power plants.
CHP system application is site-specific and are most commonly installed at relatively small scale (less than 50 MW) at facilities with steady thermal loads. Ideal sites for CHP applications include pulp and paper mills, chemicals and food processing industries, which need power and heat on a daily basis; and hospitals, universities and other institutional facilities which regularly need both electricity and thermal loads. With potential increases in fuel prices - and the fact that CHP is compatible with virtually any kind of energy source, fossil and non-fossil fuel – CHP systems are becoming more attractive and widespread in facilities seeking to reduce energy consumption and reduce CO2 emissions.
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