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What is CHP? How Combined Heat and Power Systems Work

by chris@pkwydigital.com 2. October 2018 06:26

CHP, or combined heat and power, is a method of electricity generation that captures and uses the heat byproduct naturally released when electricity is generated from fuel. CHP systems are an on-site generation technology most often used to power industrial complexes. This technology is also called cogeneration because while electricity is generated, usable heat is simultaneously generated and captured.

In traditional power generation setups, necessary electricity and heat are generated and transported separately. Heat left over from generating electricity is allowed to escape in these systems, leading to an inefficient use of fuel. The average fossil-fueled US power plant operates at 33% efficiency and producing electricity and heat separately is typically 45% efficient. In comparison, capturing and using the byproduct of heat in CHP systems allows them to boast 60 to 80% efficiency.

Fuel efficiency reduces the cost of power for organizations that opt to use CHP for part or all of their power needs. This also makes the technology more environmentally friendly than other power generation methods.

Not only is fuel consumed more efficiently because both electricity and heat are used, but because CHP systems are built on-site. This lessens the distance power needs to travel before it’s used. As an on-site generation technology, CHP reduces (or even eliminates, in some cases) reliance on the aging power grid. Businesses in many industries are drawn to this benefit, including manufacturers, hospitals, housing complexes and retailers.

Like other alternative electricity generation methods, excess power from CHP can be sold back to the grid.

How CHP Systems Work

In their most basic form, combined heat and power systems are comprised of a prime mover, generator and heat recovery mechanism, as well as electrical interconnection with the building(s) powered. Common CHP prime movers, or power sources, include:

  • Steam turbine: Like in many traditional power plants, pressurized water is heated to steam using fuel.
  • Reciprocating engine: A combination of fuel combustion and piston action powers the generator.
  • Combustion (gas) turbine: Compressed air and fuel are combined, similar to how airplanes are powered.
  • Microturbine: Smaller industrial and even residential systems often use a modified gas turbine.
  • Fuel cell: Urban CHP systems may choose this oxygen and hydrogen-powered method because it operates silently.

The prime mover is often powered by natural gas, a fuel with costs predicted to remain stable in the coming years. This protects businesses from fluctuating electricity costs, which are often a challenge for organizations completely reliant on the power grid. Cogeneration can also be designed with fuel switching capabilities. Other fuel options include biogas, coal and biomass, which is especially attractive in agriculture.

Heat is captured from both the fuel exhaust and engine jacket in most CHP setups. The system can also be integrated with industrial processes, so heat released by the process is recovered as well. The heat released from the fuel and engine are used in the form of steam or hot water. Steam may first power a steam turbine in order to further increase the amount of electricity produced by the system. All remaining thermal power is used for space heating, cooling, domestic hot water and industrial processes.

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