Technological Advances in CHP

Stirling engines

The Stirling Engine is an external combustion device and therefore differs substantially from conventional combustion plant where the fuel burns inside the machine. Heat is supplied to the Stirling engine by an external source, such as burning gas, and this makes a working fluid, e.g. helium, expand and cause one of the two pistons to move inside a cylinder. The Stirling engine has fewer moving parts than conventional engines, and no valves, tappets, fuel injectors or spark ignition systems. It is therefore quieter than normal engines.

Stirling engines also require little maintenance and emissions of particulates, nitrogen oxides, and unburned hydrocarbons are low. The efficiency of these machines is potentially greater than that of internal combustion or gas turbine devices.

There is a more that 60 years experience with this technology, what is newer is its use for micro-cogeneration boilers. For this type of boilers, there is a need for small engines with a capacity between 0.2 and 4 kWe. Gas turbines and even gas engines are unsuited for this kind of size (although the current smallest spark-ignition engine is 3 kWe), while the Stirling engine offers a good alternative.

The advantages of the Stirling engine are: less moving parts with low friction, no need for an extra boiler, no internal burner chamber, high theoretical efficiency and very well suited for mass production. The external burner allows a very clean exhaust and gives the possibility of controlling the electrical output of the engine by reducing the temperature of the hot side. So there is the possibility of varying the electricity production regardless of the need for thermal heat demand.

CHP Microturbines

Microturbines are smaller than conventional reciprocating engines, and capital and maintenance costs are lower. There are environmental advantages, including low NOx emissions of 10-25 ppm or lower. Microturbines can be used as a distributed generation resource for power producers and consumers, including industrial, commercial and, in the future, even residential users of electricity. Significant opportunities exist in five key applications:

• Traditional cogeneration,
• Generation using waste and biofuels,
• Backup power,
• Remote Power for those with ‘Black Start’ capability,
• Peak Shaving.

Fuel Cells

Fuel cells convert the chemical energy of hydrogen and oxygen directly into electricity without combustion and mechanical work such as in turbines or engines. In fuel cells, the fuel and oxidant (air) are continuously fed to the cell. All fuel cells are based on the oxidation of hydrogen. The hydrogen used as fuel can be derived from a variety of sources, including natural gas, propane, coal and renewables such as biomass, or, through electrolysis, wind and solar energy.

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© Irish CHP Association. Last Updated: Fri 13 May 2005.