Large-scale combustion of solid fuels for combined heat and power production
The simultaneous generation of electricity and heat is called cogeneration or combined heat and power (CHP). In contrast to thermal power plants, CHP uses the waste heat, which is emitted during electricity generation, and therefore increases the efficiency of the process up to over 80 %.
Construction of a CHP plant
The following components are required for the conversion of chemically stored fuel energy into useable electrical energy and heat:
- Fuel treatment (fuel filter, gasifier, …)
- Engine for the conversion of chemically stored energy into kinetic energy and heat (combustion engine, gas turbine, steam engine, stirling engine, …)
- Generator for converting kinetic energy into electrical energy and heat (not needed in case of fuel cells, where fuel is directly converted to electrical energy)
- Heat exchanger systems for recovering heat energy (from the engine heat loss, oil circulation, exhaust gas, …)
- Various electrical switchgear assemblies and control devices for current distribution and motor management
- Hydraulic equipment for heat distribution
There are various processes for the production of power and heat from biomass. Examples include biomass gasification (fixed-bed or fluidized-bed gasification), biomass combustion, and utilization of biogas from anaerobic digestion.
An excerpt of technologies is mentioned below.
- Combustion engine – This technology is state of the art. The combustion engine can be operated with biogas or syngas . Fixed-bed gasifiers, which gasify the solid biomass and use this gas for the process, are also available.
- Organic Rankine Cycle – Currently, this is used mainly for plants larger than 400kWel, but there are also experiments with smaller ones. For this process, solid biomass can be used.
- Steam turbine – This technology is also state of the art and can use solid biomass. It is used for systems with a performance range starting at 1MWel.
- Stirling engine – This technology can also use solid biomass for the process. Stirling engines are more suitable for smaller plants between 0,6 and 35kWel.
- Hot air turbines – These can also be operated with solid biomass. The hot air turbine is indirectly fired.
It is also possible to use solid biomass in the following processes: reciprocating engine, screw-type steam engine, thermoelectric generator etc. These are, however, still in the demonstration stage.
The inverse gas turbine and the micro gas turbine can be operated with biogas. It can also operate on syngas, but this is still under research.
Theoretically, a fuel cell can also be operated with purified biogas, but with current technologies this is not economical.