Biomass CHP
Biomass combined heat and power (CHP)
CHP (also referred as cogeneration) is the combined generation of heat and electricity in a single, integrated system and from a single primary energy source. When biomass is used as the energy source, the process is regarded as biomass CHP.
Grate combustion and fluidized bed combustion technologies are the major combustion technologies. Grate combustion is the traditional technology for burning solid fuels. Grates are still widely used for both hot water boilers and steam production in small-scale plants. Fluidized bed combustion is increasingly being used for biomass CHP plants.
Usually, the combustion boiler raises steam for power generation in a turbo-generator, while the waste heat is recovered for producing hot water or raising low pressure steam.
New technologies are being developed for biomass CHP systems. Gasification technologies for biomass CHP production have been researched intensively. Stirling engine, organic Rankin cycle, air bottoming cycle, evaporative gas turbine, externally-fired gas turbine, pulverized wood-fired gas turbine, powdered fuel combustion engine are technologies being tried.
Large biomass power generation systems can have comparable efficiencies to fossil fuel systems, but the costs are higher due to the special design of the boilers to facilitate combustion of biomass. CHP systems have much higher overall efficiency than systems generating electricity alone. Conventional power plants usually have an efficiency of around 35%. When the waste heat is recovered in a CHP system, the overall efficiency can reach as higher as 80%.
The economics of a biomass CHP system depends on the availability of fuel, the technology used and the efficiency of the plant, and the demand for heat and power. The cost for collecting and pre-treating biomass and distributing the heat and power generated will add cost to the overall system. Therefore, biomass CHP is viable where there is a sufficient supply of feedstock in the vicinity and there is a local demand for the heat and electricity.
