Introduction to biomass
What is bioenergy?
Bioenergy is the energy contained in "Biomass". Biomass means any plant-derived organic matter available on a renewable basis.
Why is biomass a renewable source of energy?
The capture of solar energy as fixed carbon via photosynthesis is the key initial step in the biomass growing:
Burning biomass returns the CO2 that was absorbed as the plants grew to the atmosphere. There is "no net release of CO2" if the cycle of growth and harvest is sustained.
How is biomass used to create energy?
Biomass energy systems can be based on a wide range of feedstock. They use many different conversion technologies to produce solid, liquid and gaseous fuels. These can then be used to provide heat, electricity and fuels to power vehicles; using burners, boilers, generators, internal combustion engines, turbines or fuel cells.
Power can be generated by:
- co-firing a small portion of biomass on existing power plants;
- burning biomass in conventional steam boilers;
- biomass gasification; and
- anaerobic digestion.
Heat. The same power plants that produce power also yield useful steam and heat in combined heat and power (CHP). Biomass can be used in fireplaces and kilns to heat homes and at a bigger scale for "district heating".
Fuel. Unlike other renewable energy sources, biomass can be converted directly into liquid fuels for transport. The two most common biofuels are ethanol and biodiesel.
What are the main forms of biomass used for energy production?
Biomass includes the biodegradable fraction of products, waste and residues from agriculture (including vegetal and animal substances), forestry and related industries, as well as the biodegradable fraction of industrial and municipal waste
The main biomass sources in use for energy production are: forest residues, agricultural residues, pulp and paper operation residues, animal waste, landfill gas and energy crops.
Overview of the technology
Various aspects of the technology and its applications
Many of the techniques employed for exploiting biomass have been used for a number of years (e.g. stokers for combustion) while others are only just being tested and demonstrated (e.g. gasification). Others appear to have good potential for becoming conceivable future techniques, although they have not yet been fully tested (e.g. ethanol from lignocellulose).
The techniques of greatest current interest are:
- Direct combustion in boilers
- Advanced thermal conversion of biomass into a secondary fuel by thermal gasification or pyrolysis, followed by use of the fuel in an engine, turbine or fuel cell.
- Biological conversion into methane by anaerobic bacterial digestion
- Thermochemical or biochemical conversion of organic material into hydrogen, methanol, ethanol or diesel fuel.
In summary, different technologies can be applied to biomass to generate the commodities tabulated below.
|Anaerobic digestion||fuel gas||boiler, gas engine gas turbine, fuel cell||heat power/heat|
|Fermentation extraction||liquids||oil burners, liquid motor fuels, fuel cells||power/heat transport|
|Combustion||hot exhaust gas||boiler/steam engine||space heating, process heat, hot water, power/heat|
|Gasification||fuel gas||boiler, gas engine gas turbine, fuel cell||heat power/heat|
| ||synthesis gas||synthetic natural gas, liquid motor fuels, chemicals, heat||heat, transport|
| ||Liquids (fuel oil) char (solid fuel) boiler engine|| ||power/heat|
Although all these technologies are used in Europe, not all are fully developed. A number of obstacles must be overcome before the technology can advance to the stage in which it can be developed commercially.