Biomass plant – how it works

A biomass-fired power plant produces electricity and heat by burning biomass in a boiler. The most common types of boilers are hot water boilers and steam boilers.

Wood chips, residues and other types of biomass are used in the boilers, in the same way as coal, natural gas and oil.

Co-firing biomass with coal

Co-firing biomass with coal (replacing a portion of coal with biomass) is an effective method of using biomass for energy purposes and to reduce CO2 emissions. Coal plants can be made suitable to replace part of the coal by biomass or even to convert fully to biomass – turning a coal plant into a 100% renewable energy plant.

Biomass for electricity generation

Forest productsWoody biomass from multi-functional forests constitutes the majority of today's biomass.  Pellets and briquettes are manufactured by compressing by-products from the forestry industry, such as sawdust, bark or small diameter roundwood.  They are easy to transport, and therefore suitable for export.

Waste, by-products and residues – Residues include manure, sewage, sludge and other degradable waste. Liquid biomass waste, such as manure, household waste and sewage plant residues, can be digested to biogas.

Energy crops - Energy crops are not used on a large scale for electricty or heat production today. As demand for sustainable biomass increases over time such energy crops may play a more important role in the future. Examples include woody short rotation forestry/crops such as eucalyptus, poplar and willow. But also herbaceous (grassy) energy crops such as miscanthus can be used. Especially with the use of energy crops it is important to ensure these plantations are established and managed in a sustainable manner. 

Carbon neutrality

Carbon dioxide is emitted into the atmosphere when biomass is burned, in the same way as when fossil fuels are burned. But when biomass grows it binds carbon dioxide through photosynthesis.

The carbon dioxide released through biomass combustion is captured by growing biomass. Properly managed biomass is therefore carbon neutral over time. 

There is currently a debate on the time period within which biomass is truly carbon neutral. Vattenfall is of the opinion that biomass can and must make a meaningful contribution to the goal of limiting global warming to a maximum of two degrees.

As such Vattenfall actively contributes to the debate on the carbon neutrality of different biomass types and is also directly involved in the definition of criteria that ensure timely carbon neutrality; for example in the Netherlands where sustainability criteria for biomass are defined that include criteria that ensure such timely carbon neutrality. 

Biomass - a short CO2 cyclus

1. Trees take up CO2.
2. Wood residues are chipped.
3. CO2 is released during combustion in the power plant.
4. Trees take up CO2 and so on.

Enlarged illustration

Biomass typically leads to more than 80% CO2 emission reductions

Biomass production, processing and transport leads to CO2 emissions in the supply chain. Vattenfall monitors these emissions and the biomass we use typically leads to more than 80% CO2 emission reductions. This also holds true for imported biomass.

Sea transport by ship is extremely efficient and wood pellets imported from North America achieve more than 80% emission reductions on average when compared to coal. Vattenfall is a member of the Sustainable Biomass Partnership that develops and implements standards and tools to ensure the sustainability of imported biomass. This includes a detailled standard for the CO2 emission savings of the biomass we import, which includes the emissions of all stages in the supply chain.

The generation of electricity with biomass produces flue gases that must be cleaned before they are emitted into the atmosphere. This is done by utilising well-developed techniques such as flue gas washing and particulate filters.

CO2-emissions biomass pellets over the entire chain

Enlarged illustration

CO2 emissions from coal have been set at 100. This makes it easier to compare CO2 emissions from various energy sources. The figures are indicative; the exact figures depend on the characteristics of the chain.

The figures are based on scientifically accepted sources. The biomass pellets are assumed to come from the USA, and the wood chips are assumed to come from the local region.

Biomass becomes electricity and heat

Enlarged illustration

Fuel is stored in a bunker for a further transport to the boiler. In the boiler, water is heated to high temperature under pressure. Steam from the boiler powers the turbine, which is connected to the generator. Steam that has passed through the turbine heats district heating water, which is distributed through the district heating network's piping.

Last updated: 2016-08-24 16:18