How It Works

The process used to convert biomass into heat and energy depends on its source. The most common processes for achieving this are outlined below:

Combustion

Biomass combustion systems burn biomass in specially designed, high-efficiency boilers, furnaces or wood stoves. 

This is one of the most common ways for using biomass. Under this system, the biomass is used on its own or by co-firing it with fossil fuels in power stations. This reduces greenhouse gas emissions by replacing a component of the fossil fuel required.

Suitable biomass - woody biomass (including cardboard, wood chips, pellets, forest products, straw) and animal waste).

Output - heat, electricity.

Anaerobic digestion (AD) 

Anaerobic digestion (AD) is used to convert biomass into biogas, which is suitable for energy production. The digestion process takes place in a warmed, sealed airless container which creates the perfect conditions for decomposition.

In the absence of oxygen, natural bacteria break down the biomass, which is fed into a digester, either continuously or in batches. 

There are two basic AD processes, which take place over different temperature ranges:

  • Mesophilic digestion takes place between 20ºC and 40ºC and typically takes between 15 days and a month to complete.
  • Thermophilic digestion takes place from 50-65ºC and is significantly faster, usually completing within 14 days. 

Suitable biomass - slurry, animal manure, wastewater.

Output - the process generates three main products:

  • Biogas - a mixture of carbon dioxide (CO2) and methane (CH4), which can be burnt to generate heat and/or electricity.
  • Fibre - for use as a nutrient-rich soil conditioner
  • Liquor - for use as liquid fertiliser

Fermentation

Fermentation is another anaerobic process. It occurs when anaerobic digestion converts sugars into ethanol using micro-organisms, usually yeast.

Suitable biomass - sugar cane or beet is the most efficient source but potatoes, corn, wheat and barley can also be used.

Output - bioethanol, which can be used as a transport fuel by mixing it with petrol or using it directly in a modified combustion engine.

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