Application to the home

The issues to considered when planning to install a biomass boiler include

• supply and storage– biomass is not piped into buildings and has a lower energy density than oil for heating so it is necessary to find space for fuel storage
• fuel quality must be considered when planning the system and purchasing fuel
• domestic boilers are larger than their fossil fuel equivalents

Sources

The list of biomass sources includes:

Wood

• firewood, logs or wood prepared for burning in a stove or fireplace,
• wastes and by-products of forest industry, bark, sawdust and shavings, wood chips, trimmings and other tree logging remains,
• energy crops: the common willow, poplar

Straw and farming wastes

• straw from corn, oil plants (rape) and leguminous plants
• harvest waste, shells from coconuts, remains of corn cobs
• wastes and by-products of the processing industry, remains after processing sugar cane

Wood briquette is produced from fragmented timber wastes such as sawdust, shavings or wood chips, which are compressed under high pressure. Thanks to its low moisture content, the fuel value of briquette is higher than that of wood. Also, due to high density relative to volume, the process of combustion proceeds slowly and gradually.

Pellets In the EU, production of granulate obtained from timber wastes have risen several fold in recent years. Pellets have been used for heating public buildings and households for many years and the industry is most advanced in Sweden and Austria which have large areas that are forested.

Pellets are manufactured from timber wastes produced in sawmills and timber processing companies, as well as from forest timber wastes. The most common wastes are sawdust and wood shavings. Technically, it is also possible to produce pellets from bark, wood chips, energy crops and straw.

Energy crops There is limited possibility of utilising forest firewood, waste timber from timber industry or straw from farming. As a result, in order to increase the amount of biomass used for energy purposes, it may be necessary to establish energy crop plantations.

Energy crops are characterised by a high annual growth rate, high fuel value, high resistance to diseases and pests and relatively low soil requirements. It is crucial to mechanise the agro-technical actions involved in setting up a plantation and crop harvesting. Energy crops can be harvested every two to three years on average for a period of 15-20 years before rotating with other crops.

Conversion of biomass to energy

Combustion is used to generate the most widespread and simplest method of acquiring energy from biomass. The process of burning generates up to 90% of energy obtained worldwide from biomass. Biomass in all states of aggregation is suitable for direct combustion.

Fuel values of biomass products are lower than those of conventional fuels and are as follows:

• yellow straw 14.5 MJ/kg
• grey straw 15.2 MJ/kg
• waste timber 13 MJ/kg
  Compared with
• hard coal 25 MJ/kg
• natural gas 48 MJ/kg

Environmental impact

Biomass is important for a variety of reasons

• not harmful to the environment: the amount of carbon dioxide released to the atmosphere during its combustion is compensated by the same amount of carbon dioxide absorbed by plants during photosynthesis
• release of sulphur dioxide and nitrogen oxides (the underlying factors causing acid rain) are lower than in the case of fossil fuels
• heating with biomass is becoming more cost-effective, as biomass prices are becoming more competitive on the fuel market. Also, using biomass allows for wasteland management and refuse utilisation.

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