Biomass

An NBS section on solid fuel boilers, was published as part of NBS Engineering Services update 7. Technical author Brian Ware is hot on the topic of alternative fuels.

Section T24 (Solid fuel boilers) gives specifiers a choice of fuel sources – conventional solid fuels such as coal, or alternative fuels such as biomass. Existing sections T20 (Gas and oil fired boilers) and T25 (Combined heat and power units) are being updated to also include alternative fuels, such as biogas and biofuel.

The use of fossil fuels to power homes and businesses is a major cause of climate change, which is a real threat to our future. These fuels are also non-renewable. Renewable carbon-neutral energy, combined with energy efficiency, offers a sustainable solution to countering the effects of global warming and to meeting energy needs in the long term.

What is biomass?

Biomass, also known as biofuel or bioenergy, is obtained from organic matter, either directly from plants or indirectly from certain industrial, commercial, domestic and agricultural waste products.

Because the carbon dioxide released during the generation of energy is balanced by that absorbed by plants during their growth, the use of biomass is generally classed as ‘carbon-neutral’. There are three main groups of biomass:

Dependent resources: These are the waste products generated from agricultural, industrial and commercial processes. Included are forest products, waste wood, straw, slurry, chicken litter and industrial and municipal wastes (such as food processing wastes). For every tonne of wheat that is harvested, a certain amount of ‘waste’ straw is created, and for every tree felled for furniture production, a certain percentage cannot be used. These can serve as biomass.
Dedicated energy crops: These are short-rotation crops, such as coppice (willow and poplar) and miscanthus (elephant grass) which are specifically grown to generate biomass.
Multi-functional crops: These are crops that can be used to create different types of energy, e.g. the ears of wheat can be used to create biofuel (bioethanol and biodiesel), while straw can be used in electricity generation as biomass.

Biomass fuelled systems for buildings

Energy can be produced from woody biomass sources (including forest products, waste wood, straw, and cardboard) by combustion, which can be used as a heat source for log fires, domestic stoves, hot water system boilers and large commercial installation boilers. Boilers fuelled by woody biomass can help reduce waste removal costs in industrial or agricultural use when the biomass is consumed at source.

For domestic and small commercial installations, pellet fuelled boilers are attractive as they can incorporate an integral hopper that is topped up daily with the fuel fed automatically into the combustion chamber. A store is used for larger installations with an auger drive feed to supply the pellets to the boiler. Domestic and small commercial boilers are often designed so they can burn both pellets and chips.

Biomass boilers can replace conventional boilers. They do however rely on a reliable source of fuel.

Other applications

Many of the prominent biomass projects in the UK have been community heating schemes or local authority projects where a biomass heat source has been used to provide both heating and hot water. Biomass can be used on its own or can be co-fired with fossil fuels in power stations, reducing greenhouse gas emissions. Likely areas for development are smaller-scale regional energy projects, and the promotion of energy crops such as short-rotation coppice.

Grants

The UK government has set a target of 10% of the UK’s energy demand to be provided from renewable sources by 2010. Launched on 1 April 2006, phase one of the DTI’s low carbon buildings programme (www.lowcarbonbuildings.org.uk/home/) will run over three years and replaces the previous DTI Clear Skies grant programme. Open to householders, public, not for profit and commercial organisations across the UK (except the Channel Islands and the Isle of Man), it provides grants for microgeneration.

The Scottish Executive has funded the Scottish Community and Household Renewables Initiative (SCHRI) (www.energysavingtrust.org.uk/schri) which operates in a similar manner to the UK wide DTI scheme.

In Northern Ireland the Energy Saving Trust (NI) operates a similar scheme to the DTI scheme. However, schemes cannot receive grant funding from both the SCHRI or the Energy Saving Trust (NI) and the Low carbon buildings programme.

Conclusion

Biomass can make a significant contribution to future UK heat and energy generation, although the development of some forms of biomass may be constrained by limited resources. There is the potential for many biomass feedstocks to be grown on a larger scale within the UK. In some cases, crop yields will need to be improved before the process becomes economic.

The appropriate use of biomass to fuel part of our future is seen by most to be an effective means of reducing global warming.

Amended July 2007