Ian Gaunt, Associate Director at Gravis, explains what biomass is, how it differs from biofuels, and walks us through the processes used to generate energy from organic materials. He also covers the impact of biomass on the renewable energy landscape, discussing both the advantages and the challenges, and highlights Gravis' pioneering role in biomass gasification and anaerobic digestion technologies in the UK. You can watch the full video below, or read more about this below.

Biomass is a general term we use to describe any organic matter that can be used as a fuel, such as plants, animals, or waste. Typically, biomass power stations burn a variety of fuels from virgin or waste wood, straw, energy crops such as miscanthus, or indeed food processing residues such as olive pellets or oat husks.

Put simply, biomass is the term given to the organic raw material which can be used directly in power plants, or alternatively be subject to additional processing and used to produce biofuels. Biofuels are usually in liquid form and are typically used in transportation as a renewable additive to fossil derived liquid fuels such as petrol or diesel. Because they have been subject to processing, biofuels tend to have a higher energy content than biomass.

Most biomass power plants use the biomass in a similar way as coal or oil is used in a fossil fired power station. The biomass is burned as a fuel in a boiler which raises high pressure and high temperature steam which is then passed through a steam turbine. The turbine drives a generator from which electricity is produced.

Some biomass power plants may allow the biomass to decompose first, releasing biogas which is then combusted.

Alternatively, some biomass can be partially heated under oxygen depleted atmospheres and instead produce a synthetic gas which again can be combusted to raise steam. Such gasification processes can produce different residual fractions that could be used in the development of biofuels and/or renewable plastics.

Around 41.8% of our electrical generation in the UK is from renewable sources of which ~14% is biomass. Worldwide, biomass accounts for ~6% of global energy supply.

For Virgin biomass, the advantages focus on the principles of the carbon cycle; that is to say the CO2 that is released as a product of combustion in the process is reabsorbed by biomass vegetation through photosynthesis prior to being harvested and then used back in the power station. As a result, biomass power plants are largely carbon neutral.

For recycled or waste biomass, then the principle is more one of preventing that biomass decomposing and releasing methane directly to atmosphere. It should be remembered that Methane is a greenhouse gas which is more than 28 times as potent as carbon dioxide. Instead the waste biomass is used either directly through combustion or indirectly by first harvesting the methane and then combusting in a boiler or internal combustion engine.

Virgin biomass sourced in the UK has stringent sustainability criteria that it must satisfy to safeguard biodiversity, sustainable forestry and arable land use. Proof of appropriate licencing and membership of Quality Assurance programmes such as “Red Tractor” or the Forestry Commission is a prerequisite when purchasing biomass for electricity production.

Biomass, unlike other renewable sources of power, can be available 24/7 and is not reliant on when the wind blows or when the sun shines. It is the technology most closely comparable with fossil fuelled power stations and, as such, is most suited to the requirements of the electrical grid network.

Ultimately, biomass plants still emit carbon dioxide, all be it as part of the carbon cycle in which this carbon is absorbed by growing vegetation such as trees or crops. To safeguard the neutrality of these emissions, such crops harvested for use in the power station must be replaced and allowed to grow before being harvested again for use. In some plantations around the world, the time scales between respective harvesting can be decades and therefore the actual carbon neutrality of large scale biomass use has been questioned.

Biomass is also a fuel that comes at a cost. Whereas the wind and sunshine are “free” at the point of use, biomass needs to be purchased so has a greater marginal cost and a requirement for a mature and reliable supply chain.

Some crops are grown and harvested specifically for energy use. The early adoption of some otherwise edible crops for processing into biofuels has been contentious where the demands for feeding populations were at odds with demands for carbon neutral liquid fuels. The second generation of biofuels however, are utilising other sources such as household waste or seeking to combine hydrogen and carbon dioxide to form complex hydrocarbon fuels which are no longer reliant on edible crops as feedstock.

In the UK, generation from biomass is a mature technology which has cross over applications in the Energy from Waste field. Waste wood gasifiers built over the last decade have pioneered the development of pyrolysis applied to domestic and commercial waste streams, providing heat and waste fractions that can be refined to produce bio chars and liquid fuels.

While the sustained and continuous operation of these plants has its challenges, such issues are not insurmountable and has great potential for the future. Similarly the refinement of the anaerobic digestion (AD) process can readily lend itself to the capture of carbon dioxide for use in local industries whose organic waste products can form part of the AD feedstock, thereby promoting a circular economy.

Opportunities are also available to retrofit carbon capture technologies to existing and future biomass power plants such that they become net negative emitters of carbon dioxide. However, such opportunities are going to be restricted by the access to appropriate carbon dioxide transmission and sequestration pipeline infrastructure, currently identified along the Firth of Forth, Tees, Humber, Mersey and Dee estuaries.

Gravis was a first mover in biomass gasification technology in the UK, with its interests in Birmingham Bio Power. This plant uses four gasifier units fed with up to 72,000 tonnes of waste wood per year sourced from the West Midlands, and has been operational since 2016.

Gravis also lends against waste wood projects in Widnes and Northern Ireland that use a more traditional moving or vibrating grate boiler and steam turbine power island.

We also have portfolios of smaller AD plants in Scotland and Northern Island where we are looking to retrofit carbon capture technology to grow an alternative industrial CO2 income stream.

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