Biomass Gasification in the UK—Where are we Now?
Biomass can be thermally converted into energy by a variety of methods. The main three ways are combustion, pyrolysis and gasification. Gasification is a thermochemical conversion process that reacts carbon-based materials at high temperatures (800-1,200 degrees Celsius) with a limited amount of oxygen, air and/or steam. The reaction yields a combustible gas, mainly comprised of carbon monoxide and hydrogen. This gas can be used to generate heat and power or converted into a number of useful products, including fuels such as ethanol, synthetic diesel or jet fuel; and chemicals such as methanol or synthetic lubricants.
The gasification process itself can be either autothermal or allothermal. In autothermal gasifiers, the energy necessary for gasification is provided within the gasifier by partial combustion. Allothermal gasifiers are externally heated, for example by electricity in the case of plasma gasifiers or via heated bed material. The type of gasifier used will depend on the input feedstock, its characteristics and the required end use.
Gasification is capable of converting a wide range of sustainable and low-cost feedstocks into energy. In countries with low-population densities and high resources this might be wood or energy crops, but in the U.K. it is more likely we will see novel forms of biomass being used in gasification, such as leftover food and municipal solid waste (MSW).
Market Development in the U.K.
Over the past 10 years, investment in biomass gasification in the U.K. has been small, particularly in comparison to countries such as Sweden, Germany and the U.S. Project Arable Biomass Renewable Energy (ARBRE)—built near Eggborough (Northeast England) in 2001—was among the first of its kind in the U.K., producing energy from gasified biomass. The plant cost £30 million ($48 million) but closed after only eight days of operation never to reopen. The closure of the project left nearly 50 local farmers without a market to sell their biomass, having planted 1,500 hectares (3,700 acres) of short-rotation coppice willow. However, ARBRE’s failure was less a result of the gasification technology, and more due to a change in the commercial strategy of the projects parent company and bankruptcy of the turnkey contractor appointed to oversee the project.
Now nearly 10 years after the doors closed at ARBRE, gasification is undergoing something of a renaissance in the U.K. New technologies are allowing a variety of different feedstocks to be used and end products to be produced.
Current Research and Development
The U.K. has a growing research and development network for biomass gasification (Figure 1). Universities—Newcastle, Leeds, Cranfield and UCL—are playing an important role in the design of advanced gasification systems, particularly with a view to tackling some of the more traditional problems associated with biomass gasification of ash clinker and tar production.
Much of the primary research and development on gasification has involved using wood as the feedstock, because in most parts of the world it is the largest source of biomass. However, the U.K. is unique in that it has a comparatively small and localized wood resource but a high population density. As a result, waste is often a more readily available feedstock for gasification than wood.
The U.K. produces more than 17 million metric tons (18 million tons) of MSW each year, compared to just 4.6 million metric tons of surplus wood. Recovering the energy stored in MSW will help tackle the dual problems of climate change and constraints on landfill space; by 2015 the U.K. must reduce the amount of waste sent to landfills to less than 35 percent of that sent in 1995. This has led to technology providers developing novel processes for converting waste to energy, although most are currently at the planning or demonstration scale.
Commercial Production of Energy and Fuels from Biomass
New biomass gasification projects are emerging across the U.K., highlighting the growing interest in the technology as a mechanism for creating fuel and energy from renewable sources. This includes energy-from-waste projects, which use the renewable (biogenic) and nonrenewable parts of the feedstock, as well as plants using traditional sources of biomass or utilizing the biogenic fraction of MSW by advanced separation.
For example, in Newport on the Isle of Wight, Energos Ltd. has been operating its commercial gasification plant since 2009. The plant is designed to run on 30,000 metric tons of fuel annually, produced from 60,000 to 70,000 metric tons of MSW. The technology generates more than 2 megawatts of electricity, enough to power up to 3,000 homes.
Elsewhere, Ineos Bio plans to produce renewable energy and bioethanol, via gasification and fermentation, using prepared biomass waste (Figure 2). Its commercial-scale biorefinery (planned for construction on Teesside, England) is due to be operational by 2012. Approximately 50 percent of the input energy is expected to be recovered, mainly as ethanol with some electricity being exported to the National Grid.
At a site near London, British Airways and U.S. bioenergy group, Solena, are planning to produce jet fuel from gasified waste. Eventually, BA hopes the project will produce at least half of the airline's fuel needs for its London City Airport operations.
Biossence has been granted planning permission to develop the East London Sustainable Energy Facility. This facility will gasify local waste left after recycling into renewable electricity, at efficiencies of 35 to 40 percent. Eventually ELSEF hopes to produce enough energy to power about 10,000 homes a year.
Together these projects, among others, will leapfrog the U.K. into a world-leading position with respect to the advanced gasification of biomass. Challenges remain before this can be achieved, however, including securing finance for projects and developing strong and sustainable feedstock supply chains.
Author: Matthew Aylott
Staff Writer, U.K. National Non-Food Crops Centre