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54 Evaluation of Opportunities for Converting Indigenous UK Wastes to Wastes and Energy AEA/ED45551/Issue 1 Currently the majority of these residues are recycled to agricultural land. The high water content makes large scale transportation unfeasible, and so utilisation for energy or fuel generation would likely be at a local scale. Dry Agricultural Residues There has been much interest in the use of dry agricultural residues for energy for some time. The UK Government (then Department of Energy) supported a significant programme in the 1980s-early 1990s to examine the potential and support demonstration projects. Two main dry agricultural residues were identified as: poultry litter and straw. Straw Straw is available from cereal and other 'combinable' crops such as oil seeds. The recent report by CSL for NNFCC gives a broad description of the straw market. 78 It is produced seasonally and is localised to arable farming areas. Straw is produced during crop harvest and often remains on the ground after the passage of stage one collection – the seed crop. It must then be collected and baled in a second handling stage. For an estimation of regional crop area potentially generating straw, by crop type and region of the UK please see Appendix 1. The three main types of straw that are available in the UK are barley, wheat and oil seed rape (OSR). It is common for barley and oat straw to be consumed almost entirely by the livestock industry as part of the winter diet with additional straw used for bedding, so this must be borne in mind when considering the following figures. Cereal straw is also used to protect some crops, such as carrots, against frost and to keep others, such as strawberries, off the ground. OSR straw is not suitable for either of these uses. Other potential industrial uses for straw are for paper-making, or in the production of industrial fibre, including constructional board manufacture. 79 Straw can also be used as a feedstock for power generation, as is the case at the EPRL Power station in Ely (see later chapter). OSR straw is popular for combustion, as it burns fiercely due to the presence of residual oilseeds. To moderate this, such straw is mixed with cereal straws to contain this volatility at lower levels. To prevent deterioration during storage, crops are generally harvested dry, i.e. moisture content below 15% and, as straw is usually harvested immediately after harvesting the associated cereal or oilseed crop, its moisture content will be around the same. During poor weather, however, the crops may be harvested at higher moisture contents, meaning the straw will be wetter, or the straw may spoil in the field, reducing that year’s yield. Straw is harvested over a short period (typically around 70 days), and for the remainder of the year storage is required. This storage may be done in Dutch barns or in stacks on the field. There will usually be some losses in dry matter during storage, mainly due to degradation of biomass. This loss is estimated to be around 10-20% of dry matter. Straw stored in the open (piles of bales in the field) can also be damaged by rainwater and the outer bales in the stack may rot and be lost. Problems can be avoided by choosing the storage sites carefully. If stored damp and under cover, some self-heating can occur – a potential fire hazard. A number of estimates for the quantity of straw available across the UK have been made, however in reality it varies from year to year, depending on the harvest and on alternative market demand for straw. Existing traditional agricultural uses such as livestock bedding and feed, animal feed compounding, crop protection and composting consume significant and varying amounts of straw each year. 80 78 National and Regional Supply/demand balance for agricultural straw in Great Britain, Copeland, J., Turley, D., Central Science Laboratory for the NNFCC, 2008. 79 ETSU New and Renewable Energy: Prospects in the UK for the 21st Century: Supporting Analysis. 80 ETSU BM/04/00056/REP/3 (1999) Energy from Biomass: summaries of the biomass projects carried out as part of the Department of Trade and Industry’s New and Renewable Energy Programme Volume 5: Straw, poultry litter and energy crops.
Evaluation of Opportunities for Converting Indigenous UK Wastes to Wastes and Energy AEA/ED45551/Issue 1 The Carbon Trust’s biomass study for 2003 estimated straw production to vary between 10 and 12 million tonnes per annum of which around 25% would be available for use in future energy solutions. 81 The Royal Commission on Environmental Pollution (RCEP) report indicated an availability of 24 million tonnes in 2002. 82 The Biomass Task Force, provided an estimate of 3-4.5 million tonnes of straw available for energy generation per annum. 83.84 The most recent report by the CSL in 2008 estimated that 60% of straw could be recovered from the field, approximately 2.75 – 4 t/ha, and of this 4.9 million tonnes would be available for non-traditional uses in Great Britain, once operational and future straw burning Power Stations had been taken into account (total straw arising 11.9 million tonnes). Most of these figures refer only to England and Wales. Work for SEERAD indicated that most of the straw in Scotland has a ready market and there is no or very little surplus in Scotland. 85 The straw arising figures below have used the assumption of 3.5 tonnes of straw produced per ha in the UK, together with an availability of 25% for non-traditional uses (such as future energy solutions and fuels) as described in the Carbon Trust report. 86 Using the above assumptions, an estimation of the straw arisings can be made, as well as the amount of straw that might be available for non-traditional uses such as energy generation and transport fuels. 81 Biomass sector review for the Carbon Trust, 2005, Paul Arwas Associates and Black & Vetch Ltd. 82 Royal Commission on Environmental Pollution, 2004, Biomass as a renewable energy source, www.rcep.org.uk/biomass/Biomass%20Report.pdf 83 According to Defra Statistics the amount of land on which cereals were harvested varied from 3,014,000 to 4,026,000 ha over the pass 20 years. As the yield of straw varies from 3-4 t/ha, this translates into a range of just over 9Mt just over 16Mt of straw produced in the UK per annum. The availability of straw for energy will then depend on the market for alternative use, but is typically about a third of the total available. See: www.defra.gov.uk/esg/publications/auk/200/3-2.xls 84 Biomass Task Force report to Government, October 2005. 85 MLURI, SAC and AEA Technology 2003 Energy from Crops in Scotland. Timber and Agricultural residues Technical Annex. 86 J Nix Farm Management Handbook, 3 rd Edition 2005. 55
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Appendix 3 MBT Methods Specific in
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Figure 27 Orchid Environmental proc
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