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142 Evaluation of Opportunities for Converting Indigenous UK Wastes to Wastes and Energy AEA/ED45551/Issue 1 Current key topics for research are the improvement of the organisms used in the process to improve yields and efficiency and the combination of several processes in the same unit operation to reduce capital costs. Current plans in the USA indicate that one of the most promising configurations for a demonstration will be to install the hydrolysis stages on a corn ethanol site to process the maize harvesting residue. Scale of operation – Regional The reliance on clean feedstock would suggest that this would be a regional technology drawing from agricultural residues such as straw and chipped wood fuels. The low bulk densities would tend to reduce the economic transport radius. However the process involves complex process engineering which responds well to the economies of scale. Hydrolysis feed stocks Feed stocks for hydrolysis based processes need to be clean waste, virgin wood or agricultural residues. The microbial fermentation is susceptible to poisoning if contaminated waste biomass is used as a feedstock. Table 72 The suitability of feedstocks for hydrolysis processes SRF Waste Wood Clean Wood Domestic Pellet Industrial Pellet Unsorted Waste Wet Wastes Agricultural Residues T C Fuels – Thermochemical Fuels A contrary view on the necessity for clean feedstocks is taken by Aquegen who propose using MSW fractions at their installation to be built in the UK at South Milford in West Yorkshire. The chemical process appears to be acid hydrolysis of the cellulose and hemi cellulose but the impact on the fermentation stage is unclear and operating data is scarce. UK Biomass to Ethanol Plant Mytum and Selby have planning permission for the creation of a biomass to ethanol facility at South Milford in West Yorkshire, as a joint venture with AqueGen. The intended site will be capable of processing 400,000 tonnes of waste food, ABP (Animal By Product) and liquids into 100 million litres of alcohol each year. It is hoped that the site will be operational by 2011. 274 Table 73 Risks Associated with Ethanol from lignocellulose waste Level of Risk Comment Technical High The technology remains innovative with only small demonstration and pilot projects built so far. Feedstocks are currently limited to clean wood and agricultural residues. Contamination from other sources could damage the fermentation process. Social & Planning Medium Process should be no more difficult to implement than a biomass power plant. Implementation is likely to be on an existing grain ethanol site Financial High The combination of expensive processing and the need for good quality feedstock means that product will be more expensive than imported ethanol for some time. Plant economics will be sensitive to price competition for feedstock and competition from improved cane sugar ethanol processes for final product. This may make it T C Fuels
Evaluation of Opportunities for Converting Indigenous UK Wastes to Wastes and Energy AEA/ED45551/Issue 1 Level of Risk Comment unsuitable for use in the UK. Regulatory Medium Would require additional subsidy from Renewable transport fuels obligation. 9.4 Conclusions for Biological Processes Biological processes for waste include anaerobic digestion for the production of methane fuel gas and the hydrolysis and subsequent fermentation to ethanol fuels of the hemi-cellulose and cellulose fractions of lignocellulosic materials. Following our review of these technologies our conclusions are as follows; • Anaerobic digestion processes are technically viable and available for most wet waste feedstocks including sewage bio-solids. • There is much discussion concerning whether AD is economically viable for standard fee waste at the moment. Greater interest in applying this disposal method is being stimulated by the revised Waste Framework Directive, and interest in biogas for transport. • Using a proportion of food waste is important to the economics of anaerobic digestion due to its high gas generation potential and gate fee. Manures are bulky and have poor gas potential. • Digestate disposal is becoming difficult due to constraints in nitrogen sensitive areas. • Composting is a lower cost alternative to AD but does not produce energy and can be regarded as a competitor to AD. It is popular with waste managers due to the cost and its status as a recovery, rather than a disposal process. Disposal of compost to land suffers from the same constraints as AD digestates. • Hydrolysis and subsequent fermentation to ethanol fuels of the hemicellulose and cellulose fractions of lignocellulosic materals is still at the development stage although there are plans for demonstrations in the EU and USA. • Feedstocks are limited at present to clean wood and agricultural residues. o We question whether hydrolysis and fermentation should be a priority for the UK at present where clean residues are relatively expensive and could potentially be used in more efficient ways. 143
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Figure 27 Orchid Environmental proc
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