The techno-economic viability of bio-synthetic natural gas production utilising willow grown on contaminated land

摘要

The growth of energy crops on contaminated land offers two potential advantages over their growth on agricultural land. Firstly, it can clean the land of contaminants, remediating it for future development or agricultural use. Secondly by growing energy crops on such land there is no conflict with land that is suitable for other uses (primarily agriculture). This study examines the opportunity to grow willow on contaminated land and to use this crop to produce bio-synthetic-natural-gas via the gasification processing route. The impact on the gasification system of using the contaminated materials as a feedstock is examined. A process that utilises a steam and oxygen blown gasifier with a plasma gas cleaning step and subsequent syngas cleaning is found most effective. An economic analysis of the process is undertaken to assess the viability of the opportunity. The results show that the costs associated with using the system to remediate land are lower than conventional alternatives, but require forward temporal planning which is not often evident or possible. Cost viability, if considered only for energy production, depends on the feedstock selling for a significantly lower price than virgin feedstock (in many cases requiring a gate fee), alongside a combination of strong policy incentives, natural gas prices and a long-term demand for gas products. For a 20 MW output system the feedstock would require a gate fee of ￡30 or ￡70 per tonne (depending on the policy support claimed), whilst for a 50 MW system a ￡25 gate fee or ￡30 cost per tonne are needed. Larger gasifiers are more economically viable, but provision of material grown from contaminated land would be unlikely to fulfil demand. Therefore, coupling systems with waste material as a feedstock is beneficial, but has resultant policy implications as current financial incentives are different for such materials.