Combustion characteristics of some imported feedstocks and short rotation coppice (SRC) willow for UK power stations

The availability and sustainability of biomass is very crucial in the production of energy using biomass. Currently nearly two thirds of the biomass in the UK is being imported due to the limited supply of indigenous resources. The Green House Gas (GHG) emissions from importing these fuels are very high. The imported feed stocks studied here (PKE, shea, olive and DDGS) exhibited high N and ash contents and also high slagging and fouling tendencies which are undesirable fuel traits. The high N contents and S content (in the case of DDGS) emit NOx and SOx emissions respectively which cause acid rain and photochemical smog and are harmful to human health. Due to the poor quality of these fuels for use in boilers and furnaces, and the need for Green House Gas savings, indigenous fuels with better combustion properties need to be produced. Energy crops like SRC willow and Miscanthus have remarkably better fuel properties (eg low ash and nitrogen contents) and there is potential to grow them in the UK. In order to help farmers to increase the yields and grow these crops in a more sustainable way, some agronomic studies have been carried out. The influence of 6 different fertilizer treatments with varying nitrogen levels, (0, 150 and 250 Kg/hectare), the addiition of K (150Kg N + 100Kg K), the addition of S (150 Kg N + 80 Kg S) and sewage pellets on SRC willow are studied. These crops are sampled twice a year for 3 years. It was found that fertilizer treatments do have an impact on the fuel properties (eg the application of N and K increase the C content and the CV of the fuel). Different parts of the crop also exhibit different fuel properties (eg leaves have higher nitrogen and ash contents which are undesirable qualities during combustion) hence it is important to avoid such parts. Sampling time also has a very big impact as the composition of the crop changes over the growth period. The optimum harvest time for SRC willow would be spring, after senescence when the leaves have fallen and some of the nutrients have translocated into the soil for the next growing season. Different genotypes of SRC willow with varying biochemical compositions were also studied to enable farmers to try and breed different genotypes with desired fuel properties for the next generation. 6 genotypes with varying biochemical composition (highest and lowest hemicelluloses, cellulose and lignin contents) were studied. From these, one genotype S.elaeagnos Scop showed remarkably different properties compared to the other 5 genotypes. All the genotypes except S.elaeagnos Scop had very high ash melting temperatures (>1500oC) and low slagging and fouling tendencies. S.elaeagnos Scop exhibits good grinding properties. The pyrolysis products of SRC willow are highly sensitive to its hemicelluloses and lignin contents. Due to its different properties S.elaeagnos Scop is of great interest for further investigation especially for its grinding ability. Overall, there is a potential for the UK to grow its own SRC willow. A larger dataset is required for the fertilizer application experiment to make firm conclusions since it is insufficiently small at the moment. A larger selection of genotypes would also need to be studied in order to help farmers breed a larger variety of SRC willow.