Influence of various machinery combinations, fuel proportions and storage capacities on costs for co-handling of straw and reed canary grass to district heating plants

Autumn-harvested cereal straw and spring-harvested reed canary grass (Phala ris arundinacea L.) are renewable energy sources with similar material char acteristics. The fuels can be harvested and handled with the same machines, stored in the same stores, and fired with the same equipment. Thus, there is a possibility to reduce costs and increase supply reliability at many lo cations by using reed canary grass (RCG) as a complementary fuel in straw-f ired district heating plants. The objective of this study was to find appro priate machinery combinations, straw/RCG proportions and storage capacities in order to reduce the total costs of the fuel system. The tool for the an alyses was a modified dynamic simulation model for straw handling called SH AM (Straw HAndling Model). To include handling of RCG, SHAM was extended wi th submodules for calculation of daily fuel use, soil moisture contents and early crop growth. The model was applied to a fictitious heating plant in Enkoping in central Sweden as a case study. The simulations showed that the total costs can be lowered by using both straw and RCG in suitable proport ions instead of solely using straw, although the primary fuel cost for RCG is more than three times higher per GJ than for straw. The choice of reserv e base load fuel had a significant impact on the results, particularly when the RCG proportion was small, because the consumption of the reserve fuel became proportionally higher in such cases. (C) 2001 Elsevier Science Ltd. All rights reserved.