In order to evaluate the fuel maize cobs regarding its combustion related properties a comprehensive fuel evaluation based on fuel analyses, lab­scale reactor tests as well as combustion trials at a pilot­scale grate­fired biomass combustion plant have been performed. The results and experiences gained from these investigations form an important basis for the development of combustion systems which are tailored to the demands of maize cob combustion. Maize cobs show a significantly lower energy density than wood fuels which has especially to be considered regarding fuel transport and storage as well as regarding the fuel feeding system and the grate design. Especially regarding their comparably high N, S and Cl contents as well as their unfavourable ash melting behaviour maize cobs distinguish themselves from conventional chemically untreated woody biomass fuels. Nevertheless, they could be utilised in the pilot­scale combustion plant at very low CO and OGC as well as acceptable NOx, HCl and SOx emissions which indicate that with the exception of HCl most probably no secondary emission control measures are needed for a real­scale plant. Fine PM emissions dominated the total dust emissions and due their high level (90.7 mg/Nm³, dry flue gas and 13 vol% O2) advanced filter concepts such as ESP or baghouse filters will be needed for PM emission control. Special respect must be regarded to boiler tube deposits since they most probably will contain considerable amounts of KCl thus increasing corrosion risks. Moreover, K­Si­phases in the bottom ash with melting temperatures in the range of 1,050°C were found which underlines the need for an optimised fuel bed temperature control by appropriate combustion air settings as well as flue gas recirculation below the grate in order to avoid severe slagging problems. Summing up, it can be concluded that if all measures proposed in this paper are implemented in a medium sized combustion plant, maize cobs represent an interesting alternative to traditional wood fuels especially for decentralised systems where the fuel is available within short transport distances.

Proceedings of the 19th European Biomass Conference and Exhibition, 6-10 June 2011, Berlin, Germany, pp. 944-951