Determination of the optimal ratio of coal to biomass in the co-firing process: feed mixture properties

Abstract

This study presents research that was conducted to determine the impact of biomass chemical composition on the characteristic ash melting behaviour of a biomass–coal blend made for use in the co-firing of power plants. It was conducted using two different types of biomass: wood biomass—pine (Pinus sylvestris L.) residue from sawmill, and agrarian biomass—miscanthus (Miscanthus giganteus). The design-of-experiments matrix was prepared using the simplex–lattice design method with four independent variables (i.e. coal A and B and biomass A and B). The characteristic melting points of ash (ash fusibility temperatures, i.e. the sintering, softening, melting and flowing temperatures) were used as the dependent variables, which were analysed under two atmospheres (e.g. oxidative and reductive). The analysis of the ash fusibility temperatures in oxidized and reduced atmospheres was conducted under accredited standards and test procedures using a PR-25/1750 furnace that was capable of reaching a maximum temperature of 1650 °C at a heating rate of 30 K min−1 to 1200 °C and 10 K min−1 between 1200 and 1650 °C, which provided an adequate zone of uniform temperature. In addition to the analyses of the ash melting point, full characterization of the physico-chemical properties of the applied fuels and their mixtures was performed. Based on the results of these analyses, the ash deposit behaviour was calculated, and its impact was discussed.