Abstract
To reduce the exhaustion of carbon dioxide in power plants, the operating technology for co-firing of woody biomass at existing coal-fueled power plants has come to attract attention. In the present study, it is assumed that the domestic forestry biomass transported from mountain regions is used as a fuel in pulverized coal fired power plants. The forestry biomass in Japan is the most promising domestic resource. However, most of the forests in Japan locate in the mountain region, and hence the overland transportation of biomass to the power station is indispensable. The pretreatment of semi-carbonization and chipping before transportation is effective in reducing the energy consumption for transportation of forestry biomass. The main purpose of the study is to clarify the comminution and combustion properties of the mixture of semi-carbonized woody biomass and coal. From the experimental investigations, the following results are obtained. (1) The comminution energy of mixture decreases with pyrolysis temperature. The increase in the biomass mixing ratio increases the comminution energy in the temperature range below 300°C. In the “W region” below 200°C, the density of wood exerts great influence on the comminution energy. (2) The estimation method of comminution energy based on the biomass mixing ratio, which is called “biomass mixing ratio method”, is compared with the experimental results. The comminution energy of the mixture is overestimated by the biomass mixing ratio method, when the woody biomass is mixed. The overestimation is due to the wedge effect induced by pulverized coal. The comminution energy of the mixture of coal and the semi-carbonized biomass for the pyrolysis temperature ranging from 200 to 400°C can be predicted by the biomass mixing ratio method. (3) The estimation method based on the work index of the Bond's Law is proposed. The experimental comminution energy can be estimated by using the empirical correlations of the work index within accuracy of ±30%. (4) In the case of mixing with the biomass produced by pyrolysis at a temperature below 200°C, the ignition delay time and the total combustion time linearly decrease with the biomass mixing ratio. The increase in the biomass mixing ratio causes the increase in the volatile gas, which leads to the improvements of ignitability and the decrease in total combustion time. In the case of mixing with the biomass produced by pyrolysis at a temperature of 400°C, the total combustion time is not affected by the biomass mixing ratio.
