Wet biomass comprises diverse organic wastes, which are discarded in large amount from our society. Energy production from them, therefore, poses great challenges both in quality and in quantity. However, anaerobic digestion is practically the only method currently available and due to its limited applicability, the alternative technologies are desired. In this paper, an energy-efficient dryer called the VRC (vapor re-compression) dehydrator that the author have developed for years, is proposed to be applied to wet biomass. The dried biomass would be used as a fuel for thermochemical energy conversions. The VRC dehydrator compresses evaporated steam and recovers its latent heat, which is used for the subsequent evaporation. Test results on a prototype dehydrator showed that the compression energy is as little as one tenth of the latent heat of water evaporation. Based on the experience, generated electricity from the hypothetical wet biomass was estimated in two processes: VRC dehydration followed by the ther-mochemical generation; and anaerobic digestion followed by the biogas generation. It was found that the VRC dehydration process would obtain more electricity than the anaerobic digestion process, even after the dehydrator's consumption was subtracted from the generator output. Additional advantages and future possibilities of the VRC dehydration system are also mentioned.
To understand agglomeration phenomena of ash particles in a hot gas ceramic filter system, actual tests were carried out on candle filters with a 4MWth pressurized internally circulating fluidized bed boiler (PICFB) pilot plant. Coal ashes build up on the ceramic filters were analyzed by computer controlled scanning electron microscopy (CCSEM) and thermo- mechanical analyzer (TMA). The dust cake taken at 800°C did not show any sign of bridging or cleaning difficulty, while those at 950°C showed some difficulty in cleaning because of ash bridging between the adjacent ceramic filters. The initial deformation temperatures of the non-bridge dust were about 800°C. The index of R2O/ (Al2O3+SiO2) (R2O=Na2O or K2O) for the non-bridge dust cake showed in the range of 1 to 25wt%, and the particle size of the potassium rich particles was in the range of 0.5 to 2.2m. However, the index for the bridge cake approached to below 5% and the particle size of the potassium rich particles shifted to the larger range of 2.2 to 10m. It was observed that weak sintering takes place by the reaction of potassium rich particles and the ash particles that adjoins the particles. Ther-modynamic equilibrium has been also examined for this system.
It is difficult to recycle effectively the waste plastic mixture. Plastics were employed in the coal liquefaction process as a source of hydrogen. Mixture of a coal and three kinds of plastics was liquefied by using a non-hydrogen donor solvent, and the effects of reaction temperature and time on the coprocessing were investigated. Radicals are derived from coal at about 300°C, and those attack plastics. Therefore, the possibility of a lowering of the initial reaction temperature on this coprocessing was suggested. The combination of radicals from coal and plastics produced radicals having large molecular weight, so the yield of residue increased. The residue decomposed with the increase of the reaction time. As the reaction temperature increased, the decomposition rate of residue was becoming faster. However, the over-decomposition of plastic radicals occurred, and the interaction of radicals from plastics and coal would be inhibited. The result was linked to the increase of the final yield of residue. In conclusion, the increase of reaction time rather than that of reaction temperature was effective for the appearance of interaction of coal and plastics to bring about the decrease of residue.