Production of Bio-Coal Fuel from Low Rank Coal and Woody Biomass Mixture by Using a Bench-Scale Continuous Hydrothermal Equipment

Hydrothermal treatments of mixtures of Beluga coal and Cryptomeria Japonica were conducted by using a slurry of 10wt% density, fed at 10 kg/h rate in the reactor of a bench-scale continuous equipment, the temperature and pressure of which were set at 300°C and 12 MPa, respectively. The reaction time was 30 minutes. It was found that, during the hydrothermal treatment, the yield of solid phase decreased and the total organic carbon (TOC) of liquid phase increased as the biomass-mixing ratio increased. That means that the biomass was more decomposable than the coal. Besides, volatile matter in the material sample showed a higher decomposability, as compared with fixed carbon, and part of the decomposed volatile matter was considered to produce new aromatic compounds and carboxylic acids through repolymerization to fixed carbon. As a consequence, the gross calorific value of the solid phase of the hydrothermally treated mixture became higher with increasing biomass-mixing ratio on a dry basis. Considering ash content, the solid phase showed negligible change in gross calorific value, independent of the mixing ratio; it was ca. 7300 kcal/kg on a dry ash-free basis. In addition, it is worth mentioning that a five-hour run using a bench-scale continuous equipment was conducted successfully.