Simultaneous Pyrolysis of Coal and Biomass in a Drop-Tube–Fixed-Bed Reactor

Copyrolysis of coal and biomass has been extensively studied to exploit its inherent synergistic effects; however, the different pyrolysis temperature zones of coal and biomass seriously affect the realization of these effects. Therefore, a new copyrolysis method (preheating the coal to a certain temperature and then adding the biomass in a drop-tube-fixed-bed reactor, denoted as M1) was designed herein to achieve "simultaneous" pyrolysis of coal and biomass. The yields of products and the characteristics of M1-produced tar were estimated and compared with those of tar obtained by fixed-bed-reactor (denoted as M2)-based copyrolysis. M1 achieved a higher tar yield and lower water content than M2. The M1-generated tar exhibited a lower free-radical concentration, higher H/C ratio, higher levels of uncondensed aromatic hydrogen, and shorter side-chains than that produced by M2. The temperature of HLBE coal at which the WSs were fed to the reactor in M1, denoted as T F, affects the "simultaneous" pyrolysis. T F values of 300, 400, and 500 °C were studied, and it was found that the tar yield obtained at a T F of 400 °C (the main pyrolysis temperature of coal) is the highest, the water yield is the lowest, and the free-radical concentration of the tar is also the lowest among the investigated samples.