Experimental study of the solar-driven steam gasification of coal in an improved updraft combined drop-tube and fixed-bed reactor

Solar-driven steam gasification of coal particles promises a new approach for efficiently storing concentrated solar power (CSP) in producer syngas and achieving solid fuels energetic upgrade. A 1.5-kWth improved updraft solar reactor combined with drop-tube and fixed-bed for the steam gasification of coal was designed, fabricated, and experimentally studied under a 7-kWe high-flux solar simulator (HFSS). The gasifier retains the advantages of the efficient radiative heat transfer, long particle residence time and excellent particle size adaptation to the conventional combined drop-tube and fixed-bed reactors (CDFR) while, however, improving pyrolysis conditions by changing the moving direction of the steam and feedstock to use the high-temperature producer gas to preheat coal particles. The aim of this work was to achieve a proof of concept for the newly designed solar gasifier applied to coal gasification. Additionally, a comprehensive parametric study considering different H2O/coal molar ratios (0.8-2.2), coal feeding rates (1.0-1.5 g/min), carrier gas flow-rates (2.5-3.5 Nl/min), temperature (1050 C and 1150 C) and heights of reticulate porous ceramic (3 cm and 6 cm) was conducted for optimizing the syngas composition and evaluating the gasification performance. The experimental data indicated the syngas yield increased obviously from 57.92% to 64.63% with the increasing temperature, while the increasing steam content favored H-2, CO2 and CH4 and reduced CO mole fraction. The increasing heights of the reticulate porous ceramic (RPC) extended the particle residence time, resulting in the carbon conversion rate increasing over 8%. Maximum amounts of produced syngas over 100 mmol/min and carbon conversion rates over 70% were achieved. The coal energy content was solar-upgraded by a factor of 1.17 at 1150 C. Compared with the conventional CDFR, the carbon conversion rate was promoted from 51.66% to 64.63% with the increasing pyrolysis temperature (up to 400 C).