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

•A 1.5-kWth improved updraft combined drop-tube and fixed-bed reactor was developed.•Different gasification operating conditions were experimentally investigated.•The highest value of carbon conversion rate above 65% was achieved.•The peak of the energy upgrade factor was 1.18.•The average solar-to-fuel conversion efficiency above 20% was obtained. 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 H2, 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).