Experimental study on air/steam gasification of leather scraps using U-type catalytic gasification for producing hydrogen-enriched syngas

• A new U-type gasification-catalysis system is delicately designed.
• Operating conditions can greatly affect gasification performance of leather scraps.
• Water vapor can increase the yield of hydrogen twice.
• The highest hydrogen yield of 74.7 g per kg ISW is obtained for leather residue.
• Pore structure of bottom ash is analyzed to evaluate the gasification results.

The development of clean and low-cost hydrogen production method is of great research interests and environmental benefits. In this paper, a U-type gasification system which consisted of a downdraft gasifier, a cyclone separator and a catalytic tar cracking bed was delicately designed for producing hydrogen-enriched syngas from artificial leather scrap, typical industrial solid waste (ISW) discharged from shoes and suitcase manufactures. The influences of air/fuel equivalence ratio (ER), gasifying agent, catalyst, and reaction temperature were experimentally studied to achieve the optimal hydrogen yield and carbon conversion rate. Results showed that when saturated air was used as gasifying agent, H2 yield reached a highest value of 74.75 g per kg ISW at ER = 0.3 and further increasing ER would decrease the yield of H2 and deteriorated the syngas quality due to the promoted oxidation reaction and the dilution of N2. Compared with the pure air gasification, the addition of water vapor could significantly enhance the yield of hydrogen from 37.67 g/kg to 74.58 g/kg. Moreover, lower heat value (LHV) of syngas and carbon conversion efficiency increased by 22.5% and 17.9% at the gasification temperature of 700 °C, respectively, when replacing air with air/steam as the gasifying agent. The use of calcined dolomite could not only crack tar species in the syngas into light components efficiently, but also could reduce the concentration of CO2 due to the recarbonation effect of CaO. Higher gasification temperature could promote H2 yield, but the heat value of syngas would decrease. For ISW sample investigated in this study, the highest energy conversion efficiency of 84.4% was obtained at the gasification temperature of 700 °C and the ER of 0.2 when air/steam and calcined dolomite were used as gasifying agent and catalyst.