Ex-situ catalytic cracking of gasifier tar using Ni-loaded pigeonpea stalk char catalyst

Abstract Purpose Tar in producer gas causes detrimental effects in downstream pipelines in gasifier based power generation system. Ni-supported char based catalysts have been proven to be effective and low-cost solution for cracking of tar. Use of simple method to make the catalyst with locally available biomaterial and its optimization can effectively solve this problem. Methods This paper includes efficacy of ex-situ catalytic cracking temperature, Ni-loading, particle size of char catalyst and catalyst bed depth on cracking efficiency. Producer gas generated from pigeonpea stalk pellets using a laboratory scale downdraft gasifier was passed through a hot catalyst bed in an ex-situ reactor. Taguchi method was used for de-compositional analysis of the variables affecting tar-cracking efficiency. Results Experiments showed increase in cracking efficiency with increasing temperature, Ni loading, bed depth and with decrease in particle size. Optimum values of operating parameters were 700 °C catalyst bed temperature, 0.3 M Ni loading, 5–10 mm particle size and 400 mm bed depth. Improvement in gas composition with the increase in Ni-loading was observed. Conclusion These findings confirmed that using pigeonpea stalk char supported with Ni, tar in producer gas can be decomposed to the tune of 84% at 600°C which can be easily achievable at the peripheral space of oxidation zone in a downdraft gasifier. With further increase in temperature to 700°C and using low size of 1–5 mm catalysts cracking efficiency can be achieved up to 93%. Catalytic cracking also improved the quality of producer gas.