Steam gasification of oat hull pellets over Ni-based catalysts: Syngas yield and tar reduction

Abstract

Renewable and clean energy generated from agricultural crops wastes can displace fossil fuels in heating and power generation. The abundant and low-value byproduct from agricultural industries can have a positive impact on the economy and environment of agricultural provinces in Canada and elsewhere. In this work, the effects of catalytic and non-catalytic steam gasification of oat hull pellets on syngas production and tar reduction were evaluated. For non-catalytic gasification, the impacts of temperature, between 650 and 850 °C, and steam-to-biomass ratio, between 0.25 and 0.50, were tested. Higher temperature increased fuel gas production and heating value, and decreased tar and char yields. Similar effects were observed with increasing steam-to-biomass ratio, except for char yield, which was not affected. For catalytic gasification, Ni/Al2O3 catalysts, with and without Ce, were synthesized and characterized. All catalytic gasification experiments were performed in a two-stage fixed bed reactor at 650 °C and catalyst-to-biomass ratio of 0.5. Among unpromoted catalysts, 10% Ni loading showed the lowest tar formation. Furthermore, adding cerium promoter increased metal dispersion, decreased reduction temperature, and lowered coke formation as observed in TGA. Increasing catalyst to biomass ratio from 0.2 to 1 reduced tar formation from 2.3 to 1.3% but had insignificant influence on syngas yield. As compared to non-catalytic process, using Ni-based catalysts improved the efficiency of steam gasification of oat hull pellets by increasing syngas production and decreasing tar formation. Improving the efficiency will make steam gasification a promising method to convert the agricultural wastes to a clean energy.