Experimental study on the optimization of parameters during biomass pyrolysis and char gasification for hydrogen-rich gas

Abstract

In order to achieve the efficient conversion of biomass char into hydrogen-rich gas at lower temperatures and investigate the different effects of potassium during biomass pyrolysis and char conversion, gasification experiments of the chars derived from wheat straw were carried out in steam atmosphere based on Response Surface Methodology. The response surface was set up with three parameters (pyrolysis temperature, K2CO3 loading concentration and the content of K-based catalyst in bed materials) for char gasification performances of carbon conversion efficiency, hydrogen yield and reaction rate to make analysis and optimization about the experimental conditions. The results showed that suggested conditions of char steam gasification were 650 °C for pyrolysis temperature, 22% for K2CO3 loading concentration and 70% for the content of K-based catalyst in bed materials. In these conditions, the confirmatory experiment indicated that carbon conversion efficiency was 95.1% while hydrogen yield and reaction rate reached 182.5 mol/kg-char and 1.55%/min, which was in good agreement with the model prediction. In addition, H2 concentrations were able to attain 70%. The X-ray diffractometry (XRD), scanning electron microscopy (SEM) and Fourier-transform infrared (FTIR) spectroscopy were employed to draw conclusions of char characterizations and account for the optimization results: i) chars obtained by the pyrolysis around 650 °C were liable to be gasified due to the cracked structures without carbonization occurring, and ii) properly loaded K2CO3 tended to cause the formation of porous sponge-like textures on char surfaces and contributed to maintaining the variety of functional groups with H and O, resulting in enhanced char reactivity.