Catalytic effect of potassium in thermochemical gasification of biogenic resources in a floating fixed bed gasifier

Abstract

The floating fixed bed wood gasifier has a potential to use low-cost residues from agriculture and forestry. Those feedstocks often contain relevant amounts of potassium salts that are known to lower the ash melting point and to catalytically accelerate the Boudouard reaction, which is one of the main reactions in the gasification process. The influence of varying amounts and types of potassium salts on the reaction rate of the Boudouard reaction was quantified in previous works. Basing on these findings, an ASPEN-Plus®-based tool (SBR-Sim 3.0) was developed to simulate the product gas composition and temperature profile in the floating fixed bed gasifier, caused by potassium-induced changes of the reaction kinetics of the Boudouard reaction. The main findings from the simulations were that the CO content of the product gas and the carbon conversion rate can be increased when increasing the reaction rate of the Boudouard reaction up to a factor of two, thus improving product gas quality. With a higher enforcement of the reaction rate of the endothermic Boudouard reaction, the reaction lowers the overall temperature in the reactor, thus leading to undesirably increased CO2 output. Conclusions are drawn on how the potassium content of potassium-containing feedstock will influence product gas quality and temperature profile in the reactor to predict gasification behavior by analyzing the chemical composition of the raw material.