Kinetic study of steam gasification of lignocelullosic biomass char obtained from pyrolysis

Abstract

Hydrogen plays a key role in the energy transition towards a more sustainable model based on renewable energies, as it has the capacity to solve two major problems: i) reducing dependence on fossil fuels and ii) reducing greenhouse gas emissions. Currently, approximately 85 % of the world hydrogen production comes from fossil fuel technologies without CO2 capture. In this sense, a promising alternative for the substitution of these fuels may be biomass gasification with water vapor, due to its high availability and low cost, where the gas produced can be used directly as fuel or raw material to produce high value-added chemicals. The aim of this work is to perform the steam gasification of the solid residue obtained from biomass pyrolysis to optimize the hydrogen production. Three types of lignocellulosic biomass (almond shell, olive stone and hemp) were evaluated as raw material for steam gasification. Biomass samples were obtained by conventional pyrolysis in a fixed-bed reactor at a temperature of 800 °C, a heating rate of 10 °C/min for 1 h, obtaining a char that was later gasified in a downdraft fixed-bed reactor, using steam as the reacting agent (30 % vol.), in a temperature range between 800 °C and 900 °C. A kinetic model that takes into account the gas product distribution and the weight loss during the gasification reaction was developed using representative gas-solid models such as the volumetric model (VM), the grain model (GM) and the random pore model (RPM).