Insights into biomass mild gasification based on mass-energy balance: Establishing condition, thermodynamic mechanisms, and product properties

Abstract

To alleviate the challenge of gas and char quality competition arising from over oxidation during the biomass gasification. A new concept of biomass mild gasification based on mass and energy balance was proposed, wherein the energy produced during the oxidation stage precisely equals the energy consumed in the pyrolysis and reduction stages. An energy balance index (EBI), obtained through the combined use of TG-DSC-MS-FTIR and Gaussian model fitting to represent the relationship between mass loss and endothermic/exothermic properties among different reaction stages, was optimized by response surface methodology (RSM) to obtain the critical conditions of biomass mild gasification. Under two typical mild gasification conditions, the quality characteristics of mild gasification biochar were analyzed and the gas evolution characteristics and sequence were determined through the combination of two-dimensional correlation spectroscopy (2D COS). The results indicated that mild gasification can be achieved within a heating rate range of 21 °C/min to 26 °C/min, with the oxidation temperature ranging from 776 °C to 869 °C. Under mild gasification conditions, the biochar produced at 850 °C-20 °C/min had higher COOH content, which can regulate soil pH, promote organic matter degradation, and enhance biological activity. Under the 800 °C-25 °C/min mild gasification condition, more CO and CH4 were generated during the pyrolysis stage, but slightly more CO2 was also produced during both the pyrolysis and oxidation stages. This work provides comprehensive thinking on the precious control of gasification process, which lays a foundation for co-generation of high-quality char and gas.