Self-heating and thermal runaway of biomass – Lab-scale experiments and modeling for conditions resembling power plant mills

Review on Self-Heating of Biomass Materials: Understanding and Description

“…The simplest model is based only on the energy equation (eq ) with a single or multiple reactions to predict the spontaneous ignition in stockpiled materials with temporary and spatial variability . With the consumption of the reactants considered, additional equations for mass transport of such as oxygen through diffusion are integrated; − convective heat and mass transport can also be considered by applying Darcy’s law. , These allow the model to accommodate the effects of the process factors in the self-heating process. To investigate the self-heating of moist materials and the influence of moisture, heat effects of physical and chemical processes associated with the moisture have been considered as heat sources in numerical models. , Heat generation due to biological processes, which is critical to moist biomass and biomass-originated materials, can also be included in the models. ,, With the transport of heat and mass as well as momentum through the porous medium and the reactions of multiple heat sources integrated (eqs and ), the model has been developed and generalized to be capable of simulating the process from self-heating to the consequent self-ignition and smoldering combustion.…”

“…The state-of-the-art numerical models ,, theoretically describe the transport processes involved in the self-heating process and are therefore able to fully cover the process factors including pile size and configuration, ambient conditions, , and air flow inside and outside the pile . However, to cover the reaction and material related factors requires characterizing the properties and especially the kinetics of different biomass materials. , In particular, the submodels for the heat sources, that is, microbial activity and chemical oxidation, are still not so mechanistically based. This means that current models are far from an engineering tool for practical predictions.…”

“…The kinetic parameters may also be applied as model inputs to predict spontaneous ignition . With the help of a mechanistic model, the kinetic analysis is able to provide insight into processes associated with low temperature oxidation, including pyrolysis and oxidation of biomass chemical components, and provide kinetic parameters for properly predicting the self-ignition of various biomass materials . Nevertheless, limited by the sensitivity of the weight loss measurement, reliable kinetics is obtainable only at higher temperatures even than those of hot storage tests, which may limit the applicability of the kinetics for prediction of self-heating at relatively lower temperatures.…”

“…Schwarzer et al developed a mechanistic kinetic model considering the parallel pyrolysis and oxidation in detail, based on stepwise-isothermal TGA of biomass materials at 150–250 °C . The model and its kinetics were applied to simulate the self-ignition of various biomass materials, which underlines the necessity of determining accurate reaction mechanisms and kinetic models for low temperature reactions of biomass …”

Analysis of Spontaneous Ignition of Grass: Chemical Oxidation and Water Vapor Sorption

“…The self-heating and thermal runaway of four types of biomass without vapor sorption have also been studied by Schwarzer et al [34] at the lab-scale and modelled satisfactorily, taking into account all the external and internal mass and heat transfer in cylindrical samples.…”