Interdependency of pyrolysis and combustion: a case study for lignocellulosic biomass

It is intriguing to see how a storm kills a candle but catalyzes the spread of a forest or residential fire. The question is difficult to answer and requires a holistic approach. The underlying study employs a holistic approach to studying the fundamental of lignocellulosic biomass combustion. The study involves analysis of ignition properties, energy, and mass transport limitations, and the quantity of energy released/demanded at various stages of the combustion process. Combustion in a solid involves three primary stages such as pyrolysis, gasification, and oxidation. Pyrolysis, which is also the first step of the combustion process, is endothermic and requires energy from external sources to progress. On the other hand, gasification and oxidation are exothermic processes. The study hypothesizes that pyrolysis as an energy-demanding process has much influence on the overall combustion process. In this study, pyrolysis and combustion experiments are conducted using a thermogravimetric analyzer (TGA) at various heating rates (5, 10, 15, 20, 25 degrees C min(-1)) in N-2 and air atmospheres, respectively. Mass loss (TG), differential curve (DTG), differential thermal analysis, and heat flow concerning temperature and time for both processes are recorded. The isoconversional methods such as Flynn-Wall-Ozawa and Kissinger-Akahira-Sunose are employed to estimate the activation energy of the process with respect to the conversion. The differential calorimetry analysis of the process reveals that the combustion process has two exothermic zones: one related to the combustion of volatiles released during the pyrolysis step and another one related to the combustion of char. In the terms of magnitude, the second exothermic step is predominated by the first one. The FTIR analysis of the raw biomass and char produced from the isothermal reveals the structural transformation of the biomass concerning temperature and conversion.