Kinetic analysis of pyrolysis and combustion of botswana Morupule coal and its blend with municipal and industrial waste Using iso-conversional and model-fitting methods

Abstract

Several mathematical tools for interpreting experimental data for non-isothermal heating protocols have been established. Such methods may generally be classified into two categories: model-fitting and model-free. Model-fitting methods have always been common because they can precisely identify the kinetic triplet (i.e., frequency factor [A], activation energy [Eα] and model). However, there are several issues with these methods, one of which is that they do not correctly predict the response model. As a result, these techniques have become less popular in favor of isoconversional (model-free) techniques that examine kinetics without relying on model assumptions. Isoconversional approaches on the other hand, do not compute a frequency factor or determine a reaction model, both of which are required for a complete and accurate kinetic analysis. Critical analysis was done on the TGA data results from various models. Proximate and ultimate analysis of the coal from different active mining sites were performed following ASTM standard methods. Thermogravimetric-mass spectrometry studies were carried out for determining the evolved gas analysis during pyrolysis and combustion of Morupule coal. The municipal waste, high density polyethylene (HDPE) plastic was used in the coal-blending process at a 5wt% addition rate based on the literature point of view. Volatile and combustion products (H2, CO, CO2, H2O,CH4) were released based on their relative intensities. The pyrolysis behavior of the three kinds of Morupule sub-bituminous coal (EM1, WM1 and S3-5) were carried out under various heating rates with the temperature range 25-900 °C under both argon and oxygen atmosphere. The coal was washed with water to remove dirt and dried under static conditions. The samples were dried and pulverized to millimeter size with particle sizes of (0.6, 0.850, 1.0, 1.18 and 2.0 mm). Isoconversional and model fitting methods (Kissinger Akahira Sunose (KAS), Ozawa Flynn Wall (OFW), Kissinger, Friedman, Advanced integral Vyazovkin, linear regression and Coats Redfern) were applied to calculate the kinetic parameters of the coal, including activation energy and pre- exponential factor. The Arrhenius parameters from Friedman and advanced integral Vyazovkin showed a similar trend in the activation energy of the three coals. Among all the methods, advanced integral Vyazovkin method was considered to be best in order to evaluate kinetic parameters of coal pyrolysis. The mean activation energy calculated from the advanced integral Vyazovkin method was 155.77-284.59 kJ/mol for the three coals, the HDPE plastic, and the coal mixture.