Application of weibull mixture model to illustrate wheat straw black liquor pyrolysis kinetics

Abstract

Wheat straw soda black liquor is by-product of agricultural based paper industry. It is a promising resource of renewable energy. It is evaluated using thermogravimetric technique at different heating rates (e.g. 5, 10, 15 and 20 °C/min) in nitrogen atmosphere. From thermogravimetric analysis (TGA) graph it is found that there are three different mass loss processes, such as moisture or water molecule separating process, volatile material burning process and alkali salts reacting and fixed carbon burning process. TGA and Differential Thermogravimetric curves slightly move towards higher temperature side with increase in the heating rate. Weibull mixture model proposed allows for fitting an overall TGA curve of soda black liquor solid pyrolysis.The TGA curves of soda black liquor solids at different heating rates (5, 10, 15 and 20 °C/min.) have been analyzed and found the corresponding adjusted R- squared value greater than 0.99 in each case, thus the calculated TGA data by Weibull mixture model are in agreement with the actual experimental TGA data. Therefore, the TGA curve of soda black liquor solids pyrolysis can be understood as combination of three parallel reactions, where each single component represents one single reaction. Ozawa and Kissinger methods are used to find out the kinetic parameters such as activation energy and pre-exponential factor for the pyrolysis of soda black liquor solids. The activation energy of soda black liquor solids is almost equal in both methods. The experimental data and data driven models can help in smooth plant operations.