Thermodynamic Quasi-Equilibrium Model for the Energetic Performances Analysis of the Air and Air–Steam Gasification of Raw and Pretreated Cotton Stalks by Torrefaction and Carbonization

Abstract

Numerical and experimental study of the gasification of raw and pretreated (torrefied and carbonized) cotton stalks were investigated. The experimental results were used to calibrate the quasi-equilibrium model by multiplying the equilibrium reaction constant with coefficient varying from 0.01 to 10 and by fixing the methane molar fraction. Values varying from 0.15 to 0.7, 0 to 0.8 and 400 to 900 K were considered for air equivalence ratio (ER), the ratio of steam to fuel (SF) and the temperature of steam respectively. LHV and energy efficiency decreased from 4528 kJ Nm− 3 and 73.5% for the raw cotton stalks to 3984 kJ Nm− 3 and 68.9% for torrefied cotton stalks and to 3815 kJ Nm− 3 and 69.6% for carbonized cotton stalks. The energy efficiency was improved by steam injection to 80, 78 and 75% for the gasification of raw, torrefied and carbonized CS respectively due to the increase of H2 and CH4. The air–steam gasification was more efficient to air gasification at a temperature of steam over than 500 K for raw cotton stalks. However, only the air–steam gasification of pretreated cotton stalks was recommended since it has the net energy efficiency (which consider the steam energy) superior to 60%.