Estimation of synergetic effects of CO2 in high ash coal-char steam gasification

Abstract

Char particles of high ash Turkish coal with different sizes are produced in a thermo-gravimetric apparatus furnace using three heating rates. The effect of coal particle size on char production under various heating rates is evaluated. The gasification experiments of the produced char in steam and blended (steam+CO2) ambiences were performed over the temperature range of 850–950°C under ambient pressure conditions. It is observed that the changes in char structure porosity for various heating rates affect its gasification rates. Also, char gasification is affected by the parametric conditions such as reaction temperature, char production method, and particle size in addition to chemical composition and physical structure of char. The maximum reaction rate is shifted to higher conversion levels when the chars are produced from high heating rate pyrolysis conditions. In the argon, steam and CO2 blended ambience, the substitution of CO2 for argon improves the char gasification rate. There is no CO2 inhibition effect observed in the char-steam gasification, whereas some synergetic effects are anticipated. Three kinetic models are used to describe the char gasification kinetics: volumetric model, grain model, and random pore model. The variation of activation energy during gasification is based on the char generation method, particle size and reactant concentrations. The activation energy for steam gasification is 156–173kJ/mol, whereas in the steam blended with CO2 gasification values are in between 162and196kJ/mol for 3mmparticles. Besides, these values are considerably low for 800μm particles. Similar trends are observed from Arrhenius constant values for both sized particles.