The effect of carbon dioxide partial pressure on the gasification rate and pore development of Highveld coal chars at elevated pressures

Abstract

Char structural changes occurring during gasification are normally only related to conversion and few data is published on the effect of carbon dioxide partial pressure on the extent of pore development. In this study, the char–CO2 reactivity and consequential pore development of different Highveld coal chars were investigated over a wide pressure range. Reactivity experiments were performed in a fixed bed reactor under reaction controlled conditions. The initial reaction rate was found to be solely a function of temperature and CO2 partial pressure and was well described by the Langmuir Hinshelwood rate equation. Surface analyses were performed on fresh and partially converted chars to quantify the effect of CO2 partial pressure on pore development. It was found that pores development more rapidly with conversion if the CO2 partial pressure is increased. This outcome has fundamental implications for the interpretations of gasification reaction kinetics. The term describing the total amount of active sites in the Langmuir Hinshelwood equation might not be constant at all partial pressures, and the possible impact of that is shown in this work. More work is required to further understand these effects and incorporate them appropriately into high pressure rate equations