Structural Characteristics of Lignite Char from Different Pyrolysis Reactors and the Influence on Their Gasification Reactivity

Ying Zhang,Xiaoqin Wang,Haitang Wang

doi:10.21577/0103-5053.20210145

Abstract

The gasification reactivity of coal char is affected by numerous experimental variables, and char structure is one of the dominant factors. In this work, Raman spectroscopy, powder X-ray diffraction (XRD), and N2 adsorption were used to investigate the physical and chemical structure of char prepared under different pyrolysis conditions. Three kinds of pyrolysis reactors, fluidizedbed reactor (FL), entrained-flow-bed reactor (EF), and fixed-bed reactor (PT), were designed and used to prepare the char samples. Lignite was pyrolyzed in a fixed-bed reactor with a heating rate of 10 ºC min-1, and the final temperature was 1000 ºC. The gasification reactivity of char was characterized in a quartz fixed-bed reactor under CO2, H2O, and their mixtures at 750 ºC. FB reactor produces chars with a smaller interlayer spacing of aromatic layers (d002), and FL reactor produces chars with a larger mean crystallite size along the c-axis (Lc) and aromaticity (ƒa) but inhibits the growth of mean crystallite size along the a-axis (La). The content of small aromatic rings, which is higher in the FL reactor, positively affects the initial intrinsic reactivity.

Highlights

Coal continues to be an essential energy source in many parts of the world, especially in China and Australia
It can be seen that the 002 peak of L-1000FL is much thinner and higher than that of L-1000EF and L-1000PT, and the 002 peak position of L-1000FL is moved to a higher degree, which indicates a better crystalline structure and a higher content of aromatic
The interlayer spacing of aromatic layers (d002) of L-1000FL and L-1000PT seems less than L-1000EF. This could be attributed to that a longer holding time in the pyrolysis reactor contributes to a denser microcrystalline structure for lignite char

Summary

Introduction

Coal continues to be an essential energy source in many parts of the world, especially in China and Australia. Developing and utilizing coal resources rationally, efficiently, and environmentally is a reasonable way to alleviate the pressure of energy demand. The existing lignite reserves in China are about 129 billion tons, accounting for 12.9% of the total Chinese coal reserves. High moisture content (25‐50%) in lignite causes serious application problems, and it is generally difficult to be ground, separated, and classified. Approaches such as drying and pyrolysis are often used to upgrade lignite before the subsequent utilization process.[6,7,8] Nowadays, gasification has been an efficient thermal conversion process to upgrade lignite

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