Study on oxidation and pyrolysis characteristics of lignite damaged by liquid CO2 at low-temperature

Abstract

• Effect of low temperature action of liquid CO 2 on coal pore and fissure. • Changes of characteristic temperature and functional groups of coal samples with different particle sizes treated with liquid CO 2 . • Changes in heat release of coal samples with different particle sizes before and after CO 2 treatment. In order to study the oxidation and pyrolysis characteristics of lignite damaged by liquid CO 2 (L-CO 2 ) at low-temperature, the coal sample was treated by L-CO 2 leaching device, TG-DSC-FTIR experiment and scanning electron microscopy were carried out to study the variation characteristics of parameters such as TG-DSC characteristic temperature, gas generation, functional groups and surface structure of lignite damaged by L-CO 2 at low-temperature. The results show that the coal pores change from micropore (<2nm) to mesopore (2–50 nm) to macropore (>50 nm) after low-temperature L-CO 2 leaching; The spectral peak intensity and peak area of the coal samples treated with L-CO 2 increased in different degrees compared with that of the raw coal. The absorption strength of C(D H ) coal samples increased by 500% compared with that of R(D H ), and the relative contents of C O, C O and COOH increased by 54.9%, 121.4% and 700%, respectively; The critical temperature and drying temperature of L-CO 2 leached coal sample decreased by 1.5–10℃ compared with that of raw coal sample, and the growth rate temperature, weight loss temperature, ignition temperature, maximum weight loss temperature and burnout temperature advanced by 8–20℃; The total heat release of treated coal samples is higher than that of raw coal, among which the change of coal samples with particle size of D H is the most obvious, and Its heat release reaches 5.18×10 3 J·g −1 , increased by 175%; The contents of CO decreased after the treatment of three coal samples with particle sizes of D H , D M and D L , while the contents of H 2 O and CO 2 increased. The intensity of CO 2 absorption peak was 1.65 times, 1.57 times and 1.29 times of raw coal respectively; The research results have important theoretical and practical significance for the prevention and control of coal reburning after L-CO 2 fire extinguishing.