Pyrolysis behaviors and product distributions of coal flotation sample separated by float and sink test

Abstract

Flotation has been widely applied in coal processing to separate mineral matter from coal and enrich macerals. In this work, four kinds of coal samples were chosen from different coal fields, and the thermogravimetric analyzer and fixed bed reactor were used to study the pyrolysis behavior and product distribution of coal sample with different densities prepared by the float-sink method. The results indicated that the releasing temperature of volatiles in pyrolysis of different coal samples is mainly in the range of 350–550 ℃, and the amount of volatiles decreases obviously with the increase of flotation density. The maximum difference of char yield at final pyrolysis temperature of ZC, HCG, DLT and HSQ flotation coal samples is 27.97 wt.%, 26.71 wt.%, 12.67 wt.% and 6.24 wt.%, respectively. The distribution of pyrolysis products reveals that the char yield increases gradually with the increase of flotation density, while the tar yield decreases. In addition, the pyrolysis gases（H2O, H2, CO, CH4 and CO2) of different flotation coal samples do not change regularly. The chars from pyrolysis of different coal samples were characterized by N2 adsorption/desorption and electron paramagnetic resonance. The specific surface area of char first increases and then decreases with the increase of flotation density. The stable radical concentration of the all char samples is on the order of 10 to the 16th. With the decreasing in flotation sample density, the stable radical concentration of char increases, and the mineral matter may be unfavorable to the formation of stable radicals during coal pyrolysis. The pyrolysis behaviors, yield, specific surface and stable radical concentration of coal/char are greatly related to coal types. The kinetic studies show that the differences in activation energy of pyrolytic conversion between the initial reaction region and the main pyrolysis region. With the change of flotation density of coal samples, the reaction rate, E and A factors are different from those of raw coal, which proves the accumulation of intrinsic minerals (or organic macerals) changes the pyrolysis process and mechanism of coal.