Influence of lumping properties of coking coal by pyrolysis shrinkage

Abstract

The performance of coke in blast furnace has higher requirement under the carbon emission peak & carbon neutrality goal and hydrogen-rich blast furnace development in China. Except for the thermal performance, the lump size of coke gets more attention. The pyrolysis shrinkage of coking coal is an important factor to determine the lumping performance of coke. The coking tests of coal with different deterioration were carried out with 2 kg coke oven, the effect of fineness of coal on coke lumping property was analyzed. An improved Audibert-Arnu dilatometer was used to study the shrinkage performance of eight kinds of coking coals with different degrees of metamorphism during the pyrolysis process at 300 ℃ to 900 ℃. The influence of the shrinkage coefficient of coal pyrolysis and its shrinkage dynamic characteristics on the caking performance of coke was discussed, and the mathematical relationship between the shrinkage coefficient of pyrolysis and the activation energy of pyrolysis of the average caking size of coke was established. It attempts to predict the average lumpiness of coking coal by its pyrolysis shrinkage characteristics. The results show that the average lumpiness of coke is increased with the increase of coking coal metamorphism. The average lumpiness of YK gas coal is only 38.9 mm, while the SAJ coking coal and BBG lean coal are 50.5 mm and 48.5 mm respectively. Among the eight kinds of coking coals, except for BBG lean coal, the average lumpiness of coke formed is the largest when the fineness of coal into furnace is 75%. The average lumpiness of coke is the best when BBG lean coal is 85% in fineness. On the pyrolysis process, the shrinkage coefficient and activation energy of the first shrinkage peak of coking coal with different metamorphic degrees are obviously different. The pyrolysis shrinkage coefficient of low-metamorphic YK gas coal and SYS1/3 coking coal is higher than 8.33×10−4 ℃−1, and the pyrolysis activation energy is lower than 77 kJ/mol. The pyrolysis shrinkage coefficient of LH coking coal, SAJ coking coal and BBG lean coal is lower than 4.55×10−4 ℃−1, but the activation energy required for pyrolysis is all higher than 106.1 kJ/mol. It indicates that the coking coal with high metamorphism requires higher energy to complete the shrinkage process during pyrolysis. The larger the shrinkage coefficient of coking coal, the smaller the average lumpiness of coke, and the pyrolysis shrinkage coefficient has a good linear relationship with the average lumpiness of coke, the correlation coefficient is 0.90. At the same time, the activation energy of pyrolysis shrinkage is also closely related with the average lumpiness of coke. Therefore, pyrolysis shrinkage coefficient and shrinkage activation energy can be used to effectively predict the average lumpiness of coke generated from coking coal with different metamorphic degrees.

Keywords

• coking coal
• pyrolytic shrinkage coefficient
• lumping property
• average particle size
• activation energy of contraction