Occurrence, migration pathways, and multifactorial regulation of chlorine in coking coal

Chlorine migration is a serious issue in coking process due to the existence of chlorine in coking coal and its harmful effects such as equipment corrosion and environmental pollution. This study aims to investigate the speciation and migration behavior of chlorine in nine typical coking coals during cooking process simulating industrial coking in 5 kg pilot-scale coke oven (final temperature:1050°C; coke cake center: 960°C) by proximate analysis, X-ray photoelectron spectrometer (XPS), thermogravimetry-mass spectrometry (TG-MS) and JF-WK-2000A microcoulometric chlorine analyzer. The speciation of different forms of chlorine and its migration to coke, tar and gas were systematically studied. The results are summarized as follows:1) Speciation: Chlorine in coking coal mainly exists in organic form (average 66.3%) and bonded in aromatic structure with C-Cl bond. 2) Migration: After coking, more than 60% of initial chlorine in coal was retained in coke and condensate water, and the amount of chlorine transferring to tar and gas phases was less than 40%. 3) The influence of different factors on chlorine migration was explored: The chlorine conversion rate transfer to coke was the highest for fat coals and the lowest for prime coking coal (average 21.5%). In addition, high-temperature rapid heating would increase 2 to 4 times of chlorine releasing to gas phase. The results show that the chlorine migration in coking process is regulated by multiple factors, including coal properties and process parameters, which provides an experimental basis for steel enterprises to optimize coal blending, alleviate equipment corrosion and treat chlorinated condensate water.