The Influence Law Of Hydrothermal Treatment On Pollutants Release And Migration During Thermal Conversion Process Of Lignite

Dehydration technologies of lignite, which can improve coal utilization efficiency and reduce energy losses, have become a focus of the large-scale use of low quality coal. As a high-efficiency and practical dewatering method, hydrothermal treatment has become a hot research issue. Influence law of hydrothermal treatment on nitrogen and sulfur pollutants release and migration of three kinds of low quality coal during thermal conversion process has been studied in this paper.First, Zhundong bituminous coal, Yimin lignite and Zhaotong lignite were hydrothermally modified at200℃,250℃and300℃by using high-heat and high-pressure reaction kettle. Results showed that hydrothermal treatment greatly removed the moisture in coal and improved the low-level combustion calorific value.(1)X-ray photoelectron spectroscopy technology was adopted to better analyze the species of nitrogen and sulfur in raw coal and hydrothermal-modified coal. XPS-peak-differentation-imitating analysis was performed by using the XPSPEAK points peak software. Results showed that hydrothermal treatment badly destroyed micro-structures and functional groups of nitrogen and sulfur in coal, bringing about phenomenons that N-5structure converted to N-6or N-Q, N-Q of polycyclic aromatic hydrocarbon converted to N-6and N-Q in edge of coal molecule converted to N-X. Mercaptan, sulfide, sulfoxide and sulfone may be converted to thiophene. Mercaptan and sulfide may be converted to pyrite sulfur, sulfoxide and sulfone would be converted to sulfate sulfur possibly.(2)Gas chromatograph mass spectrometer coupled with fast pyrolysis apparatus(Py-GC/MS) was used to study the release characteristics of nitrogen and sulfur macro-molecular volatile of raw and modified coal. Results showed that hydrothermal treatment affected the content and species of nitrogen and sulfur macro-molecular volatile. After sorting different types of nitrogen and sulfur volatile into category, the result was found that hydrothermal treatment have effect on the release of nitrogen substance in volatile such as amine, amide, oxime, nitriles, azonle, and sulfur substance, that is mercaptan and sulfide. (3)The tubular furnace experiment platform was employed to investigate the release mechanism on the nitrogen and sulfur emitted from three kinds of raw and modified coal during the pyrolysis and combustion process. Hydrothermal treatment reduced the release of nitrogen and sulfur pollutants of Zhundong and Zhaotong coal and increased that of Yimin coal during pyrolysis process. Hydrothermal treatment made it easier to emit sulfur pollutants and harder to emit nitrogen pollutants of Zhundong coal during combustion process. After hydrothermal treatment, nitrogen pollutants of Yimin coal greatly enhanced and sulfur pollutants cut down during combustion. The NO emission-peak of Zhaotong coal specifically increased a bit, the first SO2emission-peak declined and the second SO2peak become climb up during combustion.