Influence of hydrothermal treatment on selenium emission -reduction and transformation from low -ranked coal


Ullah H., Chen B., Shahab A., Naseem F., Rashid A., Lun L., ...More

JOURNAL OF CLEANER PRODUCTION, vol.267, 2020 (Journal Indexed in SCI) identifier identifier

  • Publication Type: Article / Article
  • Volume: 267
  • Publication Date: 2020
  • Doi Number: 10.1016/j.jclepro.2020.122070
  • Title of Journal : JOURNAL OF CLEANER PRODUCTION
  • Keywords: Selenium emission, Hydrothermal treatment, Low-rank coal, Coal gasification, BROWN-COAL, COMBUSTION CHARACTERISTICS, PHYSICOCHEMICAL STRUCTURE, SURFACE-PROPERTIES, SHENGLI LIGNITE, BITUMINOUS COAL, XIMENG LIGNITE, BIOMASS, GASIFICATION, PYROLYSIS

Abstract

One of the key environmental limitations in coal usage is selenium emission whose removal is focused in this study. We employed hydrothermal treatment to remove Se element and upgrade low rank Huainan coal at 200-300 degrees C. Pyrolysis temperature given during coal treatment was evaluated to simulate coal transformation into high-rank industrial grade by emphasizing O/C ratio, removal of oxygen functional groups and moisture and chemical structure stability. Following hydrothermal treatment, different characterization techniques including XPS, FTIR, XRD and Raman spectroscopy were used to determine the chemical structure of coal. Findings revealed that hydrothermal treatment process has an important influence on the crystalline structures of low rank coals. The results of XRD and Raman spectroscopy analysis demonstrated much graphitized and aromatic microcrystalline structure. The chemical structure developed was orderly, stable and dense. Selenium XPS spectra comprising of 3D peaks has confirmed several oxidation states including selenide, selenates and oxide species. The removal proportion of Se was significant and increased up to 50.7% with increased HTT temperature (300 degrees C). This study provides some unique findings pertaining to solubility of sub-critical water and rate of change in pyrolysis temperature as determinant factors in the removal of Se. Our simulation model further concludes that transformation of low rank coal into high rank is a function of temperature treatment coupled with optimization of fixed carbon. We infer that hydrothermal treatment derived coal possesses sufficient lucid attributes to be considered as environmentally safe fuel.