Speciation and thermal transformation of sulfur forms in high-sulfur coal and its utilization in coal-blending coking process: A review

Modes of occurrence of beryllium in the Ge-rich coal deposit, Lincang, SW China: Theoretical insight into organic association and distribution

The coal-hosted germanium (Ge) deposit in Lincang, China, contains an abnormally high concentration of beryllium (Be), which is of significant organic affinity. However, the specific species of Be at the atomic scale remain unclear. In this study, thirteen model compounds representing O/S/N-containing functional groups in coal were calculated to probe the local environment of Be. The results indicate that hydroxyl and carboxyl groups are the primary acceptors of Be. Various Be-O complexes with a saturated four coordination of Be can achieve best stabilization. In contrast, the heteroatoms S and N are less likely to act as the acceptors for Be. In addition, the calculation results provide theoretical insights into the vertical distribution of Be. Unlike the upper coal seam, a fraction of Be in the middle and lower seams occurs in a mineral phase, which can be attributed to the limited capacity of organic matter to bond with all available Be. Furthermore, competition from other organically-associated metals, such as Ge and W, for bonding sites affects the local distribution of Be. This study reveals the molecular mechanism for Be enrichment in the organic matter of the Lincang Ge deposit, and suggests potential strategies for the removal of organically bonded Be in coal through the destruction of O-bridged complexes.

The behavior of organic sulfur species in fuel during chemical looping gasification

Uncoupling chemical looping gasification (CLG), the organic sulfur evolution was simulated and explored qualitatively and quantitatively using typical sulfur compounds on TG-MS and temperature-programmed fixed bed. The HS radical in the reductive atmosphere easier converted to H₂S and COS. H₂O activated the evolution of S which was stably bonded to carbon, and H₂ generated from gasification and oxidation of reductive Fe by H₂O contributed to the release of sulfur. The proportion of H₂S released from sulfur compounds was greater than 87% in steam gasification, and more than 60% during CLG. Oxygen carriers promoted the conversion of sulfur to SO₂ in the mid-temperature region (500 °C-700 °C), and H₂S in the high temperature region (700 °C-900 °C). Sulfur species played a pivotal role in sulfur evolution at low temperature of CLG. The organic sulfur in mercaptan and benzyl were more easily converted and escaped than in thiophene and phenyl. The thermal stability of sulfur species, the presence of steam and OC affected the initial temperature and peak concentration of gas sulfur release as well as sulfur distribution. Consequently, CLG strengthened the sulfur evolution, and made it possible to targeted restructure the distribution of sulfur by regulating process parameters, or blending fuel with different sulfur species for emission reduction, and selective conversion of sulfur.

Effects of S and Al on K Migration and Transformation during Coal and Biomass Co-combustion

The co-combustion of biomass and coal has both environmental and economic benefits in terms of pollutants and greenhouse gas emissions. However, one of the key factors affecting the feasibility of this technology is the ash deposition and corrosion caused by the high alkali metal content of biomass, especially K. After the addition of elemental S to corn stalk/Xiaolongtan lignite blended fuel and Al₂O₃ to corn stalk/Datong lignite, combustion experiments were carried out in a tubular furnace to explore the effects of S and Al in coal on K migration and transformation. The experimental results show that when S/K < 6, an increase in the S/K ratio inhibited the release of K. When S/K > 6, the sulfation become saturated, and an increase in S promoted the release of K. When S/K = 6, the higher the temperature was, and the more obvious the inhibitory effect on the release of K was. Increasing the S/K ratio not only increased the CaSO₄ content of the ash but also increased the content of water-soluble K compounds, such as K₂SO₄, and decreased the contents of acid-soluble K compounds and insoluble K compounds, such as KAlSi₃O₈. After Al₂O₃ was added, as the Al/K ratio increased, the K release rate gradually decreased. When the sample with Al/K = 2.5 and the original samples were burned at 600-700 °C, the difference in the K release rates of the two samples was relatively small. When the temperature was higher than 700 °C, the higher the temperature was, and the greater the difference in the K release rates of the samples was, which indicates that a high temperature promotes the formation of aluminosilicates containing K.