Characteristics Of Gasification Of Char With CO₂, H₂O Or CO₂/H₂O

Gasification is one of the most promising coal utilization technologies. The gasification medium is one of the key factors affecting gasification process. CO2 and H2 O are the most commonly used coal gasification agents. Numbers of domestic and overseas researchers have investigated the effect of CO2 or H2 O on char gasification characteristics in recent decades. In recent years, with the developing of the coal gasification technology, the effects of H2O/CO2 on char gasification characteristics have received the widespread attention.In this study, a bituminous coal(from Hongshaquan coal mine) was selected as experimental sample, and gasification experiments were conducted on a vertical fixed bed reactor.The influences of residence time and CO2 concentration on coal char yield during gasification process were firstly investigated. The chemical structure and reactivity of resulted coal chars were determined by using raman spectroscopy and thermogravimetry(TG), respectively. The results showed that the gasification characteristics of coal char were significantly affected by different CO2 concentration. The char yield decreased with the increasing of CO2 concentration. Under the same condition of CO2 concentration, the char yield decreased with the increase of residence time. CO2 concentration also had a significant impact on the char chemical structure in the gasification process.As the CO2 concentration increased from 0% to 70%, the polycondensation degree of coal char structure increased corresponding to the results of raman spectroscopy. The CO2 concentration was further elevated to 100%, the I(Gr+Vl+Vr)/ID increased significantly.The effect of H2 O on char gasification characteristics was further investigated in the study. The results showed that gasification rate of coal char with H2 O was higher than that with CO2. The char yield decreased with the increasing of H2 O concentration. Under the condition of the same H2 O concentration,, char yield decreased with the increase of residence time. Different H2 O concentration had a significant impact on the char chemical structure in the gasification process.As the H2 O concentration increased from 0% to 30%, more 3-5 ring aromatic structure in char was consumed or changed into a over 6 ring aromatic structure. When H2 O concentration was further increased to 50%, the I(Gr+Vl+Vr)/ID increased significantly. The char reactivity was lower. The variation discipline of chars reactivity was in accordance with that of chars chemical structure.Finally, the synergic effect of CO2/H2 O on char gasification characteristics was studied under different conditions such as different proportion of CO2 / H2 O and residence time. The experimental results showed that under CO2 and H2 O atmosphere, the synergic effect of CO2/H2 O existed in coal char gasification. The coal char gasification characteristics in CO2 and H2 O atmosphere can not be simply superposed by that in single H2 O or CO2 atmosphere.H2O/CO2-char has high degree of polycondensation than CO2-char, H2O/CO2-char has lower degree of polycondensation than H2O-char. The reactivity of H2O/CO2-char is higher than that of H2O-char and less than that of CO2-char.