Sulfur Behavior In Integrated Process Of Coal Pyrolysis With Steam Reforming Of Methane

Sulfur is one of the main heteroatoms in coal and a serious obstacle for clean and effective utilization of coal. Gaseous sulfurs (mainly SO2) released from coal combustion directly lead to acid rain and the destruction of ozone layer. Therefore, it is a vital practical significance to realize clean and effective utilization of coal from the perspective of energy conservation and environmental protection. Aim at newly proposed technique on the integrated process of coal pyrolysis with steam reforming of methane (CP-SRM) by our group, this work is to investigate the pyrolysis behavior and sulfur behavior in the integrated process.Two Chinese coal samples, Xinghe coal (XH) with high organic sulfur and Inner Mongolia lignite (IM) with high pyritic sulfur, were used in this work. Coal pyrolysis experiments were performed in a thermogravimetric analyzer (TGA), a pyrolysis-time of flight mass spectrometry (Py-TOF-MS) and a fixed-bed reactor to investigate the pyrolysis behavior and products distribution of coal pyrolysis. The results show that there is a certain difference of pyrolysis behavior between XH and IM coals due to relatively high pyrite in IM coal, and that the evolution of H2S and SO2 is associated with decomposition of pyrite in coal. The results also demonstrate that the integrated process has the highest tar yield under different atmospheres and char yield in CP-SRM is similar to that under N2 atmosphere.Coal pyrolysis experiments were conducted in a fixed-bed reactor to investigate the effects of coal properties and pyrolysis conditions (pyrolysis temperature, residence time, H2O/CH4 ratio, CH4 flow rate, catalyst, ect.) on sulfur behavior during coal pyrolysis. The results indicate that pyrolysis temperature has significant influence on the sulfur removal and sulfur distribution in CP-SRM. High pyrolysis temperature is preferable to the release of sulfur from coal. Longer residence time, higher H2O/CH4 ratio, faster CH4 flow rate and catalyst contribute to increasing sulfur removal and reducing sulfur content in char. The appropriate conditions in CP-SRM are 650 ℃, holding 20 min at preset temperature, H2O/CH4 ratio of being 1:1,140 ml/min CH4 flow rate and 1 g N1/Al2O3 for higher tar yield and higher sulfur removal. The sulfur distribution in pyrolysis product was investigated by using IM coal as an example. In CP-SRM, most of sulfur in coal transfers to char and gas, less sulfur to tar. Compared with pyrolysis under N2 atmosphere, the release of sulfur from coal in CP-SRM is greatly improved, and more sulfur is transferred to the gas phase.A two-step desulfurization process for high sulfur coals was proposed to improve sulfur removal in CP-SRM. XH and IM coals with the addition of sodium carbonate (Na2CO3) were carried out in the integrated process, then the pyrolytic char was washed with hot deionized water. The results indicate that sulfur removal of coal pyrolysis increases and sulfur content in char evidently decreases in the two-step desulfurization process. In this process, the sulfur removal of XH and IM coals is higher than 80% when 10% Na2CO3 is added to coals via impregnation. With the increase of the addition of Na2CO3, sulfur content in char decreases and sulfur removal increases. The effect of atmosphere on the sulfur removal during coal pyrolysis is related to the sulfur forms in coals.