Influence Of CaO On Coal Pyrolysis And Steam Gasification

Coal gasification with in-situ CO2 capture has the potentiality to produce syngas with rich H2/CH4. By adding CaO as sorbent in coal gasifier, the product gas CO2 can be captured, and as a result, the equilibrium of water gas shift reaction tends to produce more H2 and CO. Coal gasification with in-situ CO2 capture is a promising field which can significantly promote the coal gasification efficiency, as well as shorten the gasification processes, reduce investments and CO2 capture costs. In the present work, kinetic analysis of coal pyrolysis, influences of experimental conditions on coal/CaO pyrolysis gas production rate and tar, influences of CaO on coal steam gasification rate, as well as hydrogasification of coal/CaO mixture were carried out with fix-bed reactors. The main work includes four parts as follows:1. Kinetic analysis of coal pyrolysisKinetic analysis of temperature-programmed pyrolysis and isothermal pyrolysis of Inner Mongolia coal were studied, the results showed that based on temperature ranges coal pyrolysis process can be divided into three characteristic stages, and the reaction order of the second and third characteristic stages were almost first order. With the increase of residence time, the total weight loss per gram coal of isothermal pyrolysis increased follow the logarithm law.2. Influences of Ca-based additives on coal pyrolysis productsInfluences of Ca/C molar ratio and the final temperature of pyrolysis on coal pyrolysis gas production rate were studied with the Inner Mongolian coal. And on this basis, the effectiveness of Ca-based additives on the increase of Zhangjiakou coal pyrolysis effective gas production (H2+CO+CH4+C2) and low weight components of tar were studied. The results showed that Ca-based additives can promote coal pyrolysis reaction rate, as well as the effective gas production (H2+CO+CH4+C2). As for Zhangjiakou coal, the gas production rate per gram coal under H2 atmosphere was much higher than under N2 atmosphere. Furthermore, compositions of CH4, C2H4 and C2H6 increased sufficiently, as well as the low weight components of tar. In addition, CaO was able to improve the quality of coal pyrolysis products, but not so sufficient as hydropyrolysis. The CaO and Ca(OH)2 additives both can promote the effective gas (H2+CO+CH4+C2) content and low weight components of tar in pyrolysis products. While CaCO3 additive would decrease the effective gas production and nearly has no apparent improvement on tar quality.3. Influences of CaO on coal steam gasification rateInfluences of three different char-CaO mixing methods on the Inner Mongolia coal char steam gasification rate and their apparent activation energies were studied. Conclusions that the more sufficiently the mixing extent of CaO and char the better the promotion effect of CaO on char steam gasification rate were obtained. The apparent activation energies of three mixing methods were 136.56-200.54 kJ/mol. Influences of Ca/C molar ratio, temperature and steam partial pressure on char/CaO steam gasification rate and coal/CaO directly steam gasification were studied. The residual solid materials of coal/CaO direct steam gasification under different experimental conditions were analyzed to study the eutectic phenomena of CaO/Ca(OH)2/CaCO3 mixture.4. Influences of CaO on coal steam hydrogasificationInfluences of CaO on Inner Mongolia coal direct steam hydrogasification and coal char steam hydrogasification were studied. Results showed that hydrogasification can promote the CH4 and C2 gas production. Furthermore, with the increasing of hydrogen pressure, the reaction rate of coal/CaO direct steam hydrogasification and CH4, C2 gas production increased sufficiently, while CO and CO2 gas production decreased.