Research On Gasification Characteristics Of Inferior Coal With High Ash Content Under Carbon Dioxide Atmosphere

The coal resources in china have the feature of high content of ash and sulfur. Theaverage ash content of the raw coal content reaches nearly23.6%, and the sulfur1.1%.In the southwest area, that maybe higher. With the tense increasingly of the shortsupply of domestic bunker coal, the efficient use of the inferior coal cause widespreadattention. Now the new coal chemical industry has a vigorous development. As aleading technology of this industry, the coal gasification attracts more and moreresearchers,attention for the efficiency of coal utilization and reduction the pollutionemissions. Combine the situation of the domestic coal resources and the actual needs ofthe enterprises, enhance the theoretical and experimental research for the technology ofcoal chemical industry, especially for the gasification of the inferior coal, haveimportant academic significance and engineering value.On the basis of in-depth analysis of the status of coal gasification research, Thetemperature-programmed thermogravimetry was applied to study the effects of heatingrate and particle size on the gasification characteristics of two kinds of inferior coal withCO₂by Synthesized Thermogravimetry Analyzer，explore the catalysis of ash contentwith different coal ash ratio, calculate the kinetics parameters under each gasificationcondition. Adopt the method of acid wash and coal dipping, study the effects of threekinds of typical metal ions Na⁺, Ca²⁺and Fe³⁺,which exist in the coal ash. In addition,the inferior coal gasification experiments with different temperature and oxygenconcentration were carried on a self-designed gasification reactor, and a gaschromatograph was used to analysis the gas composition and calorific value. Thecharacteristics of gasification reaction with oxygen-enriched and steam were discussedin the article.The heating rate and particle size have a major impact on inferior coal gasificationwith CO₂. With the decrease of coal particle size and the increase of the heating rate, theapparent activation energy of both kinds of the coal decreased in the gasification. Whenthe reaction order is equal to1, the kinetic equation of the reaction to NT coal showed abest linear relation, however, to SZ coal that is1.2, and there exists kineticcompensation relationship between the activation energy of the gasification andfrequency factor as Ln A=a·E+b. The coal ash shows some catalytic effect on thegasification reaction. With the increasing of the ratio of ash, the gasification reaction rate constant increases and reaction rate accelerated.Results indicated that metal ions Na⁺, Ca²⁺and Fe³⁺in coal ash have obviouscatalytic effect on the gasification. They can effectively reduce the activation energy,enhance the reaction rate, and reduce the reaction temperature. The weight loss peak ofthe gasification reaction DTG curves shift to low temperature zone after the coalsamples impregnated metal ions. The corresponding temperature decrease about100°C, and the gasification reaction gets more intense. Compare of the catalytic effect to thegasification of the three metal ions, Ca²⁺> Fe³⁺> Na⁺.The results of fixed bed gasification experiment shows that the gasification has lowreactivity under CO₂atmosphere, and the gas heating value and carbon conversion areboth low. While using O₂/H₂O as gasifying agent, temperature and oxygenconcentration have obvious effect on the gasification of inferior coal. High reactiontemperature and oxygen concentration are benefit of the conversion of carbon in thecoal, however, the highest conversion rate of carbon in the coal is not correspondingwith the best gas calorific value. To enhance the gasification temperature, theconcentration of CO in the gasification gas increases quickly and continually, thehighest content reaches27.4%, while the concentration of H2decreased after theincreasing in prophase. With the increase of the oxygen concentration in thegasification agent, the concentration of CO₂in the gasification gas increase rapidly,the contents of H2and CO increases first and then show a decreasing trend.