| China is the world’s biggest energy producer and consumer, and fixed number of year for using the residual coal reserves is greatly reducing year by year. The accumulative total proven reserve of Xinjiang Zhun Dong coalfield is 213.6 billion tons, which can be used for coal supply in China. But Zhun Dong coal contains high sodium content, which can make it easy to stain the facility in the combustion process, and affect the normal operation of the equipment. While the alkali metal sodium,whichcan be used as a catalytic, can make influence on co al pyrolysis and gasification process. So studying the transformation of the sodium in coal and its influence on pyrolysis characteristics is beneficial to optimiz ing the utilization of coal. Zhun Dong raw coal,acid washing coal(H-form coal), sodium ion exchange coal(Na-form coal) and secondary acid washing coal coal(H-form-1) had been used in a horizontal tube furnacefor pyrolysis at different temperature, and with the aid of Portable Gas Analyzer, Thermogravimetric Analyzer and Fourier Transform Infrare d Spectrometer to studying thecomposition of pyrolysis products,the reactivity of char and the change of functional groups in char.With the increase of pyrolysis temperature, carboxylic sodium in coal transformed to water soluble sodium gradually, and the total volatile yield increased. For different gaseous productsin different temperature range, carboxylic sodium had different effects. When pyrolyzed under 700℃carboxylic sodium inhibited the release of CO. And when the temperature reached at 800℃ or higher, carboxylic sodium promoted its release. At lower temperature carboxylic sodium could promote the generation of CH4, and at the temperature of 500℃ or higher, it inhibited, considering the fat chain hydrocarbon functional groups for generating CH4 primary pyrolyzedat 600℃~700℃, and the aromatic side chain structure crackedat 800℃~900℃. At 600℃~700 ℃, the release of C2H4 can attribute to the dehydrogenation reaction of C2H6, when the temperature reached at 900 ℃, dehydrogenation reaction of C2H4 and C2H6resulted in the release of C2H2, C2H4 greatly reduced and C2H6 approached to zero. In addition, carboxylic sodium inhibitedthe tar yield at high temperature, and at 700℃the effect was most evident.Na-form charmade at 500℃, 700℃ and 900℃presented different reactivity. The reactivity increased and later decreasedto the char rate, and the maximumactivity appeared at 700℃. With the increase of pyrolysis temperature, the kinds and contents of aromatic structure, oxygen containing functional groups, fat structure and hydroxyl groups in char were gradually reduced. At different temperature, there’s mutual transformation between the functional groups of Na-form coal and char. Combined with the analysis of functional groups in the char we can includethat the substance with active catalysis was likely to be some fatstructure.Some pyrolysis experiments of different treatments at different temperatures were carried out in the horizontal tube furnace, to preliminarily explore the interaction between volatile and char. At 500℃ with two kinds of processing mode, layered tile and mixing uniformityof H-form and Na-form, CO release concentration curve were similar, but the release concentration curve of CO of mixing treatment at 900℃ lay between H-form and Na-form but stratified flat peak was very high. It showed that the interaction between volatile and char at high temperature was even more significant, and this promoted the further decomposition of macromolecules in volatile to release CO.In addition, some experiments were carried in the fluidized-bed/fixed-bed to study the mechanism of volatile and char reaction, and its influence on the release of sodium futher. It’s found that hydrogen radical may interact with char to replace the sodium in the char matrix to promote the release of sodium. |
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