| Natural gas is a kind of efficient and clean energy product, but the contradiction between gas supply and demand in China is particularly conspicuous because of its uneven energy structure:"rich in coal, but short of oil and gas". As an effective way of coal utilization, coal hydrogenation methanation is of great importance to relieve this contradiction. Young lignite with high hydrogenation activity is a benign raw material to produce methane. With the progress of the lignite’s hydrogenation reaction, the active component in coal is decreasing while the inert one is increasing. This situation makes the reaction harder to continue and decreases hydrogenation rate, resulting in residue with high carbon content. Gasifying the hydrogenation residue can greatly improve the economy of the direct coal hydrogenation to methane. The characteristics of the lignite semi-coke, such as microcrystalline, specific surface and functional groups, have chanced significantly after hydrogenation under high pressure and temperature, which have a vital effect of the gasification progress.The hydrogasification residue of Inner Mongolia lignite semi-coke is used as raw material. The residue made in different final temperature is analyzed by the analytical techniques such as XRD, FTIR, SEM and XPS, etc. Non-isothermal thermogravimetry is used to research the CO2gasification characteristics of the residue at different temperature. Study of Steam gasification characteristics with different steam-coal ratio and different temperature is carried out in fixed bed. The experiment also research the residue co-gasification characteristics at800℃under the thermostatic and constant pressure. The main conclusions are as follows:1. As the increase of the final hydrogasification temperature of the Inner Mongolia lignite semi-coke, the content of Hdaf, Ndaf, Odaf, Vad and FCad gradually decreased while the content of Cdaf and Aad increased. The aromaticity increased from0.81to0.84. The activity of the residue decreased as a result of the hydrogasification of semi-coke, but still stronger than that of the general anthracite. In the semi-coke hydrogasification process, the graphite sheet layer increases and amorphous carbon turns into high density graphite sheet layer. The residue structure tends to graphite, generating more cracks and pore structures in its surface. The absorption peaks of the residue mainly appear at3030cm-1,2920cm-1、1610cm-1、1375cm-1、1070cm-1and750cm-1. The absorption strength of the characteristic absorption bands of the main functional group generally decreases with the enhancement of the final temperature.2.There are five carbon forms in the residue surface:C-C、 C-H、 C=O、C-O and π-π*. High final hydrogasification temperature is conducive to the reaction between hydrogen and active group of semi-coke. As the increase of the final temperature, the content of C-O and C-H fluctuates irregularly. The relative content of C-O increases from8.15%to14.31%, while the content of C=O appears a downward trend. There are three oxygen forms in the residue surface, among which the content of the phenolic hydroxyl group and ether-oxygen bond is more than91%, and increases slowly as the hydrogenation temperature increases. In the hydrogasification process, the stability of C=O is weaker than that of C-O, and the content of C=O in HR4decreases to2.15%.3.As the final hydrogasification temperature increases, the initial reaction temperature, maximum rate temperature and the final conversion temperature all increases, while the maximum reaction rate decreases. The relationship between the maximum reaction rate and heating rate can be described by the equation of r=mβ+l.4.In the10℃/min heating rate rising reaction, with the rise of methanation final temperature, residue gasification time will prolong, and the cumulative gas production will decrease. What’s more, with the increase of gasification agent flow, the670℃HR1final reaction temperature will decrease from1000℃to900℃.The carbon conversion rate will be improved with the increase of the gasification agent flow; When the gasification temperature is900℃, the maximum carbon conversion rate will increase from4.45%/min to6.23%/min, in contrast, the reaction time will reduce from50minutes to30minutes; When the gasification temperature rise from900℃to1000℃, gasification rate will slightly increase and there will be an great enhancement of the carbon conversion rate if the sample has relative high carbon content; In addition, it is worthwhile to mention that the semi-coke and the residue can convert completely within30-35minutes under the condition that the gasification agent flow is550mL/min and gasification temperature is1000℃5.In the CO2and steam gasification experiment, as the content of CO2increases, HR4reaction time maintain at about35minutes, the most reaction gas output ratio will decrease from405mL/min to364mL/min, and mixed coal gas H2/CO will decrease.6.Under the high pressure of3.0Mpa, the co-gasification reaction between O2and steam is carried out using HR4as the raw material. With the increase of the steam-oxygen ratio, the yield of hydrogen increases and carbon monoxide shows a downward trend. While the steam-oxygen ratio varies from4.30kg/Nm3to4.80kg/Nm3, the efficient gas content increases from58.77%to68.32%. Steam-oxygen ratio continues to increase, the effective gas content will decrease. There is little change in effective gas content when the pressure of gasification rises.7.The residue gasification reaction can be explained by the adsorption theory. The adsorption rate ra is affected by heating rate, reaction temperature and residue surface active site θσn, etc. The kinetic equation is r=da/dt=k(1-α)n Reaction order of CO2varies from1.09to2.31, while the activation energy changes from161.36to289.20kJ/mol. Activation energy and heating rate accord with E=aβ2+bβ+c; Hydrogenation final temperature and residue CO2activation energy accord with E=aβTF2+bβTF+cβ. Activation energy and pre exponential factor exist kinetic compensatory relation:lnA=eE+f. The residue and steam reaction order is1.29to2.04, and gasification reaction activation energy ranges from143.42to240.38kJ/mol. |
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