| For the natural gas shortage and the rigid requirements of environmental protection, methanation of coal has aroused wide concern. Methanation technology is of great significance to ensure the supply of natural gas, emission reduction and station energy security. The hydrogasification technology is of lower investment, higher heat efficiency and methane production. However, the hydrogenation activity of high rank coal is poor, which lead to low carbon conversion and methane yield, the hydrogenation activity of low rank coal is much higher, but its oxygen content is high too, which result in high hydrogen consumption. Effects of operational conditions, catalyst, inlet gas composition on the hydrogasification of Inner Mongolian lignite semi-coke was investigated by using a self-developed high-temperature and high-pressure fixed-bed reactor with a design parameter of 1000℃ and 12 MPa; Changes of the properties of semi-coke during hydrogasification process were studied by means of XRD, FT-IR, BET, XPS analysis technology; reaction mechanism of semi-coke hydrogasification was investigated too. The main conclusions were list as follows:1. During the hydrogasification process, two methane peaks, about 500-600℃ and 750-800℃, were included; The formation of C2H、C2H6、CO and CO2 were finished before 700℃; Hydrogasification of semi-coke was a ideal means of fuel gas production.2. As the decrease of semi-coke grain size and the increase of hydrogen flow rate, the heat transfer and mass transfer were improved, as the semi-coke grain size<0.25-0.35mm and the hydrogen flow rate> 1200mL/min, effect of internal diffusion and external diffusion on the hydrogenation reaction has been basically eliminated. As the Increase of reaction temperature the C, H atomic energy were improved, as the reaction temperature Increased from 700℃ to 800℃, the carbon conversion was improved from 61.7% to 92.3%, the optimal reaction temperature is 800℃. as the reaction pressure increasing, hydrogasification rate was improved however the increase rate of methane production and carbon conversion were gradually reduced.3. The Fe(NO3)3 and the ash could promote the hydrogasification of semicoke; The order of the catalytic effect were Fe(NO3)3>Fe2(SO4)3>FeCl3; the optimal loading amount of Fe(NO3)3 was 3w%;4. At 700℃, methane in the inlet gas had little effect on the hydrogasification of semicoke, the methane in the inlet gas and the methane which was formed by hydrogasification were superimposed; at 850℃, the increase of methane concentration of inlet gas would inhibit the hydrogasification of semicoke, which resulted in the desease of methane yield and the carbon conversion.5. During the hydrogasification process, the volatile and H, O, N, S containing active groups of semicoke were preferentially consumed. As it was shown in the XRD and FT-IR results, at early reaction stage, hydrogasification mainly occurred in non-crystalline structures such as -CH3,-CH2, C=O,-NH etc., so the intensity of peak C(002) did not change much; at late reaction stage, the hydrogasification of microcrystalline structures occurred, and the decrease of the size and quantity of microcrystalline structures led to the decrease of peak C(002) intensity.6. At the first 60min of hydrogasification reaction, pore structure parameters of semi-coke changed a little; at 60-90min, the amount of microporous and mesoporous in semicoke was increasing, BET of semicoke was increased from 15.14 m2/g to 259.27 m2/g; during slow hydrogasification stage, BET of semicoke was decreased gradually and the mean pore size of semicoke was increased.7. Hydrogasification of Inner Mongolian lignite semi-coke included three stages:hydro-pyrolysis of active functional groups such as oxygen-containing functional groups, alkyl side chains etc., rapid hydrogasification of carbon structures with high hydrogenation activity for example, hydrogen-rich low aromatic rings structures, heterocyclic structures, and slow hydrogasification of hydrogen-deficient skeleton carbon structures. |
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