Research Of Catalyst And Technology For One-Step Production Of Synthetic Natural Gas Based On Coal

Energy is the foundation of social and economic development. In view of the basic national conditions that our country is rich in coal resources and the shortage of natural gas developing the clean coal technology is the important guarantee to realize our energy security. One-step production of synthetic natural gas (SNG) based on coal is referred to coal gasification and methanation in one reactor to products SNG. The process is about the reaction of coal and H2O in the presence of catalyst. The methanation reaction heat released in the technology can provide part required heat for coal gasification reaction, which decreases the energy consumption of the process. One-step production of SNG based on coal has the advantage of less investment, low energy compared with the traditional coal gasification technology (two-step), which results in a novel research topic in last few years. Both the experimental study of catalysts for one-step production of SNG based on coal in a fixed-bed reactor, and the process parameters influencing on reaction are investigated in this paper. The reaction kinetics model was established. Moreover, the recovery catalysts and the improvement of the process was discussed tentatively. The main results are as follows:1. K-Ni composite catalyst were prepared using impregnate method. The activity of catalysts and the influence of different types of coal on the catalyst behavior have been studied in fix-bed reactor. The experimental results showed that the active component K and Ni of K-Ni composite catalyst have synergistic effect by forming K2NiO2 and K3Ni2O4 with high activity, which could increase the speed of chemical reaction. When the rate of K and Ni in K-Ni composite is 1:2, the catalytic efficiency is 2-3 times as that of the single component catalyst K2SO4. The introduction of CaO in the composite catalyst could effectively absorb CO2, and accelerate the methanation reaction. When the K:Ni:Ca is 2:1:1.5 in the composite catalyst, the content and selectivity of methane were increased by 40% compared with that of without CaO.2. The influence of reaction parameters, such as temperature, pressure, initial water/coal ration and the amount of catalyst used were investigated. The optimum process technical parameters were obtained. The results showed that the carbon conversion increases obviously with the temperature increasing. When the temperature is less than 700℃, the thermodynamic equilibrium has not been achieved, and the formation of gas is controlled by dynamics. The appropriate temperature is about 600-700℃. Higher pressure could increase CH4 production rate obviously, the appropriate reaction pressure is 2.0 MPa. The carbon conversion increases with the increasing of the water/carbon ratio. When the ratio is 1.0, the surface of carbon particles close to the water vapor saturated, continue to increase the water/carbon ratio lead to the decrease of carbon conversion slowly. CH4 yields increases first and then decrease with the water/carbon ratio increasing, and the highest value is at the ratio of 1.0. Adding catalyst can improve the CH4 yield obviously, and the loading saturation of K-Ni binary compound is 10%.3. The Modified random pore model could well describe the kinetic curve for catalytic gasification among three kinetic models (Homogeneous model, shrinking core model Modified random pore model). The K-Ni-Ca ternary composite catalyst could lower the activation energy of Shenmu char 101.88 kJ·mol-1, so the gasification reaction could be conducted in a gentle condition.4. The recovery of catalysts was discussed briefly. Using the method of water washing step by step and slag-water separation, the catalyst was concentrated in the solution and loaded on the fresh char by one-step coal to SNG. The research has shown that when washing time is 4 h, slag-water is 1:20, number of washing for 4 times, and stirring peed of 400 r·min-1, catalyst can be recycled about 80%. At last, the preliminary process improvement for the catalytic gasification of coal and H2O in the production of SNG was proposed.