Research On The Characteristics Of Coal Hydrogasification In A Pressurized Fixed-bed Reactor

Coal combustion, a traditional method of coal utilization, has many disadvantages. The clean coal technologies which were developed in recent years, becomes more and more popular because near-zero emissions might be achieved. But coal gasification under high temperature and pressure in a gasifier in order to generate methane consists of many complex chemical reactions and laws that have not been well established. Research on the characteristics of coal hydrogasification is very important for coal gasification technology. This paper focused on the system of coal hydrogasification, utilized experimental method and numerical simulation method to study the important factors of coal hydrogasification on the fixed-bed reactor to obtain their impacts on the gasification products.A fixed-bed reactor was established for coal hydrogasification experiments and the operating methods of the experiments were set up for the coal hydrogasification and pyrolysis. A series of gas tightness test was examined for the gas tightness ensurance of the test bed. A series of coal hydrogasification experiments in full range of conditions for a standard coal was carried out to study the effects of temperature and pressure on the gasification composition. A series of orthogonal coal hydrogasification experiments with four standard coals, was carried out to study the effects of pressure and temperature and components of coal on the gasification composition. The orthogonal principle was utilized to obtain the the optimal gasification conditions. And finally coal pyrolysis experiments with these four coals, were carried out to study the effects of coal pyrolysis on the CH4 production.The experiments show that at a particular temperature, there is a turning point. After the pressure is greater than the pressure at that point, more carbon of the pulverized coal was converted to CH4 gas with the increase of pressure. This means that carbon has been utilized effectively. In the whole range of the parameters of the orthogonal experiments, pressure, temperature and coal components are listed in descending order of impacts on CH4 production as:temperature, coal components and pressure. Among them, temperature and coal components have significant impacts on the production of CH4, while pressure has no significant impacts. The amount of CH4 generated by coal pyrolysis is very small. Therefore, coal pyrolysis has little effect on the production of CH4 during coal hydrogasification. Simulations of coal hydrogasification were carried out using chemical equilibrium thermodynamic model of Chemkin to predict the composition of the gasification products.The results were compared with experimental data. In the whole range of simulation parameters, the values of the concentration of methane calculated under different conditions have little difference. Therefore, taking factors such as equipment cost, safety, the reaction rate and so on into accounts, high-temperature and low-pressure operating conditions were suggested be applied to coal hydrogasification, which is consistent with the result of the orthogonal experiments. The results with the thermodynamic equilibrium model are consistent with the experimental results in the overall trend, but the value of carbon conversion rate is over predicted. The model needs for further improvements and refinements.