基于超临界水气化制氢的煤炭利用技术研究进展

Coal will continue to play an important role as energy source in the near future in China. Traditional combustion utilization of coal inevitably produces large amounts of SO_x, NO_x, dust and greenhouse gas, which are main causes of environmental problems such as haze and global warming. A coal-to-hydrogen power generation multi-generation process based on supercritical water gasification was originally proposed by the team of Liejin Guo at the State Key Laboratory of Multiphase Flow in Power Engineering, Xi’an Jiaotong University, China. Coal is completely gasified in a supercritical water homogeneous environment to produce hydrogen-rich mixtures. The hydrogen is completely oxidized to form supercritical H₂O/CO₂ mixed working fluid which is then sent into the turbine for power generation. The exhaust gas from the turbine is separated and the carbon dioxide is further captured. The development status of the key technologies in the schemes were reviewed, especially the research progress in the last decade by the State Key Laboratory of Multiphase Flow in Power Engineering, Xi’an Jiaotong University. In terms of strengthening the gasification process of coal in supercritical water, it was revealed that the ring-opening reaction of polycyclic aromatic hydrocarbon is the rate-limiting step of coal gasification. The gasification model of porous coke particles in supercritical water was established and the gasification mechanism was obtained. The gasification rate of coal was increased by about 17% by circulating the fluid with high free radical concentration. The low-temperature and low-velocity side reaction zone was reduced by adjusting the nozzle jet angle. In-situ coupling matching of endothermic-exothermic reactions was achieved by adding catalysts. In terms of multiphase flow and heat transfer in a supercritical water fluidized bed, a new energy minimum multi-scale (EMMS) drag model was proposed based on the experimental results of flow characteristics of mesoscale structures. The characteristics of fluidized bed internal flow pattern evolution and the corresponding calculation criteria were obtained based on the pressure difference experimental data. The dynamic characteristics of bubbles in the fluidized bed were revealed and the calculation criteria of bubble chord length and rising velocity were presented. The bed-wall heat transfer correlation and the heat transfer model based on the particle renewal theory in the homogeneous expansion were established. In terms of kinetics of hydrogen oxidation in supercritical water, the reaction pathways and kinetic parameters of hydrogen oxidation were obtained from the atomic level sing the reactive force field (ReaxFF) method. The global reaction rate expression of hydrogen oxidation was established based on the experimental data. An elementary model of hydrogen oxidation in supercritical water was established, and the reaction path analysis and sensitivity analysis were conducted. The above research results provide a guidance for the regulation and strengthening of supercritical water coal gasification reaction, and the design of gasification reactor and oxidation reactor.