基于超临界水气化制氢的煤炭利用技术研究进展

Research progress of coal utilization technology based on supercritical water gasification for hydrogen production

  • 摘要: 中国以煤炭为主体的能源结构短期内无法改变。 传统“ 一把火烧” 的煤炭利用方式不可避 免产生大量的SOx、NOx、粉尘及温室气体,是雾霾和全球气候变暖等环境问题的重要成因。 郭烈锦 院士团队原创性地提出基于超临界水气化的煤制氢发电多联产技术,该技术可将煤在超临界水均 相环境中实现完全气化制得富氢混合物,其中的氢被完全氧化形成超临界 H2 O / CO2 混合工质后进 入透平做功发电,透平出口的乏汽经气液分离可实现 CO2 的自然富集。 针对上述方案中关键技术 的发展现状进行综述,重点介绍西安交通大学动力工程多相流国家重点实验室近 10 a 来在该领域 取得的研究成果。 在超临界水煤气化反应过程强化方面,揭示了超临界水中煤气化过程的受控步 骤在于稠环芳烃的开环反应;建立了超临界水中多孔焦颗粒气化模型并获得其气化机理与影响规 律;通过将烷烃重整区高自由基浓度的流体循环注入反应器底部提高煤气化率约 17%;通过调整 喷嘴射流角度缩小了低温低流速的副反应区;通过添加催化剂实现了吸热-放热反应的原位耦合 匹配。 在超临界水流化床多相流动与传热方面,基于介尺度结构流动特性实验结果提出了新型能 量最小多尺度( EMMS) 曳力模型;基于压差实验数据获得了流化床内流型演变特性及相应计算准 则;基于实验结果揭示了流化床气泡动力学特性并提出气泡弦长与上升速度的计算准则式;建立了 流化床均质膨胀区和鼓泡区的床层-壁面传热关联式与基于颗粒团更新理论的传热模型。 在超临 界水环境氢氧化反应动力学方面,基于反应力场方法从原子层面获得了超临界水中氢氧化反应路 径与动力学参数;基于氧化反应段出口氢气体积分数数据建立了超临界工况下氢氧化总包反应速 率方程;建立了适用于超临界水工况的氢氧化基元反应模型并开展了反应路径分析与敏感性分析。 上述研究成果为超临界水煤气化反应调控与强化、气化反应器与氧化反应器的设计优化提供指导。

     

    Abstract: Coal will continue to play an important role as energy source in the near future in China. Traditional com⁃ bustion utilization of coal inevitably produces large amounts of SOx, NOx, 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 com⁃ pletely 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 pow⁃ er generation. The exhaust gas from the turbine is separated and the carbon dioxide is further captured. The develop⁃ ment 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 strength⁃ ening 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 su⁃ percritical water was established and the gasification mechanism was obtained. The gasification rate of coal was in⁃ creased by about 17% by circulating the fluid with high free radical concentration. The low⁃temperature and low⁃veloc⁃ ity side reaction zone was reduced by adjusting the nozzle jet angle. In⁃situ coupling matching of endothermic⁃exother⁃ mic 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 re⁃ sults 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 dy⁃ namic 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 par⁃ ticle renewal theory in the homogeneous expansion were established. In terms of kinetics of hydrogen oxidation in su⁃ percritical 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 es⁃ tablished based on the experimental data. An elementary model of hydrogen oxidation in supercritical water was estab⁃ lished, 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 gasi⁃ fication reactor and oxidation reactor.

     

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