Cool-Flame-Assisted Combustion of High Pressure CH4/air Mixtures for Hydrogen Synthesis

最近对富燃料甲烷/空气混合物在高压下的自燃行为的研究表明，当量比约为4的混合物可以在高于8个大气压的压力下迅速反应，因此有可能在改进的燃烧器配置中稳定该过程，以连续生产产品气体。目前富燃料甲烷燃烧的机制——用于模拟甲烷的“冷焰”行为——预测这种燃烧产生的产物气体的氢产量将超过目前的燃烧方法，氢：水比为3或更好。在这项工作中，设计和建造了一个高压反应器，用于燃烧甲烷/空气混合物，当量比约为4。反应器的设计是为了促进这些流动的稳定，其特点是长感应时间和低热量释放。此外，该反应器具有完整的光学通道，可以在流动中进行详细的温度和物质浓度测量，并与动力学模型的预测进行优化比较。利用该反应器，对非常丰富的甲烷/空气混合物在高压下的燃烧进行了广泛的表征。温度和甲醛的空间分布，诱导时间，和详细的产品产量测量作为一个函数的过程参数，并倾向于烟灰的形成进行了检查。利用这些数据，在这些条件下对当前的动力学模型进行了评估和分析。本研究旨在证明从天然气中合成氢气的高压空气燃烧技术的可行性，以及开发计算过程分析和优化工具，同时生成关于这种重要混合物独特燃烧行为的广泛而详细的数据集。经济地将天然气转化为氢燃料是实现大规模使用氢作为交通和工业燃料的关键。此外，燃料电池的广泛使用同样需要廉价的氢源。目前大多数氢合成方案，例如蒸汽甲烷重整和催化部分氧化，仍然过于昂贵，部分原因是与这些过程中固有的催化剂相关的高成本。燃烧技术通过天然气的非催化部分氧化生成一氧化碳和氢气（合成气），为廉价制氢提供了希望。这样的技术可以同时产生电能和氢气，并且可以设计成包括简单的反应堆设施，需要更少的资本成本。目前工业上至少使用两种这样的燃烧过程。如果1)产品气体中氢与水的比例（目前为1比2）可以显著提高，2)所需的氧化剂是空气而不是氧气，则可以显著降低氢合成燃烧过程的成本。

Recent studies on the autoignition behavior of fuel-rich methane/air mixtures at elevated pressures suggests that mixtures at equivalence ratios of around 4 can be made to react rapidly for pressures above 8 atmospheres, and thus it may be possible to stabilize the process in a modified burner configuration for continuous production of product gases. Current mechanisms for fuel-rich methane combustion--those used to model 'cool-flame' behavior of methane--predict that the product gases resulting from such combustion will have hydrogen yields that exceed current combustion approaches and hydrogen:water ratios of 3 or better. In this work, a high-pressure reactor for combustion of methane/air mixtures at equivalence ratios of approximately 4 is designed and constructed. The reactor is designed to facilitate stabilization of these flows, which are characterized by long induction times and low heat release. In addition, the reactor has complete optical access, enabling detailed temperature and species concentration measurements in a flow that is optimized for comparison with the predictions of a kinetic model. Using this reactor, an extensive characterization of the combustion of very rich methane/air mixtures at elevated pressures is conducted. Temperature and formaldehyde spatial profiles, induction times, and detailed product yields are measured as a functions of process parameters, and the propensity for soot formation is examined. Using these data, current kinetic models are evaluated and analyzed under these conditions. This study is designed to demonstrate the feasibility of elevated pressure, air-based combustion techniques for hydrogen synthesis from natural gas, as well as to develop the tools for computational process analysis and optimization, while simultaneously generating an extensive and detailed dataset on the unique combustion behavior of this important mixture.Economical conversion of natural gas to hydrogen fuel is critical to realization of large-scale use of hydrogen as a fuel for transportation and for industry. In addition, widespread use of fuel cells likewise requires an inexpensive source for hydrogen. Most current hydrogen synthesis schemes, for example steam methane reforming and catalytic partial oxidation, remain too costly, in part due to high costs associated with the catalysts that are inherent in these processes. Combustion technologies offer the promise of inexpensive hydrogen production through non-catalytic partial oxidation of natural gas to carbon monoxide and hydrogen (syngas). Such technologies can generate power and hydrogen simultaneously and can be designed to involve simple reactor facilities that require smaller capital costs. At least two such combustion processes are currently used by industry. Significant cost reduction in combustion process for hydrogen synthesis can be obtained if 1) the hydrogen:water ratio in the product gases (currently ~1 to 2) can be significantly improved, and 2) the required oxidizer is air rather than oxygen.