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

最近对富含燃料的甲烷/空气混合物在加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8个大气压以上的压力下快速反应，因此有可能在改进的燃烧器结构中稳定这一过程，以连续生产产品气。目前用于模拟甲烷冷火焰行为的燃料丰富的甲烷燃烧机制预测，这种燃烧产生的气体的氢产率将超过当前的燃烧方法，氢水比为3或更高。在这项工作中，设计和建造了一个甲烷/空气混合物当量比约为4的高压燃烧反应器。该反应堆的设计是为了促进这些流动的稳定，这些流动的特点是诱导时间长，热释放低。此外，该反应器具有完整的光学通道，能够在经过优化以与动力学模型的预测进行比较的流动中进行详细的温度和物种浓度测量。利用该反应器，对富含甲烷/空气混合物在高压下的燃烧进行了广泛的表征。测量了温度和甲醛的空间分布、诱导时间和详细的产品产率作为工艺参数的函数，并检查了碳烟形成的倾向。利用这些数据，对现有的动力学模型在这些条件下进行了评估和分析。这项研究旨在论证天然气加压空气燃烧制氢技术的可行性，并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。天然气向氢燃料的经济转化对于实现大规模使用氢作为交通和工业燃料至关重要。此外，燃料电池的广泛使用同样需要廉价的氢气来源。目前的大多数氢气合成方案，如蒸汽甲烷重整和催化部分氧化，成本仍然太高，部分原因是这些过程中固有的催化剂成本较高。燃烧技术通过天然气非催化部分氧化生成一氧化碳和氢气(合成气)，提供了廉价的氢气生产前景。这类技术可以同时产生电力和氢气，而且可以设计成只需简单的反应堆设施，需要较小的资本成本。目前，工业中至少使用了两种这样的燃烧过程。如果1)产品气体中的氢水比(目前为~1：2)能够显著提高，以及2)所需的氧化剂是空气而不是氧气，则可以显著降低氢气合成的燃烧过程的成本。

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.