RETRACTED: Catalytic Combustion Characteristics of Methane-Air Mixtures in Small-Scale Systems at Elevated Temperatures

Abstract

The catalytic combustion characteristics of methane-air mixtures in small-scale systems were investigated at elevated temperatures, with particular emphasis on identifying the main factors that affect formation and removal of combustion-generated pollutants. Computational fluid dynamics simulations were performed using detailed chemical kinetic mechanisms, and more insights were offered into the phenomena occurring in the temperature range where homogeneous and heterogeneous reaction pathways are both important. Reaction engineering analysis was performed to provide an in-depth understanding of how to achieve low emissions of pollutants. Spatial distributions of the major species involved were presented to gain insight into the interplay between the two competing pathways involved. The results indicated that the distribution of oxidized products depends critically on the feed composition, dimension, temperature, and pressure. Small-scale catalytic systems enable low emissions of pollutants even in a high temperature environment, along with high combustion efficiency. The interplay between the two competing pathways via radicals is strong, and the heterogeneous pathway can significantly inhibit the homogeneous pathway. The inhibiting effect also accounts for the low emissions of nitrogen oxides. Almost all of the nitrogen oxides emitted by small-scale catalytic systems are nitric oxide. Catalytic combustion technology can be used to reduce the formation of undesired products, especially pollutant nitrogen oxide gases far below what can be achieved without catalysts. Recommendations for the design of small-scale catalytic systems are provided.

RETRACTED: Chen et al. Catalytic Combustion Characteristics of Methane-Air Mixtures in Small-Scale Systems at Elevated Temperatures. Catalysts 2018, 8, 439

“…We have become aware that figures and experimental data in the published article [1] are identical to a previously published paper by the same authors [2]. While the authors claim that the work was sufficiently different to that of the previously published paper, our Editorial Board did not agree and we have therefore decided to retract the paper.…”

“…MDPI is a member of the Committee on Publication Ethics and takes the responsibility to enforce strict ethical policies and standards very seriously. To ensure the addition of only high quality scientific works to the field of scholarly publication, [1] is retracted and shall be marked accordingly. We apologize to the readership of Catalysts for any inconvenience caused.…”

Experimental Insights into the Coupling of Methane Combustion and Steam Reforming in a Catalytic Plate Reactor in Transient Mode

“…On the basis of process requirements, the operating temperature for the catalytic methane combustor can be categorized into low (300–700 °C) and high (700–1400 °C) . MSR is a highly endothermic reaction, requiring a large amount of heat at temperatures up to 1000 °C for attractive equilibrium conversion, which makes a high-temperature catalytic combustor desirable. The scaled-down version of the industrial reformer shows poor performance and responds slowly to throughput variation, mainly because of heat transfer limitations between the flame and the catalyst pellet, and also due to mass transfer limitations. , Furthermore, flames quench on small scales, and catalytic combustion is needed . By improving transport limitations, microreactor technology provides unique opportunities to realize compact and modular steam reformers. − In a microreactor, the improved heat and mass transport rates lead to 1–3 times higher throughput of hydrogen .…”

“…27,28 Furthermore, flames quench on small scales, and catalytic combustion is needed. 29 By improving transport limitations, microreactor technology provides unique opportunities to realize compact and modular steam reformers. 30−33 In a microreactor, the improved heat and mass transport rates lead to 1−3 times higher throughput of hydrogen.…”