Effect of diffusion on the combustion characteristics and flame stability of catalytically supported thermal combustion systems
Creators: name: Chen, Junjie
Publisher: name: figshare
Year: 2022
Subjects: subject: 90403 Chemical Engineering Design
subject: FOS: Chemical engineering
subject: 90499 Chemical Engineering not elsewhere classified
subject: 90402 Catalytic Process Engineering
subject: 91501 Computational Fluid Dynamics
subject: FOS: Other engineering and technologies
subject: 91502 Computational Heat Transfer
subject: 91505 Heat and Mass Transfer Operations

description: Catalytically-supported, thermal combustion surmounts the mass transfer limitation. If the operating temperature of the catalyst is increased substantially into the mass transfer limited region, the reaction rate again begins to increase exponentially with temperature. This is an apparent contradiction of catalytic technology and the laws of mass transfer kinetics. The phenomena may be explained by the fact that the catalyst surface and the gas layer near the catalyst surface are above a temperature at which thermal combustion occurs at a rate higher than the catalytic rate, and the temperature of the catalyst surface is above the instantaneous autoignition temperature of the fuel-air admixture. The fuel molecules entering this layer spontaneously burn without transport to the catalyst surface. As combustion progresses, it is believed that the layer becomes deeper. The total gas is ultimately raised to a temperature at which thermal reactions occur in the entire gas stream rather than only near the surface of the catalyst. Once this stage is reached within the catalyst, the thermal reactions continue even without further contact of the gas with the catalyst as the gas passes through the combustion zone. The term "instantaneous auto-ignition temperature" for a fuel-air admixture as used herein is defined to mean that the temperature at which the ignition lag of the fuel-air mixture entering the catalyst is negligible relative to the residence time in the combustion zone of the mixture undergoing combustion. Catalytically-supported thermal combustion is achieved by contacting at least a portion of the carbonaceous fuel intimately admixed with air with a solid oxidation catalyst having an operating temperature substantially above the instantaneous auto-ignition temperature of the fuel-air admixture. At least a portion of the fuel is combusted under essentially adiabatic conditions. Combustion is characterized by the use of a fuel-air admixture having an adiabatic flame temperature substantially above the instantaneous auto-ignition temperature of the admixture but below a temperature that would result in any substantial formation of oxides of nitrogen. The adiabatic flame temperature is determined at catalyst inlet conditions. The resulting effluent is characterized by high thermal energy useful for generating power and by low amounts of atmospheric pollutants. Where desired, combustible fuel components, for example, un-combusted fuel or intermediate combustion products contained in the effluent from the catalytic zone, or fuel-air admixture which has not passed through a catalytic zone, may be combusted in a thermal zone following the catalytic zone. Sustained catalytically-supported, thermal combustion occurs at a substantially lower temperature than in conventional adiabatic thermal combustion and therefore it is possible to operate without formation of significant amounts of nitrogen oxides. Combustion is no longer limited by mass transfer as in the case of conventional catalytic combustion, and at the specified operating temperatures the reaction rate is substantially increased beyond the mass transfer limitation. Contributor: Junjie Chen, ORCID: 0000-0001-5055-4309, E-mail address: komcjj@gmail.com, Department of Energy and Power Engineering, School of Mechanical and Power Engineering, Henan Polytechnic University, 2000 Century Avenue, Jiaozuo, Henan, 454000, P.R. China