The numerical simulations of reactive turbulent flows and heat transfer in an industrial slab reheat furnace in which the combustion air is highly preheated have been carried out. The influence of the ratio of the air and fuel injection velocities on the NOx production rate in the furnace has also been studied numerically. A moment closure method with the assumed β probability density function (PDF) for mixture fraction was used in the present work to model the turbulent non-premixed combustion process in the furnace. The combustion model was based on the assumption of instantaneous full chemical equilibrium. The turbulence was modeled by the standard k-ε model with a wall function. The numerical simulations have provided complete information on the flow, heat, and mass transfer in the furnace. The results also indicate that a low NOx emission and high heating efficiency can be achieved in the slab reheat furnace by using low NOx regenerative burners. It is found that the air/fuel injection velocity ratio has a strong influence on the NOx production rate in the furnace.
A study of the effects of nitric oxide (NO) models on the prediction of NO formation in a gas-fired regenerative furnace with highly preheated air was undertaken. Three chemical kinetic processes for NO formation/depletion, i.e., thermal NO, prompt NO, and NO reburning, are included. In the thermal NO model, the sensitivity encountered when using two different approaches, namely the equilibrium approach and the partial equilibrium approach, for determining the O radical concentration was studied. The effects of the third reaction in the thermal NO mechanism, NO reduction (reburning) mechanism, and different types of probability density functions (PDFs) on the NO predictions have also been tested. The sensitivity of the excess air ratio on the NO generation rate in the furnace has been investigated. Finally, the impact of the temperature on the NO formation rate in the regenerative furnace was discussed. [S0195-0738(00)00304-6]
Thermal and chemical characteristics of the flames obtained from an industrial size regenerative combustion furnace have been obtained spectroscopically. The combustion characteristics of diffusion or premixed flames in the regenerative high-temperature air combustion facility have been examined using coal gas as the fuel. The fuel gas composition consisted of H2, hydrocarbon, CO, and N2. Monochromatic images of the flames have been observed in the emission mode using a CCD camera fitted with an optical band pass filter at the desired wavelength. The two-dimensional temperature distribution in the furnace has been determined using the two-line method by utilizing the Swan emission bands from within the flame. The emission intensity profiles of NO, as well as OH and CH radicals have also been observed spectroscopically. The results showed quite uniform two-dimensional temperature distribution and emission intensity of OH and CH radical species for the diffusion flame case as compared to the premixed case using high-temperature combustion air. The premixed flame case showed high local values and large fluctuations in the combustion zone for both emission intensity and temperature distribution. The temperature distribution of soot particles in the premixed flame was also determined using the two-color optical method. The results showed high local value of temperature, similar to that found for the gas temperature using signatures for C2 species at two different wavelengths. In contrast the distribution of temperature for soot particles was different. The location of the maximum soot temperature shifted to downstream positions of the flame as compared to the maximum gas temperature regions measured from the C2 species. The experimental results are discussed in conjunction with those obtained from the heat simulation analyses.
A numerical procedure is presented to predict the turbulent non-premixed combustion flames in regenerative furnaces. A moment closure method with the assumed β probability density function (PDF) for the mixture fraction is used in the present work. The procedure is applied to an experimental regenerative slab reheat furnace developed in NKK to demonstrate its predictive capability. The predictions are compared with the experimental data. The comparison is favorable. [S0022-1481(00)01302-5]
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