Numerical investigation of the effect of constant velocity and constant residence time scaling criteria on the natural gas MILD combustion

Abstract

This paper concerns with effect of scaling on performance of MILD combustor when increasing its geometry and thermal throughput from the 0.58 MW prototype to its scaled-up versions of 5.8 MW. The constant velocity (CV) and constant residence time (CRT) scaling approaches were used in this work. Their performances were simulated with a numerical model for MILD combustion which was thoroughly validated against existing experimental data. It was found that despite MILD condition could be successfully maintained with both scaling approaches up to the scaling factor of 10, the effect of CV scaling could lead to elevated NOx emission due to increase in flow retention time in hot environment. The results were also discussed in term of Damköhler number. Despite of promising technology of MILD combustion for low-NOx emission, care must be taken on NOx emission level when scaling up with large scale factor under the CV criteria. As for the CRT criteria with increasing inlet velocity with the scale factor, the fuel and air supply pressure should be considered as a constrain when scaling up with large scale factor.

Estudio Numérico Del Escalado De Un Sistema De Combustión Sin Llama Y El Efecto Del Número De Boquillas De Descarga De Aire

“…Mantener todos los factores constantes durante el escalado no es posible, dado que ello requeriría una similitud tanto cinemática como dinámica del sistema. Por lo tanto, dependiendo de cuál o cuáles factores se quieran conservar durante el escalado, existen diferentes criterios que permiten hacer un óptimo escalado de un sistema de combustión, siendo los más utilizados en sistemas de combustión industriales el criterio de velocidad constante y el de tiempo de residencia constante (Kumar, Paul, & Mukunda, 2005;Suksam & Charoensuk, 2019) lo cuales dependen de la potencia del prototipo a escalar y la potencia a la que se quiere llegar con el sistema de calentamiento escalado.…”

“…donde ρo, Uo y Do son la densidad del fluido, la velocidad del quemador y el diámetro del quemador por donde se descarga el fluido, respectivamente, mientras K representa una constante de proporcionalidad (Suksam & Charoensuk, 2019).…”

Short overview on combustion systems scale‐up with emphasis on NOx emissions of gas‐fired furnaces

“…An ideal scaling of all relevant processes, such as the mixing process and chemical reaction kinetics, at varying thermal input power levels in the laboratory and industrial scale is not possible. 8,[28][29][30] Since the value of a dimensionless parameter can cover considerably more operating points than a value of a dimensional parameter, 31,32 common scaling approaches are based on keeping dimensionless parameters constant. With the CV approach, the characteristic inlet velocity U 0 and consequently the ratio U 01 ∕U 02 between system 1 and system 2 is kept constant.…”