Numerical Study On The Effect Of Diluent On Micromix Combustion Of Syngas

Micromix combustion technology is a new type of combustion technology that achieves ultra-low emissions by reducing the mixing scale of fuel and air.Its unique micro-nozzle array arrangement can decompose a complete long flame into many short micromix flames,reduce the flame length and width,shorten the residence time of flue gas in the high temperature area,and then achieve low NOx emissions.This paper is based on the single nozzle micromix burner which is designed b y the research group independently,using syngas as fuel and three inert gases of N 2,CO2 and Ar as diluents.The influence of changes in flow rates,dilution rates and diluent types on the related combustion characteristics of the micromix burner were studied.And based on the simulation data of the single nozzle burner,the cold and hot flow field distribution law and related combustion characteristics in the case of multiple nozzles were studied.This paper first analyzed the structure of the single nozz le micromix burner and established its fluid domain model and structure grid of the fluid domain.The number of grids used in subsequent simulations was determined by grid independence verification.After consulting and analyzing the literature,and comparing different syngas combustion mechanisms,a 16-step simplified syngas combustion mechanism was finally used for the thermal simulation of the micromix burner.After determining the grid model of the burner and combustion mechanism,this paper used the uniformity of fuel distribution at the outlet of the micromix burner,the reflow rate,the shape of the temperature field and the combustion temperature as the evaluation indicators.The effects of changes in swirl hole flow rates,dilution rates and diluent types on the flow field and combustion characteristics of the micromix burner were studied when the composition of syngas were H2: CO = 1: 1 and H2: CO = 2: 1.The range of the swirl hole flow rates,dilution rates and diluent types suitable for different syngas composition of the micromix burner were determined.Then,this paper analyzed two common flame modes in turbulent premixed combustion,studied the effect of burner downsizing on the turbulent premixed combustion flame.The flame modes of micromix combustion under different flow rates,dilution rates and diluent types under the two syngas compositions were calculated.Finally,based on the simulation data of single nozzle micromix burner,the layout structure of three multi-nozzle micromix burners was studied,and the cold and hot flow fields and combustion characteristics of the burner under each structure were analyzed.It is finally determined that for the multi-nozzle layout structure of the micromix burner,the micromix array burner combined with a single nozzle micromix swirl burner as the unit nozzle is the most reasonable,which can not only achieve stable combustion but also ensure higher combustion efficiency.