Experimental And Numerical Study Of Trapped Vortex Combustor

The development of IGCC and CO₂ Zero Emission technology has brought forward ademand of using hydrogen or hydrogen rich syngas as fuel in gas turbine combustionchambers. Presently, combustors in industrial gas turbines mostly are swirl burners whichtake natural gas as fuel. Due to the big difference between the chemical characteristics ofhydrogen and natural gas, there might be many problems for a traditional swirl burner touse hydrogen rich fuel, such as flame instability, local high-temperature, and high NO_xemissions. Therefore, a novel combustion technology and a new type of combustor forhydrogen rich fuel use must be developed.Trapped vortex combustion technology, which was firstly developed from theaero-engine after burner, is considered the most potential candidate among the newgeneration of hydrogen rich fuel combustion technologies. However, research works aboutthis subject have just been started, and the feasibility of the technology has not beenconfirmed yet. Therefore, in this paper, an experimental trapped vortex combustor wasmanufactured, and a numerical simulation model was fabricated for realizing premixedcombustion of hydrogen rich fuel in a trapped vortex combustor. Experimental andnumerical studies were carried out focusing on combustion characteristics of purehydrogen and hydrogen rich syngas in the model combustion chamber.First of all, some structure parameters, such as the dimension scale of cavity walls, thelocation of primary flow injection holes, the entrance angle of main flow, and so on, havebeen studied, focusing on their influence to the cavity flow field, the forming of vortexes,and the pressure drop in the combustor. Based on the studing results, principles for a modelTVC design have been put forward, and appropriate structure parameters for theexperimental combustor have been chosen.Then the characteristics of flow field, the shape of the flames, and the instantaneousOH images have been studied. Results showed that a trapped vortex is realized in themodel combustor, and a two-vortex structure could be achieved in the cavity zone whenunder suitable flow conditions.Flame stability performances in the experimental trapped vortex combustor were carried out by doing the lean-blow-out experiments, monitoring the dynamic pressue,analysing the root mean square images of OH, and PDF statistic of OH signal intensity.Results showed that, flame stability of the model combustor is better when burninghydrogen than burning syngas, the combustion mode in the cavity zone has few influencetowards flame stability, flame stability performance turns worse when increasing the heatloading of the combutor or decreasing the overall equivalent ratio. The characteristicoperating parameter when flame stability is relatively better is S_f=0.4.Pollutants emission was tested in the experiments for both fuels. Results showed thatNOx emission for hydrogen was in the range of 3～10ppmvd (15%O₂). When the primaryflow is in a premixed mode, NOx emission for hydrogen was 3～5ppmvd lower than that ofin non-premixed mode. When taking syngas as fuel, NOx emission was about 3ppmvdlower than taking hydrogen as fuel, at the same operating condition. NOx emission of thecombutor was reduced when the overall equivalence ratio decreased or when the heat dutyincreased. The characteristic operating parameter for a relatively lower pollutants emissionin the model combustor isΦ_p=0.4.A numerical research, in which the combustor was divided into three reaction zones,showed that, for pollutants deduction, the residence time needed by hydrogen and syngasin each reaction zone is different. For hydrogen, NO_x emission would decrease as theresidence time of reactants in the cavity and mixing zone increases, whereas, the situationof syngas is just on the opposite. Shortening the residence time of both fuels in the maincombustion zone is good for NO_x deduction, but for syngas, the residence time can't be tooshort to complete the combustion of CO.Through the research work of this paper, a general view of hydrogen rich fuelcombustion characterisitcs in a trapped vortex combustor has been portrayed, and thefeasibility of trapped vortex technology as a potential hydrogen rich fuel combustiontechnology has been preliminarily confirmed. Corresponding characteristic operatingparameters for relatively high flame stability performance and relatively low pollutantsemission have been put forward seperately. In general, the work of this paper has provideda data basis for further research of adopting trapped vortex combustion technology intohydrogen rich fuel combustion chambers and IGCC gas turbine systems.