Investigation Of Flameless Combustion Technology For Hydrogen-rich Fuels In Micro Gas Turbine

With the development of gas turbine technology, the small gas turbine is more and more widely used as key equipment of distributed energy supply system. The traditional fuels for small gas turbines include light oil and natural gas. However, natural gas resources becoming increasingly strained, so hydrogen-rich fuels can be an effective supplement/replacement of natural gas. The representative hydrogen-rich fuels contain synthesis gas, coke oven/blast furnace gas, chemical exhaust gas, biomass gasification gas and city gas and so on. Common grounds of these fuels are high flame propagation speed, low calorific value and instability combustion. The mainstream low-polluting combustion technologies currently encounter difficulties when hydrogen-rich fuels is applied:The diluted combustion, which is the most current used, can control the NOx emission under 25ppm@15%02.But in small gas turbines the diluents are difficult to obtain, and excessive dilution will also lead to the decline in combustion efficiency and combustion instability; the other mature technology is lean premixed combustion, whose biggest problems are flashback and acoustic oscillations. In particular, the oscillation contains a nondeterministic factor, which is difficult to obtain diagnosis and control. To meet this challenge, several new low emission technologies, including catalytic combustion(CA), Rich-quench-lean(RQL), and flameless combustion, as well as flameless combustion in this paper, have become research hotspots.It is great believed that flameless combustion is the most promising applications to solve the problem in distributed energy supply system with hydrogen-rich fuels. Flameless combustion can be obtained by mixing a large amount of high-temperature burnt gas with fresh air so as to decrease the O2 concentration in oxidants while reaching the temperature of the self-ignition point of the fuel-oxidants mixture.. When fuel is injected into this kind of oxidant with high speed, combustion proceeds spatial homogeneously without a clear flame brush. Flameless combustion is particularly suitable for small gas turbine combustor with hydrogen-rich fuel, because small gas turbine usually has a recuperator which can just match the high inlet temperature in flameless combustion, and flameless combustion can reduce the NOx and CO emissions at the same time. At present, there is no systematically studies focus on flameless combustion with hydrogen-rich fuels in public literatures.In this paper, studies for flameless combustion with hydrogen-rich fuels were mainly focused, which contains theoretical analysis, mechanism experimental, mode combustor design and performance tests at atmospheric and higher pressure.First of all, though path analysis and sensitivity analysis, the author found that in flameless combustion a lot of characteristics changed including path and rate of elementary reactions, laminar flame thickness, laminar flame propagation velocity and ignition delay time. Flameless combustion has a correlation length scale close to the flame thickness, and the correlation volume is much larger.. Combustion can be understood as a continuous process of deflagration and extinguished.This paper concentrates on the characteristics of syngas'flameless combustion. The autor took different C/H ratios in a unique heat value, oxidant temperatures, O2 concentration and equivalence ratios into consideration. The experimental results showed the key feature to approach low NOx emission is the reduced O2 content in oxidation. However, this will narrow the flammable range and cause combustion instability. In this paper,10% O2 content in oxidation is a suitable percentage, in which the pollution can be controlled efficiently and less O2 content is not necessary to avoid extra flame instability.This paper designed a model combustor using flameless technology, and the author introduced parametric design approach into the design procedure, so the design cycle was reduced greatly and duplication of effort was avoided. By determination of parameters such as recirculation amount, the structure was specified. And in this paper, Eddy Dissipation Concept model, which took detailed chemical reaction mechanism and turbulence-chemistry interaction into account, was taken to three-dimensional CFD calculation, so detailed velocity distribution, temperature distribution, species distribution were obtained.The author took natural gas, diluted natural gas (to simulate heat value of synthesis gas), hydrogen-rich synthesis gas and coke oven gas in the test. The results demonstrated that the pressure loss, combustion efficiency and heat of combustion intensity of heat were in line with design goals. Different fuels could all reach ultra-low pollutant emissions, so the combustor had certain fuel flexibility. Dynamic characteristics of the combustion chamber test results illustrated the flameless combustion is a stable combustion, less prone to thermoacoustic oscillation. Laser-induced fluorescence measurements of the combustion flame structure analysis shows that a state of flameless combustion flame brightness is lower than the conventional combustion mode.