Yufeng Cui

Flashback Limit and Mechanism of Methane and Syngas Fuel

Flashback is one of the major problems in lean premixed combustion of gas turbine combustor. Due to the effulgent future of co-product system and IGCC, lean premixed combustion, one of the approaches to ultra low NOx for rich hydrogen syngas fuel need farther research on anti-flashback and low pressure drop combustor. Mechanism and characteristics of methane and syngas flashback for 2 types of flame holders, i.e. ring shape and rod shape have been researched through experiment as well as numerical simulation. The partial premix model has been selected to simulate premixed combustion flashback process since it combined the advantage of PDF model and TFC model. Experiments demonstrate that, the flashback velocity of different fuel compositions or flame holder size generally can be correlated to the same dimensionless function by using Peclet number model if the structures of flame holders are the same. Peclet function curves were used to compare the anti-flashback performance of the 2 types of flame holders mentioned above with swirl holder. Boundary coaxial jet can change flashback through the wall into flashback in the core flow and significantly improve the anti-flashback performance of the ring-type flame holder on condition that the velocity of the boundary coaxial jet is in an optimal range. As the result, ring shape holder shows the best while swirl holder the worst on anti-flashback performance.© 2006 ASME

The Effects of Fuel Dilution With Steam on Gas Turbine Combustor Performance

The formation of nitrogen oxides (NOx ) in combustion systems is a significant pollutant source in the environment, and How to control NOx emission is a worldwide concern as the utilization of fossil fuels continues to increase. Syngas is produced from variety of fossil fuels through a gasification process. Though syngas is regarded as one kind of clean fuel, its NOx emission control techniques in combustion systems still remain many problems for further development. Steam dilution of fuel is an effective method for NOx reduction in practical gas turbine systems. This paper describes the study focusing on the influence about steam dilution of fuel for reducing the NOx emission. Experimental investigations are conducted on a 40MW gas turbine fired with syngas. The pollutant emissions, combustor dynamic pressure, metal temperature distribution of liner and combustion efficiency are analyzed at the base load of gas turbine with different steam injection rate to fuel flow. Three-dimensional CFD numerical simulation of combustor according to experiment parameters is applied to investigate the influence of steam dilution on NOx emission and the combustion liner wall temperature. Comparisons are made between experiment data and CFD simulation results for further understandings about NOx formation characteristics in steam diluted syngas and its influence to gas turbine combustion system. The investigation of this paper’s work shows tha steam dilution is an effective method of NOx emission control technique in practical gas turbine combustion systems fired with syngas. The CFD simulation results show that steam in flame can remarkably reduce temperature of the flame for its high thermal capacity and it can remarkably reduce formation of NOx in gas turbine combustor. Moreover, as the steam flowrate added to fuel increase the wall temperature of some zone of liner may increase because of the convection heat transfer is strengthened and the combustion oscillation will be weaken.Copyright

The Effects of Pressure on Gas Turbine Combustor Performance: An Investigation via Numerical Simulation

Performance tests of a gas turbine combustor are usually conducted at atmospheric or medium pressure which is quite different from its real operating condition. The effects of pressure on the performance of a gas turbine combustor for burning medium-heating-value syngas are researched by numerical simulation in this paper. The geometry of the combustor is modeled by coupling all its components including nozzle, combustor liner and sealant tube. In the simulation a laminar flamelet model and P-1 radiation model are adopted. The numerical results show that at the same fuel and air inlet temperature and the same equivalence ratio, the operation pressure has less effect on the flow fields, but its effect on the temperature distribution is obvious. Both the highest temperature in the combustor and the outlet temperature increase with increasing operating pressure because of the weakening of the dissociation of the H2 O, CO2 and so on. Moreover, as pressure increases, the concentration of H2 O and CO2 in the combustor increase, and so to does the absorption coefficient and the emissivity of gas inside the liner. As a result, the radiation heat transfer between the gas and the combustion liner wall is enhanced, and the wall temperature of the liner increases. The NOx emissions of the combustor are also distinctly higher at high pressure than at low pressure.Copyright

Numerical Investigation of a Stagnation Point Reverse Flow Combustor

Flameless combustion is characterized by ultra-low NOx emissions, high combustion efficiency and very stable flame, which is able to operate stably at very lean fuel-air mixtures without problems of combustion oscillation and flashback. Stagnation Point Reverse Flow (SPRF) combustors, as an important application of flameless combustion, have been experimentally studied by various optical diagnostic techniques. In this paper, Eddy Dissipation Concept (EDC) model with detailed chemical reaction mechanisms of natural gas GRI 2.11 is used to investigate the flame characteristics of a SPRF combustor operating at premixed mode with various mass flow rates and equivalence ratios of CH4 and air mixtures. The numerical results indicate that as the fuel and air mixture injection velocities increase, there are no distinct changes in the jet penetrations. However, flame temperatures and NOx emissions decrease, CO emissions increase, and OH is distributed in wider area and more evenly. For turbulent flow, intense reactions take place in the shear layer and the stagnation zone and they gradually shift to the combustor outlet as the jet velocities increase. As the equivalence ratios increase from 0.5 to 1, the NOx emissions always increase, although they are very low when equivalence ratio is below 0.7. However, the CO emissions decrease firstly, reaching the minimum value at equivalence ratio of 0.58, and then increase. The numerical results are compared with experimental data and it is verified that EDC model can capture the important flow field characteristics and flame structure and is appropriate for modeling SPRF combustor.Copyright

Design and Development Test of a Gas Turbine Combustor for High Hydrogen Medium Heating Value Syngas Fuel

When gas turbine is used in coal co-production system, its combustor needs to burn syngas produced by coal gasification. The syngas’ main combustible compositions are CO and H2 , and it has a nominal lower heating value of 10920kJ/ncm. In this paper, three modification schemes of a heavy-duty gas turbine combustor burning syngas are proposed. Flow fields, temperature profile and chemical reaction characteristics are compared using three-dimensional CFD numerical simulation and two of them have been chosen for medium-pressure, full-scale tests at the Gas Turbine Combustor Laboratory of the Institute of Engineering Thermophysics, Chinese Academy of Sciences. Laboratory tests show good result in exhaust emissions, combustor efficiency, exhaust temperature profile, and metal temperature distribution of liner and transaction pieces, which indicate that the retrofitting schemes satisfied the design specification. In addition, the dynamic characteristics of the combustors are researched applying FFT and wavelet analyses.Copyright

Experimental Test on a Syngas Model Combustor With Flameless Technology

The research of combustor for gas turbine using flameless combustion technology is in the stage of laboratory. This paper designs a flameless model combustor using syngas, which has similar flow structure with reverse-flow can-type combustors and therefore could be used in typical small gas turbine system. In this combustor, either the premixed or non-premixed mode can be selected, meanwhile the difference is discussed. CFD methods are used to design the flow field and emissions of a combustor with detailed mechanisms. How the distance between the nozzle and axis influences the recirculation zone is discussed and optimized in the Isight platform. In the experimental test, the emissions and dynamic pressure characteristics are the main focus. The results demonstrate that flameless combustion technology has potential to be applied in gas turbine with syngas for the aim of Ultra-low pollutant emission combustion, which can restrict emission in a low level meanwhile maintain combustion stability. Flameless combustion is a rising ultra-low-pollution combustion technology. However, in this combustor when pilot flame existed, in some conditions the thermoacoustic oscillation was observed. The CFD results illuminates that this combustor ensures the recirculation in the primary zone, meanwhile the position of the nozzle and injection’s velocity have significant effect to the flow field.Copyright

Influence of Humid Air on Gaseous Combustion of Gasturbines

Combustion with humid air is a key process of humid air turbine (HAT) cycle. In the present study, the influence of humid air on gas turbine combustion was studied both experimentally and numerically. Performance of a full-scale can-type combustor equipped with a diffusion burner was investigated when burning propane and syn-gas with various humidity of intake air. The results indicate that the effect of humid air on pollutant emission depends on fuel type due to the difference of chemical mechanisms. For the syn-gas flames, moisture addition can effectively reduce NO emission without increasing CO. A numerical model was developed to simulate the 3D flow field in the combustor when burning syn-gas. The mixture fraction approach and the laminar flamelet model were applied to simulate the diffusion flame. The thermochemical quantities of the flamelets were computed by adopting a detailed chemical reaction mechanism for the H2 -CO-N2 -O2 system. The numerical results show that an oval hot zone above 2100 K is formed near the axis of the combustor due to flow recirculation. The hot zone mainly accounts for the thermal NO in the syn-gas flames. With the moisture addition into intake air, the volume of this zone is substantially decreased, and, therefore, the NO production is suppressed. This explains the NO reduction due to humid air observed in the experiment.© 2005 ASME