Bidhan Dam

Laminar flame velocity of syngas fuels

The paper presents the experimental measurements of the laminar burning velocity of H2 -CO mixtures. Hydrogen (H2 ) and carbon monoxide (CO) are the two primary constituents of syngas fuels. Three burner systems (nozzle, tubular, and flat flame) are used to quantify the effects of burner exit velocity profiles on the determination of laminar flame propagation velocity. The effects to N2 and CO2 diluents have been investigated as well, and it is observed that the effects of N2 and CO2 on the mixture burning velocity are significantly different. Finally, the burning velocity data of various syngas compositions (brown, bituminous, lignite and coke) are presented.Copyright

Effect of Local Flow Field Fluctuations on the Characteristics of Turbulent Flames

This paper focuses on the experimental measurements of turbulence and its effect on the local consumption speed of premixed syngas-air mixtures. The flow field visualization using Particle Imaging Velocimetry (PIV) technique is also implemented to make a better understanding of the turbulence characteristics of syngas (H2-CO)-air combustion. The velocity fluctuations, turbulence intensities and local propagation velocities along the burner exit had been determined at different blockage ratios. With the increase of blockage ratios the velocity fluctuations increased in axial direction for both isothermal and reacting flows at a fixed Reynolds number (Re=2000) and equivalence ratio(Ф=.9).For reacting flows the fluctuations decreased up to the reaction zone then increased substantially at both blockage ratios. Turbulent flame propagation velocities were also determined at constant laminar burning velocity for different syngas mixtures. The effect of diluents (N2 and CO2) on turbulent burning velocities of syngas is determined at a constant adiabatic flame temperature of 1900K and at different blockage ratios. Turbulent flame propagation velocities increase with the increase in the blockage ratios. Turbulent flame propagation velocities increase with increase in hydrogen content in the syngas mixtures at constant laminar burning velocity.

Investigation of Flashback Propensity in Turbines with Syngas Fuels

The paper presents experimental measurements of combustion induced vortex breakdown (CIVB) flashback propensity for hydrogen (H2)-carbon Monoxide (CO) flames. The effects of H2 concentration, diluents and swirl number on the flashback propensity of H2-CO flames are discussed. For a given Ubulk, the stoichiometric ratio (%F) at which the CIVB flashback occurs decreases with the increase in H2 concentration in fuel mixtures. However, the flashback propensity decreases with the increase in the swirl number. Combustor flashback maps for syngas compositions derived from different coal source shows the distinct behavior due to the presence of various diluents in fuel mixtures.

Large eddy simulation of reacting centerbody stabilized swirled flow in a gas turbine combustor

This study is focused on understanding the changes in the flowfield when the operating conditions of a gas turbine combustor shift closer to the flashback regime. Flow visualization techniques and Computational Fluid Dynamics (CFD) technologies are used to analyze the complex flow-flame interactions that develop in the combustor. It is concluded in this study that when the combustor is operating in a stable condition, there is a bubble type recirculation zone anchored at the centerbody of the swirler. However, when the operating conditions shift closer to the flashback point, the bubble type vortex breakdown transforms into a spiral type vortex, which is characterized by a rapid deceleration of the flow, followed by a corkscrew-shaped twisting of the flow.

Characterization of Oxy-Fuel Flames in a Swirl Based Combustor

This paper focuses on the experimental measurements of the flow field characteristics of premixed CH4/21%O2/79%N2 and CH4/38%O2/72%CO2 mixtures at contant firing input of 7.5 KW, constant, equivalence ratio of .8, constant swirl number of .92 and constant Reynolds Number of 4500. The flow field visualization using Particle Imaging Velocimetry (PIV) technique is implemented to make a better understanding of the turbulence characteristics of CH4/air and CH4/38%O2/72%CO2 combustion. The velocity fluctuations, turbulence intensities and local propagation velocities along the combustion chamber have been determined. The turbulent intensities increase as we move away from the combustor axis. CH4-38%O2-72%CO2 flames have low radial velocity and turbulent intensity distributions at different axial distances when compared with CH4-Air flames.

Effect of CO2 and H2O diluents on radiative heat release rates of Oxy-fuel flames

Oxy-fuel combustion is the burning of fuel (typically a hydrocarbon) in oxygen instead of air. The flue gases are recycled from the exit of the boiler/combustor/furnace and combined with oxygen to maintain allowable combustion temperature. The process generates concentrated CO2 with H2O in the exhaust. Producing concentrated CO2 from fossil fuel power station is important because it is much easier and efficient to capture and store the gas. It is expected that oxy-fuel incorporated with carbon capture and storage (CCS) would be a viable retrofit technology as well as an option for new build projects to reduce anthropogenic global warming. Currently Department of Energy (DOE) is considering oxy-fuel turbine cycle as an alternative to hydrogen based power generation. The oxy-fuel turbine cycle, the burning of pure fossil fuel and pure oxygen, offers same system efficiencies to the H2 turbine with an additional 10 percent CO2 capture. Since the oxidant does not include significant concentrations of nitrogen it has the benefits of near zero NOx emissions. Table 1 presents a summary of recent studies investigating oxy-fuel combustion systems.

Determination of Radiative Heat Release Rates of Oxy-fuel Flames

The development of alternative hydrocarbon combustion techniques that can accommodate capture and sequestration of CO2 were encouraged due to concerns about green house gas emissions. Oxy-fuel combustion technique has potential to capture CO2 effciently and meet the sequestration goals, however, this technique has brought a number of concerns, especially flame dynamics and flame radiaiton characateristics. This paper presents experimental measurements of radiative heat release rates of CH4-O2 flames and CH4-air flames at similar operating conditions. The effects of recirculated CO2 to the oxyfuel combustion conditions were investigated in this article. The radiative heat release rates of CH4-O2 flames were greater than CH4-air flames. The radiative heat release rate of CH4-O2 flame is almost constant for the lean flames, yielded F value 4.1%, 8.9% by using solar radiometer and Mark IV radiometer respectively. Once the equivalence ratio reached more fuel rich conditions (φ >1) the radiative factor increases as the equivalence ratio increases further. No significant differences were observed for radiative heat release rates of 75%CH425%CO2-O2 and CH4-O2 flames at a constant firing input.

An Experimental Investigation of Combustion Induced Vortex Breakdown Flashback in a Swirl Stabilized Burner

This paper presents an experimental investigation of combustion induced vortex breakdown (CIVB) flashback propensity for flames yielded from Hydrogen (H2) - Carbon Monoxide (CO) fuel blends and actual synthesized gas (syngas) mixtures. A two-fold experimental approach, consisting of a high definition digital imaging system and a high speed PIV system, is employed. The main emphasis was on the effect of concentration of different constituents in fuel mixtures on flashback limit. In addition, the effect of Swirl Number on flashback propensity was discussed. The percentage of H2 in fuel mixtures played the leading role to cause CIVB flashback. For a given air mass flow rate, the mixture containing higher percentage of H2 underwent flashback at much leaner condition than that containing less H2. Flashback map for actual syngas fuel compositions showed distinct behavior due to the presence of various diluents in the mixture. CO had significant dominance over H2 that helped retarding flashback propensity. Of the two major diluents carbon dioxide (CO2) and nitrogen dioxide (NO2), CO2 was more dominant. It appeared that the flashback propensity decreased with an increase in Swirl Number. The analysis of flow field of reacting flames revealed the complex vortex-chemistry interaction leading to vortex breakdown and flashback. Based on the experiential results a parametric model similar to Peclet Number approach was developed employing flame quenching concept. A value of the quench parameter, Cquench was obtained from the correlation of flow Peclet Number and flame Peclet Number, which was observed to be dominated by the fuel composition rather than Swirl Number.

Flashback Propensity in Swirl Stabilized Burner With Syngas Fuels

In swirl stabilized burner, combustion induced vortex breakdown (CIVB) flashback is a significant phenomenon. This paper presents experimental measurements of CIVB flashback propensity for hydrogen (H2 )-carbon monoxide (CO) flames. The effects of H2 concentration, and swirl number on the flashback propensity of H2 -CO flames are discussed. For a given air mass flow rate, the stoichiometric ratio (%F) at which the CIVB flashback occurs decreases with the increase in H2 concentration in fuel mixtures. However it appears that near the CIVB flashback limit, the swirl strength plays a more dominating role over the H2 concentration in the fuel mixture. The flashback propensity decreases with the increase in swirl number. An analysis of the nonreacting flow field (Air 6 g/s) as well as reacting (CH4 -Air and H2 -CO-Air) flame near the CIVB transient velocity field was conducted. The analysis revealed that a complex vortex-chemistry interaction leading to vortex breakdown and flashback occurred. The vector flow field showed that the high swirling flow generates a more stabilized and wider recirculation zone. It also showed that the presence of H2 dictates the intensity of the flashback process.Copyright

Flashback Propensity of Syngas Fuels

The paper presents experimental measurements of flashback propensity of H2 -CO mixtures (primary constituents of syngas fuels). Effects of H2 concentration, external excitation and swirl on the flashback propensity of H2 -CO flames are discussed. The flashback behavior of H2 -CO flames changes nonlinearly with the increase in H2 contents in the mixture. The critical velocity gradient (gF ) values of 5%–95% and 15%–85% H2 -CO mixtures somewhat agree with the scaling relation (gF = c(SL 2 /α)) and yield an average c value of 0.035. However, the gF values of 25%–75% H2 -CO mixture show higher order variations with the SL 2 /α ratio (especially for SL 2 /α < 19,000 s−1 ). At a lower SL 2 /α ratio, burner diameters have small effects on critical velocity gradient measurements; however, the effect is significant at higher SL 2 /α ratio. The effect of external excitation on the flashback propensity of H2 -CO flames with more than 5% H2 is not significant. Flashback through two mechanisms and their dependence on combustor parameters were also identified for swirl stabilized H2 -CO flames.Copyright