Gas turbines combustors

Combustors All gas turbine combustors perform the same function They increase the temperature of the high-pressure gas at constant pressure. The gas turbine combustor uses veiy little of its air (10 percent) in the combustion process. The rest of the air is used for cooling and mixing. The air from the compressor must be diffused before it enters the combustor. The velocity leaving the compressor is about 400-500 ft/sec (130-164 m/sec), and the velocity in the combustor must be maintained at about 10-30 ft/sec (3-10 iTi/sec). Even at these low velocities, care must be taken to avoid the flame to be carried downstream. To ensure this, a baffle creates an eddy region that stabi-hzes the flame and produces continuous ignition. The loss of pressure in a combustor is a major problem, since it affecls both the fuel consumption and power output. Total pressure loss is in the range of 2-8 percent this loss is the same as the decrease in compressor efficiency. 

All gas turbine combustors perform the same function, they increase the temperature of the high-pressure gas. The gas turbine combustor uses very little of its air (10%) in the combustion process. The rest of the air is used for cooling and mixing. New combustors are also circulating steam for cooling purpose. The air from the compressor must be diffused before it enters the... 

All gas turbine combustors provide the same function however, there are different methods to arrange combustors on the gas turbine. Designs fall into three major categories ... 

The majority of the NOx produced in the combustion chamber is called thermal NOx. It is produced by a series of chemical reactions between the nitrogen (N2) and the oxygen (O2) in the air that occur at the elevated temperatures and pressures in gas turbine combustors. The reaction rates are highly temperature dependent, and the NOx production rate becomes significant above flame temperatures of about 3300 °F (1815 °C). Figure 10-19 shows schematically, flame temperatures and therefore NOx production... 

Ballal, D.R., and Lefebvre, A.H., A Proposed Method for Calculating Fibn Cooled Wall Temperatures in Gas Turbine Combustor Chambers, ASME Paper 72-WA/HT-24, 1972. 

Hilt, M.B., and Johnson, R.H., Nitric Oxide Abatement in Heavy Duty Gas Turbine Combustors by Means of Aerodynamics and Water Injection, ASME Paper 72-GT-22, 1972. 

Of course, there is no methane at exit from the PO reactor, and no oxygen. The hydrogen content is quite high, over 15% and comparable to that in Lloyd s example of the steam/TCR cycle, but the CO content is also nearly 8%. It is interesting to note that the calculated equilibrium concentrations of these combustible products from the reactor are reduced through the PO turbine (because of the fall in temperature) before they are supplied to the gas turbine combustor where they are fully combusted, but it is more likely that the concentrations would be frozen near the entry values. 

In a first-generation PFBC plant, the PFBC is used as the gas turbine combustor. For this application, the temperature to the gas turbine is limited to a bed temperatnre of about 870°C (1,600°F). This temperature level limits the effectiveness of this cycle as a coal-fired alternative. 

Diagram and photograph of a model gas turbine combustor operating on CH4/air at atmospheric pressure. Fuel is injected from an annulus separating two swirhng air streams. (From Meier, W., Duan, X.R., and Weigand, R, Combust. Flame, 144,225,2006. With permission.)... 

Comparison of perovskite and hexaaluminate-type catalysts for CO/H2-fiieled gas turbine combustors. 

Gas Turbine Combustors GT combustor design has been altered to handle low BTU gas with high mass flow due to problems encountered in gas turbines. 

Duplex 20-200 Gas turbine combustors Simple, Cheap, Wide spray angle, Good atomization over a wide range of liquid flow rates Narrowing spray angle with increasing liquid flow rate... 

Fan spray atomizers have been widely used in the spray coating industry (Fig. 2.5), in some small annular gas turbine combustors, and in other special applications that require a narrow elliptical spray pattern rather than the normal circular pattern. In particular, fan spray atomizers are ideal for small annular combustors because they can produce a good lateral spread of fuel, allowing to minimize the number of injection ports. 

Considering the wake of a flame holder as a stirred reactor may be inconsistent with experimental data. It has been shown [66] that as blowoff is approached, the temperature of the recirculating gases remains essentially constant furthermore, their composition is practically all products. Both of these observations are contrary to what is expected from stirred reactor theory. Conceivably, the primary zone of a gas turbine combustor might approach a state that could be considered completely stirred. Nevertheless, as will be shown, all three theories give essentially the same correlation. 

Stirred reactor theory was initially applied to stabilization in gas turbine combustor cans in which the primary zone was treated as a completely stirred region. This theory has sometimes been extended to bluff-body stabilization, even though aspects of the theory appear inconsistent with experimental measurements made in the wake of a flame holder. Nevertheless, it would appear that stirred reactor theory gives the same functional dependence as the other correlations developed. In the previous section, it was found from stirred reactor considerations that... 

The primary zone of a gas turbine combustor is modeled as a perfectly... 

Pressure oscillations with RMS value up to 10 kPa in two models of lean-burn gas turbine combustors, with heat release around 100 kW, have been actively controlled by the oscillation of fuel flow. The flames were stabilized behind an annular ring and a step in one arrangement, and downstream of an expansion and aided by swirl in the other. Control was sensitive to the location of addition of oscillated fuel. Oscillations in the annular flow were attenuated by 12 dB for an overall equivalence ratio of 0.7 by the oscillation of fuel in the core flow and comprising 10% of the total fuel flow, but negligibly for equivalence ratios greater than 0.75. Oscillation of less than 4% of the total fuel in the annulus flow led to attenuation by 6 dB for all values of equivalence ratio considered. In the swirling flow, control was more effective with oscillations imposed on the flow of fuel in a central axial jet than in the main flow, and oscillations were ameliorated by 10 dB for equivalence ratio up to 0.75, above which the flame moved downstream so that the effectiveness of the actuator declined. The amelioration of pressure oscillations resulted in an increase in NOj, emissions by between 5% and 15%. 

Paschereit, C. O., E. Gutmark, and W. Weisenstein. 1998. Control of thermoacoustic instabilities and emissions in an industrial type gas turbine combustor. 27th Symposium (International) on Combustion Proceedings. Pittsburgh, PA The Combustion Institute. 

Bhidayasiri, R., S. Sivasegaram, and J.H. Whitelaw. 1997. Control of combustion oscillations in a gas turbine combustor. 7th Asian Congress of Fluid Mechanics Proceedings. 107-9. 

High-pressure loss in a gas turbine combustor would result in excess specific fuel consumption and thus should be avoided. When (j> = 0.237 and p = 8 ppcm, the porous layers created an additional pressure drop of about 150 Pa for one 2.5-centimeter-thick porous layer and about 300 Pa for a 5.1-centimeter-thick foam. The loss of efficiency due to the pressure drop is estimated as 0.086% for 2.50-centimeter-thick insert and 0.17% for 5.1-centimeter-thick insert. 

Catalytic combustion for gas turbines has received much attention in recent years in view of its unique capability of simultaneous control of NOX) CO, and unbumed hydrocarbon emissions.1 One of the major challenges to be faced in the development of industrial devices is associated with the severe requirements on catalytic materials posed by extreme operating conditions of gas turbine combustors. The catalytic combustor has to ignite the mixture of fuel (typically natural gas) and air at low temperature, preferably at the compressor outlet temperature (about 350 °C), guarantee complete combustion in few milliseconds, and withstand strong thermal stresses arising from long-term operation at temperatures above 1000°C and rapid temperature transients. 

The flow conditions are chosen to represent a range of gas-turbine-combustor conditions, covering a range of physical parameters that include inlet velocities from 0.5 to 5 m/s and pressures from 1 to 10 bar. These conditions can be characterized in terms of a Reynolds number based on channel diameter and inlet flow conditions, which is varied over the range 20 < Rej = V nd/v < 2000. The upper limit of Rej = 2000 is chosen to ensure laminar flow, hence removing the need to model turbulence. It should be noted that the validity of the boundary-layer approximations improve as the Reynolds number increases. 

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