Lean Low NOx Primary Zones Using Radial Swirlers

1988 ◽  
Author(s):  
H. S. Alkabie ◽  
G. E. Andrews ◽  
N. T. Ahmad
Keyword(s):  
Natural Gas ◽  
Recirculation Zone ◽  
Fuel Injection ◽  
Swirling Flow ◽  
Combustion Efficiency ◽  
Flame Stability ◽  
Nox Emissions ◽  
Primary Zone ◽  
Outer Expansion ◽  
Curved Blade

Swirling flow primary zones with between 30% and 60% simulated primary zone air flow were investigated using curved blade radial swirlers. Two radial swirlers were compared with the same open area but different outlet diameters, d, giving different expansion ratios, D/d, from the swirler to the combustor diameter, D. Two combustors were used, 76 mm and 140 mm diameter, the larger one corresponding to the size of several gas turbine can combustors. There was no influence of D/d on the weak extinction. It was demonstrated that an adequate efficiency was not achieved in the weak region until there was a significant outer expansion and associated recirculation zone. It was shown that these systems with central gaseous fuel injection had good flame stability with very low NOx emissions. Propane and natural gas were compared and the NOx emissions were 50% lower with natural gas. The optimum NOx emissions, compatible with a high combustion efficiency, were close to 10 ppm NOx emissions corrected to 15% oxygen.

scholarly journals Reduced NOx Emissions Using Low Radial Swirler Vane Angles

1991 ◽  
Author(s):  
H. S. Alkabie ◽  
G. E. Andrews
Keyword(s):  
Gas Turbines ◽  
Fuel Injection ◽  
Combustion Efficiency ◽  
Inlet Temperature ◽  
Nox Emissions ◽  
Primary Zone ◽  
Industrial Gas Turbines ◽  
Curved Blade ◽  
Swirl Vane ◽  
Vane Angle

The influence of vane angle and hence swirl number of a radial swirler on the weak extinction, combustion inefficiency and NOx emissions was investigated at lean gas turbine combustor primary zone conditions. A 140mm diameter atmospheric pressure low NOx combustor primary zone was developed with a Mach number simulation of 30% and 43% of the combustor air flow into the primary zone through a curved blade radial swirler. The range of radial swirler vane angles was 0–60 degrees and central radially outward fuel injection was used throughout with a 600K inlet temperature. For zero vane angle radially inward jets were formed that impinged and generated a strong outer recirculation. This was found to have much lower NOx characteristics compared with a 45 degree swirler at the same pressure loss. However, the lean stability and combustion efficiency in the near weak extinction region was not as good. With swirl the central recirculation zone enhanced the combustion efficiency. For all the swirl vane angles there was little difference in combustion inefficiency between the swirlers. However, the NOx emissions were reduced at the lowest swirl angles and vane angles in the range 20–30 degrees were considered to be the optimum for central injection. NOx emissions for central injection as low as 5ppm at 15% oxygen and 1 bar were demonstrated for zero swirl and 20 degree swirler vane angle. This would scale to well under 25 ppm at pressure for all current industrial gas turbines.

Radial Swirlers With Peripheral Fuel Injection for Ultra-Low NOx Emissions

1990 ◽  
Author(s):  
H. S. Al Kabie ◽  
G. E. Andrews
Keyword(s):  
Natural Gas ◽  
Recirculation Zone ◽  
Fuel Injection ◽  
Air Flow ◽  
Inlet Temperature ◽  
Nox Emissions ◽  
Gas Oil ◽  
Primary Zone ◽  
Wall Injection

A 76mm outlet diameter radial swirler with a dump expansion into a 140mm diameter combustor was investigated with a simulated 43% primary zone air flow at a 600K inlet temperature and one bar pressure. Two modes of peripheral fuel injection were investigated: at the 76mm swirler outlet and at the 140mm combustor wall just downstream of the swirler. This 140mm wall injector resulted in fuel injection into the swirler expansion outer recirculation zone. It was shown that the 140mm wall injection gave much higher NOx emissions than for the 76mm swirler outlet injector. These results were compared with other methods of fuel injection and the 76mm peripheral injection was shown to have superior NOx emissions than vane passage injection for all fuels except gas oil. Ultra low NOx emissions of 1ppm with 20 ppm CO, both at 15% oxygen, were demonstrated for propane and natural gas.

Jet Shear Layer Turbulent Diffusion Flames for Ultralow NOx Emissions

1992 ◽  
Vol 114 (1) ◽  
pp. 55-62 ◽  
Author(s):  
A. F. Ali Al-Shaikhly ◽  
G. E. Andrews ◽  
C. O. Aniagolu
Keyword(s):  
Natural Gas ◽  
Shear Layer ◽  
Gas Turbine ◽  
Fuel Injection ◽  
Diffusion Flames ◽  
Stability Margin ◽  
Operating Conditions ◽  
Nox Emissions ◽  
Turbulent Diffusion Flames ◽  
Primary Zone

Direct fueling of each shear layer generated by an array of holes in a grid plate was shown to have ultralow NOx emissions combined with a good flame stability, compared with a premixed system. Two methods of fuel injection were investigated that had opposite NOx/stability characteristics. Four shear layers in a 76-mm combustor were used at gas turbine primary zone operating conditions with 60 percent simulated primary zone air at one bar pressure. The fuels used were propane and natural gas and a minimum NOx emission of 2.5 ppm at 15 percent oxygen, compatible with a 0.1 percent inefficiency, was demonstrated for natural gas with a reasonable stability margin. These designs have the potential for a dry NOx solution to any current or proposed gas turbine NOx regulation for natural gas.

Conical Grid Plate Flame Stabilizers: Stability and Emissions for Liquid Fuels

1986 ◽  
Author(s):  
A. F. Ali ◽  
G. E. Andrews
Keyword(s):  
Mach Number ◽  
Fuel Injection ◽  
Combustion Efficiency ◽  
Liquid Fuels ◽  
Injection System ◽  
Flame Stability ◽  
Gas Oil ◽  
Air Jets ◽  
Primary Zone ◽  
Grid Plate

Flame Stability and Emission results are presented for a jet shear layer primary zone design consisting of a 90° conical flame stabiliser with a central annular vaporiser fuel injection system feeding an array of air jets. The performance with kerosene and gas oil fuels is compared with previous work with propane. The influence of the primary zone residence time or Mach number is shown to be much more significant for liquid fuels than for propane. An acceptable combustion efficiency was only achieved at a Mach number of 0.03, corresponding to 60% of the combustion air in the primary zone, provided that the pressure loss was maintained as the Mach number was reduced by using a stabiliser of higher blockage. NOx emissions with kerosene were compatible with those for propane, but for gas oil there was a significant increase in NOx.

scholarly journals Ultra Low NOx Emissions for Gas and Liquid Fuels Using Radial Swirlers

1989 ◽  
Author(s):  
H. S. Alkabie ◽  
G. E. Andrews
Keyword(s):  
Gas Turbines ◽  
Fuel Injection ◽  
Air Flow ◽  
Combustion Efficiency ◽  
Liquid Fuels ◽  
Inlet Temperature ◽  
Flame Stability ◽  
Nox Emissions ◽  
Gas Oil ◽  
Industrial Gas Turbines

Curved blade radial swirlers using all the primary air were investigated with applications to lean burning gas turbine combustor primary zones with low NOx emissions. Two modes of fuel injection were compared, central and radial swirler pássage injection for gaseous and liquid fuels. Both fuel systems produced low NOx emissions but the upstream mixing in the swirler passages resulted in ultra low NOx emissions. A 140mm diameter atmospheric pressure combustor was used with 43% of the combustor air flow into the primary zone through the radial swirler. Radial gas composition measurements at various axial distances were made and these showed that the flame stability and NOx emissions were controlled by differences in local mixing at the base of the swirling shear layer downstream of the swirler outlet. For radial passage fuel injection it was found that a very high combustion efficiency was obtained for both propane and liquid fuels at 400K and 600K inlet temperatures. The flame stability, although worse than for central fuel injection was considerably better than for a premixed system. The NOx emissions at one bar pressure and 600K inlet temperature, compatible with a high combustion efficiency, for propane and kerosene were 3 and 6 ppm at 15% oxygen. For Gas Oil the NOx emissions were higher, but were still very low at 12ppm. Assuming a square root dependence of NOx on pressure these results indicate that NOx emissions of 48ppm for Gas Oil and less than 12ppm for gaseous fuels could be achieved at 16 bar pressure, which is typical of recent industrial gas turbines. High air flow radial swirlers with passage fuel injection have the potential for a dry solution to the NOx emissions regulations.

scholarly journals Conical Grid Plate Flame Stabilizers for Combustor Primary Zones

1985 ◽  
Author(s):  
A. F. Ali ◽  
G. E. Andrews
Keyword(s):  
Residence Time ◽  
Fuel Injection ◽  
Combustion Efficiency ◽  
Shear Layers ◽  
Injection System ◽  
Fuel Injection System ◽  
Nox Emissions ◽  
Fuel Injector ◽  
Primary Zone ◽  
Grid Plate

Emission results are presented for a jet shear layer flame stabiliser design consisting of a 90° conical flame stabiliser with an array of holes and a central annular vaporiser fuel injection system. This design was tested with premixed propane and air and with direct propane injection into the vaporiser at two blockages and approach velocities. The results showed that an array of jet shear layers could be fuelled by a single fuel injector without incurring excessive NOx emissions. An increase in the primary zone residence time was found to result in an improved combustion efficiency, with no increase in NOx, provided that the stabiliser blockage was increased to maintain the pressure loss.

scholarly journals Mixing and Fuel Atomisation Effects on Premixed Combustion Performance

1983 ◽  
Author(s):  
G. E. Andrews ◽  
M. M. Abdul Aziz ◽  
N. A. Al-Dabbagh
Keyword(s):  
Liquid Fuel ◽  
Fuel Injection ◽  
Constant Pressure ◽  
Combustion Efficiency ◽  
Premixed Combustion ◽  
Flame Stability ◽  
Nox Emissions ◽  
Jet Mixing ◽  
Mixing Effects ◽  
Single Droplets

The main objective was to compare a flame stabiliser at constant pressure loss and identical isothermal aerodynamics with three modes of fuel injection: premixed, direct propane injection and direct kerosene injection. A Jet Mixing type of flame stabiliser was used at simulated gas turbine primary conditions. The influence of gaseous mixing effects was to deteriorate the combustion efficiency solely by increasing the CO emissions and to increase the NOx emissions. The flame stability was increased and low CO emissions were achieved at weaker mixtures. Liquid fuel atomisation effects resulted in a further deterioration in combustion efficiency due solely to un-burnt hydrocarbons. However, the NOx emissions were reduced indicating that local stoichiometric burning around single droplets does not occur.

Low NOx Primary Zones Using Jet Mixing Shear Layer Combustion

1988 ◽  
Author(s):  
U. S. Abdul Hussain ◽  
G. E. Andrews ◽  
W. G. Cheung ◽  
A. R. Shahabadi
Keyword(s):  
Natural Gas ◽  
Shear Layer ◽  
Gas Turbines ◽  
Scale Up ◽  
Combustion Efficiency ◽  
Operating Conditions ◽  
Nox Emissions ◽  
Fuel Injector ◽  
Jet Mixing ◽  
Primary Zone

An interacting radial and axial multi jet shear layer combustion system is described that has the rapid fuel and air mixing characteristics necessary for low NOx emissions. The radial jet has the fuel mixed with a proportion of the total primary zone flow and a 30% proportion was investigated. This radial jet was fuel rich at most primary zone operating conditions and ensured a flame stability far superior to the premixed situation. The scale up of the design from a 76mm to a 140mm diameter combustor was investigated. It was demonstrated that the distance the radial jet travelled before encountering the rapid mixing with the axial jets, had a strong influence on the combustion efficiency and NOx emissions. For both the 76 and 140mm combustors it was shown that the NOx emissions with propane were 50% greater than those for natural gas. It was also demonstrated that the low NOx emissions of the 76mm system were retained in the larger combustor with the same single central fuel injector design. There was a significant increase in NOx for some 140mm combustor configurations, but the emissions corrected to 15% oxygen below 10ppm were demonstratred, with a high combustion efficiency. The design thus demonstrated, in a practical combustor size, the potential for a dry solution to the NOx emissions problem of natural gas fired industrial gas turbines.

Shear Layer Mixing for Low Emission Gas Turbine Primary Zones

1984 ◽  
Author(s):  
N. A. Al-Dabbagh ◽  
G. E. Andrews ◽  
R. Manorharan
Keyword(s):  
Shear Layer ◽  
Gas Turbine ◽  
Fuel Injection ◽  
Flame Temperature ◽  
Stability Margin ◽  
Air Injection ◽  
Flame Stability ◽  
Nox Emissions ◽  
Primary Zone ◽  
Air Mixing

Shear layer turbulent fuel and air mixing has been utilised in a simulated gas turbine primary zone combustor. Two methods of fuel injection and two values of the number of air injection holes have been investigated at a constant pressure loss of 4% at a reference Mach number of 0.047. The method of fuel injection and the number of air injection holes was found to influence the flame stability and NOx emissions. A large number of holes produced much higher NOx emissions which was not compensated for by the ability to operate at weaker equivalence ratios due to the greater flame stability. An optimum primary zone operating condition, for very low NOx and high combustion efficiencies involving a flame temperature of approximately 1600K was identified and there was a wide flame stability margin on this condition.

scholarly journals Jet Shear Layer Turbulent Diffusion Flames for Ultra-Low NOx Emissions

1990 ◽  
Author(s):  
A. F. Ali Al-Shaikhly ◽  
G. E. Andrews ◽  
C. O. Aniagolu
Keyword(s):  
Natural Gas ◽  
Shear Layer ◽  
Gas Turbine ◽  
Fuel Injection ◽  
Diffusion Flames ◽  
Stability Margin ◽  
Operating Conditions ◽  
Nox Emissions ◽  
Turbulent Diffusion Flames ◽  
Primary Zone

Direct fuelling of each shear layer generated by an array of holes in a grid plate was shown to have ultra-low NOx emissions combined with a good flame stability, compared with a premixed system. Two methods of fuel injection were investigated that had opposite NOx/stability characteristics. Four shear layers in a 76 mm combustor were used at gas turbine primary zone operating conditions with 60% simulated primary zone air at one bar pressure. The fuels used were propane and natural gas and a minimum NOx emission of 2.5 ppm at 15% oxygen, compatible with a 0.1% inefficiency, was demonstrated for natural gas with a reasonable stability margin. These designs have the potential for a dry NOx solution to any current or proposed gas turbine NOx regulation for natural gas.

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