JPS638373B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION In recent years, gas turbine manufacturers have become increasingly concerned with pollutant emissions. Of particular interest is nitrogen oxide (NOx) emissions. This is because such oxides pollute the air the most.

As is well known, NOx generation increases with increasing flame temperature and residence time. Therefore,
Theoretically, by reducing the flame temperature and/or the time the reactant gases remain at maximum temperature.
It is possible to reduce NOx emissions. However, this is difficult to accomplish due to the turbulent diffusion flame characteristics of today's gas turbine combustors. Combustion in such combustors occurs in a thin layer surrounding the vaporized fuel droplets with a fuel-to-air equivalent ratio close to unity regardless of the total reaction zone equivalent ratio. This is the condition that produces the highest flame temperature, so a relatively large amount of
NOx is generated. As a result, conventional single-stage, single-fuel nozzle atomizing combustors may not meet newly established emissions standards at any lean nominal reaction zone equivalent ratio.

It is known that in order to meet the requirement that conventional combustors emit small amounts of NOx, the amount of NOx produced can be reduced by injection of significant amounts of water or steam. However, such injection also has many drawbacks. For example, increased equipment complexity, increased operating costs due to required water treatment, and deterioration of other performance factors.

Various attempts to obtain a homogeneous lean reaction zone by pre-vaporizing the fuel and mixing it with air in a lean equivalent ratio externally have limited applicability. These designs are typically used for regeneration cycles (high combustor inlet temperatures) and also for clean, highly volatile fuels at relatively low pressures (less than 10 atmospheres), such as gasoline, jet fuel, etc. has been used for. Besides the increased complexity, a significant drawback of this approach is the risk of self-ignition and backfire. At 10 atmospheres, the residence time required for complete evaporation of distillate fuel is approximately equal to the residence time required for self-ignition. See, eg, ASME Preprint 77-GT-69.

The problem of achieving low NOx emissions becomes even more complex when it must meet other combustion design criteria. Such criteria include, for example, good ignition properties, good cross-ignition properties, stability over the entire load range, high turndown ratios,
The ratio of the maximum fuel flow rate before explosion to the minimum fuel flow rate before extinguishment. A high turndown ratio is desirable because it allows the fuel flow rate to be adjusted to a lower amount without terminating combustion, thereby reducing the generation of undesirable localized thermal stresses. ) Standards for long life, safe driving ability, etc.

Some of the factors that generate nitrogen oxide from fuel nitrogen and air nitrogen are already known;
Efforts have been made to adapt various combustor operations to these factors. See, eg, US Pat. Nos. 3,958,416, 3,958,413 and 3,946,553. However, the methods used in the past have been either inapplicable to combustors for quantitative gas turbines or have been unsuitable for the reasons described below.

The object of the present invention is to provide a novel two-stage dual combustion device for gas turbines using various gaseous and distillate fuels and working over the entire gas turbine cycle with flame temperatures that reduce pollutant emissions to acceptable levels. The goal is to provide the following. These and other objects of the invention will be well understood by those skilled in the art from the following detailed description.

The present invention relates to a combustor for a quantitative gas turbine, e.g.
A combustion apparatus comprising a plurality of combustors and a method for operating each combustor to reduce NOx emissions. More specifically, the combustor of the present invention has two combustion chambers connected through a neck, separate fuel introduction means for each chamber, and a fuel flow rate of each fuel introduction means to be connected to another fuel introduction means. and means for adjusting. In preparation for the occurrence of blowout, the combustor group is constructed by connecting the first chambers of each adjacent combustor and the second chambers of each adjacent combustor by a crossing fire tube. A high-load ignition system is provided. When the combustor is used, fuel is first introduced into only the first chamber and is combusted there. The fuel flow is then transferred into the second chamber until the combustion in the first chamber is completed, after which the fuel is distributed again into the first chamber for mixing purposes, and this redistribution is continued until the desired NOx reduction is achieved. be exposed.

1 and 2, the combustor 1 of the present invention generally comprises a first combustion zone 2, a neck or throat zone 3 connected thereto, and a second combustion zone connected to this zone 3. Consists of 4.

The first combustion zone 2 may be of a conventional lean combustor design utilizing a single, preferably axisymmetric fuel nozzle 5. The second combustion zone 4 is supplied with fuel from a plurality of fuel nozzles 6 . Although FIGS. 1 and 2 show four radial nozzles arranged symmetrically around the combustor, any number of nozzles may be used as desired. Air from a gas turbine compressor (not shown) is introduced into the combustor at high pressure, typically about 10 to 30 atmospheres. For example, the air is introduced through one or more air inlets 7. The inlet 7 arranged in the first combustion zone 2 is preferably arranged in such a way as to cause a reflux which results in stable combustion over a wide range of use. Also provided are means for quenching the combustion products in zone 4 with a suitable heat exchange fluid. For example, cooling air may be introduced into zone 4 through a plurality of openings 8 . The amount of heat exchange fluid used is sufficient to cool the combustion products to reduce the fluid temperature to the desired gas turbine ignition temperature.

The preferred cross-sectional shape of zones 2, 3, and 4 is circular, but any shape may be adopted. The structural material may be metal or ceramic. Each zone may be surface cooled by various cooling techniques such as water cooling, closed system cooling, steam film cooling, conventional air film cooling, etc. By way of example only, a useful arrangement of schematically spaced loopers in multiple annular rows along a zone wall for air film cooling is shown by the Dibelius and Schiefer. ), and a useful slot cooling structure is described in Corrigan and Plemmons, US Pat. No. 3,728,039.

The neck or throat 3 connects the first combustion zone 2 and the second
It will be appreciated that it acts as an aerodynamic separator or separator with the combustion zone 4. In order to properly perform this function, network 3 is connected to the first area 2 and the second area.
It is necessary to have a suitably small diameter relative to zone 4. Generally, the ratio of the diameter of the first combustion zone 2 and the diameter of the second combustion zone 4, whichever is smaller, to the diameter of the neck zone 3 is at least 1.2:1, preferably at least about 1.5:1. 1st combustion zone 2
To facilitate a smooth transition between
The most downstream part 2a of the zone 2 has an evenly decreasing diameter, ie a conical cross section. The longitudinal length of the net 3 is not critical; any distance may be used as long as it fulfills the separating and restricting functions of the net 3. Generally, the longitudinal length of first combustion zone 2 is at least about three times that of neck 3, preferably at least about five times. The overall shape of the second combustion zone 4 is similar to that of the first zone 2. However, of course, the conical transition part is in the most upstream part 4a of the area 4 which meets the net 3.

A second preferred embodiment of the invention is shown in FIG. In this figure, parts similar to those in FIG. 1 are designated by the same reference numerals. The configuration shown in FIG. 2 differs from the configuration shown in FIG. 1 in the following points. First, the diameter of the throat region 3 is reduced to increase the average air velocity within the region, and this design is most effective in preventing flashback. The height (ie longitudinal length) of the tapered conical portion 2a is also increased. In this embodiment, the fuel nozzle 6 has been moved from the throat 3 to a diverging conical portion 4a of the second region 4, forming a small combustion chamber or swirl cup 9.
being pulled inside. Here, the operation of the secondary fuel nozzle 6 is more stable, and the possibility of blowout occurring during fuel switching, which will be described later, is relatively low.

FIG. 3 illustrates three interconnected combustors of the present invention. The first combustion zone 2 of each combustor 1 is connected to the adjacent combustor 1 by a crossfire tube 10 in a conventional manner.
The first combustion zone 2 is connected to the first combustion zone 2 of the combustion chamber. Furthermore, in the present invention, the second combustion zone 4 of each combustor 1 is connected to the second combustion zone 4 of each adjacent combustor 1 via a crossfire tube 11. As will be described later, when the present combustor is operating at a designed high load condition, combustion occurs only in the second zone 4 and does not occur in the first zone 2. If for some reason one combustor were to blow out under such high load conditions, a crossfire could not occur in the conventional structure. This is because the standard crossfire tube 10 is upstream of the reaction zone 4 and the network 3 serves to prevent flashback. In the embodiment shown in FIG. 3, the second set of crossfire tubes 11 acts as a high-load ignition system. Although it is preferred to provide two sets of crossfire tubes (i.e., tubes 10, 11), any high-load reignition system may be incorporated into the combustion device as desired.

The operation of the combustor of the present invention is illustrated graphically in FIG. Combustion begins by ignition of a mixture of hydrocarbon fuel and air in the first combustion zone 2. This is done in a conventional manner by means of a spark plug 12 arranged close to the fuel nozzle 5 in the first combustion zone 2 (spark plugs are normally provided only in the first combustion zone 2). . In a typical conventional device, 10 combustors are arranged in a ring, and usually only two combustors are provided with spark plugs 12, and the remaining eight combustors are connected to the crossfire by crossfire tubes 10. be done. During ignition and crossfire, and also while the combustor is working at low loads, only the primary fuel nozzle 5 delivers fuel to the combustor 1. Combustion up to this point exhibits the single stage heterogeneous turbulent diffusion flame combustion characteristics of a conventional combustor.

Under moderate load conditions, the secondary fuel nozzle 6 is utilized. Note that the precise timing of this condition is related to stability limits, the pollutant emission characteristics of each combustion type, and the fuel split between the stages. The ignited fuel is the first
Proceeding from zone 2 into second zone 4, ignition occurs within second zone 4. The combustor is then working in a two-stage heterogeneous mode, which continues until the desired base load is obtained. After a short period of time for stabilization and warm-up, combustor operation is converted from two-stage heterogeneous combustion to single-stage homogeneous combustion. The conversion is initiated by increasing the fuel flow to the secondary nozzle 6 while decreasing the fuel flow to the primary nozzle 5 while keeping the total fuel flow constant. The ratio of fuel flow rates to nozzles 5 and 6 may be controlled by a fuel flow control device 13 coupled to nozzles 5 and 6.
The change in fuel distribution continues until the flame is extinguished within the primary combustion zone 2. This extinguishing occurs in most cases when the entire fuel flow is transferred to the secondary nozzle 6.

Fuel flow to nozzle 5 is then regenerated or increased and fuel flow to nozzle 6 is reduced, while keeping the total fuel flow substantially constant. Combustor 1
The first region 2 is made sufficiently long so that the flow cross section resembles that of a well-developed turbulent pipe flow, and the throat 3 is made sufficiently narrow to increase the flow velocity and prevent backfire under normal operating conditions. It is designed to prevent this from happening. As a result, most of the fuel and air are premixed in the first stage (ie, first zone 2) and combusted evenly in the second stage, ie, second zone 4. The switching of fuel distribution from the secondary nozzle 6 to the primary nozzle 5 continues until the pollutant emissions reach a desired low level. The desired emission level is obtained when the majority of the fuel flow passes through the nozzle 5, and in most cases at least 60% of the fuel flow passes through the nozzle 5.

An important feature of the combustor of the present invention is that in the event of a flashback, because the premixing is done within the combustion chamber, structural damage will not occur as would occur with typical conventional premix designs. I hope you understand that this is true. However, significant NOx may be produced, and control measures must be taken to redirect the fuel distribution and return the combustor to homogeneous combustion mode.

Upon shutdown of the gas turbine, steps are taken to reignite the first zone 2. This is because the homogeneous method provides only a small turndown ratio. Reignition of the first stage means a return to heterogeneous two-stage combustion, where the system has a large turndown ratio and the turbine can come to a slow stop, relieving undesirable thermal stresses. Ru.

To demonstrate the reduction in NOx emissions achieved by the present invention, a combustor constructed in accordance with the present invention was compared to a conventional commercial combustor using an MS7001E device. The combustor of the present invention has the structure shown in FIG.
It utilized an MS7001E nozzle and four smaller pressure spray secondary nozzles 6. Data collection was performed at approximately 2080〓 (1138℃), i.e.
The laboratory equivalent values for base load (values corrected for radiation losses from thermocouples) were performed. Under these conditions, the conventional standard combustor
showed laboratory NOx emissions of 120 ppmv, whereas the combustor made according to the present invention had only a
It was 56 ppmv. This test was conducted using a dirty air source. This means that the combustion products from the direct heater (eg, propane heater) used to raise the air temperature to the appropriate inlet level are utilized as the combustion oxidant during testing. Therefore, the NOx emissions are less than would be obtained using clean air (indirectly reserved air, which does not contain combustion products). Based on these laboratory test results, it is expected that if the combustor of the present invention is used in a homogeneous manner under field conditions (i.e., using a real turbine with clean air), The expected reduction in NOx emissions would be comparable to the above reduction. Therefore, a combustor made according to the present invention has a low level
Evaluated to meet NOx emission requirements.

A second test was conducted on the two-stage compound combustion apparatus of the present invention. During this test, a dirty air source was utilized and the ignition temperature was kept constant at approximately 2070°. At some point during the increase in fuel flow in the secondary fuel nozzle 6 when the fuel flow through the primary nozzle 5 is 20% and combustion is occurring in both combustion zone 2 and combustion zone 4, NOx Emissions are approx.
It was 95 ppmv. Two-stage heterogeneous combustion method (Two-stage means that combustion occurs in both the first combustion zone 2 and the second combustion zone 4.Heterogeneity means that in the case of two-stage combustion, there is a Since there is no mixing (homogenization), combustion is not uniform when looking at the cross section of the combustion zone.) After switching from the homogeneous combustion method to the homogeneous combustion method, approximately 14% of the fuel is transferred to the primary nozzle (first stage nozzle). At a certain point in time while flowing through the
It was 93.5 ppmv. The amount of fuel flowing to the primary nozzle 5 increased from 14% to the point where approximately 70% of the total fuel flow passed through the primary nozzle 5, and NOx emissions continued to decrease from 93.5 ppmv to approximately 49 ppmv.

A third test was conducted in a manner similar to the first test above, but using a source of clean air, ie, indirectly preheated air free of combustion products. At an ignition temperature of about 2060㎓, the conventional combustor emitted about 260 ppmv of NOx, while the combustor of the present invention emitted about 65 ppmv of NOx in the homogeneous combustion mode. The fuel used in each of the above tests was No. 2 distillate.

From the laboratory test data described above, and in particular from the third test utilizing a source of clean air, it is clear to those skilled in the art that a combustor made in accordance with the present invention
It can be noticed that the NOx emissions are reduced to a considerable extent (by a factor of 4). By using such a combustor, NOx emissions can be significantly reduced,
Will meet most NOx emission requirements.

Having described two embodiments of the present invention and their mode of operation, those skilled in the art can better understand how the present invention differs from the prior art patents mentioned above. In particular, Roberts et al., US Pat. No. 3,946,553, appears to disclose a two-stage combustor with multiple fuel nozzles for emission control.
However, in this case the fuel and air are mixed outside the combustion liner wall, which is different from the present invention. Also, with the combustor of the present invention, there are several conditions (ie, during start-up, during part load, and during base load transients) where the reaction occurs in a heterogeneous manner without premixing. This method of operation is not possible with the combustor patented by Roberts et al.
The mode of operation of the present invention facilitates ensuring important characteristics of practical design such as large turndown ratio, easy ignition and cross-fire, and flame stability. Also, switching from a heterogeneous combustion regime to a homogeneous combustion regime is achieved according to the present invention by changing the fuel split between the first and second stage fuel nozzles, as described by Roberts et al. This is an undisclosed characteristic.

Cornelius et al. U.S. Patent No.
No. 3958413 and Hammond, Giunia (Hammond,
Jr. et al., U.S. Pat. No. 3,958,416, relates to a two-stage combustor in which the stages are separated by a medium-narrow throat. Also, the first stage in both patents is used as the part where combustion occurs at some times in the cycle and as the part where premixing occurs at other times in the cycle.
Therefore, flashbacks do not cause structural failure as in the Roberts et al. patent. The Cornelius et al. patents and the Hammond, Giunia et al. patents also require that air be used between both stages to achieve a transition from heterogeneous combustion in the first stage or first and second stages to homogeneous combustion in only the second stage. It appears to disclose a variable air inlet geometry to vary the volume dispensed. In contrast, the present invention utilizes fuel distribution adjustment between stages, utilizes multiple fuel nozzles (rather than variable geometry), and varies the rate of fuel split rather than air split.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of a first embodiment of the present invention, FIG. 2 is a schematic cross-sectional view of a second embodiment of the present invention, and FIG. 3 is a three-piece combustor of the present invention having a high-load ignition system. FIG. 4 is a graph showing fuel flow rate as a function of time during use of the combustor. 1... Combustor, 2... First combustion area, 3... Throat area (neck area), 4... Second combustion area, 5, 6
... Fuel nozzle, 7 ... Air inlet, 8 ... Opening,
9...Small combustion chamber, 10,11...Intersection fire tube,
12...Spark plug, 13...Fuel flow rate control device. A...Total fuel flow, B...Primary nozzle fuel flow,
C...Secondary nozzle fuel flow.

Claims (1)

Claims: 1 comprising first and second combustion chambers interconnected by a throat chamber, said first combustion chamber having a first fuel introduction means, and said throat chamber and said second combustion chamber having first fuel introduction means; A method for reducing exhaust NOx from a gas turbine combustor in which at least one of the chambers has a second fuel introduction means, the method comprising: (a) continuously introducing fuel into the first chamber by the first fuel introduction means; and the fuel is introduced into said first
(b) initiating the introduction of fuel into the second chamber by the second fuel introduction means, and introducing the introduced fuel flow through all of the fuel introduction means; increasing the flow rate of fuel introduced until it is approximately the desired flow rate of fuel introduced, and ignition of fuel in the second chamber is initiated as a result of passage of combustion products from the first chamber to the second chamber; (c) reducing the flow rate of fuel introduced through said first fuel introduction means and correspondingly increasing the flow rate of fuel introduced through said second fuel introduction means, such that the total introduced fuel flow rate is (d) increasing the flow rate of fuel introduced through the first fuel introduction means so as to increase the flow rate of the fuel introduced through the first fuel introduction means and accordingly reducing the flow rate of fuel introduced through said second fuel introduction means, such that the total introduced fuel flow rate remains substantially constant until NOx emissions from said combustor reach a desired level; A method consisting of sequentially performing 2. In step (c), the flow rate of fuel introduced through the first fuel introduction means is reduced until the entire fuel introduction is by the second fuel introduction means. Method. 3. The method of claim 2, wherein the fuel distribution at the end of step (d) is such that the majority of the fuel is introduced via the first fuel introduction means. 4. The method of claim 3, wherein the fuel distribution at the end of step (d) is such that at least 60% of the total fuel is introduced via the first fuel introduction means. 5. The method of claim 1, wherein the fuel distribution at the end of step (d) is such that the majority of the fuel is introduced via the first fuel introduction means. 6. The method of claim 1, wherein said first fuel introduction means is an axisymmetric fuel nozzle and said second fuel introduction means comprises a plurality of symmetrically arranged fuel nozzles. 7. A plurality of adjacent combustors, each combustor having first and second combustion chambers interconnected by a neck and at least one combustor having means for igniting fuel in the first chamber. the first chamber of one combustor and the first chamber of the adjacent combustor.
a plurality of first crossfire tubes connecting a second chamber of one combustor and a second crossfire tube of an adjacent combustor;
A stationary gas turbine combustion device comprising a plurality of second crossfire tubes connected to a combustion chamber. 8. The stationary gas turbine combustion apparatus according to claim 7, comprising ten combustors, each combustor adjacent to another combustor.