NL7909203A - TWO-STAGE BURNER WITH LOW NITROGEN OXIDE EMISSIONS FOR A GAS TURBINE. - Google Patents

Description

P & c "* W 2348-1007 Ned.

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Two-stage burner with low nitrogen oxide emissions for a gas turbine

In recent years, gas turbine manufacturers have increasingly paid attention to air-polluting exhaust gases. Particularly important here is the emission of nitrogen oxides (NO) as these oxides are a precursor to air pollution.

5 It is known that the formation of Ν0χ increases with increasing flame temperature and with increasing residence time. Therefore, it is theoretically possible to reduce NO emissions by lowering the flame temperature and / or the time in which the reacting gases remain at peak temperatures.

In practice, however, this is difficult to achieve due to the turbulent flame diffusion characteristics of today's gas turbine burners. With these burners, combustion takes place in a thin layer around the diluting droplets of the liquid fuel at a fuel / air equivalence ratio in turn of one independent of the average equivalence ratio in the entire reaction zone. Since this is the condition giving the highest flame temperature, quite large amounts of NO are produced. As a result, the known single-stage single fuel burners with atomizing nozzles do not meet the new emission conditions, regardless of how low the nominal equivalence ratio is in the reaction zone.

It is known that by injecting large quantities of water or steam the Ν0χ production can be reduced in such a way that the known burners can meet the low ΝΟχ emission requirements. However, this injection also has many drawbacks, including greater system complexity, increased operating costs due to the need for water treatment, and deterioration of other operating parameters.

Attempts to achieve a homogeneous lean reaction zone by pre-diluting the fuel and premixing it with air at a low equivalence ratio have only limited applications. These designs have been used, for example, for clean, highly volatile fuels such as gasoline, jet fuel, etc., for regenerative cycles (high burner inlet temperature), and at lower pressures (less than 980 kPa). In addition to the increase in complexity, a serious drawback of this measure is the danger of auto-ignition and flashback. At a pressure of 980 kPa, the residence time required for complete evaporation of distillate fuel and for auto ignition is almost equal. See, for example, ASME Preprint ^ 77-GT-69.

The problem of obtaining low ΝΟχ emissions becomes even more complicated when it is necessary to meet other burner design requirements 7 § ö 9 2 Ö 3 Ϋ -2-. Among these requirements are those of good ignition qualities, good possibility of transverse ignition, stability over the entire load range, large ratio of possible fuel supply extremes, low throughput, long life and safe operation.

Some of the factors causing the formation of nitrogen oxides from fuel nitrogen and from air nitrogen are known, and attempts have been made to adapt different burner operations in light of these factors. See, for example, U.S. Pat. Nos. 3,958,416 / 3,958,413 and 3,946,553. However, hitherto applied methods 10 have either hitherto failed to adapt to use in a stationary gas turbine burner or are unsuitable for the reasons set forth below.

The object of the invention is to provide a new two-stage combustion system with two modes of operation / for a gas turbine, allowing the operation of flame temperatures throughout the gas turbine cycle, thereby significantly reducing pollutant emissions to an acceptable level, when using different gaseous and distillate fuels.

The invention will be explained in more detail below with reference to the drawing, in which two exemplary embodiments of a gas turbine burner according to the invention are shown.

Fig. 1 is a schematic longitudinal section through the first embodiment.

Fig. 2 is a schematic longitudinal section through the second embodiment.

. Fig. 3 schematically shows three burners according to the invention with a high load ignition system.

Fig. 4 is a graph of fuel delivery to the burner of the invention as a function of time.

The invention relates to a burner for a stationary gas turbine. For example, an arrangement of burners and the method by which they are used to "achieve a reduction in χ0χ emissions. In particular, the burner has two combustion chambers which are connected by a narrowed neck, separate fuel feed means for each chamber. and means for controlling the fuel supply of each fuel supply member relative to the others In the event that the flames should extinguish, the burners are equipped with a high-load ignition system by connecting each first chamber of adjacent burners, as well as each second chamber of 7909203 »-3- the adjacent burners, through transverse ignition tubes. The burner is commissioned by first feeding fuel only into the first chamber and having it burned therein. Then the fuel supply is moved to the second chamber until the combustion in the first chamber 5 stops, followed by another v transfer the fuel supply to the first chamber for mixing purposes until the desired NO reduction is achieved

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reached.

The burner 1 according to the invention, shown in Figs. 1 and 2, mainly consists of a first combustion zone or chamber 2, which is connected to a narrowed neck or throat 3 which in turn is connected to a second combustion zone or chamber 4 .

The first combustion chamber 2 may be of the conventional lean combustion type using a single, preferably axisymmetric nozzle 5 or atomizer. The second burner chamber 4 is supplied with fuel from a number of fuel nozzles 6. In Figs. 1 and 2, four radial nozzles are arranged symmetrically about the burner circumference, but any number of nozzles can be used if desired. Air from the gas turbine compressor (not shown) is supplied to the burner at high pressure, for example from 980 to 2940 kPa. For example, the air can be supplied through one or more air supply ports 7. The ports 7 in the first burner chamber 2 are preferably positioned to cause recirculation of the flow, resulting in stable combustion over a large operating area. Measures have been taken for a rapid cooling of the combustion products in the second chamber 4 with a suitable heat exchange medium. For example, cooling air can be admitted to chamber 4 through a number of openings 8. The amount of heat exchange medium used is that sufficient to cool the combustion products such that the medium temperature is lowered to the desired gas turbine ignition temperature.

Zones 2, 3 and 4 preferably have a circular cross section, but any other shape of the cross section can also be used. The construction material can be metal or ceramic material and the chambers can be surface cooled by a variety of techniques including water cooling, closed system cooling, steam film cooling and the known air film cooling. As an example, a useful device is an arrangement of annular rows of schematically indicated blinds along the walls of the chambers to provide air film cooling, as described in U.S. Patent 3,777,484, while 7909203 V 'f -4- describes favorable slot cooling in U.S. Patent 3,728,039.

It is clear that the neck or throat 3 acts as an aerodynamic separator or insulator between the first burner chamber 2 and the second 5 burner chamber 4. In order to properly perform this function, the neck 3 must have a suitably reduced diameter with respect to the first chamber 2 and the second chamber 4. In general, a ratio of the smaller of the two chambers, namely the first burner chamber 2 or the second burner chamber 4, namely the diameter thereof to the diameter of the neck 3, of at least 1, is applied. 2: 1 and preferably at least about 1.5: 1. To facilitate a smooth transition between the first burner chamber 2 and the neck 3, the most downstream part 2a of the chamber 2 is formed with an evenly decreasing diameter, ie conical. The length of the neck 3 is not critical and any distance can be used for this purpose, whereby the separation function and the throttling function of the neck 3 are obtained. Generally, the length of the first burner chamber 2 is at least three times that of the neck 3 and preferably at least about five times that of the neck 3. The second burner chamber 4 has the same general shape as the first burner chamber 2 except, of course, that the conical transition part of this chamber is located in the upstream part 4a of the chamber 4 near the neck 3.

A second and preferred embodiment of the invention is shown in Figure 2, in which the same reference numerals are used for the same parts as in Figure 1. The device of Figure 2 differs from that of Figure 1 in the following points. First, the diameter of the neck 3 has been made smaller in order to increase the average air velocity in this range, which design is more effective in preventing flashback. The height, i.e. the length, of the converging conical part 2a is also increased. In this embodiment, the fuel nozzles 6 have been moved from the throat 3 to the diverging conical portion 4a of the second chamber 4, and the nozzles are additionally placed back into mini burner chambers or vortex chambers 9, in which the operation of the second fuel nozzles 6 is more stable and they are less likely to be blown out during the change of fuel supply, which is described below.

Fig. 3 shows as an example three connected burners according to the invention. The first burner chamber 2 of each burner 1 is connected to the first burner chamber 2 of the adjacent burners 1 by a transverse ignition tube 10, in a known manner. In addition, each second burner chamber 4 7909203 * -5- of each burner 1 is connected to the second burner chamber 4 of each adjacent burner 1 by a transverse ignition tube 11. As described below, combustion under full load conditions of the design of the burners takes place only in the second chambers 4 and no combustion takes place in the first chambers 2. When, for any reason, one chamber is extinguished at these full load conditions, the transverse ignition cannot take place in the known arrangement since the standard transverse ignition tubes 10 are upstream are located from the reaction chamber 4 and since the neck 3 prevents the surfaces from kicking back. In the embodiment according to Fig. 3, the second set of transverse ignition tubes 11 serves as a full load ignition system. Although it is preferable to provide the double set of transverse ignition tubes, i.e. the tubes 10 and 11, any full load re-ignition system may be fitted to the burner of the invention if desired.

The operation of the burners according to the invention is shown graphically in fig. 4. The combustion starts by igniting a mixture of hydrocarbon fuel and air in the first burner chamber 2. This is obtained in known manner with a spark plug 12, which is arranged near the fuel nozzle 5 in the first burner chamber 2. In installations known as example 20, ten burners are arranged in a ring and usually only two of the burners are provided with spark plugs 12, while the other eight burners are ignited by transverse ignition by means of transverse ignition tubes 10. During ignition and transverse ignition and also during low-load operation of the burner, only the primary fuel nozzle 5 supplies fuel to the burner 1. Until now, combustion is in one step and heterogeneous, the combustion characteristic with turbulent flame diffusion occurs from the known burners.

At about half load, the second fuel nozzles 6 are actuated, the exact timing depending on stability limits and the characteristic pollutant emission of the two modes of operation and the distribution of the fuel over the two stages. By flowing the ignited fuel from the first chamber 2 to the second chamber 4, the gases in the second chamber 4 are ignited.

The burner now operates as a heterogeneous two-stage burner, which continues until the desired base load is achieved. After a short period of stabilization and warming, the action is changed from the heterogeneous two-stage combustion to a homogeneous single-stage combustion. This procedure starts by simultaneously increasing the amount of fuel supplied 79 0 92 0 3.

* Y '-6- to the secondary nozzles 6 and reducing the amount of fuel supplied to the first fuel nozzle 5, while keeping the total fuel flow constant. The relative amounts of fuel supplied to the nozzles 5 and 6 can be controlled with a fuel supply controller 13 connected to the nozzle 5 and nozzles 6. The change in fuel distribution continues until the flames extinguish in the first burner chamber 2, which in most cases t occurs when all fuel is supplied to the second nozzles 6 ...

Thereafter, the fuel supply to the nozzle 5 is reset or increased and the supply to the nozzles 6 is reduced, while the total amount of fuel supplied remains almost constant.

The burner 1 is designed not to cause flame retardation in normal operation because the first chamber 2 is made long enough so that the flow section is similar to that of a fully developed turbulent pipe flow, while the neck 3 is narrow enough to maintain speed to a level above which the flame speed cannot be overcome. As a result, most of the fuel and air pre-mix in the first stage or first chamber 20 2 and then burn homogeneously in the second stage or second chamber 4.

The switchover of the fuel distribution from the second nozzles 6 to the first nozzle 5 continues until the desired low emission level of the building is obtained. The desired levels are achieved when most of the fuel is supplied through the nozzle 5, and in most cases at least 60% of the fuel is supplied through the nozzle 5. - ·

It is noted that an important feature of the burner according to the invention is that the flames would recoil in this way, resulting in damage to the construction parts, such as with burners with a premixing section. However, this creates a lot of gases and must be regulated in such a way that the switching procedure is repeated and * the burner is reset to homogeneous operation.

When the gas turbine is switched off, measures are taken to re-ignite the first chamber 2 since only a small fuel supply ratio without quenching is possible in the homogeneous mode of operation. Re-igniting the first stage means a return to the heterogeneous two-stage combustion, allowing the system to achieve a large fuel supply ratio without quenching, allowing the turbine to be slowed to a halt to reduce unwanted heat stresses.

In order to demonstrate the reduction in NO emissions obtained with the invention, a burner according to the invention works compared to a commercially available known burner with device according to MS 700IE. The burner of the present invention was in the form of Figure 1 and used a single MS 700IE air atomized nozzle as the primary nozzle 5 and four smaller secondary atomizers 6 with pressure atomizing. The data was collected at approximately 1138 ° C, which is the laboratory equivalent to the base load (corrected for radiation losses from thermocouples). Under these conditions, the standard known burner exhibited NO emissions in the laboratory of 120 volumes x parts per million, while a burner according to the invention had only 56 volumes parts per million. This test was done with so-called "tainted" air, meaning that the combustion products of a direct heater, for example a propane heater, which is used to raise the air temperature to the correct inlet level, are used as the oxidizing agent for combustion during the trial. As a result, ΝΟχ emissions are lower than would be obtained with ~ unspoiled air. Based on these laboratory results, it is expected that the operation of the burner according to the invention under practical conditions, i.e. when used in a turbine with unspoiled air, with a homogeneous effect, will show a comparable reduction in NO emissions. It is therefore believed that the burners according to the invention will meet the requirements of low NO emissions.

x 25 A second test with the combustion system of the invention using two stages and two combustion modes was conducted using a "spoiled" air supply, while the burning temperature remained constant at about 1132 ° C. At a time during the increase of the fuel supply to the secondary fuel nozzles 6, while the fuel supply through the primary nozzle 5 was 20% and combustion occurred in both chamber 2 and chamber 4, the ΝΟχ emissions about 95 parts by volume per million.

After switching from the two-stage heterogeneous combustion to the homogeneous combustion, at a time when about 14% of the fuel was supplied through the primary first stage nozzle, the NO

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emissions 93.5 parts by volume per million. The amount of fuel supplied to the primary nozzle 5 was then increased from 14% to about 70%, with NO emissions continuing to decrease from 93.5 to about 49

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parts by volume.

7909203 4 -8- • 5 4

A third test was performed in a manner similar to the first test described above, using unrepaired air, i.e. indirect preheated air without combustion products.

At a burning temperature of about 1127 ° C, the known burner delivered about 5260 parts by volume per million,, while the burner according to the invention, operating in the homogeneous manner, delivered about 65 parts by volume per million.

The fuel used in the above two tests was distillate No. 2.

If the above laboratory test data, and in particular from the third test, in which uncontaminated air was used, it will be clear to a person skilled in the art that a significant reduction in NO emissions occurs, by a factor of four, obtained by the burner according to the invention. By using these burners, the level of ΝΟχ emissions will be significantly reduced and meet most NO requirements. e. As the embodiments of the burner according to the invention and its operation have now been described, one skilled in the art will be able to better understand how the invention differs from the prior art in the above patents. In particular, US patent 3,946,533 describes a two stage burner with a number of fuel nozzles for controlling emissions. However, the fuel and air are mixed outside the burner lining wall, which is different from the invention. Furthermore, with the burner of the invention, there are some conditions in which the reaction takes place heterogeneously in an unmixed state, ie during starting, at partial load and during base load transition periods, which mode of operation is not possible. with the burner of said patent. The operations of the burner according to the invention facilitate a large ratio of the possible fuel supply amounts without extinguishing the combustion, good ignition and transverse ignition, as well as flame stability, which are essential features for a practical design. Furthermore, the switch from the heterogeneous to the homogeneous operation according to the invention is obtained by changing the fuel distribution over the nozzles of the first and second stages, which feature is not described in this patent.

U.S. Pat. Nos. 3,958,413 and 3,958,416 relate to two-stage burners, the stages of which are separated by a converging-divergent throat section. Also, the first stage of these two patents is used at some times during the cycle as a combustion chamber and at others 7909203-9% times in the cycle as a premix chamber. As a result, kickback of the flames does not cause damage to the parts / as is the case with the burner according to US patent 3,946,533. Patent 3,958,413 further appears to describe a variable size of the air inlet, for changing the air distribution over the stages, for obtaining the heterogeneous combustion transition in the first stage or in the first and second stages. -r the homogeneous combustion only in the second stage. In contrast, according to the invention, change of the fuel distribution over 10 stages is applied, using a number of fuel nozzles instead of variable size of the opening thereof, and by changing the fuel distribution instead of changing the air distribution.

* 790920?

Claims (12)

A method of operating a gas turbine burner so as to produce low NO emissions, which burner consists of a first and a second burner chamber connected by a neck, the first chamber having first fuel supply means and at least the neck or the second chamber is provided with second fuel supply means, the method being characterized by the successive steps of ê a) continuously supplying fuel to the first chamber through the first fuel supply means and igniting the fuel in this chamber; B) starting the fuel supply to the second chamber by the second fuel supply means and increasing the amount of fuel supplied per unit of time until the fuel supply through all fuel supply means is approximately the desired amount per unit of time, the fuel in the second chamber starting to ignition as a result of passage of combustion products from the first to the second chamber; c) reducing the fuel supply by the first fuel supply means and correspondingly increasing the fuel supply by the second fuel supply means such that the total fuel supply 20 remains almost constant until at least the combustion of fuel in the first chamber ceases; and d) increasing the fuel supply by the first fuel supply means and correspondingly reducing the fuel supply by the second fuel supply means such that the total fuel supply 25 remains approximately constant until the desired level of NO emissions from the burner is obtained. 2. Method according to claim 1, characterized in that the fuel supply through the first fuel supply members in step c) is reduced until all fuel supply takes place via the second fuel supply members. Method according to claim 2, characterized in that the fuel distribution at the end of step d) is such that the major part of the fuel is supplied via the first fuel supply means. Method according to claim 3, characterized in that the fuel distribution at the end of step d) is such that at least 60% of the total fuel supply takes place via the first fuel supply means. Method according to claim 1, characterized in that the fuel distribution at the end of step d) is such that the major part of 7909203 -11-. V V fuel is supplied through the first fuel feeders. 6. Method according to claim 1, characterized in that the first fuel supply members consist of an axisymmetric fuel nozzle, while the second fuel supply members consist of a number of symmetrically arranged fuel nozzles. 7. Stationary gas turbine burner capable of reducing Ν0χ emissions from the combustion of a hydrocarbon fuel, which burner is characterized by a first combustion chamber, first fuel supply means arranged for supplying fuel to the first chamber, by 10 means for supplying compressed air to the first chamber, by a neck or throat, connected to the first chamber and with a smaller cross-sectional area than the first chamber, by a second burner chamber, connected to the neck and with a cross-sectional area larger than that of the neck, by means for supplying compressed air to the second chamber by second fuel supply means, arranged for supplying fuel to at least either the neck or the second chamber, by means for supplying a cooling amount of a heat exchange medium to the second chamber downstream of the compressed air supply means to the second chamber mer, and the means for modifying the relative fuel supply amounts supplied by the first and second fuel supply means. 8. Burner according to claim 7, characterized in that the first fuel supply members consist of a single axisymmetric fuel nozzle, while the second fuel supply members consist of a number of symmetrically arranged fuel nozzles. Burner according to claim 8, characterized in that each of the nozzles of the second fuel supply means are arranged for supplying fuel to a third burner chamber, which is provided with means for supplying compressed air therein, said third burner chamber 30 such that they transfer the fuel and air therein to the second combustion chamber. * Burner according to claim 9, characterized in that the first, second and third burner chambers and the neck each have a circular cross section. to have. 11. Stationary gas turbine burner arrangement, comprising a plurality of adjacent burners, each having a first and a second burner chamber connected by a neck, characterized in that at least one burner is provided with ignition means of a fuel in its first chamber, wherein a plurality of 7909203 -12- * 4 first transverse ignition tubes are provided, each connecting the first chamber of one burner to the first chamber of an adjacent burner, while a plurality of second transverse ignition tubes are provided, which each connecting the second chamber of a burner to the second chamber of an adjacent burner. Burner device according to claim 11, characterized in that the device comprises ten burners, which are arranged adjacent to each other. ♦ 7909203