EP0713058B1 - Multi-stage combustion chamber - Google Patents

Description

Technical field

The invention relates to a method for operating a multi-stage Combustion chamber, with at least one primary burner Premix type, in which within a premixing room the Fuel injected via nozzles prior to ignition is intensively mixed with primary combustion air, and with at least an afterburner, downstream of the pre-combustor is arranged and introduced into the secondary combustion air becomes. It also relates to a combustion chamber for implementation of the procedure.

State of the art

Such a two-stage combustion chamber and a method for its operation is known from DE-C2 31 49 581. Vortex cups with central fuel injection nozzles are used there as primary burners of the premix type. The combustion chamber is a so-called "rich / lean two-stage combustion chamber", the gases having a fuel / air equivalence ratio in the first combustion stage which is greater than 1. In the second combustion stage, the gases have a fuel / air equivalence ratio that is less than 1. The transition from the rich to the lean mixture can be realized as quickly as possible. The mixture is therefore accelerated and the secondary combustion air is injected into the accelerated mixture. The purpose of the acceleration is to keep the duration of the mixture in the zone in which the fuel / air equivalence ratio is 1 as short as possible. This is because the formation rate of NO _{X is} greatest at this medium ratio.

Modern burners of the premix type offer the possibility of also operating the first combustion stage lean, which has an advantageous effect on the NO _x formation due to the large air ratio and the lower flame temperatures. With such a premixed combustion technology, it only has to be ensured that the flame stability, especially at partial load, does not reach the extinguishing limit. As a rule, such premix burners, when operated in one stage and when temperatures of 1800K (approx. 1530 ° C) are required, produce about 25-30 ppm NO _X.

Presentation of the invention

The object of the invention is to create a "lean / lean" process and the associated combustion chamber using such modern premix burners, with which extremely low NO _x emissions are achieved.

• dass der Primärbrenner ein flammenstabilisierender Vormischbrenner ist, welcher an der unteren Stabilitätsgrenze betrieben wird,
• dass zwischen Vorbrennraum und Nachbrennraum das Rauchgas beschleunigt wird,
• und dass in die den Vorbrennraum verlassende Rauchgasströmung zwecks Bildung eines selbstzündenden Gemisches Kühlluft aus der doppelwandigen Brennkammerbegrenzung und Zusatzbrennstoff eingeführt wird.

According to the invention, this is achieved by

• that the primary burner is a flame-stabilizing premix burner which is operated at the lower stability limit,
• that the flue gas is accelerated between the pre-combustion chamber and the after-combustion chamber,
• and that cooling air from the double-walled combustion chamber boundary and additional fuel is introduced into the flue gas flow leaving the pre-combustion chamber to form a self-igniting mixture.

A combustion chamber for carrying out this method draws arranged from one at the head end of the combustion chamber Double-cone burner of the premix type, with a subsequent one Pre-combustion chamber, by one following the pre-combustion chamber Acceleration path for the flue gas, which in one Afterburner opens, and through air inlets in the area of the acceleration section in the double wall Combustion chamber boundary are arranged, as well as by at the entrance of the afterburner arranged injection means for Additional fuel.

It is from DE-A1 37 07 773 in connection with process heat already a two step process and a corresponding combustion chamber known, which with a flame-stabilizing double cone burner as primary burner works in which between pre-combustion chamber and post-combustion chamber the gas is accelerated and at which of the second Stage air is added. However - as with the State of the art already mentioned at the beginning - this Pre-combustion chamber sub-stoichiometric with an air ratio Lambda = 0.7 operated. This achieves the partially burned Gas a temperature of 1800-1900 ° C. At the in the accelerated gas flow introduced air so-called quenching air (quench air), which quickly enters the The main flow is to inject to oxidize the atmospheric nitrogen to avoid.  

The advantage of the invention can be seen in particular in the fact that the premix burner can be operated at the lower extinguishing limit, with only about 9 ppm NO _x initially being produced; The self-igniting afterburning process delivers gases with the desired high temperature of 1800K (approx. 1530 ° C), which gases only have NO _x values below 6 ppm due to the supply of additional air and due to the short residence times.

Brief description of the drawing

In the drawing are two embodiments of the invention schematically represented by gas turbine combustion chambers.

Fig. 1

einen Teillängsschnitt einer ersten zweistufigen Brennkammer;

Fig. 2

einen Teillängsschnitt einer zweiten fünf stufigen Brennkammer;

Fig. 3A

einen Querschnitt durch einen Vormischbrenner der Doppelkegel-Bauart im Bereich seines Austritts;

Fig. 3B

einen Querschnitt durch denselben Vormischbrenner im Bereich der Kegelspitze;

Show it:

Fig. 1

a partial longitudinal section of a first two-stage combustion chamber;

Fig. 2

a partial longitudinal section of a second five-stage combustion chamber;

Figure 3A

a cross section through a premix burner of the double cone type in the region of its outlet;

Figure 3B

a cross section through the same premix burner in the region of the cone tip;

It is only essential for understanding the invention Elements shown. For example, are not shown the complete combustion chamber and its assignment to a Plant, fuel supply, control devices and the like, the flow direction of the work equipment is marked with arrows.  

Way of carrying out the invention

In Fig. 1, 50 is a jacketed plenum, which is usually the one not shown Compressor-fed combustion air and one for example, supplies annular combustion chamber 60. This The combustion chamber has two stages and essentially exists a pre-combustion chamber 61 and a downstream one located post-combustion chamber 62, both with a combustion chamber wall 63 are covered. Of all the combustion air part a of the pre-combustion chamber 61 is fed directly, while parts b and c initially have cooling functions exercise.

On the pre-combustion chamber 61, which is at the head end of the combustion chamber 60 is located and its combustion chamber through a front panel 54 is limited, an annular dome 55 is placed. A burner 110 is arranged in this dome in such a way that the burner outlet is at least approximately flush with the Front plate 54. The longitudinal axis 51 of the primary burner 110 runs coaxially to the longitudinal axis 52 of the combustion chamber 60 a number of such burners are distributed around the circumference 110 side by side on the annular front plate 52 arranged. About the dome wall perforated at its outer end the combustion air a flows from the plenum 50 into the Dominnere and acts on the burners. The fuel will fed to the burner via a fuel lance 120 which penetrates the cathedral and plenum walls.

In the premix burner shown schematically in FIGS. 3A and 3B 110 is a so-called Double cone burner, such as from EP-B1-0 321 809 is known. Essentially it consists of two hollow, conical part-bodies 111, 112, which are nested in the direction of flow.  

The respective central axes 113, 114 of the two Partial body offset from each other. The neighboring walls of the two partial bodies form in their longitudinal extent tangential slots 119 for the combustion air that on this way gets into the interior of the burner. There is one arranged first fuel nozzle 116 for liquid fuel. The fuel is injected into the at an acute angle Hollow cone injected. The resulting tapered fuel profile is from the tangentially flowing combustion air enclosed. In the axial direction, the concentration of the Fuel continuously as a result of mixing with the Combustion air reduced. In the example, the burner can can also be operated with gaseous fuel. For this purpose, in the area of the tangential slots 119 in the Walls of the two partial bodies distributed in the longitudinal direction Gas inflow openings 117 are provided. Starts in gas operation the mixture formation with the combustion air is therefore already in the zone of the entry slots 119. It is understood that in this way also a mixed operation with both types of fuel is possible.

At the burner outlet 118 of the burner 110 there is one if possible homogeneous fuel concentration over the acted upon circular cross-section. It arises on A defined dome-shaped recirculation zone emerges from the burner 122, at the tip of which the ignition takes place. The flame itself is through the recirculation zone in front of the burner stabilized without the need for a mechanical flame holder.

In the example, the premix burner is operated with approx. 56% of the total available combustion air and that close to the lower extinguishing limit; ie the corresponding amount of fuel is set so that a temperature of 1640K (approx. 1370 ° C.) and a NO _x content of 9 ppm prevail in the combustion chamber 61.

1 forms the transition from the pre-combustion chamber 61 in the Afterburner 62 is a constriction, which is an acceleration zone 70 represents for the work equipment. This is supposed to a suitable temperature / speed field for a stable auto-ignition downstream of fuel lances be created.

Such fuel lances are at the entrance to the afterburning chamber 62 121 arranged. In the case of an annular combustion chamber several such lances are distributed over the circumference. Out the additional fuel is supplied to them - evenly over the Flow cross section distributed - injected into the main flow.

The remaining ones are upstream of this fuel injection 44% air is appropriately mixed into the combustion process. This is the air that initially is used to cool the combustion chamber walls. These combustion chamber walls are both in the area of the pre-combustion chamber 61 and in the area of the afterburner 62 double-walled. The inner wall 63a is in the Plane of the intended air supply with inlet openings 64 see. The amount of air that is added to the main flow is composed of two partial flows. On the one hand the cooling air b of the pre-combustion chamber, which is approximately 16% of the total and the cooling air c of the afterburner, which makes up about 28% of the total.

It is understood that this process involves pressure loss connected is. For example, the pressure drop is the air via the wall cooling approx. 4%, that via the Mixture of combustion gases and cooling air approx. 2%.  

The mixing temperature after admixing the cooling air to the combustion gases in the pre-combustion chamber is approximately 980 ° C., so that the fuel / air mixture present at the inlet into the afterburning chamber 62 is self-igniting. The amount of additional fuel is selected so that the desired final temperature of 1700 K (approx. 1430 ° C.) prevails in the afterburning chamber 62. The NO _x content of 9 ppm resulting from the pre-combustion is reduced to less than 6 ppm by the dilution.

It is understood that the afterburning chamber 62 is in its axial Extension is dimensioned so that it is complete Burnout takes place.

2 schematically shows a five-stage combustion chamber which can be operated as follows:
Fuel is fed to the premix burner 110 via the fuel lance 120 and burned with approximately 10% of the combustion air a. The amount of fuel supplied via the lance 120 is adjusted so that a temperature of 1640 K (approx. 1370 ° C.) and a NO _x content of 9 ppm prevail in the combustion chamber A. The mixture is accelerated; A further 8% of air, in this case wall cooling air, is introduced in level b, and a corresponding amount of fuel is introduced via fuel lances 121, so that a temperature of 1500 K (approx. 1230 ° C.) prevails in combustion chamber B. A further 14% of air is introduced in level c and a corresponding amount of fuel is introduced via fuel lances 130, so that a temperature of 1500 K (approx. 1230 ° C.) also prevails in combustion chamber C. A further 26% of air is introduced in level d and a corresponding amount of fuel is introduced via fuel lances 131, so that a temperature of 1500K (approx. 1230 ° C.) also prevails in combustion chamber D. The remaining 42% air is introduced in level e and the remaining amount of fuel is introduced via fuel lances 132, so that the desired final temperature of 1700 K (approx. 1430 ° C.) prevails in combustion chamber E. As a result of the successive reduction in the NO _x created on the basis of the pre-combustion, it is entirely possible that the NO _x content in the combustion chamber E is only 3 ppm.

As a result, it can be determined that the optimal number of combustion stages with regard to the NO _x value to be achieved is to be selected as a function of the pressure loss to be accepted and the combustion chamber length.

Claims (3)

1. Method of operating a multi-stage combustion chamber, having at least one primary burner (110) of the premixing type of construction, in which the fuel injected via nozzles is intensively mixed with primary combustion air inside a premixing space in advance of the ignition, and having at least one secondary combustion space (62, B, C, D, E) which is arranged downstream of the precombustion space (61, A) and into which secondary combustion air is directed, characterized

   in that the primary burner (110) is a flame-stabilizing premixing burner which is operated at the lower stability limit,

   in that the burnt gas is accelerated between precombustion space (61, A) and secondary combustion space (62, B, C, D, E),

   and in that, for the purpose of forming a self-igniting mixture, cooling air from the double-wall combustion-chamber boundary and additional fuel are introduced into the burnt-gas flow leaving the precombustion space.
2. Combustion chamber for carrying out the method according to Claim 1,

   a premixing burner (110), having an adjoining precombustion space (61, A), being arranged at the head end of the combustion chamber, characterized

   in that an acceleration section (70) for the burnt gas is provided, which acceleration section (70) follows the precombustion space and leads into a secondary combustion space (62, B, C, D, E),

   in that inflow openings (64) are arranged in the area of the acceleration section (70) in the double-wall combustion-chamber boundary,

   and in that injection means for additional fuel are arranged at the inlet of the at least one secondary combustion space (62, B, C, D, E).
3. Combustion chamber according to Claim 2, characterized in that the premixing burner is a double-cone burner (110) without a mechanical flame retention baffle.