DE19542644B4 - premixed - Google Patents

Abstract

contraption for premixing combustion, wherein fuel (7, 8) and gaseous working means (3, 4, 9) previously the ignition for premix burning at least two stages (1, 2) are used, in a first stage (1) fuel (7) and combustion air (3) with excess air in a mixer (21), the resulting mixture (23) by means of a Flame stabilization (11) is stabilized and burned in one second stage (2) fuel (8) and combustion air (4) and / or Flue gas (9) are mixed in a mixer (22), the resulting Mixture (24) is added to the resulting in the first stage exhaust gases (25) and this mixture is post-combusted (12), characterized in that in a burner (30) at least one inner annular combustion channel (32) and an external one Ring combustion channel (31) are arranged coaxially with each other, wherein the inner annular combustion channel (32) through an inner, closed tube (33) and a middle pipe 34 and the outer ring combustion channel (31) through an outside Pipe (35) and the middle pipe ...

Description

Technical area

The The invention relates to a process for premix combustion, wherein Fuel and gaseous work equipment previously the ignition be mixed. The invention also relates to a device for execution of the procedure.

State of the art

Such methods and devices for premix combustion are known for example from EP-B1-0 321 809 known. There, the lower limit of nitrogen oxide production is determined by the lean extinction limit, which depends on the fuel used, air preheating, etc. Starting from a stoichiometric mixture, the excess air can now be increased until the lowest possible flame temperature is reached, without the flame being extinguished.

One Part of the excess air may also be due to recirculated flue gas be replaced. The deletion limit but then shifts to higher Flame temperatures, thereby reducing the nitrogen oxide emissions on the value from approx. 5-15 ppm (normalized for 3% residual oxygen).

at Burners with thermal power up to about 100 kW can be low Nitrogen oxide emissions can also be achieved by active flame cooling. This is the heat of combustion transferred to internals and from there to the burner walls radiated.

Out DE 195 10 744 A1 a combustion chamber with two-stage combustion has become known, which combustion chamber consists of a pre-combustion chamber and a secondary combustion chamber. In the pre-combustion chamber a plurality of individual burners is distributed over the circumference, which are arranged side by side on an annular front plate. In the afterburner opens a number of secondary burners, which are also arranged in a ring. The operation of such a structure is not easy to handle, bearing in mind that pollutant emissions will only remain low if uniform burns are consistently occurring across all burners.

Furthermore, it is off DE 36 06 625 A1 a burner configuration has become known, which consists of a main burner and a pilot burner, wherein the central pilot burner has a premix with a simple supply line for the supply of a fuel, and wherein a further parallel supply line is present, are introduced via which inert materials. The reduction of NOx emissions is achieved here by the admixture of an inert material, but this adversely affects the efficiency of the combustion.

Furthermore, it is off DE 44 16 650 A1 a heat generator has become known, which basically consists of a central burner, wherein the heat generator has a further system of mixers, which serve for the operation of Nachverbrennungszonen, and which act in the cross-sectional widening of the central burner. These mixers have the function of providing a mixture of air and fuel. If, however, the set goals of minimizing the pollutant emissions, in particular the NOx values, are to be achieved in this initial configuration, further mixers must be arranged on the circumference of the flame tube, which fulfill the same function as the mixer operating in the cross-sectional enlargement of the central burner , so in addition to be used, so that in the secondary and tertiary combustion zones can also be acted on the minimization of NOx emissions.

Presentation of the invention

Of the Invention is based on the object in a method and a Premix combustion devices of the type mentioned in the introduction for any Thermal services, in particular for thermal services greater than 100 kW, to obtain lowest nitrogen oxide emissions.

According to the invention this is achieved in that for premix combustion at least two Stages are used in a first stage fuel and Combustion air with excess air be mixed in a mixer such that the resulting mixture stabilized and burned by flame stabilization, that in a second stage fuel and combustion air and / or Flue gas can be mixed in a mixer, that is the resulting Mixture mixed with the resulting in the first stage exhaust gases and that this mixture is burned.

The Advantages of the invention are, inter alia, that the first stage with a part of the fuel used at the lean extinction limit can be operated and that the remaining part of the fuel in the second stage is burned so that in the second stage no significant increase the nitrogen oxide emission takes place.

When using flue gases in the second stage, it is advantageous to incinerate the remaining second stage fuel with the first stage residual oxygen. Due to the amount of flue gas used, the Flammentempe be set and the formation of additional nitrogen oxides can be kept to a minimum.

A Apparatus for carrying out of the method is characterized by the fact that at least one internal Ring combustion channel and an external Annular combustion channel are arranged coaxially to each other and that in the Ring combustion channels Mixing elements are arranged. This can, for example, the education carbon monoxide even at very low flame temperatures be prevented. For example, the second stage is the inner Assigned annular combustion channel, which prevents the cold flue gas / fuel mixture with cold burner walls comes into contact, which would lead to high carbon monoxide emissions.

Short description of the drawing

In The drawings are exemplary embodiments represented the invention.

It demonstrate:

1 a schematic representation of the premixing process;

2 a partial longitudinal section through a concentric burner;

3 a partial cross section through the concentric burner along the plane III-III in 2 ;

4 a partial longitudinal section through a burner with axially displaced annular combustion channels;

5 a partial longitudinal section through a burner with axially displaced annular combustion channels;

6 a partial longitudinal section through a burner with arranged therein double-cone burner.

It are only for the understanding the invention essential elements shown. The flow directions the work equipment are indicated by arrows.

Way to execute the invention

This in 1 schematically illustrated Vormischverfahren consists essentially of a first stage 1 and a second stage 2 wherein the stages are operated substantially lean. The first stage 1 consists of a mixer 21 in which combustion air 3 with fuel 7 is mixed, and a flame stabilization 11 , That in the mixer 21 resulting mixture 23 is thus stabilized and ignited by means of flame stabilization. The amount of combustion air 3 and fuel 7 is chosen so that the premix flame thus generated is operated with excess air at the lean extinction limit (for example, with an air ratio λ ≈ 1.7 for natural gas without air preheating, which corresponds to an adiabatic temperature of about 1,600 K Kung).

In the second stage 2 will now also combustion air 4 and / or recirculated flue gas 9 with fuel 8th in a mixer 22 mixed. That in the mixer 22 resulting mixture 24 becomes the hot exhaust 25 mixed in the first stage and in the second stage 2 burned and the flue gases 9 derived.

Will be in the mixer 22 combustion air 4 with fuel 8th mixed, becomes the second stage 2 also operated with excess air at the lean extinction limit. The air ratio can then be compared to the air ratio in the mixer 21 the first stage 1 be increased without the flame extinguished. As a result, low flame temperatures and thus very low nitrogen oxide emissions can be achieved.

Will be in the mixer 22 recirculated flue gas 9 with fuel 8th mixed, the fuel becomes 8th by means of residual oxygen of exhaust gases 25 from the first stage 1 in the second stage 2 burned. By the appropriate choice of the amount of flue gas 9 can be a nitric oxide formation in the second stage 2 be avoided completely constantly, since the fuel was premixed with the flue gas. As a result, the flue gas must also be heated during combustion and hot spots where nitrogen oxides could form are avoided.

The aim of the peak temperature is again to aim for the smallest achievable adiabatic flame temperature. The required amount of flue gas 9 For example, depends on the flue gas temperature, the mixing mechanism between fuel 8th and flue gas 9 , the heat loss at the burner walls during the mixing and the extraction of the flue gas 9 , By the recirculation of flue gas 9 the total air ratio λ _{total can} be reduced. When applied to a boiler, the thermal efficiency of the boiler increases as the total air ratio decreases.

Numerical example:

For a total air ratio λ _total of 1:05 and an oxygen content of less than one percent in the exhaust gas is obtained for natural gas as fuel and without air heating:
First stage: λ = 1.7; 100% combustion air; 62% total fuel (≅ fuel 7 )
Second stage: 38% total fuel (≅ fuel 8th ); Flue gas quantity ≤ 62% combustion air quantity

To 2 There is a two-stage burner 30 essentially coaxially about an axis of symmetry 29 arranged annular combustion channels, an inner annular combustion channel 32 and an outer annular combustion channel disposed around the inner annular combustion channel 31 , The ring combustion channel 32 is through an inner, closed tube 33 and a middle tube 34 limited, the annular combustion channel 31 is through an outer tube 35 and the middle tube 34 limited.

At the downstream end of the annular combustion channels 31 . 32 , at the burner exits 36 . 37 , the flow-through cross section expands, forming a backflow zone, which serves for flame stabilization. The burner 30 is on a front panel 6 the combustion chamber 5 assembled. On the front panel can be a partition 40 be arranged. This partition 40 encloses the outer ring combustion channel 31 annular and extends downstream into the combustion chamber 5 , The partition 40 serves to adjust the cross-sectional widening at the downstream end of the outer annular channel and thus the flame stabilization.

To 3 and 2 are upstream of the Brenneraustritte 36 . 37 over the circumference of the annular combustion channels 31 . 32 several vortex generators 20 distributed. The non-illustrated, for example, tetrahedral vortex generator 20 is from the EP-A1-0 623 786 known. Such a vortex generator 20 consists essentially of three freely flowing around triangular surfaces, which protrude into the annular combustion channels. These are a roof surface and two side surfaces that run at certain angles in the direction of flow. The two side surfaces are usually perpendicular to the walls of the annular combustion channels 31 . 32 and are fixed with one side on these walls. The two side surfaces are symmetrical in shape, size and orientation. The roof surface lies with a transversely to the flow-through channel extending, curved edge on the walls of the annular combustion channels 31 . 32 at. The connecting edge of the two side surfaces forms the downstream edge of the vortex generator, which is also perpendicular to the walls of the annular combustion channels 31 . 32 runs. The transverse to the flow-through channel curved edge of the roof surface is the first acted upon by the flow edge. As the edges of the vortex generator flow around, the flow is converted into a pair of opposing vortexes. Their vortex axes lie in the axis of the flow. The swirl number and the location of vortex break down, if the latter would be desired, are determined by appropriate choice of the angle of attack of the roof surface and the angle that enclose the two side surfaces. With increasing angles, the vorticity or swirl number is increased and the location of vortex perturbation migrates upstream. The vortex generator 20 can have different heights h relative to the respective annular combustion channel height H. As a rule, the height h will be coordinated with the channel height H such that the generated vortex immediately downstream of the vortex generator already reaches such a size that the full channel height H is filled, which leads to a uniform velocity distribution in the applied cross section. Another criterion which can influence the chosen ratio h / H is the pressure drop which occurs when the vortex generator flows around. With a larger ratio h / H, the pressure loss coefficient increases. The ratios h / H can also be found in the different ring burners 31 . 32 be designed differently, which can support the mixing of the partial streams.

Downstream of the vortex generators are fuel injections 38 . 39 intended. The fuel feeds to the fuel injections are not shown, but they usually become inside the tubes 33 . 34 and 35 arranged. The downstream route of the annular combustion channels 31 . 32 until the burner outlet 36 . 37 thus serves as Vormischstrecke. The length of this premix is dependent on the design of the vortex generators 20 and is tuned so that at the burner exits 36 . 37 an optimal mixture is achieved.

The steps 1 and 2 can now essentially the inner and the outer annular combustion channel 32 . 31 be assigned arbitrarily. In the following, the first stage will now be defined by the outer annular combustion channel. Through the outer ring combustion channel 31 becomes combustion air 3 and about the fuel injections 38 fuel 7 into the combustion air 3 mixed. The mixture thus obtained 23 emerges from the outer ring combustion channel 31 out and through the cross-section jump at the burner outlet 36 a backflow zone forms. The premix flame produced by ignition of the mixture is stabilized by this backflow zone. Through the inner ring combustion channel 32 For example, recirculated flue gas 9 directed and about the fuel injections 39 fuel 8th mixed. This mixture 24 is the flue gases of the premix flame of the first stage 1 admixed. This is done by the jump in cross section at the burner outlet 37 , Not shown is the possibility of supporting the mixing of the partial streams of the first and the second stage by the burner 30 Downstream any mixing systems.

To 4 and 5 can the two stages 1 . 2 also along the axis of symmetry 29 be moved axially. This allows the location of Ver Mixing the flow of the first stage 1 with the flow of the second stage 2 be set exactly. Again, can the partition 40 to adjust the cross-sectional widening be arranged on the front panel.

In 4 the inner annular combustion channel extends downstream into the combustion chamber 5 into it. The outer ring combustion channel 31 forms the first step 1 , the inner annular combustion channel 32 the second stage. This is particularly advantageous in the use of recirculated flue gas 9 in the second stage. The flue gases 9 They do not come into contact with the cold outer walls of the burner and are surrounded by the hot exhaust gases of the first stage. This minimizes the risk of carbon monoxide formation.

In 5 the inner annular combustion channel extends upstream into the burner 30 into, ie the burner outlet 37 of the inner annular combustion channel 32 lies upstream of the burner outlet 36 of the outer ring combustion channel 31 , The äusse re ring burning channel 31 here forms the second stage 2 , the inner annular combustion channel 32 the first stage 1 , Here the exhaust gases of the first stage do not come into contact with the cold outer walls of the burner.

To 6 can the inner ring combustion channel 32 and the inner tube 33 be replaced by another mixing system, for example by a premix burner 15 , In this premix burner shown schematically 15 it is a so-called double-cone burner, as he, for example, from the EP-B1-0 321 809 is known. It consists essentially of two hollow, conical body parts, which are nested in the flow direction. The respective central axes of the two body parts are offset from each other. The adjacent walls of the two body parts form tangential slots in their longitudinal extent 18 for the combustion air 3 , which thus enters the burner interior. To operate the burner with gaseous fuel are in the range of tangential slots 18 provided in the walls of the two part body in the longitudinal direction distributed gas inlet openings in the form of nozzles. These nozzles can be with special lines or by means of the fuel lance 17 be supplied. In gas operation, the mixture formation begins with the combustion air 3 already in the zone of the slots 18 , At the burner exit 16 of the burner 15 In each case, the most homogeneous possible fuel concentration is established over the applied cross-section. At the burner outlet, a defined dome-shaped recirculation zone is created, at the top of which the ignition takes place. The flame itself will pass through the recirculation zone in front of the burner 15 stabilized without the need of a mechanical flame holder.

Of course it is the invention is not limited to the embodiments shown and described limited. The vortex generators and the double cone burners can also by any other mixing elements used for mixing fuel and combustion air or flue gas are suitable to be replaced. These can be, for example, delta wings, half delta wings, wing profiles etc. act. The number of ring burners can of course for a finer gradation of Premixing and combustion are also increased. The ring combustion channels can be arbitrary be formed and must not cylindrical as shown. You can, for example also tapered so that the inner tube substantially is designed as a cone or a truncated cone whose tip is oriented downstream is.

1

First step

2

Second step

3

combustion air

4

combustion air

5

combustion chamber

6

front panel

7

fuel first stage

8th

fuel second step

9

flue gas

11

flame stabilization

12

afterburning

15

premix

16

burner outlet

17

fuel lance

18

tangential slots

20

Vortex generator

21

mixer first stage

22

mixer second step

23

mixture Combustion air / fuel

24

mixture Combustion air or flue gas / fuel

25

exhaust first stage

29

axis of symmetry

30

burner

31

outer Ring combustion channel

32

internal Ring combustion channel

33

inner pipe

34

middle pipe

35

outer pipe

36

outer burner outlet

37

internal burner outlet

38

Fuel injection external Ring combustion channel

39

Fuel injection inside Ring combustion channel

40

partition wall

H

channel height

H

Height vortex generator

Claims (5)

Premix combustion device, wherein fuel ( 7 . 8th ) and gaseous working materials ( 3 . 4 . 9 ) are mixed prior to ignition, for premix combustion at least two stages ( 1 . 2 ), in a first stage ( 1 ) Fuel ( 7 ) and combustion air ( 3 ) with excess air in a mixer ( 21 ), the resulting mixture ( 23 ) by means of flame stabilization ( 11 ) is stabilized and burned, in a second stage ( 2 ) Fuel ( 8th ) and combustion air ( 4 ) and / or flue gas ( 9 ) in a mixer ( 22 ), the resulting mixture ( 24 ) the exhaust gases produced in the first stage ( 25 ) and this mixture is post-combusted ( 12 ), characterized in that in a burner ( 30 ) at least one inner annular combustion channel ( 32 ) and an outer annular combustion channel ( 31 ) are arranged coaxially with each other, wherein the inner annular combustion channel ( 32 ) through an inner, closed tube ( 33 ) and a middle tube 34 and the outer annular combustion channel ( 31 ) through an outer tube ( 35 ) and the middle tube ( 34 ) and that in the annular combustion channels ( 31 . 32 ) Mixing elements ( 20 ) are arranged. Premix combustion device, wherein fuel ( 7 . 8th ) and gaseous working materials ( 3 . 4 . 9 ) are mixed prior to ignition, for premix combustion at least two stages ( 1 . 2 ), in a first stage ( 1 ) Fuel ( 7 ) and combustion air ( 3 ) with excess air in a mixer ( 21 ), the resulting mixture ( 23 ) by means of flame stabilization ( 11 ) is stabilized and burned, in a second stage ( 2 ) Fuel ( 8th ) and combustion air ( 4 ) and / or flue gas ( 9 ) in a mixer ( 22 ), the resulting mixture ( 24 ) the exhaust gases produced in the first stage ( 25 ) and this mixture is post-combusted ( 12 ), characterized in that in a burner around a premix burner ( 15 ) in the form of a double-cone burner concentric at least one outer annular combustion channel ( 31 ) is arranged and that in the annular channel ( 31 ) Mixing elements ( 20 ) are arranged. Apparatus according to claim 1 or 2, characterized in that the mixing elements vortex generators ( 20 ) are. Device according to claim 1 or 2, characterized in that the burner outlets ( 16 . 36 . 37 ) of the inner annular combustion channel ( 32 ) or premix burner ( 15 ) and that of the outer annular combustion channel ( 31 ) in the flow direction of the mixtures ( 23 . 24 ) are axially displaced. Apparatus according to claim 1 or 2, characterized in that the annular combustion channels ( 31 . 32 ) are cylindrical.