DE10301316B3 - Fuel dust combustion method for preventing nitrous emissions e.g. for steam generator, with tangential injection of fuel rich stream and fuel impoverished stream into combustion chamber - Google Patents

Abstract

The combustion method uses a vertical combustion chamber (2) with a rectangular cross-section, containing a fuel dust burner (6) in each combustion chamber wall (4) or at each combustion chamber corner (5) in at least one horizontal plane. The fuel/air mixture is divided into a fuel rich stream (8) and a fuel impoverished stream (9), supplied to the combustion chamber tangential to concentric circles together with a secondary air flow. An independent claim for a fuel dust combustion device is also included.

Description

The invention relates to a method and an apparatus for low-NO _x combustion of fuel dust in a vertical combustion chamber with a substantially square cross-section, in which at least one fuel dust burner is arranged in at least one horizontal plane in each combustion chamber wall and / or each combustion chamber corner each fuel dust burner, at least one fuel-air mixture (primary air) and secondary air are blown into the combustion chamber tangentially aligned with at least one imaginary circle lying in the horizontal plane, and additional air required for combustion is supplied to the combustion chamber.

By the publication "low _NOx Steinkohlentangentialfeuerung" in EVT report 118/96 (1996) has disclosed a method and an apparatus for the combustion of fuel fines in a steam generator. In this known method of combustion of coal is burned in a vertical furnace of a steam generator The fuel is blown together with primary air in four horizontal planes through the dust burner tangentially onto an imaginary or imaginary circle in the combustion chamber for combustion. The respective secondary air is tangentially injected via secondary air nozzles of the dust burner into another second imaginary circle enveloping the first imaginary circle In order to avoid reducing and thus corrosive conditions on the combustion chamber walls, which consist of steam generator tube walls, wall air is also conducted parallel to the combustion chamber walls by means of additional nozzles.

In order to reduce the NO _x emissions caused by the combustion, the principle of axial and radial air grading is used, i.e. the air flow is designed so that to avoid NO _x formation, a substoichiometric (air - or lack of oxygen) combustion zone. Appropriate air is metered in towards the combustion chamber or surrounding walls or towards the end of the combustion chamber (the combustion or flue gas generated during combustion flows from the bottom upwards within the vertical combustion chamber or to the end of the combustion chamber) so that there is by means of radial air gradation) or at the end of the combustion chamber (through axial air gradation) set above-stoichiometric (excess air or oxygen) conditions. The setting of over-stoichiometric ratios is particularly important in the wall area in order to keep the carbon monoxide which occurs in sub-stoichiometric zones and which has a corrosive effect away from the surrounding walls.

This known method requires an elaborate air duct with numerous targets aimed at the combustion chamber or surrounding walls additional nozzle to build up the radial air gradation. This wall air curtain should seamless in all operating conditions to prevent CO corrosion attacks. By the impulse of this Nozzles in unfavorable make the possibility, that due to the suction effect of these nozzles, the fireball in the combustion chamber or in the combustion chamber could be shifted to the surrounding walls, which means under circumstances Slagging on the walls can be.

As a rule, the adjustment of the air quantities to maintain the axial and radial air grading requires precise measuring and control devices and experienced operating personnel for all load cases. Furthermore, when existing furnaces are converted to such low-NO _x furnaces, there is a considerable cost involved in retrofitting the additional nozzles.

By publication DE 197 31 474 C1 A method for operating a corner burner for tangential firing and corner burner for carrying out the method has become known. In this method, at least one stream of coal dust and primary air is introduced into the firing chamber via the corner burner, oriented tangentially to an imaginary, essentially horizontal circle in the combustion chamber of the tangential furnace, and at least one further air flow can be set via a nozzle of the corner burner at an offset angle to the stream of coal dust and introducing primary air toward a wall of the furnace into the furnace. The offset angle is adjusted by a mixture of at least two partial air jets of different flow speeds.

By publication US Pat. No. 4,294,178 a tangential combustion system has become known, each has coal dust burners in the corners of the combustion chamber. Starting from these corner burners are tangential to a first or inner one, imaginary horizontal Circle of coal and primary air, recirculated to a second and the first enclosing circle Flue gas and a third and the second enclosing circle secondary air entered in the firebox.

The object of the invention is now to provide a method and an apparatus for low _NOx combustion of fuel fines to provide, or with which the above-mentioned disadvantages and the large number of costly Wandluft- or sheath air nozzles can be avoided in the well as a less expensive Provide measuring and control equipment.

The above object is achieved with regard to the method by the characterizing Features of claim 1 and with respect to the device solved by the characterizing features of claim 4.

Advantageous embodiments of the Invention are the dependent claims refer to.

• – Durch die Eindüsung eines brennstoffreichen Gemischstroms tangential auf einen feuerraumzentrumsnahen gedachten Kreis oder direkt auf das Feuerraumzentrum ausgerichtet und eines brennstoffarmen Gemischstroms tangential auf einen den ersten gedachten Kreis umhüllenden zweiten gedachten Kreis ausgerichtet wird in dem Feuerraum ein Brennstoffkonzentrationsgefälle von der Mitte zur Wand hin erzeugt, d.h. es liegt eine hohe Brennstoffkonzentration in der Mitte, eine geringer werdende Brennstoffkonzentration zur Wand hin vor, so dass die Stöchiometrie der Verbrennung ebenfalls von der Mitte zur Wand hin zunimmt. Somit kann gewährleistet werden, dass in der Hauptverbrennungszone in der Mitte des Feuerraumes unterstöchiometrische und somit NO_x-arme Verbrennungsbedingungen herrschen, während an den Umfassungs- bzw. Feuerraumwänden ausreichend Sauerstoff zur Vermeidung der CO-Korrosion vorhanden ist,
• – durch die Aufkonzentration eines brennstoffreichen Gemischstroms und örtlich getrennte Einblasung dieses Gemischstroms von dem brennstoffarmen Gemischstrom in Richtung des Feuerraumzentrums kann vermieden werden, dass Brennstoff in die Nähe der Feuerraumwand gelangt und dort verbrennt, d. h. das Feuer wird konzentrierter in der Feuerraummitte gehalten, so dass die Rauchgastemperaturen in Wandnähe gegenüber den herkömmlichen Verfahren geringer werden, was somit die Verschlackungsneigung an den Feuerraumwänden reduziert. Die Vermeidung von zur Feuerraumwand hin abgelenkten Luftdüsen begünstigen diesen Sachverhalt, da kein direkt an die Wand gerichteter Impuls und somit keine entsprechende Brennstoffansaugung vorliegt,
• – aus der Tatsache, dass der Brennstoff hochkonzentriert in den Feuerraum eingebracht wird, wird die Zündstabilität der Brenner verbessert, was insbesondere im Teillastfall zu einem stabileren Betrieb der Feuerung führt,
• – durch den Wegfall von zu den Feuerraumwänden hin abgelenkten Luftdüsen mit entsprechenden Mess- und Regeleinrichtungen kann der Brennstoffstaubbrenner einfacher, kompakter und somit kostengünstiger ausgeführt werden,
• – der Aufwand bei Umbauten von konventionellen Tangentialfeuerungen auf NO_x-arme Feuerungen ist beim Einsatz der erfindungsgemäßen radialen Brennstoffstufung deutlich geringer als beim Einsatz der radialen Luftstufung, da auf zusätzliche Luftdüsen, Mess- und Regeleinrichtungen weitestgehend verzichtet werden kann, es sind ggf. lediglich Modifikationen an den Brennstoffstaubleitungen bzw. der Brennstoffstaubaustrittsdüsen erforderlich,
• – der Betrieb der erfindungsgemäßen Feuerung mit Brennstoffstufung ist im Vergleich zu einer Feuerung mit radialer Luftstufung aufgrund der nicht vorhandenen Mess- und Regeleinrichtungen für zusätzliche Luftdüsen einfacher, der Betrieb entspricht der einer konventionellen Tangentialfeuerung.

The solution according to the invention creates a method or a device which has the following advantages:

• - By injecting a fuel-rich mixture flow tangentially to an imaginary circle near the center of the combustion chamber or directly to the center of the furnace and a fuel-poor mixture stream tangentially aligned to a second imaginary circle enveloping the first imaginary circle, a fuel concentration gradient is generated in the furnace from the center to the wall, ie there is a high fuel concentration in the middle, a decreasing fuel concentration towards the wall, so that the stoichiometry of the combustion also increases from the center towards the wall. This ensures that the main combustion zone in the middle of the combustion chamber is under-stoichiometric and therefore low in NO _x , while there is sufficient oxygen on the surrounding or combustion chamber walls to avoid CO corrosion.
• - By concentrating a fuel-rich mixture flow and locally blowing this mixture flow from the low-fuel mixture flow towards the center of the combustion chamber, it can be avoided that fuel gets near the combustion chamber wall and burns there, ie the fire is held more concentrated in the center of the combustion chamber, so that the Flue gas temperatures near the wall are lower than with conventional methods, which reduces the tendency to slagging on the walls of the combustion chamber. The avoidance of air nozzles deflected towards the combustion chamber wall favors this situation, since there is no impulse directed directly at the wall and therefore there is no corresponding fuel intake.
• The fact that the fuel is introduced into the combustion chamber in a highly concentrated manner improves the ignition stability of the burners, which leads to more stable operation of the furnace, in particular under part-load conditions,
• By eliminating the air nozzles deflected towards the combustion chamber walls with appropriate measuring and control devices, the fuel dust burner can be made simpler, more compact and therefore more cost-effective,
• - The effort for conversions from conventional tangential furnaces to low-NO _x furnaces is significantly lower when using the radial fuel gradation according to the invention than when using the radial air gradation, since additional air nozzles, measuring and control devices can be largely dispensed with, there may only be modifications required on the fuel dust lines or the fuel dust outlet nozzles,
• - The operation of the combustion according to the invention with fuel gradation is easier compared to a combustion with radial air gradation due to the lack of measuring and control devices for additional air nozzles, the operation corresponds to that of conventional tangential combustion.

In an advantageous embodiment of the invention is the circular flow of the secondary air flow inside the firebox the same as that of the fuel-rich and low-fuel mixture flow. This will make an even, vortex-free Mixing of the secondary air achieved with the fuel mixture.

An advantageous embodiment of the Invention provides that if there are several horizontal planes the tangential alignment of the fuel-rich and the fuel-poor Mixture flow on an imaginary first and / or second circuit with the same dimensions. In other words, that the imaginary first and / or second circles to which the mixture flows as well the secondary air are directed tangentially in all Horizontal planes have the same dimensions. This measure will a uniform Burns achieved and all Burner simplified in design.

Another advantageous training The invention provides the dust burner nozzles for blowing in the fuel-rich and low-mixture flow in the horizontal direction side by side to arrange. This makes the design of the two dust burner nozzles simple be solved and at the same time the mixture flows in desired Way into the firebox.

Below are exemplary embodiments the invention with reference to the drawing and the description explained in more detail.

It shows:

1 schematically shown in longitudinal section a vertical combustion chamber with four horizontal levels equipped with fuel dust burners,

2 schematically shown a combustion chamber in cross section according to section AA of the 1 .

3 schematically shown a combustion chamber in cross section according to section BB of the 1 .

4 schematically represented a combustion chamber in cross section within the horizontal planes,

5 schematically shown a fuel dust burner with upstream Device for dividing and separating the fuel-air mixture.

1 shows schematically shown in longitudinal section a vertical firebox 2 of a steam generator 1 , The firebox 2 has essentially a square cross section, but can also have a rectangular cross section. The firebox 2 is to the side of the combustion chamber walls 4 limited, which usually consists of membrane walls or tube walls that are part of a steam generator 1 are formed. The lower end of the vertical firebox 2 usually forms a furnace funnel 19 , through which part of the ashes generated during combustion and unburned material from the combustion chamber 2 can be carried out. The vertical firebox sits upwards 2 through a flue gas flue 20 through which the flue gas generated during combustion is discharged.

The firebox shown 2 has four spaced horizontal planes 3a . 3b . 3c and 3d on, each with a fuel dust burner 6 per firebox corner 5 are trained. Instead of in the corners of the firebox 5 can the fuel dust burner 6 also in the firebox walls 4 or be located in both locations. The fuel dust burner 6 comprises a dust burner nozzle for injecting a fuel-air mixture (primary air) and at least one secondary air nozzle 16 for the injection of secondary air 15 , The firebox 2 according to 1 each has a fuel dust burner 6 a secondary air vent 16a and a secondary sub-air nozzle 16b on, which are arranged immediately above and below the dust burner nozzle.

According to the invention, the fuel-air mixture (the air is primary or carrier air), which is caused by dust lines 21 to the respective dust burner 6 is brought upstream of each fuel dust burner 6 by means of a device 7 into a fuel-rich 8th and a low fuel 9 Mixture flow divided and separated the dust burner nozzles 10 . 11 of the dust burner 6 fed, being through the burner nozzle 10 the fuel-rich 8th and through the burner nozzle 11 the low-fuel mixture 9 in the firebox 2 is blown in. In an advantageous embodiment of the invention, the burner nozzles are 10 . 11 arranged in a plane next to each other - separated by a partition, so to speak. The burner nozzles 10 . 11 but can also be more or less spaced apart in the horizontal direction or vertically one above the other.

According to the fuel-rich mixture stream 8th through the burner nozzle 10 of the dust burner 6 tangential to one in the respective horizontal plane 3 imaginary circle close to the center of the combustion chamber 13 or directly to the furnace center 12 aligned in the firebox 2 blown in and the low-fuel mixture flow 9 through the burner nozzle 11 of the dust burner 6 tangential to the first imaginary circle 13 enveloping second imaginary circle 14 aligned in the firebox 2 blown in and thus a common circular flow 24 of the two mixture flows 9 . 10 generated around the combustion chamber axis. 2 that have a cross section through the firebox 2 at the level of the horizontal plane 3a (lowest level) shows the injection of the fuel-rich according to the invention 8th and low fuel 9 Mixture flow within the horizontal plane 3a in the firebox 2 ,

The respective to the fuel-air mixture 8th . 9 secondary air introduced 15 per dust burner 6 is according to the invention by secondary air nozzles 16a . 16b tangential to the second imaginary circle 14 aligned in the firebox 2 blown in, see 3 that have a cross section through the firebox 2 at the level of the horizontal plane 3a (lowest level). The secondary upper air and the secondary lower air nozzles 16a . 16b are directly above or below the dust burner nozzles 10 . 11 arranged. Instead of a secondary upper air and lower air nozzle 16a . 16b it is also possible to have only one secondary air nozzle 16 above or below or to the side of the dust burner 6 provided. The secondary air 15 is preferably tangent to the second imaginary circle 14 directed into the firebox 2 blown in that the secondary air 15 the same circular flow 24 takes like that of the fuel-air mixture 8th . 9 , For reasons of mixing, the secondary air 15 but also tangential to the second imaginary circle 14 directed into the firebox 2 be blown in that the circular flow 24 the secondary air 15 opposite to that of the fuel-air mixture 8th . 9 is. The secondary air 15 is through a secondary air line 27 to the secondary air nozzles 16 . 16a . 16b introduced.

The measure according to the invention achieves that in the middle 12 of the firebox 2 - each on the burner levels 3a . 3b . 3c . 3d related - a concentration of the fuel dust takes place, whereas towards the outside to the combustion chamber wall 4 the fuel concentration steadily decreases or there is essentially no fuel dust in the wall area. Because of the fuel concentration in the middle 12 of the firebox 2 be in this area 22 substoichiometric conditions, ie lack of air or oxygen, which in turn leads to low NO _x combustion. In contrast, prevail in the wall area 23 of the firebox 2 hyperstoichiometric conditions, ie excess air or oxygen, and the formation of corrosive carbon monoxide is largely prevented ( 4 ).

With several horizontal levels - starting from at least one level used - within the firebox 2 - 1 has four horizontal planes 3a . 3b . 3c . 3d on - the burn -rich 8th and low fuel 9 Mix flows preferentially tangential to imaginary circles 13 . 14 directed, the dimensions of which are the same or substantially the same. However, it would be possible to vary the dimensions, for example the imaginary circles 13 . 14 of the upper horizontal levels to be gradually reduced.

The combustion of the dusty fuel in the axial direction of the combustion chamber 2 to be able to lock at the end of the firebox - the one in the firebox center 12 under substoichiometric conditions or incompletely burned fuel under lack of oxygen still requires an afterburning and thus a further oxygen supply - it is necessary to the combustion chamber 2 in the direction of flue gas flow 25 seen after the last or top horizontal plane 3d additional air required for combustion 17 supply. This is done by the above the top horizontal level 3d arranged air nozzles 18 ,

For the division and separation of the fuel-air mixture into a fuel-rich 8th and low fuel 9 Mixture flow used device 7 are known establishments. For example, as a dividing and separating device 7 the separation or sifter of a coal grinding plant 26 according to 5 be used. Furthermore, one can be in the immediate vicinity and upstream of the dust burner nozzles 10 . 11 located device 7 are used, which has, for example, separating plates, U-beams or the like. The enumeration of the aforementioned examples limits further design variants of the device 7 not a.

1

steam generator

2

firebox

3

WL

4

Furnace wall

5

Firebox corner

6

Fuel coal burner

7

contraption for fuel dust separation

8th

fuel Empire mixture

9

fuel arm mixture

10

Staubbrennerdüse

11

Staubbrennerdüse

12

Firebox center

13

first or circle near the combustion center

14

second circle

15

secondary air

16

secondary air

16a

Sekundäroberluftdüse

16b

Sekundärunterluftdüse

17

air

18

air nozzle

19

Firebox funnel

20

flue

21

dust line

22

stoichiometric Area

23

superstoichiometric Area

24

circular flow

25

Flue gas flow direction

26

coal mill

27

Secondary air line

Claims (5)

Method for low-NO _x combustion of fuel dust in a vertical combustion chamber with a substantially square cross-section, in which at least one fuel dust burner is arranged in at least one horizontal plane in each combustion chamber wall and / or each corner of the combustion chamber, at least one fuel-air mixture from each fuel dust burner (Primary air) and secondary air are blown tangentially into at least one imaginary circle lying in the horizontal plane, and additional air required for the combustion is fed into the combustion chamber, characterized in that the fuel-air mixture upstream of the fuel dust burner into a fuel-rich one and split a low-fuel mixture stream and the two mixture streams are fed separately to the dust burner and the fuel-rich mixture stream is tangent to an imaginary circle near the combustion chamber center or directly to the combustion chamber center is blown into the combustion chamber and the low-fuel mixture flow is directed tangentially to a second imaginary circle enveloping the first imaginary circle and is blown into the firebox and the secondary air is discharged tangentially to the second imaginary circle is blown into the firebox. A method according to claim 1, characterized in that the circular flow of the fuel-rich and low-fuel mixture flow and of the secondary air flow is the same inside the firebox. A method according to claim 1 or 2, characterized in that that if there are several horizontal planes, the tangential alignment of the fuel-rich and the low-fuel mixture flow an imaginary first and / or second circle, each with the same Dimensions is. Device for carrying out the method according to one of the preceding claims, with a vertical combustion chamber ( 2 ) with an essentially square cross section for low-NO _x combustion of fuel dust, in which at least one horizontal plane ( 3a . 3b . 3c . 3d ) in each combustion chamber wall ( 4 ) and / or every corner of the furnace ( 5 ) at least one fuel dust burner ( 6 ) is arranged from each fuel dust burner ( 6 ) at least one fuel-air mixture (primary air) and secondary air tangential to at least one imaginary circle lying in the horizontal plane ( 13 . 14 ) aligned in the firebox ( 2 ) and the firebox ( 2 ) additional air required for combustion ( 17 ) via air nozzles ( 18 ) is supplied, characterized in that the fuel-air mixture upstream of the fuel dust burner ( 6 ) by a device ( 7 ) into a fuel-rich and a low-fuel mixture flow ( 8th . 9 ) and the fuel-rich mixture flow ( 8th ) through the dust burner nozzle ( 10 ) tangential to an imaginary circle close to the center of the combustion chamber ( 13 ) or directly to the furnace center ( 12 ) aligned in the firebox ( 2 ) and the low-fuel mixture flow ( 9 ) through the dust burner nozzle ( 11 ) tangential to the first imaginary circle ( 13 ) enveloping second imaginary circle ( 14 ) aligned in the firebox ( 2 ) is blown in and the secondary air ( 15 ) through the secondary air nozzle ( 16 ) tangent to the second imaginary circle ( 14 ) aligned in the firebox ( 2 ) is blown in. Device according to claim 4, characterized in that the dust burner nozzles ( 10 . 11 ) for blowing in the fuel-rich and low-fuel mixture flow ( 8th . 9 ) are arranged side by side in the horizontal direction.