EP0483678A2 - Steam boiler - Google Patents

Abstract

The steam boiler has several trains and a DeNO _x system as a catalyst with an NH₃ injector to reduce the NO _x content in the flue gas. The catalyst lies in the direction of flow of the flue gases before the last draft in a boiler section leading down the flue gases. The passage section upstream of this section of the boiler can be regulated as a function of the flue gas temperature prevailing upstream of the catalytic converter. This passage cross section can be enlarged with a decreasing flue gas temperature. The boiler section upstream of the catalytic converter is designed as a flue pipe (4). One of the smoke pipes (6) forming this smoke pipe train (4) has an enlarged diameter compared to the other smoke pipes (5) of this train. The passage cross section of this smoke tube (6) can be regulated with a throttle valve (9). The end of the train (4) which can be regulated in the passage cross section opens into a chamber (7). The catalyst-side end of the smoke pipe (6) with the enlarged diameter merges in the chamber (7) into an upward-pointing, pipe-like extension (25). A perforated plate (27) lying essentially horizontally is provided at a distance from the mouth opening of this pipe-like extension (25).

Description

The invention relates to a steam boiler with the features of the preamble of claim 1. A steam boiler of this type is the subject of European patent application 91 103 143.3.

It is known, among other things, to denitrify the flue gases in steam boiler systems, to reduce the nitrogen oxides content in the flue gas, for which purpose catalysts are used. The operation of this known method is based on the reaction of nitrogen oxides with the NH₃ introduced into the flue gases under the action of the catalyst mentioned. The efficiency of the catalyst is temperature-dependent, the optimal reaction temperature is about 350 ° C. A method is known in this context (AT-PS 379 677) in which the flue gases are passed through two flue gas aftertreatment devices connected in series, the Flue gas temperature in the second flue gas aftertreatment device is higher than that in the first. The heat of the flue gases is used to reheat the flue gases and also to preheat the air. Such systems are indeed suitable for heating the flue gas entering the catalyst to the reaction temperature required here, but the associated outlay on equipment is extremely large and therefore expensive, so that such facilities are only suitable for large systems. Such systems cannot be used with steam boilers for medium power, i.e. for power between 10 and 30 MW, because they are too complex and too expensive.

Another known steam boiler system of the type mentioned is described and shown in DE-OS 27 33 408. In this known construction, provision is made to arrange a shunt line to the secondary preheater, the cross section of which is regulated as a function of temperature. This construction is not considered to be expedient: the construction of such a shunt channel is very complex and expensive. Above all, a functional disadvantage is particularly important here. The shunt line is introduced into the flue gas duct immediately upstream of the catalytic converter, so that there is a sharp temperature gradient directly upstream of the catalyst and across the cross section of the flue gas duct prevails, it can be assumed that the flue gas stream experiences a temperature gradient of several hundred degrees in the secondary preheater. The cross section of the catalytic converter is therefore struck by a flue gas stream which has a very different temperature across its cross section, with relatively hot flue gas flowing in laterally. In order to mix this flue gas stream with different temperatures in front of the condenser across its cross section, neither devices are provided here, nor is there sufficient time for this - taking into account the flow velocity.

The efficiency of the DeNO _x system with a catalyst and an NH₃ injector is the better, the more uniform the temperature of the flue gas is over the entire cross section of the flue; Flue gas of the same temperature flows over the entire cross section of the catalyst.

Starting from a steam boiler of the type mentioned, this object is achieved in the manner according to the invention by those features which are the subject and content of claim 1. Thanks to this proposal, the flue gas leaving the flue pipe, which has different temperatures over the cross section of the flue pipe or the chamber following the flue pipe, is intensively mixed and mixed, so that the catalyst consequently has flue gas at essentially the same temperature over its entire cross section is flowed to. Appropriate embodiments of the invention are defined in the subclaims. All of these measures serve one and the same purpose, namely to intensify the mixing of the flue gas, so that the entire cross-section is flown with flue gas of the same temperature.

Fig. 1

die stirnseitige Ansicht eines drei Züge aufweisenden Dampfkessels mittlerer Leistung (15 MW);

Fig. 2

einen horizontalen Schnitt nach der Linie II - II in Fig. 1;

Fig. 3

das katalysatorseitige Ende des Rauchrohrzuges bei geöffneter Kesseltüre in einem gegenüber den Fig. 1 und 2 vergrößerten Maßstab;

Fig. 4

einen Schnitt nach der Linie IV - IV in Fig. 3;

Fig. 5

einen Horizonatalschnitt nach der Linie V - V in Fig. 4.

Der über einen Ölbrenner 1 mit Öl befeuerte Heizkessel besitzt ein Flammrohr 2, das endseitig in einen ersten als Wasserrohrzug ausgebildeten Umlenkzug 3 übergeht. An diesen Umlenkzug 3 schließt ein zweiter als Rauchrohrzug 4 ausgebildeter Zug an, wobei die Rohre 5 dieses Zuges 4 im wesentlichen parallel zur Längsachse des Flammrohres 2 verlaufen. Eines dieser Rauchrohre, nämlich das Rauchrohr 6 besitzt einen Durchmesser, der um ein Mehrfaches, beispielsweise um das 6-fache des Durchmessers der anderen Rauchrohre 5 des Rauchrohrzuges 4 beträgt. Der Rauchrohrzug 4 mündet in eine stirnseitig am Dampfkessel angeordnete Kammer 7, die hier mit einer Kesseltüre 8 verschließbar ist.The drawing illustrates the invention. Show it:

Fig. 1

the front view of a three-pass steam boiler of medium power (15 MW);

Fig. 2

a horizontal section along the line II - II in Fig. 1;

Fig. 3

the catalyst-side end of the flue pipe when the boiler door is open on an enlarged scale compared to FIGS. 1 and 2;

Fig. 4

a section along the line IV - IV in Fig. 3;

Fig. 5

a horizontal section along the line V - V in Fig. 4.

The boiler, which is fired with oil via an oil burner 1, has a flame tube 2, which at the end merges into a first deflection cable 3 designed as a water tube cable. A second train, designed as a smoke pipe train 4, adjoins this deflection train 3, the pipes 5 of this train 4 running essentially parallel to the longitudinal axis of the flame pipe 2. One of these flue pipes, namely the flue pipe 6, has a diameter that is a multiple, for example 6 times the diameter of the other flue pipes 5 of the flue pipe 4. The flue pipe 4 opens into a chamber 7 arranged on the front of the steam boiler, which can be closed here with a boiler door 8.

The flue pipe 6 with the enlarged diameter lies in the central region of the flue pipe 4. The chamber-side end of the flue pipe 6 has an upward, pipe-like extension 25 (FIGS. 3 and 4), the mouth of which has openings 26 above the throttle valve 9. A perforated plate 27 is arranged above the mouth opening of this pipe-like, upwardly directed extension 25 and at a distance therefrom, which extends over the entire cross section of the flue pipe 28. The mouth opening of the pipe-like extension 25 lies in or above the plane of the uppermost pipes 5 of the smoke pipe duct 4 (FIGS. 3 and 4).

To the side of this pipe-like extension 25 and at a distance from it are separating plates 29 which extend over the entire depth of the chambers 7 and delimit chamber sections 7 'in which throttle valves 30 are likewise pivotably mounted. These throttle valves are in the plane of the uppermost pipes 5 of the smoke pipe 4 or somewhat above the same. The Partitions 29 are substantially parallel to the longitudinal center plane of the smoke pipe 6 having the pipe-like extension 25. They extend over the upper edge of the flue pipe 4. The axes of all three throttle valves 9 and 30 are parallel to each other and are passed through the chamber door 8. A single servomotor 10 is expediently provided for all throttle valves.

The chamber 7 merges into a first rising boiler section 11 and an adjoining falling boiler section 12, with an NH₃ injector 13 being arranged in the falling boiler section 12 and at a distance below the actual catalyst 14, followed by the third boiler train 15, which in the chimney 16 opens. The trains 4 and 15 connected upstream and downstream of the catalytic converter 14 are arranged horizontally and essentially parallel to one another.

In the falling boiler section 12 between the NH₃ injection device 13 and the catalyst 14, a temperature sensor 17 is provided, which is operatively connected to the servomotor for the throttle valves 9 and 30 via a controller 18, which can be equipped with a temperature display device.

The function of the parts of the steam boiler described above results directly from what has been said. If the boiler is running at full load, the flue gases reach the catalytic converter 14 at approx. 350 ° C when the throttle valve 9 is closed. On the other hand, if the boiler runs in the partial load range, the flue gas temperature drops considerably and is significantly below the operating temperature for the catalytic converter, which then no longer has its optimal performance. Thanks to the invention, this temperature drop via the controller 18 is now effective via the temperature sensor 17 in such a way that the controller 18 activates the servomotor 10 for the throttles 9 and 30, namely in the sense of opening the throttle valve 9. By opening the throttle valve will the Passage cross section of the smoke pipe train 4 upstream of the catalytic converter 14, which determines the flow resistance of this train, is reduced, so that the hot flue gas reaches the catalytic converter 14 more quickly and with less cooling, so that its operating temperature can be kept essentially constant. The flue gas leaving the flue pipe 4 and entering the chamber 7 has - viewed over the cross section of the chamber 7 - quite different temperatures. Thanks to the proposed device according to the invention, the flue gas located here and flowing through this section is intensively mixed, so that above the perforated plate 27 there is a flue gas which has a uniform temperature over the entire cross section of the flue gas duct. If the steam boiler is driven to a higher load again, the throttles are actuated in the sense of a closing movement in section 12 via the temperature sensor 17, the controller 18 and the servomotor because of the consequent rise in the flue gas temperature.

Legend for the reference numbers

1

Oil burner

2nd

Flame tube

3rd

Deflection cable

4th

Flue pipe

5

Smoke pipe

6

Smoke pipe

7

chamber

8th

Boiler door

9

throttle

10th

Servomotor

11

rising boiler section

12

falling boiler section

13

NH₃ injector

14

catalyst

15

third train

16

chimney

17th

Temperature sensor

18th

Regulator

25th

pipe-like approach

26

Breakthroughs

27th

Perforated sheet

28

Smoke train

29

Divider

30th

throttle

Claims (9)

Steam boiler with several, especially three trains (3, 4, 15) for medium outputs and with a DeNO _x system in the form of a catalyst (14) and an NH₃ injection device (13) to reduce the NO _x content (denitrification) in Flue gas, the catalyst (14), viewed in the flow direction of the flue gases, being arranged before the third draft (15) of the steam boiler in a boiler section (12) leading down the flue gases and the boiler section upstream of this boiler section (12) depending on the upstream of the catalyst ( 14) prevailing flue gas temperature with regard to its passage cross-section is adjustable, and for controlling the passage cross-section a temperature sensor (17) is provided, which is preferably between the NH 3 injection device (13) and the catalyst (14), this passage cross-section being able to be increased with decreasing flue gas temperature and the boiler section upstream of the catalyst (14) is designed as a flue pipe (4) is formed and at least one of the flue pipes (6) forming this flue pipe has an enlarged diameter compared to the other flue pipes (5) of this train, and the passage cross section of this flue pipe (6) can be regulated by means of a throttle valve (9) and the end of the catalytic converter in the passage cross section controllable train (4) opens into a chamber (7) which can preferably be closed by means of a door or flap (8), characterized in that the catalyst-side end of the smoke pipe (6) having the enlarged diameter in the chamber (7) is directed into an upward direction , pipe-like approach (25) merges and at a distance from the mouth of this pipe-like approach (25) perforated plate (27) lying essentially horizontally is provided. Steam boiler according to claim 1, characterized in that the perforated plate (27) extends over the entire cross section of the flue. Steam boiler according to claim 1, characterized in that openings (26) are provided in the wall of the pipe-like extension (25). Steam boiler according to claim 1 or 3, characterized in that on both sides of the pipe-like extension (25) and at a distance therefrom there are vertical separating plates (29) which extend over the depth of the chimney or the chamber (7) are essentially parallel to the longitudinal center plane of the smoke pipe (6) having the pipe-like extension (25). Steam boiler according to claim 4, characterized in that the separating plates (27) extend over the upper edge of the flue pipe (4). Steam boiler according to claim 4 or 5, characterized in that in the chamber sections (7 ') formed by the separating plates (27) there are provided throttle valves (30) influencing their cross sections. Steam boiler according to one of claims 1 to 6, characterized in that the axes of all throttle valves (9, 30) are parallel to one another. Steam boiler according to claim 7, characterized in that all throttle valves (9, 30) have a common drive. Steam boiler according to claim 1, characterized in that the smoke pipe (6) having the enlarged diameter lies in the central region of the smoke pipe train (4).

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