EP2364414B1 - Continuous steam generator - Google Patents

Description

The invention relates to a continuous steam generator having a combustion chamber with a number of burners for fossil fuel and a surrounding gas-tight welded steam generator tubes Umfassungswand, wherein the combustion chamber is connected downstream of the gas side in an upper region via a horizontal gas a vertical gas train, wherein the vertical gas train facing part of the surrounding wall is inclined inwardly below the horizontal gas train and thereby forms with the bottom of the adjacent horizontal gas flue a projecting into the combustion chamber nose.

In a fossil-fueled steam generator, the energy of a fossil fuel is used to generate superheated steam, which can then be supplied to power a steam turbine, for example, in a power plant. In particular, in the usual in a power plant environment steam temperatures and pressures steam generators are usually designed as a water tube boiler, d. h., The supplied water flows in a number of tubes which receive the energy in the form of radiant heat of the burner flames and / or by convection of the resulting during combustion flue gas.

In the field of burners, the steam generator tubes usually form the combustion chamber wall by being welded together in gas-tight fashion. In further, the combustion chamber downstream side of the combustion chamber arranged Dampfampfererrohe can be provided in the exhaust duct.

Fossil fueled steam generators can be categorized by a variety of criteria: Steam generators may generally be designed as natural, forced circulation or continuous flow steam generators. In a continuous steam generator, the heating of a number of evaporator tubes leads to a complete Evaporation of the flow medium in the evaporator tubes in one go. The flow medium - usually water - is supplied to the evaporator tubes downstream superheater tubes after its evaporation and overheated there. This description is strictly valid only for partial loads with subcritical pressure of water (P _Kri ≈ 221 bar) in the evaporator. For the sake of clarity, however, this illustration will be used throughout the following description. The position of the evaporation end point, ie the location at which the water content of the flow is completely evaporated, is variable and mode-dependent. During full load operation of such a continuous steam generator, the evaporation end point is, for example, in an end region of the evaporator tubes, so that the overheating of the evaporated flow medium already begins in the evaporator tubes.

In contrast to a natural or forced circulation steam generator, a continuous steam generator is not subject to any pressure limitation, so that it can be designed for live steam pressures far above the critical pressure of water.

During low load operation or during startup, such a continuous steam generator is usually operated with a minimum flow of flow medium in the evaporator tubes in order to ensure reliable cooling of the evaporator tubes. For this purpose, just at low loads of, for example, less than 40% of the design load, the pure mass flow through the evaporator usually no longer suffices for cooling the evaporator tubes, so that an additional throughput of flow medium is superimposed on the passage of flow medium through the evaporator in circulation. The operationally provided minimum flow of flow medium in the evaporator tubes is thus not completely evaporated during startup or during low load operation in the evaporator tubes, so that in such a mode at the end of the evaporator tubes still unvaporized flow medium, in particular a water-steam mixture is present.

However, since the evaporator tubes of the continuous steam generator are usually designed for a flow through unvaporised flow medium after passing through the combustion chamber walls, continuous steam generators are usually designed so that even when starting and in low load operation, a water ingress into the superheater tubes is reliably avoided. For this purpose, the evaporator tubes are usually connected to the superheater tubes connected downstream via a Wasserabscheidesystem. The water separator causes a separation of the emerging during the start or in low load operation of the evaporator tubes water-steam mixture in water and in steam. The steam is supplied to the water separator downstream superheater tubes, whereas the separated water can be fed back to the evaporator tubes, for example via a circulating pump or discharged through a decompressor.

Based on the flow direction of the gas flow, steam generators may continue to be classified, for example, into vertical and horizontal types. In fossil-fueled steam generators in vertical construction usually a draw-in and two-pass boiler are distinguished.

In a feeder or tower boiler, the flue gas produced by the combustion in the combustion chamber always flows vertically from bottom to top. All arranged in the flue gas heating surfaces are flue gas side above the combustion chamber. Tower boilers offer a comparatively simple construction and easy control of the stresses caused by the thermal expansion of the tubes. Furthermore, all heating surfaces of the arranged in the flue gas duct steam generator tubes are horizontal and therefore completely drainable, which may be desirable in frost-prone environments.

When Zweizugkessel a horizontal gas train is downstream of flue gas side in an upper region of the combustion chamber, which opens into a vertical gas train. In this second vertical Gas train usually flows the gas vertically from top to bottom. It takes place at the two-pass boiler so a multiple deflection of the flue gas. Advantages of this design are, for example, the lower height and the resulting lower production costs.

In a steam generator designed as a two-pass boiler, the walls are usually arranged hanging in a boiler stand, so that they can expand freely during heating during operation downwards. In this case, the two-steam generator usually comprises four walls per train, in which care must be taken to ensure that the walls of the individual trains extend uniformly, since otherwise unacceptable stresses can occur in the connections of the individual walls.

Furthermore, such Zweugugkessel often include a so-called combustion chamber nose. This nose is a projection which is formed from the combustion chamber wall inclined inwardly at the transition to the horizontal gas flue and the bottom of the horizontal flue. Such a combustion chamber nose improves the flow of the flue gas at the transition to the horizontal gas flue.

• Beispielsweise kann das obere und das untere Ende der Nase mittels Zugstangen und Federn bzw. so genannten Konstanthängern, die trotz Änderung des Federwegs immer annähernd die gleiche Kraft übertragen, geschehen. Eine derartige Konstruktion passt sich also der unterschiedlichen Ausdehnung der Wände an. Unterschiedliche Lasten z. B. durch wechselnden Innendruck bzw. durch Ascheablagerungen verursachen jedoch hohe Spannungen an den Verbindungen zu den Seitenwänden. Außerdem sind diese Konstanthänger kostenaufwändig.

The disadvantage here, however, that the bore of the combustion chamber rear wall, ie the horizontal gas flue and the second vertical gas train facing wall is interrupted by the combustion chamber. The weight of the rear wall must therefore usually be introduced by a separate construction between the upper and lower end of the nose in the boiler structure such that when heated or load -. As by internal pressure, ash deposition or weight - the back wall moves to the same extent as the other walls. To solve this problem, there are different approaches:

• For example, the upper and the lower end of the nose by means of tie rods and springs or so-called constant pendants, which always transfer despite changing the spring travel almost the same force happen. Such a construction So adapts to the different extent of the walls. Different loads z. B. by changing internal pressure or by ash deposits cause high voltages at the connections to the side walls. In addition, these constant hangers are expensive.

Another possibility is the simple continuation of the tubes of the lower combustion chamber in the vertical direction to the suspension point in the boiler frame. Thus, the connection from the lower end of the nose to the boiler frame has approximately the same temperatures as the side walls and the front wall. However, the nose must then be carried out separately, which means an additional burden on connecting pipes.

Another possibility is to divide the tubes of the combustion chamber rear wall at the bottom of the nose flow medium side, so that a part of the tubes is guided in the tube of the nose, another part parallel to it vertically to the boiler frame. But this is only a part of the tubes and the flow medium for the nose available, which can sometimes lead to insufficient cooling of the nose, as this has a relatively high heat input by their exposed position in the combustion chamber. In contrast, the heat input for the removed, vertically upwardly guided support tubes is correspondingly lower, which can cause problems in terms of the distribution of the mass flow. All wall pipes above the nose and the support tubes should have the same possible steam temperatures at the outlet. Furthermore, a complex transition into the nose tube z. B. by changing the pipe pitch or other tube geometry required.

The DE 12 44 803 B shows a continuous steam generator with a combustion chamber with a number of burners for fossil fuel and a formed from gas-tight welded together steam generator tubes Umfassungswand, wherein the combustion chamber is connected downstream of the gas side in a gasizzug in a top region via a horizontal gas train, a vertical gas train a vertical gas flue facing the Umfassungswand below the horizontal gas flue is inclined inwardly and thereby forms with the bottom of the adjacent horizontal flue a nose projecting into the combustion chamber, wherein at least a portion of the steam generator tubes of the nose at the upper end a number of support tubes downstream of the flow medium side, the are guided substantially vertically to the lower end of the nose.

The invention has for its object to provide a continuous steam generator of the type mentioned above, which has a simplified construction with a particularly high reliability in operation.

This object is achieved by at least part of the steam generator tubes of the nose at the upper end of a number of support tubes downstream of the flow medium side, which are guided substantially vertically to the lower end of the nose.

The invention is based on the consideration that a particularly simple technical construction of a continuous steam generator in Zweizugbauweise would be possible if the suspension of the rear wall could happen in the nose in particular by vertically arranged support tubes and thus no additional springs or constant hanger are necessary. In the interests of operational safety, care should be taken to ensure that the nose is adequately cooled due to the high heat input. Against this background, therefore, the largest possible part of the tubes of the lower region of the rear wall of the combustion chamber should be led into the nose, so that almost the entire medium flow is available for cooling the nose. However, then there are no pipes available as support tubes for the rear wall. However, complicated distribution systems or separate nose drills as a remedy mean that additional technical design effort is required.

To solve these apparently conflicting interpretation goals, therefore, at least a portion of the tubes should be performed against the usual flow direction of the bore of the combustion chamber from top to bottom only at the upper end of the nose. These tubes can then serve as support tubes for the rear wall when connected to the lower end of the nose.

In an advantageous embodiment of a further part of the steam generator tubes of the nose at the upper end of a number of support tubes downstream of the flow medium side, which are guided substantially vertically to a ceiling of the combustion chamber. This also support tubes are available, which connect the nose and connected to the nose lower part of the combustion chamber with the ceiling and so for a reliable Hang up. Since these support tubes are flowed through with flow medium, they expand as well as the other parts of the combustion chamber and there is a uniform expansion of all four combustion chamber walls and there are no inadmissible stresses on the connections of the walls.

In a further advantageous embodiment, all steam generator tubes of the vertical gas train facing part of the surrounding wall flow medium side steam generator tubes downstream of the nose. This ensures that the entire flow medium from the combustion chamber rear wall or its lower steam generator tubes flows into the nose and thus ensures sufficient cooling of the nose. Because of its exposed position inside the combustion chamber, the nose has a particularly high heat input.

Advantageously, the guided to the lower end of the nose support tubes downstream of a arranged in the region of the lower end of the nose collector. This collector can then collect the branched off for the support tubes flow medium and continue to provide the system via an appropriate forwarding available.

For this purpose, the guided to the lower end of the nose support tubes downstream of a number of connecting pipes, which open into the steam generator tubes of the upper portion of the combustion chamber downstream pipes. Thus, the branched off for the support tubes medium flow to the other steam generator tubes of the upper portion of the combustion chamber is connected in parallel and fed back to the system. Thus, a full use of the medium flow of the support tubes is possible.

The advantages associated with the invention are, in particular, that by the flow-medium side downstream of a number of support tubes, which are guided substantially vertically to the lower end of the nose, at least a portion of the steam generator tubes of the nose at the upper end a particularly simple technical construction while high operational reliability of the steam generator is possible. On the one hand, steam boiler tubes are used to load transfer through the boiler frame and no separate constructions such as constant hanger used, on the other hand stands by this construction, the entire water-steam flow of the rear wall for the nose available and it is ensured sufficient cooling of the combustion chamber. Incidentally, in the tube walls, largely the same temperatures occur, without a separate and elaborate bore of the nose or a complicated transition with changes in the geometry of the tubes would be required.

FIG 1

schematisch einen fossil beheizten Durchlaufdampferzeuger in Zweizugbauweise, und

FIG 2

eine schematische Darstellung der Verschaltung der einzelnen Dampferzeugerrohre der Brennkammerwand.

An embodiment of the invention will be explained in more detail with reference to a drawing. Show:

FIG. 1

schematically a fossil-heated continuous steam generator in Zweizugbauweise, and

FIG. 2

a schematic representation of the interconnection of the individual steam generator tubes of the combustion chamber wall.

Identical parts are provided in both figures with the same reference numeral.

The continuous steam generator 1 according to the FIG. 1 comprises a trained as a vertical gas flue combustion chamber 2, which is connected downstream of a horizontal region 4 in an upper region 4. At the horizontal gas train 6, another vertical gas train 8 connects.

In the lower region 10 of the combustion chamber 2, a number not shown burner is provided which burn a liquid or solid fuel in the combustion chamber 2. The Umfassungswand 12 of the combustion chamber 2 is formed from each other gas-tight welded steam generator tubes, in the flow through a pump not shown in detail - usually Water - is pumped, which is heated by the heat generated by the burners. In the lower region 10 of the combustion chamber 2, the steam generator tubes can be aligned either spirally or vertically. In a spiral arrangement, a relatively higher design effort is required, but the resulting imbalances - different mass flows and temperatures of the flow medium in parallel pipes - comparatively lower than in the vertical-bore combustion chamber. 2

The continuous steam generator 1 further comprises, to improve the flue gas duct, a nose 14 which merges directly into the bottom 16 of the horizontal gas flue 6 and projects into the combustion chamber 2. Due to its exposed position in the interior of the combustion chamber 2, the nose 14 has a particularly high heat input and should therefore have a particularly high throughput of flow medium, so that care is taken to ensure adequate cooling of the nose 14.

The trains of the steam generator 1 are arranged suspended in a frame 18, so that the trains of the steam generator 1 can expand unhindered when heated down. So that the walls of the combustion chamber 2 of the steam generator 1 are as uniform as possible, all surrounding walls 12 of the combustion chamber 2 should have approximately the same temperature, so that a uniform heating and expansion takes place. This is easiest to accomplish by the entire support structure consists of steam generator tubes.

On the one hand to allow a support structure in particular of the horizontal gas flue 6 facing part of the peripheral wall 12 of the combustion chamber 2 and on the other hand to ensure sufficient cooling of the nose 14, the steam generator tubes of the horizontal gas flue 6 facing the surrounding wall 12 of the combustion chamber 2 are interconnected as in FIG. 2 shown.

The steam generator tubes 20 of the lower region of the rear wall of the combustion chamber 2 first open at the point A (for the geometric position of the points A to D, these are also in FIG. 1 shown) in a collector 22 and are passed on to point B. Here, first of all the mass flow of A is performed in the tubing of the nose 14. Thus, the entire mass flow from the steam generator tubes 20 of the combustion chamber rear wall is available for cooling the nose.

At point C, the mass flow is divided, a part of the tubes runs as a support tubes 24 to the point D on the ceiling of the steam generator, another part is guided from point C as support tubes 26 down to point B. Thus, the support tubes 24, 26 form a continuous support structure for the rear wall of the combustion chamber from steam generator tubes. The support tubes 26 open into a collector 28 at point B and the medium flow is supplied via a connecting line 30 to the point B downstream pipes or a water-steam separation system. Thus, a use of the medium flow from the support tubes 26 is possible.

Claims (5)

1. Continuous steam generator (1) with a combustion chamber (2) with a number of burners for fossil fuel and a surrounding wall (12) formed of steam generator pipes welded together (20) in a gas-tight manner, wherein a vertical gas flue (8) is connected downstream of the combustion chamber (2) on the hot gas side in an upper area (4) by means of a horizontal gas flue (6), wherein a part of the surrounding wall (12) facing the vertical gas flue (8) and below the horizontal gas flue (6) is inclined inwards and thereby forms, with the bottom (16) of the adjacent horizontal gas flue (6) a nose (14) projecting into the combustion chamber (2) and wherein a number of support pipes (26) are connected downstream of at least one part of the steam generator pipes (20) of the nose (14) at the upper end thereof on the flow medium side, said support pipes (26) being routed essentially vertically to the lower end of the nose (14),
   characterised in that the piping is so arranged that the entire mass flow is routed out of the part of the surrounding wall (12) facing the vertical gas flue(8) below the nose (14) into the nose (14).
2. Continuous steam generator (1) according to claim 1, in which a number of support pipes (24) are connected downstream of a further part of the steam generator pipes (20) of the nose (14) at the upper end thereof on the flow medium side, said support pipes (24) being routed essentially vertically to a cover of the combustion chamber (2).
3. Continuous steam generator (1) according to claim 1 or 2, in which steam generator pipes of the nose (14) are connected downstream of all steam generator pipes (20) of all the steam generator pipes (20) of the part of the surrounding wall (12) facing the vertical gas flue (8) on the flow medium side.
4. Continuous steam generator (1) according to one of claims 1 to 3, in which a collector (28) arranged in the area of the lower end of the nose (14) is downstream of the support pipes (26) routed to the lower end of the nose (14).
5. Continuous steam generator (1) according to one of claims 1 to 4, in which a number of connecting pipes (30) are connected downstream of the support pipes (26) routed to the lower end of the nose (14), said connecting pipes (30) leading into the pipes downstream of the steam generator pipes of the upper area of the combustion chamber (2).

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