EP2473782B1 - Forced-flow steam generator for using at steam temperatures of above 650°c - Google Patents

Description

The invention relates to a forced once-through steam generator for the use of steam temperatures of about 650 ° C, the forced flow steam generator having a combustion chamber and a subsequent end of the upper flue and this surrounding Umfassungswände, wherein the Umfassungswände are formed from tube walls whose tubes the working fluid water / Steam lead, the combustion chamber has at least one burner and are arranged in the flue gas Nachschaltheizflächen.

Continuous or forced circulation steam generators are from the publication " Kraftwerkstechnik ", Springer-Verlag, 2nd edition 1994, Chapter 4.4.2.4-Forced circulation (pages 171 to 174 ), Prof. Dr.-Ing. Karl Strauß known, which are used in power plants for the production of electrical energy by combustion of, for example, fossil fuels. In a continuous flow or continuous flow steam generator, the heating of the combustion chamber or the gas flue forming tube walls or enclosing walls - in contrast to a natural circulation or forced circulation steam generator with only partial evaporation of circulating water-steam mixture - leads to an evaporation of the flow or working medium in the tubes of the pipe walls or enclosing walls in a single pass.

The desire for forced flow steam generators with higher efficiencies, which among other things help to reduce the specific CO ₂ emissions into the atmosphere, leads, among other things, to an increase in the steam parameters of the once-through steam generator. Achieving or realizing higher steam parameters, ie higher pressures and temperatures of the working medium steam at the outlet of the once-through steam generator (fresh steam outlet), places high demands on the material concept of the forced-circulation steam generator. Forced-circulation steam generators with steam parameters of approx. 280 bar / 600 ° C (live steam parameters) represent the current state of the art. The highly stressed parts (helical winding and vertical bore) the perimeter walls formed as tube walls are made of the special materials T23 (a material approved by ASME (American Society of Mechanical Engineers)), T24 (7CrMoVTiB10-10) or other materials of similar chemical composition, all of which are of the generic type of the modified, heat-resistant 2.25-2.5% chromium steels count. The material T23 is listed, for example, in VdTÜV Material Data Sheet 511/2, issue 06.2001, and the material T24 is listed, for example, in the standard sheet DIN EN 10216-2, October 2007 issue. These materials have the advantage that they are best suited for the aforementioned steam parameters and that they can be welded without post-heat treatment and thus the creation of the perimeter walls or pipe walls and their installation on the site are easy to carry out.

If forced circulation steam generators with even higher steam parameters are desired in the course of a further improvement of the efficiency, e.g. with 350 bar / 700 ° C (live steam parameter), so the steam temperature and thus the associated calculation temperature in the enclosure walls of the steam generator continues to increase. At these elevated ambient wall temperatures, however, the above-mentioned materials T23, T24 or other materials with a similar chemical composition are no longer sufficient in terms of their strength characteristics. Possible materials for these increased boundary wall temperatures are martensitic 9-12% chromium steels such as T91 (X10CrMoVNb9-1), T92 (X10CrWMoVNb9-2) and VM12-SHC (factory designation of the company Vallourec-Mannesmann) or Ni-base alloys such as Alloy 617 ( NiCr23Co12Mo) or Alloy 617mod. (NiCr23Co12Mo mod) The aforementioned materials are mostly listed in material sheets, for example the material T91 in VdTÜV-Materialblatt 511/2, issue 06.2009; the material T92 in VdTÜV-Materialblatt 552/2, issue 03.2008; the material Alloy 617 in VdTÜV Material Data Sheet 485, Edition 09/2001 and the material VM12 in VdTÜV Material Data Sheet 560/2, Edition 03/2009.

Using marlensitic 9-12% chromium steal or Ni base alloys for the perimeter walls requires complicated manufacturing and assembly operations. The martensitic 9-12% chromium steels must be heat treated after welding in the workshop and during assembly. In addition, in the workshop special tempering furnaces as well as on the construction site special annealing cassettes needed. In the production or assembly of Ni-base alloys excessively large shrinkage processes must be mastered. In addition, with Ni base alloys, their procurement costs are significantly higher than those of steels. For both of these solutions are therefore expected to higher costs, both in terms of the cost of materials and the manufacturing and assembly costs.

As mentioned above, natural circulation and forced circulation steam generators are known in addition to forced circulation steam generators. In these known circulation or circulating steam generators with subcritical steam parameters, only a certain amount of heat can be absorbed by the evaporator of the steam generator. This is defined by the operating pressure of the system. Due to the properties of the fuel (ash composition, melting characteristics of the ash), the amount of heat to be transferred from the combustion in the combustion chamber or in the combustion chamber can be higher than that which can be absorbed by the evaporator. When circulating steam generators Schottenheizflächen have been used to limit the amount of heat to be transferred to the evaporator and to deliver the excess amount of heat to the Schottenheizfläche. In contrast to the natural and forced circulation steam generators, the heat absorption in the evaporator is not limited in a forced once-through steam generator, since the medium temperature at the evaporator outlet in forced continuous operation is already overheated and the amount of overheating can be set variably. The associated temperature level of the steam or the associated calculation temperature in the enclosure walls is governed by a suitable choice of materials with respect to the enclosure walls.

The document US 5146878 discloses a steam generator according to the prior art.

The object of the invention is therefore to provide a forced once-through steam generator for the use of steam temperatures of over 650 ° C, in which the aforementioned disadvantages are avoided or in terms of Umfassungswände or pipe walls of the once-through steam generator simple and not complicated and difficult to control manufacturing and assembly operations are to be carried out.

The above object is solved by the entirety of the features of claim 1.

Advantageous embodiments of the invention can be found in the dependent claims.

• Vermeidung eines kompliziertem Fertigungs- und Montagekonzeptes der Umfassungswände des Zwangdurchlaufdampferzeugers.
• Reduzierung von Materialkosten sowie Fertigungs- und Montagekosten der Umfassungswände des Zwangdurchlaufdampferzeugers,
• Einsparung der Verwendung von Glühöfen und -kassetten und deren Betriebskosten.

By the solution according to the invention a forced once-through steam generator for the use of steam temperatures of over 650 ° C is created, which has the following advantages:

• Avoidance of a complicated manufacturing and assembly concept of the surrounding walls of the once-through steam generator.
• Reduction of material costs as well as production and assembly costs of the surrounding walls of the once-through steam generator,
• Saving on the use of annealing furnaces and cassettes and their operating costs.

An advantageous embodiment provides that in the region of the combustion chamber, a part of the enclosing walls covering Schottenheizfläche between the upper edge of the uppermost situated burner and lower edge of the lowermost Nachschaltheizfläche is arranged. By this measure, a certain area of the combustion chamber is covered with a Schottenheizfläche on which otherwise a large part of the heat from the combustion chamber would reach the Umfassungswände and their medium temperature in the enclosure wall and the wall temperature itself would increase so that higher quality materials would have to be used ,

In an advantageous embodiment of the invention, at least part of the enclosing walls is formed from one of the materials T23, T24 or another material having a similar chemical composition. In this case, at least the part of the surrounding walls is formed with the aforementioned materials, which is thermally highly loaded or higher than the remaining part of the surrounding walls. The materials T23, T24 or another material with a similar chemical composition are high-quality materials which are commercially available and which meet the desired requirements or, after their welding, no heat post-treatment must be carried out on them.

An advantageous embodiment of the invention provides for the Schottenheizfläche of martensitic materials with 9-12% chromium, austenitic materials or nickel-based alloys form or manufacture. This ensures that the requirements of the exposed in the combustion chamber Schottenheizfläche is satisfied in terms of temperatures.

It is advantageous that the bulkhead heating surface is designed as a superheater or reheater heating surface. Thus, the Schottenheizfläche is efficiently integrated into the water / steam cycle of the forced flow steam generator or in the water / steam cycle of a power plant, which includes such a forced flow steam generator.

An advantageous embodiment provides that the bulkhead heating surface is arranged parallel to the surrounding wall. This ensures that the Schottenheizfläche as well as the surrounding wall is arranged vertically and provides a minimum possible attack surface for ash or slag from the combustion chamber.

An expedient embodiment provides that the bulkhead heating surface extends adjacent to the surrounding wall. This ensures that the enclosure wall is optimally covered by the bulkhead heating surface and that the lowest possible amount of heat reaches the enclosure wall.

Embodiments of the invention with reference to the drawings and the description are explained in more detail below.

It shows:

FIG.

1 schematically shows a longitudinal section through a forced-circulation steam generator according to the invention,

Fig. 2

as FIG. 1 , but alternative design.

FIG. 1 schematically shows a continuous flow or continuous flow steam generator 1 (both terms mean the same thing, namely the generation of steam within the steam generator in one run) in tower construction, ie the pipe walls 5 (as surrounding walls 4) and all Nachschaltheizflächen 7 are on or in housed in a single vertical throttle cable. The vertical throttle cable, which is formed or bounded by gas-tight enclosure walls 4, includes in the lower region of the combustion chamber 2 and the subsequent flue 3. The combustion chamber 2 usually closes down with a combustion chamber funnel and extends up to to the lowest Nachschaltheizfläche 7. In the lower part of the combustion chamber 2, one or more burners 6 are arranged for burning a fossil fuel. The burners 6 can be arranged either in the corners (corner burners) or in the walls (wall burners) of the combustion chamber 2. In the flue 3, the various Nachschaltheizflächen 7 are arranged as Berührungsheizflächen. These are typically economizer heating surfaces, superheater and reheater heating surfaces. The flue 3 closes up with a ceiling and he has at its upper end laterally a flue gas outlet 9.

According to the invention, the once-through steam generator 1 has at least one steam heating surface 8, which covers a part of the surrounding walls 4 in the region of the combustion chamber 2 and whose area-side size is determined such that the heat absorption of the surrounding walls 4 and consequently their temperature is reduced to a value which reduces the formation the perimeter wall 4 of modified, heat-resistant 2.25-2.5% chromium steels permits, which require no post-treatment after their welding technology processing. In other words, the enclosing wall 4 in the region of the combustion chamber 2 with a predetermined surface-side size covering Schottenheizfläche 8 takes from the combustion chamber 2 so much heat that the heat absorption of the perimeter wall 4 is reduced due to the cover such that the maximum medium temperature at the perimeter wall. 4 remains below a value indicating the use of modified, heat-resistant 2.25-2.5% chromium steels permits, which require no heat aftertreatment after their welding technical processing. These may be, for example, the materials T23 (a material approved by the American Society of Mechanical Engineers), T24 (7CrMoVTiB10-10) or another material of similar chemical composition covering steam temperatures up to about 500-510 ° C and listed, for example, in the booklet "The T23 / T24 Book, New Grades for Waterwalls and Superheaters by Vallourec & Mannesmann Tubes" (booklet on modified, heat-resistant 2.25-2.5% chromium steels). By reducing the temperature of the medium in the enclosure wall 4 by means of the Schottenheizfläche 8 arranged according to the invention can be dispensed with the use of ultra-high temperature materials such as martensitic, chromium-containing steels or nickel-base alloys for the perimeter wall 4, which costly after treatment by heat treatment aftertreated (martensitic, 9-12% chromium-containing steels) or because of the high shrinkage properties consuming processes (nickel-base alloys) would have to.

The now used high-quality materials that do not require after-treatment heat treatment and no elaborate processing can either be used anywhere on the Umfassungswand 4 or according to a commercially advantageous variant, at least on the parts of the enclosing walls 4, their high thermal load this is required. These are, for example, the areas on the burners 6 and directly above the burners 6 within the combustion chamber 2. On the parts of the Umfassungswände 4, the thermal load is lower, such as in the lower part of the combustion chamber 2 (below the burner 6 including combustor funnel) with Medium temperatures of about ≤ 400-460 ° C in the tube walls, to reduce the investment costs compared to the aforementioned high quality materials lower valued materials, such. 8. 16Mo3 or 13CrMo45, used. These materials also need after their welding technology no postheat treatment or no further elaborate processing.

The enclosing walls 4, which are formed as tube walls 5, are usually made of a welded pipe-web-tube combination, wherein the tubes of the Pipe walls 5, the working medium water / steam and lead within the enclosure walls 4 either obliquely or vertically or can be formed from a combination of oblique and vertical. The arranged in the Umfassungswänden 4 tubes are used in the lower and middle part of the combustion chamber 2 as evaporator tubes, ie, the fed and preheated water is evaporated in these evaporator tubes. In the upper part of the combustion chamber 2, which is usually bored vertically, the pipes arranged in the surrounding wall 4 can already be connected as a superheater heating surface.

The Schottenheizfläche 8 itself, which now receives a portion of the heat from the combustion chamber 2 is formed according to the temperature requirements with suitable materials. Since very high temperatures are to be controlled, martensitic 9-12% chromium-containing steels, austenitic steels or nickel-based alloys have proven suitable for this purpose. These may be, for example, the martensitic materials T91 (X10CrMoVNb9-1), T92 (X10CrWMoVNb9-2) or VM12-SHC, the austenitic steels SUPER 304H, HR3C, DMV304HCu, DMV3101N or Ni base alloys such as Alloy 617 (NiCr23Co12Mo) or Alloy 617mod ( NiCr23Co12Mo mod). The Schottenheizfläche 8 may consist of individual, closely spaced and parallel tubes or a pipe-web-tube construction. The tubes of the Schottenheizfläche 8 usually run horizontally within the heating surface, but can also extend vertically.

The Schottenheizfläche 8 is preferably arranged parallel to the Umfassungswand 4 and more preferably adjacent to the latter. By this arrangement it is ensured that the enclosure wall 4 is covered very efficiently by the Schottenheizfläche 8 and thus the transfer of heat to the enclosure wall 4 is largely prevented. By FIG. 2 an advantageous variant of the Schottenheizfläche invention 8 is shown. In this case, the perimeter wall 4 or pipe wall 5, which generally include the front and rear walls and two side walls of the once-through steam generator, in the region of the combustion chamber 2 between the upper edge of the uppermost burner 6 and lower edge of the lowest Nachschaltheizfläche 7 {the area is in FIG. 2 marked with "S"), for Part covered by one or more Schottenheizfläche (s) 8, according to FIG. 2 By way of example, a Schottenheizfläche 8, ie a total of four, are arranged on each individual tube wall. The targeted arrangement of the Schottenheizfläche 8 especially in this area of the combustion chamber 2 can glossy targeted the usually hottest area of the perimeter wall 4 and tube wall 5 are covered within the combustion chamber 2. The Schottenheizfläche 8 can be advantageously used as a superheater heating within the forced flow steam generator 1. However, it is also possible to use it as a reheater heating surface.

LIST OF REFERENCE NUMBERS

1

Once-through steam generator

2

combustion chamber

3

flue

4

containment

5

pipe wall

6

burner

7

heat recovery area

8th

Schottenheizfläche

9

Flue gas outlet

Claims (8)

1. Once-through steam generator for the use of steam temperatures of above 650°C, the once-through steam generator (1) having a combustion chamber (2), a flue gas pass (3) which adjoins the upper end of said combustion chamber (2), and enclosure walls (4) which enclose them, the enclosure walls (4) being formed from tube walls (5), the tubes of which conduct the working medium water/steam, the combustion chamber (2) having at least one burner (6), and downstream heating surfaces (7) being arranged in the flue gas pass (3), part of the enclosure walls (4) being covered in the region of the combustion chamber (2) by at least one platen heating surface (8), characterized in that the enclosure walls (4) consist of modified, heat-resistant 2.25-2.5% chromium steels which do not require any thermal post-treatment after they have been processed using welding technology.
2. Once-through steam generator according to Claim 1, characterized in that the platen heating surface (8) which covers part of the enclosure walls (4) in the region of the combustion chamber (2) is arranged between the upper edge of the uppermost burner (6) and the lower edge of the lowermost heating surface (7).
3. Once-through steam generator according to Claim 1, characterized in that at least part of the enclosure walls (4) is formed from one of the materials T23, T24 or another material with a similar chemical composition.
4. Once-through steam generator according to at least one of the preceding claims, characterized in that the platen heating surface (8) is formed from martensitic steels with a 9-12% chromium proportion, austenitic steels or nickel-based alloys.
5. Once-through steam generator according to at least one of the preceding claims, characterized in that the platen heating surface (8) is configured as a superheater heating surface.
6. Once-through steam generator according to at least one of the preceding claims, characterized in that the platen heating surface (8) is configured as a reheater heating surface.
7. Once-through steam generator according to at least one of the preceding claims, characterized in that the platen heating surface (8) is arranged parallel to the enclosure wall (4).
8. Once-through steam generator according to at least one of the preceding claims, characterized in that the platen heating surface (8) extends such that it bears against the enclosure wall (4).

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