EP2473783B1 - Forced-flow steam generator for burning dry brown coal - Google Patents

Description

The invention relates to a forced once-through steam generator for the combustion of dry lignite without the aid of recirculated flue gas in the combustion chamber, 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 medium 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.

A continuous flow steam generator fired with dry lignite (TBK) or a power plant designed therewith has a considerable efficiency increase potential compared to a forced flow steam generator conventionally fired with crude lignite (RBK) or a power plant formed therewith. The TBK is generated in a process upstream of the combustion energetically favorable from RBK. Due to the reduced water content of the TBK compared to the RBK, the calorific value and the amount of heat to be transferred in the combustion chamber of the steam generator increases considerably. According to the ash properties of the RBK or the TBK, the combustion chamber must be designed so that a final combustion chamber temperature in the range 950-1150 ° C is established with the heat absorption of the surrounding walls of the combustion chamber. The Due to the heat absorption of the surrounding walls resulting medium-side steam temperature is crucial for the choice of materials used as Umfassungswände tube walls, which are made of a pipe-land-pipe connection. In continuous flow steam generators with high, supercritical steam parameters, when TBK is burnt to reduce the heat absorption of the perimeter walls in the combustion chamber, a certain amount of flue gases must be returned to the combustion chamber (flue gas recirculation) so that the highly stressed parts (helical and vertical bore) of the perimeter walls, are made of tube materials 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 modified type , heat-resistant 2.25-2.5% chromium steels count. These materials have the advantage that they are ideally suited for high 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 construction site are easy to carry out. 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.

When using a flue gas recirculation a flue gas recirculation system with a flue gas recirculation blower is necessary. The convection heating surfaces used may be larger than if no flue gas recirculation is used. The flue gas recirculation system and the additional heating surfaces represent high investment costs. The flue gas recirculation system increases in a further disadvantageous way the electrical self-consumption of the power plant and increases the ongoing operating 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, ash melting properties), the amount of heat to be transmitted from the combustion in the combustion chamber or in the combustion chamber to 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 controlled by a suitable selection of materials and in the combustion of TBK by a suitable flue gas recirculation into the combustion chamber.

The document US 5,146,878 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 burning of dry lignite, in which the aforementioned disadvantages are avoided or avoided in the burning of dry lignite the use of a flue gas recirculation and the medium temperature in the Umfassungswänden or the pipe walls in comparison Forced lignite-fired forced-circulation steam generator is not increased.

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 von Rauchgasrezirkulation und damit verbunden eine Verbesserung des Dampferzeugerwirkungsgrades durch Absenken der Rauchgastemperatur nach Rauchgasluft-Vorwärmer.
• Reduzierung von Investitionskosten und Betriebskosten für das Rauchgasrezirkulationssystem.
• Reduzierung der Konvektionsheizflächengröße gegenüber einer Ausführung mit Rauchgasrezirkulation

The inventive solution provides a once-through steam generator for the burning of dry lignite, which has the following advantages:

• Prevention of flue gas recirculation and associated improvement of the steam generator efficiency by lowering the flue gas temperature after flue gas air preheater.
• Reduction of investment costs and operating costs for the flue gas recirculation system.
• Reduction of the convection heating surface size compared to a version with flue gas recirculation

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 specific area of the combustion chamber is covered with a Schotten heating surface 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 to reduce the wall temperature a flue gas recirculation system 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 efficient in integrated into the water / steam cycle of the forced flow steam generator or in the water / steam cycle of a power plant comprising 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 is arranged 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.

Fig. 1

schematisch dargestellt einen Längsschnitt durch einen erfindungsgemäßen Zwangdurchlaufdampferzeuger,

Fig. 2

wie Figur 1, jedoch alternative Ausführung.

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 its lower region The combustion chamber 2 usually closes down with a combustion chamber funnel and extends up to the lowest Nachschaltheizfläche 7. In the lower part of the combustion chamber 2, one or more burners 6 for burning of Dry lignite arranged. 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 that allows the use of modified, heat-resistant 2.25-2.5% chromium steels, which do not require post heat treatment after their welding 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 present invention arranged Schottenheizfläche 8 can on the use of Flue gas recirculation systems are dispensed with, the otherwise cooler flue gas lead into the combustion chamber 2 and thus lower the temperatures within the combustion chamber 2 and consequently the medium temperature in the enclosure wall 4.

These aforementioned high-quality materials, which do not require postheating after their welding processing, can be used either everywhere on the surrounding wall 4 or according to a commercially more advantageous variant, at least on the parts of the surrounding walls 4, the high thermal load makes this necessary. 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 pipe walls, to reduce the investment costs in comparison to the aforementioned high quality materials lower valued materials, such as 16Mo3 or 13CrMo45. These materials also do not require post heat treatment after their welding processing.

The surrounding walls 4, which are formed as tube walls 5, are usually made of a welded pipe-web-tube combination, wherein the tubes of the tube walls 5, the working medium water / steam and within the enclosure walls 4 either obliquely or vertically or out a combination of oblique and vertical may be formed. The arranged in the Umfassungswänden 4 tubes are used in the lower and middle part of the combustion chamber 2 as evaporator tubes, i. 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, have for this martensitic 9-12% chromium-containing steels, austenitic steels or nickel-based alloys have proven suitable. These can 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 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 enclosing wall 4 or pipe wall 5, which usually include the front and rear walls and two side walls of the forced once-through steam generator, in the combustion chamber 2 between the upper edge of the uppermost burner 6 and lower edge of the lowest Nachschaltheizfläche 7 (the range is in FIG. 2 denoted by "S"), partially covered by one or more bulk heating surfaces 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 be specifically covered in the rule hottest area of the perimeter wall 4 and tube wall 5 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 burning dry brown coal without the aid of recycled flue gas in its combustion chamber, 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 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 posttreatment 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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