RU2546888C2 - Forward-flow steam generator for use at steam temperatures above 650-c - Google Patents

Abstract

FIELD: power industry.

SUBSTANCE: invention relates to heat engineering and may be used in steam generators with forced flow for use at steam temperatures above 650°C. Steam generator with forced flow includes combustion chamber, channel of fuel gas connected to its upper edge, and peripheral walls around this channel. These walls are formed by pipes which transmit steam-water working medium. Combustion chamber includes at least one burner, and burners arranged downstream the heating surface are in the channel of fuel gas. In the area of combustion chamber part of peripheral walls is covered with at least one slabby heating surface, which size on the surface side is determined in such a way, that thermal absorption of peripheral walls and consequently their temperature is reduced to the level which allows manufacturing of peripheral walls from modified heat-resistant steel containing 2.25-2.5% of chrome, which doesn't require any consequent thermal treatment after welding; the slabby heating surface is made from martensitic steels containing 9-12% proportion of chrome, austenitic steel or nickel-based alloys.

EFFECT: improvement of structure.

7 cl, 2 dwg

Description

The present invention relates to a once-through steam generator for use at steam temperatures above 650 ° C, and this once-through steam generator contains a combustion chamber, a flue gas channel that borders the upper edge of the specified combustion chamber, and surrounding walls that surround them, and the surrounding walls are formed by tubular walls whose tubes conduct a working steam-water medium, where the combustion chamber contains at least one burner, and the heating surfaces are in the flue gas channel.

Direct-flow steam generators are known from the publication entitled “Kraftwerkstechnik” (Power Plant Technology), Springer Publishing House, second edition, 1994, chapter 4.4.2.4 “Forced Flow”, p. 171-174), authored by Professor Karl Straus (Karl Strauß), Doctor of Technical Sciences, and used in power plants to generate electricity by burning, for example, fossil fuels. In a once-through steam generator, heating of the walls of the pipes or enclosing walls that form the combustion chamber or gas ducts, unlike the steam generator with natural circulation or forced circulation with only partial evaporation of the steam-water mixture, circulating, to the evaporation of the flow or working medium in the pipes of the tubular walls or covering walls in a single stream.

The need for once-through steam generators with increased degrees of efficiency, whose forced-flow steam exchangers allow, among other things, to reduce specific emissions of CO ₂ into the atmosphere, leads, in particular, to increase the parameters of the once-through steam generator steam. The achievement or provision of increased steam parameters, in other words, increased values of steam pressure and temperature as a working medium at the outlet of the once-through steam generator (release of fresh steam), creates high requirements for the choice of material of the once-through steam generator. Direct-flow steam generators with steam parameters of approximately 280 bar (28 MPa) / 600 ° C (fresh steam parameters) represent the current state of the art. Here, the parts under high load (inclined bend and perpendicular hole) of the enclosing walls, which have the configuration of tubular walls, are made of special materials T23 (material that is approved by the American Society of Mechanical Engineers (ASME)), T24 (7CrMoVTiB10-10) or other materials with a similar chemical composition, and they all belong to the category of modified heat-resistant steels containing 2.25-2.5% chromium. Material T23 is indicated, for example, in the technical specifications of material VdTÜV, document 511/2, edition of June 2001, and material T24 is indicated, for example, in the technical specifications of DIN EN 10216-2, edition of October 2007. Advantage of these materials lies in the fact that they are particularly suitable for the aforementioned parameters of the steam, and they can be welded without subsequent heat treatment, and thus, it is possible to simply manufacture the enclosing walls or tubular walls and their installation at the construction site.

If in the course of a further increase in the degree of efficiency, direct-flow steam generators with even higher steam parameters, such as 350 bar (35 MPa) / 700 ° C (fresh steam parameters) are required, the steam temperature increases further and, consequently, the design temperature of the enclosing walls associated with it steam generator. At the indicated elevated temperatures, the enclosing walls, however, the aforementioned materials T23, T24 or other materials with a similar chemical composition are no longer sufficient with respect to their strength parameters. Possible materials for these elevated temperatures covering the walls are martensitic steels containing 9-12% chromium, such as T91 (X10CrMoVNb9-1), T92 (X10CrWMoVNb9-2) and VM12-SHC (brand name from Vallourec & Mannesmann) or nickel-base alloys such as alloy 617 (NiCr23Co12Mo) or alloy 617mod (modified NiCr23Co12Mo). The above materials are indicated mainly in the technical specifications of the materials, for example, T91 material in the technical specifications of VdTÜV 511/2, revised June 2009; T92 material in VdTÜV 552/2 specifications, revised March 2008; alloy 617 in the technical specifications of VdTÜV 485, revised September 2001; and VM12 material in VdTÜV 560/2 specifications, revised March 2009

If martensitic steels containing 9-12% chromium, or nickel-based alloys are used for covering walls, complicated manufacturing and installation operations are necessary. Martensitic steels containing 9-12% chromium require heat treatment after welding at the factory and during installation. For this purpose, the workshop requires special hardening furnaces and special chambers for annealing at the installation site. It is necessary to suppress the processes of excessive compression during the production and / or installation of parts from nickel-based alloys. In addition, nickel-based alloys are distinguished by the fact that their acquisition cost significantly exceeds the cost of steel. Thus, a higher cost of both of these solutions should be expected, since it includes both the cost of materials and the cost of manufacturing and installing parts.

As already mentioned above, in addition to direct-flow steam generators, natural circulation and forced circulation steam generators are also known. In these known recirculating or circulating steam generators with subcritical steam parameters, only a certain amount of heat can be absorbed by the steam generator evaporator. The indicated amount of heat is determined by the operating pressure of the installation. As a result of fuel properties (ash composition, ash melting properties), the amount of heat transferred during combustion in the combustion chamber may exceed the amount of heat that can be absorbed by the evaporator. Then, stove heating surfaces in circulating steam generators are used to limit the amount of heat transferred to the evaporator and / or to transfer excess heat to the stove heating surface. Unlike steam generators with natural circulation and forced circulation, the heat absorption in the direct-flow steam generator is not limited to its evaporator, since the medium at the outlet of the evaporator is already overheating during the forced flow, and it is possible to set a different level of overheating. The associated steam temperature level or the corresponding design temperature of the enclosing walls is controlled by the selection of a suitable material for the enclosing walls.

Thus, it is an object of the present invention to provide a once-through steam generator for use at a steam temperature above 650 ° C. so that the above-mentioned drawbacks are absent in this once-through steam generator or, with respect to covering walls or tubular walls of the once-through steam generator, simple manufacturing processes can be carried out and installation, not complex operations that are difficult to manage.

The above goal is achieved by the combination of distinctive features listed in claim 1 of the claims of the present invention.

Useful features of the present invention are described in the dependent claims.

The solution according to the present invention provides a direct-flow steam generator for use at steam temperatures above 650 ° C, and this direct-flow steam generator has the following advantages:

- the exception of the complex manufacture and assembly of the covering walls of the once-through steam generator;

- reducing the cost of material and the cost of manufacturing and assembly of the covering walls of the once-through steam generator;

- savings on the use of furnaces and chambers for annealing and their operating costs.

One preferred embodiment provides that the stove heating surface, which covers part of the enclosing walls in the region of the combustion chamber, is located between the upper edge of the uppermost burner and the lower edge of the lowermost downstream heating surface. As a result of such a measure, a certain region of the combustion chamber is closed by means of a stove heating surface, and in this area a significant part of the heat would otherwise exit the combustion chamber to the enclosing walls and increase the temperature of the medium in the enclosing walls and the temperature of the walls in such a way that it would be necessary to use higher quality materials.

In one useful improvement of the present invention, at least a portion of the enclosing walls is made of one of materials T23, T24, or another material with a similar chemical composition. Here, at least that part of the enclosing walls which is subjected to a high thermal load or a higher load than the rest of the enclosing walls is made from the aforementioned materials. Materials T23, T24 or other materials with a similar chemical composition are high-quality materials that are commercially available and satisfy the desired requirements or for which, after welding, no additional heat treatment is required.

One preferred embodiment of the present invention provides that the stove heating surface is formed or made of martensitic materials containing 9-12% chromium, austenitic materials or nickel-based alloys. This ensures that the requirements are met with respect to the temperatures that the stove heating surface facing the combustion chamber must withstand.

Preferably, the stove heating surface is configured as a superheater heating surface or an intermediate superheater heating surface. A stove heating surface is thus effectively integrated into the steam-water circuit of a once-through steam generator or into the steam-water circuit of a power plant, which includes a direct-flow steam generator of this type.

One preferred embodiment provides that the stove heating surface is parallel to the enclosing wall. Thus, a situation is achieved in which the stove heating surface is arranged vertically, similarly to the wall, and creates the smallest possible surface for the deposition of ash or slag from the combustion chamber.

One advantageous embodiment provides for a stove heating surface that extends so as to abut against the enclosing wall. This provides the most satisfactory coverage of the enclosing walls of the stove heating surface and the transfer of the minimum possible amount of heat to the enclosing wall.

The following are exemplary embodiments of the present invention are presented in more detail by way of description and drawings, in which:

figure 1 schematically represents a longitudinal section through a once-through steam generator according to the present invention and

figure 2 represents the same view as figure 1, but in an alternative embodiment.

Figure 1 schematically represents a once-through steam generator 1 (the number indicates the generation of steam in the steam generator in one pass) of a tower structure; in other words, the tubular walls 5 (as covering walls 4) and all heating surfaces 7 are placed on or in one vertical gas duct. The vertical duct, which is formed or limited by gas-tight enclosing walls 4, contains, in its lower part, a combustion chamber 2 and a flue gas channel 3, which is adjacent from above to said combustion chamber 2. Typically, the combustion chamber 2 ends at the bottom with the hopper of the combustion chamber and at the top reaches the lowermost heating surface 7. One or more burners 6 for burning fossil fuels are installed in the lower part of the combustion chamber 2. Burners 6 can be positioned at the corners (corner burners) or on the walls (wall burners) of the combustion chamber 2. Various heating surfaces 7 are set as convection heating surfaces in the flue gas channel 3. Typically, these heating surfaces 7 are economizer heating surfaces, superheater heating surfaces, and intermediate superheater heating surfaces. The flue gas channel 3 ends at the top of the ceiling and has a flue gas outlet 9 on the side at its upper end.

According to the present invention, the once-through steam generator 1 has at least one stove heating surface 8, which covers part of the enclosing walls 4 in the region of the combustion chamber 2 and whose size on the surface side is determined so that the heat absorption of the enclosing walls 4 and, therefore, their temperature is reduced to level, which allows to produce the covering wall 4 of the modified heat-resistant steels containing 2.25-2.5% chromium, which do not require any additional heat treatment abotki after treatment using welding technology. In other words, the stove heating surface 8, which covers the enclosing wall 4 in the region of the combustion chamber 2 with a predetermined size on the surface side, absorbs so much heat from the combustion chamber 2 that the heat absorption of the enclosing wall 4 decreases due to the coating to such a level that the maximum temperature of the medium the surrounding wall 4 remains below the value that allows the use of modified heat-resistant steels containing 2.25-2.5% chromium, which do not require any additional term processing after their processing using welding technology. These can be, for example, T23 (a material approved by the American Society of Mechanical Engineers (ASME)), T24 (7CrMoVTiB10-10) or other materials with a similar chemical composition that can withstand steam temperatures up to approximately 500-510 ° C and which are listed, for example, in the brochure “New T23 / T24 steel grades for furnace screens and superheaters from Vallourec & Mannesmann Tubes” (the brochure describes modified heat-resistant steels containing 2.25-2.5% chromium). By reducing the temperature of the medium in the enclosing wall 4 using the stove heating surface 8, which is located according to the present invention, it is possible to exclude the use of heat-resistant materials, such as martensitic steels containing 9-12% chromium, or nickel-based alloys for the manufacture of enclosing walls 4, which after their manufacture using welding technology would have to be subjected to complex additional heat treatment (martensitic steels containing 9-12% chromium) or It would be difficult to process due to their significant compression properties (nickel-based alloys).

High-quality materials that are currently used and do not require any additional heat treatment after their processing using welding technology or which do not require complex processing, can be used anywhere on the enclosing wall 4 or, according to one more economical option, at least at least in those parts of the enclosing walls 4 where high thermal loads make this necessary. These are, for example, the areas near the burners 6 and directly above the burners 6 inside the combustion chamber 2. In order to reduce investment costs compared to the aforementioned high-quality materials, materials of a lower quality, such as 16Mo3 or 13CrMo45, are used for those parts of the enclosing walls 4 where the thermal load is lower, such as in the lower part of the combustion chamber 2 (below the burners 6, including the hopper combustion chambers), where the temperature of the medium in the tubular walls does not exceed approximately 400-460 ° C. Similarly, these materials do not require any additional heat treatment after they are processed using welding technology, or they do not require additional complex processing.

Surrounding walls 4, which have the configuration of the tubular walls 5, are usually made as a welded construction of the "pipe-wall-pipe" type, pipes from the tubular walls 5 conduct a working steam-water medium and can be placed inside the enclosing walls 4 in a spiral or vertical position , or in a combination of spiral and vertical positions. Pipes, which are located in the enclosing walls 4, are used in the lower and middle parts of the combustion chamber 2 as evaporation pipes; in other words, the water that enters and heats up evaporates in the indicated evaporation tubes. In the upper part of the combustion chamber 2, which, as a rule, contains perpendicular pipes, pipes that are located in the enclosing wall 4 can already be connected as a superheater heating surface.

The stove heating surface 8 itself, which then absorbs some of the heat from the combustion chamber 2, is formed using suitable materials according to temperature requirements. Since it is necessary to work at very high temperatures, martensitic steels containing 9-12% chromium, austenitic steels or nickel-based alloys have proven to be suitable for this purpose. This can be, for example, martensitic materials T91 (X10CrMoVNb9-l), T92 (X10CrWMoVNb9-2) or VM12-SHC, austenitic steels SUPER 3 04H, HR3C, DMV304HCu, DMV3101N or nickel-based alloys, such as alloy 617o12 NiC or alloy 617mod (modified NiCr23Co12Mo). The stove heating surface 8 may consist of separate pipes that are located close to each other and parallel to or form a pipe-wall-pipe-type structure. The pipes of the stove heating surface 8, as a rule, extend horizontally along the heating surface, but may also extend vertically.

The plate heating surface 8 is preferably parallel to the enclosing wall 4 and is preferably so that it abuts against the latter. This arrangement ensures that the enclosing wall 4 is very effectively covered by the stove heating surface 8, and therefore, heat transfer to the enclosing wall 4 is suppressed as much as possible. Figure 2 represents one preferred embodiment of a stove heating surface 8 according to the present invention. Here, the covering wall 4 and the tubular wall 5, which, as a rule, contain front and rear walls and two side walls of a once-through steam generator, partially cover one or more stove heating surfaces 8 in the area of the combustion chamber 2, more precisely, between the upper edge of the uppermost burner 6 and the lower edge of the lowermost heating surface 7 (this area is marked or marked with the letter "S" in figure 2), one stove heating surface 8 is located on each individual tubular wall, that is, only four, according but figure 2. As a result of the predetermined location of the stove heating surface 8, especially in a given area of the combustion chamber 2, that region of the enclosing wall 4 or of the tubular wall 5 inside the combustion chamber 2, which is the hottest, can usually be coated in a precisely defined manner. The cooker heating surface 8 can advantageously be used as a superheater heating surface in a once-through steam generator 1. However, it can also be used as an intermediate superheating heating surface.

List of designations:

1 - Direct-flow steam generator

2 - Combustion chamber

3 - flue gas channel

4 - Covering wall

5 - Tubular wall

6 - Burner

7 - heating surface

8 - Plate heating surface

9 - Flue gas discharge

Claims (7)

1. A once-through steam generator for use at steam temperatures above 650 ° C, wherein the once-through steam generator (1) has a combustion chamber (2), a flue gas channel (3) adjacent to the upper end of said combustion chamber (2), and enveloping walls ( 4) which surround them, and the enclosing walls (4) are formed of tubular walls (5), the pipes of which conduct a working steam-water medium, the combustion chamber (2) has at least one burner (6), and the heating surfaces located downstream (7) located in the flue gas channel (3), part of the enclosing walls (4) is covered in the region of the combustion chamber (2) by at least one stove heating surface (8), the size of which on the surface side is determined in such a way that the heat absorption of the enclosing walls (4) and, therefore, their temperature are reduced to a level which allows the configuration of the enclosing walls (4) of modified heat-resistant steels containing 2.25-2.5% chromium, which do not require any additional heat treatment after their processing using welding technology, while litnaya heating surface (8) is made of martensitic steels containing 9-12% chrome proportion, austenitic steels or nickel base alloys. 2. A once-through steam generator according to claim 1, characterized in that the stove heating surface (8), which covers part of the enclosing walls (4) in the region of the combustion chamber (2), is located between the upper edge of the uppermost burner (6) and the lower edge of the lower heating surface (7). 3. A once-through steam generator according to claim 1, characterized in that at least a portion of the enclosing walls (4) is made of one of the materials T23, T24 or another material with the same chemical composition. 4. Direct-flow steam generator according to claim 1, characterized in that the stove heating surface (8) is made as a superheater heating surface. 5. A once-through steam generator according to claim 1, characterized in that the stove heating surface (8) is made as an intermediate superheater heating surface. 6. Direct-flow steam generator according to claim 1, characterized in that the stove heating surface (8) is parallel to the enclosing wall (4). 7. A once-through steam generator according to claim 1, characterized in that the stove heating surface (8) extends in such a way that it abuts against the enclosing wall (4).

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