JP5709995B2 - Forced once-through steam generator - Google Patents

Description

  The present invention has a surrounding wall formed of a steam generating pipe that is hermetically welded and can flow in the vertical direction. A passage header is arranged in the surrounding wall, and a plurality of parallel-connected outlet side outlets are arranged by the header. The present invention relates to a forced through-flow steam generator for connecting a first steam generation pipe on a fluid medium side to a plurality of parallel-connected inlet-side second steam generation pipes connected in series to the first steam generation pipe. The invention further relates to a power generation facility comprising such a steam generator.

  A steam generator is a facility for generating steam from a fluid medium. In this type of equipment, the fluid medium, typically water, is heated and converted to steam. The steam is then used for driving the machine or generating electrical energy. The steam generator generally has an evaporator for generating steam and a superheater for heating the steam to a temperature necessary for the user. Often, the evaporator is pre-connected with a preheater that uses waste heat, further increasing the efficiency of the entire facility.

  Steam generators are now generally implemented industrially as water tube boilers, i.e. a fluid medium is introduced into the steam generator tube. In this case, the steam generating pipes can be welded together in an airtight manner to form a wall, in which the hot gas supplying heat is guided. The steam generator can be formed vertically or horizontally, i.e. hot gas is guided vertically or horizontally.

  The steam generator can also be designed as a forced through-flow steam generator, in which case the flow through the fluid medium is forced by a feed pump. In this case, the fluid medium is supplied from the feed water pump to the boiler and sequentially flows through the preheater, the evaporator and the superheater. Since the heating, evaporation and superheating of the feed water up to the saturated steam temperature takes place continuously in the through-flow-at least at full load-no special water and steam separators are required. The once-through steam generator can also be operated under supercritical pressure. The definition of the individual heating surfaces, the preheater, the evaporator and the superheater is not very important because, strictly speaking, this mode of operation produces a continuous phase course.

  In a variant of a vertically piped once-through steam generator, the surrounding pipe is divided into a lower part and an upper part, the lower part having a number of first steam generator tubes connected in parallel, the upper part Has a number of parallel-connected second steam generation pipes connected in series downstream of the first steam generation pipes. The lower and upper parts are connected to each other by passage headers. This achieves on the one hand a pressure balance between the steam generator tubes connected in parallel, and on the other hand at least a partial mixing of the flow medium from the different steam generator tubes.

  In this type of once-through steam generator with a steam generator pipe and a flow header that run vertically, the individual pipes in the upper part of the enclosure will be unacceptably hot and in some cases damage to the pipe wall may occur. It has recently been found that it occurs. In this case, the occurrence of such an excessive temperature is associated with certain operating parameters.

  The object of the present invention is therefore to provide a forced once-through steam generator of the kind described above which has a particularly long life and a particularly low repair frequency, irrespective of the operating conditions.

According to the present invention, the problem is that, according to the present invention, the setting parameters of the steam generator pipes connected downstream of the passage header are set as follows, that is, the average mass flow density of the steam generator pipes connected in parallel in the surrounding wall is This can be solved by choosing not to go below 1200 kg / m ² s at full load.

  In this case, the invention departs from the consideration that the overheating of the individual steam generator tubes is attributed to inadequate removal of the heat introduced by the fluid medium. Insufficient heat transfer occurs when the steam generator tube has an excessively low mass flow. In the case where the amount of introduced steam is very small and the heat supply is very small, and in the case of obvious natural circulation characteristics, the hydrostatic pressure drop in these tubes is already almost between the inlet and outlet of the steam generating tube. It is almost the same or the same size as the total pressure difference. The residual pressure difference as the driving force of the flow is therefore very small or completely extinguished, so that in the worst case the flow stops.

  Of course, the passage header works to weaken such an action because it establishes a certain balance between the pipes connected downstream of the passage header. However, the passage header provides a perfect pressure balance, but does not result in a complete mixing of the flowing fluid medium leading to the balance of water and steam components in the steam generator tube connected downstream of it. It turns out. Based on a small amount of steam from the lower heating steam generating tube in the lower part and an additional local separation phenomenon in the header, nevertheless a constant operating condition when entering the individual tubes of the upper vertical pipe Then, the amount of steam may become zero. Therefore, such a phenomenon must be avoided by sufficiently weakening the natural circulation characteristics.

This can be achieved particularly easily without taking additional structural measures on the individual pipes by appropriately selecting the setting parameters of the steam generating pipes connected downstream of the passage header. However, these parameters are not adapted as expected for a certain operating condition, but are made constant over the full load range of the steam generator, so that for easy setting, the corresponding value at full load is appropriate. The criteria to do will have to be discovered. As recognized by the present invention, the natural circulation characteristics are sufficiently weakened so that the average mass flow density of the steam generator tubes connected in parallel in the enclosure does not fall below 1200 kg / m ² s at full load of the steam generator. This is achieved by selecting a setting parameter.

  In each advantageous embodiment, the number and / or inner diameter of the steam generating tubes are taken into account as parameters in setting the mass flow density of the enclosure. These parameters thus have a significant influence on the flow characteristics in the enclosure, and at the same time can be set without special expense during the construction of the steam generator.

The vertical wall of the steam generator can have various horizontal cross sections. A particularly simple structure is possible when the cross section is approximately square. In this type of steam generator, the steam generator tube, particularly located in the edge region, is furthest particularly weak because it is farthest from the center of the hot gas channel and at the same time has a particularly slight heat transfer surface. As a result, the amount of steam in the individual edge pipes in the lower part of the vertical pipe is reduced to zero. In this case, an unevenly distributed water / steam mixture flows into the intermediate header. The intermediate header again does not show a sufficient mixing action, so that the mass flow in the post-connected edge tube is interrupted, which results in insufficient heat transfer. Therefore, in this type of steam generator, it is exactly the case that the average mass flow density of the steam generator pipes connected in parallel in the surrounding wall is not later than 1200 kg / m ² s at the full load of the steam generator. It is particularly advantageous to select the setting parameters for the connected steam generator tubes.

The passage header can be arranged continuously in a horizontal manner in the horizontal direction, i.e. the passage header connects all steam generating tubes arranged below or above the enclosure. Separation of water and vapor components can occur despite complete pressure balance across all tubes. Therefore, even in this type of forced once-through steam generator, the steam generation pipe connected downstream of the passage header has an average mass flow density of the steam generation pipes connected in parallel of the surrounding wall of 1200 kg / at the full load of the steam generator. It is advantageous if it is set so as not to fall below m ² s.

The piping below the passage header can be arranged so as to surround the spiral. The piping is arranged so as to surround the entire surrounding wall. This, of course, creates a complex structure and also reduces the number of steam generation tubes in the lower range, and in particular this greatly balances the heating differences in the various ranges of the enclosure. Nevertheless, even with this type of structure, accidental local separation occurs in the passage header, which can lead to the above-mentioned problems of excessively low mass flow in the tube post-connected to the passage header. Therefore, even in this type of structure, the steam generating pipe connected downstream of the passage header has an average mass flow density of steam generating pipes connected in parallel of the surrounding wall of 1200 kg / m ² s at the full load of the steam generator. It is set not to fall below.

  In a steam generator by burning fossil fuel, heat is not carried into the steam generating pipe of the combustion chamber exclusively by convection, but most of the heat component is brought about by heat radiation to the steam generating pipe. Particularly in this type of steam generator, the heating difference of the individual steam generating tubes can therefore be particularly large. Therefore, it is advantageous for a steam generator with a combustion chamber having a number of combustors for fossil fuels to set the mass flow density of the steam generating tube of the surrounding wall at full load as described above.

  In a preferred embodiment, the forced once-through steam generator is connected downstream of the steam medium, for example for generating electric current, on the fluid medium side. Furthermore, it is advantageous if the power plant has such a steam generator.

  The advantage obtained by the present invention is in particular that sufficient heat transfer in each pipe is ensured by appropriate selection of the setting parameters of the steam generating pipes connected downstream of the enclosure header, thereby causing damage to the pipe walls. This is to avoid unacceptably high temperatures that lead to Such treatment is then based on the recognition that there is a natural circulation characteristic that is not negligible even in a forced once-through steam generator and weakens the predetermined minimum mass flow density at full load. Ultimately, this avoids restrictions during operation of the power plant.

  Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a schematic view of a vertically piped forced once-through steam generator with a passage header. FIG. 2 is a graph of mass flow density and fluid temperature at the outlet of a relatively weakly heated edge tube of a forced through-flow steam generator with various mass flow densities at full load.

  The same parts are denoted by the same reference numerals in all the drawings.

FIG. 1 shows a fossil combustion type vertically forced steam generator 1 according to the present invention. The forced once-through steam generator 1 has a surrounding wall 4 formed from a steam generating pipe 2 which is hermetically welded. The enclosure 4 in this case has a substantially square horizontal cross section 6. A combustion chamber 8 is arranged in the lower region of the forced once-through steam generator 1, and a number of combustors not shown in detail for burning fossil fuels prepare the heat supply to the steam generator tube 2 .

  The surrounding wall 4 is divided into an upper part 10 and a lower part 12, and these parts 10, 12 are connected to each other via a passage header 14. The piping of the lower portion 12 is arranged vertically here, but can also be arranged in a spiral shape so as to surround the surrounding wall. The passage header 14 collects all the flowing medium flowing out of the steam generating pipe 2 of the lower part 12 and enables a pressure balance between the steam generating pipes 2 connected in parallel. Subsequently, the fluid medium is led from the passage header 14 to the steam generating pipe 2 of the upper part 10 where it is further heated and possibly superheated. The superheated steam is further heated on a heating surface (not shown) and supplied to a steam turbine (not shown) of the power generation facility.

  Most of the heat generated by the combustor is absorbed by the steam generator tube 2 by heat radiation. Especially in the edge pipe 16 of the lower part 12, the position is farthest from the center of the forced once-through steam generator 1, and the amount of heat carried in is small due to the geometrical arrangement of the surface that receives particularly little heat. The flowing medium entering the passage header 14 from the edge tube 16 of the portion 12 has a relatively small amount of steam.

  Passage header 14 provides complete pressure balance but does not provide complete mixing of the incoming fluid medium. Due to the small amount of steam exiting the edge tube 16 of the lower part 12 as described above and the additional local separation phenomenon in the passage header 14, the amount of steam entering the individual steam generating tubes 2 of the upper part 10 is very small. May be. When the setting of the piping of the upper portion 10 is inconvenient depending on the operation state of the forced once-through steam generator 1, the through-flow of the individual steam generation pipes 2 may clearly break down and stop. This can likewise result in inadequate heat transfer and unacceptably high fluid temperatures, so that eventually the tube wall becomes unacceptably high and is destroyed.

In order to avoid such damage, the steam generating pipe 2 post-connected to the passage header 14 of the upper part 10 is set to 1230 kilograms per second per square meter (kg / m ² s). This increases the total pressure loss for all parallel tubes. As a result, the hydrostatic pressure drop in each steam generating tube 2, in particular in the edge tube 16, is relatively reduced. Therefore, a sufficient pressure difference as a flow driving force always remains. This effect will be described with reference to FIG.

FIG. 2 shows various settings of the average mass flow density of the piping of the upper part 10 at full load and relatively little heat supply and the flow in the edge pipe 16 of the upper part 10 for partial load operation of the steam generator 1. The media parameters are shown graphically. The left scale shows the mass flow density of the edge tube 16 in kg / m ² s, and the right scale shows the fluid temperature at the outlet of the edge tube 16 in degrees Celsius (° C.). Is shown.

Curve 20 shows the mass flow density of edge tube 16 when the pipe is set to an average mass flow density of 870 kg / m ² s at full load. The drop in the curve 20 on the left side of the graph clearly shows that the mass flow density of the edge tube 16 decreases as the vapor component decreases. When the vapor component is zero, the mass flow density is reduced to 40 kg / m ² s, which substantially corresponds to a flow stagnation in the tube. Sufficient heat transfer in the tube is no longer guaranteed, and accordingly the temperature of the fluid medium, and therefore the edge tube 16, rises significantly as shown in curve 22 from a vapor component of about 0.2.

But the average mass flow density 1200 kg / m ² s total load of the steam generation tube 2 of the upper portion 10, in this embodiment natural circulation characteristics as described above is reduced in the case of setting to 1230kg / m ² s , Excessive relative hydrostatic pressure drop in the edge tube 16 is reduced. Curve 24 of course shows that the mass flow density of edge tube 16 decreases as the vapor content decreases. However, in this case, the mass flow density value is significantly higher (330 kg / m ² s in this case) than when the average mass density at full load is set to 870 kg / m ² s even when the steam component is zero. . As the curve 26 shows, this results in a sufficient heat transfer in the edge tube 16 whatever the vapor component, i.e. the temperature rises only slightly or remains constant. This avoids damage to the enclosure 4 in the upper range 10 due to excessive temperatures, and a longer overall life of the forced flow steam generator 1 is achieved.

DESCRIPTION OF SYMBOLS 1 Forced through-flow steam generator 2 Steam generating pipe 4 Enclosure 6 Horizontal cross section 8 Combustion chamber 10 Upper part 12 Lower part 14 Passage header 16 Edge pipe

Claims (8)

Has a horizontal square cross section (6) comprises a surrounding wall (4) formed from a plurality of steam generator tubes which can flow in the vertical direction is hermetically welded to (2), passage tube to said enclosure (4) in A plurality of first steam generation pipes (2) connected in parallel to the lower part (12) of the surrounding wall (4), and the upper part of the surrounding wall (4) ( a plurality of second steam generator tubes connected in parallel to 10) and (2) to be connected in a fluid medium side, steam downstream connected the upper part (10) in said passage tube jogger (14) generating tube configuration parameters (2) as follows, namely the average mass flow density of the upper portion a plurality of second steam generator tubes connected in parallel (10) of said enclosure (4) (2) steam generator Forced once-through steam generator selected so that it does not fall below 1200 kg / m ² s at full load. The forced once-through steam generator according to claim 1, wherein the number of the plurality of second steam generation pipes (2) connected in parallel to the upper part (10) of the surrounding wall (4) is one of the setting parameters. The forced flow-through steam generator according to claim 1 or 2, wherein an inner diameter of the plurality of second steam generation pipes (2) is one of set parameters. A first plurality of steam generating pipes (2) and a surrounding wall (4) are arranged so that the passage header (14) surrounds the surrounding wall in the horizontal direction, and all of them are arranged under the surrounding wall (4) and connected in parallel. A forced through-flow steam generator according to one of claims 1 to 3 , further comprising a second plurality of steam generating pipes (2) arranged in parallel and connected in parallel on the upper side. The forced through-flow steam generation according to one of claims 1 to 4 , wherein the steam generating pipe (2) connected in front of the passage header (14) is arranged so as to spirally surround in the surrounding wall (4). vessel. Forced once-through steam generator according to one of claims 1 5 comprising a combustion chamber having a plurality of combustors for fossil fuels. Forced once-through steam generator according to one of claims 1 to 6 which connected downstream of the steam turbine flow medium side. A power generation facility comprising the forced once-through steam generator according to one of claims 1 to 7 .

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