WO2012016750A2

WO2012016750A2 - Forced-flow steam generator

Info

Publication number: WO2012016750A2
Application number: PCT/EP2011/059989
Authority: WO
Inventors: Joachim Brodesser; Jan BRÜCKNER; Martin Effert; Joachim Franke; Tobias Schulze
Original assignee: Siemens Aktiengesellschaft
Priority date: 2010-08-04
Filing date: 2011-06-16
Publication date: 2012-02-09
Also published as: AU2011287836A1; ZA201300582B; JP5709995B2; JP2013532814A; AU2011287836B2; DE102010038885B4; WO2012016750A3; KR20130098993A; EP2601442A2; CN103052848B; DE102010038885A1; CN103052848A

Abstract

A forced-flow steam generator (1) having a surrounding wall (4) formed from steam generator pipes (2) which are welded in a gas-tight fashion and traversable by flow in the vertical direction, in which within the surrounding wall (4) there is arranged a passage collector (14) by means of which the outlet side of a first multiplicity of steam generator pipes (2) in parallel configuration is connected at the flow medium side to the inlet side of a second multiplicity, in series configuration with and downstream of the first multiplicity, of steam generator pipes (2) in parallel configuration, should have a particularly long service life and particularly low susceptibility to faults, independently of the operating state. For this purpose, the design parameters of the steam generator pipes (2) downstream of the passage collector (14) are selected such that the mean mass flow density in the steam generator pipes (16), in parallel configuration, of the surrounding wall (4) at full load of the steam generator (1) does not lie below 1200 kg/m2s.

Description

description

The invention relates to a forced once-through steam generator with a surrounding gas-tight welded, formed in the vertical direction steam generator tubes wall, in which a Durchgangs ^¬ collector is arranged within the enclosure, the first plurality of parallel switched steam generator tubes outlet side with a two ^¬ th, the first A plurality of series connected downstream plurality of steam generator tubes connected on the inlet side flow medium side. It further relates to a power plant with such a steam generator.

A steam generator is a plant for producing steam from a flow medium. In such a plant is a flow medium, typically water is heated, and vice ^¬ converts into steam. The steam is then used to drive machinery or generate electrical energy. Typically, a steam generator comprises an evaporator for generating the steam and a superheater, in which the steam is heated to the temperature required for the consumer. Frequently, the evaporator is preceded by a preheater for the use of waste heat, which further increases the efficiency of the overall system.

Steam generators are industrially today usually designed as ^¬ serrohrkessel, ie, the flow medium is guided in steam generator tubes. The steam generator tubes can be welded gas-tight with each other and thus form a order ^¬ fassungswand, within which the heat-supplying hot gas is guided. Steam generators can be designed either in a vertical or horizontal design, ie, the hot gas is guided in the vertical or horizontal direction. Steam generators can furthermore be designed as forced-circulation steam generators, the passage of the flow medium being forced by a feed pump. The flow medium is conveyed by the feed pump into the boiler and successively the preheater, the evaporator and the superheater are flowed through. The heating of the feed water to the saturated steam temperature, the evaporation and superheating occur continuously in one pass, so that - at least in full load operation - no separate separation device for water and steam is required. Continuous steam generators can also be operated at supercritical pressures. The definitions of the individual heating surfaces preheater, evaporator and superheater are strictly speaking no longer useful in this mode of operation, as a continuous phase transition takes place.

In a variant of vertically tubed Durchlaufdampf- generator, the tubing of the containment is subdivided into a unte ^¬ ren and an upper section, said lower section includes a first plurality of parallel-connected steam ^¬ generator tubes and the upper portion of a second, the first plurality serially downstream Plural parallel connected steam generator tubes. The lower and upper From ^¬ section are connected by a passage collectors. As a result, on the one hand pressure equalization between the parallel connected steam generator tubes is achieved, on the other hand, an at least partial mixing of the flow medium from different steam generator tubes.

In such continuous steam generators with through-flow in the vertical direction steam generator tubes and through-collector has now been found that individual tubes of the upper portion of the perimeter wall can assume unacceptably high tempera ^¬ tures, which can lead to destruction of the pipe wall under certain circumstances. The occurrence of these excessive temperatures is linked to certain operating parameters. The invention is therefore based on the object to provide a forced ^once- through steam generator of the type mentioned above, which has a particularly long life ^¬ life and a particularly low susceptibility to repair regardless of the operating condition.

This object is achieved according to the invention by the interpretation ^¬ supply parameters of the downstream of the passage collector steam generator tubes are selected so that the mean mass flow density in the parallel-connected steam generator tubes is not less than 1200 kg of the surrounding wall at full load of the steam generator / is m2s.

The invention proceeds from the consideration that the overheating of individual steam generator tubes is due to a unzurei ^¬ sponding derivative of the incoming heat by flow medium. Inadequate heat removal occurs when the steam generator tube in question has too low a mass flow. With a pronounced natural circulation characteristic, with very low inlet steam content and very low heat input, the hydrostatic pressure drop in these tubes is already approximately as large or equal to the total pressure difference between the inlet and outlet of the steam generator tube. The remaining pressure difference as a driving force of the flow is therefore very low or disappears completely, so that in the worst case the flow stagnates.

Although the passage collector should bring some balance between the tubes downstream to mitigate this effect. However, it was recognized that the

Throughput collector causes a complete pressure equalization, but not complete mixing of the incoming flow medium, which would lead to a balance of water and vapor content in the downstream steam generator tubes. Due to the low vapor content of the lower heated steam boiler tubes of the lower section and additional local segregation phenomena in the Collector can thus still go at entry into individual tubes of the upper vertical bore in certain operating conditions of the vapor content to zero. Thus, this phenomenon should be avoided by a sufficient weakening of the natural circulation characteris- tics.

This is particularly easy without additional constructive measure ^¬ took possible on single tubes by an appropriate choice of the design parameters of the downstream passage collector steam generator tubes. However, since these are not specifically adaptable to certain operating conditions, but remain constant over the entire load range of the steam generator, appropriate criteria should be found at full load for easy design. As recognized inventive, is achievable by a sufficient attenuation of the natural circulation characteristic, by the design parameters are chosen such that the mean mass flow density is not / is located in the paral ^¬ lel-connected steam-generator tubes of the surrounding wall at full load of the steam generator under 1200 kg m2s.

In an advantageous embodiment, the number and / or the inner diameter of the steam generator tubes come as a parameter in the design of the mass flow density of Umfas ^¬ sungswand into consideration. These parameters essentially influence the flow characteristic within the enclosure wall and at the same time can be influenced in the design of the steam generator without any special effort.

The surrounding wall of a steam generator in a vertical construction can have different horizontal cross sections. A particularly simple construction is possible if the cross section is substantially rectangular. In such steam generators, in particular, the steam generator tubes arranged in the corner regions are heated particularly weakly, since they are furthest away from the center of the hot gas duct and at the same time have a particularly small heat input surface. As a result, the vapor content of individual corner tubes of the lower section of the vertical bore can be reduced to zero. hen, so that here an unevenly distributed water-steam mixture enters the intermediate collector. Since the intermediate collector does not cause sufficient mixing here, too, the mass flow in the downstream corner tubes can come to an end and thus the heat dissipation can be insufficient. Especially with such a steam generator, it is therefore of particular advantage to select the design parameters of the through-flow collector downstream steam generator tubes such that the average mass flow density is not less than 1200 kg / m2s in the parallel connected steam generator tubes of Umfassungswand at full load of the steam generator.

The through-collector can be arranged horizontally all around, d. h., It connects all below or above arranged steam generator tubes of

Surrounding wall with each other. Despite the complete pressure equalization over all pipes, segregation of water and steam can still occur. Advantageously, therefore, even in such a once-through steam generator, the steam generator tubes downstream of the throughput collector are designed such that the average mass flow density in the paral ^¬ lel switched steam generator tubes of Umfassungswand at full load of the steam generator is not less than 1200 kg / m2s. The tubing below the passage collector can be designed spiral ^¬ circumferentially. The tubes run around as surrounding the entire enclosure wall. Although this causes a more complex construction and also a smaller number of steam generator tubes in the lower area, but this heating differences in various areas of the enclosure wall are largely compensated. Nevertheless, he was ^¬ known that even with such a construction in the through-collector to random local segregation can occur, the above-described problems of too low a mass flow in the passage collector downstream

Cause pipes. Therefore, even with such a construction, the steam generator tubes connected downstream of the throughput collector are designed such that the average mass current density in the parallel-connected steam generator tubes of the surrounding wall at full load of the steam generator does not un ^¬ ter is 1200 kg / m2s. In fossil-fired steam generators, the heat input to the steam generator tubes of the combustion chamber does not occur exclu ^¬ Lich convectively, but a large part of the heat content is introduced by heat radiation in the steam generator tubes. In particular, in such steam generators, therefore, the differences in the heating of individual steam generator tubes can be particularly large. Therefore advantageously has

Steam generator with a number of burners for fossil fuel combustion chamber having a corresponding interpretation ^¬ tion of the mass flow density of the steam generator tubes of the Umfas- sungswand at full load.

In an advantageous embodiment, the forced-circulation steam generator is followed by a steam turbine, for example for generating electricity, downstream of the flow medium. Furthermore, a power plant advantageously has such a steam ^¬ generator.

The advantages achieved by the invention are, in particular, that a sufficient heat ^¬ removal is guaranteed in each tube and thus unzu ^¬ casually high temperatures that lead to damage to the pipe wall by the appropriate choice of design parameters of the passage collector downstream steam generator tubes can be avoided. In this case, this measure is based on the knowledge that a non-negligible NaturumlaufCharakte ^¬ ristik is present in a forced-circulation steam generator, which is attenuated by a predetermined Mindestmas- senstromdichte at full load. Ultimately ^¬ thereby the restrictions on the operation of a power plant avoided.

The invention will be explained in more detail with reference to a drawing. Show: 1 shows schematically a vertically contacted

Forced circulation steam generator with throughput collector, and

2 shows a graphical representation of the mass flow density and the fluid temperature at the outlet of a comparatively weakly heated corner tube of the once-through steam generator with different mass flow density designs at full load.

Identical parts are provided in all figures with the same Bezugszei ^¬ chen. 1 schematically shows a fossil-fired, vertically bored forced once-through steam generator 1 according to the invention. The once-through steam generator 1 comprises an enclosing wall 4 formed from gas-tightly welded steam generator tubes 2. The enclosing wall 4 has a substantially rectangular horizontal cross-section 6. In the lower region of the once-through steam generator 1, a combustion chamber 8 is arranged with a number of burners not shown in detail for the combustion of a fossil fuel, which provide the heat supply to the steam generator tubes 4.

The enclosure wall 4 is divided into an upper portion 10 and ei ^¬ NEN lower portion 12, wherein the portions 10 and 12 are connected to each other via a through-collector 14. The tubing in the lower portion 12 is arranged vertically here, but may also be arranged spirally around the Umfas ^¬ sungswand circumferentially. The passage collector 14 collects all of the flow medium exiting from the steam generator tubes 2 of the lower section 12 and thus enables a pressure equalization between the parallel connected

Steam generator tubes 2. Subsequently, the flow medium from the passage collector 14 is introduced into the steam generator tubes 2 of the upper portion 10, where it is further heated and optionally superheated. The superheated steam is going down further overheating in not shown heating surfaces of a steam turbine not shown in a power plant ^¬ fed system. The heat generated by the burner is largely absorbed by heat radiation through the steam generator tubes 2. In particular, in the corner tubes 16 of the lower portion 12 is due to their location in the greatest distance to the center of the once-through steam generator 1 and due to the geometri-see arrangement of particularly low heat-treated surface of the heat input so low that from the corner ^¬ tubes 16 of the lower portion 12 in the passage header 14 entering flow medium has a comparatively low vapor content.

Although the passage collector 14 now effects a complete pressure equalization, however, no complete mixing of the incoming flow medium. Due to the described low vapor content at the exit from the corner tubes 16 of the lower section 12 as well as additional local segregation phenomena in the passage header 14, the vapor content at the entrance to individual steam generator tubes 2 of the upper section 10 can become very small. Depending on the operating state of the once-through steam generator 1, this can lead to a significant drop in the flow through individual steam generator tubes 2 as far as stagnation given an unfavorable design of the bore of the upper section 10. This in turn can result in insufficient heat removal and inadmissibly high fluid temperatures, so that ultimately the pipe wall assumes inadmissibly high temperatures and is destroyed.

To avoid such damage, the collector passage 14 downstream of the steam generator tubes 2 in the upper portion 10 for a mean mass flow density of 1230 kilograms per square meter and second (kg / m2s) ^¬ be inserted. This increases the total pressure loss for all parallel tubes. This causes the hydrostatic pressure waste in the respective steam generator tubes 2, in particular in the corner tubes 16 is relatively reduced. Thus, a sufficient pressure difference always remains as the driving force of the flow. This effect is illustrated by FIG. 2:

2 shows a graphical representation of the parameters of the flow medium in a corner tube 16 of the upper portion 10 for various designs of mean mass flow density of the upper section 10 at full load, namely at comparatively low heat and for a partial load ^¬ operation of the steam generator 1. The left scale shows the Mas ^¬ senstromdichte in the corner pipe 16 in kg / m2s, in the right scale shows the fluid temperature at the outlet of Eckrohres 16 in degrees Celsius (° C), in each case plotted against the vapor portion of the flow medium at the pipe inlet.

Curve 20 shows the mass flow density in the corner tube 16 in a design of the tubing for a mean mass flow density at full load of 870 kg / m2s. The drop of the curve 20 to the left of the graph clearly shows how towards lower steam files the mass flow density in the corner tube 16 decreases. With a vapor content of 0, the mass flow density drops to a value of 40 kg / m2s, which practically equates to a stagnation of the flow in the pipe. A sufficient heat dissipation in the pipe is no longer guaranteed and accordingly increases the temperature of the flow medium and thus of the corner tube 16 from a Dampfan ^¬ part of about 0.2 significantly, as curve 22 represents.

A design of the steam generator tubes 2 of the top portion 10 for a mean mass flow density at full load of about 1200 kg / m2s in the exemplary embodiment 1230 kg / m2s reduced depending ^¬ but the natural circulation characteristic as described above, thus reducing an excessive relative hydrostatic

Pressure drop in the corner tube 16. Although curve 24 also shows that towards lower vapor contents, the mass flow density in the corner tube 16 decreases. But the value of the mass current density even at a steam level of from 0 to a ^¬ we sentlich higher value (here 330 kg / m2s) than in an arrangement with a design for a mean mass flow density at full load of 870 kg / m2s. As curve 26 illustrates, this means that at any steam content sufficient heat dissipation in the corner tube 16 is ensured, ie, the temperature increases only slightly or remains constant. Damage to the enclosure wall 4 in the upper region 10 due to excessive temperatures is thereby avoided and an overall longer service life of the forced continuous steam generator 1 is achieved.

Claims

claims

1. forced-circulation steam generator (1) with a welded gas-tight welded, in the vertical direction steam generator tubes (2) formed Umfassungswand (4), wherein within the Umfassungswand (4) a passage collector (14) is arranged, the first plurality of parallel connected Steam generator tubes (2) on the outlet side with a second, the first plurality serially connected downstream plurality of steam generator tubes (2) on the inlet side flow medium side connects, the design parameters of the passage collector (14) downstream steam generator tubes (2) are selected such that the average mass current density in the parallel connected steam generator tubes (2) of the perimeter wall (4) at full load of the steam generator (1) is not less than 1200 kg / m2s.

2. Continuous flow steam generator (1) according to claim 1, wherein the number of parallel connected steam generator tubes (2) is a design parameter.

3. Continuous flow steam generator (1) according to any one of the preceding claims, wherein the inner diameter of the steam generator tubes (2) is a design parameter.

4. Forced once-through steam generator (1) according to any one of the preceding claims, wherein the peripheral wall (4) has a ^¬ We sentlichen rectangular horizontal cross-section (6).

5. forced once-through steam generator (1) one of the preceding claims, wherein the passage collector (14) horizontally around the Umfassungswand (4) is arranged circumferentially and the first plurality all below in the enclosure wall (4) arranged, parallel steam generator tubes (2) encompasses and the second plurality comprises all arranged above in the Um ^¬ fassungswand steam generator tubes (2).

6. forced-circulation steam generator according to one of the preceding claims, in which the passage collector (14) upstream steam generator tubes (2) are arranged spirally encircling in the enclosure wall (4).

7. forced once-through steam generator according to one of

preceding claims with a combustor having a number of fossil fuel burners.

8. forced once-through steam generator according to one of

preceding claims with a flow medium side downstream steam turbine.

9. power plant with a forced once-through steam generator according to one of the preceding claims.