EP0657010A1

EP0657010A1 - Steam generator.

Info

Publication number: EP0657010A1
Application number: EP93917528A
Authority: EP
Inventors: Wolfgang Koehler; Rudolf Kral; Eberhard Wittchow
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 1992-08-19
Filing date: 1993-08-06
Publication date: 1995-06-14
Anticipated expiration: 2013-08-06
Also published as: EP0657010B2; CN1043680C; JPH08500426A; US5701850A; CZ287735B6; RU2109209C1; DK0657010T3; GR3022186T3; SK22295A3; CN1083573A; KR950703135A; DK0657010T4; DE4227457A1; JP3188270B2; ATE145980T1; WO1994004870A1; EP0657010B1; TW228565B; ES2095660T5; CA2142840A1

Abstract

A fossil-fired steam generator includes a gas flue having a surrounding wall being formed by tubes which are mutually joined gas-tightly and which are disposed substantially vertically and can conduct an upward flow through them on the medium side. The tubes in a first or lower part of the gas flue have a greater internal diameter than the tubes in a second part of the gas flue located above. On one hand, this ensures reliable cooling of the tubes. On the other hand, even additional or above-average heating of individual tubes does not lead to inadmissible temperature differences between outlets of the tubes.

Description

Steam generator

The invention relates to a fossil-fired steam generator with a gas flue, the peripheral wall of which is formed from tubes which are connected to one another in a gas-tight manner and which are arranged essentially vertically and through which the medium can flow in parallel from bottom to top.

The surrounding wall is often exposed to different levels of heating from heating surface element to heating surface element. In the lower part, in which a number of burners for the fossil fuel is arranged, the heating is usually much stronger than in the upper part. The reason for this also lies in the fact that additional heat exchanger surfaces are often arranged in this upper part, which shield the peripheral wall against excessive heating, in particular by heat radiation.

In the steam generator known from European Patent Specification 0 054 601, the peripheral wall of the vertical throttle cable serves only in the lower part as an evaporator heating surface. The steam - or the water-steam mixture at partial load - is then fed to a downstream convection evaporator. The upper part of the surrounding wall is formed from pipes serving as superheater heating surfaces. Since only a part of the surrounding wall is used as an evaporator surface, only a relatively small temperature difference occurs at the outlet of these tubes in the case of multiple heating or above-average heating of individual tubes. An uneven distribution of the water-steam mixture on the tubes of the convection evaporator downstream of the evaporator heating surface can be controlled due to the low heating of this evaporator. However, since the cooling the upper part of the surrounding wall with superheated steam at a high pressure of about 280 to 320 bar, high chromium-containing steel is used in this upper part of the surrounding wall, which requires complicated heat treatment during production. In addition, this known device is very costly owing to the necessary connecting lines and collectors to and from the convection evaporator and requires an increased outlay on regulation in the convection train, in particular due to the installation of flue gas-side control trains. A similar device is also described in the publication VGB Kraftwerkstechnik, issue 7, 1991, pages 637 to 643.

In the case of a continuous steam generator with a spiral pipe arrangement of the surrounding wall, in which the mass flow density in the pipes is usually about 2500 kg / m ² s, the effect of additional heating on temperature differences between the pipes can be increased by increasing the pipe inside diameter in the upper part of the vertical throttle cable can be reduced. However, this principle cannot be applied to surrounding walls with vertically arranged pipes, since the comparatively small mass flow density, which is a measure of the flow velocity in the pipes, is then reduced to such an extent that steam pressures nearby the critical point safe cooling of the pipes is no longer guaranteed. Another complicating factor is that, on the one hand, high mass flows are required for reliable cooling of the pipes, and on the other hand, high mass flows can lead to large temperature differences between individual pipes. Furthermore, when using an intermediate collector in the wet steam area due to segregation, there is a risk of an uneven distribution of water and steam, so that large temperature differences can occur in a pipe system connected downstream of this intermediate collector. The invention is therefore based on the object of developing a steam generator of the type mentioned at the outset in such a way that, on the one hand, sufficient cooling of the pipes of the surrounding wall is ensured, and on the other hand, additional heating of individual pipes does not result in inadmissible temperature differences between the individual ones Pipes leads. This should be achieved at low cost.

According to the invention, this object is achieved in that the tubes in a first part of the throttle cable located below have a larger inner diameter than the tubes in a second part of the throttle cable lying above them.

The first part of the throttle cable, which is also referred to below as the first section of the surrounding wall, is characterized by very high heat flow densities and good internal heat transfer in the pipes and is e.g. in the burner area. The overlying second part of the throttle cable, which is also referred to below as the second section of the surrounding wall, is likewise distinguished by high heat flow densities, but a deteriorated internal heat transfer in the pipes and is e.g. in the so-called gas jet room of the steam generator, which connects to the burner area.

The first section of the surrounding wall expediently comprises, to improve the internal heat transfer, internally finned tubes arranged vertically. These are preferably dimensioned such that the average mass flow density in the tubes at full load is preferably less than 1000 kg / m ² s. The steam has an average steam content at the outlet of the first section, which is between 0.8 and 0.95 at a partial load of about 40%. With these prerequisites, the flow conditions are so favorable that additional heating of individual pipes increases Throughput through these pipes leads so that only small temperature differences occur at the outlet of the pipes.

Depending on the operating state, a heat transfer crisis, ie a so-called "dry out", can occur in the second section of the surrounding wall. In order to avoid impermissibly high tube wall temperatures in the case of this deteriorated internal heat transfer, the mass flow density is preferably increased to more than 1000 kg / m ² s. Therefore, the inside diameter of the pipes at the transition from the first to the second section is reduced while maintaining the same number of parallel pipes or pipe divisions. By reducing the inside diameter, reliable pipe cooling is ensured even with a high heat flow density in the second section.

The tubes with a smaller inner diameter of the second section are advantageously connected directly to the tubes of larger inner diameter of the first section, so that the tubes of the two sections merge directly into one another. The tubes of the second section can also have internal ribbing at least in the part through which flow first.

In a heated evaporator parallel pipe system, a pressure drop occurs between the inlet and outlet, which leads to

Escaping is essentially generated by friction due to high steam speeds. A high drop in frictional pressure has the effect that the mass flow is either reduced by more heated pipes, or else increases less compared to the heating. If you now arrange a pressure compensation vessel in an area in which the friction pressure drop increases sharply due to the formation of steam, the system in front of the pressure compensation vessel can adapt to the heating differences almost ideally, i.e. stronger heating results in an approximately equally stronger mass flow. Therefore, in a practical embodiment, a pressure compensation tube is connected to each tube in the upper half of the first part of the throttle cable, for example in the vicinity of the transition from the first to the second section. The pressure compensation tubes are expediently led to one or more pressure compensation containers provided outside the vertical gas flue. The pressure equalization largely decouples the two sections on the flow side. The relatively high friction pressure loss in the second section due to the comparatively large mass flow density therefore has no effect on the favorable flow conditions in the first section. This means that no temperature imbalances (temperature drop above the pipe cross-section) can occur due to additional heating at the outlet of the first section. The direct transition of the pipes from the first section to the pipes from the second section reliably prevents water-steam separation in the wet steam area.

In the case of a steam generator with a high throttle cable, e.g. a steam generator in a retractable construction, the tubes have a larger inner diameter in a third upper part of the gas flue than in the second part of the gas flap underneath. This third part of the throttle cable, which is also referred to below as the third section of the surrounding wall, is characterized by a low heat flow density and a moderate internal heat transfer in the pipes and is located in the so-called convection cable of the steam generator,

At the transition from the second to the third section of the

The surrounding wall reduces the mass flow density due to the low heat flow density prevailing there compared to that in the second section in order to keep the friction pressure loss in the pipes low. In the third section, the tubes can be designed without internal fins. In the further course of the vertical throttle cable, the heat flow density drops so far that in the third part of the gas cable, ie in the third section of the peripheral wall, half the number of tubes of the second part of the gas cable, ie the second section of the peripheral wall, is sufficient. The number of tubes in the third section is halved in that two tubes each of the second part of the throttle cable open into a jointly assigned tube of the third part of the gas cable.

Embodiments of the invention are explained in more detail with reference to a drawing; show in it:

1 shows a steam generator with a throttle cable divided into three sections, and

Figure 2 shows a detail II of Figure 1 on a larger scale with tubes with different inner diameters in different sections.

Corresponding parts are provided with the same reference symbols in both figures.

The vertical throttle cable of the steam generator 1 according to FIG. 1 with a rectangular cross section is formed by a surrounding wall 2 which merges into a funnel-shaped base 3 at the lower end of the gas cable. The tubes 4 of the surrounding wall 2 are on their long sides - e.g. via fins 9 (Figure 2) - gas-tightly connected to each other, e.g. welded. The bottom 3 comprises a discharge opening 3a for ashes, not shown in detail.

In a lower or first part 5 of the throttle cable, ie in a first section of the surrounding wall 2, for example four burners for a fossil fuel are each installed in an opening 6 in the surrounding wall 2. On one of these term opening 6 tubes 4 of the surrounding wall 2 are curved; they run on the outside of the vertical throttle cable. Similar openings can also be formed, for example, for air nozzles or flue gas nozzles.

Above the first lower part 5 of the throttle cable is a second part 7 of the throttle cable, i.e. a second section of the surrounding wall 2, over which a third or upper part 8 of the throttle cable, i.e. a third section of the peripheral wall 2 is provided.

The first section 5 in the burner area is distinguished by a very high heat flow density and good internal heat transfer in the tubes 4. The second section 7 is located in the gas jet chamber and is also distinguished by a high heat flow density, but also by a lower, deteriorated internal heat transfer in the tubes 4. The third section 8 is located in the convection train and is characterized by a low heat current density and a moderate internal heat transfer in the tubes 4. This third section 8 is present, in particular, in the case of a steam generator in a pull-in construction.

The medium side, i.e. of water or a water-steam mixture, through which tubes 4 of the surrounding wall 2 flow in parallel from bottom to top are connected with their inlet ends to an inlet header 11 and with their outlet ends to an outlet header 12. The inlet header 11 and the outlet header 12 are located outside the throttle cable and are e.g. each formed by an annular tube.

The inlet header 11 is connected via a line 13 and a header 14 to the outlet of a high-pressure preheater or economizer 15. The heating surface of the economizer 15 lies in the third section 8 of the surrounding wall 2 covered space. The economizer 15 is connected on the input side to the water / steam circuit of a steam turbine via a collector 16 during the operation of the steam generator 1,

The outlet header 12 is connected to a high-pressure superheater 19 via a water-steam separating vessel 17 and a line 18. The high-pressure superheater 19 is arranged in the region of the second section 7 of the surrounding wall 2. It is connected on the output side to a high-pressure part of the steam turbine via a collector 20 during operation. In the area of the second section 7 there is also an intermediate superheater 21 which is connected via collectors 22, 23 between the high-pressure part and a medium-pressure part of the steam turbine. Water occurring in the water-steam separating vessel 17 is discharged via a line 24.

In a region 25 of the transition from the first section 5 to the second section 7 of the surrounding wall 2, a pressure compensation vessel 26 is provided outside the throttle cable, which is formed by an annular tube.

As can be seen from FIG. 2, each pipe 4 running in sections 5 and 7 is connected to the pressure compensation vessel 26 via a pressure compensation tube 27.

In area 25, in which the pipes 4 pass from the first section 5 into the second section 7, the clear width of the pipes 4 tapers. In other words: the pipes 4 have a larger inner diameter d in the lower part 5 of the gas flue, on as the pipes 4 in the overlying second part 7 of the throttle cable, the inner diameter of which is denoted by d ₂ . The tubes 4 with the smaller inner diameter d _{2 are} connected directly to the tubes 4 with the larger inner diameter d-, ie the tubes 4 merge into one another in the region 25. The tubes 4 in section 5 have a thread in a manner not shown shaped internal ribs. The tubes 4 are dimensioned in section 5 such that the mean mass flow density there is less than or equal to 1000 kg / m ² s at full load. The average mass flow density in the tubes 4 is then greater than 1000 kg / m ² s in the second or middle section 7.

In the third or upper section 8 of the surrounding wall 2, the pipes 4 again have a larger inner diameter than in the section 7 below. While the pipes 4 in the second section 7 also preferably have a thread-like internal ribbing over their entire length, the pipes 4 are of the third section 8 is provided with a thread-like inner ribbing only over part of its length. However, it is expedient to dispense with internal ribbing.

The number of pipes 4 in the upper section 8 of the surrounding wall 2 is only half as large as in the second section 7. Therefore, two pipes 4 of the second section 7 each open in a region 30 into a pipe 4 of the third section 8 that is assigned to them (Figure 1).

As shown in Figure 2, the outer diameter of the tubes 4 in sections 5 and 7 is different and adapted to the respective inner diameter d ,, d ₂ such that the wall thickness of the tubes 4 in all sections 5, 7, 8 is approximately the same size is. However, the outer diameter of the tubes 4 can also be the same in all sections 5, 7, 8, so that the wall thickness of the tubes 4 in the middle or second section 7 is greater than in the first section 5 and / or in the third section 8 As already mentioned, the tubes 4 are provided on their long sides with fins 9 which serve for the gas-tight connection of the tubes 4.

Characterized in that the pipes 4 of the surrounding wall 2 on their

Length in different sections 5, 7, 8 or areas of the steam generator 1 have a different inside diameter d ,, d ₂ , the dimensioning of the tubes 4 of the surrounding wall 2 is adapted to different heating of the throttle cable. On the one hand, reliable cooling of the tubes 4 is ensured. On the other hand, additional heating of individual tubes 4 does not lead to impermissible temperature differences between the outputs of the individual tubes 4.

Claims

1. Fossil-fired steam generator with a gas flue, the peripheral wall (2) of which is formed from tubes (4) which are gas-tightly connected to one another and which are arranged essentially vertically and can be flowed through from bottom to top on the medium side, characterized in that the tubes (4) have a larger inner diameter (d-) in a lower part (5) of the throttle cable than the tubes (4) in an overlying second part (7) of the gas cable.

2. Steam generator according to claim 1, characterized in that the tubes (4) with the smaller inside diameter (d ₂ ) are connected directly to the tubes (4) with the larger inside diameter (d,) or pass into them.

3. Steam generator according to claim 1 or 2, so that each pipe (4) is connected via a pressure compensating pipe (27) to a pressure compensating vessel (26) provided outside the throttle cable.

4. Steam generator according to claim 3, so that each pressure compensation tube (27) in the upper half of the first part (5), preferably in the upper third of the first part (5), e.g. in the area (25) of the transition from the first part (5) to the second part (7) of the throttle cable.

5. Steam generator according to one of claims 1 to 4, characterized in that the tubes (4) in the first part (5) of the throttle cable have a threaded internal ribbing.

6. Steam generator according to one of claims 1 to 5, d a d u r c h g e k e n n z e i c h n e t that the tubes (4) in the second part (7) of the throttle cable have a thread-like internal ribbing over at least part of their length.

7. Steam generator according to one of claims 1 to 6, characterized in that the average mass flow density in the tubes (4) of the first part (5) of the throttle cable at full load is less than or equal to 1000 kg / m ² s.

8. A steam generator according to claim 1, that the pipes (4) in an upper third part (8) of the

Throttle cable have a larger inner diameter than in the second part (7) of the gas cable underneath.

9. Steam generator according to claim 8, characterized in that the tubes (4) of the third part (8) with the larger inner diameter are directly connected to the tubes (4) of the second part (7) with the smaller inner diameter (d ₂ ) , or merge into them.

10. Steam generator claim 8 or 9, characterized in that the number of tubes (4) in the third part (8) of the throttle cable is only half as large as in the second part (7) of the throttle cable, two tubes (4) of the second Part (7) open into a jointly assigned tube (4) of the third part (8).