EP3585985A1

EP3585985A1 - Preservation method

Info

Publication number: EP3585985A1
Application number: EP18720124.9A
Authority: EP
Inventors: Uwe Juretzek; Michael Rziha; Edwin Gobrecht; Michael SCHÖTTLER
Original assignee: Siemens AG
Current assignee: Siemens Energy Global GmbH and Co KG
Priority date: 2017-04-11
Filing date: 2018-04-10
Publication date: 2020-01-01
Anticipated expiration: 2038-04-10
Also published as: WO2018189176A1; JP2020516808A; KR102216364B1; US10895172B2; EP3585985B1; JP6880232B2; PT3585985T; ES2887407T3; KR20190131118A; US20200149435A1

Abstract

The invention relates to a power plant (1) comprising a steam turbine (2) with a shaft (3), further comprising a condenser (4) mounted downstream of the steam turbine (2) in the direction of flow of the steam, a vacuum pump (5) mounted downstream of the condenser (4), a compressed steam system (6) with shaft seals (7), and a compressed steam supply line (8) extending into the shaft seals (7); a first nitrogen line (9) extends into the condenser (4), and a second nitrogen line (10) as well as a recirculation line (11) that branches off the vacuum pump (5) extend into the compressed steam supply line (8). The invention especially relates to a method for preserving a power plant (1).

Description

description

The invention relates to a power plant and a method for preserving a power plant.

In a power plant with a steam turbine, the steam turbine and the condenser must be conserved for longer standstills in order to limit corrosion. At the same time, in the case of thermal power plants with a water-steam cycle, it is the aim to be able to restart them quickly after a long standstill and to achieve chemical vapor purity quickly during start-up in order to be able to put the steam turbine back into operation as soon as possible.

So far, the vacuum was broken during longer stoppages, i. Steam turbine and condenser were filled with ambient air. The ambient air thus contained in the steam turbine and condenser was dried by dryers so far that corrosion was sufficiently contained by the substantial absence of moisture. A critical point in this context is the condensate collector, from which the condensate is either completely drained or at least the level is reduced. This makes it difficult to restart. In addition, by the vacuum breaking on the ambient air and "pollution" registered in the steam turbine and in the condenser, so that the required steam purity when restarting is correspondingly difficult to achieve and the startup process takes longer.

Corrosion can be prevented either by the absence of moisture (previously most common approach to steam turbine and condenser) or oxygen. For example, nitrogen is already commonly used today for preventing and conserving corrosion in the steam-conducting area of the boiler and in the steam line area. The object of the invention is to provide a power plant with which a preservation method is possible, which is advantageous both in terms of effectiveness and cost efficiency as well as in terms of quick start capability of Kraftwerksan- plant. Another object of the invention is to provide a corresponding method for preservation.

The invention solves the task directed to a power plant by providing that in such a power plant comprising a steam turbine with a shaft, a steam turbine in the steam flow downstream condenser, a condenser downstream vacuum pump, a sealing steam system with shaft seals and a in the In the condenser, a first nitrogen line opens and in the sealing steam supply line a second nitrogen line and a branching off from the vacuum pump

Recirculation line open. Due to the possibility of introducing nitrogen into the

Sealing steam system and also directly into the condenser, the steam turbine / the condenser can be brought during the shutdown in the conserved state to a low (a few mbar) nitrogen pressure. The nitrogen requirement can be kept comparatively low via the recirculation line.

The use of nitrogen to preserve the steam turbine as an alternative to drying leads to reduced water consumption - the condensate in the condensate collection is no longer discarded, resulting in a reduction of the wastewater attack.

Generally, the operating costs for the dryer are eliminated.

In an advantageous embodiment of the invention, the shaft seals comprise sealing steam chambers and vapor vapor chambers, the sealing steam supply line being inserted into the blocking chamber. dam fkämmern opens and the Wrasendampfkammern are connected to a Wrasendampf blower to suck in the shaft seals penetrating air and a partial flow of steam from the sealing vapor chambers and fed to a Wrasendampf- capacitor. By means of this arrangement, in the case of preservation with nitrogen, the nitrogen can also be collected or withdrawn in a controlled manner and optionally fed to further use. In particular, nitrogen, which is needed in a case of a standing, conserved plant to a significant extent or accumulates, can be recovered.

In a further advantageous embodiment, an electric superheater is connected in the sealing steam supply line and the nitrogen line opens into the sealing steam supply line upstream of the superheater. If necessary, the warming / warming of the steam turbine can be assisted by warming up the nitrogen via the electrical superheater present in the sealing steam system (actually auxiliary steam superheater).

The object directed to a method is achieved by a method for preserving a power plant comprising a steam turbine, a condenser downstream of the steam turbine, a vacuum pump downstream of the condenser and a sealing steam system, wherein when the steam turbine is shut down into a conserved state, nitrogen is introduced into the sealing steam system and is introduced into the condenser, and the steam turbine and the condenser are brought to nitrogen overpressure and the vacuum pump is turned off, being diverted at startup of the steam turbine to the exhaust air of the vacuum pump nitrogen and fed back to the sealing steam system.

It is advantageous if nitrogen upstream of an electrical superheater in a sealing steam supply line of the

DichtdampfSystems is initiated. The electrical superheater in the sealing steam system ensures that the over The nitrogen vapor system fed nitrogen has sufficiently high temperatures for the shaft sealing steam supply.

By switching to nitrogen supply earlier, the sealing steam can be reduced after it has been lowered, leaving more heat in the boiler and keeping it hot and warm-startable for longer.

It is therefore expedient if, when the power plant system 1 is shut down, nitrogen is fed together with steam into the sealing steam supply line (8) as soon as the vacuum can be broken.

With regard to an economical use of nitrogen, it is advantageous if, after the steam turbine has been shut down after reaching a nitrogen overpressure in the steam turbine and in the condenser, the nitrogen supply of the sealing steam system is taken out of operation during the preservation phase. After reaching a slight nitrogen overpressure in

Steam turbine or condenser, the pressure can be through the

Nitrogen make-up can be maintained on the capacitor. This procedure reduces the consumption of sticks.

It is important to pay attention to temperature fluctuations. In particular, it is advantageous if a nitrogen pressure in the steam turbine or in the condenser is increased before an expected temperature change, in particular cooling, in the steam turbine or in the condenser. Otherwise, in the worst case ambient air can be sucked into the steam turbine or the condenser. Such a temperature fluctuation and associated pressure fluctuation in the steam turbine or condenser can be caused, for example, by the operation of the main cooling water system during the preservation. Such recirculation of the cooling water during prolonged shutdowns are from time to time from a chemical / biological point of view necessary. In order to avoid these problems, a corresponding nitrogen pressure control strategy is necessary, which also takes into account changes in operating conditions, eg before the cooling water pumps are switched on, the nitrogen pressure can be increased slightly beforehand. Regular checking of the residual oxygen in the preserved volume is also necessary.

Advantageously, when the power plant starts up, as long as there is no sufficient sealing steam, nitrogen is continuously supplied via the sealing steam system. In particular, this takes place during the condenser evacuation to block the steam turbine shaft seal. This prevents subsequent flow of ambient air into the steam turbine and, as a result, contamination of the water-steam cycle. A sealing steam supply independent of the heat recovery steam generator is thus not necessary, i. it could possibly be saved a separate auxiliary steam generator. This also leads to energy savings. It is particularly advantageous for nitrogen to be recirculated from the condenser to the sealing steam system in order to start up the power plant, specifically after air has been expelled from the condenser to the sealing steam system in a recirculation line and after a sufficient negative pressure has been reached in the condenser, which opens vapor diverter stations allowed. Sufficient negative pressure typically means 600 mbar.

It is also advantageous if the warming or heating of the steam turbine is assisted by heating the nitrogen via an electric superheater arranged in the auxiliary steam system.

It is expedient for the nitrogen-enriched exhaust air to be compressed from the vapor vapor chambers and made available to a nitrogen generator as input air. Furthermore, it is expedient if a comparatively small, high-purity amount of nitrogen is provided for the preservation during shutdown and during standstill and for starting up a larger, impure amount of nitrogen per time in comparison.

Advantageously, the WrasendampfSystem is at least temporarily during a targeted nitrogen filling of the condenser and the steam turbine in operation.

With the invention, numerous advantages. For example, the invention, in addition to a much improved over the present day concept (dryer based) preservation (eg greatly reduced corrosion in the condensate collection) also cost savings (while investing as well as in operation) with maximum shortened startup from the longer downtime and this without an external auxiliary steam source is needed. The preparation time to the actual start time are shortened, for example, compared to the prior art, that the condensate collecting tank is already filled or that does not have to wait for the sealing steam supply.

The investment cost savings result from the elimination of the previous dryer including connecting lines, the auxiliary steam boiler including auxiliary equipment or additional starting devices for early sealing steam supply from the cold reheat and thus from the boiler, etc. The countersigned costs for the nitrogen supply are significantly lower and include Essentially, the nitrogen storage, piping and valves for nitrogen supply or for nitrogen removal to the outside.

If a nitrogen recovery plant is present on site, in addition to this still a sufficiently large compressed air generating plant and advantageously a nitrogen collecting area are added to the nitrogen-containing exhaust air receives and the compressed air generating unit is available as supply air.

At least, however, there are synergy effects with respect to the preservation of other parts of the steam cycle. Although these savings are to be offset by the operating costs for nitrogen consumption and, in particular, compressed air generation. But these are comparatively low.

Further synergy effects arise if a factory air system is installed in relation to the compressed air system required for on-site nitrogen production. In addition, fuel savings result from significantly faster cold starts, since the waiting time for chemical vapor purity can be omitted in principle. The prerequisite for this, however, is that other parts of the water-steam cycle are sufficiently preserved and equipped against the intrusion of ambient air and operated accordingly.

Compared to a plant operated with a fossil-fueled auxiliary boiler, an emission source to be taken into account for the approval would also be omitted.

The invention will be explained in more detail by way of example with reference to the drawings. Shown schematically and not to scale: Figure 1 shows a power plant according to the invention and

Figure 2 expiry of a method for preserving a

Power plant.

1 shows schematically and by way of example a power plant 1 comprising a steam turbine 2 with a shaft

3, one of the steam turbine 2 in the steam flow direction downstream condenser 4 and a condenser 4 downstream vacuum pump 5. For sealing the shaft 3 comes over Licher way a sealing steam system 6 with an opening into the shaft seals 7 sealing steam supply line 8 is used. The shaft seals 7 comprise sealing vapor chambers 12 and steam vapor chambers 13. The sealing steam supply line 8 coming from the auxiliary steam generator 19 opens into the sealing steam chambers 12. For overheating the auxiliary steam or sealing steam, an electric superheater 16 is connected in the sealing steam supply line 8. Within a steam vapor system 18, the vapor steam chambers 13 are connected to a steam blower 14 in order to suck air which penetrates into the shaft seals 7 and a partial flow of steam from the sealing steam chambers 12. The extracted vapor is fed to a steam vapor condenser 15. According to the invention, a first nitrogen line 9 opens into the condenser 4. A second nitrogen line 10 opens into the sealing steam supply line 8 upstream of the electric superheater 16. Further, a recirculation line 11 branching off from the vacuum pump 5 discharges into the sealing steam supply line 8. The recirculated amount of nitrogen can overflow a valve 40 in the recirculation line 11 can be adjusted. A pressure control of the vacuum pump 5 can also be done via valve 41 or in combination of the two valves 40 and 41. The nitrogen supply is carried out in the embodiment of Figure 1 via a nitrogen generator and a nitrogen storage 20. Since the vacuum pump 5 with regard to the funded flow as expected not for the

Recirculation of nitrogen is designed for preservation and tends to be oversized for this purpose, Figure 1 shows two further measures with which an operation with the vacuum pump 5 is nevertheless meaningfully possible. On the one hand, excessively pumped nitrogen can be recirculated to the inlet of the vacuum pump 5 via the return line 42 with valve 43; on the other hand, nitrogen can be conveyed directly into the nitrogen storage 20 via line 44 with compressor 45. In the method according to the invention for the preservation of a power plant 1, nitrogen is fed upstream of an electric superheater 16 into the sealing steam supply line 8 of the sealing steam system 6 and into the condenser 4 when the steam turbine 2 is shut down in a conserved state, as shown in FIG. 2. As long as the steam turbine 2 is still synchronized with the network, the condenser pressure to avoid ventilation problems on the steam turbine 2 may be raised only limited by nitrogen supply. As in the case of driving off, as well as when starting up the steam turbine 2, nitrogen may be temporarily fed together with steam into the sealing steam supply line 8, 22 but in particular only when the vacuum can be broken. The vacuum pump 5 is switched off only after it has been disconnected from the grid and the turn speed has been reached. 23. A corresponding condenser-side shut-off at the air suction of the condenser is closed. The vacuum breaker is not used (it may be omitted if it is replaced by a sufficiently large nitrogen feed on the condenser). Subsequently, the pressure in the condenser 4 / in the steam turbine 2 is raised to overpressure via the nitrogen supply 24.

In the sealing steam system is always during the nitrogen filling process (this can already start slowly during the shutdown of the power plant, ie steam turbine set is still synchronized with the grid) maintained an overpressure 25 (either by nitrogen feed, conventional sealing steam supply from the boiler or a combination of both), so that no ambient air can penetrate this way. This is to ensure that the system is always ready to start quickly from a chemical point of view (no waiting for steam purity) and that corrosion does not occur even when the condensate collector in the area of the steam turbine and condenser is full.

After the complete shutdown of the steam turbine 2 and after reaching a nitrogen overpressure in the steam turbine. 2 and in the condenser 4, the nitrogen supply of the sealing steam system 6 is taken out of service during the preservation phase 26. The steam vapor system 18 is at least temporarily during a targeted nitrogen filling of the condenser and the steam turbine in operation.

Nitrogen-enriched exhaust air from the vapor vapor chambers 13 can be compressed and made available to a nitrogen generator 17 as input air 28. For the preservation during the shutdown and during the stoppage of the steam turbine 2, a comparatively small, high-purity first amount of nitrogen is required 29.

A warming or warming of the steam turbine 2 is supported 30 by heating the nitrogen via an arranged in the sealing steam supply line 8 electrical superheater 16.

Before an expected temperature change in the steam turbine 2 or in the condenser 4, a nitrogen pressure in the

Steam turbine 2 or in the condenser 4 increases 31.

When starting the power plant 1, in particular during the condenser evacuation, to block the steam turbine shaft seal, continuously nitrogen 32 is fed via the sealing steam system 32, as long as there is no sufficient sealing steam.

When starting up the steam turbine 2, the vacuum pump 5 is put back into operation 33. In particular, a vacuum sufficient for opening the steam diverter stations or starting enable of the gas turbine is drawn via the vacuum pumps. Nitrogen is blown off via a corresponding exhaust pipe to the vacuum pumps on the roof 34 or, in the case of

Nitrogen production on site (for example by means of pressure change -

Adsorption), a special supply air range at a compressed air generation plant for nitrogen production supplied 35. Thus, it makes sense, the heavily nitrogen-containing exhaust gas from the WrasendampfSystem 18 and the exhaust air from the vacuum pump 5 again to compress and the nitrogen generator 17 as input compressed air available. In this way, the nitrogen recovery plant as well as the necessary "amount of compressed air" can be greatly reduced.

The nitrogen required may be either via a reservoir (e.g., bottle battery) to be filled externally, or nitrogen may be recovered on-site (e.g., by adsorption by pressure swing) and may be stored in a reservoir. The dimensioning of the storage tank and / or the nitrogen recovery plant must be sufficient to at least the

To ensure filling of steam turbine / condenser and the subsequent pressure maintenance. In addition, the restart concept must also be taken into account, that is, it must be considered from when the nitrogen make-up can be replaced by conventional sealing steam again. If there is no nitrogen production on site, the delivery logistics must also be taken into account in the storage dimensioning.

In order to limit the nitrogen requirement, nitrogen is branched off at least temporarily at the exhaust air of the vacuum pump 5 nitrogen and fed to the sealing steam system 6 36. Der

Of course, nitrogen does not enter the sealing steam system 6 immediately, but only after a certain period of operation

recirculates, and then when air in one

Recirculation line 11 was driven from the condenser 4 to the sealing steam system 6 and after a sufficient negative pressure in the condenser 4 was reached, the opening of

Steam diverter stations allowed. This is ensured by appropriate shut-off devices.

In the case of on-site nitrogen production, varying the nitrogen purity level can vary the capacity of a given nitrogen feed. As described above, it is necessary to provide a smaller but high purity amount of nitrogen for preservation. This is required during shutdown and standstill and results from the comparatively low nitrogen losses via the vapor steam system, since the nitrogen excess pressure in the steam turbine / condenser is kept very low for conservation purposes. It would now be possible to switch a nitrogen production from "high purity" in the start-up preservation case to provide a relatively larger, less-polluted second nitrogen amount 37. The provision of a larger amount of impure nitrogen for the start-up is necessary in view of the amount Nitrogen must be provided with a higher pressure in the sealing steam system 6, which increases the nitrogen losses through the vapor steam system 18. On the other hand, the increased impurity is not a problem due to the shortness of the start-up process, moreover it becomes highly pure Nitrogen recirculated via the vacuum pump 5.

With regard to operational safety, it should be noted that the vapor steam system 18 (in particular the fans for suction) remains in operation during the entire time (even during possibly longer standstill preservation) and the nitrogen which otherwise escapes via the shaft seals 7 into the machine house discharges a corresponding pipeline through the roof or a special (correspondingly well shielded) Zuluftbereich on an optionally additional, provided only for the compression of the nitrogen-containing exhaust air, compressed air generation plant. The existing engine room ventilation ensures as further security that any accumulations of nitrogen (eg in case of malfunction of the exhaust fans on WrasendampfSystem 18), which could prevent a sufficient supply of oxygen for humans, not even arise. As a further security, corresponding alarm systems can indicate that the vapor steam system 18 and / or the building ventilation have failed and, in addition, corresponding gas detectors are used which detect either a high nitrogen concentration or a low oxygen concentration and speak clearly. For this stationary or even by the individual employee zuzulagende gas detectors can be used. Thus, any problems with respect to personal safety are very well manageable. Overall, it should also be noted that the molecular nitrogen emitted in gaseous form is non-toxic per se and, as the main constituent of the air, also no environmentally relevant emission.

Claims

Power plant (1) comprising a steam turbine (2) with a shaft (3), a steam turbine (2) downstream of the steam condenser (4), a condenser (4) downstream vacuum pump (5), a sealing steam system (6) with shaft seals (7) and in the shaft seals (7) opening sealing steam supply line (8), characterized in that in the condenser (4) a first nitrogen line (9) opens and in the sealing steam supply line (8) has a second nitrogen line (10) and a from the vacuum pump (5) branching recirculation line (11) open.

Power plant (1) according to claim 1, wherein the shaft seals (7) sealing vapor chambers (12) and Wrasendampf- chambers (13), wherein the sealing steam supply line (8) opens into the sealing vapor chambers (12) and the Wrasendampfkammern (13) with a Wrasendampf blower (14) are connected to suck in the shaft seals (7) penetrating air and a partial flow of steam from the sealing vapor chambers (12) and fed to a steam vapor condenser (15).

Power plant (1) according to one of claims 1 or 2, wherein an electric superheater (16) in the sealing steam supply line (8) is connected and the first

Nitrogen line (9) upstream of the electric superheater (16) opens into the sealing steam supply line (8).

Method for preserving a power plant (1) comprising a steam turbine (2), a condenser (4) connected downstream of the steam turbine (2), a vacuum pump (5) connected downstream of the condenser (4) and a sealing steam system (6), wherein when the steam turbine is shut down (2) into a preserved state nitrogen is introduced into the sealing steam system (6) and into the condenser (4), and the steam turbine (2) and the condenser (4) be brought to nitrogen pressure and the vacuum pump (5) is switched off, characterized in that when starting the steam turbine (2) the vacuum pump (5) is put back into operation and at least temporarily branched off at the exhaust air of the vacuum pump (5) nitrogen and the sealing steam system (6) is supplied.

A method according to claim 4, wherein nitrogen is introduced upstream of an electric superheater (16) into a sealing steam supply line (8) of the sealing steam system (6).

Method according to one of claims 4 or 5, wherein when shutdown of the power plant (1) nitrogen together with steam in the sealing steam supply line (8) is fed as soon as the vacuum can be broken.

Method according to one of claims 4 to 6, wherein after the shutdown of the steam turbine (2) after reaching a nitrogen overpressure in the steam turbine (2) and in the condenser (4), the nitrogen supply of the sealing steam system (6) is taken out of service during the preservation phase ,

Method according to one of claims 4 to 7, wherein before an expected temperature change in the steam turbine (2) or in the condenser (4), a nitrogen pressure in the steam turbine (2) or in the condenser (4) is increased.

Method according to one of claims 4 to 8, wherein when starting the power plant (1), as long as there is no sufficient sealing steam, nitrogen is continuously fed via the sealing steam system (6).

Method according to one of claims 4 to 9, wherein for starting the power plant (1) nitrogen from the condenser (4) in the sealing steam system (6) is recirculated, after air in a recirculation line (11) from Kon- Was driven (4) to the sealing steam system (6) and after a sufficient negative pressure in the condenser (4) has been reached, which allows opening of Dampfumleitstatio- nen. Method according to one of claims 4 to 10, in which a warming or warming of the steam turbine (2) is supported by heating of the nitrogen via a in the sealing steam supply line (8) arranged electrical superheater (16). Method according to one of claims 4 to 11, in which compressed nitrogen-enriched exhaust air from the Wrasendampf- chambers (13) and a nitrogen generator (17) is provided as input air available. Method according to one of claims 4 to 12, wherein for the conservation during the shutdown and during the stoppage of the steam turbine (2) a comparatively small, high-purity first amount of nitrogen and for starting a comparatively larger, impure second amount of nitrogen per time is provided , Method according to one of claims 4 to 13, wherein a WrasendampfSystem (18) at least temporarily during a targeted nitrogen filling of the condenser (4) and the steam turbine (2) is in operation.