EP2126291B1 - Method for operating a gas and steam turbine plant and a gas and steam turbine plant for this purpose - Google Patents

Description

The invention relates to a method for operating a gas and steam turbine plant in which the flue gas emerging from a gas turbine is passed through a heat recovery steam generator and in which a fluid used for driving a steam turbine is guided in a fluid circuit comprising a number of pressure stages, wherein at least one the pressure stages having an evaporator circulation with a steam drum, with a number of downpipes connected to the steam drum and with a number of the downcomers downstream, also connected to the steam drum and heated by the flue gas in the heat recovery steam riser riser. The invention further relates to a gas and steam turbine plant designed for such an operating method.

An example of such a gas and steam turbine plant with a high and a low pressure stage discloses the US 4,501,233 ,

In a gas and steam turbine plant contained in the relaxed working fluid or flue gas from the gas turbine heat for the evaporation of a fluid, usually water used. The (water) steam thus generated is then used to drive a steam turbine. The heat transfer takes place in one of the gas turbine flue gas downstream heat recovery steam boiler or heat recovery steam generator, are arranged in the heating surfaces in the form of tubes or tube bundles in which the fluid to be evaporated is performed. These heating surfaces are usually part of a steam turbine and a downstream of their fluid downstream capacitor fluid circuit, z. B. a water-steam cycle, wherein the emerging from the steam turbine relaxed fluid is returned to the heating surfaces of the heat recovery steam generator after its condensation in the condenser. In addition to the evaporator heating surfaces, further heating surfaces, in particular for preheating the condensate or feed water or for overheating the generated steam, can also be provided in the waste heat steam generator. Furthermore, in the heat recovery steam generator also an additional firing, z. As a Ölfeuerung be integrated to either raise the temperature of the flue gas over the existing at its exit from the gas turbine level, or to be able to maintain steam production in the heat recovery steam boiler at decoupled or decommissioned gas turbine (so-called oil operation).

Usually, the fluid circuit comprises several, for example three, pressure stages, each with its own evaporator section. A design and design concept for such an evaporator section which has proved its worth because of its comparatively simple structure and its relatively simple operability is based on the natural circulation principle, at least in the area of subcritical vapor pressures. It serves a above the flue gas flow channel of the heat recovery steam generator arranged steam drum, which is sometimes referred to as "top drum", as a reservoir for the condensate or feed water ago her running, optionally preheated by a condensate preheater or economizer condensate or feed water. During operation, driven by its own weight or by the hydrostatic pressure of the water column, a portion of the water supply decreases continuously by down to the bottom or bottom of the steam drum, unheated downpipes. Via an intermediate manifold, which is sometimes referred to as a "sub-drum", the sunken water is on a number of parallel connected and bundled to heating surfaces, by the heat contained in the flue gas and / or heated by the radiant heat generated by an additional burner of Abhitzedampfkessels risers distributed, in which the desired evaporation takes place. The heating surfaces formed from the riser tubes can be arranged part of the enclosure wall of the heat recovery steam boiler or in the manner of Schottheizflächen within the enclosed by the surrounding wall flue gas flow channel.

Due to its reduced density relative to the liquid state, the water-vapor mixture produced in the riser pipes by (partial) evaporation of the water rises and finally re-enters the steam drum above the liquid level, whereby the evaporator circulation is closed. In the steam drum, the water-steam separation also referred to as phase separation takes place; the water vapor present above the water level under saturated steam conditions is withdrawn via a steam extraction line connected to the top of the steam drum and, if necessary, overheating of its further use, eg. B. for driving a steam turbine supplied.

Evaporator stages based on the forced circulation principle have a similar structure, but still have a circulating pump connected in the evaporator loop, which supports or forces the circulation of the water or of the water / steam mixture.

Due to the limited thermal load capacity of the commonly used pipe wall materials for the heating pipes and risers is to ensure in accordance with the prior state of science and technology necessarily that when operating a gas and steam turbine plant of the type mentioned above, the risers of each evaporator stage in all operating conditions sufficiently fluid , usually water or water-steam mixture, are supplied. The aim is to ensure a certain minimum cooling of the tube walls as a result of the heat transfer from the pipe inner wall surface on the thereby partially evaporating fluid and thus any damage to the evaporator circulation and thus to avoid associated operational hazards. In other words: so-called dry operation of the evaporator or operation with lowered water level, in which the liquid column in the steam drum and in the downpipes connected to it sinks to a level below the connection of the downpipes or even the downpipes and the riser pipes connected downstream. be driven dry, so that virtually no fluid flows through it is to be avoided under all circumstances.

An example of how such "dry driving" can be avoided is in the CA 1 273 856 in which a connection for a level measuring device, which is connected to a monitoring and control device (a float and a pump), is provided on a downpipe.

Such considerations are also based on the previously applied, internationally valid regulations DIN EN 12952, according to Part 1 for "water tube boiler with a volume of more than 2 liters for the production of steam and / or hot water with an allowable pressure of more than 0.5 bar and a temperature of over 110 ° C ", which, in accordance with Part 7, sets the minimum permissible water level in the steam drum to" 150 mm above the highest heated point of the drum and the highest connection of the downpipes to the boiler drum ". The internationally accepted successor standards DIN IEC 61508 and DIN IEC 61511, which were introduced in Germany in 2002, do not expressly contain such detailed requirements, but the safety requirements specified therein have generally not fallen by any means, despite more flexible frameworks.

In order to comply with the said minimum fill levels of liquid fluid in the steam drum also z. B. to guarantee for fast load changes of the heat recovery steam generator or about an unforeseen interruption or lockout of the feedwater safely and in particular in the latter case existing in the system To be able to dissipate residual heat in a safe and material-saving manner, the volume of the steam drum and the amount of fluid (feed water) stored in it during normal operation is usually comparatively large, taking into account a "safety impact". However, this is associated with a correspondingly high production cost and thus high production costs.

According to the particular relevance, which is attributed to the maintenance of the minimum water level in the steam drum, in existing systems continues to be a triple redundant measurement or monitoring of the drum base or on the upper edge of the downpipes current fill level, which is a relatively expensive interpretation of the associated safety Devices conditional. Once a two-by-three selection from the three level measurements, a drop in water level below a predetermined threshold, e.g. B. 150 mm according to DIN EN 12952, signaled by the safety system, a further supply of hot gas turbine exhaust gases is prevented in the heat recovery steam generator, z. B. by rapid shutdown of the gas turbine, or by by pressing a corresponding flap the exhaust gases in a bypass chimney, d. H. past the heat recovery steam generator, to be diverted. However, in the interests of the highest possible system availability, such an emergency shutdown is extremely undesirable.

In addition, the current compliance with the medium pressure drum (MD drum) and low pressure drum (LP drum) levels above the minimum oil level requires complex inlet temperature control for the economizers of the high and medium pressure systems and the condensate preheater. Changes in stationary conditions due to different operating conditions in oil operation result in internal heat shifts in the heat recovery steam generator, which influence the heat absorption of the medium-pressure and low-pressure evaporator. This can, for example, fluctuations in the drum water levels of the MD and ND drum and cause an unintentionally high pressure rise in the LP drum. In order to be able to keep these fluctuations within the required operating limits, the quantities of water must additionally be superimposed accordingly via the HP and MD economizer bypass valves, which requires increased control effort.

Finally, the currently required compliance with the minimum water level in the LP steam drum, especially in the case of the basic concept ago particularly interesting, in the patent DE 100 04 178 C1 in detail explained driving style "Sleeping Mode", in the z. B. during a quick closure of the steam turbine of the HD-steam generated in the HD stage is diverted via a bypass line directly into the condenser (diverter), while by a targeted pressure shift and a shift of heat dissipation and absorption in heat recovery steam generator, the production of MD and LP steam to be brought to a standstill, at additional cost due to a comparatively large dimensioned LP steam drum. The drop in the water level in the low-pressure drum during a quick-closing of the steam turbine is particularly drastic here due to the deliberately induced increase in pressure in the low-pressure system. Contrary to the original orientation of the concept can therefore not be completely dispensed with in practice on a Niederdruckumleitstation that reduces the drop in water level at a quick closing of the steam turbine accordingly.

The invention is therefore based on the object of specifying a method for operating a gas and steam turbine plant of the type mentioned, which is particularly flexible adaptable to various operating conditions of the system with high reliability and high operational safety, and a particularly cost-effective design of the components respective evaporator circulation possible. Furthermore, a suitable for carrying out the process gas and steam turbine plant should be specified.

With regard to the method, the object is achieved by monitoring the height of the liquid column formed by the flow medium in the downpipes connected to the steam drum.

According to the concept presented here, a metrological detection of the filling level height of the liquid column formed by the liquid flow medium within the downpipes of the evaporator circulation is provided above the hitherto customary level measurement in the steam drum. In other words, the measuring device not only provides information as to whether the liquid level is actually dropping below a minimum level in the steam drum or below the level of the downpipe connections, but quantifies this state even more closely by detecting at least one further height level or a plurality of discrete height measuring points within the downpipe monitors and metrologically dissolves. Of course, a continuous or quasi-continuous measurement of the level height can be provided in the downpipe, expediently with the arranged at the lower end of the manifold manifold as a reference point.

If several downcomers are connected to the steam drum and connected in the manner of a flow-side parallel connection with a common manifold, adjusts itself in accordance with the principle of communicating tubes usually in all downpipes the same level height, so that advantageously only the level in one of the tubes must be monitored ,

The invention is based on the consideration that, due to the advances recently achieved in the material technology and material development for evaporator, contrary to hitherto considered in the professional opinion interpretation of a combined cycle power plant conceivable both technically possible and under the given economic conditions in the Practice is competitive, at least temporarily during special operating conditions a partial or complete dry operation of an evaporator circuit, that is, a drop in the liquid level in the downpipes below the level of the steam drum, is tolerable.

In order to avoid permanent material damage and associated operational hazards, on the one hand arranged in the flow channel of the heat recovery steam riser or the heating surfaces formed from them should be designed in terms of their temperature resistance to the usually occurring during plant operation flue gas temperatures in the region of their installation position, for example 300th ° C for an MD evaporator or 200 ° C for a LP evaporator. The hitherto always existing cooling by the normally conducted in the pipes fluid should therefore now not be included in the temperature design for a possible dry operation in the temperature design. Such requirements are readily met by a variety of steels known in the art, the temperature limit is partly over 400 ° C and their use can be justified in economic terms.

On the other hand, the hitherto customary monitoring and safeguarding concept for such a gas and steam turbine plant and in particular for those evaporator circuits in which a temporary dry running is considered, consistently to the previous design principles changed thermal loads and hazards to the structural integrity of the evaporator components be adjusted. As a central input for the associated monitoring system and for deciding on the type and extent of security measures to be initiated, a measured variable should first be recorded which reliably provides information about an incipient dry operation as well as about its "extent".

In an advantageous embodiment, the temperature of the flue gas is also monitored in the riser, wherein in an operating condition with a lying below the connection to the steam drum liquid level in the downcomers a safety measure is initiated as soon as the temperature of the flue gas in the downstream of the downcomers risers exceeds a predetermined limit.

In this way, the heating temperature acting from the outside on the riser tubes is thus monitored, especially in an operating state associated with a particularly high risk situation, with a possibly imminent or already occurring dry operation or with a reduced throughput of fluid, and a safety reaction is triggered when a critical value is exceeded. In this case, in particular, a cascade of staggered limit values can also be defined, whereby, when a first limit value is exceeded, a relatively "mild" countermeasure is initially introduced, but increasingly more drastic countermeasures upon further increase in temperature.

Advantageously, the respective temperature limit value is determined as a function of the liquid level in the downpipes determined by measurement, so that the cooling influence of the remaining amount of the fluid flowing through the downstream riser pipes and taken into account appropriately takes into account when deciding on the type and timing of initiation of safety measures can be.

A first, relatively mild safety measure preferably consists in opening a bypass line of a condensate preheater upstream of the evaporator circuit or of a feedwater preheater on the flue gas side in order to generally exceed the permissible values during different load change states, in particular when the gas and steam turbine system is started or stopped Prevent flue gas temperatures from the relevant evaporators. If the regular operation is then resumed and steam is again generated in the relevant evaporator stage, then the respective evaporator system is filled with hot water from the upstream economizer (in the MD evaporator) or from the condensate preheater (in the LP evaporator). By deliberately closing the cold condensate preheater bypass or the economizer bypass, the respective heating temperature is increased and steam production reintroduced.

Especially in a three-pressure system with a condensate preheater, an MD economizer downstream of the condensate preheater for the feed water of the MD evaporator and an MD economizer downstream HD economizer for the feed water of the HP stage leads to the opening of the condensate preheater bypass line or the bypass line of the MD economizer in the standard case that, as in the DE 100 04 187 C1 described, the HD evaporator flue gas side of the MD evaporator and this in turn upstream of the LP evaporator, to the advantageous side effect that now the evaporator circulation of the HD stage is supplied with comparatively cooler feed water, so that the flue gas of the gas turbine already in the Entry area of the heat recovery steam generator comparatively much heat is withdrawn. The temperature load in the area of the MD and LP heating surfaces, which is in any case moderate in comparison to the high pressure stage, is thereby reduced particularly quickly and effectively when required. Especially with such an effective, if necessary activatable safety measure, a temporary drying of the MD and / or LP evaporator circulation can therefore be tolerated particularly well.

Advantageously, both the height of the liquid column in the downcomers of the MD and / or the LP evaporator and the respective flue gas temperature are monitored, with a possible overload state of the two pressure levels based on the two associated parameters level and flue gas temperature at the installation of the heating surfaces is derived. When establishing temperature limits for the initiation of safety measures, both the spatially varying heating profile and possibly a different choice of material and temperature design for the various evaporator circuits are expediently taken into account.

Another, more drastic security measure may be to initiate a power reduction or an emergency shutdown of the gas turbine or, for. B. by pressing a bypass valve, passing the flue gas leaving the gas turbine at least partially on the heat recovery steam generator.

With regard to the device, the object mentioned above is achieved by a gas and steam turbine plant, in which a fill level measurement in the steam drum beyond a level measuring device that monitors at least yet another height level within the downpipe and dissolves metrologically, to measure the height of the Flow medium formed liquid column in the connected to the steam drum downpipes signal output side is connected to a monitoring and control device for the gas and steam turbine plant.

Advantageously, the monitoring and control device is further connected on the signal input side to a temperature measuring device monitoring the temperature of the flue gas in the region of the riser tubes and configured to introduce a safety measure in an operating condition with a below the connection to the steam drum liquid level in the downpipes, as soon as temperature measured by the temperature measuring device exceeds a predetermined limit.

The advantages achieved by the invention are in particular that it is due to the consistent design of the plant architecture and the associated hedging and Überwanenanlage with a heat recovery steam generator on demand on the natural circulation principle based evaporator system, in particular the MD and / or LP evaporator system, safe to operate at a water level far below the currently set minimum water level or the heating even dry, without having to stop the operation of the heat recovery steam generator or the gas turbine. In particular, an adjustment of flexible minimum water levels in the respective evaporator circulation depending on certain modes without loss of security is possible.

It can be demonstrated that such a concept also meets or exceeds the safety standards set by the new standards DIN IEC 61508 and DIN IEC 61511. The rapid shutdown risk of the waste heat steam generator with a quick closing of the steam turbine control valves or in rapid load changes namely drops significantly when the water level in the evaporator circulation can safely fall below the drum level. Thus, the availability of gas and steam turbine plant is further increased, especially in quick launches, which comes to compensate for short-term demand and supply fluctuations in the power grid of increasing importance. In particular, in gas and steam turbine without bypass chimney flap has a lower risk of rapid shutdown of the heat recovery steam generator lower loads and thus less equivalent operating hours for the gas turbine result. This allows the maintenance intervals at the gas turbine can be extended while maintaining the same level of safety.

In addition, the inventive concept allows a more cost-effective design and construction of production costs usually particularly costly components of the evaporator system, since in particular the MD and LP steam drums can be made more compact than previously necessary. This is especially in the context of the above-mentioned operation "Sleeping Mode" in the absence of Niederdruckumleitstation for the LP evaporator of relevance, since the otherwise required for carrying out this mode drum enlargement now be correspondingly lower or even eliminated altogether. Finally, the control engineering effort to comply with the Kondensatvorwärmer- and economizer inlet temperatures in oil operation is lower than before.

With a corresponding modification and adaptation, the concept presented here can also be used in gas and steam turbine plants with evaporator stages based on the forced circulation principle.

FIG 1

eine Gas- und Dampfturbinenanlage, und

FIG 2

einen Ausschnitt aus FIG 1, wobei im Interesse einer besseren Erkennbarkeit wesentlicher Komponenten der Gas- und Dampfturbinenanlage einige Details aus FIG 1 weggelassen oder in zeichnerisch leicht abgewandelter Form dargestellt wurden.

An embodiment of the invention will be explained in more detail with reference to a drawing. In it show in a schematic representation:

FIG. 1

a gas and steam turbine plant, and

FIG. 2

a section from FIG. 1 , wherein in the interest of better visibility of essential components of the gas and steam turbine plant some details FIG. 1 omitted or have been shown in slightly modified form.

Identical parts are provided in both figures with the same reference numerals.

The gas and steam turbine 1 according to FIG. 1 includes a gas turbine plant 1a and a steam turbine plant 1b.

The gas turbine plant 1a comprises a gas turbine 2 with a coupled air compressor 4 and a combustion chamber 6 upstream of the gas turbine 2 in which fuel B is burned while supplying compressed air from the air compressor 4 to the working medium or fuel gas A for the gas turbine 2. The gas turbine 2 and the air compressor 4 and a generator 8 are seated on a common turbine shaft 10.

The steam turbine installation 1 b comprises a steam turbine 12 with a coupled generator 14 and a condenser 18 connected downstream of the steam turbine 12 and a waste heat steam generator 20 in a water circuit 16 designed as a water-steam circuit. The steam turbine 12 has a first pressure stage or a high-pressure component 12 a and a second pressure stage or a medium-pressure part 12b and a third pressure stage or a low-pressure part 12c, which drive the generator 14 via a common turbine shaft 22.

For supplying relaxed in the gas turbine 2 working fluid or flue gas R in the heat recovery steam generator 20, an exhaust pipe 24 to the heat recovery steam generator 20 is connected on the input side. The expanded flue gas R from the gas turbine 2 leaves the heat recovery steam generator 20 on the output side in the direction of a fireplace, not shown.

The heat recovery steam generator 20 comprises, as heating surfaces, a condensate preheater 26, which is fed on the input side with condensate K from the condenser 18 via a condensate line 28, into which a condensate pump 30 is connected. The condensate preheater 26 is guided on the output side to the suction side of a feedwater pump 34. For bypassing the condensate preheater 26 as required, it is bridged with a bypass line 36 into which a motor-actuated valve 38 is connected.

The feedwater pump 34 is formed in the embodiment as a high-pressure feed pump with medium pressure extraction. It brings the condensate K to a pressure level suitable for a high-pressure stage 40 of the fluid circuit 16 assigned to the high-pressure part 12 a of the steam turbine 12. The guided through the feedwater pump condensate K, which is referred to as the feed water S on the pressure side of the feedwater pump 34 is supplied to a feedwater heater 42 with medium pressure. This is the output side connected to a medium-pressure steam drum 44. Analogously, the condensate preheater 26 is connected on the output side via a motor-actuatable valve 46 to a low-pressure steam drum 48.

The medium-pressure steam drum 44 is connected to a medium pressure evaporator 50 arranged in the heat recovery steam generator 20 to form a medium pressure evaporator circulation 52. The evaporator circuit 52 includes a number of in FIG. 1 indicated only schematically, outside of the heated flue gas R flow channel of the heat recovery steam generator 20 extending downcomers 54 which are connected at their upper end respectively to the bottom of the steam drum 44 and open at its lower end in a distributor collector not shown here. About the manifold collector a plurality of parallel connected, arranged in the heat recovery steam generator 20 heating surfaces 50 bundled risers 56 with liquid fluid, here water, from the steam drum 44 or from the downpipes 54 fed, which evaporates when flowing through the risers 56 in part, thereby up rises and enters the steam drum 44 again as a water-steam mixture.

On the steam side, a medium-pressure superheater 58 is connected to the medium-pressure steam drum 44 and is connected on the output side to an exhaust steam line 62 connecting the high-pressure part 12a on the output side to a reheater 60. The reheater 60, in turn, is connected on the output side via a steam line 64, into which a motor-actuatable valve 66 is connected, to the central-pressure part 12b of the steam turbine 12.

High-pressure side, the feedwater pump 34 via a first high-pressure economizer 68 and a feed water side downstream and within the heat recovery steam generator 20 upstream flue gas second high pressure economizer 70 is guided to a high pressure steam drum 72. The high pressure steam drum 72 is in turn connected to a high pressure evaporator 74 disposed in the waste heat steam generator 20 to form an evaporator circuit 80 comprising a number of downcomers 76 and risers 78. For discharging live steam F, the high-pressure steam drum 72 is connected to a high-pressure superheater 82 arranged in the heat recovery steam generator 20, which is connected on the output side to the high-pressure part 12a of the steam turbine 12 via a live steam line 84 to a motor-actuated valve 86. The first high-pressure economizer 68 is also bridged with a bypass line 88, into which in turn a motor-operated valve 90 is connected.

The feedwater preheater 42 and the medium-pressure evaporator 50 and the medium-pressure superheater 58 together with the reheater 60 and the medium-pressure part 12b of the steam turbine 12, the intermediate pressure stage 92 of the designed as a water-steam cycle fluid circuit 16. Analog forms in the heat recovery steam generator 20th arranged and to form an evaporator circuit 94 with the low-pressure steam drum 48 connected low-pressure evaporator 96 together with a low-pressure superheater 98 connected to the low-pressure steam drum 48 and the low-pressure part 12c of the steam turbine 12 the low-pressure stage 100 of the fluid circuit 16. Analogous to the high-pressure evaporator circuit 80 and the medium-pressure evaporator circuit 52, the low-pressure evaporator circuit 94 consists of a number of connected to the steam drum 48 downcomers 102 and a number of these downstream of the flow side risers 104 together. On the output side, the low-pressure superheater 98 is connected to the inlet of the low-pressure part 12 c of the steam turbine 12 via a steam line 106 into which a motor-actuated valve 108 is connected.

For bypassing or diverting the high-pressure part 12a of the steam turbine 12 on demand, the live steam line 84 connecting the high-pressure superheater 82 to the high-pressure part 12a is connected directly to the condenser 18 via a steam line 110 into which a motor-actuated valve 112 is connected. In this case, the steam line 110 serving as high-pressure bypass is connected in the flow direction of the live steam F upstream of the valve 86 to the main steam line 84.

In order to enable a flexible adaptation of the operation to different requirements with a particularly low design and manufacturing costs, the gas and steam turbine plant 1 is designed such that the level of liquid fluid in the downpipes 54, 102 of the medium-pressure evaporator circuit 52 and the low pressure Evaporator circuit 94 may at least temporarily drop below the level of the connection to the respective steam drum 44, 48, if necessary, up to a complete dry operation of the evaporator circuit 52 and 94, respectively.

For this purpose, the tube wall material of the downpipes 54, 102 downstream of the flow side, by contact with the flue gas R convectively heated risers 56, 104 are each selected with respect to its temperature resistance such that its temperature limit above that in this area the heat recovery steam generator 20 is normally present or maximum expected temperature of the flue gas R. For example, the temperature of the flue gas R in the region of the medium-pressure evaporator 50 under ordinary circumstances around 300 ° C, in the region of the low-pressure evaporator 96 around 200 ° C. If, for example, the riser pipes 56 of the medium-pressure evaporator 50 are designed for a continuous temperature resistance of about 400 ° C. and the risers 104 of the low-pressure evaporator 96 to a continuous temperature resistance of about 300 ° C., then as a rule sufficient safety reserves are available in order to temporarily dry them , z. B. at startup or shutdown of the gas and steam turbine 1 or during rapid load changes to tolerate. Thus, in particular the medium-pressure steam drum 44 and the low-pressure steam drum 48 can be built very compact, since the date each to compensate for different steam production rates and to ensure a continuous feeding of the risers 56, 104 with fluid vorgehaltene liquid volume may be relatively small.

However, in order to be able to react adequately even in the case of unforeseen temperature peaks during an imminent or already occurring dry operation of the medium-pressure evaporator circuit 52 and / or the low-pressure evaporator circuit 94 by the introduction of safety measures, the gas and steam turbine plant 1 with a specific equipped for monitoring and control of such operating conditions designed monitoring and control system. In particular, the medium-pressure evaporator circulation 52 and the low-pressure evaporator circulation 94 are monitored independently of one another in a manner to be described below.

The monitoring of the low pressure evaporator circuit 94 is done as follows: In addition to the hitherto customary monitoring of the water level in the low pressure steam drum 48, in FIG. 2 indicated schematically by the double arrow 114, is now a level monitoring provided, which also includes the connected to the low-pressure steam drum 48 downpipes 102, here indicated schematically by the double arrow 116. A fill level measuring device not shown here so measures the reference to the lowest point of the downpipes 102 height of the water column during the normal operation of the gas and steam turbine plant 1 extends into the steam drum 48, while special situations now but also - as described above - can fall below the height level of the upper downpipe connections. It can also be provided to refer the fill level to the downcomer connections, that is to say to the lowest point of the steam drum 48, and to indicate, for example, an overlying level with a positive sign, an underlying level with a negative sign. So if z. For example, if the height of the downcomers 102 is two meters, a level of "minus 1.9 meters" would indicate a potentially imminent complete dry operation.

The so measured level of liquid flow medium in the downpipes 102 of the low-pressure evaporator circuit 94 is transmitted to a central evaluation unit, not shown here, a monitoring and control device for the combined cycle power plant 1. A further input for monitoring the pressure prevailing in the area of the riser tubes 104 temperature T ₁ of the flue gas R, which in the embodiment of FIG. 2 by a seen in the flow direction of the flue gas R just before the risers 104 in the heat recovery steam generator 20 arranged, here only schematically indicated temperature measuring device 118 and its temperature sensor is detected. The monitoring and control device is configured or programmed to initiate a safety measure at least in an operating condition with a liquid level in the downcomers 102 below the connection to the steam drum 48 as soon as the temperature T ₁ measured by the temperature measurement device 118 reaches a predetermined limit exceeds. This limit value can be predetermined in particular depending on the liquid level in the downpipes 102.

For example, if the temperature input limit for the risers 104 of the low-pressure evaporator circuit 94 at 300 C, so may be set at about half height with water-filled downpipes 102, a first limit at 290 ° C, in the first in the bypass line 36 of the Kondensatvorwärmers 26 lying valve 38 is opened. In the case of a complete dry operation, this first limit is suitably set correspondingly lower, z. At about 270 ° C.

The opening of the valve 38 causes the condensate K on the suction side of the feedwater pump 34 has a mixing temperature T _M , which adjusts due to the at least partial recirculation of the condensate preheater 26. This mixed temperature T _M is smaller than the condensate temperature T _K "with completely flowed, ie not flow around condensate 26. Also in preheating a partial flow K 'in the condensate 26, a mixing temperature T _M , which is smaller than the temperature T _K " des During operation of the steam turbine 12 the condensate preheater 26 leaving condensate K. In this way, both in the feedwater 42 and in the first high pressure economizer 68 comparatively cold feed water S with the result that the flue gas R in the flow direction before the low pressure stage 100 comparatively strong is cooled. As a result, the low-pressure stage 100, ie in particular the low-pressure evaporator 96, receives comparatively little heat, while at the same time comparatively cooler condensate K flows through the condensate line 120 into the low-pressure steam drum 48. Thus, depending on the position of the valve 38, the temperature load for the risers 104 of the low-pressure stage 100 is greatly reduced and at the same time the water level in the low-pressure steam drum 48 and in the downpipes connected to it 102 increases again, so that potentially dangerous operating conditions due to the temporary dry operation of the low pressure evaporator circulation 94 can be actively and effectively counteracted if necessary.

Should despite the measures described, the temperature T _{1 of} the flue gas R in the region of the low-pressure evaporator 96 continue to increase and a second limit of z. B. 320 ° C in half filled with water downpipes 102 or z. B. exceed 300 ° C in dry operation, then initiates the monitoring and control device for the combined cycle power plant 1 further security measures, eg. B. an emergency shutdown of the gas turbine plant 1a.

For the monitoring of the medium-pressure evaporator circulation 52 applies accordingly. That is, it is on the one hand a level measuring device, indicated by the double arrow 124, for measuring the height of the fluid column formed by the flow medium in the connected to the steam drum 44 downcomers 54 and on the other hand arranged in the flue gas duct just before the risers 56 temperature measuring device 126 for measuring the in Area of the riser pipes 56 prevailing flue gas temperature T ₂ provided. Analogous to the low-pressure evaporator circuit 94, a monitoring and control device connected to the temperature and level sensors is configured to initiate a safety measure in an operating condition with a liquid level in the downcomers 54 below the connection to the medium-pressure steam drum 44 as soon as the measured by the temperature measuring device 126, the flue gas temperature T ₂ exceeds a predetermined limit.

For example, a first safety measure may be to open the valve 38 in the bypass line 36 for the condensate preheater 26. Alternatively or additionally, the valve 90 may be opened in the bypass line 88 for the first high-pressure economizer 68, so that comparatively cooler feed water S is supplied to the second high-pressure economizer 70. The second high pressure economizer 70 therefore removes the pressure in this area of the heat recovery steam generator 20 flowing flue gas R compared to the operation with closed bypass valves 38, 90 in addition heat that the flue gas side downstream medium-pressure heating surfaces and the risers 56 is no longer available. As a result, in particular during dry operation, the temperature load for the riser pipes 56 can be reduced. A second, more drastic security measure can in turn consist in an emergency shutdown of the gas turbine plant 1a.

Particularly advantageous is the ability to temporarily drive the medium-pressure evaporator circuit 52 or the low-pressure evaporator circuit 94, during the so-called bypass operation. Such a bypass operation, which is provided in particular when starting or stopping the steam turbine 12 and at a steam turbine short circuit, leads to a diversion of the generated live steam F, bypassing the steam turbine 12 directly into the condenser 18. For this purpose, the valve 86 is closed and the valve 112th open. In parallel, the condensate preheater 26 is at least partially flowed around by opening the valve 38 located in the bypass line 36. Optionally, the valve 90 is opened in the bypass line 88, so that due to the above-described heat shifts in the heat recovery steam generator 20, the production of low-pressure steam and optionally also throttled by medium-pressure steam or even brought to a complete halt. Thus, only high-pressure steam or live steam F is generated, which is, however, introduced directly into the condenser 18 via the vapor line 12 bypassing steam line 110. Due to the possibility of being able to drive the medium pressure evaporator circuit 52 and / or the low pressure evaporator circuit 94 safely, the enlargement of the medium pressure steam drum 44 or the low pressure steam drum 48, which is otherwise necessary in gas and steam turbine plants without diverter stations, is opposite those systems where diverter stations are present avoided.

Claims (9)

1. Method for operating a gas and steam turbine plant (1) in which the flue gas (R) coming out of a gas turbine (2) is conducted via a waste heat steam generator (20), and in which a flow medium used to drive a steam turbine (12) is conducted in a flow medium circuit (16) comprising a number of pressure stages (40, 92, 100), with at least one of the pressure stages (100) featuring an evaporator circuit (94) with a steam collection drum (48) with a number of downpipes (104) connected to the steam collection drum (48) and with a number of riser pipes (104) connected downstream from the downpipes (102) likewise connected to the steam collection drum (48) and heated by the flue gas (R) in the waste heat steam generator (20).
   characterised in that beyond a fill level measurement in the steam collection drum (48) the height of the column of liquid formed by the flow medium in the downpipes (102) connected to the steam collection drum (48) is monitored by at least one further height level being monitored within a downpipe (102) and resolved for measurement.
2. Method according to claim 1,
   characterised in that the temperature (T₁) of the flue gas (R) is monitored in the area of the riser pipes (104), in which case in an operating state with a liquid level lying below the connection to the steam collection drum (48) in the downpipes (102) a safety measure is initiated as soon as the temperature (T₁) of the flue gas (R) in the area of the riser pipes (104) connected downstream from the downpipes (102) exceeds a predetermined threshold value.
3. Method according to claim 2,
   characterised in that the threshold value is predetermined as a function of the liquid level in the downpipes (102).
4. Method according to claim 2 or 3,
   characterised in that as a safety measure a bypass line (36) of a condensate preheater (26) connected downstream from the evaporator circuit (94) on the flow medium side or the feed water preheater (68) arranged before the evaporator circuit (94) on the flue gas side is opened.
5. Method according to one of claims 2 to 4,
   characterised in that, as a safety measure, a power reduction or a rapid shutdown of the gas turbine plant (1a) is initiated, and/or the flue gas coming out of the gas turbine (2) is at least in part directed past the waste heat and steam generator (20).
6. Method according to one of claims 1 to 5,
   characterised in that, for a flow medium circuit (16) comprising at least three pressure stages (40, 92, 100) each with one evaporator circuit (80, 52, 94), with the riser pipes (78, 56, 104) of the evaporator circuits (18, 52, 94) seen in the flow direction of the flue gas (R) being arranged behind one another in the waste heat steam generator (20), the height of the column of liquid in the downpipes (102) in the last evaporator circuit (94) seen in the direction of flow of the flue gas (R) which is preferably embodied as a low-pressure evaporator circuit, is monitored.
7. Method according to claim 6,
   characterised in that the height of the column of liquid in the downpipes (54) of the last but one evaporator circuit (52) seen in the direction of flow of the flue gas (R), which is preferably embodied as a medium-pressure evaporator circuit, is also monitored.
8. Gas and steam turbine plant (1) with a gas turbine (2) and with a waste heat steam generator (20) connected downstream from this on the exhaust gas side, as well as with a flow medium circuit (16) comprising a number of pressure stages (40, 92, 100), in which a flow medium used for driving a steam turbine (12) is conducted, with at least one of the pressure stages (100) featuring an evaporator circuit (94) with a steam collection drum (48) with a number of downpipes (102) connected to the steam collection drum (48) and with a number of riser pipes (104) connected downstream from the downpipes (102) likewise connected to the steam collection drum (48) and heated by the flue gas (R) in the waste heat steam generator (20), characterised in that beyond a fill level measurement in the steam collection drum (48) a level measurement facility, which monitors at least one further height level within the downpipe (102) and resolves them for measurement, for measuring the height of the column of liquid formed by the flow medium in the downpipes (102) connected to the steam drama (48), is connected on the signal output side to a monitoring and control facility for the gas and steam turbine plant (1).
9. Gas and steam turbine plant (1) according to claim 8,
   characterised in that the monitoring and control facility is linked on the signal side to a temperature measurement facility (118) monitoring the temperature (T₁) of the flue gas (R) in the area of the riser pipes (104) and is configured such that, in an operating state with a liquid level lying below the connection to the steam collection drum (48) in the downpipes (102), a safety measure is initiated as soon as the temperature (T₁) measured by the temperature measurement facility (118) exceeds a predetermined threshold value.

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