WO2016188671A1 - Water/steam circuit of a gas and steam turbine system - Google Patents

Abstract

The invention relates to a water/steam circuit (1) of a gas and steam turbine system (2) comprising a steam turbine (3) and a waste heat steam generator (4), comprising at least one high-pressure superheater heating surface (47, 49, 51), a high-pressure evaporator heating surface (52), a high-pressure preheater heating surface, at least one average-pressure superheater heating surface (48, 50, 54), an average-pressure evaporator heating surface (56), an average-pressure preheater heating surface (57), and a low-pressure evaporator stage (5) comprising a low-pressure superheater heating surface (6) and a low-pressure evaporator heating surface (7), wherein a low-pressure evaporator stage (8) comprising a low-pressure evaporator heating surface (9) is arranged in the waste heat steam generator (4) downstream of the low-pressure evaporator stage (5) in the flow direction of gas turbine exhaust gases. The invention further relates to a gas and steam turbine system (2) comprising a water/steam circuit (1) and to a method for operating a gas and steam turbine system (2).

Description

description

The invention relates to a water-steam circuit of a gas and steam turbine plant and a method for its operation.

For gas and steam power plants, fuel costs and investment costs are the cost blocks with the greatest impact on economic efficiency. Accordingly, an object depending ^¬ plant optimization to achieve the highest possible overall plant efficiency at the lowest possible investment costs. The location of the optimum is thereby determined by the amount of the specific payable by the operator

Fuel price determined. Particular importance is attached to the water-steam cycle concept for the steam part of the gas and steam power plant operated with the waste heat of the gas turbine. This is important to make the given amount of waste heat from the exhaust of the gas turbine as well as possible but also kostenspa ^¬ rend.

Typically, in the water-steam cycle, even at low specific fuel prices, a low-pressure evaporator stage is used, since thus the exhaust gas temperature at Abhitzedampferzeugeraustritt greatly reduced and thus the waste heat can be greatly improved at relatively low additional cost. At high fuel prices may come even more, z.T. strongly cost-increasing measures for increasing efficiency, such as a third evaporator pressure stage and / or a reheat, for carrying.

This low evaporation pressure stage is always settled in the range around 4 to approximately 10 bar and the ^generated steam in the heat recovery steam generator subsequently clearly overheats there (overheating in the range of 50K to 150K are usual) for the steam introduction conditions of the steam turbine - to fill. In ISO conditions, exhaust gas temperatures at the waste heat steam generator outlet of around 85 ° C were thus made possible. This ge ^¬ schah with respect to an optimization with respect to utilization of the residual exhaust gas heat (downstream of higher Verdampferdruck- stages) at a sufficiently high temperature level on the one hand and as far as possible cooling of the exhaust gas ^¬ mass flow (at even technically / economically viable low-pressure steam volume flows the corresponding a Steam line and valves are to be integrated into the steam turbine) on the other side.

The object of the invention is to provide a water-steam cycle for a combined cycle power plant of the aforementioned type, which allows an improved utilization of heat at the cold end of the heat recovery steam generator and which is to be equal ^¬ as simple and inexpensive to manufacture. Furthermore, a corresponding gas and steam turbine plant is to be provided. Another object of the invention is to provide a corresponding method for operating a gas and steam turbine plant.

The invention solves the ge ^¬ directed to a water-steam cycle task by providing that in a derarti ^¬ gen water-steam circuit of a combined cycle power plant comprising a steam turbine and a heat recovery steam generator having at least one high-pressure superheater, a High-pressure evaporator, a high-pressure preheater ^¬ heating surface, at least one medium-pressure Überhitzerheizfläche, a medium-pressure Verdampferheizfläche, a medium-pressure Vorwärmerheizfläche and with a low-pressure evaporator stage comprising a low-pressure Überhitzerheiz ^¬ area and a low-pressure Verdampferheizfläche, im

Abhitzedampferzeuger a Niederstdruck-evaporator stage ^¬ including a Niederstdruck evaporator heating in the direction of flow of gas turbine exhaust gases after the low-pressure evaporator stage is arranged. The previous water-steam cycle concepts with a Nie ^¬ derdruck evaporator stage at a pressure level of about 4 to about 10 bar with subsequent significant overheating of the steam generated there so according to the invention by a further stage, a "low-pressure evaporator stage" be completed. This will be the one to continue as in the past, much of the rest of the exhaust heat utilized at a comparatively high tem ^¬ peraturniveau on the low-pressure evaporator stage and secondly the heat efficiency of the boiler at the "cold end" sels even further ge a Niederstdruck-evaporator stage ^¬ increases (with "sulfur-free" fuels and a minimum condensate inlet temperature of 55 ° C derived from this, the exhaust gas temperature can be reduced from approx. 85 ° C to approx. 65 ° C without dew point undershooting).

Is a desirable effect of the combination of low-pressure evaporator stage and Niederstdruck evaporator stage that said generated in the Niederstdruck-evaporator stage vapor masses ^¬ current (and thus the resulting there steam flow rate) is limited by the limitation of the available heat range about the low-pressure evaporator stage. The latter is of importance to keep the dimensions of the piping and valves which introduce the steam into the Niederstdruck-evaporator stage he testified ^¬ into the steam turbine, in a "meaningless full" frame (overall volume, cost, etc.).

In an advantageous embodiment, at least a first part of a condensate in the waste is Vorwärmerheizfläche ^¬ arranged directly between the Niederstdruck-evaporator and the low-pressure evaporator heating ^¬. In order to integrate the steam generated in the low-pressure evaporator stage into the steam turbine, it must generally be ensured that the steam is sufficiently overheated. How strong the overheating must be depends on the usable binding point on the steam turbine. The lower the pressure at the binding site, the lower the requirements for overheating. The saturated steam generated in the low-pressure evaporator stage is intended are not overheated in the heat recovery steam generator itself via a superheater heating surface in order to avoid the resulting pressure losses. Each pressure loss must be compensated by a higher vapor pressure in the low-pressure evaporator stage, which in turn means the additional usable heat and thus the possible steam production in the low-pressure evaporator stage

Low pressure evaporator stage restricts.

It is expedient for the low-pressure evaporator stage to be followed by a second part of the condensate preheater heating surface in the flow direction of gas turbine exhaust gases.

Furthermore, it is expedient for a first steam line to be associated with one of the low-pressure evaporator heating surfaces

Low-pressure steam drum connects to the steam turbine.

In an advantageous embodiment, a valve for relaxing a vapor is arranged in the first steam line. In this way, saturated steam produced in the low-pressure evaporator stage, which is conducted via a separate pipeline to the steam turbine, can be easily expanded before it enters the steam turbine and thereby be easily overheated. This type of steam integration is suitable for integrally depressions on the steam turbine of about 0.5 to 1.2 bar.

In a further advantageous embodiment, a second steam line connecting an associated one of Niederstdruck-evaporator Niederstdruck steam drum with a superheater, is arranged which reasonable outside the heat recovery steam generator, and a third steam line branches off from the overheating ^¬ zer and opens into the steam turbine. This type of steam integration is suitable for immersion pressures of approx. 1 to 3 bar. Conveniently, the superheater is electrically, steam, feed water or condensate heated. In yet another advantageous embodiment, a fourth steam line connects a low pressure steam drum associated with the low pressure evaporator heating surface to a vapor compressor, and the vapor compressor is connected to the steam turbine via a fifth steam line. Thus, steam produced in the low-pressure evaporator stage (possibly after a slight overheating - this can be represented, for example, by expansion via a valve) is compressed and thus simultaneously overheated, before it is guided to the steam turbine and integrated into the steam turbine.

This type of steam incorporation is suitable for integrally pressures of approx. 1.5 to 5 bar. If the pressure is thereby raised to the pressure ^¬ level of supplied from the low-pressure evaporator stage low-pressure steam line, thereby eliminating the otherwise necessary separate steam pipes / valves for the integration of the steam generated in the Niederstdruck-evaporator stage in the steam turbine.

Conveniently, the vapor compressor is electrically driven.

Alternatively, in the Niederstdruck-evaporator stage he ^¬ begat saturated steam can be integrated into the steam turbine without further overheating, when provided at the steam turbine corresponding special water protection measures on the integration point or is included at such low pressures, that the air flowing into the steam turbine Steam is already present as saturated steam / wet steam. It is therefore advantageous, when provided in the steam turbine ^¬ wet protection measures at a integration point for the saturated steam from the lower of pressure evaporator stage of the heat recovery steam generator.

It is advantageous if a sixth steam line branches off from the second, third, fourth or fifth steam line and opens into an intake air preheating system of a gas turbine plant. Whenever not the full power of force ^¬ work is required, the steam can (partially or completely) held in the steam turbine for the Air intake Gas turbine plant are passed. Thus, the performance of the gas turbine plant and thus also of the entire system decreases without the partial closing of the Vorleitstufen the efficiency of the system drops sharply. The use of the steam generated in the low-pressure evaporator stage has the ^{advantage ¬} part that for the intake air preheating low heat (because of comparatively low temperature levels) is used. Thus a significant increase in the Teillastwir ^¬ kung degree and also a very high speed Laständerungsge- (upward or downward) of the power plant si ^¬ is chergestellt. The load rate of change is be ^¬ Sonder high when a direct steam-heated air intake heater is used. In addition to the reaction speed, an intake air preheater heated directly with low-pressure steam also has the advantage that it can be controlled by the control of the

Vapor pressure can be controlled very accurately. Both together ^¬ quantitative accepted makes it possible to increase the intake air temperature to close to the allowable limit of the respective gas turbine plant and reduce hitherto conventional large safety margins, which take into account the inertia of a conventional filled with water or glycol intake air system.

Furthermore, it is advantageous if a seventh steam line branches off from the second, third, fourth or fifth steam line and opens into a heat exchanger, which ends in a

Main condensate system is arranged before entering the heat recovery steam generator. In the heat exchanger, the vapor condenses from the low-pressure evaporator stage, whereby the main condensate ^¬ sattemperatur is raised accordingly. The im

Heat exchanger accumulating condensate is on a corre sponding ^¬ pump again in the water-steam cycle ^{eingebun ¬} the. Thus, the steam ^generated in the low-pressure evaporator stage (or a part thereof) can be used with varying sulfur contents in the fuel to increase the condensate inlet temperature into the heat recovery steam generator if required (increased sulfur content). It is expedient if the low-pressure evaporator stage is designed for pressures between 1 and 3.5 bar. The limitation of the minimum pressure level in the entire system (from the low-pressure evaporator stage to the valve at the inlet of the steam ^¬ turbine) to greater than 1 bar (slight pressure over ambient pressure) has the advantage of limiting the flow, avoids the dew point below the exhaust and avoids simple Make the air entry into the water-steam cycle and resulting problems with the power plant chemistry. With further reduction of the evaporator pressure level in the negative pressure range, the heat ^¬ utilization at the cold end of the heat recovery steam generator improved even further, but also the problems dew point undershoot and the cost of steam flow and avoidance of ambient air intake increase. In addition, the usable enthalpy gradient becomes smaller and smaller.

Advantageously, a gas and steam turbine plant comprises a water-steam cycle according to the invention.

The object directed to a method is achieved by a method for operating a combined cycle power plant with a steam turbine and a heat recovery steam generator comprising a low-pressure evaporator stage and a low-pressure evaporator stage arranged in the flow direction of a gas turbine exhaust gas downstream of the low-pressure evaporator stage, in which The low-pressure evaporator stage generated rich ^¬ steam is removed from the heat recovery steam generator.

Advantageously, the saturated steam from the evaporator stage of the heat recovery steam generator Niederstdruck for superheating, via a valve is released before ^¬ supplied to the steam turbine.

Alternatively, it may be advantageous if the saturated steam from the low-pressure evaporator stage of the heat recovery steam generator is overheated by means of a heat recovery steam generator-external superheater before it is fed to the steam turbine. Further, it may be advantageous if the saturated steam is condensed from the evaporator stage of the heat recovery steam generator Niederstdruck-with ^¬ means of a steam compressor before it is supplied to the steam turbine.

It is expedient if the saturated steam from the low-pressure evaporator stage of the heat recovery steam generator is supplied at pressures of the steam turbine in which a steam flowing in the steam turbine is already present as saturated steam or wet steam.

Furthermore, it is expedient if the difference in the pressures of the low-pressure evaporator stage and the low-pressure evaporator stage is less than 10 bar.

Advantageously, the saturated steam from the low pressure evaporator stage of the heat recovery steam generator is fed to an intake air preheating system of a gas turbine plant.

Likewise advantageously, the saturated steam heated from the

Low-pressure evaporator stage of the heat recovery steam generator in heat exchange condensate before entering the heat recovery steam generator.

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 is a gas and steam turbine plant according to the prior

 Technology,

Figure 2 according to the invention It ^¬ a first gas and steam turbine installation, Figure 3 is a second gas and steam turbine plant according to the

Invention and Figure 4 shows a third gas and steam turbine plant according to the invention.

1 shows a gas and steam turbine plant according to the prior art. It comprises a gas turbine plant 24 and a steam turbine plant 28. The gas turbine plant 24 comprises a gas turbine 29 with coupled air compressor 30 and a gas turbine 29 upstream combustion chamber 31 which is connected to a compressed air line 32 of the compressor 30. The gas turbine 29 and the air compressor 30 and a

Generator 33 are arranged on a common shaft 34. The fuel supply takes place via a fuel line 35. The steam turbine plant 28 comprises a steam turbine 3 with a coupled generator 36 and a water-steam cycle 45 of the steam turbine 3 downstream capacitor 37 and a heat recovery steam generator 46. The steam turbine 3 is usually in large plants from several Druckstu - fen (portrait 38, middle 39 and the low pressure stage 40) ^¬ typi cally via a common shaft 41 to the generator 36 at ^¬ drive.

In operation, the still about 550 to 650 ° C hot exhaust gases of the gas turbine 29 are fed to the heat recovery steam generator 46 via an exhaust gas line 42, flow through this from the exhaust gas inlet 43 to the exhaust outlet 44 and leave the

Heat recovery steam generator 46 in the direction of a fireplace, not shown.

On their way through the heat recovery steam generator 46, in the example of FIG. 1, the hot exhaust gases of the gas turbine 29 supply their heat to a third high pressure superheater heating surface 47, further to a third medium pressure superheater heating surface 48, a second high pressure superheater ^{heating surface} 49, a second medium pressure Superheater heating surface 50, a first high ^¬ pressure superheater heating surface 51, a high-pressure evaporator heating surface 52, a third high-pressure preheater heating 53, then a first medium-pressure Überhitzerheizfläche 54, a second high-pressure Vorwärmerheizfläche 55, a ^¬ medium-evaporator heating surface 56, a low-pressure superheater ^¬ heating surface 6, a medium-pressure Vorwärmerheizfläche 57, a first high-pressure Vorwärmerheizfläche 58, then a low ^¬ pressure evaporator heating surface 7 and finally a

Condensate preheater 10.

The condensate preheater 10 can be fed with condensate from the condenser 37 via a condensate line 59 into which a condensate pump unit 60 is connected.

A first part of the heated condensate is fed to the low pressure evaporator stage 5 in the heat recovery steam generator 46, a second part is brought by means of a feedwater pump 61 to a suitable pressure level. About the medium-pressure 62 and high-pressure extraction 63 to the feedwater pump 61, the feed water of a corresponding pressure level in

Heat recovery steam generator 46 is supplied via a feedwater preheater (medium-pressure preheater heating surface 57, first 58, second 55 and third high-pressure preheater heating surface 53), which is connected on the output side to a steam drum 65, 66. The steam drums 64, 65, 66 are each provided with an im

Heat recovery steam generator 46 arranged evaporator heating surface 7, 56, 52 connected to form a water-steam circulation. For discharging live steam, the steam drums 64, 65, 66 are each connected to a superheater arranged in the heat recovery steam generator 46, possibly with a plurality of superheater heating surfaces 6, 54, 50, 48 and 51, 49, 47, the output side via steam lines 67, 68 , 69 is connected to a steam inlet of the steam turbine 3.

The steam superheated in the heat recovery steam generator 46 and fed to the steam turbine 3 is released there by performing mechanical work. The notify by ^¬ stretched in the steam turbine 3 high-pressure steam is supplied to a reheat heat recovery steam generator 70 in the 46th The remaining steam is after the relaxation in the middle 39 and low pressure part 40 of Steam turbine 3 condensed in the condenser 37, and the so ent ^¬ standing condensate is fed back to the heat recovery steam generator 46 via the condensate pump 60, so that a water-steam cycle 45 is formed.

FIG. 2 shows a gas and steam turbine plant 2 according to the invention. The water-steam circuit 1 comprises erfindungsge ^¬ Mäss a Niederstdruck-evaporator stage 8 comprising a Niederstdruck-evaporator 9, which is arranged in the flow direction of gas turbine exhaust gases to the low pressure evaporator stage. 5 An at least first part 10 of a condensate preheater heating surface is arranged directly between the low-pressure evaporator heating surface 9 and the low-pressure evaporator heating surface 7. A second part 11 of the condensate preheater heating surface is in the flow direction of

Gas turbine exhaust of Niederstruck evaporator stage 8 nachge ^¬ switches. Because of overheating of the generated

Low-pressure steam in the heat recovery steam generator 4 is dispensed with according to the invention, a first steam line 12 connects one of the Niederstdruck evaporator 9 associated

Low-pressure steam drum 71 with the steam turbine 3. In the ^¬ se first steam line 12, a valve 13 is arranged to relax the steam. The saturated steam from the low-pressure evaporator stage 8 can also be supplied to the steam turbine 3 without overheating. Then wet protection measures 21 should be provided at a binding point 20 for the saturated steam in the steam turbine 3. Figure 3 shows a second steam line 14, which the

Niederstdruck- evaporator 9 and the low-pressure steam drum 71 connects with a superheater 15, which is arranged outside of the heat recovery steam generator 4. A third steam line 16 branches off from the superheater 15 and opens into the steam turbine 3. The superheater 15 may be electrically, steam, feed water or condensate heated. FIG. 4 shows a further overheating variant of FIG

Niederstdruck vapor. Here 17 connects a fourth Dampflei ^¬ tung the Niederstdruck-evaporator 9 and the associated Niederstdruck ^¬ to steam drum 71 with a Dampfkom- pressor 18, which is in turn connected to the steam turbine 3 via a fifth steam line nineteenth The vapor compressor 18 is typically powered electrically.

Furthermore, FIGS. 2 to 4 show a sixth steam line 22, which branches off from the second 14, third 16, fourth 17 or fifth steam line 19 and discharges into an intake air preheating system 23 of a gas turbine plant 24.

Another application for the evaporator stage in the Niederstdruck-comparison 8 generated steam is also shown in Figures 2 to 4, and although the condensate preheating for fuel change or a change in the sulfur content in the combustion ^¬ material. For this purpose, a seventh steam line 25 branches off from the second 14, third 16, fourth 17 or fifth steam line 19 and ends in a heat exchanger 26, which is arranged in a main condensate system 27.

Claims

claims 1. water-steam cycle (1) of a gas and steam turbine plant (2) comprising a steam turbine (3) and a A heat recovery steam generator (4) having at least one high pressure superheater heating surface (47, 49, 51), a high pressure evaporator heating surface (52), a high pressure preheater heating surface, at least one medium pressure superheater heating surface (48, 50, 54), a medium pressure evaporator heating surface (56 ), a medium pressure Vorwärmerheizfläche (57) and with a Nie ^¬ the pressure evaporator stage (5) comprising a low-pressure superheater heating surface (6) and a low-pressure evaporator heating surface (7), characterized in that (in the heat recovery steam generator 4) a Niederstdruck-evaporator stage (8) comprising a Niederstdruck evaporator heating surface (9) in the flow direction of gas turbine exhaust gases after the low-pressure evaporator stage (5) is arranged. 2. Water-steam circuit (1) according to claim 1, wherein immediately between the Niederstdruck evaporator heating surface (9) and the low-pressure Verdampferheizfläche (7) at least a first part (10) of a condensate Vorwärmerheizfläche in Heat recovery steam generator (4) is arranged. 3. Water-steam circuit (1) according to any one of claims 1 or 2, wherein the low-pressure evaporator stage (8) is followed by a two ^¬ ter part (11) of the condensate Vorwärmerheizfläche in the flow ^¬ direction of gas turbine exhaust. 4. Water-steam cycle (1) according to one of the preceding claims, wherein a first steam line (12) one of Low-pressure evaporator heating surface (9) associated Low-pressure steam drum (71) ver ^¬ binds with the steam turbine (3). 5. water-steam circuit (1) according to claim 4, wherein in the first steam line (12), a valve (13) is arranged to relax a vapor. 6. water-steam cycle (1) according to one of claims 1 to 3, wherein a second steam line (14) one of the Niederst ^¬ pressure evaporator ^heating surface (9) associated Niederstdruck- steam drum (71) with a superheater (15) connects, wel ^¬ cher outside the heat recovery steam generator (4) is arranged and a third steam line (16) branches off from the superheater (15) and flows into the steam turbine (3). 7. water-steam circuit (1) according to claim 6, wherein the superheater (15) is electrically, steam, feed water or condensate heated. 8. Water-steam cycle (1) according to one of claims 1 to 3, wherein a fourth steam line (17) one of the Niederst ^¬ pressure evaporator ^heating surface (9) associated Niederstdruck- steam drum (71) with a vapor compressor (18) connects and the vapor compressor (18) is connected to the steam turbine (3) via a fifth steam line (19). 9. water-steam cycle (1) according to claim 8, wherein the vapor compressor (18) is electrically driven. 10. Water-steam circuit (1) according to claim 4, wherein at a binding point (20) for the saturated steam from the  Low-pressure evaporator stage (8) of the heat recovery steam generator (4) in the steam turbine (3) Wet protection measures (21) are provided. A water-steam circuit (1) according to claim 4, wherein a sixth steam line (22) branches off from said second (14), third (16), fourth (17) or fifth steam line (19) and into an intake air preheating system (23 ) of a gas turbine plant (24) opens. 12. Water-steam cycle (1) according to claim 4, wherein a seventh steam line (25) branches off from the second (14), third (16), fourth (17) or fifth steam line (19) and in a heat exchanger (26) opens, in a Main condensate system (27) is arranged. 13. Water-steam circuit (1) according to any one of the preceding claims, wherein the low-pressure evaporator stage (8) for Pressures between 1 and 3.5 bar is designed. 14. Gas and steam turbine plant (2) with a water-steam circuit (1) according to one of the preceding claims. 15. A method for operating a gas and steam turbine plant (2) with a steam turbine (3) and a heat recovery steam generator (4) comprising a low-pressure evaporator stage (5) and arranged downstream of the low-pressure evaporator stage (5) in the flow direction of a gas turbine exhaust gas Low-pressure evaporator stage (8), characterized in that in the Low-pressure evaporator stage (8) generated saturated steam is removed from the heat recovery steam generator (4). 16. The method of claim 15, wherein the saturated steam from the low-pressure evaporator stage (8) of the heat recovery steam generator (4) for overheating via a valve (13) is relaxed before ^¬ the steam turbine (3) is supplied. 17. The method of claim 15, wherein the saturated steam from the Niederstdruck-evaporator stage (8) of the heat recovery steam generator (4) by means of a heat recovery steam generator external superheater (15) is superheated before it is fed to the steam turbine (3). 18. The method according to claim 15, wherein the saturated steam from the low-pressure evaporator stage (8) of the heat recovery steam generator (4) by means of a vapor compressor (18) is compressed before ^¬ the steam turbine (3) is supplied. 19. Method according to claim 15, wherein the saturated steam from the low-pressure evaporator stage (8) of the heat recovery steam generator (4) is supplied at pressures of the steam turbine (3) in which A steam flowing in the steam turbine (3) is already present as saturated steam or wet steam. 20. The method of claim 15, wherein the saturated steam from the low-pressure evaporator stage (8) of the heat recovery steam generator (4) via wet protection measures (21) in the steam turbine (3) is initiated. 21. The method according to any one of claims 15 to 20, wherein the difference of the pressures of the low pressure evaporator stage (5) and the low pressure evaporator stage (8) is less than 10 bar. 22. The method of claim 15, wherein the saturated steam from the low-pressure evaporator stage (8) of the heat recovery steam generator (4) is supplied to an intake air preheating system (23) of a gas turbine plant (24). 23. The method of claim 15, wherein the saturated steam from the low-pressure evaporator stage (8) of the heat recovery steam generator (4) in the heat exchange condensate before entering the Heat recovery steam generator (4) heated.