EP2801759A1 - Steam bypass in a waste heat steam generator - Google Patents

Abstract

The invention relates to a heat recovery steam generator (1) comprising a pressure stage (3, 4) with at least two superheaters (5, 6, 7, 8), of which one in the steam flow direction the last superheater (5, 6) of the pressure stage (3, 4 ) and the other of the penultimate superheater (7, 8) of the pressure stage (3, 4), wherein the penultimate (7, 8) and the last superheater (5, 6) via a steam line (9, 10) are interconnected, wherein a steam bypass (11, 12) to the penultimate superheater (7, 8) opens into the steam line (9, 10). The invention further relates to a gas and steam turbine plant (2).

Description

The invention relates to a heat recovery steam generator and relates to a steam temperature control by means of steam diversion. The invention further relates to a gas and steam turbine plant.

To protect the thermally highly loaded areas of the heat recovery steam generator and the steam turbine, the steam temperature must be carefully controlled in the gas and steam turbine plant or limited to a maximum value.

As a standard solution for steam temperature control usually injection coolers are used. The feed water is injected into the superheated steam, thereby achieving a cooling effect.

The main disadvantages of this method are above all the loss of efficiency, thermal stresses and the risk of droplet entry.

The object of the invention is therefore to provide a heat recovery steam generator of the type mentioned, which allows a high efficiency and a material-saving operation. Another object of the invention is the specification of a gas and steam turbine plant.

The invention solves this problem by providing that in such a heat recovery steam generator, comprising a pressure stage with at least two superheaters, one of which is the last superheater of the pressure stage in the steam flow direction and the other of the penultimate superheater of the pressure stage, the penultimate and the last superheater are connected to each other via a steam line, a steam bypass to the penultimate superheater opens into the steam line. By this measure, the usual Zwischeneinspritzkühler be replaced by steam bypasses. The provision of steam instead of water eliminates the risk of droplet entry. Furthermore, it is ensured by feeding the colder steam before the last superheater, that its material is not thermally overstressed during operation.

In an advantageous embodiment, the heat recovery steam generator is designed as a multi-pressure boiler. Here, several (usually up to three) steam generators, which operate at different pressure levels and each include superheater, evaporator and economizer, connected in series with one another on the flue gas side. The steam temperature control can then either alternatively or additionally perform both in the medium-pressure stage and in the high-pressure stage, when the pressure stage with the vapor bypass is corresponding to a medium or high pressure stage.

The invention is not limited to a particular type of boiler. In an advantageous embodiment, the heat recovery steam generator is a drum boiler (forced circulation or natural circulation boiler), and in an alternative advantageous embodiment, the heat recovery steam generator is a forced flow boiler (e.g., Benson).

In the medium-pressure stage of the heat recovery steam generator, the steam bypass branches off in order to be as short as possible in the steam flow direction behind a mixing point of medium pressure steam and cold reheater steam from a steam line leading to the next to the last superheater. In principle, however, the steam bypass can also take place before the mixing point from the cold reheater steam line.

The steam bypass is not limited to the bypass of a single superheater. If more than two superheaters provided in a pressure stage, it may be advantageous if the Steam bypass already branches off from a steam line leading to a first superheater of the pressure stage.

Finally, it is advantageous for a gas and steam turbine plant to comprise a gas turbine, a waste heat steam generator connected downstream of the gas turbine on the exhaust gas flow side, and a steam turbine downstream of the waste heat steam generator on the steam side.

One of the numerous advantages of the invention is the elimination of the intermediate sprays. Only the final spray for startup is needed, i. the injection cooler in the main steam line to the high-pressure part of the steam turbine or in the hot superheater line to the medium-pressure part of the steam turbine. During normal load operation, this spray is inactive, i. There is no danger from droplet entry. Likewise, thermal stresses due to large temperature differences in the injection of water during normal load operation no longer represent a danger.

Furthermore, no long hot reheater mixing sections are needed. There is also greater flexibility in the heat recovery steam generator design. The efficiency disadvantage of unintentionally oversized superheaters can be compensated with the steam bypasses.

In addition, there is also an increase in the GUD efficiency at full load and high ambient temperatures or at partial loads and when starting.

At high ambient temperatures, there is no performance difference between forced-circulation boilers (e.g., Benson) and drum boilers (forced circulation or natural circulation).

Due to a higher steam production results in a higher Benson evaporator stability at partial loads.

Finally, the bypass volumes on the last high-pressure economizer are reduced.

• Figur 1 eine Gas- und Dampfturbinenanlage nach dem Stand der Technik und
• Figur 2 eine Gas- und Dampfturbinenanlage nach der Erfindung.

The invention will be explained in more detail by way of example with reference to the drawings. Shown schematically and not to scale:

• FIG. 1 a gas and steam turbine plant according to the prior art and
• FIG. 2 a gas and steam turbine plant according to the invention.

The FIG. 1 shows schematically and by way of example a gas and steam turbine plant 2 with a gas turbine 17, a steam turbine 18 and a heat recovery steam generator 1. About a shaft 19, a rotor of the gas turbine 17, a rotor of a generator 20 and a rotor of the steam turbine 18 are coupled together, the Runners of the steam turbine 18 and the rotor of the generator 20 via a clutch 21 are rotationally separable from one another and coupled. The rotor of the generator 20 and the gas turbine 17 are rigidly connected to each other via the shaft 19. An exhaust gas outlet 22 of the gas turbine 17 is connected via an exhaust pipe 23 to the heat recovery steam generator 1, which is provided for generating the operating steam of the steam turbine 18 from waste heat of the gas turbine 17.

During operation of the gas and steam turbine plant 2, a compressor 24 is driven by the rotating rotor of the gas turbine 17 via the shaft 19, which sucks combustion air from the environment and a combustion chamber 25 supplies. There, the combustion air is mixed with fuel supplied from a fuel supply 26 and burned and the hot, pressurized exhaust gases are supplied to the turbine part 27 of the gas turbine 17 and there relaxed under the power of work. The still about 550 to 650 ° C hot exhaust gases are then fed through the exhaust pipe 23 to the heat recovery steam generator 1 and flow through this from the exhaust gas inlet 53 to the exhaust outlet 54, and pass through a chimney 28 in the area.

The heat recovery steam generator 1 in the example of FIG. 1 is carried out as a multi-pressure boiler with natural circulation and includes a low pressure stage 29, a medium pressure stage 3 and a high-pressure stage 4. On their way through the heat recovery steam generator 1, the hot exhaust gas turbine 17 lead their heat a third high pressure superheater, ie the last superheater 6 of the high pressure stage 4 to , then a second reheater, ie the last superheater 5 of the medium-pressure stage 3, a second high-pressure superheater, ie the penultimate superheater 8 of the high-pressure stage 4, a first reheater, ie the penultimate superheater 7 of the medium-pressure stage 3, and a first high-pressure superheater 15, the other one High-pressure evaporator 30, a high-pressure preheater 31, then a medium-pressure superheater 32, a medium-pressure evaporator 33, a medium-pressure preheater 34, then a low-pressure superheater 35, a low-pressure evaporator 36 and finally a condensate preheater 37th

Overheated steam in the third high-pressure superheater 6 is supplied to a high-pressure stage 39 of the steam turbine 18 by a steam discharge 38, where it is released under the power of work. With the work is - analogous to the work done in the gas turbine 17 - the shaft 19 and thus the generator 20 for generating electrical energy moves. The partially relaxed in the high-pressure stage 39 hot steam is then fed together with steam from the medium pressure superheater 32 the reheaters 7, 5 there again or further superheated and fed via a derivative 40 a medium-pressure stage 41 of the steam turbine 18 and there under power of mechanical work relaxed. The there partially relaxed steam is supplied via an internal supply line of a low pressure stage 42 of the steam turbine 18 and there further relaxed under the release of mechanical energy.

The expanded steam is condensed in the condenser 43 of the steam turbine 18, and the resulting condensate is directly via a condensate pump 44 after heating in the condensate preheater 37 of the low-pressure stage 29 of the heat recovery steam generator. 1 or via a feedwater pump 45 - and provided by this with appropriate pressure - the medium-pressure stage 3 or the high-pressure stage 4 of the heat recovery steam generator 1 fed where the condensate is evaporated. After steam generation and overheating, the steam is supplied via the corresponding outlets 38, 40 of the heat recovery steam generator 1 back to the steam turbine 18 for relaxation and performance of mechanical work.

FIG. 1 also shows injection cooler 46 - 49, for controlling the steam temperature in the steam discharge 38 after the last superheater 6 of the high-pressure stage 4, in the discharge line 40 after the last superheater 5 of the medium-pressure stage 3, in the steam line 9 between the penultimate superheater 7 and the last Superheater 5 of the medium-pressure stage 3 and in the steam line 10 between the penultimate 8 and last superheater 6 of the high pressure stage 4 are arranged and their use mainly brings a loss of efficiency, thermal stresses and the risk of droplet entry with it.

To avoid these disadvantages, in the example of FIG. 2 According to the invention, the injection coolers 48 and 49 replaced by a respective vapor bypass 11, 12th

When steam bypass 12 of the high pressure stage 4, a portion of the high pressure saturated steam directly behind the high pressure evaporator 30 of the steam line 16, which connects the high pressure evaporator 30 and the high pressure drum 50 to the first superheater 15 of the high pressure stage 4, and taken both on the heating surfaces of the first superheater 15 and the heating surfaces of the second and thus last but one superheater 8 of the high-pressure stage 4 and before the heating surface of the third and thus last superheater 6 of the high-pressure stage 4 in the steam line 10, which connects the penultimate superheater 8 with the last superheater 6 of the high-pressure stage 4 , fed and thus fed back into the cycle.

When steam bypass 11 of the medium-pressure stage 3, it is also referred to as HZÜ steam bypass, a part of the cold reheat steam is taken directly behind the mixing point 13 of the medium-pressure steam with the cold reheat steam leading to the penultimate superheater 7 steam line 14 of the medium pressure stage 3 and the penultimate superheater. 7 the medium-pressure stage 3, ie at the first hot reheater heating surface, passed and before the heating surface of the last superheater 5 of the medium-pressure stage 3 in the steam line 9, which connects the penultimate 7 with the last superheater 5 of the medium-pressure stage 3, and thus the cycle again fed. If one accepts a prolonged steam bypass line compared with the solution shown, the steam bypass can in principle also be effected before the mixing point 13, for example from the cold reheater steam line 55.

The desired steam temperature is achieved by a controlled mixture of the steam mass flows at different temperatures. For regulation, corresponding valves 51, 52 are provided in the vapor bypasses 11, 12. In order to be able to divert a sufficient amount of steam, it is also possible to arrange throttle valves or throttle valves 56, 57 in the steam lines 14 and 16 in the steam flow direction either comparatively shortly after branching off of the steam bypasses 11, 12 or shortly before the steam bypasses 11, 12 are integrated ,

Claims (9)

A heat recovery steam generator (1) comprising a pressure stage (3, 4) with at least two superheaters (5, 6, 7, 8), of which the one in the steam flow direction is the last superheater (5, 6) of the pressure stage (3, 4) and the other the penultimate superheater (7, 8) of the pressure stage (3, 4), wherein the penultimate (7, 8) and the last superheater (5, 6) via a steam line (9, 10) are interconnected, characterized that a steam bypass (11, 12) around the penultimate superheater (7, 8) into the steam line (9, 10). Heat recovery steam generator (1) according to claim 1, wherein the heat recovery steam generator (1) is designed as a multi-pressure boiler. Heat recovery steam generator (1) according to one of the preceding claims, wherein the pressure stage (3) is a medium-pressure stage (3). Heat recovery steam generator (1) according to one of the preceding claims, wherein the pressure stage (4) is a high-pressure stage (4). Heat recovery steam generator (1) according to one of the preceding claims, wherein the heat recovery steam generator (1) is a drum boiler. Heat recovery steam generator (1) according to any one of claims 1 to 5, wherein the heat recovery steam generator (1) is a once-through boiler. A heat recovery steam generator (1) according to any one of claims 1 to 3, 5 or 6, wherein the steam bypass (11) is downstream of a mixing point (13) of medium pressure steam and cold reheater steam in the steam flow direction to the penultimate superheater (7) leading steam line (14) branches off. A heat recovery steam generator (1) according to any one of claims 1, 2 and 4 to 6, wherein the steam bypass (12) branches off from a steam line (16) leading to a first superheater (15) of the pressure stage (4). Gas and steam turbine plant (2), comprising a gas turbine (17), a gas turbine (17) downstream of the exhaust gas downstream heat recovery steam generator (1) according to one claims 1 to 8 and the heat recovery steam generator (1) downstream steam turbine (18).

Images