EP0822320B1 - Gas and steam turbine plant - Google Patents

Description

The invention relates to a gas and steam turbine plant according to the preamble of claim 1. Such Appendix is shown in JP-A-4362207. Other gas and steam turbine plants with heat recovery steam generators and fossil-fired Steam generators are from the patents DE 38 15 536 C1 and US 4,852,344 known.

When combining a steam turbine process and one Gas turbine process there are basically two ways to use the exhaust gas from the gas turbine to generate steam. As in the article "Combined gas / steam turbine processes" described in fuel-thermal power (BWK) 31 (1979), No. 5, May, serve in a possible combination process with downstream Steam generator the oxygen-rich exhaust gases from the Gas turbine as combustion air for the fossil-fired Steam generator. In another combination process with a downstream Heat recovery steam generators become gas turbine and steam turbine processes combined by the waste heat of the gas turbine in the Heat recovery steam generator is used. A gas and Steam turbine power plant with waste heat generator and solar heated Steam generator and with an additional combustion chamber downstream fossil heat exchanger is from the DE-OS 41 26 036 known.

In a combined process, the performance of the steam turbine and the gas turbine and the fired steam generator from each other dependent, so that when interpreting such System must be coordinated. This does not only apply to retrofitting an existing one Steam turbine plant, but also for a new plant. The Coordination usually takes place in such a way that during nominal load operation the oxygen demand of the fired steam generator can be covered by the exhaust gases from the gas turbine. It However, gas turbines with only a few different ones Output sizes, for example with 50 MW, 150 MW or 200 MW, manufactured and offered, so that their adaptation to the performance of the steam turbine and that of the steam generator extremely is difficult. Therefore delivers - at a given Plant size - the gas turbine compared to that used as combustion air required amount of exhaust gas for the fired steam generator in the full load range either too large or too small amount of exhaust gas. If the amount of exhaust gas is too small, Full load range only a low efficiency of the system reach, which then gets better in the partial load range.

In contrast, an excessive amount of exhaust gas from the gas turbine can do this cause that in the case of a combination process in which the excess Exhaust gases from the gas turbine at a combustion chamber of the fired steam generator over to a boiler or feed water preheater (Economizer) are passed through this the excessive heat input in an undesirable manner the evaporation begins. Or it has to be with a too large amount of exhaust gas at an early stage in the partial load range the performance of the gas turbine can be reduced. With increasing However, the reduction in the power of the gas turbine takes place Efficiency of the system in the partial load range. With others Words: In both cases, the overall efficiency achieved only limited. Especially when retrofitting one Existing steam turbine plant must therefore have an increase in performance be dispensed with from the gas turbine if the Exhaust heat of the gas turbine is not fully used or an acceptable part-load behavior cannot be achieved.

In contrast to the combined process with downstream fired The steam generator is suitable for the combined process with a downstream one Heat recovery steam generator especially for retrofitting one already existing gas turbine plant. When creating a new system usually a number of gas turbines with a corresponding one Number of heat recovery steam generators on a common Steam turbine switched. Because in this combination process steam generation is limited to pure heat recovery, the overall efficiency of the system is also only limited. In addition, it is also problematic with this combination process when a replacement is required or desired the gas turbine against a gas turbine with a comparatively high Performance to find a suitable gas turbine model. Because with a given power of the steam turbine and thus given design of the heat recovery steam generator would be the Heat input with the exhaust gas from a comparatively large Gas turbine in the heat recovery steam generator too large, so in particular in preheaters arranged inside the steam generator (Economizer) already evaporation in an undesirable manner would take place.

The invention is therefore based on the object of a gas and Specify steam turbine plant, in which at the same time particularly high overall efficiency using one from one Variety of gas turbines of different sizes freely selectable gas turbine is possible.

With regard to the gas and steam turbine system of the aforementioned This object is achieved according to the invention by Art the characterizing features of claim 1.

In the water-steam cycle of the steam turbine is a fossil fired steam generator switched, the water / steam side a heat recovery steam generator is connected in parallel, both the fired steam generator via a first partial flow line as well as the heat recovery steam generator via a second Partial flow line of the gas turbine connected on the exhaust gas side are. The feed water is preheated for both steam generators in several stages.

A first partial flow of the exhaust gas is generated to generate steam the gas turbine for burning a fossil fuel used. A second partial flow of the exhaust gas from the gas turbine is used to generate waste heat, with both the Steam generation by burning the fossil fuel as also waste heat generation in a common water-steam cycle the steam turbine. This is advantageous pressurized feed water of the water-steam cycle preheated in partial flows, the Preheating a first partial flow of the feed water by means of resulting from the combustion of fossil fuel Flue gas occurs. The preheating of a second partial flow of the Feed water takes place by means of the second, the heat recovery steam generator flowing part of the exhaust gas from the Gas turbine. A third partial flow of the feed water is by means of Tap steam preheated from the steam turbine. This is done the preheating of the three partial flows of the feed water expediently multi-stage, the preheating of the first Partial stream and the third partial stream in a common second preheating stage by means of combustion of the flue gas produced from fossil fuel.

The steam turbine process can consist of one or more pressure stages be constructed. A two-pressure system is expedient provided with reheating and condensate preheating. For this purpose, the waste heat steam generator includes a condensate preheater and this upstream medium pressure heating surfaces with a reheater and advantageously arranged at least partially parallel to these on the exhaust side and high pressure heating surfaces connected in parallel on the water / steam side. The reheater located in the heat recovery steam generator is another conveniently provided Reheater of the fired steam generator on the water / steam side connected in parallel.

The invention is based on the consideration that by the combination of pure waste heat use and use as Combustion air divides these types of use of the exhaust gas from the gas turbine regardless of its output size best possible with regard to the overall efficiency of the system is tunable if additionally in the exhaust gas from the gas turbine and in the combustion of fossil fuel Flue gas contained and not for steam generation more usable residual heat is used for preheating the feed water becomes.

In the fired steam generator can advantageously large range of fuels are used. For example as fossil fuel oil, gas, coal or special fuels, such as. Garbage, wood or waste oil can be used. Since when using e.g. Coal as fuel for the fired steam generator the exhaust gas temperature behind the Gas turbine at around 500 ° C for coal drying under certain circumstances is too high, can suitably as combustion air serving first partial flow of the exhaust gas from the Gas turbine be mixed with a cold air stream.

The oxygen-containing exhaust gas from the gas turbine, for example 15% oxygen content serves as the sole combustion air for those to be burned in the fired steam generator fossil fuels, the fired steam generator expediently only with the one required for combustion Exhaust gas volume is applied. A possible one Flue gas cleaning system must therefore only for the first partial flow of the exhaust gas from the gas turbine and not for the whole Exhaust gas volume can be designed, this as combustion air serving first partial flow of the exhaust gas from the Gas turbine along with that when burning the fossil The resulting flue gas is cleaned.

The fired steam generator is in a practical embodiment a flue gas cleaning system downstream of the flue gas side. Since the flue gas cleaning system is only for the first Partial flow of the exhaust gas from the gas turbine and for that in the fossil fired steam generator designed amount of flue gas must not occur with a new system or with a Retrofitting an old system Problems with a required Limiting the size of the cleaning system Space constraints. An undesirable reduction in steam generator output in the case of a cleaning system to be retrofitted, due to the space available on site only for one limited exhaust gas volume is sufficient is therefore not necessary.

To the in the flue gas from the fired steam generator in the first Partial stream of the exhaust gas from the gas turbine still contained To be able to use residual heat as completely as possible is the fired Steam generator a series connection of two flue gas-heated high-pressure preheaters on the water / steam side upstream. This is done in a first high-pressure preheater or boiler economizer all of the fired steam generator supplied feed water preheated while in one second downstream of the boiler economizer on the flue gas side second high pressure preheater or boiler parts economizer only the first partial flow of the feed water is preheated.

The advantages achieved with the invention are in particular in that by combining a fired steam generator and a heat recovery steam generator at the same time Distribution of the exhaust gas from the gas turbine in the steam generators supplied partial streams not only in the fired steam generator a wide range of fuels, e.g. Coal, heavy oil, Low gases or special fuels, e.g. Garbage, wood or Waste oil, can be used. Rather, it can decrease Boiler output of the fired steam generator as a result a fuel conversion of e.g. Oil on coal or as a result of Conversion to a low nitrogen oxide firing is still a special one high steam turbine output and thus a higher system efficiency due to the additional steam generator output be maintained from the heat recovery steam generator.

Because the fired steam generator only with that for combustion required exhaust gas from the gas turbine is applied, is the installation or even in confined spaces Retrofitting a flue gas cleaning system is unproblematic, since the flue gas cleaning system only for a partial flow of the Exhaust gas from the gas turbine and not for the total amount of exhaust gas must be interpreted. In addition, with old systems with high power reserves of the steam turbine system these power reserves through the additional steam production be used in the heat recovery steam generator.

Since the entire exhaust gases of the gas turbine are used almost without loss be a particularly high overall utilization of the Plant achieved. In particular, when replacing an older one Gas turbine model by a modern unit with one comparatively high waste heat supply this waste heat or excess Residual heat is used as best as possible in the heat recovery steam generator become.

An embodiment of the invention is based on a Drawing explained in more detail. The figure shows a circuit diagram a combined gas and steam turbine system with the gas turbine downstream of both a fossil-fired Steam generator as well as a heat recovery steam generator.

The gas and steam turbine system 1 according to the figure comprises a gas turbine system with a gas turbine 2 with coupled Air compressor 3 and one of the gas turbine 2 upstream Combustion chamber 4, which is connected to a fresh air line 5 of the air compressor 3 is connected. In the combustion chamber 4 of the gas turbine 2 opens a fuel or fuel gas line 6. Die Gas turbine 2 and the air compressor 3 and a generator 7 sit on a common shaft 8.

The gas and steam turbine system 1 further comprises a steam turbine system with a steam turbine 10 with coupled Generator 11 and in a water-steam cycle 12 one of the Steam turbine 10 downstream capacitor 13 and a fired steam generator 14 and a heat recovery steam generator 15.

The steam turbine 10 consists of a high pressure part 10a and a medium pressure part 10b and a low pressure part 10c, which drive the generator 11 via a common shaft 16.

A first partial flow line 18 is connected to an inlet 14a of the fired steam generator 14 in order to supply working fluid or exhaust gas A relaxed in the gas turbine 2 to the fired steam generator 14. A first partial flow t _{1 of} the exhaust gas A from the gas turbine 2 with an oxygen content of approx. 15%, which is conducted via the partial flow line 18, serves as combustion air during the combustion of a gaseous, liquid or solid fuel B. This is fired via an inlet 14b Steam generator 14 connected fuel line 20 led into the fired steam generator 14. A control flap 22 connected to the partial flow line 18 is provided for setting the first partial flow t ₁ . During the combustion of the fossil fuel B, the flue gas R formed and the partial flow t _{1 of} the exhaust gas A serving as combustion air from the gas turbine 2 leave the fired steam generator 14 via a flue gas line 24 and after it has been cleaned in a cleaning system 26 in the direction of a (not shown) Stack. The flue gas cleaning system 26 comprises a flue gas desulfurization device and a denitrification device (DeNO _x system) and a dedusting device in a manner not shown. To feed a second partial flow t _{2 of} the exhaust gas A from the gas turbine 2 into the waste heat steam generator 15, a second partial flow line 28 with a control flap 29 is connected to an inlet 15a of the waste heat steam generator 15. The partial flow t _{2 of} the relaxed exhaust gas A from the gas turbine 2 leaves the heat recovery steam generator 15 via its outlet 15b in the direction of the chimney.

Via a third partial flow line or bypass line 30 with a flap 32 is - e.g. when starting and stopping the system 1 - neither for the fired steam generator 14 nor for the waste heat steam generator 15 required exhaust gas A from the gas turbine 2 led. In particular, however, this bypass line 30 is used to discharge the exhaust gas A from the gas turbine 2, if operated alone in so-called single-cycle operation becomes.

A fresh air line 34, into which a blower 36 and a steam-heated heat exchanger 38 and a flap 40 are connected, opens into the partial flow line t ₁ . In comparison to the exhaust gas A from the gas turbine 2, cold fresh air KL can be mixed into the partial flow t _{1 of} the exhaust gas A from the gas turbine 2 via this fresh air line 34.

The heat recovery steam generator 15 comprises a preheater as heating surfaces 42, between its inlet and outlet a circulation pump 44 is switched. The preheater 42 is on the input side connected to the output of a condensate preheater 46, which in turn on the input side via a condensate pump 48 with the Capacitor 13 is connected. The condensate preheater 46 will via one with the low pressure part 10c of the steam turbine 10 connected tap 50 heated with steam. Two the condensate preheater 46 downstream and also over with the Low pressure part 10c connected tap lines 52 and 54 heated Preheaters 56 and 58 are in the heat recovery steam generator 15 arranged preheater 42 connected in parallel and on the output side connected to a feed water tank 60. The heat recovery steam generator 15 further comprises one as heating surfaces Medium pressure preheater or economizer 62 and a medium pressure evaporator 64 and a medium pressure superheater 66, the output side to one with the high pressure part 10a Steam turbine 10 connected steam line 68 and with a reheater 70 is connected. The medium pressure heating surfaces 62, 64, 66 are via the reheater 70 to one in the Medium pressure part 10b of the steam turbine 10 opening steam line 72 connected. The medium pressure heating surfaces 62, 64, 66 and the reheater 70 and the medium pressure part 10b of the Steam turbine 10 thus form a medium pressure stage of the water-steam cycle 12th

The heat recovery steam generator 15 further comprises in a high pressure stage two high-pressure preheaters connected in series as heating surfaces or -Economizer 74 and 75 and a high pressure evaporator 76 and a high pressure superheater 78. The High-pressure superheater 78 is on the outlet side via a steam line 80 with the entrance of the high pressure part 10a of the steam turbine 10 connected.

While the medium-pressure economizer 62 and the high-pressure economizer 74, 75 are arranged within the heat recovery steam generator 15 in the region of the same exhaust gas temperature, the high-pressure evaporator 76 and the high-pressure superheater 78 are off in the flow direction of the partial flow t _{2 of} the exhaust gas A from the gas turbine 2 before the series connection the medium pressure evaporator 64 and the medium pressure superheater 66, the intermediate superheater 70 and the high pressure superheater 78 being arranged in the region of the same exhaust gas temperature.

The feed water tank 60 is via a high pressure pump 82 and a heat exchanger arrangement with a series connection from three preheaters 84, 86, 88 with the fired Steam generator 14 connected. The feed water tank 60 is also via a medium pressure pump 90 with the medium pressure economizer 62 connected.

On the pressure side of the high pressure pump 82 is in the fired steam generator 14 leading feed water line 92 a partial flow line 92a connected via a boiler part economizer 94 between preheaters 86 and 88 the feed water line 92 is connected. This is also via a further partial flow line 92b with the high-pressure economizer 74 connected. The boiler parts economizer 94 and the preheater or boiler economizer 88 are in the Flue gas line 24 of the fired steam generator 14 switched.

The fired steam generator 14 is on the output side via a High-pressure superheater 96, the steam line on the outlet side 80 is connected to the input of the high pressure part 10a of the steam turbine 10 connected. One in the heat recovery steam generator 15 arranged reheaters 70 connected in parallel Intermediate heater 98 is on the input side via the Steam line 68 with the outlet of the high pressure part 10a and on the output side with the medium pressure part 10b of the steam turbine 10 connected. The preheaters 84 and 86 are via steam lines 100 and 102 using bleed steam from the medium pressure section 10b or the high pressure part 10a of the steam turbine 10 is heated.

When the combined gas and steam turbine system 1 is operated, a fuel B ′ is fed to the combustion chamber 4 of the gas turbine 2 in a manner not shown in detail via the fuel line 6. The fuel B 'is burned in the combustion chamber 4 with compressed fresh air L from the air compressor 3. The hot combustion gas V formed during the combustion is conducted into the gas turbine 2 via a gas line 6a. There it relaxes and drives the gas turbine 2, which in turn drives the air compressor 3 and the generator 7. The hot exhaust gas A emerging from the gas turbine 2 is conducted in the first partial flow t ₁ via the partial flow line 18 as combustion air into the fired steam generator 14. The second partial flow t _{2 of} the hot exhaust gas A from the gas turbine 2 is conducted via the partial flow line 28 and through the heat recovery steam generator 15.

The hot flue gas R which is produced by supplying the partial flow t _{1 of} the exhaust gas A from the gas turbine 2 during the combustion of the fossil fuel B is used there to generate steam and then leaves the fired steam generator 14 via the flue gas line 24 in the direction of the flue gas cleaning system 26, previously has first been cooled in the boiler economizer 88 and then in the boiler part economizer 94 by heat exchange with feed water from the feed water tank 60.

The feed water is preheated in three partial flows S ₁ to S ₃ . In this case, a first partial flow S ₁ of the feed water under high pressure, which is adjustable by means of a valve 104 connected to the partial flow line 92 a, is passed through the boiler part economizer 94 and preheated by means of the flue gas R and the partial flow t _{1 of} the exhaust gas A of the gas turbine 2. A second partial flow S ₂ , which can be set by means of a valve 106 connected to the partial flow line 92b, is led through the high-pressure economizers 74 and 75 and preheated by heat exchange with the second partial flow t _{2 of} the exhaust gas A from the gas turbine 2. The preheating of a third partial flow S _{3, which can be} adjusted by means of a valve 108 connected to the feed water line 92, of the feed water under high pressure takes place in the preheaters 84 and 86 by means of bleed steam from the steam turbine 10.

The preheating of the feed water both for the fired steam generator 14 and for the waste heat steam generator 15 is thus carried out in several stages. A two-stage preheating of the feed water partial stream S _{2 takes place} within the heat recovery steam generator 15 in the high pressure economizers 74 and 75 connected in series on the water / steam side. The feed water for the fired steam generator 15 is preheated in three stages. The third partial flow S _3, which is preheated in two stages in the preheaters 84 and 86, is then preheated together with the partial flow S ₁ preheated in parallel in the boiler part economizer 94 in the boiler economizer 88 in the common third stage. This multi-stage preheating of the feed water in three partial streams S ₁ to S ₃ enables a particularly advantageous distribution or division of the feed water between the two steam generators 14 and 15, so that undesired evaporation within their gas-heated preheaters 74, 75 and 88, 94 as a result of an increased Heat input from the partial streams t ₁ and t _{2 of} the exhaust gas A from the gas turbine 2 and from the flue gas R is practically avoided even when using a particularly powerful gas turbine 2.

The steam generated in the waste heat steam generator 15 in the high pressure evaporator 76 and superheated in the high pressure superheater 78 is conducted together with the steam generated in the fired steam generator 14 and superheated in the superheater 96 into the high pressure part 10a of the steam turbine 10. The steam which is partially expanded in the high pressure part 10a is partly overheated again in the superheater 70 arranged in the waste heat steam generator 15 and partly in the intermediate superheater 98 of the fired steam generator 14 and then fed to the medium pressure part 10b of the steam turbine 10. The steam which is further expanded in the medium pressure part 10b is used partly for heating the feed water in the feed water tank 60 and partly for preheating the feed water partial flow S ₃ led through the preheater 84, and partly directly into the low pressure part 10c of the steam turbine 10. The steam released in the low-pressure part 10c is used via the bleed lines 50 to 54 for preheating condensate K fed into the feed water tank 60. The steam emerging from the low-pressure part 10c is condensed in the condenser 13 and conveyed as condensate K via the condensate pump 48 and the preheaters 46, 56 and 58 into the feed water tank 60. The water-steam circuit 12 common to the fired steam generator 14 and the waste heat steam generator 15 is thus closed.

Claims (4)

1. Gas and steam turbine plant, with a steam generator (14) fired by fossil fuel, which is connected into a water/steam circuit (12) of the steam turbine (10) and to which a waste-heat steam generator (15) is connected in parallel on the water/steam side, the gas turbine (2) being followed on the exhaust-gas side both by the fired steam generator (14) via a first part-stream line (18) and by the waste-heat steam generator (15) via a second part-stream line (28), and with a number of preheaters (74, 75, 84, 86, 88, 94) for the multistage preheating of feed water (S₁ to S₃) both for the fired steam generator (14) and for the waste-heat steam generator (15), at least one of the preheaters (88, 94) which precedes the fired steam generator (14) being capable of being heated by flue gas, characterized in that the waste-heat steam generator (15) comprises heating surfaces (42) for condensate preheating and medium-pressure heating surfaces (62, 64, 66) preceding these on the exhaust-gas side and having an intermediate superheater (70), and also highpressure heating surfaces (74, 75, 76, 78) arranged at least partially parallel to these on the exhaust-gas side and connected in parallel with these on the water/steam side.
2. Gas and steam turbine plant according to Claim 1, characterized in that the fired steam generator (14) is followed on the flue-gas side by a flue-gas purification plant (26).
3. Gas and steam turbine plant according to Claim 1 or 2, characterized in that the fired steam generator (14) is preceded on the water/steam side by a series connection of two boiler preheaters (88, 94) heated by flue gas.
4. Gas and steam turbine plant according to one of Claims 1 to 3, characterized in that the fired steam generator (14) is connected to a feed-water tank (60) via at least one preheater (84, 86) heated by means of steam from the steam turbine (10).

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