EP0783619B1 - Method of operating a gas and steam turbine plant - Google Patents

Description

The invention relates to a method for operating a gas and steam turbine plant according to the preamble of Claim 1. Such a method is from the patents DE 38 15 536 C 1 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 heat recovery steam generator and solar heated Steam generator and with an additional combustion chamber downstream Fossil heated heat exchanger is out of 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 is extremely 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 method to operate a gas and steam turbine plant, with a particularly high overall efficiency the plant uses one of a variety of gas turbines freely selectable gas turbine of different output sizes is possible.

With regard to the method of the type mentioned at the beginning, this is Object achieved by the characterizing Features of claim 1.

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 sub-stream of the feed water is preheated from the steam turbine by means of bleed steam. Here the three partial flows of the feed water are preheated 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 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 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 will.

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 plant 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 stream 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 heating surfaces a medium pressure preheater or economizer 62 and one 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 as well 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 as well as a high pressure evaporator 76 and a high pressure superheater 78. The High-pressure superheater 78 is on the output 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 economizers 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 in the flow direction of the partial flow t _{2 of} the exhaust gas A from the gas turbine 2 arranged before the series connection of 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 supplied 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 arises when the partial flow t _{1 of} the exhaust gas A from the gas turbine 2 is produced during the combustion of the fossil fuel B is used there to generate steam and then leaves the fired steam turbine 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 waste heat 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 heat recovery 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 passed} 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. Method for operating a gas-turbine and steam-turbine plant (1), in which the oxygenous exhaust gas (A) from the gas turbine (2) is utilized for steam generation, a first part stream (t₁) of exhaust gas (A) from the gas turbine (2) being used as combustion air for the combustion of a fossil fuel (B), and a second part stream (t₂) of exhaust gas (A) from the gas turbine (2) being utilized for waste-heat steam generation, in which method the steam generation takes place by the combustion of the fossil fuel (B) and the waste-heat steam generation takes place in a common water/steam circuit (12) of the steam turbine (10), feed water of the water/steam circuit (12) being preheated in part streams (S₁ to S₃), characterized in that the preheating of a first part stream (S₁) of feed water takes place by means of flue gas (R, t₁) occurring during the combustion of the fossil fuel (B), the preheating of a second part stream (S₂) of feed water takes place by means of the second part stream (t₂) of exhaust gas (A) from the gas turbine (2) and the preheating of a third part stream (S₃) of feed water takes place by means of steam from the steam turbine (10).
2. Method according to Claim 1, characterized in that the preheating of the three part streams (S₁ to S₃) of feed water takes place in a multi-stage manner, the preheating of the first part stream (S₁) and of the third part stream (S₃) taking place in a second preheating stage (88) common to these by means of the flue gas (R, t₁) occurring during the combustion of the fossil fuel (B).
3. Method according to Claim 1 or 2, characterized in that a cold-air stream (KL) is admixed with the first part stream (t₁) of exhaust gas (A) from the gas turbine (2) serving as combustion air.
4. Method according to one of Claims 1 to 3, characterized in that the first part stream (t₁) of exhaust gas (A) from the gas turbine (2) serving as combustion air is purified together with the flue gas (R) occurring during the combustion of the fossil fuel (B).

Images