NO343989B1 - Efficient combined cycle power plant with CO2 capture and a combustion chamber arrangement with separate streams - Google Patents

Description

Title: Efficient combined cycle power plant with CO2 capture and a combustor arrangement with separate streams.

Description

The subject area of the invention

The present invention generally relates to a method for increasing the energy and cost efficiency of a gas power plant or cogeneration plant by capturing CO2. The invention further relates to one or more gas power plants or cogeneration plants and in particular the invention relates to the integration of one or more combined cycle gas turbine plants and a CO2 exhaust gas cleaning plant which is adapted to pressurized flue gas with concentrated CO2 content.

Background

The invention also relates to an adapted combustion chamber. In recent decades, there has been a significant global increase in the amount of emissions of carbon dioxide (CO2). Based on the Kyoto agreement and the "precautionary" principle, it is therefore desirable to limit the emission of greenhouse gases such as CO2 in order to counteract changes in the climate. One measure is to ensure the capture of CO2 in connection with the conversion of energy from fossil fuels in gas power plants and/or cogeneration plants. The various elements in the CO2 value chain include technology for capture, transport and further final storage or use of CO2 for, for example, increased oil recovery in reservoirs (IOR).

Technology development within CO2 capture from combustion processes can be divided into three main categories, where there is currently existing technology that can be realized in plants:

Removal of CO2 before combustion (hydrogen power plant, Pre Combustion Type).

Removal of CO2 after combustion (exhaust gas purification, Post Combustion Type)

Stoichiometric combustion of natural gas and oxygen (oxyfuel type)

Of these three main groups, exhaust gas purification is the technology that has come the furthest, and there are today such facilities in operation on a medium scale. Exhaust gas purification also has the greatest potential for cost reductions, and can most quickly be tested in a demonstration plant.

The existing technology for exhaust gas purification is based on the absorption of carbon after combustion has taken place. A gas power plant of this type is described in open literature, textbooks and publications.

Emissions of CO2 are usually reduced by 85-90% compared to a plant without exhaust cleaning. The exhaust gas from a standard combined cycle gas turbine power plant contains approx. 3.5 volume % CO2 and the exhaust must be cooled down to the normal operating temperature for amine washing, which is around 40-55°C. In the atmospheric absorption tower, CO2 in the gas is transferred to the liquid phase by chemical absorption in the amine solution. It is important to have a large contact surface between gas and liquid, and the tower will be tall and can reach over a meter. For a gas power plant of 400 MW, the amount of gas is approx. 2,500,000 Nm3/h, and the required cross-section in the absorption column will then be 260-320 m2.

In the power plant's regeneration plant, CO2 is then removed from the amine solution by heating the solution to 120-125°C. Steam from the gas power plant is used both for heating, dilution and transport of CO2 out of the plant. After cooling and condensation, CO2 and water are separated, and a desorption column is used to create mass transfer from liquid to steam. The desorption column can have a height of approx. 20 meters and a cross section of 60-150 m2.

The amine solution can then be used for absorption after the heat in the solution has been recovered and the temperature reduced. The desorption process produces a waste that must be handled. For a 400 MW gas power plant, the waste amounts to approx. 90-1500 tonnes/year, of which approx. 30-500 tonnes/year of amine, salts and organic carbon. The regeneration process has a significant energy requirement, and this results in an approx. 20% reduced efficiency in a normal gas power plant for electricity production. A standard gas power plant with this type of exhaust gas cleaning therefore has the disadvantage that both the investment costs and the operating costs are very high, in addition to the fact that the plant is also very space-consuming.

It is also known that more cost-effective plants for CO2 capture exist for other applications, for example CO2 capture from the well flow from natural gas fields, for example as at the Sleipner field in the North Sea, or from synthesis gas production. However, these plants work with completely different operating conditions, i.e. higher pressure and/or higher 3 CO2 concentration, in relation to exhaust gas purification where existing plants usually work at atmospheric pressure and a low CO2 concentration of approx. 3.5 volume %.

In the North Sea, there are platform installations that use an amine absorption plant and a desorption plant, but this CO2 capture plant is significantly smaller in size, cheaper and requires less added energy.

Furthermore, it is known to use CO2 membranes, for example of the polymer type, for pressurized well flow and process gas in facilities, for example in the USA. These plants are even more energy- and cost-efficient. Unlike amine plants, CO2 membrane plants have no liquid part and therefore no regeneration of liquid that would have required added energy.

Another advantage is that it is possible to use a higher temperature, typically 40-100 °C, into the CO2 membrane system. A certain leakage current of N2 can escape through the CO2 membrane, and N2 can be removed after compression to a pressure where CO2 is liquefied so that N2 gas can be separated. However, for injection into oil reservoirs for increased oil recovery, it is probably not necessary to separate N2 and CO2, and it may in some cases be advantageous to have the mixture of N2 and CO2 for increased oil recovery.

Capture plants of the amine plant type for exhaust gas with concentrated CO2 content and/or higher pressure are known from other publications, such as for example WO 95/21683 or WO 00/57900.

To achieve lower NOx emissions from combustion plants, it is known to recycle cooled flue gas using a booster fan back to the combustion chamber.

The document WO 01/75277 describes a power generation system for solid fuel with CO2 capture. In this technique, oxygen is separated from the air and divided into first and second oxygen streams. The first flow of oxygen and a solid fuel, such as coal, is introduced into a solid fuel gasifier to create a combustible gas. The gas is combusted in the presence of the second oxygen stream and water is introduced into the combustor to generate an exhaust stream of CO2 and steam. The exhaust gas is then passed through a turbine to drive the turbine and generate electricity.

The document US 5 937 652 describes a process for coal or biomass fuel gasification with carbon dioxide extracted from a flue gas boiler stream. In this technique, CO2 is separated from a flue gas boiler stream, recycled and used for gasification of coal or biomass to increase fuel utilization and reduce CO2 emissions into the atmosphere.

Summary of the invention

One purpose of the invention is to lay the foundations for power plants where emissions of greenhouse gases and environmentally harmful substances such as amines, salts, etc. are reduced to a minimum or eliminated.

Another purpose is to find more energy- and cost-effective solutions and to reduce, preferably halve, both investment costs and operating costs in relation to existing technology. It is of particular interest to achieve an energy-efficient solution in that the temperature at the inlet to the turbine part is as high as possible, and that a favorable and greatest possible heat transfer is also achieved in the combustion chamber, where the high-quality heat energy can be transferred to the gas sub-flow that goes to the turbine .

It is also an aim to find cost-effective solutions for gas power plants, similar to those used, for example, to capture CO2 from the well flow from natural gas fields, where new capture systems for exhaust gas with concentrated CO2 and higher pressure can be used.

According to the invention, the objectives are achieved by a method, by a combustion chamber and by a power plant, as stated in the independent claims 1, 14 and 16 respectively.

According to the invention, a more efficient power plant is achieved where emissions of CO2 can be reduced by preferably 85-90%, but can also be a lower reduction, i.e. from 0-90%.

Furthermore, a facility is achieved that is simpler to build and does not require such large areas compared to traditional facilities for amine washing, this in particular because a CO2 membrane has a simpler structure and is not based on a liquid part to separate out CO2. Effective utilization of such a CO2 membrane solution, for example of the polymer type, for cleaning flue gas requires that the flue gas is both pressurized and has concentrated CO2.

A further advantage of the solution according to the invention is that the need for large gas/gas heat exchangers can be reduced or eliminated completely. Such large heat exchangers can be difficult to build for temperatures above 600 °C without having to use costly solutions and costly materials.

According to the invention, an energy-efficient heating is achieved in the combustion chamber part, and steam injection in this gas sub-flow before heating in the combustion chamber part can further contribute more positively because the specific heat capacity of the steam is greater than air.

The steam injection also contributes significantly to keeping the turbine's output at a high level by compensating for the volume of CO2 that has been removed in the CO2 membrane system. The consequences are achieved/become a consequence of the invention:

Higher efficiency due to higher temperature at the inlet to the turbine section

Can carry out CO2 separation with a polymer membrane Can use steam injection in one or more of the gas sub-flows.

Can use a semi-closed gas turbine cycle (semi-closed gas turbine cycle) and high CO2 content, because the combustion chamber part is supplied with both compressed air and recycled exhaust gas, so that stable combustion of natural gas is achieved.

Can provide low NOx formation as the combustion chamber part receives both fresh air and recycled exhaust gas so that combustion can take place at an optimal combustion temperature.

Brief description of the figures

In the following, the invention will be described in more detail with reference to the accompanying figures, where:

figure 1 shows schematically in diagram form the principle of a preferred embodiment of a gas power plant according to the invention, where the gas power plant is equipped with a combustion chamber part with separate gas flows according to the invention, the gas power plant being of the type combined cycle gas turbine power plant (CCGT power plant);

figure 2 shows schematically in diagram form the principle and an improved combustion chamber system according to the invention;

figure 3 shows a preferred further embodiment of the principle and a combustion chamber system according to the invention; and

figure 4 shows details of a preferred embodiment that a combustion chamber.

Detailed description of preferred embodiments

In the process that is principally and schematically shown in Figure 1, a gas power plant or cogeneration plant is used, comprising in principle a power plant unit in the form of a combined cycle gas turbine plant and an integrated CO2 capture unit B, for example a CO2 membrane plant 11 which is to separate CO2 from pressurized flue gas with concentrated CO2 content from the combustion chamber 10. The collection unit 11 can be of the polymer membrane type. Alternatively, the CO2 capture unit 11 can be of the amine system type.

Two integrated gas turbine plants 12,12' are used which have common combustion chamber(s) and which work with essentially 6 two separate gas streams, a stream consisting of impure flue gas and a stream consisting, among other things, of purified flue gas.

The gas turbine plant 12' can, for example, be of the semi-closed type.

The combustion chamber comprises a flame tube and a surrounding mantle or jacket 27.

The combustion chamber and its operation will be described in greater detail below with reference to Figures 2-4.

The power plant part also includes one or more exhaust gas boilers 17,18, heat exchangers 19 and, for example, generators 20, 21 for the production of electricity.

As indicated in Figure 1, the plant is supplied with natural gas and air and produces purified exhaust or flue gas, purified CO2 and energy, for example in the form of heat and electricity. Flue gas is led into the CO2 capture unit 11 at a pressure equal to or greater than bar and with a CO2 concentration that preferably exceeds 10%. The flue gas released from the plant is essentially cleaned of CO2.

The CO2 that is secreted in the CO2 capture unit 11 can, for example, be used for increased oil recovery in reservoirs (IOR).

Figure 2 shows a preferred embodiment of a combined cycle gas turbine plant and a CO2 capture plant 11. The gas turbine plant comprises a first gas turbine 12 comprising a compressor part 13, a turbine part 14 and a generator 21 which is driven on the same shaft. The compressor 13 supplies pressurized air to a combustion chamber 10 flame tube through a conduit 15. The air has a temperature of around 400 °C and has a pressure of the order of bar. Fuel in the form of natural gas is also injected into the flame tube 40. The flue gas from the flame tube 40 drives the turbine part 14' of the second turbine plant 12'.

The temperature of the flue gas out of the combustion chamber 10 can typically be in the range of 1200-1400°C, which is the usual inlet temperature for the turbine part of advanced gas turbines. With such a solution, it is desirable that the distance from the combustion chamber 10 to the turbine part 14' is short, in order thereby to be able to reduce the use of expensive high-temperature materials. In this context, reference is made to Figures 1 and 2.

From the turbine part 14', the flue gas with a temperature of approximately 500 °C is led to an exhaust boiler 18 where the flue gas is cooled. The flue gas leaves the flue gas boiler 18 at a temperature of the order of 100 °C and is carried on via a water cooler 16, a water separator 22 and a subsequent booster fan 23 after which the pressurized flue gas is led to the inlet of the compressor part 13' in the second gas turbine 12', where the flue gas is compressed. The water separated in the water separator 22 is led back into the gas flow from the booster 23 in order to thereby regulate the flue gas's molar weight at the inlet of the compressor part 13'. If too little or too much water is separated in the water separator 22, water can be removed or supplied from an external source (not shown).

After the compressor part 13', the pressurized flue gas stream is divided into two sub-streams, with one sub-stream continuing via a simple heat exchanger 19 to the CO2 capture system 1 1. The purified flue gas returns via the heat exchanger 19 and into the jacket 27 on the outside of the flame tube 40. After the purified exhaust gas has circulated through the mantle 27, it is led to the turbine part 14 of the first gas turbine 12 through the pipeline 29. This gas flow typically has a temperature of approximately 800 - 1000°C or higher. From the turbine part 14, the purified flue gas is led through a pipeline to a second exhaust gas boiler 17 for the production of steam using the heat in the purified flue gas before it is released into the environment.

The second partial flow from the outlet of the compressor part 13' in the second gas turbine 12' continues in a recirculation line 24 back to the combustion chamber 10 and into the flame pipe 40 together with fuel and air from the compressor part 13 of the first gas turbine 12. The purpose of the recirculation is to concentrate up the flue gas optimally in front of the CO2 membrane system.

The steam from the exhaust boilers 17 and 18 drives a steam turbine which drives a generator 26. In addition, the exhaust boiler(s) 17,18 supply steam which is introduced into the cleaned flue gas before it is led into the jacket 27 around the flame tube 40. This steam is introduced to compensate for the volume of the 8 secreted CO2. Steam can additionally or as an alternative supply heat to an industrial plant.

Figure 3 shows a similar solution to the solution shown in the figure, but where the only significant difference is that the ethylene unit 28 for additional firing is placed in the pipeline 29 after the outlet from the casing 27 and before the inlet to the turbine part 14 in the first gas turbine 12. The additional firing is done with for example natural gas. This afterburner device raises the temperature of the cleaned exhaust gas from a typical temperature of about 800 QC or higher up to about 1200 - 1400 QC. This will lead to an improvement in the overall plant's efficiency, but will reduce the degree of CO2 removed from the power plant.

In the design example shown in Figures 1-3, two different gas turbines are initially used with regard to usable shaft power, for example in a ratio of 1:3. But other ratios can also be used or similar gas turbines can be used, i.e. ratios between 1:3 and 1:1 can be used with regard to usable shaft power.

However, the gas turbine's other parameters, such as pressure ratio, should be approximately the same. As available gas turbines on the market are only found in standard models with a given design and shaft power, the process shown in Figure 3 can be adapted to given gas turbines.

The gas power plant's combined cycle gas turbines 12, 12' may be of a standard type, with the possible exception of the common combustion chamber 10, which may involve a modification in relation to a standard combustion chamber. It may be possible to modify different types of combustion chambers, such as, but not limited to, external combustion chambers, "silo" type combustion chambers or "canned" type combustion chambers. In addition, there is integration of the CO2 capture facility 1 1 which is of the CO2 membrane type, for example of the polymer type, which is arranged as best as possible for practical implementation and cost efficiency.

Captured CO2 and possible nitrogen that has escaped through the CO2 membrane are removed from the CO2 separator and pumped back, for example, to an oil well for increased oil recovery (IOR = Increased Oil Recovery) or to a suitable landfill.

Reference is made to Figure 4 which shows details of a preferred embodiment of a combustion chamber 10 according to the invention. The combustion chamber is formed by a flame tube 40 and a surrounding mantle or jacket 27. In the process shown in figures 1-3, a standard combustion chamber 10 is used, modified somewhat with regard to controlling the air flows. The constructive design of such a typical standard combustion chamber can be found described in open literature, textbooks and publications. However, a standard combustion chamber is usually used in a different way, as the air is usually first led to the outside of the flame tube 40 (between the mantle 27 and the flame tube 40), and is then led further into the flame tube 40 to the primary zone of the combustion process.

But in the present plant the procedure (air management) is different, as the combustion chamber 10 works with essentially two separate gas streams, one of which goes inside the flame tube 40 and the other goes on the outside of the flame tube 40. It is only the partial flow that goes inside the flame pipe 40 which goes to the CO2 capture system 11.

Compressed air from the compressor 13, natural gas and recycled exhaust gas from the combustion chamber are led into one end 34 of the flame tube 40 through the air supply line 3 1, the natural gas supply 32 and the supply line 33 for recycled exhaust gas, respectively. The burnt exhaust gas leaves the combustion chamber 10 at its opposite end 35.

The purified flue gas, on the other hand, is fed into the mantle 27 at the outlet end of the combustion chamber and is made to circulate around the flame tube 40 on its outside to cool it down, and then leave the mantle 27 in the area of the flame tube 40's primary zone.

Thereby, the combustion in the combustion chamber 10 can take place at an optimal combustion temperature and excess air in order to thereby meet the requirement for a necessary low NOx emission.

A combustion chamber 10 according to the invention is consequently a combination of a combustion chamber and a heat exchanger. Thereby, the combustion in the combustion chamber 10 can take place at an optimal combustion temperature and excess air in order to thereby meet the requirement for a necessary low NOx emission.

Although in the present plant one combustion chamber is described, it may be possible to use several combustion chambers. Furthermore, it should be stated that the combustion chamber is shown entirely schematically, where parts that are obvious to a person skilled in the art are not shown. An example of such an omission is, among other things, the pressure jacket that necessarily surrounds the combustion chamber.

According to the embodiments shown and described, CO2 membrane systems are used, for example of the polymer type, as it is appropriate to use polymeric membranes, for example of cellulose acetate. This type of membrane solution is both well-proven and affordable in acquisition and use, but has limitations with regard to selectivity as a relatively large amount of nitrogen and oxygen in addition to CO2 can escape through the membrane. It may, however, be relevant to use new types of polymer membranes for CO2 capture without thereby deviating from the invention, as such new polymer membranes will make it possible to use higher inlet temperatures and thereby reduce the need for gas/gas heat exchangers.

Claims (20)

Patent claims 1. Method for increasing the energy and cost efficiency of a combined cycle gas turbine power plant and for energy and cost-effective CO2 capture from a pressurized flue gas with concentrated CO2, where the method includes: at least one of providing and operating a combined cycle gas turbine power plant comprising one or more gas turbine plants (12, 12') and/or combined plant with steam and gas turbine cycles, comprising one or more compressor parts (13, 13') and one or several turbine parts (14, 14') and further comprising a combustion chamber (10); in that flue gas from the combustion chamber (10) is cooled and passed through a purification unit (11), where the method further comprises removing at least significant parts of the CO2 content from the flue gas to obtain purified flue gas and where the purified flue gas is heated again and together with pressurized steam they drive one or more turbine parts (14, 14 ') and where the steam is depressurized before being released into the atmosphere, characterized in that the combustion chamber (10) works with mainly two separate gas sub-flows where one gas sub-flow goes inside the combustion chamber (10) flame tube (40) and where the second gas sub-flow goes on the outside of the flame tube (40), the first gas sub-flow comprising additional air and recycled impurity flue gas from the combustion chamber which is burned together with fuel inside the flame tube (40), and the second gas sub-flow comprises purified flue gas which is heated on the outside of the flame tube (40) at the same time as the flame tube (40) cools down. 2. Method according to claim 1, characterized in that the gas power plant is equipped with a first (12) and a second (12') gas turbine, each with its own compressor part (13, 13') and a turbine part (14, 14)'), where the the uncleaned flue gas from the combustion chamber (10) is compressed in the compressor part (13') of the second gas turbine system (12'), the gas sub-flow of flue gas being cleaned and used for heat exchange in the combustion chamber (10) in order to achieve optimal heating of this gas sub-flow in the combustion chamber ( 10), where the heat energy is transferred at the highest possible temperature and where the purified gas partial flow is then supplied to the inlet to the turbine part (14) of the turbine part of the first gas turbine plant (12) in order to operate the first gas turbine plant (12). 3. Method according to claim 2, characterized in that the pressurized part of the flue gas to be cleaned is passed through a CO2 capture unit (11), for example of the polymer type, to remove CO2 from the flue gas. 4. Method according to claim 2, characterized in that steam is injected into the purified gas partial stream before the inlet of the jacket (27) which encloses the flame tube (40) of the combustion chamber (10) to compensate for removed CO2 in the CO2 capture unit (11) and to increase the heat transfer in the combustion chamber (10). 5. Method according to claim 4, characterized in that a gas partial flow from the compressor (13) is supplied to the casing (27) at the outlet of the combustion chamber (10) and is led out of the casing (27) in the area of the combustion chamber (10)'s combustion zone. 6. Method according to any one of claims 1-5, characterized in that the second part of the pressurized, untreated flue gas from the compressor part (13') is recycled back to the flame pipe (40) together with pressurized air and fuel. 7. Method according to any one of claims 1-6, characterized in that the pressure of the flue gas is increased after expansion and cooling, and where parts of the pressurized flue gas are recycled back to the combustion chamber (10) for optimal concentration of CO2 before introduction into CO2- the capture unit (11), preferably in the area of the combustion chamber (10) combustion zone (34). 8. Method according to any one of claims 1-7, characterized in that water is removed from the flue gas prior to a booster fan (57), which pressurizes the flue gas, after which water is added again after passing through the booster fan (57), thereby regulate the molar weight of the flue gas at the inlet to the compressor (13 '). 9. Method according to any one of claims 1-8, characterized in that the flue gas from the gas turbine plant (ones) is fed through a heat recovery steam generator (17, 18) for the production of steam, where parts of the produced steam are fed back to the gas partial flow in front of the jacket (47 ) to the combustion chamber (10). 10. Method according to claim 9, characterized in that the remaining part of the produced steam drives one or more steam turbines (25). 11. Method according to any one of claims 1-10, characterized in that part of the flue gas partial flow is led via a heat exchanger (19) to the CO2 capture unit (11), after which the purified flue gas is returned back via the heat exchanger (19) where it is heated again and possibly mixed with steam and additional air from the compressor (13) to the first gas turbine plant (12), which forms the gas partial flow that goes on the outside of the flame tube (40). 12. Method according to any one of claims 1-11, characterized in that a first and a second series-connected gas turbine plant (12, 12') are used which have common combustion chamber(s) (10), the gas being heated on the outside of the flame pipe (40), possibly passed through a unit (28) for additional firing, and supplied to the turbine part (14) of the first gas turbine plant (12) and where the flue gas formed in the flame pipe (40) goes to the turbine part (14') of the second gas turbine plant (12'), after which the flue gas is supplied to a heat recovery steam generator (18) where the flue gas is cooled and then led via a water cooler (16) to the inlet of the compressor part (13') of the second gas turbine plant (12') where the flue gas is compressed and divided into two flue gas sub-streams. 13. Method according to claim 12, characterized in that a flue gas partial flow goes via a heat exchanger (19) to the CO2 capture unit (11), after which the purified flue gas returns via the heat exchanger (19) where the flue gas is heated again and then mixed with steam and then is circulated around the outside of the flame tube (40). 14. Combustion chamber for use in a heat or gas power plant which comprises at least one gas turbine plant or a combined cycle gas turbine plant and which further comprises a combustion chamber (10) which has a flame pipe (40), a heat exchanger (19), a plant (11) for C02 capture from the flue gas from the combustion chamber (10) and at least one heat recovery steam generator (17, 18) and associated pipelines between the various parts of the gas turbine plant, where the combustion chamber (10) comprises a combustion zone (34), pipelines (31, 32) for supplying air and fuel and an outlet pipe (29) for exhaust gas at the opposite end (35) of the combustion zone (34), where the jacket (27) for circulation of a cooling gas is arranged around the flame pipe (40), the inlet for the cooling gas is arranged in the area of the outlet pipe (29) for the flue gas, while the outlet from the jacket (27) is arranged in the area of the combustion zone (34), so that the cooling gas is caused to circulate through the jacket (27) in the direction from the outlet pipe (29) for the exhaust gas towards the burning zone (34). 15. Combustion chamber according to claim 14, characterized in that the combustion chamber (10) is equipped with a supply line (33) for recycled exhaust gas. 16. Power plant comprising at least one gas turbine plant or a combined cycle gas turbine plant, comprising at least two gas turbine plants (12, 12 '), each comprising a compressor part (13, 13') and a turbine part (14, 14 '), where the thermal power plant further comprises a combustion chamber (10) according to claim 14, a heat exchanger (19), a plant (11) for capturing CO2 from the flue gas from the combustion chamber (10) and at least one heat recovery steam generator (17, 18) and associated pipelines between the various plants and units in the gas turbine plant , characterized in that a purified gas partial flow from the flame pipe (40) is led through a pipe from the compressor part (13') of the gas turbine plant (12') and injected steam to a jacket (27) which surrounds the combustion chamber (10) and is led further through an outlet pipe (29) ) from the jacket (27) to the inlet of a turbine part (14) in the first gas turbine plant (12), the gas circulating through the jacket (27) being used to cool the combustion chamber (10) in order to achieve optimal heating thereof. 17. Power plant according to claim 16, characterized in that the CO2 capture unit (11) comprises a CO2 membrane system, preferably of the polymer type. 18. Power plant according to claims 16 and 17, characterized in that a second impure gas partial flow from the flame tube (40) is injected into the flame tube (40) together with additional air and fuel. 19. Power plant according to claim 17 or 18, characterized in that the supply pipe for purified flue gas is connected to the jacket (27) at the outlet side of the combustion chamber (10), while the outlet pipe (29) from the jacket (27) is connected to the jacket (27) at the combustion zone of the combustion chamber (10). 20. Power plant according to any one of claims 17-19, characterized in that the turbine plant comprises two connected gas turbine plants where the first gas turbine plant (12) is powered by purified flue gas from the combustion chamber (10), while the second gas turbine plant (12') is powered by purified flue gas from the combustion chamber (10), which is possibly mixed with steam supplied from a steam source (17, 18) and air supplied from the compressor part (13) of the first turbine plant (12).