Power generation system and method including a gas turbine with heat recovery steam generator and carbon dioxide capture

Abstract

The gas turbine system (1) comprises a gas turbine engine (3), a first fuel line (4) adapted to deliver fuel to the gas turbine engine (3), a heat recovery steam generator (11) adapted to receive flue gas exhausted from the gas turbine engine (3), and a second fuel line (39) adapted to deliver fuel to a post burner (37) of the heat recovery steam generator (11). The carbon dioxide capture unit (31) is fluidly coupled to a chimney (25) of the heat recovery steam generator (11). The recirculation line (33) recirculates the flue gas from the chimney (25) of the heat recovery steam generator (11) to the post burner (37) in the heat recovery steam generator (11). The carbon dioxide return lines (51, 61) recirculate a stream of carbon dioxide-containing gas from the carbon dioxide capture unit (31) towards the gas turbine engine (3) or towards the post burner (37). Also disclosed herein is a method for generating electricity with improved carbon dioxide capture.

Description

[Technical field]

[0001] The present disclosure relates to removing carbon dioxide from the flue gases of a gas turbine system. In particular, embodiments disclosed herein relate to removing carbon dioxide from the flue gases of a combined gas turbine cycle by post combustion. [Background technology]

[0002] Carbon dioxide represents the largest proportion of greenhouse gases, which are the main cause of climate change and the increase in environmental temperature. Numerous human activities involve the production of carbon dioxide. Among them, electricity generation using fossil fuels, including coal, oil, and natural gas, plays a major role. Recently, in an attempt to stimulate research into technological solutions aimed at reducing carbon dioxide emissions into the atmosphere, many governments have applied a carbon tax on every tonne of greenhouse gas emissions. Businesses as well as consumers, who ultimately bear the additional costs caused by the tax, are prompted to take steps such as switching from fossil fuels to renewable energy sources or adopting new technologies to reduce greenhouse gas emissions and thus limit the amount of carbon tax they pay.

[0003] Carbon dioxide emissions can be reduced and prevented from being released into the atmosphere by switching to alternative energy sources or by capturing carbon dioxide from flue gases produced by the combustion of fossil fuels. Several techniques have been developed aimed at capturing carbon dioxide from flue gases to reduce the amount of greenhouse gases released into the atmosphere.

[0004] When designing large-scale power plants, it will become increasingly important to implement effective measures to improve carbon dioxide capture, in addition to the efficiency of the thermal cycle that converts thermal energy into useful mechanical energy and ultimately electrical energy.

[0005] The main problem in removing carbon dioxide from flue gas produced by a combustion process, such as the combustion of fossil fuels in a gas turbine engine, is presented by the low concentration of carbon dioxide in the flue gas and the low pressure of the flue gas (near ambient pressure). These factors make the capture process inefficient and expensive. Carbon dioxide capture becomes an effective method of reducing carbon dioxide emissions only if the savings in terms of carbon taxes are higher than the costs of the carbon dioxide capture process, both in capital expenditures as well as the costs to operate the system.

[0006] In reality, carbon dioxide capture systems are not only expensive to build and space-demanding, but also require significant power to operate.

[0007] Gas turbine combined cycles include a top gas turbine cycle (Bryton cycle) and a bottom steam cycle (Hirn cycle or Rankine cycle) that recovers heat from the flue gas of the gas turbine to generate additional power for a steam turbine. The flue gas from the gas turbine is cooled in a heat recovery steam generator (HRSG) to generate superheated steam, which is then expanded in the steam turbine to generate mechanical power. The mole percentage of carbon dioxide in the exhausted flue gas at about ambient pressure and about 90°C is about 3-3.5%. Processing such CO2-lean flue gas in a carbon dioxide capture unit has been found to be inefficient and adversely affects the overall plant efficiency.

[0008] Embodiments of combined cycles and simple gas turbine cycles including a heat recovery steam generator and a carbon dioxide recovery unit are disclosed in EP 3756752. In these known embodiments, a flue gas stream from a gas turbine power plant is split into a first flue gas stream and a second flue gas stream. The first flue gas stream flows through a first heat recovery steam generator and the second flue gas stream bypasses the first heat recovery steam generator. A portion of the first flue gas stream can be discharged to the environment through a stack. The remaining first and second flue gas streams are joined together and fed through a further heat recovery steam generator combined with a nitric oxide removal unit for selective catalytic removal. The nitric oxide removal unit is fed with a reducing agent for catalytic reaction with the nitric oxides. The temperature of the flue gas flowing through the nitric oxide removal unit is adjusted by modulating the flow rates of the first and second flue gas streams and the amount of flue gas discharged to the environment downstream of the first heat recovery boiler so that an optimal temperature is achieved in the nitric oxide removal unit. Once nitric oxides are removed from the flue gas flowing through the nitric oxide removal unit, the flue gas is treated in a carbon dioxide capture unit. Carbon dioxide is removed from the flue gas and the carbon dioxide-free flue gas is discharged to the environment. The captured carbon dioxide can be compressed and further processed for storage or transport purposes. These known systems do not effectively improve the efficiency of the carbon dioxide capture facility. Summary of the Invention [Problem to be solved by the invention]

[0009] Therefore, it would be beneficial to provide a system and method for concentrating the carbon dioxide content in flue gas to make carbon dioxide capture more efficient.

[0010] According to one aspect, a gas turbine system is disclosed herein that includes a gas turbine engine, a first fuel line adapted to deliver fuel to the gas turbine engine, and a heat recovery steam generator adapted to receive flue gas exhausted from the gas turbine engine. The system further includes a second fuel line adapted to deliver fuel to a post burner of the heat recovery steam generator. A carbon dioxide capture unit is fluidly coupled to a chimney of the heat recovery steam generator and adapted to capture carbon dioxide from the flue gas exhausted from the heat recovery steam generator. A recycle line recirculates the flue gas from the chimney of the heat recovery steam generator to the post burner in the heat recovery steam generator to increase the carbon dioxide concentration in the flue gas flowing through the carbon dioxide capture unit.

[0011] To further increase the carbon dioxide concentration in the flue gas processed by the carbon dioxide capture unit, according to embodiments disclosed herein, at least one carbon dioxide return line is provided to recirculate the stream of carbon dioxide-containing gas that has been at least partially processed by the carbon dioxide capture unit towards the gas turbine engine, the post burner, or both.

[0012] Thus, the mechanical power generated by the gas turbine engine may be used to drive a rotating machine, such as a compressor or a compressor train, and in some embodiments, the mechanical power may be converted, fully or partially, to electrical power.

[0013] The steam produced by the heat recovery steam generator can be used in any process where high temperature steam is needed, such as in the paper industry. The thermal power contained in the steam can also be used for air conditioning or heating purposes, such as district heating.

[0014] In some embodiments, the steam generated by heat recovery steam generation is used as a working fluid in a bottom heat cycle, such as a Rankine cycle or Hirn cycle, to generate additional mechanical and / or electrical power.

[0015] In an advantageous embodiment, the gas turbine system of the present disclosure may be part of a natural gas liquefaction plant to provide electrical, mechanical, and thermal energy.

[0016] As described in more detail below, with reference to an exemplary embodiment of a system according to the present disclosure, the carbon dioxide-containing stream may be diverted downstream of the carbon dioxide capture unit, where the stream contains a majority of carbon dioxide. In other embodiments, the carbon dioxide-containing gas stream may consist of or contain flue gas from a heat recovery steam generator that has been cooled by the carbon dioxide capture unit, for example in a direct contact cooler of a cooled ammonia process system.

[0017] The flow of carbon dioxide-containing gas returned from the carbon dioxide capture unit can be delivered to the suction side of the air compressor of the gas turbine engine. This option is particularly beneficial, for example, when the recirculated carbon dioxide-containing gas stream contains cooled flue gas discharged by a direct contact cooler of a cooled ammonia process. In other embodiments, the carbon dioxide can be recirculated to a fuel skid that feeds the combustor of the gas turbine engine and / or the post-combustor of a heat recovery steam generator.

[0018] According to a further aspect, provided herein is a method for generating electrical power using a gas turbine system, the method comprising the steps of: delivering air and fuel to a gas turbine engine to generate mechanical power; flowing flue gas exhausted from the gas turbine engine through a heat recovery steam generator; providing fuel to a post burner of a heat recovery steam generator; generating steam in a heat recovery steam generator; recirculating a portion of the flue gas exhausted from the heat recovery steam generator to the post burner; treating the remaining flue gas exhausted from the heat recovery steam generator in a carbon dioxide capture unit to remove carbon dioxide from the flue gas; and recirculating a stream of carbon dioxide containing gas from the carbon dioxide capture unit towards at least one of the gas turbine engine and the post burner.

[0019] Further embodiments of the systems and methods of the present disclosure are generalized below and claimed in the accompanying claims. [Brief description of the drawings]

[0020] Reference will now be made briefly to the accompanying drawings, in which: [Figure 1] FIG. 1 illustrates a system including a combined gas turbine cycle with post-combustion and carbon dioxide capture, according to one embodiment. [Diagram 2] FIG. 2 illustrates a system including a combined gas turbine cycle with post combustion and carbon dioxide capture, according to a further embodiment. [Diagram 3] FIG. 3 illustrates a system including a combined gas turbine cycle with post combustion and carbon dioxide capture, according to a further embodiment. [Figure 4] FIG. 4 illustrates a system including a combined gas turbine cycle with post combustion and carbon dioxide capture, according to yet a further embodiment. [Diagram 5] FIG. 5 illustrates a schematic of a cooled ammonia process for carbon dioxide capture that can be used in the systems of FIGS. [Figure 6] FIG. 6 is a flow chart summarizing the method of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] To improve the carbon dioxide capture efficiency in a system including a gas turbine engine and a heat recovery steam generator with a post-combustor, a stream of carbon dioxide-containing gas is diverted from the carbon dioxide capture unit and recirculated to the gas turbine engine, to the post-combustor of the heat recovery steam generator, or both. Specifically, the stream of carbon dioxide-containing gas can be diverted from the carbon dioxide exhaust of the carbon dioxide capture unit, where the recirculated stream contains mainly carbon dioxide. Alternatively or in combination, the flue gas exhausted from the heat recovery steam generator is cooled in a section of the carbon dioxide capture unit as a first step of the carbon dioxide capture process. A portion of the cooled flue gas is diverted and recirculated to the gas turbine engine, and the remaining cooled flue gas is further processed through the carbon dioxide capture unit.

[0022] Referring now to the drawings, FIG. 1 illustrates a first embodiment of a power generation system 1 including a gas turbine engine and a carbon dioxide capture unit.

[0023] The system 1 includes a gas turbine engine 3 drivingly coupled to a first generator 5. The gas turbine engine 3 may include any type of gas turbine adapted to drive the generator 5. For example, the gas turbine engine 3 may include a heavy duty gas turbine, or an aero-derivative gas turbine, such as a 1-spool, 1.5-spool, 2-spool, or 3-spool gas turbine engine.

[0024] The gas turbine engine 3 generally includes an air compressor section 3.1, which may include one or more air compressors, e.g., a low pressure air compressor and a high pressure air compressor. The gas turbine engine 3 further includes a gas turbine combustor 3.2, which is fed with fuel through a fuel line 4 and a turbine section 3.3. The turbine section 3.3 may include one or more turbine wheels. One or more shafts 6 connect the turbine wheels to the air compressor and a first generator 5.

[0025] The first generator 5 may be electrically connected to an electrical grid 7 that may power the electrical devices and machines of the system. In particular, the electrical power generated by the first generator 5 may be used to power an electric motor, which in turn drives a machine, such as a turbomachine, e.g., a compressor or compressor train.

[0026] In other embodiments, the gas turbine engine 3 may be drivingly coupled to a driven machine, such as a compressor or compressor train, such that the mechanical power generated by the gas turbine engine 3 is used to directly drive the driven machine without converting the mechanical power to electrical power.

[0027] In some embodiments, the compressor or compressor train powered directly or indirectly by the gas turbine engine 3 may be a refrigerant compressor in a natural gas liquefaction system adapted to liquefy natural gas, or a gas compressor for a natural gas pipeline, etc.

[0028] The exhaust end of the gas turbine engine 3 is fluidly coupled through a flue gas duct 9 to a heat recovery steam generator 11. As described in more detail herein below, the heat recovery steam generator removes heat from the flue gases of the gas turbine engine 3, thereby generating steam. In the embodiment of FIG. 1, the system 1 is a combined gas turbine cycle, and the steam generated in the heat recovery steam generator is used in a bottom cycle 13 including a steam turbine 15 that can be drivingly coupled to a second generator 17. The steam turbine 15 converts a portion of the thermal power contained in the hot pressurized steam into mechanical power to drive the generator 17. This latter can be coupled to an electrical grid 7.

[0029] 1, steam turbine 15 includes a high pressure steam turbine section 15.1 and a low pressure steam turbine section 15.2. In other embodiments, not shown, a different number of steam turbine sections may be envisioned.

[0030] The superheated steam may be delivered to the inlet of the high pressure steam turbine section 15.1 through a superheated steam line 15.3. The partially expanded steam from the high pressure steam turbine section 15.1 may be returned to the heat recovery steam generator 11 through a steam return line 15.4 to be re-superheated at a lower pressure before being delivered to the low pressure steam turbine section 15.2 through a second superheated steam line 15.5.

[0031] In other embodiments, overheating twice may be avoided or overheating more than twice may be envisaged.

[0032] The bottom cycle 13 further comprises a condenser 19 and a pump 21 which circulates the pressurized water back to the heat recovery steam generator 11 along a water duct 23 .

[0033] In the embodiment shown in the drawings, the bottoms cycle is a Rankine cycle with regeneration. In the exemplary embodiment shown in Figure 1, a partial flow of partially expanded steam is diverted from the low pressure steam turbine section 15.2 or a point upstream thereof in regeneration line 15.6 and added to the cold pressurized water delivered by pump 21 (at 15.7) before reaching the heat recovery steam generator 11.

[0034] In other embodiments, regeneration may be omitted or more than one regeneration step at different temperature and pressure levels may be foreseen.

[0035] In another embodiment, not shown, system 1 may be a cogenerative system that generates mechanical power through gas turbine engine 3 to generate heating steam in heat recovery steam generator 11, which is used in a steam turbine for purposes other than generating electricity.

[0036] The exhaust flue gas from the heat recovery steam generator 11 is discharged through a chimney 25. The exhaust flue gas still contains a certain amount of residual oxygen, which is at least partially utilized in a post-combustion process in the heat recovery steam generator 11 for the purpose of increasing the carbon dioxide content of the flue gas.

[0037] The flue gas stream from the chimney 25 is split into a main stream which is delivered via line 29 to a carbon dioxide capture unit 31 and a recirculated stream which is delivered again via a recirculation line 33 including a blower 35 to the heat recovery steam generator, more specifically to a post burner 37 of the heat recovery steam generator 11. Reference numeral 39 denotes a fuel line which delivers fuel to the post burner 37. Flue gas from the gas turbine engine 3 is mixed with the recirculated flue gas stream from the recirculation line 33 and mixed with fuel from the fuel line 39 to combust the fuel in the post burner 37.

[0038] Post-combustion in post burner 37 increases the mole percentage (%mol) of carbon dioxide and reduces the residual oxygen content in the flue gas delivered to the carbon dioxide capture unit 31. The additional heat power generated by the post-combustion of the heat recovery steam generator 11 generates an additional amount of steam, i.e., because higher heat power is made available by the combustion of the fuel delivered through fuel line 39, the amount of steam generated by the heat recovery steam generator is increased relative to the amount of steam generated by a heat recovery steam generator that does not include a post burner.

[0039] The carbon dioxide capture unit 31 can be based on any suitable carbon dioxide capture technology. In some embodiments, the carbon dioxide capture unit 31 can be based on the so-called chilled ammonia process (CAP), which uses an ammonia solution to cool the flue gas and remove carbon dioxide therefrom. According to other embodiments, the carbon dioxide capture unit 31 can for example perform a mixed salt process (MSP), or include a membrane separation facility, or can be based on any other technically and economically feasible carbon dioxide capture process.

[0040] Regardless of the nature of the carbon dioxide separation and the abatement process used by the carbon dioxide capture unit 31, the effect of the flue gas treatment in the carbon dioxide capture unit 31 is to remove at least a portion of the carbon dioxide from the flue gas delivered through line 29. Through line 41, a CO2-lean flue gas containing a reduced amount of carbon dioxide or no carbon dioxide is discharged to the atmosphere. The carbon dioxide removed from the flue gas forms a stream consisting almost entirely of carbon dioxide, which is delivered through a carbon dioxide exhaust duct 43. The carbon dioxide from the exhaust duct 43 can be stored in a suitable CO2 storage site, such as, for example, abandoned oil and gas fields, deep saline formations, or other storage sites adapted for this purpose.

[0041] In some embodiments, a portion of the steam generated by the heat recovery steam generator 11 may be used to operate the carbon dioxide capture unit 31, to which steam may be delivered directly from the heat recovery steam generator 11 through a water steam line 47. In addition to or instead of the water steam line 47, steam may also be delivered to the carbon dioxide capture unit 31 through a line that branches partially expanded steam from the steam turbine 15, specifically from the low pressure steam turbine section 15.2 as pictorially represented by line 47X, or from the high pressure steam turbine section 15.1 (not shown).

[0042] Due to the higher carbon dioxide concentration in the flue gas processed through the carbon dioxide capture unit 31, the recirculation of the exhaust gases through recirculation line 33 and post-combustion in post burner 37 improves the efficiency of the carbon dioxide capture unit 31. Although the overall efficiency of the system 1 is reduced by the increased amount of fuel required to operate the post burner, the increased efficiency of capturing carbon dioxide makes the system economically viable and environmentally friendly due to a significant (approximately 90%) reduction in greenhouse gas emissions.

[0043] The mole percentage of carbon dioxide in the flue gas delivered to the carbon dioxide capture unit 31 through line 29 may be increased from 3-3.2% (the typical mole percentage of carbon dioxide in gas turbine flue gas without post combustion or recirculation of exhaust flue gas in a heat recovery steam generator) to about 8.2-8.5%.

[0044] To provide better results in terms of increasing the mole percentage of carbon dioxide in the flue gas released by the heat recovery steam generator 11, a carbon dioxide diversion line 51 is provided connecting the carbon dioxide exhaust duct 43 to a fuel treatment skid 53 which can provide fuel to the gas turbine combustor 3.2 (fuel line 4) and / or to the post burner 37 (fuel line 39). The carbon dioxide from the exhaust duct 43, pressurized to around 120 bar, is blended with the fuel and the fuel / CO2 mixture is delivered to the gas turbine combustor 3.2 or to the post burner 37 or both. The amount of carbon dioxide added to the fuel is such that it does not adversely affect the combustion process, but increases the proportion of total carbon dioxide in the exhaust flue gas in the chimney 25 of the heat recovery steam generator 11, thus improving the efficiency of the carbon dioxide capture process performed by the carbon dioxide capture unit 31.

[0045] 1, a proportion of about 8.7-8.8% (molar) carbon dioxide can be expected in the exhaust flue gas released by the heat recovery steam generator 11 and delivered to the carbon dioxide capture unit 31. An increase in the carbon dioxide molar content in the flue gas is beneficial with regard to the efficiency of the carbon dioxide capture process performed by the carbon dioxide capture unit 31.

[0046] In some embodiments, as shown diagrammatically in FIG. 1, a supplemental oxidant supply line 60 may deliver oxidant (air, pure oxygen, or other oxygen-containing gaseous mixture) to the post burner 37.

[0047] Continuing with reference to Figure 1, Figure 2 illustrates a further embodiment of a system according to the present disclosure. The same reference numbers represent the same or equivalent components or parts of the system already shown in Figure 1 and described above, and will not be described in detail again.

[0048] In the system 1 of FIG. 2, the carbon dioxide diversion line 51 is omitted and all of the carbon dioxide stream delivered by the carbon dioxide capture unit 31 is removed through the carbon dioxide exhaust duct 43 .

[0049] To improve the carbon dioxide capture efficiency of the carbon dioxide capture unit 31, the embodiment of Figure 3 provides a flue gas recirculation line 61 connecting the carbon dioxide capture unit 31 to an air inlet of the gas turbine engine 3. The inlet of the recirculation line 61 may be fluidly coupled to a section of the carbon dioxide capture unit 31 in which cooled flue gas is present. For example, the flue gas recirculation line 61 may collect flue gas at a temperature in the range of about 5°C to about 20°C, preferably about 5°C to about 15°C.

[0050] FIG. 5 illustrates a schematic diagram of a known chilled ammonia process plant for capturing carbon dioxide. Details regarding such a system are disclosed, for example, in "Chilled Ammonia Process Scale-up and Lessons Learned" by Ola Augustons et al., available at www.sciencedirect.com, paper presented at the 13th International Conference on Greenhouse Ga Control Technologies, GHGT-13, November 14-18, 2016, Lausanne, CH. The system, generally designated 81, includes a direct contact cooler 83, in which flue gas from the gas turbine is cooled before being delivered to a carbon dioxide absorber 85. The system further includes a regenerator 87, a stripper 89, a water washing station 91, and a direct contact heater 93, in which the flue gas from which carbon dioxide has been removed in the absorber 85 is heated before being discharged to the environment. The structure and operation of the system are known and will not be described. Furthermore, the schematic of FIG. 5 is provided merely as an example of a chilled ammonia processing system. Several modifications to the basic layout of the system are known.

[0051] Generally, a portion of the cooled flue gas exiting the direct contact cooler 83 may be recirculated along the cooled flue gas recirculation line 61 towards the suction side of the air compressor 3.1 of Figures 1-4.

[0052] The cooled flue gas recirculated through line 61 is fed to the suction side of the air compressor 3.1 of the gas turbine engine 3 and blended with the air suctioned by the air compressor 3.1.

[0053] The effect of recirculating the cooled flue gas is twofold: on the one hand, it increases the proportion of carbon dioxide in the stream entering the gas turbine combustor 3.2, thereby increasing the mole percentage of carbon dioxide and reducing the amount of residual oxygen in the flue gas entering the heat recovery steam generator 11. A reduction in the exhaust flue gas recirculation through line 33 and blower 35 can be foreseen, thereby reducing the amount of power required to recirculate the flue gas.

[0054] On the other hand, since the temperature of the flue gas recirculated through line 61 is typically lower than the ambient temperature, an improvement in the thermal efficiency of the upper thermodynamic cycle performed by the gas turbine engine 3 is expected.

[0055] Continuing with reference to Figures 1 and 2, Figure 3 illustrates a further embodiment of system 1 in which the improvements of Figures 1 and 2 are combined in a single system to provide high carbon dioxide concentrations in the flue gases that are processed by the carbon dioxide capture unit 31. The same reference numbers used in Figures 1 and 2 are used in Figure 3 to indicate the same parts and components of the system and will not be described in detail again.

[0056] In FIG. 3, a cooled flue gas recirculation line 61 and a carbon dioxide diversion line 51 are used in combination to increase the carbon dioxide content in the flue gas treated by the carbon dioxide capture unit 31 .

[0057] Continuing with reference to Figures 1, 2 and 3, Figure 4 illustrates an alternative embodiment for improving the carbon dioxide content at the suction side of the air compressor 3.1 of a gas turbine engine 3. The same reference numbers used in Figures 1 and 2 indicate the same or equivalent parts and components already described in connection with Figures 1 and 2 and will not be described in detail again.

[0058] In the embodiment of Figure 4, an exhaust flue gas recirculation line 71 connects the discharge end of the gas turbine engine 3 to its inlet. Thus, a portion of the flue gas exhausted from the turbine section 3.3, which contains a higher percentage of carbon dioxide compared to the atmosphere due to the combustion process, is blended with ambient air to increase the percentage of carbon dioxide in the combustion air delivered to the gas turbine combustor 3.2. This results in a higher concentration of carbon dioxide in the flue gas of the chimney 25 and ultimately in the flue gas that is processed through the carbon dioxide capture unit 31.

[0059] The recirculated exhaust flue gas in the exhaust flue gas recirculation line 71 is cooled in a cooler 73 arranged along the exhaust flue gas recirculation line 71 before being blended with fresh air. The recirculated flue gas in the exhaust flue gas recirculation line 71 may be subjected to a flow treatment aimed at removing particulate matter or other pollutants therefrom that may adversely affect the operation of the gas turbine engine 3. For this purpose, a general flow treatment unit 75 is provided along the exhaust flue gas recirculation line 71, preferably downstream of the cooler 73.

[0060] Thermal energy (arrow Q) removed from the recirculated exhaust flue gas flowing in the exhaust flue gas recirculation line 71 can be used in one or more sections of the system 1 or in a separate process or system (not shown). For example, heat from the cooler 73 can be used to preheat fuel delivered to the post burner 37 and / or the gas turbine combustor 3.2. Thermal energy Q from the cooler 73 can also be utilized in the carbon dioxide capture unit 31 and / or the bottom cycle 13, for example, to preheat water from the condenser 19 before it is delivered to the heat recovery steam generator 11.

[0061] In Figure 4, the cooled flue gas recirculation line 61 (Figures 2 and 3) has been omitted. However, the combination of recirculation lines 71 and 61 in the same system is not excluded. Additionally, also disclosed herein is a system 1 including combined recirculation lines 61 and 71, but omitting the carbon dioxide diversion line 51.

[0062] FIG. 6 is a flow chart summarizing the method of the present disclosure. The method illustrated in FIG. 6 includes step 101, where air and fuel are delivered to a gas turbine engine 3 to generate mechanical power. In step 102, flue gas exhausted from the gas turbine engine 3 is passed through a heat recovery steam generator 11. In a further step 103, fuel is delivered to a post burner 37 of the heat recovery steam generator 11 to generate steam therein (step 104). As explained above, the flue gas exhausted from the heat recovery steam generator is partially recirculated to the post burner (step 105), while the remaining portion of the flue gas is treated in the carbon dioxide capture unit 31 to remove carbon dioxide therefrom (step 106). A stream of carbon dioxide-containing gas from the carbon dioxide capture unit is returned towards the gas turbine engine and / or the post burner (step 107).

[0063] Exemplary embodiments are disclosed above and illustrated in the accompanying drawings. It will be understood by those skilled in the art that various modifications, omissions, and additions may be made to what is specifically disclosed herein without departing from the scope of the invention as defined in the following claims.

[0064] For example, an additional fuel delivery line 26 and an additional oxygen or air delivery line 28 may be provided to deliver lower quality fuel to the post-combustor and additional oxygen if necessary. The fuel delivered to the gas turbine engine via the fuel skid 53 may be a gaseous fuel or any other high quality fuel, but the additional fuel delivery line 26 may deliver a base fuel, for example a fuel different from the fuel delivered by the fuel skid 53, coal, waste from other processes, such as products that are normally intended to be burned, etc. If necessary, a fuel pre-treatment unit may be provided in the additional fuel delivery line, or a combustion gas post-treatment unit may be provided at the exhaust of the post-combustor or heat recovery steam generator.

Claims

1. A gas turbine system (1), comprising: A gas turbine engine (3); a first fuel line (4) adapted to deliver fuel to said gas turbine engine (3); a heat recovery steam generator (11) adapted to receive flue gas exhausted from said gas turbine engine (3); a second fuel line (39) adapted to deliver fuel to a post burner (37) of said heat recovery steam generator (11); a carbon dioxide capture unit (31) fluidly coupled to the chimney (25) of the heat recovery steam generator (11) and adapted to capture carbon dioxide from the flue gas exhausted from the heat recovery steam generator (11); a recirculation line (33) adapted to recirculate flue gas from the chimney (25) of the heat recovery steam generator (11) to the post burner (37) within the heat recovery steam generator (11); and at least one carbon dioxide return line (51, 61) adapted to recirculate a stream of carbon dioxide-containing gas at least partially processed by the carbon dioxide capture unit (31) towards at least one of the gas turbine engine (3) and the post burner (37).

2. 2. The gas turbine system (1) of claim 1, further comprising a bottom thermodynamic cycle (13) including a steam turbine (15) adapted to expand steam generated by the heat recovery steam generator (11) and generate mechanical power therefrom.

3. The gas turbine system (1) of claim 2, further comprising an electrical generator (17) drivingly coupled to the steam turbine (15).

4. 4. The gas turbine system (1) of claim 1, 2 or 3, further comprising an electric generator (5) drivingly coupled to the gas turbine engine (3).

5. 5. The gas turbine system (1) according to any one of claims 1 to 4, wherein the carbon dioxide return line comprises a carbon dioxide diversion line (51) fluidly connected to a carbon dioxide exhaust duct (43) of the carbon dioxide capture unit (31) and to a fuel processing skid (53) fluidly connected to at least one of the first fuel line (4) and the second fuel line (39), and in use, carbon dioxide diverted through the carbon dioxide diversion line (51) is blended into the fuel.

6. 6. The gas turbine system (1) according to any one of claims 1 to 5, wherein the carbon dioxide return line comprises a cooled flue gas recirculation line (61) fluidly connected to the carbon dioxide capture unit (31) and to a suction side of an air compressor (3.1) of the gas turbine engine (3), and in use, the cooled flue gas recirculation line (61) diverts a quantity of cooled flue gas from the carbon dioxide capture unit (31) to the air compressor (3.1) of the gas turbine engine (3).

7. 7. The gas turbine system (1) of any one of claims 1 to 6, further comprising a turbine recirculation line (71) having an inlet fluidly connected to a discharge of a turbine section (3.3) of the gas turbine engine (3) and an outlet fluidly connected to the suction side of the air compressor (3.1) of the gas turbine engine (3), wherein, in use, a quantity of flue gas from the turbine section (3.3) of the gas turbine engine (3) is recirculated through the turbine recirculation line (71) to the suction side of the air compressor (3.1) of the gas turbine engine (3).

8. The gas turbine system (1) of claim 7, wherein the turbine recirculation line (71) includes a cooler (73).

9. The gas turbine system (1) according to claim 7 or 8, wherein the turbine recirculation line (71) comprises a flow treatment unit (75).

10. 1. A method for generating electrical power using a gas turbine system, the method comprising: delivering air and fuel to a gas turbine engine (3) to generate mechanical power; flowing flue gas exhausted from said gas turbine engine (3) through a heat recovery steam generator (11); delivering fuel to a post burner (37) of the heat recovery steam generator (11); generating steam in the heat recovery steam generator; recirculating a portion of the flue gas exhausted from the heat recovery steam generator (11) to the post burner (37); treating the remaining flue gas exhausted from the heat recovery steam generator in a carbon dioxide capture unit (31) to remove carbon dioxide from the flue gas; and recirculating a stream of carbon dioxide containing gas from the carbon dioxide capture unit (31) towards at least one of the gas turbine engine (3) and the post burner (37).

11. 11. The method of claim 10, further comprising using the steam generated by the heat recovery steam generator (11) to generate mechanical power in a bottom thermodynamic cycle (13) including a steam turbine (15).

12. The method of claim 11 , further comprising converting the mechanical power generated by the steam turbine into electrical power.

13. The method of claim 10, 11 or 12, further comprising converting mechanical power generated by the gas turbine engine (3) into electrical power.

14. The method according to any one of claims 10 to 13, wherein the step of recirculating the stream of carbon dioxide containing gas comprises blending the recirculated stream of carbon dioxide containing gas with fuel delivered to at least one of the gas turbine engine (3) and a post combustor (37).

15. The method according to any one of claims 10 to 14, wherein the step of recirculating the stream of carbon dioxide containing gas comprises diverting flue gas cooled in the carbon dioxide capture unit (31) to the suction side of the gas turbine engine (3).

16. The method according to any one of claims 10 to 15, further comprising the step of recirculating flue gas exhausted from an exhaust side of the gas turbine engine (3) to a suction side of the gas turbine engine (3).

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