Power generation system and method

Abstract

A power generation system includes: a compressor; a burner section; a turbine section; an exhaust gas recirculation path adapted to establish a fluid connection between the turbine exhaust port and the suction side of the compressor section. The power generation system further comprises an exhaust emission chimney and a carbon dioxide emission device. The power generation system further includes a flow regulating arrangement adapted to regulate: a flow of air to the compressor section; an oxidant stream from the air separation unit to the combustor section; and an exhaust gas flow recirculated to the suction side of the compressor section through an exhaust gas recirculation path.

Description

TECHNICAL FIELD

[0001] Disclosed herein are power generation systems and methods of operating these systems. BACKGROUND

[0002] A large amount of mechanical and electrical power is still generated by thermal cycles involving the combustion of fossil fuels. In particular, gas turbine engines are used to drive large rotating equipment, such as compressors and generators, for converting mechanical power to electrical power.

[0003] The combustion of fossil fuels, including natural gas, produces carbon dioxide (CO2) and other polluting gaseous substances, such as nitrogen and sulfur oxides. The release of CO2 into the atmosphere has a negative impact on the climate, including being a significant factor in global warming.

[0004] There are active efforts to reduce the amount of carbon dioxide released into the atmosphere by human activities. Carbon capture systems (CCS for short) are being developed with the goal of removing carbon dioxide from the flue gas produced by thermal cycles used for power generation. Since gas turbine machines operate with a large excess of air, the turbine exhaust gas contains a relatively low concentration of carbon dioxide, in the range of 3% to 4%.

[0005] Such a low percentage of carbon dioxide content makes the carbon capture process not only complex, but also very costly. The complexity and expense are due in part to the need to handle a large flow of flue gas. Carbon capture systems also require a considerable amount of electrical power, equipment, and administrative costs, and the electrical power required for carbon dioxide capture reduces the overall efficiency of the thermal cycle used for power generation.

[0006] Accordingly, power generation equipment has been developed that uses exhaust gas recirculation with the goal of increasing the concentration of carbon dioxide in the exhaust gas. Techniques for this purpose provide for the partial recirculation of exhaust gas from the turbine of a gas turbine engine to an air compressor. The compressor processes a fluid that is partially composed of air and partially composed of exhaust gas that has been previously cooled, where the exhaust gas contains a percentage of carbon dioxide. As a result, the concentration of carbon dioxide in the exhaust gas is increased, for example, from 3% to 4% to about 8% to 9%. Having a higher concentration of carbon dioxide in the gas exiting the thermal cycle allows for easier removal of carbon dioxide and reduces the cost of carbon capture.

[0007] The recently developed oxy-fuel combustion cycle aims to address the same problem, namely to improve carbon capture and reduce the release of carbon dioxide into the environment. Oxy-combustion technology has been identified as one of the most promising technologies for carbon dioxide capture and sequestration / storage. In the oxy-fuel combustion cycle, nitrogen is removed from the process gas and a high pressure mixture consisting primarily or almost entirely of carbon dioxide and oxygen is mixed with a fuel, typically natural gas (CH4), and combusted. The resulting high temperature pressurized combustion gas contains carbon dioxide and water and is expanded in an expander to generate electrical power. The spent flue gas is cooled and water is removed from it by condensation. The majority of the resulting dry combustion exhaust gas, which contains almost only carbon dioxide, is recycled and a small portion is removed to compensate for the addition of oxygen and fuel in the cycle. The high concentration of carbon dioxide in the stream removed from the cycle facilitates carbon capture and sequestration.

[0008] The current oxy-fuel combustion cycle is efficient and environmentally friendly, but the process is complex and technically challenging given the high pressure and high temperature of the compressed combustion gas.

[0009] Therefore, a high efficiency oxy-fuel combustion cycle at low pressure is desirable in the art. SUMMARY

[0010] According to a first aspect, there is disclosed a power generation system comprising a gas turbine engine comprising: a compressor section comprising a suction side adapted to receive exhaust gas and air, in particular ambient air drawn from the environment; a combustor section fluidly coupled to a delivery side of the compressor section and configured to generate a flow of hot, compressed combustion gas (flue gas); and a turbine section having a turbine intake and a turbine exhaust, the turbine intake being fluidly coupled to the combustor section. The system further comprises an exhaust gas recirculation path adapted to establish a fluid connection between the turbine exhaust and the suction side of the compressor section. The power generation system further comprises an exhaust gas discharge stack adapted to release exhaust gas, i.e. flue gas, from the gas turbine engine at least under certain operating conditions. A carbon dioxide discharge device is fluidly coupled to the exhaust gas recirculation path to remove carbon dioxide from the power generation system under certain operating conditions. An air separation unit of the power generation system is adapted to provide an oxidant flow to the combustor section. The power generation system comprises a flow regulation arrangement adapted to control: a flow of air, i.e. ambient air, to the suction side of the compressor section; the oxidant flow from the air separation unit to the combustor section; and a flow of exhaust gas recirculated to the suction side of the compressor section through the exhaust gas recirculation path; a flow of exhaust gas released through the exhaust gas discharge stack; a carbon dioxide discharge flow removed from the power generation system; in order to gradually switch the power generation system from a gas turbine operating mode under open cycle to an oxy-fuel combustion operating mode under semi-closed cycle.

[0011] In embodiments disclosed herein, the flow regulating arrangement is adapted to switch the power generation system from a first operating mode, in which the gas turbine engine is operated in open loop conditions with 100% air, where air is obtained completely from the environment, to semi-closed operating conditions, in which the gas turbine engine is operated in oxygen-fuel combustion mode.

[0012] In embodiments disclosed herein, the flow regulating arrangement comprises an air flow regulator at the air inlet, an oxidant flow regulator between the air separation unit and the combustor section, an exhaust emission flow regulator at the exhaust emission stack, and a carbon dioxide flow regulator at the carbon dioxide emission device.

[0013] In some embodiments, the flow regulating arrangement further comprises a recirculation flow regulator in the exhaust gas recirculation path between the turbine exhaust and the suction side of the compressor section.

[0014] Each flow regulator disclosed herein can comprise a device adapted to regulate, i.e. to govern, modulate or control, the flow and thereby the flow rate of the respective fluid flow. The regulation can be achieved, for example, by a flow restriction member adapted to change the cross section or geometry of the respective duct and thereby to partiallyize the fluid flow therethrough and to regulate the fluid flow rate. The flow regulator may, for example, regulate the flow rate from 100% to zero by acting on the geometry or cross section of the respective flow duct.

[0015] According to another aspect, a method for operating a power generation system as described above is disclosed herein.

[0016] According to the embodiments disclosed herein, the method comprises a start-up step, wherein the power generation system starts running in open cycle gas turbine operating mode with 100% air. The gas turbine engine of the power generation system operates according to the standard Brayton cycle. Ambient air is drawn by the compressor of the gas turbine engine, mixed with fuel and ignited in the combustor section of the gas turbine engine to generate high pressure hot combustion gases. The combustion gases expand in the turbine section of the gas turbine engine to produce power to drive the compressor section and useful power available on the output shaft of the gas turbine engine. The exhaust flue gas is released to the environment. The rotational speed and the ignition temperature of the gas turbine engine are increased until the base load condition is reached. Once the base load condition is reached, the exhaust gas flow released from the gas turbine engine through the exhaust gas discharge stack is gradually reduced. At the same time, the exhaust gas flow that is gradually increased is recirculated to the intake of the gas turbine engine through an exhaust gas recirculation path arranged between the outlet of the gas turbine engine and the intake of the gas turbine engine. The air flow towards the intake of the gas turbine engine is gradually reduced. In response to the oxygen content in the gas turbine engine being below a predetermined threshold value required for combustion, the operation of the air separation unit of the power generation system is started to deliver an oxidant flow to the gas turbine engine and to maintain the oxygen content in the gas turbine engine at a predetermined value. In some embodiments, for example, the air separation unit can be started in advance and the oxygen can be stored in a storage unit. The exhaust gas flow discharged through the exhaust gas discharge stack continues to be reduced, the air flow towards the intake of the gas turbine engine also continues to be reduced, while at the same time the exhaust gas flow recirculated towards the gas turbine engine continues to be increased until the gas turbine engine operates in semi-closed cycle operating mode with oxy-fuel combustion.

[0017] Further features of the method and system according to the present disclosure are described hereinafter and set out in the appended claims.

[0018] By the above steps, the gas flow is processed by the compressor section from an air flow to a flow consisting mainly of carbon dioxide or consisting of carbon dioxide and oxygen. BRIEF DESCRIPTION OF DRAWINGS

[0019] Reference will now be made in detail to the drawings, in which:

[0020] Figure 1 is a schematic view of a system according to the present disclosure; and

[0021] Figure 2 is a flow chart summarizing a method for operating the system according to the present disclosure. DETAILED DESCRIPTION

[0022] A novel system for operating a power generation system including a gas turbine engine is disclosed herein. The system includes an exhaust gas recirculation arrangement, an air separation unit, and a flow regulating device adapted to handle a transition in operating mode from an open cycle gas turbine operating mode (Brayton cycle) to a semi-closed oxy-fuel combustion cycle. When the system is started, the gas turbine is fed with air and fuel and produces exhaust gas. The amount of exhaust gas that is gradually increased is recirculated towards the suction side of the compressor of the gas turbine engine, and the amount of exhaust gas that is released to the environment is correspondingly reduced. Thus, the gas turbine engine processes a gas that contains an increased percentage of carbon dioxide from the recirculated exhaust gas, and the amount of ambient air is reduced. As the concentration of carbon dioxide in the loop increases and the fresh air flow decreases, the air separation unit starts to feed the loop with oxidant. At the end of the transient period, the fresh air flow to the compressor stage becomes zero, and no more exhaust gas is discharged in the loop. A carbon dioxide stream is removed from the loop to compensate for the carbon dioxide produced by the combustion of the oxidant and the fuel fed to the combustor of the gas turbine engine, and the power generation system operates according to an oxy-combustion cycle with a semi-closed loop.

[0023] Figure 1 A power generation system 1 in an embodiment is illustrated. The power generation system 1 includes a gas turbine engine 3 that forms part of a top thermodynamic cycle 5. The top thermodynamic cycle 5 converts thermal energy into mechanical power and ultimately into electrical power. In some embodiments, the power generation system 1 also includes a bottom thermodynamic cycle 7 that converts waste heat from the top thermodynamic cycle 5 into mechanical power and ultimately into electrical power.

[0024] The gas turbine engine 3 includes an air intake 3A and an air exhaust 3B, between which are arranged: a compressor stage 11, a combustor stage 13, and a turbine stage 15. In some embodiments, the compressor stage 11 can include a single compressor. In other embodiments, the compressor stage 11 can include two or more compressors arranged in series. In the illustrated embodiment, the compressor stage 11 includes a low pressure compressor 11.1 and a high pressure compressor 11.2 arranged in series. Figure 1 In the illustrated embodiment, the compressor stage 11 includes a first compressor and a second compressor arranged in series. More specifically, the compressor stage 11 includes a low pressure compressor 11.1 and a high pressure compressor 11.2. The low pressure compressor 11.1 includes a suction side 11.11 and a delivery side 11.12. The high pressure compressor 11.2 includes a suction side 11.21 fluidically coupled to the delivery side 11.12 of the low pressure compressor 11.1, and a delivery side 11.22 fluidically coupled to the combustor stage 13.

[0025] The compressor section 11 can include an intercooler 11.3. In this case, the delivery side 11.12 of the low-pressure compressor 11.1 can be fluidly coupled with an inlet of a hot side of the intercooler 11.3, and an outlet of the intercooler 11.3 can be fluidly coupled with the suction side 11.21 of the high-pressure compressor 11.2. A coolant fluid flows through a cold side of the intercooler 11.3 to remove heat generated by compression from the partially compressed process gas flowing from the first compressor 11.1 to the second compressor 11.2.

[0026] In some embodiments, the first low-pressure compressor 11.1 can include an axial flow compressor, and the second high-pressure compressor 11.2 can include a radial flow compressor, in particular a centrifugal compressor.

[0027] The turbine section 15 can include one or more turbine wheels. In Figure 1 In the exemplary embodiment, the turbine section 15 includes a high-pressure turbine 15.1 and a low-pressure turbine 15.2. A shaft arrangement 17 drivingly connects the turbine section 15 to the compressor section 11 such that power generated by the turbine section is used to drive the compressor section 11. The shaft arrangement 17 can include a single shaft or two or more coaxial shafts. For example, the high-pressure turbine 15.1 can be drivingly coupled to the high-pressure compressor 11.2 by a first shaft, and the low-pressure turbine 15.2 can be drivingly coupled to the low-pressure compressor 11.1 by a second shaft that is coaxial with the first shaft. An output shaft drivingly couples the low-pressure turbine 15.2 to a load, for example a generator 17. The generator 17 is electrically coupled to an electrical power distribution grid 19.

[0028] In other embodiments, different loads can be connected to the output shaft of the gas turbine engine 3. For example, the gas turbine engine 3 can be used to drive a turbomachine, such as a compressor or a compressor train.

[0029] The structure of the gas turbine engine 3 described above and shown in Figure 1 Fig. 1 is given by way of example only. A person skilled in the art of gas turbine engines will understand that different gas turbine layouts can be provided, for example a gas turbine engine comprising more than two coaxial shafts and comprising more than two compressors and two turbines in series.

[0030] For example, in some embodiments, the high-pressure turbine wheel can be drivingly coupled to the high-pressure compressor 11.2, and the intermediate-pressure turbine wheel can be drivingly coupled to the low-pressure compressor 11.1. The low-pressure turbine wheel can be provided with a separate shaft that is coupled to a load. This allows the various turbine sections to rotate at different rotational speeds. A single shaft heavy-duty gas turbine engine can also be used, which includes a single shaft drivingly coupling one or more compressors to one or more turbine wheels and to a load.

[0031] The turbine section 15 includes a turbine intake 15.3 fluidly coupled with the combustor section 13, and a turbine exhaust 15.4 at an outlet 3B of the gas turbine engine 3.

[0032] The power generation system 1 also includes an exhaust gas recirculation path 21 having an inlet end 21.1 fluidly coupled with the turbine exhaust 15.4 and an outlet end 21.2 fluidly coupled with the compressor intake section 11.4.

[0033] In some embodiments, the exhaust gas treatment skid 23 can be positioned along the exhaust gas recirculation path 21.

[0034] The exhaust gas recirculation path 21 is fluidly coupled with an exhaust gas discharge stack 22 through which exhaust gas is discharged from the top thermodynamic cycle under certain operating conditions of the power generation system 1, as will be described later.

[0035] In some embodiments, the power generation system 1 can include a regenerator 25. The exhaust gas recirculation path 21 can extend through a hot side of the regenerator 25. A compressed gas conduit 11.5 from the delivery side 11.22 of the second compressor 11.2 to the combustor section 13 extends through a cold side of the regenerator 25. This arrangement is such that heat from the exhaust gas flowing from the turbine section 15 is recovered in the regenerator 25 and used to preheat the compressed gas stream from the compressor section 11.

[0036] As mentioned above, in Figure 1 embodiments, the power generation system 1 includes a bottom thermodynamic cycle 7. In a waste heat recovery heat exchanger 29, low temperature waste heat is transferred from the top thermodynamic cycle 5 to the bottom thermodynamic cycle 7. The exhaust gas recirculation path 21 extends through a high temperature side of the waste heat recovery heat exchanger 29 in heat exchange relationship with a process fluid flowing in the bottom thermodynamic cycle 7, the low temperature of which circulates through the waste heat recovery heat exchanger 29.

[0037] The bottom thermodynamic cycle 7 can be any cycle suitable for converting relatively low temperature heat into mechanical power. As understood herein, “relatively low temperature” is a temperature equal to or lower than the lower temperature of the top thermodynamic cycle. As a non-limiting example, the bottom thermodynamic cycle is a closed cycle. In some example, but non-limiting, embodiments, the bottom thermodynamic cycle can be a Rankine cycle, such as an organic Rankine cycle (ORC), rather than a steam (water vapor) Rankine cycle.

[0038] In Figure 1In the schematic diagram of Figure 1, the bottom thermodynamic cycle 7 is represented as comprising a heater and an evaporator 7.1 located in the cold side of the waste heat recovery heat exchanger 29, in which pressurized working fluid, such as an organic fluid, is heated and vaporized. The pressurized and vaporized working fluid is expanded in a turbine or expander 7.2. The discharged working fluid is condensed in a condenser 7.3 and pumped back by a pump 7.4 to the waste heat recovery heat exchanger for vaporization.

[0039] In other embodiments, not shown, a heat transfer loop can be provided between the waste heat recovery heat exchanger 29 and the bottom thermodynamic cycle. In this case, the heat transfer loop is interposed between the waste heat recovery heat exchanger and the bottom thermodynamic cycle. A heat transfer fluid circulates in the heat transfer loop. The heat transfer fluid is heated by flowing through the cold side of the waste heat recovery heat exchanger and transfers heat to the working fluid of the low temperature cycle in the evaporator.

[0040] The expander 7.2 is drivingly coupled to a load, such as an electrical generator 31, which converts the mechanical power produced by the expander 7.2 into electrical power. The electrical generator 31 can be electrically coupled to an electrical power distribution grid 19.

[0041] In other embodiments, the bottom thermodynamic cycle 7 can be omitted. In yet another embodiment, the waste heat from the exhaust gas recirculation path can be used in a different way to produce additional mechanical power or electrical power. For example, the power generation system 1 can be a cogeneration system for producing mechanical power / electricity by the top thermodynamic cycle 5 and heat from the waste heat recovery heat exchanger, which can be used for heating purposes or other processes.

[0042] The exhaust gas recirculation path 21 further comprises a cooler 21.3 located between the waste heat recovery heat exchanger 29 and the outlet end 21.2 of the gas recirculation path 21. Between the cooler 21.3 and the outlet end 21.2 of the exhaust gas recirculation path 21, a water gas separator 21.4 can be arranged, in which water condensed in the cooler 21.3 can be removed from the gas stream recirculated in the exhaust gas recirculation path 21. The water can be removed at the bottom of the water gas separator 21.4 (line 21.5) and the dried exhaust gas is delivered to the outlet end 21.2 of the exhaust gas recirculation path 21.

[0043] The power generation system 1 further comprises an air separation unit 33 adapted to separate oxygen from ambient air. The air separation unit 33 separates oxygen from air and, under certain operating conditions, delivers oxygen (or, more generally, an oxidizing agent comprising oxygen) to the top thermodynamic cycle 5, as will be described in more detail below. In Figure 1In the schematic illustration, the air separation unit 33 is fluidly coupled directly to the combustor section 13 by an oxidant supply line 35. In other embodiments, the output of the air separation unit 33 can be fluidly coupled at a different location, for example, upstream of the combustor section 13. For example, the oxidant from the air separation unit 33 can be supplied upstream of the regenerator 25, or upstream of one or both of the compressors 11.1 and 11.2.

[0044] The air separation unit 33 can be configured to supply a flow of substantially pure oxygen in the flow path of the working fluid of the top thermodynamic cycle. In other embodiments, the air separation unit 33 can be configured to supply an oxidant comprising, for example, a blend of oxygen and carbon dioxide. The carbon dioxide can be cooled, for example, in the cooler 21.3 and delivered through the exhaust gas recirculation path 21 after water removal in the water gas separator 21.4.

[0045] The power generation system 1 further comprises a flow regulation arrangement adapted to regulate the gas flow in the various sections of the power generation system 1 in order to gradually switch the operating mode of the power generation system from a gas turbine operating mode in open cycle to an oxy-fuel combustion operating mode in semi-closed cycle.

[0046] In Figure 1 In embodiments of the power generation system 1, the flow regulation arrangement comprises an air flow regulator 41 arranged to control and regulate the air flow in an air intake 42 at the inlet of the compressor section 11. As will be explained in more detail below, the air flow regulator 41 is adapted to regulate the air intake from the compressor section 11.

[0047] The flow regulation arrangement can further comprise an oxidant flow regulator 43 along the oxidant supply line 35. The oxidant flow regulator 43 is adapted to regulate the oxidant flow from the air separation unit 33 to supply the oxidant flow at the required flow rate depending on the operating conditions of the power generation system 1, as will be explained in detail below.

[0048] In embodiments, a flue gas discharge flow regulator 45 is further provided between the exhaust gas recirculation path 21 and the flue gas discharge stack 22. The flue gas discharge flow regulator is adapted to control and regulate the flue gas flow through the flue gas discharge stack 22 under certain operating conditions, as will be described below.

[0049] In some embodiments, the flow regulation arrangement further comprises a carbon dioxide flow regulator 47 located at the carbon dioxide exhaust 49, which can be fluidly coupled with the exhaust gas recirculation path 21 downstream of the water gas separator 21.4. The carbon dioxide flow regulator 47 is adapted to control and regulate the flow of carbon dioxide exiting the top thermodynamic cycle under certain conditions, as described in more detail below. The carbon dioxide exhaust 49 can be fluidly coupled with a carbon capture system 51 adapted to capture the carbon dioxide exiting the top thermodynamic cycle 7.

[0050] The flow regulation arrangement can further comprise a recirculation flow regulator 53 arranged along the exhaust gas recirculation path 21, for example between the water gas separator 21.4 and the outlet end 21.2 of the exhaust gas recirculation path 21. The recirculation flow regulator 53 is adapted to control and regulate the flow of exhaust gas recirculated through the exhaust gas recirculation path 21 towards the compressor inlet section 11.4.

[0051] The power generation system 1 is adapted to operate in a 100% air gas turbine operation mode, wherein the power generation system 1 performs a standard open Brayton cycle, and in an oxygen-fuel combustion operation mode according to a semi-closed cycle. Moreover, the power generation system 1 is configured to gradually transition from the open loop operation mode (standard Brayton cycle) to the semi-closed loop operation mode (oxygen-fuel combustion cycle) without interruption.

[0052] The process of transitioning from the open loop operation mode to the semi-closed loop operation mode is as follows.

[0053] At start-up, the power generation system 1 is set to operate according to the standard Brayton open cycle with 100% air. Operating with 100% air means that the gas expanded in the turbine section 15 is produced by igniting an air-fuel mixture, without recirculation of flue gas. The exhaust gas discharge flow regulator 45 and the air flow regulator 41 are fully open. The oxidant flow regulator 43 is closed. The carbon dioxide flow regulator 47 and the recirculation flow regulator 53 are fully closed. The gas turbine engine 3 is started and gradually reaches nominal conditions (base load). The compressor section 11 sucks in ambient air and delivers compressed air to the combustor section 13. Fuel, for example methane (CH4), is fed to the combustor section 13 from a fuel source 55 through a fuel line 57. The fuel flow is regulated via a fuel control valve 59.

[0054] When the gas turbine engine 3 reaches base load conditions, this preliminary step is finished. Base load conditions can be determined by the rotational speed of the gas turbine engine or the ignition temperature. According to the gas turbine engine, base load can be reached when the design operating speed is reached, or when the design ignition temperature is reached. The ignition temperature or rotational speed can be detected by standard sensors and transducers.

[0055] Once the base load has been reached and a gradual switchover (i.e. transition) to an oxy-fuel combustion cycle is desired, the intermediate mode of operation of exhaust gas recirculation is initiated with a gradual increase. This is achieved by gradually closing the exhaust gas discharge flow regulator 45 so that the flow of exhaust gas released to the atmosphere is gradually reduced. At the same time, the air flow regulator 41 is gradually closed and the recirculation flow regulator 53 is gradually opened. The increased flue gas (i.e. combustion exhaust gas) flow is recirculated from the outlet 3B of the gas turbine engine 3 towards the gas turbine engine's intake 3A.

[0056] As understood herein, the term "gradual" or "gradually" refers to a transition from one operating condition to another operating condition being performed as a function of time over a limited time interval and not abruptly. The gradual opening or closing of a flow regulator and the gradual change (increase or decrease) of the corresponding controlled flow that follows can be a linear change that occurs over a time interval from to ti, where to is the instant at which the gradual change starts from a first flow value and ti is the instant at which the gradual change ends at a second flow value. As will be described in more detail below, the gradual increase of the flow typically starts from a zero flow and ends at a steady state flow value, which can depend on the operating conditions of the power generation system, e.g. on the power required by the load drivingly coupled to the output shaft of the gas turbine engine 3. While a linear transition from the starting value to the final value is possible, this is not the only feasible trend. The time interval to - ti can be selected based on the needs, e.g. also taking into account the load applied to the gas turbine engine.

[0057] As the flow of recirculated exhaust gas is gradually increased, the compressor section 11 handles a blend of air and recirculated exhaust gas, which includes an increasing percentage of exhaust gas and a decreasing percentage of fresh air.

[0058] As the percentage of recirculated exhaust gas is increased and the air at the gas turbine engine's intake 3A is reduced, the percentage of carbon dioxide in the flow handled by the gas turbine engine 3 gradually increases.

[0059] The content of carbon dioxide and oxygen in the blend of air and recirculated exhaust gas handled by the compressor section 11 is detected (i.e. monitored).

[0060] Any suitable device can be used to detect the percentage of carbon dioxide and oxygen in the flow of gas handled by the gas turbine engine 3, either directly or indirectly.

[0061] In some embodiments, the percentage of carbon dioxide and oxygen in the gas being processed by the gas turbine engine 3 can be detected by, for example, suitable carbon dioxide and oxygen detectors arranged at the intake 3A of the gas turbine engine 3. In some embodiments, the carbon dioxide and oxygen percentages can be calculated based on the air flow and the fuel flow. The air flow at the intake 3A and the fuel flow delivered to the combustor section 13 can be detected with suitable transducers. For example, a flow meter can detect the fuel flow. Pressure and temperature transducers at the intake 3A of the gas turbine engine 3 can be used to calculate the air flow.

[0062] Monitoring (i.e., detecting) the carbon dioxide and oxygen content in the gas being processed by the gas turbine engine 3 has a dual purpose. On one hand, changes in the composition of the gas mixture being processed by the compressor section 11 can require changes in the rotational speed of the compressor to adapt the operating point of the compressor section 11 and maintain a constant value of the corrected speed, while the speed of sound in the gaseous blend decreases with the increase of the carbon dioxide percentage. On the other hand, once the oxygen content in the working fluid drops below the percentage required for the correct operation of the gas turbine engine, the oxidizer flow regulator gradually opens to supply additional oxygen to the working fluid, so that the flow of oxygen delivered to the combustor section 13 relative to the fuel flow is always at the correct value to maintain stable combustion in the combustor section 13 and reduce or avoid the emission of unburned fuel at the outlet 3B of the gas turbine engine. The required oxygen flow depends on the amount of fuel delivered to the combustor section 13, which in turn depends on the load applied to the gas turbine engine 3.

[0063] At the end of this transition operating mode, the air flow regulator 41 and the exhaust emission flow regulator 45 will be fully closed. The recirculation flow regulator 53 will be fully open. The cycle cannot be fully closed due to the introduction of oxygen and fuel into the cycle. To compensate for the addition of chemical species (O2; CH4), the carbon dioxide flow regulator 47 is opened to allow a corresponding amount of carbon dioxide produced by the combustion process to escape the circuit. The carbon dioxide removed by the carbon dioxide flow regulator 47 can be captured in the carbon capture system 51. The flow processed by the carbon capture system 51 is small since it is essentially composed of carbon dioxide. The power required by the carbon capture system 51 is minimized, thereby optimizing the overall efficiency of the power generation system 1.

[0064] The top thermodynamic cycle 5 now operates according to an oxy-combustion semi-closed cycle. Fuel and oxygen are fed into the cycle, and a corresponding amount of water (from the water gas separator 21.4) and carbon dioxide (through the carbon dioxide flow regulator 47 and the carbon dioxide emission device 49) produced by the combustion are removed from the cycle.

[0065] In Figure 2The above-mentioned transition from open to semi-closed cycle operation is outlined in the flow chart as follows: block 101 represents the step of starting the gas turbine according to the open Brayton cycle with 100% air. Once the base load conditions are reached (block 102), the exhaust gas recirculation is started by gradually closing the exhaust discharge flow regulator, gradually closing the air flow regulator and gradually opening the recirculation flow regulator. This step is shown in block 103. As mentioned above, the CO2 content in the air and recirculated exhaust gas mixture entering the gas turbine engine 3 is detected, see block 104, to adapt the rotational speed of the compressor to the variation of the carbon dioxide content in the process gas. The oxygen content is also detected so that when the oxygen content drops below the amount required for combustion, the operation of the air separation unit is started and oxygen is supplied from this air separation unit to the gas turbine engine 3 according to the control of the oxidant flow regulator, as shown in block 105. According to the CO2 concentration, the operating point of the gas turbine compressor stage is controlled and varied by varying the rotational speed of the gas turbine compressor stage, as shown in block 106. When the exhaust discharge flow regulator and the air flow regulator are fully closed and the recirculation flow regulator is fully open, the carbon dioxide flow regulator is opened and the excess carbon dioxide produced by combustion is removed from the semi-closed cycle, as shown in block 107.

[0066] The above-mentioned flow regulators and valves can be controlled by a control unit 60, which is functionally connected to these flow regulators and valves, as illustrated by the dashed lines in Figure 1 More specifically, the control unit 60 can be functionally connected to the air flow regulator 41 to reduce the air flow from full air flow to zero. Furthermore, the control unit 60 can be functionally coupled to the exhaust discharge flow regulator 45 and the recirculation flow regulator 53 to control the decrease of the exhaust gas flow released through the stack 22 and the simultaneous increase of the exhaust gas flow recirculated from the gas turbine engine outlet 3B to the gas turbine inlet 3A through the water gas separator 21.4. By functionally connecting the control unit 60 with the carbon dioxide flow regulator 47, this carbon dioxide flow regulator can be opened to control the flow of carbon dioxide removed from the circuit when the power generation system 1 is operated in the semi-closed oxy-fuel combustion mode. The oxidant flow regulator 43 is controlled by the control unit 60 to provide supplemental oxidant to the combustor stage 13 when the oxygen content in the process fluid is insufficient. In Figure 1 The oxygen and carbon dioxide content is detected by, for example, a sensor block 64 arranged at the gas turbine engine 3 intake 3A and delivered to the control unit 60, which is functionally connected to said sensor block 64, in

[0067] Additionally, the control unit 60 can be functionally coupled to, for example, a rotational speed sensor 66 adapted to detect the rotational speed of the gas turbine engine 3 and / or of one or more of its shafts, and to a temperature sensor 68 adapted to detect the ignition temperature of the gas turbine engine 3, so that it can be detected by the control unit 60 whether the base load is reached.

[0068] In some embodiments, the power generation system can comprise means or arrangements adapted to start the system directly in oxygen-fuel combustion mode, without the need for a preliminary operating phase in gas turbine mode. In some embodiments, these arrangements can be used to speed up the transition or switching process from gas turbine operating mode to oxygen-fuel operating mode.

[0069] Such arrangements or means can comprise a carbon dioxide tank or carbon dioxide source adapted to be fluidically coupled with the suction side of the compressor section 11. In Figure 1 In some embodiments, the reference 61 denotes a general carbon dioxide source. In Figure 1 In some embodiments, the carbon dioxide source 61 is illustrated as a tank, which can be placed in fluid communication with the exhaust gas recirculation path 21 and / or with the suction side 11.4 of the compressor, through a valve 63. In other embodiments, the carbon dioxide source can be a separate process or facility from which a carbon dioxide flow can be obtained. The valve 61 can be functionally connected to the control unit 60.

[0070] For example, the carbon dioxide source can be used if one or more of the above-mentioned flow regulators required to perform a gradual transition from gas turbine operating mode to oxygen combustion operating mode are not available. The carbon dioxide source 61 can also be used to speed up the transition from gas turbine operating mode to oxygen-fuel combustion mode. This can be achieved by supplementing the carbon dioxide to the compressor section 11, thereby increasing the carbon dioxide concentration in the exhaust gas recirculation path 21 at a faster rate.

[0071] In some embodiments, in order to achieve a more smooth operation of the power generation system, one or more dampers can be provided at one or more points along the exhaust gas recirculation path 21. This can be particularly useful downstream of the intersection points between the pipes, where different gas streams intersect and merge with each other. For example, and by way of non-limiting example, a damper 65 can be provided downstream of the intersection point between the exhaust gas recirculation path 21 and the intake 42.

[0072] Exemplary embodiments have been disclosed above and illustrated in the accompanying drawings. Those skilled in the art will appreciate that various changes, omissions and additions can be made to the specifics set forth herein without departing from the scope of the present application as defined by the following claims.

Claims

1. A power generation system, the power generation system comprising: The compressor section includes an intake side adapted to receive exhaust gas and air; A burner section, which is fluidly connected to the delivery side of the compressor section, and is configured to generate a hot, compressed flue gas flow. A turbine section having a turbine inlet and a turbine exhaust outlet, the turbine inlet being fluidly connected to the combustor section; An exhaust gas recirculation path is adapted to establish a fluid connection between the turbine exhaust port and the intake side of the compressor section. Exhaust gas is emitted from chimneys; A carbon dioxide emission device, wherein the carbon dioxide emission device is fluidly connected to the exhaust gas recirculation path; An air separation unit adapted to provide an oxidant flow to the burner section; and A flow regulation arrangement adapted to control the airflow toward the intake side of the compressor section; The oxidant flow from the air separation unit to the burner section; the exhaust gas flow recirculated to the intake side of the compressor section via the exhaust gas recirculation path; the exhaust gas flow released through the exhaust gas emission chimney; the carbon dioxide emission flow removed from the power generation system; the flow regulation arrangement is configured to gradually switch the power generation system from an open-cycle gas turbine operation mode to a semi-closed-cycle oxygen-fuel combustion operation mode.

2. The system according to claim 1, wherein, The flow regulation arrangement includes: An airflow regulator, wherein the airflow regulator is located at the air inlet; An oxidant flow regulator is located at the outlet of the air separation unit; An exhaust gas flow regulator, the exhaust gas flow regulator being located at the exhaust gas emission chimney; and A carbon dioxide flow regulator, located at the carbon dioxide emission device.

3. The system according to claim 2, wherein, The airflow regulator is configured to control and regulate the airflow in the inlet at the inlet of the compressor section, and to gradually reduce the airflow to the compressor section as the power generation system gradually switches from the gas turbine operating mode to the oxygen-fuel combustion operating mode; wherein the oxidant flow regulator is configured to gradually open to supply additional oxygen to the working fluid circulating in the system, while the airflow regulator gradually reduces the airflow to the compressor section.

4. The system according to claim 2 or 3, wherein, The exhaust gas flow regulator is configured to gradually close to reduce the flow rate of exhaust gas released into the atmosphere, while the airflow regulator gradually reduces the airflow to the compressor section, and the oxidant flow regulator gradually opens; wherein the carbon dioxide flow regulator is adapted to emit carbon dioxide when the system is operating in the oxygen-fuel combustion mode.

5. The system according to claim 2, 3, or 4, wherein, The flow regulation arrangement also includes a recirculation flow regulator located in the exhaust gas recirculation path between the turbine exhaust port and the intake side of the compressor section.

6. The system according to claim 5, wherein, The recirculation flow regulator is configured to open gradually while the airflow regulator closes gradually, to switch the system from the gas turbine operating mode under open cycle to the oxygen-fuel combustion operating mode under semi-closed cycle.

7. The system according to any one of the preceding claims, wherein, The exhaust gas recirculation path includes an exhaust gas cooler.

8. The system according to claim 7, wherein, when subordinate to claim 4, The recirculation flow regulator is positioned downstream of the exhaust gas cooler relative to the flow direction of the exhaust gas in the exhaust gas recirculation path.

9. The system according to any one of the preceding claims, wherein, The exhaust gas recirculation path includes an exhaust gas treatment slide rail adapted to treat the exhaust gas recirculated in the exhaust gas recirculation path.

10. The system according to any one of the preceding claims, wherein, The compressor section is driven to the turbine section and is driven to rotate therefrom.

11. The system according to any one of the preceding claims, wherein, The compressor section includes: a first compressor having an intake side and a delivery side; and a second compressor having an intake side and a delivery side; wherein the first compressor and the second compressor are arranged in series.

12. The system according to claim 11, wherein, The compressor section also includes an intercooler fluidly connected to the delivery side of the first compressor and the suction side of the second compressor.

13. The system according to claim 11 or 12, wherein, The first compressor is an axial compressor, and the second compressor is a radial compressor, particularly a centrifugal compressor.

14. The system according to any one of the preceding claims, further comprising a regenerator adapted to transfer heat from the exhaust gas circulating in the exhaust gas recirculation path to compressed gas delivered by the compressor section upstream of the burner section.

15. The system according to any one of the preceding claims, further comprising a bottom recirculation system adapted to convert waste heat contained in the waste gas recirculated in the waste gas recirculation path into mechanical power; wherein, The waste heat recovery heat exchanger is arranged between the turbine section and the compressor section along the exhaust gas recirculation path and is adapted to transfer waste heat from the exhaust gas recirculated in the exhaust gas recirculation path to the bottom circulation.

16. The system according to claim 15, wherein, The bottom cycle is the organic Rankine cycle.

17. The system according to claim 15 or 16, wherein, when subordinate to claim 11, The regenerator is positioned upstream of the waste heat recovery heat exchanger relative to the flow direction of the waste gas in the waste gas recirculation path.

18. The system according to any one of the preceding claims, the system further comprising a carbon capture system fluidly coupled to the carbon dioxide emission device.

19. The system according to any one of the preceding claims, the system further comprising at least one damper located in the exhaust gas recirculation path.

20. The system according to any one of the preceding claims, further comprising a carbon dioxide source adapted to be fluidly coupled to the system to supply carbon dioxide to the compressor section.

21. A method of operating a power generation system, the method comprising the following steps: The power generation system is started and operated in open-loop gas turbine mode with 100% air. Determine if the basic load conditions have been met; Gradually reduce the exhaust gas flow from the gas turbine engine through the exhaust stack; gradually increase the exhaust gas flow recirculated to the gas turbine engine's intake through an exhaust gas recirculation path arranged between the gas turbine engine's outlet and the gas turbine engine's intake; and gradually reduce the airflow toward the gas turbine engine's intake. In response to the oxygen content in the gas turbine engine falling below a predetermined threshold required for combustion, an oxidant stream is started to be supplied to the gas turbine engine; and Further reduce the exhaust gas flow through the exhaust chimney; continue to reduce the airflow toward the intake of the gas turbine engine; and continue to increase the exhaust gas flow circulating toward the gas turbine engine until the gas turbine engine operates in a semi-closed-loop operation mode of oxygen-fuel combustion.

22. The method according to claim 21, wherein, The step of starting to supply an oxidant stream to the gas turbine engine includes starting to operate the air separation unit of the power generation system to generate the oxidant stream.

23. The method according to claim 21 or 22, wherein, The step of gradually reducing the exhaust gas flow through the exhaust gas chimney includes the step of gradually closing the exhaust gas flow regulator located between the outlet of the gas turbine engine and the exhaust gas chimney.

24. The method according to claim 21, 22 or 23, wherein, The step of gradually increasing the exhaust gas flow recirculated toward the intake of the gas turbine engine includes the step of gradually opening a recirculation flow regulator adapted to connect the exhaust gas recirculation path to the intake of the gas turbine engine.

25. The method according to any one of claims 21 to 24, wherein, The step of gradually reducing the airflow toward the air intake of the gas turbine engine includes the step of gradually closing the airflow regulator between the air inlet of the gas turbine engine and the air intake.

26. The method according to any one of claims 21 to 25, wherein, The step of delivering an oxidant stream from the air separation unit to the gas turbine engine includes controlling an oxidant stream regulator to maintain the oxygen content in the combustor section of the gas turbine engine at a predetermined level.

27. The method according to any one of claims 21 to 26, the method further comprising the step of activating a carbon dioxide flow regulator to remove excess carbon dioxide from the power generation system.

28. The method according to claim 27, wherein, When the flow rate of exhaust gas discharged through the exhaust gas chimney is approximately zero, the step of opening the carbon dioxide flow regulator and removing excess carbon dioxide from the power generation system begins.

29. The method according to any one of claims 21 to 28, further comprising the step of: Controlling the carbon dioxide content in the gas flow at the intake side of the gas inlet of the gas turbine engine; The rotational speed of the compressor section is adjusted in response to the carbon dioxide content to maintain a substantially constant calibrated speed in the compressor section.

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