An OXY-combustion power generation system and method

Abstract

The power generation system includes an expander with a combustor and an expansion turbine. A heat exchange unit having a hot side with a hot-side inlet and a hot-side outlet, is further provided, wherein the hot-side inlet is fluidly coupled with the outlet of the expansion turbine and adapted to receive the expanded combustion gas stream and transfer heat therefrom to the recycling carbon dioxide stream. A recycling carbon dioxide compressor section pressurizes recycling carbon dioxide in an intercooled compression process, maintaining the process gas in a gaseous or supercritical, non-liquid phase.

Description

AN OXY-COMBUSTION POWER GENERATION SYSTEM AND METHODDESCRIPTIONTECHNICAL FIELD

[0001] The present disclosure concerns thermodynamic systems and methods for the generation of power. Embodiments disclosed herein specifically concern systems using oxy-combustion cycles for power generation purposes.BACKGROUND ART

[0002] Fossil fuels are a major source of chemical energy used for the generation of mechanical power. Fossil fuels are mixed with air and combusted to generate a combustion gas at high pressure and temperature, which expands in an expander. The expander converts combustion gas enthalpy into mechanical power available on the output shaft of the expander and used to drive a load, such as a compressor or compressor train, or to rotate an electric generator and convert mechanical power into electric power.

[0003] One of the major concerns regarding combustion of fossil fuels relates to the production of carbon dioxide, a greenhouse gas which is considered one of the main contributors of global warming and climate changes.

[0004] To reduce the environmental impact of power generation through combustion of fossil fuels, the option of post combustion capture of carbon dioxide has been investigated. Carbon dioxide capture facilities have been developed, to process flue gas exhausted from gas turbines and remove carbon dioxide therefrom, prior to discharging the flue gas in the environment. The cost of a carbon dioxide capturing facility are high, both in term CAPEX, as well as in terms of energy required to run the facility, which reduces the overall thermodynamic efficiency of the system. The percentage of carbon dioxide in flue gas is low. This requires large volumes of flue gas to be processed through the carbon dioxide capturing facility and renders the capturing process particularly inefficient.

[0005] In recent years oxy-combustion cycles, also known as oxy-fuel cycles or oxy-fuel combustion cycles, have been developed, wherein fuel, such as natural gas or another fossil fuel, is blended into a mixture of an oxidant consisting mainly of oxygen (O2) and carbon dioxide (CO2) at high pressure. The blend of fuel, oxidant and carbon dioxide bums in a combustor of an expander producing a pressurized flue gas consisting exclusively or almost exclusively of carbon dioxide and water.

[0006] The flue gas is expanded in the expander to generate mechanical power. The exhaust flue gas discharged at the discharge side of the expander is cooled in a regenerative heat exchanger and further chilled to condensate water which can thus be removed from the chilled flue gas. The low-temperature flue gas, consisting mainly or exclusively of carbon dioxide is pressurized and recycled through the regenerative heat exchanger towards the combustor of the expander.

[0007] Oxygen supplied to the combustor of the expander can be obtained by separation from ambient air, removing nitrogen therefrom, such that the working fluid supplied to the combustor mainly consists of oxygen and carbon dioxide and does not include nitrogen. The resulting flue gas mainly consists of water and carbon dioxide. Water is removed from the flue gas by condensation and the part of water-free flue gas, which is not recycled to the combustor, can be efficiently processed in a carbon dioxide capturing unit.

[0008] The oxy-combustion cycle summarized above is a semi-closed cycle, in that only a fraction of the flue gas exits the cycle after water has been removed therefrom.

[0009] Oxy-combustion cycles, such as those described above, are particularly interesting in terms of efficiency, reduction of noxious emissions and ease of CO2 sequestration. However, they operate under CO2 supercritical conditions at the inlet of the expander and are characterized by high pressure and temperature values inside the expander and specifically inside the combustor. These operating conditions pose difficult constraints in the casing design. Moreover, complex machinery arrangements for pressurizing the recycling carbon dioxide are needed, which include a sequence of compressors and pumps, as the recycling carbon dioxide is present in liquid for at the outlet of the pressurizing section of the thermodynamic cycle. The pressurizing arrangement is expensive and difficult to control. Moreover, the arrangement of several differentpressurizing turbomachines increases the footprint of the system.

[0010] Improvements in the design of the power generation systems based on oxycombustion cycles, aimed at simplifying the overall arrangement would be highly desirable.SUMMARY

[0011] According to the present disclosure, a power generation system, is provided, which includes an expander comprising a combustor and an expansion turbine. The combustor is adapted to receive a fuel, oxygen, and a recycling carbon dioxide stream, and to combust the fuel with the oxygen in the presence of the recycling carbon dioxide stream, producing a compressed combustion gas stream containing carbon dioxide. The expansion turbine is fluidly coupled with the combustor, and comprises an outlet for discharging an expanded combustion gas stream containing carbon dioxide. A heat exchange unit having a hot side with a hot-side inlet and a hot-side outlet, is further provided, wherein the hot-side inlet is fluidly coupled with the outlet of the expansion turbine and adapted to receive the expanded combustion gas stream and transfer heat therefrom to the recycling carbon dioxide stream. A recycling carbon dioxide compressor section includes an inlet fluidly coupled with the hot-side outlet of the heat exchange unit, and an outlet fluidly coupled with an inlet of a first cold side of the heat exchange unit, the first cold side of the heat exchange unit being in heat exchange with the hot side of the heat exchange unit and adapted to receive heat therefrom. The recycling carbon dioxide compressor section is adapted to pressurize recycling carbon dioxide from the hot-side outlet of the heat exchange unit. The recycling carbon dioxide compressor section comprises a plurality of sequentially arranged compressor units. At least one intercooler is arranged between two compressor units arranged in sequence. The compressor units and the at least one intercooler are configured and controlled such that the recycling carbon dioxide stream processed through the recycling carbon dioxide compressor section is maintained in a supercritical condition along the whole compression process, up to the inlet of the most downstream compressor unit. The use of pumps is thus avoided, making the system simpler an easier to control compared to systems of the prior art.

[0012] In embodiments disclosed herein, the recycling carbon dioxide compressor section does not include a pump. I.e., the recycling carbon dioxide compressor section consists only of compressor units. The delivery side of the most downstream compressor unit of the recycling carbon dioxide compressor section is directly coupled to the inlet of the first cold side of the heat exchange unit. Directly coupled means that there are no further pressurizing units in-between, and the delivery pressure at the recycling carbon dioxide compressor section is approximately the same pressure at the inlet of the first cold side of the heat exchange unit. In embodiments disclosed herein, the compressor units and the intercooler(s), of which the compressor section consists, are configured and controlled such that all points of a compression line in an enthalpy -vs-pressure diagram, are on the right side of the isothermal curve which passes through the critical point.

[0013] According to another aspect, disclosed herein is a method for power generation, comprising:introducing a fuel, oxygen, and a recycling carbon dioxide stream into a combustor;combusting the fuel and generating a combustion gas stream comprising carbon dioxide;expanding the combustion gas stream across an expansion turbine fluidly coupled with the combustor, to generate power;releasing an expanded combustion gas stream from the expansion turbine; withdrawing heat from the expanded combustion gas stream by passing the expanded combustion gas stream through a heat exchange unit;removing water from the cooled expanded combustion gas stream to obtain a recycling carbon dioxide stream;supplying recycling carbon dioxide to a carbon dioxide compressor section comprising a plurality of sequentially arranged compressor units and at least a first intercooler arranged between two compressor units arranged in sequence;compressing the recycling carbon dioxide in the recycling carbon dioxide compressor section to a final pressure maintaining the recycling carbon dioxide in a gaseous or supercritical state, i.e. without liquefying the recycling carbon dioxide; delivering the compressed recycling carbon dioxide at said final pressurethrough the heat exchange unit and heating said recycling carbon dioxide with heat released by the expanded combustion gas; anddelivering the heated recycling carbon dioxide to the expander.

[0014] Further features and embodiments of the system and of the method according to the present disclosure are outlined in the enclosed claims and described with reference to the attached drawings.BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Reference is now made briefly to the accompanying drawings, in which:Fig.1 illustrates a schematic of a power generation system using an oxy-com-bustion cycle according to the present disclosure, in one embodiment;Fig.2 illustrates an enthalpy-pressure diagram of the cycle performed by the system of Fig.1; andFig.3 illustrates a schematic of a power generation system using an oxy-com-bustion cycle according to the present disclosure, in another embodiment.DETAILED DESCRIPTION

[0016] In short, the power generation system and method described herein use an oxy-combustion cycle wherein the recycling carbon dioxide is pressurized using only compressors and without the use of pumps. To reduce the compression work, the compressor arrangement is intercooled, i.e. heat is removed from partially compressed recycling carbon dioxide prior to reaching the final pressure. Using compressors and avoiding the use of pumps, as is currently done in known systems and methods, provides several advantages over the prior art, including of cost reduction, easier control of the rotating turbomachinery, and reduction of overall footprint of the system.

[0017] Fig.l illustrates schematically an embodiment of a power generation system 1 according to the present disclosure.

[0018] The power generation system 1 comprises a turbine or expander 3, which in turns comprises a combustor 3.1 and an expansion turbine 3.2. The combustor 3.1 is fluidly coupled to a fuel line 5 and is adapted to receive a fuel therefrom, for instance natural gas.

[0019] The combustor 3.1 is further fluidly coupled to an oxidant line 7, which supplies an oxidant containing oxygen to the combustor 3.1. In some embodiments, the oxidant consists of a mixture containing oxygen and carbon dioxide.

[0020] The combustor 3.1 is further fluidly coupled to at least one recycling carbon dioxide line 9, which supplies high-pressure recycling carbon dioxide to the expander 3.

[0021] The combustor 3.1 is configured to combust the fuel with the oxygen contained in the oxidant stream delivered by the oxidant line 7 in the presence of the recycling carbon dioxide stream delivered by recycling carbon dioxide line 9, thus producing a compressed combustion gas stream containing mainly or almost exclusively carbon dioxide and steam.

[0022] The expansion turbine 3.2 is fluidly coupled with the combustor 3.1 to receive the compressed and hot combustion gas from the combustor 3.1, and to expand the combustion gas converting gas enthalpy into power, available on an output shaft 3.3 of the expander 3. The expansion turbine 3.1 comprises an outlet 3.4 for discharging expanded and exhausted combustion gas containing mainly, or almost exclusively carbon dioxide and steam.

[0023] The output shaft 3.3 can be drivingly coupled to an electric generator 11, or to another load. In some embodiments, not shown, the output shaft 3.3 can be drivingly coupled to one or more compressors of the power generation system 1, described below.

[0024] The power generation system 1 further comprises a heat exchange unit 13, which is adapted to remove heat from the expanded process gas discharged by the expander 3, and to recover thermal energy which is used to heat a compressed recycling carbon dioxide stream.

[0025] The heat exchange unit 13 comprises a hot side 13.1 with a hot-side inlet 13.2 and a hot-side outlet 13.3. The hot-side inlet 13.2 is fluidly coupled with the outlet 3.4 of the expansion turbine 3.2 and is adapted to receive the expanded combustion gas stream and transfer heat therefrom to the recycling carbon dioxide stream which isdelivered to the expander 3 through the recycling carbon dioxide line 9.

[0026] In some embodiments, the power generation system 1 further includes a cooler 15, which is fluidly coupled with the hot-side outlet 13.3. The partially cooled expanded combustion gas delivered through the hot side 13.1 of the heat exchange unit 13 is further cooled in the cooler 15 to condensate water contained therein.

[0027] The outlet of the cooler 15 can be fluidly coupled with a water separator 17, having an inlet 17.1, which is adapted to receive the cooled combustion gas containing condensed water from the cooler 15, a gas outlet 17.2, and a water outlet 17.3. Condensed water is removed from the gaseous flow at the water outlet 17.3 and the resulting dehydrated gaseous flow leaves the water separator 17 through the gas outlet 17.2.

[0028] After water removal, the resulting gaseous flow consists mainly or almost exclusively of carbon dioxide. The resulting gaseous stream exiting the water separator 17 is referred to in the present disclosure as carbon dioxide or recycling carbon dioxide, even though it shall be understood that the gaseous stream can contain a percentage of other species. In some embodiments, typically the gas streaming from the water separator 17 at the gas outlet 17.2 and recycled towards a cold side of the heat exchange unit 13 contains at least 70% by volume of carbon dioxide, and preferably at least 80% of carbon dioxide.

[0029] A recycling carbon dioxide compressor section 19 is fluidly coupled with the gas outlet 17.2 of the water separator 17 and is adapted to re-compress the recycling carbon dioxide stream received from the water separator 17 and which is recycled towards the expander 3 as described below.

[0030] As shown in Fig.1, the recycling carbon dioxide stream exiting the water separator 17 is divided into a main stream, which is delivered through a line 23 to the recycling carbon dioxide compressor section 19, and a bypass stream, which is delivered through a line 25 to an oxidant supply line 27.

[0031] The recycling carbon dioxide compressor section 19 comprises in turn an inlet 19.1 fluidly coupled with the hot-side outlet 13.3 of the heat exchange unit 13 through the water separator 17 and the cooler 15, and possible additional ancillary devices, notshown. The recycling carbon dioxide compressor section 19 further includes an outlet 19.2 fluidly coupled with an inlet 13.4 of a first cold side 13.5 of the heat exchange unit 13. The first cold side 13.5 is in turn fluidly coupled with the expander 3.

[0032] The first cold side 13.5 of the heat exchange unit 13 is in heat exchange with the hot side 13.1 of the heat exchange unit 13 and is adapted to receive therefrom heat released by the expanded and exhausted combustion gas which circulates through the hot side 13.1 of the heat exchange unit 13.

[0033] The recycling carbon dioxide compressor section 19 is therefore configured to pressurize recycling carbon dioxide received from the hot-side outlet 13.3 of the heat exchange unit 13 after water removal at the water separation separator 17, and deliver the compressed recycling carbon dioxide stream to the first cold side 13.5 of the heat exchange unit 13, to recover heat from the expanded and exhausted combustion gas flowing through the hot side 13.1 of the heat exchange unit 13.

[0034] The recycling carbon dioxide compressor section 19 comprises a plurality of sequentially arranged compressor units. In the embodiment schematically shown in Fig.l, the recycling carbon dioxide compressor section 19 includes a first compressor unit 30 comprised of a first compressor 31, and a second compressor unit 32 comprised of a second compressor 33.

[0035] In other embodiments, the recycling carbon dioxide compressor section 19 can comprise more than two compressor units.

[0036] One, some or all compressors (such as compressors 31, 33) of the compressor units 30, 32 of the recycling carbon dioxide compressor section 19 can be a multi-stage compressor, i.e., can include one or more compressor stages in sequence.

[0037] The recycling carbon dioxide compressor section 19 is intercooled, i.e. includes at least one intercooler positioned between two sequentially arranged compressor units, or between two compressors or between two compressor stages of the same compressor. The intercooler is adapted to remove compression heat generated in a first compression phase, before performing a second compression phase. In the embodiment of Fig.1, an intercooler 35 is positioned between the first compressor unit 30 andthe second compressor unit 32.

[0038] While in the schematic of Fig.1 a single intercooler 35 is foreseen, in other embodiments, the recycling carbon dioxide compressor section 19 may include more than one intercooler. For instance, one or both compressor units 30, 32 upstream and downstream of the intercooler 35 may be in turn intercooled, e.g. may include one or more intercoolers between compressors or compressor stages forming part of the respective compressor unit 30, 32.

[0039] As will be described in more detail with reference to Fig.2, the compressor units 31, 33 and the at least one intercooler 35 are configured and controlled such that the recycling carbon dioxide stream processed through the recycling carbon dioxide compressor section 19 reaches a supercritical condition but does never reach a liquid state. Specifically, at the outlet of the last intercooler, where the lowest enthalpy content of the recycling carbon dioxide is achieved, the recycling flow is still in a supercritical, and not liquid condition. The recycling carbon dioxide reaches the inlet of the first cold side of the heat exchange unit, without being liquefied along the recycling carbon dioxide compressor section 19.

[0040] The line 25 diverts a fraction of the recycling carbon dioxide stream delivered by the water separator 17, and feeds said diverted fraction of recycling carbon dioxide stream to an oxidant compressor section 41. The oxidant compressor section 41 comprises at least one compressor 43. In other embodiments, not shown, the oxidant compressor section 41 can include two or more compressors. One, some or each compressor of the oxidant compressor section 41 can be a multistage compressor.

[0041] The oxidant compressor section 41 comprises an oxygen inlet 41.1 fluidly coupled with an oxygen source 45, and a carbon dioxide inlet 41.2, which is in turn fluidly coupled with the line 25. The oxygen source 45 may be, or include, an air separation unit, which separates nitrogen from air, and feeds oxygen or oxygen and additional gaseous components contained in air and not removed by the air separation unit, to the oxygen inlet 41.1. The composition and the thermodynamic conditions of the gas supplied by the oxygen source depend on the air separation technology used. In any event, the predominant component of the gas is oxygen and the unit 45 is thereforereferred to as an oxygen source.

[0042] An outlet 41.3 of the oxidant compressor section 41 is fluidly coupled with an inlet 13.6 of a second cold side 13.7 of the heat exchange unit 13, in heat exchange with the hot side 13.1 of the heat exchange unit 13 and adapted to receive heat therefrom. The second cold side 13.7 has a cold-side outlet 13.8, which if fluidly coupled with the oxidant line 7, supplying the oxidant to the expander 3.

[0043] Recycling carbon dioxide is added through line 25 to the gaseous stream delivered by the oxygen source 45, such that the oxidant flow processed through the oxidant compressor unit 41 contains a certain amount of carbon dioxide. The carbon dioxide percentage can even be predominant over the oxygen percentage of the oxidant flow. For instance, the oxidant flow processed through the oxidant compressor unit 41 can contain around 15-25% in molar weightof oxygen and around 85-75% of carbon dioxide. Minor quantities of other gaseous species contained in air and not removed by the air separation unit can also be contained in the oxidant.

[0044] The oxidant compressor section 41 is adapted to pressurize the oxidant stream, consisting mainly of recycling carbon dioxide from line 25 and oxygen from the oxygen source 45, up to the pressure required for supply to the expander 3.

[0045] Fig.2 shows an enthalpy-vs-pressure diagram of the cycle performed by the power generation system 1 of Fig.1. The main points of the cycle are labeled with letters A-B-C-D-E-F-G-H. Corresponding letters are reported on the schematic of Fig.l. Specifically, A indicates the conditions at the inlet of the expansion turbine 3.2 and B indicates the condition at the discharge 3.4 of the expansion turbine 3.2. The line A-B in Fig.2 therefore represents the expansion of the combustion gas through the expansion turbine 3.2. Along line B-C the combustion gas is cooled in the hot side of the heat exchange unit 13 and in the cooler 15. Point C represents the thermodynamic conditions at the inlet of the recycling carbon dioxide compressor section 19.

[0046] The compression phase of the recycling carbon dioxide flowing through the recycling carbon dioxide compressor section 19 is represented by the line C, D, E, F, G, H. In Fig.2 a first compression step is shown along line C, D, E, and includes an intercooling phase in an intercooler, not shown in Fig.l and contained in the firstcompressor unit 30. Thus, the curve C, D, E, F shows how the compression in the recycling carbon dioxide compressor section 19 can include more than two compression phases separated by more than one inter-refrigeration step.

[0047] Between point F and point G the partially compressed recycling carbon dioxide delivered by the first compressor unit 33 is cooled in the intercooler 35. The final compression step between G and H is performed in second compressor unit 32, which in the exemplary embodiment of Fig.1 is the most downstream compressor unit.

[0048] In the diagram of Fig.2 the dashed line between points C and I represents the oxidant stream processed through the oxidant compressor section 41.

[0049] The compressor units 31, 33 and the intercool er(s) 35 are configured and controlled such that in point G the process fluid, mainly consisting of partly compressed carbon dioxide, is in a supercritical, non-liquid phase. This means that the thermodynamic cycle is controlled such that in the enthalpy-vs-pressure diagram point G is on the right side of the isothermal curve Tc which passes through the critical point CP of the diagram of Fig.2.

[0050] Specifically, in some embodiments the cycle is controlled such that the process fluid in point G, consisting mainly of carbon dioxide, has a compression factor, i.e. a compressibility factor, higher than 0.1, and for instance lower than 0.6. In some embodiments, the compression factor is comprised between 0.1 and 0.6, or between 0.15 and 0.45.

[0051] As known, the compressibility factor, aka compression factor is defined as:pVz = — —nRTwherep is the pressuren is the number of molesR is the gas constantT is the absolute temperatureV is the unit volume.

[0052] This allows pressurization of the recycling carbon dioxide to be performed using only compressors and avoiding the use of pumps. Thus, a simpler and more controllable system and cycle is obtained compared to the systems of the current art, wherein the last pressurization phase is performed in a pump and the recycling carbon dioxide is in a liquid phase.

[0053] The one or more intercooling steps along the curve C, D, E, F, G, H reduce the compression work. The simplification in terms of plant layout offsets the partial reduction of the efficiency of the compression phase, since the entire pressurization step is performed with the process fluid in a gaseous or supercritical, non-liquid phase.

[0054] Performing the entire pressurization step with compressors, avoiding the use of pumps, can be particularly beneficial in small power generation systems, for instance having a rated power between 50 and 250 MW, or preferably between 50 and 150 MW, for instance between 50 and 120 MW. With a small power rate, the advantage in terms of plant simplification is more significant than the potential reduction in energy efficiency, originating from the need to operate constantly with the process fluid in the non-liquid phase, i.e. in the gaseous or supercritical phase till the cold-side inlet 13.4 of the first cold side 13.5 of the heat exchange unit 13.

[0055] In the embodiment of Figs. 1 and 2 the recycling carbon dioxide, which is blended with the oxygen from the oxygen source 45 to form the oxidant flow, is diverted from the main recycling carbon dioxide stream at the lowest cycle pressure, i.e. at the pressure at the discharge side of the expander 3. This, however, is not the only possible solution. In general, the pressure of the recycling carbon dioxide which is added to the oxygen forming the oxidant stream can be chosen, e.g., based on the operating pressure of the oxygen source 45, i.e. as a function of the pressure at which oxygen is made available at the inlet 41.1 of the oxidant compressor section 41.

[0056] In Fig.3 a second embodiment of a power generation system 1 is shown, which differs from the system 1 of Fig.1 primarily in that carbon dioxide is supplied to the oxidant compressor section 41 at a higher pressure than in the system shown in Fig.l. In Fig.3 parts or elements corresponding to those of Fig. 1 are labeled with the same reference numbers and are not described again. The main difference betweenFig.3 and Fig.1 is that the carbon dioxide supplied to the suction side of the oxidant compressor section 41 is taken at the discharge side of the first compressor unit 31 rather than upstream of the recycling carbon dioxide compressor section 19.

[0057] Exemplary embodiments have been disclosed above and illustrated in the ac-companying drawings. It will be understood by those skilled in the art that various changes, omissions and additions may be made to that which is specifically disclosed herein without departing from the scope of the invention as defined in the following claims.

Claims

CLAIMS1. A power generation system, comprising:an expander comprising a combustor and an expansion turbine; wherein the combustor is adapted to receive a fuel, oxygen, and a recycling carbon dioxide stream, and to combust the fuel with the oxygen in the presence of the recycling carbon dioxide stream, producing a compressed combustion gas stream containing carbon dioxide; and wherein the expansion turbine is fluidly coupled with the combustor, and comprises an outlet for discharging an expanded combustion gas stream containing carbon dioxide;a heat exchange unit having a hot side with a hot-side inlet and a hot-side outlet; wherein the hot-side inlet is fluidly coupled with the outlet of the expansion turbine and adapted to receive the expanded combustion gas stream and transfer heat therefrom to the recycling carbon dioxide stream; anda recycling carbon dioxide compressor section, comprising: (i) an inlet fluidly coupled with the hot-side outlet of the heat exchange unit; (ii) and an outlet fluidly coupled with an inlet of a first cold side of the heat exchange unit, the first cold side of the heat exchange unit being in heat exchange with the hot side of the heat exchange unit and adapted to receive heat therefrom; wherein the recycling carbon dioxide compressor section is adapted to pressurize recycling carbon dioxide from the hot-side outlet of the heat exchange unit;wherein the recycling carbon dioxide compressor section comprises a plurality of sequentially arranged compressor units; wherein at least one intercooler is arranged between two compressor units arranged in sequence; and wherein the compressor units and the at least one intercooler are configured and controlled such that the recycling carbon dioxide stream processed through the recycling carbon dioxide compressor section is maintained in a supercritical condition.

2. The power generation system of claim 1, wherein the recycling carbon dioxide stream in the recycling carbon dioxide compressor section maintains a compressibility factor higher than 0.1, or higher than 0.15, or between 0.1 and 0.6, or between 0.15 and 0.45.

3. The power generation system of claim 1 or 2, wherein the recyclingcarbon dioxide compressor section consists of compressor units and at least one intercooler; and wherein a delivery side of the most downstream compressor unit of the compressor section is directly coupled to the inlet of the first cold side of the heat exchange unit.

4. The power generation system of any one of the preceding claims, wherein the recycling carbon dioxide compressor section comprises a most-downstream compressor unit having a delivery side directly coupled to the inlet of the first cold side of the heat exchange unit; wherein a suction side of the most downstream compressor unit is fluidly coupled to the at least one intercooler; and wherein the at least one intercooler is controlled such that the recycling carbon dioxide stream delivered by the at least one intercooler to the suction side of the most downstream compressor unit is in a supercritical, non-liquid condition.

5. The power generation system of any one of the preceding claims, comprising an oxidant compressor section; wherein the oxidant compressor section comprises: (i) an inlet fluidly coupled with an oxygen source and with a recycling carbon dioxide stream inlet; (ii) and an outlet fluidly coupled with an inlet of a second cold side of the heat exchange unit, in heat exchange with the hot side of the heat exchange unit and adapted to receive heat therefrom; wherein the oxidant compressor section is adapted to pressurize an oxidant stream; the oxidant stream comprising a mixture of recycling carbon dioxide and oxygen from the oxygen source.

6. The power generation system of claim 5, wherein the oxidant compressor section and the recycling carbon dioxide compressor section are configured to receive recycling carbon dioxide at approximately the same pressure.

7. The power generation system of claim 5, wherein the oxidant compressor section has an inlet fluidly coupled with a delivery side of one of said plurality of sequentially arranged compressor units of the recycling carbon dioxide compressor section.

8. The power generation system of claim 7, wherein the inlet of the oxidant compressor section is fluidly coupled downstream of the first intercooler.

9. The power generation system of any one of claims 5 to 8, wherein an outlet of the second cold side of the heat exchange unit is fluidly coupled with the expander.

10. The power generation system of any one of the preceding claims, wherein an outlet of the first cold side of the heat exchange unit is fluidly coupled with the expander.

11. The power generation system of any one of the preceding claims, wherein the recycling carbon dioxide compressor section and the oxidant compressor section are fluidly coupled with the hot-side outlet of the heat exchange unit such that a first partial stream of recycling carbon dioxide at the inlet of the recycling carbon dioxide compressor section and a second partial stream of recycling carbon dioxide at the inlet of the oxidant compressor section are at a pressure approximately equal to or lower than a pressure at the outlet of the hot-side of the heat exchange unit.

12. The power generation system of any one of the preceding claims, further comprising a water separation unit having a gas inlet, fluidly coupled with the hot-side outlet of the heat exchange unit, and a gas outlet fluidly coupled with the inlet of the recycling carbon dioxide compressor section.

13. The power generation system of claim 12, when depending upon claim 6, wherein the gas outlet of the water separation unit is fluidly coupled with an inlet of the oxidant compressor section.

14. The power generation system of claim 12 or 13, further comprising a cooler positioned between the hot-side outlet and the gas inlet of the water separation unit, the cooler adapted to condensate water contained in the expanded combustion gas.

15. The power generation system of any one of the preceding claims, wherein the oxidant compressor section does not include a cooler.

16. The power generation system any one of claims 1 to 14, wherein the oxidant compressor section includes a cooler.-16-17. The power generation system of any one of the preceding claims, wherein the oxidant compressor section comprises a single compressor.

18. The power generation system comprising a carbon dioxide exporting line.

19. The power generation system of any one of the preceding claims, wherein the recycling carbon dioxide compressor section and the oxidant compressor section are configured such that a mass flow rate processed by the recycling carbon dioxide compressor section is at least twice a mass flow rate processed by the oxidant compressor section.

20. The power generation system of any one of the preceding claims, wherein the recycling carbon dioxide compressor section and the oxidant compressor section are configured such that a mass flow rate of the first partial stream of recycling carbon dioxide is approximately at least three times a mass flow rate of the second partial stream of recycling carbon dioxide.

21. A method for power generation, comprising:introducing a fuel, oxygen, and a recycling carbon dioxide stream into a combustor;combusting the fuel and generating a combustion gas stream comprising carbon dioxide;expanding the combustion gas stream across an expansion turbine fluidly coupled with the combustor, to generate power;releasing an expanded combustion gas stream from the expansion turbine; withdrawing heat from the expanded combustion gas stream by passing the expanded combustion gas stream through a heat exchange unit;removing water from the cooled expanded combustion gas stream to obtain a recycling carbon dioxide stream;supplying recycling carbon dioxide to a carbon dioxide compressor section comprising a plurality of sequentially arranged compressor units and at least a first intercooler arranged between two compressor units arranged in sequence;compressing the recycling carbon dioxide in the recycling carbon dioxide-17-compressor section to a final pressure maintaining the recycling carbon dioxide in a gaseous or supercritical state;delivering the compressed recycling carbon dioxide at said final pressure through the heat exchange unit and heating said recycling carbon dioxide with heat released by the expanded combustion gas; anddelivering the heated recycling carbon dioxide to the expander.

22. The method of claim 21, wherein during the step of compressing the carbon dioxide is maintained with a compression factor higher than 0.1, or higher than 0.15, or between 0.1 and 0.6, or between 0.15 and 0.45.

23. The method of claim 21 or 22, wherein the step of compressing the recycling carbon dioxide is performed using compressors and not using pumps.

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