GB2600180A

GB2600180A - Oxy-fuel power generation and optional carbon dioxide sequestration

Info

Publication number: GB2600180A
Application number: GB2100460.1A
Authority: GB
Inventors: Austin Hastings Robert; Dawn Hastings Alison
Original assignee: Tigre Technologies Ltd
Current assignee: Tigre Technologies Ltd
Priority date: 2021-01-14
Filing date: 2021-01-14
Publication date: 2022-04-27
Anticipated expiration: 2041-01-14
Also published as: GB202100460D0; GB2600180B

Abstract

A turbine system 100 comprising an oxy-fuel gas turbine generator comprising a combustion chamber and a turbine. Liquid oxygen is pumped to a liquid oxygen feed connected to the combustion chamber, liquid fuel is pumped to a liquid fuel feed connected to the combustion chamber, wherein oxygen and fuel are injected into and combusted in the combustion chamber in the presence of steam which is fed into the combustion chamber via a steam feed. Exhaust fluids are expanded through the turbine to drive an electrical generator. Water and/or steam from the exhaust fluids is separated and recirculated as steam to the steam feed of the combustion chamber by way of an integrated recuperator and separator. The integrated recuperator and separator comprises an evaporator heat exchanger, an economiser heat exchanger, a first stage condenser and a second stage condenser. The second stage condenser comprises a separated carbon dioxide outlet, a separated water outlet, and a cooling water outlet.

Description

OXY-FUEL POWER GENERATION AND OPTIONAL CARBON DIOXIDE

SEQUESTRATION

[0001] The present disclosure relates to methods and systems for oxy-fuel power generation.

BACKGROUND

[0002] The use of natural gas as a fuel in gas turbine power plants is well-established. In known gas turbine systems, a gaseous oxidant (typically air) is pressurised in a compressor and fed to a combustion chamber. A fuel (typically natural gas, which is primarily methane) is injected into the combustion chamber where it mixes with the pressurised oxidant and combusted at a high temperature. The combustion process produces a high temperature, high pressure exhaust gas stream that enters and expands into a turbine section of the turbine system. As the hot combustion gas expands through the turbine section, it causes rotation of typically several sets of turbine rotors. The rotation of the turbine rotors is used to spin an electromagnetic generator in order to generate electricity. In addition, rotation of the turbine rotors also drives the compressor to draw more pressurised oxidant into the combustion chamber.

[0003] However, it will be appreciated that the efficiency of known gas turbine generators leaves room for improvement. For example, a substantial amount of energy from the expansion of the hot combustion gas is used to drive the rotors of the compressor, rather than being converted to electrical energy. Moreover, compression of gaseous oxidant by a compressor is a relatively inefficient process.

[0004] A further drawback of known gas turbine power plants is that combustion using air as an oxidant results in exhaust products containing a relatively low concentration of carbon dioxide relative to nitrogen, oxygen and other gases. This can make the separation of carbon dioxide from the exhaust products difficult. Additionally, using air as an oxidant can result in the generation of NOx pollutants in the exhaust gas output from the gas turbine.

[0005] Accordingly, it has been proposed to use substantially pure oxygen, rather than air, as the oxidant in a gas turbine power plant. An oxy-fuel gas turbine has a number of advantages over an air-fuel gas turbine. One advantage is that oxy-fuel combustion yields exhaust gases that is rich in carbon dioxide (when the fuel is a hydrocarbon), and mixed substantially only with water in the steam phase. As such, separation of carbon dioxide from the exhaust gas mix is facilitated.

[0006] Accordingly, challenges remain in connection with improving the efficiency of such systems.

BRIEF SUMMARY OF THE DISCLOSURE

[0007] Viewed from a first aspect, there is provided a turbine system comprising an oxy-fuel gas turbine generator comprising a combustion chamber section and an expander turbine section, a pumped liquid oxygen feed connected to the combustion chamber, a pumped liquid fuel feed connected to the combustion chamber, and a steam feed connected to the combustion chamber, wherein oxygen and fuel are injected into and combusted in the combustion chamber in the presence of steam, and exhaust fluids from the combustion chamber are expanded through the expander turbine section to drive an electrical generator, wherein water from the exhaust fluids from the expander turbine section is separated and recirculated as steam to the steam feed of the combustion chamber.

[0008] The oxy-fuel gas turbine generator of the present disclosure does not include a compressor or compression section to compress air and/or fuel prior to combustion. Instead, the combustion chamber is supplied with oxygen and fuel that have been pumped to high pressures in the liquid phase and then injected into the combustion chamber for combustion. In some embodiments, the liquid oxygen and liquid fuel may be pumped to pressures of 2MPa (20 bar) to 7MPa (70 bar). The temperature and pressure at injection may be chosen to achieve a stoichiometric reaction of high efficiency with combustion exhaust products at temperatures and pressures suitable for expansion through the expander turbine section so as to create mechanical energy that drives one or more electrical generators. High pressure steam is also introduced into the combustion chamber. In some embodiments, the steam may also be at a pressure of 2MPa (20 bar) to 7MPa (70 bar). Because the oxygen and fuel are in the liquid phase for pressurisation, they can be pumped to high pressures. Pumping liquids to high pressure with pumps is a much more efficient process than compressing gases with a compressor. Additionally, by obviating the need for a compressor driven by the expander turbine section, more of the energy from the hot exhaust gases can be converted into kinetic energy by rotating one or more turbine rotors so as to drive the electrical generator, rather than also having to drive compressor rotors.

[0009] The liquid oxygen feed may be at least 90vol% oxygen, at least 95vo1% oxygen, or at least 98vo1% oxygen.

[0010] The addition of high pressure steam to the combustion chamber is also advantageous.

[0011] Firstly, the presence of steam helps to increase the density of the expander turbine section working fluid. A working fluid, in this context, is a fluid that primarily converts thermal energy into mechanical or kinetic energy expansion through one or more turbine rotors. In a conventional gas turbine generator, using air as an oxidant, there will be a high proportion of nitrogen in the air (typically around 78volcY0) to act as a useful component of the working fluid. However, a large amount of energy is needed to heat the nitrogen component of the working fluid, and much of this heat will be lost in the exhaust fluid if this is simply vented to atmosphere. The oxy-fuel gas turbine generator of the present disclosure does not use nitrogen as a significant component of the working fluid, but instead uses steam. The steam is recycled to the combustion chamber, thus helping to reduce heat loss and to improve efficiency.

[0012] Secondly, the presence of steam can help to reduce or manage the combustion temperature, which can be useful when oxy-fuel combustion takes place at temperatures substantially higher than conventional air-fuel combustion. This can help to keep the temperature of the exhaust fluids within a range that can be tolerated by the expander turbine section.

[0013] In some embodiments, the combustion chamber section and the expander turbine section may together define a first stage of the oxy-fuel turbine generator, and a combustion reheater section and an additional expander turbine section may be provided as a second stage of the oxy-fuel turbine generator.

[0014] The combustion reheater section is configured to introduce additional fuel (and, if required, additional oxidant) into the exhaust fluids from the expander turbine section of the first stage of the oxy-fuel turbine generator so as to enable a second stage combustion process. The second stage combustion process increases the temperature of the exhaust fluids from the expander turbine section of the first stage, but does not significantly change the pressure of the exhaust fluids. This helps to increase the enthalpy of the exhaust fluids, and allows them to be further expanded through the additional expander turbine section to rotate one or more additional turbine rotors so as to help drive the electrical generator also driven by the first stage of the oxy-fuel turbine generator, and/or to drive an additional electrical generator, while helping to avoid unwanted condensation of components of the exhaust fluid.

[0015] The combustion reheater can therefore be used to extract additional energy from the exhaust gases. The first stage combustion chamber section and expander turbine section operate on high temperature, high pressure fluid, and as such are highly efficient and allow a large amount of energy to be extracted from the fluid. However, if too much energy is extracted by expansion through the expander turbine section, some components of the fluid may condense to the liquid phase. Turbines are generally optimised either for gas phase or liquid phase operation, and do not operate efficiently with a mixture of phases. The exhaust fluids from the expander turbine section will still have a substantial amount of residual energy, being at a relatively high pressure but a lower temperature. Accordingly, reheating the exhaust fluids in a second stage combustion reheater allows the temperature of the exhaust fluids to be raised, thereby allowing a second stage expansion through an additional expander turbine section while avoiding unwanted condensation of components of the exhaust fluid from the first stage expander turbine section.

[0016] An oxy-fuel turbine generator does not have include nitrogen as a working fluid component. Accordingly, embodiments of the present disclosure use steam as a working fluid component to compensate for the absence of nitrogen. By recycling the steam, it is possible to recycle heat to the oxy-fuel turbine generator as well as increasing the mass density of the working fluid.

[0017] In a typical gas turbine generator with an air compressor, efficiency tends to be around 40% at most. By avoiding the need for an air compressor, and instead using pumped liquid oxygen and pumped liquid fuel, both at high pressure, it is possible to raise the efficiency of a turbine generator to around 75 to 80%. Using liquid oxygen and liquid fuel and pumping these to a high pressure (for example, 2MPa (20 bar) to 7MPa (70 bar) before vaporisation in the combustion chamber is highly efficient.

[0018] However, there is a significant energy overhead required to generate liquid oxygen. Embodiments of the present disclosure may be supplied with liquid oxygen from a cryogenic air separator. Cryogenic air separation is a convenient process for separating atmospheric air into its primary components by cooling air until it liquefies, and then performing fractional distillation to separate out the components as required. Because this is all done at very low temperature, the separated oxygen can easily be returned to the liquid phase for pumping. Although this is an energy-intensive process, when offset against the efficiency gain obtained by omitting a compressor section in the oxy-fuel turbine generator, an overall efficiency of around 45 to 50% may be achieved, which is better than the 40% efficiency obtained by a traditional gas turbine generator. Recycling steam, as described above, can help to boost the overall efficiency to around 50 to 60%.

[0019] The oxy-fuel turbine generator may be configured to use natural gas a fuel. In this case, the natural gas may be extracted from an underground natural gas reservoir. In some embodiments, the oxy-fuel turbine generator may be located above or close to the underground natural gas reservoir. This may be at an offshore or onshore location. In embodiments using natural gas as a fuel, carbon dioxide generated by way of combustion of the natural gas fuel may be separated from the exhaust fluids from the oxy-fuel turbine generator and returned to the underground reservoir for sequestration as described in more detail below. Oxy-fuel combustion of natural gas yields exhaust gases that are rich in carbon dioxide and mixed primarily only with water in the steam phase. As such, separation of carbon dioxide from the exhaust gas mixture is a simpler process that can be designed to be relatively efficient. A substantial proportion of the exhaust gas mixture is steam, which is condensable and thus facilitates separation of carbon dioxide. The latent heat energy released through condensation of the steam can be captured and reused within the cycle, rather than lost as in conventional processes where exhaust gases are discharged to atmosphere.

[0020] Alternatively, the oxy-fuel turbine generator may be configured to use hydrogen as a fuel. In these embodiments, little or no carbon dioxide is generated by combustion, and the primary product of combustion is water. The use of oxygen, rather than air, as an oxidant in the combustion process helps to avoid the generation of NO pollutants.

[0021] Alternatively, the oxy-fuel turbine generator may be configured to use hydrocarbons other than natural gas as a fuel. Carbon dioxide generated in the combustion process can be separated from the exhaust fluids and sequestered.

[0022] Using recycled water in the steam phase as a working fluid component has a number of advantages. The presence of steam in the working fluid can help to moderate temperatures in the combustion chamber and/or the combustion reheater. The presence of steam in the working fluid may increase the heat capacity of the working fluid and help to moderate temperature fluctuations. The presence of steam in the working fluid may increase the density of the working fluid, and thus create fluid mechanical conditions which improve the thermodynamic energy efficiency of the turbine system.

[0023] As noted above, the fuel for the oxy-fuel turbine generator may be natural gas, which is primarily methane, sometimes including varying amounts of other higher alkanes, and possibly a small percentage of carbon dioxide, nitrogen, hydrogen sulphide or helium. The fuel may be provided by a natural gas production system connected to new or pre-existing wells and producing reservoirs.

[0024] In embodiments where the fuel is natural gas or another hydrocarbon, the oxy-fuel turbine generator is preferably installed at or close to one or more natural gas producing reservoirs, for reasons that will be explained hereinbelow.

[0025] Hydrocarbon fuel for the oxy-fuel gas turbine generator may be received into the system from a subsurface reservoir at a production well head. The fuel may be received at any pressure above 100kPa (1 bar). The fuel may be in a temperature range from -20°C to +60°C. The fuel may be condensed to liquid phase and pumped to a pressure of 2MPa (20 bar) to 7MPa (70 bar) nominal operating pressure. The nominal respective gas temperature resulting from adiabatic compression may be from 60°C to 200°C. The compressed fuel may be vaporised and injected into the combustion chamber of the oxy-fuel gas turbine generator at any temperature above 0°C.

[0026] As noted above, a pumped liquid oxygen feed may comprise at least 90vo1%, at least 95vo1% or at least 98vo1% oxygen. Liquid oxygen may be produced by a cryogenic air separation module. The cryogenic air separation module may be configured to take ambient air at a pressure of around 100kPa (1 bar). The cryogenic air separation module may be configured to take ambient air at temperatures between -40°C and +60°C. The cryogenic air separation module produces oxygen through a fractionation process. Byproducts of the fractionation process, such as nitrogen, argon and other trace gases, may be used as a heat sink to pre-cool compressed ambient air prior to entering the fractionation process. The warmed heat sink gases may subsequently be released to atmosphere.

[0027] The oxygen feed is pumped to a pressure of 2MPa (20 bar) to 7MPa (70 bar) in the liquid phase. The liquid phase pumped oxygen may be heated to a temperature sufficient to vaporise into the gas phase prior to or at injection into the combustion chamber. Steam may be injected at the steam feed of the first stage oxy-fuel gas turbine generator at pressures between 2MPa (20 bar) and 7MPa (70 bar). Steam may be injected at the steam feed of the combustion chamber at temperatures between 220°C and 500°C. The steam may help to moderate fluid temperatures and to increase the density of the working fluid. Fluid conditions are maintained below allowable temperature, pressure and flow rate conditions as determined by the mechanical properties of the first stage expander turbine section of the oxy-fuel gas turbine generator. In some embodiments, the maximum allowable inlet temperature of the first stage expander turbine section of the oxyfuel gas turbine generator is 1350°C. In some embodiments, the maximum allowable inlet pressure of the first stage expander turbine section of the oxy-fuel gas turbine generator is 7MPa (70 bar). However, the maximum temperature and/or pressure will depend on actual fluid density and flow rates.

[0028] The fluids entering the first stage expander turbine section of the oxy-fuel gas turbine generator may be in a temperature range from 800°C to 1350°C. The fluids entering the first stage expander turbine section of the oxy-fuel gas turbine generator may be in a pressure range from 2MPa (20 bar) to 7MPa (70 bar). The fluids may undergo adiabatic expansion in the first stage expander turbine section of the oxy-fuel gas turbine generator. The exhaust from the first stage expander turbine section of the oxy-fuel gas turbine generator may comprise fluids in a pressure range from 600kPa (6 bar) to 1MPa (10 bar). The exhaust from the first stage expander turbine section of the oxy-fuel gas turbine generator may comprise fluids in a temperature range from 320°C to 780°C. The expansion of fluids in the first stage expander turbine section produces work that can drive an electrical generator. In some embodiments, the generator may be an asynchronous generator. In some embodiments, the generator may be connected to an electricity supply grid.

[0029] The exhaust fluids from the first stage expander turbine section may be heated by the combustion reheater to temperatures in a range from 525°C to 1350°C. The pressure of the exhaust fluids may be in a range from 600kPa (6 bar) to 1MPa (10 bar).

[0030] The reheated fluids may be fed into the additional expander turbine section to undergo adiabatic expansion. The exhaust from the additional expander turbine section may be in a temperature range from 320°C to 650°C. The exhaust from the additional expander turbine section may be at a pressure of around 120kPa (1.2 bar). The expansion of fluid in the additional expander turbine section produces work that can drive an electrical generator, which may be the same electrical generator as driven by the first stage expander turbine section, and/or may be an additional electrical generator. In some embodiments, the additional generator may be an asynchronous generator. In some embodiments, the additional generator may be connected to an electricity supply grid.

[0031] An integrated recuperator and separator may be provided to take the exhaust fluids from the expander turbine section, or (where provided) the additional expander turbine section, and to condense water and extract gas phase carbon dioxide from the exhaust fluids. The integrated recuperator and separator may comprise an integrated system including a heat exchanger, a heat recuperator, a condenser and a multiphase separator. The integrated recuperator and separator may be configured to perform two-phase separation on the exhaust fluids. At entry into the integrated recuperator and separator, heat may be recovered from the exhaust fluids by way of a heat exchanger to heat recirculated water to form steam at a temperature in a range of 225°C to 400°C. The steam may be at a pressure from 2MPa (20 bar) to 7MPa (70 bar). The resultant pre-heated steam is then returned for recycling through the oxy-fuel gas turbine generator. The steam may be fed to the first stage combustion chamber of the oxy-fuel gas turbine generator.

[0032] Water at ambient temperature and pressure, for example seawater On the case of offshore or coastal installations), may be used as a tertiary cooling source for the exhaust fluids from the oxy-fuel gas turbine generator in the integrated recuperator and separator.

The water may be in a temperature range from 5°C to 30°C. The exhaust fluids may be cooled to a temperature of 30°C to 95°C prior to carbon dioxide separation. The cooled exhaust fluids may be passed through a two-phase separator to separate carbon dioxide and water components. A proportion of the produced water is recirculated to the oxy-fuel gas turbine generator, and any remainder may be degassed of residual carbon dioxide and disposed of.

[0033] The produced carbon dioxide, for example at a concentration from 92vo1% to 96vo1%, may be compressed by one or more compressors and cooled with water, for example seawater, to dehydrate the carbon dioxide and to condense to the liquid phase.

The one or more compressors may be electrically driven using power generated by the oxy-fuel gas turbine generator. Any residual water produced during compression may be separated at each compression stage.

[0034] The liquid phase carbon dioxide may be discharged into the same underground reservoir from which the fuel for the turbine system has been extracted. The carbon dioxide may be discharged into the reservoir through one or more injection wells. The carbon dioxide remains in a dense phase, and depending on the depth of the reservoir, may be in a supercritical phase. This may have the effect of increasing reservoir pressure over time. This may assist fuel, for example natural gas, production through the process of re-pressurisation of the reservoir.

[0035] The oxy-fuel gas turbine generator may thus be or form part of a mostly closed circuit system in which carbon dioxide generated from combustion is sequestered back into the reservoir from which the fuel for the oxy-fuel gas turbine generator is extracted. This helps to reduce the greenhouse gas emissions resulting from combustion of natural gas and electricity generation by the oxy-fuel gas turbine generator. In addition, by using an oxy-fuel combustion process, generation of NOx gases is also significantly reduced.

[0036] Viewed from a second aspect, there is provided an integrated recuperator and separator comprising: an evaporator heat exchanger having an exhaust fluid inlet and an exhaust fluid outlet, and a water inlet and a steam outlet; an economiser heat exchanger having an exhaust fluid inlet connected to the exhaust fluid outlet of the evaporator heat exchanger and an exhaust fluid outlet, and a water inlet and a water outlet, the water outlet being connected to the water inlet of the evaporator heat exchanger; a first stage condenser having an exhaust fluid inlet connected to the exhaust fluid outlet of the economiser heat exchanger and an exhaust fluid outlet, and a cooling water inlet and a cooling water outlet; and a second stage condenser and separator having an exhaust fluid inlet connected to the exhaust fluid outlet of the first stage condenser, a separated carbon dioxide outlet, a separated water outlet connected to the water inlet of the economiser heat exchanger, a cooling water inlet and a cooling water outlet, the cooling water outlet connected to the cooling water inlet of the first stage condenser.

[0037] A pump may be provided between the separated water outlet of the second stage condenser and separator and the water inlet of the economiser heat exchanger.

[0038] A pump may be provided between the water outlet of the economiser heat exchanger and the water inlet of the evaporator heat exchanger.

[0039] A surplus produced water drainage outlet may be provided between the water outlet of the economiser heat exchanger and the water inlet of the evaporator heat exchanger.

[0040] The second stage condenser and separator may be configured as a substantially vertical column with a main body and a top portion. The separated carbon dioxide outlet may be at a top end of the top portion of the column, and the separated water outlet may be at a bottom end of main body of the column. The exhaust fluid inlet of the second stage condenser and separator may be disposed on a side wall of the main body of the column. The top portion of the column may have a shell and tube configuration, with the cooling water inlet and cooling water outlet being shell-side, and the separated carbon dioxide outlet being tube-side. The input to the tube-side of the top portion of the column receives gaseous phase carbon dioxide, separated from the exhaust fluid, from the main body of the column. The cooling water inlet and cooling water outlet may both be disposed on the top portion of the column. The cooling water inlet may be closer to the separated carbon dioxide outlet, and the cooling water outlet may be closer to the separated carbon dioxide inlet. The main body of the second stage condenser and separator may be configured as a largely empty vessel, optionally provided with internal horizontal and/or angled baffles to increase a dwell time of the separated water as it passed through the main body. This may encourage additional release of dissolved carbon dioxide.

[0041] The evaporator heat exchanger may have a shell and tube configuration. The exhaust fluid inlet and exhaust fluid outlet may be shell-side. The water inlet and steam outlet may be tube-side. It is generally preferred for higher pressure fluids to be tube-side in a shell and tube heat exchanger.

[0042] The economiser heat exchanger may have a shell and tube configuration. The exhaust fluid inlet and exhaust fluid outlet may be tube-side. The water inlet and water outlet may be shell-side. This configuration is most appropriate for the pressures and heat transfer coefficients pertaining in the economiser heat exchanger, as well as the preferred geometry of the connection between the economiser heat exchanger and the first stage condenser.

[0043] The first stage condenser may have a shell and tube configuration. The cooling water inlet and cooling water outlet may be shell-side. The exhaust fluid inlet and outlet may be tube-side. The cooling water outlet of the first stage condenser may be connected to a cooling water disposal system.

[0044] The integrated recuperator and separator may be configured as a single unit with the evaporator heat exchanger connected to the economiser heat exchanger, the economiser heat exchanger connected to the first stage condenser, and the first stage condenser connected to the second stage condenser and separator. The evaporator heat exchanger, economiser heat exchanger and first stage condenser may be arranged endto-end in a substantially horizontal, linear arrangement, and the second stage condenser and separator may be arranged vertically at one end of the first stage condenser.

[0045] The integrated recuperator and separator of the second aspect is particularly well-suited to receive exhaust fluids from oxy-fuel gas turbine generator of the first aspect, to generate steam for injection into the combustion chamber oxy-fuel gas turbine generator of the first aspect, and to separate carbon dioxide from the exhaust fluids from the oxy-fuel gas turbine generator of the first aspect.

[0046] The integrated recuperator and separator of the second aspect may be connected with the exhaust fluid inlet of the evaporator heat exchanger connected to an exhaust of the oxy-fuel gas turbine generator of the first aspect, for example an exhaust of the second stage additional expander turbine section, and with the steam outlet of the evaporator heat exchanger connected to the steam feed of the first stage combustion chamber of the oxy-fuel gas turbine generator of the first aspect.

[0047] The separated carbon dioxide output by the second stage condenser and separator may be compressed and cooled to the liquid phase before being pumped into the subsurface reservoir as discussed hereinabove.

[0048] When the integrated recuperator and separator of the second aspect is connected to the oxy-fuel gas turbine generator of embodiments of the first aspect, exhaust fluids from the second stage expander turbine section are passed into the exhaust fluid inlet of the evaporator heat exchanger. The exhaust fluid may be input at a temperature from 320°C to 650°C. The exhaust fluid may be input at a pressure of around 120kPa (1.2 bar).

[0049] Preheated, high pressure water is passed to the water inlet of the evaporation heat exchanger and may be output as high pressure, saturated steam from the steam outlet. The water at the water inlet may be at a temperature from 65°C to 95°C. The water at the water inlet may be at a pressure from 2M Pa (20 bar) to 7M Pa (70 bar). The steam at the steam outlet may be at a temperature from 225°C to 450°C. The steam at the steam outlet may be at a pressure from 2MPa (20 bar) to 7MPa (70 bar). If the evaporator heat exchanger is a shell and tube evaporator heat exchanger, it is preferable for the water inlet and steam outlet to be tube-side, since the water/steam is at higher pressure than the exhaust fluid, which is preferably shell-side.

[0050] Exhaust fluid may exit the exhaust fluid outlet of the evaporator heat exchanger and enter the exhaust fluid inlet of the economiser heat exchanger at a temperature from 150°C to 275°C. Exhaust fluid may exit the exhaust fluid outlet of the evaporator heat exchanger and enter the exhaust fluid inlet of the economiser heat exchanger at a pressure of around 110kPa (1.1 bar). Water may enter the water inlet of the economiser heat exchanger at a temperature from 25°C to 65°C. Water may enter the water inlet of the economiser heat exchanger at a pressure of around 200kPa (2 bar). Water may exit the water outlet of the economiser heat exchanger at a temperature from 62°C to 93°C.

Water may exit the water outlet of the economiser heat exchanger at a pressure of around 200kPa (2 bar). In certain embodiments, the exhaust fluid inlet and exhaust fluid outlet of the economiser heat exchanger are tube-side, and the water inlet and water outlet are shell-side. The water exiting the water outlet of the economiser heat exchanger may have its flow managed by control valves to split the output between a pump that feeds water at high pressure to the water inlet of the evaporator heat exchanger and a surplus water drainage outlet [0051] Exhaust fluid may exit the exhaust fluid outlet of the economiser heat exchanger and enter the exhaust fluid inlet of the first stage condenser at a temperature from 55°C to 65°C. Exhaust fluid may exit the exhaust fluid outlet of the economiser heat exchanger and enter the exhaust fluid inlet of the first stage condenser at a pressure of around 100kPa (1 bar). Cooling water may enter the cooling water inlet of the first stage condenser at a temperature from 15°C to 45°C. Cooling water may exit the cooling water outlet of the first stage condenser at a temperature from 45°C to 65°C. The cooling water exiting the cooling water outlet of the first stage condenser may be disposed of by way of a managed cooling water disposal system. Exhaust fluid may exit the exhaust fluid outlet of the first stage condenser at a temperature from 25°C to 65°C. Exhaust fluid may exit the exhaust fluid outlet of the first stage condenser at a pressure of around 80kPa (0.8 bar) to 90kPa (0.9 bar). In certain embodiments, the exhaust fluid inlet and exhaust fluid outlet of the first stage condenser are tube-side and the cooling water inlet and cooling water outlet of the first stage condenser are shell-side.

[0052] Exhaust fluid may exit the exhaust fluid outlet of the first stage condenser and enter the exhaust fluid inlet of the second stage condenser and separator at a temperature from 25°C to 65°C. Exhaust fluid may exit the exhaust fluid outlet of the first stage condenser and enter the exhaust fluid inlet of the second stage condenser and separator at a pressure of around 80kPa (0.8 bar) to 90kPa (0.9 bar). The exhaust fluid entering the exhaust fluid inlet of the second stage condenser and separator may comprise or consist of liquid water, water vapour, carbon dioxide and trace elements.

[0053] Cooling water may enter the cooling water inlet of the second stage condenser and separator at a temperature from 5°C to 25°C. Cooling water may exit the cooling water outlet of the second stage condenser and separator at a temperature from 15°C to 45°C and be passed to the cooling water inlet of the first stage condenser. The cooling water inlet and outlet of the second stage condenser and separator may be in a top portion of the second stage condenser and separator configured as a shell and tube heat exchanger. The cooling water inlet and outlet may be shell-side.

[0054] Gaseous components (primarily carbon dioxide and water vapour) of the exhaust fluid in the second stage condenser and separator may pass through the top portion of the second stage condenser and separator tube-side. Water vapour may condense from the exhaust fluid in the top portion of the second stage condenser and separator and fall down as water into the main body of the second stage condenser and separator. The top portion of the second stage condenser and separator includes a separated carbon dioxide outlet through which separated carbon dioxide is output. The separated carbon dioxide may be output at a temperature of 25°C to 45°C. The separated carbon dioxide may be output at a pressure of 80kPa (0.8 bar) to 90kPa (0.9 bar).

[0055] Separated water from the second stage condenser and separator may exit the separated water outlet at a temperature from 25°C to 65°C. Separated water from the second stage condenser and separator may exit the separated water outlet at a pressure of around 80kPa (0.8 bar) to 90kPa (0.9 bar). The separated water exiting the second stage condenser and separator may be fed to a pump. The pump may pressurise the separated water to a pressure of around 200kPa (2 bar). The pressurised separated water is then fed to the water inlet of the economiser heat exchanger.

[0056] The pump between the separated water outlet of the second stage condenser and separator and the water inlet of the economiser heat exchanger may be powered by electricity generated by the oxy-fuel gas turbine generator of the first aspect. The pump between the water outlet of the economiser heat exchanger and the water inlet of the evaporator heat exchanger may be powered by electricity generated by the oxy-fuel gas turbine generator of the first aspect.

[0057] Embodiments of the second aspect may provide one or more advantages, in particular but not exclusively in combination with embodiments of the first aspect. Increasing the mass density of the working fluid in the oxy-fuel gas turbine generator of the first aspect can improve thermodynamic efficiency. Selection of the components of the working fluid stream requires consideration of the compressibility of the components and any consequent latent energy effects through the process cycle for the working fluid. Using water, in both liquid and steam phases, as a component of the working fluid helps to increase the mass density of the working fluid. Latent energy losses arising from condensation and evaporation through the cycle may be managed by way of a system of partially closed circuit evaporators, condensers and two phase separators, for example by way of the integrated recuperator and separator of the second aspect.

[0058] To increase thermodynamic efficiency, it is preferable that water is not condensed from the exhaust fluid in the integrated recuperator and separator at too low a temperature so as to ensure that sufficient energy remains available from the recovery process for re-evaporating the condensed water into steam for recycling. However, condensation at too high a temperature results in less efficient separation of water from carbon dioxide. As a result, the separated carbon dioxide will contain more water vapour, and would require additional water separation processing subsequent to compression of the produced carbon dioxide into the dense liquid or supercritical phase. The exemplary operating temperatures and pressures set out hereinabove may facilitate efficient operation of the integrated recuperator and separator in this regard.

[0059] Viewed from a third aspect, there is provided a turbine system comprising an oxyfuel gas turbine generator comprising a combustion chamber section and an expander turbine section, a pumped liquid oxygen feed connected to the combustion chamber, a pumped liquid fuel feed connected to the combustion chamber, and a steam feed connected to the combustion chamber, wherein liquid oxygen and liquid fuel are vaporized injected into and combusted in the combustion chamber in the presence of steam, and exhaust fluids from the combustion chamber are expanded through the expander turbine section to drive an electrical generator, wherein water and/or steam from the exhaust fluids from the expander turbine section is separated and recirculated as steam to the steam feed of the combustion chamber by way of an integrated recuperator and separator comprising: an evaporator heat exchanger having an exhaust fluid inlet connected to an exhaust fluid outlet of the oxy-fuel gas turbine generator and an exhaust fluid outlet, and a water inlet and a steam outlet connected to the steam feed of the combustion chamber; an economiser heat exchanger having an exhaust fluid inlet connected to the exhaust fluid outlet of the evaporator heat exchanger and an exhaust fluid outlet, and a water inlet and a water outlet, the water outlet being connected to the water inlet of the evaporator heat exchanger; a first stage condenser having an exhaust fluid inlet connected to the exhaust fluid outlet of the economiser heat exchanger and an exhaust fluid outlet, and a cooling water inlet and a cooling water outlet; and a second stage condenser and separator having an exhaust fluid inlet connected to the exhaust fluid outlet of the first stage condenser, a separated carbon dioxide outlet, a separated water outlet connected to the water inlet of the economiser heat exchanger, a cooling water inlet and a cooling water outlet, the cooling water outlet connected to the cooling water inlet of the first stage condenser.

[0060] Fuel for the turbine system may be drawn from a subsurface reservoir, for example a subsurface natural gas reservoir. The separated carbon dioxide output by the second stage condenser and separator may be condensed and sequestered in the subsurface reservoir as discussed hereinabove.

[0061] Viewed from a fourth aspect, there is provided a method of electrical power generation, wherein: i) liquid oxygen and liquid fuel are pumped to a predetermined pressure, vaporised and combusted in a combustion chamber of an oxy-fuel gas turbine generator in the presence of steam; ii) exhaust fluids from the combustion chamber are expanded through an expander turbine section of the oxy-fuel gas turbine generator so as to drive an electrical generator; and iii) water from exhaust fluids from the oxy-fuel gas turbine generator is separated and recirculated as steam to the combustion chamber.

[0062] Viewed from a fifth aspect, there is provided a method of electrical power generation, wherein: i) liquid oxygen and liquid fuel are pumped to a predetermined pressure, vaporised and combusted in a combustion chamber of an oxy-fuel gas turbine generator in the presence of steam; ii) exhaust fluids from the combustion chamber are expanded through an expander turbine section of the oxy-fuel gas turbine generator so as to drive an electrical 30 generator; iii) exhaust fluids from the oxy-fuel gas turbine generator are passed through an evaporator heat exchanger having an exhaust fluid inlet and an exhaust fluid outlet, and a water inlet and a steam outlet; iv) the exhaust fluids are then passed through an economiser heat exchanger having an exhaust fluid inlet connected to the exhaust fluid outlet of the evaporator heat exchanger and an exhaust fluid outlet, and a water inlet and a water outlet, the water outlet being connected to the water inlet of the evaporator heat exchanger; v) the exhaust fluids are then passed through a first stage condenser having an exhaust fluid inlet connected to the exhaust fluid outlet of the economiser heat exchanger and an exhaust fluid outlet, and a cooling water inlet and a cooling water outlet; vi) the exhaust fluids are then passed through a second stage condenser and separator having an exhaust fluid inlet connected to the exhaust fluid outlet of the first stage condenser, a separated carbon dioxide outlet, a separated water outlet connected to the water inlet of the economiser heat exchanger, a cooling water inlet and a cooling water outlet, the cooling water outlet connected to the cooling water inlet of the first stage condenser; viii) separated carbon dioxide is extracted by way of the separated carbon dioxide outlet; and ix) steam from the steam outlet of the evaporator heat exchanger in step iv) is recirculated and provided to the combustion chamber of the oxy-fuel gas turbine generator as the steam in step i).

[0063] The exhaust fluids from the expander turbine section may be reheated in a combustion reheater and subsequently further expanded through an additional expander turbine section so as to drive the electrical generator and/or a further electrical generator.

[0064] The pumped liquid oxygen feed may be supplied by a cryogenic air separator.

[0065] The fuel may be a hydrocarbon [0066] The fuel may be natural gas, and may be extracted from a subsurface natural gas reservoir. Carbon dioxide separated from the exhaust fluids of the oxy-fuel gas turbine generator may be condensed and returned to the subsurface natural gas reservoir. The separated carbon dioxide may be compressed to a liquid or supercritical phase before being returned to the subsurface natural gas reservoir by pumping.

[0067] Alternatively, the fuel may be hydrogen.

[0068] Viewed from a sixth aspect, there is provided a method of separating carbon dioxide from water in turbine exhaust fluids, wherein: i) the turbine exhaust fluids are passed through an evaporator heat exchanger having an exhaust fluid inlet and an exhaust fluid outlet, and a water inlet and a steam outlet; ii) the turbine exhaust fluids are then passed through an economiser heat exchanger having an exhaust fluid inlet connected to the exhaust fluid outlet of the evaporator heat exchanger and an exhaust fluid outlet, and a water inlet and a water outlet, the water outlet being connected to the water inlet of the evaporator heat exchanger; iii) the turbine exhaust fluids are then passed through a first stage condenser having an exhaust fluid inlet connected to the exhaust fluid outlet of the economiser heat exchanger and an exhaust fluid outlet, and a cooling water inlet and a cooling water outlet; iv) the turbine exhaust fluids are then passed through a second stage condenser and separator having an exhaust fluid inlet connected to the exhaust fluid outlet of the first stage condenser, a separated carbon dioxide outlet, a separated water outlet connected to the water inlet of the economiser heat exchanger, a cooling water inlet and a cooling water outlet, the cooling water outlet connected to the cooling water inlet of the first stage condenser; and v) separated carbon dioxide is extracted by way of the separated carbon dioxide outlet.

BRIEF DESCRIPTION OF THE DRAWINGS

[0069] Embodiments of the invention are further described hereinafter with reference to the accompanying drawings, in which: Figure 1 is a schematic outline of a system for natural gas production and oxy-fuel combustion of natural gas to generate electrical power; Figure 2 is a schematic outline of a system for oxy-fuel combustion of hydrogen to generate electrical power; Figure 3 shows a first view of an integrated recuperator and separator that may be implemented in the system of Figure 1; Figure 4 shows a second view of the integrated recuperator and separator of Figure 3; Figure 5 shows detail A of Figure 4; and Figure 6 shows detail B of Figure 4.

DETAILED DESCRIPTION

[0070] Figure 1 shows a schematic outline of a system for natural gas production and oxy-fuel combustion with direct steam injection and expansion through an electrical turbine generator incorporating full carbon dioxide capture and underground storage.

[0071] The system is configured for installation above or close to a subsurface natural gas producing reservoir 1, which may be a naturally-occurring store of geologically-trapped natural gas. The installation may be onshore or offshore. Where the installation is offshore, the water required by the system may be obtained from seawater.

[0072] Natural gas is extracted from the reservoir 1 by way of known extraction techniques, for example by way of a well head and ancillary equipment. The natural gas may be processed as required to remove contaminants such as sand or water. The natural gas is received into the system from the subsurface reservoir 1 at the production well head at any pressure above 100kPa (1 bar) and at temperatures between -20°C and +60°C to be compressed at processing module 2 to between 2M pa (20 bar) and 7MPa (70 bar) nominal operating pressures and consequential respective gas temperatures resulting from adiabatic compression.

[0073] An oxygen separation module 3 takes ambient air and extracts oxygen from the ambient air to provide a high purity oxygen feed with an oxygen content of at least 90vol%, preferably at least 95vo1%, ideally at least 98vo1%. The ambient air may be at atmospheric pressure of around 100kPa (1 bar) and a temperature of -40°C to +60°C. The oxygen separation module 3 can be a cryogenic air separation module that separates oxygen by a fractionation process. By-products of nitrogen, argon and other trace gases produced by the cryogenic separation process may be used as a heat sink to pre-cool compressed ambient air prior to entering the fractionation process, and the warmed by-products can subsequently be released to atmosphere. The oxygen separation module 3 may make use of freshwater or seawater for cooling, and electrical power. The oxygen produced by cryogenic fractional separation is in the liquid phase and at a pressure of around 100kPa (1 bar), and will therefore be at a temperature of around -183°C. The liquid oxygen is then pumped to a pressure of 2MPa (20 bar) to 7MPa (70 bar). The liquid oxygen may be used as a cold source for pre-cooling air being drawn into the cryogenic air separation module 3, and the temperature of the pressurised oxygen may therefore rise, in some cases up to ambient air temperatures. The increase in temperature may be sufficient to vaporise the pressurised liquid oxygen into the gas phase prior to combustion. It is important to note, however, that the main pressurisation, to a pressure of 2MPa (2 bar) to 7MPa (7 bar), takes place while the oxygen is in the liquid phase, and is achieved by pumping.

[0074] A turbine system 100 comprises an oxy-fuel gas turbine generator provided with an oxygen feed, a fuel feed and a steam feed. The first stage oxy-fuel gas turbine generator includes a combustion chamber 4. Oxygen from the oxygen separation module 3 and natural gas from the natural gas processing module 2 are pumped in the liquid phase to the required pressure, for example 2MPa (2 bar) to 7MPa (7 bar). The liquid oxygen and liquid natural gas are vaporised and injected into the combustion chamber 4 and combusted in the presence of steam. The natural gas fuel is injected into the combustion chamber 4 at any temperature above 0°C and at a pressure between 2Mpa (20 bar) and 7MPa (70 bar). The oxygen is injected into the combustion chamber 4 at a pressure between 2Mpa (20 bar) and 7MPa (70 bar). The temperature of the oxygen at the point of injection into the combustion chamber 4 will be somewhere between -183°C and ambient air temperature depending on prior processing and storage, as well as on specific prevailing conditions such as volumetric flow rates, ramp rates of the flow, and system latencies of any heat exchangers employed in upstream cryogenic processes for oxygen production. The oxygen and natural gas are mixed and combusted in an oxy-fuel combustion process to provide a heat source through combustion to further mix with injected steam of between 2MPa (20 bar) and 7MPa (70 bar) and between 220°C and 400°C for the purpose of both moderating fluid temperatures and increasing fluid density. Fluid conditions can be maintained below allowable first stage expander turbine inlet temperatures of 1350°C at 7MPa (70 bar), depending on actual fluid density and flow rates. The combustion exhaust fluids are presented to a first stage expander turbine section 5 at a temperature range of between 845°C and 1350°C and pressures from 2MPa (20 bar) to 7MPa (70 bar) to undertake adiabatic expansion to pressures from 600kPa (6 bar) and 1MPa (10 bar) and temperatures between 380°C and 750°C. The exhaust fluids expand through one or more turbine rotors in the first stage expander turbine section 5 to produce work to drive an asynchronous, grid connected electrical generator and generate electrical power at (a).

[0075] The exhaust fluids from the first stage expander turbine section 5 are passed to a second stage oxy-fuel combustion reheater 6 to reheat the exhaust fluids. The reheated exhaust fluids may have temperatures between 525°C and 1350°C at pressures between 600kPa (6 bar) and 1MPa (10 bar) [0076] The reheated exhaust fluids are presented to a second stage expander turbine section 7 to undertake adiabatic expansion of the exhaust fluids to a pressure of around 120kPa (1.2 bar) and temperatures between 320°C and 650°C. The exhaust fluids expand through one or more turbine rotors in the second stage expander turbine section 7 to produce work to drive an asynchronous, grid connected electrical generator and generate electrical power at (b).

[0077] Exhaust fluids from the second stage expander turbine section 7 are passed to an integrated system of heat exchangers, heat recuperators, condensers and multiphase separators 8 that condenses water within the exhaust fluids in order to extract gas phase carbon dioxide from the exhaust fluids through two phase separation. At entry to the integrated system 8, heat is recovered from the exhaust fluids through a heat exchanger component to heat recirculated water to temperatures between 225°C and 400°C. The heated recirculated water, in the form of steam, is pumped to a pressure of 2MPa (20 bar) and 7MPa (70 bar), indicated generally at 9. The resultant preheated steam is presented to the combustion chamber 4 of the turbine system 100.

[0078] Fresh water or seawater at temperatures between 5°C and 30°C is used as a tertiary cooling source for the exhaust fluids to achieve fluid temperatures of between 60°C and 95°C prior to separation of carbon dioxide in a two-phase separator 10. The cooled exhaust fluids are passed through the two-phase separator 10 to separate the carbon dioxide and water components. A proportion of the produced water is recirculated to the combustion chamber 4 and the remainder is degassed from any residual carbon dioxide and disposed of at 11.

[0079] The produced carbon dioxide, at concentrations from 92vo1% and 96vo1%, is compressed through a multi-stage process and cooled with fresh or seawater to dehydrate the carbon dioxide and to condense to a liquid or supercritical dense phase at module 12.

Compressors are electrically driven using power generated by the turbine system, and residual produced water is separated at each of the compression stages and drained at 11.

[0080] The liquid or supercritical phase carbon dioxide produced by module 12 is discharged into the same subsurface reservoir 1 from which the natural gas providing fuel for the oxy-fuel combustion process is extracted. This may be done through injection wells that are separate from the extraction wells. The carbon dioxide remains in the dense liquid or supercritical phase and has the effect of increasing reservoir pressure over time which assists natural gas production through re-pressurisation of the reservoir 1.

[0081] In this way, embodiments of the disclosure provide a system whereby electrical power can be obtained from oxy-fuel combustion of natural gas extracted from a subsurface reservoir 1, and carbon dioxide produced by the oxy-fuel combustion process can be sequestered back into the reservoir 1. This has the dual purpose of both sequestering the carbon dioxide so as to reduce or avoid greenhouse emissions, and also re-pressurising the reservoir 1 so as to facilitate natural gas extraction. Additionally, the oxy-fuel combustion process produces little or no NOx pollution, which is also of environmental benefit.

[0082] Figure 2 shows a schematic outline of a system similar in some respects to that of Figure 1, but configured to use hydrogen as a fuel rather than natural gas. Many of the elements of the system are the same as or substantially similar to those of Figure 1, and are labelled accordingly. However, since hydrogen fuel is not extracted from natural subsurface reservoirs, and since oxy-fuel combustion of hydrogen does not generate carbon dioxide, these aspects of the Figure 1 embodiment are omitted.

[0083] Compressed hydrogen, at a pressure of 2MPa (20 bar) to 6MPa (60 bar) is provided at 150. The temperature of the compressed hydrogen may be any appropriate temperature. The hydrogen is pumped in the liquid phase to the combustion chamber 4 as fuel.

[0084] An oxygen separation module 3 takes ambient air and extracts oxygen from the ambient air to provide a high purity oxygen feed with an oxygen content of at least 90vor/o, preferably at least 95vo1%, ideally at least 98vo1%. The ambient air may be at atmospheric pressure of around 100kPa (1 bar) and a temperature of -40°C to +60°C. The oxygen separation module 3 can be a cryogenic air separation module that separates oxygen by a fractionation process. By-products of nitrogen, argon and other trace gases produced by the cryogenic separation process may be used as a heat sink to pre-cool compressed ambient air prior to entering the fractionation process, and the warmed by-products can subsequently be released to atmosphere. The oxygen separation module 3 may make use of freshwater or seawater for cooling, and electrical power.

[0085] A turbine system 100 comprises an oxy-fuel gas turbine generator provided with an oxygen feed, a fuel feed and a steam feed. The first stage oxy-fuel gas turbine generator includes a combustion chamber 4. Oxygen from the oxygen separation module 3 and hydrogen from the hydrogen supply 150 are pumped in the liquid phase to the required pressure, for example 2MPa (2 bar) to 7MPa (7 bar). The liquid oxygen and liquid hydrogen are vaporised and injected into the combustion chamber 4 and combusted in the presence of steam. The hydrogen fuel is injected into the combustion chamber 4 at a pressure between 2Mpa (20 bar) and 6MPa (60 bar). The oxygen is injected into the combustion chamber 4 at a pressure between 2Mpa (20 bar) and 7MPa (70 bar). The temperature of the oxygen at the point of injection into the combustion chamber 4 will be somewhere between -183°C and ambient air temperature depending on prior processing and storage, as well as on specific prevailing conditions such as volumetric flow rates, ramp rates of the flow, and system latencies of any heat exchangers employed in upstream cryogenic processes for oxygen production. The oxygen and hydrogen are mixed and combusted in an oxy-fuel combustion process to provide a heat source through combustion to further mix with injected steam of between 2MPa (20 bar) and 7MPa (70 bar) and between 220°C and 400°C for the purpose of both moderating fluid temperatures and increasing fluid density. Fluid conditions can be maintained below allowable first stage expander turbine inlet temperatures of 1350°C at 7MPa (70 bar), depending on actual fluid density and flow rates. The combustion exhaust fluids are presented to a first stage expander turbine section 5 at a temperature range of between 845°C and 1350°C and pressures from 2MPa (20 bar) to 7MPa (70 bar) to undertake adiabatic expansion to pressures from 600kPa (6 bar) and 1MPa (10 bar) and temperatures between 380°C and 750°C. The exhaust fluids expand through one or more turbine rotors in the first stage expander turbine section 5 to produce work to drive an asynchronous, grid connected electrical generator and generate electrical power at (a).

[0086] The exhaust fluids from the first stage expander turbine section 5 are passed to a second stage oxy-fuel combustion reheater 6 to reheat the exhaust fluids. The reheated exhaust fluids may have temperatures between 525°C and 1350°C at pressures between 600kPa (6 bar) and 1M Pa (10 bar).

[0087] The reheated exhaust fluids are presented to a second stage expander turbine section 7 to undertake adiabatic expansion of the exhaust fluids to a pressure of around 120kPa (1.2 bar) and temperatures between 320°C and 650°C. The exhaust fluids expand through one or more turbine rotors in the second stage expander turbine section 7 to produce work to drive an asynchronous, grid connected electrical generator and generate electrical power at (b) [0088] Exhaust fluids from the second stage expander turbine section 7 are passed to an integrated heat recovery system 8 that condenses water within the exhaust fluids through two phase separation. At entry to the integrated system 8, heat is recovered from the exhaust fluids through a heat exchanger component to heat recirculated water to temperatures between 225°C and 400°C. The heated recirculated water, in the form of steam, is pumped to a pressure of 2MPa (20 bar) and 7MPa (70 bar), indicated generally at 9. The resultant preheated steam is presented to the combustion chamber 4 of the turbine system 100. A proportion of the produced water is recirculated to the combustion chamber 4 and the remainder may be disposed of at 11.

[0089] Figure 3 shows an example of an integrated recuperator and separator 8 that may be implemented in the system of Figure 1. The integrated recuperator and separator 8 comprises an evaporator heat exchanger 22 having an exhaust fluid inlet 21 and an exhaust fluid outlet 23, and a water inlet 38 and a steam outlet 40. The integrated recuperator and separator 8 further comprises an economiser heat exchanger 24 having an exhaust fluid inlet 41 connected to the exhaust fluid outlet 23 of the evaporator heat exchanger 22 and an exhaust fluid outlet 42, and a water inlet 34 and a water outlet 35, the water outlet 35 being connected to the water inlet 38 of the evaporator heat exchanger 22. The integrated recuperator and separator 8 further comprises a first stage condenser 26 having an exhaust fluid inlet 43 connected to the exhaust fluid outlet 42 of the economiser heat exchanger 24 and an exhaust fluid outlet 44, and a water inlet 27 and water outlet 25 (which may be connected to drainage). The integrated recuperator and separator 8 further comprises a second stage condenser and separator 32 having an exhaust fluid inlet 45 connected to the exhaust fluid outlet 44 of the first stage condenser 26, a separated carbon dioxide outlet 29, a separated water outlet 33 connected to the water inlet 34 of the economiser heat exchanger 24, a cooling water inlet 28 and a cooling water outlet 46, the cooling water outlet 46 connected to the water inlet 27 of the first stage condenser 26. A pump 47 is connected between the separated water outlet 33 of the second stage condenser and separator 32 and the water inlet 34 of the economiser heat exchanger 24. A pump 37 is connected between the water outlet 35 of the economiser heat exchanger 24 and the water inlet 38 of the evaporator heat exchanger 22. Control valves 49 at the water outlet 35 of the economiser heat exchanger 24 allow surplus water to be drained at 36.

[0090] The exhaust fluid inlet 21 of the evaporator heat exchanger 22 may be connected to the exhaust fluid outlet of the second stage expander turbine generator 7 of Figure 1.

The steam outlet 40 of the evaporator heat exchanger 22 may provide the steam feed for the combustion chamber 4 of the first stage oxy-fuel gas turbine generator of Figure 1.

[0091] Increasing the mass density of the working fluid can improve the thermal energy efficiency of the oxy-fuel combustion driven turbine system of Figure 1. Selection of the components of the fluid stream requires consideration of the compressibility of the components and any consequent latent energy effects through the process cycle for the working fluid. The integrated recuperator and separator 8 of Figure 3 allows the use of water as a component of the working fluid in both liquid and steam phases and the management of latent energy losses arising from condensation and evaporation through the cycle with the use of a system of partially closed circuit evaporators, condensers and two phase separators.

[0092] With reference to Figure 3, exhaust fluids comprising steam, carbon dioxide and trace components received from the second stage expansion turbine generator 7 of Figure 1 are input at the exhaust fluid inlet 21 of the evaporator heat exchanger 22 at a temperature between 380°C and 750°C and a pressure of around 120kPa (1.2 bar). The exhaust fluid inlet 21 is on the shell side of the evaporator shell and tube heat exchanger 22.

[0093] Preheated high pressure water at temperature of 65°C to 95°C and a pressure of 2MPa (20 bar) to 7MPa (70 bar) passed through the tube side water inlet 38 of the evaporator heat exchanger 22. High pressure saturated steam at a temperature of 225°C to 400°C and a pressure of 2MPa (20 bar) to 7MPa (70 bar) is output from the tube side steam outlet 40.

[0094] Exhaust fluids at a temperature of 150°C to 275°C and a pressure of around 110kPa (1.1 bar) are transferred from the evaporator heat exchanger 22 shell side exhaust fluid outlet 23 to the tube side exhaust fluid inlet 41 of the economiser heat exchanger 24, as shown in more detail in Figures 3 and 5. The exhaust fluids exit the economiser heat exchanger 24 at tube side exhaust fluid outlet 42.

[0095] Exhaust fluids enter the tube side of first stage condenser 26 at tube side exhaust fluid inlet 43 from tube side exhaust fluid outlet 42 at a temperature of 55°C to 65°C and around 100kPa (1 bar) pressure. Cooling water enters the shell side water inlet 27 of the first stage condenser 26 at a temperature of 15°C to 45°C and exits from the shell side cooling water outlet 25 at a temperature of 45°C to 65°C. The cooling water output from cooling water outlet 25 can be drained, or may be discharged into the sea after appropriate drainage processing. Exhaust fluids exit the tube side exhaust fluid outlet 44 of the first stage condenser 26 at a temperature of 25°C to 65°C and a pressure of around 80kPa (0.8 bar) to 90kPa (0.9 bar).

[0096] Exhaust fluids consisting of liquid water, water vapour, carbon dioxide and trace components enter the exhaust fluid inlet 45 of the second stage condenser and separator 32 at a temperature of 25°C to 65°C and a pressure of around 80kPa (0.8bar) to 90kPa (0.9 bar). A top portion 30 of the second stage condenser and separator 32 has a shell and tube configuration, while a main body 50 of the second stage condenser and separator 32 is configured as a largely empty vessel that may have horizontal baffles or trays to increase the dwell time of the condensed water so as to facilitate further separation of dissolved carbon dioxide. Cooling water at a temperature of 5°C to 25°C enters a top portion 30 of the second stage condenser and separator 32 at shell side cooling water inlet 28 and exits via shell side cooling water outlet 46 at a temperature of 15°C to 45°C before being passed to shell side cooling water inlet 27 of the first stage condenser 26.

[0097] Carbon dioxide saturated with water vapour passes through the tube side of the top portion 30 of the second stage condenser and separator 32, resulting in condensed water returning to the main body 50 of the second stage condenser and separator 32.

Separated carbon dioxide exits from the tube side separated carbon dioxide outlet 29 of the second stage condenser and separator at a temperature of 25°C to 45°C and a pressure of around 80kPa (0.8 bar) to 90kPa (0.9 bar). Details of the top portion 30 of the second stage condenser and separator 32 are shown in Figures 4 and 5.

[0098] Carbon dioxide and any exhaust gas trace components are transferred from separated carbon dioxide outlet 29 to a module 12 an Figure 1) by way of pipeline 31 in order to dry, compress and liquify the carbon dioxide prior to sequestration in the subsurface reservoir 1.

[0099] Produced water is collected from the main body 50 of the second stage condenser and separator 32 through the separated water outlet 33 at a temperature of 25°C to 65°C and a pressure of around 80kPa (0.8 bar) to 90kPa (0.9 bar). Pump 47 is operable to pump the separated water to a pressure of around 200kPa (2 bar) before transferring the pressurised water at a temperature of 25°C to 65°C to the shell side water inlet 34 of the economiser heat exchanger 24.

[00100] Preheated water at a temperature of 62°C to 93°C exits through the shell side water outlet 35 of the economiser heat exchanger 24 with flow managed by control valves 49 to split the flow rates between a recycled water return and surplus produced water disposal 36. Pump 37 is operable to pump recycled water to a pressure of 2MPa (20 bar) to 7MPa (70 bar) into the tube side water inlet 38 of the evaporator heat exchanger 22 at a temperature of 65°C to 95°C and a pressure of 2MPa (20 bar) to 7MPa (70 bar).

[00101] High pressure saturated steam at a temperature of 225°C to 400°C and a pressure of 2MPa (20 bar) to 7MPa (70 bar) is output from the tube side steam outlet 40 and fed to the combustion chamber 4 of the first stage oxy-fuel gas turbine generator as shown in Figure 1.

[00102] Throughout the description and claims of this specification, the words "comprise" and "contain" and variations of them mean "including but not limited to", and they are not intended to (and do not) exclude other moieties, additives, components, integers or steps. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

[00103] Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

Claims

CLAIMS: 1. An oxy-fuel gas turbine generator comprising a combustion chamber section and an expander turbine section, a pumped liquid oxygen feed connected to the combustion chamber, a pumped liquid fuel feed connected to the combustion chamber, and a steam feed connected to the combustion chamber, wherein oxygen and fuel are injected into and combusted in the combustion chamber in the presence of steam, and exhaust fluids from the combustion chamber are expanded through the expander turbine section to drive an electrical generator, wherein water from the exhaust fluids from the expander turbine section is separated and recirculated as steam to the steam feed of the combustion chamber.
2. The oxy-fuel gas turbine generator as claimed in claim 1, further comprising a combustion reheater to reheat exhaust fluids from the expander turbine section and an additional expander turbine section to expand exhaust fluids from the combustion reheater to drive the electrical generator and/or an additional electrical generator.
3. The oxy-fuel gas turbine generator as claimed in claim 1 or 2, wherein the pumped liquid oxygen feed is supplied by a cryogenic air separator.
4. The oxy-fuel gas turbine generator as claimed in any preceding claim, wherein the fuel is a hydrocarbon.
5. The oxy-fuel gas turbine generator as claimed in claim 4, wherein the liquid fuel feed is connected to a subsurface natural gas reservoir and wherein carbon dioxide separated from the exhaust fluids of the oxy-fuel gas turbine generator is condensed and returned to the subsurface natural gas reservoir.
6. The oxy-fuel gas turbine generator as claimed in claim 5, further comprising a compressor module comprising at least one compressor configured to condense the separated carbon dioxide to a liquid or supercritical phase before return to the subsurface natural gas reservoir.
7. The oxy-fuel gas turbine generator as claimed in any one of claims 1 to 3, wherein the fuel is hydrogen.
8. An integrated recuperator and separator comprising: an evaporator heat exchanger having an exhaust fluid inlet and an exhaust fluid outlet, and a water inlet and a steam outlet; an economiser heat exchanger having an exhaust fluid inlet connected to the exhaust fluid outlet of the evaporator heat exchanger and an exhaust fluid outlet, and a water inlet and a water outlet, the water outlet being connected to the water inlet of the evaporator heat exchanger; a first stage condenser having an exhaust fluid inlet connected to the exhaust fluid outlet of the economiser heat exchanger and an exhaust fluid outlet, and a cooling water inlet and a cooling water outlet; and a second stage condenser and separator having an exhaust fluid inlet connected to the exhaust fluid outlet of the first stage condenser, a separated carbon dioxide outlet, a separated water outlet connected to the water inlet of the economiser heat exchanger, a cooling water inlet and a cooling water outlet, the cooling water outlet connected to the cooling water inlet of the first stage condenser.
9. The integrated recuperator and separator as claimed in claim 8, further comprising a pump between the separated water outlet of the second stage condenser and separator and the water inlet of the economiser heat exchanger.
10. The integrated recuperator and separator as claimed in claim 8 or 9, further comprising a pump between the water outlet of the economiser heat exchanger and the water inlet of the evaporator heat exchanger.
11. The integrated recuperator and separator as claimed in any one of claims 8 to 10, wherein the evaporator heat exchanger and the economiser heat exchanger are shell and tube heat exchangers, wherein the exhaust fluid inlet and exhaust fluid outlet of the evaporator heat exchanger are shell-side, and wherein the exhaust fluid inlet and exhaust fluid outlet of the economiser heat exchanger are tube-side.
12. The integrated recuperator and separator as claimed in any one of claims 8 to 11, wherein the second stage condenser and separator is configured as a substantially vertical column having a main body and a top portion, wherein the cooling water inlet, the cooling water outlet and the separated carbon dioxide outlet are provided in the top portion.
13. The integrated recuperator and separator as claimed in claim 12, wherein the exhaust fluid inlet of the second stage condenser and separator is provided in a side wall of the main body.
14. The integrated recuperator and separator as claimed in claim 12 or 13, wherein the separated water outlet of the second stage condenser and separator is provided at a bottom of the main body.
15. The integrated recuperator and separator as claimed in any one of claims 12 to 14, wherein the top portion of the second stage condenser and separator has a tube and shell configuration, and wherein the cooling water inlet and cooling water outlet are shell-side, and wherein water is separated from carbon dioxide tube-side.
16. A turbine system comprising an oxy-fuel gas turbine generator comprising a combustion chamber section and an expander turbine section, a pumped liquid oxygen feed connected to the combustion chamber, a pumped liquid fuel feed connected to the combustion chamber, and a steam feed connected to the combustion chamber, wherein oxygen and fuel are injected into and combusted in the combustion chamber in the presence of steam, and exhaust fluids from the combustion chamber are expanded through the expander turbine section to drive an electrical generator, wherein water and/or steam from the exhaust fluids from the expander turbine section is separated and recirculated as steam to the steam feed of the combustion chamber by way of an integrated recuperator and separator comprising: an evaporator heat exchanger having an exhaust fluid inlet connected to an exhaust fluid outlet of the oxy-fuel gas turbine generator and an exhaust fluid outlet, and a water inlet and a steam outlet connected to the steam feed of the combustion chamber; an economiser heat exchanger having an exhaust fluid inlet connected to the exhaust fluid outlet of the evaporator heat exchanger and an exhaust fluid outlet, and a water inlet and a water outlet, the water outlet being connected to the water inlet of the evaporator heat exchanger; a first stage condenser having an exhaust fluid inlet connected to the exhaust fluid outlet of the economiser heat exchanger and an exhaust fluid outlet, and a cooling water inlet and a cooling water outlet; and a second stage condenser and separator having an exhaust fluid inlet connected to the exhaust fluid outlet of the first stage condenser, a separated carbon dioxide outlet, a separated water outlet connected to the water inlet of the economiser heat exchanger, a cooling water inlet and a cooling water outlet, the cooling water outlet connected to the cooling water inlet of the first stage condenser.
17. The turbine system as claimed in claim 16, wherein the oxy-fuel gas turbine generator further comprises a combustion reheater to reheat exhaust fluids from the expander turbine section and an additional expander turbine section to expand exhaust fluids from the combustion reheater to drive the electrical generator and/or an additional electrical generator.
18. The turbine system as claimed in claim 16 or 17, wherein the pumped liquid oxygen feed is supplied by a cryogenic air separator.
19. The turbine system as claimed in any one of claims 16 to 18, wherein the fuel is a hydrocarbon.
20. The turbine system as claimed in claim 19, wherein the fuel feed is connected to a subsurface natural gas reservoir and wherein carbon dioxide separated from the exhaust fluids of the oxy-fuel gas turbine generator is condensed and returned to the subsurface natural gas reservoir.
21. The turbine system as claimed in claim 20, further comprising a compressor module comprising at least one compressor configured to condense the separated carbon dioxide to a liquid or supercritical phase before return to the subsurface natural gas reservoir.
22. The turbine system as claimed in any one of claims 16 to 18, wherein the fuel is hydrogen.
23. A method of electrical power generation, wherein: i) liquid oxygen and liquid fuel are pumped to a predetermined pressure, vaporised and combusted in a combustion chamber of an oxy-fuel gas turbine generator in the presence of steam; ii) exhaust fluids from the combustion chamber are expanded through an expander turbine section of the oxy-fuel gas turbine generator so as to drive an electrical generator and iii) water from exhaust fluids from the oxy-fuel gas turbine generator is separated and recirculated as steam to the combustion chamber.
24. A method of electrical power generation, wherein: i) liquid oxygen and liquid fuel are pumped to a predetermined pressure, vaporised and combusted in a combustion chamber of an oxy-fuel gas turbine generator in the presence of steam; exhaust fluids from the combustion chamber are expanded through an expander turbine section of the oxy-fuel gas turbine generator so as to drive an electrical generator; iii) exhaust fluids from the oxy-fuel gas turbine generator are passed through an evaporator heat exchanger having an exhaust fluid inlet and an exhaust fluid outlet, and a water inlet and a steam outlet; iv) the exhaust fluids are then passed through an economiser heat exchanger having an exhaust fluid inlet connected to the exhaust fluid outlet of the evaporator heat exchanger and an exhaust fluid outlet, and a water inlet and a water outlet, the water outlet being connected to the water inlet of the evaporator heat exchanger; v) the exhaust fluids are then passed through a first stage condenser having an exhaust fluid inlet connected to the exhaust fluid outlet of the economiser heat exchanger and an exhaust fluid outlet, and a cooling water inlet and a cooling water outlet; vi) the exhaust fluids are then passed through a second stage condenser and separator having an exhaust fluid inlet connected to the exhaust fluid outlet of the first stage condenser, a separated carbon dioxide outlet, a separated water outlet connected to the water inlet of the economiser heat exchanger, a cooling water inlet and a cooling water outlet, the cooling water outlet connected to the cooling water inlet of the first stage condenser; viii) separated carbon dioxide is extracted by way of the separated carbon dioxide outlet; and ix) steam from the steam outlet of the evaporator heat exchanger in step iv) is recirculated and provided to the combustion chamber of the oxy-fuel gas turbine generator as the steam in step i).
25. The method according to claim 23 or 24, wherein the exhaust fluids from the expander turbine section are reheated in a combustion reheater and subsequently further expanded through an additional expander turbine section so as to drive the electrical generator and/or a further electrical generator.
26. The method according to any one of claims 23 to 25, wherein the pumped liquid oxygen feed is supplied by a cryogenic air separator.
27. The method according to any one of claims 23 to 26, wherein the fuel is a hydrocarbon.
28. The method according to claim 27, wherein the fuel is extracted from a subsurface natural gas reservoir and wherein carbon dioxide separated from the exhaust fluids of the oxy-fuel gas turbine generator is condensed and returned to the subsurface natural gas reservoir.
29. The method according to claim 28, wherein the separated carbon dioxide is compressed to a liquid or supercritical phase before being returned to the subsurface natural gas reservoir by pumping.
30. The method according to any one of claims 23 to 26, wherein the fuel is hydrogen.
31. A method of separating carbon dioxide from water in turbine exhaust fluids, wherein: i) the turbine exhaust fluids are passed through an evaporator heat exchanger having an exhaust fluid inlet and an exhaust fluid outlet, and a water inlet and a steam outlet; ii) the turbine exhaust fluids are then passed through an economiser heat exchanger having an exhaust fluid inlet connected to the exhaust fluid outlet of the evaporator heat exchanger and an exhaust fluid outlet, and a water inlet and a water outlet, the water outlet being connected to the water inlet of the evaporator heat exchanger; iii) the turbine exhaust fluids are then passed through a first stage condenser having an exhaust fluid inlet connected to the exhaust fluid outlet of the economiser heat exchanger and an exhaust fluid outlet, and a cooling water inlet and a cooling water outlet; iv) the turbine exhaust fluids are then passed through a second stage condenser and separator having an exhaust fluid inlet connected to the exhaust fluid outlet of the first stage condenser, a separated carbon dioxide outlet, a separated water outlet connected to the water inlet of the economiser heat exchanger, a cooling water inlet and a cooling water outlet, the cooling water outlet connected to the cooling water inlet of the first stage condenser; and v) separated carbon dioxide is extracted by way of the separated carbon dioxide outlet.