Installation for capturing CO2 from feed gas streams

Abstract

The invention relates to an installation (1) for recovering CO2 from a feed gas stream (FG), comprising: - a unit (2) for treating the feed gas stream (FG) in order to produce a CO2-enriched gas stream (FCO2) and a nitrogen-enriched gas stream (FN) from the feed gas stream; - a compression stage (5) for compressing the feed gas stream (FG); - an expansion stage (8) capable of outputting mechanical energy generated by expansion of the nitrogen-enriched gas stream; - a thermal device (10) arranged to enable heat transfer between the gas stream leaving the compression stage (5) and the nitrogen-enriched gas stream before expansion; and - a device (4) for utilizing the mechanical energy output by the expansion stage.

Description

[Technical field]

[0001] The present invention relates to an installation for capturing CO2 from a feed gas stream, particularly a flue gas stream. [Background technology]

[0002] Hydrogen is an energy carrier that plays an increasingly large role in decarbonizing various sectors, especially in transport and industry. Hydrogen can be produced from the reforming reaction of natural gas (in an SMR [steam methane reforming] reactor). In the SMR unit, significant CO2 is generated during hydrogen production. To reduce the carbon footprint of hydrogen production by SMR, a CO2 capture unit of the PSA type (pressure swing adsorption device) can be added to the SMR. CO2 capture (e.g. CO2 processing and liquefaction for food applications or sequestration) can be performed cryogenically or non-cryogenically, e.g. amine washing. In this case, a high-pressure nitrogen-rich gas stream is generated in the PSA unit.

[0003] The invention proposes to improve the energy efficiency of an installation. Summary of the Invention [Means for solving the problem]

[0004] Thus, one subject of the present invention is an installation for recovering CO2 from a feed gas stream, in particular a flue gas, comprising: - a unit for treating the feed gas stream by pressure swing adsorption to produce a CO2-enriched gas stream and a nitrogen-enriched gas stream from the feed gas stream; - a compression assembly including at least one compression stage for compressing the feed gas stream prior to entering the processing unit; a turbine including at least one expansion stage and capable of providing mechanical energy generated by the expansion of a nitrogen-enriched gas stream in said expansion stage; - a thermal device arranged to allow a transfer of heat between the feed gas stream exiting the compression stage and the nitrogen-enriched gas stream prior to expansion in the expansion stage, for heating the nitrogen-enriched gas stream prior to expansion thereof; a device for utilizing the mechanical energy provided by the expansion stage.

[0005] The feed gas stream upstream of the compression assembly may contain, by way of example, 10-60 mol% CO2, particularly 15-50 mol% CO2. The remainder is mostly nitrogen and small amounts of O2. Argon Ar and trace amounts of impurities, particularly NOx, on the order of magnitude of 1 mol% or less may possibly be present.

[0006] The feed gas stream may originate, for example, from an SMR reformer, a cement plant, an oxy-combustion unit, or a lime plant.

[0007] The feed gas stream may have been pre-treated before entering the facility, for example by a scrubbing or filtration unit.

[0008] The high pressure nitrogen-rich gas stream exiting the PSA unit may contain, in addition to nitrogen, potentially the least adsorbable components such as O2, Ar, NO.

[0009] The proportion of nitrogen in the nitrogen-enriched stream is in particular between 50 and 90 vol.%.

[0010] The CO2 is a portion of the CO2-rich gas stream, for example 50-85 vol%.

[0011] Generally, compositions are given on a dry basis, i.e., water (H2O) is removed from the composition of the gas and the remaining components are standardized to 100.

[0012] According to one aspect of the invention, the feed gas stream, after being compressed in the compression assembly, arrives at the treatment unit at a pressure in the range of 3-15 bar abs, particularly 6-12 bar abs, in particular 8-10 bar abs, and at a temperature close to ambient temperature, for example 5-45°C.

[0013] According to one embodiment of the invention, the nitrogen-enriched gas stream leaves the treatment unit at high pressure, in particular at a pressure of 8-10 bar.

[0014] According to one of the aspects of the invention, the compression assembly comprises a centrifugal compressor capable of accelerating the feed gas flow through one or more wheels rotated by a motor, in particular an electric motor. The energy thus obtained by the gas flow is converted into an increase in its static pressure in a diffuser located at the outlet of each wheel. The arrangement of the wheels of the compression assembly depends on the characteristics of the process, e.g. flow rate, compression ratio, gas composition, but also on the technology specific to different compressor manufacturers.

[0015] Typically, a motor drives a main rotating shaft associated with a main gear and possibly an auxiliary gear. These gears are mechanically connected to pinions coupled to a counter rotating shaft. Each gear can therefore drive several pinions. The dimensions of each of the gears and pinions determine the rotational speed of the counter shaft as a function of the rotational speed of the motor.

[0016] If there is a single compression stage, the countershaft drives a single wheel to compress the gas stream to a selected pressure.

[0017] Where the compression assembly includes several wheels for achieving a selected overall compression ratio, i.e. the ratio of outlet pressure to inlet pressure of the compression assembly, various arrangements of these wheels are possible.

[0018] It should also be noted that if compression is performed in several stages, a compression ratio per stage is defined, i.e. the ratio of the outlet pressure of the stage to its inlet pressure.

[0019] It should also be noted in this case that it is possible to partially adjust the compression ratio of each of the different stages in order to obtain an overall compression ratio, and to do so while remaining within the range of possible dimensions, and in particular while respecting the maximum allowable speeds and temperatures. This flexibility can make it possible to more easily incorporate different compression wheels in the compression assembly.

[0020] The present invention provides a compression assembly associated with one or more wheels of an expansion turbine to recover mechanical energy generated by the expansion of a nitrogen-enriched gas stream, thus making it possible to reduce the energy that needs to be provided by the motor.

[0021] In the present invention, a turbine, also called an expansion turbine, is an item of equipment that makes it possible to expand a fluid from its high pressure to its low pressure, the ratio of these pressures being called the expansion ratio.

[0022] A turbine includes one or more expansion stages, the number of which depends on the operating conditions, in particular the expansion ratio.

[0023] If the expansion is carried out in several stages, the expansion ratio per stage is also defined, i.e. in this case the ratio between the inlet and outlet pressures of the stage in question.

[0024] The expansion of the gas is very commonly performed via one or more wheels rotated by the gas and slowed down by brakes. In practice, a turbine may thus include several wheels in series with respect to the gas flow, each wheel may have its own shape and its own rotational speed.

[0025] According to one aspect of the invention, the utilization device is a generator capable of utilizing the mechanical energy provided by the expansion stage to generate electricity.

[0026] This generator makes it possible to harness the energy of expansion by producing electricity that can be used locally or via the power grid.

[0027] In one variation, the utilization device includes a compression stage positioned to receive the mechanical energy provided by the expansion stage.

[0028] In this case, the invention may make it possible to transfer the energy provided by the turbine directly in mechanical form to the compression assembly of the installation.

[0029] In fact, from an economic point of view, it has generally proven to be more advantageous to modify the compressor by adding an expansion wheel than to install a generator.

[0030] It should be noted that in this type of expansion, the expanded gases are significantly cooled, which creates a risk of condensation in the wheel or at the outlet, which can lead to erosion problems or even corrosion problems in the presence of components such as NOx.

[0031] Heating the nitrogen-enriched gas stream prior to expansion makes it possible both to increase the recoverable energy and to avoid excessively low temperatures at the outlet of the expansion wheel(s).

[0032] In the case of several expansion stages, it is possible to adjust the expansion ratio of each stage to obtain an overall expansion ratio and to do so while staying within the range of possible dimensions and, in particular, while respecting the maximum permissible peripheral speed. This flexibility can make it possible to add expansion wheels to the compression assembly more easily.

[0033] The expansion wheel of the turbine can have different positions. - located on the same axis as the compressor stage, preferably on the other side of the pinion. It should be noted that in this case the turbine wheel and the compressor wheel rotate at the same speed. Nevertheless, the internal velocity of the gases in the wheels, especially the circumferential velocity, depends on the geometry of each wheel. - or on a second shaft, still in mechanical connection with the main gear, but through a second pinion. In this case, the rotational speed of the turbine wheel is independent of the rotational speed of the compression wheel, but depends only on the diameter of the main gear and of the second pinion, respectively. It should be noted that the main gear can be in mechanical connection with several pinions of different diameters, thus rotating several shafts, each at a selected speed. - or on a separate shaft that is mechanically connected to the secondary gear via a separate pinion. Thus, the speed of the expansion wheel is adaptable. - or possibly on a shaft including a counter pinion in mechanical connection with the pinion driving the compression stage. In this case too, the speed of the expansion wheel can be adapted by choosing the diameter of the counter pinion. In this case, the compression stage receives torque from both the motor and the expansion wheel.

[0034] It will be appreciated that depending on the configuration selected, the energy produced by the expansion of the nitrogen-enriched gas stream is transferred directly to the rotating shaft of the compression stage or to the main shaft of the motor to supply the energy from the expansion to the compression assembly.

[0035] The secondary gear can be located in any way on the motor shaft, i.e. on the same side of the motor as the main gear, or in the extension of the shaft on the other side of the motor, for example between the motor and the main gear, or after the main gear.

[0036] The two wheels of the turbine are possibly on the same shaft and may be mechanically connected to the motor shaft through a pinion in contact with the main or secondary gear, or to the shaft of the compression wheel.

[0037] As mentioned above, the energy of the expansion is directly fed to the shaft of the compression wheel or to the shaft of the motor, and thus the energy released by the expansion is fed to the compression assembly.

[0038] Where the installation includes at least two compression stages in a compression assembly and a turbine including at least two expansion stages operable with a nitrogen-enriched gas stream, the compression ratio and expansion ratio of at least one of the compression stages and at least one expansion stage, respectively, are selected such that the compression wheel of the compression stage and the expansion wheel of the expansion stage have the same rotational speed and are mounted on the same shaft.

[0039] If the installation comprises a turbine comprising at least two expansion stages operable with a nitrogen-enriched gas stream, the expansion ratio of each of the two expansion stages is selected so that the corresponding wheels have the same rotational speed and are mounted on the same shaft.

[0040] In the present invention, the expansion of a nitrogen-rich gas stream from high pressure to low pressure takes place in one or more expansion stages of a turbine, this expansion having the effect of rotating, for example, a turbine wheel, the rotation being damped by a utilization device, for example a compression assembly. The present invention thus makes it possible to improve the efficiency of the installation by recovering mechanical energy from the nitrogen-rich gas stream, which is at high pressure and capable of driving one or more expansion stages of the turbine. The efficiency is significantly improved with respect to the case where the compressed nitrogen stream is simply discarded into the atmosphere without being subject to energy recovery.

[0041] In the present invention, the expanded nitrogen stream is vented to the atmosphere.

[0042] According to one aspect of the invention, the number of expansion stages in the turbine is adjusted as needed.

[0043] According to one aspect of the invention, the expansion and compression stages of the turbine each include a rotary shaft, the shafts being connected such that rotation of the shaft of the expansion stage of the turbine provides torque to the shaft of the compression stage.

[0044] According to one aspect of the invention, the installation comprises at least two compression stages in a compression assembly and a turbine including at least two expansion stages operable by a nitrogen-enriched gas flow, each expansion stage of the turbine being arranged to transmit mechanical energy to the compression assembly, in particular whether this is directly to one of the compression stages, or to a rotating shaft common to several compression stages, or to the shaft of a motor actuating the compression stages.

[0045] According to one aspect of the invention, the plant includes at least two compression stages in a compression assembly and at least two expansion stages for expanding a nitrogen-enriched gas stream, the expansion stages being arranged to provide mechanical energy to the compression stages.

[0046] According to one aspect of the invention, the expansion stages are arranged in series such that the nitrogen-enriched gas stream passes first through one of the expansion stages and then through the other expansion stage.

[0047] According to one aspect of the invention, each expansion stage is arranged to transfer mechanical energy to one of the compression stages.

[0048] According to one aspect of the invention, the expansion stage or stages which convert the energy of the nitrogen-enriched gas stream may be dimensioned to provide at least 25%, in particular about 40% or 50%, of the mechanical energy required to operate the compression stage.

[0049] The invention is therefore particularly advantageous as it allows for the reuse of energy and thus for a reduction in the consumption of external energy in the installation.

[0050] The nitrogen-enriched gas stream prior to expansion in the expansion stage is at, for example, ambient temperature as it passes through the thermal device, and the feed gas stream leaving the compression stage is at a higher temperature.

[0051] The present invention therefore makes it possible to utilize a nitrogen-rich gas stream, which is at substantially ambient temperature at the outlet of the PSA unit, to cool a feed gas stream and to heat a nitrogen-rich gas stream, so as to improve the overall thermodynamic performance of the facility. Advantageously, the nitrogen cools the feed gas stream before compression, making this compression more efficient (less volume is compressed, therefore less energy required for compression), while at the same time the feed gas stream heats the nitrogen before expansion, increasing the recoverable energy.

[0052] According to one aspect of the invention, the thermal device includes at least one gas / gas heat exchanger arranged to enable the transfer of heat between a feed gas stream exiting the compression stage and the nitrogen-enriched gas stream prior to expansion in the expansion stage, for heating the nitrogen-enriched gas stream prior to its expansion.

[0053] The present invention makes it possible to avoid the nitrogen-rich stream becoming too cold.

[0054] According to one aspect of the invention, the gas / gas heat exchanger is located at the outlet of the compression stage such that the feed gas stream first passes through the compression stage before passing through the heat exchanger.

[0055] The gas / gas heat exchanger thus makes it possible to cool a feed gas stream which has experienced an increase in temperature due to compression in the compression stage.

[0056] According to one aspect of the invention, the thermal device includes at least two gas / gas heat exchangers for exchanging heat between a nitrogen-enriched gas stream and a feed gas stream, each gas / gas heat exchanger being disposed at the outlet of a compression stage.

[0057] According to one aspect of the invention, two gas / gas heat exchangers are arranged in series with the nitrogen-enriched gas stream such that the nitrogen-enriched gas stream passes first through one of the gas / gas heat exchangers and then through the other gas / gas heat exchanger.

[0058] According to one aspect of the invention, an expansion stage of the turbine is provided downstream of each gas / gas heat exchanger such that the nitrogen-enriched gas stream first passes through a gas / gas heat exchanger and then through an expansion stage used to transmit mechanical torque to a device for utilizing the mechanical energy.

[0059] According to one embodiment of the invention, the exchanger used, of the gas / gas or gas / heat transfer fluid type, is a shell-and-tube exchanger with grilles.

[0060] Depending on the flow rates, pressures and temperatures, these exchangers may also be plate exchangers.

[0061] According to one aspect of the invention, the nitrogen-rich gas stream passes through the same exchanger several times, for example once before expansion in the first expansion stage and then upon exiting this expansion stage, and a second time through the same exchanger before the second expansion in the second expansion stage is performed, in which case the exchanger is equivalent to two exchangers in parallel for the heat transfer fluid.

[0062] Such parallel switch configurations are described below along with examples of implementations of the present invention.

[0063] According to one aspect of the invention, the heat exchange in the gas / gas exchanger is performed by a pair of heat regenerators, one of which recovers heat from the compressed feed gas stream with cooling, and the other regenerator returns this heat to the nitrogen-enriched gas stream with cooling by said stream. The use of such a pair of heat regenerators instead of a gas / gas heat exchanger forms part of the invention.

[0064] According to one aspect of the invention, the thermal device comprises one or more gas / heat transfer fluid heat exchangers for exchanging heat between the feed gas stream and a heat transfer fluid other than the nitrogen-enriched gas stream, this fluid being, for example, glycol water belonging to a cooling circuit.

[0065] According to one aspect of the invention, a compression assembly includes a number of compression stages, one or more gas / gas heat exchangers for exchanging heat between a nitrogen-enriched gas stream and a feed gas stream, and one or more gas / heat transfer fluid heat exchangers for exchanging heat between the feed gas stream and a cooling fluid other than the nitrogen-enriched gas stream, each heat exchanger being positioned at the outlet of one of the compression stages such that the feed gas stream first passes through the compression stage before passing through the heat exchanger.

[0066] According to one aspect of the invention, all of the compression stages are followed by a heat exchanger, either of the gas / gas type or of the gas / heat transfer fluid type.

[0067] In one variant, at least one of the compression stages is directly connected to the next compression stage, with no heat exchanger between these two compression stages.

[0068] According to one aspect of the invention, the compression assembly includes four compression stages, two stages each followed by a gas / gas heat exchanger, and two stages each followed by a gas / heat transfer fluid heat exchanger.

[0069] According to one embodiment of the invention, in the circulation direction of the feed gas flow, each of the two first stages is followed by a gas / heat transfer fluid heat exchanger and each of the two last stages is followed by a gas / gas heat exchanger.

[0070] The nitrogen-enriched gas stream therefore serves to cool the feed gas stream at the outlet of the two compression stages.

[0071] According to one aspect of the invention, the turbine includes two expansion stages, one of which is located downstream of one of the gas / gas heat exchangers and the other expansion stage is located downstream of the other gas / gas heat exchanger.

[0072] According to one aspect of the invention, the expansion stages and gas / gas heat exchangers are therefore in series such that the nitrogen-enriched gas stream passes successively through one of the gas / gas heat exchangers, then through one of the expansion stages, then through the other gas / gas heat exchanger and finally through the other expansion stage.

[0073] According to one aspect of the invention, the nitrogen-enriched gas stream is at substantially atmospheric pressure when it leaves the last expansion stage, and preferably at a temperature above -10°C, more preferably above 0°C.

[0074] Such a temperature may be achieved by sufficiently heating the nitrogen-enriched gas stream and, optionally, limiting the expansion rate of the turbine, for example by a valve located in the circuit of the nitrogen-enriched gas stream, preferably at the outlet of the last expansion stage.

[0075] This allows for the avoidance of expensive materials, the avoidance or minimization of thermal insulation equipment, and the creation of ice-cold water.

[0076] Finally, the nitrogen-enriched gas stream may be used for additional heat exchange before being exhausted to the atmosphere.

[0077] According to one aspect of the invention, one or more gas / heat transfer fluid heat exchangers may be provided downstream of the last gas / gas exchanger to further cool the feed gas stream before it reaches the PSA processing unit.

[0078] According to one aspect of the invention, a single gas / gas heat exchanger is provided in the installation, which is located downstream of one of the compression stages.

[0079] The two expansion stages are arranged in series downstream of the gas / gas heat exchanger such that the nitrogen-enriched gas stream first passes through the gas / gas heat exchanger and then, successively, through the two expansion stages.

[0080] This can be advantageous when the turbine expansion rate from high pressure to low pressure is relatively low, but still too high to be implemented in a single expansion stage, so rather than providing two exchangers it is preferable to heat the turbine inlet to the maximum.

[0081] According to one aspect of the invention, one of the compression stages is directly connected to the next compression stage, e.g., the third compression stage is directly connected to the fourth compression stage, and there is no heat exchanger between the two compression stages.

[0082] According to one aspect of the invention, the installation comprises the steps of: continuously supplying a nitrogen-enriched gas stream from the outlet of the treatment unit with: - a first gas / gas heat exchanger; a first expansion stage; - a second gas / gas heat exchanger; a second expansion stage; Including, The first and second heat exchangers are arranged in parallel with each other with respect to the feed gas flow and downstream of the compression stages, in particular the first compression stage.

[0083] Thus, in this example, the nitrogen-enriched gas stream is used at the outlet of the first compression stage to cool a feed gas stream in two exchangers arranged in parallel.

[0084] According to one embodiment of the invention, the feed gas streams further split into two exchangers in parallel are combined at the outlet of the two exchangers to reform a single feed gas stream passing through a gas / heat transfer fluid exchanger.

[0085] As can be seen, for the feed gas stream the two gas / gas exchangers are interpreted as being in parallel, and for the nitrogen-enriched gas stream these two gas / gas exchangers are interpreted as being in series.

[0086] According to one aspect of the invention, the installation includes an intermediate heat circuit using an intermediate heat transfer fluid different from the nitrogen-enriched gas stream and the feed gas stream, the intermediate circuit being arranged to enable heat exchange between the nitrogen-enriched gas stream and the feed gas stream via the intermediate heat transfer fluid.

[0087] According to one aspect of the invention, when there are multiple compression stages, the nitrogen-enriched gas stream is heated directly by a gas / gas exchanger or indirectly by a gas / heat transfer fluid exchanger via a heat transfer fluid by extracting heat from a feed gas stream leaving a compression stage, preferably having a maximum temperature above 100°C, more preferably above 120°C, this temperature being obtained by ensuring that said compression stage has a higher compression ratio or a higher inlet temperature than the other stages.

[0088] According to one aspect of the invention, when there are multiple compression stages, the nitrogen-enriched gas stream is heated directly by a gas / gas exchanger or indirectly by a gas / heat transfer fluid exchanger via a heat transfer fluid by extracting heat from a feed gas stream leaving a compression stage, preferably having a maximum temperature above 100°C, more preferably above 120°C, which temperature has been obtained by ensuring that said compression stage has a compression ratio higher than the average of the compression ratios and / or an inlet temperature higher than the average of the inlet temperatures.

[0089] According to one aspect of the invention, this maximum temperature level is used at least twice to heat the nitrogen-rich gas stream before it enters the at least two expansion stages.

[0090] The present invention therefore makes it possible to utilize the highest temperature level of the feed gas stream in order to maximize heating of the nitrogen-rich gas stream prior to each expansion stage.

[0091] If necessary, the nitrogen-enriched gas stream which is heated by the feed gas stream via the gas / gas exchanger may be pre-heated by one or more, particularly gas / heat transfer fluid exchangers, to carry out the first part of the heating and to make the most of the highest temperature levels.

[0092] According to one aspect of the invention, the intermediate circuit includes a pump for circulating the intermediate fluid.

[0093] Conventionally, equipment may include instruments (temperature sensors, pressure sensors, vibration sensors, analyzers, etc.), fittings (full-open and full-close valves, regulators, etc.), and auxiliary equipment (filters, valves, bypasses, etc.).

[0094] According to one aspect of the invention, the intermediate circuit is arranged such that the intermediate heat transfer fluid passes through at least one gas / heat transfer fluid heat exchanger for enabling exchange of heat between the heat transfer fluid and the feed gas stream, and another gas / heat transfer fluid heat exchanger for enabling exchange of heat between the heat transfer fluid and the nitrogen-enriched gas stream, said gas / heat transfer fluid exchanger being arranged upstream of the expansion stage such that the nitrogen-enriched gas stream passes through this exchanger and is heated by the intermediate heat transfer fluid before being expanded in the expansion stage.

[0095] According to one aspect of the invention, a gas / heat transfer fluid heat exchanger for enabling the exchange of heat between a heat transfer fluid and a feed gas stream is arranged downstream of the first compression stage such that the feed gas stream is cooled by an intermediate fluid at the outlet of this first compression stage.

[0096] According to one aspect of the invention, the intermediate circuit is arranged to pass through two gas / heat transfer fluid heat exchangers for enabling the exchange of heat between the heat transfer fluid and the nitrogen-enriched gas stream, each of which is arranged upstream of an expansion stage.

[0097] According to one aspect of the invention, these two gas / heat transfer fluid heat exchangers for enabling the exchange of heat between a heat transfer fluid and a nitrogen-enriched gas stream are arranged in parallel with respect to an intermediate heat transfer fluid such that this intermediate fluid is further divided into two streams, each passing through one of these exchangers.

[0098] According to one aspect of the invention, in the nitrogen-enriched gas stream, for its part, is contemplated a series arrangement of a gas / heat transfer fluid heat exchanger and two expansion stages.

[0099] According to one aspect of the invention, the nitrogen-enriched gas stream produced from the wet feed gas stream is dried to contain less than 50 ppm HO, preferably less than 5 ppm HO, prior to expansion in the expansion stage.

[0100] A further object of the present invention is a method for recovering CO2 from a feed gas stream, in particular a flue gas, comprising the following steps: - compressing the feed gas stream using a compression stage; - treating the previously compressed feed gas stream by pressure swing adsorption using a processing unit to produce a low pressure CO2-enriched gas stream and a high pressure nitrogen-enriched gas stream from the feed gas stream; - using a turbine comprising at least one expansion stage and capable of providing mechanical energy generated by the expansion of the nitrogen-enriched gas stream in said expansion stage; - allowing heat to be transferred between the feed gas stream exiting the compression stage and the nitrogen-enriched gas stream prior to expansion in the expansion stage, for heating the nitrogen-enriched gas stream prior to expansion thereof; - utilizing the mechanical energy provided by the expansion stage to either drive a compression assembly or to generate electricity using a generator; Includes.

[0101] According to one aspect of the invention, a portion of the thermal energy of compression is recovered by the nitrogen-enriched gas stream by direct heat exchange with the feed gas stream at the outlet of at least one compression stage and / or by indirect heat exchange via a heat transfer fluid.

[0102] According to one aspect of the invention, the nitrogen-enriched gas stream is heated prior to expansion through each expansion stage of the turbine.

[0103] According to one aspect of the invention, a torque transfer device is implemented between the shafts of one or more expansion stages and one or more compression stages of the turbine, the torque transfer device including, among other things, a gear and pinion for transferring torque from the turbine to the compression assembly.

[0104] According to one aspect of the invention, the feed gas stream is wet and contains greater than 10 ppm NOx, and the nitrogen-enriched gas stream is dried prior to expansion to contain less than 50 ppm HO, preferably less than 5 ppm HO.

[0105] This makes it possible to avoid the possibility of condensation during cooling due to expansion and the formation of nitric acid.

[0106] According to one aspect of the invention, drying of the nitrogen-enriched gas stream is carried out using a hydrophilic adsorbent in a unit for treating the feed gas.

[0107] The present invention may allow for the use of dry nitrogen to create ice-cold water.

[0108] The CO2-enriched gas coming from the PSA unit can, if necessary, undergo further processing, including, for example, complementary enrichment of CO2. Thus, the residual nitrogen extracted from the CO2-enriched gas can be recycled and participate in the expansion and energy recovery.

[0109] The invention will be better understood on reading the following description and on examining the accompanying figures, which are given purely for the purpose of illustration and which do not in any way limit the invention. [Brief description of the drawings]

[0110] [Figure 1] 1 is a schematic partial view of an installation according to a first example of the invention; [Diagram 2] FIG. 2 is a schematic partial view of an installation according to a second embodiment of the invention. [Diagram 3]FIG. 4 is a schematic partial view of an installation according to a third embodiment of the invention. [Figure 4] FIG. 11 is a schematic partial view of an installation according to a fourth embodiment of the present invention. [Diagram 5] FIG. 11 is a schematic partial view of an installation according to a fifth embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0111] FIG. 1 shows an installation 1 for recovering CO2 from a feed gas stream FG, which in the example described is a flue gas, comprising: - a unit 2 for treating a feed gas stream FG by pressure swing adsorption in order to produce from said feed gas stream a CO2-enriched gas stream, designated FCO2, and a nitrogen-enriched gas stream, designated FN, said unit 2 being a PSA unit; - a compression assembly 3 including at least one compression stage 5 for compressing the feed gas stream FG before it enters the treatment unit 2; a turbine 6 including at least one expansion stage 8 and capable of providing mechanical energy generated by the expansion of a nitrogen-enriched gas stream FN in this expansion stage 8; a thermal device 10 arranged to allow the transfer of heat between the feed gas stream FG leaving the compression stage 5 and the nitrogen-enriched gas stream FN before expansion in the expansion stage 8, in order to heat the nitrogen-enriched gas stream FN before its expansion; - a device 4 for utilizing mechanical energy provided by an expansion stage 8; Includes.

[0112] The feed gas stream FG upstream of the compression assembly 3 may contain, by way of example, 10-60 mol% CO2, in particular 15-50 mol% CO2. The remainder is mostly nitrogen and small amounts of O2. Argon Ar and trace amounts of impurities, in particular NOx, on the order of magnitude of 1 mol% or less may possibly be present.

[0113] The feed gas stream FG may originate from an SMR reformer, a cement plant, an oxy-combustion unit, or a lime plant.

[0114] The feed gas stream FG may have been subjected to pre-treatment before entering the facility, for example by a scrubbing or filtration unit.

[0115] The high pressure nitrogen-rich gas stream FN leaving type 2 of unit may contain, in addition to nitrogen, possibly the least adsorbable components such as O2, Ar, NO.

[0116] The proportion of nitrogen in the nitrogen-enriched stream FN is in particular between 50 and 90 vol.%.

[0117] The CO2 is a portion, for example 50-85 vol. %, in the CO2-rich gas stream FCO2.

[0118] Generally, the compositions are provided on a dry basis.

[0119] The feed gas stream FG, after being compressed in the compression assembly 3, arrives at the treatment unit 2 at a pressure in the range of 8-10 bar abs and at a temperature close to ambient temperature, for example 5-45°C.

[0120] The nitrogen-enriched gas stream FN leaves the treatment unit 2 at high pressure, in this case at a pressure of 8-10 bar.

[0121] The plant 1 comprises an electric motor 20 having a rotating shaft 21 fixed to a main gear 22 .

[0122] The plant 1 further comprises a pinion 23 which drives the wheels of the compression stage 5 via a rotating axle or shaft 24 .

[0123] A further pinion 25 associated with the main gear 22 is arranged to transmit, via a rotating shaft 26 , the rotational torque generated by a wheel of the expansion stage 8 of the turbine 6 .

[0124] After compression, the feed gas stream FG is separated in a treatment unit 2. The dry, pressurized nitrogen-enriched gas stream FN is heated in a thermal unit 10.

[0125] The expansion stage 8 transfers the energy resulting from the expansion of the hot compressed gas FN in the turbine 6 to a lower pressure to the main gear 22 and thus to the compression assembly 3 .

[0126] The energy required in the compression stage 5 is therefore partly provided by the motor 20 and partly by the expansion turbine 6. Such an arrangement allows the electrical energy consumed by the motor 20 to be very significantly reduced, for example by half.

[0127] In the example described, the utilization device 4 includes a compression stage 5 arranged to receive the mechanical energy provided by the expansion stage 8, and a pinion 25 and a rotating shaft 26 ensuring the transmission of the rotational torque.

[0128] Of course, various connections are possible between the wheels of the compression stage(s) and the wheels of the expansion stage(s).

[0129] FIG. 2 illustrates an exemplary embodiment of the present invention in which a compressor assembly 3 includes four compression stages 5 and a turbine 6 includes two expansion stages 8 .

[0130] These expansion stages 8, each equipped with a wheel, are arranged in series such that the nitrogen-enriched gas stream FN first passes through one of the expansion stages 8 and then through the other expansion stage 8.

[0131] The expansion stage 8 converting energy from the nitrogen-enriched gas stream FN may provide approximately 40% of the energy required to operate the compression stage.

[0132] In the example shown in FIG. 2, the thermal device 10 is positioned to allow the transfer of heat between the nitrogen-enriched gas stream FN and the feed gas stream FG.

[0133] The nitrogen-enriched gas stream FN is, for example, at ambient temperature and the feed gas stream FG is at a higher temperature.

[0134] The invention therefore makes it possible to utilize a nitrogen-enriched gas stream FN, which is at substantially ambient temperature at the outlet of the PSA unit, to cool the feed gas stream FG so as to improve the overall thermodynamic performance of the installation 1.

[0135] The thermal device 10 includes two gas / gas exchangers 11 in the compression assembly 3 arranged to enable heat exchange between the nitrogen-enriched gas stream FN and the feed gas stream FG to heat the nitrogen-enriched gas stream FN and cool the feed gas stream FG.

[0136] Each gas / gas heat exchanger 11 for exchanging heat between the nitrogen-enriched gas stream FN and the feed gas stream FG is arranged at the outlet of one of the compression stages 5 such that the feed gas stream FG first passes through the compression stage 5 before passing through the heat exchanger 11.

[0137] The gas / gas exchanger 11 therefore makes it possible to cool the feed gas stream FG which has experienced an increase in temperature due to compression in the compression stage 5 .

[0138] The two gas / gas exchangers 11 are arranged in series such that the nitrogen-enriched gas flow FN first passes through one of these gas / gas exchangers 11 and then through the other gas / gas exchanger 11.

[0139] Each expansion stage 8 is provided downstream of the respective gas / gas heat exchanger 11 such that the nitrogen-enriched gas stream FN first passes through the gas / gas heat exchanger 11 and then through the expansion stage 8 which is used to transfer the mechanical torque to a dedicated compression stage 5.

[0140] The compression assembly 3 includes three gas / heat transfer fluid heat exchangers 12 for exchanging heat between the feed gas stream FG and a cooling fluid other than the nitrogen-enriched gas stream, which in this case is glycol water belonging to the cooling circuit.

[0141] Each heat exchanger 11 or 12 is positioned at the outlet of one of the compression stages 5 such that the feed gas stream FG first passes through the compression stage 5 before passing through the heat exchanger 11 or 12 .

[0142] In the example of FIG. 2, all of the compression stages 5 are followed by a heat exchanger, either of the gas / gas type 11 or of the gas / heat transfer fluid type 12 .

[0143] In the circulation direction of the feed gas flow FG, each of the two first compression stages 5 , stage number 1 and stage number 2 , is followed by a gas / heat transfer fluid heat exchanger 12 .

[0144] The two last stages 5 are each followed by a gas / gas heat exchanger 11 .

[0145] The nitrogen-enriched gas stream FN thus serves to cool the feed gas stream FG at the outlet of the two compression stages 5, stage numbers 3 and 4.

[0146] A final gas / heat transfer fluid exchanger 12 is positioned downstream of the final gas / gas exchanger 11 to further cool the feed gas stream before it reaches the PSA processing unit.

[0147] The nitrogen-enriched gas stream is for its part heated by the feed fluid FG via exchanger 11 .

[0148] Each turbine stage 8 is arranged downstream of one of the gas / gas exchangers 11 .

[0149] The expansion stage 8 and the two gas / gas exchangers 11 are therefore in series such that the nitrogen-enriched gas stream FN passes successively through one of the gas / gas exchangers 11, then through one of the expansion stages 8, then through the other gas / gas exchanger 11 and finally through the other expansion stage 8.

[0150] The nitrogen-enriched gas stream FN is at substantially atmospheric pressure when it leaves the final turbine 6 and is preferably at a temperature above -10°C, more preferably above 0°C.

[0151] In the variant shown in Figure 3, one of the compression stages 5 is directly connected to the next compression stage 5, and there is no heat exchanger 11 or 12 between these two compression stages 5. As in the example of Figure 2, two expansion stages 8 are provided.

[0152] In the example of FIG. 3, a single gas / gas heat exchanger 11 is provided in the installation 1, which is arranged downstream of the last of the four compression stages 5.

[0153] Thus, the nitrogen-enriched gas stream FN first passes through a heat exchanger 11 and then passes successively through two turbines 6 .

[0154] In the example shown in FIG. 4, the installation 30 continuously supplies the nitrogen-enriched gas stream FN from the outlet of the treatment unit with: a first gas / gas heat exchanger 31, a first expansion stage 33, a second gas / gas heat exchanger 32; a second expansion stage 34; Including, the first gas / gas heat exchanger 31 and the second gas / gas heat exchanger 32 are arranged in parallel with each other and downstream of the first of the four compression stages 5 with respect to the feed gas flow FG;

[0155] Thus, in this example, the nitrogen-enriched gas stream FN is used at the outlet of the first compression stage 5 to cool the feed gas stream FG in two exchangers 31 and 32 arranged in parallel.

[0156] The feed gas stream FG, which is further split into two branches 41 and 42 in the two parallel exchangers 31 and 32, joins at the outlets of these two exchangers 31 and 32 to reform a single feed gas stream FG which passes through the gas / heat transfer fluid exchanger 12.

[0157] As can be seen, in the feed gas flow FG, the two gas / gas exchangers 31 and 32 are interpreted as being in parallel, and in the nitrogen-enriched gas flow FN, these two gas / gas exchangers 31 and 32 are interpreted as being in series.

[0158] The compression stage 5 is arranged to bring the feed gas stream FG from a pressure slightly below atmospheric to the operating pressure of the PSA unit, approximately 8 or 9 bar abs.

[0159] On a dry basis, the feed gas stream contains 22 mol% CO2, 75 mol% N2, 2 mol% O2, 1 mol% Ar, and a few tens of ppm impurities. The temperature is around 60° C., thus avoiding condensation of liquid water.

[0160] The compression assembly 3 includes an electric motor (not shown) that powers four compression stages 5 in series. An expansion stage 8 of a turbine 6, also in series, provides some of the energy required for compression in the compression assembly 3. In the present case, the wheels of the expansion stage 8 provide about 40% of this energy.

[0161] The gas to be expanded in the expansion stages 8 is a high pressure stream coming from the PSA unit. This gas contains 94 mol% N2, 3 mol% CO2, 2 mol% O2 and 1 mol% Ar. This gas is available at about 8 bar abs and is expanded to a pressure slightly above atmospheric pressure. To increase the energy recoverable during expansion, this stream is heated to a temperature of 70-80°C before entering each expansion stage. The corresponding heat is recovered from the feed gas stream FG leaving the first compression stage 5.

[0162] The interstage pressures of the compression assembly 5 are of the order of 2 bar abs (outlet of stage 1), 3.5 bar abs (outlet of stage 2) and 5.5 bar abs (outlet of stage 3). The interstage pressure of the expansion 8 is 3 bar abs. Similarly, the outlet temperatures of the compression stages are of the order of 140-150°C (outlet of stage 1) and 75-85°C in the next stage, respectively. The discharge temperature of the expansion stage 8 is around 0°C.

[0163] The staging of the pressures, and more generally of the operating conditions, is selected so that the wheels of the stage of the compression assembly and the wheels of the second expansion stage 8 have the same rotational speed. These two wheels may therefore have the same axis of rotation, for example on either side of the pinion.

[0164] This may be true for the first expansion stage and another compression stage as well.

[0165] At the thermal level, the feed gas stream leaving the first compression stage 5 is first cooled by exchange with a nitrogen-enriched stream FN. These exchanges are carried out by means of two gas-gas exchangers 31 and 32, which are U-tube exchangers, in parallel with respect to the feed gas stream FG, which is essentially split in half between the two exchangers 31 and 32.

[0166] At the outlet of these exchangers 31 and 32 the feed gas stream is cooled to ambient temperature by refrigeration water, separated from any condensed water and led to the second compression stage 5. At the outlet of each stage 5 the feed gas stream is then cooled to ambient temperature by refrigeration water and separated from any condensed water.

[0167] It should be noted that the feed gas stream FG is used at the highest temperature to heat the intake of the expansion stage 8, thus making it possible to increase the recoverable energy.

[0168] In the exemplary embodiment of FIG. 5, the installation 50 comprises an intermediate heat circuit 51 using an intermediate heat transfer fluid different from the nitrogen-enriched gas stream FN and the feed gas stream FCO2, the intermediate circuit 51 being arranged to enable heat exchange between the nitrogen-enriched gas stream FN and the feed gas stream FCO2 via the intermediate heat transfer fluid.

[0169] The intermediate circuit 51 includes a pump 52 for circulating the intermediate fluid. A temperature sensor 53 may be provided in the intermediate circuit 51.

[0170] The intermediate circuit 51 is arranged so that the intermediate heat transfer fluid passes through a gas / heat transfer fluid heat exchanger 55 arranged to enable exchange of heat between the intermediate heat transfer fluid in the circuit 51 and the feed gas stream FG, and two other gas / heat transfer fluid heat exchangers 56 each arranged upstream of the expansion stage 8 so that the nitrogen-enriched gas stream FN passes through this exchanger 56 to be heated by the intermediate heat transfer fluid in the circuit 51 before being expanded in the expansion stage 8.

[0171] A gas / heat transfer fluid heat exchanger 55 for cooling the feed gas flow FG is arranged downstream of the first compression stage 5 such that the feed gas flow FG is cooled by an intermediate fluid at the outlet of this first compression stage 5.

[0172] The two exchangers 56 are arranged in parallel with respect to the intermediate fluid such that the intermediate fluid is further divided into two streams 61 and 62 each passing through one of these exchangers 56 .

[0173] For the nitrogen-enriched gas stream FN, for its part, there is interpreted a series arrangement of exchangers 56 and expansion stages 8. Each expansion stage 8 is arranged downstream of one of the exchangers 56.

[0174] In said installation, a unit 65 is provided for producing ice-cold water using a dry nitrogen stream FN. A stream of ice-cold water 66 coming from the unit 65 is used in a heat exchanger 67 for further cooling the gas stream FG entering the PSA unit. A pump 68 is provided for circulating the stream of ice-cold water. Stream FN is finally exhausted to the atmosphere at point 69.

[0175] The CO2-enriched gas stream FCO2 coming from the PSA unit can, if necessary, undergo further processing, including, for example, complementary enrichment of CO2. Thus, the residual nitrogen extracted from the CO2-enriched gas can be recycled and participate in the expansion and energy recovery.

Claims

1. 1. An installation (1) for recovering CO2 from a feed gas stream (FG), in particular a flue gas, comprising: a unit (2) for treating said feed gas stream (FG) by pressure swing adsorption in order to produce from said feed gas stream a CO2-rich gas stream (FCO2) and a nitrogen-rich gas stream (FN); a compression assembly (3) comprising at least one compression stage (5) for compressing said feed gas stream before it enters said processing unit; a turbine (6) including at least one expansion stage (8) and capable of providing mechanical energy generated by the expansion of said nitrogen-enriched gas stream (FN) in said expansion stage; a thermal device (10) arranged to allow the transfer of heat between said feed gas stream (FG) leaving the compression stage (5) and said nitrogen-enriched gas stream (FN) before its expansion in said expansion stage, in order to heat said nitrogen-enriched gas stream (FN) before its expansion; a device (4) for utilizing the mechanical energy provided by the expansion stage, Including, facilities.

2. 2. The installation of claim 1, wherein the utilization device is a generator capable of utilizing the mechanical energy provided by the expansion stage to generate electricity.

3. 2. The installation according to claim 1, wherein the utilization device (4) comprises the compression stage (5) arranged to receive the mechanical energy provided by the expansion stage.

4. 4. An installation according to claim 3, comprising at least two compression stages (5) in said compression assembly, and a turbine (6) comprising at least two expansion stages operable by said nitrogen-enriched gas flow (FN), each expansion stage of said turbine being arranged to transmit mechanical energy to said compression assembly, whether this be directly to one of said compression stages, or to a rotating shaft common to several compression stages, or to the shaft of a motor which actuates said compression stages.

5. 5. The installation according to claim 4, wherein the expansion stages (8) are arranged in series such that the nitrogen-enriched gas stream (FN) passes first through one of the expansion stages and then through the other of the expansion stages.

6. 6. An installation according to any one of claims 3 to 5, wherein the expansion stage or stages (8) are dimensioned to provide at least 25%, in particular about 40% or 50% of the mechanical energy required to operate the compression stage (5).

7. 7. Installation according to any one of claims 1 to 6, wherein the thermal device (10) comprises at least one gas / gas heat exchanger (11) arranged to allow the transfer of heat between the feed gas stream (FG) leaving the compression stage (5) and the nitrogen-enriched gas stream (FN) before expansion in the expansion stage, in order to heat the nitrogen-enriched gas stream (FN) before its expansion.

8. 8. The installation according to claim 7, wherein the gas / gas heat exchanger (11) is arranged at the outlet of the compression stage (5) such that the feed gas stream (FG) first passes through the compression stage (5) before passing through the heat exchanger (11).

9. The installation according to any one of claims 1 to 8, wherein the thermal device (10) comprises one or more gas / heat transfer fluid heat exchangers (12) for exchanging heat between the feed gas stream (FG) and a heat transfer fluid other than the nitrogen-enriched gas stream, this fluid being for example glycol water belonging to a cooling circuit.

10. With respect to the nitrogen-enriched gas stream (FN), continuously from the outlet of the treatment unit: a first gas / gas heat exchanger (11), a first expansion stage (8), a second gas / gas heat exchanger (11), a second expansion stage (8), Including, the first and second heat exchangers are arranged in parallel with each other and downstream of a compression stage (5), in particular the first compression stage, with respect to the feed gas stream (FG); 10. The installation according to claim 8 or 9.

11. 11. The installation according to any one of claims 1 to 10, comprising an intermediate heat circuit (51) using an intermediate heat transfer fluid different from the nitrogen-enriched gas stream (FN) and the feed gas stream (FG), the intermediate circuit being arranged to allow heat exchange between the nitrogen-enriched gas stream and the feed gas stream via said intermediate heat transfer fluid.

12. 12. The installation according to any one of claims 1 to 11, wherein the nitrogen-enriched gas stream (FN) produced from the wet feed gas stream (FG) is dried to contain less than 50 ppm HO, preferably less than 5 ppm HO, prior to expansion in the expansion stage.

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