Method and apparatus for separating a gas stream by partial condensation and / or distillation and / or solidification

Abstract

Title: Process and apparatus for separating a gas stream by partial condensation and / or distillation and / or solidification. In a process for separating a gas stream containing a first component, at least one second component and water, the gas stream is compressed in a compressor (14) to form a compressed flow (18), the compressed flow is cooled to form a cooled compressed flow, the cooled compressed flow is purified of water by a purification apparatus operating by adsorption (19) to form a compressed and dried flow (23), the compressed and dried flow is cooled in a heat exchanger and separated (20) by partial condensation and / or distillation and / or solidification to form a flow (3) enriched in the first component relative to the dry basis gas stream and a flow depleted (21) in the first component relative to the dry basis gas stream.The flow, depleted in the first component, is expanded in a turbine (22) coupled to the compressor, and when the compressor stops, a portion (15) of the compressed and dried flow is taken upstream of the heat exchanger and sent to the turbine inlet. Figure from the abstract: FIG. 1,

Description

Title of the invention: Method and apparatus for separating a gas stream by partial condensation and / or distillation and / or solidification

[0001] The present invention relates to a method and apparatus for separating a gas stream by partial condensation and / or distillation and / or solidification.

[0002] In a separation and / or liquefaction unit, the fluid to be treated generally needs to be compressed in a compressor. Furthermore, the compression energy of certain co-products or intermediate fluids can be recovered as cooling and / or mechanical energy in a turbine. In particular, there are two main families of compression wheels mechanically coupled to expansion wheels: • Those where the turbine drives the compressor, without any other energy source on the common shaft. • Those where the compressor and turbine are placed on the same shaft and a motor or steam turbine or more generally another mechanical source completes the energy to be supplied to the compressor because the turbine does not provide enough.

[0003] It is known from US 1992486 to compress a combustion gas containing 18% CO2, to separate the CO2 it contains by solidification and to expand a portion of the gas not having been solidified in a turbine which drives a combustion gas compressor, the whole forming a compression and expansion machine.

[0004] When the compression and expansion machine stops abruptly or is shut down for safety reasons due to a process disturbance, the compression wheels continue to rotate for a few minutes due to kinetic energy, thus driving the wheels of the turbine(s). The mechanical inertia of the compressor is higher when the compression wheels have a large diameter (i.e., when the flow rate to be processed is high, for example, 355,100 m³ / h with a compression power of several megawatts). The rotation of the turbine without sufficient fluid at the inlet can cause the turbine materials to overheat and be damaged.

[0005] This problem may also exist during the start-up of the turbine and / or during the start-up of the compressor to which the turbine is coupled.

[0006] To overcome the problem of overheating and / or damage to the turbine, either a backup fluid is supplied to the turbine in case of machine stoppage, or more expensive materials that withstand a higher temperature are chosen for the turbine (which makes the unit cost higher while the machines represent a significant part of the unit cost).

[0007] The problem with a backup fluid is that it takes a few seconds to open the valves and supply the fluid, which allows time for the materials to heat up (even with ultra-fast opening valves, particularly due to the large size of the valves). Therefore, in machines where the turbine drives a compressor, the backup fluid is generally a gas taken directly from the compressor outlet. However, this is not always possible, for example, when the fluid to be compressed is saturated with water and the fluid to be expanded must be dry. This problem arises, for instance, in combustion gas separation devices for producing CO2 that include a nitrogen turbine, due to the risk of freezing and / or the potential formation of hydrates at low temperatures after expansion.

[0008] The present invention consists of taking as a backup fluid the compressed gas downstream of a cooling unit and an adsorption drying unit, so that the backup fluid is dry and cooled.

[0009] According to one object of the invention, a process is provided for separating a gas stream containing a first component, at least a second component, and water, in which the gas stream is compressed in a compressor to form a compressed flow, the compressed flow is cooled to form a cooled compressed flow, the cooled compressed flow is purified with water by a purification apparatus operating by adsorption to form a compressed and dried flow, optionally the compressed and dried flow is enriched in the first component, the compressed and dried flow, and optionally enriched in the first component, is cooled in a heat exchanger and separated by partial condensation and / or distillation and / or solidification to form a flow enriched in the first component relative to the dry gas stream and a flow depleted in the first component relative to the dry gas stream,The flow, depleted in the first component, is reheated by heat exchange with the compressed and dried flow, which cools in the heat exchanger and is then expanded in a turbine coupled to the compressor, characterized in that, during a compressor shutdown or a reduction of at least 1% / sec in the compressed molar flow rate, or during the start-up of the compressor and / or turbine, a portion of the compressed and dried flow is taken upstream of the heat exchanger and sent to the turbine inlet.

[0010] According to other optional aspects: • The portion of the compressed and dried flow upstream of the exchanger is sent to the turbine inlet only if the compressed flow and / or its pressure and / or the pressure at the turbine inlet falls below a threshold and / or if the temperature at the outlet of the passes above a threshold and / or in the event of a stop signal for the compressor wheels. • The first component is carbon dioxide. • the compressed flow rate includes at least 15 mol% wet-based carbon dioxide. • at least one second component is chosen from the group: nitrogen, oxygen, argon, carbon monoxide, methane. • the portion of the compressed and dried flow taken upstream of the heat exchanger and sent to the turbine inlet consists of gas present in a free space of at least one adsorbent bottle of the adsorption apparatus, this at least one bottle being in the adsorption phase. • an opening means, for example a pressure regulator, downstream of at least one adsorbent cylinder of the adsorption apparatus opens when the pressure of the compressed flow and / or at the turbine inlet falls below a threshold. • The adsorption unit comprises at least two adsorbent bottles and at least two opening means, which may be regulators, each bottle being connected to a respective opening means downstream of the bottle in the direction of flow of the flow to be dried. • the opening mechanism, for example the regulator of each cylinder, is calibrated to open from the same threshold. • the compressed gas flow in the compressor is at least 50,000m3 / h, or even at least 150,000m3 / h. • the compressed and dried flow is enriched in the first component and depleted in at least one second component by adsorption. • the flow depleted in the first component is enriched in at least one second component, which may be nitrogen, oxygen, argon, carbon monoxide or methane, by partial condensation and / or distillation. • after sending the portion of the compressed and dried flow taken upstream of the heat exchanger to the turbine, a gas flow from another source is sent to the turbine. • in the case where an enrichment device for the first component is present, the portion of the compressed and dried flow taken upstream of the heat exchanger is taken upstream of the enrichment device.

[0011] According to another object of the invention, a device for separating a gas stream containing a first component, at least a second component, and water is provided, comprising a compressor for compressing the gas stream to form a compressed flow, cooling means for cooling the compressed flow to form a cooled compressed flow, a purification device operating by adsorption for purifying the cooled compressed flow with water to form a compressed flow, and dried, possibly an enrichment apparatus in the first component of the compressed and dried flow, a heat exchanger for cooling the compressed and dried flow connected to the purification apparatus and possibly to the enrichment apparatus, a separation apparatus by partial condensation and / or distillation and / or solidification to separate the compressed and dried flow to form a flow enriched in the first component relative to the dry-based gas flow and a flow depleted in the first component relative to the dry-based gas flow, means for sending the flow depleted in the first component to the heat exchanger to be heated by heat exchange with the compressed and dried flow which is cooled in the heat exchanger,a turbine coupled to the compressor and means for sending the depleted flow in the first component and heated in the heat exchanger to the turbine characterized in that it comprises means connected to the inlet of the turbine for sending compressed and dried gas, taken downstream of the purification apparatus or in the purification apparatus and upstream of the heat exchanger and means for triggering the sending if the compressor stops or if the compressed flow decreases by at least 1% / sec.

[0012] Preferably, the apparatus includes means for regulating the sending of the compressed and dried gas to the turbine inlet as a function of the pressure at the turbine inlet and / or as a function of the flow rate of the compressed flow and / or as a function of the temperature at the turbine inlet and / or as a function of the temperature of the turbine outlet.

[0013] The compressor is preferably coupled to the turbine by a shaft to which a gas turbine or an electric motor is coupled.

[0014] A non-return valve or an isolation valve (in English "block valve") can be placed between the compressor and the adsorption unit.

[0015] Typically, a TSA air purification process cycle comprises the following steps: a. Purification of a gas stream by adsorption of impurities at superatmospheric pressure and ambient temperature, b. possibly depressurizing the adsorber to atmospheric pressure or below atmospheric pressure, c. regeneration of the adsorbent at atmospheric pressure, in particular by a residual gas, in the case of air separation typically of impure nitrogen from an air separation unit, and heated to a temperature usually between 100 and 200°C by means of one or more heat exchangers, d. cooling the adsorbent to ambient or subambient temperature, in particular by continuing to introduce said residual gas, but without heating it, e. possibly repressurization of the adsorber with the purified gas stream from, for example, another adsorber in the production phase.

[0016] Alternatively, regeneration can take place at the same pressure as adsorption.

[0017] Usually, a PSA process cycle for purifying a gas stream involves substantially the same steps a), b) and e), but differs from a TSA process by the absence of heating of the residual gas(s) during the regeneration step (step c)), therefore the absence of step d) and, in general, a shorter cycle time than in the TSA process.

[0018] Generally, adsorption drying units comprise at least two adsorbers, operating alternately, i.e. at least one of the adsorbers is in production phase, while another is in regeneration phase.

[0019] In general, the removal of water vapor is carried out on a bed of adsorbents, intended to preferentially stop water, for example a bed of activated alumina, silica gel or zeolites.

[0020] In a particularly efficient embodiment of the invention, a pressure regulator is added downstream of the adsorption unit and upstream of the expansion wheels, which are mechanically coupled to the compressor on the same shaft. This allows for the instantaneous supply (due to mechanical opening) of backup fluid to the turbine during a sudden shutdown (or significant disturbance) of the compressor. This is achieved by utilizing the gas inventory stored in the temperature-switching adsorption (TSA) or pressure-switching adsorption (PSA) cylinders of the drying unit. Backup fluid can also be supplied by a distillation column or a tank, in addition to the fluid supplied downstream of the adsorption drying unit.If the gas inventory in the adsorbent cylinders of the adsorption unit between the compressor and the turbine proves insufficient to supply the turbine in the event of a compressor stoppage, the solution with a pressure regulator still allows gas to be supplied to the turbine during the first few seconds after activation while waiting for a slower system to be activated (for example, a valve with ultra-fast opening, a backup gas from a storage tank, a backup gas from a liquid to be vaporized).

[0021] The invention will be described in more detail with reference to the figures where:

[0022] [Fig.1] illustrates a device according to the invention.

[0023] [Fig.2] illustrates a device according to the invention.

[0024] [Fig.3] illustrates an adsorption drying apparatus according to the invention

[0025] [Fig.4] illustrates the relationship between the rotation speed and the time of a compressor of a device according to the invention.

[0026] [Fig-1] illustrates an apparatus according to the invention comprising a compressor 14 of the flow gaseous 13 containing a first component, at least one second component and water, the second component being able to be heavier or lighter than the first component. The content of the first component may be greater than that of the second component or vice versa.

[0027] The flow rate of the gas flow 13 is preferably at least 50,000m3 / h, or even at least 150,000m3 / h.

[0028] In normal operation, the flow 13 is compressed in the compressor 14 forming a compressed flow 18 which is cooled in a cooler which may be the last water cooler of the compressor, an indirect heat exchange cooler or a direct heat exchange cooler, such as a water scrubber tower.

[0029] In the diagram, the cooling means are considered an integral part of the compressor 14, as they constitute the final cooling downstream of the last impeller. The cooled flow is then dried in a TSA or PSA type adsorption scrubber 19 to remove the water it contains, forming a dried flow 23 which feeds a partial condensation and / or distillation and / or solidification separation unit 20. The dried flow in the scrubber 19 can be enriched in the first component, for example by treating it by adsorption upstream of the unit 20. The unit 20 includes a heat exchanger to cool the dried flow 23 to a temperature below 0°C. The unit 20 separates the dried and partially condensed and / or distilled and / or solidification flow, forming a fluid 3 enriched in the first component compared to the flow 23, and this fluid 3 is sent to a customer 4 or to a storage facility.The apparatus also produces a gas 21 depleted in the first component compared to the flow 23 at a pressure higher than atmospheric pressure, this gas 21 being able to come from a partial condensation stage and / or a distillation stage and / or a solidification stage and this gas 21 is heated in the exchanger where the dry gas 23 is cooled and then expanded in a turbine 22 coupled to the compressor 14. An electric motor 17 or a gas turbine can also be coupled to the shaft 16 common to the compressor 14 and the turbine 22.

[0030] In the event of a reduction in the compressed flow rate 18, for example in the event of a failure or stoppage of the compressor 14, the inertia of the compressor wheels means that they can continue to rotate, driving the rotation of the turbine wheels 22 via the shaft 16, which can thus be supplied with too little gas 21 from the separation, causing the turbine to heat up.

[0031] The problem also arises in the event of a sudden reduction in the compressed flow rate in the compressor 14, for example a reduction of at least 10% of the molar flow rate in the space of ten seconds, that is to say of at least 1% of the molar flow rate per second.

[0032] The problem also occurs when starting the compressor 14 and / or the turbine 22.

[0033] To solve this problem, when the compressor stops or when the compressed molar flow rate is reduced by at least 1% / sec or when the compressor and / or turbine is started, cooled and dried gas 15 is sent directly from the drying unit 19 to the turbine 22, without separation or cooling in the separation unit 20. The operating pressure of the adsorption unit is such that the gas 15 quickly reaches the inlet of the turbine 22.

[0034] In some cases, the flow 23 can be enriched in an enrichment unit producing a gas enriched in the first component and depleted in the second component which is then sent to the cooling and separation unit 20. According to this variant, the gas 15 is taken upstream of the enrichment unit.

[0035] In a typical example, the first component may be carbon dioxide and the second component may be nitrogen, oxygen, carbon monoxide, hydrogen, or methane. The gas stream may contain other impurities such as at least one NOx, at least one SOx, mercury...

[0036] The gas stream 13 contains, for example, 20 molar percent of carbon dioxide, 20 molar percent of water and 60 molar percent of nitrogen (wet base).

[0037] [Fig.2] illustrates an apparatus according to the invention of [Fig.1] with more detail of the means of sending emergency gas 15.

[0038] To prevent the inventory of gas coming from the bottles of the drying unit 19 from depressurizing towards the compressor 14 rather than towards the turbine 22, a non-return valve C or an isolation valve (in English "block valve") must be placed between the compression wheels of the compressor 14 and the inventory of gas present in the bottles of the drying unit.

[0039] An opening means, for example a pressure regulator D, is placed on the emergency gas line 15 coming from the drying unit 15 to the turbine 22.

[0040] The role of the pressure regulator D (or other equivalent system) is to open when its downstream pressure drops below its set threshold. The opening is mechanical, using a spring-loaded system like a valve, which ensures a very fast (virtually instantaneous) opening time and good reliability. This also has the advantage of not involving the distributed control system (DCS), which would add a reaction time of approximately 3-4 seconds, due to the DCS scan time of ~1s, plus the time to information transfer and processing. In total, for a pneumatic valve of adequate size associated with a DCS, the opening time would be 5-10 seconds (including the waiting time related to the DCS).

[0041] Thus, the pressure regulator D opens if the pressure at the turbine inlet falls below a threshold and rapidly supplies the turbine with dry gas stored in at least one cylinder of the drying unit. The system thus behaves like a weir.

[0042] The sending of gas 15 can be triggered using a regulating means other than a regulator.

[0043] The sending of gas 15 can be triggered as a function of the pressure at the inlet of the turbine 22 and / or as a function of the compressed flow rate and / or as a function of the temperature at the inlet of the turbine and / or as a function of the temperature at the outlet of the turbine and / or as a function of a stop signal of the compression wheels of the compressor 14.

[0044] This gas shipment 15 can be followed by a gas shipment from another source, for example a pressurized gas storage, a liquid storage associated with a vaporizer, a gas withdrawn from a pipeline.

[0045] The gas 15 can be taken directly from at least one bottle of adsorbent 20A, 20B, 20C, 20D.

[0046] Depending on the application, a single or staggered set pressure may be preferred for the different pressure regulators (if there are several, for example, if there are several adsorption cylinders). In the case of adsorption cylinders, the set pressure will preferably be the same in order to minimize the risk of fluidization of the adsorbent bed (so that the cylinders empty simultaneously and not successively).

[0047] [Fig. 3] illustrates an adsorption drying apparatus 19 of an example of an apparatus according to the invention. This apparatus comprises four adsorbent bottles 20A, 20B, 20C and 20D, connected in parallel, to dry the gas 13 compressed in the compressor 14 forming a compressed gas 18 which is dried in the three bottles 20A, 20B, 20C during adsorption, the bottle 20D being regenerated in a known manner by sending a dry gas from the separation apparatus 20.

[0048] In normal operation, three cylinders are in the adsorption phase while the fourth is in the regeneration phase. The selection of the cylinders in the adsorption phase is cyclical in order to regenerate all the cylinders in turn. The three cylinders each produce a dried gas 23A, 23B, 23C, and the flow rates are mixed to form the gas 23 that feeds the separation unit 20.

[0049] [Fig.4] illustrates the relationship between the rotation speed and the time of a compressor of a device according to the invention with time in seconds on the abscissa and the rotation speed of the compressor 14 of the gas flow of figures 1 and 2 on the ordinate in rpm.

[0050] To give one example among many, a compressor 14 takes approximately 10 minutes to stop if triggered. Furthermore, its rotational speed is halved during the first few seconds (~30-40 seconds) and the flow rate decreases by half during the first 2 minutes.

[0051] A certain amount of gas is contained in the TSA cylinders per cylinder when they are depressurized to 2 bar, this value corresponding to the free volume of gas contained in the cylinders plus the desorbed gas. Three cylinders 20A, 20B, and 20C are in production, and one 20D is being regenerated (at a similar pressure but at a high temperature, which limits the available gas inventory). Considering only the three cylinders in production, the available gas inventory for the turbine 22 allows the turbine 22 to be supplied for 5 minutes, for example, with a constant flow rate of 20,000 Nm³ / h. This makes it possible to supply gas 15 to the turbine 22 during the first moments after a shutdown or sudden reduction in the flow rate of the compressor 14, these first few minutes being the most critical with regard to the risk of the machine overheating.

Claims

Claims

1. A method for separating a gas stream containing a first component, at least one second component and water, wherein the gas stream is compressed in a compressor (14) to form a compressed flow (18), the compressed flow is cooled to form a cooled compressed flow, the cooled compressed flow is purified of water by a purification apparatus operating by adsorption (19, 20A, 20B, 20C, 20D) to form a compressed and dried flow (23, 23A, 23B, 23C, 23D), optionally the compressed and dried flow is enriched in the first component, the compressed and dried flow and optionally enriched in the first component is cooled in a heat exchanger and separated (20) by partial condensation and / or distillation and / or solidification to form a flow (3) enriched in the first component relative to the gas stream on a dry basis and a flow (21) depleted in the first component relative to the gas stream on a dry basis,the flow depleted in the first component is reheated by heat exchange with the compressed and dried flow which cools in the heat exchanger then expanded in a turbine (22) coupled to the compressor characterized in that when the compressor stops or when the compressed molar flow (18) is reduced by at least 1% / sec or when the compressor and / or the turbine is started, a part (15, 15A, 15B, 15C, 15D) of the compressed and dried flow is taken upstream of the heat exchanger and sent to the turbine inlet.,

2. Method according to claim 1 in which the part (15) of the compressed and dried flow taken upstream of the heat exchanger is sent to the inlet of the turbine (22) only if the compressed flow and / or its pressure and / or the pressure at the inlet of the turbine falls below a threshold and / or if the temperature at the outlet of the turbine falls above a threshold and / or in the event of a signal to stop the compression wheels of the compressor (14).

3. A method according to claim 1 or 2 wherein the first component is carbon dioxide.

4. Method according to one of the preceding claims in which at least one second component is chosen from the group: nitrogen, oxygen, argon, carbon monoxide, methane.

5. Method according to one of the preceding claims in which the part (15) of the compressed and dried flow taken upstream of the heat exchanger and sent to the inlet of the turbine consists of gas present in a free space of at least one adsorbent bottle (20A, 20B, 20C, 20D) of the adsorption apparatus (19), this at least one bottle being in the adsorption phase.

6. Method according to one of the preceding claims when dependent on claim 2 in which an opening means (D, DA, DB, DC, DD), for example a pressure reducer, downstream of at least one adsorbent bottle (20A, 20B, 20C, 20D) of the adsorption apparatus opens when the pressure of the compressed flow (18) and / or at the inlet of the turbine (22) falls below a threshold.

7. Method according to one of the preceding claims in which the adsorption unit (19) comprises at least two adsorbent bottles (20A, 20B, 20C, 20D) and at least two opening means (D, DA, DB, DC, DD), which may be pressure reducers, each bottle being connected to a respective opening means downstream of the bottle in the direction of flow of the flow to be dried.

8. Method according to claim 7 in which the opening means (D, DA, DB, DC, DD), for example the regulator of each bottle (20A, 20B, 20C, 20D), is calibrated to open from the same threshold.

9. Method according to one of the preceding claims in which the compressed gas flow in the compressor (14) is at least 50,000 m3 / h, or even at least 150,000 m3 / h.

10. Method according to one of the preceding claims in which the flow (21) depleted in the first component is enriched in the at least one second component, which may be nitrogen, oxygen, argon, carbon monoxide or methane.

11. Apparatus for separating a gas stream (13) containing a first component, at least one second component and water comprising a compressor (14) for compressing the gas stream to form a compressed flow (18), cooling means for cooling the compressed flow to form a cooled compressed flow, a purification apparatus (19) operating by adsorption to purify the cooled compressed flow with water to form a compressed and dried flow (23), optionally an apparatus for enriching the first component of the compressed and dried flow, a heat exchanger (20) for cooling the compressed flow to form a cooled compressed flow, a purification apparatus (21) operating by adsorption to purify the cooled compressed flow with water to form a compressed and dried flow, optionally an apparatus for enriching the compressed and dried flow with water, a heat exchanger (22) for cooling the compressed flow to form a cooled compressed flow, a purification apparatus (23) operating by adsorption to purify the cooled compressed flow with water to form a compressed and dried flow, optionally an apparatus for enriching the compressed and dried flow with water, a heat exchanger (24) for cooling the compressed flow to form a cooled compressed flow, a purification apparatus (25) operating by adsorption to purify the cooled compressed flow with water to form a compressed and dried flow, optionally an apparatus for enriching the compressed and dried flow with water, a heat exchanger (26) operating by adsorption to purify the cooled compressed flow with water to form a compressed and dried flow, optionally an apparatus for enriching the compressed and dried flow with water, a heat exchanger (27) operating by adsorption to purify the cooled compressed flow with water to form a compressed and dried flow, optionally an apparatus for enriching the compressed and dried flow with water, a heat exchanger (28) operating by adsorption to purify the cooled compressed flow with water to form a compressed and dried flow, optionally an apparatus for enriching the compressed and dried flow with water, a heat exchanger (29) operating by adsorption to purify the cooled compressed flow with water to form a compressed and dried flow, optionally an apparatus for enriching the compressed and dried flow with water, a heat exchanger (30) operating by adsorption to purify the cooled compressed

12. heat to cool the compressed and dried flow connected to the purification apparatus and possibly to the enrichment apparatus, a separation apparatus (20) by partial condensation and / or distillation and / or solidification to separate the compressed and dried flow to form a flow (3) enriched in the first component compared to the dry-based gas flow and a flow (21) depleted in the first component compared to the dry-based gas flow, means for sending the flow depleted in the first component to the heat exchanger to be heated by heat exchange with the compressed and dried flow which cools in the heat exchanger, a turbine (22) and means for sending the flow depleted in the first component and heated in the heat exchanger to the turbine, means connected to the inlet of the turbine to send compressed and dried gas (15) therein,taken downstream of the purification device or in the purification device and upstream of the heat exchanger and means for triggering the sending as a function of a stoppage of the compressor or as a function of a reduction speed of the compressed flow (18) characterized in that it comprises means for regulating the sending of the compressed and dried gas towards the inlet of the turbine (22) as a function of the pressure at the inlet of the turbine and / or as a function of the flow rate of the compressed flow (18) and / or as a function of the temperature at the inlet of the turbine and / or as a function of the temperature of the outlet of the turbine and in that the turbine is coupled to the compressor., Apparatus according to claim 11 wherein the compressor (14) is coupled to the turbine (22) by a shaft (16) to which a gas turbine or electric motor (17) is coupled.

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