Method and device for separating a gas flow via partial condensation and / or distillation and / or solidification
Patent Information
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2024-04-15
- Publication Date
- 2026-03-11
AI Technical Summary
In gas separation and liquefaction processes, sudden shutdown or startup of compression and expansion machines can cause turbine overheating due to mechanical inertia, leading to potential damage, especially when the turbine is not adequately supplied with fluid, particularly in large-scale systems where emergency fluids may not be promptly available or effective.
The method involves using a compressed and dried gas flow from a cooling and adsorption unit as a relief fluid, which is cooled and purified, then sent to the turbine inlet during compressor shutdown or reduced flow rates, or during startup, to prevent overheating by providing a quick supply of dry, cooled gas, leveraging the gas inventory in adsorption bottles and regulators for rapid delivery.
This approach effectively mitigates turbine overheating and damage by rapidly supplying a dry, cooled gas to the turbine, reducing the risk of mechanical stress and extending equipment lifespan, even in high-flow rate systems where emergency fluids may be insufficient or delayed.
Smart Images
Figure EP2024060172_07112024_PF_FP_ABST
Abstract
Description
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. In addition, the compression energy of certain co-products or intermediate fluids can be recovered in the form of cold and / or mechanical energy in a turbine. There are two main families of compression wheels mechanically coupled to expansion wheels: Those where the turbine drives the compressor, without any other source of energy on the common shaft. Those where the compressor and the turbine are placed on the same shaft and a motor or a steam turbine or more generally another mechanical source supplements the energy to be supplied to the compressor because the turbine does not provide enough.
[0003] It is known from US1992486 to compress a combustion gas containing 18% CO2, to separate the CO2 it contains by solidification and to expand a portion of the gas which has not been solidified in a turbine which drives a compressor of the combustion gas, the assembly forming a compression and expansion machine.
[0004] When the compression and expansion machine stops suddenly or is put into safety shutdown due to a disturbance in the process, the compression wheels continue to rotate for a few minutes by kinetic energy and thus drive the wheels of the turbine(s). The mechanical inertia of the compressor is higher when the compression wheels have a large diameter (i.e. the flow to be treated is large, for example 355,100 m 3 / h with a compression power of several megawatts). Rotating the turbine without sufficient fluid at the inlet can cause the turbine materials to heat up and damage it.
[0005] This problem can also exist when starting the turbine and / or when starting the compressor to which the turbine is coupled.
[0006] To overcome the problem of heating and / or damage to the turbine, either a backup fluid is supplied to the turbine in case of machine shutdown, or more expensive materials that withstand a higher temperature are chosen for the turbine (which makes the cost of the unit higher while the machines represent a significant part of the cost of the units).
[0007] The problem with a backup fluid is that it takes a few seconds to trigger the valves and supply the fluid, which gives the materials time to heat up (even with ultra-fast opening valves, particularly due to the large valve sizes). This is why, on machines where the turbine drives a compressor, the backup fluid is generally made up of a gas taken directly from the compressor discharge. 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 example, in devices for separating a combustion gas to produce CO2 including a nitrogen turbine, due to the risk of freezing and / or possibly the formation of hydrates at low temperature after expansion.
[0008] The present invention involves taking as 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 an object of the invention, there is provided a method for separating a gas stream containing a first component, at least one 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 of 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 gas stream on a dry basis and a flow 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 coupled to the compressor characterized in that when the compressor stops or when the compressed molar flow is reduced by at least 1% / sec or when the compressor and / or the turbine starts, part 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 part 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 falls above a threshold and / or in the event of a signal to stop the compressor's compression wheels. the first component is carbon dioxide. the compressed flow comprises at least 15 mol% of carbon dioxide on a wet basis. the at least one second component is chosen from the group: nitrogen, oxygen, argon, carbon monoxide, methane. the part 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 reducer, downstream of at least one adsorbent bottle 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 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. the opening means, for example the pressure reducer of each bottle, is calibrated to open from the same threshold. the compressed gas flow in the compressor is at least 50,000m. 3 / h, or at least 150,000m 3 / h.the compressed and dried flow is enriched in the first component and depleted in the at least one second component by adsorption.the flow depleted in the first component is enriched in the at least one second component, which may be nitrogen, oxygen, argon, carbon monoxide or methane, by partial condensation and / or distillation.after sending the part 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 a device for enriching in the first component is present, the part 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, there is provided an apparatus for separating a gas flow containing a first component, at least one second component and water comprising a compressor for compressing the gas flow to form a compressed flow, cooling means for cooling the compressed flow to form a cooled compressed flow, a purification apparatus operating by adsorption for purifying the cooled compressed flow with water to form a compressed and dried flow, optionally an apparatus for enriching 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 optionally 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 compared to the dry-based gas flow and a flow 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 coupled to the compressor and means for sending the flow depleted 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 to send compressed and dried gas therein, taken downstream of the purification apparatus or in the purification apparatus and upstream of the heat exchanger,means for detecting a compressor stoppage or means for detecting a compressed flow reduction speed and means for triggering the sending following a compressor stoppage or as a function of the compressed flow reduction speed.,
[0012] Preferably, the apparatus comprises means for regulating the delivery of the compressed and dried gas to the inlet of the turbine 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 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.
[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 check valve or block valve can be placed between the compressor and the adsorption unit.
[0015] Conventionally, a TSA air purification process cycle comprises the following steps: purification of a gas stream by adsorption of impurities at super-atmospheric pressure and at ambient temperature, optionally depressurization of the adsorber to atmospheric pressure or below atmospheric pressure, regeneration of the adsorbent at atmospheric pressure, in particular by a residual gas, in the case of air separation typically 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, cooling to ambient or subambient temperature of the adsorbent, in particular by continuing to introduce said residual gas, but not heated, optionally repressurization of the adsorber with the purified gas stream originating, for example, from 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 comprises substantially the same steps a), b) and e), but is distinguished from a TSA process by the absence of heating of the residual gas(es) 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 the production phase, while another is in the regeneration phase.
[0019] Typically, water vapor removal is performed 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 variant of the invention, an expander is added downstream of the adsorption unit and upstream of the expansion wheels mechanically coupled on the same shaft to the compressor to instantly supply (because of mechanical opening) the emergency fluid to the turbine during a sudden stop (or significant disturbance) of the compressor by taking advantage of the gas inventory stored in the adsorption bottles of the temperature swing adsorption (TSA) or pressure swing adsorption (PSA) type of the drying unit. Emergency fluid can also be supplied by a distillation column or a capacity, in addition to the fluid coming downstream of the adsorption drying unit.If the gas inventory in the adsorbent cylinders of the adsorption unit between the compressor and the turbine is not sufficient to supply the turbine in the event of a compressor shutdown, the solution with a pressure reducer still allows the 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, an emergency gas from storage, an emergency gas from a liquid to be vaporized).
[0021] The invention will be described in more detail with reference to the figures where:
[0022] illustrates an apparatus according to the invention.
[0023] illustrates an apparatus according to the invention.
[0024] illustrates an adsorption drying apparatus of an apparatus according to the invention
[0025] illustrates the relationship between the rotational speed and the time of a compressor of an apparatus according to the invention.
[0026] illustrates an apparatus according to the invention comprising a compressor 14 of the gas flow 13 containing a first component, at least one second component and water, the second component possibly being heavier or lighter than the first component. The content of the first component may be higher than that for the second component or vice versa.
[0027] The flow rate of the gas stream 13 is preferably at least 50,000m 3 / h, or at least 150,000m 3 / 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 wash tower.
[0029] In the diagram, the cooling means are considered to be an integral part of the compressor 14, as this is the last cooling downstream of the last wheel. The cooled flow is then dried in an adsorption purification device 19 of the TSA or PSA type to remove the water it contains, forming a dried flow 23 which feeds a partial condensation and / or distillation and / or solidification separation device 20. The dried flow in the purification device 19 may be enriched in the first component, for example by treating it by adsorption upstream of the device 20. The device 20 comprises a heat exchanger for cooling the dried flow 23 to a temperature below 0°C. The device 20 separates the dried and cooled flow by partial condensation and / or distillation and / or solidification forming a fluid 3 enriched in the first component relative to the flow 23 and this fluid 3 is sent to a customer 4 or to storage.The apparatus also produces a gas 21 depleted in the first component relative to the flow rate 23 at a pressure higher than atmospheric pressure, this gas 21 possibly coming from a partial condensation step and / or a distillation step and / or a solidification step and this gas 21 is reheated in the exchanger where the dry gas 23 cools 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 to the turbine 22.
[0030] In the event of a reduction in the compressed flow 18, for example in the event of a breakdown or shutdown of the compressor 14, the inertia of the compressor wheels means that they can continue to rotate, driving the wheels of the turbine 22 via the shaft 16 to rotate, 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 within ten seconds, i.e. at least 1% of the molar flow rate per second.
[0032] The problem also occurs when starting compressor 14 and / or 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 start, 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 arrives at the inlet of the turbine 22.
[0034] The apparatus comprises means for detecting a stoppage of the compressor 14 or means for detecting a reduction speed of the compressed flow in the compressor 14.
[0035] 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.
[0036] 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, etc.
[0037] Gas stream 13 contains, for example, 20 mol% carbon dioxide, 20 mol% water and 60 mol% nitrogen (wet basis).
[0038] illustrates an apparatus according to the invention with more detail of the emergency gas sending means 15.
[0039] To prevent the gas inventory 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 gas inventory present in the bottles of the drying unit.
[0040] An opening means, for example a pressure regulator D (in English “pressure regulator”), is placed on the emergency gas line 15 coming from the drying unit 15 to the turbine 22.
[0041] The role of the D regulator (or other equivalent system) is to open when its downstream pressure drops below its setting threshold. The opening is mechanical, using a spring-loaded system like a valve, which guarantees a very fast opening time (almost instantaneous) and good reliability. This also has the advantage of not going through the distributed control system (DCS) control, which would add a reaction time of around 3-4s, coming from the DCS scanning time of ~1s, plus the information transfer and processing time. In total, for a pneumatic valve of an adequate size associated with a DCS, it would be necessary to allow 5-10s of opening time (including the waiting time linked to the DCS).
[0042] Thus, the regulator D opens if the pressure at the turbine inlet falls below a threshold and quickly supplies the turbine with dry gas stored in at least one bottle of the drying unit. The system thus behaves like a spillway.
[0043] The sending of gas 15 can be triggered using a means of regulation other than a regulator.
[0044] 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 of the outlet of the turbine and / or as a function of a signal to stop the compression wheels of the compressor 14.
[0045] This sending of gas 15 can be followed by a sending of gas from another source, for example a pressurized gas storage, a liquid storage associated with a vaporizer, a gas withdrawn from a pipeline.
[0046] The gas 15 can be taken directly from at least one adsorbent bottle 20A, 20B, 20C, 20D.
[0047] Depending on the application, an identical or staggered setting pressure may be preferred for the different pressure reducers (if there are several, for example if there are several adsorption bottles). In the case of adsorption bottles, the setting pressure will preferably be identical so as to minimize the risk of fluidization of the adsorbent bed (so that the bottles are emptied simultaneously and not successively).
[0048] 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, for drying 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.
[0049] In normal operation, three bottles are in the adsorption phase while the fourth is in the regeneration phase. The selection of bottles in the adsorption phase is cyclical in order to regenerate all the bottles in turn. The three bottles each produce a dried gas 23A, 23B, 23C and the flows are mixed to form the gas 23 feeding the separation device 20.
[0050] illustrates the relationship between the rotation speed and the time of a compressor of a device according to the invention with the 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.
[0051] To give one example among others, a compressor 14 takes about 10 minutes to stop in the event of a trip. In addition, its rotation speed is halved during the first few seconds (~30-40s) and the flow rate decreases by half during the first 2 minutes.
[0052] A certain gas inventory is contained in the TSA cylinders per cylinder when they are depressurized to 2 bara, this value corresponding to the free volume of gas contained in the cylinders plus the desorbed gas. Three cylinders 20A, 20B, 20C are in production and one 20D in regeneration (at a similar pressure but at high temperature, which limits the available gas inventory). Considering only the three cylinders in production, the gas inventory available for turbine 22 allows turbine 22 to be supplied for 5 minutes, for example, with a constant flow rate of 20,000 Nm 3 / h. This makes it possible to supply gas 15 to the turbine 22 during the first moments after stopping or abruptly reducing the flow rate of the compressor 14, these first minutes being the most critical with regard to the risk of the machine overheating.
Claims
Method for separating a gas stream containing a first component, at least one second component and water in which 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 depleted (21) 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., 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). A method according to claim 1 or 2 wherein the first component is carbon dioxide. 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. 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. 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. 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. 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. Method according to one of the preceding claims in which the compressed gas flow in the compressor (14) is at least 50,000m 3 / h, or at least 150,000m 3 / h. Method according to one of the preceding claims in which the flow (21) depleted in the first component is enriched in at least one second component, which may be nitrogen, oxygen, argon, carbon monoxide or methane. 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 for cooling the compressed and dried flow connected to the purification apparatus and optionally 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) coupled to the compressor and means for sending the flow depleted 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 to send compressed and dried gas (15) therein, taken downstream of the purification apparatus or in the purification apparatus and upstream of the heat exchanger,means for detecting a compressor stoppage or means for detecting a compressed flow reduction speed and means for triggering the sending following a compressor stoppage or as a function of the compressed flow reduction speed (18., Apparatus according to claim 11 comprising 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. Apparatus according to claim 11 or 12 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.