Method and device for separating a gaseous mixture containing co2
The method and apparatus for CO2 separation at a single pressure reduce the need for compressors and simplify the system, lowering costs and energy use while maintaining efficiency in CO2 production.
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- LAIR LIQUIDE SA POUR LETUDE & LEXPLOITATION DES PROCEDES GEORGES CLAUDE
- Filing Date
- 2026-01-19
- Publication Date
- 2026-07-23
AI Technical Summary
Existing methods for separating CO2 from gas mixtures require multiple compressors and complex systems, leading to high investment costs and energy consumption, particularly when producing CO2 at two different pressures.
A method and apparatus that allows CO2 production at a single pressure by recycling and compressing a two-phase mixture, eliminating the need for a product compressor and optimizing heat exchange processes to reduce complexity and energy consumption.
Reduces the number of machines required, decreases investment and maintenance costs, and slightly lowers energy consumption while maintaining efficient CO2 separation, with potential for higher CO2 production pressures without additional compressors.
Smart Images
Figure EP2026051189_23072026_PF_FP_ABST
Abstract
Description
[0001] Description
[0002] Title of the invention: Method and apparatus for separating a gaseous mixture containing CO2
[0003] The present invention relates to a method and apparatus for separating a gaseous mixture containing CO2, for example, containing at least 50 mol% CO2. It is known to separate a gaseous mixture containing CO2 at a temperature below 0°C by partial condensation and distillation. After compression and drying of the inlet gas, a low-temperature treatment produces a CO2-poor gas, still under pressure; as well as purified CO2, available at at least two pressures, typically 5.5 and 11 bara. The process is constructed such that it is necessary to produce the CO2 at two pressures. Thus, when the CO2 is to be produced as a gas, a compressor is indispensable, if only to reduce the CO2 at 5.5 bar to the pressure of the CO2 stream at 11 bara. [FIG.Figure 1 illustrates a process of this kind in which a gaseous mixture containing at least 50 mol% CO2 and at least one lighter component is compressed by a compressor, dried by a dryer, cooled in a heat exchanger E, and then separated by at least one partial condensation stage, for example, either a single partial condensation stage (called the main stage) or two partial condensation stages, one of which (called the main stage) is preceded by a first partial condensation stage (called the auxiliary stage). The liquids from the two condensate pots S1 and S2 are sent to the top of a simple column K, which operates at a first pressure. The gas from the main pot is enriched in the at least one component lighter than CO2, called "non-condensable." The gas at the top of column K is heated in the heat exchanger E and is returned upstream of a blower S for the gas to be separated.The use of the terms "principal" and "auxiliary" only indicates that the principal step is essential to the invention while the auxiliary step is not. They do not characterize the two separations, for example, by indicating that the separation is more complete in one step than in the other.
[0004] Part of the tank liquid is vaporized in the heat exchanger and sent partly to the column tank as reboiling gas and partly to the product compressor. Another portion of the tank liquid is expanded, forming a two-phase flow. The resulting gas and liquid are heated in the exchanger and mixed, forming a gas at a second pressure lower than the first, which is also compressed by the product compressor.
[0005] The invention allows, in several cases, the production of the CO2 gaseous flow at a single pressure, preferably relatively high to avoid the need for a compressor. The compression work would be transferred to the compressor from the feed flow.
[0006] More precisely :
[0007] • The compressed feed flow is cooled in the cryogenic exchanger, in a partial condensation at at least one or two stages
[0008] • A portion of the liquid from at least one partial condensation pot or pots is expanded and purified in a distillation column operated at the desired CO2 production pressure.
[0009] • Liquid CO2 recovered in the column tank is vaporized in the exchanger to provide cooling at the temperature level of the first partial condensation, and recovered as vapor at the desired production pressure, in several variants.
[0010] • according to one variant, at least a portion of the non-condensables recovered at the top of the main partial condensation pot, as well as a portion of the liquid CO2 recovered from the auxiliary partial condensation pot (if present) or the main partial condensation pot, and possibly gas from the column head, are mixed in order to generate cold at the temperature level of the second partial condensation:
[0011] • According to one variant, a portion of the non-condensables recovered at the top of the auxiliary partial condensation pot, as well as a portion of the liquid CO2 recovered from the auxiliary partial condensation pot and possibly some gas from the column head, are mixed to generate cooling at the temperature level of the second partial condensation: • According to another variant, a portion of the non-condensables recovered at the top of the auxiliary pot and the main partial condensation pot, as well as a portion of the liquid CO2 recovered from the first partial condensation pot and possibly some gas from the column head, are mixed to generate cooling at the temperature level of the second partial condensation:
[0012] The amount of CO2 released is adjusted to provide sufficient cooling for the condensation of the feed flow.
[0013] o The quantity of non-condensables is adjusted in order to have the correct temperature level of the mixture.
[0014] o The pressure of the mixture is adjusted to optimize the exchange diagram, and to be able to judiciously recycle this fluid to the compressor: for example at a pressure between 10-12 bara.
[0015] o Vaporizing an impure two-phase fluid causes a large temperature glide, allowing cooling to be applied at the correct temperature level without having to expand the pressure from 2 to 5 bar. • If the fluid produced by heating the two-phase mixture is recycled, it is preferably recompressed and reprocessed in the cryogenic section.
[0016] Here the term "cryogenic" is used to cover temperatures below -30°C.
[0017] According to one aspect of the invention, a method is provided for separating a mixture containing CO2 and at least one component lighter than CO2 in which:
[0018] a) The gaseous mixture, preferably containing at least 50 mol% CO2, is compressed in a compressor and optionally dried, then cooled in a heat exchanger, and separated by at least one partial condensation step forming at least one liquid and at least one gas, for example by being sent to a first condenser forming a first gas and a first liquid, at least part of the first gas being partially condensed and sent to a second condenser forming a second gas and a second liquid
[0019] b) At least a portion of at least one liquid, for example, a portion of the first liquid recovered in the first condenser, and all of the second liquid separated in the second condenser, is depressurized and sent to a distillation column operated at a first pressure, producing a liquid enriched in CO2 and depleted in at least one lighter component and a gas enriched in at least one lighter component and depleted in CO2
[0020] c) CO2-enriched liquid recovered from the column tank is vaporized and
[0021] i) heated in the heat exchanger forming a gas produced enriched in CO2 at the first pressure and / or
[0022] ii) sent to another column to be separated and
[0023] d) Gas formed by at least one partial condensation step, which may be part of the first gas exiting the first condenser pot and / or at least part of the second gas exiting the second condenser pot and / or a gas formed by separating at least part of the first and / or second gas (G1, G2), is mixed with liquid formed during at least one partial condensation step, which may be part of the liquid recovered in the first partial condenser pot and possibly with the gas enriched in at least one lighter component recovered at the top of the column, forming a two-phase mixture, the two-phase mixture is heated in the exchanger to vaporize the liquid it contains and the heated gas thus produced is possibly recycled to the gas mixture upstream of the heat exchanger and is possibly compressed with the gas mixture.
[0024] According to one aspect of the invention, a method is provided for separating a mixture containing CO2 and at least one component lighter than CO2 in which:
[0025] (e) the gaseous mixture, preferably containing at least 50 mol% CO2, is compressed in a compressor and optionally dried, then cooled in a heat exchanger, and separated by at least one partial condensation step forming at least one liquid and at least one gas,
[0026] (f) At least a portion of the at least one liquid is depressurized and sent to a distillation column operated at a first pressure, producing a liquid enriched in CO2 and depleted in at least one lighter component and a gas enriched in at least one lighter component and depleted in CO2
[0027] g) CO2-enriched liquid recovered from the column tank is vaporized and
[0028] i) heated in the heat exchanger forming a gas produced enriched in CO2 at the first pressure and / or
[0029] ii) sent to another column to be separated and
[0030] h) Gas formed by at least one partial condensation step is mixed with liquid formed during at least one partial condensation step, forming a two-phase mixture; the two-phase mixture is heated in the exchanger to vaporize the liquid it contains.
[0031] The heated gas thus produced is possibly recycled to the gas mixture upstream of the heat exchanger and is possibly compressed with the gas mixture.
[0032] According to other optional aspects: • At least one condensation pot operates at a temperature below -50°C or even below -52°C but above -56°C.
[0033] • part of the gas from partial condensation, for example from the last pot is heated in the heat exchanger to its hot end without having been mixed with another fluid.
[0034] • the part of the gas from the partial condensation, for example from the last pot, heated in the heat exchanger until its hot end is then expanded in a turbine and returned to the heat exchanger to provide cooling.
[0035] • the portion of the gas resulting from partial condensation, for example from the last pot heated in the heat exchanger until its hot end is then separated by permeation forming a permeate enriched in CO2
[0036] • the permeate is expanded in a turbine and returned to the heat exchanger to provide cooling.
[0037] • at least part of the permeate constitutes the gas formed by separating at least part of the second gas which mixes with liquid formed by partial condensation, for example the liquid from at least one of the pots and possibly with the gas enriched in at least one lighter component and depleted in CO2.
[0038] • the permeate is cooled in the heat exchanger before being mixed with the liquid from at least one of the pots and possibly with the gas enriched in at least one lighter component and depleted in CO2.
[0039] • The turbine is coupled to a gas mixture compressor upstream of the heat exchanger.
[0040] • The first gas is expanded in a turbine after being heated in the heat exchanger.
[0041] • the gas mixture contains at least one component heavier than CO2 and at least part of the CO2 enriched liquid recovered in the column tank is vaporized and sent to another column (K2) to be separated, forming a CO2 rich gas at the top of the column and a liquid enriched with at least one heavier component in the column tank.
[0042] According to another object of the invention, an apparatus for separating a mixture containing CO2 and at least one component lighter than CO2 is provided, comprising a compressor, a partial condensation system including a heat exchanger, at least one condenser pot and optionally a second auxiliary condenser pot, a distillation column, means for sending the gaseous mixture, preferably containing at least 50 mol% CO2, to be compressed in the compressor and optionally dried, then cooled in the heat exchanger of the system, to partially condense it, means for sending the partially condensed flow to at least one condenser pot of the partial condensation system, producing a liquid and a gas, and expansion means for expanding a portion of the liquid recovered in the partial condensation system.means for sending the expanded fluid in the expansion means into the distillation column operated at a first pressure, producing a liquid enriched in CO2 and depleted in at least one lighter component and a gas enriched in at least one lighter component and depleted in CO2; means for sending CO2-enriched liquid recovered in the column tank to the heat exchanger to form a CO2-enriched product gas at the first pressure; and optionally means for sending the product gas to another column for separation; means for mixing a gas recovered in the partial condensation system with a liquid recovered in the partial condensation system and optionally with the gas enriched in at least one lighter component recovered at the top of the column, forming a two-phase mixture.means for sending the two-phase mixture to be heated in the exchanger to vaporize the liquid it contains, and optionally means for sending the heated gas thus produced to mix with the gas mixture upstream of the heat exchanger and optionally upstream of the compressor. According to one object of the invention, a method is provided for separating a mixture containing CO2 and at least one component lighter than CO2 in which:
[0043] a) The gaseous mixture, preferably containing at least 50 mol% CO2, is compressed in a compressor and optionally dried, then cooled in a heat exchanger to partially condense it. The partially condensed flow is optionally sent to a first auxiliary condenser, forming a first gas and a first liquid. At least a portion of the first gas is partially condensed and sent to a second main condenser, forming a second gas and a second liquid.
[0044] b) A portion of the first liquid recovered in the auxiliary condenser, and all of the second liquid separated in the main condenser, are expanded and sent to a distillation column operated at first pressure, producing a liquid enriched in CO2 and depleted in at least one lighter component and a gas enriched in at least one lighter component and depleted in CO2. c) CO2-enriched liquid recovered in the column vessel is vaporized and i) reheated in the heat exchanger, forming a CO2-enriched product gas at first pressure and / or
[0045] ii) sent to another column to be separated
[0046] d) a part of the first gas exiting the auxiliary condenser pot and / or at least a part of the second gas exiting the main condenser pot and / or a gas formed by separating at least a part of the first and / or second gas is mixed with a part of the first liquid recovered in the auxiliary partial condenser pot and possibly with the gas enriched in at least one lighter component recovered at the top of the column forming a two-phase mixture, the two-phase mixture is heated in the exchanger to vaporize the liquid it contains and possibly the heated gas thus produced is recycled to the gas mixture upstream of the heat exchanger and is possibly compressed with the gas mixture.
[0047] Depending on other optional characteristics:
[0048] • the main condensation pot operates at a temperature below -50°C or even below -52°C but above -56°C.
[0049] • Part of the second gas from the main pot is heated in the heat exchanger to its hot end without having been mixed with another fluid.
[0050] • The portion of the second gas coming from the main pot, heated in the heat exchanger until its hot end is then expanded in a turbine and returned to the heat exchanger to provide cooling.
[0051] • The portion of the second gas coming from the main pot, heated in the heat exchanger until its hot end is then separated by permeation, forming a permeate enriched in CO2
[0052] • the permeate is expanded in a turbine and returned to the heat exchanger to provide cooling.
[0053] • at least part of the permeate constitutes the gas formed by separating at least part of the second gas which mixes with the liquid of the first pot and possibly the gas enriched in at least one lighter component and depleted in CO2.
[0054] • the permeate is cooled in the heat exchanger before being mixed with the liquid (L1b) from the first pot and possibly the gas enriched in at least one lighter component and depleted in CO2.
[0055] • the portion of the second gas mixed with the gas enriched in at least one lighter component exiting the column is heated in the heat exchanger before being mixed.
[0056] • The turbine is coupled to a gas mixture compressor upstream of the heat exchanger.
[0057] • The first gas is expanded in a turbine after being heated in the heat exchanger. • The mixture contains at least one component heavier than CO2 and at least part of the CO2-enriched liquid recovered in the column tank is vaporized and sent to another column to be separated, forming a CO2-rich gas at the top of the column and a liquid enriched with at least one heavier component in the column tank.
[0058] • The column tank liquid vaporizes at a single pressure before forming a process product.
[0059] • the liquid in the column tank vaporizes at the pressure of the column from which it is withdrawn.
[0060] • The heated gas formed by heating the two-phase mixture is expanded before being sent to the compressor.
[0061] • the first pressure is greater than 10 bars abs, or even greater than 25 bars abs.
[0062] • The gas at the top of the column is heated in the heat exchanger without having been mixed with another fluid
[0063] • The column's overhead gas constitutes part of the two-phase mixture. • The permeate is enriched in CO2 relative to the second gas.
[0064] • the residue is depleted in CO2 compared to the second gas
[0065] • The two-phase mixture is heated in the exchanger after being separated into a gaseous part and a liquid part; the liquid part is heated to vaporize, and the gaseous part is simply heated. The two heated parts are then mixed downstream of the heat exchanger.
[0066] According to another object of the invention, an apparatus for separating a mixture containing CO2 and at least one component lighter than CO2 is provided, comprising a compressor, a heat exchanger, optionally a first (auxiliary) condenser, a second (main) condenser, a distillation column, means for sending the gaseous mixture, preferably containing at least 50 mol% CO2, to be compressed in the compressor and optionally dried, then cooled in the heat exchanger, to partially condense it, optionally means for sending the partially condensed flow to the first condenser forming a first gas and a first liquid, means for sending at least a part of the first partially condensed gas to the second condenser forming a second gas and a second liquid, and expansion means for expanding a portion of the first liquid recovered in the first condenser.and the entirety of the second liquid separated in the second condenser pot, means for sending the expanded fluid in the expansion means to the distillation column operated at a first pressure, producing a liquid enriched in CO2 and depleted in at least one lighter component and a gas enriched in at least one lighter component and depleted in CO2, means for sending CO2-enriched liquid recovered in the column tank to the heat exchanger to form a CO2-enriched product gas at the first pressure and optionally means for sending the product gas to another column for separation,means for mixing a gas which is a part of the first gas exiting the first condenser pot and / or at least a part of the second gas exiting the second condenser pot and / or a gas formed by separating at least a part of the first and / or second gas with a part of the first liquid recovered in the first partial condenser pot and possibly with the gas enriched in at least one lighter component recovered at the top of the column forming a two-phase mixture,Means for sending the two-phase mixture to be heated in the exchanger to vaporize the liquid it contains, and optionally means for sending the heated gas thus produced to mix with the gas mixture upstream of the heat exchanger and possibly upstream of the compressor. The apparatus may include a second connected column for separating a portion of the tank liquid from the column vaporized in the heat exchanger, and means for drawing a liquid enriched in a component heavier than CO2 from the tank of the second column as a purge liquid.
[0067] The apparatus may include means for compressing the overhead gas from the second column after heating in the heat exchanger, for use, for example, as a gaseous and / or liquid product. The apparatus may include means for liquefying the compressed overhead gas. The apparatus may include means for sending the liquefied overhead gas, via liquefaction means, to the head of the second column to serve as a reflux.
[0068] [FIG.2] illustrates the heat exchange diagram with temperature on the x-axis and heat exchanged H on the y-axis. It shows the large temperature glide of the process according to the invention.
[0069] The advantages of this solution are as follows:
[0070] The process requires one less machine, which reduces investment costs, the floor space used by the unit, and maintenance requirements.
[0071] However, this invention has several disadvantages in certain variations:
[0072] • The compressor recycler increases in size in its second section. • The unit's energy consumption increases slightly (~5%). • The cryogenic heat exchanger is more complex and requires a larger surface area.
[0073] • Integration begins to reach its limits beyond 20 bara.
[0074] Depending on the composition and pressure of the non-condensables drawn off at the top of the second partial condensation unit, their expansion to the mixture pressure may cause the gas to drop below the triple point of CO2 (-56.5°C). Although the non-condensables are relatively unsaturated with CO2 and the gas expansion poses little risk of CO2 freezing, mixing this cold gas with CO2-rich fluids presents a high risk of freezing. If this risk arises, slight modifications to the process can mitigate the mixing risk:
[0075] It is always possible to expand the non-condensable gases from the hot end of the heat exchanger, which significantly raises the temperature of the expanded fluid away from the triple point. To maintain the desired temperature at the cold end, more non-condensable gases and CO2 must be expanded.
[0076] • In cases where non-condensable gases are expanded in a turbine to provide cooling in the heat exchanger, a portion of the exhaust gas from the turbine can be drawn off to form part of the two-phase mixture. This potentially requires raising the turbine pressure to the pressure of the two-phase mixture, but it allows for the expansion of all the non-condensable gases, thus increasing the cooling capacity of the process and slightly reducing the flow rate of the two-phase mixture.
[0077] A variant of this process may consist of expanding some of the non-condensables generated by the cryogenic treatment, possibly after treatment (for example in a membrane unit) to drive a compressor further increasing the pressure of the CO2 produced, making it possible to obtain a product above 25 bara.
[0078] Another variant is suitable for units that separate a gas mixture in which at least one component lighter than CO2 includes hydrogen. Such units are used for the production of decarbonized hydrogen. One variation involves replacing the non-condensable gas stream from the second partial condenser with the second permeate from a membrane separation unit. This permeate is already recycled at the compressor; using some of it to add the lighter components to the mixture does not incur an energy penalty like expanding non-condensables. Furthermore, this eliminates any risk of freezing.
[0079] The slight energy gain (~1%) must be weighed against a more complicated exchanger.
[0080] The invention will be described in more detail with reference to the figures where:
[0081] [FIG. 3] represents a method according to the invention
[0082] [FIG. 4] represents a method according to the invention
[0083] [FIG. 5] represents a method according to the invention
[0084] [FIG. 6] represents a process according to the invention [FIG. 7] represents a process according to the invention for a gas containing at least one component heavier than CO2.
[0085] [FIG. 8] represents a method according to the invention which is a variant of [FIG. 7],
[0086] [FIG. 9] represents a method according to the invention which is a variant of [FIG. 3],
[0087] [FIG. 3] represents a process for separating a mixture containing CO2 and at least one component lighter than CO2, in which the gaseous mixture 1, preferably containing at least 50 mol% CO2 and at least one lighter component, such as nitrogen, oxygen, carbon monoxide, methane, or hydrogen, is compressed in a compressor C1 and optionally dried in a dryer D, compressed by a compressor C2 on the same axis as compressor C1, and then cooled in a plate and finned heat exchanger E. In the exchanger E, it partially condenses; optionally, the partially condensed flow exits an intermediate level of the exchanger E and is sent to an auxiliary condenser S1, forming a first gas G1 and a first liquid. The first gas is partially condensed and sent to a main condenser S2, forming a second gas and a second liquid at -52.5°C.
[0088] A portion Lia of the first liquid recovered in the auxiliary condensation pot S1, and the entirety of the second liquid separated in the main condensation pot are decompressed and sent to the top of a simple distillation column K operated at a first pressure as liquid L, containing about 95% mol CO2, producing a liquid L6 enriched in CO2 and depleted in at least one lighter component and a gas G3 enriched in at least one lighter component and depleted in CO2.
[0089] The CO2-enriched liquid L6 recovered from the column tank is vaporized and heated in the heat exchanger, forming a CO2-enriched product gas G8 at the first pressure, for example, 15 bar. Thus, all the liquid from the column K1 tank is vaporized at a single pressure, which is the product production pressure. In this way, no product compressor is required.
[0090] The gas G3 enriched in at least one lighter component recovered at the top of the column is first mixed with at least a part G2b of the second gas exiting the main condenser pot S2 then with a part L1b of the first liquid L1 recovered in the auxiliary partial condenser pot S1 and / or with a part L2b of the second liquid L2 recovered in the main partial condenser pot S2 forming a two-phase mixture, the two-phase mixture M is heated in the exchanger to vaporize the liquid it contains and the heated gas thus produced can be recycled to the gas mixture upstream of the heat exchanger and compressor C2.
[0091] It will be understood that the G2b gas and the L1 liquid and / or the L2 liquid can form the two-phase mixture on their own, with the G3 gas being heated separately in dedicated passages of the heat exchanger.
[0092] It will be understood that, according to one variant, a gas, which is gas G2b and / or a portion of gas G1, is / are mixed upstream of the heat exchanger E with liquid L1 and / or liquid L2 to constitute the two-phase mixture M, with gas G3 being heated separately in dedicated passages of the heat exchanger. Thus, it is possible to mix gas G2b, a portion of gas G1, and liquid L1 and / or L2 to form mixture M. The remaining gas G1 is then partially condensed to supply the pot S2.
[0093] If the mixture M only includes the part of the gas G1 and the liquid L1, the gas G2b does not exist and all the gas G2 is heated separately in the exchanger E. The mixture M is heated in the exchanger preferably at a pressure between 10 and 12 bar.
[0094] The remaining gas G2a, containing between 15 and 25 mol% CO2, exiting the main condenser S2, is heated in the heat exchanger. This gas can be expanded in a turbine after being heated in the heat exchanger E. [FIG.4] represents a variant of [FIG.3] in which the gas G2 from the main condenser S2 is heated in the heat exchanger E and is separated in a unit PT, forming a residue R depleted in CO2 relative to the second gas and a permeate P enriched in CO2 relative to the second gas. The permeate P is expanded in a turbine T, and the expanded permeate is sent to the cold end of the exchanger E, where a portion P2 of the permeate is heated, providing cooling for the separation process. The remainder P1 of the expanded permeate P is mixed with the gas G3 upstream of the arrival of the liquid L1b and / or L2b forming the mixture M. This requires raising the turbine pressure to the pressure of the mixture M.
[0095] It will be understood that the gas P and the liquid L1b and / or L2b can constitute the two-phase mixture alone, the gas G3 being heated separately in dedicated passages of the heat exchanger.
[0096] The rest of the process is that of [FIG.3],
[0097] Note the absence of compressor C3. Since all the liquid in the tank of column K1 is vaporized at a single pressure, which is the product production pressure, no product compressor is required.
[0098] [FIG.5] represents a variant of [FIG.4] in which the expanded permeate P is not sent to mix with gas G3 and is not heated. A portion G2b of gas G2 from the second pot S2 mixes with gas G3. Gas G2b can be heated in the exchanger E before being mixed with gas G3. It will be understood that, according to one variant, a gas which is gas G2b and / or a portion of gas G1 is / are mixed upstream of the heat exchanger E with liquid L1b and / or L2b to constitute the two-phase mixture M, with gas G3 being heated separately in dedicated passages of the heat exchanger.
[0099] The gas resulting from the vaporization of the tank liquid can be compressed by a C3 compressor coupled to the T turbine, making it possible to obtain a G8 gas at up to 25 bar.Y1
[0100] [FIG.6] represents a variant of [FIG.3], without expansion of the permeate P. The permeate P is cooled in the heat exchanger E to its cold end to be mixed with gas G3. Separation in the PT unit produces at least one other permeate P', and a portion Pa of the permeate P is taken before cooling to be mixed upstream of compressor C2 with gas 1. The PT unit also produces a residue R. Note the absence of compressor C3.
[0101] It will be understood that gas P and liquid L1b can constitute the two-phase mixture M on their own, being mixed upstream of the heat exchanger E, with gas G3 being heated separately in dedicated passages of the heat exchanger. All the liquid in the tank of column K1 is vaporized at a single pressure, which is the production pressure of product G8. In this way, no product compressor is required.
[0102] [FIG. 7] represents a process for separating a mixture containing CO2 and at least one component lighter than CO2 and at least one component heavier than CO2. Dryer D is not shown here but may obviously be included. The gas mixture 1, preferably containing at least 50 mol% CO2 and at least one lighter component, such as nitrogen, oxygen, carbon monoxide, methane, or hydrogen, as well as at least one heavier component, such as NO2, is initially separated as in FIG. 1. The flue gases, for example, contain nitrogen oxides (NOx) that must be removed from the CO2 produced to meet its purity specifications. NOx exists as NO (lighter than CO2) and NO2 (heavier than CO2). Furthermore, NO can oxidize to NO2 in the presence of oxygen.
[0103] NOx is removed by distillation: NO by stripping, along with oxygen and other light gases, in column K1, and NO2 by washing in column K2. However, these operations cannot be performed in just any order if the specification for the CO2 produced is particularly strict. Removing NO2 before partial condensation will leave NO in the gas, which will partially oxidize to NO2 that will not be removed in the stripping column. To obtain CO2 that is particularly free of NO2, NO2 must be removed after the removal of NO and oxygen. Given that the CO2 is produced at at least two different pressures in two separate streams, this implies locating this step after recompression, with all the resulting complexity regarding the specification and control of the machine, interconnections, etc.
[0104] The invention consists of producing the gaseous CO2 flow at a single pressure, in order to be able to locate the NOx removal column K2 upstream of the CO2 compressor. C3. To do this, the coldest CO2 vaporization stage is replaced by the vaporization of a two-phase mixture of CO2 and nitrogen recycled to the compressor of the gaseous mixture to be separated (as described above).
[0105] More specifically, the compressed gas is cooled in heat exchanger E, in a one- or two-stage partial condensation. All or part of the CO2 from the main condenser pot, as well as some from any auxiliary condenser pot, is expanded and purified in a first distillation column K1 operated at the desired production pressure for the CO2 produced. The liquid CO2 collected in the first column tank is vaporized in heat exchanger E to provide cooling at the temperature level of the first partial condensation, and the vapor G6 is recovered.
[0106] Part of the vaporized CO2 G6B is then introduced into the tank of a second NOx removal column K2, where the NO2 is scrubbed with liquid CO2. The purified G9 gas at the top of the second column K2 is heated in the heat exchanger E and then sent to the CO2 compressor C3.
[0107] Optionally, some of the tank liquid taken from the first column tank can be recovered as a liquid product or vaporized to form a liquid product comprising at least one heavier component, if such a composition is desired.
[0108] At an intermediate point in the compression or discharge of machine C3, a fraction G10 of the CO2 is withdrawn, introduced into the exchanger E, and condensed. The resulting liquid CO2, L10, is then introduced into the second column K2 where it serves as a reflux. A purge liquid N, enriched in NO2 relative to the gas, G6B, is also used.
[0109] The gas at the top G3 of the first column K1, a portion G1a of the non-condensable gases G1 recovered at the top of the auxiliary partial condensation pot S1 and / or a portion G2a of the non-condensable gases G2 recovered at the top of the main partial condensation pot S2, as well as a portion L1b of the liquid CO2 L1 recovered from the auxiliary partial condensation pot and / or a portion L2b of the liquid CO2 L2 recovered from the main partial condensation pot are mixed to generate cooling at the temperature level of the partial condensation pot S2. Here, the remaining gas G1 is sent to the separator S2 after partial condensation.: The gas at the top G3 of the first column K1 can be mixed with a part of the non-condensables G1, G2 recovered at the top of the first and / or second partial condensation pot S1, S2 as well as a part L1b of the liquid CO2 L1 recovered from the first auxiliary partial condensation pot and / or a part L2b of the liquid CO2 L2 recovered from the main partial condensation pot in order to generate cold at the temperature level of the second partial condensation S2. The pressure of the mixture M is adjusted to optimize the exchange diagram, and to be able to recycle this fluid judiciously to the compressor C1, C2: for example 10-12 bara.
[0110] The vaporization of an impure two-phase fluid causes a large temperature glide, making it possible to bring cold to the right temperature level without having to expand CO2 to 5 bara.
[0111] In one variation, the gas G3 at the top of the column is not mixed with the liquid CO2 L1 / L2 and the non-condensable gases G1a / G2a, and is heated in the heat exchanger in dedicated passes. Depending on the CO2 content of this gas, this can reduce the amount of non-condensable gases to be added to the mixture. This results in a slight energy saving at the cost of a slightly larger and more complex heat exchanger. In this case, the mixture M contains only the gas G1a / G2a and the liquid L1b / L2b. Here, the two-phase mixture is separated into two parts, liquid and gaseous, using a phase separator S3. Thus, the liquid part vaporizes and heats up separately from the gas, which is heated in the heat exchanger E. This separator S3 is not strictly necessary in [FIG.7] and [FIG.8]. Similarly, the separator S3 could be used in the preceding figures.
[0112] The recycled fluid is recompressed and reprocessed in the cryogenic section.
[0113] [FIG.8] illustrates a variant of the process in [FIG.7] for the production of liquid CO2. Only the elements that differ from those in [FIG.7] will be described. The process described above only produces gaseous CO2. However, minor modifications would easily allow its adaptation to the production of liquid CO2. It would simply be a matter of compressing the gaseous CO2 produced by the cryogenic treatment to a high pressure before cooling and condensing or densifying the CO2. The liquid CO2 thus produced could be introduced into the heat exchanger line, cooled, then expanded and produced at the coil boundary. Some of this CO2 could be used to provide cooling in the heat exchanger and / or to supply the reflux necessary for the NOx removal column. This process greatly simplifies the CO2 compressor, which is particularly large in the case of liquid production, and allows it to operate at higher pressures.
[0114] Thus, compressor C3 compresses gas G8, which is cooled by a water cooler and then cooled in a heat exchanger E1. It is then expanded to produce a two-phase mixture and sent to a phase separator S4. The liquid in separator S4 is split in two: one portion, L11, is vaporized in exchanger E1, mixed with the gas from phase separator S4, and then mixed with gas G13 upstream of the compressor. The remaining liquid, L12, is sent in liquid form to exchanger E for cooling and is split into two portions: liquid L13, which vaporizes in exchanger E to form gas G13, and L15, which is a liquid product. Liquid L10 serves as the reflux from the top of column K2. In Figure 9, there is only one partial condensation stage upstream of the distillation. Only the differences with Figure 3 are described. All the gas from the compressor is cooled in the heat exchanger E1, where it partially condenses.After separation in the separator pot S2, a portion of the resulting liquid is sent to the top of column K1. Another portion of the liquid is mixed with the gas from the top of column K1. A portion of the gas from separator S2 is mixed with the gas from the top of column K1 as gas G2b, with the separator gas being mixed before the liquid from the separator with the column's top of gas. Another portion of the gas from the single separator S2 is reheated and sent to PT treatment as shown in Figure 3.
[0115] Liquid and gas from the single separator S2 can alternatively be mixed together and heated together in the exchanger E1, without having been mixed with the top gas from the column.
[0116] In all figures:
[0117] The amount of CO2 released is adjusted to provide sufficient cooling for the condensation of gas 1. This is adjusted via a regulating valve. The control loop aims to maintain the temperature of the feed gas leaving the heat exchanger and flowing to the second pot S2 at the setpoint temperature.
[0118] The quantity of non-condensables G1 and / or G2b and / or P is adjusted to obtain the correct temperature level of mixture M.
[0119] The pressure of mixture M is adjusted to optimize the heat exchange diagram and potentially allow for the efficient recycling of this fluid to compressor C1 or C2: for example, at a pressure between 10 and 12 bar. The pressure is maintained by a control valve V at the hot end of the heat exchanger E (after vaporization), which reduces the pressure of mixture M to compressor C1 or C2.
[0120] The vaporization of an impure two-phase fluid M causes a large temperature glide, making it possible to provide cooling at the correct temperature level without having to expand CO2 to 5 bar.
Claims
DEMANDS 1. A process for separating a mixture (1) containing CO2 and at least one component lighter than CO2 in which: (i) the gaseous mixture, preferably containing at least 50 mol% of CO2, is compressed in a compressor (C1, C2) and optionally dried, then cooled in a heat exchanger (E), and separated by at least one partial condensation stage forming at least one liquid (L1, L2) and at least one gas (G1, G2), for example by being sent to a first condensation pot (S1) forming a first gas (G1) and a first liquid (L1), at least part of the first gas being partially condensed and sent to a second condensation pot (S2) forming a second gas (G2) and a second liquid (L2) (j) At least a portion (Lia) of at least one liquid, for example, a portion (Lia) of the first liquid recovered in the first condenser pot, and the entirety of the second liquid separated in the second condenser pot, is depressurized (L) and sent to a distillation column (K1) operated at a first pressure, producing a liquid enriched in CO2 and depleted in at least one lighter component (L6) and a gas (G3) enriched in at least one lighter component and depleted in CO2 k) CO2-enriched liquid recovered from the column tank is vaporized and i) heated in the heat exchanger forming a product gas (G8) enriched in CO2 at the first pressure and / or ii) sent to another column (K2) to be separated and (l) Gas formed by at least one partial condensation step, which may be a part (G1a) of the first gas exiting the first condenser pot and / or at least a part (G2b) of the second gas exiting the second condenser pot and / or a gas (P) formed separating (PT) at least a part of the first and / or second gas (G1, G2), is mixed with liquid formed during at least one partial condensation step, which may be a part (L1b) of the first liquid recovered in the first partial condenser pot and possibly with gas (G3) enriched in at least one lighter component recovered at the top of the column, forming a two-phase mixture (M), the two-phase mixture is heated in the exchanger to vaporize the liquid it contains and the heated gas thus produced is possibly recycled to the gas mixture upstream of the heat exchanger and is possibly compressed with the gas mixture.
2. Method according to claim 1 wherein at least one condensation pot (S1, S2), for example the second condensation pot (S2), operates at a temperature below -50°C or even below -52°C but above -56°C.
3. Method according to claim 1 or 2 wherein a part (G2a) of the gas from the partial condensation, for example from the last pot (S2) is heated in the heat exchanger (E) to its hot end without having been mixed with another fluid.
4. Method according to claim 3 wherein the part (G2a) of the gas from the partial condensation, for example of the last pot, heated in the heat exchanger to its hot end is then expanded in a turbine (T) and returned to the heat exchanger (E) to provide cooling.
5. A method according to claim 3, wherein the portion of the gas from the partial condensation, for example from the last pot (S2) heated in the heat exchanger to its hot end, is then separated by permeation (PT) forming a permeate (P) enriched in CO2 6. Method according to claim 5 wherein the permeate (P) is expanded in a turbine (T) and returned to the heat exchanger to supply cooling.
7. A process according to claim 5 or 6 wherein at least a part of the permeate (P, P') constitutes the gas formed by separating at least a part of the second gas which mixes with liquid formed by partial condensation, for example the liquid (L1b / L2b) from at least one of the pots (S1, S2) and optionally with the gas enriched in at least one lighter component and depleted in CO2.
8. A process according to claim 5 and 7 in which the permeate (P, P') is cooled in the heat exchanger (E) before being mixed with the liquid (L1b / L2b) from at least one of the pots and optionally with the gas (G3) enriched in at least one lighter component and depleted in CO2.
9. Method according to claim 5 or 6 in which the turbine (T) is coupled to a compressor of the gas mixture (C1, C2) upstream of the heat exchanger.
10. A method according to any one of the preceding claims in which the first gas (G1) is expanded in a turbine (T) after heating in the heat exchanger.
11. A process according to any one of the preceding claims wherein the gas mixture (1) contains at least one component heavier than CO2 and at least a part of the CO2-enriched liquid recovered in the column tank is vaporized and sent to another column (K2) to be separated forming a CO2-rich gas (G8,G9) at the top of the column and a liquid (N) enriched in at least one heavier component in the column tank.
12. Apparatus for separating a mixture containing CO2 and at least one component lighter than CO2, comprising a compressor (C1, C2), a partial condensation system comprising a heat exchanger (E), at least one condenser pot (S2) and optionally an auxiliary condenser pot (S1), a distillation column (K1), means for sending the gaseous mixture, preferably containing at least 50 mol% CO2, to be compressed in the compressor and optionally dried, then cooled in the heat exchanger of the system, for partial condensation, means for sending the partially condensed flow to at least one pot of the partial condensation system, producing a liquid and a gas, expansion means for expanding a portion (Lia) of the liquid recovered in the partial condensation system, means for sending the expanded fluid in the expansion means to the distillation column operated at a first pressure,producing a liquid enriched in CO2 and depleted in at least one lighter component and a gas enriched in at least one lighter component and depleted in CO2, means for sending CO2-enriched liquid recovered in the column tank to the heat exchanger to form a CO2-enriched product gas at the first pressure and optionally means for sending the product gas to another column for separation, means for mixing a gas recovered in the partial condensation system with a liquid recovered in the partial condensation system and optionally with the gas enriched in at least one lighter component recovered at the top of the column forming a two-phase mixture,means for sending the two-phase mixture to be heated in the exchanger to vaporize the liquid it contains, and possibly means for sending the heated gas thus produced to mix with the gas mixture upstream of the heat exchanger and possibly upstream of the compressor.