Method and apparatus for separating a mixture of CO2 and NOx by partial condensation
The use of two NOx scrubbing columns in CO2 capture processes addresses NO2 freezing and conversion issues, reducing energy consumption and investment costs while ensuring low NOx concentrations in the final product.
Patent Information
- Application Number
- FR2024003035
- Authority / Receiving Office
- FR · FR
- Patent Type
- Patents
- Current Assignee / Owner
- Filing Date
- 2024-03-26
- Publication Date
- 2026-02-20
- Estimated Expiration
- 2044-03-26
AI Technical Summary
Current CO2 capture processes struggle to achieve low NOx concentrations in the final product due to insufficient conversion of NO to NO2, leading to NO2 freezing and migration issues, especially in high-NO and NO2-loaded fumes, and require excessive energy consumption and investment.
Implementing two NOx scrubbing columns, with the first column before and the second after the light distillation column, to manage NOx conversion and reduce recycled purge flow rates, optimizing liquid use and pressure for efficient CO2 separation.
Reduces energy consumption, investment costs, and improves CO2 separation efficiency by minimizing recycled purge flow rates and optimizing liquid use, while maintaining low NOx concentrations in the final product.
Smart Images
Figure 00000012_0000 
Figure 00000013_0000 
Figure 00000014_0000
Abstract
Description
Title of the invention: Method and apparatus for separating a mixture of CO2 and NOx by partial condensation
[0001] The present invention relates to a method and apparatus for separating a mixture of CO2 and NOx by partial condensation. The mixture also contains at least one component lighter than CO2.
[0002] In CO2 capture processes at temperatures below 0°C, the incoming gas is compressed, dried, cooled, and separated by partial condensation. In the case of gases containing NOx, the gas is scrubbed upstream of the partial condensation, as illustrated in WO13 / 135993 and WO15 / 148927. As the specifications for the purity of the CO2 produced become increasingly stringent, it is becoming necessary to consider new scrubbing methods to achieve the new required levels.
[0003] The present invention proposes a scheme with two columns dedicated to washing heavy molecules.
[0004] For these schemes, the present invention also proposes possibilities for interconnecting the refluxes allowing gains in investment and energy consumption. State of the art
[0005] In current low-temperature CO2 capture schemes, the separation of nitrogen oxides from the flue gases occurs throughout the process. A large portion of the NO is oxidized to NO2 during compression and within the dryer adsorbents (and the PSA in schemes that include it). Some of the NO2 is removed in the condensate after hydrolysis to HNO3. At the outlet of the adsorption stage(s), the NOx are present mainly in the form of NO2.
[0006] These remaining NOx are usually washed in the cryogenic section by combining an adsorbent bed that accelerates the conversion of NO to NO2 and a washing column. In the latter, the NO2 is mostly removed by direct contact with liquid CO2 from the downstream CO2 separation process. This method makes it possible to achieve a NOx content of less than 10 ppm mol in the final product.
[0007] With lower NOx concentrations in the CO2 produced (on the order of 1 ppm mol or even lower), the conversion to NO2 may prove insufficient before the scrubbing column. One solution would be to relocate this column further downstream in the process where temperatures are favorable for the conversion of NO to NO2, as illustrated in WO09 / 007937. However, in this case, the other heavy molecules (if present) that were separated in the scrubbing column along with the NO2 will They can migrate downstream of the process where they risk freezing. Furthermore, in certain applications where the treated fumes are heavily loaded with NO and NO2, NO2 or its dimer N2O4 can freeze during the vaporization of liquid CO2 at low pressure (approximately 5.5 bara).
[0008] In this case, it is preferable to keep the first scrubbing column and install a second one after the light distillation column, as in an inverted column arrangement. Indeed, low temperatures and high pressures accelerate the oxidation of NO to NO2. Thus, even if the majority of the NO2 is removed in the first scrubbing column, NO2 can form again between the first scrubbing column and the light distillation column from the NO remaining at the top of the scrubbing column. This NO will then end up in the final product and will prevent the desired concentration from being achieved. A scrubbing column, installed after the distillation column, can therefore remedy this problem.
[0009] The use of two NOx scrubbing columns thus provides greater confidence regarding the NOx content in the final product. Furthermore, it allows for greater flexibility in the NOx content of the gas exiting the first column, as this column is no longer solely responsible for the NOx purity of the product. It is therefore possible to degrade the quality of the liquid used for refluxing this column or to perform a less effective scrubbing without impacting the NOx content of the final product. Problems solved by the invention
[0010] A system using two NOx scrubbing columns results in a higher flow rate of NOx-rich liquid being processed in the tanks of these columns compared to a system using only one scrubbing column. Typically, the purge from a NOx scrubbing column is recycled upstream of the filtration system as described in WO09 / 007937.
[0011] The scheme proposed by this invention has the advantage of reducing the recycled purge flow rate upstream of the process. A reduced flow rate results in lower energy consumption thanks to the saved compression energy, as well as lower investment due to machines being sized for a lower volumetric flow rate. This impact is primarily felt in the initial equipment of the process, particularly the compressor and the wet flue gas dryer.
[0012] The invention also has the advantage of overcoming a lack of cooling capacity in the process. Indeed, using less liquid from partial condensation allows it to be utilized as cooling in the main heat exchanger (particularly at the outlet of the light distillation column). This also reduces the volume of the main heat exchanger.
[0013] Finally, the invention makes it possible to increase the pressure at the outlet of the turbo-blower and therefore the partial condensation, thus improving its efficiency. This is made possible by subcooling the reflux of the first column, reducing its evaporation at the top of the column and therefore minimizing the flow rate at the inlet of the blower.
[0014] According to one object of the invention, a process is provided for separating a mixture of CO2, NOx and at least one component lighter than CO2 by partial condensation in which: i. The mixture is cooled and sent to the tank of a first scrubbing column fed at the top with a liquid containing at least 90 mol% CO2. A gas depleted in NOx and enriched in CO2 relative to the mixture exits the top of the first scrubbing column, and a liquid enriched in NO2 and depleted in CO2 relative to the mixture exits the tank of the first scrubbing column. ii. The NOx-depleted gas is separated by partial condensation and possibly by distillation, forming at least one liquid enriched in CO2 relative to the NOx-depleted gas and at least one gas depleted in CO2 relative to the NOx-depleted gas. iii. at least a part of at least one CO2-enriched liquid is vaporized, compressed, cooled and sent as a gas into the tank of a second scrubbing column fed at the top by a liquid containing at least 90% mol of CO2, a gas depleted in NOx and enriched in CO2 relative to the gas sent into the tank of the second scrubbing column exits from the top of the second scrubbing column and a liquid enriched in NO2 and depleted in CO2 relative to the gas sent into the tank of the second scrubbing column exits into the tank of the second scrubbing column.
[0015] According to other optional features: • at least part of the liquid sent to the top of the first scrubbing column is a liquid produced by partial condensation and / or distillation of the NOx-depleted gas from the top of the first scrubbing column. • at least part of the liquid sent to the top of the first wash column is tank liquid from the second wash column. • The tank liquid from the second wash column is the only liquid sent to the top of the first wash column. • at least part of the liquid sent to the top of the first wash column is pressurized by a pump. • The second washing column is arranged vertically above the first washing column. • The tank liquid from the second wash column is cooled before being sent to the top of the first wash column. • The tank liquid of the second washing column is cooled by indirect heat exchange with the overhead gas of the second washing column and / or the overhead gas of the first washing column. • The flow rate of the tank liquid from the second wash column is regulated before being sent to the top of the first wash column, in order to adjust the reflux rate of the first wash column. • the gaseous mixture contains between 35 and 95% mol of CO2, • the gaseous mixture contains at least one component lighter than CO2, for example nitrogen, oxygen, carbon monoxide • the gas mixture contains at least one component heavier than CO2, including NOx, and possibly at least one other heavier component such as mercury. • The first scrubbing column operates at between 15 and 40 bar, for example between 20 and 25 bar
[0016] According to another object of the invention, an apparatus for separating a mixture of CO2, NOx and at least one component lighter than CO2 by partial condensation is provided, comprising a first washing column, a second washing column, means for cooling the mixture, means for sending the cooled mixture to the tank of the first washing column, means for supplying the top of the first mixing column with a liquid containing at least 90 mol% CO2, means for exiting a gas depleted in NOx and enriched in CO2 relative to the mixture from the top of the first washing column, means for exiting a liquid enriched in NO2 and depleted in CO2 relative to the mixture into the tank of the first washing column, at least one phase separator, means for sending the gas depleted in NOx to separate by partial condensation in at least one phase separator and optionally by distillation in a distillation column,forming at least one liquid enriched in CO2 relative to the NOx-depleted gas and at least one gas depleted in CO2 relative to the NOx-depleted gas, means for vaporizing at least part of one of the at least one CO2-enriched liquid, a compressor for compressing the vaporized liquid, means for cooling the vaporized liquid compressed in the compressor and means for sending the cooled vaporized liquid as a gas to the tank of the second washing column, means for supplying the top of the second washing column with a liquid containing at least 90 mol% CO2, means for exiting a gas depleted in NOx and enriched in CO2 relative to the gas sent to the tank of the second washing column from the top of the second washing column and means for exiting a liquid enriched in NO2 and depleted in , CO2 relative to the gas sent to the tank of the second washing column.
[0017] Description of the invention
[0018] The invention will be described in more detail with reference to the figures where:
[0019] [Fig-1] schematically represents a method according to the invention.
[0020] [Fig.2] schematically represents a method according to the invention which is a variant of that of [Fig.1].
[0021] [Fig.3] schematically represents a method according to the invention which is a variant of that of [Fig.2]
[0022] [Fig.4] schematically represents a process according to a simplified variant according to the invention.
[0023] [Fig.5] schematically represents a process according to a simplified variant according to the invention.
[0024] Fig. 1 shows an apparatus for separating a gaseous mixture 1 containing between 35 and 95 mol% of CO2, at least one component lighter than CO2, for example nitrogen, oxygen, carbon monoxide and at least one component heavier than CO2 including NOx and possibly at least one other heavier component such as mercury.
[0025] The gas mixture 1 is cooled in a first heat exchanger HX1 and is sent to the tank of a first scrubbing column Kl operating at between 15 and 40 bara, for example between 20-25 bara. The column is fed at the top with a scrubbing liquid 45 rich in CO2, containing, for example, at least 90 mol% CO2, and produces in the tank a liquid enriched in NOx but also containing CO2. The overhead gas 5 is enriched in CO2 and in at least one lighter component compared to mixture 1.
[0026] A liquid 3 is drawn from the tank of column Kl, enriched in NOx relative to gas 1. This liquid can be sent upstream of the heat exchanger HX1 in a part of the process where the NOx is removed.
[0027] The overhead gas 5 is heated in the heat exchanger HX1 and then compressed in a compressor B to a pressure greater than that of the column KL
[0028] The booster B is preferably coupled to a turbine in which a gas 47 expands.
[0029] The pressurized gas 5 is cooled in a second heat exchanger HX2 to an intermediate temperature and partially condenses. The resulting two-phase flow is separated in a phase separator S1, forming a gas 9 depleted in CO2 and enriched in at least one lighter component compared to gas 5, and a liquid 11 enriched in CO2 and depleted in at least one lighter component compared to gas 5. The gas 9 is partially condensed in the heat exchanger HX2, then sent to the phase separator S2 forming a gas 15 depleted in CO2 and enriched in at least one lighter component compared to gas 9 and a liquid 17 enriched in CO2 and depleted in at least one lighter component compared to gas 9.
[0030] At least part of the liquid 11 and / or the liquid 17 constitutes at least part of the liquid 45 sent to the top of the column Kl.
[0031] At least a portion of the liquid 11 and / or the liquid 17 constitutes at least a portion of the liquid 21 sent to the top of column K2 after expansion through valve V2. Column K2 operates as a stripping column at a pressure between 7 and 20 bar to reduce the content of at least one lighter component of the liquid 21, producing a gas 37 at the top of the column. The CO2 concentrates in the tank of column K2 with the remaining NOx in the form of NO2 and is withdrawn as liquid 23.
[0032] The liquid 23 is divided into two flows 25, 27, the flow 27 being vaporized in the heat exchanger HX2 forming a gas containing CO2 and NOx MP CO2. The flow 25 is expanded in a valve V3 to partially vaporize it and separated in a phase separator S3 forming a gas 31 and a liquid 29. The gas 31 is heated in the heat exchanger HX2 where the liquid 29 vaporizes and the heated gas and the vaporized liquid mix to form a gas 33 which is CO2 containing NOx at a lower pressure than that of the gas 38.
[0033] The gas 33 and / or the gas 38 may constitute at least a portion of the gas 39 containing more NOx than desired in the final product. The gas 39 is preferably at a pressure between 10 and 50 bar, following a compression step (not shown). The gas 39 is cooled in the heat exchanger HX1 and is sent to the tank of a second scrubbing column K3, which is fed at its top with liquid CO2 51 containing less NOx than the gas 39 and containing, for example, at least 90 mol% CO2. A NOx-purified gas 41 is drawn off at the top of column K3. A liquid 43 is drawn off from the tank of column K3, enriched in NOx relative to the gas 39. This liquid 43 can be sent upstream of the heat exchanger HX1 to a part of the process where the NOx is removed.
[0034] Alternatively, according to a variant, which is the one illustrated, the liquid 43 is sent as reflux for the first column KL
[0035] To implement this scheme, two configurations can be considered. The first, illustrated in [Fig. 1], consists of using a pump P to convey the liquid from column K3 to column K1 and thus avoid any problems related to a pressure difference between the two columns due to their location in the process.
[0036] A second version illustrated in [Fig. 2] consists of superimposing column K3 vertically above column K1 in order to take advantage of the hydrostatic head and thus be able to convey the liquid from the second washing column to the first wash column. This scheme is possible when the second wash column K3 has an operating pressure sufficiently higher than the first Kl.
[0037] According to one variant, the pressure of column K3 can be greater than the pressure of column Kl and the liquid 45 can be expanded, without column K3 necessarily being above column Kl.
[0038] Depending on the liquid flow rate 43, 45 available at the outlet of the second washing column K3, the available reflux may not be sufficient to guarantee a liquid charge allowing efficient distillation in the first column K1. This flow rate can therefore be supplemented by adding a portion of the liquid from the separation process 11 and / or 17 (such as that from partial condensation) in order to achieve a sufficient liquid charge.
[0039] Another solution consists of ensuring an excess reflux in the second washing column K3 in order to obtain a sufficient liquid charge in the first washing column K1. It is obviously possible to consider intermediate solutions where the reflux of the second column K3 exceeds the minimum value required for its proper functioning and is nevertheless replenished with liquid from the separation process.
[0040] In order to limit the evaporation of the reflux from the second washing column K3 upon entering the first column Kl, it is possible to subcool this liquid 43, as illustrated in [Fig. 3]. In particular, if the first column Kl is entirely fed at its top by the purge 43 from the second washing column K3, this operation makes it possible to significantly reduce the reflux in the second column K3 to ensure a sufficient liquid charge in the first column Kl and thus to reduce the specific energy because the draw on production (origin of the reflux from the second washing column K3) is lower.
[0041] The previous point also shows the possibility, in the case of a single feed of the first column Kl by the second washing column K3, of the direct control of the liquid charge of the first column Kl by this reflux 43. A variation of the reflux 43 coming from the second column K3 will allow to have the desired liquid / vapor ratio in the first column.
[0042] In this case, the liquids 11,17 do not feed the Kl column.
[0043] As noted above, the NOx content of the gas 5 exiting the first column K1 may be higher than according to the prior art, since the latter is no longer the sole source of the NOx purity of the product 41. It is therefore possible to degrade the quality of the liquid 45 used for refluxing this first column. Thus, liquid 45 may contain less CO2 and / or more NOx than liquid 51, containing, for example, at least 90 mol% CO2, used for refluxing the second washing column K3.
[0044] Similarly, it is possible to carry out a less efficient washing without impacting the NOx content of the final product. Thus, the flow rate of liquid 45 can be reduced or the column Kl can have fewer theoretical plates.
[0045] In some cases, it is possible to eliminate column K2, the entire separation of the at least component lighter than CO2 being carried out by at least one partial condensation step, the liquid produced being vaporized, compressed and sent to the second washing column K3.
[0046] [Fig.4] is a simplified variant of [Fig.2] where column K2 is not present. At least part of the liquid 21 is vaporized and heated and potentially compressed to form gas 39.
[0047] [Fig. 5] is a simplified variant of [Fig. 3] where column K2 is not present. At least part of the liquid 21 is vaporized and heated to form gas 39. It differs from [Fig. 4] by the subcooling of liquid 43.
Claims
Demands
1. A process for separating a mixture of CO2, NOx and at least one component lighter than CO2 by partial condensation in which: i. the mixture is cooled and sent to the tank of a first scrubbing column (Kl) fed at the top with a liquid (13, 43, 45) containing at least 90 mol% CO2, a gas (5) depleted in NOx and enriched in CO2 relative to the mixture exits from the top of the first scrubbing column and a liquid (3) enriched in NO2 and depleted in CO2 relative to the mixture exits into the tank of the first scrubbing column ii. the gas depleted in NOx is separated by partial condensation and optionally by distillation forming at least one liquid (21, 33, 38) enriched in CO2 relative to the gas depleted in NOx and at least one gas (15, 37) depleted in CO2 relative to the gas depleted in NOx iii.at least a part (39) of one of the at least one CO2-enriched liquid is vaporized, compressed, cooled and sent as a gas into the tank of a second washing column (K3) fed at the top by a liquid (51) containing at least 90% mol of CO2, a gas (41) depleted in NOx and enriched in CO2 relative to the gas sent into the tank of the second washing column exits from the top of the second washing column and a liquid (43) enriched in NO2 and depleted in CO2 relative to the gas sent into the tank of the second washing column exits into the tank of the second washing column.
2. A method according to claim 1 wherein at least a part of the liquid (13) sent to the top of the first scrubbing column (Kl) is a liquid produced by partial condensation and / or distillation of the NOx-depleted gas (5) from the top of the first scrubbing column.
3. Method according to claim 1 or 2 wherein at least a part (43) of the liquid sent to the top of the first washing column (Kl) is tank liquid from the second washing column (K3).
4. Method according to claim 3 wherein the tank liquid (43) of the second washing column (K3) constitutes the only liquid sent to the top of the first washing column (Kl).
5. A method according to any one of claims 2, 3 or 4 wherein at least a part of the liquid sent to the top of the first washing column (Kl) is pressurized by a pump (P).
6. A method according to any one of claims 1 to 5 wherein the second washing column (K3) is arranged vertically above the first washing column (Kl).
7. A method according to any one of claims 3 to 6 wherein the tank liquid of the second washing column (K3) is cooled before being sent to the top of the first washing column (Kl).
8. A method according to claim 7 wherein the tank liquid (43) of the second washing column (K3) is cooled by indirect heat exchange with the head gas (41) of the second washing column and / or the head gas (5) of the first washing column (Kl).
9. A method according to any one of claims 3 to 8 wherein the flow rate of the tank liquid (43) from the second wash column (K3) is regulated before being sent to the top of the first wash column (Kl), in order to adjust the reflux rate of the first wash column.
10. Apparatus for separating a mixture of CO2, NOx and at least one component lighter than CO2 by partial condensation comprising a first scrubbing column (K1), a second scrubbing column (K3), means for cooling the mixture (HX1), means for sending the cooled mixture (1) to the tank of the first scrubbing column, means for supplying the top of the first mixing column with a liquid (45) containing at least 90 mol% CO2, means for exiting a gas (5) depleted in NOx and enriched in CO2 relative to the mixture from the top of the first scrubbing column, means for exiting a liquid (3) enriched in NO2 and depleted in CO2 relative to the mixture into the tank of the first scrubbing column, at least one phase separator (S1, S2), means for sending the NOx-depleted gas to separate by partial condensation in at least one phase separator and optionally by distillation in a distillation column (K2),forming at least one liquid enriched in CO2 (33, 38) relative to the NOx-depleted gas and at least, a gas (37) depleted in CO2 relative to the gas depleted in NOx, means (HX2) for vaporizing at least a part of one of at least one liquid enriched in CO2, a compressor for compressing the vaporized liquid, means for cooling the vaporized liquid (HX1) compressed in the compressor and means for sending the cooled vaporized liquid as a gas (39) into the tank of the second washing column, means for supplying the top of the second washing column with a liquid (51) containing at least 90% mol of CO2, means for exiting a gas (41) depleted in NOx and enriched in CO2 relative to the gas sent into the tank of the second washing column from the top of the second washing column and means for exiting a liquid (43) enriched in NO2 and depleted in CO2 relative to the gas sent into the tank of the second washing column into the tank of the second washing column.