A method and system for deeply removing trace NO from high-concentration CO2 X ​

Abstract

The present invention discloses a method for deeply removing trace NO from high-concentration CO2, belonging to the technical field of CO2 purification, and comprising the following steps: dehydrating the CO2 raw material gas containing NO and NO2 and then introducing it as a heat source into the evaporators of a first rectification column and a second rectification column respectively, and collecting the raw material gas output from the two evaporators and then liquefying it to obtain liquid CO2 containing NO and NO2; removing NO from the liquid CO2 containing NO and NO2 through the first rectification column and removing NO2 through the second rectification column. The present invention also discloses a system for deeply removing trace NO from high-concentration CO2 X , including a dehydration subsystem, a refrigeration subsystem and a rectification subsystem. The present invention adjusts the flow rate of the raw material gas entering the two evaporators by detecting whether the NO gas at the top gas outlet of the second rectification column exceeds a set threshold value to achieve closed-loop control, and can achieve the deep removal of trace NO in high-concentration CO2 X , and reduce the contents of trace NO and NO2 in high-concentration CO2 to below 1.5 ppm respectively. X X ​​

Description

Technical Field

[0001] The present invention belongs to the technical field of CO2 purification, and particularly relates to a method and system for deeply removing trace NO from high-concentration CO2 X and the system. Background Art

[0002] The flue gas emitted by ship engines generally contains 5% CO2, 70% N2, 24% O2, and small amounts of SO2 and NO X . The flue gas first passes through a desulfurization system, and generally uses the alkalinity of seawater to absorb and remove SO2 and NO2 in the flue gas. The flue gas after desulfurization mainly contains N2, O2, CO2, and NO, and enters a carbon capture system. The CO2 in the flue gas is absorbed by an organic amine solution at room temperature. Most of the O2, N2, and NO are discharged into the air from the top of the absorption tower because they are not absorbed by the amine solution. However, a small amount of N2, O2, and NO will be entrained by the amine solution into the stripping tower and stripped from the amine solution together with CO2 at high temperature. After dehydration and purification, the content of NO in CO2 is about 30 ppm. In the presence of oxygen, a very small amount of NO will be converted into NO2

[0003] If the above CO2 is made into food-grade, the NOx content in CO2 should be below 5 ppm. In addition, in some countries and regions, the captured CO2 is sequestered underground and in rock formations. Since NO X will cause erosion and damage to rock formations and geology, a higher requirement for NO in CO2 is proposed in this case, requiring NOx to be lower than 1.5 ppm. In the existing technology, the existing denitrification technologies, whether catalytic reduction, low-nitrogen combustion, or activated carbon adsorption, are very rough for the removal of trace NOx. Therefore, the existing technology is not applicable to the deep removal of trace NO X in high-concentration CO2 and cannot meet the requirements of some application scenarios for the extremely low content of NOx in CO2 (such as <1.5 ppm). X The depth removal of NO in high-concentration CO2 cannot meet the requirements of some application scenarios for the extremely low content of NOx in CO2 (such as <1.5 ppm). Summary of the Invention

[0004] In view of one or more of the above-mentioned defects or improvement requirements of the existing technology, the present invention provides a method and system for deeply removing trace NO from high-concentration CO2 X and the system, which can realize the removal of trace NO in high-concentration CO2 x and obtain a high-purity CO2 product.

[0005] To achieve the above object, according to one aspect of the present invention, a method for deeply removing trace NO from high-concentration CO2 X is provided, including the following steps:

[0006] S1: Dehydrate the CO2 feed gas containing NO and NO2

[0007] S2: Set up a first distillation column with a first evaporator at the bottom and a second distillation column with a second evaporator at the bottom; introduce the dehydrated raw material gas in S1 into the two evaporators as a heat source respectively, and collect the raw material gas output from the two evaporators and then liquefy it to obtain liquid CO2 containing NO and NO2.

[0008] S3: Introduce the liquid CO2 in S2 into the first distillation column, control the flow rate of the raw material gas introduced into the first evaporator, and reach the boiling point of CO2 under the heat it provides to evaporate part of the CO2, and remove NO while discharging from the top gas outlet of the first distillation column, and discharge the liquid CO2 containing NO2 from the bottom liquid outlet of the first distillation column.

[0009] S4: Introduce the liquid CO2 in S3 into the second distillation column, control the flow rate of the raw material gas introduced into the second evaporator, and evaporate CO2 under the heat it provides and discharge and collect it from the top gas outlet of the second distillation column, and at the same time discharge NO2 in liquid form from the bottom liquid outlet of the second distillation column to remove NO2.

[0010] As a further improvement of the present invention, by detecting NO X in the gas at the outlet of the second distillation column whether it exceeds the set threshold, adjust the amount of the dehydrated raw material gas entering the first evaporator and the second evaporator;

[0011] If it is detected that NO exceeds the set threshold, increase the amount of the raw material gas introduced into the first evaporator; if it is detected that NO2 exceeds the set threshold, decrease the amount of the raw material gas introduced into the second evaporator.

[0012] As a further improvement of the present invention, in step S2, the dehydrated raw material gas is divided into three paths, including a first pipeline leading to the first evaporator, a second pipeline leading to the second evaporator, and a third pipeline for direct liquefaction.

[0013] As a further improvement of the present invention, when the total flow rate of the introduced raw material gas is constant, the control process of the flow rate of the raw material gas in the three pipelines is as follows:

[0014] Detect NO X in the gas at the outlet of the second distillation column whether it exceeds the set threshold;

[0015] If it is detected that NO exceeds the set threshold, increase the amount of the raw material gas introduced into the first pipeline, and decrease the amount of the raw material gas introduced into the second pipeline or decrease the amount of the directly liquefied raw material gas; if it is detected that NO2 exceeds the set threshold, decrease the amount of the raw material gas introduced into the second pipeline, and increase the amount of the raw material gas introduced into the first pipeline or increase the amount of the directly liquefied raw material gas.

[0016] As a further improvement of the present invention, when the total flow rate of the raw material gas introduced is constant, the control process of the raw material gas flow rate in the three pipelines is as follows:

[0017] 1) Introduce the raw material gas into the first pipeline, and gradually increase the amount of the raw material gas introduced into the first pipeline. Detect the amount of NO output from the outlet of the first distillation column, and compare the amount of NO with the amount of NO in the raw material gas until the output amount of NO is not greater than the set threshold value, thereby obtaining the minimum flow rate of the raw material gas introduced into the first pipeline;

[0018] 2) Introduce all the remaining raw material gas into the second pipeline, and detect the amount of NO2 in the outlet of the second distillation column. If it is less than the set threshold value, the maximum flow rate of the introduced gas is obtained; if it is greater than the set threshold value, gradually reduce the flow rate introduced into the second pipeline until the output amount of NO2 is not greater than the set threshold value, thereby obtaining the maximum flow rate of the raw material gas introduced into the second pipeline;

[0019] 3) Introduce the remaining raw material gas into the third pipeline and directly liquefy it.

[0020] According to another aspect of the present invention, a system for deeply removing trace NO from high-concentration CO2 is provided. X The system includes a dehydration subsystem, a refrigeration subsystem, and a distillation subsystem;

[0021] The distillation subsystem includes a first distillation column with a first evaporator at the bottom and a second distillation column with a second evaporator at the bottom. Both the first distillation column and the second distillation column are provided with a liquid inlet, a gas outlet at the top, and a liquid outlet at the bottom;

[0022] The dehydration subsystem is connected to the inlets of the first evaporator and the second evaporator through pipelines respectively, so as to dehydrate the CO2 raw material gas containing NO and NO2 and introduce it into the two evaporators as a heat source respectively; the outlets of the first evaporator and the second evaporator are connected to the inlet of the refrigeration subsystem to liquefy the CO2 raw material gas and obtain liquid CO2 containing NO and NO2;

[0023] The outlet of the refrigeration subsystem is connected to the liquid inlet of the first rectification column to introduce the liquid CO2 into the first rectification column. Under the heat provided by the first evaporator, the boiling point of CO2 is reached to evaporate part of the CO2, and NO is removed while discharging from the gas outlet of the first rectification column. The liquid outlet of the first rectification column is connected to the liquid inlet of the second rectification column to introduce the liquid CO2 containing NO2 discharged from the liquid outlet of the first rectification column into the second rectification column. Under the heat provided by the second evaporator, CO2 is evaporated and discharged and collected from the gas outlet of the second rectification column, and at the same time, NO2 is discharged in liquid form from the liquid outlet of the second rectification column to remove NO2.

[0024] As a further improvement of the present invention, a NO X analyzer is provided corresponding to the gas outlet of the second rectification column. By detecting whether the NO X gas at the gas outlet of the second rectification column exceeds the set threshold, the amounts of the dehydrated raw material gas entering the first evaporator and the second evaporator are adjusted;

[0025] If it is detected that NO exceeds the set threshold, the amount of the raw material gas introduced into the first evaporator is increased; if it is detected that NO2 exceeds the set threshold, the amount of the raw material gas introduced into the second evaporator is decreased.

[0026] As a further improvement of the present invention, the dehydrated raw material gas is divided into three paths. The dehydration subsystem is connected to the first evaporator through the first pipeline, connected to the second evaporator through the second pipeline, and directly connected to the refrigeration subsystem through the third pipeline.

[0027] As a further improvement of the present invention, a NO X analyzer is provided corresponding to the gas outlet of the second rectification column. Under the condition that the total flow rate of the introduced raw material gas is constant, the control process of the raw material gas flow rates in the three pipelines is as follows:

[0028] If it is detected that NO exceeds the set threshold, the amount of the raw material gas entering the first evaporator is increased, and the amount of the raw material gas entering the second evaporator is decreased or the amount of the raw material gas directly introduced into the refrigeration subsystem is decreased; if it is detected that NO2 exceeds the set threshold, the amount of the raw material gas introduced into the second evaporator is decreased, and the amount of the raw material gas entering the first evaporator is increased or the amount of the raw material gas directly entering the refrigeration subsystem is increased.

[0029] As a further improvement of the present invention, a waste gas flow meter is provided corresponding to the gas outlet of the first rectification column, and a NO X analyzer is provided corresponding to the gas outlet of the second rectification column. Under the condition that the total flow rate of the introduced raw material gas is constant, the control process of the raw material gas flow rates in the three pipelines is as follows:

[0030] 1) Feed the raw material gas into the first pipeline, gradually increase the amount of the raw material gas fed into the first pipeline, detect the amount of NO output from the outlet of the first distillation column, and compare the amount of this NO with the amount of NO in the raw material gas until the amount of the output NO is not greater than the set threshold value, then the minimum flow rate of the raw material gas fed into the first pipeline can be obtained;

[0031] 2) Feed all the remaining raw material gas into the second pipeline, and detect the amount of NO₂ at the outlet of the second distillation column. If it is less than the set threshold value, then the maximum flow rate of the feed can be obtained; if it is greater than the set threshold value, then gradually reduce the flow rate fed into the second pipeline until the amount of the output NO₂ is not greater than the set threshold value, then the maximum flow rate of the raw material gas fed into the second pipeline can be obtained;

[0032] 3) Feed the remaining raw material gas into the third pipeline and directly liquefy it.

[0033] As a further improvement of the present invention, the dehydration subsystem includes a first molecular sieve adsorber and a second molecular sieve adsorber arranged in parallel. The inlet ends and outlet ends of the first molecular sieve adsorber and the second molecular sieve adsorber are respectively connected to the raw material gas main pipe through valves;

[0034] And the outlet ends of the first molecular sieve adsorber and the second molecular sieve adsorber are respectively connected to the outlet end of the heater through valves. The inlet end of the heater is connected to the raw material gas main pipe through a valve; at the same time, the inlet ends of the first molecular sieve adsorber and the second molecular sieve adsorber are respectively connected to the inlet end of the cooler. The outlet end of the cooler is connected to the raw material gas main pipe through a valve; through the alternate control of the valves, when one molecular sieve adsorber adsorbs, the other molecular sieve adsorber is regenerated.

[0035] As a further improvement of the present invention, a water analyzer is provided on the raw material gas main pipe at the outlets of the first molecular sieve adsorber and the second molecular sieve adsorber, which is used to judge whether the first molecular sieve adsorber or the second molecular sieve adsorber is saturated with adsorption, so as to control the valve connecting one of the molecular sieve adsorbers to the raw material gas main pipe to open, and the other molecular sieve adsorber is communicated with the heater and the cooler to realize regeneration.

[0036] As a further improvement of the present invention, the gas outlet at the top of the second distillation column is connected to the refrigeration subsystem through a valve, so that when the content of NO X detected by the NO analyzer exceeds the set threshold value, the top gas of the second distillation column is re-liquefied and then fed into the first distillation column for re-separation;

[0037] The gas outlet at the top of the second distillation column is also connected to a refrigerator through a valve, so as to liquefy the CO₂ gas with the required purity at the top of the column for storage.

[0038] Generally speaking, compared with the prior art, the above technical solution conceived by the present invention has the following beneficial effects:

[0039] (1) In the present invention, NO and NO2 are respectively removed through the first rectification tower and the second rectification tower. An evaporator is provided at the bottom of the rectification tower, and the dehydrated raw material gas is introduced into the evaporator as a heat source. This not only enables the utilization of the heat source and reduces the power of cooling and liquefaction, but also by controlling the flow rates of the raw material gas introduced into the first evaporator and the evaporator, the contents of trace NO and NO2 in high-concentration CO2 can be respectively reduced to below 1.5 ppm, obtaining a high-purity CO2 product.

[0040] (2) In the present invention, by detecting whether the NO X gas at the top outlet of the second rectification tower exceeds a set threshold value, the flow rates of the raw material gas entering the two evaporators are adjusted to achieve closed-loop control, thereby ensuring deep removal of trace NO X in high-concentration CO2.

[0041] (3) In the present invention, the dehydrated raw material gas is further divided into three paths. Under the condition of a certain flow rate of the raw material gas introduced, by directly liquefying one path of the dehydrated raw material gas, the flow rates of the raw material gas entering the first evaporator and the second evaporator can be further balanced. By controlling the flow rate distribution of the raw material gas introduced into the first evaporator, the second evaporator, and the direct liquefaction, as little CO2 as possible can be lost in the first rectification tower while NO is removed as much as possible, and at the same time, CO2 can be evaporated as much as possible while preventing NO2 from evaporating in the second rectification tower, thereby achieving optimized heat energy utilization and reducing the loss of CO2.

[0042] (4) In the present invention, dehydration is carried out through two groups of molecular sieve adsorbers arranged in parallel. A water analyzer corresponding to the molecular sieve adsorber is used to judge whether adsorption is saturated. By switching the valves, when one group of molecular sieve adsorbers is adsorbing, the other group of molecular sieve adsorbers can be controlled to be connected to the heater and the cooler, so that the moisture in the molecular sieve adsorbers is desorbed, thereby realizing regeneration and repeated use. And the present invention can realize regeneration by using the raw material gas of the system itself. A small amount of raw material gas in the raw material gas main pipe is heated by the heater and then introduced into the molecular sieve adsorber for regeneration, and after cooling, it re-enters the raw material gas main pipe. Description of the Drawings

[0043] Figure 1 Schematic diagram of the system for deeply removing trace NO X from high-concentration CO2 in an embodiment of the present invention.

[0044] In all the accompanying drawings, the same reference numerals denote the same technical features, specifically: 1. First rectification column; 2. Second rectification column; 3. First evaporator; 4. Second evaporator; 5. First refrigerator; 6. Exhaust gas flowmeter; 7. NO X analyzer; 8. First molecular sieve adsorber; 9. Second molecular sieve adsorber; 10. Heater; 11. First cooler; 12. Second cooler; 13. Water analyzer; 14. Second refrigerator. Detailed implementation mode

[0045] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various implementation modes of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0046] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as limiting the present invention.

[0047] In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance or implicitly indicating the quantity of the technical features indicated. Thus, the features defined with "first" and "second" may explicitly or implicitly include at least one of such features. In the description of the present invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise specifically defined.

[0048] In the present invention, unless otherwise clearly specified and defined, the terms "installed", "connected", "connected", "fixed", etc. should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or integrated; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium, and it may be the internal communication of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0049] In the present invention, unless otherwise clearly specified and defined, the first feature being "on" or "under" the second feature may mean that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, the first feature being "above", "over" and "on top of" the second feature may mean that the first feature is directly above or obliquely above the second feature, or simply indicates that the first feature has a higher horizontal height than the second feature. The first feature being "under", "beneath" and "underneath" the second feature may mean that the first feature is directly below or obliquely below the second feature, or simply indicates that the first feature has a lower horizontal height than the second feature.

[0050] As a preferred embodiment of the present invention, an embodiment of the present invention provides a method for deeply removing trace NO from high-concentration CO2 X The method includes the following steps:

[0051] S1: Dehydrate the CO2 feed gas containing NO and NO2.

[0052] S2: Set up a first rectification column with a first evaporator at the bottom and a second rectification column with a second evaporator at the bottom; introduce the dehydrated feed gas in S1 into the two evaporators as a heat source respectively, and liquefy the feed gas output from the two evaporators after collection to obtain liquid CO2 containing NO and NO2.

[0053] S3: Introduce the liquid CO2 in S2 into the first rectification column, control the flow rate of the feed gas introduced into the first evaporator, and evaporate part of the CO2 at the boiling point of CO2 under the heat provided, and remove NO while discharging from the top gas outlet of the first rectification column, and discharge the liquid CO2 containing NO2 from the bottom liquid outlet of the first rectification column.

[0054] S4: Introduce the liquid CO2 in S3 into the second rectification column, control the flow rate of the feed gas introduced into the second evaporator, evaporate the CO2 under the heat provided and discharge and collect it from the top gas outlet of the second rectification column, and at the same time discharge NO2 in liquid form from the bottom liquid outlet of the second rectification column to remove NO2.

[0055] In step S3, due to the application scenario of the embodiment of the present invention being to remove trace NO from high-concentration CO2 X where the content of NO in CO2 is trace (about 30 ppm) and the content of NO2 is even less, it is necessary to discharge NO carried by the evaporated part of the gaseous CO2 from the gas outlet of the rectification column.

[0056] Therefore, the heat provided by the first evaporator needs to reach the boiling point of CO2, for example, at or slightly above the critical temperature of CO2 evaporation, but below the evaporation temperature of NO2. As a result, during the heat exchange process of CO2, part of it evaporates into gas, and part condenses and is located at the bottom of the first distillation column in liquid form. In the rising steam, at the same pressure, the high-boiling CO2 and NO2 (in the mixed liquid containing NO, NO2, and CO2, a small amount of NO2 will evaporate) continuously condense into liquid, and the low-boiling NO in the down-flowing liquid continuously evaporates into gas. At the same time, part of the CO2 evaporates and is discharged from the top gas outlet of the first distillation column to remove NO.

[0057] In step S4, since the boiling point of CO2 is much lower than that of NO2 at the same pressure, in order to separate CO2 and NO2, the heat provided by the second evaporator in the second distillation column needs to reach the boiling point of CO2 and be lower than the boiling point of NO2. During the distillation process, the CO2 in the liquid continuously evaporates into the top of the column, and pure low-boiling CO2 gas is obtained at the top of the column. At the same time, NO2 is discharged from the bottom liquid outlet of the second distillation column in liquid form to remove NO2. Usually, the liquid CO2 rich in NO2 is obtained at the bottom of the column, and only the purity of the evaporated CO2 gas needs to be ensured.

[0058] In the actual evaporation process, due to the mutual influence between different gases in the mixed gas, a small amount of NO2 will evaporate during the evaporation process of CO2 in step S4. However, during the upward movement of the evaporated gas, the CO2 gas containing NO2 continuously contacts and exchanges heat with the liquid CO2 containing NO2 introduced into the second distillation column. As a result, the high-boiling NO2 gas continuously condenses into liquid, ensuring that the NO2 content in the output CO2 gas is lower than the set threshold, thereby ensuring the purity of the separated CO2 gas.

[0059] In a preferred embodiment, the amount of the dehydrated raw material gas entering the first evaporator 3 is about 8-10% of the amount entering the second evaporator 4. At this distribution ratio, the evaporation requirements of the first distillation column and the second distillation column can be met.

[0060] In the preferred embodiment, by detecting whether the NO X gas at the gas outlet of the second distillation column exceeds the set threshold, the amounts of the dehydrated raw material gas entering the first evaporator and the second evaporator are adjusted, thereby performing closed-loop control on the heat provided by the two evaporators at the bottom of the corresponding distillation columns to achieve the distribution of the raw material gas, and thus ensuring the deep removal of trace NO X in high-concentration CO2.

[0061] If it is detected that the NO exceeds the set threshold, the amount of the raw material gas entering the first evaporator is increased; if it is detected that the NO2 exceeds the set threshold, the amount of the raw material gas entering the second evaporator is decreased. When the flow rate of the raw material gas introduced is constant, when increasing the flow rate of the raw material gas introduced into one of the evaporators, if reducing the flow rate of the raw material gas introduced into the other evaporator has a relatively small impact on the rectification effect of the rectification column, the flow rate is balanced by reducing the flow rate of the raw material gas introduced into the other evaporator; vice versa. Otherwise, it is necessary to adjust the flow rate of the raw material gas introduced to balance the flow rate of the pipeline.

[0062] It should be noted that the set threshold of NO X ≥0, and it is specifically set according to the NO X removal standard that needs to be achieved in the CO2. In this embodiment, the set threshold of NO X ≥1.5 ppm.

[0063] In a preferred embodiment, in step S2, the dehydrated raw material gas is divided into three paths, including a first pipeline leading to the first evaporator, a second pipeline leading to the second evaporator, and a third pipeline for direct liquefaction. Among the first pipeline and the second pipeline, the raw material gas output from the two evaporators is collected and liquefied to obtain liquid CO2 containing NO and NO2; the raw material gas in the third pipeline is directly liquefied to obtain CO2 liquid containing NO and NO2.

[0064] In one embodiment, when the flow rate of the raw material gas introduced is constant, the control process of the flow rate of the raw material gas in the three pipelines is as follows:

[0065] If it is detected that the NO exceeds the set threshold, the amount of the raw material gas entering the first evaporator is increased. If reducing the amount of the raw material gas in the second evaporator at this time affects the rectification effect of the second rectification column, the amount of the raw material gas for direct liquefaction is reduced; similarly, if it is detected that the NO2 exceeds the set threshold, the amount of the raw material gas entering the second evaporator is reduced. If increasing the amount of the raw material gas in the first evaporator at this time affects the rectification effect of the first rectification column, the amount of the raw material gas for direct liquefaction is increased.

[0066] In this embodiment, by directly liquefying one path of the dehydrated raw material gas, the flow rate of the raw material gas entering the first evaporator and the second evaporator can be further balanced. By controlling the flow rate distribution of the raw material gas introduced into the first evaporator, the second evaporator, and the direct liquefaction, it is ensured that as little CO2 as possible is lost in the first rectification column while NO is removed as much as possible, and at the same time, as much CO2 as possible is evaporated in the second rectification column while avoiding the evaporation of NO2.

[0067] In another embodiment, when the flow rate of the raw material gas introduced is constant, the control process of the flow rate of the raw material gas in the three pipelines is as follows:

[0068] 1) Feed the raw material gas into the first pipeline, gradually increase the amount of the raw material gas fed into the first pipeline, detect the amount of NO output from the gas outlet of the first rectification column, and compare the amount of this NO with the amount of NO in the raw material gas until the output amount of NO is not greater than the set threshold value, then the minimum flow rate of the raw material gas fed into the first pipeline is obtained;

[0069] 2) Feed all the remaining raw material gas into the second pipeline, and detect the amount of NO2 in the gas outlet of the second rectification column. If it is less than the set threshold value, then the maximum flow rate of the feed-in is obtained; if it is greater than the set threshold value, then gradually reduce the flow rate fed into the second pipeline until the output amount of NO2 is not greater than the set threshold value, then the maximum flow rate of the raw material gas fed into the second pipeline is obtained;

[0070] 3) Feed the remaining raw material gas into the third pipeline and directly liquefy it.

[0071] In this embodiment, by determining the minimum flow rate of the raw material gas fed into the first evaporator and the maximum flow rate of the raw material gas fed into the second evaporator, it is possible to further ensure that as little CO2 as possible is lost in the first rectification column while removing as much NO as possible in the first rectification column. At the same time, in the second rectification column, as much CO2 as possible is evaporated while avoiding the evaporation of NO2. And on the premise of meeting the feed-in amounts of the first evaporator and the second evaporator, the amount of the raw material gas for direct liquefaction is made as little as possible, so as to achieve a more ideal flow rate distribution method.

[0072] As Figure 1 shown, the embodiment of the present invention also provides a system for deeply removing trace NO from high-concentration CO2 X including a dehydration subsystem, a refrigeration subsystem, and a rectification subsystem.

[0073] Among them, the dehydration subsystem is used to dehydrate the CO2 raw material gas containing NO and NO2; the rectification subsystem includes a first rectification column 1 and a second rectification column 2. The bottoms of the first rectification column 1 and the second rectification column 2 are provided with a first evaporator 3 and a second evaporator 4, and both the first rectification column 1 and the second rectification column 2 are provided with a liquid inlet, a gas outlet at the top, and a liquid outlet at the bottom. The dehydration subsystem is connected to the inlets of the first evaporator 3 and the second evaporator 4 through pipelines respectively, and the outlets of the first evaporator 3 and the second evaporator 4 are connected to the inlet of the refrigeration subsystem; the outlet of the refrigeration subsystem is connected to the liquid inlet of the first rectification column 1, and the liquid outlet of the first rectification column 1 is connected to the liquid inlet of the second rectification column 2.

[0074] The CO2 raw gas containing NO and NO2 entering the system is dehydrated through the dehydration subsystem and then introduced into the first evaporator 3 and the second evaporator 4 as a heat source respectively. The raw gas output from the first evaporator 3 and the second evaporator 4 is introduced into the refrigeration subsystem for liquefaction to obtain liquid CO2 containing NO and NO2, and the liquid CO2 is pumped into the first rectification tower 1 from the liquid inlet at the top of the first rectification tower 1 and flows downward to the bottom of the tower, where it is heated by the raw gas in the first evaporator 3 to generate rising steam. During the rising process, the high-boiling CO2 and NO2 are continuously condensed into liquid, and the low-boiling NO in the downward-flowing liquid is continuously evaporated into gas. In this way, waste gas rich in NO is obtained at the top of the tower, and liquid CO2 containing NO2 is obtained at the bottom of the tower, thereby removing the NO impurity component in the CO2.

[0075] Furthermore, the liquid CO2 containing NO2 is pumped into the first rectification tower 1 from the liquid inlet at the top of the second rectification tower 2 and flows downward to the bottom of the tower, where it is heated by the raw gas in the first evaporator 3 to generate rising steam. Since the boiling point temperature of NO2 is much higher than that of CO2 under the same pressure, during the rectification process, the rising high-boiling NO2 gas is continuously condensed into liquid, and the low-boiling CO2 in the downward-flowing liquid is continuously evaporated into gas. In this way, pure CO2 gas is obtained at the top of the tower, and liquid CO2 rich in NO2 is obtained at the bottom of the tower.

[0076] In a preferred embodiment, valves V11 and V12 are respectively provided on the pipelines connecting the dehydration subsystem to the inlets of the first evaporator 3 and the second evaporator 4, and at the same time, a NO X analyzer 7 is provided corresponding to the gas outlet of the second rectification tower 2.

[0077] According to the above, by the NO X analyzer 7 detects whether the NO X at the gas outlet of the second rectification tower 2 exceeds the set threshold value, and adjusts the amount of the dehydrated raw gas entering the first evaporator 3 and the second evaporator 4, so as to control the heat provided by the two evaporators at the bottom of the corresponding rectification tower. The heat of the first evaporator 3 needs to evaporate part of the CO2 and discharge it from the gas outlet at the top of the first rectification tower while removing NO, and at the same time, discharge the CO2 liquid containing NO2 from the liquid outlet at the bottom of the first rectification tower. The heat of the second evaporator 4 needs to evaporate the CO2 and discharge and collect it from the gas outlet at the top of the second rectification tower, and at the same time, discharge the NO2 in liquid form from the liquid outlet at the bottom of the second rectification tower to remove NO2.

[0078] More preferably, the dehydration subsystem is also directly connected to the inlet of the refrigeration subsystem through valve V19. When the flow rate of the raw material gas introduced is constant, by dividing the dehydrated raw material gas into one path for direct liquefaction, it is possible to further balance the flow rate of the raw material gas entering the first evaporator and the second evaporator, enabling the first rectification column to remove NO as much as possible with as little loss of CO2 as possible, and evaporating CO2 as much as possible while avoiding the evaporation of NO2 in the second rectification column. The control process of the flow rate of the raw material gas in the three pipelines is as described above and will not be elaborated here.

[0079] In the preferred embodiment, the middle parts of the first rectification column 1 and the second rectification column 2 are filled with packing (such as stainless steel structured packing). The falling liquid and the rising steam come into contact with the packing, which is beneficial to increasing the heat exchange area between the rising high-temperature steam and the falling low-temperature liquid to achieve a better heat exchange effect.

[0080] In the preferred embodiment, an exhaust gas flowmeter 6 is also provided at the gas outlet corresponding to the top of the first rectification column 1. By comparing the amount of NO detected by the exhaust gas flowmeter 6 with the known amount of NO in the raw material gas, on the one hand, it can provide a reference for whether the content of NO in the raw material gas has been removed to below the set threshold. Then, according to the NO X analyzer 7 provided at the gas outlet at the top of the second rectification column 2 to detect NO X gas whether it exceeds the set threshold, and adjust the amount of the dehydrated raw material gas entering the first evaporator and the second evaporator to remove NO and NO2 impurities to below the set threshold. On the other hand, when setting the three pipelines, it can cooperate with the NO X analyzer 7 to determine the minimum flow rate of the raw material gas introduced into the first evaporator and the maximum flow rate of the raw material gas introduced into the second evaporator, further optimizing the flow rate distribution in the three pipelines.

[0081] In the preferred embodiment, the gas outlet at the top of the second rectification column 2 is also connected to the refrigeration subsystem (the first refrigerator 5) through a valve (not shown in the figure). If the NO X analyzer 7 detects that the content of NO or NO2 exceeds the threshold, then the gas at the top of the second rectification column 2 will be controlled by the valve to be re-introduced into the first refrigerator 5 for liquefaction and then enter the first rectification column 1 for re-separation.

[0082] In the preferred embodiment, the gas outlet at the top of the second rectification column 2 is also connected to the second refrigerator 14 through valve V16. Through the valve, the high-purity CO2 gas at the bottom is cooled into liquid CO2 by the second refrigerator 14 for storage, and the liquid CO2 containing NO2 at the bottom is introduced into the treatment system for waste liquid treatment.

[0083] Since the CO2 feed gas from carbon capture and compressed by a compressor contains a certain amount of saturated water, dehydration treatment is required before entering the refrigerator for liquefaction to prevent blockage caused by ice formation of water under low temperature conditions. Therefore, in the present invention, the feed gas is dehydrated by a dehydration subsystem before rectification, and the dehydration subsystem includes at least one group of molecular sieve adsorbers.

[0084] In a preferred embodiment, the dehydration subsystem includes a first molecular sieve adsorber 8 and a second molecular sieve adsorber 9 arranged in parallel. The inlet ends and outlet ends of the first molecular sieve adsorber 8 and the second molecular sieve adsorber 9 are respectively connected to the main feed gas pipe through valves. Specifically, the inlet end and outlet end of the first molecular sieve adsorber 8 are respectively connected to the main feed gas pipe through valves V2 and V4, and the inlet end and outlet end of the second molecular sieve adsorber 9 are respectively connected to the main feed gas pipe through valves V3 and V5.

[0085] Moreover, the outlet ends of the first molecular sieve adsorber 8 and the second molecular sieve adsorber 9 are respectively connected to the outlet end of a heater 10 through valves V7 and V8, and the inlet end of the heater 10 is connected to the main feed gas pipe through a valve V6; at the same time, the inlet ends of the first molecular sieve adsorber 8 and the second molecular sieve adsorber 9 are respectively connected to the inlet ends of a first cooler 11 and a second cooler 12. The outlet end of the first cooler 11 is connected to the main feed gas pipe through a valve V9, and the outlet end of the second cooler 12 is connected to the main feed gas pipe through a valve V10.

[0086] By controlling the valve switching, when one molecular sieve adsorber is adsorbing, the other molecular sieve adsorber is regenerated. Preferably, a water analyzer 13 is provided on the main feed gas pipe at the outlets of the first molecular sieve adsorber 8 and the second molecular sieve adsorber 9 to determine whether the first molecular sieve adsorber 8 or the second molecular sieve adsorber 9 is saturated with adsorption. Thus, through the automatic valve switching program, the valve connecting one molecular sieve adsorber to the main feed gas pipe is opened, the valve connecting the other molecular sieve adsorber to the main feed gas pipe is closed, and this molecular sieve adsorber is connected to the heater and the cooler, so that the moisture in the molecular sieve adsorber is desorbed, thereby achieving regeneration and reuse.

[0087] The specific control process is as follows: When the first molecular sieve adsorber 8 is performing the adsorption work, the CO2 feed gas containing NO and NO2 (i.e., Figure 1CO2 in the system enters through valve V1. Valves V2 and V4 are opened for adsorption (valves V3, V5, V6, V7, and V9 are closed). The dehydrated raw gas is sent out through valves V11, V12, and V19. The first molecular sieve adsorber 8 is monitored by the water analyzer 13 to check if it is saturated with adsorption. If saturated, valves V2 and V4 are closed, and valves V3 and V5 are opened. The second molecular sieve adsorber 9 starts the adsorption operation. Meanwhile, valve V6 is opened, and a set amount (about 15% of the total gas volume) of the dehydrated raw gas is heated by the heater 10. Valves V7 and V9 are opened, and the heated CO2 gas is used to regenerate the first molecular sieve adsorber 8. The regenerated CO2 gas is cooled by the first cooler 11 and then merged into the main raw gas pipe for dehydration adsorption. Thus, one adsorption and regeneration cycle is completed. Similarly, if the water analyzer 13 detects that the second molecular sieve adsorber 9 reaches the adsorption saturation state, the second molecular sieve adsorber 9 is controlled for regeneration according to the above principle, and the first molecular sieve adsorber 8 performs adsorption. The adsorption and regeneration of the two molecular sieves are carried out simultaneously, which will not be elaborated here.

[0088] It should be noted that in a specific embodiment shown in the drawings of the present invention, the first molecular sieve adsorber 8 and the second molecular sieve adsorber 9 are connected to the same heater 10 through valves V7 and V8, that is, the raw gas is heated by the same heater and used as the heat source for regeneration. Of course, corresponding heaters can also be set for the first molecular sieve adsorber 8 and the second molecular sieve adsorber 9 according to the actual situation, that is, the raw gas is heated by controlling the corresponding heaters through valves respectively, serving as the heat sources for the regeneration of the two molecular sieve adsorbers. Moreover, the first molecular sieve adsorber 8 and the second molecular sieve adsorber 9 are respectively provided with a first cooler 11 and a second cooler 12, and the two coolers are respectively connected to the main raw gas pipe through valves V9 and V10. Similarly, according to the actual situation, the first molecular sieve adsorber 8 and the second molecular sieve adsorber 9 can also be connected to the same cooler, and the regenerated CO2 gas output from the two molecular sieve adsorbers shares one cooler for cooling.

[0089] It should also be noted that other valves, such as valves V13, V14, V15, V17, V18, etc., can be set in the corresponding connecting pipelines in the system shown in the drawings as needed. These valves only play the role of opening and closing, and existing valves can be used.

[0090] In addition, at the same pressure, the boiling points of NO, CO2, and NO2 increase in sequence. However, at different pressures, the boiling points of NO, NO2, and CO2 are different. Therefore, by controlling the tower pressures of the first distillation column 1 and the second distillation column 2, the boiling points of NO, NO2, and CO2 can be controlled. Preferably, before introducing the raw material gas into the system in the present invention, the tower pressures of the first distillation column 1 and the second distillation column 2 are first reached by introducing pure CO2 gas, and the specific tower pressures can be adjusted according to the actual situation.

[0091] In a specific application, during the distillation process, the tower pressure of the first distillation column is 17.0 - 17.8 barA, and the temperature inside the tower is -32 to -23 °C; the tower pressure of the second distillation column is 17.0 - 17.8 barA, and the temperature inside the tower is -23 to -20 °C. The evaporation temperature requirements of the two distillation columns can be met at the above tower pressures and temperatures, and trace amounts of NO in high-concentration CO2 X can be deeply removed. In addition, in the embodiment of the present invention, the raw material gas after being dehydrated by the molecular sieve has a temperature of about 40 °C and a pressure of 18 barA; the temperature of the raw material gas exiting the first evaporator decreases, and the temperature is about -18 to -20 °C. The low-temperature raw material gas is cooled to a liquefied and supercooled state by the first refrigerator 5, and the temperature of the liquid CO2 output from the first refrigerator 5 is about -35 °C.

[0092] It is easy for those skilled in the art to understand that the above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for deeply removing trace NO from high-concentration CO2 X , characterized in that It includes the following steps: S1: Dehydrate the CO2 feed gas containing NO and NO2. S2: Set up a first distillation column with a first evaporator at the bottom and a second distillation column with a second evaporator at the bottom; Introduce the dehydrated feed gas in S1 into the two evaporators respectively as a heat source, and collect the feed gas output from the two evaporators and then liquefy it to obtain liquid CO2 containing NO and NO2. S3: Introduce the liquid CO2 in S2 into the first distillation column, control the flow rate of the feed gas introduced into the first evaporator, and evaporate part of the CO2 at the boiling point of CO2 under the heat provided by it, and remove NO while discharging from the top gas outlet of the first distillation column, and discharge the liquid CO2 containing NO2 from the bottom liquid outlet of the first distillation column. S4: Introduce the liquid CO2 in S3 into the second distillation column, control the flow rate of the feed gas introduced into the second evaporator, evaporate the CO2 under the heat provided by it and discharge and collect it from the top gas outlet of the second distillation column, and at the same time discharge NO2 in liquid form from the bottom liquid outlet of the second distillation column to remove NO2. In step S2, the dehydrated feed gas is divided into three paths, including a first pipeline introduced into the first evaporator, a second pipeline introduced into the second evaporator, and a third pipeline for direct liquefaction; When the total flow rate of the feed gas introduced is constant, the control process of the feed gas flow rate in the three pipelines is as follows: 1) Introduce the feed gas into the first pipeline, and gradually increase the amount of the feed gas introduced into the first pipeline, detect the amount of NO output from the gas outlet of the first distillation column, and compare the amount of this NO with the amount of NO in the feed gas until the output amount of NO is not greater than the set threshold, that is, obtain the minimum value of the flow rate of the feed gas introduced into the first pipeline. 2) Introduce all the remaining feed gas into the second pipeline, and detect the amount of NO2 in the gas outlet of the second distillation column. If it is less than the set threshold, obtain the maximum value of the flow rate introduced; If it is greater than the set threshold, gradually reduce the flow rate introduced into the second pipeline until the output amount of NO2 is not greater than the set threshold, that is, obtain the maximum value of the flow rate of the feed gas introduced into the second pipeline. 3) Introduce the remaining feed gas into the third pipeline and directly liquefy it.

2. A system for deeply removing trace NO from high-concentration CO2 X is characterized in that It includes a dehydration subsystem, a refrigeration subsystem and a distillation subsystem. The distillation subsystem includes a first distillation column with a first evaporator at the bottom and a second distillation column with a second evaporator at the bottom, and both the first distillation column and the second distillation column have a liquid inlet, a gas outlet at the top, and a liquid outlet at the bottom. The dehydration subsystem is connected to the inlets of the first evaporator and the second evaporator respectively through pipelines to dehydrate the CO2 feed gas containing NO and NO2 and then introduce it into the two evaporators as a heat source respectively; The outlets of the first evaporator and the second evaporator are connected to the inlet of the refrigeration subsystem to liquefy the CO2 feed gas to obtain liquid CO2 containing NO and NO2. The outlet of the refrigeration subsystem is connected to the liquid inlet of the first rectification column to introduce the liquid CO2 into the first rectification column. Under the heat provided by the first evaporator, the boiling point of CO2 is reached to evaporate part of the CO2, and NO is removed while discharging from the gas outlet of the first rectification column. The liquid outlet of the first rectification column is connected to the liquid inlet of the second rectification column to introduce the liquid CO2 containing NO2 discharged from the liquid outlet of the first rectification column into the second rectification column. Under the heat provided by the second evaporator, CO2 is evaporated and discharged and collected from the gas outlet of the second rectification column, and at the same time, NO2 is discharged in liquid form from the liquid outlet of the second rectification column to remove NO2. The dehydrated raw material gas is divided into three paths. The dehydration subsystem is connected to the first evaporator through a first pipeline, connected to the second evaporator through a second pipeline, and directly connected to the refrigeration subsystem through a third pipeline; a waste gas flowmeter is provided corresponding to the gas outlet of the first distillation column, and a NO X analyzer is provided corresponding to the gas outlet of the second distillation column; when the total flow rate of the raw material gas passing through is constant, the control process of the raw material gas flow rate in the three pipelines is as follows: 1) Introduce the raw material gas into the first pipeline, and gradually increase the amount of the raw material gas introduced into the first pipeline. Detect the amount of NO output from the gas outlet of the first rectification column, and compare the amount of this NO with the amount of NO in the raw material gas until the output amount of NO is not greater than the set threshold, then the minimum flow rate of the raw material gas introduced into the first pipeline is obtained. 2) Introduce all the remaining raw material gas into the second pipeline, and detect the amount of NO2 in the gas outlet of the second rectification column. If it is less than the set threshold, then the maximum flow rate of the introduced gas is obtained. If it is greater than the set threshold, then gradually reduce the flow rate introduced into the second pipeline until the output amount of NO2 is not greater than the set threshold, then the maximum flow rate of the raw material gas introduced into the second pipeline is obtained. 3) Introduce the remaining raw material gas into the third pipeline and directly liquefy it.

3. The system for deeply removing trace NO from high-concentration CO2 according to claim 2 X , characterized in that The dehydration subsystem includes a first molecular sieve adsorber and a second molecular sieve adsorber arranged in parallel. The inlet ends and outlet ends of the first molecular sieve adsorber and the second molecular sieve adsorber are respectively connected to the raw material gas main pipe through valves. And the outlet ends of the first molecular sieve adsorber and the second molecular sieve adsorber are respectively connected to the outlet end of the heater through valves. The inlet end of the heater is connected to the raw material gas main pipe through a valve. At the same time, the inlet ends of the first molecular sieve adsorber and the second molecular sieve adsorber are respectively connected to the inlet end of the cooler. The outlet end of the cooler is connected to the raw material gas main pipe through a valve. Through the alternate control of the valves, when one molecular sieve adsorber adsorbs, the other molecular sieve adsorber is regenerated.

4. The system for deeply removing trace NO from high-concentration CO2 according to claim 3 X , characterized in that A water analyzer is provided on the raw material gas main pipe at the outlets of the first molecular sieve adsorber and the second molecular sieve adsorber, which is used to judge whether the first molecular sieve adsorber or the second molecular sieve adsorber is saturated with adsorption, so as to control the opening of the valve connecting one molecular sieve adsorber to the raw material gas main pipe, and the other molecular sieve adsorber is communicated with the heater and the cooler to realize regeneration.

5. A system for deeply removing trace NO from high-concentration CO2 according to any one of claims 2-4 X , characterized in that The gas outlet at the top of the second rectification column is connected to the refrigeration subsystem through a valve, so that when the content of NO X detected by the NO analyzer or the content of NO2 exceeds the set threshold, the overhead gas of the second rectification column is re-liquefied and then introduced into the first rectification column for re-separation; The top gas outlet of the second rectification column is also connected to the refrigerator through a valve to liquefy the CO2 gas with the required purity at the top of the tower for storage.

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