Ammonia recovery method

Abstract

The present invention provides a method for recovering ammonia, including: step S1 of providing a mixed gas containing ammonia; step S2 of dissolving ammonia in water; step S3 of degassing the ammonia water containing the dissolved ammonia to separate water and ammonia gas; and step S4 of purifying the degassed ammonia.

Description

[Technical Field]

[0001] The present invention relates to a method for recovering ammonia from a mixed gas, and more particularly to a method for recovering ammonia, which selectively separates ammonia from process intermediates containing various constituents (NH, H, S, CO, H, O, etc.) to recover high purity ammonia of 90% or more, while preventing the formation of solid salts during the recovery process, thereby achieving high ammonia recovery efficiency. [Background technology]

[0002] Ammonia is a compound of nitrogen and hydrogen with the chemical formula NH3. Ammonia boils at -33.34 °C (-28.012 °F) at 1 atmosphere of pressure, so liquid form of ammonia must be stored in a high-pressure or low-temperature environment.

[0003] One of the commercial uses of ammonia is as a process gas in semiconductor manufacturing. For example, ammonia is used in the epitaxial deposition of semiconductor materials in a process called metal-organic chemical vapor deposition (MOCVD).

[0004] Among the many gases used in MOCVD LED fabrication, ammonia is one of the most expensive. This is due, in part, to the high purity required for the ammonia process gas. Because ammonia requires high flow rates during nitride crystal growth, even trace amounts of impurities in the gas can result in significant numbers of unwanted atoms being incorporated into the device. For example, if water (H2O) or oxygen (O2) molecules are present in ammonia gas, even at trace concentrations exceeding a few parts per billion (ppb), oxygen atoms can be incorporated into the crystalline structure of the LED device. Therefore, modern LEDs are typically fabricated using ammonia containing less than 1 ppb of water or oxygen.

[0005] Ammonia is also used in chemical reactions, one example of which is as a NOx reducing agent in SCR (selective catalytic reduction). SCR technology is used to remove NOx generated in combustion facilities such as stationary sources like power plants, or in mobile sources like automobiles. In this case, urea water is used as the reducing agent, and the urea water is decomposed at high temperatures to convert into ammonia, which then reacts with NOx, so it can be said to be the same technology.

[0006] Recently, as environmental problems have increased, the number of SCR facilities for removing NOx has increased, and as a result, the amount of ammonia used has also tended to increase, so there is a need for technology to supply large amounts of high-purity ammonia.

[0007] Meanwhile, the general technology for synthesizing and separating ammonia involves synthesizing H2 from natural gas, reacting it with nitrogen separated by an air separation unit (ASU) to synthesize NH3, and then separating it from the product. In most cases, this separation is achieved by taking advantage of the difference in boiling points between ammonia and hydrogen and nitrogen.

[0008] However, this invention focuses on recovering high concentrations of NH3 generated during industrial processes. Because it is difficult to immediately recover ammonia, conventional techniques have involved burning it at high temperatures to generate heat. However, this invention provides a method and apparatus for selectively separating ammonia from process intermediates containing various constituents.

[0009] Meanwhile, in addition to ammonia, process intermediates include H2S, CO2, H2O, etc. H2S and CO2 in particular are highly reactive with ammonia and can form salts when cooled at room temperature, which can cause line narrowing. For this reason, in order to selectively separate ammonia, it is necessary to not only consider the difference in boiling points, but also to adjust the process so that solid salts do not form.

[0010] In addition, NH3, H2S, and CO2 are all highly soluble in water, so a technology for selective separation is required. Meanwhile, NH3 can dissolve in water up to about 30%, but the solubility of H2S is relatively low at 3g / L and that of CO2 is 1.3g / L. Therefore, high-purity NH3 can be recovered by taking advantage of the difference in solubility. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Korean Patent Registration No. 1925612 Summary of the Invention [Problem to be solved by the invention]

[0012] The present invention provides a method for removing impurities, except ammonia, from a gas mixture and recovering high purity ammonia. [Means for solving the problem]

[0013] According to one embodiment of the present invention, there is provided an ammonia recovery apparatus including: A mixed gas cooler 1; an ammonia absorption tower 2; an absorption liquid supply pump 3; an absorption liquid cooler 4; an absorption liquid degassing tower 5; a cooler 6 for the degassing tower; a reboiler 7 for the degassing tower; a cooler 8 at the upper and rear ends of the degassing tower; a cooler 9 at the lower and rear ends of the degassing tower; a first ammonia purification tower 10; a cooler 11 for the first ammonia purification tower; a reboiler 12 for the first ammonia purification tower; a second ammonia purification tower 13; a cooler 14 for the second ammonia purification tower; and a reboiler 15 for the second ammonia purification tower.

[0014] According to another embodiment of the present invention, there is provided a method for recovering ammonia, including: step S1 of providing a mixed gas containing ammonia; step S2 of dissolving ammonia in water; step S3 of degassing the ammonia water containing the dissolved ammonia to separate water and ammonia gas; and step S4 of purifying the degassed ammonia. [Effects of the Invention]

[0015] According to the present invention, it is possible to provide a method for effectively removing hydrogen sulfide, carbon dioxide, etc. from a mixed gas and effectively recovering ammonia at a high concentration. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a diagram illustrating the components of the ammonia recovery apparatus of the present invention and their connection relationships. [Figure 2] 1 is a diagram illustrating the ammonia recovery method of the present invention, showing the flow of fluid streams ([A] to [S]) that appear during the implementation of the ammonia recovery method. DETAILED DESCRIPTION OF THE INVENTION

[0017] The present invention will be described in detail below with reference to the accompanying drawings, in which: FIG. 1 is a block diagram of a semiconductor device according to a first embodiment of the present invention; FIG. 2 is a block diagram of a semiconductor device according to a first embodiment of the present invention; FIG. 3 is a block diagram of a semiconductor device according to a first embodiment of the present invention;

[0018] According to one embodiment of the present invention, there is provided an ammonia recovery apparatus including the following equipment.

[0019] A mixed gas cooler 1; an ammonia absorption tower 2; an absorption liquid supply pump 3; an absorption liquid cooler 4; an absorption liquid degassing tower 5; a cooler 6 for the degassing tower; a reboiler 7 for the degassing tower; a cooler 8 at the upper and rear ends of the degassing tower; a cooler 9 at the lower and rear ends of the degassing tower; a first ammonia purification tower 10; a cooler 11 for the first ammonia purification tower; a reboiler 12 for the first ammonia purification tower; a second ammonia purification tower 13; a cooler 14 for the second ammonia purification tower; and a reboiler 15 for the second ammonia purification tower.

[0020] According to another embodiment of the present invention, there is provided a method for recovering ammonia, including: step S1 of providing a mixed gas containing ammonia; step S2 of dissolving ammonia in water; step S3 of degassing the ammonia water containing the dissolved ammonia to separate water and ammonia gas; and step S4 of purifying the degassed ammonia.

[0021] Each step of the method of the present invention will now be described in more detail with reference to FIGS.

[0022] In step S1, a mixed gas containing ammonia can be provided, and the mixed gas can be cooled by a mixed gas cooler 1 in order to make the ammonia more easily dissolve in water in the following step S2.

[0023] For example, the mixed gas may be cooled to 5°C to 80°C, more preferably 10°C to 40°C.

[0024] 80°C or higher means that the process temperature is used as is without heat exchange. If the temperature is cooled to a temperature lower than 5°C, solid salt may be generated, which may cause operational difficulties.

[0025] Step S2 is a step of producing ammonia water by cooling and absorbing ammonia with water in the ammonia absorber 2. The ammonia contained in the mixed gas can be recovered by supplying water to the mixed gas. Such ammonia recovery is a commonly used method, in which ammonia is absorbed by injecting a large amount of water into the mixed gas to produce ammonia water. For example, the mixed gas can be separated into water that has absorbed ammonia and residual gas that is not dissolved in water by injecting water into the mixed gas. In this case, it is preferable to inject the water in a countercurrent direction to the flow of the mixed gas.

[0026] Highly concentrated ammonia can be recovered from the ammonia water produced in the S2 stage, and if necessary, a portion of the produced ammonia water can be separated and used as an absorbent for removing acid gases in the COG.

[0027] The dissolution reaction of ammonia in water is an exothermic reaction (the enthalpy change ΔH o =-30.50 kJ / mol), and in the S2 stage, water cooled via the absorption liquid cooler 4 can be supplied.

[0028] More specifically, the temperature of the sprayed water may be 5 to 45°C, and more preferably 10 to 40°C.

[0029] If the water temperature is below 5°C, cooling water must be produced using equipment such as a chiller, which can increase the power costs required. Conversely, if the water temperature exceeds 45°C, the increase in temperature can decrease the gas solubility, which can reduce the amount of ammonia absorbed into the water.

[0030] In the S2 stage, in addition to ammonia, hydrogen sulfide (H2S) and carbon dioxide (CO2) can also dissolve. However, compared to ammonia, which can dissolve at 30% at room temperature, hydrogen sulfide has a solubility of 3g / L and carbon dioxide has a solubility of 1.3g / L, which are very small amounts. Therefore, impurity gases can be removed by purifying them in the subsequent distillation column, and high-purity ammonia can be recovered.

[0031] The ammonia water generated in step S2 can be collected at the bottom of the ammonia absorber 2, and impurity gases such as hydrogen sulfide (HS) and carbon dioxide (CO) that are not dissolved by the injected water can be separated from the ammonia gas and discharged or collected at the top of the ammonia absorber 2.

[0032] In the step S2, 99% or more of impurity gases such as hydrogen sulfide (H2S) and carbon dioxide (CO2) initially introduced in the step S1 are separated from the ammonia gas and can be discharged or collected from the top of the ammonia absorption tower 2.

[0033] The S3 stage is a stage in which ammonia gas is degassed from the ammonia water produced in the S2 stage via the absorbent degassing tower 5, and can be carried out by utilizing the difference in boiling points between ammonia and water.

[0034] In the S3 stage, the ammonia water can be vaporized by heating in the reboiler 7 of the degassing tower, and the vaporized ammonia water can be cooled again by the cooler 6 of the degassing tower. At this time, the difference in boiling points between ammonia and water causes the water to liquefy and be collected at the bottom, which can cause degassing.

[0035] To carry out the above-mentioned S3 step, the internal temperature of the absorbent degassing tower 5 may be 100 to 200°C, more specifically 110 to 170°C.

[0036] If the internal temperature of the absorbent degassing tower is below 100°C, it is not possible to recover a large amount of dissolved ammonia, and if ammonia remains in the recirculated fluid, the absorption capacity will decrease, which may affect the absorber. Conversely, if the internal temperature of the absorbent degassing tower 5 exceeds 200°C, not only ammonia but also water will vaporize, which may prevent the degassing tower from performing its function of recovering and separating ammonia from the solution.

[0037] At this time, the pressure inside the absorbent degassing tower 5 was 1 kg / cm 2 ~20kg / cm 2 More specifically, 6 kg / cm 2 ~10kg / cm 2 may be.

[0038] If the internal pressure of the absorbent degassing tower is 1 kg / cm 2If the temperature is less than 20 kg / cm, as described above, the high internal temperature of the absorbent degassing tower 5 may cause water to evaporate, making it impossible for the degassing tower to perform its function of recovering and separating ammonia from the solution. 2 If the temperature exceeds 100°C, ammonia must be recovered at an excessively high temperature, which may result in an increase in energy costs.

[0039] The degassed ammonia is collected from the upper end of the absorbent degassing tower 5, and then cooled by a cooler 8 at the upper rear end of the degassing tower, and can be introduced into a first ammonia purification tower 10. The ammonia can be cooled to 20 to 50°C by the cooler 8 at the upper rear end of the degassing tower.

[0040] On the other hand, the water from which ammonia has been degassed is recovered from the lower end of the absorbent degassing tower 5, cooled by a cooler 9 at the rear end of the lower end of the degassing tower, and then introduced into the ammonia absorption tower 2, where it can be reused for absorbing ammonia in the S2 stage.

[0041] Step S4 is a step of purifying the degassed ammonia, and impurity gases such as residual carbon dioxide, hydrogen sulfide and / or water vapor can be removed through step S4.

[0042] The step S4 is not particularly limited as long as it can separate the remaining impurity gas from the ammonia. For example, the step S4 can be performed by a membrane separation process, temperature swing adsorption, pressure swing adsorption, temperature and pressure swing adsorption, or distillation, and more preferably by distillation.

[0043] More specifically, when step S4 is carried out by distillation, the input ammonia gas can be separated from residual impurity gases such as carbon dioxide, hydrogen sulfide, and water vapor by gas-liquid equilibrium at a specific temperature and pressure.

[0044] When step S4 is carried out by distillation, it can be carried out using a purification column, which may be equipped with a cooler at the top and a reboiler at the bottom, and may be filled with packing material.

[0045] In the purification column, ammonia gas-liquid equilibrium is formed in each stage formed by packing material, and at this time, ammonia gas and remaining impurity gas can be separated from each other due to the difference in boiling point and volatility of the mixed gas.

[0046] The step S4 can be performed in multiple steps.

[0047] More specifically, in the step S4, residual carbon dioxide and hydrogen sulfide The method may include a primary purification step for removing gas, and a secondary purification step for removing water or water vapor from the ammonia gas that has been purified in the primary purification step.

[0048] The primary purification step may be performed in a first ammonia purification tower 10 to remove residual carbon dioxide and hydrogen sulfide using distillation.

[0049] More specifically, the primary purification step may further include a step of cooling the input ammonia gas; a step of removing residual gaseous impurity gases; and a step of reheating the ammonia gas from which the residual impurity gases have been removed; and each of the above steps may be performed intermittently or continuously.

[0050] When the first purification step is performed by distillation, the first ammonia purification tower 10 may further include a first ammonia purification tower cooler 11 and a first ammonia purification tower reboiler 12.

[0051] The step of cooling the introduced ammonia gas may be performed by the first ammonia purifying tower cooler 11. The first ammonia purifying tower cooler 11 may serve to send the ammonia gas among the gases introduced into the first ammonia purifying tower 10 to the lower end and separate it.

[0052] In addition, the step of reheating the ammonia gas from which the residual impurity gases have been removed can be performed by the reboiler 12 of the first ammonia purification tower. The reboiler 12 of the first ammonia purification tower can play a role in sending CO2 and H2S from the input gas to the top end and separating them.

[0053] When the first purification step is carried out, the ammonia gas may be cooled to 0°C to 5°C, more preferably 0°C to 3°C, by the cooler 11 of the first ammonia purification tower.

[0054] If the temperature of the ammonia gas cooled by the cooler 11 of the first ammonia purification tower is less than 0°C, a problem may occur in that a lot of energy is consumed in the cooling process, increasing the process cost. Conversely, if the temperature exceeds 5°C, a problem may occur in that the ammonia is not cooled sufficiently, reducing the amount recovered at the bottom.

[0055] In addition, when the first purification step is performed by distillation, the internal pressure of the first ammonia purification tower 10 is 1 kg / cm 2 ~20kg / cm 2 and more specifically 3 kg / cm 2 ~10kg / cm 2 may be.

[0056] If the internal pressure of the first ammonia purification column 10 is 1 kg / cm 2 If it is less than 20 kg / cm, there may be a problem of ammonia being discharged and lost at the top. 2 If the distillation column temperature exceeds 100° C., a large amount of energy will be required for reboiling the bottom end of the distillation column, which may result in poor economic efficiency.

[0057] The temperature of the ammonia gas can be raised to 6°C to 10°C by the reboiler 12 of the first ammonia purification column.

[0058] In the process in which the input ammonia gas is cooled by the cooler 11 of the first ammonia purification tower and heated by the reboiler 12 of the first ammonia purification tower, ammonia having a relatively high boiling point is recovered from the lower end of the first ammonia purification tower 10, and impurity gases such as CO and HS having relatively low boiling points can be separated and removed in a gaseous state from the upper end of the first ammonia purification tower 10.

[0059] The ammonia gas recovered from the first ammonia purification tower 10 may be input into a second ammonia purification tower for a second purification step, which may remove water or water vapor remaining in the ammonia gas.

[0060] The secondary purification step is not particularly limited as long as it can separate the water remaining in the ammonia gas, but it is more preferably carried out by distillation.

[0061] More specifically, the second purification step may further include a step of cooling the input ammonia gas; a step of removing residual water in a liquid state; and a step of reheating the ammonia gas from which the residual water has been removed, and each of the above steps may be performed intermittently or continuously.

[0062] When the second purification step is performed by distillation, the second ammonia purification column 13 may further include a second ammonia purification column cooler 14 and a second ammonia purification column reboiler 15.

[0063] Therefore, the step of cooling the input ammonia gas may be performed by the cooler 14 of the second ammonia purifying tower. The cooler 14 of the second ammonia purifying tower may serve to send water or water vapor remaining in the gas input into the second ammonia purifying tower 13 to the lower end and separate it.

[0064] In addition, the step of reheating the ammonia gas may be performed by the reboiler 15 of the second ammonia purification tower. The reboiler 15 of the second ammonia purification tower may serve to separate the ammonia in the input gas by sending it to the top end.

[0065] When the second purification step is carried out, the ammonia gas may be cooled to -35°C to 0°C, more preferably -10°C to -3°C, by the cooler 14 of the second ammonia purification tower.

[0066] If the temperature of the ammonia gas cooled by cooler 14 of the second ammonia purification tower is below -35°C, there may be problems that the cooling process consumes a lot of energy, increasing process costs, and that the water is supercooled, forming ice and clogging the pipes. Conversely, if the temperature is above 0°C, the ammonia may not be cooled sufficiently to separate the water and ammonia, and impurities may not be sufficiently removed at the bottom, which may result in a problem that ammonia of sufficient purity cannot be recovered.

[0067] In addition, when the second purification step is performed by distillation, the internal pressure of the second ammonia purification tower 13 is 1 kg / cm 2 ~20kg / cm 2 More specifically, 3 kg / cm 2~10kg / cm 2 may be.

[0068] If the internal pressure of the second ammonia purification column 13 is 1 kg / cm 2 If it is less than 20 kg / cm, the separation ratio of impurities other than ammonia will be low, which may result in a problem of low ammonia purity. 2 If the distillation column temperature exceeds 100° C., a large amount of energy will be required for reboiling the bottom end of the distillation column, which may result in poor economic efficiency.

[0069] The ammonia gas may be heated to 50°C to 100°C, more preferably 55°C to 70°C, by the reboiler 15 of the second ammonia purification column.

[0070] In the process in which the input ammonia gas is cooled by the cooler 14 of the second ammonia purifying tower and heated by the reboiler 15 of the second ammonia purifying tower, ammonia having a relatively low boiling point is recovered from the upper end of the second ammonia purifying tower 13, and water having a relatively high boiling point is separated and removed from the lower end of the second ammonia purifying tower 13.

[0071] The ammonia gas purified by the second purification step can be recovered and stored after being cooled by the cooler 14 of the first ammonia purification tower.

[0072] The purity of the ammonia purified, recovered and stored according to one embodiment of the present invention may be 99.0% or higher, more preferably 99.9% or higher, and even more preferably 99.99% or higher. [Example]

[0073] <Example> However, the present invention can be modified in various different forms and the scope of the present invention is not limited to the following examples.

[0074] FIG. 1 shows the configuration of an ammonia recovery apparatus according to one embodiment of the present invention.

[0075] FIG. 2 is a flowchart of the ammonia recovery process carried out via the ammonia recovery apparatus.

[0076] Tables 1 and 2 below show the temperature and pressure of each fluid stream in the flow chart of Figure 2, as well as the components and contents of the gases identified from each stream. Streams A to S in Tables 1 and 2 correspond to [A] to [S] in Figure 2, respectively.

[0077] [Table 1]

[0078] [Table 2]

[0079] Referring to FIGS. 1 and 2 and Tables 1 and 2, a mixed gas containing ammonia was pre-cooled through a mixed gas cooler 1 and then introduced into an ammonia absorption tower 2, in step S1.

[0080] In the ammonia absorber 2, the water supplied through the absorbent supply pump 3 was cooled by the absorbent cooler 4 and then injected into the ammonia absorber 2 to absorb ammonia, in step S2.

[0081] In the S2 stage, most of the carbon dioxide and hydrogen sulfide It can be seen that the is separated into stream [D] in a state that is not dissolved in water.

[0082] The water that absorbed ammonia in the ammonia absorber 2, that is, ammonia water, was introduced into the absorbent degassing tower 5 to perform a step of degassing ammonia gas from the ammonia water, that is, the S3 step.

[0083] At this time, the water liquefied by the cooler 6 of the degassing tower was cooled through a cooler at the rear end of the lower end of the degassing tower, and then re-introduced into the ammonia absorption tower 2 for reuse in the S2 stage.

[0084] The degassed ammonia gas was cooled again by a cooler 8 at the rear end of the top of the degassing tower, and then introduced into a first ammonia purification tower 10 to carry out the first purification step of the S4 step.

[0085] The first purification step is carried out by distillation, and as a result, carbon dioxide and hydrogen sulfide It was confirmed that the gas was separated into stream [M].

[0086] The ammonia gas that had undergone the first purification step was introduced into the second ammonia purification tower 13, where it underwent a second purification step.

[0087] The second purification step was carried out by distillation, which resulted in the separation of some of the remaining water into stream [P].

[0088] The ammonia purified through steps S1 to S4 is recovered in stream [O] and is confirmed to have a purity of 99.99% or more.

[0089] On the other hand, 99.8% (3284.1 kg / h) of the carbon dioxide in the mixed gas introduced was removed from the introduced flow rate (3289.9 kg / h). hydrogen sulfide It can be seen that 99.3% (1749.0 kg / h) of the input flow rate (1760.8 kg / h) is separated and removed into stream [4] at the S2 stage.

[0090] Therefore, according to the method of the present invention, carbon dioxide and hydrogen sulfide More than 99% of the carbon dioxide and CO2 are separated and removed in the S2 stage. hydrogen sulfide It can be seen that the possibility of forming salts and causing line stenosis is significantly reduced. [Explanation of symbols]

[0091] 1: Mixed gas cooler 2: Ammonia absorption tower 3: Absorbent supply pump 4: Absorption liquid cooler 5: Absorbent degassing tower 6: Degassing tower cooler 7: Degassing tower reboiler 8: Cooler at the top and rear end of the degassing tower 9: Cooler at the rear end of the degassing tower 10: First ammonia purification tower 11: Cooler for the first ammonia purification tower 12: Reboiler for the first ammonia purification tower 13: Second ammonia purification tower 14: Cooler for the second ammonia purification tower 15: Reboiler for the second ammonia purification tower

Claims

1. a step S1 of providing a gas mixture containing ammonia; Step S2 of dissolving ammonia in water; Step S3 of degassing the ammonia water containing dissolved ammonia to separate water and ammonia gas; and A method for recovering ammonia, comprising: a step S4 of purifying the degassed ammonia.

2. 2. The method of claim 1, wherein the step S1 further comprises cooling the provided mixed gas to 5°C to 80°C.

3. 2. The method for recovering ammonia according to claim 1, wherein the step S2 is carried out by injecting water in a countercurrent direction to the flow of the mixed gas.

4. 4. The method for recovering ammonia according to claim 3, wherein the temperature of the injected water is 5 to 45°C.

5. 2. The method of claim 1, wherein the step S4 comprises a first purification step and a second purification step.

6. 6. The method of claim 5, wherein the primary purification step further comprises: cooling the input ammonia gas; removing residual gaseous impurity gases; and heating the ammonia gas from which the residual impurity gases have been removed.

7. The step of cooling the ammonia gas introduced in the first purification step is performed at a temperature of 0 to 5°C and a pressure of 1 kg / cm ２ ~20 kg / cm ２ The ammonia recovery method according to claim 6, wherein the ammonia recovery method is carried out by

8. 6. The method of claim 5, wherein the secondary purification step further comprises: cooling the input ammonia gas; removing residual water in a liquid state; and heating the ammonia gas from which the residual water has been removed.

9. 9. The method for recovering ammonia according to claim 8, wherein the secondary purification step is carried out at a temperature of −35° C. to 0° C. and a pressure of 1 bar to 20 bar.

10. An ammonia recovery apparatus comprising: a mixed gas cooler 1; an ammonia absorption tower 2; an absorption liquid supply pump 3; an absorption liquid cooler 4; an absorption liquid degassing tower 5; a cooler 6 for the degassing tower; a reboiler 7 for the degassing tower; a cooler 8 at the upper rear end of the degassing tower; a cooler 9 at the lower rear end of the degassing tower; a first ammonia purification tower 10; a cooler 11 for the first ammonia purification tower; a reboiler 12 for the first ammonia purification tower; a second ammonia purification tower 13; a cooler 14 for the second ammonia purification tower; and a reboiler 15 for the second ammonia purification tower.

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