Liquid seal system for amine tank

Abstract

This invention discloses an amine liquid tank liquid sealing system, belonging to the petrochemical field. The amine liquid tank liquid sealing system includes an amine liquid tank and an amine liquid sealing tank, wherein the bottom of the amine liquid sealing tank is higher than the top of the amine liquid tank; the top of the amine liquid tank is connected to the top of the amine liquid sealing tank; and the bottom of the amine liquid sealing tank is connected to the amine liquid tank. This invention solves the problem of hydrogen sulfide emissions from amine liquid tank exhaust gas under normal and stable operating conditions by optimizing the on-site layout of the water sealing tank and improving the liquid sealing medium of the water sealing tank. This provides technical support for the control of odor sources in the plant and the creation of an odor-free factory.

Description

Technical Field

[0001] This invention belongs to the field of petrochemicals, specifically relating to an amine liquid tank sealing system. Background Technology

[0002] Amine liquid tanks, commonly referred to as amine liquid main tanks in process production, are a common piece of equipment in desulfurization processes within the petroleum and petrochemical industry. These are atmospheric pressure storage tanks; both overpressure and negative pressure can damage the tank. Therefore, amine liquid main tanks are typically equipped with a nitrogen self-regulating valve and a breather valve at the top to prevent overpressure or negative pressure. However, due to improper maintenance over time, the breather valve may experience problems such as leakage, jamming, adhesion, and blockage, affecting the normal operation of the atmospheric pressure tank.

[0003] In recent years, newly built amine liquid tanks generally no longer have breather valves, but are usually equipped with water seal tanks. These water seal tanks are dual-function water seal tanks, and the equipment process is as follows: Figure 1 As shown. The principle of the dual-function water seal tank is as follows. Figure 2-1 , Figure 2-2 , Figure 2-3 As shown, the height of the positive pressure water seal depends on the depth of the inner tube inserted into the lower vertical baffle. Generally, the negative pressure liquid seal height of the liquid seal tank is 50mm, and the positive pressure liquid seal height is 150-200mm. The specific liquid seal height can be set according to the process requirements of the device, thereby achieving stable pressure control of the amine liquid tank between -50 and 150 (200) mm liquid column. The horizontal line of the liquid seal tank is the upper baffle. A fresh water supply line is set at the top of the water seal tank. Normally, it is open. Water forms a water seal layer at the top of the tank, sealing the bottom of the air inlet pipe and forming a negative pressure water seal. Excess water overflows to the bottom of the tank through the upper baffle, forming a lower water seal, sealing the central baffle of the tank, forming a positive pressure water seal. Water is then discharged from the bottom side, realizing the function of breaking the water seal to prevent overpressure when the pressure is high and drawing in air to prevent negative pressure when the pressure is low. The pressure of the normal amine liquid tank is controlled between the positive pressure liquid seal height and the negative pressure liquid seal height, gradually replacing the breather valve in function. During normal operation, the condition of the water seal tank can be determined simply by checking whether the drainage at the bottom of the water seal tank is normal, making it easy to maintain.

[0004] However, Figure 1 The existing process shown has the following drawbacks: The medium in the amine liquid tank is generally lean amine liquid after regeneration in the solvent regeneration tower. The hydrogen sulfide content in the amine liquid is controlled at 0.5-1.5 g / L, so a small amount of hydrogen sulfide is normally present in the lean amine liquid. When a large amount of lean amine liquid is stored in the atmospheric pressure amine liquid tank, the small amount of hydrogen sulfide dissolved in the lean amine liquid will be continuously released. This process will cause the pressure in the amine liquid tank to rise slowly. When the pressure exceeds the water seal height of the water seal tank, the hydrogen sulfide-containing waste gas in the tank will break through the water seal and be discharged into the atmosphere from the waste gas outlet of the water seal tank, causing environmental pollution.

[0005] As can be seen from the above, the main function of the water seal tank in the above process is to replace the breather valve, maintain the pressure stability of the amine liquid tank, and ensure the normal and stable operation of the amine liquid tank. However, there is no solution for the hydrogen sulfide-containing waste gas released from the amine liquid in the tank. The emission of hydrogen sulfide-containing waste gas into the atmosphere will cause on-site odor and environmental pollution, which is inconsistent with the existing environmental protection requirements. This is a common environmental problem faced by equipment containing amine liquid tanks. Summary of the Invention

[0006] Currently, water-sealed tanks are commonly used in processes to ensure the safe and stable operation of amine liquid tanks. However, existing water-sealed tanks cannot effectively address the problem of environmental pollution caused by exhaust gas emissions from the tank top into the atmosphere. This invention aims to solve the problem of hydrogen sulfide emissions from the exhaust gas at the top of amine liquid tanks by optimizing the process flow and the liquid level medium in the water-sealed tank, ensuring normal and stable operation of the amine liquid tank. This provides technical support for controlling odor sources in the plant and creating an odor-free factory.

[0007] In a first aspect, the present invention provides an amine liquid tank liquid sealing system, comprising an amine liquid tank and an amine liquid sealing tank, wherein the amine liquid sealing tank contains lean amine liquid; the bottom of the amine liquid sealing tank is higher than the top of the amine liquid tank; and the top of the amine liquid tank is connected to the top of the amine liquid sealing tank.

[0008] Both the amine liquid tank and the amine liquid seal tank contain lean amine solution (an aqueous solution of methyldiethanolamine with a concentration of 25% to 40%).

[0009] As a preferred technical solution, the bottom of the amine liquid sealing tank is connected to the amine liquid tank.

[0010] As a preferred technical solution, the bottom of the amine liquid sealing tank is connected to the amine liquid tank via pipeline P1, and the section of pipeline P1 adjacent to the amine liquid tank is U-shaped or V-shaped.

[0011] Amine tanks are usually equipped with level gauges, which have upper and lower leads.

[0012] The return port of P1 (the location where P1 connects to the amine liquid tank) is 10-20cm higher than the upper lead-out point of the level gauge.

[0013] Secondly, as a preferred technical solution, the pressure control device for the amine tank further includes an absorption tower; the waste gas absorption tower is filled with packing material; the packing material is usually made of lightweight sulfur-resistant materials, such as stainless steel 304 or 316L, plastic, etc.

[0014] The bottom of the amine liquid sealing tank, the absorption tower, and the amine liquid tank are connected in sequence.

[0015] As a preferred technical solution, the packing is located in the middle of the absorption tower; the bottom of the amine liquid sealing tank is connected to the upper part of the absorption tower; the exhaust gas outlet of the amine liquid sealing tank (the negative pressure port in Figure 2) is divided into two streams; one stream (with a valve) is connected to the upper part of the absorption tower, and the other stream (with a valve) is connected to the lower part of the absorption tower, and the flow direction of the exhaust gas is controlled by switching valves.

[0016] As a preferred technical solution, the bottom of the absorption tower is connected to an amine liquid tank.

[0017] As a preferred technical solution, the bottom of the absorption tower is connected to the amine liquid tank via pipeline P2, and the section of pipeline P2 near the amine liquid tank is U-shaped. The return port of P2 (the location where P2 connects to the amine liquid tank) is 10-20cm higher than the upper lead-out point of the level gauge, ensuring that the return port is above the normal liquid level of the amine liquid tank.

[0018] As a preferred technical solution, the amine liquid sealing tank has a positive pressure liquid seal height; the height difference between the lowest and highest points of the U-shape is the liquid seal height; the liquid seal height is greater than the positive pressure liquid seal height.

[0019] Thirdly, the present invention provides a method for controlling pressure using the amine liquid tank liquid seal system described in the first aspect above, wherein both the amine liquid tank and the amine liquid seal tank contain lean amine liquid, the exhaust gas from the top of the amine liquid tank is introduced into the amine liquid seal tank, and the lean amine liquid at the bottom of the amine liquid seal tank flows by gravity to the amine liquid tank through pipeline P1.

[0020] Fourthly, the present invention provides a method for controlling pressure using the amine liquid tank liquid seal system described in the second aspect above. Both the amine liquid tank and the amine liquid seal tank contain lean amine liquid. The exhaust gas from the top of the amine liquid tank is introduced into the amine liquid seal tank. The lean amine liquid at the bottom of the amine liquid seal tank flows by gravity to the upper part of the absorption tower, and then flows by gravity from the bottom of the absorption tower through pipeline P2 back to the amine liquid tank. The exhaust gas from the amine liquid seal tank is introduced into the lower part of the absorption tower, where hydrogen sulfide is absorbed and treated before being discharged.

[0021] The method of controlling the pressure of the amine tank and the purification of exhaust gas using any of the above-described amine tank liquid seal systems is as follows: the amine flow rate is sufficient to wet the packing material, with no specific limitations; the amine tank is under normal pressure control, and is normally controlled at -50 to 200 mmH2O (i.e., the positive and negative liquid seal heights of the liquid seal tank) through a nitrogen self-regulating valve.

[0022] Technical effects of the present invention:

[0023] (1) Breaking with traditional thinking, the liquid sealing medium was changed to lean amine liquid, which solved the problem of non-recovery of continuously flowing water in the liquid sealing tank. At the same time, the lean amine liquid, as the liquid sealing medium, can absorb hydrogen sulfide in the waste gas to a certain extent, reducing hydrogen sulfide emissions. Through the amine liquid liquid sealing tank, the pressure of the amine liquid tank is stabilized.

[0024] (2) Breaking away from the conventional thinking of placing liquid seal tanks on the ground, the liquid seal tanks are placed at a high place, and the height difference is used to achieve lean liquid gravity flow, thus solving the problem of amine liquid recovery.

[0025] (3) The absorption tower is in the form of a chimney, with removable and washable packing material in the middle as a re-absorption site for waste gas. The chimney effect (i.e., utilizing the density difference between the bottom and top of the chimney to create natural convection, also known as draft) is used to solve the pressure drop problem of the packing material, ensuring that the pressure below the packing material in the absorption tower is at atmospheric pressure. Through the absorption tower, hydrogen sulfide components in the gas discharged after the amine tank breaks through the positive pressure liquid seal can be further absorbed, completely solving the problem of tail gas emissions from the amine tank.

[0026] (4) The absorption tower is a cut-out device. After the packing has been running for a certain period of time, the reabsorption tower can be cut out, the packing can be cleaned and then reinstalled.

[0027] (5) To prevent the gas phase of the amine liquid tank from short-circuiting, a U-shaped bend is set as a liquid seal in the gravity flow process of the amine liquid, and the height of the liquid seal is greater than the height of the positive pressure water seal of the water seal tank. Attached Figure Description

[0028] Figure 1 This is a common pressure control flowchart for amine tanks in existing technologies;

[0029] Figure 2-1 , Figure 2-2 , Figure 2-3 This is a schematic diagram of an existing dual-function water seal tank.

[0030] Figure 3 One specific embodiment of the amine liquid tank liquid sealing system of the present invention;

[0031] Figure 4 The second specific embodiment of the amine liquid tank liquid sealing system of the present invention;

[0032] In the diagram, 1 is the amine liquid tank, 2 is the amine liquid seal tank, and 3 is the absorption tower. Detailed Implementation

[0033] The present invention will be further illustrated by the following embodiments, but the following embodiments do not in any way limit the scope of the present invention.

[0034] The various devices and pipelines in this invention are connected by flanges, which facilitates disassembly, assembly, and maintenance.

[0035] The pipelines between the amine liquid tank and the amine liquid seal tank, and between the amine liquid seal tank and the absorption tower, are typically DN150 and PN2.0.

[0036] The amine liquid seal tank has a lean liquid pipeline. The liquid level between the bottom of the amine liquid seal tank and the absorption tower is DN40 or PN2.0.

[0037] The bottom of the absorption tower has a diameter of DN800 and PN2.0, and a height of about 1500mm. It is equipped with removable packing material with a height of about 500mm.

[0038] The upper chimney of the absorption tower is DN200, PN2.0, and about 5000mm high.

[0039] Since hydrogen sulfide is present in the medium, the materials used for the above-mentioned equipment and pipelines are preferably carbon steel or stainless steel that are resistant to hydrogen sulfide corrosion.

[0040] Example 1: Amine Liquid Tank Liquid Sealing System

[0041] like Figure 3 As shown, the amine liquid tank liquid sealing system includes an amine liquid tank 1 and an amine liquid sealing tank 2 (the structure of the amine liquid sealing tank 2 is as follows). Figure 2-1 , Figure 2-2 , Figure 2-3 The dual-function water seal tank is shown in the diagram; the bottom of the amine liquid seal tank 2 is higher than the top of the amine liquid tank 1; the top of the amine liquid tank 1 is connected to the top of the amine liquid seal tank 2; the amine liquid seal tank 2 contains lean amine liquid; both amine liquid tank 1 and amine liquid seal tank 2 contain lean amine liquid (an aqueous solution of methyldiethanolamine, with a concentration of 25% to 40%), and the lean amine liquid is within this concentration range to meet the desulfurization effect. The amine liquid tank 1 is equipped with a level gauge (not shown in the diagram), which has an upper lead-out point and a lower lead-out point. The bottom of the amine liquid seal tank 2 is connected back to the amine liquid tank 1 via pipeline P1, and the section of pipeline P1 adjacent to the amine liquid tank is U-shaped; the position of P1 connecting to the amine liquid tank 1 is 10 to 20 cm higher than the upper lead-out point of the level gauge. The height difference between the lowest and highest points of the U-shaped position is the liquid seal height, which is greater than the positive pressure liquid seal height. Figure 2-1 (The positive pressure liquid seal height is shown in the figure).

[0042] Example 2: Amine Liquid Tank Liquid Sealing System

[0043] like Figure 4 The amine liquid tank liquid sealing system shown includes amine liquid tank 1 and amine liquid liquid sealing tank 2 (the structure of amine liquid liquid sealing tank 2 is as follows). Figure 2-1 , Figure 2-2 , Figure 2-3The diagram shows a dual-function water seal tank and a waste gas absorption tower 3; the bottom of the amine liquid seal tank 2 is higher than the top of the amine liquid tank 1; the top of the amine liquid tank 1 is connected to the top of the amine liquid seal tank 2; the amine liquid seal tank 2 contains lean amine liquid; both the amine liquid tank 1 and the amine liquid seal tank 2 contain lean amine liquid (an aqueous solution of methyl diethanolamine, with a concentration of 25% to 40%), and the lean amine liquid is within this concentration range to meet the desulfurization effect. The amine liquid tank 1 is equipped with a level gauge (not shown in the diagram), which has an upper lead-out point and a lower lead-out point. The bottom of the waste gas absorption tower 3 is connected back to the amine liquid tank 1 via pipeline P2, and the section of pipeline P2 adjacent to the amine liquid tank 1 is U-shaped; the position of P2 connecting to the amine liquid tank 1 is 10 to 20 cm higher than the upper lead-out point of the level gauge. The height difference between the lowest and highest points of the U-shaped position is the liquid seal height, which is greater than the positive pressure liquid seal height. Figure 2-1 (The positive pressure liquid seal height is shown in the figure).

[0044] The waste gas absorption tower 3 is equipped with removable packing material, which is located in the middle of the waste gas absorption tower 3; the bottom of the amine liquid sealing tank 2 is connected to the upper part of the waste gas absorption tower 3; the bottom of the waste gas absorption tower 3 is connected to the amine liquid tank 1.

[0045] The exhaust gas outlet of the amine liquid sealing tank 2 is divided into two streams; one stream is controlled by valve d and connected to the upper part of the exhaust gas absorption tower 3, and the other stream is controlled by valve c and connected to the lower part of the exhaust gas absorption tower. Under normal operating conditions, valve c is opened and valve d is closed; under operating conditions when the exhaust gas absorption tower is shut off for packing replacement, valve d is opened and valve c is closed; the exhaust gas is discharged from the upper part of the absorption tower 3.

[0046] Example 3: Method for controlling pressure in an amine liquid tank liquid seal system

[0047] The method for controlling pressure using the amine liquid tank liquid seal system of Example 1 includes: introducing the exhaust gas from the top of amine liquid tank 1 into amine liquid seal tank 2, and changing the liquid seal medium from water to lean amine liquid to maintain stable operation of amine liquid tank 1 and prevent equipment damage caused by overpressure or negative pressure. The amine liquid at the bottom of amine liquid seal tank 2 flows by gravity through valve b (no additional pump is required, it flows downwards by gravity) to amine liquid tank 1, and the gas phase is discharged to the atmosphere through valve d, without affecting the normal operation of the water seal tank.

[0048] Example 4: Method for controlling pressure in an amine liquid tank liquid seal system

[0049] The method for controlling pressure using the amine liquid tank liquid seal system of Example 2 includes: introducing the exhaust gas from the top of amine liquid tank 1 into amine liquid seal tank 2, and changing the liquid seal medium from water to lean amine liquid to maintain stable operation of amine liquid tank 1 and prevent equipment damage caused by overpressure or negative pressure. The amine liquid at the bottom of amine liquid seal tank 2 flows by gravity through valve a to the upper part of the absorption tower, and then flows by gravity from the bottom of the absorption tower through valve e back to amine liquid tank 1.

[0050] This invention provides a solution to the long-standing problem of waste gas treatment in amine liquid tanks. By changing the liquid sealing medium from water to lean amine liquid, the problem of amine liquid not being able to be recovered after the water-sealed tank is converted to lean amine liquid is solved. In addition, the addition of a waste gas re-absorption tower in the process flow can effectively reduce hydrogen sulfide emissions from the waste gas and solve on-site environmental protection problems.

Claims

1. An amine liquid tank liquid sealing system, comprising an amine liquid tank and an amine liquid liquid sealing tank, characterized in that, The bottom of the amine liquid sealing tank is higher than the top of the amine liquid tank; The top of the amine liquid tank is connected to the top of the amine liquid seal tank; The bottom of the amine liquid sealing tank is connected to the amine liquid tank.

2. The amine liquid tank liquid sealing system according to claim 1, characterized in that, The bottom of the amine liquid sealing tank is connected to the amine liquid tank via pipeline P1, and the section of pipeline P1 adjacent to the amine liquid tank is U-shaped.

3. The amine liquid tank liquid sealing system according to claim 1 or 2, characterized in that, The pressure control device for the amine liquid tank also includes an absorption tower; The bottom of the amine liquid sealing tank, the absorption tower, and the amine liquid tank are connected in sequence.

4. The amine liquid tank liquid sealing system according to any one of claims 1-3, characterized in that, The absorption tower is filled with packing material; preferably, the packing material is located in the middle of the absorption tower. The bottom of the amine liquid sealing tank is connected to the upper part of the absorption tower.

5. The amine liquid tank liquid sealing system according to claim 4, characterized in that, The exhaust gas outlet of the amine liquid sealing tank is connected to the lower part of the absorption tower; Preferably, the exhaust gas outlet of the amine liquid sealing tank is divided into two streams; one stream is connected to the upper part of the absorption tower, and the other stream is connected to the lower part of the absorption tower.

6. The amine liquid tank liquid sealing system according to any one of claims 3-5, characterized in that, The bottom of the absorption tower is connected to an amine liquid tank.

7. The amine liquid tank liquid sealing system according to claim 6, characterized in that, The bottom of the absorption tower is connected to the amine liquid tank via pipeline P2, and the section of pipeline P2 adjacent to the amine liquid tank is U-shaped.

8. The amine liquid tank liquid sealing system according to any one of claims 1-7, characterized in that, The amine liquid seal tank has a positive pressure liquid seal height; The height difference between the lowest and highest points of the U-shape is the liquid seal height; The liquid seal height is greater than the positive pressure liquid seal height.

Images