Nitrogen and oxygen containing tail gas treatment device

Abstract

The utility model relates to the technical field of tail gas treatment in chemical production, in particular to a nitrogen and oxygen-containing tail gas treatment device which comprises an absorption tower, a water scrubber, a water tank, a liquid separation tank and an incinerator, the absorption tower is connected with a methanol pipeline and a tail gas pipeline, the water scrubber is connected with the absorption tower and the water tank, a tower kettle of the water scrubber is connected to a wastewater system, and the tower top of the water scrubber is connected with the liquid separation tank. The device has the following beneficial effects that the emission standard is reached, the process operation is simple, the switching is convenient, on one hand, residual propylene and methanol in the tail gas can be recovered, and the material loss is reduced; on the other hand, by-product low-temperature process condensate of the device can be used as washing liquid of the washing tower, energy is fully utilized, and waste water is reduced.

Description

Technical Field

[0001] This utility model relates to the field of tail gas treatment technology in chemical production, and in particular to a nitrogen- and oxygen-containing tail gas treatment device. Background Technology

[0002] Propylene oxide is an important basic organic chemical raw material, ranking third in production volume among propylene derivatives after polypropylene and acrylonitrile. Currently, the main industrial production processes for propylene oxide are the chlorohydrin process and the co-oxidation process. However, the chlorohydrin process consumes large amounts of chlorine, lime, and water resources, suffers from severe equipment corrosion, generates large quantities of wastewater and waste residue, causing serious environmental pollution, and has low raw material utilization. Therefore, this method is gradually being phased out by various countries. The co-oxidation process, based on the type of co-product, is further divided into the PO / SM (styrene) process, the PO / TBA (tert-butanol) process, and the PO / MTBE (methyl tert-butyl ether) process. The disadvantages of the co-oxidation process are large co-product yields, complex production processes, and high investment costs.

[0003] The direct hydrogen peroxide oxidation (HPPO) process for propylene oxide is an effective method for producing propylene oxide. This process boasts high hydrogen peroxide conversion, high propylene oxide selectivity, and low byproduct production, representing a future direction for propylene oxide production. The exhaust gas generated during propylene oxide production contains nitrogen oxides, propylene, methanol, and other gases. Direct emission of these gases into the atmosphere would pollute the environment; therefore, pretreatment is necessary before emission.

[0004] To treat the tail gas from propylene oxide production, researchers have developed various treatment processes and procedures, such as:

[0005] The invention application with application number 200910187942.4 discloses an energy-saving and emission-reducing process for producing propylene oxide by epoxidizing propylene with hydrogen peroxide. The process uses a circulating solvent to absorb propylene in the tail gas, and the remaining gas phase tail gas is then passed through a water washing tower to obtain a mixture of oxygen and water before being discharged from the system.

[0006] The invention application with application number 201610008220.8 discloses a tail gas treatment device and process for preparing propylene oxide by epoxidation of propylene with hydrogen peroxide. The process mainly includes a tail gas emission device for an epoxidation reactor, a deoxygenation reactor, and a propane separation tower. The process uses methanol as an absorbent to first absorb propylene in the tail gas through a propylene absorption tower, and the remaining non-condensable gases are discharged from the top of the propylene absorption tower.

[0007] However, the exhaust gas treatment processes of the above-mentioned methods are relatively complex, and the exhaust gas they ultimately emit still contains a small amount of organic matter and nitrogen oxides that have not been properly treated, which will still cause pollution to the environment. Utility Model Content

[0008] The purpose of this invention is to provide a nitrogen-containing exhaust gas treatment device that meets emission standards and reduces environmental pollution.

[0009] The above-mentioned technical objective of this utility model is achieved through the following technical solution: a nitrogen-oxygen tail gas treatment device, comprising an absorption tower, a water washing tower, a water tank, a liquid separator, and an incinerator. The absorption tower is connected to a methanol pipeline and a tail gas pipeline. The water washing tower is connected to the absorption tower and the water tank. The bottom of the water washing tower is connected to a wastewater system. The top of the tower is connected to the liquid separator. The bottom of the liquid separator is connected to the wastewater system. The top of the liquid separator is connected to the incinerator.

[0010] Preferably, the absorption tower is also connected to a nitrogen pipeline, and a first analyzer for monitoring oxygen content is installed on the pipeline between the absorption tower and the water washing tower.

[0011] Preferably, the water tank is connected to both demineralized water and process condensate at its inlet, and the water inlet of the water tank is switched between the demineralized water and process condensate using a valve.

[0012] Preferably, a second check valve is installed on the pipeline between the water tank and the demineralized water.

[0013] As a preferred option, the top of the water washing tower is also connected to a flare incineration system.

[0014] As a preferred option, a second analyzer for monitoring the content of combustible gases is also installed at the top outlet of the water washing tower.

[0015] Preferably, the separator is equipped with a fourth pressure gauge that can trigger an alarm when the pressure exceeds a preset range.

[0016] Preferably, the separator is equipped with a third level gauge, which has low and high level alarms, and a third shut-off valve is installed on the pipeline at the bottom of the separator.

[0017] Preferably, a third pressure regulating valve is installed on the pipeline from the separator to the incinerator.

[0018] Preferably, a nitrogen purging line is connected to the pipeline between the separator and the incinerator.

[0019] In summary, this utility model has the following beneficial effects:

[0020] This device uses solvent absorption and water washing to recover propylene and methanol from the tail gas. The remaining nitrogen- and oxygen-containing tail gas is discharged to the incinerator for incineration treatment, achieving emission standards. The process is simple to operate and easy to switch. On the one hand, it can recover residual propylene and methanol in the tail gas, reducing material loss. On the other hand, it can utilize the low-temperature process condensate by-product of the device as the washing liquid in the water washing tower, making full use of energy and reducing wastewater generation. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the connection relationships within this device.

[0022] In the diagram, 1. Absorption tower; 2. Methanol pipeline; 3. Nitrogen pipeline; 4. Tail gas pipeline; 5. First pressure gauge; 6. First analyzer; 7. Water washing tower; 8. Second pressure gauge; 9. Second analyzer; 10. First flow meter; 11. First check valve; 12. First manual valve; 13. Tower bottom pump; 14. Cooler; 15. First shut-off valve; 16. Second check valve; 17. First level gauge; 18. Third pressure gauge; 19. Water tank; 20. Second level gauge; 21. Separator; 22. Fourth pressure gauge; 23. Third level gauge; 24. Second manual valve; 25. Third pressure regulating valve; 26. Fifth pressure gauge; 27. Third check valve; 28. Second shut-off valve; 29. ​​Third shut-off valve; 30. Incinerator; 31. Water washing pump; 32. Regulating valve. Detailed Implementation

[0023] The present invention will be further described in detail below with reference to the accompanying drawings.

[0024] This specific embodiment is merely an explanation of the present utility model and is not intended to limit the present utility model. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but as long as they are within the scope of the claims of the present utility model, they are protected by patent law.

[0025] Example:

[0026] like Figure 1 As shown, it mainly includes an absorption tower 1, a water washing tower 7, a water tank 19, a separating tank 21, and an incinerator 30.

[0027] The upper, middle, and lower parts of the side of the absorption tower 1 are connected sequentially to a methanol pipeline 2, a nitrogen pipeline 3, and a tail gas pipeline 4. A first pressure gauge is installed at the top of the absorption tower 1. The material at the top of the absorption tower 1 is connected to a water washing tower 7, and a first analyzer 6 is installed on the pipeline connecting the two.

[0028] Water tank 19 is externally connected to demineralized water and process condensate, a byproduct of the propylene oxide unit. A first hand valve 12 is installed on the pipeline used to transport the process condensate, and a second hand valve 24 and a second check valve 16 are installed on the pipeline used to transport the demineralized water. Water tank 19 is also connected to a second level gauge 20 and a third pressure gauge 18. The outlet of water tank 19 is connected to the upper part of absorption tower 1, and a water washing pump 31 and a first flow meter 10 are connected between the two.

[0029] The upper and lower parts of the water washing tower 7 are connected to the water tank 19 and the absorption tower 1, respectively, and a first level gauge 17 is installed on the water washing tower 7. The bottom of the water washing tower 7 is connected to the wastewater system via the tower bottom pump 13. A branch pipeline returning to the water washing tower 7 is connected to the pipeline from the water washing tower 7 to the wastewater system, and a cooler 14 is connected to this pipeline.

[0030] After the top pipeline of the water washing tower 7 is connected to the second pressure gauge 8 and the second analyzer 9, one path is connected to the liquid separator 21 via the first check valve 11, and the other path is connected to the flare incineration system via the first shut-off valve 15.

[0031] The separator 21 is connected to a fourth pressure gauge 22 and a third level gauge 23. An emergency discharge line is installed at the bottom of the separator 21, which connects to the wastewater system and is equipped with a third shut-off valve 29 and a regulating valve 32 in parallel. The top of the separator 21 is piped to the incinerator 30. A third pressure regulating valve 25 and a fifth pressure gauge 26 are installed on the pipeline between the top of the separator 21 and the incinerator 30. A nitrogen purging line is installed between the separator 21 and the incinerator 30, and a third check valve 27 and a second shut-off valve 28 are installed on the nitrogen purging line.

[0032] The basic working principle of this device is as follows:

[0033] Methanol and tail gas enter absorption tower 1 through methanol pipeline 2 and tail gas pipeline 4, respectively, where methanol absorbs propylene from the tail gas. The top gas phase of the tail gas from absorption tower 1 then enters water washing tower 7 for water washing to absorb methanol and other organic components from the tail gas. Demineralized water or process condensate enters water tank 19 through a valve, and the water in water tank 19 is then pumped into water washing tower 7 by water washing pump 31 to absorb organic components from the tail gas. The top gas phase of the tail gas containing nitrogen and oxygen from water washing tower 7 enters separating tank 21, where gas-liquid separation is performed, and the separated water is discharged from the bottom of the tank to the wastewater system. The top gas phase of separating tank 21 enters incinerator 30 for incineration. The liquid phase from the bottom of water washing tower 7 is sent to the wastewater system by bottom pump 13.

[0034] The working principle of the above-mentioned nitrogen- and oxygen-containing exhaust gas treatment method is as follows:

[0035] Methanol and the tail gas from the reaction enter absorber 1 through methanol pipeline 2 and tail gas pipeline 4, respectively, while nitrogen enters absorber 1 through nitrogen pipeline 3. Absorber 1 uses methanol as a solvent to absorb propylene from the tail gas. The methanol solution after propylene absorption is then discharged from the bottom of absorber 1 into other units for use. A first pressure gauge is used to monitor the pressure of absorber 1, which is controlled between 1.6 and 1.8 MPa. A first analyzer 6 is used to monitor the oxygen content in the tail gas. When the oxygen content is high, the nitrogen flow rate in nitrogen pipeline 3 is adjusted to control the oxygen content in the system and prevent excessive oxygen levels from forming an explosive mixture.

[0036] After the tail gas from the top of the absorption tower 1 enters the water washing tower 7, it is washed with demineralized water or process condensate. The demineralized water or process condensate is first delivered to the water tank 19, and then delivered to the water washing tower 7 by the water washing pump 31. The water washing flow rate is controlled by the first flow meter 10. During normal production, the first hand valve 12 is opened to use the process condensate as makeup water for the water washing tower 7; when the process condensate is interrupted, the second hand valve 24 is opened, the first hand valve 12 is closed, and the demineralized water is switched to make up the water for the water tank 19.

[0037] After washing and absorption in the water washing tower 7, the liquid phase containing methanol and other organic matter is transported to the wastewater system via the tower bottom pump 13. The nitrogen- and oxygen-containing tail gas from the top of the water washing tower 7 is transported to the separator 21. The first check valve 11 between the top of the water washing tower 7 and the separator 21 prevents material backflow. The fourth pressure gauge 22 and the third level gauge 23 on the separator 21 are used to monitor the pressure and level of the separator 21. The level of the separator 21 is controlled by the regulating valve 32 to maintain a stable level. When the level detected by the third level gauge 23 is higher than 80%, the third shut-off valve 29 is opened in an emergency, and the liquid is discharged to the wastewater system through the emergency discharge pipeline.

[0038] The exhaust gas from the top of the separator 21 is transported to the incinerator 30 for combustion via pipeline. The third pressure regulating valve 25 between the top of the separator 21 and the incinerator 30 stabilizes the pressure to the incinerator 30 after the valve is closed to <50 kPa. When the exhaust gas is not in use, the second shut-off valve 28 is opened, and the pipeline between the separator 21 and the incinerator 30 is purged through the nitrogen purging line to prevent the accumulation of combustible exhaust gas in the pipeline and avoid potential risks.

[0039] When the incinerator 30 malfunctions or experiences an abnormal operating condition, the first shut-off valve 15 is opened to send the exhaust gas to the flare incineration system for combustion.

Claims

1. A nitrogen- and oxygen-containing exhaust gas treatment device, characterized in that, It includes an absorption tower (1), a water washing tower (7), a water tank (19), a liquid separator (21), and an incinerator (30). The absorption tower (1) is connected to a methanol pipeline (2) and a tail gas pipeline (4). The water washing tower (7) is connected to the absorption tower (1) and the water tank (19). The bottom of the water washing tower (7) is connected to the wastewater system, the top of the tower is connected to the liquid separator (21), the bottom of the liquid separator (21) is connected to the wastewater system, and the top of the tank is connected to the incinerator (30).

2. The nitrogen-oxygen-containing tail gas treatment device according to claim 1, characterized in that, The absorption tower (1) is also connected to a nitrogen pipeline (3), and a first analyzer (6) for monitoring oxygen content is installed on the pipeline between the absorption tower (1) and the water washing tower (7).

3. The nitrogen-oxygen-containing tail gas treatment device according to claim 1, characterized in that, The inlet of the water tank (19) is connected to demineralized water and process condensate, and the water inlet of the water tank (19) is switched between demineralized water and process condensate by a valve.

4. The nitrogen-oxygen-containing tail gas treatment device according to claim 3, characterized in that, A second check valve (16) is installed on the pipeline between the water tank (19) and the demineralized water.

5. The nitrogen-oxygen-containing tail gas treatment device according to claim 1, characterized in that, The top of the water washing tower (7) is also connected to the flare incineration system.

6. The nitrogen-oxygen-containing tail gas treatment device according to claim 1, characterized in that, A second analyzer (9) for monitoring the content of combustible gas is also installed at the top outlet of the water washing tower (7).

7. The nitrogen-oxygen-containing tail gas treatment device according to claim 1, characterized in that, The separator (21) is equipped with a fourth pressure gauge (22) that can alarm when the pressure exceeds the preset range.

8. The nitrogen-oxygen-containing tail gas treatment device according to claim 1, characterized in that, The separator (21) is equipped with a third level gauge (23), which is equipped with low level alarm and high level alarm. The bottom pipeline of the separator (21) is equipped with a third shut-off valve (29).

9. The nitrogen-oxygen-containing tail gas treatment device according to claim 1, characterized in that, A third pressure regulating valve (25) is installed on the pipeline from the separator (21) to the incinerator (30).

10. A nitrogen-oxygen-containing tail gas treatment device according to claim 1, characterized in that, A nitrogen purging line is connected between the separator (21) and the incinerator (30).

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