Recovery system of DMT-containing methanol tail gas

Abstract

The utility model discloses a DMT-containing methanol tail gas recovery system which comprises a tail gas absorption tank and a methanol circulation pipeline, a first ejector and a second ejector are installed on the top of the tail gas absorption tank, the first ejector is connected with a first tail gas pipeline, and the second ejector is connected with a second tail gas pipeline. One end of the methanol circulating pipeline is connected to the bottom of the tail gas absorption tank, the other end of the methanol circulating pipeline is connected to the first ejector and the second ejector in a branched mode, the top of the tail gas absorption tank is connected with a methanol supplementing pipeline, and the methanol circulating pipeline is connected with a methanol output pipeline. Methanol liquid is used as driving liquid to circularly enter and exit the tail gas absorption tank, tail gas can be continuously brought in through circulation of the driving liquid, the tail gas is effectively recycled in the tail gas absorption tank, the tail gas recycling problem is solved, liquid level control and DMT content control can be achieved in the tail gas absorption tank, and the tail gas recycling efficiency is improved. And redundant DMT can orderly flow to a methanol output pipeline along with the methanol liquid to be discharged.

Description

Technical Field

[0001] This utility model relates to the field of exhaust gas treatment technology, and more specifically, to a recovery system for exhaust gas containing DMT methanol. Background Technology

[0002] The production of polyester chips using a chemical recycling method involves a series of steps, including crushing waste polyester fabric, alcoholysis of the crushed fabric to generate BHET, transesterification of BHET to obtain crude DMT (dimethyl terephthalate), crude DMT crystallization, multi-stage centrifugation, DMT distillation, DMT transesterification reaction, polymerization reaction, and pelletizing. In the multi-stage centrifugation step, the DMT powder separated by the last centrifuge enters a DMT remelting tank. The remelting tank needs to dissolve the DMT powder, and the temperature must be maintained at 150-165℃. However, the DMT powder contains 10% to 15% methanol. At high temperatures, the methanol rapidly volatilizes, carrying some DMT vapor and escaping to form tail gas. Both the methanol and DMT components in the tail gas have recycling value. However, the DMT in the tail gas is prone to precipitation during the recovery process due to cooling, which can cause pipeline blockages. How to recover the DMT-containing methanol tail gas is a difficult problem encountered in production and urgently needs to be solved. This case arises from this need. Utility Model Content

[0003] The purpose of this invention is to overcome the shortcomings of the prior art and provide a recovery system for methanol tail gas containing DMT. This invention uses methanol liquid as the driving liquid to circulate in and out of the tail gas absorption tank. The circulation of the driving liquid can continuously bring in the tail gas, so that the tail gas can be effectively recovered in the tail gas absorption tank, thereby solving the problem of tail gas recovery. The tail gas absorption tank can realize liquid level control and DMT content control. Excess DMT can flow orderly with the methanol liquid to the methanol output pipeline for external discharge treatment.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] A system for recovering methanol tail gas containing DMT includes a tail gas absorption tank and a methanol circulation pipeline. A first injector and a second injector are installed on the top of the tail gas absorption tank. The first injector is connected to a first tail gas pipeline, and the second injector is connected to a second tail gas pipeline. One end of the methanol circulation pipeline is connected to the bottom of the tail gas absorption tank, and the other end of the methanol circulation pipeline branches and connects to the first injector and the second injector. A methanol replenishment pipeline is connected to the top of the tail gas absorption tank, and a methanol output pipeline is connected to the methanol circulation pipeline.

[0006] Furthermore, two discharge pumps are installed on the methanol circulation pipeline, and the two discharge pumps are connected in parallel. A filter is installed at the input end of each discharge pump.

[0007] Furthermore, a first control valve is installed on the methanol replenishment pipeline, and a DMT content detector is installed on the tail gas absorption tank. The first control valve and the DMT content detector are linked for control.

[0008] Furthermore, the methanol output pipeline is connected to the pipeline after the output end of the discharge pump, the methanol output pipeline is equipped with a second control valve, and the tail gas absorption tank is equipped with a level gauge. The second control valve and the level gauge are linked for control.

[0009] Furthermore, the first injector includes a gas chamber, a throat, and a tail pipe. The two ends of the throat are connected to the gas chamber and the tail pipe, respectively. The gas chamber, throat, and tail pipe are interconnected. A liquid inlet pipe is inserted into the top of the gas chamber, and a tail gas inlet is connected to the side of the gas chamber. The first injector and the second injector have the same structure. The liquid inlet pipes of both the first injector and the second injector are connected to the methanol circulation pipeline. The tail gas inlet of the first injector is connected to the first tail gas pipeline, and the tail gas inlet of the second injector is connected to the second tail gas pipeline.

[0010] Furthermore, the liquid inlet pipe is installed vertically in the air chamber, with a portion of the liquid inlet pipe inserted into the air chamber. There is a gap between the outer wall of the liquid inlet pipe and the inner wall of the air chamber. The top of the liquid inlet pipe is provided with an inlet, and the bottom of the liquid inlet pipe is provided with a nozzle. The diameter of the nozzle is smaller than the diameter of the inlet.

[0011] Furthermore, the top of the exhaust gas absorption tank is connected to a volatile gas treatment pipeline, and a first condenser and a second condenser are installed in series on the volatile gas treatment pipeline. The outlet ends of the first condenser and the second condenser are both connected back to the exhaust gas absorption tank.

[0012] The beneficial effects of this utility model are:

[0013] 1. This utility model has a reasonable design layout. Methanol liquid is used as the driving liquid to circulate in and out of the tail gas absorption tank. The circulation of the driving liquid can continuously bring in the tail gas, so that the tail gas can be effectively recovered in the tail gas absorption tank to solve the problem of tail gas recovery. The tail gas absorption tank can realize liquid level control and DMT content control. Excess DMT can flow orderly with the methanol liquid to the methanol output pipeline for external discharge treatment.

[0014] 2. The injector used in this utility model has the advantages of good gas entrainment effect and small size. This utility model has the advantages of small footprint, low equipment investment cost and good practical effect. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the connection principle of a recovery system for methanol tail gas containing DMT in this embodiment;

[0016] Figure 2This is a schematic diagram of the structure of the first injector in this embodiment.

[0017] Reference numerals in the attached diagram: 1. Tail gas absorption tank; 11. DMT content detector; 12. Level gauge; 2. First injector; 21. Gas chamber; 22. Throat pipe; 23. Tail pipe; 24. Liquid inlet pipe; 241. Liquid inlet; 242. Nozzle; 25. Tail gas inlet; 3. Second injector; 4. First tail gas pipeline; 5. Second tail gas pipeline; 6. Methanol circulation pipeline; 61. Discharge pump; 62. Filter; 7. Methanol replenishment pipeline; 71. First control valve; 8. Volatile gas treatment pipeline; 81. First condenser; 82. Second condenser; 9. Methanol output pipeline; 91. Second control valve. Detailed Implementation

[0018] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present utility model.

[0019] like Figure 1 and Figure 2The diagram illustrates a DMT-containing methanol tail gas recovery system. This system includes a tail gas absorption tank 1 and a methanol circulation pipeline 6. The tail gas absorption tank 1 is used to recover DMT-containing methanol tail gas, primarily from the production of DMT remelting tanks, and secondarily from the DMT finished product storage tanks. Therefore, this invention installs a first injector 2 and a second injector 3 on the top of the tail gas absorption tank 1. The first injector 2 and the second injector 3 correspond to the two tail gas sources, respectively, and continuously introduce tail gas for recovery. The first injector 2 is connected to a first tail gas pipeline 4, which corresponds to... The first tail gas line 4 receives the tail gas output from the DMT finished product storage tank. The second injector 3 is connected to the second tail gas line 5, which corresponds to the top gas outlet of the DMT remelting tank. The second tail gas line 5 receives the tail gas generated during the production of the DMT remelting tank. In this invention, the top of the tail gas absorption tank 1 is connected to a methanol replenishment line 7, which replenishes the tail gas absorption tank 1 with methanol liquid. This invention utilizes the characteristic that DMT is slightly soluble in methanol, and dissolves the DMT particles in the tail gas by replenishing a large amount of clean methanol liquid into the tail gas absorption tank 1. Since DMT needs to be kept at a low content to ensure its dissolution... Therefore, clean methanol liquid needs to be continuously supplied through methanol replenishment line 7. In this invention, the exhaust gas is carried in through the first injector 2 and the second injector 3. The activation of the first injector 2 and the second injector 3 requires a driving fluid. In this invention, the methanol liquid in the exhaust gas absorption tank 1 is used as the driving fluid for the first injector 2 and the second injector 3. Therefore, this invention installs a methanol circulation line 6 in the exhaust gas absorption tank 1. One end of the methanol circulation line 6 is connected to the bottom of the exhaust gas absorption tank 1, and the other end of the methanol circulation line 6 is branched and connected to the first injector 2 and the second injector 3. The methanol circulation line 6 circulates the methanol liquid in the exhaust gas absorption tank 1 and simultaneously supplies it to the first injector 2 and the second injector 3. Injector 3 is used as a driving fluid. Due to the continuous replenishment of tail gas recovery and clean methanol liquid in tail gas absorption tank 1, the liquid level in tail gas absorption tank 1 will gradually rise. In order to balance and stabilize the liquid level in tail gas absorption tank 1, this invention connects a methanol output pipeline 9 to the methanol circulation pipeline 6. The methanol output pipeline 9 can carry out excess methanol liquid to subsequent equipment while circulating methanol liquid. The methanol liquid output through the methanol output pipeline 9 contains DMT components dissolved in it. This methanol liquid needs to be output to the DMT methanol dilution tank equipment for separate recovery of methanol and DMT. The recovered clean methanol can be used in methanol replenishment pipeline 7. This invention can solve the problem of DMT methanol tail gas recovery.

[0020] like Figure 1As shown, two discharge pumps 61 are installed on the methanol circulation pipeline 6. The methanol liquid in the tail gas absorption tank 1 is circulated by the discharge pumps 61. The two discharge pumps 61 are connected in parallel and are not turned on at the same time. They are set to a standby and start working mode, which can be used without stopping the machine. A filter 62 is installed at the input end of the discharge pump 61. The filter 62 is a basket filter, which can filter out large pieces of insoluble DMT and other impurities. After the filter 62 of one discharge pump 61 has filtered out a lot of impurities, the other discharge pump 61 is switched to use to achieve maintenance and cleaning operations without stopping the machine.

[0021] like Figure 1 As shown, a first control valve 71 is installed on the methanol replenishment line 7, and a DMT content detector 11 is installed on the tail gas absorption tank 1. The first control valve 71 and the DMT content detector 11 are linked for control. The DMT content detector 11 can detect the DMT content in the methanol liquid in the tail gas absorption tank 1. If fresh methanol is not replenished, the DMT content in the methanol liquid in the tail gas absorption tank 1 will gradually increase as the tail gas continues to enter and be recovered. This will affect the solubility of DMT, causing the generation and increase of large pieces of insoluble DMT. Therefore, it is necessary to monitor the DMT content in the methanol liquid in the tail gas absorption tank 1. When the DMT content detector 11 detects that the DMT content in the methanol liquid is close to the critical value, it will promptly open the first control valve 71 and then replenish fresh methanol liquid through the methanol replenishment line 7, so that the DMT content in the methanol liquid in the tail gas absorption tank 1 remains at a low level.

[0022] As a recovery system, it continuously recovers exhaust gas, replenishes fresh methanol liquid, and also requires methanol liquid containing DMT to be output. This ensures both subsequent separation and recovery operations and maintains a stable liquid level in exhaust gas absorption tank 1 to prevent tank explosion. Figure 1 As shown, the methanol output pipeline 9 is connected to the pipeline after the output end of the discharge pump 61. When the methanol output pipeline 9 is opened, a portion of the methanol liquid pumped by the discharge pump 61 is output from the methanol output pipeline 9. The methanol output pipeline 9 is equipped with a second control valve 91, and a level gauge 12 is installed on the tail gas absorption tank 1. The second control valve 91 and the level gauge 12 are linked for control. The level gauge 12 controls the highest liquid level in the tail gas absorption tank 1. After the liquid level in the tail gas absorption tank 1 reaches the set value of the level gauge 12, the second control valve 91 on the methanol output pipeline 9 will be opened, and the methanol output pipeline 9 will output methanol liquid containing DMT.

[0023] The first injector 2 and the second injector 3 are the main devices used to introduce exhaust gas into the exhaust gas absorption tank 1, such as... Figure 2As shown, the first injector 2 includes a gas chamber 21, a throat 22, and a tail pipe 23. The two ends of the throat 22 are connected to the gas chamber 21 and the tail pipe 23, respectively. The gas chamber 21, the throat 22, and the tail pipe 23 are interconnected. The tail pipe 23 is fixedly connected to the top of the exhaust gas absorption tank 1 and is connected to the inner cavity of the exhaust gas absorption tank 1. A liquid inlet pipe 24 is inserted into the top of the gas chamber 21, and an exhaust gas inlet 25 is connected to the side of the gas chamber 21. The first injector 2 and the second injector 3 have the same structure. The liquid inlet pipes 24 of both the first injector 2 and the second injector 3 are connected to the methanol circulation pipeline. 6. Methanol liquid supplied from methanol circulation pipeline 6 enters the injectors through inlet pipe 24. This portion of methanol liquid is used as the driving fluid for gas input. The exhaust gas inlet 25 of the first injector 2 is connected to the first exhaust gas pipeline 4, and the exhaust gas inlet 25 of the second injector 3 is connected to the second exhaust gas pipeline 5. The first exhaust gas pipeline 4 and the second exhaust gas pipeline 5 respectively introduce DMT-containing methanol exhaust gas into the two injectors. Under the action of the driving fluid, the exhaust gas is carried and flushed into the exhaust gas absorption tank 1. The exhaust gas is thus recovered into the methanol liquid in the exhaust gas absorption tank 1. Figure 2 As shown, the inlet pipe 24 is vertically installed in the gas chamber 21, with a portion of the inlet pipe 24 inserted into the gas chamber 21. A gap exists between the outer wall of the inlet pipe 24 and the inner wall of the gas chamber 21, allowing exhaust gas to pass through. The inlet pipe 24 has an inlet port 241 at its top and a nozzle 242 at its top. The methanol liquid is input through the inlet port 241 and output through the nozzle 242. Because the diameter of the nozzle 242 is smaller than the diameter of the inlet port 241, the methanol liquid is pressurized and ejected at the nozzle 242. The temperature of the methanol liquid inside the inlet pipe 24 is lower than that inside the gas chamber 21. The temperature of the exhaust gas flowing between the outer wall of the liquid inlet pipe 24 and the inner wall of the gas chamber 21 is such that when the exhaust gas passes through the space between the outer wall of the liquid inlet pipe 24 and the inner wall of the gas chamber 21, methanol liquefaction and DMT precipitation will occur. In addition, there is a pressurized methanol liquid jet at the nozzle 242 position. The methanol liquid jet will quickly carry the methanol formed by the liquefaction of the exhaust gas and the precipitated DMT into the exhaust gas absorption tank 1. During the above process, a local negative pressure can be formed at the nozzle 242 position to attract the continuous entry of exhaust gas. Therefore, the methanol liquid passing through the liquid inlet pipe 24 is called the driving fluid carried in by the exhaust gas.

[0024] Methanol in exhaust gas absorption tank 1 will evaporate, therefore... Figure 1As shown, the top of the exhaust gas absorption tank 1 is connected to a volatile gas treatment pipeline 8. A first condenser 81 and a second condenser 82 are installed in series on the volatile gas treatment pipeline 8. The outlet ends of the first condenser 81 and the second condenser 82 are both connected back to the exhaust gas absorption tank 1. The first condenser 81 and the second condenser 82 provide a two-stage condensation effect. The condensed methanol liquid flows back to the exhaust gas absorption tank 1 for continued use. The first condenser 81 is a primary condenser, and the cooling medium is 32°C cooling water or 7°C chilled water. The second condenser 82 is a secondary condenser, and the cooling medium is 7°C chilled water. After two stages of condensation, the methanol content at the condenser outlet is significantly reduced.

[0025] In this invention, DMT is slightly soluble in methanol. Methanol is easily volatilized when the temperature is too high, and DMT will crystallize and precipitate when the temperature is too low. Therefore, the tail gas absorption tank 1 needs to maintain the temperature at 55-60℃. The tail gas conveying pipelines of the first tail gas pipeline 4 and the second tail gas pipeline 5 need to be equipped with 6 kg steam jackets for heating to ensure that DMT will not cool and condense and block the pipeline during tail gas conveying.

[0026] The first injector 2 and the second injector 3 of this utility model have the advantages of good performance and small size. The first injector 2 and the second injector 3 can be directly installed on the top of the exhaust gas absorption tank 1. The whole set of equipment of this utility model has the advantages of small footprint, low equipment investment cost and good practical effect.

[0027] The above description is merely a preferred embodiment of this utility model. The protection scope of this utility model is not limited to the above embodiments. All technical solutions falling within the scope of this utility model's concept are protected. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principle of this utility model should also be considered within the protection scope of this utility model.

Claims

1. A system for recovering methanol tail gas containing DMT, characterized in that, The system includes a tail gas absorption tank (1) and a methanol circulation pipeline (6). The tail gas absorption tank (1) is equipped with a first injector (2) and a second injector (3) on its top. The first injector (2) is connected to a first tail gas pipeline (4), and the second injector (3) is connected to a second tail gas pipeline (5). One end of the methanol circulation pipeline (6) is connected to the bottom of the tail gas absorption tank (1), and the other end of the methanol circulation pipeline (6) is forked and connected to the first injector (2) and the second injector (3). The top of the tail gas absorption tank (1) is connected to a methanol replenishment pipeline (7), and the methanol circulation pipeline (6) is connected to a methanol output pipeline (9).

2. The recovery system for DMT-containing methanol tail gas according to claim 1, characterized in that, Two discharge pumps (61) are installed on the methanol circulation pipeline (6), and the two discharge pumps (61) are connected in parallel. A filter (62) is installed at the input end of the discharge pump (61).

3. The recovery system for DMT-containing methanol tail gas according to claim 1, characterized in that, A first control valve (71) is installed on the methanol replenishment pipeline (7), and a DMT content detector (11) is installed on the tail gas absorption tank (1). The first control valve (71) and the DMT content detector (11) are linked for control.

4. The recovery system for DMT-containing methanol tail gas according to claim 2, characterized in that, The methanol output pipeline (9) is connected to the pipeline after the output end of the discharge pump (61). The methanol output pipeline (9) is equipped with a second control valve (91). The tail gas absorption tank (1) is equipped with a level gauge (12). The second control valve (91) and the level gauge (12) are linked for control.

5. The recovery system for DMT-containing methanol tail gas according to claim 1, characterized in that, The first injector (2) includes a gas chamber (21), a throat (22) and a tail pipe (23). The two ends of the throat (22) are connected to the gas chamber (21) and the tail pipe (23) respectively. The gas chamber (21), the throat (22) and the tail pipe (23) are interconnected. A liquid inlet pipe (24) is inserted into the top of the gas chamber (21). A tail gas inlet (25) is connected to the side of the gas chamber (21). The first injector (2) and the second injector (3) have the same structure. The liquid inlet pipes (24) of the first injector (2) and the second injector (3) are both connected to the methanol circulation pipeline (6). The tail gas inlet (25) of the first injector (2) is connected to the first tail gas pipeline (4). The tail gas inlet (25) of the second injector (3) is connected to the second tail gas pipeline (5).

6. The recovery system for DMT-containing methanol tail gas according to claim 5, characterized in that, The liquid inlet pipe (24) is installed vertically in the air chamber (21). Part of the liquid inlet pipe (24) is inserted into the air chamber (21). There is a gap between the outer wall of the liquid inlet pipe (24) and the inner wall of the air chamber (21). The top of the liquid inlet pipe (24) is provided with a liquid inlet (241), and the bottom of the liquid inlet pipe (24) is provided with a nozzle (242). The diameter of the nozzle (242) is smaller than the diameter of the liquid inlet (241).

7. The recovery system for DMT-containing methanol tail gas according to claim 1, characterized in that, The top of the exhaust gas absorption tank (1) is connected to a volatile gas treatment pipeline (8), and a first condenser (81) and a second condenser (82) are connected in series on the volatile gas treatment pipeline (8). The outlet ends of the first condenser (81) and the second condenser (82) are both connected back to the exhaust gas absorption tank (1).

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