A wastewater recovery system for trioxymethylene synthesis wastewater and polymerization wastewater

Abstract

The invention discloses a wastewater recovery system for trioxymethylene synthesis wastewater and polymerization wastewater, comprising: a wastewater recovery tower, wherein the wastewater recovery tower is sequentially provided with a tower top gas phase extraction system, a feed pipe, a first side extraction system, a second side extraction system and a tower bottom recovery system from top to bottom; the wastewater recovery tower can effectively recover recyclable components, and the recombinant components and salts that can cause catalyst deactivation are concentrated and then sent for incineration; through system control of an optimal recovery scheme, formaldehyde, benzene, trioxymethylene and the like can be effectively recovered, and the recombinant components, SS, salts and sulfuric acid can be concentrated in the bottom discharge of the wastewater recovery tower, thereby achieving the purpose of energy saving and emission reduction.

Description

Technical Field

[0001] The invention relates to the technical field of trioxymethylene synthesis wastewater recovery and polymerization wastewater recovery, and in particular to a wastewater recovery system for trioxymethylene synthesis wastewater and polymerization wastewater. Background Art

[0002] With economic development, countries around the world are paying more and more attention to environmental protection. Currently, countries have increasingly higher requirements for waste disposal and discharge in various industries. The formaldehyde index in the wastewater discharge standard generated by the polyformaldehyde-related industry is 5 mg / l. In the existing technology, due to the inability to well separate the triformaldehyde synthesis wastewater, polyformaldehyde, and copolymer synthesis wastewater, the polymerization wastewater is mainly recovered by pressurized distillation to recover formaldehyde, while other components such as triformaldehyde are wasted and incinerated. In addition, pressurized distillation (>0.3MPa) will lead to the disproportionation reaction of formaldehyde, which not only has high energy consumption but also increases carbon emissions, pollutes the environment, and corrodes equipment. Summary of the Invention

[0003] In view of the problems mentioned in the background technology, the purpose of the present invention is to provide a wastewater recovery system for trioxymethylene synthesis wastewater and polymerization wastewater.

[0004] The above technical objectives of the present invention are achieved through the following technical solutions: A wastewater recovery system for trioxymethylene synthesis wastewater and polymerization wastewater, comprising: a wastewater recovery tower, wherein the wastewater recovery tower is provided with a tower top gas phase extraction system, a feed pipe, a first side extraction system, a second side extraction system and a tower bottom recovery system in order from top to bottom;

[0005] The tower top gas phase extraction system is provided with a tower top condensation reflux tank, and the tower top gas phase extraction system controls the tower top temperature to be stable within a specific range by extracting benzene and a small amount of trioxymethylene in the extraction system, and controls a specific reflux ratio to maintain the operation of the distillation tower;

[0006] The first side extraction system can remove the entrained liquid foam in the side extraction gas phase. The gas phase after demisting is extracted by gas phase condensation to extract trioxymethylene and part of the water in the extraction tower. The temperature and the composition distribution in the tower are controlled by the gas phase extraction amount; the temperature of the first side extraction system is maintained above 102°C; the extracted composition trioxymethylene is maintained at about 30%.

[0007] The second side extraction system removes the liquid foam entrained in the side extraction gas phase, and the gas phase after demisting is extracted through gas phase condensation to extract the dilute formaldehyde and a large amount of water in the extraction tower, and the recombined formaldehyde is concentrated at the bottom of the distillation tower;

[0008] The bottom recovery system is provided with a reboiler, which uses 0.4MPa steam as the separation power of the distillation tower. The reboiler is provided with an external discharge device, and the waste water from the bottom of the tower is sent to the incinerator by the external discharge device after cooling.

[0009] Preferably, the top pressure of the wastewater recovery tower is 5 to 25 kPa, and the bottom pressure is 40 to 90 kPa.

[0010] Preferably, the temperature at the top of the wastewater recovery tower is between 65 and 75°C, and the temperature at the bottom of the tower is between 104 and 106°C.

[0011] Preferably, the wastewater recovery tower is provided with 50 layers of sieve plates, and the 50 layers of sieve plates are numbered 1-50 from top to bottom.

[0012] Preferably, the first side extraction system is located on the gas phase side above the 38th sieve plate. It condenses the gas phase after passing through the first side extraction demister to recover trioxymethylene, formaldehyde, methanol, and the like. The first side extraction system's side extraction rate controls the temperature and pressure above the 44th sieve plate at specific values. This allows the TOX content in the upper extraction to be controlled at approximately 30%, while the TOX concentration in the lower extraction is kept below 0.2%.

[0013] Preferably, the second side extraction system is located on the gas phase side above the 48th sieve plate. It condenses the extracted gas phase after passing through the second side extraction demister to recover formaldehyde, while simultaneously extracting water from the system. The extraction ratio is such that the formaldehyde emission concentration after subsequent biochemical treatment of methylal wastewater after reconstitution from the extracted material is below 5 mg / l. This reduces the total amount of water in the bottom wastewater. The extraction rate is based on approximately 90% of the total feed volume from the top extraction, the first side extraction system, and the second side extraction system, and is fine-tuned based on operational data.

[0014] Preferably, the wastewater recovery tower (1) is connected to a defoamer tank via a defoamer pump. The defoamer is added to the feed and the bottom of the wastewater recovery tower in a certain proportion.

[0015] Preferably, a first side extraction demister is provided in the first side extraction system, the first side extraction demister is connected to the first side extraction condenser, and the first side extraction condenser is connected to the extraction reflux tank.

[0016] Preferably, a second side extraction demister is provided in the second side extraction system, the second side extraction demister is connected to the second side extraction condenser, and the second side extraction condenser is connected to the dilute formaldehyde tank.

[0017] In summary, the present invention mainly has the following beneficial effects: a wastewater recovery system for triformaldehyde synthesis wastewater and polymerization wastewater can effectively recover recyclable components, and the recombinant components and salts that can cause catalyst deactivation are concentrated and sent for incineration. Through system control of the optimal recovery scheme, formaldehyde, benzene, triformaldehyde, etc. can be effectively recovered, and the recombinant components, SS, salts, and sulfuric acid can be concentrated in the bottom discharge of the wastewater recovery tower, thereby achieving the purpose of reducing unit consumption, saving energy and reducing emissions. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a system schematic diagram of the present invention.

[0019] Explanation of the accompanying drawings: 1-wastewater recovery tower, 2-tower top gas phase extraction system, 21-tower top condensing reflux tank, 22-water phase extraction pipe, 23-oil phase extraction pipe, 24-reflux pipe, 3-feed pipe, 4-first side extraction system, 41-first side extraction demister, 42-first side extraction condenser, 43-extraction reflux tank, 5-second side extraction system, 51-second side extraction demister, 52-second side extraction condenser, 53-dilute formaldehyde tank, 6-tower bottom recovery system, 61-reboiler, 62-boiling water cooler, 63-incinerator, 7-defoaming pump, 8-defoaming agent tank. DETAILED DESCRIPTION

[0020] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0021] A wastewater recovery system for trioxymethylene synthesis wastewater and polymerization wastewater, comprising: a wastewater recovery tower 1, wherein the wastewater recovery tower 1 is provided with a tower top gas phase extraction system 2, a feed pipe 3, a first side extraction system 4, a second side extraction system 5, and a tower bottom recovery system 6 in order from top to bottom; the tower top pressure of the wastewater recovery tower 1 is 5-25 kPa, and the tower top temperature is 65-75°C; the tower bottom temperature of the wastewater recovery tower is 104-106°C;

[0022] The top gas phase extraction system 2 is provided with a top condensation reflux tank 21. The top gas phase extraction system 2 controls the top temperature of the tower to be stable within a specific range by extracting benzene and a small amount of trioxymethylene in the system, and controls a specific reflux ratio to maintain the operation of the distillation tower. The top condensation reflux tank 21 of the top gas phase extraction system 2 mainly separates benzene and some light components in the feed. The top gas phase extraction system 2 is provided with a water phase extraction pipe 22, an oil phase extraction pipe 23 and a reflux pipe 24. The reflux pipe 24 is mainly used to maintain the composition and temperature distribution in the tower. It is a conventional design of a distillation tower, and the minimum reflux is generally used here. The top condensation reflux tank 21 is integrated, and the liquid level control adopts overflow extraction. The U-shaped tube design and insertion into the liquid prevent the gas phase pressure from affecting the stratification control on both sides. The reflux pump maintains reflux and spraying on the upper tube plate of the condenser.

[0023] The first side extraction system 4 can remove the liquid foam entrained in the side extraction gas phase. The gas phase after demisting is extracted through the first side extraction condenser 42 to extract the trioxymethylene and part of the water and formaldehyde in the tower. The temperature and the composition distribution in the tower are controlled by the gas phase extraction amount.

[0024] The second side extraction system 5 can remove the liquid foam entrained in the side extraction gas phase. The gas phase after demisting is extracted and the dilute formaldehyde and a large amount of water in the extraction tower are extracted through the second side extraction condenser 52, and the recombined formaldehyde is concentrated at the bottom of the distillation tower.

[0025] The bottom recovery system 6 is provided with a reboiler 61, and the reboiler 61 uses 0.4MPa steam as the separation power of the distillation tower. The tower bottom is provided with an external discharge of produced wastewater, which is cooled and then sent to the incinerator 63 by the external discharge device; the tower bottom is partially produced and cooled and then sent to the incinerator 63 to dispose of SS, recombinants and salts that are difficult to recover.

[0026] A set of distillation towers is used to distill and separate the triformaldehyde synthesis tower bottoms, polymerization unit wastewater, and deweighting tower wastewater. The top of the tower is temperature-controlled to extract benzene and a small amount of triformaldehyde from the extraction system, and a specific reflux ratio is controlled to maintain the operation of the distillation tower. The first side extraction system 4 removes droplets from the gas phase extracted during the side extraction. The demisted gas phase is extracted through gas phase condensation to extract the triformaldehyde and some water in the tower. The temperature, pressure, and composition distribution above the 44th tray are controlled by the gas phase extraction volume. The second side extraction system 5 removes droplets from the side extraction gas phase. The demisted gas phase is extracted through gas phase condensation to extract the dilute formaldehyde and a large amount of water in the tower. The recombined components are concentrated at the bottom of the distillation tower. A reboiler 61 is installed at the bottom of the tower as the separation power of the distillation tower, and a certain proportion of the exhaust gas is cooled and sent to the incinerator.

[0027] Furthermore, the first side extraction system 4 condenses the gas phase after passing through the first side extraction demister 41 to recover triformaldehyde, formaldehyde, methanol, etc.; the very small amount of condensate captured by the first side extraction demister 41 enters the gas phase after demisting at the bottom of the tower and enters the first side extraction condenser 42 for condensation, mainly to achieve triformaldehyde recovery, and the recovery rate of triformaldehyde after recovery is greater than 99%.

[0028] Furthermore, the second side extraction system 5 condenses the produced gas phase after passing through the second side extraction demister 51 to recover formaldehyde, and at the same time extracts water from the system. The extraction ratio is such that the formaldehyde emission concentration after subsequent biochemical treatment of the methylal wastewater after recombining the produced material is lower than 5 mg / l, thereby achieving high-proportion concentration of the wastewater and maximum-proportion recovery of formaldehyde.

[0029] Furthermore, the wastewater recovery tower 1 is connected to the defoamer tank 8 via a defoamer pump 7; the defoamer pump 7 adds defoamers to the feed of the wastewater recovery tower 1 and the reactor of the synthesis tower to prevent flooding in the wastewater recovery tower. Under normal circumstances, the ratio of the defoamer added by the defoamer pump 7 to the feed of the wastewater recovery tower 1 is 2 ml / m 3 Defoaming pump 7 in the synthesis tower reactor to add defoamer 1ml / m 3Feeding; slight tower flooding will cause tower pressure fluctuation. When the tower pressure fluctuation is >3KPa / min, increase the defoaming agent dosage by 10%.

[0030] Furthermore, the wastewater recovery tower 1 is provided with 50 layers of sieve plates, which are numbered 1-50 from top to bottom, with the topmost sieve plate being the 1st layer and the bottommost sieve plate being the 50th layer.

[0031] Furthermore, the first side extraction system 4 is located on the gas phase side above the 38th sieve plate; a first side extraction demister 41 is provided within the first side extraction system 4, which is connected to a first side extraction condenser 42, which is connected to an extraction reflux tank 43; the first side extraction demister 41 is primarily used to prevent droplets from being carried over and recombined into the first side extraction system 4. The very small amount of condensate captured by the first side extraction demister 41 enters the demisted gas phase at the bottom of the tower and enters the first side extraction condenser 42 for condensation, primarily to recover trioxymethylene. Since the material in the first side extraction system 4 contains formaldehyde, spray wetting of the upper tube sheet is used to prevent formaldehyde scaling during phase change.

[0032] Furthermore, the second side extraction system 5 is arranged on the gas phase side above the 48th sieve plate, and the second side extraction demister 51 is provided in the second side extraction system 5, and the second side extraction demister 51 is connected to the second side extraction condenser 52, and the second side extraction condenser 52 is connected to the dilute formaldehyde tank 53; the side lines of the first side extraction system 4 and the second side extraction system 5 are all materials without recomposition after distillation in the wastewater recovery tower 1. The removal of the recomposition of the materials will not cause subsequent disposal problems for the methylal unit wastewater when recycled, and the salt will also be separated during the distillation process. The materials recovered after defoaming will not be poisoned by the triformaldehyde synthesis catalyst and the methylal synthesis catalyst due to the salt.

[0033] Furthermore, a reboiler 61 and a wastewater cooler 62 are provided in the bottom recovery system 6. The discharge pipe of the wastewater recovery tower 1 is connected to the reboiler 61 and the boiling water cooler 62 respectively. The discharge pipe of the reboiler 61 is connected to the wastewater recovery tower 1, and the discharge pipe of the boiling water cooler 62 is connected to the incinerator 63; the reboiler 61 is the power of the distillation tower and is of conventional design. A tower bottom pump is used for forced circulation here to prevent corrosion and scaling.

[0034] Example:

[0035] Examples 1, 2, and 3 are for normal production processes; Examples 1, 4, and 7 all achieve recovery of the recombination and triformaldehyde, but relatively high amounts of formaldehyde and water are incinerated, making them uneconomical. Examples 2, 5, and 8 are preferred solutions; Examples 3, 6, and 9 involve excessive recovery, which can cause the recombination to enter the second side extraction system of the recovery tower, leading to subsequent problems with the final recovery. (Because the recombination is not thoroughly separated, the formaldehyde concentration in the methylal wastewater after subsequent biochemical treatment is >5 mg / l.)

[0036] Three compositions of feed:

[0037] Polymerization wastewater: Existing technology mainly recovers formaldehyde through pressurized distillation, in which other components such as trioxymethylene are wasted and incinerated. In addition, high-pressure distillation causes the disproportionation reaction of formaldehyde at high temperature to increase formic acid, which will cause corrosion to equipment; in addition, the energy consumption is much higher than that of low-pressure distillation.

[0038] The bottom of the third trioxymethylene distillation tower is mainly sent to incineration in the existing technology. The bottom of the synthesis tower is about 70% of the formaldehyde, which is mainly sent to incineration in the existing technology due to the recombination.

[0039] The following is a detailed introduction: (In the following examples, SS is suspended solids; COD is the amount of reducing substances that need to be oxidized in the water sample measured by chemical methods;)

[0040] Example 1:

[0041] The tower top pressure is 7-9 kPa, and the tower bottom pressure is 44-46 kPa. The wastewater recovery tower top temperature is 66-68°C, and the tower bottom temperature is 104-106°C. The reflux ratio is 1.0; a defoamer is added to prevent flooding; the bottom discharge of the triformaldehyde synthesis tower is 150 L / h; the bottom discharge of the triformaldehyde deweighting tower is 170 L / h; and the polymerization wastewater is 5000 L / h.

[0042] Temperature control of the top gas phase extraction system 2 of the recovery tower;

[0043] The first side extraction system 4 of the recovery tower controls the temperature distribution in the extraction tower to be stable under the condition of stable reflux, and the concentration of trioxymethylene in the extracted material is controlled at about 30%; the extracted material is sent to the trioxymethylene extraction reflux tank for recovery;

[0044] The second side extraction system 5 of the recovery tower controls the extraction from the bottom of the tower;

[0045] The extraction rate of the tower bottom recovery system 6 was controlled at approximately 12%, and the content of unknown components at the bottom of the tower was observed. Defoamers were added to prevent flooding in the recovery tower. Observe whether the biochemical treatment results of the methylal wastewater met the standards.

[0046] Methylal wastewater after 24 hours

[0047] formaldehyde 623mg / l Methanol 12mg / l Ethylene glycol 89mg / l COD 1121mg / l Unknown COD 322mg / l

[0048] Biochemical wastewater after 48 hours

[0049] formaldehyde 2.55mg / l COD 135mg / l

[0050] formaldehyde 2.61mg / l COD 141mg / l

[0051] formaldehyde 2.45mg / l COD 132mg / l

[0052] Conclusion: Recombinant compounds that influence biochemical treatment can be separated using this treatment unit; the effect of SS on distillation can be controlled by adding a defoamer; cations, sulfuric acid, and fines in the feed are separated and discharged from the bottom of the tower. Side streams passing through a demister prevent liquid foam carryover; triformaldehyde recovery rates exceed 99%, and formaldehyde recovery can exceed 90%. Under controlled conditions for recombinant compounds and the effects of fines within the tower, recovery rates can be appropriately increased.

[0053] Example 2:

[0054] The tower top pressure is 7-9 kPa, and the tower bottom pressure is 44-46 kPa. The wastewater recovery tower top temperature is 66-68°C, and the tower bottom temperature is 104-106°C. The reflux ratio is 1.0; the triformaldehyde synthesis tower bottom discharge is 150 L / h; the triformaldehyde deweighting tower bottom discharge is 170 L / h; and the polymerization wastewater is 5000 L / h.

[0055] Temperature control of the gas phase extraction system 2 at the top of the recovery tower;

[0056] The extraction temperature of the first side extraction system 4 of the recovery tower is controlled, and the concentration of trioxymethylene is controlled at about 30%.

[0057] The second side extraction system 5 of the recovery tower controls the extraction from the bottom of the tower.

[0058] Control the extraction rate of tower bottom recovery system 6 to approximately 8%. Observe the content of unknown components at the bottom of the tower. Observe whether there is flooding in the recovery tower. Observe whether the biochemical treatment results of the methylal wastewater meet the standards.

[0059] Methylal wastewater data and biochemical wastewater data:

[0060] Methylal wastewater after 24 hours

[0061] formaldehyde 623mg / l Methanol 12mg / l Ethylene glycol 89mg / l COD 1121mg / l Unknown COD 322mg / l

[0062] Biochemical wastewater after 48 hours

[0063] formaldehyde 4.15mg / l COD 255mg / l

[0064] formaldehyde 4.33mg / l COD 262mg / l

[0065] formaldehyde 4.26mg / l COD 265mg / l

[0066] Conclusion: Recombinant compounds that affect biochemical treatment can be separated using this treatment unit; the effect of SS on distillation can be controlled by adding a defoamer. Cations, sulfuric acid, and powder in the feed are separated and discharged from the bottom of the tower in this wastewater recovery unit; side streams pass through a demister to prevent liquid foam carryover. Triformaldehyde recovery is >99%, and formaldehyde recovery exceeds 94%. Monitoring of the methylal biochemical wastewater indicates that a small amount of recombinant compounds has already entered the methylal system via the recovery tower's second side draw system 5; further increases in recovery rates are not recommended.

[0067] Example 3:

[0068] The tower top pressure is 7-9 kPa, and the tower bottom pressure is 44-46 kPa. The wastewater recovery tower top temperature is 66-68°C, and the tower bottom temperature is 104-106°C. The reflux ratio is 1.0; the triformaldehyde synthesis tower bottom discharge is 150 L / h; the triformaldehyde deweighting tower bottom discharge is 170 L / h; and the polymerization wastewater is 5000 L / h.

[0069] Temperature control of the gas phase extraction system 2 at the top of the recovery tower;

[0070] The temperature of the first side extraction system 4 of the recovery tower is controlled, and the concentration of trioxymethylene is controlled at about 30%;

[0071] The second side extraction system 5 of the recovery tower controls the extraction from the bottom of the tower;

[0072] Control the extraction rate of the tower bottom recovery system 6 to approximately 6%. Observe the content of unknown components at the tower bottom. Observe whether the recovery tower is flooded. Observe whether the biochemical treatment results of the methylal wastewater meet the standards.

[0073] Methylal wastewater data and biochemical wastewater data:

[0074] Methylal wastewater after 24 hours

[0075] formaldehyde 611mg / l Methanol 11mg / l Ethylene glycol 92mg / l COD 1325mg / l Unknown COD 536mg / l

[0076] Biochemical wastewater after 48 hours

[0077] formaldehyde 6.41mg / l COD 311mg / l

[0078] formaldehyde 6.25mg / l COD 312mg / l

[0079] formaldehyde 6.32mg / l COD 310mg / l

[0080] Conclusion: When the second side extraction system 5 of the recovery tower recovers excessively, recombination will be carried over, causing the recombination to be carried to the methylal unit and affecting the methylal synthesis wastewater.

[0081] The second side extraction system 5 of the recovery tower needs to recover an appropriate amount, control the appropriate recovery tower bottom displacement, and maintain the bottom recombinant concentration.

[0082] Example 4:

[0083] The tower top pressure is 7-9 kPa, and the tower bottom pressure is 44-46 kPa. The wastewater recovery tower top temperature is 66-68°C, and the tower bottom temperature is 104-106°C. The reflux ratio is 1.0; the bottom discharge of the triformaldehyde synthesis tower is increased to approximately 1000 L / h to cope with special operating conditions; the bottom discharge of the triformaldehyde deweighting tower is 170 L / h; and the polymerization wastewater is 5000 L / h.

[0084] Temperature control of the gas phase extraction system 2 at the top of the recovery tower

[0085] The temperature of the first side extraction system 4 of the recovery tower is controlled, and the concentration of trioxymethylene is controlled at about 30%;

[0086] The recovery tower's secondary side extraction system 5 controls the tower bottom extraction, and the bottom recovery system 6 maintains a extraction ratio of approximately 12%. The team monitored the concentration of unknown components at the bottom of the tower, observed whether there was flooding in the recovery tower, and observed whether the biochemical treatment results of the methylal wastewater met standards. The team also observed the impact of the recombined trioxymethylene synthesis tower bottoms on the recovery tower and its distribution of formaldehyde.

[0087] Methylal wastewater data and biochemical wastewater data:

[0088] Methylal wastewater after 24 hours

[0089] formaldehyde 609mg / l Methanol 11mg / l Ethylene glycol 93mg / l COD 1105mg / l Unknown COD 317mg / l

[0090] Biochemical wastewater after 48 hours

[0091] formaldehyde 2.42mg / l COD 132mg / l

[0092] formaldehyde 2.38mg / l COD 129mg / l

[0093] formaldehyde 2.38mg / l COD 131mg / l

[0094] Conclusion: Recombinant factors that affect biochemical treatment can be separated using this treatment unit; the effect of SS on distillation can be controlled by adding a defoamer; cations, sulfuric acid, and fines in the feed are separated and discharged from the bottom of the tower. Side streams passing through a demister prevent liquid foam carryover; triformaldehyde recovery rates exceed 99%, and formaldehyde recovery can exceed 84%. Under controlled conditions for recombinant factors and the influence of fines in the tower, recovery rates can be appropriately increased, but formaldehyde and COD levels in the biochemical treatment of methylal wastewater will increase.

[0095] Embodiment 5:

[0096] The tower top pressure is 7-9 kPa, and the tower bottom pressure is 44-46 kPa. The wastewater recovery tower top temperature is 66-68°C, and the tower bottom temperature is 104-106°C. The reflux ratio is 1.0; the bottom discharge of the triformaldehyde synthesis tower is increased to approximately 1000 L / h to cope with special operating conditions; the bottom discharge of the triformaldehyde deweighting tower is 170 L / h; and the polymerization wastewater is 5000 L / h.

[0097] Temperature control of the gas phase extraction system 2 at the top of the recovery tower;

[0098] The temperature of the first side extraction system 4 of the recovery tower is controlled, and the concentration of trioxymethylene is controlled at about 30%;

[0099] The second side extraction system 5 of the recovery tower controls the extraction from the bottom of the tower;

[0100] The extraction rate of the tower bottom recovery system 6 was controlled at approximately 12%. The content of unknown components at the bottom of the tower was observed, as was the presence of flooding in the recovery tower. The biochemical treatment results of the methylal wastewater were also observed to ensure that they met the standards. The impact of the recombined trioxymethylene synthesis tower bottoms on the recovery tower and the distribution of formaldehyde were also observed.

[0101] Methylal wastewater data and biochemical wastewater data:

[0102] Methylal wastewater after 24 hours

[0103] formaldehyde 669mg / l Methanol 11mg / l Ethylene glycol 90mg / l COD 1310mg / l Unknown COD 462mg / l

[0104] Biochemical wastewater after 48 hours

[0105] formaldehyde 4.45mg / l COD 251mg / l

[0106] formaldehyde 4.53mg / l COD 266mg / l

[0107] formaldehyde 4.48mg / l COD 266mg / l

[0108] Conclusion: The recombinant that affects the biochemical treatment can be separated by this treatment device. The influence of SS on distillation can be controlled by adding a defoaming agent; the cations, sulfuric acid, and powder in the feed are separated in this wastewater recovery device and discharged from the bottom of the tower. The side stream passes through the demister to prevent liquid foam entrainment; the triformaldehyde recovery rate is >99%, and the formaldehyde recovery can reach more than 88%. Under the conditions where the recombinant and the influence of the powder in the tower can be controlled, the bottom discharge of the wastewater recovery tower can be appropriately reduced to increase the recovery rate; however, the formaldehyde and COD in the biochemical treatment results of methylal wastewater increase. If the bottom discharge of the waste recovery tower is further reduced, it may cause a small part of the recombinant to be discharged from the second side extraction system 5 to the methylal system, thereby causing the methylal biochemical wastewater to exceed the standard.

[0109] Example 6:

[0110] The tower top pressure is 7-9 kPa, and the tower bottom pressure is 44-46 kPa. The wastewater recovery tower top temperature is 66-68°C, and the tower bottom temperature is 104-106°C. The reflux ratio is 1.0; the triformaldehyde synthesis tower effluent is increased to approximately 1000 L / h to cope with special operating conditions; the triformaldehyde deweighting tower bottom effluent is 170 L / h; and the polymerization wastewater is 5000 L / h.

[0111] Temperature control of the gas phase extraction system 2 at the top of the recovery tower;

[0112] The temperature of the first side extraction system 4 of the recovery tower is controlled, and the concentration of trioxymethylene is controlled at about 30%;

[0113] The second side extraction system 5 of the recovery tower controls the extraction from the bottom of the tower;

[0114] The extraction rate of the tower bottom recovery system 6 was controlled at approximately 12%. The content of unknown components at the bottom of the tower was observed, as was the presence of flooding in the recovery tower. The biochemical treatment results of the methylal wastewater were also observed to ensure that they met the standards. The impact of the recombined trioxymethylene synthesis tower bottoms on the recovery tower and the distribution of formaldehyde were also observed.

[0115] Methylal wastewater data and biochemical wastewater data:

[0116] Methylal wastewater after 24 hours

[0117] formaldehyde 709mg / l Methanol 12mg / l Ethylene glycol 85mg / l COD 1450mg / l Unknown COD 564mg / l

[0118] Biochemical wastewater after 48 hours

[0119] formaldehyde 6.69mg / l COD 325mg / l

[0120] formaldehyde 6.81mg / l COD 326mg / l

[0121] formaldehyde 6.82mg / l COD 325mg / l

[0122] Conclusion: When the recovery of the bottom row of the trioxymethylene synthesis tower is increased, it is necessary to control the second side extraction system 5 and appropriately reduce the proportion of the second side extraction system 5 of the recovery tower.

[0123] Embodiment seven:

[0124] The tower top pressure is 7-9 kPa, and the tower bottom pressure is 44-46 kPa. The wastewater recovery tower top temperature is 66-68°C, and the tower bottom temperature is 104-106°C. The reflux ratio is 1.0; the triformaldehyde synthesis tower bottom discharge is 150 L / h; the triformaldehyde deweighting tower bottom discharge is 170 L / h; and the polymerization wastewater is 3000 L / h.

[0125] Temperature control of the gas phase extraction system 2 at the top of the recovery tower;

[0126] The temperature of the first side extraction system 4 of the recovery tower is controlled, and the concentration of trioxymethylene is controlled at about 30%;

[0127] The second side extraction system 5 of the recovery tower controls the extraction from the bottom of the tower;

[0128] Control the extraction rate of the tower bottoms recovery system at approximately 12%. Observe the content of unknown components at the bottom of the tower. Observe whether there is flooding in the recovery tower. Observe whether the biochemical treatment results of the methylal wastewater meet the standards. Observe the impact of the recombined triformaldehyde synthesis tower bottoms on the recovery tower and its distribution.

[0129] Methylal wastewater data and biochemical wastewater data:

[0130] Methylal wastewater after 24 hours

[0131]

[0132]

[0133] Biochemical wastewater after 48 hours

[0134] formaldehyde 3.01mg / l COD 158mg / l

[0135] formaldehyde 3.04mg / l COD 152mg / l

[0136] formaldehyde 3.06mg / l COD 155mg / l

[0137] Conclusion: The recombinant fractions that influence biochemical treatment can be separated using this treatment unit; the effect of SS on distillation can be controlled by adding a defoamer; cations, sulfuric acid, and powder in the feed are separated and discharged from the bottom of the tower; side streams pass through a demister to prevent liquid foam entrainment; triformaldehyde recovery rates exceed 99%, and formaldehyde recovery can exceed 90%. Under controlled conditions for recombinant fractions and the effects of powder in the tower, recovery rates can be appropriately increased.

[0138] Embodiment 8:

[0139] The tower top pressure is 7-9 kPa, and the tower bottom pressure is 44-46 kPa. The wastewater recovery tower top temperature is 66-68°C, and the tower bottom temperature is 104-106°C. The reflux ratio is 1.0; the triformaldehyde synthesis tower bottom discharge is 150 L / h; the triformaldehyde deweighting tower bottom discharge is 170 L / h; and the polymerization wastewater is 3000 L / h.

[0140] Temperature control of the gas phase extraction system 2 at the top of the recovery tower;

[0141] The temperature of the first side extraction system 4 of the recovery tower is controlled, and the concentration of trioxymethylene is controlled at about 30%;

[0142] The second side extraction system 5 of the recovery tower controls the extraction from the bottom of the tower;

[0143] Control the extraction rate of tower bottom recovery system 6 at approximately 12%. Observe the content of unknown components at the bottom of the tower. Observe whether there is flooding in the recovery tower. Observe whether the biochemical treatment results of the methylal wastewater meet the standards. Observe the impact of the reconstituted triformaldehyde synthesis tower bottoms on the recovery tower and its distribution.

[0144] Methylal wastewater data and biochemical wastewater data:

[0145] Methylal wastewater after 24 hours

[0146] formaldehyde 689mg / l Methanol 11mg / l Ethylene glycol 86mg / l COD 1326mg / l Unknown COD 461mg / l

[0147] Biochemical wastewater after 48 hours

[0148] formaldehyde 4.53mg / l COD 298mg / l

[0149] formaldehyde 4.62mg / l COD 302mg / l

[0150] formaldehyde 4.55mg / l COD 309mg / l

[0151] Conclusion: The recombinant that affects the biochemical treatment can be separated by this treatment device. The effect of SS on distillation can be controlled by adding a defoaming agent. The cations, sulfuric acid, and powder in the feed are separated in this wastewater recovery device and discharged from the bottom of the tower. The side stream passes through the demister to prevent liquid foam entrainment; the triformaldehyde recovery rate is >99%, and the formaldehyde recovery can reach more than 88%. Under the conditions that the recombinant and the influence of the powder in the tower can be controlled, the recovery rate can be appropriately increased; adding the second side extraction system 5 of the recovery tower can appropriately increase the formaldehyde recovery rate, but the formaldehyde and COD in the biochemical treatment results of acetal wastewater show a significant increase.

[0152] Embodiment 9:

[0153] The tower top pressure is 7-9 kPa, and the tower bottom pressure is 44-46 kPa. The wastewater recovery tower top temperature is 66-68°C, and the tower bottom temperature is 104-106°C. The reflux ratio is 1.0; the triformaldehyde synthesis tower effluent rate is 150 L / h; the triformaldehyde deweighting tower bottom effluent rate is 170 L / h; and the polymerization wastewater rate is 3000 L / h.

[0154] Temperature control of the gas phase extraction system 2 at the top of the recovery tower;

[0155] The temperature of the first side extraction system 4 of the recovery tower is controlled, and the concentration of trioxymethylene is controlled at about 30%;

[0156] The second side extraction system 5 of the recovery tower controls the extraction from the bottom of the tower;

[0157] Control the extraction rate of tower bottom recovery system 6 at approximately 12%. Observe the content of unknown components at the bottom of the tower. Observe whether there is flooding in the recovery tower. Observe whether the biochemical treatment results of the methylal wastewater meet the standards. Observe the impact of the reconstituted triformaldehyde synthesis tower bottoms on the recovery tower and its distribution.

[0158] Methylal wastewater data and biochemical wastewater data:

[0159] Methylal wastewater after 24 hours

[0160] formaldehyde 658mg / l Methanol 11mg / l Ethylene glycol 86mg / l COD 1450mg / l Unknown COD 619mg / l

[0161] Biochemical wastewater after 48 hours

[0162] formaldehyde 5.89mg / l COD 383mg / l

[0163] formaldehyde 5.91mg / l COD 3.89mg / l

[0164] formaldehyde 5.78mg / l COD 386mg / l

[0165] Conclusion: When the recombination at the bottom of the recovery tower is concentrated to a certain ratio, the risk of further concentration and the recombination being carried out from the second side extraction system 5 of the recovery tower will increase rapidly.

[0166] In summary, this patent effectively recovers recyclable components, concentrates recombinant components, and incinerates salts that may cause catalyst deactivation. System control optimizes recovery strategies, effectively recovering formaldehyde, benzene, and trioxymethylene, while concentrating recombinant components, SS, salts, and sulfuric acid in the bottom effluent of the wastewater recovery tower. This achieves energy conservation and emission reduction.

[0167] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A wastewater recovery system for trioxymethylene synthesis wastewater and polymerization wastewater, characterized in that: include: A wastewater recovery tower (1), wherein the wastewater recovery tower (1) is provided with a tower top gas phase extraction system (2), a feed pipe (3), a first side extraction system (4), a second side extraction system (5) and a tower bottom recovery system (6) in sequence from top to bottom; The tower top gas phase extraction system (2) is provided with a tower top condensation reflux tank (21), and the tower top gas phase extraction system (2) controls the tower top temperature to be stable within a specific range by extracting benzene and a small amount of trioxymethylene in the extraction system, and controls the specific reflux ratio to be 1.0, thereby maintaining the operation of the distillation tower; The first side extraction system (4) can remove the liquid foam entrained in the side extraction gas phase, and the gas phase after demisting is extracted to extract trioxymethylene and part of the water in the extraction tower through gas phase condensation, and the temperature and the composition distribution in the tower are controlled by the gas phase extraction amount; The second side extraction system (5) can remove the liquid foam entrained in the side extraction gas phase, and the gas phase after demisting is extracted by gas phase condensation to extract the dilute formaldehyde and a large amount of water in the extraction tower, and the distillation tower is recombined and concentrated at the bottom of the distillation tower; The tower bottom recovery system (6) is provided with a reboiler (61), and the reboiler (61) uses 0.4MPa steam as the separation power of the distillation tower. The reboiler (61) is provided with an external discharge device, and the waste water from the tower bottom is sent to the incinerator (62) through the external discharge device after cooling. The top pressure of the wastewater recovery tower (1) is 5-25 kPa, and the bottom pressure is 40-90 kPa; the top temperature of the wastewater recovery tower (1) is 65-75°C, and the bottom temperature of the wastewater recovery tower (1) is 104-106°C; The wastewater recovery tower (1) is provided with 50 layers of sieve plates, and the 50 layers of sieve plates are numbered 1-50 from top to bottom; The first side extraction system (4) is arranged on the gas phase side above the 38th sieve plate, and the first side extraction system (4) condenses the gas phase after passing through the first side extraction demister (41) to recover trioxymethylene, formaldehyde, and methanol; The second side extraction system (5) is arranged on the gas phase side above the 48th sieve plate. The second side extraction system (5) condenses the extracted gas phase after passing through the second side extraction demister (51) to recover formaldehyde, and simultaneously extracts water from the system. The extraction ratio is such that the formaldehyde emission concentration after subsequent biochemical treatment of methylal wastewater after recombining the extracted material is lower than 5 mg / l. The wastewater recovery tower (1) is connected to the defoaming agent tank (8) via a defoaming pump (7), and the defoaming agent is added in a certain proportion at the feed of the wastewater recovery tower (1) and the bottom of the wastewater recovery tower (1); A first side extraction demister (41) is provided in the first side extraction system (4), the first side extraction demister (41) is connected to a first side extraction condenser (42), and the first side extraction condenser (42) is connected to an extraction reflux tank (43) via a pump; A second side extraction demister (51) is provided in the second side extraction system (5), the second side extraction demister (51) is connected to a second side extraction condenser (52), and the second side extraction condenser (52) is connected to a dilute formaldehyde tank (53).

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