Method for comprehensive treatment of polyformaldehyde wastewater

Abstract

The application discloses a polyformaldehyde wastewater comprehensive treatment method, which comprises the following steps: pumping polyformaldehyde wastewater to a gas-liquid mixer, introducing ozone into the gas-liquid mixer to mix with the polyformaldehyde wastewater, preheating, and then entering a fixed-bed catalytic reactor, under the action of a catalyst, the ozone oxidizes formaldehyde and methanol in the wastewater into formic acid; pumping the oxidized material liquid to a neutralization tank, adding sodium hydroxide solution into the neutralization tank, so that the sodium hydroxide reacts with the formic acid in the wastewater to generate sodium formate, pumping the neutralized material liquid to a buffer tank; sending the wastewater in the buffer tank to a two-effect evaporator to evaporate and concentrate, after heat exchange and condensation, the steam flows into a wastewater tank, the residual wastewater is pumped to a sewage treatment plant for treatment and discharge, the concentrated liquid is cooled and flows into a concentrated liquid storage tank, and the concentrated liquid can be used as a single carbon source or a raw material of a composite carbon source to be regularly loaded and sold. The application fully recycles useful components in the polyformaldehyde wastewater, by-products of 20-30% sodium formate solution products are obtained, and resource waste is avoided to the maximum extent.

Description

TECHNICAL FIELD

[0001] The present application relates to a wastewater treatment method, more particularly to a method for comprehensive treatment of polyformaldehyde wastewater. BACKGROUND

[0002] The polyformaldehyde wastewater is a kind of high-COD, high-salt and strong-acid wastewater generated in the production process of a polyformaldehyde device. Under stable production conditions, the COD of the polyformaldehyde wastewater is 8000-12000 mg / L, and the pH is 2-3. The polyformaldehyde wastewater has complex components, contains 96.5-97 wt.% of water, 1.1-1.3 wt.% of sodium formate, 1.2-1.5 wt.% of formic acid, 600-800 ppm of formaldehyde, and a small amount of methanol, trioxymethylene, dioxolane and other substances. The sodium formate, formic acid and formaldehyde with high content together account for more than 95% of the total COD of the wastewater. For the treatment of the polyformaldehyde wastewater, the commonly used method in the industry is the biochemical method. However, due to the high COD, strong acidity and high formaldehyde concentration (when the formaldehyde concentration exceeds 200 ppm, it will seriously inhibit the growth and reproduction of bacteria), the wastewater has exceeded the tolerance limit of the bacteria. Therefore, the polyformaldehyde wastewater needs to be adjusted to a certain pH by adding alkali and diluted to a large extent before entering the biochemical system, which greatly increases the total amount of the wastewater to be treated, increases the wastewater treatment load of the wastewater treatment plant, and also indirectly affects the treatment of other wastewater in the park. In addition, the biochemical method for treating the polyformaldehyde wastewater will cause waste of resources to some extent because the high-value organic components are indiscriminately biodegraded. SUMMARY

[0003] The present application aims to overcome the deficiencies in the prior art and provides a method for comprehensive treatment of polyformaldehyde wastewater. The method of the present application converts and recycles the useful components in the condensation wastewater through a series of treatments such as ozone catalytic oxidation, alkali neutralization and evaporation concentration, obtains a high-value sodium formate acid solution product, and then sends the residual wastewater with greatly reduced COD and formaldehyde concentration and weakened acidity to the wastewater treatment plant for standard treatment by the biochemical method.

[0004] The present application is achieved by the following technical scheme.

[0005] The method for comprehensive treatment of polyformaldehyde wastewater of the present application comprises the following steps:

[0006] First step: polyformaldehyde wastewater raw water in a polyformaldehyde wastewater raw water tank is pumped into a gas-liquid mixer, an ozone generator is started, and ozone is introduced into the gas-liquid mixer to make the ozone and the polyformaldehyde wastewater fully mixed in the gas-liquid mixer. After mixing, the material liquid is preheated by a heat exchanger and then enters a fixed-bed catalytic reactor, where the ozone oxidizes the formaldehyde and methanol in the material liquid into formic acid under the action of a catalyst. The oxidized material liquid flows into an oxidation completion liquid storage tank for standby use.

[0007] The second step is to pump the liquid in the oxidation completion liquid tank to the neutralization tank, then pump the sodium hydroxide solution in the lye tank to the neutralization tank, so that the sodium hydroxide and the formic acid in the liquid are neutralized to convert the formic acid into sodium formate; when the pH online detector detects that the pH is 7-8, stop adding lye to the neutralization tank; finally, pump the neutralized liquid to the buffer tank for standby;

[0008] The third step is to pump the liquid in the buffer tank to the primary evaporator for primary evaporation, so that part of the water in the wastewater and unoxidized formaldehyde and methanol light components are evaporated; the evaporated gas is used as secondary steam from the top of the primary evaporator to enter the secondary evaporator to provide heat source; the liquid not evaporated at the bottom of the primary evaporator flows into the secondary evaporator for further evaporation and concentration, so that part of the water and residual formaldehyde and methanol light components are evaporated; the gas evaporated from the top of the secondary evaporator is combined with the secondary steam condensate of the secondary evaporator after passing through the heat exchanger to enter the evaporated gas condenser, and then enters the wastewater tank after being cooled to 30-40°C, and the non-condensable gas is sent to the flare; the concentrated liquid at the bottom of the secondary evaporator is cooled to 20-30°C by the concentrated liquid cooler and then enters the concentrated liquid storage tank;

[0009] The fourth step is to pump the remaining wastewater in the wastewater tank to the sewage treatment plant by the wastewater transfer pump for further biochemical treatment and discharge after reaching the standard;

[0010] The fifth step is to start the loading pump to load the sodium formate solution in the concentrated liquid storage tank as a single carbon source or a raw material of a composite carbon source for sale.

[0011] The flow rate of the polyformaldehyde wastewater in the polyformaldehyde wastewater raw water tank in the first step to the gas-liquid mixer is 80-100 m 3 / h, the ozone concentration of the mixed liquid in the gas-liquid mixer is controlled at 300-500 ppm, the mixed liquid is preheated to 50-70°C in the heat exchanger, the space velocity of the fixed bed catalytic reactor is 15-25 h -1 , and the catalyst used is titanium dioxide-zinc oxide or titanium dioxide-copper oxide.

[0012] In the second step, the liquid in the oxidation completion liquid storage tank is pumped to 50-60% of the effective volume of the neutralization tank, and then the lye is added; the concentration of sodium hydroxide in the lye tank is 40-50 wt.%.

[0013] The heat source of the one-effect evaporator in the third step is derived from the low-pressure steam of the existing production system on site, with a pressure of 0.6-0.8 MPa and a temperature of 220-280 DEG C, and the steam condensate is returned to the system; the operating pressure of the one-effect evaporator is 0.03-0.05 MPa, and the operating pressure of the two-effect evaporator is -0.01-0.01 MPa; the feed flow of the one-effect evaporator is 80-100 t / h, the evaporation amount of the evaporated gas of the feed liquid of the one-effect evaporator is 48-60 t / h, the evaporation amount of the evaporated gas of the feed liquid of the two-effect evaporator is 24-30 t / h, the flow of the concentrated liquid is 8-10 t / h, and the mass fraction of sodium formate in the concentrated liquid is 20-30%.

[0014] The flow of the wastewater transfer pump in the fourth step is 72-90 t / h.

[0015] Compared with the prior art, the technical scheme of the present application has the beneficial effects that:

[0016] (1) The present application realizes comprehensive treatment of polyformaldehyde wastewater while recycling as much useful components as possible, and by-products of sodium formate solution with a mass fraction of 20-30% are obtained, which can be sold as raw materials of single carbon source or composite carbon source, thereby avoiding resource waste, enriching the product structure of the enterprise, and also bringing considerable economic benefits to the enterprise.

[0017] (2) In the present application, formaldehyde and methanol in the wastewater are oxidized into formic acid, which is reacted with the added sodium hydroxide solution to generate sodium formate together with the formic acid originally existing in the system, thereby increasing the content of sodium formate and reducing the pH of the system. After the two-effect evaporation, the COD of the evaporated liquid is reduced from 8000-12000 mg / L to below 1500 mg / L, the pH is increased from 2-3 to 7-8, and the formaldehyde content is reduced from 600-800 ppm to below 100 ppm, so that the formaldehyde can be treated by the sewage treatment plant to avoid the inhibition of formaldehyde on microorganisms, and the water dilution and pH adjustment are not needed, thereby saving water, greatly reducing the total amount of wastewater to be treated, reducing the treatment load of the sewage treatment plant, and also saving the cost of reagents. In addition, due to the reduction of the total amount of COD, the difficulty of biochemical treatment is also reduced, and the treatment time is shortened. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 The present application is a schematic diagram of the process flow of the method for comprehensive treatment of polyformaldehyde wastewater.

[0019] Attached reference numerals: 1-Polyoxymethylene wastewater raw water tank, 2-Polyoxymethylene wastewater raw water pump, 3-Gas-liquid mixer, 4-Ozone generator, 5-Heat exchanger, 6-Fixed bed catalytic reactor, 7-Oxidation-completed liquid storage tank, 8-Oxidation-completed liquid transfer pump, 9-Alkali tank, 10-Alkali pump, 11-Neutralization tank, 12-pH online detector, 13-Buffer tank feed pump, 14-Buffer tank, 15-First-effect evaporator feed pump, 16-First-effect evaporator, 17-Second-effect evaporator, 18-Concentrate cooler, 19-Concentrate storage tank, 20-Loading pump, 21-Evaporator gas condenser, 22-Wastewater tank, 23-Wastewater transfer pump. Detailed Implementation

[0020] The present invention will now be further described with reference to the accompanying drawings.

[0021] like Figure 1 As shown, the process flow of the comprehensive treatment method for polyoxymethylene wastewater of the present invention mainly includes a polyoxymethylene wastewater raw water tank 1, a polyoxymethylene wastewater raw water pump 2, a gas-liquid mixer 3, an ozone generator 4, a heat exchanger 5, a fixed-bed catalytic reactor 6, an oxidation-completed liquid storage tank 7, an oxidation-completed liquid transfer pump 8, an alkali tank 9, an alkali pump 10, a neutralization tank 11, a pH online detector 12, a buffer tank feed pump 13, a buffer tank 14, a first-effect evaporator feed pump 15, a first-effect evaporator 16, a second-effect evaporator 17, a concentrate cooler 18, a concentrate storage tank 19, a loading pump 20, an evaporative gas condenser 21, a wastewater tank 22, a wastewater transfer pump 23, and related connecting pipelines.

[0022] The outlet of the polyoxymethylene wastewater raw water tank 1 is connected in sequence via pipelines to a gas-liquid mixer 3, a heat exchanger 5, a fixed-bed catalytic reactor 6, an oxidation-completed liquid storage tank 7, a neutralization tank 11, a buffer tank 14, and a single-effect evaporator 16. The gas-liquid mixer 3 is connected to an ozone generator 4 via pipelines. The neutralization tank 11 is equipped with an online pH meter 12, and the inlet of the neutralization tank 11 is connected to an alkali tank 9 via pipelines. The heat source medium inlet of the double-effect evaporator 17 is connected to the liquid evaporation gas outlet at the top of the first-effect evaporator 16 via a pipeline. The liquid inlet of the double-effect evaporator 17 is connected to the liquid outlet at the bottom of the first-effect evaporator 16 via a pipeline. The liquid evaporation gas outlet at the top of the double-effect evaporator 17 is connected to the wastewater tank 22 via a pipeline, passing through the heat exchanger 5 and the evaporation gas condenser 21 in sequence. The heat source medium outlet of the double-effect evaporator 17 is connected to the wastewater tank 22 via a pipeline, passing through the evaporation gas condenser 21. The concentrate outlet at the bottom of the double-effect evaporator 17 is connected to the concentrate storage tank 19 via a pipeline, passing through the concentrate cooler 18.

[0023] In the above process, a polyformaldehyde wastewater raw water pump 2 is arranged on the pipeline connecting the polyformaldehyde wastewater raw water tank 1 and the gas-liquid mixer 3, an oxidation completed liquid transfer pump 8 is arranged on the pipeline connecting the oxidation completed liquid storage tank 7 and the neutralization tank 11, an alkali liquid pump 10 is arranged on the pipeline connecting the alkali liquid tank 9 and the neutralization tank 11, a buffer tank feed pump 13 is arranged on the pipeline connecting the neutralization tank 11 and the buffer tank 14, and a one-effect evaporator feed pump 15 is arranged on the pipeline connecting the buffer tank 14 and the one-effect evaporator 16. The outlet of the concentrated liquid storage tank 19 is provided with a loading pump 20, and the sodium formate solution in the concentrated liquid storage tank 19 can be used as a raw material of a single carbon source or a composite carbon source, and is sold after being loaded by the loading pump 20. The outlet of the wastewater tank 22 is provided with a wastewater transfer pump 23, and the wastewater in the wastewater tank 22 is sent to a sewage treatment plant by the wastewater transfer pump 23 and is discharged after reaching the standard.

[0024] In the above process, the heat exchanger 5 is arranged in a shell-and-tube structure, and the heat source passes through the shell and the liquid passes through the tube. The liquid inlet of the heat exchanger 5 is connected to the liquid outlet of the gas-liquid mixer 3 through a pipeline, the liquid outlet of the heat exchanger 5 is connected to the feed inlet of the fixed-bed catalytic reactor 6 through a pipeline, the heat source inlet of the heat exchanger 5 is connected to the liquid vapor gas outlet at the top of the two-effect evaporator 17 through a pipeline, and the heat source outlet of the heat exchanger 5 is connected to the vapor condenser 21 through a pipeline. At the same time, the heat source inlet of the heat exchanger 5 is also connected to a first steam pipeline for use in the start-up stage, and the heat source outlet of the heat exchanger 5 is also connected to a first steam condensate pipeline for use in the start-up stage. The steam used can be low-pressure steam of an existing production system, with a gauge pressure of 0.2-0.3 MPa and a temperature of 140-160℃. In the start-up stage, when there is no material at the top of the two-effect evaporator 17, the steam in the first steam pipeline can be used to preheat the feed in the heat exchanger 5; after the process is started, when there is liquid vapor gas at the top of the two-effect evaporator 17, the steam in the first steam pipeline can be used as the heat source of the heat exchanger 5, and the heat exchanger 5 can be switched to the normal heat exchange process and use the vapor gas at the top of the two-effect evaporator 17 as the heat source. In addition, in order to meet the above switching process, valves can be arranged on the pipelines connecting the heat source inlet and the heat source outlet of the heat exchanger 5.

[0025] In the above process, the primary evaporator 16 is arranged in a shell-and-tube structure, with steam in the shell side and liquid in the tube side. The shell side inlet and outlet of the primary evaporator 16 are connected to the second steam pipeline and the second steam condensate pipeline, respectively, as the heat source medium inlet and outlet. The tube side inlet, top tube side outlet and bottom tube side outlet of the primary evaporator 16 are connected to the primary evaporator feed pump 15, the heat source medium inlet of the secondary evaporator 17 and the liquid inlet of the secondary evaporator 17, respectively, as the liquid inlet, the liquid evaporation gas outlet and the liquid outlet.

[0026] In the above process, the secondary evaporator 17 is arranged in a shell-and-tube structure, with steam in the shell side and liquid in the tube side. The shell side inlet and outlet of the secondary evaporator 17 are connected to the secondary evaporator feed pump 14, as the heat source medium inlet and outlet. The tube side inlet, top tube side outlet and bottom tube side outlet of the secondary evaporator 17 are connected to the concentrated liquid cooler 18 and the concentrated liquid storage tank 19, respectively, as the liquid inlet, the liquid evaporation gas outlet and the concentrated liquid outlet.

[0027] In the above process, the evaporator condenser 21 is arranged in a shell-and-tube structure, with evaporation gas in the tube side and cooling medium in the shell side. The tube side inlet, top tube side outlet and bottom tube side outlet of the evaporator condenser 21 are connected to the heat source outlet of the heat exchanger 5 and the heat source medium outlet of the secondary evaporator 17, as the evaporation gas inlet, the non-condensable gas outlet and the condensate outlet. The non-condensable gas outlet of the evaporator condenser 21 is connected to a flare, and the non-condensable gas generated in the evaporator condenser 21 is sent to the flare through the non-condensable gas outlet. The condensate outlet of the evaporator condenser 21 is connected to the waste water tank 22.

[0028] In the above process, the concentrated liquid cooler 18 and the evaporator condenser 21 can use cooling water as the cooling medium.

[0029] In the above process, the steam (delivered through the second steam pipeline) used by the primary evaporator 16 can be sourced from the low-pressure steam of the existing production system on site, with a gauge pressure of 0.6-0.8 MPa and a temperature of 220-280°C. The steam condensate is returned to the production system. The steam generated at the top of the primary evaporator 16 is used as secondary steam to provide heat source for the secondary evaporator 17. The liquid that has not been evaporated at the bottom of the primary evaporator 16 enters the secondary evaporator 17 for further evaporation and concentration. The steam generated at the top of the secondary evaporator 17 is delivered to the heat exchanger 5 as a heat source to preheat the feed of the heat exchanger 5.

[0030] Based on the above process, the application provides a method for comprehensive treatment of polyformaldehyde wastewater, and the specific implementation process comprises the following steps:

[0031] First step: start the polyformaldehyde wastewater raw water pump 2, and pump the polyformaldehyde wastewater in the polyformaldehyde wastewater raw water tank 1 into the gas-liquid mixer 3 at a flow rate of 80-100 m 3 / h. At the same time, start the ozone generator 4, and introduce ozone into the gas-liquid mixer 3, so that the ozone and the polyformaldehyde wastewater are fully mixed in the gas-liquid mixer 3, and the ozone concentration in the mixed material liquid is controlled at 300-500 ppm. The mixed material liquid enters the heat exchanger 5, is preheated to 50-70 DEG C, and then enters the fixed-bed catalytic reactor 6, under the action of the catalyst, the ozone oxidizes the formaldehyde and the methanol in the material liquid into formic acid, so as to increase the total content of formic acid in the material liquid system, and the oxidized material liquid flows into the oxidation completed liquid storage tank 7 for standby.

[0032] The polyformaldehyde wastewater raw water has a COD of 8000-12000 mg / L, a pH of 2-3, contains 96.5-97 wt.% of water, 1.1-1.3 wt.% of sodium formate, 1.2-1.5 wt.% of formic acid, 600-800 ppm of formaldehyde, and a small amount of methanol, trioxymethylene, dioxolane and other substances. The space velocity of the fixed-bed catalytic reactor 6 is 15-25 h -1 , and the catalyst used is titanium dioxide-zinc oxide (TiO2-ZnO) or titanium dioxide-copper oxide (TiO2-CuO).

[0033] Second step: start the oxidation completed liquid transfer pump 8, and pump the material liquid in the oxidation completed liquid storage tank 7 to the 50-60% liquid level of the neutralization tank 11. Start the lye pump 10, pump the 40-50 wt.% sodium hydroxide solution in the lye tank 9 into the neutralization tank 11, so that the sodium hydroxide and the formic acid in the material liquid are neutralized to convert the formic acid into sodium formate, so as to increase the content of sodium formate in the system. When the pH online detector 12 detects that the pH is 7-8, stop the lye pump 10, and stop adding lye to the neutralization tank 11. Start the buffer tank feed pump 13, and pump the neutralized material liquid into the buffer tank 14 for standby.

[0034] Third step: start the first evaporator feed pump 15 to pump the liquid in the buffer tank 14 to the first evaporator 16 for primary evaporation, and evaporate part of the water and unoxidized formaldehyde, methanol and other light components in the wastewater. The evaporated gas is used as secondary steam to enter the second evaporator 17 from the top of the first evaporator 16 to provide heat source for the second evaporator 17. The liquid not evaporated in the first evaporator 16 flows into the second evaporator 17 to continue evaporation and concentration, and further evaporate part of the water and residual formaldehyde, methanol and other light components. The gas evaporated from the top of the second evaporator 17 is combined with the secondary steam condensate of the second evaporator 17 after heat exchange in the heat exchanger 5, and then enters the evaporated gas condenser 21, and is cooled to 30-40℃ and then enters the wastewater tank 22, and the non-condensable gas is sent to the flare. The concentrated liquid in the second evaporator 17 is mainly composed of sodium formate, water and trace amounts of trioxymethylene, dioxolane and the like, which is cooled to 20-30℃ by the concentrated liquid cooler 18 and then enters the concentrated liquid storage tank 19.

[0035] In the start-up stage, when there is no material in the top of the second evaporator 17, the preheater 5 can use steam provided by the first steam pipeline to preheat the feed; when the process is connected, there is liquid evaporated gas in the top of the second evaporator 17, the heat exchanger 5 can stop using steam provided by the first steam pipeline as heat source, and switch to normal heat exchange process using the evaporated gas in the top of the second evaporator 17 as heat source.

[0036] The heat source for the first evaporator 16 is low-pressure steam from the existing production system, with a pressure of 0.6-0.8 MPa and a temperature of 220-280℃, and the steam condensate is returned to the system. The operating pressure of the first evaporator 16 is 0.03-0.05 MPa, and the operating pressure of the second evaporator 17 is -0.01-0.01 MPa. The feed flow rate of the first evaporator 16 is 80-100 t / h, the evaporation amount of the liquid evaporated gas of the first evaporator 16 (i.e. the secondary steam flow rate) is 48-60 t / h, the evaporation amount of the liquid evaporated gas of the second evaporator 17 (i.e. the steam flow rate produced in the top of the second evaporator 10) is 24-30 t / h, the concentrated liquid flow rate is 8-10 t / h, and the mass fraction of sodium formate in the concentrated liquid is 20-30%. The above pressures are measured in terms of gauge pressure.

[0037] Fourth step: start the wastewater transfer pump 23 to pump the remaining wastewater (with COD <1500 mg / L, formaldehyde concentration <100 ppm, and pH 7-8) in the wastewater tank 22 to the sewage treatment plant for further biochemical treatment, and then discharge after reaching the standard. The flow rate of the wastewater transfer pump 23 is 72-90 t / h.

[0038] Fifth step: start the loading pump 20 to load the sodium formate solution in the concentrated liquid storage tank 19 as raw material for single carbon source or composite carbon source for sale.

[0039] The invention fully recycles the useful components in polyformaldehyde wastewater, by-products are obtained, the product of sodium formate solution with high added value, the waste of resources is avoided to the greatest extent, the product structure of the enterprise is enriched, the economic benefits of the enterprise are brought, the remaining wastewater enters the sewage treatment plant without dilution, the water is saved, the cost of the reagent for adjusting pH is saved, the treatment difficulty is reduced, and the treatment time is shortened.

[0040] Example 1

[0041] The polyformaldehyde wastewater comprehensive treatment method of the embodiment is as follows: the COD of the condensation wastewater raw water is 8000 mg / L, the pH is 2.5, the water content is 97 wt.%, the sodium formate content is 1.3 wt.%, the formic acid content is 1.35 wt.%, the formaldehyde content is 700 ppm, and a small amount of methanol, trioxymethylene, dioxolane and other substances are also contained.

[0042] First step: start the polyformaldehyde wastewater raw water pump 2, and pump the polyformaldehyde wastewater in the polyformaldehyde wastewater tank 1 into the gas-liquid mixer 3 at a flow rate of 80 m 3 / h. At the same time, start the ozone generator 4, and introduce ozone into the gas-liquid mixer 3, so that the ozone and the polyformaldehyde wastewater are fully mixed in the gas-liquid mixer 3. The ozone concentration in the mixed material liquid is controlled at 400 ppm. After mixing, the material liquid enters the heat exchanger 5, is preheated to 60 DEG C, and then enters the fixed-bed catalytic reactor 6. Under the action of the catalyst, the ozone oxidizes the formaldehyde and methanol in the material liquid into formic acid, increases the total content of formic acid in the material liquid system, and the oxidized material liquid flows into the oxidation completion liquid storage tank 7 for standby. The space velocity of the fixed-bed catalytic reactor 6 is 20 h -1 , and the catalyst used is TiO2-ZnO (titanium dioxide-zinc oxide).

[0043] Second step: start the oxidation completion liquid transfer pump 8, and pump the material liquid in the oxidation completion liquid storage tank 7 to the 50% liquid level of the neutralization tank 11. Start the lye pump 10, pump the 45 wt.% sodium hydroxide solution in the lye tank 9 into the neutralization tank 11, so that the sodium hydroxide and the formic acid in the material liquid are neutralized to convert the formic acid into sodium formate, so as to increase the content of sodium formate in the system. When the pH online detector 12 detects that the pH is 7, stop the lye pump 10, and stop adding lye to the neutralization tank 11. Start the buffer tank feed pump 13, and pump the neutralized material liquid into the buffer tank 14 for standby.

[0044] Third step: start the first evaporator feed pump 15 to pump the liquid in the buffer tank 14 to the first evaporator 16 for primary evaporation, and evaporate part of the water and unoxidized formaldehyde, methanol and other light components in the wastewater. The evaporated gas is used as secondary steam to enter the second evaporator 17 from the top of the first evaporator 16 to provide heat source for the second evaporator 17. The liquid not evaporated in the first evaporator 16 flows into the second evaporator 17 to continue evaporation and concentration, and further evaporate part of the water and residual formaldehyde, methanol and other light components. The gas evaporated from the top of the second evaporator 17 is combined with the secondary steam condensate of the second evaporator 17 after heat exchange in the heat exchanger 5, and then enters the evaporated gas condenser 21, and is cooled to 30℃ and then enters the wastewater tank 22. The non-condensable gas is sent to the flare. The concentrated liquid in the second evaporator 17 mainly contains sodium formate, water and trace amounts of trioxymethylene, dioxolane and other substances, which is cooled to 20℃ by the concentrated liquid cooler 18 and then enters the concentrated liquid storage tank 19.

[0045] The heat source for the first evaporator 16 is obtained from the low-pressure steam of the existing production system on site, with a pressure of 0.6 MPa and a temperature of 220℃, and the steam condensate is returned to the system. The operating pressure of the first evaporator 16 is 0.04 MPa, and the operating pressure of the second evaporator 17 is -0.01 MPa. The feed flow rate of the first evaporator 16 is 80 t / h, the evaporation amount of the liquid evaporated gas of the first evaporator 16 (i.e. the secondary steam flow rate) is 48 t / h, the evaporation amount of the liquid evaporated gas of the second evaporator 17 (i.e. the steam flow rate produced at the top of the second evaporator 10) is 24 t / h, and the flow rate of the concentrated liquid is 8 t / h. The mass fraction of sodium formate in the concentrated liquid is 25%. The above pressures are measured in terms of gauge pressure.

[0046] Fourth step: start the wastewater transfer pump 23 to pump the remaining wastewater (COD is 1260 mg / L, formaldehyde concentration is 85 ppm, and pH is 7) in the wastewater tank 22 to the sewage treatment plant for further biochemical treatment and discharge.

[0047] Fifth step: start the loading pump 20 to load the sodium formate solution in the concentrated liquid storage tank 19 as a single carbon source or a raw material for a composite carbon source for sale.

[0048] Example 2

[0049] The method for comprehensive treatment of polyformaldehyde wastewater in this embodiment is as follows: the COD of the raw polyformaldehyde wastewater is 10000 mg / L, the pH is 2, the water content is 96.5 wt.%, the sodium formate content is 1.1 wt.%, the formic acid content is 1.2 wt.%, the formaldehyde content is 600 ppm, and the methanol, trioxymethylene, dioxolane and other substances are trace amounts.

[0050] First step: start the polyformaldehyde wastewater raw water pump 2 to pump the polyformaldehyde wastewater in the polyformaldehyde wastewater raw water tank 1 at a flow rate of 90 m3 The flow rate of the stream of the polyformaldehyde waste water is pumped into the gas-liquid mixer 3. At the same time, the ozone generator 4 is started to supply ozone into the gas-liquid mixer 3, so that the ozone and the polyformaldehyde waste water are mixed in the gas-liquid mixer 3. The ozone concentration in the mixed stream is controlled at 300 ppm. The mixed stream is then introduced into the heat exchanger 5, preheated to 50°C, and then introduced into the fixed-bed catalytic reactor 6. Under the action of the catalyst, the ozone oxidizes the formaldehyde and the methanol in the stream into formic acid, so as to increase the total content of the formic acid in the stream. The oxidized stream is then introduced into the oxidized stream storage tank 7 for standby. The space velocity of the fixed-bed catalytic reactor 6 is 15 h -1 The catalyst used is TiO2-CuO (titanium dioxide-copper oxide).

[0051] The second step is to start the oxidized stream transfer pump 8 to pump the stream in the oxidized stream storage tank 7 to the 55% liquid level of the neutralization tank 11. The alkali pump 10 is started to pump the 40 wt.% sodium hydroxide solution in the alkali tank 9 into the neutralization tank 11, so that the sodium hydroxide and the formic acid in the stream are neutralized to convert the formic acid into sodium formate, so as to increase the content of the sodium formate in the system. When the pH online detector 12 detects that the pH value is 7.5, the alkali pump 10 is stopped to stop adding the alkali into the neutralization tank 11. The buffer tank feed pump 13 is started to pump the neutralized stream into the buffer tank 14 for standby.

[0052] The third step is to start the first-effect evaporator feed pump 15 to pump the stream in the buffer tank 14 into the first-effect evaporator 16 for primary evaporation to evaporate part of the water and the unoxidized formaldehyde, methanol and other light components in the waste water. The evaporated gas is introduced into the second-effect evaporator 17 from the top of the first-effect evaporator 16 as secondary steam to provide heat source for the second-effect evaporator 17. The stream not evaporated in the first-effect evaporator 16 flows into the second-effect evaporator 17 for further evaporation and concentration to evaporate part of the water and the residual formaldehyde, methanol and other light components. The evaporated gas in the top of the second-effect evaporator 17 is cooled to 35°C by the heat exchanger 5, and then introduced into the waste water tank 22 after being condensed in the evaporation gas condenser 21. The non-condensable gas is sent to the flare. The concentrated stream in the bottom of the second-effect evaporator 17 mainly contains sodium formate, water and trace amounts of trioxymethylene and dioxolane, which is cooled to 30°C by the concentrated stream cooler 18 and then introduced into the concentrated stream storage tank 19.

[0053] The heat source for the first evaporator 16 is derived from the low-pressure steam of the existing production system on site, with a pressure of 0.7 MPa and a temperature of 250°C, and the steam condensate is returned to the system. The operating pressure of the first evaporator 16 is 0.05 MPa, and the operating pressure of the second evaporator 17 is 0.01 MPa. The feed flow rate of the first evaporator 16 is 90 t / h, the evaporation amount of the vaporized gas of the feed liquid of the first evaporator 16 (i.e., the secondary steam flow rate) is 54 t / h, the evaporation amount of the vaporized gas of the feed liquid of the second evaporator 17 (i.e., the steam flow rate produced at the top of the second evaporator 10) is 27 t / h, the concentrated liquid flow rate is 9 t / h, and the mass fraction of sodium formate in the concentrated liquid is 20%. The above pressures are measured in terms of gauge pressure.

[0054] Fourth step: Start the wastewater transfer pump 23 to pump the remaining wastewater (COD of 1180 mg / L, formaldehyde concentration of 75 ppm, and pH of 7.5) in the wastewater tank 22 to the sewage treatment plant for further biochemical treatment and discharge in accordance with the standards. The flow rate of the wastewater transfer pump 23 is 81 t / h.

[0055] Fifth step: Start the loading pump 20 to load the sodium formate solution in the concentrated liquid storage tank 19 as a single carbon source or a composite carbon source for sale.

[0056] Example 3

[0057] The method for comprehensive treatment of polyformaldehyde wastewater in this embodiment is as follows: the COD of the raw polyformaldehyde wastewater is 12000 mg / L, the pH is 3, the water content is 96.75 wt.%, the sodium formate content is 1.2 wt.%, the formic acid content is 1.5 wt.%, the formaldehyde content is 800 ppm, and the methanol, trioxane, dioxolane, and other substances are present in trace amounts.

[0058] First step: Start the polyformaldehyde wastewater raw water pump 2 to pump the polyformaldehyde wastewater in the polyformaldehyde wastewater raw water tank 1 into the gas-liquid mixer 3 at a flow rate of 100 m 3 / h. At the same time, start the ozone generator 4 to introduce ozone into the gas-liquid mixer 3, so that the ozone and the polyformaldehyde wastewater are fully mixed in the gas-liquid mixer 3, and the ozone concentration in the mixed liquid is controlled at 500 ppm. After mixing, the liquid is preheated to 70°C in the heat exchanger 5 and then flows into the fixed-bed catalytic reactor 6, where the ozone oxidizes the formaldehyde and methanol in the liquid into formic acid under the action of the catalyst, thereby increasing the total content of formic acid in the liquid system. The oxidized liquid flows into the oxidation completion liquid storage tank 7 for standby use. The space velocity of the fixed-bed catalytic reactor 6 is 25 h -1 , and the catalyst used is TiO2-ZnO (titanium dioxide-zinc oxide).

[0059] Step 2: Start the oxidation completed liquid transfer pump 8 to pump the liquid in the oxidation completed liquid tank 7 to the 60% liquid level of the neutralization tank 11. Start the lye pump 10 to pump the 50wt.% sodium hydroxide solution in the lye tank 9 to the neutralization tank 11 to make neutralization reaction between sodium hydroxide and formic acid in the liquid, and convert all formic acid into sodium formate to increase the content of sodium formate in the system. When the pH online detector 12 shows that the pH is 8, stop the lye pump 10 to stop adding lye to the neutralization tank 11. Start the buffer tank feed pump 13 to pump the neutralized liquid to the buffer tank 14 for standby.

[0060] Step 3: Start the primary evaporator feed pump 15 to pump the liquid in the buffer tank 14 to the primary evaporator 16 for primary evaporation to evaporate part of water, unoxidized formaldehyde, methanol and other light components in the wastewater. The evaporated gas is used as secondary steam to enter the secondary evaporator 17 from the top of the primary evaporator 16 to provide heat source for the secondary evaporator 17. The liquid not evaporated in the primary evaporator 16 flows into the secondary evaporator 17 to continue evaporation and concentration, and further evaporate part of water, residual formaldehyde, methanol and other light components. The gas evaporated from the top of the secondary evaporator 17 is cooled to 40℃ by the heat exchanger 5, and then enters the wastewater tank 22 after being cooled to 40℃, and the non-condensable gas is sent to the flare. The concentrated liquid in the secondary evaporator 17 mainly contains sodium formate, water and trace amounts of trioxymethylene, dioxolane and the like, which is cooled to 25℃ by the concentrated liquid cooler 18 and then enters the concentrated liquid storage tank 19.

[0061] The heat source for the primary evaporator 16 is obtained from the low-pressure steam in the existing production system, with a pressure of 0.8 MPa and a temperature of 280℃, and the steam condensate is returned to the system. The operating pressure of the primary evaporator 16 is 0.03 MPa, and the operating pressure of the secondary evaporator 17 is 0 MPa. The feed flow rate of the primary evaporator 16 is 100 t / h, the evaporation amount of the liquid evaporated gas of the primary evaporator 16 (i.e. the secondary steam flow rate) is 60 t / h, the evaporation amount of the liquid evaporated gas of the secondary evaporator 17 (i.e. the steam flow rate produced at the top of the secondary evaporator 10) is 30 t / h, and the flow rate of the concentrated liquid is 10 t / h. The mass fraction of sodium formate in the concentrated liquid is 30%. The above pressures are measured in terms of gauge pressure.

[0062] Step 4: Start the wastewater transfer pump 23 to pump the remaining wastewater (with a COD of 1150 mg / L, a formaldehyde concentration of 79 ppm and a pH of 8) in the wastewater tank 22 to the sewage treatment plant for further biochemical treatment and discharge.

[0063] Step 5: Start the loading pump 20 to load the sodium formate solution in the concentrated liquid storage tank 19 as raw material for single carbon source or composite carbon source for sale.

[0064] Although the functions and working processes of the present application are described above in combination with the drawings, the present application is not limited to the specific functions and working processes described above, and the specific embodiments described above are merely illustrative but not restrictive, and those of ordinary skill in the art can make many forms under the inspiration of the present application without departing from the purpose of the present application and the scope protected by the claims, which all belong to the protection of the present application.

Claims

1. A method for comprehensive treatment of polyformaldehyde wastewater, characterized in that, The method comprises the following steps: The first step: polyformaldehyde wastewater raw water in polyformaldehyde wastewater raw water tank (1) is pumped into gas-liquid mixer (3) at a flow rate of 80-100 m 3 / h, ozone generator (4) is started, ozone is introduced into gas-liquid mixer (3), ozone is fully mixed with polyformaldehyde wastewater in gas-liquid mixer (3), and the ozone concentration of the mixed material liquid is controlled at 300-500 ppm; after mixing, the material liquid is preheated to 50-70 DEG C through heat exchanger (5) and then enters fixed bed catalytic reactor (6), the space velocity of fixed bed catalytic reactor (6) is 15-25 h -1 / h, under the action of the catalyst, ozone oxidizes formaldehyde and methanol in the material liquid into formic acid, the oxidized material liquid flows into oxidation completion liquid storage tank (7) for standby use; wherein the catalyst is titanium dioxide-zinc oxide or titanium dioxide-copper oxide; The second step: the liquid in the oxidation completion tank (7) is pumped into the neutralization tank (11), and then the sodium hydroxide solution in the lye tank (9) is pumped into the neutralization tank (11), so that the sodium hydroxide and the formic acid in the liquid are neutralized to convert the formic acid into sodium formate; when the pH online detector (12) detects that the pH is 7-8, the addition of the lye into the neutralization tank (11) is stopped; finally, the neutralized liquid is pumped into the buffer tank (14) for standby; The third step: the liquid in the buffer tank (14) is pumped into the first evaporator (16) for primary evaporation, so that part of the water in the wastewater and the unoxidized formaldehyde and methanol light components are evaporated; the evaporated gas is used as secondary steam from the top of the first evaporator (16) to enter the second evaporator (17) to provide heat for the second evaporator (17); the liquid not evaporated in the first evaporator (16) flows into the second evaporator (17) for continuous evaporation and concentration, and further evaporates part of the water and residual formaldehyde and methanol light components; the gas evaporated from the top of the second evaporator (17) is combined with the secondary steam condensate of the second evaporator (17) after heat exchange in the heat exchanger (5) to enter the evaporated gas condenser (21), and then enters the wastewater tank (22) after being cooled to 30-40℃, and the non-condensable gas is transported to a flare; the concentrated liquid at the bottom of the second evaporator (17) is cooled to 20-30℃ by the concentrated liquid cooler (18) and then enters the concentrated liquid storage tank (19); The fourth step: the remaining wastewater in the wastewater tank (22) is pumped to a sewage treatment plant by a wastewater transfer pump (23) for biochemical treatment and discharge; The fifth step: the loading pump (20) is started to load the sodium formate solution in the concentrated liquid storage tank (19) as a single carbon source or a composite carbon source for sale.

2. The method for comprehensive treatment of polyformaldehyde wastewater according to claim 1, characterized in that, In the second step, the liquid in the oxidation completion tank (7) is pumped to 50-60% of the effective volume of the neutralization tank (11), and the sodium hydroxide in the lye tank (9) has a concentration of 40-50wt.%.

3. The method for comprehensive treatment of polyformaldehyde wastewater according to claim 1, characterized in that, In the third step, the heat source of the first evaporator (16) is derived from the low-pressure steam of the existing production system, with a pressure of 0.6-0.8 MPa and a temperature of 220-280℃, and the steam condensate is returned to the system; the operating pressure of the first evaporator (16) is 0.03-0.05 MPa, and the operating pressure of the second evaporator (17) is -0.01-0.01 MPa; the feed flow rate of the first evaporator (16) is 80-100 t / h, the evaporation amount of the liquid evaporation gas of the first evaporator (16) is 48-60 t / h, the evaporation amount of the liquid evaporation gas of the second evaporator (17) is 24-30 t / h, the flow rate of the concentrated liquid is 8-10 t / h, and the mass fraction of sodium formate in the concentrated liquid is 20-30%.

4. The method for comprehensive treatment of polyformaldehyde wastewater according to claim 1, characterized in that, In the fourth step, the flow rate of the wastewater transfer pump (23) is 72-90 t / h.

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