Phosphorus chemical sulfur-containing sewage treatment method and system

Abstract

The invention discloses a phosphorus chemical sulfur-containing sewage treatment method and system, the system comprises a circular reaction box, the circular reaction box is divided into a reaction area and a lifting area by a partition plate with a hole in the lower section, the front section of the circular reaction box is provided with a stirrer, and the rear section of the circular reaction box is provided with a screen drum; a sewage outlet lifting pump at the bottom of the lifting area is respectively connected with a feed port and a discharge pipeline of the hydrocyclone, an overflow conduit at the top of the hydrocyclone is connected with the reaction area of the circular reaction box, and an underflow port at the bottom of the hydrocyclone is detachably connected with the screen drum. According to the method, chemical oxidation is combined with centrifugal separation, sulfides in the sulfur-containing sewage are directionally oxidized into elemental sulfur, and the elemental sulfur is filtered by a screen drum; and oxidizing the residual sulfur element in the sewage into sulfate radicals. The system is extremely simple, low in operation and investment cost, small in equipment occupied area and high in treatment efficiency, the production rhythm of phosphorus chemical enterprises is effectively matched, and the requirement for centralized and safe treatment of sewage discharged by the phosphorus chemical enterprises is met.

Description

Technical Field

[0001] The present invention relates to the field of sewage treatment, in particular to a method and system for treating sulfur-containing sewage from the phosphorus chemical industry. Background Art

[0002] Phosphorus chemical companies intermittently discharge arsenic removal wastewater and washing wastewater during their production processes. This wastewater contains high sulfide concentrations, sometimes exceeding 5,000 to 8,000 mg / L. These wastewaters are highly toxic and corrosive, and are collectively referred to as sulfur-containing wastewater. Furthermore, phosphorus chemical companies produce large quantities of highly acidic products, which also generate significant amounts of acidic wastewater. To save costs and improve treatment efficiency, companies often seek to centrally treat these wastewaters. However, for sulfur-containing wastewater, when the pH is ≤ 5.5, sulfide primarily exists as hydrogen sulfide. Directly mixing highly concentrated sulfur-containing wastewater with acidic wastewater can result in the release of large amounts of hydrogen sulfide gas, potentially causing safety incidents. Therefore, for large phosphorus chemical companies, achieving safe and effective centralized treatment of these high-concentration sulfur-containing and acidic wastewater remains a crucial technical challenge.

[0003] Currently, vacuum stripping and chemical precipitation are the most common methods used to remove sulfides from sulfur-containing wastewater in China. Vacuum stripping involves controlling the wastewater pH to below 4 and the water temperature to around 70°C, separating hydrogen sulfide from water under negative pressure. However, this method requires vacuum and negative pressure equipment, resulting in high engineering investment and operating costs. Chemical precipitation removes sulfides by reacting metal ions with sulfides to form a precipitate. However, this method requires high precipitant consumption and produces a large amount of sludge, requiring the installation of sludge-water separation equipment. Furthermore, the sludge cannot be recycled.

[0004] CN 203382605U discloses a system for treating sulfur-containing industrial wastewater, comprising a circulating oxidation reactor, a crystallizer, a centrifuge, and a vibrating fluidized bed dryer, all of which are sequentially connected. This system uses chlorine as the oxidant. The crystallizer, centrifuge, and vibrating fluidized bed dryer can recover high-purity elemental sulfur. The waste steam from the recovered elemental sulfur is condensed into water in a condenser cooler and collected for use in preparing an alkaline solution, thereby reducing clean water usage. This system involves virtually no wastewater discharge, and the small amount of liquid produced by the centrifuge is also collected. This system is suitable only for small enterprises with high sulfur content and low wastewater discharge. Summary of the Invention

[0005] The purpose of the present invention is to solve the above technical problems and provide a method for treating sulfur-containing wastewater from the phosphorus chemical industry, which has extremely simple process, low operation and investment costs, small equipment footprint, high treatment efficiency, effectively matches the production rhythm of phosphorus chemical enterprises, and meets the centralized and safe treatment needs of wastewater discharged by phosphorus chemical enterprises.

[0006] The present invention also provides a phosphorus chemical industry sulfur-containing wastewater treatment system used in the above treatment method.

[0007] The phosphorus chemical industry sulfur-containing wastewater treatment system of the present invention includes a circulating reaction box, which is divided into a reaction zone and a lifting zone by a partition with holes in the lower section. The reaction zone is provided with a sewage inlet, a front section of which is equipped with an agitator, and a rear section of which is equipped with a sieve drum; a sewage outlet is provided at the bottom of the lifting zone, and the sewage outlet is respectively connected to the feed port and the external discharge pipe of a hydrocyclone through a lifting pump; the overflow conduit at the top of the hydrocyclone is connected to the reaction zone of the circulating reaction box, and the underflow port at the bottom is detachably connected to the sieve drum.

[0008] The reaction zone is provided with a pH online monitor, an oxidation-reduction potential online monitor, and a turbidity online monitor. The data output ends of the pH online monitor, the oxidation-reduction potential online monitor, and the turbidity online monitor are connected to the data input end of the PLC. The control signal output end of the PLC is respectively connected to the control ends of the hydrogen peroxide solution dosing device, the acid dosing device, and the alkali dosing device.

[0009] The sieve filter aperture of the sieve cylinder is 100 μm.

[0010] A sight glass is installed near the screen cylinder.

[0011] The upper section of the hydrocyclone is a cyclone chamber, and the lower section is a cone.

[0012] The cone angle is 6°.

[0013] The present invention provides a method for treating sulfur-containing wastewater from the phosphorus chemical industry. The sulfur-containing wastewater is fed into a circulating reaction box in batches for treatment. The above-mentioned phosphorus chemical industry sulfur-containing wastewater treatment system is used. The treatment method for each batch of sulfur-containing wastewater is as follows:

[0014] 1) First, hydrogen peroxide solution is added to the reaction zone of the circulating reaction tank to control the redox potential of the sulfur-containing wastewater to 30-60 mV, and acid or alkali is added to adjust the pH value to 6.3. While stirring, the sulfide in the sulfur-containing wastewater is directionally oxidized to elemental sulfur. The wastewater in the lifting zone of the circulating reaction tank is circulated into the hydrocyclone for centrifugation through a lifting pump. The overflow liquid at the top of the hydrocyclone is returned to the circulating reaction tank, and the solid-liquid bottom is filtered through a screen and returned to the circulating reaction tank;

[0015] 2) When the turbidity of the sulfur-containing wastewater drops below 5NTU, the lift pump stops working, and an excessive amount of hydrogen peroxide solution is added to the circulation reaction tank to control the wastewater redox potential at 200-240mV. The reaction is stirred for 5-10 minutes to oxidize the remaining sulfur in the wastewater into sulfate ions. Finally, all the wastewater in the circulation reaction tank is discharged through the lift pump and sent to the subsequent centralized wastewater treatment process.

[0016] In the step 1), the stirring speed is controlled to be 20-60 rpm.

[0017] In step 2), the stirring speed was controlled to 80 rpm.

[0018] In response to the problems existing in the background technology, taking into account the characteristics of intermittent discharge of sulfur-containing wastewater by phosphorus chemical enterprises during the production process, a circulating reaction box is set up, and the sulfur-containing wastewater is collected in batches by using the circulating reaction box for intermittent treatment. After each batch of sulfur-containing wastewater is treated and discharged, the next batch of sulfur-containing wastewater is collected, which just matches the production rhythm of the phosphorus chemical enterprises.

[0019] During each batch of treatment, the redox potential and pH value of the sulfur-containing wastewater are controlled by adding hydrogen peroxide solution and acid or alkaline agents. Studies have shown that in the initial stage, the sulfide concentration in the sulfur-containing wastewater is high. At this time, by controlling the redox potential in the sulfur-containing wastewater at 30-60mV, it is conducive to the occurrence of oxidation reactions, so that a large amount of sulfide is directional oxidized to elemental sulfur. Too high a redox potential will peroxidize the sulfide into positive sulfur, and too low a redox potential will reduce the generation rate of elemental sulfur. At the same time, the pH value is strictly controlled to be 6.3. In this pH environment, the wastewater can avoid the overflow of hydrogen sulfide gas and cause safety accidents, and can also ensure the oxidizing ability of the hydrogen peroxide solution to directionally oxidize the sulfide into elemental sulfur. It is also conducive to the rapid growth of elemental sulfur crystals and facilitates separation. That is, under the weakly acidic conditions of pH 6.3, it can not only ensure the oxidizing ability of hydrogen peroxide but also make the sulfide mainly oxidized as HS - It exists in a form that facilitates the controlled directional oxidation of sulfides. Since the oxidant in the oxidation reaction is a hydrogen peroxide solution, in order to improve the efficiency of liquid-liquid mixing, an agitator is set in the reaction zone. The stirring effect allows the sulfur-containing wastewater to be fully mixed with the reagent in the reaction zone, while also increasing the collision and agglomeration speed of the generated elemental sulfur, rapidly increasing the particle size of the elemental sulfur. The partition is set to separate the reaction zone and the lifting zone, reducing the disturbance of the liquid phase in the lifting zone, allowing more grown elemental sulfur crystals to settle at the bottom, and then be lifted by the lifting pump from the lifting zone into the hydrocyclone for efficient centrifugal separation. The density of elemental sulfur is greater than that of water. Under the action of inertial centrifugal force, large particles flow out from the bottom flow port, and light phase or small particles are discharged from the overflow pipe.

[0020] Here, a sieve drum located below the hydrocyclone is also provided in the reaction zone. On the one hand, the solid-containing liquid flowing out of the bottom of the hydrocyclone is circulated into the circulation reaction box after the large particles are intercepted by the sieve drum. After several cycles, the elemental sulfur crystals attached to the screen of the sieve drum will gradually grow and become more and more. The purpose of removing most of the elemental sulfur can be achieved through an extremely simple structure. On the other hand, since the sulfur-containing wastewater produced by phosphorus chemical industry is discharged intermittently, and the method of the present invention is also processed in batches, the sieve drum is detachably connected, and there is enough time to clean the sieve drum between two treatments to prepare for the next batch of processing. Preferably, the sieve filter aperture of the sieve drum is 100 μm. This aperture takes into account the particle size of the separated elemental sulfur crystals. It can not only intercept the elemental sulfur crystals by the sieve and use the sewage circulation to allow the elemental sulfur crystals to grow gradually, but also avoid the sieve being blocked too quickly, resulting in increased resistance.

[0021] Furthermore, when the turbidity of the sulfur-containing wastewater drops below 5 NTU, the sulfur in the wastewater becomes difficult to remove using the above method. At this point, the process is discontinued and the dosage of hydrogen peroxide solution is increased to control the wastewater's redox potential between 200 and 240 mV. This oxidizes the remaining sulfur in the wastewater into sulfate ions, further reducing the sulfide content. The resulting wastewater can then be sent to a subsequent centralized wastewater treatment process and mixed with other wastewater for treatment, effectively preventing the sulfide from mixing with other acidic wastewater and overflowing with hydrogen sulfide gas. Preferably, the reaction time is 5-10 minutes with stirring to ensure the peroxidation effect.

[0022] The present invention can monitor the pH and redox potential of sewage online, thereby automatically controlling the dosage of the reagent through PLC; it can also monitor the turbidity of sewage online, thereby flexibly controlling the timing of excessive addition of hydrogen peroxide solution, realizing automatic control and saving time and labor.

[0023] The beneficial effects of the present invention are:

[0024] 1. The method of the present invention adopts "chemical oxidation" combined with "centrifugal separation" technology to directionally oxidize sulfides in sulfur-containing wastewater into elemental sulfur, and uses a sieve drum to achieve simple and efficient interception. Subsequently, the remaining sulfur element in the wastewater is cleverly oxidized into sulfate ions through excessive addition of hydrogen peroxide solution, effectively removing residual sulfides. Through the pretreatment of sulfur-containing wastewater, it can avoid the overflow of hydrogen sulfide gas after high-concentration sulfur-containing wastewater mixes with other phosphorus chemical acidic wastewater, causing safety accidents, thereby meeting the needs of centralized and safe treatment of wastewater discharged by phosphorus chemical enterprises.

[0025] 2. The system of the present invention is simple, with low investment and operating costs, compact equipment, small footprint, effective matching of the production rhythm of phosphorus chemical enterprises, strong applicability to high-concentration sulfur-containing wastewater intermittently discharged by phosphorus chemical industry, stable pollutant removal effect, and can treat sulfur-containing wastewater with a sulfide concentration of 5000 to 8000 mg / L in chemical enterprises. The sulfide removal rate can reach more than 99%, with high treatment efficiency, easy maintenance and overhaul, and long-term stable operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a process flow chart and system diagram of the present invention.

[0027] Among them, 1-circulation reaction box, 1.1-sewage inlet, 1.2-sewage outlet, 2-agitator, 3-pH online monitor, 4-oxidation-reduction potential online monitor, 5-hydrogen peroxide solution dosing equipment, 6-acid dosing equipment, 7-alkali dosing equipment, 8-hydrocyclone, 8.1-overflow conduit, 8.2-cyclone chamber, 8.3-cone, 8.4-bottom flow outlet, 9-lifting pump, 10-sieve drum, 11-PLC, 12-turbidity online monitor, 13-first shut-off valve, 14-second shut-off valve, 15-partition, 15.1-hole, 16-sight mirror, 17-external discharge pipe, A-reaction zone, B-lifting zone. DETAILED DESCRIPTION

[0028] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not intended to limit the present application.

[0029] System Example: See Figure 1 The phosphorus chemical industry sulfur-containing wastewater treatment system includes a circulating reaction tank 1, which is divided into a reaction zone A and a lifting zone B by a partition 15 with a lower opening 15.1. Reaction zone A has a wastewater inlet 1.1, an agitator 2 at the front, and a sieve drum 10 at the rear, with a sight glass 16 installed nearby for observing sieve drum blockage. A wastewater outlet 1.2 is located at the bottom of lifting zone B. This outlet 1.2 is connected to the feed inlet and an external discharge pipe 17 of a hydrocyclone 8 via a lift pump 9 and then, respectively, through a first shut-off valve 13 and a second shut-off valve 14. An overflow conduit 8.1 at the top of the hydrocyclone 8 connects to the reaction zone A of the circulating reaction tank 1, and an underflow port 8.4 at the bottom is detachably connected to the sieve drum 10, whose mesh has a filtration aperture of 100 μm. The upper section of the hydrocyclone 8 comprises a cyclone chamber 8.2, and the lower section comprises a cone 8.3 with a cone angle of 6°.

[0030] As another embodiment, the reaction zone A is provided with a pH online monitor 3, an oxidation-reduction potential online monitor 4 and a turbidity online monitor 12. The data output ends of the pH online monitor 3, the oxidation-reduction potential online monitor 4 and the turbidity online monitor 12 are connected to the data input end of the PLC 11, and the control signal output end of the PLC 11 is respectively connected to the control ends of the hydrogen peroxide solution dosing device 5, the acid dosing device 6 and the alkali dosing device 7.

[0031] Process Example:

[0032] Sulfur-containing wastewater from a phosphorus chemical plant enters the circulating reactor 1 in batches through wastewater inlet 1.1. This process operates in a sequential batch mode. During the treatment of a batch of sulfur-containing wastewater, an online pH monitor 3 and an online redox potential monitor 4 installed in reaction zone A output wastewater pH and redox potential signals to a programmable logic controller (PLC) 11. After analyzing and comparing these data, PLC 11 outputs control signals to the control terminals of the hydrogen peroxide dosing device 5, the acid dosing device 6, and the alkali dosing device 7, controlling the dosage of hydrogen peroxide and the acid / alkali dosage. Ultimately, the wastewater pH in reaction zone A is maintained at 6.3 and the redox potential at 30-60 mV. This environment prevents hydrogen sulfide gas overflow and potential safety hazards, while ensuring that the oxidizing properties of the hydrogen peroxide solution oxidize sulfides to elemental sulfur. Simultaneously, the stirring speed of agitator 2 in reaction zone A is controlled at 20-60 rpm, enabling rapid diffusion of the reagent throughout the wastewater and increasing the collision and agglomeration rate of elemental sulfur, rapidly increasing the particle size of the sulfur to facilitate elemental sulfur crystal growth. The solid-liquid bottom layer in reaction zone A flows through opening 15.1 below partition 15 to lifting zone B. It is then pressurized by lifting pump 9 through sewage outlet 1.2 and fed into the feed port of hydrocyclone 8 (first shut-off valve 13 is open and second shut-off valve 14 is closed). The sewage forms a vortex under the centrifugal action of cyclone chamber 8.2 of hydrocyclone 8. The light phase at the top and overflow water containing small particles are circulated back to circulation reaction tank 1 through overflow conduit 8.1. Elemental sulfur of a certain particle size has a greater density than water and, under the action of inertial centrifugal force, accelerates its sinking through cone 8.3, flowing out of bottom flow outlet 8.4 and into sieve drum 10. The elemental sulfur crystals in the sewage are intercepted by the screen of sieve drum 10. The filtered sewage is then circulated back to circulation reaction tank 1 for further oxidation reaction. After several rounds of recycling, most of the elemental sulfur in the sewage is removed.

[0033] The turbidity of the sulfur-containing wastewater in the reaction zone A is continuously monitored by an online turbidity monitor 12. When the turbidity drops below 5 NTU, the lift pump 9 is controlled to stop working, the first shut-off valve 13 is closed, and the PLC 11 controls the hydrogen peroxide solution dosing device 5 to add an excess amount of hydrogen peroxide solution to the circulating reaction tank 1. The redox potential of the wastewater is controlled to be between 200 and 240 mV. The stirring speed is increased to 80 rpm and the reaction is carried out for 5-10 minutes to rapidly oxidize the remaining sulfur in the wastewater into sulfate ions. After the reaction is completed, the second shut-off valve 13 and the lift pump 9 are opened, and all the wastewater in the circulating reaction tank 1 is sent to the subsequent centralized wastewater treatment process via the lift pump 9 and the external discharge pipe 17. At this time, it can be subsequently treated together with other wastewater from the phosphorus chemical enterprise. This can prevent the overflow of hydrogen sulfide gas after the high-concentration sulfur-containing wastewater mixes with other phosphorus chemical acidic wastewater, causing safety accidents, and meet the centralized safety treatment needs of phosphorus chemical enterprises.

[0034] Among them, the sieve filtration aperture of the sieve drum 10 is 100μm, and the sight glass 16 installed nearby can observe the operation of the sieve at any time. When a large amount of elemental sulfur crystals adhere to the sieve and affect normal filtration, the sieve drum 10 can be removed and cleaned during the intervals of batch operation, or it can be removed and cleaned regularly to filter and intercept the elemental sulfur.

[0035] The present invention utilizes chemical oxidation to oxidize most sulfides to elemental sulfur. After centrifugal separation and physical filtration, the elemental sulfur is removed, and the remaining sulfur is peroxidized to sulfate. After treatment with the method of the present invention, the sulfide removal efficiency in the wastewater discharged through the external discharge pipe 17 reaches over 99%. The treated wastewater can be mixed with other acidic wastewater and safely treated in a centralized manner, without hydrogen sulfide gas spillage. The capacity of the circulating reaction tank 1 is rationally designed based on the amount of sulfur-containing wastewater generated by the corresponding phosphorus chemical enterprise during a certain period of time, matching the enterprise's production rhythm, and achieving high operating efficiency. The entire system is simple in structure, requiring only cleaning of the screen drum 10, making it easy to maintain and overhaul, and capable of long-term stable operation.

Claims

1. A phosphorus chemical sulfur-containing wastewater treatment system, comprising a circulating reaction box, characterized in that: The circulating reaction box is divided into a reaction zone and a lifting zone by a partition with holes in the lower section. The reaction zone is provided with a sewage inlet, a stirrer is installed in the front section, and a screen drum is installed in the rear section. A sewage outlet is provided at the bottom of the lifting zone, and the sewage outlet is connected to the feed port and the external discharge pipe of the hydrocyclone respectively through a lifting pump. The overflow conduit at the top of the hydrocyclone is connected to the reaction zone of the circulating reaction box, and the underflow port at the bottom is detachably connected to the screen drum.

2. The phosphorus chemical sulfur-containing wastewater treatment system according to claim 1, characterized in that: The reaction zone is provided with a pH online monitor, an oxidation-reduction potential online monitor, and a turbidity online monitor. The data output ends of the pH online monitor, the oxidation-reduction potential online monitor, and the turbidity online monitor are connected to the data input end of the PLC. The control signal output end of the PLC is respectively connected to the control ends of the hydrogen peroxide solution dosing device, the acid dosing device, and the alkali dosing device.

3. The phosphorus chemical sulfur-containing wastewater treatment system according to claim 1, characterized in that: The sieve filter aperture of the sieve cylinder is 100 μm.

4. The phosphorus chemical sulfur-containing wastewater treatment system according to claim 1, characterized in that: A sight glass is installed near the screen cylinder.

5. The phosphorus chemical sulfur-containing wastewater treatment system according to any one of claims 1 to 4, characterized in that: The upper section of the hydrocyclone is a cyclone chamber, and the lower section is a cone.

6. The phosphorus chemical sulfur-containing wastewater treatment system according to claim 5, characterized in that: The cone angle is 6°.

7. A method for treating sulfur-containing wastewater from a phosphorus chemical industry, wherein the sulfur-containing wastewater is fed into a circulating reaction box in batches for treatment, characterized in that: The phosphorus chemical sulfur-containing wastewater treatment system according to any one of claims 1 to 6 is used, and each batch of sulfur-containing wastewater is treated by: 1) First, hydrogen peroxide solution is added to the reaction zone in the circulating reaction box to control the redox potential of the sulfur-containing wastewater to 30-60mV, and acid or alkali is added to adjust the pH value to 6.

3. While stirring, the sulfide in the sulfur-containing wastewater is directionally oxidized to elemental sulfur. The wastewater in the lifting zone of the circulating reaction box is circulated and sent to the hydrocyclone for centrifugation through the lifting pump. The overflow liquid at the top of the hydrocyclone is returned to the circulating reaction box, and the solid and liquid at the bottom are filtered through a screen and returned to the circulating reaction box; 2) When the turbidity of the sulfur-containing wastewater drops below 5NTU, the lift pump stops working, and an excessive amount of hydrogen peroxide solution is added to the circulation reaction tank to control the wastewater redox potential at 200-240mV. The reaction is stirred for 5-10 minutes to oxidize the remaining sulfur in the wastewater into sulfate ions. Finally, all the wastewater in the circulation reaction tank is discharged through the lift pump and sent to the subsequent centralized wastewater treatment process.

8. The method for treating sulfur-containing wastewater from phosphorus chemical industry according to claim 7, wherein: In the step 1), the stirring speed is controlled to be 20-60 rpm.

9. The method for treating sulfur-containing wastewater from phosphorus chemical industry according to claim 7, wherein: In step 2), the stirring speed was controlled to 80 rpm.

Images