Device and method for synchronously removing floating objects and ammonia nitrogen in blast furnace gas washing water

Abstract

The invention relates to a device and a method for synchronously removing floating objects and ammonia nitrogen in blast furnace gas washing water. The device comprises a high-density sedimentation tank, a skimmer and a chemical reaction unit, the high-density sedimentation tank comprises a mixing area, a reaction area and a sedimentation area, and the skimmer is located above the mixing area of the high-density sedimentation tank; the chemical reaction unit comprises a physicochemical reaction tank and a breakpoint oxidation tank, the physicochemical reaction tank comprises a reaction zone and a settling zone, the breakpoint oxidation tank comprises a first-stage oxidation tank, a second-stage oxidation tank and a third-stage oxidation tank, and the second-stage oxidation tank and the third-stage oxidation tank respectively comprise a pH adjusting zone, an oxidation zone and a settling zone. Blast furnace gas washing water enters the high-density sedimentation tank, floating objects are separated and removed by the skimmer, and after the remaining washing water sequentially flows through the mixing area, the reaction area, the sedimentation area, the physicochemical reaction tank and the breakpoint oxidation tank, effluent reaches the standard and is discharged or recycled. According to the invention, the problem of up-to-standard treatment of blast furnace gas washing water is solved, smooth production is guaranteed, and zero discharge of wastewater is realized.

Description

Technical Field

[0001] The invention relates to the technical field of steel smelting and water treatment, and in particular to a device and method for synchronously removing floating matter and ammonia nitrogen in blast furnace gas washing water. Background Art

[0002] The gas drawn from the blast furnace is generally first passed through a gravity dust collector to remove large dust particles, and then introduced into the gas washing system through a pipeline for cleaning and cooling. The wastewater generated after repeated cycles of cleaning and cooling is the blast furnace gas washing water. This wastewater not only has a water temperature of more than 60°C, but also contains a large amount of suspended matter composed of iron ore powder and coke powder, as well as phenol, cyanide, ammonia nitrogen, sulfide and zinc. Due to the large amount of water and heavy pollution of this type of wastewater, it must be fully treated before it can be recycled.

[0003] In recent years, affected by the changes in blast furnace charges, the ammonia nitrogen content of blast furnace gas washing water has increased significantly, with the average value rising from 50 mg / L to more than 200 mg / L, and various floating objects in the return water are difficult to settle, resulting in the continuous deterioration of the effluent water quality, which seriously affects the safety of blast furnace water supply. At present, the common blast furnace gas washing water treatment process mainly includes coagulation and sedimentation (adding PAC and PAM), water quality stabilization (adding scale inhibitors), cooling (cooling), and sludge treatment. It basically does not have the ability to treat ammonia nitrogen and floating objects. Therefore, how to efficiently treat the ammonia nitrogen in blast furnace gas washing water, and at the same time let the floating objects settle quickly so that the total outlet water quality meets the standards, is a problem that needs to be solved urgently.

[0004] Blast furnace gas washing water has the characteristics of high salinity and complex components. It also contains a certain concentration of ammonia nitrogen. Therefore, it has poor biodegradability and is difficult to treat using conventional biological methods. The stripping method is one of the effective treatment methods for high ammonia nitrogen wastewater. The main disadvantages of this method are that the aeration fan has high energy consumption and there is a certain amount of noise pollution. In addition, part of the ammonia gas blown out is absorbed by the acidic solution, and the other part is discharged at a high point, causing the transfer of pollution factors. Therefore, the stripping method is not an environmentally friendly treatment method. Although the breakpoint oxidation method has the advantages of high ammonia nitrogen removal efficiency, no influence of water temperature, convenient operation, and investment saving, it also has problems such as high treatment cost. More importantly, a large amount of chloride remains in the treated water, which will cause secondary pollution and is not conducive to the reuse of wastewater. The chemical precipitation method is more suitable for the treatment of high-concentration ammonia nitrogen wastewater due to its simple equipment and high removal efficiency, but the cost of the precipitant is high and there are problems in large-scale application.

[0005] In short, the existing treatment methods for high-ammonia nitrogen wastewater cannot be directly used for blast furnace gas washing water. Summary of the invention

[0006] The main purpose of the present invention is to solve the above-mentioned problems existing in the prior art, and to provide a device for synchronously removing floating objects and ammonia nitrogen in blast furnace gas washing water, which includes: a high-density sedimentation tank, a skimmer, and a chemical reaction unit; the high-density sedimentation tank includes a mixing zone, a reaction zone, and a sedimentation zone arranged in sequence along the water flow direction, and the skimmer is located above the mixing zone of the high-density sedimentation tank; the chemical reaction unit includes a physicochemical reaction tank and a turning point oxidation tank arranged in sequence along the water flow direction, and the sedimentation zone of the high-density sedimentation tank is connected to the physicochemical reaction tank of the chemical reaction unit. The blast furnace gas washing water enters the high-density sedimentation tank, and the floating objects are separated and removed by the skimmer. The remaining washing water flows through the mixing zone, the reaction zone, the sedimentation zone, the physicochemical reaction tank, and the turning point oxidation tank in sequence, and the effluent meets the discharge standards.

[0007] Furthermore, the device also includes a sludge storage tank, a collecting tank, a spiral pump, and a water pump. The water outlet of the skimmer is connected to the collecting tank. A spiral pump is arranged on the top of the collecting tank, and the spiral pump pushes the floating objects into the sludge storage tank; a water pump is arranged at the bottom of the collecting tank, and the water pump transports the wastewater obtained by solid-liquid separation back to the mixing area of ​​the high-density sedimentation tank.

[0008] Furthermore, stirring devices (such as stirrers or stirring paddles) are provided in the mixing zone and the reaction zone of the high-density sedimentation tank.

[0009] Furthermore, the reaction zone is composed of a stirring tank and a plug flow reaction tank connected in series.

[0010] Furthermore, the sedimentation area includes an inclined plate and a mud scraper, the inclined plate is arranged at the upper part of the sedimentation area, the mud scraper is arranged at the bottom of the sedimentation area, and the sedimentation area is connected to the mud storage tank.

[0011] Furthermore, the physicochemical reaction pool includes a reaction zone and a sedimentation zone arranged in sequence along the water flow direction, and the sedimentation zone is connected to the mud storage tank.

[0012] Furthermore, the inflection point oxidation pond comprises a primary oxidation pond, a secondary oxidation pond, and a tertiary oxidation pond arranged in sequence along the water flow direction, wherein the secondary oxidation pond and the tertiary oxidation pond both comprise a pH adjustment zone, an oxidation zone, and a precipitation zone arranged in sequence along the water flow direction.

[0013] Furthermore, the sedimentation areas of the secondary and tertiary oxidation tanks are both connected to the mud storage tank.

[0014] The second object of the present invention is to provide a method for simultaneously removing floating matter and ammonia nitrogen in blast furnace gas washing water, comprising: inputting the blast furnace gas washing water into a high-density sedimentation tank, and using a skimmer to separate and remove floating matter therein; then transporting the remaining washing water into a physicochemical reaction tank to remove ammonia nitrogen therein; finally, transporting the treated washing water into a breakpoint oxidation tank to remove cyanide and ammonia nitrogen therein, and the effluent meets the standards for discharge or reuse.

[0015] Furthermore, polyaluminium chloride (PAC) and polyacrylamide (PAM) need to be added to the mixing zone of the high-density sedimentation tank and stirred sufficiently.

[0016] Furthermore, a precipitant Na3PO4 or its hydrate needs to be added to the reaction zone of the physicochemical reaction tank and stirred sufficiently to control the P:N molar ratio in the mixture to be 1.5-1.8:1.

[0017] Furthermore, polyacrylamide needs to be added to the precipitation area of ​​the physicochemical reaction tank.

[0018] Furthermore, sodium hypochlorite (NaClO) needs to be added to the primary oxidation tank of the inflection point oxidation tank, sodium hydroxide (NaOH), sodium hypochlorite and polyacrylamide need to be added to the pH adjustment zone, oxidation zone and precipitation zone of the secondary oxidation tank, respectively; hydrochloric acid (HCl), sodium hypochlorite and polyacrylamide need to be added to the pH adjustment zone, oxidation zone and precipitation zone of the tertiary oxidation tank, respectively.

[0019] Furthermore, the blast furnace gas washing water is alkaline (pH 7-9), with a total alkalinity of 700-950 mg / L, suspended solids (ss) of 500-3500 mg / L, ammonia nitrogen of 150-240 mg / L, and chloride of 1300-4000 mg / L.

[0020] Compared with the existing similar technologies, the advancement of the present invention is mainly reflected in the following points:

[0021] (1) The blast furnace gas washing wastewater is treated by using high-density sedimentation tanks, skimmers, physicochemical reaction tanks, inflection point oxidation tanks, etc., so that it can be reused in this process after meeting the standards. This achieves zero discharge of blast furnace gas washing wastewater and avoids the pollution to the environment caused by traditional treatment methods.

[0022] (2) A set of special blast furnace gas washing wastewater treatment equipment was assembled using a number of relatively conventional equipment. The entire treatment process is relatively simple, easy to maintain and repair, has a wide range of applications, and is very easy to transform or operate on site.

[0023] (3) The method of the present invention is used to treat blast furnace gas washing wastewater, which, on the one hand, reduces the amount of wastewater discharged, and on the other hand, can reduce the water cost of related processes, while achieving multiple purposes such as energy saving and environmental protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Schematic diagram of the process for simultaneously removing floating matter and ammonia nitrogen from blast furnace gas washing water.

[0025] Figure 2 The diagram below shows the working principle of the skimmer.

[0026] Figure 3 This is a real picture of the skimmer. DETAILED DESCRIPTION

[0027] In order to enable ordinary technicians in the field to fully understand the technical solutions and beneficial effects of the present invention, the following is further described in conjunction with specific embodiments and drawings. It should be emphasized that the embodiments listed below are only preferred implementations of the present invention, and simple replacements or improvements made on the basis thereof still fall within the scope of protection of the present invention.

[0028] Example 1

[0029] The complete set of equipment for synchronously removing floating matter and ammonia nitrogen in blast furnace gas washing water provided by the present invention is as follows: Figure 1-3 As shown, the corresponding process flow is as follows:

[0030] (1) The blast furnace gas washing water to be treated is the wastewater (total amount 10L) generated by the wet dust removal of the blast furnace, which is the sewage discharged multiple times after coagulation, sedimentation and cooling treatment and recycling. The water quality indicators of the blast furnace gas washing water are shown in Table 1.

[0031] (2) First, the above-mentioned blast furnace gas washing wastewater is sent to the mixing zone of the high-density sedimentation tank. The high-density sedimentation tank is provided with a mixing zone, a reaction zone and a sedimentation zone. 20 mL of PAC with a mass concentration of 5% and 10 mL of PAM with a mass concentration of 0.1% are added to the mixing zone, and a rapid mixer is used to fully stir the coagulant material so that the added coagulant material is quickly dispersed and fully mixed with the wastewater in the tank to form small flocs.

[0032] (3) A set of water inlet baffles is installed on the top of the mixing area of ​​the high-density sedimentation tank. Figure 2-3 The skimmer shown. In the process of sending the blast furnace gas washing wastewater into the mixing area of ​​the high-density sedimentation tank, the skimmer is used and the principle of gravity is used to separate the floating objects from the wastewater under the push of the water flow. The water discharged from the skimmer is sent to the collection tank. A spiral pump is set at the top of the collection tank. The spiral pump pushes the surface floating objects into the mud storage tank (that is, the separated floating objects enter the mud storage tank). A water delivery pump is set at the bottom of the collection tank. The water delivery pump adopts liquid level control to return the separated wastewater to the mixing area of ​​the high-density sedimentation tank.

[0033] (4) The washing water in the mixing zone of the high-density sedimentation tank flows into the bottom of the circular guide pipe in the reaction zone, and is stirred and mixed evenly from bottom to top by the stirring paddle in the guide pipe. The reaction zone of the high-density sedimentation tank is a series reaction unit composed of a stirring tank and a plug-flow reaction tank. After the washing water fully reacts here and obtains larger flocs, it is transported to the sedimentation zone of the high-density sedimentation tank for rapid sedimentation. During this period, the flocculated alum flowers flow slowly into the sedimentation zone to avoid damage to the alum flowers. The flocculated alum flowers gather into sludge at the bottom of the sedimentation zone and are concentrated, and then transported to the sludge storage tank through a pipeline.

[0034] In order to achieve the above purpose and effect, an inclined plate for removing excess alum flowers is set at the top of the sedimentation area of ​​the high-density sedimentation tank, and the inclined plate is used to ensure the effluent quality of the sedimentation area. A sludge scraper is set at the bottom of the sedimentation area of ​​the high-density sedimentation tank. The sludge scraper continuously scrapes and sweeps to promote the concentration of sludge in the sedimentation area. The concentrated sludge is first sent to the sludge storage tank and then dehydrated.

[0035] (5) The effluent from the sedimentation area of ​​the high-density sedimentation tank flows into the chemical reaction unit. The chemical reaction unit includes two reaction tanks connected in series, which respectively treat ammonia nitrogen and cyanide in the wastewater. The first reaction tank is a physicochemical reaction tank, and the second reaction tank is a breakpoint oxidation tank.

[0036] The physicochemical reaction tank includes a reaction zone and a precipitation zone. After the wastewater enters the reaction zone, Na3PO4·12H2O is added as a precipitant. Phosphate ions are added to the blast furnace gas washing water containing ammonia nitrogen, and the Mg in the blast furnace gas washing water is used to react at a certain pH value to generate ammonium magnesium phosphate precipitation. The main reaction is:

[0037] Mg 2+ +NH 4+ +PO4 3- +6H2O=NH4MgPO4·6H2O.

[0038] When the ammonia nitrogen content in the wastewater is about 180 mg / L, the molar ratio of P:N is controlled to be 1.5-1.8:1, thereby pre-treating the ammonia nitrogen in the wastewater. The physicochemical reaction time is about 60 minutes, and magnetic stirring is performed after the addition is completed. The speed is controlled between 250-300 r / min, and the ammonia nitrogen removal efficiency is measured to be 20%-40%.

[0039] The reason why Na3PO4·12H2O is selected as the precipitant in this process is that it can increase the pH value of the wastewater. The pH value determines the existence form and activity of various ions that make up the precipitate when they reach equilibrium in the water, which is beneficial to the removal of ammonia nitrogen within a certain range.

[0040] The effluent from the reaction zone of the physicochemical reaction tank enters the sedimentation zone, and an appropriate amount of PAM with a mass concentration of 0.1% is added and left to stand for 15-20 minutes. The separated supernatant enters the next step of the inflection point oxidation tank for oxidation treatment, and the sludge at the bottom of the sedimentation zone enters the sludge storage tank for dehydration treatment.

[0041] (6) The breakpoint oxidation pond is divided into three levels, namely the primary oxidation pond, the secondary oxidation pond, and the tertiary oxidation pond. The secondary oxidation pond and the tertiary oxidation pond include a pH adjustment zone, an oxidation zone, and a precipitation zone. The raw materials added to each functional zone are different.

[0042] The supernatant first enters the primary oxidation tank of the breakpoint oxidation tank, where sodium hypochlorite solution (the effective chlorine content of the solution is about 6%) is added according to the mass ratio of ammonia nitrogen to chlorine = 1:7.6-8. After 25-35 minutes of oxidation reaction, the ammonia nitrogen removal rate is measured to be 70-80%.

[0043] (7) The effluent from the primary oxidation pool of the inflection point oxidation pool enters the pH adjustment zone, oxidation zone and precipitation zone of the secondary oxidation pool in turn. Sodium hydroxide is added to the pH adjustment zone of the secondary oxidation pool according to the pH value of the wastewater to control the pH value of the mixed solution not to exceed 10 (such as 9-10), and the hydraulic retention time is 5-8 minutes. Due to the increase in pH, heavy metal elements such as Pb and Zn contained in the wastewater can form hydroxide precipitation and precipitate in the subsequent precipitation zone.

[0044] The effluent from the pH adjustment zone of the secondary oxidation tank enters the oxidation zone, where the oxidant sodium hypochlorite is added to carry out oxidation decyanation and oxidation treatment of some residual ammonia nitrogen. The dosage of sodium hypochlorite is controlled at more than 40 mg / L, and the oxidation reaction time is 10-12 minutes. After the feeding, a stirring device is used for stirring, and the stirring speed is about 200r / min.

[0045] The effluent from the oxidation zone of the secondary oxidation tank enters the sedimentation zone, where an appropriate amount of PAM with a mass concentration of 0.1% is added and left to stand for 8-10 minutes. The separated supernatant is sent to the tertiary oxidation tank for further oxidation treatment, and the sludge at the bottom of the sedimentation zone of the secondary oxidation tank is discharged for dehydration treatment.

[0046] (8) The supernatant in the sedimentation zone of the secondary oxidation tank first enters the pH adjustment zone of the tertiary oxidation tank, where an appropriate amount of HCl solution is added to control the pH of the mixed solution between 7.5 and 8 and stay for 5 to 8 minutes.

[0047] The effluent from the pH adjustment area of ​​the tertiary oxidation tank enters the oxidation area, where the oxidant sodium hypochlorite is added and fully stirred using the matching stirring device to continue oxidation to remove cyanide and residual ammonia nitrogen. The amount of sodium hypochlorite added is controlled below 20 mg / L, and the reaction time is controlled within 25-30 minutes.

[0048] The effluent from the oxidation zone of the tertiary oxidation pond enters the sedimentation zone, where an appropriate amount of PAM with a mass concentration of 0.1% is added and left to stand for 8-10 minutes. The separated supernatant re-enters the system for reuse, and the sludge at the bottom of the sedimentation zone is discharged for dehydration. The supernatant in the sedimentation zone can be reused in the system's reagent preparation, sludge dehydration, filter press belt washing, etc.

[0049] The physical and chemical parameters of blast furnace gas washing water before and after treatment are shown in Table 1.

[0050] Table 1 Comparison of water quality before and after blast furnace gas washing water treatment

[0051]

[0052] It can be seen from Table 1 that the suspended matter and ammonia nitrogen contents in the effluent after the treatment of blast furnace gas washing wastewater are greatly reduced, wherein the removal rate of suspended matter is more than 85%, and the removal rate of ammonia nitrogen is more than 70%. This shows that the treatment device and treatment method of the present invention are feasible, and the treated water quality also meets the reuse standard.

[0053] In summary, the present invention solves the following problems: (1) In the case of a drastic change in water quality, the blast furnace gas washing water is treated to meet the standards, thereby ensuring smooth production; (2) The blast furnace gas washing water is treated by this method and can be reused in this process after meeting the standards, thus truly achieving zero discharge of blast furnace gas washing wastewater without causing pollution to the environment.

Claims

1. A device for simultaneously removing floating matter and ammonia nitrogen from blast furnace gas washing water, characterized in that: The device comprises a high-density sedimentation tank, a skimmer, and a chemical reaction unit. The high-density sedimentation tank comprises a mixing zone, a reaction zone, and a sedimentation zone arranged in sequence along the water flow direction, and the skimmer is located above the mixing zone of the high-density sedimentation tank; the chemical reaction unit comprises a physicochemical reaction tank and a turning point oxidation tank arranged in sequence along the water flow direction, and the sedimentation zone of the high-density sedimentation tank is connected to the physicochemical reaction tank of the chemical reaction unit.

2. The device according to claim 1, characterized in that: The device also includes a mud storage tank, a collection tank, a spiral pump, and a water pump. The water outlet of the skimmer is connected to the collection tank. A spiral pump is arranged on the top of the collection tank. A water pump is arranged on the bottom of the collection tank. The water pump is connected to the mixing area of ​​the high-density sedimentation tank.

3. The device according to claim 1, characterized in that: A stirring device is arranged in the mixing zone and the reaction zone of the high-density sedimentation tank, and the stirring device comprises a stirrer and a stirring paddle.

4. The device according to claim 1, characterized in that: The reaction zone of the high-density sedimentation tank is composed of a stirring tank and a plug-flow reaction tank connected in series.

5. The device according to claim 1, characterized in that: The sedimentation area of ​​the high-density sedimentation tank includes an inclined plate and a mud scraper. The inclined plate is arranged at the upper part of the sedimentation area, the mud scraper is arranged at the bottom of the sedimentation area, and the sedimentation area is connected with the mud storage tank.

6. The device according to claim 1, characterized in that: The physicochemical reaction pool comprises a reaction zone and a sedimentation zone which are sequentially arranged along the water flow direction, and the sedimentation zone is communicated with the mud storage tank.

7. The device according to claim 1, characterized in that: The inflection point oxidation pond comprises a primary oxidation pond, a secondary oxidation pond, and a tertiary oxidation pond which are sequentially arranged along the water flow direction, wherein the secondary oxidation pond and the tertiary oxidation pond both comprise a pH adjustment zone, an oxidation zone, and a sedimentation zone which are sequentially arranged along the water flow direction, and the sedimentation zones of the secondary oxidation pond and the tertiary oxidation pond are both connected to the mud storage tank.

8. A method for synchronously removing floating matter and ammonia nitrogen from blast furnace gas washing water using the device according to any one of claims 1 to 7, characterized in that The method comprises: inputting blast furnace gas washing water into a high-density sedimentation tank, separating and removing floating matter therein by a skimmer, and then conveying the remaining washing water to a physicochemical reaction tank and a breakpoint oxidation tank in sequence for treatment, and discharging or reusing the effluent when it meets the standards.

9. The method according to claim 8, characterized in that: PAC and PAM need to be added to the mixing zone of the high-density sedimentation tank and stirred sufficiently; Na3PO4 or its hydrate needs to be added to the reaction zone of the physicochemical reaction tank and stirred sufficiently, and the P:N molar ratio in the mixture should be controlled to be 1.5-1.8:1; PAM needs to be added to the sedimentation zone of the physicochemical reaction tank; NaClO needs to be added to the primary oxidation tank of the inflection point oxidation tank, NaOH, NaClO and PAM need to be added to the pH adjustment zone, oxidation zone and sedimentation zone of the secondary oxidation tank respectively, and HCl, NaClO and PAM need to be added to the pH adjustment zone, oxidation zone and sedimentation zone of the tertiary oxidation tank respectively.

10. The method according to claim 8, characterized in that: The blast furnace gas washing water has a pH value of 7-9, a total alkalinity of 700-950 mg / L, suspended solids (ss) of 500-3500 mg / L, ammonia nitrogen of 150-240 mg / L, and chloride of 1300-4000 mg / L.

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