CN101462801A - A system and process for iron and steel comprehensive wastewater reuse double-membrane desalination - Google Patents

Abstract

The invention discloses a system and a process for desalination of iron and steel comprehensive sewage reuse water by a double-membrane method, belonging to the technical field of sewage treatment and reuse. The system includes cooling tower, raw water tank, micro-flocculation filter device, bypass activated carbon filter tank, laminated filter, ultrafiltration system, precision filter, reverse osmosis system, reverse osmosis desalination tank. It is used to solve the problem of double-membrane desalination of comprehensive sewage reuse water in iron and steel enterprises. The double-membrane method is used to desalinate, and the pretreated water is first treated by an ultrafiltration device to meet the requirement of SDI≤3, and then desalted by a reverse osmosis device. The combination of pre-oxidation, micro-flocculation filtration, side-flow activated carbon filtration and self-cleaning filtration is used to treat the reused water of iron and steel comprehensive sewage, which greatly improves the operation stability and service life of the double-membrane desalination system, and effectively realizes the sewage Recycling and "zero discharge" of sewage have important practical value for the desalination of iron and steel comprehensive sewage reuse water.

Description

A system and process for iron and steel comprehensive wastewater reuse double-membrane desalination

technical field

The invention belongs to the technical field of iron and steel sewage treatment and reuse, and in particular relates to a system and process for desalination of iron and steel comprehensive sewage reused by a double-membrane method, which is suitable for advanced treatment and desalination and reuse of iron and steel comprehensive sewage.

Background technique

Sewage reuse is an important way for iron and steel enterprises to achieve "water saving and emission reduction". In order to save water and increase the reuse rate of water resources in the entire iron and steel plant, iron and steel companies, which are large water users, have successively invested in sewage treatment plants to reuse the treated water in order to save the replenishment of water sources; at the same time, Due to factors such as concentration and evaporation of the entire steel plant water system, the sewage water entering the sewage treatment plant has complex water quality and high salt content, and the sewage without deep desalination treatment is reused, resulting in an increase in the salt content of the steel plant water system and the concentration multiple. Increase difficulty and exacerbate the corrosion tendency of the system, etc.

At present, most domestic iron and steel companies use lime softening-clarification-filtration-disinfection process for comprehensive sewage (production wastewater containing no more than 30% of domestic sewage) to meet the water reuse requirements and then perform double-membrane desalination and reuse. Due to the complex and fluctuating quality of reclaimed water in sewage treatment plants, the life of the double-membrane desalination system is very short and its operation is very unstable. Therefore, some companies have added some pretreatment measures before the double-membrane desalination system, such as increasing the cooling tower to cool down in summer, adding micro-flocculation to remove some suspended solids, colloids and COD, and adding laminated filters to remove some suspended solids. Injection of powdered activated carbon before the raw water tank to remove part of the dissolved organic matter, or even a combination of these measures. Obviously, these measures can only improve the water quality entering the double-membrane desalination system from some aspects; although some measures can solve some problems, they have created new problems. For example, the method of injecting powdered activated carbon can be more economical. Reduce the content of dissolved organic matter, but it is easy to block the subsequent laminated filter and UF.

The above situation leads to the following main problems in the existing dual-membrane desalination system for comprehensive sewage reuse water: ①The ultrafiltration system is susceptible to colloidal fouling, which leads to an increase in transmembrane pressure difference, a decrease in membrane flux, and a significant increase in cleaning frequency; ② The reverse osmosis system is easily polluted by heavy metal ions such as iron and manganese in sewage, or microorganisms can grow due to the presence of organic matter in some dead ends. ③ All kinds of fouling will increase the operating pressure, chemical consumption and power consumption of the double-membrane desalination system. In view of the above problems, the double-membrane desalination technology for iron and steel comprehensive wastewater reuse should be continuously improved. The core issue is to strengthen the ability of double-membrane desalination pretreatment.

Contents of the invention

The purpose of the present invention is to overcome the deficiencies of the prior art and provide a system and process for iron and steel comprehensive sewage reuse double-membrane desalination, so as to realize the resource utilization of sewage and "zero discharge" of sewage in iron and steel plants.

The system of the present invention includes a cooling tower 1, a raw water tank 2, a raw water pump 3, a microflocculation filter device 4, a side flow water pump 5, a side flow activated carbon filter tank 6, a water pump 7, a laminated filter 8, an ultrafiltration system 9, Precision filter 10, reverse osmosis system 11. Among them, cooling tower 1, raw water tank 2, raw water pump 3, microflocculation filter device 4, side flow water pump 5, side flow activated carbon filter tank 6, water pump 7, and laminated filter 8 are connected by pipelines in turn to form a double-membrane method The desalination pretreatment system, the ultrafiltration system 9, the precision filter 10, the reverse osmosis system 11, and the reverse osmosis desalination tank 12 are sequentially connected by pipelines to form a double-membrane desalination system.

The micro-flocculation filter device of the present invention is connected to the water pump and the laminated filter successively through pipelines, and on the pipeline between the micro-flocculation filter device and the water pump, a side-flow water pump, a side-flow activated carbon filter tank, and a side-flow water pump are arranged. It is connected with the side flow activated carbon filter tank through the pipeline.

The filtration precision of the laminated filter in the present invention is 20-200 μm; the filtration precision of the precision filter is 5-20 μm.

Technology of the present invention is carried out as follows:

1. Double-membrane desalination pretreatment: After the comprehensive steel sewage is treated, the reused water with suspended solids less than 25mg/L, COD _Cr less than 40mg/L, mineral oil less than 3mg/L, and temporary hardness less than 100mg/L is passed through sequentially. After cooling, pre-oxidation, micro-flocculation filtration, side-flow activated carbon filtration and laminated filter treatment, most of the heavy metal ions, colloids, organic matter and mineral oil are removed to make the suspended matter less than 5mg/L and COD _Cr less than 10mg/L , Mineral oil less than 0.5mg/L, iron less than 0.5mg/L, manganese less than 0.5mg/L.

2. Double-membrane method for desalination: the pretreated water is first treated by an ultrafiltration device to meet the requirement of SDI≤3, and then enters a reverse osmosis device for desalination treatment after passing through a precision filter.

The pre-oxidation in the present invention utilizes the sump of the cooling tower or the raw water tank to carry out the pre-oxidation, and the pre-oxidation can adopt the method of aeration or oxidation by adding medicine to promote the oxidation of iron and manganese.

The filter material of the micro-flocculation filter device of the present invention adopts quartz sand or manganese sand, hydraulic retention time (hydraulic retention time, English abbreviation is HRT, is exactly " contact time " or " action time " in popular terms.) HRT=5～ 30min, the design filtration rate is 8-20m/h.

The flocculant of the micro-flocculation filtration device of the present invention is selected from FeCl ₃ (ferric chloride), PFC (polymeric ferric chloride) or PFS (polymeric ferric sulfate), and the dosage is 2-15mg/L, or adding PAC (polyaluminum chloride), the dosage is 1-15mg/L.

The side flow activated carbon filter tank of the present invention adopts granular activated carbon as the filter material, adopts the fixed bed method, and the side flow water volume is 0.1 to 100% of the total water volume, and the specific ratio needs to be set according to the water quality of the recycled water, and the hydraulic retention time HRT=1 ~15min.

The present invention has two innovative technical improvements: one is to improve the removal capacity of iron and manganese, and this effect is realized by pre-oxidizing in the sump or raw water tank of the cooling tower; The turbidity, colloid, and organic matter have a synergistic degradation effect, and the use of granular activated carbon is not easy to block subsequent devices, and the installation of laminated filters can ensure that the ultrafiltration system will not be blocked.

Advantage and positive effect of the present invention are:

The combination of pre-oxidation, micro-flocculation filtration, side-flow activated carbon filtration, and self-cleaning filtration is used to treat the reuse water of iron and steel comprehensive wastewater, which greatly improves the double-membrane method of desalination with only a small increase in investment and land occupation. The stable operation and service life of the system greatly reduce the consumption of chemicals and electricity, effectively realize the recycling of sewage and the "zero discharge" of sewage, and have good economic effects.

② Micro-flocculation filtration-activated carbon filtration combined process has a synergistic degradation effect on turbidity, colloids, and organic matter of sewage. Adding pre-oxidation before micro-flocculation filtration can further strengthen the degradation of iron, manganese, and organic matter. The invention has important practical value for the double-membrane desalination of iron and steel comprehensive sewage reuse water.

Description of drawings

Fig. 1 is a diagram of a double-membrane desalination system for iron and steel comprehensive sewage reuse water of the present invention. Among them, cooling tower 1, raw water tank 2, raw water pump 3, microflocculation filter device 4, side flow water pump 5, side flow activated carbon filter tank 6, water pump 7, laminated filter 8, ultrafiltration system 9, precision filter 10. Reverse osmosis system 11, reverse osmosis demineralized water tank 12, compressed air or oxidizing agent for pre-oxidation 13, flocculant for micro-flocculation 14, bactericide 15, hydrochloric acid for pH adjustment 16, scale inhibitor 17, reducing agent 18, Sodium hydroxide 19 for pH adjustment, 20 for iron and steel comprehensive sewage reuse, 21 for demineralized water supply, 22 for ultrafiltration concentrated water, 23 for reverse osmosis concentrated water.

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings.

The invention is suitable for the advanced treatment and desalination reuse of iron and steel comprehensive sewage.

1. Double-membrane desalination pretreatment: After the comprehensive steel sewage is treated, the reused water with suspended solids less than 25mg/L, COD _Cr less than 40mg/L, mineral oil less than 3mg/L, and temporary hardness less than 100mg/L is passed through sequentially. Cooling, pre-oxidation, microflocculation filtration, side-stream activated carbon filtration and stack filter treatments. Through technical and economical comparison, the present invention confirms that the aeration pre-oxidation in the water collection tank of the cooling tower or the raw water tank is more economical than the chemical oxidation, and there is basically no damage to the subsequent double-membrane desalination system. For the side-flow activated carbon filter tank, granular activated carbon is not easy to block the follow-up device, and the installation of a laminated filter can ensure that the ultrafiltration system will not be blocked. The fixed-bed method is adopted, and the side-flow water volume is 0.1-100% of the total water volume. The specific ratio It can be adjusted according to the water quality of the recycled water, and the hydraulic retention time HRT=1～15min.

Comprehensive sewage reuse water can remove most heavy metal ions, colloids, organic matter and mineral oil after pretreatment, so that the suspended matter is less than 5mg/L, COD _Cr is less than 10mg/L, mineral oil is less than 0.5mg/L, and iron is less than 0.5mg /L, manganese is less than 0.5mg/L.

2. Double-membrane desalination system: The pretreated water is first treated by an ultrafiltration device to remove colloidal silicon, biological pollutants, particulate matter, turbidity, and bacteria in the water to meet the requirements of SDI≤3 and meet the requirements of entering reverse osmosis. Requirements, enter the ultrafiltration product water tank. After passing through the precision filter, its filter holes are in a tapered structure, and the filter can penetrate deep to form a deep filter, which has a large amount of dirt holding capacity, long life, and is easy to replace quickly, which plays a very good role in security for the subsequent reverse osmosis device. Then enter the reverse osmosis device for desalination treatment. The main function of the reverse osmosis device is to remove the salt in the water, and the desalination rate is greater than 96%.

Specific examples are provided below:

1. Double-membrane desalination pretreatment: A steel company mixed smelting and steel rolling wastewater and the remaining about 24% of domestic sewage to produce comprehensive steel wastewater through coarse screen-fine screen-lime softening-high-density clarifier —pH adjustment—V-type filter—after adding NaClO for disinfection, the suspended solids are less than 20mg/L, COD _Cr is less than 30mg/L, mineral oil is less than 3mg/L, temporary hardness is less than 100mg/L, and residual chlorine is 0.5 mg/L reuse water, and then through cooling to control the water temperature at 8-30 ℃, aeration pre-oxidation in the cooling tower sump, raw water tank, raw water pump, choosing quartz sand as the filter material and adding 3-10mg/L FeCl ₃ (Ferric chloride) for micro-flocculation filtration, setting 10-50% of the total water volume for side-flow activated carbon filtration, and then processed by a laminated filter with a filtration accuracy of 55 μm. In addition, in order to inhibit the growth of bacteria in the water, a bactericide should be added after the raw water pump for sterilizing treatment. The bactericide can be NaClO (sodium hypochlorite), and the dosage is 0.5-3mg/L. In order to ensure the bactericidal effect of NaClO, the pH needs to be adjusted At 5.5-7.0, a certain amount of hydrochloric acid can be added. After pretreatment of comprehensive sewage reuse water, most heavy metal ions, colloids, organic matter and mineral oil can be removed to ensure that suspended matter is less than 5mg/L, COD _Cr is less than 10mg/L, mineral oil is less than 0.5mg/L, and iron is less than 0.1mg /L, manganese is less than 0.05mg/L.

2. Double-membrane desalination system: the pretreated water is first treated by an internal pressure ultrafiltration device to meet the requirements of SDI≤2, and then sent to the ultrafiltration water tank, while the ultrafiltration concentrated water is discharged to the drainage pipe network . After passing through a precision filter with a precision of 5 μm, it is boosted by a high-pressure pump and then enters a reverse osmosis device for desalination treatment. Before the ultrafiltration product water enters the precision filter, reducing agent and antiscaling agent need to be added and mixed through a pipeline mixer. The antiscaling agent can be PTP0100 high-efficiency antiscaling/dispersing agent produced by Qingli Company of the United States, and the dosage is 3~5mg/L; NaHSO ₃ (sodium bisulfite) is used as the reducing agent, and the dosage is 1~3mg/L to ensure that the chlorine content before entering the reverse osmosis device is less than 0.1mg/L. Concentrated water from reverse osmosis is discharged to remove stewed steel slag, and NaOH (sodium hydroxide) is added to adjust the pH to about 7.0 through the reverse osmosis water, and mixed with a pipeline mixer and sent to the desalinated water tank for relevant users such as steelmaking slab continuous casting It can also be used as supplementary water for circulating water system or other production water.

Claims (7)

1. A system for iron and steel comprehensive wastewater reuse double-membrane desalination, characterized in that , the system includes a cooling tower (1), a raw water tank (2), a raw water pump (3), a microflocculation filter device (4), a bypass water pump (5), a bypass activated carbon filter tank (6), a water pump (7) , laminated filter (8), ultrafiltration system (9), precision filter (10), reverse osmosis system (11), reverse osmosis desalted water tank (12); among them, cooling tower, raw water tank, raw water pump , micro-flocculation filtration device, side flow pump, side flow activated carbon filter tank, water pump, and laminated filter are connected by pipelines in turn to form a double-membrane desalination pretreatment system, ultrafiltration system, precision filter, reverse osmosis system, The reverse osmosis desalination tanks are sequentially connected by pipelines to form a double-membrane desalination system. 2. The system according to claim 1, characterized in that, the micro-flocculation filter device is connected to the water pump and the laminated filter in turn through pipelines, and a side filter is set on the pipeline between the micro-flocculation filter device and the water pump. The flow water pump and the side flow activated carbon filter tank are connected through pipelines between the side flow water pump and the side flow activated carbon filter tank. 3. The system according to claim 1, characterized in that, the filtration precision of the laminated filter is 50-200 μm; the filtration precision of the precision filter is 5-20 μm. 4. A method for desalination using the double-membrane method for the reuse of steel and iron comprehensive wastewater in the system according to claim 1, characterized in that, (1) Double-membrane desalination pretreatment: After the steel comprehensive sewage is treated, the reuse water with suspended solids less than 25mg/L, COD _Cr less than 40mg/L, mineral oil less than 3mg/L, and temporary hardness less than 100mg/L is sequentially After cooling, pre-oxidation, micro-flocculation filtration, side-flow activated carbon filtration and laminated filter treatment, most of the heavy metal ions, colloids, organic matter and mineral oil are removed, so that the suspended matter is less than 5mg/L, and the COD _Cr is less than 10mg/ L. Mineral oil less than 0.5mg/L, iron less than 0.5mg/L, manganese less than 0.5mg/L; (2: Double-membrane desalination: the pretreated water is first treated by an ultrafiltration device to meet the requirement of SDI≤3, and then enters a reverse osmosis device for desalination after passing through a precision filter. 5. The process according to claim 4, characterized in that the pre-oxidation is carried out by using the sump of the cooling tower or the raw water tank, and the pre-oxidation adopts the method of aeration or chemical oxidation to promote the oxidation of iron and manganese. 6. The process according to claim 4, characterized in that the filter material of the micro-flocculation filtration is quartz sand or manganese sand, the hydraulic retention time HRT=5-30min, and the design filtration rate is 8-20m/h; The agent is FeCl ₃ , polyferric chloride or polyferric sulfate, the dosage is 2-15mg/L, or polyaluminum chloride is added, the dosage is 1-15mg/L. 7. The process according to claim 4, characterized in that granular activated carbon is used as the filter material for the side-flow activated carbon filtration, and the hydraulic retention time (HRT) is 1-15 min.

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