CN116835803A - Demineralized water production system and process adopting double-membrane method - Google Patents
Demineralized water production system and process adopting double-membrane method Download PDFInfo
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- CN116835803A CN116835803A CN202310898277.XA CN202310898277A CN116835803A CN 116835803 A CN116835803 A CN 116835803A CN 202310898277 A CN202310898277 A CN 202310898277A CN 116835803 A CN116835803 A CN 116835803A
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- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 title claims abstract description 332
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- 238000002360 preparation method Methods 0.000 claims abstract description 10
- 238000011033 desalting Methods 0.000 claims abstract description 6
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- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 claims description 66
- KRKNYBCHXYNGOX-UHFFFAOYSA-N citric acid Chemical compound OC(=O)CC(O)(C(O)=O)CC(O)=O KRKNYBCHXYNGOX-UHFFFAOYSA-N 0.000 claims description 51
- 239000007788 liquid Substances 0.000 claims description 40
- 239000005708 Sodium hypochlorite Substances 0.000 claims description 36
- SUKJFIGYRHOWBL-UHFFFAOYSA-N sodium hypochlorite Chemical compound [Na+].Cl[O-] SUKJFIGYRHOWBL-UHFFFAOYSA-N 0.000 claims description 36
- 238000001914 filtration Methods 0.000 claims description 18
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- 230000001590 oxidative effect Effects 0.000 claims description 16
- 229910001220 stainless steel Inorganic materials 0.000 claims description 15
- 239000010935 stainless steel Substances 0.000 claims description 15
- ZAMOUSCENKQFHK-UHFFFAOYSA-N Chlorine atom Chemical compound [Cl] ZAMOUSCENKQFHK-UHFFFAOYSA-N 0.000 claims description 14
- 239000000460 chlorine Substances 0.000 claims description 14
- 229910052801 chlorine Inorganic materials 0.000 claims description 14
- 239000003638 chemical reducing agent Substances 0.000 claims description 13
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- SNRUBQQJIBEYMU-UHFFFAOYSA-N dodecane Chemical compound CCCCCCCCCCCC SNRUBQQJIBEYMU-UHFFFAOYSA-N 0.000 claims description 6
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- 238000009285 membrane fouling Methods 0.000 claims description 6
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- BVKZGUZCCUSVTD-UHFFFAOYSA-L Carbonate Chemical compound [O-]C([O-])=O BVKZGUZCCUSVTD-UHFFFAOYSA-L 0.000 claims description 3
- KCXVZYZYPLLWCC-UHFFFAOYSA-N EDTA Chemical compound OC(=O)CN(CC(O)=O)CCN(CC(O)=O)CC(O)=O KCXVZYZYPLLWCC-UHFFFAOYSA-N 0.000 claims description 3
- DWAQJAXMDSEUJJ-UHFFFAOYSA-M Sodium bisulfite Chemical compound [Na+].OS([O-])=O DWAQJAXMDSEUJJ-UHFFFAOYSA-M 0.000 claims description 3
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- 239000004289 sodium hydrogen sulphite Substances 0.000 claims description 3
- 235000010267 sodium hydrogen sulphite Nutrition 0.000 claims description 3
- 235000019832 sodium triphosphate Nutrition 0.000 claims description 3
- 238000012360 testing method Methods 0.000 claims description 3
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- 208000037584 hereditary sensory and autonomic neuropathy Diseases 0.000 claims 5
- 230000009471 action Effects 0.000 claims 1
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- 229910000831 Steel Inorganic materials 0.000 description 10
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- 238000011161 development Methods 0.000 description 9
- VTYYLEPIZMXCLO-UHFFFAOYSA-L Calcium carbonate Chemical compound [Ca+2].[O-]C([O-])=O VTYYLEPIZMXCLO-UHFFFAOYSA-L 0.000 description 8
- 239000000706 filtrate Substances 0.000 description 8
- WQYVRQLZKVEZGA-UHFFFAOYSA-N hypochlorite Chemical compound Cl[O-] WQYVRQLZKVEZGA-UHFFFAOYSA-N 0.000 description 8
- 239000002351 wastewater Substances 0.000 description 7
- 239000012459 cleaning agent Substances 0.000 description 6
- QWPPOHNGKGFGJK-UHFFFAOYSA-N hypochlorous acid Chemical compound ClO QWPPOHNGKGFGJK-UHFFFAOYSA-N 0.000 description 6
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Classifications
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F9/00—Multistage treatment of water, waste water or sewage
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D65/00—Accessories or auxiliary operations, in general, for separation processes or apparatus using semi-permeable membranes
- B01D65/02—Membrane cleaning or sterilisation ; Membrane regeneration
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2321/00—Details relating to membrane cleaning, regeneration, sterilization or to the prevention of fouling
- B01D2321/04—Backflushing
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2321/00—Details relating to membrane cleaning, regeneration, sterilization or to the prevention of fouling
- B01D2321/08—Use of hot water or water vapor
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2321/00—Details relating to membrane cleaning, regeneration, sterilization or to the prevention of fouling
- B01D2321/16—Use of chemical agents
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/001—Processes for the treatment of water whereby the filtration technique is of importance
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/44—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis
- C02F1/441—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis by reverse osmosis
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/44—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis
- C02F1/444—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis by ultrafiltration or microfiltration
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/50—Treatment of water, waste water, or sewage by addition or application of a germicide or by oligodynamic treatment
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/70—Treatment of water, waste water, or sewage by reduction
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/72—Treatment of water, waste water, or sewage by oxidation
- C02F1/76—Treatment of water, waste water, or sewage by oxidation with halogens or compounds of halogens
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F2101/00—Nature of the contaminant
- C02F2101/30—Organic compounds
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F2209/00—Controlling or monitoring parameters in water treatment
- C02F2209/06—Controlling or monitoring parameters in water treatment pH
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F2209/00—Controlling or monitoring parameters in water treatment
- C02F2209/11—Turbidity
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F2303/00—Specific treatment goals
- C02F2303/14—Maintenance of water treatment installations
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F2303/00—Specific treatment goals
- C02F2303/16—Regeneration of sorbents, filters
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F5/00—Softening water; Preventing scale; Adding scale preventatives or scale removers to water, e.g. adding sequestering agents
- C02F5/08—Treatment of water with complexing chemicals or other solubilising agents for softening, scale prevention or scale removal, e.g. adding sequestering agents
Landscapes
- Chemical & Material Sciences (AREA)
- Life Sciences & Earth Sciences (AREA)
- Hydrology & Water Resources (AREA)
- Engineering & Computer Science (AREA)
- Environmental & Geological Engineering (AREA)
- Water Supply & Treatment (AREA)
- Organic Chemistry (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Separation Using Semi-Permeable Membranes (AREA)
Abstract
The invention discloses a desalted water production system and a process adopting a double-membrane method, wherein the system comprises an ultrafiltration system and a reverse osmosis system; the ultrafiltration system comprises: the ultrafiltration water distribution channel, the ultrafiltration unit, the ultrafiltration water production suction pump, the ultrafiltration cleaning unit, the ultrafiltration backwashing unit, the ultrafiltration medicine preparation and adding unit, the ultrafiltration product water tank and the compressed air storage tank; the ultrafiltration system is used for removing suspended solids in water and providing qualified water inflow for reverse osmosis: ensuring that the turbidity of reverse osmosis inflow water is less than 0.2NTU and the SDI is less than 3; the reverse osmosis system comprises a full-automatic reverse osmosis unit, a dosing system and a flushing system. The sewage firstly enters the water distribution channel after chemical treatment, then enters the bottom of the ultrafiltration unit membrane pool, is driven by the negative pressure of an ultrafiltration water production suction pump to penetrate through the membrane wall and enter the membrane fiber cavity, is filtered by the immersed ultrafiltration membrane, and then enters the middle water tank, and the ultrafiltration water is treated by the reverse osmosis system and then is sent to the desalting water pool of the combined pump station, so that the recycling of the water is realized.
Description
Technical Field
The invention relates to a desalted water production system and a desalted water production process adopting a double-membrane method, and belongs to the technical field of sewage water treatment.
Background
The yield of the iron and steel enterprises is rapidly developed, but the iron and steel enterprises are also industries with high energy consumption, high water consumption and high pollution, and are large households with energy and resource consumption, wherein the water consumption of the iron and steel industries accounts for more than 9% of the water consumption of the national industry, especially the production processes of iron making, steel rolling and the like in the iron and steel production process, on one hand, the water consumption per ton of steel is continuously reduced through technical innovation and technical transformation, the optimization design and the flow are also positively responded to the national call, and the green development and the recycling and the reutilization of resource waste are carried out.
Disclosure of Invention
In order to meet the demands of the demineralized water used in the production line of the Tai steel stainless steel, realize the reutilization of waste and the sustainable development of green development, the invention provides a demineralized water production system which performs the treatments of disinfection, ultrafiltration, pressurization, reverse osmosis and the like on the reclaimed water to produce the demineralized water, the pressurization is supplied to users through a demineralized water pipe network, the automation degree of the treatment system is high, the operation is safe and stable, the economic benefit and the social benefit are high, the yielding water quality is stable and controlled, the production water of the stainless steel system is met, the reutilization of waste water is realized, and enterprises are led to walk on a green and low-carbon sustainable development cyclic development road.
The invention mainly adopts a double-membrane technology, ultrafiltration adopts an immersed ultrafiltration membrane element, reverse osmosis adopts an anti-pollution membrane element, and is matched with a dosing system, a cleaning system, a sterilizing system, a backwashing system and a chemical cleaning system to form a water production system, wherein the ultrafiltration system mainly has the functions of removing colloid, suspended matters, macromolecular organic matters and the like in water, the turbidity of the product water is less than or equal to 0.2NTU, the SDI is less than or equal to 3, filtered water enters a reverse osmosis device through a reverse osmosis lifting pump, a security filter and a high-pressure pump, the produced water of the reverse osmosis system is sent to a desalted water pond, and the reverse osmosis concentrated water is discharged after further treatment.
The invention provides a desalted water production system adopting a double-membrane method, which comprises an ultrafiltration system and a reverse osmosis system;
the ultrafiltration system comprises: an ultrafiltration water distribution channel (containing a filter screen), an ultrafiltration unit, an ultrafiltration water production suction pump, an ultrafiltration cleaning unit, an ultrafiltration backwashing unit, an ultrafiltration medicine preparation and adding unit, an ultrafiltration product water tank and a compressed air storage tank. The ultrafiltration system is used for removing suspended solids in water, including colloid, bacteria and other impurities, and providing qualified water inflow for reverse osmosis: ensuring that the turbidity of reverse osmosis inflow water is less than 0.2NTU and the SDI is less than 3; ensure the safe operation of the reverse osmosis system, reduce the chemical cleaning frequency of the reverse osmosis system and prolong the service life of the reverse osmosis membrane.
The ultrafiltration unit comprises an ultrafiltration membrane tank and an ultrafiltration membrane tank trolley, wherein an ultrafiltration membrane element, an ultrafiltration membrane hanger (stainless steel), a water collecting pipe, a gas distribution pipe and the like are arranged in the ultrafiltration membrane tank.
The ultrafiltration membrane tank is a main reaction tank of a CS membrane filtration system, adopts a concrete structure form, and has the characteristics of low cost, corrosion resistance, firmness, no deformation and the like.
The ultrafiltration membrane element consists of tens of thousands of polyvinylidene fluoride (PVDF) hollow fiber membranes, a plastic net cover is externally covered, and polyurethane plastic sealing heads are used at two ends. The membrane element upper head may allow filtered water to flow from the hollow fiber membrane lumens to the water collection lines, while the bottom head seals the fiber membrane outlets but allows low pressure process air to pass from a series of openings in the head into the outer surface of the membrane bundles during backwashing. The membrane elements are also referred to as membrane columns, which can be removed for repair and replacement.
The ultrafiltration membrane hangers (stainless steel) are totally installed with 54 membrane hangers, and each membrane hanger is provided with 9 groups of membrane columns and 1944 membrane assemblies. And 9 membrane hangers and 324 membrane assemblies are arranged in each column of membrane tanks. The membrane hanger is a movable device, and the membrane hanger can be lifted out of the water surface for maintenance through a membrane pool maintenance trolley.
The ultrafiltration membrane tank trolley is arranged above the membrane tank, is convenient to install membrane elements of the ultrafiltration system, is convenient to maintain the ultrafiltration system in the future, is arranged above the membrane tank, can lift a series of ultrafiltration membrane hangers from the membrane tank, and overhauls a membrane column on the trolley.
In the system, 6 ultrafiltration water-producing suction pumps are adopted and are respectively and correspondingly connected with the membrane tanks of 6 sets of ultrafiltration units. The ultrafiltration water-producing suction pump provides the filtration power of the ultrafiltration unit, unlike other types of ultrafiltration, the filtration power of submerged ultrafiltration comes from the suction force of the water pump. The ultrafiltration water-producing suction pump also has the function of being used as a chemical cleaning pump, and when in chemical cleaning, the suction pump circulates through a pipeline inside the unit, so that cleaning liquid continuously permeates the membrane wires, and deep cleaning is carried out inside the membrane wires.
The ultrafiltration backwashing unit consists of a blower, a backwashing water pump and related meters;
the ultrafiltration backwash unit consists of a blower, a backwash water pump and related instruments. The ultrafiltration blower consists of 3 variable-frequency Roots fans (1 for 2), an inlet filter, an inlet silencer, an outlet silencer and a monitoring instrument. The blower adopts a frequency conversion speed regulation mode according to the flowmeter on the pipeline, so that the flow of the blower is ensured to meet the backwashing process condition. The ultrafiltration backwash water pump consists of a variable-frequency water pump and a monitoring instrument. The water pump adopts a frequency conversion speed regulation mode according to a flowmeter on the pipeline and a pressure sensor of the ultrafiltration unit, so that the flow and the pressure of backwash water are ensured to meet backwash process conditions.
The ultrafiltration medicine preparation and adding unit comprises a sodium hypochlorite dispensing and conveying device, a hydrochloric acid dispensing and conveying device and a citric acid dispensing and conveying device. In order to inhibit the propagation of bacteria in water, the sodium hypochlorite dispensing and conveying device needs ultrafiltrationSterilizing the water supply; the bactericide adopts 10% sodium hypochlorite, and the dosage is 3mg/L. Sodium hypochlorite dispensing and conveying device consists of 1 table and 5m 3 Sodium hypochlorite storage tank, 1 sodium hypochlorite discharge pump, 2 sodium hypochlorite discharge pumps and 2 sodium hypochlorite discharge pumps 2 m 3 The device comprises a metering box, 2 mechanical metering pumps (for raw water sterilization) and 2 pneumatic diaphragm metering pumps (for ultrafiltration cleaning). The sodium hypochlorite measuring box and the measuring pump 1 are 1. The dosage is automatically regulated according to the flow rate. The dosage of the ultrafiltration cleaning sodium hypochlorite dosing pump is controlled by time, so that the concentration of the chemical cleaning liquid is ensured. The hydrochloric acid dispensing and conveying device consists of 1 hydrochloric acid storage tank, 1 hydrochloric acid discharge pump, 2 hydrochloric acid discharge pumps and 2 hydrochloric acid discharge pumps 2 m 3 The device comprises a metering box, 2 mechanical diaphragm metering pumps (for regulating pH by raw water) and 2 pneumatic diaphragm metering pumps (for ultrafiltration cleaning). The dosage is automatically adjusted according to the PID of the pH change. The dosage of the ultrafiltration cleaning hydrochloric acid dosing pump is controlled by time, so that the concentration of the chemical cleaning liquid is ensured. The citric acid dispensing and conveying device consists of 1 table 2 m 3 The metering box and 2 pneumatic diaphragm metering pumps. The citric acid batch meter is provided with 1 stirrer. The dosage is quantitatively added, and the chemical cleaning liquid concentration is ensured by controlling the dosage by time.
The compressed air storage tank is used for storing compressed air, the compressed air for the ultrafiltration unit process has 2 functions, and one is used for removing air in a suction inlet pipeline of an ultrafiltration water production suction pump; another function is to perform an integrity test on the ultrafiltration membrane. When the system is started for the first time, compressed air is pumped into the pipeline through the vacuum aspirator, so that ultrafiltration product water fills the suction inlet pipeline of the suction water pump, and cavitation is avoided.
The ultrafiltration cleaning unit consists of an ultrafiltration cleaning water tank, an ultrafiltration cleaning heater and an ultrafiltration cleaning water pump. The PLC determines when to perform maintenance cleaning and chemical cleaning according to time and membrane permeation pressure difference, and the maintenance cleaning and chemical cleaning processes are all completed automatically without human intervention. The cleaning system is provided with a pneumatic butterfly valve, a temperature sensor, a liquid level meter, a flowmeter, a heater and other matched equipment, and the cleaning process comprises the steps of flushing a cleaning water tank, dispensing, heating, transferring liquid medicine to an ultrafiltration membrane tank, carrying out closed-loop circulation in the device, evacuating the ultrafiltration membrane tank, rinsing the ultrafiltration membrane and the like. The ultrafiltration cleaning unit mainly cleans the membrane component, and has the following functions: preventing membrane fouling and membrane fouling, the system includes gas/water backwash, chemically Enhanced Backwash (CEBW), chemical in-line Cleaning (CIP).
CIP chemistry online cleaning system, when system TMP (membrane permeation pressure) or time combination reaches the upper limit of process setting or reaches the cleaning cycle of setting, the system stops water filtration operation, carries out the chemical online cleaning of full scope. The complete CIP can be accomplished automatically by PLC control. The normal membrane permeation pressure is 15-35kPa. The complete CIP cleaning must be performed beyond the film pressure, after which the normal film pressure is reached. The method comprises the following specific steps:
first step, backwashing
Before complete CIP cleaning, the membrane filter tank is backwashed to remove redundant solid impurities so as to furthest improve the chemical cleaning efficiency.
Second, chemical cleaning solvent is poured in
And (5) adding chemical cleaning agent after filling the membrane filter tank with 38 ℃ hot water to fill up.
Third step, soaking
The membrane module is immersed in the cleaning liquid in the membrane tank for a predetermined period of time (the time can be adjusted by an operator), and the blower is started, so that low-pressure air is adopted to enter the membrane fiber bundles, and the strength of CIP is enhanced.
Fourth step, the chemical cleaning agent is emptied
The cleaning liquid is discharged from the membrane pool to a sewage drain pipe, and is discharged after being diluted by utilizing the concentrated water of the reverse osmosis system.
Fifth step, rinsing
Before the membrane filter tank returns to a standby or filtering working state, the membrane filter tank is fed with water again, and back flushing and pipeline rinsing are carried out on residual chemical cleaning agent solution.
Chemically Enhanced Backwash (CEBW): the difference from the intact CIP is that the concentration and time of the cleaning liquid is used during the cleaning process, the intact CIP process takes 6 to 8 hours to complete, whereas the CEBW takes only 30 minutes, with a lower concentration of cleaning solution used. The system is designed to be a cleaning period for 96 hours, and the medicines adopt sodium hypochlorite or hydrochloric acid. When a CEBW cycle is required, the CEBW system must be ready and the CEBW process steps operate as a complete CIP process.
Gas/water backwash system: the system must carry out comprehensive back flushing in the membrane wires within a certain time, mainly preventing the deposition of particulate matters in the membrane wires, maintaining the flux of the membrane and being beneficial to protecting the normal operation of the membrane system. When the particle impurities of the inlet water are trapped on the surface of the membrane, the flow resistance is increased continuously along with the filtration time. After reaching a preset value, the system starts automatic back flushing, so that the flux of the membrane is ensured, the set value can be the membrane passing pressure (TMP), the set value can also be time setting or membrane flux, and the back flushing process can be started by the membrane passing pressure, resistance increase or flux decrease, time and the like. The backwash water is pumped and conveyed from the micro-filtration water tank by a backwash pump, and backwash wastewater of the membrane filter tank flows to a wastewater pipeline by gravity and enters a wastewater tank.
The ultrafiltration system comprises the following working processes: the reclaimed water enters the bottom of the membrane tank through the water distribution channel, and after being filtered by the filtering fiber membrane, clean water is driven by siphon negative pressure to pass through the membrane wall and enter the membrane fiber cavity. The filtered water is collected by each water collecting cross pipe and pumped out of the filtrate pump to be combined and flow to the filtering water tank. The filtrate pump of the membrane filtration device produces suction to provide a transmembrane pressure (TMP) of up to 85kpa, and flow control is achieved by variable speed actuation of the filtrate flow meter and the filtrate pump.
The reverse osmosis system comprises a full-automatic reverse osmosis unit, a dosing system and a flushing system.
The full-automatic reverse osmosis unit comprises: 8 rows (7 is 1 for 8 sets of reverse osmosis units, and the net water yield of the single set of units is 200 m) 3 And/h) comprises a lift pump, a cartridge filter, a high-pressure water supply pump and a reverse osmosis device. Reverse osmosis lift pump: the anti-corrosion centrifugal pump is adopted, the material of the overflow part of the pump is stainless steel material, 5 water pumps (1 standby water pump) are adopted, and the pressure provided by the reverse osmosis lifting pump is mainly used for overcoming the resistance of the security filter and providing stable water inflow for the high-pressure pump. And a PH meter and a conductivity meter are arranged on the front water inlet pipeline of the primary lifting pump. Is used for detecting the water quality condition of the water inlet of the reverse osmosis system. Said security device And (3) a filter: according to the large-flow filtration requirement, 8 sets of large-flow folding filter cores with the diameters of 6 'and the lengths of 40' and horizontal filters made of stainless steel are adopted. When the pressure difference between the inlet and the outlet of the filter is larger than a set value (usually 0.2 MPa), the filter element should be replaced timely. The high-pressure water supply pump comprises: the outlet water of the cartridge filter is boosted by the high-pressure water supply pump and then enters the reverse osmosis device. The inlet and outlet of the high-pressure water supply pump are respectively provided with a high-pressure switch and a low-pressure switch, the inlet pressure is low, the alarm is stopped, and the outlet pressure is high, and the alarm is delayed, so that the high-pressure pump is protected. The high-pressure water supply pump is a famous-brand horizontal centrifugal pump, and the pump body is made of corrosion-resistant stainless steel. The reverse osmosis device comprises: the reverse osmosis device is divided into 8 sets (1 for 7). The reverse osmosis device selects a membrane product with strong pollution resistance and has high desalination rate. The membrane system is configured as follows: film model: BW30-400FR; number of pressure vessels per set: 40, a step of performing a; arrangement: 26:14; number of elements per pressure vessel: 7.
the dosing system comprises a scale inhibitor dosing device, a reducing agent dosing device and a non-oxidative bactericide dosing device. The scale inhibitor dosing device comprises: the scale inhibitor dosing device of the system consists of 2 electric stirring metering boxes and 8 metering pumps. The electromagnetic diaphragm metering pump is selected as the metering pump, and the pump head is made of PVC material, so that the metering pump is corrosion-resistant and has no leakage. The metering pump is quantitatively added into the reverse osmosis water inlet according to the water supply flow. The metering box is provided with a liquid level switch for protecting the dosing pump and reminding operators of timely dosing and switching the solution box. The scale inhibitor metering pump is started, stopped, interlocked with the high-pressure pump and quantitatively added.
In the reverse osmosis operation process, when the recovery rate is 75% -80%, the salt content of the concentrated water is 4-5 times higher than that of the inlet water (the ion concentration of the reverse osmosis membrane is ignored). As the concentration of each ion on the concentrated water side is increased, the insoluble salts reach the solubility product, and are extremely easy to form precipitates on the surface of the reverse osmosis membrane to be separated out (such as calcium carbonate CaCO3 precipitates, and the like), so that the water permeability and the desalination rate of the reverse osmosis membrane are reduced, namely the rated output cannot be achieved during operation. In severe cases, the recovery is impossible by chemical cleaning, so that the membrane element is damaged and the equipment cannot operate.
The addition of the scale inhibitor can prevent CaCO 3 In reverse osmosisThe precipitation of the surface of the membrane is delayed by delaying the growth of salt crystals, so that the crystals are not precipitated in the membrane due to the formation of a certain size and enough concentration, namely insoluble salt in the reverse osmosis concentrated water is not precipitated on the surface of the membrane, and the insoluble salt is discharged out of the reverse osmosis device along with the concentrated water, thereby achieving the aim of scale prevention.
The reducing agent is NaHSO 3 The method comprises the steps of carrying out a first treatment on the surface of the The reductant dosing device includes: naHSO (NaHSO) 3 The dosing device consists of 2 electric stirrer metering boxes and 2 metering pumps. The electromagnetic diaphragm metering pump is selected as the metering pump, and the pump head is made of PVC material, so that the metering pump is corrosion-resistant and has no leakage. The metering box is provided with a liquid level switch for protecting the dosing pump and reminding operators of timely dosing and switching the solution box. The start and stop of the metering pump are interlocked with the lifting pump, and the metering pump is quantitatively added.
The purpose of adding sodium bisulphite into the feed water of the first-stage reverse osmosis is as follows: residual chlorine remained in the CMF-S membrane filtration treatment process is removed, and the reduction of the desalination rate caused by oxidation of the reverse osmosis membrane is prevented. Since the free residual chlorine in water exists mostly in the form of dissolved molecules, about 1/3 of the free residual chlorine undergoes hydrolysis to generate hypochlorous acid, which is a weak acid, and when the PH is more than 6.5, a part of the free residual chlorine is ionized into hypochlorite, so that the residual chlorine exists in the water mainly as hypochlorous acid, hypochlorite and chlorine molecules. Hypochlorous acid generated by hydrolysis has strong oxidizing property, and can damage the structure of a reverse osmosis membrane.
The non-oxidizing bactericide dosing device consists of 1 metering box and 2 metering pumps. The metering pump is a mechanical diaphragm metering pump, and the pump head is made of PVC material, so that the metering pump is corrosion-resistant and has no leakage. The metering box is provided with a liquid level switch to protect the dosing pump and remind operators of timely dosing, and a given quantitative value is adjusted according to actual working conditions by using the SX-402 non-oxidative bactericide.
The flushing system comprises a water cleaning device and two chemical cleaning devices, wherein the water cleaning device consists of a reverse osmosis flushing water tank and two flushing pumps, and the chemical cleaning device consists of two chemical cleaning water tanks (with heating devices), two cleaning pumps (1 for 1) and 2 cartridge filters. And after the reverse osmosis membrane is blocked, cleaning the reverse osmosis membrane manually.
The saidChemical cleaning: in operation, RO membranes may become contaminated or clogged with inorganic scale, colloids, microorganisms, metal oxides, and the like. These materials deposit on the membrane surface, which will cause a decrease in RO membrane permeation and a decrease in desalination rate. Therefore, in order to restore the permeation and desalination performance of RO membranes, chemical cleaning of RO is required periodically. The system is provided with two sets of chemical cleaning devices, and the flow rate of a chemical cleaning pump is 238m 3 And/h, the lift is 32m, and the volume of the chemical cleaning water tank is 20m 3 The flow rate of the cartridge filter is 270m 3 And/h. The RO cleaning system consists of a medicine dissolving tank with corrosion resistance, a cleaning filter (5 mm security filter), a cleaning pump and a pipeline. The chemical cleaning adopts the modes of manually preparing liquid and manually controlling the cleaning process.
The chemical cleaning formula comprises: the alkaline washing is suitable for organic matter and microorganism pollution, and the dosage is as follows: EDTA 2%, sodium tripolyphosphate 2%, dodecane 0.125%; the PH value is ensured to be 11-12 by ensuring that alkali is added in the cleaning process. Hydrochloric acid or citric acid, is suitable for iron pollution, pollution caused by carbonate crystallization and partial colloid, and is used for preparing the following medicines: hydrochloric acid or citric acid, and the pH is ensured to be 2-2.5 by adding acid during the cleaning process.
Generally, alkali washing is adopted, and then acid washing is adopted, and acid washing and alkali washing can be carried out according to pollution reasons. In order to prevent the first-stage pollutant from entering the second-stage to cause the second-stage pollution, the first-stage cleaning is performed in a sectional manner, and the second-stage cleaning is performed first and then the first-stage cleaning is performed. The reverse osmosis system must be flushed with reverse osmosis water for 10-30 minutes before cleaning. The flow is regulated to be 100-160m during the second cleaning stage 3 And/h, the PH is ensured to be within a specified range in the whole cleaning process, and the temperature is less than or equal to 38 ℃ and the pressure difference is less than or equal to 0.25Mpa. The cleaning flow rate of each pressure container can reach 9m 3 And/h, the second section has good cleaning effect, and the first section can be poured.
Cleaning one section of adjusting flow rate of 200-240m 3 And/h, the pH value is ensured to be within a specified range in the whole cleaning process, and the temperature is less than or equal to 38 ℃ delta P and less than or equal to 0.25MPa. The cleaning flow rate of each pressure container can reach 9m 3 And/h, the cleaning effect is good, and the cleaning can be finished. After each cleaning, the reverse osmosis water is used for flushing the reverse osmosis until the pH value is close to the pH value of the inlet water. If neededNon-oxidants may be used for cyclic sterilization. The pH value of the cleaning liquid is measured once per hour in the whole cleaning process, the color of the cleaning liquid is observed, the pH value is adjusted in time, the cleaning liquid is replaced when the color becomes dark, and the temperature, the inlet and outlet pressure, the pressure difference, the flow, the pH value and the like are recorded once per hour.
The invention provides a desalted water production process adopting a double-membrane method, which is used for treating reclaimed water after domestic sewage treatment, and comprises the following steps of:
the sewage is firstly disinfected by adding chlorine and enters a water distribution channel, then enters the bottom of a membrane tank, is driven by an ultrafiltration water production suction pump to pass through a membrane wall to enter a membrane fiber cavity under negative pressure, and is filtered by an immersed ultrafiltration membrane and then enters an intermediate water tank. The ultrafiltration system has the main functions of removing colloid, suspended matters, macromolecular organic matters and the like in water, the turbidity of the product water is less than or equal to 0.2NTU, the SDI is less than or equal to 3, the requirement of reverse osmosis inflow water quality is met, and the reverse osmosis system is protected. The ultrafiltration effluent enters a reverse osmosis system through a reverse osmosis lifting pump, a cartridge filter and a high-pressure pump, and the produced water of the reverse osmosis system is sent to a desalting water pond of a combined pump station and is sent to a Tai steel desalting water pipe network for production water of a stainless cold rolling plant, a new steelmaking plant and a stainless hot rolling plant, so that the recycling of domestic sewage is effectively realized, and the recycling of water is realized.
The invention has the beneficial effects that:
(1) In order to adapt to the development concepts of green development, low carbon development, ultra-low emission and sustainable development of enterprises, the resource recycling and reutilization are realized, the reclaimed water after the domestic sewage treatment is subjected to the advanced treatment of the system, high-quality desalted water is produced, and the high-quality desalted water is conveyed to a Tai steel desalted water pipe network for production water of a stainless cold rolling plant, new steelmaking and a stainless hot rolling plant;
(2) The technology is advanced, the optimal technological process and the automatic control scheme are selected, the equipment with the optimal performance is selected, and the key parts reach the international advanced and domestic first-class level;
(3) The economic benefit and the social benefit are excellent, the quality, the safety and the reliability are ensured, and the system cost and the water production cost are reduced as much as possible on the premise of fully considering the economical efficiency of long-term operation, so that the optimal water quality standard of the cost performance is achieved;
(4) The process and equipment type selection can have larger flexibility and adjustment margin in the production operation process, can adapt to various changes of water quality, water quantity and water temperature through the setting and proportioning of various parameters, and ensures stable and controllable water quality of produced water;
(5) The system has complete protection measures, and can meet various abnormal treatments by various measures such as system sterilization, cleaning and control of various protection measures of the system, thereby greatly prolonging the service life of equipment.
Drawings
FIG. 1 is a schematic diagram of the ultrafiltration system of the present invention;
FIG. 2 is a schematic diagram of the reverse osmosis system of the present invention.
In the figure: 1 is a water distribution canal, 2 is an ultrafiltration membrane pool, 3 is an ultrafiltration water production suction pump, 4 is an ultrafiltration product pool, 5 is an ultrafiltration cleaning water tank, 6 is an ultrafiltration cleaning water pump, 7 is a blower, 8 is a sodium hypochlorite dispensing and conveying device, 9 is a hydrochloric acid dispensing and conveying device, 10 is a citric acid dispensing and conveying device, 11 is a compressed air storage tank, 12 is a lifting pump, 13 is a security filter, 14 is a reverse osmosis device, 15 is a scale inhibitor dosing device, 16 is a reducing agent dosing device, 17 is a non-oxidizing bactericide dosing device, 18 is a reverse osmosis flushing water tank, 19 is a chemical cleaning water tank, 20 is a factory self-use water pipe, and 21 is a factory steam pipe. A is sewage, B is water from an ultrafiltration water producing tank, and C is water for factories.
Detailed Description
The present invention is further illustrated by, but not limited to, the following examples.
Examples
As shown in fig. 1-2, the desalted water producing system adopting the double-membrane method provided by the invention comprises an ultrafiltration system and a reverse osmosis system;
the ultrafiltration system comprises: an ultrafiltration water distribution channel 1 (containing a filter screen), an ultrafiltration unit, an ultrafiltration water production suction pump 3, an ultrafiltration cleaning unit, an ultrafiltration backwashing unit, an ultrafiltration medicine preparation and adding unit, an ultrafiltration product water tank 4 and a compressed air storage tank 11. The ultrafiltration system is used for removing suspended solids in water, including colloid, bacteria and other impurities, and providing qualified water inflow for reverse osmosis: ensuring that the turbidity of reverse osmosis inflow water is less than 0.2NTU and the SDI is less than 3; ensure the safe operation of the reverse osmosis system, reduce the chemical cleaning frequency of the reverse osmosis system and prolong the service life of the reverse osmosis membrane.
The ultrafiltration water distribution channel 1 is connected with a sewage pipe, a filter screen is arranged in the water distribution channel, the other end of the ultrafiltration water distribution channel 1 is connected with a plurality of ultrafiltration units, a membrane pool of each ultrafiltration unit is provided with an ultrafiltration water production suction pump 3, an ultrafiltration cleaning unit and an ultrafiltration backwashing unit are respectively connected with the membrane pools of the ultrafiltration units, and the membrane elements are cleaned regularly; the ultrafiltration medicine preparation and adding unit is connected with the sewage pipe and is used for carrying out chemical treatment on ultrafiltration water supply; the outlet of the ultrafiltration unit is connected with an ultrafiltration product water tank; the compressed air storage tank is connected with the membrane tank of the ultrafiltration unit;
the ultrafiltration unit comprises an ultrafiltration membrane tank 2 and an ultrafiltration membrane tank trolley, wherein an ultrafiltration membrane element, an ultrafiltration membrane hanger (stainless steel), a water collecting pipe, a gas distribution pipe and the like are arranged in the ultrafiltration membrane tank 2.
The ultrafiltration membrane tank is a main reaction tank of the CS membrane filtration system, and the embodiment adopts a concrete structure form, and has the characteristics of low cost, corrosion resistance, firmness, no deformation and the like.
The ultrafiltration membrane element consists of tens of thousands of polyvinylidene fluoride (PVDF) hollow fiber membranes, a plastic net cover is externally covered, and polyurethane plastic sealing heads are used at two ends. The membrane element upper head may allow filtered water to flow from the hollow fiber membrane lumens to the water collection lines, while the bottom head seals off the fiber membrane outlets, but allows low pressure process air to pass from a series of openings in the head through to the outer surface of the membrane bundles during backwashing. The membrane elements are also referred to as membrane columns, which can be removed for repair and replacement.
The ultrafiltration membrane hangers (stainless steel) are totally installed with 54 membrane hangers, and each membrane hanger is provided with 9 groups of membrane columns and 1944 membrane assemblies. And 9 membrane hangers and 324 membrane assemblies are arranged in each column of membrane tanks. The membrane hanger is a movable device, and the membrane hanger can be lifted out of the water surface for maintenance through a membrane pool maintenance trolley. In this example, six membrane tanks are provided.
The ultrafiltration membrane tank trolley is arranged above the membrane tank, is convenient to install membrane elements of the ultrafiltration system, is convenient to maintain the ultrafiltration system in the future, is arranged above the membrane tank, can lift a series of ultrafiltration membrane hangers from the membrane tank, and overhauls a membrane column on the trolley.
In the embodiment, 6 ultrafiltration water-producing suction pumps are adopted and are respectively and correspondingly connected with the membrane tanks of the 6 sets of ultrafiltration units. The ultrafiltration water-producing suction pump provides the filtration power of the ultrafiltration unit, unlike other types of ultrafiltration, the filtration power of submerged ultrafiltration comes from the suction force of the water pump. The ultrafiltration water-producing suction pump also has the function of being matched with a chemical cleaning pump, and when in chemical cleaning, the suction pump circulates through a pipeline inside the unit, so that cleaning liquid continuously permeates the membrane wires, and deep cleaning is carried out inside the membrane wires.
The ultrafiltration cleaning unit consists of an ultrafiltration cleaning water tank 5, an ultrafiltration cleaning heater and an ultrafiltration cleaning water pump 6. The PLC determines when to perform maintenance cleaning and chemical cleaning according to time and membrane permeation pressure difference, and the maintenance cleaning and chemical cleaning processes are all completed automatically without human intervention. The cleaning system is provided with a pneumatic butterfly valve, a temperature sensor, a liquid level meter, a flowmeter, a heater and other matched equipment, and the cleaning process comprises the steps of flushing a cleaning water tank, dispensing, heating, transferring liquid medicine to an ultrafiltration membrane tank, carrying out closed-loop circulation in the device, evacuating the ultrafiltration membrane tank, rinsing the ultrafiltration membrane and the like.
The ultrafiltration backwashing unit consists of a blower 7, a backwashing water pump and related instruments; the ultrafiltration blower consists of 3 variable-frequency Roots fans (1 for 2), an inlet filter, an inlet silencer, an outlet silencer and a monitoring instrument. The blower adopts a frequency conversion speed regulation mode according to the flowmeter on the pipeline, so that the flow of the blower is ensured to meet the backwashing process condition. The ultrafiltration backwash water pump consists of a variable-frequency water pump and a monitoring instrument. The water pump adopts a frequency conversion speed regulation mode according to a flowmeter on the pipeline and a pressure sensor of the ultrafiltration unit, so that the flow and the pressure of backwash water are ensured to meet backwash process conditions.
The ultrafiltration medicine preparation and adding unit comprises a sodium hypochlorite dispensing and conveying device 8, a hydrochloric acid dispensing and conveying device 9 and a citric acid dispensing and conveying device 10. Sodium hypochlorite dispensing and conveying deviceIn order to inhibit the propagation of bacteria in water, ultrafiltration water is sterilized; the bactericide adopts 10% sodium hypochlorite, and the dosage is 3mg/L. Sodium hypochlorite dispensing and conveying device consists of 1 table and 5m 3 Sodium hypochlorite storage tank, 1 sodium hypochlorite discharge pump, 2 sodium hypochlorite discharge pumps and 2 sodium hypochlorite discharge pumps 2 m 3 The device comprises a metering box, 2 mechanical metering pumps (for raw water sterilization) and 2 pneumatic diaphragm metering pumps (for ultrafiltration cleaning). The sodium hypochlorite measuring box and the measuring pump 1 are 1. The dosage is automatically regulated according to the flow rate. The dosage of the ultrafiltration cleaning sodium hypochlorite dosing pump is controlled by time, so that the concentration of the chemical cleaning liquid is ensured. The hydrochloric acid dispensing and conveying device consists of 1 hydrochloric acid storage tank, 1 hydrochloric acid discharge pump, 2 hydrochloric acid discharge pumps and 2 hydrochloric acid discharge pumps 2 m 3 The device comprises a metering box, 2 mechanical diaphragm metering pumps (for regulating pH by raw water) and 2 pneumatic diaphragm metering pumps (for ultrafiltration cleaning). The dosage is automatically adjusted according to the PID of the pH change. The dosage of the ultrafiltration cleaning hydrochloric acid dosing pump is controlled by time, so that the concentration of the chemical cleaning liquid is ensured. The citric acid dispensing and conveying device consists of 1 table 2 m 3 The metering box and 2 pneumatic diaphragm metering pumps. The citric acid batch meter is provided with 1 stirrer. The dosage is quantitatively added, and the chemical cleaning liquid concentration is ensured by controlling the dosage by time.
The compressed air storage tank 11 is used for storing compressed air, the compressed air for the ultrafiltration unit process has two functions, one is used for removing air in a suction inlet pipeline of an ultrafiltration water production suction pump; another function is to perform an integrity test on the ultrafiltration membrane. When the system is started for the first time, compressed air is pumped into the pipeline through the vacuum aspirator, so that ultrafiltration product water fills the suction inlet pipeline of the suction water pump, and cavitation is avoided.
The reverse osmosis system comprises a full-automatic reverse osmosis unit, a dosing system and a flushing system.
The full-automatic reverse osmosis unit comprises: 8 rows (7 is 1 for 8 sets of reverse osmosis units, and the net water yield of the single set of units is 200 m) 3 And/h) comprises a lift pump 12, a cartridge filter 13, a high pressure feed pump and a reverse osmosis device 14.Reverse osmosis lift pump: adopts a corrosion-resistant centrifugal pump, the material of an overflow part of the pump is stainless steel material, 5 water pumps (1 for 4) are used for reverse osmosisThe pressure provided by the transparent lifting pump is mainly used for overcoming the resistance of the cartridge filter and providing stable water inflow for the high-pressure pump. And a PH meter and a conductivity meter are arranged on the front water inlet pipeline of the primary lifting pump. Is used for detecting the water quality condition of the water inlet of the reverse osmosis system. The cartridge filter comprises: according to the large-flow filtration requirement, 8 sets of large-flow folding filter cores with the diameters of 6 'and the lengths of 40' and horizontal filters made of stainless steel are adopted. When the pressure difference between the inlet and the outlet of the filter is larger than a set value (usually 0.2 MPa), the filter element should be replaced timely. The high-pressure water supply pump comprises: the outlet water of the cartridge filter is boosted by the high-pressure water supply pump and then enters the reverse osmosis device. The inlet and outlet of the high-pressure water supply pump are respectively provided with a high-pressure switch and a low-pressure switch, the inlet pressure is low, the alarm is stopped, and the outlet pressure is high, and the alarm is delayed, so that the high-pressure pump is protected. The high-pressure water supply pump is a famous-brand horizontal centrifugal pump, and the pump body is made of corrosion-resistant stainless steel. The reverse osmosis device comprises: the reverse osmosis device is divided into 8 sets (1 for 7). The reverse osmosis device selects a membrane product with strong pollution resistance and has high desalination rate. The reverse osmosis device comprises a reverse osmosis membrane pool, wherein a membrane assembly and a pressure vessel are arranged in the reverse osmosis membrane pool; the membrane system is configured as follows: film model: BW30-400FR; number of pressure vessels per set: 40, a step of performing a; arrangement: 26:14; number of elements per pressure vessel: 7.
The dosing system comprises a scale inhibitor dosing device 15, a reducing agent dosing device 16 and a non-oxidizing bactericide dosing device 17. The scale inhibitor dosing device comprises: the scale inhibitor dosing device of the system consists of 2 electric stirring metering boxes and 8 metering pumps. The electromagnetic diaphragm metering pump is selected as the metering pump, and the pump head is made of PVC material, so that the metering pump is corrosion-resistant and has no leakage. The metering pump is quantitatively added into the reverse osmosis water inlet according to the water supply flow. The metering box is provided with a liquid level switch for protecting the dosing pump and reminding operators of timely dosing and switching the solution box. The scale inhibitor metering pump is started, stopped, interlocked with the high-pressure pump and quantitatively added.
The lifting pump of the full-automatic reverse osmosis unit is connected with the water outlet pipe of the ultrafiltration produced water, the other end of the lifting pump is connected with a security filter, and the water outlet of the security filter is led to the reverse osmosis device; the scale inhibitor dosing device and the reducing agent dosing device of the dosing system are respectively connected with a water outlet pipe of ultrafiltration water production, and are used for carrying out chemical treatment on water; the non-oxidative bactericide dosing device of the dosing system is connected with the reverse osmosis device, the membrane is sterilized in the operation process, and the reverse osmosis device is connected with the flushing system to clean the membrane assembly. As shown in fig. 2.
The invention provides a desalted water production process adopting a double-membrane method, which is used for treating reclaimed water after domestic sewage treatment, and comprises the following steps of:
the sewage is firstly subjected to chemical treatment and then enters a water distribution channel, then enters the bottom of a membrane pool of an ultrafiltration unit, is driven by an ultrafiltration water production suction pump to pass through a membrane wall to enter a membrane fiber cavity under negative pressure, is filtered by an immersed ultrafiltration membrane, and then enters an intermediate water tank, and the ultrafiltration system has the functions of removing colloid, suspended matters, macromolecular organic matters and the like in the water, wherein the turbidity of the product water is less than or equal to 0.2NTU, the SDI is less than or equal to 3, the water quality requirement of reverse osmosis water inlet is met, and a reverse osmosis system is protected; the ultrafiltration effluent enters a reverse osmosis device through a reverse osmosis lifting pump, a cartridge filter and a high-pressure water supply pump, and the produced water of the reverse osmosis device is sent to a desalting water pond of a combined pump station, so that the water can be recycled.
Specifically, the ultrafiltration system works as follows: the reclaimed water enters the bottom of the membrane tank through the water distribution channel, and after being filtered by the filtering fiber membrane, clean water is driven by siphon negative pressure to pass through the membrane wall and enter the membrane fiber cavity. The filtered water is collected by each water collecting cross pipe and pumped out of the filtrate pump to be combined and flow to the filtering water tank. The filtrate pump of the membrane filtration device produces suction to provide a transmembrane pressure (TMP) of up to 85kpa, and flow control is achieved by variable speed actuation of the filtrate flow meter and the filtrate pump.
The technical parameters in the ultrafiltration system in this example are shown in table 1 below.
TABLE 1
The ultrafiltration cleaning unit mainly cleans the membrane component, and has the following functions: preventing membrane fouling and membrane fouling, the cleaning process comprising gas/water backwash, chemically Enhanced Backwash (CEBW), chemical in-line Cleaning (CIP).
CIP chemistry online cleaning system, when system TMP (membrane permeation pressure) or time combination reaches the upper limit of process setting or reaches the cleaning cycle of setting, the system stops water filtration operation, carries out the chemical online cleaning of full scope. The complete CIP can be accomplished automatically by PLC control. The normal membrane permeation pressure is 15-35kPa. The complete CIP cleaning must be performed beyond the film pressure, after which the normal film pressure is reached. The method comprises the following specific steps:
first step, backwashing
Before complete CIP cleaning, the membrane filter tank is backwashed to remove redundant solid impurities so as to furthest improve the chemical cleaning efficiency.
Second, chemical cleaning solvent is poured in
And (5) adding chemical cleaning agent after filling the membrane filter tank with 38 ℃ hot water to fill up.
Third step, soaking
The membrane module is immersed in the cleaning liquid in the membrane tank for a predetermined period of time (the time can be adjusted by an operator), and the blower is started, so that low-pressure air is adopted to enter the membrane fiber bundles, and the strength of CIP is enhanced.
Fourth step, the chemical cleaning agent is emptied
The cleaning liquid is discharged from the membrane pool to a sewage drain pipe, and is discharged after being diluted by utilizing the concentrated water of the reverse osmosis system.
Fifth step, rinsing
Before the membrane filter tank returns to a standby or filtering working state, the membrane filter tank is fed with water again, and back flushing and pipeline rinsing are carried out on residual chemical cleaning agent solution.
Chemically Enhanced Backwash (CEBW): the difference from the intact CIP is that the concentration and time of the cleaning liquid is used during the cleaning process, the intact CIP process takes 6 to 8 hours to complete, whereas the CEBW takes only 30 minutes, with a lower concentration of cleaning solution used. The system is designed to be a cleaning period for 96 hours, and the medicines adopt sodium hypochlorite or hydrochloric acid. When a CEBW cycle is required, the CEBW system must be ready and the CEBW process steps operate as a complete CIP process.
Gas/water backwash system: the system must carry out comprehensive back flushing in the membrane wires within a certain time, mainly preventing the deposition of particulate matters in the membrane wires, maintaining the flux of the membrane and being beneficial to protecting the normal operation of the membrane system. When the particle impurities of the inlet water are trapped on the surface of the membrane, the flow resistance is increased continuously along with the filtration time. After reaching a preset value, the system starts automatic back flushing, so that the flux of the membrane is ensured, the set value can be the membrane passing pressure (TMP), the set value can also be time setting or membrane flux, and the back flushing process can be started by the membrane passing pressure, resistance increase or flux decrease, time and the like. The backwash water is pumped and conveyed from the micro-filtration water tank by a backwash pump, and backwash wastewater of the membrane filter tank flows to a wastewater pipeline by gravity and enters a wastewater tank.
The operating parameters of the cleaning system (gas/water combined backwash, chemically enhanced backwash CEBW, chemical on-line cleaning CIP) in this example are shown in table 2 below:
TABLE 2
The reverse osmosis system is specifically described as follows:
in the reverse osmosis operation process, when the recovery rate is 75% -80%, the salt content of the concentrated water is 4-5 times higher than that of the inlet water (the ion concentration of the reverse osmosis membrane is ignored). As the concentration of each ion on the concentrated water side is increased, the insoluble salts reach the solubility product, and are extremely easy to form precipitates on the surface of the reverse osmosis membrane to be separated out (such as calcium carbonate CaCO3 precipitates, and the like), so that the water permeability and the desalination rate of the reverse osmosis membrane are reduced, namely the rated output cannot be achieved during operation. In severe cases, the recovery is impossible by chemical cleaning, so that the membrane element is damaged and the equipment cannot operate.
Technical parameters of each set of reverse osmosis device of the reverse osmosis unit in this embodiment are shown in the following table 3:
TABLE 3 Table 3
Reverse osmosis operating parameters are shown in table 4 below.
TABLE 4 Table 4
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The addition of the scale inhibitor can prevent CaCO 3 The precipitation is carried out on the surface of the reverse osmosis membrane, the precipitation process is delayed by delaying the growth of salt crystals, and the crystals are promoted not to form a certain size and enough concentration in the membrane to be precipitated, namely insoluble salt in reverse osmosis concentrated water is not precipitated on the surface of the membrane, so that the insoluble salt is discharged to the outside of the reverse osmosis device along with the concentrated water, and the purpose of scale prevention is achieved.
The reducing agent is NaHSO 3 The method comprises the steps of carrying out a first treatment on the surface of the The reductant dosing device includes: naHSO (NaHSO) 3 The dosing device consists of 2 electric stirrer metering boxes and 2 metering pumps. The electromagnetic diaphragm metering pump is selected as the metering pump, and the pump head is made of PVC material, so that the metering pump is corrosion-resistant and has no leakage. The metering box is provided with a liquid level switch for protecting the dosing pump and reminding operators of timely dosing and switching the solution box. The start and stop of the metering pump are interlocked with the lifting pump, and the metering pump is quantitatively added.
The purpose of adding sodium bisulphite into the feed water of the first-stage reverse osmosis is as follows: residual chlorine remained in the CMF-S membrane filtration treatment process is removed, and the reduction of the desalination rate caused by oxidation of the reverse osmosis membrane is prevented. Since the free residual chlorine in water exists mostly in the form of dissolved molecules, about 1/3 of the free residual chlorine undergoes hydrolysis to generate hypochlorous acid, which is a weak acid, and when the PH is more than 6.5, a part of the free residual chlorine is ionized into hypochlorite, so that the residual chlorine exists in the water mainly as hypochlorous acid, hypochlorite and chlorine molecules. Hypochlorous acid generated by hydrolysis has strong oxidizing property, and can damage the structure of a reverse osmosis membrane.
The non-oxidizing bactericide dosing device consists of 1 metering box and 2 metering pumps. The metering pump is a mechanical diaphragm metering pump, and the pump head is made of PVC material, so that the metering pump is corrosion-resistant and has no leakage. The metering box is provided with a liquid level switch to protect the dosing pump and remind operators of timely dosing, and a given quantitative value is adjusted according to actual working conditions by using the SX-402 non-oxidative bactericide.
The flushing system comprises a water cleaning device and two chemical cleaning devices, wherein the water cleaning device consists of a reverse osmosis flushing water tank 18 and two flushing pumps, and the chemical cleaning device consists of two chemical cleaning water tanks 19 (with heating devices), two cleaning pumps (1 for 1) and 2 cartridge filters. And after the reverse osmosis membrane is blocked, cleaning the reverse osmosis membrane manually.
The chemical cleaning: in operation, RO membranes may become contaminated or clogged with inorganic foulants, colloids, microorganisms, metal oxides, and the like. These materials deposit on the membrane surface, which will cause a decrease in RO membrane permeation and a decrease in desalination rate. Therefore, in order to restore the permeation and desalination performance of RO membranes, chemical cleaning of RO is required periodically. The system is provided with 2 sets of chemical cleaning devices, and the flow rate of a chemical cleaning pump is 238m 3 And/h, the lift is 32m, and the volume of the chemical cleaning water tank is 20m 3 The flow rate of the cartridge filter is 270m 3 And/h. The RO cleaning system consists of a medicine dissolving tank with corrosion resistance, a cleaning filter (5.00 m security filter), a cleaning pump and a pipeline. The chemical cleaning adopts the modes of manually preparing liquid and manually controlling the cleaning process.
The chemical cleaning formula comprises: the alkaline washing is suitable for organic matter and microorganism pollution, and the dosage is as follows: EDTA 2%, sodium tripolyphosphate 2%, dodecane 0.125%; the PH value is ensured to be 11-12 by ensuring that alkali is added in the cleaning process. Hydrochloric acid or citric acid, is suitable for iron pollution, pollution caused by carbonate crystallization and partial colloid, and is used for preparing the following medicines: hydrochloric acid or citric acid, and the pH is ensured to be 2-2.5 by adding acid during the cleaning process.
Generally, alkali washing is adopted, and then acid washing is adopted, and acid washing and alkali washing can be carried out according to pollution reasons. In order to prevent the first-stage pollutant from entering the second-stage to cause the second-stage pollution, the first-stage cleaning is performed in a sectional manner, and the second-stage cleaning is performed first and then the first-stage cleaning is performed. The reverse osmosis system must be flushed with reverse osmosis water for 10-30 minutes before cleaning. The flow is regulated to be 100-160m during the second cleaning stage 3 And/h, the PH is ensured to be within a specified range in the whole cleaning process, and the temperature is less than or equal to 38 ℃ and the pressure difference is less than or equal to 0.25Mpa. The cleaning flow rate of each pressure container can reach 9m 3 And/h, the second section has good cleaning effect, and the first section can be poured.
Cleaning one-stage flow adjustment 200-240m 3 And/h, the pH value is ensured to be within a specified range in the whole cleaning process, the temperature is less than or equal to 38 ℃ and the delta P is less than or equal to 0.25MPa. The cleaning flow rate of each pressure container can reach 9m 3 And/h, the cleaning effect is good, and the cleaning can be finished. After each cleaning, the reverse osmosis water is used for flushing the reverse osmosis until the pH value is close to the pH value of the inlet water. Non-oxidants may be used for cyclic sterilization if desired. The pH value of the cleaning liquid is measured once per hour in the whole cleaning process, the color of the cleaning liquid is observed, the pH value is adjusted in time, the cleaning liquid is replaced when the color becomes dark, and the temperature, the inlet and outlet pressure, the pressure difference, the flow, the pH value and the like are recorded once per hour.
The embodiment adopted in the Tai steel stainless advanced water treatment station is designed to be on the scale of 50000m of water inflow 3 And/d, adopting an ultrafiltration and reverse osmosis process, wherein the water source is reclaimed water obtained after domestic sewage is treated, and the produced water enters a desalting water system of a combined pump station, and the current important indexes are shown in table 5.
TABLE 5
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Claims (10)
1. A demineralized water producing system adopting a double-membrane method is characterized in that: comprises an ultrafiltration system and a reverse osmosis system;
the ultrafiltration system comprises: the ultrafiltration water distribution channel, the ultrafiltration unit, the ultrafiltration water production suction pump, the ultrafiltration cleaning unit, the ultrafiltration backwashing unit, the ultrafiltration medicine preparation and adding unit, the ultrafiltration product water tank and the compressed air storage tank; the ultrafiltration system is used for removing suspended solids in water and providing qualified water inflow for reverse osmosis: ensuring that the turbidity of reverse osmosis inflow water is less than 0.2NTU and the SDI is less than 3;
the ultrafiltration water distribution channel is connected with a sewage pipe, a filter screen is arranged in the water distribution channel, the other end of the ultrafiltration water distribution channel is connected with a plurality of ultrafiltration units, a membrane pool of each ultrafiltration unit is provided with an ultrafiltration water production suction pump, an ultrafiltration cleaning unit and an ultrafiltration backwashing unit are respectively connected with the membrane pools of the ultrafiltration units, and the membrane elements are cleaned regularly; the ultrafiltration medicine preparation and adding unit is connected with the sewage pipe and is used for carrying out chemical treatment on ultrafiltration water supply; the outlet of the ultrafiltration unit is connected with an ultrafiltration product water tank; the compressed air storage tank is connected with the membrane tank of the ultrafiltration unit;
The ultrafiltration unit comprises an ultrafiltration membrane tank and an ultrafiltration membrane tank trolley, wherein an ultrafiltration membrane element, an ultrafiltration membrane hanger, a water collecting pipe and a gas distribution pipe are arranged in the ultrafiltration membrane tank; the ultrafiltration membrane tank is a main reaction tank of a CS membrane filtration system and adopts a concrete structure; the ultrafiltration membrane element consists of tens of thousands of PVDF hollow fiber membranes made of polyvinylidene fluoride materials, a plastic net cover is externally wrapped, polyurethane plastic sealing heads are used at two ends, the sealing heads at the upper end of the membrane element allow filtered water to flow from the inner cavity of the hollow fiber membranes to a water collecting pipeline, the outlet of the bottom sealing head for sealing the fiber membranes allows low-pressure process air to pass through a series of openings in the sealing heads to enter the outer surface of a membrane fiber bundle during backwashing, and the membrane element can be taken out for repair and replacement; the ultrafiltration membrane pool trolley is arranged above the membrane pool;
the ultrafiltration backwashing unit consists of a blower, a backwashing water pump and related meters;
the ultrafiltration medicine preparation and adding unit comprises a sodium hypochlorite dispensing and conveying device, a hydrochloric acid dispensing and conveying device and a citric acid dispensing and conveying device; the sodium hypochlorite dispensing and conveying device comprises a sodium hypochlorite storage tank, a sodium hypochlorite discharge pump, a metering box and a metering pump, and is used for sterilizing ultrafiltration water supply; the hydrochloric acid dispensing and conveying device comprises a hydrochloric acid storage tank, a hydrochloric acid discharge pump, a metering box and a metering pump; the citric acid dispensing and conveying device comprises a metering box and a metering pump;
The compressed air storage tank is used for storing compressed air, and the ultrafiltration unit process uses the action of the compressed air, firstly, the air in the suction inlet pipeline of the ultrafiltration water production suction pump is discharged; another function is to perform an integrity test on the ultrafiltration membrane;
the ultrafiltration cleaning unit consists of an ultrafiltration cleaning water tank, an ultrafiltration cleaning heater and an ultrafiltration cleaning water pump; determining when maintenance cleaning and chemical cleaning are performed by a PLC according to time and membrane permeation pressure difference, wherein an ultrafiltration cleaning unit is provided with a pneumatic butterfly valve, a temperature sensor, a liquid level meter, a flowmeter and a heater; the ultrafiltration cleaning unit cleans the membrane component and has the following functions: preventing membrane fouling and membrane fouling;
the reverse osmosis system comprises a full-automatic reverse osmosis unit, a dosing system and a flushing system;
the full-automatic reverse osmosis unit comprises a lift pump, a cartridge filter, a high-pressure water supply pump and a reverse osmosis device; the reverse osmosis lifting pump adopts a corrosion-resistant centrifugal pump, and the effluent of the security filter enters the reverse osmosis device after being boosted by the high-pressure water supply pump; the reverse osmosis device comprises: the reverse osmosis device comprises a reverse osmosis membrane pool, wherein a membrane assembly and a pressure vessel are arranged in the reverse osmosis membrane pool;
The dosing system comprises a scale inhibitor dosing device, a reducing agent dosing device and a non-oxidative bactericide dosing device; the scale inhibitor dosing device comprises an electric stirring metering box and a metering pump; the reducing agent dosing device comprises an electric stirrer metering box and a metering pump; the non-oxidizing bactericide dosing device comprises a metering box metering pump;
the flushing system comprises a water cleaning device and two chemical cleaning devices, wherein the water cleaning device consists of a reverse osmosis flushing water tank and two flushing pumps, and the chemical cleaning device consists of two chemical cleaning water tanks with heating devices, two cleaning pumps and 2 security filters; when the reverse osmosis membrane is blocked, cleaning the reverse osmosis membrane manually;
the lifting pump of the full-automatic reverse osmosis unit is connected with the water outlet pipe of the ultrafiltration produced water, the other end of the lifting pump is connected with a security filter, and the water outlet of the security filter is led to the reverse osmosis device; the scale inhibitor dosing device and the reducing agent dosing device of the dosing system are respectively connected with a water outlet pipe of ultrafiltration water production, and are used for carrying out chemical treatment on water; the non-oxidative bactericide dosing device of the dosing system is connected with the reverse osmosis device, the membrane is sterilized in the operation process, and the reverse osmosis device is connected with the flushing system to clean the membrane assembly.
2. The demineralized water producing system employing the double membrane method according to claim 1, wherein: the ultrafiltration membrane hanging frames are provided with 54 membrane hanging frames in total, the ultrafiltration membrane hanging frames are made of stainless steel, and each column of membrane tanks is provided with 9 membrane hanging frames and 324 membrane assemblies; the ultrafiltration membrane hanging frame is movable equipment, and the membrane hanging frame is lifted out of the water surface for maintenance through a membrane pool maintenance trolley.
3. The demineralized water producing system employing the double membrane method according to claim 1, wherein: the air blower of the ultrafiltration backwashing unit consists of 3 variable-frequency Roots fans, an inlet filter, an inlet silencer, an outlet silencer and a monitoring instrument, and adopts a variable-frequency speed regulation mode according to the flowmeter on the pipeline to ensure that the flow of the air blower meets backwashing process conditions, and the ultrafiltration backwashing water pump consists of a variable-frequency water pump and the monitoring instrument; the variable-frequency water pump adopts a variable-frequency speed regulation mode according to a flowmeter on a pipeline and a pressure sensor of the ultrafiltration unit, so that the flow and the pressure of backwash water are ensured to meet backwash process conditions.
4. The demineralized water producing system employing the double membrane method according to claim 1, wherein: in the ultrafiltration medicine preparation and adding unit, a sodium hypochlorite dispensing and conveying device consists of 1 table and 5m 3 Sodium hypochlorite storage tank, 1 sodium hypochlorite discharge pump, 2 sodium hypochlorite discharge pumps and 2 sodium hypochlorite discharge pumps 2 m 3 The sodium hypochlorite metering box and the metering pump 1 are prepared by 1; the hydrochloric acid dispensing and conveying device consists of 1 hydrochloric acid storage tank, 1 hydrochloric acid discharge pump, 2 hydrochloric acid discharge pumps and m hydrochloric acid discharge pumps 3 The metering box, 2 mechanical diaphragm metering pumps and 2 pneumatic diaphragm metering pumps are formed; the citric acid dispensing and conveying device consists of 1 table 2 m 3 The metering box and 2 pneumatic diaphragm metering pumps.
5. The demineralized water producing system employing the double membrane method according to claim 1, wherein: in the full-automatic reverse osmosis unit, the pressure provided by the reverse osmosis lifting pump is mainly used for overcoming the resistance of a security filter and providing stable water inflow for the high-pressure pump, and a PH meter and a conductivity meter are arranged on a front water inlet pipeline of the lifting pump; the method is used for detecting the water quality condition of the water inlet of the reverse osmosis system; the cartridge filter comprises: according to the large-flow filtering requirement, 8 sets of large-flow folding filter cores with the diameters of 6 'and the lengths of 40' and horizontal filters made of stainless steel are adopted; when the pressure difference between the inlet and the outlet of the filter is more than 0.2 MPa, the filter element is replaced; the inlet and outlet of the high-pressure water supply pump are respectively provided with a high-pressure switch and a low-pressure switch, the inlet pressure is low, the alarm is stopped, the outlet pressure is high, the alarm is delayed, the stop is performed, so that the high-pressure pump is protected, the high-pressure water supply pump is a horizontal centrifugal pump, and the pump body is made of corrosion-resistant stainless steel; the reverse osmosis device comprises: the reverse osmosis device comprises 8 sets of membrane types: BW30-400FR.
6. The demineralized water producing system employing the double membrane method according to claim 1, wherein: in the dosing system, the scale inhibitor dosing device consists of 2 electric stirring metering boxes and 8 metering pumps, wherein the metering pumps are electromagnetic diaphragm metering pumps, pump heads are made of PVC materials, the metering pumps are quantitatively added into reverse osmosis water according to water supply flow, the metering boxes are provided with liquid level switches to protect dosing pumps and remind operators to timely dispense and switch solution boxes, and the starting and stopping high-pressure pumps of the scale inhibitor metering pumps are interlocked for quantitative addition; the reducing agent dosing device consists of 2 electric stirrer metering boxes and 2 metering pumps, the metering pumps are electromagnetic diaphragm metering pumps, pump heads are made of PVC materials, the metering boxes are provided with liquid level switches for protecting dosing pumps, operators are reminded of timely dosing and switching solution boxes, and the starting and stopping of the metering pumps are interlocked with the lifting pumps for quantitative dosing; the non-oxidizing bactericide dosing device consists of 1 metering box and 2 metering pumps; the metering pump is a mechanical diaphragm metering pump, and the pump head is made of PVC material, so that the metering pump is corrosion-resistant and has no leakage. The liquid level switch is arranged on the metering box to protect the dosing pump and remind operators of timely dosing, and a given quantitative value is adjusted according to actual working conditions.
7. A process for producing demineralized water by adopting a double-membrane method, which adopts the demineralized water producing system adopting the double-membrane method as claimed in any one of claims 1 to 6, and is characterized by comprising the following steps:
the sewage is firstly subjected to chemical treatment and then enters a water distribution channel, then enters the bottom of a membrane pool of an ultrafiltration unit, is driven by an ultrafiltration water production suction pump to pass through a membrane wall to enter a membrane fiber cavity under negative pressure, is filtered by an immersed ultrafiltration membrane, and then enters an intermediate water tank, and the ultrafiltration system has the functions of removing colloid, suspended matters, macromolecular organic matters and the like in the water, wherein the turbidity of the product water is less than or equal to 0.2NTU, the SDI is less than or equal to 3, the water quality requirement of reverse osmosis water inlet is met, and a reverse osmosis system is protected; the ultrafiltration effluent enters a reverse osmosis device through a reverse osmosis lifting pump, a cartridge filter and a high-pressure water supply pump, and the produced water of the reverse osmosis device is sent to a desalting water pond of a combined pump station, so that the water can be recycled.
8. The process for producing demineralized water by adopting a double membrane method according to claim 7, wherein the process is characterized in that: the process for carrying out chemical treatment on sewage by the ultrafiltration system comprises the following steps:
the sodium hypochlorite dispensing and conveying device performs sterilization treatment on ultrafiltration water supply; the bactericide adopts 10 percent sodium hypochlorite, and the dosage is 3mg/L; the dosing amount is automatically regulated according to the flow rate change in proportion, and the dosing amount of the ultrafiltration cleaning sodium hypochlorite dosing pump is controlled by time, so that the concentration of the chemical cleaning liquid is ensured; the dosing amount of the hydrochloric acid dosing and conveying device is automatically adjusted according to the PID of pH change, and the dosing amount of an ultrafiltration cleaning hydrochloric acid dosing pump is controlled by time, so that the concentration of chemical cleaning liquid is ensured; the citric acid dispensing and conveying device is characterized in that the citric acid metering box is provided with a stirrer 1. The dosage is quantitatively added, and the chemical cleaning liquid concentration is ensured by controlling the dosage by time.
9. The process for producing demineralized water by adopting a double membrane method according to claim 7, wherein the process is characterized in that: the membrane component is cleaned in the ultrafiltration system, including gas/water back flushing, chemical enhanced back flushing CEBW and chemical on-line cleaning CIP;
the IP chemical online cleaning system stops water filtering operation when the system film-penetrating pressure or time combination reaches the upper limit of process setting or reaches the set cleaning period, and carries out full-range chemical online cleaning; the complete CIP is automatically finished under the control of a PLC, the normal membrane permeation pressure is 15-35kPa, the complete CIP cleaning is required to be carried out when the membrane permeation pressure exceeds the membrane permeation pressure, and the normal membrane permeation pressure is reached after the cleaning;
chemically enhanced backwash CEBW: the difference from the intact CIP is that the concentration and time of the cleaning liquid are used in the cleaning process, the intact CIP treatment is completed in 6 to 8 hours, while the CEBW only takes 30 minutes, and the concentration of the used cleaning solution is lower;
gas/water backwash system: the system must carry out comprehensive back flushing in the membrane wire within a certain time to prevent the deposition of particulate matters in the membrane wire, maintain the flux of the membrane and facilitate the normal operation of the protection membrane system.
10. The process for producing demineralized water by adopting a double membrane method according to claim 7, wherein the process is characterized in that: in the reverse osmosis operation process, when the recovery rate is 75% -80%, the salt content of the concentrated water is 4-5 times higher than that of the inlet water; because the concentration of each ion on the concentrated water side is increased, the insoluble salts reach the solubility product, so that the water permeability and the desalination rate of the reverse osmosis membrane are reduced, namely the rated output can not be reached during operation; the addition of the scale inhibitor can prevent CaCO 3 Separating out on the surface of the reverse osmosis membrane; the reducing agent is NaHSO 3 The method comprises the steps of carrying out a first treatment on the surface of the The purpose of adding sodium bisulphite into the reverse osmosis water is as follows: residual chlorine remained in the CMF-S membrane filtration treatment process is removed, and the reduction of the desalination rate caused by oxidation of the reverse osmosis membrane is prevented; the non-oxidizing bactericide uses SX-402 non-oxidizing bactericide, and a given quantitative value is adjusted according to actual working conditions;
the chemical cleaning in the flushing system comprises the following cleaning formulas: the alkaline washing is suitable for organic matter and microorganism pollution, and the dosage is as follows: EDTA 2%, sodium tripolyphosphate 2%, dodecane 0.125%; in the cleaning process, the pH is ensured to be 11-12 by ensuring that alkali is added; the acid washing is suitable for iron pollution, pollution blocking of carbonate crystallization and partial colloid, and the dosage is as follows: hydrochloric acid or citric acid, and the pH value is ensured to be 2-2.5 by adding acid in the cleaning process.
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