CN100357202C - Liquid flow type capacitance pretreatment method for sea water desalination - Google Patents

Abstract

The invention relates to a pretreatment method for seawater desalination by a liquid-flow capacitor method, and belongs to the field of seawater desalination treatment. The pretreatment method of the present invention has a plurality of pretreatment procedures, and its specific process steps are: seawater passes through a multi-media filter unit, a carbon filter unit, a fine filter unit, an ultrafiltration unit, and a nanofiltration membrane unit in sequence, and finally obtains a suitable liquid flow The water supply required by the capacitive seawater desalination device. The method of the present invention has the advantages of being able to remove most of the hardness ions in seawater, solving the scaling problem of seawater desalination equipment, prolonging the service life of seawater desalination equipment; The treatment effect of the seawater desalination equipment is greatly improved, and at the same time, the water production rate is greatly improved, and the cost of seawater desalination is further reduced.

Description

Pretreatment method of seawater desalination by liquid flow capacitive method

Technical field:

The invention relates to a pretreatment method for seawater desalination by a liquid-flow capacitance method, and belongs to the field of seawater desalination treatment.

Background technique:

Today, the shortage of fresh water resources has become a worldwide problem. At present, 500 million people in the world do not have access to clean water. By 2025, this number will increase fivefold to 2.8 billion, accounting for about 35% of the estimated global population of 8 billion. %. The solutions to the water shortage problem include continuing to find water, remote water transfer, waste water recycling, and formulating water conservation measures. However, to take advantage of

Modern technology has opened up new water sources on a large scale, and seawater desalination has become an effective way. In fact, this has become an inevitable trend all over the world. Due to the increasingly prominent water resource crisis, most countries are directly or indirectly involved in the development trend of seawater desalination technology.

Seawater desalination, also known as seawater desalination, is a process in which salt in seawater is removed and desalinated through devices and equipment. The existing seawater desalination methods mainly include distillation (multi-stage flash evaporation MSF, multi-stage evaporation MED and compressed air distillation VC) and membrane method (reverse osmosis SWRO and electrodialysis ED), as well as FTC mentioned in patents US5538611, US6413409, US5547581, etc. (flow-through capacitor) seawater desalination method (we have applied for a patent for this method in China). At present, seawater desalination devices are developing in the direction of increasing the production capacity of a single machine, and reducing the energy consumption of seawater desalination has always been the development goal of seawater desalination technology. FTC seawater desalination has the advantages of low energy consumption, low cost, high desalination rate and long service life, so its application prospect is very promising.

Seawater is a complex dilute solution system with high salt content and high hardness. Under the condition of pH 8.2, the carbonates, bicarbonates, sulfates and chlorides formed by calcium and magnesium ions in seawater make seawater have great High hardness, easy to form scale in seawater desalination process. At the same time, the turbidity of seawater varies greatly, and there are organic and inorganic particles of different particle sizes in suspension, as well as microorganisms of different sizes. It is easy to block the pipeline and pollute the membrane elements; and the oxygen dissolved in the seawater is enough for the survival of marine organisms. During the desalination process, the presence of dissolved oxygen makes the metal materials of the desalination device easy to corrode and produce oxide scale. Therefore, the success of seawater desalination firstly depends on the rationality of the pre-treatment.

At present, in the seawater desalination process such as distillation method and membrane method, a series of pretreatment combined processes such as chlorine or sodium hypochlorite sterilization, FeCl ₃ flocculation precipitation, acid adjustment of pH and multimedia filtration are generally used to remove suspended solids and colloidal particles. , bacteria and macromolecular suspended matter, but the water quality of seawater after treatment is unstable, and it is difficult to meet the water inlet requirements of reverse osmosis membranes. Although conventional treatment has been running smoothly for many reverse osmosis seawater desalination plants for many years, conventional pretreatment has high requirements in terms of design, operation and maintenance, otherwise membrane fouling will occur. The distillation method is serious in scaling and corrosion, which has become one of the important factors limiting its application. For FTC (fluid capacitance method) seawater desalination, there is no report on its pretreatment, but combined with the FTC influent index, the existing pretreatment method cannot meet its influent requirements, so it is necessary to adopt a new technology to solve this problem.

A lot of research has been done on seawater desalination pretreatment at home and abroad. Patent US20030130088A1 uses adsorption as pretreatment; US20030121856A1 uses secondary filtration pretreatment; US20020189987A1 uses filtration as pretreatment; and device, using coarse filter, microporous filtration and dosing as reverse osmosis pretreatment; Chinese patent CN1328867A reverse osmosis seawater desalination microfiltration membrane pretreatment method, using flocculation scale inhibitor, microfiltration as pretreatment; Chinese patent CN1155518A seawater desalination equipment adopts activated carbon filter and hollow fiber filter; Chinese patent CN2583096Y seawater desalination processor adopts dosing, activated carbon adsorption and precision filtration as pretreatment; Chinese patent CN2583087Y reverse osmosis membrane seawater desalination device adopts fine filtration, Security filtration and ultrafiltration are used as pretreatment; Chinese patent CN2346787Y marine seawater desalination device adopts fine filtration and microfiltration as pretreatment. The preparation method of Chinese patent CN1241535A membrane treatment type seawater desalination adopts pre-filter and ultra-filtration as pre-treatment. However, using the existing seawater desalination pretreatment method to provide water for FTC (fluid flow capacitor method) still has the following disadvantages: (1) The operation is complicated, and if the protection is not proper, it is easy to cause biological pollution. (2) The problem of high hardness and high salinity of seawater cannot be solved, resulting in high energy consumption of FTC seawater desalination, serious scaling, high washing frequency, low water production rate, and difficulty in reducing desalination costs. (3) It is necessary to add medicine for sterilization and anti-scaling, resulting in complicated equipment and high investment. Therefore, according to the FTC influent index, none of the existing pretreatment methods can meet the FTC seawater desalination influent requirements.

Contents of the invention

The purpose of the present invention is to provide a kind of pretreatment method that combines multiple membrane separation processes and other treatment processes for the flow capacitive method (FTC) aiming at the technical deficiencies and defects of the existing conventional seawater desalination pretreatment methods.

An object of the present invention is to effectively remove solid particles, colloidal particles, bacteria, viruses and most of the magnesium ions in seawater by each program step of the method, and reduce the total dissolved solids in the influent of the liquid flow capacitance method Quantity (TDS).

The above object of the present invention is achieved through the following technical solutions.

A pretreatment method for seawater desalination by liquid flow capacitive method, characterized in that it has multiple pretreatment procedures, and its specific process steps are: seawater passes through a multimedia filter unit-carbon filter unit-fine filter unit -ultrafiltration unit-nanofiltration membrane unit-water supply that meets the requirements of seawater desalination; the multi-media filter unit uses quartz sand as the filter material; the carbon filter unit uses shell-type granular activated carbon; , bacteria, rocks, silica, iron corrosion products, iron precipitates, manganese precipitates, hardness precipitates, aluminum hydroxide flocs are filtered out, and then enter the activated carbon filter, the fine filter unit, using the filter element as the inner diameter Hollow polysulfone fibers smaller than 5 μm; the ultrafiltration membrane used in the ultrafiltration unit is an organic polymer ultrafiltration membrane or an inorganic ceramic ultrafiltration membrane with a molecular weight cut-off of 20,000 to 50,000 Daltons; the nanofiltration membrane unit adopts composite nanofiltration Membrane, the composite nanofiltration membrane is a three-layer structure, that is, aromatic polyamide, polyester non-woven fabric, polysulfone polymer; the final treated seawater is used for seawater desalination.

The above-mentioned effluent treated by the ultrafiltration unit needs to be pressurized by the booster pump and directly adopts the nanofiltration membrane unit; the nanofiltration membrane unit adopts a plurality of nanofiltration membrane components composed of double nanofiltration membranes; The nanofiltration membrane unit adopts the above-mentioned nanofiltration membrane modules of 1-5 stages.

The effluent treated by the above-mentioned ultrafiltration unit needs to be boosted by a booster pump. The operating pressure used is 0.1-1.50 MPa, and the operating temperature is 0-30°C.

The main function of the above-mentioned multimedia filter unit is to remove suspended solids, and the multimedia filter is usually used first to remove impurities in water. Prevent any medium from transferring from the front equipment to the back, and reduce the degree of pollution to the subsequent processing equipment.

The main function of the above-mentioned carbon filter unit is to remove the odor in seawater, natural and synthetic dissolved organic matter, and micro-polluting substances; it has obvious removal effects on free chlorine and dissolved oxygen in seawater, and protects the downstream membrane elements; further removes Impurities in seawater to ensure that the following components can fully function.

The main function of the above-mentioned fine filter unit is to remove fine particles with a particle size of 1-5 μm, further reduce the total dissolved solids (TDS) pollution index, and prevent activated carbon powder from entering the downstream membrane module. The fine filter membrane adopts hollow polysulfone fiber.

The main function of the above-mentioned ultrafiltration unit is to further remove impurities such as particles, colloids, bacteria, algae and various organic substances in seawater, especially bacteria and algae substances; to prevent bacteria and algae from rapidly multiplying and growing on the pipeline and membrane surface, blocking waterways and polluting NF Membrane; the FI value of the seawater entering the NF reaches 0-1, and almost all bacteria and algae are removed, prolonging the service life of the NF. The material of the ultrafiltration membrane is polypropylene, polyetherphenol or polyacrylonitrile; the material of the inorganic ceramic ultrafiltration membrane is aluminum oxide membrane.

The main function of the above-mentioned nanofiltration unit is to further reduce turbidity (SDI) and microorganisms; use the selective permeability of nanofiltration membrane to remove scaling ions and remove harmful substances in seawater to the desalinator, which can significantly reduce RO, etc. Inlet water pressure and energy consumption of seawater desalinator.

The most important link in the pretreatment method of the present invention is the nanofiltration process of seawater desalination by the liquid-flow capacitive method. The nanofiltration membrane element used is a new type of separation membrane, and the pore size of the membrane surface is in the nanometer range; The composite nanofiltration membrane used is a three-layer structure, that is, aromatic polyamide, polyester non-woven fabric, and polysulfone polymer.

The seawater desalination pretreatment method of the present invention is a technological process that simultaneously integrates various membrane separation processes such as ultrafiltration and nanofiltration, and processes such as multi-media filtration, activated carbon adsorption, and fine filtration. Using seawater as the source water, it goes through five treatment steps of multi-media filtration, activated carbon filtration, fine filtration, ultrafiltration and nanofiltration in sequence, and finally obtains feed water with a lower concentration that meets the requirements of the seawater desalination water flow test capacitance method.

Adopting the seawater desalination and treatment method of the present invention, its treatment method has the following advantages relative to the existing methods: (1) most of the hardness ions in seawater are removed, which solves the FTC fouling problem and reduces the cost of electrodes. The number of flushing reduces energy consumption, saves flushing water, and prolongs the service life of FTC; (2) reduces the concentration of FTC influent, which will greatly improve the treatment effect of FTC, thereby reducing energy consumption and increasing water production rate It has been greatly improved, further reducing the cost of seawater desalination. (3) The method of the present invention not only removes a large amount of microorganisms, suspended solids, odor and organic matter, particles, and metal ions in seawater, but also removes most of the scaling ions in seawater, reducing the total dissolved solids in seawater , (4) The method of the present invention has the advantages of simple process, convenient operation, rapid separation, high efficiency, high degree of automation, and low cost.

Description of drawings

Fig. 1 is a schematic flow chart of the seawater desalination treatment method of the present invention by the liquid flow test capacitance method.

The meanings of the numbers in the figure are as follows:

1-water supply pump, 2-sea water tank, 3-flush water discharge port, 4-float switch, 5-water inlet booster pump, 6-discharge port, 7-multimedia filter unit, 8-activated carbon filter unit, 9- Fine filter unit, 10-Ultra filter unit, 11-Low pressure switch, 12-Boost pump, 13-Nano filter unit, 14-Rinse water tank, 15-Rinse pump, 16-Concentrated water outlet, 17-Sea water desalination device water tank.

Detailed ways

Now the embodiment of the inventive method is described in the back:

Example 1: Referring to Figure 1, seawater with a concentration of 35000mg/L is used as the water source, and the impurities in the seawater are filtered out through the multimedia filter unit 7, and then enters the activated carbon filter unit 8 to remove the odor in the seawater, natural and synthetic dissolved organic matter , micro-polluting substances, etc., and then enter the fine filtration unit 9 to remove fine particles with a particle size of 1-5 μm, and at the same time further reduce the pollution index and prevent activated carbon particles from entering the downstream membrane module. Then pass through the ultrafiltration membrane unit 10 to remove pollutants on the order of microorganisms and bacteria, as well as pollutants on the order of harmful poisons, carcinogens, and viruses. At this time, the seawater has become clean brine after the above treatment, the turbidity of the effluent is NTU<0.1, suspended solids<1mg/L, total organic carbon content is 8-10mg/L, SDI<1, bacteria CFU/100mL<10 ; After the above treatment, the seawater has become a clean brine, which fully meets the water inlet requirements of the nanofiltration membrane. Then the booster pump enters the nanofiltration unit 13 at an operating pressure of 1.2Mpa and a temperature of 20°C. After the nanofiltration treatment, 92% of the hardness, 95% of sulfate, and 40% of the chloride in the water are removed, and the TDS is reduced by 46%. %.

Embodiment 2: Using 20000mg/L seawater along the coast of China as the water source, after the same treatment process as the above-mentioned embodiment, the seawater has become clean brine, and then the booster pump enters the nanofiltration unit at 1.3Mpa and a temperature of 20°C Treatment 13 was used to remove 96% of hardness, 98% of sulfate, and 51% of chloride in water, and the TDS was reduced by 61%.

Through the examples, it can be known that the pretreatment method of the present invention can supply water to the seawater desalinator that meets the water quality requirements, and the water production rate can reach up to 70%, and the removal rate can reach more than 70%.

Claims (4)

1. A pretreatment method for liquid flow capacitance seawater desalination, characterized in that: it has a plurality of pretreatment procedures, and its concrete process steps are: seawater passes through multimedia filter unit-carbon filter unit-finish filter unit -ultrafiltration unit-nanofiltration membrane unit-water supply that meets the requirements of seawater desalination; the multi-media filter unit uses quartz sand as the filter material; the carbon filter unit uses shell-type granular activated carbon; , bacteria, rocks, silica, iron corrosion products, iron precipitates, manganese precipitates, hardness precipitates, aluminum hydroxide flocs are filtered out, and then enter the activated carbon filter, the fine filter unit, using the filter element as the inner diameter Hollow polysulfone fibers smaller than 5 μm; the ultrafiltration membrane used in the ultrafiltration unit is an organic polymer ultrafiltration membrane or an inorganic ceramic ultrafiltration membrane with a molecular weight cut-off of 20,000 to 50,000 Daltons; the nanofiltration membrane unit adopts composite nanofiltration Membrane, the composite nanofiltration membrane is a three-layer structure, that is, aromatic polyamide, polyester non-woven fabric, polysulfone polymer; the final treated seawater is used for seawater desalination. 2. The pretreatment method for seawater desalination by a liquid-flow capacitive method according to claim 1, characterized in that: the effluent treated by the ultrafiltration unit needs to be pressurized by a booster pump and directly adopts a nanofiltration membrane unit ; The nanofiltration membrane unit adopts a plurality of nanofiltration membrane components composed of double nanofiltration membranes; the nanofiltration membrane unit adopts the above-mentioned nanofiltration membrane components of 1-5 levels. 3. the pretreatment method of a kind of liquid flow capacitive seawater desalination according to claim 1, is characterized in that: The effluent treated by the ultrafiltration unit needs to be pressurized by a booster pump. The operating pressure used is 0.1-1.50MPa, and the operating temperature is 0-30°C. 4. the pretreatment method of a kind of liquid flow capacitive seawater desalination according to claim 1, is characterized in that: The organic polymer material of the ultrafiltration membrane used in the ultrafiltration unit is polypropylene or polyetherphenol or polyacrylonitrile; the material of the inorganic ceramic ultrafiltration membrane is aluminum oxide membrane.

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