Research on EDI membrane stacks used in China market and their application status and development

I. Achievements of EDI membrane reactor products and application technologies launched in the China market since 2000

Since 2000, under the concepts of reducing consumption and emission reduction, cleaner production, and making the sky bluer and the water greener, China has developed rapidly in EDI membrane stack production and application technology. Dozens of EDI membrane stack products, more than a hundred EDI equipment products, and more than a thousand complete sets of equipment containing EDI technology have been put on the market in China, achieving consumption reduction and emission reduction, saving water and electricity, and making clean production. It has made great contributions.

95% of the more than ten domestic and foreign EDI membrane stack products put on the China market are plate EDI membrane stacks. Plate EDI membrane stacks are divided into 1-stage EDI membrane stacks, 2-stage EDI membrane stacks, and multi-stage EDI membrane stacks (see [ZCYX Plate EDI Membrane Stack Classification]). EDI membrane reactor products from GE in the United States, Siemens in Germany, and ellecpure in the United States all belong to Class 1 EDI membrane reactors. These Level 1 EDI membrane stacks have been widely used in the [industrial pure water] production process in all walks of life in China.

2-stage and multi-stage EDI membrane stacks are inventions in China. [Secondary EDI technology],[Secondary EDI membrane stack],[Secondary EDI equipment] and [Multi-level EDI technology],[Multi-level EDI membrane stack],[Multi-level EDI equipment] The terms are senior engineer Zou Jinyuan The concepts of these terms have been elaborated in relevant papers published since 2000; In 2014, Guangzhou City Jingyuan Seawater Desalination and Water Treatment Co., Ltd. also developed level 2 and multi-stage EDI membrane stacks, which have been rapidly promoted and applied in the production equipment of [laboratory analytical water] and [ultrapure water for the pharmaceutical and electronic industry] in hospitals, universities and national statutory testing centers with high water quality requirements at home and abroad.

So far, there are the following pure water, high-purity water, and ultrapure water production processes including EDI membrane stack technology used in various industries

* The combined process of Level 1 RO+ Level 1 EDI produces deionized water (stable produced water resistivity 0.1-5MΩ.CM).

* The combined process of Level 1 RO+ Level 2 EDI produces pure water (stable produced water resistivity of 5-10MΩ.CM).

* Level 1 RO+ Level 3 EDI combination process produces high-purity water (stable produced water resistivity of 10-15MΩ.CM).

* The 2-level RO+1-level EDI combination process produces high-purity water (stable produced water resistivity of 10-15MΩ.CM).

* The 2-level RO+2-level EDI combination process produces ultrapure water (stable produced water resistivity of 15-17MΩ.CM).

* The 2-level RO+3-level EDI combination process produces ultrapure water (stable produced water resistivity of 17-18.2MΩ.CM).

The above-mentioned various RO+ EDI combination application processes can produce pure water, high-purity water, and ultra-pure water used in all walks of life without the use of polishing resin purification processes, basically meeting the high-end water requirements of my country's industrial enterprises.

In the EDI membrane stack market in China, the process used by the [Level 1 EDI membrane stack] represented by GE membrane stack in the United States and ionpure in Germany in the metallurgical, power and petrochemical industry basically adopts a 2-level RO+ Level 1 EDI combination process. Most of the stable produced water resistivity is 5-10 MΩ.CM, and a small part of the stable produced water resistivity is 10- 1 - 5 MΩ.CM. The actual water resistivity index is about 1-5 M Ω.CM, and the service life is generally 1-3 years.

The process used in the [ZCYX]-brand multi-level EDI membrane stack produced by Guangzhou City Jingyuan Seawater Desalination and Water Treatment Co., Ltd. basically adopts a 2-level RO+2-level EDI combination process to stabilize the resistivity of produced water at 15-18.2 MΩ.CM. The actual water resistivity index is>10MΩ.CM, and the service life is generally 5-10 years to replace it; The processes applied in the [pharmaceutical level laboratory] and the [electronic level laboratory] basically adopt a 2-level RO+3-level EDI combination process, which stabilizes the produced water resistivity at 17-18.2 MΩ.CM, and the actual water resistivity index is>17.5 MΩ.CM, and the service life is generally 3-6 years.

To sum up, the application status of various EDI membrane reactors put on the China market is summarized as follows:

* When tap water with a salt content of <250us/cm is used as raw water, a laboratory pure water machine using a combined process of Level 1 RO+ Level 1 EDI can produce a resistivity of 1-5MΩ within 1 year.CM laboratory Class III pure water can produce a resistivity of 0.1-1MΩ within 2 years.CM laboratory Class IV pure water; The high-purity water machine adopting the combined process of Level 1 RO+ Level 2 EDI can produce pure water with a resistivity of 5-10MΩ.CM II within 1 year, and can produce pure water with a resistivity of 1-5MΩ.CM III, and can produce pure water with a resistivity of 0.1-1MΩ.CM IV within 3 years; The ultrapure water machine using the combined process of Level 1 RO+ Level 3 EDI can produce pure water with a resistivity of 10- 1 - 5 MΩ. CM Laboratory Class I pure water with a resistivity of 5-10MΩ within 2 years.CM Laboratory Class II pure water can produce pure water with a resistivity of 1-5MΩ within 3 years.CM Laboratory Class III pure water with a resistivity of 0.1-1MΩ. CM Laboratory Class IV pure water with a resistivity of 0.1-1MΩ within 4 years.

* When using tap water with a salt content of <500us/cm as raw water, a high-purity water machine with a combined process of 2-stage RO+1-stage EDI can stably produce a resistivity of 10- 1 - 5 MΩ. CM laboratory Class I pure water can stably produce a resistivity of 5-10MΩ within 2 years.CM laboratory Class II pure water can stably produce a resistivity of 1-5MΩ.CM laboratory Class III pure water can stably produce a resistivity of 1-5MΩ within 3 years; The ultrapure water machine using the 2-level RO+2-level EDI combined process can stably produce a resistivity of 1 - 5 -18MΩ within 1 year.CM Medical Laboratory Class I ultrapure water can stably produce a resistivity of 10- 1 - 5 MΩ. CM Medical Laboratory Class II high pure water can stably produce a resistivity of 5-10MΩ within 3 years.CM Medical Laboratory Class III pure water can stably produce a resistivity of 1-5MΩ within 4 years.CM Medical Laboratory Class IV pure water; The ultrapure water machine using the 2-stage RO+3-stage EDI combined process can stably produce ultrapure water with a resistivity of 17- 18.2 M Ω.CM Electronics Class I ultrapure water with a resistivity of 15-17MΩ.CM Electronics Class II pure water with a resistivity of 10-15MΩ.CM Electronics Class III ultrapure water with a resistivity of 5-10MΩ. CM Electronics Class IV ultrapure water with a resistivity of 5-10MΩ.CM Electronics Class IV ultrapure water with a resistivity of 4 years. Within 5 years, electronic V-level ultrapure water with a resistivity of 1-5MΩ.CM can be stably produced.

Practice has proved that under the condition of using the same water source and using EDI membrane stack water, the multi-level EDI application effect has the following rules

● Impact of RO stages used for pretreatment. Under the conditions of using the same stage of EDI membrane reactors, the quality of EDI water produced by using stage 2 RO pretreatment is one level higher than that of the system using stage 1 RO pretreatment, and the service life of the EDI membrane reactor is one year longer.

● Produced water quality of multi-stage EDI membrane reactor: Under the conditions of RO pretreatment with the same number of stages, the produced water resistivity of stage 3 EDI membrane reactor> the produced water resistivity of stage 2 EDI membrane reactor> the produced water resistivity of stage 1 EDI membrane reactor. For every additional level of EDI membrane stack, the quality of produced water will be improved by one level.

● Service life of multi-stage EDI membrane stack: Under the conditions of using the same number of RO pretreatment and the same requirements for water resistivity indicators, the service life of level 3 EDI membrane stack> the service life of level 2 EDI membrane stack> Service life of level 1 EDI membrane stack. For every additional level of EDI membrane stack, the service life will be increased by one year.

● The amount and cost of polishing resin used in multi-stage EDI membrane stacks: Taking ultrapure water with a resistivity of 15- 18.2 M Ω.CM as the standard, and using the same 300us/cm water source as the standard, the production process of ultrapure water containing various EDI technologies is as follows

*1 stage RO+1 stage EDI+3 stage cation-anion mixed polishing mixed bed exchange column combination process produces ultrapure water.

* The combination process of level 1 RO+ level 2 EDI + level 2 mixed polishing mixed bed exchange column produces ultrapure water.

* The combination process of Level 1 RO+ Level 3 EDI + Level 1 polished mixed bed exchange column produces ultrapure water.

*2-stage RO+1-stage EDI+1-stage polished mixed bed exchange column combination process produces ultrapure water.

* The 2-level RO+2-level EDI combination process produces ultrapure water.

* The 2-level RO+3-level EDI combination process produces ultrapure water.

The above-mentioned system using level 1 RO pretreatment uses a higher number of EDI membrane stacks, and the smaller the number of stages using polishing mixed beds, the lower the amount used and the cost incurred; the system using level 2 RO pretreatment uses a higher number of EDI membrane stacks, and the fewer number of stages using polishing mixed beds, and even does not use polishing resin mixed beds, saving a lot of polishing resin resources and consumables.

● Impact of multi-stage EDI membrane stacks on the service life of secondary reverse osmosis membrane elements: Under the same water quality requirements (based on 15-18.2 MΩ.CM), under the conditions of using second-stage reverse osmosis pretreatment, In order to ensure that the polishing mixed bed resin replacement frequency is lower, the level 1 EDI membrane stack requires higher water quality (the general requirement for inlet water conductivity is <1-3us/cm). The replacement of level 2 reverse osmosis membrane elements is generally about 1-2 years; the replacement of level 2 reverse osmosis membrane elements is generally about 3 - 4 years; the replacement of level 2 reverse osmosis membrane elements is generally about 2-3 years; the replacement of level 3 EDI membrane elements is generally about 3 years; the replacement of level 2 reverse osmosis membrane elements is generally about 3-4 years.

Using a Level 3 EDI membrane stack, reverse osmosis membrane elements are replaced only once within 4 years; using a Level 2 EDI membrane stack, reverse osmosis membrane elements are replaced only once within 3 years; using a Level 1 EDI membrane stack, reverse osmosis membrane elements need to be replaced once within 2 years. Practice has proved that the higher the number of EDI membrane stacks used, the longer the usable life of reverse osmosis membrane elements. It not only saves the cost of replacing reverse osmosis membrane elements, but also saves reverse osmosis membrane element resources. 

● Application conclusion of using multi-stage EDI membrane stacks: Using multi-stage EDI membrane stacks in hospitals, laboratories, national statutory testing centers, electronics industry, pharmaceutical industry, thermal power generation industry, nanomaterials and fine chemical materials with high water quality requirements, and other applications in industries such as materials can produce ultrapure water in one step without using polishing resins, which has extremely high application advantages and development prospects. It not only saves the cost of consumables for reverse osmosis membrane elements in the pretreatment system, but also saves the cost of polishing resin consumables used in the ultrapure water purification section. Compared with first-stage EDI membrane reactors, multi-stage EDI membrane reactors have important advantages such as high water quality, long service life, water conservation, electricity conservation, resources conservation, water production costs, and reduced pretreatment investment scale.