The infiltration/electrodeionization (RO/EDI) integrated membrane technology is the latest generation of ultrapure water manufacturing technology that has rapidly developed and matured in recent years and has been used in large-scale industrial applications. It has gradually become the mainstream of pure water technology in the world.
Membrane Ultrapure Water Preparation
RO/EDI’s integrated membrane technology has unique advantages in electronics water, laboratory water systems, and power plant water.
The tap water enters the original water tank, is pressurized by the original water pump, passes through the sand filter, the carbon filter, the scale inhibitor, and the security filter, reaches the reverse osmosis unit, and enters the EDI unit through two-stage reverse osmosis filtration to reach a resistivity of 15 MΩ⋅cm ( 25°C) into the pure water tank.
The pure water supply is designed in a circulating mode. It is pressurized by a pure water supply pump. It is connected to the pure water supply pipe through a UV sterilizer, a polishing mixed bed, and a 0.22-micron filter to reach the point of use.
Membrane method for ultrapure water preparation equipment mainly through pretreatment unit, membrane system unit, reverse osmosis module, EDI module, water supply unit
Quartz sand filtration activated carbon filtration, and security filtration is used as pretreatment for two-stage reverse osmosis.
Membrane System Unit
The membrane system unit is the core of the system and is responsible for removing most of the harmful substances in the water and ensuring that the terminal water production meets the standard requirements. In this design, two-stage reverse osmosis with pH adjustment is used as the primary desalination process, and the EDI module is used as the deep desalination process.
Reverse Osmosis Module
The reverse osmosis membrane is a liquid membrane separation method that uses a pressure difference as a driving force and can be regarded as a reverse action of permeation. Under pressure, the water molecules in the solution pass through the membrane, while other molecules, ions, bacteria, viruses, etc. are trapped, thereby achieving the desalination effect and achieving the purification purpose.
The entire reverse osmosis system consists of a high-pressure pump, a reverse osmosis membrane, a pressure vessel, and corresponding instruments, instruments, valves, frames, pipes, and fittings; in addition to an independent chemical cleaning device.
EDI technology is a new process combining membrane method and ion exchange method. The basic principles mainly include ion exchange, selective migration of ions under DC electric field and electrical regeneration of the resin.
The ions in the water are first adsorbed to the resin particles by exchange and then migrate to the surface of the film via the “ion transport channel” composed of the resin particles under the action of the electric field and enter the rich chamber through the ion exchange membrane.
Since the exchange and migration of ions and the electrical regeneration of the ion exchange resin occur, it is like a mixed bed ion exchange resin column that is regenerated while working, so that high-quality pure water and high-purity water can be continuously produced.
The EDI system consists of a booster pump, a membrane stack, a power supply, and corresponding instruments, meters, valves, racks, and pipes.
Water Supply Unit
The pure water supply cycle uses 254nm ultraviolet sterilization, polishing mixed bed desalination, and 0.22-micron filtration to meet the user’s pure water quality requirements.
In order to ensure the quality of pure water and biological indicators, a microfiltration membrane filter with an accuracy of 0.22 μm is set at the terminal of pure water preparation for intercepting particles and bacterial corpses in the effluent of the desalination equipment.
Since the 0.22 μm microfiltration membrane filter is the last processing equipment of the entire desalination process, it is also called the terminal filter.
The filter is equipped with a folded microporous membrane with a filtration precision of 0.22μm and a pressure gauge at the outlet of the filter. After a period of operation of the filter, a large number of impurities are trapped on the surface of the filter membrane, causing the filter membrane to clog, resulting in an increase in working pressure. When the inlet and outlet pressure difference increases to a certain set value, the filter membrane is replaced.
The terminal filter consists of a tank, a 0.22μm filter, and a pressure gauge.
Main Equipment for Ultrapure Water Manufacturing
Original water tank, raw water booster pump, sand filter, carbon filter tank, multi-way valve, scale inhibitor metering pump, scale inhibitor (amino trimethylene phosphonic acid ATMP) canister, security filter, security filter, level one RO high-pressure pump, first stage RO membrane, secondary RO high-pressure pump, secondary RO membrane, membrane shell, pH adjustment metering pump, EDI booster pump, EDI module, ultrapure water tank, pure water booster pump, polishing mix Bed can, polishing resin, 0.22-micron filter, 0.22imicron filter, etc.
Ultrapure water equipment is a combination of reverse osmosis equipment and ion exchange mixed bed or ED. The ion exchange mixed bed is carried out in an electrolyte solution by an ion exchange resin. It can remove various anions and cations in water. It is an irreplaceable means in the current process of preparing high purity water.
Ion exchangers are classified into cation exchangers, anion exchangers, and the like. When the raw water passes through the ion exchange column, the cations in the water and the anions in the water (HCO3 plasma) are exchanged with the H ions of the cation resin in the exchange column and the OH ions of the anion resin, thereby achieving the purpose of desalination. Different combinations of positive and negative mixing columns can achieve higher water quality requirements.