EDI is the abbreviation for Electrodeionization. It is a novel deep desalination process that organically combines electrodialysis and ion exchange technologies. It leverages the deep desalination capability of ion exchange to overcome the incomplete desalination drawback of electrodialysis, while utilizing the polarization-induced generation of H? and OH? on the surfaces of electrodialysis membranes and ion exchange resins under an electric field, along with the selective permeability of electrodialysis membranes, to achieve automatic regeneration of ion exchange resins. This eliminates the need for acid and alkali regeneration after resin exhaustion. EDI is the product of the integration of ion exchange and electrodialysis technologies, thus inheriting all the operational characteristics of both during the desalination process. The electrodeionization system includes the main unit, chemical cleaning device, auxiliary systems, supporting instruments, valves, piping, main frame, and dosing equipment. The EDI unit is a critical device for post-RO polishing treatment, with EDI membrane elements being the core component of the EDI system. It is widely used in the preparation of electronic ultrapure water and industrial high-purity water. It employs a fully filled concentrate compartment, requires no salt addition or concentrate recirculation, operates continuously without shutdown for regeneration, and offers a broader application range and superior performance. **Main Unit Design Requirements:** - The electrodeionization unit adopts a modular frame design and is supplied as a complete set. The unit is equipped with all necessary modules, rectifiers, instruments, controls, piping, and valves to meet the required water quality and output. The EDI unit operates fully automatically, with internal equipment and piping arranged neatly. The combination of components is determined based on factors such as water quality, recovery rate, and production capacity. - Valves are installed on the main inlet and outlet pipes of each unit within the assembly. Sampling points are provided on the product water, feed, and drain pipes of each unit (each unit’s product water pipe shall have an independent sampling point). The number and location of sampling points should allow effective diagnosis and identification of system defects. Sampling points are centrally located for easy access. - The unit frame includes all piping and fittings, as well as all supports, fasteners, and clamps. The electrodeionization unit frame should facilitate maintenance and disassembly. The design of the EDI unit frame must comply with local seismic intensity requirements. - **Types and requirements of chemical cleaning solutions:** | Cleaning Formula | Purpose | Composition | Requirement | |------------------|----------------------------------|-------------------------|-----------------| | Formula 1 | Scaling/Residual chemical solution | 2% Hydrochloric Acid | Chemically Pure | | Formula 2 | Organic fouling | 5% NaCl + 1% NaOH | Chemically Pure | | Formula 3 | Biofouling/Organic fouling | 0.04% PAA + 0.2% H?O? | Chemically Pure | - Instruments, dosing metering pumps, and automatic valves in the electrodeionization unit shall be high-quality, reliable imported products. The system should enable automatic operation. - Each EDI module is equipped with a fully independent DC power control box, ensuring that if any module overheats due to operational reasons, its power supply is automatically cut off while other modules in the system continue to operate normally. - EDI does not generate chlorine gas or salt bridges during operation. - The EDI rectifier complies with relevant national technical standards and displays current and voltage parameters. - The EDI unit is assembled in a modular format for easy maintenance and replacement. Each EDI module has corresponding inlet and outlet pipes and valves, allowing isolation in case of failure while other modules continue to operate normally. All components within the module are pre-assembled before shipment.