Existing problems in the technology and application of various EDI membrane stack products put into the China market

● Fouling is the cause of damage to the EDI membrane stack. First, the process design of the water production system is imperfect. For example, the system lacks EDI membrane reactor pH adjustment equipment, CO2 removal equipment, and cleaning equipment, resulting in incomplete removal of calcium, magnesium ions and carbon dioxide in pretreatment, and the water into the EDI membrane reactor cannot meet the requirements of the indicator, resulting in scaling. Although most systems are equipped with external EDI membrane stack cleaning devices, the market supply quality of special cleaning agents for EDI membrane stacks is uneven, which often causes cleaning failures and damages the membrane stack; moreover, periodic timed chemical cleaning cannot deal with EDI membrane stacks in a timely manner. The problem of frequent fouling often causes poor flow in concentrated water channels, increased working voltage, increased energy consumption, and even clogging, causing overheating, burning and damage to the membrane stack. Nearly 60% of the damage caused by a large number of EDI membrane stacks used in industry is caused by fouling.

Therefore, the problem of fouling determines the desalination efficiency and service life of the EDI membrane stack. How to prevent fouling of EDI membrane stacks and timely chemical cleaning during fouling is a key issue in the current research and development of EDI membrane stack technology. It is unrealistic to rely entirely on users to improve the application and management technology of EDI membrane stacks. The only way to completely solve the popularization and application of EDI membrane stacks must be innovatively developed.

● Energy consumption is the second problem existing in EDI membrane stacks. A large number of EDI membrane stack application cases have proved that 30% of EDI membrane stack failures are due to energy consumption issues. Most brands of EDI resins are easy to break into powder and flow out of the resin chamber after long-term use, causing the resin in the membrane stack to become loose and the resistance increased. The limited working voltage of the configured DC power supply reaches the peak, the migration current becomes smaller, energy consumption increases, and even no migration current is generated, making the membrane stack unusable. How to improve the quality of resins used in EDI is a problem. How to reduce the working voltage of the membrane stack is another problem.

● Water utilization rate is the third problem existing in EDI membrane stacks. The concentrated water channel of the EDI membrane stack flows through the produced water of stage 2 reverse osmosis. Generally, the water utilization rate of EDI membrane stacks is designed to be within the range of 10%-5%. In order to prevent fouling by concentrated water and increase the working current, under normal circumstances, the concentrated water flow rate is large, exceeding the water utilization index given by EDI membrane reactors. Due to the high cost of desalinated water by stage 2 reverse osmosis, water reflux reuse technology is generally used for the part where the concentrated water flow exceeds the water utilization ratio (this technology has been widely used). However, this concentrated water reflux and recycling has caused a further increase in energy consumption. How to control concentrated water within the allowable water utilization rate range, save renewable energy consumption, and provide stable working current is also an important issue that needs to be solved.