Countercurrent regeneration cation exchanger

Working principle: After the raw water passes through the cation exchanger, it enters an anion exchanger filled with OH-type anion exchange resin. This causes the various anions present in the water to react with the OH- groups on the ion exchange resin as follows: Cl- + ROH → RCl + OH-, SO42- + 2ROH → R2SO4 + 2OH-, CO32- + 2ROH → R2CO3 + 2OH-. As a result of these reactions, the various anions in the water get adsorbed onto the ion exchange resin, while the OH- groups from the resin end up in the water. The anions in the water then consist almost entirely of OH-, which reacts with other anions present in the water to form various bases. Water quality after treatment: SiO2 < 100 μg/L; Conductivity (at 25°C) < 5 μs/cm. Brief description of the structure: 1. Water inlet device – A water inlet device is located at the upper part of the equipment, enabling the water to be distributed evenly over the exchange resin layer. 2. Middle-row device The middle-row device is installed at the interface between the cation exchange resin layer and the fat compression layer; it is used to discharge the regenerated alkali waste liquid as well as the water used for backwashing. It comes in a branch-pipe main-pipe design, with small holes in the pipes for liquid distribution, and the pipes are covered with triangular-shaped winding wires. Both the pipes and the wiring are made of 316L stainless steel. 3. Drainage system Type: rubber-lined steel dome-shaped perforated plate and quartz sand cushion. 　　In addition, a sight glass is installed at the contact surface between the cushion layer at the bottom of the exchanger and the resin, another sight glass is placed 100 mm away from the resin interface, and two sight glasses are installed at the maximum backwashing expansion height, all of which are used to monitor the conditions inside the device. Space is reserved next to the peephole for the lamp holder used for lighting. The upper manhole is equipped with a maintenance platform and a straight ladder, and guardrails and protective cages are installed in accordance with relevant regulations. Considering the hydraulic loading and unloading of the resin, a resin inlet is provided at the upper part of the cylinder, while a resin outlet is located at the lower part of the cylinder near the bottom of the resin. Usage Method 1: Resin treatment 　Before putting the resin into the exchanger, it should first be screened. It is then soaked in an 8–10% NaCl solution for 20 hours; after that, the saline solution is drained and the resin is rinsed with water until the water flowing out is no longer yellow. Alternatively, soak it in a 5% HCl solution for 2–4 hours; after draining the acid, rinse the resin with water until the drainage water is nearly neutral. Then fill the resin into the equipment to the specified height. 　　Perform a backwash once after the resin is installed. 2. Operation 　　A sufficiently high water cushion should be maintained inside the device to prevent water from directly impacting the fat-pressure layer on the resin layer. A forward wash must be performed before putting it into operation. That is: open the inlet valve and the exhaust valve; once the tank is full, close the exhaust valve promptly, open the rinse drain valve, and close it as soon as the water quality meets the standards. Then open the outlet valve to resume normal operation. 3. Regeneration 　　When the quality of the effluent water is not satisfactory or after a certain volume of deionized water has been produced, the ion exchanger needs to be stopped and regenerated. The steps for regeneration are as follows: ⑴ Light backwashing: 　　Before regeneration, a light backwash should be performed on the fat layer located above the intermediate drain pipe, in order to remove the dirt that has accumulated there during operation. During minor backwashing, first close the inlet valve and the outlet valve, then open the minor backwashing inlet valve and the backwashing drain valve. The flow rate is generally 5–10 meters per hour, and the duration is 3–5 minutes. After the minor backwash is completed, close the minor backwash inlet valve and the backwash drain valve. ⑵　Feed of regeneration liquid: Open the valve for feeding the regeneration liquid, and introduce it into the device from the bottom; then open the intermediate discharge valve, so that the regenerated waste liquid is discharged through the intermediate unit. To ensure effective regeneration, the regeneration flow rate should be controlled at 5 meters per hour, and the concentration of the regeneration alkali solution should be maintained between 3% and 5%. (Replacement is carried out after regeneration is completed.) ⑶ Light rinsing: During the injection of the regeneration solution, some of the alkaline solution seeps into the fat compression layer. To reduce the water consumption for rinsing and shorten the rinsing time, a light rinsing is performed first to wash away this excess liquid. During light cleaning, open the water inlet valve and then the intermediate drainage valve; water is discharged through the drainage device, with a flow rate of 10–15 meters per hour, for a duration of about 5–10 minutes. ⑷ Normal washing: After the short normal washing cycle is completed, the intermediate drain valve is closed, and the normal washing drain valve is opened to carry out the washing process; the flow rate remains the same as that during normal operation. Once the quality of the water discharged meets the requirements, the drain valve is closed and the outlet valve is opened to resume normal operation. ⑸　Heavy backwashing: Since the exchange medium can become compacted or contaminated, which affects its proper functioning, a heavy backwashing must be carried out after several cycles of operation. The interval between such backwashings can be determined based on factors such as the turbidity of the water entering the plant, the quality of the water exiting the plant, the operating pressure difference, and the exchange capacity of the medium; generally, it is performed every 10 to 20 cycles. After a heavy backwash, the exchange resin layer becomes disrupted; to restore its normal exchange capacity, during the first regeneration after the heavy backwash, the amount of regenerant used should be 0.5 to 1.0 times higher than that used in the first regeneration. During heavy backwashing, open the heavy backwashing inlet valve, gradually increasing the flow rate; the intensity of backwashing should be adjusted based on the center line indicated on the backwashing sight glass. Open the backwashing drain valve to carry out the backwashing process, which lasts approximately 10 to 15 minutes.