Reductant dosing device

DAWT·2022-05-09

System Introduction

Adding a reducing agent before the reverse osmosis unit can reduce the content of residual chlorine to ensure the normal operation of the reverse osmosis system. It is generally controlled at 0.3-1.0 mg/L; if the residual chlorine in the water exceeds this value, it is mostly caused by the excess of disinfectant at the factory. The chemical reduction removal method is generally used for removal, which is simple in process, low in operating cost, moderate in equipment investment and convenient for automatic control.

How it works

The reduction of residual chlorine by sodium bisulfite is a redox reaction. The redox reaction has the fastest reaction rate among so many reactions. Generally, the dosage of the reducing agent will be more, which will eliminate the interference of other ions in the water. According to the theoretical calculation, 1.34mg/l food grade sodium bisulfite (SMBS) can remove 1.0mg/l residual chlorine. In actual engineering, 3.0 mg/l of SMBS is required for every 1.0 m/l of residual chlorine removed.

Principle of automatic control

The 4-20ma signal output by the residual chlorine detection instrument is transmitted to the PLC. The PLC compares with the standard value and outputs the signal to the inverter. The inverter controls the output frequency of the dosing pump through PID to adjust the dosing amount to achieve the control target.

In order to make the reaction between the medicament and the water more rapid and evenly mixed after dosing, a mixing tank is added to ensure the accuracy of residual chlorine detection.