Instrument keywords: Equal-proportional nitrogen flow rate distributor, chlorine calibration method, unattended

A high-chlorine wastewater COD digester that uses an imported proportional regulating distributor to control the nitrogen flow rate;
A high-chlorine wastewater COD digester that fully complies with the national standard HJ/T 70-2001 "Determination of Chemical Oxygen Demand of High-chlorine Wastewater - Chlorine Correction Method";

Product development background:
The determination of COD in industrial wastewater generally refers to the national standard "Determination of Chemical Oxygen Demand in Water Quality - Dichromate Method" (HJ828-2017). However, for industrial wastewater containing high concentrations of chloride, such as wastewater from the oil extraction industry, dye chemical industry, organic chlorination industry, and salt lake brine development industry, the chloride ions are easily oxidized by potassium dichromate when COD is measured under strong acidic conditions, which will affect the accuracy of the measurement results. Therefore, for the determination of COD in high-chlorine industrial wastewater with a concentration higher than 1000 mg/L and less than 20000 mg/L, it is generally required to be carried out in accordance with the standard HJ/T70-2001 "Determination of Chemical Oxygen Demand in High-Chlorine Wastewater - Chlorine Correction Method".

Principle of the method:
Add known amounts of potassium dichromate solution and mercuric sulfate solution to the water sample, and use silver sulfate as a catalyst in a strong acid medium. After 2 hours of boiling and refluxing, use 1.10-phenanthroline as an indicator and ammonium ferrous sulfate to titrate the unreduced potassium dichromate in the water sample. The amount of ammonium ferrous sulfate consumed is converted into the mass concentration of oxygen consumed, which is the expressed COD. The chlorine gas formed by the uncomplexed and oxidized part of the chloride ions in the water sample is led out, and then absorbed by sodium hydroxide solution, potassium iodide is added, and the pH is adjusted to about 3-2 with sulfuric acid. Starch is used as an indicator and titrated with sodium thiosulfate standard titration solution. The amount of sodium thiosulfate consumed is converted into the mass concentration of oxygen consumed, which is the chloride ion correction value. The difference between the expressed COD and the chloride ion correction value is the true COD of the measured water sample.

Instrument use:
Used for dechlorination and digestion of COD samples in high-chloride water bodies (water and wastewater, chloride ion concentration greater than 1000mg/L and less than 20000mg/L).

Applicable industries:
COD determination in high-chlorine wastewater such as oil fields, coastal refineries, oil depots, chlor-alkali plants, steel mills, power plants, pesticides, food, textile printing and dyeing enterprises, and deep-sea discharge of wastewater.

Main advantages of the product:
1. The heating unit adopts far-infrared ceramic heating technology, and the heating rate is stable and controllable;
2. Digestion unit: 1-6 positions, all with single hole and single control;
3. The nitrogen flow rate control adopts imported proportional adjustment distributor, which ensures uniform flow distribution and stable flow rate;
4. The digestion time is controlled by computer program and can be set freely. It can stop automatically when the digestion is finished.
5. The cooling system adopts built-in compressor cooling, and the cooling water automatically circulates internally without external cooling water;
6. The main unit is equipped with a nitrogen automatic anti-backflow unit to prevent the absorption liquid from being sucked back after heating.
7. The whole machine adopts PLC module control and touch-screen LCD tablet computer, which can be operated remotely and conveniently.