Chlorine dioxide is also declining due to its excellent killing characteristics and cost of production. Chlorine dioxide is used as a biocide for industrial circulating cooling water treatment. It has a chlorine system in terms of effect, operation, safety and cost. The trend of biocides and non-oxidizing biocides.
Based on the actual application data and experience, we will give a general introduction to the practical application of chlorine dioxide in circulating cooling water treatment.
1. Method of adding chlorine dioxide
Due to the good sterilization of chlorine dioxide and the long duration of action, it is usually possible to use regular feeding.
The practical application of the tracking test shows that the maximum sterilization rate after the addition of chlorine dioxide often occurs 1 to 3 days after the addition.
In laboratory tests, the number of days in which chlorine dioxide maintains more than 99% of the heterotrophic bacteria sterilization rate sometimes reaches about 5 days. The chlorine dioxide dosing cycle and dosage are related to the system condition, concentration factor, water temperature, water treatment agent and the amount of reducing substances in the water. Usually, the chlorine dioxide addition cycle is 3 to 5 days, and the length is also up to one week. If the amount of investment is large, the investment cycle can be longer.
Chlorine dioxide not only can be strongly sterilized, but also control algae and slime is very effective, which is unmatched by chlorine disinfection. Chlorine dioxide is mainly used for stripping and rapidly reversing the deterioration of water quality. This aspect is often more than non-oxygen.
Chemical fungicides (such as alkyl dimethyl quaternary ammonium salt - 1227, etc.) are superior.
When chlorine dioxide is added as a primary biocide, it may be added periodically or irregularly with a small amount of chlorine to enhance synergistic killing, reduce the amount of biocide and maintain residual chlorine. In areas where the chlorine source is tight and the price is high, chlorine gas may not be added, and chlorine dioxide is used as a biocide.
The use of chlorine dioxide as an auxiliary biocide is mainly used in areas where the chlorine source is cheap and readily available as a daily primary biocide. When the effect of chlorination is not obvious or chlorine is not added, chlorine dioxide may be added periodically or irregularly to control the deterioration of water quality or maintain the killing effect.
Simultaneous or alternating use of chlorine dioxide and chlorine not only provides significant savings in terms of cost, but also provides better biocidal effects, can also weaken microbial resistance and reduce the production of carcinogens such as trihalomethanes (THM) in water. To improve the safety of drainage.
2. The dosage of chlorine dioxide
The amount of chlorine dioxide added is also related to many factors, such as system conditions, dosing cycles, and reducing substances that leak into the system. Under normal circumstances, when used for normal sterilization, the dosage of chlorine dioxide is about 0.4~0.6mg/L. If it is converted into a stable chlorine dioxide solution with a content of 2%, it is 20~ 30mg / L, the dosing cycle is long, and the dosage is also increased accordingly. For example, when adding once in 3 days, the dosage of CLO2 commercial liquid is 25mg/L. If it is changed once every 5~6 days, the dosage should be 50mg/L. When supplemented with chlorine, the amount of chlorine dioxide added can be reduced according to the amount of chlorine added.
When the water quality deteriorates and the microorganisms multiply, the chlorine dioxide can be added or impacted periodically (such as several weeks or once a month). The dosage is usually about 0.6~1.2mg/L CLO2, which is converted into CLO2 commodity. The liquid is 30~60mg/L.
Due to the excellent bactericidal and algae-killing properties of chlorine dioxide and the excellent control of biological slime in actual use, chlorine dioxide can replace all or most of the non-oxidizing biocides with high price and large dosage. When the biocide is used for impact dosing, its commercial dosage is often above 100 mg/L.
3. The killing effect of chlorine dioxide
(1) Several circulating cooling water treatment plants of Yangzi Petrochemical and Qilu Petrochemical Company will use CLO2 commercial liquid 20mg/L for 3 days in summer and 60mg/L of CLO2 commercial liquid once a month. The total number of bacteria is generally maintained at About 103 / mL, the treatment effect is very significant.
(2) 30 tons of synthetic ammonia circulating cooling water treatment in a chemical plant, originally based on CL2 sterilization. When the water quality deteriorates, even if 75mg/LCL2 is added per shift, the residual chlorine often fails to reach the index; Add 1227 cationic surfactant, the dosage is as high as 100mg/L, but the effect is still very poor. Even if 1227 is added frequently, the residual chlorine is still not up to standard and the cost increases suddenly. After the change to the monthly impact of adding CLO2 commercial liquid 30mg / L, each shift supplemented with the addition of 10mg / L of CL2, the residual chlorine can reach the standard, the number of bacteria also dropped from the original 106 / mL to 103 / In the mL, the bactericidal rate of the heterotrophic bacteria was maintained above 99% by the fifth day.
(3) A synthetic ammonia plant is added with chlorine dioxide once every 3 days, each time adding 35mg/L of commercial liquid, and after 4 consecutive doses, the drug is stopped for a period of time, 1 week in summer, 4 weeks in winter, and so on. The total number of bacteria can be controlled below 105 / mL.
(4) A petrochemical company's alkylbenzene plant will add CIO2 commercial liquid 70mg/L every other week, and add quaternary ammonium salt biocide 50~100mg/L once every other week. The two will be used alternately. The total number of bacteria can be controlled at 103. ~104 / mL.
(5) A petrochemical plant's 25,000 tons/year C5 separation plant circulating water plant is cleaned and stripped before parking. The impact is added CIO21.7~2.0mg/L, and it is cycled for 24 hours without substantial sewage. The turbidity of circulating water before treatment was 5mg/L, C5112mg/L, total iron 0.4mg/L; after 24 hours of administration, the turbidity increased to 35mg/L, the total iron was 53.6mg/L, the water body obviously changed, and chlorine dioxide was visible. The effect of removing iron and cleaning and stripping is obvious.
It can be seen from the above that for different processing purposes and requirements and different system conditions, through the on-site adjustment, the optimal dosing scheme for the biocide suitable for the system can be designed, thereby achieving the objective of achieving obvious treatment effect and saving cost.
4, cost accounting
At present, the price of 2% CLO2 stabilized chlorine dioxide solution for water treatment is about 10 yuan/kg, and the average price of liquid chlorine rises to about 3 yuan/kg, but the dosage of chlorine dioxide is small and the dosage period is long. It can replace non-oxidizing biocides such as 1227, which cost about 12 yuan/kg, so the cost is obviously reduced when the same effect is achieved.
For impact feeding, the dosage of CIO2 commercial liquid per 1,000 tons of water is 30~60kg, the cost is 300~600 yuan/kilogram; and the dosage of 1227 is 100kg/kt, the cost is 1000~1200 Yuan / thousand tons, so the use of chlorine dioxide to kill can save 50 to 75%. For the ammonia plant, due to the use of chlorine dioxide for impactful or auxiliary dosing, the daily chlorine content can be reduced by 50~70%, and the chlorination cycle can be doubled, which can save 50~75% of liquid. chlorine.
For petrochemical plants, the amount of water per 1,000 tons of water is 20 kg/kt of chlorine dioxide commercial liquid per month, and a total of 240 kg/kt CIO2 of commercial liquid is added every month. The cost is 2,400 yuan / kiloton. The circulating cooling water treatment of Yangzi Petrochemical Olefin Plant is added according to this scheme. The total number of bacteria is controlled at 103/mL, and the annual cost is about 160,000 yuan. The original CI2 and 1227 are used as biocides, and the annual cost is 210,000 yuan. After switching to CIO2, it will be 23%. If the above-mentioned annual processing cost of kilotons of water is changed to the chlorine dioxide generator produced by our factory [3], the monthly fee is only 100 yuan/ton.
The circulating cooling water treatment of the water supply workshop of a petrochemical plant originally added CL240kg per day, and added 1227 calories per two weeks, with a monthly cost of 13,800 yuan. After switching to chlorine dioxide, the monthly CLO2 commercial liquid dosage is 1200kg. According to 8 yuan/kg, the monthly cost is 0.96 million yuan, which can save 0.42 million yuan/month and the annual savings of 50,000 yuan.
Current experts agree that controlling microbes remains the key to water treatment in fertilizer plants and refineries, especially when using alkaline water treatment formulations. The use of chlorine dioxide as a biocide for such cooling water is particularly effective and cost-effective compared to CL2 and 1227.
5, the operation of the addition
Due to the small amount of chlorine dioxide added, the short filling time and the long feeding period, the total amount of work is reduced and the labor intensity is reduced.
The stabilized chlorine dioxide commercial solution needs to be activated by an activator for 15 minutes before being put into the system. If activated and filled in an open container, a large amount of CLO2 gas will escape, which not only causes loss, pollutes the environment, but also has strong stimulation to the upper respiratory tract of the operator and is harmful to health. The United States stipulates that the allowable emission limit of chlorine dioxide in the air is 0.3 mg/m3, and the short-term exposure limit is 0.9 mg/m3. In order to protect the safety and health of operators and protect the environment, we have specially developed and produced chlorine dioxide activation and filling equipment. It can be activated without chlorine dioxide leakage and the chlorine dioxide activation solution can be quickly and effectively filled into the system. It can be continuously filled (such as Wuhu Water Company) or intermittently filled with impact ( For example, in Yangzi Petrochemical Company, it is easy to operate, safe and reliable, and is well received by users.
6. On-site determination of residual chlorine
The analytical test method for the residual amount of chlorine dioxide in water is the same as chlorine. When using the o-toluidine visual colorimetric method, the yellow color produced by the same concentration of CLO2 is about half lighter than the residual chlorine of CL2, so the residual chlorine reading is multiplied by 1.9 [4] after colorimetry.
CL2 can be determined by ferrous iron DPD (N,D-diethylphenyleneamine) visual colorimetry, and CLO2 can also be determined. The color depths of the two are nearly doubled. Since the color development is bright and stable red, the visual colorimetric result is more accurate, and the free effective chlorine and the combined effective chlorine can be better distinguished. With the promotion and application of chlorine dioxide, the development and production of field test instruments in this area is also very urgent.
[The following models of chlorine dioxide are suitable for use in the treatment of cyanide-containing wastewater]
1, high purity chlorine dioxide disinfectant
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2, stable chlorine dioxide solution
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3, one yuan chlorine dioxide disinfection powder
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