Chlorine is a very good disinfectant but it is very hazardous. So we need to find some alternatives of hazardous chlorine gas for water treatment. Here I present about the alternatives of chlorine. One of the best alternative is chlorine di-oxide(ClO2). What are the advantages of ClO2, how to generate everything discussed here.

1. Presented by: Team: Chemlife
Badal Majhi
Raghab Gorain
Sushobhan Adhikary
Arnab Bisui
Professional Circle
Date- 28/12/2020NTPC TSTPS
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2. 2
1)Why treatment of water require?....................................................................................................................................... 3
2)Biocides:............................................................................................................................................................................ 4-6
3)Flow Diagram of Chlorination...........................................................................................................................................7
4)Limitations of Chlorine(Cl2)...............................................................................................................................................8-9
5)Chlorine incidents……………………………………………………………………………………………………….10-11
6)Alternative of Chlorine Gas.............................................................................................................................................12-13
7)Safety consideration of (ClO2)…………………………………………………………………………………..…..…...14
8)Generation method of ClO2 ………………………………………………………………………………………....….15
9)ClO2 generation flow diagram…………………………………………………………………………………..…..…..16
10)Effectiveness Comparison………………………………………………………………………………………..….…17-18
11)ClO2 production at TSTPS………………………………………………………………………………………….….19
12)Cost effective…………………………………………………………………………………………………………….20
13)Conclusion……………………………………………………………………………………………………………....21
14)Thank you………………………………………………………………………………………………………………22
Content

3. 3
Raw water contains many contaminants like
Colloidal form
Dissolved solid
Micro-organism, bacteria, algae etc
Suspended form.
Colloidal, dissolved & suspended contaminants are removed by treating water with
alum, lime, Pac etc. But raw water & cooling water contains microorganisms also.
These to be removed to prevent biofouling, biofilm, scaling & corrosion. So we dosed
biocides.
Why treatment of water require?

4. 4
Biocides are used to control microbiological fouling and organic fouling in cooling water. Continuous
chlorine dosing is done for better bio-fouling control.
Two types of biocides are there
1) Non oxidizing biocides:
Prevent normal cell metabolism in any of the following ways :
Alter permeability of cell wall
Destroy protein groups
Precipitate protein
Block metabolic enzyme reactions
Biocide:
Examples:
Methylene bis-thiocyanate (MBT)
Organo tin compound
Quaternary ammonium salts
Organo sulphur
Copper salts
DBNPA (2,2-dibromo-3-nitrilopropionamide)ti
Biocides:

5. 5
Oxidising Biocides:
Have the ability to oxidise organic matter eg. protein groups
 Chlorine and its various products
 Bromine
 Chlorine dioxide
 Ozone
 Hydrogen Peroxide
 Sodium hypo chloride
Biocides

6. 6
Why do we use chlorine?
 Highly effective biocides
 To remove organic and micro organism from raw water, drinking water & cooling water
 To prevent fouling inside the condenser
 Various other industries like paints, paper, pharma, agriculture etc.
Chlorination:
Chlorine reacts with water to produce HOCl which destroys the physical structure of the organisms. The
physical structure i.e. the cell-wall of the organism contains amino group which is destroyed by chlorine.
H2O + Cl2 = HCl + HOCl
HOCl = H+ + OCl-
( AT pH more than 6.0)
NH3 + HOCl = NH2Cl + H2O (monochloramine)
NH2Cl + HOCl = NHCl2 + H2O (dichloramine)
NHCl2 + HOCl = NCl3 + H2O (nitrogen trichloride)
Destroying reactions
Biocide: Chlorine

7. 7
Header
Chlorinator
Cl2 Tonner
Booster Pump
Stilling Chamber
HOCL
Ejector
Cl2
H2O
Flow Diagram of Chlorination

8. 8
 Chlorine is a toxic gas and hence storage and handling chlorine poses
severe risk
 Efficacy of chlorine is pH dependent
 Chlorine is highly corrosive
 Chlorine reacts with organics to produce Trihalomethanes (THM) which
are known carcinogens
 Chlorine does not have the ability to penetrate and remove biofilms
Limitations of Chlorine(Cl2)

9. 9
Symptoms Chlorine limit
Least amount to produce slight symptom 1ppm
Least detectable odor 3.5ppm
Max amt that may inhaled for 1 hr without serious disturbance 4 ppm
Noxiousness, impossible to breathe 5 ppm
Least amt to cause irritation to throat 15 ppm
Least amount to cause coughing 30-32 ppm
Amount dangerous in 30 min. to 1 hr 40 to 60ppm
Amount likely to be fatal after few deep breaths 1000ppm
Limitations of Chlorine(Cl2)
Health hazard of chlorine

10. 10
5000 gallon tanker tipped over, 6th January 2020 The Graniteville Chlorine Disaster, 6th January, 2005
Chlorine incidents

11. 11
Cuttack SCB medical college, Nov 2017 Mumbai chlorine leak from tonner, July 2010
Chlorine incidents

12. 12
Biocides Disadvantages
Bromine(Br2) Toxic & same drawbacks of chlorine
Ozone(O3) 1)High reactive so highly skilled & patioanate
technician required.
2) Very unstable
3) Particularly high pH
Hydrogen Peroxide(H2O2) 1) Not so much effective
2) Quick decomposition
Sodium hypochloride(NaOCl) 1) Corrosive to metal
2) Crystallizes, can clog pipes, valves etc
3) Limited shelf life
Chlorine di-oxide: There are so many biocides, each one has advantages as well as drawbacks.
So we are finding such a chemical , where drawbacks are minimized & effectiveness is maximized
Chlorine dioxide(ClO2) is one of them.
Alternatives of Chlorine :

13. 13
Best alternative of chlorine gas is chlorine di-oxide(ClO2)
Advantages of chlorine di-oxide(ClO2)
 2.5 times more powerful & highly effective oxidizer
 Not effected with pH
 Excellent biofilm removal - rapidly penetrates and oxidizes biofilms
 Less corrosive compared to chlorine
 Does not form trihalomethanes with organic matter like chlorine
 Does not hydrolyze to form acid
Alternatives of Chlorine :

14. 14
It is much more safe to use comparing chlorine as
 Not handled as gas
 In-situ generation of ClO2
Chlorine dioxide has excellent bactericidal, virucidal, sporicidal and algicidal
properties, hence used as disinfectant in water and inhibit growth of algae.
Safety Consideration of ClO2

15. 15
Sodium chlorite(NaClO2) is the precursor to generate chlorine dioxide. In situ
generation of chlorine di-oxide can be done.
Sodium chlorite reacts with hydrochloric acid(HCl) to form chlorine di-oxide
1) Chlorine Method
2NaClO2 + Cl2 = 2ClO2 + 2NaCl
2) Acid Activation Method
5NaClO2 + 4HCl = 4ClO2 + 5NaCl + 2H2O
 Required gaseous chlorine
 Formation of THM
 Safety issue for transporting, handling
 Higher Corrosion
Disadvantages
Advantages
 Gaseous Chlorine not required
 THM formation minimized
 Most robust & safe system
Generation Method of ClO2

16. 16
NaClO2
(25%)
HCl(33%)
ClO2 Generator Dilution water pump
Power water
ClO2 SolutionMetering pump
Metering pump
ClO2 Generation Flow Diagram

17. 17
Effectiveness comparison
Effectiveness on pH

18. 18
•ClO2 penetrates through slimy deposit as it is in gas
form, removes the same & kills the target.
ClO2
ClO2
ClO2 ClO2
Cl2 Cl2 Cl2
Cl2 Cl2
Effectiveness on concentration
Effectiveness comparison

19. 19
Parameters Stage1 Stage2
ClO2 Generator 3 2
Capacity(kg/hr) 80 60
Operating hr/day 4 4
NaClO2 required(lt/hr) 1126.37 563.18
HCl required(lt/hr) 1110.52 555.26
Parameters Stage1 Stage2
No. of p/ps 4(3W +
1S)
3(2W + 1S)
Capacity(m3/hr) 80 60
Dilution water required(m3) 160 80
ClO2 Generator Dilution Water Pump
Chemical Consumption
Parameters NaClO2(31%) HCl(33%)
No of Tanks 2 2
Tank capacity(m3) 120 120
No of dosing p/ps 4(3W + 1S) 3(2W + 1S) 4(3W + 1S) 3(2W +1S)
p/p capacity required(lt/hr) 375.46 281.59 370.17 277.63
p/p capacity provided(lt/hr) 940 940 940 940
Calculation of ClO2 production: TSTPS ongoing project

20. 20
Total Chlorine dosing per annum= 1287.72 MT
Rate = Rs 5618 per MT
Total cost per annum = 72.34 Lakh
Sod. chlorite cost =Rs.1920.52Lakh/annum
Hydrochloric acid cost= Rs.62.01Lakh/annum
Total Chem. Cost = Rs.1982.53Lakh/annum
Chlorine Chlorine di-oxide
Cost Comparison

21. 21
Chlorine di-oxide is costlier than chlorine but in the aspect of safety & effectiveness chlorine di-
oxide is much much safer than chlorine.
 We have to run chlorine 24 hrs for maintaining chlorine demand, but ClO2 dosing not required
so much time. So man power requirement is also low for ClO2.
Conclusion

22. 22
Thank You