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Nitrogen ttrichloride ---   revised
Nitrogen ttrichloride ---   revised
Nitrogen ttrichloride ---   revised
Nitrogen ttrichloride ---   revised
Nitrogen ttrichloride ---   revised
Nitrogen ttrichloride ---   revised
Nitrogen ttrichloride ---   revised
Nitrogen ttrichloride ---   revised
Nitrogen ttrichloride ---   revised
Nitrogen ttrichloride ---   revised
Nitrogen ttrichloride ---   revised
Nitrogen ttrichloride ---   revised
Nitrogen ttrichloride ---   revised
Nitrogen ttrichloride ---   revised
Nitrogen ttrichloride ---   revised
Nitrogen ttrichloride ---   revised
Nitrogen ttrichloride ---   revised
Nitrogen ttrichloride ---   revised
Nitrogen ttrichloride ---   revised
Nitrogen ttrichloride ---   revised
Nitrogen ttrichloride ---   revised
Nitrogen ttrichloride ---   revised
Nitrogen ttrichloride ---   revised
Nitrogen ttrichloride ---   revised
Nitrogen ttrichloride ---   revised
Nitrogen ttrichloride ---   revised
Nitrogen ttrichloride ---   revised
Nitrogen ttrichloride ---   revised
Nitrogen ttrichloride ---   revised
Nitrogen ttrichloride ---   revised
Nitrogen ttrichloride ---   revised
Nitrogen ttrichloride ---   revised
Nitrogen ttrichloride ---   revised
Nitrogen ttrichloride ---   revised
Nitrogen ttrichloride ---   revised
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Nitrogen ttrichloride --- revised

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  • 1. RISKS & CONTROLS OF NITROGEN TRI-CHLORIDE Presented by H S.SEHGAL, DY.GM Gujarat Alkalies & Chemicals Ltd Vadodara, Gujarat (India)
  • 2. PREFACE
    • The Production of Chlorine has expanded rapidly in the recent years and larger quantities are stored, used and transported.
    • Nitrogen tri chloride is an extremely hazardous chemical which is synthesized in small quantities in all chlorine manufacturing plants.
    • Nitrogen tri chloride under certain circumstances is extremely unstable and can produce violet explosion.
    • It must be handled and disposed off with extreme cautions.
  • 3. AREAS OF POTENTIAL CONCERNS
    • Chlorine Liquefiers
    • Chlorine Storages
    • Mobile Containers
    • Liquid Chlorine Tonners/ Cylinders
    • Vaporizers
    • Upset Conditions in Process or Preparation for Maintenance
    • Recycling of various streams
    • Modification Jobs
    • Destruction Process of Nitrogen Tri Chloride
  • 4. OBJECTIVE OF STUDY
    • PURPOSE - To highlight the potential problem with accumulation of reactive material Nitrogen Tri Chloride in liquid Chlorine.
    • - To describe the constraints which need to be observed in order to avoid the risks associated with its presence in routine Chlorine storage, transport and use.
    • Any Chlorine user who is uncertain of the potential problem which can arise from accumulation of NCl 3 , should consult the Chlorine suppliers to confirm acceptable level and level of risk.
  • 5. OCCURRENCE & FORMATION OF NCl 3
    • Nitrogen Tri-Chloride was first observed in 1811 from the action of Chlorine on the solution of Ammonium Chloride.
    • This compound is a yellow oil with a pungent Chlorine like Odour.
    • It is insoluble in water and soluble in most organic solvents.
    • A drop of oil explodes violently when touched with a feather dipped in turpentine .
    • Nitrogen Tri-Chloride is formed during the production of Chlorine when Ammonical Nitrogen is present in the brine fed to the electrolytic cells.
    • Any ammonical compound in the brine or water will be converted to NCl 3 in short time. 30 ppm of ammonia in water is converted to NCl 3 in 20 seconds .
    • NCl 3 is soluble to the extent of 7.3 mg/l in liquid Chlorine.
  • 6. OCCURRENCE & FORMATION OF NCl 3
    • Once NCl 3 forms in the electrolytic cells, it will pass with Chlorine gas through the coolers, scrubbers, acid seal pumps and will be condensed with the liquid Chlorine.
    • NCl 3 Vapor pressure is a function of temperature. Under the usual brine electrolysis conditions NCl 3 will be readily swept out of the cells with chlorine .
    • NCl 3 concentrates itself in the layer of liquid Chlorine next to vapor phase. As the liquid Chlorine is used up, the concentration of NCl 3 keeps increasing at vapor-liquid inter-phase.
    • Chemical reaction is as under---
    • NH 3 + Cl 2 ------NH 2 Cl+HCl
    • NH 2 Cl+Cl 2 ------NHCl + HCl
    • NHCl+ Cl 2 ------ NCl 3 +HCl
  • 7. ASSOCIATED HAZARDS
    • Nitrogen Tri-Chloride is one of the most hazardous material in Chlor-Alkali industry.
    • Fatalities have occurred and workers have been injured by NCl 3 explosions.
    • The explosive power of small quantity of NCl 3 can be catastrophic & can cause
      • release of Chlorine &
      • large scale damage to personnel, plant equipment .
    • NCl 3 is
      • sensitive to light, impact and ultrasonic radiation
      • A spontaneous explosive compound.
      • Explosive potential is 30% of TNT.
    • The compound has +72 Kcal/mol free energy of formation and decomposition gives 54.7 Kcal/mol.
    • On detonation at constant volume, a temperature of 2128 0 C and pressure of 5361 atm is reached.
    • Decomposition of as little as 0.3 gm/cm 2 of exposed wall area in a confined volume can overstress steel and can create a very hazardous situation.
  • 8. ASSOCIATED HAZARDS (CONTD)
    • Increasing the number to 1.5 gm/cm 2 results in fracture.
    • The hazard is less when Chlorine contaminated with NCl 3 is spread in a wide pool than it collects in a nozzle or section of piping.
    • NCl 3 is much less volatile (Boiling point:71 0 C) than Liquid Chlorine (Boiling point:-34 0 C). It tends to accumulate at different points in the process. Any NCl 3 present in the gas shall concentrate in liquid chlorine. Vapor pressure of NCl 3 is 0.11 atm and for chlorine is 3.68 atm at 0 0 C which shows NCl 3 will remain on evaporation of liquid chlorine.
    • Yellow oil of NCl 3 explodes violently :
      • When heated in greater than 93 0 C
      • Exposed to light
      • Brought in contact with Ozone, Phosphorous, Arsenic, Alkali and organic matter.
    • Spill of NCl 3 is a hazardous residue. Spilled NCl 3 can detonate on simple walking through it.
  • 9. ASSOCIATED HAZARDS (CONTD)
    • The use of containers are cause of concern. When liquid chlorine is exhausted in containers and gas is withdrawn to storage, vaporization or other process use then decomposition of NCl 3 starts. Once decomposition begins, the exothermic heat of reaction causes to propagates very rapidly and move on to detonation.
  • 10.  
  • 11. SOURCES OF NITROGENOUS IMPURITY
    • Nitrogen compounds may be present in salt and other chemicals added during processing.
    • Nitrogenous explosives used to break the beds in the mines.
    • Anti-caking agent present in ppm concentration.
    • Salt delivery vehicle is a potential source of contamination.
    • Dissolving water is the source of nitrogenous matter in solution mining.
    • Calcium Chloride used in some brine systems – a by-product of Solvay Process of Soda Ash is a source of Ammonical impurity.
  • 12. SOURCES OF NITROGENOUS IMPURITY
    • KCl salt recovered by the use of Amines as separator can add Nitrogenous impurity.
    • H 2 SO 4 used in Chlorine drying is also source of Ammonia compounds sometimes.
    • Plant utilities are likely sources like
      • use of impure water to prepare treatment chemicals,
      • flushing water on rotating equipments seals,
      • water recycle from waste minimization systems,
      • direct contact cooling water.
    • Steam and its condensate are also potential sources. The culprits are usually the amines used as corrosion inhibitors in steam system.
  • 13. SOURCES OF NITROGENOUS IMPURITY
    • Higher risk of Nitrogen Tri-Chloride formation or accumulation during
      • periods of start up,
      • shut downs,
      • process modifications,
      • maintenance,
      • process upsets or process fluctuations
    • Not all compounds are converted to Nitrogen Tri-Chloride. Water contaminated with nitrogenous material like Caprolactum does not contribute rise in NCl 3 (used in mine brine).
    • Nitrogen gas introduced into Chlorine is not converted to NCl 3 .
    • Fully oxidized form of Nitrate salts ( Potassium Nitrate or Sodium Nitrate ) do not form NCl 3 with interaction with Chlorine.
  • 14. Awareness to the suppliers
    • Suppliers to be made aware about the importance of preventing contamination of the materials and the hazards involved in chlor-alkali industry.
    • 1 ppm of Ammonia in the feed brine can produce >50 ppm of NCl 3 in dry
    • Chlorine and 1 ppm of Ammonia in salt can produce about 12 ppm of NCl 3 in the Chlorine .
    • Salt to be mined with the help of an explosive which is free from Nitrogenous matter .
    • Salt to be stored without anti-caking agent .
    • Safer type of water for the manufacture of salt.
    • Rigid analytical programme for the analysis of the salt.
    • Dedicated vehicles for the transportation of salt to avoid any nitrogen compound contamination.
  • 15.
    • To Control the formation of NCl 3 in liquid chlorine, it is essential to limit the entry of Nitrogen compound in Salt and Brine solution in process continuously.
    • Analysis on line :-
    • An on line analysis has been developed by a French organization website :- www.seres-france.com . It works in on principle of sequential analysis
    • It can measure Ammoniac salt(NH4) Concentration in Brine & Ncl3 Concentration in Cl2 gas at the exit of Cl2 Compressor.
    • Magnetic fields & photo sensibility of Ncl3 influence the analyzer. Therefore the analyzer must be installed:-
      • At a sufficient distance from the Cells House.
      • In a close Cabinet with air conditioning & with no external light.
      • All Transparent piping (Teflon etc) has to be covered.
    DETECTION
  • 16. DETECTION
    • ANALYSIS OF NCL3 IN LIQUID CL2 :-
      • Instrument technique & chemical determinations based on conversion to ammonium ions are available.
      • Instrument technique is based on absorption of ultra violet or infrared radiation, Gas chromatography or liquid chromatography. The Instrument technique can not analyze Ncl3 that has decomposed to Ammonium chloride & also not applicable for whole concentration range.
      • Chemical determinations of Ncl3 are based on the determinations of ammonium ions that are formed When the equilibrium is moved to the right. Chemical principle method is preferred as compared to the other methods.
      • The Chemical method is suitable for 0.2-20000mg/kgs Ncl3 in Cl2.
  • 17. DETECTION
      • In this process Liquid Cl2 sample is taken in a refrigerated special steel trap (-60 C) . Max. sample capacity is 500ml.
      • Liquid Cl2 is evaporated in the presence of Hydrochloric acid & the gas is scrubbed by hydrochloric acid to form Ammonium chloride.
      • After removal of the dissolved Chlorine ,the hydrochloric acid solution is carefully neutralized & the Ammonium ion is determined either by Spectrophotometry of the Indophenols Complex or by an Ammonia gas sensing Electrode for level up to 200mg/kg Ncl3 Or by Distillation & titration for higher levels.
      • For lowest level of Ncl3 5mg/kg of Cl2, the Spectrophotometry method is preferred.
      • Results achieved by these methods are claimed to be reliable.
  • 18. DETECTION
    • NCl 3 is assayed by the old Kjedahl Nitrogen test. It is
      • Time consuming (6.5 hours)
      • Not very sensitive at low concentration.
      • Is off-line process
      • Can be used for grab samples only.
      • This method of analysis is a three distinct process –
        • digestion,
        • distillation
        • titration
        • moreover, it over-reports Nitrogen.
    • Chromatographic method
      • Is rapid and precise.
      • Time required for analysis is 20 minutes.
      • Detector uses ultra-violet light.
      • Has been certified by ASTM (E2036-99) and has been further modified to take low concentration of sample for better results. This process is suitable for carbon tetrachloride system and require dilution 100:1 for safety reasons.
      • Depends on partial evaporation of Chlorine from chilled sample of liquid followed by addition of chromatographic elluent (methanol + dilute acetate buffer at PH-4) and injection into column.
  • 19. METHODS OF CONTROLL
    • When Ammonia compounds are in brine despite preventive measures, destruction can be done by
      • controlled Chlorination at pH > 8.5 to form very volatile monochloroamine
      • allowing Nitrogen content to be removed by venting or surging with air.
    • NCL3 IN CL2 GAS IS CONTROLED BY ;
      • Irradiating the Chlorine gas exiting in the cells with ultra-violet light in the spectrum of 3600-4400 before the Chlorine enters the scrubbers ,
      • UV system is used to remove the small quantities of NCl 3 formed.
  • 20. METHODS OF CONTROLL
    • Due to thermal instability of NCl 3, decomposition becomes useful at 70 o C.Temperature in excess of this are found in Chlorine compressors. (Reciprocating and centrifugal)
    • Iron and its compounds can also cause decomposition.
    • Destruction of NCl 3 by scrubbing with cold HCl and contact with reducing agents can be done. But this practice is not followed widely.
    • Because of the possibility of combustion of Chlorine with Iron as well as higher activity of copper alloys, the grease free Mone l shaving would be preferred.
    • Treatment of filtered dry gas
      • with activated carbon—this process is not in use. It was used in some plants, few years ago.
      • Silica and Alumina are other candidates.
      • These may be impregnated to increase their reactivity.
    • This process is not in commercial use as it requires careful management due to possible exothermic reaction
  • 21.  
  • 22. METHODS OF CONTROLL
    • NCl 3 in liquid cl2 is Removed by passing through carbon tetrachloride solvent or equivalent as under :-
    • Cl2 gas containing Ncl3 is passed through purifying tower containing liquid cl2.
    • Ncl3 impurity in gas is washed out by liquid cl2
    • This liquid cl2 + Ncl3 is passed through purge drain tank containing carbon tetrachloride maintained at 50 c-60 c.
    • Ncl3 impurity accumulates carbon tetrachloride & cl2 gas recycled through dryer system.
    • Contaminated carbon tetrachloride is reacted with Naoh or suitable reducing agents.
    • Waste Solvent is incinerated & caustic is neutralized appropriately.
    • The Solvent carbon tetrachloride has to be replaced at scheduled interval & conc. Of C4 vapors to be minimized & recorded.
    • Flow sheet of the process is attached for reference.
    • NCl 3 in liquid Cl 2 can be controlled/destroyed by,
    • Purging
    • Purging NCl 3 + liquid Chlorine from the vaporizer is a method of reducing concentration of NCl 3 . In this process NCl 3 enriched liquid chlorine is bottled in Tonners / Cylinders in a scheduled way. Toleration in Cl 2 tonners is higher(20ppm) than storage tanks(2ppm). Moreover the tonners becomes empty frequently at the customer end which eliminate the possibility of NCl 3 accumulation in the system.
    • Purging and destruction process.
    • Collection of NCl 3 + liquid chlorine from the bottoms of chiller/evaporator gives another opportunity for thermal decomposition. Part of the Material is collected in a separate pot and decomposed by heating with steam upto 80 0 C.
    • Spill of NCl 3
      • is a hazardous residue.
      • Spilled NCl 3 can detonate on simple walking through it.
    • A spray of approximately 5% solution of reducing agents and washing with water will remove all traces of NCl 3 .
  • 23. FLOW SHEET
  • 24. METHODS OF CONTROLL
    • NCl 3 in liquid Cl 2 can be controlled/destroyed by,
    • Purging
    • Purging NCl 3 + liquid Chlorine from the vaporizer is a method of reducing concentration of NCl 3 . In this process NCl 3 enriched liquid chlorine is bottled in Tonners / Cylinders in a scheduled way. Toleration in Cl 2 tonners is higher(20ppm) than storage tanks(2ppm). Moreover the tonners becomes empty frequently at the customer end which eliminate the possibility of NCl 3 accumulation in the system.
    • Purging and destruction process.
    • Collection of NCl 3 + liquid chlorine from the bottoms of chiller/evaporator gives another opportunity for thermal decomposition. Part of the Material is collected in a separate pot and decomposed by heating with steam upto 80 0 C.
    • Spill of NCl 3
      • is a hazardous residue.
      • Spilled NCl 3 can detonate on simple walking through it.
    • A spray of approximately 5% solution of reducing agents and washing with water will remove all traces of NCl 3 .
  • 25. DECOMPOSITION OF NCl 3
    • THERMAL
    • 2NCl 3 N 2 + 3Cl 2 (CHAIN REACTION)
    • NCl 3 NCl 2 + Cl, Cl + NCl 3 NCl 2 + Cl 2
    • NCl 2 + NCl 3 N 2 + 2Cl 2 + Cl
    • VAPOUR PHASE - MAY LEAD TO EXPLOSION
    • LIQUID PHASE - HIGHLY UNSTABLE
    • SOLID PHASE - MAY DETONATE ON THAWING
    • SOLUTION NCL3 - STABLE 1.5 WT % < 30 O C
    • BEYOND INITIATION TEMPERATURE
    • SELF ACCELERATING – EXPLOSION
    • AT ~ 100 O C. CATALYZED BY HEAT,
    • LIGHT, TRANSITION METAL OXIDES.
  • 26. DECOMPOSITION OF NCl 3
    • REDUCTION - BY A NUMBER OF COMPOUNDS
    • NCl 3 + 4 HCl NH 4 Cl + 3Cl 2
    • 3Na 2 SO 3 + NCL 3 + 3H 2 O NH 4 Cl + 3Na 2 SO 4 + 2HCl
    • RADIATION
    • 2NCl 3 N 2 + 3Cl 2
    HEAT U.V.
  • 27. NCl 3 SAFE OPERATION LIMITS
    • 20 ppm w/w NCl 3 is generally accepted maximum level
    • for liquid Chlorine .
    VESSEL CAPACITY MAXIMUM CONCENTRATION OF NCL 3 PPM W/W CALCULATED RECOMMENDED 50 KG 200-300 20 1000 KG 50- 60 20 20 T 15 5 50 T 8 2
  • 28. EXPERIENCES WITH NCl 3 MANAGEMENT
    • Different types of compressor being used for compressing chlorine in chlor - alkali industries.
      • Reciprocating Chlorine Compressor.
      • Centrifugal chlorine Compressor.
      • Liquid seal ring type Compressor with sulphuric acid as sealing material.
      • The management of Nitrogen tri chloride is well managed in reciprocating and centrifugal compressor due to the achievement of decomposition temperature 90 0 C .NCl3 is not controlled in liquid seal ring type compressors as the operating temperature range is 40 to 50 0 C
    • Practices adopted to control NCl 3 Concentration in liquid chlorine evaporator:-
      • Purging system – part of the quantity at the bottom of the evaporator is filled in tonners/cylinders at regular intervals
      • Purging & decomposition of part quantity of NCl 3 +Liquid Chlorine at regular intervals is collected in a separate pot and heated with steam at 80 0 C/25 Kg/cm 2 .
      • The decomposed material is released to chlorine neutralization system.
  • 29. EXPERIENCES WITH NCl 3 MANAGEMENT
    • Problems with liquid seal type compressors:
      • Some sulphuric acid mists are carried over to liquid chlorine evaporators & cause iron sulphate formation.
      • This problem becomes more serious with the break down of mist eliminator filter candle .
      • Under these conditions liquid chlorine + NCl 3 drain line (used for transferring material) to tonners / cylinders gets chocked.
      • To continue the NCl 3 monitoring process, liquid chlorine + NCl 3 at the bottom of the evaporators is transferred in the main 100m 3 storage tank through the evaporator liquid chlorine inlet line during plant stoppage.
      • No suitable online analyzer available for analysis of NCl 3 or to check grab sample of NCl 3 control.
      • Details of agency to carry out analysis of NCl 3 is also not available.
      • Withdrawal and collection of NCl 3 sample for analysis is also difficult.
      • By using other type of compressors, discharge temperature can go upto 90 0 C (NCl 3 decomposition point) against 40 0 C with liquid seal ring type compressor. NCl3 decompositions is not appreciable with this type of compressor
  • 30. EXPERIENCES WITH NCl 3 MANAGEMENT
    • In the second process
      • Part of the quantity of liquid chlorine +NCl 3 mixture is decomposed at 80 0 C in a steam heated jacketted catch pot.
      • The passage of liquid chlorine+NCl 3 catch pot can be reason of explosion due to local hotspot.
      • The operation is done in gradual and cautious way.
      • After decomposition chlorine is released to chlorine neutralizing system
    • Unreliability factor of analyzer and non availability of analysis facility makes the case serious.
    • In order to avoid a problem of NCl 3 in the system all specifications of raw material and chemicals are analyzed in the laboratory on schedule basis. Possibility of online analyzers for brine is being explored to check nitrogen compounds in the brine system.
    • No new material is added without thorough analysis for nitrogenous matter.
  • 31. NEED FOR DEVELOPMENT
    • Need is felt for
      • Availability and installation of online analyzer for brine to check nitrogen compound
      • Development of foolproof system of collecting samples of NCl 3
      • On line analysis at various NCl 3 accumulating pockets in chlorine handling system.
      • To set up authorized agency for rechecking of on line analysis
      • Safe carriage of sample to external areas.
      • Development of a speedy and reliable test, coupled with more frequent monitoring,
      • A mechanism to call for repeat analysis,
      • More frequent checks after one analysis has exceeded the usual range.
  • 32. CONCLUSION AND RECOMMENDATIONS
    • To establish practices & policies which will ensure the safety of the process.
    • IT IS RECOMMENDED THAT ALL PRODUCERS AND CONSUMERS SHOULD REVIEW THEIR SYSTEM AND OPERATION PERIODICALLY.
    • The process review should inspect/analyze the various NCl 3 pockets in this process vessels.
    • In this process review, knowledge of the operating condition to:
      • eliminate hazardous conditions,
      • for example, keep the NCl 3 concentration below 1.5% and temperature below 30 o C in NCl 3 accumulating pockets.
  • 33. CONCLUSION AND RECOMMENDATIONS
    • The most important control over the potential level of NCl 3 is
      • At source in Chlorine producing process.
    • Use of salt without anti-caking agent and mined salt without nitrogenous explosives.
    • Use of safer type of water.
      • Whenever any raw material is changed a check should be made to ensure that new NCl 3 risk has not been introduced.
    • Frequency level of NCl 3 analysis
      • Should be once in 3 months when NCl 3 is in 5-20 ppm .
      • Once in one year for NCl 3 concentration below 5 ppm is suggested as guideline.
  • 34. The Chlorine industry has gone several years with only one serious incident associated with Nitrogen Tri-Chloride. We always need to work aggressively to prevent NCl 3 from accumulating and reaching dangerous levels.
  • 35. THANK YOU

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