Ecosterile Marketing Private Limited, Surat, Chlorine Dioxide CLO2
CHLORINE DIOXIDE PROCESS - University of Georgiapplant.uga.edu/tappi/ClO2 Process.pdf · Filtration...
Transcript of CHLORINE DIOXIDE PROCESS - University of Georgiapplant.uga.edu/tappi/ClO2 Process.pdf · Filtration...
CHLORINE DIOXIDE PROCESS
The Basics
Tom PoweSr. Technology
Services Engineer
CHLORINE DIOXIDE PROCESSThe Basics
• ClO2 Properties/Safety
• General Introduction to ClO2 Processes
• Vacuum Processes
• Control Strategy
CHLORINE DIOXIDE PHYSICAL PROPERTIES
• General – Formula ClO2
– Molecular Weight 67.45
• Appearance
– Gaseous Greenish Yellow– Aqueous Solution Pale Yellow to Deep Green
(Color proportional to strength)
CHLORINE DIOXIDE PHYSICAL PROPERTIES
• Exposure Limits– TLV 0.1 ppm per 8 hr shift– Exposure 5 ppm
• Odor– Detectable 1 - 2 ppm – Noticeable 2 - 5 ppm– Irritating 5 - 10 ppm – Dangerous 10 - 18 ppm – Fatal 19 ppm
CHLORINE DIOXIDE SOLUBILITY in Water
0
5
10
15
20
0 20 40 60 80 100 120 140
ClO 2 gas Partial Pressure [mmHg]
ClO
2 So
ln C
once
ntra
tion
[gpl
]
0 5 10 15
Temperature °C
DECOMPOSITIONS
• Initiators– Heavy Metals– Rust– Organic Materials– Sunlight – High Temperature– High
Concentration – Electrical Sparks
Reaction
2 ClO2 ⇒ Cl2 + 2 O2 + Heat
ClO2 DECOMPOSITIONSEVERITY
• > ClO2 gas concentration, > decomposition.
• > initial operating pressure, > decomposition.
• > the volume of gas, > decomposition.
CHLORINE DIOXIDE PRODUCTION
ClO3- + H+ + Reducing Agent ⇒ ClO2 + H2O
Chlorate Supply • Any Alkali Metal Chlorate Will Work
– (NaClO3, KClO3, etc) • Industry Practice uses NaClO3
– 99.9+% of All ClO2 Processes use NaClO3
CHEMISTRY FUNDAMENTALS
REDUCING AGENT
Choice of Reducing Agent Determines the By-
Product GasR Agent Gas
• CH3OH CH2O2
• H2O2 O2
ACID
Acid Saltcake• H2SO4 Na2SO4
PROCESS TYPES
• ATMOSPHERIC
• VACUUM
• OTHER
VACUUM PROCESS
• React the Chlorate, Acid & Reducing Agent in a Vacuum Crystallizer
• The Generator/Crystallizer operates in the range from 150 - 250 mmHg absolute.
• Acidity Varies by Process Chemistry
• The By-Product Salt is Discharged as a Dry Crystal
WHY A VACUUM PROCESS?
• Advantages
– Sulphate By-Product may be used by the Mill
– Very Efficient NaClO3 use
– Safer to operateLess violent decomposition
• Disadvantages
– Higher Capital Cost Versus Atmospheric Systems
– More complex operation
VACUUM PROCESS FLOW DIAGRAM
ClO2 GeneratorClO2 Generator
Heat AdditionHeat Addition
Gas CondensingGas Condensing
ClO2 AbsorptionClO2 AbsorptionClO2 StorageClO2 Storage Vacuum SystemVacuum System
Vent ScrubbingVent Scrubbing Chilled Water
Saltcake FiltrationSaltcake
Filtration
Saltcake DissolvingSaltcake
Dissolving
Gas CondensingGas CondensingCooling WaterClO2 ProductCooling Water
HP Steam or vacuum pump
Cooling WaterCausticCooling Water Water
Sulfuric Acid
Sodium Chlorate
Reducing Agent
LP Steam Saltcake Solution To MillAirWaterCondensate
VACUUM PROCESS FLOW DIAGRAMHP Steam
Reboiler
Vent
Filter Receiver
Filter Ejector System EjectorVentFan
GeneratorCirc. Pump
LP Steam
CondensatePump
CondensateTank
Generator
GeneratorCondenser
Absorber
To BleachPlant
AbsorberPump
ClO2Storage
HotWater
SaltcakeFilter
Air
VentScrubber
Misc.Vents
ScrubberPump
Chilled Water
Chilled Water
SystemCondenser
NaClO3Feed
SaltcakeFilter Pump
SaltcakeSol. Pump
DissolvingTank
AcidFeed
Deluge/SprayQuench
Reducing Agent Feed
Cooling Water
Saltcake Soln.
Cooling Water
Condensate
VACUUM PROCESS FLOW DIAGRAMwith Saltcake Washing
Vent
ClO2 GeneratorClO2 Generator
Heat AdditionHeat Addition
Gas CondensingGas Condensing
ClO2 AbsorptionClO2 AbsorptionClO2 StorageClO2 Storage Vacuum SystemVacuum System
Vent ScrubbingVent Scrubbing Chilled Water
Saltcake Filtration No.1Saltcake
Filtration No.1Saltcake
RecrystallizerSaltcake Recrystallizer
Water
Saltcake Solution To Mill
Saltcake Filtration No.2Saltcake
Filtration No.2Filtrate StorageFiltrate Storage
Saltcake DissolvingSaltcake
Dissolving
AirWater
Gas CondensingGas CondensingCooling WaterClO2 ProductCooling Water
HP Steam
Cooling WaterCooling Water Air
Sulfuric Acid
CausticSodium Chlorate
Methanol
LP SteamCondensate
YIELD
95
96
97
98
99
100
Yie
ld (%
)
Lite
/R-8
SC
W/R
-10
HP
Yield Components
• Feeds– Chlorate Feed
• Losses – Chlorate for side reactions– Chlorate in Saltcake– Chlorate lost as ClO2 in the
vents• Calculation
Yield = (Feeds-Losses)/Feeds
SALTCAKE FILTRATION REQUIREMENTS
0
0.5
1
1.5
2
2.5
3
T Sa
ltcak
e/T
ClO
2
Lite SCW HP
PROCESS TRADE NAMES
Reducing Agent Acid Acidity Salt Form Name By
NaCl H2SO4 Low Crystal SVP-Conventional EkaH2SO4 Low Crystal R-3 Process SterlingH2SO4 High Solution R-2 Process Hooker
CH3OH H2SO4 Moderate Crystal SVP-Lite EkaH2SO4 Moderate Crystal SVP-SCW EkaH2SO4 High Crystal R-8 Process SterlingH2SO4 High Solution Solvay SolvayH2SO4 High Crystal R-10 Sterling
H2O2 H2SO4 Low Crystal SVP-HP EkaH2SO4 High Solution HP-A Eka
SO2 H2SO4 High Solution Mathieson Olin-Mathieson
PROCESS COMPARISONS - Chemicals
ITEM MethanolBased
MethanolBased withWashing
PeroxideBased
Chlorate,Ton/TonClO2
1.64 1.64 1.64
ReducingAgent,Ton/TonClO2
0.16 0.16 0.33
Sulfuric Acid,Ton/TonClO2
1.0 0.75 0.75
Salt Cake,Ton/TonClO2
1.44 1.06 1.06
PROCESS COMPARISONS - Utilities
ITEM MethanolBased
MethanolBased withWashing
PeroxideBased
LP Steam,Ton/Ton ClO2
4.3 5.1 4.6
HP Steam,Ton/Ton ClO2
0.92 1.26 1.76
Chilled Water,Ton/Ton ClO2
91.0 89.1 91.2
Cooling &Hot Water,Ton/Ton ClO2
298 341 292
KEY PROCESS CONTROL VARIABLES
• Generator Level
• Generator Chemistry
• Generator Solids Level
• Chemical Feed Flows
• Generator Pressure
• Generator Temperature
• ClO2 Solution Concentration
Do They correlate?
RULE OF 10 GUIDELINES
SODIUM CHLORATE SULFURIC ACIDGPL MOLARITY GPL NORMALITY100 0.94 250 5.10110 1.03 260 5.30120 1.13 270 5.51130 1.22 280 5.71140 1.32 290 5.91150 1.41 300 6.12160 1.50 310 6.32170 1.60 320 6.53180 1.69 330 6.73190 1.79 340 6.93200 1.88 350 7.14210 1.97 360 7.34220 2.07 370 7.54230 2.16 380 7.75240 2.25 390 7.95250 2.35 400 8.16260 2.44 410 8.36270 2.54 420 8.56280 2.63 430 8.77290 2.72 440 8.97300 2.82 450 9.18
TARGET: 10.0 RANGE: 9.0 - 10.5
To calculate the "Rule of 10" number: Find the chlorate molarity and the acid normality on the above chart that corresponds to the test performed on the generator solution. Add these two numbers together. Make the appropriate chemical feed flow adjustment
GENERATOR LIQUOR TARGET ZONE
“Rule of 10”
01234567
5 6 7 8 9 10 11Acidity (N)
Chl
orat
e (M
)
A + C = 9 A + C = 10 A + C = 11
White-Out Zone
Sluggish Reaction
GENERATOR LEVEL CONTROL
• Maintaining a constant level in the generator is critical for controlling generator concentrations.
• If an excess of water is boiled away in the generator, the level will decrease and generator concentrations will increase. An inverse effect occurs when not enough water is boiled away.
• Also small adjustments, generally 500#/hr or less, of low-pressure steam to the reboiler should be made to minimize level swings.
PROCESS ADJUSTMENTS
• When making adjustments to the generator operation keep in mind that the generator holds a large inventory of chemicals.
• To avoid overshooting your target adjustments should be made slowly.
• Change the steam flow at the same time you change the feed flows.
• The changes in production rate must be done slowly.
SUMMARY
• The chlorine dioxide manufacturing process has evolved from salt-based atmospheric systems to the methanol and peroxide based vacuum systems that dominate the industry today.
• The operation of a chlorine dioxide vacuum process is mill specific.
• The key to smooth operation of a chlorine dioxide vacuum process is generator level control.
Questions?