SPENT CAUSTIC
TREATMENT OPTIONS
Hadi Saudi
M. Al-Daghman,
2014
Aramco: Company General Use
Outline
 Background
 Treatment Options
 Most Common Treatment
 Conclusion
Saudi Aramco: Company General Use
BACKGROUND
What is Spent caustic ?
Spent Caustic is the wastewater generated
from using Caustic to remove
1. Hydrogen Sulfide (H2S) and
2. Mercaptanes (R-SH)
from hydrocarbon product stream.
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BACKGROUND
Major Sources of Spent Caustic
1. MEROX Processing Unit:
 Gasoline
 Kerosene
 Jet fuel
2. Isomerization Processing Unit
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BACKGROUND
Type Of Spent Caustics
1. Sulfidic Spent Caustic
2. Non-Sulfidic Spent Caustic
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BACKGROUND
Saudi Aramco: Company General Use
BACKGROUND
Saudi Aramco: Company General Use
BACKGROUND
Composition of Spent Caustic
 Toxic and Highly Odorous
 The list below shows typical analytical results:
 Chemical Oxygen Demand (COD):
10,000 to 100,000 mg/L
 Biochemical Oxygen Demand (BOD): 5,000 to 50,000 mg/L
 Total Organic Carbon (TOC):
1,000 to 5,000 mg/L
 Sulfides:
5,000 to 35,000 mg/L
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TREATMENT OPTIONS
 Chemical oxidation
 Neutralization
 Dilution Treatment
 Wet Air Oxidation
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CHEMICAL OXIDATION
Hydrogen Peroxide
Spent Caustic
Feed/Heating
Cooling
Process
REACTOR
Catalyst
SEPARATOR
Off Gas to
Thermal
Oxidizer
Knock Out Drum
Oxidized Spent Caustics
to Neutralization and WTTP
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CHEMICAL OXIDATION
Advantages of Chemical Oxidation :
 Oxidized most of spent caustic
Disadvantages :
 Very high operating cost
 High explosion risks
 Requires special handling needs (H2O2 is highly
corrosive and degrades in heat)
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NEUTRALIZATION
REACTOR
SEPARATOR
Sulfuric
Acid
Fuel Gas
Spent Caustic
Acid
Brine
Solvent and Acid oils to fuel oil
Fresh Caustic
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STRIPPING
COLUMN
Solvent
Off Gas
to Sulfur Plant
Neutralized
Brine to WWTP
NEUTRALIZATION
Advantages of Neutralization:
 Low Operating Cost
Disadvantages :
 Multiple chemical feed
 Complex separation steps
 Safety concerns: H2S is generated as a result of the
neutralization process
 Equipment life reduction: H2S is highly corrosive
 Odors Concerns
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DILUTION
Water
Supply
Dilution Tank
Diluted Caustic to WWTP
Spent Caustic
Stream
Routing Sampling
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DILUTION
Advantages of Dilution:
 Low capital cost
 Lower safety concerns
Disadvantages :
 Not complete removal (No chemical reactions)
 Risk on downstream processes
 Very critical operations
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WET AIR OXIDATION
Off Gas to Thermal
Oxidizer
Spent
Caustic
High
Pressure
Pump
Cooling
Process
SEPARATOR
Heating
REACTOR
Oxidation Air Compressor
Knock Out Drum
Oxidized Spent Caustics
toGeneral
Neutralization
and WTTP
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Use
WET AIR OXIDATION
Advantages of Wet Air Oxidation:




Treat all types of spent caustics
Mostly oxidized the spent caustic
Equipment is highly resistance to corrosion
Low operating and maintenance cost
Disadvantages :
 Safety concerns is minimal if it is high pressure
and high temperature
 Consume Energy
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THE MOST COMMON SPENT
CAUSTIC TREATMENT
WAO is the most common Spent Caustics Treatment
 The best combination of cost control
 Ease of operation and implementation
 WAO can treat all type of Spent Caustics at different
pressure and temperature.
 No byproducts to handle or excess sulfur within off-gas
stream
 Reuse spent caustic after WAO process
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CONCLUSION
 Type of Spent Caustic can determine the best treatment
technique .
 WAO found to be the most common treatment method to
treat all type of Spent Caustics.
 Safety factor plays a major role in spent caustic treatment.
Saudi Aramco: Company General Use
Thank You!
Questions?
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