1. SPENT CAUSTIC TREATMENT OPTIONS Hadi M. Al-Daghman, 2014
Good morning everyone and I an very happy to be here and to participate in this very important Environmental event.
My name is Hadi Al-Daghman, I work for Saudi Aramco (SA) in the Environmental Protection Department’s WW Mgmt. & Water Conservation Unit.
SA is committed to protect the environment, promote water conservation practices, ensure that industrial and sanitary wastewater treatment systems operate adequately, and to be compliant with all environmental regulations.
In this presentation I will give you an overview about Spent Caustic Treatment Options and emphasize on the most common treatment.
Hadi M. Al-Daghman, 2014

2. Outline Background Treatment Options Most Common Treatment Conclusion
In my presentation, I will provide you with a background regarding spent caustic which is a very complex and difficult wastewater to deal with. I will touch base on the different types of spent caustic, the composition of each type, and how they are produced.
Then, I will talk about the different treatment technologies (options) available to treat this wastewater.
Advantages and disadvantages of each options will be also presented and I will elaborate on the most common treatment technology.
Finally, I will conclude.

3. BACKGROUND What is Spent caustic ? Talk about what is Caustic????
Spent Caustic is the wastewater generated from using Caustic to remove
Hydrogen Sulfide (H2S) and
Mercaptanes (R-SH)
from hydrocarbon product stream.
Talk about what is Caustic????
It is a highly concentrated hydroxide solution (for example: sodium hydroxide – NAOH, or Potassium Hydroxide – KOH) with a pH above 12.
Spent Caustic is the wastewater stream generated from using Caustic to remove the two major constituents:
1- Caustic is used to remove (H2S)
2 - Mercaptanes (RSH) from hydrocarbon product stream.

4. Major Sources of Spent Caustic
BACKGROUND
Major Sources of Spent Caustic
MEROX Processing Unit:
Gasoline
Kerosene
Jet fuel
Isomerization Processing Unit
At refineries and gas plants,
Two major sources of spent caustics are generated:
The first one is the Merox Process
Merox processing (Mercapetens Oxidation) : is a process used in oil refineries and natural gas plants to remove mercaptans from LPG , propane , butanes, light naphtha, kerosene, and Jet fuel by converting them to liquid hydrocarbon disulfides.
The second one is the isomerization Process
Isomerization is a process in petroleum refining that converts n-butane, n-pentane and n-hexane into their respective isoparaffins of substantially higher octane number. The isomerate is washed (caustic and water), acid stripped, and stabilized before going to storage.

5. BACKGROUND Type Of Spent Caustics Sulfidic Spent Caustic
Non-Sulfidic Spent Caustic
Generally, Spent caustic is classified in two main categories : sulfidic and non-sulfidic.
Sulfidic spent caustics: it is the most common spent caustics type. It contains high concentration of SULFIDE which might be converted to hydrogen sulfide if the pH of wastewater is reduced. This hydrogen sulfide will be emitted as a gas from the wastewater. This a very serious issue and need to be handled cautiously and carefully. The lower the pH the higher the conversion of sulfide to hydrogen sulfide. Therefore, it is best to oxidize the sulfide prior to any neutralization process take place.
Non-Sulfidic Spent Caustic: it is any other spent caustic that does not contain sulfide, such as:
phenolic
cresylic
chloridic
spent caustics.

6. BACKGROUND You can see from the Graph that as the pH ……..
Talk about the safety of H2S (toxic level)

7. BACKGROUND

8. Composition of Spent Caustic
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
This slide shows why earlier I said that this a very difficult waste stream to deal with.
As you can see from the analytical data, this waste stream can not be send directly (without any pre-treatment) to the sewers system especially if the treatment method is biological.
Certain pretreatment procedure has to be done before spent caustic is disposed of.
In the next slide , I will talk about the available treatment options

9. TREATMENT OPTIONS Chemical oxidation Neutralization Dilution Treatment
Wet Air Oxidation
Four treatment options of spent caustic are available
Chemical oxidation
Neutralization
Dilution Treatment
Wet Air Oxidation
Next slides , I will explain each treatment concept and it is advantages and it is disadvantages.

10. CHEMICAL OXIDATION SEPARATOR REACTOR Hydrogen Peroxide Cooling Process
Off Gas to Thermal Oxidizer
Oxidized Spent Caustics
to Neutralization and WTTP
Spent Caustic
Feed/Heating
Knock Out Drum
Cooling Process
Catalyst
Hydrogen Peroxide
Chemical Oxidation process is a treatment process which can provide a deep (very low pH) neutralization and oxidized the spent caustic by adding a strong chemical oxidizing agent such Hydrogen Peroxide (ozone may also be used)
Heated spent caustic, Hydrogen Peroxide along with catalyst (a Fenton reagent - peroxide with Fe+2 catalyst) is introduced into the reactor to neutralize the waste . Then, the oxidized waste stream is cooled and sent into a separator where the liquid effluent is send to the wastewater treatment plant while the off-gas is treated thru thermal oxidizer for VOC removal .
Alkaline conditions are favored for complete conversion to sulfates (note: refer to slide number 5).

11. CHEMICAL OXIDATION Advantages of Chemical Oxidation : Disadvantages :
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)
Advantages of Chemical Oxidation :
Oxidized most of spent caustic
Disadvantages :
Operating expense is the highest
High explosion risks
Safety concerns is high since H2O2 requires special handling needs
H2O2 is highly corrosive and degrades in heat

12. Neutralized Brine to WWTP Solvent and Acid oils to fuel oil
NEUTRALIZATION
SEPARATOR
STRIPPING
COLUMN
Fuel Gas
Sulfuric Acid
Solvent
Acid Brine
Fresh Caustic
Off Gas
to Sulfur Plant
Spent Caustic
Neutralized Brine to WWTP
Solvent and Acid oils to fuel oil
REACTOR
The neutralization of spent caustic treatment process involves mixing the caustic stream along with sulfuric acid to enable separating the caustic stream into multiple stream.
As shown in the slide, spent caustic is fed into a low pH reactor using sulfuric acid with resulting stream mixed with solvent. An acidified stream is produced which is directed to a separator along with fuel gas where the stream is separated into acid oils , brine, and off gas . The acid brine is then directed to a stripping column to further separate the mixture. A fresh caustic prior to discharge to the wastewater treatment plant is injected into the liquid effluent to neutralize the pH. The off-gas is sent to the sulfur plant for additional treatment.

13. NEUTRALIZATION Advantages of Neutralization: Disadvantages :
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
Advantages of Neutralization:
Low operating cost
Disadvantages :
Multiple chemical feeds
Complexity of the separation activity
Safety concerns is high since it creates H2S rich gases resulted from the neutralizer .
H2S is highly corrosive and reduce the equipment life
Odors due to the presence of H2S and mercaptans

14. DILUTION Dilution Tank Diluted Caustic to WWTP Spent Caustic Stream
Water Supply
Spent Caustic Stream
Diluted Caustic to WWTP
Routing Sampling
This treatment option is basically the simplest one.
It consists of:
water supply
dilution tank,
pumps
the spent caustic is pumped from the SC collection or storage tank to the dilution tank where water is added (to dilute the concentration of spent caustic.
the desired dilution factor is in most cases 100 of water :1 part of spent caustic.

15. DILUTION Advantages of Dilution: Disadvantages : Low capital cost
Lower safety concerns
Disadvantages :
Not complete removal (No chemical reactions)
Risk on downstream processes
Very critical operations
Dilution has advantages and disadvantages and are as following:
Capital cost is low
Safety concern is low since there is no reaction and H2S emissions is minimal at the final pH Effluent (7.5 to 8)
(monitoring H2S level remains “a must” just like the other treatment options)
The main disadvantages of this option
that there is no chemical treatment is provided.
Risk of residual Sulfides, mercaptans and acids since they will be presented in the stream at low concentration .
This option needs to be operated full time since Improper dilution or operator error could lead to damage the biological treatment

16. WET AIR OXIDATION SEPARATOR REACTOR Oxidation Air Compressor Heating
Off Gas to Thermal Oxidizer
Oxidized Spent Caustics
to Neutralization and WTTP
Spent Caustic
Knock Out Drum
Cooling Process
Oxidation Air Compressor
High Pressure Pump
Heating
Wet Air Oxidation process is the oxidation of the spent caustic in an aqueous environment using oxygen (from air) as the oxidizing agent. The oxidation reactions occur at high temperatures (150C-320 C) and high pressures (10 to 220 Bar).
The required operating conditions are determined by the desired treatment level and type of spent caustic.
The typical Wet Air oxidation system uses rotating equipment to raise the feed stream and air to the required operating pressure Heat exchanger is preheating the feed mixed with air entering the reactor, Since WAO is exothermic reaction, the effluent mixture from the reactor is cooled while the gas and liquid streams are separated.
The liquid effluent from the separator will send to the wastewater treatment facility for polishing while the off-gas is passed through a thermal oxidizer to remove the excess VOC and H2S.

17. WET AIR OXIDATION Advantages of Wet Air Oxidation: Disadvantages :
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
WAO has advantages and disadvantages and are as following:
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 medium if it is high pressure and high temperature WAO process
Consume Energy

18. 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
As an outcome from the previous studies , WAO process was found to be the most common Spent Caustics Treatment ) due to the following reasons :
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

19. 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.
I will conclude my presentation will the following remarks:
The handling and disposal of spent caustics is a paramount problem to the refining and LPG industries.
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 is a major role in spent caustic treatment.

20. Thank You!
Questions?