Sulfur unit

n the context of oil and gas plants, the sulfur process primarily refers to the treatment and
management of sulfur compounds present in crude oil and natural gas. Sulfur compounds, such
as hydrogen sul de (H₂S) and sulfur dioxide (SO₂), are common impurities that must be removed
to prevent corrosion, environmental pollution, and health hazards. Here’s an overview of the sulfur
process in oil and gas plants:
1. Hydrogen Sul de Removal
Gas Sweetening:
• Amine Gas Treating: One of the most common methods for removing H₂S and CO₂ from
natural gas. In this process, the gas is contacted with an amine solution (e.g.,
monoethanolamine, diethanolamine) that absorbs the acidic gases. The "sweetened" gas, now
free of H₂S and CO₂, is then separated from the amine solution, which is regenerated and
recycled.
• Physical Solvents: Physical solvents like Selexol and Rectisol can also be used for gas
sweetening, especially when dealing with high-pressure gas streams and higher concentrations
of H₂S and CO₂.
Claus Process:
• The Claus process is widely used to convert H₂S into elemental sulfur. It involves two main
steps:
◦ Thermal Step: H₂S is partially oxidized to sulfur dioxide (SO₂) in a furnace at high

temperatures.
◦ Catalytic Step: The remaining H₂S reacts with the produced SO₂ over a catalyst (typically

alumina or titanium dioxide) to form elemental sulfur and water. The overall reaction is:
◦ 2

→
3

+
2

2H
• 2 •
•
• S+SO

• →3S+2H
𝑂
𝐻
𝑆
𝑂
𝑆
𝑆
𝐻
fi
fi
 • O
◦ The sulfur produced is condensed and collected, while the remaining gases are treated further
to recover more sulfur.
2. Sulfur Dioxide Management
Tail Gas Treatment:
• SCOT Process (Shell Claus O -gas Treating): Tail gases from the Claus process, which still
contain small amounts of sulfur compounds, are further treated to maximize sulfur recovery. The
SCOT process involves hydrogenating the sulfur compounds to H₂S, which is then absorbed in
an amine solution and recycled back to the Claus unit.
Flue Gas Desulfurization (FGD):
• In combustion processes, such as re ning or power generation, sulfur in fuels can form SO₂.
FGD technologies are used to remove SO₂ from ue gases. Common methods include:
◦ Wet Scrubbing: Flue gas is passed through a scrubber where it reacts with a slurry of

limestone (calcium carbonate) or lime (calcium hydroxide), forming gypsum (calcium sulfate)
as a byproduct.
◦ Dry Scrubbing: Involves injecting a dry sorbent, such as lime, into the ue gas stream, where

it reacts with SO₂ to form a dry byproduct.

3. Desulfurization of Crude Oil
Hydrodesulfurization (HDS):
• This process removes sulfur compounds from crude oil fractions during re ning. The oil is mixed
with hydrogen and passed over a catalyst (typically cobalt-molybdenum or nickel-molybdenum)
at high temperatures and pressures. The sulfur compounds are converted into H₂S, which is
then removed from the gas stream using gas sweetening methods.
4. Sulfur Recovery and Utilization
• Sulfur Storage and Transportation: Recovered sulfur is often stored in solid form or as liquid
sulfur, depending on the ambient temperature and speci c requirements.
• Sulfur Use: Elemental sulfur has various industrial uses, including the production of sulfuric acid
(a key industrial chemical), fertilizers, and in vulcanization of rubber.
5. Environmental and Safety Considerations
• Regulations: Stringent environmental regulations govern sulfur emissions from oil and gas
plants to prevent air pollution and acid rain. Compliance with these regulations is critical for
plant operations.
• Safety: Handling H₂S and SO₂ is hazardous. H₂S is highly toxic and ammable, requiring strict
safety protocols, including monitoring, ventilation, and personal protective equipment (PPE).
By e ciently managing sulfur through these processes, oil and gas plants can minimize
environmental impact, ensure safety, and comply with regulatory standards while producing
cleaner fuels and products.
The sulfur recovery process in oil and gas plants involves several critical units: the boiler, reheater,
converter, and condenser. These components are part of the larger sulfur recovery unit (SRU),
which typically includes the Claus process and various tail gas treatment steps. Below is a
detailed overview of the process and the structure of each component.
Overview of the Claus Process
The Claus process is the primary method for sulfur recovery from hydrogen sul de (H₂S) in gas
streams. It consists of thermal and catalytic stages to convert H₂S into elemental sulfur.
1. Boiler (Thermal Stage)
Structure and Function:
• Combustion Chamber: The process begins in a combustion chamber, where H₂S-rich gas is
burned in the presence of air. This partial combustion converts about one-third of the H₂S into
sulfur dioxide (SO₂) while the remaining H₂S is left unreacted.
• Reaction: The overall combustion reaction is:
• 2

2
𝑆
𝐻
ffi
ff
fi
fl
fi
fl
fl
fi
fi
 +
3

→
2

+
2

+
heat

2H
• 2 •
•
• S+3O

• →2SO

• +2H

• O+heat
• 2

→
3

+
2
𝐻
𝑆
𝑂
𝑆
𝑆
𝐻
𝑂
𝐻
𝑂
𝑆
𝑂
 2

2H

• S+SO

• →3S+2H

• O
Heat Recovery:
• Waste Heat Boiler: The hot gases from the combustion chamber are passed through a waste
heat boiler to recover heat, generating steam for use in other plant processes.
2. Reheater
Structure and Function:
• Heat Exchangers: Reheaters are typically heat exchangers that raise the temperature of the
gas stream before it enters the catalytic converters. This ensures the reaction conditions are
optimal for the catalytic conversion of H₂S and SO₂ to elemental sulfur.
Types of Reheaters:
• Indirect Reheaters: Use steam or other heat transfer uids to raise the gas temperature without
direct contact.
• Direct Reheaters: Use combustion of fuel gas to directly heat the process stream.
3. Converter (Catalytic Stage)
Structure and Function:
• Catalytic Reactors: These reactors contain catalysts such as activated alumina or titanium
dioxide. The gas mixture from the reheater is passed over these catalysts, where H₂S reacts
with SO₂ to form elemental sulfur.
• Multiple Stages: Typically, there are two or three catalytic stages to maximize sulfur recovery.
Each stage converts a portion of the remaining H₂S.
Reactions:
• 2

→
3

+
2

2
𝑂
𝐻
𝑆
𝑂
𝑆
𝑆
𝐻
fl
 2H
• 2 •
•
• S+SO

• →3S+2H

• O
4. Condenser
Structure and Function:
• Sulfur Condensers: After each catalytic stage, the gas stream passes through a condenser
where the temperature is lowered to condense elemental sulfur.
• Sulfur Collection: The condensed sulfur is collected in liquid form and can be further
processed or solidi ed for storage and transport.
Process Flow:
• The gas stream from the catalytic converter is cooled in the condenser, causing sulfur vapor to
condense into liquid sulfur. The condensed sulfur is collected at the bottom of the condenser.
• The remaining gas, still containing some H₂S and SO₂, is reheated and sent to the next catalytic
stage.
Tail Gas Treatment (Optional)
Additional Treatment:
•
• SCOT (Shell Claus O -gas Treating): Tail gas from the nal condenser, which still contains
some sulfur compounds, is treated to reduce sulfur emissions further. This typically involves
catalytic hydrogenation to convert all sulfur compounds back to H₂S, which is then absorbed
and recycled.
Process Flow Summary
1. Feed Gas Entry: H₂S-rich gas enters the Claus unit.
2. Combustion and Thermal Stage: Partial combustion in the boiler produces SO₂ and residual
H₂S.
3. Heat Recovery: Waste heat boiler recovers heat to produce steam.
4. Reheating: Gas stream is reheated to optimal catalytic conversion temperature.
5. Catalytic Conversion: Multiple catalytic stages convert H₂S and SO₂ to elemental sulfur.
6. Condensation: Sulfur vapor is condensed and collected as liquid sulfur.
7. Tail Gas Treatment: (If applicable) Further treatment of residual gases to maximize sulfur
recovery and minimize emissions.
Structural Diagram (Simpli ed)
1. Combustion Chamber: Initial conversion of H₂S to SO₂.
2. Waste Heat Boiler: Heat recovery and steam generation.
3. Reheater: Heats the gas stream before catalytic conversion.
4. First Catalytic Converter: Initial catalytic conversion stage.
5. Sulfur Condenser: Condenses and collects sulfur.
6. Reheater: Heats the gas stream before the second catalytic conversion.
7. Second Catalytic Converter: Further catalytic conversion stage.
8. Sulfur Condenser: Additional sulfur collection.
9. Tail Gas Treatment Unit: (Optional) Additional gas treatment for emission control.
𝑂
fi
ff
fi
fi
 By e ciently utilizing these units, the Claus process in oil and gas plants achieves high sulfur
recovery rates, converting hazardous H₂S into useful elemental sulfur while minimizing
environmental impact.
+--------------------+
| Feed Gas (H₂S-rich)|
+---------+----------+
|
v
+--------------------+
| Combustion |
| Chamber (Boiler) |
+---------+----------+
|
v
+--------------------+
| Waste Heat Boiler |
| (Heat Recovery) |
+---------+----------+
|
v
+--------------------+
| First Reheater |
+---------+----------+
|
v
+--------------------+
| First Catalytic |
| Converter |
+---------+----------+
|
v
+--------------------+
| First Sulfur |
| Condenser |
+---------+----------+
|
v
+--------------------+
| Second Reheater |
+---------+----------+
|
v
+--------------------+
| Second Catalytic |
| Converter |
+---------+----------+
|
v
+--------------------+
| Second Sulfur |
| Condenser |
+---------+----------+
|
v
+--------------------+
| Tail Gas Treatment |
| (Optional, e.g., |
| SCOT Process) |
+---------+----------+
|
ffi
 v
+--------------------+
| Final Emission or |
| Recycle |
+--------------------+

Description of the Layout

1. Feed Gas Entry: The H₂S-rich gas stream enters the SRU.
2. Combustion Chamber (Boiler): The gas stream is partially combusted with air, converting
some H₂S to SO₂.
3. Waste Heat Boiler (Heat Recovery): Heat from the combustion gases is recovered to
generate steam.
4. First Reheater: The gas stream is reheated to the optimal temperature for catalytic
conversion.
5. First Catalytic Converter: The reheated gas undergoes catalytic conversion, where H₂S and
SO₂ react to form elemental sulfur.
6. First Sulfur Condenser: The gas stream is cooled, condensing the sulfur vapor into liquid
sulfur which is collected.
7. Second Reheater: The remaining gas is reheated again for further catalytic conversion.
8. Second Catalytic Converter: Additional catalytic conversion occurs, further converting H₂S
and SO₂ to elemental sulfur.
9. Second Sulfur Condenser: The gas stream is cooled again, condensing more sulfur vapor
into liquid sulfur.
10. Tail Gas Treatment (Optional): The remaining tail gases are treated to maximize sulfur
recovery and reduce emissions.
11. Final Emission or Recycle: The treated gas is either emitted safely or recycled back into the
process.
Notes
• Combustion Chamber: The initial stage where partial oxidation of H₂S occurs.
• Waste Heat Boiler: Recovers heat from the combustion process, improving energy e ciency.
• Reheaters: Ensure the gas stream reaches the optimal temperature for e ective catalytic
conversion.
• Catalytic Converters: Multiple stages to maximize the conversion of H₂S and SO₂ into
elemental sulfur.
• Sulfur Condensers: Collect sulfur produced in each catalytic stage.
• Tail Gas Treatment: Enhances overall sulfur recovery and reduces emissions.
This simpli ed layout provides a clear representation of the sulfur recovery process in an oil and
gas plant. For an actual implementation, the design would be more complex and would consider
additional factors like material selection, safety measures, and compliance with environmental
regulations.

Sss
fi
ff
ffi