1. Chapter 5 Sulfur Recovery and Claus Off-Gas Treating
Gas Processing I NGT 140
Chapter 5
Sulfur Recovery and
Claus Off-Gas Treating
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2. Ch 3
Ch 5
Ch 2
Ch 7 & 8
Ch 10
Ch 4
Ch 6
Ch 9
Ch 2
Ch 9

3. Gas treating plants must comply with standards and regulations concerning emissions and pollution.
In Chapter 4 discussed the removal of H2S and CO2 from the sour gas stream.
Next these removed components must be dealt with.
Limits on H2S and CO2 vary but generally fall in to the range of a few pounds per day into the atmosphere (some cases 99.9% removal - USA)
The acid gas stream from the processing plant is fed to a sulfur recovery unit (SRU)

4. The SRU converts the H2S and other sulfur compounds into recoverable non-toxic elemental sulfur (S).
Tail gas (gas leaving a SRU) still contains some sulfur components
These are converted to SO2 in an incinerator before being released into the atmosphere.

5. The Claus Process – discovered by Carl Claus in 1883.
Reduced H2S to elemental sulfur and water
However the process was difficult in inefficient
Today the process is vastly improved by breaking the process into two steps.
Thermal Step
Oxygen injected during high temperature combustion to produce SO2 and water (p. 67)
Catalytic Step
SO2 formed in step 1 reacts with the unburned H2S to form gaseous elemental sulfur. (Catalyst – activated alumina or titanium dioxide)

6. Figure 5.2 Claus sulfur-recovery unit (SRU) – Catalytic Recovery
Following the thermal reaction furnace and waste heat recovery units, the catalytic recovery of sulfur consists of three substeps: heating, catalytic reaction, and cooling plus condensation. The three steps usually repeated three times.

7. Figure 5.4 Shell Claus Off-Gas Treating process (SCOT)
The Claus process converts 96% of the sulfur compounds to elemental sulfur.
The off gas from the Claus process still contains more sulfur than emission regulations allow.
The Shell Claus Off-Gas Treating process can reliably recover greater than 99.8% of the sulfur. (p. 70)