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The Claus Process Analysis
H
2
S is toxic at 10 ppm, entirely lethal at 800 ppm, highly corrosive to equipment, flammable when in excess of 4.3% by volume in air, and unpleasantly odorous at a threshold of less than 1 ppb.
Unfortunately, H
2
S occurs abundantly in the world’s fossil fuel reserves. The sulfur recovery unit (SRU) of a refinery is dedicated to processing the H
2
S stripped from the hydrocarbon fuel through a series of operations that convert it into water and harmless elemental sulfur, which can be sold and repurposed in fertilizer, gunpowder, and more.
The Claus process is the industry standard for treating the H
2
S-rich “sour” gas . In the reaction furnace, H
2
S is combusted:
3H
2
S +
3
/
2
O
2
SO
2
+ H
2
O + 2H
2
S
A catalytic converter reacts the products of the combustion to create elemental sulfur in it various crystalline forms:
2H
2
S + SO
2
2H
2
O +
3
/
X
S
X
As can be deduced from the 2nd reaction above, the typical Claus reaction runs most efficiently when the stoichiometric ratio of H
2
S to SO
2
is controlled at 2:1. The 1st reaction above demonstrates that this ratio is controlled by adjusting the amount of available oxygen.
The efficiency of sulfur recovery therefore hinges on the “Air Demand” signal which informs the oxygen adjustment in the DCS. The
Air Demand is calculated by multiplying the expression (2[SO
2 requires continuous, reliable measurement of the H to measure COS and CS
2
2
S and SO
2
] - H
2
S) by a scaling factor. Obtaining the real-time Air Demand value
concentrations in the Claus tail gas. Additionally, it can be valuable
in the tail gas as high levels can be indicators of reduced efficiency or potential catalyst issues.
Applied Analytics’ TLG-837 provides continuous, ultra-safe measurement of all these critical parameters in the tail gas stream.
Other applications for Applied Analytics technology within the Sulfur Recovery Unit include:
Feed Forward — measuring H
2
Sulfur Pit — measuring H
2
S in the acid feed gas to the sulfur recovery unit to predict Air Demand [
S and SO
2
in pit gas to warn of toxic gas buildup and sulfur fires [ OMA H
2
OMA H
S Analyzer ]
2
S Analyzer ]
Typical SRU Claus Process Schematic
AT# = analyzer location
CLAUS
PROCESS
[3]
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