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Exploring the Claus Process

     There are few processes that have served the chemical industry better than the Claus Process.  For years, this process has helped remove hydrogen sulfide (H2S) gas from combustion streams and turn it into salable elemental sulfur.

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Figure 1:  Simplified Flow Diagram of the Claus Process

     A gas containing H2S is fed with oxygen to a waste heat boiler.  Oxygen is used to help the boiler reach the
temperature necessary for combustion from 1562 to 2462 0F (850 to 1350 0C).   The combustion products are cooled between 500 to 572 0F (260 to 300 0C) and fed to the catalytic stage of the process.  The process gas passes over an Al2O3 based catalyst with a surface area specification of 200-300 m2/g.  The following reaction results:

2 H2S  +  SO2  ---> 3 S  +   2 H2O

     The elemental sulfur is drawn off at various locations throughout the process and is sent to storage.  The remaining gases in the process stream are sent to the desulfurization section (not shown in Figure 1) for further sulfur removal.  In the desulfurization section, additional sulfur removal lowers the concentration of sulfur in the process stream to between 100 and 1000 ppmv (parts per million by volume).  The residual sulfur is then transformed to sulfur dioxide in a furnace via the following reaction:

S  +  O2  --->  SO2

     Heat in the hot furnace gas is recovered by heat exchange with a portion of the process stream leaving the desulfurization unit.  The cooled, SO2 rich furnace gas is treated in downstream equipment for SO2 removal.  A portion of the heated process stream is recycled to the waste heat boiler while the balance is vented to the atmosphere.

     The Claus Process has been used to produce soot-free sulfur for years due to it's unique dual chamber combustion compartment.   If the feed rate to the Claus plant becomes too low, a sustaining combustion chamber reaction is necessary to prevent soot from forming.

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     An interesting aspect of the Claus Process is the strange behavior of molten sulfur.  The temperature of molten sulfur must be controlled carefully.  If the sulfur is allowed to cool too much it can begin to polymerize. Below is the characteristic viscosity curve associated with molten sulfur.

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     For further reading about the Claus Process, visit the links below:

Bryan Research and Engineering

Sulfur Experts Online

By: Christopher Haslego, Owner and Chief Webmaster (read the author's Profile)

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