Hydrogen Sulfide can be very dangerous in poorly ventilated spaces. Although very pungent at first, it
quickly deadens the sense of smell, so potential workers may be unaware of its presence until it is too
late. 800 ppmv is the lethal concentration for 50% of humans for 5 minutes exposure.
This Hydrogen Sulfide gas is a common off-gas which is produced in the Steel and Mining industry. At
even very low concentration levels H2S is considered a fatal gas. H2S is commonly reduced by
thermal oxidation to SO2 and SO3 for possible usage in other plant processes or if not utilized for
other applications may be removed by the use of a granulated carbon biofiltration system.
Many industrial engineers and H2S application specialist have been involved with thermal oxidizer
systems which have been used in the treatment of H2S and CS2 pollutants. Many, after being
involved in many failed or sub-standard trials have devoted the time in research and product
development to design and manufacture regenerative thermal oxidizers that works. A regenerative
thermal oxidizer (RTO) is utilized to improve fuel efficiencies and to reduce NOX production that would
come from a standard direct-fired thermal oxidizer.
Many steel and mining facilities are currently utilizing direct-fired thermal oxidizers and have recently
realized that a regenerative thermal oxidizer would be a better piece of equipment when considering
direct fired thermal oxidizers usage of fuel costs.
Limiting factors have to be considered while designing the regenerative thermal oxidizer. Some
considerations include; blocking any H2S from possible leakage from the regenerative thermal oxidizer
system, leaking can cause premature degradation and drastically reduce the overall life of the
equipment; blocking any possible fatal H2S gas to be emitted directly into the immediate atmosphere
causing severe health and safety issues.
With the potential of high operating pressures, consideration should be given to the thickness of
material and flow design. Many of the systems that have been installed had not taken into
consideration of the high pressure which resulted in fractured welded seams emitting and exposure of
high levels of H2S.
Design considerations should also be given to the type and metal thickness to obtain high outlet
temperatures. These temperatures need to be above any possible condensation levels of
by-products, this will reduce any formation of sulfuric acid within the exhaust system. With the high
outlet temperatures the exhaust may be used to generate high pressure steam which may be used in
steam operations or to power a turbine creating offset electricity.
Usually the stack or its inlet process line is normally equipped with sampling ports to allow periodic
stack testing. In certain global areas regulations may also require continuous monitoring of SO2
emissions. The decision of whether or not to apply waste heat recovery to regenerative thermal
oxidizer depends on plant size and utility costs. Economic evaluations comparing regenerative thermal
oxidizers with and without waste heat recovery should be performed.
|Hydrogen Sulfide Reduction Using Regenerative Thermal Oxidizer
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Air Pollution Control Equipment
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