Steel Mills Environmental Emissions



Posted: Monday, October 04, 2010

by Scott Manes
American Environmental Fabrication & Supply,LLC

Hydrogen Sulfide is dangerous to the environment, colorless, very poisonous, highly flammable gas with the characteristic foul odor of rotten eggs. With density greater than air, it tends to accumulate at the bottom of 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.

Hydrogen Sulfide gas is produced as a common off-gas in the Steel and Mining Industry. At even very low concentration levels H 2 S is considered a fatal gas. H 2 S is commonly reduced by thermal oxidation to SO 2 and SO 3 for possible usage in other plant processes or if not utilized for other applications may be removed by the use of a wet scrubber.

Air pollution control by industrial engineers and H 2 S application specialist have often decided to use direct fired thermal oxidizer systems for the treatment of H 2 S and CS 2 pollutants.

Many, after being involved with high fuel costs have devoted the time in research and product development to design and manufacture a regenerative thermal oxidizer that works with much reduced fuel consumption.

A Regenerative Thermal Oxidizer (RTO) is utilized to improve fuel efficiencies and to reduce NOX production that normally comes with a standard Direct-Fired Thermal Oxidizer.

Many steel and mining facilities are currently utilizing Direct-Fired Thermal Oxidizers and have more recently realized that a Regenerative Thermal Oxidizer would be a better piece of equipment when considering a direct fired thermal oxidizer's usage of fuel costs.

Many limiting factors have to be considered while designing the H2S reduction thermal oxidizer. Some considerations include; blocking any H 2 S 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 H 2 S 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 systems that have been installed have not taken into consideration high pressures which resulted in duct protrusion and fractured welded seams emitting exposure of high levels of H 2 S.

The type and metal thickness should be considered in the design phase 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 power to a micro turbine generator creating offset electricity. Frequently the exhaust stack and/or the inlet process line is normally equipped with a sampling port to allow periodic stack testing. In certain global areas regulations may also require continuous monitoring of SO 2 emissions. The decision of whether or not to apply waste heat recovery to regenerative thermal oxidizer depends on plant size and utility costs. Waste heat recovery economic evaluations comparing regenerative thermal oxidizers with and without systems shoudl be performed.

For more information about H2S reduction systems, please visit: American Environmental Fabrication & Supply
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