The Austrian engineering company Kanzler Verfahrenstechnik (KVT) has developed a proprietary process, Oxysulf, for which a thermal efficiency of > 85% and a tail gas sulfur dioxide (SO₂) emission value of < 5 ppm(v) have been demonstrated in a recently commissioned plant.

KVT has been active in the field of environmental technologies for more the 30 years, with experience in supply of turnkey off-gas treatment plants worldwide. The Oxysulf technology can handle sulfuric compounds such as SO₂, H₂S, COS or CS₂ in wide range of concentration. Plant sizes up to 200.000 Nm³/h and concentrations of sulfur bearing compounds from 2–200 g/Nm³ can be managed. Treated off-gas streams come from various sources, for example:

• Natural gas refining
• Furnace waste gases
• Metal smelter
• Viscose fiber industry
• Spent acid regeneration
• Oleum production

The process is based on thermal and/or catalytic oxidation of Sulfur-bearing compounds, by forming sulfuric acid.
The off-gas passes a pre-treatment system; depending on the application, this is a combination of a pre-filter, a scrubber, a DRY-FIL-hot gas filter, or a preheating. The pre-treatment is followed by the catalytic oxidation or thermal and catalytic oxidation, depending on concentration and kind of pollutant. In all applications the off gas is routed over a multi bed catalytic converter, followed by a concentration column and a tail gas treatment.

The catalytic oxidation of the sulfur-bearing compounds is exothermic, operating within the range of 360–550 °C, the resulting heat is typically recovered by a steam system. After the reactor, the process gas is passed through a concentration column where sulfuric acid is condensed and concentrated up to 98w%. The remaining sulfuric acid aerosols contained in the gas are precipitated in the wet electrostatic precipitator (WESP). To achieve lowest SO₂ emissions, further tail gas treatment is generally required.

The governmental regulations for SO₂/SO₃ emissions are becoming more and more stringent. Up to now the existing solutions to reduce the emission in the wet sulfuric acid process were limited:

• Exceeding the oxidation rate of 99% in a single step wet oxidation process is impossible due to the reaction equilibrium.
• Adding of second catalytic stage, as in the dry process, results in an enormous increase of the investment and operational costs.
• Adding a scrubber system with hydrogen peroxide or caustic soda has a considerable influence on the operational and disposal costs.

For reaching a sulfur recovery rate of > 99,9% and lowest SO₂ emission of < 5 ppm(v), KVT has developed its own technology: the Oxytail reactor. Instead of an additional conventional high temperature process step, the company’s Oxytail offers the possibility of SO₂ reduction with low investment and low operational costs.

In the Oyxtail reactor the remaining SO₂ contained in the gas is converted, washed out with demineralized water, and recycled to the process as weak sulfuric acid, without any extra utilities and avoiding any disposal costs.
KVT´s recently installed plant is treating 50,000 Nm³/h of high loaded gas up to 130 g/Nm³ of SO₂ at inlet of the main catalyst bed. While the inlet concentration to the KVT Oxytail reactor is within the range of 2 g/Nm³, SO₂ in the outlet of the reactor it is reduced to the value of 2–3 ppm(v).

With the new Oxytail unit KVT is setting a new standard for SO₂ emission control and makes the sulfuric acid recovery process more cost-effective.

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