Sulfur Oxidation Process (SOP) – Efficient Sulfuric Acid Production

Sulfuric acid is a basis of industrial chemistry, used in:

• Fertilizer production (especially phosphate-based)
• Rubber and plastics manufacturing
• Cosmetics and pharmaceuticals
• Steel refining and metallurgy
• Pigments and dyes
• Catalysis in Alkylation processes
• Viscose fibre production

Hydrogen sulfide (H₂S) or COS, CS2 is commonly found in:

• Natural gas processing
• Acid gases from Industrial and refinery gases
• Oil refining and coal gasification processes
• In viscose synthesis byproducts

Depending on the source, H₂S concentrations can range from ppm levels to over 75% by volume. If not properly treated, these gases release sulfur oxides (SOₓ) into the atmosphere, contributing to acid rain, which harms ecosystems and infrastructure.

The SOP (Sulfur Oxidation Process) is a high-efficiency, customizable process designed to:

• Clean wet or dry exhaust gases containing sulfur compounds
• Convert these compounds into Sulfuric Acid or Oleum
• Produce energy in the form of high-pressure superheated steam for e.g. steam turbines

The system uses single or double contact, single or double conversion  technology (optional an additional TGTU Stage) and is suitable for both elemental sulfur combustion and sulfur containing waste gas treatment.

Typical Gas Sources:

• Acid gas from refinery units (e.g. sour gas strippers, crude benzene hydrogenation)
• Acid gas from amine scrubber systems and high flash columns
• Waste gas from viscose production:
  • Rich gas: ~56% H₂S, 21% CS₂ (from spin bath degassing)
  • Lean gas: ~0.3% H₂S, 0.2% CS₂ (off-gas from spinning machines)

Liquid sulfur is also burned to provide the thermal energy needed and to ensure sulfuric acid production meets upstream process demand.

The SOP Plant treats sulfur-containing waste gases and liquids using a wet oxidation process in the presence of water vapor to produce Sulfuric Acid 98% Min – Industrial Grade sulfuric acid.

Key Process Steps

1. Gas cleaning (Hot gas filtration, scrubber, WESP, …)
2. Preheating – Acid gases are pre-heated via e.g. glass tube heat exchangers to reach reaction temperature.
3. Catalytic Oxidation – SO₂ is oxidized to SO₃ over a catalyst bed; exothermic reaction heat is recovered by special molten salt system which converted to superheated steam.
4. Acid Formation – SO₃ is hydrated and condensed into H₂SO₄; hydration energy is reused in the process at highest efficiency
5. Aerosol removal – Acid mist is removed by Wet ESPs ; weak acid is recycled back to the process increasing total sulfur recovery rate to reach almost zero emission levels.
6. Tail Gas Cleaning – Remaining SO₂ traces are  removed to meet strongest emission limits.

Energy Efficiency Features

• Catalysts active at very low temperature enable complete  SO₂ conversion.
• Glass tube heat exchangers recover heat from partially condensed acid up to 300°C.
• Heat transfer molten salt system  enables efficient operation from 180–630°C.
• Optimized equipment design ensures low process gas pressure drop leads to reduced energy demand.

• No process-related liquid and solid effluents aside from sulfuric acid and clean steam
• Highest Energy recovery via high-pressure steam generation for electricity and utilizing the excess heat within the process almost completely
• Efficient heat transfer using:
  • PFA lined glass-tube heat exchangers (up to 300°C)
  • Molten salt systems for high-temperature heat transfer (180°C–630°C) without high-pressure equipment
• Catalyst technology:
  • Locally manufactured precious metal-promoted catalysts
  • Operate from 250°C up to 750°C with >12 vol% SO₂
• Low power consumption due to optimized low pressure drop reactor and acid condenser design