Sulfur Dioxide (SO₂) is a colorless, pungent, and highly reactive gas primarily produced by the combustion of sulfur-containing fuels such as coal, oil, and petroleum products. It is one of the most common and harmful air pollutants regulated globally due to its severe environmental and health effects. SO₂ is classified as a criteria pollutant by agencies like the USEPA, CPCB (India), and the European Environment Agency. Its presence in industrial exhaust must be strictly controlled using an appropriate sulfur dioxide removal process to meet emission norms and environmental regulations.

Sources of SO₂ Emissions

SO₂ is mostly formed by the oxidation of sulfur (S) in fuels during combustion processes:

Common industrial sources include:

• Coal-fired power plants
• Refineries
• Smelting of metal ores (e.g., copper, zinc, lead)
• Cement kilns
• Fertilizer and sulfuric acid plants
• Pulp and paper industries
• Marine engines and heavy-duty diesel generators

Why is SO₂ Harmful?

Health Impacts:

• Respiratory irritation: Triggers asthma, bronchitis
• Cardiovascular stress
• Particulate formation: SO₂ reacts with moisture to form fine PM2.5

Environmental Effects:

• Acid rain: Forms sulfuric acid (H₂SO₄) when combined with water vapor
• Crop damage
• Soil and water acidification

SO₂ Removal – Process Overview

The process of removing sulfur dioxide from industrial exhaust gases is known as flue gas desulfurization (FGD). This can be achieved using physical absorption, chemical reaction, or catalytic conversion depending on application, space, and regulatory constraints.

Common SO₂ Removal Technologies

Here are the most widely used methods, each offering a unique sulfur dioxide removal process depending on plant size and effluent conditions:

1. Wet Scrubbing (Wet FGD)

The most widely used sulfur dioxide removal process, especially in power plants and refineries.

Process:

• Flue gas passes through a scrubber tower where it contacts a liquid slurry (usually lime or limestone-based).
• SO₂ reacts with the alkaline reagent to form calcium sulfite (CaSO₃) or gypsum (CaSO₄·2H₂O).

2. Dry and Semi-Dry Scrubbing

Used in industries where space is limited or water use is restricted. This sulfur dioxide removal is ideal for retrofits and cement plants.

3. Sorbent Injection Systems (Dry Sorbent Injection – DSI)

This compact sulfur dioxide removal process involves direct injection of sorbents into the flue gas.

4. Catalytic Oxidation (SNOX Process)

An advanced sulfur dioxide removal process that converts SO₂ into sulfuric acid using a catalyst.

5. Biological Desulfurization

Biological oxidation of SO₂ by bacteria in biofilters or bioscrubbers—an eco-friendly sulfur dioxide removal process for low-flow exhaust streams.

SO₂ Removal Efficiency by Technology

Each sulfur dioxide removal process offers a different efficiency range:

Technology	SO₂ Removal Efficiency
Wet FGD	90–98%
Semi-Dry Scrubbing	80–90%
Dry Sorbent Injection	50–80%
SNOX Process	>99%
Bio-desulfurization	60–90%

Design Considerations

To implement an effective sulfur dioxide removal process, consider:

• Flue gas flow and SO₂ concentration
• Reagent availability (lime, limestone, NaHCO₃)
• Disposal or reuse of by-products

Regenerative Thermal Oxidizer System

Global SO₂ Norms

Region	SO₂ Limit (mg/Nm³)
India (CPCB)	100–600
EU IED	<200
USA (EPA)	~300

 

Sulfur Dioxide Scrubber Installation kenya

 

Packed Tower Wet Scrubber Rubber Plant

Conclusion

A well-engineered sulfur dioxide removal is essential to meet environmental regulations and protect air quality. Whether using wet scrubbing, dry injection, or catalytic systems, selecting the correct sulfur dioxide removal process ensures efficient, cost-effective SO₂ mitigation.

Looking for an experienced provider of complete sulfur dioxide removal solutions? Contact our team for design, manufacturing, and performance guarantees.