Proven methods for reducing sulfur dioxide (SO2) emissions

Risks associated with SO₂

Short-term exposure to SO₂ can harm the human respiratory system and make breathing difficult. SO₂ and other sulfur oxides can contribute to acid rain, which can harm sensitive ecosystems.

SO₂ emissions that lead to high concentrations of SO₂ in the air generally also lead to the formation of other sulfur oxides (SO_x). SO_x can react with other compounds in the atmosphere to form small particles, which contribute to particulate matter (PM) pollution. Small particles may penetrate deeply into the lungs and, in sufficient quantities, can contribute to health problems.

At high concentrations, gaseous SO_x can harm flora by damaging foliage and contaminating soil.

The largest source of SO₂ in the atmosphere is from the burning of fossil fuels by power plants as well as other industrial facilities in mining and oil and gas production and refining.

For example, in Ontario alone, SO₂ is released in the following sectors:

Solutions adapted to each situation

SO₂ emissions are proportional to feed sulphur content. If it is not feasible to reduce the amount of SO₂ released from the combustion process by switching to a burning product (mainly fuel) that has lower sulphur content, other options can be implemented.

For industrial companies, there are many solutions that take into account multiple factors: targeted emissions reduction, staggered/phased options, monetization opportunities of a sulphurous by-product, availability of utilities and processing feedstock.

For instance:

Removal of sulphur after combustion

SO₂ emissions generated during combustion/oxidation can be reduced by treating the flue gases before they are emitted into the atmosphere via a stack; this is termed flue gas desulphurisation (FGD).

Wet systems

This process is the most globally used FGD system. This system is relatively simple : crushed limestone / lime is mixed with water, or caustic soda diluted in water to form a slurry or liquid, which is then sprayed into the sulphur containing flue gases. The sorbent reacts with the SO₂ to form an aqueous slurry of manageable sulphur species that could have the potential to be monetized or at least safely disposed.

Dry / Semi-Dry Systems

Within the spray dry system, a slurry of alkali sorbent, usually slaked lime, is injected into the flue gases in a fine spray. The heat from the flue gases causes the water to evaporate, cooling the gases as it does so. The present SO₂ reacts with the drying sorbent to form a solid reaction product, with no waste water.

Depending on the site and connected operations, other systems can be assessed: ammonia injection, oxidation type, magnesium based as lime, alkaline ash based, sodium/lime based, even biological sulphur recovery, among multiple others.

SO₂ reduction due to processing of acid gas streams

Commonly found in oil and gas facilities (gas production or refineries), SO₂ reduction can be accomplished by further processing the acid gas stream containing mainly hydrogen sulfide (H₂S).

Several methods are possible. Additional stages of reaction, in addition to fine tuning the sulphur recovery unit, can increase the conversion of H₂S into elemental sulfur and subsequently reduce SO₂ emissions. Possibilities cover adding stages of conversion, based on Claus or Selective oxidation reactions, or further treatment of the tail gas (tail gas treating units).

Other possibilities to be considered are sulphur degassing at the sulphur pit or oxygen enrichment. These may increase processing capacity and gain some additional SO2 removal for a relatively low ratio of extra investment.

Count on our experts to help you

There are various methods for reducing atmospheric SO2 emissions that must be considered in light of tightened regulations and necessary environmental protection. Each method has both advantages and limitations related to cost, removal efficiency, operational experience and produced waste products. Therefore, the choice of the control technology should be based on the specific criteria required.

The challenge for facility owners is to develop monitoring and mitigation plans, suited for the specific facilities and reduction targets in the most cost-effective way. Our experts can help you perform a thorough analysis, from emissions to SO2 removal facilities, while considering associated CAPEX and OPEX. Give us a call!