Reducing Sulfur Oxide Emissions
- The removal of sulfur from fossil fuels can either take place pre-combustion or post-combustion
- The oxides of sulfur, SO2 and SO3, are both acidic and toxic gases
- Sulfur dioxide is produced naturally during volcanic eruptions, but large quantities have been and continue to be emitted by burning coal, oil and natural gas
Pre-combustion
- Pre-combustion of sulfur takes place for coal and petroleum, although it is expensive to remove all the sulfur, so a small percentage often remains
- For example, the average sulfur content of gasoline is 347ppm (this is the same as 347 mg per litre)
- It is essential to remove most of the sulfur as it damages the workings of internal combustion engines
- The sulfur is removed by reacting it with hydrogen in a process called hydrodesulfurization
- The sulfur is recovered and used in the manufacture of sulfuric acid
Post-combustion
- Post-combustion is carried out on in coal-fired power stations
- The waste gases from burning the coal contain sulfur dioxide
- The waste gases are passed through a wet slurry of calcium oxide and calcium carbonate which react with the SO2 and produce calcium sulfate
CaO (s) + SO2 (g) + ½O2 (g) → CaSO4 (s)
CaCO3 (s) + SO2 (g) + ½O2 (g) → CaSO4 (s) + CO2 (g)
- The calcium sulfate is also known as gypsum and is used to make plasterboard and other useful building materials
What does the future hold?
- Global policies working towards combating global warming will have the additional benefit in reducing acid deposition
- As we switch away from burning fossil fuels for energy there will be a fall in the emission of oxides of sulfur and nitrogen, which can only be a good thing for the environment
- Ultimately reducing the emission of primary pollutants is achieved by greater use of renewable energy sources, greater use of public transport and more efficient energy transfer systems
