Flue Gas Desulphurization

Flue Gas Desulphurization

What is flue gas desulphurisation?

Flue gas desulphurisation (FGD) describes a process that removes sulphur dioxide (SO2) from a flue gas (exhaust gas) stream. Sulphur dioxide is released to the atmosphere when fossil fuels are burnt and it is a leading contributor to acid rain. The FGD process has become critical to many industrial plants due to increasingly stringent environmental legislation. Although the FGD process is present in many industries, this article focuses upon FGD equipment associated with the power generation industry, particularly for coal fired power stations.

Why do we need flue gas desulphurisation?
Most fossil fuels (coal, oils etc.) contain some sulphur. When a fossil fuel is burnt, the sulphur it contains is released to atmosphere via the process of combustion. Some coals may contain up to 4% sulphur, which is a significant amount considering that a coal power station may burn in excess of 5,000 tonnes of coal per day.

Sulphur dioxide combines readily with water and consequently combines readily with moisture clouds in the atmosphere. Once a cloud has become sufficiently saturated with moisture, water droplets form and fall to the ground due to gravity; this process is known as precipitation (rain).

Unfortunately, as water absorbs sulphur dioxide it becomes more acidic. Consequently, as clouds of moisture absorb the sulphur dioxide gas in the atmosphere, the pH value of the suspended water molecules (moisture) decreases, and it becomes more acidic. The acidic rain -colloquially referred to as acid rain- then falls to the ground due to gravity.