Flue Gas Desulphurisation (FGD); the next battlefield
Dr John McCullough, Chartered Engineer

There has been a number of disputes (e.g. arbitrations etc.) relating to retrofitted FGD installations. The problems or issues known to Cadogans concern performance, materials, construction, corrosion and delays.

FGD has been retrofitted to coal-fired power stations across Europe to comply with the EU Large Combustion Plant Directive (LCPD); there are about 12 such retrofits in the UK.

LCPD is applicable to combustion plant with a thermal output in excess of 50MW and its objective is to mitigate acidification and levels of particulates and ozone by controlling emissions of sulphur dioxide (SO2), particulate matter (PM) and nitrous oxides (NOX) from power stations, refineries and other industrial plant.

It is proposed to replace the LCPD with a new Industrial Emissions Directive (IED) in 2016. The SO2 emission level for coal-fired plant will reduce from the current LCPD value of 400 mg/m3 to the IED level of 200 mg/m3. There will also be a reduction in the allowable emission levels of NOx and PM.

FGD is for SO2 control and its main component is an absorption tower to remove SO2 from flue gases. This is generally preceded by some form of particulate removal, for example using an electrostatic precipitator (ESP).

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Limestone (CaCO3) and water are mixed to form a slurry which is sprayed into the tower to react with SO­2 to form calcium sulphite (CaSO3­). The CaSO3 is then exposed to air and reacts with oxygen to form calcium sulphate (CaSO4) which is known as gypsum.

The gypsum slurry is dewatered and the gypsum is used to manufacture products such as plasterboard. The removed water is used to make more limestone slurry which is returned to the tower

Limestone (CaCO3) and water are mixed to form a slurry which is sprayed into the tower to react with SO­2 to form calcium sulphite (CaSO3­). The CaSO3 is then exposed to air and reacts with oxygen to form calcium sulphate (CaSO4) which is known as gypsum.

 

The gypsum slurry is dewatered and the gypsum is used to manufacture products such as plasterboard. The removed water is used to make more limestone

slurry which is returned to the tower.

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