Award as “Low Carbon Model Company of the Year”
Wet flue gas desulphurisation is usually based on the use of calcareous absorbents (for example limestone, calcium hydrate, quicklime or chalk). Industrially, the use of limestone as an absorbent has prevailed in the area of power stations. The limestone-gypsum method produces gypsum as an end product, which is marketable for industrial re-use. So-called lime scrubbing reliably removes sulphur dioxide, hydrogen chloride, hydrogen fluoride, and ash from the flue gases and is one of the most widely used desulphurisation methods. Steinmüller Babcock Environment has 120 reference plants worldwide for this technology, with absorber sizes of up to 3.2 million Nm3/h respectively 1,100 MWel
The reaction of sulphur dioxide with limestone in the form of suspension is initiated in a spray tower that acts as an absorber. The absorber is divided into three distinct zones, the absorber sump, the contact zone and the absorber head. In the bottom area, the absorber sump, the lime suspension is agitated, supplemented with fresh absorbent, and ventilated. The agitation supports the dissolving of the limestone in the suspension, promotes the even crystallisation of the gypsum, and at the same time prevents the solid material from settling. To oxidise the sulphur dioxide to sulphate (gypsum), finely-distributed oxygen is required. Therefore air is blown into the absorber sump in front of the agitators and distributed or dispersed very finely in the suspension with the agitator flow.
The solid absorbent for the process can either be supplied as powder or ground in a milling unit at the power plant. In the lime milk dosing station the ground limestone is mixed with water before it is injected into the absorber sump.
From the absorber sump some suspension is pumped to the dewatering unit, where the dewatered gypsum is extracted as a marketable product. The surplus water is reused within the limestone/gypsum process.
The flue gas enters the absorber above the sump, and flows upwards through the contact zone. Here are many levels with spray nozzles, which disperse the scrubbing suspension from the sump very finely into the flue gases.
In the contact zone the gaseous sulphur dioxide from the flue gas is dissolved into the scrubbing liquid. After flowing through the contact zone, the flue gas reaches the absorber head and passes through horizontal droplet separators where liquid droplets are removed. When leaving the absorber the cleaned gas is saturated with water vapour has been cooled down to the respective saturation temperature.
Advantages of the limestone-gypsum method
Marketable product (gypsum)
Optimised material and plant concepts