HF and SO₂ Multipoint Monitoring on Large Gas Treatment Centers (GTCs) with Prewarning Abilities

During dry scrubbing, alumina and pot gas are distributed inside the GTC into multiple (typical 10–30) filtering modules where the adsorption of HF takes place on the surface of the alumina. Unintended distribution patterns due to blockages or mechanical failures inside the reactors and filter modules may give too high HF emissions due to oversaturation of the alumina inside the various modules. Although not widely implemented yet, several systems are available today for HF monitoring in individual modules. These systems will be reviewed in this paper. The capabilities of the HF extractive multipoint method are verified with manual measurements on an 18-compartment size GTC in the Middle East. HF molecules have a higher affinity to the alumina surface when compared to SO₂ molecules that are also contained in the pot gas. When HF molecules diffuse to the alumina surface, SO₂ molecules are pushed off because of the weaker bond to the alumina surface. Because of this phenomenon the system is therefore capable of giving off an early warning about 2–3 h ahead before HF emissions start to exceed normal limits when SO₂ concentration monitoring is added to the individual filter modules. This principle is also described in this paper.