PROCESS FOR REMOVING HYDROGEN FLUORIDE FROM GASES CONTAINING IT

摘要

1486871 Hydrogen fluoride removal VEREINIGTE ALUMINIUM WERKE AG and METALLGESELLSCHAFT AG 22 Jan 1975 [24 Jan 1974] 2882/75 Addition to 1474215 Heading C1A [Also in Division C7] In a process for the removal of hydrogen fluoride from exhaust gases of electrolytic aluminium production, by introducing the gases into a fluidized bed reactor containing solid absorbent for HF such that the solids concentration in the expanded fluidized bed decreases upwardly and from which the absorbing solids are discharged upwardly and subjected to solid-gas separation by elastrostatic precipitation, the improvement comprises removing solid impurities from the gases in an additional electrostatic precipitatior before introduction into the reactor. In one embodiment (see Figure), the crude gas is conditioned with water in chamber 1, and a major part of dust impurities are separated in precipitator 3 and fed to pyrohydroylsis furnace 5, from which the purified gas flows into fluidized bed reactor 7 and is contracted with alumina absorbent 8 to which water is added via conduit 9. The gassolids mixture passes into a second electrostatic precipitator 12 which is divided into several electric fields. Pure gas leaves the electrostatic precipitator 12. The fraction of separated solids having the lowest impurity content is withdrawn from dust-collecting bin 13, and heat-treated in rotary kiln 17, and can then be fed to the electrolytic bath. The majority of dust collected in precipitator 12 is discharged from dust-collecting bins 14 and returned to fluidized-bed reactor 7. The expelled gases from pyrohydrolysis furnace 5, containing mainly HF are fed to fluidized-bed reactor 7 together with the exhaust gases from the rotary kiln 17.