Dust Deposition from Chimney Stacks

Abstract

Economic competition compels many firms to operate processes which emit gases carrying a dust burden many thousand times that of atmospheric air. Even after treatment in the most expensive deduster this effluent will still hold some 5 per cent of its original dust, so that it must be discharged up a tall chimney. Wind eddies then dilute the chimney gases until they can be tolerated at ground level; however, during dilution the coarser dust is liable to settle and cause objectional deposits in the vicinity. The problem of designing an installation to avoid nuisance is therefore to remove the coarser grits in a deduster and to arrange the stack to dilute the finer residue so that deposits will not be noticed. The authors have developed a set of reasonably simple formulae and charts for predicting the path of particles emitted from a stack and spread by the wind. Experimental checks have been applied to the predictions, but the subject is complex, and at this stage it is unlikely that it will be possible to predict the rate of deposit within a factor of 2. In order to illustrate the implications of the paper a worked example is given on a powdered-coal boiler installation. This shows that with properly designed cyclones and a moderately high stack there will be no noticeable deposits. The implication is that it should be possible in time to extend the treatment given in the paper to specify a deduster exit which will avoid nuisance with fair certainty and at a relatively moderate cost.