DUST CAKE DETACHMENT FROM GAS FILTERS

Most forms of barrier filter for particulate removal from gases are cl eaned periodically by administering a short pulse of pressurized gas t o the downstream side. This is intended to remove the dust cake which deposits during filtration. The mechanisms of dust cake detachment fro m both rigid and flexible filter media are considered, with particular reference to the effect of the 'cake loading', the cake mass per unit area of filtration medium. Small-scale experimental methods for the q uantitative determination of the conditions necessary for cake detachm ent are reviewed, and experimental data on cake detachment at ambient temperature are summarized. At low cake loadings (particularly below 3 00 g/m(2)) experiments carried out under conditions of reverse gas flo w and acceleration show different trends: in general, the 'cake detach ment stress' measured in an acceleration test increases with increase in cake loading while the opposite is true for cake detachment by reve rse Bow. At higher cake loadings (about 1000 g/m(2)) the results of th e two methods converge. Cakes are removed much more easily from rigid media than from flexible ones under corresponding conditions. Experime nts on rigid media show that if the cake detachment stress under rever se flow conditions is taken at the first point of significant cake rem oval, (the 'burst pressure'), the resulting values are in good agreeme nt with median detachment stresses obtained by acceleration. It is lik ely that cake removal by reverse flow is influenced by 'hinging' of ca ke patches, which remain loosely attached to the surface after their a pparent detachment stress has been overcome.