Influence of shear force and analysis of operating parameters on filter cake stability and deliquoring in a belt filter press

Belt filter press is among those technical set-ups used for mechanical deliquoring of sludge. The purpose of this study is to analyze the effect of operating parameters in the high-pressure zone on the deliquoring performance and cake stability. The investigated operation parameters are the velocity of the belt, the number of pressure cycles together with the exerted pressure, and the quantity of substance. The deliquoring performance is evaluated in terms of final cake dryness and specific throughput, while the stability is defined as the capacity of the cake to suffer a certain level of pressure without an excessive spreading or breaking its structure. Experiments are performed with two different types of sludge. To estimate the effect of each process parameter, different series of experiments are carried out in the high-pressure zone simulation equipment. In each series, only one parameter is modified to isolate the single effect. Other series of experiments are carried out in the high-pressure zone simulation equipment to investigate the re-wetting and to analyse the so-called F factor used to link the experimental result with the specific throughput of a full-scale equipment. Finally, the effect of shear force on the deliquoring performance is studied through the use of a filter press unit cell. The belt speed has an influence on the final dry solid content: a low belt speed produces drier cakes with lower lateral sludge migration on the belt. At low belt speed, pressure is more gently applied to the initial sludge, enabling a slow structuring of the cake and leading to better water release. The number of pressure cycles has an influence on the cake stability which means that the pressure must be gradually increased during the belt filter press to avoid excessive migration. Re-wetting occurs and it has a negative effect on the final dry solid content. The combination of shear and compression force leads to an effective improvement on deliquoring performance.