Investigations on the caking behaviour of bulk solids—macroscale experiments

Abstract

The storage of bulk solids is often a neglected process step in many industries like chemical, pharmaceutical, and food industries. It is of great importance that the bulk solids do not solidify partly or completely, even after a long storage time. If the bulk solid cakes, then machinery, manpower, and time are needed for deagglomeration of these unwanted agglomerates, adding costs to the customer. Mechanisms that induce caking are, for example, liquid bridge formation, sintering, cohesion, adsorption, crystallisation, and/or deformation. The caking of bulk solids is mainly influenced by storage conditions like humidity, temperature, storage time, and the stress that acts on the bulk solid during storage. The influence of these storage conditions can be investigated in macroscale experiments, among others, either with a Schulze ring shear tester or a uniaxial test. In this paper, a uniaxial consolidation test is used for measuring the unconfined failure strength. To simulate real storage conditions, the material is placed in a climatic chamber at different–but constant–humidity, temperature, and stress levels during different consolidation times. The porous material of the cylindrical container ensures a homogenous humidity and temperature level in the whole sample. After this consolidation, the unconfined failure strength of the caked sample is determined with a material testing machine. The results for ammonium chloride are presented.