Pressure agglomeration in solids processing— fundamentals and recent developments

Abstract

Pressure agglomeration is a commonly used process to produce larger compacts of defined size, density and also of a more or less uniform shape, depending on the equipment type used. Size enlargement is based on the densification of the bulk material. The control of the agglomerate and bulk density allows to improve the storage and handling characteristics and also to control stability and dispersibility via a defined surface area and porosity. Compared with other agglomeration processes the size enlargement by pressure agglomeration is caused by the application of external mechanical forces to the solid bulk material, which has been filled into a press die or press channel before. Particle binding is then due to different mechanisms, in certain cases additionally supported by binding agents or thermal treatment. A principal distinction of pressure agglomeration processes can be made with respect to the magnitude of the applied forces and the pressing rate or impact velocity, both having a significant effect on the resulting agglomerate density and the mechanical strength. In the first part of this review theoretical and experimental aspects of the process principles within pressure agglomeration are discussed in order to point out the effect of the various solid feed material properties and different process parameters on the agglomerates’ technological properties relevant to their utilization. This also involves a short discussion of the diverse measuring techniques applied. In the second part recent developments and special applications in pressure agglomeration are discussed, in particular referring to the compaction of different types of biomass as a renewable resource for the production of biofuels and other bio-based products, the recycling of metal-bearing residues and by-products in the form of agglomerates with defined characteristics to be used in metallurgical processes, and as special cases the application of high velocity impact forces as applied in the compaction of metal powders and large compact densification within the pre-treatment of coal in metallurgical cokemaking.