Nanosized powders are becoming widely used in powder processing techniques, and especially in Spark Plasma Sintering, thanks to their high potential for the production of materials with outstanding mechanical properties and advanced components. Some examples are the high surface area components used in supercapacitors, rechargeable batteries and gas absorbers. Nanopowders are nevertheless very prone to agglomeration issues, which lead to the formation of hierarchical porous structures and non-uniform densification. A combined analytical and FEM model for the study of shrinkage kinetics and mechanical properties of agglomerated powders is proposed. Both densification kinetics and mechanical properties are derived as functions of the different-size porosities, and tools are developed to individuate the optimal thermal regime to achieve in-situ de-agglomeration. Comparisons with experimental data are provided.