A system includes a solid feed pump having a housing, a rotor disposed in the housing, a curved passage disposed between the rotor and the housing, a solid feed inlet coupled to the curved passage, and a solid feed outlet coupled to the curved passage. Also, a solids packing device is coupled to the solid feed inlet of the solid feed pump. The solids packing device includes a first channel configured to receive a solid feed with a first range of sizes, a second channel configured to receive transport assisting particles (TAP) with a second range of sizes. The first range is different from the second range. A third channel is configured to receive and mix the solid feed and the TAP to provide a solid feed-TAP mixture with the TAP filling interspatial spaces between the solid feed. The third channel is coupled to the solid feed inlet.