Preventing Ash Agglomeration during Gasification of High-Sodium Lignite

Various additives were evaluated to assess their ability to prevent ash agglomeration during the gasification of high-sodium lignite. Additives that showed promise in simple muffle furnace tests included meta-kaolin, vermiculite, two types of silica fume, and one type of bauxite. Additives that were tested and rejected included dolomite, calcite, sand flour, kaolinite, fine kaolin, and calcined bauxite. Based on the muffle furnace test results, the meta-kaolin was selected for a follow-on demonstration in a pilot-scale coal gasifier. Pilot-scale testing showed that the addition of coarse (minus 14-mesh, 920-mu m mean size) meta-kaolin at a feed rate roughly equivalent to the ash content of the lignite (similar to 10 wt%) successfully prevented agglomeration and deposition problems during gasification of high-sodium lignite at a maximum operating temperature of 927 degrees C (1700 degrees F).