Impact of sodium and sulfur species on agglomeration and defluidization during spouted bed gasification of South Australian lignite

Abstract

Transformations of inorganic elements during steam gasification of a high-sodium, high-sulfur lignite were investigated in a 77 mm i.d. spouted bed reactor. The role of sodium and sulfur in agglomeration and defluidization of the bed material is assessed by analysis of inorganics in the bed char, in cyclone dust, in any agglomerates formed, and in deposits formed at the gas inlet to the reactor. It was found that a sodium disilicate-quartz eutectic was the key species in causing stickiness of the surface of mineral particles within the coal. The present data indicate that sodium and silica from the coal are reacting to form sodium silicate species, which forms the “glue” causing solid ash particles to cohere, initiating particle growth and agglomeration. This finding agrees with a fundamental study conducted by other authors. Sodium−calcium−sulfur eutectics, which have been found by other authors to cause agglomeration for similar coals under combustion conditions in a fluidized bed, were only found to form near the steam−air inlet to the reactor and thus do not play a significant part in agglomerate chemistry under the reducing conditions which exist throughout the majority of the bed under gasification conditions