ASH AGGLOMERATION DURING FLUIDIZED-BED GASIFICATION OF HIGH SULFUR-CONTENT LIGNITES

Intensive ash agglomeration has hampered the fluidized bed gasification of lignites from the Elhovo deposit (Bulgaria) containing 5.9 wt% sulphur in the dry state. Samples of slag and agglomerates from the pilot plant have been examined by means of chemical, X-ray analysis, IR spectroscopy and scanning electron microscopy. Pyrrhotite (FeS) and wustite (FeO) have been established in the agglomerates, where junctions between ash particles have been found to consist of magnetite, spinel and garnet grains. The chemical reactions leading to garnet formation have been studied. Centres of sintering and centres of melting during the ash agglomeration process have been distinguished. The pyrite product, an eutectic of FeS and FeO melting at 924-degrees-C, is assumed to be responsible for the cessation of lignite gasification with steam and air under pressure at a bed temperature of 930-degrees-C.