Fouling in a 160 MWe FBC boiler firing coal and petroleum coke

The 160 MWe fluidized bed combustor (FBC) boiler owned and operated by the Tennessee Valley Authority (TVA) has recently been co-fired with coal and petroleum coke (up to 50%). However, it has suffered some fouling problems. On examination of the deposits it became clear that, in only a few cases could the fouling be partially attributed to alkali metals, and even in those cases the primarily limestone-derived materials were almost quantitatively sulphated to a level which was sufficient to cause strength development by itself. In other cases, it appeared that the fouling mechanism was carbonation of the free lime component of the deposit followed by sulphation. Finally, in a few deposits which were less sulphated than bed materials and fly ash, strength development appeared to have occurred by conversion of the free lime in the deposits to Ca(OH)2, followed by carbonation. This type of agglomeration has not been reported previously in a FBC.