A MECHANISTIC DESCRIPTION OF ASH DEPOSITION DURING PULVERIZED COAL COMBUSTION - PREDICTIONS COMPARED WITH OBSERVATIONS

A mechanistic model of ash deposition is based on the transformations of mineral species in coal during transport of particles through an ar bitrary combustion environment. Quantitative predictions include the e lemental composition of boiler ash deposits as a function of location, operating conditions and coal type. Qualitative predictions relating to practical aspects of boiler operation are also included. Model pred ictions are compared with experimental results at pilot and utility sc ales. A three-week test burn of a Wyoming coal in a power plant boiler designed for midwestern and eastern coal is described. Data reported include deposit accumulation rate, strength, morphology, removability, emissivity and elemental composition. Similar data are also reported for the Sandia multifuel combustor, a pilot-scale facility. Deposits f rom the Wyoming coal accumulated at about the same rate as those from the fuel used previously. The deposits from the Wyoming coal were gran ular and friable. They were easily removed from boiler heat transfer s urfaces by normal soot blowing practices. They were light-coloured and highly reflective. All these qualitative trends are consistent with m odel predictions. The measured elemental composition of the ash deposi ts from the Wyoming coal is within approximately 5% (absolute) of the predicted composition.