Ash Deposition as a Function of Coal Type, Location in a Boiler, and Boiler Operating Conditions: Predictions Compared To Observations

A mechanistic model of ash deposition is compared with pilot- and utility-scale experiments. The model is based on the transformations of mineral species in coal during transport of particles through an arbitrary combustion environment. Quantitative model predictions include the elemental 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. Comparisons of model predictions with experimental results at pilot and utility scales are presented. A three-week utility test burn of a Wyoming (Hanna Basin) coal in a boiler designed for midwestern and eastern coal is described. The test burn occurred in the tangentially fired boiler of a 600 MWe power plant located in illinois. Data acquired from the test bum include deposit accumulation rate, strength and morphology, removability, emissivity, and elemental composition. Deposit samples were collected during and after the test burn for comparison with model predictions. Ash deposit removability, as indicated by soot blower effectiveness, was monitored during the test burn. Deposit strength is indicated by friability of deposits collected during a boiler inspection following the test bum. Deposit emissivity was qualitatively determined by monitoring the furnace exit gas temperature. Similar data are also reported from the Sandia multifuel combustor, a pilot-scale facility. Experimental observations and data are compared with model predictions. Deposits from the Wyoming coal were observed to accumulate at about the same rate as those from the fuel used previously in this boiler. The deposits from the Wyoming coal were granular and friable (had little strength). They were easily removed from boiler heat transfer surfaces by normal soot blowing practices. They were light colored and highly reflective. All of these qualitative trends are consistent with model predictions. The measured elemental composition of the ash deposits from the Wyoming coal is within approximately 5 % (absolute) of the predicted composition.