MODELING OF FOULING AND SLAGGING IN COAL-FIRED UTILITY BOILERS

In a current study, models are under development to predict the impact of ash deposition in a pulverized coal-fired boiler. These models are being incorporated into a coal quality expert software product being developed under a DOE Clean Coal Technology Program. Slagging and foul ing are addressed by two separate submodules that interact with each o ther and with a boiler performance model to account for changes in coa l input properties and boiler operation. The input to these models inc ludes results from detailed analysis of coal mineralogy obtained from computer-controlled scanning electron microscopy, coal size-distributi on data, boiler design details, and boiler operating conditions. The o utput from the models is an assessment of boiler performance associate d with the use of the coal specified in the model. This paper describe s the slagging and fouling algorithms, the rationale used in their dev elopment, and algorithm validation with laboratory, pilot, and field t est data, Submodel validation for slag deposition growth and heat tran sfer was carried out using data from well-controlled, pilot-scale comb ustor testing. Composition of the different layers within the deposit was compared with the model prediction to validate the ash particle st ickiness model. In addition, the measured temporal heat flux profile w as used to check the consistency of the parameters describing the depo sit growth submodel. The fouling submodel was developed using informat ion from a bench-scale drop-tube furnace, along with data from other l aboratory- and pilot-scale studies. The fly-ash particle-size distribu tion, as a function of distance from the deposition tube, was compared for both upstream and downstream deposits in bench- and pilot-scale s tudies.