Modelling of fouling and slagging in coal-fired utility boilers

Abstract

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 fouling are addressed by two separate submodules that interact with each other and with a boiler performance model to account for changes in coal input properties and boiler operation. The input to these models includes results from detailed analysis of coal mineralogy obtained from computer-controlled scanning electron microscopy, coal size-distribution data, boiler design details, and boiler operating conditions. The output from the models is an assessment of boiler performance associated with the use of the coal specified in the model. This paper describes the slagging and fouling algorithms, the rationale used in their development, and algorithm validation with laboratory, pilot, and field test data. Submodel validation for slag deposition growth and heat transfer was carried out using data from well-controlled, pilot-scale combustor testing. Composition of the different layers within the deposit was compared with the model prediction to validate the ash particle stickiness model. In addition, the measured temporal heat flux profile was used to check the consistency of the parameters describing the deposit growth submodel. The fouling submodel was developed using information from a bench-scale drop-tube furnace, along with data from other laboratory- and pilot-scale studies. The fly-ash particle-size distribution, as a function of distance from the deposition tube, was compared for both upstream and downstream deposits in bench- and pilot-scale studies.