The UK Collaborative Research Programme on Slagging Pulverised Coal-Fired Boilers: Summary of Findings

Abstract

A major UK collaborative research programme to address all aspects of slagging in bituminous coal-fired boilers has recently been completed. The 3 1/2-year programme comprised an integrated package of full-scale plant trials; rig and laboratory-scale tests; coal, flyash, and deposit characterisation by Computer Controlled scanning Electron Microscopy (CCSEM); and the development of computer models. The major findings are presented in this paper.

It is concluded that the key to the behaviour of ash deposits lies in understanding their consolidation by a viscous flow sintering mechanism. For UK coals, iron and calcium (derived from pyrite and calcite respectively) are the main fluxing elements that affect ash viscosity and it is, therefore, the degree of assimilation of these elements into the aluminosilicate glass that ultimately determines the slagging characteristics of the coal.

CCSEM can be used to quantify the mineral matter distribution in coals and a novel slagging index based on CCSEM analysis that takes account of the effectiveness of the fluxing elements present, in particular the pyrite-derived iron, is proposed. A methodology for studying the ash deposition characteristics of coals using a laboratory-scale Entrained Flow Reactor (EFR) has also been established. CCSEM analysis of deposits formed in the EFR shows the potential for coalescence and provides the basis for an alternative slagging index.