INFLUENCE OF ASH DEPOSIT CHEMISTRY AND STRUCTURE ON PHYSICAL AND TRANSPORT-PROPERTIES

Boiler ash deposits generated during combustion of coal, biomass, blac k liquor, and energetic materials affect both the net plant efficiency and operating strategy of essentially all boilers. Such deposits decr ease convective and radiative heat exchange with boiler heat transfer surfaces. In many cases, even a small amount of ash on a surface decre ases local heat transfer rates by factors of three or more. Apart from their impact on heat transfer, ash deposits in boilers represent pote ntial operational problems and boiler maintenance issues, including pl ugging, tube wastage (erosion and corrosion), and structural damage. T his report relates the chemistry and microstructural properties of ash deposits to their physical and transport properties. Deposit emissivi ty, thermal conductivity, tenacity, and strength relate quantitatively to deposit microstructure and chemistry. This paper presents data and algorithms illustrating the accuracy and limitations of such relation ships. (C) 1998 Elsevier Science B.V. All rights reserved.