Doctor of Philosophy
Department of Materials Engineering
Nightingale, Robert John, The development and application of hearth voidage estimation and Deadman Cleanliness Index for the control of blast furnace hearth operation, Doctor of Philosophy thesis, Department of Materials Engineering, University of Wollongong, 2000. http://ro.uow.edu.au/theses/1522
The lower part of the blast furnace contains a coke bed, which is of fundamental importance to the process and its stability. The properties of this bed are determined the qualities of the coke lumps charged to the process, their response to the harsh furnace environment and the deposition of debris particles generated within the system. The coke bed may also retain solid slag residues or kish graphite.
Accordingly, the properties of the coke bed, particularly its permeability to fluids, dynamically in response to operational changes. The present work is the first attempting to find methods for the routine monitoring of these critical process dynamics.
A method for estimating the hearth coke bed voidage in the plane of the taphole has been developed which employs data routinely collected in the course of furnace casting operations. It is shown that casting practice itself can influence this voidage due to ability of high buoyancy forces, as experienced by coke particles in an iron bath, to cleanse the coke bed of small particles when the iron bath height is high.
The Deadman Cleanliness Index (DCI) has been developed for routine monitoring of the status of the coke bed in this crucial region. Calculation of this index relies on fact that metal dripping through the deadman coke bed does not generally reach chemical equilibrium with the bed. Accordingly, the degree of departure from saturation with carbon is influenced by the permeability of the bed and provides one basis for estimating the bed's cleanliness. This is reinforced by a term recognising the risk associated when insufficient superheat is available to the dripping slag phase, which must also percolate through the bed.
Several operational and raw material influences on deadman cleanliness have been identified. Practical process improvement strategies for stable operation and long lining life based on these learnings are presented and discussed.