Various sections of the hearth will show different wear mechanisms and have a different life expectancy. Most likely, wear of the taphole (s) is more severe than the bottom, and (local) interim repairs permit safe campaign extension. Of all known attack mechanisms, water damage and carbon deposition caused by CO disintegration appear to be the most dangerous attack mechanisms. To obtain a good impression of wear progress, installing a large array of thermocouples (200 to 256) in critical locations and making regular "hearth health" review reports is suggested. These reports should primarily be based on TC analysis, but all other relevant information regarding hearth condition should be reviewed as well. The results should be compared with and verified by thermal computer models, with specific emphasis on the tuning of the boundary condition of the models. The nonlinear effects of the formation of a brittle zone will usually make any thermocouple analysis and computer model calculation unreliable. We recommend also performing a series of core drillings into the hearth sidewall when the life of the hearth exceeds a certain age, and when the presence of a brittle zone must be verified. Each individual hearth design should set up a well-defined "extension strategy" by defining maximum temperature limits of individual thermocouples and safe distances of solid material with a temperature below 450 deg C. Further management of a hearth must be done by translating these limits into operational action plans and even repair projects. If the general condition of the hearth and or the taphole has become worse because of progressive wear and the predefined wear or temperature limits are exceeded, a number of technologies are available to repair the hearth from the outside, while leaving the burden inside. Usually this is done for tapholes, but similar repairs can also be done in the lower "elephant foot" areas. The installation of high conductivity graphite directly against the shell in these areas greatly improves the life expectancy and reduces operational risks during the remaining years of the campaign.
展开▼
