The mechanical wear of tuyere refractory and stirring plugs in BOF steelmaking

University dissertation from Luleå : Luleå tekniska universitet

Abstract: Water modelling investigations of pressure change at tuyere tip or back attack and wear of H3B03 disks, as well as high temperature modelling wear tests of BOF refractory using single- or double-tuyere and Ar or N2 gas, have been carried out to study mechanisms for mechanical wear of the refractory for BOF stirring tuyeres and plugs. A new nominal Mach number, M'', was defined and adopted as the criterion for correlating test data. Both the back attack frequency and the Wr, wear rate of H3B03 disks, increase with M'' at M''<1, reach the maximum near M''=1 and start to decrease after M''>1. The wear rate, Wr, of MgO-C bricks tested using steel at 1550°C depends strongly on tuyere characters and increases with M'' until M''=l, similar to the trends for the back attack and disk Wr. Another brick wear parameter, the radius of deep wear area, RDA, displays a behaviour similar to that of the Wr. The estimated refractory wear rate, Wr', at M''<_1 can be related to mM'', the defined nominal momentum rate from tuyere gas injection. The RDA measured from single-tuyere tests can be used to estimate influences of tuyere interaction on the refractory wear rate. When the DTC, the distance between tuyeres for a double-tuyere test, is less than twice the RDA, values of Wr are increased. The refractory wear rate will no be influenced with DTC>2RDA. Tuyere gas flowrate can also be reduced to diminish the interaction. Equations are derived, based on proposed bubble expansion wear mechanism, to compute values of estimated RDA, as well as RSA (Radius of Shear wear Area), at M''<_1 which can be used to eliminate detrimental effects of tuyere interaction and for the plug design. The M'' values for tuyeres should be either less than 0.5 or greater than 1.5 and values of mM'' should be low to reduce the refractory wear for the stirring tuyeres and plugs in BOF steelmaking. A smaller tuyere inner diameter sets the maximum wear parameters to a lower level and can be chosen to decrease the wear, without decreasing the gas flowrate.

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