Assessment of the State of the Blast Furnace High Temperature Region by Tuyere Core Drilling

Abstract

Tuyere core drillings give a unique opportunity to probe the blast furnace and detect changes in both physical and chemical conditions of its high-temperature region. In this paper the findings from drill cores taken from a blast furnace are used to characterize the internal state of the furnace hearth, quantified by an erosion model estimating the available hearth volume. The complex relation is studied by entertaining neural network models using different combinations of inputs consisting of the extent of the distinct tuyerelevel zones (raceway, bird's nest, dead man, etc.) of the core samples. The resulting model can be used to gain knowledge of the relation between tuyere level conditions and hearth states, and to classify the findings from future core drillings. The results also throw light on possible reasons for thermal cycles observed in the hearth of the furnace studied.KEY WORDS: tuyere core drillings; blast furnace; hearth state; neural network pruning. 203© 2009 ISIJ ternative, tuyere core drillings have been used at many plants since the 1990's 5-7) : A steel pipe is drilled into the furnace through an opened tuyere at a stoppage, and the pipe with its core filled with the bed is withdrawn, quenched and opened for analysis. Typically, the length of the distinct regions, the particle size of the coke, the metallurgical and mineralogical state of the materials and the presence of iron and slag in the sample are analyzed.Tuyere drillings are performed regularly at Rautaruukki's two blast furnaces during shorter stoppages.9) The sample tubes are 5.5 m long and the withdrawn core has a diameter of 205 mm; typically, the core length is shorter than the maximum drill penetration, l max , into the bed due to compression of the core. The drill penetration, in turn, depends on the physical state of the dead man. After drilling, the core samples are analyzed physically and chemically. In the present work, the modeling effort is focused on the lengths of the different sections identified in the drill core (cf. Fig. 1). Based on the characteristics of the sampled coke and iron, the core is divided in to six regions (with the corresponding number given in parentheses): (1) bosh, (2) flame, (3) raceway, (4) bird's nest, (5) iron agglomerate, and (6) dead man, and their lengths l i (iϭ1...6) are recorded. The difference between the maximum penetration of the drill and the total core length, l c ϭ∑ 6 iϭ1 l i represents the total compression of the sample, Dlϭl max Ϫl c . These lengths from twenty two drill core samples from one of the Rautaruukki furnaces were used for modeling (cf. Table 1). Figure 2 shows a photograph of a core with the different regions indicated. Lining Temperatures and Heath VolumeThe internal state of the furnace hearth can be assessed on the basis of refractory temperatures measured by thermocouples in the hearth bottom and sidewall lining. These temperature measurements can be used to estimate the remaining thickness of the lining and also formation of buildup material (skull) on the hot fa...

Model for Fast Computation of Blast Furnace Hearth Erosion and Buildup Profiles

“…The model has been applied to study the evolution of the hearth erosion and buildup processes in three industrial furnaces, and the results have been found to agree reasonably well with observations in the operation and with the furnace hearth states found at midcampaign repairs. In a forthcoming work, the results of the model will be used for throwing light on the complex interaction between hearth liquid flow patterns, dead-man state, 14 and erosion/buildup formation. Literature Cited…”

Numerical Estimation of Hearth Internal Geometry of an Industrial Blast Furnace

“…Several earlier investigators have reported similar findings. [9,[16][17][18] It is believed that the coke and coal rate have a crucial influence on permeability (especially in the center zone) and floating of the deadman and thus impose a strong influence on the bottom temperature. In particular, a lower coke rate leads to higher burden density and gravity forces, which Skull [9,10,28] 0 0 2.0 facilitate a sitting deadman in the hearth where the flow velocities and temperature at the bottom are low.…”

GA-PARSIMONY: A GA-SVR approach with feature selection and parameter optimization to obtain parsimonious solutions for predicting temperature settings in a continuous annealing furnace

“…Developing parsimonious models presents a promising approach [7][8][9][10]. According to the parsimony criterion, the model with the least complexity that performs with similar accuracy is always preferred.…”