Effect of casting parameters on permeability in lower part of blast furnace

Abstract

Maintenance of adequate permeability in the lower zone of a blast furnace is crucial for stable and efficient furnace operation. Permeability in the lower zone is influenced by the changing levels of hot metal and slag in addition to other operational factors. Thus, accumulation of liquids in the hearth and inadequate drainage will lead to deterioration in permeability, thereby limiting wind acceptance and furnace productivity. Therefore, the knowledge of the liquid level in the hearth and factors influencing drainage would be helpful for ensuring high permeability. Effort has been made in the present study to analyse the effect on liquid level of casting parameters such as casting rate (CR), production rate, gun up to knock out time (GKT), slag delay, cast duration (CD) and number of casts (NC). The relationships between casting parameters, liquid level and permeability resistance in the lower zone have been derived mathematically based on material balance. From known casting parameters, the liquid levels have been estimated. The prediction of liquid levels by the model was in good agreement with the furnace data on permeability resistance. In order to maintain high permeability in the lower zone, the optimum values of GKT, NC and CR for different production rates have been suggested to the plant. List of symbolsA Area of hearth, m 2 CD Cast duration, min CP Casting to production ratio CR Casting rate, t min 21 GKT Gun up to knock out time, min H 1 Height of metal and slag when tap hole is closed, m H 2 Height of metal and slag during iron only flow, m H 3 Height of hot metal and slag during iron and slag casting, m H i Height of metal when tap hole is closed, m H s Height of slag when tap hole is closed, m K_Low Permeability resistance in the lower part of the furnace NC Number of casts P Hot metal production, thm day 21 P m Production rate of metal, t min 21 P s Production rate of slag, t min 21 Q m Casting rate of metal, t min 21 Q s Casting rate of slag, t min 21 S Slag rate, kg thm 21 t m Duration of iron only flow, mint ms Duration of combined iron and slag flow, min V s Ascending velocity of slag level, m h 21 r m Density of liquid metal, t m 23 r s Density of slag, t m 23 e Porosity of dead man (0.33) ß

Improvement in casting practice by controlling the drainage rate and hearth liquid level to develop an efficient casthouse management practice in blast furnace

“…This time interval allows building up of the liquid level inside the hearth, however if this time interval is too short, the cast duration will be reduced and would demand more cleaning in casthouse. GUTKO time is always another key parameter and the operational practice of controlling liquid level is developed by standardising GUTKO time [19] as shown in Figure 5.

Figure 3. Effect of increasing the drill bit size on casting rate.

Figure 4. Controlling the average liquid level by increasing the casting duration/cast.

Figure 5. Standardisation of GUTKO time for all the tapholes.

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“…This time interval allows building up of the liquid level inside the hearth, however if this time interval is too short, the cast duration will be reduced and would demand more cleaning in casthouse. GUTKO time is always another key parameter and the operational practice of controlling liquid level is developed by standardising GUTKO time [19] as shown in Figure 5.…”

“…The stable blast furnace operation means maintaining gas permeability [19] in the lower part of the furnace with reduced loss of heat. Here, circuit #3 heat loss is referred to the tuyere zone area or high heat zone.…”