Measuring temperature of the atmosphere in the steelmaking furnace

The paper presents a measurement of temperature in a steelmaking furnace with an oxygen refining process, specifically in a tandem furnace. Knowledge of the temperature is important for optimizing the manufacturing process and extending of the life cycle of the inner furnace lining. Conditions in the furnace are very demanding; the temperature may temporarily exceed 2000 °C and exhibits changes of 60 °C s−1. The atmosphere in the furnace is mainly oxidizing and its chemical composition is very variable. In the atmosphere there are also present liquid and solid compounds which act chemically and abrasively on the lining and on the sensor. These conditions make it impossible to use a suction pyrometer, contactless optical or acoustic measurement methods. It was decided to use a thermocouple in a protective tube. The sensor was inserted into the furnace through a steel bushing with water cooling. For the first measurement the type B thermocouple in Al2O3 protective tube inside an outer shielding tube made from SiC was used. The second sensor used the type C thermocouple in a special thick-walled protective tube made from sintered SiC. The sensor does not measure the temperature of the gas itself, since it is affected by radiation of the surrounding areas. Conditions for heat transport from the furnace to the sensor are variable and difficult to determine; therefore, the accurate identification of the atmosphere temperature is not possible. Limit values of the temperature interval of the atmosphere were determined, for hypothetical cases of athermanous and ideally diathermic atmospheres.