Described below is a method for non-contact determination of a temperature T of a metal melt in a furnace having at least one burner-lance unit, which is fed above the metal melt through a wall of the furnace in a furnace chamber, by a temperature measurement unit assigned to the at least one burner-lance unit. Also described is a device for non-contact determination of a temperature T of a metal melt in a furnace, wherein the device includes at least one burner-lance unit which is fed above the metal melt through a furnace wall of the furnace into the furnace chamber. Also described is a furnace, especially an arc furnace, with such a device.
Furnaces for producing and/or accommodating metal melts are in general use in the steel industry. This type of furnace can generally typically involve an arc furnace, a ladle furnace, a degassing plant or another secondary metallurgy plant. In the production of steel it is important to find out at any given point in time about a temperature of the metal melt. This can be done by contact-based measurement, as a rule by manual temperature measurement and sampling via a lance, or via a non-contact measurement based on electromagnetic radiation emitted by the metal melt.
A device for continuous non-contact measurement of the temperature of a metal melt in a furnace is known from EP 1 440 298 B1. This is equipped with a heat analysis instrument disposed in a lance, which blows inert gas against a surface of a slag located on the metal melt in the furnace or container.
A device for optical analysis of a metal melt in a furnace is known from WO 2004/083722 A1. The device includes a lance with an exit opening for a coherent gas flow which is directed onto the metal melt, a viewing window on the lance which is arranged such that optical data can be captured along the direction of propagation of the coherent gas flow and also an analyzer and a transmitter for transmitting the optical data to the analyzer.
Burner-lance units are also known, which form a combination of a burner and a lance, with such a unit able to be operated in burner mode or in lance mode.
Metallurgical furnaces, especially arc furnaces, generally have burners installed on the furnace wall directed towards the surface of the metal melt in the furnace chamber in order to introduce energy into the metal melt or in order to accelerate the melting process in the furnace. A flame is generated from such a burner in burner mode. In such cases fuel, especially natural gas, oil and such like is burned by mixing it with a combustion gas containing oxygen.
Lances are usually introduced into the furnace chamber locally and frequently only for a restricted time, in order to supply gas for example, such as oxygen for freshening the metal melt, for performing measurements or for taking samples.
As with a known burner, with a burner-lance unit as well, when it is operated in burner mode a flame is generated and energy is introduced into the furnace chamber. The burner-lance unit can however be used a lance, via which a gas flow is blown into the furnace chamber and measurements can be taken at the metal melt, after burner mode is switched off, i.e. the flame is switched off. For this purpose, in addition to the connections for fuel and combustion gas present on a known burner, gas connections for at least one gas to be blown in, in lance mode, are present on a burner-lance unit. The use and modification of a known burner to a burner-lance unit, such that the unit can also be used as a lance, thus means that no additional expense is incurred and no space is required for additional devices.
In lance mode the inside of the burner-lance unit can be used to carry out a temperature measurement on the metal melt by a temperature measuring unit in the furnace chamber. In particular in this case gas to be blown in, in lance mode, is injected at supersonic speed into the furnace chamber in the direction of the metal melt in order to blow away slag forming on the metal melt and expose the surface of the metal melt locally for non-contact temperature measurement. In order to generate a flow of gas at supersonic speed, the burner-lance unit especially features a Laval nozzle in which the gas to be blown is injected at pressure of a few bar.
Standard operation of a metallurgical furnace with at least one burner-lance unit thus usually consists of the following processes:
During the charging of the material to be melted into the furnace chamber the burner-lance unit is operated with a protective flame in order to keep the opening of the burner-lance unit directed towards the furnace chamber free. Subsequently the burner-lance unit is operated in burner mode and the power is increased in stages in order to assist melting of the material in the furnace chamber. As soon as a sufficient amount of metal melt is present, the burner-lance unit is switched over into lance mode and oxygen or gas containing oxygen for freshening the metal melt is injected at supersonic speed into the furnace chamber. During lance mode the protective flame which surrounds the injected gas flow usually continues to burn. As soon as the furnace can be discharged, i.e. the furnace chamber can be emptied, the gas flow is switched off, the burner-lance unit continues to be operated with the protective flame being formed, and the metal melt is removed. Standard operation now begins again with the charging of material to be melted into the furnace chamber.
To carry out non-contact temperature measurement on the metal melt formed, a burner-lance unit can have at least one temperature measurement unit assigned downstream from it, which is arranged close to the end of the burner-lance unit facing away from the metal melt. In this case the temperature is measured for example via a central opening in the burner-lance unit which extends along a longitudinal axis of the burner-lance unit through the latter and through which the electromagnetic radiation emitted by the metal melt can be detected.
It has been shown however that a burner-lance unit cannot readily be used in the standard operating mode described above for non-contact temperature measurement. This is because interference influences are present during burner mode as a result of the inherent radiation of the flame, which lead to incorrect measurement of the temperature T of the metal melt. During lance mode in which, in standard operation, oxygen or gas containing oxygen is injected into the furnace chamber, the oxygen is burnt exothermally in the furnace chamber, so that interference influences are also present here as a result of the combustion process, which lead to an incorrect measurement of the temperature T of the metal melt.