In many metal making processes, such as for example, steelmaking processes, water-cooled lances are inserted into a furnace vessel. In the steelmaking environment, a lance may be inserted into a basic oxygen furnace (BOF), electric arc furnace (EAF), etc., to promote melting, decarburization, refining and other processes useful in converting iron-containing scrap material within the vessel into steel. A typical lance may inject gaseous materials such as oxygen, hydrocarbon gas and/or inert gas at high velocity at various times to achieve desired treatment of the scrap metal and/or maintenance of the interior of the vessel. Some lances may also inject particulate carbon and/or lime (or similar substances) to achieve desired properties in the metal ultimately produced.
Water-cooled lances generally comprise an adapter portion, an elongated barrel portion connected at a first end thereof to the adapter portion and lance tip portion connected to a second end of the barrel portion.
The adapter portion comprises at least one inlet for receiving the gaseous and/or particulate matter to be injected into the furnace vessel, which matter will hereinafter be generally referred to as “active material.” The adapter portion also includes a water inlet and a water outlet for circulating pressurized cooling water throughout the lance.
The barrel portion comprises at least three substantially concentrically arranged metal, typically steel, pipes for communicating the cooling water and/or active material(s) between the adapter portion and the lance tip portion. The outermost and first innermost pipes normally define an annular water return passageway for conveying coolant water from the lance tip portion to the adapter portion. The first and second innermost pipes normally define an annular water delivery passageway for conveying coolant water to the lance tip portion from the adapter portion. And, the interior of the second innermost pipe (and any additional pipes arranged concentrically interiorly thereof) defines at least one passageway for conveying active material from the adapter portion to the lance tip for injection into the furnace vessel.
The lance tip portion usually comprises an assembly having one or more parts which may be secured by welding, soldering or the like to the concentric pipes of the barrel portion. The lance tip assembly comprises at least one nozzle in communication with the at least one active material passageway of the barrel portion for injecting or discharging the active material into the furnace vessel. The tip assembly further comprises passage means for connecting the water delivery and return passageways of the barrel portion to one another. So constructed, water or other coolant fluid may be continuously circulated through the lance to cool the lance, especially the lance tip assembly which is exposed to the greatest temperatures during lance operation. Indeed, if coolant water is not effectively conveyed through the lance tip portion then the assembly may become non-uniformly heated. This, in turn, may lead to so-called “hot-spots” or “burn-through” sites which often result in premature failure of the lance tip. Examples of lances including systems and methods for detecting potential lance tip burn-through prior to the occurrence of burn-through or automatically responding in the event of failure are found in U.S. Pat. Nos. 6,599,464 and 4,533,124 and German Offenlegungsschrift DE 3543836. Among these, U.S. Pat. No. 6,599,464 describes an assembly where a temperature sensor is received within a post disposed in a sealed chamber behind the working face and in front of the inner face of the lance tip.
Another type of lance failure may occur when slag is “ingested” by the lance. Slag may be ingested through lances nozzles in either of two ways: “blow-back” and flow interruption. Blow-back is the reaction of the burner flame bouncing from the scrap onto the burner housing and possibly into inactive burner ports when a metal making lance is functioning in a burner mode (if a particular lance is equipped to function as a burner). Blow-back can carry furnace slag into the inactive ports or nozzles of the lance tip. Slag ingestion may also occur as a result of a gas flow interruption when the ferrostatic pressure differential of the slag/steel emulsion surrounding the lance/burner forces the slag into the lance nozzles.
In either case, ingested slag can lead to catastrophic lance failure if it is not quickly detected. When high velocity oxygen gas flow through the lance is restarted, potentially explosive conditions can arise at the inner wall of the lance tip. Sources of heat, oxygen and fuel must be simultaneously present for dangerous spontaneous combustion to occur within a lance assembly. This confluence of circumstances happens when slag has been ingested by a lance and a flow of oxygen comes into contact with the slag such as when the lance is refining the metal within a furnace vessel. The ingested slag (which may typically range in temperature from about 2300° F. and 3000° F. depending on the elapsed heat time) provides the heat. The oxygen provides an oxygenating atmosphere and the copper or carbon in the copper or steel inner wall of the lance tip provides a source of combustible fuel. When the copper or carbon begins to combust in the highly oxygenated environment, the lance tip inner wall is consumed. If the process is not quickly detected and the oxygen gas flow stopped, a burn-through occurs, thereby resulting in an violent coolant water breach that may cause severe damage not only to the lance but the surrounding furnace vessel and equipment as well.
An advantage exists, therefore, for a system and method for rapidly and reliably detecting the ingestion of slag within a metal making lance tip.
A further advantage exists for a system and method for immediately and automatically ceasing oxygen-containing gas flow through a metal making lance upon detection of the ingestion of slag within the lance tip.