Heating – Heating or heat retaining work chamber structure
Reexamination Certificate
2000-02-09
2001-05-22
Lu, Jiping (Department: 3749)
Heating
Heating or heat retaining work chamber structure
C432S248000, C432S252000, C266S280000, C266S286000
Reexamination Certificate
active
06234790
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a refractory wall structure for a furnace, in particular for a metallurgical furnace, such as for example a blast furnace with a high process temperature during operation, which wall structure is subjected to a high thermal loading, comprising
a steel outer wall,
a refractory lining consisting of one or more layers of a well heat-conducting material on the inside of the outer wall, and
means for cooling the refractory wall structure.
BACKGROUND OF THE INVENTION
With the wall structure of this furnace, the refractory lining is exposed to a high temperature. As a consequence of this, considerable wear of the refractory lining occurs and its service life is reduced. At the state of the art the reference temperature is kept low by cooling and attempts are made to keep the interior temperature low by using refractory materials with a high heat conductivity, such as graphite, semi-graphite or other refractory materials containing graphite. The means for cooling the refractory wall structure can consist of means on the outside of the steel wall, such as for example spray-cooling, air-cooling or cooling ducts for fluid coolants, or of other means on the inside of the steel wall such as for example water-cooled cooling elements such as stave coolers or cooling plates which are generally made from copper.
SUMMARY OF THE INVENTION
The object of the invention is to reduce the wear of this wall structure and to improve the service life.
The object of the invention is also to create a repair process for the refractory wall structure of a furnace which prolongs the service life.
With the invention this is achieved because the wall structure also comprises a permanent, well heat-conducting metallic filling in a gap in the refractory wall structure, which filling has been molten inside the gap and then after solidifying forms a low heat resistance across the gap.
The invention relies on the notion that the gaps which inevitably occur or form in the refractory wall structure which is always of a composite nature, form considerable heat resistances for the flow of dissipating heat passing through, so that the interior temperature of the refractory lining remains high. The filling, which in molten state has a close thermal contact with the gap walls, which contact remains unchanged following solidification, and the good heat conductivity of the material of the filling, together provide a low heat resistance across the gap, so that the interior temperature of the refractory lining falls. In certain cases, a layer such as slag can even solidify onto and build up on the inside. This results in a permanent, wear-resistant layer.
In WO95/22732 a construction of a wall lining for a furnace is described in which high thermal conductivity elements extend from a cooled metal outer shell into a refractory lining. These elements may themselves consist of a refractory material of which the pores have been impregnated with a metal. This patent application does not deal with the reduction of heat barriers which are formed by gaps between refractory bricks or between elements and refractory bricks.
Preferably the gap with a good heat conducting metallic filling is a gap in the refractory lining, or a gap between the steel outer wall and the refractory lining, or, if the means for cooling the refractory wall structure are water-cooled copper cooling elements, a gap between the refractory lining and a cooling element. A gap in the refractory lining can be a gap between two layers of the refractory lining, or a gap between two elements such as blocks or bricks of the refractory lining, or a gap such as a heat crack in the material of the refractory lining. The most effective are fillings in gaps which lie at right-angles to the flow of heat, so that the heat resistance for the heat dissipation is reduced.
The melting temperature of the metallic filling is preferably lower than the process temperature, higher than 200° C. and lower than 1,100° C. and the filling has a coefficient of heat conductivity of over 15 W/m ° C.
The filling is preferably selected from the group consisting of tin, lead, zinc, aluminium, silver, copper and alloys of these and combinations of these.
Preferably the filling is obtained during operation by melting of foil which is applied in the gap during assembly of the refractory wall structure, the filling is cast into the gap in molten state during assembly or the filling is obtained during operation by melting a metal which is applied in the gap in the form of a mass containing metal particles during assembly of the refractory wall structure. These embodiments of the invention are all very effective.
The embodiment with a mass containing metal particles is also suitable for wider gaps such as joints which are normally filled up with mortar, concrete, ramming mass, cement or other binding agents such as for example the joint between jacket (
1
) and graphite layer (
3
′) in FIG.
2
. Metal particles in the form of powder, grains, granulated material, chips, needles, small wires or similar are added to this mass. This metal-laden mass is applied in a joint during assembly of the refractory wall structure. In this state the metal particles are evenly divided present in the relevant joint, but still do not form a heat bridge over the joint. Following melting and solidification again of the metal, however, the joint is not homogeneously filled with metal but at sufficient loading of the mass with metal particles of for example 10-40% vol a continuous metal lattice with a spongy or biscuit-like structure forms throughout the joint with a low heat resistance owing to the good heat conductivity of the metal and thus forms a heat bridge.
Also preferably the filling is obtained during operation by melting metal in the form of one or more pellets which are placed into one or more cavities in the refractory wall structure before or after the start of the operation of the furnace. In some cases in an alternative embodiment pellets can also be applied during operation. In this context pellets are taken to be a form of the filling which can be applied into the cavity singly or in multiples, such as tablets of round, oval or cylindrical shape, but also shaped parts which fit into the cavity, or for example in rod-shaped pieces in the case where they are applied subsequently during operation. Capsules with a dosing opening are also possible so that the filling is discharged over a longer period of time or several times, for example where the refractory wall structure breathes in the event of temperature fluctuations.
Preferably the filling is obtained during operation by melting metal which is introduced in the form of a pumpable mass containing the metal into the refractory wall structure through a duct. The pumpable mass can for example be a slurry or a suspension, which is laden with the metal in finely divided state such as powder or grains to such an extent, for example 10 to 60% wt, that it does not sag. Preferably the pumpable mass also contains an oil product such as tar or pitch or a thermosetting resin as a carrier and the pumpable mass also contains graphite for example in the form of powder. Mortar and cement can also be added. After the pumpable mass has been introduced into the gap by pumps the metal melts and forms a heat bridge over the gap. Following coking the tar or the pitch forms a skeleton which for example effects a certain gas tightness of the gap. The same effect can be obtained by the resin following setting, while the graphite can yield extra wear resistance and/or heat conduction of the refractory wall structure. The embodiments of the invention with pellets and with a pumpable mass are particularly suited to be applied after starting the operation of the furnace.
Preferably during assembly of the refractory wall structure cooling elements are used which, at least partly, have been provided with a coating with the substance of the metallic filling. By a coating here is understood a layer which during its application has obtai
Gleijm Gerardus
Teerhuis Cornelis Pieter
Toxopeus Hisko Leon
van Laar Jacobus
Corus Staal B.V.
Lu Jiping
Stevens Davis Miller & Mosher LLP
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