SHAFT FURNACE WITH A MELT COLLECTING CHAMBER

Abstract: A shaft furnace for preparing a melt for feeding a mineral wool spinner and having a melt collecting chamber (4) located on the side of the shaft furnace and communicates with the lower end of the furnace chamber through a hole (3) in the furnace wall (1), and which contains a molten mass (11) during operation, the side wall (7) of the melt collecting chamber being provided with a hole (14) for discharging melt, said hole (14) being located below the surface of the molten mass in the chamber (4). An essentially constant melt flow to the mineral wool spinner is obtained with the shaft furnace.

Description: Shaft furnace with a melt collecting chamber This invention relates to a shaft furnace for preparing a melt for mineral wool production and having a melt collecting chamber which is located on the side of the shaft furnace and which communicates with the lower end of the furnace chamber through a hole in the side wall of the shaft furnace and which during operation contains a molten mass, the surface of said molten mass being located a distance above the bottom of the collecting chamber and the chamber having means for discharging melt for mineral wool production. US patent specification No. 2,900,764 discloses a tank furnace for the manufacture of glass. This tank furnace has a side wall with a passage which communicates with a heat insulated receptacle having a bottom outlet for molten glass and serving for the discharge of the glass melt containing air bubbles as such a bubble-containing melt creates problems in the processing of the glass melt, e.g. in the manufacture of drawn glass products. US patent specification No. 4,664,691 discloses a cupola furnace of the type mentioned above wherein the melt collecting chamber is constituted by a crucible having a free surface from which melt is discharged by means of an overflow which melt through a passage is passed to a cascade spinner for the production of mineral wool. During the operation of the prior art cupola furnace melt formed in the furnace chamber flows into said crucible which partly serves to equalize variations in the melt flow from the furnace chamber and partly to homogenize the melt with respect to both composition and temperature. The overflow may e.g. have the shape of a groove having a U or V shaped cross section. Even though the volume of said crucible and the size of the melt surface are chosen in such a manner so as to allow only small variations in the surface level of the crucible the use of the discharge means does prevent considerable variations of the melt flow from the crucible to the fibre spinner. Thus, in connection with the charging of the furnace and in case of sudden collapses of the furnace content generated by combustion of solid fuel and/or melting of the starting material, sudden violent changes in the surface level of the melt collecting chamber may occur, said changes inevitably causing violent changes in the melt flow in connection with the discharge of melt through an overflow. Such variations in the melt flow require a corresponding adjustment of the production speed of both the fibre spinner and the cooperating apparatus such as collecting conveyors, curing oven and sawing and packing machines. The object of the invention is to provide a shaft furnace of the type mentioned above which produces a more constant melt flow than the prior art apparatus. This object is obtained with the shaft furnace according to the invention, said shaft furnace being characterized in that the means for discharging melt comprise at least one hole in the side wall of the melt collecting chamber, the hole being located below the melt surface in the chamber. The use of a melt collecting chamber with a "submerged" discharge hole having a constant cross section results in a melt flow which only to a limited degree is dependent on the surface level in the melt collecting chamber. Thus, the discharge amount, Q, is determined by the equation: Q = μ • f • J 2g . h Q where μ - the discharge coefficient, f = the discharge area, g - the acceleration of gravity, h_ = the distance from the liquid surface to the center of the discharge hole. As it appears from the formula above the melt flow from the shaft furnace according to the invention will only vary with a factor which is the square root of the variation, Δh, of the distance, h , from the liquid surface to the center of the discharge hole, whereas the variation in the melt flow, when using a U or V shaped overflow, can be exponential . In a preferred embodiment of the shaft furnace according to the invention two discharge holes are provided in the side wall of the melt collecting chamber thereby making it possible to feed two fibre spinner production lines from one shaft furnace at the same time. An adjustable valve is preferably mounted in the discharge hole or holes for adjustment of the cross sectional area of the discharge hole(s) to a desired value and/or for closing the hole or holes in case of a production line stop. The valve is preferably a water- cooled valve. The walls of the melt collecting chamber preferably consist of a refractory, ceramic material and the bottom and side walls may be surrounded by a water-cooled steel jacket. The chamber may have a cover at the top which is also made from a refractory, ceramic material. A heat source, e.g. in the form of a burner, which is supplied with a mixture of oxygen and fuel or in the form of an electric arc formed between two graphite electrodes may be provided in an appropriate distance from the melt surface within the interior of the chamber. The heat source serves to maintain the melt in the melt collecting chamber at a desired temperature. The invention will now be described in further detail with reference to the drawing showing part of a cross sectional view of a preferred embodiment of a shaft furnace according to the invention. The shaft furnace shown in the drawing comprises a furnace wall 1 and a furnace bottom 2. The lower end of the furnace wall is provided with a hole 3 through which the furnace chamber communi¬ cates with a melt collecting chamber generally designated 4. The melt collecting chamber 4 is defined by the two end walls 5, a vertical side wall 6, an oblique side wall 7, a bottom wall 8 and a cover 9, all made from a refractory, ceramic material, such as aluminum oxide. The end walls 5, the oblique side wall 7 and the bottom wall 8 are surrounded by by a steel jacket 10. In the lower portion of the furnace chamber and in the melt collecting chamber 4 there is a mineral melt 11, the surface of which is located at a lower level in the furnace chamber, wherein a superatmospheric pressure prevails, than in the melt collecting chamber which, via a hole 13 formed at the upper end of the oblique side wall 7 and acting as overflow in case of clogging of the hole 14 mentioned below, communicates with the ambient atmosphere. A distance below the melt surface the oblique side wall 7 is provided with a hole 14, and in the embodiment shown a valve 15 having an adjustable discharge opening is mounted in said hole. Finally, a heater 16 is mounted in the area above the melt 11 in the melt collecting chamber 4. The discharge hole 11 is connected with means (not shown) for carrying the melt 11 to a fibre spinner apparatus (not shown).

Claims: C L A I M S 1. A shaft furnace for preparing a melt for mineral wool production and having a melt collecting chamber (4) which is located on the side of the shaft and communicates with the lower end of the shaft through a hole (3) in the furnace wall (1), and which during operation contains a molten mass (11), the surface of said molten mass being located a distance above the bottom (8) of the collecting chamber (4) and the chamber (4) having means for discharging melt for mineral wool production, c h a r a c t e r i z e d in that the means for discharging melt comprise at least one hole (14) in the side wall (7) of the melt collecting chamber, the hole (14) being located below the melt surface in the chamber (4). 2. A shaft furnace according to claim 1, c h a r a c t e r i z e d in that two holes (14) are provided in the melt collecting chamber (4). 3. A shaft furnace according to claims 1 or 2, c h a r a c t e r - i z e d in that an adjustable valve (15) is mounted in the hole or the holes (14). 4. A shaft furnace according to any of the preceding claims, c h a r a c t e r i z e d in that the walls (5, 6, 7 and 8) of the melt collecting chamber (4) are made from a refractory, ceramic material . 5. A shaft furnace according to any of the preceding claims, c h a r a c t e r i z e d in that the melt collecting chamber has a cover (9) at the top. 6. A shaft furnace according to any of the preceding claims, c h a r a c t e r i z e d in that a heat source is mounted in the interior of the melt collecting chamber (4) above the melt surface.

Inventors: HOLTZE ERIK, MADELUNG HANS, HOLTZE, ERIK, MADELUNG, HANS
Applicants: ROCKWOOL INT, ROCKWOOL INTERNATIONAL A/S
Application year: 1989
Main classification: C03B5
IPC codes: C03B5, C03B7