JPH0525819B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a process for the continuous and controlled melting of essentially non-metallic inorganic materials, particularly inorganic oxides, for the production of mineral or ceramic fibers.

Mineral fibers are mainly used in the field of insulation and for reinforcing products based on plaster cement. The quality and behavior of mineral fibers in use depends on the consistency of their physical and chemical properties, and these properties depend on the uniformity of the liquid bath in which they are drawn.

It is known that even very slight inhomogeneities in the liquid bath in terms of composition or heat have a negative effect on the quality of the produced fibers as well as on the yield in the drawing equipment located at the exit of the melting furnace.

Currently known equipment for melting raw materials for the production of mineral fibers is mainly cupora-type furnaces (95%) and arc or submerged arc furnaces (5%).
%). An induction furnace is in the experimental stage.

A notable feature common to known furnaces and the liquid baths formed within them is that the volume of the liquid bath is extremely small compared to the volume of the total charge of the furnace. actually,
This ratio is between 1:10 and 1:50 in the case of cupora furnaces. A small bath volume is extremely disadvantageous, since even the smallest variations in the properties of the charge material have a greater effect on the uniformity of the bath the smaller the total bath volume.

Continuous tapping of molten inorganic oxides is a laborious operation in which changes in temperature or chemical composition, as well as factors affecting the uniformity of the liquid material, are dependent on the ability of the drawing equipment to produce the desired fibers. Tends to interfere with proper operation. For example, a failure of the drawing equipment due to a disturbance caused by premature solidification of the withdrawn liquid material affects the entire production facility.

Additionally, when using known continuous flow melting methods, fluctuations in furnace pressure act on a relatively limited volume of molten material, and temperature fluctuations cause variations in the diameter of the extraction orifice. , it has been observed that the flow of liquid leaving the extraction port becomes irregular. Such fluctuations upstream of the extraction port are
Due to the non-uniformity of the molten material at this location, it is difficult to control.

The aim of the present invention is to overcome the above-mentioned drawbacks of known processes for continuously melting non-metallic inorganic substances for producing mineral fibers.

The purpose of this is to continuously control the melting of non-metallic inorganic materials to produce mineral fibers in a closed furnace electrically heated and provided with a refractory lining of graphite. The inorganic material is charged as a function of the discharge rate of the furnace such that the amount of liquid bath in the furnace is always at least 8 tons of molten material, and the liquid bath is filled with a neutral or reducing gas by means of a neutral or reducing gas. The molten material is removed from the furnace by creating a positive pressure in the furnace space and controlling the discharge amount of the molten material by adjusting the positive pressure in the furnace space.
This is achieved by a continuous controlled melting method for non-metallic inorganic substances, which is characterized in that the amount of liquid discharged per hour is approximately half of the total amount of the liquid bath.

"Charging the closed furnace with non-metallic inorganic substances as a function of the furnace discharge" means that the discharge from the closed furnace is adjusted so that the amount of bath liquid in the closed furnace is always at least 8 tons. Refers to charging non-metallic inorganic materials to a closed furnace in substantially the same amount or flow rate.

The basic idea of the invention is significantly different from the melting principle in cupora furnaces. A cupola furnace melts a relatively small amount, which is then extracted directly and used to convert it into fiber. With cupora reactors the special requirements of special environments can be taken into account. In vertical furnaces such as cupola furnaces, there is always a relatively large amount of unmelted material in the furnace, which makes the molten product non-uniform, so such furnaces can produce Not suitable for melting inorganic materials. To overcome this problem, the method of the invention uses an electrically heated closed furnace, ie a closed electric furnace. In addition, in the method of the invention, heating and homogenization are provided which make it possible to refill the furnace and replenish the discharged molten material within a given time without falling into the difficult situations encountered in cupola furnaces. A predetermined minimum volume of molten material is maintained in the furnace to act as a reservoir for the molten material. In the present invention, this minimum amount of molten material is, of course, greatly influenced by the downstream spinning capacity, but it is determined by the normal total charging amount in the furnace (i.e., the total liquid bath amount).
The total liquid bath volume is at least 8 tons. The downstream spinning capacity should be at least 4 to make best use of the melting capacity of one furnace.
It needs to be ton/hour. Depending on the downstream spinning capacity to which the molten material is fed, for example, a furnace that can accommodate 8 tons of molten material and receive a replenishment of 4 tons/hour, or a multiple of this and receive a multiple replenishment. It is a matter of no problem for the furnace builder to select an advantageous design, volume and other characteristics of the furnace. In the present invention, it is necessary to have at least 8 tons of molten material in the furnace at all times in order to be able to process approximately the same weight of raw material per hour and take out the same weight of uniform molten material. I discovered that. In the method of the invention, it is important to achieve a residence time sufficient to sustain the various intra- and intermolecular effects that occur during the melting of the raw materials and to ensure chemical and thermal homogeneity of the liquid bath. I can do it.

Blast furnace slag 70-65% by weight and silica 30-35% by weight
In the case of a mixture with , it is necessary to set the residence time to about 2 hours, and this residence time is determined by the method of the present invention (for example, when the effective liquid bath volume is 8 tons, the discharge flow rate is set to 4 tons/hour). ) is achieved. Uniformity of the liquid bath is achieved by a sufficiently long residence time, as well as high thermal uniformity due to the high inertia of the liquid bath, even with respect to unforeseen temperature changes. This inertia allows adjustment of the amount of heat required to offset the heat losses due to continuous addition of raw materials (the extent of which depends on the discharge from the liquid bath) by adjusting the pressure occupying the furnace. It allows you to do it accurately. Since in the process of the invention a completely closed furnace is used, the pressure can be regulated very precisely, for example by means of a butterfly valve in the chimney.

In the process of the invention, neutral or reducing gases are injected above the level of the liquid bath, or such gases or gas mixtures are introduced directly into the liquid bath via the bottom of the furnace or through immersed hollow electrodes. By doing so, a positive pressure can be created and maintained above the liquid bath level. All that is required to maintain a constant positive pressure above the liquid bath is to adjust the butterfly valve according to the required and measured pressure. A constant positive pressure can also be created by trapping the smoke from the liquid bath in the furnace and adjusting the butterfly valve to maintain the desired degree of pressure.

The range of pressure variations that can be achieved within the scope of the method of the invention is of the order of 0.51 Kg/cm ² (0.5 bar);
This range of pressure variation is sufficient during operation to adjust the output from the outlet as a function of variations in the bath height within the furnace and the diameter of the outlet to achieve a constant flow rate. This is important to achieve optimum yields when producing consistent quality fibers from drawing equipment.

Regarding the feeding to the furnace, the solid raw material or the already melted raw material, such as, for example, blast furnace slag, can be charged continuously or batchwise. Obviously, the energy consumption in the melting equipment can be significantly reduced when feeding liquid raw materials, and
Problems encountered during start-up of the equipment when charging 100% solids can be avoided.

Continuous or batch supply of liquid raw materials can easily be carried out from fixed or movable closed containers provided with an insulating lining and heating means.

The already molten raw material can be transferred from the vessel to the furnace by means of a closed conduit whose inner wall is graphite. Transfer can be by gravity if the container is properly positioned with respect to the furnace, or by pressurizing the container with a neutral or reducing gas.

In a particularly advantageous embodiment of carrying out the method of the invention, the liquid bath can be homogenized by blowing in a neutral or reducing bubbling gas through the furnace bottom or through the electrodes.

Since the process of the invention is carried out in a neutral or reducing controlled atmosphere, a carbon or graphite lining can be used in the furnace. There are two main advantages in this case: First, graphite refractories do not become wetted by molten inorganic oxides, and second, with external cooling, operation at temperatures in excess of 2000°C is possible, thereby saving costs. I can do it.

The first condition for proper behavior of graphite refractories is, of course, the absence of molecules or oxygen that are likely to release oxygen during thermal decomposition. In fact, if blast furnace slag is to be used as a raw material, it is necessary to take into account the possibility that residual iron oxide may be present in the slag, which may be in considerable amounts.

According to the method of the invention, a refractory lining of graphite is prepared by injecting powdered reducing additives, such as carbon, petroleum coke, graphite or tar, into a liquid bath together with bubbling gas or by incorporating them into the charge. can be protected from oxidation. In the method of the invention, a kind of cementing of the furnace wall can be achieved on the one hand by injecting carbonaceous material, in particular tar or a mixture of tar and graphite, and on the other hand the desired reducing gas can be produced continuously, reducing the consumption of highly expensive neutral gases (nitrogen, argon), and in extreme cases even making neutral gases unnecessary. .

In addition, in the method of the invention, a certain amount of additives, which can decompose under the action of high temperatures and release neutral or reducing gases, can be injected into the liquid bath, for example together with bubbling gas. .

Claims (1)

[Scope of Claims] 1. In continuously controlled melting of non-metallic inorganic substances to produce mineral fibers, in a closed furnace that is electrically heated and provided with a refractory lining of graphite, Charge the pre-molten inorganic material as a function of the furnace output such that the amount of liquid bath in the furnace is always at least 8 tons of molten material, and charge the liquid bath with a neutral or reducing gas. By creating a positive pressure in the upper furnace space and controlling the discharge rate of the molten material by adjusting the positive pressure in the furnace space, the molten material is removed from the furnace until the total discharge amount per hour is A continuously controlled method for melting non-metallic inorganic substances, characterized in that the amount is taken out in an amount that is approximately half of the amount of a liquid bath. 2. The method according to claim 1, wherein a neutral or reducing gas is injected into the liquid bath to maintain a constant positive pressure above the liquid bath. 3. A method as claimed in claim 1 or 2, in which a portion of the smoke is evacuated from the closed furnace to maintain a constant positive pressure above the liquid bath. 4. The method according to any one of claims 1 to 3, wherein the liquid bath is made uniform by blowing neutral or reducing bubbling gas through the bottom of the furnace or through the electrodes. 5. The method of claim 4, wherein a reducing atmosphere is created in the furnace by injecting a powdered reducing additive, such as carbon or petroleum coke, into a liquid bath together with the bubbling gas. 6. Cementing of refractory linings of closed furnaces during the melting process by injecting powdered additives such as graphite, tar or mixtures thereof into a liquid bath together with bubbling gas, as claimed in claim 2. The method described in any one of paragraphs 1 to 5. 7. The method according to any one of claims 4 to 6, wherein an additive that releases neutral or reducing gas upon thermal decomposition is injected into the liquid bath together with the bubbling gas. .