GB2118929A

GB2118929A - Process for producing glass and apparatus for carrying out the process

Info

Publication number: GB2118929A
Application number: GB08306607A
Authority: GB
Inventors: Christian Richard
Original assignee: Rhone Poulenc Chimie de Base SA
Current assignee: Rhone Poulenc Chimie de Base SA
Priority date: 1982-03-11
Filing date: 1983-03-10
Publication date: 1983-11-09
Also published as: FR2523115B1; GB2118929B; FR2523115A1; GB8306607D0

Abstract

Glass is made by introducing a glassmaking composition into a plug flow type feed region, with a temperature gradient imparted to it, where the composition melts and is refined, and then passed into an agitated region. The composition is prepared by forming an alkaline solution of formative oxides having the same molar ratio as the final glassmaking composition, and a suspension of modifier oxides of the same anion as the preceding solution and having the same molar ratio, drying the said suspension putting the resulting product in suspension in the alkaline solution of formative oxides having solution of formative oxides having the same molar ratio, and drying the suspension. The process is carried out in particular by means of an electric pot furnace, and a suitable furnace comprises a double-wall casing (1) for the introduction of a hot circulation fluid; a sealing wall (4) which separates the two compartments, a cold arch compartment (2) and a hot arch compartment (3), and is fixed with respect to a double arch means (7); a space (5) forming a communicating passage between the two compartments; electrodes (8); heating elements (9); and an agitator (10). <IMAGE>

Description

SPECIFICATION Process for producing glass and apparatus for carrying out the process The present invention concerns a process and apparatus for producing glass, particularly from a glassmaking composition produced by chemical synthesis.

European Patent Application No. 15,794 describes a process for producing a glassmaking composition from a solution of alkali metal silicates and solutions of soluble metal salts which enter the glassmaking composition in such a way that the metals at least partially replace the initial aikali metal.

That process therefore provides compositions of a eutectic character.

In European Appiication No. 44,236, the metals may be introduced directly by operating in the presence of a miscible polar organic liquid such as methanol. It is thus easier to monitor the molar ratios, which condition the formation of the eutectic composition.

Those processes make it possible to produce a composition having a lower melting point and enhanced fining characteristics.

In accordance with the present invention, a process for the production of a glass from a glassmaking composition comprises forming an alkaline solution of formative oxides having the same molar ratio as the final glassmaking composition, and a suspension of modifier oxides of the same anion as the preceding solution and having the same molar ratio, drying the said solution, putting the resulting product in suspension in an alkaline solution of formative oxides having the same molar ratio, and drying the suspension; introducing the resulting composition into a plug-flow feed region with a temperature gradient imparted to it, where the composition melts and is subsequently refined; passing the molten composition into an agitated region and collecting it from the agitated region.

In practice, the operations of melting and fining the composition are performed in the first region and the temperature gradient imparted must be such that the melting, fining and gathering operations can be considered as being performed substantially at the same temperature.

The present process has been found to be particularly advantageous in situations which involve using a glassmaking composition of eutectic character, as described in European Patent Application No. 1 5,794.

The procedure comprises, first, forming an alkaline solution of formative oxides having the same molar ratio as the finial glassmaking composition, and a suspension of modifier oxides of the same anion as the previous solution and of substantially the same molar ratio, drying the suspension, suspending the resulting product in the alkaline solution of formative oxides having the same molar ratio, and drying the suspension on which the melting, fining and gathering operations are performed, at the same temperature.

In practical operation in accordance with European Patent Application No. 15,794 the molar ratio of the solution of formative oxide (e.g. Six2), from which the metal silicates that the mixture is composed of will be precipitated, is determined. This molar ratio Rm is given by the equation Molar concentration of formative oxide le.g. Six2) Rm= Total molar concentration of K20, Na20, etc.

Thus, a part of the alkaline solution of formative oxides serves to form the suspension of modifier oxides, which are added to the remaining part of the initial alkaline solution. The alkali metals used are in particular potassium and sodium.

In accordance with European Patent Application No. 44,236, as before, the procedure involves forming an alkaline solution of formative oxides of the same molar ratio as the final composition and a solution of modifier oxides, but the latter may be added directly to the solution of formative oxides, by making use of a water-miscible organic liquid such as methanol. T hat results in a suspension of the glassmaking composition. This is dried and the melting, fining and gathering operations are performed on it at the same temperature.

The organic liquid may be added in various ways, such as to the alkaline solution of formative oxides, or by way of an organic solution of modifier oxides, which is added to the alkaline solution of formative oxides.

In both types of process, the oxide is usually silica but it is also possible to use other oxides such as boron oxide or alumina. The metals of the modifier oxides are those which are normally used, in particular Ca, Pb, Ba and Zn. The product obtained is remarkable in regard to its performance, which is of eutectic type.

The present invention also provides apparatus suitable for carrying out the process comprising a double-wall casing for the introduction of a hot circulation fluid; a sealing wall which separates the two compartments, a cold arch compartment and a hot arch compartment, and is fixed with respect to a double arch means; a space forming a communicating passage between the two compartments; electrodes; heating elements; and an agitator.

A preferred form of such apparatus is shown by way of example in the single figure of the drawing. The apparatus is an electric pot furnace comprising double-wall casing 1, which permits of the introduction at 6 of a hot circulatory liquid such as Dowtherm or Gillotherm. A sealing wall 4 separates two compartments, a cold arched compartment 2 and a hot arched compartment 3. The wall 4 is fixed with respect to a double-arch structure 7. Communication between the two compartments is provided by the space 5 and heating is provided by electrodes 8 for the interior of the pot and heater elements 9 for the hot compartment 3 in which an agitator 10 is disposed.

Glassmaking composition 1 3 is supplied to the apparatus by a conveyor belt 1 The pot may be of any material, such as steel, possibly protected by an internal lining 12 of refractory material. The sealing wall 4 may also be of refractory material. It is also possible to use metals, for example platinum.

The nature of the submerged electrodes depends on the glass being produced.

The furnace according to the invention can operate continuously or intermittently; the feed of material to the furnace may be proportional to the amount of material removed from it, or it is possible to tolerate a drop in the level of glass in the pot. The furnace can if desired easily be put into a "waiting mode", at minimum output, and it may even be completely shut down. The furnace can be restored to operation by heating the sealing wall 4.

Temperature control of the glass is very easy, due to the combination of the cooling and heating system, the flexibility in the supply of heat or cold being one of the advantages of this mode of operation, which permits of total automation.

One of the advantages of the invention is that it makes profitable use of the remarkable properties of a chemical glassmaking composition, in particular: its homogeneity, its melting, fining and working temperatures, and its speed of transformation into fine glass.

By way of illustration, the mode of operation of the above-described furnace, when supplied with the composition as described in European Patent No. 15,794, in Example 8, is as follows: The composition is introduced into the compartment 2. It melts at a temperature of about 7500C and in melting region 14 it is rapidly transformed into a mass charged with bubbles. As that mass moves downwardly in the reaction vessel, it rapidly reaches the operating temperature of 12000 C. The fining mechanism operates in the same manner, and large bubbles are formed in refining region 15.

When the glass arrives at a level below the sealing wall 4, it is refined and homogenized (region 16).

The glass rises again in the compartment 3; in contact with the agitator 10, it undergoes perfect homogenization at the temperature appropriate for the gathering operation (region 1 7).

Many advantages can result from the above-described novel design of furnace, which can be adapted to any size of furnace and in particular, to a furnace especially suitable for manual glassmaking works, as it may be of low intermittent daily output, less than 500 kg/furnace, while retaining the advantages of electric melting.Among the advantages are a high level of thermal efficiency, which is enhanced here by the possibility of recovering the heat absorbed by the cooling fluid, which may be either water or a liquid circulating at a high temperature above 1 00 C; absence of pollution, by virtue of the possible feed of material to the cold arch; flexibility in operation, bearing in mind the single temperature in the furnace and the control system; reduced volume of the installation and the resulting low level of capital investment; the exceptionai quality of the glass, with very reduced contact between the glass and the refractory material, homogeneity of the glass being ensured by the composition used; the rhythm of operation of the furnace, which can be easily adapted to the working rhythm; and the service life of the furnace and the electrodes, bearing in mind the limited convention currents and the relatively low, uniform temperature.

Claims

1. A process for producing glass from a glassmaking composition, comprising forming an alkaline solution of formative oxides having the same molar ratio as the final glassmaking composition, and a suspension of modifier oxides of the same anion as the preceding solution and having the same molar ratio, drying the said solution, putting the resulting product in suspension in an alkaline solution of formative oxides having the same molar ratio, and drying the suspension; introducing the resulting composition into a plug-flow feed region with a temperature gradient imparted to it, where the composition melts and is subsequently refined; passing the molten composition into an agitated region and collecting it from the agitated region.

2. A process according to Claim 1, in which the melting, refining and gathering operations are performed at the same temperature.

3. A process according to Claim 1 or 2, in which an alkaline solution of formative oxides having the same molar ratio as the final composition is prepared, and a solution of modifier oxides is added to the alkaline solution of formative oxides in the presence of a water-miscible polar organic liquid so as to produce a suspension of the glassmaking composition which is dried and used in the melting, refining and gathering operations.

4. A process according to Claim 3, in which the organic liquid is supplied to the alkaline solution of formative oxides.

5. A process according to Claim 3 or 4, in which an organic solution of the modifier oxides is formed and the alkaline solution of formative oxides is added to it.

6. A process according to any one of Claims 3 to 5, in which the organic liquid comprises methanol.

7. A process according to any one of Claims 1 to 6, in which the formative oxide is silica, boron oxide or alumina and the metal of the modifier oxides is Ca, Pb, Ba or Zn.

8. An electric furnace for carrying out the process according to one of Claims 1 to 7, comprising a double-wall casing for the introduction of a hot circulation fluid; a sealing wall which separates the two compartments, viz. a cold arch compartment and a hot arch compartment, and is fixed with respect to a double arch means; a space forming a communicating passage between the two compartments; electrodes; heating elements; and an agitator.

9. A furnace according to Claim 8 substantially as hereinbefore described with reference to the accompanying drawing.

10. Glass obtained by a process according to any one of Claims 1 to 7.