GB2097381A

GB2097381A - Method and apparatus for preheating glass-making ingredients before charging them into a glass-making furnace

Info

Publication number: GB2097381A
Application number: GB8211015A
Authority: GB
Original assignee: Gerresheimer Glas AG
Current assignee: Gerresheimer Glas AG
Priority date: 1981-04-28
Filing date: 1982-04-15
Publication date: 1982-11-03
Also published as: DE3116755A1; DE3116755C2; FR2504513A1; BE892949A; IT1148540B; IT8248274A0

Abstract

In order to preheat glass-making ingredients before charging them to a melting furnace, the materials are gently and only slightly moved and during their movement are exposed to a flow of hot gas derived from the melting end of the furnace, the gas flowing at a low speed. This technique enables the materials to be preheated in a loose state, that is without briquetting them, without causing segregation. Apparatus for effecting the preheating comprises a casing 3 having a hot gas inlet 7 at its bottom and a gas outlet 7 at its top. A shaft 1, which rotates at 0.5 r.p.m., extends through the casing and carries pans 2. The material to be preheated enters the casing through an inlet 13 on to the top tray 2. It is then caused by strippers 12 and funnels 4 to trickle downwards from pan to pan in countercurrent to the hot gas flow to an outlet 18 whence it is discharged to the furnace. <IMAGE>

Description

SPECIFICATION Method and apparatus for preheating glassmaking ingredients before charging them into a glass-making furnace The invention relates to methods and apparatus for preheating materials which are subsequently subjected to a glass melting process, before the materials are charged into the melting end of a glass-making furnace.

Hitherto in the glass making industry it has not been usual to preheat batches of glass-making materials on a commercial scale before feeding them to the melting furnace. Also no cullet which arose from the glass-making or from other sources has been preheated before melting.

In laboratory experiments and in pilot plants heating of the materials has been attempted and this heating was recognized as advantageous, but the materials were not employed in a loose state, but for fear of segregation only in an agglomerated state, for example in the form of pellets or briquettes.

From the point of view of outlay in investment and energy, pelletizing or briquetting is expensive and disadvantageous because of the plant necessary for the purpose as well as for the fine grinding of the raw materials which is necessary for the pelletizing and the amount of water, of up to 10% which is necessary for the binding of the raw materials in the pellets or briquettes, but which must later be evaporated again.

The object of the present invention therefore, is to provide a method and apparatus whereby glass-making ingredients, and preferably cullet also may be preheated in a loose state, i.e., not agglomerated, by means of hot gas from glassmaking furnaces of any construction, but preferably from regeneratively heated tank furnaces.

According to this invention, we provide a method of preheating materials which are subsequently subjected to a glass melting process, before the materials are charged into the melting end of a glass-making furnace, wherein the materials are gently and only slightly moved and during their movement are exposed to a flow of hot gas derived from the melting end of the furnace, the gas flowing at a low speed.

The temperatures of the gases emanating from the actual melting process are generally between 4000 and 500"C.

The temperature of the heating gas may be increased by additional burners acting directly on the gas or lying in combustion chambers, in order to preheat the material to such an extent that at from 750-8500C, preferably at substantially 8000C, a preliminary reaction takes place which is effected with greater efficiency than in the glass furnace itself, whereby the overall heat balance of the glass melting process is considerably improved.

The segregation of the ingredients is kept within justifiable limits, i.e., it is not injurious to the melt. Significant segregation is avoided by the gentle movement of the material during the heating as well as by the conductioi I of the hot gas through or over the material at low speed.

By this means the large amounts of heat which are present in the furnace gas at a relatively low temperature are returned directly into the furnace within the limits of a permissible drop in temperature through its introduction into the cullet and loose ingredients. Thus the use of indirect heat exchange via a heat carrier, such as steam, for which after use for heat exchange, during the hotter part of the year there is generally no further use, is avoided.

The invention also consists, according to another of its aspects, in apparatus for carrying out the method in accordance with the invention, the apparatus comprising a heat exchanger comprising a casing having an inlet for hot gas from the melting end of a glass-making furnace, a gas outlet, an upright rotary shaft extending through the casing, a plurality of material receiving pans mounted one above the other on the shaft, means for supplying the materials to the uppermost pan, means for moving the materials on the pans and causing the materials to trickle from the uppermost pan to each lower pan and means for feeding materials from the lowermost pan to the melting end of the furnace.

An example of a method and of apparatus in accordance with the invention will now be described with reference to the accompanying drawings in which: Figure 1 is a vertical section through the apparatus as seen in the direction of the arrows on the line A-B of Figure 2; and Figure 2 is a cross section through the apparatus as seen in the direction of the arrows on the line C-D of Figure 1.

The apparatus consists of a rotary heat exchanger comprising an upright shaft 1 which supports at least two, and preferably from three to ten, in this example there being six, disc-shaped material receiving pans 2.

The shaft 1 with the pans 2 is surrounded by a cylindrical or tapered casing 3 through which hot gases led away from the melting end of a glassmaking furnace flow to give up their heat.

Between the pans 2, funnels 4 of frusto-conical shape are built into the casing 3 which is provided with inspection doors 5 and with an insulating jacket 6 to reduce the loss of heat.

The funnels 4 are arranged between every adjacent pair of disc-shaped pans 2. On the outside, the funnels 4 are fixed to the casing and have a central opening which is smaller than the diameter of the pan 2 lying below the funnel.

The hot gases which are preferably exhaust gases from a glass melting furnace, take a zigzag path through the heat exchanger enforced by the pans 2 and the funnels 4, and in so doing heat both the pans 2 and also the funnels 4. In their passage the hot gases also get brought directly into contact with glass making material resting on the pans 2.

The material including cullet, which if required it may contain, is heated up both by contact with the funnels 4 and the pans 2 and also in trickling down through the exhaust gases from one pan to a funnel and then the next pan and so on.

The apparatus has a gas inlet 7 at its bottom and a gas outlet 7 at its top and in the inlet and outlet are baffles 8 having adjustable tongues 9 which ensure uniform distribution of the hot gases around the whole circumference of the casing. The hot gases may be led in counter-flow, directflow, crossflow or in combinations of these flows by changing over the inlet and outlet.

The low speed of gas flow previously mentioned is in the region of the outlet preferably less than 0.4 m/sec.

The speed of rotation of the shaft 1 with the material receiving pans 2 attached to it is slow, for example from 0.2 to 1 r.p.m., preferably 0.5 r.p.m.

Above the material receiving pans 2, armoured ploughs 10, rakes 11 and strippers 12 are adjustably mounted to move the material which is being heated. Their angle of attack may be of any magnitude in order to be able to perform any required movement of the material from each pan downwards.

In addition to the exhaust gases led from the glass furnace, further hot gas may be generated.

For this purpose additional burners or additional combustion chambers are used, which are not shown or further described.

The distance between the material receiving pans 2 is kept such that the material which is to be heated does not have any great height to cover in moving from one pan to the next. The ploughs and blades 10 and the strippers 12 which are preferably flat, as well as the rakes 11 exert through their angle of attack a mixing action upon the material. Together with the described low speed of movement and gas flow the heating up of the loose materials is effected without significant segregation.

The heat exchanger, or parts of it, are made of a material which is suitable for withstanding temperatures of preferably up to 8500C e.g., heat resistant steels. It may also be lined with refractory bricks.

During the passage of the glass making materials, conditioning of the furnace exhaust gases used for heating takes place. Their corroding action upon a succeeding dust-extraction filter as well as the emission of injurious substances are reduced.

In detail the apparatus operates as follows:- The material which is to be preheated is delivered into the heat exchanger via charging valve 13 and an inlet chute 14 on to the uppermost material receiving pan 2. Owing to the rotation of the pans 2 and the action of the ploughs and blades 10 and the rakes 11 a distribution as well as thorough mixing of the material takes place on the pan 2. In doing this heat is taken up by the material by contact with the metal parts which are being heated up by the hot gases flowing through the exchanger.

Armoured strippers 12 at arbitrary points situated upstream, in the direction or rotation of the pans, of the chute 14, throw the material from the receiver pan 2 via baffles or chutes 1 5 as well as the funnel 4 lying next below the pan on to the next lower pan 2.

In trickling down the material falls through the gas flow and in so doing is further heated up. On the following pans 2 the heating process as described is repeated at progressively higher temperatures. Furthermore, the introduction of heat takes place directly from the gas into the material resting on the pans 2, because the gas, directed by the funnel 4 lying above the pan, comes into contact with the material on the pan.

The annular zigzag path of the gas flow is designated by arrows 1 6.

The material thus heated up flows via a funnel 1 7 through a discharge valve 18 into the entry to the glass making furnace.

Claims

1. A method of preheating materials which are subsequently subjected to a glass melting process, before the materials are charged into the melting end of a glass-making furnace, wherein the materials are gently and only slightly moved and during their movement are exposed to a flow of hot gas derived from the melting end of the furnace, the gas flowing at a low speed.

2. A method according to Claim 1, in which the materials consist of loose, not agglomerated, ingredients for glass making, or cullet or a mixture of the ingredients and cullet.

3. A method according to Claim 1 or Claim 2, in which after preheating by the flow of hot gas, the materials are further heated to a temperature of from 7500 to 8500C by burners acting on the materials directly or via a combustion chamber.

4. A method according to Claim 3, in which the temperature is substantially 8000 C.

5. A method according to any one of the preceding Claims, in which the speed of the flow of the hot gas in the region after it has contacted the materials is less than 0.4 m/sec.

6. Apparatus for carrying out the method in accordance with Claim 1, the apparatus comprising a heat exchanger comprising a casing having an inlet for hot gas from the melting end of a glass-making furnace, a gas outlet, an upright rotary shaft extending through the casing, a plurality of material receiving pans mounted one above the other on the shaft, means for supplying the materials to the uppermost pan, means for moving the materials on the pans and causing the materials to trickle from the uppermost pan to each lower pan and means for feeding materials from the lowermost pan to the melting end of the furnace.

7. Apparatus according to Claim 6, in which there are from three to ten pans.

8. Apparatus according to Claim 6 or Claim 7, in which the shaft has a driving mechanism which, in operation, rotates the shaft at a speed of from 0.2 to 1 r.p.m.

9. Apparatus according to Claim 8, in which the speed is 0.5 r.p.m.

10. Apparatus according to any one of Claims 6 to 9-, in which the means for moving the materials comprises an armoured plough, a rake and a stripper mounted above each-pan, the ploughs, rakes and strippers having means for adjusting their angle of attack.

11. Apparatus according to any one of Claims 6 to 10, in which the casing is cylindrical or tapered with an upright axis and has an insulating jacket and inspection doors.

12. Apparatus according to any one of Claims 6 to 11, in which a funnel of frusto-conical shape is connected to the casing between a pair of adjacent pans.

13. Apparatus according to Claim 12, in which the funnel is fixed rigidly at its outside to the casing.

14. Apparatus according to Claim 13, in which the opening in the funnel is smaller than the diameter of the pan immediately above it.

1 5. Apparatus according to any one of Claims 12 to 14, in which a funnel is provided between every adjacent pair of pans.

1 6. A method according to Claim 1, substantially as described with reference to the accompanying drawings.

1 7. Apparatus according to Claim 6, substantially as described with reference to the accompanying drawings.