The present invention relates to a glass melting furnace with

- A melting chamber containing a glass melt which forms a top surface,

- A device for conveying glass batch material into the melting chamber through an orifice in a wall of the melting chamber which orifice is positioned below the level of the glass melt top surface, the device having a chamber communicating with the interior of the melting chamber via the orifice,

- whereby the chamber has a conveying section, in which the glass batch material is conveyable in conveying direction towards the melting chamber by means of a piston or a conveyor screw arranged in the conveying section of the chamber,

- whereby the chamber has further a feeding section connecting the conveying section with the wall of the melting chamber,

- the chamber further communicating with a supply tube via an outlet cross section of the supply tube.

Further, the invention relates to a method for feeding glass batch material into a glass melting furnace according to the preamble of claim 12.

The device for conveying glass batch material into the melting chamber can also be called “batch charger”.

The chamber has a conveying section as well as a feeding section, whereby the conveying section is the area where the glass batch material is introduced into the chamber and forwarded to the melting chamber of the furnace. Within the conveying section the conveying means are arranged. If the conveying means are formed by a piston the movement of the piston takes place within the conveying section. The feeding section is the area in between the conveying section and the melting chamber. As there are no conveying means in the feeding section there is always glass batch material in the feeding section. The batch material enters into the melting chamber by being pushed by new batch material being forwarded by the conveying means. The batch material laying in the feeding section serves as heat insulation and as plug, which prevents melt from entering into the chamber in a backward direction. State of the art

Glass melting furnaces are commonly known in the state of the art. Typically, glass furnaces can be grouped according to the location of the energy source (U flame or cross fired furnaces), depending on the type of the oxidant (oxygen or air) for fuel and also depending on the quality of the produced glass such as container, tableware, float or fiberglass. The present invention concerns all types of glass melting furnaces mentioned before.

Since the production of glass in a glass melting furnace runs continuously, raw batch material is regularly added to the glass melt in the melt chamber, whereas good quality glass is continuously pulled from the furnace for the production. In conventional furnaces the raw batch material, also named as batch, is added to the furnace in powder form by distributing the same on top of the existing glass melt, burners being arranged above the glass melt. This method has many drawbacks, for example the well-known insulating effect of the batch material on top of the melt, which results in a higher energy consumption. Further, the introduction of the batch material causes an undesired dusting effect and a lot of air is introduced in the melt, which causes unwanted bubbles in the melt requiring a long mixing process.

To solve the aforesaid problems, the document US 9,394,192 B2 proposes to introduce the batch below the melt level, which can be called “submerged feeding”, so that the disadvantages about an insulating layer on top of the melt, if the batch is introduced on top of the glass melt, are avoided for the most part. A drawback of the submerged feeding can occur, if the orifice of the furnace would be clogged or if parts of the batch charger might be damaged and have to be replaced. In such a case the feeding of the furnace is not possible any more so that the continuous process of the glass production is endangered. To solve this problem it is proposed in document US 9,394,192 B2 to arrange a slide gate damper, which is closed in case of maintenance work. To prevent damage to parts of the slide gate damper it is equipped with a cooling system. Another possibility to avoid problems caused by a clogged batch charger is to arrange a second batch charger to achieve a redundant feeding system.

Further, a glass melting furnace, which can be fed beneath the level of molten glass, is known from the US 1,761,229 A. The known furnace has a cylinder in communication with the furnace, a reciprocating plunger operable within the cylinder in order to force the batch into the furnace. The cylinder itself is fed with batch material via a vertical inlet, the inlet corresponding with a storage tube, which is arranged at substantially a 45° angle to the inlet. The piston itself is designed very long so that the inlet of the cylinder is closed by the piston when moving towards the furnace to avoid further batch material falling into the cylinder. Only when the piston moves back entirely, new batch material can fall into the cylinder to be fed again.

Also the document WO 2016/120351 A1 discloses a glass melting furnace with a feeder suitable to feed the batch material under melt level. The feeder consists of a feeding barrel with a feeding piston moving within the barrel. The feeding barrel is fed via an input opening, which is closed by the piston when moving towards the furnace.

Problem

The problem to be solved with the present invention is to find an alternative method for feeding glass batch material into a glass melting furnace as well as an alternative glass melting furnace.

Solution

Based on the state of the art mentioned above, the aforesaid problem is solved by a furnace characterized in that the conveying section of the chamber of the device is inclined with respect to the horizontal, the angle between the horizontal and a central axis of at least the conveying section of the chamber being in a range of 30 degrees to 60 degrees. Further, an angle of inclination of a central axis of the supply tube with respect to the horizontal is greater than the angle of the inclination of the axis of the conveying section with respect to the horizontal.

The inclination of at least the conveying section of the chamber has the advantage that the gravitational force can be used to move the batch material towards the orifice of the melting chamber. It is self-evident that this effect depends on the angle between the horizontal and the central axis of the conveying section: The greater the inclination from the horizontal, the greater the effect of the gravitational force. So, the force to be applied by the conveyor means of the invention is lower than it is necessary by means arranged in a horizontal chamber. In addition, stacking of the glass batch material as well as of the conveyor means is counteracted.

The inclination of the supply tube has the advantage that loose batch material does not get stuck in the supply tube as easily as in a tube arranged vertically. Nevertheless, the gravitation force is used partially because of the inclined arrangement of the supply tube.

By using a piston as conveyor means only cyclic feeding of the batch is possible. That means that only portions of batch material can be fed into the furnace by displacing the piston in direction to the orifice. To feed another portion of the batch it is first necessary to retract the piston and to place another portion of the batch material in front of the piston. Advantageously, by using a piston it is possible to feed conventional batch, which is typically loose material, as well as to feed batch rods, that are pre-shaped as rods, into the glass melting furnace. Consequently, it is possible to feed sodium hydroxide into the furnace which is typically coated or encapsulated with non-corrosive components of the batch. By feeding the batch material by means of a piston, the batch material is not mixed so that no parts of the batch feeder and no parts of the furnace come into contact with the batch material.

It goes without saying that the piston has the same or a slightly smaller cross section as the free cross section of the chamber, so that a movement of the piston inside the chamber is easily possible. For example, the outer diameter of the piston can be 0,5 mm to 2 mm smaller than the inner diameter of the chamber, dependent on the particle size of the batch composition. If the batch composition has very small particles, for example less than 1 mm, the piston and the tube diameter difference should be less than 1 mm.

When the batch is fed into the furnace by means of a conveyor screw a continuous feeding is possible, wherein different components of the batch are mixed because of the rotary motion of the screw.

According to a preferred embodiment of the invention it is foreseen that the supply tube has a horizontal inlet cross section being at least at the level of the top surface of the glass melt or higher. So, the advantages analogous to the communicating vessels principle can be used according to which the pressure of the liquid in two vessels should be in the same height.

Molten glass in the furnace and the second vessel batch itself produces the pressure for feeding the solid raw materials. As molten glass is viscous liquid it is preferable to create a counter pressure to enable the feeding of solid particles. Then, the feeding piston works to route the pressure inside the furnace into the molten glass. Consequently, the piston acts like a pressure directing equipment.

As regards the supply tube it is preferred that the central axis of the conveying section encloses an angle with the central axis of the supply tube, the angle being in a range of 15 degrees to 45 degrees.

Advantageously, it is foreseen according to another preferred embodiment of the invention that the glass batch material is conveyable into the melting chamber by means of a piston arranged in the conveying section of the chamber, the piston being elongated with a circular cross section, the length of the piston being at least as long as a maximal width of the outlet cross section of the supply tube. Thus, the piston serves as closure element to open and to close the outlet cross section of the supply tube and no other closure element is necessary as regards the outlet cross section. As the piston moves forward towards the orifice, the outlet cross section of the supply tube is progressively closed until the whole outlet cross section being closed. Consequently, no more batch material can fall into the conveying section of the chamber. By retracting the piston the outlet cross section is gradually opened again and the batch material enters the chamber again. Of course, the piston stroke is provided in such a way that -viewed in the conveying direction - the top dead center (the most upward position of the piston ^' s front end) is located behind the outlet cross section and the bottom dead center is located in front of the outlet cross section.

As regards the piston it is advantageous that it is tubular with a hollow interior, whereby in view of the conveying direction a front end of the piston being closed with a circular front disc and a back end of the piston being open. According to this preferred embodiment it is possible to attach a piston rod to a rear side of the front disc, an axis of the piston rod coincides with an axis of the piston. Further, a piston with a hollow inside is more lightweight than a solid cylindrical body.

Additionally, it is advantageous as regards a piston with a hollow interior, when the piston has radially running holes that are distributed over its surface, the holes connecting an external environment of the piston with the hollow interior of the piston. The holes can be arranged in different ways: For example, it would be possible to arrange the holes only in an area corresponding to the outlet cross section of the supply tube. Alternatively, the holes can be distributed over the entire shell surface of the piston. The holes can be arranged in parallel rows, the holes of one row being equidistant to each other. Alternatively, the holes can be arranged in other patterns. The diameter of the holes should have a diameter dependent on the particle size of the batch material. It is advantageous if the diameter of the holes does not exceed the three times of the raw material biggest particle size. For example, the diameter should not exceed 12 mm if the maximal particle size is 4 mm.

The distance between adjacent holes should be selected dependent on the stroke of the piston. It is recommended that the distance of the holes should be in the range of 20 % to 40 % of the stroke of the piston.

Providing the piston with holes has the advantage that batch material that gets into the space between the piston and the chamber wall can drop through the holes into the interior of the piston. In this way, sticking of the piston is counteracted. When the interior of the piston is filled or partially filled with batch material, it is possible to empty the interior of the piston via the open back end of the piston, for example by sucking the batch material.

Further, it can be advantageous if the front disc of the piston is provided with holes so that a retraction of the piston is easier because there is no vacuum created. The holes of the inner disc should have a similar or same diameter as the aforementioned holes in the shell surface of the piston.

According to another preferred embodiment of the inventive furnace the piston has a front surface, which is facing the orifice, the surface enclosing an angle with an axis of the piston, the angle being in a range of 30 degrees to 90 degrees, preferably in a range of 45 degrees to 75 degrees.

Advantageously, it is foreseen according to another preferred embodiment of the invention that the glass batch material is conveyable into the melting chamber by means of a conveyor screw arranged in the chamber, the conveyor screw being arranged in the conveying section and below the outlet cross section of the supply tube. With the conveyor screw a continuous feeding is possible.

According to a further preferred embodiment of the invention the device has a circumferentially arranged heat exchange device, preferably in the form of a jacket, being positioned in the feeding section of the chamber. This heat exchange device can be used both for cooling and heating. During operation of the batch charger it is useful to cool the feeding section in order to reduce the stress of the construction. It is required to have a sharp temperature interface between raw material and molten glass. Molten glass has a temperature in the range of 1200 to 1400 degree Celsius and the raw materials should have a temperature in the range of 200 to 400 degree Celsius in order to prevent clogging. So, water cooling enables to create the sharp temperature interface between raw materials and molten glass.

In the event that the batch charger is out of service because of maintenance work or similar, the heat exchange device can be used to at least partially freeze the feeding section of the chamber so that the conveying section and a portion of the feeding section can be maintained, disassembled or repaired. After the maintenance work the heat exchanger device can be used to heat the frozen section in order to speed up the defrosting time to restart the feeding process.

As regards the feeding section of the chamber it is advantageous, if the feeding section has a curved part on its end facing the conveying section so that the connection of the chamber with the wall of the melting chamber can be made easier in terms of construction. With the curved part it is possible to compensate the inclination the conveying section of the chamber.

Additionally, it can be advantageous if the feeding section has a horizontal part on its end facing the melting chamber so that the connection with the wall of the melting chamber is feasible with standard parts.

The problem mentioned above is further solved by a method for feeding glass batch material into a glass melting furnace containing a volume of a glass melt which forms a top surface, wherein the glass batch material is fed into the glass melt of the furnace through an orifice that is positioned below the level of the glass melt top surface, with the following process steps:

- Conveying a certain quantity of the glass batch material into a chamber arranged outside the glass melting furnace, which communicates with the aforementioned orifice, the displacement of the aforementioned quantity from the chamber through the orifice into the glass melt is carried out by means of a piston moving in a conveying direction or by means of a conveyor screw,

- A conveying section of the chamber being supplied with glass batch material via an outlet cross section of a supply tube, characterized by the process step that:

The displacement of the glass batch material is carried out in a conveying direction which is inclined with respect to the horizontal, the angle between the horizontal and the conveying direction being in a range of 30 degrees to 60 degrees.

The advantages described in connection with the inventive furnace apply analogously to the inventive method.

According to a further preferred embodiment of the invention the method is characterized in that the displacement of the glass batch material is made by means of the piston and that the glass batch material is fed in form of rods.

Description of the drawings: The present invention is illustrated with reference to the appended figures, in which

Figure 1 shows: a vertical cross section of an inventive glass melting furnace with a device for conveying glass batch material into the furnace,

Figure 1a: the furnace of figure 1 with batch rods,

Figures 2a to 2d: a vertical cross section of the inventive device of figure 1 with the piston being in different positions,

Figure 3 shows: a three-dimensional view of the inventive device of figure 1 ,

Figure 4 shows: a vertical cross section of a second inventive furnace and

Figure 5 shows: a three-dimensional view of a third inventive furnace.

Figure 1 shows an example for a preferred embodiment of an inventive glass melting furnace 1 with a melting chamber 2 from which only a part is shown. The melting chamber 2 is filled with glass melt, the level of glass melt being shown with dotted line 3. Next to the melting chamber 2 a device 4 for conveying glass batch material 5 is arranged, the device 4 and the melting chamber 2 being connected via an orifice 6. The device 4 for conveying glass batch material 5 has an elongated tubular chamber 7 with a circular cross section and a cylindrical side wall 8. The orifice 6 is arranged in a side wall 9 of the melting chamber 2 and has the same cross section than a free cross section of the tubular chamber 7. So, the orifice 6 has also a circular cross section.

A piston 10 with a piston rod 11 is arranged within the chamber 7, the piston 10 being displaceable in longitudinal direction 12 of the chamber 7. The piston 10 is composed of an elongated cylindrical element 13 and a circular front disc 14, which closes a front end 15 of the cylindrical element 13. At a back end 16 the cylindrical element 13 is open. So, the piston 10 has a hollow interior 17 in which the piston rod 11 runs as the piston rod 11 is attached to a rear side of the circular front disc 14. So, an axis 18 of the piston rod 11 coincides with an axis 19 of the piston 10. The piston 10 as well as the piston rod 11 is made of steel material.

The cylindrical element 13 of the piston 10 has four rows 20 of holes 21, the rows 20 running parallel to the axis 19 of the piston 10. The holes 21 are arranged radially and connect an external environment of the piston 10 with its hollow interior 17. In figure 1 only one row 20 of three equidistant holes 21 is shown, one of the holes 21 being placed adjacent to the front disc 14. It is alternatively possible to arrange the holes in another number and other patterns. To ensure that the piston 10 is movable in the longitudinal direction 12 of the chamber 7 without risk of sticking, an outer diameter of the piston 10 is slightly smaller than an inner diameter of the chamber 7. In the present example the deviation of the diameters needs only to be in a range of 0,5 mm to 2 mm. Optionally, it can be advantageous to arrange holes in the front disc 14 of the piston 10 so that a possible vacuum is avoided between the front disc 14 and the chamber 7 when the piston 10 is retracted.

As shown in figure 1 the chamber 7 has a conveying section 22, in which the batch material 5 is conveyable in conveying direction 23 towards the orifice6 by means of the piston 10. In other words, the section of the chamber 7 in which the piston 10 is displaceable is defined as conveying section 22 of the chamber 7. It goes without saying that the conveying section 22 is made in a straight manner to ensure that the piston 10 can move in between a top dead center 24 and a bottom dead center 25.

The conveying section 22 is followed by a feeding section 26 which connects the conveying section with the wall 9 of the melting chamber 2.

The conveying section 22 is inclined with respect to the horizontal. In detail, the axis 27 of the conveying section 22 encloses an angle 28 of 45 degrees with the horizontal. Consequently, the piston 10 is inclined in the same manner.

The feeding section 26 has a bended part 29 and a horizontal part 30 so that a connection with the wall 9 of the melting chamber 2 is feasible easily.

Further, the device 4 for conveying glass batch material 5 has a supply tube 31 with an outlet cross section 32 communicating with the chamber 7. The supply tube 31 is also inclined with respect to the horizontal, the angle 33 of inclination being 75 degrees. So an axis 34 of the supply tube 31 encloses an angle 35 of 30 degrees with the axis 27 of the conveying section 22. Consequently, the outlet cross section 32 of the supply tube 31 is inclined accordingly. The supply tube 31 has an inlet cross section 36 which is horizontal and which is above the level of melt.

With the device 4 according to figure 1 it is possible to feed loose batch material 5 via the supply tube 31. In the position of the piston 10 shown in figure 1 the outlet cross section 32 of the supply tube 31 is entirely opened and the loose batch material 5 falls down into the chamber 7. When the level of batch material 5 reaches an upper point 37 of the outlet cross section 32 the piston 10 is moved towards the orifice 6 so that the outlet cross section 32 is closed by the cylindrical wall of the piston 10 and the batch material 5 is advanced via the orifice 6. After reaching the bottom dead center 25 the piston 10 is retracted and the outlet cross section 32 is opened again. New batch material 5 falls into the chamber 7. After reaching the top dead center 24 the piston 10 is moved towards the orifice 6 again and the former inserted batch material 5 is pushed by the new batch material 5 and enters the melt chamber 2. It is evident that there is always batch material 5 in the feeding section 26 of the chamber 7, which serves as plug to prevent the entrance of melt into the chamber 7. For the sake of a better overview of the figure 1 the loose batch material is not shown.

As described before, the piston 10 serves as closing element as regards the outlet cross section 32 of the supply tube 31. In consequence, a length 38 of the piston 10 is at least as long as a maximal width of the outlet cross section 32 of the supply tube 31.

Alternatively, it is possible with the inventive device 4 according to figure 1 to feed batch material 5 into the melting chamber 2 the batch material 5 being formed as rods 43 with a circular cross section. In this event batch rods are positioned in the supply tube 31 the batch rods falling into the conveying section 22 of the chamber 7 when the piston 10 is retracted in such a way that it releases the outlet cross section 32 of the supply tube 31. The inventive device 4 with batch rods 43 inside is shown in figure 1a.

The embodiment of the invention shown in figure 1 further has a heat exchange device 39 in form of a jacket 40 that is circumferentially arranged in the feeding section 26 of the chamber 7 and adjacent to the wall 9 of the melting chamber 2. With the heat exchange device 39 it is possible to cool and to heat the feeding section 26 according to the requirements needed.

Figures 2a to 2d each show a vertical cross section of the inventive furnace 1 of figure 1, the piston 10 being in different positions. For purpose of a better overview the batch material, which can be loose material or batch rods, is not shown in the figures. In figure 2a the piston 10 is forwarded until its bottom dead center 25 so that the outlet cross section 32 is entirely closed. It can be seen that the length 38 of the piston 10 is slightly longer than the maximal width of the outlet cross section 32. Figure 2b shows the piston 10 in a position in which it is partly retracted, so that a part of the outlet cross section 32 is opened. In figure 2c the piston 10 is pulled back even more so that a big part of the outlet cross section 32 is opened. Figure 2d shows the piston 10 in its top dead center 24 so that the outlet cross section 32 is entirely free.

Figure 3 shows the inventive furnace 1 of figure 1 in a three-dimensional view.

In figure 4 another embodiment of the inventive furnace is shown. The only difference to the embodiment shown in the figures 1 to 3 is that the conveying means are composed of a conveyor screw 41 arranged in the conveying section 22 of the chamber 7. With the conveyor screw 41 it is only possible to feed loose material which is not shown in the figure.

Figure 5 shows a three-dimensional view of a third inventive furnace 1 which differs from the furnace 1 shown in figure 1 only in that it has a container 42 on the supply tube 31. The container 42 helps to feed the furnace 1 with loose batch material 5, which is put in the container 42 before the batch material 5 descends the supply tube 31.

Reference numerals:

1 glass melting furnace

2 melting chamber

3 dotted line 4 device

5 glass batch material

6 orifice

7 chamber

8 side wall of the chamber 9 side wall of the melting chamber

10 piston 11 piston rod 12 longitudinal direction of the chamber 13 cylindrical element 14 front disc

15 front end

16 back end

17 interior

18 axis piston rod 19 axis piston

20 row

21 hole 22 conveying section

23 conveying direction

24 top dead center

25 bottom dead center 26 feeding section

27 axis conveying section

28 angle

29 bended part

30 horizontal part 31 supply tube

32 outlet cross section

33 angle

34 axis supply tube

35 angle 36 inlet cross section

37 upper point

38 length

39 heat exchange device

40 jacket 41 conveyor screw

42 container

43 rod