Method and installation for producing hollow microbeads of glass

Abstract

Hollow microbeads of glass are produced during a number of operating phases in which an upwardly directed hot gas flow is produced in a firing chamber by firing a vertical furnace. The firing chamber is continuously charged with microparticles of a starting glass material and the microparticles are expanded in the hot gas flow into the hollow microbeads. Expanded hollow microbeads are discharged out of the firing chamber with the gas flow through a gas outlet at the upper end of the vertical furnace. Between successive operating phases there is respectively provided a charging break, during which the charging of the firing chamber with the microparticles is suspended. In these charging breaks, the microparticles remaining in the firing chamber are respectively removed from the firing chamber.

Claims

1. A method for producing hollow microbeads of glass, the method comprising: during each of a plurality of operating phases: producing an upwardly directed hot gas flow in a vertical furnace by firing in a firing chamber of the vertical furnace; continuously charging the firing chamber with microparticles of a starting glass material; expanding the microparticles in the hot gas flow to form the hollow microbeads; and discharging expanded hollow microbeads out of the firing chamber with the gas flow through a gas outlet at an upper end of the vertical furnace; and setting a duration of the operating phases so that the discharging of the firing chamber takes place before operation of the vertical furnace is significantly impaired by the microparticles collecting therein; providing a charging break between mutually successive operating phases, and during the charging break: suspending the charging of the microparticles into the firing chamber; and removing the microparticles remaining in the firing chamber from the firing chamber.

2. The method according to claim 1, which comprises: during each charging break, reducing the gas flow to allow the microparticles remaining in the firing chamber to sink to a bottom of the firing chamber; and removing the microparticles from the firing chamber through an outlet opening provided in the bottom of the firing chamber.

3. The method according to claim 2, which comprises reducing a temperature of the gas flow during the charging breaks prior to reducing the gas flow by introducing cold gas.

4. The method according to claim 1, which comprises: during each charging break, increasing the gas flow by blowing cold gas into the firing chamber, to blow the microparticles remaining in the firing chamber out from the firing chamber by way of the gas outlet at the upper end of the vertical furnace.

5. The method according to claim 4, which comprises reducing a temperature of the gas flow during the charging breaks prior to increasing the gas flow by introducing cold gas.

6. The method according to claim 1, which comprises performing operating phases and charging breaks following one another in a regular cycle over time.

7. The method according to claim 1, wherein the operating phases have a uniform duration, which exceeds a duration of the charging breaks.

8. The method according to claim 1, which comprises setting a duration of each charging break to between 5 seconds and 60 seconds.

9. An installation for producing hollow microbeads of glass, the installation comprising: a vertical furnace having a firing chamber with a gas outlet formed at an upper end thereof; a burner disposed in said firing chamber and configured to produce an upwardly directed hot gas flow in said firing chamber; a charging device for charging said firing chamber with microparticles of a starting glass material, whereupon the microparticles are expanded in the hot gas flow into the hollow microbeads, and the microbeads are discharged out of the firing chamber with the gas flow through the gas outlet; and a control unit configured to automatically carry out the method according to claim 1.

10. The installation according to claim 9, which comprises an outlet opening at a bottom of the firing chamber for removing microparticles remaining in said firing chamber.

11. The method according to claim 1, which comprises carrying out the operating phases with a duration of each operating phase between 4 minutes and 30 minutes.

12. A method for producing hollow microbeads of glass, the method comprising: during each of a plurality of operating phases: producing an upwardly directed hot gas flow in a vertical furnace by firing in a firing chamber of the vertical furnace; continuously charging the firing chamber with microparticles of a starting glass material; expanding the microparticles in the hot gas flow to form the hollow microbeads; and discharging expanded hollow microbeads out of the firing chamber with the gas flow through a gas outlet at an upper end of the vertical furnace; and carrying out the operating phases with a duration of each operating phase between 4 minutes and 30 minutes; providing a charging break between mutually successive operating phases, and during the charging break: suspending the charging of the microparticles into the firing chamber; and removing the microparticles remaining in the firing chamber from the firing chamber.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

(1) FIG. 1 is a highly schematic and simplified representation of an installation for producing hollow microbeads of glass with a vertical furnace, a hot gas flow in which introduced microparticles of a starting glass material are expanded into the desired hollow microbeads being produced in a firing chamber of the vertical furnace by means of a burner;

(2) FIG. 2 shows in six synchronous diagrams arranged one above the other the sequence over time of a method carried out by means of the installation according to FIG. 1 for producing hollow microbeads on the basis of six operating parameters of the installation, to be specific (from the top downward) on the basis of the flow velocity of the gas flow within the firing chamber, the temperature of this gas flow, the burner output, the blower output of a cold-gas blower, the charging rate at which the microparticles are introduced into the firing chamber and the position of a reject valve, which is arranged downstream of an outlet opening arranged in the bottom of the firing chamber;

(3) FIG. 3 shows in a representation according to FIG. 1 an alternative configuration of the installation there;

(4) FIG. 4 shows in a representation according to FIG. 2 the sequence of the method carried out by means of the installation according to FIG. 3 on the basis of once again six parameters of this installation, to be specific (from the top downward) on the basis of the flow velocity of the gas flow in the firing chamber, the temperature of this gas flow, the burner output, the blower output of a cold-gas blower, the charging rate and the position of a three-way valve arranged in a flue duct of the firing chamber; and

(5) FIG. 5 shows in a representation according to FIG. 1 a variant of the shaft furnace according to FIG. 1 or FIG. 3 with a double-wall furnace shell in the form of a detail.

DETAILED DESCRIPTION OF THE INVENTION

(6) Referring now to the figures of the drawing in detail and first, particularly, to FIG. 1 thereof, there is shown, in highly schematic simplification, an installation 1 for producing hollow microbeads 2 of glass G. The central component part of the installation 1 is a vertical furnace 3 with a substantially hollow-cylindrical, peripheral (furnace) shell 4, which surrounds the firing chamber 5, which is elongated in the manner of a shaft and aligned vertically with regard to its longitudinal extent. In a preferred form of the vertical furnace 3, the shell 4 comprises an inside wall 6 of steel directly bounding the firing chamber 5 and a thermal insulation 7, provided on the outside of the inside wall 6. In an alternative configuration of the installation 1, the shell 4 may however also have a fiber insulation on the inside (i.e. directly adjacent the firing chamber 5), which is stabilized by a ramming compound.

(7) At its lower end, the shell 4 is formed by a conical (frustoconical) bottom 8, which opens out into an outlet opening 9. This outlet opening 9 is adjoined by a reject line 10, which can be reversibly opened and closed by a reject valve 11. The reject line 10 opens out into a reject reservoir 12, which is formed for example by a silo or a container.

(8) At its upper end, the shell 4 is closed off by a likewise frustoconical (alternatively curved) dome 13, which opens out into a gas outlet 14. The gas outlet 14 is adjoined by a pipeline referred to as a flue duct 15, which opens out into a solids separator 16. A lower end (solids outlet) of the solids separator 16, preferably formed as a cyclone separator, is adjoined by a product line 17, which is closed off by a product valve 18 in a pressure-tight manner, though allowing deposited products (that is to say hollow microbeads 2 produced) to pass through. The product valve 18 is formed for example in the form of a double swing valve or a rotary feeder. The product line 17 opens out into a product reservoir 19, which once again is formed for example by a silo or a container.

(9) In a region of the vertical furnace 3 near the bottom, a burner 20 operated by a combustible gas B is arranged within the firing chamber 5. The combustible gas B is fed to the burner 20 by way of a combustible-gas line 21, in which a gas valve 22 is arranged to control the gas inflow. The burner output Lb can be variably set here by way of the gas valve 22.

(10) On the other hand, the installation 1 comprises a (cold-gas) blower 23, in order to blow cold gas K (here by way of example outside air at ambient temperature) into the firing chamber 5. In the representation according to FIG. 1, the blower 23 is for this purpose connected to the burner 20 by way of a cold-gas line 24. The cold gas K is consequently blown into the burner 20. In alternative embodiments of the installation 1, the cold-gas line 24 opens out into cold-gas nozzles, which are arranged separately from the burner 20 in the lower part of the firing chamber 5.

(11) Furthermore, the installation 1 comprises a charging device 25, with which microparticles 26 of a starting glass material A can be introduced into the firing chamber 5 as a starting product for the production of the hollow microbeads 2.

(12) The charging device 25 comprises a output head 27, which is arranged above the burner 20 in the firing chamber 5 and by way of which the microparticles 26 are output into the firing chamber 5. The output head 27 is connected to a supply line 28, by way of which the microparticles 26 are transported into the firing chamber. Arranged in the supply line 28 is an actuating unit 29, by way of which the charging rate r can be set. Here, the charging rate r refers to the amount (weight or volume) of microparticles 26 output into the firing chamber 5 per unit of time. Optionally, the charging unit 25 comprises means for preheating the microparticles 26 to a temperature lying below the softening point of the starting glass material, for example to approximately 800° C. The microparticles 26 are thereby output into the firing chamber 5 in a correspondingly preheated state. A hot-air blower or an electrically heated supply line 28 are provided for example as means for preheating the microparticles 26.

(13) Finally, the installation 1 comprises a control unit 30, which in the embodiment represented comprises a control computer 31 with a control program 32 to be executed by the computer. The control unit 30 serves for automatically controlling the installation 1 in its operation and for this purpose is connected, for example by way of an indicated fieldbus 33, to the outlet valve 11, the gas valve 22, the blower 23 and the actuating unit 29, in order to control these components of the installation automatically.

(14) In the operation of the installation 1, the firing chamber 5 is fired by means of the burner 20. Produced as a result within the firing chamber 5 is an upwardly directed hot gas flow H, into which the microparticles 26 are output by means of the output head 27. As input variables for controlling the aforementioned components of the installation, measured values of the flow velocity v and the temperature T of the gas flow H, which are collected by the sensor unit 34 arranged in the firing chamber 5, are fed to the control unit 30 by way of the fieldbus 33.

(15) The microparticles 26 are melted by the hot gas flow H, the microparticles 26 being inflated (expanded) into the desired hollow microbeads 2 by gas formation of a blowing agent contained in the starting glass material A. On account of their very much lower apparent density in comparison with the microparticles 26, the expanded hollow microbeads 2 are discharged out of the firing chamber 5 with the gas flow H through the gas outlet 14 and fed to the solids separator 16. Here, the hollow microbeads 2 are separated from the furnace offgases. While the offgas cleaned in such a way is output to the environment or passed on for further offgas treatment, the hollow microbeads 2 separated in the solids separator 16 are fed to the product reservoir 19 by way of the product line 17.

(16) Essential boundary conditions for this process are the temperature T and the flow velocity v of the gas flow H produced in the firing chamber 5. Both parameters are set by the control unit 30 indirectly by way of the setting of the burner output Lb and the blower output Lk. The burner output Lb is controlled here by the control unit 30 by activation of the gas valve 22. By contrast, the blower output Lk is controlled by the control unit 30 by activation of the blower 23.

(17) The method automatically carried out by the control unit 30 running the control program 32 is represented in FIG. 2 on the basis of the variation over time of the flow velocity v, the temperature T, the burner output Lb, the blower output Lk and the charging rate r. Also represented in FIG. 2 is the variation over time of the valve position S1 of the reject valve 11 activated by the control unit 30. In this representation, the valve position S1 assumes a positive value, other than zero, when the reject valve 11 is open, while the valve position S1 assumes the value zero when the reject valve 11 is closed.

(18) It can be seen from the representation that the installation 1 is not in continuous operation in the course of the method. Rather, the operation of the installation 1 according to the method is distinguished by a regular alternation over time of operating phases 35 and charging breaks 36. The operating phases 35 have a much greater time duration here than the charging breaks 36. Thus, in an example of how the method is carried out, the operating phases 35 have a duration of in each case 20 minutes, while the charging breaks 36 have in each case a time duration of 30 seconds.

(19) In each of the operating phases 35, hollow microbeads 2 are produced by means of the installation 1 in the way described above. Correspondingly, the charging rate r in the operating phases 35 always has a positive value. In the operating phases 35, the gas flow H is steadily produced with an approximately constant flow velocity v and approximately constant temperature T between approximately 1400° C. and 1900° C. by firing the firing chamber 5 while admixing a comparatively small amount of cold gas K. Consequently, the operating phases 35 are distinguished by a comparatively high burner output Lb and comparatively low blower output Lk. Moreover, the reject valve 11 is always kept closed in the operating phases 35.

(20) With the beginning of each charging break 36, the charging of the firing chamber 5 with the microparticles 26 is suspended by the control unit 30 by corresponding activation of the actuating unit 29. Correspondingly, the charging rate r returns to the value zero. At the same time, the burner 20 is switched by the control unit 30 to a standby mode, in that the control unit 30 lowers the burner output Lb to a small value by corresponding activation of the gas valve 22.

(21) In a cooling-down phase 40, of for example approximately 5 sec, at the beginning of each charging break 36, the flow velocity v prevailing in the firing chamber 5 is at least approximately maintained by increased blowing in of cold gas K. The reduction in the burner output Lb is consequently compensated by a temporary increase in the blower output Lk. As a result, in the cooling-down phase 40 on the one hand the (non-expanded or partly expanded) microparticles 26 still remaining in the firing chamber 5 are kept in suspension. On the other hand, the microparticles 26 are cooled down abruptly to below 800° C. by the increased blowing in of cold gas K (which can be seen in FIG. 2 from the drop in the temperature T), whereby the sticking of the microparticles 26 to one another and to the inside wall 6 of the vertical furnace 3 is avoided or at least reduced.

(22) After the cooling-down phase 40, in an emptying phase 41 on the one hand the blower output Lk is also lowered by the control unit 30 (with the still lowered burner output Lb), whereby the flow velocity v in the firing chamber 5 drops sharply. At the same time, the reject valve 11 is opened by the control unit 30, which is manifested in the representation according to FIG. 2 by the value of the valve position S1 jumping from zero to one.

(23) Due to the interruption in the gas flow H, the microparticles 26 remaining in the firing chamber 5 sink to the bottom 8 of the vertical furnace 3 and fall from there through the outlet opening 9 and the reject line 10 into the reject reservoir 12. If it is not possible for these microparticles 26 to be transported in the reject line 10 by gravitational force alone, suitable transporting means are provided in the reject line 10, for example a feed screw or a blower, with which the microparticles 26 withdrawn from the firing chamber 5 are actively transported into the reject reservoir 12.

(24) After the emptying phase 41—lasting for example 15 seconds—the valve 11 is closed again by the control unit 30, whereby the valve position S1 jumps back again to the value zero. Subsequently, in a heating-up phase 42 lasting for example for 10 seconds, the burner output Lb and the blower output Lk are raised by the control unit 30 to their values typical for the operating phase 35, whereby on the one hand the flow velocity v of the gas flow H assumes its operating value and on the other hand the temperature T of the gas flow H also increases again

(25) After the heating-up phase 42, the next operating phase 35 is started by the control unit 30, in that the control unit 30 starts renewed charging of the firing chamber 5 by corresponding activation of the actuating unit 29. The method steps described above are cyclically repeated.

(26) FIG. 3 shows an alternative embodiment of the installation 1. Apart from the differences described below, this embodiment corresponds to the installation 1 shown in FIG. 1. As a difference from the embodiment there, in the case of the installation 1 according to FIG. 3 however there is no outlet opening 9 in the bottom 8 of the vertical furnace 3. Instead, provided in the flue duct 15 in the case of the installation 1 according to FIG. 3 is a branching 50, by which the flue duct 15 is divided into a product branch 51 and a reject branch 52. The three-way valve 53, which is provided at the branching 50 and is activated by the control unit 30 by way of the fieldbus 33, allows the gas outlet 14 to be connected in a reversibly switchable manner either to the product branch 51 or to the reject branch 52 of the flue duct 15.

(27) While—as in the case of the embodiment according to FIG. 1—the product branch 51 opens out into the solids separator 16 intended for separating the hollow microbeads 2, the reject branch 52 opens out into a second solids separator 54. This solids separator 54 is preferably likewise formed by a cyclone separator, which is in particular structurally identical to the solids separator 16. On its underside, the solids separator 54 opens out into the reject line 10, which—as in the case of the exemplary embodiment according to FIG. 1—is connected to the reject reservoir 12. Instead of the reject valve 11, provided in the reject line 10 in the case of the exemplary embodiment according to FIG. 3 however is a modified reject valve 55, which closes off the solids separator 54 from the environment in a pressure-tight manner, though allowing the microparticles 26 withdrawn from the firing chamber 5 to pass through. In a way similar to the case of the product valve 18, the reject valve 55 is formed for example by a double swing valve or a rotary feeder. The reject valve 55 here is formed in particular as structurally identical to the product valve 18.

(28) The sequence of the method carried out with the installation according to FIG. 3 for producing the hollow microbeads 2 is represented in FIG. 4. This representation corresponds to the representation according to FIG. 2, although a valve position S2 of the three-way valve 53 is indicated instead of the valve position S1. The valve position S2 here assumes a positive value, other than zero, when the reject branch 52 is connected to the gas outlet 14 of the vertical furnace 3 by the three-way valve 53. If, on the other hand, the product branch 51 of the flue duct 15 is connected to the gas outlet 14, the valve position S2 in the representation according to FIG. 4 has the value zero.

(29) Except as otherwise described below—the method carried out by way of the installation 1 according to FIG. 3 is identical to the method described on the basis of FIG. 2. In particular, also in the case of the installation according to FIG. 3, the charging of the firing chamber 5 with the microparticles 26 is suspended by the control unit 30 during the charging breaks 36 (r=0) and, after the initial cooling-down phase 40, the burner output Lb is lowered.

(30) However—as a difference from the method according to FIG. 2—during the emptying phase 41 the lowered burner output Lb is overcompensated by a further increase in the blower output Lk. This causes a sharp rise in the flow velocity v in the firing chamber 5 during the emptying phase 41, whereby the non-expanded or only partly expanded microparticles 26 that remained in the firing chamber 5 at the completion of the preceding operating phase 35 are also blown out upwardly through the gas outlet 14.

(31) In order to prevent this rejected matter being separated together with the properly expanded hollow microbeads 2 in the solids separator 16, the control unit 30 switches over the three-way valve 53 at the beginning of the emptying phase 41, so that the gas outlet 14 is connected to the reject branch 52. In the representation according to FIG. 4, this can be seen by the value of the valve position S2 assuming a value other than zero.

(32) The microparticles 26 discharged out of the firing chamber 5 during the emptying phase 41 are consequently separated in the solids separator 54 and in turn pass by way of the reject line 10 into the reject reservoir 12.

(33) FIG. 5 shows a variant of the vertical furnace 3 in the form of a detail, in which the shell 4 is formed with a double wall. The shell 4 comprises here in addition to the inside wall 6 an outside wall 60 of steel, which surrounds the inside wall 6 at a distance. The insulation 7 is provided here on the outside of the outside wall 60. The inside wall 6 does not bear any insulation.

(34) The inside wall 6 is formed by a shell that is welded, and consequently of one piece in the finished state. By contrast, the outside wall 60 is preferably made up of three parts, to be specific a boiler head (in particular a standard part as used conventionally for boilers or storage tanks), which forms the dome 13, and also two half-shells, which respectively form one half of the middle region and the bottom 8. These three parts are screwed to one another or reversibly joined together in some other way, in order to be able to dismantle the vertical furnace 3 easily for maintenance and repair purposes. The vertical separation of the outside wall 60 into the two half-shells advantageously makes it possible here—by removing at least one half-shell—to have good accessibility to the inside wall 6, without the vertical furnace 3 having to be completely dismantled for this.

(35) In order to make stress-free thermal expansion of the inside wall 6 possible, the inside wall 6 is exclusively suspended from the boiler head, that is to say the dome region of the outside wall 60, and is not otherwise in contact with any other rigid part of the installation 1. In this case, the suspension of the inside wall 6 on the outside wall 60 is also expediently configured in a flexible manner, so that a radial movement of the inside wall 6 with respect to the outside wall 60 is made possible.

(36) Formed between the inside wall 6 and the outside wall 60 is an air gap—annular in horizontal section through the vertical furnace 3—which is referred to as a shell interspace 61 and the thickness of which (measured in each case perpendicularly to the inside wall 6) is for example about 20 to 30 cm. At its lower periphery, the shell interspace 61 is closed off by a temperature-resistant and flexible seal (not explicitly represented).

(37) The double-wall shell 4 is used for cooling the inside wall 6. For this purpose, the lower region of the shell interspace 61 is connected by way of a warm-air line 62 to a mixer 63, into which the cold-gas line 24 opens out on the other side. On the output side, the mixer 63 is connected to the burner 20 by way of an air line 64. In the mixer 63, the cold gas K fed in by way of the cold-gas line 24 is mixed with the warm air W, fed in by way of the warm-air line 62, in a ratio that can be variably set.

(38) In the operation of the vertical furnace 3, cold air is introduced—by means of a not explicitly represented blower, for example a rotary blower—by way of an air line 65 in a volumetrically metered manner and under positive pressure into an upper region of the shell interspace 61. On account of the positive pressure, the heated warm air W escapes from the lower region of the shell interspace 61 by way of the warm-air line 62. The air circulation consequently produced in the shell interspace 61 has the effect that the inside wall 6 of the shell 4 is cooled in countercurrent in relation to the gas flow H.

(39) In the case of the variant of the vertical furnace 3 according to FIG. 5, the temperature of the air L fed to the burner 20 is set by the mixer 63. As a result, the temperature T of the gas flow H in the firing chamber 5 is also indirectly influenced.

(40) The double-wall shell 4 and cooling-air ducting described above may be provided both in the case of the installation 1 according to FIG. 1 and in the case of the installation 1 according to FIG. 3. The bottom 8, of different designs in FIGS. 1 and 3, of the firing furnace 3 is therefore only partially represented in FIG. 5.

(41) The invention becomes particularly clear from the exemplary embodiments described above, but is nonetheless not restricted to these exemplary embodiments. Rather, further embodiments of the invention can be derived from the claims and the foregoing description.

(42) The following is a summary list of reference numerals and the corresponding structure used in the above description of the invention:

(43) 1 Installation

(44) 2 Hollow microbeads

(45) 3 Vertical furnace

(46) 4 (Furnace) shell

(47) 5 Firing chamber

(48) 6 Inside wall

(49) 7 Insulation

(50) 8 Bottom

(51) 9 Outlet opening

(52) 10 Reject line

(53) 11 Reject valve

(54) 12 Reject reservoir

(55) 13 Dome

(56) 14 Gas outlet

(57) 15 Flue duct

(58) 16 Solids separator

(59) 17 Product line

(60) 18 Product valve

(61) 19 Product reservoir

(62) 20 Burner

(63) 21 Combustible-gas line

(64) 22 Gas valve

(65) 23 (Cold-gas) blower

(66) 24 Cold-gas line

(67) 25 Charging device

(68) 26 Microparticles

(69) 27 Output head

(70) 28 Supply line

(71) 29 Actuating unit

(72) 30 Control unit

(73) 31 Control computer

(74) 32 Control program

(75) 33 Fieldbus

(76) 34 Sensor unit

(77) 35 Operating phase

(78) 36 Charging break

(79) 40 Cooling-down phase

(80) 41 Emptying phase

(81) 42 Heating-up phase

(82) 50 Branching

(83) 51 Product branch

(84) 52 Reject branch

(85) 53 Three-way valve

(86) 54 Solids separator

(87) 55 Reject valve

(88) 60 Outside wall

(89) 61 Shell interspace

(90) 62 Warm-air line

(91) 63 Mixer

(92) 64 Air line

(93) 65 Air line

(94) r Charging rate

(95) t Time

(96) v Flow velocity

(97) A Starting glass material

(98) B Combustible gas

(99) G Glass

(100) H Gas flow

(101) K Cold gas

(102) L Air

(103) Lb Burner output

(104) Lk Blower output

(105) S1 Valve position

(106) S2 Valve position

(107) T Temperature

(108) W Warm air