WO1980002833A1

WO1980002833A1 - Infrared batch level control for a glass furnace

Info

Publication number: WO1980002833A1
Application number: PCT/US1980/000497
Authority: WO
Inventors: H Moody
Original assignee: Owens Corning Fiberglass Corp
Priority date: 1979-06-18
Filing date: 1980-04-30
Publication date: 1980-12-24

Abstract

System for maintaining a predetermined thick blanket of batch (11) over a body of molten glass (13) in a glass melting furnace (14). An infrared sensor (18) remotely measures the surface temperature of the blanket of batch (11). The measured surface temperature is compared with a set point temperature for controlling the rate at which batch is fed to the furnace (14).

Description

D E S C R I P T I O N

INFRARED BATCH LEVEL CONTROL FOR A GLASS FURNACE

TECHNICAL FIELD This invention relates to glass making and more particularly an improved system for maintaining a desired level of batch in a glass melting furnace.

BACKGROUND ART In one type of glass melting furnace, a plurality of parallel electrodes are submerged within a pool of molten glass. An electric current is caused to flow through the molten glass between the electrodes to heat the glass by the Joule effect. A layer of raw glass batch material is maintained on the surface of the molten glass in the furnace. The batch is gradually melted to form additional glass and also forms an insulating layer or crust on the upper surface of the molten glass. As the batch is gradually melted and the thickness of the layer drops, there will be an increase in the heat loss from the body of molten glass in the furnace through the batch. Conversely, as additional batch material is distributed over the upper surface of the molten glass, there will be a decrease in the heat loss through the thicker layer of batch material.

United States Patent 3,930,460 is directed to a feeder for distributing a glass batch over the upper surface of a body of molten glass in a glass melting furnace. A sensor, such as a thermocouple or thermistor, senses the air temperature at some distance above the crust of batch floating on the molten glass. As the temperature increases, power is increased to a motor to increase the rate at which additional batch is added to the furnace. Conversely, as the temperature decreases, the motor is slowed down to decrease the rate at which batch is added to the furnace. With a conventional electric glass furnace having submerged electrodes, the batch is maintained in a blanket on the order of 5.2 cm to 20.3 cm (six to eight inches) thick. A control of this type has not been satisfactory for use with electric glass melting furnaces of a design which maintains a very thin layer of batch on the upper surface of a body of molten glass. For example, a batch thickness on the order of 9.5 mm (3/8 inch) to 1.28 cm (1/2 inch) is maintained in a furnace of the type known as a "paramelter". A paramelter furnace is much smaller than other glass melting furnaces and is provided with a platinum screen submerged within a body of molten glass. Electric current passes through and heats the platinum screen which in turn heats the molten glass. DISCLOSURE OF THE INVENTION

According to the present invention an improved system is provided for controlling the thickness of a thin layer of batch floating on a body of molten glass in a furnace of the type known as a paramelter furnace. The system also is suitable for other types of glass melting furnaces in which a relatively thin blanket of batch is maintained over a pool of molten glass, namely, a blanket of no more than 2.54 cm (one inch) of batch. A conventional batch distributor is positioned for uniformly distributing batch over the surface of the furnace. An infrared sensor is mounted on or adjacent the batch distributor for obtaining a non-contact measurement of the temperature of the outer batch surface. The sensor is connected to a remotely located control which indicates the batch surface temperature. A set point temperature, which is manually entered into the control, is compared with the indicated temperature of the batch surface for generating a control signal which drives the batch distributor. The batch distributor either is turned on or its speed is increased in response to a slight increase in the measured batch surface temperature. Or, the batch distributor is stopped or slowed down in response to a slight decrease in the measured batch thickness is accurately controlled, for example, to 9.5 mm (3/8 inch) or .64 cm (1/4 inch) or 1.28 crn (1/2 inch) or 1.92 cm (3/4 inch), as desired, to maintain optimum conditions for the furnace. BRIEF DESCRIPTION OF THE DRAWINGS

The single figure is a schematic illustration of infrared control apparatus for maintaining a predetermined level of batch material on the surface of a body of molten glass in a glass melting furnace. BEST MODE OF CARRYING OUT THE INVENTION

Referring to the drawing, apparatus 10 is illustrated for distributing and controlling the thickness of a blanket of batch 11 floating on the surface 12 of a body of molten glass 13 in a glass melting furnace 14. The furnace 14, which is illustrated in section, is of the parametric type and includes a platinum screen 15 which is spaced parallel to and typically a few inches below the upper surface 12 of the molten glass 13. An electric current is passed through the screen 15 for heating the screen 15 to a high temperature to in turn melt and heat the glass 13. In a furnace of this type, it is desirable to maintain the blanket of batch 11 as a uniform, relatively thin layer over the molten glass 13. For example, the blanket of batch 11 may be on the order of 9.5 mm (3/8 inch) or 1.28 cm (1/2 inch) and is always less the 2.54 cm (1 inch) in thickness.

A feeder 16 is mounted for distributing the blanket of batch 11 over the molten glass 13 in the furnace 14. The feeder 16 may be of any desired configuration, for example, such as the feeder illustrated in United States Patent No. 3,980,460. Batch is discharged from the feeder 16 at a rate determined by the speed of a motor 17 which drives the feeder 16. The feeder 16 also is reciprocated across the furnace 14 to uniformly distribute the batch 11 over the upper surface 12 of the molten glass 13, as is known in the prior art. An infrared sensor 18 is mounted on or adjacent the feeder 16 for remotely sensing the temperature of the upper surface of the blanket of batch 11. The infrared sensor 18 is aimed to measure the temperature of the batch 11 at the area in which the feeder 16 is adding or is about to add additional batch without contacting the furnace 14 or the blanket of batch 11. The infrared sensor 18 is connected to a control 19. The infrared sensor 18 and control 19, for example, may consist of a Modline 6000 infrared sensor and control manufactured by Ircon of Skokie, Illinois. The controller 19 includes an analogue or a digital display 20 which indicates to a system operator, the temperature of the surface of the blanket of batch 11 as measured by the infrared sensor 18. A plurality of knobs 21 also are provided on the controller 19. At least some of the knobs 21 permit the system operator to enter a set point into the controller 19. For example, if it is desired to maintain a surface temperature of 298.9°C. (750°F.) on the blanket of batch 11, the knobs 21 may be used to enter this temperature into the controller 19. The controller 19 has an output 22 which is used to control the motor 17 which drives the batch feeder 16. The output 22 from the controller 19, for example, may comprise a DC control signal which varies from 0 volts to some predetermined maximum voltage. If necessary, this signal may be modified in a conventional manner to vary between any two voltages or to v ary in frequency for controlling the motor 17, depending upon the type and range of control signals required by the motor 17.

In operation, a system operator initially operates the apparatus 10 manually through the use of the knobs 21. Through the knobs 10, the operator drives the motor 17 at a maximum speed to build up the blanket of batch 11 over the molten glass 13 in the furnace 14. As the blanket of batch 11 builds up, the temperature, as indicated on the controller 19, gradually decreases due to the insulating effect of the batch 11. When the batch 11 reaches a desired thickness, a temperature corresponding to this thickness will be displayed on the indicator 20. The operator then switches the controller 19 over to an automatic mode of operation. At this point, the currently displayed temperature is stored in the controller 19 as a set point. So long as the temperature of the surface of the batch 11 is at or below the stored set point temperature, the feeder 16 will either operate at a minimum rate or will be stopped. As the sensor temperature increases slightly above the set point temperature, the speed of the motor 17 will be increased to supply batch from the feeder 16 to the furnace 14 at an increased rate until the sensed temperature returns to or drops below the set point temperature.

The particular set point temperature entered into the controller 19 will depend upon the type of glass melted in the furnace 14. It has been found, for example, that when a "C" type glass is melted in the furnace 14, the surface of the blanket of batch 11 may have a temperature of about 232°C. (450°F.) when the batch 11 has an optimal thickness. On the other hand, when an " S" type glass is melted in the furnace 14, the set point temperature may be on the order 398.9°C. (750°F.) .

It should be noted that the body of molten glass 13 will have an appreciably higher temperature than the upper surface temperature than the blanket of batch 11. Since there will be a high temperature differential across the thickness of the blanket of batch 11 and the blanket of batch 11 is relatively thin, small changes in the thickness of the batch 11 will cause a relatively large change in the surface temperature. This change will be detected quickly by the infrared sensor 18 and supplied to the controller 19. As a consequence, the thickness of blanket of batch 11 can be accurately controlled with the apparatus 10.

It will be appreciated that various modifications and changes may be made in the above-described apparatus for controlling the thickness of a blanket of batch over a body of molten glass in a glass melting furnace without departing from the spirit and the scope of the following claims.

Claims

C L A I M S 1. An apparatus for maintaining at a predetermined thickness of not more than 2.54 cm (one inch) a blanket of batch floating on a body of molten glass in a glass melting furnace comprising feeder means for distributing batch over the body of molten glass, infrared sensor means mounted for remotely measuring the surface temperature of the blanket of batch, said surface temperature varying as an inverse function of the thickness of the blanket of batch, means for comparing the measured surface temperature with a predetermined set point temperature corresponding to the surface temperature when said blanket of batch has the predetermined thickness and means responsive to said comparing means for controlling said feeder means to maintain the blanket of batch at the predetermined thickness wherein the measured surface temperature corresponds with the set point temperature.

2. A method of maintaining at a predetermined thickness of not more than 2.54 cm (one inch) a blanket of batch floating on a body of molten glass in a glass melting furnace comprising the steps of feeding batch to the surface of the blanket of batch, remotely sensing the surface temperature of the blanket of batch, comparing the sensed surface temperature with a set point temperature which the surface has wh e n t he b l a n ket o f b at c h h a s t h e p redet erm ined th ic kn es s , and controlling feeding of the batch in response to the compared temperatures to maintnin the blanket of batch at the predetermined thickness.

3. A method for maintaining at a predetermined thickness of not more than 2.54 cm (one inch) a blanket of batch floating on a body of molten glass, as set forth in claim 2, wherein said temperature is sensed by sensing from a location spaced from the surface infrared energy emanating from the surface of the blanket of batch.

4. A method for maintaining at a predetermined thickness of not more than 2.54 cm (one inch) a blanket of batch floating on a body of molten glass, as set forth in claim 3, wherein the feeding of batch is controlled by progressively increasing the speed of a feeder motor as the measured surface temperature progressively increases above the set point temperature.

5. A method for controlling the delivery of batch to a glass melting furnace comprising the steps of manually controlling a batch feeder to distribute an increasingly thick blanket of batch over a body of molten glass in the furnace, remotely sensing the surface temperature of the blanket of batch, storing as a set point temperature the sensed batch surface temperature when the blanket of batch has a predetermined thickness, and subsequently automatically controlling said batch feeder to maintain said sensed surface temperature at said stored set point temperature.