Patent Description:
Typically, the natural gas burners that provide energy for a glass melting furnace are located in the walls of the furnace. The flames from the burners extend across the width or the length of the furnace, slightly above and approximately parallel to the top surface of the glass melt within the furnace. Heat energy is transferred from the burner flames to the top surface of the glass melt primarily by conduction and radiation. In a typical furnace, raw batch materials are added to the furnace by distributing the raw materials on top of the existing glass melt, creating a batch 'blanket' of raw materials on the top surface of the glass melt. The raw batch materials consist of dry particles, ranging in grain size from approximately <NUM> to <NUM>.

Adding the raw batch materials into a glass furnace in this manner presents several operational difficulties. First, the dry batch materials are poor conductors of heat due to their low heat transfer coefficients and radiation emissive factors. As a result, the blanket of raw batch materials on the surface of the melt functions as an insulating layer that decreases the amount of heat energy that is transferred from the burners to the glass melt.

Another issue is the disturbance of the dry materials by the glass burner flames. The flow of air from the flames causes turbulence that disturbs and picks up the dry materials. The dry materials become entrained in the exhaust gases that exit the furnace flue or stack, a situation referred to as 'batch carryover', resulting in environmental air emissions such as opacity and particulate matter emissions. A third issue caused by the blanket of dry batch materials is the loss of light chemical elements such as sodium from the glass melt due to volatilization of these light elements. The loss of batch materials due to carryover or volatilization alters the chemistry of the glass melt, resulting in a final glass chemistry that is outside of the desired chemical specification, which alters the properties of the final glass product. To avoid these problems with dry batches, glass melting furnace feedstock is typically wetted with water (<NUM>-<NUM>% by weight). Although batch wetting mitigates many of the problems discussed herein, it can cause others such as poor batch transport conditions, segregation, and additional energy consumption in the glass melting furnace to drive off the added water. <CIT> discloses a stack with sloped baffles and supported by a hearth and a conventional tank having an end wall which serves as a dam to obstruct the flow of unmelted materials from the melting stack. <CIT> discloses a glass melting furnace and a pit located outside an inlet to the furnace. <CIT> discloses a glass furnace with batch feeder. <CIT> discloses a glass furnace with screw conveyors for feeding batch material from below the melt level.

A general object in accordance with one aspect of the disclosure is to provide a raw batch material feeder for glass furnaces that eliminates the raw batch material blanket that may be formed on the top surface of the melt when batch material is fed onto the top surface of the melt, and the problems associated with such a batch blanket.

Another object in accordance with another aspect of the disclosure is to eliminate the raw batch material blanket that reduces the amount of heat energy that is transferred from the gas burners to the glass, thereby increasing the efficiency of the furnace, by increasing the amount of heat energy that is transferred from the burner flames to the glass melt.

Another object in accordance with another aspect of the disclosure is to eliminate the loss of light chemical elements such as sodium from glass melt due to volatilization at high temperature.

A still further object in accordance with another aspect of the disclosure is to eliminate batch carryover. The present disclosure embodies a number of aspects that can be implemented separately from, or in combination with, each other.

The object of the present disclosure is achieved by subject matter of the independent claims.

A glass furnace in accordance with the present invention includes a furnace melt chamber to contain a glass melt having a top surface; a screw conveyor as a batch feeder to receive glass batch material and feed said material to the furnace melt chamber below the level of the glass melt top surface, and a dam wall disposed such that batch material from the screw conveyor must flow upward over the dam wall before entering the furnace melt chamber.

The disclosure, together with additional objects, eatures, advantages and aspects thereof, will be best understood from the following description, the appended claims and the accompanying drawings, in which:.

<FIG> illustrates a schematic top view of a glass melting furnace generally designated by the reference numeral <NUM>. The furnace has a furnace melt chamber <NUM> for melting the raw batch materials which in operation contains a pool <NUM> of molten glass as understood by those skilled in the art. One or more batch feed chutes <NUM> may be connected to the furnace <NUM>, for example, at a bottom portion thereof. A batch feed inlet <NUM> may be coupled to each batch feed chute <NUM> for the introduction of raw batch materials to the feed chute. Each of the batch feed chutes <NUM> may contain a batch feeder in the form of a screw conveyor <NUM>. Each of the batch feed chutes <NUM> may be coupled to a heater <NUM> having an outlet <NUM> as more fully described below. A dam wall <NUM> may be disposed between the screw conveyor <NUM> and the melt chamber <NUM>. The dam wall <NUM> creates a well <NUM> or a series of wells prior to the melt chamber <NUM> and may contain the heaters <NUM>. The dam wall <NUM> may be positioned between the heater outlets <NUM> and the remainder of the furnace and separates the heaters <NUM> and the heater outlets <NUM> from the remaining volume of the furnace <NUM>.

<FIG> is a side view of the glass melting furnace <NUM> of <FIG> showing one of the batch feed chutes <NUM> and a feed path for raw batch materials fed into the furnace <NUM>. Heat in the furnace <NUM> may be provided by top mounted heating elements <NUM> which may be powered by natural gas. Other types of heating elements may be used and in any suitable locations. An outlet of the feed chute <NUM> may be coupled to the heater <NUM>.

The heater <NUM> may comprise an enclosure <NUM> which may have an outlet <NUM> on the top thereof, and a heating element contained within the enclosure <NUM>. The heating element may comprise a gas or an electric heater element as desired. The heater <NUM> may also include an internal screw conveyor <NUM>. The screw conveyor <NUM> may provide a flow of the raw batch material from the screw conveyor <NUM> of the feed chute <NUM> to the heater outlet <NUM>. The heater <NUM> may be positioned in the well <NUM> within the furnace prior to the glass melt chamber <NUM> that may be established by the dam wall <NUM>.

The dam wall <NUM> creates a well <NUM> in which the raw batch materials are heated and partially melted by the heaters in the well <NUM> before the batch flows over the dam wall <NUM> and enters the main volume of the furnace melt chamber <NUM>. The top <NUM> of the dam wall <NUM> may be below the top surface of the glass melt level <NUM> in the furnace melt chamber <NUM>. The melt level <NUM> may be an upper surface of the molten glass in the chamber <NUM>.

In operation, raw batch materials are fed into the feed inlet <NUM> and the screw conveyor <NUM> transports the raw batch materials through the feed chute <NUM> into the heater <NUM>. The heater <NUM> heats and partially melts at least some of the raw batch materials and the conveyor <NUM> in the heater <NUM> drives the batch material to the heater outlet <NUM> and into the lower portion of the well <NUM> formed by the dam wall <NUM> for partial melting prior to entering the melt chamber <NUM>. The partially melted raw batch materials flow upward over the dam wall <NUM> out of the well <NUM> and into the furnace melt chamber <NUM>.

The dam wall <NUM> creates a well in which CO2 may be released from the raw materials as the heaters <NUM> provide heat to, and partially melt, the raw materials. The release of CO2 from the raw materials in the well reduces the amount of CO2 bubbles that may form in the glass as the raw materials fully melt in the melt chamber <NUM>. The removal of CO2 bubbles from the molten glass is referred to as refining. Removal of the CO2 in the well reduces the amount of time required to refine the glass in the melt chamber. As more partially melted batch material flows from the heater outlet <NUM> into the well <NUM>, the melted batch material flows over the top <NUM> of the dam wall <NUM> into the melt pool <NUM> contained in the furnace melt chamber <NUM>.

The height of the dam wall <NUM> can be varied to obtain different objectives. A short dam wall <NUM> will protect the feeder mechanism. A mid-height dam wall <NUM> will cause the batch material to be fed in the middle of the melt pool <NUM>, or at the top surface of the melt pool <NUM>. The percentage of batch material that is melted by the heater <NUM> in the mix of melted and unmelted batch material that flows over the dam wall <NUM> can be varied from approximately <NUM>% to <NUM>%, and more particularly from <NUM>% to <NUM>%, as desired.

<FIG> shows another illustrative embodiment of a glass melting furnace <NUM>. This embodiment is similar in many respects to the embodiment of <FIG>, and like numerals among the embodiments generally designate like or corresponding elements throughout the several views of the drawing figures. Accordingly, the descriptions of the embodiments are incorporated into one another, and description of subject matter common to the embodiments generally may not be repeated here.

The glass melting furnace <NUM> has a chamber <NUM> in which a hopper <NUM> may be positioned adjacent to a wall <NUM> of the furnace melt chamber <NUM>. The hopper <NUM> contains raw batch material <NUM> which is fed by gravity to a feed chamber <NUM> containing a screw conveyor <NUM>, which may be carried at a level that is proximate a bottom portion <NUM> of the furnace <NUM>. As used herein, the terminology proximate a bottom portion <NUM> may include at the bottom portion <NUM> or spaced apart therefrom but closer to the bottom than the top or at a position below the top surface of the molten glass pool <NUM> within the furnace melt chamber <NUM>.

The screw conveyor <NUM> may be coupled by a high thermal resistance joint <NUM> to the output shaft <NUM> of a motor <NUM> contained in a motor housing <NUM>. The motor housing <NUM> may be coupled to a source of cooling fluid <NUM> that circulates through the housing <NUM> to maintain the motor <NUM> at an acceptable operating temperature. The batch feed chamber <NUM> may be separated from the rest of the furnace melt chamber <NUM> by a dam wall <NUM>. A top <NUM> of the dam wall <NUM> may be below the top surface of the melt level <NUM> in the furnace melt chamber <NUM>. The height of the dam wall <NUM> can be varied to obtain different objectives. A short dam wall <NUM> will protect the screw conveyor <NUM> from the high temperatures of the melt pool <NUM> in the furnace melt chamber <NUM>. A mid-height dam wall <NUM> will cause the batch material to be fed into the middle of the melt pool <NUM>, and a high dam wall <NUM> will cause the batch material to be fed into the upper portion of the melt pool <NUM>.

A heater <NUM> may be provided to heat the batch material in the feed chamber <NUM> and well <NUM> before it is driven over the top <NUM> of the dam wall <NUM>. The heater <NUM> may span the gap between the dam wall <NUM> and the wall <NUM> of the furnace melt chamber <NUM> so that batch material exiting the feed chamber <NUM> may be forced through the heater <NUM>. Alternatively, the heater <NUM> may be positioned on the side of the dam wall <NUM> facing the incoming batch material, and on the side of the furnace wall <NUM> that is in contact with the batch material within the well <NUM> so that batch material exiting the feed chamber <NUM> may be forced past the heater <NUM>, or the heater <NUM> may be located in any other position. The heater <NUM> may be an electric heater, an induction heater, a gas radiation tube, or other suitable heating device.

In operation, gravity feeds batch material <NUM> from the hopper <NUM> into the feed chamber <NUM>, and rotation of the screw conveyor <NUM> by the motor <NUM> drives the raw batch material <NUM> through the feed chamber <NUM> and upward through or past the heater <NUM>. The heater <NUM> heats and partially melts at least some of the raw batch material <NUM> before it is introduced into the melt pool <NUM> in the furnace melt chamber <NUM>. The outlet of the heater <NUM> may be below the melt level <NUM> in the furnace.

<FIG> shows an alternative embodiment of a glass melting furnace <NUM> having a furnace melt chamber <NUM> and a side mounted hopper <NUM> that supplies batch material <NUM> to a feed chamber that is part of a well <NUM> formed by a dam wall <NUM> located in the furnace melt chamber <NUM>. The well <NUM> contains a vertical screw conveyor <NUM> that is located proximate the bottom wall <NUM> of the furnace <NUM>, and heater elements <NUM> and <NUM> that are located on the side of the dam wall <NUM> and the side wall <NUM> of the furnace <NUM>, respectively. Heat in the furnace <NUM> may be provided by top mounted heating elements <NUM>. The batch material <NUM> in the hopper <NUM> is fed by gravity to a feed channel <NUM> having a sloped bottom feed wall <NUM> that is angularly related to the vertical side wall <NUM> of the hopper <NUM> and the bottom wall <NUM> of the furnace <NUM>. The sloped bottom feed wall <NUM> may be angled between <NUM>° and <NUM>° to the bottom wall <NUM> of the furnace <NUM>, and the sloped bottom feed wall <NUM> aids in maintaining an even flow of batch material <NUM> to the vertical screw conveyor <NUM>.

The vertical screw conveyor <NUM> is arranged to convey batch material <NUM> upward from the well <NUM> to a top <NUM> of the dam wall <NUM>. The vertical screw conveyor <NUM> may be coupled by a high thermal resistance joint <NUM> to the output shaft <NUM> of a motor <NUM> contained in a motor housing <NUM>. The motor housing <NUM> may be coupled to a source of cooling fluid <NUM> that circulates through the motor housing <NUM> to maintain the motor <NUM> at an acceptable operating temperature. The well <NUM> is separated from the furnace melt chamber <NUM> by the dam wall <NUM>. The top <NUM> of the dam wall <NUM> may be below a melt level <NUM> in the furnace melt chamber <NUM>. The heater elements <NUM> and <NUM> heat the batch material flowing upward from the well <NUM> over the top <NUM> of the dam wall <NUM> into the melt pool <NUM> in the furnace melt chamber <NUM>. The heater elements <NUM> and <NUM> may be an electric heater, an induction heater, a gas radiation tube, or other suitable heating device.

<FIG> shows another embodiment of a glass melting furnace <NUM> having a furnace melt chamber <NUM> including a side wall <NUM> and a bottom wall <NUM>. The furnace melt chamber <NUM> contains a melt pool <NUM> of glass having a melt level <NUM>. A batch feed hopper <NUM> is positioned adjacent to the side wall <NUM> of the furnace melt chamber <NUM> to supply batch material <NUM> under gravity to the bottom <NUM> of the hopper <NUM>. A feed opening <NUM> in the side wall <NUM> of the furnace melt chamber <NUM> feeds batch material <NUM> from the bottom <NUM> of the hopper to the melt pool <NUM> of glass below the melt level <NUM>. A screw conveyor <NUM> proximate the bottom wall <NUM> of the hopper <NUM> feeds the batch material <NUM> from the bottom <NUM> of the hopper <NUM> through the feed opening <NUM> and into the furnace melt chamber <NUM>. The screw conveyor <NUM> is oriented generally horizontally proximate the bottom wall <NUM> of the hopper. Submerged heaters <NUM> proximate the bottom wall <NUM> of the furnace melt chamber <NUM> heat the melt pool <NUM> of glass in the furnace melt chamber <NUM>. The feed opening <NUM> defines a plane and is positioned below the melt level <NUM> in furnace melt chamber <NUM>. The screw conveyor <NUM> may be coupled by a high thermal resistance joint <NUM> to the output shaft <NUM> of a motor <NUM> contained in a motor housing <NUM>. The motor housing <NUM> may be coupled to a source of cooling fluid <NUM> that circulates through the housing <NUM> to maintain the motor <NUM> at an acceptable operating temperature. The end <NUM> of the screw conveyor <NUM> is in approximate alignment with the plane of the feed opening <NUM>. The submerged burners <NUM> create turbulence in the melt pool <NUM> in the furnace melt chamber <NUM> to provide mixing of the batch material <NUM> with the melt pool <NUM> of glass in the furnace melt chamber <NUM> as it passes thorough the feed opening <NUM> into furnace melt chamber <NUM>.

The present disclosure is directed to the concept of feeding glass batch material into a furnace at a location below the melt level to eliminate problems associated with the glass batch "blanket" otherwise formed on the top surface of the melt. A screw conveyor is used to feed the batch material into the melt pool in the furnace.

This application is a divisional application of European Patent Application <CIT> (<CIT>).

Claim 1:
A glass furnace (<NUM>, <NUM>, <NUM>, <NUM>) comprising:
a furnace melt chamber (<NUM>, <NUM>, <NUM>, <NUM>) to contain a glass melt (<NUM>) having a top surface; and
a screw conveyor (<NUM>, <NUM>, <NUM>, <NUM>) as batch feeder to receive glass batch material and feed said material to the furnace melt chamber below the level of the glass melt top surface;
a dam wall (<NUM>, <NUM>, <NUM>) disposed with respect to thescrew conveyor (<NUM>, <NUM>, <NUM>, <NUM>) such that batch material from the screw conveyor (<NUM>, <NUM>, <NUM>, <NUM>) must flow upward over the dam wall (<NUM>, <NUM>, <NUM>) before entering the furnace melt chamber (<NUM>, <NUM>, <NUM>, <NUM>), wherein a top (<NUM>, <NUM>, <NUM>) of the dam wall is below the top surface of the glass melt level (<NUM>) in the furnace melt chamber.