WO1999015466A2

WO1999015466A2 - Glass furnace exhaust gas filter combined with raw material preheater

Info

Publication number: WO1999015466A2
Application number: PCT/SE1998/001650
Authority: WO
Inventors: Jeffery C. Alexander
Original assignee: Praxair, Inc.
Priority date: 1997-09-23
Filing date: 1998-09-16
Publication date: 1999-04-01
Also published as: WO1999015466A3

Abstract

A method and apparatus for glass manufacturing are described which utilizes waste heat from glass furnace exhaust gases, removes fine particulate dust from the exhaust gases, purifies ecological cullet, and incinerates organic compounds contaminating ecological cullet. Factory cullet is heated directly with the hot furnace gases and this hot cullet in turn is used to dry batch and ecological cullet. By means of a counter flow, solid-to-to-solid heat exchanger, hot factory cullet is also used to vaporize organic material mixed with the ecological cullet as well as preheat the ecological cullet and batch raw materials. Pollutant organic fumes are incinerated by venting into the channels carrying hot exhaust gases, and fine particulate matter is trapped in moving bed filters.

Description

GLASS FURNACE EXHAUST GAS FILTER COMBINED WITH RAW

MATERIAL PREHEATER

BACKGROUND OF THE INVENTION

Glass is made by heating and melting a mixture of solid raw materials to a liquid state. The melting is done Inside of a furnace and necessarily requires substantial amounts of heat. Typically, this heat is generated by the combustion of fossil fuels and the exhaust gases from the combustion leave the furnace. Exhaust gas temperatures immediately after the furnace are quite high, typically 1300-1450 °C. Combustion air preheaters are normally included which recover some of the heat in these gases. Nevertheless, gas temperatures at the discharge to atmosphere are quite high. Therefore, substantial amounts of heat are wasted. The cost of fuel for the furnace is a major component in the cost of making glass and it is beneficial to recover as much heat as possible.

Solid raw materials for glass making generally fall into three categories; batch, ecological cullet and factory cullet. Each of these three categories are discussed below.

Batch generally refers to various pulverous materials including silica sand, limestone, soda ash, salt cake, and a variety of other minor ingredients. The material and mixture ratios are carefully chosen to produce glass of the desired properties and quality. Generally these materials are prepared in a finely divided form to promote their melting rates. Sizes are typically 100 to 200 μm diameter with a maximum size of 1 mm. To promote more rapid melting, these materials are thoroughly mixed prior to their introduction to the furnace. Poor mixing can result in inferior glass quality. After mixing, poorly designed handling techniques can result in segregation of materials, which can also lead to problems with glass quality. Often, the batch is wetted during or after mixing to prevent such segregation. The water acts as a temporary binder to prevent individual grains of the batch material from separating and also acts to dissolve water soluble components in the glass batch for better homogeneity of the mixed batch. Upon drying in the furnace, these water soluble components are then evenly distributed on the surfaces of the batch grains.

Cullet refers to previously formed glass which is introduced into the furnace and melted into new glass. Cullet source can be either rejects from the manufacturing process in the factory, thus called factory cullet, or cullet which is brought into the glass factory from the outside, i.e., post-consumer sources, Generally, the motivation for the latter source of cullet is ecological concern from the community to reduce amounts of waste material which require expensive disposal. Thus this material can be called "ecological cullet." Progressively improving awareness of environmental issues has increased recycling efforts and the amounts of ecological cullet returned to glass factories are continuously increasing. Some regional authorities even mandate usage of post consumer recycled material in the manufacturing process.

Factory cullet is necessarily of chemical composition and purity consistent with the desired glass production from the furnace and can be reintroduced directly to the furnace without much concern. Ecological cullet, on the other hand, is from a variety of original glass manufacturing sources and is contaminated with various impurities which render it more difficult for use in the glass furnace. The impact of impurities in ecological cullet are an increasing problem for the glass maker. Many glass makers are investing in equipment to purify ecological cullet before melting in the glass furnace. Impurities in ecological cullet generally fall into three categories: 1. Metals - these are typically bottle caps, foil wrappers, and other metallic objects which are deposited into recycle bins by the recycler along with the glass. 2. Ceramics - these are typically plates, cups, mugs, etc- which are inadvertently deposited into recycle bins by the recycler. If introduced to the glass furnace, they cause serious problems with glass output quality, since the large ceramic pieces will not melt. 3. Organic compounds - these are food and drink residues left in bottles and containers, as well as paper and plastic labels and glues used to adhere them. Also, loose paper, rags, gloves, clothing, etc. all have been found in varying amounts in ecological cullet. When introduced to the glass furnace, these materials will volatilize and burn, but their presence makes good control of the fuel combustion in the furnace difficult. Efficient furnace operation is then difficult. As well, improper combustion of these materials in the furnace can result in formation of carcinogenic pollutants, for example dioxins, which can be emitted to the atmosphere.

The metal problem is resolved with equipment installed in the glass factory. Cullet only needs to be crushed down to sizes (< 50 mm) convenient for material handling, Ferrous metals can be then easily removed by magnets, Non- ferrous metals can be removed by electrical eddy current separators. Both of these purification technologies are routinely and effectively used.

The ceramic problem is resolved by pulverizing all the ecological Cullet to sizes less than 1 mm. Then, all the ceramic places will be small enough to melt into glass. Several factories use this approach at the present time. However, it has been discovered that this approach can lead to new problems in glass making. When ecological cullet Is pulverized, the organic materials in the cullet are also pulverized and uniformly mixed with the cullet which in turn is mixed with the batch. When this "blanket" of material is fed into the furnace, the organic material becomes "trapped" inside the batch blanket. Depending upon the type of organic and the quantity, this can lead directly to problems with quality of glass output from the furnace. Also, the normal problem of combustion control in the furnace from organic content remains. Many glass makers refrain from using cullet pulverization for this reason.

Organic impurities can be reduced by various mechanical means, but complete organic purification of cullet has heretofore been impossible. Crushing cullet (to sizes <50 mm) will free some of the labels, which can then be removed from the cullet by air sweeping hoods. Some manufacturers have tried washing cullet in water to remove more of the labels and organic compounds, but the waste water generated was intolerable. Even so the cullet could not be completely purified.

Normally, batch and both types of cullet are mixed together before being fed into the glass melting furnace. Various attempts at direct and indirect contact preheating of batch and cullet using the heat of exhaust gases from the glass furnace have appeared in the art. Because of problems with material flow, preheaters have only been successful at treating either pure cullet, or cullet/batch mixtures with high percentages of cullet.

Direct contact preheaters bring the hot furnace exhaust gases directly into contact with the material to be heated. In the case of preheating cullet only, direct contact has proven to be very effective at transferring heat from gas to the cullet and such technologies have found industrial use. In the case of preheating cullet / batch mixtures, direct contact of gases invariably leads to large carryover of dust from the batch into the gases. This has been unacceptable to the industry because of limitations in allowable dust emissions from the furnace.

Although filters to capture entrained dust can be implemented, the complexity of such systems have precluded their practical use in the industry. There are no technologies in use today which involve pure direct contact preheaters for batch. Indirect preheaters generally take the form of channels containing batch/cullet mixtures alternated with channels containing hot gases. Heat is transferred through the metallic plates which divide the channels. Batch/cullet flows downward by gravity, while gas flow is typically horizontal. While such systems remedy the problem of dust carryover, they have been less than satisfactory because of dust build-ups on the gas side of the metal plates. Heat transfer rates are very low, requiring inordinately large devices. Also, solid material flow by gravity has proved unreliable because some of the batch materials are water soluble and form clumps upon drying Inside of the preheater. Indirect preheaters with high proportions of cullet mixed with batch have proved operational, but again they are quite large and expensive. Generally, the efficiency of indirect preheaters has been disappointing, because the batch and cullet cannot be heated to temperatures approaching the exhaust gas temperature.

The primary air pollutant in the exhaust gas stream from a glass making furnace is particulate matter, or dust. This has proved to be an especially difficult problem because the dust particle size is almost exclusively less than 1 μm diameter (submicron). This size is the most difficult to capture in any type of air pollution control device. Additionally, the exhaust gas stream is at a high temperature. Various types of air pollution technologies have been tried for the cleanup of glass furnace exhaust gas streams, most notably electrostatic precipitators and bagfiiters. While effective, they have proved to be extremely expensive because of the high temperature exhaust gases and very small particle sizes of the dust pollutants.

SUMMARY OF THE INVENTION

In view of the foregoing, the following are objects of the present invention:

1. Utilize waste heat from glass furnace exhaust gases to preheat batch, factory cullet and ecological cullet, that is 100% of the material fed into the glass furnace. In this way, fuel consumption of the furnace can be substantially reduced, thereby reducing the overall cost of manufacturing glass.

2. Remove fine particulate dust from the furnace exhaust gases to levels which comply with strict regulatory limits, thus satisfying the governmental requirements for pollution emissions from the furnace.

3. Purify ecological cullet, so that it can easily be used as a raw material for the glass production, specifically, remove a high percentage of the organic material from the ecological cullet.

4. Incinerate the organic material which enters the process with the ecological cullet with high efficiency so that objectionable emissions of organic compounds to the atmosphere are eliminated.

One aspect of the present invention is directed to a method for heating glass manufacturing raw materials including the following steps:

a) classifying the raw materials into small size particles and large size particles, b) providing a moving bed of the large size particles having a top and a bottom, c) introducing large particles of the raw material to the top of the moving bed, d) Passing hot exhaust gases from a glass melting furnace through the moving bed so that heat is transferred from the gases to the large size particles to give hot, large size particles, e) removing the hot, heated large size particles from the bottom of the moving bed, f) dividing the hot, large size particles removed from the bottom of the moving bed into a first portion, a second portion, and a third portion, g) introducing the first portion of the hot, large size particles into the glass melting furnace, h) mixing the second portion of the hot, large size particles with the small size particles transferring heat to the small size particles and releasing any moisture present as water vapor,

I) venting any water vapor released in step h) into an exhaust gas channel of the glass melting furnace, j) separating the dry, small size particles from the large size particles, k) introducing the large size particles separated in step j) to the top of the moving bed according to step c),

I) introducing the third portion of the hot, large size particles into a solid-to- solid heat exchanger, m) introducing the small size particles separated in step j) into the solid-to- solid heat exchanger transferring heat from the hot, large size particles to the small size particles, to give hot, small size particles, n) removing the hot, small size particles from the heat exchanger and introducing them into the glass melting furnace, o) venting any water vapor and organic fumes released in step m) into the exhaust gas channel of the glass melting furnace, and p) removing the large size particles from the solid-to-solid heat exchanger and introducing them to the top of the moving bed according to step c).

Another aspect of the present invention is directed to an apparatus for carrying out the foregoing process.

In one embodiment of the invention where the raw material has a low moisture content, the hot large size particles removed from the bottom of the moving bed are divided into only two portions and steps (h) through (k) are omitted, and in step (m) the small size particles of raw material are introduced directly into the heat exchanger rather than from step (j).

Another embodiment of the invention is a method for heating and purifying glass manufacturing raw materials and removing pollutants from exhaust gases from the glass melting furnace including the following steps: a) providing a portion of the raw materials as coarse cullet the particles of which are substantially free of impurities and are substantially greater than about 4 mm in diameter, b) providing a portion of the raw materials as glass batch the particles of which are substantially less than about 1 mm in diameter, c) providing a portion of the raw materials as contaminated cullet the particles of which have been pulverized to be substantially less than about I mm, d) providing a moving bed consisting of the coarse cullet, introducing the cullet to the top of the moving bed and removing said cullet from the bottom of the moving bed, e) providing electrode means in the moving bed to electrically polarize the cullet, f) passing furnace exhaust gases first through an electrostatic ionizer, the ionizer generating corona discharge which imparts electrical charge onto the dust particles in the gases. g) passing furnace exhaust gases subsequently through the moving bed so that heat is transferred from the gases to the coarse cullet, creating hot, coarse cullet, and so that electrically charged dust particles are deposited onto the surface of the polarized coarse cullet, h) dividing the hot, coarse cullet which exits the moving bed into a first portion and a second portion,

I) introducing the first portion of the hot, coarse cullet to a glass melting furnace, j) providing a heat exchanger and introducing the second portion of the hot, cullet into the heat exchanger, k) introducing the batch and pulverized cullet into the heat exchanger so that the heat from the hot, cullet dries and heats the batch and pulverized cullet and releases volatilizes organic impurities from the pulverized cullet, I) venting the volatilized organic material from the heat exchanger into a gas flow which is mixed with the furnace exhaust gases in a flue channel of furnace to elevate their temperature and incinerate the volatilized organic material, m) removing heated batch and pulverized cullet from the heat exchanger and introducing it to the furnace, and n) removing cooled, coarse cullet from the heat exchanger and introducing it to the top of the moving bed according to step d.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a schematic diagram showing the process and system of the present invention.

Figure 2 is a cross sectional, schematic diagram of a counterflow solid-to-solid heat exchanger.

Figure 3 is a detailed, cross sectional, schematic diagram of drying screen 28.

Figure 4 is a schematic diagram showing the process and system of alternate embodiment A of the present invention.

Figure 5 is a schematic diagram of a counterflow solid-solid heat exchanger showing details of the spiral, vibratory trough conveyor.

Figure 6 is a schematic diagram illustrating the operation of a counterflow solid- solid heat exchanger.

Figure 7 is a schematic diagram showing the process and system of alternate embodiment B of the present invention. Figure 8 is a schematic diagram illustrating the heat transfer theory of a counterflow solid-solid heat exchanger.

DETAILED DESCRIPTION OF THE INVENTION

General Process Description

One embodiment in accordance with the present invention is depicted in figure 1. Referring to figure 1 , ecological cullet 1A is passed through a pulverizer 14 which grinds the cullet to particles less than about 1 mm in diameter. Removal of any metallic impurities from the cullet is performed prior to pulverizing using conventional methods of the art. Pulverized ecological cullet 1B is deposited into storage silo 15 along with factory cullet 2a and batch 3. Factory cullet 2a has been crushed to particles less than about 50 mm in diameter and typically very little of this material is less than about 2 mm in diameter. Particles of batch 3 are typically less than about 1 mm in diameter. Storage silos are normally used in the art of glass making for storage of the mixed raw materials prior to their being fed into a glass melting furnace.

Exhaust gases at very high temperatures (typically 1450°C) from glass melting furnace 24 are delivered via exhaust gas channel 25 to the primary heat recovery device 26, which preheats combustion air for the glass melting furnace 24 by regenerative or recuperative heat exchange. In a regenerative type glass melting furnace, the exhaust gas temperature is typically 400°C. In a recuperative type of glass furnace, the exhaust gas temperature is typically 650°C. In the case of oxygen-fuel firing, no primary heat recovery can be employed, in which case the exhaust gas temperature is typically 1300-1400°C. Therefore, the temperature of exhaust gas 10 may be about 400°C to about 1400°C.

Depending upon the furnace type and outlet gas temperature, a gas cooler 31 may be employed to reduce the temperature of the exhaust gas 10 before entering the ionizer 17, and cullet filter module 18 to that suitable for electrostatic filtration. For present purposes, this temperature may be between 250° and 550° depending upon the specific situation but will typically be about 400°C. The gas cooler 31 may operate by any of a variety of means known in the art, such as injection of dilution air, injection of water, or indirect heat transfer, etc.

Cooled exhaust gases 12 are drawn through a combination of ionizer 17 and cullet filter module 18 by exhaust gas fan 19. Cooled and cleaned exhaust gases 13 are discharged to atmosphere. The operation of ionizer 17 and cullet filter module 18 are consistent with existing technology taught in the art.

Particulate matter in the exhaust gas stream is given an electrostatic charge in the ionizer 17 by a corona discharge process. Then the particle bearing exhaust gases are caused to flow through a moving bed of cullet 18a within cullet filter module 18. The cullet in the moving bed is electrically polarized so that the particulate matter is attracted to the cullet surfaces, thus cleaning the exhaust gases. Also, the cullet is heated by the hot exhaust gas to nearly the exhaust gas temperature by direct contact of the gases with the cullet. As a result of the transfer of heat from the exhaust gas to the cullet, the exiting exhaust gas is cooled. Hot cullet 6 leaving the cullet filter module 18 is typically at a temperature close to the incoming gas 12 temperature. Thus, for a 400°C inlet gas temperature, the exiting cullet 6 would be at about 380°C. Hot cullet 6 is divided into a first hot cullet stream 7, a second hot cullet stream 8, and a third hot cullet stream 29. The first hot cullet stream 7 is fed directly into the glass melting furnace

24. Generally, the mass flow rate of this stream will match the mass flow rate of factory cullet 2a delivered to cullet filter module 18.

The third hot cullet stream 29 is fed onto the batch drying screen 28. Moisture bearing raw material stream 4 from storage silo 15 Is also fed onto the screen. On the drying screen 28, as third hot cullet stream 29 and moisture bearing raw material stream 4 mix, moisture is removed from the raw material stream 4 and exits as water vapor stream 31. Batch and ecological cullet leave the drying screen in a dry and partially heated condition as cullet/batch material stream 32. Factory cullet 2 leaves the drying screen as material stream 33a, the temperature of which is significantly less than material stream 29. Details of the drying screen operation are presented below.

Second hot cullet stream 8 is fed into the counterflow solid-to-solid heat exchanger 16. Cullet/batch material flow 32 from the drying screen 28 is also fed into the solid-to-solid heat exchanger 16, where the two solid materials (heated cullet and batch/ecological cullet mixture) are directly contacted with each other as they are traveling in a counterflow arrangement. Details of the solid-to-solid heat exchanger 16 operation are given later. Batch and ecological cullet heated mixture 5 exiting solid-to-solid heat exchanger 16 is fed into the glass melting furnace 24. Because of the efficient counterflow design of solid-to-solid heat exchanger 16, mixture 5 can be at a temperature approaching that of the second hot cullet stream 8 temperature, typically 350°C. Cooled cullet exits the heat exchanger as cullet material flow 33b.

Both cullet material stream 33a and cullet flow 33b are conveyed by a conventional conveying device 30, such as a bucket elevator, to the top of the cullet filter module 18 where they enter the cullet filter module 18 as cullet material flow 9, which is all cullet of size greater than about 2 mm in diameter. The feed rate of hot cullet directly into the furnace and the delivery rate of fresh factory cullet 2a will most preferably be substantially the same to keep the cullet filter module 18 filled with cullet at all times.

One alternate arrangement is to deliver factory cullet directly to the top of the cullet filter module, as shown by the dashed line 2c, which would avoid handling the fresh factory cullet in the drying screen. However, it is generally more convenient for the glass manufacturer to deliver all of its raw materials to the silo mixed together, thus avoiding the necessity of added material handling equipment and operational complexity.

Inside of the solid-to-solid heat exchanger 16, the ecological cullet is heated to temperatures which will volatilize most of the organic impurities into fumes. These fumes 20 are vented from the solid-to-solid heat exchanger 16 and mixed with vapors from the drying screen. Fan 22 operates to provide a slight underpressure inside of the drying screen 28 and the solid-to-solid heat exchanger 16, thus preventing the escape of any pollutant vapors to the atmosphere. Although some air may become mixed with the fumes 20 and water vapor 31 because of leakage, the effect on the method of this invention is negligible.

Certain amounts of dust will be generated inside of the drying screen 28 and the solid-to-solid heat exchanger 16 because of mechanical agitation of the pulverous materials. This dust is carried away with the fumes 20 and water vapor 31 and is collected in cyclone 21. Collected dust 23 can be either returned to the material storage silo 15 or fed into the glass melting furnace 24 along with first hot cullet stream 7 or heated mixture 5. The preference will depend upon the quantity and composition of the dust.

Vapors 27 (water vapor and volatilized organic compounds, i.e., organic fumes) are discharged from fan 22 into flue gas channel 25 where they are mixed with hot furnace exhaust gases. Because the mass flow of the vapors is much less than the mass flow of the furnace exhaust gases (typically 2%, maximum 5%), the mixed gas temperature inside of the exhaust gas channel will remain quite high. At these high temperatures, the organic fumes will be completely incinerated, converting them into harmless carbon dioxide and water vapor.

It is important that the gas temperature entering the primary heat recovery device 26 remain at the very high temperature, otherwise, the air preheating function of the device will be unacceptably compromised. As a result, the mass flow rate of the vapors must be less than about 5% of the furnace exhaust gas mass flow rate. Any copious amounts of air infiltration to vapor stream 20 vented from the solid-to-solid heat exchanger 16 must be avoided.

The temperatures and residence times of ecological cullet in the solid-to- solid heat exchanger 16 may not be sufficient to volatilize 100% of the organic material. However, this is not a problem, because the ecological cullet is introduced directly into the furnace after being discharged from the heat exchanger. Any residual organic material entering the glass melting furnace 24 will then be released and incinerated in the furnace, so there will be no organic emissions to the atmosphere. Moreover, the amount of residual organic material is so small that glass production quality or furnace combustion control is not effected.

Referring to Figure 3, a detailed, cross sectional, schematic diagram of drying screen 28, the third hot cullet stream 29 first mixes with the cold, wet raw material stream 4 on a solid conveyor deck 37. Heat from the third hot cullet stream 29 dries the cold, wet infeed raw material stream 4. Water vapor released during drying is vented away as water vapor stream 31. After the mixing and drying, the mixture of raw material and cullet passes over a screen deck typically with openings to allow passage of a particle of about 2 mm in diameter. All of the batch and pulverized ecological cullet pass through the screen in a dry and partially heated condition and exit the unit as feed material flow 32. The oversize material, which consists of the fresh factory cullet 2 and cullet from the filter module 29 (now cooled) exit the unit as recycle material flow 33a to be transported to the top of the moving bed of cullet 18a in cullet filter module 18.

It is important that the initial contact of wet batch be onto hot cullet. The batch dries quickly upon direct contact heating, but the water soluble components of the batch will leave tightly adhered residues on the hot surface. If the hot surface were to be fixed in place, then over time, residues would build up and clog the device. Using cullet as the heating/drying surface alleviates this problem by two methods. First of all, the cullet is constantly renewed, with fresh cullet coming in and old cullet going out. Any small amount of tightly adhered residue on the exiting cullet will not cause any problems in the equipment. Secondly, the mechanical agitation of the coarse cullet will serve to scrub off any residues adhering onto the surrounding metallic structures in the heat exchanger.

Referring to the cross sectional schematic diagram of Figure 2, a counterflow solid-solid heat exchanger 16 is based on a spiral design vibratory trough conveyor. With proper design of the vibration amplitude and angle, material can be made to flow up an inclined trough at angles of from 5° to 10°. Essentially, the conveyed material is sequentially thrown up the conveyor trough by the vibration, The incline of the trough is less than the angle which will allow the material to slide back down. The trough is built in a spiral arrangement, creating a tower, the entire tower being supported on a spring at the top. A mechanical drive assembly is located at the bottom. The trough floors are constructed of perforated plate, with opening size of nominally 2 mm. The size is selected so that 100% of the batch and pulverized ecological cullet will easily pass through the plate while 100% of the hot cullet will not pass through the plate. Cullet is fed onto the trough at the bottom of the tower, and is discharged at the top.

Still referring to Figure 2, second hot cullet stream 8 is fed into counterflow solid-solid heat exchanger 16 through port 28 and is introduced onto the spiral perforated trough 29. The spiral perforated trough 29 is continuous up to the discharge port 30 and carries the large sized cullet upward. The coarse cullet forms a bed of cullet material 34 residing on top of the spiral perforated trough 29. The bed thickness depends upon the conveyor vibration design and the input feed rate of hot cullet. The spiral perforated trough 29 is secured to a vibrating central column 50 mounted on a spring assembly 42. The mechanical drive 43, provides the necessary vibration to propel bed of cullet material 34 up the spiral inclined trough and to keep the bed constantly agitated. A static central column 51 is provided for support with base 52 secured a rigid, stable platform such as a floor or steel structure.

The dry and partially heated cullet / batch material stream 32 is fed into the top of counterflow solid-solid heat exchanger 16 through port 31 which allows the material to freely fall onto the top of bed of cullet material 34. Because of the size difference between the particles of the cullet / batch material stream 32 and those of bed of cullet material 34, the former will percolate down through the latter as a result of the constant agitation provided by mechanical drive 43. During this percolation, the fine material will be heated by direct contact with the coarse material. Upon reaching the perforated trough floor, the fine material will fall through the openings.

After failing through the perforated trough, the fine material will then fall on top of the bed of cullet directly below, repeating the heat exchange action until the fine material reaches the bottom of the heat exchanger. After passage through the lowest bed of cullet, the fine material collects on the nonperforated catch pan 53 and is discharged from counterflow solid-solid heat exchanger 16 through port 35 as heated mixture 5.

Inside of counterflow solid-to-solid heat exchanger 16, the organic impurities on the ecological cullet will be volatilized and released. The outer edges of the troughs are comprised of a trough end 54 to retain the cullet bed 34 with gap 55 between successive flights which will allow the volatilized organic compounds, i.e., organic fumes, to easily leave the spiral trough areas. If these areas are not effectively vented, pressures could build up inside of the spiral areas which could impede material flows. The spiral elevator is provided with a stationary cover 36 to contain the released organic fumes and dust as well as provide thermal insulation. The cover is provided with a vent 56 to allow discharge of volatilized organic material, dust, and water vapor. The ports for material inlet and outlet have sealed connections 57 to the cover, thus preventing air infiltration.

Alternative Embodiment A When the drying requirement of batch 3 and pulverized ecological cullet

1b is slight, both can be introduced directly into solid-to-solid heat exchanger 16 as illustrated schematically in Figure 4. The drying screen 28 is eliminated and any drying occurs inside of solid-solid heat exchanger 16, and water vapor is vented away with the organic fumes. When this embodiment is possible, it is preferred because of the reduction in required equipment.

Alternative Embodiment B

In some cases it is not desirable to pulverize the ecological cullet. These cases require an alternate design of solid-solid heat exchanger 16. Coarse ecological cullet is heated along with batch in the Double Helix Design Heat Exchanger as depicted in figure 5. The unit consists of two separate spirals interspersed with each other. The first is the conventional design, where the flights are mounted on a "vibrating" column, and hot factory cullet is carried from bottom to top of the unit. The second spiral is used to carry ecological cullet from the top of the unit to the bottom. These flights are mounted on the "semi- static" central column as shown in the detail. The support brackets for this spiral extend through holes In the "vibrating" central column. Because this flight is pitched downward (in direction of material flow), much less vibrational intensity is required to move the material. This column is connected to the base of the unit which in turn is mounted to the floor or structural steel via rubber pads or springs which permit some vibration of the "semi-static" central column.

Perforated troughs are used for both of the spirals, allowing batch to fall through. Figure 6 shows a schematic representation of the process. Mixed batch and coarse ecological cullet are introduced at the top of the unit. Batch falls through the perforations and would heat when contacted with the hot factory cullet. Then the heated batch would transfer heat to the ecological cullet on the next stage down. Of course several stages of the heat transfer would be required to heat both the batch and the coarse ecological cullet to a high degree. This is easily accommodated in the heat exchanger design. The bottommost flight is not perforated and collects the heated batch and ecological cullet for discharge from the unit.

The entire double helix heat exchanger is enclosed and water vapor and organic fumes are vented to the glass melting furnace as previously described. Alternate embodiment B as illustrated schematically in figure 7 is then used. The pulverization is eliminated, so raw ecological cullet 1 is delivered directly to storage silo 15, along with batch. A second storage silo 40 receives and stores factory cullet 2a, which is then fed by feed stream 41 directly into conveying device 30, e.g., a bucket elevator for transport to the top of the cullet filter module 18. Material 4 then consists of cold batch and coarse ecological cullet, while heated mixture 5 consists of heated batch and ecological cullet.

Of course such a design would require the spiral to have significantly more flights that the simpler design and the use of pulverized cullet would always be preferred. But in cases where this is not possible, the additional cost for the larger double helix heat exchanger would be generally less than the cost of pulverization equipment.

Electrical Conductivity of Cullet In Filter Module

Again referring to Figure 1 , the media in the cullet filter module 18 is cullet which is continually renewed. Factory cullet 2a is delivered to the storage silo 15 along with batch 3 and pulverized ecological cullet 1b. Because factory cullet 2a is most preferably of a large particle size, drying screen 28 sends it to the top of the cullet filter module 18 along with some of the large size cullet which has already been through the filter module. Because the cullet filter module 18 is continuously discharging some hot material directly to the furnace, there is a constant requirement for fresh cullet to be added to cullet filter module 18. While any one cullet piece might make several traverses through the filter module, eventually it will leave and be replaced by fresh material. The average number of traverses which a given piece of cullet makes through the cullet filter module 18 depends upon the ratio of the two hot material streams 7 and 8+29.

The electrostatic filtration process in the cullet filter module 18 requires that the cullet be electrically polarized by applying an electrical potential across the moving bed of cullet 18a, and such process necessitates that the cullet bed electrical conductivity be less than a practical maximum. Otherwise, the power consumption required to maintain the electrical potential would be excessive.

As the cullet circulates through cullet filter module 18, it collects particulate matter from the exhaust gases. This particulate matter is primarily sodium sulphate, which clings tenaciously to the cullet surface and cannot be completely cleaned off. Over many subsequent passes through the cullet filter module 18, a continuous layer of sodium sulphate will form on the surface of the cullet. At the temperatures of interest in the method of this invention, this continuous layer of sodium sulphate will make the electrical conductivity of the cullet become too high for effective electrical polarization. Most glass batch formulations include significant amounts of soda ash

(sodium carbonate). This material is water soluble, Since batch is wet when it is first contacted with the hot cullet, there will be residues of soda ash tightly adhered to the cullet pieces when the water is evaporated off. This soda ash will also eventually form a continuous layer on the cullet and would also serve to increase the electrical conductivity of the cullet.

Electrostatic filtration performance of the filter is enhanced if cullet is continuously refreshed in the above described process. Otherwise, after several days, the particulate capture efficiency of the filter would deteriorate. It is possible to operate a system in accordance with the present invention where no material, i.e., first hot cullet stream 7, from the cullet filter module 18 is delivered directly to the glass melting furnace 24. However, such a system could achieve material heating only. In this case, the material would not have to be cullet, but could be any sort of durable granular heat transfer media. Also, all the material delivered to the storage silo 15 would have to be of size which would pass through the perforations of solid-to-solid heat exchanger 16.

Solid to Solid Heat Exchanger for Coarse Solids An alterative arrangement for heating ecological cullet which is not pulverized is depicted in figure 9. The heat exchanger unit 60 is based on a spiral design vibratory trough conveyor, as previously described. This design, though, includes a bifurating trough wall 61 to create an inner trough 62 and an outer trough 63. The inner trough 62 has a solid bottom to prevent any material from passing through, while the outer trough is perforated as before, to allow material smaller than about 2mm to pass through. The bottommost trough 64 is not bifurcated and has a solid bottom. It is designed so that fine material collected here is directed to enter the inner trough 62 and travel upward in the spiral. The upper most trough 65 is also not bifurcated and is perforated to allow fine material to pass through. It is designed to receive fine material from the top end of inner trough 62 and combine it with coarse material traveling upward on outer trough 63. As the mixture passes over trough 65, the fine material falls through, so that only coarse material 34a can exit the top of the machine. A portion of the hot factory cullet flow 6 is separated out as material flow

8a and is delivered via chute 66 to trough 63a, which is approximately in the middle of the machine. This cullet forms a bed 67 of factory cullet which travels upward in trough 63 until it exits the machine as material stream 34a. A heat transfer media, including fine durable particles of size less than 2mm, percolates downward through the bed 67 and trough 63 perforations. As the material travels downward, it is heated by direct contact with the hot factory cullet bed 67. Ecological cullet stream 1a is delivered via chute 69 to trough 63b, which is near the lower end of the machine. This cullet forms a bed 70 of ecological cullet which travels upward on trough 71 until the material exits the machine via chute 72 as material stream 5a. Chute 72 is fed by trough 73 which is arranged so that all the material of bed 70 exits the machine before it can reach trough 63a. In this way, the integrity of the two material streams 8a-34 and 1a-5a is maintained. However, fine material 74 (>2mm) passing through trough 63a will fall onto trough 73.

Fine material 74 has been heated by cullet stream 8a-34a. As it further percolates downward through the spiral, it transfers its heat to material stream 1a-5a which is traveling upward. Thus material stream 5a will be heated to a temperature approaching that of material stream 8a. The heat from material stream 8a is first transferred to the fine heat transfer material 74 and then to material stream 5a. Because of the counterflow design, the fine heat transfer material 75 passing through trough 63b is cooled substantially. This material is collected in bottom pan 64 where it forms bed 76 and is directed to inner trough 62 and conveyed to the top of the machine. This material then serves as the fine heat transfer material 68 in the upper portion of the machine. Materials 68, 73, and 75 are in actuality the same material, recycled in a closed loop.

The fine heat transfer media can be any durable particulate material. In theory it only need to be loaded once, then it remains as a closed loop in the machine. In actuality, some of the fine heat transfer media will exit the machine along with material flow 5a, thus some fresh material will have to be added continuously. As such, it is important that the heat transfer media be chemically consistent with the glass to be manufactured, since it is ultimately introduced to the glass melting furnace. Suitable choices would be silica sand, limestone, or other batch ingredients.

A preferred heat transfer media would be fine pieces of cullet. Cullet streams 8a and 1a inherently contain some percentages of fine pieces, sized less than 2mm. these would naturally pass through the trough perforations and become the heat transfer media. In fact, in most cases, the inherent supply of this fine cullet would exceed the amount of fine material which naturally exits the machine along with material flow 5a, and would then build up excessively inside of the machine. In order to prevent this excessive buildup, the bifurcating wall between the inner trough and outer trough 73 would be of a lower height than in the rest of the machine. Then depth of bed 62 would be dictated by this reduced wall height, with excess fine material falling over into trough 73. This would then increase the amount of fine material exiting the machine along with material flow 5a until a material balance is achieved, where the amount of fine material entering the machine along with material flows 8a and 1a is equal to the amount of fine material exiting the machine along with material flow 5a.

Pelletized Glass Batch Operation

In another embodiment of the invention pelletized glass batch could be substituted for, or added to the coarse ecological cullet of the heat exchangers of figure 5 or figure 9. Batch pelletizing has certain advantages, such as reduced energy required for melting and reduced dust generation inside of the furnace. If these advantages out-weigh the rest of the pelletizing operation, the glass maker might choose to operate with pelletized batch.

Claims

What is claimed is:

1. A method for heating a mixture of glass manufacturing raw materials comprising: a) separating the raw materials into small size particles and large size particles, b) providing a moving bed of the large size particles having a top and a bottom, c) introducing the large size particles of the raw material to the top of the moving bed, d) passing hot exhaust gases from a glass melting furnace through the moving bed so that heat is transferred from the gases to the large size particles to provide hot large size particles, e) removing the hot large size particles from the bottom of the moving bed, f) dividing the hot large size particles removed from the bottom of the moving bed into a first portion, a second portion, and a third portion, g) introducing the first portion of the hot large size particles into the glass melting furnace, h) mixing the second portion of the hot large size particles with the raw material small size particles thereby transferring heat to the small size particles,

I) separating the dry, small size particles from the large size particles, j) introducing the large size particles separated in step (I) to the top of the moving bed according to step (c), k) introducing the third portion of the hot large size particles into a solid-to- solid heat exchanger,

I) introducing the small size particles separated in step( I) into the solid-to- solid heat exchanger transferring heat from the hot, large size particles to the small size particles, to provide hot small size particles, m) removing the hot, small size particles from the heat exchanger and introducing them into the glass melting furnace, n) removing the large size particles from the solid-to-solid heat exchanger and introducing them to the top of the moving bed according to step (c).

2. The method of Claim 1 , further comprising venting any water vapor released in step h) into an exhaust gas channel of the glass melting furnace.

3. The method of Claim 1 , further comprising venting any water vapor and organic fumes released in step (I) into the exhaust gas channel of the glass melting furnace.

4. The method of Claim 1 , wherein the large size particles of raw material are pieces of cullet and the small size particles of raw material are glass batch.

5. The method of Claim 4, wherein the pieces of cullet are a size greater than about 2 mm.

6. The method of Claim 1 , wherein the solid-to-solid heat exchanger is of a counter flow design.

7. The method of Claim 6, wherein the heat exchanger comprises a spiral elevator vibratory conveyor.

8. The method of Claim 1 , wherein at least a portion of the small size material is contaminated ecological cullet which has been pulverized to size less than I mm.

9. The method of Claim I, further comprising removing impurities from the furnace exhaust gas stream by passing said furnace exhaust gases through an electrostatic ionizer where a corona discharge imparts electrical charge onto dust particles in the gas wherein said moving bed includes an internal electrode with an electrical potential applied to it to polarize the cullet pieces

10. An apparatus for heating a mixture of glass manufacturing raw materials comprising: a) means for separating the raw materials into small size particles and large size particles, b) a moving bed of the large size particles having a top and a bottom, c) means for introducing the large size particles of the raw material to the top of the moving bed, d) means for passing hot exhaust gases from a glass melting furnace through the moving bed so that heat is transferred from the gases to the large size particles to provide hot large size particles, e) means for removing the hot large size particles from the bottom of the moving bed, f) means for dividing the hot large size particles removed from the bottom of the moving bed into a first portion, a second portion, and a third portion, g) means for introducing the first portion of the hot large size particles into the glass melting furnace, h) means for mixing the second portion of the hot large size particles with the raw material small size particles thereby transferring heat to the small size particles,

I) means for separating the dry, small size particles from the large size particles, j) means for introducing the large size particles separated in step (I) to the top of the moving bed according to step (c), k) means for introducing the third portion of the hot large size particles into a solid-to-solid heat exchanger, I) means for introducing the small size particles separated in step( I) into the solid-to-solid heat exchanger transferring heat from the hot, large size particles to the small size particles, to provide hot small size particles, m) means for removing the hot, small size particles from the heat exchanger and introducing them into the glass melting furnace, n) means for removing the large size particles from the solid-to-solid heat exchanger and introducing them to the top of the moving bed according to step (c).

11. A method for heating glass manufacturing raw materials comprising the following steps: a) classifying the raw materials into small size particles and large size particles, b) providing a moving bed of the large size particles having a top and a bottom, c) introducing large particles of the raw material to the top of the moving bed, d) passing furnace exhaust gases through the moving bed so that heat is transferred from the gases to the large size particles to provide hot large size particles, e) removing the hot large size particles from the bottom of the moving bed, f) dividing the hot large size particles removed from the bottom of the moving bed into a first portion and a second portion, g) introducing the first portion of the hot large size particles into a glass melting furnace, h) introducing the second portion of the hot large size particles into a solid to solid heat exchanger, I) introducing the small size particles of raw material into the heat exchanger so that heat is transferred from the hot large size particles to the small size particles to provide hot small size particles, j) removing the hot small size particles from the heat exchanger and introducing them into the glass melting furnace, and k) removing the large size particles from the heat exchanger and introducing them to the top of the moving bed according to step c).

12. An apparatus for heating glass manufacturing raw materials comprising: a) means for classifying the raw materials into small size particles and large size particles, b) means for providing a moving bed of the large size particles having a top and a bottom, c) means for introducing large particles of the raw material to the top of the moving bed, d) means for passing furnace exhaust gases through the moving bed so that heat is transferred from the gases to the large size particles to provide hot large size particles, e) means for removing the hot large size particles from the bottom of the moving bed, f) means for dividing the hot large size particles removed from the bottom of the moving bed into a first portion and a second portion, g) means for introducing the first portion of the hot large size particles into a glass melting furnace, h) means for introducing the second portion of the hot large size particles into a solid to solid heat exchanger,

I) means for introducing the small size particles of raw material into the heat exchanger so that heat is transferred from the hot large size particles to the small size particles to provide hot small size particles, j) means for removing the hot small size particles from the heat exchanger and introducing them into the glass melting furnace, and k) means for removing the large size particles from the heat exchanger and introducing them to the top of the moving bed according to step c).

13. A method for heating and purifying glass manufacturing raw materials and removing pollutants from exhaust gases from the glass melting furnace comprising: a) providing a portion of the raw materials as coarse cullet, b) providing a portion of the raw materials particles of which are smaller than the course cullet, c) providing a moving bed of the coarse cullet, introducing the cullet to the top of the moving bed and removing said cullet from the bottom of the moving bed, d) providing electrode means in the moving bed to electrically polarize the cullet, e) passing furnace exhaust gases first through an electrostatic ionizer, the ionizer generating corona discharge which imparts electrical charge onto the dust particles in the gases, f) passing furnace exhaust gases subsequently through the moving bed so that heat is transferred from the gases to the coarse cullet, creating hot coarse cullet, and so that electrically charged dust particles are deposited onto the surface of the polarized coarse cullet, g) dividing the hot coarse cullet which exits the moving bed into a first portion and a second portion, h) introducing the first portion of the hot coarse cullet to a glass melting furnace,

I) providing a heat exchanger and introducing the second portion of the hot cullet into the heat exchanger, j) introducing the portion of the raw materials particles of which are smaller than the course cullet into the heat exchanger so that the heat from the hot cullet heats the portion of the raw materials particles of which are smaller than the course cullet batch providing heated particles which are smaller than the course cullet batch, k) removing heated particles which are smaller than the course cullet batch, and m) removing cooled, coarse cullet from the heat exchanger and introducing it to the top of the moving bed according to step c).

14. The method of claim 13, wherein said portion of the raw materials particles of which are smaller than the course cullet are less than about 1 mm on average.

15. The method of claim 13, wherein said coarse cullet is greater than about 4 mm in diameter on average

16. The method of claim 13, wherein said portion of the raw materials particles of which are smaller than the course cullet comprise pulverized contaminated cullet.

17. The method of claim 13, wherein said portion of the raw materials particles of which are smaller than the coarse cullet comprise glass batch.

18. A solid to solid heat exchanger that transfers heat between a large size material and a small sized material comprising: a) an upwardly inclined conveying means having a top end, a bottom end, and a plurality of flights arranged in a spiral configuration so that the flights are substantially above one another on a vertical axis, b) a plurality of passing means in the flights of a size which allows substantially all of the small sized material to pass through while preventing substantially all of the large sized material from passing through, c) a means for vibrating the upwardly inclined conveying means in such a way that the large size material travels up the upwardly inclined conveying means.

19. A method for exchanging heat between particluates of different size comprising, a) providing an upwardly inclined conveying means having a top end, a bottom end, and a plurality of flights arranged in a spiral configuration so that the flights are substantially above one another on a vertical axis, b) providing a plurality of passing means in the flights of a size which allows substantially all of the small sized material to pass through while preventing substantially all of the large sized material from passing through, c) providing a means for vibrating the upwardly inclined conveying means in such a way that the large size material travels up the upwardly inclined conveying means. d) introducing the large size material proximate the bottom end of the upwardly inclined conveying means so that it flows upwardly along the trough conveyor, e) introducing the small sized material proximate the upper end of the upwardly inclined conveying means so that the small sized material passes through the passing means during its downward passage through the upwardly inclined conveying means, f) removing the large size material from the upper end of the upwardly inclined conveying means. g) Capturing and removing small sized material after it falls through the passing means.

20. The heat exchanger of Claim 18, wherein the flights are inclined at an angle to horizontal of between 2┬░ and 20┬░.

21. The heat exchanger of Claim 18, wherein the small sized material is on average several times smaller than perforation opening size.

22. A method for heating cullet prior to introduction to a glass furnace comprising: a) providing cullet which has been contaminated and uncontaminated cullet, b) pulverizing substantially all of the contaminated cullet to size less than 1mm, c) heating the clean uncontaminated cullet by direct contact with furnace exhaust gases, d) exchanging heat from the clean cullet to the contaminated cullet by direct contact in an enclosed chamber, and e) collecting the organic vapors released in the chamber for incineration, f) incinerating the organic vapors.

23. The method of Claim 22, wherein the heated contaminated cullet is separated from the cooled clean cullet of step d and the heated contaminated cullet is directed to the furnace and the cooled clean cullet is reheated by direct contact with the furnace exhaust gases.

24. The method of Claim 22, wherein the heat exchange of step d is achieved by using an upwardly inclined conveying means having a top end, a bottom end, and a plurality of flights arranged in a spiral configuration so that the flights are substantially above one another on a vertical axis, a plurality of passing means in the flights of a size which allows substantially all of the small sized material to pass through while preventing substantially all of the large sized material from passing through, and a means for vibrating the upwardly inclined conveying means in such a way that the large size material travels up the upwardly inclined conveying means.

25. A method for heating cullet and batch prior to introduction to a glass furnace comprising: a) providing contaminated cullet and uncontaminated cullet, b) providing batch in a finely divided form with particle sizes less than 1 mm on average, c) heating the uncontaminated cullet by direct contact with furnace exhaust gases, d) providing an enclosed double helix heat exchanger comprising a first and second spiral trough conveyors with top ends and bottom ends, having a plurality of flights, said flights arranged vertically above and alternately interspersed with one another, said troughs having a plurality of passing means to allow batch to flow through the passing means while retaining cullet having a larger particle size, e) vibrating the first spiral trough conveyor so that cullet will flow in an upward direction and vibrating the second spiral trough conveyor so that cullet will flow in a downward direction, f) introducing hot clean cullet to the bottom of the first spiral trough conveyor, g) introducing contaminated cullet to the top of the second spiral trough conveyor, h) introducing batch to top of the double helix heat exchanger so that it falls successively through the perforation so the trough of both spiral conveyors, I) removing cooled clean cullet from the top end of the first trough and returning it to be reheated by direct contact with the furnace exhaust gases, j) removing heated contaminated cullet from the bottom end of the second spiral trough conveyor and introducing it to the glass furnace.

K) capturing and removing heated batch material after it falls through the perforations and introducing it to the glass furnace, I) collecting the organic vapors released in the enclosed heat exchanger and directing them into the exhaust gases in or leaving the glass furnace so the organic vapors are incinerated.

26. A solid to solid heat exchanger that transfers heat from a first granular material to a second granular material comprising: a) an upwardly inclined conveying means having a top end, a bottom end, and a plurality of flights arranged in a spiral configuration so that the flights are substantially above one another on a vertical axis, b) a solid particulate heat transfer media which is on average smaller than both of the first and the second granular materials, c) a plurality of passing means in the flights of a size which allows substantially all of the heat transfer media to pass through while preventing substantially all of the two granular materials from passing through, d) a means for vibrating the upwardly inclined conveying means to convey particles of said first and second granular materials up the upwardly inclined conveying means, e) means to introduce the first granular material to a middle flight, f) means to remove the first granular material from an upper flight, g) means to introduce the second granular material to a lower flight, h) means to remove second granular material from a middle flight, below the level of flight of step e.

27. Apparatus of claim 26, which further includes an integral upwardly inclined conveying means comprising of a plurality of flight arranged in a spiral configuration which transports the solid particulate heat transfer media from the bottom of the apparatus to the top.

28. Apparatus of claim 26, where first granular material is factory cullet and second granular material is ecological cullet.

29. Apparatus of claim 26, where first granular material is cullet and second granular material is pelletized batch.