Pollution abating, energy conserving glass manufacturing process

Some free water containing glass batch agglomerate formulations when attempted to be dried and heated in a vertical bed prior to being discharged to a glass melter for vitrification convert into large aggregates which cannot be suitably supplied to the melter. The present invention solves this process disabling aggregate formation by treating such agglomerates in a preconditioning chamber(s) prior to supplying them into a vertical bed so as to preclude serious aggregate formation in either the preconditioner or the vertical bed. Such treatment is employed in manufacturing glass with a fossil fuel fired melter or an electrically operated melter.

TECHNICAL FIELD 
The present invention relates to the art of glass manufacturing; more 
specifically the present invention relates to the art of glass 
manufacturing wherein glass forming batch ingredients are formed into 
agglomerates which are fed to a melter for vitrification. Even yet more 
particularly the present invention relates to a process of glass 
manufacturing wherein agglomerated glass batch ingredients are dried and 
preheated to an elevated temperature by direct contact with products of 
combustion, e.g. flue gases from a fossil fuel fired melter, so as to 
provide an economical glass manufacturing process with improved throughput 
and which enhances pollutant recovery and minimizes energy losses and/or 
energy consumption. 
BACKGROUND AND SUMMARY OF THE INVENTION 
The glass industry, in general, is aware that glass forming batch 
ingredients can be combined with water to form agglomerates which 
agglomerates may be dried and heated and then charged to a glass melting 
furnace. It is also recognized in the glass industry that the flue gases 
emanating from a fossil fuel fired melting furnace can have a significant 
roll in such processes. That is, instead of wasting energy in such flue 
gases, including flue gases which have undergone heat exchange in a 
recuperator or regenerator, as had previously been done by discharging 
such gases to the ambient, the flue gases may be used as a source of 
energy. It is also known to minimize pollutant discharge to the 
atmosphere, and simultaneously beneficially employ such energy, by 
transferring at least a portion of otherwise wasted flue gas energy to the 
agglomerated glass batch by direct contact therewith prior to discharge 
into the melting furnace. 
Some of the most economical of such process teachings of the prior art work 
well for many glass batch formulations but these teachings are entirely 
unsuitable for an economical, industrial exploitation of such processes as 
applied to certain other agglomerated glass batch formulations. Such 
unsuitability is especially acute in instances of agglomerating certain 
glass batch formulations with water into the form of pellets. Such water 
containing agglomerates, to which the teachings of the prior art are 
ill-suited will henceforth be referred to as "hydrologically unstable" 
agglomerates. The term hydrologically unstable will be subsequently 
clarified and the term agglomerate includes within its scope any 
composite, intergral, discrete, self-supporting mass which includes 
substantially all essential glass forming batch ingredients. Unless the 
contrary is indicated, the term agglomerates comprehends within its scope 
extrusions, disks, briquettes, pellets or other discrete geometric shapes. 
Normally a maximum dimension of either height, length, or width or 
diameter of such agglomerates will be on the order of one or two inches 
and specifically with regard to pellets the maximum diameter will be 
preferably less than one inch and more typically in a size range of about 
3/8 of an inch to about 5/8 of an inch. 
It should be borne in mind that the glass industry is a highly capital 
intensive industry generally operating on low profit margins and high 
production rates. Thus, for any process to merit industrial exploitation 
in the glass industry such process must be compatible with the economic 
nature of the industry. Some of the factors involved include the necessity 
of low capital expenditures for new equipment installations, and a process 
which has low operating cost. Included in the latter consideration are not 
only manpower requirements but also, for example, floor space 
requirements, as such space is at a premium in virtually all glass 
industry plants, equipment susceptible to minimal breakdown and damage, 
and equipment utilizing a minimum amount of operating power. In the 
context of drying and heating water-containing, glass batch agglomerates 
with flue gases from a fossil fuel fired melting furnace, the most 
desirable process equipment of the prior art is a shaft type heater, or 
chamber, i.e., a vertical bed of substantial height, and preferably a bed 
in which the agglomerates flow downwardly through the chamber and in which 
the flue gases flow counter-current to the agglomerates, to substantially 
continuously, in a single processing operation, dry and preheat them. 
Some glass batch agglomerates are, however, unstable and substantially 
continuous drying and heating in a single operation in a vertical bed is 
not obtainable. When such water-containing glass batch agglomerates, and 
especially pellets, are processed in direct contact with, for example, 
flue gases from a glass melting furnace, which flue gases have passed 
through a dry portion of the bed to preheat them, the wet agglomerate 
containing portion of the bed, when at a height in excess of a 
characteristic value, will aggregate into a strong, rather massive, 
monolithic type structure, or structures, which plug the shaft heater. 
This unacceptably necessitates shutdown and results during drying and at 
temperatures which are well below those which would cause the agglomerates 
to thermally sinter or fuse together. The height at which aggregate 
formation occurs is greater for a vertical bed dried and preheated with 
hot, or warm, dry air, or dry combustion products than where the drying 
and preheating is done with wet air or wet combustion products, like the 
flue gases from a fossil fuel fired glass melting furnace. If ambient air 
is heated, or warmed, at constant humidity, or if combustion is practiced 
with a large excess of air, such gaseous heating medium may typically, for 
example, have a wet bulb temperature on the order of about 80.degree. F. 
to 85.degree. F. (26.degree.-30.degree. C.) and perhaps less. In contrast 
however, the flue gases from a fossil fuel fired glass melting furnace are 
the products of stoichiometric combustion and are more humid, or wet; 
typically they have a wet bulb temperature on the order of about 
130.degree. to about 140.degree. F. (54.degree.-60.degree. C.) or higher. 
This indicates that a significant factor in aggregate formation is the 
psychrometry of the gaseous heating and drying medium, for example the wet 
bulb temperature. This is not to imply however, that the use of warm, dry 
air is satisfactory. First of all, relative to the use of a fossil-fuel 
fired melter, if such warm dry air had to be separately provided it would 
increase cost and would not be compatible with the purpose of recovering 
at least some of the energy normally wasted in the furnace flue gases, nor 
with attempting to remove pollutants from the furnace flue gas. 
Furthermore, even the use of such heated dry air does not eliminate 
aggregate formation. For example, it has been found when directly heating 
a bed of free water containing pellets with a gaseous heating medium 
comprising combustion products and having a web bulb temperature of about 
80.degree.-85.degree. F. by passing such medium through the bed, that a 
bed of a height of up to about 8 or 9 inches was characterized by the 
pellets generally remaining as discrete, free flowing individual pellets. 
Above that height, however, the pellets were aggregated and no longer free 
flowing. Such occurrence obviously is unsuitable inasmuch as a typical 
shaft type heater, or vertical bed of agglomerates, must be in excess of 
several feet, e.g., ten or more, to maintain compatibility with the pull 
rate on a melting furnace and provide a sufficient retention time so as to 
be able to preheat the pellets to the maximum temperature possible, but 
short of causing the agglomerates to sinter together, and also to allow 
sufficient agglomerate-flue gas contact time to separate pollutants from 
the flue gases. 
Thus, it will be seen from the above that there is a problem in the glass 
manufacturing industry with the above type indicated processes in that 
certain types of free water-containing, glass batch agglomerates simply 
cannot be suitably processed in a vertical bed. In accordance with the 
present invention, this problem has now been solved and an improved 
process is provided. Some of the advantageous features of the present 
improved process include the ability to substantially continuously dry and 
preheat such glass batch agglomerates, using a vertical bed, while 
substantially simultaneously recovering pollutants from flue gases of a 
glass melting furnace in the bed for recycle into the glass melter. With, 
for example, Na.sub.2 O and B.sub.2 O.sub.3 containing glasses, otherwise 
potentially wasted boron values are recovered in the vertical bed as a 
sodium borate, e.g. NaBO.sub.2, and recycled to the melter. This has the 
advantage of enhancing the quality of the atmosphere and additionally 
saves on raw material costs. In conjunction with that, the process 
recovers otherwise wasted energy, reduces the amount of energy which is 
normally consumed in a glass melter for melting glass batches and will 
significantly increase furnace throughput per square foot of melter area. 
In fact, it is not uncommon to double the throughput per square foot of 
melter area. Furthermore, the improved process recognizes the economic 
nature of the glass manufacturing industry and provides for a maximization 
of economic benefit with a minimization of economic detriment in order to 
obtain that benefit. Thus, for example, the improved process is not highly 
capital intensive and is characterized by low operating costs. The 
significance of the above in light of today's economic conditions, will be 
appreciated by all. 
In passing it should be mentioned that realization of the above type 
advantages, is not limited to the use of a fossil-fuel fired melter. They 
may, likewise, be obtained in manufacturing glass by using a melter in 
which the energy is electrically supplied. In the latter instance instead 
of using melter flue gases, agglomerate drying and preheating is effected 
by using separately provided products of combustion for the heating medium 
and, thereby, the amount of more expensive electrical energy needed for 
the melter is significantly decreased. Corresponding increased throughputs 
will also be realized. The heating medium is obtained by the combustion, 
preferably with a substantial stoichiometric excess, e.g. at least about 
50%, typically about 50% to about 400%, of air with any suitable fuel such 
as coal, oil, natural gas, propane, or the like, depending on cost and 
availability. In some instances it may even be economically expedient that 
the heating medium be heated air, for example electrically heated air. 
The foregoing problem is solved, and the advantageous features attained, by 
providing for an improvement in glass manufacturing processes of the type 
comprising combining glass-forming batch ingredients and water into free 
water-containing glass batch agglomerates, preferably pellets, 
continuously directly contacting glass batch agglomerates in a vertical 
bed with flue gases from a glass melting furnace so as to preheat the 
agglomerates, discharging preheated agglomerates from a lower portion of 
the bed, charging preheated agglomerates to a melting furnace and melting 
the charged agglomerates therein. The improvement resides in adapting such 
processes to the use of free water-containing glass batch agglomerates 
which are hydrologically unstable and further comprises accumulating a 
predetermined amount of such agglomerates in a preconditioning chamber, 
preferably a plurality of separate chambers operated in a sequential, 
parallel flow fashion, so as to form a preconditioning bed(s) of a 
predetermined height, directing flue gases from said vertical bed into 
said preconditioning chamber and passing said gases through said 
preconditioning bed so as to heat the bed for a sufficient period of time 
to form a hydrologically stabilized bed of agglomerates and discharging 
the agglomerates of the hydrologically stabilized bed and supplying them 
to the vertical bed. Generally, the height of the preconditioning bed or 
beds will be significantly less than the height of the vertical bed, e.g. 
typically less than 5% of the height of the vertical bed. 
In accordance with another aspect of the present invention, the foregoing 
advantageous features are obtained by providing an energy efficient, 
pollution abating, substantially continuous glass manufacturing process 
comprising, forming separate beds of free water-containing glass batch 
agglomerates, discharging the agglomerates of the beds, after at least 
some heating, into a shaft-type preheating chamber having a vertical bed 
of agglomerates therein, substantially continuously releasing dry, further 
heated agglomerates from the vertical bed, charging the dry, further 
heated agglomerates to a combustion-fired melting furnace, melting the 
agglomerates therein and, substantially simultaneously conveying flue 
gases from the furnace to the chamber, through the vertical bed therein so 
as to further heat the agglomerates of said bed, and then from the 
vertical bed through said separate beds so as to heat the agglomerates of 
the separate beds. The separate beds will be heated prior to discharging 
the agglomerates of the respective beds for a sufficient period of time to 
assure that they will not form process disabling aggregates in the 
preheating chamber but the period of time will be insufficient to cause 
the respective separate beds themselves to convert, or cement, into 
process disabling aggregates. Preferably, the separate beds are 
sequentially formed and sequentially heated for the prescribed period of 
time. That is, while an individual bed is treated in a batch-like 
sequence, the cycles of the respective plural beds will be such that 
overall, the heating of the separate beds, and discharging, will be 
generally along the lines of a continuous processing step. Desirably, the 
separate beds will be disposed downstream of the vertical bed in a general 
parallel flow arrangement and will be located adjacently upwardly of the 
preheating chamber with the flue gases from the chamber being conveyed to 
the beds also in a parallel flow type manner. 
In accordance with another aspect of the invention, there is provided a 
glass manufacturing process comprising forming separate beds of free-water 
containing, glass batch agglomerates, and, after at least some heating, 
discharging the agglomerates of said beds, and supplying them into a shaft 
type preheating chamber having a vertical bed of agglomerates therein, 
substantially continuously releasing dry, further heated agglomerates from 
said vertical bed, charging said dry, further heated agglomerates to a 
glass melter and melting said agglomerates therein, while conveying 
gaseous combustion products to said chamber, through said vertical bed so 
as to further heat said agglomerates, and then from said vertical bed 
through said separate beds so as to heat the agglomerates therein. The 
gaseous combustion products may be flue gases from a melter, or the melter 
may be electrically powered and the combustion products provided by 
burning air and a fuel. 
Yet another aspect of the invention provides an improved glass 
manufacturing process of the type comprising, combining glass forming 
batch ingredients and water into free water containing glass batch 
agglomerates, continuously directly contacting glass batch agglomerates in 
a vertical bed with gaseous combustion products so as to preheat the 
agglomerates, discharging said preheated agglomerates from a lower portion 
of said bed, charging said preheated agglomerates to a melting furnace and 
melting said charged agglomerates therein. The improvement resides in 
preventing hydrologically unstable agglomerates from forming large 
(process disabling) aggregates by continuously supplying said 
hydrologically unstable agglomerates to a preconditioning chamber so as to 
form a preconditioning bed of progressively increasing height, 
discontinuing the supply to said chamber and directing said gaseous 
combustion products from said vertical bed into said preconditioning 
chamber and passing said gaseous combustion products through said 
preconditioning bed so as to heat said preconditioning bed of 
hydrologically unstable agglomerates for a sufficient period of time to 
form a hydrologically stabilized bed of agglomerates, discharging the 
agglomerates of said hydrologically stabilized bed into said vertical bed. 
Further in accordance with the present invention there is provided an 
improved glass manufacturing process comprising discharging a supply of 
free water containing, hydrologically unstable, glass batch agglomerates 
gravitationally downwardly, discontinuing said discharging at a 
predetermined interval and intercepting said gravitationally downwardly 
discharged supply so as to form said supply into a shallow static bed of 
substantially uniform height, directly heating said static bed so as to 
remove at least some free water from the agglomerates and convert said bed 
to a hydrologically stabilized bed, discharging the agglomerates of said 
stabilized bed and supplying them to a vertical bed, said vertical bed 
being maintained at a predetermined minimum height, gravitationally 
flowing the discharged agglomerates generally downwardly through said 
vertical bed, heating said vertical bed, including said generally 
downwardly flowing discharged agglomerates to an elevated temperature by 
direct contact with a gaseous heating medium passing through said vertical 
bed, supplying said heated flowing agglomerates after flowing through said 
vertical bed to a glass melting furnace and melting said agglomerates 
therein. 
The present invention, in addition to the previously indicated advantages, 
provides outstanding pollution-abatement features when the heating medium 
are the flue gases of a fossil-fuel fired melter. That is, materials in 
the heating medium, especially flue gases, which normally decrease 
environmental quality are reclaimed and recycled into the melting 
operation. Particulates, for example, are separated by a filter-type 
action. If desired, a cyclone, downstream of the agglomerate beds, may be 
employed to effect further reclamation of materials. Some materials are 
reclaimed by an in-situ reaction and some gaseous polluting species, 
because of the progressive temperature drop of such flue gases during 
operation, are reclaimed by a condensation type mechanism. Of course, 
however, the temperature of the gases during operation will not be allowed 
to drop to the point where water vapor therein will undergo condensation. 
EXEMPLARY PRIOR ART 
U.S. Pat. No. 3,880,639 discloses a process for heating agglomerates with 
flue gases from a glass melting furnace to recover SO.sub.x values. The 
patent generally indicates that drying of the pellets may be done by means 
of heated air or in an oven after which the pellets may be supplied to a 
heat exchanging reactor. There is no recognition in this patent of, let 
alone a solution to, the problem noted above inasmuch as the patent 
indicates that wet pellets may be fed directly to the heat 
exchanger-reactor and contacted therein with furnace flue gases. 
Similarly, difficient are the teachings of U.S. Pat. No. 3,788,832, which 
discloses drying agglomerates, for example briquettes, in warm air and 
then preheating the dried material with combustion gases prior to delivery 
to the furnace, as this patent also states that compacted glass batch can 
be dried and simultaneously preheated. 
U.S. Pat. No. 3,767,751 appears to generally allude to problems with drying 
certain types of batches in Column 2 but the solution to that problem is 
allegedly obtained by special pelletizing equipment so as to pelletize at 
temperatures between 100.degree. C. to about 600.degree. C. 
U.S. Pat. No. 3,728,094 discloses a process wherein agglomerated particles, 
e.g. pellets, are fed to a compartmentalized belt drier with the drying 
gas being waste gas originating at a glass melter and passing through a 
stack furnace wherein the particles are heated after leaving the drier. 
Such a drier would appear to be a rather massive piece of equipment 
requiring high capital expenditures and would be subject to high operating 
cost and hence is not desirable. Not insignificant factors of such 
operating costs will be water condensation and belt plugging problems. 
Furthermore, there is no recognition of the aggregate formation problem in 
that patent, as the patent indicates that the compartmentalized drier may 
be by-passed or eliminated. The drying and preheating process with flue 
gases from a melting unit, as set forth in FIG. 4 of U.S. Pat. No. 
4,113,459, likewise has no recognition of the aggregate formation problem. 
U.S. Pat. Nos. 3,726,697 and 4,026,691 represent high capital expenditure 
processes with high operating cost since the rotary driers and traveling 
bed vessels they respectively disclose are relatively massive structures. 
Furthermore, both of these patents teach an affirmative prereaction of the 
alkali metal oxide source compound and the alkaline earth metal oxide 
source compound prior to formation of pellets or granules. Such an 
additional step is not needed in accordance with the present invention and 
it only serves to increase manufacturing costs. 
In Glass, February 1965, pages 68 and 69, there is a discussion with regard 
to drying granules of soda containing glass batch. The discussion 
indicates that with a brick shaft and also a cellular drier, granules 
adhered into a compact mass and that a special belt drier was developed 
for the use of flue gases. The provided design data with regard to the 
drier would indicate it to be impractical for use. In a translation of 
"Moglichkeiten der industriellen Pelletierung von Glasgomengen", 
Glastechnische Berichte 50 (1): 19-23 (1977) it is also indicated that 
pellets of alkali metal oxide containing glass batch may be heated with 
oil, natural gas, coal or flue gases from a melting furnace in what would 
appear to be a special unit which is termed a drying belt. The drying belt 
is described as consisting of a traveling grate in the form of a revolving 
series of troughs with perforated bottom; the pellets are said to be dried 
by introducing them into these troughs or containers using a temperature 
program which can vary with different batches. 
U.S. Pat. No. 2,366,473 relates to a process of producing nodular or pebble 
like units and refers to a chemical set taking place with powdered glass, 
or ground silica, and soda ash. The patent indicates that drying may be 
effected in a rotary drum employed in the nodulating operation, or by 
conveying the nodules on suitable conveyors through drying rooms or the 
use of other convenient driers. It is also indicated that hardening of 
calcium oxide or hydroxide containing batches may be hastened by exposing 
the bodies in trays or on moving conveyors to flue gas or another gas rich 
in carbon dioxide but no specifics are provided. U.S. Pat. No. 2,220,750 
discloses drying soda containing ingredients during a milling operation or 
by exposure to the atmosphere or that dryers of the rotary, belt or other 
convenient type may be used. It is indicated that the agglomerated masses 
may be dried to any desired free water content so long as the masses are 
non-sticky. Preference is expressed for removal of all water but it is 
indicated that this is not necessary since the remaining water will be 
driven off in the melting pot or tank. 
DESCRIPTION 
The present invention is generally applicable to glass batch formulations 
which when agglomerated with water form hydrologically unstable 
agglomerates. Usually the amount of water used to form the agglomerates 
will be between about 5 to about 20% by weight on a (dry basis) and will 
vary with different glass batches and the agglomerate forming technique. 
When, for example, forming pellets on a rotating disc, typical water 
contents of the formed pellets will be about 10 to about 15%. As a general 
matter it will be preferred to form the pellets, and agglomerates 
generally with the minimum amount of water that can be employed and yet 
provide adequate wet, or green, strength; too much water will tend to 
complicate processing because, so to speak, the agglomerates will be 
stickier. Of course, as will be readily apparent, well mixed batch should 
be employed to reliably produce consistent quality pellets. Specific glass 
batch formulations to which the present invention is especially uniquely 
adapted are exemplified by the alkali metal oxide containing glasses in 
which the alkali metal oxide source in the batch ingredients is present in 
a sufficient quantity to cause free water-containing batch agglomerates to 
be hydrologically unstable. By hydrologically unstable is meant that when 
batch ingredients are formed into agglomerates with water the following 
characteristic of the agglomerates will result. This characteristic is the 
propensity, or natural inclination, of such agglomerated glass batches, 
when individual agglomerates are positioned on themselves in a vertical 
bed and then dried, to form, or coalesce into, a rather massive aggregate, 
or aggregates, i.e., monolithic structures composed of a multitude of 
firmly adhered individual agglomerates. That is, when attempting to 
simultaneously dry and preheat agglomerates containing free, or bound, 
water to a temperature in excess of the boiling point of water in a shaft 
type vertical bed by continuously passing a gaseous drying-and-heating 
medium containing combustion products and having a wet bulb temperature 
between about 130.degree. F. to about 140.degree. F., or higher, 
therethrough, i.e., a wet bulb temperature like that of melter flue gases, 
the wet agglomerates will form an aggregate, or aggregates, of the 
individual agglomerates and the agglomerates no longer remain as 
substantially individual units. Aggregate formation precludes free flow 
under the influence of gravity through and from the bed and likewise 
dramatically decreases passage of the drying and heating medium through 
the bed. In short, such aggregate formation is process-disabling. Such 
occurrence is the result of drying and is not caused by sintering of 
agglomerates, i.e., the problem is in the nature of forming a cement 
during drying and not sintering. When so drying (i.e., removing 
substantially all free water, for example to less than about 0.5% on a dry 
basis), such hydrologically unstable agglomerates, a given formulation 
generally will have an easily determinable characteristic aggregate 
forming height and such height precludes the practical utilization of a 
vertical bed, or shaft type heater, to dry and preheat agglomerates in a 
single processing operation. This height may be only a few inches, whereas 
the vertical bed will commonly need to be in excess of, for example, 10 
feet and typically 15-20 feet. 
More specifically, exemplary hydrologically unstable batch formulations are 
the sode containing glasses. The source of soda (Na.sub.2 O) in such 
batches will be a sodium carbonate, e.g., soda ash, or sodium hydroxide or 
combinations of these materials. The sodium hydroxide may be employed as 
an anhydrous material, e.g. flakes, or in the form of a convenient aqueous 
solution thereof in which case the water of that solution may supply some 
or even all of the water employed in forming the agglomerates. Typically, 
hydrological instability will be observed when the soda content of the 
glass, on a theoretical oxide basis, is in excess of several percent by 
weight, for example in excess of about 5% or 6% by weight of Na.sub.2 O, 
and will be especially serious in pellets at a Na.sub.2 O content between 
about 10-20% by weight on a dry theoretical oxide basis. 
It will thus be seen that the instability characteristic will exist in some 
quite common glasses, including fiberizable glasses, container glasses, 
and plate, or flat glasses. Such glasses may contain Na.sub.2 O in an 
amount between about 5% and about 25% by weight of the final glass and 
more commonly between about 10% and about 20% by weight. Exemplary of such 
glasses are the glasses which are predominantely soda lime silica glasses. 
That is, glasses in which the cumulative amount of silica and calcium 
oxide and sodium oxide are in excess of about 60% by weight of the total 
glass. Typically, for containerglass and sheet, or flat glass this amount 
will be in excess of about 75% and even more commonly in excess of about 
90% by weight of the glass. Exemplary of such soda lime silica glasses are 
those in which the silica content is between about 60% to about 75% by 
weight, alumina between about 0% to about 15% by weight, calcium oxide 
between about 5% and 20% by weight, magnesium oxide between 0% to about 
20% by weight, sodium oxide between about 10% to about 20% by weight. The 
raw materials employed in the batch for such compositions typically 
include sand, soda ash and/or sodium hydroxide, limestone, clay, and burnt 
dolomite. Quite typically these glasses will include from 0% to 5% by 
weight of one or more of potassium oxide and/or lithium oxide and 
occasionally between 0% to about 5% by weight of barium oxide. 
Exemplary of the fiberizable glass compositions which are outstandingly 
adapted for use in the present contemplated process are the 
alkali-alkaline earth-aluminoborosilicate glass compositions, for example, 
those compositions wherein the cumulative total weight percents of silica, 
aluminum oxide, boron oxide, alkali metal oxides and alkaline earth metal 
oxides is in excess of about 75% or 80% by weight of the glass composition 
and more typically in excess of about 97% by weight. The 
soda-lime-aluminoborosilicate compositions are most common. Typically, 
such latter type compositions include the following ingredients on an 
oxide basis in approximate weight percents: silica about 55% to about 65%; 
alumina about 3% to about 6.5%; calcium oxide about 6% to about 10%; 
sodium oxide about 11% to about 16.5%; and B.sub.2 O.sub.3 about 3% to 
about 12%; those compositions may also generally include about 0.1% to 
about 3% by weight of K.sub.2 O, about 0.1% to about 0.5% Fe.sub.2 
O.sub.3, and, optionally, 0% to about 0.5% TiO.sub.2 , 0% to about 3% BaO, 
0% to about 0.2% Li.sub.2 O, and 0% to about 0.5% SrO as well as 0% to 
about 4.5% of MgO. The raw materials which are employed for such 
compositions include burnt dolomite, clay, limestone, sand, soda ash, 
and/or sodium hydroxide, with soda ash being especially preferred. The 
sources of B.sub.2 O.sub.3 for these glasses will preferably be calcium 
borates and/or sodium calcium borates, e.g., probertite, ulexite and/or 
colemanite supplying minerals or materials. If colemanite is employed, the 
material, prior to utilization, will be treated by heating it above its 
decrepitation temperature so as to release water of crystallization. In 
fact, with regard to any of the raw materials employed, if they are 
characterized by a sudden, rather violent release of any gases, i.e., they 
decrepitate, it is recommended that they be so calcined, or burnt, prior 
to being used to form agglomerates. Such calcium borates and sodium 
calcium borates are preferred B.sub.2 O.sub.3 sources because they have 
relatively high decomposition and/or melting points which thereby allows 
the agglomerates containing such materials to be preheated, e.g. with flue 
gases emanating from a fossil-fueled fired furnace, to a temperature which 
is quite high, e.g., in excess of about 500.degree. C., and even in excess 
of 600.degree. C. This, therefore, will allow for a maximum heat recovery 
from the flue gases in contrast to using other sources which could not 
tolerate such a high temperature of preheat. In the context of electric 
melting, more expensive electrical energy is saved because the high degree 
of preheat can be done with cheaper energy (fuel) sources. If a borax is 
employed, e.g. 5 mole borax, it will be desirable for most suitable 
operation to limit its amount to less than about 2 or 3% by weight of the 
batch. 
As has been indicated above when free water containing, hydrologically 
unstable glass batch agglomerates are attempted to be dried to substantial 
total dryness (less than about 0.5% and more typically to virtually 0% 
water) in a vertical bed by passing combustion products directly 
therethrough, having a wet bulb temperature of generally between about 
130.degree. F. to about 140.degree. F. or higher, the wet agglomerate bed 
will, by a cementing type action, convert into a process disabling 
aggregate, or aggregates. It has been found that, when so drying 
hydrologically unstable agglomerates with combustion products having a wet 
bulb temperature corresponding to the approximate wet bulb temperature of 
furnace flue gases, the agglomerates will have an "inherent, or imminent, 
aggregate forming height" below which no serious aggregation of a bed 
results when substantially totally dried but above which it does. 
Furthermore, it has been found that the height of the bed of wet 
agglomerates at which serious aggregate formation results is not 
independent of the psychrometry of the drying and/or heating medium. That 
is, the imminent aggregate forming height may be adjusted ("adjusted 
imminent aggregate forming height"), for example, upwardly by decreasing 
the wet bulb temperature of the drying medium. The latter can be, for 
example, easily accomplished by dilution of furnace flue gases with air, 
or by combustion with substantial excess air. While this will be more 
specifically subsequently exemplified, as an example, an "inherent 
aggregate forming height" may be on the order of about 2 inches, whereas 
an "adjusted imminent aggregate forming height" may be on the order of 
about 8 or 9 inches with a drying medium having wet bulb temperature of 
about 80.degree. F.-85.degree. F. Such heights may vary with different 
agglomerate compositions, but they indicate how a bed of wet agglomerates 
can be preconditioned to a "hydrologically stabilized" state. That is, as 
indicated, if the height of a wet agglomerate bed is less than certain 
values, e.g. 2 inches when using a heating medium with a wet bulb 
temperature of about 130.degree.-140.degree. F., or 8-9 inches when the 
wet bulb is about 80.degree.-85.degree. F., the bed can be substantially 
totally dried without serious aggregation; furthermore the dry 
agglomerates of such beds can then be further heated to an elevated 
temperature in another bed, likewise, without serious aggregation. The 
latter bed for preheating to an elevated temperature can be a vertical bed 
in a shaft type preheating chamber with the height of the vertical bed 
being maintained at a suitable predetermined minimum value which is 
significantly greater than the above indicated aggregate forming heights. 
It has also been further found that when drying a bed of wet hydrologically 
unstable agglomerates, the bed passes through a unique state where, after 
at least some heating so as to remove some free water, the bed may also be 
termed "hydrologically stabilized". This has been observed with beds of 
hydrologically unstable agglomerates under conditions which, if the bed 
were to be substantially totally dried, would seriously aggregate. That 
is, the amount of free water which has been removed when the bed is in 
this hydrologically stabilized state has not yet reached the point which 
causes the bed itself to convert into process disabling aggregates and, 
surprisingly, if the bed is discharged during that state, for example by 
dropping the bed into another chamber, the agglomerates can then be 
further heated to not only remove the remaining free water, (without 
process disabling aggregate formation in the latter chamber) but also 
preheated in the same chamber to a substantially elevated temperature for 
feeding to the glass melter. The latter chamber, may be a shaft type 
preheating chamber having a vertical bed of substantial height in it. This 
finding makes it possible to employ a bed of the hydrologically unstable 
agglomerates which has a height that is greater than the inherent 
aggregate forming height of the agglomerates, and even greater than the 
adjusted imminent aggregate forming height of the bed corresponding to the 
wet bulb temperature of the medium passing therethrough, by discharging 
such bed and supplying the agglomerates which formed the bed to a main 
vertical bed, for preheating to an elevated temperature, when the bed has 
been properly preconditioned to its hydrologically stabilized state. 
Thus, by employing plural, e.g. at least 2, separate preconditioning beds, 
preferably operating on a sequential or cyclic basis, those beds can be 
discharged to a main vertical bed of a shaft type preheater and further 
processed therein without encountering operation-discontinuing aggregation 
in either the preconditioning beds or the main vertical bed. The height of 
the vertical bed is thus maintained at some predetermined minimum value by 
the cyclic, sequential discharging of the preconditioning beds thereto. 
Generally, the amount of hydrologically unstable agglomerates which will 
be accumulated to form the separate preconditioning beds will be such that 
the height of the formed bed will be no greater than, and typically will 
be less than, the adjusted imminent aggregate forming height which 
corresponds to substantially completely drying the bed with ambient air 
which has been heated at substantially constant humidity. Bearing in mind 
that it is desired to preheat dry agglomerates to an elevated temperature 
by counter-current, direct, heat exchanging contact of the agglomerates 
and a heating medium (e.g. flue gases from a furnace or separately 
provided combustion products) in a vertical bed, it will be apparent that 
the temperature of the heating medium will progressively decrease as it 
passes through the bed. It is also desired to use such medium after such 
heat exchange to precondition hydrologically unstable agglomerates to a 
hydrologically stabilized state, also by a direct contact operation, in 
which the agglomerates of the preconditioning bed have substantially no 
relative movement, so as to further remove pollutants from the drying 
medium. The temperature to which the medium is cooled in a vertical bed 
before it is used to precondition the preconditioning beds will vary with 
different installations and will be routinely selected based on various 
considerations including, for example, the maximum temperature to which 
the agglomerates can be heated without sintering, the desired temperature 
to which the agglomerates will be heated, the temperature of the flue 
gases (after cooling in a recuperative or regenerative type heat 
exchanger) supplied to the vertical bed, the heat capacity of the 
agglomerates which, in turn, will depend on glass composition, production 
rates, radiation heat losses from the shaft type preheater in which the 
vertical bed is maintained, and the like. That temperature may for example 
be 200.degree. F.-800.degree. F., more typically about 350.degree. F. to 
700.degree. F., e.g. 400.degree. F. to 600.degree. F. Consequently, in 
order to determine a typical desirable maximum bed height for the 
preconditioning chambers the adjusted imminent aggregate forming height 
will be determined using a heating medium having a dry bulb temperature of 
that selected temperature and a wet bulb temperature approximately that of 
ambient air. Thus, the maximum height may be approximately determined by, 
for example, determining the adjusted imminent aggregate forming height of 
a bed of hydrologically unstable agglomerates which corresponds to using a 
heating medium which is ambient air that has been heated at constant 
humidity to that selected dry bulb temperature, e.g. a heating medium 
having a dry bulb of 350.degree. F. and a wet bulb of about 80.degree. F. 
The above generally shows that various options exist with regard to process 
operation and, more specifically, with regard to preconditioning. It is 
thus possible to operate such preconditioning beds by passing flue gases 
therethrough, after counter current heat exchange contact with 
agglomerates in the vertical bed, by employing a preconditioning bed 
height which is less than the inherent aggregate forming height. 
Similarily, it is possible to use a preconditioning bed height in excess 
of the inherent aggregate forming height by diluting, or combining, the 
flue gases (so as to decrease the wet bulb temperature) of the main 
vertical bed prior to entry into the preconditioning beds with ambient air 
and operating the bed at a height which is less than the adjusted inherent 
aggregate forming height corresponding to the psychrometry of the diluted 
flue gases. No process disabling aggregation will result with the above 
even if the preconditioning beds are totally dryed prior to discharging 
them to a main vertical bed for further heating. Likewise, by diluting the 
flue gases with air after passage through the main vertical bed and prior 
to their being directed into the preconditioning beds, it is possible to 
operate the preconditioning beds at a height in excess of the adjusted 
imminent aggregate forming height corresponding to the psychrometry of 
such diluted flue gases by discharging the preconditioning beds when they 
are in their unique hydrologically stabilized condition to a vertical bed. 
The same considerations apply when electric melting is contemplated in 
which case, instead of using flue gas from a melter, separate combustion 
products are provided; the psychrometry of such products may be controlled 
during combustion by the use of excess air or by dilution. If desired the 
heating medium for electric melter operation may be heated ambient air. 
Generally the process will be operated so that the temperature of the gases 
will not drop so low as to create water condensation problems. To assist 
in this regard the air, with which the combustion products, e.g. flue 
gases, are combined or diluted prior to entry into the preconditioning 
beds, may be heated. Such combination will also increase the drying rate 
of the preconditioning beds. Such heated air may be produced by combustion 
of a suitable fuel with an excess of stoichiometric air or available 
"spill air" may be employed. Spill-air generally is the excess of needed 
combustion make-up air after heating of air in a recuperator, or 
regenerator.

Referring now to FIG. 1 of the drawings, there is set forth a schematic 
flow diagram which represents a desirable manner of industrially 
exploiting the present invention. In the drawing, the flow paths of vapor 
are indicated by dashed lines and the agglomerate flow paths by solid 
lines. Referring to the drawing there is generally shown a combustion 
fired glass melter 1 from which molten glass issues. The products of 
stoichiometric combustion, as is known in the art, are passed through a 
heat exchanger 2, for example a recuperator or a regenerator, where they 
undergo indirect heat exchange contact with combustion makeup air (not 
shown). There is also provided a shaft type preheater 3 maintaining a 
vertical bed of agglomerates, with the preheater preferably containing an 
upper substantially cylindrical portion and a lower inverted 
frusto-conical portion. Preferably, the ratio of the height of the 
cylindrical portion to the height of the frusto-conical, or funnel, 
portion is about 0.8 to 1, with the height of the cylindrical portion 
being about one and one-half (1.5) to about twice the diameter of the 
cylindrical portion. Desirably, the superficial velocity of the flue gases 
through the cylindrical portion will be between 60 to about 130 standard 
feed per minute. The included angle between diametrically opposed side 
wall portions of the funnel desirably will be 30.degree.-40.degree., 
preferably 36.degree.. Flue gases from heat exchanger 2, e.g. having a 
temperature of 1000.degree. F. to 1500.degree. F. or even higher, are 
conveyed through a duct 51 and then directed to a lower portion of 
preheater 3 and passed counter currently to the gravitationally downwardly 
flow of the agglomerates therein so as to preheat the agglomerates to an 
elevated temperature. The flue gases enter, in a preferred arrangement, 
the preheater on diametrically opposed sides of the funnel and beneath an 
inverted V, or wedge shaped, flow distributor. The flow distributor is in 
the form of a bar extending between the entry ports for the flue gases and 
has an included angle of about 60.degree.. Desirable gas distribution 
through the preheater will be obtained if the level of pellets above the 
flue gas inlets are maintained at a height of about equal to, to about 1.5 
times, the diameter of the cylindrical portion. While for any given 
installation some adjustments will need to be made, it will be desirable 
to locate the wedge in the funnel portion such that its base, or bottom 
terminous, is at a level, beneath the juncture of the funnel and 
cylindrical portion, equal to about 0.1 to about 0.5 times the diameter of 
the cylindrical portion. As will be appreciated by those skilled in the 
art, as the agglomerates flow past the wedge shaped distributor, a void 
area, or more exactly a void volume, will generally form adjacently 
beneath the apex of the wedge. This area may be viewed as diamond shaped 
with the uppermost portion being defined by the internal surfaces of the 
inverted V-shaped bar and the lowermost portion, which is largely governed 
by the angle of repose of the agglomerates employed, being a V-shaped 
portion. Suitably, the wedge will be positioned in the funnel such that 
the open area, for pellet and gas flow around the wedge, will 
approximately be equal to about the total surface of the V-shaped 
lowermost portion. Prior to entry into preheater 3, it is preferred to 
pass the flue gases through a chamber 4, in the nature of a slag box, so 
as to separate some of the larger entrained, materials therefrom. 
Generally the agglomerates will be heated to as high an elevated 
temperature as practicable but short of causing the agglomerates to sinter 
together. The heated agglomerates are discharged from a lower portion of 
the bed and, without significant cooling, are directly transmitted by a 
suitable conveyor 7, e.g. a screw conveyor, to a melter for vitrification. 
The shaft type preheater may include, in an upper portion, of the upper 
cylindrical portion, a heat exchanger of a type containing a plurality of 
generally rectangular elongate ducts (not shown). For further details 
reference may be had to copending application U.S. Ser. No. 924,274, filed 
on behalf of Messrs. Erickson and Hohman. The heat exchanger includes an 
inlet manifold 10 to receive a suitable heat transfer medium, for example 
air, and outlet manifold 12 through which the heat transfer medium is 
withdrawn from the ducts of the heat exchanger proper. Generally the heat 
exchanger provides flexibility in the operation by allowing for control of 
the dry bulb temperature of the flue gases. 
Located downstream of the shaft type preheater 3 are at least two 
preconditioning chambers and further downstream is an agglomerator 4. The 
agglomerator itself may be any conventional piece of equipment available 
in the art for combining glass forming batch ingredients and water into 
free water containing agglomerates. Typically the amount of water, as 
previously indicated, in the agglomerates will be about 5 to about 20% by 
weight. Preferably the agglomerator will be a conventional rotary disc 
pelletizer. The amount of water typically employed to produce the pellets 
will generally be between about 10 to about 15% by weight and more 
typically on the order of about 10 to 14% by weight. While pelletizing is 
an art and the pelletizer will need to be adjusted for optimum results on 
any specific glass batch, it is desirable to control the pelletizer using 
the water control scheme generally set forth in copending application U.S. 
Ser. No. 965,632 filed on behalf of Mr. Seng. That is a pivotally 
supported paddle type sensor which may be spring biased or counterweighed, 
is employed to control the feed of water to the pelletizer. Preferably the 
paddle will be located in the finished pellet stream, as set forth in 
copending application Ser. No. 974,470 filed on behalf of Mr. Henry, 
generally in a central portion of a sector of the disc defined between 
about an 8 to 9 o'clock position and positioned away from the disc wall 
about 40% of the disc radius. The water supply will include one duct 
supplying a constant flow of water to a main supply line and a second duct 
containing a solenoid valve also in fluid communication with the main 
supply. The paddle sensor is used to operate the solenoid valve in an 
on-off fashion, as set forth in the above Seng application so as to 
produce substantially uniform size pellets. Generally, when facing the 
inclined rotary disc pelletizer and considering the uppermost portion as 
the 12 o'clock position, batch will be supplied to the pelletizer along a 
chord of the disc between about the 5:30 and 6:30 positions with the water 
supply being furnished by sprays located generally on a chord between the 
4 and 8 o'clock positions and to the right of a diameter running through 
the 6 and 12 o'clock positions of the circular disc of the pelletizer. 
Desirably the pelletizer will also be equipped with a rotary scraper 
device. This device includes two pairs of generally normally related arms 
with each arm having a radius of about one-half the radius of the 
pelletizer disc and has its axis of rotation about midway along the radius 
of the disc drawn to about the 3 o'clock position. One pair of arms, which 
may be viewed as a diameter of the circle through which the device 
rotates, includes scrapers at its diametric end portions adapted to scrape 
the sidewall of the rotating disc pelletizer. The other pair of arms 
include diametrically opposed scrapers operating closely adjacent to the 
bottom of the disc of the pelletizer. The disc will also be provided with 
a stationary plow extending inwardly from about the 11:30 position and 
intersecting a diameter through the 6 and 12 o'clock positions at an angle 
of about 45.degree.. Excellent results have been obtained using a rotary 
disc having about a 6-8 min. dwell time. Ser. No. 974,470 illustrates an 
alternate water control scheme. When manufacturing pellets, it is also 
preferred, although not shown, to coat the pellets with a thin layer of 
particulate batch material so as to enhance the handling characteristics 
of the pellets. This may be done in accordance with the teachings of 
copending application U.S. Ser. No. 031,290. It is also preferred to pass 
the pellets through a suitable sizing device (not shown) such that the 
pellets to be further processed generally have a maximum dimension in the 
range of about 1/4 to about 1 inch and most desirably between about 3/8 to 
about 5/8 of an inch. Undersize pellets may, if desired, be recycled 
directly to the pelletizer. 
The free water containing agglomerates are then conveyed by a suitable 
conveyor 5, preferably a FLEXOWALL conveyor, in a generally cyclic, or 
sequential, manner and in parallel flow paths, to preconditioning chambers 
11, 21, 31 and 41 so as to form separate preconditioning beds. Typically 
these preconditioning chambers will be located adjacently upwardly of the 
preheater, for example, within a distance of only several feet, like for 
example, within 5 feet of the preheater and more commonly will be mounted 
directly on the upper wall of the preheater. More specific details as to a 
preferred mechanism for implementing the present process are set forth in 
copending application U.S. Ser. No. 031,369 and in copending application 
U.S. Ser. No. 095,871 filed concurrently herewith, both of which are 
hereby incorporated by reference. Generally agglomerates from conveyor 5 
are supplied to a main pellet duct 14 and sequentially diverted to ducts 
16 and 18. The pellets supplied to duct 16 are then, in turn, cyclically 
diverted to ducts 20 and 22 and pellets from duct 18, subsequently and 
sequentially, diverted to ducts 24 and 26. Suitable diverting valves will 
be employed to effect the above sequential, or cyclic, operation. Ducts 
20, 22, 24, and 26 serve to cyclically supply agglomerates, preferably 
pellets, to the respective preconditioning chambers 11, 21, 31 and 41 so 
as to form separate static preconditioning beds in the preconditioning 
chambers. 
Generally, a supply of agglomerates will be discharged downwardly through 
one of the ducts, e.g. 20, by operating an appropriate diverter valve for 
a predetermined time interval at which time the supply to that duct will 
be discontinued and supply to another duct will be initiated. The 
discharged agglomerates fall downwardly from duct 20 into preconditioner 
11 and they are intercepted in the preconditioner by a pellet detaining 
member and formed into a static bed. This member is actually a movable 
bottom wall of the preconditioner and allows gases to pass therethrough 
but does not allow the agglomerates to so pass. The formed static bed is 
then preconditioned after which time it is discharged and the agglomerates 
dropped downwardly to preheater 3. This is effected by moving the pellet 
detaining member outwardly from the preconditioner and pushing the 
agglomerates, as with a doctor blade technique, off the member. Each of 
the preconditioners has such a pellet detaining bottom wall member, with 
each sequentially operating to intercept a supply of agglomerates and then 
discharge preconditioned agglomerates to a main vertical bed. 
The heating and drying medium, e.g. the flue gases, enter the bottom 
portion of the preheater, pass upwardly therethrough, whereby they 
exchange heat by direct contact with the gravitationally downwardly 
flowing agglomerates of the vertical bed therein, and then, in a generally 
parallel flow path, as represented respectively by arrows 28, 30, 32 and 
34 are directed to respective preconditioning chambers 11, 21, 31 and 41. 
In a parallel flow pattern the respective flue gas streams then pass 
upwardly through the static beds, of the preconditioners and then are 
exhausted from the chambers in parallel flow paths (43, 45, 47, 49) and 
then exhausted through a main duct 36. In actual operation exhaust duct 36 
will be operatively connected to a suitable fan (not shown) which 
generally maintains the preheater and the preconditioning chambers under a 
negative pressure. Prior to being directed to the preconditioning 
chambers, it is preferred to dilute the flue gases with air and, for 
purposes of thermal efficiency, it is preferred that this dilution be done 
subsequent to the flue gas entry into the preheater. Since the preheater 
and preconditioners are under a negative pressure leakage of ambient air 
into the system affects dilution and the adjusted inherent aggregate 
forming height. Preferably the dilution is effected in the head-space 
above the bed. The air may be introduced by a duct or ducts 40. As 
previously indicated such air may be ambient air or it may be heated air, 
e.g. spill air or heated air produced by the combustion of a suitable 
fuel, e.g. natural gas, with an excess of stoichiometric air. This serves 
to alter the height of aggregate formation and can also supply energy to 
increase the drying rate in the preconditioners. After the respective 
static preconditioning beds of chambers 11, 21, 31, 41 have been heated 
for a time sufficient to form hydrologically stabilized beds, they are 
discharged into the vertical bed in preheater 3 as generally represented 
by parallel flow paths 23, 25, 27 and 29. They are then further heated in 
preheater 3 to an elevated temperature, discharged from the preheater in a 
generally continuous fashion and directly supplied by suitable means, like 
conveyor 7, to melter 1. Preferably the discharging of the preconditioning 
beds will be in a cyclic, or sequential manner, and will be done by a mere 
dropping of the beds, e.g. a drop of at least about 1 foot, unto the 
vertical bed. This dropping action can also serve to separate individual 
agglomerates from any minor aggregates which may have formed, but the 
dropping height should not be so high as to fracture the agglomerates. 
The preconditioning chambers, as indicated, are preferably operated in 
cyclic or sequential manner. That is, preferably, each preconditioning 
chamber has its own cyclic pattern and the respective chamber patterns are 
desirably sequenced to provide quasi-continuous processing. Each chamber 
will accumulate a predetermined amount of agglomerates and, since the 
chamber will be of a fixed dimension, for example a 2'.times.2'.times.2' 
box, each will have formed therein a static preconditioning bed of a 
predetermined height. This may be done, for example to chamber 11, by 
supplying pellets from conveyor 5, to duct 16, and to duct 20, whereby a 
bed of progressively increasing height will form, then discontinuing the 
supply to chamber 11 by diverting the pellets in duct 16 from duct 20 to 
duct 22 and thereby supplying pellets to chamber 21 for its 
preconditioning cycle. The preconditioning bed of chamber 11 is then 
preconditioned to a hydrologically stabilized bed with gases (28) passing 
upwardly through the bed and the gases exhausted through duct 43 to main 
exhaust duct 36. After preconditiong, the static bed is discharged (arrow 
23) unto the main vertical bed in preheater 3. 
In the preferred embodiment, the respective preconditioners will be mounted 
directly on the top wall of preheater 3. An opening will be provided in 
the preheater top wall for each of the preconditioners, with the gases 
from preheater 3 entering the preconditioner through such opening and the 
agglomerates of the preconditioned beds falling into the preheater through 
the same opening. That is, for example, with respect to preconditioner 11, 
such an opening would be common for agglomerate stream 23 and gas stream 
28. 
In order to initially start-up the process it is generally preferred to 
employ separately provided combustion products to form an initial vertical 
bed in the preheater 3 after which time the system is changed from the 
separately provided combustion products to the flue gas coming from the 
melter. This mode of operation is illustrated in the drawing wherein it is 
shown that air and fuel are provided, for example, to a burner (not shown) 
and these combustion products are then passed into the preheater through a 
duct 50 for a time sufficient to provide the initial vertical bed. As in 
the case with the flue gases, the temperature of the combustion products 
in duct 50 should not be so high as to cause the agglomerates in the 
preheater to sinter into aggregates. Preferably, using natural gas as the 
fuel, the combustion will be with at least a 25% excess of stoichiometric 
air so that the wet bulb temperature is less than that of normal flue 
gases (130.degree.-140.degree. F.). Desirably the excess will be 25% to 
about 300% and preferably about 50% to about 100%. Exemplary dry bulb 
temperatures will be about 1000.degree. F. to about 1500.degree. F. with 
suitable wet bulbs being about 100.degree. F. to about 125.degree. F. In 
fact, when it is desired to apply the teachings of the present invention 
to a non combustion fired melter, that is, to a melter wherein the energy 
is electrically supplied, the system will operate as described herein, by 
usage of separately provided fuel and air combustion products. In such 
electric melting embodiment, obviously, melter 1 will be electrically 
powered and the heating medium will be the combustion products supplied by 
duct 50 since there will be no furnace flue gases to be supplied by duct 
51. If desired, however, a vent may be provided from the electric melter 
to the preheater, so as to enhance pollutant recovery and recycle. 
In passing, it should be mentioned that whether involved with the start-up 
phase of the process for use of a combustion fired melter, whether the 
embodiment is practiced wherein air and fuel are separately fired and 
those combustion products used to effect the preheating and drying of the 
agglomerates which are subsequently electrically melted, or whether actual 
operation is underway employing a combustion fired melter, it will be 
important, for most reliable operation, when supplying the agglomerates to 
the preconditioning chambers that beds be formed which have as 
substantially a uniform height as reasonably possible. Preferably this is 
accomplished by using suitable agglomerate flow diverters to distribute 
the agglomerates substantially uniformly in the chamber. The preferred 
arrangement for effecting such flow distribution is that set forth in 
application Ser. No. 031,288. 
While actual operating conditions will vary with different installations, 
the following generally exemplifies typical process parameters. The 
temperature of the gases entering the preheater, whether they be 
combustion products resulting from separate firing intended for an 
electric melter operation or whether they be flue gases coming from the 
heat exchanger of a combustion fired melter, will be no greater than the 
temperature at which the specific glass formulation will sinter into 
massive aggregates. Typically, such temperatures will be in excess of 
750.degree. F., preferably about 1000.degree. F. to 1500.degree. F. and a 
more exemplary temperature being about 1100.degree. F. to about 
1250.degree. F. The velocity of the gases passing through the preheater 
will vary, but suitable ranges will be from about 60 to about 130 standard 
feet per minute (superficial velocity). As previously generally indicated, 
the wet bulb temperature of the flue gases from a combustion fired melter 
will be on the order of about 130.degree. F. to 140.degree. F. but, in the 
electrical melting embodiment, it will be preferred to practice the 
combustion with an excess of stoichiometric air such that the wet bulb 
temperature of the gases supplied to the preheater will be less and 
desirably in the range of about 100.degree. F. to about 125.degree. F. and 
preferably between about 110.degree. F. to about 120.degree. F. For 
convenient operation it will generally be preferred, especially in the 
case when flue gases from a combustion fired melter are employed, to 
dilute the gases prior to entry of the combustion products into the 
respective preconditioners. Generally, suitable operation will be obtained 
by diluting the flue gases about 100%, i.e. diluting them in a volume 
ratio of one part of ambient air to one part of combustion gases. 
Temperatures of the gases, after having passed through the preconditioning 
chambers will generally be about 200.degree. F. to 500.degree. F. In 
actual operation it will be desirable to adjust the temperature of the 
gases entering the preconditioning chambers such that, after passing 
therethrough, they will be exhausted at a temperature which is as low as 
possible, but without causing the wet bulb temperature of the gases to be 
reached as that would cause undesirable condensation. The height of the 
preconditioning beds may vary with different compositions and can be 
selected for different operating conditions, but generally they will not 
be very high. Preferably, especially for a soda-lime-aluminoborosilicate 
glass, the height will be in the range of about 2 to about 8 or 9 inches. 
Exemplary actual superficial velocities of the gaseous medium passing 
through the respective preconditioners will generally be in the range of 
about 200 to about 500 feet per minute. The optimum actual preconditioning 
cycle of the respective preconditioning chambers will vary depending, for 
example, on the composition employed, the water content of the 
agglomerates employed, the desired production rate, and on the velocities 
and psychrometry of the heating medium. An exemplary operation, however, 
when supplying pellets to the preconditioners having a moisture content of 
about 11.5 to 13% and employing a preconditioning bed height of about 2-3 
inches with the dry bulb temperature of the heating medium entering the 
preconditioner being 400.degree. F. to 600.degree. F. with a calculated 
wet bulb temperature of about 111.degree. F. (equivalent to about 200% 
dilution) at a superficial velocity of about 450 (standard) feet per 
minute through the preconditioner was a cycle wherein the preconditioners 
were charged and formed to a bed over a period of about 2 minutes, then 
preconditioned for a period of 6 minutes and then discharged to the main 
vertical bed. 
Some adjustments will, of course, be made in actual operation for purposes 
of optimization once the general operating parameters have been 
determined. In order, however, to assist those in making and using the 
present invention in its fullest scope the following represents laboratory 
experimental work which can be easily done to obtain the general design 
and operating parameters for the system. Additionally, the following 
exemplifies some of the terminology previously employed. 
In the following a soda-lime-aluminoborosilicate glass was employed which 
on a theoretical oxide basis contained about 61.3% silica, about 4% 
alumina, about 8.4% CaO, about 1.3% MgO, about 7.4% B.sub.2 O.sub.3, about 
15% Na.sub.2 O, about 0.1% K.sub.2 O, about 0.2% Fe.sub.2 O.sub.3, about 
0.5% SrO, about 0.1% TiO.sub.2, and about 0.4% sulfur as SO.sub.3. The 
batch employed included about 45.3% (by weight) sand, about 1.1% 
limestone, about 7.8% clay, about 2.8% burnt dolomite, about 23% by weight 
of a sodium calcium borate bearing material (ulexite) and about 20% soda 
ash. The borate material was ground prior to use, such that approximately 
100% by weight of the material was minus 200 mesh. It contained about 21% 
CaO, about 27% B.sub.2 O.sub.3, about 4% Na.sub.2 O, about 9% SiO.sub.2 
and 3% MgO and minor amounts of other oxides and its loss on ignition was 
about 31%. The particle size of the sand employed was: about 5% by weight 
(minus 12 and plus 30) mesh: about 55% between 30 and 100 mesh and about 
40% by weight was minus 100 mesh. The soda ash was of the granular type 
and contained: about 11% by weight minus 12 and plus 20 mesh; about 69% by 
weight between 20 and 100 mesh and about 20% by weight minus 100 mesh. The 
particle size of the limestone was: 2% minus 8 and plus 20 mesh; about 68% 
between 20 and 100 mesh and about 30% minus 100 mesh. The clay was very 
fine and was approximately 98% to 99% by weight, minus 325 mesh. The burnt 
dolomite was about 55% to about 90% by weight minus 100 mesh with the 
balance being essentially between 20 and 100 mesh. The particle size 
analysis of the composite batch, as measured by a Leeds and Northrup Micro 
Trac particle size analyzer, showed that the batch had: a surface area of 
about 0.3 to about 0.4 sq. meters per cubic cm of batch; an average 
particle size of about 110 about 120 microns with 100% of the particles 
smaller than 300 microns, about 69-70% smaller than 212 microns, about 
51-52% smaller than 106, about 45-46% smaller than 53 microns, about 
25-26% smaller than 13 microns, and about 6-7% smaller than about 4-5 
microns. In all subsequent cases the above batch was pelletized on a 
rotary disc pelletizer with water to produce pellets containing between 
about 13 to about 14% by weight water (dry basis). The tested pellets 
generally had diameters in the range of about 3/8 of an inch to about 5/8 
of an inch. 
Unless otherwise indicated, when reference is made to the water content of 
the pellet bed, or of the pellets, that means the water content of a 
pellet in the uppermost layer of the bed. Care was taken such that the 
respective beds that were formed had as uniform an upper surface, or as 
uniform a height, as practicable. The following represents an easy way of 
simulating the drying conditions, that is, drying wet agglomerates with 
gases that have passed through the preheater where they have given up some 
of their heat to preheat dry pellets in the preheater and have 
consequently had their dry bulb temperature substantially reduced with 
virtually no change in wet bulb temperature. The following procedures are 
employed to obtain the needed design and operating data for any 
installation or glass composition or agglomerate type. 
EXEMPLIFICATION OF INHERENT AGGREGATE FORMING HEIGHT AND ADJUSTED INHERENT 
AGGREGATE FORMING HEIGHT 
The following equipment was employed to determine the "inherent aggregate 
forming height" as well as to demonstrate and determine the various 
"adjusted aggregate forming heights" which correspond to various wet bulb 
temperatures. Essentially the equipment includes a cylindrical drying 
chamber having a diameter of about 20 inches and a height of about 24 
inches. Along the 24 inch axial height of the drying chamber there is 
provided a plurality of sample ports such as, for example, at about 3 inch 
intervals. The top wall includes a vapor outlet duct and is either 
removable or has suitable port means providing access to the internal 
portions of the chamber so as to allow agglomerate charging. A bottom 
portion of the chamber is defined by a perforate, or foraminous, pellet 
retaining metal plate. The actual size of openings in this plate were 
about 1/4 inch. Flanged to the bottom of the drying chamber, beneath the 
perforate plate, is another substantially similarly dimensioned 
cylindrical chamber. In this lower cylindrical chamber is provided a bed 
of E-type glass marbles whose function is to provide a flow straightening 
effect to gases entering the bottom thereof. A head space is provided 
above the marbles and beneath the perforate plate, with a gas bypass duct 
communicating with that head space. Adjacently downwardly of the perforate 
plate is a solid plate, traversing the transverse dimension of the 
equipment, whose function is to operate in the nature of a blank. The 
blank is manually movable outwardly and inwardly in a direction 
perpendicular to the axis of the test equipment. Pellets are accumulated 
in the upper chamber on the perforate, pellet retaining metal plate in the 
form of beds having different predetermined heights for successive runs. 
In operation, the heating medium will be provided to the lower portion of 
the flow straightening marble bed, the gases pass upwardly therethrough 
and until the psychrometry and flow is stabilized, the blank is closed and 
the bypass employed so as to preclude gas-pellet contact. The blank is 
then moved outwardly to allow the heating medium to pass through the bed 
and flowing, direct drying contact is then achieved, and maintained, 
between such drying medium and the pellets for a sufficient period of time 
to dry the pellets to substantially total dryness. Dryness is monitored, 
if desired, by removing a pellet of the upper layer of the bed and 
determining its moisture content. The drying medium utilized was produced 
by combustion of natural gas in a burner with controllable amounts of air, 
with the combustion products conveyed in a duct member to the marble bed. 
Intermediate the burner and entry into the marble bed, a pipe arrangement 
was provided which allowed for the introduction of controlled amounts of 
steam to adjust the wet bulb temperature of the heating medium. Primarily 
to control the dry bulb temperature of the combustion products, air was 
supplied to the burner by means of a variable speed centrifugal blower. In 
order to obtain the most meaningful information, the pellet bed should be 
of a substantially uniform height so as to provide for substantially 
uniform flow of the gases through the pellet bed and minimize short 
circuiting type effects. In the following, the actual superficial velocity 
of the heating medium through the drying chamber varied between about 200 
to about 400 feet per minute. Thus, as will be appreciated, various bed 
heights are employed in successively different runs and heated to 
substantial dryness with the condition of the bed qualitatively evaluated 
as by inspection through the sample ports. The chart below summarizes such 
operation in which H refers to the approximate height of the bed, T (wb) 
is the approximate calculated wet bulb temperature of the drying medium 
and, in the column entitled "Bed Condition", S refers to the fact that the 
pellets were stuck in the bed as aggregates and NS refers to no 
substantial sticking when the respective beds were taken to substantially 
total dryness. The chart below was developed employing a dry bulb 
temperature of approximately 350.degree. F. 
______________________________________ 
H T(wb) Bed Condition 
______________________________________ 
&lt;2 inches 137.degree. F. 
NS 
2 inches 137.degree. F. 
S 
3 inches 120.degree. F. 
S 
3 inches 111.degree. F. 
NS 
6 inches 104.degree. F. 
S 
6 inches 100.degree. F. 
NS 
9 inches 80.degree. F. 
NS 
&gt;9 inches 80.degree. F. 
S 
______________________________________ 
The above wet bulb temperatures approximately correspond on a calculated 
basis to the following equivalent levels of dilution of flue gases from a 
gas fired melting furnace: 137.degree. F. about 0% dilution; 120.degree. 
F. about 100% dilution; 111.degree. F. about 200% dilution; 104.degree. F. 
about 300% dilution; 100.degree. F. approximately 400% dilution. The wet 
bulb temperature of 80.degree. F. corresponds to, in affect, infinitely 
diluted flue gas (e.g. about 800% dilution) inasmuch as the wet bulb 
temperature approached that of the ambient. Percent dilutions as referred 
to herein are the volume ratios of ambient air used for dilution to the 
volume of flue gases so diluted, multiplied by a value of 100. Thus for 
example, a 100% dilution is effected by diluting one volume of flue gases 
with one volume of dilution air. 
The foregoing chart indicates that the "inherent aggregate forming height" 
(drying to substantially total dryness with flue gases from a melter, 
wherein, substantially stoichiometric amounts of air and fuel are employed 
or drying with a gas having a wet bulb essentially the same as such flue 
gas) is approximately 2 inches. Thus, the height of the preconditioning 
beds in the preconditioning chambers may be less than about 2 inches and 
satisfactory operation will be obtained when pellets are totally dryed 
using a drying medium having a wet bulb temperature of about 130.degree. 
F. to about 140.degree. F., e.g., melter furnace flue gases which have 
passed through a vertical bed of dry pellets to preheat them; such flue 
gases need not be diluted with air but dilution will cause no difficulty 
using such a height. The chart also exemplifies how the inherent aggregate 
forming height may be adjusted; thus, it shows the various "adjusted 
inherent aggregate forming heights" as they correspond to various wet bulb 
temperatures of the drying medium (or flue gas dilution levels). For 
example, an adjusted inherent aggregate forming height of about 3 inches 
corresponds to a wet bulb temperature of about 111.degree. F. (about 200% 
flue gas dilution). Consequently, the height of the static preconditioning 
beds can be about 3 inches when the drying medium has a wet bulb 
temperature of about 111.degree. F. and the preconditioning bed will be 
hydrologically stabilized when totally dried; with that same height, the 
bed will also be hydrologically stabilized when totally dried, by using a 
wet bulb temperature of less than about 111.degree. F. (greater than about 
200% flue gas dilution). Using a wet bulb temperature greater than about 
111.degree. F. (less than about 200% flue gas dilution) will require a bed 
height less than about 3 inches. Similarly, an adjusted aggregate forming 
height of about 6 inches corresponds to a wet bulb temperature of about 
100.degree. F. (about 400% flue gas dilution). Consequently, the 
preconditioning bed, when at a height of about 6 inches (or less), will be 
hydrologically stabilized when substantially totally dried with a medium 
having a wet bulb of about 100.degree. F., or less, (about 400% dilution 
or greater). Totally drying a bed having a height greater than about 6 
inches, so as to form a dry hydrologically stabilized bed, will require a 
heating medium with a wet bulb less than about 100.degree. F. The maximum 
bed height without serious aggregate formation, when the bed was 
substantially totally dried, was on the order of about 8-9 inches when the 
wet bulb temperature of the heating medium was about 80.degree. F.; that 
substantially represents the use of infinitely diluted flue gases as the 
drying medium i.e., the virtual equivalent of heating ambient air at 
constant humidity to indicated dry bulb. 
Obviously, the same operational characteristics exist for the embodiment 
wherein the pellets are to be electrically melted, that is, in that 
embodiment wherein the heating medium is provided by the separate 
combustion of a fuel and air, the pellets preheated and preconditioned 
therewith, and the preheated pellets or agglomerates supplied to an 
electric melter. The above can be implemented by, for example, selecting a 
desired height for the preconditioning bed in the preconditioning 
chambers, say about 6 inches. The amount of air used for combustion is 
then selected so that the combustion products will have the maximum 
tolerable dry bulb temperature (less than the temperature which will cause 
dry agglomerates to sinter) but a wet bulb temperature no greater than, 
and preferably slightly less than the wet bulb temperature corresponding 
to the adjusted imminent aggregate forming height of the bed height 
selected--about 100.degree. F. for the 6 inch selection or about 
111.degree. F. for a 3 inch selection. Such combustion products are then 
supplied through duct 50 to the vertical bed of preheater 3 and to the 
respective preconditioning chambers 11, 21, 31, 41 for substantially 
totally drying the beds therein prior to discharge to the vertical bed of 
preheater 3 for further heating. Alternatively, if the separate combustion 
is selected such that the wet bulb temperature of the combustion products 
in duct 50 is greater than that corresponding to that of a selected bed 
height having an adjusted imminent aggregate forming height of such 
selected height (e.g. greater than 111.degree. F. for a 3 inch selection 
or greater than 100.degree. F. for a 6 inch selection) then these gases, 
after passage through the vertical bed and prior to entry into the 
preconditioners, may be diluted with air, as by duct 40, to a wet bulb 
temperature which is less than the wet bulb temperature corresponding to 
the adjusted imminent aggregate forming height of a bed with the selected 
height (e.g. less than about 111.degree. F. for a 3 inch selection). 
No dramatically different results, relative to the above table, were 
observed when employing dry bulb temperatures of the heating medium 
varying between about 200.degree. F. to about 500.degree. F. 
The foregoing indicates the manner in which the bed of hydrologically 
unstable agglomerates, e.g. pellets, may be converted to a hydrologically 
stabilized bed of agglomerates by heating, to substantially totally dry 
the agglomerates of the bed, and then, without fear of massive aggregate 
formation, discharging the bed to a main vertical bed in a preheater for 
subsequent processing so as to preheat the agglomerates to a substantially 
elevated temperature, for example a temperature in excess of 450.degree. 
C., preferably in excess of about 500.degree. C., or even 600.degree. C., 
depending on the composition employed. 
PRECONDITIONING BEDS WITH A HEIGHT GREATER THAN THE ADJUSTED INHERENT 
AGGREGATE FORMING HEIGHT 
It has been previously indicated that in accordance with this invention it 
is also possible to operate the preconditioning bed at a height which in 
excess of the inherent aggregate forming height and even in excess of the 
adjusted inherent aggregate forming height corresponding to the wet bulb 
temperature of the drying medium employed. This unique state, also 
representing a state wherein the bed is hydrologically stabilized (no 
massive aggregation in either the preconditioning bed or vertical bed), is 
obtained when the wet agglomerates have been heated for a sufficient 
period of time to remove some, but not all, of the free water content 
thereof. The following will exemplify the manner of determining such a 
state. 
In FIG. 2 of the drawing, there is schematically illustrated the laboratory 
arrangement which may be employed to develop any characteristic operating 
curve for the system employed. In the drawing there is generally shown a 
heating and drying chamber 10, generally having the same shape as the 
preconditioning chambers and being a scaled down model thereof, e.g. a 
chamber with a 1 foot-square cross section. The chamber includes an upper 
chamber portion 12, which simulates the preconditioning chamber, and a 
lower chamber 14 to which pellets of the bed in chamber 12 are dropped. 
Element 16 is a suitable pellet detaining, or supporting member which is 
porous, or permeable to the drying medium; that is it provides the support 
for the bed to be preconditioned and allows the heating medium to pass 
therethrough with a minimal pressure drop. Additionally element 16 is 
movable, for example manually, inwardly into an outwardly from chamber 12. 
Desirably, however, element 16 will be moved inwardly and outwardly by an 
air operated piston and cylinder, for example one delivering a force of 
about 250 pounds. Additionally, the wall of chamber 12 will be provided 
with a wiper or scraper which functions in the nature of a doctor blade to 
scrape the pellets of the bed from element 16 as it moves outwardly from 
its inward position in the chamber 12, thereby discharging the pellets of 
the preconditioned bed gravitationally downwardly into lower chamber 14. 
Most expediently element 16 will be, and was, a scaled down substantial 
duplicate, or model, of the actual device contemplated for use in the 
preconditioners to form the preconditioning bed. In this instance element 
16 was a drawer-like receptacle having a bottom formed of a plurality of 
parallel rods, displaced on about 1/4 inch centers, and included an inner 
end wall, extending upwardly from the rods, sidewalls and an outer end 
wall with the receptacle being suitably supported for movement inwardly 
and outwardly of chamber 12 by the above-indicated air operated piston and 
cylinder. Reference may be had to the above-incorporated application, Ser. 
No. 031,369 and Ser. No. 095,871, for fuller particulars of the 
arrangement for the pellet detaining receptacle and the wiper for 
discharging the pellets of the bed thereon. Chamber 14 includes, at a 
bottom portion, a perforate metal plate 18 which functions to retain 
pellets discharged from chamber 12 to chamber 14 and also provides for a 
substantially uniform flow of heating medium through both chamber 14 and 
12. Beneath perforate metal plate 18 is a slidable blank-type plate 20. At 
the lowest portion of chamber 10 is a flow straightening means, in the 
form of a bed of E-glass marbles (not shown), which are disposed beneath 
another perforate plate 22. Blank type slide gate 20, when closed, directs 
gases from the head space above plate 22 to a bypass line. Appropriate 
valving (not shown), is of course, provided and in this manner the gas 
flow, and its psychrometry, can be stabilized by passing gases through the 
bypass before contact with the pellets. In a manner similar to that 
described above, the heating medium is provided by burning a combustible 
fuel, for example natural gas, with controlled amounts of air. Steam is 
injected into the products of combustion to adjust the wet bulb 
temperature of the heating medium, and the dry bulb temperature is 
primarily controlled by employing controlled excess amounts of 
stoichiometric air for combustion. The drying medium exhausts from chamber 
10 through a duct in the top wall. A suitable, sealed releasable access 
opening or door (not shown) is provided in the upper wall of chamber 10 to 
allow predetermined amounts of pellets to be added to chamber 12 so as to 
form a preconditioning bed on element 16 when the latter is in its inward 
position. The sidewall of upper chamber portion 12 is provided with a 
plurality of sample and observation ports (not shown) in the axial 
direction of the chamber and, closely adjacent to perforate plate 18, 
chamber 14 is provided with a sealed, removable door (also not shown) for 
withdrawing pellets from chamber 14. The fuel, air and steam are 
appropriately adjusted to obtain the desired psychrometry of the drying 
and heating medium with blank plate 20 being closed and the gases exiting 
through the bypass until the desired conditions are obtained and 
stabilized. A total heating and drying cycle is then selected, such as for 
example a fifteen minute cycle. Pellets are then added, with receptacle 16 
being inward in chamber 12 so as to form a wet bed of pellets having a 
height of about 2 inches, with care being taken to have a bed of 
substantially uniform height. The bypass valve (not shown) is then closed 
and slide gate 20 opened. Operation then is allowed to take place for a 
predetermined interval, for example two minutes, at which time a pellet is 
removed from the upper surface of the bed in chamber 12, the air cylinder 
activated to move receptacle 16 outwardly so as to contact the bed with a 
wiper, push it therefrom and drop the pellets of the bed approximately one 
foot into chamber 14 onto plate 18. The moisture content of the withdrawn 
pellet is determined and the balance of the heating cycle, in this case, 
thirteen minutes, is continued. The characteristics of the pellets in the 
static bed in chamber 12 are noted at the time of discharge, especially as 
to their state of aggregation, if any, and their ability to be discharged 
from receptacle 16 to plate 18. The characteristics of the bed in chamber 
14, i.e., the degree of aggregation, if any, is noted at the end of the 
total 15 minute cycle, i.e., after the thirteen additional minutes. The 
pellets are removed from chamber 14 and another run made with a 2 inch 
bed. This run however, will alter the time for heating in chamber 12 to 4 
minutes followed by 11 minutes of heating in chamber 14 with the same 
procedures and observations being made. With a two inch bed, successive 
runs are similarly made in which heating in chamber 12, prior to 
discharging the bed into chamber 14, will be 6 minutes, 8 minutes, 10 
minutes, 12 minutes and 14 minutes and, correspondingly, the time for 
heating in chamber 14 will respectively be 9, 7, 5, 3 and 1 minute. In all 
instances, the characteristics of the bed at discharge will be observed, a 
moisture content of a pellet in the top layer will be taken, and the 
characteristics of the pellets in bottom chamber 14 will be observed at 
the end of the heating cycle. This same procedure was then repeated using 
bed heights in chamber 12 of about 4 inches, about 6 inches, and 8-9 
inches. Under some conditions it will be noted that the beds in chamber 12 
convert to a large aggregate, or aggregates, whereas under other 
conditions, upon discharge to chamber 14, the pellets aggregated in that 
chamber. In all instances the pellets are substantially totally dry after 
the 15 minute cycle. The data is then collated and a operating curve 
developed. 
FIG. 3 is an example of such developed operating curve. That curve was 
developed using pellets having a water content of about 13.6% by weight 
(dry basis). The heating medium approximately corresponded on a calculated 
basis to the use of flue gases from a melter which had been diluted about 
150% as the calculated wet bulb was about 115.degree.-116.degree. F.; the 
dry bulb temperature of the heating medium entering chamber 14 was about 
350.degree. F. and its actual superficial velocity through chambers 14 and 
12 was about 400 feet per minute. 
Referring now to FIG. 3, it will be seen that the curve includes a line AB. 
That line means that the ratio (W.sub.f /W.sub.i) on a dry basis, of the 
water content of pellets in the upper layer of a bed with a height H in a 
preconditioning chamber, (W.sub.f), relative to the water content of the 
wet pellets initially charged into that chamber, (W.sub.i), be less than a 
prescribed value; otherwise, when the pellets are discharged from a 
preconditioning chamber (12, or for example 21) to another chamber, for 
example to a vertical bed in preheater 3 (or chamber 14) and the heating 
cycle continued, they will aggregate in the latter chamber when heated to 
total dryness. FIG. 3 shows this value of W.sub.f /W.sub.i to be about 
0.96. In the present instance, as indicated, W.sub.i generally was about 
13.6% and W.sub.f was the determined water percentage of the pellets taken 
from the top layer at the time of discharging the bed from chamber 12. 
There is another consideration with regard to the operation of the 
preconditioning beds. That is, if the heating is done in a preconditioning 
chamber (12 or e.g. 21) for a time such that the amount of water removed 
will cause the W.sub.f /W.sub.i ratio to be approximately to the right of 
curve CE, undesirable pellet sticking and aggregation will occur in the 
preconditioning chamber itself. The line ED generally indicates that the 
pellets may be substantially totally dried without serious aggregate 
formation in the preconditioner when the height of the preconditioning bed 
is less than about the adjusted inherent aggregate forming height 
corresponding to the wet bulb temperature of the drying medium employed. 
Thus, for most reliable performance under such conditions the moisture 
content of the upper layer of pellets in the preconditioning chamber just 
prior to discharging the bed by dropping it to a main vertical bed for 
preheating should be such that the W.sub.f /W.sub.i ratio generally falls 
within the approximate area ABCED of FIG. 3. For example, when using a bed 
height equal to, or less than, the inherent aggregate forming height, i.e. 
about 2 inches or less, serious aggregate formation neither occurs in 
lower chamber 14 nor in the preconditioning bed of chamber 12 so long as 
the bed of chamber 12 be discharged into chamber 14 after heating for a 
sufficient period of time such that the water content ratio (W.sub.f 
/W.sub.i) is less than about 0.96. At a 4 inch bed height (which is 
greater than the adjusted inherent aggregate forming height corresponding 
to the wet bulb temperature of the drying medium used), the bed was 
hydrologically stabilized, in that no serious aggregate formation was 
noted in either chamber, so long as the water content ratio, when the 
preconditioning bed was discharged, was less than about 0.96 but greater 
than about 0.7. Similarly, the ranges for the 6 inch bed were between 
about 0.96 to about 0.85 to produce a hydrologically stabilized bed. 
The dotted lines in FIG. 3 at the 2, 4, 6, and 8-9 inch bed heights, hence 
represent operating "tie-lines" and it will be observed that the operating 
range of the tie-line decreases with height. Thus, by operating in 
conformity with such tie lines, the pellets of the preconditioning bed can 
be moved to a main vertical bed prior to the point of interpellet adhesion 
reaching an irreversible state of unacceptable aggregate formation in the 
preconditioner and a point at which such formation will likewise not occur 
in the vertical bed of the preheater when the agglomerates are further 
heated to an elevated temperature. 
In the above, the tie line for the 8-9 inch bed amounts to preconditioning 
for about 7 and one-half (7.5) minutes to about 8 minutes prior to bed 
discharge. The tie-line for the 6 inch bed is preconditioning heating for 
about 6 to about 8 minutes prior to bed discharge, and about 3 to about 8 
minutes for the 4 inch tie-line. Thus, for example, consistent with the 
foregoing discussion, bed heights of about 4 to about 8-9 inches may be 
hydrologically stabilized by heating a hydrologically unstable pellet bed 
for about 3 to about 8 minutes prior to discharge to a vertical bed for 
further heating to elevated temperatures. Lower drying times will be used 
with higher dry bulb temperatures. Generally, the water content of pellets 
during drying will depend on the velocity of the drying medium, the height 
of the bed, the dry bulb temperature of the drying medium, the initial 
water content of the pellets to be dryed, the drying time, pellet diameter 
and the wet bulb temperature of the medium. 
Substantially the same results were obtained for the 4 inch tie-line using 
a heating medium which on an approximate calculated basis corresponded to 
about 75% dilution of flue gases. 
It will be most desirable, for conservative design, to design the operation 
of the preconditioning chambers to operate at a certain predetermined 
height but that the bed be discharged based upon operation on a tie-line 
for a height which is in excess of that predetermined height. For example, 
for at least initial operation, a 4 inch height can be suitably selected 
for the preconditioning bed but the bed, prior to discharge, be operated 
on the tie-line for the 6 inch height. In this way, a margin of error is 
provided. This margin of error can be further increased, if desired, by, 
in the case of using melter furnace flue gases, diluting them to a higher 
level or, in the case of electric melting, either diluting the gases 
employed or increasing the amount of air used for combustion. It is then 
possible to further optimize the system if desired. 
Hydrologically unstable allgomerates will usually also be characterized by 
a non-linear strength drying curve in which, as wet, or green agglomerates 
having an initial water content, W.sub.i, are dried and the strength 
thereof is measured at various times during the drying process and the 
water content thereof, W.sub.f, also being determined at that time, the 
strength of the agglomerates will show a minimum value prior to their 
being totally dry. That is, the strength will initially decrease as the 
W.sub.f /W.sub.i ratio decreases and, subsequently, the strength will 
increase as the W.sub.f /W.sub.i ratio continues to decrease and goes to 
zero. The foregoing free water containing alkali-alkaline earth 
aluminoborosilicate pellet batch composition, for example, when plotting 
compressive strength (ordinate) against the ratio W.sub.f /W.sub.i 
(abscissa) shows a decrease in strength from a ratio of one (1) to a 
general minimum value of about two pounds when the ratio is generally 
between about 0.8 to about 0.64 and then the strength increases to a value 
of about 70 to 90 pounds as the ratio reaches zero. With such type 
compositions, in order to minimize the possibility of inadequate pellet 
strengths complicating the desired process operation as, for example, when 
the pellets of the preconditioning beds are to be dropped more than a 
couple of feet, it will be desirable to discharge the preconditioning beds 
when the pellets, especially those in the upper layer of the bed, are 
either substantially totally dry or such that the pellet strength will be 
increasing during further drying in the vertical bed. Thus, desirably, the 
preconditioning beds will be discharged when the W.sub.f /W.sub.i ratio is 
at, at least, the strength minimum. Thus, for example, the beds are 
suitably discharged in a hydrologically stabilized state where the W.sub.f 
/W.sub.i ratio is less than about 0.6 and even more suitably, for strength 
considerations, when the ratio is less than about 0.3. At about 0.3 the 
strength is about 6 pounds and this strength goes to about 70-90 pounds as 
the water content ratio approaches zero. As will be apparent a balance may 
need to be made, on one hand, between the selected preconditioning bed 
heights, and the operating conditions to hydrologically stabilize such 
beds, and, on the other hand, the above indicated strength considerations. 
In those circumstances where the above strength considerations are 
somewhat sacrificed it will, in general, be desired to provide for a 
minimum dropping height of the pellets from the preconditioning bed(s) to 
the main vertical bed, e.g. a dropping height of around two feet, or even 
less, like 1 to 2 feet. 
The following further exemplifies the present invention in which a gas 
fired melter (about 80 sq. feet) was employed to produce glass at a rate 
of about 3600 pounds per hour and a rotary disc pelletizer having a 
diameter of about 6 feet operating at about 10 RPM and inclined at an 
angle of about 49.degree. was employed to produce water containing 
pellets. A rotary scraper was employed which revolved at about 20 RPM. In 
parts by weight the batch was about 1043--sand, 161--clay, 71--burnt 
dolomite, 526--ulexite (containing about 23% B.sub.2 O.sub.3), 444--soda 
ash and 54--5 mole borax. The particle size of the batch, as measured by a 
Micro Trac size analyzer was as follows with the percentage being the 
weight percent smaller than the specified size: 300 microns--100%; 212 
microns--63%; 106 microns--59.6%; 53 microns--44%; 27 microns--31.9%; 13 
microns--22.8%; 4.7 microns--8.8%; the batch having a surface area of 
0.313 square meters per square centimeter and an average particle size of 
about 118 microns. The batch was formed into pellets and screened to 
produce pellets having a size of 3/8 to 5/8 inch; the pellets had a water 
content of about 11-12% by weight (dry basis) and prior to preconditioning 
were coated with the same dry batch in a rotary drum with about 3 parts by 
weight of the dry batch per 100 parts by weight of the pellets. 
The flue gases (after passage through a recuperator) entering the preheater 
had a temperature of about 1200.degree. F. (649.degree. C.)-1250.degree. 
F. (677.degree. C.). The preheater had a diameter (cylindrical portion) of 
about 7 feet. It is estimated that the flue gases were diluted about 
200%-300% by leakage of ambient air into the preheater through the heat 
exchanger and into the preconditioners through their attachments to the 
preheater. Additionally a gas fired burner (using a substantial excess of 
stoichiometric air--about 300%) was positioned in duct 40 and regulated to 
produce a heated mixture having a temperature of about 1200.degree. F.; 
the burner was periodically employed so that the temperature of the gases 
after passage through the preconditioning beds was generally in excess of 
about 350.degree. F.-400.degree. F. The temperature of the gases supplied 
to the preconditioners varied between about 400.degree. or 500.degree. F. 
to about 700.degree. F. with the velocity of the gases (actual 
superficial) through each of four preconditioners being about 400-500 feet 
per minute. The heights of the preconditioning bids generally varied 
between about 4-6 inches with each preconditioner operating on a two 
minute fill--6 minute heat cycle with the area of each bid being about 2 
feet.times.2 feet. The height of the vertical bed in the preheater was 
generally maintained about 10-11 feet above the wedge shaped gas 
distributor with the temperature of the dry pellets leaving the preheater 
being about 1200.degree. F. An exhaust blower was employed having a 
capacity of about 5000-7000 scfm with the temperature of the gases near 
the suction inlet of the blower being about 300.degree. F.-410.degree. F. 
Excellent results were obtained in total operation and energy savings. 
Having described the invention it will, of course, be apparent that 
modifications of the invention may be made which pursuant to the patent 
statutes and laws, do not depart from the spirit and scope thereof.