CA1244484A - Process and apparatus for producing an expanded mineral material - Google Patents

Process and apparatus for producing an expanded mineral material

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Publication number
CA1244484A
CA1244484A CA000462676A CA462676A CA1244484A CA 1244484 A CA1244484 A CA 1244484A CA 000462676 A CA000462676 A CA 000462676A CA 462676 A CA462676 A CA 462676A CA 1244484 A CA1244484 A CA 1244484A
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Canada
Prior art keywords
pellets
stream
reactor
gas
expanded
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Expired
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CA000462676A
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French (fr)
Inventor
Hans B. Fehlmann
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Construction Research and Technology GmbH
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Individual
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Classifications

    • CCHEMISTRY; METALLURGY
    • C03GLASS; MINERAL OR SLAG WOOL
    • C03BMANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
    • C03B19/00Other methods of shaping glass
    • C03B19/10Forming beads
    • C03B19/108Forming porous, sintered or foamed beads
    • C03B19/1085Forming porous, sintered or foamed beads by blowing, pressing, centrifuging, rolling or dripping
    • CCHEMISTRY; METALLURGY
    • C04CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04BLIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B20/00Use of materials as fillers for mortars, concrete or artificial stone according to more than one of groups C04B14/00 - C04B18/00 and characterised by shape or grain distribution; Treatment of materials according to more than one of the groups C04B14/00 - C04B18/00 specially adapted to enhance their filling properties in mortars, concrete or artificial stone; Expanding or defibrillating materials
    • C04B20/02Treatment
    • C04B20/04Heat treatment
    • C04B20/06Expanding clay, perlite, vermiculite or like granular materials

Abstract

INVENTOR: HANS BEAT FEHLMANN

INVENTION: PROCESS AND APPARATUS FOR PRODUCING
AN EXPANDED MINERAL MATERIAL

ABSTRACT OF THE DISCLOSURE

An expanded mineral material suitable for use as a filler, e.g. instead of or in addition to sand or gravel in concrete mixes, is produced by dropping a stream of solid pellets in-to a rising stream of heated gas contained in a substanti-ally vertical reactor space; the pellets consist essentially of a fusible mineral composition and a latent blowing agent;
while falling in counter-current to the gas stream the pel-lets are heated progressively and expand at least to the point where they are capable to float in the gas stream and are carried in concurrent motion with the gas stream out of the reactor space. This reversal of motion of the expanding particles provides for a substantially self-regulating resid-ence period of the particles in the expansion zone resulting in substantially improved process control and economy.
An apparatus for carrying out this process is disclosed.

Description

8~

l BACKGROUND OF THE INVENTION
I
ThlA inv~ntion relate~ to the ~roduction o~ an ex~and~d mlner-al material sultable for use as a con~tltuent or filler for ¦ concrete and other compo~lte materials that contaln a hydraul-¦ ic or other type of blndar and at lea~t one particulate inor-¦ ganic filler havlng a particle ~ize ln the range of typlcally ¦ from 0.1 to 20 mm.

¦ Conventional concrete mixes con~ist essentially of cement, ¦ water, and a mineral flller whlch, dep~nding upon lts graln ¦ size, ls termed "sand" or "gravel" and preferably consl~ts of ¦ alluvlal ma~ter or "pebbles", i.e partlcles of stone worn I round and smooth by geo~formative forces and having a typic-¦ al diameter of up to about 50 mm. Accordingly, both the sand ¦ a~ well as the gravel constituent of concrete may con~ist of ¦ "pebbles" and this latter term is u~ed herein generically to ¦ lndicate a generally round or spheroidal outer shape of indi-¦ vidual mineral particles regardless of whether their diameters ¦ would be that of fine, medium or coarse sand (up to about 2 mm) ¦ or that of f~ne to medium gravel (above 2 mrn). Particle sizes given herein are the maximum dimension~ or "dlameters" of gen-¦ erally spherical or spheroidal particles.
.
For producing improved cons-truction materials including light-weight concrete it is known in the art to use bulky mineral 1.24~8'~ ~

"fillers" or addltives ~uch as expanded gla~s, expanded clay, or expanded mica. These conventional addltive~ are obtalned by heatlng a mlneral composltlon, generally ln the ~orm of a stream of individual particleQ or pellet~ that contaln a "latent blowing agent", i.e. a compound or constituent capable of producing gaseous matter, e.g. carbon dioxide or water va-por, when heated; the latent blowlng agent may be incorporat-ed into a preblend that is used to form precur~or particlPQ or pellets for subsequent thermal expansion, or may be a natu,ral constituent, such as chemically bound water or a carbonate component of a mineral substance.

Specifically, expanded clay or expanded mica for use a~ a min-exal filler is generally produced by passing a stream of par-tlculated mineral material through a rotary kiln, that is, a cylindrical furnace revolvlng about an axis lnclined at an angle of S to 20 towards the horizontal. The particle~ within the rotary kiln move or roll in contact with the furnace wall so that the outer layer or skin of the final particles wlll be rough and broken. Further, the structure of the internal voids will, in general, be "porous" in the sense that most voids, e.g. more than 50 ~ communicate with each otheri "cel-lular" structures,.on the other hand, have fewer and typically less than 50 ~ voids that communioate with one or more other voids.

~ _ A proce~s for producing thermally expanded clay ls disalo~ed ln U~S. Patent 2,676,892, for cxample, and use o~ vertical kilns or expanslon reactor~ is known for producing expanded glass particles, e.g. as disclosed ln U.S. Patent 3,838,998 for making small hollow glass spheres, or in U.S. Patents
2,978,339 and 3,030,215 for production of glass particle~ of which a desired majorlty (typically 70 ~) has a ~ingle void and an undesirable minority (typically 10 ~) has a porou~
structure while anoth~r undesirable portion (typically 20 ~) .
consists of unexpanded massive glass globules.

Prior art expanded mineral fillers suitable for concrete and the like have one or more of the followlng defect3: the skin of the particles i6 rough and broken a~ a cons~quence of con-tact with the wall of tha kiln during thermal expan~ion; the lnternal structure is porous rather than cellular in thP ~ense defined above; mechanical or/and chemlcal stability under the conditions of use as a filler in concrete mixe~ is/are lnsuf-flcient elther becau~e the expanded partlcle~ have an inher-ently low structural strength and/or low resistance against the environment typical in concrete mixes, or because the aqueous cons-ti-tuent of the mix will penetrate through the skin or its broken portions into the voids within the expanded par-tlcles; further, prior art production methods are co~tly and/or dlfflcult to control.

~L~ 384 ¦ Because of these defects, expanded materials obtained by prior ¦ art methods are far from ldeal for u~e as a light-wolght sand ¦ or gravel constituent of concrete or for other purpo~es where ¦ a generally stable and reslstant low-cost li~ht-weight miner-¦ al filler is desirable.

¦ Such ~n improved light-~eight material, also termed "expanded ¦ pebble material" herein, would be of u3e to replace, entirely ¦ or in part, sand and gravel constituent~ of concrete mi~:es, ¦ notably for construction purpose~ or for production of pre-¦ formed co~struction elements, such as panels or blocks, and ¦ other USeQ where a substantially decreased speciflc weight ¦ and lmproved insulation (thermal and acoustic) of a ~tructure ¦ or construction would be advantageous.

¦ Now, according to the best knowledge of the inventor, no prior ¦ art method is capable to produce such a material and it la a ¦ main object of the present invention to provide for an improv-¦ ed process of producing an expanded mineral material suitable ¦ for the above descrlbed uses.

¦ For production of small hollow glaqs spheres as disclosed in ¦ the above cited U.S. Patents 2,978,339 and 2,978,340 and for production of hollow glass micro-spheres it is known to avold contact between the fused glass and the oven by continuously dropping pellets of glass or glass-forming matter and a latent ~.~

:lZ~ 8~ 1 blowing agent into a vertlcal chamber in which a hot ga~ is movlng upward and in counter-current to the pellet~ whlch are progreisively heated to fuse and to expand.

According to these prior art methods, the expanded particles continue to move ln a downward direction toward~ the lower end of the chamber where they are cooled and collected. The ma~s of the unexpanded pellets is crltical because the amount of heat required for expanding the pellets to form the hollow globules increases geometrically with such mass. The extreme-ly cloqe process control required is prohibitive when product-lon of a low-cost lelght-weight filler for use as expanded pebbles in concrete is considered.

Further, and even more important, the aand and gravol constl-tuent of a concrete mix must consist of granules or pebble~ of differing diameters; if the sand and gravel con~tituent of a concrete mix 1~ to consi~t substantially of expanded particles, such particle~ must be provided ln reLatlvely wlde dl~trlbution of particle sizes, e.g. between 0.2 and 10 mm. So, if a prior art expansion method would be used whereln a ~ubstantlally con-~tant partlcle mass 1~ crltical becau~e of heat transfer pro-blems, simultaneous production of expanded par~icle~ of dlffer-ing diameters would not be possible.

~Z~8~ 1 SUMMARY OF THE INVENTION

Now, lt ha-~ been found accordin~ to the lnventlon that import-ant advantages will be achieved in the production of expanded mineral materlals when the motlon of the pellet~ dropped into the hot gas stream is reversed during expansion in the sense that the unexpanded pellets are allowed to flr~t fall ln coun-ter-current motion to the ri~ing stream of hot gas until they have expanded to a degree at which they begin to float in the gas ~tream; as a consequence, the motion of the unexpanded particles counter-current to the hot gas stream will be qlow-ed down to virtual standstill of the particles wlthin the reactor and then reversed so that the fully expanded parti-cles will move with the gas stream, i~e. ln concurrent motion therewith, and will be fed out of the reactor together wlth that gas stream for subsequent recovery of the expanded part-icles.

. I
The use of gas streams for carrying solid particles in con-current motion with the stream i~ known per se from many ty-pes of pneumatlc conveyors and al~o for formation of gla~
sho~ as disclosed, for example, ln U.S. Patent 2,947,115;
however, the solid particles move in the same direction as the gas stream and no reversal of partlcle motion relatlve to the carrier stream is involved or intended and no advantage would be obtained by reversal of particle motion when the intended product consists oE massive glass ylobules.

'L2D~8~

Three different types, or modes, of movement of pellets (having a spherical or spheroidal shape, a diameter of be-tween 0.1 and 20 mm and a speciic weight in the range of 1 to
3) dropped into a rising gas stream can be envisaged: when gas velocity is relatively low and specific part.icle mass relatively high, the particle will fall in-to the gas stream; soon, an equi-librium between gravitation and aerodynamic resistance is reached and the particle will continue to fall at a substantially const-ant speed throu~h the gas; this will be referred to herein as the first or counter-current mode of movement; for simplicity it can be assumed here that the velocity of the falling pellets and the velocity of the rising gas stream are roughly substractive in first-mode movement.

In the other extreme, at high gas velocity and low specific part-icle mass, the aerodynamic resistance will exceed the gravit-ational pull and the particle will not fall into the stream but move concurrently therewith, i.e. rise with the gas stream, though generally at a lower speed because of the residual effect of gravlty; because of the intermediate mode described below, concurrent movement of a solids particle in a rising stream of gas will be referred to as the third or concurrent rnode of move-~nent.

. 1 .. ~

The type of motion in-termediate between counter-current and concurrent mouvement of a solids particle in a rising gas stream will be achieved when the force of gravi.ty acting upon the part icle will be the same as the counteracting "aerodynamic force"
exerted by the rising gas stream upon the particle; such "aero-dynamic force" is a complex entity including friction, turbulent suction as well as other factors including viscosity of the gas, limited areas of transition from laminar to non-laminar flux, and the like parameters of non-ideal behaviour. Floating of a particle in a gas stream, i.e. virtual stand-still with refer-ence to an external point of reference, will also be termed second-mode motion herein.

While full mathematical analysis and definit on of the "aero-dynamic force" required to balance gravitation would be extreme-ly complex, second-mode motion is observed phenomenologically and can be easily manipulated as explained in more detail below.
It should be understood, however, that the inventive process does not aim at any particular length of the floating state of a particle but at complete reversal of particle motion from the first to the third motion of the particle in the reaction ~one.

lZ~8~

Optimum conditions for carrying out the inventive process in a given system (including pellet size, usion temperature, activ-ation temperature and activity of the latent blowing agent, heat exchange between pellets and gas, temperatuxe gradient within gas stream, gas velocities in various parts of the reaction zone) need no-t be limited because the result to be achieved - reversal of particle motion - can be controlled in a simple test run in which the pellets to be used are dropped into the part,lcular reactor while maintaining a velocity of the rising hot gas such that all pellets will start to move in counter-current motion (1st mode) through the reactor space that contains the xising hot:
gas stream over a reactor space length sufficient for fusion of the mineral composition and activation of the latent blowing ag-ent to achieve thermal expansion of substantially all pellets.

As a consequence of thermal expansion of the particles while in counter-current motion, their volume increases typically by a factor of from about 1.5 to 15, depending upon the intended end use of the expanded pebbles; while the increase of volume can be influenced by the type and amount of the latent blowing agent as explained in more detail below, the essential reversal of part-icle motion will always be achieved when the velocity of the rising gas stream is lower -than required for second-mode motion of the unexpanded pellets but high enough for second-mode motion of pellets in the state of partial or incipient expansion.

,, , . . . _ _ _ _ ____ _ ~ Z'1'19~

~ny volume increase of the pellets will increase the aerodynamic force tha-t counteracts the gravitational force and one or more of the process parameters mentioned above could be varied; as a mat-ter of practice, proper selection of the velocity of the rising hot gas stream is a particularly preferred con-trol parameter be-cause this provides for self-regulation when expanding pellets of differing parameters. For example, assuming that a target product consis~ing of a mixture of expanded pebbles suitable as the only sand/gravel constituent of a concrete mix is to be made accordlng to the invention, the product must consist of expanded pebbles having differing diameters at least in the range of from about 0.2 to about 10 mm. Assuming a typical medium expansion factor of about 5 to about IO, the star-ting pellets should be a mixture of pellets having diameters in -the range of from about 0.1 to about 3 mm. I ' Pellets of such differing diameters require quite different am-ounts of heat for fusion and expansion because of the cubic rel-ation between diameter and volume. Since heat transfer is, to so-me extent at least, a time-dependent parameter, pellets of differ ing diameters require substantially different heating or residenc times for adequate expansion. However, for operation of the in-ventive process it will generally be sufficient to provide for second-mode motion of the largest pellets near the lower end of the reaction zone and this may be reached well before full expan-sion of the pellets is reached.

_ _ _ lZ~4~14 Then, additional heat will be exchanged while second-mode motion continues and while third-mode motion carries the expanded part-ic18 out of the expansion zone. Assuming, as an example, a length of the heating zone in the range of from about 20 to about 40 me~
ters and a velocity of the rising gas stream in the range of from 5 to 1Q meters per second (m/sec) this will normally result in an effective (relative to an outside point of reference) falling velocity of the unexpanded pellets in the range of from 1 to 4 m/sec. Consequently, pellets can remain in heat exchange with the rising gas stream for periods between 5 and 40 seconds in counter current motion and for an additional period in floating and in concurrent motion. In general, the reaction zone will have its hottest area te.g~ 1000-1400C) near its lower end.

Now, as the pellets start to expand while still in first or coun-ter-current motion and as the aerodynamic force acting against gravity increases progressively with the volume of the expanding pellets, motion of all pellets will be reversed at some point of the reaction zone if the pellets with the largest unexpanded diameter reach second-mode motion somewhere above the lower end of the reaction zone.

Generally, the smaller a given pellet or particle is, the smaller will be the amount of heat required for fusion and expansion, and such parti~les will reach transition from first into third mo-~Z~8~

de of motion within a shorter t.ime and a shorter path of travelin the first mode of motion so that they will start to float in the rising gas s-tream at a comparatively higher level within the reactor, i.e. closer to the upper reactor end.

A relatively larger pellet or particle, on the other hand, requi~
res more heat for fusion and expansion and, hence, a longer path of travel in the firs-t mode of motion and will start to float at a comparatively lower level within the reactor, i.e. closer to its lower end. If a pellet or particle fails to achieve the second mo-de of motion at the lower reactor end, it will not form an expand-ed pebble; however, a relatively small increase of the hot-gas-velocity throughout the reactor, or near its lower end, will norm-ally be sufficient to assure that substantially all pellets that have a predetermined upper diameter or maximum mass will start to float above the lower reactor end. Generally, well defined upper and lower limits of the pellet diameter range are desirable and can be achieved by simple methods such as sieving.

Generally, the reversion of particle movement as a consequence of expansion even though unexpanded pellets of substantially differ-ing diameters are dropped into the hot gas stream provides for an essentially self-regulating process according to the invention in that each pellet and expanding particle will choose the residence time it needs for expansion, and tha-t such self-regulation can be achieved by such simple means as sieving the pellets and/or con-trolling the hot gas velocity.

. . ~

Fusible mineral materials sultable for producing expanded pebbles according to the invention gener~lly are silicaceous composition~
that contain silica (SiO2) and at least one further inorganic and preferably o~idic compound capable of reducing the fusion temper-ature of the composition to below about 1400C. In general, the silica content will be in the range of from about 35 to about 95 by weight; the further inorganic compound preferably is an oxide selected from alumina (Al2O3), calcium oxide (CaO), magnesium ox-ide (MgO), iron oxide (Fe2O3), oxides of the alkali metals (Me2O), and binary, tertiary, quaternary or higher order mixtures thereof as most of the remaining portion.

Other inorganic compounds known as constituents of fusible mineral compositions may be present, e.g. TlO2, MnO, B2O3, P2O5, etc., or mixtures thereof, in minor amounts in a typical total of below ab-out 10 % by weight.

1%'~

The above constltuents are recited a~ oxldes but thl~ 1~ ln-dlcatlve merely of analyals; the constltuent~ actually u~ed for produclng the pellets may include complex oxidlc compounda such as naturally occuring minerals as well as precur90r com-pounds of oxides, eOg. carbonatea, that yield the re~uired ox-idlc componen~ when heated for fusion~

In vlew of the low-cos~ objective, waste or refuae-type sub-stances of natural or man-made origin are preferred for the fusible mineral compositlon; speclflc preferred examples in-clude vitreous materials, such a~ waste glass, mlneral a~hes, such as fly ash, obtained upon combustion of coal or other organlc matter, alluvial sediment sub~tancea, such as finea obtained from gravel production Iwashing flnes) or from sed-iments in natural water bodies, such aa rivers, lakes and the sea (e.g. dredged-up depoaits~, sand, solld alag-type com-buatlon residues and mixtures o~ the above mater~al..

Some compositlon ranges typical of mineralic re~ldues for use herein are given in Table I below.

_ ~ _ lZ~4'~4 TA~LE I
Analysis Data of Mineral Waste Material~
(in ~ by weight after heatlng at 1500UC
to constant weigh~

Type Alluvial Se~i- Fly-~shVitreous Waste ments (Fines) Substance ~ _ SiO2 35-60 5-50 35-95 Al23 5-20 5-30 0-30 CaO 10-50 10-50 0-15 MgO 2-15 10-40 0-12 Fe23 2-8 5-20 0-2 Na2O 0.5-2.5 0.S-5 0.5-15 K2O 0.5-2.5 0.5~5 0-20 Others (e.g.
TiO2, P205, B2O3) 0-5 0-5 0-2 Generally, the mlneral composltion of the pellets Rhould yield expanded partlcles that are substantlally ln oluble in aqueous media even at pH values in the moderately acid or moderately basic range. Potentially toxic constituents are not preferred.

Preferably, the fusion or softening temperature of the mlneral composition is in the range between 800 and 1400C, the range of from 1000 to 1300C being particularly preEerred.

~ _ ~Z~48~

For preparing pellets suitable for the inventive process, the min-eral substance and all solid constituents of the pellets should be ln a finel~ divided state, i.e. have a particle ~ize of below 100 lum and preferably below 50 ~um. Many silicaceous mineral waste mat-erlals such as alluvial sedlments and fly-ash meet thls requlre-ment; other materials or additives may require ~illing. However, as particle size reduction adds to processing costs, the use of mineral waste fines is preferred, at least for a major portion of the pellet constituents.

A second necessary constituent of the pellets is the latent blow-ing agent; its selection will depend upon the fusion or softening temperature of the mineral composition because the activity of the blowing agent, i.e. the development of a significant amount of a gaseous product such as carbon dioxide, oxygen or nltrogen, should not start until the outermost portion or skin of a pellet has been fused. Generally, the activation temperature of the latent blowing agent should be higher than the fusion or softening temperature of the mineral composition.

Many examples of latent blowing agents having activation temperat-ures in the range of interest hereln are known and include such compounds as inorganic carbonates, sulfates, nitrates, and oxides of metals selected from alkali metals, alkaline earth metals, al-uminum, iron, cobalt, manganese, titanium, chromium, nickel, cop-per, and zink.

1~ 8~

Other compounds suitable for use as a latent blowlng agent are inorganic compounds, such as carbides, known to be stable at temperatures of up to 800C but are reactive with constituents of the fuslble mineral composition. Silican carbide is a specific example and a known blowlng agent for produclng expanded glass.

Further examples include inorganic compounds that catalyse or promote decomposition of lnorganic oxides at temperatuxes in the range of from 1100 to 1300C.

Numerous inorganic compounds are known to decompose at specified temperatures above 800C and to liberate a gaseous component;
: various metal carbonates and ~ulfates belong into this group and carbonates of alkali metals or alkaline earth metals are a pre- .
ferred group; for example, zink sulfate will decompose at 770C, sodium . ~ _, ~ 2~

carbonate at about 1100C. Generally, the term l'decompo~ltion temperature" refer~ to the temperature of transltion o~ a com-pound into a thermally more stable form, frequently an oxide.
For example, manganese dioxlde (MnO2) i3 capable of generat-ing oxygen at various temperatures that may be determlned by an addltive, such as a ferric compound, e.g. FeC or FeSlN. In general, latent blowing agents for use in the lnvention are normally solid inorganic compounds that form at leaqt one gase-ous product when heated to the activation temperature whlch, frequently, wlll be ln the range of from about 800 to 1400~C.
Fusion (meltlng) of the latent blowing agent below lt~ actlv-ation temperature does not detract from ita utili~y. The lat-ent blowing agent ~hauld be dispersed in the pellets as homo-geneou~ly as poq~ible and the formatlo~ of many small voida wi~hln the expanding pellets i9 greatly preferred over form-ation of few large voids.

Pellets may be formed from aqueous slurrieq, e.g. by prill-ing, by mechanical compaction and qimilar prior art methods of forming granular particles or agglomerates from pulverulent solids. To that end, use of an additlve known ln the art and commonly called an agglomeratlon adjuvant or blnder may be advantageous. Water-soluble silicates ~uch as '!waterglas~"
are an example. Some latent blowing agents, such as sodium carbonate in a dissolved or molten form, may also serve as ..~

agglomeration adjuvants. Adjuvants may be inorganlc or organ-lc and need not, but can, be thermally ~table durlng expansion of the pellets.

Depending upon the method used for forming the pellat~, drying or heating of the raw pellets may be of advantage. Generally, the pellets should have ~ufficlent cohesion to with~tand siev-ing and normal handlinc without substantlal breakage.
. '.

~RIEE` DESCRIPTION OF THE DRAWINGS
~ ' ' .' The inventlon will be explalned in more detail with reference to the annexed drawings which illustrate preferred exemplary embodiments of the invention and wherein:

Figure 1 is a diagrammatic illustLation of an embodiment of the inventive process when operating ~ith a flame-heated react-or;

Figure 2 ls a dlagra~natic lllu~tration of an embodlment of the inventlve process when operating with an electrically heat-ed reactor;

Flgure 3 is a dlagra~natic and enlarged sect~onal vlew of a pellet for use in -the lnventiv~ proces~; and Figure 4 ls a diagrammatic and enlarged sectional view of an expanded pebble obtained by the inventive proce~s.

~ _ 1,.Z~48~

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The diagrammatlc scheme of an integral system for carrying out the inventive process shown in Figure 1 includes a reactor/sep-arator unit and a pellet-producing unit.

The reacto~ 10 of unit 1 represented schematically as a section-ed tube or hollow cylinder is made of a heat-resistant structur-al material such as steel and/or ceramics, and has an external heat insulation layer (not shown). The length/width-ratio of re-actor 10 is typically in the range of from 50:1 to 250:1 and the diameter may be constant or may vary continually or in a step-wise manner for optimization of aerodynamic parameters in the ; temperature regions explained below.

A gas infeed conduit 11 near the lower end 101 of reactor 10 provided with a blower 111 blows a gas, eOg. air, into the react-or in the direction of arrow A; the gas may be preheated in a heat exchange unit 112 operated e.g. with waste heat from the process. Burner 12 is provided to produce a heat control flame 121 generated by controlled combustion of a gaseous or liquid fuel.

, . . ~ _ _ _ ___ _ Near ~he lower end 101 of reactor 10~the temperature T4 of the rl~ing gaa stream will be at a maximum, e.g. in thu ran-ge of from 900 to 1200C, typically ~bou~ 1000C, and ~uch temperatures are suitable for pellets consisting predominant-ly of vitreous materials.

Near the upper reactor end 102 the temperature T1 of the gas stream rlslng in reactor 10 will be lowest, e.g. ln the range of from 200 to 400C. The temperature gradient or profile be-tween T1 and T2 may be steady and the intermediate temp~rat-ure zones T2 and T3 are indicated for purposes of explaining differentlstages of the fusion/expanslon proce~ o~ t~e ex pandlng particles.

A charging valve 14 feeds a stream of agglomerated particles or pellets 15 falling in a substantially vartical direction indicated by arrow B, i.e. in counter-current to the stream of hot gas indicated by arrow C rising sub~tantlally in vert-ical direction ln reactor 10. Typically, a reac~or 10 may have a length in the range of from 10 to 40 m and a diameter in the range of from 0~1 to 0.5 m.

The velocity of the rising gas stream within reactor 10 may be in the range of from 1 to 10 m/sec or more.

.

~z~

Pellets 15 are made in a pellet-producing unit 13 e.g. compris-ing an extruder plus cut-ter unit 130 for producing granular part-icles, and a sieving machine 139 for producing particle size fractions within a predetermined range and/or size distribution;
silicaceous mineral fines are supplied from source 132 and a lat-ent blowing, agent, e.g. in the form of a solution or slurry, is supplied from source 138; the blowing agent composition may also serve as agglomeration adjuvant or contain the latter as an add-itional component.

The mineral fines may be provided from a first source 131, e.g. a milling and sieving unit, for reducing vitreous waste to a finely divided powder of predetermined particle sizes, and/or from a ¦second source 134 for supplying sieved mineral fines produced in la combustion unit or oven 133. Generally, the particle size of the ¦fines in source 132 should be below 50 ~m, preferably in the range ¦of from 1 to 10 lum. The volume ratio of the pellet stream to the ¦gas stream preferably is low, e.g. in the range of from 1:1000 to ¦10,000.

¦Pellets 15 composed of vitreous or othe- silicaceous fines, lat-¦ent blowing agent/and optional agglomeration adjuvant dropped in-¦to the rising gas stream will be dried while falling at a typical ¦speed of about 3 m/sec through the first temperature zone T1~ e.g.
200 to 400C for lower-melting vitreous materials and 300 to 600 C for higher melting vitreous or non-vitreous materials); when us-ing alkali silicate in aqueous solution as the agglomeration ad-~ _ ~ 41~4 juvant, a silicaceous phase may be formed that connects the par~-icles of pellets 15 and may serve as a skin-forming cornponent.

The pellets will be heated progressively while falling through temperature zone T le.gO 400 to 700C for lower-melting vltreous and 500 to 800C for higher-melting vitreous or non-vitreous mat-erials) where fusion will be limited to low-melting constituents and/or sintering effects. Substantial softening or fusion will occur in zone T (e.g. 700 to 900C for low-melting vitreous and 800 to 1100C for high-melting vitleous or non-vitreous materials) at least in surface portion of the pellets, and a substantially coherent skin will be formed; the activation temperature of the latent blowing agent will be reached and after formation of such skin the pellets will begin to expand and to form partly expanded particles 151.

The increase of diameter of the particles 151 will continually de-crease their falling velocity in the rising gas s-tream ~typical gas velocity of about 8 m/sec) until, at a level designated as G
between temperature zones T3 and T4 (e.g. 800 to 1200C), any pel-let will stop to fall counter-current (arrow B), possibly float for some time at a relatively constant level, and then start to rise concurrently with the gas stream in the direction of arrow C.
A predominant portion, at least, and preferably all particles 152 will be carried by and with the rising gas stream into progressive ly cooler zones T , T1 and a stream of relatively cool expanded particles will be fed out of reactor 10 via conduit 16 near the lZ444~4 upper reactor end together with a poxtion, at least, of the gas stream; conduit 16 opens into a separator 17, e.g. a cyclone conn-ected to a storage bin 18 where the particles are separated from the gas stream and recovered as the target product.

A recirculation conduit 19 is connected with the separator for recirculation of the heat transfer gas into the process. An anti-adhesion device (no-t shown) may be provided, e.g. in the form of stationary or mobile electrodes or similar means capable of gen-erating electrostatic charges or fields that will decrease ad-hesion of particles to the wall of reactor 10. An outlet (not shown) may be arranged at the lower reactor end 101 for discharge of molten mineral mass that may accumulate there as a result of particle adhesion to the reactor wall or because of the failure of some particles to become sufficiently expanded for reversal of motion.

Figure 2 shows a diagrammatic view of a preferred process when using pellets of mineral compositions fusing in the higher temp-erature range, e.g. between 1000 and 1400C. To this end, reactor system 2 comprises a lower portion 20 serving as an expansion furnace and an upper portion 21 serving as a preheating reactor portion or pellet preheater. Furnace 20 comprises a central tubul-ar member 23 made of a material capable to support worklng temp-eratures of up to about 1400C, e.g. a ceramic material. A therm-ally lnsulating jacket 24 surrounds a number of electric heating elements 25 (indicated by s~uares~ arranged within a tubular in-terspace 240 between jacket 24 and central tube 23; the cylindric-1~

al space 230 encompassed by tube 23 forms the expansion chamber.Spaces 230 and 239 form ~he reactor space for the inven~ive pro-cess.

The upper reactor portion 21 is connected to an elongated heat exchanger 27 continuing through a number of turns and ending in separator 28. Inner tube 231 of the pellet preheater 21 is a functional extension of central tube 23 in an upward directlon in that the elongated and substantially vertically extending react-or space is formed consisting of the pellet expansion ~pace 230 as its lower part and the pellet preheating space 239 as its upper part.

Both the outer tube 241 and the inner tube 231 extend from the pellet preheatisr 21 into the heat exchanger so that an essentially coaxial system is formed for circulation of heat exchange gas through system 20 by means of a blower 29 that will cause and maintain a stream of heat exchange gas, e.g. air, to enter (arrows E) into chamber 240 where it is heated, e.g. by a series of elec trical resistance heaters 25 (indicated in rectangular cross-sect-ion) and e~ters (arrows F) into expansion chamber 230 formed by tube 23 and having a tapered lower end 234. The temperature o the gas entering chamber 230 will typically be in the range of from 1200 to 1400C and this hot gas stream rises as indicated by arrow G towards the upper end of furnace 20.

~2~4~

A shunt condult 26 with a control valve ~not shown) may be provid~
ed to introduce gas of a somewhat lower temperature, e.g. about 800C, that may be withdrawn at an appropriate portion from the heat exchanger 27 so as to form a temperature delimitation between the reactor spaces 230 and 239 and to maintain a predetermined tempera-ture differential (fusion/non-fusion-temperature) between the expansion portion 230 and the preheatin~ poxtion 239 of the reactor. The embodiment of the inventive process illustrated in Figure 2 will be operated, for example, as follows:

A stream of individual pellets (not shown in Fig. 2) having diff-ering particle diameters between 0.1 and 2 mm is fed via a pellet port 211 into preheating portion 239. The pellets can be prepared as explained above and the mineral composition of the pellets will have a fusion or softening temperature of typically above 1000C
and up to 1400C; the latent blowing agent will be activated with-in that temperature range. The pellets are dropped continuously in-to the hot gas stream near the upper end of the preheating portion 239 of the reactor so as to maintain a low (e.g. 0.01 to 0.1 %) pellet stream volume relative to the volume of the gas stream; the velocity of the gas stream will be in the range of from about 6 to about 10 m/sec so that the pellets will fall through space 239 at a speed of about 3 m/sec. Typically, the temperature of the gas stream rising through preheating portion 239 will be about 600C
near its upper end (where the pellets are dropped into the stream) and about 800C near its lower end (where the shunt conduit 26 opens into the reactor space).

~ 4~3~

Generally, the temperature threshold produced between spaces 230 and 239 by the gas introduced via conduit 26 will be determined by the fuslon or meltlng temperature o~ the mineral composltlon of the pellets so -that fusion or softening of the pellets will occur but in the expansion portion 230 of the reactor.

Reactor dimensions can be essentially as explained above ~ut the main factor is an effective residence time of the pellets and/or expanding particles within chamber 230 sufficient for reversal of motion (1st mode to 3rd mode) of the largest pellets as e~plained above; this, in turn, can be influenced by the physical length of the preheating chamber, the temperature gradient in the rising gas stream and aerodynamic factors including gas velocity, pellet mass and pellet shape.

Depending upon the mass of a given pellet, expanslon and reversal of motion may occur shortly ater entering chamber 230 or at any portion thereof above the tapered lower end 234 that forms a gor-ge where the velocity of the gas stream rising in chamber 230 will be at a maximum; as a consequence, the aerodynamic lifting force for counteracting gravity will increase significantly near the lower reactor end so as to act as dynamic stopper ~or pellets that have not become expanded sufficiently for second or third mode motion.

~ 4~4 Still, some pellets might fall through chamber end 234 and a coll-ector 24S is provided for withdrawing any molten mass that accum-ulates at the lower reactor end. Again, the expanded particles formed within chamber 230 will be carried with the gas stream; be-cause of the temperature gradient caused by shunt 26 at the trans-ition from the expansion chamber 230 to the preheating chamber 239 problems of adhesion between expanded particles rising in third-mode motion with the hot gas stream and the pellets falling in first-mode motion into the gas stream can be minimized.

The expanded particles carried in third-mode motion with the gas stream through chamber 239 enter the heat exchanger27 formed by extending tubes 231, 241 of the pellet preheater into tubes 237, 247 of heat exchanger 27 which, in essence, consists of a pair of coaxial spaces 271, 272 in which the inner part 271 carries the stream of expanded particles mixed with a major portion( at least, of the hot gas into the separator or cyclone,28; there, the expand ed particles are recovered from collector 281.

The gas stream and the expanded particles entering through conduit 283 into separator 28 (arrow ~) will have transferred most of their heat content through tube 237 to the gas stream that flows back from separator 28 through conduit 282, blower 29, and the annular conduit 272 formed between tubes 237, 247 and 231, 241 to the heat-ing space 240 where the gas stream for feeding into chamber 230 is heated to the temperatures required for expansion of the pellets.

i'~ 8~

Heat losses and environmental problems can be mini~ized in this manner.

Figure 3 shows an enlarged diagrammatic cross-sectional view of a pellet 30 for use in the inventive process prior to expansion;
it has a generally compact shape in that length, width and thick-ness of each particle approach unity (1:1:1). Preferred pellets 30 have a maximum diameter or largest cross-sectional dimension in the range of from 0.1 to 10 mm, and consist of an agglomerated mass of small particles 31 that, in turn, have maximum diameters of below lO0 ~m and preferably below 50 ~m. Preferably, the latent blowing agent (not shown in Fig. 3) is a further particulate con-stituent homogeneously dispersed throughout the body of each pel-let. The optional agglomeration adjuvant can be an interfacial film (not shown) between the particles 31.

An illustrative example of the composition of a pellet 30 is an agglomerated mass of natural fines obtained as a sediment from sand and gravel washing; the fusion points of such fines obtained from varying sources was in the range of from 1180 to 1260~C.
Sodium carbonate (2 to 3 ~ by weight of the pellet) was used as an agglomera-tion adjuvant. The latent blowing agent was a mixture of equal parts by weight oE MnO2 and FeSiN used in an amount of 1 to 2 ~ by weight of the pellet. Alternatively, the MnO2 may be omitted and the FeSiN replaced by silicon carbide because SiC re-acts with ~any silicaceous melts to generate a gaseous reaction product.

`\ l'Z~

The analytical eomposition (in percent by weight; a~ter heating at 1500C to constant weight) of the natural fines was as follows:

42.4 to 56.5 ~ SiO2 6.1 to 14.0 ~ Al2O3 2.3 to 6.1 ~ Fe2O3 . 0.3 to 0.7 % TiO2 14.0 to 35.0 % CaO
2.4 to 11.0 % MgO
0.05 to 0.2 ~ MnO
1.0 to 2.6 % K2O
0.6 to 1.8 % Na2O
0.1 to 0.2 % P2O5 summing up to 100 ~.

Figure 4 shows an enlarged diagrammatic eross-sectional view of an expanded pebble 40 obtained from a pellet as shown in Fig. 3 by the expansion method illustrated in Fig. 2. Each sueh pebble has a spheroidal shape and a generally smooth and eoherent i.e.
unbroken outer skin 41. The inner strueture is that of a eontinu-ous phase or matrix 42 in whieh numerous spherieal voids 43 with diameters in the microseopie (0.1 to 10 ~um) to macroseopie (0.01 to 0.5 mm),range are dispersed. The voids are substantially elos-ed, i.e. few if any voids 43 eommunicate with eaeh other thus re-presenting what is generally termed a cellular strueture (as op-pcsed to a "porous" structure of intercommunicating voids).

;~ 84 In general, cellular structures having more and smaller voids are preferred over those having fewer and larger voids and the actual structure of a pellet 4 would show many additional but minute voids.

The specific weight of the pellets 30 will generally be in the range of from 1.5 to 3 while the specific weight of the expanded pebbles 40 according to the invention will be in the light-weight range of from 0.1 to 1.2. Preferably, an expanded light-weight filler according to the invention consists of pebbles 40 of diff-ering diameters within the general range of from about 0.1 to ab-out 20 mm and having a specific weight in the ran~e of from 0.2 to 0.8, notably 0.2 to O.S.

While preferred embodiments of the present invention are shown and described herein, it is to be understood that the invention is not limited thereto but ma~ be embodled and practiced wlthin the scope of the following claims. :

- 30a -_ ~. _ _

Claims (8)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A process for producing an expanded mineral material consisting essentially of a multiplicity of discrete spheroidal particles having a generally cellular structure and being suit-able for use as a sand or gravel constituent of a concrete mix;
said process comprising the steps of:
(a) providing a stream of individual pellets comprising a fusible mineral composition and a latent blowing agent, (b) continuously dropping said pellets into a hot gas stream contained in an elongated, vertically extending reactor space and moving essentially in an upward direction counter-curr-ent to said pellets for heat exchange between said pellets and said hot gas to progressively heat said pellets while moving counter-current to said hot gas;
(c) allowing said pellets to fall through a sufficient length of said elongated reactor space for causing fusion of said mineral composition, activation of said blowing agent, and ex-pansion of said pellets until a major portion, at least, of said pellets becomes expanded sufficiently for floating in and moving with said stream of hot gas to form a stream of expanded particles carried by said hot gas stream;
(d) guiding said stream of expanded particles with a por-tion, at least, of said gas stream out of said reactor space;
and (e) separating said expanded particles from said hot gas stream.
2. The process of claim 1, wherein each of said pellets is a generally spheroidal agglomerate formed of said fusible mineral composition in a finely divided pulverulent state; said pellets having a diameter in the range of from about 0.1 to about 3 mm and containing said latent blowing agent in a substantially homogeneous distribution.
3. The process of claim 2, wherein each of said pellets is formed by agglomeration of a pulverulent mixture comprising said mineral composition, said latent blowing agent, and an agglomer-ation adjuvant, said pulverulent mixture being formed of part-icles each having a diameter of below about 0.05 mm.
4. The process of claim 2, wherein said mineral composition is selected from vitreous materials, fly-ash, mineral sediment substance, sand, solid combustion residues, and mixtures thereof.
5. The process of claim 1, wherein said pellets of said stream have differing diameters within the range of from about 0.1 to about 3 mm and wherein said expanded particles obtained in step (e) have differing diameters within the range of from about 0.2 to about 10 mm.
6. The process of claim 1, wherein a decreasing temperat-ure gradient is provided within said reactor space extending from a lower zone having temperatures above the fusion temperature of said mineral composition to an upper zone having temperatures below the fusion temperature of said mineral composition.
7. An expansion reactor for continuously producing an ex-panded mineral filler material, said reactor comprising (i) an elongated and essentially vertical chamber;
(ii) an upper end for feeding a falling stream of substanti-ally unexpanded mineral pellets into said chamber;
(iii) a lower end for feeding a rising stream of gas into said chamber counter-current to said falling stream;
(iv) means to heat said riding stream of gas to a temperat-ure for expanding said pellets to a degree of expansion suffici-ent to produce expanded particles floating in said rising stream of gas;
(v) means to carry said expanded particles with said stream of gas out of said vertical chamber; and (vi) means to separate said expanded particles from said gas.
8. The reactor of claim 7, comprising at least one means for cooling said expanded particles within said reactor.
CA000462676A 1983-09-13 1984-09-07 Process and apparatus for producing an expanded mineral material Expired CA1244484A (en)

Applications Claiming Priority (2)

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CH4979/83A CH664356A5 (en) 1983-09-13 1983-09-13 METHOD FOR PRODUCING FLOWED MINERAL GRAIN.

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JPS6212646A (en) * 1985-07-09 1987-01-21 宇部興産株式会社 Manufacture of minute inorganic formed body
EP0242872A1 (en) * 1986-04-23 1987-10-28 Helmut Dipl.-Ing. Pieper Process for foaming glass-forming mineral substances, especially fly ashes, etc., and furnace for carrying out this process
DE19951453A1 (en) * 1999-10-25 2001-04-26 Alstom Power Schweiz Ag Baden Oxidic mineral composition
NZ521491A (en) 2000-03-14 2004-06-25 James Hardie Res Pty Ltd Fiber cement building materials with low density additives and cellulose fibers
US7574930B2 (en) * 2002-02-15 2009-08-18 Implant Sciences Corporation Trace chemical sensing
US7455798B2 (en) 2002-08-23 2008-11-25 James Hardie International Finance B.V. Methods for producing low density products
CA2495696C (en) * 2002-08-23 2012-01-31 James Hardie International Finance B.V. Synthetic hollow microspheres
US7993570B2 (en) 2002-10-07 2011-08-09 James Hardie Technology Limited Durable medium-density fibre cement composite
US20090156385A1 (en) 2003-10-29 2009-06-18 Giang Biscan Manufacture and use of engineered carbide and nitride composites
KR100541411B1 (en) * 2004-02-11 2006-01-11 주식회사 재원 expansion apparatus of expansive stone
US7998571B2 (en) 2004-07-09 2011-08-16 James Hardie Technology Limited Composite cement article incorporating a powder coating and methods of making same
NZ560872A (en) 2005-02-24 2010-08-27 Hardie James Technology Ltd Alkali resistant glass compositions
CA2632760C (en) 2005-12-08 2017-11-28 James Hardie International Finance B.V. Engineered low-density heterogeneous microparticles and methods and formulations for producing the microparticles
EP1832560A3 (en) * 2006-03-07 2010-03-24 Omega Minerals Germany GmbH Method for manufacturing ceramic or vitreous micro hollow balls
NZ571874A (en) 2006-04-12 2010-11-26 Hardie James Technology Ltd A surface sealed reinforced building element
US20070275335A1 (en) * 2006-05-25 2007-11-29 Giang Biscan Furnace for heating particles
US8209927B2 (en) 2007-12-20 2012-07-03 James Hardie Technology Limited Structural fiber cement building materials
US20140144319A1 (en) * 2012-11-27 2014-05-29 John J. Paoluccio Orbit filter magnets for cyclonic cleaners
AT15001U1 (en) * 2015-06-03 2016-10-15 Binder + Co Ag METHOD AND DEVICE FOR PRODUCING A BLOWN GRANULATE
MX2021000767A (en) * 2018-07-26 2021-03-29 Basf Se Hollow spherical glass particles.
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US2947115A (en) * 1955-12-01 1960-08-02 Thomas K Wood Apparatus for manufacturing glass beads
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EP0134584B1 (en) 1988-03-16
ATE33016T1 (en) 1988-04-15
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FI843571A0 (en) 1984-09-12

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