US2925336A - Process for the production of hard burned agglomerates - Google Patents

Description

Feb. 16, 1960 2,925,336

PROCESS FOR THE PRODUCTION OF HARD BURNED AGGLOMERATES w. F. STOWASSER, JR

2 Sheets-Sheep 1 Filed July 22, 1957 2,925,336 PROCESS FOR THE PRODUCTION OF HARD BURNED AGGLOMERATES Filed July 22, 1957 Feb. 16o, 1960 W. F. STOWASSER, JR

2 Sheets-Sheet 2 5 E E n TW A mm mm H M 5w M PROCESVSY'IFOR THE moment-mm BURNED AGGLOMYERATES r William F. Stowassen' Jr., Milwaukee, Wis-,hssignor to;

Allis-Chalmers Manufacturing Company, Milwaukee,

Y a lication July 22, la /{s rial ism-673,219 11 Claims. c1. 75-3 This invention relates? generally to'processesl for agglomerating iron ores and particularly to processes for P s ca )f'lent fl 16. 1 69 subieQted to"'a .tu'r'ribling' test' developed {to establish an index o'fpellet-res'i'stance todeg radation; It" has been determined that thesepellets-"when subjected to the established-tumblingtest-produc from 13 to 1 5' percent minus 28 nieshffihes." Thesefines have been observed to result fromboth pellet breakage and'surface abrasion.

Such fines produced --bytheihandling and shipping of the pellets are detrimental to smelting processes.

The principal object"of the. -present'-invention is to t tumbling test referred-Ito willproduce virtually no broken making hardened separate pellets of iron ore from finely divided iron oxide ores and concentrates thereof such as magnetite produced from taconites.

It is well known that fine powdery; ore is unsuitable for treatment in blast furnaces, open hearth. furnaces, and the like used in the iron and steel industries.

number of methods have been tried with varying degrees 7 4 of success for agglomerating such fine ore particles to make them suitable for. handling, shippingv'and use in blast. furnaces or other types of smelting furnaces.- Briquetting presses and extrusion pelletizers have been used,

however operatingmaintenance costs vhavefbeen undesirably high. Sintering, a commonlyg used-method, requires highfuel consumption andas a process for finely divided concentrates has not been acceptable to industry.

Sintering is generally nsed forscreened ore jfines of minus I one-half inch orless. The product ,ofsintering is ,a brittle, slag bonded, porous cake and will varyin physical I characteristics. ,Sintering is a process that is usedl of necessity to reclaim flue dust. and ore fines of theisizesobtained as a result of steel plant operations.,

Rotary kilns have also been used to makenodules ;of powdered ore, however to produce the nodules it is necessary to have a slag bondingcomponentor:the nodule ,will notform. An' additional result however of j .thelpresence of theslag component is theformationof an' accretion build-up or ring inside .the kiln. Thek l n therefore must periodically be bored out to maintain operation. Pelletsiof ore concentrates arealso-burned in shaft type kilns.. But the 'shaft kiln' is znot always dependable (because; of diificulties in obtaining uniform charging and discharging and uniform movement of ma-v terial and gases-through the interior of the shaft. Ihese difiiculties in shaft'kiln operation: canlead to nonuniform burning, hanging of the, charge, and sintering togetherof pelletsin parts of the kilnso as to hinder gas flow and promote further irregularities such as'overburned clusters of material-in some parts of thecharge'and underburned'. pellets in other parts of the charge.- Pellets of ore con centrates are also burned on horizontal traveling grates;

Several variations of burning -on grates have heen cle veloped,-s uch as one variation int which.finely divided;

fuel is mixed with the ore before it is pelletized, and i13 another variation thepellets after they have been formed are coated .with a finely divided fuel. With grate type heat hardening equipment side wall- -struc ture of some, kind; must beprovidedto keep the pellets on the grate; ,As a result-of this sidewall; structure a nonuniform heattransfer to the pellets .takesplace,

7 It has beenestablished that the product farm, t e

ing grate and the shaft kiln have certain physical chatty acterisjtics which are evidencedby -the ability of; pellets,- p'roduced by these two means to withstand degradation! fromhandling, shipping andstockpiling which thepellets are subjected to before they-are finally placed in a blast; Iu 3 =f l 9t;f m ths srrrgq ss lisse zs a;

provide a new and improved process for heat treating agglomerates of finely divided-ironore to produce hard durable pellets which rwhen- -subject to the established pelletssand will'reduce-fines produ ced by abrasion to the order of onlyj1 to'5 percent; thus producing a pellet of {vastly superior resistance to degradation frorn'handling and'shipping; Another object formlyburned pellet of finely divided iron ore.

Another object .of'ihe present inventionis to provide a new-and improved .process .fo'riheat treating pellets of iron ore in which'dust and fins pro duced during early stagesofthe' process will' during later stages ofthe process be weldedto. the'pelle'ts'beforethepellets have com-' pletedtheir. processing and are discharged from the proc essing equipment. r v l The process according to this-invention is applied to a material comprising finely divided magnetite iron ore ina moist condition-such; as'dsgener'ally produced by magnetic-concentration of magnetic taconites.

'The finely ground moist ore concentrate is first formed into. small agglomerates'ofgrenwa'ter bound pellets.

. The pellets-may be-formed inany' desired known manner.

such as bybriquetting, extrusion processes, balling drums or balling pansi Briquettingor extrusion processes are less desirable than balling. drumsor pans. -Withballing drums or balling pans it is well known that pellets be producedwithout a'" hinder or plasticizer other than water,..however it may sometimes be desirable to utilize an additive such as'a fraction of a percent of bentonite.

.The green pellets are formed into a body'of pellets that is movableiama bodywith individual pellets being .at:rest:within thef body. :This may be accomplished by" forming the "pellets ina-layer' upon-a movable'gas per- .meable support such as "agrate -lt has beenjfound that a layer ofabout seven inchesdeep will 'give'good results with green pellets averaging in size; between one-half and threeefourthsof an inch in diameter.

, At leastfirst'and second gas confining zones are establishedithrough whichthebody of the pellets can be con-;

, veye'd. With. a body: of pellets such' as a layer on a moving grate, the firstand'second gas confining zones may be established'by all=structi1re around the grate.

ally horizontal rotary kiln. Rotation of the rotary kiln.

about its central axis will achieve the 'desired'tumbling action of the pellets.

A flowv of highly he'atedis'trongly oxidizing gases is V eifectedthat is countercurrenfto 1 path of movement' 'of the tumbling pelletsi 'l'hisjmay be accomplished by' pro -f" viding a combustion device "at the discharge end ofitlle rotary 'kiln an admitting airto the dischargeend brute I f kilnin quantities in excess of therequirements to support combustion. of fuel. After the highly neatedjn vd' gases have passed thrqu gh the third aone'tliesejgaseg .e- I passed through the bodyofithe pellets.withinlthe second u Ea d gamma the dandy. of el e s; min

of 'theapresent'invention is to provide a new andimproved process for producing a more uni-'- The body ofgpellets'is conveyed through the first and secon'd'": zonesanddischzirged intola 'third'zone. The pellets are s,- tumbled "through-thisnthird 'zone. vThe third zone may] -beestablis'h'ed by providing apparatus such as a gener first zone. This may be accomplished by directing the gases discharged from the rotary kiln into the wall structure defining the second zone and directing these gases 9 Pas d w r thml t bo y r l ts O the within thesecond zone. The gases after they have passed through the body of pellets in the second ,zone can be directed from the wall structure defining the secondzone to, the wall structure'defining the firstzone and then directed to make a second pass downwardly through the body of pellets in thefirst zone.

The "temperature of the oxidizing gases and the rate of movement of the body of pellets through :the first and second zones are correlated to -heat treat thepellets sufiiciently to withstandthe tumbling. aotion in the third zone wherein the final hardening of thegpellets takes place. This is accomplished'by first .he ating. the pellets inthe first zone sufficiently to drive 91f themoistureirom the pellets and dry them. .Ihen. additional-heatwis applied to the pellets in the seeond zone to preheatand initiate the conversion of the magnetite in the pellet to. hematite. This is accomplished by heating the pellets in'the highly xi izingatm sphere -to.=a temperature between approximately 16 QO F. and'lSOO? This transformationcan be symbolically expressed by theformula After having reached a temperature, of at least approximately 1600 F., the grains comprising the pellets are at'least superficially oxidized tqllematite. During the oxidation reaction, individual grains of transformed hematite bridge together by grain growth and-recrystallization, in the solid state, witho ut reaction with available silica, to initiate a structure oiithe mineral component forming the, pellet. .The oxidized pellet, havingv been raised toa temperature of from 1600f F. tol800 F. has developed, from the grain growth ofits mineral constituent, sufiicient strength to withstand the. tumbling action in the third zone. This crushing strength ofpellets on the "'second'is of the order of one to two, hundred pounds. The amount of bridgingof the grains of the pellets in the temperature range, existing in. the second zone, is sufiicient to give strength, tothe pellet to withstand tumbling in the third zone but willnot causethe pellets to stick together because of the small amount of contact between the.,P6llets.

To provide final heattreating of-the pellets, the pellets are discharged from the second zone. into thethird zone where. they are tumbled and subjected, to highly heated oxidizing gases to maintain and develop the. hematite structure within each pellet to. complete the network of bridged hematite crystals. Thisis accomplishedby subjecting the pellets to a maximum temperature in the range ot-at least about 2200 F. but.not=morethan about 245Q F. thereby maintaining thepellets at a temperature caused an increase, in. pellet strength. In additiondust orfines that might have. resulted. from'the movement ofthe pellets prior to. their. attaining adequate strength to resist degradation are picked up by the tumbling-pellets inthethird zone and canbefusedlo the tumbling pellets thus providing an extremely. low. percentage of fines and dustin the gases passing through the second and.first. zones. The additional filtering action, of the. gases ,passr ing through the body of pelletsin the. second and first zones results in an overall redu'ction of dust and fines pr du d.

"Since the maximum temperature of the pellets is not.

permitted to'exceed app'roXirnately'2450" F. the hematite in the pellets will not thermally decompose back to mag netite. Since there will be no magnetite in the pellets and since the pellets will not be raised to decomposition temperatures there will be no slag produced. By eliminating the possibility of slag formation the danger of ring formation in a rotary kiln is also eliminated. High pellet strength is assured by the absence of slag. or iron silicates are the weakest component in the pellet and pellets containing such are brittle and have a much lower crushing strength than that attained by the heat treatment in the third zone of this process.

The pellets produced by this process are so hard that they wiil scour the lining of rerractory equipment such as the rotary kiln which may be used for the final burning.

For convenience and clarity, the process will be further described as proposed to be continuously carried out on equipment of the traveling grate and rotary kiln type shown schematically in Fig. l of the drawings.

Fig. 2 is a drawing of a microphotograph of a pellet that 'has'been dried and preheated to initiate the conversion of magnetite inthe pellet to hematite. This figure also shows that individual grains of hematite are bridging together by grain growth and recrystallization in the solid state. The gray area in "the grain shown is magnetite and the white area is oxidized magnetite, transformed to hematite. I

Fig. 3 is'a drawing of a microphotograph of a pellet as shown in Fig. 2 when very little of the magnetite remains in the grains and substantialbridging of the grains has taken place; 7

Fig. 4 is'a drawing of a microphotograph of a pellet that has been heated sufiiciently to substantially complete the conversion of magnetite to hematite and develop a network of bridged crystals having sufiicient strength to withstand the tumbling action during the final burning of the pellets according to this process: v

Fig. 5 is a drawing of a microphotograph'similar to Fig. 4 but. to greater magnification showing the bridging together of individual grains of hematite to provide the network referred toi Fig; 6 is a drawing of a microphotograph of a pellet after final burning according to this invention. In this figure it can be seen that when a pellet has been burned according to this invention in a temperature range of at least about 2200"F. but not more than about 2450 F. that recrystallization and grain growth will have taken place to p'rovide a continuous network of hematite crystals within the pellet to provide greatly increased pellet strength over that shown in Figs. 4 and 5 Fig. 7' is a drawing of'a microphotograph of a pellet showing the effect of overheating the pellet during final burning: This shows a. pellet that has been burned to over 2400 F: It can be seen that the gray areas which are magnetite'are beginm'g to reappear as the hematite in this temperature range converts back to magnetite.

'For convenience and' clarity; the process will be further described as it may be continuously carried out on the equipmentshown schematically in Fig. lot the drawing. Green water bound pellets of concentrated magnetite ore may be formed in a pelletizing pan 10 of conventional construction. The pelletizing pan 10 may discharge pellets on a conveyer belt 11 for'transferring them to ahopper 12; that in turn deposits them-on a moving gratel3z' i y The grateli! is a gas permeable grate with openings fine enough to retainthe pellets being handled, and'will be'of heavy cast-iron bar or perforated plateconstruction of heatresistant steel. As shown, the grate 13is of the same general type as is now known in the sintering machine art and consists ofan endless chain of grates traveling-over mechanically rotated supporting rolls 15: The' upper portions of the grate 13 will be supported mechanically by known structure (not shown) placed between the rolls.

' Beneath the generally horizontal'working surface of the grate 13 andunder the feed end,a first suction box 16 is arranged with an opening connected to an'exhaust Slag 6 fan 19 and a stack 20 for dischargingigases from the first suction box 16 to the atmosphere. Above the-suction box 16 and adjacent the feed end of the grate 13is a hood 21' extending over the grate 13 to create afirst chamber 22 through which all material on .the grate 13mustpass.

Adjacent the first hood 21 and in the direction of grate travel is a second hood 23 over a second suction' box 24 which with wall structure 25 forms a second zone 26 through which all material on the grate mustv pass, Thesecond suction box 24 which is beneath the second zone 26 is connected to'the first hood 21 by a.tube 27 to direct gases that have passed through the gratej13 in the second zone 26 to the first hoodffor passing siic'h;

gases through the grate moving through the first' zone Adjacent the'end of thefti'avelinggrate13. remote from the feed -hopper 12 is an inclined surface30 "for receiving pellets from the traveling grate and discharging the'pelletsinto a third zone 31 within a rotary kiln 3 2. The rotary kiln '32 may be of relatively conventional 1; in the' rotary kilni'32 counter- 'rlnblin g' pellets within the kiln; iorfof "th'e hoodf23 defining the second zone 6 oyer the;pellets' on the moving grate. n19 associatedj with thestack ZQ will draw- 'dizing gases from these'c'pnd zone 26' above grate 13. through the pellets 'on'the moving o". the second, wind box' 24 below the. grate the first'f zoneirom 'wherefthegasesljwill pass to the atmospliere through the stack "-Sutficient quantity of :air must be provided to coolthepellets to atempera tui egatwhich they can be handled; maintain ;-,combus- .tionjof the incl admitted through: the burner and to main construction having roller supports 33 for supporting the kiln at various points along its entire length. The kiln may be rotated in the conventional manner by providing 2. motor driven shaft 34 and gear 35 for engaging a girth gear 36 around the body of the kiln 32. The end of the rotary kiln 32 remote from the traveling grate 13 is enclosed with a firing hood 40. A burner 41 may be; provided that projects inwardly through the hood ({0 that is supplied with fuel through a tube 42 and primary combustion air through a tube "43,. A cooler 50may be provided directly beneath therfiring hood for receiving the burned pellets from the kiln 32f Secondaryair for cooling the pellets may' be injected into .the cooler structure by a secondary blow'er51. It is; desirable that the cooler be of the type having cooling air passing upwardly or counter-current to descending pellets. After the heat" 11 motor 53 driving a speed reducer 54 which in turn drives a gear 55 that turns vertical axis. we I h The process is carried out'on the des the cooler body. about a central 'bed apparatus byplacing the greenvwater bound pellets on the grate 13 thus forming a body of pelletsthat is 'movable'as-a body with individual pellets being addressed withinthe body of pellets. As previously stated, it has been found that a layer of about seven inches deepwill give-good; 4

results with green pellets averaging in size between 'onehalf and three-quarters of an inch'indiameter." The bodyof pellets established on the grate..13 i s; then passed through the firstzone 22 and then' throughthe second zone 26 and discharged into the third zone I 31 established within therotary kiln 32. The pellets are. then'tumbled through the thirdizone 31 the.kiln 32 and discharged into the cooler 50. The pellets wilk tumble through the kiln as a .result o'f thearotationfofz the rotary kiln about its central axis and the fact that;

the vkiln is tilted' downwardlytoward the cooler.

A flow of highly heated strongly oxidizing gases/isefiected that is .countercurrent to the'movement,.of;the:

pellets through the third zone 3l.- Fuel and primary combustion air-delivered through the tubes 42, 43, con- 1- nected, to the burner will provide a flame extending into the rotary kiln. The quantity of air supplied-by the secondary r-blower- 51 forcountercurrent flow through the pellets in the cooler 50 will insure a sufficient excess of;

airbeing admitted to therrotary cooler to provide :the"

strong y idi i a d qu red by hi p o 1 taiiia flow of strongly oxidizing gases through thezones V It has been 1 determined thatfthese requirements can be met by. admitting sutiicient air through the cooler to provide in the kiln about SOfpercent'lrriore air th'an'that theoretically required 'to maintain the combustionof fuel. Ithas alsobeendeterminedthat optimum thermal efliciency for the; 1

'process will result trom providingl about 240 percent more air th'an th at required to maintain combustion of of treatrnent'established tojtreat the pellets.

thefuel'necesssafy to'create; the temperatures required to .in. h pr s-;

The temperature 'otthe"oxidizing gases required in thisprocessisdetermin'ed and controlled. by the amount of fuel burned and the arnountjoffair and the preheat temperatureof such air admittedto the rotarykiln. The

temperature of the oxidizing" gasesand the rate of movementlof the] body of 'pellet sv through the system is cor related. so'that the oxidizinggascs;whichat thedischarge of J-therotaryCkiln 32 are maintained at .about12450 'F., are. at thegr'ate'end offthefrotary kiln about 1800 E; As the'j'gases passinto the'second. zone .26 and down-. wardly'through the bediofrfpellet'sinto ,the second wind box 24f'sonLe'of the heat will'be transferred from the gases to the movin'g pellets. The depthiof the layer of'pelletson the grate. 13 and .the rate at 7,.whichthe pellets are moved through the second'zone will determine how much.

thei'pellets arej-heatfedin the second zone and how much l r'emain inthe gases that reach thesecond .wind

box; These factors are to befcontrolleduso ,thatthe gases delivered to the first zone 22 above the moving. grate will be at the order of 500 to 900 F. The temperature rangesreferred to in each of the three zones, the first two over'the moving grate and the third in the rotary kiln, have'been determined to be practical so that the rate of pelleti transfer through the three zones can -be' controlled inaccordaiicejwith the'objects of this invention. I With the temperatures of the order referred to thefrat'e of pellet transfer through the zones 22, 26,

31 can be controlled so that within. the first zone the; pelletswill be heated sufiiciently to driveofiz substantially all ofjthemoistur'e from the pelletsqand provide dry pellets f o'n treatirient in the second zone. 1 Additional heat is applied to the pellets within thesecond zone to preheat them 'and'initiateth'e conversion. of the magnctitein the pelletto -hematite...-As previously stated this is accomplished, byheatingthe-pellets in the highly oxidizing atmosphere to a temperature between approxi-' I mately1600 F. and 1800". F. Figs 2, -3,4 and 5 showthe; transformation that takes place within the pellets before they are discharged into the third zone 31 within the rotary kiln32. Fig; 2" shows a grain of what was magnetite as; it is changing to hematite. The white area is hematite, and the light, gray area magnetite. v The dark fgrayspots within thepellet shown in Fig.36 are." pa ti lesxqf silica which are slag'iorming'agents" and would; form a slag if they-were tocombine with mag netite; Howevenibefore the'pellet reachesa' tempera ox d z g oase te zt ey have passedough the tube 27 tojthehood21 defining.

fthe first. zone H over the moving grateLfFromfthe first zoriel22 the gaseswill be drawn downwardly, through thefpelle on thegrateintojthe first windbox 16 beneath ture which will allowthe Silica. to react with the magnetite, the magnetite willhaye,changedtojhematite. As the magnetite changes to hematite ihe. needles of j'her'natite.

that can be seen in Fig. 2 projectthemselves into the remaining areas of magnetitejas the conversion takes place. This figure also shows thebeginning ofgrain. gEowth and recrystallization of the pelletthat begins ltqform a network of bridged grains. Fig.v 3 which is) Slightly greater magnification than Fig.2 shows grains of the.

a pellet thathas completely convertedfrom magnetite to hematite. It can beseenjn this figure. thatvrecrystallization has taken place and i-graingrowthhas proceeded sufficiently to create a networkof joined-grains .,that can be seen in Figs. 4 and 5. Fig. 5 is similar to Fig. 4 but to greater magnification. The graingrowth and bridging of individual grains to initiate amnetwork of crystals shown in Figs. 2, 3; 4 and 5, will impart increased physical strength to the pellet in the range of from one to two hundred pounds. crushing. strength depending on the extent of the development of the network within the pellet. Pellets are therebyprovided having sufficient strength to withstand the .tumbling action in the, third zone 31 within the rotary kiln 32. At the temperature ranges established in thejfirst and second zones there will not be sufiicientsbridging of grains of the mineral constituents to cause-(separate pellets to stick together because of the. merely .slight amount of physical contact between the separate-pellets.

When the pellets are discharged from themoving grate 13 into the third zone 31 within the rotary kiln 32 they are burned to a temperature of about at least2200 F. but not morethan about 2450 F. As th'epellets are heated to this temperature range they are tumbled through the rotary kiln thus continually exposing new. surface areas-of the pellets to the hot gases withir'rthatzone and thereby producing a very uniformly burned-pellet.

During this stageof the heat treatment -of,,the -"pellet,

the tumbling pellets may pick up and forgelonto the pellet dust or fines.

The final burning that takes place in the. third. zone 31 within the rotary kiln 32' produces a pelletshown in Fig. 6. This figure shows how grain growth and recrystallization has proceeded to a pointwh'erea con tinuous network of hematite crystals exists. This con- As the pellets ;continne to tinuous network provides a pellet with greatly increased strength. This figure also shows a portion of silica embedded in the hematite network. The silica shown'in this figure has not become slagbut has remained as a dormant particle of silica within a surrounding body of hematite. If the temperature of the pellets inthe third zone within the rotary kiln is permitted to get above photograph it can be seen that the gray areas of the in dividual grains which are magnetite. arebeginning to reappear. Continued exposure to'temperature above approximately 2450 F. wouldcomplete, the conversion of hematite b ack' 'to magnetite and-result in the magnetite combining with silica to form slag. With the process controlled soj as to burn the pellets-to a temperature of 2200 tosapproximately 2450 F; but not ovser approxi mately-.;-24-50 F.'the pellet; shownrin-Fig. 6 -will be pro- 8 duced. This pellet has the desired strength to withstand handling, shippingand' charging to av smelting furnace. This pellet has been subjected to thetumbling testpreviously referred'to and iit has been determined that'this pelletwill'be so hard that it will not break as the result of the tumbling test and that fines produced by abrasion of one pellet on another will be reduced to. the order of one to live percent or an improvement of from 2 /2" to 15 times that which is produced by burning on a traveling grate alone or in a shaft type kiln.

From the foregoing it will be apparent to those skilled in, this art that the process described provides. a new and improved way. of producing pellets of concentrated iron ore for use ,in a blast furnace or other smelting apparatusandaccordingly accomplishes the objects of this invention. On the other hand, it will also be obvious to those, skilled in theartthat the processmaybe varied or modified without'necessarily departing from thespirit of the'invention' or sacrificing all of the advantages thereof. Accordingly; the disclosure herein is illustrative only, and the inventionis not limited thereto.

What is claimed is: i i

1. For making hard, unsintered, dense, discretehernatite pellets from finely divided iron ore, the process comprising: making individual green pellets of a preselected size out of said finely dividedore; forming said individual green pellets into a movable gas permeable .body with said pellets at rest relative to each other within said body; establishing at least first, second-and third gas confining zones; conveyingsaid'body of pellets through said first and second zones at a first 'preselected rate; discharging said body irom'said thirdl zone while simultaneously disrupting said body and imparting movement to said pellets relative to each other; tumbling said pellets through said third zone at a second'preselected lrate to maintain the-movement of said pellets relative to each other; efiecting a flow of highly heated gases containing a surplus of oxidant successively through vsaid third zone count'ercurrently to said movement of saidtumblingpellets therein, through said body in said second zone, and through said body in said first zone; and correlating the temperature of said heated gases simultaneously with'said preselected pellet size and said first preselected rate to transform said individual green pellets into dry, preheated discrete pellets containing hematite (as evidenced by the growth of individual grains of hematite intobridging relationship with adjacent grains-and a pellet strength capable of withstandingsaid tumbling) for discharge from said second zone to said third zone, and with said preselected pellet size and said secondpreselected rate to transform said dry, preheated discrete ,pellets containinghernatite into hard, unsintered discrete pellets, each. having a continuous network of bridged hematite there-v through.

2. For making hard, unsintered, dense, discrete hematite. pellets from finely divided iron ore, the process comprising: making individual green pellets of a preselected size out of said finely divided ore; forming said-individual green pellets into a .movable gas permeable: body with said pellets stationary relative to each otherwithin said body; establishing at least first, second and third gas confining zones; conveying said body of pellets through said first and second zones at a first preselected rate; dis: charging said body from said second zone to said third' zone while simultaneously disrupting said body'and' imparting free movement to said pellets relative to each other; tumbling said pellets through said third zoneat a second preselected rate to maintain the free movement of said pellets relative to each other; effecting allow" ofhighly heated oxidizing gases counter-currently to saidmovement of said pellets successively through said free moving pellets in said third zone; through said "body of saidrelativelystationary pellets in said second zone,- and through said body of said-relatively stationary pellets" in said-first zone, and the temperature-of "said heated oxidizing gases being correlated simultaneously with said preselected pellet size andsaid-first preselectedrate to transform said individual green pellets into dry, preheated discrete pellets containing hematite (as evidenced by the growth-of individual grains o-fhematite into bridging relationship with adjacent grains and a pelletstrength capable of withstanding said tumbling) fordischarge'from said secondzone to said third zone, and with said preselected pellet size and said second preselected rate to transform said dry, preheated discrete pellets containing hematite into hard, unsintered discrete pellets, each having a continuous network of bridged hematite therethrough.

. 3. Formaking hard, unsintered, dense, discrete hematite pellets from finely diided iron ore, the process comprising: making individual green pellets of apreselected size. out of said finely divided ore; forming said individual green pellets into a movable gas permeable body with said pellets at rest relative to each other within said body; establishing at, least first, second and third gas confining zones; conveying said body of pellets through said first and second zones at a first preselected rate; discharging said body from said second zone to said third zone while simultaneously disrupting said body and imparting movement' to said pellets relative to each other; tumbling said pellets through said third zone at a second preselected rate to maintain the movement of said pellets relative to eachother; burning fuel to provide a flame; supplying saidfiame with oxygen of 50 to 240 percent in excess of the oxygen required to support the combustion of said fuel to provide. a supply of highly heated strongly oxidizing gases; effecting a.,fiow of said highly heated strongly oxidizing gases from said supply successively through said third zone countercurrently to said movement of said tumbling pellets therein, through said body in 'said second zone, and through said body in said first zone, said gases being at a temperature with respect to said preselected pellet size and said first preselected rate to transform said individual green pellets into dry, preheated discrete pellets containing hematite (as evidenced by the growth of individual grains of hematite into bridg-. ing relationship with adjacent grains and a pellet strength capable of withstanding said tumbling) for discharge from said second zone to said third zone, and said gases being me temperature with respect to said preselected pellet size and said second preselected rate to transform said: dry, preheated discrete pellets containing hematite into hard, unsintered discrete pellets, each having a continuous network of bridged hematite therethrough.

' 4. For makinghard, unsintered, dense, discretehematite pellets from finely divided iron ore, the process comprising: making individual green pellets of a preselected size, out of said, finely divided ore; forming said individual green pellets into a movable gas permeable,

body withsaid pellets at rest relative to each other within said body; establishing at least first, secondv and third gas confining zones; etfecting aflow of highly heated oxidizing gases successively through said third, said second and said first zones; conveying said body pf pellets through said first and second zones at a first preselected rate while simultaneously passing said heated gases through said body in said second and first zones until said individual green pellets are transformed into dry; preheated discrete pellets containing hematite (as evidenced by the growth of individual grains of hematite into'bridging relationship with adjacent grains and a pellet strength capable of withstanding the forging action of impact during tumbling); discharging said body of dry, preheated discrete pellets from said second zone to said third zone while simultaneously disrupting said body into a plurality of discrete pellets and fines movable relative -to each other and tumbling said pellets through said third zone at a second preselected rate to maintain the movement of said pellets and said fines relative to each other and to promote collision impact therebetween to forge said fines to said pellets while passing aeaaase 10 said heated gases countercurrentlyto said movement of said tumbling forging pellets therein until said dry, preheated discrete; pellets and fines containing hematite are transformed into hard, unsintered discrete pellets vwith substantially no fines, each of said pellets having a continuous network of bridged hematite therethrough.

5. For. making hard, unsintered, dense, discrete hematite pellets from finely divided iron ore, the process comprising: making individual green pellets of said finely divided ore; forming said individual green pellets into a-movable gas permeable body with said pellets at rest relative to' each other within said body; establishing first, second and ,third zones: conveying said body of pellets through said first and second zones; disrupting said body of pellets and tumbling said pellets through said-third zone; effecting a flow of heated oxidizing gases successively through said third, second and first zones, the temperature in each of said zones being main-J tained below ,thesintering temperature of said ore; maintaining said body of pellets in said second zone until said pellets are dry, preheated, and have individual grains of hematite within, each pellet, which have commenced to grow into bridging relationship with adjacent grains of hematite; then, before said grain growth becomes a continuous network therethrough, discharging said pellets into said third zone; and continuing said tumbling of said pellets in said third zone until said grain growth becomes a continuous completed network of bridged grains of hematite in each of said pellets.

6. For, making hard, unsintered, dense, discretehema tite pellets from finely divided iron ore, the process comprising: making individual green pellets of said finely divided ore; forming said individual green'pellets into va movable gas permeable body with said pellets at rest relative to each other within said body; establishing first, second and third zones; conveying said body of pellets throughvsaid first and second zones; disrupting said body of pellets and tumbling said pellets through said third zone; effecting a fiow of heated oxidizing gases successively through said pellets in said third zone and through said body in said second and first zones to heat said pellets and said body while maintaining their respective-temperatures below the sintering temperature of said ore; maintaining said body of pellets in said secondzone until said pellets are dry, preheated, and

have individual grains of hematite within each pellet, which have commenced to grow into bridging relationship with adjacent grains of hematite; then, before said grain growth becomes a continuous network'therethrough, discharging said: pellets intosaid-third zone; and continuing said tumblingof said pellets in said third zone to complete growth of hematite grains and recrystallization thereof untilsaid grain growth becomes a continuous completednetwork of bridged hematite crystals throughout each of said pellets.

:7. For making'hard, unsintered, dense, discrete hematite pellets from finely divided iron ore, the process comprising: making individual green pellets of said finely divided ore; forming said individual green pellets into a movable gas permeable body with said pellets'at rest relative to each other within said body; establishing first, second and third zones; conveying said body of pellets through said first and second zones; disrupting said body of pellets and tumbling said pellets through 7 of hematite within each pellet, which have commenced to grow into bridging relationship with adjacent grains of hematite; then, before said grain growth becomes a continuous network therethrough, discharging said pellets into said third zone; and continuing said tumbling of said pellets in said third zone until said grain growth becomes a continuous completed network of bridged grains of hematite in each of said pellets.

8. For making hard, unsintered, dense, discrete hematite pellets from finely divided iron ore, the process comprising: making individual green pellets of said finely divided ore; forming said individual green pellets into a movable gas permeable body with said pellets at rest relative to each other within said body; establishing first, second and third zones; conveying said bodyof pellets through said first and second zones; disrupting said body of pellets and tumbling said pellets through said third zone; efiecting a flow of heated oxidizing gases successively through said third, second and first Zones; maintaining said body of pellets in said second zone at-a temperature of approximately 1600 F. to 1800 F. until said pellets are dry, preheated, and have individual grains of hematite within each pellet, which have commenced to grow into bridging relationship with adjacent grains of hematite; then, before said grain growth becomes a continuous network therethrough, discharging said pellets into said third zone; and continuing said tumbling of said pellets in said third zone at a temperature beneath the fusion temperature of said iron ore, said temperature being from about 2200 F. to about 2450 F., until said grain growth becomes a continuous completed network of bridged grains of hematite in each of said pellets.

9. A process for making hard, unsintered, separate pellets from finely divided magnetite iron ore, said process comprising the steps of making green pellets of said finely divided ore, forming said pellets into a movable body with individual pellets at rest within said body, drying said pellets in said body by heating them to drive ofi moisture, then preheating said pellets in said body and oxidizing said magnetite to hematite to cause individual grains of hematite to bridge together by grain growth but without slag formation; then, before said grain growth becomes a continuous network therethrough, tumbling and heating said tumbling pellets in an oxidizing atmosphere to complete growth of hematite grains and recrystallization thereof to provide a continuous network of bridged hematite crystals throughout each pellet without formation of slag while maintaining the temperature of said pellets below the sintering temperature of said ore.

10. A process for making hard, unsintered, separate pellets from finely divided magnetite iron ore, said process comprising the steps of making green pellets of said finely divided ore, forming said pellets into a movable body with individual pellets at rest within said body, drying said pellets by heating them to drive ofi moisture, then preheating said pellets in said body and 12 oxidizing said magnetite to hematite by raising the temperature of said pellets in a'highly oxidizing atmosphere to 1600 to 1800 F. to cause individual grains of hematite to commence to grow into bridging relationship with adjacent grains of hematite; then, before said grain growth becomes a continuous network therethrough, tumbling and heating said tumbling pellets until said grain growth becomes a continuous network of bridged hematite crystals in each of said pellets without the formation of slag, said heating of said tumbling pellets being in an oxidizing atmosphere having a maximum temperature of 2200 F. to 2450 F.

11. For making hard, unsintered, dense, discrete hematite pellets from finely divided iron ore containing magi netite, the process comprising: making individualvgreen pellets of said finely divided ore; forming said individual green pellets into a movable gas permeable body. with said pellets at rest relative to each other within said body; establishing first, second and third zones; conveying said body'of pellets through said first and second zones; disrupting said body of pellets and tumbling said pellets through said third zone; burning fuel to pro+ vide a flame; supplying oxygenvto said flame in excess of requirements for combustion of said fuel to provide a supply of heated oxidizing gases; efiecting a flow of said heated oxidizing gases successively through said pellets in said third zone and transversely through said body in said second and first zones; maintaining said body of pellets in said second zone at a temperature of approximately 1600 to 1800 F. untilsaid pellets are dry, preheated, and have individual grains of hematite within each pellet, which have commenced to grow into bridging relationship with adjacent grains of hematite; then, before said grain growth becomes a continuous network therethrough, discharging said pellets into said third zone; and continuing said tumblingof said pellets in said third zone at a temperature beneath the fusion temperature of said iron ore, said temperature being from about 2200" F. to about 2450 F., until said grain growth becomes a continuous completed network of bridged grains of hematite in each of said pellets.

References Cited in the file of this patent UNITED STATES PATENTS 1,153,203 Drefahl Sept. 14, 1915 2,590,090 De Vaney Mar. 25, 1952 2,750,272 Lellep June 12, 1956 2,766,109 Komarek et al Oct. 9, 1956 OTHER REFERENCES Mining Engineer (1), December 1952, pp. 1223 1230.

Mining Engineering (2), November 1952, pp. 1053- 1058.

Blast Furnace and Steel Plant, July 1955, pp. 745-752.

UNITED STATES PA ENT oFFIcE CERTIFICATE OF CORRECTION Patent No 2 925-,536 February 16, 1960 William F. StoWasser Jr.

It is hereby certified that error appears in the-printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 8, line .32 after "said", second 0ccurrence,-. insert second zone to said column 9, line 14,. for "diided" read divided column 10,- line 13 for "zones'fi read zones; o

.Signed and sealed this 9thday of August 1960.

(SEAL) Attest:

KARL H; AXLINE Attesting Officer ROBERT C. WATSON Commissioner of Patents 7' 7 Q i

Claims (1)

1. FOR MAKING HARD, UNSINTERED, DENSE, DISCRETE HEMATITE PELLETS FROM FINELY DIVIDED IRON ORE, THE PROCESS COMPRISING: MAKING INDIVIDUAL GREEN PELLETS OF A PRESELECTED SIZE OUT OF SAID FINELY DIVIDED ORE, FORMING SAID INDIVIDUAL GREEN PELLETS INTO A MOVABLE GAS PERMEABLE BODY WITH SAID PELLETS AT REST RELATIVE TO EACH OTHER WITHIN SAID BODY, ESTABLISHING AT LEAST FIRST, SECOND AND THIRD GAS CONFINING ZONES, CONVEYING SAID BODY OF PELLETS THROUGH SAID FIRST AND SECOND ZONES AT A FIRST PRESELECTED RATE, DISCHARGING SAID BODY FROM SAID THIRD ZONE WHILE SIMULTANEOUSLY DISRUPTING SAID BODY AND IMPARTING MOVEMENT TO SAID PELLETS RELATIVE TO EACH OTHER, TUMBLING SAID PELLETS THROUGH SAID THIRD ZONE AT A SECOND PRESELECTED RATE TO MAINTAIN THE MOVEMENT OF SAID PELLETS RELATIVE TO EACH OTHER, EFFECTING A FLOW OF HIGHLY HEATED GASES CONTAINING A SURPLUS OF OXIDANT SUCCESSIVELY THROUGH SAID THIRD ZONE COUNTERCURRENTLY TO SAID MOVEMENT OF SAID TUMBLING PELLETS THEREIN, THROUGH SAID BODY IN SAID SECOND ZONE, AND THROUGH SAID BODY IN SAID FIRST ZONE, AND CORRELATING THE TEMPERATURE OF SAID HEATED GASES SIMULTANEOUSLY WITH SAID PRESELECTED PELLET SIZE AND SAID FIRST PRESELECTED RATE TO TRANSFORM SAID INDIVIDUAL GREEN PELLETS INTO DRY, PREHEATED DISCRETE PELLETS CONTAINING HEMATITE (AS EVIDENCED BY THE GROWTH OF INDIVIDUAL GRAINS OF HEMATITE INTO BRIDGING RELATIONSHIP WITH ADJACENT GRAINS AND A PELLET STRENGTH CAPABLE OF WITHSTANDING SAID TUMBLING) FOR DISCHARGE FROM SAID SECOND ZONE TO SAID THIRD ZONE, AND WITH SAID PRESELECTED PELLET SIZE AND SAID SECOND PRESELECTED RATE TO TRANSFORM SAID DRY, PREHEATED DISCRETE PELLETS CONTAINING HEMATITE INTO HARD, UNSINTERED DISCRETE PELLETS, EACH HAVING A CONTINUOUS NETWORK OF BRIDGED HEMATITE THERETHROUGH.

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