US2799573A - Method of sintering ores - Google Patents

Description

July 16, 1957 Filed April 7, 1953 4 Sheets-Sheet. 1

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S/N TER/NG Macy/N5 SCREEN F//VE S July 16 1957 J. c. BARNET-r ETAL 2,799,573

METHOD oF SINTERING oREs Y Filed April 7, 195s 4 sheets-sheet 3 July 16, 1957 J. c. BARNETT Erm. 2,799,573

METHOD OF SINTERING ORES Filed 'April 7, 1955 4 Sheets-Sheet 4 /0 /z /4 /6 /a za Z2 96 czwr F550 /va/srz/Ff.

United States 2,799,573 METHOD oF SINTERING onus James C. Barnett, Dayton, l1io, and James D. Barnllill, Columbia, Tenu., assignors to Monsanto Chemical Company, St. Louis, Mo., a corporation of Delaware Application April 7, 1953, Serial No. 347,372

6 Claims. (Cl. 75--5) phosphate ores by blast roasting on a vDwight `and Lloyd sintering machine.

An object of the invention is to provide .an improved method of sintering which results in a substantial in-v crease in sinter production and a substantial improve- 4ment in sinter quality as compared to prior art methods of sintering.

Another object of the invention is to Provide an imfines, have heretofore been mixed simultaneously, resulting in a sinter feed which possesses a rather'low burning rate, thus limiting the production obtainable from the machine. In addition, this procedure has Vsuffered from excessively high maintenance on the mixing device `since the recycle material is very abrasive.

We have made the surprising discovery that the ilimita- Ations encountered in ythe aforesaid method of sintering ores, and particularly phosphate ores, are overcome by Ithe novel procedure hereinafter described. In accordance with this procedure, finely divided ore, a carbonaceous fuel and water are first intimately and uniformly mixed together Vin a pug millor another suitable mixing device. Then at, or substantially at, the end of the mixing or pugging operation, recycle fines from a prior sintering operation are thoroughly blended with the mixture of ore, fuel vand water. After completing this operation, the

v resulting feed'ischarged to the sintering machine and proved sintering method in which higher sinter yields are' obtained when using the optimum amount of water in the Ysinter feed rthan has been heretofore possible vby the methods of the prior art.

An additional object of the invention is to provide an improved -sintering method :in which the maximum Eproduction previously obtainable by prior art methods is now obtainable by `using a sinter feed having a much wider range of water content.

An additional object of the invention is to provide an improped sintering method which permits burning tof isubstantially deeper sinter beds and thereby increases the productive capacity of the sinter machine.

A further object of the invention is -to providean im' proved method of sintcring involving the use of a sinter feed which permits higher gas flow through the bed and thus an increased flame propagation -rate with a correspondingly higher production rate and ywithout anii-ncrease in windbox suction. v

Afstill further objectlof the invention is to provide au improved method of sintering ywhich involves the; use of a sinter feed having improved heat transfer charaeteristi-cs during sintering and which resultsin decreased wear on the mixer'during the mixingoperation. I

Other objects and advantages will become apparent to those skilled in the art as the description-,of theinventiori proceeds. 7

in the sintering of ores on a Dwight and Lloyd. or equivalent sintering machine, a mix-ture ofore, carbonaceous fuel, water and recycle material from ,the prior .operation of the machine is charged onto a moving grate and :ignited by a ame vwhile air is drawn downwardly Ithrough the grate into wind boxes whichare connected to asouree of reduced pressure. wardly through the material :on the grate and thus combustionis propagated down ythrough this material. Once the bed is ignited, the ignition flame is removed. and the fuel content lofythe bed continues to burn as additional air is forced through `the bed. .The heat from such combustion causes the' :fine ore to sinter together and form a porous aggregate.

In ,the sintering-of ores on a machine of this type, it

has been the practice to use a sinter feed prepared byy mixing 'together finely ,divided ore, coke or other :carbonaceous fuel, a relatively small pr oportion of Vrecycle fines and water. These materials, including the recycle This serves to force the air downsubjected to sintering in the usual manner. The sintered product is then crushed between rolls, on a metal bar grizzly screen or another suitable crushing device and screened to separate the fines from the oversize material Awhich Ais the desired product. The fines thus obtained are recycled and used inthe manner previously described in the production of kfurther quantities of sintered product.

For a more complete understanding of the instant invention, reference is made to the accompanying drawings and the illustrative example hereinafter presented.

'Figure l illustrates a ow sheet ofthe improved method of sinteringof the instant invention.

.As a modification of the method illustrated in Figure 1, the sintered product from the crushing rolls is passed through a `two-inch grizzly screen to separate a +2 material as sintered product and a 2" undersized material. This undersized material is treated on a Vibrating screen yand separated into three fractions, namely, a -2/-{% sintered Vproduct which is mixed with the +2 material, a -1'-8mesh material (recycle fines) and a .-8-mesh product (dust) which is incorporated with the finely divided ore, carbonaceous fuel and water and charged to the pug mill or another suitable mixing device. The -recycleliines are returned to the process in the manner shown inthe flow sheet.

"Figure 2 graphically illustrates phosphate sinter production as a' function of feed moisture when varied amounts ofrecycle fines were admixed with the sinter feed before and after pugging.

As indicated in Figure 2, curves A, B and C demonstrate the effect of feed moisture on phosphate sinter production when 0%, 10% and 20% by weight of recycle fines were'pugged in feed, whereas curves B and C' show the effect of feed moisture when 10% and 20% by weight of recycle fines were added after pugging the feed.

Figure 3 graphically illustrates in curves F, Fand G, G phosphate sinter production as a function of feed moisture when 420% ,fines were admixed with different types of sinter feeds before and after pugging.

figure -4 graphically illustrates in curves D, D and E E phosphate sinter production as a function of feed moisture and bed depth when the recycle lines were admixed with a typical sinter feed before and after puggingvThe description fof a typical method and apparatus used in practicing the instant invention will now be given.

.The apparatus used in practicing this invention consisted essentially of a laboratory pug mill and a sinter pot pilot plant.

The pug -millhad a 24-inch diameter shell which was 32 inches long and rotated at 9.1 R. P. M. Inside this Shell .there was an .eccentrically mounted shaft containing four rows of S-inch cutter blades (12 blades per 2,799,573 e N p e row) which rotated at a speed of 177 R. P. M. and in an opposite direction from the shell.

The sinter pot pilot plant consisted of an 18-inch x l8-inch pot, which was l1 inches in depth and whose sides tapered downward to a l41/z-inrch x 14Vzinch grate. Underneath the grate there was provided a 12- inch wind box with a 4-inch exhaust main about which the pot was pivoted so that it could be inverted to dump the charge. A blower fan was employed to draw air through the wind box at a rate which was measured by an orifice and controlled by an externally located control valve. Above the sinter pot there was a retractable ignition hood which was fired by a propane-air mixture.

The sinter feeds were prepared from stocks ofV sinter grade phosphate matrix, phosphate concentrates, recycle fines, recycle dust and anthracite dust. They were all prepared in the same manner except in those instances where the fines were withheld from the pug mill and mixed with the feed after the pugging operation. In these cases, the fines were mixed with the pugged feed by pouring the two through a l-inch sample splitter, simultaneously. After the first split the two halves were vsimultaneously poured into a large pan and then poured back through the splitter and combined again.

The two types of sinter feeds were charged to the sinter pot pilot plant in exactly the same manner, that is, sixty pounds of the wet feed, except in those runs using sinter beds of varying depths, was charged into the sinter pot in such a manner as to provide a bed depth of about 6% inches. After a layer of coke fines had been sprinkled over the top of the charge to assure its complete ignition, a reduced pressure of 8 inches of water was produced in the wind box by opening the air flow control valve. The gas flow rate at this standard 8-inch suction was used as a criterion of the beds initial po- Table I Sinter Feed Anal- Gas Flow (Standard ysis Cu. Ft. Per Min.) Percent lbs. +8M Sinter -8-Mesh Min-Ft.2 Cake, After Grate Comments H20, per- C, per- Average lbs. Crushing Area cent cent 8 H2O After Ignition 42 gg 0% Fines Pugged In Feed, 70 30-70 Ratio.

10% Fines Pugged In Feed,

30-70 Ratio.

10% Fines Added After Pugging Feed, 30-70 Ratio.

% Fines Pugged In Feed,

-70 Ratio.

20% Fines Added After Pngging Feed, 30-70 Ratio.

20% FinesPugged I n Feed,

0-100 Ratio.

20% Fines Added After Pngging Feed, 0100 Ratio.

20% Fines Pugged In Feed,

-50 Ratio.

20% Fines Added After Pngging Feed, 50-50 Ratio.

20% Fines Pugged In Feed, 30-70 Ratio, 72 lbs. Charge, B-Inch Bed.

20% Fines Added After comoccolenenooooocnoenooenoocenocnoooenoomenocenmmcxcoccnonwoocenmcnomoxoo 'armas-vs Yro'sity. At this point the ignition hood was :placed over the sinter pot and the wind box control valve opened further to allow the full application of reduced pressure.

The sinter bed was ignited for 40 .seconds using a n flame temperature vof about 1350 C., whereupon the ignition hood was removed. In exactly 5 minutes after vignition commenced, the blower fan was .cut off. During this period, the gas fiow rate, the wind'box suction 'and the wind box temperature were measured at one minute intervals. The sinter pot was then inverted and the cake dumped into a heavy metal pan. After the recovered charge had been weighed, the sinter cake was scraped free of all non-sintered material and weighed. When the sinter cake had cooled, it was crushed in a ,l-inch roll crusher (7/s inch roll spacing). The crushed fragments were screened through 3/s-incll and 8-mesh screens, the percentage of -S-mesh material being used as'a Acriterion of sinter quality.

The instant invention is further illustrated by .the following 'specific example which clearly demonstrates the advantages obtained by admixing recycle fines with the sinter feed after pugging. In this example, the sintering operation was carried out in the manner described above, using a sinter feed containing 0%, 10% and 20% by weight (dry basis) of recycle fines.

The properties of the sinter feed and sinter bed, the amount of carbon used and the quantity of sinter produced `are given in Table I.

The expression ratio as used in ythis table has reference 4to the weight ratio vof thephosphate sinterlgrade matrix to phosphate concentrates. f

All feeds had same weight of fuel vadded except those used for `deeper bed depths wherefuel was proportionately increased. Variations `in carbon content shown in the above table are due to experimental and analytical error.

The results recorded in this table are graphically illustrated in Figures 2, 3 and 4 of the accompanying drawings. From these figures, it will be observed that, regardless of the moisture content of the sinter feed, the amount of fines and the feed 'proportions used, or the bed depth, the sinter production was consistently increased when the recycle fines were added after the pugging operation.

In the practice of the instant invention, the recycle fines, i. e., the -%/|8mesh materials, are employed in an amount varying from about 5% to about 25% by weight of the sinter bed or, more specifically, from about to about 20% by weight and within these limits about by weight is preferred.

The fuel content of the sinter bed varies with the ore being sintered, but in general it falls within the range of about 2% to about 15 or, more specifically, in the range of about 7% to about 12% by Weight of the bed.

More particularly, in the sintering of phosphate ores, the practice is to use a fuel content of about 6% to about 12% or, more specifically, about 7% to about 8% by weight of the bed.

Illustrative examples of fuels which may be used in the practice of the instant invention are coke, coal, peat, charcoal, hydrocarbons and other carbon-containing fuels.

The amount of water used in preparing the sinter feed may vary within the range of about 5% to about 21% by weight or, more specifically, within the range of about 16% to about 20% by weight of the sinter bed. Within the above range, a sinter feed moisture content of about 18.5% by weight is preferred.

The optimum percentages and percentage ranges stated above apply to phosphate sintering and it is to be understood that these variables will vary with the ore being sintered. Suffice it to say that they may be readily determined in each case by those skilled in the art and so no attempt Will be made to state them here.

The admixing of the recycle fines with the sinter feed 6 substantially Yat the 'end of or 'after the pugging opera- "tion, instead of before or during the principal portion lof the pugging operation leads to a number of highly advantageous results.

For example, when using an optimum feed moisture of about "18.5%, the maximum yield of sintered product obtained by the method of the instant invention is invariably higher than that obtainable by the prior art method in which the recycle fines are pugged in the feed. lThis fact is clearly demonstrated by the accompanying graphs and also by the following typical experimental results.

Fines Pugged Fines Added Optimum I nSinter AfterPuggng Type of Sinter Feed (Matrix. Feed Feed, Sinter Feed,

to Concentrate Ratio) .Moisture Sintered Sintered Percent Product Product Produced, Produced,

bs. Lbs.

0-100 feed ratio 18. 5 29. 8 32.2 i30470 feed ratioA 1s. 5 31.8 33. 3 fso-soteed'ratim 18.5 30. 8 33. 5

y"Moreover, .by the method of the instant invention, the maximum-sinter production achieved by the prior art .methods at Jan optimum feed moisture of 18.5% may be obtained .by .the present invention over a wider range :of :sinter feed moisture content. As evidence of this .fact, reference is made to the following typical experimental data.

Feed Moisture Feed Moisture Resulting In Resulting In Typeof Sinter Feed (Matrixto Con Maximum Sin- Equivalent centrate Ratio) ter Production Maximum Sin- By Prior Art 'ter Production Methods By Method Of Instant Invention Percent Percent 18. 5 16. 6-20. 2 18. 5 16. 8-20. 0 50-50 feed ratio. 18. 5 16A-.19.4

In view of the normal fluctuations which occur in the sinter feed moisture, the widening of the effective feed moisture range has the desirable effect of increasing sinter production and facilitating the control over the sintering operation.

In addition, the method of the instant invention makes passible the use of deeper sinter beds because of the higher sintering rate which may be employed. This burning of deeper beds not only. results in increasing the productive capacity of the sinter machine but lowers the percentage of recycle to the machine. The reason for this is that thick sinter cakes have less abrasive surface and therefore yield less dust and fines. Thus, the addition of fines after pugging in accordance with this invention provides increased sinter production and better sinter quality.

Furthermore, the recycle fines retain their jagged edges when they are admixed after pugging; Whereas, when they are pugged with the otherrcomponents of the feed, they are coated with mud and converted into round, wet pellets which have poor heat transfer properties.

Also, the recycle fines are very abrasive and cause excessive wear and tear on the cutter blades of the pug mill when they are pugged in the sinter feed. In contrast thereto, the addition of the recycle fines to the sinter feed at, or substantially at, the end of the pugging operation results in a substantial reduction in the cost of maintaining the cutter blades.

What is claimed is:

1. The method of sintering ores, which comprises intimately mixing together finely divided ore, fuel and water, blending with said mixture recycle fines from a previous sintering operation and then subjecting the `blended product to blast roasting at atemperature sucient to eiect agglomeration of said ore; said nes, said fuel and said water respectively constituting about to about 25%, about 2% to about 15%, and about 5% to about 21%, by weight of said blended product, and said blending step being carried out substantially at the end of said mixing operation.

2. The method of sintering ores, which comprises intimately mixing together iin-ely divided ore,vfue1 and Water, blending with said mixture recycle fines from a previous sintering operation and then subjecting the blended product to blast roasting at a temperature sutlicient to effect agglomeration of said ore; said lines, said fuel and said Water respectively constituting about to about 20%, about 7% to about 12%, and about 16% to about 20%, by weight of said blended product, and said blending step being carried out at the end of said mixing operation.

3. The method of sintering phosphate ores, which comprises intimately mixing together nely divided phosphate ore, a carbonaceous fuel and water, blending with said mixture recycle lines from a previous phosphate sintering operation and then subjecting the blended product to blast roasting at a temperature suicient to eiect agglomeration of said ore; said fines, said fuel and said water respectively constituting about 10% to about 20%, about 7% to about 12%, and about 16% to about 20%, by Weight of said blended product, and said blending step being carried out substantially at the end of said mixing operation.

4. The method of sintering phosphate ores, which comprises intimately mixing together in a pug mill finely divided phosphate ore, carbon and Water, blending with said mixture recycle nes from a previous phosphate sintering operation and then subjecting the blended product to blast roasting at a temperature sufficient to effect agglomeration of said ore; said tines, said fuel and said water respectively constituting about 10% to about 20%, about 7% to about 8%, and about 16% to about 20%, by weight of said blended product, and said blending step being carried out at the end of said mixing operation.

5.-The method of sintering-phosphate ores, which comprises intimately mixing together in a pug mill finely divided phosphate ore, coke and water, blending with saidmixture recycle fines from a previous phosphate fsintering operation and then subjecting the blended product to blast roasting at a temperature sufficient toeect agglomeration of said ore; said tines, said coke and said water respectively constituting 15%, about 7% to about 8%, and about 18.5%, by weight of said blended product, and said blending step being carried out at the end of said mixing operation.

6. In the method of sintering phosphate ores, which comprises intimately mixing together sinter feed components comprising finely divided phosphate ore, carbonaceous fuel and Water, and then subjecting the resulting product to blast roasting at a temperature sutiicient to elect agglomeration lof said ore, the improvement which comprises blending recycle lines from a previous phosphate sintering operation with said mixture; said lines, said fuel and said water respectively constituting about 10% to about 20%, about 7% to about 12%, and about 16% to about 20%, by weight of said blended product, and said blending step being carried out substantially at the end of said mixing operation.

References Cited in the le of this patent UNITED STATES PATENTS McAfee June 3, 1919 1,444,955 Davis Feb. 13, 1923 2,052,329 Wendeborn Aug. 25, 1936 2,343,270 Agnew Mar. 7, 1944 2,412,104 Stewart Dec. 3, 1946 2,533,142 rRoyster Dec. 5, 1950 FOREIGN PATENTS Great Britain Feb. 26, 1925 OTHER REFERENCES Min-

Claims (1)

1. THE METTHOD OF SINTERING ORES, WHICH COMPRISES INTIMATELY MIXING TOGETHER FINELY DIVIDED ORE, FUEL AND WATER, BLENDING WITH SAID MIXTURE RECYCLE FINES FROM A PREVIOUS SINTERING OPERATION AND THEN SUBJECTING THE BLENDED PRODUCT TO BLAST ROASTING AT A TEMPERATURE SUFFICIENT TO EFFECT AGGLOMERATION OF SAID ORE; SAID FINES, SAID FUEL AND SAID WATER RESPECTIVELY CONSTITUTING ABOUT 5% TO ABOUT 25%, ABOUT 2% TO ABOUT 15%, AND ABOUT 5% TO ABOUT 21%, BY WEIGHT OF SAID BLENDED PRODUCT, AND

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