proceeding of the fertilizer industry round table

8/13/2019 Proceeding of the Fertilizer Industry Round Table

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PRO EEDINGS OF TH

FERTILIZER INDUSTRYROUND T BLE

Granulation nd mmoniation

Held October 11-12 1955Washington D C


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Industry Fertilizer Round TableV I N C E N T SAUCHELLI chairmanII L MARSHALL secretary

o port of these proceedings is to be reprintedwithout the permission of authors or

Industry Publications Inc.

Articles reprinted from the January, February, March and April 19 )6issues o ACRICULTCRAL CHEMICALS.


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THE SWIFT PROCESSof

GR NUL TION11 1 . C. 41

Blaw Knox Co.Chemical Plants Division

HIS paper describes a systemof producing granular mixedfertili4er. The process differs in

many important characteri6tics fromthose with which most manufac'turers are familiar. The process wasdeveloped by Swift Co. and isnow used by it to produce both semi,granular and granular fertili4er.maw,Knox Co . Chemical Plants Di,vision, has been licensed by Swiftt de5ign, fabricate, and erect equip'ment to produce fertili4er by thisprocess, and Blaw,Knox is the licensing agent.

The research laboratories ofSwift (1 CO. 5 Plant Food Divisionseveral years ago* embarked on aprogram of research with the objective of developing a process andequipment with the following char,acteristics:

A. High rate of production.B. Low investment cost.C. Low labor cost.D. Low raw material cost.E. Production of high analysisgrades.F. Complete flexibility in the use of

liquid and gaseous raw materialsinterchangeably with solid rawmaterials.

G. Use of the heat of reaction toproduce a dry product.

In January 1950 application was made, byCharles Davenport and Walter Horn. for apatent covering the continuous process whichwas developed. and in November 1952. U. S.Patent No. 2.618.5417 was granted. Theprocess is now in operation at a number ofSwift's Plant Food Factories' and more unitsare currently being installed.

H. Virtually complete elimination ofnitrogen loss from gaseous am'monia or liquid nitrogen solu,tions.

I. Improved mechanical conditionof the product.J. Granulation of high nitrogengrades without drying.

Process And EquipmentT HE Swift granulation proce s isadaptable to operation with abatch weighing system. This in'volves batch weighing, screening, andpre-mixing of the s::lid raw ma'terials, and is the manner in whichthe process has been operated. Solidraw materials may also be suppliedby continuous weighing, whichwould eliminate the need for premixing. With the batch weighingsystem illustrated, dry materials areweighed and discharged to a batchhopper on a definite time cycle. Thishopper feeds the two ton batch mixeron the same cycle, and each batchis discharged to the surge hopper.The feed screw to the Swift reactori equipped with a variable speeddrive. The feed screw speed is ad,justed so that the pre mixed ma'terial level in the surge hopper ismaintained within minimum andmaximum limits. In this way, the rateis controlled by the frequency of thepreparation of batches, and a can'stant flow of pre,mixed dry materialsis maintained to the reactor.

Liquid raw materials are supplied by pumping or by pressuri4edstorage tanks, and are fed to thereactOr through individual rotameters. The reactor is vented througha vapor stack, and the product discharged to storage or to drying, depending on the type of product beingmade.

The reactor is a rotating shell,38 feet long by 5 z feet in diameter,set on a 3.75 0 slope (pitch of 13/16inch/foot). The speed of rotation is5.5 rpm. The first 5 foot section ofthe tube is equipped with spiralflights, which move the dry materialrapidly into the lifting flight 2;One.The lifting flights are 24 long by8 deep, and 12 are spaced aroundthe inside circumference. The flightpattern is repeated at a 13 0 staggerto within '5 feet of the tube outlet.

The liquid feed dischargesthrough noz;z;les directed toward theshowering material, in the fir t 10feet of the reactOr. Hammers areprovided to insure that no materialsticks to the shell. Vapor is ventedfrom the hooded discharge end bymeans of a gravity stack through theroof. Vapor tightness at the inlet endof the reactOr is accomplished byoverlapping the head ring with a:>tationary head sheet.

When sulfuric or phosphoricacid is reacted with ammonia in mix,ing fertili4er, a large volume ofsteam is developed. In a batch mixer,the escaping steam carries with itmuch of the unreacted ammoniavapor, resulting in substantial lossesof nitrogen and local nuisance effects.In the Swift Process, ammonia thatdoes not react in the feed z;one travelsthe entire length of the reactorthrough a continuous curtain of falling olids, resulting in practicallycomplete absorption of ammonia bythe time the vapors reach the exitof the unit. Reaction of ammoniawith superphosphates is promoted bythe presence of water, and it is believed that the presence of watervapor is a factor in the high absorp'tion efficiency. The spray methodof feeding liquid5 into the so:ids permits the evaporation of large quanti,ties of water, and the obtaining ofa solids outlet temperature of from


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200,250 F through use of rawmaterials, which develop a high heatof reaction. This results in a muchdrier product at the discharge of thereactor, and permits granulation witha relatively small &olution phase,as calculated by Hardesty's method.

and Ross, as published in Industrialand Engineering Chemistry 1937.The heat of reaction of ammonia andsulfuric acid was calculated fromheat of formation data.

Table illustrates a formulat ionthat can be used in the Swift Processto produce a 12- 12, 12 grade ferti-

practice it is found that evaporationamounts to 60,100 lbs. per ton, leav'ing a product containing 1 to 3%moisture,

Table III illustrates a formula'tion for making granular 5,20,20 bythe Swift Proce s, with the samedata. Deducting the sensible heat of

GFormulation

RANULATION requires aminimum of about 175,300 T BLE II12 12 12 Formulation

Weight/Ton Plant FoodProduct Analysis

Raw Material lb . %Free

Waterlb

Free NHEquivalent

Lbs.Approx. Heat

af ReadionBtu/Ton

NHa 119 82.2NSolution 50 40.8 NH 2S0 4 (60 0 Be) 332(NH')2 8 4 593 205 NTSP 457 46.0 APANSP 149 20.0APAKCl 400 60,0 K20

2100

97328

9

119

+1191389537.055

0

264,00058,000

8,000

330,000

pounds/ton of 60 Be sulfuric acidin order to provide enough heat. Thisamount of acid requires 2.0,3.3units of nitrogen from free ammoniafor neutralization. With a 5,20,20grade, the degree of ammoniationmay be as low as 3.0 lbs. NH3 perunit APA. For grades containing 6%or more nitrogen, a normal degree ofammoniation (350,4.25 lbs. NH3 perunit APA) can be used. To granu'late grades contai ning 4 % or lessnitrogen, with economical raw ma'terials, the water content must be in'creased, and the production rate istherefore decrea&ed for the same sizedrying equipment.

Degree of Ammoniation=3.54 Ibs, NIh/Unit APA

The mechanism of granulationin this process apparently dependson the formation of a liquid phasecontaining solids, which have veryhigh solubilities at elevated tempera'tures. The high temperature thus in'crea es the liquid phase far beyondwhat would be expected from theamount of water in the formulation,Agglomeration occurs in and im'mediately following the acid stage ofthe reactor. Hardening and dryingof the granules continues throughcontact with hot ammonia and watervapors, as the material passes to theexit end of the reactor.

Table I shows the heat de'veloped in the ammoniation of nor'mal superphosphate, triple super'phosphate, phosphoric acid and ul,furic acid. The first three were cal,culated from the data of Hardesty

lizer. The tabulation also shows, forthe raw materials used, 1) the plantfood analysis, 2) the free water con'tained, 3) the free ammonia whichis contained in (plus) or which willreact with (minu&) each material,and 4) the approximate heat of re'action developed. The degree of am'moniation of the superphosphate isalso shown.

To calculate the heat availablefor the evaporation of water, thespecific heat of the dry mixture isestimated at about 0.25 Btu/lb, OF,based on the data of Hardesty andRoss, f the initial temperature is70F, and the final temperature230F, the heat available for evap'orating water is 330,000 Btu/ ton(1981 pounds per ton) x (0.25 Btu/lb. OF) x (230 7 F)--(119pounds per ton) x (1.0 Btu/lb, OF)x (230 70 F) 232,000 Btu/ton. This heat is reduced by radia'tion losses from the reactor. and in

T BLE IHeats of Reaction

Reactants End ProductsBTU'S Per UnitOf N Reacted

NH:) SuperphosphateNHs + Triple superphosphateNHa + Ha PONHa H 2S0 4

3.3 Ibs,N/Unit APA3.25 Ibs.N/Unit APANH. z PO.(NH4h sal

35,78037,66946,21471.500

solids and water in raising the temp'erature from 70F to 230F leaves143,000 Btu/ton available for evap'oration, About the same amount ofwater (60 to 100 lbs./ton) is evap'orated, also leaving 1% to 3% mois'ture in the product.

Semi'granular material can bemade over a wide range of gradessuch as 5,10,10, 5,20,20, 12-12-12,10-20,10, etc., with economical rawmaterials,

For a very high analysis ma'terial, or when prices are favorable,phosphoric acid may be substitutedfor sulfuric add, but it is necessaryto use a &tainless steel reactor toavoid corrosion. The use of phos'p.horic acid is well worked out sincethis material has frequently beenused when triple superphosphate wasunavailable or too high in cost.

OperationT HE process is convenient tooperate, since it is normallyput on stream in 10 minutes. Thispermits the operation of the processon a non-continuous basis, that is,the sy tem may be operated for asmany hours per day as are neces'sary to meet production require'ments, and a variety of grades mayhe produced during one operatingday,


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T BLE5-20-20 Formulation

Weight/Ton Plan FoodProduct Analysis

Raw Material lbs. %NH3 97 82.2 NSolution 50 40.8 NH 2S0 1 (60 0 Be) 185TSP 736 45.0 APANSP 345 20.0 APAKCl 667 60.0 K0

2080

WalerFreelbs.

9414421

115

EquivalentFree NH

lb .+97+13- 5 0--49.7-10.3

o

Approx. Heotof Reaction

B:u/Ton

148,00077,00015,000

240,000Degree of Ammoniation=3.0 lbs. NH,/Unit APA

The granules, as produced in thereactor, are hard and will retain the;ridentity very well if the material iscooled (without drying) prior tostockpiling. Some evaporation take&place in cooling, of course. However,this method is not as reliable as drying, since the results vary somewhatwith the conditions of productionand the atmospheric humidity, temperature, etc.

In producing granular fertilizerby this proce&>, the best method toassure the complete absence of caking is drying the material to 1 % orless moisture content. In this case, nocooling is necessary, unle&> it is desired to bag or otherwise manuallyhandle the material as it is produced.No caking results when the materialis put in storage at a temperatureof 200F. This sy&tem also offers theoption of using the dryer as a coolerby cutting off the fuel supply, andsaving fuel costs when conditions arefavorable for granulation.

Production RatesU SING the Swift Reactor only,without succeeding drying,cooling. or screening equipment, aproduction rate of 60 tons per hourmay be obtained.

Using the Swift Reactor, followed by a cooler, a production rateof 60 ton& per hour is also possible,depending on the cooler capacityand the required maintenance ofgranular form in storage.

For production of a completelygranular fertilizer, the equipmentconsists of the reactor, dryer, screens,oversize crus.hing, and recycle conveying equipment. The factors limiting production are the capacities of

the dryer and screen. Blaw-Knox isprepared to supply &tandardizedunits for the production of 15 or 30tons per hour of 6 + 20 meshgranular goods.

ProductsScreen analysis of a sample of

12 12 12 taken at the reactor discharge shows:Mesh Size 10

+ 4 20.8- 4 +20 61.8- 2 0 +40 15.2- 4 0 2.2

which would certainly be satisfactoryfor sale in many areas without screening.

T BLE VScreen Analyses

Mesh Size 12-12-12 5-20-20% %(A) B) (A) B)

6 5.8 1.8 1.0 0.56 10 55.9 31.9 38.0 37.2

--10 +20 35.8 46.5 46.1 48.8--20 +40 2.3 19.2 13.6 11.6- 4 0 0.2 0.6 1.3 1.9

Table IV shows two typicalanalyse& of each of two productsafter screening, when made by theformulations given, and shows variations due to local operating conditions. Screen sizes are 5 mesh and20 mesh. The amount of materialrecycled to obtain the particle sizedistribution "hown may vary from5 to 20 . Screening efficiency islow in some cases, since the production units are being operated at ratesexceeding 250 of design capacityat times.

Ordinary 3-ply paper bags(without water-proof layers) areused, and no caking i5 experiencedwhen granular material is made bydrying to 1 % moisture or less.

Operating CostsW HEN this process is operatedto produce a semi-granularmaterial without drying and screening equipment as previously de"cribed, savings are made in operating costs over a batch system producing a pulverized material. Aton batch mixer system has a capacityof 30 to 35 tons per hour; the samesy.tem with the addition of a SwiftReactor has a capacity of 60 tons perhour with the "ame numher ofoperators.

Operating costs for the fullgranulation system compare withother granulation systems as follows:1. Fuel-The cost of fuel for drying

the product is greatly reducedsince no sensible heat need besupplied to the fertilizer material,and the water to be evaporatedis normally only 1 to 3 ofthe weight of the product.

2. Power-With the elimination ofthe cooler and its exhaust fan, thereduction in size of the dryershell and exhaust fan capacity,and the reduction in the totalnumber of piece" of operatingequipment, the power costs arelower.

3. Maintenance - Maintenance costis decreased not only by the reduction in the total number of

of equipment, but also inthe elimination of the distributorfor liquid which operates beneatha bed of material in the TVAprocess.

4. Labor-Labor costs for weighingand batch mixing are typical ofthe type in"tallation which maybe used. Operation of the ammoniation, granulation, and drying equipment does not requirethe full time attention of oneman.

5. Royalties--When used by producers other than those who ownthe patent, there is an additionalexpense for royalty payments.The licensor has fixed this cost at


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30 per ton of material producedfor a period of 5 year5.

Investment and Material Costs

THE Swift Reactor with onlysurge bin, feeder, and liquidflow indicators, can be furnished forabout 25,000. Most manufacturerswho are not now producing granular fertiliz;cr will also require sulfuric acid and anhydrous ammoniaunloading and storage equipment andpossibly also nitrogen solution unloading and 5torage equipment.

Many combinations and variations of equipment are possible, depending on the of granulationdesired and local conditions. Betweenthe limits stated, a wide variety ofcosts of installation may be found.

The cost of materials will depend on location and may be easilycalculated for granular 12-12-12 and; -20-20 from the formulations previously given. Generally speaking,material costs are lower than forbatch produced pulveriz;ed fertiliz;er,but in some cases are higher thanother granulation processes, such astho5C using the TVA ammonia tor.For many producers, these highermaterial costs and the royalty payments will be more than offset by thehigh production rate and flexibilityof operation, the savings in nitrogenloss, and investment, operating, andbag costs.

P ocess AdvantagesSemi Granular

The advantages of this processusing Swift Reactor only, ascompared with conventional fertiliz;ermixing, are a higher production ratewith the same labor requirements, theuse of lower cost raw materials, alower nitrogen lower moisturecontent in the product, less reversionof P205 and the production of a&emi-granular fertilizer with theproduct particle siz;e as high as 75within the 4 mesh range.Granular

The Swift process for the continuous rroduction of a granularmixed fertilizer provides:1. Low investment cost.2. High production rate.3. Low rate material costs:

Use 01 anhydrous ammonia andnitrogen solution, in place produc-

don of ammonium suliate and lorammonium phosphate. and low nitrogen 105s.4. Low operating cost:Labor, maintenance, fuel and powercosts are all lower than in othercomparable granulation systems.

), Superior product condition:No caking of granular material,and use of non-water-proof bags.

6. Flexibility of operation:Semi-granular or complete granularproduction, and quick start-up andchange of grades.7. Proven operation:The process has been commerciallyproven with 4 plants currently inoperation, more under construction,2nd more than 1 million tons of

product sold to date .

Granulation of Mixed FertilizersTheory v ractice

Nt john t J I I a ~Fertiliz;er and Agricultural Lime Section

Agricultural Research ServiceU. S. Department of AgricultureBeltsville, Maryland

I N attempting to incorporate themost desirable qualities in agranular mixed fertiliz;cr, themanufacturer of the product is facedwith the problem of bridging a widega p between thecry and practice.Theory, in this instance, is defined asan analysis of a given set of fa.ctorsin their idt:al relationship:; to one an'other. The ideal may often be at Var-iance with practice, which is actualperformance of the process or theproduct. However, practice is seldomImproved without aiming, at 111the direction of the ideal. For thepurpose of discussion in this article,the following spCC111cations are theauthor's conception of the ideal properties for a granular mixed fertiliz;er:

1 Particle size; 10-14 Tyler Standardmesh (screen openings 1.6)1 -1.168mm.)

2 Particle shape; sphetical.3 Particle structu.re; 95% of the par

ticles to remain intact under a loadequivalent to 100 lb./sq. in.4. Homogeneity each granule u p-tograde.5 . Drillability; product to be free of

lumps and to maintain its originaldrilling rate for 1 hour when exposed to 88% relative humidity at76 Fahrenheit.6. Fertilizing efficiency; optimum delivery of nutrients to the growing

plant.Some of these specifications are

beyond the realm of practical attainmc:nt, but none of them are beyond

practical approach. For this reason,it seems desirable to give them morccritical consideration.Particle size

At present, there is no generallyaccepted definition of the particlesiz;e limits between which a fixed proportion of a fertiliz;er should fall, forthe product to be classed as granular.Manufacturing convenience and theattainment of improved physical condition determine largely the particlesize. Examination of 28 r p r s s t ~ -tive samples of typical, commercialgranular mixed fertiliz;er (8) showedan average particle'size distribution asfollows:

Mesh Tyler)+6 126-8 218-14 3814-20

20-35 11-35 7

I t is evident that the ir.dicatedideal particle siz;e (10- 14 mesh) iswell within the particle-size range ofthe average granular product. Thegranule siz;e of the proposed idealproduct is large enough to provide insurance against setting and caking,


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(1)

( 2)

(3)

( 4)

( 5)

Literature CitedClark, K. G. and Hoffman, W. M.Forms and Solubility of Phosphorusin Mixed Fertilizers. Farm Chemicals115, No.5, 17(1952).Cooke, G. W. Field Experimentson Phosphate Fertilizers. GreatBrit. :Natl. Agr. Adv. Servo i(uart-erly Rev. 27, 95(1955).Dion, H. G., Dehm., J. E., andSpinks, J. W. T. Study of Fer-tilizer Uptake Using RadioactivePhosphorus IV. The Availabilityof Phosphate Carriers in CalcareousSoils. Sc Agr. 29, 512(1949).Hardesty, J. O. and Ross, W. H.Factors Affecting Granulation ofFertilizer Mixtures. Ind. Eng. Chem.30, 668 1938).Hardesty, J. O. Agglomeration-AChemical Engineering Tool forGranulating Mixed Ferti l izers.Chem. Eng. Progress 51,291(1955).

(6)

(7)

(8)

(9)

Jacob, K. D. and Hill, W. L. Lab-oratory Evaluation of PhosphateFertilizers. Chap. 10 Vol. IV. Agronomy Monographs, AcademicPress, New York, 1953.Lawton, Kirk, and Vomocil, J. A.The Dissolution and Migration ofPhosphorus from Granular Superphosphate in Some Michigan Soils.Soil Science Soc . A m Proc. 18, No.1 26(1954).Magness, R. M., and Hardesty, J O.Particle Size and CompositionStudies of Granular Fertilizers. Agr.Chemicals 9, No.4 63-4(1954).Owens, L. Lawton, K., Robertson,L. S., and Apostolakis, C. Labora-tory, Greenhouse, and Field StudiesWith Mixed Fertilizers Varying inWater-Soluble Phosphorus Contentand Particle Size. Soil Sci. Soc. Am.Proc. 19, No.3 , 315(1955).(1955).

Pilot Plant Studies of Granulationo High nalysis Fertilizers

By T. P. HignettTennessee Valley Authority

Wilson Dam, Alabama

G R A N U L A T I O N of high,analysis fertilizers has beenstudied by TVA on a pilot,plant scale for nearly three years.The objective of this project is todevelop effective and economicalmethods and equipment for granulation as a means of improving thephysical properties of high'analysisfertilizers. The results of the pilot,plant studies were reported in a paperpresented at the 128th national meeting of the American Chemical Society(1). The present report brieflydescribes the pilot plant and presents in some detail the results ob,tained with one fertilizer, 5,20,20,since many manufacturers are particularly interested in this grade.Pilot plant results for other gradesare reviewed briefly.

The experimental work wasdone in a pilot plant that had a capacity of about three tons of granu,

lar product per hour. Figure 1 (page143) is a diagram of the pilot plant.

Superphosphate, potassium chloride, recycled fines, and any othersolid materials that were requiredwere fed by volumetric feeders toa collecting belt and thence to thecontinuous ammoniator. No preparatory treatment of the materials wasneeded, unless they were caked orcontained large lumps that mightclog the feeders; in this case thematerials were crushed to pass a 4,mesh screen. Finer grinding was notrequired and was not considered tooffer any particular advantage.

The continuous ammoniator(2)is 3 feet in diameter by 3 feet long.It usually was rotated at 15 r.p.m.The bed depth in the ammoniatorwas 9 inches, and the retention timewas about 3 minutes when operatedat a throughput of 3 tons per hour.Ammonia or ammoniating solution

10) Ross, W. H., and Hardesty, J. O.The Granulation of Fertilizer Mixtures. Com. Fertilizer, 1937 Year-bool{ p. 28.

(11) Sayre, C. B. and Clarke, A. W.Changes in Composition of Granular and Powdered Fertilizers in theSoil. ]. Am. Soc. Agron. 30, 30(1938).

( 12) Starostka, R. W., Caro, J. H., andHill, W. L. Availability of Phos-phorus in Granulated Fertilizers.Soil Sci. Soc. Am. Proc. 18. 67(1954).

( 13) Starostka, R. W., and Hill, W. 1.Influence of Soluble Salts on theSolubility of and Plant Response toDicalcium Phosphate. Soil Sci. Soc.Am. Froc. 19, 193(1955).

( 14 ) Webb, J. R. Significance of WaterSolubility on Phosphatic Fertilizers.Agr. Chemicals 10, No . 3 44or mixtures of the two were injectedunder the bed of material through aspecial distributor. Sulfuric acid,phosphoric acid, or steam was supplied through an adjacent distributor.Air for cooling and controlling granule size was supplied from a drilledpipe located over the bed of material. The drilled holes in thepipe were located so as to direct airjets onto the surface of the bed.When water was needed for granulation, it was either sprayed on thesurface of the bed, or mixed withthe ammonia or ammoniating solutionin the pipe line leading to the ammonia distributor. The latter ar. rangement was preferable. A streamof air was drawn through the ammoniator to sweep out water vaporand fumes.

The material flowed from theammonia or through a chute to thegranulator, which was an open cylinder 24 inches in diameter by 6 /zfeet long. It usually was rotated at20 r.p.m. From the granulator, thematerial flowed to a cooler, whichwas 3 feet in diameter by 24 feetlong and contained flights. The flowof air in the cooler was countercurrent to the flow of solids. Thetemperature of the material leavingthe cooler was about 100 F. In afew cases the cooler was used as adryer with cocurrent firing.

A set of screens, a crusher, andconveying equipment were used tosize the product at approximatelyminus 6 plus 28 mesh. The undersizewas recycled to the ammonia or.


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ROLLCRUSHER

PRODU T

OOLEROR DRYER

FINES RECYCLE

ACID

Figure 1Flow diagram of TV A pilot plant for granulation of high. analysis fertilizer.

Factors Affecting GranulationHE most important factor affecting granulation was the formu

lation. The formulation determinedthe heat of reaction and the amountand character of the soluble salts;these factors strongly influencedgranulation. The best results wereobtained when the formulation wasself granulating or nearly so. By aself, granulating formulation we meanthat, when the constituents arebrought together, the Oluble salt con'tent, the moisture content, and thetemperature resulting from the heatof reaction are such as to impart aa suitable consistency for forminggranules with only minor adjust,ment of the temperature or moisturecontent.

Poor results were obtained whenthe formulation was such that a largeamount of water was required forgranulation. Although it was posible to induce granulation at lowtemperatures by addition of large

amounts of water, the granules oftenwere weak and disintegrated duringdrying, which was required becauseof the high moisture content.

Poor results also were obtainedwhen the formulations led to exces,sive agglomeration due to too muchheat of reaction. The formation oftoo much oversize led to impairedefficiency of ammoniation and fume

formation and interfered with effi,ciency of the subsequent coolingoperation.

No method has been developedfor predicting accurately the granu,lation characteri5tics of a formulation. It seems probable that the granulation obtained with a given formulation may vary depending on suchfactors as design of the ammoniator,heat losses from the ammoniator,effectiveness of temperature controlin the ammoniator, physical proper'ties of the superphosphate, and ini,tial temperature of materials enteringthe ammoniator. For these rearons,it should be expected that some experimentation would be required ineach plant to find the best formulation for good granulation of any par'ticular grade.

In addition to the selection ofa formulation that provides properconditions for granulation, it is verydesirable to provide operating con'troIs to obtain the most efficientgranulation. One effective and con'venient method that was developedand used in the pilot plant was theuse of air jets directed onto the bedof material in the ammoniator. Theair jets cooled the material in theammoniator and evaporated waterfrom the .surface of the granules,thereby decreasing the amount ofoversize formed. Control of granula

tion by air cooling was effectivewhen the formulation was such thattoo much agglomeration would occurotherwise.

Recycling of some of the cooledproducts was found to be effectivein controlling overagglomeration.However, this method was not generally used in the pilot plant becauseit was inconvenient to handle thelarge amount of recycle that wouldbe required for effective control. Inmost runs, only the fines normallyproduced were recycled, whichamounted to 10 to 25 per cent of theproduct.

When the formulation was suchthat the extent of granulation wasinsufficient, additions of steam orwater were sometimes effective inincreasing it.

Production of Granular 5-20-20J UDGING from comments thatwe have received from fertilizermanufacturers, 5,20,20 is an important grade that has given an unusualamount of difficulty in granulationplants. For this reason, several formulations for producing this grade werestudied in the pilot plant. The formu,lations used and typical data obtainedin these runs are shown in Table 1.The formulations were calculatedfrom actual feed rates; due to inaccuracies of the feeders, the propor'tions of the ingredients were sometimes appreciably different from theintended proportions. For this andother reasons, some of the formulations are not consistent with produc'tion of ongrade product.

In test J,I, ammoniating solution Y (26 free ammonia) wasU5ed to supply all of the nitrogen:water addition was the only meansof granulation control. The heat re'leased by the ammoniation reactionwas not sufficient to permit granu,lation at low moisture content. t wasnecessary to add water to increasethe moisture content to about 13 percent to obtain granulation. The ef,ficiency of granule formation was satisfactory, but the percentage of bothoversize and undersize increased dur'ing drying, leaving only 42 per centin the desired size range. After crush,ing the oversize, only 72 per cent was


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onsize. The dried granules were weakand dusty.

The need for artificial dryingwas eliminated and the stability ofgranules was improved by adding sulfuric acid to the formulation. Theheat generated by the reaction of theacid with the free ammonia increasedthe temperature in the ammoniator.At the higher temperature, moreliquid phase was formed by the solution of soluble salts, and no wateraddition wa;;, needed for granulation.This use of acid to promote granulation is illustrated by test }2. Bestoperation was obtained when the addrate was 143 pounds of add per tonof product. Fifty-seven per cent ofthe granulator product was onsize.There was very little breakdown ofparticles in the cooler. Onsize material, including the crushed oversize,amounted to 80 per cent of the totalproduct. The moi;;,ture content of theproduct was only 1.7 per cent eventhough artificial drying was not used.

During a part of test J'2 the acidrate was increased to 170 pounds perton of product. Overagglomerationresulted, and operation was inferiorat the higher acid rate. When theacid rate was reduced to 90 poundsper ton, there was too little granula,tion.

In test }2 the degree of ammoniation was low, ahout 1 pound ofammonia per unit of P ~ o . . Consequently, the ammonia loss was verylow, 0.1 per cent or less, and thewater solubility of the PzO was veryhigh, about 7) per cent.

The foregoing tests showed thatoperation with nitrogen solution asthe source of nitrogen was much improved when sulfuric acid was addedto supply heat by reacting with thefree ammonia. Two additional testwere made to determine whether similar results could be obtained by adding part of the nitrogen as anhydrousammonia. Thus, the amount of freeammonia available to react with thesuperphosphate was increased, andmore heat from this source was released in the ammoniator. The nitro'gen solution (solution X in thesetests), anhydrous ammonia, and water required for granulation were allinjected through the same distributor.

T BLE I.Pilot Plant Data for Production of Granular 5 20 20 Ferti izers

Tell No. J-1 J-2 J-3 J-4 J-5 J-6 J-7Formulation, lb./ton of productAnhydrous ammonia 103 50 129 127.\Iitrogen solutiona

(X, Y, or Z) 259 (y) 252(y) 85(x) 180(x) 308(z)Sulfuric acid (66 0 Be.) 143 92 139 123Ordinary superphosphate 398 260 292 293 278 774 460Concentrated superphosph;.lte 675 741 807 810 769Calcium metaphosphate 513Phosphoric acid 380. Potassium chloride 690 669 628 630 643 645 641

Total 2022 2065 2003 1963 1958 1926 2045Recycle. lb./ton 441 397 386 356 304 829 330Means of granulation control Vater Varia- Water Water \Vater \Vater Watertion of and air and airacid rateAmmoniator temperature, OF. 140 206 235 176 207 176 166Moisture content of product, o cFrom ammonia or 12.6 4.4 3.7 7.5 5.9 9.0Final product 4.1< 1.7 2.0 4.5 3.9 0.6(;ranuiation, ; {Oversize 34 35 36 31 28 31 29Onsize 55 57 63 65 70 58 66Undersize 8 4 2 11 5Onsize recovery aftercrushing oversize, 83 88 81 87 91 86 9'Composition of nitrogen solution:Per Cent h Product 'as cooled but not dried except as indicated.Solution Nfl, NH,NO. H2O


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11 per cent of the potassium chloridewere plus 28 mesh improved granulation considerably. Substituting granular potassium chloride (73% +28mesh) further improved granulation.In a few te ts with grades other than8-16-16 the particle size of the patas'sium chloride had little effect ongranulation.

A few tests were made in which0.5 or 1.0 pound of an anionic surfactant per ton of product was added to the mixture entering the am'moniator. Some increase in the percentage of onsize granules was notedin some of the tests, but the effect wasnot conc1usive.**

Gahu atifJh t tileSpencer ARK-MO Plant

8 , . glt,a. tp*Spencer Chemical Co.Kansas City, Mo.

SINCE March 7, 1955, when theArk-Mo Plant went through itsshake-down run, much valuableinformaticn has been developed onthe granulation of many grades ofmixed fertilizers, u ing the most eco'nomical formulas, based on presentsupply of raw materials. Basically,plant design has proven sound, butexperience has shown us where somechanges will e beneficial. Thesechanges are being recommended toother companies converting to granulation.

This discussion describes thepre&ent process and indicates desirable changes.Solids

The flow diagram is shown inFigure I In Figure II, the warehouseon the left is dry raw material storage; in the center, the process J:>uild-ing; and on the right, a con'Verted air'plane hangar for finished product.Normal superphosphate, triple superphosphate, pota&h, and inerts are fedinto the elevator in the center of thewarehouse, which discharges onto aconveyor that connects with the process building. The conveyor that car'

ries the finished product to storagemay also be seen between the proc'i':ssbuilding and the hangar.

Figur'i': III is a picture of a moddof the process building and equipmenttaken from the raw material side.The four storage hoppers (A) nearthe center are for the various n.wmaterials. The hopper (B) at theleft end of the building is for recyclestorage. Each dry material and recycle is weighed continuously withgravimetric feeders and flows onto thecommon conveyor belt leading to theelevator on the right. The elevator

Figure J.

References1. Hein, L.B., Hicks, G. C., Silverberg,Julius, and Seatz;, L. F. Granulation

of High-Analysis Fertiliz;ers. October28,195,. (Presented at the 128thNational Meeting of the AmericanChemical Society, Minneapolis, Minnesota, September 19552. Yates, L. D., Nielsson, F. T., andHicks, G. C. Farm Chemicals 1177, 38-48; No.8, 34-41 (1954).

discharges onto either or both of twoten-mesh screens. The rejects fromthe screens pass through either orboth of two crushers and back intothe base of the elevator. Actually inthe operation at Ark-Mo, only onescreen and one crusher ha'lle been usedat the same time. We feel the extraones are not needed.

Figure IV shows the finishedproduct side of the model. The tenmesh mixture of dry materials flowsinto a TVA,type ammoniator (C)which can be seen on the second ele'vation at the left in the picture. Thiscylindrical vessel i 7 feet in diameterand 8 feet long. There is a 27 -inchretarding ring in the center and theammoniation takes place in the fronthalf.Liquids

Ammoniating solutions, anhy'drous ammonia, sulfuric acid, phosphoric acid, and water are eitherpumped or pressured through flow'meters, and are fed into the ammonia'tor through spargers. When ammon'iating solution, anhydrous ammonia,and water are used in the same formula, they are mixed in a pipe aheadof the ammoniating sparger, A ep';lI'ate sparger is used for add.


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SteamSteam and acid are not used in

the same formula, so the same spargeris used for either material.

The back half of the 7 foot by 8foot vessel is used to firm up androuml off the pellets formed in theammoniator. The product then flowsinto the 8 foot by 40 foot dryer. Thefirst three feet of this cylindrical ves-sel contain di rectional flights to movethe material forward. The next threefeet contain no flights, and the pelletsare further firmed and rounded. Theremainder of the vessel is equippedwith lifting flights . A vibratory con veyor carries the product from thedryer to the 7 foot by 30 foot cooler.It then flows into an elevator that liftsit to a doubledeck screen. The 6mesh material from the top screengoes through a crusher and back intothe elevator. The material that flowsover th e bottom screen (14 or 20mesh, depending on grade beingmade) flows onto the finished product belt. The fin es going through thebottom screen and dust from the dryerand cooler cyclones dr op into the recycle hopper.

A discussion on all the gradesthat have been made is not containedin this article, although some 30 di fferent formulations have been madein the Ark-Mo plant. The two gradesdiscussed below represent extreme

n d i t i n s ~ that is, a grade that requires a great amount of liquids tosupply the nitrogen, and one thatrequires a small amount, namely, 14-14-14 and 3-9-27. The 14 -14-14

T BLE 1Ark-Mo Fertilizer Granulation Plant

Grade 14- 14-14FO RMULTION Plant Food / Tan FLOWSSpensol C 37 762 Prociuction RateAnhydrous Recycle RateAmmonium Sulfat e Total ThroughputSulfuric Acid 66Be 194 Gas Con sumedSuperphosphate 20 210 Air Flow DryerTriple Super 47 516 Air Flow CoolerPotash 60 468Filler TEMPERATURESAtmosphericTolal 2160 Burner AirAmmoniator

Drye r ThroatDryer StackDryer DischargeCooler StickCooler Discha rgeFinishe d Prod uct

UM IDITIES H 20I Dry Air Dry BulbAtmospheric 0.0094 62c FDryer Stack 0.052 175FCooler Stack 0.026 140F

SIEt E NAL L ;l S (%)Ammaniator Cooler Finished

Exit Exit ProductHeld on 6 38.6 28.4 4.7Held on 14 58.8 52.7 92.4Held on 20 78.3 75.5Held on 40Held on 65

CHE1HfCAL ANALLSISAmmonialor Ammonialor

Feed ExitMoisture 1.80 3.00N 11.14 13 .46Available P 15.82 14.12Insoluble P 2 0 0.18 0.17Total P20 0 15.00 14.30K20 16.99 15 .25

8 T/hr.27 T/hr.35 T/hr.2,100 CFH14,000 CFM

15,000 CFM- - - - - -OF

6265180

420195190145120

Relative791829

Recycle

.051.1872FinishedProduct2.4013 .7114.500.18

14 6814.04


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T BLE 2OPERATIONAL DATA

Ark-Mo Fertilizer Granulation PlantGrade 3-9-27FORMULATION Plant Food /TonsSpensol CAnhydrousAmmonium SulfateSulfuric AcidSuperphosphateTriple SuperPotashFillerTotal

HUMIDITIESAtmosphericDryer StackCooler Stack

3782.2

200

10925

900900110

2044

20 Dry Air0.0190.0940.024

SIEVE i\ ALYSIS (J

Held all 6Held on 14Held all 20Held all 40Held all 65

AmmoniatorExit9.161.022.47.10.4

CHEMICAL VALYSIS

FLOWSProduction RateRecycle RateTotal ThroughputGas ConsumedAir Flow DryerAir Flow CoolerTEMPERATURESAtmosphericBurner AirAmmoniatorDryer ThroatDryer StackDryer DischargeCooler StackCooler DischargeFinished Product

CoolerExit14 .860.019.65.60.0

Dry Bulb79F190F

130 F

FinishedProduct

1.565.033.00.50.0

Ammoniator AmmoniatorFeed Exit

Moisture 4.60 4.68N 1.39 4.81Available P 2 0 5 9.55 8.89Insoluble P 205 0.08 0.06To tal P20, 9.63 8.95K20 27.05 23.28* Spensol requirement below flowmeter calibration.

Corrected by ins talling smaller owmeter.

10 T/hr.4.5 T/hr.

14 .5 T/hr.3,500 CFH10,650 CFM4 095 CFM

OF7986

205410197200150121120

Relotive921

25

Recycle0.00.021.065.0

14.0

FinishedProduct

1.48* 4.748.970.089.0526.8 4

formula has 956 pounds of liquids,whereas, the 3-9-27 has only 134pounds of liquids. Formulas and operational data on these grades areshown in Tables 1 and 2.

The operational data on 14-14-14shows that 27 tons per hour of recycle at an 8 ton per hour productionrate was required. This dried andcooled recycle served to absorb theliquids, and thus prevent a slurry frombeing formed in the ammoniator. Thefinished product temperature was120 F. With greater cooling capacity, the amount of recycle could havebeen reduced, because temperature ofthe recycle greatly affects the solution phase in the ammoniator. Wenow recommend that the cooler bethe same si e as the dryer. The dataalso show that the cooler exit has 28.4per cent held on a 6-mesh sieve. Withthe present system, much of this material is broken up to finished product si e. This causes too many jaggedshaped particles in the finished product. Furthermore, the particles beingmade from larger particles are notsufficiently dry to ensure propermechanical condition. The +6-meshmaterial should be removed at the endof the dryer, crushed, and returnedto the head of the dryer. Thi changeeliminates the need for a doubledeck screen, but it requires two singledeck screens instead. Two per centof diatomaceous earth is added to14-14-14 and other high nitrogen


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Fraction60 Potash (Coarse)/6 0.0

6/14 31.514/20 51.120 40 13.540/65 2.7651 1.2

Particle TolalGrade Size Tolal N P2 0 S3-12-12 Blank 3.0 11.2

6/8 2.9 11.98/14 2.9 11.0

14/ 3.1 11.23-9-18 Blank 2.9 8.96/10 2.7 9.2

10/16 2.9 8.7161 3.2 9.0

3-9-27 Blank 2.7 8.16/10 2.9 9.4

grades as a parting agent to enhancemechanical condition.

The operational data sheet on 3-9-27 shows 4.5 tons per hour of recycle for a 10 ten per hour production rate. The only reason for thisrecycle is to remove the ~ 2 meshmaterial from the finished product.Since the liquids in the formula arelow, this recycle hinders granulationby competing with the other materialsfor the liquids preseot. In additionto the liquids shown in the formula,it is necessary to add 100 pounds ofwater as such per ton and 74 poundsof steam to bring about granulation.In this case, it would be better to recycle the hot fines, instead of coldfines.

A system of chutes in connectionwith the two single-deck screens willallow hot or cold recycle to be used,to suit the grade being made.

T BLE 3SIEVE ANALYSIS - RAW MATERIALS

. Acc. 60 Potash Fine)0.0 1631.5 6/1482.6 14120

96.1 20/4098.8 40 6565/

T BLE 4ANALYSIS SIEVE FRACTIONS

PartideK O Free H2O Grade Size12.5 1.0 10/1611.0 0.9 16/13.2 0.8 10-10-10 Blank13.7 0.9 6/1017.9 0.6 10/1615.5 0.6 16/19.1 0.6 14-14-14 Blank18.2 0.6 6/1027.6 0.7 10/1621.7 0.8 161

Coarse potash was used in thisformula. The sieve analyses areshown in Table 3. As can be seenin the picture of a bisected pellet,Figure V, the potash particle is thenucleus. Figure VI contrasts granulesmade with fine potash, where the potash particles are sticking loosely to thesurface.

Table 4 &hows analyses of various sieve fractions. The 3-12-12, 3-9,18, and 3,9,27 were made withcoarse potash, and the 10-10-10 and14, 14-14 with fine potash. Attemptsto granulate high potash grades withfine potash have been unsatisfactory.SummaryTHE Ark-Mo Plant has successfully granulated 16-20-0, 13,39,0, 10-20-0, 14-14-14, 13-13-13, 12,12-12, 10-10-10, 8-8-8, 10-20-10, 8-24-8, 6,8,12, 4-12-4, 5-10,5 , 3,12-12,

Fraction Ace.0.0 OJ}0.5 0.518.1 18.664.3 82.914.3 97.22.8

ToialTolal N p OC, K2 F r ~ J H:. ()2.4 7.7 29.3 0.62.7 7.9 29.0 0.610.0 10.9 10.8 0.810.0 11.5 9.4 0.810.1 10.9 12.6 0.810.4 10.8 11.8 0.713.3 13.7 13.8 2.613.2 13.9 14.0 2.613.1 14.6 13.4 2.412.2 13.7 15.4 2.2

3-9-18, 3-9-27 and 5 ,20,20. All thenitrogen was derived from Spel1501,or a combination of Spensol and anhydrous ammonia. In addition to using low-cost nitrogen, these high ananalysis materials allow more roomfor normal superphosphate, which often further reduces formulation costs.

We recommend the eliminationof one raw material screen and oneraw mate.rial crusher. Also, the cooler5hould be the same si;;:e as the dryer.The process should be changed to remove the +6-mesh material at theend of the dryer, which will replacethe double-deck screen with twosingle-deck screens for finished product. A system of chutes should beprovided to permit the use of eitherhot or cool recycle. Spencer Chemical Co. Technical service is availableto assist in these problems.**


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TEMPER TURE MOISTURERelationships n ranulation

Eastern States Farmers' Exchange, Inc.West Springfield, Massachusetts

THE search for some method ofeffectively reducing the problemof mechanical condition or bagset has been a long one. Of the manytechniques and additives which havemade their contribution to fertilizermanufacturing, the method known asgranulation i now generally regardedO S a practical and economical way ofaccomplishing good mechanical condition.

Within recent years, when thoseof us at Eastern States Farmers' Ex'change, and other organizations began working on granulation techniques, there occurred serious questions on whether 0 not it was apractical answer to the- problem nfbag set. Virtuc.Jy the o;.ly methodof granulatiol1 being [It.1ctlced wasthat used in an increa&ing numberof European mixed fertilizer plantswhereby mixed fertilizer is removedfrom the storage pile, placed in abatch mixer with sufficient water toaccomplish agglomeration, and thendischarged to a granulator . . . fromwhich the material passes to dryingand cooling facilities. Approximate'Iy 15'-18% moisture is necessary toaccomplish agglomeration with thatmethod. Obviously, the importantmatter of cost causes serious objec'tions to that method. Each step inthat process represents additionalcapital and operating costs. Otherobjections are apparent.

Fortunately, when Eastern Statesand others in the United States commenced study of granulation, therewas some basic work completed on

the properties of common fertilizermaterials, the ammoniation of superphosphates, and some of the factorsimportant to granulation. Work hadbeen done principally by W. H. Ross,]. H. Hardesty and their associatesin the U.S. Bureau of Plant Industry, which i referred to in part inthis article. At that time, ammoniation of superphosphate was common,and the studies by John Hardestyand others suggested the extent towhich ammonia could be reactedwith superphosphates of various con'centrations and physical propert:es.Data was available on the heatresulting from the ammoniation re'actions. Solubility of salts commonlyused as fertilizer ingredient:;, hadbeen determined. This informationled to the gradual recognition thatuse of ammonia as anhydrous orin nitrogen solutions not onlycould reduce the cost of nitrogenin the mixture, but would contrib,ute to granulation in the follow,ing ways:(1) Use of sufficiently highamounts of ammonia in the mixtureincreases the temperature of thebatch substantially, and according toa fairly definite ratio.

(2) Large amounts of the saltscontained in the m i x ~ u r of ingredients are dissolved at the tempera'tures attainable through high am'moniation. These salts dissolved inthe free water increase the solutionphase of the mixture.

(3) Ammonium nitrate andurea are the most soluble of salts

used commonly in mixed fertilizers.They have also the greatest increases.in solubility with increases in temperature, which s of particular importance.

(4) During the drying and cooling steps, low moisture content andlarge amounts of salts in solutioncontribute to rapid crystallization ofsalts and, therefore, permanency ofthe granules formed during agglomeration.

From this very brief review, it15 apparent that temperature andmoisture relationships are extremelyimportant considerations in granulation. They can be regarded as thekeys to granulation, although muchof our effort has necessarily con'cerned equipment o accon:plish thesE verai steps ill granulation. Veryappropriately, much of this conference concerns suitable equipment.In summarizing some of the temperature and moisture relationships,let us begin first with f o n ~ u l t i o nand then consider the steps in theprocess individually.Formulation

RADES which are generallybeing granulated, contain ,

or more nitrogen. Granulation is fadltated directly with increasing nitrogencontent, which in turn is directly related to the amount of the more solu'ble nitrogen salts contained. The relative solubilities in water at 68 F. ofsome common fertili;;:ers are as follows:

Weight Per entAmmonium Nitrate 66.0Calcium Nitrate, Anhydrous 56.4Urea 52.0Sodium Nitrate 46.7Ammonium Sulfate 42,8Diammonium Phosphate 40.8Mono-ammonium Phosphate 27.2Ammonium Chloride 27.1Potassium Nitrate 24.0(Crittendon: Allied Chemical and DyeCorporation)

As this table indicates, ammonium nitrate is the most watersoluble fertilizer material, with ureahigh on this list. t is of importance,also, that the solubility of these twomaterials increases substantially withincrease in temperature. Monoammonium phosphate and potassium


18/32

nitrate respond similarly through alower temperature range. With in'creases from to 2 2 F., am'monium nitrate increases in percent&olubility by weight from 54 to 89%and urea from 39 to 87%.

Eastern States Farmers' Ex'change has used ammonium nitrate-ammonia solutions in granulation,with only limited experience withurea'ammonia solutions. Our observa'tion indicates that smaller granules arcformed with the urea'ammonia solu'tions. Attempts to formuiate, usingboth ammonium nitrate and urea,have been discouraging in that theproportion of desirable granules hasbeen reduced substantially.

The volume of the liquid phasedepends upon the ingredients used,the concentration of the mixture and,


19/32

balance between moisture and tem,perature necessary.

The compo&ite of all materialsintroduced into the mixer determineslargely the temperature and moisturerelationships which occur, and thequality of granulation. However,construction and characteristics ofequipment do have their effeet ontemperature and moisture, and thequality of granulation attained.Granulator

I T is important to provide condi,tions which encourage agglomera'tion at the stage in the process whenthe temperature and moi6ture leve:sfor a given formula encourage rapidcrystallization and hydration. Withformulas of high soluble salt can'tent and low moisture dischargefrom the mixer at high temperature,granulation can be attained immed;,ately following discharge from themixer. With formulas of relativelylow soluble salt content, and necessarily high moisture content, agglomeration i more gradual and related to the reduction of moisturecontent. Agglomeration may occurin a so' called granulator , the dryeror the cooler, '-depending upon theformula of the mixture and thecharacteristics of the equipmentused.

A granulator essentially pro'vides agitation or tumbling of thefertilizer during temperature reduc'tion. A thin layer of material isimportant, the rate of production notexceeding 1000 pounds per squarefoot per hour of effective granulatorsurface. Either a rotary cylinder ormechanism providing horizontallyvihrating surface can be used.

ryer

A DRYER i n s t a l l a t i o ~ should at'tempt to accomplIsh at l e a 5 ~the following:

1. Moisture reduction of thefertilizer.

2. Low fertilizer discharge tem'perature.

3. Maintain or increase agglom,eration.

The quantity of heat, the vol,ume of air and the direction of airflow principally determine moistureand temperature relationships in thedryer and affect agglomeration. Di,ameter and length of dryer and con'struction of flights also affect ag'glomeration. Temperature of thefertilizer must be maintained or il1creased to sufficiently high tempera'tures to evaporate water. Applica'tion of excessive heat can reduce themoisture content more than neces'sary, and result in unnecessarily highex,dryer fertilizer temperature. Ade'quate volume of air is required toconvey the evaporated moisture. Toolarge air volume can reduce dryingefficiency, requiring excessive consumption of fueL The fact that thedischarge temperature of the ferti,lizer is sometimes less than the' temperature of the fertilizer entering thedryer, leads to the occasional state'ment that fertilizer dryers are actual,ly coolers.

These relationships can be illus,trated by the average temperatures(see table below) on several weeksproduction of an 8 nitrogen gradeat an Eastern States plant. Fertilizerexdryer temperatures, fertilizer excooler temperatures and fertilizer excooler moistures are summarized ac'cording to air ex,dryer temperatures.

f 2 moisture is assumed tobe satisfactory, it can be concludedfrom this data that with this grade,an air ex,dryer temperature of about2 0 F. is adequate in this particulardryer and with the given air volumt:.Iiigher ex,dryer air temperatureswould increase both the fertilizer exdryer and ex'cooier t e m p e r a t u r e ~

A large dryer with substantialrange of air volume and heat inputoffers advantage,:;. Temperature andmoisture conditic'l1s and mechanicalfeatures can e adjusted more sads'factorily in a large dryer to accomplish considerable agglomeration, therequired drying and the partial cool,ing within the dryer. Co,currentair flow is generally employed andassumed in this discussion.

Counter air flow in a dryer per'mits attaining lower moisture can'

tent with a given heat input, butresults in substantially higher fer'tilizer ex-dryer temperatures, and ismore likely to cause reduction ofnitrates, with resulting evolution ofnitrous oxide. In the summary above,there is less than 50 decrease infertilizer temperature in the cooler.In an Eastern States granulation unithaving counter'current air flow andsimilar air volume and fuel consump'tion, the fertilizer dryer dischargetemperature ranges between 225 and26 F, but the fertilizer decreasesapproximately 100 in the cooler.With these temperatures, agglomera,tion tends to occur in the cooler.

oolerDEDUCTION of fertilizer tern'.1. - perature in the cooler is a result of transfer of heat from thegranules to air, and the evaporationof limited amounts of moisture. Theprinciples of the fertiliz.er rotarycooler, as first developed by Keenenand associates of the DuPont Co., areapplicable today. With less moisturein granular fertilizer to evaporate inthe cooler, there is less reduction oftemperature of fertilizer per givenvolume of air. By study of air flow,air volume, air temperature, fertilizertemperature and fertilizer moisture,maximum efficiency of a cooler canbe determined, Granulation has accentuated one factor and that is time.Increased time during which fertilizeris in the cooler encourages the trans'fer of heat to the surface of granulesand then tran&fer to the air.

Typical Moisture and Temperature

I T may be helpful to summarizewhat can be considered approxi'mate moisture and temperature levelsat several locations in the process,which contribute to granulation.Formulation and other' factors affectthese figures.

ontrol

U NIFORMITY of granular prod,uct is important. An unsatls'factory granular product can be moreobjectionable than pulverized fer'tilizer. Lack of control of tempera'ture and moisture levels is likely to


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moniation and subsequent drying processes. The reasoning here was basedon experience with urea in conventional fertilizers, in which urea isknown to hydrolyze in long-continuedhot storage. Since conditions aresomewhat different in granulationprocesses, with lower moisture content of the finished product, and withcooling generally practiced, it was feltexpedient to explore the behavior ofurea; to ascertain if hydrolysis was aserious factor, and i f S0, where; andto determine the granulating characteristics of urea with re::;pect tostorage qualitites, granule hardness,and hygroscopic behavior.

T BLEANALYSES

No. Description381 8-16-16 dryer 180, cooled382 8,16-16 dryer 180, 16 hrs. 140391 8-16,16 ammoniator 185, cooled392 8-16-16 dryer 140 cooled393 8,16-16 dryer 174 cooled401 10,10-10 ammoniator 170 0 cooled402 10-10-10 dryer 195 cooled403 10-10-10 ammoniatDf 186 cooled404 10-10-10 dryer 180 0 cooled405 10-10-10 ammoniator 202 cooled406 10-10-10 dryer 175 cooled407 10-10-10 dryer 175 30 min., 160411 5-20-20 ammoniator 1n cooled412 5-20,20 dryer 180 ' cooled413 5-20-20 ammoniator 1 H O cooled414 5-20-20 dryer 180 cooled415 ;-20-20 dryer 150 0 cooled416 ;-20-20 ammoniator 155 cooled

Nitrogen%

8.007.337.207.708.70

10.0010.5;9.159.609.80

10.1510.2;

5.837.004.855.204.934.65

Urea NitrogenCalculoted Found Recovery% % %

3.55 353 003.25 3.42 1053.20 3.11 973.42 3.31 973.86 3.49 903.23* 3.37 1043.23* 3.44 1063.23* 3.47 1073.23* 3.43 1064.35 4.08 944.50 4.10 914.55 4.26 942.59 2.45 953.11 2.97 962.15 2.10 982.31 2.23 972.19 2.13 972.07 1.93 93

This, then, is an account of test3,first in a pilot plant, and then in plantscale equipment, using Du PontUramon Ammonia Liqnors A and

B, hereinafter referred to as UAL-Aand UAL-B. T h c ~ tests w{ rc begunabout a year ago, and are still COflt puing. They have been explor.1toryin nature, and e ) pretense is made . ~ funcovering any new granulation technique. Most worhrs in the field willconcede that granulation tod:\y is an

a r ~ more


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23/32

T A 8 L E 8 Properties of Uramon Ammonia Liquors~ . ~ ~ ~ ~

UAL-A UAL B UAt-C UAL A UALB UAt-CTotal N 45.5 45.5 37.0 Total N 45.5 45.5 37.0Composition Vapor PressureUREA 32.5 43.3 26.5 100 104 F, p.s.i. 64 50 22AMMONIUM CARBf\MATE to10.5 15.0 8.6

AMMONIA 32.2 24.1 26.3 . Salting Out Temp. F 5 34 6WATER 24.8 17.6 38.6 Lbs Water /Unit of N 11.0 7.8 21.0100.0 100.0 100.0 Lbs Water/5 Lbs NH. 3.4 2.9 6.5

- - ~ - - - - ~ - ~ - - - - - - -

hard lumps. Granule hardness wasjudged to be quite satisfactory.

In another plant scale test, twogrades, a 121212 and a ;20,10,were tried with UALA. The processwas again a modified TVA design,with ammoniator'granulator and co'current dryer. There was no cooler.In the 121212, 7.5 units of N werederived from UALA and 1.5 unitsfrom solid urea, this combination be'ing equivalent to 9.0 units fromUAL,B. In the 5,20,10, all of thenitrogen was derived from UAL,A,and a small amount of calcium oxideand sulfuric acid was included to pro'vide additional heat. The formulasare listed in Table 6.

Granulation of the 12,12,12 wasstarted at 10T hour, and after Onehour stepped up to 1; T /hour. Prod,uct from the ammoniator was estimated at 200 to 22; F, and had a mois'ture content of 5.8 to 7.1 . Productfrom the dryer had a temperature of19;0 F, and a moisture content of0.6 to 0.9 . Yield was estimatedat 60 to 67 , - 6 2 0 mesh. In gen'eral, good granulation was secured,but some difficulty was experiencedin maintaining the optimum granulat-ing conditions in the ammoniator'granulator. Control of water addedwas not as good as could be desired,

and the amount of water in the form'ulation appeared to be too dose tothe critical amount to allow adjust,ment by added water. The productin storage was very free flowing, andhad good granule characteristics. The

urface of the pile cooled rapidly, butthe interior appeared to increase intemperature (over 160 0 F) with adistinct odor of ammonia. Rehandlingand moving the product broughtdown the temperature so that nofurther free ammonia could be de'tected. It was quite apparent fromthis test that to make and store thisgrade successfully cooling is necessary.

llhe ;,2010 grade proved to bedifficult to granulate with UAL,A(as it had been with other solutions),and repeated runs varying the amountof water produced erratic granula'tion, the material becoming alternate'ly too dry or too wet. It was concluded that for this grade, the amountof urea (71. 5 Ibs.jT) was insufficientfor good granulation.

In another plant test, UAL,Bwas used in completely differentequipment making 5,20,20 formulat'ed with all N from UAL,B: a 5,20-20with 3 units from UAL,B and 2 unitsfrom anhydrous ammonia, plus suI,furic acid; and a 12,12,12, 7.2 unitsfrom UAL,B and 4.8 units from am'

monium sulfate, plus sulfuric acid.Granulation was satisfactory, but nodata or analyses are available.

As indicated at the beginning,the work reported here was concerned principally with the question ofurea hydrolysis under conditions ofhigh ammoniation rates and granu,lation. The properties of urea do notpreclude its consideration in granu'lating processes. From the standpointof solubilities, urea is close to ammonium nitrate, and therefore affordsa good agglomerating and adhesiveeffect. Only slight modification informulating might be necessary insome cases to utilize UAL in anyprocess now employing nitrate solu'tions.

In conclusion, we believe thatthis exploratory work has shown:(1) that urea is stable in granulating

processes involving high tempera'tures, provided the product iscooled before storage.

(2) that urea solutions afford satisfac'tory granulation from the stand,point of yield, desirable granulesize, hardness of granule, appear'ance, freeflowing qualities, andcomparati've freedom from subsequent reactions that may induceexcessive pile set or caking inbag storage.**


24/32

C Key to low iagram(1) SUPPLY HOPPERS AND BATCHWEIGHING EQUIPMENT-Cranes equipped

with 20 yard (approximately 20 ton)clam-shell buckets pick up the raw materials from bins in the crane,bay andload the overhead large supply hoppers.From these hoppers the required weightof each material called for in the form-ula is weighed into hopper scales anddumped on conveyor belts which emptyinto a vertical bucket elevator to lift thematerials into the mixer for blending.(2) MIXING AND SCREENING UNIT-A l l of the dry materials afe assembledby batch method and thoroughly blendedthrough a Sackett gravity I-ton mixer.From the mixer each blended batch isdumped mto a vertical bucket elevator andlifted to a single-deck Tyler-Niagara 4' x 8'screen. The screen 40 mesh) throwsout all of the foreign material, sends the

oped and patent pending equipment. Theammoniator is 7 feet in diameter and 7 feetlong, rotates at 8 revolutions per minuteand is equipped with I , H.P. variablespeed motor. The granulator is 6 feet indiameter and 8 feet long also rotates at 8revolutions per minute and equipped with10 H.P. variable speed motor. Vapors,principal moisture generated by the chemical reaction in the ammoniator, are forcedthrough a stack into the atmosphere by asuction fan equipped with , H.P. motor.Sometimes the mixture becomes too wetfor rolling, and when this happens air isblown on the bed of material in the ammoniator for some drying. The fan usedis equipped with 3 H.P. motor. Most ofthe granul tion takes place in the ammoniator, and the granulator is used foradditional rolling of the product.

, ) DRYING EQUIPMENT-The dampgranular product flows from the granulator by chute directly into the dryer. Therotary dryer is 6 feet in diameter and 50

o / ~ - . . . .,mHQPHRS C ~ E S f( . :-.__ e RYER

- .. .. .. . - . : . . - - - - - - - - > - - > - . . . . : ; =

over size to a Sackett # 1 5 pulverizer forrecycling and conditions the batch for ammoniation. From the screen the blendedconditioned batched materials dump intoa supply hopper directly over a continuousbelt weighing machine.(3) SOLID AND LIQUID PROPORTIONINGEQUIPMENT-The continuous operationbegins at this stage. The batch blend ofsolid ingredients is converted to an accurately controlled Poidometer belt scalereceiving its feed continuously from thesupply hopper directly above. Rotometers and flowraters cont rol continuO llsly

the flow of liquid nitrogen solutions,sulphuric acid, and water. The dry rnaterials flow from scalebelt into the am'moniator and the liquids feed into theammoniator under a deep cascading bed ofsolid materials.(4) CoNTINUOUS AMMONlATOR ANDGRANULATOR-The rotary ammoniator

and rotary granulator are T.V.A. devel-

feet long and is driven by a 50 H.P.motor. A co-current 15 million B.T.U.capacity Natural Gas' Fired combustion-:hamber feeds the hot gases thru the dryer.The first several feet of the dryer has directional flights to move the material awayfrom intake of dryer, and from this pointlifting flights move the material to the discharge end. Combustion air is furnishedby a fan equipped with 20 H.P. Motor.Moisture is removed from the dryerthrough a stack to the atmosphere. Dualcyclones recover the fine dust. A 50 H.P.motor is used to drive the cyclone fan.

(6) COOLING EQUIPMENT-Materialfrom the dryer empties into a verticalbucket elevator, which feeds the cooler.The rotary cooler is 6 feet in diameter and40 feet long, and is driven by a 40 H.P.motor. A coun ter-cur rent air flow is usedfor cooling. The cooler flights are similarto the dricr flights. Additio nal moistureduring the cooling process is removed

through the stack to the atmosphere. Dualcyclones recover the fine dust. A 40 H.P.motor is used to drive the cyclone fan.(7) PRODUCT CLASSIFYING EQUIP-

MENT-The cooler discharges onto a conveyor flowing the material into a verticalbucket elevator which lifts the product toa double deck 4' x 15 classifying screen.This screen gives us 3 classifications: Oversille, fines, and finished product. Theoversize passes through a large pulverizer,equipped with 15 H.P. motor, and is returned via a belt conveyor to the dryerfor reworking. The fines are then returnedvia a belt conveyor to the ammoniator andthe desired product flows on a belt conveyor to storage p t for the crane to pickup to store to desired bin.

(8) CRUSHED OVERSIZE-Pulverizerand belt conveyor taking the crushed oversize to the dryer.

(9) FINES RETURN FOR GRANULA-TION-Fines from dryer and cooler cyclones and from classifying screen flow

on conveyor belt back to the ammoniatorfor reworking.10) AMMONIATING AND COOLINGPOWDERED MIXED GooDs-Conventionalpowdered mixed goods is batch-weighed

and the dry materials required for theformula desired are assembled and blendedsimilar to the granular dry materials. TheT.V.A. ammoniator is used for blendingthe dry materials with the required nitrogen solution. The granulator and dryerare not needed, therefore, this equipmentis by passed. The finished ammoniatedpowdered mixed goods flows from the ammoniator onto a conveyor belt emptyinginto the cooler. From the cooler the product flows onto a conveyor belt to a verticalelevator by passing the classifying equip,ment used for the granular product delivering directly to the belt conveyor to takethe product to the crane pit to be pickedup by crane to deliver to desired bin storage.


25/32

THIS business of granulation isno Utopia . It takes a greatdeal of hard work, continuousresearch and experimenting to continue improving manufacturing methods, formulation and quality .

Although it was anticipated, Fertilizer Manufacturing Cooperative,Inc. had its problems getting started.For several weeks all kinds of difficulties were encountered, Viz: Material fr om the ammonia or was toowet, too dr y, too much oversize, toomany fines too much recycle, chuteplugups, pulverizer plugging, screenblinding, too much heat, too littleheat, high moistures, not enough cooling, ammonia fumes, cyclone dusting,etc., etc. During this shakedown period, day by day; we were learningmore and more about the behaviour

erations from day to day, during thestartup period, was the real key togetting us started on full productionby April 1st, 1955. We are continuing to keep records of each day'soperation, showing grade granulated ,formula used, water in materials,water added at the ammoniator, ammoniation rate, moisture driven off hydrier heat and sulfuric acid, cubicfeet of gas consumed per ton of finished product, temperatures, moistures from finished product , cooler,ammoniator, granulator, recycle fines,and oversize; also screen analysesfore class ifying finished product,oversize, fines from classifying screenand cyclones. N.P.K. analyses aremade once per shift, and the othertests are made periodically throughthe shift. This control and permanent

AMMONIATION nd GRANULATION ATFERTILIZER MANUFACTURING COOP

Fertilizer Manufacturing CooperativeBaltimore, Md.

of our equipment, finding troublespots, eliminating previous operatingerrors, stationing our crew whereneeded, and getting straightenedaround on formulation.

Keeping accurate records of op-

The 4' x 8' Tyler-N iagara singledeck screen for screening the drymaterial batch before enteringT.V.A. Ammoniator.

record work, I am sure, has helped usto stay on the right track as much asany of the other major controls used

our process.Since starting on full production,

April 1 1955 to June 30, 1955, one

Twin dryer cyclones and the double deck Tyler 5' x 15' vibratingclassifying screen.

eight -hour shift per J ay, FMCI manufactured 14,000 tons of granularmixed goods. Four grades were madeduring this period. Most of the tonnage was 10-10-10 and 8-16-16 and asmall tonnage of 6-12 -12 and 6- 18-18.Nitrogen solution carrying 22.2%free ammonia was used in the 10-10-10 and 8-16-16, and nitrogen solutioncarrying 16.6% fre e ammonia wasused in the 6-12-12 and 6-18-18. SinceJuly 1st FMCI has improved its pro duction operation, using 22.2% freeammonia in 6 nitrogen formulas.Types of nitrogen so lution used mayhave to vary from time to time, depending on the formula desired.

FMCI had no difficulty granulat ing the higher nitrogen grades 10- 10-10 and 8-16-16 by adjusting the wateradded if the material from the ammoniator was too dry, or by not add ing water, or taking out 25 lbs. to 50lbs. of nitrogen solution and substituting sulfate of ammonia, if the material from the ammoniator was toowet. Lower nitrogen grades 6-12-12and 6-18-18 were more difficult togranulate. We got nowhere withthese grades until we added 100 lbs.of 60 Baume sulfuric acid to give additional heat to help plasticity andalso added considerable water. SinceJuly 1st we have experimented with acoarse potash, almost 100% through10 mesh and about 85% on 20 mesh,and find we can do a better granulating job with 6% nitrogen mixtures byusing a combination fine and coarse orall coarse potash. We have done considerable experimentin g with Minco

Conveyor takes the fines from thecyclones and fines from the classifying screen back to the ammoniator for reworking.


26/32

Another view of the ammoniatingfloor showing conveyor on right,which takes the finished screenedproduct to pit for cranes, to carryback to storage and conveyor,

Conditioner , a fine clay dolomiticlimestone and find this material helpedgranulation.

Most of the 14,000 tons of granular made from March 15th to June-30, 195 5 was shipped within 48 hoursafter manufacture, and in some casesthe fertilizer was shipped direct fromproduction with no trouble on condition. However, several complaints onsevere packing of 6 -18-18 shippedduring hot weather, July and earlyAugust were encountered. I believewe could have eliminated these complaints had the mixture been dustedwith a fine clay at time of bagging.We plan to do considerable experimenting by dusting the mixtures witha fine clay at time of shipment to findout what improvement we can expectin mechanical condition when thegoods are stored for long periods.

A surge hopper carries thescreened dry material and empties into a continuous poidomet erfor delivery to T.V.A. ammoniatoron floor below.

At the present we are on aone shift basis, working 8 hours perday. After each shift all of the equipment is thoroughly cleaned . This procedure is very important to keep operating with practically no downtime. Granulation at present is moreof an art than a science. The man as-signed to watch the continuous ammoniator must stay on the job at alltimes. He is the most important ofthe entire crew. All of the controlsfor feeding the dry material, solution,sulfuric acid, water, return finesand oversize belts are near the ammoniator easily accessible to the operator. This procedure permits the ammoniator operator to make the necessary changes within seconds.

As we approach the end of ourfirst year of granular production, substantially over 40,000 tons of granu-

The intake to the TVA ammoniator, showing piping for ammonia,sulfuric acid and water. The drybatch flows into the hopper fromthe floor above,

lated mixed goods ha,ve been made inthe following 7 grades: 6-12-12 , 6-1218,6-18-18,8-16-16,8-16-16 carrying3 units magnesium from sulfate ofpotash magnesium, 10-10-10 and 10-20-10.

In general, the process as shown111 Figure 1 has given a very goodac-:ount of itself in that the hourlyproduction estimates made by theequipment manufacturer have beencompletely fulfilled, and in most caseshave been substantially exceeded.

The flow diagram (Pg. 40) showsthe ammoniating, granulating, drying,cooling and classifying equipment.The entire unit, building changes,foundations, all engineering, designand equipment was engineered andbuilt by the A. ]. Sackett Sons Co ,Baltimore, Md.**


27/32

THEORIES nd PRACTICESn MMONI TION

CInuvJ e. Pe vdneAllied Chemical and Dye Corp.Nitrogen Division

New York, N. Y.

Jt MMONIA is the lowest cost ni'trogen. Thus from the eco-nomic angle alone, it behooves

management to use as much of thisproduct as practical whether it beammonia contained in the ammoniating solutions or as anhydrous ammonia. In addition to the price advantage,many persons believe that much of thegood condition of ordinary fertilizer isachieved through high rates of am'moniation, and that extreme rates arealmost mandatory in granulation.Also the heat of the ammoniationreaction is desirable in more casesthan in granulation alone. W e are notunmindful of the possibility of re'version in the P205 and of some otherdisturbing features related to highas well as to low rates of ammoniation.

f anhydrous ammonia alonecould supply all of the nitrogen required in all of our formulas, theproblems would be greatly simplified.It so happens that the second lowestcost nitrogen is derived from chemi,cals that are logically in combinationwith anhydrous ammonia. This combination forms the very popular am'moniating solutions. The makers ofthese solutions are constantly tryingto meet the demands of performancethat are being put on their products.

One of the most significant developments in the fertilizer industryin recent years has been the doublingof the old long-time rate of 3 poundsof ammonia per unit of P205 in 20%superphosphate. As more suitableammoniating media are developed andsome of the shortcomings are circum'vented, the demands focus more ongetting a few more pounds of ammonia into the superphosphate. This

is just alxJUt the number one problem; and it is through an understanding of the theories and practices ofammoniation that this problem canbe solved.

Ammoniation can be effected alittle more readily with nitrogensolutions than with anhydrous ammonia this discussion, however.deals with ammonia regardless of itssource. The principles remain thesame although it is necessary to varythe techniques a little in handling anhydrous ammonia. Superphosphatein this article refers to a normal 20%product. The same principles applyto the ammoniation of triple superphosphate, but the practical limit ofammoniation seems to be about halfthat for the 20% material. It shouldbe noted too that the presence ofmany large particles reduces the ammonia take-up seriously, as shown ina study on particle size by theUSDA.

About the same amount of ammonia can be added to a given amountof superphosphate, whether the superphosphate is in a nitrogewphosphor'ous base or in such dilute formula asthe 3, 12-12. It is necessary only toprovide a little mixing of the dry ingredients prior to introducing theammonia into complete goods.

Normal superphosphate has sucha high affinity for ammonia that aI,most any scheme that brings the twomaterials into reasonable proximityfor a short time will result in 25 to3.0 pounds of ammonia being takenup per unit of P 2 0 ~ \Vith 20% superphosphate the theoretical limit is 9.6pounds of ammonia plus about onepound of each three pounds of free

acid present. Until 6 or 7 yearsago, ammoniating arrangements weresuch that in the initial steps, mostof the ammonia was taken up byless than half of the superphosphate. Some operators werc neverconverted to modern techniques, andan apaIling number have gone backto the old methods because of theirfailure to understand the newerdevelopments.

The reactions at the lower levelsare almost instantaneous and permanent. Today, however, we are attempt'ing to make all of the superphosphatedo its share of the work.

Superphosphate probably takesup ammonia beyond 3 pounds perunit of P20 5 more slowly than before this point is reached. The gas

::0/::'1/55 INCHES lRtE.t l>Nt

will react more slowly with dry m;vterials than will the liquid fromwhich this gas escaped. We certainlymust provide means for reacting thisgas when we go beyond 3 poundrates of ammoniation at the tons perhour rates that payoff. This requiresintimate contact, combined with eithercontinual or repeated exposure of thesuperphosphate to the gas. As thetask of reacting the gas is the mostserious of the ammoniating problems,it is advisable to generate the gasonly as fast as it can be taken up inthe reactions.

1 OfAl. l :x. IN 1&C()l6) ITO.tnL X 6.5 l 'OUNl) or }I'll, PR\ UIIl t '2S (2o:l aUl lft

::t-'0]}C

1/..

: : o l ~ - - - : : r l - Ji I I i \ i}.o 4.0 5.0 6.0 6.S 7 0SICJUBl)$ OJ l"'il\ WIT 'aOs SUrDThese production problems are

almost the same with both nitrogensolutions and anhydrous ammonia.They differ only in degree and not


28/32

nearly as much in degree as is generally supposed.These principles are more easilyunderstood when applied to the con'ventional rotary batch mixer. The

TVA type of continuous ammonia'tor uses different means to implementthe principles. But the principles willhelp in getting the very best performance regardless of the type of ammoniator used.

All of the finely screened materials should be in the mixer beforeammoniation is started. It is usuallybest to use the full capacity of themixer. This will assure' better contact with the ammonia and providefor maximum scrubbing of the gasby the showering mass. We havefound no improvement in ammoniatake-up nor in condition of the goodswhen the superphosphate is ammoniated in the mixer prior to admittingthe balance of the materials. Someoperators attempt to ammoniate themass collectively, or the superphosphate separately, as the materials aresliding into the mixer. How could anammonia distributor pipe be drilledto successfully achieve this feat?

The distribution of the massin the rotary mixer has probably be'come constant after one revolution ofthe mixer. You can watch a smallglass mixer and see this. Most continuous ammoniators rightly providefor some mixing ahead of the am'moniator to conserve its capacity forthe important function of getting theammonia into the superphosphate.It is possible to locate the holesin the ammonia distributor pipe witha pattern that will introduce the rightamount of ammonia for the amount

of superphosphate that exists alongevery inch of the length of the mixer.And it is extremely important to dothis. In the conventional mixer thismeans a pipe that extends throughthe entire length of the mixer. Insome cases, it s necessary to offset aportion of the end to clear the move'ments of the discharge door. In somemixers, it means cutting off some ofthe width of the extremely wideflights to allow clearance between theflights and the discharge door. Somemixers are so long that it is difficultto support the pipe.

All of these problems are beingmet, and quite easily in most mixers.But it would pay to throwaway evena costly new mixer that can not bemade to accomodate the higher am'moniation rates . . . for that is in'deed a costly mixer. Were it notthat stainless steel does the job per'fectly well, it would be profitable tomake a good ammonia distributorpipe even of gold or platinum forthe savings in the cost of nitrogencan run over $200 per operating day.Actually, this distributor pipe isa metering device or manifoldwhether it is so recognized or not.And it had better be a good one.It contends with requirements asexacting as many of the manifolds inthe chemical industry. Both typesshould be given the same close a::cntion that they deserve.

For years enough has beenknown about the requirements of adistributor pipe to justify making thenext one of stainless steel. We admitthat there is room for improvement.The holes of an ordinary steel pipesoon corrode, thus destroying anyability to correctly meter the ammoniato the desired points in the desiredvolume. So then you have to reducethe amount of low-cost nitrogen thatcan be used, buy a dm;en gas masks,and start on the hunt for that nitro'gen that the state chemist failed tofind in your fertilizer.

The problems of gas are greatlyreduced when the ammomatmgmedium is applied in its liquid statein such a manner that every particleof superhosphate can be contacted atleast once by the liquid. It is quiteconceivable that in batch rotarymixing the particles are returnedseveral times for repeat baptisms ofammonia, thus effecting an accumula,tive, or multi'stage ammoniation. Itdoes not require much imagination tobelieve that this s also happening inthe TVA unit, and just as effectively.

Judged by the speed by whichmoderate rates of ammoniation areperformed with good equipment,there is much evidence to indicatethat as much as 4 pounds of ammonia can be taken up from thesolution while it is still in solution.The duration of the act of ammonia'

tion for these moderate rates need notexceed 25 or 30 seconds.Atomizing sprays have beentried. f it were practical to retainthe fogging effect that is so easilydemonstrated outdoors, we would beammoniating at much higher rates.

But the very heavy showering cur'tains of fertilizer blanket any knownatomizing spray. The effect is thatof a very few holes in a pipe andthose very poorly placed.

One continued slot for thclength of the pipe with additionalshort slots to effect a good patternwas tried. This failed, probably be'cause the very thin sheets of liquidlacked driving power for penetra'tion. The ammonia was depositedin a thin layer on the surface of thethick curtains of materiaL f timewere of no concern, this, as well asmany other discarded methods, wouldsuffice.

Much more superphosphate iscontacted in a short time throughthe modern distrihutor pipe by its12 to 30 powerful streams locatedstrategically, each of which can pene'trate the heavy loose curtains anddisperse inside for yet more contact.I t delivers the milk along the streetas called for by the concentration ofmilk drinkers along the street.

f no scale or rust can enter thesystem, the holes in the pipe may be3 16 inch drilled in one row on oneside of the pipe. This size of holepermits twice the number of pointsof contact that will result from Yinch holes. There is no justificationfol 'Ising ordinary steel in such avital place as the distributor pipe.Where any ordinary steel exists else'where in the system, the holes in thepipe should be Y inch, even thoughthe pipe itself be of stainless steeL

Even the most ardent supporterof the principles which have beenoutlined will concede that gas is acertainty at 5 pounds of ammoniaper unit of P205 in 20 superphosphate and probably at a lower leveLAt the popular high rates of am'moniation and of plant productionthe problems of gas take on magni'tude. No mixer is tight enough tohold the gas if provisions are notmade to take care of it inside the


29/32

mixer as it is generated. Any suc'cessful high rate ammoniating system surely does generate gas. Theunsuccessful ones release it to theatmosphere before it can be reacted.

There are two factors which makeit necessary to add ammonia at ratesabove 4 or ) pounds progressivelymore and more slowly. One: sincethe mass of the material into whichthe ammonia is injected is gettinghotter and hotter, a higher portionof the ammonia is being transformed into gas. The reaction of gaswith the dry super is slow. Two:the reaction of any form of ammoniawith &uperphosphate is apparentlyslower as the reactions reach theupper practical limits.

Cascading superphosphatethrough the confines of a machinein the manner as is done in therotary mixer is a very fine means ofscrubbing ammonia out of the atmosphere, whether that atmosphere contains 1% or 99% ammonia. Eventhe more efficient of the present modern systems do not give wholly uniform contact between the superparticles and the ammonia while theammonia is in the liquid stage. TheUSe of gas, unintentional and troublesome as it is, does permit eveningup the irregular or spotty work ofthe liquid. Gas seems to be the mostfeasible method of getting uniformexposure.P,rovisions For Reacting Ammonia Gas

ITH the liquid stage accounted for, we can now turn our

attention to the problems of scrubbing the ammonia gas from the atmosphere inside the mixer. Themixer, it must be remembered, isessentially an open or at best a nonpressure machine. Conditions aresuch that there is a vaporizing actionin one sense, and there can be anequal scrubbing action i operationsare geared to it. The problem is tolimit the production of gas to theability of the cascading superphosphate to rick up the gas. This takestime. And there is time for this actiO


30/32

Hro.o t of" 100~ ~ : . 90[ O s ~ i t O r :Ht . ned

10 11155

'0

'10

- - - - ~ - ~ ~ - T ~ _ _ _ _ _ _ r - - - ' . 5 7.0 ' ..S 8.0 8.5 9.0 9.S

AJI,ClClA j,ppm FiR UNl't 0 "20s {2 ' ) 1 J l ' a \ J ' l t 0 6 ~ .

Eeottomca 0'- t.lt:QtIl,\flliiG10(1 ',. d lQ UTl a ; N THE J i ~ f EC081' USING 1I"1T1t00&l4 $OWflot "1$ N Ail .) CC4ltAt:NINQ ~ .II }IL HO A,l);>11 lcg/.:.-t}.OO -:::: ---- m r a C

:O:l.1.00 . - . - - r - r - t - . ~ - - - -

6 5 7 0 1. 6,1) 8.5 \1.010/ll/S'J

tion of 65 pounds of ammonia inputper unit of 20% superphosphate, itis possible to hold as much as 8 poundswhen 9 pounds are applied. This in'wIves a loss of one pound of ammonia. I t means that 8 pounds isabout all of the ammonia that it ispractical to hold without the aid ofacid. The addition of 10, 11 or even12 pounds fails to give any morethan 8.0 pounds retention. Howmuch ammonia is taken up as gas Inthis scheme?

Acid-Its Use and Mis-UseM OST of the mixers, includingthe TVA continuous, arecapable of retaining 100% of anammonia input

proceeding of the fertilizer industry round table

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