ZINC COATED UREABY: ABHISHEK ANAND

Msc Chemistry & B.E. ChemicalBITS PILANI

UREA: THE FERTILISER GIANT

•NITROGEN BASED FERTILISER & MACRO-NUTRIENT&IS PREPARED IN GRANULE,PRILLS AND CRYSTALS•HEART OF AGRICULTURE INDUSTRY

•. USED IN PREPARATION OF PIGMENTS AND ADHESIVES•UREA HAS HIGHEST NITROGEN CONTENT OF ALL NITROGEN BASED FERTILISER AND HENCE LOWEST TRANSPORTATION COST PER UNIT OF NITROGEN.

•IMPORTANT RAW MATERIAL FOR OTHER INDUSTRIAL & HOUSEHOLD PRODUCTS•MORE THAN 90% OF UREA IS DESTINED FOR NITROGEN BASED FERTILISER

PROPERTIES OF UREA

NH2CONH2

STRUCTURES OF UREA

TATA CHEMICALS: A HUB OF UREASUSTAINIBILTY

WORK ETHICS

INNOVATION

AIM

UREA PRODUCTION

RAW MATERIALS

BASIC CHEMICAL REACTION

PROCESS INVOLVED

RAW MATERIALS

Liquid ammonia

Utilities like cooling

water, steam and

electricity

Gaseous carbondi-

oxide

Urefix-a chemical for increasing crushing

strength of urea

BASIC CHEMICAL REACTION

Rkn Condition: (1850C,160kg/cm2/s)2NH3 (l)+ CO2 (g) NH2COONH4(l) + 38.1 Kcal/mol

Rkn Condition: (1800C)NH2COONH4(l) NH2CONH2(l) + H20(l) -7.1 Kcal/mol

KEY POINTS IN THE REACTION

MOLE RATIO•For higher yield a mole ratio of 3.3-3.6 : 1 maintained for NH3/CO2

BIURET FORMATION(NH2CONHCONH2)•2NH2CONH2 NH2CONHCONH2 + NH3•Avoid this as it lowers yield of urea and also kills plant

WATER CONTENT•A low H2O/CO2 ratio favours urea synthesis•If too low water is there,then crystallization of water results in choking of pipeline

PROCESS INVOLVEDUREA SYNTHESIS

& HIGH PRESSURE RECOVERY

UREA PURIFICATION & MEDIUM LOW

PRESSURE RECOVERY

UREA CONCENTRATIO

N

UREA PRILLING

WASTE WATER TREATMENT

UREA PLANT BLOCK DIAGRAM

NH3

CO2

Reactor StripperTK-1/ K-01

MPD LPD

Pre-Vacuum & Vacuum System

Prilling SystemUREA

CarbamateCondenser

MPAbsorber

WWTSection

AmmoniaReceiver

DMplant

PERCENTEGE COMPOSITIONCONTAINERS NH3% CO2% H2O% UREA%

REACTOR 32.82 13.78 20 33.4

STRIPPER 24.73 6.66 24.56 44.05

MP DECOMPOSER 6.44 1.38 29.62 62.56

LP DECOMPOSER 1.75 0.77 27.66 69.82

PRE-VACCUM CONCENTRATOR

0.38 0.1 16.32 83.2

AFTER PRILLING THE SOLUTION CONTAINS MORE THAN 99% OF UREA w/w.

ZINC DEFICIENCY-A REAL THREAT!!!

• Zinc is essential micronutrient for growth of plants.

• Generally Zinc is marketed as Zinc heptahydrate i.e. ZnSO4.7H2SO4

• Zinc deficiency is widespread in rice growing tracts of northern India

• Beside N,P,K & S, Zn has gained maxium attention of late owing to its deficiency in soil.

IND0-GANGETIC PLAIN

• A Micronutrient essential for plants• It’s deficiency is widely spread

ZINC

ZINCATED UREA-A SOLUTION??

WHAT TO CHOOSE-DILEMMA OR CLARITY??

Water souble,hygroscopic,low %

of eleme

ntal Zinc

ZnSO4ZnCO3

ZnCl2 &Zinc

chelates

Water insoluble and non-hygroscopic

High % of Zinc

Zno

CONVENTIONAL METHODS FOR INCORPORATING ZINC ON UREA

Dry Blending

Coating

Solution Dispersion Method

Dry-Blending Technique

• Dehydrated powders are mixed together to achieve a uniform blend of macro and micro nutrient

• The method is less capital intensive and more energy efficient

• Dry ingredients are blended in large batches in a ribbon blender

• Blending is done until the nutrients of the ingredients are distributed throughout the batch.

• The blended product is then passed through a sifter to remove the oversize and extraneous particles

• The process is not suitable as zinc salts combining with urea is hygroscopic and hence results in agglomiration or cake formation.

• Furthermore,powdery zinc salts separate resulting in waste of zinc

Solution-Dispersion Method

• Zinc oxide is not suitable here as it is insoluble in water.Here a liquid dispersion medium is used.

• Other zinc salts are tried but face the threat of higher hygroscopic value.

• Toovercome the water absorption rate many binders such as Clay or ammonium nitrate can be used,but they too are ineffective

Coating

• When granules of urea coated with a micronutrient is wetted with water or steam,then micronutrient react with fertiliser component to form in situ stable complexes

• The urea is first dried and then mixed vigorously for at least 3 minutes with micronutrient

• The micronutrient is incorporated intimately into the structure of urea granule rather than a shell structure surrounding it.

• The batch and continuous test were still unsatisfactory with uniformity,adherence of zinc particles were bwlow par.

WHAT WE LOOK FOR IN COATING ZINC ON UREA??

UNIFORMITY ADHERENCE

NO AGGLOMIRA

TION OR CAKE

FORMATION

HYGROSCOPIC

VALUE=ZERO

ZINC OXIDE:THE PERFECT CHOICE

Proposed Solution 1

•Excellent adherence and uniformity is obtained•Conventional technique like dry blending with calcination is used

Proposed Solution 2

•Very well suited for urea plant•Coating of metal oxide to urea followed by heating

PROPOSED SOLUTION 1Homogenous coating of Zinc

High elemantal zinc content

OBJECTIVE

WHAT WE REQUIRE??• ZnO having purity of 90 to 99%• ZnO of particle size 90% less than 12

micron & 95 % less than 37 micron• Also carbon content 0.05 to 2% can be

blended• Binding agent like clay and ammonium

nitrate can be added to maintain adherence

• Traces of FeO,MgO,CaO also increase adherence and uniformity.

EXPERIMENTAL PROCEDURE• Particle size distribution is obtained

from wet screen analysis and by soil dispersion method

• Adherence are obtained by using/exposing coated samples to vigorous air flow for 5 minutes

• In Calcining ,Zinc oxide samples were heated at 16000 F,ground to less than 400 mesh and used to coat urea prill with 8% of calcined material

ANALYSIS OF BEST RESULT• Purity of ZnO from 95% to 99%• Uniform particle size of at least 90% less

than 8 microns and 98% less than 37 microns

• Carbon content from 0.2 to 0.5 %• Bulk density from 28 to 38 lbs per cubic

foot• Binders such as clay and ammonium

nitrate may be used if required

PROPOSED SOLUTION 2Coating of at least one metal oxide

Heati

ng t

he c

oate

d

particles t

o

have reacti

on

bet

wee

n

metal

oxi

de a

nd

urea

Facilitate the addition of micronutrient sulphur

Relatively non-caking of micronutrient containing nitrogenous substance

OBJECTIVE

WHAT WE REQUIRE??

• Containers like Conventional pan and drum granulators & Fluidized Bed dryers

• Addition of liquid(usually water) for particle adhesion

• Burner or Impinging heated gases such as heated air or gases from combustion

• Sieve Analysis for particle size distribution

• Screw conveyors

EXPERIMENTAL PROCEDURE

• Mixing prilled urea with dry powdered metal oxide(ZnO) in Screw Conveyor

• The above mixture is allowed to fall in rotating pan granulators

• The pan granulator is heated by a burner placed under it

• Addition of hot gases directly to the mixture to maintain temperature of pan between 100 to 1330C

• Water is sprayed(0.5 to 5% of weight of urea-ZnO mixture) to ensure particle adhesion.

• Product discharge from Pan passed through Sieve,which removes finer particles for recycle to pan

• And is then cooled below 500C before being placed in storage.

HOW SULPHUR IS INCORPORATED??

• Product discharge from the pan(ZnO coated urea) is passed through another granulator where molten sulphur is sprayed.

• After cooling ,it is again kept for storage. • Hence,adhesion of three particles

namely urea,ZnO and sulphur is achieved.

CHALLENGES OF THE PROPOSED METHOD

Problem

A side reaction occurs at urea metal

oxide interface .

Addition of Sulphur increases the prodcut cost

Dust formation in the drum