Physical Characterization Of Urea Binder Extrude At Various Weight Concentration.

UNIVERSITI TEKNIKAL MALAYSIA MELAKA

This report submitted in accordance with requirement of the Universiti Teknikal Malaysia Melaka (UTeM) for the Bachelor Degree of Manufacturing Engineering

(Manufacturing Process) (Hons.)

by

MUHAMMAD YAZUAN BIN YAAKUP B050810104

89080105069

FACULTY OF MANUFACTURING ENGINEERING 2012

PHYSICAL CHARACTERIZATION OF UREA BINDER

EXTRUDE AT VARIOUS WEIGHT CONCENTRATION

BORANG PENGESAHAN STATUS LAPORAN PROJEK SARJANA MUDA

TAJUK: Physical Characterization of Urea Binder Extrude at Various Weight

Concentrations

SESI PENGAJIAN: 2011/12 Semester 2

Saya MUHAMMAD YAZUAN BIN YAAKUP

mengaku membenarkan Laporan PSM ini disimpan di Perpust akaan Universit i Teknikal Malaysia Melaka (UTeM) dengan syarat -syarat kegunaan sepert i berikut :

1. Laporan PSM adalah hak milik Universit i Teknikal Malaysia Melaka dan penulis.

2. Perpust akaan Universit i Teknikal Malaysia Melaka dibenarkan membuat salinan

unt uk t uj uan pengaj ian sahaj a dengan izin penulis.

3. Perpust akaan dibenarkan membuat salinan laporan PSM ini sebagai bahan

pert ukaran ant ara inst it usi pengaj ian t inggi.

4. **Sila t andakan (√)

SULIT

TERHAD

TIDAK TERHAD

(Mengandungi maklumat yang berdarj ah keselamat an at au kepent ingan Malaysia yang t ermakt ub di dalam AKTA RAHSIA RASMI 1972)

(Mengandungi maklumat TERHAD yang t elah dit ent ukan oleh organisasi/ badan di mana penyelidikan dij alankan)

Alamat Tet ap:

BATU 3 ½, KG. KUALA PAH,

71600, KUALA KLAWANG,

JELEBU, N. SEMBILAN

Disahkan oleh:

PENYELIA PSM

Tarikh: ______________________

** Jika Laporan PSM ini SULIT at au TERHAD, sil a l ampirkan surat daripada pihak berkuasa/ organisasi

DECLARATION

I hereby, declared this report entitled “Physical Characterization of Urea Binder Extrude at Various Weight Concentration” is the results of my own research except as

cited in references.

Signature : ……….

Author’s Name : Muhammad Yazuan Bin Yaakup

APPROVAL

This report is submitted to the Faculty of Manufacturing Engineering of UTeM as a partial fulfillment of the requirements for the degree of Bachelor of Manufacturing Engineering (Manufacturing Process) (Hons.). The member of the supervisory committee is as follow:

ABSTRAK

Tujuan kajian ini adalah untuk menentukan peranan sifat-sifat fizikal Urea pengikat meleler pada pelbagai nisbah kepekatan. Analisis akan dilakukan dengan menggunakan mesin Pemampatan, Penganalisis Saiz Butir dan Densimeter Elektronik di pelbagai nisbah kepekatan. Hasil dari ujian pemampatan, analisis saiz butir dan ujian ketumpatan akan memberitahu kita sifat-sifat fizikal Urea Pengikat. Parameter yang digunakan dalam kajian ini adalah kepelbagaian nisbah kepekatan Urea Pengikat. Ujian Pemampatan ini digunakan untuk melihat kekuatan menghancur butir Urea Pengikat. Analisis saiz butir Urea Pengikat digunakan untuk mencari sama ada terdapat sebarang butir bahan-bahan mentah yang hilang atau tidak hilang selepas proses penyemperitan. Daripada analisis saiz butir, ia juga boleh menunjukkan sama ada bahan mentah telah digabungkan dengan baik atau tidak baik. Keputusan bagi ujian ketumpatan Urea Binder adalah untuk mencari sama ada terdapat mana-mana yang ketumpatan berbeza yang terhasil akibat pelbagai nisbah kepekatan Urea Pengikat. Akhirnya data yang diperolehi akan memberitahu kita hubungkait antara kekuatan menghancur butir Urea Pengikat, saiz butir Urea Pengikat dan ketumpatan Urea Pengikat untuk memahami lebih lanjut mengenai proses Butiran baja.

ABSTRACT

The aim of this study is to determine the role on the physical properties of Urea Binder extrude at various weight concentrations. The analysis will be done using the Compress machine, Particle Size Analyzer and Electronic Densimeter at various weight concentrations. The result from compress test, particle size analysis and density test will tell us the physical properties of Urea binder.The parameters that are used in this study are concentration of Urea binder. The compress test is used to look the granule crushing strength of Urea binder. The analysis of particle size is to find whether there is any particle of raw materials lost or not after extrusion process. From particle size analysis it also can show either the raw materials had combined and granule well or not. The results for density test is to find whether there is any different of density occur because of the various weight concentration of Urea binder. Finally the data obtained will tell us the correlation between granule crushing strength, particle size and density in order to understand more about the fertilizer granulation process.

DEDICATION

I especially dedicate this report to my father and my mother.

Without their patience, understanding, support, and most of all love, the completion of this study would not have been possible.

I also dedicate this report to my friends no matter where they are now. We have built this tight relationship and being together for many years.

Without all of you, surely I could not all the challenges.

ACKNOWLEDGEMENT

Firstly I would like to take this chance to thank all lecturer and friend for giving an advice and support since the beginning of Final Year Project1 until today Final Year Project 2. A very thankful for my Supervisor, Mr. Mohd Fairuz Bin Dimin @ Mohd. Amin for giving me much support and guidance in order to complete this project and report within the given period. He gave me so many ideas and suggestions in order to perform well along this period.

I also would like to thank all my friends for giving an opinion and helping me in searching for information and guidelines for my study. I believed that all the knowledge I got here might be useful later in my career. I would like to convey my appreciation to all Manufacturing Engineering Faculty Lecturers and staff for being so kind and helpful along this period of studies. Without all of them, I am nothing and my four years studies may be useless.

TABLE OF CONTENT

Abstrak i

Abstract ii

Dedication iii

Acknowledgement iv

Table of Content v

List of Tables viii

List of Figures ix

List of Abbreviations, Symbols and Nomenclature x

1.0 INTRODUCTION 1

1.1 Background 1

1.2 Problem Statement 2

1.3 Objectives 2

1.4 Scopes 3

2.0 LITERATURE REVIEW 4

2.1 Fertilizer 4

2.2 Urea Fertilizer 5

2.3 Urea Manufacturing Process 6

2.3.1 Synthesis 6

2.3.2 Purification 6

2.3.3 Concentration 7

2.3.4 Granulation Process 7

2.3.4.1 Wet Granulation 8

2.3.4.2 Dry Granulation 8

2.4 The Physical Characteristic of Urea 9

2.4.1.1 Effects on Agronomic Response 10

2.4.1.2 Effects on Granulation and Process Performance 11

2.4.1.3 Effects on Storage, Handling, and Application Properties 11

2.4.1.4 Effects on Blending Properties 12

2.4.1.5 Particle Size Analysis 14

2.4.2 Density 14

2.4.2.1 Bulk Density 14

2.4.2.2 Apparent Density 15

2.4.2.3 True Density 15

2.4.3 Granule Hardness 16

2.4.3.1 Crushing Strength 16

2.4.3.2 Abrasion Resistance 17

2.4.3.3 Impact Resistance 18

2.5 The Parameters in Urea 18

2.5.1 Concentration of Urea 18

3.0 METHODOLOGY 20

3.1 Planning of the Study 20

3.2 Flow Chart of Methodology 21

3.3 Machines and Equipment 22

3.3.1 Extruder machine 22

3.3.2 Particle Size Analyzer 24

3.3.3 Electronic Densimeter MD-300S 26

3.3.4 Compression Tester 28

3.4 The Materials 30

3.4.1 Pure Urea (CH4N2O) 30

3.4.2 Soy Bagasse 31

3.4.3 Wheat Flour 32

4.0 RESULT AND DISCUSSION 33

4.1.1 Compression Test 35

4.1.2 Density Test 37

4.1.3 Particle Size Analysis 38

4.2 Discussion 41

5.0 CONCLUSIONS AND RECOMMENDATIONS

5.1 Conclusions 44

5.2 Recommendations 45

REFERENCES 46

APPENDICES

A Gantt chart for PSM 1

B Gantt chart for PSM 2

C Parts of Extruder machine

D Parts of Extruder machine

E Parts of Extruder machine

LIST OF TABLES

3.1 Sample Ratio by Gram 23

3.2 Sample Ratio by Percentage 23

4.1 Result of Compression test 35

4.2 Result of Density test 36

4.3 The Range size of Soy Bagasse for Particle Size analysis 38

4.4 The Range size of Wheat Flour for Particle Size analysis 39

4.5 The Range size of Urea for Particle Size analysis 40

LIST OF FIGURES

2.1 Schematic representation of Urea synthesis 5

3.1 Flow Chart for Methodology 21

3.2 Extruder machine 22

3.3 Particle Size Analyzer 24

3.4 Flow Chart for Particle Size Analyzer 25

3.5 Electronic Densimeter 26

3.6 Flow Chart for Electronic Densimeter 28

3.7 Compression Tester 28

3.8 Flow Chart for Compression Tester 30

3.9 Pure Urea (CH4N2O) 30

3.10 Soy Bagasse 31

3.11 Wheat Flour 32

4.1 Sample A (Soy Bagasse 50%: Wheat Flour 25%: Urea 25%) 33

4.2 Sample B (Soy Bagasse 25%: Wheat Flour 50%: Urea 25%) 34

4.3 Sample C (Soy Bagasse 25%: Wheat Flour 25%: Urea 50%) 34

4.4 Sample D (Soy Bagasse 33.34%: Wheat Flour 33.34%: Urea 33.34%) 35

4.5 Graph of Compression test 36

4.6 Graph of Density test 37

4.7 Graph of Soy Bagasse for Particle Size analysis 38

4.8 Graph of Wheat Flour for Particle Size analysis 39

4.9 Graph of Urea for Particle Size analysis 40

LIST OF ABBREVIATIONS, SYMBOLS AND

NOMENCLATURE

C - Carbon

H - Hydrogen

He - Helium

ISO - International Organization for Standardization

K Potassium

MTPD - Mertic Tonne per Day

N - Nitrogen

Ne - Neon

No.exp - Number of experiment

O - Oxygen

P - Phosphorus

QC - Quality control

R - Correlation coefficient

R2 - The value of coefficient of determination

UPM - Universiti Putra Malaysia

USM - Universiti Sains Malaysia

UTeM - Universiti Teknikal Malaysia Melaka

CHAPTER 1

INTRODUCTION

Fertilizer is known as a catalyst or supply the plant nutrient essential to growth the plant. Typically the term of fertilizer is used to refer to the industry of agriculture that researches, designs, manufactures, operates, and maintains the growth of the plant on the earth. Fertilizer is very important in agriculture industry because it also contribute in the economy of country. These specifications narrowed the manufacturing processes of fertilizer of Urea.

1.0 Background

OneBaja group that contains four Universities that is UTP, UPM, USM, and UTeM had been assigned a Project entitle “Next Generation Green and Economical Urea” under Kementerian Pengajian Tinggi Malaysia. UTeM will be doing research about “Biodegradable Urea Granules”. Physical characterization of Urea binder extrude at various weight concentration is one of minor scope that will be review. A single line urea granulation plants nowadays have reached capacities of more than 3,500 MTPD. With increasing environmental and health awareness, more and more attention is paid to the insoluble binder being used in the urea granules and the ammonia emissions from such plants. These nondegradable binders such as formaldehyde may well be absorbed by the plant and get into the food cycle. If large amount is consumed and untreated in a prolong period of time it may cause a detrimental effect to human. The challenge is to come up with a new biodegradable binder for the urea granulation process with

comparable quality and cost against the current available technology. A compound fertilizer is a complex homogenous product containing two or more of nutrients that has undergone chemical interaction during the manufacturing process. The chemical compounding is followed by the process of granulation with the addition of anti caking agents to form free-flowing compound granules. One of the processes in fertilizer manufacturing is blending process. In this process, Urea will be blended in various weight concentrations. The types of the processing parameters are various weight concentrations. This process is done to combine Urea and binder to produce fertilizer. From this process, there are some physical properties that being used which are hardness, particle size and density. This three characteristic are used to see whether there is changes when Urea binder is blend in various weight concentrations. Besides, the compress test, particle size analysis and densitometer are the tools that being used to test the hardness, particle size and density of Urea binder.

1.2 Problem statement

(a) The physical properties of Urea binder extrude at various weight concentrations. (b) Hence this study, will determine whether there is any changes when the granule

crushing strength, particle size and density against various weight concentrations.

1.3 Objectives

The objectives of this study are:

(a) To determine the physical characterization of Urea binder extrudes at various weight concentrations.

(b) To deliver the granule crushing strength, particle size and density of Urea binder using Compression machine, Particle Size Analyzer and Densimeter when extrude at various weight concentrations.

(c) To analyze the correlation between the granule crushing strength, particle size and density against various weight concentrations whether, if there is any changes in the physical properties of Urea binder.

1.4 Scope

The aim of this project is to determine the physical characterization of Urea binder extrudes at various weight concentrations. Parameter that will be used is various weight concentrations of Urea binder will eventually influence the quality of the product produced. The Urea binder characteristic which is physical properties will be analyzed using Compression test, Particle size Analyzer and Densimeter.

CHAPTER 2

LITERATURE REVIEW

2.1 Fertilizer

Fertilizers are soil amendments applied to promote plant growth. The main nutrients added in fertilizer are nitrogen, phosphorus, potassium, and other nutrients are added in smaller amounts. Collectively, the main nutrients vital to plants by weight are called macronutrients, including nitrogen, phosphorus, and potassium. Ammonia is main source of nitrogen. Urea is the main product for making nitrogen available to plant. Phosphorous is made available in form of super phosphate, Ammonium phosphate. Potassium Chloride is used for supply of potassium. Synthetic macronutrient fertilizer can be referred to as artificial or straight, where the product predominantly contains the three main nutrients. Compound fertilizers are N-P-K fertilizers with other elements purposely intermixed. Fertilizers are classified according to the content of these three elements. Labeling is according to relative amounts of each of the three elements by weight Nitrogen percentage is reported directly, however phosphorus is reported as the mass fraction of phosphorus pentoxide and potassiumis reported as the mass fraction of potassium oxide (Mayer, 1996).

2.2 Urea Fertilizer

Urea (NH2CONH2) is very importance to the agriculture industry as a nitrogen-rich fertilizer. Ammonia and carbon dioxide are the two elements that are produced Urea in two equilibrium reactions. The ammonia and carbon dioxide are fed into the reactor at high pressure and temperature, and the urea is formed in two steps reaction:

2NH3 + CO2 NH2COONH4 (ammonium carbamate)

NH2COONH4 H2O + NH2CONH2 (urea)

Unreacted NH3 and CO2 and ammonium carbamate are the several elements that is contains in urea. The ammonia and carbon dioxide are recycled as the pressure is reduced and heat applied the NH2COONH4 decomposes to NH3 and CO2. The urea solution is then concentrated to give 99.6% w/w molten urea, and granulated for use as fertiliser and chemical feedstock (Copplestone and Kirk, 1991).

2.3 Urea manufacturing process

2.3.1 Synthesis

Ammonium carbamate is form from the reaction of a mixture of compressed CO2 and ammonia at 240 barg. This is an exothermic reaction, and heat is recovered by a boiler which produces steam. The first reactor achieves 78% conversion of the carbon dioxide to urea and the liquid is then purified. The solution from the decomposition and concentration sections are recycle after second reactor receives gas from the first reactor. Conversion of carbon dioxide to urea is approximately 60% at a pressure of 50 barg. The solution is then purified in the same process as was used for the liquid from the first reactor (Copplestone and Kirk, 1991).

2.3.2 Purification

Water from the urea production reaction and unconsumed reactants (ammonia, carbon dioxide and ammonium carbamate) are the major impurities in the mixture at this stage. The unconsumed reactants are removed in three stages. Firstly, the solution is heated after the pressure is reduced from 240 to 17 barg, which causes the ammonium carbamate to decompose to ammonia and carbon dioxide:

NH2COONH4 2NH3 + CO2

At the same time, some of the ammonia and carbon dioxide will be flashed off. With more ammonia and carbon dioxide being lost at each stage, the pressure is then reduced to 2.0 barg and finally to -0.35 barg,. Then, after the mixture is at the level of -0.35 barg, the solution of urea dissolved in water and free of other impurities remains. The unconsumed reactants are absorbed into a water solution which is recycled to the secondary reactor at each stage. The excess ammonia is purified and used as feedstock to the primary reactor (Copplestone and Kirk, 1991).

2.3.3 Concentration

75% of the urea solution is heated under vacuum, which fade off some of the water and increase the urea concentration from 68% w/w to 80% w/w. At this stage some urea crystals also form. The solution is then heated from 80 to 110°C to redissolve these crystals prior to evaporation. In the evaporation stage molten urea (99% w/w) is produced at 140°C. The remaining 25% of the 68% w/w urea solution is processed under vacuum at 135°C in a two series evaporator-separator arrangement (Copplestone and Kirk, 1991).

2.3.4 Granulation process

Granulation is the process of collecting particles together by creating bonds between them. Bonds are formed by compression or by using a binding agent called as binder. The granulation process combines one or more powders and forms a granule that will allow the tablet process to be predictable and will produce quality tablets within the required tablet-press speed range. A tablet formulation contains several ingredients, and the active ingredient is the most important among them. The remaining ingredients are necessary because a suitable tablet cannot be composed of active ingredients alone. The tablet may require variations such as additional bulk, improved flow, better compressibility, flavoring, improved disintegration characteristics, or enhanced appearance. If the active ingredient in a formulation represents a very small portion of the overall tablet, then the challenge is to ensure that each tablet has the same amount of active ingredient. Sometimes, blending the ingredients is not enough. The active ingredient may segregate from the other ingredients in the blending process. The ingredients may be incompatible because of particle size, particle density, flow characteristics, compressibility, and moisture content. These incompatibilities can cause problems such as segregation during blending or during transfer of the product to the press as well as separation of the active on the tablet press. Two basic techniques are

used to prepare powders for compression into a table that is wet granulation and dry granulation (Tousey, 2002).

2.3.4.1Wet Granulation

Wet granulation, the process of adding a liquid solution to powders, is one of the most common ways to granulate. The process can be very simple or very complex depending on the characteristics of the powders, the final objective of tablet making and the equipment that is available. Some powders require the addition of only small amounts of a liquid solution to form granules. The liquid solution can be either aqueous based or solvent based. Aqueous solutions have the advantage of being safer to deal with than solvents. Although some granulation processes require only water, many actives are not compatible with water. Water mixed into the powders can form bonds between powder particles that are strong enough to lock them together. However, once the water dries, the powders may fall apart. Therefore, water may not be strong enough to create and hold a bond. In such instances, a liquid solution that includes a binder (pharmaceutical glue) is required. The existing binder that had been use in Urea NPK is Formaldehyde (Tousey, 2002).

2.3.4.2Dry Granulation

The dry granulation process is used to form granules without using a liquid solution because the product to be granulated may be sensitive to moisture and heat. Forming granules without moisture requires compacting and densification the powders. Dry granulation equipment offers a wide range of pressures and roll types to attain proper densification. This equipment is loud and dusty compared with other process machinery. Material feed rates are critical for attaining the final objective. The process may require repeated compaction steps to attain the proper granular end point. Typically, a percentage of products does not get compacted and may require screening to remove

excessive fines. Again, successful compaction depends on the compatibility of the products being compressed. If fines are not removed or reprocessed, then the batch may contain too many of them, a situation that can contribute to capping, laminating, weight, and hardness problems on the tablet press. The need for screening large amounts of fines is common to roller compaction, and the degree to which it can be managed depends on the nature of the ingredients. Any product that is removed from the rest of the batch because of particle size must be analyzed to determine what is being removed (Tousey, 2002).

2.4 The Physical Characteristic Of Urea

Sastry and Fuerstenau (1973)detailed the mechanisms for granule growth (granulation) which included: nucleation; growth; random coalescence; pseudo-layering, and crushing and layering. Litster and Liu (1989) in their studies on the granulation of fertilizer have found that coalescence is the most probable mechanism for low-temperature fertilizer granulation using a feed with a broad particle size distribution. To establish an understanding of the fundamental mechanisms of granule formation, the forces involved in the collision of two spherical particles were investigated by a number of researchers. The capillary and viscous contributions were both found to significantly affect the bonding mechanism of colliding particles and were correlated using the viscous number. The regime map theory of Iveson and Litster (1998)postulates that the type of granule growth behavior is a function of the amount of granule deformation during collision and the maximum pore saturation. The amount of granule deformation has been characterized by Tardos et al. (1998) as a Stokes deformation number. The maximum

pore saturation and the Stokes deformation number characterize the growth regime in which granulation takes place. The exact boundary between the regimes depends on the type of granulation equipment and properties of the binder such as viscosity. Miyazaki et al. (1998) had stated that in order to obtain solid granules, it is important to pay

2.4.1 Particle Size

Particle size distribution of Urea fertilizer products or Urea raw materials is defined as the particle diameter range of the material. Particle size analysis is typically measured by sieving, a process of separating a mixture of particles according to their size fraction. Particle size affects agronomic response, granulation and process performance, and blending, storage, handling, and application properties. Some of the reasons for size control follow (Hoffmeister, 1979).

2.4.1.1 Effects on Agronomic Response

Hoffmeister (1979) had stated that fertilizer of very low water solubility generally must

be ground to small particle size to ensure sufficiently rapid dissolution in the soil and utilization by plants. For example, the effectiveness of raw phosphate rock generally increases with fine grinding down to a particle diameter of about 150 μm; below that, little further benefit has been established. Other materials of low solubility that require relatively fine grinding include basic slag, limestone, dolomite, dicalcium phosphate, and fused phosphates. Micronutrient or secondary nutrient sources of low solubility, such as sulfur, metallic oxides, and glasses, likewise require fine grinding. The fine grinding required for these materials often results in undesirable dustiness and other handling difficulties. Therefore, some research and development has been directed toward retranslating the pulverized materials. For example, in the United States, there are currently a few small commercial limestone granulation plants. Method of dust control other than granulation includes spraying the pulverized materials lightly with oil, water, or amine formulations. Others fertilizer that benefit agronomical from particle size control is some of the sparsely soluble slow release nitrogen fertilizers such as urea formaldehyde, isobutylidene diurea, and oxamide. The rate of dissolution and hence the rate of nitrogen availability from these materials, has been shown to be dependent on particle size; the larger the particles, the slower the release.

2.2 Urea Fertilizer

Urea (NH2CONH2) is very importance to the agriculture industry as a nitrogen-rich

fertilizer. Ammonia and carbon dioxide are the two elements that are produced Urea in two equilibrium reactions. The ammonia and carbon dioxide are fed into the reactor at high pressure and temperature, and the urea is formed in two steps reaction:

2NH3 + CO2 NH2COONH4 (ammonium carbamate)

NH2COONH4 H2O + NH2CONH2 (urea)

Unreacted NH3 and CO2 and ammonium carbamate are the several elements that is

contains in urea. The ammonia and carbon dioxide are recycled as the pressure is reduced and heat applied the NH2COONH4 decomposes to NH3 and CO2. The urea

solution is then concentrated to give 99.6% w/w molten urea, and granulated for use as fertiliser and chemical feedstock (Copplestone and Kirk, 1991).

2.3 Urea manufacturing process

2.3.1 Synthesis

Ammonium carbamate is form from the reaction of a mixture of compressed CO2 and

ammonia at 240 barg. This is an exothermic reaction, and heat is recovered by a boiler which produces steam. The first reactor achieves 78% conversion of the carbon dioxide to urea and the liquid is then purified. The solution from the decomposition and concentration sections are recycle after second reactor receives gas from the first reactor. Conversion of carbon dioxide to urea is approximately 60% at a pressure of 50 barg. The solution is then purified in the same process as was used for the liquid from the first reactor (Copplestone and Kirk, 1991).

2.3.2 Purification

Water from the urea production reaction and unconsumed reactants (ammonia, carbon dioxide and ammonium carbamate) are the major impurities in the mixture at this stage. The unconsumed reactants are removed in three stages. Firstly, the solution is heated after the pressure is reduced from 240 to 17 barg, which causes the ammonium carbamate to decompose to ammonia and carbon dioxide:

NH2COONH4 2NH3 + CO2

At the same time, some of the ammonia and carbon dioxide will be flashed off. With more ammonia and carbon dioxide being lost at each stage, the pressure is then reduced to 2.0 barg and finally to -0.35 barg,. Then, after the mixture is at the level of -0.35 barg, the solution of urea dissolved in water and free of other impurities remains. The unconsumed reactants are absorbed into a water solution which is recycled to the secondary reactor at each stage. The excess ammonia is purified and used as feedstock to the primary reactor (Copplestone and Kirk, 1991).

2.3.3 Concentration

75% of the urea solution is heated under vacuum, which fade off some of the water and increase the urea concentration from 68% w/w to 80% w/w. At this stage some urea crystals also form. The solution is then heated from 80 to 110°C to redissolve these crystals prior to evaporation. In the evaporation stage molten urea (99% w/w) is produced at 140°C. The remaining 25% of the 68% w/w urea solution is processed under vacuum at 135°C in a two series evaporator-separator arrangement (Copplestone and Kirk, 1991).

2.3.4 Granulation process

Granulation is the process of collecting particles together by creating bonds between them. Bonds are formed by compression or by using a binding agent called as binder. The granulation process combines one or more powders and forms a granule that will allow the tablet process to be predictable and will produce quality tablets within the required tablet-press speed range. A tablet formulation contains several ingredients, and the active ingredient is the most important among them. The remaining ingredients are necessary because a suitable tablet cannot be composed of active ingredients alone. The tablet may require variations such as additional bulk, improved flow, better compressibility, flavoring, improved disintegration characteristics, or enhanced appearance. If the active ingredient in a formulation represents a very small portion of the overall tablet, then the challenge is to ensure that each tablet has the same amount of active ingredient. Sometimes, blending the ingredients is not enough. The active ingredient may segregate from the other ingredients in the blending process. The ingredients may be incompatible because of particle size, particle density, flow characteristics, compressibility, and moisture content. These incompatibilities can cause problems such as segregation during blending or during transfer of the product to the press as well as separation of the active on the tablet press. Two basic techniques are

used to prepare powders for compression into a table that is wet granulation and dry granulation (Tousey, 2002).

2.3.4.1Wet Granulation

Wet granulation, the process of adding a liquid solution to powders, is one of the most common ways to granulate. The process can be very simple or very complex depending on the characteristics of the powders, the final objective of tablet making and the equipment that is available. Some powders require the addition of only small amounts of a liquid solution to form granules. The liquid solution can be either aqueous based or solvent based. Aqueous solutions have the advantage of being safer to deal with than solvents. Although some granulation processes require only water, many actives are not compatible with water. Water mixed into the powders can form bonds between powder particles that are strong enough to lock them together. However, once the water dries, the powders may fall apart. Therefore, water may not be strong enough to create and hold a bond. In such instances, a liquid solution that includes a binder (pharmaceutical glue) is required. The existing binder that had been use in Urea NPK is Formaldehyde (Tousey, 2002).

2.3.4.2Dry Granulation

The dry granulation process is used to form granules without using a liquid solution because the product to be granulated may be sensitive to moisture and heat. Forming granules without moisture requires compacting and densification the powders. Dry granulation equipment offers a wide range of pressures and roll types to attain proper densification. This equipment is loud and dusty compared with other process machinery. Material feed rates are critical for attaining the final objective. The process may require repeated compaction steps to attain the proper granular end point. Typically, a

excessive fines. Again, successful compaction depends on the compatibility of the products being compressed. If fines are not removed or reprocessed, then the batch may contain too many of them, a situation that can contribute to capping, laminating, weight, and hardness problems on the tablet press. The need for screening large amounts of fines is common to roller compaction, and the degree to which it can be managed depends on the nature of the ingredients. Any product that is removed from the rest of the batch because of particle size must be analyzed to determine what is being removed (Tousey, 2002).

2.4 The Physical Characteristic Of Urea

Sastry and Fuerstenau (1973)detailed the mechanisms for granule growth (granulation) which included: nucleation; growth; random coalescence; pseudo-layering, and crushing and layering. Litster and Liu (1989) in their studies on the granulation of fertilizer have found that coalescence is the most probable mechanism for low-temperature fertilizer granulation using a feed with a broad particle size distribution. To establish an understanding of the fundamental mechanisms of granule formation, the forces involved in the collision of two spherical particles were investigated by a number of researchers. The capillary and viscous contributions were both found to significantly affect the bonding mechanism of colliding particles and were correlated using the viscous number. The regime map theory of Iveson and Litster (1998)postulates that the type of granule growth behavior is a function of the amount of granule deformation during collision and the maximum pore saturation. The amount of granule deformation has been characterized by Tardos et al. (1998) as a Stokes deformation number. The maximum pore saturation and the Stokes deformation number characterize the growth regime in which granulation takes place. The exact boundary between the regimes depends on the type of granulation equipment and properties of the binder such as viscosity. Miyazaki et al. (1998) had stated that in order to obtain solid granules, it is important to pay sufficient attention to the viscosity of the solvent and surface tension.

2.4.1 Particle Size

Particle size distribution of Urea fertilizer products or Urea raw materials is defined as the particle diameter range of the material. Particle size analysis is typically measured by sieving, a process of separating a mixture of particles according to their size fraction. Particle size affects agronomic response, granulation and process performance, and blending, storage, handling, and application properties. Some of the reasons for size control follow (Hoffmeister, 1979).

2.4.1.1 Effects on Agronomic Response

Hoffmeister (1979) had stated that fertilizer of very low water solubility generally must be ground to small particle size to ensure sufficiently rapid dissolution in the soil and utilization by plants. For example, the effectiveness of raw phosphate rock generally increases with fine grinding down to a particle diameter of about 150 μm; below that, little further benefit has been established. Other materials of low solubility that require relatively fine grinding include basic slag, limestone, dolomite, dicalcium phosphate, and fused phosphates. Micronutrient or secondary nutrient sources of low solubility, such as sulfur, metallic oxides, and glasses, likewise require fine grinding. The fine grinding required for these materials often results in undesirable dustiness and other handling difficulties. Therefore, some research and development has been directed toward retranslating the pulverized materials. For example, in the United States, there are currently a few small commercial limestone granulation plants. Method of dust control other than granulation includes spraying the pulverized materials lightly with oil, water, or amine formulations. Others fertilizer that benefit agronomical from particle size control is some of the sparsely soluble slow release nitrogen fertilizers such as urea formaldehyde, isobutylidene diurea, and oxamide. The rate of dissolution and hence the rate of nitrogen availability from these materials, has been shown to be dependent on particle size; the larger the particles, the slower the release.