Production of Urea by ACES Process

TOYO’S ACES Process for UREA Synthesis This report is submitted to department of Chemical Engineering, Wah Engineering College, University of Wah, Wah Cantt, Pakistan For the partial fulfillment of the requirements for the Bachelor’s Degree In CHEMICAL ENGINEERING

Session 2010-2014

Group Members Hafiz Adeel Hassan

UW-10-Ch.E-BSc-011

Muhammad Imran Salim

UW-10-Ch.E-BSc-025

Noman Rasool

UW-10-Ch.E-BSc-028

Muhammad Usman

UW-10-Ch.E-BSc-036

Department of Chemical Engineering Wah Engineering College University of Wah

DEDICATION The project is dedicated to our beloved parents, who nurtured us from our childhood and not only prayed for our better future but even did struggle for while getting all troubles on their own heads. In addition, we would also like to dedicate this project to our honorable and respected teachers who helped us in compiling this report.

i

PREFACE UREA is a major FERTILIZER product. Different processes are available for the production of urea. This design report is about the “TOYO’S ACES process for Urea synthesis”. This report is divided in different sections. First of all the introduction of ACES process is given, which highlights the importance of this process. Different manufacturing processes for urea are also described. Detail description of “TOYO’S ACES process for Urea synthesis”. Afterwards material and energy balance of equipments is presented. In preceding chapters introduction to different equipments of plant along with their designing procedure and specification sheets are presented. Hazop study, Instrumentation & Control and Cost Estimation for this plant are also included in this report.

ii

ABSTRACT Urea is in many ways the most convenient form for fixed nitrogen. It has the highest nitrogen content available in a solid fertilizer (46 %).It is easy to produce as prills or granules and easily transported in bulk or bags with no explosive hazard. It leaves no salt residue after use on crops. Its specific gravity is 1.335, decomposes on boiling and is fairly soluble in water. The principal raw materials required for this purpose are NH3 & CO2.Two reactions are involved in the manufacture of urea. First, ammonium carbamate is formed under pressure by reaction between CO2 & NH3. CO2 + 2NH3

→

NH2COONH4

∆H= -37.4 Kcal

This highly exothermic reaction is followed by an endothermic decomposition of the ammonium carbamate. NH2COONH4

↔

NH2CONH2 + H2O ∆H= + 6.3 Kcal

Various processes of urea manufacture are: 1) Advanced Cost and Energy Saving (ACES) Process 2) Stamicarbon CO2 stripping process 3) Snamprogetti ammonia stripping process 4) Once through urea process

We selected the Advanced Cost and Energy Saving process for the manufacture of urea. The preference of ACES process to other urea manufacturing processes is briefly discussed in first chapter. Some advantages of ACES process include High CO2 conversion, efficient stripping, maximum heat recovery, less corrosion and product quality.

Energy balance & material balance of the plant is done. The selected capacity of the plant is 6, 00,000 tons/year of urea producing 75, 583.33 kg/hr of urea with 98.5 % purity. Urea reactor is mechanically designed. The volume of reactor is calculated & found to be 129 m3. The length & diameter of the reactor are 25 m & 2.5 m respectively. The Reactor used is of plug flow type.

iii

Advanced Cost and Energy Saving process involves a high NH3 to CO2 ratio in the reactor, usually 4/1 and 66-68% conversion of CO2 is done. CO2 is used as stripping agent. NH3 (l) is entered into reactor and CO2 (g) into stripper. Uses of Urea: • About 56 % of Urea manufactured is used in solid fertilizer. • About 31 % of Urea manufactured is used in liquid fertilizer. • Urea-formaldehyde resins have large use as a plywood adhesive. • Melamine-formaldehyde resins are used as dinnerware & for making extra hard surfaces.

The wide nature of the subject and the size restrictions left many areas to be touched very briefly, however an effort has been made to cover significant facet of the topic.

iv

ACKNOWLEDGEMENT We express gratitude and praise to ALMIGHTY ALLAH, The Creator of universe, who is beneficent and merciful, guided us in difficult circumstance, who endowed us with the will to undertake this design project. Great respect our Holy Prophet Hazrat Muhammad (PBUH), who taught us to learn till lap of grave. We are highly thankful to honorable Prof. Dr. A.K Salariya who provided us with a chance to work on such an interesting topic. His constructive suggestions, constant guidance and friendly attitude encouraged us to work in a better manner. We are grateful to our honorable group advisor Prof. Dr. G.M. Mamoor and group supervisor Mr. Kashif Iqbal for their nice cooperation in our design work. We also show appreciation to our friends who encouraged and cooperated with us throughout our work.

v

TABLE OF CONTENTS CHAPTER 1 INTRODUCTION TO UREA

1.1 Fertilizer 1.2 Characteristics of Urea 1.3 Commercial Production of Urea 1.4 Fertilizers Available In Pakistan 1.5 Demand and Supply of Urea in Pakistan

2 4 5 8 11 CHAPTER 2 PROCESS SELECTION AND DESCRIPTION

2.1 Conventional Processes 2.2 Process Comparison 2.3 Selection of Process 2.4 Detail Process Description of ACES process 2.5 Process Flow Diagram of ACES Process

13 19 20 22 26 CHAPTER 3 MASS BALANCE CALCULATIONS

3.1 Material Balance on Overall Plant 3.2 Reactor Balance 3.3 Stripper Balance 3.4 Balance around Medium Pressure Decomposer 3.5 Balance around Carbamate Condenser 3.6 Balance around Lower Pressure Decomposer 3.7 Balance around Lower Pressure Absorber 3.8 Balance around Medium Pressure Absorber 3.9 Balance around Scrubber 3.10 Balance around Condenser 3.11 Balance around Evaporator 3.12 Balance around Prilling Tower

29 31 32 34 35 36 38 39 40 41 43 45

C H A P TE R 4 E N ER G Y B A LA N C E C A LC U LA T I O N S 4.1 Specific Heat Calculations 4.2 Energy Balance around Reactor 4.3 Energy Balance around Stripper 4.4 Energy Balance around Scrubber

47 49 51 53

4.5 Energy Balance around Carbamate Condenser 4.6 Energy Balance around Medium Pressure Decomposer 4.7 Energy Balance around Low Pressure Absorber 4.8 Tabulated Heat Balance

53 55 56 57 CHAPTER 5 PROCESS DESIGN

5.1 Reactor Design 5.2 Specification Sheet 5.3 Stripper Design 5.4 Specification Sheet 5.5 Condenser Design 5.6 Specification Sheet 5.7 Evaporator Design 5.8 Specification Sheet 5.9 Absorber Design 5.10 Specification Sheet 5.9 Selection of Pump 5.10 Specification Sheet 5.11 Selection of Compressor 5.12 Specification Sheet

59 62 63 73 74 81 82 87 88 97 98 101 102 104 CHAPTER 6 MECHANICAL DESIGN

6.1 Mechanical Design of Reactor 6.2 Specification Sheet 6.3 Mechanical Drawing of Reactor

106 112 113 CHAPTER 7 INSTRUMENTATION AND PROCESS CONTROL

7.1 Instrumentation and Control 7.2 Components of Control System 7.3 Typical Control Systems 7.4 Consideration of PFR in ACES Urea Plant

115 116 118 120 CHAPTER 8 HAZOP STUDY

8.1 Hazard and Operability Study 8.2 Steps Conducted In HAZOP Study 8.3 Safety of the Urea Plant 8.4 Hazard Identification 8.5 First Aid (Emergency Procedure)

123 123 125 126 126

CHAPTER 9 ENVIRONMENTAL IMPACT

9.1 Environmental Impact Assessment 9.2 Impact of the Urea Plant on the environment 9.3 Emission to air 9.4 Emission to water 9.5 Emission to land 9.6 Elimination Methods

129 130 130 131 131 132 CHAPTER 10 COST ESTIMATION

10.1 Purchased Equipment Cost 10.2 Total Capital Investment 10.3 Total Product Cost 10.4 Profitability Analysis

135 137 138 140 CHAPTER 11 SIMULATION IN ASPEN HYSYS

11.1 Introduction to ASPEN HYSYS 11.2 Simulation of Synthesis Section

143

REFERENCES References

143

CHAPTER 01: Introduction To Urea

1.1 FERTILIZER Fertilizers restore soil fertility by supplying nutrients to the soil. These nutrients are utilized by crops for their growth and development. Without the addition of fertilizers, crop yield would be significantly reduced as our soils are deficient in major nutrients, like, N, P & K. Mineral fertilizers are used to increase the nutrient concentration of the soil and these minerals can be quickly absorbed and used by the crops. Urea is the most concentrated solid straight nitrogen fertilizer. fertilizer Its prills or granules are white in color and free flowing. Urea is readily soluble in water. It contains 46 per cent Nitrogen N in amide (NH2) form which is changed to ammonium (NH4+) in the soil. Because of its high water solubility, it is well suited for use in solution fertilizers or foliar sprays. Urea is an organic compound with chemical formula (NH2)2CO. Urea is also known by international nonproprietary name (INN) carbide, as established by world health organization. Other names include Carbide Resin, R Isourea, Carbonyl Diamide, and Carbonyl Diamine.

Figure 1.1 Chemical structures of urea molecules

2

Production of Urea by ACES process

Synthetic Urea: It was first organic compound to be artificially synthesized from inorganic starting materials, in 1828 by friedrich Wohler, who prepared it by reaction of potassium cyanate with maximum sulfate. Although Wohler was attempting to prepare ammonium cynate by foaming urea, he inadvertently discredited vitalism the theory that the chemicals of living organisms are fundamentally different from inanimate matter, thus starting the discipline of organic chemistry. This artificially urea synthesis was mainly relevant to human health because of urea cycle in human beings. Urea was discovered: synthesis in human liver in order to expel excess nitrogen from the body. So in past urea was not considered as a chemical for agriculture and industrial use. Within 20th century it was found to be a best for the iatrogenic fertilizer for the plant and become widely used as a fertilizer. Urea was the leading fertilizer worldwide in 1990s. Apart from the urea is being utilized in many other industries. Urea is produced on a scale of some 100,000,000 ton per year worldwide. For use in industry, urea is from produce synthetic ammonia and carbon dioxide. Urea can be produce as prillers, granuls, flakes, pellets, crystal and solution. More than 90% of world production is destined for use as a fertilizer. Urea has the highest nitrogen content of all nitrogenous fertilizer in common use (46.7%). Therefore, it has the lowest transportation cost per unit of nitrogen nutrient. Urea is highly soluble in water and is therefore, also very suitable for use in fertilizer solution (in combination of ammonium nitrate).

3

CHAPTER 01: Introduction To Urea

1.2 CHARACTERISTICS OF UREA Urea is white odorless solid. Due to extensive hydrogen bonding with water (up to six hydrogen bonds may forms –two from the oxygen atom and one from each hydrogen urea is very soluble) Table 1.1 Physical Characteristics of Urea Density

1.33 × 10

Melting point

solid

132.7°c (406 °k) decompose

Boiling point

NA

Solubility in water

108

(20°c)



167

(40°c)



251

(60°c)



400

(80°c)



733

(100°c)



Vapor pressure