This document provides details about the production process of urea. It discusses that the main raw materials needed are ammonia and carbon dioxide. Ammonia is typically produced via the Haber-Bosch process using hydrogen derived from methane or other light hydrocarbons. Carbon dioxide is obtained from atmospheric air or as a byproduct of ammonia synthesis. The urea production process involves reacting ammonia and carbon dioxide to form ammonium carbamate, which is then dehydrated to produce molten urea. It also outlines different process variations and discusses economic and environmental aspects of urea production.

1. CH 4202 Comprehensive Design Project
Assignment 1
Design of an Urea Manufacturing Plant
Group Members: -
Wellappili A.Y.G
090556N
Wijesinghe C.D
090577E
Silva G.G.S.N
090488G
Pathiraja P.D.T.P
090361L
Ariyaratne V.T
090029d
Rashara G.A.D.D
090428B
Gamage G.P.S
090147L
Abeywickrama T.D
090010L
Dayananda L.K
090079E
Date of Submission:-
Department of Chemical and Process Engineering
University of Moratuwa

2. Table of Contents
1)
INTRODUCTION ..................................................................................................................................... 4
1.1)
1.2)
Nitrogen sources and fertilizers .................................................................................................... 4
1.3)
About Urea .................................................................................................................................... 6
1.4)
Importance of Urea as a fertilizer ................................................................................................. 7
1.5)
2)
Importance of Nitrogen for plant growth ..................................................................................... 4
Other applications......................................................................................................................... 8
PRODUCTION PROCESS OF UREA........................................................................................................ 10
2.1)
Raw materials for manufacturing Urea ....................................................................................... 10
2.1.1)
Ammonia ............................................................................................................................. 10
2.1.2)
Carbon dioxide .................................................................................................................... 11
2.2)
Sources and availability of raw materials ................................................................................... 11
2.2.1) Hydrogen Production ............................................................................................................... 11
2.2.2) Nitrogen .................................................................................................................................... 12
2.3)
Synthesis of Ammonia ................................................................................................................ 12
2.3.1) Steam Reforming method ......................................................................................................... 12
2.4)
Process in general production of Urea ....................................................................................... 19
2.5)
Process variation of Urea manufacturing ................................................................................... 22
2.5.1) Once-through processes ........................................................................................................... 22
2.5.2) Partial recycle processes ........................................................................................................... 23
2.5.3) Total recycle processes ............................................................................................................. 24
3)
ECONOMIC ASPECTS OF UREA PRODUCTION ..................................................................................... 33
4)
ENVIRONMENTAL AND SAFETY ISSUES............................................................................................... 34
4.1) Health and Safety............................................................................................................................. 34
4.1.1) Health........................................................................................................................................ 34
4.1.2) Safety ........................................................................................................................................ 35
4.2) Safety Procedures ............................................................................................................................ 37
4.3) Inherent Safe Design ........................................................................................................................ 37
4.4) Layers of Process Safety................................................................................................................... 38
4.5) conclusions ...................................................................................................................................... 39
4.6) recommendations............................................................................................................................ 39
4.7) Environment .................................................................................................................................... 39

3. 5)
GREEN CONCEPTS USED IN PLANT DESIGNING .................................................................................. 40
5.1) why should we care about green buildings? ................................................................................... 40
5.2) Current methods used in industries ................................................................................................ 41
6)
HISTORY OF UREA PRODUCTION IN SRI LANKA .................................................................................. 44
7)
PROCESS SELECTION AND DESIGN DECISIONS.................................................................................... 46
REFERENCES ................................................................................................................................................ 58
LIST OF TABLES
LIST OF FIGURES

4. 1) INTRODUCTION
1.1) Importance of Nitrogen for plant growth
Nitrogen is considered the most important component for supporting plant growth. While
nitrogen is a natural element existing as N2 (gas) accounting for 78% of the earth’s atmosphere,
plants cannot absorb it in this natural form (N2 molecules are inert under normal environmental
conditions due to their high bond energy). The nitrogen in the environment is synthesized into
fertilizers which are readily available to plants. Nitrogen is the main nutrient and regulator of
plant growth – it supplements and promotes all of a plant’s growth processes.
Nitrogen is a part of all living cells and an integral component of all chemical
compounds-proteins, enzymes, hormones and metabolic processes involved in the
synthesis and transfer of energy.
Nitrogen is a constituent of chlorophyll, the green pigment present in chloroplasts in
certain plant cells (esp. in green leaves-green leaves get their color due to chlorophyll) of
the plant that is responsible for photosynthesis.
Helps accelerate plant growth, increasing seed and fruit production and improving the
quality of leaf and forage crops.
1.2) Nitrogen sources and fertilizers
Nitrogen often comes from fertilizer application and from the air (legumes get their N from the
atmosphere, water or rainfall contributes very little nitrogen)
Nitrogen in the air is the ultimate source of all soil nitrogen.
Nitrogen may enter the soil through rainfall, plant residues, fixation by soil organisms,
animal manures and organic fertilizers (i.e. compost) and commercial fertilizers.
Nitrogen may be lost from the soil by plant removal, volatilization, leaching or erosion.
The earth's atmosphere is the ultimate source of nitrogen. In most areas of the world, the nitrogen
found in soil minerals is negligible. Nitrogen may be added to or lost from soil by a number of
processes. In the soil, nitrogen can undergo a number of transformations.

5. Rainfall adds about 10 lbs. of nitrogen to the soil per acre per year. The nitrogen oxides
and ammonium that are washed to earth are formed as a result of lightning during storms,
by internal combustion engines and through oxidation by sunlight. Crop residues
decompose in the soil to form soil organic matter. This organic matter contains about 5%
nitrogen. An acre-foot of soil having 2 percent organic matter would contain about 3,500
lbs. of nitrogen. Generally, about 1- 3% of this organic nitrogen is annually converted by
microorganisms to a form usable by plants.
Legumes fix atmospheric nitrogen through their symbiotic association with Rhizobium
bacteria. If plant roots are well modulated, the legume plant does not benefit from the
addition of fertilizer nitrogen. Perennial legumes, such as alfalfa, can fix several hundred
pounds of nitrogen per acre per year.
Manure contains an appreciable amount of nitrogen. Most of this nitrogen is present as
organic compounds. Cattle manure contains about 10-40 lbs. of nitrogen per ton. About
half of this nitrogen is converted to forms available to plants during the first growing
season. Lesser amounts are converted during succeeding seasons. Each ton of applied
manure is equal to about 5-20 pounds of commercial fertilizer nitrogen.
Commercial fertilizer nitrogen comes in three basic forms: gas, liquid and dry. All forms
are equally effective when properly applied. Once applied, fertilizer nitrogen is subject to
the same transformations as other sources of nitrogen. There is no difference between the
ammonium (NH4+) or nitrate (NO3-) which are absorbed by the plant from commercial
fertilizers and that supplied by natural substances.
Nitrogen exists in a number of chemical forms and undergoes chemical and biological reactions.
1. Organic nitrogen to ammonium nitrogen (mineralization). Organic nitrogen comprises
over 95% of the nitrogen present in soil. This form of nitrogen cannot be used by plants but is
gradually transformed by soil microorganisms to ammonium (NH4+). Ammonium is not leached
to a great extent. Since NH4+ is a positively charged ion (cation), it is attracted to and held by the
negatively charged soil clay.
2. Ammonium nitrogen to nitrate nitrogen (nitrification). In warm, well-drained soil,
ammonium transforms rapidly to nitrate (NO3-). Nitrate is the principle form of nitrogen used by

6. plants. It leaches easily, since it is a negatively charged ion (anion) and is not attracted to soil
clay.
3. Nitrate or ammonium nitrogen to organic nitrogen (immobilization). Soil microorganisms
use nitrate and ammonium nitrogen when decomposing plant residues. These forms are
temporarily "tied-up" (incorporated into microbial tissue) in this process. This can be a major
concern if crop residues are high in carbon relative to nitrogen. Examples are wheat straw, corn
stalks and sawdust. The addition of 20 to 70 lbs. of nitrogen per ton of these residues is needed to
prevent this transformation. After the residues are decomposed, the microbial population starts
dying out and processes 1 and 2 take place.
4. Nitrate nitrogen to gaseous nitrogen (de-nitrification). When soil does not have sufficient
air, microorganisms use the oxygen from NO3- in place of that in the air and rapidly convert NO3to nitrogen oxide and nitrogen gases (N2). These gases escape to the atmosphere and are not
available to plants. This transformation can occur within two or three days in poorly aerated soil
and can result in large losses of nitrate-type fertilizers.
5. Ammonium nitrogen to ammonia gas (ammonia volatilization). Soils that have a high pH
(> 7.5) can lose large amounts of NH4+ by conversion to NH3 gas. To minimize these losses,
incorporate solid ammonium-type fertilizers, urea- CO(NH2)2 and anhydrous ammonia below the
surface of a moist soil.
1.3) About Urea
Urea (also known as carbamide) is an organic compound with the chemical formula CO(NH2)2.
The molecule has two —NH2 (amine) groups linked to a carbonyl (C=O) functional group.
Molecular Formula CO(NH2)2
Molec
Physical properties

7. Molar mass:
Density:
Solubilty Melting point:
Urea serves an important role in the metabolism of nitrogen-containing compounds by animals
and is the main nitrogen-containing substance in the urine of mammals. It is a colorless, odorless
solid, although the ammonia that it gives off in the presence of water, including water vapor in
the air, has a strong odor. It is highly soluble in water and practically non-toxic. Dissolved in
water, it is neither acidic nor alkaline. Urea would hydrolyze in both acidic and basic aqueous
media. The body performs nitrogen excretion by means of urea. Urea is widely used in fertilizers
as a convenient source of nitrogen. It is also an important raw material for the chemical industry.
Urea was first discovered in urine in 1727 by the Dutch scientist Herman Boerhaave. In 1828,
the German chemist Friedrich Wöhler was the first to artificially synthesize urea from an
inorganic precursor-this was an important breakthrough in organic chemistry since it
demonstrated that an organic compound present in living organisms could be obtained from
inanimate materials. It was done by treating silver isocyanate (AgNCO) with ammonium
chloride (NH4Cl).
1.4) Importance of Urea as a fertilizer
More than 90% of world production of urea is destined for use as a nitrogen-release
fertilizer. Urea has the highest nitrogen content of all solid nitrogenous fertilizers in
common use. Therefore, it has the lowest transportation costs per unit of nitrogen
nutrient. The standard crop-nutrient rating of urea is 46-0-0.

8. Many soil bacteria possess the enzyme urease, which catalyzes the conversion of the urea
molecule to two ammonia molecules and one carbon dioxide (CO2) molecule, thus urea
fertilizers are very rapidly transformed to the ammonium form in soils. Among soil
bacteria known to carry urease, some ammonia-oxidizing bacteria (AOB), such as species
of Nitrosomonas, are also able to assimilate the carbon dioxide released by the reaction to
make biomass via the Calvin Cycle, and harvest energy by oxidizing ammonia (the other
product of urease) to nitrite, a process termed nitrification. Nitrite-oxidizing bacteria,
especially Nitrobacter, oxidize nitrite to nitrate, which is extremely mobile in soils and is
a major cause of water pollution from agriculture. Ammonia and nitrate are readily
absorbed by plants, and are the dominant sources of nitrogen for plant growth.
Urea is also used in many multi-component solid fertilizer formulations. Urea is highly
soluble in water and is, therefore, also very suitable for use in fertilizer solutions (in
combination with ammonium nitrate: UAN), e.g., in 'foliar feed' fertilizers.
1.5) Other applications
Chemical Industry-Urea is an important raw material in the manufacture of several chemical
compounds. They include: plastics (such as urea-formaldehyde resins), adhesives (urea
formaldehyde or urea melamine formaldehyde) and Potassium Cyanate. Chemical Formulae and
relevant reactions.
Explosives-Urea is also used to produce urea nitrate which is a highly explosive substance.
Automobiles-Urea is used in Selective Non-Catalytic Reduction (SNCR) and Selective Catalytic
Reduction (SCR) reactions to reduce nitrous oxides (NOx) in exhaust fumes from combustion of
diesel.
Other commercial uses
Stabilizer in nitrocellulose explosives

9. A component of animal feed, providing a relatively cheap source of nitrogen to promote
growth
A flavor-enhancing additive for cigarettes
A main ingredient in hair removers
An ingredient in skin cream, moisturizers and hair conditioners
A flame-proofing agent, commonly used in dry chemical fire extinguisher charges such as
the urea-potassium bicarbonate mixture
An ingredient in many tooth whitening products
Along with ammonium phosphate, as a yeast nutrient, for fermentation of sugars into ethanol
As a solubility-enhancing and moisture-retaining additive in dye baths for textile dyeing or
printing

10. 2) PRODUCTION PROCESS OF UREA
2.1) Raw materials for manufacturing Urea
The industrial process of manufacturing urea basically involves two main steps. The first step is
the formation of ammonium carbamate (NH2COONH4) which is done by reacting ammonia
(NH3) and gaseous carbon dioxide (CO2).
The second step is dehydration of ammonium
carbamate to produce molten urea (NH2CONH2). So main reactants needed for the process
would be ammonia and carbon dioxide.
2.1.1) Ammonia
Ammonia is a colourless gas having density 0.589 times that of air, with a sharp unpleasant
smell. At atmospheric pressure the boiling point of ammonia is -33.34 0C. So the storage must be
done under high pressure at low temperature. Due to the presence of strong hydrogen bonds
between molecules it can be easily liquefied and well miscible in water.
Natural occurrence of ammonia happens due to decay process of nitrogenous animal and
vegetable matter. In addition ammonia salts such as ammonium chloride, ammonium sulfate and
ammonium bicarbonate are available in soil and rain water. Biosynthesis of ammonia from
atmospheric nitrogen by enzymes called nitrogenase happens in certain organism which is called
nitrogen fixing. Ammonia is also produced through amino acid metabolism and is converted to
urea through series of reactions inside the liver.
The commercial production of ammonia is very important since it is not available as a natural
resource and it is essential in large quantities for urea manufacturing. Worldwide, the annual
production of synthetic ammonia is about 120 million tones, of which about 85% is used in
fertilizers, including urea [1]. Most of the industrial processes for synthesis of ammonia are
based on Haber Bosch process, developed in Germany 1904-1913. In that process ammonia is
produced by the reaction between gaseous hydrogen and nitrogen under high temperature and
pressure in the presence of iron based catalyst. Formation of ammonia from nitrogen and
hydrogen is basically a reversible reaction which the yield depends on the conditions employed.
Unreacted hydrogen and nitrogen are usually separated and recycled.

11. 2.1.2) Carbon dioxide
Carbon dioxide is available in atmospheric air in trace amount which is known as a pollutant gas.
In most of industrial plants carbon dioxide is emitted as a result of burning fossil fuels. Carbon
dioxide is produces as a byproduct of ammonia synthesis itself. So carbon dioxide which is
produced as a byproduct can be removed and used in the production of urea.
When overall production process is consider primary raw materials needed to manufacture urea
are
Hydrogen (H2)
Nitrogen (N2)
2.2)
Sources and availability of raw materials
2.2.1) Hydrogen Production
There are many sources that hydrogen can be obtained. The process of ammonia synthesis
basically depends on the hydrogen source used for the process.
Hydrogen can be produced from natural gas i.e. methane, liquid petroleum gases such as
propane and butane or petroleum naphtha. When light hydrocarbons mentioned above are
used as the source for hydrogen the production process used for ammonia synthesis is
known as ―Steam Reforming‖.
Heavy fuel oil or vacuum residue can be used to obtain hydrogen when partial oxidation
process for ammonia synthesis is used.
Although coal gasification and electrolysis of water can be used to produce hydrogen
those methods are no longer used in industrial scale ammonia production. In addition
hydrogen gas emitted as a byproduct of petroleum cracking can also be used to produce
hydrogen to manufacture urea.
Since different process techniques should be employed depending on the feedstock, energy
consumption, investment cost and production cost will be vary depending on the feedstock.

12. Following table gives an approximate comparison of the energy consumption, investment cost
and production cost for main three sources of hydrogen production [2]
Natural Gas
Heavy oil
Coal
Energy consumption
1.0
1.3
1.7
Investment cost
1.0
1.4
2.4
Production cost
1.0
1.2
1.7
In addition availability of raw materials is also important in deciding the production process.
2.2.2) Nitrogen
The most abundant source for nitrogen is atmospheric air. Dry air contains roughly 78% of
gaseous nitrogen (N2) by volume. Pure nitrogen needed for the Haber process can be easily
extracted by removing oxygen, carbon dioxide and other gases by liquefaction or law
temperature distillation. But if steam reforming process is used, no such method is needed. In
that process, oxygen is removed by simple combustion and carbon dioxide is removed by using
absorption process.
2.3)
Synthesis of Ammonia
There are two methods available for synthesis of ammonia. Steam reforming method can be used
for natural gas and other light hydrocarbons such as liquid petroleum gas and naphtha. If the
feedstock is residual heavy oil or vacuum residue from a refinery, then the process will be partial
oxidation. Steam reforming process of natural gas is identified as the most efficient method for
synthesis of ammonia.
2.3.1) Steam Reforming method
This method is known as the best available technique for the synthesis of ammonia. Steam
reforming method can be divided into three as mentioned below [3].

13. Conventional steam reforming with fired primary reformer and stoichiometric air
secondary reforming (stoichiometric H/N- ratio)
Steam reforming with mild conditions in fired primary reformer and excess air in
secondary reformer (Under-stoichiometric H/N ratio)
Heat exchange auto thermal reforming, with a process gas heated steam reformer (heat
exchange reformer) and a separate secondary reformer, or in a combined auto thermal
reformer using excess or enriched air (under- stoichiometric or stoichiometric H/N-ratio)
Among these three techniques conventional steam reforming method is the oldest and most
widely used technique.
2.3.1.1) Conventional Steam Reforming method
Desulphurization
Sulphur and sulphorous compounds which contain in natural gas poison the catalyst used in
ammonia synthesis process. The feed gas is pre heated up to 350-400 0C in the primary reformer
convection section and then passed to the desulphurization vessel. In that section sulphur
compounds are hydrogenated to hydrogen sulphide (H2S) using cobalt molybdenum catalyst and
then H2S is removed by reacting with Zinc Oxide (ZnO).
R-SH +
H2
H2S
+
RH
ZnO
H2S
ZnS
+
H2O
+
Hydrogen gas needed for hydrogenation of sulphur compounds is usually recycled from the
synthesis section of the plant and consumed zinc oxide or zinc sulphide remains in the adsorption
bed.
Primary Reforming
Primary reformer consists of nickel or iron containing catalyst. Desulphurized gas reacts with
superheated steam which is heated up to 500-600 0C in the convection section before entering the
primary reformer. Following reactions take place in the primary reformer.
CH4 (g) +
H2O (g)
CO (g) +
3H2 (g)
H=206 kJ.mol-1

14. CO (g) +
H2O (g)
CO2 (g) +
4H2 (g) +
H=-41 kJ.mol -1
H2 (g)
CO2 (g)
The overall reaction would be
CH4 (g) +
2H2O (g)
In modern plants preheated steam and gas mixture is passed through an adiabatic pre reformer
which uses pre reformer catalyst to reheat the mixture in the convection section. In some plants
part of process steam is obtained from feed gas saturation. The amount of steam that should be
supplied is given by steam to carbon molar ratio. It is usually maintained at 3.0 for an efficient
process. The optimum ratio depends on factors such as feedstock quality, purge gas recovery,
primary reformer capacity, shift operation, and the plant steam balance.
The reaction between methane and steam takes place between 780-830 °C. At this temperature
the above equilibrium reaction is driven to the right, giving high yield of hydrogen, carbon
dioxide and small quantities of carbon monoxide. Since the overall reaction is highly
endothermic additional heat should be supplied to maintain optimum temperature by burning
natural gas or other gaseous fuel. The output from the primary reformer is commonly known as
synthesis gas.
Secondary Reforming
The synthesis gas, small amount of carbon monoxide and unreacted methane leaving the primary
reformer enters the secondary reformer where it is mixed with calculated amount of air. At actual
operating conditions only 30-40% of hydrocarbons are reformed and temperature must be
increased to increase the conversion. Addition of air converts methane molecules that are not
reacted during primary steam reforming in to synthesis gas.
Following reaction takes place in the secondary reforming process.
Ni Catalyst
2CH4 (g) +
O2 (g) +
4N2 (g)
2CO (g) +
4H2 (g) +
4N2 (g)
CO produced in the above reaction is converted to CO2 as mentioned in the following reaction.
CO (g) +
H2O (g)
So the overall reaction would be
CO2 (g) +
H2 (g)

15. 2CH4 (g) +
O2 (g) +
4N2 (g) +
2H2O (g)
2O2 (g) +
6H2 (g) +
4N2 (g)
This internal combustion is highly exothermic and supplies necessary heat and also gives high
yield of hydrogen. The temperature at the outlet of secondary reformer is around 1000 °C and
99% of hydrocarbons coming from primary reformer is converted leading to reduced methane
fraction of 0.2-0.3% on dry gas basis. This reaction also removes oxygen from air and provides
nitrogen for final synthesis of ammonia. In the conventional reforming process the degree of
primary reforming is adjusted so that air supplied to the secondary reformer balances both heat
requirement and stoichiometric nitrogen gas requirement. Finally gas leaving is cooled to 350400 °C in a waste heat steam boiler downstream from the secondary reformer.
Shift Conversion
In order to increase the efficiency of the process there should be a very lower amount of carbon
monoxide (CO) content where as the process gas leaving the secondary reformer contains 1215% of CO. It is reduced up to 3% on dry base in high temperature shift (HTS) conversion. For
that gas is passed through a bed of iron oxide or chromium oxide catalyst at around 400 0C. The
use of copper containing catalyst increases the conversion. The gas from HTS converter is
cooled and passed through a Low temperature shift(LTS) converter, which has a bed of copper
oxide or zinc oxide-based catalyst and operates at about 200-220 °C. The final amount of CO
content is about 0.2-0.4% on dry base. Following reaction takes place in the shift conversion.
Iron Oxide Catalyst
CO (g) +
H2O (g)
CO2 (g) +
H2 (g)
H=-41 kJ.mol -1
Water Removal
Iron catalyst used in ammonia synthesis can be oxidized due to the presence of water, carbon
dioxide and carbon monoxide. Because of that those compounds must be removed using above
mentioned shift conversion and following water removal and carbon dioxide removal methods.
Water is removed by cooling the mixture up to 400C and allowing it to condense. The condensate
may contain some amount of ammonia, methanol, and minor amounts of amines, formic acid and

16. acetic acid. These compounds can be stripped and recycled for more efficient process. The heat
released during condensation can be used for the stripping of carbon dioxide, driving an
absorption refrigeration unit and boiler water preheating.
Carbon Dioxide Removal
The process gas now contains mainly H2, N2 and CO2. CO2 can be easily removed by
absorption process. Mono ethanol Amine (MEA), Activated Methyl Di Ethanol Amine
(AMDEA) or potassium carbonate solutions can be used for chemical absorption. Glycol Di
Methyl Ethers (Selexol) and propylene carbonate can be considered as physical absorption
solutions. When MEA is used it needs high amount of regeneration energy and because of that
it is not considered as an efficient process.
Finally absorbed carbon dioxide is stripped and recycled back to use as a raw material for
manufacturing of urea.
Methanation
Even after the shift conversion and CO2 removal, still there can be a trace amount of CO and
CO2 which is poisonous for the ammonia synthesis catalyst. So in methanation process they are
converted to methane by reacting with hydrogen. Following reactions take place in the reactor
filled with nickel catalyst at about 3000C.
CO (g) +
3H2 (g)
CH4 (g)
+
H2O (g)
CO2 (g) +
4H2 (g)
CH4 (g)
+
2H2O (g)
Although methane is an inert gas in ammonia synthesis, water produced in the reaction oxidizes
the iron catalyst used in ammonia synthesis. So water is removed in two stages at the
downstream of the methanator and in ammonia synthesis loop by condensation.
Synthesis of ammonia

17. Synthesis of ammonia is done by Haber-Bosch process. Following reaction takes place in the
reactor when incoming gas (N2 and H2) is passed over iron catalyst at a pressure usually in the
range 100-250 bar and at the temperature range of 350-5500C.
N2 (g)
+
H2 (g)
2NH3 (g)
H=-46 kJ.mol -1 NH3
The required pressure is achieved by centrifugal compression which is driven by a steam
turbine. The required amount of steam for the turbine can be obtained from the steam produced
in the ammonia plant itself.
At this equilibrium conditions, the conversion of reactants are only 20-30% per pass. So
unreacted gas is separated and recycled. The synthesis is typically carried out in a loop as
shown in the diagram. Ammonia formed is separated from the recycle gas by condensation. The
refrigeration compressor needed for this task is also driven by a steam turbine that uses steam
produced in the plant itself. In order to maintain the pressure and to shift the reaction forward,
fresh make up synthesis gas is supplied to the reactor.
Synthesis loop can be designed in many different ways with respect to the points which make
up gas is added and ammonia and purge gas is removed. . The best arrangement is to add the
make-up gas after ammonia condensation and ahead of the converter. The loop purge should
be taken out after ammonia separation and before make-up gas addition. This configuration is
dependent on the make-up gas being treated in a drying step before entering the loop. [4].
since the reaction is exothermic there should be a method to remove excess heat to maintain
equilibrium conditions. Ammonia produced in this process can be used as raw material for
urea manufacturing process.
2.3.1.2) Steam reforming with excess air secondary reforming
In conventional process the marginal efficiency of primary reforming is very low. So the
process designed to reduce the primary reforming and to move some of duty to secondary
reforming is known as Steam reforming with excess air secondary reforming. Following
features can be observed in this process compared to a conventional process.
Decreased firing in the primary reformer

18. Since the amount of heat supplied to the primary reformer is comparatively lower the process
outlet temperature is also generally lower. This will increase the firing efficiency, reduce the
size and the cost of primary reformer and prolong catalyst due to mild operating conditions. But
the degree of primary reforming is reduced due to law supply of heat which results lower
temperatures.
Increased process air supply to the secondary reformer
Since the degree of reforming is lower in the primary reformer there should be an increased
amount of internal firing or combustion in the secondary reformer in order to achieve the same
degree of overall conversion at the outlet of secondary reformer. The process air requirement is
50% higher than in the conventional method.
Cryogenic final purification
In this process all the methane and excess nitrogen is removed from the synthesis gas using a
cryogenic purifier. The purified gas is very pure except a trace amount of argon. Purge gas from
the synthesis section is also sent to this unit where it delivers an off gas for fuel.
Lower synthesis gas inert level
In the traditional process impurities such as CO and CO2 are removed by methanation. In this
process a significant improvement of purity level can be achieved in synthesis gas. This leads to
a higher conversion per pass and reduce purge gas flow which results a more efficient process
than the conventional process.
2.3.1.3) Heat exchange auto-thermal reforming
From a thermodynamic point of view it is wasteful to use the high-level heat of the secondary
reformer outlet gas and the primary reformer flue-gas, both at temperatures around 1,000°C,
simply to raise steam. Recent developments are to recycle this heat to the process itself, by using
the heat content of the secondary reformed gas in a newly-developed primary reformer (gas heated
reformer, heat exchange reformer), thus eliminating the fired furnace. Surplus air or oxygen-

19. enriched air is required in the secondary reformer to meet the heat balance in this auto thermal
concept.
When auto thermal reforming is used nitrogen dioxide emissions to the atmosphere is
significantly reduced due to the elimination of flue gas in the primary reformer.
2.4) Process in general production of Urea
The main principle of manufacture of urea has two main reactions.
2NH3 + CO2
NH2COONH4
-37.4 Kcal/gm mol
NH2COONH4
NH2CONH2 + H2O
+ 6.3 Kcal/gm mol
While going main reactions undesirable side reaction taking place is
2NH2CONH2
NH2CONHCONH2 (Biuret) + NH3
The synthesis is further complicated by the formation of a dimmer called biuret,
NH2CONHCONH2, which must be kept low because it adversely affects the growth of some
plants. The structure of these compounds is shown in Figure

20. Figure. Schematic representation of urea synthesis
We can consider that the totally process which can be divided to fore sub processes.
Synthesis
Ammonia & CO2 are compressed separately and fed to the high pressure (180 atms) then a
mixture of urea, ammonium carbamate, H2O and unreacted (NH3+CO2) is produced. Both 1st &
2nd reactions are equilibrium reactions. The 1st reaction almost goes to completion at 185-190
oC & 180-200 atms. The 2nd reaction (decomposition reaction) is slow and determines the rate
of the reaction.
Purification
The major impurities in the mixture at this stage are water from the urea production reaction and
unconsumed reactants (ammonia, carbon dioxide and ammonium carbamate). This liquid
effluent is let down to 27 atms and fed to a special flash-evaporator containing a gas-liquid
separator and condenser. Unreacted NH3, CO2 & H2O are thus removed & recycled. An
aqueous solution of carbamate-urea is passed to the atmospheric flash drum where further
decomposition of carbamate takes place NH2COONH4
2NH3 + CO2 The pressure is then
reduced a solution of urea dissolved in water and free of other impurities remains. At each stage
the unconsumed reactants are absorbed into a water solution which is recycled to the secondary
reactor. The excess ammonia is purified and used as feedstock to the
primary reactor.
Concentration
75% of the urea solution is heated under vacuum, which evaporates off some of the water,
increasing 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 110oC to redissolve these crystals prior to evaporation. In the
evaporation stage molten urea (99% w/w) is produced at 140oC.
Granulation

21. Figure. Schematic representation of granulation
Urea is sold for fertilizer as 2 - 4 mm diameter granules. These granules are formed by spraying
molten urea onto seed granules which are supported on a bed of air. This occurs in a granulator
which receives the seed granules at one end and discharges enlarged granules at the other as
molten urea is sprayed through nozzles. Dry, cool granules are classified using screens.
Oversized granules are crushed and combined with undersized ones for use as seed.
All dust and air from the granulator is removed by a fan into a dust scrubber, which removes the
urea with a water solution then discharges the air to the atmosphere. The final product is cooled
in air, weighed and conveyed to bulk storage ready for sale.

22. 2.5) Process variation of Urea manufacturing
Once– through processes
Process
partial recycle processes
Total recycle processes
1 Gas recycles process
 CPI-Allied gas recycle urea process
 Inventa gas recycle urea process
2
Liquid recycles process
 Stamicarbon CO2 stripping urea process
 Montecatini complete recycle urea
process
 Pechiney total recycle urea process
 Inventa liquid recycle urea process
3 Gas / liquid recycle process
 Mitsui Toatsu total recycle D improved
urea process
 Stamicarbon total recycle process
 SNAM PROGETTI ammonia stripping
urea process
 Chemico total recycle urea process
 Lonza- Lummus urea process
The basic process chemistry of urea manufacturing is relatively simple. However, because
operating parameters vary; particularly in the initial formation of the urea solution, numerous
process designs have been utilized. Design differences occur in the separation and recycle of
component streams. There are three major classes of urea processes, based on the type or
quantity of recycle: once– through processes, partial recycle processes and total recycle processes. At
least 75% of the urea produced today is by total recycle systems.
2.5.1) Once-through processes
Figure below is generalized flow diagram of a once- urea process.

23. Figure. Once– through processes
In this process liquid NH3 is pumped through a high pressure plunger pump and gaseous CO2 is
compressed through a compressor up to the urea synthesis reactor pressure at an NH3 to CO2
feed mole ratio of 2/1 or 3/1. The reactor usually operates in a temperature range from 175 to
190 0C. The reactor effluent is let down in pressure to about 2 atm and the carbamate
decomposed and stripped from the urea-product solution in a steam heated shell & tube heat
exchanger. The moist gas, separated from the 85-90 % urea product solution, & containing about
0.6 tons of gaseous NH3 per ton of urea produced is usually sent to an adjacent ammonium
nitrate or ammonium sulfate producing plant for recovery. An average conversion of carbamate
to urea of about 60 % is attained. Excess heat is removed from the reactor by means of a low
pressure steam-producing coil in an amount of about 280,000 cal/Kg urea produced.
2.5.2) Partial recycle processes
Partial recycle processes as shown in figure bellow. This process is termed partial recycle
because only excess ammonia is recovered and recycles to the reactor.

24. Figure. partial recycle processes
The synthesis is carried out with as much as 200% excess ammonia. This process is also similar
to that of the once through process, with one additional step : the reactor effluent contacting urea
ammonium carbamate, water, and excess ammonia. Passes though an expansion valve reducing
the pressure to a few hundred KPa depending on the particular process design. The steam goes to
an ammonia separator where excess ammonia is removed, condensed, and recycled to the
reactor. This is necessary to recover some of the cost of using excess ammonia. Also if passed
directly to the carbamate decomposer, the excess ammonia could hinder the decomposition of the
carbamate. The steam containing urea, cabamate and water goes to a carbamate decomposer
which dissociates the cabamate to ammonia and carbon dioxide. The aqueous urea solution is
separated and goes to further processing or shipment.
2.5.3) Total recycle processes
The total recycle process is most widely used process in the urea manufacturing industry. There
are three variations of the total recycle process.
1. Decomposed carbamate gases are separated and recycled in their pure states.
2. Carbamate solution is recycled to the reactor.
3. A combination gas/ liquid recycle may occur.
2.5.3.1) Gas recycles process

25. Figure. Gas recycles process
The material leaving the reactor is a mixture of urea, ammonium carbamate, water, and excess
ammonia. This stream goes to a decomposer which separates the carbamate into ammonia and
carbon dioxide. The separated gases may both be recycled, or one may be purified at the expense
of the other and returned to the process. In the partial recycle process, however, the excess
ammonia is recovered and the ammonia or carbon dioxide in the unreacted carbamate is lost to
the process. In the total recycle process, the entire quantity of ammonia is reused; i.e., excess
plus decomposed carbamate ammonia. Two examples of the gas recycle process will be
discussed; the CPI – Allied and inventa processes.
 CPI
-Allied gas recycle urea process
Higher operating temperature (1940C -2330C) at 30.3 MPa and Conversion rate is 80%-85%.
Ammonia and carbon dioxide feed entering with ration ratio- 4:1.
The reactor products pass through an expansion valve to primary carbamate decomposer where
90% of the carbamate is flashed and stripped along with water vapor. The urea solution contains
approximately 1.5% of the initial carbon dioxide feed. This stream is sent to an ammonia
separator, where excess ammonia is stripped, and on to secondary decomposer where any
remaining carbamate dissociates at atmospheric pressure.The overheads from both decomposers
are passed through a two – unit series of absorbers where monoethanolamine (MEA) selectively
absorbs carbon dioxide and water, leaving ammonia for recycle to the reactor. The carbon
dioxide – rich solvent is sent to a stripper which thermally regenerates the MEA creating a rich
carbon dioxide stream which is recycled to the reactor. The urea solution leaving the secondary

26. decomposer passes through a centrifugal Min-film evaporator unit. The product contains less
than 0.7% biuret and 0.20% water.
Figure. CPI-Allied gas recycle urea process
 Inventa gas recycle urea process
The Inventa process utilizes a reactor operating at 20.2 MPa and 180 0C to 2000C. The molar
feed ratio of ammonia to carbon dioxide is 2:1 with a maximum carbon dioxide conversion to
urea of 50%. The reactor effluent containing excess ammonia, ammonium carbamate, urea, and
water passes through an expansion valve where it is lowered to 549 kpa and heated to 1200C in
the carbamate decomposer. The ammonia and carbon dioxide go to an absorber where the
ammonia is selectively absorbed and the carbon dioxide exits for recycle. The resulting
ammoniacal solution of ammonium carbamate goes to a desorber to remove ammonia for recycle

27. Figure. Inventa gas recycle urea process
2.5.3.2) Liquid recycle process
Figure. Liquid recycle process
This process is similar to the gas recycle process except that the gases are condensed with the
addition of water when needed, to form a carbamate solution for recycle. Those processes which
will be discussed in this category are the Stamicarbon CO2 Stripping, Montecatini, Pechiney, and
inventa processes.

Stamicarbon CO2 stripping urea process
In the Stamicarbon CO2 Stripping urea process ammonia and carbon dioxide are reacted
in the
molar ratio of 2.4:1 to 2.9:1 at 1700C to 1900C and 12.1 MPa to 15.1 MPa . The
reaction product (1850C, 14.1 MPa) goes immediately to a high pressure stripper.

28. Operating at 14.1 MPa and 1900C (1), where the reactor stream is stripped by incoming carbon
dioxide. The stream containing 15% unconverted carbamate is then let down for further
decomposition in the low pressure decomposer operating at 300 kpa and 1200C. the ammonia
and carbon dioxide are condensed in the low pressure to the high pressure condenser where it
combines with the off-gas from the high pressure stripper and a split from the ammonia feed line.
The condensed stream from the high pressure condenser operating at 1700C and 14.1MPa, goes
to the reactor. An equivalent amount of 345 kpa steam is produced in the high pressure
condenser and is used in other sections of the plant.
This process claims ammonia and carbon dioxide consumption of 0.57 metric ton and 0.755
metric ton per metric ton of urea produced, respectively. Conversion efficiencies for ammonia
and carbon dioxide are 65% to 85% and 70% to 85%, respectively.
Figure. Stamicarbon CO2 stripping urea process
 Montecatini complete recycle urea process
Montecatini process ( Montedison) in which preheated liquid ammonia and carbon dioxide are
compressed to 20.2 MPa and enter the reactor operating at 1950C (12,16). The reactor mole ratio
for NH3:CO2 is 3.5.1;for H2O : CO2 it is 0.6.1 (17).the effluent containing urea, excess

29. ammonia, ammonium carbamate, and water enters a first – stage decomposer/separator operating
at 8.1 MPa and 1850C. In this decomposer/ separator most of the ammonia is driven off along
with the carbamate decomposition products. This stream, along with 20% to 30% of the carbon
dioxide feed stream, is fed to the first – stage carbvamate condenser which operates at 8.1 MPa
and 1450C
The effluent form the first – stage condenser passes to an auxiliary condenser operating at the
same pressure but at 1150C so that condensation is completed. The gas leaving this condenser is
washed to remove ammonia. The liquid stream is recycled to the reactor.
The liquid stream leaving the first – stage decomposer/ separator proceeds to a second- stage unit
operating at the same temperature as stage one and 1.2 MPa, and finally to a third stage operating
at 202kpa to 303 kpa before leaving the facilities. The gaseous effluents from the stage two and
three decomposer/ separators are condensed in carbamate condensers three and four,
respectively. In condenser three the gas stream is mixed with liquid effluent from both wash
vessels and the liquid carbamate is sent to the first stage condenser. In condenser four an
ammonia bearing gas stream from the solidification section is washed with cold ammonium
carbamate, and the resulting effluent is cycled through a wash vessel before going to condenser
three.

30. Figure. Montecatini complete recycle urea process
 Inventa liquid recycle urea process
Figure. Inventa liquid recycle urea process
2.5.3.3) Gas/Liquid recycle process
Figure. Gas / liquid recycle process

31. It is characterize by ammonia recycle with carbon dioxide being recycled in the form of
carbamate. The following processes of this type will be considered: Mitsui Toatsu (Total Recycle
D Improved) , Stamicarbon, SNAM PROGETTI ,chemico, and Lonza-lummus.

Stamicarbon total recycle process
The stamicarbon total recycle process is shown in below the reaction take place at 20.2 MPa and
1700C to 1900C. The reactor effluent is lowered to approximately 505 KPa before going to the
preseparater. The liquid stream form the preseparater passes through to additional separation
steps before finally leaving the process. The various ammonia and carbon dioxide streams are
condense, and the carbomate formed is recycle to the reactor. A wet scrubber is used on the gas
stream to recover ammonia for recycle.
Figure. Stamicarbon total recycle process
 SNAM PROGETTI ammonia stripping urea process
The SNAM PROGETTI urea process ,as shown in below is similar to the stamicarbon CO2
stripping process , but the stripping is done by ammonia rather than carbon dioxide. The process

32. as shown can operate at two different reactor pressure, 13MPa to 16MPa or 20.2MPa to 25 MPa.
Operating temperature is 180C to 190C.malar ratio is 3.5:1.
The effluent leaving the reactor is passed to a stripping operating at 10 MPa to 15MPa and 160C
to200C. Most (>90%) of the ammonia and carbon dioxide are removed in the stripper with the
remainder being removed in the flash separator. These overheads are collected and the cabomate
is recycled; excess ammonia is also recycled to storage.
The unique feature in the SNAM PROGETTI process is the cabomate ejector which introduces
carbomate and ammonia to the reactor. The ammonia pressure drop through the ejector of
41MPa supplies the necessary driving force
.
Figure. SNAM PROGETTI ammonia stripping urea process

33. 3) ECONOMIC ASPECTS OF UREA PRODUCTION

34. 4) ENVIRONMENTAL AND SAFETY ISSUES
4.1) Health and Safety
4.1.1) Health
Ammonia is a material that is widely used in chemical industry and it has its own toxicity, health
issues and safety measures that require attention. Therefore it is required for the designers of
ammonia and derivatives plant to have a clear understanding about these aspects of ammonia. In
analyzing the effects of releases of ammonia the toxicity of ammonia should be considered.
The threshold limit value (TLV) for ammonia is 25 PPM (TWA), short term exposure limit
(STEL) 35 PPM and initialism for Immediately Dangerous to Life or Health (IDLH) 300 PPM
[51]. Ammonia gas is irritating to skin, nose, eyes, throat, respiratory tract and mucous
membranes. Even though at lower concentrations below TLV there has been no evidence of
affect to lung functioning. Various concentrations of ammonia gas cause following health
concerns.
Concentration
400-700 PPM
Affect
Severe eye and respiratory irritation.
Potential Permanent damage
1700 PPM
Convulsive coughing and bronchial
spasms
Exposure more than half an hour can be
fatal
2500 PPM
Can be life threatening
5000-10000 PPM
Death by suffocation
[36], [52]
Ammonia vapor can be extremely irritant to eyes and mists or liquid ammonia can course
permanent blindness. Cryogenic burns can be coursed by liquid ammonia. Ammonia has not
been found to be carcinogenic or has the ability to reproductive or developmental toxicity in
human body. [36], [52]

35. 4.1.2) Safety
When the safety of ammonia and its derivatives plant is considered, a common accident that has
occurred over the years is accidental releases of ammonia. Metals and alloys of particularly
copper and zinc are extremely vulnerable to corrosion when exposed to ammonia. In general
ammonia can be stored in iron or steel containers, transferred through iron and steel piping and
fittings. [36]. It should be noted that under certain conditions with few specific steels ammonia
can produce embrittlement [35]. Therefore it is required to follow strict guidelines when
choosing materials to avoid releases of ammonia liquid or gasses to the atmosphere. Ammonia
can flash in case of loss of containment when ammonia is stored under refrigerated conditions or
liquefied gas under pressure. Quantity flashed will depend on the temperature conditions [35].
Even though ammonia has lower density than air, the resultant clouds formed by flashing are
found to have higher densities than air. This will result in ground level ammonia clouds [54].
Past events
In order to get an idea about the safety measures that should be taken when designing an
ammonia and derivatives plant, it is required to have an understanding about the incidents that
have occurred with the presence of ammonia and in ammonia production.
In 1976, a release of 19 tons of ammonia from a road tanker in Texas, USA caused 6 deaths. It
should be noted that just after 2.5 hours the levels of ammonia has returned to the background
levels.[39] [40]
Even though there were no human fatalities, a massive 600 ton spill of ammonia to a
watercourse, caused a severe environmental hazard in Arkansas, USA in 1971 killing thousands
of fish [59]. The reason for the spill was accidently filling a tank with warm ammonia. The warm
ammonia transferred to the tank from the bottom, formed a layer at the bottom. Afterwards this
layer suddenly rose to the surface due to higher vapor pressure of the warmer ammonia causing
the tank to burst.
A very important fact to note is that with ammonia, brittle fractures can occur in metal
containments. Brittle fractures are catastrophic since the fracture can propagate at a velocity

36. closer to the velocity of sound. What appears to be the worst accident involving ammonia is the
release of approximately 38 tons of ammonia which caused 18 deaths. The release was due to a
brittle fracture in an ammonia tank. The accident occurred in Potchefstroom, South Africa in
1973. The post incident investigation revealed neither over pressure nor over temperature nor
other triggering event. The fracture started in a carbon steel dished end. The minimum transition
temperatures were 200C for fragment and 1150C for remaining part of the dished end. The
investigation showed that the operating conditions were below these temperatures which made
the material brittle. A gas cloud of 150m in diameter and 20m deep was resulted from this
failure. [39] [58].
Another type of accidents that has occurred in ammonia production plants over the years is vapor
cloud explosions. This is due to sudden releases of hydrogen rich synthesis gases being ignited
after a while. The flammable region of these clouds is spread from 4%-74% v/v. Due to the
diffusivity, these vapor clouds are not often formed in unconfined or semi-confined areas. But in
confined spaces, (eg: compressors) ignition of such a vapor cloud is catastrophic.
Another possible, yet uncommon type of accident is ammonia explosions. Ammonia explosions
are rare because of the unusually high, lower explosive limits (LEL-16%, HEL- 25%). The auto
ignition temperature of ammonia is about 6500C. There are no reports of ammonia explosions in
unconfined spaces due to the fact that it is not easier to get a 16% concentration in open air. In
Oklahoma, in 1978, a refrigeration system failed causing the ammonia storage to warm up. The
pressure eventually rose and the pressure relief valves discharged ammonia, which was ignited
by a nearby flare. In New Zealand in 1991, a welder was killed due to an explosion occurred
when he was welding a tank which supposed to be empty, yet which was later found out to have
a flammable mixture of ammonia vapor and air.[16]
Common avoidable mistakes
In the famous book ―What Went Wrong‖ by Trevor Kletz, it has been identified that many of the
failures have occurred due to the use of wrong material other than the one that has been
specified. There has been one incident where the converter has been pushed over due to the
reaction forces from a hydrogen leak out. The reason for the leak out is the use of a carbon steel

37. exit pipe for the converter instead of 1.25% Cr, 0.5% Mo alloy, in which a hole was created due
to the hydrogen attack [16]
An interesting investigation was done to check the materials delivered to a new ammonia plant.
5480 items (1.8% of the total) was found to delivered in the wrong material. This included 2750
furnace roof hangers. Had this investigation been not done, the roof would probably have failed.
[16]. A specific reason has not been found for the delivery of wrong materials (Can be cost
cutting or unavailability). Therefore the engineers are advised to check the items before they are
used in the plant to avoid severe accidents in future. [16]
4.2) Safety Procedures
It should be noted that not all the failures, problems or hazards can be anticipated. Events such as
those are eye openers for everyone, reminding that never be complacent with safety and the
importance of following the procedures to prevent accidents.
One such widely accepted procedure is ―Inherent safety design‖.
4.3) Inherent Safe Design
Inherent safety is an approach to process design and operation which builds in safety, health and
environmental considerations at the start. This is done to ensure that even if something goes
wrong, the level of danger is minimized. Practically it is impossible to have an inherently safe
design. But one can have an inherently safer design.
―What you don’t have can’t leak!‖
- Trevor Kletz, (Author: What Went Wrong)
There are four guidewords that drive inherent safety.
Substitute:
Replace hazardous substances and procedures with less hazardous substances and
procedures
Minimize:
Use as less as possible hazardous materials when it is not avoidable. Perform
hazardous procedures as few times as possible.
Moderate:
Use hazardous materials in the least hazardous forms and identify processing
options that involve less severe process conditions.

38. Simplify:
Finish the design, processing equipment and procedures to eliminate the chances
of errors by eliminating excessive use of safety features and protective devices.
Less equipment of any kind means that there is less to go wrong.
4.4) Layers of Process Safety
Inharrent
Passive
Active
Procedural
Inharent Safety:
Elimination of hazards from the design
Passive Safety:
Protection to the design so that it cannot be easily changed
Eg: process conditions
Active Safety:
Prevent. Eg: high level trip isolates flow into a tank before it can overfill
Control. Eg: A restrictive orifice plate limits the rate of loss of
containment if a line fails.
Mitigate. Eg: heat activated links open deluge valves to spray water in
case of fire
Procedural Safety:
Risk management systems
Eg: company policies, site rules, operating procedures, training,
maintenance, test procedures, emergency response plans

39. There will be a conflict of interest when implementing inherent safety concepts due to many
reasons like workload, motivation, complexity, time, communications, organizational structure,
cost cutting, poor working environment etc.
It should be strictly noted that alarm systems are less complicated and work properly to make
sure that alarms are not ignored due to the fact that they are often activated due to
malfunctioning.
4.5) conclusions
4.6) recommendations
4.7) Environment

40. 5) GREEN CONCEPTS USED IN PLANT DESIGNING
Green concepts are used frequently in industrial plant designing recently, as the whole world is
aware of the sustainability of the environment and the energy sources. These concepts mainly
addresses the issues with renewable energy sources, minimizing the pollutants which affects the
environment, Life cycle management of each raw material used, Efficient usage of natural
resources and protecting occupational health of the employees.
In a green building design, application of green concepts comes throughout the designing stage
to maintenance stage. This focuses on energy and resources efficiency, overall impact to the
environment, indoor environment quality and any other sustainable concepts (1). Life cycle of
each material used will be focused to make its’ use maximum and impact to the environment
minimum. Green building has the potential to save 30%-40% of energy while reducing the
operating cost and improving good health and a comfortable environment to work in (2).
5.1) why should we care about green buildings?
For last 20-30 years, mankind faced bad experiences with global warming, ozone depletion,
resource depletion, energy scarcity, ecological toxicity, humantoxicity, acid rains etc. (1). These
have made them think about how they use the environment for their uses. Although it’s really
hard to stop the environment impact under current circumstances, idea of green industries is to
minimize the effect to the environment done by human activities.
There are lots of tangible and intangible benefits that an industry would get by applying green
concepts into its design (3).
 Tangible benefits
o Sustained savings

Energy saving- 30%-40%

Water saving-20%-30%

Reduction in initial investments
o Reduce operational costs
o Optimize life cycle
o Waste minimization

41.  Intangible benefits
o Reduce the impact to the environment
o Enhance occupant comfort
o Improve productivity of occupants
There are several aspects of green building concepts which can be taken to our consideration.
1. Site design, Preparation and development
2. Resource efficiency
a. Energy efficiency
b. Water efficiency
c. Other resources efficiency
3. Impact to the environment
a. Carbon foot print
b. Waste minimization
c. Life cycle management
4. Indoor environment quality
5.2) Current methods used in industries
Main areas addressed in the effort are
Search for renewable energy sources
Main renewable sources considered currently are
o Solar power
PV cells are used in different scales to create electricity from solar rays. Usage of
these has being increasing, but still the initial investment and the payback period
are problems related with this option. Still this stands as one of the main
renewable options to go with mainly for countries as Sri Lanka.
o Wind power

42. This is the other main energy source considered as a renewable option for
industries. Companies have widely tried to get wind power to their plant designs.
Optimize current energy consumption
This is the best starter for a current industry to go green. Most of the factories have their
problems in consuming energy in an optimum way, so that they will surely find their
energy demand decreased by concerning on the current energy plan.
Break-up of energy consumption in an industrial building(3)
Most of the energy consumed in industrial buildings are for ventilation and lighting. So,
most common way to save electricity is through upgrades to more energy-efficient
lighting systems, the use of energy management systems and upgrade to their HVAC
system.
Minimize greenhouse gas emission

43. Minimizing the carbon foot print on earth is the other main area stressed with green
concepts. For this, most industries have started acting on minimizing the emission of
greenhouse gasses. As CO2 being the main greenhouse gas produced in industries the
impact you do to the environment is measured as CO2.
Optimizing the usage of natural resources, waste treatment and life cycle management
Usage of natural resources as water and other raw materials takes a major role.
Management of life cycle of each raw material will help to minimize the waste and
improve the productivity of natural sources.

44. 6) HISTORY OF UREA PRODUCTION IN SRI LANKA
There many views being aired about the Fertilizer and the Fertilizer plant that was closed down
in 1986. The plant was constructed by British Company to manufacture 980 tons of urea per day
at a cost 250 million US $.
Feedstock used for the process was Naphtha (fuel even lighter than petrol), which is a byproduct
of the oil refinery at Sapugaskanda. Naphtha has a severe demand in the world market for
making many petroleum products. CPC invariable preferred to sell naphtha to foreign markets
for obvious reason mentioned below.
In Middle East and in most countries Urea is manufactured using Natural gas, which can be
tapped easily in oil producing countries. Therefore it is a known fact that urea manufacture using
Natural gas is much more economical than using Naphtha. Under these circumstances Naphtha
based plants could not compete with natural gas plants particularly in a country like Sri Lanka
where there was only one oil refinery. Since our cost of production was extremely high treasure
could no settle the feedstock bills to refinery. CPC in return curtailed the live wire to Urea plant
as the Government was of the view that it would be cheaper to import urea and sell naphtha to
foreign market thereby eliminating the burden on the treasury.
The other factor that contributed to uneconomical operating cost was the regular breakdown in
the machinery and the lack of trained staff. Engineers and the Technicians who were trained
abroad for this specialized industry were gradually leaving for stabilized industries with the
development of uncertainty in the organization. Liberalized policy of the then government did
not want the staff to be retained by force. For practically all the spare parts and equipment we
had to depend purely on foreign suppliers. Probably a country like India could manage Naphtha
based plant because of the many refineries that they possess and also because of their welldeveloped infrastructure. India not only could manufacture their own spares but also they could
manufacture all the required plant equipment.

45. Chlorophyl – C55H54N4Mg - Photosynthesis
Mol Wt – 55x12 +54x1+14x4+24x1 = 794
N – Wt % = 56/794 = 7.05%
C-
= 660/794 = 83%
Mg -
= 24/794 = 3.02%
Cellulose – (C12H10O5)n = 234 : C – 61%
2NH3 + CO2 ------- (NH2)2CO + H2O
At STP 1 gmol of a gas occupies 22.4 litres of volume
At STP 3 gmol (78 g) of a gas occupies 67.2 litres of volume
At 600 Bar pressure 67.2 litres will contain - 600x3gmols (23,400g)
Atmosphere – 0.03% CO2
Urea – CO(NH2)2
N – 28/60 – 46.7%
C – 12/60 – 20%
(NH4)2SO4 – 28/132 – 21%
NH4NO3 – 28/80 – 35%
MSDS of Methane, Ammonia, Urea, CO, CO2
Demand for Natural Gas – CH4 + 2O2 ---- CO2 + 2 H2O
16
44
Cal Value – 16,000 + kcals/kg
Other hydrocarbons – LPG - 12,000 + kcals/kg
Gasoline - 12,000 + kcals/kg

46. 7) PROCESS SELECTION AND DESIGN DECISIONS
Cost effective study of raw materials for production of Hydrogen
Considering the literature review done on existing processes to produce Hydrogen, following raw
materials are considered as possible major options for the production process of Hydrogen for
manufacturing of Ammonia for Urea.
1.
2.
3.
4.
Natural Gas
Heavy oil
Coal
Water/Alkaline electrolysis
1.Natural Gas
Currently natural gas is nor produced, imported or consumed in Sri Lanka. Although there are new
prospects of natural gas wells in Sri Lanka, unavailability of natural gas is the main challenge with
Natural gas. So we assume importing of natural gas which is the only option if we are going with this
option.
CH4(g) + H2O(g)
CO(g) + 3H2(g)
Production cost
Price of natural gas in international market
Density
= Rs 53,300/103m3
=0.5kg/m3
= (Rs 53,300/103m3)*6/(16*0.5)
Price to produce 1kg of H2
= Rs.79.50/kg of H2
Shipping cost
Shipping cost of avg 2.8kg of natural gas = Rs. 39/2.8kg of natural gas
(which is equalant to 1kg of H2 )
Total cost for 1kg of H2
=
Rs.118.50/=

47. Heavy fuel oil
Heavy fuel will be bought from petroleum corperation.
C50H102(l) + 25O2 (g)
5CO(g)+51H2(g)
Price per 1liter of Heavy fuel oil in Sri Lanka
= Rs. 90/=
Avg. specific gravity of heavy oil
= 0.95
Price to produce 1kg of H2
=
Rs.(90*702)/(102*0.95)
= Rs. 648.88/=
Coal
Although producing hydrogen from coal is a matured industry, it is not considered as a cost effective
option for the countries which don’t have coal.
C(s)+ H2O(g)+heat
CO(g)+H2(g)
This process need very high temperatures and considering the unavailability of coal in Sri Lanka and the
electricity consumption, this is not considered as a favorable option.
4.Water/Alkaline electrolysis
H2O + electricity
H2 + 1/2O2
With non-renewable fuels been decaying, cost forecast for electrolysis has shown good signs with the
statistics.

48. With above factors, this can also be considered as a possible candidate.But the high electricity
consumption and lack of R&D in industrial scale have hold this option from being a cost effective option
for the process, for Sri Lanka.
When above analysis is considered, the best cost effective option seems to be natural gas. Natural gas
has a high calorific value, which attracts the attention as a potential fuel. This leads the designers to be
considerate about the future prices of natural gas.
In this regard, there were two forecasts referred. Both of the forecasts are done by United States Energy
Information Administration (EIA). Forecasts were done from 2009 – 2030 time period which is likely to
be the core operating time period of the proposed plant.

49. The first graph is of the price forecast of crude oil until 2030. Heavy oil is the heavy facture of the crude
oil. If the liquid fuel consumption is broken down to sectors it can be clearly seen that the major
consumption is for transportation (i.e. the consumption of gasoline and diesel). Therefore it is safe to
assume that the world will focus on producing light fuels even from the heavier fractions.

50. When taking a look at the current price of a barrel of crude oil (2013 ≈$95) it is clear that the predictions
are almost at reference prediction. Furthermore, the forecasted price varies from $50-$200.
In contrary the natural gas price tend to increase by maximum of $4 and seems very stable.
Therefore the overall conclusion is to use natural gas as a raw material.
According to the economical analysis mentioned above, it can be seen that using natural gas as
the feed is more cost effective than using heavy oils or coal. Because of that ―Steam reforming‖
process should be used for production of ammonia. New technologies can be used along with the
conventional steam reforming technology in order to increase the efficiency and thereby to
reduce the overall operating cost. Although the process layout is identical to the process that has
been used for decades, the performance is expected to be significantly improved due to
incorporation of modern technologies with the proposed plant.
Two main areas that have significant impact on the performance and the cost of an ammonia
production section are the reforming section and the synthesis section. Improvements for those
sections have been a major concern in this process design. Following improvements are basically
considered in designing the process for ammonia synthesis.
1) Reducing the duty of primary reformer
In every reforming ammonia process the reformer furnace and the flue gas duct represents about
25% of total investment cost of ammonia production plant.[1] Because of that the concept of
reducing the size of primary reformer and shifting duty to secondary reformer or another heat
exchange reformer is very important. Although there are so many methods to achieve this such
as Braun Purifier Process, ICI AMV process and Foster Wheeler process etc, The Topsoe
Process is selected in this design which is considered as the latest and energy efficient process
[2]. According to that process the size of the primary reformer can be reduced by following steps
Installation of pre reformer upstream to the primary reformer
Natural gas basically contains methane. But it may contain varying amount of other
hydrocarbons depending on the source. In the pre reformer all higher hydrocarbons are converted
in to a carbon oxides, hydrogen and methane. When a pre reformer is installed the primary

51. reformer has to reform methane only. Adiabatic reforming can be used for steam reforming of
feed stocks ranging from natural gas to heavy naphtha. Because of that the process also becomes
more flexible. In case of shortage of natural gas in Sri Lanka, Naphtha can be used as the feed
stock which can be obtained as a byproduct of petroleum refinery. At the same time pre
reforming catalyst will pick up any sulphur components in the feed and will allow much higher
heat flux in the primary reformer. The pre reformed feed can be reheated to 650°C before
entering the primary reformer. This will result in reduced firing in the primary reformer, and
thereby reduced fuel consumption [3].
Figure 1- Installation of Pre reformer
Installation of heat exchange reformer downstream of the secondary reformer
The temperature of the flue gas emitted from a conventional primary reformer is usually about
9000C and the process gas at the outlet of the secondary reformer is also at around 10000C. From
a thermodynamic point of view it is waste of energy to use this high amount of heat simply for

52. raising steam and preheating process air for the secondary reformer. The boiling temperature in a
125bar main boiler on the secondary reformer outlet is only 3250C.
According to the Haldor Topsoe process a heat exchange reformer unit which is named as
HTER-p (Haldor Topsøe Exchange Reformer) can be installed at the downstream of the
secondary reformer. The HTER-p is heated by the process gas exit from the secondary reformer,
and thereby the waste heat normally used for High pressure steam production can be utilized for
the reforming process down to 750–850°C approximately. Operating conditions in the HTER-p
are adjusted independently of the primary reformer in order to get the optimum performance of
the overall reforming unit. As shown in the diagram around 20% of the natural gas feed can be
by-pass the primary reformer according to this concept. [3]
Figure 2- Arrangement of Heat exchanger reformer unit
2) Pre heat combustion air for the primary reformer and process air to the secondary
reformer.
Although the duty of primary reformer is reduced using new technologies, the flue gas from the
primary reformer is expected to be at a temperature higher than 650 0C. This heat can be
recovered to preheat combustion air for the primary reformer up to about 4000C and to pre heat
the process air for the secondary reformer. Rest of the heat that is needed to heat process air up to

53. 6000C can be recovered from the gas emitted from the secondary reformer. Any remaining heat
from the flue gas can be used to preheat fuel to 1000C and to pre heat boiler water. According to
the energy efficient Topsoe process permitted stack temperature is lowered to 100 0C using about
energy recovery methods.
3) Raising steam using waste heat steam boiler at the downstream of the HTER-p unit
The process gas at the outlet of the HTER-p is around 750–850°C. Temperature should be
reduced up to 350-4000C to feed the High Temperature Shift converter unit. This heat can be
recovered to raise high pressure steam which can be utilized in other heating requirements of the
plant.
4) S-350 Ammonia Synthesis Loop produced by Haldor Topsoe
There are various typical arrangements of ammonia synthesis loop based on the point at which
the fresh make up gas is delivered and ammonia formed is condensed. Since make up gas is
absolutely free from catalyst poisoning agents such as sulphur, water and carbon dioxide can be
directly sent to the converter. After that ammonia leaves the converter can be condensed out by
cooling. This can be considered as the most favorable arrangement in the minimum energy point
of view because it results the lowest ammonia concentration at the converter and highest
ammonia content at the condensation.
S-350 ammonia synthesis loop is the latest development of ammonia synthesis technology with
related to the above configuration. As shown in the diagram it contains two ammonia converters
which are known as S-300 converter follows by S-50 converter. This will increase overall
ammonia conversion than conventional loops. S-300 converter is the most updated version of
radial flow converter which is designed to increase the conversion with reduced catalyst volume.
[4] In addition this increased conversion will results improved steam generation. Considering
above facts S-350 synthesis loop is proposed to incorporate in the plant design.

55. Reasons for selecting ACES 21 process
ACES21 Process
Advanced process for Cost and Energy Saving (ACES) urea production is one of the latest
technologies which were introduced by TOYO Engineering Corporation, Japan. Newest version
of ACES was currently used in many urea plants worldwide. (ACES 21)
ACES 21 advanced technology for urea production ascertain initial investment cost and energy
consumption and other operating costs are lower compared to other technologies. Operating
conditions of the urea synthesis reaction have been optimized under lower temperature and lower
pressure than normal conditions without reducing reaction rate significantly. As a result, energy
consumption and other related operating costs were reduced noticeably.
Synthesis of Urea by ACES 21 Advanced Process
ACES21 process synthesis section consists of three sections as follows,
1. Reactor
2. Stripper
3. Vertical Submerged Carbamate Condenser
Reactor
Liquid ammonia is fed to the reactor via the HP Carbamate Ejector which provides the driving
force for circulation in the synthesis loop instead of the gravity system of the original ACES. The
reactor is operated at an N/C ratio of 3.7, 182 °C and 152 bar. The CO2 conversion to urea is as
high as 63% at the exit of the reactor.

56. Following reactions were carried out in the reactor,
NH2COONH4
NH2CONH2 + H2O
: ΔH = +23 kJ/mol
2NH3 + CO2
NH2COONH4 + heat
: ΔH = -84 kJ/mol
Stripper
Urea synthesis solution leaving the reactor is fed to the stripper where unconverted carbamate is
thermally decomposed and excess ammonia and CO2 are efficiently separated by CO2 stripping.
The stripped off gas from the stripper is fed to the Vertical Submerged Carbamate Condenser.
Part of original CO2 is fed to the stripper as stripping agent. The rest carbon dioxide is supplied
to the synthesis reactor.
Vertical Submerged Carbamate Condenser
Vertical Submerged Carbamate Condenser (VSCC) operated at an N/C ratio of 3.0, 180°C and
152 bar. Ammonia and CO2 gas condense to form ammonium carbamate and subsequently urea
is formed by dehydration of the carbamate in the shell side. Reaction heat of carbamate
formation is recovered to generate 5 bar steam in the tube side. A packed bed is provided at the
top of the VSCC to absorb uncondensed ammonia and CO2 gas into a recycle carbamate solution
from the MP absorption stage. Inert gas from the top of the packed bed is sent to the MP
absorption stage.
Medium Pressure Absorber
Ammonia and carbon dioxide separated from urea solution in medium pressure decomposer are
recovered in medium pressure absorber. Then condensation heat is transferred to the aqueous
urea solution feed in the final concentration section.
2NH3 + CO2 ↔ NH2COONH4
; ΔH = -84 kJ/mol

57. Low Pressure Absorber
Ammonia and carbon dioxide separated from urea solution in low pressure decomposer are
recovered in low pressure absorber. Heat is released from the reaction inside low pressure
absorber. That heat is used to produce steam at 2bar. This steam is used for the evaporation
process of lower and upper separator.
2NH3 + CO2 ↔ NH2COONH4
; ΔH = -84 kJ/mol
Flash Separator
In this unit, water is evaporated by reducing pressure in order to concentrate the urea solution.
This unit is operated at 1.0 bar and 110 °C.
H2O(l) → H2O(g)
Lower Separator
In this unit, purified urea is further purified. The head required for this process is taken from
steam produced in low pressure absorber. This is operated at 0.55 bar vacuum pressure and at
110 °C. Calendria evaporator is used for this.
Upper Separator
Urea solution coming from lower separator is further concentrated in this unit. This is operated at
0.55 bar vacuum pressure and at 112 °C. 99.2% pure urea can be obtained from unit.

58. Granulation Plant
In here the basic principle of the process involves the spraying of the melt onto recycled seed
particles circulating in the granulator. These seed particles gradually increase in size as the
process continues. This is operated at 110-115oC and at slightly negative pressure. Then the heat
of solidification is removed by cooling air to about 90ºC.
REFERENCES