The document is an advanced book on fertilizer technology, focusing on ammonia and urea production processes and related equipment design. It covers various chapters detailing ammonia plant operations, fertilizer types, urea production methods, corrosion issues, pressure vessel design, explosive risks, and safety procedures. This resource is intended for engineers and managers to support plant commissioning, troubleshooting, and educational purposes in the field of fertilizer technology.

1. AN ADVANCE BOOK ON
FERTILIZERS TECHNOLOGY
(The Pure Knowledge)
BY
PREM BABOO

2. 2
INDEX
Sr.
No.
Description Page No.
1 About this book 2
2 Chapter-1 7
3 Chapter-1(Introduction & Ammonia Plant) 7
4 Introduction 7
5 Ammonia Plant 7-9
6 Thermodynamic Properties Graph 10
7 Ammonia Density 11
8 Process description Ammonia Plant and different section 11-15
9 Primary Reformer 16-18
10 Secondary reformer 18-19
11 Shift Section 19-23
12 Methanator 24-26
13 CO2 Removal Section 26-27
14 CO2 Breakthrough in Process 27-28
15 Ammonia Synthesis section 28-31
16 Ammonia synthesis converter 31-32
17 Effect of Optimum Inlet 32-33
18 Isothermal and adiabatic converter 33-40
19 Purge gas recovery unit 41
20 Difference between Horizontal and Vertical Converter 41-44
21 Refrigeration Circuit 44-45
22 Different Methane leakage Curve 45-52
23 Commercial uses of ammonia 53-55
24 Direct use as a Fertilizers. 55-56
25 Chapter-2 58
26 Types of Fertilizers, NPK and complex 59-60
27 Bio Fertilizers 60=64
28 Chapter-3 65
29 Urea Plant and Different Urea Process 66-67
30 Urea properties 67=8
31 Vapour Pressure of Urea 68
32 Neem Oil properties 69-70
33 Graduals and Prilled Urea 69=70
34 Advantages of Granular Urea 70-75
35 Process Technology 75-76
36 Brief Description of Urea Process 76
37 Once through process, partial recycle process 76=77
38 Total Recycle Process 77=78
39 Monticatni Process 78=79
40 Stripping Process 79-80
41 Ammonia stripping Process ,Saipem Process 80-81
42 CO2 Stripping Process, Stamicarbon Process 81-84
43 Total recycle Process Vs Stripping Process 84-85
44 Stamicarbon CO2 stripping Process N=3 85-87
45 Pool Condenser and Pool Reactor 87-88
46 Stamicarbon Mega Urea Process,4500 TPD single train 88-89
47 Development History of TEC Process. 89
48 ACES-21 Process 89
49 Comparison of ACES-21 and Pool reactor 89=90
50 Casale Urea Technology 90-94

3. 3
51 Granulation Process 95-97
52 Chemistry of Urea Synthesis 97-99
53 NH3/CO2 ratio 99-100
54 Vapour liquid Binary diagram 100-101
55 Effect of Excess water 100-101
56 Residence Time of Urea Reactor 102-103
57 Operation with High Efficiency Tray(HET) 103
58 Biuret Formation 104-105
59 Binary Azeotrope 105
60 Liquid gas equilibrium system 105-106
61 Vapour liquid equilibrium 106-107
62 Effect of Molar ratio 107
63 Theory of stripping 107-109
64 Technical realization of stripping process 108
65 Difference between Stripper and decomposer 108-110
66 Water carryover from decomposers and stripper 110
67 Theory of Hydrolysis 110
68 Others factors of conversion 111-112
69 Super Conversion in urea reactors with Super Cup High efficiency 112-113
70 Design Principle of super cup 113-114
71 Plant Performance after Installation of Super Cups 114-115
72 MRT 115-116
73 Plant Performance after Installation of Super Cups 117
74 Granulation 117-118
75 Granulator dust scrubber and cooler scrubber 118-119
76 Avearage product Diameter 119-120
77 Granulation Technology for urea 120-121
78 Storage condition Product Temperature 121-122
79 Urea Storage 122
80 Urea process Description 122-126
81 Advantages of pre concentrator 127-128
82 Urea Concentration Section 128
83 Urea prilling 128-129
84 Waste water Treatment 129
85 Urea Hydrolysis Theory 129-130
86 Bilk Flow Cooler(Solex)
87 The design for Fertilizer Important operational Parameters 131-135
88 CFD(Cooling Fluidized dryer) 135-136
89 Detail of Urea Prills quality 137-142
90 FCO(Fertilizers Control order) 143
91 Zincated Urea 143
92 Vapour pressure of Urea 144
93 Polymer formation after installation of Pre concentrator 144-145
94 Pressure, Temperature, Concentration Chart of Urea 145-148
95 Chapter-4 Corrosion in Urea Plants 149-150
96 Corrosion in Urea Plants 150-151
99 Crevice corrosion 152-153
100 Inter granular corrosion 153-154
101 Stress Corrosion cracking(SCC) 154-155
102 Condensation corrosion 155
103 Galvanic corrosion 155
104 Pitting Corrosion 156-157
105 Role of Oxygen and Stainless steel 157-158
106 Titanium 158

4. 4
107 Zirconium 159
108 Role of temperature and other process parameters in corrosion 159
109 Corrosion due to urea dust 159
110 Concrete Corrosion 160
111 Corrosion prevention and material selection 160
112 Duplex stainless steel 160-161
113 Safurex 162
114 Urea Reactor Pressure vessel 162-163
115 Chapter-5 Design of Pressure vessel 164
116 Design of High Pressure Vessel 165
117 Design of Urea reactor 167=170
118 Urea Reactor Trays Vs density 171
119 Urea Reactor N/C meter 171-172
120 Advantages of N/C meter 172
121 HP stripper 173
122 Titanium Bimetallic stripper 174-175
123 About 2RE-69 material 176
124 Urea stripper design 176-180
125 CO2 Stripping Stripper 180
126 HP carbamate condenser 180-182
127 Risky section of ammonia/CO2 stripping 183
128 High pressure Scrubber 183
129 Start-up and shut down operation mode 185-186
130 Hydrogen Contents too high 186
131 Carbamate solution too low. 186
132 Design of urea solution Tank and medium pressure absorber 187-191
133 Chapter -6,Explosive in Urea Plants & Urea Product quality 192-193
134 Explosive check 194-184
135 Water contents in ammonia Tank 195-195
136 Urea Finishing technology 196
137 Prilling 196
138 Zones of Free Fall height 197
139 Granulation 198
140 Prilling Tower Scrapper 199
141 Design of Prilling Tower 199
142 Chapter-7 203
143 Effluent Treatments in fertilizers Complex 204
144 Treatments of Non- Ammonical Effluents 204
145 Treatments of Ammonical Effluents 205
146 Sewage treatment Plants 205
147 Effluent Storage pond 206
148 Chapter-8 206
149 Hazard and risk appreciation 207
150 Toxicity of chemicals and Catalyst 207
151 Specific Safety warnings, start up Heater 208
150 CO2 Product vent silencer 208
151 Nitrogen risk 208
152 First aid Procedure 208
153 Health Hazards inhalation 209
154 Maximum allowable concentration 209
155 First aid procedure ,if ammonia is inhaled 209
156 Protective equipments recommendation 209
157 Fire and Explosion hazards 209
158 Ammonia 210

5. 5
159 Carbon Dioxide 213
160 Fire Extinguisher 214
161 First aid Procedure 214
162 Special storage handling 214
163 Urea 215
164 Health Hazard Inhalation 215
165 Urea Formaldehyde 216
166 Maximum Allowable Concentration 216
167 References 217
About this book
This book covers design of high Pressure equipment and developments, Process flow diagram of
different section of Ammonia, Urea and others fertilizers .Fundamentals of ammonia urea plant
trouble shooting risk assessment corrosion in different vessels and remedies. This book is useful for
Engineers and Sr. Managers for plant commissioning and trouble shooting and Engineering Students.
This book contains about 51 tables and 144 useful diagram and chart graphics etc. Detail description
of ammonia/CO2 stripping process and new developments. Design Parameters of High pressure
vessel and comparison. Study of corrosion for various equipments and control. How to control
corrosion by changing of equipments material. The life time of the reactor of course strongly
depends on the material used for this protective layer. The design of the vessel, construction
materials used, as well as the layout of the leak detection system, is to be considered before a re-
lining job is undertaken when liner to be changed after 25-30 years of services. There are generally
three main types of urea reactor vessels which are built as follows: solid wall, multi-layer, or multi-
wall. Urea synthesis processes have been carried out at relatively high temperature (160–270 °C) and
high pressure (120–250 bar). This book intended how to increase life of urea reactor liner and energy
saving with low passivation air and high N/C ratio, Ammonia is the noncorrosive and ammonia to
CO2 Ratio is an important parameter for process optimization occurring less losses and less
explosion probability in urea reactor because it affects the amount of produced urea and corrosion to
the material in the reactor. Corrosion or erosion is particularly caused in urea reactors by contact
with solutions of ammonium carbamate at the high temperatures and pressures necessary for the
synthesis of urea. There are numerous metals and alloys capable of withstanding for sufficiently long
periods, the potentially corrosive conditions arising inside a synthesis reactor of urea. In recent years,
considerable progress has been made in research of urea reactor liner and there is an increase in the
production of urea by reducing the liner leakage and fewer breaks down has been observed
throughout the world. Generally we are using urea reactor liner 316L (urea grade), now we can
change 2-RE-69 for large capacity plant and Duplex stainless steel. Detail description of Product
quality and risk assessments and explosiveness checking and remedies.
Prem Baboo
Jan-2021

6. 6
CHAPTER-1
INTRUDUCTION
&
AMMONIA
PLANT

7. 7
INTRODUCTION
Urea is produced by synthesis from liquid ammonia and gaseous carbon dioxide. Ammonia and
carbon dioxide react to form ammonium carbamate, a portion of which dehydrates to form urea and
water. Fertiliser is defined as any material, organic or inorganic, natural or synthetic which supplies
one or more of the chemical elements required for the plant growth. Carbon, hydrogen and oxygen
are the most essential elements which are drawn by plants from nature. Based on nutrient
requirement for plant growth, fertilizer elements are divided in three categories, i.e. Primary,
Secondary and Micro nutrients. Nitrogen, phosphorus and potassium are termed as primary nutrients.
Concentration of primary nutrients in chemical compound is expressed as percentage of total
nitrogen (as N), available phosphate (as P2O5) and soluble potash (as K2O). Calcium, magnesium and
sulphur are termed as secondary nutrients which also play an important role in the growth of specific
plants. There are about seven nutrients essential to plant growth and health that are only needed in
very small quantities. They are known as micronutrients or trace elements. Boron, chlorine, copper,
iron, manganese, molybdenum and zinc are micronutrients. Some important chemical fertilisers are
as under
Nitrogenous fertilisers In case of nitrogenous fertilisers, nitrogen may be in the form of Ammonical,
nitrate (a combination of thereof) or amide. Some of the nitrogenous fertilisers are as under.
1. Urea
2. Urea (Coated)
3. Ammonium nitrate
4. Ammonium Sulphate
5. Ammonium Chloride
6. Calcium Ammonium Nitrate
7. Calcium Nitrate
8. Anhydrous Liquid Ammonia
9. Urea-Ammonium Nitrate Solution
AMMONIA PLANT
Properties of Ammonia
Ammonia is a colorless gas with a characteristically pungent smell. It is lighter than air,
its density being 0.589 times that of air. It is easily liquefied due to the strong hydrogen bonding
between molecules; the liquid boils at −33.3 °C, and freezes to white crystals at −77.7 °C .
Sr. No. Parameters Values
1 Molecular weight 17.03
2 Freezing Point -77.70
C
3 Boiling Point -33.40
C
4 Latent Heat 1370 KJ/Kg
5 Ignition Temperature 6510
C
6 Flame Range,% 15-28
7 Density,00
C, 1 atm 0.77 kg/m3
8 Solubilty of water at 200
C 532 g/L
Table-1
Ammonia reacts with copper ions to produce a blue precipitate, copper (II) hydroxide.
NH3 +H2O=NH4(aq) +OH(aq)
Cu2+
(aq)+ 2OH(aq)=Cu(OH)2(Solid)
(Blue Precipitate)

8. 8
“Copper is not used in ammonia system because if there is a little amount of moisture or water
is present ammonia will react rapidly with it to form ammonium hydroxide which contains
OH-
ions, these ions react with copper to form the copper hydroxide of blue colour.”
Fig-1
Chemical, Physical and Thermal Properties of Ammonia. Phase diagram
Sr. No. Property Value Unit
1 Gibbs free Energy of formation, ΔGf -16.6 KJ/Kg
2 Heat (Enthalpy) of combustion, ΔHc (gas) 382.8 KJ/Kg
3 Heat (Enthalpy) of evaporation, ΔHv,
at boiling point
23.37 KJ/Kg
4 Heat(Enthalpy) of formation, ΔHf (gas) -45.9 KJ/Kg
Table-2
Ammonia is a gas at standard conditions. However, at low temperature and/or high pressures the gas
becomes a liquid. The phase diagram for ammonia shows the phase behavior with changes in
temperature and pressure. The curve between the triple point and the critical point shows the
ammonia boiling point with changes in pressure. As shown in the figure-1
In the diagram-(Fig-1) the triple point temperature, ammonia becomes a solid, this phase will also be
present at very high pressure (> 10 000 bar) and ambient temperature.
At the critical point there is no change of state when pressure is increased or if heat is added.
The triple point of a substance is the temperature and pressure at which the three phases (gas, liquid,
and solid) of that substance coexist in thermodynamic equilibrium. As shown in the figure-2.

9. 9
Fig-2

10. Fig-3
PROCESS DESCRIPTION AMMONIA PLANT
In the plant, ammonia is produced from synthesis gas containing hydrogen and nitrogen in the ratio
of approximately 3:1. Besides these components, the synthesis gas contains inert gases such as argon
and methane to a limited extent. The source of H
natural gas. The source of N2 is the atmospheric air. The source of CO
natural gas feed. Product ammonia and CO
illustrated in the following sketch, figure
Fig-4
The ammonia plants include the following section:
Desulphurization •Reforming •Shift Conversion •CO
•Ammonia Refrigeration •Process condensate stripping a
recovery section •Nitrogen start-up blower circuit •Recycle hydrogen compressor circuit •
condensate system •a MDEA solution storage system
Short Description of the Process
PROCESS DESCRIPTION AMMONIA PLANT
In the plant, ammonia is produced from synthesis gas containing hydrogen and nitrogen in the ratio
3:1. Besides these components, the synthesis gas contains inert gases such as argon
and methane to a limited extent. The source of H2 is demineralised water and the hydrocarbons in the
is the atmospheric air. The source of CO2 is the hydrocarbons in the
natural gas feed. Product ammonia and CO2 is sent to urea plant. The main function of the plant is
strated in the following sketch, figure-4.
the following section:
•Reforming •Shift Conversion •CO2 removal •Methanation •Ammonia Synthesis
•Process condensate stripping and common facilities as •Ammonia
up blower circuit •Recycle hydrogen compressor circuit •
MDEA solution storage system.
Short Description of the Process
10
In the plant, ammonia is produced from synthesis gas containing hydrogen and nitrogen in the ratio
3:1. Besides these components, the synthesis gas contains inert gases such as argon
water and the hydrocarbons in the
is the hydrocarbons in the
is sent to urea plant. The main function of the plant is
removal •Methanation •Ammonia Synthesis
nd common facilities as •Ammonia
up blower circuit •Recycle hydrogen compressor circuit •off spec

11. 11
The process steps necessary for production of ammonia from the above-mentioned raw materials are
as follows: - The hydrocarbon feed is desulphurized to the ppb level in the desulphurization section. -
The desulphurized hydrocarbon feed is reformed with steam and air into raw synthesis gas (process
gas). The gas contains mainly hydrogen, nitrogen, carbon monoxide, carbon dioxide and steam. - In
the gas purification section, the CO is first converted into CO2. Then the CO2 is removed from the
process gas in the CO2 removal section. - The CO and CO2 residues in the gas outlet of the CO2
removal unit are converted into methane by reaction with H2 (methanation) before the synthesis gas
is sent to the ammonia synthesis loop.
The purified synthesis gas is compressed and then routed to the ammonia synthesis loop, where it is
converted into ammonia. In order to limit the accumulation of argon and methane in the loop, a
purge stream is taken. The liquid ammonia product is depressurised during which the dissolved
gases, letdown gas and inert gas, are flashed off.
Desulphurization General Information
The natural gas feedstock coming from battery limit contains minor quantities of sulphur compounds
which have to be removed in order to avoid poisoning of the reforming catalyst in the primary
reformer and the low temperature shift catalyst in the CO converter, particularly the low temperature
shift.converter, is sensitive to deactivation by sulphur and sulphur-bearing compounds. Prior to
hydrogenation, the feed gas is mixed with Hydrogen rich recycle stream which is coming from syn
gas compressor 2nd stage discharge. Then the Feed gas is heated in heaters and in the reformer flue
gas section. Since the gas contains organic sulphur compounds, the desulphurization takes place in
two stages. The organic sulphur compounds are converted to H2S by the hydrogenation catalyst and
the H2S absorption takes place in the sulphur absorption catalyst. After desulphurization, the content
of sulphur is less than 0.1 vol. ppm. A sketch of the desulphurization section is given in Figure 2.
Hydrogenation
The preheated natural gas is fed to the hydrogenator. The vessel contains HTAS Hydrogenation
Catalyst which is a cobalt-molybdenum based catalyst. catalyzes the following reactions:
RSH + H2 → RH + H2S
R1SSR2 + 3H2 → R1H + R2H + 2H2S
R1SR2 + 2H2 → R1H + R2H + H2S
(CH)4S + 4H2 → C4H10 + H2S
COS + H2 → CO + H2S
Where R is hydrocarbon radical.

12. 12
The hydrogenation catalyst must not get into contact with hydrocarbons without the presence of
hydrogen. The result would be poor conversion of the organic sulphur compounds causing an
Fig-5
Increased sulphur slip to the reforming section. The temperature also plays an important role with
regard to catalyst activity; at low temperatures the hydrogenation reactions progress very slowly and
conversion is not optimal while at high temperatures undesirable cracking reactions may occur with
deactivation of catalyst due to carbon lay-down on the catalyst itself. The optimum temperature
range is between 350 and 400°C. In case natural gas containing CO and CO2 is fed to the
Hydrogenator, the following reactions will take place:
CO2 + H2 ⇔ CO + H2O
CO2 + H2S ⇔ COS + H2O
Therefore, the presence of CO, CO2 and H2O influences the sulphur slippage from downstream the
Sulphur absorbers, The catalyst is oxidized at delivery and resumes its activity when sulphided. The
Catalyst can be sulphided during initial start-up with natural gas feedstock at not high temperature
and not high H2 flow to minimize the possibility of the MoO3 being reduced to MoO2 that means
catalyst irreversible deactivation. In the sulphided state the catalyst is pyrophoric and it must be not
exposed to air at temperatures above 70°C.
H2S Absorption

13. 13
The hydrogenated natural gas is fed to the sulphur absorbers. The two sulphur absorbers, located in
series, are identical acts as a guard in case of sulphur breakthrough is taken out of service for catalyst
replacement. Each vessel has one catalyst bed which contains catalyst. This zinc oxide catalyst is in
the form of 4 mm extrudates. The normal operating temperature is approximately 355°C. The zinc
oxide reacts with the hydrogen sulphide and carbonyl sulphide in the following equilibrium
reactions:
ZnO + H2S ⇔ ZnS + H2O
ZnO + COS ⇔ ZnS + CO2
The equilibrium composition for the reaction between the zinc oxide and hydrogen sulphide is
expressed by the following equation:
Kp(T)=
( )
( )
= 2.5 X10-6
at 3800
C.
The catalyst is not reacting with oxygen or hydrogen at any practical temperature. Zinc sulphide is
not pyrophoric and no special care during unloading is required. Steam operations should not be
carried out. The zinc oxide would hydrate and it would then be impossible to regenerate the ZnO
material in the reactor.
Reforming Section
General information
In the reforming section, the desulphurized gas is converted into synthesis gas by catalytic reforming
of the hydrocarbon mixture with steam and the addition of air. The steam reforming process can be
described by the following reactions:
1. CnH2n+2 + 2H2O ⇔ Cn-1H2n + CO2 + 3H2 - heat
2. CH4 + 2H2O ⇔ CO2 + 4H2 - heat (39.4 kcal/mol)
3. CO2 + H2 ⇔ CO + H2O - heat (9.84 kcal/mol)
Reaction (1) describes the mechanism of reforming the higher hydrocarbons, which are reformed in
stages to lower and lower hydrocarbons, finally resulting in methane, which is reformed as shown in
reaction (2). The heat input required for the reverse shift reaction (3) is very small compared to the
heat input required for reaction (1) and (2). The reactions take place in two steps, primary reforming
and secondary reforming as illustrated in Figure 3: Reforming section. Thus, the reforming unit
consists of a primary reformer with a waste heat section and a secondary reformer.
Carbon Formation
During operation, undesirable carbon formation may occur outside and/or inside the catalyst particles
in the primary reformer. Carbon deposits outside the particles will increase the pressure drop over
the catalyst bed, and deposits inside the particles will reduce the activity and mechanical strength of
the catalyst. Thermal cracking is favored by higher temperature and by lower steam/carbon ratio;
generally, if the S/C ratio is higher than 1.4 formed carbon will not damage the catalyst in a not

14. 14
reversible way. The higher S/C ratio, the lower will be the methane leakage that is desirable since
Fig-6
Methane is an inert gas in the synthesis ammonia section; on the other hand, increasing too much the
S/C ratio means very high operation cost. The design steam/carbon ratio is 2.85, sufficiently above
the ratio where carbon formation on an active catalyst is possible and sufficiently high to reduce the
methane leakage. Only during reformer start-up or shut down the S/C ratio will be kept higher;
during start up, load is gradually increased and the S/C ratio is decreased from an initial value of 6-8
towards normal operating value; during shut down, load is reduced and S/C ratio is gradually
increased towards even above a value of 10.
Reaction heat
In the primary reformer the heat necessary for the reaction is supplied in the form of indirect heat
from firing; in the secondary reformer the heat is direct heat from combustion of the gas mixture
with air. The introduction of air at the same time provides the nitrogen required for ammonia
synthesis. Since the H2/N2 ratio in the purified synthesis gas should be maintained at a value close to
3.0, the amount of air is fixed. Overall, adjusting the duty of the primary reformer controls the
reforming reaction and thus the methane leakage from the secondary reformer.
Operating Pressure
Since methane is an inert gas in the ammonia synthesis process, it is desirable to reduce the methane
content of the synthesis gas to the lowest possible level in order to keep the level of inert gases low.
The methane content in the synthesis gas is governed by the equilibrium of reforming reaction (2) at
the outlet temperature and by the catalyst activity. According to reaction (2), lower methane content

15. 15
can be obtained by increasing the temperature, lowering the pressure, or adding more steam. On the
other hand, a relatively high reforming pressure results in considerable savings in the power
necessary for the subsequent synthesis gas compression. An operating pressure of approximately 40
kg/cm2
g at the inlet of the primary reformer provides a reasonable economic compromise.
Primary Reformer
The first step of the steam reforming process takes place in the Primary reformer. The desulfurized
hydrocarbon and steam mixture is preheated to 520°C in the Feed gas/steam preheater before
entering the Primary reformer. The process gas passes downwards through vertical tubes containing
the nickelbased catalyst. The required heat is transferred by radiation from a number of wall burners
to the catalyst tubes. In order to ensure complete combustion of the fuel gas, the burners are operated
with an excess air ratio of about 10%, which corresponds to about 2 vol % (dry) of oxygen in the flue
gas. The hydrocarbons in the feed to the Primary reformer are converted into hydrogen and carbon
oxides, and the gas from the Primary reformer contains approximately 11.6 mole% (dry) of methane
with a Primary reformer outlet temperature of about 821°C. The Primary reformer has a total of 244-
300 reformer tubes installed in two chambers. The chambers are placed side by side in a duplex row
arrangement and function as one unit. The two furnace chambers have a common flue gas duct and
flue gas heat recovery section.
Each furnace chamber contains a number of vertically mounted, high alloy Cr-Ni steel tubes filled
with reforming catalyst. The tubes are mounted in a single row along the centre line of the chamber.
The process gas is flowing downwards with the gas being distributed to the top of the tubes from a
header through "hairpins" at a temperature of about 520°C. The gas leaves the tubes through bottom
"hairpins" and enters a refractory lined collector through high alloy hot collectors. The tubes are
heated by a number of burners located in each side wall of the furnace chambers and arranged in
horizontal rows at several elevations to provide easy control of the uniform temperature profile along
the length of the catalyst tubes. In this manner, the optimal utilization of the expensive high alloy
tubes is obtained. Flue gas flow is upwards with outlet near the top of the radiant chamber. The flue
gas outlet system comprises a common flue gas collector mounted between the two radiation
chambers. The flue gas temperature is about 1085°C. The upper part of the reformer tubes is loaded
with catalyst ,while the middle part of the reformer tubes is loaded with catalyst and the bottom part
with other catalyst. The reduced catalyst is stable in air up to 80°C. If it is exposed to air at higher
temperature it will oxidize.
Using Improved Materials for Reformer Tubes
The reformer contains about 250-450 tubes made off chromium nickel steel, 10-13 meters long, with
an inner diameter of 75-140 mm and a wall thickness of 11-18mm . Under the severe conditions
taking place in the reformer the tubes start to creep and rupture. Determining factors for such
deformation are the internal pressure and the tube-wall temperature. Figure-7 shows the stress to
rupture of different materials. To avoid tube rupture, lower pressures are employed, leading to higher
power use for compression in ammonia synthesis. The reaction in the reformer is endothermic and
proceeds with an increase in volume. To compensate for the lower conversion rate due to the
increased pressure the reaction temperature needs to increase. However, tube materials limit the
allowable increase in temperature.
The standard material for many years was the HK 40. The HP modified (1.5% Nb) material, due to
its improved temperature properties (40 bar reforming pressure at a tube wall temperature of 900o
C),
has been used in many tube replacements and tubes in new plants . The use of micro alloys
containing Ti and Zr are another improvement (see Figure 8). Their use permits the reduction of
tube-wall thickness while maintaining the same tube lifetime (100,000 hours). By installing tubes
with smaller wall thickness and/or wider diameter the capacity of the front end of an ammonia plant
can be increased.

16. The use of micro alloyed tubes with minimum wall thickness can increase the catalyst volume,
increase firing and lower the pressures drop
new improvements in materials it is possible to increase the life time of the reformer tubes (by up to
20 000 hours) and have higher tube
Fig-7
tubes with minimum wall thickness can increase the catalyst volume,
the pressures drop. According to Fertilizer Association of India, with the
new improvements in materials it is possible to increase the life time of the reformer tubes (by up to
20 000 hours) and have higher tube-wall temperatures (up to 906 o
C)
16
tubes with minimum wall thickness can increase the catalyst volume,
Fertilizer Association of India, with the
new improvements in materials it is possible to increase the life time of the reformer tubes (by up to

17. Fig-8
Flue gas heat recovery section
The flue gas passes via the flue gas duct to the flue gas heat recovery section, in which the sensible
heat of the flue gas is utilized for the following duties:
mixture going to primary reformer,
Final superheating of high pressure steam,
desulphurization, Superheating of hi
reformer, Preheating of natural gas,
temperature is reduced to approx. 189
Secondary reformer
For detail up to 218 pages 144 useful
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The flue gas passes via the flue gas duct to the flue gas heat recovery section, in which the sensible
heat of the flue gas is utilized for the following duties: - Preheating of the hydrocarbon/steam
to primary reformer, Final preheating of the process air for the Secondary reformer,
gh pressure steam, Final preheating of natural gas going to the
Superheating of high pressure steam, Preheating of process air for the S
ng of natural gas, Boiler feed water preheating, At the outlet the flue gas
temperature is reduced to approx. 189°C. A Flue gas blower takes the flue gas to the Flue gas stack.
144 useful drawing/graphics
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17
The flue gas passes via the flue gas duct to the flue gas heat recovery section, in which the sensible
Preheating of the hydrocarbon/steam
econdary reformer,
Final preheating of natural gas going to the
Preheating of process air for the Secondary
At the outlet the flue gas
takes the flue gas to the Flue gas stack.