A REPORT OF 6-WEEKS INDUSTRIAL TRAINING

at
NATIONAL FERTILIZERS LIMITED, NANGAL UNIT

SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENT FOR THE AWARD

OF DEGREE OF

BACHELOR OF ENGINEERING
Chemical
SEMESTER- 06

JULY-AUGUST, 2021

SUBMITTED BY
VIKRANT SINGH
CH18184

Dr. S.S. BHATNAGAR UNIVERSITY INSTITUTE OF CHEMICAL ENGINEERING &

TECHNOLOGY
PANJAB UNIVERSITY, SECTOR-14, CHANDIGARH
 CHE 404: INDUSTRIAL INTERNSHIP TRAINING

DECLARATION

I affirm that the Industrial Internship Training report titled “INDUSTRIAL INTERNSHIP
TRAINING AT NATIONAL FERTILIZERS LIMITED, NANGAL UNIT” being submitted in

partial fulfilment of the requirements for the award of the Degree of BACHELOR OF

ENGINEERING IN CHEMICAL is the original work carried out by me. It has not formed the

part of any other project work submitted for award of any degree or diploma, either in this or
any other Institution.

Vikrant Singh

CH18184

i
ii
 ACKNOWLEDGEMENT
The internship opportunity I had with National Fertilizers Limited, Nangal Unit was a great
chance for learning and professional development. Therefore, I consider myself as a very lucky
individual as I was provided with an opportunity to be a part of it. I am also grateful for having
a chance to meet so many wonderful people and professionals who led me though this
internship period.

Bearing in mind previous I am using this opportunity to express my deepest gratitude and
special thanks to the MD of National Fertilizers Limited who allows me to carry out my project
at their esteemed organization.

I express my deepest thanks to Mr. Handa Sir, Shift Engineer for taking part in useful decision
& giving necessary advices and guidance and arranged all facilities to make life easier. I choose
this moment to acknowledge his contribution gratefully.

It is my radiant sentiment to place on record my best regards, deepest sense of gratitude to Mr.
Vinod Sir, Mr. Sanjay Sir, Mr. Kanchan Sir, and others for their careful and precious guidance
which were extremely valuable for my study both theoretically and practically.

Finally, but most importantly, I want to thank my family and friends. Without their patience,
support and encouragement I would not have been able to go through the sequence of stages
required to complete this internship.

I perceive this opportunity as a big milestone in my career development. I will strive to use
gained skills and knowledge in the best possible way, and I will continue to work on their
improvement, in order to attain desired career objectives. Hope to continue cooperation with all
of you in the future.

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 ABSTRACT
I carried out my 6 weeks internship at National Fertilizers Limited, Nangal Unit. I have done
my internship in the production department where I overviewed the production of Nitric Acid,
Urea and Ammonia. The production of Nitric acid was done according to Ostwald Process
where ammonia and oxygen firstly react to form NO in the presence of Pt catalyst and then NO
oxidizes to NO2 and then form Nitric acid after reacting with water. The production of
ammonia was done by the Haber’s process where nitrogen and hydrogen in ratio of 1:3 react
with each other in the presence of iron catalyst to give the product as ammonia. When this
ammonia reacts with the carbon dioxide at an optimum temperature and pressure, we get urea.
Alongside all this I saw various equipment and their working which was required for the
production of all these compounds. Equipment’s like Heat Exchanger, Prilling Tower,
Reformer, Vaporizer, etc. their working in real life was an amazing experience. Along with
technical knowledge it also improves my interpersonal skills and help me in knowing how to
do a work professionally.

As a result of what we have done we get the 54% nitric acid, 99.85 wt.% pure Ammonia and
99.7% pure urea. Alongside these three major products, byproduct like sodium nitrite and
sodium nitrate also produced in the NOx abatement plant to balance the economical aspect of
the plant.

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 LISTS OF FIGURES
Figure Page No.

Figure 2.1.1 – Structure of Nitric Acid 3

Figure 2.1.2 – Process Flow Diagram of Nitric Acid Plant 7

Figure 2.1.3 – Deaerator 8

Figure 2.2.1 – Structure of Ammonia 10

Figure 2.2.2 – Process Flow Diagram of Ammonia Plant 14

Figure 2.2.3 – Horton Sphere 15

Figure 2.3.1 – Structure of Urea 16

Figure 2.3.2 – Process Flow Diagram of Urea Plant 19

Figure 2.3.3 - Prilling tower:(a) schematic diagram; (b) side view of the prilling tower 20

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 LIST OF TABLES
Table Page No.

Table 2.1.1 - Properties of Nitric Acid 3

Table 2.2.1 - Properties of Ammonia 10

Table 2.2.2 – Compositions of Lean and Rich Gas 10

Table 2.2.3 - Different Steam Header Conditions 11

Table 2.3.1 – Properties of Urea 16

Table 2.3.2 - Operating conditions of the two synthesis sections 17

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 Table of Contents
Topic Page No.
Candidate Declaration ⅰ

Industry Certificate ⅱ

Acknowledgement ⅲ

Abstract ⅳ
Lists of Figures ⅴ

Lists of Tables ⅵ

CHAPTER 1: INTRODUCTION TO THE ORGANISATION 1-2

CHAPTER 2: TRAINING WORK UNDERGONE 3-20
2.1: Nitric Acid Plant 3-9

2.2: Ammonia Plant 10-15

3.3: Urea Plant 16-20

CHAPTER 3: CONCLUSION 21
CHAPTER 4: REFERENCES 22
APPENDIX 23
 INTRODUCTION
National Fertilizers Limited, a Schedule ‘A’ & a Mini Ratna (Category-I) Company, having its
registered office at New Delhi was incorporated on 23rd August 1974. Its Corporate Office is at
NOIDA (U.P). It has an authorized capital of Rs. 1000 crore and a paid-up capital of Rs. 490.58
crore out of which Government of India’s share is 74.71 % and 25.29 % is held by financial
institutions & others.

The company has a Vision i.e. “to be a leading Indian company in fertilizers and beyond with
commitment to all stakeholders” and a Mission “to be a dynamic organization committed to
serve the farming community and other customers to their satisfaction through timely supply of
fertilizers and other products & services; continually striving to achieve the highest standards in
quality, safety, ethics, professionalism, energy conservation with a concern for ecology and
maximizing returns to stakeholders”.
NFL has five gas-based Ammonia-Urea plants viz. Nangal & Bathinda plants in Punjab,
Panipat plant in Haryana and two plants at Vijaipur at District Guna, in Madhya Pradesh. The
Panipat, Bathinda & Nangal plants were revamped for feed stock conversion from Fuel Oil to
Natural Gas, an eco-friendly fuel during 2012-13 / 2013-14. Vijaipur plants of the company
were also revamped for energy savings & capacity enhancement during 2012-13, thus
increasing its total annual capacity from 20.66 LMT from 17.29 LMT, an increase of 20%. The
company currently has a total annual installed capacity of 35.68 LMT (Re-assessed capacity of
32.31 LMT) & is the 2 nd largest producer of Urea in the country with a share of about 16% of
total Urea production in the country.
Company has a Bio-Fertilizers Plant at Vijaipur with a capacity of 600 tons of solid & liquid
Bio-Fertilizers to produce four strains of Bio-Fertilizers viz. PSB, ZSB, Rhizobium and
Azotobacter are produced.
NFL is engaged in manufacturing and marketing of Neem Coated Urea, four strains of Bio-
Fertilizers (solid & liquid), Bentonite Sulphur and other allied Industrial products like
Ammonia, Nitric Acid, Ammonium Nitrate, Sodium Nitrite and Sodium Nitrate. The brand
name of the company is popularly known in the market as ‘KISAN’.
The company has also started production of certified seeds under its Seeds Multiplication
Program for sale under its own brand name as Kisan Beej.
NFL has taken various initiatives in adopting best practices for Environment Management,
Energy Conservation and Social Upliftment leading to sustainable development.
Use of cleaner and greener fuel i.e., Natural Gas as feed and fuel in NFL Plants.
One of the major milestones achieved by NFL in this direction is switchover of all its fuel oil
feedstock plants at Nangal, Panipat and Bathinda, to Natural Gas (NG), the cleaner and energy
efficient fuel. With this initiative, Company’s 100% Urea production is now based on gas as
feedstock. In addition to above, specific energy consumption has also come down by more than
20 %.

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NFL has also switched over the support fuel in the coal fired boilers at Panipat, Bathinda
Nangal to NG from fuel oil. This has eliminated use of fuel oil besides improving reliability
and reducing carbon footprints.
100 KW Solar Power Plant at Corporate Office has been commissioned in August’ 2014 is
running satisfactorily. Also, 90 KW Solar Power Plant at Bathinda Unit has been installed in
December 2014.
To increase the subsoil water level, Manufacturing Units of NFL have installed Rainwater
Harvesting.
All conventional lights at Units and Corporate Office have been replaced with LED lights.
Development of Township at Vijaipur as Mini Smart City:
Under new development model as per directives of the Hon’ble PM during CPSEs Conclave
2018, NFL has committed to convert its Vijaipur Township into a mini–Smart City by March
2022.
In order to build mini smart city at Vijaipur Unit, the company is currently undertaking various
activities such as Zero Water discharge, Modern Sewage System, Solid Waste Management
System, Rain Water Harvesting System, CCTVs, High Speed Wi-Fi, LED Lighting etc.
Company is constantly working towards inclusive growth in society through CSR. Through its
CSR programmes, Company is supporting sectors like health, education, skill development,
environment and empowerment of underprivileged sections of the society. One of the major
CSR projects of FY 2020-21 that the company undertook was for Training of Apprentices at a
budget of Rs. 152.78 Lakh over and above the minimum mandate of 2.5% of total manpower.
The project was envisaged to help youth in various placements linked skill training and
capacity building through practical industrial experience.
Total manpower of the company as on 31-03-2021 was 3220.
I had undergone 6 weeks summer internship in Nangal Unit of the Plant where the main
objective of my training was to overview the production department of the plant. I have been
appointed in three different production plant within the Nangal Unit namely Nitric Acid Plant,
Urea Plant and Ammonia Plant where I have learned, observe and gained the basic of how the
production of these things happen. I got opportunity to see various equipment in real whose
working I used to study in books and it was an amazing experience. Seeing the working of
104 m tall prilling tower to the 830℃ hot reformers always motivate me to learn in-depth the
working of such equipment’s.
Apart from technical knowledge the internship also teaches me professional way of doing a
work and give the experience to work me on the field which help me to grow my interpersonal
skills as well as it gave me the experience of how a plant engineer works which definitely help
me in choosing my future.

2
 TRAINING WORK UNDERGONE
NITRIC ACID PLANT
Nitric Acid is a strong acid with chemical formula HNO3. It is also known as the spirit of niter
and aqua fortis. In its pure form, it is colourless but as it gets older it turns into a yellow cast
due to the decomposition of Nitric acid to oxides of nitrogen and water.

Properties of Nitric Acid

Table 2.1.1 – Properties of Nitric Acid

Molecular formula HNO3

Molecular Weight/ Molar Mass 63.01 g/mol
Density 1.51 g/cm3 at 25℃
Boiling Point 83℃
Melting Point -42°C
Appearance Colourless, yellow or red fuming liquid

Structure of Nitric Acid

Figure 2.1.1 - https://study.com/learn/lesson/nitric-acid-chemical-formula-struture.html

Introduction of Plant Design

Plant is designed to produce 560 Te./Day of Nitric Acid in two independent but equal streams
of 280 Te./Day of HNO3 in the form of 54% acid. The plant is divided into two main sections:

1. Combustion Section 2. Condensation Section

Combustion Section comprises of

I. Air scrubbing tower (common for the streams)

II. Ammonia Vaporizer
III. Ammonia Preheater
IV. Turbo-compressor unit consisting of a steam turbine along with a condenser, an air
blower and a recovery turbine.
V. Air-ammonia mixing nozzle
VI. Filter chambers
VII. Burner, superheater and waste heat boiler assembly
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VIII. Tail gas heater
IX. Boiler feed water system consisting of feed water tank, deaerator and dosing tank, etc.
Condensation Section comprises of

I. Condensators
II. Oxidation towers each with one brine cooled and four water cooled acid coolers
III. Production tower with two water cooled coolers for the upper segment and three for the
lower segment.
IV. Six absorption towers
V. Drop separator
VI. De nitration towers
VII. Condensate cooler and tank
VIII. Brine equalizing tank
IX. Leakage acid tank
X. Acid storage tanks

Process Description
The ammonia is oxidized by oxygen present in air to produce NO, which is further oxidized to
NO2 and absorbed in H2O to form 54% nitric acid.

Gaseous System
Atmospheric air is sucked by turbo compressor through an air scrubbing tower & a drop
separator. The scrubbing of the air is done by spraying water in the counter current to the air.
Then the air enters the cyclone type drop separator where entrained droplets get separated. The
compressor compresses the air from about 0.95 ata to 3.55 ata, whereby the temperature rises to
218℃.

The liquid ammonia from the ammonia plant is vaporized in the ammonia vaporizer by means
of brine solution. The ammonia vapor from the vaporizer which is at about -2℃ is heated to
50℃ by means of secondary air in the ammonia preheater. This preheated NH3 vapor at 4 ata
is mixed with the compressed air in the mixing nozzle at about 3.5 ata to form a mixture with
10% of ammonia by volume.

Then this mixed gas passes through ceramic filters candles fitted in filter chambers. The filtered
mixed gas from each filter passes through a burner. In each burner there are 5 catalyst gauzes
(95% Pt & 5% Rh), arranged one over other and a recovery gauze underneath them in each
burner. The oxidation of ammonia takes place in presence of platinum catalyst at 830℃
according to the following reaction:

4NH3 + 5O2 → 4NO + 6H2O + 217 Kcal (2.1.1)

Some possible side reactions depending upon various factors are:

4NH3 + 3O2 → 2N2 + 6H2O (2.1.2)

2NH3 + 2O2 → N 2O + 3H2O (2.1.3)

4N3 + 7O2 → 4NO2 + 6H2O (2.1.4)

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 2NH3 → N2 + 3H2 (2.1.5)

4NH3 + 6NO → 5N2 + 6H2O (2.1.6)

2NO → N2 + O2 (2.1.7)

By careful control in maintaining the specified optimum condition’s reaction will proceed as
per equation number 1.1, then pass over a superheater coil and through a waste heat boiler
which are situated below the burners. With the help of this steam is generated at 17 ata and
300℃, which is utilized for driving the steam turbine, which in turn drives the turbo
compressor. The gases leaving the four waste heat boilers at about 250℃ combines into one
stream and flow through the tail gas heater where some more heat is recovered by heating the
tail gases, in doing so nitrous gases get cooled to 150℃ and from here they pass on to the
condensators in the condensation section.

The gases are cooled down to 50℃ by means of cooling water into two vertical shell and tube
type condensator connected in series, whereby about 90% of the water vapor resulting from the
oxidation in the burners is condensed and a weak nitric acid of about 30% concentration on the
average of the two is produced. Weak acid collected in the first condensator goes to Absorption
Tower No.-2 and that collected in the second condensator goes to the Absorption Tower-1.

The nitrous gases after the second condensator get mixed with the exit air from the De nitration
tower and enter the two oxidation towers in parallel. By the time the gases reach the oxidation
towers 60% of NO is already converted to NO 2 . The balance of the NO still carried in the gases
is oxidized in the oxidation towers according to the equation:
2NO + O2 → 2NO2 + 26.9 Kcal (2.1.8)
While cooling down from 50℃ to 30℃ here, the rest of water vapor contained in the gases gets
condensed and form 60% acid, absorbing NO 2 according to the following equation:

2NO2 + H 2O ↔ 2HNO3 + NO + 32.5 Kcal (2.1.9)

As both the above reactions are exothermic, the heats of oxidation and absorption are removed
by circulating the acid through four water cooled coolers and one brine cooled coolers and
spraying it on the top of the oxidation tower which is packed with Raschig Rings for further
absorption. The gases from both the oxidation tower join together and enters the lower segment
of production tower from there they pass into the upper segment of the same and subsequently
through all the six Absorption Towers in series. All these are packed with Raschig Rings, in
each tower the gases travel upward from bottom to top, whereas the acid which is recirculated
through the respective coolers and sprayed at the top of the tower flows down through Raschig
rings. Due to this intermingling between liquid and gaseous phases, NO 2 reacts with H2O and
NO according to 1.9 and then this NO is re oxidized to NO 2 as per equation (1.8). The heat is
eliminated by coolers and 30℃ is maintained throughout.

The gases out of the sixth absorption tower go to the drop separator where the entrained mist is
separated. The water collected at the bottom of the drop separator flows back to the Absorption
Tower-6. The tail gases leaving the drop separator which are at a pressure of 2.95 ata and
temperature of 30℃ then pass to the tail gas heater in the combustion section, where they are

5
heated to about 160℃. From there the tail gases flow through the expansion turbine thereby
supplying a part of the driving force for the turbo compressor. Here the tail gas pressure drops
down from 2.84 ata to 1.02 ata and temperature falls down to 70℃ then the gases pass through
the air mixing nozzle where they get diluted and are blown to the atmosphere.

Acid System

Demineralized water is taken in the condensate storage tank from where it is pumped to the
Absorption Tower-6. While the liquid in each tank is recirculated a small portion of it flows
from that tower to previous tower by gravity as their level are arranged in a gradual descending
order. Because of this the acid concentration enriched in different absorption tower. The flow
of the upper segment of the production tower which obviously cannot takes place by gravity is
maintained by tapping the acid recirculation line of Absorption Tower-1 and taking a portion of
the acid flow through a branch pipe line to spray at the top of the production tower upper.

The 60% acid formed in the oxidation towers flows from the first oxidation tower to second
oxidation tower and from there to the production tower lower. The overall strength of the acid
here comes to 54%. From the acid recirculation line of the lower segment of the production
tower, a part equivalent to the production is sent to the de nitration tower where the dissolved
nitrous gases are removed by secondary air and thus the aid is bleached. As already stated, the
secondary air along with the NO stripped from the acid is introduced in the main gas stream
before the oxidation towers. The bleached acid flows to the acid storage tank.

The leakage acid from various places is collected in the leakage acid tank and pumped to
Absorption Tower -2 & 3.

Brine System
The brine, which is a 20% solution of ammonia in water, enters the ammonia vaporizer at 12℃,
supplies heat for vaporization of ammonia, and thereby gets cooled to 5℃. This cooled brine is
then circulated through the three-brine cooled acid coolers in the condensation section. While
cooling the acid, it again gets heated up to 12℃ and returns to the ammonia vaporizer.

Cooling Water System

1000 ppm water lines distributes as follows:

a. To the ‘Air Scrubbing Tower’ and from there to the drain.

b. To the coolers and condensators which branches into 4 lines:
i. To the coolers of production tower (upper and lower segment)
ii. To the coolers of Absorption Tower-2 and from there to the coolers of the Absorption
Tower-1.
iii. To the coolers of Absorption Tower-3 and from there to the coolers of oxidation tower-
1.
iv. To the coolers of Absorption Tower 5 and from there to the cooler of Absorption
Tower-4 and then to the coolers of oxidation number-2.
The outlet lines of ⅰ & ⅱ join together and go to inlet of condensator no-2 and flows out of the
condensator into the drain. Similarly, the outlet of ⅲ & ⅳ join together and go to the inlet of
condensator no-1 and flows out of the condensator into the drain.
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c. To the condensate coolers and from there to the drain.

Water Steam System

The exhaust from the steam turbine is condensed in a surface condenser maintained at a
vacuum of 700-720 mmHg. The cooing is done by water. The condensate is extracted and sent
to the feed water deaerator where the dissolved gases are expelled by heating with steam which
is taken as a bleeder steam from the turbine at a pressure of 2 ata the deaerated water is then
flows down to the feed water tank from where it is pumped to the waste heat boilers.

A demineralized water supply line also joins the deaerator for the makeup of feed water. The
demineralized water though free from any acid content still has a dissolving tendency and even
after deaeration slight traces of CO2 and O2 continue to remain in the water. For preventing
from both these effects we dissolve chemicals like Trisodium Phosphate, in the water before it
is fed to the boilers.

Process Flow Diagram of Nitric Acid Plant

Figure 2.1.2 – Process Flow Diagram of Nitric Acid Plant

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Deaerator
A deaerator is a device that removes oxygen and other dissolved gases from liquids and
pumpable compounds.

The deaerator system works according to the principle of two laws. They are

 Henry’s Law
 Inverse solubility Law

Henry’s Law

In conformity to Henry, the pressure available inside the equipment is directly proportional to
the solubility of gases. Whenever the pressure present inside is decreased such that the solubility
of gases also gets reduced. Hence, the pressure is reduced by the introduction of steam inside the
deaerator.

Inverse Solubility Law

In conformity to Inverse solubility Law, the temperature inside the equipment is inversely
proportional to the solubility of gases. Whenever the temperature is increased such that the
number of dissolved gases inside will be reduced. Thus, the temperature is increased by the
introduction of steam inside the deaerator.

Therefore, this is the basic principle of how does a deaerator system work by removing the
dissolved gases from the feedwater before supplying it to the boiler. They are removed either by
decreasing pressure or by increasing temperature but both will be practiced by the introduction
of steam.

Figure 2.1.3 - Deaerator

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Uses of Nitric Acid
Nitric acid is used in the:
 Production of ammonium nitrate for fertilizers.
 Making plastics.
 Manufacturing of dyes.
 It is also used for making explosives such as nitro-glycerine and TNT.
 When it is combined with hydrochloric acid, an element called aqua regia is formed.
This is a reagent that is capable of dissolving gold and platinum.
 Used in a colorimetric test to distinguish heroin and morphine.

9
 AMMONIA PLANT
A pungent colourless gaseous alkaline compound of nitrogen and hydrogen NH 3 that is very
soluble in water.

Properties of Ammonia
Table 2.2.1 – Properties of Ammonia

Molecular formula NH3

Molecular Weight/ Molar Mass 17.031g/mol
Density 0.73g/cm3 at 25℃
Boiling Point -33.34℃
Melting Point -77.73°C
Appearance Colourless gas

Structure of Ammonia

Figure 2.2.1 - https://www.informationpalace.com/uses-of-ammonia/

Introduction of Ammonia Plant

The plant is based on the KBR Purifier TM technology. The plant is set up to produce 950
MTPD of ammonia. The feed and fuel to the ammonia plant is natural gas with the following
compositions and conditions.
Table 2.2.2 – Compositions of Lean and Rich Gas

Composition, dry mol% Lean Gas Rich Gas

CH4 97.97 84.50
C2H6 1.79 9.00
C3H8 0.14 3.00
C4H10 0.00 2.00
C5H12 0.00 0.25
CO2 0.00 0.00
N2 0.10 1.25
Total 100.00 100.00
LHV (Kcal/kg) 11908 11515
Total Sulfur (as H2S), ppmv ≤10 ≤10
Pressure at Plant Battery Limit 40.5 40.5
(kg/cm2)
Temperature, ℃ 30.0 30.0

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The main process steps are as follows:

 Feed Gas Compression, Preheating and Desulfurization

 Primary Reforming
 Process Air Compression
 Secondary Reforming
 Shift Conversion
 Carbon Dioxide Removal
 Methanation
 Drying
 Cryogenic Purification
 Syngas Compression
 Ammonia Synthesis
 Purge Gas Ammonia Recovery
 Process Condensate Stripping
Table 2.2.3 - Different Steam Header Conditions

Header Pressure Kg/cm2 (g) Temperature ℃

High Pressure (HP) 90 500
Medium Pressure (MP) 63 462
32 kg/cm2(g) Header 32 386
10 kg/cm2(g) Header 10 332
2.5 kg/cm2(g) Header 2.5 146

Process Description
Feed Gas Compression, Preheating and Desulfurization
Natural gas for feed and fuel is supplied at the plant battery limit at 57.3 kg/cm2 and 30℃. Part
of the natural gas is sent to the primary reformer furnace as fuel. The natural gas feed is mixed
with a small amount of syngas recycled from the synthesis loop which provides the required
hydrogen for the downstream hydrotreater. The mixture of natural gas and hydrogen is heated
to 371℃, first using condensing LP steam in the LP Steam/Feed Gas Preheater (190-C), and
then in the Feed Gas Coil located in the convection section of the Primary Reformer (101-B).
The hot gas then enters a two steps desulfurization system. In the first step, the hot gas passes
through a Hydrotreater (108-DA), which contains cobalt/molybdenum (CoMo) catalyst. The
catalyst ensures hydrogenation of organic sulfur compounds, if present in the feed gas, such as
mercaptans (RSH), carbonyl sulfide (COS), to hydrogen sulfide.

COS + H2 → CO + H2 S (2.2.1)

RSH + H2 → RH + H2 S (2.2.2)

In the second step, hydrogen sulfide in the feed gas is removed in two Desulfurizers,
(108DB/DC). Each desulfurizer contains a bed of ZnO. Hydrogen sulfide reacts with the zinc
oxide and is retained as a ZnS, thereby producing an effluent stream containing < 0.1 ppmv of
sulfur.

11
 H2S + ZnO → ZnS + H2 O (2.2.3)

Primary Reforming
Desulfurized feed gas is mixed with process steam to give a steam to organic carbon molar
ration of 2.7:1. The mixture is preheated to about 495℃ in the convection section of the
primary reformer (101-B). Steam reforming reactions take place over the nickel based
reforming catalyst in the radiant tubes to form carbon dioxide, carbon monoxide and hydrogen.

CH4 + H2O → CO + 3H2 (2.2.4)

The water gas shift reaction converts carbon monoxide to carbon dioxide and additional
hydrogen:

CO + H2O → CO2 + H2 (2.2.5)

The 101-B effluent at 48.0 kg/cm2 and 721℃ contains about 29.9 mol % (dry basis) of
unreacted methane. The effluent is sent to the Secondary Reformer via Primary Reformer
Effluent Transfer Line (107-D). Heat for the endothermic steam reforming reactions in 101-B is
supplied by the combustion of fuel gas in burners located at the top of the furnace.

Process Air Compression

Process air is drawn in through an air filter (101-L) which removes any dust particles. Process
air is compressed to a pressure of 50.8 kg/cm2. Compressed process air is then preheated to
about 510℃ in the air preheat coil located in the convection section of 101-B, and sent to the
secondary reformer. Steam is continuously added to prevent the backflow of hot gas from the
Secondary Reformer.

Secondary Reforming
Spontaneous combustion occurs at the top of the reformer, heat released during this combustion
reaction supplies the heat for the steam reforming reactions in the lower section converting
methane to more CO2 and CH4. The unreacted methane content leaving 103-D is about 1.8%.
The heat in the 103-D effluent is recovered by generating HP steam (104 kg/cm2) in the
secondary reformer waste heat boiler (101-C).

Shift Conversion

The cooled secondary reformer effluent is sent to the High Temperature Shift (HTS) Converter
(104-D1) reactor. Here the gas flows over a bed of HTS catalyst and carbon monoxide reacts
with steam to form carbon dioxide and hydrogen via the water gas shift reactions.

CO + H2O → CO2 + H2 (2.2.6)

About 72% of the CO is shifted to CO 2 in the HTS converter. The CO content in the HTS
effluent is about 2.9% (dry basis). The gas leaving the HTS converter is cooled by generating
HP steam in the HTS effluent/Steam Generator (103-C), and by heating HP boiler feed water in
HTS effluent/BFW Preheater (186-C).

The gas then passes through a LTS Guard Bed (104-D3) which is packed with LTS catalyst.
The effluent is then sent to the LTS converter (104-D2) at about 208℃ and almost all CO is
12
converted to CO2 in the LTS. Then LTS effluent is cooled against BFW in the LTS Effluent /
BFW Preheater (131-C) and by raising LP steam in the Steam Generator (131-C1). The gas is
further sent to the CO2 stripper reboiler and then further cooled in the LTS Effluent/DMW
Exchanger to about 70℃. The process condensate is separated out in the Raw Gas Separator.

Carbon Dioxide Removal

The process gas enters the bottom of the CO2 absorber at about 70℃. It is contacted first with
the semi lean aMDEA solution and then with the lean aMDEA solution. The gas then sent to
the CO2 overhead knockout drum to remove any trace of the solution. The overhead gas
contains less than 500 ppmv (dry basis) of CO2 and is sent to the methanation section.

Methanation

The vapor from the knockout drum is preheated to the methanation section reaction
temperature, using methanator feed/Effluent Exchanger and using condensing HP steam in the
methanator start up heater. The preheated gas then flows to the methanator where carbon
oxides in the gas are converted to the methane by reaction with hydrogen over a nickel catalyst.

CO2 + 4H2 ↔ CH4 + 2H2O (2.2.7)

CO + 3H2 ↔ CH4 + H2O (2.2.8)

Residual carbon dioxide leaving the methanator are less than 5ppmv (dry basis).

Drying
In preparation for drying, the methanator is cooled by heat exchanger with methanator feed
114℃ to 79℃ and against cooling water in the Methanator Effluent Cooler to 38℃. Then it is
chilled with ammonia refrigerant in the Methanator Effluent Chiller to about 4℃. The chilled
gas is then sent to Methanator Effluent Separator which process condensate is separated out.
The overhead from separator is then sent to the Molecular Sieve Driers which are packed with
zeolite based desiccant and operate cyclically.

Cryogenic Purification
Dried raw synthesis gas is then sent to the cryogenic purification section. The gas is cooled in
the top section of the Purifier and then it expands in the Purifier Expander. The expander
effluent is further cooled and partial condensed in the bottom section of the Purifier and enters
the Purifier Rectifier at -17℃. Liquid will evaporate from the bottom section of the rectifier
and provide cooling for the condenser and reflux for the column. The rectifier bottom contains
the excess nitrogen, most of the methane, and some of the inlet argon. The make-up syngas
from the top is reheated and sent to the existing Synthesis Gas Compressor at 1.8℃.

Ammonia Synthesis
Make up and recycle gas mixture from the synthesis gas compressor is preheated by heat
exchanger with converter effluent in the Hot Exchanger. It then flows to the ammonia
converter. Ammonia concentration in the feed to the converter is about 2.76%. Ammonia is
synthesized in two adiabatic beds provided with an intercooler and an aftercooler. The
converter effluent 17.70 mol% ammonia at about 453℃. It is cooled by generating HP steam in
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the Synloop Waste Heat boiler and by heating boiler feed water in the Converter Effluent BFW
Preheater. The converter effluent is further cooled to 38℃ by cooling water in Converter
Effluent Cooler. The gas is finally chilled to about -4℃ against ammonia refrigeration in the
Ammonia Chiller. Liquid ammonia is separated out from the converter effluent in the Separator
while the vapor is recycled to the last stage of Synthesis Gas Compressor while a small fraction
of vapor is purged to maintain the inert composition to 3.20%. Liquid ammonia along with
recovered ammonia is sent to the Horton Sphere as product ammonia. The expected ammonia
purity is about 99.85 wt.% ammonia. The Horton sphere operates at about 4.2kg/cm2.

Process Flow Diagram of Ammonia Plant

Figure 2.2.2 – Process Flow Diagram of Ammonia Plant

Horton Sphere
The Horton sphere is a spherical pressure vessel, which is used for storage of compressed gases
such as propane, liquefied petroleum gas or butane in a liquid gas stage.

The main advantage of the spherical construction is that the stress concentration in a spherical
shape will be minimal while storing pressurized gases. The stress resistance will be uniform.

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The cost - the wall thickness of a spherical shell will be about half the wall thickness needed for
a cylindrical shell for holding in the same pressure. So, in a spherical container you use a
thinner shell which means lesser cost and weight.

Area: Volume ratio -the area that a sphere occupies will be lesser compared to a cylindrical
container of the same volume.

Figure 2.2.3 – Horton Sphere

Uses of Ammonia
 Around 90 per cent of the ammonia which is produced tends to get used up in fertilizers
to help in sustaining the production of food for the population of the world.
 Ammonia is used as an ingredient or on its own in several household products used for
cleaning many household surfaces such as sinks, toilets, tubs, tiles, kitchen countertops,
etc.
 Ammonia is also used in the production of nitric acid, synthetic fibres (e.g., Nylon),
explosives, pharmaceuticals (sulphonamides).
 As a refrigerant and in air-conditioning equipment.

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 UREA PLANT
Urea, also known as carbamide, is an organic compound with chemical formula CO(NH2)2.
This amide has two –NH2 groups joined by a carbonyl (C=O) functional group.

Properties of urea
Figure 2.3.1 – Properties of Urea

Molecular formula NH2CONH2

Molecular Weight/ Molar Mass 60.06 g/mol
Density 1.32 g/cm3 at 25℃
Appearance White solid
Melting Point 133 °C

Structure of Urea

Figure 2.3.1-https://www.acs.org/content/acs/en/molecule-of-the-week/archive/u/urea.html

Process Description
The urea plant has been divided into three main sections for operation reasons:

Section 1: Urea Synthesis Section

This section comprises the synthesis loop, existing and new items, and the three decomposition
and recovery stages working at 70, 12 and 3 ata pressure respectively.

Section 2: Vacuum Concentration Section

This section located at the top of the prilling tower includes two vacuum concentration stages at
0.35 and 0.04 ata respectively in order to concentrate the dilute urea solution (about 73%)
coming from the synthesis section to about 99.7% urea melt followed by the prilling performed
in the new natural draft prilling tower located near the old tower.

Section 3: Ammonia Recovery Section

This section consists of the rectification column operating at about 2 ata followed by absorption
column for the NH3 recovery from the process condensates coming from the vacuum
concentration.

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Section 1: Urea Synthesis Section
The CO 2 coming from the ammonia plant is fed to the urea plant by means of two separate
headers at two different pressures: 11 ata for the existing line and 1.2 ata for the new line.

Then it is compressed at the synthesis pressure of 220 ata by means of the two compressors
CA-1, existing, and K-1/N, new.

The liquid ammonia coming from ammonia plant at a pressure of 20-30 ata is compressed at
the synthesis operating pressure by means of the two of the three ammonia pumps, PA-1,
PA-1r, existing, and PA-1/N new, running in parallel.

The quantity of CO2 correspondent to the desired capacity of the new synthesis section and in
consideration of the expected conversion (72%) is fed to the carbamate condenser E-1/N under
flow control, whereas the residual part of total CO2 is fed to the existing reactor R-1/N.
The same thing is valid for the fresh ammonia to be fed to the two reactors.

Carbamate solution coming from decomposition stage is fed to the existing reactor only with
the help of carbamate pumps.
Table 2.3.2 Operating conditions of the two synthesis sections

New Section Old Section

Capacity (TPD) 600 1050
Pressure (ata) 220 220
Temperature (℃) 195 195
Molar ratio: NH3/CO2 3.1 2.9
Molar ratio: H2O/CO2 0 0.7
Conversion (%) 72 57

The desired fresh CO2 and NH3 are mixed in the mixer X-1/N, are fed to the carbamate
condenser E-1/N where part of the ammonium carbamate is formed and part of the reaction
heat is taken out generating steam at about 7.5 ata. The hot carbamate is from E-1 flows to the
new reactor R-2/N where the residence time is enough to convert 72% of the carbamate to urea.

2NH3 (g) + CO2 (g) ↔ NH2COONH4 (s) ∆H= -37.4 Kcal/gm mol (2.3.1)
(Ammonium Carbamate)

NH 2COONH4 (s) ↔ NH2 CONH2 (s) + H2O (l) ∆H= + 6.3 Kcal/gm mol (2.3.2)
(Urea)

CO2 (g) + 2NH3 (g) ↔ NH2CONH2 (s) + H2 O (l) ∆H = -31.32 kcal/gm mol (2.3.3)

The urea solution produced in the new reactor joins the one coming from the existing reactor
upstream. The resulting urea solution containing about 36% of urea, unconverted carbamate,
excess NH 3 and water is depressurized to about 70 ata in the letdown valve PV-1/N, and heated
to about 190℃ in the first distiller HE-1 by means of the saturated HP steam. The vapors
released by means of heating are separated from the urea solution concentrated up to about
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55% in the existing first stage separator, SD-1 and absorbed in the first partial condenser HE-2a
with major part of the second recycle carbamate solution. The thermo-siphon type boiler in the
first stage partial condenser removes the condensation heat where 3.5 ata steam is generated.
About 65% of the total condensation heat to be removed in the first decomposition state is
removed in partial condenser HE-2a whereas the balance unabsorbed gases are sent to the first
stage total condenser HE-2b where heat of condensation removed by circulating condensate.
The resulting carbamate solution is recycled to existing reactor using pump PA-2. The outlet
gases from the total condenser HE-2b containing mainly NH3 with small amount of CO2 and
non-condensable inert gases are first sent to the washing column C-1 and then further into inert
washing column C-6 and then inert gases are vented to the atmosphere. The urea carbamate
solution from the first stage separator SD-1 containing about 55% is again let down to about
11kg/cm2 and heated to 155℃ in the second stage distiller HE-3 with 7.5 ata saturated steam
which we have produced in carbamate condenser E-1/N. The gases released from the 2 nd stage
distiller HE-3 are then separated in the 2 nd stage separator SD-2 and then condensed in 2 nd stage
condenser HE-4 with the 3rd recycle carbamate solution and uncondensed gases are vented to
atmosphere after washing in inert washing column C-6. The 66% urea solution from the
second separator is finally let down to about 2.5kg/cm2 and heated in the 3 rd stage distiller
HE-5/N to 130℃ by means of 3.5 ata saturated steam. The decomposed gases are then
separated in the 3 rd stage separator SD-3. The decomposed vapors from SD-3 are sent to the 3rd
stage partial condenser HE-6b for partial condensation by cooling water. The condensed
carbamate solution and the unabsorbed gases are fed into 3 rd stage washing column C-3 where
the gases are absorbed and inert gases are vented into atmosphere.

Section 2: Urea Vacuum Concentration

The urea solution at about 73% urea, is pumped to the first vacuum stage distiller, HE-7 A/B,
divided in two parts, where the urea solution is heated to 130℃ by means of 3.5 and 7.5 ata
steam respectively. The gases are separated from the urea solution at about 92% in the 1st
vacuum separator SD-4, which is maintained at 0.35 ata with the help of ejector EJ-6. The
vapor containing mainly steam with little NH 3 and CO2 are fed to the first vacuum condenser
HE-8 where they are condensed and incondensable gases are ejected by ejector EJ-6 through
vent gas washing column C-7. The urea solution is pumped to the 2 nd vacuum stage distiller
HE-9/N where it is heated to 140℃ by means of 7.5 ata steam. The released steam is separated
from melt urea in the 2nd vacuum stage separator SD-5, whose vacuum is maintained by five
stage ejector system which also suck the released vapors from the 2 nd vacuum stage separator
and condensed in condensers E-2/N, HE-19 & HE-20 A/B/C. Condensate are collected into
condensate tank SR-7. The 99.7% melt urea from the bottom of the separator SD-5 is fed by
pump PC-3 to the top of the new prilling tower Z-1. A three-way valve is provided which feed
the prilling bucket Z-2 located at the top of the prilling tower which also divert the melt urea to
storage tank in case of any problem. Periodical flushing with steam is done to ensure choke free
return line. The prilling buckets are driven by electric motor. Speed is increased to reduce the
size and vice versa. Melt urea comes out of the holes of rotating prilling bucket uniformly
because of the centrifugal force imparted by rotation of prilling bucket. Ambient air enters the
bottom of the tower through louvers and rises upwards which cool the urea drop and solidify
into prills. The heat of solidification and cooling is dissipated to the ambient air which makes
18
air lighter and rises upwards. The solidify prills fall on the floor scraped by rotating double arm
rotary scraper Z-4 through a slit into the prilling tower belt conveyer Z-5A/N & Z-5B/N which
then go for weighing and storage using belt conveyor.

Section 3: Ammonia Recovery Section

The process condensate obtained from the 2 nd vacuum stage condenser are collected into tank
SR-7 from where the greater part is sent to the inerts washing column C-6. Similarly,
condensate from 1st vacuum condenser HE-8 together with the condensate coming from the
column C-7 and the ammonia solution coming from C-6 are collected in SR-6. This ammonia
enriched condensate is fed to the rectification column C-4/N by means of the pump and
preheater. In this rectification column ammonia is stripped off from the process condensate.
Then this off gases which mainly contain NH3 & CO2 is fed to partial condenser E-3/N where
they are partially condensed by raw water. Then the mixture of liquid carbamate solution and
the uncondensed gases flows into the recovered vapor condensation column C-5 where the
vapor are absorbed with weak carbamate solution. A part of recirculation solution after
pressurizes sent to the washing column C-3. In order to reduce the water content in the
recovered ammonia solution we can send it to the hydrolysis section by means of pump. The
bottom of the column C-4 containing small quantities of NH3 , CO2 and urea is sent to the
hydrolysis section where they are recovered under the form of carbamate solution. The
recovered carbamate solution from hydrolysis unit is recycled to the urea plant to the 3 rd stage
washing column C-3.

Process Flow Diagram of Urea Plant

Figure 2.3.2 – Process Flow Diagram of Urea Plant

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Prilling Tower
Prilling is a process in which a melted substance is sprayed against upward-flowing air in
a tower to form solid particles. The urea particles are produced by prilling, in which a urea melt
is cooled by contact with a gas, for example cold air, and solidified to form particles.

Figure 2.3.3- Prilling tower: (a) schematic diagram; (b) photo, side view of the prilling tower.

Source- https://www.mdpi.com/2227-9717/5/3/37/htm

Salient feature of Prilling tower used for production

Prilling Tower Height = 104 m
Prills Free fall Height = 80 m
Prilling tower ID = 22 m

Uses of Urea
 About 56 % of Urea manufactured is used in solid fertilizer.
 About 31 % of Urea manufactured is used in liquid fertilizer.
 Urea-formaldehyde resins have large use as a plywood adhesive.
 Melamine-formaldehyde resins are used as dinnerware & for making extra hard
surfaces.

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 CONCLUSION
The product that we get from three different plant i.e., Urea Plant, Nitric Acid Plant and
Ammonia Plant is the result that we get.

In the Nitric Acid Plant, the final acid that we obtained is 54% concentrated although as per our
need and requirements we can increase or decrease the concentration of the acid by adding or
removing the water that we gave in absorption column in the counter current direction. Along
with nitric acid two side product is also obtained by adding a NOx abatement plant and the
compounds are Sodium Nitrate and Sodium Nitrite whose production help us in the economical
aspect as well.

In the Ammonia plant, the final ammonia product which we store in the Horton sphere is the
product whose purity is about 99.85 wt.%. along with this we also get CO 2 in this plant as a
byproduct which also help us to produce urea and that would be good as per the economical
aspect of the plant.

In the Urea plant, the final product melt urea which we sent to the prilling tower and then to the
urea bagging plant after prills formation, purity of urea is about 99.7%.

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REFERENCES
 https://study.com/learn/lesson/nitric-acid-chemical-formula-struture.html
 https://www.watelectrical.com/deaerator-working-types-applications/
 https://byjus.com/chemistry/uses-of-nitric-acid/
 https://www.informationpalace.com/uses-of-ammonia/
 https://www.quora.com/Why-is-LPG-stored-in-spherical-tanks
 https://www.acs.org/content/acs/en/molecule-of-the-week/archive/u/urea.html
 https://www.mdpi.com/2227-9717/5/3/37/htm
 Process Description Manual by NFL.

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APPENDIX
1. Introduction
2. Training Work Undergone
2.1 Nitric Acid Plant
2.1.1 Properties of Nitric Acid

2.1.2 Structure of Nitric Acid

2.1.3 Introduction of Plant Design

2.1.4 Process Description

2.1.5 Process Floe Diagram of Nitric Acid Plant

2.1.6 Deaerator

2.1.7 Uses of Nitric Acid

2.2 Ammonia Plant

2.2.1 Properties of Ammonia
2.2.2 Structure of Ammonia

2.2.3 Introduction of Ammonia Plant

2.2.4 Process Description

2.2.5 Process Flow Diagram of Ammonia Plant

2.2.6 Horton Sphere

2.2.7 Uses of Ammonia

2.3 Urea Plant

2.3.1 Properties of Urea

2.3.2 Structure of Urea

2.3.3 Process Description

2.3.4 Process Flow Diagram of Urea

2.3.5 Prilling Tower

2.3.6 Uses of Urea

3. Conclusion
4. References

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