1. .Developments in Ammonia Production Technology
Ammonia is an intermediate product in the manufacture of nitrogenous fertilizers. It is
also used for direct application to the soil and in aqua condition with solutions of other
nitrogenous fertilisers like ammonium nitrate and/or urea. Besides these, ammonia finds
application in the production of nitric acid, soda ash, cleaning agents, leather tanning,
petroleum refining, pulp & paper industry, textiles, refrigeration, rubber & synthetic resin
industries, explosives and food & beverage industries.
(I) Raw materials used
Ammonia is produced by the reaction between nitrogen (N2) and hydrogen (H2)
N2 + 3 H2 ------> 2 NH3
Source of Nitrogen is atmospheric air and following hydrocarbons are generally used as
the source of hydrogen:
a) Natural gas
b) Naphtha
c) Heavy Oil
Other sources of hydrogen which were used earlier for manufacture of Ammonia, are:
a) Semi-water gas made by gasification of coke/ coal with steam.
b) Hydrogen produced by electrolysis of water.
c) By product Hydrogen from chlorine production.
(II) Methods for manufacture of Ammonia
Ammonia is compound of nitrogen and hydrogen in the mole ratio of 1:3. The
manufacturing process, depending upon the raw materials used, involves four successive
steps:
• Gasification
• Conversion of CO
• Gas purification
• Synthesis
Various processes for the production of synthesis gas for the production of ammonia are
given below:
1) Electrolysis process
Purified water is used as feed stock in electrolysis process. Potassium hydroxide is
added to increase conductivity, but it does not participate in the reaction. Chemical
components of water, i.e. hydrogen and oxygen, are obtained in pure state through
electrolysis.

2. H2 O -----> H2 + ½ O2
Hydrogen thus obtained is mixed with required nitrogen from the air separation plant to
get synthesis mixture.
Electrolysis process is very energy intensive process. Typical power consumption is 4.3
KWH/m3 of hydrogen, which corresponds to about 8600 KWH/MT of ammonia.
Additional energy is required for the air separation plant to produce nitrogen. Energy is
also required for compression of Hydrogen & nitrogen and recirculation of loop gases.
The total energy requirement is 10,200 KWH/MT of ammonia (8.8 Gcal/MT). The plants
based on this process are located where low cost hydro-electricity is available.
By product of electrolysis process are oxygen and heavy water that have use in other
industries.
2) Partial oxidation of hydrocarbons
In the partial oxidation process the hydrocarbon (usually naphtha or heavy oil) and
oxygen are burnt with flame in the top of reactor. Steam is added to the reactor mainly to
moderate the temperature. In the flame, a part of hydrocarbon is burnt completely, the
feedstock is cracked to shorter chain hydrocarbons and cracked products are reformed.
The normal flame temperature is 1300-15000C, which is high enough to give residual
methane content below 0.3% at the pressure of 30 kg/ cm2g.
The exit gas from reactor passes through waste heat boiler, which is designed to avoid
clogging by the carbon formed in burner. The carbon is carried on with the gas through a
trap & scrubber and may be separated as pellets. The amount of carbon produced is 1-
3% of weight of hydrogen.
Final purification of synthesis gas is done through cryogenic scrubbing where carbon
oxides are removed and methane & argon contents are reduced to a low level so that
little or no purging is required.
Partial oxidation of hydrocarbons is a simpler and more rugged process than steam
reforming. The advantages of the process are:
a) Prior sulfur removal is not required
b) No sensitive catalyst is involved
c) All the reforming can be accomplished in one step
d) Flexible to any feed stock; almost any liquid or gaseous hydrocarbon can be used from
NG to heavy residential fuel oil and the shift from one to another can be made quickly.
e) Lower total hydrocarbon for process and fuel
f) Purer synthesis because of the cold wash purification
The drawbacks that increase the process cost are:
a) Oxygen or oxygen enriched gas is required unless there is a nitrogen removal step.
b) The product gas has much higher CO : H2 ratio than that obtained by steam reforming.
c) A “Cold” plant is required for air separation, purification or both.
3) Adiabatic prereforming
The adiabatic pre reforming in case of vaporised naphtha feed is done to decompose the

3. higher hydrocarbons into lower hydrocarbons for example CH4, and other components
like H2, CO and CO2.
The vaporized naphtha is mixed with steam and preheated to about 490oC. The gas is
passed through the pre reformer containing Nickel catalyst. The typical composition of
the pre-reforming catalyst is Ni-25%, Al2O3-11%, MgO-balance.
In the pre reformer the endothermic reforming reactions are followed by the exothermic
methanation and shift reactions. The overall process is normally exothermic.
The gas from adiabatic pre reformer is sent to primary reformer and secondary reformer
for further reforming.
The adiabatic pre reformer reduces the heat load on the primary reformer thus the life of
reformer tubes becomes longer. Pre reformer also acts as an efficient sulfur guard for the
primary reformer catalyst.
4) Coal Gasification Process
The coal gasification process can be classified according to the method of gasification:
a) Fixed bed (Lurgi Process)
b) Fluidised bed (Winkler Process)
c) Entrained bed (Koppers-Totzek (KT)Process).
a) Fixed bed coal gasification process (Lurgi Process)
Lump Coal (5 – 30 mm) is charged at the top of gasifier and it descends counter currently
to the gas stream. As it descends, it is first dried & preheated, then carbonised and finally
gasified by the oxygen & steam entering at the bottom. The coal ash is discharged from
the bottom through a gate or as a slag. Because the counter current method results in
good heat exchange and very high thermal efficiency, this method requires less heat and
hence less oxygen than other methods.
This method requires least oxygen with respect to other gasification processes. The
requirement of oxygen is one half as much as entrained coal gasification. Also less purity
oxygen of 90% can be used. The gas leaves the top at 4500C and is cooled & washed to
remove tar, liquid hydrocarbons, dust etc. The washed gas contains CO, H2, CO2, CH4
and other hydrocarbons. It is treated by a series of steps including steam reforming, CO
shift conversions, CO2 and H2S removal, liquid nitrogen wash, steam reforming of
methane that is separated by nitrogen wash, nitrogen addition and compression to
produce ammonia synthesis gas.
b) Fluidised bed coal gasification process (Winkler Process)
In fluidised bed gasification 15 mm size lignite coal is introduced into fluidised bed
through feed screws near the bottom. Steam and oxygen are injected near the bottom of
the fluidised bed. The fluidised bed is essentially isothermal (10000C), consequently
there is no tar or other liquid hydrocarbons and gas contains mainly H2 and CO with less
than 1% CH4. The hot gas is cooled by waste heat boilers and scrubbed to remove ash
and then purified in the same manner as Lurgi process.
The Winkler gasifier is a low - pressure gasifier (1-3 atm). It can work with almost any

4. grade of coal or lignite. Disadvantage of the process is high compression cost.
c) Entrained bed coal gasification process (Koppers-Totzek (KT) Process)
Most of the coal based ammonia plants use KT process nowadays. In the KT process,
coal is dried and finely ground to about 75% through 200 mesh. The powdered coal is
picked up by stream of oxygen and blown in to gasification chamber through two burners
facing each other. Steam enters through annular openings around the burners. The
gasification is complete in one tenth of second in the temperature range of 1000 –
12000C. Part of ash is fused and removed from bottom of gasifier. The exit gas typically
Contains 56% CO, 31% H2, 11% CO2 and less than 0.1% CH4. After cooling in waste
heat boilers, the ash is removed by wet scrubbing and electrostatic precipitation. The rest
of ammonia synthesis gas preparation is similar to partial oxidation.
Disadvantages of the process are the need for fine grinding of coal, operation at low
pressure (1-3 atm) and higher oxygen consumption than other gasification process.
5) Steam reforming
Steam reforming is usually carried out in two stages using primary and secondary
reformers. Desulphurised naphtha or natural gas is subjected to steam (thermal)
reforming at about 28-30 kg/cm2g) pressure and around 8000C temperature in the
primary reformer consisting of a large number of centrifugally cast, high temperature,
vertical alloy steel tubes packed with nickel catalyst. The overall reaction is endothermic
and requires a large amount of heat. The gas leaving the primary reformer containing 5-
15% methane is sent to an autothermal secondary reformer. The required amount of
nitrogen is fed to the secondary reformer through addition of air to give the desired 3:1
hydrogen to nitrogen ratio in the synthesis gas. Herein methane is converted to H2, CO &
CO2 over a single bed of catalyst.
The carbon monoxide content of the gas is converted to carbon dioxide and hydrogen by
passing over catalyst in presence of steam, thus generating hydrogen by the water-gas
shift reaction and is carried out in two stages. The first stage, High-Temperature (HT)
shift conversion, is carried over iron-chromium catalyst at 350oC-430oC,while the second
stage, Low Temperature (LT) shift conversion, is carried over copper based catalyst at
200o-280oC. In the HT shift conversion, level of CO is reduced from 12% to around 3%
and in the L.T. shift conversion the CO level is reduced to around 0.2%.
The process gas after shift conversion, containing over 18% CO2 and less than 1%CO
undergoes further purification in CO2 removal section.
The purified syn-gas mixture from containing N2 and H2 in the mole ratio of 1:3 is reacted
at elevated temperature of the order of 450o-500oC and 150-250 kg/cm2g pressure over
an activated iron catalyst promoted with potassium and alumina. The gas is cooled first
by heat exchanger and finally by refrigeration to condense ammonia as liquid.
Conversion of synthesis gas to NH3 Is about 20-30% per pass. The gas remaining after
ammonia condensation is recycled to the convertor. The inert gases built up in the
synthesis gas are purged.
(III) New developments in Ammonia technology
With the focus on energy reduction several processes incorporating novel features to
achieve energy savings have been developed. Brief outlines of newly developed energy
efficient processes are given below:

5. 1) ICI – Leading Concept Ammonia (LCA) Process
This process combines the use of excess air (upto 25%) in the secondary reformer with a
very active synthesis catalyst. In LCA process the heat generated in the secondary
reformer is utilised in primary reformer by direct heat exchange in a tubular Gas Heated
Reformer (GHR). The CO shift is performed in a single stage shift reactor at 2500C using
special copper basic catalyst. CO2, inerts and excess nitrogen are removed from raw
synthesis gas by pressure swing absorption. Ammonia synthesis takes place at low
pressure of below 100 kg/cm2g using ICI’s highly active cobalt promoted catalyst. Net
energy consumption of around 7.2 Gcal/ MT ammonia has been demonstrated for 450
MT per day plant.
2) Haldor Topsoe A/S process
The company’s low energy ammonia process uses the conventional sequence of process
steps which are optimised by the introduction of improved catalysts, new equipment
design and extensive process optimisation studies. A pre-reformer containing nickel
catalyst has been also provided upstream of primary reformer for converting all the higher
hydrocarbons, so that only methane, carbon monoxide, carbon dioxide, hydrogen and
steam are present in the product gas. Firing in primary reformer is reduced by 15% due
to pre-reformer. Highly active shift catalyst ensures the lowest carbon monoxide at the
exit of converters and thus highest utilisation of feedstock. New temperature resistant iron
free catalyst makes it possible to operate at low steam to carbon ratio at high
temperature shift converter. The company has also developed Heat Exchange Reforming
Process (HERA). Low energy CO2 removal processes, such as selexol, MDEA or low
heat potassium carbonate, are used. Topsoe has developed new converters especially
for high conversion loops. The S-250 loop features an S-200 two bed radial flow
converter followed by a boiler and a S-50 single bed radial flow converter in series. A new
three bed radial flow S-300 converter has also been developed which is cheaper than S-
250 configuration and conversion is about the same.
3) Kellogg Brown and Roots Advanced Ammonia Process (KAAP)
KAAP uses a high-pressure heat exchange based steam reforming process integrated
with a low-pressure advanced ammonia synthesis process. Raw synthesis gas is
produced by steam reforming of hydrocarbon in a heat exchange based system under
pressure, based on Kellogg Brown and Root Reforming Exchange System (KRES).
KRES also reduces energy consumption and capital cost besides reduced emission and
enhanced reliability.
After sulfur removal, the autothermal reformer and reforming exchanger which operate in
parallel, convert 100% feed into raw synthesis gas in the presence of steam using nickel
catalyst. In autothermal reformer, enriched air supplies nitrogen. The heat of combustion
of partially reformed gas supplies energy to remaining hydrocarbon feed. The exit gas of
autothermal reformer is fed on the shell side of the KRES and thus heat of combustion is
supplied to the reforming reaction taking place inside the tubes. KRES exit gas is cooled
in waste heat boiler where high pressure steam is generated. After cooling, the gas is
sent to the CO shift converters (high temperature and low temperature). CO2 is removed
from the process gas using hot potassium carbonate solution, methyl diethanol amine
(MDEA) etc.
After CO2 removal, methanation and gas drying processes are carried out. The gas is
then compressed and mixed with recycle stream of synthesis loop where gas mixture is

6. sent to converter designed by KAAP. KAAP uses a high activity graphite supported
ruthenium catalyst which is claimed to have an activity 20 times greater than traditional
iron catalyst. Thus a very high conversion at low pressure is achieved.
The main features of this technology are
• Single case compression
• Four bed, intercooled, radial flow, hotwall design converter contained in one shell.
• Combined drive synthesis and refrigeration compressor
• Combined drive air compressor and electrical generator
• Low pressure synthesis-loop
• High activity synthesis catalyst
4) Krupp Uhde GmbH ammonia Process
The Krupp Uhde Gmbh process uses conventional steam reforming for synthesis gas
generation (front end) and a medium-pressure ammonia synthesis loop. The primary
reforming is carried out at pressure 40 bar and temperature range of 800-8500C. The
steam reformer is top fired and tubes are made of centrifugal high alloy steel which
enhances reliability. Process air is added in secondary reformer through nozzles installed
in the wall of vessel. This provides proper mixing of the air and reformer gas. Subsequent
high pressure steam generation & superheating, guarantee maximum heat usage to
achieve energy efficiency. Carbon monoxide is converted to carbon dioxide in HT and LT
shift converters. The MDEA or Benfield system is used for carbon dioxide removal. The
ammonia synthesis loop uses two ammonia converters with three catalyst beds with
waste heat boiler located downstream of each reactor. The converters have small grain
iron catalyst. The radial flow concept minimizes pressure drop and allows maximum
ammonia conversion.
5) The Linde Ammonia Concept (LAC) ammonia process
The LAC process consists essentially of a modern hydrogen plant, a standard nitrogen
unit and a high efficiency ammonia synthesis loop. Secondary reformer, one shift
conversion and methanation steps have been eliminated in this process. The primary
reformer is top fired and operates at an exit temperature of about 8500C. The CO shift
conversion is carried out at 2500C in a single stage in the tube cooled isothermal shift
converter and gas is sent to pressure swing absorption (PSA) unit wherein the process
gas is purified to 99.99 mole % hydrogen. A low temperature air separation in cold box is
used to produce pure nitrogen. BASF’s MDEA process is have been eliminated in this
process used for CO2 removal. The ammonia synthesis loop is based on Casale axial-
radial three-bed converter with internal heat exchanger giving a high conversion. The
energy consumption (feed + fuel) is 7 Gcal/ MT of ammonia.

7. sent to converter designed by KAAP. KAAP uses a high activity graphite supported
ruthenium catalyst which is claimed to have an activity 20 times greater than traditional
iron catalyst. Thus a very high conversion at low pressure is achieved.
The main features of this technology are
• Single case compression
• Four bed, intercooled, radial flow, hotwall design converter contained in one shell.
• Combined drive synthesis and refrigeration compressor
• Combined drive air compressor and electrical generator
• Low pressure synthesis-loop
• High activity synthesis catalyst
4) Krupp Uhde GmbH ammonia Process
The Krupp Uhde Gmbh process uses conventional steam reforming for synthesis gas
generation (front end) and a medium-pressure ammonia synthesis loop. The primary
reforming is carried out at pressure 40 bar and temperature range of 800-8500C. The
steam reformer is top fired and tubes are made of centrifugal high alloy steel which
enhances reliability. Process air is added in secondary reformer through nozzles installed
in the wall of vessel. This provides proper mixing of the air and reformer gas. Subsequent
high pressure steam generation & superheating, guarantee maximum heat usage to
achieve energy efficiency. Carbon monoxide is converted to carbon dioxide in HT and LT
shift converters. The MDEA or Benfield system is used for carbon dioxide removal. The
ammonia synthesis loop uses two ammonia converters with three catalyst beds with
waste heat boiler located downstream of each reactor. The converters have small grain
iron catalyst. The radial flow concept minimizes pressure drop and allows maximum
ammonia conversion.
5) The Linde Ammonia Concept (LAC) ammonia process
The LAC process consists essentially of a modern hydrogen plant, a standard nitrogen
unit and a high efficiency ammonia synthesis loop. Secondary reformer, one shift
conversion and methanation steps have been eliminated in this process. The primary
reformer is top fired and operates at an exit temperature of about 8500C. The CO shift
conversion is carried out at 2500C in a single stage in the tube cooled isothermal shift
converter and gas is sent to pressure swing absorption (PSA) unit wherein the process
gas is purified to 99.99 mole % hydrogen. A low temperature air separation in cold box is
used to produce pure nitrogen. BASF’s MDEA process is have been eliminated in this
process used for CO2 removal. The ammonia synthesis loop is based on Casale axial-
radial three-bed converter with internal heat exchanger giving a high conversion. The
energy consumption (feed + fuel) is 7 Gcal/ MT of ammonia.