1. Indian J. Fert., Vol. 4 (12), pp. 17-20 (4 pages)
Recent Efforts in Energy Conservation in
Ammonia and Urea Plants
Ammonia and urea plants have improved their energy efficiency over the
years. Improvement in energy efficiency is a result of concerted efforts of the
S. NAND
industry by implementing various energy saving schemes and adopting efficient
and
technologies for the new plants. The declining trend in weighted average
energy consumption of ammonia and urea plants over the years is the MANISH GOSWAMI
testimony to these efforts. The weighted average energy consumption of all The Fertiliser Association of India
FAI, House, 10 Shaheed Jit Singh Marg
ammonia and urea plants in 2007-08 was reduced by about 30% from the level
New Delhi-110067
of 1987-88. The article reviews the development in ammonia and urea industry tech@faidelhi.org
and the energy conservation efforts so far. The recent energy conservation
efforts of the industry are covered in more detail.
1.0 INTRODUCTION development of fertiliser industry in India. Table 1 – Capacity build-up of
Commercial production took off in 1951 ammonia plants (for selective years)
with first large scale ammonia plant using
I NDIAN AMMONIA AND UREA INDUSTRY
has been in existence for more than half
a century. Initial period of development
coke oven gas as raw material. It was only
after a decade that another ammonia plant
Year
1987-88
Ammonia capacity(MMT)
8.6
emphasized on indigenisation since came up in 1961 at Nangal using 1990-91 10.0
foreign exchange was a scare commodity electrolysis of water as source of 1993-94 10.1
and also there was emphasis on self- hydrogen. Major nitrogenous fertiliser 1996-97 11.3
reliance. The next phase of development products initially were ammonium 1998-99 12.7
witnessed the efforts for improving sulphate and calcium ammonium nitrate. 1999-00 12.0
reliability and operating factors. Spiraling It was only in 1959 that first urea plant of 2000-01 13.7
energy costs in the decade of 1970’s 70 tonnes per day (tpd) based on once 2002-03 13.4
shifted the attention to improvement in through process was commissioned at 2005-06 13.2
operating efficiency in the energy Sindri. 2006-07 13.2
intensive industry. Energy is a major cost 2007-08 13.2
item in the cost of production of ammonia In the beginning, capacity of both the
and urea and hence the efforts for energy ammonia and urea plants was less than In the initial phase of development of the
conservation intensified in 1980’s and 500 tpd. These plants used turbo fertiliser industry world wide, energy
continued to the present time. FAI has compressors for high pressure efficiency was not a focus area in design
been monitoring the energy efficiency of reactions. Capacity leap frogged with of plants. This was due to the fact that
ammonia and urea plants since mid- the advent of centrifugal compressors. energy in various forms viz. natural gas,
1980’s. Status papers were published at A 600 tpd ammonia and matching urea naphtha, electricity, etc. was very
regular intervals reviewing the energy capacity was the norm for several inexpensive. However, then came the oil
conservation efforts of the industry and projects in India. Centrifugal shock of the year 1973 when energy prices
results obtained. Two of these reviews compressors not only enabled large trebled in short time. Designers of the plant
published were in 2003 (1) and 2006 (2). capacity in single stream, but also paid attention to the energy efficiency as
This paper traces the developments in used waste heat of the plant in form of a parameter in addition to the capital cost
ammonia and urea industry in brief from steam as motive force. This made a of the plant.
the old times and reviews the major significant improvement in the energy
efforts for energy conservation impacting efficiency of ammonia production. A few modern energy efficient ammonia
the energy intensity of the industry. The Subsequently developments in plants were commissioned in 1984-85 with
most recent efforts of the industry in this technology, catalysts and equipments specific energy consumption figures close
area are covered in more detail. allowed the capacity to increase to 900 to 7.0 GCal/MT of ammonia. These plants
and 1350 tpd. Industry is now operating of about 1000 tpd each included one at
2.0 DEVELOPMENT OF a large number of ammonia plants with Court right, Ontario in Canada, Sluiskil in
AMMONIA INDUSTRY capacity of more than 1500 tpd and urea Netherlands and at Ludwigshafen in
plants of almost 3000 tpd. The build of Germany. Large scale ammonia plants of
HISTORY OF DEVELOPMENT OF AMMONIA ammonia capacity in recent times is 1350 tpd using gas as feedstock also came
industry in the country runs parallel to the shown in Table 1. up in India around the same time. However,
INDIAN JOURNAL OF FERTILISERS December 2008 17

2. energy consumption of these plants was equipments offered opportunity to all continued even in 1990’s in various units,
higher than the plants mentioned above. existing plants old and new to improve there was renewed emphasis on recovery
This was due to the fact that Indian energy efficiency. Therefore, revamp/ of additional waste heat from the off-gases
project owners wanted plants with proven retrofit/replacement measures were of reformer furnace. The temperature of
technology and equipment. This was after implemented as an ongoing exercise. off-gases was brought down to as low as
the experience of poor performance of 150-160ºC from more than 200ºC earlier in
plants commissioned in 1970’s with 4.1 Energy Conservation Efforts in the relatively new plants. Along with other
emphasis on experimentation in Ammonia Plants heat integration steps in the ammonia
technology and indigenization of the plant, these steps reduced energy
equipment. Local environmental 4.1.1 Phase I (1980’s) consumption by 0.1-0.2 GCal/MT of
conditions (hot and humid) and ammonia. There was also revamp of CO2
configuration of plants also increases the Production of ammonia is the most removal system by way of change to better
energy consumption by 2-3%. technologically complex and energy solvent, better packing in absorption and
intensive process. Ammonia production desorption towers for higher mass transfer
3.0 DEVELOPMENT OF takes about 80% of total energy required efficiency. For example, in one of the units,
UREA INDUSTRY for production of urea and other energy consumption was reduced from
fertilisers. Hence, there has always been 36,000 KCal/Mol CO2 to 26,000 Kcal/Mol
DEVELOPMENT OF UREA INDUSTRY RUNS sharp focus on the energy conservation CO2 with change of solvent from ammine
parallel to build up of ammonia in the efforts in ammonia plants. The first phase to MDEA.
country. Urea being the main product for of energy conservation measures in 1980’s
supply of nitrogen, urea plants were included installation of Purge Gas The next generation efforts in energy
installed along with all ammonia plants Recovery Unit (PGRU) for recovery of conservation included a number of
with a few exceptions. First large scale (500 hydrogen from the purge gas. All these significant measures. The highlight of
tpd) urea plant based on total recycle units were based on cryogenic separation these efforts were change of internals of
process was commissioned in 1966 at of hydrogen which was recycled back to synthesis converter in old plants form
Neyveli. It was part of ammonia-urea the synthesis loop. Till then, the purge gas axial flow to radial-axial or radial flow
complex using gasification of lignite as was burnt as fuel in the reformer. This which allowed the use of more active
source of hydrogen for making ammonia. measure alone reduced specific energy catalyst of finer particle size without
A number of plants with total recycle consumption by 0.15-0.25 GCal/MT of increasing the pressure drop through the
process were commissioned in the decade ammonia. reactor. This in turn resulted in increase
of 1970’s. Stripping processes were in conversion per pass and thus reducing
developed by Stamicarbon and The second most significant the energy consumption in recycle of
Snamprogetti. Most plants commissioned development was availability of reformed synthesis gas. This measure alone saved
in 1980’s and 1990’s adopted tubes of better metallurgy than that of 0.20-0.25 GCal/MT of ammonia.
Snamprogetti ammonia stripping process HK-40 or equivalent used in most
with lower steam and power consumption. reformers. The new metallurgy like IN519 Almost all ammonia and urea units
These plants consumed steam and power had higher strength and it was possible changed from analog to digital
equivalent to about 1.0 GCal/MT of urea to use thinner wall tubes for the same instrumentation with screen based
compared to energy consumption of earlier operating condition of temperature in the controls. Installation of Distributed
total recycle plants equal to or higher than reformer. This allowed larger inner space Control Systems (DCS) and Programmable
1.5 GCal/MT of urea. for packing of catalyst and hence higher Logic Controllers (PLC) became the norm
throughput. This not only increased the in the decade of 1990’s. Ammonia plants
4.0 ENERGY CONSERVATION reformer capacity but also helped to save designed for 8.0-8.2 GCal brought down
EFFORTS energy consumption. their energy consumption to 7.7-7.8 GCal/
MT ammonia.
IT I S EARLIER STATED THAT L ATER Other measures included use of solvent
generation plants were designed with low promoters in CO2 removal section, more Major energy conservation measures
energy consumption in view of escalating heat recovery in the convection zone of implemented in the decades of 1980’s and
energy prices in the 1970’s. However, older reformer furnace, etc. 90’s helped to bring down the energy
plants needed to modernize and reduce consumption in existing plants. Table 2
energy consumption to remain 4.1.2 Phase II (1990’s) shows the level of energy consumption of
competitive. Continuous developments in ammonia plants in 1987-88 and than of the
process technology, catalyst and design In reformer section, while change to same plants in 1999-2000. Further
and materials of construction of better metallurgy of reformer tubes improvement in energy efficiency in the
18 INDIAN JOURNAL OF FERTILISERS December 2008

3. existing plants is possible only in small
13.0
increments. 12.48
12.5
Table 2 – Reduction in energy consumption
12.0
of ammonia plants after implementation of
Energy (GCal/MT)
energy conservation measures in old plants 11.5
(GCal/MT) 11.0
Feedstock 1987-88 1999-2000
10.5
Gas 9.96 9.60 10.0
Naphtha 12.26 10.56 9.5
Fuel oil 13.92 13.71 8.97
9.0
Total 11.70 11.31
8.5
4.1.3 Phase III (2000 onwards)
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
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5
6
7
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-8
-8
-9
-9
-9
-9
-9
-9
-9
-9
-9
-9
-0
-0
-0
-0
-0
-0
-0
-0
-0
87
88
89
90
91
92
93
94
95
96
97
98
99
00
01
02
03
04
05
06
07
19
19
19
19
19
19
19
19
19
19
19
19
19
20
20
20
20
20
20
20
20
Energy prices witnessed a steep climb
Year
during last 5-6 years. At the same time
cost of revamp and retrofit measures have
Figure 1 – Energy consumption trends in ammonia plants
also increased multifold during last decade
or so. Increasing cost and lack of
Liquid ammonia wash of synthesis gas As a result of the energy conservation
incentives in the pricing policy in
has helped to remove impurities of CO2 efforts of the industry and addition of
general slowed the investment in
and moisture. Discharge from synthesis capacity through more efficient plants, the
debottlenecking and energy saving
gas compressor was originally going to 1st weighted average ammonia energy con-
schemes. Nevertheless, improvement
stage ammonia separator via chillers and sumption of ammonia plant was reduced
continued to occur with technical
then to convertor. After additional from 12.48 GCal/MT in 1987-88 to 8.97 in
innovations in operation and maintenance
purification, it is going directly to the 2007-08. The best plant achieved energy
and projects with small investment.
convertor and thus saving energy in consumption of 7.70 GCal/MT of ammonia
However, there are a few units which made
chillers. In a separate measure in some during 2006-07. Table 4 gives the
large investment in energy saving projects
units, chilling of make up synthesis gas feedstockwise energy consumption of
with significant energy saving.
has helped to save the compression ammonia plants during 2007-08. Figure 1
Low Temperature Shift (LTS) guard with energy in the synthesis compressor. shows the trends in energy consumption
additional heat recovery to preheat boiler of ammonia plants over a period of 20
There are numerous small measures
feed water helped to reduce CO slip from years.
implemented by a large number of plants.
0.20 to 0.10 % mole percent at the exit of Table 4 – Feedstock-wise energy
For example, even feed gas saturation with
LTS convertor resulting in energy saving consumption of ammonia plants
process condensate has helped to
of order of 0.02 GCal/MT in a number of Feedstock Production Energy
conserve energy. Most plants are
units. In carbon dioxide removal section, (MMT) consumption
operating with the DCS and take full (GCal/MT)
change from single to two stage
advantage of automation. A number of Gas 9.86 8.49
regeneration allowed better heat
units have installed Advanced Process Naphtha 0.94 9.85
integration. Changing of single stage flash
Control (APC). While energy savings are Fuel Oil 1.43 11.72
vessel system in regenerator section with
small of the order of 0.05-0.1 GCal/MT Overall 12.24 8.97
5-stage flash vessel with ejectors
ammonia, operation of plant becomes very
including a mechanical steam compressor
smooth with control of most operating 4.2 Energy Conservation Efforts in Urea
was carried out by another unit. One of
parameters within the narrow range. APC Plants
the units has also installed hydraulic
also enables the optimization of plant
turbine to recover energy from high Urea reactor has been revamped by
operation to minimize energy consumption
pressure process gas in a recent revamp. almost all units by replacement of old trays
and / or maximize production. The result
There have also been some process with hydro-dynamically more efficient
of recent energy conservation efforts are
modifications in the synthesis loop. trays. This measure improved conversion
shown in Table 3.
Installation of S-50 converter with MP in the reactor. Installation of vacuum pre-
Table 3 – Result of recent energy
waste heat boiler is reported to have given concentrator and pre-decomposer helped
conservation efforts
energy saving of the order of 0.13 GCal/ Company Savings GCal/MT Percentage
to reduce energy consumption and
MT. Additional converter has increased of ammonia improvement improve product quality in a number of
conversion from 14% to 19% resulting in (%) units. Installation of pre-concentrator
saving in recycle energy. Similarly one of A 0.837 9 reduced the heat load on the first stage
B 2.26 > 20 evaporator resulting in steam saving. Pre-
the units has installed S-300 converter
C 0.255 >3
with energy saving of 0.34 GCal/MT. decomposer reduced the load of stripper
INDIAN JOURNAL OF FERTILISERS December 2008 19

4. and MP/LP sections improving reliability
9.5
of these equipments. In one of the units
commissioned in 1984-85, a saving of 120 9.0
8.87
kg/MT urea was realised in all the four
Energy (GCal/MT)
8.5
streams. In a 1981 plant, 200 kg LP steam/
MT was saved with installation of pre- 8.0
concentrator. In the same plant
7.5
replacement of urea old stripper with new
bimetallic stripper resulted in saving of 7.0
0.05 MT steam/MT. In yet another unit of
6.5
1984 vintage, vacuum pre-concentrator, 6.29
MP pre-decomposer, additional trays in 6.0
urea reactor, steam booster ejector for
1*
8
1
2
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-0
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-0
-0
-0
-0
-0
-0
-0
87
90
91
92
93
94
95
96
97
98
99
01
02
03
04
05
06
07
00
19
19
19
19
19
19
19
19
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19
19
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20
20
20
20
20
20
utilisation of surplus LP steam in MP
20
decomposer and new bimetallic stripper Year
saved 120 kg/MT of steam. Figure 2 – Energy consumption trends in urea plants
Carbon dioxide compressor is major
energy consumer in urea plants. The weighted average energy capacity. New projects would be based on
Refurbishing the compressor with better consumption of the urea plants in the the most efficient process technologies.
design impellers and change of motor has country for the year 2007-08 is given in Further, fuel oil based plants accounts for
improved the efficiency of compressors. Table 5. The best plant achieved energy about 10% ammonia production capacity.
Similarly revamp / refurbishing of turbines consumption of 5.16 GCal/MT urea for the These plants are expected to convert to
helped to reduce the consumption of year 2007-08. Figure 2 shows the trend gas in near future. This will improve the
steam. A few units have replaced the in energy consumption of urea plants energy efficiency of these plants
turbine and / or compressor for large reflecting about 30% improvement in significantly
energy savings and improvement in energy over a 20-year period. 6.0 CONCLUSION
reliability. Table 5 – Feedstock-wise energy AMMONIA AND UREA INDUSTRY HAS COME
Change of cooling tower fans, consumption of urea plants a long way in terms of capacity expansion
replacement of insulation, steam trap Feedstock Production Energy and improvement in energy efficiency.
(MMT) consumption Modernization of old plants and
management, etc. have helped to save (GCal/MT)
energy. A number of units have modified installation of new plants with better
Gas 16.12 5.97
internals of pumps (e.g. trimming of feedstock and technology have helped to
Naphtha 1.60 7.17
impeller) to match the load and reduce the Fuel Oil 2.17 7.99 reduce the energy intensity of the industry.
steam / power consumption. Installation of Overall 19.89 6.29 The energy consumption was reduced
more efficient impellers also reduced the from 12.48 GCal/MT in 1987-88 to 8.97
steam consumption. For smaller duty 5.0 FUTURE DEVELOPMENTS GCal/MT in 2007-08 for ammonia plants.
pumps (1 MW) motor drives are more THE PLANTS WOULD CONTINUE TO CARRY For the same period the energy
efficient than steam drives. Wherever, out the measures to improve their consumption of urea plants came down
there are both types of drives (including efficiencies. Revamp and retrofit measures from 8.87 GCal/MT (1987-88) to 6.29 GCal/
stand by), mere operational changes has are under implementation in a number of MT (2007-08). Revamp and retrofit
saved energy. Elsewhere, even units. According to an estimate the projects are under way in a number of
replacement of drives has been found to demand for urea production is expected to units. This alongwith conversion of non-
be an attractive measure. There has been reach 28.8 million tonnes by 2011-12 i.e. a gas plants to gas would help to further
emphasis in recent years to save energy short fall of about 2.8 million tonnes from increase the efficiency of this energy
in various pumps by way of modification the 2007-08 production level. Part of the intensive segment of the fertiliser sector.
of pumps to improve efficiency to optimize demand would be met by de-bottlenecking REFERENCES
their operation to reduce energy the present capacities and the rest to be 1. S. Nand & V. Sood, “Energy Conservation
Efforts in Indian Ammonia and Urea Plants”,
consumption. Changes in operational met by expansion and greenfield projects.
Proceedings of the FAI Workshop on Energy
philosophy and minor changes in The de-bottlenecking projects are Conservation and Management in Fertiliser
hardware are also helpful. One of the expected to be bundled with energy Industry, 3-4 March, 2003, New Delhi.
units has installed a small booster cooling efficiency schemes. One of the companies 2. S. Nand & Manish Goswami, “Energy
water pump and now run only 3 regular has already implemented the energy Efficiency Gains in Indian Ammonia Plants:
Retrospect and Prospect”, IFA Technical
pumps along with a booster pump instead saving schemes in all its units to improve Symposium, 25-28 April, 2006, Vilnius,
of running 4 regular pumps. energy efficiency as well as increase in Lithuania.
20 INDIAN JOURNAL OF FERTILISERS December 2008