A company
of ThyssenKrupp
Technologies
Uhde
TK
Nitric acid
2
Table of contents
Page
1. Company profile
3
2. The nitric acid process
4
3. Uhde and nitric acid
6
4. The Uhde medium-pressure process
8
5. The Uhde high-pressure process
10
6. The Uhde dual-pressure process
12
7. The Uhde azeotropic nitric acid process
14
8. The Uhde N2O/NOX abatement process – EnviNOx®
16
9. Typical consumption figures
18
10. References
Don’t settle for less in nitric acid
Whether a mono or dual-pressure process
– Uhde applies technologies which meet your specific
requirements, while at the same time providing efficient
energy utilisation, reduced emissions and a high
on-stream time. Why settle for less?
Cover (photos from left to right)
Dual-pressure,
Egypt: 1,850 mtpd HNO3
Mono-medium-pressure, Germany: 350 mtpd HNO3
Mono-high-pressure, Thailand: 210 mtpd HNO3
Azeotropic dual-pressure, Germany: 1,500 mtpd HNO3
19
1. Company profile
3
Uhde’s head office
in Dortmund, Germany
With its highly specialised workforce of more than 4,900 employees and its
international network of subsidiaries and branch offices, Uhde, a Dortmund-based
engineering contractor, has, to date, successfully completed over 2,000 projects
throughout the world.
Uhde’s international reputation has been built on the successful application of
its motto Engineering with ideas to yield cost-effective high-tech solutions for its
customers. The ever-increasing demands placed upon process and application
technology in the fields of chemical processing, energy and environmental protection
are met through a combination of specialist know-how, comprehensive service
packages, top-quality engineering and impeccable punctuality.
2. The nitric acid process
4
Although the basic chemistry of the nitric acid
process has not changed in the last hundred
years, today’s highly efficient, compact and environmentally friendly plants have been developed
by a process comparable with the advances made
in automobile technology in the same period.
BP Köln,
Cologne, Germany
Capacity: 1,500 mtpd HNO3 (100%)
Air
Compression
Air
Ammonia
Combustion
NO gas
NO gas
Energy recovery
Tail gas
Excess energy
NO gas
Gas cooling
NO gas
+ Acid condensate
Process
water
Absorption
Tail gas
Block diagram of
nitric acid process
Tail gas treatment
Tail gas
Nitric acid
The oxidation of ammonia over a platinum catalyst to nitrogen oxides, and their absorption in
water to form nitric acid was first carried out in
1838 by C.F. Kuhlmann. However, this discovery
was not then commercialised as ammonia was
too expensive compared with the Chile saltpetre
used to manufacture nitric acid in those days.
The Birkeland-Eyde process,
invented at the beginning of
the 20th century, which
involves the direct combination
of atmospheric oxygen and
nitrogen in an electric arc, was
also of limited application due
to poor energy utilisation.
The history of the modern
nitric acid process really begins
in 1901 when W. Ostwald established the ammonia oxidation
conditions necessary for high
nitrogen oxide yields. The first
plants using the Ostwald process
were started up in the first
decade of the 20th century.
Since then many improvements have been made by
various workers. Milestones
include the use of larger ammonia combustion units employing
flat platinum-rhodium gauzes
instead of Ostwald’s rolled up platinum gauze
strip and the recovery of the heat of reaction for
steam raising or electricity generation. The
development of strong, affordable, corrosion
resistant stainless steel materials of construction
made feasible the absorption of the nitrogen
oxides in water under pressure, thus reducing the
size and cost of the absorption equipment, while
progress in turbo-machinery technology led to
the adoption of the more energy efficient dual
pressure process. From the 1920s onwards,
advances in the synthesis of ammonia from
hydrogen and atmospheric nitrogen by the
Haber-Bosch process have given the Ostwald
route to nitric acid an additional boost by lowering its feedstock costs. Nowadays practically all
nitric acid is manufactured by this process.
5
Nitric acid is a strong acid and occurs naturally
only in a combined state as nitrate salt. As with
other industrial inorganic acids, nitric acid is
hardly of importance in itself but rather as a key
intermediate in the production of industrial goods.
Nowadays around 55 million tonnes a year of
nitric acid of various concentrations are produced
worldwide. Approximately 80% of this is used as
an intermediate in the production of nitrogenous
mineral fertilisers, primarily ammonium
2 mole
nitrate and its derivatives such as calcium
nitrate, calcium ammonium nitrate and
O2
urea ammonium nitrate solution. The
remainder goes into the production of porous
prilled ammonium nitrate for the mining industry,
and as an intermediate for the production of
special chemicals such as caprolactam or adipic
acid. There is a growing demand for azeotropic
nitric acid (approximately 68% concentration),
which is used as a nitrating agent in the production of nitrobenzene, dinitrotoluene and other
chemicals. These are further processed to TDI
or MDI, and finally used for the production of
polyurethane. Among the great variety of other
applications, those most worthy of mention are
its use as a chemical in metallurgy, for example
as an etching and pickling agent for stainless
steel, and its employment in the manufacture of
dinitrogen tetroxide for rocket fuels.
3/2
1 mole
NH3
mole
1 mole
H2O
H2O
Combustion
5/4
1 mole
mole
O2
3/4
NO
mole
3/2
O2
1/2
H2O
1/2
mole
mole
NO2
Oxidation
mole
NO
Absorption
1 mole
Stoichiometry of
nitric acid process
HNO3
Nitric acid
~ 20% consumption
~ 80 % consumption
Fertiliser
Uses of nitric acid
AN : ammonium nitrate
NP : nitrophosphate
CN : calcium nitrate
CAN : calcium ammonium nitrate
UAN : urea ammonium nitrate solution
ASN : ammonium sulphate nitrate
TDI : toluene diisocyanate
MDI : methylene diphenyl diisocyanate
CN
Non-Fertiliser
AN
NP
CAN
UAN
AN (technical grade)
ASN
Caprolactam
Polyamide 6
Adipic
acid
Polyamide 6.6
Chemicals
Dinitrotoluene
Nitrobenzene
TDI
MDI
Polyurethane
Polyurethane
(flexible PU)
(rigid PU)
6
3. Uhde and nitric acid
As early as 1905, Dr. Friedrich Uhde, the founder
of Uhde GmbH, designed and constructed, in
cooperation with Prof. Wilhelm Ostwald, a pilot
plant for the production of nitric acid by burning
ammonia with air in the presence of a catalyst.
Since the company’s foundation in 1921, the
number of plants for the production of weak and
concentrated nitric acid as well as ammonia
combustion units for nitrogen oxide production
and absorption plants for nitrous waste gases,
which have been designed, constructed and commissioned by Uhde under a variety of climatic
conditions total some 200.
Uhde thus ranks among the world’s leading
engineering companies engaged in the design
and construction of nitric acid plants and
ammonia combustion units.
The processes have been continually refined in
order to meet ever more stringent requirements,
particularly with regard to air pollution control
and energy cost constraints.
The plants designed and constructed by Uhde
are characterised by high reliability, profitability
and on-stream time.
Shutdown periods are now almost entirely limited
to catalyst changes and equipment inspections.
The number of follow-up orders Uhde receives
bears witness to the satisfaction of our customers.
Today, nitric acid is produced exclusively from
ammonia oxidised by combustion with air in the
presence of a noble-metal catalyst.
Non-noble-metal catalysts do not play a
significant role.
The catalysts used in the process consist of a
pack of platinum-rhodium gauzes, the number
depending on the operating pressure and burner
construction. The gauzes are produced nowadays
by knitting thin wires, usually with a diameter of
60 or 76 µm. Woven gauzes are used only in a
few specialised applications.
A platinum recovery system made from palladium
can easily be installed underneath the platinum
catalyst. Combined catalyst and catchment systems are also available.
Nowadays, it is possible to manufacture catalyst
gauzes with a diameter of more than 5.5 m. More
than 1,500 tonnes per day of nitric acid can be
produced from a single burner.
Even larger burners can be manufactured;
the upper limit is dictated solely by transport
restrictions and flange machining.
The production of nitric acid takes place in
3 process steps shown by the following main
equations:
1. Ammonia combustion
4 NH3 + 5 O2
4 NO + 6 H2O + 905 kJ
2. Oxidation of the nitric oxide
2 NO + O2
2 NO2 + 113 kJ
3. Absorption of the nitrogen dioxide in water
3 NO2 + H2O
2 HNO3+ NO + 116 kJ*
In practice, these three process steps can be
carried out in different ways, resulting in several
different nitric acid processes. Modern nitric acid
plants are designed according to the monopressure or the dual-pressure process.
Within the group of mono-pressure processes, a
distinction is made between the medium-pressure
process with a 4 - 6 bar abs. operating pressure
and the high-pressure process which operates
at 8 - 12 bar abs.
The dual-pressure process employs a medium
pressure of approx 4 - 6 bar abs. for ammonia
combustion and a high pressure of approx.
10 - 12 bar abs. for nitric acid absorption.
The optimum process is selected taking into
account the costs of feedstocks and utilities,
energy and capital investment as well as local
conditions.
In compliance with stringent pollution
abatement requirements, it is possible to achieve
a NOX tail gas content of below 50 ppm.
Furthermore, emissions of nitrous oxide, an
unwanted by-product in the ammonia oxidation
step, can be reduced to a minimum by appropriate catalyst-based methods.
*
The heat of reaction shown
applies to the production of acid with
a concentration of 60% by wt.
7
The large photograph in the background
shows the glowing catalyst gauze in an
ammonia burner.
The photograph shows an ammonia burner
of a nitric acid plant built in 1924 and in
operation until 1965. The throughput was
0.1 t of nitrogen per day.
In order to achieve a daily throughput of
20 tonnes of nitrogen, 200 of these burners
were formerly arranged in parallel.
Dual-pressure nitric acid plant:
Two ammonia burners
Capacity: 1,850 mtpd HNO3 (100%)
corresponding to a burner load
of 430 mtpd of nitrogen
Abu Qir, Egypt
8
4. The Uhde medium-pressure process
In this process, the air required for burning the
ammonia is supplied by an uncooled air compressor. The compressor set can be designed
either as an inline train configuration or preferably
as a bull gear type with an integrated tail gas
turbine.
The operating pressure is governed by the maximum final pressure obtainable in an uncooled
compressor, i.e. 4 - 5 bar abs. in the case of
radial compressors and 5 - 6 bar abs. with axial
flow compressors.
Plant capacities of up to 500 mtpd of nitric acid
(100%) can be realised using a single ammonia
combustion unit and one absorption tower. Due
to the process pressure, higher capacities of up
to about 1,000 mtpd are feasible if a second
absorption tower is used.
The medium pressure process is the process of
choice when maximum recovery of energy is
required. The air compressor is usually driven by
a tail gas expansion turbine and a steam turbine,
the steam being generated within the plant. If
the credit for exported steam is high then the
compressor train can be driven by a high voltage
synchronous or asynchronous electric motor
rather than a steam turbine so that all the steam
generated can be exported.
With this plant type, it is possible to produce
one type of nitric acid with a max. concentration
of 65% or two types of acid with different concentrations, e.g. 60% nitric acid and 65% nitric acid,
while the NOX content in the tail gas can be
reduced by absorption to less than 500 ppm.
The NOX content has to be further reduced to the
required value by selective catalytic reduction
using a non-noble-metal catalyst and ammonia
as the reducing agent.
Nitric acid plant for SKW
in Wittenberg, Germany
Capacity: 350 mtpd HNO3 (100%)
(Mono medium-pressure)
The ammonia combustion unit was designed for
a capacity equivalent to 500 mtpd HNO3 (100%).
It supplies the existing plant for the production of
highly concentrated nitric acid with nitrous gases.
The medium-pressure process is characterised by
a high overall nitrogen yield of about 95.7% or
95.2% in conjunction with the tail gas treatment
process, a low platinum consumption and a high
steam export rate.
The catalyst gauzes only need to be changed
once every 6 months due to the low burner load.
9
Flowsheet of a medium-pressure nitric acid plant
Primary air
Tail gas
1
STH
Tail gas
turbine
WB
HP steam
HP
steam
8
2
NO gas
Steam
turbine
Tail gas
Ammonia (gas)
Process water
CW
Air
3
11
Condensate
Air
compr.
WB
9
LP steam
4
CW
10
AW
WB
6
BFW
BFW
CW
Ammonia (liquid)
CW
Secondary air
CW
CW
CW
5
7
Acid
condensate
Nitric acid
product
1 Reactor
2 Process gas cooler
3 Tail gas heater 3
4 Economizer
5 Cooler condenser & feedwater preheater
6 Absorption
7 Bleacher
8 Tail gas heater 1 & 2
9 Tail gas reactor
10 Ammonia evaporation & superheating
11 Turbine steam condenser
5. The Uhde high-pressure process
10
In the high-pressure process, a radial multi-stage
compressor with an intercooler section is used
to compress the process air to a final pressure
of 8 - 12 bar abs. Preferably, the bull gear type
with integrated tail gas turbine is selected but
alternatively an inline machine can be used.
Due to the higher pressure, all equipment and
piping can be of a smaller size and only one
absorption tower is required.
If lower NOX values are required, an additional
catalytic tail gas treatment unit can be easily
integrated. The nitrogen yield attained by the
high-pressure process is in the order of 94.5%.
Thai Nitrate Company,
Rayong, Thailand
Capacity: 210 mtpd HNO3 (100%)
The arrangement of all equipment is very compact
so that the building for the machine set and the
burner unit can be kept small, but this does not
pose a problem for maintenance work.
(right) Enaex S.A.,
Mejillones, Chile
Capacity: 925 mtpd HNO3 (100%)
This type of plant is always recommended when
a quick capital return is desirable.
In such cases, Uhde can offer a greatly simplified
process which does not include tail gas and steam
turbines. The heating of the tail gas downstream
of the absorption section is not necessary.
Special design concepts for the process gas
cooler unit, condenser and bleacher reduce the
cost even further.
Two high-pressure nitric acid plants:
(left)
Plant capacities between 100 mtpd (100%) and
1,000 mtpd of nitric acid can be realised.
The achieved acid concentrations of up to 67%
are slightly higher than with the medium-pressure process. Two or more product streams with
different concentrations are likewise possible.
The compressor may be driven by a steam
turbine or an electric motor.
The NOX concentration in the tail gas can be
lowered to less than 200 ppm by absorption alone.
For capacities below 100 mtpd, a low capital
investment cost may be much more preferable
to an optimum recovery of energy.
The operating pressure required by such a process depends on the maximum permissible NOX
content in the tail gas. If the specified NOX limit is
below 200 ppm, a pressure of at least 7 bar abs.
must be considered, depending on the cooling
water temperature.
Lower NOX values of less than 50 ppm can be
achieved, if required, by integrating a catalytic
tail gas treatment process. Uhde also provides a
similar process without the ammonia evaporation
and heat recovery units for recovering acid from
the waste gas in, for example, adipic acid plants.
11
Flowsheet of a high-pressure nitric acid plant
Secondary air
Tail gas
1
Primary air
LP
steam
STH
Tail gas
turbine
WB
HP steam
HP
steam
Steam
turbine
2
8
NO gas
Tail gas
Ammonia (gas)
Process water
CW
Air
11
Condensate
3
CW
WB
Air
compr.
CW
12
9
WB
4
6
CW
LP steam
CW
CW
10
AW
Ammonia (liquid)
BFW
BFW
CW
CW
CW
5
7
Acid
condensate
Nitric acid
product
1 Reactor
2 Process gas cooler
3 Tail gas heater 3
4 Economizer
5 Cooler condenser & feedwater preheater
6 Absorption
7 Bleacher
8 Tail gas heater 1 & 2
9 Tail gas reactor
10 Ammonia evaporator & superheater
11 Turbine steam condenser
12 Air intercooler
6. The Uhde dual-pressure process
12
The dual-pressure process was developed to
accommodate ever more stringent environmental pollution control requirements.
The process air is compressed to a final pressure
of 4 - 6 bar abs.
The NO gas from the ammonia combustion unit is
cooled in a heat exchanger train, producing steam
and preheating tail gas, and then compressed to
Two dual-pressure nitric acid plants:
(left)
Abu Qir Fertilizers and Chemical
Ind. Co., Abu Qir, Egypt
Capacity: 1,850 mtpd HNO3 (100%)
NOX in tail gas: less than 50 ppm
as a result of a catalytic tail gas
treatment process
(right) AMI Agrolinz Melamine International,
Linz, Austria
Capacity: 1,000 mtpd HNO3 (100%)
NOX in tail gas: less than 10 ppm
as a result of the Uhde N2O/NOX
abatement process – EnviNOx®
10 - 12 bar abs in the NOX compressor. The final
pressure is selected so as to ensure that the
absorption section is optimised for the specified
NOX content of the tail gas and that the compressors, driven by a steam turbine, can be
operated using only the steam generated in the
process gas cooler unit while ensuring that
some excess steam will always be available in
order to guarantee steady operating conditions
at all times. Alternatively the compressor set can
be driven by either a high voltage asynchronous
or synchronous motor and the steam generated
can be exported. The dual-pressure process
combines in an economical way the advantages
of the low pressure in the combustion section
and the high pressure in the absorption section.
Plant capacities of up to 1,500 mtpd of nitric
acid (100%) can be achieved in a single-train
configuration. The machine set can be designed
either as an inline-shaft set or optionally as a
bull gear type unit with integrated air/NOX compression and tail gas expander stages. The inline
machine concept is favourable in the case of
higher plant capacities in excess of 1,100 mtpd
up to 2,200 mtpd or if an increased energy export
is required. For plant capacities in excess of
1,500 mtpd the ammonia combustion and process gas cooler unit needs only to be duplicated.
The nitrogen yield in a plant of this type is more
than 96% with a NOX content in the untreated tail
gas of less than 150 ppm (vol.) being possible.
The NOX content may be further reduced to less
than 50 ppm, if required, by selective catalytic
reduction using a non-noble-metal catalyst and
ammonia as the reducing agent.
Acid concentrations of more than 68% can be
achieved. (See also chapter 7: The Uhde azeotropic nitric acid process.) Two or more product
streams with different concentrations are also
possible. In addition, external streams of weak
nitric acid (various concentrations) can be processed if required.
Due to the low burner load, the catalyst gauzes
can remain in the burner for an operating period
of 6 to 8 months or longer before being partially
or completely replaced.
13
Flowsheet of a dual-pressure nitric acid plant
Secondary air
Primary air
1
6
STH
CW
WB
Air
compr.
Air
Tail gas
HP
steam
CW
2
NO gas
7
9
Tail gas
Tail gas
turbine
Process water
Steam
turbine
3
CW
Ammonia (gas)
NOx
compr.
HP steam
CW
14
Condensate
10
4
WB
8
Tail gas
LP steam
BFW
CW
BFW
CW
CW
LP steam
CW
11
Ammonia (liquid)
AW
12
CW
5
13
Nitric acid
product
Acid
condensate
1 Reactor
2 Process gas cooler
3 Tail gas heater 3
4 Economizer
5 Cooler condenser 1 & feedwater preheater
6 Tail gas heater 2
7 Cooler condenser 2
8 Absorption
9 Tail gas heater 1
10 Tail gas reactor
11 Ammonia evaporation & superheating
12 Ammonia evaporation
13 Bleacher
14 Turbine steam condenser
7. The Uhde azeotropic nitric acid process
14
Azeotropic nitric acid with an elevated concentration of 68% by weight can replace concentrated
nitric acid in some applications such as nitrations.
Due to increased market demand, Uhde has
developed an enhanced process for the reliable
production of azeotropic nitric acid without any
further weak nitric acid co-production. The basic
process design is mainly an extended dualpressure process.
To satisfy the overall water balance, it is
mandatory at some locations to eliminate the
water carried with the incoming air taken in by
the air compressor. The necessary measures
depend on climatic conditions, in particular air
humidity and temperature. In the case of extreme
conditions the installation of an additional air
cooler/condenser operating partly with chilled
water is recommended. Normally in the Uhde
dual-pressure process, there is an extra chilled
water circuit linked to the ammonia evaporation.
This uses to a large extent the ammonia evaporation heat, especially in the absorption section,
in order to establish the required acid strength
and the NOX level at the absorption outlet. It is
also possible to provide an external chilled water
set. However, this solution is expensive and
energy consuming and would only be considered
by Uhde if all other measures prove insufficient.
The design of the absorption column is of
particular importance especially for producing
azeotropic acid. At Uhde a sophisticated computer
program is used to predict the exact limits of acid
concentration, heat loads, NOX in tail gas, etc.
Another important feature of the Uhde azeotropic
nitric acid process is the drying section for the
secondary air. This air is used for stripping
nitrous gases from the crude acid leaving the
absorption unit. During this stripping process,
the humidity of the secondary air dilutes the
product acid. The water vapour in the secondary
air is absorbed by a small circulating stream of
product acid in a special drying section within
the bleacher.
Two azeotropic nitric acid plants:
(left)
BP Köln,
Cologne, Germany
Capacity: 1,500 mtpd HNO3 (100%)
(right) Namhae Chemical Corporation
operated by HU-CHEMS,
Yosu, Korea
Capacity: 1,150 mtpd HNO3 (100%)
Important process features for the production
of azeotropic acid are, in addition to sufficient
absorption pressure and cooling, the overall water
balance of the plant. Furthermore, the ratio of
dinitrogen tetroxide to nitric oxide in the process
gas at the absorption tower inlet has to be adjusted to a level that is in equilibrium with the
acid concentration required.
Taking the above into consideration, Uhde is
able to offer individual customers tailor-made
solutions for azeotropic nitric acid plants.
The equipment shown as an example is fully integrated in Uhde´s compact bull gear concept, which
is applicable for capacities up to 1,100 mtpd.
Above this capacity an inline machine set is
employed as shown on page 13. The first pressure
level delivered by the air compressor is advantageous for the ammonia combustion section, while
the final pressure delivered by the NOX compressor promotes absorption and the formation of
azeotropic acid.
15
Flowsheet of an azeotropic nitric acid plant
(optional)
Secondary air
Primary air
1
6
CW
15
STH
AW
CW
Tail gas
WB
Air
compr.
HP
steam
CW
2
NO gas
7
9
Tail gas
Tail gas
turbine
Ammonia (gas)
Process water
Air
HP steam
3
Steam
turbine
CW
CW
NOx
compr.
8
WB
14
Condensate
10
4
Tail gas
BFW
LP steam
CW
CW
BFW
CW
LP steam
CW
Ammonia (liquid)
11
12
CW
5
13
AW
Acid
condensate
Nitric acid product
1 Reactor
2 Process gas cooler
3 Tail gas heater 3
4 Economizer
5 Cooler condenser 1 & feedwater preheater
6 Tail gas heater 2
7 Cooler condenser 2
8 Absorption
9 Tail gas heater 1
10 Tail gas reactor
11 Ammonia evaporation & superheating
12 Ammonia evaporation
13 Bleacher
14 Turbine steam condenser
15 Air condenser (optional)
16
8. The Uhde N2O/NOX abatement process – EnviNOx®
Nitrous oxide (N20) – also known as “laughing
gas” - is formed in the ammonia burner as an
unwanted by-product. Depending on the performance of this burner around 1% to 2% of the
ammonia feed is lost in this way, with a similar
amount being lost due to the formation of nitrogen.
The nitrous oxide passes through the rest of the
nitric acid plant unchanged and is discharged to
atmosphere with the tail gas.
Neglected for many years, nitrous oxide emissions
are now coming under scrutiny by regulators since
nitrous oxide is a potent greenhouse gas some
300 times stronger than carbon dioxide and is
implicated in the destruction of the ozone layer.
Uhde, having at an early stage recognised this
trend, have developed a catalyst and a process for
the lowering of nitrous oxide emissions from nitric
acid plants. An added bonus is that emissions
of nitrogen monoxide and dioxide (NOX) are also
reduced.
The Uhde EnviNOx® nitrogen oxide abatement
process features a tail gas reactor installed
directly upstream of the tail gas turbine. Uhde
has developed specific process variants to cater
for the range of temperatures found in different
nitric acid plants. The nitrous oxide decomposition
variant is particularly suited to tail gas temperatures above about 420°C. In this variant nitrous
oxide is decomposed to oxygen and nitrogen in
a first catalyst bed.
N20
N2 + 1/2 O2 + 82 kJ
The tail gas is then mixed with ammonia before
entering the second bed in which NOX is catalytically reduced to water vapour and nitrogen:
4 NO + 4 NH3 + O2
3 NO2 + 4 NH3
4 N2 + 6 H2O + 1628 kJ
7/ N
2 2
+ 6 H2O + 1367 kJ
Further removal of nitrous oxide also takes
place in this bed.
For lower temperatures Uhde’s solution is based
on the catalytic reduction of nitrous oxide with
hydrocarbons, such as natural gas, combined
with the reduction of NOX by ammonia. In most
situations the removal of both N2O and NOX can
take place in parallel in a single catalyst bed. The
quantity of the greenhouse gas carbon dioxide,
that is produced due to the use of hydrocarbons
is insignificant in comparison to the amount of
greenhouse gas emission reduction that the
EnviNOx® process achieves by the removal of
nitrous oxide.
In both EnviNOx® process variants the tail gas
leaving the reactor has a greatly reduced concentration of N2O. The low outlet NOX concentration is significantly smaller than that commonly
attained in conventional DeNOX units, and results
in an invisible stack plume. The NOX reduction
component is also available without the N2O
removal component and is applicable to temperatures between about 200°C and 500°C.
Uhde’s EnviNOx® technology is suited equally
well to retrofits or to new plants. As it is an
end-of-pipe process there is no contact with the
product nitric acid or intermediate NO gas, thus
eliminating any possibility of product loss or
contamination.
17
Flowsheet of tail gas section of a nitric acid plant with EnviNOx® reactor
Tail gas
2
Tail gas
Process water
Tail gas
turbine
CW
1
3
Ammonia (gas)
CW
NO gas
Nitric acid
Flowsheet of tail gas section of a nitric acid plant with EnviNOx® reactor
(for lower temperature applications)
Tail gas
2
Ammonia (gas)
Tail gas
Hydrocarbon
Process water
Tail gas
turbine
Uhde EnviNOx® reactor at AMI
Agrolinz Melamine International,
Linz, Austria
Capacity: 1,000 mtpd HNO3 (100%)
CW
For more details,
please refer to our brochure:
EnviNOx® - Climate protection
solutions for nitric acid plants
1
NO gas
3
CW
1 Absorption
2 Tail gas heating
Nitric acid
3 EnviNOx® reactor
18
9. Typical consumption figures
The dual-pressure nitric acid plant in
Donaldsonville, Louisiana, USA.
Capacity: 870 mtpd HNO3 (100%)
Plant type
Mediumpressure
process
Highpressure
process
Dualpressure
process
Operating
pressure pabs
5.8 bar
10.0 bar
4.6/12.0 bar
Ammonia
284.0 kg
286.0 kg
282.0 kg
Electric power
9.0 kWh
13.0 kWh
8.5 kWh
Platinum,
primary losses
0.15 g
0.26 g
0.13 g
with recovery
0.04 g
0.08 g
0.03 g
Cooling water
(∆t =10 K)
100 t
130 t
105 t
Process water
0.3 t
0.3 t
0.3 t
LP heating steam,
8 bar, saturated
0.05 t
0.20 t
0.05 t
HP excess steam,
40 bar, 450 ∞C
0.76 t
0.55 t
0.65 t
including water
for steam turbine condenser
Table: Comparison of typical consumption figures for steam
turbine-driven and inline compressor set nitric acid plants,
per tonne of nitric acid (100%), with a NOX content in the tail gas
of less than 50 ppm
10. References
19
Year of
Commissioning
Client
Location
Pressure in
Combustion
bar abs.
Acid
conc.
%
Capacity
mtpd HNO3
100%
2009
Ferrostaal AG
Point Lisas
Trinidad and Tobago
4.2
11.0
60
1,518
2005
Rashtriya Chemicals &
Fertilizers Ltd.
Mumbai
India
7.5
7.5
60
352
2003
Namhae Chemical Corporation
operated by HU-CHEMS
Yosu
Korea
4.6
12.0
67
1,150
2001
BP Köln GmbH
Cologne
Germany
4.6
12.0
68.25
1,500
2001
Radici Chimica GmbH
Zeitz
Germany
10.0
10.0
65
250
2001
ACE Pressureweld
Singapore
4.4
4.4
60
12
2000
Queensland Nitrates Pty Ltd
Moura
Australia
10.0
10.0
60
405
1999
Enaex S.A.
Mejillones
Chile
10.0
10.0
60
925
1999
Namhae Chemical Corporation
operated by HU-CHEMS
Yosu
Korea
10.0
10.0
65
300
1998
SKW Stickstoffwerke
Piesteritz GmbH
Wittenberg
Germany
5.6
5.6
62
350/500*
1998
CF Industries Inc.
Donaldsonville,
Louisiana/USA
4.6
11.0
57.5
870
Absorption
bar abs.
* Capacity of ammonia combustion is equivalent to the higher figure.
Dual-pressure nitric acid plants
BASF, Antwerp, Belgium
Capacities:
550 and 2 x 945 mtpd HNO3 (100%) NOX
in tail gas: less than 100 ppm as a result of
the catalytic tail gas treatment process
PDF 22.1.2009
Fl 130e/1500e 05/2007 DÖ/Hi/ Printed in Germany