uhde nitric acid process brochure

8/13/2019 Uhde Nitric Acid Process Brochure

1/20

Nitric acid

ThyssenKrupp Uhde


2/20

Table of contents

22

1. Company prole 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/NO

Xabatement process EnviNOx 16

9. Typical consumption gures 19


3/20

33

Uhdes head office

Dortmund, Germany

1. Company prole

With its highly specialised workforce of more than 5,600 employees

and its international network of subsidiaries and branch ofces, Uhde,

a Dortmund-based engineering contractor, has to date successfully

completed over 2,000 projects throughout the world.

Uhdes international reputation has been built on the successful

application of its motto Engineering with ideasto yield cost-effective

high-tech solutions for its customers. The ever-increasing demands

placed upon process and application technology in the elds ofchemical processing, energy and environmental protection are met

through a combination of specialist know-how, comprehensive

service packages, top-quality engineering and impeccable punctuality.


4/20

4

2. The nitric acid process

Although the basic chemistry of the nitric

acid process has not changed in the last

hundred years, todays highly efficient,

compact and environmentally friendly plants

have been developed by a process compa-

rable with the advances made in automobile

technology in the same period.

The oxidation of ammonia over a platinum

catalyst to nitrogen oxides, and their ab-

sorption in water to form nitric acid was firstcarried out in 1838 by C.F. Kuhlmann. How-

ever, this discovery was not then commer-

cialised 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 in-

volves the direct combination of atmos-

pheric oxygen and nitrogen in an electric

arc, was also of limited application due to

poor energy utilisation.

BP Kln, Cologne, GermanyCapacity: 1,500 mtpd HNO

3(100%)

Compression

Combustion

Energy recovery

Gas cooling

Absorption

Tail gas treatment

Air

Ammonia

Tail gas

Processwater

Air

NO gas

NO gas

Nitric acid

NO gas+ Acid condensate

Tail gas

Excess energy

NO gas

Tail gas

O2

O2

NH3

O2

HNO3

NO

2 mole 3/4mole

5/4mole

1 mole

1 mole

1/2mole

Oxidation

Combustion

Absorption

Block diagram of nitric acid process Stoichiometry of nitric acid process


5/20

5

Nitric acid

Non-Fertiliser

AN (technical grade)

Capro-lactam

Fertiliser

Chemicals

Adipicacid

Dinitro-toluene

Nitro-benzene

TDI MDI

Poly-amide 6

Poly-amide 6.6

Poly-urethane(flexible PU)

Poly-urethane

(rigid PU)

AN NP

CN CAN UAN ASN

~ 80 % consumption ~ 20 % consumption

The history of the modern nitric acid pro-

cess really begins in 1901 when W. Ostwald

established the ammonia oxidation condi-

tions 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 im-

provements have been made by various

workers. Milestones include the use of larger

ammonia combustion units employing flat

platinum-rhodium gauzes instead ofOstwalds rolled up platinum gauze strip

and the recovery of the heat of reaction for

steam raising or electricity generation. The

development of strong, affordable, corro-

sion resistant stainless steel materials of

construction made feasible the absorption

of the nitrogen oxides in water under pres-

sure, thus reducing the size and cost of the

absorption equipment, while progress in

turbo-machinery technology led to the adop-

tion of the more energy efficient dual pres-

sure 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 prac-

tically all nitric acid is manufactured by this

process.

Nitric acid is a strong acid and occurs natu-

rally only in a combined state as nitrate salt.As with other industrial inorganic acids, nitric

acid is hardly of importance in itself but ra-

ther 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. Ap-

proximately 80% of this is used as an inter-

mediate in the production of nitrogenous

mineral fertilisers, primarily ammonium

nitrate and its derivatives such as calcium

nitrate, calcium ammonium nitrate and 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 azeotr opic nitric acid (approximately

68% concentration), which is used as a

nitrating agent in the production of nitro-

benzene, dinitrotoluene and other chemi-

cals. These are further processed to TDI orMDI, and finally used for the production of

polyurethane.

Among the great variety of other applica-

tions, 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.

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

NO

H2O H

2O

H2O

NO2

mole

2mole 1 mole

2mole

1/2mole


6/20

* The heat of reaction shown applies to the productionof acid with a concentration of 60% by wt.

6

3. Uhde and nitric acid

As early as 1905, Dr. Friedrich Uhde, the

founder of Uhde GmbH, designed and con-

structed, 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 companys foundation in 1921,

the number of plants for the production of

weak and concentrated nitric acid as well

as ammonia combustion units for nitrogenoxide production and absorption plants

for nitrous waste gases, which have been

designed, constructed and commissioned

by Uhde under a variety of climatic condi-

tions total some 200.

Uhde thus ranks among the worlds lead-

ing 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 require-ments, 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 re-ceives 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 pres-sure and burner construction. The gauzes

are produced nowadays by knitting thin

wires, usually with a diameter of 60 or 76

m. Woven gauzes are used only in a few

specialised applications.

A platinum recovery system made from

palladium can easily be installed under-

neath the platinum catalyst. Combined

catalyst and catchment systems are also

available.

Nowadays, it is possible to manufacturecatalyst 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 trans-

port 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 O

24 NO + 6 H

2O + 905 kJ

2. Oxidation of the nitric oxide

2 NO + O22 NO

2+ 113 kJ

3. Absorption of the nitrogen dioxide in water

3 NO2+ H

2O

2 HNO

3+ NO + 116 kJ*


7/20

77

The large photograph in the background shows the glowing

catalyst gauze in an ammonia burner.

The photograph on the left 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.

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 ac-

cording to the mono-pressure or the dual-

pressure process.

Within the group of mono-pressure pro-

cesses, a distinction is made between the

medium-pressure process with a 4 - 6 bar

abs. operating pressure and the high-pres-sure process which operates at 8 - 12 bar

abs.

The dual-pressure process employs a me-

dium 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 util-

ities, energy and capital investment as well

as local conditions.

In compliance with stringent pollution abate-

ment requirements, it is possible to achieve

a NOXtail gas content of below 50 ppm.

Furthermore, emissions of nitrous oxide, an

unwanted by-product in the ammonia oxi-

dation step, can be reduced to a minimum

by appropriate catalyst-based methods.

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


8/20

4. The Uhde medium-pressure process

8

Flowsheet of a medium-pressure

nitric acid plant

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

Nitric acid plant for SKW

in Wittenberg, Germany

Capacity: 350 mtpd HNO3(100%)

(Mono medium-pressure)

The ammonia combustion unit was desi-

gned 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.


9/20

9

Ammonia (liquid)

CW

LP steam

CW

Nitric acidproduct

Process water

CW

CW

Tail gas

Secondary air

WB

NO gas

Ammonia (gas)

Tail gas

turbine

Steam

turbine

Air

compr.

HP steam

Air

Tail gas

1

8

3

4

510 7

9 6

CW CW

WB

STH

HPsteam

WB

11

CW

Condensate

AW

BFWBFW

Primary air

2

Acid

condensate

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 configura-

tion 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 - 6bar 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 absorp-

tion tower. Due to the process pressure, high-

er capacities of up to about 1,000 mtpd are

feasible if a second absorption tower is used.

The medium pressure process is the pro-

cess of choice when maximum recovery of

energy is required. The air compressor is

usually driven by a tail gas expansion tur-

bine 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 syn-

chronous or asynchronous electric motor

rather than a steam turbine so that all thesteam generated can be exported.

With this plant type, it is possible to pro-

duce 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

NOXcontent in the tail gas can be reduced

by absorption to less than 500 ppm.

The NOXcontent 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.

The medium-pressure process is charac-

terised by a high overall nitrogen yield of

about 95.7% or 95.2% in conjunction withthe tail gas treatment process, a low plati-

num consumption and a high steam ex-

port rate.

The catalyst gauzes only need to be changed

once every 6 months due to the low burner

load.


10/20

10

5. The Uhde high-pressure process

Flowsheet of a high-pressure

nitric acid plant

1 Reactor


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



12 Air intercooler

In the high-pressure process, a radial multi-

stage compressor with an intercooler sec-

tion is used to compress the process air to

a final pressure of 8 - 12 bar abs. Prefer-

ably, 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.

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 main-

tenance work.

This type of plant is always recommended

when a quick capital return is desirable.

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 me-

dium-pressure process. Two or more prod-

uct streams with different concentrations

are likewise possible.

The compressor may be driven by a steam

turbine or an electric motor.

The NOXconcentration in the tail gas can

belowered to less than 200 ppm by absorp-

tion alone.

If lower NOXvalues are required, an addi-

tional 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%.

For capacities below 100 mtpd, a low capitalinvestment cost may be much more prefer-

able to an optimum recovery of energy.

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.

The operating pressure required by such aprocess depends on the maximum permis-

sible NOXcontent in the tail gas. If the spec-

ified NOXlimit is below 200 ppm, a pressure

of at least 7 bar abs. must be considered,

depending on the cooling water temperature.

Lower NOXvalues 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 gasin, for example, adipic acid plants.


11/20

11

Tail gas

turbine

Steam

turbine

Air

compr.

Air

Tail gas

CW

CW

Ammonia (liquid)

CW

LP steam

Acidcondensate

Nitric acidproduct

CW

CW

Process water

Tail gas

LP

steam

WB

NO gas

8

3

4

510 7

9 6

Secondary air

CW

12WB

CW

BFWBFW

CW

AW

Ammonia (gas)

HP steam

11

CW

Condensate

Primary air1

WB

STH

HPsteam

2

Two high-pressure nitric acid plants:

(left) Enaex S.A., Mejillones, Chile


(right) Thai Nitrate Company,

Rayong, Thailand



12/20

12

6. The Uhde dual-pressure process

Flowsheet of a high-pressure nitric acid plant

1 Reactor


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


12 Ammonia evaporation

13 Bleacher


The dual-pressure process was developed

to accommodate ever more stringent envi-

ronmental 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, pro-

ducing steam and preheating tail gas, and

then compressed to 10 - 12 bar abs in theNOXcompressor. The final pressure is se-

lected so as to ensure that the absorption

section is optimised for the specified NOX

content of the tail gas and that the com-

pressors, 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 oper-

ating conditions at all times. Alternatively

the compressor set can be driven by either

a high voltage asynchronous or synchro-

nous motor and the steam generated canbe exported. The dual-pressure process

combines in an economical way the advan-

tages of the low pressure in the combustion

section and the high pressure in the absorp-

tion 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/NOXcompression 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 com-

bustion 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 NOXcontent may be

further reduced to less than 50 ppm, if re-

quired, 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 concentrationsare 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 oper-

ating period of 6 to 8 months or longer be-

fore being partially or completely replaced.


13/20

13

Tail gas

turbine

Air

compr.

NOxcompr.

Steam

turbine

CW

Ammonia (liquid)

LP steam

LP steam

CW

WB

Nitric acidproduct

CW

CW

Process water

CW

CW

CW

Air

HP steam Condensate

Tail gas

Secondary air

NO gas

Tail gas

BFW

Tail gas

Ammonia (gas)

1 6

7 9

3

4

511 1312

10 8

2

14

CW

BFW

CW

Primary air

Acid

condensate

WB

STH

HPsteam

AW

Two dual-pressure nitric acid plants:

(left) Abu Qir Fertilizers and Chemical Ind. Co.,

Abu Qir, Egypt

Capacity: 1,850 mtpd HNO3(100%)

NOXin tail gas: less than 50 ppm as a result

of a catalytic tail gas treatment process

(right) Borealis AG, Linz, Austria


NOXin tail gas: less than 10 ppm

as a result of the Uhde N2O/NO

X

abatement process EnviNOx


14/20

14

7. The Uhde azeotropic nitric acid process

Flowsheet of an azeotropic nitric acid plant

1 Reactor


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


12 Ammonia evaporation

13 Bleacher


15 Air condenser (optional)

Azeotropic nitric acid with an elevated con-

centration of 68% by weight can replace

concentrated nitric acid in some applica-

tions such as nitrations. Due to increased

market demand, Uhde has developed an

enhanced process for the reliable produc-

tion of azeotropic nitric acid without any

further weak nitric acid co-production. The

basic process design is mainly an extended

dual-pressure process.

Important process features for the produc-

tion of azeotropic acid are, in addition to

sufficient absorption pressure and cooling,

the overall water balance of the plant. Fur-

thermore, the ratio of dinitrogen tetroxide to

nitric oxide in the process gas at the absorp-

tion tower inlet has to be adjusted to a level

that is in equilibrium with the acid concen-

tration required.

To satisfy the overall water balance, it is

mandatory at some locations to eliminate

the water carried with the incoming air takenin by the air compressor. The necessary

measures depend on climatic conditions, in

particular air humidity and temperature. In

the case of extreme conditions the installa-

tion of an additional air cooler/condenser

operating partly with chilled water is recom-

mended. Normally in the Uhde dual-pres-

sure 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 absorp-

tion section, in order to establish the re-quired acid strength and the NO

Xlevel at the

absorption outlet. It is also possible to pro-

vide an external chilled water set. However,

this solution is expensive and energy con-

suming 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 produc-

ing azeotropic acid. At Uhde a sophisticated

computer program is used to predict the

exact limits of acid concentration, heat loads,

NOXin tail gas, etc.

Another important feature of the Uhde azeo-

tropic nitric acid process is the drying sec-

tion 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 sec-

ondary 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.

Taking the above into consideration, Uhde isable to offer individual customers tailor-made

solutions for azeotropic nitric acid plants.

The equipment shown as an example is fully

integrated in Uhdes compact bull gear con-

cept, 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 am-

monia combustion section, while the final

pressure delivered by the NOXcompressorpromotes absorption and the formation of

azeotropic acid.


15/20

15

NOxcompr.

Tail gas

turbine

Steam

turbine

Air

compr.

HP steamAir

CW

Ammonia (liquid)

LP steam

CW

AW

LP steam

Acid

condensate

CW

WB

BFW

3

511 12

Nitric acid product

CW

CW

Process water

CW

CW

Tail gas

Tail gas

1 6

13

Tail gas

15

Ammonia (gas)

CW

(optional)

AW

NO gas

2 7 9

410

8

14

CW

BFW

Secondary air

Primary air

CW

Condensate

WB

STH

HPsteam

Two azeotropic nitric acid plants:

(left) BP Kln, Cologne, Germany


(right) Namhae Chemical Corporation

operated by HU-CHEMS, Yosu, Korea



16/20

16

8. The Uhde N2O/NO

Xabatement process EnviNOx

Uhde EnviNOxreactor at

Borealis AG, Linz, Austria

Capacity:

1,000 mtpd HNO3(100%)

For more details, please refer to our

brochure: EnviNOx- Climate protection

solutions for nitric acid plants

Nitrous oxide (N20) also known as laugh-

ing 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 mono-

xide and dioxide (NOX) are also reduced.

The Uhde EnviNOxnitrogen oxide abate-

ment process features a tail gas reactor

installed directly upstream of the tail gas

turbine. Uhde has developed specific pro-

cess variants to cater for the range of tem-

peratures found in different nitric acid plants.

The nitrous oxide decomposition variant is

particularly suited to tail gas temperatures

above about 420C. In this variant nitrous

oxide is decomposed to oxygen and nitro-

gen in a first catalyst bed.

N20 N

2 + O

2+ 82 kJ

The tail gas is then mixed with ammonia

before entering the second bed in which

NOXis catalytically reduced to water vapour

and nitrogen:

4NO + 4NH3+O

24N

2+ 6H

2O + 1628 kJ

3NO2+ 4NH

37/2N2+ 6H2O + 1367 kJ

Further removal of nitrous oxide also takes

place in this bed.

For lower temperatures Uhdes solution isbased on the catalytic reduction of nitrous

oxide with hydrocarbons, such as natural

gas, combined with the reduction of NOXby

ammonia. In most situations the removal of

both N2O and NO

Xcan take place in paral-

lel 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

EnviNOxprocess achieves by the removal

of nitrous oxide.

In both EnviNOxprocess variants the tail

gas leaving the reactor has a greatly re-

duced concentration of N2O. The low outlet

NOXconcentration is significantly smaller

than that commonly attained in conventional

DeNOXunits, and results in an invisible stack

plume. The NOXreduction component is

also available without the N2O removal com-

ponent and is applicable to temperatures

between about 200C and 500C.

Uhdes EnviNOx

technology is suitedequally 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 inter-

mediate NO gas, thus eliminating any pos-

sibility of product loss or contamination.


17/20

Ammonia (gas)

Tail gas

turbine

Hydrocarbon

Nitric acid

CW

CW

Process water

Tail gas

Tail gas

1

NO gas

3

2

17

Tail gas

turbine

Nitric acid

CW

CW

Process water

Tail gas

Tail gas

1

NO gas

Ammonia (gas)3

2

1 Absorption

2 Tail gas heating

3 EnviNOx combiningDeN

2O and DeNO

x

functions

1 Absorption

2 Tail gas heating

3 EnviNOx combining

DeN2O and DeNO

x

functions

Flowsheet of tail gas section of a nitric acid plant with EnviNOx reactor

Flowsheet of tail gas section of a nitric acid plant with EnviNOx reactor

(for lower temperature applications)


18/20

18

The dual-pressure nitric acid plant in

Donaldsonville, Louisiana, USA.



19/20

19

9. Typical consumption figures

Table: Comparison of typical consumption gures for steam turbine-driven and inline compressor set nitric acid plants,

per tonne of nitric acid (100%), with a NOXcontent in the tail gas of less than 50 ppm

Plant type Medium-pressure

process

High-pressure

process

Dual-pressure

process

Operatingpressure pabs

Ammonia

Electric power

Platinum,primary losses

with recovery

Cooling water(t =10 K)including waterfor steam turbine condenser

Process water

LP heating steam,8 bar, saturated

HP excess steam,

5.8 bar

284.0 kg

9.0 kWh

0.15 g

0.04 g

100 t

0.3 t

0.05 t

0.76 t

10.0 bar

286.0 kg

13.0 kWh

0.26 g

0.08 g

130 t

0.3 t

0.20 t

0.55 t

4.6/12.0 bar

282.0 kg

8.5 kWh

0.13 g

0.03 g

105 t

0.3 t

0.05 t

0.65 t40 bar, 450 C


20/20

130e/150004/20

12ThyssenKruppUhde/TKprintmedia/PrintedinGermany

ThyssenKrupp Uhde

Friedrich-Uhde-Strasse 15

44141 Dortmund, Germany

Tel.: +49 231 5 47-0 Fax: +49 231 5 47-30 32 www.uhde.eu

uhde nitric acid process brochure

Documents