Nitric acid

TK

A companyof ThyssenKrupp

TechnologiesUhde

Table of contents2

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 19

Page

Don’t settle for less in nitric acidWhether a mono or dual-pressure process

– Uhde applies technologies which meet your specificrequirements, 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 HNO3Mono-high-pressure, Thailand: 210 mtpd HNO3

Azeotropic dual-pressure, Germany: 1,500 mtpd HNO3

1. Company profile

With its highly specialised workforce of more than 4,900 employees and itsinternational network of subsidiaries and branch offices, Uhde, a Dortmund-basedengineering contractor, has, to date, successfully completed over 2,000 projectsthroughout the world.

Uhde’s international reputation has been built on the successful application ofits motto Engineering with ideas to yield cost-effective high-tech solutions for itscustomers. The ever-increasing demands placed upon process and applicationtechnology in the fields of chemical processing, energy and environmental protectionare met through a combination of specialist know-how, comprehensive servicepackages, top-quality engineering and impeccable punctuality.

Uhde’s head office in Dortmund, Germany

3

2. The nitric acid process4

Although the basic chemistry of the nitric acidprocess has not changed in the last hundredyears, today’s highly efficient, compact and envir-onmentally friendly plants have been developedby a process comparable with the advances madein automobile technology in the same period.

BP Köln, Cologne, GermanyCapacity: 1,500 mtpd HNO3 (100%)

The oxidation of ammonia over a platinum cata-lyst to nitrogen oxides, and their absorption inwater to form nitric acid was first carried out in1838 by C.F. Kuhlmann. However, this discoverywas not then commercialised as ammonia wastoo expensive compared with the Chile saltpetreused to manufacture nitric acid in those days.

The Birkeland-Eyde process,invented at the beginning ofthe 20th century, whichinvolves the direct combinationof atmospheric oxygen andnitrogen in an electric arc, wasalso of limited application dueto poor energy utilisation.

The history of the modernnitric acid process really beginsin 1901 when W. Ostwald estab-lished the ammonia oxidationconditions necessary for highnitrogen oxide yields. The firstplants using the Ostwald processwere started up in the firstdecade of the 20th century.Since then many improve-ments have been made byvarious workers. Milestonesinclude the use of larger ammo-nia combustion units employingflat platinum-rhodium gauzes

instead of Ostwald’s rolled up platinum gauzestrip and the recovery of the heat of reaction forsteam raising or electricity generation. Thedevelopment of strong, affordable, corrosionresistant stainless steel materials of constructionmade feasible the absorption of the nitrogenoxides in water under pressure, thus reducing thesize and cost of the absorption equipment, whileprogress in turbo-machinery technology led tothe adoption of the more energy efficient dualpressure process. From the 1920s onwards,advances in the synthesis of ammonia fromhydrogen and atmospheric nitrogen by theHaber-Bosch process have given the Ostwaldroute to nitric acid an additional boost by lower-ing its feedstock costs. Nowadays practically allnitric acid is manufactured by this process.

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

Block diagram ofnitric acid process

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

O2

O2

NH3

O2

HNO3

NO

NO

H2O H2O

H2O

NO2

2 mole 3/4 mole

5/4 mole

1 mole

1 mole

1/2 mole

1 mole

3/2 mole 1 mole

3/2 mole

1/2 mole

Oxidation

Combustion

Absorption

Uses of nitric acid

AN : ammonium nitrate NP : nitrophosphate CN : calcium nitrateCAN : calcium ammonium nitrate UAN : urea ammonium nitrate solution ASN : ammonium sulphate nitrateTDI : toluene diisocyanate MDI : methylene diphenyl diisocyanate

Stoichiometry of nitric acid process

Nitric acid is a strong acid and occurs naturallyonly in a combined state as nitrate salt. As withother industrial inorganic acids, nitric acid ishardly of importance in itself but rather as a keyintermediate in the production of industrial goods.Nowadays around 55 million tonnes a year ofnitric acid of various concentrations are producedworldwide. Approximately 80% of this is used asan intermediate in the production of nitrogenousmineral 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 porousprilled ammonium nitrate for the mining industry,and as an intermediate for the production ofspecial chemicals such as caprolactam or adipicacid. There is a growing demand for azeotropicnitric acid (approximately 68% concentration),which is used as a nitrating agent in the produc-tion of nitrobenzene, dinitrotoluene and otherchemicals. These are further processed to TDIor MDI, and finally used for the production ofpolyurethane. Among the great variety of otherapplications, those most worthy of mention areits use as a chemical in metallurgy, for exampleas an etching and pickling agent for stainlesssteel, and its employment in the manufacture ofdinitrogen tetroxide for rocket fuels.

3. Uhde and nitric acid6

As early as 1905, Dr. Friedrich Uhde, the founderof Uhde GmbH, designed and constructed, incooperation with Prof. Wilhelm Ostwald, a pilotplant for the production of nitric acid by burningammonia with air in the presence of a catalyst.

Since the company’s foundation in 1921, thenumber of plants for the production of weak andconcentrated nitric acid as well as ammoniacombustion units for nitrogen oxide productionand absorption plants for nitrous waste gases,which have been designed, constructed and com-missioned by Uhde under a variety of climaticconditions total some 200.

Uhde thus ranks among the world’s leadingengineering companies engaged in the designand construction of nitric acid plants andammonia combustion units.

The processes have been continually refined inorder to meet ever more stringent requirements,particularly with regard to air pollution controland energy cost constraints.

The plants designed and constructed by Uhdeare characterised by high reliability, profitabilityand on-stream time.

Shutdown periods are now almost entirely limitedto catalyst changes and equipment inspections.

The number of follow-up orders Uhde receivesbears witness to the satisfaction of our customers.

Today, nitric acid is produced exclusively fromammonia oxidised by combustion with air in thepresence of a noble-metal catalyst.

Non-noble-metal catalysts do not play a significant role.

The catalysts used in the process consist of apack of platinum-rhodium gauzes, the numberdepending on the operating pressure and burnerconstruction. The gauzes are produced nowadaysby knitting thin wires, usually with a diameter of60 or 76 µm. Woven gauzes are used only in afew specialised applications.

A platinum recovery system made from palladiumcan easily be installed underneath the platinumcatalyst. Combined catalyst and catchment sys-tems are also available.

Nowadays, it is possible to manufacture catalystgauzes with a diameter of more than 5.5 m. Morethan 1,500 tonnes per day of nitric acid can beproduced from a single burner.

Even larger burners can be manufactured; the upper limit is dictated solely by transportrestrictions and flange machining.

The production of nitric acid takes place in 3 process steps shown by the following mainequations:

1. Ammonia combustion4 NH3 + 5 O2 4 NO + 6 H2O + 905 kJ

2. Oxidation of the nitric oxide2 NO + O2 2 NO2 + 113 kJ

3. Absorption of the nitrogen dioxide in water3 NO2 + H2O 2 HNO3+ NO + 116 kJ*

In practice, these three process steps can becarried out in different ways, resulting in severaldifferent nitric acid processes. Modern nitric acidplants are designed according to the mono-pressure or the dual-pressure process.

Within the group of mono-pressure processes, adistinction is made between the medium-pressureprocess with a 4 - 6 bar abs. operating pressureand the high-pressure process which operatesat 8 - 12 bar abs.

The dual-pressure process employs a mediumpressure of approx 4 - 6 bar abs. for ammoniacombustion and a high pressure of approx. 10 - 12 bar abs. for nitric acid absorption.

The optimum process is selected taking intoaccount the costs of feedstocks and utilities,energy and capital investment as well as localconditions.

In compliance with stringent pollution abatement requirements, it is possible to achievea NOX tail gas content of below 50 ppm.

Furthermore, emissions of nitrous oxide, anunwanted by-product in the ammonia oxidationstep, can be reduced to a minimum by appro-priate 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 anammonia burner.

The photograph shows an ammonia burnerof a nitric acid plant built in 1924 and inoperation until 1965. The throughput was0.1 t of nitrogen per day.

In order to achieve a daily throughput of20 tonnes of nitrogen, 200 of these burnerswere formerly arranged in parallel.

Dual-pressure nitric acid plant: Two ammonia burners

Capacity: 1,850 mtpd HNO3 (100%)corresponding to a burner loadof 430 mtpd of nitrogenAbu Qir, Egypt

4. The Uhde medium-pressure process8

In this process, the air required for burning theammonia is supplied by an uncooled air com-pressor. The compressor set can be designedeither as an inline train configuration or preferablyas a bull gear type with an integrated tail gasturbine.

The operating pressure is governed by the max-imum final pressure obtainable in an uncooledcompressor, i.e. 4 - 5 bar abs. in the case ofradial compressors and 5 - 6 bar abs. with axialflow compressors.

Plant capacities of up to 500 mtpd of nitric acid(100%) can be realised using a single ammoniacombustion unit and one absorption tower. Dueto the process pressure, higher capacities of upto about 1,000 mtpd are feasible if a secondabsorption tower is used.

The medium pressure process is the process ofchoice when maximum recovery of energy isrequired. The air compressor is usually driven bya tail gas expansion turbine and a steam turbine,the steam being generated within the plant. Ifthe credit for exported steam is high then thecompressor train can be driven by a high voltagesynchronous or asynchronous electric motor rather than a steam turbine so that all the steamgenerated can be exported.

With this plant type, it is possible to produceone type of nitric acid with a max. concentrationof 65% or two types of acid with different concen-trations, 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 therequired value by selective catalytic reductionusing a non-noble-metal catalyst and ammoniaas the reducing agent.

The medium-pressure process is characterised bya high overall nitrogen yield of about 95.7% or95.2% in conjunction with the tail gas treatmentprocess, a low platinum consumption and a highsteam export rate.

The catalyst gauzes only need to be changedonce every 6 months due to the low burner load.

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.

9

Ammonia (liquid)

CW

LP steam

CW

Nitric acidproduct

Process water

CW

CW

Tail gas

Secondary air

WB

NO gas

Ammonia (gas)

Tail gasturbine

Steamturbine

Aircompr.

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

Acidcondensate

Flowsheet of a medium-pressure nitric acid plant

1

2

3

4

5

6

7

8

9

10

11

Reactor

Process gas cooler

Tail gas heater 3

Economizer

Cooler condenser & feedwater preheater

Absorption

Bleacher

Tail gas heater 1 & 2

Tail gas reactor

Ammonia evaporation & superheating

Turbine steam condenser

5. The Uhde high-pressure process10

In the high-pressure process, a radial multi-stagecompressor with an intercooler section is usedto compress the process air to a final pressureof 8 - 12 bar abs. Preferably, the bull gear typewith integrated tail gas turbine is selected butalternatively an inline machine can be used.Due to the higher pressure, all equipment andpiping can be of a smaller size and only oneabsorption tower is required.

If lower NOX values are required, an additionalcatalytic tail gas treatment unit can be easilyintegrated. The nitrogen yield attained by thehigh-pressure process is in the order of 94.5%.

For capacities below 100 mtpd, a low capitalinvestment cost may be much more preferableto an optimum recovery of energy.

The arrangement of all equipment is very compactso that the building for the machine set and theburner unit can be kept small, but this does notpose a problem for maintenance work.

This type of plant is always recommended whena quick capital return is desirable.

Plant capacities between 100 mtpd (100%) and1,000 mtpd of nitric acid can be realised.

The achieved acid concentrations of up to 67%are slightly higher than with the medium-pres-sure process. Two or more product streams withdifferent 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.

In such cases, Uhde can offer a greatly simplifiedprocess which does not include tail gas and steamturbines. The heating of the tail gas downstreamof the absorption section is not necessary.Special design concepts for the process gascooler unit, condenser and bleacher reduce thecost even further.

The operating pressure required by such a pro-cess depends on the maximum permissible NOXcontent in the tail gas. If the specified NOX limit isbelow 200 ppm, a pressure of at least 7 bar abs.must be considered, depending on the coolingwater temperature.

Lower NOX values of less than 50 ppm can beachieved, if required, by integrating a catalytictail gas treatment process. Uhde also provides asimilar process without the ammonia evaporationand heat recovery units for recovering acid fromthe waste gas in, for example, adipic acid plants.

Two high-pressure nitric acid plants:

(left) Thai Nitrate Company, Rayong, ThailandCapacity: 210 mtpd HNO3 (100%)

(right) Enaex S.A., Mejillones, ChileCapacity: 925 mtpd HNO3 (100%)

11

Tail gasturbine

Steamturbine

Aircompr.

Air

Tail gas

CW

CW

Ammonia (liquid)

CW

LP steam

Acidcondensate

Nitric acidproduct

CW

CW

Process water

Tail gas

LPsteam

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

Flowsheet of a high-pressure nitric acid plant

1

2

3

4

5

6

7

8

9

10

11

12

Reactor

Process gas cooler

Tail gas heater 3

Economizer

Cooler condenser & feedwater preheater

Absorption

Bleacher

Tail gas heater 1 & 2

Tail gas reactor

Ammonia evaporator & superheater

Turbine steam condenser

Air intercooler

6. The Uhde dual-pressure process12

The dual-pressure process was developed toaccommodate ever more stringent environmen-tal pollution control requirements.

The process air is compressed to a final pressureof 4 - 6 bar abs.

The NO gas from the ammonia combustion unit iscooled in a heat exchanger train, producing steamand preheating tail gas, and then compressed to

Two dual-pressure nitric acid plants:

(left) Abu Qir Fertilizers and Chemical Ind. Co., Abu Qir, EgyptCapacity: 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, AustriaCapacity: 1,000 mtpd HNO3 (100%)NOX in tail gas: less than 10 ppm as a result of the Uhde N2O/NOXabatement process – EnviNOx®

either as an inline-shaft set or optionally as abull gear type unit with integrated air/NOX com-pression and tail gas expander stages. The inlinemachine concept is favourable in the case ofhigher plant capacities in excess of 1,100 mtpdup to 2,200 mtpd or if an increased energy exportis required. For plant capacities in excess of1,500 mtpd the ammonia combustion and pro-cess gas cooler unit needs only to be duplicated.

10 - 12 bar abs in the NOX compressor. The finalpressure is selected so as to ensure that theabsorption section is optimised for the specifiedNOX content of the tail gas and that the com-pressors, driven by a steam turbine, can beoperated using only the steam generated in theprocess gas cooler unit while ensuring thatsome excess steam will always be available inorder to guarantee steady operating conditionsat all times. Alternatively the compressor set canbe driven by either a high voltage asynchronousor synchronous motor and the steam generatedcan be exported. The dual-pressure processcombines in an economical way the advantagesof the low pressure in the combustion sectionand the high pressure in the absorption section.Plant capacities of up to 1,500 mtpd of nitricacid (100%) can be achieved in a single-trainconfiguration. The machine set can be designed

The nitrogen yield in a plant of this type is morethan 96% with a NOX content in the untreated tailgas of less than 150 ppm (vol.) being possible.The NOX content may be further reduced to lessthan 50 ppm, if required, by selective catalyticreduction using a non-noble-metal catalyst andammonia as the reducing agent.

Acid concentrations of more than 68% can beachieved. (See also chapter 7: The Uhde azeo-tropic nitric acid process.) Two or more productstreams with different concentrations are alsopossible. In addition, external streams of weaknitric acid (various concentrations) can be pro-cessed if required.

Due to the low burner load, the catalyst gauzescan remain in the burner for an operating periodof 6 to 8 months or longer before being partiallyor completely replaced.

13

Tail gasturbine

Aircompr.

NOx

compr.

Steamturbine

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

Acidcondensate

WB

STH

HPsteam

AW

Flowsheet of a dual-pressure nitric acid plant

1

2

3

4

5

6

7

8

9

10

11

12

13

14

Reactor

Process gas cooler

Tail gas heater 3

Economizer

Cooler condenser 1 & feedwater preheater

Tail gas heater 2

Cooler condenser 2

Absorption

Tail gas heater 1

Tail gas reactor

Ammonia evaporation & superheating

Ammonia evaporation

Bleacher

Turbine steam condenser

7. The Uhde azeotropic nitric acid process14

Azeotropic nitric acid with an elevated concentra-tion of 68% by weight can replace concentratednitric acid in some applications such as nitrations.Due to increased market demand, Uhde hasdeveloped an enhanced process for the reliableproduction of azeotropic nitric acid without anyfurther weak nitric acid co-production. The basicprocess design is mainly an extended dual-pressure process.

To satisfy the overall water balance, it is mandatory at some locations to eliminate thewater carried with the incoming air taken in bythe air compressor. The necessary measuresdepend on climatic conditions, in particular airhumidity and temperature. In the case of extremeconditions the installation of an additional aircooler/condenser operating partly with chilledwater is recommended. Normally in the Uhdedual-pressure process, there is an extra chilledwater circuit linked to the ammonia evaporation.This uses to a large extent the ammonia evap-oration heat, especially in the absorption section,in order to establish the required acid strengthand the NOX level at the absorption outlet. It isalso possible to provide an external chilled waterset. However, this solution is expensive andenergy consuming and would only be consideredby Uhde if all other measures prove insufficient.

The design of the absorption column is of particular importance especially for producingazeotropic acid. At Uhde a sophisticated computerprogram is used to predict the exact limits of acidconcentration, heat loads, NOX in tail gas, etc.

Another important feature of the Uhde azeotropicnitric acid process is the drying section for thesecondary air. This air is used for strippingnitrous gases from the crude acid leaving theabsorption unit. During this stripping process,the humidity of the secondary air dilutes theproduct acid. The water vapour in the secondaryair is absorbed by a small circulating stream ofproduct acid in a special drying section withinthe bleacher.

Taking the above into consideration, Uhde isable to offer individual customers tailor-madesolutions for azeotropic nitric acid plants.

The equipment shown as an example is fully inte-grated in Uhde´s compact bull gear concept, whichis applicable for capacities up to 1,100 mtpd.Above this capacity an inline machine set isemployed as shown on page 13. The first pressurelevel delivered by the air compressor is advanta-geous for the ammonia combustion section, whilethe final pressure delivered by the NOX compres-sor promotes absorption and the formation ofazeotropic acid.

Important process features for the production of azeotropic acid are, in addition to sufficientabsorption pressure and cooling, the overall waterbalance of the plant. Furthermore, the ratio ofdinitrogen tetroxide to nitric oxide in the processgas at the absorption tower inlet has to be ad-justed to a level that is in equilibrium with theacid concentration required.

Two azeotropic nitric acid plants:

(left) BP Köln, Cologne, GermanyCapacity: 1,500 mtpd HNO3 (100%)

(right) Namhae Chemical Corporation operated by HU-CHEMS, Yosu, KoreaCapacity: 1,150 mtpd HNO3 (100%)

15

NOx

compr.

Tail gasturbine

Steamturbine

Aircompr.

HP steamAir

CW

Ammonia (liquid)

LP steam

CW

AW

LP steam

Acidcondensate

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 gas2 7 9

4108

14

CW

BFW

Secondary air

Primary air

CW

Condensate

WB

STH

HPsteam

Flowsheet of an azeotropic nitric acid plant

Reactor

Process gas cooler

Tail gas heater 3

Economizer

Cooler condenser 1 & feedwater preheater

Tail gas heater 2

Cooler condenser 2

Absorption

Tail gas heater 1

Tail gas reactor

Ammonia evaporation & superheating

Ammonia evaporation

Bleacher

Turbine steam condenser

Air condenser (optional)

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

8. The Uhde N2O/NOX abatement process – EnviNOx®16

Nitrous oxide (N20) – also known as “laughinggas” - is formed in the ammonia burner as anunwanted by-product. Depending on the perform-ance of this burner around 1% to 2% of theammonia feed is lost in this way, with a similaramount being lost due to the formation of nitrogen.The nitrous oxide passes through the rest of thenitric acid plant unchanged and is discharged toatmosphere with the tail gas.

Neglected for many years, nitrous oxide emissionsare now coming under scrutiny by regulators sincenitrous oxide is a potent greenhouse gas some300 times stronger than carbon dioxide and isimplicated in the destruction of the ozone layer.

Uhde, having at an early stage recognised thistrend, have developed a catalyst and a process forthe lowering of nitrous oxide emissions from nitricacid plants. An added bonus is that emissionsof nitrogen monoxide and dioxide (NOX) are alsoreduced.

The Uhde EnviNOx® nitrogen oxide abatementprocess features a tail gas reactor installeddirectly upstream of the tail gas turbine. Uhdehas developed specific process variants to caterfor the range of temperatures found in differentnitric acid plants. The nitrous oxide decompositionvariant is particularly suited to tail gas tempera-tures above about 420°C. In this variant nitrousoxide is decomposed to oxygen and nitrogen ina first catalyst bed.

N20 N2 + 1/2 O2 + 82 kJ

The tail gas is then mixed with ammonia beforeentering the second bed in which NOX is cata-lytically reduced to water vapour and nitrogen:

4NO + 4NH3 +O2 4N2 + 6H2O + 1628 kJ

3NO2 + 4NH37/2N2 + 6H2O + 1367 kJ

Further removal of nitrous oxide also takesplace in this bed.

For lower temperatures Uhde’s solution is basedon the catalytic reduction of nitrous oxide withhydrocarbons, such as natural gas, combinedwith the reduction of NOX by ammonia. In mostsituations the removal of both N2O and NOX cantake place in parallel in a single catalyst bed. Thequantity of the greenhouse gas carbon dioxide,that is produced due to the use of hydrocarbonsis insignificant in comparison to the amount ofgreenhouse gas emission reduction that theEnviNOx® process achieves by the removal ofnitrous oxide.

In both EnviNOx® process variants the tail gasleaving the reactor has a greatly reduced con-centration of N2O. The low outlet NOX concen-tration is significantly smaller than that commonlyattained in conventional DeNOX units, and resultsin an invisible stack plume. The NOX reductioncomponent is also available without the N2Oremoval component and is applicable to tempera-tures between about 200°C and 500°C.

Uhde’s EnviNOx® technology is suited equallywell to retrofits or to new plants. As it is anend-of-pipe process there is no contact with theproduct nitric acid or intermediate NO gas, thuseliminating any possibility of product loss orcontamination.

Tail gasturbine

Nitric acid

CW

CW

Process water

Tail gas

Tail gas

1

NO gas

Ammonia (gas)3

2

Ammonia (gas)

Tail gasturbine

Hydrocarbon

Nitric acid

CW

CW

Process water

Tail gas

Tail gas

1

NO gas

3

2

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

1

2

3

Absorption

Tail gas heating

EnviNOx® reactor

17

Uhde EnviNOx® reactor at AMI Agrolinz Melamine International, Linz, AustriaCapacity: 1,000 mtpd HNO3 (100%)

For more details, please refer to our brochure: EnviNOx® - Climate protection solutions for nitric acid plants

Flowsheet of tail gas section of a nitric acid plant with EnviNOx® reactor (for lower temperature applications)

9. Typical consumption figures18

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

The dual-pressure nitric acid plant inDonaldsonville, Louisiana, USA.Capacity: 870 mtpd HNO3 (100%)

Plant type Medium- High- Dual-pressure pressure pressureprocess process process

Operating 5.8 bar 10.0 bar 4.6/12.0 barpressure pabs

Ammonia 284.0 kg 286.0 kg 282.0 kg

Electric power 9.0 kWh 13.0 kWh 8.5 kWh

Platinum, 0.15 g 0.26 g 0.13 gprimary losses

with recovery 0.04 g 0.08 g 0.03 g

Cooling water 100 t 130 t 105 t(∆t =10 K)including water

for steam turbine condenser

Process water 0.3 t 0.3 t 0.3 t

LP heating steam, 0.05 t 0.20 t 0.05 t8 bar, saturated

HP excess steam, 0.76 t 0.55 t 0.65 t40 bar, 450 ∞C

10. References 19

Dual-pressure nitric acid plantsBASF, Antwerp, Belgium

Capacities: 550 and 2 x 945 mtpd HNO3 (100%) NOXin tail gas: less than 100 ppm as a result ofthe catalytic tail gas treatment process

Year of Client Location Pressure in Acid CapacityCommissioning Combustion Absorption conc. mtpd HNO3

bar abs. bar abs. % 100%

2009 Ferrostaal AG Point Lisas 4.2 11.0 60 1,518Trinidad and Tobago

2005 Rashtriya Chemicals & Mumbai 7.5 7.5 60 352Fertilizers Ltd. India

2003 Namhae Chemical Corporation Yosu 4.6 12.0 67 1,150operated by HU-CHEMS Korea

2001 BP Köln GmbH Cologne 4.6 12.0 68.25 1,500Germany

2001 Radici Chimica GmbH Zeitz 10.0 10.0 65 250Germany

2001 ACE Pressureweld Singapore 4.4 4.4 60 12

2000 Queensland Nitrates Pty Ltd Moura 10.0 10.0 60 405Australia

1999 Enaex S.A. Mejillones 10.0 10.0 60 925Chile

1999 Namhae Chemical Corporation Yosu 10.0 10.0 65 300operated by HU-CHEMS Korea

1998 SKW Stickstoffwerke Wittenberg 5.6 5.6 62 350/500*Piesteritz GmbH Germany

1998 CF Industries Inc. Donaldsonville, 4.6 11.0 57.5 870Louisiana/USA

* Capacity of ammonia combustion is equivalent to the higher figure.

Fl 1

30e/

1500

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/200

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