Ammonia

A companyof ThyssenKrupp

TechnologiesUhde

Thys

senK

rupp

Table of contents2

1. Company profile 3

2. Uhde’s ammonia experience 5

3. The Uhde ammonia process 7

3.1 Steam reforming 8

3.2 CO2 removal 10

3.3 Ammonia synthesis 11

3.4 Steam system 12

3.5 Concept variants 13

3.6 The Uhde Dual-Pressure Process 14

4. Uhde proprietary equipment designs 16

4.1 The primary reformer with a cold outlet manifold system 17

4.2 The secondary reformer 20

4.3 Process gas cooling train downstream of the secondary reformer 21

4.4 Ammonia converter and waste heat recovery 22

4.5 Production and Consumption Figures per Metric Ton of Ammonia 25

5. Services for our customers 26

6. Recent references 27

Page

Ammonia technology has evolvedEvolution has brought perfect proportion for a new era in

ammonia technology. A new 4,000 plus mtpd plant design fromthe world-leading ammonia partnership between Uhde and

Johnson Matthey Catalysts. The Uhde Dual-Pressure Processminimises both compression requirements and equipment

dimensions. Based on fully-proven, dependable equipment, itoffers total reliability with no risks or surprises.

Are you looking for cost-effective investment and operationthrough economies of scale?

Then see page 14.

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-basedengineering contractor, has, to date, successfully completed over 2,000 projectsthroughout 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 itscustomers. The ever-increasing demands placed upon process and application technology in the fields of chemical processing, energy and environmental protectionare met through a combination of specialist know-how, comprehensive service packages, topquality engineering and impeccable punctuality.

4

Process flow sheet of Uhde’s first ammonia plant in Herne, Germany, completed in 1928

Ammonia plant in fertiliser complex in Tecen, Turkmenistan Capacities: 600 mtpd of ammonia

1,050 mtpd of urea synthesis1,050 mtpd granulation unit

2. Uhde’s ammonia experience 5

Ever since the company was established in1921, Uhde has been involved in the designand construction of ammonia plants and hasplayed a leading role in the development ofammonia technology. As far back as 1928, thefirst ammonia plant to use an Uhde proprietaryprocess went on-stream at the site of the Mont-Cenis coal mine at Herne-Sodingen. The planthad an output of 100 mtpd of ammonia andcomprised four reactors with a capacity of25 mtpd each, the loop operating at a pressureof 100 bar.

The fact that the first Uhde-engineered ammoniareactors were equipped with an internal heatexchanger and a synthesis loop with an integratedtwo-stage refrigeration unit deserves a specialmention. Unfortunately, this efficient system wassoon considered outdated, and it was not untilthe seventies that these design principles weretaken up again.

Rising energy prices have posed an increasingchallenge for ammonia plant designers since thisperiod. As early as 1968, Uhde took up thechallenge and engineered a plant with an energyconsumption of only 7.8 Gcal per tonne ofammonia.

This natural gas-based plant with a capacity of880 mtpd incorporated the following essentialelements for reducing energy consumption:

• Maximum heat recovery from the primaryreformer flue gas by cooling it to 135°C atthe stack inlet.

• Preheating of the combustion air for theprimary reformer.

• Generation of 125 bar steam from processwaste heat downstream of the secondaryreformer and in the ammonia synthesis unit.

• High-pressure steam superheating with wasteprocess heat downstream of the secondaryreformer.

• Three-bed ammonia reactor with heatexchangers between catalyst beds.

All subsequent ammonia plants designed by Uhde have incorporated most of these low-energy features.

In recent years, ammonia plant technology hasundergone radical developments in terms ofboth design and equipment. In order to improveplant efficiency, efforts have had to be focusedon reducing power consumption, improvingprocess heat recovery, minimising stack lossesand cutting energy consumption for CO2 removal.

Uhde’s objective of making a substantial improve-ment in energy efficiency has relied heavily onexperience and involved a broad spectrum oftechnical expertise including a technical reviewof process design, engineering design, researchand development and the evaluation of operat-ing data. Equally important has been theenhancement of plant operability and reliability.Hence, much attention has been paid to pastsuccessful experience and proven energy-savingfeatures.

In 1998, Uhde joined forces with Synetix, nowJohnson Matthey Catalysts (JMCatalysts), to further improve the Uhde ammonia process.This partnership builds on the traditional strengthsof the two companies and takes advantage ofJM Catalysts know-how in catalysis, ammoniaplant operation and support services togetherwith Uhde’s experience in design, engineeringand project execution. The partnership allowsstrong collaboration between JM Catalysts andUhde engineers so that the Uhde ammoniaprocess can be further optimised to take bestadvantage of the latest high-performance cata-lysts from JM Catalysts, thus improving efficiencyand lowering cost.

The most recent successful implementations ofthe Uhde ammonia process include a plant inTurkmenistan with a capacity of 600 mtpd, a2,000 mtpd plant for Qatar Fertiliser Co. (QAFCO)in Mesaieed, Qatar, and five 1,200 mtpd plantsin Egypt, where three more 1,200 mtpd plantsbased on the Uhde ammonia process are alsounder construction.

A new milestone in ammonia technology hasnow been achieved with the plant built for SaudiArabian Fertilizer Company (SAFCO) in Al Jubail,Saudi Arabia. It is the first plant to be based onthe "Uhde Dual Pressure Process" and, with asingle-train capacity of 3,300 mtpd, it is by farthe world's largest ammonia plant. It has beenin operation since 2006. A second plant of thistype is now under construction in Ras As Zawr,Saudi Arabia.

6

3. The Uhde ammonia process 7

The adjacent block diagram of an Uhde ammo-nia plant shows the conventional sequence ofprocess steps that form the basis of most present-day ammonia processes. However,ammonia processes cannot be judged solely onthe basis of a block diagram. A more detailedscrutiny of the facts and figures shows that whatappears to be a conventional set-up is in fact amost up-to-date ammonia plant concept.

The total consumption figure (feed + fuel + elec-tric power) per metric ton of ammonia producedis in the range of 6.6 to 7.2 Gcal (27.6 - 30.1 GJ),depending on local conditions (e.g. coolingwater temperature) and project-specific require-ments (such as the natural gas price, etc.).

The following process areas have undergonemajor modifications in order to achieve thesefigures:

• The steam reforming section including itswaste heat recovery system.

• The CO2 removal unit.

• The ammonia synthesis unit.

Assuming the reader to be familiar with thefundamentals of ammonia technology, attentionin the following sections has been restricted tothose aspects specific to the Uhde low-energyconcept.

1,500 mtpd ammoniaplant and fertiliser complex,Saskferco, Canada

Desulphurisation

Primary reformer

Secondary reformer

CO shift

CO2 removal

Methanation

NH3 synthesis

H2 recovery

Refrigeration

Natural gas feed

Fuel Process steam

Process air

Syngas compressor

H2 to syngas compressor

Combustionair

HP steamsuperheated

BFW

CO2

HP steam tosuperheater

NH3

Product

Fuel

Block diagram of an Uhde ammonia plant

3.1 Steam reforming8

The following modifications to conventionalplant designs have contributed to improvementsin overall efficiency:

• Shift of part of the reforming reaction fromthe primary to the secondary reformer as aresult of the following measure:

Installation of a purge gas recovery unit, bymeans of which hydrogen is recycled to thesuction side of the syngas compressor,thereby allowing operation of the secondaryreformer with excess air while the hydrogen-to-nitrogen ratio of the make-up gas is keptclose to 3:1.

• Preheating of the process air for the secondary reformer to a higher temperature (540°C).Shifting part of the reaction to the secondaryreformer leads to lower operating tempera-tures in the primary reformer and therefore tofuel savings.

• Optimum use of the reduced primary reformerload is achieved by increasing the reformerpressure to about 40 bar whilst maintainingthe estimated lifetime of the reformer tubes at100,000 hours. This step entails a reduction inoverall energy consumption as the aggregatepower required for the compressors is reduced.

• Increase in the feed/steam mixture preheattemperature. This reduces the firingrequirements in the primary reformer byshifting the heat transfer duty from theradiant section to the convection section.

• Decrease in the steam-to-carbon ratio to 3.0.This includes an adequate safety marginagainst the formation of carbon deposits onthe primary reformer catalyst. Reducing theadmixture of steam to the feed results in lessheat being absorbed in the primary reformerradiant section and therefore lower fuelconsumption. Nevertheless, the steam-to-gasratio is high enough to minimise by-productformation in the HT shift through the use ofcommercially proven catalysts.

The process data of the reforming section aresummarised below:

Steam/carbon ratio 3.0

Feed/steam, primary reformer inlet °C 530 - 580

Pressure, primary reformer exit bar 39 - 43

Methane, primary reformer exit vol.% 10 - 13

Methane, secondary reformer exit vol.% 0.3 - 0.6

Process air temperature °C 520 - 600

Combustion air temperature °C 250 - 440

125 bar steam, superheated °C 530 - 540

Stack temperature °C 120 - 180

Primary and secondary reformerof the AFC ammonia plant in Egypt.

➀ ➄➁ ➂ ➃

Fuel

HP steam

Feed

Desulphurisation

MP steam

Process air

Combustion air

Reformer

Secondaryreformer

Steam drum

LT shift HT shift

HP steam

BFW

Process gas

BFW

Convection bank coils

➀ HP steam superheater

➁ Feed/steam preheater

➂ Process air preheater

➃ Feed preheater

➄ Combustion air preheater

HP steamsuperheater

Processgas cooler

9

Steam reformingand CO shift

Special mention should be made of an essentialitem of equipment in the steam reforming section:the steam superheater, located in the processtrain downstream of the secondary reformer.

In a low-energy plant, the objective is to recoveras much heat as possible from the convectionsection for direct process use, thereby reducingthe fuel requirement. This reduces the heatavailable in the convection section for super-heating HP steam. The balance of the energyrequired for this purpose is therefore recoveredin the superheater downstream of the secondaryreformer. The duty of this superheater is in therange of 15 to 40% of the heat availablebetween secondary reformer exit and HT shiftinlet, depending on the process parametersselected.

The lower the consumption figure, the moreprocess gas heat is utilised to superheat the HPsteam, whereas the total HP steam generated isreduced. In other words: fuel savings also reducethe net energy export.

A superheater of this type was installed by Uhdefor the first time in the Gewerkschaft Victor plant,which went on stream in 1970. This same designconfiguration was also used for the CIL plant inCanada (on-stream since 1985) and is now the

superheater of choice in all of the ammoniaplants recently built by Uhde. On the one hand,this arrangement provides the necessaryflexibility to adapt the plant to any given set ofprocess requirements, and on the other, itenables the steam system to operate safelyunder any normal, or abnormal, operatingconditions. An internal bypass in the evaporationsection permits the shifting of heat transferduty between the evaporator and the steamsuperheater. In normal operation, the internalbypass remains partially open. By closing it, thegas temperature at the superheater inlet can bereduced, thus increasing steam generation. Thisis important in overcoming partial plant failures,e.g. in the case of a loss of steam production inthe ammonia synthesis section.

Process gas

LP steam

Fuel

CO2 (high purity)

Stripper

Flashvessel

C.W. C.W.

Absorber

Pure

gas

Various chemical and physical absorptionsystems are available for the removal of CO2,e.g. aMDEA®, Benfield, Amine Guard and Selexol.Uhde has used all these processes in the pastand has the experience of many years of com-mercial operation. The lowest energy consump-tion is achieved using the activated aMDEA®

process licensed by BASF. The key to these energysavings is that the solution is primarily regeneratedby flashing rather than steam stripping.

The activated aMDEA® process uses a solutionof N-methyldiethanolamine and water with aspecial activator as the solvent. As the aMDEA®

solution isotherms for CO2 are between those of a typical chemical solvent and a physicalsolvent, this process combines the benefits ofboth chemical and physical CO2 removalprocesses.

The design selected incorporates a two-stageabsorber. Most of the CO2 is removed in thelower part using a semi-lean solution that hasbeen regenerated in a two-stage flash loop

without any need for stripping energy. Finalpurification to the ppm range then takes place inthe upper part of the absorber with a relativelysmall portion of the total circulating solvent. It isonly this portion that has to be thermally regen-erated by a stripping process in a reboiling col-umn. This process scheme permits a reductionin the specific energy consumption of the CO2recovery system to 1,340 kJ/Nm3 of CO2(13,000 BTU/lb mole of CO2).

In addition, the process offers the followingadvantages:

• High CO2 recovery rate (> 96%) andCO2 purity (> 99% by volume).

• No need for corrosion inhibitors as thesolution is not corrosive to carbon steel.

• Minimisation of solution losses becauseaMDEA® has a low vapour pressure and doesnot degrade during operation. No reclaimingof the solution is required.

• No toxic solvents.

• No crystallisation problems.

3.2 CO2 removal10

aMDEA® CO2removal system

HP steam

BFW

Make-up gas

C.W.

Ammonia converter

Syngas compressor

NH3

Refrigeration

(liquid)

Purge

The most fundamental improvements to earlierdesigns have been effected in the ammoniasynthesis unit.

The main feature of this unit is its highconversion rate which is achieved by a largecatalyst volume. In order to minimise reactorsize and cost while keeping the pressure droplow, the large catalyst volume requires:

• The use of small grain-size catalyst.

• Application of the radial-flow concept in the ammonia reactor.

Uhde has always advocated three-bed reactorswith high ammonia conversion rates per pass.Therefore, the Uhde ammonia synthesis unit isbased on a three-bed reactor system, each bedwith a radial flow. A high-conversion synthesisloop offers considerable advantages since therecycle gas quantity is considerably reduced and,consequently, power requirements for the circu-lator are lower and heat exchanger surfacessmaller. Refrigeration requirements also decreaseoverproportionately because most of the ammo-nia produced is condensed upstream of the loopchiller.

Studies on innovative high-activity precious-met-albased catalysts have revealed that no economicadvantage can be gained through their use inview of the uncertainty of future prices for theprecious metals required. Furthermore, due tothe different physical properties operational pro-blems can be expected.

For maximum reliability and cost-effectivenessUhde therefore uses only well-proven magnetite-based catalysts in all three beds. The first of thethree beds will typically be filled with prereducedcatalyst to accelerate the initial start-up.

Depending on the site-specific and project-specificconditions, the three catalyst beds are arrangedin either one or two ammonia reactors.

Designs with one ammonia reactor and one wasteheat boiler cannot optimally exploit the reactionheat for the generation of high-pressure steam.However, optimum heat recovery can beachieved if an additional waste heat boiler isintroduced between the second and third bed.

This arrangement improves the gas-sidetemperature of the boilers and provides anadditional advantage in that it permits a higherboiler feed water temperature at the boiler inlet,which means that the preheating of the boilerfeed water can be enhanced by using the low-level heat available in other plant sections, forexample downstream of the LT shift.

The effect of a two-boiler system on high-pressuresteam generation is significant:it is increased from 1.1 to 1.5 t/t of ammonia.The process parameters of the synthesis loopdesign are shown below:

H2/N2 ratio, methanation exit 2.95

Synthesis loop pressure bar 140 - 210

NH3 reactor inlet vol.% 3 - 5

NH3 reactor outlet vol.% 20 - 25

HP steam generation t/t NH3 1.1 - 1.5

Number of reactors 1 or 2

11

Ammonia synthesis

3.3 Ammonia synthesis

3.4 Steam system12

Process gas Flue gas

HP steam header

112 bar, 530 °CTurbine syngas compressor

Turbine process aircompressor and alternator

C.W. Surface condenser

Condensate pump

Condensatetreatment

MP steam header

415 °C, 49 bar

Process gas

Process gas

Process steam

LP steam consumers

LP steam header

BFW pump

Steam drum125 bar

NH3

synthesis

BFW

Condensate

Process gas

Steam system

The diagram shows the heat management systemunderlying Uhde’s low-energy ammonia plantconcept, the essence of which is the optimumutilisation of process waste heat for the generationof superheated high-pressure steam.

High-pressure boiler feed water is heated in afirst step downstream of the LT shift; the streamis then split into two, one part-stream going tothe ammonia synthesis unit and the other to theHT shift for further preheating.

High-pressure steam is only generated fromprocess waste heat at two locations:

• Downstream of the secondary reformer.

• In the ammonia synthesis unit.

Superheating of high-pressure steam takesplace downstream of the secondary reformerand in the primary reformer convection bank.

The superheated steam is expanded in the high-pressure part of the syngas compressor turbineand fed to the medium-pressure system.

Medium-pressure steam at 49 bar, 415°C, is used as process steam or for the followingequipment:

• Condensing turbine driving the syngas compressor.

• Condensing turbine driving the process aircompressor/alternator.

• Back-pressure turbine driving the boiler feedwater pump.

Depending on the plant requirements, the processair compressor turbine or the refrigeration com-pressor turbine can be fed with HP-steam. Allother machines are driven by electric motors.

133.5 Concept variants

The plant concept presented here constitutesthe basis of Uhde’s low-energy ammonia tech-nology. The design can easily be adapted to suitthe specific conditions of any project. Variationsmay range from minor process modifications(e.g. in the steam system) to the replacement ofentire units (e.g. substitution of the aMDEA® CO2

removal system for an Amine Guard, Benfield orSelexol unit).

Moreover, gas turbines can be incorporated as acompressor driver (e.g. process air compressor)or alternator driver. The exhaust gases can beutilised as high preheat combustion air for theprimary reformer or to generate export steam ina heat recovery steam generator (HRSG).

3.6 The Uhde Dual-Pressure Process14

Chemical plant capacities have for a long timebeen taking on ever greater dimensions. Thereason lies in the reduction of the specificproduction costs through economies of scale.More than ever before, the plant constructionsector is facing the challenge of exploiting thisadvantage while at the same time continuing toemploy proven technologies and equipment.

Uhde and Johnson Matthey Catalysts have risento this challenge and developed a processbased on existing technology which now enablesammonia plants to produce very large capacities.This new process (see flowsheet) delivers acapacity of 3,300 mtpd using well-tried andtested equipment. It also provides the basis foreven larger plants (e.g. 4,000 - 5,000 mtpd).

The first plant based on this process is theSAFCO IV ammonia plant in Al-Jubail, SaudiArabia. With a capacity of 3,300 mtpd it isby far the largest ammonia plant worldwide.The plant has been in operation since 2006.Engineering for the next plant using the dual-pressure process is ongoing.

The key innovation in Uhde's new dual-pressureammonia process is an additional medium-pressure once-through ammonia synthesis connected in series with the conventional high-pressure ammonia synthesis loop as follows:

1. The once-through ammonia synthesis involvesthe compression of the make-up gas in a two-stage inter-cooled compressor. This is the low-pressure (LP) casing of the syngas compressor. The pressure at the discharge of the compressor is about 110 bar. At this pressure the three-bed, inter-cooled, once-through converter produces approximately one third of the total ammonia output. The syngas-ammonia mixture leaving this con-verter is cooled and 85% of the ammonia produced is separated from the gas as liquid.

2. The remaining syngas is then compressed in the high-pressure (HP) casing of the syngas compressor to the operating pressure of the ammonia synthesis loop (up to 210 bar). Sincethe syngas has been cooled down the HP casing can operate at a much lower tem-perature than in the conventional ammmoniaprocess. The high synthesis loop pressure is achieved through a combination of the chilledsecond casing of the syngas compressor anda slightly elevated front-end pressure. In this conventional ammonia synthesis loop the re-maining two thirds of the total ammonia is produced.

Secondammoniaconverter

LPcasing

Firstammoniaconverter

HPsteam

HPsteam

~ 110 bar

NH3 chiller

NH3chiller

CW

CW

Note: Molecularsieves (dryers)not shown

H2O

Make-up gas from front-end

Low pressure section

High pressure section

15

Technology highlights

• Well-proven magnetite-based catalysts canbe used in all stages of the new process.

• Energy efficiency is improved by 4% comparedto the conventional Uhde process.

• A high conversion rate in the high-pressuresynthesis loop combined with the reducedproduction requirement results in reducedpiping sizes in the high-pressure loop.Standard piping can be used for capacitiesof 4,000 mtpd and more.

• The syngas compressor of a 3,300 mtpddual-pressure plant is the same size as that incurrent 2,000 mtpd ammonia plants; severalreference compressors are in operation.

• Only 2/3 of the hydrogen recovered fromthe purge gas has to be recompressed tothe loop; 1/3 is converted to ammonia in theonce-through synthesis.

• The process design is extremely flexiblewith a large number of process parametersavailable to optimise the use of catalyst andmachinery.

• It is now possible to achieve a synthesiscapacity of about 3,300 mtpd of ammoniausing conventional equipment and catalyststhat have proved to be reliable and efficientin existing plants.

• There are no major deviations from provenprocess conditions.

• The front-end of the plant is very similar tothe current Uhde design except that itoperates at a pressure of about 3 bar higher,a process condition which is well withinUhde’s proven long-term design andoperating experience.

HPcasing

Once-throughammonia converters

Off-gas

PGR unit

CW

Purge gas recovery

NH3 chiller NH3

AmmoniafromHP loop

HPsteam

NH3 chiller

Ammonia from once-through conversion

~ 210 bar

NH3

4. Uhde proprietary equipment designs16

A good process alone is not sufficient.

It is at least as important to have proven andreliable designs for critical items of equipment.Only the two combined will make a good plant.

Uhde has pioneered the development ofessential items of equipment for ammoniaplants and is one of the leading contractors inthis field. These developments include:

• Primary reformer with a cold outlet manifoldsystem.

• Secondary reformer.

• Process gas cooling train downstream of thesecondary reformer for- generating high-pressure steam- superheating high-pressure steam.

• High-efficiency ammonia converter systemwith three beds, indirect heat exchange andradial flow.

• Ammonia synthesis waste heat boiler.

Uhde holds, or has pending, a number ofpatents for such equipment and has grantednumerous manufacturing and marketinglicences to equipment manufacturers andchemical engineering contractors.

Cold outlet manifold system

Inlet manifold

Burners

Reformer

tubes

Cold outlet

manifold system

Process air

Water jacket

Refractory

Catalyst bed

Gas outlet

Reformer radiant section, outlet manifoldsystem and secondary reformer

Primary reformer

Secondary reformer

4.1 The primary reformer with a coldoutlet manifold system

17

The primary reformer is a furnace in which amultiplicity of tubes filled with catalyst areheated by burning fuel. The process gas tem-perature required at the outlet of the catalyst-filled tubes is about 800°C at a pressure ofapproximately 45 bar. Inevitably, the service lifeof components such as the reformer tubes islimited. Material deterioration occurs through thecombined effects of creep, alternating thermaland mechanical stresses, external and internaloxidation and carburisation.

Consequently, the furnace designer is facedwith two main tasks:

• Firstly, to minimise the number of com-ponents subject to wear and tear due to thecombined effects of high temperatures andpressures.

• Secondly, to allow as smooth and safe anoperation as possible.

The following main features show Uhde’sapproach to fulfilling the above requirements:

• Top-firing for an optimum uniformity of thetube skin temperature profile.

• Small number of burners (in comparison witha side-fired reformer).

• Internally-insulated cold outlet manifoldsystem made from carbon steel and locatedexternally under the reformer bottom.

• Internally-insulated reformer tube-to-manifoldconnection which operates at moderatetemperatures.

• Each tube row is connected to a separateoutlet manifold.

Advantages of the Uhde reformer:

• No high-alloy outlet pigtails and/or outlet manifolds or risers which work at creepconditions.

• Minimum number of components exposed to the severe process conditions.

• Uniform temperature profile over the entirelength of the reformer tube with the lowestpossible peak temperature, resulting inoptimum utilisation of the reformer tubematerial.

• No thermal expansion problems with theoutlet manifold system. The slight remainingthermal expansions do not have to be com-pensated by materials exposed to the severeprocess conditions. The design of very largesingle-box reformers is possible.

• The process gas outlet temperature ismonitored for each tube row and isadjustable during operation for optimumreformer performance and temperatureuniformity.

• Almost unlimited service life of the Uhdeoutlet manifold system with no maintenancerequired other than painting.

• Considerable operational allowance of theoutlet manifold system with regard to processgas temperature and pressure.

More than 60 reformers of this type have so farbeen designed and constructed since 1966.All have given excellent performance.The two largest units are equipped with 630 and960 tubes, respectively.

Reformer tube-to-manifold connectionwith skin temperature profile

Skin temperature [°C]300 600 900

Refractory

Catalyst grid

Furnace bottom

Bellow

Gas conducting tube

Shop weld

Field weld

Carbon steel

Outlet manifold

Skin temperatureprofile

18Fertiliser complex of AFCin Abu Qir (near Alexandria), Egypt.Capacities: 1,200 mtpd of ammonia

1,925 mtpd of urea2,000 mtpd granulation unit

19

4.2 The secondary reformer20

Combustionzone

Arch

Refractory

Catalyst

Process air

Process gas

Process gas

Water jacket

Secondary reformer CFD optimisation

The process gas leaving the primary reformerenters the secondary reformer at the bottom.The gas is routed through the central internalriser pipe into the combustion chamber at thetop of the secondary reformer. Process air isintroduced into this combustion chamber vianozzles, arranged at equal intervals round thecircumference of the combustion chamber intwo rows. The partially oxidised gas passesthrough the catalyst bed from top to bottom, thecatalyst bed being supported by a ceramic arch.Finally, the gas leaves the secondary reformerthrough the outlet nozzle at the bottom.

Particularly challenging areas in secondaryreformer design include:

• The transfer line from the primary reformer outlet to the secondary reformer.

• The refractory lining including the ceramic arch which bears the catalyst weight.

• The burners.

Uhde’s answer to a safe and reliable secondaryreformer comprises the following features:

• A refractory-lined transfer line between the primary and secondary reformer which is only short as it is connected to the lower nozzle of the secondary reformer. Once in thesecondary reformer, the gas passes through an central internal riser into the combustion chamber. This design eases ducting and eliminates thermal stress between the transfer line and the secondary reformer.

• A multi-layer refractory lining with high-alumina bricks in the hot zones.

• A ring-shaped arch made of high-alumina bricks that provides a highly stable support for the catalyst. Due to the internal riser, the arch spans only half of the vessel diameter, resulting in improved stability compared to other designs.

• A multiple nozzle burner system comprised ofnozzles equally distributed round the circum-ference of the combustion chamber at two levels.

• Discharge of the process gas from the cen-tral internal riser into the dome by reversing the flow direction. Air is added via a specific number of nozzles installed in the vessel wall at a defined angle, thus creating a vortex flow in the combustion chamber. The vortex flow ensures optimised mixing of air and process gas. The flames do not come into contact with the vessel refractory or the central riser pipe.

• A proprietary burner design, first applied in 1992, which avoids any metallic parts com-ing into contact with the hot reacting processgas.

Since its introduction in 1968, the Uhde second-ary reformer has proved to be a reliable item ofequipment with a long service life.

21

The process gas from the secondary reformerhas to be cooled from 1,000°C to a controlledtemperature suitable for the downstream COshift. The sensible heat can best be utilised inthe generation and superheating of high-pressure steam.

The challenge in designing suitable cooling trainequipment is to arrive at a concept which pro-vides safe temperature limitation for all partsaccording to their particular load sensitivity andmaterials of construction. In addition, the equip-ment should be available at competitive prices.

Since 1966, Uhde has both used and promotedthe use of the horizontal fire-tube boiler for thispurpose. In 1969, the process gas cooling trainwas first modified to include a high-pressuresteam superheater.

4.3 Process gas cooling traindownstream of the secondary reformer

Uhde secondary reformerand process gas cooling train

Features of the Uhde process gas cooling train

Horizontal fire-tube boiler with:

• Thin flexible tube-sheet design.

• Full penetration tube to tube-sheets welds.

• Tube inlets protected by ferrules to limit thehead flux at the tube inlet.

• Double layer refractory lining for the inlet and,if necessary for the outlet chamber with highduty bricks on the hot surface.

• Internal gas bypass for temperature controlwith steam cooled damper blades.

• Steam drum mounted on top of the boiler andsupported by downcomers and risers.

High-pressure steam superheater with:

• Process gas inlet and outlet at the bottom.

• Preferably vertical arrangement of thesuperheating coil.

• Pressure shell in contact with the cooledprocess gas only.

• Internal bypass for temperature control.

Advantages of the horizontal fire-tube boiler:

• Simple, fixed-tubesheet design.

• No crevice corrosion.

• Reliable natural water circulation.

• No heated dead ends on water side wheredebris can settle.

• Low metal temperatures at and neartubesheets due to efficient insulation andferrules.

• Simple and reliable process gas temperaturecontrol.

• Easy access for inspection and maintenance.

• Low erection costs due to shop assembly ofboiler and drum.

Advantages of the high-pressure steamsuperheater:

• Coil designed for high mechanical flexibility.

• Thermal expansions compensated within the coil.

• Safe metal temperatures maintained byefficient bypass control.

• Temperature of the pressure-bearing shellgoverned by cooled outlet gas.

• Simple steam and process gas temperaturecontrol.

4.4 Ammonia converter and waste heat recovery22

The demand for energy-efficientammonia production dictates thefollowing criteria for the designof the ammonia synthesis unit:

• High conversion rates and therefore large catalystvolume.

• Maximum utilisation ofreaction heat for the gener-ation of high-pressure steam.

• Low pressure drop in the loop.

Such criteria, in turn, call for the:

• Use of small grain-size catalyst.

• Application of the radial-flowprinciple.

• High-pressure steam gener-ation wherever feasible.

The Uhde ammonia synthesisdesign therefore incorporatesthree radial-type catalyst bedsarranged in either one or twoammonia converters.

Features ofthe single-converter design:

• Heat exchanger betweencatalyst beds for indirectcooling of synthesis gas;consequently, highly-efficienttemperature control.

• Radial flow from outside toinside through all catalystbeds.

• Design adaptable to full-boreor drawn-in top closureof converter, depending onproject constraints.

• Heat exchangers extractablewithout removal of cartridge.

• An externally-arranged BFWpreheater/HP steam boilerdownstream of the third bed.

Three-bed ammonia converter,radial flow

Fertiliser complex of EFCin Ain Shukna (near Suez), Egypt.Capacities: 1,200 mtpd of ammonia

1,925 mtpd of urea2,000 mtpd granulation unit

Start-up gas

Gas inlet

Bypass

control

First bed

Second bed

Third bed

Gas outlet

23

Features ofthe two-converter design:

• Location of the first twocatalyst beds in the firstconverter vessel and of thethird bed in the secondconverter vessel.

• Radial flow from outside toinside through all catalystbeds.

• Simple U-tube heat ex-changer between first andsecond catalyst beds forindirect cooling of thesynthesis gas.

• Design adaptable to full-boreor drawn-in top closure of

HP Steam boilerAmmonia converter I,radial flow, catalyst beds 1 and 2

Start-up gas Gas inlet

First bed

Second bed

Gas outlet

Features ofthe HP steam boilers:

• Tubesheet cooling to preventnitriding.

• Channels in contact solely with the cooled synthesis gasleaving the boiler.

• Freely-movable U-tubedesign of the bundle.

• Internal bore welding, theheat exchanger tubes beingjoined to the tubesheet bymeans of full-penetrationwelds.

• Steam/boiler water separ-ation in the upper part of thewaste heat boiler.

The design of HP synthesisloop boilers is a long-standingtradition at Uhde, dating backto 1969 when equipment ofthis type was pioneered.

Advantages ofHP steam boilers:

• All components fabricatedfrom hydrogen-resistant,easy-to-handle, low-alloymaterials.

• Elimination of stresscorrosion cracking andcrevice corrosion.

• Low thermal stress.

• Integrated boiler feed waterpreheating.

• Tube-to-tubesheet weldsall subjected to non-destructive tests.

converter, depending onproject constraints.

• Easy withdrawal of internal heat exchanger without removing catalyst.

• Smaller dimensions andlower weight of vessels toreduce transport andhandling problems.

• An external HP steam boilerdownstream of the secondcatalyst bed.

• An externally arranged BFWpreheater/HP steam boilerdownstream of the third bed.

Ammonia converter II ,radial flow, catalyst bed 3

Third bed

Gas outletGas inlet

Steam outlet

Gas outletGas

inlet

BFW inlet

Temp.

blow down

Cont.

blow downBFW

bypass

Vane

separator

24

SAFCO IV fertiliser complex.Capacities: 3,300 mtpd of ammonia

3,250 mtpd of urea3,600 mtpd granulation unit

25

Overall view of the QAFCO 4ammonia/urea complex successfully commissioned by Uhde as early as 2004.Capacities: 2,000 mtpd of ammonia

3,200 mtpd of urea3,500 mtpd granulation unit

Feed and Energy ConsumptionNatural gas as feed and fuel Gcal(1) 6.8 to 7.4Elctric power kWh 15 to 90Overall feed and energy(2) Gcal(1) 6.7 to 7.4

UtilitiesCooling water ( T = 10 K) mt 120 to 260Demineralised water (net cons.) mt 0.65 to 0.75

EffluentsTreated process condensate(3) mt 0.85 to 1.15

Product QualityAmmonia content % by wt. 99.8 to 100.0Water content % by wt. 0.0 to 0.2Oil content ppm by wt. max. 5

(1) expressed as lower heating value of natural gas per ton of ammonia(2) electric power and steam export converted into fuel equivalents(3) routed back to the demineralisation unit for re-use

All consumption figures are per metric ton of liquid ammonia and serve as general information only.Local climatic conditions and gas composition may have a considerable influence on the performance figures.

4.5 Production and consumption figures per metric ton of ammonia

5. Services for our customers26

Uhde is dedicated to providing its customerswith a wide range of services and to supportingthem in their efforts to succeed in their line ofbusiness.

With our worldwide network of subsidiaries,associated companies and experienced localrepresentatives, as well as first-class backingfrom our head office, Uhde has the idealqualifications to achieve this goal.

We at Uhde place particular importanceon interacting with our customers at an earlystage to combine their ambition and expertisewith our experience.

Whenever we can, we give potential customersthe opportunity to visit operating plants and topersonally evaluate such matters as processoperability, maintenance and on-stream time.We aim to build our future business on theconfidence our customers place in us.

Uhde provides the entire spectrum of servicesassociated with an EPC contractor, from theinitial feasibility study, through financing conceptsand project management right up to the com-missioning of units and grass-roots plants.

Our impressive portfolio of services includes:

• Feasibility studies/technology selection

• Project management

• Arrangement of financing schemes

• Financial guidance based on an intimateknowledge of local laws, regulations andtax procedures

• Environmental studies

• Basic/detail engineering

• Utilities/offsites/infrastructure

• Procurement/inspection/transportation services

• Civil works and erection

• Commissioning

• Training of operating personnel

• Plant operation/plant maintenance

The policy of the Uhde group and itssubsidiaries is to ensure utmost quality in theimplementation of our projects. Our head officeand subsidiaries worldwide work to the samequality standard, certified according to:DIN/ISO 9001/EN29001.

We remain in contact with our customers evenafter project completion. Partnering is ourbyword.

By organising and supporting technical sympo-sia, we promote active communication betweencustomers, licensors, partners, operators andour specialists. This enables our customers tobenefit from the development of new technolo-gies and the exchange of experience as well astroubleshooting information.

We like to cultivate our business relationshipsand learn more about the future goals of ourcustomers. Our after-sales services includeregular consultancy visits which keep the ownerinformed about the latest developments orrevamping options.

Uhde stands for tailor-made concepts andinternational competence. For more informationcontact one of the Uhde offices near you or visitour website:

www.uhde.eu

Further information on this subject can be foundin the following brochures:

• The Uhde Steam Methane Reformer Technology

• Urea• UFT fluid bed granulation• Nitric acid• Nitrate fertilisers

6. Recent references 27

E EngineeringP ProcurementC Construction

Completion Customer Plant Site Plant Capacity Contract Project Notes

2010 Orascom Construction Arzew, Ammonia 2 x 2,200 t/d E, PIndustries for Sonatrach AlgeriaOrascom Fertiliser Company (Sorfert)

2010 Saudi Arabian Mining Co. Ras Az Zawr, Ammonia 3,300 t/d E, Pvia Samsung Engineering Saudi ArabiaCo., Ltd.,

2010 Egyptian Agrium Nitrogen Damietta, Ammonia 2 x 1,200 t/d TurnkeyProducts Co. SAE Egypt(EAgrium)

2008 Misr Oil Processing Co. Damietta, Ammonia 1,200 t/d TurnkeyEgypt

2008 Kuibyshev Azot Togliatti, Ammonia 1,800 t/d E ExpansionRussia

2007 Duslo a.s. Sala, Ammonia 1,300 t/d E ExpansionSlovakia Expansion by 300 t/d

2007 Helwan Helwan, Ammonia 1,200 t/d TurnkeyFertilizer Co. Egypt

2006 Egyptian Fertilizer Ain Sukhna/Suez, Ammonia 1,200 t/d TurnkeyCo. (EFC II) Egypt

2006 Alexandria Fertilizers Co. Alexandria, Ammonia 1,200 t/d Turnkey(AlexFert) Egypt

2006 Saudi Arabian Fertilizer Al Jubail, Ammonia 3,300 t/d TurnkeyCompany (SAFCO IV) Saudi Arabia

2004 Turkmendokunhimiya Tecen, Ammonia 600 t/d E,Pvia Gap Insaat Turkmenistan

2004 Qatar Fertiliser Mesaieed, Ammonia 2,000 t/d TurnkeyCompany (QAFCO IV) Qatar

2003 ASEAN Bintulu Fertilizer Bintulu, Ammonia 1,350 t/d E 3. ExpansionSdn Bhd (ABF) Malaysia Expansion by 30 t/d

2000 Egyptian Fertilizer Co. Ain Sukhna/Suez, Ammonia 1,200 t/d Turnkey(EFC) Egypt

1999 Istanbul Gübre Körfez, Ammonia 1,200 t/d E, P ExpansionSanayii A.S. (IGSAS) Turkey Expansion by 50 t/d

1998 Abu Qir Fertilizers and Abu Qir, Ammonia 1,200 t/d TurnkeyChemical Ind. (AFC) Egypt(Abu Qir III)

1997 ASEAN Bintulu Fertilizer Bintulu, Ammonia 1,320 t/d E, P 2. ExpansionSdn Bhd (ABF) Malaysia Expansion by 120 t/d

1997 Saskferco Products Inc. Belle Plaine, Ammonia 1,800 t/d E ExpansionCanada Expansion by 300 t/d

1997 SASTECH (Pty) Ltd. Sasolburg, Ammonia 830 t/d E ExpansionSouth Africa Expansion by 100 t/d

1997 Qatar Fertiliser Mesaieed, Ammonia 1,500 t/d TurnkeyCompany (QAFCO 3) Qatar

1993 SASTECH (Pty) Ltd. Sasolburg, Ammonia 730 t/d TurnkeySouth Africa

1992 Saskferco Products Inc. Belle Plaine, Ammonia 1,500 t/d TurnkeyCanada

1991 BASF Antwerpen N.V. Antwerp, Belgium Ammonia 1,800 t/d Turnkey

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