Snamprogetti Urea Technology

THEUREATECHNOLOGY

A company of Saipem

spm_ureasp_L01_07_10_17:Layout 1 11-01-2008 16:55 Pagina b

The UreaTechnology

A company of Saipem

spm_ureasp_L01_07_10_17:Layout 1 11-01-2008 16:55 Pagina 1


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ContentsPROCESS DESCRIPTION 4

TECHNOLOGICAL ADVANTAGES 11

MAKE UREA AT LOWER COST 22IN A HIGHLY RELIABLE PLANT

REVAMPING 24

INTEGRATION WITH 26MELAMINE PLANT

LICENSING 28

AFTER SALES SERVICE 30


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ProcessDescriptionThe Snamprogetti urea process is known worldwide.The process is divided into six sections:

• Synthesis and high pressure (HP) recovery

• Medium pressure (MP) purification and recovery

• Low pressure (LP) purification and recovery

• Vacuum concentration

• Process condensate treatment

• Finishing: prilling


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SYNTHESIS AND HIGH PRESSURE (HP)RECOVERYIn addition to the HP machinery required tofeed ammonia and carbon dioxide and torecycle ammonium carbamate solution, thissection includes: the reactor where urea isformed; the stripper necessary to strip outas vapours, from the urea solution leavingthe reactor, a large amount of ammonia andcarbon dioxide not converted to urea in thereactor; the carbamate condenser thatcondenses these vapours; the ejector thatrecycles the ammonium carbamate solutionto the reactor. In this equipment thepressures are of a similar level, 150 bar,while the temperatures of the outletsolutions are 188, 205 and 155°C for thereactor, the stripper and the carbamatecondenser, respectively.In the Snamprogetti technology, the ureareactor is characterised by a high ammonia-carbon dioxide ratio (NH3/CO2 = 3.2 - 3.4

molar) and a low watercarbon dioxide ratio(0.4 - 0.6 molar). Inside the reactora matching number of trays of a very simpledesign are installed to improve theconversion. Under these conditions 62÷64%(conversion) of the total CO2 entering thereactor is converted to urea. The total carbondioxide conversion in the HP section (or loop)is 85-90%. All the equipment in this section,the heaviest of the urea plant, is installed atground level, thus providing a horizontallayout with all the relevant benefits.The stripper and the hydrolyzer in the wastewater section are the only two itemsof equipment in the plant that consumemedium pressure steam. The amount ofsteam consumed in the stripper is practicallycompletely recovered in the carbamatecondenser: its pressure is lower but stillsufficient to be used in the urea plant itself.Even under severe conditions, all theequipment in this section has a safe life

of more than 20 years. The quantity ofoxygen introduced into the plant as air is0.25% vol of the fresh feeding carbondioxide. This minimum amount guarantees,at the same time, excellent equipmentpassivation and the absence ofexplosive mixtures where the “inerts”are released from the plant into theatmosphere after practically all the ammoniacontained therein has been washed.Thanks to the proper choice of the materialsin contact with the process fluids and to thepresence of excess ammonia, it is possible,during unscheduled shutdowns lasting onlya few days, to bottle-in the high pressuresynthesis loop by operating a few valves,thus keeping all the process solutions insidethe loop. In this way obvious pollution andstart-up problems are completely averted.All kinds of machinery (reciprocating andcentrifugal) is utilised according to localconditions or client requests.


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MEDIUM PRESSURE (MP)PURIFICATION AND RECOVERYThe purpose of this section is to partiallystrip out the reactants, ammonia and carbondioxide from the urea solution and, aftertheir condensation in water, to recycle theobtained solution to the reactor, togetherwith the ammonia and carbon dioxideaqueous solution resulting from thedownstream sections of the plant.The ammonia excess is separated inthis section and recycled to the reactorseparately. A distillation column is providedfor this purpose. The operating pressureis 17 bar g. A particular feature is includedin this section. Ammonia and carbon dioxideare partially condensed in the shell of apreheater within the vacuum section, thusrecovering some energy in the form of 200kg of steam per ton of urea, with aninvestment cost that, even in existing plants,has a pay-back time of less than two years.Another particular characteristic of theMP section is the washing of the so-calledinerts (CO, H2 and CH4 contained mainlyin the carbon dioxide and the passivationair). As already emphasised, the quantityof passivation air in the Snamprogettitechnology is very small (one third comparedwith other technologies). It is therefore easyto recover ammonia from the inerts withoutthe risk of explosion mainly due to H2/O2mixtures. No hydrogen removal fromcarbon dioxide is required. Upon special

requests, different washing systems havebeen designed by Snamprogetti and havealready been installed in industrial plants.For the complete abatement of the ammoniacontained in the inerts, in completelysafe conditions with regard to explosions,Snamprogetti has patented a washingmethod that has already been applied insome plants. This consists of washing theinerts with water after the addition of aquantity of flammable gas, as for examplenatural gas, in such an amount that afterthe ammonia has been eliminated, thecomposition of the inerts is out of theexplosive field due to the excess offlammable gas. The washed inerts are sentto a burner together with the natural gas.It should be emphasised that the presenceof the MP section provides great plantflexibility, which can be operated over awide range of NH3/CO2 ratios, with excessammonia present in the urea stream fromthe stripper being recovered and condensedby the MP section. Furthermore, although inprinciple the control of the NH3/CO2 ratio inthe synthesis loop is important, in practice,owing to the presence of the MP section,some fluctuations are acceptable and thereis no need for strict control of the NH3/CO2ratio in the Snamprogetti process.


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LOW PRESSURE (LP) PURIFICATIONAND RECOVERYFurther stripping of ammonia and carbondioxide is made in the LP section, operatingat 3.5 bar g. The vapours, containingammonia and carbon dioxide, arecondensed and recycled to the reactor viathe MP section. An appropriately sized tankis provided in this section to collect all thesolutions from the plant when it is shutdown for long time. Therefore,in no circumstances are solutionsdischarged from the plant.

VACUUM CONCENTRATIONThe urea solution leaving the LP sectionis about 70% b.w. and contains smallquantities of ammonia and carbon dioxide.The final concentration of the urea solution

(99.8% b.w.) is made under vacuum intwo steps at 0.3 and 0.03 bar abs. forthe prilled product, and in one or twosteps for the granular product, accordingto the granulation technology chosen.An important feature of this sectionis the preconcentration of the urea solution to about 86% b.w. The necessary heat is provided by partialcondensation of the vapours (ammoniaand carbon dioxide essentially) from theMP section evaporator. Particular care istaken by Snamprogetti in the design ofthis section to minimise temperaturesand residence times so as to keep thebiuret at minimum values.A simple solution has been found to theproblem of lump formation in the secondvacuum separator: lump formation is

prevented by wetting the internal walls ofthe separator by means of a small recycleof molten urea.

PROCESS CONDENSATE TREATMENTThe excellent result achieved bySnamprogetti in the treatment of wastewater from urea plants has receivedworldwide recognition.Snamprogetti’s success in dischargingthe large amount of process water with1 ppm of urea and 1 ppm of ammoniashows it is possible to reduce pollutionwhile obtaining urea at a lower cost(lower specific consumption of ammoniaand reutilization of process water as BFW).All possible and convenient heat recoverieshave been introduced into this section inorder to minimise energy consumption.


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FINISHING: PRILLINGPrilling is the easiest technology tomanufacture solid urea with commerciallyvalid chemical and physical characteristics.Molten urea (99.8% b.w.) is sprayed at thetop of the prilling tower, at a height of 55-80m, according to climatic conditions; at thebottom, essentially spheroidal urea particles,namely prills, are collected and sufficientlycooled in order to be sent to storage ordirectly to the bagging section withoutscreening, coating or any other treatment. Ina few plants based on the Snamprogettitechnology, plant owners have requestedthat formaldehyde (0.2-0.3% b.w.) be added

to the molten urea just before the prillingsection in order to improve the free-flowingcharacteristics of the prilled urea and toachieve a slight increase in hardness. A risingdraught of air inside the prilling tower is thecooling medium that removes thesolidification heat and cools the prills.The prilling process, although it is a simpleone, conceals some critical problems:• the bucket must be specially designed to

limit the quantity of fine and oversize prills to a negligible value. In fact, the Gauss distribution curve must be as narrow as possible to avoid severe cakingproblems in storage;

• too much air can cool the product excessively resulting in undesirable absorption of humidity from the air in humid climates, again with possible serious product caking problems in storage;

• too much air can entrain too much ureadust at the top of the prilling tower.

This last problem constitutes an increasein consumption of specific raw materials,which not only means plant inefficiency, butprincipally represents a serious pollutionproblem. With regard to urea dust,Snamprogetti has its patented dedustingsystem, already applied in some plants,


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which is able to reduce urea dust from 40 to15 mg/Nm3 of air. In the case of ammonia,the problem is not so easily solved due tothe extremely low partial pressure ofammonia in the air from the prilling tower.As for the abatement of ammonia, the onlypossible method is to wash the air withslightly acidified water. Unfortunately, dueto the large quantity of air, such a system hasa rather high investment cost as well as aconsiderable operating cost. Snamprogettihas patented and applied a very simplesolution in one plant that consists of the addition of an inorganic acidto the urea melt, just before the prilling

tower, in order to drastically reduce thequantity of ammonia in the air from theprilling tower. The values obtained are20-70 mg/Nm3. An interesting side-resultof this method is that the quantity of freeammonia in the prills is greatly reduced andthere is a drastic reduction in the presenceof ammonia in the work environment(conveyor belt chutes, storage). Of coursethe prilled urea contains about 2,000 ppmof relevant salt, with no detrimental effecton the use of urea as a fertiliser and otherindustrial uses.



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TechnologicalAdvantagesAll industrial urea production plants are based on direct synthesis between ammoniaand carbon dioxide according to the following exothermic reaction:


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The Snamprogetti process leads to a ureasolution of about 70% b.w., which is followedby a finishing step in order to obtain the solidproduct, either prilled or granular.Although simple, the reaction has severalcomplex aspects:• The reaction is governed by an

equilibrium requiring the removaland recycle of the reactants not transformed into urea.

• The temperatures and pressuresare rather high.

• The solutions are very corrosive.• The physical and chemical

characteristics of the solid ureaare critical.

• A urea plant can be a source of air and water pollution.

Snamprogetti has completely solved all theabove problems by providing high qualitysolutions that are the strong points of itstechnology, i.e.:• High process efficiency (low

raw material consumption, low energy requirement).

• Sustainable environmental pollution.

• High quality product.• Process condensate recovery

as BFW.• The stripper.• High reliability (easy and safe

operation, low corrosion, high on stream factor).

• Easy maintenance - Horizontal layout - Ejector.

• First-rate client assistance.• Intensive R&D support -

Mathematical modelling.

The first industrial urea plant based onSnamprogetti’s NH3 stripping technology wasput into operation in 1971. Since then morethan 100 urea plants based on thistechnology have been in operation or arecurrently being implemented. There hasbeen a steady increase in the demandfor urea over the last few decades.Snamprogetti has responded by designingurea plants with increasingly highercapacities. For the first time in 1998, a plantwas designed with a capacity greater than3,000 t/d. The Profertil plant in Argentinadesigned by Snamprogetti has a singleline design capacity of 3,250 t/d.The plant was started up in 2001 andhas demonstrated a yearly averagecapacity of 3,600 t/d, reaching a record

production of almost 1.2 million tonsof urea per year.On the basis of this experience, Snamprogettihas already started designing a newgeneration of large-scale single line plantsthat will cross the threshold of 5,000 t/d.Performance meets the most stringentrequirements for energy conservation andenvironmental control. The unique featuresof the Snamprogetti technology are theresult of continuous and intensive R&D work with feedback from plants operatedby its licensees and tests made on the sameplants, regarding the process itself,construction materials and the size ofequipment and machinery. Snamprogettimakes its urea technology availableworldwide to all sectors of the industry(soil and leaf fertilisers, cattle feed, resinmanufacturing, etc.) by:• Licensing directly or through selected

contractors.• Performing plant engineering and

construction entirely within its organisation,from basic design to turnkey jobs. Snamprogetti urea technology can be used for plants of any capacity, in addition to revamping existing plants.


HIGH PROCESS EFFICIENCYThe process is extremely efficient as regardsboth raw material consumption and energyrequirements. Almost the entire quantity ofraw materials, namely ammonia and carbondioxide, is transformed into urea.This means low consumption of rawmaterials, as close as possible to thetheoretical value and, at the same time,sustainable environmental pollution(more than 99.8% of the ammonia istransformed into urea). The high NH3/CO2 ratio in the reactorensures a high conversion of ammoniumcarbamate, an intermediate compound in thereaction, to urea (up to 64%). This result, together with the highly efficientammonia-stripping operation, drasticallyreduces the recycle of unconvertedcarbamate and the size of equipment incarbamate decomposition and recoverysections. Some important heat recoverieshave been introduced, with a pay-back timeof less than two years. High conversion, highstripping efficiency and heat recoveriesminimise the energy requirement, i.e.steam, electric power and cooling waterconsumption.

SUSTAINABLE ENVIRONMENTALPOLLUTIONOver the last decade, pollution control hasbecome a basic parameter in the design ofnew urea plants and in the management ofexisting plants. In both cases it is necessary tocomply with antipollution regulations in orderto obtain permits required for building newplants and operating existing ones.Snamprogetti has anticipated the increasinglyrestrictive antipollution regulations withexcellent patented and tried solutions thatreduce pollution to sustainable values. Thevalues of pollutants are shown in table 1. Hereare a few remarks we feel are worth making:• a particular feature of the Snamprogetti

technology reduces to nearly zero the quantity of ammonia in the plant vents where the so-called inerts are discharged into the atmosphere. This result is also facilitated by the fact that the quantity of passivation air introduced into the plant isvery low compared with other technologies;

• the proprietary design of the natural-draught prilling tower guarantees urea dust emission lower than 40 mg/Nm3

in air without a provisional dedusting system;

• process water discharged from the plant with 1 ppm of urea and 1 ppm of ammonia is an important result in reducing water pollution, consideringthe huge quantity of process water discharged from urea plants.For example, a prilled urea plant with a capacity of 2,000 t/d discharges about 1,100 t/d of process water.

HIGH QUALITY PRODUCTUrea is mainly produced as a solid product,prilled or granular. The difference in qualitybetween the two solid products issignificant: both are round, but the firstproduct (prills) has a smaller shape andlower hardness, while the second one(granules) has a bigger shape and higherhardness. For both products, Snamprogettiassures excellent free-flowing quality thatprevents caking in bulk storage andguarantees easy handling downstreamof the production plant. Excess ammoniain the high pressure synthesis loop andthe right choice of process conditionsminimise biuret formation, an undesirableby-product in urea.

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SOURCE OF POLLUTION UREA CONTENT NH3 CONTENTProcess water 1 ppm 1 ppmFrom prilling tower 15 mg/Nm3 20 mg/Nm3

From granulation stack 15 mg/Nm3 20 mg/Nm3

Table 1 - Values of pollutants from the plant.



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PROCESS CONDENSATE RECOVERY AS BFWAs stated above, process water can bedischarged with a content of 1 ppm of ureaand 1 ppm of ammonia. Snamprogettiobtained this outstanding result at thebeginning of the eighties, as demonstratedby a long list of operating plants achievingthis result. This applies not only to nearly allthe plants based on the Snamprogettitechnology, but also to plants based on thirdparty technology to which the Snamprogettitechnology has been applied. With suchnegligible values of pollutants, threesimultaneous targets are reached whichcontribute to reducing the cost of urea:specific consumption of ammonia isdecreased, environmental pollution is alsoreduced and the possibility of reusing theprocess water is guaranteed for severaltechnical purposes such as BFW for theproduction of steam at pressures reachingas high as 110 bar.

THE STRIPPERThe stripper is the primary piece ofequipment in any urea stripping technology.Its function is the decomposition ofcarbamate into ammonia and carbon dioxidefrom the urea solution leaving the reactor.This separation is made at practically thesame pressure as in the reactor, in severeand unfavourable conditions: high pressure,high temperature, high corrosiveness of thesolution and in the presence of both liquidand vapour phases, which is always apotential source of corrosion. The stripperconsists of a vertical tube bundle with theprocess solution flowing down along theinternal walls of the tubes so as to ensurelow residence time (to prevent biuretformation) and obtain high heat transfercoefficients. In the Snamprogetti technology,the separation of ammonia and carbondioxide is made in the presence of ammoniaas the stripping agent while the necessaryheat is supplied by condensing steamin the shell. In the first industrial plants

Snamprogetti used titanium as the tubematerial. At the end of the eighties titaniumwas replaced with bimetallic. The bimetallictube consists of two coaxial tubes: anexternal tube made of 25-22-2 Cr-Ni-Moand an internal tube made of zirconium.The two tubes are produced separatelyaccording to Snamprogetti specifications.They are then assembled and drawn toobtain a proper mechanical bonding.No welding is required.New options have been recently developedand implemented for the stripper design:• The full Zirconium Stripper• The OMEGABOND® StripperBoth of these strippers can withstandmore severe conditions (in terms of bottomtemperature) allowing long life of equipment,optimisation of plant operating conditionsand minimisation of required maintenance.In the full Zirconium Stripper, both lining andtubes are made of zirconium, which hasproven to be perfectly resistant to erosionand corrosion. The OMEGABOND® Strippertakes advantage of the long experience fromthe Titanium Stripper, overcoming its limitsdue to erosion of full titanium tubes by theuse of the OMEGABOND® tubes (developedin collaboration with ATI Wah Chang, USA)obtained by extrusion of titanium (external)and zirconium (internal) billets, forming ametallurgical bond of the two materials.


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HIGH RELIABILITY(EASY AND SAFE OPERATION,LOW CORROSION, HIGHON STREAM FACTOR)The plant is very easy to operate without anyparticularly strict control. As a matter of fact,the presence of the Medium Pressure section(17 bar), a buffer for any upsets of the HighPressure synthesis loop, assures greaterflexibility. The possibility of blocking-inthe process fluids in the High Pressuresynthesis loop (i.e. without discharging themfrom the plant) during emergency shutdownsgreatly simplifies plant restart. Corrosion hasbeen one of the main problems ever sincethe beginning of the development ofindustrial urea plants based on the directreaction between ammonia and carbondioxide. Excess ammonia, the mildcomposition of process fluids, and the rightchoice of construction materials guaranteelow corrosion. Flexibility, blocking-in, lowcorrosion and the right choice of machineryand control instrumentation assure a highon stream factor. Explosive mixtures havealways been a serious problem for ureaplants: in some cases, serious explosionshave resulted in the loss of human lives andplant damage. Explosive mixtures are due tothe simultaneous presence of flammablecompounds (CH4, C2H6, H2), introduced intoa urea plant with the raw materials(ammonia and carbon dioxide), the presenceof oxygen that enters with passivation airand the NH3. When all these so-called“inerts” are released from the plant to theatmosphere, their compositions are typical

of an explosive mixture. In the Snamprogettitechnology, excess ammonia, jointly with theuse of a particular material (zirconium) in thestripper, minimises the oxygen (as air)required for passivation, thus avoiding theformation of explosive mixtures. Indeed noexplosion has ever occurred in plants basedon the Snamprogetti technology. Removal ofhydrogen by catalytic combustion from thecarbon dioxide feedstock is not necessary.Furthermore, no mechanical failures haveever occurred thanks to the particularmechanical solutions and controls requiredby Snamprogetti during equipmentconstruction. All of these special featuresaccount for the Snamprogetti technologybeing fully reliable, which is extremelyimportant for urea plants. The excellentreliability of urea plants based on theSnamprogetti technology is essentially due,not only to the soundness of the process, butalso to accurate engineering, improvedequipment design and equipment materialchoice. Solid technology coupled with goodmaintenance can assure safe operations forup to a year with an on stream factor of over350 days/year, on average, including plantshutdowns for scheduled maintenance.


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EASY MAINTENANCE - HORIZONTALLAYOUTMaintenance has an important impacton the urea plant on stream factor andconsequently on the cost of urea.Urea plants based on the Snamprogettitechnology have an annual maintenancecost that is lower than 1.5% of theinvestment cost. Good maintenanceimproves the stream factor of the plantand in particular can avert plant shutdownsdue to unexpected equipment failure.Preventive maintenance has been introduced

with new methods for non-destructivetesting of the equipment. This allowsequipment condition to be checked duringand, in some cases, between scheduledshutdowns, and to forecast the status,particularly the remaining lifetime ofequipment, thus making it possible for themost appropriate action to be taken. OfSnamprogetti’s urea technology, the mostcritical items (i.e. High Pressure synthesisloop equipment) are located at ground levelthus facilitating inspections and repairs ifnecessary. The recycle of unreacted NH3 and

CO2 to the reactor is ensured by an ejector:a simple, static and maintenance-free devicethat has ammonia as its driving fluid.Horizontal layout is the key element inSnamprogetti’s technology. Besidessubstantially reducing both investment andmaintenance costs, it results in easier andsafer plant operation and maintenance.In fact, all the heavy equipment (reactor,stripper, carbamate condenser) is installed atground level, contrary to other technologieswhere the same equipment is installed highup on the structure (vertical layout).


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FIRST-RATE CLIENT ASSISTANCEExchanging information with clientsto keep the plant in optimum operatingconditions and to support Snamprogetti’scontinuous research and developmentwork is one of the most important aspectsof our client assistance programme.Assistance also covers maintenanceand equipment inspection. SnamprogettiUrea Users Symposiums are organisedperiodically (worldwide or limited tocertain areas of the world) to furtherexchange know-how and experience.

INTENSIVE R&D SUPPORT -MATHEMATICAL MODELLINGLeadership in technology is ensured only bycontinuous efforts in development work.That is why Snamprogetti conducts ongoingresearch and development tests in plantsbased on its technology in order to improvethe process, equipment design, constructionmaterials, machinery, etc. Close contacts aremaintained with all qualified manufacturersfor this purpose. This ensures that not onlythe latest, but also fully proven technology isprovided to clients. The investment made by

Snamprogetti is of paramount importancefor developing a mathematical model tosimulate the performance of the HighPressure synthesis loop equipment, i.e.the reactor, stripper and carbamatecondenser. Through the solution ofdifferential equations, the model enablesthe calculation of the material and heatbalance of two mono-dimensional streamsin a non-equilibrium status, gaseousand liquid, in:• equi-current bubbled (reactor);• counter-current falling film (stripper);


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• equi-current bubbled, plug, slug, film, mist (carbamate condenser).

The model takes into account the processof mass transfer between the variouscomponents, as well as the heat exchangebetween the different phases, through

appropriate transfer coefficients relevant tothe fluid-dynamic and geometric conditions.Kinetic aspects related to the formation ofurea from carbamate are simulated on thebasis of equations available from literature.The thermodynamic model is based on over

one hundred experimental data itemsobtained from literature (Kawasumi,Durish, Inoue), as well as on experimentaldata derived from dedicated testsperformed in the laboratory uponSnamprogetti’s request.

(1) Including c.w. consumption for CO2 compressor intercoolers and turbine condenser.

(2) 15 mg/Nm3 with dedusting system.

(3) With acidification.

(4) Climatic local conditions can affect electricity consumption. NH3 refrigeration system is included.

(5) Injected into steam turbine.

(A) CO2 compressor driven by electric motor.

(B) CO2 compressor driven by steam turbine.

Table 2 - Product quality, raw materials and utilities consumption, recoveries.

PRILLING GRANULATIONExpected Product QualityNitrogen % b.w. 46.4 46.3Biuret % b.w. 0.85 0.7Moisture % b.w. 0.3 0.25Prill size (average diameter) mm 2 3.2Formaldehyde % b.w. - 0.45Crushing strength kgf 0.8 (on 2 mm) 3.5 (on 3 mm)

Raw Materialsand Utilities Consumption A B A BAmmonia (as 100%) kg 566 566 563 563Carbon dioxide (as 100%) kg 733 733 731 731HP steam (110 bar g, 510°C) kg - 840 - 810MP steam (23 bar g, 220°C) kg 620 - 620 -Cooling water (DELTA T=10°C)(1) m3 85 95 85 95Electric power kWh 120 23 160 (4) 75 (4)

RecoveriesLP steam export (3.5 bar g, 147°C) kg 50 - (5) 150 -(5)Total condensate export kg 900 1,100 720 900

Effluents• Process condensate

- Ammonia ppm b.w. <1 <1- Urea ppm b.w. <1 <1

• Air emission- Urea dust mg/Nm3 40 (2) 15- NH3 mg/Nm3 20 (3) 20 (3)

PERFORMANCE DATAExpected product quality, raw materials and utilities consumption, recoveries, referred to 1,000 kg of urea product are given below.


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Make Urea at Lower Costin a Highly Reliable PlantWhen illustrating urea technology, steam consumption (or even sometimes energy consumption) is notinfrequently the only parameter taken into consideration. It would be more accurate to talk about the cost ofurea, which is affected by several parameters (including steam consumption). The diagram below shows allthese parameters, i.e. the advantages of the Snamprogetti urea technology and their impact on the cost ofthe product together with high plant reliability.


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A new urea plant often requires a huge capital investment and the price of ureais usually not sufficient to justify a new unit. In nearly all market situations,manufacturers are considering the revamp of their existing plants.

Revamping

A revamp ordinarily reduces the cost of theproduct, does not require an excessiveinvestment and has a shorter payout timethan that required for a new plant.Revamping a plant usually includes one ormore of the following changes:• Increasing production capacity• Reducing raw materials and utilities

consumption• Reducing pollution• Reducing maintenance costs• Increasing the on stream factor• Reducing labour• Improving product quality.Some of these changes can be in mutualconflict: improvement of one element can

entail deterioration of another.The Snamprogetti ammonia strippingtechnology appears to be particularlysuitable when stripping and conventionaltotal recycle plants are to be revamped.An increased production capacity of at least20-30% over the design capacity of theplant can be regarded as a standard goalto achieve through unit revamping, and inparticularly favourable machinery conditions,the capacity increase can easily be muchhigher than the above-mentioned value:even a 50% increase in capacity has beenobtained together with lower utilitiesconsumption and reduced pollution. Thestatus of existing conventional total recycle

plants is particularly favourable for reducingsteam consumption. To strongly reducesteam consumption in these examples, it is sufficient to introduce the typical stepof the Snamprogetti HP stripping andrecovery section. In fact, the steamconsumed in the added stripper is almostentirely recovered in the added carbamatecondenser, at a lower pressure, yet sufficientfor use in the existing downstream sectionsof the plant. For example, steam consumptioncan be reduced from 1,300 kg downto 700 kg per ton of urea. These resultscannot be generalised because eachrevamp should be reviewed ona case-by-case basis.


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Ammonia and urea are the raw materials used to producemelamine with melamine plants having an output ofmelamine and vapours (off-gas) containing ammonia,carbon dioxide and water.

Integration withMelamine Plant


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The composition and pressure of thesevapours vary depending on the melamineprocess. Ammonia must be recovered fromthese vapours either through a selectiveprocess or by sending the vapours to aneutralisation plant with the consequentproduction of an ammonium salt. Anotherway to recover ammonia and carbon dioxidesimultaneously from the off-gas is to makeurea from them, and then to recycle this ureaas molten urea to the melamine plant.In this case the urea plant can be regardedas a recycle unit of the melamine plant:if the ammonia content in the off-gas ishigher than the stoichiometric one, then theurea production unit will also releaseammonia, which can be recycled to the melamine plant. A further hypothesis maybe contemplated with a urea plant thatproduces urea, not only from off-gas, butalso from fresh ammonia and carbon dioxide.In this case, urea is ready to be partiallydisposed of and partially recycled to themelamine plant. The Snamprogetti ureatechnology can be applied in all of thesituations outlined above. One particularlyinteresting scenario entails excess ammoniain the off-gas. This excess is released by theMP section of the urea plant. Depending onthe melamine technology used, the off-gasesmay be released at different pressures: low,

medium and high at about 3, 20 and 150bar g, respectively. They may be condensed inthe LP, MP or HP section of the Snamprogettiprocess, in a condenser in parallel to theexisting one or directly in the existing one.This possibility is particularly interestingwhen the off-gas is at 150 bar g andcontains a small amount of water; it can becondensed at such pressures with the smallamount of water favouring conversion in theurea reactor. In the intermediate case (forexample 80 bar g), the off-gas can becondensed and then pumped as a solutioninto Snamprogetti’s HP section.


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Snamprogetti’s urea technology license and know-how areavailable to urea manufacturers.

Licensing

The technology, based on the ammoniastripping process, has already been proven inmore than 100 plants throughout the worldfor capacities ranging from a few tenths tonearly 4,000 t/d in one line. The majorityof these plants were engineered bySnamprogetti, a factor which greatlycontributes to improving the technicaldetails, especially those relating toequipment and machinery. Several plantsengineered by Authorised Contractorsare available worldwide to meet all specificneeds such as financing, local engineering,procurement, etc. The issue of a CustomisedBasic Engineering Package enablesthe appointed contractor to perform thedetailed engineering and all other projectimplementation. In principle, the CBEPincludes the following documentation:• process flowsheet with mass balance

of process fluids and utilities;• P&I diagrams;• equipment specifications with material

of construction;• quality and quantity of effluents;• suggested layout;• area classification;• instrument data sheet and interlock

system;• computer controlled plants (DCS);

• data for safety valves;• vendor list;• commissioning and operating manual;• recommendations for maintenance;• checking of some detailed engineering;• performance test-run procedures;• analytical manual;• training programmes for client personnel;• commissioning services.During the design stage of detailedengineering, Snamprogetti is in closecontact with the Authorised Contractorfor the above-mentioned checks andfor the selection of the main equipmentand machinery. Assistance at the vendor’sworkshop is provided on request.Tailor-made training programmes for clientpersonnel include “on-the-job” and “hands-on” training. The most up-to-date trainingaids such as dynamic simulators areavailable.


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After Sales ServiceSnamprogetti is proud to be a leader in the field of ureatechnology and makes every possible effort to maintain itshigh-ranking status.


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Accordingly, its ongoing goal is to updateand improve its technology on the basisof increasingly more appropriate calculations,taking advantage of mathematical modelsthat have been verified by a considerableamount of screened data collected fromclient operating plants. This data iscontinuously collected by Snamprogettiduring visits to the plants in operation, orsupplied by clients themselves, in the frameof the already mentioned “Client Assistance”or the “After Sales Service” programmeoffered by Snamprogetti in order to:• keep clients constantly informed

of developments;• provide revamping to achieve the

objectives described in the section entitled “Revamping” i.e. increase capacity, reduce raw materialsand utilities consumption, reducepollution, etc.;

• inspect equipment;• troubleshoot any problem. Symposiums are an ideal way to foster theexchange of information between clients andSnamprogetti or directly between clients.These information and experience exchangesgreatly benefit both Snamprogetti, inimproving plant design, and clients,in improving plant performance.


The Urea Team

We are readyto design 5,000 MTPDsingle line urea plants.


Snamprogetti S.p.A.Viale De Gasperi, 16 - 20097 San Donato Milanese, Milan - ItalyTel. +39.02520.1 - www.saipem.eni.it

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A company of Saipem

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Snamprogetti Urea Technology

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