Latest Urea Technology for Improving Performance and

Product Quality

by

EIJI SAKATA, Senior Process Engineer

TAKAHIRO YANAGAWA, Process Engineer

Technology & Knowledge Research Center

L TOYO ENGINEERING CORPORATIONTOKYO JAPAN

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ABSTRACTToyo Engineering Corporation (TEC) has started licensing an advanced version of its ACESurea process named “ACES 21”, being established based on a close collaboration with PT PupukSriwidjaja (PUSRI), Indonesia. ACES 21 is featured by ground level reactor and verticalsubmerged carbamate condenser, combined with CO2 stripping technology, aiming at both plantcost reduction and further energy saving from the original ACES process. TEC also owns thegranulation technology featured by unique Spout-Fluid Bed Granulator. A 2,000 mtpd ureagranulation plant using TEC granulation technology started operation successfully in 2000,demonstrating its excellent performance.

This paper introduces the TEC’s latest urea technologies to improve plant performance andproduct quality with the following features and references:n Features of ACES 21 technology, remarkable plant cost reduction and energy saving, and

advantages in view of operation and maintenancen A typical study to revamp a conventional solution recycle urea plant with ACES 21 for

capacity increase and energy saving, fully utilizing the existing urea reactor.n Features of TEC granulation technology for improving product qualityn Recent commissioning experience in urea granulation plant based on TEC technologies.

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INTRODUCTION

Toyo Engineering Corporation (TEC), a worldwide engineering contractor and one of threemajor urea process licensers, has made continual efforts to improve the urea process as theprocess licenser and the E-P-C contractor, and has contributed to the fertilizer industry bysupplying reliable, efficient and economical urea plants since its establishment 40 years ago.TEC has engineered and constructed, as of the end of 2000, 93 urea plants and 10 ureagranulation plants based on TEC technologies, giving a quarter of the world’s total productioncapacity by the three major urea processes licensors. Realizing the future technical demands forthe urea process technologies during the 21st Century, TEC has improved the existing ACESProcess to realize further reducing investment costs while maintaining all features of the ACESProcess. The improved process has been named the ACES 21 Process.

A 2,000 mtpd urea granulation plant which is the latest and the largest experience for TECstarted operation successfully in 2000, demonstrating its excellent performance with aqueousurea solution feed. Some details of the project are outlined in the later sections in this paper.

THE ACES PROCESS

The main concept of the original ACES Process is to minimize energy input to the urea plant bycombining the features of solution recycle process and stripping process i.e. a high CO2

conversion and the highly efficient separation of unreacted materials. The ACES Processdrastically reduced steam consumption compared to Total Recycle Process.

The ACES Process, by ensuring NH3 to CO2 molar ratio (N/C ratio) of 4.0 and an operatingtemperature of 190 °C in the reactor give CO2 conversion of 68%, the highest among modernurea processes. The high CO2 conversion reduces the energy required for decomposition ofunconverted materials. The proprietarily designed tray-falling film Stripper efficientlydecomposes and separates ammonium carbamate and excess ammonia in urea synthesis solutionfrom the reactor. Fig. 1 shows the simplified flow diagram of the ACES Process synthesissection.

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Fig. 1

ACES Process Synthesis Section

NO.1 & NO.2CARBAMATECONDENSER

REACTOR

STRIPPER

SCRUBBER

LP STM+BFW

CO2

NH3

TO MP ABSORPTION

FROM MP ABSORPTION

BFW

MP STM

COND.

TO MP DECOMPOSITION

The unique heat integration between the synthesis section and downstream sections furtherreduces energy requirement (See Fig. 2). MP steam is supplied to synthesis section todecompose and separate excess NH3 and carbamate in the stripper. The stripped NH3 and CO2

gas mixture is sent to the carbamate condenser and the condensation heat is recovered by the twoparallel carbamate condensers. One is utilized for decomposition in the medium pressure sectionand the other is for low pressure steam generation to be utilized in the low pressure andevaporation sections. Condensation heat in medium pressure section is also utilized inevaporation section. This multiple heat integration concept, originally invented and developedby TEC, gives the most energy efficient urea process.

The ACES Process has been employed in 13 urea plants since its first application in 1983 (seeTable 1). Over last 10 years, 11 urea plants in 5 countries have employed this process.

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Fig. 2

heat Integration Scheme

C.W.

C.W.

C.W.

UREA NH3 + CO2 + H2O

MEDIUM PRESSURESECTION

LOW PRESSURESECTION

EVAPORATIONSECTION

HEAT RECOVERYSECTION

REACTOR

NH3 CO2

UREAMELT

NH3 + CO2 + H2O

H2O

UREA NH3 + CO2 + H2O

UREA H2O

WATER(BY-PRODUCT)

L.P. STEAM(GENERATED)

M.P. STEAM

Table 1 Experience List of ACES Process

1. KOREA FERTILIZER AND KOREA 600 MAY 1983CHEMICALS CO.

2. FERTIBERIA S.L. SPAIN 750 OCT. 1988

3. UREA FERTILIZER FACTORY BANGLADESH 1,422 FEB. 1993LTD.

4. P.T. PUPUK SRIWIDJAJA INDONESIA 1,725 MAR. 1994

5. P.T. PETROKIMIA GRESIK INDONESIA 1,400 MAY 1994

6. P.T. PUPUK SRIWIDJAJA INDONESIA 1,725 FEB. 1994

7. WEIHE CHEMICAL FERTILIZER CHINA 1,760 MAY 1996

8. WEIXIAN CHEMICAL FERTILIZER CHINA 180 JAN. 1997

9. PAK - AMERICAN FERTILIZER PAKISTAN 1,050 SEP. 1998

10. ENGRO CHEMICAL PAKISTAN LTD. PAKISTAN 1,755 OCT. 1998

11. CHAMBAL FERTILIZERS AND INDIA 2,350 OCT. 1999 CHEMICALS LTD.

12. P.T. PUPUK ISKANDAR MUDA INDONESIA 1,725 (2002)

13. P.T. PUPUK KUJANG INDONESIA 1,725 (2004)

PLANTCLIENT COUNTRY CAPACITY ON-STREAM

(MT/D)

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THE ACES 21 PROCESS

ACES 21 Process Concept

In CO2 stripping technology, the reactor, the largest and the heaviest vessel in urea plant, isnormally installed at 20-22 meter level so as to feed urea synthesis solution to the stripper bygravity. If the reactor is installed on the ground level, civil and erection cost can be greatlyreduced. TEC and PUSRI jointly developed this process incorporating a unique two-stagesynthesis concept comprised by:

n A vertical submerged carbamate condenser, functioning as carbamate condenser, HPscrubber and the primary urea reactor

n A vertical reactor to complete reaction from carbamate to urea, as the secondary reactorn A vertical falling film type stripper to decompose and separate unreacted carbamate and

excess ammonia by CO2 stripping.n A HP ejector motivated by HP liquid ammonia to supply driving force for the HP loop

circulation, so that the reactor is installed on the ground level and other HP vessels are laid-out horizontally, as well as to increase N/C ratio in the reactor high enough so as to achievethe high CO2 conversion.

ACES 21 Synthesis Section

Fig. 3 shows the ACES 21 Process synthesis section. The reactor, stripper, carbamate condenserand ejector comprise the synthesis section as major equipment. Liquid ammonia is fed into thereactor via the ejector. Most of the CO2 is fed to the stripper as stripping media and the rest is fedto the reactor as a source of passivation air and a raw material for urea synthesis in the reactor.Carbamate solution from the carbamate condenser is fed to the reactor after being pumped by theejector that is motivated by high pressure liquid ammonia. Urea synthesis solution leaving thereactor is fed to the stripper. Stripped urea solution is sent to MP decomposition stage. Thestripped off gas is fed to vertical submerged-type carbamate condenser. NH3 and CO2 gascondenses to form ammonium carbamate and urea in the shell side of the carbamate condenser.The condensation heat is recovered to generate low pressure steam in the tube side. Packed bedis provided at the top to absorb uncondensed NH3 and CO2 into recycle carbamate solution fromMP absorption stage. Inert gas from top of the packed bed is sent to MP absorption stage. Thedriving force for liquid and gas circulation in the synthesis loop is mainly provided by the ejector,while appropriate elevation of the carbamate condenser supplies additional driving force bygravity.

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Fig. 3ACES 21 Process Synthesis Section

CARBAMATE CARBAMATE CONDENSERCONDENSER REACTORREACTOR STRIPPERSTRIPPER

EJECTOREJECTOR

INERTS TO ABSORPTION STAGE

FROM ABSORPTION STAGE

MP STM

S.C.

TO DECOMPOSITION STAGE

BFW LP STM

CO2

LIQ. NH3

Vertical Submerged Carbamate Condenser

Vertical submerged design is employed for the carbamate condenser. From process view point,this provides the following advantages:(1) High gas velocity, appropriate gas hold up and sufficient liquid depth in the bubble column

promote mass and heat transfer;(2) The appropriate number of baffle plates distribute gas bubbles in the column effectively

without pressure loss;(3) A vertical design inevitably requires smaller plot area

Optimized N/C Ratio

In the ACES 21 Process, the N/C ratio in the carbamate condenser differs from that in the reactor.A lower N/C in the carbamate condenser lowers vapor pressure, reducing vapor loss from thecarbamate condenser. A higher N/C ratio in the reactor raises CO2 conversion, reducing the heatrequired for decomposition of carbamate in the stripper. Equilibrium vapor pressure becomes itslowest level at around an N/C ratio of 3.0 at which the carbamate condenser is operated. Thereactor N/C ratio should be as high as possible to maximize CO2 conversion as far as itsoperating pressure has appropriate excess pressure to that of the equilibrium.

Since different levels of N/C ratio are employed for the carbamate condenser and the reactor,urea synthesis reaction takes place in two steps.

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Advantages

Features and advantages of the ACES 21 Process are summarized below:

1. The horizontal layout of HP vessels has the following advantages compared to the verticallayout.(a) less HP piping and construction materials are used;(b) easier erection using commonly available construction equipment and techniques;(c) easier operation and maintenance

2. Combining the functions for carbamate formation, heat recovery, urea synthesis, and inertgas scrubbing into one vertical submerged carbamate condenser has the followingadvantages in comparison with conventional separate reactor and falling film carbamatecondenser:(a) fewer and smaller sized HP vessels;(b) a smaller heat transfer area for heat recovery;(c) less HP piping and construction material are required

3. Simplified synthesis loop offers the followings advantages over conventional strippingtechnologies:(a) less HP piping and construction materials are required;(b) easier operation and maintenance

4. Improved design for the reactor and the stripper give the following advantages incomparison to conventional ones:

(a) less volume and weight for both the reactor and the stripper;(b) easier reactor and stripper fabrication

5. Optimizing N/C ratios at different levels for the carbamate condenser and the reactor atlower synthesis pressure results in the following advantages over the ACES Process:(a) lower mechanical design pressure of HP vessels and rotating equipment;(b) less energy consumption

TEC and PUSRI confirmed the combined effect of the above improvements, based on the one-year demonstration with the pilot plant and the following engineering study for an industrialscale plant, reduces the urea plant direct cost by approximately 10% and energy consumption by5-20% from the original ACES process.

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REVAMPING OF CONVENTIONAL SOLUTION RECYCLE UREA PROCESS

Revamping Technology Options

Table 2 shows the revamping technology options offered by TEC to improve plant efficiency andproduct quality. Those options are so selected to meet the objectives for the revamp and/orrenovation project.

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PP

PP

PPP

Table 2 REVAMPING TECHNOLOGY OPTIONS

ACES 21

D PROCESS

GRANULATION PROCESS

VACUUM CONCENTRATION

PROCESS CONDENSATE TREATMENT

CENTRIFUGAL TYPEHP ROTATING MACHINE

ACOUSTIC GRANULATOR

DUST SCRUBBER

Capacity Energy Product Environment MaintenanceIncrease Saving Quality

P PP P

PP

ACES 21 Process Features for Revamping

ACES 21 is also suitable for revamping conventional solution recycle urea plants in an efficientway. For example, TEC’s Total Recycle C-Improved Process plant can be revamped to have 130– 150% capacity of original nameplate together with 30 – 40 % saving of specific energyconsumption per metric ton of the product, simply adding a carbamate condenser, a stripper andan ejector to the synthesis section. The ACES 21 revamp concept thus renovates conventionalless efficient urea plants to be the most advanced and efficient ones, owing to the followingfeatures:

(1) ACES 21 adopts two-stage reaction with a vertical submerged condenser and a reactor. Thisenables to increase the synthesis section capacity to 150% of original nameplate by re-utilizing the existing reactor on the ground level without adding a new reactor, resulting ingreat reduction of equipment cost;

(2) Horizontal lay-out of HP equipment greatly reduces erection and construction cost;(3) Lowered synthesis pressure of 155 kg/cm2G greatly reduces energy for raw material feed;(4) Adoption of ACES 21 synthesis loop maximizes heat recovery in the synthesis section.

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Revamp Case Study

A revamp study to increase capacity to 150% of nameplate capacity and 30-40% energyreduction for TEC Total Recycle C-Improved plants has been carried out. Fig. 4 shows a blockflow diagram for the overall revamped urea plant. The study result has shown positive feasibilityin view of profitability, environmental protection and energy saving. The following paragraphsoutline the modifications in each section.

Fig. 4

Block flow diagram

NH3 FEED

SYSNTHESIS(ACES 21)

PURIFICATION

CRYSTALLIZATION

PRILLING

CO2COMPRESSION

RECOVERY

CONCENTRATION

GRANULATION

NH3 CO2

MODIFICATION

NEW

MODIFICATION ORREPLACEMENT

NEW

MINORMODIFICATION

MINORMODIFICATION

1,725 T/DUREA

875 T/DUREA

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Outline of Revamp Schemes

1. Synthesis section and raw material feeding section

Fig. 5 shows process flow of the revamped synthesis section. Existing reactor is fully re-utilizedas ACES 21 reactor without relocation. Stripper, carbamate condenser and ejector are newlyadded and NH3 pre-heater and CO2 compressor are modified or added.

Fig. 5Revamped Synthesis Section

CO2

NH3

REACTOR STRIPPER CONDENSER HP DECOMPOSER

TO LP DECOMPOSER

HP ABSORBER

FROM LP ABSORBER

CARBAMATE FEEDPUMPNH3 PUMPCO2 COMPRESSOR

EJECTOR

BFW LPSTEAM

COND.

MP STEAM

TO NH3 CONDENSER

NEW EQUIPMENT

Raw material feed equipments are evaluated as follows:

(i) CO2 compressorReduction of the discharge pressure from 250 Kg/cm2G to 160 Kg/cm2G greatly reducesthe energy for CO2 compression. In general, following two options are consideredpractical to meet the increased capacity.(a) Replace the existing reciprocating compressor(s) to new one centrifugal compressor

aiming maintenance free and oil free.(b) Add a reciprocating compressor equivalent to the additional capacity aiming

minimum investment cost.

(ii) Turbine for CO2 compressorDepending on the steam system, turbine for CO2 compressor may be required to bemodified to extraction-admission-condensing type to supply middle pressure steam forHP stripper and to utilize low-pressure steam generated in ACES 21 condenser.

(iii) Ammonia pumpNo modification is required and pumping energy is significantly reduced due to decreaseof required capacity. The existing pumps originally have sufficiently high dischargepressure to supply motive energy for HP ejector

(iv) Carbamate pumpNo modification is required and pumping energy is greatly reduced because requiredcapacity is same and discharge pressure is decreased from 250 Kg/cm2G to 160 kg/cm2G.

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(v) Hydrogen removalHydrogen removal unit is installed in the CO2 compression section to avoid flammablecondition in the synthesis section since passivation air requirement increases afterrevamp.

2. Purification section

Purification section is utilized without major modifications. An additional pre-heater for HPDecomposer, heated by 5 kg/cm2G steam, is installed to utilize low pressure steam generatedafter revamp.

3. Recovery section

Recovery section is utilized without major modifications. Additional stage for NH3 recoveryabsorber is installed as the inert gas to high pressure recovery system increases due to increasedair supply for passivation and hydrogen removal.

4. Finishing section

Finishing section revamp options can be categorized into the following schemes depending onthe prospective market conditions, environmental regulations and owners requirement:

i) Minimum Investment without Improving Product Quality and Pollution Abatement:n Total production capacity is by prilled urea only. Crystallization section is utilized

without modification and new evaporators equivalent to the additional capacity (875mtpd) are added. Existing prilling tower is utilized by modifying induced fans toincrease air flow rate and replacing distributors for prilling.

n As an alternative, the existing crystallization process can be converted to vacuumevaporation process aiming at maintenance free and energy saving operation. Theexisting crystallizer is utilized as a vacuum concentrator.

ii) Product Quality Improvement and Pollution Abatement for Additional Capacity byInstalling a Granulation Plantn The existing crystallization section and prilling tower is utilized without modification.

New vacuum evaporation section and a granulation plant equivalent to the additionalcapacity (875 mtpd) are newly installed.

iii) Product Quality Improvement and Pollution Abatement for Total Capacity by Installing aGranulation Plantn The existing crystallization process is totally converted to vacuum evaporation process.

Existing prilling tower is totally converted to granulation.

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Process Performance and Economic Evaluation

Table 3 summarizes three typical revamp options. Case-1 needs the highest investment amongthe three, however it provides the most simple steam system and the lowest operation andmaintenance cost, owing to the all centrifugalization of CO2 compressor. Case-2 shows thesecond lowest investment, however it requires more complicated modification of steam systemand higher operation and maintenance cost than Case-1. Case-3 shows the lowest investment, solong as 875 mtpd urea can be sold as 70% urea solution with appropriate margin to other plant.Preliminary economic evaluation study has indicated that considerable steam saving by 0.4 T/Tachieved by ACES 21 concept and reasonable assumption of 20-30 US$ margin to netproduction cost per metric ton of urea product will recover the investment within 3 – 5 years inthose three cases.

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Table 3 Revamp Option

1,725 mtpd TR-CI 2,600 mtpd ACES 21

Replacement of Addition ofCO2 Compression Centrifugal Reciprocating

Compressor and Turbine CompressorSynthesis ACES 21Purification /Recover No Modification

Addition of Export 850 mtpdConcentration 850 mtpd Evaporation Urea Solution

Addition ofFinishing 850 mtpd Granulation

Steam System Optimum Simple Complicated ComplicatedConstruction / Modification Simple Complicated ComplicatedOperating / Maintenance Cost Low High MediumOperation Flexibility High Medium Low

CASE-1 CASE-2 CASE-3

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Example of A Revamping Study

Typical revamping study to renovate a TEC TR-C urea plant with ACES 21 technology has beenrecently carried out based on the conditions shown in Table 4. The case-2 is to convert prilling togranulation.

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Table 4 Study Cases

EXISTING CASE-1 CASE-2Capacity 1300 MTPD 1300 MTPD 1300 MTPD

CO2 Booster Driver Back Turbine Extraction Admission Extraction AdmissionCondensing Turbine Condensing Turbine

Synthesis TR-C ACES 21 ACES 21Urea Reactor Titanium Re-lined with S.S Re-lined with S.S

lining with Baffle Plates with Baffle Plates

Finishing Crystallization Vacuum Evaporation Vacuum Evaporation

Product Forming Conventional Prilling with Spout-Fluid BedPrilling Acoustic Granulator Granulation

with Natural Draft + ID FanDust Recovery Urea Solution Urea Solution Packed Bed

Spray Spray + Demister Dust ScrubberProcess Condensate None Hydrolyzer & Stripper Hydrolyzer & Stripper Treatment

Table 5 summarizes utility and energy consumption for each case. Energy consumption toproduce one metric ton of prilled or granulated urea is reduced by 0.36 – 0.40 Gcal. This drasticenergy reduction considerably improves the competitiveness of the urea plants.

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Table 5 Performance Summary : Utilities Consumption

EXISTING CASE-1 CASE-2Steam (T/T)

Import 43 Kg/cm2G x 385oC 1.67 1.14 1.1312 Kg/cm2G x 215oC 0.09 - -

Export 21 Kg/cm2G x 318oC - -0.16 -0.1612 Kg/cm2G x 265oC -0.32 - -

Net 1.44 0.98 0.97

Electricity (kWh/T) 83 66 82

Energy (Gcal/T)Steam 1.101 0.747 0.740Electricity 0.204 0.162 0.201Total 1.305 0.909 0.941Saving Base 0.396 0.364Note : 2475 kcal/kWh for Electricity.

30% Saving 28% Saving

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TEC GRANULATION PROCESS

TEC has developed own granulation technology so called Spout-Fluid Bed Granulation since theearly 1980s. In the year 2000, a 2,000 mtpd urea granulation plant which is the latest and thelargest experience for TEC started operation successfully, demonstrating its excellent andreliable performance with aqueous urea solution feed.

1) Mitsui Toatsu Chemicals, Inc. Chiba, Japan 50 19752) Petrochem Ltd. Kapuni, New Zealand 470 19833) Mitsui Toatsu Chemicals, Inc. Osaka, Japan 100 19834) SKW Piesteritz GmbH Piesteritz, Germany 1,200 19955) Petrochem Ltd. Kapuni, New Zealand 750 19976) SKW Piesteritz GmbH Piesteritz, Germany 500 19987) Ningxia Chemical Works of CNPC Ningxia China 1,740 19998) P.T. Pupuk Iskandar Muda North Aceh, Indonesia 1,725 (2002)9) Lutianhua Group Inc. Sichuan, China 2,000 200010) Zhanyi Fertilizer Plant Yunnan,China 600 (2002)

OWNER LOCATION CAPACITY ON(MTPD) STREAM

Table 6 Experience List of TEC Granulation Process

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Process Description

Figure 6 shows a typical flow diagram of TEC Urea Granulation Process. The Urea Granulationprocess consists of following three sections.• granulation section• recycle and product cooling section• dust removal and recovery section

Fig.6: TEC urea granulation process flow diagram

Aqueous urea solution from urea plant is fed to the granulator to enlarge recycle particles in thegranulator. In the granulator, the granules are dried and cooled simultaneously. The granulator isoperated at 110-115ºC and at slightly negative pressure. Enlarged urea particles are cooled toabout 90ºC in the after-cooler inside the granulator to be transported to the recycle section.

The discharged granules are separated into three sizes, product, small and large size by thescreen. Product size granules are further cooled below 60ºC in the product cooler to be sent tothe urea storage or bagging facility. Large size granules are crushed by the crusher. The crushedparticles and smaller size particles from the screen are recycled to the granulator as seed.

Urea dust contained in the exhaust air from the granulator and the product cooler is scrubbed inthe dust scrubber by contacting counter currently with aqueous urea solution. The urea dustcontent in the exit air of the dust scrubber is 30 mg/Nm3 or less. Urea recovered in the dustscrubber, approximately 3-4 % of production rate, is recycled to the urea plant as 45 wt% ureasolution.

Any other urea granulation processes available in the world have similar flow schemes, howevercharacteristics and performance of the process strongly depend upon the granulator design. Thefeatures of TEC Urea Granulation Process are given below:

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(i) High Energy Efficiency:n No requirement of compressed atomizing air for granulator reduces power consumption;n Seed circulation at moderately high temperature (= 90ºC) minimizes cooling air

requirement and heat removal in the process;n Optimal bed depth minimizes pressure loss in the granulator;n Uniquely designed low pressure drop dust scrubber minimizes power consumption of

induced fan(s)

Table 7 shows a typical steam and power consumption of TEC Urea Granulation Process.

Table 7Typical specific utilities consumption

Steam (MT/MT) 0 – 0.03Power (kWh/T) 23 – 25 (Fluid Bed Cooler)

19 – 21 (Bulk Flow Cooler)Note: ambient temperature = 30 - 35ºC

In the case that water cooled bulk flow cooler is applied for product cooling instead of fluidizedbed cooler, the power consumption is further reduced by about 4 kWh/MT. Since its firstapplication in 1993, TEC has been ready to apply the both options in granulation plant design,i.e. the bulk flow cooler and the fluidized bed cooler considering site conditions, energy cost andclient’s requirement.

(ii) High Product Qualityn Rapid cooling of granules in the granulator with minimum residence time reduces biuret

formation to negligibly small;n Efficient drying in the granulator reduces granule moisture low enough to increase

product hardness;n Optimal combination of spouted bed and fluidized bed produces round and uniform

granules.

Table-8 shows typical quality of the granules produced by TEC Urea Granulation Process.

Table 8Typical product quality

Total Nitrogen 46.3wt%Biuret 0.7wt%

Moisture 0.25wt%Formaldehyde 0.45wt%Size (2-4mm) 95wt%

Hardness 3.5kg at 3mm

(iii) Low Urea Dust Emissionn Optimal spouted bed air velocity minimizes dust formation in the granulator.n Uniquely designed low delta-P dust scrubber proven through application to twelve

prilling towers and seven urea granulators reduces urea dust to less than 30 mg/Nm3.

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TEC Spout-Fluid Bed Granulator

Figure 7 shows a schematic diagram of TEC Spout-Fluid Bed Granulator. The granulatorconsists of spouted beds and fluidized bed on the perforated plate, spray nozzles and air ductmanifolds. Each spouted bed has one spray nozzle. Recycle urea granules are enlarged whilepassing through the spouted beds and the fluidized bed. Aqueous urea solution ( > 95wt% ) issprayed into the spouted beds through pressure spray nozzles.

Fig. 7: TEC spout-fluid bed granulator

Vigorous mixing in the spouted bed gives round and uniform granules. Since air introduced forspouting and fluidizing not only removes urea solidification heat but also evaporates watercontained in the sprayed aqueous urea droplets and granules, the urea granules are dried to lessthan 0.25wt% moisture content at the exit of the granulator. Owing to the drying effect in thegranulator, cost and energy consumption in the urea process plant can be reduced.

Industrial scale granulator has multi-stage spouted bed arrangement, therefore the granulator issimply scaled-up by increasing the number of the spouted beds.

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Equipment Layout

Figure 8 shows a bird’s-eye view of a typical 1,700 mtpd TEC Urea Granulation Process plant.As can be seen, the building for granulator and other solid handling equipment is very compact.

Fig. 8: 3-D graphic representation of TEC granulation plant

TEC Urea Granulation Process has alternative layout options, i.e. the dust scrubber can beinstalled on the top to reduce the plot area. This option can be attractive for the case thatavailable area is very limited, for example, the case for prill tower conversion to granulation.Four granulation plants have employed this layout.

Large Scale Granulation Plants in China

Two large scale urea granulation plants based on TEC technology, of which respectivenameplate capacity is 1,740 mtpd and 2,000 mtpd, have been commissioned in China in 1999and 2000. Both plants have single train TEC Spout-Fluid Bed Granulator designed to receiveaqueous urea solution as feed. The both plants are designed to be capable to produce either 2-4mm product or 5-8 mm product, depending upon the market demand. In the 2,000 mtpd unitproject for Lutianhua Group Inc., (LTH) which aimed at the total conversion of existing prillingtower to granulation, the following advantages have been demonstrated:• 2,000mtpd production with aqueous urea solution feed• Remarkably low urea dust emission (= 5 mg/Nm3) by uniquely designed dust scrubber• Low production cost owing to low utilities consumption• Easy and smooth start-up in large capacity unit

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Fig. 9 LTH 2,000 mtpd granulation plant

This project came into effect in May 1999. TEC supplied the process design package andproprietary equipment as process licenser. China Wuhuan Chemical Engineering Corporation(CWCEC) carried out detail engineering and LTH performed procurement and construction.Owing to the efficient project coordination and cooperation among TEC, CWCEC and LTH, theplant started operation in July 2000, within only 14 month after the effective date of contract.Some details of the project are introduced below.

Operation history

The plant went into operation in the beginning of July 2000 and the plant load reached 100%very smoothly. Performance test run was completed in October 2000. Performance test waspostponed due to a repair work of bucket elevator and urea prill production required by marketreason. Maximum daily capacity reached 107% in October 2000. The plant has operatedsuccessfully producing good quality product for both export and domestic use.

CONCLUSION

TEC, the only urea process licenser that covers by itself all the proven essential technologies, i.e.urea synthesis, prilling, granulation and pollution abatement, has improved the ACES ureaprocess to establish the most advanced urea process “ACES 21” cooperating with PUSRI. TECSpout-Fluid Bed Granulation Process has been adopted in 8 revamps and 2 grass roots plants.Several revamp studies have proved that conventional urea plant can be revamped to be the mostcompetitive one with ACES 21 technology and Spout Fluid Bed Granulation in very efficientway. The recent successful commissioning of a large scale granulation plants further promotesprilling tower conversion to granulation aiming at drastic improvement of product quality. TheTEC-PUSRI ACES 21 and TEC Spout-Fluid Bed Granulation provide the most realistic solutionto improve efficiency and product quality of conventional urea plants.