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Technology Profile
Urea
Overview With more than four decades of experience in the design and construction of urea plants, Uhde is regarded as one of the top international contractors in this field. We have access to the leading urea technologies, such as: • CO2 stripping processes, Stamicarbon, licensing subsidiary of DSM, Netherlands • Fluidised-bed granulation The carbon dioxide stripping process first introduced by Stamicarbon in the 1960s has undergone significant improvement in the last 10 years, resulting in the innovative Stamicarbon Urea 2000plusTM technology. The first step in this technology development was the pool condenser. This is basically a horizontal high-pressure carbamate condenser with a submerged U-tube bundle. It combines the function of the falling film-type carbamate condenser with part of the reactor function of the conventional CO2 stripping process. Following on from this, Stamicarbon then developed the horizontal pool reactor. This reactor further simplified the urea synthesis section by reducing the number of highpressure components. As Uhde is an approved engineering partner of Stamicarbon, our customers can now seize the opportunity to take advantage of this latest technology: • Urea 2000plusTM technology with pool condenser • Urea 2000plusTM technology with pool reactor Of course, we can also supply the conventional Stamicarbon CO2 stripping process with standard falling film-type carbamate condenser if required. In conjunction with our partners, we continually search for innovative technologies to enhance our portfolio and to offer our customers state-of-the-art technology.
Uhde Technology Profile: Urea
Page 1 of 7
Copyright © Uhde GmbH 2002
Conventional CO2 stripping process In all CO2 stripping processes, ammonia and carbon dioxide are fed directly to the synthesis section. In a first fast exothermic reaction between ammonia and carbon dioxide ammonium carbamate is formed. The second reaction is the endothermic dehydration of carbamate to urea and water. Optimum process conditions of approx. 145 bar and 180 °C and a nitrogen / carbon (N/C) ratio of 3 are maintained. The dehydration of ammonium carbamate is an equilibrium reaction. For this reason, the reaction mixture from the reactor is subjected to a high-pressure stripping, using carbon dioxide as stripping gas to remove unreacted ammonia and carbon dioxide. The stripper offgases are returned to the reactor after condensation in the high-pressure carbamate condenser. The carbamate solution from the high-pressure scrubber and fresh ammonia are added. Exhaust gases, which are separated from the liquid at the reactor top, are scrubbed in a high-pressure and a low-pressure scrubber, thus minimising ammonia emissions.
LP absorber Atmospheric absorber
Reactor
HP carb. cond.
HP scrubber
Rectifying column & sep.
LP carb. con.
NH3 CO2
HP heat
Air
exchang. (stripper)
Cond. Pre-/evaporator
Gases Liquids Urea Steam/Cond. Cool. Water
Hydrolyser
Reflux cond. 1st & 2nd desorber
Flash tank
Flash tank cond.
Urea melt Purif. Process water
In view of the low ammonia and carbon dioxide concentrations in the stripped urea solution, a separate high-pressure ammonia recycling stage is not necessary. The ammonia and carbon dioxide still contained in the urea solution discharged by the stripper are recovered in the low-pressure recirculation stage. The urea solution leaving the recirculation section is further concentrated in the evaporation section from approx. 74% to 96% by weight, thus meeting the requirements of the downstream fluidised-bed granulation process. Evaporation takes place in a vacuum section to minimise biuret formation.
Uhde Technology Profile: Urea
Page 2 of 7
Copyright © Uhde GmbH 2002
The entire process condensate is treated in the desorption and hydrolysis section. Ammonia and carbon dioxide are spelled off in a stacked two-desorber column whereas small amounts of urea are dissociated in the hydrolysis column. The purity of the treated condensate allows it to be used as make-up water for the cooling water cycle or it may also be added to the boiler feedwater after polishing. Consequently, the Stamicarbon urea process has no waste water effluent.
Urea synthesis with pool condenser (Stamicarbon Urea 2000plusTM technology) The pool condenser is basically a horizontal vessel with a submerged U-tube bundle. It combines the function of the falling film-type carbamate condenser with part of the reactor function of the conventional CO2 stripping process. A 30-40% reduction in the reactor volume is achieved by shifting a part of the reaction volume to the pool condenser. This is of particular advantage for high-capacity single-line plants since the reactor is one of the heaviest items of equipment. The stripper gases are condensed together with fresh ammonia and overhead vapours from the HP scrubber in a pool of liquid, while low-pressure steam is generated within the tubes of the bundle.
to LP absorber
Carbamate solutions HP scrubber Pool condenser Reactor
Gases Liquids Urea NH3 CO2
HP heat exchanger (stripper)
to dissociation
Air
Uhde Technology Profile: Urea
Steam/Cond. Cool. Water
Page 3 of 7
Copyright © Uhde GmbH 2002
Urea synthesis with pool reactor (Stamicarbon Urea 2000plusTM technology) A further step towards the full integration of equipment within the urea synthesis section is the horizontal pool reactor, first introduced by Stamicarbon in 1996. By combining the functions of the urea reactor and the carbamate condenser in one vessel, the number of high-pressure items in the synthesis unit has been reduced from 4 to 2 (stripper and pool reactor) and a considerable amount of interconnecting high-pressure piping has been dispensed with. The condensing section of the reactor contains the U-tube bundle, already used in the pool condenser technology, while the rest of the pool reactor forms the reaction zone for the dehydration of the carbamate.
Carbamate solutions
to LP absorber
HP scrubber sphere
Pool reactor
Gases Liquids Urea Steam/Cond. Cool. Water NH3
HP heat exchanger (stripper)
CO2 to rectifying column
Air
Uhde Technology Profile: Urea
Page 4 of 7
Copyright © Uhde GmbH 2002
Technology highlights CO2 stripping process highlights
Advantages of the Urea 2000plusTM technology
•
low energy consumption
•
•
high process efficiency / low raw material consumption figures
Savings in investment costs due to the reduction in size and the number of high-pressure items
•
Operational advantages:
•
high on-stream times (reliability)
•
low corrosion rates
•
high safety standards
•
low emissions
•
simple operation
•
easy maintenance
Uhde Technology Profile: Urea
-
more stable level / pressure control
-
less sensitivity to changes in the load or the N/C ratio
-
fast capacity change of the plant due to self-regulating heat transfer characteristics
•
Reduced construction height, resulting in reduced construction costs
•
Improved heat transfer / reduced heat exchanger area
Page 5 of 7
Copyright © Uhde GmbH 2002
Fluidised-bed granulation The urea melt from the evaporation section is fed to the fluidised-bed granulation unit and further processed to high-grade solid granules. Formaldehyde is injected into the urea melt as a granulation agent before it is atomised in the granulator. The granulation mode permits accretion, which means that the granules grow from seed material by solidification of thousands of tiny urea droplets on their surface. The granulated product extracted from the granulator is cooled down and lifted to the screening section. The oversize material is crushed and returned as seeding particles to the granulator together with the undersize grains. After final cooling, the specification-grade product is sent to the storage facility. The granules produced by this technology are round and very hard and therefore highly resistant to crushing and abrasion. They can be produced in a wide range of defined sizes. Urea dust, which is entrained in the air from the granulator, the fluidised-bed coolers and various dedusting points, is recovered in a scrubbing system. Process condensate from the desorption section is used as make-up water for the scrubbing liquid, which is recycled to the evaporation section. Because of its high efficiency and a granulator that ensures excellent product quality with extremely low solid recycle rates, the fluidised-bed granulation process is the leading granulation technology. It permits the construction of single-train granulation plants which are in line with the largest synthesis units so far constructed. The process conforms to the most stringent environmental laws as there is no waste water and only minimum dust emission. Maximum operating flexibility and reliability as well as minimum maintenance and operating staff requirements are further features of this advanced process.
Uhde Technology Profile: Urea
Page 6 of 7
Copyright © Uhde GmbH 2002
Experience Uhde's experience in the engineering and construction of urea plants spans several decades. We are an approved engineering contractor of the world-renowened licensor Stamicarbon. We engineered and constructed the first urea plant using Stamicarbon's carbon dioxide stripping process and were also chosen as Stamicarbon’s engineering partner for the first pool reactor unit in DSM’s new urea plant at Geleen, Netherlands. In the last 10 years Uhde has commissioned or revamped nine urea plants. These references include the world's largest single-train plant with a capacity of 2,850 mtpd of urea which we engineered and constructed for Saskferco, Canada. Ammonia and urea fertiliser complex, Saskferco, Canada
Uhde Technology Profile: Urea
Page 7 of 7
Copyright © Uhde GmbH 2002
Urea
Overview With more than four decades of experience in the design and construction of urea plants, Uhde is regarded as one of the top international contractors in this field. We have access to the leading urea technologies, such as: • CO2 stripping processes, Stamicarbon, licensing subsidiary of DSM, Netherlands • Fluidised-bed granulation The carbon dioxide stripping process first introduced by Stamicarbon in the 1960s has undergone significant improvement in the last 10 years, resulting in the innovative Stamicarbon Urea 2000plusTM technology. The first step in this technology development was the pool condenser. This is basically a horizontal high-pressure carbamate condenser with a submerged U-tube bundle. It combines the function of the falling film-type carbamate condenser with part of the reactor function of the conventional CO2 stripping process. Following on from this, Stamicarbon then developed the horizontal pool reactor. This reactor further simplified the urea synthesis section by reducing the number of highpressure components. As Uhde is an approved engineering partner of Stamicarbon, our customers can now seize the opportunity to take advantage of this latest technology: • Urea 2000plusTM technology with pool condenser • Urea 2000plusTM technology with pool reactor Of course, we can also supply the conventional Stamicarbon CO2 stripping process with standard falling film-type carbamate condenser if required. In conjunction with our partners, we continually search for innovative technologies to enhance our portfolio and to offer our customers state-of-the-art technology.
Uhde Technology Profile: Urea
Page 1 of 7
Copyright © Uhde GmbH 2002
Conventional CO2 stripping process In all CO2 stripping processes, ammonia and carbon dioxide are fed directly to the synthesis section. In a first fast exothermic reaction between ammonia and carbon dioxide ammonium carbamate is formed. The second reaction is the endothermic dehydration of carbamate to urea and water. Optimum process conditions of approx. 145 bar and 180 °C and a nitrogen / carbon (N/C) ratio of 3 are maintained. The dehydration of ammonium carbamate is an equilibrium reaction. For this reason, the reaction mixture from the reactor is subjected to a high-pressure stripping, using carbon dioxide as stripping gas to remove unreacted ammonia and carbon dioxide. The stripper offgases are returned to the reactor after condensation in the high-pressure carbamate condenser. The carbamate solution from the high-pressure scrubber and fresh ammonia are added. Exhaust gases, which are separated from the liquid at the reactor top, are scrubbed in a high-pressure and a low-pressure scrubber, thus minimising ammonia emissions.
LP absorber Atmospheric absorber
Reactor
HP carb. cond.
HP scrubber
Rectifying column & sep.
LP carb. con.
NH3 CO2
HP heat
Air
exchang. (stripper)
Cond. Pre-/evaporator
Gases Liquids Urea Steam/Cond. Cool. Water
Hydrolyser
Reflux cond. 1st & 2nd desorber
Flash tank
Flash tank cond.
Urea melt Purif. Process water
In view of the low ammonia and carbon dioxide concentrations in the stripped urea solution, a separate high-pressure ammonia recycling stage is not necessary. The ammonia and carbon dioxide still contained in the urea solution discharged by the stripper are recovered in the low-pressure recirculation stage. The urea solution leaving the recirculation section is further concentrated in the evaporation section from approx. 74% to 96% by weight, thus meeting the requirements of the downstream fluidised-bed granulation process. Evaporation takes place in a vacuum section to minimise biuret formation.
Uhde Technology Profile: Urea
Page 2 of 7
Copyright © Uhde GmbH 2002
The entire process condensate is treated in the desorption and hydrolysis section. Ammonia and carbon dioxide are spelled off in a stacked two-desorber column whereas small amounts of urea are dissociated in the hydrolysis column. The purity of the treated condensate allows it to be used as make-up water for the cooling water cycle or it may also be added to the boiler feedwater after polishing. Consequently, the Stamicarbon urea process has no waste water effluent.
Urea synthesis with pool condenser (Stamicarbon Urea 2000plusTM technology) The pool condenser is basically a horizontal vessel with a submerged U-tube bundle. It combines the function of the falling film-type carbamate condenser with part of the reactor function of the conventional CO2 stripping process. A 30-40% reduction in the reactor volume is achieved by shifting a part of the reaction volume to the pool condenser. This is of particular advantage for high-capacity single-line plants since the reactor is one of the heaviest items of equipment. The stripper gases are condensed together with fresh ammonia and overhead vapours from the HP scrubber in a pool of liquid, while low-pressure steam is generated within the tubes of the bundle.
to LP absorber
Carbamate solutions HP scrubber Pool condenser Reactor
Gases Liquids Urea NH3 CO2
HP heat exchanger (stripper)
to dissociation
Air
Uhde Technology Profile: Urea
Steam/Cond. Cool. Water
Page 3 of 7
Copyright © Uhde GmbH 2002
Urea synthesis with pool reactor (Stamicarbon Urea 2000plusTM technology) A further step towards the full integration of equipment within the urea synthesis section is the horizontal pool reactor, first introduced by Stamicarbon in 1996. By combining the functions of the urea reactor and the carbamate condenser in one vessel, the number of high-pressure items in the synthesis unit has been reduced from 4 to 2 (stripper and pool reactor) and a considerable amount of interconnecting high-pressure piping has been dispensed with. The condensing section of the reactor contains the U-tube bundle, already used in the pool condenser technology, while the rest of the pool reactor forms the reaction zone for the dehydration of the carbamate.
Carbamate solutions
to LP absorber
HP scrubber sphere
Pool reactor
Gases Liquids Urea Steam/Cond. Cool. Water NH3
HP heat exchanger (stripper)
CO2 to rectifying column
Air
Uhde Technology Profile: Urea
Page 4 of 7
Copyright © Uhde GmbH 2002
Technology highlights CO2 stripping process highlights
Advantages of the Urea 2000plusTM technology
•
low energy consumption
•
•
high process efficiency / low raw material consumption figures
Savings in investment costs due to the reduction in size and the number of high-pressure items
•
Operational advantages:
•
high on-stream times (reliability)
•
low corrosion rates
•
high safety standards
•
low emissions
•
simple operation
•
easy maintenance
Uhde Technology Profile: Urea
-
more stable level / pressure control
-
less sensitivity to changes in the load or the N/C ratio
-
fast capacity change of the plant due to self-regulating heat transfer characteristics
•
Reduced construction height, resulting in reduced construction costs
•
Improved heat transfer / reduced heat exchanger area
Page 5 of 7
Copyright © Uhde GmbH 2002
Fluidised-bed granulation The urea melt from the evaporation section is fed to the fluidised-bed granulation unit and further processed to high-grade solid granules. Formaldehyde is injected into the urea melt as a granulation agent before it is atomised in the granulator. The granulation mode permits accretion, which means that the granules grow from seed material by solidification of thousands of tiny urea droplets on their surface. The granulated product extracted from the granulator is cooled down and lifted to the screening section. The oversize material is crushed and returned as seeding particles to the granulator together with the undersize grains. After final cooling, the specification-grade product is sent to the storage facility. The granules produced by this technology are round and very hard and therefore highly resistant to crushing and abrasion. They can be produced in a wide range of defined sizes. Urea dust, which is entrained in the air from the granulator, the fluidised-bed coolers and various dedusting points, is recovered in a scrubbing system. Process condensate from the desorption section is used as make-up water for the scrubbing liquid, which is recycled to the evaporation section. Because of its high efficiency and a granulator that ensures excellent product quality with extremely low solid recycle rates, the fluidised-bed granulation process is the leading granulation technology. It permits the construction of single-train granulation plants which are in line with the largest synthesis units so far constructed. The process conforms to the most stringent environmental laws as there is no waste water and only minimum dust emission. Maximum operating flexibility and reliability as well as minimum maintenance and operating staff requirements are further features of this advanced process.
Uhde Technology Profile: Urea
Page 6 of 7
Copyright © Uhde GmbH 2002
Experience Uhde's experience in the engineering and construction of urea plants spans several decades. We are an approved engineering contractor of the world-renowened licensor Stamicarbon. We engineered and constructed the first urea plant using Stamicarbon's carbon dioxide stripping process and were also chosen as Stamicarbon’s engineering partner for the first pool reactor unit in DSM’s new urea plant at Geleen, Netherlands. In the last 10 years Uhde has commissioned or revamped nine urea plants. These references include the world's largest single-train plant with a capacity of 2,850 mtpd of urea which we engineered and constructed for Saskferco, Canada. Ammonia and urea fertiliser complex, Saskferco, Canada
Uhde Technology Profile: Urea
Page 7 of 7
Copyright © Uhde GmbH 2002
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