EA040954B1 - METHOD AND PLANT FOR PRODUCING UREA WITH HEAT INTEGRATION IN LOW PRESSURE REGENERATION SECTION - Google Patents

Description

The field of technology to which the invention belongs

The invention relates to a method and plant for the production of urea by stripping, as well as to a method for modifying an existing plant for the production of urea.

State of the art

Known methods for producing carbamide using a high pressure stripper (HP) and without a high pressure stripper (HP). In the urea production process without a high pressure stripper, the heat supplied to the urea synthesis solution is generally applied only once; thus, this type of process can be called an N=1 process. In high pressure stripping urea processes, heat is supplied to the first heater (stripper), regenerated in the high pressure carbamate condenser, and reused in the low pressure heaters. The supplied heat is effectively applied twice; thus, the term process n=2 is used. The average energy consumption in the stripping process is 0.8-1.0 tons of steam per ton of carbamide.

In one example of a typical Stamicarbon CO2 stripping carbamide process, the gas from the low pressure digester is passed through a distillation column (for countercurrent contact with the incoming urea solution) and then fed directly into a low pressure carbamate condenser that uses a cooling agent. water. The urea solution from the low pressure digester is fed to a flash vessel and then to a pre-evaporator where it is heated (Ullmann's Encyclopaedia, chapter Urea, 2010).

In Ullmann's Encyclopaedia, chapter Urea, 2010, it was mentioned that some methods were described in the 1980s to reduce energy consumption even further by further applying the fold effect to N=3, in which the heat supplied to the first heater (the stripper) ), effectively applied three times (N=3). Specifically, in conceptual form, a urea synthesis solution is converted to a urea melt by passing through three heaters in succession, the second heater applying the heat of condensation of a gas condenser from the first heater; the third heater uses the condensation heat provided by the condenser used to condense the gas from the second heater.

US 2015/0119603 describes a process for the production of urea from ammonia and carbon dioxide in a urea plant comprising a high pressure synthesis section with a horizontal pool condenser. The method includes exchanging heat from a high-pressure process medium supplied to the casing section of the pool condenser to a medium-pressure urea-containing solution supplied to the first heat exchange section provided in the pool condenser for at least decomposing ammonium carbamate into NH3 and CO2. In one embodiment, the gas produced in the first heat exchange section is fed to a medium pressure condenser evaporator where the gas is at least partially condensed and the water from the mixture of urea and water is evaporated under vacuum. It can be seen that heat is effectively applied three times in the process described in US 2015/0119603.

The disadvantage of the method proposed in US 2015/0119603 is that the first heat exchange section, such as a U-shaped tube bundle, is in contact with the process fluid from both sides. The process fluid contains ammonium carbamate and is highly corrosive at temperatures associated with high pressure and medium pressure service. This makes it difficult to create a horizontal pool condenser, in particular connecting a pipe to a tube sheet, given that the corrosive fluid in the pipes passes through bored holes in the tube sheet, and the tube sheet consists of carbon steel located between two corrosion-resistant layers.

US 2015/0086440 describes a method for assembling a tube sheet and a U-tube heat exchanger, including the use of sleeves inserted into the tube sheet; Couplings are made of corrosion resistant duplex stainless steel. The Launch Melt Ultra Low Energy Design brochure at www.stamicarbon.com mentions that through direct thermal integration between the high pressure condenser and the medium pressure fractionating heater, followed by direct heat exchange between the medium pressure condenser and the first stage evaporator heater, the steam supply to the plant for urea production is minimized to unprecedented low levels of less than 600 kg of steam per tonne of urea produced. As used herein, direct heat transfer and direct thermal integration refer to heat transfer between separate flows through a wall without the use of a heat transfer fluid.

US 2018/0258034 describes a process for the production of urea, in which, in one embodiment, the ammonia feedstock is heated with steam generated by the condensation heat of the decomposed gas.

US 2012/0302789 describes a urea production process in which the urea solution from the stripper is subjected to adiabatic expansion and vapor-liquid separation before the liquid enters the first regeneration section. The steam can be condensed and the resulting heat of condensation can be used to concentrate the urea solution.

- 1 040954

The aim of the present invention is to provide an energy efficient process and plant for the production of urea with a simple design of the high pressure section.

Statement of the Invention

In a first aspect, the present invention relates to a process for the production of urea, comprising:

A) creating conditions for the formation of urea from ammonia and carbon dioxide in the reaction zone of high pressure, thus forming the first urea solution, which also contains carbamate;

B) subjecting the first urea solution to high pressure stripping to decompose the carbamate using heat, thereby forming a gas stream and a second urea solution also containing carbamate, and subjecting said gas stream to condensation in a high pressure carbamate condenser, thereby forming a first carbamate-containing solution and isolating the heat of condensation, wherein the carbamate-containing solution is fed into the high-pressure reaction zone;

C) subjecting said second urea solution to low pressure decomposition of the carbamate or first treating said second urea solution under medium pressure and subjecting the treated second urea solution to low pressure decomposition, said low pressure decomposition of the carbamate comprising heating in a low pressure decomposition apparatus urea solution containing carbamate using said heat of condensation from a high pressure carbamate condenser to decompose the carbamate, whereby a first vapor and a third urea solution also containing carbamate are obtained, and expansion of the third urea solution to subatmospheric pressure, thereby obtaining an expanded third urea solution;

D) subjecting said first vapor to condensation in a first low pressure carbamate condenser, thereby producing a second carbamate-containing solution and a second vapor, and releasing additional heat of condensation, wherein the first low-pressure carbamate condenser has an outlet for a second carbamate-containing solution that is in fluid communication with the reaction inlet. high pressure zones, and subjecting said expanded third urea solution to decomposition of the carbamate in a subatmospheric decomposition apparatus using said additional heat of condensation from said first low pressure carbamate condenser by heat transfer through a heat exchange wall between said first low pressure carbamate condenser and said device for performing decomposition under subatmospheric pressure, thereby obtaining a fourth carbamide solution and a third pair; And

E) subjecting said third vapor to condensation in a subatmospheric carbamate condenser in indirect heat exchange with a cooling fluid, thereby obtaining a fourth carbamate-containing solution.

In another aspect, the present invention relates to a plant for the production of urea, containing:

A) a high pressure reaction zone for creating conditions for the formation of urea from ammonia and carbon dioxide, thus forming the first urea solution, which also contains carbamate;

B) a high pressure stripper for subjecting the first urea solution to high pressure stripping to decompose the carbamate using heat, thereby forming a gas stream and a second urea solution also containing carbamate, and a high pressure carbamate condenser for subjecting said gas stream to condensation, thereby forming a first carbamate-containing solution and the release of heat of condensation;

C) a low pressure decomposition apparatus, wherein the low pressure decomposition apparatus is configured to subject said second urea solution to low pressure decomposition, or the apparatus is configured to first treat at least a portion of the second urea solution at a medium pressure of a medium pressure section to form a treated second urea solution, and a low pressure decomposition device configured to subject said treated second urea solution to low pressure decomposition, wherein said low pressure decomposition of the carbamate comprises heating the carbamate-containing urea solution using said heat of condensation from the high pressure carbamate condenser to decompose the carbamate, thereby producing a first vapor and a third urea solution also containing carbamate, and expanding an expansion system for expanding the third urea solution to subatmospheric pressure, thereby obtaining an expanded third urea solution;

D) a first low pressure carbamate condenser for subjecting said first vapor to condensation, thereby obtaining a second carbamate-containing solution and a second vapor and separating

- 2 040954 receiving additional heat of condensation, wherein the first low pressure carbamate condenser has an outlet for a second carbamate-containing solution, which is in fluid communication with the high pressure reaction zone, and a subatmospheric decomposition device for subjecting said expanded third urea solution to decomposition of the carbamate using said additional condensation heat from said first low pressure carbamate condenser by heat transfer through a heat exchange wall between said first low pressure carbamate condenser and said subatmospheric decomposition apparatus, thereby producing a fourth urea solution and a third vapor; And

E) a subatmospheric carbamate condenser configured to subject said third vapor to condensation by indirect heat exchange with a cooling fluid, thereby obtaining a fourth carbamate-containing solution, and preferably having an outlet for all or part of the fourth carbamate-containing solution, in fluid communication with inlet of the high pressure reaction zone.

Brief description of graphic materials

In FIG. 1 is a diagram of an exemplary embodiment in accordance with the present invention.

In FIG. 2 is a diagram of an exemplary embodiment in accordance with the present invention.

In FIG. 3 is a diagram of an exemplary embodiment in accordance with the present invention.

In FIG. 4 schematically shows an exemplary embodiment of a method in accordance with the present invention for retrofitting an existing plant.

Detailed description

The present application is generally based on the reasonable notion that, in the high pressure stripper type urea production process, the gas from the decomposition device of the low pressure regeneration section is supplied in series to two condensers, and the condensation heat generated in the upstream condenser from said two condensers, for subatmospheric pressure decomposition of carbamate in the urea solution obtained from the low pressure decomposition apparatus.

Thus, the heat is firstly applied in the high pressure stripper (S) and then released in the high pressure carbamate condenser (HPCC), the heat from the high pressure carbamate condenser is applied a second time in the low pressure (LP) carbamate decomposition device (LPD ) to carry out the decomposition of carbamate, and is released in the upstream first LP carbamate condenser (LPC1), which is used to partially condense the gas from the device for performing LP decomposition, and the heat generated in the first LP carbamate condenser is used for the third time to decompose carbamate in the urea solution obtained from the low pressure decomposition device (LPD) in the subatmospheric pressure decomposition device (LLPD) by heat exchange through the wall between the first carbamate condenser LP and the subatmospheric decomposition device, thus without heat transfer heating fluid to transfer heat from LPC1 to LLPD. This ensures good thermal integration in the low pressure recovery sections. In addition, part of the water evaporates from the urea solution in the apparatus for carrying out decomposition under pressure below atmospheric pressure (LLPD).

Accordingly, the first LP carbamate condenser (LPC1) is characterized by thermal integration with a subatmospheric pressure decomposition (LLPD) device by heat exchange through the wall rather than by heat transfer fluid between these blocks. The use of such a subatmospheric decomposition apparatus is preferably combined with high pressure stripping at a lower stripping efficiency α (alpha) of the high pressure stripper, such as a stripping efficiency α of less than 75%, more preferably 60-70% and preferably with CO ₂ as a stripping gas compared to a stripping efficiency of over 78% α in the known CO2 stripping urea production process. In a preferred embodiment, the HP stripper operates at a stripping efficiency (α) of 75% or less, eg 50-75% or preferably 6070%, eg 63-68%, the stripper preferably using CO2 as the stripping gas.

Accordingly, high pressure stripping with lower stripping efficiency (eg, α less than 75%) requires significantly less heat, i. provides much lower steam consumption. In addition, high pressure stripping involves lower temperatures, which reduces urea hydrolysis in the stripper compared to stripping, with higher stripping efficiency. Reduced hydrolysis provides an effective increase in convert

- 3 040954 these or at least an increase in the yield of urea. Accordingly, the feed flow (CO2 and NH3 in kg/h) can be reduced (with the same urea production in kg/h), resulting in a longer residence time (with a fixed reaction zone volume). This further increases the urea conversion rate (or urea yield). In one embodiment, a total of about 7% to about 10% additional urea production can be achieved (based on a constant reaction zone volume), or alternatively, the reaction zone can be 7-10% smaller by volume for the same urea production. The reaction zone is often a urea-grade steel reactor, which is an expensive construction material. In addition, lower stripping efficiency reduces the heat transfer load (condensation load) of the HPCC, for example by more than 25%, for example 30-40%, which can provide a smaller heat exchange surface area (for example, a smaller tube bundle) or, in the case of a fixed area heat exchange surface, to increase the pressure of the steam raised in the HPSS, for example, to increase the pressure by 1 bar, which makes the steam more suitable for further use.

In addition, the use of the condensation heat released in the LPC1 to separate NH ₃ , CO ₂ and water from the urea-containing stream (under conditions below atmospheric pressure) in the LLPD provides an advantageously low heat exchanger wall temperature (for the LPHX wall) due to the smaller difference temperatures. This provides a reduction in the formation of biuret. The heat exchanger wall temperature is in particular lower than when using a typical heat transfer fluid such as LP steam at approximately 4.5 bar absolute pressure. Similarly, in an optional embodiment, the heat exchange wall of the MPPHX wall with the medium pressure carbamate condenser MPC can be lower than when using LP steam for pre-evaporation.

The lower stripping efficiency also advantageously results in reduced biuret formation compared to a stripper.

The overall effect of utilizing the heat of carbamate condensation in LPC1 and preferred MPC, along with lower stripping efficiency, is quantified as a 0.04 to 0.06 wt% reduction in biuret content in the final product. The vapor from the subatmospheric decomposition apparatus is condensed in a subatmospheric pressure condenser (LLPC) to form a carbamate-containing solution which contains water, carbamate and some urea (e.g. 35-45 wt% carbamate, the rest is mostly water). and about 0.5-2% (eg wt %) of captured urea). In preferred embodiments of the present invention, this carbamate-containing solution is fed partially or completely into the high pressure reaction zone, preferably completely, although it contains a fraction with a high water content (for example, at least 40 wt.% water, for example 65-55 wt.% water ). The slightly higher water recirculation to the reaction zone is balanced by the advantage of significantly reduced steam consumption, in particular for high pressure stripping. The sub-atmospheric decomposition apparatus ensures sufficient purification of the urea solution even at a lower high pressure stripping rate. In preferred embodiments, the carbamate-containing solution from LLPC is partially or completely, preferably completely, indirectly fed into the inlet of the high pressure reaction zone, for example, first by feeding a carbamate-containing solution containing, for example, at least 50 wt.% water, to another carbamate condenser, where the aqueous fraction is mainly used to prevent crystallization of the carbamate.

In contrast, in known urea plants, water streams containing a small amount of ammonia and urea (or, respectively, containing most of the water), and these streams are obtained, for example, using condensers of the vacuum evaporation section, as a rule, are sent to the waste treatment section water for cleaning. Purification may, for example, include stripping (to remove ammonia) and hydrolysis (to remove urea). Cleaning is highly energy intensive (characterized by high steam consumption), in particular for the hydrolyser. Thus, it is an advantage that the condensate from the LLPC can be completely returned to the reaction zone of the HP synthesis, thus not increasing the load on any wastewater treatment section, while still providing a satisfactory conversion.

The presence of urea in the LLPC condensate is believed to be primarily or wholly due to physical entrainment of droplets from the LLPD in the vapor stream, without being bound by any theory.

In an optional embodiment, part or all of the carbamate-containing solution, e.g. condensate, from LPCC is treated in a stripper or wastewater treatment section, e.g. to the high pressure reaction zone, and a portion fed to a desorption column or wastewater treatment section. When the condensate is treated in the stripper and/or the wastewater treatment section, two streams are formed - purified condensate (for example, substantially pure water) as the first stream, and the purified condensate is usually not reintroduced into the process streams in the high pressure reaction zone. The second stream is usually

- 4 040954 bamate-containing solution containing more than 10 wt.% carbamate, and it is returned, for example, to the high pressure reaction zone. The vapor (non-condensed gases including NH ₃ and CO2) in the first LP carbamate condenser is optionally condensed in a second downstream LP carbamate condenser (LPC2) using cooling water; the condensate (carbamate-containing solution) is returned to the reaction zone for the synthesis of carbamide; in some other embodiments, instead, the steam is vented to the atmosphere after optional purification. In a first preferred embodiment, the carbamate-containing solution from LPC2 is fed into LPC1, since LPC1 often requires water to be fed to prevent the carbamate from crystallizing into LPC1. In a second preferred embodiment, the carbamate-containing solution from LPC1 is fed to LPC2, and the carbamate-containing solution from LLPC is fed to LPC1. In this embodiment, in particular, vapor (V2) and liquid (C2) are supplied, for example, as a mixture, from LPC1 to LPC2 for additional condensation of vapor (V2) relative to a cooling fluid (for example, cooling water) in the presence of a liquid ( C2) derived from LPC1. The carbamate-containing solution (C2) from LPC2, for example, is fed into the high-pressure synthesis section, in particular is returned to the HP reaction zone. Thus, the carbamate (C4) from LLPC first provides the necessary water supply to LPC1 to avoid carbamate crystallization in LPC1. Liquid (C2) from LPC1 supplied to LPC2 provides the necessary water supply to LPC2. This second preferred embodiment is less preferred than the first preferred embodiment in terms of energy advantages, but still provides significant energy advantages over existing CO ₂ stripping urea production processes.

The carbamide solution from the stripper is preferably expanded to medium pressure (MP) and subjected to medium pressure treatment, after which it is expanded to low pressure and fed to an apparatus for performing LP decomposition. More preferably, the medium pressure treatment is an adiabatic flash to produce an evaporated urea solution and medium pressure steam. In an alternative embodiment, the medium pressure treatment is medium pressure decomposition to produce treated urea solution and medium pressure steam. Medium pressure decomposition may include heating; the heat used therein can be supplied, for example, in the form of steam, for example from the HPCC. Heat can, for example, also be supplied by heat exchange through the wall with the condensing medium in the HPRS, more specifically if the HPRS is a shell and tube heat exchanger containing a tube bundle, by supplying a medium pressure urea solution through the HPRS pipes while a high pressure process medium is present. from the side of the casing and condenses from the side of the casing, thereby releasing heat. For both types of preferred MP treatment, MP flash and MP decomposition, the MP vapor is preferably condensed in an MP condenser (MPC) which preferably also receives a carbamate-containing solution from LPC1 and/or from an optional LPC2 (the solutions contain some water) to avoid carbamate crystallization. The obtained carbamate-containing solution is pumped and fed into the high pressure reaction zone, for example through a high pressure carbamate condenser. The heat of condensation generated in the pressure condenser MP is preferably used to vaporize water from the carbamide solution from the subatmospheric decomposition apparatus by heat exchange through the wall.

A significant advantage is that no special design of the high pressure section is required (for greenfield plants), nor is there any need for special modifications to the high pressure section (to retrofit existing urea plants). Accessories such as the LPC1/LLPD heat exchange vessel are low pressure equipment, optionally with medium pressure accessories such as the MPC/PEV heat exchange vessel, and therefore operate at lower temperatures where the carbamate is less corrosive. This significantly reduces equipment costs compared to high-pressure equipment, for example by eliminating the need for special corrosion-resistant materials such as duplex stainless steel alloys. The method for producing urea according to the present invention includes creating conditions for the formation of urea from ammonia and carbon dioxide in the reaction (R) high pressure zone, thus forming the first urea solution (U1), which also contains carbamate. The method further comprises subjecting the first urea solution to high pressure stripping (S) to decompose the carbamate using heat (H1, S1), thereby forming a gas stream (SG) and a second urea solution (U2) also containing carbamate, and subjecting the gas stream ( SG) condensing in a high pressure carbamate condenser (HPCC), thereby forming a first carbamate-containing solution (C1) and generating heat of condensation (H2, S2), wherein the carbamate-containing solution (C1) is fed into the high pressure reaction zone.

The method further includes subjecting the second urea solution (U2) to low pressure decomposition of the carbamate, or first treating said second urea solution (U2) under medium pressure (MPP) and subjecting the treated second urea solution (U2a) to low pressure decomposition. Low pressure decomposition of carbamate involves heating in

- 5 040954 apparatus for carrying out low pressure decomposition (LPD) of a carbamide solution (U2, U2a) containing carbamate, using said heat of condensation (H2, S2) from a high pressure carbamate condenser to decompose the carbamate, thereby obtaining a first vapor (V1 ) and a third urea solution (U3) also containing carbamate, and expanding the third urea solution to subatmospheric pressure (F1, X1), thereby obtaining an expanded third urea solution (U3a). The method further includes subjecting the first vapor (V1) to condensation in the first low pressure carbamate condenser (LPC1), thereby obtaining a second carbamate-containing solution (C2) and a second vapor (V2) and generating additional heat of condensation (H3). The first low pressure carbamate condenser has an outlet for a second carbamate solution (C2) which is in fluid communication with the inlet of the high pressure reaction zone (R).

The method further includes subjecting said expanded third carbamide solution (U3a) to carbamate decomposition in a subatmospheric pressure decomposition device (LLPD) using said additional heat of condensation (H3) from said first low pressure carbamate condenser (LPC1) by heat exchange through a heat exchange wall (LPHX) between said first low pressure carbamate condenser (LPC1) and said subatmospheric pressure decomposition device (LLPD) to thereby obtain a fourth urea solution (U4) and a third vapor (V3). The method further includes subjecting said third vapor (V3) to subatmospheric pressure carbamate condenser (LLPC) condensation in indirect heat exchange with a cooling fluid, thereby obtaining a fourth carbamate-containing solution (C4).

The method optionally further comprises subjecting the second vapor (V2) to condensation in a second low pressure carbamate condenser (LPC2) in indirect heat exchange with a cooling fluid (CW) to thereby obtain a third carbamate-containing solution (C3), wherein the second low pressure carbamate condenser (LPC2) has an outlet for a third carbamate-containing solution (C3) which is in fluid communication with the inlet of the high pressure reaction zone (R).

In some embodiments, the second vapor (V2) is vented to the atmosphere instead, optionally after purification.

In a preferred embodiment, a subatmospheric carbamate condenser (LLPC) has an outlet for at least a portion of a fourth carbamate-containing solution (C4) that is in fluid communication with the high pressure reaction zone (R).

The plant for the production of urea (UP) according to the present invention contains a reaction zone of high pressure (R) for creating conditions for the formation of urea from ammonia and carbon dioxide, thus forming the first urea solution (U1), which also contains carbamate; and a high pressure stripper (S) for stripping the first urea solution under high pressure to decompose the carbamate using heat (H1, S1), thereby obtaining a gas stream (SG) and a second urea solution (U2) also containing carbamate, and a carbamate condenser high pressure (HPC) for subjecting said gas stream (SG) to condensation, thereby forming a first carbamate-containing solution (C1) and releasing the heat of condensation (H2, S2).

The urea plant further comprises a low pressure decomposition (LPD) device. The low pressure decomposition (LPD) device is configured to subject said second urea solution (U2) to low pressure decomposition, or the plant is configured to initially treat at least a portion of the second urea solution (U2) at medium pressure (MPP) in a medium pressure section (MPP) to form a treated second urea solution, and a low pressure decomposition (LPD) device configured to subject said treated second urea solution to low pressure decomposition. The low pressure decomposition of carbamate involves heating a carbamate-containing carbamide solution using said condensation heat (H2, S2) from a high-pressure carbamate condenser to decompose the carbamate, thereby obtaining a first vapor (V1) and a third urea solution (U3) also containing carbamate. The urea plant further comprises an expansion system (F1, X1) for expanding the third urea solution to subatmospheric pressure, thereby obtaining an expanded third urea solution (U3a). The urea plant further comprises a first low pressure carbamate condenser (LPC1) for subjecting said first vapor (V1) to condensation, thereby obtaining a second carbamate-containing solution (C2) and a second vapor (V2) and releasing additional condensation heat (H3). The first low pressure carbamate condenser (LPC1) has an outlet for a second carbamate solution (C2) in fluid communication with the high pressure reaction zone (R). The urea production plant further comprises a subatmospheric pressure decomposition (LLPD) device for subjecting said expansion

decomposing the carbamate using said additional heat of condensation (H3) from said first low pressure carbamate condenser (LPC1) by heat exchange through a heat exchange wall (LPHX) between said first low pressure carbamate condenser (LPC1) and said apparatus for carrying out decomposition under subatmospheric pressure (LLPD), thereby obtaining a fourth urea solution (U4) and a third pair (V3).

The urea production plant further comprises a subatmospheric pressure carbamate condenser (LLPC) which is configured to subject said third vapor (V3) to condensation by indirect heat exchange with the cooling fluid, thereby obtaining a fourth carbamate-containing solution (C4), and which preferably has an outlet for all or part of the fourth carbamate-containing solution (C4) which is in fluid communication with the inlet of the high pressure reaction zone (R). The present invention relates to a method for the production of urea and a plant for the production of urea, which is preferably made for this method. An exemplary method and setup is shown in FIG. 1.

The urea plant (UP) comprises an HP synthesis section containing an HP reaction zone (R), an HP stripper (S), and an HP carbamate condenser (HPCC). The reaction zone HP (R) is configured to create conditions for the formation of urea from ammonia and carbon dioxide, thus forming the first urea solution (U1), which also contains carbamate (ammonium carbamate), and usually also contains water and ammonia. The method includes creating conditions for the formation of urea from ammonia and carbon dioxide in the reaction zone HP (R) thus forming the first urea solution (U1). The reaction is carried out, for example, at an N/C ratio of 2.5-3.5, preferably 3.0-3.2. The N/C ratio is the molar ratio of NH3 and CO ₂ in the reaction zone based on the theoretical feed mixture.

The stripper HP (S) is configured to subject the first urea solution (U1) (urea synthesis reaction) to high pressure stripping to decompose part of the carbamate into NH3 and CO2 using heat (H1), in particular using the first steam (S1) to form thus a gas flow (SG) (eg mixed gas) which contains NH3 and CO2 and a second urea solution (U2) (stripped urea solution) also containing carbamate, ammonia and water. The HP stripper uses, for example, CO2 as the stripping gas in the urea plant of the CO2 stripper, as shown in FIG. 1. Ammonia stripping and self-stripping can also be applied; in combination with CO2 feed to the reaction zone (R). High pressure stripping typically involves countercurrent contact between the incoming first urea solution and a gas stream having a lower vapor pressure of NH3 or CO2 compared to the first urea solution.

In a preferred embodiment, the first urea solution (U1) has an N/C ratio of about 3 (e.g. 2.5-3.5), the stripped urea solution (U2) at the outlet of the stripper has an N/C ratio of about 2.0-2 ,3, optionally from 2.10 to 2.30.

The first steam (S1), for example, is taken from the steam turbine of the CO ₂ supply compressor of the urea plant. The first steam, for example, is usually obtained from an engineering plant, such as a dedicated fossil fuel boiler system, optionally via a steam turbine, or, for example, is obtained from an upstream ammonia plant, or it is, for example, saturated steam ( e.g. 18 to 20 bar abs) obtained from any plant.

The HP carbamate condenser (HPCC) comprises a process medium side, a cooling fluid side and a heat exchange wall between these sides and is configured to subject said gas stream (SG) to condensation, thereby forming a first carbamate-containing solution (C1) from the process medium side. Such condensation of the carbamate includes the release of the heat of condensation (H2), preferably by generating a second vapor (S2) from the side of the cooling fluid. The high pressure carbamate condenser (HPCC) has a connection for supplying the first carbamate-containing solution (C1) to the high pressure reaction zone (R). The plant for the production of urea is configured to supply the first carbamate-containing solution (C1) from the high pressure carbamate condenser (HPCC) to the high pressure reaction zone, optionally by means of a connection between separate vessels or by transporting the solution inside the combined vessel. The method includes supplying a carbamate-containing solution (C1) to a high-pressure reaction zone.

The process includes feeding NH3 feed to the HP reaction zone, optionally via an HPCC. Already in the high pressure carbamate condenser some amount of urea can be formed, for example more than 10 wt.%, more than 30 wt.% and/or less than 90 wt.% of the total amount of urea formed during the process. Accordingly, the HP reaction zone in some embodiments is provided at least partially in the HP carbamate condenser. The HP carbamate condenser is, for example, a heat exchanger using cooling water as the cooling liquid, such as a shell and tube heat exchanger, such as a U-shaped

- 7 040954 tube bundle and, for example, with cooling water in the pipes and the process medium on the shell side.

The urea plant may comprise one or more HP reaction zones. In some embodiments, the HP reaction zone is a reactor, such as a vertical reactor, which is a vessel separate from the HP carbamate condenser. In some embodiments, the HP reaction zone and the HP carbamate condenser may be provided in separate vessels. In some embodiments, the HP reaction zone or at least one of the HP reaction zones and the HP carbamate condenser are combined in a single vessel, with one vessel preferably being a vessel with a horizontally submerged condenser portion; optionally, the plant contains an additional reaction zone HP downstream of the vessel, for example in the form of a vertical reactor. The condenser in such a combined vessel is, for example, a shell and tube heat exchanger with a tube bundle. The tube bundle may be, for example, a U-shaped tube bundle or a straight tube bundle. During operation, the cooling fluid is typically supplied through the tubes and the gas stream (SG) from the stripper is supplied to the housing section. The vessel is, for example, in a pool reactor as described in US 5,767,313 or a vertical combination reactor as described in US 6,680,407.

HP equipment, such as the HP carbamate reactor, stripper, and condenser, is made of, for example, a corrosion-resistant material such as urea-grade steel, such as ferritic-austenitic duplex stainless steel, at least for parts in contact with the process fluid. The urea plant comprises a connection between the outlet of the HP reaction zone and the inlet of the HP stripper for the first urea solution, a connection between the outlet of the stripper and the inlet of the HP carbamate condenser for gas flow (SG), and in some embodiments, the connection between the outlet of the HP carbamate condenser and the inlet of the reaction HP zones for the first carbamate solution. The stripper preferably has a stripping gas inlet and the HP carbamate condenser preferably has an ammonia feed inlet.

In some embodiments, the urea plant comprises an HP scrubber for scrubbing gases from the outlet of the HP synthesis section, such as HPCC. These gases are in particular inert components (eg passivating air, if used). In preferred medium pressure condenser embodiments, the urea plant preferably does not include an HP scrubber.

The urea plant further comprises a low pressure regeneration section receiving at least a portion, e.g. all, of the second urea solution (U2) from the stripper, and optionally a medium pressure section (MPP) between the stripper and the low pressure regeneration section for processing at least a portion of optionally all of the second urea solution (U2) to obtain a treated second urea solution (U2a).

The urea plant, in particular the LP regeneration section, comprises a low pressure decomposition (LPD) device. The low pressure decomposition (LPD) device is configured to subject the second urea solution (U2) and/or the treated second urea solution (U2a) to low pressure decomposition of carbamate and has an inlet for these streams with a connection to a stripper outlet and/or a connection with medium pressure section outlet (MPP). The decomposition of LP comprises heating an optionally treated second urea solution containing carbamate (U2, U2a) using the heat of condensation (H2) from the carbamate condenser HP to decompose the carbamate, preferably by heat exchange with the second vapor (S2), thereby producing the first vapor ( V1) which contains CO2 and NH3 as well as water vapour, and a third urea solution (U3) also containing carbamate and water.

The device for carrying out the decomposition of LP contains, for example, a distillation column for contact between the incoming (optionally processed) second carbamide solution containing carbamate (U2, U2a) and the first vapor (V1), in particular for countercurrent contact between these streams. A distillation column is used, for example, to reduce the water content of the first vapor (V1). The distillation column contains, for example, a packing and has, for example, a heat exchanger zone for heat exchange with steam in the lower part.

In a preferred embodiment, a portion of the CO2 feed is fed to an atmospheric evaporator (F1) to control the N/C ratio of the first vapor (V1) to obtain the desired lower N/C ratio for better condensation of the first vapor (V1). In a preferred embodiment, the adiabatic flash vessel (F1) is configured for countercurrent contact between the CO2 gas flow and the urea solution, thus stripping a portion of the NH3 species in the urea solution, preferably under adiabatic conditions.

The evaporator vessel (F1) preferably contains a packing layer to effect such contact. In a preferred embodiment, the flash vessel (F1) is an atmospheric pressure stripper. In a preferred embodiment, part of the supplied CO2 is fed into the atmospheric evaporator (F1), and this part is, for example, from 1 to 10 wt.%,

- 8 040954 more preferably from 3 to 8 wt.% of the total amount of CO2 supplied to the plant for the production of urea. In a preferred embodiment, the stripping effect of the CO2 supplied to the atmospheric evaporator reduces the N/C ratio from about 4.0 at the urea solution inlet (U3) to about 2.6 at the urea solution outlet (U3a). The advantage of N/C correction in the flash vessel is that the dew point in the LLPC is high enough (e.g. above 30°C) to use the standard available cooling water (e.g. 30-40°C) in the LLPC to condense the carbamate under pressure below atmospheric.

The installation, in particular the low pressure regeneration section, further comprises an expansion system (F1, X1) for expanding the third urea solution (U3) to a subatmospheric pressure (less than 1.0 bar abs, for example 0.10-0.9 bar abs, preferably 0.3-0.5 bar abs.) thus obtaining an expanded third urea solution (U3a). The method further includes such an extension. In a preferred embodiment, the expansion system comprises an atmospheric flash vessel (F1) having an inlet for a third urea solution (U3) to expand the urea solution to atmospheric pressure (e.g. 1 to 2 bar abs, e.g. 1.0 to 1.8 bar abs or preferably 1.0-1.3 bar abs), for example with adiabatic flashing to produce a fourth vapor (V4) and a urea solution, and an expansion valve (X1) to further expand the urea solution to subatmospheric pressure to obtain expanded third urea solution (U3a). The method preferably further comprises condensing the fourth vapor (V4) in an atmospheric pressure condenser (APC) to obtain a fifth carbamate-containing solution (C5). The atmospheric pressure condenser (APC) has an outlet for a fifth carbamate-containing solution (C5) which is in indirect fluid communication with the high pressure reactor (R) to recycle the carbamate. The method preferably includes feeding the fifth carbamate-containing solution (C5) to the first and/or second low pressure carbamate condenser (LPC1, LPC2). Thus, the aqueous fraction of the fifth carbamate-containing solution (C5) is advantageously used to prevent carbamate crystallization in the first and/or second low pressure carbamate condenser (LPC1, LPC2).

The low pressure regeneration section further comprises a first low pressure carbamate condenser (LPC1) for subjecting the first vapor (V1) to condensation of the carbamate, thereby obtaining a second carbamate-containing solution (C2) and a second vapor (V2) and generating additional condensation heat (H3). The condensation is partial. The first low pressure carbamate condenser (LPC1) has an inlet connected to the first vapor outlet (V1) of the low pressure decomposition device. The operating pressure of the LPC1 is preferably 6-9 bar abs, more preferably it is 8 bar abs; these pressures provide the optimal condensing temperature in the LPC1 for thermal integration with the LLPD.

The first low pressure carbamate condenser (LPC1) has an outlet for a second carbamate solution (C2) in fluid communication with the high pressure reaction zone (R). The process thus includes indirectly supplying a second carbamate-containing solution (C2) to the high pressure reaction zone (R), optionally via a second carbamate condenser LP and, for example, via a carbamate condenser HP, by means of a pump. The process thus includes returning the carbamate to the HP synthesis section.

The urea production plant further comprises a subatmospheric pressure decomposition (LLPD) device that is configured to subject said expanded third urea solution (U3a) to decomposition of the carbamate using additional heat of condensation (H3) from the first low pressure carbamate condenser (LPC1) thus obtaining a fourth urea solution (U4) and a third pair (V3). The subatmospheric decomposition device (LLPD) has an inlet with a connection to an expanded third urea solution outlet (U3a) of the expansion system and has a fourth urea solution outlet (U4) and a third vapor outlet (V3).

The urea plant comprises a heat exchange wall (LPHX) between said first low pressure carbamate condenser (LPC1) and said subatmospheric decomposition device (LLPD). Thus, in practice, the low pressure carbamate condenser (LPC1) and said lower pressure decomposition device (LLPD) are combined in the same vessel, more specifically in a heat exchanger, such as a shell and tube heat exchanger, while the expanded third urea solution (U3a) is at the first side (eg tube side) and the first vapor (V1) on the second side of the heat exchanger (eg shell side) separated for mass transfer by a heat exchanger wall (LPHX). One vessel is preferably in the form of a shell-and-shell tube-side shell-and-tube heat exchanger, which is more preferably a shell-side immersion condenser (LPC1) with tubes immersed in the liquid phase on the shell side, and with falling film evaporation in the tubes (LPD1) and the flow in the pipes in countercurrent to the flow in the casing side.

The method includes heat transfer through this heat exchange wall (LPHX). Fourth urea

- 9 040954 solution (U4) preferably contains at least 60 wt.% urea, more preferably at least 70 wt.% urea, for example, from 70 to 80 wt.% urea, for example from 70 to 76 wt.% urea.

The urea plant further comprises a second low pressure carbamate condenser (LPC2) which is configured to subject said second vapor (V2) to condensation by indirect heat exchange, typically with a cooling fluid such as cooling water (CW), to thereby image of the third carbamate-containing solution (C3).

The second low pressure carbamate condenser (LPC2) has an inlet connected to the second vapor outlet (V2) of the first low pressure carbamate condenser (LPC1) and has an outlet for a third carbamate containing solution (C3) which is in fluid communication with the inlet of the reaction zone HP (R), to feed the third carbamate-containing solution (C3) eventually into the reaction zone HP (R), usually through the HP carbamate condenser and by means of a pump. The second low pressure carbamate condenser (LPC2) is, for example, a shell and tube heat exchanger.

In an optional embodiment, LPC2 may be omitted. Under appropriate operating conditions for the LPC1/LLPD unit and with thermal integration between LPC1 and LLPD, LPC2 can have very little or no heat load (heat load for cooling water). Thus, in an optional embodiment, LPC2 is omitted. In such an embodiment, the carbamate solution (C4) from the subatmospheric pressure condenser (LLPC) is fed to, for example, the first LP condenser (LPC1) and the vapor (V2) from the first LP condenser (LPC1) is vented to the atmosphere, optionally after purification.

The urea production plant further comprises a subatmospheric pressure carbamate condenser (LLPC) which is configured to subject the third vapor (V3) to condensation of the carbamate in indirect heat exchange with the cooling fluid (CW) to thereby obtain a fourth carbamate-containing solution (C4). The subatmospheric pressure carbamate condenser (LLPC) has a third vapor inlet (V3) connected to the third vapor outlet (V3) of a subatmospheric pressure decomposer (LLPD) and has an outlet for a fourth carbamate-containing solution (C4).

The fourth carbamate-containing solution (C4) contains, for example, at least 20 wt.% carbamate and, for example, less than 70 wt.% carbamate, for example, 30-50 wt.% carbamate, as a rule, with the remainder in the form of essentially water.

The subatmospheric pressure carbamate condenser (LLPC) outlet is preferably for all or part of the fourth carbamate solution (C4) and is preferably in fluid communication with the high pressure reaction zone inlet (R). Optimally, the subatmospheric carbamate condenser (LLPC) has an outlet for all or part of the fourth carbamate-containing solution (C4) in fluid communication with the inlet of the desorption column and/or the wastewater treatment section. The method preferably includes feeding all or part of the fourth carbamate-containing solution (C4) to the high pressure reaction zone (R), preferably through the first and/or second low pressure carbamate condensers (LPC1, LPC2) and then through the HP carbamate condenser. The subatmospheric carbamate condenser (LLPC) is preferably a shell-and-tube heat exchanger with shell-side condensing and cooling water in the tubes; in addition, preferably a horizontal surface condenser with a horizontal tube bundle and condensation on the surface of the tubes, or further preferably a vertical falling film condenser with a vertical tube bundle. Preferably the pipes are in the form of a straight tube bundle. The pipes are preferably provided with stainless steel material on both sides (inner and outer surfaces of the pipe wall) since the pipes on both sides are exposed to the process medium containing carbamate. In a particularly preferred embodiment, a straight tube bundle is used with 316L steel on the casing side (outer surface of the pipe) and 304L steel on the tube side (inner surface of the pipe).

In a preferred embodiment, the subatmospheric pressure carbamate condenser (LLPC) has an outlet for at least a portion of the fourth carbamate-containing solution (C4) which is in fluid communication with the high pressure reaction zone (R), preferably through the first and/or second carbamate condensers. low pressure (LPC1, LPC2) and optionally through an HP carbamate condenser (HPCC). In an optional embodiment in which the urea plant does not include a medium pressure condenser, the fourth carbamate-containing solution is preferably fed to the HP scrubber of the urea plant, the HP scrubber having a carbamate solution outlet connected to an HP carbamate condenser inlet.

In a preferred embodiment, the third carbamate solution (C3) is fed to the first low pressure carbamate condenser (LPC1) and the fourth carbamate solution (C4) is fed to the second low pressure carbamate condenser (LPC2); and the installation respectively contains a connection between the LPC2 outlet and the LPC1 inlet for the third carbamate-containing solution (C3)

- 10 040954 and connection from the LLPC outlet to the LPC2 inlet for the fourth carbamate-containing solution (C4). The second carbamate-containing solution (C2) is fed into the HP reaction zone. This provides an energy efficient process and plant for the production of urea. In FIG. 1 is a flow diagram of an example of such an embodiment in which the stripper is additionally a CO ₂ stripper and the preferred atmospheric condenser (APC) is used. Optionally, a medium pressure processing unit (MPP) is used. Part of the supplied CO2 is used to correct N/C in the atmospheric evaporator (F1). In addition, expansion valves (not shown) are provided for each expansion/depressurization step, for example between the HP stripper and the low pressure digester. In addition, pumps and/or ejectors (not shown) are provided to increase the pressure of fluid streams, for example in the C4 stream from LLPC to LPC. In addition, LLPC, LPC2 and MPC (not shown) typically have outlets for uncondensed vapors (particularly inert components, such as from the optional passivation air and/or traces of hydrogen and/or N2 from the CO2 feed and /or supplied NH3). The HP HPCC carbamate condenser in some embodiments has a gas outlet connected to an HP scrubber or an MP scrubber (not shown); in other embodiments, the HP synthesis section does not include an HP scrubber. These outlets are not shown in FIG. 1. In addition, the arrows for heat (HI, H2, H3) indicate schematic heat flows, not process flows; the same applies to the heat flux H4 as shown in FIG. 3.

In another embodiment, the second carbamate-containing solution (C2) is fed from the outlet of the first low pressure carbamate condenser (LPC1) to the inlet of the second low pressure carbamate condenser (LPC2), and the fourth carbamate-containing solution (C4) is fed from the outlet of the subatmospheric carbamate condenser (LLPC). ) to the inlet of the first low pressure carbamate condenser (LPC1); and the setup contains the connections between these inputs and outputs.

In FIG. 2 schematically illustrates an example of such an embodiment in which C4 solution is fed from LLPC to LPC1, this embodiment being less preferred than the embodiment shown in FIG. 1. Each of the first low pressure carbamate condenser (LPC1) and the second low pressure carbamate condenser (LPC2) is independently preferably a liquid-continuous immersion condenser and is, for example, a shell-and-tube heat exchanger, preferably with cooling fluid in the tubes; the first and second low pressure carbamate condensers are preferably such condensers. The first low pressure carbamate condenser (LPC1) is an integral unit with a subatmospheric decomposition (LLPD) unit, and this integral unit is preferably a shell-and-tube heat exchanger with tube bundle and vapor condensation (V1) on the shell side and heating of the urea solution (U3a) in pipes, more preferably in the form of an immersion condenser. Preferably heating the urea solution comprises falling film evaporation in tubes, alternatively rising film evaporation can be used in tubes; in addition, the pipes are preferably located on the side of the shell immersed in the liquid phase of the carbamate-containing solution, alternatively on the side of the shell, for example, falling film condensation can be used. The tube bundle is preferably vertical. The first low pressure carbamate condenser (LPC1) preferably operates at a higher temperature than the second low pressure carbamate condenser (LPC2), such as at least 10°C or at least 20°C higher. LPC1 is preferably used to partially condense the vapor, and LPC2 is used to condense the remaining CO2 and NH3 in the V2 vapor to carbamate. In some embodiments, LPC1 and LPC2 are integrated into the same housing.

The LP refresh section contains, for example, LPD, LPC1, LPC2, F1, APC, LLPD and LLPC blocks; although F1, APC, LLPD and LLPC operate at less than 2 bar abs. In a preferred embodiment, the method comprises first processing said second urea solution (U2) at medium pressure (MPP) and subjecting the treated second urea solution (U2a) to low pressure carbamate (LPD) decomposition. The medium pressure treatment preferably includes the removal of ammonia and/or carbamate from the carbamide solution, and as a result of this treatment, a treated second urea solution (U2a) also containing carbamate, and a fifth pair (V5) containing NH ₃ and CO 2, for example 60 wt. .% CO2, 5 wt.% water and the remainder as NH ₃ . Reducing the pressure of the stripped carbamide solution (U2) to medium pressure allows the decomposition of the carbamate. The method preferably includes condensing the fifth vapor in a medium pressure condenser (MPC) to obtain a sixth carbamate-containing solution (C6). Preferably, the second carbamate-containing solution (C2) from said first low-pressure carbamate condenser (LPC1) and/or the third carbamate-containing solution (C3) from the subatmospheric pressure carbamate condenser (LLPC) is fed to a medium pressure condenser (MPC) and the plant comprises connections between inputs and outputs for such streams. Preferably, the medium pressure condenser (MPC) has an outlet for the sixth carbamate-containing solution (C6) in fluid communication with the inlet of the high-pressure reaction zone (R), and preferably the process comprises feeding the sixth carbamate-containing solution (C6) directly or indirectly into high pressure reaction zone (R).

Preferably, the method further comprises heating a fourth urea solution (U4) from a sub-atmospheric pressure carbamate condenser (LLPD) (optionally via a urea storage tank) in a pre-evaporator (PEV) to evaporate water from the urea solution, optionally also decomposing some of the remaining carbamate, applying the heat of condensation (H4) generated by the condensation of the carbamate in said medium pressure condenser (MPC), thereby obtaining a fifth carbamide solution (U5) with reduced water content and a sixth vapor (V6) which is mainly water vapor. The sixth steam, for example, is condensed, and the condensate, for example, is sent to the wastewater treatment section. The fifth urea solution (U5) contains, for example, at least 80 wt.% urea, preferably at least 85 wt.% urea, for example, 86-95 wt.% urea, for example, 93 wt.% urea. An example of the method according to this embodiment is shown in FIG. 3.

Preferably the medium pressure carbamate condenser (MPC) is an integral pre-evaporator vessel (PEV) and more preferably a shell and tube heat exchanger with tube bundle MP(V5) vapor condensation on the shell side and heating of the urea solution (U4) in the tubes, more preferably made in the form of an immersion condenser. Preferably heating the urea solution comprises falling film evaporation in tubes, alternatively rising film evaporation can be used in tubes; the pipes are preferably located on the side of the casing immersed in the liquid phase of the carbamate-containing solution. Preferably, the shell and tube heat exchanger is configured to provide flow in the tubes in countercurrent to the shell side flow such that the steam inlet is adjacent to the urea solution outlet. The MPC tube bundle is preferably vertical.

Preferably, the medium pressure treatment comprises adiabatically flashing the second urea solution (U2) in a medium pressure flash vessel (MPF), whereby the treated urea solution is the evaporated second urea solution (U2a). This embodiment is shown in FIG. 3.

In combination with the low pressure regeneration section according to the present invention, a very energy efficient process can advantageously be achieved by adiabatic flashing as a medium pressure treatment. In addition, the medium pressure adiabatic evaporator vessel is a relatively simple piece of equipment.

In FIG. 3 is a schematic representation of an illustrative embodiment with a medium pressure flash vessel (MPF) for adiabatically flashing a second urea solution (U2) from an HP stripper. In FIG. 3 also shows schematically that the same process as in FIG. 1; those. solution C2 is fed from LPC1 to LPC2, and solution C4 is fed from LLPC to LPC1; this configuration is independent of the application of MP processing, and other configurations are also possible. For example, in a further example, the urea plant comprises a medium pressure flash vessel (MPF) and the regeneration section LP is configured as shown in FIG. 2.

In another embodiment, the medium pressure treatment comprises heating the second urea solution (U2) in a medium pressure decomposition apparatus to decompose the carbamate. In medium pressure heating, for example, steam is used as the heating fluid. In one embodiment, medium pressure heating comprises heat exchange through the wall with a high pressure condensing process fluid in an HP carbamate condenser; for example, in an HP carbamate condenser having two tube bundles, one for the second urea solution (U2), optionally after the evaporator, and the other for the cooling water to generate steam.

The urea solution (U4) from the subatmospheric pressure decomposition device (LLPD) and/or the urea solution (U5) from the pre-evaporator (PEV) are fed, for example, to the evaporation section of the urea plant (UP), which contains, for example , one, two, three or more vacuum evaporation stages arranged in series to evaporate water to produce steam and urea melt (for example, with at least 95 wt.% or at least 99 wt.% urea); the steam is, for example, condensed and fed to the wastewater treatment section. The Waste Water Treatment Section (WWT) contains, for example, a desorption column and a deep hydrolysis unit. Deep hydrolysis typically involves heating using steam, such as steam at pressures greater than 10 bar, as the heating fluid. The cleaned condensate from the WWT is generally not returned to the HP synthesis section as a process fluid, but optionally, after being used as a cooling fluid, it is disposed of at the plant boundary. The carbamide melt, for example, is fed to a final treatment section for curing to form a solid urea product, such as a granulator or a granulation tower. The urea solutions can also be used, for example, as a fluid for the production of diesel exhaust fluid (DEF) and/or liquid fertilizer such as urine ammonium nitrate (UAN). The present invention also relates to a method for modifying an existing urea plant to obtain a plant in accordance with the present invention.

In a preferred method of retrofitting an existing urea plant, the existing carbamate condenser LP becomes an optional second carbamate condenser LP and a heat exchange vessel for LPC1/LLPD is added, optionally adding an MP treatment section containing a heat exchanger for MPC/PEV and, for example, a flash vessel MP MPF or medium pressure decomposition device.

For a preferred method of retrofitting an existing urea plant, the existing urea plant comprises: a high pressure reaction zone (R) to form a first urea solution (U1) which also contains urea; a high pressure stripper (S) for subjecting the first urea solution to high pressure stripping to decompose carbamate with heat (H1, S1), thereby forming a gas stream (SG) and a second urea solution (U2) also containing carbamate; and a high pressure carbamate condenser (HPCC) for subjecting said gas stream (SG) to condensation, thereby forming a first carbamate-containing solution (C1) and generating condensation heat (H2, S2), wherein the high-pressure carbamate condenser (HPCC) has a connection for supplying carbamate-containing solution (C1) into the high pressure reaction zone. The existing plant further comprises a low pressure decomposition (LPD) device, wherein the low pressure decomposition (LPD) device is configured to subject said second urea solution (U2) to low pressure decomposition, or the low pressure decomposition device (LPD). pressure (LPD) is configured to subject the treated second urea solution to low pressure decomposition of the carbamate, and wherein the existing plant is configured to initially process said second urea solution (U2) at medium pressure (MPP) in a medium pressure section to obtain said treated second urea solution. The low pressure decomposition of carbamate involves heating a second urea solution containing carbamate (U2) using said heat of condensation (H2, S2) from a high pressure carbamate condenser to decompose the carbamate, thereby producing a first vapor (V1) and a third urea solution (U3 ), also containing carbamate.

The method includes adding an existing low pressure carbamate condenser configured to subject the first vapor (V1) to condensation and an expansion system (F1, X1) to expand the third urea solution to a subatmospheric pressure, thereby obtaining an expanded third urea solution (U3a), if the existing installation does not contain such an expansion vessel. The method further includes adding a unit comprising a first low pressure carbamate condenser (LPC1) and a subatmospheric pressure decomposition device (LLPD), wherein the first low pressure carbamate condenser (LPC1) is configured to subject said first vapor (V1) to condensation to obtain thus the second carbamate-containing solution (C2) and the second vapor (V2) and the release of additional condensation heat (H3), wherein the first low pressure carbamate condenser (LPC1) has an outlet for transporting the second carbamate-containing solution (C2) to the high pressure reaction zone (R) , and wherein the subatmospheric pressure decomposition (LLPD) device is configured to subject said expanded third urea solution (U3a) to decomposition of carbamate using said additional heat of condensation (H3) from said first low pressure carbamate condenser (LPC1) by through a heat exchange wall (LPHX) between said first low pressure carbamate condenser (LPC1) and said subatmospheric pressure decomposition device (LLPD), thereby obtaining a fourth urea solution (U4) and a third vapor (V3). The method optionally further comprises modifying an existing low pressure carbamate condenser into a second low pressure carbamate condenser (LPC2) having an inlet for said second vapor (V2) and configured to condense the second vapor (V2) in indirect heat exchange with a cooling fluid (CW), thus obtaining a third carbamate-containing solution (C3), and having an outlet for transporting the third carbamate-containing solution (C3) to the high pressure reaction zone (R). The method further includes adding a subatmospheric pressure carbamate condenser (LLPC) configured to subject said third vapor (V3) to condensation by indirect heat exchange with a cooling fluid, thereby obtaining a fourth carbamate-containing solution (C4) and having an outlet for transporting part or all of fourth carbamate-containing solution (C4) into the high pressure reaction zone (R). The modified plant is preferably a plant according to the present invention and is preferably configured to carry out the urea production process according to the present invention, preferably with the preferred process features and plant features as described above herein. In FIG. 4

- 13 040954 presents an example of such a method of modifying an existing installation for the production of urea. The existing plant comprises an HP synthesis section with a reactor R, a stripper S and an HP HPCC carbamate condenser and an LP regeneration section containing a device for performing LP LPD decomposition, as well as an existing LP condenser using CW cooling water for the V1 steam from the LPD, for example in the form of a shell and tube heat exchanger with a U-shaped tube bundle. A heat exchanger unit is added to provide a first carbamate condenser LP LPC1, as well as a subatmospheric decomposition apparatus LLPD, such as a vessel as described, preferably a straight tube bundle shell and tube heat exchanger, and a subatmospheric carbamate condenser LLPC. The blocks added in this method are indicated by shading. The existing capacitor LP does not necessarily become LPC2 receiving the V2 pair from the added LPC1 block. The C4 carbamate solution from LLPC, for example, is fed to LPC2, and the C3 carbamate solution from LPC2, for example, is fed to LPC1. Alternatively, the configuration shown in FIG. 2. Preferably, in the modified plant, the atmospheric condenser (APC) has an outlet for the fifth carbamate-containing solution (C5) connected to a second low pressure carbamate condenser (LPC2).

In yet another preferred embodiment, the plant retrofit method comprises adding an MP processing section (MPP), preferably an adiabatic flash vessel (MPF), as described herein.

The method according to the present invention is preferably carried out in a plant according to the present invention. The installation according to the present invention is preferably suitable for the installation according to the present invention. The preferences described in connection with the installation also apply to the method. The preferences described in connection with the method also apply to the installation. In the context of this document, HP is at least 100 bar abs, e.g. 110-160 bar abs, MP is 20-60 bar abs, LP is 4-10 bar abs, atmospheric pressure is 1-2 bar abs, e.g. 1.0 -1.8 bar abs, and the pressure below atmospheric pressure (LLP) is less than 1.0 bar abs, for example, 0.2-0.5 bar abs; these pressure ranges are for process applications and are not necessarily the same for steam and heating fluids. Reducing bar abs. means bar absolute pressure. The term fluid communication refers to a flow line (eg, tubes or channels) allowing fluid to pass between two units, optionally through multiple intermediate units. Fluid communication does not include gas phase transport, and hence the two units connected by the evaporator, vapor flow line, and condenser are not in liquid communication, although they are in fluid communication (which includes both gas phase transport and liquids). The first block is in fluid communication with the second block, for example, if the liquid outlet of the first block is connected to the inlet of the condenser, and the liquid outlet of the condenser is connected to the inlet of the second block. Stripper efficiency (alpha) is defined as the amount of ammonia converted to urea (and biuret) divided by the total amount of ammonia, which is typically measured at the stripper fluid outlet. This definition is equivalent to the definition of NH3 conversion based on the stripper output. Thus, alpha = (2* wt.% urea/60)/((2* wt.% urea/60)+(wt.% NH ₃ /17)), measured at the outlet of the stripper fluid, with wt.% NH ₃ includes all ammonia compounds, including ammonium carbamate. One skilled in the art will understand that stripping efficiency refers to the purity of the urea at the stripper fluid outlet, not the energy efficiency of the stripper.

Carbamate condenser condensation refers to the so-called carbamate condensation, which involves the reaction of NH ₃ and CO ₂ to form ammonium carbamate, which is a liquid, whereby the gaseous NH ₃ and CO 2 are converted into a liquid phase. Carbamate decomposition refers to the dissociation reaction of carbamate into NH ₃ and CO 2 .

Example 1

An example of the method is implemented according to the method diagram shown in FIG. 3. The HP stripper operates with a typical stripping efficiency (alpha) of 0.63 and the stripper outputs a stripped U1 urea solution at 170-180°C and 140-145 bar (HP) (all pressures are absolute) , which adiabatically vaporizes in the MPF to produce a vaporized urea solution U2a at a pressure of 20-30 bar (MP) and a temperature of 140-150°C. The U2a stream is fed into an LPD decomposition device for carbamate decomposition, which has a distillation column, to obtain a U3 stream at a pressure of 5-8 bar (LP) and a temperature of 130-140°C, which is evaporated in the flash vessel F1 to a pressure of 1-1 .3 bar and expands in valve X1 to a pressure of 0.3-0.5 bar (LLP) at a temperature of 60-70°C at the LLPD inlet. Optionally, some fresh CO2 is added to flash vessel F1 to correct N/C. Steam V3 from LLPD is at a temperature of 70-85°C and a pressure of 0.3-0.5 bar. The urea solution U4 at the LLPD outlet and the PEV inlet is at a pressure of 0.3-0.5 bar and a temperature of 75-90°C, and it is heated to obtain a urea solution U5 at a pressure of 125-135°C and a temperature of 0.3-0 .5 bar. Vapor V5 from MPF is at a pressure of 20-30 bar and a temperature of 140-150°C and condenses in MPC with the formation of carbamate solution C6 at a pressure of 20-30 bar and a temperature of 105-115°C. MRS is a shell-and-tube heat exchange

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Claims (15)

nick for countercurrent flow in shell and pipes with gas inlet temperature at 140150°C on the side of the shell which is at the same end as the outlets of the urea solution pipes. LLPC heats cooling water CW from 32 to 35°C, C4 solution at the LLPC outlet is at a pressure of 0.3-0.5 bar and a temperature of 35-40°C and is pumped into LPC2 to obtain C3 carbamate solution at a pressure of 5-8 bar and a temperature of 75-85°C, heating the cooling water CW from 55 to 65°C, which is fed into the LPC1. Steam V2 from LPC1 is at a temperature of 85-95°C and a pressure of 5-8 bar. Very low energy consumption is 580-660 kg of steam per ton of urea product. In addition, the heat load of the HP carbamate condenser is reduced by 37%. In the absence of MPF (eg as shown in FIG. 1) a low energy consumption of 720-800 kg of steam per tonne of urea product is still achieved. These steam consumption figures are based on steam at 18-23 bar abs. and a temperature of approximately 300°C; it is also possible to use, for example, saturated steam at a pressure of 18-23 bar abs. In this example, the stripped urea solution U2 contains in this example 44 wt.% urea, 15 wt.% NH3, 16 wt.% CO ₂ and 25 wt.% H ₂ O. The U5 urea solution from PEV has a urea concentration of 86-95 wt.%, preferably 93 wt.%. The urea solution U4 from LLPD has a urea concentration of 70-76% by weight, preferably 73% by weight. CLAIM 1. A method for the production of carbamide, including the stages in which: A) creating conditions for the formation of urea from ammonia and carbon dioxide in the reaction zone (R) high pressure with the formation of the first urea solution (U1), which also contains carbamate; B) subjecting the first urea solution to high pressure (HP) stripping (S) to decompose the carbamate using heat (H1, S1) to obtain a gas stream (SG) and a second urea solution (U2) also containing carbamate, and subjecting said gas stream to (SG) condensing in a high pressure carbamate condenser (HPCC) to form a first carbamate-containing solution (C1) and generating heat of condensation (H2, S2), wherein the carbamate-containing solution (C1) is fed into the high pressure reaction zone; C) subjecting said second urea solution (U2) to low pressure decomposition of carbamate or first treatment of said second urea solution (U2) at medium pressure (MPP) and subjecting said second urea solution (U2a) to low pressure decomposition, said carbamate decomposition under low pressure includes heating in a device (LPD) to carry out decomposition under low pressure of a urea solution (U2, U2a) containing carbamate, using the specified heat of condensation (H2, S2) from the high pressure carbamate condenser to decompose the carbamate, thus obtaining the first vapor (V1) and a third urea solution (U3) also containing carbamate, and expanding the third urea solution to subatmospheric pressure (F1, X1) to thereby obtain an expanded third urea solution (U3a); D) subjecting said first vapor (V1) to condensation in a first low pressure carbamate condenser (LPC1) to obtain a second carbamate-containing solution (C2) and a second vapor (V2) and releasing additional heat of condensation (H3), wherein the first low pressure carbamate condenser has an outlet for the second carbamate-containing solution (C2) which is in fluid communication with the inlet of the high-pressure reaction zone (R), and subjecting said expanded third urea solution (U3a) to decomposition of carbamate in a device (LLPD) to carry out decomposition under subatmospheric pressure using said additional heat of condensation (H3) from said first low pressure carbamate condenser (LPC1) by exchanging heat through a heat exchange wall (LPHX) between said first low pressure carbamate condenser (LPC1) and said device (LLPD) for performing decomposition under subatmospheric pressure to obtain such in the manner of the fourth carba mid solution (U4) and third steam (V3); And E) subjecting said third vapor (V3) to condensation in a subatmospheric carbamate condenser (LLPC) in indirect heat exchange with a cooling fluid, thereby obtaining a fourth carbamate-containing solution (C4). 2. Process according to claim 1, characterized in that the subatmospheric carbamate condenser (LLPC) has an outlet for at least a portion of the fourth carbamate-containing solution (C4) which is in fluid communication with the high pressure reaction zone (R). 3. The method according to claim 1 or 2, further comprising subjecting said second vapor (V2) to condensation in a second low pressure carbamate condenser (LPC2) in indirect heat exchange with a cooling fluid (CW), thereby obtaining a third carbamate-containing solution (C3), wherein the second low pressure carbamate condenser (LPC2) has an outlet for a third carbamate-containing solution (C3) which is in fluid communication with the high pressure reaction zone (R) inlet. 4. The method according to any one of the preceding claims, characterized in that the extension of the third - 15 040954 subatmospheric urea solution includes atmospheric evaporation (F1) to obtain a fourth vapor (V4) and a urea solution, which is further expanded to a subatmospheric pressure to obtain an expanded third urea solution (U3a), and moreover, the method includes condensing the fourth vapor (V4) in an atmospheric pressure condenser (APC) to obtain a fifth carbamate-containing solution (C5) and feeding the fifth carbamate-containing solution (C5) to said first low-pressure carbamate condenser (LPC1) and/or to said second low-pressure carbamate condenser (LPC2). 5. Process according to any one of the preceding claims, comprising first treating said second urea solution (U2) at medium pressure (MPP), said treatment yielding a treated second urea solution (U2a) further containing carbamate, and a fifth pair (V5) , and condensing said fifth vapor in a medium pressure condenser (MPC) to obtain a sixth carbamate-containing solution (C6), wherein said second carbamate-containing solution (C2) from said first low-pressure carbamate condenser (LPC1) and/or a third carbamate-containing solution (C3) from the second low pressure carbamate condenser (LPC2) is fed into said medium pressure condenser (MPC), wherein said medium pressure condenser (MPC) has an outlet for a sixth carbamate-containing solution (C6) in fluid communication with the inlet of the high pressure reaction zone (R). pressure, the method further comprising subjecting the treated second urea solution (U2a) to said low pressure decomposition of carbamate (LPD) and heating said fourth urea solution (U4) in a pre-evaporator (PEV) to evaporate water using the heat of condensation (H4) released in said medium pressure condenser (MPC), with obtaining the fifth carbamide solution (U5) and the sixth pair (V6). 6. Process according to claim 5, wherein said medium pressure treatment comprises adiabatically flashing the second urea solution (U2) in a medium pressure flash vessel (MPF), wherein the treated urea solution is the vaporized second urea solution (U2a). 7. Method according to claim 5, characterized in that said medium pressure treatment comprises heating the second urea solution (U2) in a medium pressure decomposition apparatus, thereby decomposing the carbamate. 8. Method according to any one of claims 3 to 7, characterized in that the third carbamate-containing solution (C3) is fed into the first low-pressure carbamate condenser (LPC1), wherein the fourth carbamate-containing solution (C4) is fed into the second low-pressure carbamate condenser (LPC2) . 9. Method according to any one of claims 3 to 7, characterized in that said second carbamate-containing solution (C2) is fed from said first low-pressure carbamate condenser (LPC1) to said second low-pressure carbamate condenser (LPC2), wherein the fourth carbamate-containing solution ( C4) is fed into the first low pressure carbamate condenser (LPC1). 10. Method according to any one of the preceding claims, characterized in that the high pressure stripper uses CO ₂ as the stripping gas and the stripping efficiency is 60-70%. 11. Installation for the production of urea (UP), designed to implement the method according to any one of claims 1 to 10, containing: A) a high pressure reaction zone (R) to create conditions for the formation of urea from ammonia and carbon dioxide with the formation of the first urea solution (U1), which also contains carbamate; B) a high pressure stripper (S) for subjecting the first urea solution to high pressure stripping to decompose carbamate using heat (H1, S1), thereby forming a gas stream (SG) and a second urea solution (U2) also containing carbamate, and a condenser (HPC) high pressure carbamate for subjecting said gas stream (SG) to condensation, thereby forming a first carbamate-containing solution (C1) and releasing heat of condensation (H2, S2); C) a low pressure decomposition device (LPD), wherein the low pressure decomposition device (LPD) is configured to subject said second urea solution (U2) to decomposition at low pressure, or the plant is configured to initially treat at least part of the second urea solution (U2) at medium pressure (MPP) in the medium pressure section (MPP) to obtain a treated second urea solution, and a low pressure decomposition device (LPD) is configured to subject said treated second urea solution to low pressure decomposition. pressure, wherein said low pressure decomposition of the carbamate comprises heating a carbamate containing urea solution using said heat of condensation (H2, S2) from a high pressure carbamate condenser to decompose the carbamate, thereby producing a first vapor (V1) and a third carbamate an ideous solution (U3) also containing carbamate, and an expansion system (F1, X1) for expanding the third urea solution to subatmospheric pressure to obtain an expanded third urea solution (U3a); - 16 040954 D) a first low pressure carbamate condenser (LPC1) for subjecting said first vapor (V1) to condensation, thereby obtaining a second carbamate-containing solution (C2) and a second vapor (V2) and generating additional condensation heat (H3), wherein the first condenser (LPC1) low pressure carbamate has an outlet for a second carbamate solution (C2) in fluid communication with the high pressure reaction zone (R) and a subatmospheric decomposition device (LLPD) for subjecting said expanded third urea solution (U3a) to decomposition of the carbamate with said additional heat of condensation (H3) from said first low pressure carbamate condenser (LPC1) by heat exchange through a heat exchange wall (LPHX) between said first low pressure carbamate condenser (LPC1) and said subatmospheric decomposition device (LLPD) with thus obtaining the fourth arbamide solution (U4) and third steam (V3); And E) a subatmospheric carbamate condenser (LLPC) configured to subject said third vapor (V3) to condensation by indirect heat exchange with a cooling fluid, thereby obtaining a fourth carbamate-containing solution (C4). 12. The urea production plant of claim 11, wherein the subatmospheric carbamate condenser (LLPC) has an outlet for all or part of the fourth carbamate-containing solution (C4) in fluid communication with the inlet of the high pressure reaction zone (R). 13. The plant for the production of urea according to claim 11 or 12, further comprising a second low pressure carbamate condenser (LPC2), configured to subject said second vapor (V2) to condensation by indirect heat exchange with a cooling fluid (CW), thereby obtaining a third carbamate-containing solution (C3) and having an outlet for the third carbamate-containing solution (C3) in fluid communication with the inlet of the high pressure reaction zone (R). 14. A plant for the production of urea according to any one of claims 11 to 13, characterized in that the plant comprises a medium pressure processing section (MPP) for processing said second urea solution (U2) at medium pressure, wherein said processing results in a treated second urea solution (U2a) also containing carbamate, and a fifth vapor (V5), wherein said plant further comprises a medium pressure condenser (MPC) for condensing said fifth vapor to obtain a sixth carbamate-containing solution (C6) and having an outlet for said second carbamate solution (C2 ) from said first low pressure carbamate condenser (LPC1) and/or an outlet for a third carbamate-containing solution (C3) from a second low pressure carbamate condenser (LPC2) connected to said medium pressure condenser (MPC), and said condenser (MPC) medium pressure has an outlet for the sixth carbamate-containing solution (C6), which is in liquid in direct communication with the inlet of the high pressure reaction zone (R), wherein the medium pressure treatment section (MPP) has an outlet for said treated second carbamide solution (U2a) connected to said device (LPD) for carrying out low pressure carbamate decomposition, wherein the installation is additionally contains a pre-evaporator (PEV) for heating said fourth urea solution (U4) to evaporate water using the heat of condensation (H4) generated in said medium pressure condenser (MPC), thereby obtaining a fifth urea solution (U5) and a sixth vapor ( V6), wherein the medium pressure treatment section (MPP) is a medium pressure flash vessel (MPF) for adiabatically flashing the second urea solution (U2). 15. A method for modifying an existing urea plant to obtain a urea plant according to claim 11, wherein the existing urea plant comprises: A) a high pressure reaction zone (R) to form a first urea solution (U1) which also contains carbamate; B) a high pressure stripper (S) for subjecting the first urea solution to high pressure stripping to decompose the carbamate using heat (H1, S1) to thereby form a gas stream (SG) and a second urea solution (U2) also containing carbamate, and a condenser (HPCC) of high pressure carbamate for subjecting said gas stream (SG) to condensation, thereby forming a first carbamate-containing solution (C1) and generating heat of condensation (H2, S2), wherein the high-pressure carbamate condenser (HPCC) has a connection for supplying a carbamate-containing solution ( C1) into the high pressure reaction zone; C) a low pressure decomposition device (LPD), wherein the low pressure decomposition device (LPD) is configured to subject said second urea solution (U2) to low pressure decomposition, or a low pressure decomposition device (LPD). pressure is configured to subject the treated second urea solution to decomposition of carbamate under low pressure, and while the existing installation is configured to initially process the specified second urea solution (U2) at medium pressure (MPP) in the medium pressure section to obtain indicated