EA044065B1 - THERMAL STEAMING INSTALLATION AND METHOD FOR UREA PRODUCTION - Google Patents

Description

Field of technology

The invention relates to the production of urea and, in particular, to a plant and method for the production of urea using a high-pressure thermal stripping type (also known as self-cleaning type) steamer.

Basic information

The invention relates to the production of urea from raw materials NH3 and CO2 in a high-pressure reaction zone. The synthesis stream from the reaction zone contains urea, water, ammonium carbamate, ammonia (partially in the gas phase) and inert gases. The synthesis stream must be purified to product urea using a urea production plant and method.

Inert gases are formed from raw material NH ₃ and raw material CO2; noble gases, for example, include H2. The NH ₃ feedstock in some embodiments of the invention contains some CH ₄ . In many existing urea production plants, passivating air is added to the raw CO2; this air is also included in the inert gases. Oxygen in passivation air is used to prevent corrosion of parts of high pressure (HP) equipment in urea production plants.

Urea plants are often of the full return to production type. In such plants, the urea synthesis stream from a high pressure reaction zone, which contains urea, water, ammonia and ammonium carbamate, is expanded and undergoes decomposition of the carbamate to produce a purified urea solution and a gas stream containing NH ₃ and CO2. The gas stream condenses to form a carbamate solution, which is pumped back into the high-pressure reaction zone. This carbamate return solution contains water to avoid solidification of the ammonium carbamate. Since water is a by-product of the urea formation reaction, water return is undesirable and it is desirable to minimize the water content of the urea return stream.

In general, it is desirable to minimize the specific volume of water introduced into the HP reaction zone from the low and medium pressure sections.

Processes such as urea stripping are based on a full return to production scheme and use a high pressure steamer. This invention generally relates to a process for producing urea using a stripping type process. In a urea production process using a stripping type process, the synthesis stream from the reactor is at least partially, eg completely, stripped under high pressure in a stripper to decompose the ammonium carbamate into a gas stream containing NH3 and CO2. The steamer operates, for example, at substantially the same pressure as the reactor. This gas stream leaving the steamer is condensed in a high pressure carbamate condenser (HPCC). High pressure stripping in urea production plants typically involves heating the urea synthesis solution and contacting the liquid with a countercurrent gas stream, the gas stream having a lower partial pressure of NH ₃ and/or CO2 vapor than the liquid , which ensures stripping efficiency.

In urea stripping processes, the HP steamer and HP urea condenser are typically shell-and-tube heat exchangers with a tube bundle consisting of thousands of tubes. The high pressure reactor is often a vertical vessel with trays. The steamer, as a rule, is a film-type shell-bran heat exchanger, in the pipes of which there is a urea solution, and the stripping gas rises upward. The HP carbamate condenser is typically a shell-and-tube heat exchanger with a horizontal or vertical tube bundle, with straight or U-tubes and with coolant or process fluid(s) in the tubes.

In CO2 stripping plants, the stripping gas is the CO2 feed; the N/C ratio in the reactor is about 3.0, and the N/C ratio in the distilled urea solution is relatively low. In CO ₂ strippers, the HP reactor typically has separate outlets for the inert gases sent to the HP scrubber and for the urea synthesis solution sent to the HP stripper.

This invention relates to a method for producing urea using a thermal stripping type (also known as self-cleaning type) process.

In thermal stripping plants, the urea reactor operates at a relatively high N/C ratio in excess of 3.0, in snamprogetti plants often at an N/C ratio of 3.2-3.6, for example 3.2-3.4. The reactor operates, for example, at 150-160 bar.

Thus, the urea synthesis stream fed to the thermal steamer is relatively rich in NH3, and the stripping gas is generated by heating (or reboiling) the liquid at the bottom of the HP thermal steamer to form a gas stream rich in NH3, which is in countercurrent contact with the incoming flow of urea synthesis, which provides a stripping effect. The thermal steamer does not receive raw CO ₂ as stripping gas. In some embodiments, a quantity of passivating air may optionally be supplied to the bottom of the thermal steamer.

The stripped urea solution from the thermal steamer has a relatively high N/C ratio and is fed to a medium pressure (MP) recovery section, which includes an MP digester, an MP carbamate condenser, and a separate MP ammonia condenser. The MP decomposition apparatus produces a urea solution, which is sent to the LP (low pressure) regeneration section, and a gas stream containing CO2 and a relatively large amount of NH ₃ . The gas stream is condensed in an MP carbamate condenser to produce a carbamate solution and the remaining NH ₃ gas. The remaining NH ₃ gas from the MP condenser is condensed in the MP ammonia condenser. The condensed solution of ammonia and carbamate is pumped separately back from the MP section to the HP section, typically by two different liquid streams at different temperatures and using different pumps.

An example of a method for producing urea using a thermal stripping type process is the snamprogetti process for producing urea, illustrated in Ullmann's Encyclopaedia of Industrial Chemistry, Chapter Urea, 2010, FIG. 25. In the process illustrated in this figure, the high pressure (HP) reactor has one outlet and the entire urea synthesis stream from the reactor is fed to the HP stripper, which is a thermal stripper type. Inert gases pass through the HPSS, wherein the oxygen contained in the inert gases provides corrosion protection to the HPSS, and the inert gases are separated from the HP condensate in the HP carbamate separator and supplied as a gas stream to the MP regeneration section, where they are discharged from the ammonia scrubber, located after the ammonia condenser. Thus, the exhausted inert gases do not contain much NH3, despite the relatively high N/C ratio of the urea solution in the thermal steamer. In the Snamprogetti design, the medium pressure regeneration section typically operates at 18 bar.

There is a need for large-scale urea production plants in which, preferably, the high-pressure stripper and high-pressure condenser are relatively small compared to the plant capacity. This will avoid such disadvantages of the steamer and condenser (usually shell-and-tube heat exchangers), such as their weight, bulkiness and difficulty in transporting them for the construction of the installation, for example, in the case of a new installation (installation from scratch). In addition, there is a desire to increase the capacity of existing thermal stripper urea units (ie, retrofit) without the need to modify the HP steamer and condenser or without adding an HP steamer or condenser.

US 2004/0116743 A1 mentions that the HP stripper stage and the HP condensation stage are largely responsible for the fact that it is only to a limited extent possible to increase the capacity of an existing plant without modifying or replacing expensive high pressure equipment. US '743 proposes increasing plant productivity by modifying the plant so that a portion of the urea synthesis solution is transferred from the synthesis zone to a medium pressure processing zone operating at a pressure of 1-4 MPa; and so that the other part is sent to the HP steamer. US '743 illustrates the design of HP type steamers using CO ₂ but mentions that thermal steam can also be used. However, details of this embodiment of the invention are not given, and FIG. 2 and 4 of US '743 use a CO2 stripper and a stream of inert gas RG from the top of the reactor to the scrubber. This is not desirable with the HP thermal steamer due to the higher N/C ratio.

There remains a need for improved urea production processes and thermal stripping plants, for example having relatively higher throughput and lower water turnover, as well as corresponding modernization methods.

The essence of the invention

The invention relates, in a first aspect, to a method for the production of urea, carried out in a thermal stripping type urea production plant comprising a high pressure (HP) synthesis section and first and second medium pressure (MP) regeneration sections, wherein the HP synthesis section contains an HP reaction zone , an HP thermal stripper and an HP carbamate condenser, wherein the HP steamer has an outlet for stripped urea solution connected to the first MP regeneration section and a gas outlet connected to the HP carbamate condenser, wherein the HP synthesis section further includes a separator . Said method comprises: separating a reaction mixture from a reaction zone at high pressure in said separator into a first stream, for example an ammonia-rich first stream, and a second stream, wherein both the first stream and the second stream contain a liquid phase containing urea, wherein the first the stream (eg, the ammonia-rich first stream) preferably has a lower gravimetric density than the second stream, while the first stream (eg, the ammonia-rich first stream) preferably has a higher ammonia concentration than the second stream; supplying a first stream (e.g., an ammonia-rich first stream) at least partially (e.g., fully

- 2 044065 stu), into the steamer; and supplying the second stream at least partially (eg, completely) to a second medium pressure regeneration section. Preferably, the first stream has a lower gravimetric density than the second stream and the first stream is an ammonia-rich first stream having a higher ammonia concentration than the second stream; and/or preferably the second stream is expanded from high pressure to medium pressure in an adiabatic MP flash unit included in the second MP regeneration section, resulting in a gas stream and a flashed MP urea solution.

The invention also relates to a urea production plant, preferably suitable for the inventive urea production process described herein, said plant comprising a high pressure synthesis section containing a reaction zone, a thermal steamer and a urea condenser, the plant also comprising a first medium pressure recovery section. pressure having an inlet connected to an outlet for stripped urea solution from said thermal steamer, the high pressure section comprising a high pressure separator configured to separate the high pressure reaction mixture from the reaction zone into a first stream and a second stream, wherein as the first stream , and the second stream contain a liquid phase containing urea and the first stream preferably has a lower gravimetric density than the second stream; and wherein the high pressure separator has a first outlet for a first stream connected to an inlet of said thermal steamer, and a second outlet for a second stream connected to a second medium pressure recovery section.

The invention also relates to a method of modifying an existing thermal stripper type urea plant, preferably to the inventive plant described herein, wherein the existing plant comprises a high pressure synthesis section containing a reaction zone, a thermal stripper and a urea condenser, wherein said existing plant further comprises a first section medium pressure regeneration having an inlet connected to an outlet for stripped urea solution from said thermal steamer. The method includes: adding a high pressure separator to the high pressure synthesis section, configured to separate a high pressure reaction mixture from the reaction zone into a first stream and a second stream, wherein both the first stream and the second stream contain a liquid phase containing urea, the first the stream preferably has a lower gravimetric density than the second stream; and adding a second medium pressure (MP) regeneration section, the high pressure separator having a first outlet for a first stream connected to an inlet of said thermal steamer, and a second outlet for a second stream connected to said second medium pressure regeneration section.

Brief description of drawings

In fig. 1 schematically illustrates a typical process flow diagram of the invention.

In fig. 2 schematically illustrates a typical flow diagram of the second medium pressure regeneration section used in the invention.

In fig. 3 schematically illustrates a typical high pressure separator used in the invention.

In fig. 4 schematically illustrates a typical high pressure separator used in embodiments of the invention.

Any embodiments of the invention illustrated in the figures are examples only and do not limit the invention.

Detailed description

Embodiments of the present invention are generally based on the intelligent approach of separating the urea synthesis stream from a reaction zone in a high pressure separator into a first stream and a second stream, both containing a liquid phase and both containing urea, the first stream being preferably richer in ammonia than the second flow.

In some embodiments, the first ammonia-rich fluid stream from the high-pressure separator has a higher ammonia concentration than the second fluid stream from the high-pressure separator, wherein the ammonia concentration is based on both gas and liquid together for two-phase fluid streams.

In some embodiments, the second stream may have a lower, higher, or the same NH3 concentration as compared to the first stream.

Preferably, a flash step and/or N/C measurement is used for the second stream.

Preferably, said method includes determining the N/C ratio of the second stream. The determination of the N/C ratio is advantageously particularly simple in preferred embodiments of the invention where the second stream consists of a degassed liquid. It is very beneficial in these embodiments that the degassed second stream consists of liquid rather than

- 3 044065 two-phase gas/liquid fluid flow, and accordingly the N/C ratio can be conveniently measured.

In the most preferred embodiment of the invention, the second stream is adiabatically flashed and the flash vapor is fed directly or indirectly to an ammonia condenser to form an ammonia condensate which is returned to the HP synthesis section. In this way, substantially water-free recirculation of the ammonia condensate is effectively achieved while achieving a low water content in the carbamate return stream from the second MP regeneration section.

Preferably, the flash vapor is supplied to the first MP regeneration section, in particular directly or indirectly to the ammonia condenser of the first MP regeneration section, to be condensed as ammonia condensate, which is returned to the synthesis section using an ammonia pump. Thus, the equipment of the first MR regeneration section is successfully used.

The first stream preferably contains both vapor and liquid and is preferably a two-phase fluid. The second stream preferably consists essentially of liquid. Preferably, the separation includes degassing the second stream. The first stream (the total stream including both gas and liquid in the case of a two-phase fluid) has a higher ammonia concentration than the second stream. Such separation can be performed at high pressure based on, for example, gravimetric density separation.

The ammonia-rich first stream preferably has a lower gravimetric density than the second stream. This refers to the gravimetric density of the entire flow (gas and liquid together in the case of two-phase fluid flows), as well as the density at the separation stage and/or within the separator. The flux density may increase or decrease after the separation stage.

In a preferred embodiment of the invention, the separator comprises a funnel with a liquid outlet down through the narrow opening of the funnel, preferably for the second stream and alternatively for the first stream. Preferably, the separator includes a funnel having a lower portion and an upper portion, a narrow opening at the bottom and a wide opening at the top, the narrow opening being connected to an outlet for the second separator stream. Preferably, the surface area of the wide opening is at least 2 or at least 4 times the surface area of the narrow opening of the funnel. In this document, up and down refer to gravity. In addition, the funnel is preferably located at the top of the vertical urea reactor. The urea reactor has an inlet at the bottom, directly or indirectly connected to the outlet of the HP urea condenser for receiving liquid from the HP urea condenser.

The funnel structure, for example, tapers conically from a wide opening to a narrow opening. Preferably, during operation the funnel is completely immersed in the reaction mixture phase containing the urea solution. The reaction mixture flows relatively slowly down the funnel and becomes a degassed urea solution, which is preferably removed as a second stream or, alternatively, as a first stream. A wide funnel (at a wide opening) results in a low downward velocity of the liquid inside the funnel, which allows the liquid to degas. The funnel outlet (narrow opening), for example, is connected to a drain.

Preferably, the method includes degassing the second stream in the HP separator. Preferably, the method includes supplying the degassed second stream to the second MP regeneration section, preferably by bypassing the thermal stripper, such that the second MP regeneration section receives degassed unstripped urea synthesis solution. Preferably, the method includes determining the N/C ratio in the degassed second stream.

In another embodiment of the invention, the first stream is degassed in an HP separator, and the degassed first stream is fed to a thermal steamer. Preferably, in this embodiment of the invention, the method includes determining the N/C ratio in the first stream.

Preferably, the first and second streams have different compositions immediately after separation. Preferably, the first and second streams have different compositions at high pressure, prior to any expansion step to reduce the pressure. Preferably, the first and second streams have different compositions at the separator outlets, and have a pressure at the separator outlets that is the same as the reactor operating pressure, or which is less than 10 bar lower than said reactor operating pressure.

Such embodiments of this invention fundamentally deviate from US 2004/0116743 A1, and the first part of the synthesis solution sent to the steamer and the second part sent to the MP section have the same composition (before the pressure of the second part is reduced from HP to MP).

In other, less preferred embodiments of the invention, the first and second streams have the same composition, as in US 2004/0116743 A1, for example, if an N/C measuring device is not used.

The two streams from the HP separation step are at least partially, for example completely, subjected to different treatments in accordance with the invention, in particular the streams are at least partially

- 4 044065 for example, completely, supplied to different blocks. The processing of the two streams can be tailored to the specific composition of each stream.

The first stream is at least partially, for example completely, for example at least 90% by weight of the liquid phase, directed to a thermal stripping type HP steamer. The stripped urea solution from the thermal steamer, at least partially, for example completely, for example at least 90 wt.%, is sent to the first MP regeneration section.

The first MP regeneration section preferably comprises an MP decomposition apparatus, an MP carbamate condenser and an MP ammonia condenser, and preferably also an MP carbamate separation column and an MP ammonia receiver. The first MP regeneration section preferably has a separate return flow circuit for the condensed ammonia stream and the first carbamate solution to return these streams separately to the HP section.

In some embodiments of the invention, the first stream may be divided into sub-streams and one or more of these sub-streams is supplied, at least in part, for example in its entirety, to the thermal steamer. For example, if the first stream is a two-phase fluid, then the first stream, for example, undergoes gas-liquid separation, the liquid stream, for example, being supplied to a stripper, and the gas stream, for example, being supplied to a high pressure carbamate condenser. In such an embodiment of the invention, only a portion of the first stream is supplied to the thermal steamer.

Typically, the first stream undergoes gas-liquid separation after the HP separation stage and the liquid is distributed to the inlets of the tube bundle in the thermal steamer. This gas-liquid separation, for example, takes place in the upper chamber of a thermal steamer. Gas-liquid separation can also be carried out in an additional separation tank located between the HP separator and the steamer, with liquid supplied to the thermal steamer and gas to the HPSS.

The gas from gas-liquid separation, containing inert gases and NH3, is preferably sent to the HPSS, for example, mixed with the gas stream released during stripping in the tube bundle of a thermal steamer. Thus, the oxygen contained in the inert gases helps prevent corrosion in both the reactor and the HPSS.

Preferably, the first stream is completely or substantially completely (for example, at least 95 wt.% of the liquid phase) is sent to the thermal steamer.

The second stream preferably bypasses the HP steamer and is sent at least partially, for example completely, to the second MP regeneration section, preferably the second stream is completely or substantially completely (for example, at least 95 wt.%) is sent to the second MP regeneration section. As an advantage, the capacity of the HP steamer and HP carbamate condenser may be small compared to the capacity of the urea unit.

Preferably, the second MP regeneration section receives at least 95 or at least 99 wt.% of the second stream provided by the high pressure separator. The second MP regeneration section preferably receives unstripped urea solution from the HP reactor as said second stream.

Preferably, the second MP regeneration section receives 5-50 wt.% of the urea produced in the HP synthesis section, more preferably 15-30 wt.%

The second MP regeneration section contains a second MP decomposition apparatus, a second MP carbamate condenser and, preferably, an MP adiabatic flash unit. The second MP regeneration section preferably operates independently of the first MP regeneration section. This allows the use of optimal technological modes in each section.

The preferred MP adiabatic flash unit receives at least a portion, preferably all, of the second stream, preferably the degassed second stream, and has a first outlet for flashed vapor and a second outlet for flashed urea solution. The MP flash unit is preferably adiabatic in the sense that it is preferably not actively heated. The advantage of this is that the endothermic decomposition reaction of the carbamate occurs with difficulty or only to a limited extent, so the flash vapor has a relatively low CO2 content. In addition, adiabatic flashing provides low water evaporation and advantageously low water content in the flash vapor. Preferably, the flash vapor contains at least 90% by weight NH ₃ or substantially pure NH ₃ . The N/C ratio of the urea solution is reduced by flash evaporation, which results in less water being returned to the urea from the second MP regeneration section and improves urea conversion. The MP adiabatic flash unit preferably operates at a higher pressure than the second MP decomposition apparatus, preferably at least 1.0 bar higher or, for example, at least 5 bar higher, or, for example, at least 10 bar higher, generally less than 30 bar higher and preferably also at least 1.0 bar or at least 2

- 5 044065 bar higher than the first MR regeneration section. The pressure of the flashed urea solution is preferably correspondingly reduced between the MR adiabatic flash unit and the second MR decomposition apparatus by at least 1.0, at least 5 or, for example, at least 10 bar.

The MR adiabatic flash unit is preferably operated at a pressure of at least 20 bar (absolute), for example at a pressure in the range of 20 to 60 (absolute), for example 25 to 40 bar, for example 25 to 35 or, for example 30 to 40 bar. The pressure from the adiabatic flash stage of MP can be effectively used to control the composition of carbamate return streams.

The urea solution at the outlet of the MP flash unit, for example, contains 15-25 mol.% NH3 (both in free form and in the form of carbamate) and 5-15 mol.% CO ₂ (both in free form and in the form carbamate), for example at a pressure of 20-30 bar.

As an example, the urea solution leaving the MP flash unit is, for example, 23 mol% NH3 (both free and carbamate), 10 mol% CO2 (both free and form of carbamate), 19 mol.% urea and 32 mol.% water, at 25 bar and 133°C.

The flash vapor is preferably condensed to form liquid condensate, which is typically returned to the HP section, preferably using a pump. In some embodiments of the invention, a special ammonia condenser is used. In the most preferred embodiment of the invention, the vapor from the adiabatic flash is supplied to the MP carbamate condenser of the first MP regeneration section. This MR carbamate condenser has a gas outlet connected to the gas supply to the ammonia condenser of the first MR regeneration section. Thus, the excess NH3 contained in the vapor from the adiabatic flash is effectively condensed in the ammonia condenser of the first MP regeneration section as a relatively pure liquid NH3. Due to flashing, a second high N/C ratio stream, for example in embodiments of the invention with a reactor operating at an N/C ratio in the range of 3.0 to 3.4, can be effectively combined with a high quality carbamate return solution from the second section of MR regeneration. In addition, this method takes advantage of the first MP regeneration section after the HP thermal stripper, adapted to process the stripped urea solution with a relatively high N/C ratio and substantially anhydrous return of ammonia from the ammonia condenser to the HP synthesis section.

Thus, the preferred embodiment of the invention uses an adiabatic MP flash unit that receives a portion of the urea synthesis stream from the reactor (second stream) and the flash vapor is supplied to the MP carbamate condenser of the first MP regeneration section. In this embodiment, but also in other embodiments of the invention, the second stream, for example, may have the same, higher or lower gravimetric density than the first stream, and the second stream may have a higher, the same or more lower NH3 concentration than the first flow.

The MP adiabatic flash unit preferably operates at a higher pressure than the first MP digester and the first MP carbamate condenser, preferably at least 1.0 bar higher, to ensure vapor transfer.

In the case of modification of an existing urea plant (reconstruction), the urea condenser and ammonia condenser in the existing first MR regeneration section usually have a reserve to produce steam from adiabatic flash evaporation. Adiabatic flash pressure can be used to control the amount of gas flashed.

The second MP digester has an inlet for the preferably flashed urea solution or a second stream (if the preferred adiabatic flash is not used), a steam outlet and an outlet for the urea solution. The second MP decomposition apparatus typically comprises a heat exchanger, preferably comprises a shell and tube heat exchanger, and preferably uses steam as a heat transfer medium. The second apparatus for MP decomposition contains, for example, a vertical straight-tube shell-and-tube heat exchanger with a rectifier on top. The rectifier contains a nozzle that provides contact between the incoming liquid film and the rising gas. The gas outlet is preferably located at the top. The liquid inlet is preferably located at the top of the rectifier. The second MP decomposition apparatus operates, for example, at a pressure of 15 to 25 bar.

The first and second MP decomposition apparatuses can operate effectively at different pressures. The second MP digester, for example, operates at a higher pressure than the first MP digester, for example at least 1.0 or at least 5.0 bar higher, for example 5-15 bar higher. This may contribute to the relatively high condensation temperature in the second MP carbamate condenser.

- 6 044065

Steam from the second MP decomposition apparatus is supplied to a second MP carbamate condenser, which has an outlet for the carbamate solution. The second MP carbamate capacitor may be provided in one or more units. For example, it is offered as two shell-and-tube heat exchangers. The second MPC (medium pressure carbamate condenser) contains, for example, a first heat exchanger for indirect heat exchange with the urea solution, which needs to be heated, for example, to evaporate water, and a second heat exchanger for cooling water. The second MP digester and the second MP carbamate condenser preferably operate at substantially the same pressure. A higher condensing temperature in such embodiments of the invention is desirable for the first heat exchanger.

The carbamate solution is directly or indirectly returned to the HP synthesis section, for example, to the HPSS of a thermal stripper unit, in particular, to a part of the process medium of such HPSS, for example, to the pipe part of the boiler-type HPSS. This return typically involves pumping the carbamate solution using an HP carbamate pump.

In one embodiment of the invention, the carbamate solution formed in the second carbamate condenser MP is pumped to the HP section using a carbamate pump for the first regeneration section. For example, the carbamate solution generated in the second carbamate condenser MP is supplied to the MP separation column, and the carbamate solution outlet of the MP separation column is connected (for liquid flow) directly or indirectly to the inlet of the HP carbamate pump of the first regeneration section. This exemplary embodiment of the invention is less preferred because the carbamate solution formed in the second MP carbamate condenser then becomes saturated with ammonia.

More preferably, the carbamate solution formed in the second MP carbamate condenser is pumped to the HP synthesis section using a dedicated pump that is separate from the pump used to transfer the carbamate solution from the first MP carbamate condenser to the HP synthesis section. Preferably, the carbamate solution formed in the second carbamate condenser MP does not flow through the MP separation column. This has the advantage that the carbamate solution does not absorb NH ₃ in said separation column, so that the flow volume pumped by the additional pump is relatively small. Thus, the portion of the NH ₃ feed supplied to the first MP regeneration section, which is pumped by the ammonia pump, is relatively large, which effectively reduces the specific amount of water returned to the HP section.

The second MP regeneration section preferably further has an inlet for the CO2 feed gas stream such that the MP CO2 feed is supplied directly or indirectly to the second MP carbamate condenser where it is condensed with ammonia (derived from the second stream, e.g. from a second apparatus for the decomposition of MP) to form a carbamate solution.

Advantageously, therefore, part of the CO2 feedstock can be supplied at medium pressure and pumped to reach high pressure in the form of a carbamate solution. Thus, in case of refurbishment, the existing HP CO ₂ compressor (usually present in the existing urea plant for supplying HP CO ₂ gas to the high pressure synthesis section) does not require modification. In the case of a greenfield installation, the CO ₂ HP compressor may be relatively small. The CO2 HP compressor generally requires higher capital costs compared to the carbamate pump and _CO2 MP compressor. In some embodiments of the invention, said installation comprises a CO2 MP compressor for compressing the CO2 feedstock to medium pressure, in particular to a pressure above the operating pressure of the second MP carbamate condenser. In some embodiments, the MP CO2 feedstock is obtained from the intermediate stage of a multi-stage HP CO2 compressor.

Typically, CO2 is available at the low pressure limit (eg 1-5 bar abs) from an ammonia production plant (in particular a synthesis gas plant). The CO2 MP feedstock is, for example, compressed to MP using a _CO2 MP compressor or by recovering the _CO2 feedstock from the intermediate stage of a _CO2 HP compressor. In some embodiments of the invention, no passivating oxygen is added to the MP CO2 feedstock and/or no oxygen is added to the MP CO2 feedstock for the hydrogen converter unit. This advantageously provides a low inert gas content in the second urea condenser MR, which is particularly effective in embodiments in which the second urea condenser includes a first heat exchanger for indirect heat exchange with the urea solution to be heated.

In a preferred embodiment of the invention, the CO2 MP feedstock is supplied to a CO2 MP steamer included in the second MP regeneration section. In this MP stripper, preferably, the urea solution from the MP decomposition apparatus is stripped (in countercurrent contact with a flow of CO2 gas) to produce a steam stream and an MP stripper solution. The stripping in the CO2 MP steamer is preferably adiabatic. The CO2 MP steamer contains, for example, a compacted layer adapted for countercurrent contact of gas and liquid.

The urea solution at the liquid outlet of the _CO2 MP steamer typically has a lower N/C ratio than the urea solution at the liquid inlet from the CO2 MP steamer. Thus, the urea solution at the outlet is more suitable for processing in the subsequent LP regeneration section.

The steam flow from the CO2 MP steamer is directed to the second MP carbamate condenser.

Supplying the CO2 MP feedstock to the second MP carbamate condenser, optionally via a CO ₂ MP steamer, provides the advantage that the carbamate solution formed in the second MP carbamate condenser has a relatively low N/C ratio and therefore, for a fixed amount of carbamate, has less volume. A smaller volume is effective for pumping MR carbamate solution. The adiabatic flash can be adjusted to have sufficient NH3 in the second MP carbamate condenser.

The first stream has, for example, an N/C ratio in the range of 3.3-3.6 at the reactor outlet and at the HP separator outlet.

The urea solution at the outlet of the HP thermal steamer contains, for example, 23-25 wt.% NH ₃ (both in free form and in the form of carbamate) and 6-7 wt.% CO2 (both in free form and in the form carbamate).

The carbamate solution from the first MP carbamate condenser has an N/C ratio of, for example, 3 to 4, or 3.50 to 4.50

In an illustrative embodiment of the invention, the liquid obtained from the bottom of the separation column, before mixing with the carbamate solution from the second MP regeneration section, contains 5060 mol.%, for example, 56 mol.% NH ₃ (both free and as carbamate), 10-20 mol.%, eg 14 mol.% CO2 (both free and carbamate) and 25-35 mol.%, eg 29 mol.% H2O. The high N/C ratio necessitates a high water content.

Preferably, the carbamate solution from the second MP carbamate condenser has an N/C ratio of 2.10 to 2.50, for example 2.20 to 2.40.

For example, the carbamate solution from the second MP carbamate condenser contains 50-60 mol%, e.g. 55 mol.% NH3 (both free and carbamate), 20-25, e.g. 22 mol.% CO2 (as in free form and in the form of carbamate), and 20-25 mol.%, for example 23 mol.% H ₂ O. The specified solution, for example, has a pressure of 17-18 bar.

Preferably, the carbamate solution from the first MP regeneration section entering the HP section (i.e., exiting the HP carbamate pump) has a water content of 23-27 wt.%, and the carbamate solution from the second MP regeneration section entering the HP section , has a water content of 18-22 wt.%, for example 20 wt.%

Preferably, the carbamate solution from the first MP carbamate condenser has a water content of 23-27 wt%, for example 25 wt%, and the carbamate solution from the second MP carbamate condenser has a water content of 18-22 wt%, for example 20 wt. %.

The carbamate solution from the second MR carbamate condenser is thus of better quality using the design of this invention, in particular due to the high separation rate and/or the preferred adiabatic flash of the MR.

The purified urea solution from both the first MP regeneration section and the second MP regeneration section is sent to the LP regeneration section of the urea plant, for example, to two separate LP regeneration sections or to the same LP regeneration section. One or more LP regeneration sections typically comprise an LP decomposition apparatus and an LP carbamate condenser. The carbamate solution LP from the carbamate condenser LP is supplied, for example, to the first and/or second carbamate condenser MP.

In fig. 1 schematically illustrates a typical process diagram of the invention, which does not limit the invention or limit the claims. In the following description, the reference numerals shown in FIG. 1 are for convenience only and do not limit the invention in any way.

The urea production method according to the invention is typically carried out in a urea production plant (UPP) of the thermal stripping type. The installation contains a high pressure synthesis section (HP) and the first and second medium pressure recovery sections (MPR1, MPR2). The first and second MR regeneration sections receive a urea-containing stream from the HP synthesis section and obtain a urea solution MR, which, as a rule, is further processed in the LP regeneration section to produce a urea solution LP, which, for example, is further concentrated in the evaporation section to form urea melt. The urea melt is often sent to a finishing section where a solid urea product is formed, such as a granulator or granulation tower. The evaporation section is used to remove water, the resulting water vapor is condensed, and the condensate is usually treated in a waste water treatment (WWT) section consisting of a hydrolyzer and a stripper. Typically, WWT has relatively high power consumption.

Other uses of urea melt and urea solution are also possible.

- 8 044065

The HP synthesis section contains a high pressure reaction (HPR) reaction zone, a high pressure stripper (HPSt) and a high pressure carbamate condenser (HPCC).

The HP reaction zone (HPR), for example, is provided with one or more urea HP reactors. If two or more urea HP reactors are used, they are, for example, arranged in parallel or in series. One or more HP reactors are typically vertical bubble columns with trays. In the present invention, the reactor is, for example, operated at 180-195°C, for example 185-195°C, and/or at a pressure of at least 140 bar, for example 140-160 or 150-160 bar. The reactor operates, for example, at an N/C ratio in the range of 3.00 to 3.40, for example in the range of 3.1 to 3.2.

The urea production process, for example, involves introducing oxygen (O2) for passivation purposes into the HP reaction zone (HPR), for example, in an amount of at least 0.010 vol.% based on fresh feed CO2, for example, by introducing air in an amount of at least at least 0.10 vol.% and generally less than 1.0 vol.% relative to fresh CO2 feed. Passivating air or oxygen, for example, is supplied as part of the feed CO ₂ . Passivating air or oxygen, for example, is supplied directly to the HP urea reactor.

The HP steamer (HPSt) has an outlet for stripped urea solution (2) connected to the first MP regeneration section (MPR1), and a gas outlet (3) connected to the HP urea condenser (HPCC). The HP Steamer (HPSt) is typically a vertical film-type shell-and-tube heat exchanger with urea stripping solution in the tubes, with an outlet for the gas mixture at the top connected to an HP urea condenser (HPCC) and with an outlet for the stripped urea solution at the bottom. The HP steamer is preferably designed as a thermal steamer. The steamer tubes are not limited to, for example, being bimetallic tubes or containing, for example, Ti and/or Zr, or, for example, being made of a suitable stainless steel, for example, duplex ferritic-austenitic stainless steel, for example, duplex stainless steel, such as described in WO 2017/014632.

In the method according to the invention, the thermal steamer operates, for example, at 200-210°C, these temperatures indicate the outlet temperature of the urea solution.

The HP carbamate condenser (HPCC) is preferably a shell and tube heat exchanger, more preferably a horizontal U-tube bundle heat exchanger. For example, the HPSS is designed to work with liquid as a continuous phase in the process part. The HP carbamate condenser is preferably of the boiler type with a horizontal bank of U-shaped tubes, having an inlet for receiving gas to be condensed within the tubes and an inlet for receiving coolant in the casing. Other types of HP carbamate condenser are possible, such as with a vertical bank of U-tubes or with a horizontal bank of U-tubes, with an inlet to receive gas to be condensed in the shell, and with an inlet to receive coolant in the tubes.

Preferably, the HPSS additionally supplies a medium-pressure carbamate solution from the first MP regeneration section to the process part, for example, to the tubes for a boiler-type condenser.

In some embodiments of the invention, the HP process fluid stream (4) from the HPCC contains a carbamate solution and inerts and is supplied to a carbamate separator (CSp) operating at high pressure and configured for gas-liquid separation to produce a liquid stream (5) and gas flow (6). The liquid carbamate stream (5) is fed into the reactor, typically using an ammonia-fuelled ejector (Ej). The gas (6) from the carbamate separator (CSp) contains inerts and ammonia and is preferably supplied to the first MP regeneration section, for example, to the lower part of the MP decomposition apparatus. The supply of gas (6) to the first MP regeneration section (MPR1) is particularly effective in embodiments of the invention in which a degassed urea solution is supplied to a medium pressure flash (MPF) unit.

In the invention, the HP synthesis section further includes a high pressure liquid separator (HPLS), in particular a high pressure liquid separator, more specifically a high pressure liquid separator. The separator operates at high pressure. The separator is, for example, a special block or located inside the reactor vessel. If two or more reactors are used in series, the separator is preferably located in the downstream reactor. The separator, offered as a special unit, is preferably located after the reactor. The separator is preferably located at the bottom of the reaction zone. The separator preferably receives a reaction mixture in which the conversion (urea formation) is already at least 90% complete with respect to the total conversion achieved in the HP synthesis section. The reaction mixture at the inlet of the separator contains, for example, at least 30 wt.% urea, for example, 30-35 wt.% urea. It is preferable that NH3 and/or gaseous components are not removed from the reaction mixture in the reaction zone prior to separation in the HP separator.

- 9 044065

The claimed method for producing urea involves separating the reaction mixture from a reaction zone (HPR) at high pressure in a separator (HPLS) into a first stream, for example an ammonia-rich first stream (S1), and a second stream (S2). Both the first and second streams contain a liquid phase; this liquid phase contains urea. The ammonia-rich first stream (S1) preferably has a lower gravimetric density when separated than the second stream (S2). The separation may be based, for example, on gravimetric density separation. The first stream (S1) has, for example, a higher concentration of ammonia than the second stream (S2) based on the total volume of the two streams (including gas and liquid in the case of two-phase fluid streams). In particular, the second stream is optionally substantially free of gas, such that the gaseous fraction of the gaseous components of the reaction mixture is present in the first stream; these gaseous components may be rich in ammonia. Accordingly, the first stream (S1) contains inert substances and, in particular, the first stream (S1) has a higher content (wt.%) of inert components than the second stream (S2). The inert components of a urea plant include H ₂ and O ₂ . For example, the first stream (S1) has a higher wt.% H ₂ content and a higher O2 content than the second stream (S2). The inert components included in the first stream (S1) pass through the HP Steamer (HPSt) and through the HP Carbamate Condenser (HPCC), thereby assisting in the passivation of said HP blocks and preventing corrosion of said blocks.

In this process, the ammonia-rich first stream (S1) is supplied at least partially, for example completely, to a thermal stripping type HP steamer. The second stream (S2) is supplied at least partially, for example completely, to the second MP regeneration section (MPR2).

In a preferred embodiment of the invention, the HP separator is located at the lower end of the reaction zone. This provides the advantage that the liquid phases of the first and second streams have substantially the same composition, in particular may have substantially the same composition in the connection circuit (pipes) for transferring the first stream, at least in part, to the thermal steamer and for transferring the second flow into the second MR regeneration section.

Preferably, said method includes determining the N/C ratio of the second stream.

Preferably, the method includes determining the N/C ratio in the degassed stream from the HP separator.

The determination of the N/C ratio is advantageously particularly simple in preferred embodiments of the invention where the second stream consists of a degassed liquid. It is very beneficial in these embodiments that the degassed second stream consists of a liquid rather than a two-phase gas-liquid fluid stream, and accordingly the N/C ratio can be conveniently measured. Thus, very preferably, the N/C ratio in the liquid phase contained in the first stream can also be determined since it is substantially the same as the measured N/C ratio in the second stream. This can be used to better control the operation of the synthesis section, for example, the reactor and thermal stripper, as well as the first MP regeneration section; for example, during installation startup. Information about the N/C ratio in the liquid phase is useful because in the reactor the urea formation reaction occurs only in the liquid phase.

Preferably, the installation includes an N/C measuring device for the degassed stream supply line, preferably in the degassed second stream supply line to the MP regeneration section. Preferably, a small portion of the degassed HP liquid stream is withdrawn and supplied to the N/C measuring device.

Continuous N/C measuring devices for the effluent stream from a liquid urea reactor are known in the art and use, for example, the relationship (correlation) between liquid density and N/C ratio, for example at a fixed temperature and pressure. The N/C measuring device is based, for example, on measuring the density of a liquid using, for example, a Coriolis density measurement, a radioisotope density meter, or, for example, a vibrating element technology for measuring liquid density. Other methods may also be used. Information about the N/C ratio of the first stream supplied to the thermal stripper is particularly useful in the process of the invention, in which the operation of the first and second regeneration sections, for example, preferential adiabatic flash, provides increased flexibility for optimizing urea yield.

By measuring the N/C ratio, the NH ₃ feed and/or the CO2 feed to the synthesis section can be adjusted to obtain optimum yield, preferably by adjusting the NH ₃ return flow rate. Preferably, the method includes adjusting the NH ₃ supply and/or the CO2 supply to the HP synthesis section, in particular the NH ₃ return flow rate, depending on the measured N/C ratio.

The introduction of an N/C metering device ensures stable plant operation with lower energy consumption and lower ammonia emissions, especially since the two MP regeneration sections typically produce carbamate solutions with different N/C ratios.

In the first MP regeneration section (MPR1), in general, a urea solution MP (7) is obtained containing, for example, 55-65 wt.% urea, for example, 60-65 wt.% urea, the return flow of urea is 10 044065 mate (8 ) and a separate liquid return stream of ammonia (9), as well as a gas stream containing inert substances (10).

Preferably, the first MP regeneration section (MPR1) includes a first MP decomposition apparatus (MPD-1), a first MP carbamate condenser (MPCC-1) and an ammonia condenser (AC), and preferably an MP separation column (medium pressure separation column (MPSC) and ammonia receiver (AR).

In fig. 2 schematically illustrates a typical first MP regeneration section (MPR1). The first MP decomposer (medium pressure decomposer, MPD-1) receives the expanded stripped urea solution (2) and uses heat to decompose the carbamate contained in the stripped urea solution and also to remove NH ₃ . For example, the decomposition apparatus has a solution inlet (2) at the top and a gas outlet (18) at the top, a nozzle and a casing heat exchange portion, and a solution outlet (7) at the bottom, and optionally an inlet hole (6), preferably at the bottom , to receive gas from the HP carbamate separator (CSp).

The first MP carbamate condenser (MRCC-1) has an inlet for receiving gas (18) from the MP decomposition apparatus (MPD-1) and is configured to at least partially condense CO ₂ and NH ₃ contained in said gas into solution carbamate, usually after also receiving some carbamate solution from the LP regeneration section. A relatively high water content of the LP carbamate solution can be used to avoid crystallization of the MP condensate. The carbamate solution MP (8) formed in the first carbamate condenser MP (MRCC1) is generally supplied directly or indirectly to the HP synthesis section as a return carbamate solution using a pump.

Most preferably, the first carbamate condenser MP (MPCC-1) also receives a gas stream (11) from the adiabatic flash. Thus, components of this gas stream (11) that do not condense in MPCC-1, such as excess NH3, are preferentially purified in the MPSC and can be condensed as relatively pure liquid ammonia in an ammonia condenser (AC), e.g. ammonia condenser MR. The ammonia condensate (22) from the ammonia condenser (AC) contains (almost) no carbamate. The ammonia condensate (22) may accordingly have a low water content. The ammonia condensate (22) is preferably substantially pure ammonia.

Condensation can be carried out using one or more heat exchangers, and also using as a cooling fluid, for example, cooling water and/or urea solution, which must be heated. The first MP carbamate condenser (MRCC-1) is proposed, for example, as an MP condenser/pre-evaporator for indirect heat exchange with a heated urea solution, optionally with an additional MP condenser downstream for condensing at least a portion of the uncondensed gases from the first MP carbamate condenser (MRSS-1). The MP condenser downstream works with cooling water, for example. The MP condenser/pre-evaporator is, for example, a shell-and-tube heat exchanger in which gas is condensed in the shell and the urea solution is heated in the tubes. The heated urea solution is obtained, for example, from the LP regeneration section of the plant and using the method.

Preferably, the MP condensate (19) is supplied to an ammonia-carbamate separation column (MPSC) along with the uncondensed gas, and the uncondensed gas is, for example, refluxed with relatively cold liquid NH3 feed in said column to remove CO2 from the gas. Column (MPSC), for example, is used as a distillation column.

In a preferred embodiment of the invention, the MP condensate (19) is fed to the bottom of the column and heated, and the feed liquid NH3 is fed to the top of the column. Preferably, the column contains trays. Preferably, an additional water stream is supplied just below the top of the column. Advantageously, the gas stream (21) from the top of the separation column contains only NH3 and inert substances. This gas stream (21) is preferably supplied to an ammonia condenser (AC). The bottom product of the ammonia-carbamate separation column (MPSC) is a carbamate solution MP (8), which contains relatively high amounts of NH ₃ and water.

The uncondensed gas stream from the first MP carbamate condenser (MRCC-1), preferably after purification to purer ammonia gas, is supplied to the (first) ammonia condenser (AC), which is a heat exchanger that preferably uses cooling water as the cooling fluid . The ammonia condenser preferably operates at a temperature in the range of 20 to 50°C.

The condensed ammonia (9) is returned to the HP synthesis section, preferably after separating the inert gaseous components (10) from the liquid in the ammonia receiver (AR), which also receives the liquid NH3 feed. Liquid ammonia from the ammonia receiver (AR) is partially (9) pumped to the HP section and partially (23) used in the MP separation column (MPSC).

The gas stream (10) is fed, for example, into a scrubber (not shown), where washing occurs with an aqueous stream, for example, steam condensate, from which the liquid is usually returned to the HP synthesis section, for example, by feeding it into ammonia carbamate separation column (MPSC).

The WWT section contains, for example, a hydrolyzer and a stripper. In particular, in embodiments of the invention in which degassed urea solution is supplied to the MP flash unit, the amount of inerts in the gas stream (10) may be relatively low, and accordingly, the power consumption of the WWT section may preferably be relatively low.

The second MP regeneration section (MPR2) contains a second MP decomposition apparatus (MPD2) and a second MP carbamate condenser (MPCC2). An exemplary second MP regeneration section is illustrated in FIG. 1.

Preferably, the method includes expanding a preferably degassed second stream (S2) from high pressure to medium pressure in a second MP regeneration section in a preferred adiabatic MP flash (MPF) step as contemplated to produce a gas stream (11) (flash vapor). evaporation) and flashed urea solution MR (12). Preferably, the flash vaporization of the MP is carried out at a pressure in the range of 25 to 40 bar. Preferably, the second MP digester operates at a slightly lower pressure than the MP flash unit, for example 1 bar lower. Preferably, the installation comprises an expansion valve between the MP adiabatic flash unit and the second MP decomposition apparatus.

Preferably, the flashed urea MR solution (12) is subjected to ammonium carbamate decomposition in the above MR decomposition apparatus (MPD2) to produce a treated urea solution (13) and a gas stream (14). The second apparatus for MP decomposition (MPD2), as a rule, is a heat exchanger for indirect heat exchange with steam. The gas stream (14) is condensed in a second carbamate condenser MP (MRCC2) to produce a gas stream (20) of carbamate solution (15), which is returned to the HP section (HPS). Any non-condensed gases (20) can be supplied, for example, to a carbamate condenser LP, which is located in the regeneration section LP. A particular advantage is that the uncondensed gases (20) have a low inert gas content, so they can be condensed and scrubbed in the LP recovery section to produce a low water content LP carbamate stream which is returned directly or indirectly to the synthesis section HP. The carbamate solution (15) from the second carbamate condenser MP (MRCC2) is pumped, for example, into the carbamate condenser HP, preferably using a special carbamate pump, for example if MPCC-2 operates at a higher pressure than MPCC-1.

Preferably, the installation comprises, as separate pumps, an HP ammonia pump, a carbamate pump of the first MP regeneration section and a carbamate pump of the second MP regeneration section for pumping these three streams separately to the HP section. This, in particular, allows the streams to have different temperatures and/or different pressures across the MR range, which advantageously contributes to lower water content in the return stream (15).

In other possible embodiments of the invention, the carbamate solution (15) bypasses the MP separation column (MPSC) and is supplied to the carbamate pump used in the first regeneration section (MPR1) to pump the carbamate solution (8) to the HP section.

Preferably, the second MP regeneration section (MPR2) further comprises a CO ₂ MP stripper (medium pressure stripper, MPS). Preferably, in this steamer, the urea solution (13) from the second MP decomponent (MPD2) is stripped/contacted in countercurrent with the feed CO2 MP in said CO2 MP steamer (MPS) to produce a further processed urea solution (16) and a gas stream (17). The gas stream (17) is condensed to form a carbamate solution in said second carbamate condenser MP (MRCC2). In this way, the desired low N/C ratio in the carbamate solution is achieved (15).

The invention also relates to a urea plant (urea production plant), which is preferably suitable for the methods of the invention. The preferences and details of the plant, units and connections discussed herein in combination with the urea production method also apply to the claimed plant. Said installation comprises a high-pressure synthesis section containing a reaction zone, a thermal steamer and a carbamate condenser. The reaction zone is, for example, one or more reactors, in particular one or more vertical reactors. Vertical urea reactors include, for example, one or more inlets at the bottom and outlets for first and second streams at the top of the reactor. In the case of two or more reactors, they are, for example, arranged in series, although they can also be arranged in parallel. The installation further comprises a first medium pressure regeneration section having an inlet port connected to an outlet port for stripped urea solution of said thermal steamer. The high pressure synthesis section contains a high pressure separator configured to separate the high pressure reaction mixture from the reaction zone into a first stream and a second stream. The separator is typically designed such that both the first stream and the second stream contain a liquid phase containing urea, the first stream (S1) optionally having a lower gravimetric density than the second stream (S2) . In addition, the high pressure separator has a first outlet for a first stream connected to an inlet of said thermal steamer, and a second outlet for a second stream connected to a second medium pressure regeneration section. The details of the first and second medium pressure regeneration sections are the same as described with respect to the method. The separator has, for example, a funnel-shaped structure with a wide opening at the top of the funnel and a narrow opening at the bottom, the narrow opening being connected to an outlet for the second stream. In the context of this invention, the terms upper and lower are used as defined in relation to gravity. The separator is located, for example, in the upper part of the second vertical reactor, which is located in series after the first vertical reactor. The second reactor has, for example, an inlet connected to the reaction mixture outlet of the first reactor. The second reactor has, for example, a smaller volume than the first reactor.

The details for the first and second medium pressure regeneration sections described herein for the urea production process are equally applicable to the plant of the invention.

In a preferred embodiment of the invention, the urea plant comprises an N/C measuring device for measuring the N/C ratio in the fluid, in particular in the liquid, in the supply line of the second stream from the high pressure separator to the medium pressure regeneration section, more preferably, the N measuring device /C continuous action. The N/C measuring device is, for example, selected from the group consisting of a Coriolis density measuring device, a radioisotope density meter, and vibrating element technology for measuring liquid density. The installation, for example, also includes a flow meter for measuring the flow rate in the supply line of the second stream.

In the case of a greenfield plant, the HP steamer can be kept relatively small compared to the plant capacity thanks to the second MP regeneration section.

The invention also relates to a reconstruction method. Preferably, the method relates to a method for modifying an existing thermal stripper type urea plant. Preferably, the refurbishment is used to increase the capacity of the plant, and preferably the method includes the step of increasing the reactor volume in the high pressure synthesis section, for example, by adding an additional reactor.

The existing plant is modified to the claimed plant described herein. Said method includes the step of adding an HP separator as described, whereby by adding a second MP regeneration section as described, in particular by adding a preferred adiabatic flash unit connected in-line to the outlet an opening for a second stream of added HP separator, MP digester, MP carbamate condenser and optionally MP steamer. Also added is a CO ₂ MP inlet connected to a second MP regeneration section to supply CO ₂ MP directly or indirectly to the MP carbamate condenser, preferably through a CO 2 MP steamer.

A typical upgrade method is schematically illustrated in FIG. 1, wherein the upgrading method involves adding the underlined blocks to the existing installation (added blocks: HPLS, MPF, MPD2, MPCC2 and MPS).

Preferably, an N/C measuring device is added to the flow line for the second stream. The N/C measuring device can be used, for example, to regulate the operation of added sections in a modified installation.

Preferably, the method also adds a gas supply line for the gas stream from the MP adiabatic flash unit to the first medium pressure (MP) regeneration section, more preferably to the first MP carbamate condenser.

A preferred retrofit method involves adding an additional (second) urea reactor after the existing first urea reactor to produce a reaction mixture from the top of the first reactor. Therefore, the reactors are arranged in series. Preferably, the existing first reactor has only one outlet, used for both gas and liquid, connected to a thermal steamer. The existing first reactor is, for example, a vertical reactor having only one outlet located at the top.

Preferably, the high pressure separator added as a reconstruction element is located inside said additional reactor. The second/additional urea reactor preferably contains an HP separator at the top. The second urea reactor accordingly preferably has an outlet for the first stream and a separate outlet for the second stream. The use of two vertical reactors in series allows for longer residence times and higher conversion of carbamate to urea. The outlet of the first reactor is preferably located at the top and is connected to the inlet of the second reactor at the bottom of the second reactor. The first and second reactors are preferably installed at or near ground level. The bottom of the second reactor is preferably located below the top of the first reactor.

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Claims (14)

The advantage is that the upgrade does not require extensive modifications to the HP synthesis section and the first MP regeneration section of the existing plant, and the modified plant can have significantly increased throughput. The plant according to the invention and the method for producing urea according to the invention can be used for greenfield plants as well as for upgrading existing plants. In fig. Figure 3 schematically illustrates an example of a second vertical urea reactor (R2) located downstream, which was added during the renovation of an existing thermal stripper plant. In general, in preferred embodiments of the modernization method of the invention, a second reactor is added between the vertical urea reactor of the existing plant and the thermal stripper and has an inlet at the bottom for the reaction mixture (24) coming from the top outlet of the plant before the first reactor. The second reactor has an outlet for the first stream (S1) at the top. In preferred embodiments of the urea production process of the invention, the added second reactor is completely filled and there is no liquid level (gas-liquid interface) in the reactor. The reactor contains a separator having a funnel-shaped design. The separator contains a funnel (F) with a bottom and a top, with a narrow opening at the bottom and a wide opening at the top. The lower opening is connected to the outlet for the second flow (S2), in particular to the drain. The funnel contains, for example, a ring at the top and a truncated-conical segment. The use of a wide funnel ensures a low liquid velocity, which helps degas the second stream. In fig. 4 schematically illustrates an example of a high pressure separator (HPLS) in a urea reactor (R), for example configured in the form of a funnel (F) having a lower part and an upper part, with a narrow opening at the lower part and a wide opening at the upper part. The bottom opening of the funnel is connected to the outlet of the degassed liquid stream (26), which is preferably a second stream (S2) supplied to the second MP regeneration section, but may also be a first stream (S1) supplied to the thermal steamer. The degassed flow line contains an N/C meter (27) and an expansion valve (28) for expansion to MP. The reactor also has an outlet (25) at the top for the gas-liquid mixture, which is preferably supplied as a first stream to the thermal stripper, but alternatively supplied as a second stream to the second MP regeneration section. In the context of the present invention, the N/C ratio refers, as is customary in the art for liquid streams, to the molar ratio of NH3 to CO ₂ , particularly in the reaction zone, based on the theoretical feed mixture. For gas streams, the N/C ratio indicates the molar ratio of NH3 to CO2. In the context of the present invention, high pressure (HP) is at least 100 bar, for example from 110 to 160 bar, in particular 140-160 bar; medium pressure (MP) is, for example, from 10 to 60 bar, for example 20-60 bar, and low pressure (LP) is, for example, from 4 to 10 bar; These pressure ranges are for process solutions and are not necessarily the same for steam and heating fluids. The abbreviation bar means absolute bar. In the context of this invention, pressure is absolute unless otherwise indicated. In conclusion, the invention relates to a plant and method for the production of urea using a thermal steamer, in which the reaction mixture is divided into two parts, the first part being fed at least partially, for example completely, into the thermal steamer, and the second part at least partially, for example completely, bypasses the thermal steamer and is fed into the medium pressure regeneration section. The first and second parts do not necessarily have different compositions. CLAIM 1. A method for producing urea, carried out in a thermal stripping type urea production plant (UPP), the said plant contains a high pressure (HP) synthesis section (HPS) and first and second medium pressure (MP) regeneration sections (MPR1, MPR2), wherein The HP synthesis section contains an HP reaction zone (HPR), a thermal stripper HP steamer (HPSt), a HP carbamate condenser (HPCC) and a separator (HPLS), wherein the steamer (HPSt) has an outlet for stripped urea solution connected to the first recovery section MP (MPR1), and gas outlet connected to HP carbamate condenser (HPCC), the specified method includes: separating the reaction mixture (1) from the reaction zone (HPR) at high pressure in the specified separator (HPLS) into a first stream (S1) and a second stream (S2), both the first stream and the second stream containing a liquid phase containing urea; supplying the first stream (S1), at least partially, to the HP steamer (HPSt); and supplying a second stream (S2), at least partially, to a second medium regeneration section - 14 044065 pressure (MPR2), and: the first stream (S1) has a lower gravimetric density than the second stream (S2), and the first stream is an ammonia-rich first stream (S1) having a higher ammonia concentration than the second stream (S2). 2. A method for producing urea according to claim 1, characterized in that said method includes: degassing the second stream (S2) in the separator (HPLS); measuring the N/C ratio in the degassed second stream; and supplying the degassed second stream to a second MP regeneration section (MPR2), bypassing the HP steamer (HPSt). 3. The method for producing urea according to claim 1 or 2, characterized in that the first MP regeneration section (MPR1) contains a first MP decomposition apparatus (MPD1), a first MP carbamate condenser (MPCC1), a medium pressure separation column (MPSC) and a condenser ammonia (AS), wherein the stripped urea solution (2) undergoes decomposition in the specified first MP decomposition apparatus (MPD) to obtain a urea solution MP (7) and a gas stream (18), wherein the gas stream (18) undergoes condensation in the specified first a carbamate MP condenser, wherein stream (19) from said first MP carbamate condenser (MPCC1) is separated in said medium pressure separation column (MPSC) to produce a carbamate MP solution (8) and an ammonia-containing gas stream (21), wherein the ammonia-containing the gas stream (21) is condensed in said ammonia condenser (AC) to produce an ammonia condensate stream (22). 4. A method for producing urea, carried out in a thermal stripping type urea production plant (UPP), said plant comprising a high pressure (HP) synthesis section (HPS) and first and second medium pressure (MP) regeneration sections (MPR1, MPR2), wherein the HP synthesis section comprises an HP reaction zone (HPR), a thermal stripper HP steamer (HPSt), a HP carbamate condenser (HPCC) and a separator (HPLS), wherein the HP steamer (HPSt) has an outlet for stripped urea solution connected to the first MP regeneration section (MPR1), and a gas outlet connected to an HP carbamate condenser (HPCC), the said method includes: separating the reaction mixture (1) from the reaction zone (HPR) at high pressure in the specified separator (HPLS) into a first stream (S1) and a second stream (S2), both the first stream and the second stream containing a liquid phase containing urea; supplying the first stream (S1), at least partially, to the HP steamer (HPSt); and supplying the second stream (S2), at least partially, to a second medium pressure regeneration section (MPR2), wherein the first MP regeneration section (MPR1) contains a first MP decomposition apparatus (MPD1), a first MP carbamate condenser (MPCC1), a medium pressure separation column (MPSC) and an ammonia condenser (AC), wherein the stripped urea solution (2) is decomposed in said first MP decomposition apparatus (MPD) to produce a urea solution MP (7) and a gas stream (18), the gas stream (18) is condensed in said first carbamate condenser MP, wherein stream (19) from said first carbamate condenser MP (MRCC1) is separated in said medium pressure separation column (MPSC) to produce a solution of carbamate MP (8) and ammonia-containing gas stream (21), wherein the ammonia-containing gas stream (21) is subjected to condensation in the specified ammonia condenser (AC) to obtain an ammonia condensate stream (22); wherein the second stream (S2) is expanded from high pressure to medium pressure in an adiabatic MP flash unit (MPF) included in the second MP regeneration section (MPR2), resulting in a gas stream (11) and a flashed urea solution MP. (12), while the gas stream (11) is supplied to the first carbamate condenser MP (MRCC1). 5. The method for producing urea according to claim 4, characterized in that the second MP regeneration section (MPR2) contains a second MP decomposition apparatus (MPD2) and a second MP carbamate condenser (MPCC2), wherein the flashed urea solution MP (12) is subjected to decomposition in said second MP decomposition apparatus to produce a treated urea solution (13) and a gas stream (14), wherein the gas stream (14) is condensed in said second MP carbamate condenser to produce a carbamate solution (15), wherein said carbamate solution ( 15) returns to the high pressure synthesis section (HPS). 6. The method for producing urea according to claim 5, characterized in that the second MP regeneration section (MPR2) additionally contains a CO ₂ MP steamer (MPS), and the urea solution (13) from the second MP decomposition apparatus (MPD2) is evaporated using raw materials CO ₂ MP in said CO 2 MP steamer (MPS) to produce a further treated urea solution (16) and a gas stream (17), wherein the gas stream (17) is condensed to produce a carbamate solution in said second MP urea condenser (MRCC2). 7. Urea production plant containing a high pressure synthesis section (HPS), - 15 044065 containing a reaction zone (HPR), a thermal steamer (HPSt) and a urea condenser (URCC), said unit further comprising a first medium pressure regeneration section (MPR1) having an inlet connected to an outlet for stripped urea solution of said thermal a steamer, wherein the high pressure section comprises a high pressure separator (HPLS) configured to separate the high pressure reaction mixture (1) from the reaction zone into a first stream (S1) and a second stream (S2), both the first stream and the second stream contain a liquid phase containing urea, and the first stream has a lower gravimetric density than the second stream; and wherein the high pressure separator has a first outlet for a first stream connected to an inlet of said thermal steamer, and a second outlet for a second stream connected to a second medium pressure recovery section (MPR2), wherein the apparatus comprises an N/C measuring device to measure the in-line N/C ratio for the second flow from the high pressure separator to the second medium pressure regeneration section. 8. A urea production plant comprising a high pressure synthesis section (HPS) comprising a reaction zone (HPR), a thermal steamer (HPSt) and a urea condenser (Urea Condenser), said plant further comprising a first medium pressure regeneration section (MPR1) having an inlet connected to an outlet for stripped urea solution of said thermal steamer, the high pressure section comprising a high pressure separator (HPLS) configured to separate the high pressure reaction mixture (1) from the reaction zone into a first stream (S1) and a second stream (S2), wherein both the first stream and the second stream contain a liquid phase containing urea; and wherein the high pressure separator has a first outlet for a first stream connected to an inlet of said thermal steamer, and a second outlet for a second stream connected to a second medium pressure regeneration section (MPR2); wherein the first medium pressure (MP) regeneration section (MPR1) contains a first MP decomposition apparatus (MPD1), a first MP carbamate condenser (MPCC1), a medium pressure separation column (MPSC) and an ammonia condenser (AC); wherein said first MP decomposition apparatus (MPD) is configured to subject the stripped urea solution (2) to decomposition to produce a urea solution MP (7) and a gas stream (18), wherein said first MP carbamate condenser is configured to subject the gas stream ( 18) condensation, wherein said medium pressure separation column (MPSC) is configured to separate the stream (19) from said first MP carbamate condenser (MRCC1) into a MP carbamate solution (8) and an ammonia-containing gas stream (21), wherein said ammonia condenser (AC) is configured to subject the ammonia-containing gas stream (21) to condensation to produce an ammonia condensate stream (22); in this case, the second MP regeneration section (MPR2) contains: an adiabatic MP flash unit (MPF) configured to expand the second stream from high pressure to medium pressure in the second MP regeneration section, thereby obtaining a gas stream (11) and a flashed MP urea solution (12); a second MP decomposition apparatus (MPD2) configured to subject the flashed urea solution MP (12) to decomposition to produce a treated urea solution (13) and a gas stream (14); a second carbamate condenser MP (MRCC2), configured to subject the gas stream (14) to condensation to produce a carbamate solution (15); and a gas flow line for said gas stream (11) from said MP adiabatic flash unit to said first medium pressure regeneration (MP) section (MPR1). 9. Installation for the production of urea according to claim 8, characterized in that the second MP regeneration section (MPR2) contains: CO ₂ MP steamer (MPS), configured to subject the urea solution (13) from the second MP decomposition apparatus (MPD2) to stripping using raw CO2 MP to obtain an additionally processed urea solution (16) and a gas stream (17), and flow a connection for said gas stream (17) to the inlet of said second MP carbamate condenser (MRCC2). 10. A method for modifying an existing thermal stripping type urea production plant, wherein the existing plant comprises a high pressure synthesis section containing a reaction zone, a thermal stripper and a urea condenser, wherein the existing plant further comprises a first medium pressure regeneration section having an inlet connected with outlet for stripped urea solution - 16 044065 specified thermal steamer, the specified method includes: adding a high pressure separator to the high pressure synthesis section configured to separate the high pressure reaction mixture from the reaction zone into a first stream and a second stream, wherein both the first stream and the second stream contain a liquid phase containing urea, wherein the first stream (S1) has a lower gravimetric density than the second stream (S2); and adding a second medium pressure (MP) regeneration section, the high pressure separator having a first outlet for a first stream connected to an inlet of said thermal steamer, and a second outlet for a second stream connected to said second medium pressure regeneration section. 11. The method according to claim 10, characterized in that the high-pressure separator contains a funnel having a lower part and an upper part, a narrow opening at the bottom and a wide opening at the top, wherein the narrow opening is connected to a second outlet of the separator for the second flow, and at the same time a measuring The N/C device is offered in the production line for the second flow from the high pressure separator to the second medium pressure regeneration section. 12. The method according to claim 10 or 11, further comprising the step of increasing the volume of the reactor in the high pressure synthesis section, for example, by adding an additional reactor containing a high pressure separator. 13. A method of modifying an existing thermal stripping type urea production plant, wherein the existing plant comprises a high pressure synthesis section containing a reaction zone, a thermal stripper and a urea condenser, wherein the existing plant further comprises a first medium pressure regeneration section having an inlet connected with an outlet for the stripped urea solution of said thermal steamer, said method includes: adding a high pressure separator to the high pressure synthesis section configured to separate the high pressure reaction mixture from the reaction zone into a first stream and a second stream, both the first stream and the second stream containing a liquid phase containing urea; and adding a second medium pressure (MP) regeneration section, wherein the high pressure separator has a first outlet for a first stream connected to an inlet of said thermal steamer, and a second outlet for a second stream connected to said second medium pressure regeneration section, wherein the specified method involves adding to the existing installation the following blocks as elements of the second MP regeneration section: an adiabatic MP flash unit (MPF) configured to expand the preferably degassed second stream from high pressure to medium pressure in a second MP regeneration section, thereby producing a gas stream (11) and a flashed urea MP solution (12) ; a second MP decomposition apparatus (MPD2) configured to subject the flashed urea solution MP (12) to decomposition to produce a treated urea solution (13) and a gas stream (14); a second carbamate condenser MP (MPCC2), configured to subject the gas stream (14) to condensation to produce a carbamate solution (15); and a gas flow line for said gas stream (11) from said MP adiabatic flash unit (MPF) to said first medium pressure (MP) regeneration section (MPR1), and preferably a CO ₂ MP steamer (MPS) configured to undergo urea solution (13) from the second MP decomposition apparatus (MPD2) is stripped using raw material CO2 MP to obtain an additionally processed urea solution (16) and a gas stream (17); and a flow connection for said gas stream (17) to the inlet of said second MP carbamate condenser (MRCC2). 14. The method of claim 13, further comprising the step of increasing the volume of the reactor in the high pressure synthesis section, for example, by adding an additional reactor containing a high pressure separator. -