Plant with urea manufacturing process and parallel MP unit

Abstract

Some embodiments of the present disclosure relate to a plant and process for producing a urea-containing product. The plant includes a medium pressure dissociation unit and a high pressure CO2 stripper, each of which receives a portion of a urea synthesis solution. The stripped urea solution is further processed in a medium pressure processing unit.

Description

[Technical field]

[0001] The present invention relates to the production of urea from NH3 and CO2.

[0002] introduction Urea plants are often of the type equipped with a high pressure (HP) stripper, e.g., using at least a portion of the CO2 feed as strip gas (e.g., Stamicarbon CO2 stripping process). An exemplary process scheme for a CO2 stripping type urea process is shown in Ullmann's Encyclopaedia, Urea Chapter, 2010, Figure 16. The HP stripper is operated at a stripping efficiency of, e.g., 80% and has a corresponding demand for steam as a heating fluid.

[0003] Patent document 1 attributes the HP stripping and HP condensation steps to the main cause of the fact that it is only possible to a limited extent to expand the capacity of existing facilities without modifying or replacing expensive high-pressure equipment. Patent document 1 proposes to increase the capacity of the plant by modifying it in such a way that part of the urea synthesis solution is transferred from the synthesis zone to a medium-pressure processing zone operating at a pressure of 1 MPa to 4 MPa, and the other part is sent to the HP stripper. Patent document 1 shows a plant in which the medium-pressure processing zone is equipped with a medium-pressure carbamate condenser MCC, which receives a gas stream from the medium-pressure dissociator and a gas stream from the medium-pressure stripper. The medium-pressure stripper receives the liquid from the medium-pressure dissociator and part of the CO2 feed. The medium-pressure dissociator receives the liquid directly from the urea reactor. The stripped urea solution from the high-pressure stripper is fed directly to the low-pressure stripper.

[0004] Patent Document 2 describes an integrated system for the production of urea and urea ammonium nitrate, which comprises: (i) a unit for the production of urea, the unit comprising a urea synthesis section comprising a reactor, a stripper and a condenser, which are in fluid communication with each other to form a urea synthesis loop, and a urea purification section downstream of the synthesis section, in fluid communication therewith, suitable for separating CO2 and NH3 from the urea aqueous solution containing said CO2 and NH3; and (ii) a unit for the production of ammonium nitrate from ammonia and nitric acid, in which an outlet for NH3 from the purification section of the urea plant is connected to an inlet for NH3 of a unit for the production of ammonium nitrate, and an outlet for the urea solution from the purification section and an outlet for the aqueous ammonium nitrate solution from the unit for the production of ammonium nitrate are connected to a unit for mixing the urea solution and the aqueous ammonium nitrate solution.

[0005] US Pat. No. 5,399,433 describes an integrated process for producing urea and ammonium urea nitrate.

[0006] US Pat. No. 5,399,633 describes a urea production process using an HPCO2 stripper, in which the urea solution leaving the stripper is subjected to an adiabatic expansion, vapor and liquid are produced and separated, the liquid enters a first recovery section and the vapor is condensed. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] US Patent Application Publication No. 2004 / 0116743 [Patent Document 2] European Patent Application Publication No. 3274297 [Patent Document 3] European Patent Application Publication No. 3541780 [Patent Document 4] US Patent Application Publication No. 2012 / 0302789 [Patent Document 5] U.S. Pat. No. 5,767,313 Summary of the Invention [Problem to be solved by the invention]

[0008] CO2 emissions from industrial plants are often limited for environmental reasons or require emission permits, but even if emission allowances are tradable, CO2 emissions can increase costs.

[0009] There remains a need for an energy-efficient urea production process, especially in large-scale plants. There is also a need for an integrated urea and ammonium nitrate production process with low CO2 emissions and low energy consumption. There is also a need for corresponding plants and methods for modifying existing plants. The present invention is not limited to processes for the integrated production of urea and ammonium nitrate, but also includes embodiments in which only urea is produced. In preferred embodiments, desired energy savings may be achieved. Improved energy efficiency and integrated production of urea and ammonium nitrate are preferred objectives of some embodiments of the present invention, but not necessarily all embodiments. [Means for solving the problem]

[0010] The present invention relates in a first aspect to a plant for producing a urea containing product, the plant comprising a urea production section with a high pressure (HP) synthesis section comprising an HP stripper, a reactor for forming urea from NH3 and CO2, and an HP carbamate condenser, the reactor and the HP carbamate condenser being optionally combined, the urea production section further comprising a medium pressure (MP) processing unit, an MP dissociator and an MP condenser, the reactor having an outlet for the urea synthesis solution connected to a first liquid flow path connected to the HP stripper, the outlet also being connected to a second liquid flow path connected to the MP dissociator, the HP stripper having an inlet for a CO2 feed as strip gas, the plant comprising a liquid flow path for the stripped urea solution from the HP stripper to the MP processing unit, a gas flow path for the first MP gas stream from the MP processing unit to the MP condenser, and a gas flow path for the second MP gas stream from the MP dissociator to the MP condenser.

[0011] Preferably, the plant further comprises a low pressure (LP) dissociator and a liquid flow path for the MP urea solution from the MP treatment unit to the LP dissociator.

[0012] Preferably, the plant comprises an ammonium nitrate (AN) section configured for neutralizing nitric acid with ammonia to form ammonium nitrate, the neutralization section having a nitric acid inlet and an ammonia-containing gas inlet. Preferably, the plant comprises a gas flow path for ammonia-containing LP-gas from the preferred LP dissociator to the neutralization section.

[0013] The invention further relates to a process for producing a urea-containing product carried out in a plant according to the first aspect, comprising the steps of reacting an NH3 feed and a CO2 feed in the reactor to produce a urea synthesis solution, splitting the urea synthesis solution into at least a first and a second portion, feeding the first portion to the HP stripper, thereby obtaining a stripped urea solution, subjecting the stripped urea solution to treatment at medium pressure in the MP processing unit to produce the first MP gas stream, subjecting the second portion to medium pressure dissociation in the MP dissociator to produce the second MP gas stream and MP urea solution, and at least partially feeding the first MP gas stream and the second MP gas stream to the MP condenser.

[0014] The present invention also relates to a method of modifying an existing plant for producing a urea-containing product. Preferably, the existing plant comprises a urea production section with a high pressure (HP) synthesis section comprising an HP stripper, a reactor for forming urea from NH3 and CO2, and an HP carbamate condenser, the reactor and the HP carbamate condenser being optionally combined, the HP stripper having an inlet for CO2 feed as strip gas. The method includes adding an MP dissociator and an MP condenser, and a connection from an outlet of the urea synthesis solution to the MP dissociator, if they do not already exist in the existing plant. The method also includes adding a medium pressure (MP) processing unit, a liquid flow path for the stripped urea solution from the HP stripper to the MP processing unit, a gas flow path for a first MP gas stream from the MP processing unit to the MP condenser, and a gas flow path for a second MP gas stream from the MP dissociator to the MP condenser, if the gas flow path for the second MP gas stream does not already exist in the plant. The modified plant is preferably a plant according to the first aspect of the invention. [Brief description of the drawings]

[0015] [Figure 1]1 illustrates diagrammatically an exemplary plant and process according to the present invention; [Diagram 2] 1 illustrates diagrammatically details of an exemplary plant and process according to the invention; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Any embodiments illustrated in the figures are merely examples and are not intended to be limitations of the present invention.

[0017] The disclosed urea production plant and process is generally based on the wise insight of using an MP dissociator receiving a urea synthesis solution from a reactor and an MP processing unit receiving a stripped urea solution from an HP stripper, and at least the gas streams from the MP dissociator and the MP processing unit are fed directly or indirectly to an MP condenser, where the gas streams are at least partially condensed to produce a carbamate solution. In particular, the gas stream from the MP dissociator is at least partially condensed in the MP condenser and the gas stream from the MP processing unit is at least partially condensed in the MP condenser, preferably both gas streams are at least partially condensed in the same condenser, which may be, for example, a heat exchanger.

[0018] Supplying a gas stream from the MP treatment unit to the MP condensate may advantageously contribute to lower CO2 emissions from one or more units downstream of the outlet for liquid (i.e., urea solution) of the MP treatment unit. Supplying a gas stream from the MP treatment unit to the MP condensate may contribute to condensing carbamates in the MP condensate with an advantageous N / C ratio.

[0019] By feeding a gas stream from the MP process section to the MP condenser section, relatively more CO2 can be advantageously recycled to the HP synthesis section as part of the MP carbamate solution, improving CO2 recovery and reducing emissions from the preferred ammonium nitrate (AN) section.

[0020] Advantageously, steam consumption of the HP stripper can be reduced by having the MP treatment unit treat the urea solution that is fed to the MP treatment unit.

[0021] Advantageously, more CO2 can be sent to the HP stripper compared to processes in which the MP condenser receives only gas from the MP dissociator and MPCO2 feed, which can further contribute to reduced steam consumption in the HP stripper. Lower steam consumption in the HP stripper is generally desirable and contributes to higher energy efficiency of the plant.

[0022] The size of the HP stripper can be advantageously relatively small compared to the total urea production capacity in the plant of the present invention.

[0023] The MP dissociator and the MP processing unit are arranged in parallel within the plant.

[0024] The HP synthesis section includes an HP stripper, an HP reactor, and an HP carbamate condenser. The stripper is a CO2 stripper. The plant includes a first liquid flow path from the reactor to the HP stripper and a second liquid flow path from the reactor to the MP dissociator. The HP synthesis section includes an inlet for NH3 feed, for example, at the HP carbamate condenser.

[0025] The reactor is configured to form urea from NH3 and CO2 and has an outlet for a urea synthesis solution. The urea synthesis solution has an N / C ratio of, for example, 2.85 to 3.3. The reactor is operated at a urea synthesis pressure, i.e. HP, and a urea synthesis temperature, for example, above 100 bar, for example, between 120 bar and 300 bar, for example, between 120 bar and 200 bar, and / or at a temperature of, for example, between 160°C and 240°C, preferably between 170°C and 220°C.

[0026] The reactor is, for example, a vertical reactor equipped with trays, the feed inlet is at the bottom and the urea synthesis solution is withdrawn from the top of the vertical reactor, for example using a downcomer.

[0027] For example, the reactor has a separate outlet for gas (so-called inerts). The inerts are, for example, fed as a gas stream directly or indirectly to the preferred AN section. The inerts, for example, come from the feed stream and include, for example, N2. The gas stream from the gas outlet of the reactor also includes, for example, NH3.

[0028] The urea production plant may include one or more reactors in series, such as a first reactor and a post-reactor, for example, the post-reactor receiving the reactor effluent and having a liquid outlet connected to the first and second flow paths, i.e., the split between the first and second liquid flow paths. The urea production plant may also include one or more reactors in parallel.

[0029] The reactor and HP carbamate condenser are optionally combined in a single vessel. An example is an integrated reactor / condenser as described in U.S. Pat. No. 5,399,633. An exemplary integrated condenser / reactor comprises a reaction zone and a condensation zone combined in a single vessel. The condensation zone comprises a heat exchange surface, such as, for example, a tube bundle. The reaction zone comprises, for example, a baffle. The reaction zone is typically disposed downstream of the condensation zone in the vessel. An exemplary integrated condenser / reactor comprises a horizontal vessel and a tube bundle configured to receive a cooling fluid in the tubes and a process medium in the shell space.

[0030] The reactor has a urea synthesis solution outlet connected directly or indirectly to a first liquid flow path to the HP stripper and to a second liquid flow path to the MP dissociator. The second liquid flow path bypasses the HP stripper. The plant comprises a split of the HP urea synthesis solution flow path into a first flow path and a second flow path, for example using a valve. Typically, the plant comprises a split or divider of the flow path for the HP urea synthesis solution into the first liquid flow path and the second liquid flow path. The HP urea synthesis solution flow path is connected to the urea synthesis solution outlet of the reactor. The split or divider of the urea synthesis solution is performed at high pressure. The first and second liquid flow paths are both used for the liquid flow in the HP. The second liquid flow path connected to the MP dissociator typically includes an expansion valve for expanding the urea solution from HP to MP.

[0031] The split ratio of the HP urea synthesis solution can preferably be adjusted, for example, during start-up or in a flexible manner to increase or decrease urea production, for example, the MP dissociator can be shut down to decrease urea production.

[0032] The urea synthesis solution includes urea, water, ammonium carbamate, and ammonia.

[0033] The HP stripper has an inlet for the CO2 feed as strip gas, an outlet for the stripped urea solution, and an outlet for the gas stream. The plant is preferably of the CO2 stripping type. The stripped urea solution, which contains urea, water, carbamates and ammonia, is fed to the MP treatment unit.

[0034] The HP carbamate condenser (HPCC) typically receives at least a portion, preferably all, of the raw NH3 feed. The HPCC receives at least a portion, e.g., all, of the gas stream from the HP stripper. The HP carbamate condenser has an outlet for a stream containing condensed carbamate connected to the inlet of the reactor, and in a combined condenser / reactor, the condensation zone is in fluid communication with the reaction zone.

[0035] The urea production section may comprise a CO2 compressor for compressing the CO2 feed stream to urea synthesis pressure. The compressor is, for example, a multi-stage compressor. CO2 is available at relatively low pressure (for example, below 20 bar), for example at the battery limit, from, for example, a syngas plant. The syngas plant comprises, for example, a steam reformer, a water gas shift reactor, and a CO2 removal unit. The syngas plant may also produce H2 used in the ammonia plant. The NH3 feed for the urea plant may come from the ammonia plant. Other sources of the CO2 and NH3 feed streams are possible.

[0036] Generally, in various embodiments of the invention, the HP stripper comprises a vertical shell-and-tube heat exchanger with an inlet at the top of the stripper for feeding the urea solution to be stripped, for example to the tube, an outlet at the bottom for the stripped urea solution, and an outlet at the top of the stripper for the mixed gas stream. The HP stripper is of the CO2 stripper type, with an inlet at the bottom for the CO2 feed used as stripping gas. The mixed gas stream is condensed in the HP carbamate condenser, resulting in a high pressure recycle stream containing carbamate that is fed to the reactor. In the case of a combined reactor / condenser in a single vessel, this may involve transport of the condensate from the condensation section to the reactor section in the vessel, in particular flow of the carbamate-containing liquid from the condensation zone to the reaction zone in the vessel.

[0037] The HP stripper is typically an apparatus configured to countercurrently contact a urea solution with a strip gas stream. Typically, the HP stripper is configured with a urea solution in tubes and a strip gas stream, with heat provided by shell-side steam. In the present invention, the HP stripper uses all or a portion of the raw CO2 feed as the strip gas. Stripping using CO2 as the strip gas reduces the N / C ratio of the urea solution. The stripped urea solution has a lower N / C ratio than the urea synthesis solution, e.g., N / C ratio less than 3.0, less than 2.7, or less than 2.5, such as in the range of 1.5-2.5, or in the range of 2.0-2.5.

[0038] In a preferred embodiment in which the liquid outlet for the MP carbamate solution of the MP condenser is connected to a liquid flow path to the HP synthesis section, thereby providing recycle of the carbamate solution to the HP synthesis section, the HP stripper is operated at a stripping efficiency α in the range of, for example, 60% to 80%, for example, 65% to 75%, for example, a stripping efficiency α of about 70%. In an embodiment in which the carbamate solution from the MP condenser is removed in another way, for example, by feeding the solution to an additional urea synthesis section, the stripping efficiency may be in the range of, for example, up to 92%.

[0039] Advantageously, the HP stripper can be operated at a relatively low stripping efficiency because the MP processing unit receives the stripped urea solution and is used to purify the urea solution, thereby allowing for relatively low steam consumption in the HP stripper.

[0040] In the plant and process of the present invention, the HP carbamate condenser (HPCC) is, for example, a shell-and-tube heat exchanger. The HPCC is, for example, a vertical condenser or a horizontal condenser. The shell-and-tube heat exchanger as HPCC is operated with the process medium (in particular the gas to be condensed) in the shell-side space and the cooling fluid in the tubes, or with the process medium in the tubes and the cooling fluid in the shell-side space.

[0041] In some embodiments, the HPCC is, for example, a falling film carbamate condenser with cooling fluid in the shell. In further embodiments, the HPCC is, for example, a submerged condenser. The HPCC is, for example, a shell-and-tube condenser with a horizontal U-shaped tube bundle, process medium on the shell side, and a submerged tube bundle, for example, a pool condenser. The HPCC comprises, for example, a U-shaped tube bundle or a straight tube bundle. The HPCC is, optionally, a pool reactor with a pool condenser zone and a reactor zone. The pool reactor comprises, for example, a baffle in the shell space.

[0042] The HPCC also includes an inlet for, for example, NH3 feed to the shell space.

[0043] The MP processing unit is configured to subject the stripped urea solution to a process including expansion to MP and gas / liquid separation to produce a first MP gas stream and a first MP urea solution, the process optionally also including heating. In some embodiments, the MP process is substantially adiabatic or adiabatic. In some embodiments, the MP processing unit has an inlet for a gas stream, such as a CO2 feed stream, and the process in the MP processing unit optionally includes contacting the urea solution with the gas stream, with or without heating.

[0044] Processing in the MP processing unit purifies the stripped urea solution by removing at least a portion of NH3 and CO2 from the solution and / or decomposing the carbamates to NH3 and CO2 and removing NH3 and CO2 from the solution to produce a first MP gas stream, the first MP gas stream comprising NH3 and CO2.

[0045] In some optional embodiments, countercurrent contacting of the stripped urea solution in the MP processing unit with a portion of the CO2 feed stream is used, optionally in combination with heating the urea solution in the MP processing unit.

[0046] For example, heating the stripped urea solution in a MP-operated MP processing unit using indirect heat exchange with a heating fluid, e.g., steam, can contribute to more complete removal of NH3 and ammonium carbamate from the stripped urea solution.

[0047] Removal of ammonium carbamate from the stripped urea solution of the MP treatment unit can contribute to reducing CO2 emissions from the AN neutralization section coupled to the urea production section, whereby CO2 recovery is improved by feeding the first MP gas stream to the MP treatment unit and the MP condensation section.

[0048] Preferably, the MP treatment unit is configured for flashing, more preferably for (substantially) adiabatic flashing, of the urea solution, hi some embodiments the MP treatment unit is an MP flash vessel.

[0049] Advantageously, by flashing from HP to MP in a preferably (substantially) adiabatically MP flash vessel (MPF), the first MP gas stream has a low NH3:CO2 molar ratio, such as less than 2.0, e.g., in the range of 0.8 to 1.2, and / or lower than the N / C ratio of the HP stripped urea solution. The first MP gas stream may advantageously have a relatively high CO2 concentration so that the MP condenser may operate at a more favorable N / C ratio.

[0050] In some embodiments, NH3 and CO2 are removed from the urea solution in the MP flash vessel at a molar ratio of NH3 to CO2 of less than 2.0, such as a molar ratio in the range of 0.8 to 1.2. If CO2 is added to the gas stream, the first MP gas stream may have an even lower molar ratio of NH3 to CO2.

[0051] The MP treatment unit comprises a gas / liquid separation zone, for example in a preferred flash vessel, for example by a zone or flash vessel having a top outlet for gas and a bottom outlet for liquid, where the liquid is a urea solution.

[0052] The MP treatment unit is used, for example, to expand the urea solution from high pressure to medium pressure, for example from 10 bar to 50 bar, for example from 15 bar to 40 bar. The MP treatment unit is, for example, operated at a pressure at least 1.0 bar higher, for example from 2 bar to 10 bar higher, than the pressure of the MP condenser.

[0053] The favorable adiabatic nature of the flash in the preferred MP flash vessel favorably contributes to a low N / C ratio (molar ratio of NH3 to CO2) in the formed gas stream. In particular, upon adiabatic pressure reduction, CO2 exits the urea solution from the CO2HP stripper to a greater extent than NH3.

[0054] The first MP gas stream preferably has an N / C molar ratio (NH3 to CO2 molar ratio) of less than 2.0, e.g., 0.9-1.2, e.g., 0.5-1.5, such as about 1.0. The first MP gas stream preferably contains NH3 and CO2 in a molar ratio of less than 2.0, e.g., 0.9-1.2, e.g., 0.5-1.5, such as about 1.0. The first gas stream contains, e.g., about 40%-50% NH3 by weight, about 40%-50% CO2 by weight, e.g., 10%-20% H2O by weight, these ranges may also apply to components removed from the liquid phase of the urea solution when CO2 is added to the first MP gas stream. The first gas stream received by the MP carbamate condenser, i.e. at the inlet of the condenser, preferably has such an N / C molar ratio (molar ratio of NH3 to CO2) and preferably comprises, for example, about 40% to 50% by weight NH3, about 40% to 50% by weight CO2, and, for example, 10% to 20% by weight H2O.

[0055] The MP dissociator (MPD) has an inlet connected to the second liquid flow path for receiving a portion of the urea synthesis solution, an outlet for the second MP gas stream, and an outlet for the MP urea solution. The MP is typically a heat exchanger that uses a heating fluid, e.g. steam, for indirect heat exchange to dissociate the carbamates contained in the urea synthesis solution. The use of steam as a heating fluid in the MP dissociator offers the advantage of great flexibility, in particular to ensure sufficient carbamate removal from the urea solution independent of the N / C ratio at the inlet of the MP dissociator. The MP dissociator is, for example, a shell-and-tube heat exchanger with steam in the shell and urea solution in the tubes. The MP dissociator includes, for example, a rectifier arranged upstream of the shell-and-tube heat exchanger section for the urea solution, which is configured for gas / liquid separation of the urea solution expanded from the HP to the MP, and for countercurrent contact between the urea solution and the gas stream from the heat exchange section. This contributes to good removal of carbamates from the urea solution.

[0056] The MP urea solution at the outlet of the MP dissociator has, for example, an N / C ratio of at least 4. The second MP gas stream from the MP dissociator has, for example, an N / C ratio of at least 2.5.

[0057] In some embodiments, the MP dissociator also receives other urea solution streams, such as a urea solution obtained indirectly from the HP stripper.

[0058] The MP dissociator is, for example, a shell-and-tube heat exchanger, for example, using steam as the heating fluid. For example, the MP dissociator is a vertical shell-and-tube heat exchanger with a urea solution in the tubes and a rectification unit on top.

[0059] The second MP gas stream is fed from the MP dissociator to a MP condenser (MPCC), which has a liquid outlet for the carbamate solution.

[0060] The plant comprises a gas flow path for the first MP gas stream from the MP treatment unit directly or indirectly, preferably directly, to the MP condenser, so that at least a part of said gas, preferably all of said gas, is transported as gas to the MP condenser. In this way, advantageously, the CO2 contained in the stripped urea solution may be recovered using the MP condenser.

[0061] In an embodiment with a preferred (substantially) adiabatic flash, at least a portion of the vapor from the flash can be used to correct (reduce) the N / C ratio of the MP condensate. The combined carbamate condensation of the first and second MP gas streams in the MP condensate provides an optimal N / C ratio of the formed condensate, i.e., the carbamate solution, close to 2, thereby allowing the recovery of CO2 in the form of a carbamate solution. The carbamate condensation is also advantageously achieved at a relatively high temperature (higher condensation point) in the MP condensate with an advantageous relatively low N / C ratio.

[0062] The MP treatment unit allows the CO2 originating from the HP stripper to be used and recovered in the MP condenser, so that the steam consumption of the HP stripper can be low at a constant stripping efficiency α. Thereby, relatively more CO2 can be advantageously supplied to the HP stripper. In a preferred embodiment having an ammonia consuming unit, e.g. an ammonium nitrate unit, the HP stripper can advantageously operate at a relatively lower stripping efficiency α compared to a urea production unit producing only a urea melt, so that the NH3 contained in the stripped urea solution (also as carbamate) and received by the preferred LP dissociator can be used in the preferred ammonia consuming unit and reacted, e.g., in the preferred ammonium nitrate unit. The skilled person will understand that in the context of a urea plant, a lower stripping efficiency α, a term used in the art, can provide an advantage.

[0063] The MP condenser section comprises one or more MP carbamate condensers, e.g., having a liquid outlet for the MP carbamate solution connected to a recycle flow path to the HP synthesis section. The MP condenser section also comprises an outlet for non-condensed gases. The gases are fed, e.g., to an absorber or scrubber, or, e.g., to the neutralization section of the optional AN section. Typically, the plant only comprises a recycle flow path from the MP unit to the HP synthesis section for the carbamate solution. Usually, the plant does not comprise an ammonia condenser, nor does it comprise a dedicated recycle flow path for ammonia to the HP synthesis section.

[0064] The MP condenser may optionally comprise a second MP carbamate condenser arranged downstream of the first MP carbamate condenser, the first condenser being thermally integrated with a pre-evaporator, for example as described below. The second condenser is, for example, a shell-and-tube heat exchanger. The second condenser receives, for example, both vapor and liquid from the first MP carbamate condenser. The MP condenser further comprises a gas / liquid separator, in particular for separating the carbamate solution from non-condensed gases.

[0065] The MP condenser preferably receives an aqueous stream, such as aqueous ammonia, such as an aqueous stream from a wastewater treatment unit, or, for example, steam condensate. This advantageously avoids carbamate crystallization. Optionally, the MP condenser receives LP carbamate solution, for example, from an optional LP carbamate condenser, if used.

[0066] Optionally, at least one condenser in the MP condenser (MPCC) is in heat exchange contact through a heat exchange wall with an optional pre-evaporator (PEV) used to concentrate the urea solution, e.g., urea solution received directly or indirectly from the LP dissociator, as described hereinbefore and hereinafter, by heating to produce a concentrated urea solution and a vapor stream. Carbamate condensation is exothermic. This favors heat integration.

[0067] The pre-evaporator comprises, for example, a heat exchanger and a gas / liquid separator. The urea solution in the pre-evaporator is, for example, at an absolute pressure of 0.4 bar to 0.6 bar.

[0068] The term "pre-evaporator" as used herein does not imply the need to use a further evaporator. For example, the concentrated urea solution may be so used, for example, to produce UAN (urea ammonium nitrate liquid fertilizer). The concentrated urea solution may be further concentrated, for example to provide a urea melt, and the plant may comprise an evaporation section for further concentrating the urea solution from the pre-evaporator.

[0069] The MP condenser, in particular the first MP condenser, is at least partially provided by a heat exchanger, for example with a heat exchange wall, a first zone and a second zone in heat exchange contact with each other through said wall, an MP process fluid in the first zone, in particular the first MP gas stream and the second MP gas stream to be condensed, and a urea solution in the second zone. The MP condenser is for example provided by a shell-and-tube heat exchanger, in particular the first MP condenser, with an MP process medium in the shell and a urea solution in the tubes. The second zone is for example operated at a lower pressure than the first zone. The heat exchanger advantageously provides heat integration.

[0070] The advantageously relatively low N / C ratio in the MPCC allows for carbamate condensation at relatively high temperatures, contributing to efficient water evaporation in the pre-evaporator with heat integration.

[0071] Preferably, the MP urea solution from the MP dissociator is expanded to a LP, preferably heated in the LP, and subjected to gas / liquid separation in a LP processing unit (such as a LP dissociator) to further purify the urea solution by removing ammonia and / or carbamates to produce a LP urea stream and a LP gas stream. The expansion to LP and heating in the LP may be performed, for example, in a dedicated LP processing unit or in the same LP processing unit used to process the urea solution downstream of the liquid outlet of the MP processing unit.

[0072] Thus, the plant preferably comprises a low pressure (LP) dissociator, a LP carbamate condenser, and flow paths, e.g. a liquid flow connection for a urea solution from the MP dissociator to the LP dissociator, optionally via a MP stripper, and a gas flow path from the LP dissociator to the LP carbamate condenser.

[0073] The LP gas stream is, for example, condensed in an LP carbamate condenser to an LP carbamate stream or is, for example, fed as an ammonia-containing gas stream to an ammonia-consuming unit, for example a neutralization unit, for example the neutralization unit of the AN part which is preferably used.

[0074] Preferably, the plant comprises a low pressure (LP) dissociator, a LP carbamate condenser, a flow path for the urea solution from the MP dissociator to the LP dissociator, and a gas flow path from the LP dissociator to the LP carbamate condenser. Preferably, the plant comprises a MP stripper, preferably for adiabatic MP stripping, having an inlet for the urea solution from the MP dissociator, an inlet for a CO2-containing gas stream, e.g., MPCO2 feed and / or gas, from the MP flash vessel, an outlet for the stripped MP urea solution, and an outlet for a gas stream connected to the MP condenser, and preferably the plant comprises a liquid flow path for the stripped MP urea solution from the MP stripper to the LP dissociator. Details of the MP stripper are described below.

[0075] The urea synthesis solution from the reactor is split into at least two parts, for example a first part of 50% to 90% by volume is fed to the HP stripper and a second part of 10% to 50% by volume is fed to the medium pressure dissociator (percentage based on the total volume of the urea synthesis solution). Advantageously, this ratio can be adjusted, thereby increasing the flexibility of the plant, for example using a valve in the flow path for the urea synthesis solution. For example, during periods of low demand, the urea synthesis solution may be fed less to the MP processing section, lowering the total urea production. The ratio is optimized in such a way that the recycle flows from the MP and LP sections to the synthesis are minimized. This results in less water in the synthesis section and makes the urea synthesis more efficient.

[0076] In some embodiments, the urea production process is operated for at least some periods of time with at least 30% or at least 40% by volume of urea synthesis solution fed to the MP dissociator.

[0077] The urea synthesis solution is divided, for example, by a flow divider included in the HP synthesis unit and by the HP.

[0078] In some embodiments, a portion of the CO2 feed of the urea production section is fed directly or indirectly to the MP condensation section as a MP feed CO2 stream.

[0079] In a preferred embodiment, the amount of the MP feed CO2 stream to the MP condenser is less than 70%, or less than 60%, and such as more than 10% of the amount of CO2 contained in the first MP gas stream, whereby a significant portion of the CO2 fed to the MP condenser comes from the MP processing unit processing the urea solution from the HP stripper, preferably this processing is an adiabatic MP flashing.

[0080] The MP feed CO2 stream is obtained, for example, from a CO2 compressor of a urea plant or from a battery limit. In some embodiments, the CO2 compressor is a multi-stage compressor, and an additional CO2 stream is optionally extracted from an intermediate stage of the compressor. In some embodiments, the MP feed CO2 stream is obtained from a dedicated MP CO2 compressor.

[0081] In an optional embodiment of interest, the urea solution from the MP dissociator is subjected to countercurrent direct contact in the MP stripper, preferably with or without heating, with a gas stream, for example, a CO2 gas stream and / or a first MP gas stream from the MP processing unit. This optional contact can provide a stripping effect, in particular a stripping effect of NH3 from the urea solution. Stripping without heating in the MP can be referred to as adiabatic MP stripping. The MP solution is subjected to countercurrent direct contact, i.e., in the MP.

[0082] The gas stream used for the optional MP adiabatic stripping is, for example, the first MP gas stream and / or the MP feed CO2 stream. In some embodiments, only the MP feed CO2 stream is used for the optional MP adiabatic stripping. In some embodiments, a variable combination of MP flash steam and MP feed CO2 stream is used for the optional MP adiabatic stripping. In the optional MP adiabatic stripper, the gas used for stripping is in countercurrent direct contact with, for example, a urea solution.

[0083] When used, the MP stripper is configured to adiabatically strip the urea solution from the MP dissociator, e.g., by directly contacting the urea solution with a gas stream, e.g., a first MP gas stream, and perform gas / liquid separation to produce a gas stream that is fed to the MPCC and a stripped MP urea solution that is fed to a low pressure section, e.g., the LP dissociator.

[0084] For example, any MP stripper includes a packed bed for the gas / liquid contact.

[0085] In the optional MP stripper, the N / C ratio of the urea solution is reduced, for example, from about 6 to about 3 (example values ​​only). Thus, the MP stripper provides a reduction in the N / C ratio, similar to the high pressure CO2 stripper in the HP synthesis section.

[0086] The term "stripping" is used broadly to indicate that any MP stripper in which the gas / liquid it contacts contributes to a reduction in the N / C ratio. MP stripping may involve, for example, absorbing some CO2 into the liquid and transferring some NH3 from the liquid phase to the gas phase. The outlet liquid may be, for example, 90%-110% by weight of the inlet liquid. Any MP adiabatic stripping does not necessarily involve a significant mass loss of the liquid phase.

[0087] For example, in an embodiment having such an optional MP stripper, the plant further comprises, for example, a low pressure (LP) dissociator, a LP carbamate condenser, a liquid flow path for the urea solution from the MP stripper to the LP dissociator, and a gas flow path from the LP dissociator to the LP carbamate condenser. These LP units can also be used without the optional MP stripper, in which case the plant comprises a liquid flow path for the urea solution directly or indirectly from the MP dissociator to the LP dissociator. The LP dissociator that receives the urea solution directly from the MP dissociator can be the preferred LP dissociator that receives the urea solution directly or indirectly from the MP processing unit and indirectly from the HP stripper, or an additional LP dissociator.

[0088] The LP dissociator downstream of the MP dissociator has a gas outlet connected to a gas inlet of an ammonia consuming unit, such as the described neutralization unit of a nitric acid plant, with or without an optional MP stripper.

[0089] Since the urea synthesis solution is rich in ammonia (e.g., N / C of at least 3.0), the second MP gas stream from the MP dissociator is also rich in ammonia. In order to condense this gas in the MP condenser to carbamates, the N / C ratio is advantageously adjusted (reduced) to, for example, avoid excess NH3 and / or provide greater flexibility to, for example, process a relatively large proportion of the urea synthesis solution in the MP dissociator. In the present invention, very advantageously, for example, the first MP gas stream from the preferred MP flash may be used for this adjustment of the N / C ratio. This may improve the HP stripper efficiency and urea yield and / or reduce energy consumption compared to a reference process in which most or all of the raw CO2 feed is introduced into the urea plant and processed at high pressure, especially in the HP stripper, whereby only the raw feed CO2 is used for the N / C adjustment in the MP condenser. In an embodiment with a preferred AN section, CO2 emissions from the AN section are also advantageously reduced by CO2 recovery through the MP processing unit and the MP condenser.

[0090] Bypassing a portion of the urea synthesis solution around the HP stripper to the MP process section allows for a single line (single train) urea plant with a large urea capacity without the stripper becoming too heavy and / or large to fabricate and transport.

[0091] The urea production section produces a urea solution, such as an LP urea solution. The urea solution can be used, for example, partially or totally, to produce liquid fertiliser, such as UAN, and for other purposes. The urea solution can be used, for example, partially or totally, to produce a urea melt in the evaporation section. The urea melt can be used, for example, partially or totally, to produce solid urea in the finishing section, for example, as granules or prills. The urea melt can be used, for example, partially or totally, to produce melamine. A combination of these uses is also possible.

[0092] An embodiment of the present invention relates to a plant for producing a urea-containing product.

[0093] Preferably, the plant further comprises an ammonia consuming unit with an inlet for ammonia-containing gas from a unit included in the urea production section downstream of the urea solution outlet of the MP treatment unit, for example the ammonia consuming unit having an outlet for discharging gas, and during operation, the CO2 contained in one or more gas streams received by the unit is at least partially or completely discharged via said outlet.

[0094] Preferably, the plant further comprises an ammonium nitrate section configured for neutralizing nitric acid with ammonia to form ammonium nitrate, comprising a neutralization section having an inlet for nitric acid and an inlet for ammonia-containing gas from a unit included in said urea production section downstream of the outlet for the urea solution of the MP treatment unit. For example, the neutralization section or the ammonium nitrate section has an outlet for discharging gas, and during operation, CO2 contained in one or more gas streams received by the neutralization section is at least partially or completely discharged through said outlet.

[0095] In some embodiments, at least one of the urea-containing products comprises urea and an ammonium salt, such as ammonium nitrate. The invention also relates to a plant for producing urea and ammonium nitrate, such as a plant for producing at least UAN (urea ammonium nitrate) liquid fertilizer. In some embodiments, the plant has UAN as its only product. In some embodiments, the plant produces multiple urea-containing products.

[0096] In a particular embodiment, the urea solution from the MP processing unit is processed in an LP dissociator to produce an LP urea solution and an ammonia-containing LP gas, which is fed, for example, to an ammonia consuming unit, for example an ammonium nitrate (AN) plant, in particular to provide some or all of the ammonia used to neutralize acids, for example to neutralize nitric acid to ammonium nitrate in the AN section. The LP dissociator and / or the additional LP dissociator, for example, have a gas outlet in gas flow connection with the gas inlet of the neutralization section.

[0097] In these embodiments, the plant is a plant for the integrated production of urea and ammonium nitrate and the process is a process for the integrated production of urea and ammonium nitrate. Optionally, some or all of the urea product, e.g., all or a portion of the LP urea solution from at least one LP disintegrator, is combined with ammonium nitrate to form a urea ammonium nitrate (UAN) solution that can be used, e.g., as a fertilizer. Also, in these embodiments, an optional second portion of the urea product may be used, e.g., as a feed for a melamine plant or may be fed to a finishing section to produce a solid urea product.

[0098] In an embodiment having an AN section, the LP section is operated at, for example, 1.10 bar to 3.0 bar absolute, such as about 1.5 bar absolute. The relatively low pressure contributes to better NH3 removal in the LP dissociator. The neutralization section of the AN section is operated at, for example, atmospheric pressure.

[0099] Advantageously, the MP treatment unit contributes to a relatively low CO2 emission from the AN section, thus additionally reducing the load on the HPCO2 compressor (CO2 feed to the HP stripper).

[0100] The invention also relates to a process for producing a urea-containing product carried out in a plant of the invention as described hereinbefore and hereinafter. The process comprises, for example, reacting an NH3 feed with a CO2 feed in the reactor to produce a urea synthesis solution. The urea synthesis solution is split into at least a first portion and a second portion, preferably using the split ratio described above. The first portion is fed to a HP stripper, thereby obtaining a stripped urea solution. The stripped urea solution is subjected to treatment at medium pressure in a MP processing unit to remove one or more components other than urea from the solution, producing the first MP gas stream and a MP urea solution having a higher concentration of urea. The second portion is subjected to medium pressure dissociation in the MP dissociator to produce the second MP gas stream and the MP urea solution. The process further comprises at least partially feeding the first MP gas stream and the second MP gas stream, respectively, to the MP condenser.

[0101] The urea production plant may, for example, be a grassroots plant, but may also be obtained, for example, by modifying an existing plant.

[0102] The present invention relates to a method for modifying an existing urea plant of the CO2 stripping type by adding an MP treatment unit, an MP dissociator and an MP carbamate condenser.

[0103] The present invention also relates to a method for modifying an existing urea plant, which is of the CO2 stripping type and already comprises an MP dissociator and an MP carbamate condenser, by adding an MP processing unit downstream of the HP stripper.

[0104] The present invention also relates to a method of modifying an existing plant for producing a urea-containing product. The existing plant comprises, for example, a urea production section with a high pressure (HP) synthesis section with an HP stripper, a reactor for forming urea from NH3 and CO2, and an HP carbamate condenser, the reactor and the HP carbamate condenser being optionally combined, the HP stripper having an inlet for CO2 feed as strip gas. The existing plant also typically comprises an HP CO2 compressor. The method includes, for example, adding, if not already present in the existing plant, an MP dissociator, an MP condenser, a connection from an outlet for the urea synthesis solution to the MP dissociator, and a gas flow path for the second MP gas stream from the MP dissociator to the MP condenser. The method further includes adding to the plant a medium pressure (MP) processing unit, preferably an MP adiabatic flash vessel, and a liquid flow path for the stripped urea solution from the HP stripper to the MP processing unit, and a gas flow path for the first MP gas stream from the MP processing unit to the MP condenser.

[0105] Optionally, the method further involves adding an optional MP stripper to the plant. In an advantageous embodiment, the method involves adding a dedicated CO2 compressor to an existing plant to compress the CO2 to MP, with an outlet for the CO2 connected to a gas flow path that is directly or indirectly connected to the MP carbamate condenser. This embodiment advantageously allows for an increase in plant capacity without increasing or modifying the HPCO2 compressor.

[0106] The described modification method (modifying an existing plant) preferably results in a plant of the invention as described. The preferences of the plant of the invention also apply to the method of modifying an existing plant. The unit details described in relation to the plant also apply to the units used or added in the method of modifying an existing plant. The connection of the liquid outlet from the MP carbamate condenser to the HP synthesis section may involve adding a HP carbamate pump. The method may also involve the installation of a post-reactor to effectively expand the reactor capacity.

[0107] FIG. 1 shows a schematic diagram of an exemplary embodiment of a process and a plant according to the invention.

[0108] The plant comprises a urea production section (UPS) with a high pressure (HP) synthesis section (HPSS), the HP section comprising a HP stripper (HPS), a reactor (HPR) for the formation of urea from NH3 and CO2, in particular a HP urea reactor, and a HP carbamate condenser (HPCC). The HP stripper has an inlet for CO2 feed as strip gas. The reactor and the HP carbamate condenser are optionally combined in a single vessel. The HP carbamate condenser (HPCC) is only an example, illustrated diagrammatically as a horizontal submerged condenser. Optionally, some urea formation already takes place in the HP carbamate condenser (HPCC). The HP synthesis section, e.g. the HP carbamate condenser, comprises an inlet for NH3 feed.

[0109] The urea production section further comprises a medium pressure (MP) processing unit (MPTU), a MP dissociator (MPD) and a MP condenser (MPCC). The HP urea reactor has an outlet for the urea synthesis solution (1) connected to a first liquid flow path (1a) to the HP stripper and a second liquid flow path (1b) to the MP dissociator (MPD).

[0110] The urea production section comprises a liquid flow path for the stripped urea solution (2) from the HP stripper (HPS) to the MP treatment unit (MPTU), a gas flow path for a gas stream (3) from the HP stripper, a gas flow path for a first MP gas stream (4) from the MP treatment unit (MPTU) to the MP condenser (MPCC), and a gas flow path for a second MP gas stream (5) from the MP dissociator (MPD) to the MP condenser (MPCC).

[0111] Gas (3) from the HP stripper is sent to the HP carbamate condenser (HPCC) where it is condensed. The carbamate-containing stream (6) is fed to the reactor. The MP processing unit (MPTU) has an outlet (7) for the first MP urea solution. The MP dissociator (MPD) has an outlet (8) for the second MP urea solution. The MP condenser (MPCC) has an outlet (9) for the MP carbamate solution and an outlet (10) for the gas. The MP condenser (MPCC) has a heat exchange wall in heat exchange contact with an optional pre-evaporator (PEV) used, for example, to heat the urea solution (11a) and remove water from the solution. The concentrated urea solution (11b) is fed to an optional finishing section, for example to produce solid urea.

[0112] Typically, as shown, the urea solution (7) from the MP treatment unit (MPTU) is fed directly or indirectly to an LP dissociator (LPD), which may also be described as an LP heat treatment unit, used to heat the solution. The LP dissociator (LPD) has an outlet (11) for the LP urea solution and an outlet (12) for the LP gas. The LP gas is fed directly or indirectly, for example, to an ammonia consuming unit, for example, the neutralization section of the ammonium nitrate section (AN). The reactor has, for example, an outlet (13) for gas, which is also fed, for example, to the neutralization section.

[0113] In an exemplary method of modifying an existing plant, an MP processing unit, an MP dissociator, and an MP condenser are added to the existing plant, and a pre-evaporator is also added, along with the respective flow connections.

[0114] FIG. 2 shows a schematic diagram of an exemplary embodiment of a process and plant according to the invention with an optional MP stripper (MPS). The MP optional stripper receives the urea solution (8) from the MP dissociator (MPD) and has an inlet for a CO2 stripped gas, typically an MPCO2 gas stream, e.g., a first MP gas stream (4) and / or a gaseous MPCO2 feed. The gaseous MPCO2 feed is optionally used in addition to the HPCO2 feed to the HP stripper. The optional MP stripper (MPS) has an outlet for a gas stream (15) connected to the MP condenser (MPCC) and an outlet for the urea solution (14) connected to the LP dissociation unit (LPD-2). The optional MP stripper (MPS) may also receive the first MP gas stream (4). The LP dissociation unit typically has an outlet (16) connected to the gas flow path to the LP carbamate condenser and an outlet (17) for the LP urea solution. In an alternative embodiment, the gas outlet (16) is connected to the neutralization section of the ammonium nitrate section (AN).

[0115] In this application, for process streams (i.e. not steam lines), high pressure (HP) is above 100 bar, for example from 120 bar to 300 bar, typically from 150 bar to 200 bar. Medium pressure (MP) is for example from 10 bar to 70 bar (including medium pressures from 30 bar to 70 bar), in particular from 10 bar to 40 bar, and low pressure (LP) is for example from 1.0 bar to 10 bar, in particular from 1.0 bar to 8 bar, for example from 1.5 bar to 5 bar. All pressures are in bar absolute.

[0116] The N / C ratio used here for the reactor, i.e. the NH3 to CO2 molar ratio, reflects the composition of the so-called initial mixture before urea production, consisting only of NH3, CO2 and H2O, as used in the technical field of urea plants. In particular, the N / C ratio of the reaction zone, as the term is conventionally used in the art, reflects the composition of the so-called initial mixture before urea production, consisting only of NH3, CO2 and H2O, measured at the reactor outlet. The N / C ratio of the carbamate condenser is the molar ratio of NH3 to CO2 measured at the outlet of the carbamate solution. The N / C ratio of the gas stream is the molar ratio of NH3 to CO2. The N / C ratio of the urea solution downstream of the HP synthesis section is the molar ratio of NH3 to CO2 of the actual mixture, based on the carbamate converted to the corresponding amounts of NH3 and CO3, i.e. without taking into account the urea component.

[0117] As used herein, the term "carbamate" refers to ammonium carbamate conventionally used in the art of urea plants.

[0118] The terms "exemplary" and "particularly" are used to indicate features that may be used in some embodiments, but are not required. Also, preferred features are not required.

[0119] The terms "liquid communication" and "liquid flow path" refer to a flow path (e.g., a tube or duct) that allows the passage of liquid between two units, optionally through some intermediate units. Liquid communication (and liquid flow path) does not involve gas phase transport, so two units connected by an evaporator, a flow path for vapor, and a condenser are not in liquid communication (not connected by a liquid flow path), but are in fluid communication (including both gas phase transport and liquid transport). A first unit is in liquid communication with a second unit, for example, if the liquid outlet of the first unit is connected to the inlet of the condenser, and the liquid outlet of the condenser is connected to the inlet of the second unit.

[0120] Stripper efficiency (α) is defined as the amount of ammonia converted to urea (and biuret) divided by the total amount of ammonia, typically measured at the stripper liquid outlet. This definition is equivalent to the definition of NH3 conversion based on the stripper outlet. Thus, α=(2*wt% urea / 60) / ((2*wt% urea / 60)+(wt% NH3 / 17)), where wt% NH3 includes all ammonia species, including ammonium carbamate, measured at the stripper liquid outlet. Those skilled in the art will understand that "stripping efficiency" refers to the urea purity at the stripper liquid outlet, and not the energy efficiency of the stripper.

[0121] Condensation in the carbamate condenser refers to the so-called carbamate condensation, which involves the reaction of NH3 and CO2 to liquid ammonium carbamate, resulting in the liquid phase carbamate from gaseous NH3 and CO2. Carbamate decomposition refers to the dissociation reaction of carbamate to NH3 and CO2.

[0122] As used herein, the term "shell space" refers to the shell-side space of a shell-and-tube heat exchanger.

[0123] The priorities given for the inventive plant also apply to the inventive improved method and process. The inventive urea production process is preferably implemented in an inventive plant. The integrated process is preferably implemented in an integrated plant. The inventive improved method preferably provides the inventive plant as a modified plant.

[0124] Some embodiments of the present disclosure relate to a plant and process for producing a urea-containing product. The plant includes a medium pressure dissociation unit and a high pressure CO2 stripper, each of which receives a portion of a urea synthesis solution. The stripped urea solution is further processed in a medium pressure processing unit.

[0125] Example 1 In the urea plant according to the invention, which is particularly illustrated in FIG. 2, 34,000 kg / h of CO2 was fed to the HP stripper, a gaseous MPCO2 stream of 4,000 kg / h was fed to the MP stripper (MPS) and mostly fed to the MP condenser (MPCC) via stream (15), and 7,000 kg / h of CO2 was removed from the stripped urea solution (2) in the MP treatment unit (MPTU), which is an MP adiabatic flash vessel, and fed from the MP treatment unit (MPTU) to the MP stripper (MPS) as the first MP gas stream (4). This resulted in the CO2 being completely condensed in the MP condenser (MPCC). The CO2 emissions from the ammonium nitrate section (AN) were reduced by 7,000 kg / h of CO2 and an advantageous urea concentration was achieved in the pre-evaporator (PEV). [Explanation of symbols]

[0126] 1 urea synthesis solution, 1a first liquid flow path, 1b second liquid flow path, 2 urea solution, 4 first MP gas stream, 5 second MP gas stream, 7 MP urea solution, 8 liquid flow path, 9 carbamate solution, 11 LP urea solution, 11a urea solution, 12 ammonia-containing LP gas, AN ammonium nitrate section, HP high pressure, HPCC HP carbamate condenser, HPR reactor, HPS HP stripper, HPSS high pressure synthesis section, LP low pressure, LPD low pressure dissociator, MP medium pressure, MPCC MP condenser section, MPD MP dissociator, MPF MP flash vessel, MPTU medium pressure treatment unit, PEV pre-evaporator, UPS urea production section

Claims

1. A plant for producing a urea-containing product, the plant comprising an HP stripper (HPS) and an NH ３ and CO ２ a urea production section (UPS) comprising a high pressure (HP) synthesis section (HPSS) comprising a reactor (HPR) for forming urea from and a HP carbamate condenser (HPCC), the reactor and the HP carbamate condenser being optionally combined, the urea production section further comprising a medium pressure (MP) processing unit (MPTU), a MP dissociator (MPD), and a MP condenser (MPCC), The reactor has an outlet for the urea synthesis solution (1) connected to a first liquid flow path (1a) connected to the HP stripper, the outlet also being connected to a second liquid flow path (1b) connected to the MP dissociator (MPD), the second liquid flow path (1b) bypassing the HP stripper, The HP stripper uses CO as a strip gas. ２ having an inlet for a feed; The plant comprises a liquid flow path for the stripped urea solution (2) from the HP stripper (HPS) to the MP treatment unit (MPTU), The MP processing unit (MPTU) comprises an MP flash vessel (MPF); the MP flash vessel receives the stripped urea (2) solution and has a gas outlet for a first MP gas stream (4) and a liquid outlet for an MP urea solution (7); The MP dissociator (MPD) is a shell-and-tube heat exchanger having an outlet for the second MP gas stream (5) and an outlet for the MP urea solution (8); The plant comprises a gas flow path for the first MP gas flow (4) from the MP processing unit (MPTU) to the MP condenser (MPCC) and a gas flow path for the second MP gas flow (5) from the MP dissociator (MPD) to the MP condenser (MPCC).

2. The plant of claim 1 , wherein the MP processing unit (MPTU) and the MP dissociator (MPD) are arranged in parallel.

3. 3. A plant according to claim 1 or 2, wherein the MP dissociator (MPD) is a heat exchanger using steam as heating fluid.

4. The plant further comprises an ammonium nitrate section (AN) configured to neutralize nitric acid with ammonia to form ammonium nitrate, the neutralization section having an inlet for nitric acid and an inlet for ammonia-containing gas from a unit included in the urea production section downstream of the outlet for the urea solution of the MP treatment unit, the plant further comprises a low pressure (LP) dissociator (LPD) and a liquid flow path (7) for MP urea solution (7) from the MP treatment unit (MPTU) to the LP dissociator, and a gas flow path (12) for ammonia-containing LP gas (12) from the LP dissociator to the neutralization section, the LP dissociator comprising an outlet for the LP urea solution (11) and an outlet for the LP gas (12). The plant according to any one of claims 1 to 3.

5. 5. The plant according to claim 4, further comprising a liquid flow path (8) from the MP dissociator (MPD) to the LP dissociator or to an additional LP dissociator, the additional LP dissociator having an outlet for an LP urea solution and an outlet for a second ammonia-containing LP gas stream connected to the neutralization section.

6. The plant according to any one of claims 1 to 5, wherein the liquid outlet of the carbamate solution (9) of the MP condenser (MPCC) is connected to a recirculation flow path to the HP synthesis section.

7. 7. The plant according to any one of claims 1 to 6, wherein the plant comprises a pre-evaporator (PEV) for removing water from the urea solution (11a), and the MP condenser (MPCC) comprises a heat exchange wall for exchanging heat with the pre-evaporator (PEV).

8. The plant of claim 7, comprising a shell-and-tube heat exchanger having a tube side and a shell side, the tube side providing the pre-evaporator (PEV) and the shell side providing at least a portion of the MP condenser (MPCC).

9. The plant according to any one of the preceding claims, comprising a split of a flow path for a HP urea synthesis solution into the first liquid flow path and the second liquid flow path.

10. The plant of claim 9 , wherein the split comprises a valve.

11. A plant as described in any one of claims 1 to 10, further comprising an MP stripper (MPS) for subjecting the urea solution (8) from the MP dissociator (MPD) to countercurrent direct contact with the first MP gas stream (4) from the MP treatment unit (MPTU).

12. The plant of claim 11, wherein the MP stripper (MPS) is configured to strip adiabatically.

13. A plant as described in claim 11 or 12, wherein the plant comprises a liquid flow path (8) from the MP stripper to an additional LP dissociator, the additional LP dissociator comprising a liquid outlet for the LP urea solution and a gas outlet for a second ammonia-containing LP gas stream connected to a low pressure carbamate condenser.

14. The plant of claim 13, comprising an LP dissociator (LPD) connected to receive the MP urea solution (7) from the MP flash vessel (MPF), the LP dissociator having a gas outlet connected to a gas inlet of an ammonia consuming unit, the liquid outlet of the MP urea solution (7) of the MP flash vessel being connected to an LP dissociator having a first outlet for LP urea solution and a second outlet for ammonia-containing LP gas, the second outlet for ammonia-containing LP gas being connected to an ammonia consuming unit.

15. A process for producing a urea-containing product carried out in a plant according to any one of claims 1 to 14, said process comprising the steps of: -NH ３ Feed and CO ２ reacting the feed in said reactor to produce a urea synthesis solution; - splitting said urea synthesis solution into at least a first portion and a second portion; - feeding said first portion to said HP stripper, thereby obtaining a stripped urea solution; - subjecting the stripped urea solution to treatment at medium pressure in the MP treatment unit (MPTU) comprising the MP flash vessel to produce the first MP gas stream (4); - subjecting said second portion to medium pressure dissociation in said MP Dissociator (MPD), which is a shell-and-tube heat exchanger, to produce said second MP gas stream (5) and MP urea solution; - feeding said first and second MP gas streams at least partially to said MP condenser (MPCC).

16. N.H. ３ and CO ２ NH ３ Against CO ２ 16. The process of claim 15, wherein the molar ratio of is less than 2.0 is removed from the stripped urea solution in the MP treatment unit.

17. 17. The process according to claim 15 or 16, wherein the treatment in the MP treatment unit (MPTU) involves a substantially adiabatic flashing of the stripped urea solution (2) to produce the first MP gas stream (4).

18. The process of claim 17, wherein a first urea solution (8) from the MP processing unit (MPTU) is processed in a LP dissociator (LPD) to produce a LP urea solution (11) and an ammonia-containing LP gas (12), and the ammonia-containing LP gas (12) is supplied to an ammonia consumption unit.

19. The process of any one of claims 15 to 17, further comprising the steps of subjecting a urea solution (7) received directly or indirectly from the MP Processing Unit (MPTU) to low pressure dissociation to produce a LP urea solution (11) and an ammonia-containing LP gas (12), and neutralizing nitric acid using the ammonia-containing LP gas (12) to form ammonium nitrate.

20. A method for modifying an existing plant for producing a urea-containing product, the existing plant comprising: ３ and CO ２ a urea production section (UPS) comprising a high pressure (HP) synthesis section (HPSS) comprising a reactor (HPR) for forming urea from CO2 and a HP carbamate condenser (HPCC), the reactor and the HP carbamate condenser being optionally combined, the HP stripper providing CO2 as a strip gas, ２ having an inlet for a feed; The method comprises: - if not already present in the existing plant, an MP dissociator (MPD), an MP condenser (MPCC) and a connection from the outlet of the urea synthesis solution (1) to said MP dissociator (MPD) bypassing the HP stripper, - a medium pressure (MP) processing unit (MPTU) comprising an MP flash vessel (MPF) and a liquid flow path for a stripped urea solution (2) from the HP stripper (HPS) to the MP flash vessel (MPF) and a gas flow path for a first MP gas stream (4) from the MP flash vessel (MPF) to the MP condenser (MPCC), - adding, if not already present in the plant, a gas flow path for a second MP gas stream (5) from the MP dissociator (MPD) to the MP condenser (MPCC), which is a shell-and-tube heat exchanger, thereby obtaining a plant as described in claim 1.

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