Stripping urea facilities for DEF production

Abstract

The present application provides a stripping urea plant and a urea production process suitable for producing diesel exhaust fluid (DEF) or its precursors in a DEF production unit downstream of a treatment section receiving a portion of the urea synthesis stream from a reaction zone, in particular bypassing the HP stripper.

Description

Technical Field

[0001] The present invention relates to the production of urea and in particular to the production of high purity urea solutions suitable for use as, for example, diesel exhaust fluid (DEF) in stripping-type urea plants.

[0002] introduce

[0003] Urea is usually produced in fertilizer grade quality. Urea products of higher purity are required, for example for reducing NO in combustion exhaust gases. x , such as for the production of diesel exhaust fluid (DEF). The standard for DEF is ISO 22241-1:2006 (version of October 15, 2006). DEF should have a low biuret content. DEF is used for the selective catalytic reduction of NO from exhaust gas. x urea aqueous solution (SCR solution).

[0004] Urea products with low biuret content can be prepared, for example, by crystallization from a mother liquor.The urea crystals can be dissolved to produce DEF.

[0005] Ullmann's Encyclopedia of Industrial Chemistry, chapter Urea, 2010, describes various urea production processes, including the use of crystallization to produce urea with a low biuret content, and stripping processes such as the Stamicarbon CO2 stripping process.

[0006] Many existing urea plants are of the stripping type with a high pressure stripper (eg a CO2 stripper or a thermal stripper) in the synthesis section.

[0007] US 2013 / 207035 A1 describes a process in which a first urea-containing aqueous stream is withdrawn directly from or after a recovery section in a urea production process and diluted. The recovery section is arranged downstream of the synthesis section.

[0008] US2017 / 204054 A1 describes a process for preparing DEF using flash crystallization.

[0009] US2018 / 0071653 A1 describes a process comprising stripping a urea reaction solution and diluting a portion of the aqueous urea stream with water to obtain a urea solution suitable for use in the reduction of NO. x The solution used in the unit.

[0010] EP 3862345 A1 to Casale describes a process for purifying a urea-containing aqueous stream comprising the step of removing biuret from the urea-containing stream by reverse osmosis to prepare an SCR solution.

[0011] The present invention relates to producing a urea product suitable for use as DEF or as a DEF precursor in a stripping urea plant, and in particular, a urea product suitable for dilution by the addition of water to form DEF. DEF precursors are typically converted to DEF outside a urea plant by the addition of sufficiently pure water. Producing DEF or a DEF precursor urea product of sufficiently high purity in a stripping urea plant remains challenging.

[0012] DEF is used in diesel engine vehicles to reduce NO x Emissions. The composition of DEF for automotive use has been standardized in ISO 22241-1:2006. DEF for automotive use has approximately 32.5 wt.% urea (i.e., a substantially eutectic composition) and also has very low concentrations of impurities. The product urea solution can also be used, for example, in industrial facilities and in NOx in ships and trains. x For NOx in railway and marine applications x Emission reduction, according to ISO 186111-1:2014, using about 40 wt.% urea solution. For NO (fossil fuel) power plants x The term "DEF" is used in this disclosure and also in the present invention to refer to, in particular, suitable, applicable and / or identified for use in NO x Abatement urea solution, for example a urea solution according to any of said specifications, more particularly a urea solution according to ISO 22241-1:2006.

[0013] When preparing DEF, the concentration of urea is important to ensure precise dosing of the liquid to the SCR catalyst. Low concentrations of organic impurities in DEF are crucial to avoid clogging and coke formation on the catalyst surface. Very low concentrations of inorganic impurities, particularly heavy metals, are also crucial in DEF because these impurities can poison the SCR catalyst. Metals accumulate on the catalyst, shortening its lifespan.

[0014] The maximum limits for metal impurities in the DEF reference specification approximate the typical achievable concentrations in the urea stream from a typical urea stripping plant. In particular, during upset or startup conditions, the amount of metals in the urea solution from the urea stripping plant can often exceed the DEF specification. In the case of urea plants designed for DEF production alone without solid urea production (e.g., plants without a urea solidification stage), this can result in large amounts of urea material exceeding product specifications and unable to be processed in the plant (e.g., within the plant's boundaries).

[0015] US20040116743 A1 describes a urea plant having a high pressure (HP) stripper receiving a first portion of a urea synthesis solution; a second portion is supplied to a medium pressure (MP) dissociator and the MP stripper and subsequently to a low pressure (LP) recovery section which also receives stripped urea solution from the HP stripper.

[0016] Jan Mennen, Nitrogen 2005, “The MEGA urea plant concept is now reality at SKW Piesteritz, Germany” describes a urea production process in which a first part of the urea solution from the urea reactor is supplied to an HP stripper using CO2 stripping gas, and a second part is supplied to an MP splitter, the urea solutions from the HP stripper and the MP splitter being combined and supplied to a low-pressure (LP) rectifier.

[0017] EP 2086928 B1 describes a process wherein a first portion of the urea solution from the urea reactor is supplied to an HP stripper and a second portion to an MP splitter, wherein the urea solutions from the HP stripper and from the MP splitter are combined and sent to a LP recovery section. Summary of the Invention

[0018] In a first aspect, the present invention relates to a urea production facility for producing a first urea-containing product and a second urea-containing product, wherein the second urea-containing product is diesel exhaust fluid (DEF) or a DEF precursor, the facility comprising a high-pressure (HP) synthesis section, the high-pressure synthesis section comprising a reaction zone, a high-pressure (HP) stripper, a condensation zone and a flow splitter adapted to separate a urea synthesis stream from the reaction zone into a first stream and a second stream, and a flow line for the first stream to the HP stripper, the facility further comprising a urea processing section for stripping the urea solution from the HP stripper The urea processing section comprises a recovery section comprising one or more recovery section decomposers for processing the stripped urea solution; an expansion device for expanding the second stream to give an expanded second stream; a treatment section comprising one or more treatment section decomposers for purifying the expanded second stream into a purified urea solution, wherein the one or more treatment section decomposers are arranged in parallel with the one or more recovery section decomposers; and preferably a DEF production unit for producing DEF and / or a DEF precursor from the purified urea solution.

[0019] The present invention also provides, in one aspect, a urea production process, wherein a urea synthesis stream is split into a first portion and a second portion, wherein the first portion is stripped in a high pressure (HP) stripper, recovered in a recovery section comprising one or more recovery section decomposers, and processed into a first urea-containing product, preferably a urea fertilizer product, and wherein the second stream is sent to a treatment section comprising one or more treatment section decomposers without passing through the HP stripper, wherein the one or more treatment section decomposers are separate and operated in parallel with the one or more recovery section decomposers, and wherein the treatment section produces a urea-containing stream suitable for use as a diesel exhaust fluid or for preparing a diesel exhaust fluid by dilution with water; wherein preferably no urea solution is supplied from the HP stripper to the treatment section, and wherein preferably no urea solution is supplied from the recovery section to the treatment section.

[0020] On the other hand, the present invention also provides a method for modifying an existing stripping urea facility, wherein the stripping urea facility includes a high-pressure (HP) synthesis section and a recovery section, wherein the high-pressure synthesis section includes a reaction zone, a condensation zone and a high-pressure HP stripper, wherein the recovery section includes a recovery section low-pressure (LP) decomposer, and the method includes adding to the existing facility: a splitter for dividing the urea synthesis stream from the reaction zone into a first part and a second part, the first part being supplied to the HP stripper; a treatment section for processing the second part, wherein the treatment section includes a treatment section LP decomposer connected in parallel with the recovery section LP decomposer. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 An example urea plant and process according to the present invention is schematically illustrated.

[0022] Figure 2 An example urea plant and process according to the present invention is schematically illustrated.

[0023] Figure 3 An example urea plant and process according to the present invention is schematically illustrated.

[0024] Any embodiments shown in the accompanying drawings are examples only and do not limit the invention. DETAILED DESCRIPTION

[0025] The present invention is based, in one aspect, on the insight that DEF can be produced in a stripping-type urea plant by treating a portion of the urea synthesis solution in a treatment section operating at medium and / or low pressure without passing through a high-pressure (HP) stripper, and processing the treated urea solution into a DEF product substantially without adding urea from the stripped urea solution. This advantageously allows for the preparation of a high-purity urea solution in the treatment section, in particular achieving a low metal content.

[0026] In certain aspects, the present invention relates to a urea plant and processes carried out in such a plant. The urea plant comprises a high-pressure (HP) synthesis section comprising a reaction zone, a high-pressure (HP) stripper, and a condensation zone. The urea plant is, for example, of the CO2-stripping type or the thermal stripping type.

[0027] The HP synthesis section has an inlet for NH3 feed and an inlet for CO2 feed. In this process, urea is formed by the reaction of NH3 and CO2.

[0028] The reaction zone is provided, for example, as a vertical urea reactor, although other configurations are possible. A vertical urea reactor may have, for example, one or more inlets at the bottom and one or more outlets at the top, or, for example, one or more inlets at the bottom and an outlet provided with a downcomer. The urea reactor may include horizontal trays to improve fluid flow in the reactor. The reactor may have one outlet for a urea synthesis stream containing both gas and liquid, or, for example, separate outlets for gas and liquid.

[0029] The reaction zone and the condensation zone are combined, for example, in a single vessel or, for example, in a single unit, such as a so-called pool reactor, as shown, for example, in Ullmann's Encyclopedia, chapter Urea, 2010, Figure 19. A pool reactor is a horizontal vessel comprising the reaction zone and the condensation zone.

[0030] One or more reactors can be used in series or in parallel. One or more condensers can be used, for example, in series or in parallel.

[0031] Reaction zone, condensing zone and stripper are operated under pressure in the high pressure range. Reactor, condensing zone and stripper can operate under substantially the same pressure or different pressures. For example, in a self-stripping facility, reactor is operated under 155-160 bar conventionally, and stripper is operated under 145-150 bar. In a CO stripping type facility, reaction zone, condensing zone and stripper are for example all operated under the same pressure (for example 138-142 bar).

[0032] The reactor outlet temperature is, for example, higher than 180°C, for example in the range of 180-190°C.

[0033] The urea solution at the reactor outlet has an N / C ratio of, for example, 3.0-3.8 (e.g., 3.0-3.1) in a plant with a high-pressure (HP) CO2 stripper and an N / C ratio of, for example, 3.3-3.6 in a plant with a high-pressure (HP) hot stripper.

[0034] The synthesis section may comprise further HP units, such as a high pressure (HP) scrubber, or a prereactor, or an ejector.

[0035] The HP stripper receives a portion, but not all, of the urea solution contained in the urea synthesis stream from the reactor. In particular, the HP stripper receives the first stream from the splitter. The urea solution received by the HP stripper also contains carbamate.

[0036] The stripper uses, for example, CO2 as a stripping gas or uses hot stripping (self-stripping). The stripper is typically a shell and tube heat exchanger, in which the urea solution acts as a falling film in the tube, and a heating fluid (typically steam) is in the shell side space. The gas outlet of the stripper is connected to the condensation zone. All or part of the gas from the stripper is supplied to the condensation zone. In some embodiments, a portion of the gas from the stripper is supplied to the reactor to improve the heat balance in the reactor. The stripper has an inlet for a urea synthesis solution and an outlet for the urea solution to be stripped. For example, a CO2 stripping type stripper has an inlet for a urea synthesis solution at the top, a gas outlet at the top, an inlet for CO2 used as a stripping gas at the bottom, and an outlet for the urea solution to be stripped at the bottom, all of which are connected to the stripper tubes; and an inlet and outlet for the heating fluid on the shell side.

[0037] The invention is particularly, but not exclusively, suitable for embodiments wherein the stripping in the HP synthesis section is carried out using steam having a temperature of at least 195°C (e.g. 195-225°C) and / or using saturated steam at a pressure of 14-24 bara, for example.

[0038] The stripper tubes are made, for example, of a corrosion-resistant material, such as a stainless steel alloy, in particular a ferritic-austenitic duplex stainless steel. Example duplex steel alloys are described in WO 95 / 00674 A1, WO 2017 / 013180 A1, and WO 2017 / 014632 A1. Reactor components that come into contact with the reaction mixture are also preferably made of duplex stainless steel, more preferably of the duplex steel alloys described above. This contributes to a low metal content in the urea synthesis solution.

[0039] In a specific embodiment, the stripper is a CO2 stripper comprising stripper tubes made of duplex ferritic-austenitic stainless steel.

[0040] Suitable duplex stainless steels for stripper tubes include, for example, Steel having the composition 29Cr-6.5Ni-2Mo-N, also designated by UNS S32906, or such as DP28W TMSteel with a composition of 27Cr-7.6Ni-1Mo-2.3WN, also specified by ASME Code 2496-1 and UNS S32808. Duplex steels used for stripper tubes have, for example, the following composition (mass %): C: maximum 0.05; Si: maximum 0.8; Mn: 0.3-4.0; Cr: 28-35; Ni: 3-10; Mo: 1.0-4.0; N: 0.2-0.6; Cu: maximum 1.0; W: maximum 2.0; S: maximum 0.01; Ce: 0-0.2; the balance being Fe and (unavoidable) impurities. Preferably, the ferrite content is 30-70% by volume, and more preferably 30-55%. More preferably, the steel contains (in wt. %): C max 0.02, Si max 0.5, Cr 29 to 33, Mo 1.0 to 2.0, N 0.36 to 0.55, Mn 0.3 to 1.0, the balance being Fe and (unavoidable) impurities.

[0041] It is also advantageous if the duplex stainless steel has the following composition in weight % (wt. %): C maximum 0.030; Si maximum 0.8; Mn maximum 2.0; Cr 29.0 to 31.0; Ni 5.0 to 9.0; Mo less than 4.0; W less than 4.0; N 0.25-0.45; Cu maximum 2.0; S maximum 0.02; P maximum 0.03; the balance being Fe and unavoidable impurities; and wherein the Mo+W content is greater than 3.0 but less than 5.0 (wt. %), preferably greater than 3.0 but less than 4.0 wt. %, further preferably having a steel composition as described in WO 2017 / 014632 A1, incorporated herein by reference.

[0042] The condensing zone, which serves as a high-pressure (HP) carbamate condenser, is provided, for example, as a vertical or horizontal HP carbamate condenser and is typically provided as a horizontal or vertical shell-and-tube heat exchanger for heat exchange with a cooling fluid. The gas to be condensed from the stripper is received in the tube or shell side space of the shell-and-tube heat exchanger. The condensing zone receives all or a portion of the gas stream from the HP stripper, typically at least 60 vol.%, for example at least 90 vol.%. Optionally, a portion of the gas stream from the HP stripper, for example 5-40 vol.%, is supplied to the reaction zone.

[0043] The HP carbamate condenser has an outlet for a fluid stream containing a liquid comprising ammonium carbamate. For liquid flow connection, the outlet is connected to the inlet of the reactor. Typically, a carbamate recycle solution from one or more low-pressure (LP) and / or medium-pressure (MP) carbamate condensers included in the facility is also supplied to the portion of the condenser that receives gas from the stripper. In embodiments where the gas is condensed in vertical tubes of the condenser, the carbamate solution is supplied, for example, to the top (falling film) or bottom of the tubes. In other embodiments, the gas to be condensed is supplied to the tubes of a U-shaped horizontal tube bundle (kettle type). In embodiments where the gas is to be condensed in the shell-side space, the condenser typically includes a tube bundle for a cooling fluid, wherein the tube bundle is, for example, vertical or horizontal. The HP carbamate condenser includes, for example, a straight tube bundle or a U-shaped tube bundle. The condenser may include two or more tube bundles. The cooling fluid is typically a liquid at the cooling fluid inlet of the condenser and is, for example, water used to generate steam and / or a process stream to be heated, such as a urea solution also containing carbamate. Two or more cooling fluids may be used, for example with dedicated tube bundles.An example of a horizontal submerged condenser is a pool condenser, which is shown in Ullmann's Encyclopedia, 2010, chapter Urea, figure 18.

[0044] The liquid containing ammonium carbamate is optionally supplied to the reaction zone with any uncondensed gases. Optionally, the uncondensed gases are separated from the condensate in a gas / liquid separator and supplied to another unit, for example to a scrubber or to a medium pressure (MP) section.

[0045] Feed CO2 and feed NH3 are supplied to the synthesis section in whole or in part, directly or indirectly, for example, in some embodiments, both feed CO2 and NH3 are supplied to the reactor (e.g., in combination with thermal stripping). In some embodiments employing HP CO2 stripping, part or all of the CO2 is supplied to the stripper, and part or all of the NH3 feed is supplied to, for example, the HP carbamate condenser.

[0046] The synthesis section includes a flow splitter. The flow splitter or distributor is adapted to separate the urea synthesis stream from the reaction zone into a first stream and a second stream, with the first stream being supplied to the HP stripper. Both the first stream and the second stream contain urea. In particular, the urea synthesis solution from the reaction zone is separated into the first stream and the second stream.

[0047] In some embodiments of the process, up to 50 wt.%, or for example up to 35 wt.% (e.g., 10-30 wt.%) of urea from the reaction zone is supplied as a second stream to the treatment section. The flow splitter is, for example, adapted to supply an adjustable portion of the urea synthesis solution to the HP stripper and an adjustable portion of the urea synthesis solution (e.g., a portion ranging from no urea solution to the entire urea solution) to the treatment section, to the HP stripper, or to simultaneously supply a portion of the urea synthesis solution to the HP stripper and a portion to the treatment section.

[0048] The first stream and the second stream are independently optionally liquid streams. In some embodiments, the process involves gas / liquid separation of the reaction mixture in the reaction zone upstream of the splitter (e.g., already in the reactor or in a gas / liquid separator between the reaction zone and the splitter). In such embodiments, the splitter receives only urea synthesis solution.

[0049] The urea synthesis solution comprises urea, water, ammonium carbamate and unconverted ammonia. The N / C ratio of the urea synthesis solution received by the splitter and received by the expansion device is preferably the same as that at the outlet of the reaction zone.

[0050] Preferably, the facility includes a control device for adjusting the mass ratio of the first and second streams. In this way, flexible portions of the urea synthesis solution can be supplied separately to the processing section and the HP stripper. For example, when demand for fertilizer urea products is low, relatively more urea can be supplied to the processing section to produce DEF. During certain time periods, all of the urea solution can be supplied separately to the processing section and the HP stripper.

[0051] The plant comprises a urea processing section for processing the stripped urea solution from the HP stripper into a first urea-containing product.The urea processing section comprises a recovery section and an evaporation section, eg downstream of the recovery section, and a polishing section, eg downstream of the evaporation section.

[0052] The recovery section comprises one or more recovery section decomposers for treating the urea solution from the HP stripper, and the plant generally comprises one or more condensers connected to the gas outlet of the one or more recovery section decomposers.

[0053] The term "recovery section" is used herein broadly to refer to the recovery of urea from the stripped urea solution, i.e., the processing of the stripped urea solution to at least partially remove non-urea components, such as carbamate and ammonia. The recovery section may, for example, comprise a medium-pressure (MP) decomposer and a downstream low-pressure (LP) decomposer connected in series, or, for example, an LP decomposer that receives the stripped urea solution directly from the HP stripper.

[0054] The decomposer is, for example, a heat exchanger that uses a heating fluid to decompose the carbamate and remove NH3 and CO2. The decomposer has an outlet for the gas. The decomposer is, for example, a shell-and-tube heat exchanger for indirect heat exchange with the heating fluid. The heating fluid is, for example, steam or a process stream, such as a condensed process gas stream.

[0055] The gas stream containing CO and NH from the recovery section decomposer, preferably from the MP or LP recovery section decomposer, is supplied, for example, to a carbamate condenser. The carbamate solution formed in the carbamate condenser is typically recycled to the reaction zone, optionally via the HP carbamate condenser. In this way, the recovery section is typically a "full recycle" design.

[0056] The urea solution from the decomposer may be further treated, such as by atmospheric flash evaporation, subatmospheric flash evaporation and / or in a pre-evaporator.

[0057] The recovery section comprises for example a LP decomposer, in particular with a HP CO2 stripper, optionally with an MP treatment unit such as an MP adiabatic flash unit between the outlet for the stripped urea solution of the HP stripper and the inlet of the LP decomposer.

[0058] The recovery section comprises, for example, a medium pressure (MP) decomposer with a downstream low pressure (LP) decomposer, for example with an HP hot stripper.

[0059] When the term "recovery section" is used in the present disclosure, the recovery section may include units operating at different pressures and may, for example, include both an MP recovery section and an LP recovery section.

[0060] After passing through the recovery section, for example, after passing through the LP decomposer, the stripped urea solution comprises, for example, at least 75 wt.% urea (e.g., 75 to 85 wt.% urea) and water, as well as biuret and metallic impurities. The urea solution can be used, for example, to prepare urea ammonium nitrate (UAN) liquid fertilizer. In some embodiments, the facility includes a UAN production unit downstream of the recovery section, wherein the urea solution from the recovery section is mixed with an ammonium nitrate (AN) solution.

[0061] The first urea-containing product of the process is a urea solution, for example from a LP decomposer.

[0062] The urea solution is preferably converted into a urea melt containing at least 90 wt.% urea in an evaporation section for removing water. For example, at least 90 wt.%, or at least 95 wt.%, or all of the urea in the stripped urea solution is converted into this urea melt. The urea melt may contain, for example, at least 95 wt.% urea or at least 99 wt.% urea. The evaporation section may comprise, for example, one or more vacuum evaporators.

[0063] The urea melt is subjected to urea finishing, for example by granulation or prilling, to form a solid urea product. Other uses of the urea melt are also possible, for example for melamine production. The first urea-containing product of the process is, for example, a solid urea product or a urea melt.

[0064] The water vapor removed in the evaporation stage is, for example, condensed, and the condensate is treated, for example, in a wastewater treatment (WWT) stage, which comprises, for example, a hydrolyzer and a desorber. The clean process condensate from the WWT is used, for example, for the production of DEF, in particular by dilution with a urea solution, and / or is supplied, for example, to a low-pressure (LP) carbamate condenser to prevent carbamate crystallization.

[0065] The facility optionally includes a connection for the liquid flow of the urea solution from the treatment section to the evaporation section, preferably a liquid flow line for the urea solution from the treatment section to the evaporation section. For example, the facility includes a liquid flow line from the LP decomposer in the treatment section to the evaporation section. Thus, the outlet of the treatment section for the urea solution is connected to the inlet of the evaporation section for liquid flow. Preferably, the treatment section is also connected to the inlet of the DEF production unit via a urea solution flow line connected in parallel to the flow line to the evaporation section.

[0066] The liquid flow connection can, for example, be provided as a flow line for urea solution from the treatment section to the recovery section, wherein the evaporation section receives urea solution from the recovery section. Preferably, the flow line is connected at the inlet of the flow line to a MP decomposer, a medium-pressure (MP) contact unit (such as a medium-pressure (MP) adiabatic stripper), a LP decomposer, or a residual ammonia removal unit of the treatment section. For example, the facility includes a flow line for urea solution from an MP decomposer or MP contact unit of the treatment section to the inlet of an LP decomposer of the recovery section. For example, the facility includes a flow line for urea solution from a residual ammonia removal unit to the inlet of the evaporation section.

[0067] In a preferred embodiment, the facility includes a flow line for the urea solution from the treatment section to the inlet of the evaporation section. The preferred embodiment of the liquid flow connection including the flow line offers the following advantages: in situations where there is low demand for DEF and / or high demand for (solid) urea fertilizer, the urea solution from the treatment section can be converted into a urea melt. This can also be used during plant upsets, where DEF quality may not be guaranteed, but fertilizer-grade urea can be safely produced. Thus, the liquid flow connection provides improved flexibility for the facility.

[0068] Preferably, the plant comprises a liquid flow connection for the urea solution from the treatment section LP decomposer to the inlet of the evaporation section and a liquid flow connection for the urea solution from the treatment section LP decomposer to a preferred residual ammonia removal unit, for example with a preferred steam stripper. This provides improved flexibility without increasing the load on the recovery section.

[0069] Optionally, the process comprises supplying the urea solution from the treatment section to a preferably used evaporation section, or for example to a recovery section, or for example to a UAN production section.

[0070] In yet another embodiment, the facility comprises a flow line for the urea solution from the treatment section to the UAN production unit. This similarly provides improved flexibility.

[0071] In an embodiment, the facility is of the CO2 stripping type and the HP stripper uses CO2 as the stripping gas. Preferably, the reaction zone is operated with an N / C ratio of 3.0-3.2 (reaction zone urea solution outlet) and preferably at a pressure of 140-160 bar. Preferably, the HP reactor, HP condenser and HP stripper are operated at substantially the same pressure. Preferably, gravity flow is used for fluid transport from the condenser to the reactor and from the reactor to the stripper. Preferably, the stripper tubes are made of stainless steel, for example, duplex ferritic-ferritic stainless steel, such as the steel discussed above.

[0072] Advantageously, since only a portion of the urea formed in the reaction zone is processed in the HP stripper, a relatively large portion of the CO feed can be used for stripping, which can be used to reduce energy consumption in the HP stripper and / or achieve high stripping efficiency. If only a portion of the CO feed is used for stripping, the remaining portion of the CO feed can be supplied directly to the reaction zone or used to adjust (reduce) the N / C ratio (N / C ratio measured at the carbamate solution outlet) in one or more carbamate condensers.

[0073] The stripped urea solution is supplied, for example, directly to a LP decomposer. The LP decomposer operates, for example, at 2-6 bar, for example about 4 bar.

[0074] In some embodiments, the HP stripper is a hot stripper and includes stripper tubing, such as hot stripper tubing. Similarly to hot stripping, the processes and apparatus of the present invention can achieve the advantages of lower metal content in DEF production. For example, the inner tubing of urea stripper tubing, made of, for example, Zr or Ti, can be susceptible to corrosion, resulting in metal loss into the stripped urea solution. Furthermore, if stainless steel stripper tubing is used, metal loss into the urea solution, such as through passive corrosion, can occur.

[0075] In embodiments employing hot HP stripping, the recovery section typically comprises a medium-pressure (MP) decomposer and a downstream low-pressure (LP) decomposer. The HP synthesis section typically comprises a high-pressure (HP) ejector for transporting the carbamate-containing liquid from the HP condenser to a vertical urea reactor. The HP ejector typically uses feed NH3 as the motive fluid. The reactor is operated, for example, with an N / C ratio of 3.2-3.6 at the reactor outlet.

[0076] The plant comprises expansion means for expanding the second stream to obtain an expanded second stream, for example to reduce the pressure of the second stream from a high pressure to a medium pressure. The expansion means is for example an expansion valve.

[0077] The treatment section includes one or more treatment section decomposers for purifying the expanded second stream comprising urea solution into a purified urea solution. The treatment section is used to process the unstripped urea solution. The treatment section receives a portion of the urea synthesis stream from the reaction zone, i.e., the second stream. In particular, the portion of the urea synthesis stream, i.e., the second stream, bypasses the HP stripper.

[0078] The processing stage comprises, for example, a medium pressure (MP) resolver, a low pressure (LP) resolver, or both MP and LP resolvers, for example in series.

[0079] The treatment section decomposer and the recovery section decomposer are independent units. Specifically, the treatment section decomposer is separate from and an additional component of the recovery section decomposer. The treatment section decomposer and the recovery section decomposer are arranged in parallel. This prevents mixing of the urea solution from the first and second streams.

[0080] The one or more decomposers have an inlet for a urea solution, an outlet for the urea solution, and an outlet for a gas stream containing NH3 and CO2. In operation, at least some of the carbamate contained in the urea solution is decomposed in the decomposer. The decomposer is, for example, a heat exchanger that uses a heating fluid (e.g., steam, or a condensing process stream, or steam condensate). The decomposer is typically a shell-and-tube heat exchanger.

[0081] The gas outlet of the decomposer is usually connected to a carbamate condenser. The carbamate condenser is usually a heat exchanger using a cooling fluid. The cooling fluid is, for example, water or a urea solution to be heated. The carbamate condenser has an outlet for condensate and an outlet usually for uncondensed gases. The carbamate solution from one or more carbamate condensers is recycled directly or indirectly to the reaction zone. The carbamate condenser is optionally shared with the recovery section. In particular, the gas stream from the treatment section decomposer is preferably combined with the gas stream from the recovery section decomposer, and the combined gas stream is condensed in the condenser; optionally, one or both of these gas streams have been partially condensed before being combined.

[0082] The treatment section may include additional urea solution treatment units operating at medium and / or low pressure, such as an adiabatic flash vessel. In an exemplary embodiment, the treatment section includes an adiabatic flash vessel and a downstream LP decomposer, optionally without a MP heat exchanger decomposer. The flash vessel has an inlet for the urea solution, an outlet for the urea solution, and an outlet for flash steam. The flash vessel is positioned downstream of an expansion device (e.g., an expansion valve) or includes the expansion device. The flash vessel operates at medium pressure and adiabatically flashes the urea solution from high pressure to medium pressure.

[0083] The medium-pressure flash steam is supplied to, for example, an MP carbamate condenser, for example also receiving fresh CO 2 .

[0084] Preferably, no stripped urea solution (stripped in the HP stripper) is supplied to the treatment section. For example, the urea solution at the outlet of the treatment section contains less than 5 wt.% urea originating from the stripped urea solution. This contributes to a low metal content and a low biuret content in the urea solution obtained from the treatment section.

[0085] Optionally, steam stripping, in particular the injection of steam into the urea solution, can be used to remove traces of NH 3 from the urea solution in the treatment stage.

[0086] In embodiments where the processing section comprises a processing section LP splitter, the processing section LP splitter is separate from the LP splitter comprised in the recovery section.Thus, the processing section LP splitter is arranged in parallel with the recovery section LP splitter.

[0087] In particular, the process section LP decomposer is a dedicated LP decomposer. This provides an important distinction from prior art processes, in which urea solutions from the HP stripper and from the medium pressure (MP) process section are expanded and combined, and the resulting combined urea solution is supplied to the LP decomposer.

[0088] In an embodiment, the processing section includes a medium pressure (MP) decomposer and a low pressure (LP) decomposer connected in series, optionally with a medium pressure (MP) contact unit between the MP decomposer and the LP decomposer. Gas from the MP decomposer in the processing section is typically condensed in a medium pressure (MP) carbamate condenser. The MP carbamate condenser may also optionally receive gas from the medium pressure (MP) decomposer in the recovery section.

[0089] A portion of the CO2 feed can be supplied to the MP carbamate condenser to adjust the N / C ratio therein. Optionally, the portion of the CO2 feed is first contacted with a urea solution in a treatment section to adjust the N / C ratio of the urea solution, for example in an MP contact unit arranged in a flow line for the urea solution between the MP decomposer and the LP decomposer. The MP contact unit has an outlet for the gas stream connected to the inlet of the MP carbamate condenser. The MP contact unit is used, for example, for MP stripping of the urea solution, more preferably for MP adiabatic stripping, and is preferably a medium pressure (MP) adiabatic stripper. MP stripping involves a countercurrent flow of a gas stream in direct contact with the urea solution. MP adiabatic stripping can contribute to sufficient condensation in a low pressure (LP) carbamate condenser, which is connected to the low pressure (LP) decomposer that receives the urea solution from the MP adiabatic stripping.

[0090] The treatment section optionally includes a residual ammonia removal unit, typically downstream of the LP decomposer. The residual ammonia removal unit is, for example, a steam stripper, or a stripper using an inert gas such as N2, or a unit operating at a lower pressure than the LP decomposer, for example, a unit operating below atmospheric pressure (i.e., below 1.0 bar absolute). The residual ammonia removal unit typically operates at LP (1-10 bar) or below 1.0 bar.

[0091] The residual ammonia removal unit is, for example, a steam stripper for processing urea solution from the decomposer in the treatment stage, typically processing low-pressure (LP) urea solution from the decomposer in the low-pressure (LP) treatment stage. The optional steam stripper operates, for example, at a pressure below 1.0 bar absolute. The steam stripper is, for example, a vessel having an inlet for steam and configured to inject steam into the urea solution. The steam stripper can be used to control and reduce the amount of NH3 in the DEF precursor; other units and methods can also be used to control and reduce the amount of NH3 in the DEF precursor. The urea solution at the liquid outlet of the steam stripper meets DEF specifications, for example, and has a maximum NH3 content of 0.2 wt.%, for example, a maximum alkalinity, expressed as NH3, in the urea solution at the liquid outlet of the steam stripper. Other purification devices can also be used, and in some embodiments, the urea solution obtained from the decomposer in the treatment stage already meets DEF specifications.

[0092] The plant further preferably comprises a DEF production unit downstream of the treatment section.The DEF production unit is a preferred part of the plant and is preferably also used in the urea production process.

[0093] A DEF production unit, for example, is a dilution unit configured to add water to the purified urea solution obtained from the treatment stage to achieve the desired urea concentration. In particular, high-purity water, such as clean process condensate, such as from the wastewater treatment stage of a urea plant, is added. In principle, dilution water can also or alternatively be added upstream in the process, but this is generally less preferred due to the purification steps.

[0094] In some embodiments, the DEF production unit comprises a dry flash unit, for example as described in US 2017 / 204054 A1.

[0095] The dry flash unit includes a liquid distributor, in particular a nozzle. The dry flash is preferably performed at a pressure below 15 kPa, preferably in the range of 1 to 10 kPa. Preferably, the urea solution subjected to the dry flash has a urea concentration in the range of 85 wt.% to 95 wt.%, more preferably between 87 wt.% and 92 wt.%. The DEF production unit may include an evaporator to increase the urea concentration of the urea solution upstream of the dry flash unit. Typically, in embodiments in which the DEF production unit includes a dry flash unit, the treatment section does not include a residual ammonia removal unit, such as a steam stripper. The dry flash preferably produces a free-flowing urea powder. Preferably, the DEF production unit includes a packaging unit, such as a bagging unit, for packaging the powder. Preferably, the free-flowing urea powder is packaged with a moisture content of less than 0.2 wt.%, preferably in water-tight packaging. Preferably, the facility includes a conveyor line for conveying the powder from the dry flash unit to the packaging unit. The powder can be easily transported, easily packaged and subsequently removed from its packaging, and can be dissolved to produce DEF.

[0096] By supplying the second stream from the reaction zone to the treatment section without HP stripping, the urea solution can have a lower metal content. In particular, the processing of the second stream involves less corrosive process conditions than in HP stripping. Ammonium carbamate, an intermediate reaction product contained in the urea synthesis solution, is extremely corrosive, especially at high temperatures, such as in the high-pressure stripper. In particular, in a stripping facility, the reactor can be operated at, for example, about 185°C, but the peak temperature at the top of the HP stripper is, for example, 210-220°C. In addition, the HP stripper is usually a shell and tube heat exchanger, in which the urea solution is in the stripper tubes and the steam is on the shell side, and in the HP stripper, due to the large number of tubes, the amount of metal surfaces in contact with the urea solution containing ammonium carbamate is large.

[0097] The lower metal content of the urea synthesis solution as a source of the second urea-containing product is important for use as DEF and as NO xReductants in emission reduction systems are important because these systems contain (expensive) catalysts for selective catalytic reduction (SCR). The presence of metallic species in the urea solution shortens the life of the SCR catalyst due to metal accumulation. Reducing the metal content (i.e., metal concentration) will therefore extend the service life of the SCR catalyst.

[0098] Biuret is a detrimental component in urea used in selective catalytic reduction (SCR) systems because exposure of the biuret component to the catalyst leads to the formation of isocyanuric acid, which shortens the life of the SCR catalyst. Therefore, a lower biuret content in the supplied urea solids will be used in the DEF solution, thereby extending the life of the SCR catalyst.

[0099] Compared to processes in which the DEF production unit receives a urea solution from the recovery section, the DEF produced in the DEF production unit will have significantly lower biuret and metal contents because the precursor solution used to produce DEF in the present invention is not exposed to the high temperature conditions typical of the HP stripper, and thus the process avoids the formation of biuret and the corrosion caused by these conditions.

[0100] The first urea-containing product obtained from the urea processing section and also using the urea production process of the present invention is, for example, a final product (such as a solid urea product), or, for example, an intermediate product (such as a urea melt that can be used for melamine production, or a urea solution that can be used for UAN production). The first urea-containing product is preferably fertilizer-grade urea.

[0101] The second urea-containing product, which is typically obtained downstream of the treatment stage in the DEF production unit, is preferably Diesel Exhaust Fluid (DEF) or a DEF precursor. DEF precursor designates a urea product which can be converted into DEF by adding (pure) water.

[0102] DEF broadly refers to NO x catalytic selective reduction of NO x Emission reduction) urea solution.

[0103] The high purity urea solution obtained from the treatment section is used to prepare DEF or DEF precursor, for example, by diluting the urea solution with water to a desired target urea concentration, for example to about 32.5 wt.% urea for DEF according to ISO 22241-1:2006, to about 40 wt.% urea solution according to ISO 186111-1:2014, or, for example, to about 50 wt.% urea for NO in industrial facilities. x Reduced urea solution.

[0104] The purified urea solution from the treatment section and, for example, the DEF product and / or DEF precursor product from the DEF production unit have a low impurity content. The same applies to the urea-containing stream suitable for use as or in the production of DEF produced in the process of the present invention. Preferably, the impurities are consistent with the intended use as DEF or with the intended use to form DEF by dilution with water, in particular with DEF according to ISO 22241-1:2006 (i.e., with 32.5 wt.% urea) and / or ISO 186111-1:2014. Typically, biuret is a maximum of 0.3 wt.%. Typically, NH3 is a maximum of 0.2 wt.%, for example, alkalinity expressed as NH3 is a maximum of 0.2 wt.%. Preferably, carbonates expressed as CO2 are a maximum of 0.2 wt.%. Furthermore, typically, aldehydes are a maximum of 5 ppm (by weight) and / or insoluble matter is a maximum of 20 ppm (by weight). Typically, PO4, Ca, Fe, Al, Mg, Na and K are each at a maximum of 0.5 ppm. Cu, Zn, Cr and Ni are each typically at a maximum of 0.2 ppm (all in ppm by weight). The same applies to urea-containing streams suitable for use as or in the preparation of DEF produced in the process of the present invention.

[0105] For DEF precursor solutions, impurities are preferably such that the impurity levels are obtained after dilution by adding water to the DEF specification urea content (e.g., by diluting to 32.5 wt.% urea with water). The above purity level values ​​are given at a 32.5 wt.% urea level. Generally, it is desirable and advantageous to have purity levels exceeding these limits, e.g., the DEF product or DEF precursor has a higher purity.

[0106] The purified urea solution from the treatment section and, for example, the DEF product and / or DEF precursor product from the DEF production unit preferably has a basicity expressed as NH3 of a maximum of 0.2 wt.%; a maximum of 0.3 wt.% biuret; a maximum of 0.5 ppm by weight each of PO4, Ca, Fe, Al, Mg, Na, and K; and a maximum of 0.2 ppm by weight each of Cu, Zn, Cr, and Ni, and a urea content of at least 32.5 wt.%. The same preferred levels apply to urea-containing streams suitable for use as or in the preparation of the diesel exhaust fluid prepared in the process of the present invention.

[0107] The purified urea solution from the treatment section and, for example, the DEF product and / or DEF precursor product from the DEF production unit preferably has a basicity expressed as NH3 of a maximum of 0.2 wt.%; a maximum of 0.3 wt.% biuret; a maximum of 0.5 ppm by weight each of PO4, Ca, Fe, Al, Mg, Na, and K; and a maximum of 0.2 ppm by weight each of Cu, Zn, Cr, and Ni, calculated on a 32.5 wt.% urea basis with the addition of water as required, and an actual urea content of at least 32.5 wt.%. The same preferred levels apply to urea-containing streams suitable for use as or in the preparation of DEF produced in the process of the present invention.

[0108] Advantageously, the second stream has a lower metal content relative to urea (wt. % relative to urea) than the stripped urea solution. Preferably, the relatively lower temperature in the treatment section than in the HP stripper helps maintain this relatively low metal content, which is advantageous for producing DEF or a DEF precursor.

[0109] In some embodiments, the processing section operates entirely at temperatures below 170°C, or below 165°C, or even below 160°C.

[0110] Preferably, the treatment section produces a urea solution having at least 32.5 wt.% urea and having a maximum of 0.3 wt.% biuret and / or a maximum of 0.2 wt.% NH3, calculated on a basis of 32.5 wt.% urea (i.e. for urea solutions with a higher urea content) by adding water as needed to reach 32.5 wt.% urea.

[0111] In one aspect, the present invention provides a urea production process in which a urea synthesis stream is split into a first portion and a second portion. The urea production process is preferably carried out in a facility according to the present invention, and all preferences regarding the facility also apply to the method carried out in the facility according to the present invention. The first portion is stripped in an HP stripper, recovered in a recovery section, and processed into a first urea-containing product having the preferred characteristic preferences and details described in conjunction with the facility. The recovery section includes one or more recovery section decomposers, the details of which are as discussed in conjunction with the facility.

[0112] In this process, the second stream bypasses the HP stripper and is sent to the treatment section. The treatment section includes one or more treatment section decomposers, which are separate and operated in parallel with one or more recovery section decomposers. The treatment section produces a urea-containing stream suitable for use as DEF or for preparing DEF by dilution with water. The urea-containing stream is preferably the same as the purified urea solution discussed in conjunction with the facility.

[0113] The urea-containing stream is supplied, for example, to a DEF production unit, where it is diluted, for example, by adding clean water, or subjected to a dry flash distillation. The dry flash distillation product is a DEF precursor that can be converted into DEF by adding clean water. The urea-containing stream at the inlet of the dry flash distillation unit is typically already of sufficiently high purity that it can be converted into DEF by adding water. The details of the dry flash distillation are the same as those discussed with respect to the facility. The added clean water is, for example, clean process condensate from the wastewater treatment section of the urea facility.

[0114] The treatment sections and the processes therein have as preferred features the same preferences and details as described in connection with the facility.

[0115] Preferably, the urea-containing stream obtained from the treatment section contains at least 32.5 wt.% urea and preferably has an alkalinity of a maximum of 0.2 wt.% NH3 at a 32.5 wt.% urea level; a maximum of 0.3 wt.% biuret; a maximum of 0.5 ppm by weight each of PO4, Ca, Fe, Al, Mg, Na and K; and a maximum of 0.2 ppm by weight each of Cu, Zn, Cr and Ni. These impurity limits are calculated based on 32.5 wt.% urea, i.e., based on the addition of water to the urea solution as needed to obtain 32.5 wt.% urea.

[0116] Preferably, the recovery section includes a recovery section LP decomposer, and the treatment section includes a separate treatment section LP decomposer. Preferably, these LP decomposers are arranged in parallel. Thus, the process particularly involves decomposing the urea solution in the treatment section in a dedicated LP decomposer.

[0117] Preferably, in this process, neither the stripped urea solution from the HP stripper nor the urea solution obtained from the stripped urea solution from the HP stripper is combined with the second stream or the urea solution derived from the second stream. In other words, preferably no urea solution is supplied from the HP stripper or from the recovery section to the treatment section. Consequently, the urea solution in the treatment section is not contaminated by any impurities in the stripped urea solution from the HP stripper.

[0118] Preferably, the installation therefore does not comprise a flow line for such transport of urea solution. Preferably, the installation does not comprise a flow line for the stripped urea solution coming from the HP stripper or for the urea solution obtained from the stripped urea solution coming from the HP stripper to a flow line or unit in the plant receiving a second stream or to a flow line or unit receiving a urea solution originating from said second stream.

[0119] Preferably, less than 1.0 wt.%, preferably 0 wt.%, of the urea in the DEF product, the DEF precursor product and the urea stream from the treatment section originates from the HP stripper.

[0120] In one aspect, the present invention also provides a method for converting an existing steam stripping urea facility, comprising a synthesis section and a recovery section, the synthesis section comprising a reaction zone, a condensation zone, and a HP stripper. The existing facility may also include, for example, an evaporation section and a wastewater treatment section. The method comprises adding a splitter and a treatment section to the existing facility. The splitter is configured to separate a urea synthesis stream from the reaction zone into a first portion and a second portion, the first portion being supplied to the HP stripper. The treatment section is adapted to process the second portion. The recovery section comprises a recovery section LP decomposer, and the added treatment section preferably comprises a separate treatment section LP decomposer arranged in parallel with the recovery section LP decomposer in the converted facility. Preferably, the method further involves adding a steam stripper included in the treatment section downstream of the treatment section LP decomposer. The steam stripper is configured to inject steam into the urea solution purified in the treatment section. The converted facility is preferably a urea production facility according to the present invention. The method preferably also involves adding a DEF production unit downstream of the treatment section, such as a unit for diluting the urea solution from the treatment section or for subjecting the urea solution to dry flash evaporation. Preferably, the method involves adding a flow line for cleaning process condensate from the wastewater treatment section to the DEF production unit. All details and preferences of the urea production facility of the present invention also apply to the retrofit facility of this method.

[0121] Figure 1 An exemplary urea plant and process according to the invention is schematically shown, comprising an HP synthesis section comprising a reactor (R), an HP stripper (S), a carbamate condenser (C) and a flow splitter (FS). The urea synthesis solution (1) from the reactor (R) is divided in the flow splitter (FS) into a first stream (1a) comprising urea, which is supplied to the HP stripper (S), and a second stream (1b) also comprising urea.

[0122] The gas stream (6) from the HP stripper (S) is supplied to the carbamate condenser (C), and the liquid containing carbamate (7) from the condenser is supplied to the reactor (R). NH3 feed and CO2 feed are also supplied to the synthesis section. Inert gas is removed from the synthesis section (not shown).

[0123] The stripped urea solution (2) is supplied to a recovery section (RS), where the urea content of the solution (2) is increased by removing NH3, CO2 and ammonium carbamate to obtain a urea stream (3). The recovery section (RS) comprises at least one recovery section decomposer (RSD), which is, for example, a heat exchanger for heating the urea solution. The recovery section (RS) is included in a urea processing section (UPS). The urea processing section (UPS) may further comprise, for example, an evaporation section and a finishing section downstream of the recovery section.

[0124] The second stream (1b) is expanded in an expansion device (e.g., valve (V1)) and supplied as expanded stream (1c) to a treatment section (TS) where it is processed into a high-purity urea solution (4). The high-purity urea solution (4) is used to prepare DEF and / or DEF precursor (5) in a DEF production unit (DEF). In practice, the facility includes further units, flow lines, and components, such as additional valves and control valves. The treatment section (TS) includes at least one treatment section decomposer (TSD) arranged in parallel with a recovery section decomposer (RSD).

[0125] Figure 2 An exemplary urea plant and process according to the present invention with a CO2 HP stripper (S) is schematically illustrated. Unless otherwise indicated, reference numerals are the same as Figure 1 The reactor (R) comprises a downcomer connected to a liquid outlet (1) and a separate gas outlet (not shown) at the top. The stripped urea solution (2) is directly supplied to the recovery section LP pressure decomposer (RSLPD) included in the LP recovery section (LPRS). The gas (8) from the LP decomposer (RSLPD) is condensed in the LP carbamate condenser (LPCC), and the resulting carbamate solution (9) is supplied to the HP carbamate condenser (C) which also receives NH3 feed. The treatment section (TS) comprises an MP decomposer (MPD) and an LP decomposer (TSLPD) arranged in series for treating the expanded second urea stream (1c). The gas (11) from the LP decomposer (TSLPD) is condensed in a dedicated LP carbamate condenser (not shown), or, as shown in the figure, is supplied to the LP carbamate condenser (LPCC) of the LP recovery section (LPRS). The treatment section LP decomposer (TSLPD) and the recovery section LP decomposer (RSLPD) are independent units arranged in parallel. The urea processing section may further include an evaporation section (EVAP) for concentrating the LP urea solution (3) from the recovery section LP decomposer (RSLPD) by evaporating water to form a urea melt (12). The urea melt (12) is supplied to a finishing section (FIN), such as a prilling tower or granulator, to form a solid urea product (13).

[0126] The treatment section (TS) also comprises a residual ammonia removal unit (RAR). From the residual ammonia removal unit (RAR), the high purity urea solution (4) is supplied to a DEF production unit (DEF), which is a dilution unit having an inlet (10) for clean water.

[0127] Advantageously, the precursor solution (4) used to produce DEF is not exposed to the high temperature conditions typical in the HP stripper (S) and thus avoids biuret formation and metal absorption caused by these conditions and corrosion occurring in the HP stripper (S).

[0128] In practice, the installation comprises other units, flow lines and elements such as additional valves and control valves.

[0129] Figure 3 An example urea plant and process according to the present invention is schematically illustrated. Unless otherwise indicated, reference numerals are the same as Figure 2 The residual ammonia removal unit (RAR) is implemented as a steam stripper (StS). The steam stripper (StS) is a container for injecting steam into the urea solution to achieve stripping. The steam stripper (StS) has a supply line for steam (not shown) and a gas outlet connected to a condenser (C) (not shown). The facility further comprises a flow line (14) for the LP urea solution from the treatment section LP decomposer (TSLPD) to the evaporation section (EVAP), which can be used if the demand for DEF is low and / or the demand for solid urea product is high, or in abnormal situations.

[0130] Other configurations of the preferred liquid flow connection from the treatment section (TS) to the evaporation section (EVAP) are also possible, for example via a recovery section LP decomposer (RSLPD) (not shown) or by supplying urea solution (4) to the evaporation section (EVAP) (not shown).

[0131] In summary, embodiments of the present invention provide a stripping urea plant and a urea production process suitable for producing Diesel Exhaust Fluid (DEF) or its precursors in a Diesel Exhaust Fluid (DEF) production unit downstream of a treatment section that receives a portion of the urea synthesis stream from the reaction zone, in particular bypassing the HP stripper.

[0132] As used herein, HP (high pressure) indicates a pressure of, for example, at least 100 bara, such as 120-250 bara, or, for example, 110-160 bara, MP (medium pressure) indicates a pressure of, for example, 15-80 bara, 20-80 bara, and LP (low pressure) indicates a pressure of, for example, 1-10 bara, such as 4-10 bara; these pressure ranges apply to process streams, particularly solutions, and not necessarily to steam and heating fluids. The abbreviation "bara" means bar absolute. Unless otherwise indicated, pressures are absolute.

[0133] As used herein, the term 'typically' indicates a feature that is often used but is not mandatory.

[0134] As used herein, "carbamate" refers to ammonium carbamate.

[0135] The terms 'typical', 'generally' and 'in particular' are used to indicate features that may be used in some embodiments but are not mandatory in all embodiments. Preferred features are not mandatory.

[0136] The N / C ratio used herein for the urea solution at the outlet of the reaction zone reflects the composition of the so-called initial mixture before urea production, which consists solely of NH 3 , CO 2 and H 2 O, as this term is used in the field of urea plants, and is a molar ratio. The N / C ratio of the gas stream indicates the molar ratio of NH 3 to CO 2 . The N / C ratio of the carbamate condenser indicates the molar ratio of NH 3 to CO 2 used at the outlet of the carbamate solution.

Claims

1. A urea production facility for producing a first urea-containing product and a second urea-containing product, wherein the second urea-containing product is diesel exhaust fluid (DEF) or a DEF precursor, the facility comprising a high-pressure (HP) synthesis section configured to operate at a pressure of at least 100 bara, comprising a reaction zone (R), a high-pressure stripper (S) configured to operate at a pressure of at least 100 bara, a condensation zone (C) and a flow splitter (FS) adapted to split a urea synthesis stream (1) from the reaction zone (R) into a first stream (1a) and a second stream (1b), and a flow line for the first stream (1a) to the HP stripper (S), the facility further comprising: a urea processing section (UPS) for processing the stripped urea solution (2) from the HP stripper (S) into the first urea-containing product (3), the urea processing section (UPS) comprising a recovery section (RS) comprising one or more recovery section decomposers (RCD) for processing the stripped urea solution (2); - expansion means (V1) for expanding said second stream (1b) to give an expanded second stream (1c); a treatment section (TS) comprising one or more treatment section decomposers (TCD) for purifying the expanded second stream (1c) into a purified urea solution (4), wherein the one or more treatment section decomposers (TCD) are arranged in parallel with the one or more recovery section decomposers (RCD); as well as - A DEF production unit (DEF) for producing DEF and / or a DEF precursor (5) from the purified urea solution (4).

2. The urea production facility according to claim 1 , wherein the process section comprises a process section low pressure (LP) decomposer (TSLPD) configured to operate at a pressure of 1-10 bara, and the recovery section (RS) comprises a recovery section low pressure (LP) decomposer (RSLPD) configured to operate at a pressure of 1-10 bara in parallel with the process section LP decomposer (TSLPD).

3. Urea production plant according to claim 1 or 2, wherein the treatment section (TS) comprises a steam stripper (StS) for stripping the urea solution by injecting steam.

4. Urea production facility according to claim 1 or 2, wherein the DEF production unit (DEF) comprises an inlet (10) for adding clean water to the purified urea solution (4).

5. Urea production facility according to claim 1 or 2, wherein the DEF production unit (DEF) comprises a dry flash unit.

6. Urea production plant according to claim 1 or 2, wherein the plant does not comprise a flow line for the stripped urea solution from the HP stripper (S) or for a urea solution obtained from the stripped urea solution (2) from the HP stripper (S) to a flow line or a unit in the plant receiving the second stream (1 b) or receiving a urea solution originating from the second stream (1 b).

7. A urea production facility according to claim 1 or 2, wherein at least one of the one or more recovery section decomposers (RCD) is the recovery section LP decomposer (RSLPD), wherein the recovery section (RS) optionally comprises a medium pressure (MP) decomposer configured to operate at a pressure of 15-80 bara between the outlet for the stripped urea solution (2) of the HP stripper (S) and the recovery section LP decomposer (RSLPD); wherein the facility further comprises a low pressure (LP) carbamate condenser (LPCC) configured to operate at a pressure of 1-10 bara for condensing gases (8) coming from the recovery section LP decomposer (RSLPD), wherein the LP carbamate condenser (LPCC) is optionally also used to condense gases (11) coming from a treatment section LP decomposer (TSLPD) included in the treatment section (TS).

8. Urea production facility according to claim 1, wherein the HP stripper (S) uses at least a portion of the CO2 feed for stripping.

9. Urea production facility according to claim 8, wherein the stripper (S) is a shell and tube heat exchanger comprising stripper tubes made of duplex stainless steel.

10. A urea production facility according to claim 1 or 2, wherein the urea processing section (UPS) comprises, downstream of the recovery section (RS), an evaporation section (EVAP) for converting the urea solution (2) into a urea melt (12) and a liquid flow connection (14) for the urea solution from the treatment section (TS) to the evaporation section (EVAP).

11. A urea production process, wherein a urea synthesis stream (1) is split into a first portion (1a) and a second portion (1b), wherein the first portion (1a) is stripped in a high pressure (HP) stripper (S) configured to operate at a pressure of at least 100 bara, recovered in a recovery section (RS) comprising one or more recovery section decomposers (RCD), and processed into a first urea-containing product (3), and wherein the second portion (1b) is sent to a treatment section (TS) comprising one or more treatment section decomposers (TCD) without passing through the HP stripper, wherein the one or more treatment section decomposers (TCD) are separate and operated in parallel with the one or more recovery section decomposers (RCD), and wherein the treatment section (TS) produces a urea-containing stream (4) suitable for use as diesel exhaust fluid (DEF) or for preparing DEF by dilution with water.

12. The process according to claim 11, wherein the first urea-containing product (3) is a urea fertilizer product.

13. Process according to claim 11, wherein no urea solution is supplied from the HP stripper (S) to the treatment section (TS).

14. Process according to claim 11, wherein no urea solution is supplied from the recovery section (RS) to the treatment section (TS).

15. The process according to claim 11 or 12, wherein the urea-containing stream (4) of 32.5 wt.% urea has an alkalinity of a maximum of 0.2 wt.% NH3; a maximum of 0.3 wt.% biuret; a maximum of 0.5 ppm by weight each of PO4, Ca, Fe, Al, Mg, Na and K; and a maximum of 0.2 ppm by weight each of Cu, Zn, Cr and Ni.

16. The process according to claim 11 or 12, wherein the recovery section (RS) comprises a recovery section low pressure decomposer (RSLPD) configured to operate at a pressure of 1-10 bara, and the treatment section (TS) comprises a treatment section low pressure decomposer (TSLPD) configured to operate at a pressure of 1-10 bara arranged in parallel with the recovery section low pressure decomposer (RSLPD) configured to operate at a pressure of 1-10 bara.

17. The process according to claim 11, carried out in the facility according to claim 1.

18. A method for retrofitting an existing stripping urea facility, the stripping urea facility comprising a high pressure (HP) synthesis section and a recovery section, the HP synthesis section being configured to operate at a pressure of at least 100 bara, comprising a reaction zone, a condensation zone, and an HP stripper configured to operate at a pressure of at least 100 bara, wherein the recovery section comprises a recovery section low pressure decomposer configured to operate at a pressure of 1 to 10 bara, The method comprises adding to the existing facility: a flow splitter (FS) for dividing the urea synthesis flow coming from the reaction zone into a first portion (1a) and a second portion (1b), the first portion (1a) being supplied to the HP stripper; a treatment section (TS) for processing said second portion (1 b), wherein the treatment section (TS) comprises a treatment section low pressure (LP) decomposer (TSLPD) configured to operate at a pressure of 1-10 bara in parallel with the recovery section low pressure (LP) decomposer (RSLPD) configured to operate at a pressure of 1-10 bara.

19. The process according to claim 18, wherein the added treatment section (TS) comprises a steam stripper (StS).

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