Urea production using triple MP flow

Abstract

The present disclosure relates to a urea production facility and process that uses a high-pressure CO2 stripper, a downstream medium-pressure treatment unit, and a medium-pressure dissociator that receives a urea synthesis solution from a reactor, where gases from the treatment unit and dissociator are condensed in a first condenser, and waste gases from the synthesis section are separately condensed in a second condenser. A retrofit method is also described.

Description

Technical Field

[0001] The present invention relates to NH 3 and CO 2 Production of urea.

[0002] Introduction

[0003] Urea facilities typically use at least part of the CO 2 The feed is used as stripping gas (e.g., CO from Stamicarbon). 2 The type of high pressure (HP) stripping column used in the stripping process. In the chapter on urea in Ullmann's Encyclopedia, 2010, Figure 16 shows the CO 2 An example process scheme for a stripping type urea process, which does not limit the invention. In the illustrated process, the reactor has an outlet for fluid and an outlet for gas, and the gas from the reactor is supplied to a high pressure scrubber. The urea solution from the stripper is supplied to a low pressure decomposer and then to a pre-evaporator, which is a heat exchanger using cooling water. The gas from the reactor is supplied to the high pressure scrubber. The gas from the low pressure decomposer or dissociator is condensed in a low pressure carbamate condenser and the resulting aqueous carbamate stream is recycled to the synthesis section. Low water recycle is usually required because supplying water to the reaction zone is detrimental to the urea yield. Typical CO 2 The high-pressure stripping tower in the stripping type urea process is usually operated at a stripping efficiency α of 0.87.

[0004] There is a need for a urea production facility and process having a relatively small HP stripper compared to the urea production capacity and having low energy consumption.There is also a need to improve existing urea production facilities to increase their capacity. Summary of the invention

[0005] In a first aspect, the present invention relates to a urea production facility comprising a high pressure (HP) synthesis section, the HP synthesis section comprising an HP stripping column, a urea ... 3 and CO 2 The reaction zone for forming urea and the condensation zone, wherein the HP stripper has CO as stripping gas 2an inlet for a feed, the facility further comprising a medium pressure (MP) treatment unit, an MP decomposer, a first MP carbamate condensation section and a second MP carbamate condensation section, a first flow line for urea solution from the reaction zone to the HP stripping tower and a second flow line for urea solution from the reaction zone to the MP decomposer, wherein the facility comprises a fluid flow line for the stripped urea solution from the HP stripping tower to the MP treatment unit, wherein the MP treatment unit has a gas outlet for a first MP gas stream, wherein the MP decomposer has a gas outlet for a second MP gas stream, and wherein the HP synthesis section has a gas outlet and a pressure reducing element for a third MP gas stream, and wherein two gas streams selected from the group consisting of the first, second and third MP gas streams are combined and condensed in the first MP carbamate condensation section.

[0006] Preferably, the first MP carbamate condensation section is arranged to receive the first MP gas flow from the MP treatment unit and the second MP gas flow from the MP dissociator, and wherein the second MP carbamate condensation section receives the third MP gas flow, preferably wherein the second MP carbamate condensation section comprises a condenser, a scrubber and / or an absorber.

[0007] The invention also relates to a urea production process carried out in a urea production facility having such an MP treatment unit, an MP dissociator and first and second MP carbamate condensation stages.

[0008] The present invention also relates to a method for improving an existing urea production facility, the existing urea production facility comprising: a high pressure (HP) synthesis section, the HP synthesis section comprising an HP stripping tower, a 3 and CO 2 The reaction zone for forming urea and the condensation zone, wherein the HP stripper has CO as stripping gas 2an inlet for the feed, and the HP synthesis section has a gas outlet, the facility comprising a first flow line for urea solution from the reaction zone to the HP stripper, the method comprising adding the following units and connections if not already present in the facility: a medium pressure (MP) treatment unit with a gas outlet for a first MP gas stream, an MP decoupler with a gas outlet for a second MP gas stream, a first MP carbamate condensation section and a second MP carbamate condensation section and a second flow line for urea solution from the reaction zone to the MP decoupler, a pressure reducing element for gas from the gas outlet of the HP synthesis section giving a third MP gas stream, a fluid flow line for the stripped urea solution from the HP stripper to the MP treatment unit, the method further comprising configuring the facility so that two gas streams selected from the group consisting of the first, second and third MP gas streams are combined and condensed in a first MP carbamate condensation section, and one gas stream selected from the group is condensed separately in a second MP carbamate condensation section, preferably by arranging the first MP carbamate condensation section to receive the first MP gas stream from the MP treatment unit and the second MP gas stream from the MP dissociator, and arranging the second MP carbamate condensation section to receive the third MP gas stream. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 An exemplary urea production facility and process according to the present invention is schematically illustrated.

[0010] The embodiments shown in the drawings are merely examples and do not limit the invention. DETAILED DESCRIPTION

[0011] The invention is based on the insight that in one aspect, MP treatment (particularly adiabatic flashing) of a stripped urea solution from an HP stripper in an MP treatment unit is combined to give a first MP gas stream, while MP dissociation of a portion of the urea synthesis solution bypassing the HP stripper in the MP dissociator is combined to give a second gas stream, and pressure reduction of the synthesis section offgas to MP is combined to give a third MP gas stream. Furthermore, the process involves combining and condensing two of these MP gas streams at medium pressure to form an MP carbamate solution. The MP carbamate solution recycled to the HP synthesis section advantageously has a low water content, thereby increasing the urea yield in the reaction zone, and the heat released in the combined MP condensation can advantageously be used for heat integration.

[0012] In an embodiment, the second MP gas stream from the MP dissociator and the reactor off-gas as the third gas stream undergo combined condensation at medium pressure while the first gas stream from the MP treatment unit (eg, flasher) is separately condensed.

[0013] In an embodiment, a first MP gas stream from an MP treatment unit (eg, flasher) and reactor off-gas as a third gas stream undergo combined condensation under MP while a second MP gas stream from an MP dissociator is separately condensed.

[0014] In a preferred embodiment, a first MP gas stream from an MP treatment unit (e.g. a flasher) and a second MP gas stream from an MP dissociator are combined and condensed in a first MP carbamate condensation section to give a favorable balance of the N / C ratio, and the reactor off-gas is condensed separately as a third MP gas stream. In this embodiment, by combining and condensing the second MP gas stream from the MP dissociator, it is possible to advantageously use the low N / C ratio and the low inert content of the first MP gas stream for the condensation of said gas streams. Thus, at a given MP condensation pressure, a relatively high temperature (by virtue of a relatively low inert content) and a low water content (by virtue of the N / C ratio) of the formed MP carbamate solution are achieved. The high temperature is used, for example, to heat the urea production solution by heat exchange in order to facilitate the evaporation of water from the urea solution.

[0015] The MP treatment unit is preferably a flash evaporator, in particular an adiabatic flash evaporator. Adiabatic flash evaporation provides low NH 3 With CO 2 Flash steam with a molar ratio (e.g., N / C less than 1.0). 2 The vapors of the MP adiabatic flash of the stripped urea solution of the stripping column include, for example, about 40 mol % of NH 3 and about 50 mol% CO 2 In the preferably adiabatic flash evaporation, the urea solution at the outlet of the flasher has a lower temperature than the urea solution at the inlet of the flasher.

[0016] The offgas from the synthesis section is, for example, released from a HP urea synthesis reactor included in a urea production facility. For example, the offgas contains about 65 mol % NH 3 and 20 mol% CO 2 .

[0017] The synthesis section includes HP CO 2 A stripping column having an outlet for the stripped urea solution connected to an inlet of the MP treatment unit. In an exemplary embodiment, the HP reaction zone is operated at an N / C ratio of at least 2.7 (e.g., about 3) and a pressure of at least 120 bar (e.g., about 140 bar). 2 The urea solution at the outlet of the stripper is compared to the urea solution partially received by the MP decomposer without undergoing HP CO 2The stripped urea synthesis solution has a relatively high N / C ratio. The urea synthesis solution comprises urea, water, ammonium carbamate and ammonia. The second gas stream from the MP dissociator also has a relatively high N / C ratio. The second gas stream comprises, for example, 65 mol % NH 2 and 25 mol% CO 2 .

[0018] The urea production facility and process of the present invention is CO 2 The facility includes a high pressure (HP) synthesis section, which includes an HP stripping column, a 3 and CO 2 A reaction zone and a condensation zone for forming urea. The reaction zone includes one or more reactors. A plurality of reactors can be arranged in series or in parallel. The facility includes, for example, a vertical urea reactor. The reaction zone and the condensation zone can also be combined in a single container, for example, in a horizontal container, such as in a pool reactor. The reaction zone typically has an outlet for urea synthesis solution and a separate outlet for exhaust gases. The synthesis section has an outlet for exhaust gases, an outlet for stripped urea solution and an outlet for unstripped urea synthesis solution.

[0019] The condensation zone is provided, for example, by a high-pressure carbamate condenser, preferably a shell and tube heat exchanger with a tube bundle and a shell side space. For example, a straight tube bundle or a U-shaped tube bundle is used. The gas to be condensed is preferably supplied to the shell side space and the cooling fluid is supplied to the tubes. Alternatively, the gas to be condensed is supplied to the tubes and the cooling fluid is supplied to the shell side space.

[0020] The condenser can be a horizontal or vertical condenser. The condenser is, for example, a heat exchanger with a cooling fluid side and a condensation side, which is configured to operate with the fluid as the continuous phase on the condensation side, while the gas to be condensed is present as bubbles, rising through the liquid phase. This advantageously provides (substantially) complete condensation in the condenser.

[0021] The condenser is, for example, a horizontal immersed condenser in which the cooling fluid is in the tubes, for example, of a U-shaped tube bundle, and is, for example, a pool condenser or a pool reactor, or is, for example, a vertical condenser in which the cooling fluid is in the tubes, or is, for example, a vertical condenser in which the gas to be condensed rises in the tubes as bubbles in the liquid phase. In other embodiments, the condenser is, for example, a vertical falling film condenser.

[0022] The stripping tower is a tower with CO used as stripping gas. 2 A heat exchanger is provided at the inlet of the feed and is configured for countercurrent contact between a portion of the urea synthesis solution coming from the reaction zone and the stripping gas and for heating the urea solution. 2The stripping tower is, for example, a vertical shell and tube heat exchanger configured for operation with a falling film of a urea solution to be stripped in the tubes and comprising an inlet for the urea solution at the top, an outlet for the stripped urea solution at the bottom, an inlet for the stripping gas at the bottom and an outlet for the gas at the top connected to the HP condensation section, all of which are in and out of the tubes. The stripping tower also comprises, for example, a shell for heating a fluid such as, for example, steam. In embodiments in which separate HP condensers and reactors are used, the facility comprises a flow line for the condensate from the condenser to the reactor. The HP carbamate condenser typically also receives NH 3 Feed.

[0023] The facility comprises a medium pressure (MP) treatment unit, preferably a flash evaporator, and a fluid flow line for the stripped urea solution from the HP stripper to the MP treatment unit. The MP treatment unit has a gas outlet for a first MP gas stream and a fluid outlet for the treated urea solution. The facility further comprises an MP dissociator, a first flow line for the urea solution from the reaction zone to the HP stripper, and a second flow line for the urea solution from the reaction zone to the MP dissociator. Thus, a portion of the urea synthesis solution from the reaction zone, in particular from the reactor, is supplied to the HP stripper, and another portion is supplied to the MP dissociator. In a preferred embodiment, a single reactor is connected to supply urea solution to both the HP stripper and the MP dissociator.

[0024] Preferably, the MP flasher is typically operated at a pressure of 10 to 70 bar, preferably 10 to 35 bar, for example 18 to 25 bar. Preferably, the MP flasher is preferably operated at a pressure equal to or higher than that of the MP dissociator, for example, at a pressure of 0 to 10 bar higher than that of the MP dissociator, for example, at a pressure of 1 to 10 bar higher than that of the MP dissociator, or more preferably 2 to 7 bar higher. The MP dissociator has a gas outlet for a second MP gas stream. The HP synthesis section has a gas outlet for waste gas and a pressure reducing element for the waste gas, thereby giving a third MP gas stream. The pressure reducing element is, for example, a valve, for example, a control valve. In the process and facility, two gas streams selected from the group consisting of the first, second and third MP gas streams are combined and condensed in the first MP carbamate condensation section. A gas stream selected from the group is condensed separately in the second MP carbamate condensation section.

[0025] The facility preferably comprises a gas flow line for conveying two gas streams selected from the group consisting of said first, second and third MP gas streams to the first MP carbamate condensation section. Preferably, the facility comprises a gas flow line for conveying the first and second MP gas streams to the first MP carbamate condensation section and a gas flow line for supplying the third MP gas stream to the second MP carbamate condensation section.

[0026] Preferably, the first MP carbamate condensation section is arranged to receive a first MP gas stream from the MP treatment unit and a second MP gas stream from the MP dissociator. Preferably, the facility comprises a gas flow line from the MP treatment unit to the first MP carbamate condensation section and a gas flow line from the MP dissociator to the first MP carbamate condensation section. Preferably, the facility comprises a gas flow line from the pressure reducing element (or unit) to the second MP carbamate condensation section for supplying a third MP gas stream. In an interesting embodiment, the third MP gas stream from the HP synthesis section has at the inlet of the second MP carbamate condensation section a NH 3 is the NH of the gas stream at the gas outlet(s) of the HP synthesis section 3 The content (eg, on a mass basis) is at least 90%. For example, the gas flow line for the third gas stream from the HP synthesis section to the second MP carbamate condensation section does not include a scrubber or condenser operating at HP.

[0027] Preferably, the second MP carbamate condensation section comprises a condenser, a scrubber and / or an absorber. Preferably, the second MP condensation section comprises a shell and tube heat exchanger (condenser), wherein a cooling fluid (e.g., cooling water) is in the tube, and the gas to be condensed is supplied to the shell side space. Preferably, the heat exchanger also receives a fluid containing carbamate in the shell side space, for example, the fluid is in co-current contact with the gas to be condensed. The fluid containing carbamate is, for example, supplied from a low pressure (LP) recovery section. For example, both gas and fluid are supplied to the bottom portion of the shell side space, and the heat exchanger has an outlet at the top. The heat exchanger comprises, for example, a U-shaped vertical tube bundle. The condensation section preferably further comprises a gas / fluid separator receiving a process fluid from the heat exchanger.

[0028] Preferably, the second MP condensation stage comprises a shell and tube heat exchanger and a downstream gas / fluid separator and optionally an absorber receiving the gas from said separator.

[0029] Preferably, fluid from an absorber is supplied to the heat exchanger, and LP carbamate solution is supplied to the absorber as absorption fluid.

[0030] Furthermore, in embodiments where the second MP condensation stage consists of a heat exchanger (as a condenser) and a gas / fluid separator (i.e., without an absorber), this stage may be referred to as a scrubber, similar to HP scrubbers, which are frequently used to clean the gas from CO 2 Off-gas from the HP synthesis section in stripping urea plants.

[0031] In an embodiment of the plant and process according to the invention, the MP treatment unit, which is preferably an adiabatic flash evaporator, makes the relatively CO rich 2 MP gas flow (NH 3 With CO 2 The MP dissociator that receives the urea synthesis solution bypassing the HP stripper advantageously allows a relatively large urea production capacity to be achieved with a relatively small HP stripper. The gas stream from the MP dissociator is relatively rich in NH 3 (NH 3 With CO 2 The molar ratio of N / C to CO is, for example, at least 2.3, for example, in the range of 2.50 to 3.0, for example, about 2.60). The gas stream is preferably combined with a gas stream from an MP treatment unit, preferably an adiabatic flash evaporator, and condensed in a first MP carbamate condensation section at medium pressure (e.g., 20 to 30 bar, such as 22 to 30 bar). This pressure with a small amount of inerts advantageously results in relatively high temperatures of more than 120° C. Preferably, the condensation is carried out in heat exchange contact with a urea solution to be heated for water evaporation. The N / C ratio of the carbamate solution in the first MP carbamate condensation section can be adjusted by reducing CO to CO at MP. 2 A portion of the feed is added to the first MP carbamate condensation section for correction (reduction).

[0032] CO 2 The feed typically contains some inerts and may include added oxygen, for example, for use in a hydroconverter. The CO supplied to the first MP carbamate condensation section 2 The feed can be, for example, from HP CO 2 supplied at the compressor interstage point, or from a dedicated MP CO 2 compressor. For example, for CO 2 The supply line to the first MP carbamate condensation section comprises a hydrogen converter, typically a catalytic converter, in which as CO 2 The presence of H in the feed 2 is removed. CO at the outlet of the hydrogen converter 2The feed contains, for example, 0.05 vol.% to 0.20 vol.% O 2 , preferably about 0.10 vol.% O 2 Advantageously, the CO received by the MP stripper 2 The feed stream preferably has a CO content greater than that received by the HP stripper. 2 Feed lower O 2 content, since no or less passivation air is required for units operating at medium pressure.

[0033] CO 2 The feed may originate, for example, from the synthesis gas production section of an upstream ammonia plant.

[0034] CO 2 The feed is supplied to the first MP carbamate condensation section, for example, via an MP stripper, which is preferably an adiabatic stripper. The MP stripper is, for example, configured for urea solution and CO 2 The MP stripper comprises a countercurrent contact of the feed and has a gas inlet, a gas outlet, a fluid inlet and a fluid outlet. The MP stripper comprises, for example, a packed bed for ensuring gas / fluid contact. The gas from the gas outlet of the MP stripper is supplied to the first MP condensation section. The contact causes a reduction in the amount of ammonia (free and / or as carbamate) in the urea solution, thereby providing stripping. The urea solution can absorb some CO 2 The CO supplied to the optional MP stripper 2 The feed stream comprises, for example, at least 95 vol. % CO 2 and less than 0.10 vol.% NH 3 , preferably excluding NH 3 For example, if the urea solution from the MP dissociator is supplied to the LP recovery section comprising the LP dissociator and the LP carbamate condenser for achieving good carbamate condensation, the CO is provided by the MP stripper. 2 The feed is favorable.

[0035] The urea solution from the MP treatment unit and the urea solution from the MP dissociator are directly or indirectly supplied to a LP recovery section, which comprises a LP dissociator receiving the urea solution and a LP carbamate condenser receiving the gas from the LP dissociator. The urea solution from the MP treatment unit and the urea solution from the MP dissociator can be processed in a common LP recovery section or in separate LP recovery sections. The LP carbamate condenser(s) also receives water to prevent crystallization of carbamate. The water is provided, for example, as a clean process condensate, for example, from a sewage treatment section. CO 2Part of the feed is optionally supplied to the LP carbamate condenser, optionally via an atmospheric flash tank condenser, to reduce the N / C ratio of the carbamate solution in the LP carbamate condenser, thereby ensuring good condensation and avoiding supplying high NH to the (atmospheric) absorber. 3 The carbamate solution from the LP condensation section is compressed and recycled, for example, to the second MP carbamate condenser and comprises, for example, 25 wt.% to 50 wt.% of H 2 O, for example, about 30 wt.% H 2 O.

[0036] Preferably, the facility comprises a LP dissociator and a fluid flow line for urea solution from the MP treatment unit to the LP dissociator. Preferably, the facility comprises a LP carbamate condenser and a gas flow line from the LP dissociator to the LP carbamate condenser. Preferably, the facility comprises a fluid flow line for carbamate solution from the LP carbamate condenser to a second MP carbamate condensation section (e.g., an MP scrubber). Preferably, the facility comprises a fluid flow line for carbamate solution from the second MP carbamate condensation section to the first MP carbamate condensation section. Preferably, the facility comprises a fluid flow line for carbamate solution from the first MP carbamate condensation section to the high pressure (HP) synthesis section, in particular to supply carbamate solution to the reaction zone, optionally via the HP condensation zone.

[0037] The high-pressure synthesis stage of the urea plant and process involves the use of CO 2 At least a portion of the feed is used as stripping gas to the HP stripper.

[0038] CO 2 The feed includes inert components, for example, from the produced CO 2 The upstream synthesis gas facility of the feed. Typically, the CO entering the HP synthesis section 2 The feed includes oxygen, for example, which is added to prevent corrosion in the urea synthesis section. Oxygen can also be added for CO upstream of the synthesis section. 2 H in the feed 2 The HP synthesis stage comprises one or more outlets for waste gases. The waste gases include inert components as well as uncondensed NH 3 and CO 2 The offgas from the synthesis stage is relatively rich in NH 3(e.g. N / C ratio of at least 2.2 or in the range of 2.3 to 3.0), and expanded to a pressure in the MP range and subjected to condensation in a second MP carbamate condensation section. The condensation is carried out, for example, in the presence of a carbamate recycle stream comprising water from the LP recovery section(s) included in the heat exchanger in the second MP carbamate condensation section. Preferably, the facility, in particular the HP synthesis section, does not comprise an HP scrubber. Preferably, the process does not involve contacting the synthesis section off-gas with an aqueous fluid stream at high pressure.

[0039] The condensation of the offgas from the HP synthesis stage at medium pressure offers the advantages of increased safety and reduced equipment costs compared to the use of an HP scrubber.

[0040] The second MP carbamate condensation section (e.g., MP scrubber) is operated, for example, with cooling water, and the temperature at the carbamate outlet is, for example, in the range of 80°C to 100°C. The second MP carbamate condensation section is operated, for example, at a pressure of 15 bar to 25 bar, preferably 20 bar to 25 bar. The carbamate solution from the second MP carbamate condensation section, for example, with a water content of 25 wt.% to 30 wt.%, is enriched in carbamate in the first MP carbamate condensation section. The first MP carbamate condensation section, for example, gives a carbamate solution with a water content at least 5 wt.% (percentage points) lower than that of the carbamate solution from the second MP carbamate condensation section. The carbamate solution from the first MP carbamate condensation section, for example, has a water content in the range of 15 wt.% to 20 wt.%. The first MP carbamate condensation section is operated, for example, at a temperature at least 10°C higher than that of the second MP carbamate condensation section, for example, at 110°C to 120°C. In this way, the carbamate solution in the second MP carbamate condensation stage can have a relatively high water content, thereby allowing a lower condensation temperature without the risk of carbamate crystallization. The lower temperature helps to reduce the discharge of uncondensed NH to the downstream (LP) absorber. 3 This may help to reduce energy consumption in the wastewater treatment (WWT) section and advantageously reduce recycle from the WWT. The first MP carbamate condensation section is operated, for example, at a pressure of 20 to 30 bar, preferably 22 to 27 bar, and preferably at a higher pressure than the second MP carbamate condensation section. The aqueous fluid from the LP absorber may be supplied to the WWT.

[0041] Advantageously, inerts from the HP synthesis section do not enter the first MP carbamate condensation section, thereby providing a higher condensation temperature for heat exchange which can be used, for example, to heat the urea solution for water evaporation.

[0042] The carbamate solution from the second MP carbamate condensation section is supplied to the first MP carbamate condensation section operated at a higher temperature. Thus, the water included in the carbamate solution from the LP recovery section is advantageously used to prevent carbamate crystallization in the three condensers in series. For example, in an exemplary embodiment of the process according to the invention, the carbamate solution is obtained from the LP carbamate condenser and has 30 wt.% H 2 O, and is supplied to a second MP carbamate condenser (e.g., a scrubber) to give a 26 wt.% H 2 O, which is then supplied to the first MP carbamate condenser, thereby giving a carbamate solution having advantageously 20 wt.% H 2 O to produce a carbamate solution with a lower water content, which is recycled to the HP synthesis.

[0043] Preferably, the uncondensed gases from the first MP carbamate condensation section are supplied to the second MP carbamate condensation section. In a preferred embodiment, the uncondensed gases are combined with the off-gases from the reactor and condensed in the second MP carbamate condensation section. Preferably, the second MP carbamate condensation section is operated at a lower pressure than the first MP carbamate condensation section, e.g., at least 1.0 bar lower pressure, e.g., 1.0 bar to 5 bar lower.

[0044] The non-condensed gases from the second MP carbamate condensation stage are supplied, for example, to an absorber operating, for example, at LP. Very advantageously, in a preferred embodiment, inert gases from the HP synthesis are not supplied to the second MP carbamate condenser, thereby reducing the condensable gases supplied to the absorber, and increasing the temperature in the heating zone to achieve a fixed total gas pressure in the second MP carbamate condenser.

[0045] Preferably, the uncondensed gas from the first MP carbamate condensation stage has a low H 2 content in order to avoid explosive mixtures, especially in the second MP carbamate condensation section. Low H 2 The content is supplied to the first MP carbamate condensation section by MP CO 2 Upstream H of feed 2 Advantageously, partial condensation in the first MP carbamate condensation section facilitates a simple apparatus, for example with only a single condenser in said section, and heat is transferred to the urea solution which is heated in a heating zone in heat exchange contact with said condenser, such as by turbulence at the downstream end of said condenser. For example, the condenser is provided as a shell and tube heat exchanger, with the urea solution to be heated in the tubes and the gas to be condensed in the shell side space.

[0046] Advantageously, the plant preferably does not include an ammonia condenser and preferably does not include a recycle flow line for the ammonia fluid.

[0047] Preferably, the facility further comprises a heating zone for heating the urea solution for water and ammonia removal. Preferably, the facility comprises a fluid flow line for the urea solution from the LP dissociator, optionally via an atmospheric flash tank, to the heating zone. Preferably, the heating zone is in heat exchange contact with at least a portion of the first MP carbamate condensation section; the LP dissociator is typically a LP dissociator of the LP recovery section. Preferably, the heating zone is used to heat the urea solution from the LP recovery section, in particular from the LP dissociator included in the LP recovery section, to facilitate evaporation of water from the urea solution, in particular for the preparation of a urea melt. Preferably, the first MP carbamate condensation section is at least partially provided in a shell and tube heat exchanger, for example, as described above, wherein the gas to be condensed is in the shell (shell side space) and the urea solution to be heated is in the tubes.

[0048] The heated urea solution from the heating zone (e.g., pre-evaporator) is preferably subjected to gas / fluid separation to obtain a urea solution further comprising NH 3 The concentrated urea solution may have, for example, a urea content of 75 wt.% to 85 wt.%. The urea solution received at the inlet of the heating zone has, for example, a urea content of 60 wt.% to 75 wt.% and includes, for example, about 0.7 wt.% of NH 3 Preferably, the urea concentration in the heating zone increases by 5 wt.% to 10 wt.% (percentage points). In the first MP carbamate condensation section, a relatively high urea concentration can be achieved by means of a relatively high temperature, such as 110°C.

[0049] The concentrated urea solution is optionally supplied to, for example, a vacuum evaporation section via a storage tank to give a urea melt. The urea melt is solidified, for example, in a finishing section (such as a granulator or a granulation tower). The urea melt can also be supplied, for example, to a melamine facility. Other uses are also possible.

[0050] The heating zone (pre-evaporator) is for example operated at a pressure of less than 1.0 bar absolute, for example 0.3 to 0.8 bar absolute, such as 0.4 to 0.6 bar absolute.

[0051] The heated urea solution advantageously has a low NH 3 The content is, for example, less than 0.10 wt.%, such as about 0.05 wt.%. Low NH 3 The content is desirable for storing the solution in a urea storage tank.

[0052] The heated urea solution can accordingly be used, for example, to 3 Diesel exhaust fluid (DEF) is produced with a urea content of, for example, 32.5 wt.% by adding water to obtain a desired urea concentration of, for example, 32.5 wt.%. Water of sufficiently high purity for DEF production may be added, for example, as a clean process condensate from a WWT section, as steam condensate or as demineralized water. DEF is typically an aqueous urea solution of 32.5 wt.% urea and 67.5 wt.% water, and preferably, when based on 32.5 wt.% urea, NH 3 The basicity is less than 0.2 wt.%, i.e., 32.5 wt.% urea when the basicity is converted based on the addition or removal of water as required. Advantageously, no steam stripping is required to achieve low NH 3 content.

[0053] The term "pre-evaporator" as used herein does not mean that an evaporation section must be present in the facility. In some embodiments, the facility comprises a pre-evaporator but does not comprise an evaporation section for producing a urea melt.

[0054] The present invention also relates to a method for 2 A urea production process carried out in a stripping urea facility, preferably in a urea production facility of the present invention. The urea production process comprises, for example, supplying a first portion of the urea synthesis solution from the reaction zone to an HP stripper and using CO 2 The urea solution is stripped in the HP stripper as stripping gas to give a stripped urea solution, and the stripped urea solution is supplied to the MP treatment unit to give a first MP gas stream and a treated urea solution, and a second part of the urea synthesis solution from the reaction zone is subjected to carbamate decomposition by heating in an MP dissociator to give a second MP gas stream and an MP urea solution, and a third MP gas stream from the HP synthesis section is provided by decompression. The process involves combining and condensing two gas streams selected from the group consisting of the first, second and third MP gas streams in a first MP carbamate condensation section. Preferably, the process involves combining and condensing the first and second gas streams in the first MP carbamate condensation section, and subjecting the third gas stream to condensation in a second MP carbamate condensation section.

[0055] Preferably, the first MP carbamate condensation section operates at a higher pressure, for example 1 to 10 bar higher, more preferably 1 to 5 bar higher, even more preferably 1 to 3 bar higher than the operating pressure of the second MP carbamate condensation section.

[0056] Preferably, the first MP carbamate condensation section is operated at a pressure of 15 to 35 bar. Preferably, the MP treatment unit, preferably the adiabatic flasher, is operated at a pressure of 15 to 35 bar. Preferably, the adiabatic flasher is operated at the same pressure as the first MP carbamate condensation section. Preferably, the second MP carbamate condensation section is operated at a pressure of 15 to 35 bar.

[0057] Preferably, the HP stripper is operated with a stripping efficiency α in the range of 0.65 to 0.80 (e.g., 0.70 to 0.75). A relatively low stripping efficiency advantageously provides lower energy consumption by the HP stripper, e.g., reduced steam consumption. Additionally, the HP stripper and the HP carbamate condenser can be relatively small, which can facilitate the modification of existing urea facilities to increase capacity with the desired limited improvements to the HP synthesis section. The MP processing unit, particularly the preferred adiabatic flasher, even with a relatively low stripping efficiency, can also contribute to low water recycle with carbamate recycle.

[0058] Preferably, 30 vol.% to 70 vol.% of the urea synthesis solution is supplied from the reaction zone to the MP dissociator, ie bypassing the HP stripper.Thereby, the MP dissociator can significantly unload the HP stripper.

[0059] There is also provided a method of retrofitting an existing urea production facility as described above.

[0060] Preferably, the method involves arranging the first MP carbamate condensation section to receive a first MP gas stream from an MP treatment unit and a second MP gas stream from an MP dissociator. Preferably, the method involves providing a gas flow line from the MP treatment unit to the first MP carbamate condensation section and a gas flow line from the MP dissociator to the first MP carbamate condensation section. Preferably, the method involves providing a gas flow line from a pressure reducing element to the second MP carbamate condensation section for supplying a third MP gas stream. The method generally provides an increase in the capacity of a urea plant in an advantageous manner without requiring or making few changes to the HP synthesis section.

[0061] In an interesting embodiment, the existing facility includes an MP treatment unit, in particular an MP adiabatic flasher receiving a stripped urea solution, and a first MP carbamate condenser. The first MP carbamate condenser receives the synthesis section offgas from the reactor and / or the HP carbamate condenser and gases from the MP treatment unit in the existing facility. For example, the first MP carbamate condenser is in heat exchange contact with a heating zone for urea solution in the existing facility, in particular with a pre-evaporator. A preferred inventive method for improving this existing facility involves adding an MP dissociator that receives a portion of the urea synthesis solution from the reactor to the facility, and adding a second MP carbamate condenser and a gas flow line stream for supplying a third MP gas (e.g., reactor offgas) to the second MP carbamate condenser and a gas flow line for supplying a gas flow from the MP dissociator to the first MP carbamate condenser. In this way, advantageously, the inert gas in the reactor offgas no longer negatively affects (reduces) the temperature in the pre-evaporator. In addition, various advantages as discussed in conjunction with the inventive facility and process are obtained in the improved facility. Very advantageously, an increase in the capacity of a urea plant can be obtained by means of an MP decomposer without adding or modifying HP equipment. The preferred embodiments described above for a urea production plant also apply to a modified urea plant, for example a fluid flow line for carbamate solution from an added second MP carbamate condenser to a first MP carbamate condenser. Preferably, the existing plant does not comprise an HP scrubber, and preferably, in the existing plant, the synthesis section offgas is supplied to the first MP carbamate condenser directly from the reactor and / or the HP carbamate condenser via a pressure reducing element such as, for example, a valve (e.g., a control valve).

[0062] Figure 1 An exemplary urea production process and facility according to an embodiment of the present invention is shown. The facility comprises a high pressure (HP) synthesis section (HPSS) comprising an HP stripper (HPS), a 3 and CO 2 A reaction zone (HPR) for forming urea and a condensation zone (HPCC). The reaction zone (HPR) comprises a reactor, for example a vertical urea reactor, having a fluid outlet for a urea synthesis solution (1) and a separate gas outlet for inerts (14). A first portion (1a) of the urea synthesis solution is supplied to a reactor using CO 2HP stripper (HPS) as stripping gas. The stripped urea solution (2) from the HP stripper (HPS) is supplied to the MP treatment unit (MPTU). The second part (1b) of the urea synthesis solution is supplied to the MP decomposer (MPD), which is a heat exchanger for heating the urea solution. Thus, a single reactor is connected to supply urea synthesis solution to both the HP stripper and the MP decomposer. 3 and CO 2 The gases (4) from the MP treatment unit (MPTU) and the gases (5) from the MP dissociator (MPD) are both condensed in a first MP carbamate condensation section (MPCC-1) which is in heat exchange contact with a pre-evaporation unit (PEV) for heating the urea solution (11a) to give a heated urea solution (11b). The gases (3) from the HP stripper (HPS) are condensed in an HP carbamate condenser in a condensation zone (HPCC) which also receives NH 3 The urea solution (7) from the MP treatment unit (MPTU) is supplied to a LP decomposer (LPD), which is preferably a shell and tube heat exchanger for heating the urea solution (7) in order to decompose the ammonium carbamate into NH 3 and CO 2 The urea solution (8) from the MP decomposer (MPD) is also supplied to the MP stripper (MPS) where the urea solution is reacted with the MP CO 2 feed contact. The urea solution (16) from the MP stripping tower is, for example, supplied to the LP recovery section, for example, to the LP dissociator (LPD) (not shown). The gas (14) from the HP synthesis section (HPSS), for example, the gas (14) from the reactor in the reaction zone (HPR) and / or the gas (14a) from the HP carbamate condenser is expanded to the MP in a pressure reducing element (such as, for example, one or more valves (V1)) and supplied to the second MP carbamate condensation section (MPCC-2), which also receives the non-condensable gas (10) from the first MP carbamate condensation section (MPCC-1). The non-condensable gas (18) from the second MP carbamate condensation section (MPCC-2) is, for example, supplied to an absorber operating under LP. The gas (12) obtained from the LP dissociator (LPD) is supplied to the LP carbamate condenser (LPCC), which also directly or indirectly receives CO 2part of the feed. The LP carbamate solution (13) with a relatively high water content from the LP carbamate condenser (LPCC) is supplied to the second MP carbamate condensation section (MPCC-2), where it helps to avoid carbamate crystallization. The MP carbamate solution (15) from the second MP carbamate condensation section (MPCC-2) is supplied to the first MP carbamate condensation section (MPCC-1) operated at a higher temperature, where the solution is advantageously enriched in carbamate. The resulting carbamate solution (9) is recycled to the HP synthesis section (HPSS), for example, to the HP condensation zone (HPCC). The urea solution (11) obtained from the LP dissociator (LPD) optionally still contains water after a further expansion step and is heated as a urea solution (11a) at an advantageously high temperature, for example in a pre-evaporator (PEV) using the heat released in the first MP carbamate condensation section (MPCC-1), and undergoes a gas / fluid separation to give water vapor and a concentrated urea solution. From the MP CO 2 The gas (17) (including MP CO) from the stripping tower (MPS) 2 A portion of the feed) is supplied to the first MP carbamate condensation section (MPCC-1) to facilitate a proper N / C ratio in the condensation section.

[0063] The preference for the facility also applies to the process and the renovation method (a method of improving an existing facility). The process is preferably carried out in the facility described. The renovation method is preferably given the facility described.

[0064] In the present application, for process streams (i.e. not for steam lines), high pressure (HP) is above 100 bar, for example 120 to 300 bar, typically 150 to 200 bar. Medium pressure (MP) is for example 10 to 70 bar (including intermediate pressures of 30 to 70 bar), in particular 10 to 40 bar, and low pressure (LP) is for example 1.0 to 10 bar, in particular 1.0 to 8 bar, for example 1.5 to 5 bar. All pressures are given in absolute bar.

[0065] The N / C ratio as used herein for urea solutions and carbamate streams reflects the composition of the so-called initial mixture prior to urea production, consisting only of NH 3 , CO 2 and H 2 O composition and is a molar ratio. The N / C ratio of the gas stream indicates NH 3 With CO 2 molar ratio.

[0066] The term 'carbamate' as used herein refers to ammonium carbamate, as the term is used in the urea plant art.

[0067] The terms 'typical' and 'in particular' are used to indicate features that may be used in some embodiments but are not mandatory. Preferred features are also not mandatory.

[0068] The terms 'fluid flow line' and 'fluid communication' refer to a flow line (e.g., a pipe or conduit) that allows a fluid to pass between two units, optionally through a plurality of intermediate units. Fluid communication does not involve gas phase transmission, and thus two units connected by an evaporator, a flow line for vapor, and a condenser are not in fluid communication, although they are in fluid communication (covering both gas phase transmission and fluid transmission). For example, if the outlet for fluid of a first unit is connected to the inlet of a condenser, and the outlet for fluid of the condenser is connected to the inlet of a second unit, then the first unit is in fluid communication with the second unit. For example, a pump may be present in a fluid flow line. 'Gas flow line' is a flow line for gas phase transmission of gas between two units. Gas phase transmission does not involve the transmission of a material as a fluid.

[0069] The 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 fluid outlet of the stripper (HP stripper). This definition is equivalent to the NH based on the outlet of the stripper. 3 Definition of conversion rate. Therefore, α = (2*wt.% urea / 60) / [(2*wt.% urea / 60)+(wt.% NH 3 / 17)], measured at the fluid outlet of the stripping tower, where wt.% NH 3 All ammonia species are included, including ammonium carbamate. The skilled person will understand that 'stripping efficiency' refers to the purity of the urea at the stripper fluid outlet, not the energy efficiency of the stripper.

[0070] Condensation in the carbamate condenser is the so-called carbamate condensation, which involves NH 3 and CO 2 reacts to form liquid ammonium carbamate, making the gaseous NH 3 and CO 2 The decomposition of carbamate is the decomposition of carbamate into NH 3 and CO 2 dissociation reaction.

[0071] As discussed above, the present invention relates to a urea production facility and process that utilizes high pressure CO 2a stripping column, a downstream medium-pressure treatment unit and a medium-pressure dissociator receiving the urea synthesis solution from the reactor, wherein the gases from the treatment unit and the dissociator are condensed in a first condenser and the offgases from the synthesis section are separately condensed in a second condenser. A retrofit method is also described.

[0072] Examples

[0073] The invention will now be further illustrated by the following non-limiting example. This example does not limit the invention and does not limit the claims.

[0074] Example 1

[0075] In accordance with Figure 1 In the process of , the second MP carbamate condenser was operated at 93 ° C and 21 bar and gave a NH 3 、37wt.%CO 2 of carbamate solution (both free and as for NH 3 and CO 2 urethane) and 26 wt.% H 2 O, which are supplied to the first MP carbamate condenser. The first MP carbamate condenser is operated at 114°C and 24 bar and produces a 38 wt.% NH 3 、42wt.%CO 2 and 19wt.% H 2 O carbamate solution (each content is free and used as a 3 and CO 2 carbamates), which can be supplied to the HP synthesis with an advantageously low water content.

Claims

1. A urea production facility comprising a high-pressure synthesis section, the high-pressure synthesis section comprising a high-pressure stripping column, a reaction zone for forming urea from NH3 and CO2, and a condensation zone, wherein the high-pressure stripping column has an inlet for feeding CO2 as stripping gas, the facility further comprising a medium-pressure treatment unit, a medium-pressure dissociator, a first medium-pressure carbamate condensation section and a second medium-pressure carbamate condensation section, a first flow line (1a) for urea solution from the reaction zone to the high-pressure stripping column and a second flow line (1b) for urea solution from the reaction zone to the medium-pressure dissociator, wherein the facility comprises a fluid flow line for a stripped urea solution (2) from the high-pressure stripping column to an inlet of the medium-pressure treatment unit for the stripped urea solution (2), wherein the medium-pressure treatment unit has an inlet for the stripped urea solution (2), a gas outlet for a first medium-pressure gas stream (4) and a fluid outlet for a treated urea solution (7), wherein the medium-pressure dissociator has a gas outlet for a second medium-pressure gas stream (5), and wherein the high-pressure synthesis section has a gas outlet for a third medium-pressure gas stream (14) and a pressure reducing element, and wherein two gas streams selected from the group consisting of the first, second and third medium-pressure gas streams are combined and condensed in the first medium-pressure carbamate condensation section, wherein the first medium-pressure carbamate condensation section is arranged to receive the first medium-pressure gas stream (4) from the medium-pressure treatment unit and the second medium-pressure gas stream (5) from the medium-pressure dissociator, and wherein the second medium-pressure carbamate condensation section receives the third medium-pressure gas stream (14), The facility further comprises: - a fluid flow line (7) for urea solution from the medium-pressure treatment unit to the low-pressure decoupler; - a gas flow line (12) from the low-pressure dissociator to a low-pressure carbamate condenser; - a fluid flow line (13) for carbamate solution from said low-pressure carbamate condenser to said second medium-pressure carbamate condensation section; - a fluid flow line (15) for carbamate solution from said second medium-pressure carbamate condensation section to said first medium-pressure carbamate condensation section; and - a fluid flow line (9) for carbamate solution from said first medium-pressure carbamate condensation section to said high-pressure synthesis section, And wherein the medium pressure processing unit is a flash evaporator.

2. The urea production facility according to claim 1, wherein the second medium-pressure carbamate condensation section comprises a condenser, a scrubber and / or an absorber.

3. The urea production facility according to claim 1 or 2, further comprising: a heating zone for heating urea solution for water removal, wherein the heating zone is in heat exchange contact with at least a portion of the first medium-pressure carbamate condensation section.

4. A urea production facility according to claim 3, wherein the urea production facility further comprises a fluid flow line (11a) for urea solution from the low-pressure dissociator to the heating zone, and wherein the first medium-pressure carbamate condensation stage is at least partially provided in a shell and tube heat exchanger, wherein the gas to be condensed is in the shell and the urea solution (11a) to be heated is in the tubes.

5. The urea production facility according to claim 1 or 2, further comprising: A medium pressure CO2 stripper and a fluid flow line (8) for urea solution from the medium pressure dissociator to the medium pressure CO2 stripper.

6. The urea production facility according to claim 5, further comprising: A gas flow line (17) from the medium-pressure CO2 stripping column to the first medium-pressure carbamate condensation section.

7. Urea production facility according to claim 1 or 2, wherein the second medium-pressure condensation stage comprises a shell and tube heat exchanger and a downstream gas / fluid separator.

8. The urea production facility according to claim 7, wherein the second medium-pressure condensation section further comprises an absorber receiving the gas from the separator.

9. Urea production plant according to claim 1 or 2, wherein the gas (10) from the first medium-pressure carbamate condensation section is also supplied to the second medium-pressure condensation section; And wherein the gas (18) from the second medium-pressure condensation stage is supplied to an absorber.

10. Urea production facility according to claim 9, wherein the absorber is a low-pressure absorber.

11. A urea production process carried out in a urea production facility according to any one of the preceding claims, wherein the process comprises: a first portion (1a) of the urea synthesis solution from the reaction zone is supplied to the high-pressure stripper, and the urea solution is stripped in the stripper using CO2 as stripping gas to give a stripped urea solution (2), and the stripped urea solution (2) is supplied to the medium-pressure treatment unit to give a first medium-pressure gas stream (4) and a treated urea solution (7), and a second portion (1b) of the urea synthesis solution from the reaction zone is subjected to carbamate decomposition by heating in the medium-pressure dissociator to give a second medium-pressure gas stream (5) and a medium-pressure urea solution (8), and a third medium-pressure gas stream (14) from the high-pressure synthesis section is provided by reducing pressure, wherein the process involves combining and condensing the first and second gas streams (4, 5) in the first medium-pressure carbamate condensation stage and subjecting the third gas stream (14) to condensation in a second medium-pressure carbamate condensation stage, and The first medium-pressure carbamate condensation section is operated at a higher pressure than the second medium-pressure carbamate condensation section.

12. The urea production process according to claim 11, wherein the first medium-pressure carbamate condensation section is operated at a pressure 1 to 10 bar higher than the operating pressure of the second medium-pressure carbamate condensation section.

13. The urea production process according to claim 11, - wherein the first medium-pressure carbamate condensation section is operated at a pressure of 15 to 35 bar; - wherein the medium pressure treatment unit is operated at a pressure of 15 to 35 bar; - and wherein the second medium-pressure carbamate condensation section is operated at a pressure of 15 to 35 bar.

14. Urea production process according to claim 13, wherein the medium-pressure treatment unit is an adiabatic flash vessel operated at the same pressure as the first medium-pressure carbamate condensation section or at a higher pressure.

15. The urea production process according to claim 11, wherein the high pressure stripper operates with a stripping efficiency in the range of 0.65 to 0.

80.

16. A method for improving an existing urea production facility, the existing urea production facility comprising a high pressure synthesis section, the high pressure synthesis section comprising: a high-pressure stripping column, a reaction zone for forming urea from NH3 and CO2, and a condensation zone, wherein the high-pressure stripping column has an inlet for CO2 feed as stripping gas, and the high-pressure synthesis section has a gas outlet, the facility comprising a first flow line (1a) for urea solution from the reaction zone to the high-pressure stripping column, The method includes: adding the following units and connections if they do not already exist in the facility: a medium-pressure treatment unit having an inlet for the stripped urea solution (2), a gas outlet for the first medium-pressure gas stream (4) and a fluid outlet for the treated urea solution (7), a medium-pressure dissociator having a gas outlet for a second medium-pressure gas stream (5), - a first medium-pressure carbamate condensation section and a second medium-pressure carbamate condensation section, - and a second flow line (1b) for urea solution from the reaction zone to the medium-pressure dissociator, - a pressure reducing element for the gas coming from said gas outlet of said high-pressure synthesis section giving a third medium-pressure gas stream (14), a fluid flow line for the stripped urea solution (2) from the high-pressure stripping column to the inlet of the medium-pressure treatment unit for the stripped urea solution (2), - a fluid flow line (9) for carbamate solution from said first medium-pressure carbamate condensation section to said high-pressure synthesis section, The method further comprises configuring the facility so that the first and the second intermediate-pressure gas streams (4, 5) are combined and condensed in a first intermediate-pressure carbamate condensation section and the third intermediate-pressure gas stream (14) is condensed separately in a second intermediate-pressure carbamate condensation section, The first medium-pressure carbamate condensation section is arranged to receive the first medium-pressure gas flow (4) from the medium-pressure processing unit and the second medium-pressure gas flow (5) from the medium-pressure dissociator, and the second medium-pressure carbamate condensation section is arranged to receive the third medium-pressure gas flow (14) from the high-pressure synthesis section.

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