Process and plant for producing urea

Abstract

The invention relates to a process and plant for producing urea from ammonia and carbon dioxide and can be used in the chemical industry and in the production of fertilizers. Proposed is a process for producing urea which includes: feeding ammonia and a first portion of carbon dioxide into a reactor to produce a first reaction mixture; feeding said first reaction mixture and a second portion of carbon dioxide into a stripper; feeding a gas phase from the reactor and a gas phase from the stripper into a condenser to produce a gas-liquid mixture; feeding said gas-liquid mixture and a carbamate solution into a pre-reactor to produce a second reaction mixture; and ejecting said second reaction mixture with the ammonia that is fed into the reactor. Also proposed is a plant for producing urea. The technical result consists in improving the efficiency of the urea production process, increasing the degree of carbon dioxide conversion, providing for thermal balance in the synthesis reactor, and allowing easier and more convenient placement of high-pressure equipment.

Description

[0001] METHOD AND APPARATUS FOR PRODUCING UREA

[0002] Field of technology

[0003] The group of inventions relates to a method and installations for producing urea from ammonia and carbon dioxide and can be used in the chemical industry and in the production of fertilizers.

[0004] Prior art

[0005] It is known that the only method used to obtain urea in industry worldwide is a two-stage synthesis from ammonia and carbon dioxide, under high pressure and temperature. High pressure is considered to be 12-25 MPa, high temperature is considered to be 170-250 °C. The synthesis of urea from ammonia and carbon dioxide consists of the first stage of ammonium carbamate formation and the second stage of ammonium carbamate dehydration. The second stage takes place almost entirely in the synthesis reactor and is slow, endothermic and not completely completed. At the same time, how completely the reaction will proceed in the second stage depends on its implementation conditions, namely, the chemical composition of the solution, pressure, temperature and time of implementation, which is implemented in various versions by the technologies of developers, for example, Stamicarbon AK-70 Stamicarbon AK-80, URECON®2006, TEC, Tecnimont, Snamprogetti.Creating and maintaining optimal conditions in the second stage greatly affects the quality of the target product due to the possible reduction in productivity.

[0006] A device for producing urea is known, comprising a urea synthesis reactor, a device with heat supply from an external source for distilling a high-pressure urea synthesis solution, a device with heat supply for distilling a medium-pressure urea synthesis solution, a device with heat supply for distilling a low-pressure urea synthesis solution, a device for evaporating an aqueous urea solution obtained in a low-pressure distillation device, devices for condensation-absorption during cooling of high, medium and low pressure distillation gases, means for feeding ammonia and carbon dioxide into a urea synthesis reactor, a urea synthesis solution from the synthesis reactor to a high-pressure distillation device, a urea synthesis solution from a high-pressure distillation device to a medium-pressure distillation device,a urea synthesis solution from a medium-pressure distillation device to a low-pressure distillation device, an aqueous urea solution from a low-pressure distillation device to an evaporation device, distillation gases from a high-pressure distillation device to a high-pressure distillation gas condensation-absorption device in an amount of 80-95% of the total amount obtained in the high-pressure distillation device and into a urea synthesis reactor in an amount of 5-20% of the total amount obtained in the high-pressure distillation device, distillation gases from a medium-pressure distillation device to a medium-pressure distillation gas condensation-absorption device, distillation gases from a low-pressure distillation device to a low-pressure distillation gas condensation-absorption device, an aqueous solution of U AC from a low-pressure distillation gas condensation-absorption device,into a device for condensation-absorption of medium-pressure distillation gases, an aqueous solution of UAS from a device for condensation-absorption of medium-pressure distillation gases, into a device for condensation-absorption of high-pressure distillation gases, and from a device for condensation-absorption of high-pressure distillation gases into a synthesis reactor, wherein the installation contains means for feeding fresh carbon dioxide into the film heat exchanger in an amount of 90% percent of the total amount introduced into the process (EA035936, C07C 273 / 04, 2013).

[0007] In this method for producing urea, implemented in this installation, the initial carbon dioxide is fed into the distillation zone of the urea synthesis solution with heat supplied at the high-pressure stage, which is carried out in a film heat exchanger, which is a stripper-distiller, in an amount of 90% of its total amount introduced into the process and into the urea synthesis reactor in an amount of 10% of its total amount with the simultaneous supply of distillation gases removed from the stripper-distiller into the synthesis reactor in an amount of 5-20% and to the stage of condensation-absorption of high-pressure distillation gases, which is carried out in a carbamate condenser, in an amount of 80-95%. Such a joint introduction of carbon dioxide and distillation gas flows into the synthesis reactor is carried out for the purpose of regulating the temperature in this synthesis reactor.

[0008] The disadvantage of this method is the supply of a portion of the distillation gases from the stripper-distiller to the synthesis reactor, which reduces the amount of heat that could be utilized in the carbamate condenser, and also increases the amount of gas phase supplied to the synthesis reactor in the form of ammonia, which leads to a decrease in the effective volume in the lower part of the reactor, since this part of the volume is used for condensation and dissolution of ammonia contained in the distillation gases. As a result, the degree of conversion decreases and an increase in the volume of the synthesis reactor is required.

[0009] A method for synthesizing urea is known (WO 2023145821 A1, published 03.08.2023), in which ammonia is fed into a high-pressure ejector and into a synthesis reactor. In the urea synthesis reactor, ammonia reacts with carbon dioxide at the temperature and pressure of urea synthesis to form a solution containing unreacted ammonia, carbon dioxide and water. In this case, unreacted ammonia and unreacted carbon dioxide are brought into contact with each other by heating. The urea synthesis solution containing unreacted ammonia and unreacted carbon dioxide is processed to obtain urea. The gas mixture separated from the desorber is introduced into the lower part of the condenser. Thereby condensing and circulating the resulting condensate into the urea synthesis column.In this case, steel of a special composition is used for the urea synthesis column, stripper and condenser, and the oxygen concentration in the synthesis reactor should be 100-2000 ppm relative to the carbon dioxide flow, and the N / C molar ratio at the level of 3.5-4.0.

[0010] The disadvantage of this method is the use of a desorption apparatus after the synthesis reactor without feeding a stripping agent. This leads to increased concentrations of unreacted ammonia and carbon dioxide in the urea solution at the outlet of the desorber. The consequence of this is the need to install additional equipment to extract these components from the urea solution and additional energy costs for this process.

[0011] The closest to the claimed method (prototype) is the method and device for the production of urea (RU 2788626 C1, published 23.01.2023), including a synthesis stage, in which urea is synthesized from ammonia and carbon dioxide to obtain a solution for the synthesis of urea; a decomposition stage, in which, by heating the solution for the synthesis of urea obtained in the synthesis stage, the ammonium carbamate is decomposed and a gas mixture containing ammonia and carbon dioxide is separated from the solution for the synthesis of urea to obtain a solution for the synthesis of urea with a higher concentration of urea compared to the solution for the synthesis obtained in the synthesis stage;a condensation stage in which, using an immersed condenser comprising a shell-and-tube heat exchange structure comprising a U-shaped tube, at least a portion of the gas mixture obtained in the decomposition stage is absorbed and condensed in an absorbent medium in the intertube space, and steam is generated in the tube space using heat released during condensation; a recirculation stage in which at least a portion of the liquid is recirculated to the synthesis stage, wherein said liquid is obtained in the intertube space in the condensation stage; and a water supply stage in which water is supplied to the tube space of the immersed condenser at a mass flow rate that is three or more times greater than the rate of formation by mass of the steam generated in the immersed condenser.

[0012] In the prototype, the urea synthesis reaction also occurs at the condensation stage, and the condensation stage and the synthesis stage can be carried out in one high-pressure vessel. In other words, one high-pressure vessel can be used, in which the immersion condenser and the synthesis reactor are combined.

[0013] The disadvantage of the prototype is the complexity and high cost of the design of the immersion condenser, which has the functions of a built-in heat exchanger, as well as the need to install a heavy high-pressure apparatus at a high altitude.

[0014] Disclosure of invention

[0015] The objective of the claimed invention is to create an effective, simple, environmentally friendly and safe method and installation for producing urea.

[0016] The technical result of the claimed group of inventions consists in increasing the efficiency of the process of obtaining urea by combining the following factors:

[0017] - increasing the degree of carbon dioxide conversion;

[0018] - ensuring the thermal balance of the synthesis reactor;

[0019] - simplicity and convenience of placement of high-pressure equipment.

[0020] The technical result is achieved in that the method for producing urea includes the following stages: a) feeding ammonia and a first portion of carbon dioxide into a reactor to form a first reaction mixture and a gas phase; b) feeding the first reaction mixture from stage a) and a second portion of carbon dioxide into a stripper to form a liquid phase and a gas phase; c) feeding the gas phase from stage a) and the gas phase from stage b) into a condenser to form a gas-liquid mixture; d) feeding the gas-liquid mixture from stage c) and a carbamate solution into a prereactor to form a second reaction mixture and a gas phase; e) ejecting the second reaction mixture from stage d) with ammonia fed to stage a).

[0021] The following terms are used to describe the present invention.

[0022] The liquid phase is a substance in a liquid state. In the method for producing urea, the liquid phase is, for example, a urea solution and / or a carbamate solution.

[0023] Urea solution is a liquid mixture containing urea. Urea solution typically contains urea ammonia, ammonium carbamate and / or water.

[0024] Carbamate solution is a liquid mixture containing ammonium carbamate. Typically, carbamate solution contains carbamate, ammonia and / or water.

[0025] The gas phase is the substance in the gaseous state. In the process for producing urea, the gas phase typically contains ammonia, carbon dioxide and / or water.

[0026] A gas-liquid mixture is a mixture of two phases: liquid and gas.

[0027] The first reaction mixture is the liquid phase leaving the reactor.

[0028] The second reaction mixture is the liquid phase leaving the prereactor.

[0029] The pre-reactor is a preliminary reactor.

[0030] Any known prior art corresponding devices may be used as the reactor, stripper, condenser and other devices, and any known prior art modes for producing urea may also be used, with the best modes that will allow the most efficient use of the advantages of the present invention being disclosed below.

[0031] The pre-reactor regulates the thermal load of the synthesis reactor, ensuring the required temperature regime in the synthesis reactor to achieve maximum efficiency of the urea synthesis process.

[0032] In the pre-reactor, urea is partially formed, which reduces the load on the synthesis reactor and allows the use of a smaller reactor that can be installed close to the ground, thus reducing the costs of building structures.

[0033] The heat balance of the synthesis reactor is ensured by regulating the pressure of the steam generated in the carbamate condenser. This changes the heat released in the prereactor during the condensation of gases remaining in the gas-liquid flow after the carbamate condenser and, accordingly, the heat of the flow coming from the prereactor to the synthesis reactor.

[0034] The above method allows the heaviest and most dangerous equipment, namely the urea synthesis reactor and carbamate condenser, to be placed on or near the ground, which reduces the cost of building structures. This layout of the plant simplifies its maintenance and increases the safety of the personnel servicing the plant.

[0035] In a preferred embodiment, the ratio, expressed as a volume percentage, of the second portion of carbon dioxide to the first portion of carbon dioxide is adjusted within the range of 70:30 to 89:11.

[0036] Due to the fact that the gas phase in the amount of 70-89%, containing inert gases, does not enter the synthesis reactor, but is sent to the stripper, an additional increase in the degree of conversion of carbon dioxide into urea is ensured, since the presence of inert gases reduces the degree of conversion of carbon dioxide.

[0037] In a preferred embodiment, the carbamate solution in step d) is a carbamate solution obtained by subsequent processing of the liquid phase from step b), withdrawn from the stripper, and having a pressure of 14.0-16.0 MPa and a temperature of 180-210 °C.

[0038] In a preferred embodiment, at stage a) the reactor is maintained at a pressure of 14.0-16.0 MPa and a temperature of 170-190 °C.

[0039] In a preferred embodiment, at stage b) a pressure of 14.0-16.0 MPa and a temperature of 180-210 °C are maintained in the stripper tube space, while a temperature of 175-190 °C is maintained in the lower part of the stripper, and steam with a pressure of 1.8-2.5 MPa is supplied to the intertube space of the stripper.

[0040] In a preferred embodiment, at stage c), the pressure in the condenser is maintained at 14.0-16.0 MPa and the temperature at 160-170 °C.

[0041] In a preferred embodiment, at stage d) the pressure in the pre-reactor is maintained at 14.0-14.5 MPa.

[0042] The claimed method may use any conditions and operating parameters of the process flow diagram for producing urea known from the prior art, however, the above conditions and parameters make it possible to use the advantages of the present invention as effectively as possible.

[0043] In a preferred embodiment, in step d), the gas-liquid mixture from step c) is fed into the lower part of the pre-reactor, so that at least part of the said gas-liquid mixture passes through the sectioning trays in the lower part of the pre-reactor in the bottom-up direction, while at least part of the carbamate solution is fed into the pre-reactor to irrigate the packing and / or tray in the upper part of the pre-reactor.

[0044] This allows to further increase the efficiency of the prereactor and reduce the load on the synthesis reactor. The sectioning plates can be any known from the state of the art, for example, they can be partitions made of sheet steel and containing holes for the medium to pass through them. Their main function is to divide the lower part of the prereactor into sections while maintaining the possibility of the gas-liquid mixture passing through them in the direction from bottom to top.

[0045] The packing and / or trays in the upper part of the pre-reactor may be any packing and / or trays known from the prior art, for example, these may be partitions made of sheet steel and containing openings for the passage of the medium through them and / or this may be a loose packing of steel rings. Their main function is to ensure effective contact of the gas and liquid flow and effective heat and mass exchange between them. The purpose of installing the packing and / or trays is to create a developed (large) contact surface of the gas and liquid phases, which ensures intensive heat and mass exchange between the phases.

[0046] The sectional trays allow dividing the lower part of the prereactor into several vertical sections, in each of which further condensation of the gas phase contained in the gas-liquid flow from the condenser occurs, and the packing and / or tray in the upper part of the prereactor allows for intensive interaction between the gas phase coming from the middle part of the prereactor and the carbamate solution supplied to the upper part of the prereactor. This ensures the required temperature of the reaction mixture at the outlet from the middle part of the prereactor and the required volume of the gas phase at the outlet from the upper part of the prereactor. Also, due to the use of the prereactor, the amount of formed urea increases, which additionally reduces the load on the synthesis reactor and allows for the use of a smaller reactor, which can be installed close to the ground, thus reducing the costs of building structures.

[0047] The technical result is also achieved by the fact that for obtaining urea, an installation is used, which includes: a reactor, configured with the possibility of feeding ammonia and a first portion of carbon dioxide into it, as well as removing the reaction mixture and the gas phase; a stripper, configured with the possibility of feeding the reaction mixture from the reactor and a second portion of carbon dioxide into it, as well as removing the liquid phase and the gas phase; a condenser, configured with the possibility of feeding the gas phase from the reactor and the gas phase from the stripper into it, and removing the gas-liquid mixture; a prereactor, configured with the possibility of feeding the gas-liquid mixture from the condenser and the carbamate solution into it, as well as removing the reaction mixture and the gas phase; an ejector for mixing the reaction mixture from the prereactor with the ammonia fed into the reactor.

[0048] In a preferred embodiment, the pre-reactor is a vertical column apparatus comprising: sectional trays in the lower part of the pre-reactor, at least one layer of packing and / or one tray in the upper part of the pre-reactor, inlet means designed with the possibility of feeding at least part of the gas-liquid mixture from the condenser through the sectional trays of the pre-reactor in the bottom-up direction, and feeding at least part of the carbamate solution for irrigating the packing and / or tray in the upper part of the pre-reactor, means for removing the liquid phase from the middle part of the pre-reactor, means for removing the gas phase from the upper part of the pre-reactor.

[0049] The placement of the liquid phase removal means in the middle part of the prereactor allows the liquid phase to be removed from the prereactor, which has passed through all the sectional plates in the lower part of the prereactor, and accordingly, has the required temperature and contains an increased amount of formed urea, which additionally reduces the load on the synthesis reactor and allows the use of a smaller reactor, which can be installed close to the ground, thereby reducing the costs of building structures.

[0050] The mass transfer device in the upper part of the pre-reactor (at least one layer of packing and / or one tray) allows for intensive interaction between the gas phase coming from the middle part of the pre-reactor and the carbamate solution supplied to the upper part of the pre-reactor. This results in the required volume of gas phase being provided at the outlet from the upper part of the pre-reactor. The packing may be Raschig rings / Pall rings or their analogues.

[0051] The use of a pre-reactor ensures the required temperature of the reaction mixture at the outlet of the middle part of the pre-reactor and the preliminary formation of urea, which reduces the load on the synthesis reactor and allows the use of a smaller reactor that can be installed close to the ground, thereby reducing the costs of building structures.

[0052] In a preferred embodiment, the installation comprises a carbon dioxide supply line configured to divide it into a first part and a second part, such that the ratio of the amount, expressed in volume percent, of the second part of carbon dioxide to the amount of the first part of carbon dioxide can be adjusted within the range from 70:30 to 89:11.

[0053] In a preferred embodiment, the installation includes a mixer for mixing the gas phase and the carbamate solution before feeding them to the condenser.

[0054] The mixer ensures mixing of gas and liquid flows before feeding their mixture into the condenser. As a result, the reaction of ammonium carbamate formation (condensation of the gas phase) proceeds more deeply and at a high speed.

[0055] In a preferred embodiment, the reactor and condenser are located at a distance of no more than 10 meters from the ground, more preferably at a distance of no more than 1 meter from the ground.

[0056] The above parameters allow the heaviest and most dangerous equipment, namely the urea synthesis reactor and carbamate condenser, to be placed on the ground, which reduces the cost of building structures. This layout of the plant simplifies its maintenance, and increases the safety of the personnel servicing the plant.

[0057] In a preferred embodiment, the reactor is a vertical column apparatus, the stripper is a vertical shell-and-tube heat exchanger with a falling film, the condenser is a horizontal shell-and-tube heat exchanger with U-shaped heat exchange tubes, and the ejector is designed with the ability to regulate the pressure of the working flow.

[0058] The combination of the above factors leads to a significant increase in the efficiency of the method for producing urea, which is not described in the prior art.

[0059] Brief description of the drawings

[0060] The drawings are presented for a better understanding of the invention, however, it will be obvious to a person skilled in the art that the claimed invention is not limited to the variants shown in them.

[0061] The figure shows a process flow diagram illustrating a method and installation for producing urea in accordance with the claimed group of inventions.

[0062] The following are schematically indicated on the figure:

[0063] High pressure section nodes:

[0064] R-101 - urea synthesis reactor; T-101 - stripper;

[0065] S-101 - pre-reactor;

[0066] T-102 - capacitor;

[0067] H-102 - ejector.

[0068] X-101 - mixer

[0069] 1 - line for feeding a flow containing ammonia into the ejector H-102

[0070] 2 - ammonia-containing flow feed line to the R-101 reactor

[0071] 3 - line for feeding carbamate and urea solution from the S-101 pre-reactor

[0072] 4 - carbon dioxide supply line

[0073] 4.1 - carbon dioxide feed line to the R-101 reactor

[0074] 4.2 - carbon dioxide feed line to stripper T-101

[0075] 5 - line for feeding urea solution from reactor R-101 to the upper part of stripper T-101

[0076] 6 - gas phase removal line from the R-101 synthesis reactor

[0077] 7 - line for removing urea solution (liquid phase from stage b)) from the bottom of the T-101 stripper to the next distillation stage

[0078] 8 - gas phase discharge line from stripper T-101

[0079] 9 - line for removing gas-liquid mixture from condenser T-102 to the lower part of pre-reactor S-101

[0080] 10 - mass transfer plates of the S-101 pre-reactor

[0081] 11 - nozzle of the forreactor S-101

[0082] The arrows indicate the directions of the flows.

[0083] The nodes of the medium pressure section are not shown, the abbreviation SD on the drawings means medium pressure section.

[0084] Implementation of the invention

[0085] The method for obtaining urea is carried out using a urea obtaining plant as follows.

[0086] Installation includes:

[0087] - a reactor, in particular a high-pressure urea synthesis reactor R-101, which is a vertical column apparatus with internal devices;

[0088] - a stripper, in particular the T-101 high-pressure stripper, which is a vertical shell-and-tube heat exchanger with a falling film; and

[0089] - a pre-reactor, in particular a high-pressure pre-reactor S-101, which is a vertical column apparatus with mass-exchange plates installed in the lower part and equipped with packing in the upper part, a means for introducing a gas-liquid mixture (carbamate solution and gas phase) into the lower part, a means for removing the carbamate and urea solution from the middle part and, means for introducing the carbamate solution into the upper part and removing the gas phase from the upper part.

[0090] - a condenser, in particular a high-pressure carbamate condenser T-102, which is a horizontal shell-and-tube heat exchanger with U-shaped heat exchange tubes.

[0091] - an ejector, in particular a high-pressure ejector H-102, which is a jet ejector designed with the ability to regulate the pressure of the working flow.

[0092] The reactor and condenser are installed at ground level.

[0093] Ammonia is fed through line 1 to the H-102 ejector as a working flow and then through line 2 enters the R-101 synthesis reactor.

[0094] Ejector H-102, using the working flow of ammonia, pumps a solution of carbamate and urea, supplied via line 3 from prereactor C-101, into the synthesis reactor R-101. The ammonia pressure at the inlet to ejector H-102 is regulated by changing the position of the ejector needle H-102.

[0095] Carbon dioxide enters through line 4, is compressed to 14-16 MPa using a high-pressure compressor (not shown in the diagram) and at a temperature of 120-170 °C is fed through line 4.1 (first part) to the R-101 synthesis reactor (11-30%), through line 4.2 (second part) to the lower part of the T-101 stripper (70-89%).

[0096] In the R-101 synthesis reactor, at a temperature of 170-190 °C and a pressure of 14-16 MPa, a urea solution (the first reaction mixture from stage a)) and a by-product, water, are formed from ammonia and carbon dioxide. The urea solution (the first reaction mixture from stage a)) leaving the R-101 reactor contains urea, water, unreacted carbon dioxide and ammonia. The degree of conversion of carbon dioxide into urea is 58-62%.

[0097] This urea solution (the first reaction mixture from stage a)) is fed via line 5 to the upper part of stripper T-101. The level in the upper part of synthesis reactor R-101 is regulated by the valve at the solution outlet from synthesis reactor R-101. The gas phase from synthesis reactor R-101 is withdrawn separately via line 6 and fed to carbamate condenser T-102. Stripper T-101 operates under pressure of 14-16 MPa. Urea solution (the first reaction mixture from stage a)) from synthesis reactor R-101 with temperature of 180-190 °C is fed to the upper part of stripper T-101. Carbon dioxide (second part) from compressor (not shown in the diagram) is fed to the lower part of stripper T-101 as stripping agent via line 4.2. Under conditions of supplying steam with a pressure of 1.8-2.5 MPa into the intertube space of the T-101 stripper and under the action of a stripping agent at a temperature of 180-210 °C, ammonia and carbon dioxide and a small portion of water are removed from the urea solution.The urea solution (liquid phase from stage b)) from the bottom of the T-101 stripper is transferred to the next distillation stage via line 7. The temperature in the bottom of the T-101 stripper is 175-190 °C and is set by changing the pressure of the steam supplied to the intertube space of the T-101 stripper. The level of the urea solution in the bottom of the T-101 stripper is regulated by a valve on the solution outlet to the next distillation stage. The gas phase (gas phase from stage b)) with a temperature of 185-195 °C from the top of the high-pressure stripper T-101 is sent via line 8 to the carbamate condenser T-102.

[0098] The T-102 carbamate condenser operates at a pressure of 14-16 MPa. The gas phase from the upper part of the T-101 stripper (the gas phase from stage b)), the gas phase from the upper part of the R-101 synthesis reactor (the gas phase from stage a)), and the carbamate solution from the medium-pressure distillation unit (not shown in the diagram, the carbamate solution can also be introduced through the X-101 mixer) are fed into its tube space for condensation. Condensation of the gas phase in the tubes of the T-102 carbamate condenser occurs at a temperature of 160-170 °C due to evaporation of the condensate in the intertube part with the formation of steam with a pressure of 0.50-0.60 MPa. This steam is used in the process flow chart at other stages of production and can also be exported for the needs of the plant.

[0099] The gas-liquid mixture (carbamate solution and gas phase) from the carbamate condenser T-102 (gas-liquid mixture from stage c)) with a temperature of 160-170 °C is directed through line 9 to the lower part of the prereactor C-101. Here, the uncondensed gas phase condenses with the formation of an additional amount of carbamate, heating the carbamate solution. The gas-liquid mixture (carbamate solution and gas phase) passes through the sectional plates 10 of the prereactor C-101 from the bottom up, while the carbamate solution is fed into the prereactor to irrigate the packing 11 in the upper part of the prereactor. The carbamate solution here is a carbamate solution obtained by subsequent processing of the liquid phase discharged from the stripper and having a pressure of 14.0-16.0 MPa and a temperature of 180-210°C. The conditions in the apparatus allow some of the carbamate to be converted into urea.The solution of carbamate and urea from the pre-reactor C-101 (the reaction mixture from stage d)) is directed through line 12 to the ejector H-102 and, using a flow of liquid ammonia, is fed to the synthesis reactor R-101.

[0100] The uncondensed gas phase from the lower part of the prereactor S-101 enters the upper part of the prereactor, where, passing through packing I, irrigated with a part of the medium-pressure carbamate solution, it undergoes additional condensation. The remains of the gas phase from the upper part of the prereactor S-101 are throttled to a pressure of 2.3-2.7 MPa and directed to the intertube space of the recuperative heater of the urea solution (not shown in the diagram). The carbamate solution obtained in the upper part of the prereactor is drained into the lower part of the prereactor. The level in the lower part of the prereactor S-101 is maintained using valve K 1 on the outlet of the gas phase from the synthesis reactor R-101 to the carbamate condenser T-102 (by the pressure in the reactor). The pressure of 14.0-14.5 MPa in the pre-reactor S-101 is maintained by valve K2 on the gas phase outlet from the pre-reactor S-101.

[0101] The urea solution with a concentration of 45-50% after the T-101 stripper is throttled to a pressure of 2.3-2.7 MPa and sent for further processing.

[0102] The essence of the invention is confirmed by examples, which are particular cases of the implementation of the invention, but do not limit it.

[0103] Example 1 is the best embodiment of the invention.

[0104] The production of urea is carried out in accordance with the above-mentioned general case of implementing the invention, with the difference that:

[0105] - carbon dioxide is fed into the R-101 synthesis reactor in the amount of 15%, into the lower part of the T-101 stripper in the amount of 85%;

[0106] - the degree of conversion of carbon dioxide into urea is 62%;

[0107] - the urea solution from the R-101 synthesis reactor enters the upper part of the T-101 stripper at a temperature of 183 °C;

[0108] - the pressure of steam supplied to the inter-tube space of the T-101 stripper is 2.0 MPa;

[0109] - the temperature in the tube space of the T-101 stripper is 190 °C;

[0110] - the temperature at the bottom of the T-101 stripper is 180 °C

[0111] - condensation of the gas phase in the tubes of the carbamate condenser T-102 occurs at a temperature of 165 °C due to evaporation of the condensate in the intertube part with the formation of steam with a pressure of 0.50-0.60 MPa - the gas-liquid mixture (carbamate solution and gas phase) from the carbamate condenser T-102 with a temperature of 165 °C is sent to the lower part of the prereactor S-101.

[0112] - in the S-101 pre-reactor the pressure is maintained at 14.3 MPa.

[0113] At the final stage of the method for obtaining urea, a urea solution with a concentration of 49% emerges from the T-101 stripper, which is sent for further processing.

[0114] Example 2.

[0115] The production of urea is carried out in accordance with the above-mentioned general case of implementing the invention, with the difference that:

[0116] - carbon dioxide is fed into the R-101 synthesis reactor in the amount of 11%, into the lower part of the T-101 stripper in the amount of 89%;

[0117] - the degree of conversion of carbon dioxide into urea is 59%;

[0118] - the urea solution from the R-101 synthesis reactor enters the upper part of the T-101 stripper at a temperature of 182 °C;

[0119] - the pressure of steam supplied to the inter-tube space of the T-101 stripper is 2.1 MPa;

[0120] - the temperature in the tube space of the T-101 stripper is 187 °C;

[0121] - the temperature at the bottom of the T-101 stripper is 177 °C

[0122] - condensation of the gas phase in the tubes of the T-102 carbamate condenser occurs at a temperature of 168 °C due to the evaporation of the condensate in the intertube part with the formation of steam with a pressure of 0.50-0.60 MPa

[0123] - the gas-liquid mixture (carbamate solution and gas phase) from the carbamate condenser T-102 with a temperature of 168 °C is directed to the lower part of the pre-reactor S-101.

[0124] - in the S-101 pre-reactor the pressure is maintained at 14.5 MPa.

[0125] At the final stage of the method for obtaining urea, a urea solution with a concentration of 47% emerges from the T-101 stripper, which is sent for further processing.

[0126] Example 3.

[0127] The production of urea is carried out in accordance with the above-mentioned general case of implementing the invention, with the difference that:

[0128] - carbon dioxide is fed into the R-101 synthesis reactor in an amount of 30%, into the lower part of the T-101 stripper in an amount of 70%; - the degree of conversion of carbon dioxide into urea is 58%;

[0129] - the urea solution from the R-101 synthesis reactor enters the upper part of the T-101 stripper at a temperature of 181 °C;

[0130] - the pressure of steam supplied to the inter-tube space of the T-101 stripper is 2.2 MPa;

[0131] - the temperature in the tube space of the T-101 stripper is 195 °C;

[0132] - the temperature at the bottom of the T-101 stripper is 185 °C

[0133] - condensation of the gas phase in the tubes of the T-102 carbamate condenser occurs at a temperature of 160 °C due to the evaporation of the condensate in the intertube part with the formation of steam with a pressure of 0.50-0.60 MPa

[0134] - the gas-liquid mixture (carbamate solution and gas phase) from the carbamate condenser T-102 with a temperature of 160 °C is directed to the lower part of the pre-reactor S-101.

[0135] - a pressure of 14.0 MPa is maintained in the S-101 forreactor. At the final stage of the urea production process, a urea solution with a concentration of 45% exits the T-101 stripper and is sent for further processing.

Claims

Invention formula 1. A method for producing urea, comprising the following steps: a) feeding ammonia and a first portion of carbon dioxide into a reactor to form a first reaction mixture and a gas phase; b) feeding the first reaction mixture from step a) and a second portion of carbon dioxide into a stripper to form a liquid phase and a gas phase; c) feeding the gas phase from step a) and the gas phase from step b) into a condenser to form a gas-liquid mixture; d) feeding the gas-liquid mixture from step c) and a carbamate solution into a prereactor to form a second reaction mixture and a gas phase; e) ejecting the second reaction mixture from step d) with the ammonia fed to step a).

2. The method according to claim 1, characterized in that the ratio of the amount, expressed in volume percent, of the second part of carbon dioxide to the amount of the first part of carbon dioxide is regulated within the range from 70:30 to 89:

11.

3. The method according to claim 1, characterized in that the carbamate solution in stage d) is a carbamate solution obtained by subsequent processing of the liquid phase from stage b), removed from the stripper, and having a pressure of 14.0-16.0 MPa and a temperature of 180-210 °C.

4. The method according to item 1, characterized in that at stage a) the pressure in the reactor is maintained at 14.0-16.0 MPa and a temperature of 170-190 °C.

5. The method according to item 1, characterized in that at stage b) a pressure of 14.0-16.0 MPa and a temperature of 180-210 °C are maintained in the tube space of the stripper, while a temperature of 175-190 °C is maintained in the lower part of the stripper, and steam with a pressure of 1.8-2.5 MPa is supplied to the intertube space of the stripper.

6. The method according to item 1, characterized in that at stage c) a pressure of 14.0-16.0 MPa and a temperature of 160-170 °C are maintained in the condenser.

7. The method according to item 1, characterized in that at stage d) a pressure of 14.0-14.5 MPa is maintained in the pre-reactor.

8. The method according to item 1, characterized in that at stage d) the gas-liquid mixture from stage c) is fed into the lower part of the prereactor, so that at least part of the said gas-liquid mixture passes through the sectioning plates in the lower part of the prereactor in the direction from bottom to top, SUBSTITUTE SHEET (RULE 26) wherein at least part of the carbamate solution is fed into the pre-reactor to irrigate the packing and / or tray in the upper part of the pre-reactor.

9. An installation for producing urea, comprising: a reactor configured to feed ammonia and a first portion of carbon dioxide into it, as well as to remove the reaction mixture and the gas phase; a stripper configured to feed the reaction mixture from the reactor and a second portion of carbon dioxide into it, as well as to remove the liquid phase and the gas phase; a condenser configured to feed the gas phase from the reactor and the gas phase from the stripper into it, and to remove the gas-liquid mixture; a prereactor configured to feed the gas-liquid mixture from the condenser and the carbamate solution into it, as well as to remove the reaction mixture and the gas phase; an ejector for mixing the reaction mixture from the prereactor with the ammonia fed into the reactor.

10. The installation according to claim 9, characterized in that the prereactor is a vertical column apparatus comprising: sectionalizing trays in the lower part of the prereactor, at least one layer of packing and / or one tray in the upper part of the prereactor, inlet means designed with the possibility of feeding at least part of the gas-liquid mixture from the condenser through the sectionalizing trays of the prereactor in the direction from the bottom to the top, and feeding at least part of the carbamate solution for irrigating the packing and / or tray in the upper part of the prereactor, means for removing the liquid phase from the middle part of the prereactor, means for removing the gas phase from the upper part of the prereactor.

11. The installation according to item 9, characterized in that the installation comprises a carbon dioxide supply line designed with the possibility of dividing it into a first part and a second part, such that the ratio of the amount, expressed in volume percent, of the second part of carbon dioxide to the amount of the first part of carbon dioxide can be adjusted within the range from 70:30 to 89:

11.

12. The installation according to item 9, characterized in that the reactor and condenser are designed with the possibility of their installation at a distance of no more than 10 meters from the ground, more preferably at a distance of no more than 1 meter from the ground.

13. The installation according to item 9, characterized in that the installation includes a mixer for mixing the gas phase and the carbamate solution before feeding them to the condenser. SUBSTITUTE SHEET (RULE 26) 14. The installation according to item 9, characterized in that the reactor is a vertical column apparatus, the stripper is a vertical shell-and-tube heat exchanger with a falling film, the condenser is a horizontal shell-and-tube heat exchanger with U-shaped heat exchange tubes, and the ejector is designed with the possibility of regulating the flow pressure. SUBSTITUTE SHEET (RULE 26)

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