Urea synthesis device

Abstract

The present application relates to a urea synthesis device, including a high-pressure synthesis system, a medium-pressure decomposition system, a low-pressure decomposition system and a urine evaporator; the high-pressure synthesis system includes a urea synthesis tower, a stripping tower, an ammonia preheater, a methylammonium washing condenser and a high-pressure ejector; the urea synthesis tower is a vertical tower, including a high-pressure reactor composed of a metal shell, an internal tray and a metal tube, and the methylammonium washing condenser includes a washing section and a condensing section distributed up and down, and a vertical steam drum is connected to the shell of the condensing section. The urea synthesis tower in the present invention can increase the residence time of the reaction materials and improve the reaction yield. The methylammonium washing condenser can remove the unreacted NH 3 and CO 2 It absorbs and continues to react to generate methylammonium, increasing the by-product steam, achieving the technical effect of energy saving and consumption reduction, and improving the conversion rate, reducing the steam consumption per ton of urea by 20%.

Description

Technical Field

[0001] The present application relates to the technical field of urea production, and in particular to a urea synthesis device. Background Art

[0002] At present, the main urea production technologies in the world are: CO2 stripping process of Stamicarbon in the Netherlands, NH3 stripping process of Snamprogeti in Italy, and ACES process of Toyo Corporation in Japan. No matter which process is used, the excess ammonia and carbon dioxide are reacted at a pressure of 12-40MPa(A) and a temperature of 150-250℃ to produce the following reaction:

[0003] The first step is an exothermic reaction to form ammonium carbamate:

[0004] 2NH3+CO2→H2N-CO-ONH4

[0005] The second step is an endothermic equilibrium reaction to dehydrate the formed ammonium carbamate to form urea:

[0006] H2N-CO-ONH4=H2N-CO-NH2+H2O

[0007] The above reaction is carried out at a certain temperature and pressure. Urea, ammonium carbamate, water and unreacted ammonia are generated in the high-pressure urea synthesis reaction zone. The ammonium carbamate and ammonia are removed from the solution and returned to the urea synthesis zone to continue the reaction. In addition to the solution, a gas mixture is also formed in the urea synthesis reaction. The gas mixture consists of unreacted ammonia and carbon dioxide and inert gas waste gas, and the ammonia can be recovered by water absorption.

[0008] The decomposition of ammonium carbamate that is not converted into urea in the high-pressure urea synthesis reaction zone is usually carried out by thermal stripping and decomposition by carbon dioxide and / or ammonia in a stripping tower, and the ammonium carbamate is decomposed into ammonia and carbon dioxide. The heat required for decomposition is provided by steam or other heat sources provided by an external heat source. The stripping removes the existing ammonia and carbon dioxide and condenses them in a high-pressure condenser and then returns to the urea synthesis area.

[0009] The urea after stripping is decomposed at a pressure lower than the synthesis part, and the ammonium carbamate is returned to the urea synthesis part. The recovery device is usually single or can be a multi-stage recovery set in series, which can be set according to the principle of minimum energy consumption.

[0010] At present, in the traditional CO2 stripping process, its high-pressure circle operates under the guidance of optimization theory: the synthesis pressure adopts the lowest equilibrium pressure, the ammonia / carbon ratio adopts the ammonia / carbon ratio at the lowest azeotropic composition (2.95), the operating pressure is 13.5-14.5MPa (A), the temperature is 180-183℃, the condensation temperature is 167℃, the stripping temperature is about 190℃, and the stripping efficiency is more than 80%. These parameters are relatively mild, so the main equipment material is 316L or 25-22-2CrNiMo, and with a sufficient amount of passivation air, the material can meet the requirements of strong corrosion resistance, and the equipment manufacturing and maintenance are relatively convenient. Due to the high stripping efficiency, only a low-pressure recovery section is set up to meet the requirements of material recycling, but the high-level thermal energy is not utilized, resulting in high steam consumption of the entire urea synthesis unit.

[0011] The urea synthesis tower is a key equipment in the urea production process. It reacts ammonia and carbon dioxide to react urea under high pressure and high temperature. The urea synthesis tower generally adopts an empty tower or is provided with a mixer or sieve plate. The reaction liquid flows along the axial direction of the synthesis tower. Since there are openings on the sieve plate or the mixer, the pressure drop when the gas phase perforates is greater than the pressure drop of the liquid phase passing through the annular gap of the synthesis tower, causing the liquid phase and the gas phase to mix above the tower plate, and the reaction of methylammonium dehydration to generate urea is carried out. Vortex is generated during the mixed flow process, that is, back mixing is generated. Due to the existence of back mixing, the reaction rate of methylammonium is reduced during the urea synthesis process, which is manifested as a decrease in the conversion rate of CO2. In addition, the urea synthesis tower is usually provided with a central tube inside to guide the reaction liquid, which not only occupies the space for the methylammonium reaction but also increases the equipment investment.

[0012] In the urea production process, the stripping tower decomposes most of the methylammonium in the urea solution to produce CO2 and NH3, which are condensed in the high-pressure condenser to form methylammonium solution; the inert gas leaving the urea synthesis tower is recycled through the high-pressure scrubber to recover the NH3. This process requires two high-pressure devices, the high-pressure scrubber and the high-pressure condenser. Independent settings not only increase the floor space, but also increase the equipment manufacturing costs.

[0013] In view of the above problems of high energy consumption, large equipment investment and low reaction efficiency in urea production, the present invention is proposed. Summary of the invention

[0014] The purpose of the present application is to provide a urea synthesis device, which optimizes the high-pressure reaction part, improves the reaction yield, achieves the technical effect of energy saving, and can also be used in stages to achieve the purpose of reducing energy consumption.

[0015] In order to achieve the above object, the present invention provides a urea synthesis device, comprising a high-pressure synthesis system, a medium-pressure decomposition system, a low-pressure decomposition system and a urine evaporator;

[0016] The high-pressure synthesis system comprises a urea synthesis tower, a stripping tower, an ammonia preheater, a methylammonium washing condenser and a high-pressure ejector, which are connected by pipelines;

[0017] The methylammonium washing condenser comprises a washing section and a condensing section which are distributed up and down, and a vertical steam drum is connected to the shell of the condensing section;

[0018] The medium-pressure decomposition system includes a medium-pressure distillation tower, a medium-pressure separator and a connecting pipeline, and the low-pressure decomposition system includes a low-pressure distillation tower, a low-pressure separator and a connecting pipeline;

[0019] The urea synthesis tower is a vertical tower, comprising a high-pressure reactor consisting of a metal shell, an internal tower plate and a metal tube, wherein the internal tower plate comprises a plurality of baffle plates, and the plurality of baffle plates are arranged in an axially spaced and staggered manner along the urea synthesis tower, and each of the baffle plates is a non-porous baffle plate, the interior of the urea synthesis tower is filled with urine, and the urine flows out from bottom to top through the baffle plates inside the urea synthesis tower;

[0020] The metal pipe is connected to the top of the urea synthesis tower, and the metal pipe includes a bent pipe section. The urine in the urea synthesis tower flows back to the top of the tower and then is discharged through the metal pipe and flows downward. The metal pipe includes a horizontal section of the metal pipe and a vertical section of the metal pipe. The vertical section of the metal pipe is arranged parallel to the axial direction of the urea synthesis tower.

[0021] In an optional embodiment, the metal tube is connected to the top of the stripping tower through a pipeline, the top of the stripping tower is connected to the methylammonium washing condenser through a pipeline, and the connection portion is arranged at the bottom of the washing section of the methylammonium washing condenser.

[0022] In an optional embodiment, the stripping tower includes a stripping tube and a stripping shell, and the top and bottom ends of the stripping tube are respectively provided with a stripping top head and a stripping bottom head, the metal tube is connected to the side of the stripping top head through a pipeline, and the top of the stripping top head is connected to the bottom of the washing section through a pipeline.

[0023] In an optional embodiment, the condensation section includes a heat exchanger, the heat exchanger includes heat exchange tubes, the heat exchange tubes are vertically arranged in the shell of the methylammonium washing condenser, and the vertical steam drum is connected to the shell through a pipeline.

[0024] In an optional embodiment, the cavity of the bottom head of the methylammonium washing condenser is in communication with the heat exchange tube, and the bottom of the urea synthesis tower is connected to the bottom head of the methylammonium washing condenser via a pipeline.

[0025] In an optional embodiment, the urea synthesis tower is connected to the bottom head of the methylammonium washing condenser via a drainage pipe, the high-pressure ejector is connected to the drainage pipe, and the inlet of the high-pressure ejector is connected to the ammonia preheater via a pipe.

[0026] In an optional embodiment, the medium-pressure distillation tower is connected to the bottom head of the stripping tower through a medium-pressure pressure reducing pipe, so that the urea synthesis liquid at the bottom of the stripping tower is decompressed and decomposed through the medium-pressure distillation tower, and the medium-pressure pressure reducing pipe is connected to a stripping tower liquid level regulating valve for adjusting the stripping tower liquid level.

[0027] In an optional embodiment, the downstream of the medium-pressure distillation tower is connected to the low-pressure decomposition system through a low-pressure pressure reducing pipeline, and a medium-pressure tower liquid level regulating valve is provided on the low-pressure pressure reducing pipeline to adjust the liquid level of the medium-pressure distillation tower, the bottom of the low-pressure distillation tower is connected to the urine evaporator through a pipeline, and the top of the low-pressure distillation tower is connected to a low-pressure condenser and a low-pressure separator in sequence through a pipeline, and a medium-pressure methylammonium pump and a low-pressure methylammonium pump are respectively provided at the bottom of the medium-pressure separator and the low-pressure separator, and the discharge pipes of the medium-pressure methylammonium pump and the low-pressure methylammonium pump are combined and connected to the methylammonium washing condenser, and the connection portion is arranged at the top of the washing section.

[0028] In an optional embodiment, the urine evaporator includes a urine evaporation tank and a urine heat exchanger distributed up and down, the urine evaporation tank is connected to the tube side of the urine heat exchanger, the top of the medium-pressure distillation tower is connected to the upper section of the shell of the urine heat exchanger through a pipeline, the upper section of the shell side of the urine heat exchanger is connected to the medium-pressure separator through a pipeline, and the lower section of the shell side of the urine heat exchanger uses low-pressure steam to supplement heat.

[0029] In an optional embodiment, the top of the methylammonium washing condenser is connected to a high-pressure absorption tower via a pipeline, the bottom of the high-pressure absorption tower is connected to a normal-pressure absorption tower via a pipeline, and is connected to the top side of the normal-pressure absorption tower, and the gas phase pipeline of the medium-pressure separator is combined with the gas phase pipeline of the low-pressure separator and connected to the bottom side of the normal-pressure absorption tower.

[0030] By setting up a medium-voltage decomposition system, graded energy recovery can be achieved, and energy can be recovered in the form of decomposition, making energy utilization more reasonable.

[0031] The high-pressure synthesis system only includes a urea synthesis tower, a stripping tower, an ammonia preheater, a methylammonium washing condenser and a high-pressure ejector, which simplifies the structural composition of the high-pressure system, optimizes the number of equipment in the high-pressure loop, and saves investment. The synthesis tower is arranged on the ground, which reduces the frame height of the urea device and recovers more heat.

[0032] The methylammonium washing condenser includes a washing section and a condensing section which are distributed up and down. It can integrate condensation absorption and urea synthesis on the same equipment, which is suitable for increasing the energy saving of the urea device. The vertical steam drum is connected to the shell of the condensing section, which can absorb the heat of the condensing section and produce by-product steam for evaporation in the downstream section, thereby reducing the amount of evaporation steam in the downstream section.

[0033] By arranging a baffle plate inside the urea synthesis tower and combining it with a pressure reducing decomposition device arranged downstream of the top of the urea synthesis tower, the reaction liquid can pass through the baffle plate from the bottom of the tower to the top of the tower in the urea synthesis tower, thereby extending the residence time of urine in the urea synthesis tower and improving the urea conversion rate.

[0034] A plurality of baffle plates are arranged at intervals along the axial direction of the urea synthesis tower, and each baffle plate is a non-porous baffle plate, which can increase the flow path of urine in the urea synthesis tower. The non-porous baffle plates can reduce the back mixing of urine during the upward return flow, thereby ensuring the residence time of urine in the urea synthesis tower.

[0035] The interior of the urea synthesis tower is filled with urine. A metal pipe is connected to the top of the urea synthesis tower, which can lead the urine that flows back to the bottom of the tower out through the metal pipe, and then decompose the unreacted NH3 and CO2. After further washing and condensing in the methylamine washing condenser, it is circulated back to the urea synthesis tower, thereby improving the utilization rate of raw materials and the yield of urea, and further obtaining the reaction heat of the condensation section.

[0036] The purpose of the bent pipe section included in the metal pipe is to extend the flow path of urine during the discharge process. The urine discharged from the top of the tower is discharged through the metal pipe and flows downward, and the bent pipe section can play a good buffering effect.

[0037] By arranging the bent section and the vertical section of the metal pipe to be parallel to the axial direction of the urea synthesis tower, the urine can be controlled to flow vertically after being discharged, thereby extending the flow time and facilitating the dehydration reaction.

[0038] The urea synthesis device in the present invention can realize the hierarchical utilization of energy to achieve the purpose of reducing energy consumption. At the same time, by optimizing the high-pressure reaction part, the reaction efficiency is improved to achieve the technical purpose of energy saving.

[0039] The urea synthesis device and related equipment of the present invention are as follows: the urea synthesis tower adopts an empty tower with a baffle plate without holes, the central tube of the urea synthesis tower is moved outside the tower to increase the reaction space, increase the residence time of the reaction materials, and improve the reaction yield. The methylammonium washing condenser can absorb the unreacted NH3 and CO2 in the process of generating methylammonium liquid and continue to react to generate methylammonium, and the heat recovery equipment of the absorption process is integrated on the same equipment, thereby increasing the steam by-product.

[0040] Through the above measures, the high-pressure reaction part is optimized, the reaction yield is improved, energy saving and consumption reduction are achieved, and the conversion rate is improved. The graded utilization of energy is realized, and the steam consumption per ton of urea is reduced by 20%.

[0041] Other features and advantages of the present application will be described in detail in the subsequent detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0043] Figure 1 It is a structural schematic diagram of the urea synthesis device in this application;

[0044] Figure 2 This is a schematic diagram of the structure of the urea synthesis tower and the metal tube in this application;

[0045] Figure 3 This is a schematic diagram of the structure of the methylamine washing condenser in this application.

[0046] icon:

[0047] 1-urea synthesis tower; 11-metal pipe; 12-reaction liquid pipeline; 13-baffle plate; 14-vertical section;

[0048] 2-stripping tower; 21-stripping tube; 22-stripping shell; 23-stripping top head; 24-stripping bottom head;

[0049] 3-methylammonium washing condenser; 31-washing section; 32-condensing section; 33-heat exchanger; 34-bottom end cap of methylammonium washing condenser; 35-drainage pipe; 36-high-pressure ejector;

[0050] 4-vertical steam drum;

[0051] 5- ammonia preheater;

[0052] 6-medium pressure distillation tower; 61-medium pressure pressure reducing pipeline; 62-stripping tower liquid level regulating valve;

[0053] 7- urine evaporator; 71- urine evaporation tank; 72- urine heat exchanger;

[0054] 8-Medium pressure separator;

[0055] 9- low-pressure distillation tower; 91- low-pressure pressure reducing pipeline; 92- medium-pressure tower liquid level regulating valve; 93- low-pressure condenser; 94- low-pressure separator;

[0056] 10-medium pressure methylammonium pump; 20-low pressure methylammonium pump; 30-high pressure absorption tower; 40-normal pressure absorption tower. DETAILED DESCRIPTION

[0057] In order to make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the technical scheme in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all of the embodiments. The components of the embodiments of the present application described and shown in the drawings here can be arranged and designed in various different configurations.

[0058] In the description of this application, it should be noted that the terms "inside", "outside", etc. indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship in which the product of the application is usually placed when in use, which is only for the convenience of describing this application and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on this application. In addition, the terms "first", "second", etc. are only used to distinguish the description, and cannot be understood as indicating or implying relative importance.

[0059] In the description of this application, it should also be noted that, unless otherwise clearly specified and limited, the terms "disposed" and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a direct connection, or an indirect connection through an intermediate medium, or it can be the internal communication of two elements. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0060] The urea synthesis device and related equipment in the present application are mainly used for the synthesis of urea. Specifically, by simplifying and optimizing the structure and process of the high-pressure synthesis part and recovering the self-heat of the device in a graded manner, the energy utilization is made more reasonable. Based on the optimized structure and process of the high-pressure synthesis system, the washing and condensation of NH3 and CO2 after decomposition in the synthesis tower by the circulating methylammonium liquid and the heat release of the generation of methylammonium are integrated on the same equipment, thereby increasing the amount of by-product steam and reducing the downstream steam consumption.

[0061] See also Figure 1 , and combined with Figure 2-Figure 3 The urea synthesis device of the present invention includes a high-pressure synthesis system, a medium-pressure decomposition system, a low-pressure decomposition system and a urine evaporator.

[0062] The high-pressure synthesis system comprises a urea synthesis tower 1, a stripping tower 2, a methylammonium washing condenser 3, an ammonia preheater 5 and a high-pressure ejector 36. By optimizing the process and structural composition of the high-pressure synthesis system, the high-pressure system has only five devices, namely, the urea synthesis tower 1, the stripping tower 2, the methylammonium washing condenser 3, the ammonia preheater 5 and the high-pressure ejector 36, which saves investment, allows the urea synthesis tower 1 to be arranged on the ground, and reduces the frame height of the urea device.

[0063] The methylammonium washing condenser 3 simultaneously performs the washing and condensation of NH3 and CO2 after decomposition in the urea synthesis tower 1 and the exothermic reaction of methylammonium generation. The above two perspectives are specifically performed in the methylammonium washing condenser 3, which includes a washing section 31 and a condensing section 32 distributed up and down. The urine in the urea synthesis tower 1 is decomposed into NH3 and CO2 through the metal tube 11 and then enters the bottom of the washing section 31 through the top of the stripping tower 2, and the NH3 and CO2 are washed in the washing section 31 through the circulating methylammonium liquid downstream of the urea synthesis device, and the methylammonium synthesis reaction is performed in the condensing section 32.

[0064] The methylammonium synthesis reaction carried out in the condensing section 32 generates a large amount of heat. A vertical steam drum 4 is connected to the shell of the condensing section 32 to absorb the heat generated by the methylammonium synthesis reaction. Desalted water transported from the outside is added to the vertical steam drum 4 so that it is converted into steam after absorbing heat. Combined with the heat absorbed, the steam condensate with a relatively high temperature in the vertical steam drum 4 can further produce high-quality low-pressure steam as a by-product. The steam can meet the heating requirements of subsequent processes, eliminate the high-pressure water adjustment system, simplify the process, and reduce the investment in the device.

[0065] The medium-pressure decomposition system includes a medium-pressure distillation tower 6, a medium-pressure separator 8 and a connecting pipeline. The setting of the medium-pressure decomposition system allows the medium-pressure flash steam in the medium-pressure decomposition system to enter the urine evaporator 7 for heat recovery, thereby reducing the steam consumption of the device, and allowing the medium-pressure system to be free of a medium water transfer system, thereby simplifying the process and reducing the number of equipment. The present invention can reduce the amount of steam used per ton of urea by 20%.

[0066] The urea synthesis tower 1 in the present invention is a vertical tower, including a high-pressure reactor composed of a metal shell, an internal tower plate and a metal pipe. The internal tower plate includes a plurality of baffle plates 13 arranged inside the urea synthesis tower 1. The plurality of baffle plates 13 are arranged in an axially spaced and staggered manner along the urea synthesis tower 1, so that urine can be baffled from bottom to top through the baffle plates 13 in the urea synthesis tower 1, thereby extending the flow path of the reaction liquid in the urea synthesis tower 1, ensuring the residence time of the reaction liquid in the urea synthesis tower 1, and improving the conversion rate of urea.

[0067] Each baffle plate 13 is a non-porous baffle plate, which can avoid back-mixing of the reaction liquid during the return flow. The interior of the urea synthesis tower 1 is filled with urine, and the urine flows back from bottom to top in the urea synthesis tower 1 through the baffle plates 13, which can improve the flow state of the existing reaction liquid and reduce the internal space and external dimensions of the urea synthesis tower 1, thereby reducing equipment costs.

[0068] In order to be able to extract and decompose the urine after the reaction, so that the unreacted NH3 and CO2 are precipitated and decomposed from the urine, a metal pipe 11 is connected to the top of the urea synthesis tower 1. The metal pipe 11 includes a bent pipe section, which can also help to increase the flow path of the urine outside the urea synthesis tower 1 after it flows out, and provide a dehydration space.

[0069] The urine in the urea synthesis tower 1 flows back to the top of the tower and then is discharged through the metal pipe 11 and flows downward, which can maintain the buffering effect of the urine after being discharged and is conducive to the dehydration reaction.

[0070] The vertical section 14 of the bent metal tube section is parallel to the axial direction of the urea synthesis tower. Further combined with the parallelism between the vertical section and the axial direction of the urea synthesis tower, the urine can be controlled to flow vertically after being discharged, thereby extending the flow time and ensuring a full and thorough dehydration reaction.

[0071] By connecting the vertical section 14 of the metal pipe 11 to the side wall of the urea synthesis tower 1 through the support frame, the installation of the urea synthesis tower 1 is facilitated, and the connection and installation of the metal pipe 11 and the downstream docking pipeline is facilitated.

[0072] In one specific embodiment, in order to enable the urine in the urea synthesis tower 1 to be decomposed into NH3 and CO2 in the metal tube 11, the metal tube 11 is connected to the top of the stripping tower 2 through a pipeline, so that the decomposed NH3 and CO2 can enter the top of the stripping tower 2, and enter the methylammonium washing condenser 3 through the top of the stripping tower 2 to be washed and condensed.

[0073] Specifically, the metal pipe 11 is connected to the top of the urea synthesis tower 1 so as to be able to guide the urine material in the urea synthesis tower 1 out.

[0074] The top of the stripping tower 2 is connected to the methylammonium washing condenser 3 through a pipeline, and the connecting part is arranged at the bottom of the washing section 31 in the methylammonium washing condenser 3. Through this arrangement, the NH3 and CO2 decomposed in the metal tube 11 and passing through the top of the stripping tower 2 can enter the bottom of the washing section 31 of the methylammonium washing condenser 3 to obtain effective washing condensation.

[0075] It should be pointed out that in addition to the urea synthesis tower with a vertical tower structure, the urea synthesis tower can also be a horizontal tower structure. It is also necessary to arrange baffle plates in the urea synthesis tower of the horizontal tower, so that the non-porous baffle plates are arranged in an axially staggered manner to meet the requirements of extending the flow path of the reaction liquid in the urea synthesis tower and ensuring the residence time. At the same time, the metal pipe can be used to guide the urine from the end of the horizontal urea synthesis tower, and after being bent horizontally relative to the urea synthesis tower for a certain length, it is connected to the top of the stripping tower through a pipeline, so that the analyzed NH3 and CO2 enter the methylammonium washing condenser through the stripping tower.

[0076] The stripping tower 2 includes a stripping tube 21 and a stripping shell 22. The top and bottom ends of the stripping tube 21 are respectively provided with a stripping top head 23 and a stripping bottom head 24. The metal tube 11 is connected to the side of the stripping top head 23 through a pipeline. The top of the stripping top head 23 is connected to the bottom of the washing section 31 through a pipeline, so that NH3 and CO2 decomposed in the metal tube 11 on the urea synthesis tower 1 enter the interior of the stripping top head 23 from the side of the stripping top head 23, and enter the methylammonium washing condenser 3 through the top of the stripping top head 23.

[0077] The condensation section 32 includes a heat exchanger 33, and the heat exchanger 33 includes heat exchange tubes, which are vertically arranged in the shell of the methylammonium washing condenser 3, and the vertical steam drum 4 is connected to the shell through a pipeline.

[0078] Specifically, the tube side of the heat exchanger 33 is connected to the washing section 31, and the washed condensed material can enter the reaction tube of the heat exchanger 33 and release heat in the methylammonium synthesis reaction. The vertical steam drum 4 is connected to the shell through a pipeline. Combined with the desalted water introduced into the vertical steam drum 4, the desalted water can absorb the reaction heat, be converted into steam and circulate between the vertical steam drum 4 and the shell of the methylammonium washing condenser 3. The vertical steam drum 4 is connected to a condensate pipeline. By further reducing the pressure of the steam condensate inside the vertical steam drum 4 and flashing it, high-quality low-pressure steam can be obtained, thereby realizing the recovery of heat inside the high-pressure synthesis system.

[0079] The methylammonium washing condenser 3 also includes a methylammonium washing condenser bottom head 34 located at the bottom, the cavity of the methylammonium washing condenser bottom head 34 is communicated with the reaction tube, and the bottom of the urea synthesis tower 1 is connected to the methylammonium washing condenser bottom head 34 through the reaction liquid pipeline 12.

[0080] The circulating methylammonium liquid downstream of the urea synthesis device washes the unreacted NH3 and CO2 gas phases, and the washing liquid descends through the funnel included in the washing section 31 in the methylammonium washing condenser 3, and descends through the reaction tube to the methylammonium washing condenser bottom head 34 of the methylammonium washing condenser 3.

[0081] In addition to the above-mentioned condensation washing, based on the connection between the bottom of the urea synthesis tower 1 and the bottom head 34 of the methylammonium washing condenser through the reaction liquid pipeline 12, a liquid level balance can be established between the urea synthesis tower 1 and the methylammonium washing condenser 3, so that the reaction liquid pipeline 12 plays a balancing tube effect.

[0082] The gas in the stripping tower 2 enters the methylammonium washing condenser 3 from the top of the stripping tower 2 and contacts with the methylammonium liquid, thereby forming a methylammonium synthesis reaction at the heat exchanger 33. During the reaction, a large amount of heat is released to produce low-pressure steam for subsequent urine processing, and the excess low-pressure steam is supplied to the outside.

[0083] From the perspective of returning the reaction liquid in the methylammonium washing condenser 3 to the urea synthesis tower 1, the urea synthesis tower 1 is connected to the bottom head 34 of the methylammonium washing condenser through a drainage pipe 35. Specifically, the two ends of the reaction liquid pipe 12 are respectively connected to the urea synthesis tower 1 and the bottom center of the bottom head 34 of the methylammonium washing condenser, and one end of the drainage pipe 35 is connected to the side of the bottom head 34 of the methylammonium washing condenser, and the other end is connected to the side wall of the middle and lower section of the urea synthesis tower 1, and a high-pressure ejector 36 is provided on the drainage pipe 35. The reaction liquid returned from the bottom head 34 of the methylammonium washing condenser to the urea synthesis tower 1 is pressurized by the high-pressure ejector 36 and then enters the urea synthesis tower 1 for further dehydration reaction.

[0084] The inlet of the high-pressure injector 36 is connected to the ammonia preheater 5 through a pipeline. Since the ammonia preheater 5 preheats the liquid ammonia, the high-pressure injector 36 can pressurize and inject the liquid ammonia into the urea synthesis tower 1 under the premise of maintaining the heat balance in the urea synthesis tower 1.

[0085] In the high-pressure synthesis system, high-pressure CO2 gas from the carbon dioxide compressor is sent to the stripping tower 2, and 2.5 MPa (A) medium-pressure steam is used for heating on the shell side of the stripping tower 2. The methylammonium in the reaction liquid from the urea synthesis tower 1 is decomposed into NH3 and CO2 gas in the metal tube 11 and sent from the top of the stripping tower 2 through a pipeline to the bottom inlet of the washing section 31 of the high-pressure methylammonium washing condenser 3.

[0086] During the reaction process, the reaction liquid of the urea synthesis tower 1 flows into the stripping tower 2 through the metal pipe 11 by using the pressure difference, and the unreacted NH3, CO2 and inert gas are sent to the methylammonium washing condenser 3 for condensation and absorption. The unreacted NH3, CO2 and inert gas flowing out of the stripping tower 2 enter the medium-pressure decomposition system.

[0087] Through the urea synthesis tower 1, the stripping tower 2 and the methylammonium washing condenser 3, in combination with the metal tube 11, the reaction liquid pipeline 12, the discharge pipeline 35 and the high-pressure ejector 36, a dynamic balance can be established between the urea synthesis tower 1, the stripping tower 2 and the methylammonium washing condenser 3 to achieve absorption and utilization of the heat generated in the synthesis process.

[0088] At the same time, the urine in the urea synthesis tower 1 is discharged through the metal pipe 11 and separated by reducing the pressure. The urine after sufficient reaction can be separated, and the unreacted NH3 and CO2 gases are precipitated, and after washing and condensation, they are recycled back to the urea synthesis tower 1. While enhancing the sufficient reaction, it can further create the output conditions of the implicit heat in the urea synthesis process, and produce high-quality low-pressure steam as a by-product, thereby reducing the energy consumption in the urea synthesis process from another angle.

[0089] The operating conditions of the high-pressure methylammonium washing condenser 3 are: 14.1 MPa (A), 181°C, and the conversion rate of CO2 is about 40-42%; the operating conditions of the urea synthesis tower 1 are: 14.3 MPa (A), 183°C, and the conversion rate of CO2 is about 60-63%.

[0090] The medium-pressure decomposition system includes a medium-pressure distillation tower 6, a medium-pressure separator 8 and connecting pipes. The medium-pressure distillation tower 6 is connected to the stripping bottom head 24 through a medium-pressure pressure reducing pipe 61, so that the urea synthesis liquid at the bottom of the stripping tower 2 can be decompressed and decomposed through the medium-pressure distillation tower 6. A stripping tower liquid level regulating valve 62 is provided on the medium-pressure pressure reducing pipe 61.

[0091] The urea synthesis liquid from the stripping tower 2 is depressurized to about 2.2-2.3 MPa (A) by the stripping tower liquid level regulating valve 62, and then enters the medium-pressure distillation tower 6 at 158°C. The medium-pressure distillation tower 6 is a falling film heater. The urine exiting the medium-pressure distillation tower 6 is depressurized and transported to the subsequent low-pressure decomposition system.

[0092] The downstream of the medium-pressure distillation tower 6 is connected to the low-pressure distillation tower 9 through a low-pressure pressure reducing pipeline 91, and a medium-pressure tower liquid level regulating valve 92 is arranged on the low-pressure pressure reducing pipeline 91. The bottom of the low-pressure distillation tower 9 is connected to the urine evaporation tank 71 through a pipeline, and the top of the low-pressure distillation tower 9 is connected to a low-pressure condenser 93 and a low-pressure separator 94 in sequence through pipelines. The bottoms of the medium-pressure separator 8 and the low-pressure separator 94 are respectively provided with a medium-pressure methylammonium pump 10 and a low-pressure methylammonium pump 20, and the discharge pipelines of the medium-pressure methylammonium pump 10 and the low-pressure methylammonium pump 20 are combined and connected to the methylammonium washing condenser 3, and the connection portion is arranged at the top of the washing section 31.

[0093] The urine from the medium-pressure distillation tower 6 enters the low-pressure distillation tower 9 through the low-pressure pressure reducing pipe 91 under the action of the medium-pressure tower liquid level regulating valve 92 and is reduced in pressure to 0.45MPa~0.5MPa(A). Most of the carbon dioxide and ammonia in the solution are flash evaporated, and the solution temperature is reduced from 158°C to 115°C. The gas-liquid mixture enters the top of the low-pressure distillation tower 9.

[0094] The upper part of the low-pressure distillation tower 9 is a packed tower, which plays a role in gas distillation. The lower part is a separator. The urea methylammonium liquid falling through the packed section flows into the heater at the bottom of the low-pressure distillation tower 9, and is heated by the 0.58MPa (A) steam produced by the high-pressure methylammonium washing condenser 3. The temperature rises to 135°C, and the methylammonium is further decomposed. Then the liquid of the low-pressure distillation tower 9 is returned to the urine evaporation tank 71 for heat concentration.

[0095] The gas in the low-pressure distillation tower 9 rises to the filling section of the distillation tower. The distilled gas is led out of the low-pressure distillation tower 9 from the top of the tower and sent to the submerged low-pressure condenser 93 for condensation and absorption. The pipe side of the submerged low-pressure condenser 93 is connected to a circulating water pipeline, and the heat generated by absorption is directly taken away by circulating cooling water.

[0096] The gas-liquid mixture overflows from the upper part of the submerged low-pressure condenser 93 to the low-pressure separator 94 for gas-liquid separation. The liquid in the low-pressure separator 94 is discharged from the bottom of the low-pressure separator 94, and is pressurized to above 2.8 MPa (A) by the low-pressure methylammonium pump 20, and is combined with the liquid in the medium-pressure separator 8 transported by the medium-pressure methylammonium pump 10 and returned to the high-pressure methylamine condenser. The gas separated by the low-pressure separator 94 enters the atmospheric absorption tower 40, and after being absorbed by the atmospheric absorption tower 40, it is discharged through the continuous discharge cylinder to meet environmental protection requirements.

[0097] The urine evaporator 7 in the present invention includes a urine evaporation tank 71 and a urine heat exchanger 72 distributed up and down. The urine evaporation tank 71 is mainly used to receive the bottom liquid phase of the low-pressure distillation tower 9. The urine evaporation tank 71 is connected to the tube side of the urine heat exchanger 72. The top of the medium-pressure distillation tower 6 is connected to the shell side of the urine heat exchanger 72 through a pipeline, and the shell side of the urine heat exchanger 72 is connected to the medium-pressure separator 8 through a pipeline.

[0098] The gas discharged from the top of the medium-pressure distillation tower 6 enters the heat recovery section of the urine evaporator 7, that is, enters the urine heat exchanger 72 of the urine evaporator 7, and further passes into the shell side of the urine heat exchanger 72, and heats the urine inside the urine heat exchanger 72 of the urine evaporator 7 to provide heat for urine pre-concentration.

[0099] Furthermore, after the heat exchange is completed, the gas-liquid mixture enters the medium-pressure separator 8 through the pipeline connected to the shell side of the urine heat exchanger 72 for gas-liquid separation. The liquid phase in the medium-pressure separator 8 is pressurized by the medium-pressure methylammonium pump 10 and then sent to the high-pressure methylammonium washing condenser 3. The gas phase is absorbed by the liquid phase of the medium-pressure separator 8 and is sent to the atmospheric pressure absorption tower 40 for absorption after decompression and then discharged.

[0100] From the perspective of tail gas emissions, the top of the methylammonium washing condenser 3 is connected to the high-pressure absorption tower 30 through a pipeline, and a pressure reducing valve is arranged on the pipeline. The bottom of the high-pressure absorption tower 30 is connected to the atmospheric absorption tower 40 through a pipeline, and is connected to the top side of the atmospheric absorption tower 40. The gas phase pipelines of the medium-pressure separator 8 and the low-pressure separator 94 are combined and connected to the bottom side of the atmospheric absorption tower 40, and the gas phases in the medium-pressure separator 8 and the low-pressure separator 94 are combined and passed into the atmospheric absorption tower 40 for absorption.

[0101] Through this arrangement, the liquid in the high-pressure absorption tower 30 can be sprayed in the atmospheric-pressure absorption tower 40 to spray and recover the gas phase in the medium-pressure separator 8 and the low-pressure separator 94 .

[0102] The urea synthesis device of the present invention improves the process and structure of the existing high-pressure synthesis system, effectively reduces the overall energy consumption of the device, achieves the balance of energy inside the device, reduces equipment costs, and improves urea production capacity.

[0103] It should be noted that, in the absence of conflict, the features in the embodiments of this application may be combined with each other.

[0104] The above description is only the preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A urea synthesis device, characterized in that: It includes a high-pressure synthesis system, a medium-pressure decomposition system and a low-pressure decomposition system connected in sequence; The high-pressure synthesis system comprises a urea synthesis tower, a stripping tower, an ammonia preheater, a methylammonium washing condenser and a high-pressure ejector, which are connected by pipelines; The methylammonium washing condenser comprises a washing section and a condensing section which are distributed up and down, and a vertical steam drum is connected to the shell of the condensing section; The medium-pressure decomposition system includes a medium-pressure distillation tower, a medium-pressure separator and a connecting pipeline, and the low-pressure decomposition system includes a low-pressure distillation tower, a low-pressure separator and a connecting pipeline; It also includes a urine evaporator, which is located between the medium-pressure distillation tower and the medium-pressure separator; The urea synthesis tower is a vertical tower, which adopts an empty tower and a non-porous baffle plate, and includes a high-pressure reactor composed of a metal shell, an internal tower plate and a metal tube, wherein the internal tower plate includes a plurality of baffle plates, and the plurality of baffle plates are arranged in an axially spaced and staggered manner along the urea synthesis tower, and each of the baffle plates is a non-porous baffle plate, and the interior of the urea synthesis tower is filled with urine, and the urine is turned back from bottom to top through the baffle plates inside the urea synthesis tower to reach the top of the tower and flow out; The metal pipe is connected to the top of the urea synthesis tower, and the metal pipe includes a bent pipe section. The urine in the urea synthesis tower flows back to the top of the tower and then is led out through the metal pipe and flows downward. The metal pipe includes a metal pipe horizontal section and a metal pipe vertical section. The metal pipe vertical section is arranged parallel to the axial direction of the urea synthesis tower. The metal tube is connected to the top of the stripping tower through a pipeline. The stripping tower includes a stripping tube and a stripping shell. The top and bottom ends of the stripping tube are respectively provided with a stripping top head and a stripping bottom head. The metal tube is connected to the side of the stripping top head through a pipeline. The top of the stripping tower is connected to the methylammonium washing condenser through a pipeline, and the connection part is arranged at the bottom of the washing section of the methylammonium washing condenser; The urea synthesis tower is connected to the bottom head of the methylammonium washing condenser through a drainage pipe, the high-pressure ejector is connected to the drainage pipe, and the inlet of the high-pressure ejector is connected to the ammonia preheater through a pipe.

2. The urea synthesis device according to claim 1, characterized in that: The top of the stripping top head is connected to the bottom of the washing section through a pipeline.

3. The urea synthesis device according to claim 1, characterized in that: The condensing section includes a heat exchanger, and the heat exchanger includes heat exchange tubes. The heat exchange tubes are vertically arranged in the shell of the methylammonium washing condenser, and the vertical steam drum is connected to the shell through a pipeline.

4. The urea synthesis device according to claim 3, characterized in that: The cavity of the bottom cover of the methylammonium washing condenser is communicated with the heat exchange tube, and the bottom of the urea synthesis tower is connected to the bottom cover of the methylammonium washing condenser through a pipeline.

5. The urea synthesis device according to claim 2, characterized in that: The bottom end caps of the medium-pressure distillation tower and the stripping tower are connected through a medium-pressure pressure reducing pipeline, so that the urea synthesis liquid at the bottom of the stripping tower is decompressed and decomposed through the medium-pressure distillation tower. The medium-pressure pressure reducing pipeline is connected to a stripping tower liquid level regulating valve for adjusting the stripping tower liquid level.

6. The urea synthesis device according to claim 5, characterized in that: The downstream of the medium-pressure distillation tower is connected to the low-pressure decomposition system through a low-pressure pressure reducing pipeline, and a medium-pressure tower liquid level regulating valve is provided on the low-pressure pressure reducing pipeline to adjust the liquid level of the medium-pressure distillation tower. The bottom of the low-pressure distillation tower is connected to the urine evaporator through a pipeline, and the top of the low-pressure distillation tower is connected to a low-pressure condenser and a low-pressure separator in sequence through a pipeline. A medium-pressure methylammonium pump and a low-pressure methylammonium pump are respectively provided at the bottom of the medium-pressure separator and the low-pressure separator, and the discharge pipelines of the medium-pressure methylammonium pump and the low-pressure methylammonium pump are combined and connected to the methylammonium washing condenser, and the connection portion is arranged at the top of the washing section.

7. The urea synthesis device according to claim 6, characterized in that: The urine evaporator comprises a urine evaporation tank and a urine heat exchanger which are distributed up and down. The urine evaporation tank is communicated with the tube side of the urine heat exchanger. The top of the medium-pressure distillation tower is connected with the upper section of the shell of the urine heat exchanger through a pipeline. The upper section of the shell side of the urine heat exchanger is connected with the medium-pressure separator through a pipeline. The lower section of the shell side of the urine heat exchanger uses low-pressure steam to supplement heat.

8. The urea synthesis device according to claim 7, characterized in that: The top of the methylammonium washing condenser is connected to a high-pressure absorption tower through a pipeline, the bottom of the high-pressure absorption tower is connected to a normal-pressure absorption tower through a pipeline, and is connected to the top side of the normal-pressure absorption tower, and the gas phase pipelines of the medium-pressure separator and the low-pressure separator are combined and connected to the bottom side of the normal-pressure absorption tower.

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