Low-energy-consumption urea synthesis system and method

Abstract

The invention provides a low-energy-consumption urea synthesis system and method, and the system comprises a high-pressure synthesis unit which comprises a synthesis tower, a condensation part and a stripping tower; cO2 gas, liquid ammonia and methylamine liquid from the condensation part are introduced into the synthesis tower for a synthesis reaction; the synthesis tower is connected with the stripping tower to introduce the liquid generated by the synthesis reaction into the stripping tower; the synthesis tower is connected with the condensation part to introduce NH3 and CO2 gas generated by synthesis reaction into the condensation part; the stripping tower is connected with the condensing part to introduce NH3 and CO2 into the condensing part; a medium-pressure decomposition recovery unit; a low-pressure decomposition recovery unit; and a urea solution processing unit. By simplifying the high-pressure synthesis unit for urea synthesis, arranging the efficient medium-pressure decomposition and recovery unit, designing and transforming the urea production energy-saving system and optimizing the production process, the energy consumption of urea production is greatly reduced, and the urea synthesis process meets the production requirements of energy conservation and low energy consumption.

Description

Technical Field

[0001] The present application relates to the technical field of urea synthesis, and in particular to a low-energy consumption urea synthesis system and method. Background Art

[0002] The current urea production process in the related technology mainly includes: raw material supply, urea high-pressure synthesis, separation of urea-containing solution, recovery of unreacted ammonia and carbon dioxide, concentration of urea solution, product transportation and process condensate treatment, etc. The above process includes steps carried out under high temperature and high pressure conditions, which require a large amount of energy to provide the heat energy and pressure required for the reaction; sufficient heat energy needs to be provided during the synthesis reaction to maintain the reaction; at the same time, a large amount of steam supply will be generated to provide heat energy and maintain the high temperature and high pressure conditions of the reactor, and the generation of steam requires a large amount of energy. Therefore, the urea synthesis process cannot meet the production needs of energy saving and low energy consumption. Summary of the invention

[0003] The present application aims to solve at least one of the technical problems in the related art to a certain extent. To this end, the present application proposes a low-energy urea synthesis system and method, which greatly reduces the energy consumption of urea production by simplifying the high-pressure synthesis unit of urea synthesis and setting an efficient medium-pressure decomposition and recovery unit, and by designing and transforming the urea production energy-saving system and optimizing the production process, so that the urea synthesis process meets the production requirements of energy saving and low energy consumption.

[0004] The present application proposes a low-energy consumption urea synthesis system, comprising:

[0005] A high-pressure synthesis unit, comprising a synthesis tower, a condensation unit and a stripping tower; wherein CO2 gas, liquid ammonia and methylammonium liquid from the condensation unit under set parameters are introduced into the synthesis tower for synthesis reaction; the synthesis tower is connected to the stripping tower so that the liquid generated by the synthesis reaction is introduced into the stripping tower for thermal decomposition into NH3 and CO2 gas and urea synthesis liquid; the synthesis tower is connected to the condensation unit so that the NH3 and CO2 gas generated by the synthesis reaction is introduced into the condensation unit; the stripping tower is connected to the condensation unit so that the generated NH3 and CO2 gas is introduced into the condensation unit; the NH3 and CO2 gas in the condensation unit reacts with the high-pressure methylammonium liquid to generate methylammonium while generating heat to generate low-pressure steam;

[0006] A medium-pressure decomposition and recovery unit, comprising a medium-pressure decomposition component and a pre-evaporation separation component, wherein the stripping tower is connected to the medium-pressure decomposer to pass the urea synthesis liquid into the medium-pressure decomposition component for heating and decomposition into urea solution A and a first decomposition gas; the first decomposition gas is mixed with the unreacted gas output by the condensation component and then passed into the pre-evaporation separation component and reacts with the medium-pressure methylammonium liquid to generate a gas-liquid mixture, and the pre-evaporation separation component is connected to the condensation component to pass the liquid phase separated from the gas-liquid mixture into the condensation component;

[0007] A low-pressure decomposition recovery unit; connected to the medium-pressure decomposition unit, to decompose the urea solution A at low pressure to obtain a gas-liquid mixture and to distill and heat the gas-liquid mixture to obtain a urea solution B;

[0008] A urea solution processing unit is connected to the low-pressure decomposition recovery unit to concentrate and granulate the urea solution B to obtain urea.

[0009] In some embodiments, the condensing element includes a high-pressure condenser and a high-pressure ejector, wherein the air outlet of the stripping tower is connected to the air inlet of the high-pressure condenser, and the air outlet of the high-pressure condenser is connected to the air inlet of the pre-evaporation separation element; the liquid outlet of the pre-evaporation separation element is connected to the liquid inlet of the high-pressure condenser; the liquid outlet of the high-pressure condenser is connected to the synthesis tower through the high-pressure ejector; the liquid outlet of the synthesis tower is connected to the liquid inlet of the stripping tower, and the liquid outlet of the stripping tower is connected to the medium-pressure decomposition element; the air outlet of the synthesis tower is connected to the second air inlet of the high-pressure condenser.

[0010] In some embodiments, the high-pressure condenser includes a packing filtration zone and a reaction zone connected by a liquid collecting zone and a downcomer; the high-pressure methylammonium liquid passes through the packing filtration zone, the liquid collecting zone and the downcomer, and the reaction zone in sequence, and reacts with NH3 and CO2 gases in the reaction zone; the liquid outlet of the high-pressure condenser is located below the liquid collecting zone, and the methylammonium liquid generated in the reaction zone flows through the tube path of the high-pressure condenser to its liquid outlet.

[0011] In some embodiments, the medium-pressure decomposition element includes a medium-pressure flash evaporator and a medium-pressure decomposition tower element; the urea synthesis liquid passes through the medium-pressure flash evaporator and the medium-pressure decomposition tower element in sequence, and the liquid outlet of the medium-pressure decomposition tower element is connected to the low-pressure decomposition recovery unit; the gas outlet of the medium-pressure decomposition tower element and the gas outlet of the medium-pressure flash evaporator are both connected to the pre-evaporation separation element.

[0012] In some embodiments, the medium-pressure decomposition tower component includes a medium-pressure decomposition tower, a medium-pressure decomposition heater, and a heater liquid level tank connected to the medium-pressure decomposition heater; the methylammonium liquid in the medium-pressure decomposition tower that has not generated the urea solution A is passed into the medium-pressure decomposition heater for heat exchange heating, the generated gas is passed into the medium-pressure decomposition tower, and the steam condensate is passed into the heater liquid level tank.

[0013] In some embodiments, the pre-evaporation separation element includes a medium-pressure pre-evaporator, a medium-pressure absorption tower and a low-pressure absorption tower; the first decomposition gas is mixed with the unreacted gas output by the condensation element and then passed into the medium-pressure pre-evaporator, and mixed with the methylammonium liquid output by the medium-pressure absorption tower to generate the gas-liquid mixture and the first reaction heat; the liquid outlet of the medium-pressure pre-evaporator is connected to a medium-pressure liquid level tank to separate the gas-liquid mixture into gas and liquid, the separated liquid phase is passed into the condensation element, and the separated gas phase is discharged after passing through the medium-pressure absorption tower and the low-pressure absorption tower in sequence.

[0014] In some embodiments, the low-pressure decomposition and recovery unit includes a distillation tower, which includes an upper packed tower and a lower circulating heater; the liquid inlet of the distillation tower is connected to the liquid outlet of the medium-pressure decomposition tower, and the urea solution A passes through the packed tower and the circulating heater in sequence.

[0015] According to an embodiment of the second aspect of the present application, a low-energy urea synthesis method is proposed, which is synthesized using the urea synthesis system described in any of the above embodiments, and comprises the following steps:

[0016] Carbamate, liquid ammonia and part of carbon dioxide are transported to a synthesis tower for reaction, and NH3 and CO2 gases generated by the synthesis reaction are introduced into the condenser; the liquid generated by the synthesis reaction enters the stripping tower and is decomposed into NH3 and CO2 gases and urea synthesis liquid by heat; NH3 and CO2 gases are introduced into the condenser and react with high-pressure carbamate liquid to generate carbamate while generating heat to generate low-pressure steam; the generated carbamate is introduced into the synthesis tower;

[0017] The urea synthesis liquid is heated and decomposed into urea solution A and a first decomposition gas; the first decomposition gas is mixed with the unreacted gas output by the condensing element and then reacted with the medium-pressure methylammonium liquid to generate a gas-liquid mixture, and the liquid phase separated from the gas-liquid mixture is recovered;

[0018] The urea solution A is decomposed at low pressure to obtain a gas-liquid mixture, and the gas-liquid mixture is distilled and heated to obtain a urea solution B; and the urea solution B is concentrated and granulated to obtain urea.

[0019] In some embodiments, the parameters of the NH3 and CO2 gases in the condensing member being introduced into the condensing member and reacting with the high-pressure methylammonium liquid to generate methylammonium are: pressure of 14.1 MPa (A), temperature of 181°C, and CO2 conversion rate of 40-42%; the parameters of the synthesis of the methylammonium liquid, the liquid ammonia and the carbon dioxide are: pressure of 14.3 MPa (A), temperature of 183°C, and CO2 conversion rate of about 60-63%.

[0020] In some embodiments, the urea synthesis liquid is decompressed to a pressure of 2.3 MPa and a temperature of 158°C before entering the medium-pressure decomposition component for heating and decomposition; the parameters for the low-pressure decomposition of the urea solution A are a pressure of 0.45 MPa-0.5 MPa (A) and a temperature of 115°C.

[0021] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become apparent from the description below, or will be learned through the practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The above and / or additional aspects and advantages of the present application will become apparent and easily understood from the following description of the embodiments in conjunction with the accompanying drawings, in which:

[0023] Figure 1 is a structural schematic diagram of a raw material supply unit proposed in one embodiment of the present application;

[0024] Figure 2 is a structural schematic diagram of a high-pressure synthesis unit proposed in one embodiment of the present application;

[0025] Figure 3 is a structural schematic diagram of a high-pressure condenser proposed in one embodiment of the present application;

[0026] Figure 4 It is a structural schematic diagram of a medium-pressure decomposition and recovery unit proposed in one embodiment of the present application;

[0027] Figure 5 It is a structural schematic diagram of a low-pressure decomposition and recovery unit proposed in one embodiment of the present application;

[0028] Figure 6 It is a structural schematic diagram of a urea solution evaporation unit proposed in one embodiment of the present application;

[0029] Figure 7 is a structural schematic diagram of a condensing unit proposed in one embodiment of the present application;

[0030] Figure 8 It is a schematic diagram of the structure of a water decomposition and desorption unit proposed in one embodiment of the present application.

[0031] In the figure,

[0032] 1. Raw material supply unit;

[0033] 2. High-pressure synthesis unit; 21. High-pressure condenser; 211. Packing filtration area; 212. Liquid collecting area; 213. Downcomer; 214. Reaction area; 215. Funnel; 22. Synthesis tower; 23. High-pressure ejector; 24. High-pressure liquid ammonia preheater; 25. Stripping tower;

[0034] 3. Medium-pressure decomposition recovery unit; 31. Medium-pressure flash evaporator; 32. Medium-pressure decomposition tower; 33. Medium-pressure decomposition heater; 34. Heater liquid level tank; 35. High-pressure methylammonium pump; 36. Medium-pressure pre-evaporator; 37. Medium-pressure liquid level tank; 38. Medium-pressure absorption tower; 39. Low-pressure absorption tower;

[0035] 4. Low-pressure decomposition recovery unit; 41. Distillation tower; 411. Packing tower; 412. Circulation heater; 42. Low-pressure methylammonium condenser; 43. Flash tank; 44. Low-pressure methylammonium condenser liquid level tank;

[0036] 5. Urea solution processing unit; 52. One-stage evaporator; 53. One-stage separator; 54. Two-stage evaporator; 55. Two-stage separator; 56. Granulation tower. DETAILED DESCRIPTION

[0037] Embodiments of the present application are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements with the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present application, and cannot be construed as limiting the present application. On the contrary, the embodiments of the present application include all changes, modifications and equivalents that fall within the spirit and connotation of the appended claims.

[0038] Urea is a colorless crystalline solid that is soluble in water. Urea is an important nitrogen fertilizer that is widely used in agriculture. The industrial production of urea is carried out in two steps from ammonia (NH3) and carbon dioxide (CO2) to produce urea (NH2CONH2). The first step is the reaction of ammonia with carbon dioxide to produce ammonium carbamate (NH2COONH4), also known as methylammonium. The chemical reaction is:

[0039] The second step is to dehydrate ammonium carbamate to produce urea, and the chemical reaction is:

[0040] Finally, the reaction gas-liquid mixture comes out from the top of the synthesis tower and enters the medium-pressure decomposition tower for heating, so that the unreacted substances in the gas-liquid mixture are decomposed and separated during the reduced pressure heating; the decomposition products are purified and recycled through the above-mentioned other reactors to finally obtain the finished urea product.

[0041] At present, the following problems exist in the related art: First, the process of synthesizing ammonium carbamate from ammonia and carbon dioxide involves more high-pressure equipment, which consumes a large amount of raw materials and energy, and is not conducive to energy saving and emission reduction. Secondly, the structure of the high-pressure methylammonium condenser generates methylammonium by refluxing medium-pressure methylammonium and carbon dioxide and gaseous ammonia under high pressure conditions, and uses the heat released by the reaction to heat the water outside the tube to produce low-pressure steam, but the condensation degree of the high-pressure methylammonium condenser in the related art is about 80%, and the condensed liquid and uncondensed gas flow into the synthesis tower through their respective pipelines. Finally, the setting in the medium-pressure decomposition unit is unreasonable, and a medium-pressure temperature regulating water device needs to be set up in conjunction, the cooling water consumption and the power consumption of the device are high, and the steam consumption is large, etc., resulting in an increase in energy consumption of the entire urea production system.

[0042] Based on this, the present application proposes a low energy consumption urea synthesis system such as Figure 1-Figure 8 , including: a high-pressure synthesis unit 2, a medium-pressure decomposition and recovery unit 3, a low-pressure decomposition and recovery unit 4 and a urea solution processing unit 5; wherein Figure 2 The high-pressure synthesis unit 2 includes a synthesis tower 22, a condensation part and a stripping tower 25; wherein CO2 gas, liquid ammonia and methylammonium liquid from the condensation part under set parameters are introduced into the synthesis tower 22 for synthesis reaction; the synthesis tower 22 is connected to the stripping tower 25 so that the liquid generated by the synthesis reaction is introduced into the stripping tower 25 for thermal decomposition into NH3 and CO2 gas and urea synthesis liquid; the synthesis tower 22 is connected to the condensation part so that the NH3 and CO2 gas generated by the synthesis reaction is introduced into the condensation part; the NH3 and CO2 gas react with the high-pressure methylammonium liquid to generate methylammonium while generating heat to generate low-pressure steam.

[0043] Among them, the condensing part includes a high-pressure condenser 21 and a high-pressure ejector 23, wherein the air outlet of the stripping tower 25 is connected to the air inlet of the high-pressure condenser 21, and the air outlet of the high-pressure condenser 21 is connected to the air inlet of the pre-evaporation separation part; the liquid outlet of the pre-evaporation separation part is connected to the liquid inlet of the high-pressure condenser 21; the liquid outlet of the high-pressure condenser 21 is connected to the synthesis tower 22 through the high-pressure ejector 23; the liquid outlet of the synthesis tower 22 is located at the top and connected to the liquid inlet of the stripping tower 25, and the liquid outlet of the stripping tower 25 is connected to the medium-pressure decomposition part; the air outlet of the synthesis tower 22 is located at the top and connected to the second air inlet of the high-pressure condenser 21.

[0044] In some embodiments, the low-energy urea synthesis system further includes a raw material supply unit 1, wherein the raw material supply unit 1 provides high-pressure liquid ammonia and compressed carbon dioxide to the high-pressure synthesis unit 2, and includes a liquid ammonia supply component and a compressed carbon dioxide supply component; the exemplary raw material supply unit 1 is as follows Figure 1 shown.

[0045] The liquid ammonia supply component includes a liquid ammonia filter, a liquid ammonia buffer tank and a high-pressure ammonia pump, wherein the temperature of the raw liquid ammonia is 25°C and its pressure is greater than 2.20MPa. After being filtered by the liquid ammonia filter, it enters the liquid ammonia buffer tank. The liquid ammonia output from the liquid ammonia buffer tank is pressurized to 19.9MPa by the high-pressure ammonia pump and then enters the high-pressure synthesis unit 2.

[0046] The compressed carbon dioxide supply component includes a carbon dioxide droplet separator, a carbon dioxide compressor, a desulfurization unit and a dehydrogenation unit, wherein the raw carbon dioxide gas with CO2 ≥ 98.5% (Vol) has a pressure of 0.15MPa (A) and a temperature of 35°C. The raw carbon dioxide gas is mixed with a certain amount of air and first passes through the carbon dioxide droplet separator and then enters the carbon dioxide compressor. The carbon dioxide gas is compressed to a pressure of 14.7MPa.

[0047] The CO2 gas with a pressure of 14.7 MPa cannot be directly input into the high-pressure synthesis unit 2 and needs to be dehydrogenated. Therefore, in this embodiment, before the raw carbon dioxide gas enters the carbon dioxide droplet separator, a certain amount of air is added for dehydrogenation reaction and for corrosion protection of equipment in the high-pressure synthesis unit 2 to ensure that the oxygen content entering the high-pressure synthesis unit 2 reaches 0.6% (vol).

[0048] For example, the desulfurization unit and the dehydrogenation unit in the compressed carbon dioxide supply assembly are both connected to the carbon dioxide compressor. The dehydrogenation unit uses a precious metal catalyst for dehydrogenation. The dehydrogenation unit includes a dehydrogenation reactor. The dehydrogenation reactor is provided with a three-stage outlet of the carbon dioxide compressor. Since the dehydrogenation catalyst is easily poisoned by sulfur, in order to ensure the life of the dehydrogenation catalyst, the sulfur in the compressed carbon dioxide gas is removed before dehydrogenation is required. Therefore, the desulfurization unit is arranged before the three-stage inlet of the carbon dioxide compressor. The desulfurization unit includes a desulfurization tower, which uses a fine desulfurizer. After desulfurization, the total sulfur content of the carbon dioxide gas is less than 0.1ppm.

[0049] In some embodiments, the high-pressure liquid ammonia with a pressure of 19.9 MPa output by the liquid ammonia supply assembly is preheated by the high-pressure liquid ammonia preheater 24 before entering the high-pressure ejector 23. The high-pressure liquid ammonia preheater 24 uses waste water as a heat source. The high-pressure liquid ammonia serves as the power medium of the high-pressure ejector 23 to boost the pressure of the urea synthesis liquid from the high-pressure condenser 21 and send it to the bottom of the synthesis tower 22.

[0050] In this embodiment, high-pressure compressed CO2 gas with a pressure of 14.7 MPa is sent to the stripping tower and the high-pressure condenser 21; under steam heating conditions, the liquid generated by the synthesis reaction from the synthesis tower 22 is decomposed into NH3 and CO2 gases in the stripping tower and sent to the high-pressure condenser 21, and at the same time, the NH3 and CO2 gases generated by the synthesis reaction from the synthesis tower 22 enter the high-pressure condenser 21; NH3 and CO2 gases react with the high-pressure methylammonium liquid from the high-pressure methylammonium pump 35 in the lower part of the high-pressure condenser 21 to generate methylammonium and generate heat; the reaction releases a large amount of heat for the by-product low-pressure steam for subsequent use and external supply.

[0051] Among them Figure 3 The high-pressure condenser 21 shown includes a packing filtration zone 211 and a reaction zone 214 connected by a liquid collecting zone 212 and a downcomer 213; the high-pressure methylammonium liquid passes through the packing filtration zone 211, the liquid collecting zone 212 and the downcomer 213, and the reaction zone 214 in sequence, and reacts with NH3 and CO2 gases in the reaction zone 214; the liquid outlet of the high-pressure condenser 21 is located at the funnel 215 below the liquid collecting zone 212, and the methylammonium liquid is sucked into the synthesis tower 22 through the funnel 215 by the high-pressure ejector 23.

[0052] The high-pressure condenser 21 is divided into two parts, an upper part and an lower part. In the upper packing filtration area 211, the low-temperature high-pressure methylammonium liquid from the high-pressure methylammonium pump 35 washes the unreacted gas phase (NH3 and CO2 gas). The washing liquid passes through the liquid collecting area 212 and the downcomer 213 and descends to the bottom head of the high-pressure condenser 21, i.e., the reaction area 214. The NH3 and CO2 gases output by the stripping tower react with the high-pressure methylammonium liquid to generate methylammonium. The reaction liquid containing methylammonium flows from bottom to top in the tube side of the high-pressure condenser 21, and when its liquid level reaches the liquid outlet, it is pressurized by the high-pressure ejector 23 and enters the synthesis tower 22 for further reaction. In this embodiment, since the liquid ammonia is preheated, the heat balance in the synthesis tower 22 can be maintained. The synthesis reaction liquid out of the synthesis tower 22 flows into the stripping tower by the pressure difference, and the unreacted NH3, CO2 and inert gas are sent to the high-pressure condenser 21 for condensation and absorption. The unreacted NH3, CO2 and inert gas exiting the high-pressure condenser 21 enter the medium-pressure decomposition and recovery unit 3.

[0053] Among them, in this embodiment, the operating conditions of the high-pressure condenser 21 are: pressure of 14.1MPa(A), temperature of 181°C, and CO2 conversion rate of about 40-42%; the operating conditions of the synthesis tower 22 are: pressure of 14.3MPa(A), 183°C, and CO2 conversion rate of about 61-63%. The specially designed high-pressure condenser 21 with a new structure is used to increase the reaction rate of methylammonium, quickly remove the reaction heat, and produce a higher level of low-pressure steam as a by-product for use by subsequent equipment in the device, thereby reducing the supply of external steam. Therefore, the present application simplifies the high-pressure synthesis unit 2, saves investment, and the synthesis tower 22 can be arranged on the ground, reducing the frame height of the system. Finally, compared with the relevant technology, the present application cancels the high-pressure water adjustment system, simplifies the process, and reduces the investment in system components.

[0054] like Figure 4 The medium-pressure decomposition recovery unit 3 shown includes a medium-pressure decomposition component and a pre-evaporation separation component, wherein the stripping tower 25 is connected to the medium-pressure decomposer to pass the urea synthesis liquid into the medium-pressure decomposition component for heating and decomposition into urea solution A and a first decomposition gas; the first decomposition gas is mixed with the unreacted gas output by the condensation component and then passed into the pre-evaporation separation component and reacts with the medium-pressure methylammonium liquid to generate a gas-liquid mixture, and the pre-evaporation separation component is connected to the condensation component to pass the liquid phase separated from the gas-liquid mixture into the condensation component;

[0055] The medium-pressure decomposition component includes a medium-pressure flash evaporator 31 and a medium-pressure decomposition tower 32; the urea synthesis liquid passes through the medium-pressure flash evaporator 31 and the medium-pressure decomposition tower 32 in sequence, and the liquid outlet of the medium-pressure decomposition tower 32 is connected to the low-pressure decomposition recovery unit 4; the gas outlet of the medium-pressure decomposition tower 32 and the gas outlet of the medium-pressure flash evaporator 31 are both connected to the pre-evaporation separation component.

[0056] The urea synthesis liquid from the stripping tower is decompressed to a pressure of 2.3MPa and a temperature of 158°C by a regulating valve and then enters a medium-pressure flash evaporator 31, where gas-liquid separation is performed, and the separated liquid phase enters a medium-pressure decomposition tower 32, and the separated gas phase is mixed with unreacted NH3, CO2 and inert gas in the high-pressure condenser 21 and enters a pre-evaporation separation unit. In this embodiment, the medium-pressure decomposition tower 32 includes a medium-pressure decomposition tower 32, a medium-pressure decomposition heater 33 and a heater level tank 34 connected to the medium-pressure decomposition heater 33; the methylammonium liquid in the medium-pressure decomposition tower 32 that has not generated urea solution A is passed into the medium-pressure decomposition heater 33 for heat exchange heating, and the medium-pressure decomposition heater 33 is a rising film heater that continues to heat the methylammonium liquid that has not generated urea solution A, and the generated gas-liquid mixture is passed into the medium-pressure decomposition tower 32, and the urea solution A enters the low-pressure decomposition recovery unit 4.

[0057] The pre-evaporation separation component includes a medium-pressure pre-evaporator 36, a medium-pressure absorption tower 38 and a low-pressure absorption tower 39; the first decomposition gas is mixed with the unreacted gas output by the condensation component and then introduced into the medium-pressure pre-evaporator 36, and mixed with the methylammonium liquid output by the medium-pressure absorption tower 38 to generate a gas-liquid mixture and a first reaction heat; the liquid outlet of the medium-pressure pre-evaporator 36 is connected to the medium-pressure liquid level tank 37 to separate the gas-liquid mixture into gas and liquid, and the separated liquid phase is a medium-pressure methylammonium liquid with a higher temperature, which is introduced into the high-pressure condenser 21 through the high-pressure methylammonium pump 35, and the separated gas phase passes through the medium-pressure absorption tower 38 and the low-pressure absorption tower 39 in turn and is discharged.

[0058] The gas phase separated by the medium-pressure flash evaporator 31 is mixed with the unreacted NH3, CO2 and inert gas in the high-pressure condenser 21 and then enters the medium-pressure pre-evaporator 36, and is mixed with the methylammonium liquid output from the medium-pressure absorption tower 38 to generate a gas-liquid mixture and a first reaction heat; the liquid outlet of the medium-pressure pre-evaporator 36 is connected to the medium-pressure liquid level tank 37 to separate the gas-liquid mixture into gas and liquid, and the separated liquid phase is passed into the high-pressure condenser 21, and the separated gas phase passes through the medium-pressure absorption tower 38; and is mixed and reacted with the methylammonium liquid from the medium-pressure methylammonium pump, and the reaction liquid is the methylammonium liquid output from the medium-pressure absorption tower 38; the gas phase output from the medium-pressure absorption tower 38 passes through the low-pressure absorption tower 39, and is discharged after being absorbed by the steam condensate, and the liquid phase output from the low-pressure absorption tower 39 can be passed into the atmospheric pressure absorption tower.

[0059] In this embodiment, the medium-pressure methylammonium liquid at a relatively high temperature returns to the high-pressure condenser 21, and the heat brought in produces more high-quality low-pressure steam in the high-pressure condenser 21, which can meet the heating requirements of subsequent processes. In addition, because the medium-pressure methylammonium liquid at a relatively high temperature returns to the high-pressure condenser 21, the medium-pressure decomposition and recovery unit 3 no longer needs to be provided with a medium-pressure temperature regulating water system, the process is simple, the number of equipment units is small, and the cooling water consumption and the power consumption of the device are reduced. Finally, the setting of the high-efficiency medium-pressure decomposition and recovery unit 3 allows the medium-pressure flash gas to go to the pre-evaporator and mix with the methylammonium liquid output by the medium-pressure absorption tower 38 to undergo a chemical reaction, and the reaction heat is used to preheat the urea solution, thereby reducing the steam consumption of the system.

[0060] The gas phase output from the medium-pressure absorption tower 38 passes through the low-pressure absorption tower 39 and is discharged after being absorbed by the steam condensate. The efficient venting air ammonia washing and recovery system uses ammonia recovery in the venting tail gas to avoid some problems caused by the acid washing process.

[0061] The low-pressure decomposition recovery unit 4 is connected to the medium-pressure decomposition unit to decompose the urea solution A at low pressure to obtain a gas-liquid mixture and to obtain a urea solution B by distilling and heating the gas-liquid mixture.

[0062] Among them Figure 5The low-pressure decomposition recovery unit 4 shown includes a distillation tower 41, which includes a packing tower 411 at the top and a circulation heater 412 at the bottom; the liquid inlet of the distillation tower 41 is connected to the liquid outlet of the medium-pressure decomposition tower 32, and the urea solution A passes through the packing tower 411 and the circulation heater 412 in sequence. The urea solution A from the medium-pressure decomposition tower 32 is decompressed 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, and the low-pressure decomposition is performed to obtain a gas-liquid mixture, which enters the packing tower 411 for gas distillation. The urea-methylammonium liquid falling through the packing tower 411 flows into the circulation heater 412. In this process, the urea-methylammonium liquid is heated by the 0.58MPa (A) steam produced as a byproduct of the high-pressure condenser 21, and the temperature rises to 135°C. The methylammonium is further decomposed, and the decomposed liquid flows into the flash tank 43 through the control valve, and is subjected to negative pressure flash evaporation, wherein the pressure is about 0.044MPa (A), and the temperature drops from 135°C to 95°C, and then separated to obtain urea solution B. The gas phase at the top of the flash tank 43 enters the urea solution processing unit 5 for condensation. The gas separated by the packing tower 411 rises to the packing tower 411, and the rectified gas is led out of the rectification tower 41 and sent to the submerged low-pressure methylammonium condenser 42.

[0063] Here, in the low-pressure methylammonium condenser 42, the gas from the distillation tower 41 and the reflux liquid from the reflux pump enter the low-pressure methylammonium condenser 42 from the bottom. The two phases rise in parallel for absorption, and the heat generated during absorption is directly taken away by circulating cooling water. The gas-liquid mixture overflows from the upper part of the low-pressure methylammonium condenser 42 to the low-pressure methylammonium condenser liquid level tank 44 for gas-liquid separation. The separated liquid is discharged from the bottom of the liquid level tank and pumped to a pressure of more than 2.8MPa before being sent to the medium-pressure absorption tower 38; at the same time, the separated gas enters the low-pressure absorption tower 39, and after being absorbed by the low-pressure absorption tower 39, it meets environmental protection requirements and is discharged through continuous discharge.

[0064] The urea solution processing unit 5 is connected to the low-pressure decomposition recovery unit 4 to concentrate and granulate the urea solution B to obtain urea.

[0065] Among them Figure 6-Figure 8 The urea solution processing unit 5 includes a urea solution evaporation unit, a condensation unit and a hydrolysis desorption unit; wherein the urea solution evaporation unit is as follows Figure 6As shown, it includes a medium-pressure pre-evaporator 36, a first-stage evaporator 52, a first-stage separator 53, a second-stage evaporator 54, a second-stage separator 55 and a granulation tower 56; wherein the urea solution B with a concentration of about 67% (wt) flows into the medium-pressure pre-evaporator 36, and is concentrated to a concentration of 82% in the medium-pressure pre-evaporator 36 and then sent to the first-stage evaporator 52, a urea solution is generated in the first-stage evaporator 52, and is separated by the first-stage separator 53 and then sent to the second-stage evaporator 54, the urea solution is concentrated to 99.7% (wt) at 0.003MPa (A) and 138°C to obtain molten urea, and after the molten urea is separated by the second-stage separator 55, it is pumped by the molten urea pump to the rotary nozzle located at the top of the granulation tower 56 for granulation, and the finished granular urea obtained at the bottom of the granulation tower 56 is sent to the packaging building for packaging by a belt conveyor, and in addition, the tail gas at the top of the granulation tower 56 is dust-removed and washed, and the emission index after washing meets the environmental protection requirements.

[0066] In addition, in the urea synthesis system, each section of the evaporation condensate contains a certain amount of ammonia, a small amount of carbon dioxide and a small amount of urea. The evaporation condensate of each section can be introduced into the condensation unit such as Figure 7 As shown, each section of the evaporation condensate contains a certain amount of ammonia, a small amount of carbon dioxide and a small amount of urea. Each section of the evaporation condensate can be introduced into a process condensate tank, wherein the process condensate tank is divided into two first compartments and a second compartment of different sizes by a partition, wherein the volume of the first compartment is larger than the second compartment and the first compartment and the second compartment are connected by a hole at the bottom. Therefore, the liquid level of the first compartment and the second compartment is the same but not completely mixed. The first compartment can be used to store factory discharge liquid or flushing process liquid; and the second compartment can be used to store process condensate. For example, a part of the evaporation condensate in the process condensate tank is sent to the low-pressure absorption tower 39 by a low-pressure absorption tower feed pump, and the effluent of the low-pressure absorption tower 39 enters the atmospheric absorption tower; the effluent of the atmospheric absorption tower enters the process condensate tank as shown in FIG. Figure 7 shown.

[0067] like Figure 8In the hydrolysis desorption unit shown, a portion of the evaporated condensate in the process condensate tank is heated to 117°C by the desorption tower feed pump through the desorption tower heat exchanger and sent to the upper part of the first desorption tower to desorb ammonia and carbon dioxide, wherein the operating pressure of the first desorption tower is 0.35MPa(A). The liquid from the first desorption tower is pressurized to 2.6MPa by the hydrolysis tower feed pump and heat exchanged by the hydrolysis tower heat exchanger before entering the upper part of the hydrolysis tower. Steam above 2.1MPa is introduced into the lower part of the hydrolysis tower to hydrolyze a small amount of urea contained in the liquid into ammonia and carbon dioxide. The gas phase output from the hydrolysis tower enters the upper part of the first desorption tower. The liquid phase output from the hydrolysis tower has a temperature of 151°C after heat exchange in the hydrolysis tower heat exchanger and enters the upper part of the second desorption tower. The operating pressure is 0.4MPa. The lower part of the second desorption tower is fed with 0.6MPa (A) steam for desorption. The bottom temperature of the second desorption tower is 147°C. The desorbed ammonia, carbon dioxide and water vapor are directly introduced into the lower part of the first desorption tower and exchange mass and heat with the liquid of the first desorption tower. The gas output from the first desorption tower contains less than 40% water and is condensed in the reflux condenser. A part of the condensate is refluxed to the top of the first desorption tower as reflux liquid for mass and heat exchange to reduce the water content of the gas phase out of the tower. The other part of the condensate is sent to the low-pressure methylammonium condenser. The uncondensed gas in the reflux condenser enters the atmospheric pressure absorption tower, and is further recovered and discharged after ammonia and carbon dioxide are recovered. The liquid after desorption in the second desorption tower contains less than 5ppm ammonia and less than 5ppm urea. After heat exchange in the desorption tower heat exchanger and cooling in the wastewater cooler, it is sent out of the boundary area for discharge.

[0068] According to an embodiment of the second aspect of the present application, a low-energy urea synthesis method is proposed, which is synthesized using the urea synthesis system in any of the above embodiments, and comprises the following steps:

[0069] The methylammonium liquid, liquid ammonia and part of carbon dioxide are transported to the synthesis tower 22 for reaction to obtain a synthesis reaction liquid; the liquid generated by the synthesis reaction enters the stripping tower 25 and is decomposed into NH3 and CO2 gas and urea synthesis liquid by heat; the NH3 and CO2 gas generated by the synthesis reaction and the NH3 and CO2 gas generated by the stripping tower 25 enter different air inlets at the bottom of the high-pressure condenser 21; the NH3 and CO2 gas are introduced into the condensing element and react with the high-pressure methylammonium liquid to generate methylammonium while generating heat to generate low-pressure steam; the generated methylammonium is introduced into the synthesis tower 22;

[0070] The urea synthesis liquid is heated and decomposed into urea solution A and a first decomposition gas; the first decomposition gas is mixed with the unreacted gas outputted from the condenser and then reacted with the medium-pressure methylammonium liquid to generate a gas-liquid mixture, and the liquid phase separated from the gas-liquid mixture is recovered;

[0071] Urea solution A is decomposed at low pressure to obtain a gas-liquid mixture, and the gas-liquid mixture is distilled and heated to obtain urea solution B; and urea solution B is concentrated and granulated to obtain urea.

[0072] In some embodiments, the parameters of NH3 and CO2 gases in the condensing member being introduced into the condensing member and reacting with high-pressure methylammonium liquid to generate methylammonium are: pressure of 14.1 MPa (A), temperature of 181°C, and CO2 conversion rate of 40-42%; the parameters for the synthesis of methylammonium liquid, liquid ammonia and carbon dioxide are: pressure of 14.3 MPa (A), temperature of 183°C, and CO2 conversion rate of about 60-63%.

[0073] In some embodiments, the urea synthesis liquid is decompressed to a pressure of 2.3 MPa and a temperature of 158°C before entering a medium-pressure decomposition component for heating and decomposition; the parameters for low-pressure decomposition of urea solution A are a pressure of 0.45 MPa-0.5 MPa (A) and a temperature of 115°C.

[0074] It should be noted that, in the description of this application, the terms "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance. In addition, in the description of this application, unless otherwise specified, the meaning of "plurality" is two or more.

[0075] Any process or method description in a flowchart or otherwise described herein may be understood to represent a module, segment or portion of code that includes one or more executable instructions for implementing the steps of a specific logical function or process, and the scope of the preferred embodiments of the present application includes alternative implementations in which functions may not be performed in the order shown or discussed, including performing functions in a substantially simultaneous manner or in the reverse order depending on the functions involved, which should be understood by technicians in the technical field to which the embodiments of the present application belong.

[0076] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0077] Although the embodiments of the present application have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limitations on the present application. Ordinary technicians in this field can change, modify, replace and modify the above embodiments within the scope of the present application.

Claims

1. A low energy consumption urea synthesis system, characterized in that: include: A high pressure synthesis unit, which includes a synthesis column, a condensation unit and a stripping column; The CO2 gas, liquid ammonia and methylammonium liquid from the condensing part under the set parameters are introduced into the synthesis tower for synthesis reaction; the synthesis tower is connected with the stripping tower so that the liquid generated by the synthesis reaction is introduced into the stripping tower for thermal decomposition into NH3 and CO2 gas and urea synthesis liquid; the synthesis tower is connected with the condensing part so that the NH3 and CO2 gas generated by the synthesis reaction is introduced into the condensing part; the stripping tower is connected with the condensing part so that the generated NH3 and CO2 gas is introduced into the condensing part, and the NH3 and CO2 gas in the condensing part reacts with the high-pressure methylammonium liquid to generate methylammonium and generates heat to generate low-pressure steam; A medium-pressure decomposition and recovery unit, comprising a medium-pressure decomposition component and a pre-evaporation separation component, wherein the stripping tower is connected to the medium-pressure decomposer, so that the urea synthesis liquid is passed into the medium-pressure decomposition component for heating and decomposition into urea solution A and a first decomposition gas; the first decomposition gas is mixed with the unreacted gas output by the condensation component and then passed into the pre-evaporation separation component and reacted with the medium-pressure methylammonium liquid to generate a gas-liquid mixture, the gas-liquid mixture is passed into the medium-pressure separator, and the liquid phase separated from the gas-liquid mixture is passed into the condensation component; Low-pressure decomposition recovery unit; It is connected to the medium-pressure decomposition component to decompose the urea solution A at low pressure to obtain a gas-liquid mixture and to obtain a urea solution B by distilling and heating the gas-liquid mixture. Urea solution processing unit; It is connected to the low-pressure decomposition recovery unit to concentrate and granulate the urea solution B to obtain urea.

2. The urea synthesis system according to claim 1, characterized in that: The condensing element comprises a high-pressure condenser and a high-pressure ejector, wherein the air outlet of the stripping tower is connected to the air inlet of the high-pressure condenser, and the air outlet of the high-pressure condenser is connected to the air inlet of the pre-evaporation separation element; the liquid outlet of the pre-evaporation separation element is connected to the liquid inlet of the high-pressure condenser; the liquid outlet of the high-pressure condenser is connected to the synthesis tower through the high-pressure ejector; the liquid outlet of the synthesis tower is connected to the liquid inlet of the stripping tower, and the liquid outlet of the stripping tower is connected to the medium-pressure decomposition element, and the air outlet of the synthesis tower is connected to the second air inlet of the high-pressure condenser.

3. The urea synthesis system according to claim 2, characterized in that: The high-pressure condenser includes a packing filtration zone and a reaction zone connected by a liquid collecting zone and a downcomer; the high-pressure methylammonium liquid passes through the packing filtration zone, the liquid collecting zone and the downcomer, and the reaction zone in sequence, and reacts with NH3 and CO2 gases in the reaction zone; the liquid outlet of the high-pressure condenser is located below the liquid collecting zone, and the methylammonium liquid generated in the reaction zone flows to its liquid outlet through the tube path of the high-pressure condenser.

4. The urea synthesis system according to any one of claims 1 to 3, characterized in that: The medium-pressure decomposition element comprises a medium-pressure flash evaporator and a medium-pressure decomposition tower element; the urea synthesis liquid passes through the medium-pressure flash evaporator and the medium-pressure decomposition tower element in sequence, and the liquid outlet of the medium-pressure decomposition tower element is connected to the low-pressure decomposition recovery unit; the gas outlet of the medium-pressure decomposition tower element and the gas outlet of the medium-pressure flash evaporator are both connected to the pre-evaporation separation element.

5. The urea synthesis system according to claim 4, characterized in that: The medium-pressure decomposition tower component includes a medium-pressure decomposition tower, a medium-pressure decomposition heater, and a heater liquid level tank connected to the medium-pressure decomposition heater; the methylammonium liquid in the medium-pressure decomposition tower that has not generated the urea solution A is passed into the medium-pressure decomposition heater for heat exchange heating, the generated gas is passed into the medium-pressure decomposition tower, and the steam condensate is passed into the heater liquid level tank.

6. The urea synthesis system according to claim 4, characterized in that: The pre-evaporation separation component includes a medium-pressure pre-evaporator, a medium-pressure absorption tower and a low-pressure absorption tower; the first decomposition gas is mixed with the unreacted gas output by the condensation component and then introduced into the medium-pressure pre-evaporator, and mixed with the methylammonium liquid output by the medium-pressure absorption tower to generate the gas-liquid mixture and the first reaction heat; the liquid outlet of the medium-pressure pre-evaporator is connected to the medium-pressure liquid level tank to separate the gas-liquid mixture into gas and liquid, the separated liquid phase is introduced into the condensation component, and the separated gas phase is discharged after passing through the medium-pressure absorption tower and the low-pressure absorption tower in sequence.

7. The urea synthesis system according to claim 4, characterized in that: The low-pressure decomposition recovery unit comprises a distillation tower, which comprises an upper packing tower and a lower circulating heater; the liquid inlet of the distillation tower is connected to the liquid outlet of the medium-pressure decomposition tower, and the urea solution A passes through the packing tower and the circulating heater in sequence.

8. A low-energy urea synthesis method, characterized in that: The urea synthesis system according to any one of claims 1 to 7 is used for synthesis, comprising the following steps: Carbamate, liquid ammonia and part of carbon dioxide are transported to a synthesis tower for reaction, and NH3 and CO2 gases generated by the synthesis reaction are introduced into the condenser; the liquid generated by the synthesis reaction enters the stripping tower and is decomposed into NH3 and CO2 gases and urea synthesis liquid by heat; NH3 and CO2 gases are introduced into the condenser and react with high-pressure carbamate liquid to generate carbamate while generating heat to generate low-pressure steam; the generated carbamate is introduced into the synthesis tower; The urea synthesis liquid is heated and decomposed into urea solution A and a first decomposition gas; the first decomposition gas is mixed with the unreacted gas output by the condensing element and then reacted with the medium-pressure methylammonium liquid to generate a gas-liquid mixture, and the liquid phase separated from the gas-liquid mixture is recovered; The urea solution A is decomposed at low pressure to obtain a gas-liquid mixture, and the gas-liquid mixture is distilled and heated to obtain a urea solution B; and the urea solution B is concentrated and granulated to obtain urea.

9. The urea synthesis method according to claim 8, characterized in that: The parameters of the NH3 and CO2 gases in the condensing member being introduced into the condensing member and reacting with the high-pressure methylammonium liquid to generate methylammonium are: pressure of 14.1MPa(A), temperature of 181°C, and CO2 conversion rate of 40-42%; the parameters of the synthesis of the methylammonium liquid, the liquid ammonia and the carbon dioxide are: pressure of 14.3MPa(A), temperature of 183°C, and CO2 conversion rate of about 60-63%.

10. The urea synthesis method according to claim 8, characterized in that: The urea synthesis liquid is decompressed to a pressure of 2.3 MPa and a temperature of 158°C and then enters the medium-pressure decomposition component for heating and decomposition; the parameters for the low-pressure decomposition of the urea solution A are a pressure of 0.45 MPa-0.5 MPa (A) and a temperature of 115°C.

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