Rectification and purification control process for production of adblue

Abstract

The invention discloses an adblue production rectification purification control process which comprises the following steps: introducing liquid carbon dioxide and liquid ammonia from the bottom of a urea synthesis tower for reaction to obtain a synthesis liquid; introducing the synthetic liquid into a stripping tower for stripping, and separating part of unreacted gas in the synthetic liquid; introducing the synthetic liquid subjected to steam stripping into a rectifying tower for rectification; in response to the fact that the liquid level of each layer in the tower body is lower than a preset value, each first valve and each second valve are kept in an open state, and each third valve is kept in a closed state for rectification; in response to the condition that the liquid level of a layer in the tower body is higher than or equal to a preset value, closing the first valve and the second valve of the layer of which the liquid level is higher than or equal to the preset value, opening the corresponding third valve, and stopping ventilation for rectification; heating and evaporating the rectified synthetic liquid to obtain urea crystals; and granulating the urea crystals to obtain granular urea. The method can effectively reduce the influence of the flooding condition on the urea production efficiency.

Description

Technical Field

[0001] The invention relates to the field of urea production, and in particular to a distillation and purification control process for producing automotive urea. Background Art

[0002] Diesel exhaust treatment fluid (commonly known as automotive urea, automotive urea, automotive environmentally friendly urea in China), heavy trucks, buses and other diesel vehicles must meet the National IV emission standards, and a suitable SCR system must be selected for exhaust treatment, and this system must use urea solution to treat nitrogen oxides in the exhaust. Therefore, automotive urea solution has become a necessary product for heavy trucks and buses to meet the National IV emission standards.

[0003] Automotive urea is a urea aqueous solution with a concentration of 32.5% and a solvent of ultrapure water. The raw materials for production are special raw materials for automotive urea (solid granular urea) and ultrapure water. Urea, also known as carbon amide, is a white crystal with a melting point of 132.7°C. In the production process of granular urea, stripping, distillation and other steps are generally used to separate the unreacted gas and / or impurities in the urea synthesis liquid. However, during the distillation process, foam (bubbles) will be generated due to the contact between the urea synthesis liquid and the gas. Once the gas flow rate is too large or there is a blockage in the tower, it is easy to entrain excessive liquid foam to the upper plate. The liquid foam entrained by the air flow to the upper plate can thicken the liquid layer on the plate, and the liquid foam brought out by the air flow through the thickened liquid layer is further increased. This excessive liquid foam entrainment reduces the distance between the top of the foam layer and the bottom of the upper plate, and the liquid foam entrainment continues to increase. Large droplets are easily sprayed directly onto the upper plate, and the foam can also bubble up to the upper plate, until the entire tower is filled with liquid. This phenomenon is generally called flooding. The conventional method for solving the problem of flooding is generally to stop the introduction of urea synthesis liquid and distillation gas when flooding occurs. Summary of the invention

[0004] The applicant has found through research that when a tray in the urea distillation tower is flooded, the entire distillation tower will soon be filled with liquid. In this case, the flooding has to be solved by stopping the introduction of urea synthesis liquid and distillation gas. However, this will greatly reduce the production efficiency of granular urea.

[0005] In view of the above-mentioned defects of the prior art, the technical problem to be solved by the present invention is to provide a distillation and purification control process for the production of automotive urea, aiming to solve the flooding problem generated during the distillation process of urea synthesis liquid and reduce the impact of the flooding on production efficiency.

[0006] To achieve the above object, the present invention provides a process for controlling the production, distillation and purification of automotive urea, the process comprising:

[0007] Step S1, pressurizing liquid carbon dioxide and liquid ammonia in a molar ratio of 1:3-4 and introducing them from the bottom of a urea synthesis tower; controlling the temperature in the urea synthesis tower to 143° C.-195° C. to react and obtain a synthetic liquid;

[0008] Step S2, passing the synthetic liquid into a stripping tower for stripping to separate part of the unreacted gas in the synthetic liquid; passing the stripped synthetic liquid into a distillation tower for distillation; wherein the distillation tower comprises a tower body, a liquid inlet manifold, an air inlet manifold, an exhaust manifold, a condenser, a reflux tank and a reboiler; the liquid inlet manifold is arranged on the outer side of the tower wall of the tower body, a synthetic liquid inlet is arranged on the liquid inlet manifold, the liquid inlet manifold is connected to the liquid phase outlet of the reflux tank, the gas phase outlet of the reflux tank is the gaseous product outlet, the inlet of the reflux tank is connected to the outlet of the condenser, and the inlet of the condenser is connected to the exhaust manifold; the liquid discharge port of the tower body is connected to the inlet of the reboiler, the gas phase outlet of the reboiler is connected to the air inlet manifold, the liquid phase outlet of the reboiler is the liquid product outlet, and the air inlet manifold is provided with a synthetic liquid inlet. A steam inlet is provided; the tower body is divided into a plurality of levels from top to bottom, each level includes a tower plate, an air intake chassis is provided at the lower part of the tower plate, an air outlet valve is provided at the upper part of the tower plate, the air outlet valve is connected to the air intake chassis, the air intake chassis is connected to the outlet of the pressurized air pump, and the inlet of the pressurized air pump is connected to the air intake main pipe; an exhaust plate is provided above the tower plate, a plurality of air holes are provided below the exhaust plate, and the exhaust plate is connected to the exhaust main pipe; a liquid inlet is provided on the tower wall above the side of the tower plate, the liquid inlet is connected to the liquid inlet main pipe, and a first valve is provided at the liquid inlet; an overflow port is provided on the tower wall between the liquid inlet and the tower plate, the overflow port is connected to the liquid inlet main pipe, and a second valve is provided at the overflow port; a third valve is provided on the liquid inlet main pipe corresponding to the liquid inlet and the overflow port;

[0009] Step S3, in response to the liquid level of each of the layers in the tower body being lower than a preset value, keeping each of the first valves and the second valve in an open state, and keeping each of the third valves in a closed state, so that the synthetic liquid is distilled from the synthetic liquid inlet through each of the layers from top to bottom in sequence; wherein the synthetic liquid flows from the liquid inlet to the tower plate, then to the overflow port, and finally back to the liquid inlet main pipe; the distillation gas flows from the pressurized air pump to the gas outlet valve on the tower plate, then to the gas hole into the exhaust plate, and finally from the exhaust plate into the exhaust main pipe;

[0010] Step S4, in response to the liquid level of the layer in the tower body being higher than or equal to the preset value, closing the first valve and the second valve of the layer whose liquid level is higher than or equal to the preset value, opening the corresponding third valve and controlling the corresponding pressurized air pump to stop ventilation, so that the synthetic liquid bypasses the layer whose liquid level is higher than or equal to the preset value from top to bottom for distillation;

[0011] Step S5, passing the synthetic liquid after distillation into an evaporation heater, heating and evaporating the synthetic liquid to obtain urea crystals;

[0012] Step S6: adding the urea crystals into a granulation tower for granulation to obtain granular urea.

[0013] Optionally, in step S3, the process further includes:

[0014] The liquid level information of each of the layers is obtained; and according to the liquid level information, the pressure of the gas introduced by the pressurized air pump is adjusted so that the liquid level corresponding to each of the layers is lower than the preset value.

[0015] Optionally, the first valve and the third valve are integrated valves, and the integrated valves are used to change the synthetic fluid.

[0016] Optionally, the liquid inlet is connected to a liquid inlet distribution pipe, which crosses the corresponding layer. A liquid outlet nozzle is provided on the liquid inlet distribution pipe, and the liquid outlet nozzle is used to evenly spray the synthetic liquid and puncture the bubbles generated in the distillation process by the spray.

[0017] Optionally, the air holes of the exhaust disk are provided with sharp spikes, and the sharp spikes are used to puncture bubbles during the flooding process.

[0018] Optionally, the bottommost layer is not provided with an overflow port, and the corresponding tower plate is provided with an overflow weir, and the synthetic liquid flows over the overflow weir to the liquid discharge port.

[0019] Optionally, the liquid phase outlet of the reflux drum is connected to the liquid inlet main pipe corresponding to the topmost layer, so that the recovered liquid in the reflux drum is distilled starting from the topmost layer.

[0020] Optionally, a liquid level sensor is provided in each of the levels, and the liquid level sensor is used to detect whether the liquid level in each of the levels reaches the preset value.

[0021] Optionally, the distillation tower is divided into a medium-pressure distillation tower and a low-pressure distillation tower, the medium-pressure distillation tower and the low-pressure distillation tower have the same structure and are connected, and the medium-pressure distillation tower and the low-pressure distillation tower perform graded distillation work under different gas pressure environments.

[0022] Beneficial effects of the present invention: 1. The liquid inlet main pipe of the distillation tower of the present invention is arranged on the outer side of the tower wall of the tower body, the synthetic liquid inlet is arranged on the liquid inlet main pipe, the liquid inlet main pipe is connected with the liquid phase outlet of the reflux tank, the gas phase outlet of the reflux tank is the gaseous product outlet, the inlet of the reflux tank is connected with the outlet of the condenser, the inlet of the condenser is connected with the exhaust main pipe; the liquid discharge port of the tower body is connected with the inlet of the reboiler, the gas phase outlet of the reboiler is connected with the air inlet main pipe, the liquid phase outlet of the reboiler is the liquid product outlet, and the steam inlet is arranged on the air inlet main pipe; the tower body is divided into a plurality of levels from top to bottom, each level includes a tower plate, and the lower part of the tower plate An air intake chassis is arranged at the top of the tower plate, an air outlet valve is arranged at the top of the tower plate, the air outlet valve is connected to the air intake chassis, the air intake chassis is connected to the outlet of the pressurized air pump, and the inlet of the pressurized air pump is connected to the air intake main pipe; an exhaust plate is arranged above the tower plate, a plurality of air holes are arranged below the exhaust plate, and the exhaust plate is connected to the exhaust main pipe; a liquid inlet is arranged on the tower wall above the tower plate side, the liquid inlet is connected to the liquid inlet main pipe, and a first valve is arranged at the liquid inlet; an overflow port is arranged on the tower wall between the liquid inlet and the tower plate, the overflow port is connected to the liquid inlet main pipe, and a second valve is arranged at the overflow port; a third valve is arranged on the corresponding liquid inlet main pipe between the liquid inlet and the overflow port. In response to the liquid level of a layer in the tower body being higher than or equal to a preset value, the present invention closes the first valve and the second valve of the layer whose liquid level is higher than or equal to the preset value, and opens the corresponding third valve to control the corresponding pressurized air pump to stop ventilation, so that the synthetic liquid bypasses the layer whose liquid level is higher than or equal to the preset value from top to bottom for distillation. The present invention uses the structure of the above-mentioned distillation tower to make the tower body of the distillation tower divided into multiple levels, and each level is no longer directly connected but a separate environment; and through the above-mentioned control method, when a level has an abnormal liquid level (i.e., it will flood), the level can be isolated so that the distillation gas and the synthetic liquid no longer enter the level, thereby effectively avoiding the flooding of the entire distillation tower, while other levels can still perform distillation work, greatly reducing the impact of the flooding phenomenon on the urea production efficiency. 2. The present invention can also obtain the liquid level information of each level; according to the liquid level information, adjust the pressure of the gas introduced by the pressurized air pump so that the liquid level corresponding to each level is lower than the preset value. Because the distillation gas corresponding to each level of the present invention is transmitted by a separate pressurized air pump, it can be controlled separately to adapt the gas flow rate to the situation of each level, reducing the occurrence of flooding. 3. The liquid inlet of the present invention is connected to a liquid inlet distribution pipe, which crosses the corresponding level, and a liquid outlet nozzle is arranged on the liquid inlet distribution pipe. The liquid outlet nozzle is used to evenly spray the synthetic liquid and puncture the bubbles generated during the distillation process by spraying. The present invention provides a liquid inlet distribution pipe to better redistribute the synthetic liquid, and the injected airflow can puncture the bubbles generated during the distillation process to reduce the flooding. In summary, the present invention can effectively reduce the impact of flooding on urea production efficiency through the distillation tower of the above structure and the corresponding control method. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic flow diagram of a process for controlling distillation and purification of automotive urea production provided by a specific embodiment of the present invention;

[0024] Figure 2 It is a structural schematic diagram of a distillation tower provided by a specific embodiment of the present invention. DETAILED DESCRIPTION

[0025] The present invention discloses a process for controlling the distillation and purification of automotive urea production. Those skilled in the art can refer to the content of this article and appropriately improve the technical details for implementation. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art, and they are all deemed to be included in the present invention. The method and application of the present invention have been described through preferred embodiments, and relevant personnel can obviously modify or appropriately change and combine the method and application described herein without departing from the content, spirit and scope of the present invention to implement and apply the technology of the present invention.

[0026] The applicant has found through research that when a tray in a urea distillation tower is flooded, the entire distillation tower will soon be filled with liquid. In this case, the flooding has to be solved by stopping the introduction of urea synthesis liquid and distillation gas and then repairing it. However, this will greatly reduce the production efficiency of granular urea.

[0027] Therefore, the embodiment of the present invention provides a process for controlling the distillation and purification of automotive urea. Figure 1 As shown, the process includes:

[0028] Step S1, pressurizing liquid carbon dioxide and liquid ammonia in a molar ratio of 1:3-4 and introducing them from the bottom of a urea synthesis tower; controlling the temperature in the urea synthesis tower to 143° C.-195° C. to react and obtain a synthetic liquid.

[0029] It should be noted that in the specific production process, the amount of liquid ammonia reacted should generally be sufficient to completely react with liquid carbon dioxide and have a certain amount of surplus, so that most of the liquid carbon dioxide can be completely reacted. The synthetic liquid generally includes urea, biuret, carbon dioxide, ammonia and ammonium carbamate.

[0030] Step S2, passing the synthetic liquid into a stripping tower for stripping to separate part of the unreacted gas in the synthetic liquid; passing the stripped synthetic liquid into a distillation tower for distillation.

[0031] Among them, Figure 2As shown, the distillation tower includes a tower body 1, a liquid inlet main pipe 2, an air inlet main pipe 3, an exhaust main pipe 4, a condenser 5, a reflux tank 6 and a reboiler 7; the liquid inlet main pipe 2 is arranged on the outer side of the tower wall of the tower body 1, and a synthetic liquid inlet 201 is arranged on the liquid inlet main pipe 2, the liquid inlet main pipe 2 is connected to the liquid phase outlet of the reflux tank 6, the gas phase outlet of the reflux tank 6 is the gaseous product outlet, the inlet of the reflux tank 6 is connected to the outlet of the condenser 5, and the inlet of the condenser 5 is connected to the exhaust main pipe 4; the discharge port 101 of the tower body 1 is connected to the inlet of the reboiler 7, the gas phase outlet of the reboiler 7 is connected to the air inlet main pipe 3, the liquid phase outlet of the reboiler is the liquid product outlet, and a steam inlet is arranged on the air inlet main pipe 3; the tower body 1 is divided into a plurality of levels 8 from top to bottom, and the dotted frame portion in the figure divides the levels 8, and each level 8 includes a tray 9 An air intake chassis 901 is arranged at the lower part of the tower tray 9, and an air outlet valve 902 is arranged at the upper part of the tower tray 9, the air outlet valve 902 is connected to the air intake chassis 901, the air intake chassis 901 is connected to the outlet of the pressurized air pump 10, and the inlet of the pressurized air pump 10 is connected to the air intake main pipe 3; an exhaust plate 11 is arranged above the tower tray 9, and a plurality of air holes 111 are arranged below the exhaust plate 11, and the exhaust plate 11 is connected to the exhaust main pipe 4; a liquid inlet 12 is arranged on the tower wall above the side of the tower tray 9, the liquid inlet 12 is connected to the liquid inlet main pipe 2, and a first valve 14 is arranged at the liquid inlet 12; an overflow port is arranged on the tower wall between the liquid inlet 12 and the tower tray 9, the overflow port 13 is connected to the liquid inlet main pipe 2, and a second valve 15 is arranged at the overflow port; a third valve 16 is arranged on the liquid inlet main pipe 2 corresponding to the liquid inlet 12 and the overflow port 13.

[0032] Figure 2 In the figure, the solid arrows represent the inlet and outlet flow directions of the synthetic liquid, and the dotted arrows represent the inlet and outlet directions of the distillation gas.

[0033] It should be noted that the embodiment of the present invention uses the above-mentioned distillation tower structure to divide the interior of the tower body 1 into multiple isolated levels 8, and controls the first valve 14, the second valve 15, the third valve 16 and the pressurized air pump 10 to realize whether each level 8 is isolated in the overall distillation system, so as to avoid the situation where the entire distillation tower will be flooded when one level 8 is flooded.

[0034] It is worth mentioning that both stripping and distillation are used to separate unreacted gases in the synthetic liquid to purify urea and make the urea purity higher.

[0035] Step S3, in response to the liquid level of each layer in the tower body being lower than a preset value, keeping each first valve and each second valve in an open state, and keeping each third valve in a closed state, so that the synthetic liquid can be distilled through each layer from top to bottom starting from the synthetic liquid inlet.

[0036] Among them, the synthetic liquid flows from the liquid inlet to the tower plate, then to the overflow port, and finally returns to the liquid inlet main pipe; the distillation gas flows from the pressurized air pump to the outlet valve on the tower plate, then to the exhaust plate through the air hole, and finally from the exhaust plate into the exhaust main pipe.

[0037] It should be noted that, in the absence of flooding, the distillation tower in the embodiment of the present invention allows the synthetic liquid to pass through each layer in turn for full distillation.

[0038] During step S3, the pressurized air pump remains in operation throughout the entire process.

[0039] Step S4, in response to a layer having a liquid level higher than or equal to a preset value in the tower body, the first valve and the second valve of the layer having a liquid level higher than or equal to the preset value are closed, and the corresponding third valve is opened and the corresponding pressurized air pump is controlled to stop ventilation, so that the synthetic liquid bypasses the layer having a liquid level higher than or equal to the preset value from top to bottom for distillation.

[0040] It should be noted that when the liquid level of a layer in the tower body is higher than or equal to the preset value, it means that the layer will be flooded. At this time, the first valve and the second valve of the layer with a liquid level higher than or equal to the preset value are closed to prevent the synthetic liquid from entering; the pressurized air pump stops ventilation to prevent the distillation gas from entering, forming an isolated environment, so that the layer will not be flooded due to the continuous introduction of gas and liquid. At the same time, the corresponding third valve is opened to allow the synthetic liquid to enter the next layer for normal distillation, reducing the impact of flooding on production efficiency.

[0041] Step S5, passing the rectified synthetic liquid into an evaporation heater, heating the synthetic liquid for evaporation and concentration, and obtaining urea crystals.

[0042] Step S6: adding urea crystals to a granulation tower for granulation to obtain granular urea.

[0043] In a specific embodiment, in step S3, the process further includes:

[0044] The liquid level information of each layer is obtained; according to the liquid level information, the pressure of the gas introduced by the pressurized air pump is adjusted so that the liquid level corresponding to each layer is lower than the preset value.

[0045] It should be noted that the embodiment of the present invention is different from the prior art in that gas is introduced uniformly. In the embodiment of the present invention, each level corresponds to a pressurized air pump, so that targeted air pressure control can be achieved according to the different liquid levels at different levels, which can effectively avoid liquid flooding.

[0046] In a specific embodiment, the first valve and the third valve are integrated valves, and the integrated valve is used to change the synthetic fluid.

[0047] Using such a valve can reduce costs.

[0048] In a specific embodiment, the liquid inlet is connected to a liquid inlet distribution pipe, which crosses the corresponding layer. A liquid outlet nozzle is arranged on the liquid inlet distribution pipe, and the liquid outlet nozzle is used to evenly spray the synthetic liquid and puncture the bubbles generated in the distillation process by the spray.

[0049] It should be noted that the use of the liquid inlet distribution pipe can ensure uniform liquid distribution, accelerate distillation efficiency, and reduce the generation of biuret. Secondly, the bubbles generated during the distillation process can be punctured by spraying to reduce flooding.

[0050] In a specific embodiment, sharp spikes are provided at the air holes of the exhaust disk, and the sharp spikes are used to puncture bubbles during the flooding process.

[0051] The purpose of puncturing the air bubbles is to avoid flooding.

[0052] In a specific embodiment, if Figure 2 As shown, the bottommost level 8 is not provided with an overflow port, and the corresponding tower plate 9 is provided with an overflow weir 903 , and the synthetic liquid flows over the overflow weir 903 to the liquid discharge port 101 .

[0053] It should be noted that the synthetic liquid will enter the reboiler 7 when it reaches the bottom layer, so it does not need to enter the liquid inlet main pipe. Therefore, an overflow weir 903 is provided.

[0054] In a specific embodiment, the liquid phase outlet of the reflux drum is connected to the liquid inlet manifold corresponding to the uppermost layer, so that the recovered liquid in the reflux drum is distilled starting from the uppermost layer.

[0055] The reflux liquid is generally distilled from the top tray downwards, which can ensure sufficient distillation and improve product purity.

[0056] In a specific embodiment, a liquid level sensor is provided in each level, and the liquid level sensor is used to detect whether the liquid level in each level reaches a preset value.

[0057] In a specific embodiment, the distillation tower is divided into a medium-pressure distillation tower and a low-pressure distillation tower. The medium-pressure distillation tower and the low-pressure distillation tower have the same structure and are connected. The medium-pressure distillation tower and the low-pressure distillation tower realize graded distillation work under different gas pressure environments.

[0058] It should be noted that firstly distilling through a medium-pressure distillation tower and then through a low-pressure distillation tower can ensure complete distillation and improve product purity.

[0059] The liquid inlet main pipe of the distillation tower in the embodiment of the present invention is arranged on the outer side of the tower wall of the tower body, the synthetic liquid inlet is arranged on the liquid inlet main pipe, the liquid inlet main pipe is connected with the liquid phase outlet of the reflux tank, the gas phase outlet of the reflux tank is the gaseous product outlet, the inlet of the reflux tank is connected with the outlet of the condenser, and the inlet of the condenser is connected with the exhaust main pipe; the liquid discharge port of the tower body is connected with the inlet of the reboiler, the gas phase outlet of the reboiler is connected with the air inlet main pipe, the liquid phase outlet of the reboiler is the liquid product outlet, and the steam inlet is arranged on the air inlet main pipe; the tower body is divided into a plurality of levels from top to bottom, each level includes a tower plate, and the lower part of the tower plate is provided with an inlet A gas bottom plate, an air outlet valve is arranged on the upper part of the tower plate, the air outlet valve is connected to the air intake bottom plate, the air intake bottom plate is connected to the outlet of the pressurized air pump, and the inlet of the pressurized air pump is connected to the air intake main pipe; an exhaust plate is arranged above the tower plate, a plurality of air holes are arranged below the exhaust plate, and the exhaust plate is connected to the exhaust main pipe; a liquid inlet is arranged on the tower wall above the tower plate side, the liquid inlet is connected to the liquid inlet main pipe, and a first valve is arranged at the liquid inlet; an overflow port is arranged on the tower wall between the liquid inlet and the tower plate, the overflow port is connected to the liquid inlet main pipe, and a second valve is arranged at the overflow port; a third valve is arranged on the corresponding liquid inlet main pipe between the liquid inlet and the overflow port. In response to the liquid level of a layer in the tower body being higher than or equal to a preset value, the embodiment of the present invention closes the first valve and the second valve of the layer with a liquid level higher than or equal to the preset value, and opens the corresponding third valve, so that the synthetic liquid bypasses the layer with a liquid level higher than or equal to the preset value from top to bottom for distillation. The embodiment of the present invention uses the structure of the distillation tower to divide the tower body of the distillation tower into multiple levels, and each level is no longer directly connected but is a separate environment; and through the control method, when a level abnormality occurs (i.e., flooding is about to occur) in a level, the level can be isolated so that the distillation gas and the synthetic liquid no longer enter the level, thereby effectively avoiding flooding of the entire distillation tower, while other levels can still perform distillation work, greatly reducing the impact of flooding on urea production efficiency.

[0060] The embodiment of the present invention can also obtain the liquid level information of each layer; according to the liquid level information, adjust the pressure of the gas introduced by the pressurized gas pump so that the liquid level corresponding to each layer is lower than the preset value. Because the distillation gas corresponding to each layer of the embodiment of the present invention is transmitted by a separate pressurized gas pump, it can be controlled separately to adapt the gas flow rate to the situation of each layer, reducing the occurrence of liquid flooding.

[0061] The liquid inlet of the embodiment of the present invention is connected to a liquid inlet distribution pipe, which crosses the corresponding layer, and a liquid outlet nozzle is arranged on the liquid inlet distribution pipe, which is used to evenly spray the synthetic liquid and puncture the bubbles generated during the distillation process by spraying. The embodiment of the present invention is provided with a liquid inlet distribution pipe to better redistribute the synthetic liquid, and the sprayed airflow can puncture the bubbles generated during the distillation process to reduce liquid flooding.

[0062] In summary, the embodiment of the present invention can effectively reduce the impact of flooding on urea production efficiency through the distillation tower with the above structure and the corresponding control method.

[0063] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

[0064] Each embodiment in this specification is described in a related manner, and the same or similar parts between the embodiments can be referred to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the system embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and the relevant parts can be referred to the partial description of the method embodiment.

[0065] The above are only preferred embodiments of the present invention and are not intended to limit the protection scope of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention are included in the protection scope of the present invention.

Claims

1. A process for controlling the production, distillation and purification of automotive urea, characterized in that: The process comprises: Step S1, pressurizing liquid carbon dioxide and liquid ammonia in a molar ratio of 1:3-4 and introducing them from the bottom of a urea synthesis tower; controlling the temperature in the urea synthesis tower to 143° C.-195° C. to react and obtain a synthetic liquid; Step S2, passing the synthetic liquid into a stripping tower for stripping to separate part of the unreacted gas in the synthetic liquid; passing the stripped synthetic liquid into a distillation tower for distillation; wherein the distillation tower comprises a tower body, a liquid inlet manifold, an air inlet manifold, an exhaust manifold, a condenser, a reflux tank and a reboiler; the liquid inlet manifold is arranged on the outer side of the tower wall of the tower body, a synthetic liquid inlet is arranged on the liquid inlet manifold, the liquid inlet manifold is connected to the liquid phase outlet of the reflux tank, the gas phase outlet of the reflux tank is the gaseous product outlet, the inlet of the reflux tank is connected to the outlet of the condenser, and the inlet of the condenser is connected to the exhaust manifold; the liquid discharge port of the tower body is connected to the inlet of the reboiler, the gas phase outlet of the reboiler is connected to the air inlet manifold, the liquid phase outlet of the reboiler is the liquid product outlet, and the air inlet manifold is provided with a synthetic liquid inlet. A steam inlet is provided; the tower body is divided into a plurality of levels from top to bottom, each level includes a tower plate, an air intake chassis is provided at the lower part of the tower plate, an air outlet valve is provided at the upper part of the tower plate, the air outlet valve is connected to the air intake chassis, the air intake chassis is connected to the outlet of the pressurized air pump, and the inlet of the pressurized air pump is connected to the air intake main pipe; an exhaust plate is provided above the tower plate, a plurality of air holes are provided below the exhaust plate, and the exhaust plate is connected to the exhaust main pipe; a liquid inlet is provided on the tower wall above the side of the tower plate, the liquid inlet is connected to the liquid inlet main pipe, and a first valve is provided at the liquid inlet; an overflow port is provided on the tower wall between the liquid inlet and the tower plate, the overflow port is connected to the liquid inlet main pipe, and a second valve is provided at the overflow port; a third valve is provided on the liquid inlet main pipe corresponding to the liquid inlet and the overflow port; Step S3, in response to the liquid level of each of the layers in the tower body being lower than a preset value, keeping each of the first valves and the second valve in an open state, and keeping each of the third valves in a closed state, so that the synthetic liquid is distilled from the synthetic liquid inlet through each of the layers from top to bottom in sequence; wherein the synthetic liquid flows from the liquid inlet to the tower plate, then to the overflow port, and finally back to the liquid inlet main pipe; the distillation gas flows from the pressurized air pump to the gas outlet valve on the tower plate, then to the gas hole into the exhaust plate, and finally from the exhaust plate into the exhaust main pipe; Step S4, in response to the liquid level of the layer in the tower body being higher than or equal to the preset value, closing the first valve and the second valve of the layer whose liquid level is higher than or equal to the preset value, opening the corresponding third valve and controlling the corresponding pressurized air pump to stop ventilation, so that the synthetic liquid bypasses the layer whose liquid level is higher than or equal to the preset value from top to bottom for distillation; Step S5, passing the synthetic liquid after distillation into an evaporation heater, heating and evaporating the synthetic liquid to obtain urea crystals; Step S6: adding the urea crystals into a granulation tower for granulation to obtain granular urea.

2. The controllable flooding process for producing automotive urea according to claim 1, characterized in that: In step S3, the process further includes: The liquid level information of each of the layers is obtained; and according to the liquid level information, the pressure of the gas introduced by the pressurized air pump is adjusted so that the liquid level corresponding to each of the layers is lower than the preset value.

3. The controllable flooding process for producing automotive urea according to claim 1, characterized in that: The first valve and the third valve are integrated valves, and the integrated valves are used to change the synthetic fluid.

4. The process for controlling flooding of urea for automobile production according to claim 1, characterized in that: The liquid inlet is connected to a liquid inlet distribution pipe, which crosses the corresponding layer. A liquid outlet nozzle is arranged on the liquid inlet distribution pipe, and the liquid outlet nozzle is used to evenly spray the synthetic liquid and puncture the bubbles generated in the distillation process by spraying.

5. The controllable flooding process for producing automotive urea according to claim 1, characterized in that: The air holes of the exhaust disk are provided with sharp spikes, and the sharp spikes are used to puncture bubbles in the process of liquid flooding.

6. The controllable flooding process for producing automotive urea according to claim 1, characterized in that: The bottommost layer is not provided with an overflow port, and the corresponding tower plate is provided with an overflow weir, and the synthetic liquid flows over the overflow weir to the liquid discharge port.

7. The process for controlling flooding of urea for automobile production according to claim 1, characterized in that: The liquid phase outlet of the reflux drum is connected to the liquid inlet main pipe corresponding to the uppermost layer, so that the recovered liquid in the reflux drum is distilled starting from the uppermost layer.

8. The controllable flooding process for producing automotive urea according to claim 1, characterized in that: A liquid level sensor is arranged in each of the levels, and the liquid level sensor is used to detect whether the liquid level in each of the levels reaches the preset value.

9. The controllable flooding process for producing automotive urea according to claim 1, characterized in that: The distillation tower is divided into a medium-pressure distillation tower and a low-pressure distillation tower. The medium-pressure distillation tower and the low-pressure distillation tower have the same structure and are connected. The medium-pressure distillation tower and the low-pressure distillation tower realize graded distillation work under different gas pressure environments.

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