High-pressure system for urea production process by ammonia stripping method and boosting method of high-pressure system

Abstract

The invention relates to the technical field of urea production, and discloses an ammonia stripping urea production process high-pressure system and a boosting method thereof, and the ammonia stripping urea production process high-pressure system comprises a urea high-pressure synthesis tower and a high-pressure stripping tower which are communicated in sequence; one discharging end of the high-pressure stripping tower is also sequentially communicated with a high-pressure methylamine condenser and a high-pressure methylamine separator; one discharging end of the high-pressure methylamine separator is communicated with one feeding end of the urea high-pressure synthesis tower. CO2 is fully utilized to reduce the pressure boosting operation risk of the high-pressure system, so that the high-pressure system in the urea synthesis process by the ammonia stripping method can be simply and conveniently subjected to pressure boosting treatment, the operation safety of operators is improved, and the production efficiency is improved.

Description

Technical Field

[0001] The invention relates to the technical field of urea production, and in particular to a high-pressure system for a urea production process using an ammonia stripping method and a pressure-boosting method thereof. Background Art

[0002] The ammonia stripping urea production process is a chemical process that reacts ammonia and carbon dioxide to produce urea. The process mainly includes several core stages such as synthesis, decomposition and urea crystallization. In the synthesis process, ammonia and carbon dioxide react under high temperature and high pressure to produce urea and water. The process is as follows:

[0003] 2NH3+CO2 → NH2COONH4 → (NH2)2CO+H2O (1).

[0004] In order to ensure the normal progress of the above reactions, the ammonia stripping urea production process needs to be equipped with a high-pressure system to maintain the high-pressure environment required for the reaction and ensure the safety and stability of the system. The common ammonia stripping urea production process high-pressure system mainly includes the following parts:

[0005] (1) High-pressure pump: The high-pressure pump pressurizes the raw materials, thereby transporting ammonia and carbon dioxide to the high-pressure reactor for synthesis reaction;

[0006] (2) High-pressure reactor: As a reaction vessel for ammonia and carbon dioxide, the high-pressure reactor needs to withstand pressures of tens to hundreds of bars to effectively ensure the smooth progress of the reaction. It usually adopts a multi-stage design and uses high temperature and high pressure to promote the reaction;

[0007] (3) Safety system: The high-pressure system must be equipped with a safety valve and a pressure monitoring device to prevent equipment damage or explosion due to excessive pressure, and to perform gas release and emergency shut-off when necessary;

[0008] (4) Temperature and pressure control system: By adjusting the temperature and pressure in the high-pressure reactor, the reaction environment and conditions are optimized, thereby improving the yield and quality of urea;

[0009] (5) Cooling and recovery system: Both the gas and liquid after the reaction need to be cooled to recover unreacted ammonia and carbon dioxide and improve the utilization rate of raw materials.

[0010] In the existing high-pressure system of the ammonia stripping urea production process, liquid ammonia is used as the medium for pressure increase. After being heated by high-temperature jacket steam, the liquid ammonia is vaporized and pressure is provided by a high-pressure pump. Among them, the synthetic supply liquid ammonia pressure of 1.5MPa needs to be pressurized to 2.5MPa by a booster pump before it can be supplied to the high-pressure pump, which consumes a lot of energy and has low safety. In addition, the liquid ammonia vaporization adopts multi-stage jacket steam heating, and the ammonia supply amount needs to be manually adjusted on site, and the start-up pipeline temperature at the top of the stripping tower cannot be lower than 120℃. Therefore, there are also problems such as cumbersome operation, large manpower requirements, and high risk. Summary of the invention

[0011] The technical problems to be solved by the present invention are:

[0012] In the existing high-pressure system of the ammonia stripping urea production process, liquid ammonia is used as the medium for pressure increase, and the liquid ammonia is vaporized by high-temperature heating of the jacket steam. Due to the limitations of the process means, the operator is required to manually adjust the ammonia supply during the production process, and a large number of high-temperature and high-pressure production equipment are involved, which results in low safety, high risk, and high labor intensity.

[0013] The technical solution adopted by the present invention is:

[0014] The invention provides a high-pressure system for ammonia stripping urea production process, comprising a urea high-pressure synthesis tower and a high-pressure stripping tower which are connected in sequence; a discharge end of the high-pressure stripping tower is also connected in sequence with a high-pressure methylammonium condenser and a high-pressure methylammonium separator, and a discharge end of the high-pressure methylammonium separator is connected with a feed end of the urea high-pressure synthesis tower.

[0015] Preferably, the pipeline between the high-pressure stripping tower and the high-pressure methylammonium condenser is also connected to a high-pressure liquid ammonia pump and a high-pressure methylammonium pump respectively.

[0016] Preferably, a feed end of the urea high-pressure synthesis tower is connected to a CO2 compressor, and a discharge pipe of the CO2 compressor is respectively connected to a feed end of the urea high-pressure synthesis tower and a discharge pipe of the high-pressure liquid ammonia pump.

[0017] Preferably, a high-pressure methylammonium injector is provided in the pipeline between the high-pressure methylammonium separator and the urea high-pressure synthesis tower.

[0018] Preferably, a feed end of the high-pressure methylammonium injector is also connected to a high-pressure liquid ammonia preheater.

[0019] Preferably, the pipeline between the urea high-pressure synthesis tower and the high-pressure stripping tower is equipped with a feed liquid control valve; the pipeline between the high-pressure methylammonium separator and the urea high-pressure synthesis tower is equipped with a high-pressure methylammonium liquid control valve, and the discharge pipe of the high-pressure methylammonium separator is equipped with a high-pressure pressure regulating valve.

[0020] Preferably, the pipeline between the high-pressure methylammonium pump and the high-pressure methylammonium condenser is equipped with a methylammonium inlet regulating valve, and the pipeline between the CO2 compressor and the urea high-pressure synthesis tower is equipped with a CO2 feed control valve.

[0021] Preferably, the pipeline between the high-pressure liquid ammonia preheater and the high-pressure methylammonium injector is provided with a methylammonium pressure regulating valve.

[0022] The method for increasing the pressure of the high-pressure system of the above-mentioned ammonia stripping urea production process comprises the following steps:

[0023] S1 first heats up the high-pressure system of the ammonia stripping urea production process. After the temperature is raised, the steam and condensate valves entering the NH3 start-up pipeline are closed, the condensate is exhausted, and the low-point drainage and top exhaust are closed;

[0024] S2 turns on the CO2 compressor. When the CO2 compressor reaches 1500rpm during the run-up, open the start-up pipeline valve between the CO2 compressor and the high-pressure liquid ammonia pump outlet, open the start-up pipe jacket to drain water, and control the start-up pipeline temperature at the top of the high-pressure stripping tower to be maintained at 120-175℃;

[0025] S3 When the CO2 compressor speed reaches the starting speed of 8050rpm, adjust the pressure boost rate of the high-pressure system to less than 3.0MPa / h; when the high-pressure system control pressure reaches 9.0-10.0MPa, stop boosting and complete the boosting operation.

[0026] Preferably, a combination of multiple switch valves is used as the high-pressure pressure regulating valve, and after liquid ammonia is added to the urea high-pressure synthesis tower, one of the switch valves is adjusted to maintain an opening of 5-25%, and when the high-pressure system pressure reaches 14.0MPa, the switch valve is closed.

[0027] The beneficial effects of the present invention are as follows:

[0028] The high-pressure system and the pressure-boosting method of the ammonia stripping urea production process of the present invention improve the equipment and pipeline connections in the high-pressure system, make full use of CO2 to reduce the pressure-boosting operation risk of the high-pressure system, and realize a simpler and more convenient pressure-boosting treatment of the high-pressure system in the process of synthesizing urea by the ammonia stripping method, thereby improving the operating safety of operators; and by increasing the utilization rate of materials, it can also reduce environmental pollution caused by venting ammonia losses and reduce the cost of producing urea by the ammonia stripping method. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a process flow chart of the high-pressure system of the ammonia stripping urea production process in Example 1.

[0030] Figure symbols: 1-urea high-pressure synthesis tower, 11-feed liquid control valve, 2-high-pressure stripping tower, 21-liquid level regulating valve, 3-high-pressure methylammonium condenser, 4-high-pressure methylammonium separator, 41-high-pressure methylammonium liquid control valve, 42-high-pressure pressure regulating valve, 5-high-pressure liquid ammonia pump, 6-high-pressure methylammonium pump, 61-methylammonium liquid inlet regulating valve, 7-CO2 compressor, 71-CO2 feed control valve, 8-high-pressure methylammonium injector, 9-high-pressure liquid ammonia preheater, 91-methylammonium pressure regulating valve. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0032] The invention provides a high-pressure system for a urea production process using an ammonia stripping method and a pressure-increasing method thereof. The high-pressure system for a urea production process using an ammonia stripping method comprises a urea high-pressure synthesis tower 1 and a high-pressure stripping tower 2 which are connected in sequence; a discharge end of the high-pressure stripping tower 2 is also connected in sequence with a high-pressure methylammonium condenser 3 and a high-pressure methylammonium separator 4, and a discharge end of the high-pressure methylammonium separator 4 is connected with a feed end of the urea high-pressure synthesis tower 1; a pipeline between the high-pressure stripping tower 2 and the high-pressure methylammonium condenser 3 is also connected with a high-pressure liquid ammonia pump 5 and a high-pressure methylammonium pump 6 respectively; a feed end of the urea high-pressure synthesis tower 1 is connected with a CO2 compressor 7, and a discharge pipe of the CO2 compressor 7 is respectively connected with a feed end of the urea high-pressure synthesis tower 1 and a discharge pipe of the high-pressure liquid ammonia pump 5; a high-pressure methylammonium injector 8 is passed through the pipeline between the high-pressure methylammonium separator 4 and the urea high-pressure synthesis tower 1; a feed end of the high-pressure methylammonium injector 8 is also connected with a high-pressure liquid ammonia preheater 9.

[0033] In the present invention, the connecting pipelines between the above-mentioned devices are also equipped with corresponding regulating valves and other valves. Specifically, the pipeline between the urea high-pressure synthesis tower 1 and the high-pressure stripping tower 2 is equipped with a liquid control valve 11; the pipeline between the high-pressure methylammonium separator 4 and the urea high-pressure synthesis tower 1 is equipped with a high-pressure methylammonium liquid control valve 41, and the discharge pipe of the high-pressure methylammonium separator 4 is equipped with a high-pressure pressure regulating valve 42; the pipeline between the high-pressure methylammonium pump 6 and the high-pressure methylammonium condenser 3 is equipped with a methylammonium inlet regulating valve 61, and the pipeline between the CO2 compressor 7 and the urea high-pressure synthesis tower 1 is equipped with a CO2 feed control valve 71; the pipeline between the high-pressure liquid ammonia preheater 9 and the high-pressure methylammonium injector 8 is equipped with a methylammonium pressure regulating valve 91.

[0034] In the present invention, when the high-pressure system of the ammonia stripping urea production process is used to increase the pressure, the specific pressure increasing method is as follows:

[0035] (1) First, heat up the high-pressure system of the ammonia stripping urea production process. After the temperature is raised, close the steam and condensate valves entering the NH3 start-up pipeline, and drain the condensate. After the condensate accumulated in the high-pressure system is drained, close all low-point drains and top exhausts;

[0036] (2) The CO2 compressor is started and ramped up according to the normal ITCC procedure, and the pressure of the high-pressure system is controlled by the high-pressure pressure regulating valve;

[0037] When the CO2 compressor reaches 1500rpm during the run-up, open the start-up pipeline valve between the CO2 compressor and the high-pressure liquid ammonia pump outlet, control the CO2 pressure by the CO2 compressor speed, and open the pipe jacket to drain water, so that the start-up pipeline temperature at the top of the high-pressure stripping tower is maintained at 120-175℃; when the CO2 compressor speed reaches the start-up speed of 8050rpm, adjust the pressure increase speed of the high-pressure system to control the pressure increase rate to less than 3.0MPa / h;

[0038] (3) When the high-pressure system control pressure reaches 9.0-10.0MPa, the pressure increase can be stopped, that is, the pressure increase operation is completed. Subsequently, the CO2 feed control valve is closed first, then the jacket steam is stopped, and then the feed and discharge cut-off valves of the high-pressure stripping tower are closed, and the pressure is released.

[0039] Since excess ammonia is used as a stripping agent in the high-pressure system, a small amount of methylammonium is generated by the reaction of ammonia in the high-pressure system and carbon dioxide in the high-pressure equipment before the CO2 material is added. To prevent methylammonium from crystallizing, the temperature of the high-pressure system should be guaranteed to be no less than 160°C. After liquid ammonia is added to the urea high-pressure synthesis tower, one of the high-pressure pressure regulating valves is controlled to maintain an opening of 5-25% to discharge the gaseous CO2 gas. When the pressure of the high-pressure system reaches 14.0MPa, the high-pressure pressure regulating valve is closed.

[0040] Example 1

[0041] like Figure 1 As shown, the high-pressure system of the ammonia stripping urea production process in this embodiment includes a urea high-pressure synthesis tower and a high-pressure stripping tower connected in sequence; a discharge end of the high-pressure stripping tower is also connected in sequence with a high-pressure methylammonium condenser and a high-pressure methylammonium separator, and a discharge end of the high-pressure methylammonium separator is connected to a feed end of the urea high-pressure synthesis tower; a pipeline between the high-pressure stripping tower and the high-pressure methylammonium condenser is also connected to a high-pressure liquid ammonia pump and a high-pressure methylammonium pump, respectively; a feed end of the urea high-pressure synthesis tower is connected to a CO2 compressor, and a discharge pipe of the CO2 compressor is respectively connected to a feed end of the urea high-pressure synthesis tower and a discharge pipe of the high-pressure liquid ammonia pump; a high-pressure methylammonium injector is passed through the pipeline between the high-pressure methylammonium separator and the urea high-pressure synthesis tower; a feed end of the high-pressure methylammonium injector is also connected to a high-pressure liquid ammonia preheater.

[0042] In the present invention, the connecting pipelines between the above-mentioned equipment are also equipped with corresponding regulating valves and other valves. Specifically, the pipeline between the urea high-pressure synthesis tower and the high-pressure stripping tower is equipped with a liquid control valve; the pipeline between the high-pressure methylammonium separator and the urea high-pressure synthesis tower is equipped with a high-pressure methylammonium liquid control valve, and the discharge pipe of the high-pressure methylammonium separator is equipped with a high-pressure pressure regulating valve; the pipeline between the high-pressure methylammonium pump and the high-pressure methylammonium condenser is equipped with a methylammonium inlet regulating valve, and the pipeline between the CO2 compressor and the urea high-pressure synthesis tower is equipped with a CO2 feed control valve; the pipeline between the high-pressure liquid ammonia preheater and the high-pressure methylammonium injector is equipped with a methylammonium pressure regulating valve; the high-pressure stripping tower is also connected to a connecting pipe, and the connecting pipe is equipped with a liquid level regulating valve to adjust the liquid level height of the high-pressure stripping tower, etc. In addition, the high-pressure stripping tower should also be equipped with an MS feed pipe and MC discharge pipe required for material in and out.

[0043] By adopting the high-pressure system in this embodiment, the start-up time of the CO2 compressor unit is fully utilized. The use of CO2 to pressurize the urea high-pressure system reduces the operating risk and saves the start-up cost of the ammonia stripping urea plant. Each empty urea tower start-up can save the above costs by about RMB 25,000, reducing the environmental pollution caused by the loss of ammonia due to venting.

[0044] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A high-pressure system for ammonia stripping urea production process, characterized in that: It comprises a urea high-pressure synthesis tower (1) and a high-pressure stripping tower (2) which are connected in sequence; A discharge end of the high-pressure stripping tower (2) is also connected in sequence to a high-pressure methylammonium condenser (3) and a high-pressure methylammonium separator (4), and a discharge end of the high-pressure methylammonium separator (4) is connected to a feed end of the urea high-pressure synthesis tower (1).

2. The high-pressure system for the ammonia stripping urea production process according to claim 1, characterized in that: The pipeline between the high-pressure stripping tower (2) and the high-pressure methylammonium condenser (3) is also connected to a high-pressure liquid ammonia pump (5) and a high-pressure methylammonium pump (6) respectively.

3. The high-pressure system for the ammonia stripping urea production process according to claim 2, characterized in that: A feed end of the urea high-pressure synthesis tower (1) is connected to a CO2 compressor (7), and a discharge pipe of the CO2 compressor (7) is respectively connected to a feed end of the urea high-pressure synthesis tower (1) and a discharge pipe of the high-pressure liquid ammonia pump (5).

4. The high-pressure system for the ammonia stripping urea production process according to claim 1, characterized in that: A high-pressure methylammonium injector (8) is provided through the pipeline between the high-pressure methylammonium separator (4) and the high-pressure urea synthesis tower (1).

5. The high-pressure system for urea production by ammonia stripping according to claim 4, characterized in that: One feed end of the high-pressure methylammonium injector (8) is also connected to a high-pressure liquid ammonia preheater (9).

6. The high-pressure system for urea production by ammonia stripping according to any one of claims 1 to 5, characterized in that: The pipeline between the urea high-pressure synthesis tower (1) and the high-pressure stripping tower (2) is provided with a feed liquid control valve (11); The pipeline between the high-pressure methylammonium separator (4) and the high-pressure urea synthesis tower (1) is provided with a high-pressure methylammonium liquid control valve (41), and the discharge pipe of the high-pressure methylammonium separator (4) is provided with a high-pressure pressure regulating valve (42).

7. The high-pressure system for urea production by ammonia stripping according to claim 3, characterized in that: The pipeline between the high-pressure methylammonium pump (6) and the high-pressure methylammonium condenser (3) is equipped with a methylammonium inlet regulating valve (61), and the pipeline between the CO2 compressor (7) and the urea high-pressure synthesis tower (1) is equipped with a CO2 feed control valve (71).

8. The high-pressure system for urea production by ammonia stripping according to claim 5, characterized in that: The pipeline between the high-pressure liquid ammonia preheater (9) and the high-pressure methylammonium injector (8) is provided with a methylammonium pressure regulating valve (91).

9. A method for increasing the pressure of a high-pressure system in ammonia stripping urea production process according to any one of claims 1 to 8, characterized in that: The steps include: S1 first heats up the high-pressure system of the ammonia stripping urea production process. After the temperature is raised, the steam and condensate valves entering the NH3 start-up pipeline are closed, the condensate is exhausted, and the low-point drainage and top exhaust are closed; S2 turns on the CO2 compressor. When the CO2 compressor reaches 1500rpm during the run-up, open the start-up pipeline valve between the CO2 compressor and the high-pressure liquid ammonia pump outlet, open the start-up pipe jacket to drain water, and control the start-up pipeline temperature at the top of the high-pressure stripping tower to be maintained at 120-175℃; S3 When the CO2 compressor speed reaches the starting speed of 8050rpm, adjust the pressure boost rate of the high-pressure system to less than 3.0MPa / h; when the high-pressure system control pressure reaches 9.0-10.0MPa, stop boosting and complete the boosting operation.

10. The voltage boosting method according to claim 9, characterized in that: A combination of multiple switch valves is used as a high-pressure pressure regulating valve, and after liquid ammonia is added to the urea high-pressure synthesis tower, one of the switch valves is adjusted to maintain an opening of 5-25%, and when the high-pressure system pressure reaches 14.0MPa, the switch valve is closed.

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