Substitution line and substitution method for urea synthesis system

Abstract

The present application relates to urea production technology field, specifically to a kind of urea synthesis system replacement pipeline, including steam pipeline, factory air pipeline, control valve V1 is arranged on the steam pipeline, control valve V2, first blind plate, check valve and control valve V3 are sequentially arranged on the factory air pipeline;The steam pipeline and factory air pipeline end are parallel to first flushing pipeline, temperature table is arranged on first flushing pipeline;Branch is set after first flushing pipeline, and is second flushing pipeline and third flushing pipeline respectively;Control valve V4, check valve are sequentially arranged on the second flushing pipeline, and the second flushing pipeline end is communicated with stripping column;Control valve V6, second blind plate are sequentially arranged on the third flushing pipeline, and the third flushing pipeline end is communicated with the high-pressure flushing water pipeline of urea synthesis system to stripping column;Fourth flushing pipeline is arranged between stripping column and high-pressure discharge pipe, control valve V5 is arranged on fourth flushing pipeline, and each control valve and blind plate are reasonably controlled when using open-close, the goal of safe, environmental protection, fast is realized to clean replacement urea synthesis system equipment, pipeline.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of urea production, in particular to a urea synthesis system replacement pipeline and a replacement method. BACKGROUND

[0002] The 2300 tons / day urea plant adopts a carbon dioxide gas stripping process and is mainly applied to large chemical production enterprises such as the Yuntianhua Group and the Daqing Petrochemical Branch. The raw material liquid ammonia of the existing synthesis system of the 2300 tons / day urea plant is sent from a synthetic ammonia device and is divided into three paths: the first path goes to a new low-pressure methylamine condenser; the second path goes to a low-pressure methylamine condenser; and the third path enters an ammonia preheater tube side. After the process material discharge of the urea synthesis system is completed, urea, methylamine and NH3 and CO2 media remain in the equipment and pipelines and need to be replaced to prevent crystallization and blockage of the equipment or pipelines at low temperatures and to create good conditions for equipment maintenance. The current replacement method is to fill the synthesis system with condensate and dissolve the remaining process media in water to achieve the purpose of replacing the remaining process media in the synthesis system. However, the above method has the following problems:

[0003] The synthesis system uses a water replacement method, and the pH, NH4 + of the discharged condensate is high and cannot meet the discharge standard and must be treated by a sewage device before being discharged;

[0004] The system from water addition to discharge completion not only takes a long time of 20 hours or more, but also wastes a large amount of water of about 240 m³ / time, which is a serious waste;

[0005] During the discharge of the synthesis system, the discharge rate control requirement is high, and too fast discharge rate can cause problems such as damage to the lining of the urea synthesis tower.

[0006] In order to implement the safety and environmental protection production goal of the chemical industry, it is urgent to seek a safe and environmentally friendly replacement technology to meet the replacement needs of the urea synthesis system. SUMMARY

[0007] In view of the problems existing in the replacement process of the synthesis system of the 2300 tons / day urea plant, the present application provides a urea synthesis system replacement pipeline and a replacement method.

[0008] The urea synthesis system replacement pipeline of the present application is based on a 2300 tons / day urea plant and is characterized in that the system further comprises a steam pipeline and a plant air pipeline, a control valve V1 is arranged on the saturated steam pipeline, and a control valve V2, a first blind plate, a check valve and a control valve V3 are arranged in sequence on the plant air pipeline;

[0009] The saturated steam pipeline and the plant air pipeline end in parallel to form a first flushing pipeline, and a temperature table is arranged on the first flushing pipeline; a branch is arranged after the first flushing pipeline, which is respectively a second flushing pipeline and a third flushing pipeline; the second flushing pipeline is sequentially provided with a control valve V4 and a check valve, and the second flushing pipeline is communicated with the stripping tower at the end; the third flushing pipeline is sequentially provided with a control valve V6 and a second blind plate, and the third flushing pipeline is communicated with the high-pressure flushing water pipeline of the urea synthesis system to the stripping tower at the end; a fourth flushing pipeline is arranged between the stripping tower and the high-pressure discharge pipeline, and the fourth flushing pipeline is provided with a control valve V5.

[0010] Further, an AH pipeline is used before the control valve V4 of the second flushing pipeline, that is, a pipeline meeting the ST35-8-I standard and having a nominal pressure of 2.5 MPa to meet the DIN2634 standard; and an AR pipeline is used after the control valve V4, that is, a pipeline made of X2CrNiMo18-12 / X2CrNiMo18-14 and having a nominal pressure of 25.0 MPa to meet the KC standard, which has the functions of preventing corrosion of ammonium methyl solution and urea solution.

[0011] Further, a pipeline made of 304 stainless steel is used before the control valve V6 of the third flushing pipeline, and a pipeline made of urea-grade 316L stainless steel is used after the control valve V6.

[0012] Further, the first blind plate and the second blind plate are eight-blade blind plates.

[0013] For the above urea synthesis system, when the replacement is performed, the shell side steam pocket pressure of the high-pressure ammonium methyl condenser is controlled to be 0.4-0.5 MPa, the shell side high-pressure temperature control water temperature of the high-pressure ammonium methyl scrubber is controlled to be 110-120℃, the steam pressure of the stripping tower shell side is 0.9 MPa, and the saturated steam pressure is 0.9 MPa, and the following technical operation scheme is used for the replacement:

[0014] 1) After the urea device is stopped and the discharge of the process materials of the urea synthesis system is completed, the high-pressure flushing water pipeline of the synthesis system is used to flush the pipeline according to the design process;

[0015] 2) The first blind plate and the second blind plate are opened, the control valve V2, the control valve V3, the control valve V4 and the control valve V5 are opened, air is sent into the stripping tower and finally into the high-pressure discharge pipeline, the plant air pipeline is fully opened, then the control valve V1 is opened, and the temperature of the mixture of steam and air is adjusted to about 125℃, so that the mixture of steam and air flushes the stripping tower, the high-pressure ammonium methyl condenser, the synthesis tower, the high-pressure ammonium methyl scrubber, the absorption tower and the connecting pipelines thereof, and the ammonia-containing gas replaced out is recovered and utilized, so that the entire synthesis system is replaced.

[0016] 3) After 8 hours of displacement of the synthesis system, open the sampling valve of the synthesis system to check if there is ammonia smell. If there is ammonia smell, continue to displace. If there is no ammonia smell, the displacement of the synthesis system is completed, and the control valve V1, the control valve V2, the control valve V3, the control valve V4, the control valve V5 and the control valve V6 are closed in turn, and the first blind plate and the second blind plate are blind dead.

[0017] The traditional method is the high-pressure water displacement method, which has problems such as long time, safety and environmental protection, etc. If air displacement is used, the urea, methylamine and NH3 and CO2 medium in the dead angle position of the equipment cannot be displaced completely. If pure steam displacement is used, due to the poor flowability of steam, it cannot play a displacement role after condensation in the equipment. Therefore, the method of combining air displacement is proposed, and the related process parameter control requirements are proposed. The displacement effect is good, and the shortcomings of the traditional displacement method are solved, which provides a new technology for the displacement of the urea synthesis system.

[0018] The technology can achieve the following beneficial effects:

[0019] Through parameter control, the ammonia water concentration generated in the high-pressure water flushing pipeline displacement step is low and small in amount, which does not constitute environmental protection pressure, and the goal of safely, environmentally and quickly displacing the urea synthesis system equipment and pipeline clean is achieved;

[0020] The total time of displacing the urea synthesis system clean is shortened to 8 hours;

[0021] The risk of damage to the synthesis tower lining in the drainage process of the synthesis system is reduced;

[0022] The ammonia-containing gas obtained by displacement is finally discharged into the absorption tower to realize the recycling of high-concentration ammonia-containing gas; BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 The figure is a connection diagram of the displacement pipeline of the urea synthesis system.

[0024] Figure 2 The figure is a working diagram of the displacement method of the displacement pipeline of the urea synthesis system in the existing 2300 tons / day urea device synthesis system. DETAILED DESCRIPTION

[0025] Example 1: Urea synthesis system replacement pipeline, the system is based on a 2,300-ton urea plant, characterized in that the system also includes a steam pipeline and a plant air pipeline, the saturated steam pipeline is provided with a control valve V1, and the plant air pipeline is provided with a control valve V2, a first blind plate, a check valve and a control valve V3 in sequence; the ends of the saturated steam pipeline and the plant air pipeline are connected in parallel to form a first flushing pipeline, and a thermometer is provided on the first flushing pipeline; branches are provided after the first flushing pipeline, namely a second flushing pipeline and a third flushing pipeline: a control valve V4 and a check valve are provided in sequence on the second flushing pipeline, and the end of the second flushing pipeline is connected to the stripping tower; a control valve V6 and a second blind plate are provided on the third flushing pipeline, and the end of the third flushing pipeline is connected to the high-pressure flushing water pipeline of the urea synthesis system to the stripping tower; a fourth flushing pipeline is provided between the stripping tower and the high-pressure discharge pipe, and a control valve V5 is provided on the fourth flushing pipeline.

[0026] For the above urea synthesis system, during replacement, the shell-side drum pressure of the high-pressure methylammonium condenser is controlled at 0.4-0.5 MPa, the shell-side high-pressure temperature-adjusting water temperature of the high-pressure methylammonium scrubber is controlled at 110-120°C, the shell-side steam pressure of the stripping tower is controlled at 0.9 MPa, and the saturated steam pressure is controlled at 0.9 MPa. The following technical operation scheme is used for replacement:

[0027] 1) After the urea unit is shut down and the process materials of the urea synthesis system are discharged, the pipelines are flushed according to the designed process through the synthesis system's own high-pressure flushing water pipeline. Specifically, the high-pressure flushing water pipeline flushes the pipelines after the V31 and V32 valves, that is, the pipeline after the V12 valve, the pipeline before the V16 valve, the pipeline after the V27 valve, and the V33 pipeline in turn, and then flushes the gas phase pipe discharge pipeline, the liquid phase pipe discharge pipeline, the suction pipe discharge pipeline, and the overflow pipe discharge pipeline separately; close V34 and V35, use the high-pressure flushing water pipeline to fill the high-pressure methylammonium scrubber with water for replacement, then close the drain valve, fully open V34 and V35 to drain the high-pressure methylammonium scrubber; after the high-pressure flushing water flushing points and high-pressure discharge pipelines of the synthesis system are flushed, open the gas phase pipe, liquid phase pipe, suction pipe, overflow pipe discharge valves, and fully open V23, V24, V25, V14, V15 , V18 and V19, discharge the condensate generated during the system replacement process into the circulation system; after the synthesis system is flushed and depressurized, fully open V28, V33, V36, V37, V34, V35, close the shower valve, and close V16, V17, V27, V12, V31, V32, V10 and V19.

[0028] 2) Open the first and second blind plates, open the second, third, fourth and fifth control valves, send air into the stripping tower and finally into the high-pressure discharge pipe, open the factory air pipeline, then open the first control valve, adjust the temperature of the steam and air mixture to about 125°C, and flush the stripping tower, high-pressure methylamine condenser, synthesis tower, high-pressure methylamine scrubber, absorption tower and their connecting pipelines with the steam and air mixture, wash and recover the displaced ammonia-containing gas, and displace the entire synthesis system.

[0029] 3) After 8 hours of displacement of the synthesis system, open the synthesis system sampling valve to check for ammonia odor. If there is ammonia odor, continue to displace; if there is no ammonia odor, the displacement of the synthesis system is complete, and the first, second, third, fourth, fifth and sixth control valves are closed in turn, and the first and second blind plates are blind dead.

Claims

1. A urea synthesis system replacement pipeline, which is based on a 2300 tons / day urea plant, characterized in that the system further comprises a steam pipeline and a plant air pipeline, a control valve V1 is arranged on the steam pipeline, and a control valve V2, a first blind plate, a check valve and a control valve V3 are sequentially arranged on the plant air pipeline; the steam pipeline and the plant air pipeline are connected in parallel at the end to form a first flushing pipeline, and a temperature table is arranged on the first flushing pipeline; a branch is arranged after the first flushing pipeline, which is respectively a second flushing pipeline and a third flushing pipeline; a control valve V4 and a check valve are sequentially arranged on the second flushing pipeline, and the end of the second flushing pipeline is communicated with a stripping tower; a control valve V6 and a second blind plate are sequentially arranged on the third flushing pipeline, and the end of the third flushing pipeline is communicated with a high-pressure flushing water pipeline of the urea synthesis system to the stripping tower; a fourth flushing pipeline is arranged between the stripping tower and a high-pressure discharge pipeline, and a control valve V5 is arranged on the fourth flushing pipeline.

2. The urea synthesis system replacement line of claim 1 wherein The AH pipeline, i.e. the pipeline meeting the ST35-8-I standard and having a nominal pressure of 2.5 MPa, meeting the DIN2634 standard, is used before the control valve V4 of the second flushing pipeline; and the AR pipeline, i.e. the pipeline made of X2CrNiMo18-12 / X2CrNiMo18-14 and having a nominal pressure of 25.0 MPa, meeting the KC standard, is used after the control valve V4.

3. The urea synthesis system replacement line of claim 1 wherein The pipeline made of 304 stainless steel is used before the control valve V6 of the third flushing pipeline, and the pipeline made of urea grade 316L stainless steel is used after the control valve V6.

4. The urea synthesis system replacement line of claim 1 wherein The first blind plate and the second blind plate are eight-shaped blind plates.

5. A method for displacing a line of a urea synthesis system according to any one of claims 1 to 4, characterized in that The following technical operation scheme is used for replacement: the control high-pressure methylamine condenser shell side steam pocket pressure is 0.4-0.5 MPa, the high-pressure methylamine scrubber shell side high-pressure temperature control water temperature is 110-120℃, the stripping tower shell side steam pressure is 0.9 MPa, and the saturated steam pressure is 0.9 MPa; After the urea plant is stopped and the urea synthesis system process material discharge is completed, the high-pressure flushing water pipeline of the synthesis system is used to flush the pipeline according to the design process; the first blind plate and the second blind plate are opened, the control valve V2, the control valve V3, the control valve V4 and the control valve V5 are opened, air is sent into the stripping tower and finally into the high-pressure discharge pipeline, the plant air pipeline is fully opened, then the control valve V1 is opened, the temperature of the mixture of steam and air is adjusted to 125℃, and the mixture of steam and air is used to flush the stripping tower, the high-pressure methylamine condenser, the synthesis tower, the high-pressure methylamine scrubber, the absorption tower and the connecting pipelines thereof, to wash and recover the ammonia-containing gas replaced, and to replace the entire synthesis system, after the synthesis system is replaced for 8 hours, the synthesis system sampling valve is opened to check whether there is ammonia smell, if there is ammonia smell, the replacement is continued, if there is no ammonia smell, the replacement of the synthesis system is completed, the control valve V1, the control valve V2, the control valve V3, the control valve V4, the control valve V5 and the control valve V6 are sequentially closed, and the first blind plate and the second blind plate are restored to be blind.

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