A method for automatically controlling the production process of methylhydrazine by DCS

Abstract

The present invention proposes a method for automatically controlling the production process of methylhydrazine by DCS, and presets the operating parameters by the DCS system to control the opening of the steam regulating valve, so that the kettle temperature rises steadily. After the pressure in the kettle reaches the pressure setting value for closing the steam, the steam regulating valve is closed, and then the reaction is released until the temperature in the kettle reaches the insulation temperature setting value, or the pressure in the kettle reaches the insulation pressure setting value, and then the pressure control and insulation stage is entered; according to the difference fluctuation between the actual pressure value in the kettle and the insulation pressure setting value, the pressure in the kettle is kept stable by water point operation, and after the insulation time timing reaches the insulation time setting value, the circulating water inlet and outlet valves are fully opened, and when the temperature and pressure in the kettle are reduced to reach the cooling pressure setting value, the circulating water inlet and outlet valves are closed. The present invention realizes the automated production process of methylhydrazine by the DCS system, and the reaction process is precisely controllable, effectively improves product quality, saves labor costs, avoids hidden dangers caused by manual misoperation, and ensures the safety of staff at the same time.

Description

Technical Field

[0001] The present invention relates to a method for automatically controlling a methylhydrazine production process through a DCS, and belongs to the technical field of chemical pharmacy. Background Art

[0002] Methylhydrazine, also known as monomethylhydrazine, is an important chemical product with the structural formula CH3NHNH2. Methylhydrazine can spontaneously combust in contact with strong oxidants and is highly explosive in the presence of open flames and high temperatures. It is often combined with oxidants such as nitrogen tetroxide to form a two-component liquid propellant used in monitoring systems for space shuttles, spacecraft, and satellites. In recent years, it has also been widely used in the synthesis of fine chemicals such as pharmaceuticals and pesticides.

[0003] The traditional methylhydrazine production process involves methylating hydrazine hydrochloride with methanol and hydrochloric acid. The process then pressurizes and heats the reactor, then cools it down by controlling the kettle pressure with a water injection operation during the heat preservation phase. The methylation phase in this process is part of the alkylation process, and the heat preservation phase is the most reactive and dangerous phase. In the existing process, the circulating water outlet valve is always open. Workers manually open the circulating water inlet valve by observing the on-site pressure, then use a meter to time and close the valve. This process is significantly affected by human factors. In actual operation, due to large pressure fluctuations during the water injection phase, the valve opening and closing must be pre-manipulated based on the on-site reaction conditions. This is not only labor-intensive but also requires imprecise control of the operation timing. Improper operation can easily lead to reduced product purity and even safety accidents.

[0004] DCS, or distributed computer control system, is a new generation of instrumentation and control systems based on microprocessors. It adopts the fundamental design principles of decentralized control and centralized operation and management. It employs the principles of decentralized control functions, centralized display and operation, and a balance of autonomy and comprehensive coordination. It has found widespread application in various industries, including power generation, metallurgy, and petrochemicals. However, the current methylhydrazine production process lacks a compatible DCS system. There is an urgent need for a control system and method that can adapt to the modern methylhydrazine production process to improve production efficiency while reducing safety hazards. Summary of the Invention

[0005] The purpose of the present invention is to solve the above-mentioned problems existing in the existing methylhydrazine production process and to provide a method for automatically controlling the methylhydrazine production process through DCS.

[0006] The technical solution of the present invention is a method for automatically controlling the methylhydrazine production process through DCS, which specifically includes the following steps:

[0007] 1) Setting stage: Based on the operation ticket, operating parameters are preset through the DCS system. The DCS system includes a central control device and a distributed control device. The distributed control device is respectively installed on the steam regulating valve and circulating water inlet and outlet valve outside the methylation kettle and is connected to the central control device via lines. The central control device is also connected to the kettle temperature transmitter and kettle pressure transmitter inside the methylation kettle via lines and controls the material transfer system. The preset operating parameters specifically include: shut-off steam pressure set value, holding temperature set value, holding pressure set value, holding time set value, and end pressure set value, etc.

[0008] 2) Material transfer stage: The DCS system first transfers hydrazine hydrochloride into the methylation kettle through the material transfer system, and then adds methanol and hydrochloric acid. The methylation kettle is equipped with a jacket on the outside, with steam pipes and steam regulating valves at both ends of the jacket, as well as a circulating water cooling pipe with circulating water inlet and outlet valves. The methylation kettle is also equipped with a kettle temperature transmitter and a kettle pressure transmitter. The methylation kettle is also equipped with a safety control system, including a pair of steam inlet and outlet shut-off valves connected in series on the steam pipe, which are normally open; and a set of circulating water inlet and outlet shut-off valves connected in parallel on the circulating water cooling pipe, which are normally closed. When the kettle temperature exceeds 136°C or the kettle pressure exceeds 1.15 MPa, the protection interlock is triggered, forcibly closing the steam inlet and outlet shut-off valves and opening the circulating water inlet and outlet shut-off valves.

[0009] 3) Startup phase: After the material transfer phase is completed, click the temperature increase button in the DCS system to start automatic operation, open the steam regulating valve, and introduce steam into the jacket outside the methylation kettle to start the temperature increase phase;

[0010] 4) Temperature rising stage: The DCS system uses PID to control the opening of the steam regulating valve to make the kettle temperature rise steadily. When the pressure in the kettle reaches the pressure setting value for shutting off the steam, the steam regulating valve is closed. Then, the reaction releases heat until the temperature in the kettle reaches the insulation temperature setting value or the insulation pressure setting value, and then enters the pressure control and insulation stage;

[0011] 5) Pressure control and insulation stage: The DCS system intermittently controls the opening and closing of the circulating water inlet and outlet valves according to the fluctuation of the difference between the actual pressure value in the kettle and the insulation pressure setting value. When the actual pressure value in the kettle is lower than the insulation pressure setting value, the circulating water inlet and outlet valves are closed to increase the temperature and increase the actual pressure value in the kettle. When the actual pressure value in the kettle is higher than the insulation pressure setting value, the circulating water inlet and outlet valves are opened to reduce the temperature and reduce the actual pressure value in the kettle. The pressure in the kettle is kept stable by water tapping operation. When the insulation time reaches the insulation time setting value, the pressure reduction stage begins.

[0012] 6) Pressure reduction stage: The DCS system controls the circulating water inlet and outlet valves to be fully open to reduce the temperature and pressure in the kettle. When the pressure in the kettle reaches the end pressure setting value, the circulating water inlet and outlet valves are closed and the reaction ends.

[0013] Compared with the prior art, the advantages of the present invention are:

[0014] 1) The DCS system enables the automated production process of methylhydrazine, with precise control of the reaction process and data visualization, thus improving the company's production management efficiency;

[0015] 2) The introduction of data monitoring and alarms makes the entire process monitoring intuitive and safe, allowing staff to immediately detect abnormal conditions and handle them promptly;

[0016] 3) In the existing process, the water addition process requires a dedicated person to operate on-site, and only one reactor of the same type can be used for production. In addition, the reactor pressure fluctuates greatly during manual water addition. The present invention can realize automated water addition operation, ensure the stability of the pressure in the reactor during the pressure control and heat preservation stage, make the reaction process more stable and sufficient, and allow the production of similar reactors on the production line at the same time, effectively improving product quality and production efficiency.

[0017] 4) The existing process originally required two people to perform one post. This invention only requires one person to conduct on-site inspections, and there is no need to manually control the opening and closing of valves, which saves labor costs, avoids hidden dangers caused by manual operation, and ensures the safety of workers.

[0018] 5) With the DCS system protection interlock and SIS safety protection interlock, if a fault or even loss of control occurs on site, personnel can evacuate immediately, and the system will quickly intervene to perform a series of protection actions such as cooling, reducing human error in emergency situations and buying time for personnel evacuation. DETAILED DESCRIPTION

[0019] The technical solutions of the present invention are further described below based on examples. Throughout this specification, the content of an example means that the specific technical features described therein are included in at least one embodiment of the present invention. In this specification, schematic representations of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific technical features described may be combined in any suitable manner in any one or more embodiments or examples.

[0020] This embodiment provides a method for automatically controlling a methylhydrazine production process through a DCS, which specifically includes the following steps:

[0021] 1) Setting stage: According to the operation ticket, the operation parameters are preset through the DCS system;

[0022] 2) Material transfer stage: The DCS system first transfers hydrazine hydrochloride into the methylation reactor through the material transfer system, and then adds methanol and hydrochloric acid;

[0023] 3) Startup phase: After the material transfer phase is completed, click the temperature increase button in the DCS system to start automatic operation, open the steam regulating valve, and introduce steam into the jacket outside the methylation kettle to start the temperature increase phase;

[0024] 4) Temperature rising stage: The DCS system uses PID to control the opening of the steam regulating valve to make the kettle temperature rise steadily. When the pressure in the kettle reaches the pressure setting value for shutting off the steam, the steam regulating valve is closed. Then, the reaction releases heat until the temperature in the kettle reaches the insulation temperature setting value or the insulation pressure setting value, and then enters the pressure control and insulation stage;

[0025] 5) Pressure control and insulation stage: The DCS system intermittently controls the opening and closing of the circulating water inlet and outlet valves according to the fluctuation of the difference between the actual pressure value in the kettle and the insulation pressure setting value, and maintains the pressure in the kettle stable by water tapping operation. When the insulation time reaches the insulation time setting value, it enters the pressure reduction stage;

[0026] 6) Pressure reduction stage: The DCS system controls the circulating water inlet and outlet valves to be fully open to reduce the temperature and pressure in the kettle. When the pressure in the kettle reaches the end pressure setting value, the circulating water inlet and outlet valves are closed and the reaction ends.

[0027] The methylation kettle is provided with a jacket on the outside, with steam pipes and steam regulating valves at both ends of the jacket, as well as a circulating water cooling pipe with circulating water inlet and outlet valves. The methylation kettle is also provided with a kettle temperature transmitter and a kettle pressure transmitter.

[0028] The methylation kettle is also equipped with a safety control system, including a pair of steam inlet and outlet shut-off valves connected in series on the steam pipe, which are normally in the open state; a set of circulating water inlet and outlet shut-off valves connected in parallel on the circulating water cooling pipe, which are normally in the closed state; when the kettle temperature exceeds 136°C or the kettle pressure exceeds 1.15Mpa, the protection interlock is triggered, forcibly closing the steam inlet and outlet shut-off valves and opening the circulating water inlet and outlet shut-off valves.

[0029] The DCS system includes a central control device and a distributed control device, wherein the distributed control device is respectively installed on the steam regulating valve and circulating water inlet and outlet valve outside the methylation kettle and is connected to the central control device through lines; the central control device is also connected to the kettle temperature transmitter and kettle pressure transmitter inside the methylation kettle through lines and controls the material transfer system.

[0030] The preset operating parameters in step 1) specifically include: a shut-off steam pressure setting value, a holding temperature setting value, a holding pressure setting value, a holding time setting value, and an end pressure setting value.

[0031] In step 4), the steam pressure setting value is 0.7 MPa.

[0032] In step 4), the setting value of the insulation temperature is 118° C., and the setting value of the insulation pressure is 0.82 MPa.

[0033] The setting value of the insulation time in step 5) is 4 hours.

[0034] The specific steps of the water point operation in step 5) are as follows: when the actual pressure value in the kettle is lower than the insulation pressure setting value, the circulating water inlet and outlet valves are closed to increase the temperature, thereby increasing the actual pressure value in the kettle; when the actual pressure value in the kettle is higher than the insulation pressure setting value, the circulating water inlet and outlet valves are opened to cool the kettle, thereby reducing the actual pressure value in the kettle.

[0035] The final pressure setting value in step 6) is 0.5 MPa.

[0036] The models and specifications of the components used in the above system are as follows:

[0037] DCS software system: Nanjing Sciyon NT6000; DPU controllers: KM950A and BM131A; analog module: KM231A; control valve module: KM236A; shut-off valve modules: KM234A and KM235B; industrial Ethernet switch: KN831A; UPS power supply: YTR1106L6KS; etc.

[0038] Kettle temperature transmitter: HTZPJ2-240 0-200℃; Kettle pressure transmitter: PL3051LT7E4S22M3B5 -0.1-1.6Mpa; Control valve: ZJHP-16P; Steam inlet and outlet shut-off valve: ZSHO-16K-32, fault closed; Circulating water inlet and outlet shut-off valve: ZSHO-16K-50, fault open.

[0039] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A method for automatically controlling a methylhydrazine production process by DCS, characterized in that: The method specifically comprises the following steps: 1) Setting stage: According to the operation ticket, preset the operation parameters through the DCS system; 2) Material transfer stage: The DCS system first transfers hydrazine hydrochloride into the methylation reactor through the material transfer system, and then adds methanol and hydrochloric acid; 3) Start-up phase: After the material transfer phase is completed, click the temperature increase button in the DCS system to implement automatic operation, open the steam regulating valve, and introduce steam into the jacket outside the methylation kettle to start the temperature increase phase; 4) Heating stage: The DCS system uses PID to control the opening of the steam regulating valve to make the kettle temperature rise steadily. When the pressure in the kettle reaches the pressure setting value for shutting off the steam, the steam regulating valve is closed. Then, the reaction releases heat until the temperature in the kettle reaches the insulation temperature setting value or the insulation pressure setting value, and then enters the pressure control and insulation stage. 5) Pressure control and insulation stage: The DCS system intermittently controls the opening and closing of the circulating water inlet and outlet valves according to the difference between the actual pressure value in the kettle and the insulation pressure setting value, and keeps the pressure in the kettle stable through water tapping operation. After the insulation time reaches the insulation time setting value, it enters the pressure reduction stage; 6) Pressure reduction stage: The DCS system controls the circulating water inlet and outlet valves to be fully opened to reduce the temperature and pressure in the kettle. When the pressure in the kettle reaches the end pressure setting value, the circulating water inlet and outlet valves are closed and the reaction ends; The methylation kettle is also provided with a safety control system, including a pair of steam inlet and outlet cut-off valves connected in series on the steam pipeline, which are normally in an open state; a set of circulating water inlet and outlet cut-off valves connected in parallel on the circulating water cooling pipeline, which are normally in a closed state; when the kettle temperature exceeds 136°C or the kettle pressure exceeds 1.15Mpa, the protection interlock is triggered, the steam inlet and outlet cut-off valves are forcibly closed, and the circulating water inlet and outlet cut-off valves are opened; In step 4), the steam pressure setting value is 0.7Mpa; In step 4), the insulation temperature setting value is 118° C., and the insulation pressure setting value is 0.82 MPa; The insulation time in step 5) is set to 4 hours; The final pressure setting value in step 6) is 0.5 MPa.

2. A method for automatically controlling a methylhydrazine production process by DCS according to claim 1, characterized in that: The methylation kettle is provided with a jacket on the outside, steam pipes and steam regulating valves are provided at both ends of the jacket, and a circulating water cooling pipe is provided at the same time, and a circulating water inlet and outlet valve is provided on the circulating water cooling pipe; the methylation kettle is also provided with a kettle temperature transmitter and a kettle pressure transmitter.

3. The method for automatically controlling the methylhydrazine production process by DCS according to claim 1, characterized in that: The DCS system includes a central control device and a distributed control device, wherein the distributed control device is respectively installed on the steam regulating valve and the circulating water inlet and outlet valve outside the methylation kettle, and is connected to the central control device through lines; the central control device is also connected to the kettle temperature transmitter and the kettle pressure transmitter inside the methylation kettle through lines, and controls the material transfer system.

4. The method for automatically controlling the methylhydrazine production process by DCS according to claim 1, characterized in that: The preset operating parameters in step 1) specifically include: a shut-off steam pressure setting value, a heat preservation temperature setting value, a heat preservation pressure setting value, a heat preservation time setting value and an end pressure setting value.

5. The method for automatically controlling the methylhydrazine production process by DCS according to claim 1, characterized in that: The specific steps of the water point operation in step 5) are: when the actual pressure value in the kettle is lower than the insulation pressure setting value, the circulating water inlet and outlet valves are closed to increase the temperature so that the actual pressure value in the kettle increases; when the actual pressure value in the kettle is higher than the insulation pressure setting value, the circulating water inlet and outlet valves are opened to cool down so that the actual pressure value in the kettle decreases.