CN111019692B - Method for automatically controlling large valve switching of ethylene cracking furnace - Google Patents
Method for automatically controlling large valve switching of ethylene cracking furnace Download PDFInfo
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- CN111019692B CN111019692B CN201911285395.3A CN201911285395A CN111019692B CN 111019692 B CN111019692 B CN 111019692B CN 201911285395 A CN201911285395 A CN 201911285395A CN 111019692 B CN111019692 B CN 111019692B
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- C—CHEMISTRY; METALLURGY
- C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
- C10G—CRACKING HYDROCARBON OILS; PRODUCTION OF LIQUID HYDROCARBON MIXTURES, e.g. BY DESTRUCTIVE HYDROGENATION, OLIGOMERISATION, POLYMERISATION; RECOVERY OF HYDROCARBON OILS FROM OIL-SHALE, OIL-SAND, OR GASES; REFINING MIXTURES MAINLY CONSISTING OF HYDROCARBONS; REFORMING OF NAPHTHA; MINERAL WAXES
- C10G9/00—Thermal non-catalytic cracking, in the absence of hydrogen, of hydrocarbon oils
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- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C4/00—Preparation of hydrocarbons from hydrocarbons containing a larger number of carbon atoms
- C07C4/02—Preparation of hydrocarbons from hydrocarbons containing a larger number of carbon atoms by cracking a single hydrocarbon or a mixture of individually defined hydrocarbons or a normally gaseous hydrocarbon fraction
- C07C4/04—Thermal processes
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- G—PHYSICS
- G05—CONTROLLING; REGULATING
- G05D—SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES
- G05D16/00—Control of fluid pressure
- G05D16/20—Control of fluid pressure characterised by the use of electric means
- G05D16/2006—Control of fluid pressure characterised by the use of electric means with direct action of electric energy on controlling means
- G05D16/2013—Control of fluid pressure characterised by the use of electric means with direct action of electric energy on controlling means using throttling means as controlling means
- G05D16/2026—Control of fluid pressure characterised by the use of electric means with direct action of electric energy on controlling means using throttling means as controlling means with a plurality of throttling means
Abstract
The invention discloses a method for automatically controlling the switching of a big valve of an ethylene cracking furnace, which comprises the following steps: initializing and checking initial permissibility work, switching a cracking furnace mode from a hot standby mode to a large valve automatic switching mode, starting a pressure difference stable state judgment logic, starting the closing action of a cracking gas large valve until the large valve pressure difference PDZI reaches a first set value, and stopping closing the cracking gas large valve; after the pressure difference of the PDZI large valve reaches a first set value, starting to open the coke cleaning gas large valve to act; opening the coke cleaning gas big valve for a certain valve position, starting a pressure difference stable state judgment logic, continuing to open the coke cleaning gas big valve after the pressure difference is stable until the PDZI pressure difference is less than a second set value, and stopping opening the coke cleaning gas big valve; and repeating the operation until the cracking gas big valve is completely closed/the coke cleaning gas big valve is completely opened. The method has the advantages of fast adaptive control response, reduction of manual operation, contribution to improvement of the stability of the mode switching process of the cracking furnace and the control precision of the pressure difference, and reduction of the safety risk of the device.
Description
Technical Field
The invention relates to a method for automatically controlling the switching of a large valve of an ethylene cracking furnace.
Background
The ethylene industry is a measure of the state of the petrochemical industry and has been used as a marker for petrochemical development. With the continuous development of computer application technology and automatic control technology, a process control system is an important guarantee for ensuring the safe and efficient operation of an ethylene production device, the economic benefit is obtained only from the process design and production equipment modification of the ethylene production process, and the computer control and optimization operation are carried out based on the ethylene production process, the chemical engineering technology, the computer program and the automatic control strategy are comprehensively applied, the intrinsic potential of the device is fully exerted, and the higher economic benefit of the device is obtained by energy conservation, consumption reduction, low cost consumption and high load production.
The cracking furnace is the core equipment of the ethylene device, the energy consumption accounts for 65-70% of the total energy consumption of the ethylene device, the large valve switching process is complex in operation, and the cracking furnace comprises 4 modes of a normal cracking mode (normal cracking state of the cracking furnace), a hot standby mode (steam running state of the cracking furnace), free large valve switching (coke cleaning large valve and cracking large valve can be freely switched under the state), and on-line coke cleaning (coke removal is carried out by combining coke cleaning air and diluted steam), the cracking furnace indicates normal through judging the pressure difference of the large valve of the cracking gas, slowly closing the large valve of the cracking gas with a certain valve position opening degree, starting to close, continuing to close after the pressure difference indicates stable, not exceeding a certain opening degree each time, starting to open the large valve of the coke cleaning gas after the pressure difference indicates 50kPa, not exceeding a certain opening degree each time, stopping opening the large valve of the coke cleaning gas after the pressure difference begins to reduce to 40KPa, continuing to close the large valve of the cracking gas slowly, until the operation is maintained until the cracking gas atmosphere valve is fully closed, and the coke cleaning gas is fully opened. The process has strict requirements on the operation technology of personnel and high risk, and no related control technology is developed at present; secondly, the stable operation of the cracking furnace has large demand on operators, the operators need to pay continuous attention to key parameters, and the operation fault tolerance rate is low; meanwhile, different personnel have different experiences on key operating parameters, and the equipment body caused by operation has large impact, so that the fluctuation of a downstream compression and separation system caused by the operation of the cracking furnace is easily caused.
Aiming at the situations, the invention adopts a method for automatically controlling the large valve switching of the ethylene cracking furnace, fills the blank of the large valve switching control technology of the cracking furnace, clarifies and immobilizes the operation process of the cracking furnace, and performs control optimization by combining the operation experience of the device personnel, further improves the automatic control level of the cracking process, reduces the misoperation risk of the device personnel, makes up the shortage of the post personnel, and ensures the smooth driving and stable operation of the device.
Disclosure of Invention
The invention aims to provide a method for automatically controlling the automatic switching of a large valve of an ethylene cracking furnace, which aims to realize the automatic control of the mode switching process of the cracking furnace and realize the self-adaptive valve-pressure regulation aiming at a specific chemical process by stabilizing a pressure difference matching strategy of the valve switching process.
The invention provides a method for automatically controlling the switching of a big valve of an ethylene cracking furnace, wherein a cracking gas pipeline from an outlet of the ethylene cracking furnace is connected with an inlet of a quencher, an outlet pipeline of the quencher is divided into two pipelines, one pipeline goes to a quenching water tower, the other pipeline is connected with a hearth, a cracking gas big valve and a coke cleaning gas big valve are respectively arranged on the two pipelines, a pressure difference meter PDZI is arranged on a pipeline before the outlet pipeline of the quencher is divided into two pipelines, a pressure difference display value of the PDZI is used as a controlled object, the cracking gas big valve and the coke cleaning gas big valve are used as actuators, and the controlled pressure difference is monitored in real time based on a moving window time strategy, so that the stable control of the fixed valve position of the cracking big valve/the coke cleaning big valve is realized, and the method comprises the following steps:
(1) initializing and checking initial permissibility work, and ensuring that the cracking gas main valve/coke cleaning gas main valve state is in a hot standby mode initial state by utilizing the judgment of signals/logics, namely, the cracking gas main valve is in a fully open state, and the coke cleaning gas main valve state is in a fully closed state;
(2) switching a cracking furnace mode from a hot standby mode to a large valve automatic switching mode, sending a cracking gas large valve closing command based on DCS after detecting a large valve automatic switching mode state feedback parameter, simultaneously starting a cracking gas large valve coke particle jamming fault automatic processing logic in parallel, and stopping cracking gas large valve action and large valve coke particle jamming fault monitoring when a cracking gas large valve is closed to be out of the control requirement of a valve position nonlinear change area;
(3) starting a pressure difference stable state judgment logic, firstly reading a current pressure difference value as an off-line value, monitoring the off-line value by using a real-time pressure difference value after a period of time, and when the difference value between the current pressure difference value and the real-time pressure difference value within a moving window time (such as 60 seconds) is less than 5KPa, judging that the pressure difference is stable, further closing a cracking gas big valve, and circularly executing the pressure difference stable state judgment logic until the pressure difference is stable;
(4) starting the closing action of the cracking gas big valve, detecting the automatic processing of the coke particle jamming fault of the cracking gas big valve based on the valve position change in the moving window time, and stopping closing the cracking gas big valve until the big valve pressure difference PDZI reaches a first set value (for example, 45-55kPa, further for example, 50 kPa).
(5) After the pressure difference of the PDZI large valve reaches a first set value, starting to open a coke cleaning gas large valve to act, and simultaneously starting coke particle jamming fault automatic processing logic (monitoring valve position change of the coke cleaning gas large valve for a period of time) of the coke cleaning gas large valve in parallel; and (4) after opening the coke cleaning gas main valve for a certain valve position, starting a pressure difference stable state judgment logic as described in the step (3), and continuing to open the coke cleaning gas main valve after the pressure difference is stable until the PDZI pressure difference is smaller than a second set value (for example, 35-45kPa, further about 40kPa), and stopping opening the coke cleaning gas main valve.
(6) Continuously closing the cracking gas big valve to suppress pressure to a first set value, then opening the coke cleaning gas big valve to reduce pressure to a second set value until the cracking gas big valve is completely closed/the coke cleaning gas big valve is completely opened to reach a coke cleaning mode state,
the automatic control program for switching the large valve is finished, and the system can execute coke cleaning operation.
Further, the automatic processing logic of the coke particle jamming fault of the pyrolysis gas main valve comprises the steps of detecting the valve position change amplitude of the pyrolysis gas main valve within a certain time, judging that the valve coke particles are jammed when the valve position change amplitude is too small, stopping closing the pyrolysis gas main valve at the moment, and reminding an operator.
Further, in the step (1), the mode is monitored by using the condition determination block in the process of switching from the hot standby mode to the decoking mode, and it is confirmed that the hearth COT (cracking furnace outlet temperature) and the dilution steam flow rate involved in the mode switching process are within the mode allowable range.
Further, in the step (1), initial permissibility work check is carried out on the process variables and the state variables, the program variables are descended after meeting the default state and the parameter self-check within a certain time, an alarm can be immediately sent out when any condition is not met, the associated lock state is confirmed again before the logic is started, the logic control is immediately quitted when the condition is not met, and the flexibility of manual intervention is ensured.
Further, in the circulating action logic of closing the cracking gas atmospheric valve to boost the pressure to a first set value (for example, 50kPa), and opening the coke cleaning gas atmospheric valve to reduce the pressure to a second set value (for example, 40kPa), the pressure difference abnormity real-time monitoring alarm is carried out, and by constructing a large valve position limit control strategy, the valve position limit value exceeding the current process state automatically quits the logic control, and the internal operation is timely reminded to take corresponding measures.
The control method has a valve position remote transmission signal error processing control strategy, a pyrolysis gas main valve closing in-place signal and a coke cleaning gas main valve opening in-place signal are used for replacing a transmitting signal as a downlink condition, and in the processes of closing the pyrolysis gas main valve and opening the coke cleaning gas main valve, control logic carries out circulating detection on the valve position signal until an action valve position meets the control requirement.
The patent has the following creativity and outstanding results:
aiming at the problems of complex technology, high risk and large equipment body impact and rear system fluctuation caused by operation in the ethylene cracking furnace large valve switching operation process, and no related control technology is developed at present, the patent designs and develops an automatic control method for ethylene cracking furnace large valve switching, and further fills the blank of the ethylene cracking furnace large valve switching control technology. The method realizes the self-adaptive control of the differential pressure matching control of the large valve, the quenching water tower and the combustion chamber by constructing a control strategy of 'fixed valve position closing and pressure stabilizing difference', a large valve position limiting control strategy, a valve position remote transmission signal error processing control strategy and other methods and combining functions of important parameter display, key parameter setting, coke cleaning gas large valve/cracking gas large valve coke particle jamming fault automatic processing logic and the like, can improve the stability of the cracking furnace large valve in the switching process, replaces operators to monitor key parameters in real time, reduces the operating intensity of the operators, improves the fault tolerance rate and reduces errors caused by the operation of the operators; meanwhile, the impact of the equipment body caused by manual experience operation is relieved, the fluctuation of a rear system is reduced to the minimum extent, and the requirements of process stability and equipment integrity of production operation are met.
Drawings
FIG. 1 is a schematic view of a large valve switching device of an ethylene cracking furnace;
FIG. 2 is a schematic diagram (I) of an automatic cut-out control method for a large valve of an ethylene cracking furnace;
FIG. 3 is a schematic diagram of an automatic cut-out control method of a big valve of an ethylene cracking furnace (II);
FIG. 4 is a schematic diagram of the SFC program for automatically switching and controlling the large valve of the cracking furnace.
Fig. 2 and 3 are schematic diagrams of an automatic switching control method for a large valve of an ethylene cracking furnace, wherein "MODE", "CM%", "DM%", and "PDZT" in the diagrams are respectively an operation panel remote signal display, a cracking gas large valve position display, a coke cleaning gas large valve position display, and a pressure difference meter display; the method comprises the following steps of firstly, mode state monitoring logic, secondly, coke particle jamming fault monitoring of a pyrolysis gas main valve, thirdly, pressure difference stability judging logic, fourthly, coke particle jamming fault monitoring of a coke cleaning gas main valve, and fifthly, in-place signal detection of a coke cleaning gas main valve switch of the pyrolysis gas main valve. FIG. 4 is a schematic block diagram of an SFC program of a specific implementation process of automatic switching control of a large valve of a cracking furnace, wherein the DCS is implemented, a rectangular box is used for executing actions, ten is detection logic of transfer conditions, double lines indicate parallel operation, S14/S13/S16 represents the executing actions of the box step sequence of FIG. 3, T15/T17 represents the transfer conditions of the prismatic step sequence of FIG. 3, the transfer condition judgment is carried out after the executing actions are completed, and 28.984 is the executing time of the executing actions.
Detailed Description
The invention is further described below with reference to the accompanying drawings.
As shown in fig. 1, an automatic switching device for a large valve of an ethylene cracking furnace is provided, wherein a cracked gas pipeline from an outlet of the ethylene cracking furnace is connected with an inlet of a quencher 1, an outlet pipeline of the quencher is divided into two pipelines, one pipeline goes to a quenching water tower, the other pipeline is connected with a hearth, a cracked gas large valve 3 and a coke cleaning gas large valve 4 are respectively arranged on the two pipelines, a PDZI pressure difference meter 2 is arranged on the pipeline before the outlet pipeline of the quencher is divided into two pipelines, the cracked gas large valve 3, the coke cleaning gas large valve 4 and the PDZI pressure difference meter 2 are communicated with a control system DCS, a PDZI pressure difference display value of the pressure difference meter is used as a controlled object, the cracked gas large valve and the coke cleaning gas large valve are used as an actuator, and a controlled pressure difference is monitored in real time based on a moving window time strategy, so that stable control of a positioning valve of the cracked gas large valve/coke cleaning large valve is realized.
As shown in fig. 2-4, the method for automatically controlling the large valve switching of the ethylene cracking furnace comprises the following steps:
(1) initializing and checking initial permissibility work, ensuring that the cracking gas main valve/coke cleaning gas main valve state is in a hot standby MODE initial state by utilizing the judgment of signals/logics, namely, the cracking gas main valve is in a fully open state, the coke cleaning gas main valve state is in a fully closed state, setting process parameters such as hearth COT (cracking furnace outlet temperature), dilution steam flow and the like in certain upper and lower limit ranges based on DCS, confirming that the cracking furnace MODE is in a main valve free switching MODE position according to a DCS program, and monitoring the current signal of an operation panel in real time (MODE is a monitoring signal), as shown in figure 2 ((I));
(2) as shown in fig. 2, the cracking furnace mode is switched from the hot standby mode to the large valve automatic switching mode, after detecting the state feedback parameter of the large valve automatic switching mode, a cracking gas large valve closing command is sent based on DCS, simultaneously, the cracking gas large valve scorched particle jamming fault automatic processing logic is started in parallel, when the cracking gas large valve is closed to a position outside the control requirement of the valve position nonlinear change region, the cracking gas large valve action and the large valve scorched particle jamming fault monitoring are stopped, in order to overcome the nonlinear change influence between the large valve pressure differences, a valve position limiting strategy is closed for the first time, and if the M% parameter is the cracking gas large valve first closing valve position which can be written in the background;
(3) starting a pressure difference stable state judgment logic, firstly reading a current pressure difference value as an off-line value, monitoring the off-line value by using a real-time pressure difference value after a period of time, and when the difference value between the current pressure difference value and the real-time pressure difference value within a moving window time (60 seconds) is less than PDZT1kPa (5kPa), judging that the pressure difference is stable, further closing a cracking gas big valve, and circularly executing the pressure difference stable state judgment logic until the pressure difference is stable; the method is characterized in that a control strategy of 'valve position positioning closing and pressure stabilizing difference' is implemented in the cracking gas atmosphere valve closing process, the change condition of the outlet pressure of the quenching water tower and the pressure difference of a transmission line (less than (PDZT1) kPa) is detected in real time by closing the X% valve position of the cracking gas atmosphere valve, and pressure difference stabilizing processing logic is carried out, as shown in the third step in figure 2.
(4) Starting the closing action of the cracking gas big valve, detecting the coke particle jamming fault of the cracking gas big valve based on the valve position change in the moving window time, and stopping closing the cracking gas big valve until the big valve pressure difference PDZI reaches the first set value of 50 kPa.
(5) After the pressure difference of the PDZI large valve reaches a first set value, starting to open a coke cleaning gas large valve (shown as the fourth value in figure 3), and simultaneously starting coke particle jamming fault automatic processing logic (monitoring valve position change of the coke cleaning gas large valve for a period of time) of the coke cleaning gas large valve in parallel; and (4) after opening the coke cleaning gas main valve for a certain valve position, starting a pressure difference stable state judgment logic as described in the step (3), and continuing to open the coke cleaning gas main valve after the pressure difference is stable until the PDZI pressure difference is smaller than a second set value (for example, 35-45kPa, further about 40kPa), and stopping opening the coke cleaning gas main valve. Similarly implementing the control strategy of 'valve position closing and pressure stabilizing difference', carrying out pressure difference stability judgment processing logic (the same third step) until the pressure difference is reduced to 40kPa, then repeatedly executing the step (3), and controlling the actions of closing the cracking gas atmosphere valve/opening the coke cleaning gas atmosphere valve to ensure that the pressure difference is between (40-50)
And (5) opening the coke cleaning gas big valve for several times after the cracking gas big valve is closed in place between kPa, as shown by the fifth step.
(6) And (3) repeating the step (3), controlling the actions of closing the pyrolysis gas big valve and opening the coke cleaning gas big valve to ensure that the pressure difference is between 40 and 50kPa until the pyrolysis gas big valve is closed in place and then the coke cleaning gas big valve is opened for a plurality of times, as shown in the fifth step,
when the coke cleaning mode state is reached, the large valve switching automatic control program is ended, and the system can execute coke cleaning operation.
The invention is realized by DCS background configuration SFC logic, as shown in figure 4, and each execution action execution logic finishes execution duration decision (for example, judging that the execution action finishes the detection of transfer condition lasting for 3 seconds, and does not carry out pulse signal detection for 1 second), thereby eliminating the instantaneous judgment influence of DCS signal error.
Example 1
Taking 100 ten thousand t/h ethylene cracking furnace big valve switching control process of a certain factory as an example, the method comprises the following steps:
(1) firstly, initializing and checking initial admissibility work to enable related valves such as a cracking gas big valve and the like to be in a normal working state, and meanwhile, enabling parameters of a hearth COT, a dilution steam flow, a furnace negative pressure, a furnace SS temperature, a big valve pressure difference and a big valve anti-coking steam pressure to be in a process requirement range, and confirming a preparation state of related public works of a blind plate and a root valve;
(2) switching a cracking furnace mode from a hot standby mode to a large valve automatic switching mode, sending a cracking gas large valve closing command based on DCS after detecting a large valve automatic switching mode state feedback parameter, simultaneously starting a cracking gas large valve coke particle jamming fault automatic processing logic in parallel, stopping cracking gas large valve action and large valve coke particle jamming fault monitoring when the cracking gas large valve is closed to 70% (background writable parameters), and waiting for 300 seconds (background writable parameters);
(3) starting a pressure difference stable state judgment logic, firstly reading a pressure difference value PDZT0 before 60 seconds as an offline value, and closing an X% valve position of a pyrolysis gas big valve when | PDZT.PV-PDZT0| is more than 5KPa by reading a current real-time pressure difference value PDZT.PV; and when the absolute value of PDZT, PV-PDZT0 is less than or equal to 5KPa, the valve position of the pyrolysis gas atmosphere valve is not closed.
(4) Reading a current pressure difference meter pressure difference value PDZT.PV, when the PDZT.PV is less than 50kPa, continuously closing X% valve position of a pyrolysis gas main valve and starting coke particle jamming fault automatic processing logic of the pyrolysis gas main valve, then performing the pressure difference stable state judgment logic in the step (3), and stopping closing the pyrolysis gas main valve and executing the pressure difference stable processing logic until the pressure difference PDZT.PV of the main valve is greater than 50 kPa.
(5) And opening the Y% valve position of the coke cleaning gas big valve, simultaneously starting coke particle jamming fault automatic processing logic of the coke cleaning gas big valve in parallel, then carrying out pressure difference stable state judgment logic, continuing opening the coke cleaning gas big valve after the pressure difference is stable (the pressure difference value within 60 seconds is less than 5kPa) until the pressure difference PDZT.PV of the big valve is less than 40kPa, and stopping opening the coke cleaning gas big valve.
(6) And (5) repeating the steps (3) and (5), controlling the actions of closing the cracking gas big valve by X%/opening the coke cleaning gas big valve by Y% to enable the pressure difference to be between 40 and 50kPa until a cracking gas big valve closing in-place signal is read, then opening the coke cleaning gas big valve for 5 times (background parameters can be written), completely closing the cracking gas big valve to 0% at the moment, completely opening the coke cleaning gas big valve to 100%, achieving a coke cleaning mode state, and ending the automatic control program for switching the cracking furnace big valve.
Claims (10)
1. The utility model provides a method that ethylene cracking furnace big valve switches automatic control, wherein, the pyrolysis gas pipeline that comes from ethylene cracking furnace export connects the quench cooler import, quench cooler export pipeline divide into two the tunnel, go to the quench water tower all the way, another road connects furnace, be equipped with pyrolysis gas big valve and coke cleaning gas big valve on these two tunnel pipelines respectively, be equipped with pressure differential table PDZI on the pipeline before quench cooler export pipeline divide into two tunnel, use pressure differential table PDZI pressure differential display value as the controlled object, pyrolysis gas big valve and coke cleaning gas big valve are the executor, and based on moving window time strategy real-time monitoring controlled pressure differential, realize the fixed valve position stable control of pyrolysis big valve/coke cleaning big valve, the method includes following steps:
(1) initializing and checking initial permissibility work, and ensuring that the cracking gas main valve/coke cleaning gas main valve state is in a hot standby mode initial state by judging signals and logic;
(2) switching a cracking furnace mode from a hot standby mode to a large valve automatic switching mode, sending a cracking gas large valve closing command based on DCS after detecting a large valve automatic switching mode state feedback parameter, simultaneously starting a cracking gas large valve coke particle jamming fault automatic processing logic in parallel, and stopping cracking gas large valve action and large valve coke particle jamming fault monitoring when a cracking gas large valve is closed to be out of the control requirement of a valve position nonlinear change area;
(3) starting a pressure difference stable state judgment logic, reading a current pressure difference value as an off-line value, monitoring the current pressure difference value and a real-time pressure difference value after a period of time, when the difference value of the current pressure difference value and the real-time pressure difference value within a moving window time is less than 5KPa, judging that the pressure difference is stable, closing a cracking gas big valve, and circularly executing the pressure difference stable state judgment logic until the pressure difference is stable;
(4) starting the closing action of the cracking gas big valve, detecting the automatic processing of the coke particle jamming fault of the cracking gas big valve based on the valve position change in the moving window time, and stopping closing the cracking gas big valve until the big valve pressure difference PDZI reaches a first set value;
(5) after the pressure difference of the PDZI large valve reaches a first set value, starting to open a coke cleaning gas large valve to act, and simultaneously starting coke particle jamming fault automatic processing logic of the coke cleaning gas large valve in parallel; opening the coke cleaning gas main valve for a certain valve position, starting the pressure difference stable state judgment logic in the step (3), continuing to open the coke cleaning gas main valve after the pressure difference is stable until the PDZI pressure difference is smaller than a second set value, and stopping opening the coke cleaning gas main valve;
(6) and continuing to close the cracking gas main valve to suppress pressure to a first set value, then opening the coke cleaning gas main valve to reduce pressure to a second set value until the cracking gas main valve is completely closed and the coke cleaning gas main valve is completely opened to reach a coke cleaning mode state, ending the main valve switching automatic control program, and executing coke cleaning operation by the system.
2. The method of claim 1, wherein the first set point is 45-55 kPa.
3. The method of claim 2, wherein the first set point is 50 kPa.
4. A method according to any one of claims 1-3, wherein the second set point is 35-45 kPa.
5. The method of claim 4, wherein the second set point is 40 kPa.
6. The method of claim 1, wherein the automatic processing logic for coke particle jamming failure of the pyrolysis gas main valve comprises detecting a valve position change amplitude of the pyrolysis gas main valve within a certain time, and when the valve position change amplitude is too small, the valve coke particle jamming is determined, and at the moment, the operation of closing the pyrolysis gas main valve is stopped, and an operator is reminded.
7. The method of claim 1, wherein in the steps (1) to (6), the mode monitoring is performed by using a condition judgment block in the process of switching the hot standby mode to the decoking mode, and the outlet temperature and the flow rate of the dilution steam of the hearth cracking furnace involved in the process of switching the mode are confirmed to be within the allowable range of the mode.
8. The method of claim 1, wherein: in the step (1), initial permissibility work check is carried out on the process variable and the state variable, the program variable is descended after meeting the default state and parameter self-check for a certain time, an alarm can be immediately sent out when any condition is not met, the associated lock state is confirmed again before the logic is started, the condition is not met, the logic control is immediately quitted, and the flexibility of manual intervention is ensured.
9. The method of claim 1, wherein: after the cracking gas big valve starts to act, the coke particle jamming fault monitoring logic of the big valve is provided and is controlled in a mode of 'valve position fixing closing and pressure stabilizing difference', wherein the pressure stabilizing difference timing process has a forced downlink design, and the program operation time is saved; and an operator monitors the valve position of the DCS large valve and the differential pressure remote transmission signal in real time.
10. The method of claim 1, wherein: and in the circulating action logic of closing the cracking gas main valve to boost the pressure to a first set value and opening the coke cleaning gas main valve to reduce the pressure to a second set value, carrying out abnormal pressure difference real-time monitoring and alarming, and automatically quitting the logic control by constructing a main valve position limit control strategy and exceeding the valve position limit value of the current process state so as to prompt internal operation to take corresponding measures in time.
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