CN107490245B - Automatic load-variable control method for air separation device - Google Patents
Automatic load-variable control method for air separation device Download PDFInfo
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
- F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
- F25J3/04—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream for air
- F25J3/04763—Start-up or control of the process; Details of the apparatus used
- F25J3/04769—Operation, control and regulation of the process; Instrumentation within the process
- F25J3/04848—Control strategy, e.g. advanced process control or dynamic modeling
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
- F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
- F25J3/04—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream for air
- F25J3/04763—Start-up or control of the process; Details of the apparatus used
- F25J3/04769—Operation, control and regulation of the process; Instrumentation within the process
- F25J3/04812—Different modes, i.e. "runs" of operation
- F25J3/04836—Variable air feed, i.e. "load" or product demand during specified periods, e.g. during periods with high respectively low power costs
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J2210/00—Processes characterised by the type or other details of the feed stream
- F25J2210/40—Air or oxygen enriched air, i.e. generally less than 30mol% of O2
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J2280/00—Control of the process or apparatus
- F25J2280/50—Advanced process control, e.g. adaptive or multivariable control
Abstract
An automatic load change control method for an air separation device comprises the following steps: 1) obtaining PFD data of key process parameters under various working conditions of the process design of the air separation device; 2) determining variables as final product flow, wherein the variables are set as target values in the process of changing load of a process operator; 3) determining a key intermediate variable; these key intermediate variables are used to calculate the set point of the final PID controller; 4) determining a PID controller participating in automatic variable load; 5) obtaining a fitting function between the parameters in the step 2) and the step 3) by fitting, wherein the fitting function takes the variable in the step 3) as a dependent variable and the variable in the step 2) as an independent variable; 6) obtaining a fitting function between the parameters in the step 3) and the step 4) by fitting, wherein the variable in the step 4) is used as a dependent variable, and the variable in the step 3) is used as an independent variable; 7) interpolating each working point model by a polynomial function aiming at working point data of the same process parameter under different working conditions to obtain a variable load linear change track of the process parameter; 8) the starting and stopping of the automatic variable load need to meet certain conditions; 9) the above parameters may be increased or decreased according to the flow.
Description
Technical Field
The invention relates to an automatic variable load control method of an air separation device in the air separation production process, belonging to the technical field of automatic control engineering of the air separation device.
Background
In the process flow of the air separation device, raw material air enters a lower tower after a series of operation links such as filtration, compression, precooling, purification, pressurization, expansion, heat exchange and the like. After the air is primarily rectified by the lower tower, oxygen-enriched liquid air is obtained at the bottom of the lower tower, pure liquid nitrogen is obtained at the top of the lower tower, and the pure liquid nitrogen is subcooled by a subcooler and then throttled to enter the upper tower; after further rectification in the upper tower, liquid oxygen is obtained at the bottom of the upper tower, is compressed by a liquid oxygen pump and then enters the main heat exchanger, and is reheated and taken as a gas oxygen product to be discharged from the cold box. Part of the liquid oxygen directly exits the cold box and enters a liquid oxygen storage tank as a liquid oxygen product; extracting a liquid nitrogen product from the top of the upper tower, and feeding the liquid nitrogen product into a liquid nitrogen storage tank; a certain amount of argon fraction is extracted from the middle lower part of the upper tower of the main cooling box, and a liquid argon product is obtained after the argon fraction is rectified by the crude argon tower and the fine argon tower and enters a liquid argon storage tank.
The air separation device has the characteristics of complex flow, serious coupling and the like: first, the air separation plant uses a great deal of heat integration and material recycling technology, so that the air separation plant has the characteristic of high coupling of energy and material. If the upper tower and the lower tower share one condensation evaporator, part of the liquid space of the lower tower is directly used as the middle part of the upper tower for reflux, and the other part of the liquid space of the lower tower provides cold energy for a condenser of the crude argon tower, and finally returns to the air to participate in rectification on the upper tower; these factors increase the difficulty of operating the air separation plant in varying loads. During variable loads, individual units of the device cannot be adjusted individually.
Secondly, the load-variable operation of the air separation device is a dynamic adjustment process of a group of key working points, and is the transition of a production process from one working condition to another working condition; however, in the process of increasing and decreasing the load, a user determines only the yield of the product and does not determine target values of other key process variables under the target working condition, and an empirical method cannot predict the yield, is long in time consumption and is easy to overshoot and oscillate.
Disclosure of Invention
The invention aims to overcome the defects in the prior art, and provides an automatic load change control method for an air separation device, which mainly solves the problems of mutual decoupling of energy and materials, easiness in overshoot and oscillation and the like in the load change process of the air separation device and realizes smooth and rapid transition among different working conditions on the premise of ensuring the stability and the product quality of the air separation device.
The invention aims to complete the technical scheme that the automatic load changing control method for the air separation device comprises the following steps:
1) obtaining each working condition of the air separation device flow design, and PFD data at least comprising key flow parameters under the minimum working condition and the maximum working condition;
2) determining variables as final product flow: low pressure oxygen product flow LPOG, low pressure nitrogen product flow LPNG, argon product flow ArG, liquid nitrogen product flow NL; liquid oxygen product flow OL; the variables are used as target values set in the process of changing the load of a process operator;
3) determining key intermediate variables: air quantity of air entering a cold box, NLeq liquefaction capacity, air quantity of air expanded by AIRthurb, quantity of nitrogen expanded by NGturb, air quantity of high pressure HPAIR, air quantity of high pressure HPALhp; these key intermediate variables are used to calculate the set point of the final PID controller;
4) determining a PID controller participating in automatic variable load: controlling air flow FIC1294, high pressure air HPair FIC7418, regeneration effluent nitrogen flow FIC1213, effluent nitrogen pressure PIC1626, high pressure liquid-air FIC1556, lean liquid reflux FIC1557 for adjusting reflux ratio of the lower section of the middle pressure tower and the upper end of the low pressure tower, liquid nitrogen reflux FIC1558 for adjusting reflux ratio and purity of the top of the upper tower, oxygen-enriched liquid-air liquid level LIC1601, low pressure nitrogen flow FIC1520, high pressure nitrogen flow FIC1501, low pressure oxygen flow FIC1510, argon flow FIC1540, liquid nitrogen product flow FIC1630, FIC1704 crude liquid argon flow, medium pressure nitrogen-to-fine tower evaporator flow FIC1731 and crude argon tower oxygen-enriched liquid-air liquid level LIC1701 by adjusting inlet guide vanes of a main compressor;
5) obtaining a fitting function between the parameters in the step 2) and the step 3) by fitting, wherein the fitting function takes the variable in the step 3) as a dependent variable and the variable in the step 2) as an independent variable;
6) obtaining a fitting function between the parameters in the step 3) and the step 4) by fitting, wherein the variable in the step 4) is used as a dependent variable, and the variable in the step 3) is used as an independent variable;
7) interpolating each working point model by a polynomial function aiming at working point data of the same process parameter under different working conditions to obtain a variable load linear change track of the process parameter; the key flow needs to be corrected by using components, and the liquid level needs to be limited within a certain range, so that the load of a product produced by the device after being stabilized is changed on the premise that the air separation device is stable and the purity reaches the standard;
8) the starting and stopping of the automatic variable load need to meet certain conditions;
9) the above parameters may be increased or decreased according to the flow.
Preferably, the method comprises the following steps: in the step 5), the functional relationship between the independent variable and the dependent variable is as follows:
the AIRtot = func (LPOG, OL), the function is obtained by fitting parameter values of the AIRtot, the LPOG and the OL under different working conditions,
the oxygen content of the crude argon column feed was used to correct the AIRtot;
the modified functional relationship is AIRtot = func (LPOG, OL) + AIC1716 where the correction of AIC1716 is +/-10% of the AIRtot design flow;
NLeq = func (NL, OL, FIC1704) characterizes the ability to produce liquid products;
airtime = func (AIRtot, NLeq) maintains overall cold box balance;
NGturb = func (AIRtot, NLeq) maintains the overall cold box balanced;
HPair = amount of high pressure air required for the production of low pressure oxygen by FIC 7418;
MPair = AIRtot-HPair the sum of the medium-pressure air quantity and the high-pressure air quantity is the air quantity entering the cold box;
expanding HPALhp = HPair-FIC1556 high-pressure air to obtain liquid, wherein part of the liquid enters the medium-pressure tower, and the other part of the liquid enters the low-pressure tower; the flow to the low pressure column is adjusted to maintain the reflux ratio, and the flow of the liquefied air is controlled by adjusting a feed valve FV1556 of the low pressure column by FIC 1556; HPALhp is only an intermediate variable and does not participate in variable load;
in the step 6, the crude liquid argon flow rate RSP [ FIC1704] = func (airtot);
total air amount FIC1294 = func (airtot) + IA, where IA meter air flow, generally constant;
dirty nitrogen flow FIC1213 = func (airtot);
dirty nitrogen pressure PIC1626 = func (AIRtot, LPNG);
liquid-air FIC1556 = func (airtot);
barren liquor reflux FIC1557 = func (airtot);
liquid nitrogen reflux FIC1558 = func (AIRtot, MPNG);
the oxygen-enriched liquid-air liquid level LIC1601 = func (AIRtot), wherein the upper and lower limit positions are high and low alarm set points during industrial design;
low pressure nitrogen flow FIC1520 = LPNG;
medium pressure nitrogen flow FIC1501 = func (airtot);
low pressure oxygen flow FIC1510 = LPOG;
argon flow FIC1540 = ArG;
liquid nitrogen flow rate FIC1630 = NL;
crude liquid argon flow FIC1704= func (airtot);
FIC1731 = func(FIC1704)；
LIC1701 = func (airtot), where the upper and lower limits are the high and low alarm set points for the industrial design;
air expander air flow FIC1530= airtime;
low pressure nitrogen 1-way flow FIC1502= NGturb;
component analysis stations participating in the correction: the oxygen content in the middle of the low-pressure tower and the oxygen content in the middle of the crude argon tower are compensated in a positive direction;
the top outlet is crude liquid argon (CAL), the crude liquid argon is sent into a pure argon column K11, the flow of the crude liquid argon is calculated according to the total amount of air entering a cold box, and is corrected by the output value of an AIC1705 of a purity analyzer in the middle section of the argon column;
RSP[FIC1704]* = func(AIRtot) + AIC1705；
the AIC1705 was corrected to within +/-20% of the maximum mix flow of crude liquid argon, and PID adjustments to take part in compositional analysis corrections should be slow because of the longer response time of the argon column.
Preferably, the method comprises the following steps: in the step 7), the operation rate is as follows: 0.2%/min to 0.33%/min, and changing the load by 1% every 3 to 5 minutes; the operation of device can be according to the demand of gas and liquid product automatic adjustment, through setting for the flow of final product under a certain operating mode, according to material balance, the key intermediate parameter under this operating mode is come the back to the conservation of energy, includes: air amount entering a cooling box, expanded air amount, expanded nitrogen amount, medium-pressure air amount, high-pressure liquid air amount and liquefaction capacity; further calculating the flow on the key flow pipeline and the liquid level of the key container; the PID controller is used for controlling the opening of the valve so as to adjust corresponding key parameters such as flow and liquid level, so that the product produced by the device after being stabilized is subjected to load conversion on the premise that the air separation device is stable and the purity reaches the standard;
in the step 8), the starting conditions of automatic load change are as follows:
a) the relevant PID is controlled in an automatic state;
b) the air separation device runs stably;
c) the air quantity entering the cold box is in a normal range;
d) the yield of the gas oxygen product is in a normal range;
e) switching the analyzers participating in correction to corresponding analysis measuring points;
f) the PID controller participating in the correction is in an automatic state;
after the above conditions are met, the control system displays a prompt of "allowing automatic load change", and manually clicks an "automatic load change input button";
the stop conditions for automatic load change are:
a) parking the air separation plant;
b) the air quantity in the cold box exceeds the range;
c) the yield of the gas oxygen product exceeds the range;
d) the "automatic load change release button" is manually clicked.
The automatic variable load control method can be realized by participating in a conventional control system (DCS or PLC) without adding extra software and hardware; the automatic load changing process which is stable, smooth and quick under different working conditions can be realized without complex control; the invention mainly solves the problems of mutual decoupling, easy overshoot and oscillation of energy and materials in the load changing process of the air separation device, and the like, and realizes smooth and rapid transition among different working conditions on the premise of ensuring the stability of the air separation device and the product quality.
Detailed Description
The present invention will be described in detail with reference to specific embodiments below: the invention discloses an automatic load change control method for an air separation device, which comprises the following steps:
1) obtaining PFD data of key process parameters under various working conditions (at least including minimum working conditions and maximum working conditions) of the air separation device process design; designing the flow of the air separation device, and mostly adopting general process flow simulation software such as Aspen Plus or HYSYS and the like;
2) determining variables as final product flow: low pressure oxygen product flow LPOG, low pressure nitrogen product flow LPNG, argon product flow ArG, liquid nitrogen product flow NL; liquid oxygen product flow OL; the variables are used as target values set in the process of changing the load of a process operator;
3) determining key intermediate variables: air quantity of air entering a cold box, NLeq liquefaction capacity, air quantity of air expanded by AIRthurb, quantity of nitrogen expanded by NGturb, air quantity of high pressure HPAIR, air quantity of high pressure HPALhp; these key intermediate variables are used to calculate the set point of the final PID controller;
4) determining a PID controller participating in automatic variable load: FIC1294 (air flow is controlled by adjusting the main compressor inlet guide vanes), HPair FIC7418 high pressure air, regeneration effluent nitrogen flow FIC1213, effluent nitrogen pressure PIC1626, FIC1556 high pressure liquid air, FIC1557 lean liquid reflux (adjusting reflux ratio at the lower section of the medium pressure column and the upper end of the low pressure column), FIC1558 liquid nitrogen reflux (adjusting reflux ratio and purity at the top of the upper column), LIC1601 oxygen rich liquid air level, FIC1520 low pressure nitrogen flow, FIC1501 high pressure nitrogen flow, FIC1510 low pressure oxygen flow, FIC1540 argon flow, FIC1630 liquid nitrogen product flow, FIC1704 crude liquid argon flow, FIC1731 medium pressure nitrogen to argon fine column evaporator flow, LIC1701 crude argon column oxygen rich liquid air level;
5) obtaining a fitting function between the parameters in the step 2) and the step 3) by fitting, wherein the variable in the step 3) is used as a dependent variable, and the variable in the step 2) is used as an independent variable;
6) obtaining a fitting function between the parameters in the step 3) and the step 4) by fitting, wherein the variable in the step 4) is used as a dependent variable, and the variable in the step 3) is used as an independent variable;
7) interpolating each working point model by a polynomial function aiming at working point data of the same process parameter under different working conditions to obtain a variable load linear change track of the process parameter; the key flow needs to be corrected by using components, and the liquid level needs to be limited within a certain range, so that the load of a product produced by the device after being stabilized is changed on the premise that the air separation device is stable and the purity reaches the standard;
8) the start and stop of the automatic variable load need to satisfy certain conditions.
9) The above parameters may be increased or decreased according to the flow.
Further embodiments of the invention are: in the step 5), the functional relationship between the independent variable and the dependent variable is as follows:
the AIRtot = func (LPOG, OL), the function is obtained by fitting parameter values of the AIRtot, the LPOG and the OL under different working conditions,
the oxygen content of the crude argon column feed was used to correct the AIRtot; the modified functional relationship is AIRtot = func (LPOG, OL) + AIC1716 where the correction of AIC1716 is +/-10% of the AIRtot design flow;
NLeq = func (NL, OL, FIC1704) characterizes the ability to produce liquid products;
airtime = func (AIRtot, NLeq) maintains the overall cold box balanced (cold box heat leak, heat exchanger warm end temperature difference has sent liquid to each storage tank);
NGturb = func (AIRtot, NLeq) maintains the overall cold box balance (cold box heat leak, heat exchanger hot end temperature difference has sent liquid to each storage tank);
HPair = amount of high pressure air required for the production of low pressure oxygen by FIC 7418;
MPair = AIRtot-HPair the sum of the medium-pressure air quantity and the high-pressure air quantity is the air quantity entering the cold box;
expanding HPALhp = HPair-FIC1556 high-pressure air to obtain liquid, wherein part of the liquid enters the medium-pressure tower, and the other part of the liquid enters the low-pressure tower; the flow to the low pressure column is adjusted to maintain the reflux ratio, and the flow of the liquefied air is controlled by adjusting a feed valve FV1556 of the low pressure column by FIC 1556; HPALhp is only an intermediate variable and does not participate in variable load.
In the step 6, the crude liquid argon flow rate RSP [ FIC1704] = func (airtot);
total air amount FIC1294 = func (airtot) + IA, where IA meter air flow, generally constant;
dirty nitrogen flow FIC1213 = func (airtot);
dirty nitrogen pressure PIC1626 = func (AIRtot, LPNG);
liquid-air FIC1556 = func (airtot);
barren liquor reflux FIC1557 = func (airtot);
liquid nitrogen reflux FIC1558 = func (AIRtot, MPNG);
the oxygen-enriched liquid-air liquid level LIC1601 = func (AIRtot), wherein the upper and lower limit positions are high and low alarm set points during industrial design;
low pressure nitrogen flow FIC1520 = LPNG;
medium pressure nitrogen flow FIC1501 = func (airtot);
low pressure oxygen flow FIC1510 = LPOG;
argon flow FIC1540 = ArG;
liquid nitrogen flow rate FIC1630 = NL;
crude liquid argon flow FIC1704= func (airtot);
FIC1731 = func(FIC1704)；
LIC1701 = func (airtot), where the upper and lower limits are the high and low alarm set points for the industrial design;
air expander air flow FIC1530= airtime;
low pressure nitrogen 1-way flow FIC1502= NGturb;
component analysis stations participating in the correction: the oxygen content in the middle of the low-pressure tower and the oxygen content in the middle of the crude argon tower are compensated in a positive direction;
the top outlet is crude liquid argon (CAL); the crude liquid argon is sent to a pure argon column K11; the flow of the crude liquid argon is calculated according to the total amount of air entering a cold box, and is corrected by the output value of a purity analyzer AIC1705 at the middle section of the argon tower;
RSP[FIC1704]* = func(AIRtot) + AIC1705；
the AIC1705 was corrected to +/-20% of the maximum mix flow of crude liquid argon; because of the long response time of the argon column, the PID adjustment involved in the component analysis correction should be slow;
further examples are: in the step 7), the operation rate is as follows: 0.2%/min to 0.33%/min (1% load change every 3 to 5 minutes);
the operation of the device can be automatically adjusted according to the requirements of gas and liquid products, and by setting the flow (gas oxygen, gas nitrogen, gas argon, liquid oxygen, liquid nitrogen, liquid argon and the like) of the final product under a certain working condition, according to material balance and energy conservation, key intermediate parameters under the working condition are reversely deduced, such as: air intake to the cooling box, expanded air, expanded nitrogen, medium pressure air, high pressure liquid air, liquefaction capacity, and the like; therefore, the flow on the key flow pipeline, the liquid level of the key container and the like are further calculated, and the PID controller is used for controlling the opening of the valve so as to adjust corresponding key parameters such as the flow, the liquid level and the like, so that the load of a product produced by the device after being stabilized is changed on the premise that the air separation device is stable and the purity reaches the standard.
In the step 8), the starting conditions of automatic load change are as follows:
a) the relevant PID is controlled in an automatic state;
b) the air separation device runs stably;
c) the air quantity entering the cold box is in a normal range;
d) the yield of the gas oxygen product is in a normal range;
e) switching the analyzers participating in correction to corresponding analysis measuring points;
f) the PID controller participating in the correction is in an automatic state;
after the above conditions are met, the control system displays a prompt of "allowing automatic load change", and manually clicks an "automatic load change input button";
the stop conditions for automatic load change are:
a) parking the air separation plant;
b) the air quantity in the cold box exceeds the range;
c) the yield of the gas oxygen product exceeds the range;
d) the "automatic load change release button" is manually clicked.
Claims (2)
1. An automatic load change control method for an air separation device is characterized by comprising the following steps:
1) obtaining PFD data of key process parameters under various working conditions of the process design of the air separation device;
2) determining variables as final product flow: low pressure oxygen product flow LPOG, low pressure nitrogen product flow LPNG, argon product flow ArG, liquid nitrogen product flow NL; liquid oxygen product flow OL; the variables are used as target values set in the process of changing the load of a process operator;
3) determining key intermediate variables: air quantity of air entering a cold box, NLeq liquefaction capacity, air quantity of air expanded by AIRthurb, quantity of nitrogen expanded by NGturb, air quantity of high pressure HPAIR, air quantity of high pressure HPALhp; these key intermediate variables are used to calculate the set point of the final PID controller;
4) determining a PID controller participating in automatic variable load: controlling air flow FIC1294, high pressure air HPair FIC7418, regeneration effluent nitrogen flow FIC1213, effluent nitrogen pressure PIC1626, high pressure liquid-air FIC1556, lean liquid reflux FIC1557 for adjusting reflux ratio of the lower section of the middle pressure tower and the upper end of the low pressure tower, liquid nitrogen reflux FIC1558 for adjusting reflux ratio and purity of the top of the upper tower, oxygen-enriched liquid-air liquid level LIC1601, low pressure nitrogen flow FIC1520, high pressure nitrogen flow FIC1501, low pressure oxygen flow FIC1510, argon flow FIC1540, liquid nitrogen product flow FIC1630, FIC1704 crude liquid argon flow, medium pressure nitrogen-to-fine tower evaporator flow FIC1731 and crude argon tower oxygen-enriched liquid-air liquid level LIC1701 by adjusting inlet guide vanes of a main compressor;
5) obtaining a fitting function between the parameters in the step 2) and the step 3) by fitting, wherein the fitting function takes the variable in the step 3) as a dependent variable and the variable in the step 2) as an independent variable;
6) obtaining a fitting function between the parameters in the step 3) and the step 4) by fitting, wherein the variable in the step 4) is used as a dependent variable, and the variable in the step 3) is used as an independent variable;
7) interpolating each working point model by a polynomial function aiming at working point data of the same process parameter under different working conditions to obtain a variable load linear change track of the process parameter; wherein the key flow needs to be corrected by components, and the liquid level needs to be limited, so that the load of the product produced by the device after being stabilized is changed on the premise that the air separation device is stable and the purity reaches the standard;
8) the starting and stopping of the automatic variable load need to meet conditions;
9) the above parameters can be increased or decreased according to different processes;
in the step 5), the functional relationship between the independent variable and the dependent variable is as follows:
the AIRtot = func (LPOG, OL), the function is obtained by fitting parameter values of the AIRtot, the LPOG and the OL under different working conditions,
the oxygen content of the crude argon column feed was used to correct the AIRtot;
the modified functional relationship is AIRtot = func (LPOG, OL) + AIC1716 where the correction of AIC1716 is +/-10% of the AIRtot design flow;
NLeq = func (NL, OL, FIC1704) characterizes the ability to produce liquid products;
airtime = func (AIRtot, NLeq) maintains overall cold box balance;
NGturb = func (AIRtot, NLeq) maintains the overall cold box balanced;
HPair = amount of high pressure air required for the production of low pressure oxygen by FIC 7418;
MPair = AIRtot-HPair the sum of the medium-pressure air quantity and the high-pressure air quantity is the air quantity entering the cold box;
expanding HPALhp = HPair-FIC1556 high-pressure air to obtain liquid, wherein part of the liquid enters the medium-pressure tower, and the other part of the liquid enters the low-pressure tower; the flow to the low pressure column is adjusted to maintain the reflux ratio, and the flow of the liquefied air is controlled by adjusting a feed valve FV1556 of the low pressure column by FIC 1556; HPALhp is only an intermediate variable and does not participate in variable load;
in the step 6, the crude liquid argon flow rate RSP [ FIC1704] = func (airtot);
total air amount FIC1294 = func (airtot) + IA, where IA is the meter air flow;
dirty nitrogen flow FIC1213 = func (airtot);
dirty nitrogen pressure PIC1626 = func (AIRtot, LPNG);
liquid-air FIC1556 = func (airtot);
barren liquor reflux FIC1557 = func (airtot);
liquid nitrogen reflux FIC1558 = func (AIRtot, MPNG);
the oxygen-enriched liquid-air liquid level LIC1601 = func (AIRtot), wherein the upper and lower limit positions are high and low alarm set points during industrial design;
low pressure nitrogen flow FIC1520 = LPNG;
medium pressure nitrogen flow FIC1501 = func (airtot);
low pressure oxygen flow FIC1510 = LPOG;
argon flow FIC1540 = ArG;
liquid nitrogen flow rate FIC1630 = NL;
crude liquid argon flow FIC1704= func (airtot);
FIC1731 = func(FIC1704)；
LIC1701 = func (airtot), where the upper and lower limits are the high and low alarm set points for the industrial design;
air expander air flow FIC1530= airtime;
low pressure nitrogen 1-way flow FIC1502= NGturb;
component analysis stations participating in the correction: the oxygen content in the middle of the low-pressure tower and the oxygen content in the middle of the crude argon tower are compensated in a positive direction;
the top outlet is crude liquid argon (CAL), the crude liquid argon is sent into a pure argon column K11, the flow of the crude liquid argon is calculated according to the total amount of air entering a cold box, and is corrected by the output value of an AIC1705 of a purity analyzer in the middle section of the argon column;
RSP[FIC1704]* = func(AIRtot) + AIC1705；
the AIC1705 was corrected to within +/-20% of the maximum mix flow of crude liquid argon, and PID adjustments to take part in compositional analysis corrections should be slow because of the longer response time of the argon column.
2. In the step 7), the operation rate is as follows: 0.2%/min to 0.33%/min, and changing the load by 1% every 3 to 5 minutes; the operation of device can be according to the demand of gas and liquid product automatic adjustment, through setting for the flow of final product under a certain operating mode, according to material balance, the key intermediate parameter under this operating mode is come the back to the conservation of energy, includes: air amount entering a cooling box, expanded air amount, expanded nitrogen amount, medium-pressure air amount, high-pressure liquid air amount and liquefaction capacity; further calculating the flow on the key flow pipeline and the liquid level of the key container; the PID controller is used for controlling the opening of the valve so as to adjust corresponding key parameters such as flow and liquid level, so that the product produced by the device after being stabilized is subjected to load conversion on the premise that the air separation device is stable and the purity reaches the standard;
in the step 8), the starting conditions of automatic load change are as follows:
a) the relevant PID is controlled in an automatic state;
b) the air separation device runs stably;
c) the air quantity entering the cold box is in a normal range;
d) the yield of the gas oxygen product is in a normal range;
e) switching the analyzers participating in correction to corresponding analysis measuring points;
f) the PID controller participating in the correction is in an automatic state;
after the conditions are met, the control system picture can display a prompt of 'allowing automatic load change', and manually clicks an 'automatic load change input button';
the stop conditions for automatic load change are:
a) parking the air separation plant;
b) the air quantity in the cold box exceeds the range;
c) the yield of the gas oxygen product exceeds the range;
d) the "automatic load change release button" is manually clicked.
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| CN110044134B (en) * | 2019-03-29 | 2021-06-25 | 安徽加力气体有限公司 | One-key start-stop control method for full-automatic nitrogen making machine system |
| CN110243138B (en) * | 2019-04-03 | 2021-12-10 | 上海联风能源科技有限公司 | Air separation equipment model feedforward control system and method |
| CN114484263A (en) * | 2022-01-07 | 2022-05-13 | 首钢京唐钢铁联合有限责任公司 | Automatic load changing method and system for nitrogen-oxygen liquefaction device |
| CN114674112A (en) * | 2022-04-07 | 2022-06-28 | 安阳钢铁股份有限公司 | Automatic oxygen-nitrogen conversion method for liquefaction device |
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