CN111780565A - Pressure control method for main gas pipeline of heating furnace - Google Patents

Abstract

A pressure control method for a main gas pipeline of a heating furnace comprises the following steps: step one, arranging a control mechanism for adjusting the pressure of a main gas pipeline of a heating furnace, wherein the control mechanism comprises an adjusting valve, a pressure sensor and a flow sensor; step two, calculating a feedforward quantity, and step three, calculating the valve opening degree calculated by a PID algorithm; and step four, calculating the actual control output of the regulating valve. The invention adopts the control strategy of PID algorithm, feedforward quantity, correction algorithm and cyclic debugging method to better complete the stable control of the pressure of the main pipeline. The combination strategy has the advantages that the accuracy of the PID control method is kept, meanwhile, the problem of hysteresis generated by the PID algorithm in the process of frequent switching of the pulse burner is well solved by the feedforward quantity and the correction algorithm, the actual gas flow in the production of the heating furnace is infinitely close to the calculated flow by the circulation debugging method, and the disturbance of the gas flow to the control process of the regulating valve at the moment of switching on and off the burner is reduced.

Description

Pressure control method for main gas pipeline of heating furnace

Technical Field

The invention relates to the technical field of control of heating furnaces, in particular to a pressure control method for a main gas pipeline of a heating furnace.

Background

The steel rolling process in the steel industry cannot be completed by a heating furnace, and particularly, various plates and section steels need to be heated at high temperature in the heating furnace before rolling so as to be rolled. The time sequence pulse type heating furnace controls the temperature in the furnace by controlling the burning time sequence of the burner in the heating furnace. The pulse heating furnace has important application in certain steel mills in south China with the characteristics of small temperature fluctuation, fuel saving, heat efficiency improvement and the like. However, the pulse heating furnace controls the opening and closing of a plurality of mutually independent burners in a certain area in the furnace, so that certain impact can be caused to the pressure of the gas main pipe network. This impact is further evident when the fuel calorific value is low, the flow and pressure of the fuel required increases. In recent years, as the price of liquefied petroleum gas in south China is rising, the fuel cost of a heating furnace using the liquefied petroleum gas as a raw material is increased. After the natural gas is transformed to replace liquefied petroleum gas, the natural gas has lower heat value than the liquefied petroleum gas, so that the pressure fluctuation of a fuel gas main pipe network of the heating furnace is increased, the temperature field in the heating furnace is out of control, and the hardness of the plate blank is uneven. After the fuel medium is replaced, the main interference factors of the pressure of the main gas pipeline of the heating furnace are as follows:

1) the airflow generates severe impact on the pressure of the main gas pipeline at the moment of opening and closing the burner;

2) the distribution positions of the burners with different capacities and the influence of different response times on the pressure of the main pipe network;

3) in the burner switch time sequence control, a plurality of burners are simultaneously opened to influence the pressure of a gas main pipe network.

In the current application, the conventional pressure control method is generally adopted for the pressure control of the main gas pipe network of the pulse type heating furnace using liquefied petroleum gas as fuel. However, the pulse heating furnace is different from an industrial furnace adopting a continuous control mode, and especially after a fuel medium is changed into natural gas, due to inherent reasons of increased and discontinuous fuel flow, inconsistent burner capability, uncertain burner opening time, frequent and rapid burner switching and the like, the pressure of a main gas pipeline is unstable by adopting a traditional pressure control method. Therefore, in view of the defects brought by the conventional control method and the nature of natural gas, the pressure control of the main gas pipe network of the pulse heating furnace after the fuel medium is replaced still has room for further improvement. The present control technique is invented for this particular case.

The invention relates to a pressure control method for a main gas pipeline of a heating furnace. The main solution is in pulsed heating furnace combustion system, and after fuel medium changed, the problem of the pressure stability control of gas trunk line.

Disclosure of Invention

In order to solve the technical problems in the background art, the invention provides a pressure control method for a main gas pipeline of a heating furnace, which can reduce the pressure fluctuation of the main gas pipeline and improve the stability after a fuel medium is replaced in a pulse type heating furnace.

In order to achieve the purpose, the invention adopts the following technical scheme:

a pressure control method for a main gas pipeline of a heating furnace comprises the following steps:

the method comprises the following steps that firstly, a control mechanism for adjusting the pressure of a gas main pipeline is arranged on the gas main pipeline of the heating furnace, and the control mechanism comprises a regulating valve PCV101 with a valve position feedback function and linear flow characteristics in a normal working interval, a pressure sensor PT-101 and a flow sensor FT-101;

step two, calculating feedforward quantity

1) In the debugging stage of the heating furnace, a database is added in a computer control system to store the design pressure SP of all burners of the heating furnace in a gas main pipeline_{Is provided with}Calculating gas flow value F at lower opening₁…F_nN is the number of pairs of burners, and the calculated gas flow value F corresponding to each burner is obtained by automatic retrieval and comparison in a database based on the opening state of each burner in the hearth of the current heating furnace in the production process of the heating furnace₁…F_nFront electromagnetic valves XV-201 state XV of each pair of burners of the current heating furnace₁…XV_nWhen the electromagnetic valve is opened, XV is 1, otherwise XV is 0;

2) calculating a pressure correction coefficient and a temperature correction coefficient:

3) calculating a feedforward quantity R:

taking the value of the pressure sensor PT-101 as a feedback value and taking the current set value SP of the pressure of the main gas pipeline_{Fruit of Chinese wolfberry}The set value is input into a PID regulator, and the valve opening MV calculated by the PID algorithm of the valve PCV101 is calculated_pid；

Step four, calculating actual control output MV of the regulating valve PCV101

MV＝[R×100×k₁+(MV_pid×200-100)×k₂]100 × 100 (equation 4)

Wherein: SP_{Fruit of Chinese wolfberry}: the current gas main pipeline pressure set value (bar);

SP_{is provided with}: a main gas pipeline pressure design value (bar);

T_{is provided with}: gas design temperature value (deg.C);

T_measuring: actual temperature value (DEG C) of gas;

MV: adjusting the actual output (0-100%) of the valve in a normal working range;

f: the calculated flow (Nm3/h) of each pair of burners;

n: the total number of pairs of burners of the heating furnace;

XV: the state of the front electromagnetic valve of each pair of burners is 1 or 0;

k₁,k₂: weight, range: [0 to 1 ]]；

MV_pid: and (3) calculating the opening degree (0-100%) of the valve by using a PID algorithm.

The method further comprises the following steps: arranging an orifice plate FE-201, a manual regulating valve HV-201 and an electromagnetic valve XV-201 on a gas pipeline in front of each burner of the heating furnace, adopting a cycle debugging method to manually regulate the front regulating valve of each burner at the initial debugging stage of the heating furnace to enable the actual flow of each burner to approach the designed flow, wherein the cycle iteration debugging method comprises the following steps:

step 1, inputting the calculated flow of each burner under the design pressure of a main gas pipeline when natural gas is used as fuel into a computer database;

step 2, setting PID parameters by an empirical method to control the pressure of the main gas pipeline, wherein the pressure fluctuation amount is about 20%;

step 3, controlling the opening and closing of the front electromagnetic valves of the burners for at least one period, adjusting the front hand valves of the burners on site, and simultaneously connecting the front orifice plates of the burners by adopting a handheld differential pressure transmitter to enable the actual flow of the burners to be approximately equal to the design flow, wherein the actual flow of the burners deviates from the design flow by about 30%;

step 4, modifying the PID parameter again to control the pressure of the main gas pipeline, wherein the pressure fluctuation amount is about 10 percent;

step 5, controlling the opening and closing of the front electromagnetic valves of the burners for at least one period again, and readjusting the front hand valves of the burners to enable the actual flow of the burners to be approximately equal to the design flow, wherein the actual flow of the burners deviates from the design flow by about 20%;

step 6, modifying the PID parameter again to control the pressure of the main gas pipeline, wherein the pressure fluctuation amount is about 5 percent;

and 7, repeating the steps 3-6 until the pressure of the main pipe is stable and the flow of the burner is accurate.

Compared with the prior art, the invention has the beneficial effects that:

the invention adopts the control strategy of PID algorithm, feedforward quantity, correction algorithm and cyclic debugging method to better complete the stable control of the pressure of the main pipeline. The combination strategy has the advantages that the accuracy of the PID control method is kept, meanwhile, the problem of hysteresis generated by the PID algorithm in the process of frequent switching of the pulse burner is well solved by the feedforward quantity and the correction algorithm, the actual gas flow in the production of the heating furnace is infinitely close to the calculated flow by the circulation debugging method, and the disturbance of the gas flow to the control process of the regulating valve at the moment of switching on and off the burner is reduced.

Drawings

FIG. 1 is a flow chart of a heating furnace main duct system according to an embodiment of the present invention;

FIG. 2 is a view showing a burner arrangement of a heating furnace according to an embodiment of the present invention;

FIG. 3 is a flow chart of a furnace burner foreline (TYPE1) according to an embodiment of the present invention;

FIG. 4 is a flow chart of a furnace burner foreline (TYPE2) according to an embodiment of the present invention;

FIG. 5 is a flow chart of a furnace burner foreline (TYPE3) according to an embodiment of the present invention;

FIG. 6 is a flow chart of a furnace burner foreline (TYPE4) according to an embodiment of the present invention;

FIG. 7 is a flow chart of a furnace burner foreline (TYPE5) according to an embodiment of the present invention;

FIG. 8 is a flow chart of a furnace burner foreline (TYPE6) according to an embodiment of the present invention;

FIG. 9 is a flow chart of a furnace burner foreline (TYPE7) according to an embodiment of the present invention;

FIG. 10 is a logic block diagram of a main gas pipeline pressure control system of a heating furnace according to an embodiment of the present invention;

fig. 11 is a modified curve of the main gas pipe regulating valve according to an embodiment of the present invention.

Detailed Description

The following detailed description of the present invention will be made with reference to the accompanying drawings.

According to the analysis of the production process of the pulse type heating furnace after the fuel medium is replaced, the invention finds that the stable control of the pressure of the main pipeline can be better completed by adopting the control strategy of a PID algorithm, a feedforward quantity, a correction algorithm and a circulating debugging method. The combination strategy has the advantages that the accuracy of the PID control method is kept, meanwhile, the problem of hysteresis generated by the PID algorithm in the process of frequent switching of the pulse burner is well solved by the feedforward quantity and the correction algorithm, the actual gas flow in the production of the heating furnace is infinitely close to the calculated flow by the circulation debugging method, and the disturbance of the gas flow to the control process of the regulating valve at the moment of switching on and off the burner is reduced. The basis of controlling the pressure of the main gas pipeline of the heating furnace in one embodiment of the invention is how to balance the relation between the actual flow of the gas of the heating furnace and the opening degree of the valve. The invention is analyzed and found that the main factors influencing the pressure are as follows: the number of pairs of burners, the capability of the burners, the timing sequence of the burners and the characteristics of the regulating valve. The present invention takes the above factors into full consideration.

A pressure control method for a main gas pipeline of a heating furnace comprises the following steps:

step one, as shown in fig. 1, a control mechanism for regulating the pressure of a main gas pipeline is arranged on the main gas pipeline of the heating furnace, and the control mechanism comprises a regulating valve (PCV101) with a valve position feedback function and with linear flow characteristics in a normal working interval, a pressure sensor (PT-101) and a flow sensor (FT-101).

Step two, calculating feedforward quantity

In the debugging stage of the heating furnace, a database is added in a computer control system to store the design pressure (SP) of all burners of the heating furnace in a gas main pipeline_{Is provided with}) Calculated gas flow value (F) at lower opening₁…F_nIn one embodiment of the present invention, n is 20). In the production process of the heating furnace, the opening states of all burners in the hearth of the heating furnace are taken as data bases, and the calculated gas flow value (F) corresponding to each burner is obtained by automatic retrieval and comparison in a database₁…F_n) The state (XV-201) of each pair of burner front electromagnetic valves (XV-201) of the current heating furnace₁…XV_nWhen the electromagnetic valve is opened, XV is 1, otherwise XV is 0).

As shown in fig. 2 and 3-9, in an embodiment of the present invention, the heating furnace has a total of 20 pairs of burners, is divided into seven TYPEs of burners (TYPE 1-TYPE 7), is roughly divided into a long flame burner and a short flame burner, and the computer database stores the gas design flow rates of the seven TYPEs of burners in the open state.

Calculating a pressure correction coefficient and a temperature correction coefficient:

4) calculating a feedforward quantity R:

taking the value of the pressure sensor PT-101 as a feedback value and taking the current set value SP of the pressure of the main gas pipeline_{Fruit of Chinese wolfberry}The set value is input into a PID regulator, and the valve opening MV calculated by the PID algorithm of the valve PCV101 is calculated_pid；

Step four, calculating actual control output MV of the regulating valve PCV101

MV＝[R×100×k₁+(MV_pid×200-100)×k₂]100 × 100 (equation 4)

Wherein: SP_{Fruit of Chinese wolfberry}: the current gas main pipeline pressure set value (bar);

SP_{is provided with}: a main gas pipeline pressure design value (bar);

T_{is provided with}: gas design temperature value (deg.C);

T_measuring: actual temperature value (DEG C) of gas;

MV: adjusting the actual output (0-100%) of the valve in a normal working range;

f: the calculated flow (Nm3/h) of each pair of burners;

n: the total number of pairs of burners of the heating furnace;

XV: the state of the front electromagnetic valve of each pair of burners is 1 or 0;

k₁,k₂: weight, range: [0 to 1 ]]；

MV_pid: and (3) calculating the opening degree (0-100%) of the valve by using a PID algorithm.

SP_{Fruit of Chinese wolfberry}Manually adjusted, e.g. during oven-drying, during periods of reduced production, at which time SP is present_{Fruit of Chinese wolfberry}Are all less than SP_{Is provided with}In (1).

The logic block diagram of the control system of the control method is shown in FIG. 10.

And step five, correcting a valve characteristic curve, as shown in fig. 11, when the valve works in an interval of 20-80%, the valve characteristic curve is a normal working interval, but when the valve opening is smaller (< 20%) or larger (> 80%), the valve characteristic curve is difficult to keep linear, and as can be seen from the above conversion formula, the nonlinearity of the valve causes control unbalance, so that the problem that the characteristic curve is difficult to achieve linearity when the regulating valve is in small opening or large opening is corrected, the influence of nonlinear factors caused by small opening of the valve is reduced, and the valve position of the valve is regulated according to the corrected valve opening. Due to the inherent characteristics of the regulating valve, the correction process is difficult to describe as a standardized formula, so that the correction curve of the valve is obtained by an empirical method in the process of debugging the heating furnace.

As shown in fig. 3-9, in an embodiment of the present invention, each burner front gas pipeline of the heating furnace is provided with an orifice plate (FE-201), a manual regulating valve (HV-201), and an electromagnetic valve (XV-201), and at the initial stage of the commissioning of the heating furnace, a circulation commissioning method is adopted to manually regulate each burner front regulating valve so that the actual flow rate of each burner approaches the design flow rate. The loop iteration debugging method comprises the following steps:

step 1, inputting the calculated flow of each burner under the design pressure of a main gas pipeline when natural gas is used as fuel into a computer database;

step 2, setting PID parameters by an empirical method to control the pressure of the main gas pipeline, wherein the pressure fluctuation amount is about 20%;

step 3, controlling the opening and closing of the front electromagnetic valves of the burners for at least one period, adjusting the front hand valves of the burners on site, and simultaneously connecting the front orifice plates of the burners by adopting a handheld differential pressure transmitter to enable the actual flow of the burners to be approximately equal to the design flow, wherein the actual flow of the burners deviates from the design flow by about 30%;

step 4, modifying the PID parameter again to control the pressure of the main gas pipeline, wherein the pressure fluctuation amount is about 10 percent;

step 5, controlling the opening and closing of the front electromagnetic valves of the burners for at least one period again, and readjusting the front hand valves of the burners to enable the actual flow of the burners to be approximately equal to the design flow, wherein the actual flow of the burners deviates from the design flow by about 20%;

step 6, modifying the PID parameter again to control the pressure of the main gas pipeline, wherein the pressure fluctuation amount is about 5 percent;

and 7, repeating the steps 3-6. Until the pressure of the main pipe is stable and the flow of the burner is accurate.

In one embodiment of the invention, after 6-7 debugging periods, the deviation between the actual flow and the design flow of the burner is within 1%, and the maximum pressure fluctuation is not more than 1.5%.

The above embodiments are implemented on the premise of the technical solution of the present invention, and detailed embodiments and specific operation procedures are given, but the scope of the present invention is not limited to the above embodiments. The methods used in the above examples are conventional methods unless otherwise specified.

Claims (2)

1. A pressure control method for a main gas pipeline of a heating furnace is characterized by comprising the following steps:

the method comprises the following steps that firstly, a control mechanism for adjusting the pressure of a gas main pipeline is arranged on the gas main pipeline of the heating furnace, and the control mechanism comprises a regulating valve PCV101 with a valve position feedback function and linear flow characteristics in a normal working interval, a pressure sensor PT-101 and a flow sensor FT-101;

step two, calculating feedforward quantity

1) In the debugging stage of the heating furnace, a database is added in a computer control system to store the design pressure SP of all burners of the heating furnace in a gas main pipeline_{Is provided with}Calculating gas flow value F at lower opening₁…F_nN is the number of pairs of burners, and the calculated gas flow value F corresponding to each burner is obtained by automatic retrieval and comparison in a database based on the opening state of each burner in the hearth of the current heating furnace in the production process of the heating furnace₁…F_nFront electromagnetic valves XV-201 state XV of each pair of burners of the current heating furnace₁…XV_nWhen the electromagnetic valve is opened, XV is 1, otherwise XV is 0;

2) calculating a pressure correction coefficient and a temperature correction coefficient:

pressure correction coefficient:

temperature correctionCoefficient:

3) calculating a feedforward quantity R:

taking the value of the pressure sensor PT-101 as a feedback value and taking the current set value SP of the pressure of the main gas pipeline_{Fruit of Chinese wolfberry}The set value is input into a PID regulator, and the valve opening MV calculated by the PID algorithm of the valve PCV101 is calculated_pid；

Step four, calculating actual control output MV of the regulating valve PCV101

MV＝[R×100×k₁+(MV_pid×200-100)×k₂]100 × 100 (equation 4)

Wherein: SP_{Fruit of Chinese wolfberry}: the current gas main pipeline pressure set value (bar);

SP_{is provided with}: a main gas pipeline pressure design value (bar);

T_{is provided with}: gas design temperature value (deg.C);

T_measuring: actual temperature value (DEG C) of gas;

MV: adjusting the actual output (0-100%) of the valve in a normal working range;

f: the calculated flow (Nm3/h) of each pair of burners;

n: the total number of pairs of burners of the heating furnace;

XV: the state of the front electromagnetic valve of each pair of burners is 1 or 0;

k₁,k₂: weight, range: [0 to 1 ]]；

MV_pid: and (3) calculating the opening degree (0-100%) of the valve by using a PID algorithm.

2. The method for controlling the pressure of the main gas pipeline of the heating furnace according to claim 1, further comprising: arranging an orifice plate FE-201, a manual regulating valve HV-201 and an electromagnetic valve XV-201 on a gas pipeline in front of each burner of the heating furnace, adopting a cycle debugging method to manually regulate the front regulating valve of each burner at the initial debugging stage of the heating furnace to enable the actual flow of each burner to approach the designed flow, wherein the cycle iteration debugging method comprises the following steps:

step 1, inputting the calculated flow of each burner under the design pressure of a main gas pipeline when natural gas is used as fuel into a computer database;

step 2, setting PID parameters by an empirical method to control the pressure of the main gas pipeline, wherein the pressure fluctuation amount is about 20%;

step 3, controlling the opening and closing of the front electromagnetic valves of the burners for at least one period, adjusting the front hand valves of the burners on site, and simultaneously connecting the front orifice plates of the burners by adopting a handheld differential pressure transmitter to enable the actual flow of the burners to be approximately equal to the design flow, wherein the actual flow of the burners deviates from the design flow by about 30%;

step 4, modifying the PID parameter again to control the pressure of the main gas pipeline, wherein the pressure fluctuation amount is about 10 percent;

step 5, controlling the opening and closing of the front electromagnetic valves of the burners for at least one period again, and readjusting the front hand valves of the burners to enable the actual flow of the burners to be approximately equal to the design flow, wherein the actual flow of the burners deviates from the design flow by about 20%;

step 6, modifying the PID parameter again to control the pressure of the main gas pipeline, wherein the pressure fluctuation amount is about 5 percent;

and 7, repeating the steps 3-6 until the pressure of the main pipe is stable and the flow of the burner is accurate.

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