Adjusting system of induced draft fan of cracking furnace and implementation method of adjusting system

Abstract

A cracking furnace induced draft fan adjusting system comprises a fuzzy control module used for generating induced draft fan adjusting signal increment according to the CO concentration of hearth smoke; the auxiliary control module is used for selectively adjusting an induced draft fan or a combustor air door according to the signal increment generated by the fuzzy control module and the range of the hearth negative pressure or the oxygen concentration; and the threshold module is used for automatically switching back to the manual adjustment mode under the abnormal condition to ensure the stable operation of the system. According to the invention, the problem of adjustment of mutual coupling of CO concentration, oxygen concentration and hearth negative pressure on the cracking furnace can be solved, and approximate ideal combustion is realized on the premise of ensuring that the oxygen concentration and the hearth negative pressure fluctuate in a reasonable interval.

Description

Technical Field

[0001] The invention relates to automatic control technology of ethylene cracking furnace induced draft fan, in particular to automatic control of ethylene cracking furnace induced draft fan with CO concentration as set value, and specifically to a regulation system of the cracking furnace induced draft fan and an implementation method thereof. Background Art

[0002] The induced draft fans of ethylene cracking furnaces are all adjusted by furnace negative pressure, and the main purpose is to adjust the furnace negative pressure. However, in actual operation, the furnace negative pressure is very small, and the negative pressure measurement itself is unstable, resulting in the induced draft fans still being manually adjusted and unable to achieve fine control. Therefore, the current cracking furnaces are all in an oxygen-rich state, with high NOx emissions and relatively low furnace thermal efficiency.

[0003] From the perspective of heating furnace combustion optimization technology, heating furnace combustion optimization technology can be divided into three categories:

[0004] The first type guides operators to adjust the heating furnace combustion by online detection of important furnace combustion parameters. This type of combustion optimization technology currently occupies a dominant position in China.

[0005] The second type of combustion optimization technology is based on control, as a supervisory control system for heating furnace operation, by using advanced control logic, control algorithm or artificial intelligence technology to achieve combustion optimization of heating furnace. With the gradual maturity of advanced control and artificial intelligence technology and its successful application in industry, this type of combustion optimization technology has developed rapidly.

[0006] The third type of combustion optimization technology achieves combustion optimization adjustment of the heating furnace by modifying the burner, heating surface, etc. at the equipment level.

[0007] The above three types of technologies each have their own advantages, disadvantages and applications in practice. However, the second type of technology does not require any modification of the heating furnace equipment, and can make full use of the operation data of the heating furnace. On the basis of control, through the application of advanced modeling, optimization and control technology, it can directly improve the operation efficiency of the heating furnace and reduce pollutant emissions. It has the advantages of low investment, low risk and obvious effect. The second type of technology currently mainly includes the optimization control technology of the oxygen content of the flue gas of the heating furnace and the closed-loop balanced combustion control technology.

[0008] Optimization control technology for flue gas oxygen content in heating furnaces. In general, the efficiency of heating furnaces and the oxygen content in flue gas form a convex quadratic curve relationship. Therefore, the research on operation optimization control uses this relationship curve to perform online optimization control on the flue gas oxygen content of heating furnaces to ensure the best combustion efficiency of heating furnaces. Since the efficiency of heating furnaces cannot be measured online, many studies use the relationship between oxygen content in flue gas and thermal efficiency as the basis for indirect optimization of flue gas oxygen content. This type of control system is simple and effective, but relatively rough and rarely used in practice. This is mainly due to the poor controllability of early heating furnaces and the lack of maturity of various analytical measurement instruments.

[0009] Closed-loop balanced combustion control technology. The main task of the traditional combustion control system is to ensure that the total amount of fuel entering the furnace of the heating furnace is consistent with the amount of fuel required by the unit, but this does not ensure that the fuel can be evenly distributed to each burner of the heating furnace. The imbalance of fuel distribution causes unstable combustion, offset of the center of the furnace flame, and coking. The balanced combustion control system can solve the above problems better by controlling the speed of each powder feeder on the basis of the online monitoring system of air-powder concentration. The balanced combustion control system has the effect of combustion optimization control and improves the efficiency and safety of heating furnace combustion. The balanced combustion optimization control system is based on real-time online measurement technology, and the research and application development of real-time measurement technology at that time were relatively slow. It was only actually applied in heating furnaces with hot air powder delivery, and the reliability was not very high, which seriously affected the actual use effect and wide promotion of the balanced combustion control system.

[0010] Patent document CN107152695A discloses a visual combustion control system for a heating furnace based on multi-parameter detection.

[0011] The system and control method control the speed of the induced draft fan and the opening of the damper plate according to the CO concentration, furnace negative pressure and O2 concentration detection value in the exhaust gas of the heating furnace through the DCS control system to ensure the best optimization control effect, achieve energy saving, consumption reduction and emission reduction, especially reduce NO X and CO2 emissions. In this method, the furnace negative pressure is used to adjust the induced draft fan, and the CO concentration is used to adjust the damper. However, when implemented in a cracking furnace, the effect of adjusting the damper on the CO concentration has a long lag time; the furnace negative pressure to adjust the induced draft fan and the CO concentration to adjust the damper will produce a coupling effect, so this method is not currently used in cracking furnaces. However, it cannot reasonably solve the problem of the mutual coupling adjustment of CO concentration, oxygen concentration, and furnace negative pressure in the cracking furnace. Summary of the invention

[0012] Purpose of the invention: In view of the above-mentioned problem, the present invention adopts a method of controlling the induced draft fan by measuring the CO content at the flue gas emission point, and at the same time adjusting the burner damper in conjunction with the furnace negative pressure. When the oxygen concentration exceeds the range, the induced draft fan is adjusted by tracking the oxygen concentration, which can put the cracking furnace in a critical oxygen content state and reduce gas consumption and NOx emissions.

[0013] The technical solution of the present invention is as follows:

[0014] In one aspect, the present invention provides a cracking furnace induced draft fan adjustment system, which is characterized in that it includes:

[0015] The fuzzy control module is used to generate the induced draft fan regulation signal increment according to the CO concentration of the furnace flue gas;

[0016] An auxiliary control module is used to select and adjust the induced draft fan or the burner damper according to the signal increment generated by the fuzzy control module (1) and the range of the furnace negative pressure or oxygen concentration;

[0017] The threshold module is used to automatically switch back to manual adjustment mode under abnormal circumstances to ensure smooth operation of the system.

[0018] Furthermore, the fuzzy control module has an input variable of CO concentration, a control method of fuzzy PD plus integration, and an output variable of the induced draft fan opening.

[0019] Furthermore, the auxiliary control module has input variables of gas volume, oxygen concentration, and furnace pressure, a control mode of self-optimizing control, and output variables of the induced draft fan opening and the burner damper opening.

[0020] Furthermore, the threshold module sets upper and lower limit thresholds for CO concentration, oxygen concentration, gas volume, and furnace negative pressure. When the threshold is exceeded, the system automatically switches back to manual adjustment.

[0021] On the other hand, the present invention also provides a method for implementing the above cracking furnace induced draft fan adjustment system, comprising the following steps:

[0022] ①The fuzzy control module obtains the CO concentration;

[0023] ② The fuzzy control module outputs the induced draft fan adjustment signal increment Δu(kT) through fuzzy PD plus integral operation and transmits it to the auxiliary module.

[0024] ③ The auxiliary module obtains the gas volume, furnace negative pressure, oxygen concentration and induced draft fan adjustment signal increment Δu(kT); when Δu(kT) < 0, it proceeds to step ④; when Δu(kT) > 0, it proceeds to step ⑦;

[0025] ④ When the auxiliary module determines that Δu(kT) is less than 0, if the furnace negative pressure is greater than Pcmax, the burner damper is adjusted to ensure that the furnace negative pressure is within a reasonable range.

[0026] ⑤ When the auxiliary module determines that Δu(kT) is less than 0, if the furnace negative pressure is ≤Pcmax and the oxygen concentration is less than O2cmin, the oxygen concentration is self-optimized and the induced draft fan is adjusted by tracking the oxygen concentration.

[0027] ⑥ When the auxiliary module determines that Δu(kT) is less than 0, if the furnace negative pressure is ≤ Pcmax and the oxygen concentration is ≥ O2cmin, the u(kT) signal is sent to the induced draft fan. Among them, u(kT)=u(kT-T)+Δu(kT).

[0028] ⑦ When the auxiliary module determines that Δu(kT)>0, if the furnace negative pressure is <Pcmin, the burner damper is adjusted to ensure that the furnace negative pressure is within a reasonable range.

[0029] ⑧ When the auxiliary module determines that Δu(kT)>0, if the furnace negative pressure ≥Pcmin and the oxygen concentration>O2cmax, the oxygen concentration is self-optimized and the induced draft fan is adjusted by tracking the oxygen concentration.

[0030] ⑨ When the auxiliary module determines that Δu(kT)>0, if the furnace negative pressure ≥Pcmin, and the oxygen concentration ≤O2cmax, the u(kT) signal is sent to the induced draft fan. Where u(kT)=u(kT-T)+Δu(kT).

[0031] ⑩ Return to step ①.

[0032] Where: u(kT) represents the output signal at time kT;

[0033] Pcmax represents the maximum value of the limit range of the furnace negative pressure imposed by the regulating system;

[0034] Pcmin represents the minimum value of the control system's limit on the furnace negative pressure;

[0035] O2cmax represents the maximum value of the oxygen concentration limit of the regulation system;

[0036] O2cmin indicates the minimum limit range of oxygen concentration set by the regulation system.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] 1) The system of the present invention operates stably, and the average oxygen content of the cracking furnace is reduced to 1.78% under the premise of ensuring that the CO concentration is lower than 100ppm; NO in the flue gas is X The concentration decreased by 12.88 mg / m 3 , a decrease of about 20.07%; the fuel gas consumption was reduced by 92.55kg per hour, a decrease of about 2.16%.

[0039] 2) The fuzzy control module used in the present invention generates an induced draft fan adjustment signal increment according to the CO concentration of the furnace flue gas; the auxiliary control module selects to adjust the induced draft fan or the burner damper according to the range of the furnace negative pressure or oxygen concentration based on the signal increment generated by the fuzzy control module (1); the threshold module is used to automatically switch back to the manual adjustment mode under abnormal conditions to ensure the smooth operation of the system. It can solve the problem of the mutual coupling adjustment of CO concentration, oxygen concentration and furnace negative pressure in the cracking furnace, and ensure that the oxygen concentration and furnace negative pressure fluctuate within a reasonable range to achieve near-ideal combustion. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 Schematic diagram of the induced draft fan regulating system of the cracking furnace of the present invention

[0041] Figure 2 This is the block diagram of a two-dimensional fuzzy PID controller (this is a prior art logic diagram)

[0042] Figure 3 Negative oxygen concentration, furnace negative pressure tracking adjustment block diagram

[0043] Figure 4 This is the positive oxygen concentration and furnace negative pressure tracking adjustment block diagram

[0044] Figure 5 This is the threshold module block diagram DETAILED DESCRIPTION

[0045] The detailed scheme of the present invention is further described below in conjunction with the embodiments and drawings, but the protection scope of the present invention shall not be limited thereto.

[0046] See also Figure 1 , Figure 1 This is a schematic diagram of the cracking furnace induced draft fan adjustment system of the present invention. As shown in the figure, a cracking furnace induced draft fan adjustment system adjusts the CO content at the flue gas discharge, and adjusts the induced draft fan according to the real-time CO concentration to achieve the theoretical ratio of combustion, including the present invention using the CO content at the flue gas discharge for adjustment. It mainly includes three parts: CO content two-dimensional fuzzy PID control 1; auxiliary control module 2, including furnace negative pressure tracking adjustment, oxygen concentration tracking adjustment, oxygen concentration self-optimization setting; threshold module 3.

[0047] The fuzzy control module, the controlled object is the cracking furnace, and the CO concentration of the furnace flue gas is adjusted by changing the signal input of the induced draft fan inverter, that is, the control signal u(t) to the CO concentration c(t) of the furnace flue gas can be regarded as a generalized controlled object. When the control signal decreases, the CO concentration of the furnace flue gas will gradually increase.

[0048] See also Figure 2 , the fuzzy PID controller is realized by combining a two-dimensional fuzzy controller with an integral algorithm. Figure 2 In the figure, r(kT) represents the given value at time kT; e represents the difference between the input signal and the set value; Δe represents the change in the difference; Ki / Ku are both set coefficients; u(kT-T) represents the output signal at time kT-T; + / - represents whether the signal value is positive or negative.

[0049] The premise for the normal operation of the fuzzy control module is that the oxygen concentration and the furnace negative pressure fluctuate within a reasonable range, so an auxiliary module is set. When the fuzzy control module is adjusted, the auxiliary module first confirms whether the furnace negative pressure is within the limit range. If it is not within the range, it needs to track and adjust the furnace negative pressure, and the adjustment object is the burner damper; secondly, it is necessary to confirm whether the oxygen concentration is within the limit range. If it is not within the range, it needs to track and adjust the oxygen concentration, and the adjustment object is the induced draft fan. If the furnace negative pressure and oxygen concentration are both within the limit range, the output signal of the fuzzy control module is used for adjustment.

[0050] The auxiliary module consists of three parts: positive / negative oxygen concentration tracking and adjustment, furnace negative pressure tracking and adjustment, and oxygen concentration self-learning tracking. The block diagram of negative oxygen concentration and furnace negative pressure tracking and adjustment is as follows: Figure 3 shown.

[0051] The positive oxygen concentration and furnace negative pressure tracking adjustment block diagram is as follows Figure 4 shown.

[0052] Δu(kT)=u(kT)-u(kT-T), u(kT) represents the output signal at time kT;

[0053] Pcmax represents the maximum value of the limit range of the furnace negative pressure imposed by the regulating system;

[0054] Pcmin represents the minimum value of the control system's limit on the furnace negative pressure;

[0055] O2cmax represents the maximum value of the oxygen concentration limit of the regulation system;

[0056] O2cmin represents the minimum limit of the oxygen concentration of the regulation system;

[0057] Self-learning tracking of oxygen concentration: The system automatically stores the gas volume, oxygen concentration, and furnace negative pressure into the database, and performs fitting calculations on the oxygen concentration to confirm the oxygen concentration for ideal combustion of the current gas volume, and uses it as the parameter setting value for oxygen concentration tracking and adjustment.

[0058] Threshold module, in order to ensure the smooth operation of the system, to ensure that it can automatically switch back to manual adjustment mode under abnormal circumstances, add a threshold module, such as Figure 5 When the oxygen concentration, furnace negative pressure, gas volume exceeds the upper limit or is lower than the lower limit, and the CO concentration exceeds the upper limit, it is considered an abnormal situation and the system automatically switches from automatic to manual adjustment.

Claims

1. A cracking furnace induced draft fan adjustment system, characterized in that: include: A fuzzy control module (1) is used to generate an induced draft fan regulation signal increment according to the CO concentration of the furnace flue gas; The auxiliary control module (2) is used to select and adjust the induced draft fan or the burner damper according to the signal increment generated by the fuzzy control module (1) and the range of the furnace negative pressure or oxygen concentration; The threshold module (3) is used to automatically switch back to the manual adjustment mode under abnormal circumstances to ensure smooth operation of the system.

2. The cracking furnace induced draft fan adjustment system according to claim 1, characterized in that: The fuzzy control module (1) has an input variable of CO concentration, a control method of fuzzy PD plus integration, and an output variable of the induced draft fan opening.

3. The cracking furnace induced draft fan adjustment system according to claim 1, characterized in that: The auxiliary control module (2) has input variables of fuel gas volume, oxygen concentration and furnace pressure, a control mode of self-optimization control, and output variables of induced draft fan opening and burner air door opening.

4. The cracking furnace induced draft fan adjustment system according to claim 1, characterized in that: The threshold module (3) sets upper and lower thresholds for CO concentration, oxygen concentration, fuel gas volume, and furnace negative pressure. When the thresholds are exceeded, the system automatically switches back to manual adjustment.

5. The method for implementing the cracking furnace induced draft fan adjustment system according to claim 1, characterized in that: The steps include: ①The fuzzy control module obtains the CO concentration; ② The fuzzy control module outputs the induced draft fan adjustment signal increment Δu(kT) through fuzzy PD plus integral operation and transmits it to the auxiliary module. ③ The auxiliary module obtains the gas volume, furnace negative pressure, oxygen concentration and induced draft fan adjustment signal increment Δu(kT); when Δu(kT) < 0, it goes to step ④; when Δu(kT) > 0, it goes to step ⑦; ④ When the auxiliary module determines that Δu(kT) is less than 0, if the furnace negative pressure is greater than Pcmax, the burner damper is adjusted to ensure that the furnace negative pressure is within a reasonable range; ⑤ When the auxiliary module determines that Δu(kT) is less than 0, if the furnace negative pressure is ≤Pcmax and the oxygen concentration is less than O2cmin, the oxygen concentration is self-optimized to track and adjust the induced draft fan; ⑥ When the auxiliary module determines that Δu(kT) is less than 0, if the furnace negative pressure is ≤ Pcmax and the oxygen concentration is ≥ O2cmin, the u(kT) signal is sent to the induced draft fan, where u(kT) = u(kT-T) + Δu(kT); ⑦ When the auxiliary module determines that Δu(kT)>0, if the furnace negative pressure is <Pcmin, the burner damper is adjusted to ensure that the furnace negative pressure is within a reasonable range; ⑧ When the auxiliary module determines that Δu(kT)>0, if the furnace negative pressure ≥Pcmin, and the oxygen concentration>O2cmax, the oxygen concentration is self-optimized to track and adjust the induced draft fan. u(kT) represents the output signal at time kT, and Pcmax represents the maximum value of the limit range of the furnace negative pressure imposed by the regulation system; ⑨ When the auxiliary module determines that Δu(kT)>0, if the furnace negative pressure ≥Pcmin and the oxygen concentration ≤O2cmax, the u(kT) signal is sent to the induced draft fan, where u(kT)=u(kT-T)+Δu(kT); O2cmax represents the maximum value of the limit range of the regulation system for oxygen concentration; O2cmin represents the minimum value of the limit range of the regulation system for oxygen concentration; ⑩ Return to step ①.

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