The main fan unit of the catalytic cracking unit is mainly responsible for providing the main wind to the regenerator during the production operation of the whole device, which is used to satisfy the oxygen required for scorching, and also maintains the regenerator pressure, maintains heat balance, oxygen balance, and pressure. The key role of balance and fluidization. If the main fan unit is shut down, the catalytic cracking reaction will also be forced to stop, so the operating condition of the main fan unit directly affects the safe and stable long-cycle operation of the entire catalytic cracking unit. The anti-surge control of large compressor units is the key and core part of the unit control. Because once the surge is not properly contained, and then developed into a countercurrent, continuous countercurrent will have serious consequences of the destruction.
The energy recovery unit of the 1106 t/a heavy oil catalytic cracking unit of Daqing Petrochemical Company's refinery is configured as follows: hood + axial compressor + motor/generator, which has been running continuously for nearly 17 years since it was put into production in 1989. unit. For the anti-surge control of the unit, after several upgrades and improvements, a unique control system has been formed. Through the continuous safe and stable operation in recent years, after many inspections, the reliability of the unit self-protection system The stability is very high.
2 The main fan unit anti-surge control working principle.
There are two types of control methods for preventing compressor surge. One is to make the flow of the compressor not less than the critical value, open the bypass valve when the flow is close to the surge threshold; the other is to achieve the relationship according to a certain calculation function. The trajectory of the flying point approaches a curve on the graph. When the flow / (inlet pressure - outlet pressure) is less than a certain threshold, the compressor will enter the surge region. At this point, the bypass valve should be opened to increase the intake air volume of the compressor, while reducing the inlet pressure and increasing the outlet pressure, which is beneficial to prevent surge.
The anti-surge of large axial fans should adopt a follow-up surge control scheme. There are two ways to draw an anti-surge curve. One is drawn according to the unit characteristic curve provided by the manufacturer, and the other is drawn by the operational data of the on-site measured axial flow fan.
In the anti-surge control of the axial flow fan, the anti-surge regulating valve V2 is controlled by the differential pressure of the throat, and the set value of the anti-surge regulator is taken from the function of the outlet pressure and the vane angle SV=F(P, 2), see the anti-surge line in Figure 1, the detection signal is taken from the throat differential pressure. When the axial flow machine runs below the anti-surge line, ie: PV>SP, the regulator output 20mA, the anti-surge vent valve is fully closed; and when the axial flow fan runs beyond the anti-surge line, ie: PV The anti-surge curve anti-surge curve is based on the data sheet provided by the manufacturer and the data of the critical point of surge at different vane angles at the beginning of the operation, namely: the outlet pressure value and the throat differential pressure value, and the actual measured axial flow. Fan surge curve. On this curve, the anti-surge control line is obtained by shifting the curve to the right by 10% of the surge flow as the control margin. 3 original design anti-surge control system. Daqing Petrochemical Company refinery 1106 t / a heavy oil catalytic cracking unit was built in 1992, the main fan anti-surge control system of the device by a PMK regulator for simple PID loop control, anti-surge system measurements Only the throat differential pressure PDT005, the outlet pressure PI004. shows a simple anti-asthma receipt date vibration control. The control system cannot implement complex anti-surge control, but only adjusts with PID parameters. When the measured value is lower than a certain fixed value, an alarm signal is output to make the solenoid valve energized and the regulating valve is fully open. Therefore, the anti-surge control method is relatively simple and cannot fully utilize the crew's potential. Simple anti-surge control 4ESD anti-surge control system. In June 1998, the main fan control system was rebuilt, and the ESD control system produced by American ICS Company was used for unit protection and control. In the ESD system, the main fan is started, automatic operation, safe operation, reverse flow protection, emergency stop, lubricating oil self-starting, power oil self-starting, anti-surge control and other functions. It uses a reliable triple-technology, and its CPU module, power supply, CPU bus and I/O bus are all TMR configured. The CPU module and I/O card adopt hardware fault tolerance (HIFT) technology and hardware voting method, which accelerates the system response speed and makes the control system more reliable and safe. Since the control system was used in August 1998, there have been no malfunctions or other malfunctions, which is relatively stable. 4.1 ESD anti-surge control system. The ESD anti-surge control system is implemented by an ESD internal program. There are four parameters involved in anti-surge control, namely the throat differential pressure value PDT005, the outlet pressure PT004, the inlet temperature TI011 and the inlet pressure PT005. In the ESD system, anti-surge is realized by BIC004, B1, B2 and other functional blocks. control function. It is mainly used to establish anti-surge control curve, anti-surge adjustment control and quick opening and closing of surge valve. 4.1.1 ESD anti-surge control curve is established. In the B1 and B2 function blocks, the two anti-surge curves of 14# and 28# are defined. The anti-surge curve is written in logical language segments. For the performance curves of the unit at different ambient temperatures in winter and summer, two anti-surge curves were made, namely, 14# in winter and 28# in summer. The two curves are segmented according to the percentage of the differential pressure value of the throat, and the seven line segments are connected, which is the anti-surge curve at this temperature. Then move a certain margin to the right, which is the anti-surge setting curve of the axial flow fan, and the anti-surge regulation loop adopts the PID algorithm. 4.1.2 ESD anti-surge control scheme. In the BIC004 function block, the program defines the operating point of the unit to be compared to the surge line. When the PV value is less than the SP value (ie, the operating point is far from the anti-surge line), HIC004 (surge valve control output) is fully off; when the PV value is greater than the SP value (ie, the operating point exceeds the anti-surge line), HIC004 is all turn on. At the same time, the fast opening rate and the slow closing rate of the surge valve are respectively defined to ensure the smooth running of the device. 4.2 Problems with the ESD anti-surge control system. The ESD control system produced by American ICS Company is mainly dedicated to the protection control of the unit. It is not a professional anti-surge control expert. The anti-surge system can not maximize the efficiency of the unit. When the regenerator pressure control of the unit exceeds 0.235~0.245 At MPa, the entire unit will have the disadvantages of difficulty in generating electricity, high catalyst consumption, and high energy consumption. 53C anti-surge control system. In response to the problems of the ESD control system, the device introduced the PLUS+ 104 chemical automation and instrumentation volume 37 controller of the American CCC Company in 2002 for the anti-surge system, hereinafter referred to as the 3C controller. Usually, when the unit is anti-surge, it is necessary to return some of the flow to the compressor inlet or vent to keep the compressor operating point away from its surge limit. Second, a large amount of compression work is lost when reflowing or venting part of the gas. American CCC is a company specializing in unit research. The economic problem of the compressor's compression work loss is solved in the unit control. The 3C control system is able to accurately determine how far the compressor operating point is from the surge point, thereby maintaining a sufficient but not excessively large return flow. 5.13C anti-surge control system. The 3C anti-surge control system of the main fan unit of the device performs complex calculations through parameters such as throat differential pressure value PDT005, outlet pressure PT004, inlet temperature TI011, inlet pressure PT005 and outlet temperature TI012 to control the BIC004 regulating valve. 3C controller anti-surge control indication. 5.2 Definition of anti-surge multiple control lines in the controller In the 3C controller, according to the characteristics of the axial fan surge, the controller defines a number of curves. When the compressor operating point crosses these curves, the controller then generates the action. In response, avoid compressor surge, reduce unnecessary fluctuations in production process and consumption of cycle energy. The various curves defined within the controller are as shown. Various curve 5.33C anti-surge control schemes defined in the controller. Inside the controller, the surge limit is a complex function that varies with various process conditions such as gas composition, inlet pressure and temperature, speed and inlet guide vane angle. A multivariate function is therefore used to calculate the extent to which the operating point approaches the surge limit. For small and slow disturbances, proportional-integral control is used and can be prevented from resetting when the control valve is fully closed. For fast disturbances, the controller will generate a differential response that increases the safety margin and improves the control of the proportional-integral response. The anti-surge controller uses a variety of open loop and closed loop control algorithms to develop a response to the magnitude of the disturbance, thereby avoiding a wide waste of safety margin. 5.43C anti-surge controller features. The 3C anti-surge controller can combine the accurate prediction of surge and the special control response to minimize the surge safety margin of the compressor. As a result, both the compressor and the wasteful recirculation are protected. Or the amount of venting is reduced to a minimum. This is the main reason why 3C controllers are widely used. Thanks to the advanced anti-surge control solution, the compressor can be operated very close to the surge limit without having to recirculate. The unit is low in energy consumption, more economical, and the unit is more reliable. Due to the conservative strategy control method, the controller can continue to prevent surge when the transmitter fails, and the main air outlet pressure can be controlled at 0.33 MPa. 6 Improved anti-surge control system. In view of the characteristics of the above two anti-surge control systems, in order to avoid malfunctioning parking caused by equipment failure of the instrument, a control scheme in which the 3C controller and the ESD control two sets of anti-surge control systems are used as master and standby is adopted. The 3C controller is used under normal working conditions. When the 3C controller is abnormal, it is cut into the internal control of the ESD system. 6.1 Improved anti-surge control scheme. Because of the mutual backup mode of the two control systems, the control signals of various instruments need to be connected to two sets of control systems at the same time. The field input signal enters the ESD system and the 3C system through the input and exit barriers. There are four signals that need to enter the two systems at the same time, namely PDT005, PT004, TI011, PT005. The MTL5043 safety barrier is used to divide the input 4~20mA signal into the ESD AI card and the 3C controller terminal. board. Improved anti-surge control system. 6.2 Improved switching of the anti-surge control system. Introduce 3C controller output control signal into ESD, add 3C and ESD switch on anti-surge control screen, select 3C when using 3C anti-surge controller, if there is any problem with 3C anti-surge controller, switch to ESD in time Anti-surge controller control. 6.3 Improvement of the ESD system in the control system to achieve the dynamic curve Because the original anti-surge curve of the ESD system can not move, there is a certain constraint on adjusting the flow of the axial flow fan. On the original defense 105 seventh period Sun Yonggang and so on. Anti-surge control is modified in the improved surge control of the catalytic cracking main fan group application: the 28# curve is deleted, the anti-surge curve is changed to a dynamic curve based on the 14# curve, and the curve offset button is added. Adjust the curve offset to achieve the purpose of anti-surge curve to adapt to the change of ambient temperature. The maximum offset is set to 4%. 6.4 Improved ESD system to control the temperature of the control point for temperature difference in the winter and summer of the region The influence of the medium is also calculated for the temperature and pressure of the control point in the system. The temperature and pressure of the control point are compensated by introducing the TI011 (inlet temperature) and PI005 (inlet pressure) into the control point, so that the control point can better reflect the actual working condition. At the same time, a new temperature and pressure compensation switch is added to the ESD anti-surge operation screen. The compensation and uncompensated two-speed are added. The compensation refers to the temperature and pressure compensation of the inlet flow, and the compensation is not compensated. A new display compensation and no display button is added. When the button display shows compensation, two working points are displayed on the anti-surge curve: one is for compensation, one is for no compensation, and when the temperature-compensation switch is selected, it is not known. Is another working point mis-switched in the surge zone? 6.5 Recalibration of the surge line and modification of the anti-surge line. In 2007, in order to increase the system pressure, the main fan unit of the unit increased the first-stage vane (from 14 to 15), causing the surge line of the compressor to change. In order to adapt to this situation and carry out anti-surge control more accurately, we will invite the on-site service technicians of 3C control system and ESD control system to the site. After the unit operation, the unit test and adjustment method will be used to calibrate the unit change. The real surge line and the anti-surge lines of the two systems were modified to ensure production needs and unit safety. 7 Conclusion. With the continuous development of catalytic cracking unit technology, the control system of the main fan unit has been continuously improved and improved. At the same time, all petrochemical production plants have adopted different control schemes to ensure the safety of the unit in combination with the actual working conditions of their own units. According to the characteristics of the production unit and the operation of the unit, the improved anti-surge control system ensures efficient, stable and safe production and long-term operation of the catalytic cracking unit and unit and maximizes benefits. Acrylic Products,Acrylic Sheet,Acrylic Sheets Lowes,Acrylic Sheet Blick Guangzhou One-Stop Engineering Plastics Industries (group) Co., Ltd , https://www.onestopmould.com