Control of axial compressors The control of axial compressors is complicated relative to centrifugal compressors. It mainly includes main air flow 2 vane positioning adjustment system, anti-surge regulation system and unit interlock protection control system. Anti-surge control surge is an inherent feature of turbo compressors, especially axial compressors. The hazard caused by surge is more serious. In order to prevent the axial compressor from running close to the surge point, it must be set reliably. Anti-surge protection system. The anti-surge control principle is as shown.
Taking the exhaust pressure of the axial compressor as the PV value, taking the differential pressure of the throat of the axial compressor and calculating it as an SV value by an arbitrary line function generator (anti-surge line, which is actually breathing with the axial compressor) The vibration line has a safety margin of 5% to 10%). When the unit is running under stable conditions, PV In order to ensure the reliability, sensitivity and stability of the system operation, the following special functions are set when designing the anti-surge system: (1) using any polyline function to make the anti-surge line set more accurately; (2) using proportional integral (PI) control calculation not only ensures safe and reliable operation of the unit, but also minimizes the opening of the anti-surge valve and minimizes energy consumption. (3) Sets the anti-integration saturation function to make the system run more accurately and more quickly. (4) The dynamic compensation function is set to make the system change the strength of the control at any time under the sudden change of the working condition, and avoid the unit entering the dangerous working condition; (5) setting the anti-surge line to move automatically The function enables the unit to correct the anti-surge line after the long-term operation due to various factors, so as to ensure the safety of the unit; (6) Set the asymmetric output processing function to improve the stability of the system. In the sulphur-based acid process, the supply pressure of the axial-flow compressor is very low. Due to the safety of the unit and the slightly acidic nature of the process medium, the back-flow anti-surge control scheme is usually adopted. Moreover, since the differential pressure between the anti-surge valve is small and the flow rate is large, the anti-surge valve generally has a large diameter. Constant air volume / constant air pressure vane positioning adjustment According to the sulfur acid production process requirements, under the premise of constant volume of the sulfur-burning furnace furnace, the fan is required to be fixed at a certain operating point. If the amount of charge changes, the axial compressor will automatically change the operating point according to the size of the process resistance (when the resistance is large, the pressure increases, the flow becomes smaller; when the resistance is small, the pressure decreases, the flow increases). In this way, the axial compressor will select the constant air volume/constant air pressure switching operation according to the requirements of the process conditions. The principle of constant air volume/fixed air pressure positioning adjustment is as shown. The venturi tube of the axial compressor is provided with a flow measuring venturi. The differential pressure signal is subjected to the temperature and pressure compensation calculation and the obtained value is the actual flow measurement value, and is used as the PV value of the flow adjustment, and the flow rate set by the keyboard is used as the flow rate. The SV value is outputted to the stator electric actuator through the flow adjustment PID operation, and the vane angle is changed to achieve the purpose of controlling the constant air volume adjustment of the axial compressor. The principle of constant air volume/fixed air pressure positioning adjustment is similar. When the unit selects the fixed air pressure adjustment operation, the exhaust pressure of the axial compressor is taken as the PV value, the pressure set by the keyboard is used as the SV value, and the PID operation is adjusted by the equal pressure. After the output signal to the stator electric actuator, the angle of the vane is changed to achieve the purpose of controlling the constant pressure of the axial compressor. In this paper, the switching operation of constant air volume and constant air pressure realized by the unit is a disturbance-free switching operation. Unit interlock control 313.1 unit start interlock program The unit starts the interlock program as shown. The conditions for the unit to start the interlock: (1) the lubricating oil pressure is normal; (2) the vane is at the minimum angle; (3) the anti-surge valve is fully open; (4) the lubricating oil temperature is normal; (5) the main valve is fully closed; (6) Adjust the oil pressure to normal; (7) Drive the car; (8) Memory reset. When the unit starts the interlock condition, the unit start standby indication will be displayed on the HMI to remind the operator to proceed to the next step. Unit start-up procedure The unit start-up procedure is as shown. When the starting condition of the unit is available, the operator will increase the speed of the unit according to the sound speed curve of the steam turbine. After the unit reaches the rated speed, press the automatic operation button to release the flow regulation and anti-surge control in the original control program, and load the unit. Until the process production requirements are met. Unit shutdown interlocking program unit shutdown is divided into emergency shutdown and normal shutdown. The normal stop is implemented by the stop button. When the unit has a heavy fault, the emergency stop operation will be implemented. The operation procedure is as shown. The conditions for emergency shutdown of the unit are: (1) the shaft displacement of the unit is too large; (2) the shaft vibration of the unit is too large; (3) the bearing temperature of the unit is too high; (4) the lubricating oil pressure of the unit is too low; (5) the steam exhaust of the unit The pressure is too high; (6) The oil pressure is too low. Unit control unit instrument primary component selection Because the sulfuric acid process contains acidic medium in the whole process, no matter whether it is the tower rear fan or the tower front fan control, the primary component should consider corrosion resistance. Conclusion The AV80 axial compressor supplied by Yunnan Blower Group Co., Ltd. for Yunnan Furui Co., Ltd. was successfully commissioned in early 2005 and put into normal operation. The supporting control system meets the actual operation requirements. With the large-scale process of sulfuric acid production, the application of axial compressors will be a new development direction.
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