The hottest Laigang gt078l3k3 centrifugal air comp

2022-08-10
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Anti surge control of Laigang gt078l3k3 centrifugal air compressor

Laigang gt078l3k3 centrifugal three-stage air compressor, which was put into operation in 1997, is a radial compressor driven by an integral gear produced by Atlas company of Germany. The gear has three shafts and is a horizontal split single spiral straight tooth cylindrical type. The main technical indicators are motor voltage 6000V, current 570a, power 5200kw, and the volume flow of the primary suction port 61400m3/h, When the pressure is 97.4kpa, the temperature is 30 ℃, and the ratio of outlet pressure to inlet pressure remains unchanged, the surge limit operates the reaction line 42000m3/h

1 cause analysis of surge

surge of centrifugal compressor is caused by pressure fluctuation and temperature increase caused by partial or total reflux of compressed air. It is affected by factors such as air compressor speed, suction gas temperature at all levels, inlet guide vane opening, etc

air compressor speed factor due to its reliable performance, stable power supply equipment, and shaft vibration, shaft displacement alarm protection device, the factor of pressure fluctuation caused by unstable speed can be ignored

under the same pressure ratio, if the temperature of the inhaled gas at all levels is high, the amount of gas flow to guide the enterprise at each stage will be reduced. The gas flow can be corrected by measuring the inlet gas temperature at all levels, so as to reduce the impact of temperature changes on working conditions

inlet guide vane opening factor when the inlet guide vane opening is certain, there is a certain functional relationship between the air flow ratio Q and the pressure ratio p (Q and P are the ratio of the actual value to the set value). The functional relationship can be expressed by the characteristic diagram of the compressor, as shown in Figure 1

it can be seen from Figure 1 that different guide vane opening and pressure ratio lead to different flow limits for surge of air compressor. Connect the limit flow values of surge under different states to form a surge curve, such as the PG line in Figure 1. The upper left part of the surge curve is the unstable working area of the air compressor, that is, the surge area, and the lower right part is the stable working area

(1) if the opening of the inlet guide vane remains unchanged, the flow and pressure of the air compressor form a fixed curve. When the pressure ratio increases, the operating point O of the air compressor moves along the fixed curve, and the flow value is easy to move to the surge area; If the flow decreases, the operating point O of the air compressor will also move along the fixed curve, and the pressure ratio will easily move to the surge area. In order to avoid surge caused by large pressure ratio and small flow, the opening of inlet guide vane can be adjusted to maintain the pressure and flow of the air compressor within a stable working range

(2) when the air supply to the air separation unit is stopped or the resistance of the air separation unit is large, the air flow to the air separation unit will be very small, resulting in the air compressor working in the surge area. At this time, the flow of the air compressor can be kept above the surge limit operating response line by adjusting the opening of the vent valve

2 realization of anti surge control

2.1 system composition

the system is composed of DCS and PLC. The system configuration is shown in Figure 2. DCS is the INFI90 distributed control system of elsag company in Canada, in which the INFI90 ring and multi-function processor constitute the thermal redundancy of the system to complete the data acquisition, loop control and other functions of the production process of the whole factory. The PLC system adopts the Su 945 series programmable controller of Siemens company in Germany, which is composed of a group of i/o modules and an operator panel to complete the interlocking and linkage control of air compressor equipment, and the analog display and control of important parameters (motor speed, shaft vibration, etc.). There are interrelated parameters between DCs and PLC, which are connected through their i/o modules

the anti surge control system of air compressor mainly includes three parts: inlet guide vane opening adjustment circuit, vent valve adjustment circuit, and equipment interlocking during startup and shutdown. This movement is mainly used in the vertical universal friction and wear testing machine, and the opening adjustment of the inlet guide vane is realized by DCS; The vent valve adjustment and the interlock of the startup and shutdown equipment are realized by PLC

2.2 inlet guide vane opening adjustment

inlet guide vane opening is used to adjust the inlet and outlet pressure ratio and air flow of the air compressor to ensure that the air compressor can work in a stable working area. This control adopts the scheme of flow and pressure closed-loop cross control, as shown in Figure 3

the control cable hook of the inlet guide vane opening adjustment circuit cannot be upward. Lvy has 18 production bases and 4 research and innovation centers in China, with the following functions

(1) input data processing

in addition to processing the moving average value of the input signal, it also performs temperature and pressure compensation calculation and upper and lower limit amplitude processing on the air flow signal

(2) loop control

the pressure and flow of the controlled parameters are PID controlled by separate regulators, and the low value is selected by the low selector to adjust the opening of the inlet guide vane. In this way, the fluctuation of input air pressure and flow in the air separation unit is reduced, and the surge of the air compressor is prevented

(3) interlock control

when the manual/automatic control station of fic-f2615 circuit is switched to manual, the opening of inlet guide vane is controlled by the small value in the manual output value of fic-f2615 and the automatic output value of pic-p2615

when the manual/automatic control station of pic-p2615 circuit is switched to manual, the opening of inlet guide vane is only controlled by the automatic output value of fic-f2615

2.3 adjustment of vent valve opening

once the air compressor approaches the surge area (as shown in line Ag in Figure 1), open the vent valve to reduce the discharge pressure of the air compressor and return the air compressor to the stable working area. The venting volume of the vent valve will be controlled according to the air flow corrected by temperature and pressure after secondary compression, as shown in Figure 4

2.4 equipment interlock during air compressor startup and shutdown

(1) preparation for air compressor startup: the inlet guide vane is at the minimum position; The vent valve is fully open

(2) air compressor startup: the vent valve remains fully open during startup

(3) after startup: slowly close the vent valve within 3 minutes

(4) shutdown: quickly open the vent valve

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