![]({{media url="Causes_and_judgement_of_centrifugal_compressor_surge.jpg"}})
Each centrifugal compressor corresponds to a curve between outlet pressure P and flow rate Q at different speeds n, as shown in Figure 2.
As the flow rate decreases, the outlet pressure of the compressor gradually increases. When the maximum outlet pressure at this speed is reached, the unit enters the surge zone, the compressor outlet pressure begins to decrease, and the flow rate also decreases, resulting in a compressor surge Vibrate. From the curve point of view, the reduction in flow rate is the root cause of surge. In actual production, try to avoid the compressor running under the condition of small flow rate.
②Relative molecular mass of gas
As shown in Figure 3, the curve of centrifugal compressor at constant speed and different relative molecular mass under constant pressure can be seen from the curve. Under constant pressure operating conditions, when the gas with relative molecular mass M=20 surges At this time, the operating point of the gas with relative molecular masses of M=25 and M=28 is still far from the surge region. Therefore, under constant pressure operating conditions, the smaller the relative molecular mass, the easier it is to surge.
③Inlet pressure![]({{media url="Causes_and_judgement_of_centrifugal_compressor_surge3.jpg"}})
As shown in Figure 4, the inlet pressure of the compressor is P1》P2》P3. Under the operating condition of constant pressure of the compressor, the lower the inlet pressure, the more likely the compressor to surge, which is also the increase in the pressure difference of the inlet filter. When it is necessary to replace the filter in time.
④Inlet temperature![]({{media url="Causes_and_judgement_of_centrifugal_compressor_surge4.jpg"}})
As shown in Figure 5, the curve of the centrifugal compressor under constant pressure and constant speed at different inlet gas temperatures can be seen from the curve. Under constant pressure operating conditions, the higher the gas inlet temperature, the easier it is to occur Surge. Therefore, for the same centrifugal compressor, surge is more likely to occur in summer than in winter.
⑤Speed![]({{media url="Causes_and_judgement_of_centrifugal_compressor_surge5.jpg"}})
Turbine-driven compressors often run at different speeds according to different flow requirements of the outside world. As can be seen from Figure 2, with a certain amount of external air consumption, the higher the speed, the easier the surge occurs.
In summary, the root cause of surge is that the compressor's flow rate is too small, less than the compressor's minimum flow rate (or because the compressor's back pressure is higher than its maximum discharge pressure), resulting in severe gas rotation separation in the machine The external cause is that the pressure of the pipe network is higher than the discharge pressure provided by the compressor, causing gas to flow backward and generating large-scale pulsation of the air flow.
Judgement method of centrifugal compressor surge
Once the surge occurs in the centrifugal compressor, the operation status of the unit and the pipe network will have the following more obvious characteristics:
(1) Periodic oscillation occurs between the compressor and the pipe network, and generates high and low noise. In severe cases, the unit may even produce a violent "roar" sound.
(2) The casing and bearings are strongly vibrated, and the vibration is unstable, large and small, and emit strong, periodic airflow sound; the vibration frequency of surge is generally low.
(3) The outlet pressure and inlet flow rate of the gas medium change greatly, periodic pulsation occurs, and gas backflow may occur in severe cases, which is a more dangerous working condition.
(4) The ammeter and power meter pointers of the motor driving the compressor will produce large fluctuations, and gradually increase with the increase of surge intensity.
Therefore, during the production process, by observing the sound of centrifugal compressor operation, inlet pressure and flow rate, vibration amplitude meter, you can effectively determine whether surge occurs.
How to prevent the surge of centrifugal compressor
In production practice, the following measures can be used to prevent the occurrence of surge.
Pressure adjustment
When the compressor is working under conditions higher than the set pressure, the outlet pressure can be maintained through the throttle of the inlet, or part of the pressure can be emptied by opening the anti-surge adjustment valve; a bypass pipe can also be added to adopt a bypass return flow Method, keep the discharge pressure at the set pressure, and maintain the flow rate within the minimum flow rate.
Frequency converter speed regulation
When the compressor starts to run, the load is the largest, the sensor transmits the measured data to the PLC (programmable controller), the PLC outputs the operating frequency to the inverter through operation, and controls the inverter. With the operation of the compressor, the PLC The signal of the difference and flow reduction is sent to control the frequency converter to reduce the power frequency, thereby reducing the speed of the compressor in operation, avoiding surge of the compressor, and reducing unnecessary energy loss.
Reasonably control anti-surge safety margin
According to the performance curve of the centrifugal compressor, an anti-surge line is used as the setpoint curve of the anti-surge regulator on the right side of the surge line. The area between it and the surge line is the safety boundary of the compressor. This is called the safety margin. It is the ratio of the normal flow rate to the surge flow rate at a certain working speed. When the working point of the compressor reaches the anti-surge line, the anti-surge adjustment valve opens to move the operating point to the safe zone to avoid surge.
Set up alarm instrument
Install a flow monitoring instrument at the inlet of the centrifugal compressor and a pressure monitoring instrument at the outlet. Once the compressor is close to the surge operating area, an alarm can be issued in time to take measures in advance to prevent accidents.
