How is surge control achieved in large centrifugal compressors?
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How is surge control achieved in large centrifugal compressors?
This post was last edited by Hainachuanhe on December 29, 2009, at 16:51.
(1) External causes:
a: Operating parameters that affect airflow, such as rotating stall and surge, deviate from their specified values; examples include excessively low CO2 inlet pressure, high temperature, reduced CO2 purity, and a low average molecular weight. Additionally, fluctuations in the main steam pressure, temperature, flow rate, and condenser vacuum level of the steam turbine can lead to excessive variations in unit load and rotational speed, thereby causing surge.
b: Emergency shutdowns of the system; especially when the anti-surge system is manually controlled, surge is more likely to occur.
c: High cooling water temperature and elevated temperatures between various sections can also result in surge.
(2) Other external causes:
① Mechanical equipment failures:
a: Excessive clearances in inter-stage seals and shaft seals allow excessive gas leakage between stages or from the shaft ends, leading to insufficient intake by the impellers between stages.
b: Leakage or premature activation of safety valves at inter-stage outlets, internal leaks in heat exchangers, and gas leakage from separators all reduce the amount of gas entering subsequent stages.
c: Slow response of the steam turbine control system results in prolonged transition times for load changes and significant fluctuations in flow rate under varying operating conditions.
② Operational causes:
a: Excessively high pressure within the pipeline network causes the stable operating point to shift toward regions with lower flow rates.
b: Overloading of the unit, with its operating speed far exceeding the design value, leads to a steeper characteristic curve.
c: The anti-surge system is set to manual control mode.
d: Process media entering the flow channels impedes proper airflow. The above are the reasons for compressor surge. For large compressors, our current focus is on prevention, that is, preventing surge. Given the severe damage that surge can cause to the unit, for units that have experienced surge, it is necessary to promptly reduce the load and close the shut-off valve leading to the stripping tower (to prevent leakage from the check valve in this pipeline), thereby avoiding the backflow of large amounts of ammonium methoxide into the unit.
(1) External causes:
a: Operating parameters that affect airflow, such as rotating stall and surge, deviate from their specified values; examples include excessively low CO2 inlet pressure, high temperature, reduced CO2 purity, and a low average molecular weight. Additionally, fluctuations in the main steam pressure, temperature, flow rate, and condenser vacuum level of the steam turbine can lead to excessive variations in unit load and rotational speed, thereby causing surge.
b: Emergency shutdowns of the system; especially when the anti-surge system is manually controlled, surge is more likely to occur.
c: High cooling water temperature and elevated temperatures between various sections can also result in surge.
(2) Other external causes:
① Mechanical equipment failures:
a: Excessive clearances in inter-stage seals and shaft seals allow excessive gas leakage between stages or from the shaft ends, leading to insufficient intake by the impellers between stages.
b: Leakage or premature activation of safety valves at inter-stage outlets, internal leaks in heat exchangers, and gas leakage from separators all reduce the amount of gas entering subsequent stages.
c: Slow response of the steam turbine control system results in prolonged transition times for load changes and significant fluctuations in flow rate under varying operating conditions.
② Operational causes:
a: Excessively high pressure within the pipeline network causes the stable operating point to shift toward regions with lower flow rates.
b: Overloading of the unit, with its operating speed far exceeding the design value, leads to a steeper characteristic curve.
c: The anti-surge system is set to manual control mode.
d: Process media entering the flow channels impedes proper airflow. The above are the reasons for compressor surge. For large compressors, our current focus is on prevention, that is, preventing surge. Given the severe damage that surge can cause to the unit, for units that have experienced surge, it is necessary to promptly reduce the load and close the shut-off valve leading to the stripping tower (to prevent leakage from the check valve in this pipeline), thereby avoiding the backflow of large amounts of ammonium methoxide into the unit.
Reasons for surge: 1. Machine failure. 2. Low intake pressure and flow at runtime, high outlet pressure. How to control surge: Try to increase pressure first when starting up, and reduce pressure first when shutting down.
Due to the characteristics of centrifugal compressors, vortex phenomena occur in their flow channels, causing the machine to vibrate (surge). As a result, the design and manufacturing of such machines require great care, and there are complex theories involved. There are specialists who study this issue. For each machine, during its design and manufacturing process, a curve known as the anti-surge curve is established – a curve that shows the relationship between speed, flow rate, pressure, and power. The rotor must undergo high-speed dynamic balance testing before it is installed (and this testing is also necessary after any maintenance work on the rotor). When the machine is installed and started up, the operating parameters (operating points) must remain within the anti-surge zone; entering the surge zone will trigger surge. Each machine comes with specific operating procedures that must not be altered arbitrarily. There are operating curves for increasing speed and pressure, and no one dares to ignore them.