【Q&A Question 245】December 21, 2016
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【Q&A Question 245】December 21, 2016: Why must the anti-surge valve be fully opened before starting up the circulating hydrogen compressor? The reference answers will be visible after responding; scoring is awarded by identifying the key points. (Unless otherwise specified, all questions and answers are based on hydrogenation units.) ) Because during the startup of the unit, the amount of gas is relatively low at first. To ensure a certain flow rate at the inlet of the circulator, the anti-surge valve is kept fully open. As the gas volume increases, gradually close the anti-surge valve. This ensures a smooth start-up and prevents surging. Summary post of Q&A from 2016 (updated up to December~~~~) http://bbs.hcbbs.com/thread-1597792-1-1.html Seeking sponsors for the “2016 Haichuan Top 10 Members Selection Contest” http://bbs.hcbbs.com/thread-1628108-1-1.html (Source: Haichuan Chemical Forum)
The basic working principle of a centrifugal compressor is to transfer kinetic energy to the gas through a rapidly rotating impeller, thereby accelerating it and increasing its pressure; the capacity for doing work of each impeller stage is fixed. When the flow rate at the compressor inlet drops below a certain value, the pressure difference resulting from the higher outlet pressure of the impeller compared to the inlet pressure exceeds the impeller’s own capacity to generate power; as a result, the gas at the impeller outlet flows in reverse, causing severe surging in the gas flow, which in turn leads to surge in the entire unit ； It can also be understood that when the inlet flow rate of the centrifugal compressor drops below the surge value, the outlet pressure of the compressor decreases; meanwhile, the pressure in the pipeline system at the compressor’s outlet can be even higher than the compressor’s own outlet pressure, which causes gas to flow back and results in surge. In the simplest terms, it is caused by too low inlet pressure and relatively higher outlet pressure; the backflow of gas leads to surge. Of course, in actual operation, surge must be avoided; otherwise, a single instance of surge can render the entire compression unit unusable and even threaten the entire processing process.
The anti-surge function is activated to prevent surge from occurring
Prevent low inlet flow from causing compressor surge
The basic working principle of a centrifugal compressor is to transfer kinetic energy to the gas through a rapidly rotating impeller, thereby accelerating it and increasing its pressure; the capacity for doing work of each impeller stage is fixed. When the flow rate at the compressor inlet drops below a certain value, the pressure difference resulting from the higher outlet pressure of the impeller compared to the inlet pressure exceeds the impeller’s own capacity to generate power; as a result, the gas at the impeller outlet flows in reverse, causing severe surging in the gas flow, which in turn leads to surge in the entire unit ； It can also be understood that when the inlet flow rate of the centrifugal compressor drops below the surge value, the outlet pressure of the compressor decreases; meanwhile, the pressure in the pipeline system at the compressor’s outlet can be even higher than the compressor’s own outlet pressure, which causes gas to flow back and results in surge. In the simplest terms, it is caused by too low inlet pressure and relatively higher outlet pressure; the backflow of gas leads to surge. Of course, in actual operation, surge must be avoided; otherwise, a single instance of surge can render the entire compression unit unusable and even threaten the entire processing process.
The system pressure drop is too high, which prevents too low an inlet flow rate from causing surging in the turbine
The basic working principle of a centrifugal compressor is to transfer kinetic energy to the gas through a rapidly rotating impeller, thereby accelerating it and increasing its pressure; the capacity for doing work of each impeller stage is fixed. When the flow rate at the compressor inlet drops below a certain value, the pressure difference resulting from the higher outlet pressure of the impeller compared to the inlet pressure exceeds the impeller’s own capacity to generate power; as a result, the gas at the impeller outlet flows in reverse, causing severe surging in the gas flow, which in turn leads to surge in the entire unit ； It can also be understood that when the inlet flow rate of the centrifugal compressor drops below the surge value, the outlet pressure of the compressor decreases; meanwhile, the pressure in the pipeline system at the compressor’s outlet can be even higher than the compressor’s own outlet pressure, which causes gas to flow back and results in surge. In the simplest terms, it is caused by too low inlet pressure and relatively higher outlet pressure; the backflow of gas leads to surge. Of course, in actual operation, surge must be avoided; otherwise, a single instance of surge can render the entire compression unit unusable and even threaten the entire processing process.
Prevent surge from occurring due to untimely control
A sudden increase in flow can easily cause the pipeline to enter the surge zone and experience surging; in severe cases, this can damage the equipment. Therefore, during startup, the surge valve must be kept fully open to prevent surging in the pipeline.