Seeking advice on starting up and accelerating a centrifugal compressor
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Typical acceleration process: First, maintain at 300–500 revolutions per minute for an hour or so, then increase the speed by several hundred to a thousand revolutions per minute at a time, staying at each new speed level for ten minutes; during this process, the critical speed is passed quickly, and the speed is continued to be increased until the rated speed is reached. Question: If the compressor is converted from steam-driven to electric-driven, is it also necessary to increase the speed in such a step-by-step manner? If the power grid is strong enough, can it be started and go straight to 70% of the rated speed? Is a gradual increase in speed a requirement of the compressor or of the turbine? Is the startup procedure exactly the same for an enriched gas compressor with design parameters of 2500 kilowatts and 11,000 revolutions per minute, and an propylene compressor with design parameters of 15,000 kilowatts and 5,500 revolutions per minute? Is it necessary to use nitrogen for startup except for the speed-up curve? Furthermore, for compressors with lower rotational speeds, is the first-order critical speed directly higher than the rated speed?
The acceleration rate driven by a steam turbine is slow, as thermal expansion of the turbine needs to be taken into account; a slower acceleration rate is required to ensure uniform thermal expansion across all parts. Electric drive can achieve a faster acceleration rate. The startup procedure is exactly the same for an enriched gas compressor with design parameters of 2500 kilowatts and 11,000 revolutions per minute, and an propylene compressor with design parameters of 15,000 kilowatts and 5,500 revolutions per minute. Except for the speed-up curve, the unit should be started using nitrogen, and load testing should be carried out to assess its performance, train the operating staff, identify any issues, and have the manufacturer and construction team address them, thereby laying a solid foundation for the long-term operation of the facility. Furthermore, for compressors with lower rotational speeds, the first-order critical speed is not necessarily higher than the rated speed; follow the data provided by the manufacturer.
This post was last edited by CHANGBAISHI on 2020-6-20 07:00. For turbine-driven compressor units, the factor requiring gradual acceleration is solely a requirement related to the characteristics of the turbine section; it has nothing to do with the compressor part, as long as the compressor meets its critical speed conditions. As for centrifugal compressors started with nitrogen, they are all considered to handle flammable and explosive gas media. During the startup of the compressor, mechanical friction and static electricity generated by impacts from mechanical impurities, as well as sparks, can lead to explosion accidents; therefore, nitrogen is used for startup, and only after normal operation does it be switched to the production gas. For reference.
Where is nitrogen-driven technology generally used? Conventional drives are generally steam or electric, while hydraulic couplings are used in certain special applications. Is nitrogen merely an intermediate medium used during the startup process? After normalizing, use the process medium as the driving source?
1. Nitrogen is not used for driving; it is utilized in the startup process of centrifugal compressors to compress flammable and explosive gas media. Due to the dangers that may arise during this process, it is started using nitrogen. Such as oxygen centrifugal compressors,,,。 2. Nitrogen start refers to the medium conversion within the compressor itself, and is not applicable to drive sources.
The speed increase curve is a requirement for the turbine, but 300–500 revolutions per minute seems to have an impact on the dry gas seal； It goes straight to 70% of the rated speed upon startup ； The power grid may be strong enough, but the motor might not be; overcurrent could occur ； It feels like the electric drive is very easy to drive.
At the time, I didn’t understand the exact meaning of the term \"start\" in this context; now, thanks to your explanation, I know that the proper term is gas displacement, which serves to prevent gas explosions. :victory:
Some people say that if an electric-driven compressor starts at a very high speed without gradually increasing its speed, the excessive pressure difference at that moment could potentially cause the nitrogen storage tank to collapse. Is that possible?
Do you mean that as long as the power grid and the main motor can handle it, the compressor can be started and immediately reach a high speed of 90% or more? Does it also include the nitrogen displacement condition? Is it related to the molecular weight of the medium and nitrogen?
They’re all mature products; just use them as is.