What is the critical speed? Can a centrifugal two-stage compressor operate at the primary critical speed for a long time?

Neither centrifugal compressor nor turbine compressor can be operated at critical speed for a long time, which will have a great impact on the unit!

You can ask Du Niang about what the critical speed is. The running speed of the rotor is less than 0.7 times or greater than the critical speed of 1.3 degrees, otherwise it will cause harm to the rotor.

This post was last edited by Li Yixin on 2017-10-15 22:19. In API 617-2002 (7th) Article 1.5.4, the definition of critical speed (Critical Speed) is as follows: - The speed when the rotor, bearings and their supporting systems are in resonance. - A shaft rotational speed at which the rotor-bearing-support system is in a state of resonance. As shown in the figure, a centrifugal compressor usually operates between the first-order critical speed and the second-order street speed according to API 617-2002 (7th) Chapter 2.6.1.3 regulations: When you purchase a compressor, a resonant structural support system should be included in the supplier's scope of supply. Equipment provided by the supplier, within the specified operating speed range and its safety margin (SM: Separation Margins), there should be no factors that affect the vibration amplitude of the rotor. Rotor dynamic balance analysis should take into account the effective stiffness of the rotor, bearings and their supporting systems (see 2.6.2.4 d). Resonances of structural support systems that are within the vendor's scope of supply and that affect the rotor vibration amplitude shall not occur within the specified operating speed range or the specified separation margins (SM) (see 2.6.2.10 ). The effective stiffness of the structural support shall be considered in the analysis of the dynamics of the rotor-bearing-support system (see 2.6.2.4 d). In section 1 of this standard 2.6.2.10 In the article, the safety margin (Separation Margins) is specified in detail.: The damping unbalance response analysis of the unit should meet the following three requirements for safety margins (SM: Separation Margins): The damped unbalanced response analysis shall indicate that the machine will meet the following SM: a. If the (amplification factor) AF at a specific critical speed is < 2.5, the response is regarded as critical damping, and no safety margin (SM) is required. a. If the AF at a particular critical speed is less than 2.5, the response is considered critically damped and no SM is required. b. If the (amplification factor) AF at a specific critical speed is ≥ 2.5, and the critical speed is lower than the minimum speed of the unit, the safety margin (SM: As a percentage of the minimum speed) shall not be less than SM=17(1-1/(AF-1.5)) or the value 16, whichever is smaller. b. If the AF at a particular critical speed is 2.5 or greater and that critical speed is below the minimum speed, the SM (as a percentage of the minimum speed) shall not be less than the value SM=17(1-1/(AF-1.5)) or the value 16 which ever is less. Note: In other words, when the critical speed is less than the minimum speed of the unit, the safety margin SM from the first-order critical speed is ≤ 0.16·Nmin (minimum continuous speed). 16%·Nmin is the maximum margin value in this case. c. If (amplification factor) AF ≥ 2.5 at a specific critical speed, and the critical speed is higher than the maximum continuous speed, the safety margin (SM: As a percentage of the minimum speed) shall not be less than SM=10+17(1-1/(AF-1.5)) or value 26, whichever is smaller. c. If the AF at a particular critical speed is equal to 2.5 or greater and that critical speed is above the ma * mum continuous speed, the SM (as a percentage of the ma * mum continuous speed) shall not be less than the value SM=10+17(1-1/(AF-1.5)) or the value of 26 which ever is less. Note: In other words, when the critical speed is greater than the maximum continuous speed of the unit, the safety margin SM from the second-order critical speed is ≤ 0.26·Nmax (maximum continuous speed). 26%·Nmax is the maximum margin value in this case. To sum up, the machine is not allowed to operate within the range of the first-order critical speed and its safety margin.

However, the vibration displacement of the unit is not large