Cooling Tower Resonance Problem
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In a biomass power plant, an urgent support was requested from the Resonance Institute technical team due to high amplitude vibration experienced in the cooling towers during the commissioning phase.
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During field observations, the existence of a " structural vibration " problem that also affected the cooling tower base was detected.
Problem:
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In the vibration measurements taken simultaneously with the Motion Amplification camera and the 16-channel vibration analyzer within the Structural Vibration measurement package, it was determined that the vibration amplitudes on the cooling tower gearbox and motor were around 32 mm/s RMS . As such, according to the table in the " CTI STD 163 " reference standard, vibration levels are in the range of " Zone D: Vibration damages the machine ".
Diagnosis:
Blade Pass Vibration
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Simultaneously with the measurements taken with the analyzer, reecordings were taken from outside and inside the tower with the Motion Amplification camera.
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The camera was placed on a basket attached to the crane in order to prevent the recordings from being affected by high-amplitude vibrations on the ground.
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In the recordings, it is clearly seen what kind of vibration pattern the base has at the 16.5 Hz blade pass frequency .
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As a result of examining the data collected simultaneously from the 16-channel analyzer , it was determined that high amplitude vibrations were at the tower fan blade passing frequency .
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The hump below the blade pass frequency indicates that the situation has turned into a resonance problem.
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The blade pass vibrations examined in the flow-induced vibration group occur at times the number of blades per revolution. The fact that the resulting vibrations are so high is due to the fact that this flow related frequency excites a natural frequency and creates a resonance problem.
As seen in the videos, in order to eliminate the structural vibration problem in the base, the effective natural frequency of 16.5Hz must be removed from the operating range.
For this purpose, it is recommended to use the support profiles shown in the picture below.
After the support work applied as recommended, it was observed that the vibration values decreased to acceptable levels according to the CTI STD 163 standard.
Conclusion:
