Vibrations in the boiler house
From a physical perspective, vibrations occur when oscillations propagate through solid, liquid and gaseous media. Propagation is in the form of waves, e.g. as sound energy or vibration energy. Vibrations can therefore produce audible sound and perceptible vibrations.
In the context of industrial boilers, vibrations refer to visible movements of components and assemblies, which are usually accompanied by noise.
The negative effects of undesirable, excessive vibrations are problematic:
- Risk of mechanical damage to materials (cracks, breaks)
- Risk of unplanned down time due to damage to the boiler system
- Abnormal, loud noises (e.g. rattling)
The boiler body itself does not produce noise emissions on account of its mass. Attachment parts (flue gas chamber, reversing chamber, flue gas lines) are prone to vibrations due to their lower material thicknesses. As resonating bodies, these may propagate sound more easily, resulting in unwanted noise. It is critical when the excitation frequency of the sound source (combustion) matches the natural frequency of the attachment. This leads to increased vibrations.
In order to avoid these operational problems during combustion, it is essential to observe the manufacturer’s specifications. Examples of this include thermo-acoustic faults or impairment of combustion stability or excessive vibrations in parts/components. For this reason, the flue system must be carefully planned and constructed. Low NOx combustion systems in particular are more prone to incorrect flue design due to their combustion dynamics. In addition, it is particularly important in the case of existing flue systems to clarify whether modern combustion systems can be connected to existing flue systems safely and without operating problems. The integration of several boilers into a single chimney is particularly critical. This should generally be avoided.
Information about the flue system
However, the combustion process itself is also subject to requirements in order to avoid unwanted vibrations. The combustion must therefore not transmit abnormal and excessive vibrations or shocks to the boiler at any load point. In addition, the maximum vibration velocity measured at the reversing chamber door or the flue gas chamber and the characteristic/dominant frequencies for combustion operation are defined in the manufacturer’s documentation. It is important to observe these limits. Exceeding the maximum permissible vibration speed may cause damage to boiler components such as the reversing chamber door, flue gas chamber, flue gas heat exchanger and flue gas line.
Technical Information: Requirements of an on-site combustion system