Non-sinusoidal Vibration of Crystallizer
Crystallizer is a device used to generate crystalline masses from a supersaturated solution. To produce large crystal quantities, high efficient crystallization process is needed. Unfortunately, due to different transport limitations, crystallization usually accompanied with non-sinusoidal vibration. Identifying and controlling this kind of vibration are crucial in order to improve the crystallization efficiency and process stability.
Non-sinusoidal vibration of crystallizer has several forms, including double-frequency vibration, multiple-frequencies vibration and variable-frequencies vibration. Double-frequently vibration appears in the operation with high loading capacity and low heat transfer coefficient. This phenomenon is induced by rotational wear in the agitating system. With the rotational speed speeding up, wear of the impellers increase, thus resulting double frequency vibration. Multiple-frequencies resonance usually arises from the contact between electrical motor and impellers, and this resonance is usually harder to identify. Variable-frequencies vibration originates from the differences in the mass density of different materials at different operating conditions, and it may show up when the temperature or agitation speed is varied.
Non-sinusoidal vibration leads to a lot of problems. The vibration will create a lot of noise, which is uncomfortable to the operators, and the tank wall may be damaged by the resonance in the vibration. The hydraulic force on the impeller may also be changed by the non-sinusoidal vibration, which seriously impacts the efficiency of the crystal producing process. Even more seriously, the unstable vibration may form multiple layers in the chamber, thus making the reaction uneven, which would further reduce the efficiency or lead to poor product quality.
Therefore, non-sinusoidal vibration must be detected and prevented. Usually the resonance component can be isolated and identified by frequency analysis with the help of signal-measuring instruments. After the source is identified, preventive measures can be carried out in order to reduce the vibration. The most popular solution is to add flow deflectors or vibration absorbers, which can both interfere the resonance component and reduce the vibration. Recent studies have also showed that the design of the motor and impeller can also reduce the resonance component of the non-sinusoidal vibration.
In conclusion, non-sinusoidal vibration of crystallizers can be caused by different factors, and it is important to identify and control this type of vibration in order to maintain a high efficiency and process stability. Frequency analysis and signal-measuring instruments are necessary means of solving the problem. Along with vibration-absorbing equipment and motor optimization, we can prevent the vibration and improve the overall production efficiency.
