Practical experience in reducing noise from rotary blowers used in wastewater treatment

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Why does a Roots blower produce such high noise during operation? First, let’s take a look at the causes of the noise generated by a Roots blower. Rotary vane blowers draw in and discharge large volumes of air at each cycle, with sudden changes in flow rate, which results in high noise levels; they are thus referred to as the \"noise tigers\" among mechanical products. This problem is particularly severe under high pressure, and the higher the volume of air, the greater the pressure, and the faster the rotation speed, the louder the noise becomes. Modern large-scale production, on the other hand, expects rotary vane blowers to provide higher pressure and greater air volume. The noise of rotary blowers includes mechanical noise and aerodynamic noise, with aerodynamic noise further comprising rotational noise and vortex noise. Mechanical noise mainly includes gear noise, bearing noise, and pipeline vibration noise. Rotational noise is generated by significant changes in both the circumferential aerodynamic pressure and gas flow velocity when a rotating impeller passes through the exit of a narrow channel; these changes lead to periodic suction and exhaust processes, as well as instantaneous isochoric compression, thereby creating flow velocity and pressure fluctuations that result in substantial aerodynamic noise. Eddy current noise, also known as turbulent noise, is caused by pressure fluctuations in the airflow resulting from the turbulent boundary layer and its separation. On the one hand, as the impeller rotates, vortices are formed on its surface, and these vortices generate vortex noise when they separate on the surface. On the other hand, high-pressure gas leaking from the gaps into the low-pressure area also produces noise as it passes through orifices and bends. These noises, combined with the Helmholtz resonance of the fan’s intake volume, result in noise levels at the Rohts fan that are unbearably high. Sound absorption for noise reduction is a method designed to control the intensity of noise during its propagation. Rotary vane fans primarily use materials to absorb noise; this sound-absorbing effect is quite strong and widespread, and it is closely related to indoor spaces or the absorption structures in place. The Roots blower silencer is a device designed specifically for noise reduction, developed as a result of the continuous progress in science and technology. It is used in various mechanical devices, and it proves to be quite effective at reducing noise. When installed on mechanical equipment or engines, it provides excellent sound absorption results. It has truly achieved an ideal level of noise reduction in these areas, places emphasis on wide technical recognition, and has thus established an advantage through its advanced technology. http://www.hcblower.com/wp-content/uploads/2016/10/%E9%A3%8E%E6%9C%BA%E6%B6%88%E5%A3%B0%E5%99%A8.png For fans used in field applications, different control measures can be adopted based on the level of fan noise, the conditions at the site, and the noise reduction requirements. These measures generally include installing silencers, adding soundproof enclosures, modifying the fan room, or wrapping the pipes. 1. Methods for controlling mechanical noise: For the mechanical noise of Roots blowers, the main method of control is to improve the accuracy of assembly ； Replace the old ball bearings, or use sliding bearings in place of rolling bearings, to achieve dynamic balance of the rotor ； Connect the motor and blower with an elastic coupling ； Strengthen the maintenance of equipment, including refueling and lubrication, tightening connected bolts, replacing damaged parts, and so on. These are all effective in reducing noise in Roots blowers. 2. General control methods for aerodynamic noise (1) Installation of silencers. Under normal circumstances, the aerodynamic noise emitted from the fan’s inlet and outlet is 10–20 dB(A) higher than the noise emitted from other parts. Therefore, when controlling fan noise, appropriate silencers should first be installed on the inlet and outlet ducts. Silencers are used on fans, and currently both domestically and internationally there is a tendency to use resistive silencers; silencers that are large in size and have a narrow noise reduction range are rarely used. Of course, the selection, design, and installation of silencers should be based on actual conditions. (2) Install sound insulation enclosures for rotary vane fans; related products: sound insulation enclosures for rotary vane fans. The sound insulation measure involves enclosing the entire fan unit within a sealed sound insulation enclosure. The key technical aspect lies in determining what cooling measures to use to ensure the proper operation of the fan. Currently, air cooling is used both domestically and internationally. The main cooling methods include: self-ventilated cooling, negative pressure air extraction cooling, air circulation ventilation cooling within a enclosure, and external mechanical ventilation cooling. http://www.hcblower.com/wp-content/uploads/2016/10/%E9%A3%8E%E6%9C%BA%E9%9A%94%E9%9F%B3%E7%BD%A9.jpg (3) Renovating the fan room: If there is a dedicated fan room for the fan unit, it is possible to adapt it into a sound-insulated space by taking into account the specific conditions on site. In other words, the fan is enclosed within a fan room to prevent its noise from escaping. The main technical measures include the use of soundproof doors, soundproof windows, soundproof barriers, and soundproof walls, as well as the application of appropriate sound-absorbing materials. (4) Pipe wrapping: To reduce the noise radiating from the fan ducts, the pipes can be wrapped in a spiral pattern, thereby blocking the pathways through which noise can spread. (5) Vibration isolation takes into account factors such as safety, stability, and ease of maintenance; appropriate isolators are selected in the design to eliminate the rigid connection between the machine and the unit, thereby reducing solid vibration noise. Vibration isolation ditches can also be dug as a substitute for foundation vibration isolation, achieving certain effects. Furthermore, if proper maintenance is not carried out, the noise level may increase. What should we do when the noise increases? 1. Pressure increase due to blocked pipes – in this case, it is necessary to clean or replace the pipes. 2. Vibration caused by improper installation of the belt cover – in such cases, checking and reinstalling the belt cover will suffice. 3. Wear of the motor bearings – new bearings need to be installed. 4. Dust entering the Roots blower, resulting in wear – the blower needs to be disassembled for repair (it is advisable to hire a professional for this task; do not attempt to disassemble it yourself). 5. Lack of lubrication can also cause high noise levels – in this case, check the lubrication system. 6. Poor lubrication – the oil nozzles and oil filters should be cleaned regularly. 7. Loose pulleys – tighten the set screws. 8. Slipping of the V-belt – adjust the belt tension. The points mentioned above cover the analysis of why rotary vane fans generate noise and the corresponding solutions. In such situations, these guidelines can be used to address the noise issue. If the noise from a rotary vane fan increases, there’s no need to panic; first, stop the fan and investigate the cause. If the cause cannot be identified, consult a professional manufacturer specializing in the repair of rotary vane fans. No matter how high the quality and performance of a rotary vane fan are, regular maintenance is essential – only by carrying out proper maintenance can the fan’s lifespan be extended.