There are many types of cooling towers, and closed cooling towers have an obvious cooling effect on heating equipment and have become indispensable, but the noise it produces has also become a headache. As an important part of thermal power plants, natural draft cooling towers have high noise sources. So what methods do we have for the noise control of these two cooling towers? The following will introduce to you how to control the noise of closed circuit cooling towers and the basic situation of noise of natural ventilation cooling towers.
1. How to control the noise of closed cooling towers.
In view of the noise characteristics of cooling towers, the following treatment measures are often taken.
1. Replace the ordinary motor blades with low-noise blades to fundamentally reduce the noise level from the source.
2. The noise of the exhaust outlet has the characteristics of continuous spectrum, and the sound absorption treatment is considered.
3. To avoid noise caused by mechanical resonance, the cooling tower is hard-connected for vibration damping.
4. Add rapid filtration packing in the water tray to reduce the noise of water spraying.
5. Surround the tower and the pump with a waterproof sound absorption barrier to cut off the noise transmission path.
6. Add a fixed air duct or a silencing cap to the air outlet of the closed cooling tower to orient the noise to the direction that does not require noise, and the silencing cap can reduce the frequency of sound vibration to achieve the effect of reducing noise.
7. For the sound of water flow, the noise of water flow is reduced by adding a silencing blanket.
Second, the basic situation of natural ventilation cooling tower noise.
1. Noise type of natural ventilation cooling tower.
Natural draft cooling towers will produce water spray noise, pump noise, water pipeline and valve vibration noise under normal operation. Among them, the water spraying noise is the main noise source of the natural ventilation cooling tower, that is, the water droplets that fall at high speed and have a large area of continuity collide with the water surface, and the generation of water spraying noise may also be because of the sound of nozzles sprinkling water on the filler, and the sound of falling water droplets colliding with each other, of course, these have very little impact on the noise, so they can be completely ignored.
2. Noise characteristics of natural ventilation cooling towers.
The noise generated by the natural ventilation cooling tower is equivalent to dozens of times the intensity of the storm, and the high-density water droplets have a large area and continuous impact on the ground and steel plate beams and columns, so the noise source has the characteristics of large, high-level, frequency bandwidth, and long propagation distance, which will also have an impact on the surrounding environment.
The noise intensity far exceeds the national standard.
3. The mechanism of noise generation of natural ventilation cooling tower.
1) The noise generated by the wet natural ventilation cooling tower is mainly precipitation noise, that is, the noise generated by the water falling into the pool. The water droplets at the packing layer, under the action of gravity, fall with acceleration, and their potential energy is converted into kinetic energy. When a droplet with a certain velocity hits the surface of the sump water, a portion of the kinetic energy is converted into sound energy.
Radiates high-frequency noise at a high level in all directions. At the same time, the volume pulsation of the bubbles generated by the water droplets hitting the surface of the sump will also radiate a relatively sharp noise. The precipitation noise increases with the increase of the amount of water, the density of the water, the quality of the water droplets, and the height of the water fall, and is related to the wind speed in the tower, because the upward airflow reduces the falling speed of the water droplets.
2) The noise of the cooling tower also includes the sound of nozzle water distribution on the packing, the convection of the air entering the tower will produce noise, and the sound of falling water droplets colliding with each other, but the noise is much smaller than that of precipitation. In addition, water temperature also has an effect on noise, because water temperature affects the surface tension of water, and the test shows that the water temperature of the pool increases by 10 for every 10 years.
The sound pressure is reduced by about 1db.
3) From the analysis of the sound generating mechanism, the noise of natural ventilation cooling tower is mainly caused by the high-speed falling water droplets hitting the water surface, and the sound of other nozzles distributing water to the filler, the sound of falling water droplets colliding with each other, and the air convection noise can be ignored.
4. Noise treatment measures for natural ventilation cooling towers of large power plants.
1) Start with the equipment aspect.
According to the generation, characteristics and propagation mode of noise, the control of noise can be divided into three links: sound source control to prevent noise generation, to block the propagation of noise to a large extent, and to weaken noise in the process of propagation. Noise testing is carried out at several identified locations before noise can be treated.
Near-field test, noise test at the boundary of the plant and noise test at the residential area, and noise control according to the test results. In the process of governance, it is necessary to control noise from the sound source, and an important point is to start from the equipment, and only from the place where the noise is generated can the noise generation be reduced to a large extent. The first is the choice of materials, to choose durable, impact-resistant materials.
It is important to make sure that the chosen material does not resonate, otherwise it will greatly affect the noise reduction effect.
2) Solve the problem from other aspects.
A sound barrier is a barrier between a noise source and a sound receiving point, and it is usually designed for a specific sound source and area. The noise reduction effect of this method is to create a difference in sound pressure level at a specific location while keeping the noise source, topography and climatic conditions constant.
When a noise source encounters a sound barrier, there are three paths to propagate: diffraction from the top and sides to the sound receiving point; Some of them went straight through the sound barrier; Others are reflected.