Noise control of ash removal air compressor room i

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Noise control of ash removal air compressor room in thermal power plant

Abstract: ash removal air compressor is one of the strong noise sources in thermal power plant. How to effectively control the impact of its noise on the outside world is a problem that power plants should face in environmental protection. This paper introduces the measures taken in the noise control process of the dust removal air compressor room of Chengdu Thermal Power Plant and the control effect, which has a certain reference value for the noise control of similar workshops in power plants

key words: air compressor; Noise; The control party

the ash removal air compressor of the thermal power plant is a special equipment for the gas supply of the dry positive pressure pneumatic ash removal system. The noise frequency band of this kind of air compressor is wide, and the source intensity value is generally between 95 ~ 100 dB (a), which is one of the strong noise sources of the thermal power plant. The dust removal air compressor room of Chengdu thermal power plant is equipped with 10 sets of dust removal air compressors. During operation, strong noise is radiated to the outside through the workshop doors and windows, which has a great impact on the surrounding environment

1 noise condition of ash removal air compressor

1.1 noise characteristics of sound source

air compressor is a sound generator with multiple sound sources, and its noise is mainly intake noise, exhaust noise, mechanical noise and electromagnetic noise

1.1.1 intake noise

with the intermittent opening of the air compressor cylinder intake valve, when the air flow is intermittently sucked into the cylinder, pressure fluctuations are generated near the intake port, which radiates from the intake port in the form of sound waves, resulting in a wide range of intake noise conditioning; Adopt servo electromechanical transmission technology. The air inlet noise is about 100 dB (a), and the air inlet noise is 7 ~ 10 dB (a) higher than that of other components. It is the main noise source of the air compressor

1.1.2 noise at the exhaust port

noise caused by airflow disturbance when the gas is discharged intermittently from the cylinder valve

1.1.3 mechanical noise

when the air compressor is running, many parts rotate and reciprocate rapidly, causing friction and impact, causing the noise generated by the vibration of the machine parts, and its sound level is about 90 dB (a)

1.1.4 electromagnetic noise

noise caused by the magnetic field pulsation of the drive motor

in addition, the motor cooling fan also causes air flow noise

there are 10 sets of ash handling air compressors installed in the ash handling air compressor room of Chengdu thermal power plant. Due to the high speed of the air compressor (1843 r/min), its noise shows obvious medium and high frequency characteristics. Due to the superposition of the sounds of various parts, the total sound level is quite high. The air compressor emits a lot of heat during operation, and the existing equipment has been equipped with sound insulation covers, but the doors of the sound insulation covers are mostly open or semi open during operation, so the role of the sound insulation covers is difficult to give full play. Measured at a distance of 1 m from the equipment, the operating noise of a single ash handling air compressor is up to 100dB (a) when the sound insulation cover door is opened, and it shows broadband characteristics. See Table 1 for its spectral characteristics

1.2 impact of noise in the ash handling air compressor room on the outside

the ash handling air compressors have been installed with sound insulation covers, and the operating noise can be reduced by about 15 dB when the sound insulation cover door is closed. However, since the four walls in the workshop are smooth walls, the reverberation is very serious, and the occurrence of this reverberation can increase the indoor sound pressure level by 10 ~ 12 dB

the workshop is located about 50 m away from the plant boundary, and the noise impact on residents outside the plant mainly comes from the workshop. Through the on-site investigation, it is found that the noise in the workshop is radiated to the outside through the doors and windows, and the direction of sound transmission is changed by the reflection of nearby buildings. The impact on residents outside the factory is not only from the front door of the workshop, but also an important factor that the reflection of buildings leads to the accumulation and superposition of noise. It can be seen from the monitoring results of the ash removal air compressor room (see Table 2) that the workshop door facing the factory boundary is ordinary gold, such as rice husks and straw, which can be ground into powder and added to the materials. It is a rolling shutter door. When the door is opened, the noise monitoring result at 1m outside the door is 83.8 dB (a), and when the door is closed, it is 79.6 dB (a). Because the amount of chlorinated compounds such as thin metal doors may be small, the critical frequency is high, and the sound insulation is less than 5 dB

2 noise control scheme of ash removal air compressor room

2.1 control method and principle

from the above analysis, it can be seen that the noise of air compressor is mainly concentrated in the frequency range of 250 ~ 4 K (Hz), especially in the medium and high frequency. According to the noise characteristics, using the acoustic principles of sound insulation, absorption and resonance, taking plugging measures, using external isolation, internal absorption and silencing methods for comprehensive treatment, can effectively control the noise at the plant boundary affected by it

since the air compressor has been put into normal operation, it is difficult to take further noise reduction measures for the equipment itself. Therefore, a treatment scheme focusing on sound absorption and sound insulation has been adopted for the workshop to reduce the sound pressure level of this total sound source

2.1.1 sound absorption

the workshop walls are ordinary painted walls, and the sound absorption coefficient will not exceed 0.03. When the original sound absorption is very small, the method of using sound absorption structure or materials to improve the indoor average sound absorption coefficient can effectively reduce the indoor reverberation

the amount of sound absorption and noise reduction is obtained from the following formula:

2.1.2 sound insulation

the material of the outer wall of the workshop is 240 mm brick wall, but the front door is an ordinary metal fireproof roller shutter door, and the sound insulation is very limited. There are many wall windows on both sides of the workshop, accounting for a large proportion of the wall area. From the perspective of sound insulation, the average sound insulation loss of 240 mm brick wall with two joints from 125 to 4000 Hz can reach 53 dB (a). However, due to the large total area of doors and windows, the sound insulation loss of the whole wall is not high

total sound insulation loss of sound insulation assembly with doors and windows:

where: R1 - sound insulation loss of wall itself (i.e. wall surface except doors and windows) (DB)

r2 - sound insulation loss of door or window (DB)

s1 - wall area (deducting door and window area) (m)

s2 - door and window area (m)

for buildings with brick concrete structure, the impact of indoor noise on the outside can be reduced by improving the sound insulation of weak links such as doors and windows

2.2 design principle of treatment scheme

the ash removal air compressor room is a heat generation workshop, and the noise treatment must fully consider the requirements of indoor ventilation to protect the equipment from being affected

2.3 treatment measures

in order to reduce the impact of the ash removal air compressor room on the surrounding environment and not affect the normal operation of the equipment, the following measures are mainly taken in the treatment plan:

1) the original fire shutter door and the side door of the workshop are replaced with sound insulation doors, the size of the sound insulation doors maintain the size of the original doors, and the sound insulation doors at the front of the workshop adopt the form of double doors to ensure the normal operation of forklifts during equipment maintenance

2) close the windows facing the plant boundary and residential side with ordinary 240 mm clay bricks to eliminate the impact of direct sound on the outside, fix the steel window on the other side of the workshop (not open), and add a layer of closed and fixed sound insulation windows on the outside. The spacing between the two layers of windows is 100 mm, and the sound insulation windows use 8 mm thick glass

3) centrifugal glass wool board with an average sound absorption coefficient of 0.7 is selected, and the installation method of erecting metal keel and then filling sound-absorbing materials is adopted to fix it on the internal wall and top of the workshop. Metal perforated plates and gusset plates with a perforation rate of more than 20% are used as protective decorative materials for wall and top sound-absorbing materials. The purpose of this action is to reduce the noise caused by reverberation in the workshop by 4 ~ 10 dB (a)

4) in order to meet the requirements of indoor ventilation and cooling, forced ventilation measures are taken for closed workshops. Air inlets are set at the bottom of the walls on both sides near the front door of the workshop and silencing devices are installed. At the same time, two high-power exhaust fans are installed at one side of the indoor duty room. Silencing pipes are used to send hot air out of the room, which is an instrument for detecting the impact resistance of metal materials under dynamic load

3 noise control effect of ash removal air compressor room

after the implementation of the above scheme, the noise outside the workshop has been close to the local value of the environment, and the indoor reverberation has also been significantly reduced. After testing, the sound level 1m outside the front door of the workshop decreased from 79.6db (a) before treatment to 54.0db (a), and the noise reduction amount reached 25.6db (a); The indoor reverberation sound level decreased from 82.0db (a) before treatment to 74.0db (a), and the attenuation was 8.0db (a). The effect was very significant (see Table 3)

4 conclusion

there are many noise sources in thermal power plants, and the factors leading to excessive noise at the plant boundary are complex, but the influence of high-noise workshops and equipment close to the plant boundary is dominant. From the perspective of environmental protection, it is very necessary to reduce the overall noise level of such workshops to protect residents outside the plant. The noise control methods and results of the ash removal air compressor room have certain reference value for the noise control of similar workshops in power plants. (end)

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