Noise control of 6000m3/h oxygen generator

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Noise Control of 6000m3/h Oxygen Generator The 3# oxygen generator unit of Xinlin Steel Oxygen Plant is produced by Kaikong Company and adopts molecular sieve adsorber pre-purification with booster expander and full distillation argon production process. The yield and purity of its main products are shown in Table 1. Table 1 Product output and purity of the 3# oxygen generating unit of Xinlin Steel Oxygen Making Plant Product output/(m3/h) Purity/% Pressure/kPa Oxygen 6000>99.624.5 Nitrogen 1260>99.99916.4 liquid Oxygen 200>99.6143 Liquid nitrogen>99.999447 According to the production characteristics of oxygen, Xinlingang has effectively controlled the noise of relevant equipment, thereby improving the production environment and ensuring the normal production. The main noise sources of Xinlingang 3# oxygen generator are:: Air compressor and oxygen compressor, expander and exhaust noise of polluted nitrogen, low-pressure oxygen, high-pressure oxygen, nitrogen, etc. 1 Noise control technology 1.1 Noise control technology of air compressors The noise of air compressors is mainly aerodynamic noise, mechanical noise and electromagnetic noise, with aerodynamic noise being the main component. Aerodynamic noise is composed of airflow vortex noise, impact vibration noise and rotational noise. It is related to the speed of the air compressor and the shape of the impeller structure, shaft power, number of blades, etc., as well as the size and shape of the intake and exhaust pipes. Mechanical noise is the noise generated by bearing friction and gear transmission vibration. The electromagnetic noise of the air compressor is caused by the interaction of variable forces on the air in the air gap of the motor. The control of air compressor noise mainly focuses on controlling aerodynamic noise and mechanical noise. A sound insulation cover is set up to isolate the aerodynamic noise, mechanical noise and some electromagnetic noise generated by the air compressor body and motor. At the same time, a dispersion muffler is installed to reduce the noise generated when high-pressure air is dissipated. Consider the noise generated by the gas surge at the pipe outlet and pipe sides and the vibration of the pipe wall, and adopt sound insulation bandaging. (1) Sound insulation cover. The sound insulation index used to evaluate the sound insulation cover is represented by the insertion loss IL. The calculation formula is: IL=10log(1+a／τ) (dB). It can be seen that the greater the sound absorption coefficient a of the material used in the sound insulation cover, the smaller the average transmission coefficient τ, the greater the insertion loss IL, and the better the sound insulation effect. The noise of the DH760 air compressor supporting the Xinlingang 3# oxygen generating unit is high-frequency noise. In terms of blade rotation noise at all levels, its frequency is: The level 1 fundamental frequency is 3419Hz, the level 2 fundamental frequency is 3077.4Hz, the level 3 fundamental frequency is 3816Hz, and the level 4 fundamental frequency is 3392Hz. Ultra-fine glass wool (density 25kg/m3~30kg/m3) is used in the design, with a thickness of 100mm~120mm. Its sound absorption coefficient for each frequency is shown in Table 2. Table 2 Sound absorption coefficient of ultra-fine glass wool at each frequency (density 25kg/m3~30kg/m3) Frequency/Hz125250500100020004000 Sound absorption coefficient/a0.050.240.720.770.90.98 The cover wall uses a 3mm thick cold-rolled plate protective surface, and the inner protective surface uses a 1.2mm thick perforated plate (galvanized), and is lined with glass fiber cloth to enhance the noise reduction effect of low-frequency noise and avoid material loss. The frame is 5mm thick channel steel, and rubber pads are used to isolate vibrations from the foundation or floor to prevent resonance noise. Since the air compressor is large, the overall dimensions of the sound insulation cover are 9000mm × 7600mm × 3000mm. It is assembled in a modular structure and the modules are connected with bolts. In order to dissipate the heat generated during the air compression process, four air inlet ducts and two exhaust ducts are opened on the hood, and axial flow fans are used for forced ventilation. In order to prevent the generation of secondary noise, the design uses anechoic channels. (2) Disperse the muffler. The noise control of the relief port after the air compressor relief valve uses a resistive muffler, which relies on the sound absorption effect of sound-absorbing elements or sound-absorbing structures arranged in a certain way in the pipeline. The viscous effect of the airflow in the micropores of the sound-absorbing element converts part of the sound energy in the noise propagating along the pipe into heat energy and is consumed, thereby achieving the purpose of silencing the sound. The sound attenuation amount of a resistive muffler is related to the sound absorption coefficient of the material used, the width of the airflow free channel, the airflow speed and the length of the muffler. The greater the sound absorption coefficient of the material, the narrower and longer the free channel, the lower the air flow velocity, and the better the noise reduction effect. This kind of muffler has a good silencing effect on medium and high frequency noise. (3) Pipe wrapping. The outlet pipe of the air compressor with a diameter of 450mm is wrapped with sound insulation. The sound insulation material is slag cotton felt, the thickness of the sound insulation layer is 50mm, and the outside is covered with galvanized iron sheet. By taking this measure, the noise at 1m away from the pipe can be reduced to 84dB. 1.2 Noise control process of oxygen compressor The Xinlingang 3# oxygen generating unit is equipped with a 3TYS78+2TYS56 turbine oxygen compressor (10000m3/h). Similar to an air compressor, the noise is also composed of gas dynamic noise, mechanical noise and electromagnetic noise, and gas dynamic noise is the main component. Therefore, the ideas and methods of treatment are similar to those of air compressors. By setting up a 12600mm×5400mm×3000mm sound insulation cover, the aerodynamic noise and mechanical noise generated by the compressor body and the speed increaser are isolated. The material and structure of the sound insulation cover are similar to those of the air compressor. (1) Oxygen high and low pressure dispersion muffler. Oxygen emission noise reduction also uses resistive mufflers. Only the forms of high-pressure venting and low-pressure venting are different. High-pressure vent muffler is mainly used to eliminate high-frequency noise, and its form is similar to that of air compressor vent. ； The low-pressure vent muffler uses a resistive muffler, and the sound-absorbing material is slag wool. (2) Firewall. The suction port and discharge port of the oxygen compressor, the five intercoolers and the connecting pipes can all be installed below the 5m platform. In order to prevent the spread of fire in the event of a fire, a firewall is designed. The firewall is 240mm thick and is a brick wall plastered on two sides. Where the pipes pass through, it is filled with glass wool. This setting also plays the role of sound insulation. The noise value inside the wall is 105dB-110dB, and the noise value 1m outside the wall is 90dB. 1.3 Control of other noise sources In addition to the main noise sources mentioned above, the 3# oxygen generating unit also has pollution nitrogen venting noise, low-pressure nitrogen venting noise, etc. Mid-frequency mufflers are used to reduce noise when venting nitrogen and contaminated nitrogen. During normal production, the waste nitrogen is recovered from the cooling capacity through the water cooling tower and then vented. In the water-cooling tower, the flow rate is reduced due to evaporative cooling (about 1.2m/s), and then rises during the period, so it can play a silencing effect. 2 Effect Analysis and Suggestions After taking the above measures in noise control for Xinlingang 3# oxygen generating unit, the noise prevention and control effect is obvious. The treatment effect of the sound insulation cover is shown in Table 3. Table 3 Treatment effect of sound insulation cover (unit: dB) Side measurement point Average reduction inside the sound insulation hood Outside the sound insulation hood The first floor of the air compressor 1151181169189939291.2524.75 The second floor of the air compressor 102104103808383.28282.0520.95 The first floor of the oxygen compressor * 1051071068890888888.517.5 Oxygen compressor second floor 9695.696798080777917 Note: * For the sound insulation inside the firewall. High-pressure oxygen venting and venting resistive mufflers of air compressors also play a certain role. When oxygen is vented at high pressure (5m away from the muffler) the noise is 106dB ~ 108dB ； The background value here is 73dB. When the air compressor is vented (10m away from the muffler) the noise is 93dB ~ 98dB, and the background value here is 77dB. Judging from the measurement results, if no resistive muffler is installed, such injection noise is quite large, and theoretically calculated should be greater than 125dB~128dB. It can be seen that due to the high frequency and high energy of injection noise, the effect of using previous resistive mufflers is not very satisfactory. The effect of the mid-frequency muffler used when venting nitrogen and polluted nitrogen is more obvious, with an average noise reduction of 15dB~23dB. In addition, the sound insulation effect of pipe wrapping is also ideal. Taking air pipes and high-pressure oxygen pipes as examples, the noise of the air pipes before being bandaged (at 1m) is 93dB, while after bandaging it is 84dB. ； The noise of the high-pressure oxygen pipeline before being bandaged (at 1m) is 108dB, while after bandaging it is 87dB. The situation around the unit factory is also relatively good. When measured about 5m to 8m away from the factory, the noise under the filter in front of the machine is 77dB, and the noise elsewhere does not exceed 71dB. In short, the noise prevention and control measures of Xinlingang’s 3# oxygen generating unit were relatively successful. However, for the treatment of injection noise caused by high-pressure oxygen venting and air compressor venting, the author believes that it is better to use a small hole muffler or a slit muffler.