The gas generator set consists of gas engine, generator, control cabinet and other components. The gas engine and generator are installed on the same steel chassis. The unit is fueled by combustible gases such as natural gas, wellhead associated gas, coal mine gas, water gas, refining tail gas, biogas, coke oven gas, blast furnace gas, etc. It is quick to start and has good economy. Especially due to the demand of high-quality urban life, the gas generator unit has been widely used in telecommunications, post offices, banks, libraries, hospitals, hotels and other departments as a backup power supply. At first, the gas generator unit was designed for the mine conditions, and the noise generated by the unit during operation is generally 95~110 dB (A). G
B 3096-93城市区域环境噪声标准对市区的噪声状况进行了严格的规定,对于2类区域(居住、商业、工业混杂区)昼间为60 dB(A),夜间为50dB(A);对于1类区域(居住、文教机关区)昼间为55 dB(A)、夜间为45 dB(A)。机组运行时产生的噪声给城市环境带来了严重的噪声污染,影响了人们的正常工作和生活,也限制了燃气发电机组的广泛应用。本文就是针对燃气发电机组噪声污染问题,提出了一套整改措施,以期降低机组噪声,促进燃气发电机组的推广应用。
B 3096-93 urban area environmental noise standard has strict regulations on the noise situation in the urban area. For Class 2 areas (residential, commercial and industrial mixed areas), it is 60 dB (A) in the daytime and 50 dB (A) at night; 55 dB (A) in the daytime and 45 dB (A) at night for Class 1 areas (residential, cultural and educational institutions). The noise generated by the unit operation has brought serious noise pollution to the urban environment, affected people's normal work and life, and also restricted the wide application of gas generator units. This paper proposes a set of rectification measures to reduce the noise pollution of gas generating units and promote the popularization and application of gas generating units.
1. Sound source analysis
The noise of gas engine is the main noise source of gas generator set. The noise of gas engine can be divided into aerodynamic noise, combustion noise, mechanical noise, exhaust noise and vibration noise. Aerodynamic noise mainly includes air vibration noise caused by air inlet, exhaust and fan rotation, and this part of noise spreads directly into the air. The pressure vibration generated by combustion in the cylinder passes through the cylinder head, and the noise radiated from the engine body is called combustion noise; The impact of the piston on the cylinder liner and the impact vibration noise generated by the moving parts such as the valve train and the jet system are collectively referred to as mechanical noise. When the unit is working, the exhaust gas rushes out of the exhaust valve at high speed, enters the muffler along the exhaust manifold, and finally discharges into the atmosphere from the tail pipe. Exhaust noise is the largest noise of the engine, which is usually about 15 dB (A) higher than the noise of the engine host, followed by combustion noise, mechanical noise, fan noise, and intake noise.
2. Reconstruction design
Based on the working principle of the gas generator set, it is difficult to reduce the noise of the sound source, so the main thing is to effectively block its noise transmission path. The core of noise elimination technology is to reduce the pollution surface of noise by using the law of natural attenuation of sound waves in transmission.
The specific methods to reduce noise are as follows: sound absorption, sound insulation and changing the direction of noise propagation. In practical engineering applications, only one of these methods is often used. In this paper, a new combined noise reduction technology is proposed for gas generator units by using three methods together.
(1) Combined muffler
The original muffler is mainly based on resistive noise elimination, with high power consumption and poor noise elimination effect. After careful demonstration, the muffler is transformed into a new type of combined muffler by using the three-level combined noise reduction technology. The main components of the combined muffler are the anti-jet muffler damping cavity, the porous muffler cover, the sound absorption insulation layer and the sound absorption resonance plate. The sound source can fully dissipate the noise energy of the medium and low frequency sound sources through the first stage of the anti-noise cavity. The two-stage porous resistive muffler can eliminate most of the high-frequency noise, increase the adaptability of the muffler to the high-frequency, and install high-efficiency sound absorption materials in the cavity, which can fully absorb and change the direction of the noise, so as to maximize the consumption of noise energy. The third stage is the specially designed exhaust pipe with resonance plate, which is further silenced by the vibration of the sheet.
According to the test, the new muffler is superior to the original muffler in terms of noise reduction, frequency range of noise reduction (mainly the frequency range of peak noise reduction) and resistance loss. In addition, the muffler has proper size, good structural rigidity, convenient installation and the function of suppressing regenerative noise. Moreover, the sound absorption and sound insulation layer at the rear has anti-corrosion performance, which can effectively overcome the low temperature dew point corrosion of flue gas and prolong the service life of muffler.
(2) Two-stage vibration isolation pad
The effective way to control mechanical noise and combustion noise is to isolate the unit. Composite vibration isolation and damping pads are installed between the gas engine, generator and steel chassis, and high-efficiency damping rubber pads are also installed between the chassis and the foundation. After two-stage vibration isolation treatment, not only the vibration of the unit is effectively isolated, but also the operation of the unit is more stable and the overall noise is significantly reduced.
(3) Anechoic exhaust duct
Fan noise is composed of rotating noise and eddy current noise. The rotating noise is caused by the periodic disturbance of the air flow cut by the rotating fan blades. Vortex noise is a series of vortex flows formed by gas slipping or splitting when boundary layer separation occurs on the cross section of rotating blades, which radiates a kind of unsteady flow noise. The exhaust duct is directly connected with the outside, and the air velocity is very high. The air flow noise, fan noise and mechanical noise are radiated out through this channel. In order to control the noise of fan and exhaust duct, a silencing exhaust duct is designed. This silencing exhaust duct has a large length and is composed of air duct and exhaust noise reduction chamber. The working principle of the exhaust noise reduction chamber is similar to the resistive muffler. The sound attenuation effect can be improved by changing the sound-absorbing material (changing the sound-absorbing coefficient of the material), the thickness of the sound-absorbing material, the length and width of the exhaust passage and other parameters.
(4) Anechoic inlet
The unit works in a closed machine room. In a broad sense, the air inlet system includes the air inlet channel of the unit and the air inlet system of the engine. The air inlet channel and the exhaust channel are directly connected with the outside world. The air flow rate is very high. The air flow noise and the unit operation noise are radiated to the outside through the air inlet channel. The noise of the engine intake system is caused by the pressure fluctuation caused by the periodic opening and closing of the intake valve. The noise frequency is generally in the low frequency range below 500 Hz. Two silencing air inlets are set on the wall of the machine room as the air inlet of the machine room and the air inlet of the engine. Due to the negative pressure in the room caused by the exhaust, the cold air naturally enters the machine room through the silencing inlet, and the heat emitted by the machine body is discharged smoothly. This ensures that there is enough fresh air in the machine room.