The Gas-fired power plant set is composed of gas engine, generator, control cabinet and other components. The gas engine and generator are installed on the same steel chassis. The unit uses natural gas, wellhead associated gas, coal mine gas, Water gas, refining tail gas, biogas, coke oven gas, blast furnace gas and other combustible gases as fuel. It starts quickly and has good economy. Especially because of the demand of high-quality urban life, Gas-fired power plant units have been widely used in telecommunications, post offices, banks, libraries, hospitals, hotels and other departments as backup power. Initially, the Gas-fired power plant unit was designed for the working conditions of the mine, and the noise generated by the unit during operation was generally 95~110 dB (A). The GB 3096-93 Environmental Noise Standards for Urban Areas have strict regulations on the noise level in urban areas. For Class 2 areas (residential, commercial, and industrial mixed areas), the noise level is 60 dB (A) during the day and 50 dB (A) at night; For Class 1 areas (residential, cultural and educational institutions), it is 55 dB (A) during the day and 45 dB (A) at night. The noise generated during unit operation has brought serious noise pollution to the urban environment, affected people's normal work and life, and also limited the wide application of Gas-fired power plant units. This paper proposes a set of rectification measures to solve the noise pollution problem of Gas-fired power plant units, in order to reduce the unit noise and promote the popularization and application of Gas-fired power plant units.

1.聲源分析

1. Sound source analysis

燃氣發動機噪聲是燃氣發電機組的主要噪聲來源,燃氣發動機噪聲可分為空氣動力噪聲、燃燒噪聲、機械噪聲、排氣噪聲和振動噪聲。空氣動力噪聲主要包括進、排氣和風扇旋轉引起的空氣振動噪聲,這部分噪聲直接向空氣中傳播。氣缸內燃燒所形成的壓力振動通過缸蓋，機體向外輻射的噪聲叫燃燒噪聲;活塞對缸套的撞擊,配氣機構、噴氣系統等運動部件產生的撞擊振動噪聲統稱為機械噪聲。機組工作時,廢氣從排氣門高速沖出,沿排氣歧管進入消聲器,后從尾管排入大氣。排氣噪聲是發動機的大噪聲,往往比發動機主機噪聲高15 dB(A)左右,其次分別是燃燒噪聲和機械噪聲、風扇噪聲、進氣噪聲。

Gas engine noise is the main noise source of Gas-fired power plant set. Gas engine noise can be divided into aerodynamic noise, combustion noise, mechanical noise, exhaust noise and vibration noise. Aerodynamic noise mainly includes air vibration noise caused by intake, exhaust, and fan rotation, which directly propagates into the air. The pressure vibration generated by combustion inside 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, as well as the impact vibration noise generated by moving components such as the valve train and jet system, are collectively referred to as mechanical noise. During the operation of the unit, exhaust gas rushes out at high speed from the exhaust valve, enters the muffler along the exhaust manifold, and finally discharges into the atmosphere through the tailpipe. Exhaust noise is the maximum noise of an engine, often about 15 dB (A) higher than the noise of the engine host, followed by combustion noise, mechanical noise, fan noise, and intake noise.

2.改造設計

2. Renovation design

基于燃氣發電機組的工作原理,難以用降低聲源噪聲的方法來消聲,所以主要是要有效阻斷其噪聲傳播途徑。消聲技術的核心就是利用聲波在傳播中自然衰減的規律去縮小噪聲的污染面。具體降低噪聲的方法有以下幾種:吸聲、隔聲及改變噪聲傳播方向。在實際工程應用中往往只用其中一種,本文采用三種方法并用的措施,針對燃氣發電機組提出了新型組合降噪技術。

Based on the working principle of Gas-fired power plant unit, it is difficult to reduce the noise of the sound source by reducing the noise, so the main purpose is to effectively block the Pathogen transmission of the noise. The core of noise reduction technology is to use the natural attenuation law of sound waves in propagation to reduce the pollution surface of noise. There are several specific methods to reduce noise: absorption, insulation, and changing the direction of noise propagation. In practical engineering applications, only one of them is often used. This paper proposes a new combined noise reduction technology for Gas-fired power plant units by using three methods.

（1）組合消聲器

(1) Combined silencer

原來的消聲器以阻性消聲為主,功耗大,消聲效果不理想。經仔細論證,應用三級組合降噪技術,將消聲器改造為新型組合式消聲器。該組合式消聲器的主要組成部件有對噴消聲減振腔、多孔式消聲罩及吸聲隔熱層和吸聲共振板等。聲源通過級的對噴消聲減振腔,可將中低頻聲源的噪聲能量充分進行抗性耗散。二級的多孔式阻性消聲罩可消去大部分高頻噪聲,增加了消聲器對高頻的適應性,而且在該腔內裝有高效吸聲材料,可對噪聲進行充分的吸收和變向,從而大限度地消耗噪聲能量。第三級為專門設計的帶共振板的排氣管,進一步通過薄片的振動進行消聲。經測試,新型消聲器的消聲量、消聲頻率范圍(主要為消聲量峰值的頻率范圍)及阻力損失三大指標均優于原來的消聲器。此外該消聲器尺寸適宜,結構剛性好,安裝方便,并具有抑制再生噪聲的功能。而且后部的吸聲隔音層具有防腐性能,可有效地克服煙氣的低溫露點腐蝕,延長了消聲器的使用壽命。

The original muffler mainly used resistive noise reduction, with high power consumption and unsatisfactory noise reduction effect. After careful argumentation, the three-level combined noise reduction technology has been applied to transform the muffler into a new type of combined muffler. The main components of this combined muffler include a spray muffler damping chamber, a porous muffler cover, a sound absorbing insulation layer, and a sound absorbing resonance plate. The sound source can fully resist and dissipate the noise energy of medium and low frequency sound sources through the first stage of anti noise and damping cavity. The secondary porous resistive muffler can eliminate most high-frequency noise, increase the adaptability of the muffler to high frequencies, and is equipped with high-efficiency sound-absorbing materials in the cavity, which can fully absorb and redirect the noise, thereby maximizing the consumption of noise energy. The third level is a specially designed exhaust pipe with a resonance plate, which is further silenced through the vibration of thin plates. The test shows that the three major indexes of the new muffler are better than the original muffler in terms of noise elimination amount, noise elimination frequency range (mainly the frequency range of noise elimination amount peak) and Friction loss. In addition, the muffler has a suitable size, good structural rigidity, convenient installation, and has 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 smoke and prolong the service life of the muffler.

（2）兩級隔振襯墊

(2) Two stage vibration isolation pad

控制機械噪聲和燃燒噪聲的有效辦法是對機組進行隔振處理。燃氣機、發電機與鋼制底盤間裝設復合隔振減振墊,底盤與基礎之間亦墊上高效減振膠墊。經過兩級隔振處理,不僅使機組的振動被有效隔斷,而且使機組運行更加平穩,整體噪聲顯著降低。

The effective method 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 placed between the chassis and the foundation. After two-stage vibration isolation treatment, not only is the vibration of the unit effectively isolated, but also the operation of the unit is more stable, and the overall noise is significantly reduced.

（3）消聲排風道

(3) Silencing exhaust duct

風扇噪聲是由旋轉噪聲和渦流噪聲組成。旋轉噪聲由旋轉風扇葉片切割空氣流產生周期性擾動而引起。渦流噪聲是在旋轉葉片截面上發生邊界層分離時,氣體滑脫或分裂而成的一系列的漩渦流,從而輻射出一種非穩定的流動噪聲。排風道直接與外界相通,空氣流速很大,氣流噪聲、風扇噪聲和機械噪聲經此通道輻射出去。為了控制風扇和排風通道的噪聲,設計了一個消音排風道。這個消音排風道長度較大,由導風槽和排風降噪腔組成。排風降噪腔的工作原理,類似于阻性消聲器。可通過更換吸音材料(改變材料的吸音系數),改變吸音材料厚度、排風通道長度和寬度等參數來提高消音效果。

Fan noise is composed of rotating noise and eddy current noise. Rotating noise is caused by periodic disturbances caused by the cutting of air flow by rotating fan blades. Vortex noise is a series of vortex flows formed by gas slippage or splitting when Flow separation occurs on the rotating blade section, which radiates an unstable flow noise. The exhaust duct is directly connected to the outside world, with a high air flow rate. Air flow noise, fan noise, and mechanical noise are radiated out through this channel. In order to control the noise of the fan and exhaust duct, a silencing exhaust duct has been designed. This silencing exhaust duct has a large length and is composed of an air duct and an exhaust noise reduction chamber. The working principle of the exhaust noise reduction chamber is similar to that of a resistive muffler. The sound-absorbing effect can be improved by replacing the sound-absorbing material (changing the sound-absorbing coefficient of the material), changing the thickness of the sound-absorbing material, the length and width of the exhaust channel, and other parameters.

（4）消聲進氣道

(4) Silencing intake duct

機組工作在封閉的機房里面,從廣義上講,進氣系統包括機組的進風通道和發動機的進氣系統。進風通道和排風通道一樣直接與外界相通,空氣的流速很大,氣流的噪聲和機組運轉的噪聲都經進風通道輻射到外面。發動機進氣系統的噪聲是由進氣門周期性開、閉而產生的壓力波動所形成,其噪聲頻率一般處于500 Hz以下的低頻范圍。在機房墻上設置了兩個消聲進氣道,分別作為機房的進風口和發動機的進氣口。由于排風造成的室內負壓,使冷空氣自然通過消聲進氣道進入機房內,將機體散發的熱量順利排出。從而保證了機房內有足夠的新鮮空氣 [1]  。

The unit operates in a closed computer room, and broadly speaking, the air intake system includes the unit's air intake channel and the engine's air intake system. The intake channel and exhaust channel are directly connected to the outside world, and the air flow rate is high. The noise of the airflow and the operation of the unit are radiated to the outside through the intake channel. The noise of the engine intake system is caused by pressure fluctuations caused by the periodic opening and closing of the intake valves, and its noise frequency is generally in the low-frequency range below 500 Hz. Two silencing air intakes have been installed on the wall of the computer room, serving as air intakes for the computer room and for the engine. Due to the negative pressure caused by exhaust, cold air naturally enters the machine room through a silenced intake duct, and the heat emitted by the machine body is smoothly discharged. This ensures that there is sufficient fresh air in the computer room.

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