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.声源分析

1. Sound source analysis

燃气发动机噪声是燃气发电机组的主要噪声来源,燃气发动机噪声可分为空气动力噪声、燃烧噪声、机械噪声、排气噪声和振动噪声。空气动力噪声主要包括进、排气和风扇旋转引起的空气振动噪声,这部分噪声直接向空气中传播。气缸内燃烧所形成的压力振动通过缸盖，机体向外辐射的噪声叫燃烧噪声;活塞对缸套的撞击,配气机构、喷气系统等运动部件产生的撞击振动噪声统称为机械噪声。机组工作时,废气从排气门高速冲出,沿排气歧管进入消声器,后从尾管排入大气。排气噪声是发动机的大噪声,往往比发动机主机噪声高15 dB(A)左右,其次分别是燃烧噪声和机械噪声、风扇噪声、进气噪声。

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.改造设计

2. Renovation design

基于燃气发电机组的工作原理,难以用降低声源噪声的方法来消声,所以主要是要有效阻断其噪声传播途径。消声技术的核心就是利用声波在传播中自然衰减的规律去缩小噪声的污染面。具体降低噪声的方法有以下几种:吸声、隔声及改变噪声传播方向。在实际工程应用中往往只用其中一种,本文采用三种方法并用的措施,针对燃气发电机组提出了新型组合降噪技术。

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）组合消声器

(1) Combined silencer

原来的消声器以阻性消声为主,功耗大,消声效果不理想。经仔细论证,应用三级组合降噪技术,将消声器改造为新型组合式消声器。该组合式消声器的主要组成部件有对喷消声减振腔、多孔式消声罩及吸声隔热层和吸声共振板等。声源通过级的对喷消声减振腔,可将中低频声源的噪声能量充分进行抗性耗散。二级的多孔式阻性消声罩可消去大部分高频噪声,增加了消声器对高频的适应性,而且在该腔内装有吸声材料,可对噪声进行充分的吸收和变向,从而大限度地消耗噪声能量。第三级为专门设计的带共振板的排气管,进一步通过薄片的振动进行消声。经测试,新型消声器的消声量、消声频率范围(主要为消声量峰值的频率范围)及阻力损失三大指标均优于原来的消声器。此外该消声器尺寸适宜,结构刚性好,安装方便,并具有抑制再生噪声的功能。而且后部的吸声隔音层具有防腐性能,可有效地克服烟气的低温露点腐蚀,延长了消声器的使用寿命。

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）两级隔振衬垫

(2) Two stage vibration isolation pad

控制机械噪声和燃烧噪声的有效办法是对机组进行隔振处理。燃气机、发电机与钢制底盘间装设复合隔振减振垫,底盘与基础之间亦垫上减振胶垫。经过两级隔振处理,不仅使机组的振动被有效隔断,而且使机组运行更加平稳,整体噪声显著降低。

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）消声排风道

(3) Silencing exhaust duct

风扇噪声是由旋转噪声和涡流噪声组成。旋转噪声由旋转风扇叶片切割空气流产生周期性扰动而引起。涡流噪声是在旋转叶片截面上发生边界层分离时,气体滑脱或分裂而成的一系列的漩涡流,从而辐射出一种非稳定的流动噪声。排风道直接与外界相通,空气流速很大,气流噪声、风扇噪声和机械噪声经此通道辐射出去。为了控制风扇和排风通道的噪声,设计了一个消音排风道。这个消音排风道长度较大,由导风槽和排风降噪腔组成。排风降噪腔的工作原理,类似于阻性消声器。可通过更换吸音材料(改变材料的吸音系数),改变吸音材料厚度、排风通道长度和宽度等参数来提高消音效果。

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）消声进气道

(4) Silencing intake duct

机组工作在封闭的机房里面,从广义上讲,进气系统包括机组的进风通道和发动机的进气系统。进风通道和排风通道一样直接与外界相通,空气的流速很大,气流的噪声和机组运转的噪声都经进风通道辐射到外面。发动机进气系统的噪声是由进气门周期性开、闭而产生的压力波动所形成,其噪声频率一般处于500 Hz以下的低频范围。在机房墙上设置了两个消声进气道,分别作为机房的进风口和发动机的进气口。由于排风造成的室内负压,使冷空气自然通过消声进气道进入机房内,将机体散发的热量顺利排出。从而保证了机房内有足够的新鲜空气 [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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