The power system of oil drilling rigs mainly comes from diesel engines. The power of diesel engines is relatively large, generally around 800KW. A set of 5000M drilling rig generally requires 3 diesel engines and a set of 7000M drilling rig generally requires 4 diesel engines. Diesel engines will produce noise when they are working, especially diesel engines used in drilling rigs. Due to their high power and mutual influence, the noise is particularly prominent. The sound of a diesel engine can be heard even in the wild and at great distances.

1. Analysis of noise sources of diesel generator sets

1.1 Aerodynamic noise
During the operation of the diesel unit, the disturbance to the air causes a sound source between the air and the diesel unit to form noise. This kind of noise directly radiates to the outside, specifically including: the noise of the exhaust system, the noise of the air intake system, and the rotation noise of the diesel engine cooling fan.

(1) Exhaust system noise. The most direct noise source of diesel generator sets is the noise generated by the exhaust system. This noise is relatively high in intensity and is about 10~15dB (A) higher than normal engine noise. During the operation of the generator set, high-temperature and high-pressure exhaust gas must be continuously discharged. According to the operating status of the generator set, the exhaust system has two stages of exhaust, namely free exhaust of the generator set and forced exhaust of the generator set. When the exhaust gas from the generator set is discharged from the exhaust valve, it will flow from the exhaust pipe to the muffler, and finally be discharged into the air through the rear exhaust pipe. During the entire exhaust process, a large amount of exhaust noise will be generated, which is also the main source of noise from diesel generator sets. The noise generated during the exhaust process was analyzed and it was found that the composition of the noise source was relatively complex. There are noises caused by the frequency of exhaust operations in the exhaust system per unit time, noise caused by the resonance of exhaust gases in the exhaust pipe, and blowing noise caused by the airflow ejected from the exhaust pipe. The main factors that can affect the noise of the exhaust system of the generator set are: the internal pressure of the engine cylinder, the pipe diameter of the exhaust system, the rated exhaust volume of the generator set, the operating speed and workload of the generator set, etc. Increasing the working load of the generator set or increasing the engine speed will increase the gas flow, resulting in an increase in exhaust noise.

(2) Noise from the air intake system. The noise generated by the air intake system is one of the main noises of the diesel generator set. The main reason for the formation is that the air inlet is continuously opened and closed according to the air intake demand of the generator set, which causes the pressure of the air intake system to continuously change and cause noise. When the intake system is working, a certain pressure pulse is formed in the intake pipe, causing the intake system to produce periodic noise. The audio frequency range of this noise is generally around 200Hz. At the same time, when the air flow enters the inside of the system, it will flow through the air intake pipe, causing the air to be kicked out of the body. This situation will cause high-frequency noise in the engine air intake system. Usually the air flow in the intake pipe is constantly changing, so the frequency band of this noise is also relatively fixed, generally concentrated around 1000Hz. When the noise frequency of the intake cycle and the air column in the intake system reaches consistency, airflow resonance will occur, causing the noise of the intake system to increase. The noise generated by different superchargers in different generator sets is also different. The noise intensity of a turbocharged generator set is obviously different compared to a non-turbocharged generator set. This is due to the relatively high speed of the turbocharged generator set, which causes the engine's air intake system to produce relatively strong airflow due to air cutting, resulting in higher-frequency noise. The frequency distribution range of this noise is generally between 500 and 10000Hz.

1.2 Surface radiated noise
Strictly speaking, it is difficult to distinguish the surface radiation noise of diesel generator sets. Combustion noise is generally caused by the pressure vibration generated by diesel combustion inside the cylinder acting on the mechanical components of the overall cylinder, thereby radiating a certain amount of noise to the outside. During the operation of the generator set, various mechanical components will continue to collide mechanically, thus generating mechanical noise. Usually, when the generator set speed is low, the combustion noise generated is higher than the mechanical noise.

2. Specific construction measures for noise reduction in diesel generator rooms

(1)Use high-efficiency shock-absorbing rubber pads to isolate the unit. This part of the technology is now very mature. After isolation treatment, the vibration on the surface of the unit is effectively isolated.

(2) Perform noise reduction processing on the propagation channel, and install soft damping connections on the exhaust pipe of the generator set to reduce the external radiation of the sound source. According to the principle of muffling, the muffler structure can use a resistive muffler. It uses porous sound-absorbing material - melamine foam, which is arranged in a certain way in the pipe. When the airflow passes through the resistive muffler, the sound waves cause vibrations in the air and small fibers in the pores of the melamine foam. Due to friction and viscous resistance, sound energy is converted into heat energy and absorbed, thus playing a silencing effect.
(3) Each wall of the room is made of multiple layers of noise-reducing materials, including rock wool, sound-absorbing mesh cloth and sound-absorbing mesh board. Adding a sound-absorbing wall to the wall of the generator room inside the machine room can not only reduce the reverberation sound in the machine room while improving the sound insulation effect, but also attenuate the direct transmission of strong noise when it is running to the top.

(4) When designing the air inlet and outlet, the minimum air inlet and outlet volume standards required for normal operation of the unit are fully considered. At the same time, in order to solve the heat dissipation problem in the machine room, the air inlet and the exhaust outlet of the generator set should be set on the same straight line. In addition, the air intake and exhaust openings should be equipped with resistive sheet sound absorbing grilles.

3.Conclusion
The noise from the diesel generator set of oil drilling rigs is the largest noise source at the entire drilling rig site. It has a great impact on environmental protection and does not meet the requirements of the safety and environmental management system (HSE), so it needs to be prevented. This article conducts research on the noise generated by diesel generator sets, and provides specific construction measures for noise reduction in the generator set room, which can provide reference for relevant personnel.

SINOYQX’s oil and gas generator set noise reduction solution
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