Research On The Control Of Noise Of Exhaust Pipe Of Main Exhaust Fan Of Cement Mil

When the main exhaust fan of cement mill provides negative pressure for the system to ensure the stable wind speed of gas in the coal mill system,it will produce a lot of broadband noise.The coal mill of a cement factory uses a fan with a working air volume of 265000m3·h^-1,and the noise generated is released in the air vent of the exhaust duct 40m high,exceeding the limit of the emission standard and causing serious noise pollution to the surrounding environment.Aiming at the noise of the exhaust duct,this paper designs a blocking vane muffler to solve the noise problem.The reasonableness of the design is proved by the engineering example,which provides a certain reference for solving the noise problem.Firstly,a mathematical model was established in the design process of the noise reduction scheme of the exhaust duct.The equivalent acoustic impedance Z_Ⅰand Z_Ⅱof the composite structure were solved,including the acoustic impedance of porous plate based on the acoustic circulation flow theory,the acoustic impedance of non-woven fabric based on the acoustic reflection principle,and the acoustic impedance of glass fiber cotton based on the DB-Miki model and the impedance transfer theory.It is embedded in COMSOL to solve the transfer loss.The stability analysis model of high-rise structure is established,including the nonlinear buckling analysis model of self-strength analysis,the calculation model of wind load and snow load,and the response spectrum analysis model commonly used in seismic fortification.Secondly,the AWA5688 multifunctional sound level meter is used to measure the noise.According to the spectrum diagram of the noise,it is known that the noise is within the frequency range of 50Hz～5000Hz,and the broadband noise is higher than 200Hz～1000Hz.According to the spectrum characteristics of noise,a double-row resistive chip muffler is designed.The total resistance including friction resistance and local resistance is 501Pa when the fan is working,which meets the design requirements of dynamic performance.Then,the simulation results were compared with the experimental results to verify the correctness of the equivalent acoustic impedance to solve the transmission loss of the resistive chip muffler.After that,COMSOL was used to solve the acoustic performance of the resistive chip muffler at 50Hz～5000Hz broadband noise.Ten kinds of fiberglass cotton with different specifications were compared and analyzed by taking the fiber diameter and volume density of the fiberglass cotton in the noise suppressant unit as the optimization parameters.When the volume density of 60kg·m^-3 and the fiber diameter of 10μm,the noise suppressant effect of the exhaust duct was better.Finally,a simplified equivalent model was established before and after the exhaust duct was installed with the muffler.The steady state analysis was carried out,the wind load and snow load were calculated once in 50 years,and the modal sum of the response spectrum analysis was performed by CQC method.The maximum stress of the exhaust duct is far less than the allowable stress of the steel structure of 2.35×10⁸N·m^-2after the muffler with a mass of 6230kg is installed.Because the muffler is installed at the top of the exhaust duct,the long vertical cantilever thin shell structure of the exhaust duct is changed,and the maximum displacement is reduced by 55.7%under snowstorm load.The maximum displacement under earthquake increases by only 2.2%,and the contribution of maximum displacement changes from the bending deformation of the exhaust duct and the top deformation to the bending deformation of the barrel body.Finally,the feasibility of the noise reduction scheme is proved by solving the engineering problems.