| The bag filter has been more widely used because of its advantages of the fine dust purification efficiency, wide range of air volume and long bag life. Pulse-jet cleaning is the most common and most efficient bag filter cleaning method in the current world. And the bag filter runs steadily or not depends on cleaning effect. The motivation to decide the cleaning effect and the factors to influence it were great quantity. However, the current research lacked clear elaboration on the inner relationship between flow field state in bag and parameters of pulse-jet system corresponding bag dimension and dust load, which restricted the design of cleaning system.In this article, according to the bag shape and size and resistance properties of the dust layer, in order to achieve the maximum instantaneous static pressure of air flow, using Darcy’s equation reveals the relationships between the pressure in bag and reverse flow rate; The associated formula is deduced employing jet theory, which described the relationship between air flow, average kinetic energy of each section of jet flow from nozzle to bag opening and nozzle diameter, outlet air velocity and distance; According to the gas flow rate and kinetic energy at the bag mouth must be consistent with the cleaning gas flow rate and pressure in bag, calculate the diameter of the nozzle injection system, the outlet gas velocity, jetting distance, structure and dimensions of diffusion tube (venturi); Based on the theory of one dimension adiabatic flow of compressible gas in nozzle, according to the ratio of nozzle exit pressure and injection pressure to determine the form of nozzle and calculated the nozzle structure size.Based on theoretical models, using FLUENT, software of Calculation Fluid Dynamics (CFD) to simulate high-speed and compressible gas flow field in nozzle obtain the velocity distribution of the nozzle exit. And import profile with velocity conditions to the single bag model as its boundary conditions of nozzle exit. The bag with 160×6000mm for the study, four typical conditions were selected to simulate the internal flow field when the bag mouth without limiting measures, with limiting ring or diffuser. Analyze the impact of limiting structure to flow’s form around the bag mouth, the peak pressure in bag and blowback air velocity by numerical simulation results. Under the same working conditions diffusion tube can limit the back flow of gas completely, making the peak pressure and outlet air velocity maximum, next restriction ring, while will all the gas reversed without current limiting measures, causing the entire filter bag is still in a state. Based on verification the results correct the theoretical diameter of the nozzle. The correction factor reaching about 1.18 when installing diffusion tube on bag mouth, far less than the measures with restriction ring and none measures, energy efficiency of four groups working conditions reached 48.6%,50.4%, 52.8% and 57.6%, is the highest of the three measures. According to the consumption of flow rate of nozzle and energy efficiency when reached index of cleaning to determine the optimal limiting measures is installing diffusion tube on bag mouth.Finally, integrating all the data of numerical simulation to build a complete theoretical system of formation mechanism of cleaning, and come up with design method of pulse-jet cleaning system. Laying a foundation for experimental study of theoretical models of the pulse-jet cleaning; providing guidance for the design of energy-efficient cleaning system. |
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