The Research On Flow Fields In Bag-filter With Numerical Simulation

With the rapid development of industry, the total emission of atmospheric pollutants needs to be controlled to meet the increased stringent national standards, while the bag-type dust collecting equipment has gradually become to be the key technology in dust collection processing. The paper is based on the project "Research on the Large-scale Bag-type Dust Collector in Coal-fired Power Plants" of Country Electricity Environmental Protection Group, which mainly use CFD numerical simulation to study the airflow distribution in large-scale bag-house and pulse-jet system. The purpose is to analyze the airflow distribution between bags in bag-filter, predict the location of the easily damaged bags, and measures or advanced method would be proposed to avoid it in time.The paper used the k-εturbulent current model of CFD numerical simulation to study airflow distribution in large-scale bag-house with the physical model which was similar to practical bag-filter. By simulating the airflow organization in different inlet mode, different inlet velocity and different bags-distance, it could be concluded that airflow distribution in bag-house was imparity, especially the filtration velocity of different location of the bag, and the velocity of outer part of the bag-house was higher than the inner part. The velocity gradually became low from the top down of every single bag. Based on the study, the airflow should be designed with low velocity from the bottom of the bag-house; a special plate should be installed to change the airflow direction with upper inlet mode; protection measure should be proposed to prevent the airflow damage of the bags with bottom inlet mode. The paper supposed the bag in round platform with upper diameter bigger than the bottom to average airflow distribution of a single bag in both outer and inner part of the bag-house. Through simulating the airflow of the bag house for the 240t/h circulation fluid-bed boiler which the author participated, it was showed that outer part of the bag -house, especially the first line and the last line were easily to be broken, and suggestions should be proposed to prevent it during the operation and management.The research on the pulse-jet system with CFD numerical simulation showed that the mass flow in pulse-jet ports distribution was unequal, and the airflow velocity in the front pipe was higher than the back one while the static pressure was opposite. The velocity direction of front pulse-jet ports deviated greatly, and the unbalance rate of pulse-jet mass flow in pulse-jet ports was between 20% and 140%. As a result, an advanced design to adjust the size of pulse-jet ports was given which could control its unbalance rate below 20%.According to the calculation of the pulse-jet mass flow by CFD, the static pressure and airflow distribution were also simulated, and relation between the pulse-jet mass flow and the inducing mass flow was studied.