Application Of Venturi In Pulverized Coal Dense Phase Conveying System

Flow characteristics of gas-coal mixture along venturi were obtained and analyzed by means of ECT system.Structural optimization design of venturi was carried out according to the experimental data on different structures of venturi.A pressure drop model of the contraction section of venturi in dense-phase gas-solid flow system was established,and it was appled to real-time online prediction of solid flowrate.High concentration gas-coal mixture flows through venturi with annular flow regime in the contraction section.There is a "convergence" area with core-annulus flow regime in the front end of the throat and the flow regime changes from the core-annulus flow to annular flow with the increase of gas velocity.The flow regime in the throat is annular flow after through"convergence" area.The flow regime in the expansion section is annular,and the concentration of the particles decreases rapidly with strong turbulent flow.Considering lifting effect of venturi on the upstream pressure and to ensure effective delivery pressure difference,and taking into account both the pressure drop of venturi and flow stability,the optimized structural parameters used in dense-phase gas-solid flow system were obtained with the throttle ratio between 0.35 and 0.6,the contraction angle about 5°,the expansion angle about 8° and the throat length about 21 times the throat diameter.Considering pressure drop generated by gas and solid respectively and acceleration pressure drop of gas and solid respectively,a pressure drop model of gas-solid flowing through the contraction section of venturi with high solid-gas ratio was established giving total deviation within 20%,By means of numerical calculation,the characteristics of flow parameters in contraction section were obtained.The calculation result shows that the pressure drop of accelerating the particle phase determines the pressure drop of the contraction section.The prediction of solid flowrate was carried out giving the total deviation within 20%using the established pressure drop model,and the prediction error is mainly related to the accuracy of the model itself.Solid flowrate was also predicted based on the modified St number mothod,and the prediction accuracy of this method is mainly related to the correlation coefficient of m and St number,which is obtained by pre-experiment under the specific venturi structure.