Study On Powder Flow Control Characteristics Of Dense Phase Pneumatic Conveying And Pneumatic Logistics Transmission System

As an important part of the logistics system,bulk material transportation is widely used in chemical industry,pharmaceutical industry,agriculture,mining industry,processing industry and other industries.This paper takes the coal gasification process as the research background,carries out the study of pulverized coal dense phase pneumatic conveying and its flow control characteristics.Then the research including the pneumatic logistics transmission characteristics,pressure drop and the characteristic velocity modeling are carried out.The research results provide a reference for the optimal design and efficient operation of dense phase pneumatic conveying system and pneumatic logistics transmission system.Pulverized coal dense phase pneumatic conveying experiments have been carried out to grasp the conveying characteristics,resistance characteristics and flow control laws on industrial grade pipe diameter(50mm).By adjusting the flow control valve opening and nozzle structure,the pressure distribution characteristics of the nearindustrial conveying system are obtained,providing a basis for industrial process.The effects of conveying pressure difference,flow control valve and nozzle on the control characteristics of pulverized coal are compared and analyzed.The mechanism of conveying pressure difference on pulverized coal flow is explored,and the operation characteristic range of flow control valve based on valve pressure drop ratio and pulverized coal flow variation is proposed.By analyzing the evolution of conveying flow pattern,velocity and concentration with valve opening,a prediction model of pulverized coal flow coupled with valve regulation characteristics is established.The regulation performance of different nozzle structures is analyzed,and the flow prediction model based on nozzle is established through micro-element analysis.Based on the self-built pneumatic logistics transmission system,the conveying characteristics is studied with the help of signal analysis,high-speed camera technology and data processing.The variation law of pressure signal and its fluctuation characteristics with apparent gas velocity is revealed,and a method for identifying the state of transfer bottle based on signal analysis is proposed.Taking into account the structural characteristics and the pressure drop composition between the gas and solid phases,a pressure drop model of the pneumatic logistics transmission system is established,in which the gas phase pressure drop takes into account the friction pressure drop in the straight pipe,the sudden contraction,the gap and the sudden expansion,and the solid phase pressure drop effectively describes the friction characteristics of the transfer bottle with pipe wall under the motion state.Based on the data regression,the gas phase friction coefficient is obtained,and the solid phase friction coefficient is obtained based on the force analysis,thus achieving effective prediction of pressure drop in the pneumatic logistics transmission system,the model prediction deviation is below±10%.The pressure distribution of the gas-solid two-phase flow in the transmission system is further analyzed,comparing the proportion of the pressure drop of each part of the transmission system including the pressure drop per unit pipe length in the straight pipe with that in the gap,and the pressure drop ratio in the sudden contraction and expansion.By analyzing the influence factors of resistance coefficient of pneumatic logistics transmission system,a semi-theoretical and semi-empirical formula of resistance coefficient is established based on dimensional analysis and a parametric regression is carried out by using experimental data.The prediction model for the characteristic velocity(the critical gas velocity and the transfer bottle velocity)of pneumatic logistics transmission system is developed.The critical gas velocities with different structure and friction characteristics of the transfer bottle are predicted.The transfer bottle velocity is predicted based on the energy conservation and the analysis of the pressure state of the gas chamber.The logical diagram for predicting the transfer bottle loading in the multi-bottle transmission system is proposed,combining the established pressure drop model,the continuity equation and the ideal gas state equation under the requirement of the same velocity.The multi-bottle transportation theory is developed,and the control requirements of tranfer bottle loading are proposed,which provides a new idea for the design of multi-bottle transportation system.