Investigation On Gas-solid Flow Characteristics Of High Pressure Dense Phase Pneumatic Conveying

High-efficiency and large-scale pulverized coal gasification technology is widely used in fields of energy,chemical engineering and metallurgy industries.High-pressure dense-phase pneumatic conveying of carbonaceous fuel powders is one of the key and difficult technologies in dry entrained flow gasification.High-pressure dense-phase pneumatic conveying has high solid phase concentration and complex flow patterns,and the knowledge of related transport mechanisms is yet to perfect,its research has both theoretical and industrial application significance.In this paper,based on the analysis of powder flow characteristics,the transport characteristics and transport stability of the high pressure dense phase conveying of carbonaceous powders were studied.The intrinsic mechanism of high pressure dense phase transport characteristics was obtained.Flow characteristics of a series of fuel powders,such as lignite,bituminous coal,anthracite,biomass and petroleum coke,were studied systematically,and the correlation between flowability and material properties was revealed by analyzing basic flowability parameters such as angle of repose,Hauser ratio index and compressibility index.The results show that with the increase of particle size,Hausner ratio index,compressibility index and angle of repose gradually decrease,the flowability of powder materials improves gradually.The flowability results of fluidization tests are in accordance with the results of angle of repose and Hausner ratio index.Experimental investigations of a series of powders were carried out on two sets of high-pressure blow tank test facilities.The influences of operating parameters and material properties on the transport characteristics were obtained,and the transport characteristics of different materials were compared.The results show that external water content is an important factor affecting the conveying characteristics of pulverized coal.The external water content limit values of stable transportation of two lignite coals and one bituminous coal are obtained through experiments.Lignite with smaller particle size is more sensitive to the changes of external water content.External water content limit value of bituminous coal is significantly lower than that of lignite with similar mean particle size.The study also found that using simpler and more convenient test methods such as Hausner ratio index and angle of repose can effectively predict the external water content limits for stable transportation of different pulverized coals.In this paper,the transport capacity of anthracite first increases and then decreases with the decrease of particle size.That is,an optimal particle size exists which can achieve maximum transport capacity.The transport capacity of the anthracite with smallest particle size is significantly lower than those of the other two anthracite coals.Biomass and pulverized coal have significant differences in high-pressure transport characteristics.Biomass can be effectively fluidized under smaller fluidizing gas flow rate,achieving high transport capacities and solid phase concentrations.At high superficial gas velocities,biomass can be fully suspended in the horizontal pipe;solid phase concentration in the center of pipe is relatively higher.While solid concentration of the pulverized coal in the bottom of pipe is higher than that in the upper part of the pipe.It was found for the first time that during the transportation of petroleum coke,a hard and dense petroleum coke layer was formed on the inner wall of the pipeline,and it was found that electrostatic phenomena of particles,conveying pressure,apparent oil content of petroleum coke and moving speed of particles all played significant impact on the formation of petroleum coke scale.Mixing a certain percentage of anthracite with petroleum coke can significantly reduce the formation of petroleum coke scale inside the pipeline.The resistance characteristics of high-pressure dense-phase conveying of carbonaceous fuel powders were investigated,and the resistance characteristics of different pipe sections were obtained.Pressure drop Empirical correlations of different pipe sections were obtained by using additional pressure drop method,and the predicted values of the model are in good agreement with the test results.The pressure drop correlations of horizontal pipe with different external water contents were obtained.It was found that the influence of external water content on the solid-phase friction coefficient of fine lignite was greater than that of coarse lignite.By using SHANNON entropy analysis and domain coordinate analysis(HURST index),the horizontal differential pressure signals are analyzed and the conveying stabilities of various materials are discussed.Two analysis methods have relatively consistent prediction results with the regard of the conveying stability.When fluidizing gas flow rate,supplementary gas flow rate and total differential pressure change,the influence of the change of operating parameters on the conveying stability can be successfully predicted.The differences between the same type coals with different particle sizes are not obvious by using stability prediction of both methods.