Experimental And Numerical Study On Dense Phase Pneumatic Conveying Of Pulverized Petroleum Coke In Bend Under High Pressure

Large-scale and high-efficiency entrained flow gasification technology is an important technology in petroleum coke gasification.And dense phase pneumatic conveying under high pressure is one of the most important facilities of this technology.There are some advantages in dense phase pneumatic conveying under high pressure such as high solid-gas ratio,low energy consumption,low consumption of gas and less abrasion.However,on the one hand,because of the high volume concentration of the particles,the flow pattern and the conveying mechanisms of dense phase pneumatic conveying under high pressure become very complicated,for which it is difficult to understand the mechanisms of dense phase pneumatic conveying under high pressure completely.On the other hand,subject to the experimental conditions,it is impossible to fully achieve gas-solid flow behavior during the process of dense phase pneumatic conveying under high pressure by experimental approaches directly.However,numerical simulation can make up the above limitations.Therefore,the present work is to study the gas-solid flow behavior of dense phase pneumatic conveying of pulverized petroleum coke in bend under high pressure by both experimental and simulation approaches.Based on the dense phase pneumatic conveying under high pressure system,which was developed by Southeast University independently,the influence mechanisms of supplemental gas on the conveying characteristics of dense phase pneumatic conveying of pulverized petroleum coke in bend and straight pipe under high pressure was analyzed,in the proposition that keeping other conveying conditions same.Besides,according to the Barth energy addition theory,the additional pressure loss coefficient of the solid phase in bend and straight pipe was obtained,and the pressure drop predicted was in good agreement with experimental data,which meant the relative error was within 5%.The experimental results indicated that as supplemental gas increased,injection superficial gas velocity,solid mass flow rate and solid/gas mass ratio decreased,but superficial gas velocity increased.With the same supplemental gas,the pressure drop in horizontal bend was higher than that in downstream horizontal pipe,and the pressure drop in vertical bend was higher than that in downstream vertical pipe.What's more,as supplemental gas increased,the pressure drop in horizontal bend was almost the same as that in the downstream horizontal pipe,which all first decreased and then increased,and the pressure drop in vertical bend was almost the same as that in the downstream vertical pipe,which all first decreased and then increased.Based on the Euler/Euler model,this paper used the kinetic theory of granular flows incorporating Vescovi friction stress model for solids stress,Huilin-Gidaspow drag model for the interaction between gas and particles,Johnson & Jackson wall model for solids wall boundary condition and Standard k-?-kp-?p model for gas-solid turbulence.Therefore,a two-phase flow model was established for simulating dense phase pneumatic conveying of pulverized petroleum coke in horizontal bend and vertical bend under high pressure.Using the two-phase flow model for simulating dense phase pneumatic conveying of pulverized petroleum coke under high pressure established above,the predicted pressure drop in the bend and the downstream straight pipe were in good agreement with experimental date,and the error was less than 14%,and the flow pattern of the horizontal pipe was basically consistent with the Electrical Capacitance Tomography(ECT)diagram,which confirmed the reliability of the simulation.Through the simulation of a set of experimental conditions with different supplemental gas,it was found that when the particles were in bend,the high concentration region was formed on the outer wall of the bend,and the low concentration region was formed on the inside wall of the bend because of centrifugation and inertia.Besides,the transition region was found between the high concentration region and the low concentration region.After the particles entered the downstream straight pipe from the bend,with centrifugation disappearing,the gravity and drag became prominent and dominant gradually.The frictional stress between the particles in the bend and the wall shear stress between the particles and the wall were much larger than those in the downstream straight pipe,for which the energy consumption and pressure drop in bend was much larger.