Gas-solid Flow And Pressure Fluctuation Characteristics In Component Beds

In dense-phase fluidized bed,gas exists mostly in the form of bubbles,and large bubbles not only cause uneven gas-solid contact in the bed,but also easily cause large fluctuations in the operating parameters of the bed,thereby affecting the process efficiency and the stability of the device.The provision of baffle component in the bed to suppress the bubble size has proved to be an effective method and has been more researched and applied.Previous studies have shown that a“cavity”is formed below the baffle component,and it is pointed out that the change of the“cavity”height has a great influence on the pressure fluctuation in the bed.But the systematic description that the characteristics of the“cavity”extends the whole process down and the impact of component breaks bubbles is lack.There are also few systematic research reports why the components are effective in reducing the overall bubble size in the bed within a certain range of gas velocity,what the flow state is and how the course of the“cavity”change is with the gas velocity below the component.What is the corresponding that relationship the flow state under the component and whether the component can effectively break bubbles,etc.In this regard,a low-pressure baffle-type component of“rotating sieve tray type”will be installed in the bed within a wide range of gas velocity,through comparison and analysis of the single component bed and double component bed in this study.The flow phenomena in the free bed,the standard deviation of the differential pressure fluctuation,and the standard deviation of the pressure fluctuation determine the flow and operating conditions in which the single bed and double block beds can effectively break bubbles.For the single component bed,the particles under the component flows up constantly to the above bed with superficial gas velocity increasing resulting in a continuous decrease in the density of the dense bed below the internals.In this region,three types of flow conditions appear,which directly determines whether the component can break bubbles or not.In the area below the internals,when U_g<0.44m/s,the dense bed is at a higher height,forming a bubbling fluidized bed with dense bed at the bottom,dense phase and large bubbles at the top which are alternately through the internals.At that time,the component can suppress the growth of bubbles and break bubbles.And the standard deviation of differential pressure fluctuation and pressure fluctuation in the whole bed is lower than free bed under the same conditions.When 0.44?U_g<0.66 m/s,the dense bed has lower material height.It forms a dense bed in the lower region and a single dilute turbulent fluidized bed in the upper region.And the component no longer suppresses the growth of bubbles or breaks bubbles directly.However,it can reduce the strength of pressure fluctuation under the component and at a certain height above the internals,because of the dense bed which is under the internals.When U_g?0.66 m/s,the dense bed completely disappears,which forms a dilute phase fluidization state where the gas is a continuous phase.And the component can not break bubbles and make bed pressure and the strength of differential pressure fluctuation lower any more.When a component is installed and the bed height is 0.9 m,the pressure in the bed will increase when the loading height is 0.7 m,and the speed transition point of the three kinds of flow conditions below the corresponding component will advance.In the bubble bed state,the fluctuation strength of the pressure difference increases at the bottom of the component and in the region including the component with the height of the static bed increasing in the bed.When two components are installed and the static bed height of the bed is the same,and the corresponding three flow state transition points of velocity below the first component are similar to the single component bed.The flow phenomenon between the two components is similar to the other under the first component and the component has a stronger effect on breaking bubbles.Corresponding to the standard deviation of pressure fluctuation and the standard deviation of pressure fluctuation in each zone in the bed,it is lower than the single component bed.