Characteristics and formation mechanism of plug flow in the industrial vertical pipeline of dense-phase pneumatic conveying of pulverized coal

Abstract

Plug flow, which affects the reliable feeding of pulverized coal, is one of flow patterns in dense-phase pneumatic conveying of pulverized coal. The control and formation mechanism of plug flow are very important for the industrial application and theoretical research. In this work, experiments were carried out on a pneumatic conveying test platform in the Key Lab of Coal Gasification and Energy Chemical Engineering of Ministry of Education, ECUST, to study on the plug flow in the industrial vertical pipe under a low superficial gas velocity. All the flow states and flow patterns of the dense-phase pneumatic conveying process were analyzed. The present study shows that five different particle velocity distributions were found in the plug flow. However, the time series of the pressure and solid concentration signal are almost the same. What’s more, the power spectral density function analysis provides the relationship of the solid concentration signal of the cross-section by the electrical capacitance tomography (ECT) between all four operational cases and five different kinds of plug flows. From the point view of application, five different kinds of the plug flow were characterized by the plug length, fluctuation parameter of the plug flow (the Strouhal number) and the operational parameters (Lockhart–Martinelli parameter and the Froude number of the gas phase and the solid phase). Based on the phase diagram constructed using the Strouhal number and Lockhart-Martinelli parameter, five types of plug flow could be predicted. A larger Strouhal number indicates the poorer stability of the plug flow. Moreover, the formation mechanism of the plug flow was analyzed by the Janssen equation. Finally, we found that all types of the plug flow have the same unit friction force based on a statistical discussion. Through this work, we wish that our research will give a deeper understanding of the formation and control of the plug flow in the dense-phase pneumatic conveying of pulverized coal.