Characteristics of high pressure dense-phase pneumatic conveying of pulverized coal blending extract residue of direct coal liquefaction residue

Mixing the Extraction Residue of Direct Coal Liquefaction Residue (ER) into pulverized coal as fuels for co-gasification processes demonstrates a way of multi-utilization of the ER waste. But the stability and controllability of the pneumatic conveying process of this new mixture has not been studied yet. In order to investigate on the pneumatic conveying characteristics of this mixture, the pure pulverized coal and the mixture which contains of 80% pulverized coal and 20% ER were prepared as experiment samples. The fluidity of these two samples was firstly evaluated by the Hausner Ratio (HR) and Flow Function (FF) method, with their microscopic structures analyzed using SEM (Scanning Electron Micrographs). Then the high pressure dense-phase pneumatic conveying experiments were conducted at back pressure of 4 and 2 MPa, with conveying pipe diameter of 25 mm. During the experiment, the relationship between conveyed mass flowrate particles concentration and superficial gas velocity were analyzed. The stability of conveying process was evaluated with the fluctuations level of the particles mass flowrate and pressure drop of horizontal pipe, the maximum and the averaged fluctuation level of these two measured values were calculated and recorded. Results showed that the fluidity of the coal particles blended with ER became worse when comparing to the pulverized coal, evaluated by both HR and FF functions. When conveying at same superficial gas velocity, the measured mass flowrate of the mixture is similar to the pulverized coal at a high back pressure level (4 MPa), while decreases when the back pressure level drops to a lower level (2 MPa). When conveying under a same pressure level, the mixture showed a poor concentration rate compared to the pulverized coal at low superficial gas velocity, while they performed a similar concentration rate when superficial gas velocity above the critical gas velocity. In general, when the superficial gas velocity was lower than 4 m/s, the mixture of coal particles blended with 20% ER performed a poor stability compared to the pure pulverized coal. When the superficial gas velocity above 4 m/s, this two particles performed a same stability level with the mean fluctuation of mass flow rate less than 4%, the maximum fluctuation less than 15% and the mean fluctuation of pressure drop at horizontal pipe section less than 8% and maximum fluctuation less than 40%. © 2020, Editorial Office of Journal of China Coal Society. All right reserved.