Study On Characteristics Of Flow Patterns In An Industrial-Scale Feeding Process For Pulverized Coal

In order to satisfy the requirement of high efficiency of carbon conversion in entrained-flow gasification, the dense-phase pneumatic conveying experiments were conducted by an industrial-scale vertical pipe (50 mm I.D.), in which CO2 and air were applied as carrier gas. The flow patterns in vertical and Venturi tube were visually monitored by employing electrical capacitance tomography (ECT). Furthermore, the stability of ECT signals were analyzed in terms of relative standard deviation (Rd) function, probability density function (PDF) and power spectral density (PSD) function.In the case of Venturi conveying systems at a certain aeration condition, a critical feeding vessel pressure range could be obtained, in which the conveying hed the best stability and the effective utilization rate of pipeline pressure attain to optimally. The ECT results showed that the flow patterns in contraction and throat of the Venturi were both layered annular flow and the flow stability at the entrance of contraction was higher than that in the middle of throat section, while the worst flow stability was monitored at the outlet of contraction.The higher flow stability, flow rate and the particle velocity of pulverized coal were observed when applied air as carrier gas rather than CO2. In the case of straight tube system, the compound modes of feeding gas as well as carrying gas would affect the fluidized state of pulverized coal in the feeder vessel and therefore, result in the differences of stability and flow patterns of conveying process. The ECT signals monitored at variable cross-section showed that the flow pattern in the Venturi were basically annular flow but the thickness of the particle phase near the pipe wall changed with location.Flow patterns of pulverized coal at different pressure range were investigated by the vertical pipe. With the increasing pipe pressure, a progressive transition from annular flow to the plug flow and then to plug flow patterns was observed. The flow rates were reduced as the increase of pipe pressure, instead, an ideal flow state described by a low flow velocity, high concentration and flow stability had been obtained.