The dense-phase pneumatic conveying of pulverized coal was investigated in an industrial-scale vertical pipe (50 mm I.D.). Air and CO2 was used as feeding gas or carrying gas

which consequently forms four typical cases

namely Air→Air

Air→CO2

CO2→Air and CO2→CO2. Comparison was conducted between the above cases to analyze the conveying characteristics of pulverized coal experienced different courses. The results showed that the compound modes of feeding gas and carrying gas could affect the fluidized state of pulverized coal in the feeder vessel and result in the differences of stability and flow patterns of conveying process. Electrical capacitance tomography (ECT) was employed to monitor the flow patterns

while the solid concentration signals obtained from ECT were analyzed on the basis of standard deviation (SD) function and power spectral density (PSD) function. It was concluded that the flow pattern of pulverized coal in the case of Air→Air was a stable annular flow

and the stability of the case of Air→CO2 was the worst in which the flow pattern changed from a stable flow to slug flow. Both cases of CO2→Air and CO2→CO2 performed plug flow. In comparison

in the case of CO2→CO2

the bigger plug and higher peak value of PSD were obtained.