Investigations of pulverized coal pneumatic conveying using CO2 and air

The pneumatic conveying experiments at the high solid–gas ratio (120–300 kg/m3) were carried out to compare their conveying characteristics separately using CO2 and air as carrier gas. The differences between them are found to be related with fluidized state of pulverized coal in the feeding vessel and can be explained with material properties involving particle–gas interactions, permeability. Employing electrical capacitance tomography (ECT), the transition from full pipe flow to annular flow was observed with increasing the superficial gas velocity (3.0–8.5 m/s) in the vertical pipe and the flow patterns with CO2 and air are found to be similar. The analysis shows there is a significant association between sharp fluctuations of the pressure signals and gas slug. When gas slug was observed in the pipe, there was a large pressure pulse. The occurrence of gas slug is also found to be higher in the transporting with CO2 as carrier gas. The pressure signals may therefore be used to identify gas slug appearing in the pipe. The energy analysis is presented to find that the energy consumption with CO2 is about 7.5% higher than that with air at the same gas flow rate, but the required energy with CO2 is increased by about 20% than that with air at the same solid mass flow rate.