Experimental research on pressure drop in elbows in dense phase pneumatic conveying of pulverized coal at high pressure using CO2/N2 as carriers

The pressure drop characteristics in the horizontal and vertical elbows of the pipeline for pulverized Yanzhou bituminous coal using CO2 and N2 as conveying gas separately were investigated at high operating pressures in the experimental equipment for dense phase pneumatic conveying. Then the effect of the moisture content of Yunnan lignite powder on pressure drop in the horizontal and vertical elbows was studied. The experimental results show that the pressure drop in the horizontal elbow decreased with the decrease in the apparent gas velocity using CO2 or N2 at the same total conveying differential pressure, and the concentration of the powder with CO2 was smaller than that with N2. The pressure drop in the vertical elbow decreased with the decrease in the apparent gas velocity, and the pressure drop in the vertical elbow using N2 as conveying gas reached the minimum value when the apparent velocity dropped to around 5.3 m/s, while the pressure drop change in the vertical elbow using CO2 as conveying gas had no such inflexion. Moreover, due to the change of the elbow location, the pressure drop in the vertical elbow with CO2 was higher than that with N2. Further, the pressure drop in the horizontal elbow increased with an increase in the moisture content of pulverized coal with CO2 or N2 because of the powder adhesion and agglomeration caused by the increasing moisture content. Generally, the pressure drop in the vertical elbow decreased slightly with an increase in the moisture content. The regression formulae were obtained to predict additional pressure loss coefficient of the solid phase in horizontal and vertical elbows with different conveying gas on the basis of the modeling theory and analysis on the experiment, and the predicted results are in accordance with the experimental data with the relative error of within ±5%.