The Effect of Permeability on Lignite Fly Ash Pneumatic Conveying System Design

The aim of this experimental study was to evaluate the effect of permeability on the mode of flow that lignite fly ash will support in a pneumatic conveying pipeline. This research was initiated by recurring problems with the long distance and high capacity low grade lignite ash pneumatic conveying system at the 1200 MWe thermal power plant, such as clogging, unsteady flow mode, significant increase of velocity due to pressure drop and erosive wear of pipeline. Ash samples were taken during pneumatic conveying system clogging for further analysis. The experiment was limited to measuring parameters that provide data to determine minimum fluidizing velocity and permeability. The results showed very heterogeneous materials of group B by Geldart, what caused specific phenomenon during the experimental fluidization tests. Minimum fluidizing velocity for this kind of material is not authoritative for defining pneumatic conveying system, since extremely heterogeneous materials at this air speed will remain stationary or will convey very slow or with stoppage, and that required velocities are from 10 to 15 times higher than minimum fluidizing velocity. According to the results, this ash is the most suitable for dense phase pneumatic conveying.

Flow Characteristics on Fluidized Powder Conveying in a Horizontal Rectangular Channel

This study experimentally examined the dense phase pneumatic conveying in a horizontal rectangular channel using the fluidizing air. The powder used is PVC belong to Geldart A particle, where the mean diameter is 151μm, the particle density is 1382kg/m3 and the minimum fluidizing velocity is 9.0mm/s. As the experimental conditions, the fluidizing velocity at the bottom of a vessel and the horizontal channel has been changed. Also, the mass of transported powder, the supply air pressure and the height of powder bed inside a vessel were measured. In the case of PVC, we confirmed the flow characteristics of the powder conveying and air pressure. Further, we found that the fluidizing air to the bottom of a vessel was required to the powder conveying of this system, and that the fluidizing velocity at the horizontal channel needs to be larger than the minimum fluidizing velocity. These results were also obtained on the previous study when two kinds of glass bead was used. The mass flow rate and solid loading ratio were estimated by the measured data of the mass of transported powder. In addition, these results were compared with the conveying characteristic of two kinds of glass beads belongs to Geldart A and B particle. As a result, the mass flow rate and solid loading ratio of PVC were smaller than that of two kinds of glass beads.

Influence of Fluidizing Velocity on Fluidized Powder Conveying in a Horizontal Rectangular Channel

This study experimentally investigated the high dense pneumatic conveying of glass beads in a horizontal rectangular channel using the fluidizing air. The powder used belongs to Geldart A particle, where the mean diameter is 53 μm, the particle density is 2523kg/m3 and the minimum fluidizing velocity is 4.329mm/s. The fluidized powder conveying system consists of a powder supply hopper, a horizontal rectangular channel at the side of hopper and a receiving tank. The powder was fluidized by air through the porous membrane at the bottom of hopper and horizontal channel. Then, this system could be transported the fluidized powder toward the horizontal direction. In this study, the mass of transported powder, the bed height of powder in a hopper and the supply air pressure were measured when the fluidizing velocities at the bottom of hopper and horizontal channel were changed. The mass of transported powder with the fluidizing air to the bottom of hopper multiplied rapidly when the fluidizing velocity at the bottom of horizontal channel was larger than the minimum fluidizing velocity. Therefore, the fluidizing air at the bottom of hopper and horizontal channel was important to obtain smooth powder conveying on this system. Also, the mass flow rate of powder and the solid loading ratio were estimated from the mass of transported powder against the elapsed time. As the result, the solid loading ratio has taken a one peak when the fluidizing velocity at the bottom of channel was larger than the minimum fluidizing velocity. It was found from the analyzed solid loading ratio that the high dense powder conveying was possible in this system.