Experimental Study On The Gas-Solid Flow Characteristics Inside Elbows

Bias combustion is a new combustion technology which can both decrease NOx emission and stabilize combustion under low load for the boiler. Currently, the measure of the coal concentrator installed in front of the burner is taken most widely which is the simplest way to achieve bias combustion techniques. There is usually an elbow settled in the primary air pipe before entering the burner. The addition of the elbow leads to different gas flow distribution which affects the performance of the concentrator. In order to fully understand the effect of separation on the fine particles in the elbow, an experimental study on the characteristics of gas-solid flow within and after the elbow was taken in this paper. The elbow with the curvature-to-diameter ratio of 1.5 was taken as the research object, and the glass beads were added as solid particles whose volume average particle size was 29.1μm.The distribution of particle concentration and particle velocity of main direction were measured at different positions after the exit to the horizontal-to-vertical elbow with circular cross-section using PDA test system, in which the critical position of the flow field restoring even after the exit to the elbow was obtained. By comparing the impacts of different loads on the distribution of particle concentration and velocity in the plane of bending after the exit to the elbow, it was concluded that the concentration in the elbow was enhanced with the increasing load, while the particle velocity decreased in the high concentration area near the outside wall.This paper compared the effect of elbow forms on the particle concentration distribution, in which the horizontal-to-vertical elbow and the vertical-to-horizontal elbow were considered. The particle concentration distribution after the exit to the elbow with circular cross-section was measured by the online monitor of pulverized coal. The results show that particles had a stronger secondary flow in the horizontal pipe after the exit to the vertical-to-horizontal elbow and particles of high concentration zone spread more quickly at the same time, due to the different gravity effects.For the same experimental conditions, this paper compared the measurements of particle concentration by PDA system and the online monitor of pulverized coal and explained the reason for the difference between the concentration measurements of two instruments. The results show a similar trend by two instruments, which indicates that both instruments can qualitatively describe the gas-soild two phase flow characterictics.For the vertical-up-to-horizontal elbow with rectangular section, the gas-soild two phase flow field was measured at several representative cross sections in the elbow as well as the downstream line of elbow by PDA test system. The gas-solid separation performance of the rectangular elbow was also analyzed.