Study On Characteristics And Influence Factors Of Discharging Pulverized Coal From Aerated Hopper

This paper mainly focuses on the study of powder feeding system with the background of pressurized entrained-flow gasification technology of pulverized coal. Two typical coals, Beisu and Yangchangwan coal were chosen as experimental samples. The discharge characteristics and influence factors of discharging pulverized coal from aerated hopper were investigated. Some research results will offer great support for the development of hopper discharge theory and industrial operation. Main research content is shown as the following:1. Flowability parameters of pulverized coal were measure by powder characteristics tester. Based on analysis of the criteria, such as Hausner Ratio, angle of repose, Carr flowability index, the flowabitliy of pulverized coal was determined. Due to small particle diameter and large specific surface area, Beisu and Yachangwan pulverized coal showed strong agglomeration and poor flowability, typical of Group C powders. Friction parameters of pulverized coal were measured by Shear Tracâ…¡system and used for hopper design. An unsuitable hopper with small half angle and large outlet diameter was obtained, which indicated the limitation of Jenike theory for cohesive pulverized coal. The flowability of pulverized coal within 1000kPa preconsolidation stress was investigated, which indicated the limitation of existed flowability theory at high pressure.2. Effects of aerated method on hopper discharge were discussed in two ways:aeration into cone and into standpipe. The former was further investigated based on Altiner's research including "line source case" and "distributed case". By combination of their advantages, an optimized aerated method was developed, which could not only improve the solid discharge rate but also ensure the hopper strength. Aeration into standpipe could break arches and regular the solid discharge rate in a certain degree. Proper aeration could increase the solid velocity, concentration as well as the discharge rate. However, excess aeration diluted the solid concentration so as to decrease the discharge rate.3. The discharge of pulverized coal from an aerated hopper under several aeration rates was studied. Four flow regions were developed, and the major phenomena occurred during the discharge were analyzed. The proposed mechanism of aerated discharge was confirmed by the experimental data. It was thought that the mechanism integrated the effects of several factors, including:(1) Gas injected is to overcome negative gas pressure within the solids during flow. (2) Gas can fluidize powders to a certain extent and increasing gas flow merely increases the volume of powders affected. (3) Gas flow provides the energy input necessary to overcome interparticle interactions.4. The fluidization behaviors of pulverized coal in a fluidization column and in an aerated hopper were investigated and compared. The influence of gas type (air, He, H2 and CO2) on gas-solid fluidization was discussed and used to analyze the discharge characteristics of pulverized coal including discharge rate and stability. Nedderman's mode was used to predict the discharge rate, which agreed well with the experimental data with the error kept below 20% except individual points at low aeration rate.5. The concept of fluidized-pressurization was proposed based on the investigation of effects of gas supplement method on gas-solid behaviors and hopper discharge. An operation method suitable for pressurized discharge was developed including four key parts. Effects of pressure on hopper discharge were discussed within 0-1800kPa. It was found that the increase of hopper pressure increased gas flow rate, decreased gas superficial velocity and improved solid discharge rate in a certain degree. In addition, the increase of hopper pressure reduced the discharge differences between the air and CO2 aeration series.