| China’s energy consumption is dominated by coal which result in clean coal utilization technology and improving the utilization rate of coal is the inevitable choice of China’s energy development strategy. Today, the pressurized entrained-flow pulverized coal gasification is the key technology of high efficiency and clean utilization of coal in China. Therefore, it is of important realistic significance to study the high-pressure dense phase pneumatic conveying of pulverized coal system.There is great difference of ultra-dense phase pneumatic conveying system at high pressure because of very high solid concentration and complex flow patterns, the mechanism is unclear so far and the literatures is reported little at home and abroad little. Based on the national "973" project "high pressure under different carrier das more than raw materials, ultra-dense phase pneumatic conveying mechanism and the flow characteristics", this paper studies the influencing mechanism of water content in pulverized coal on the conveying characteristics of lignite. Besides, this paper also researches the correction of the elbow section of multi-fluid CFD model, the establishment of multi-fluid CFD model of binary particles flow and pneumatic conveying of complex pipe systems based on the results of numerical simulation for nitrogen high-pressure ultra-dense phase pulverized coal pneumatic conveying in our research group.In the high pressure and dense phase pneumatic conveying device, this paper studies the transport characteristics of lignite under different conditions and different water content in pulverized coal, and get the method to judge the stability of lignite’s dense phase pneumatic conveying of pulverized coal at high pressure. Experimental results show that the liquidity, transport characteristics and transport stability change slowly at first and then change dramatically with the increase of free moisture in pulverized coal. The corresponding value of the turning point of the powder’s repose angle and the HR index changing with outer moisture is defined as the critical value of outer moisture of lignite’s dense phase pneumatic conveying of pulverized coal at high pressure which can be used to judge the stability of the lignite coal transportation.In the simulation, based on the existing wall model and kinetic theory of granular flow and given full consideration of impact of friction in the elbow, this paper modifies the elbow section of multi-fluid CFD model. Considering the interaction in particle component and between the particle components, a multi-fluid CFD model of binary particles flow is established based on the correction of the viscosity, solid pressure, radial distribution function and particle collision dissipation coefficient. According to the existing multi-fluid CFD model, this paper also simulates a 14m long pipeline transport system and describes the flow status of each section which shows the difference of flow characteristics among five kinds of curved pipe. The simulation results show that the error of elbow pressure drop between simulation and test is reduced to a reasonable range after amending the multiphase flow model of the elbow, then using the model to simulate the elbow to gain the gas-solid flow characteristics and the effect of renew gas on the gas-solid flow. In the binary particles flow, due to the bigger dragging force, the small particles are suspended on the large particles in the horizontal pipe and go upper with the increase of superficial gas velocity. In the vertical pipe, small particles are aggregated in the pipe center and in the wall around the small particles and large particles exist simultaneously, while the volume fraction of small particles with higher centrifugal acceleration is lager around outer-wall in the elbow. The error between the pressure drop predicted by multi-fluid CFD model of binary particles flow and experimental data is less than 25% in horizontal pipe and 20% in vertical pipe. |
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