Control Of Coal Oualitv Based On Electrostatic Separation In Dry-Pulverized Coal Gasification Process

The electrostatic separation provides a way of in-situ deashing for pulverized coal of high ash content in the dry-pulverized coal gasification process. The technology realizes the quantitative control of ash content which guarantees the coal quality and promotes the stability and economy of the coal gasifier, thus the research is of great significance. The cold model experiment combined with CFD simulation is the main research method adopted in this thesis to study the triboelectrification characteristics of mineral particles in pipeline triboelectrification system, dynamic characteristics of charged mineral particles in electric field and triboelectrostatic separation characteristics with or without an applied electric field in triboelectrostatic separation system, providing theoretical instruction for designing and optimizing the triboelectrostatic separation system. The main results in this thesis can be summarized as follows:Firstly, the triboelectrification characteristics of main mineral particles in coal were investigated and a triboelectrification model for pipeline triboelectrification system was developed based on the experimental results. Initially, the triboelectric series for coal, main mineral particles in coal and other common friction material was proposed, among which copper was the most suitable one. Moreover, in copper pipeline triboelectrification system, the specific charge increased with the increase of air velocity and pipe length, but decreased with the increase of mass flow rate for calcite, kaolinite, quartz and pyrite. Then a triboelectrification model during dilute phase pneumatic conveying was developed based on the mechanism of continuous collision charging between particles and the pipe wall with correlation coefficient values over0.95and average relative error values under10%.Secondly, dynamic characteristics of charged mineral particles in electric field was studied through CFD simulation. The simulation demonstrated that under simulated conditions herein, increasing the air velocity could increase the separation efficiency of kaolinite and pyrite, but had little impact on calcite and quartz; reducing the particle size was in favor of the separation for calcite and kaolinite, but for quartz and pyrite particles, the smaller particle size was not better. The distribution of mineral particles on plate electrode was also found through simulation:calcite, kaolinite, quartz and pyrite from top to bottom. This was consistent with the experimental results which proved the correctness of CFD simulation.Thirdly, the separation laws of pulverized coal without an applied electric field were discovered in triboelectrostatic separation system and a positive voltage applied to the pipe wall was found to promote the efficiency of triboelectrostatic separation significantly. The experimental results showed that longer pipe length, larger air velocity, lower mass flow rate and larger electric field intensity could increase the efficiency of triboelectrostatic separation. The triboelectrostatic separation device in this thesis was most suitable for pulverized coal mixed by Zhen Xiong Coal and Heng Yuan Coal with diameter ranging from38.5μm to74μm and the limit ash content of clean coal was7.2%after electrostatic separation for several times. Furthermore, an applied electric field was introduced to strengthen the triboelectrostatic separation of pulverized coal in triboelectrification system. A positive voltage applied to the pipe wall improved the efficiency of triboelectrostatic separation while a negative voltage could reduce it.