Characterization Of Micro-crystalline Structure And Particle Size Distribution Of Soot Generated By MILD-OCC Flame Combustion

Energy is an important pillar of sustainable social development.Coal combustion occupies a very important position in China’s energy structure,and this energy structure is difficult to change for a long time.Coal is a complex high-molecular organic compound.Soot particles will be produced in the state of incomplete combustion.The content of soot particles in the air accounts for 30%of the total pollutant content.After the human body inhales the respiratory tract,it will seriously threaten human health.Therefore,low-oxygen diluted oxygen coal combustion technology（MILD-OCC）has gradually become well known as a new type of clean combustion technology.Two types of coals and CH₄were burned with O₂in a MILD-OCC mode while taking CO₂as diluted gas.By setting the sampling point in the flame,the flame temperature distribution was obtained by the thermocouple,and the Fast plug-in sampling system was used to sample at different points and used the Transmission electron microscope to obtain the TEM images,then some software tools like MATLAB,Image J and Digital Micrograph were resorted to analyze the micro-crystalline structure and particle size distribution（PSD）of soot generated by MILD-OCC.The results showed that the flame temperature distribution was uniform as a whole,and gradually dropped after a slow increase at the radial direction of the flame,while the temperature presented decreasing trend along the height above burner（HAB）at the axial direction.The flame temperature is high and uniform in the center of the flame,and the temperature is lower at the edge of the flame,which is mainly caused by heat exchange.It can be seen that when HAB=10mm,the soot were all exist in the single state and there were oil drop-like substances attached to the surface of the particles,with irregular shape.When HAB=20mm,soot were obviously spherical,and the edges of the particles were relatively clear.Starting from HAB=30mm,the particle size of basic particles was increased.When HAB=40 mm to 50 mm,emergence of chain shaped soot could be found.Both of PSD for the soot generated from two types of coal were between 0.02μm to 0.04μm,and all had the tendency of increasing at first and then decreasing.Soot layer spacing was mainly distributed between 0.32nm to 0.45nm,and the micro-crystalline size peak was between 0.4nm to2.2nm,while the peak value of curvature occurred at 1.0 to 1.5;as the HAB increased,the micro-crystalline size gradually increased as well,the change trend of layer spacing and curvature was opposite to micro-crystal size.