Chemical Composition Determination And Formation Mechanism Of Soot In MILD-OCC Combustion Flame

Fossil fuel such as coal,oil and natural gas is the main source of energy for human society.After a long period of over-exploitation and huge consumption,it will eventually be exhausted.The accompanying environmental degradation has also attracted great attention from the international community.The coordinated development of energy and environment is the main prerequisite for achieving sustainable economic and social development goals.Severe energy pressure and environmental pressure urgently need to accelerate the development and utilization of a new cleaner,more environmentally friendly and more economical combustion mode.Combining Moderate & Intensive Low Oxygen Dilution(MILD)combustion method and Oxy Coal Combustion(OCC)method,a new coal-saving and environment-friendly combustion mode is formed: Moderate & Intensive Low Oxygen Dilution –Oxy Coal Combustion(MILD-OCC)method,which has the advantages of carbon emission reduction,high thermal efficiency and low pollution.Coal and methane were mixed and burned in the MILD-OCC flame,flame temperature was measured at different flame locations with a rapid insert thermocouple,then soot volume fraction could be gotten by thermocouple particle densitometry(TPD),combining with the mass concentration of soot by the filter weighing method to obtain the distribution characteristics of soot in the flame.Soot samples were collected at specific locations in the MILD-OCC flame and analyzed with gas chromatography-mass spectrometry(GC-MS),as well as transmission electron microscopy(TEM).The results showed that the flame temperature distribution is roughly negatively correlated with the soot concentration distribution,that is,the flame temperature rose first and then decreased in the radial direction,while soot mass concentration dropped and then increased in general.As to morphology of soot particles,it exhibited spherical particles separately in the lower part of flame while chain-like structures in the upper.It is indicated that the higher temperature is beneficial to the volatilization of organic carbon in soot to make the particle size smaller,but as the flame height increases,the collision between the particles collides and merges,and the single soot particles gradually become chain structure.Alkanes,olefins,henols,furan and aromatic compounds were determined as the main components of soot by the detection of GC-MS.The process of soot formation in the MILD-OCC flame can be speculated as coal pyrolyze and burn in the high temperature,gas precursors initiate to nucleation,then agglomerate and oxidize to form soot particles.