Oxyfuel Combustion Characteristics Of Pulverized Coal Based On Flat-Flame Assisted Entrained Flow Reactor

Oxy-fuel combustion technology （also named O₂/CO₂combustion technology） ofpulverized coal has received considerable attention as one of the potential approaches toachieve a sequestration ready CO₂gas stream from coal fired power plants. Due to thedifferenced in the experamental conditions, it was inconsistent that the effects and actionmechanisms of high content CO₂on the combustion process of pulverized coal. Thedevolatilization, ignition and burnout processes of pulverized coal were investigated indetail under the simulated flue gas, which was close to the industrial furnace and wasprovided by the flat-flame assisted entrained flow reactor.A flat-flame assisted entrained flow reactor was used to conduct the devolatilizationexperiment. The chars were prepared under oxy-fuel and air combustion conditions. Theapparent volatile yields, the physical-chemical properties and reactivites were studied. Theresults indicate that the high content CO₂inhibits the volatile release of high volatile coal（lignite and bituminous coal） and increases the apparent volatile yield of low volatile coal（anthracite coal）. The high content CO₂also increases the specific surface area of highvolatile coal and decreases the specific surface area of low volatile coal. Meanwhile, theactivity of chemical structrues of char-CO₂is higher than that of char-N₂. Compared to thechemical characteristics, the physical characteristics of char play a major role on theapparent reactivity.The ignition and devolatilization behaviors of pulverized coals under oxy-fuel and aircombustion conditions were investigated using the high speed camera. The ignition delaytime, ignition stability and delay of devolatilization were analyzed. The results indicatedthat the ignition delay time is inversely proportional to YO₂,sn，n is0.15⁰.2. The present ofhigh content CO₂lead to the increase of ignition delay time and ignition stability of highvolatile coal. To the contrary, the present of high content CO₂lead to the decrease ofignition delay time and ignition stability of low volatile coal. Meanwhile, the high contentCO₂lead the delay of devolatilization procedure.The burnout behaviors of selected Chinese and U.S. typical power coals under O₂/CO₂and O₂/N₂atmospheres were investigated in the flat-flame assisted entrained flow reactor.And the reaction kinetic parameters based on the char oxidation reaction （C+0.5O₂â†'CO）and four steps detail reactions were respectively solved from the burnout curves. The results indicated that the suppression effect of high content CO₂on char burnout is morethan promotion effect of CO₂gasificaition reaction on char consumption at the high oxygencondition. The contribution of CO₂gasificaition reaction on char consumption can beenhanced through reducing the oxygen concentration. At the low oxygen conditions, thepromotion effect of CO₂gasificaition reaction on char consumption is obvious. But thepromotion effect cann’t be observed on JC anthracite coal. The oxygen atoms chemicallyadsorbedon char surface, resulted by the char-CO₂gasification reaction, leads the reduce ofrelease rate of oxygen element. The coal burnout process was found to be the competitiveprocess between elimination of the original amorphous mass and formation of newamorphous materials. At the stage of pyrolysis, the large aromatic ring system （microcrystalgraphite） keep stable, and the aromatization of aliphatic chain caused the increase of smallaromatic ring system （amorphous carbon）. At the early and late stage of char burnout, thegeneration and consumption of amorphous carbon respectively play a dominant rolebecause of oxidation reaction. This finding is important for analyzing the change of charreactivity during char burnout.Finally, the reaction kinetic data were collected, which can be used to build a databaseand incorporated into a computational fluid dynamics model for subsequent design andscale-up purposes.