Research On Combustion Characteristics Of Typical Coal In Oxy-fuel Conditions

The CO₂volume fraction can reach more than90%in flue gas under Oxygen-enriched combustion, which is advantageous to carbon capture and storage. Inaddition, oxygen-enriched combustion technology for combined removal ofpollutants such as NO_X, SO₂, etc also has a good prospect. So research oncombustion characteristic of the typical coal under oxygen-enriched condition hasimportant significance. The coal-chars combustion occupies the longest time duringthe whole coal combustion process and is a crucial link in the burning process ofpulverized coal. In this paper, the difference of coal-chars that made at differentconditions has been studied, the combustion characteristic of coal-char which madein a simulate real coal combustion atmosphere has been researched, and the coal-char combustion kinetic parameters has been calculated.Two typical coal, datong bituminous coal and shenhua bituminous coal, wereused in this paper, and made14coal-chars in a thermostatic tube furnace and asimulator of high-temperature entrained flow reactor. Ash conservation method isused to analyze volatile release rates and fixed carbon conversion of different coal-chars, and we found that fixed carbon conversion rates increase accordingly as thevolatile release rate increase. The impact of pyrolysis atmosphere in thermostatictube furnace on volatile release rate is not obvious, the coal-chars made in simulatorof high-temperature entrained flow reactor have a lower volatile release rate, thebiggest difference is as high as44.46%, and the loss of fixed carbon is larger. Thepore structure of coal and coal-chars were measured by Automated MercuryPorosimeters, and there is a great difference between two kinds of coal-chars’ porestructure. Graphitization of coal-chars that made in thermostatic tube furnacechange part of the microporous into mesopore and macropore, so the specificsurface area decreased, and pore volume is mainly made up of hole more than10000nm. For coal-chars made in simulator of high-temperature entrained flowreactor, macroporous between5000nm¹2000nm accounted for a large proportion,specific surface peak has improved greatly, but the pore volume peak is smaller.Graphitization of coal-chars that made in thermostatic tube furnace has greatinfluence on the reactivity of coal-chars. Considering the differences between twoexperiment system in the pyrolysis temperature, atmosphere and residence time, weconcluded that the pyrolysis environment in simulator of high-temperature entrainedflow reactor closer to the true pyrolysis process of pulverized coal in the furnace.Then on the HDTF, research has been made on the effects of the initial O₂/CO₂ volume ratio and temperature on burning rate and burn-off rate of char-charsproduced by the high-temperature entrained flow reactor in oxygen-enrichatmosphere. Research results show that: the burning rate is increased with theincrease of residence time, while the increasing rate is decrease; with the sameresidence time, the burning rate is increased with the increase of oxygenconcentration and that of the temperature, and as the coal-char particle’s burningprocess going on, this effect becomes less obvious. With the increase of initialoxygen volume fraction, the average reaction rate increased in different degree, butthe trend slow down if the oxygen volume rate is greater than30%. With theincrease of the temperature in furnace, the average reaction rate is increasedobviously which makes the coal-char burns off more completely, and the rate is lesseffected by oxygen volume rate in high temperature. The pre-exponential factorsdecreases from3488.53to1669.17with the increase of oxygen volume fraction.Due to the activation energy only related to the nature of coal-char itself, so theinitial oxygen volume fraction does not much affect it.