温度对半焦非催化还原CO_(2)的影响

Effect of temperature on non⁃catalytic reduction of CO_(2) by semi⁃coke

2021年我国CO_(2)排放约120亿t,碳减排压力巨大。为实现双碳目标,将CO_(2)转化为CO等基础化工原料是减排CO_(2)、实现其资源化利用的重要途径。采用自主设计的连续给料流态化立式炉装置,以榆林半焦为原料,在CO_(2)气氛下考察了温度(900~1100℃)对半焦非催化还原CO_(2)的影响,并对底渣和飞灰(灰渣)的理化特性进行了表征。结果显示:随着温度的升高,CO_(2)还原率、CO_(2)转化率、CO体积分数、碳转化率以及煤气热值均增大,而CO_(2)体积分数大幅下降,CO_(2)被有效转化为CO,但是在温度超过1050℃后,增长趋势变缓。温度为1050℃时气体组分中CO占64%左右,CO_(2)占30%左右,CO_(2)还原率为50.37%,CO_(2)转化率为0.72 m^(3)/kg。随温度上升,榆林半焦颗粒表面由光滑致密向多孔、海绵状、粗糙过渡,底渣比表面积均超过300 m^(2)/g,比表面积变化存在先上升后下降趋势,飞灰比表面积比半焦最高提升36倍,底渣比表面积比半焦最高提升63倍,灰渣平均孔径降低超过50%。拉曼光谱分析表明,灰渣的活性点位有所增加,石墨化程度降低,由于反应环境不同,底渣的石墨化程度较高;温度上升会加剧CO_(2)与碳的反应,灰渣的活性点位容易被消耗,在1000~1050℃灰渣石墨化程度相对低,活性点位相对多。底渣和飞灰反应活性优于榆林半焦,动力学分析显示飞灰与CO_(2)的反应活化能更低,这为进一步高温转化提供了有利条件。

China emitted nearly 12 billion tons of CO_(2) in 2021,and there will be a huge pressure on carbon emission reduction.To realize carbon peaking and carbon neutrality,converting CO_(2) into basic chemical raw materials such as CO is an important way to reduce CO_(2) emissions and realize its resource utilization.Based on an independently de⁃signed continuous feeding fluidized vertical furnace apparatus,the Yulin semi⁃coke was used as raw material to investi⁃gate the effect of temperature(900-1100℃)on the non⁃catalytic reduction of CO_(2) in semi⁃coke in CO_(2) atmosphere,and the physical and chemical properties of bottom char(BC)and fly char(FC)were characterized.The results showed that with the increase of temperature,the reduction rate and conversion yield of CO_(2),the volume fraction of CO,the carbon conversion rate,and the lower heating value(LHV)of gas all increased,while the volume percent of CO_(2) decreased greatly.CO_(2) was effectively converted to CO,but the trend slowed down when the temperature was over 1050℃.When the temperature was 1050℃,CO accounted for about 64%and CO_(2) accounted for about 30%,the reduction rate of CO_(2) was 50.37%,and the conversion yield of CO_(2) was 0.72 m^(3)/kg.With the increase in temperature,the smooth and dense surface of the semi⁃coke turned porous and spongy,and then became rough,the specific surface area of BC was higher than 300 m^(2)/g,and the area of both FC and BC increased at first and then de⁃creased.The maximum specific surface area of FC was 36 times higher than that of semi⁃coke,while the maximum spe⁃cific surface area of BC was 63 times higher,and the average pore diameter of FC and BC was reduced by more than 50%.Raman spectrum analysis showed that after the reaction with CO_(2),the active sites of FC increased,and the or⁃dered carbon structure decreased,due to the different reaction environment,BC had more ordered carbon structure than FC.With the increase in temperature,the reaction between CO_(2) and carbon intensified,the active sites of FC and BC were easy to be consumed,the ordered carbon structure of FC and BC was relatively low and the active sites were rela⁃tively more between 1000-1050℃.The reaction activity of FC and BC was better than that of the Yulin semi⁃coke.Kinetic analysis showed that the reaction activation energy of FC with CO_(2) was lower,which provided favorable condi⁃tions for further high⁃temperature conversion.