流化床富氧气氛对SO2排放特性的影响

Effect of oxygen-enriched atmosphere on SO2 emission characteristics in fluidized bed

为了研究富氧燃烧气氛下煤在流化床中燃烧SO2排放特性,利用小型流化床反应器,以褐煤和无烟煤为试验原料,分别在21%、29%、42%和56%O2/CO2气氛下进行了燃烧试验,探究了燃烧气氛对流化床煤燃烧中SO2排放的影响。结果表明,在O2/CO2气氛下,随着氧气浓度的提高,2种不同类型的煤在770℃燃烧后,SO2排放量逐渐升高,褐煤SO2排放量从925×10^-6增加到6 526×10^-6,无烟煤的SO2排放量从1 310×10^-6增加到5 357×10^-6。与无烟煤相比,褐煤升高趋势更为明显。氧气浓度对SO2析出速率的影响显著,在15 s甚至更短时间使得SO2析出达到更高的峰值。氧气浓度从21%增至29%时,转化S显著增加,之后随着氧浓度增加,转化S增长趋缓。从机理上解释,高氧浓度为硫化物析出提供了更充足的氧气,促进了SO2的生成,同时高氧浓度加速了挥发分和焦炭的燃烧速度,改善了煤的燃烧和燃尽特性。通过增强煤本身的自热效应,煤燃烧过程加快,促进煤中硫元素的释放,SO2排放量也相应增加。随着氧浓度的增加,褐煤的CO保持在相对稳定的水平,说明氧浓度的变化对此影响较小。褐煤挥发分高,容易出现停留时间不足,导致不充分燃烧,烟气中含有一定量CO等气体。SO2的排放除了与氧气浓度有关外,主要还与煤中含硫量有关,通常含硫量越高,煤燃烧产生的SO2越多。由于试验煤种含硫量均较高,因此SO2排放量处于较高水平,在富氧燃烧过程中,针对含硫量较高的煤种,应充分考虑SO2排放控制问题。灰分也会影响SO2排放量,SiO2和Al2O3对SO2转化为SO3的影响较小,而CaO和MgO作用明显,煤灰中Fe2O3、K2O等含量对此转化过程也有一定影响。

In order to study the SO2 emission characteristics of coal combustion in a fluidized bed under oxygen-enriched combustion atmosphere,combustion experiments were carried out in a small fluidized bed reactor with lignite and anthracite as raw materials under 21%,29%,42%and 56%O 2/CO2 atmosphere,respectively.The influence of combustion atmosphere on SO2 emission from fluidized bed coal combustion was investigated.The results show that with the increase of oxygen concentration,the SO2 emission of two different types of coal tends to increase gradually after combustion at 770℃under the atmosphere of O2/CO2.The SO2 emission of lignite can increase from 925×10^-6 to 6526×10-6 by volume and that of anthracite can increase from 1310×10^-6 to 5357×10^-6 by volume.Compared with anthracite,the increasing trend of lignite is more obvious.The effect of oxygen concentration on SO 2 precipitation rate is also obvious.SO2 precipitation reaches a higher peak value in 15 s or even shorter time.When the oxygen concentration increases from 21%to 29%,the transformation S increases significantly,and then with the increase of oxygen concentration,the transformstion S increases slowly.It is explained from the mechanism that the high oxygen concentration provides more oxygen for sulfide precipitation and promotes the formation of SO 2.At the same time,the high oxygen concentration accelerates the combustion speed of volatile matter and char and improves the combustion and burnout characteristics of coal.By enhancing the self-heating effect of coal itself,the combustion process of coal is accelerated.Therefore,the release of sulfur element in coal is promoted and the emission of SO2 is correspondingly increased.With the increase of oxygen concentration,the CO of lignite remains at a relatively stable level,indicating that the change of oxygen concentration has little effect on it.Lignite has a high volatile content,so it is easy to be short of residence time,which leads to inadequate combustion and a certain amount of CO in the flue gas.The emission of SO2 is not only related to the concentration of oxygen,but also related to the sulfur content in coal.Generally,the higher the sulfur content is,the more SO 2 produced by coal combustion is.The sulfur content of the coal involved in this paper is high,so the SO2 emission is at a high level.In the process of oxygen-enriched combustion,the SO2 emission control should be fully considered for the coal with high sulfur content.The ash also affects SO2 emission,SiO2 and Al2O3 have little effect on SO2 to SO3,while CaO and MgO have obvious effect.The content of Fe2O3 and K2O in coal ash also has influence on the transformation process.