低氧快速热解过程中氧气体积分数对活性焦孔隙结构的影响

为研究成本低、性能高的脱硫用活性焦,以烟煤为原料,在沉降炉试验台上研究低氧快速热解条件下活化氛围中氧气体积分数对活性焦孔隙结构的影响。通过氮气吸附、骤冷密度泛函理论研究活性焦的孔隙结构的演化,通过扫描电镜的方法研究活性焦的表面烧蚀特性。结果表明,低氧快速热解为挥发分析出为主的过程。所获得活性焦的低吸附等温线的类型具备Ⅰ型和Ⅳ型等温线的特征,孔隙结构以微孔结构为主。活性焦表面发生不同程度的烧蚀,表面烧蚀缺陷近似圆形,并且随着氧气体积分数的增加,烧蚀从表面逐渐向颗粒内部发展。适当的氧气含量有利于活性焦孔隙结构的发展,氧气体积分数低于6%时,氧气体积分数的增加使微孔结构更加丰富,孔容积和比表面积均有很大程度提高。氧气体积分数增加到一定程度(8%)时,由于孔壁的塌陷,最终导致活性焦的表面积和孔容积有大幅度的降低。

Effect of oxygen concentration on activated char pore structure-during low oxygen fast pyrolysis

In order to develop cheap and high-efficiency activated chars for desulfuration，bituminous coal powders were used to prepare activated chars through fast pyrolysis process in a drop-tube reactor and the effect of oxygen concentration on pore structure was investigated.The samples were characterized by QSDFT (quenched solid density functional theory) method using nitrogen adsorption and scanning electronic microscopy (SEM).The results indicate that devolatilization is a dominate process during the pyrolysis of coal powders at low oxygen levels.The absorption isotherms of char samples show some features of type Ⅰ and type Ⅳ isotherms，characterized with a significant proportion of micropore structure.Surface ablation was studied from a microscopic view and it shows that the shape of surface ablation is nearly circular.Meanwhile，with the increase of oxygen concentration，the surface ablation develops from the surface to the interior of particle.Moreover，the results show that appropriate oxygen concentration is beneficial to the development of pore structure.When the oxygen concentration is below 6%，the pore volume and surface area increase with the increase of oxygen concentration，while when the oxygen concentration increases to a certain degree (i.e.，＞8%)，the pore volume and the surface area are obviously reduced due to the collapse of pore structure.