微圆管内甲烷催化着火的实验和数值研究

Experimental and Numerical Study of Methane Catalytic Ignition in a Micro-Tube

对负载Pt催化剂的微圆管内CH_4的催化着火进行了实验研究,比较了三种点火方式下的催化着火温度,即:1)加热反应器外壁、2)预热进口气体、3)H_2辅助催化着火,确定了最优的点火方式,并采用CFD方法对H_2辅助CH_4催化着火的深层原因进行了分析,结果表明:点火方式1)具有最高的CH_4催化着火温度,方式2)的着火温度略低于1),而方式3)的着火温最低,特别是在较高的CH_4浓度条件下,H_2可以显著地降低CH_4催化着火所需要的温度,在CH_4的催化着火过程中,O_2占据催化活性中心(O(s)),抑制了CH_4的吸附,因此着火发生在较高的温度条件下;当掺入H_2以后,H_2的燃烧消耗O(s),为CH4的吸附提供了空位活性中心(Pt(s)),从而降低了CH_4的催化着火温度.

The catalytic ignition of CH4 was experimentally studied in a Pt coated micro-tube, catalytic ignition temperatures with three different ignition inethods were compared： method 1） heating the out surface of the micro-tube, 2） preheating the inlet gases, 3） H2 assisted catalytic ignition. The optimal method was determined, and the underlying of H2 assisted CH4 catalytic ignition was analyzed by using CFD simulations. The results show that catalytic ignition of CH4 at method 1） needs the highest temperature condition, which is slightly higher than that of method 2）, while method 3） has the lowest one. Specifically, with a high CH4 concentration, addition of H2 can dramatically reduced the ignition temperature of CH4. During the ignition of CH4, the surface sites are mainly covered by 02 （O（s））, which inhibits the absorption of CH4, thus leading to a higher ignition temperature. After H2 is added, catalytic combustion of H2 and 02 decreases the coverage of O（s） and increases the mnnber of uncovered surface site （Pt（s）） for CH4 absorption. Consequently, catalytic ignition temperature of CH4 is reduced.