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1、催化剂颗粒外形对甲烷水蒸气重整反响的影响及工业反响器模拟秦雯;周志明;程振民【摘 要】Methane steam reforming (MSR) is the most widely used technology for hydrogen production in industry now, where the shape of catalyst particles and the reactor operating conditions greatly influence the reactor performance and the product composition. First
2、ly, the present study investigated the effect of catalyst shape (sphere, cylinder and ring) on the MSR using a diffusion-reaction model on the particle scale. The effectiveness factors of shaped catalysts followed the sequence:cylinderspherering. Next, a one-dimensional mathematical model was develo
3、ped by taking into account the mass, heat and momentum transfer on the reactor scale together with the diffusion- reaction equations on the catalyst scale, and used to describe an industrial MSR reactor. The effects of inlet temperature and pressure on the profiles of temperature and pressure inside
4、 the reactor, effectiveness factor, conversion of methane as well as concentration of various species were studied. Finally, the optimal inlet temperature and pressure for the industrial reactor were determined, being 773 K and 3 MPa, respectively.% 甲烷水蒸气重整工艺是现阶段最主要的工业制氢技术，催化剂颗粒外形和反响器操作条件是影响重整反响器性能和
5、产物组成的重要因素。首先从颗粒尺度争论催化剂外形对甲烷水蒸气重整反响的影响，在不同的反响温度和压力下，计算并比较了球形、柱形和环形催化剂的效率因子，其大小挨次为：柱形球形 球形 柱形，这与它们的比外表积大小挨次全都环形、球形和柱形催化剂的比外表积分别为 769、397 和 325 m1，此处只计入环形和柱形催化剂的侧面积，说明催化剂比外表积的差异导致了催化剂效率因子的差异。这是由于催化剂的比外表积对传质的影响较大，而效率因子即是反映传质对反响速率的影响。由图 2 和图 3 进一步可见，工业催化剂颗粒的效率因子普遍很低，即便是环形催化剂也不例外。图 4 显示了环形催化剂颗粒内部各组分的摩尔分数变
6、化，在催化剂外外表四周各组分的浓度梯度变化猛烈，这充分说明催化剂的内集中影响较为严峻。2.2 工业反响器的模拟本文对甲烷水蒸气重整制氢工业反响器的构造尺寸和进料组成做以下规定：工业反响器的长度、内径和壁厚分别为 12、0.1 和 0.015 m，这与 Xu 等13以及Pantoleontos 等15承受的重整反响器相像；参照 Alberton 等29使用的原料气组成，假设反响器进口物料中的 CH4、H2O 和 H2 的摩尔分数分别为 0.24、0.75 和 0.01，进口总流量为 25 kmolh1；参考 Xu 等13的报道，假设反响器外壁温度沿轴向呈线性增加的规律，且在反响器进、出口处分别为
7、 973 和 1173K。2.2.1 进口温度的影响图 5 给出了当反响器进口压力恒定为 3 MPa 而进口温度分别为 773、873 和 973 K 时，反响器内的温度和压力分布。由图可见，气体温度呈先降低0 z 球形 柱形。（2） 甲烷水蒸气重整过程中的 3 个主要反响的吸放热状况不尽一样，其效率因子也存在差异。其中，蒸气重整反响式1和式3的效率因子均为正值且相差不大，而水气变换反响式2的效率因子时正时负，取决于具体的反响条件。（3） 操作条件确实定是工业生产中一项重要内容。对于本文重点争论的环形催化剂，将其装填入反响器进展生产时，优选的工业重整反响器进口温度和压力分别为773 K 和 3
8、 MPa。A 反响器横截面积，m2bj组分 j 的吸附常数，bCH4、bCO 和 bH2 的单位为 kPa1，bH2O 为量纲 1 cp工艺气体的比热容，Jg1K1 dc催化剂颗粒直径球形和柱形，mdc,in, dc,out分别为环形催化剂内径、外径，mdce颗粒当量直径，mdt,i, dt,e分别为反响器内径、外径，m De,j组分 j 的有效集中系数，m2s1 E 活化能，kJmol1Fj,F0j分别为组分 j 的瞬时流量和初始流量，kmolh1 f 动量方程中的摩擦系数Hi第 i 个反响的焓变，kJmol1 hi给热系数，Jm2h1K1Keq,i第 i 个反响的平衡常数，bar2式1和式
9、3、量纲 1式2ki第 i 个反响的速率常数，k1、k2 和 k3 的单位分别为molkPa0.5kg1s1、molkg1s1kPa1 以及 molkPa0.5kg1s1 pb,j气体主体中组分 j 的分压，MPapc,j催化剂颗粒内部组分 j 的分压，MPa pt总压，MPaQj组分 j 的吸附热，kJmol1 Re Reynolds 数r, rc, rb分别为反响速率、催化剂内部的反响速率和气相主体的反响速率；molkg1s1T 气相主体温度，K Tw反响器外壁温度，K U传热系数，Jm2h1K1us表观速率，ms1V催化剂体积，m3 x催化剂颗粒径向位置坐标，m z反响器轴向位置坐标，m
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