Numerical simulation of particle-resolved fixed-bed reactor for selective acetylene hydrogenation process

doi:10.11949/0438-1157.20240406

Abstract

Abstract:

Ethylene production is a key indicator reflecting the development level of a country's petrochemical industry. A particle-resolved fixed-bed reactor model for selective acetylene hydrogenation process has been established. The impact of cylindrical particle packing structure on the transport processes has been analyzed and the influence of operational conditions on the reaction performance has been explored. The results showed that the pressure drop in the catalyst bed mainly happened in the entrance section of the reactor, where the reaction rate of acetylene hydrogenation is the highest. However, in the latter half of the bed, the catalyst particles are not fully utilized, and there is a significant radial temperature gradient within the reactor. In terms of operational conditions, increasing the inlet pressure and decreasing the gas velocity both favor the improvement of acetylene conversion rate, but at the same time, they would reduce the selectivity of ethylene, where the selectivity of ethylene is more sensitive to pressure, and the conversion of acetylene is more sensitive to gas velocity. The increase in reaction temperature and hydrogen-to-acetylene ratio both help to promote the acetylene conversion to ethylene, but it can lead to the enrichment of ethylene on the exterior surface of the catalyst particles, which when diffusing further into the interior zone, can be over-hydrogenated to ethane, thus reducing the selectivity of ethylene.

Key words: selective acetylene hydrogenation, fixed-bed reactor, numerical simulation, mass transfer, heat transfer

摘要：

乙烯产量是反映国家石油化工发展水平的关键指标。构建了颗粒分辨的乙炔选择性加氢固定床反应器模型，分析圆柱形颗粒堆积结构对传递过程以及操作条件对其反应性能的影响。结果表明，床层压降主要集中在反应器入口段，该段乙炔加氢反应速率最高，但在后半段催化剂颗粒未被充分利用，而且反应器内存在明显的径向温度梯度。入口压力的增加和空速的降低均有利于提升乙炔转化率，但同时会降低乙烯选择性，其中乙烯选择性对压力更敏感，而乙炔转化率对空速更敏感；反应温度和氢炔比的提高均有利于促进乙炔生成乙烯的速率，但会导致乙烯富集在催化剂颗粒的外表面，其进一步向颗粒内部扩散时过度加氢生成乙烷，使乙烯选择性降低。

关键词: 乙炔选择性加氢, 固定床反应器, 数值模拟, 传质, 传热

CLC Number:

TQ 203.2

Hongyu LI, Xiangkun LIU, Yao SHI, Yueqiang CAO, Gang QIAN, Xuezhi DUAN. Numerical simulation of particle-resolved fixed-bed reactor for selective acetylene hydrogenation process[J]. CIESC Journal, 2024, 75(10): 3610-3622.

李泓宇, 刘祥坤, 施尧, 曹约强, 钱刚, 段学志. 颗粒分辨的乙炔选择性加氢固定床反应器数值模拟[J]. 化工学报, 2024, 75(10): 3610-3622.

Figures/Tables 13

Fig.1 Reactor geometry model

Table 1 Diffusion volumes used in simulation［35］

分子	扩散体积
C₂H₂	36.42
H₂	6.12
C₂H₄	41.01
C₂H₆	45.66
C₃H₈	65.34
C₄H₈	82.08
Ar	16.10

Table 2 Empirical equations used in simulation

物性	经验公式	文献
催化剂粉末热导率	$λ_{s o l i d} = 79.6671 - 0.16625 T + 9.6265 \times 10^{- 5} T^{2}$	[36]
气体混合物热导率	$λ_{m} = \sum_{i = 1}^{N_{g}} \frac{y_{i} λ_{i}}{\sum_{j = 1}^{N_{g}} y_{j} Φ_{i j}}$	[37]
物质i和物质j的二元黏度	$Φ_{i j} = \frac{1}{\sqrt[]{8}} {(1 + \frac{M_{i}}{M_{j}})}^{- 1 / 2} {[1 + {(\frac{μ_{i}}{μ_{j}})}^{1 / 2} {(\frac{M_{j}}{M_{i}})}^{1 / 4}]}^{2}$	[37]
气体混合物比热容	$C_{p, m} = \sum_{i = 1}^{N_{g}} C_{p, i} y_{i}$	[37]
气体混合物密度	$ρ_{m} = \frac{p M_{w, m}}{R T}$	[37]
气体混合物平均摩尔质量	$M_{w, m} = \sum_{i = 1}^{N_{g}} M_{w, i} y_{i}$	[37]
反应热	$Δ H_{i} = Δ H_{i}^{􀱈} + \int_{298}^{T} Δ C_{p} d T (i = 1,2, 3)$	[33]

Table 2 Empirical equations used in simulation

物性	经验公式	文献
催化剂粉末热导率	$λ_{s o l i d} = 79.6671 - 0.16625 T + 9.6265 \times 10^{- 5} T^{2}$	[36]
气体混合物热导率	$λ_{m} = \sum_{i = 1}^{N_{g}} \frac{y_{i} λ_{i}}{\sum_{j = 1}^{N_{g}} y_{j} Φ_{i j}}$	[37]
物质i和物质j的二元黏度	$Φ_{i j} = \frac{1}{\sqrt[]{8}} {(1 + \frac{M_{i}}{M_{j}})}^{- 1 / 2} {[1 + {(\frac{μ_{i}}{μ_{j}})}^{1 / 2} {(\frac{M_{j}}{M_{i}})}^{1 / 4}]}^{2}$	[37]
气体混合物比热容	$C_{p, m} = \sum_{i = 1}^{N_{g}} C_{p, i} y_{i}$	[37]
气体混合物密度	$ρ_{m} = \frac{p M_{w, m}}{R T}$	[37]
气体混合物平均摩尔质量	$M_{w, m} = \sum_{i = 1}^{N_{g}} M_{w, i} y_{i}$	[37]
反应热	$Δ H_{i} = Δ H_{i}^{􀱈} + \int_{298}^{T} Δ C_{p} d T (i = 1,2, 3)$	[33]

Table 3 Boundary conditions for solving Eqs.（12）—（14）， Eq.（16） and Eq.（17）

位置	动量方程	质量方程	能量方程
反应器入口 ( $z = 0$ )	$u = u_{0}$	$c_{m, i} = c_{m, i, 0}$	$T_{m} = T_{0}$
反应器出口 ( $z = H_{t}$ )	$p_{表压} = 0$	$\frac{\partial c_{m, i}}{\partial z} = 0$	$\frac{\partial T_{m}}{\partial z} = 0$
反应器管壁( $r = R_{t}$ )	$u = 0$	$\frac{\partial c_{m, i}}{\partial r} = 0$	$\frac{\partial T_{m}}{\partial r} = 0$
颗粒与流体交界面	—	$c_{m, i} = c_{c a t, i}$	$T_{m} = T_{c a t}$

Table 3 Boundary conditions for solving Eqs.（12）—（14）， Eq.（16） and Eq.（17）

位置	动量方程	质量方程	能量方程
反应器入口 ( $z = 0$ )	$u = u_{0}$	$c_{m, i} = c_{m, i, 0}$	$T_{m} = T_{0}$
反应器出口 ( $z = H_{t}$ )	$p_{表压} = 0$	$\frac{\partial c_{m, i}}{\partial z} = 0$	$\frac{\partial T_{m}}{\partial z} = 0$
反应器管壁( $r = R_{t}$ )	$u = 0$	$\frac{\partial c_{m, i}}{\partial r} = 0$	$\frac{\partial T_{m}}{\partial r} = 0$
颗粒与流体交界面	—	$c_{m, i} = c_{c a t, i}$	$T_{m} = T_{c a t}$

Fig.2 Grid sensitivity analysis and schematic diagram of grid’s longitudinal and cross sections (b)

Fig.3 Simulation and experimental results along the reactor axis

Fig.4 Central longitudinal flow velocity distribution and axial pressure drop distribution of reactor

Fig.5 Central longitudinal and cross-sectional (30 mm) C2H2 concentration distribution and C2H2 concentration along axial direction of reactor

Fig.6 Central longitudinal and cross-sectional (40 mm) temperature distribution and temperature distribution along axial direction of reactor

Fig.7 Central longitudinal temperature distribution, temperature along axial direction, central longitudinal C2H2 concentration distribution, C2H2 concentration along axial direction and C2H2 conversion and C2H4 selectivity with respect to pressure

Fig.8 Central longitudinal temperature distribution, temperature along axial direction, central longitudinal C2H2 concentration distribution, C2H2 concentration along axial direction and C2H2 conversion and C2H4 selectivity with respect to GHSV

Fig.9 Central longitudinal temperature distribution, temperature along axial direction, central longitudinal C2H2 concentration distribution, C2H2 concentration along axial direction and C2H2 conversion and C2H4 selectivity with respect to inlet temperature

Fig.10 Central longitudinal temperature distribution, temperature along axial direction, central longitudinal C2H2 concentration distribution, C2H2 concentration along axial direction and C2H2 conversion and C2H4 selectivity with respect to hydrogen-acetylene ratio

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