Study on variable mass flow laws in π-shaped centripetal radial flow adsorber

doi:10.11949/0438-1157.20190231

Abstract

Abstract:

Studying the variable mass flow law of pressure swing adsorption (PSA) in the radial flow adsorber can help to accurately grasp the influence of the adsorption process and the variable factors in the bed on the oxygen production performance. An air-solid two-phase pressure swing adsorption model is established for the π-shaped centripetal radial flow adsorber, axial oxygen purity profiles, temperature wave and oxygen concentration for product gas are comparatively studied by using this model. The results show that the oxygen purity of 66.02% and the recovery of the production of 29.2% can be obtained in the outlet after the first PSA cycle. The oxygen purity increases from 66.02% to 97.5% and the recovery of the production increases from 29.2% to 38.5% during the unsteady state. The product oxygen purity and recovery are achieved to be 98.6% and 38.9% at the end of each steps in steady state, and finally the temperature difference of air-solid two-phase gradually decreases and reaches thermal balance. The mass and heat transfer between the air and the adsorbent are obtained, which provides reference for π-shaped centripetal in the PSA for oxygen production.

Key words: radial flow, adsorption, π-shaped centripetal, two phase flow, numerical simulation

摘要：

对径向流吸附器内变压吸附(PSA)制氧的变质量流动规律进行研究，有助于准确掌握吸附过程及床层内的变量因素对制氧性能的影响。对π型向心径向流吸附器建立气固耦合的两相吸附模型，并对其PSA制氧过程进行了数值模拟研究，得到了床层内氧气浓度分布、温度分布以及产品气浓度的变化规律。结果表明：首次循环结束时床层内氧气最高摩尔分数可达66.02%，回收率29.2%。非稳定循环期间，氧气摩尔分数从66.02%升高至 97.5%，回收率从29.2%提高至38.5%。循环达到稳定后，床层内氧气摩尔分数最高可达98.6%，回收率38.9%左右，且达到稳定状态后床层内气固两相温差减小，逐渐达到热平衡。获得了吸附器内部气体与吸附剂两相间的传质、传热过程，为π型向心径向流吸附器用于PSA制氧提供技术支持。

关键词: 径向流, 吸附, π型向心, 两相流, 数值模拟

CLC Number:

TG 142.71

Haoyu WANG, Yingshu LIU, Chuanzhao ZHANG, Xiong YANG, Jiangwei CHEN. Study on variable mass flow laws in π-shaped centripetal radial flow adsorber[J]. CIESC Journal, 2019, 70(9): 3385-3395.

王浩宇, 刘应书, 张传钊, 杨雄, 陈江伟. π型向心径向流吸附器变质量流动特性研究[J]. 化工学报, 2019, 70(9): 3385-3395.

Figures/Tables 16

Fig.1 Structure and physical model of π-shaped radial flow adsorber

Table 1 Structure parameters of π-shaped radial flow adsorber

结构参数	数值	结构参数	数值
吸附器半径/mm	110	中心流道宽度/mm	12
吸附器长度/mm	210	吸附剂装填层厚度/mm	62
进气口半径/mm	12	外流道宽度/mm	30
进气口长度/mm	40	气流分布孔厚度/mm	3
出气口半径/mm	12	中心流道开孔半径/mm	2
出气口长度/mm	60	外流道开孔半径/mm	4
吸附剂装填高度/mm	20	吸附剂颗粒直径/mm	3
中心流道气流分布孔开孔率/%	17	外流道气流分布孔开孔率/%	27

Table 2 Initial conditions

参数	数值
气体组分压力/ Pa	21%O₂，79%N₂ 101325
气相温度/ K	293
固相温度/ K	293
气相氧气质量分数	0.233
单位质量吸附剂氧气吸附量/( mol·kg^-1)	0.0262832
单位质量吸附剂氮气吸附量/( mol·kg^-1)	0.6328067

Table 3 Model parameters

参数	数值
床层孔隙率	0.4
颗粒密度 $ρ p$ /(kg·m³)	1035
直径 $d p$ /mm	1.6
比热容/ (J·kg^-1·K^-1)	1100

Table 3 Model parameters

参数	数值
床层孔隙率	0.4
颗粒密度 $ρ p$ /(kg·m³)	1035
直径 $d p$ /mm	1.6
比热容/ (J·kg^-1·K^-1)	1100

Table 4 Cyclic sequence

循环过程

示意图

时间/s

Table 5 Boundary condition setting of absorber 1

入口	出口	床壁	轴线
质量入口q _in(p)	壁	壁	对称轴
质量入口q _in(p)	压力出口（大气压）	壁	对称轴
压力出口（大气压）	壁	壁	对称轴
压力出口（大气压）	质量入口	壁	对称轴

Table 6 Adsorption isotherm parameters

吸附质	k ₁/(mol·kg^-1·Pa^-1)	k ₂/K	k ₃/Pa^-1	k ₄/K	ΔH/(kJ·mol^-1)
O₂	7.87×10^-9	1541.211	6.79×10^-10	1968.24	12
N₂	9.86×10^-9	2010.908	1.67×10^-9	2250	18

Fig.2 Comparison of simulation and experiment results of adsorption equilibrium curves for single component N2 and O2

Fig.3 O2 concentration distribution at the end of each step for the first PSA process in π-RFA 1

Fig.4 Distribution of O2 concentration along L position at the end of each step for the first PSA process in π-RFA 1

Fig.5 Temperature wave along L position at the end of each step for the first PSA process in π-RFA 1

Fig.6 Variation of O2 concentration for product gas in outlet of π-RFA 1 with number of cycles

Fig.7 Variation of O2 recovery in outlet of π-RFA 1 with number of cycles

Fig.8 O2 concentration distribution at the end of each step after PSA process stabilized in π-RFA 1

Fig.9 Distribution of O2 concentration along L position at the end of each step after PSA process stabilized in π-RFA 1

Fig.10 Temperature wave along L position at the end of each step after PSA process stabilized in π-RFA 1

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