Simulation of cryogenic removal of volatile organic compounds from exhaust gas in oil depots

doi:10.16085/j.issn.1000-6613.2023-0133

Abstract

Abstract:

The volatile organic compounds (VOCs) in oil depot exhaust should be removed and recycled. The present authors simulated the cryogenic condensation removal of the small quantity of propane in the mixture gas using the one-dimensional calculation method. The results showed that for gas with initial propane fraction of 2.25% the heat exchanger used in present study with a length of 2.85m was required to reduce propane molar concentration in the mixture gas to 1.26×10^-4, and the molar fraction of propane decreased by 76% in the first one meter of the heat exchanger while by only 23.6% in the next 1.85m. The length of the heat exchanger required for condensation varied with the initial concentration of propane. The shortest length, 2.84m, was required when the initial molar concentration of propane was 2.0% . When the initial molar concentration of propane was below 2.0%, the main factor affecting the removal of propane was the condensation rate, and the required heat exchanger length increased rapidly in an approximately parabolic trend as the propane initial molar concentration decreased. When the propane initial molar concentration was higher than 2.0%, the main factor affecting the removal of propane became the total quantity of propane, and the required heat exchanger length increased approximately linearly at a smaller rate as the propane concentration increased. Present study could provide a reference to the design of the length of the heat exchanger for the condensation removal of the valuable component in petroleum gas.

Key words: waste treatment, recovery, numerical simulation

摘要：

针对可挥发性有机物（VOCs）油气脱除回收问题，本文采用一维仿真模拟了典型间壁换热器中的微量丙烷的氮气低温冷凝脱除过程。结果表明：本研究中初始丙烷分数为2.25%的气体，将出口丙烷摩尔分数降至1.26×10^-4所需换热器长度为2.85m；换热器前1m中丙烷摩尔分数降低了76%，随后1.85m仅降低23.6%；冷凝所需换热器长度与丙烷初始浓度关系如下：当丙烷初始浓度为2.0%时所需长度最短，为2.84m；低于2.0%时，影响丙烷脱除的主要因素为冷凝速率。随丙烷初始浓度继续降低，所需换热器长度呈近似抛物线上升；高于2.0%时，影响丙烷脱除的主要因素为总冷凝量。随着丙烷浓度升高，所需换热器长度呈近似线性小幅上升。本文工作可为微量油气低温冷凝脱除换热器的换热长度设计提供参考。

关键词: 废物处理, 回收, 数值模拟

CLC Number:

TE85

SHAO Boshi, TAN Hongbo, ZHANG Qidong. Simulation of cryogenic removal of volatile organic compounds from exhaust gas in oil depots[J]. Chemical Industry and Engineering Progress, 2023, 42(12): 6270-6277.

邵博识, 谭宏博, 张淇栋. 油库废气中挥发性有机物的低温脱除过程模拟分析[J]. 化工进展, 2023, 42(12): 6270-6277.

Figures/Tables 11

参数	油气（热流体）侧	氮气（冷流体）侧
单层通道自由流截面积A/m²	5.91×10^-3	5.91×10^-3
冷凝换热面垂直于流动方向的宽度L/m	0.72	0.72
入口流速/m·s^-1	0.05	0.53
初始质量流量/g·s^-1	2.57	5.64
热端温度/K	238.15	190.15
入口压力/MPa	0.6	0.1
雷诺数Re	464.2	1229.5
入口丙烷摩尔分数/%	2.25	—
丙烷排放摩尔分数标准/10^-6	126	—

长度/m	T_MIX计算值/K	T_MIX文献值/K	T_MIX误差绝对值/%	T_CN2计算值/K	T_CN2文献值/K	T_CN2误差绝对值/%
0	200	200	0	177	177	0
0.1	189.77	194.10	2.23	174.14	173.70	0.252
0.2	183.32	187.20	2.07	172.20	170.92	0.746
0.3	178.98	181.69	1.49	170.83	168.82	1.19
0.4	175.92	177.29	0.771	169.82	167.23	1.55
0.5	173.71	173.78	0.0420	169.07	166.03	1.83
0.6	172.07	170.98	0.635	168.50	165.12	2.04
0.7	170.83	168.74	1.23	168.06	164.43	2.20
0.8	169.88	166.96	1.75	167.72	163.91	2.32
0.9	169.15	165.54	2.18	167.45	163.52	2.40
1.0	168.58	164.40	2.54	167.24	163.22	2.46
1.1	168.13	163.49	2.84	167.07	162.99	2.50
1.2	167.78	162.77	3.08	166.94	162.82	2.53

丙烷初始摩尔分数变化情况/%	$q m s 1 / q m s 2$	$q m ¯ 2 / q m ¯ 1$	$ε$
0.5~1.0	0.501	2.217	1.112
1.0~1.5	0.669	1.612	1.078
1.5~1.9	0.752	1.340	1.008
1.9~2.0	0.951	1.055	1.003
2.0~2.5	0.802	1.243	0.998
2.5~3.0	0.836	1.191	0.995

丙烷初始摩尔分数变化情况/%	$q m s 1 / q m s 2$	$q m ¯ 2 / q m ¯ 1$	$ε$
0.5~1.0	0.501	2.217	1.112
1.0~1.5	0.669	1.612	1.078
1.5~1.9	0.752	1.340	1.008
1.9~2.0	0.951	1.055	1.003
2.0~2.5	0.802	1.243	0.998
2.5~3.0	0.836	1.191	0.995

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