Prediction of vapor-liquid equilibrium data of uranium hexafluoride and fluoride and simulation of distillation process

doi:10.11949/0438-1157.20230960

Abstract

Abstract:

The purification of uranium hexafluoride by distillation technology is an important part of the uranium conversion process. The simulation of the distillation process can provide key support for process design and operation optimization. However, due to the lack of vapor-liquid equilibrium and physical properties data for uranium hexafluoride and fluoride, modelling and simulating the purification process of uranium hexafluoride became challenging. To address this issue, we utilized COSMOtherm and Turbomole software to predict vapor-liquid equilibrium data for UF₆-TiF₄ binary systems. We indirectly verified the accuracy of the COSMO-RS model by predicting known experimental data on vapor-liquid equilibrium for WF₆-UF₆ binary system. Additionally, Aspen Plus software's property constant estimation system was employed to estimate missing physical properties such as infinitely dilute aqueous Gibbs generating energy. The UF₆ saturated vapor pressure experimental data and simulated values in the literature were compared, and the relative error was within 1.76%. Based on experimental data and predicted vapor-liquid phase equilibrium data in the literature, Aspen Plus software was used to regress the binary interaction parameters of the NRTL model. For separating uranium hexafluoride from fluoride, two purification schemes were designed: one involving direct separation sequence and another involving indirect separation sequence. Sensitivity analysis was conducted to optimize key parameters including plate number, feed position, and reflux ratio to minimize total annual cost (TAC) while maintaining desired purity levels in UF₆ product output streams. The results indicated that TAC was lower for the indirect separation sequence purification scheme.

Key words: fluoride, physical property estimation, vapor-liquid equilibria, distillation

摘要：

精馏技术提纯六氟化铀是铀转化工艺的重要环节，该精馏工艺的模拟可为工艺设计及操作优化提供关键支撑。然而，由于六氟化铀及氟化物汽液相平衡数据及物性数据的缺乏，六氟化铀提纯精馏工艺的建模和模拟难以开展。为此，利用COSMOtherm和Turbomole软件，预测UF₆与TiF₄二元体系汽液相平衡数据。通过预测已知的WF₆-UF₆二元体系汽液相平衡实验数据以间接验证COSMO-RS模型预测的准确性。利用Aspen Plus软件的物性常数估算系统（property constant estimation system），估算出缺失的无限稀释水溶液Gibbs生成能等物性参数。文献中UF₆饱和蒸气压实验数据与模拟值进行对比，相对误差在1.76%以内。根据文献中的实验数据和预测的汽液相平衡数据，利用Aspen Plus软件回归NRTL模型的二元交互作用参数。针对六氟化铀及氟化物的分离，设计直接分离序列和间接分离序列提纯UF₆的两种方案。设定UF₆产品纯度，以总年度费用（TAC）最小化为目标，采用灵敏度分析对塔板数、进料位置和回流比的关键参数进行优化，结果表明，间接分离序列提纯UF₆方案的TAC更低。

关键词: 氟化物, 物性估算, 汽液平衡, 精馏

CLC Number:

TQ 021

Tong YANG, Huan WANG, Chun DENG. Prediction of vapor-liquid equilibrium data of uranium hexafluoride and fluoride and simulation of distillation process[J]. CIESC Journal, 2024, 75(2): 463-474.

杨同, 王欢, 邓春. 六氟化铀及氟化物汽液相平衡数据预测及精馏过程模拟[J]. 化工学报, 2024, 75(2): 463-474.

Figures/Tables 20

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温度/℃	x₁(UF₆)	x₂(TiF₄)	y₁(UF₆)	y₂(TiF₄)
56.8	0.99	0.01	0.9999	0.0001
57.2	0.98	0.02	0.9999	0.0001
58.1	0.95	0.05	0.9998	0.0002
59.9	0.9	0.10	0.9997	0.0003
61.7	0.85	0.15	0.9996	0.0004
63.5	0.8	0.20	0.9994	0.0006
65.3	0.75	0.25	0.9992	0.0008
67.3	0.7	0.30	0.9991	0.0009
69.4	0.65	0.35	0.9989	0.0011
71.6	0.6	0.40	0.9986	0.0014
74.0	0.55	0.45	0.9983	0.0017
76.7	0.5	0.50	0.9979	0.0021
79.8	0.45	0.55	0.9975	0.0025
83.3	0.4	0.60	0.9968	0.0032
87.4	0.35	0.65	0.9960	0.0040
92.4	0.3	0.70	0.9948	0.0052
98.8	0.25	0.75	0.9929	0.0071
107.2	0.2	0.80	0.9896	0.0104
119.2	0.15	0.85	0.9831	0.0169
138.4	0.1	0.90	0.9662	0.0338
176.0	0.05	0.95	0.8951	0.1049
225.1	0.02	0.98	0.6625	0.3375
251.3	0.01	0.99	0.4328	0.5672
280.5	0.001	0.999	0.0560	0.9440

温度/℃	x₁(UF₆)	x₂(TiF₄)	y₁(UF₆)	y₂(TiF₄)
56.8	0.99	0.01	0.9999	0.0001
57.2	0.98	0.02	0.9999	0.0001
58.1	0.95	0.05	0.9998	0.0002
59.9	0.9	0.10	0.9997	0.0003
61.7	0.85	0.15	0.9996	0.0004
63.5	0.8	0.20	0.9994	0.0006
65.3	0.75	0.25	0.9992	0.0008
67.3	0.7	0.30	0.9991	0.0009
69.4	0.65	0.35	0.9989	0.0011
71.6	0.6	0.40	0.9986	0.0014
74.0	0.55	0.45	0.9983	0.0017
76.7	0.5	0.50	0.9979	0.0021
79.8	0.45	0.55	0.9975	0.0025
83.3	0.4	0.60	0.9968	0.0032
87.4	0.35	0.65	0.9960	0.0040
92.4	0.3	0.70	0.9948	0.0052
98.8	0.25	0.75	0.9929	0.0071
107.2	0.2	0.80	0.9896	0.0104
119.2	0.15	0.85	0.9831	0.0169
138.4	0.1	0.90	0.9662	0.0338
176.0	0.05	0.95	0.8951	0.1049
225.1	0.02	0.98	0.6625	0.3375
251.3	0.01	0.99	0.4328	0.5672
280.5	0.001	0.999	0.0560	0.9440

物性名称	参数	估算值	单位	方法
25℃时的溶解度参数	DELTA	1.8363×10⁴	J/m³	DEFINITI
无限稀释水溶液Gibbs生成能	DGAQHG	1.1604×10⁴	J/kmol	AQU-EST1
25℃时的熵	S25HG	-38.9208	J/(kmol·K)	AQU-EST2
Helgeson OMEGA热容系数	OMEGHG	1.4241×10⁸	J/kmol	HELGESON

物性名称	参数	估算值	单位	方法
25℃时的溶解度参数	DELTA	1.8363×10⁴	J/m³	DEFINITI
无限稀释水溶液Gibbs生成能	DGAQHG	1.1604×10⁴	J/kmol	AQU-EST1
25℃时的熵	S25HG	-38.9208	J/(kmol·K)	AQU-EST2
Helgeson OMEGA热容系数	OMEGHG	1.4241×10⁸	J/kmol	HELGESON

物性名称	参数	估算值	单位	方法
在0.9临界温度下的压力	AT 0.9TC	1.9667×10⁶	N/m²	RIEDEL
临界压力	PC	4.6000×10⁶	N/m²	RIEDEL
25℃时的溶解度参数	DELTA	1.7802×10⁴	J/m³	DEFINITI
无限稀释水溶液Gibbs生成能	DGAQHG	1.1604×10⁴	J/kmol	AQU-EST1
25℃时的熵	S25HG	-38.9208	J/(kmol·K)	AQU-EST2
Helgeson OMEGA热容系数	OMEGHG	1.4241×10⁸	J/kmol	HELGESON