Investigation of the mixing loss and guiding strategy of the electrolyte flow in the tanks of a redox flow battery system

doi:10.19799/j.cnki.2095-4239.2022.0693

Abstract

Abstract:

In a running redox flow battery system, the state of charge (SOC) of the electrolyte in the tanks is not uniform and is different from that of the electrolyte in the outlet of the stack. The mixing of electrolyte with different SOC results in energy loss in tanks. Thus, this paper reports a model-based study on the performance of a redox flow battery under the conditions of complete mixing and nonmixing of electrolytes in the tanks in order to quantify the effect of electrolyte mixing in the tanks on the efficiency of the system. The transport of active species in a real tank is also analyzed and compared with that under complete mixing condition. A diversion structure is proposed to optimize the electrolyte flow in the tanks to minimize the mixing loss in the tank. The results show that the mixing of electrolytes with different SOC in the tanks reduces the utilization rate of electrolyte and the voltage efficiency of the redox flow battery system, and the influence on the voltage efficiency may reach more than 1%. The mass transfer correlated energy loss in the real tank is also affected by the dead zone, where the electrolyte is stagnant. The dead zone reduces the available volume in the tank and increases the concentration gradient adjacent to the dead zone; this leads to increased mixing loss. The use of partition contributes to the reduction of concentration gradient and cross-sectional area of diffusion. This paper also creates a preliminary design for a novel tank structure, aiming to provide ideas for the design of tanks from the perspective of reducing mixing loss.

Key words: mixing loss, electrolyte tank, electrolyte guiding strategy, system efficiency

CLC Number:

TM 911

Zhiwen WANG, Qiang YE. Investigation of the mixing loss and guiding strategy of the electrolyte flow in the tanks of a redox flow battery system[J]. Energy Storage Science and Technology, 2023, 12(4): 1148-1157.

Figures/Tables 11

Fig. 1

Table 1

Geometric parameters of the models"

参数	描述	数值
$H e l e$	电极高度/ $c m$	40
$W e l e$	电极宽度/ $c m$	50
$L e l e$	电极厚度/ $m m$	5
$L m e m$	膜厚度/ $m m$	0.207
$H t a n k ①$	储液罐高度/ $m$	6
$R t a n k ①$	储液罐半径/ $m$	1.5
$H t a n k ②$	储液罐高度/ $m$	3.375
$R t a n k ②$	储液罐半径/ $m$	2
$D p i p e$	储液罐出口直径/ $c m$	15
$L b a f f$	导流板厚度/ $c m$	2
$H b a f f$	导流板高度/ $m$	5.8

Table 1

Table 2

Electrolyte、electrode properties and kinetics"

参数	描述	数值
$σ s e$	电极电导率/( $S / m$ )	$200$
$σ l m$	膜电导率/( $S / m$ )	$5$
$ε$	电极孔隙率	$0.93$
$a$	电极比表面积/ $m$ ^-1	3.5×10⁴
$D V 2 +$	二价钒离子扩散系数/( $m 2 / s$ )	4×10^-11
$D V 3 +$	三价钒离子扩散系数/( $m 2 / s$ )	4×10^-11
$D V O 2 +$	四价钒离子扩散系数/( $m 2 / s$ )	6.5×10^-11
$D V O 2 +$	五价钒离子扩散系数/( $m 2 / s$ )	6.5×10^-11
$D H +$	氢离子扩散系数/( $m 2 / s$ )	1.55×10^-9
$D H S O 4 -$	硫酸氢根离子扩散系数/( $m 2 / s$ )	2.2×10^-10
$D S O 4 2 -$	硫酸根离子扩散系数/( $m 2 / s$ )	1.8×10^-10
$k +$	正极反应速率常数/( $m / s$ )	2.5×10^-8
$k -$	负极反应速率常数/( $m / s$ )	7×10^-8

Table 2

Table 3

Initial species concentrations"

参数	描述	数值
$c V 2 + 0, t a n k$	储罐中二价钒离子初始浓度/( $m o l / m 3$ )	1200
$c V 3 + 0, t a n k$	储罐中三价钒离子初始浓度/( $m o l / m 3$ )	300
$c H + 0, t a n k$	储罐中氢离子初始浓度/( $m o l / m 3$ )	4237.5
$c H S O 4 - 0, t a n k$	储罐中硫酸氢根离子初始浓度/( $m o l / m 3$ )	2542.5
$c S O 4 2 - 0, t a n k$	储罐中硫酸根离子初始浓度/( $m o l / m 3$ )	2857.5
$c V 2 + 0, c e l l$	负极二价钒离子初始浓度/( $m o l / m 3$ )	225
$c V 3 + 0, c e l l$	负极三价钒离子初始浓度/( $m o l / m 3$ )	1275
$c V O 2 + 0, c e l l$	正极四价钒离子初始浓度/( $m o l / m 3$ )	1275
$c V O 2 + 0, c e l l$	正极五价钒离子初始浓度/( $m o l / m 3$ )	225
$c -, H + 0, c e l l$	负极氢离子初始浓度/( $m o l / m 3$ )	3628.1
$c +, H + 0, c e l l$	正极氢离子初始浓度/( $m o l / m 3$ )	4565.6
$c -, H S O 4 - 0, c e l l$	负极硫酸氢根离子初始浓度/( $m o l / m 3$ )	2176.9
$c +, H S O 4 - 0, c e l l$	正极硫酸氢根离子初始浓度/( $m o l / m 3$ )	2739.4
$c -, S O 4 2 - 0, c e l l$	负极硫酸根离子初始浓度/( $m o l / m 3$ )	2863.1
$c +, S O 4 2 - 0, c e l l$	正极硫酸根离子初始浓度/( $m o l / m 3$ )	2300.6

Table 3

Fig. 2

Fig. 3

Fig. 4

Fig. 5

Fig. 6

Fig. 7

Fig. 8

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