Non-isothermal kinetics calculation and heat storage performance analysis of silica gel based on thermochemical reaction

doi:10.19799/j.cnki.2095-4239.2021.0633

Abstract

Abstract:

Thermochemical heat storage has the advantages of high energy storage density, good cycling performance, long storage time and small heat loss, and has a broad prospect in improving energy efficiency and reducing carbon emissions. Before the application of large-scale system process, it is of great significance to judge the applicability of heat storage materials by means of experimental detection, dynamic calculation and numerical simulation. In this paper, taking silica gel as an example, nuclear magnetic resonance instrument was used to detect the change of the internal water binding form and its content before and after heat storage, and then the thermochemical reaction equation in the process of silica gel heat storage was calculated and determined. According to the experimental data of thermogravimetric analyzer (TGA), the non-isothermal kinetic calculation of the thermal decomposition reaction of silica gel was carried out, and the activation energy of the reaction was obtained to be 66.75 kJ·mol^-1. With the advance of the reaction process, the activation energy of silica gel dehydration reaction decreased as a whole, and the most probable mechanism function was the three-dimensional diffusion model. The three-dimensional diffusion rate of water vapor at the gas-solid interface is a key step affecting the total reaction rate. According to differential scanning calorimeter (DSC) experiment, the heat absorption rate of silica gel reaches its peak at about 100 ℃, about 0.87 kW·kg^-1, and the heat storage density is 1030.89 kJ·kg^-1. The calculated kinetic parameters were used to simulate the heat storage process in the reactor in Fluent, and Pearson correlation coefficient was used as the evaluation index of the correlation between the experimental and numerical simulation results. The results show that the numerical simulation predicted value is in good agreement with the experimental value.

Key words: thermochemical heat storage, non-isothermal kinetics, nuclear magnetic resonance detection, thermal storage density

CLC Number:

TK 02

Na YANG, Chengcheng WANG, Hui YANG, Zhihao HU, Lige TONG, Zhongbo LI, Li WANG, Yulong DING, Na LI. Non-isothermal kinetics calculation and heat storage performance analysis of silica gel based on thermochemical reaction[J]. Energy Storage Science and Technology, 2022, 11(5): 1331-1338.

Figures/Tables 12

Fig.1

Fig. 2

Table 1

Fig. 3

Table 2

Integral and differential forms of different gas-solid reaction mechanisms"

动力学模型	符号	$g α$	$f α$
Contracting cylinder	R2	$1 - 1 - α 1 / 2$	$2 1 - α 1 / 2$
Contracting sphere	R3	$1 - 1 - α 1 / 3$	$3 1 - α 2 / 3$
1 dimensional diffusion	D1	$α 2$	$(1 / 2) α - 1$
2 dimensional diffusion	D2	$1 - α l n 1 - α + α$	$- l n 1 - α - 1$
3 dimensional diffusion	D3	$1 - 1 - α 1 / 3 2$	$3 1 - α 2 / 3 / 2 1 - 1 - α 1 / 3$
Avrami-Erofeev	A2	$- l n 1 - α 1 / 2$	$2 - l n 1 - α 1 / 2 1 - α$

Table 2

Fig. 4

Fig. 5

Table 3

Table 4

Fig. 6

Fig. 7

Table 5

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样品	A₂₁	A₂₂	A	A₂₁/A	A₂₂/A
未处理硅胶	3301.1	3425.2	6726.3	49.1%	50.9%
加湿处理硅胶	0	21860.8	21860.8	0	100.0%

α	R²	斜率	E/(kJ/mol)	截距	lgA/s^-1
0.1	0.9922	-4.34	79.01	14.57	29.89
0.2	0.9919	-3.98	72.45	12.92	27.64
0.3	0.9939	-3.80	69.18	12.04	26.56
0.4	0.9955	-3.68	66.99	11.44	25.88
0.5	0.9955	-3.57	64.99	10.92	25.26
0.6	0.9954	-3.48	63.35	10.47	24.74
0.7	0.9946	-3.40	61.90	10.08	24.32
0.8	0.9898	-3.36	61.17	9.75	24.03
0.9	0.9772	-3.39	61.71	9.52	24.00

储能材料	E/(kJ/mol)	储热密度	作者
Ca(OH)₂掺杂15% 六方氮化硼	164	1 000 kJ/kg	Huang等^[8]
SrBr₂·H₂O	75.7	291 kJ/kg	Stengler 等l^[9]
LiOH·H₂O掺杂8% 膨胀石墨	59.5	1 120 kJ/kg	Li 等^[10]
Cu₂O/CuO	233	520 kJ/kg	Jahromy 等^[11]
CaCO₃/CaO	253.76	168.5 kJ/mol	Chen等^[12]
MgCl₂·6H₂O	103.74	882.38 kJ/kg	Mamani 等^[13]
Co₃O₄/CoO	247.21	196.2 kJ/mol	Schrader 等^[14-15]

位置	Pearson相关系数
点1	0.966
点2	0.959

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