双轴搅拌反应器内Ca（OH）2/CaO热化学储热体系的放热研究

doi:10.11949/0438-1157.20240111

摘要/Abstract

摘要：

针对Ca（OH）₂/CaO热化学储热体系的放热过程，提出了双轴搅拌反应器并对其“三传一反”过程进行了数值研究，深入地揭示了体系反应的多物理场耦合机理，分析了双轴搅拌反应器用于热化学储热的可行性，讨论了体系在双轴搅拌反应器内进行放热反应的特性。结果表明，双轴搅拌反应器改善了体系放热反应的传热传质性能；体系1200 s放热过程的转化率为0.49，峰值放热功率和稳定放热功率分别可以达到5.4 kW和3 kW；通过调节水蒸气分压可以控制体系的反应温区，而较低的初始进口温度不仅可以加快反应进程，还能减少体系的额外预热量；反应器的换热能力会明显影响放热过程进行，特别是在高转速和高填充高度的反应条件下，实际应用中应考虑需求来匹配合适的换热装置。

关键词: 热化学储热, 双轴搅拌反应器, 放热过程, 多物理场耦合, 数值模拟

Abstract:

The Ca(OH)₂/CaO thermochemical heat storage system has the advantages of high energy density, low cost, and inter-temporal storage. A more in-depth revelation of the multi-physics field coupling mechanism of the reaction will help to improve the performance of the system. In this work, for the exothermic process of Ca(OH)₂/CaO system, a biaxial stirred reactor was proposed and its heat and mass transfer and chemical reaction processes were numerically investigated. The feasibility of the biaxial stirred reactor was analyzed, and the exothermic characteristics of the system were discussed. In addition, the effects of the reaction conditions, such as heat transfer coefficient, stirring speed, initial and inlet temperatures, steam pressure and filling height, on the exothermic process were investigated in detail by analyzing the variation of the conversion, the exothermic power and the bed temperature, so as to provide directions for the determination of suitable reaction conditions. The results show that the biaxial stirred reactor with stable flow and temperature fields improves the heat and mass transfer performance of the exothermic reaction. The conversion of the exothermic process of the system during 1200 s is 0.49, the peak and the stable exothermic power can reach 5.4 kW and 3 kW, respectively. The reaction temperature zone of the system can be controlled by adjusting the steam pressure, whereas a lower initial and inlet temperature accelerates the reaction and reduces the additional preheat of the system. The heat exchange capacity of the reactor obviously affects the exothermic process, especially under the conditions of high stirring speed or high filling height, so the demand should be taken into account to match the appropriate heat exchange device in practical applications. The model and results in this work could help optimize the stirred reactors and provide theoretical guidance for future large-scale heat storage applications.

Key words: thermochemical heat storage, biaxial stirred reactor, exothermic process, multi-physics field coupling, numerical simulation

中图分类号:

TK 02

吕潇峻, 赵长颖, 闫君. 双轴搅拌反应器内Ca（OH）₂/CaO热化学储热体系的放热研究[J]. 化工学报, DOI: 10.11949/0438-1157.20240111.

Xiaojun LV, Changying ZHAO, Jun YAN. Exothermic study of Ca(OH)₂/CaO thermochemical heat storage system in biaxial stirred reactor[J]. CIESC Journal, DOI: 10.11949/0438-1157.20240111.

图/表 19

图1 双轴搅拌反应器物理模型

Fig.1 Physical model of the biaxial stirred reactor

表1 模型的几何结构参数

Table 1 Geometrical parameters of the model

符号	几何参数	值
d₀	搅拌轴直径	15 mm
r₁	底弧1半径	47 mm
r₂	底弧2半径	75 mm
h₀	入口大小	5 mm
h₁	侧边1高度	17.5 mm
h₂	侧边2高度	47.5 mm
h₃	出口高度	70 mm
l₀	出口大小	10 mm
l₁	上部宽度	95 mm
h_b	叶片宽度	10 mm
l_b	叶片厚度	2 mm

表2 模型的重要物理参数

Table 2 Important physical parameters of the model

符号	物理参数	值
D_p	颗粒粒径	100 μm
A	指前因子	53×10³ s^-1[34]
E	活化能	83×10³ J/mol^[34]
R	气体常数	8.314 J/(mol·K)
ρ_Ca(OH)2	Ca(OH)₂的密度	2200 kg/m^3[34]
ρ_CaO	CaO的密度	3320 kg/m^3[34]
λ_s	固体的热导率	2 W/(m·K)^[34]
c_p,_Ca(OH)2	Ca(OH)₂的比热容	f₁(T)^[11]
c_p,_CaO	CaO的比热容	f₂(T)^[11]

表3 基础工况的参数设置

Table 3 Parameters of the base case

符号	参数	值
u_in	气体入口流速	0.5 m/s
S/N	水蒸气/氮气比例	0.8
p_out	初始和出口压力	1 bar
ω	搅拌转速	100 rpm
T₀	初始和进口温度	623 K
H	CaO的填充高度	20 mm
h	壁面换热系数	12 W/(m²·K)
T_f	外部自由来流温度	303 K

图2 模型独立性验证注:(a) grid independence; (b) time step independence(a)网格独立性;(b)时间步长独立性

Fig.2 Validation of model independence

图3 模型准确性验证：出口水蒸气流量和床体温度

Fig.3 Validation of model accuracy: outlet steam flow and bed temperature

图4 速度云图和速度矢量图变化

Fig.4 Variation of velocity and velocity vectors maps

图5 固相体积分数云图的变化

Fig.5 Variation of solid phase volume fraction map

图6 固体粉末量的损失变化

Fig.6 Variation of solid powder loss

图7 温度云图的变化

Fig.7 Variation of temperature map

图8 监测点的温度变化

Fig.8 Temperature variation of observation points

图9 转化率和放热功率的变化

Fig.9 Variation of conversion and exothermic power

图10 换热系数对放热过程的影响注:(a) conversion and exothermic power; (b) bed temperature(a)转化率和放热功率;(b)床体温度

Fig.10 Effect of heat transfer coefficient on exothermic process

图11 搅拌转速对放热过程的影响注:(a) conversion and exothermic power; (b) bed temperature(a)转化率和放热功率;(b)床体温度

Fig.11 Effect of stirring speed on exothermic process

图12 水蒸气分压对放热过程的影响注:(a) conversion and exothermic power; (b) bed temperature(a)转化率和放热功率;(b)床体温度

Fig.12 Effect of steam pressure on exothermic process

图13 温度对放热过程的影响注:(a) conversion and exothermic power; (b) bed temperature(a)转化率和放热功率;(b)床体温度

Fig.13 Effect of temperature on exothermic process

图14 填充高度对放热过程的影响注:(a) conversion and exothermic power; (b) bed temperature(a)转化率和放热功率;(b)床体温度

Fig.14 Effect of filling height on exothermic process

图15 不同反应条件对放热过程的影响总结

Fig.15 Summary of effects of different reaction conditions on exothermic process

图16 双轴搅拌反应器与固定床反应器的放热对比注:(a)不同填充高度;(b)不同水蒸气分压

Fig.16 Comparison between biaxial stirred reactor and fixed bed reactor on exothermic process(a) variation of filling height; (b) variation of steam pressure

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双轴搅拌反应器内Ca（OH）₂/CaO热化学储热体系的放热研究

Exothermic study of Ca(OH)₂/CaO thermochemical heat storage system in biaxial stirred reactor

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