氢氧化镁热化学储热系统流化床反应器性能分析

doi:10.19799/j.cnki.2095-4239.2021.0141

摘要/Abstract

摘要：

热化学储热具有储能密度高、储存时间长、温度范围宽的优点，是目前极具前景的储能技术，流化床反应器具有出色的传热传质性能，非常适合应用于热化学储热系统。本工作基于双欧拉模型，耦合了传热方程与反应动力学方程，构建了二维轴对称非稳态的多相流化学反应模型，以氢氧化镁和氧化镁作为储热材料，对热化学储热系统流化床反应器内的储、放热过程进行了研究，并且分析了床层膨胀率、气体流量对储放热效率的影响。通过实验验证了模型的准确性，探究了反应器内的能量流动过程与能耗优化方向。结果表明，床层温度不受传热效率的影响，反应器内不同区域间以及气相与固相间的温度差值均小于1.0 K，放热反应动力学限制了反应器性能；高温气固反应能显著提高床层膨胀率，床层膨胀率和气体流量的变化对储热效率影响较大，对放热效率影响较小；放热过程中的气体预热量和储热过程中的颗粒显热是反应器能量优化的重点方向。本研究对热化学储热系统中的流化床反应器数值建模分析以及实验设计优化具有指导价值。

关键词: 热化学储热, 氢氧化镁, 流化床反应器, 数值计算

Abstract:

Thermochemical energy storage is a promising energy storage method because of its high-energy storage density, long-term storage capability, and broad temperature ranges. A fluidized bed reactor has excellent heat and mass transfer performance, suitable for a thermochemical heat-storage system. This study established a two-dimensional axisymmetric unsteady numerical model that included the multiphase flow and chemical reaction, based on the Eulerian–Eulerian model and heat-transfer and reaction kinetics equations. The effects of bed expansion ratio and gas flow rate on the heat storage and release efficiency were analyzed based on the investigation of the reaction processes and using magnesium hydroxide and magnesium oxide as the thermochemical heat storage materials. The authors validated the numerical model and investigated the energy flow and energy consumption optimization in the fluidized bed reactor by conducting experiments. The results indicated that the heat-transfer efficiency did not limit the bed temperature. The temperature differences among the different regions inside the reactor and between the gas phase and the solid phase were less than 1.0 K. The exothermic reaction kinetics limited the performance of the reactor. A high-temperature gas-solid reaction can significantly increase the bed's expansion rate; additionally, the bed expansion ratio and gas flow rate significantly influenced the heat storage efficiency but had little influence on the heat release efficiency. The gas that was preheated in the heat release process, as well as the sensible heat within particles in the heat-storage process, were key aspects of the reactor energy optimization. This research reflects guiding value for the numerical modeling and experimental optimization of a fluidized bed reactor in a thermochemical heat storage system.

Key words: thermochemical energy storage, magnesium hydroxide, fluidized bed reactor, numerical calculation

中图分类号:

TK 02

杨博文, 闫君, 赵长颖. 氢氧化镁热化学储热系统流化床反应器性能分析[J]. 储能科学与技术, 2021, 10(5): 1735-1744.

Bowen YANG, Jun YAN, Changying ZHAO. Investigating the performance of a fluidized bed reactor for a magnesium hydroxide thermochemical energy storage system[J]. Energy Storage Science and Technology, 2021, 10(5): 1735-1744.

图/表 18

图1

表1

物理量计算公式汇总"

物理量	表达式
Gidaspow模型的相间交换系数^[28]	$K g s = K s g = 150 ε s (1 - ε g) μ g ε g d p 2 + 1.75 ε s ρ g u ? s - u ? g d p, ε g ≤ 0.8 ? 18 1 + 0.15 ε g R e s 0.67 ε g - 2.65 ε s ρ g u ? s - u ? g d p R e s, ε g > 0.8$
应力应变张量^[29]	$τ ? = ε μ ? u ? + ? u ? T - 23 ? · u ? I ?$
固体压力^[29]	$? P s = 10 - 8.686 ε s + 8.577 ? ε s$
Gidaspow模型的固体剪切黏度^[30]	$μ s = 45 ε s ρ s d p g 0, s s 1 + e s s Θ s π 0.5 + 10 ρ s d p Θ s π 96 ε s 1 + e s s g 0, s s 1 + 45 ε s g 0, s s 1 + e s s 2$
Gidaspow模型的径向分布函数^[31]	$g 0, s s = 1 - ε s ε s, m a x 13 - 1$
颗粒温度	$Θ s = 13 u ? s u ? s$
颗粒碰撞恢复系数	$e s s = 0.9$
Reynolds数	$R e s = ρ g d p u ? s - u ? g μ g$

表1

表2

表3

图2

图3

表4

图4

图5

图6

图7

图8

图9

图10

图11

表5

图12

图13

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参数	值
网格数	29×220
网格形状及面积	矩形，10^-6 m²
时间步长	0.001～0.01 s，变步长
收敛准则	最大值0.001
每个时间步长最大迭代次数	30

网格数/个	时间步长/s	床体平均温度/K
20 × 100	0.001 ～ 0.01 s，变步长	604.3
29 × 220	0.001 ～ 0.01 s，变步长	604.5
58 × 440	0.001 ～ 0.01 s，变步长	604.5
29 × 220	0.01 s，固定步长	604.5
29 × 220	0.001 s，固定步长	604.5

编号	氮气流量/(L·min^-1)	水蒸气分压/kPa	气体预加热温度/℃	反应初始温度/℃	反应物质量/g Mg(OH)₂
1	10	47.4	110	144	140
2	7	70.1	110	161	80
3	7	47.4	110	162	60
4	4	57.8	110	159	60

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