Simulations on simultaneous charging/discharging process of oil sand packed bed thermocline storage tank

doi:10.11949/0438-1157.20200485

Abstract

Abstract:

A physical mathematical model of oil sand packed bed thermal energy storage (TES) which can be applied in high temperature TES system is established. The charge/discharge outlet temperature and thermocline thickness are investigated when charge and discharge process are operated simultaneously. The results indicate that the small charging power and lower increasing rate of charge outlet temperature are obtained in the end of simultaneous charge and discharge. The smaller the net TES flow rate, the longer it takes to reach a stable charge outlet temperature under the condition of the same TES medium in the TES tank. The conventional TES tank thermocline thickness is thinner than oil sand packed bed when operated at the same net charge flow rate. The stable/unstable simultaneous charge and discharge are investigated based on cycle process of square wave thermal source. The discharge outlet temperature and the thermocline thickness gradually increase after the end of each cycle due to the effect of the superposition of the cycle process. The discharge outlet temperature fluctuates periodically.

Key words: computational fluid dynamics, heat transfer, solar energy, thermocline, packed bed, combined heat and power

摘要：

针对应用于高温储热场合的导热油砂石填充床储热，建立物理数学模型，采用数值模拟方法，重点探究在稳定热源和非稳定热源同时蓄放热工况下，蓄放热出口温度、斜温层厚度等参数。研究发现：传统蓄热罐同时蓄放热后期，换热功率较小，蓄热出口温度上升较慢；当蓄热罐内部传热工质结构相同时，净蓄放热流量越小，蓄热出口达到稳定的用时越长；同一净蓄热流量下，传统蓄热罐运行过程中斜温层厚度远远小于填充床蓄热罐运行时斜温层厚度；以热源为方波形式的周期性蓄热过程探究非稳定热源同时蓄放热。由于周期叠加性的影响，各工况每周期结束后放热出口温度上升，蓄热罐内斜温层的厚度逐渐增大，放热出口温度呈现周期性波动。

关键词: 计算流体力学, 传热, 太阳能, 斜温层, 填充床, 热电联产

CLC Number:

TK 124

Xiaohui WANG, Chao XU, Lijun YANG, Xiaoze DU. Simulations on simultaneous charging/discharging process of oil sand packed bed thermocline storage tank[J]. CIESC Journal, 2020, 71(S2): 85-91.

王小惠, 徐超, 杨立军, 杜小泽. 导热油砂石填充床单罐斜温层同时蓄放热特性模拟[J]. 化工学报, 2020, 71(S2): 85-91.

Figures/Tables 10

Fig.1 Physical mathematical model

Fig.2 Comparison of thermocline profiles between numerical and experimental results

Table 1 Parameter setting and stable outlet temperature

工质	工况	Q_cs/(kg/s)	Q_ds/(kg/s)	T_out(模拟)/K	T_out(理论)/K	误差/ %
纯导热油	4-1	1.6	0.8	552.73	553.15	0.8
	4-2	2.4	0.8	569.37	569.15	0.4
	4-3	3.2	0.8	577.85	578.15	0.5
导热油砂石填充床	4-4	1.6	0.8	552.89	553.15	0.5
	4-5	2.4	0.8	569.53	569.15	0.7
	4-6	3.2	0.8	577.89	578.15	0.4

Fig.3 Variations of outlet temperatures under stable heat source conditions

Table 2 Operating time and proportion of temperature change period

工况	运行时间/min	低温恒温段/ %	温度攀升段/ %	高温恒温段/ %
4-1	1543.55	21	10	69
4-2	858.71	25	11	64
4-3	571.78	29	10	61
4-4	622.98	60	37	3
4-5	318.52	65	31	4
4-6	210.28	70	24	6

Fig.4 Variations of thermocline thickness under stable heat source conditions

Table 3 Simultaneous charge and discharge under periodic heat source conditions

工况	Q_cs/(kg/s)	Q_ds/(kg/s)	每周期蓄热时间/min	每周期放热时间/min
4-7	1.2	0.8	30	30
4-8	1.2	0.8	30	20
4-9	1.6	0.8	30	30

Fig.5 Variations of discharge outlet temperature under unstable heat source conditions

Fig.6 Distributions of discharge outlet temperature under unstable heat source conditions

Fig.7 Variations of temperature in tank under unstable heat source conditions

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