Thermodynamic Characteristics of Phase Change Heat Exchange System for Aromatics Low Temperature Heat Recovery
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摘要: 针对芳烃联合装置塔顶低温热回收工艺存在取热介质泄漏造成催化剂及吸附剂失效的问题，提出采用中间工质相变换热以确保本质安全的取热方案。采用Aspen HYSYS及EDR建立了现场工况100 kW的芳烃低温热回收相变换热系统全流程模拟的稳态数值模型，通过实验与数值模拟相结合的方法验证了稳态数值模型的可靠性，并且进行了工艺及结构参数对系统热力特性影响规律的研究。结果表明：随着除盐水入口温度升高，系统热负荷、工质循环流量及液位高度逐渐减小，工作温度逐渐升高；随着塔顶气流量增加，系统热负荷、工作温度先增加后降低，工质循环流量、液位高度先减小后增加，且除盐水入口温度越低，临界流量值越大；随着除盐水流量增加，系统热负荷、工质循环流量、液位高度逐渐增加，工作温度逐渐降低。在大温差及除盐水流量较大情况下，为避免系统传热性能受驱动力限制，需确保安装高度不小于液位差；系统热负荷随上升管管径增大而逐渐增加，且在上升管管径大于159 mm后基本不变；在下降管“断流”情况下，系统热负荷随安装高度增加而逐渐减小，实际安装高度无需过分增加；采用卧式（再沸器）-卧式（冷凝器）组合的系统其换热量比卧式（再沸器）-立式（冷凝器）组合的系统高3%左右。Abstract: Aiming at the problem of catalyst and adsorbent failure caused by the leakage of heat taking medium in the tower top low-temperature heat recovery process of aromatics combined unit, a heat taking scheme of phase change heat exchange of intermediate working medium is proposed to ensure the intrinsic safety of the process. Aspen HYSYS and EDR are used to establish the steady-state numerical model for the whole process simulation of the aromatic low-temperature heat recovery phase change heat exchange system under the field working condition of 100 kW. The reliability of the steady-state numerical model is verified by the combination of experiment and numerical simulation. The influence of process and structural parameters on the thermal characteristics of the system is studied. The results show that with the increase of the inlet temperature of demineralized water, the system heat load, circulating work quality and liquid level height of the system gradually decrease, and the working temperature increases gradually. With the increase of overhead gas flow, the system heat load and working temperature first increase and then decrease, the circulating work quality and liquid level height first decrease and then increase, and the lower the inlet temperature of demineralized water, the greater the critical flow value. With the increase of demineralized water flow, the system heat load, circulating work quality and liquid level height gradually increase, and the working temperature gradually decreases. In case of large temperature difference and large flow of demineralized water, in order to avoid the restriction of system heat transfer performance by driving force, it is necessary to ensure that the installation height is not less than the liquid level difference. The system heat load increases gradually with the increase of the rising pipe diameter, and basically unchanged after the pipe diameter is greater than Φ159 mm. In the case of "cut-off", the system heat load decreases gradually with the increase of installation height. In fact, the installation height does not need to be increased too much; The heat exchange of the system with horizontal (reboiler) and horizontal (condenser) combination is about 3% greater than that of horizontal (reboiler) and vertical (condenser) combination.
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图 1 相变换热系统结构图（a）及工质压焓图（b）
Figure 1. Structure diagram of phase change heat exchange system (a) and pressure enthalpy diagram of working medium (b)
图 2 芳烃低温热回收相变换热系统全流程模拟的数值模型
Figure 2. Numerical model of whole process simulation of aromatic low temperature heat recovery phase change heat exchange system
图 4 塔顶气、除盐水及工质温度随热流变化关系
Figure 4. Variation of overhead gas, demineralized water and working medium temperature with heat flow
图 5 水工质相变换热系统热力特性实验平台
Figure 5. Experimental platform for thermodynamic characteristics of hydraulic medium phase change heat exchange system
1—Reboiler; 2—Working medium; 3—Electric heating rod; 4—Pressure sensor; 5—Temperature sensor; 6—Riser; 7—Condenser; 8—Downcomer; 9—Gear flowmeter; T1~T16—Temperature sensor; FT1~FT2—Flowmeter; LT1~LT2—Liquidometer
图 7 热负荷、工质循环流量随工艺参数变化关系
Figure 7. Relationship between process parameters and thermal load, circulating flow of working medium
图 8 工作温度随工艺参数变化关系
Figure 8. Relationship between process parameters and working temperature
图 9 液位高度随工艺参数变化关系
Figure 9. Relationship between process parameters and liquid level height
图 10 管径对系统热力特性影响
Figure 10. Influence of pipe diameter on system thermodynamic characteristics
图 11 热负荷与安装高度变化关系
Figure 11. Relationship between thermal load and installation height
图 12 安装高度对系统热力特性的影响
Figure 12. Influence of installation height on system thermodynamic characteristics
图 13 安装方式对系统热力特性的影响
Figure 13. Influence of installation mode on system thermodynamic characteristics
表 1 除盐水及塔顶气工艺参数
Table 1. Process parameters of demineralized water and overhead gas
Item Mass flow/(kg·h−1) Inlet temperature/℃ Dryness Outlet temperature/℃ Inlet pressure/kPa Thermal load/kW Demineralized water 1370 60 0 120.0 400 100 Overhead gas 929 144 1 120.3 119 100 
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表 2 实验值与计算值相对误差
Table 2. Relative error between experimental value and calculated value
Demineralized water
flow/(L·h−1)Relative error/% Working temperature Circulating flow Liquid level height 100 0.80 5.35 0.66 200 0.84 5.42 0.66 300 0.51 5.42 0.60
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