基于热力学第二定律的ORC蒸气发生器性能优化

doi:10.11949/0438-1157.20190272

摘要/Abstract

摘要：

为了更深入地研究低温余热驱动ORC系统的设计与优化，建立了有机朗肯循环蒸气发生器主要热力性能计算模型，基于热力学第二定律，以蒸气发生器单位换热面积工质?升作为性能优化目标函数，选取了R245fa作为循环工质，在给定烟气进口温度以及保证循环工质在蒸气发生器出口为饱和蒸气条件下，对不同工况下的工质质量流速进行优化，并分析了在一系列换热管管径下，烟气入口温度、工质入口压力、管外对流传热系数、单根换热管烟气质量流量对目标函数及工质最优质量流速的影响。结果表明：工质入口压力与管外对流传热系数对最优工质质量流速影响显著，随着工质入口压力与管外对流传热系数的增大，最优工质质量流速增大，对应的换热管径减小；而烟气入口温度、单根换热管烟气质量流量对最优工质质量流速影响甚微。

关键词: 烟道气, 余热回收, ORC, 蒸气发生器, 传热, ?, 优化

Abstract:

To study the design and optimization of the low temperature waste heat driven ORC system, the main thermal performance calculation model of the organic Rankine cycle steam generator was established. Based on the second law of thermodynamics, the exergy increase of unit heat transfer area in steam generator was proposed as optimization objective function. R245fa was selected as the working fluid. Under the condition of a given flue gas inlet temperature and ensuring the working fluid gets saturated at the steam generator exit, the optimal mass flow rate under different conditions are calculated, and the effects of inlet temperature of flue gas, inlet pressure of working fluid, convective heat transfer coefficient of outside pipe and the per tube mass flow of flue gas on objective function and optimal mass flow rate of working fluid are analyzed. The results show that the inlet pressure of the working fluid and the convective heat transfer coefficient outside the tube have a significant influence on the optimal mass flow rate, while the inlet temperature of the flue gas and the per tube mass flow of flue gas have little effect on the optimal mass flow rate. With the increase of the inlet pressure of the working fluid and the convective heat transfer coefficient outside the tube, the optimal mass flow rate increases.

Key words: flue gas, wasted heat recovery, ORC, steam generator, heat transfer, exergy, optimization

中图分类号:

TK 124

余伟, 王辉涛, 王建军, 朱道飞, 陶帅, 葛众, 黄靖伦, 赵玲玲. 基于热力学第二定律的ORC蒸气发生器性能优化[J]. 化工学报, 2019, 70(11): 4238-4246.

Wei YU, Huitao WANG, Jianjun WANG, Daofei ZHU, Shuai TAO, Zhong GE, Jinglun HUANG, Lingling ZHAO. Performance optimization of ORC steam generator based on the second law of thermodynamics[J]. CIESC Journal, 2019, 70(11): 4238-4246.

图/表 9

图1 蒸气发生器模型

Fig.1 Steam generator model

图2 换热微元示意图

Fig.2 Diagram of heat transfer micro-element

图3 换热管内工质流动分析

Fig.3 Analysis of working fluid flow in heat exchange tube

图4 蒸气发生器求解计算框图

Fig.4 Diagram of steam generator solution calculation block

表1 参数设置

Table 1 Parameter settings

参数	值
换热管壁厚δ/m	0.003
管壁热导率λ_wall/(W/(m·K))	45
局部阻力及质量力附加系数 $ζ$	0.25
环境温度T_surr/℃	20

表1 参数设置

Table 1 Parameter settings

参数	值
换热管壁厚δ/m	0.003
管壁热导率λ_wall/(W/(m·K))	45
局部阻力及质量力附加系数 $ζ$	0.25
环境温度T_surr/℃	20

图5 工质最优质量流速随烟气进口温度的变化

Fig.5 Optimum mass flow rate of working fluid changes with inlet temperature of flue gas

图6 工质最优质量流速随工质入口压力的变化

Fig.6 Optimum mass flow rate of working fluid changes with inlet pressure of working fluid

图7 工质最优质量流速随单根换热管烟气质量流量的变化

Fig.7 Optimum mass flow rate of working fluid changes with gas mass flow rate of single heat exchange tube

图8 工质最优质量流速随管外对流传热系数的变化

Fig.8 Optimal mass flow rate of working fluid changes with convective heat transfer coefficient outside tube

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