Modeling and performance analysis of a two-stage thermoelectric energy harvesting system from blast furnace slag water waste heat
Introduction
Thermoelectric generation is classified as direct power conversion [1], [2], [3], [4], [5]. It has lots of features and advantages compared with traditional generators, for example, the absence of moving components results in an increase of reliability, and reduction of extra maintenance; the modularity can provide a wide-scale application without significant losses in performance. Besides, these devices produce no noise and waste in the conversion process. Therefore, thermoelectric generator has been regarded as a useful and attractive device for direct energy conversion [6], [7], [8], [9], [10] and potential application in waste heat recovery [11], [12], [13], [14].
As energy shortage and environmental deterioration are growing, energy saving and emission reduction have become global obligation and responsibility [15], [16], [17], [18], [19]. Yu and Zhao [15] employed hot and cold water as heat reservoirs and analyzed the performance of thermoelectric generator with the parallel-plate heat exchanger. Meng et al. [16] established a numerical model of commercial thermoelectric generator with finned heat exchangers taking into account inner and external multi-irreversibilities. Gou et al. [17] established a dynamic model for waste heat recovery in thermoelectric generator to assess the effects of heat reservoirs on the dynamic characteristics. Kazuaki et al. [18] analyzed energy economy for a combined thermoelectric generator on top of a steam turbine cycle, and demonstrated the advantage of adding a thermoelectric on top of a steam turbine cycle. Stevens [19] established an energy harvesting device that produces milliwatt-scale power uses a thermoelectric generator operating between the air and ground temperatures.
Since the single stage thermoelectric generator cannot operate in the case of large temperature range [20], [21], [22], [23], [24], [25], and due to the performance limits of thermoelectric materials and requirements of adapting different heat reservoir conditions, some authors have investigated the performance of thermoelectric generator composed of two stages and more [26], [27], [28], [29], [30], [31], [32].
In the process of promoting the transformation of materials in the iron and steel industry, rich and variety of waste heat is generated. Taking advantage of these waste heats can effectively reduce energy consumption [33], [34], [35]. Chen et al. [36] provided an overview of residual heat recovery in iron and steel enterprises in China based on single stage and multi-element thermoelectric generation, and the calculations showed that electricity power of 21 kWh, 43 kWh and 60 kWh can be recovered from 1 GJ waste heat with temperature difference of 100 °C, 200 °C and 300 °C, respectively. Meng et al. [37] established a model of single stage and multi-element thermoelectric generator driven by blast furnace slag flushing water sensible heat with parallel-flow type heat exchangers, and analyzed the power and efficiency performance, as well as the recovery period of the equipment cost.
On the basis of research achievements mentioned above, this paper will establish a physical and numerical model of two stage thermoelectric energy harvesting system driven by blast furnace slag water waste heat, and analyze the effects of key parameters on the power output, efficiency, optimal electrical current as well as optimal resistance ratio of the system.
Section snippets
Harvesting system setup and model
A schematic diagram of the harvesting system driven by blast furnace slag water waste heat is shown in Fig. 1. The system is consisted of two parts. The first part contains two heat exchangers between heat reservoir and two-stage thermoelectric generator module. As is well known, the performance of counter-flow heat exchanger is better than that of parallel-flow one, this paper aims at discussing the system's performance with counter-flow type heat exchangers between blast furnace slag water
Numerical examples and analyses
The effects of some key parameters on the system's performance are investigated by numerical simulation. Since the inlet temperature of blast furnace slag water at constant pressure is less than 100 °C and the inlet temperature of cooling water is set as 20 °C, the effect of temperature on the physical properties of the thermoelectric materials is ignored. The physical properties of the thermoelectric materials at mean temperature of 50 °C are set as follows [38]: α = 2.07 × 10−4 V K−1, λ
Conclusion
This paper establishes a model of two-stage thermoelectric energy harvesting system. The performance of the two-stage thermoelectric generator system driven by blast furnace slag water waste heat is analyzed. The major results are as follows:
- (1)
The inlet temperature of flushing slag water is an important parameter which affects the performance of the two-stage thermoelectric generator system significantly. Both the maximum efficiency and the optimal working electrical current are linear increasing
Acknowledgments
This paper is supported by the National Basic Research Program of China (No. 2012CB720405) and the National Natural Science Foundation of China (No. 11305266). The authors wish to thank the reviewers for their careful, unbiased and constructive suggestions, which led to this revised manuscript.
References (38)
- et al.
Progress of thermoelectric power generation systems: prospect for small to medium scale power generation
Renew Sustain Energy Rev
(2014) - et al.
Study of the influence of heat exchangers' thermal resistances on a thermoelectric generation system
Energy
(2010) - et al.
Thermodynamic irreversibility and performance characteristics of thermoelectric power generator
Energy
(2013) - et al.
Accurate simulation of thermoelectric power generating systems
Appl Energy
(2014) - et al.
Modeling, experimental study and optimization on low-temperature waste heat thermoelectric generator system
Appl Energy
(2010) - et al.
Exhaust energy conversion by thermoelectric generator: two case studies
Energy Convers Manag
(2011) - et al.
Optimization of thermoelectric generator module spacing and spreader thickness used in a waste heat recovery system
Appl Therm Eng
(2013) - et al.
A numerical model for thermoelectric generator with the parallel-plate heat exchanger
J Power Sources
(2007) - et al.
A numerical model and comparative investigation of a thermoelectric generator with multi-irreversibilities
Energy
(2011) - et al.
A dynamic model for thermoelectric generator applied in waste heat recovery
Energy
(2013)