- 期刊
高效率n型Bi-Te系熱電合金開發及其在鋼廠廢熱回收發電應用
Development of High Performance N-type Bi-Te Alloys for Thermoelectric Power Generation in the Steel Plant
摘要
熱電模組之運作主要是利用p型與n型Bi-Te系塊材所配對而成之串聯結構。但現今之n型Bi-Te系塊材的熱電性能仍無法及得上p型塊材，因此熱電模組的發電效率受限於n型Bi-Te系材料。本研究先以電腦數值模擬技術建立Bi-Te合金區熔長晶模型，進而找出最佳化的n型晶棒生產參數；並藉由微量摻雜的選用與基材Se/Te計量比例調控技術，進而優化基材能帶結構而提升熱電性能。電腦數值模擬的結果顯示，當區熔設備的加熱器及冷卻裝置的移動速度越慢，長晶凝固界面則呈現凸面，越有利於大尺寸晶粒成長。經由模擬結果找出最佳長晶參數為：加熱器溫度達770℃、加熱器與冷卻裝置的移動速度控制在0.75cm/hr；而實驗的結果亦顯示，當適量添加碘化物並控制Se/Te計量比例為0.45/2.55時，可以使n型Bi-Te系合金達到極高的熱電勢（>200 mV/K） 並能維持一定水準的電傳導率（>1000 S/cm）。綜合區熔長晶參數最佳化、以及成分計量／摻雜優化，本研究已成功開發出直徑25 mm、長度250mm的n型Bi-Te系合金晶棒，產能>5.9 kg／批次，其最佳熱電優值（ZT）達1.34，性能已超越國際水準。所開發之高效能n型熱電晶棒已經應用於自製熱電模組，其發電效率可達6.9%（國際先進水平在5%～7.2%）、模組發電密度為0.62W/cm^2。自製熱電模組已安裝於中鋼煉鋼二廠四、五、六號連鑄機廢熱回收發電系統，整體發電量規模可達6 kW。
並列摘要
Thermoelectric modules are mainly comprised of the series structure formed by pairing p-type and n-type Bi-Te alloys. However, the thermoelectric performance of the current n-type Bi-Te bulk materials is still not as good as that of the p-type bulk materials. The power generation efficiency of the thermoelectric modules is limited by the n-type Bi-Te based materials. In this work, a zone-melting model of Bi-Te alloy was first established by numerical simulation technology, and then the optimal n-type ingot production parameters were determined. At the same time, through the selection of dopants and the adjustment in the stoichiometric ratio of Se/Te, the band structure of the substrate can be optimized to improve the thermoelectric performance. The results of numerical simulation show that when the heater and cooling device of the zone melting equipment move slower, the solidification interface will present a convex surface, which is more conducive to the growth of large-sized grains. According to the simulation results, the optimal zone-melting parameters were found: the temperature of the heater reached 770°C, and the moving speed of the heater and cooling device was controlled at 0.75 cm/hr. The experimental results also show that when adding iodide in an appropriate amount and controlling the Se/Te stoichiometric ratio to 0.45/2.55, the n-type Bi-Te alloy can achieve extremely high thermopower (>200μV/ K) and maintain a certain level of electrical conductivity (>1000 S/cm). Through the optimization of zone-melting process, matrix composition, and dopant, this study has successfully developed n-type Bi-Te based ingots with a diameter of 25 mm, a length of 250 mm, and a production capacity >5.9kg/batch. Its best thermoelectric figure of merit (ZT) reaches 1.34, which has surpassed the international advanced level. The developed high-efficiency n-type ingots has been used in the self-made thermoelectric modules, the power generation efficiency can reach 6.9% (the international advanced level: 5%~7.2%), and the power generation density of the modules is 0.62 W/cm^2. The self-made thermoelectric module has been installed in the thermoelectric power generation system of No. 4, No. 5 and No. 6 continuous casting system in CSC No.2 Steel Plant, and the overall power generation capacity can reach 6kW.