Abstract
摘要：起機程序（start-up）為固態氧化物燃料電池（SOFC）操作之重要一環。由於目前SOFC PEN所使用的材料皆屬陶瓷材料，而雙極連接板（interconnect）與框架（frame）則使用不銹鋼材。高溫操作下，因熱膨脹係數差異會造成組件的洩漏或破損，降低電池的效率，甚至造成永久損壞。經由模擬結果顯示，不良的溫昇程序將可能使PEN產生破裂，為避免造成元件損壞，並考量長期運轉之耐久性，及建立最佳起動程序，必需建立起機程序之動態模型。
本研究就操作層面考量，採用模型基礎設計（model-based design）架構以進行物理與化學函式（first principle）推導元件模型。以熱力學、氣體動力學與熱傳學等理論，考量質量及能量守恆為基礎，並根據電化學理論建立氣體分壓、溫度、操作電壓、與電流密度、與其他相關變數間關係之基本模式，以建立平板狀固態氧化物燃料電池堆之總體數學模型。應用本模型可進行暫態或動態行為分析，並藉由模擬分析結果，增進對系統響應特性之瞭解。藉由適當調整氣體入口流量與溫度進行熱氣增溫（heat-up）曲線模擬，以適切之溫升率增溫至反應溫度（約650~750℃），再經由迴授控制調整負載阻抗以得到適當的反應速率至操作區間（約70％Uf），使stack在允許之溫升率（元件設計規格）下逐漸增溫，以進行快速且安全穩定之啟動程序模擬，據以建立快速且安全起動之操作策略。
Abstract:
The start-up procedure plays an important role in Solid Oxide Fuel Cells (SOFCs) operations. The typical materials used for PEN (positive-electrolyte-negative) in SOFCs are all ceramic materials while those used for interconnects and frames are stainless materials. One of the most important issues for SOFCs is the thermal stresses caused from the thermal expansion coefficient mismatch and the temperature distribution developed inside the cells. The thermal stresses will cause low efficiency and even damage the stack permanently. For a not well-controlled temperature change during heating or starting-up, the resulting thermal stresses in a SOFC stack are likely to cause fracture in PEN according to the simulation results. To avoid any impairment and to optimize the startup of an SOFC regarding time, cell performance and long time durability, a dynamic model of the startup process is required.
This project focuses on the operation strategy for warming up the stack and the initial electrical load applied to stack. A Bulk model of SOFCs with the concept of model-based design will be constructed in this project. Comprehensive thermodynamic modeling is conducted on this model supplement with some gas dynamics in cell channel and heat transfer on stack and insulation. The developed model consists of mass and energy balances, and a electrochemical model that relates partial pressure and temperature to voltage, current density, and other relevant fuel cell variables. The system response of transient and dynamic analysis can be obtained from the dynamic model. The proper stack temperature curve during heat-up and start-up can be simulated by regulate the flow rate and inlet temperature of gas and air and load resistance with feedback control. The control strategy of heat-up and start-up process will be established under the consideration of the rate of temperature permitted to ensure the safety for a rapid operation.
Keyword(s)
固態氧化物燃料電池
起機程序
動態模擬
Solid Oxide Fuel Cells
Start-up
Dynamic simulation
