抽汽冷凝式汽電共生系統為大型石化廠最常採用之熱、電整合技術，抽汽冷凝式系統相較於背壓式系統有較佳之發電調整彈性，然而抽汽冷凝式系統之熱效率會隨有效熱能產出比例(或製程抽汽比例)變動而受影響；以實務觀點而言，如汽電共生系統於設計時未準確預估製程蒸汽需求量及最適化之發電裝置容量，就可能造成設置之汽電共生系統因熱、電比太低而無法符合「合格汽電共生」之規定，或因為抽汽增加造成發電量不夠自用及售電效益不如預期等；進一步而言，因為系統偏離設計條件及低負載運轉亦會降低能源使用效率，而背離汽電共生系統推廣之原始目的。
本研究選定台灣某石化中間原料廠之94.9 MW抽汽冷凝式汽電共生機組為研究對象，根據原設計資料建立鍋爐負載、製程抽汽與發電負載之變動關係，並參考工程熱力學方法與原系統設計廠商【三菱重工業株式會社】之性能測試報告，建立汽電共生系統之發電熱耗率及發電、抽汽負載計算模式，以供業主評估操作成本及制定操作策略之參考。本研究同時發展一套Microsoft Excel效率計算試算表，提供業主利用該系統之分散式數位控制處理器(DCS)，攫取即時運轉數據轉存入控制室個人電腦(PC)，遂行汽電共生系統即時效率監控，以及供本研究獲取實際操作數據作比較。
電腦模擬該汽電共生系統之各種抽汽與發電組合，發現該機組滿載發電時必須搭配100 t/h以上之製程用汽才符合合格汽電共生系統之規定，另於發電最低負載(約20 MW)時有效熱能須達78%以上總熱效率才可達52%，顯示低載發電之熱效率極差。
本研究亦探討該系統之節能空間，發掘出節省能源、降低損失或提高能源使用效率之方案，並評估這些方案之可行性與預期效益，以鼓勵業主作降低能源使用成本之決策，及提供相關人員之規劃與設計參考；經評估該系統經由離峰降載時提高鍋爐給水溫度、常壓閃沸蒸汽再利用於空氣預熱器、冷卻水塔風扇改變頻轉速控制，及鍋爐送風機加裝液壓聯軸器等方案，每年可進一步節約能源達2,546.44公秉油當量。

The extraction-condensing cogeneration system is a popular technology for heat and power integration which can be used by petrochemical process. To compare with back pressure system, extraction-condensing system has better flexibility for process control. However, the thermal efficiency of extraction- condensing system could be affected by the amount of effective heat to process. If the effective heat to process and the plant power demand were not well designed, the cogeneration system may violate government regulation of “qualified cogeneration system” by MOEA, or the system economics can not meet investor’s requirement. From another point of view, if the cogeneration system bias original design operating condition or it has to run under low loading, the energy efficiency will move away from the target.
A 94.9 MW extraction-condensing system of a petrochemical plant was selected as an example. For the purpose of data requisition, the author established a model to predict main steam flow, extraction steam flow, and power generation load. Moreover, a set of equations for the calculation of heat rate of turbine plant was developed. Besides, a Microsoft Excel calculation sheet was programmed to compute real time plant thermal efficiency.
The actual operation data was compared with computer simulation. Results show (1) To meet the regulation, the process steam shall exceed 100 t/h with rated power generation. (2) For the minimum generator load (about 20 MW), the effective heat to process must exceed 78% in order to ensure a 52% overall thermal efficiency. (3) Low load means low thermal efficiency of this system.
Some energy conservation ideas of this cogeneration system were assessed. Four ideas were presented, including (1) Increase boiler feed water temperature during low evaporation load. (2) Recovering of flash steam vented from blow down tank for the heating of boiler combustion air. (3) Control of cooling tower fans speed by using frequency inverter. (4) Utilization of hydraulic coupled forced draft fan. The total benefit of these energy conservation ideas is 2,546.44 kilo-liter fuel oil equivalent.

目錄………………………………………………………………….…..…..I
圖目錄…………………………………………………………………...….III
表目錄……………………………………………………………….…..….VII
符號說明……………………………………………………….…………...VIII
摘要…………………………………………………………….………..….X

第一章 緒論………………………………………………………....….…1
1-1 前言…………………………………………………………..…...….1
1-2 蒸汽渦輪機汽電共生系統……………………………………….….1
1-3 研究背景及內容……………………………………………….....….5

第二章 系統說明………………………………………………….....……6
2-1 系統設備規範簡介……………………………………………......…6
2-2 系統流程說明………………………………………………….……12
2-3 系統設計條件及性能………………………………………….……16
2-4 蒸汽渦輪機之效率評估規範………………………………….……19
2-5 影響蒸汽渦輪機熱效率之參數……………………………….……23

第三章 熱效率分析方法…………………………………………....…....27
3-1 熱經濟分析(EXERGY AND AVAILABILITY ANALYSIS)…….…..…27
3-2 熱效率定義(THERMAL EFFICIENCY, HEAT RATE, BACK WORK RATIO)……………………………………………………………....28
3-3 合格汽電共生系統有效熱能產出及總熱效率………………..…...29
3-4 熱損失法鍋爐效率……………………………………………….....31
3-5 熱進出法鍋爐效率……………………………………………….....35
3-6 汽電共生系統發電熱耗率……………………………………...…..36

第四章 熱系統效率分析…………………………………………...…...38
4-1 熱系統設備計算模式…………………………………………..….38
4-2 熱力性質………………………………...……………………..…..46
4-3 方程式推導…………………………………………………......….59
4-4 發電、抽汽影響熱效率之預估模式…………………………..….70
4-5 汽電共生系統之熱效率計算模式……………………………..….81
4-6 汽電共生系統熱效率分析…………………………………….…..82

第五章 汽電共生系統節能評估…………………………………….….109
5-1 低負載時提高鍋爐給水溫度………………………………....…...109
5-2 閃沸蒸汽再利用……………………………………………....…...112
5-3 負載變動之冷卻水塔操作管理……………………………….…..113
5-4 液壓聯軸器之應用…………………………………………….…..115

第六章 結果與討論…………………………………………..……..…..119

參考文獻…………………………………………………………………..121

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