應用HAZOP及Hazard Tree Analysis（HTA）風險分析技術於蒸汽鍋爐工場之適用性研析

鍋爐產生的蒸汽是石化工廠主要的動力來源，以供應廠區各製程使用。蒸汽鍋爐工場主要區域有：（1）鍋爐區、（2）脫硝區及、（3）脫硫區。現今的鍋爐雖已採用自動化控制且設置多重安全連鎖裝置，但是鍋爐造成的意外事故仍然頻傳。究其原因，主要是未依照規定實施設備維護保養及人員違規操作。本研究以某公司的蒸汽鍋爐工場為對象，利用危害與可操作性分析（Hazard and Operability Study, HAZOP）及危害樹分析（Hazard Tree Analysis, HTA）兩種風險分析技術藉以發現蒸汽鍋爐工場重大危害並比較兩種技術的差異性，並嘗試將嚴重度導入危害樹中，以顯示危害事件的事故原因及由事故原因所對應的相對危害等級。先使用危害樹分析技術繪製出危害樹以得知每一個可能發生的潛在重大危害事件的所有程序偏離和其相對應的矯正措施，及每一程序偏離發生的根本原因和其相對應的預防措施，再使用HAZOP系統化分析評估蒸汽鍋爐工場的製程偏離及其控管措施。研究結果發現，HAZOP與危害樹分析的結果差異性不大，若將嚴重度導入HTA後則具有下列特色：（1）以整個製程的危害思維進行風險分析；（2）導入嚴重度、可能性及風險等級的觀念，並以顏色區域顯現事故發生時的危害情境；（3）明確顯現預防事故發生的對策，如製程偏離對應矯正措施，根本原因對應預防措施。

關鍵字

蒸汽鍋爐；節點；危害與可操作性分析；危害樹分析

並列摘要

Steam generated from steam boiler is the main source of power to support petrochemical plants operations. There are three main areas in the stream boiler plant: (1) boiler area, (2) denitrification and (3) desulfurization. Unfortunately, boiler accidents still occur frequently even equipped with automated control system and set multiple safeties interlocks to the boiler. The main reasons are that specified equipment maintenance schedules and procedures are not followed properly. In addition, the operator errors were also known to contribute to the accidents. By using the techniques of Hazard and Operability Study (HAZOP) and Hazard Tree Analysis (HTA), we intended to find the potential risks of the boiler and to compare the accuracy of these two techniques on the assessment of the risks. We also tried to incorporate the effect of the severity to the HTA to demonstrate the root causes of the accidents and the corresponding degree of severity of the accidents. We first drew the hazard tree diagram and listed all possible deviations from the designed process, the effects of these deviations to the occurrences of the accidents, the associating correction actions, the root causes and the corresponding prevention actions. We then systematically applied the HAZOP analysis technique to evaluate the nature of the process deviations of the boiler and the control strategies. From the results of the analysis, we found that both techniques give similar conclusions. By incorporating the severity of accidents into HTA, we also found some characteristics as follow: (1) the entire process, instead of its individual sections of the process, is considered when the risk analysis is conducted, (2) the degree of the accident occurrence can be categorized by different colors representing the degree of severity, (3) we can clearly picture the severity and the actions to prevent the accidents from happening such as by controlling the deviation of process or by improving the process at design stage or after process had been implemented.