超低溫液體供應系統製程危害分析與風險評估

Abstract

「超低溫液體供應系統」供應各行業不同的製程使用。國內近年來此種設施引發嚴重的意外事故時有所聞，肇因於缺乏完整的風險評估及製程安全管理，使看似簡易的供氣系統，潛藏著高度的風險。本研究試圖以系統化的風險評估程序，運用PDCA管理循環於製程安全管理上，在製程規劃 (Planning) 階段以本質較安全設計為基礎，再執行 (Do) 危害評估，辨識重大危害及風險等級，輔以後果分析軟體，驗證 (Check) 受影響之範圍與結果，進而採取行動 (Action) 修正原設計或強化安全防護層(Layer of Protection, LOP)，以達到風險永續管理(Risk Continuity Management)。 危害評估方法，規劃初期以危害與可操作性分析 (Hazard and Operability Studies, HazOp) 製程危害評估技術，探討超低溫液體供應系統製程中潛在危害，運用本質較安全設計及安全防護層兩大製程危害控制技術，藉此降低操作風險。並利用後果分析軟體(PHAST 6.5) ，分別模擬氮氣及氧氣排放所造成氣體擴散對於人員或設備造成的影響，對於排放至大氣中的氮氣容許濃度經公式推導及計算結果為71429 ppm。 研究結果顯示，原始排放設計可能使人員遭受危害氣體之暴露，經採用改變排放管的方向及減少管徑增加流速之方式，再經過模擬結果顯示，已可達到完全避開人員的操作位置，確保風險已有效消除，也驗證了在製程生命週期愈早導入本質較安全設計的概念，對於安全衛生績效、環境影響愈經濟有效。

The cryogenic liquid supply systems served in various process of industry. This kind of facilities was occurred serious incidents recent year in Taiwan. The reason why the simple of gases supply system have potential risk, that caused by lack of integrated risk analysis and process safety management. The purpose of this research attempted to use systematized methodology of hazard assessment to make good process safety management use of PDCA cycle. The phase of project planning is based on the Inherently Safer Design (ISD) and performed the hazard assessment to identify major hazards and levels of risk. A software of consequence analysis should be used for verify that scope and result of influence, and then take actions to improve the original design or consolidate the Layer of Protection (LOP) so that is able to achieve the Risk Continuity Management. The Hazard and Operability (HazOp) technology is used to identify the potential hazards of Cryogenic Liquid Supply Systems for the primary stage of project, also lead the ISD and LOP concept in process hazard management. The software of PHAST 6.5 is used to simulate the Nitrogen and Oxygen dispersion for consequence analysis. The release of oxygen or asphyxiant into air may pose a flammability or asphyxiation hazard. The dispersion programs do not account for the components of air which are present prior to the dispersion of the jet. Therefore, the oxygen or asphyxiant mole fractions of concern have to adjust and calculate as input to the dispersion programs. The nitrogen concentration of interest will be 71429 ppm. The result of study shows the original vent design could be created an asphyxiating/oxygen enrichment environment at grade on the platform. The asphyxiating concentration of interest is exceeded on the platform for two of the three weather conditions. Some proposed methods to eliminate the possibility of an asphyxiating/oxygen enrichment atmosphere on the platform include reducing the vent diameter and changing the direction of the vent. That is able to demonstrate that these changes reduce the nitrogen/oxygen concentration on the platform below asphyxiating/oxygen enrichment levels. The studies also prove that conduct the ISD concept is effective in safety performance and environmental protection as soon as possible in the early phases of life cycle.