地上天然氣整壓站風險危害評估-以台灣某天然氣整壓站為例

基於考量天然氣(NG)為輕質氣體特性，為避免天然氣洩漏時產生蓄積可能引發之爆炸危害，多數整壓站皆採地面上設置，再佐以外觀之綠美化等方式設置，但從歷年相關整壓站研究中發現，危害分析都僅針對地下天然氣整壓站，因此本研究以國內地上天然氣整壓站為主要探討對象。研究首先針對整壓站製程安全資訊之蒐集與探討，接著進行整壓站現場實地訪視與探勘，並彙整現場缺失，再透過初步危害分析方法全面性的將該製程化學品之本質危害進行探討後，最後進行製程之危害及可操作性分析(HazOp)，來鑑認製程在設計和操作上之危害。研究結果發現整壓站製程缺失有：(1)未繪製整壓站供氣製程管線儀表圖(P&ID)。(2)電動調壓驅動設備安全控制機制不當。(3)採用易燃易爆之天然氣為儀表用氣體。(4)瓦斯漏氣時無法進行自動緊急關斷作業。(5)過濾系統未設置安全排氣與迫氣措施。(6)備用供氣管未設置過壓自動遮斷裝置。(7)部分整壓站未設置過壓排放系統。(8)部分整壓站內瓦斯漏氣偵測系統與火焰偵測器(IRL)未設置或設置量不足。(9)未進行火災爆炸危險性區域劃分。(10)未設置自動灑水降溫設備(11)部分遠端監測元件設置於遠端監測系統(RTU)內。(12)未設置緊急通風換氣(連動)設施等問題，最後再依據分析結果提供整個供氣製程改善建議。依據風險危害分析結果，對整壓站供氣製程進行安全改善建議與規劃，其中較為重大者為：(1)以空氣取代NG為電動調壓驅動設備儀表用氣體，並將作動原理改為空氣開啟模式(Air to open，AO)。(2) 增設差壓計於各過濾器上，並增設安全排氣/迫氣措施。(3)遠端監測系統(RTU)內禁止設置量測元件。(4)備用供氣管增設過壓自動遮斷裝置，與主管過壓遮斷後自動供氣起動模式設計。(5)增設洩漏、火焰偵測與緊急啟動排氣連動以及自動供氣遮斷連鎖機制等等。本研究成果不但獲得業者之認同外，亦有新設整壓站依此設置之。期望本研究成果亦能作為國內天然氣整壓站之製程安全設計與改善之依據，可提升風險管控與安全防護，並消彌或預防工安事故之發生。

關鍵字

天然氣；整壓站；風險評估

並列摘要

Due to the characteristics of nature gas (NG) is lighter than the air, most of the natural gas stations are set up on the ground to avoid explosion hazard from the accumulation of leakage. To make their outlook more environmental friendly, they are usually covered with horticulture landscaping on the outside. Most of the studies of hazard analysis of natural gas stations were focused on the underground stations. As such, this research would explore the risk of NG stations on the ground by collecting and studying the process safety information (PSI) of NG station, processing a series steps, such as onsite survey, preliminary hazard analysis, and Hazard and Operability (HazOp) analysis and so on, to identify the hazard and to assess the risk of NG stations. Our study shows there are several major shortcomings found from the above ground NG stations which are: 1, P&ID of the gas suppling process of the NG station is not available; 2, emergency shut down mechanism of the electric-pressure control device in gas inlet is not appropriated; 3, natural gas, which is flammable and explosive, is used as instrument gas; 4, auto-shutdown is not functioning during gas leak; 5, there is no gas discharge system in the filtration system; 6, no auto-shutdown device in the backup piping system; 7, the release system for over-pressure is not installed; 8, the number of gas leakage detectors and infrared flame (IRL) detectors are insufficient settings; 9, no fire/explosion isolation zoning in place; 10, no sprinkler system installed; 11, some remote-sensing devices are installed in the RTU (Remote Telemetry Unit); 12, no emergency ventilation with interlinkage. Suggestions for improvement has been compiled based on the above analysis results. Originated from the above-mentioned risk analysis results, the items to improve for safety enhancement with priority are suggested: 1, to employ the air to replace NG for the gas used as instrument gas and the mode of operation set on the Air to open (AO) ; 2, to have the differential pressure gauge installed on the filtration system, along with having the gas discharge/ventilation measures added; 3, to remove the detection component especially the pressure transmitter in the RTU; 4, to have the auto-shutdown for over pressure in the backup piping, and to link with the auto-shutdown in the main pipe lines; 5, to add emergency discharge/ventilation measures for leaking, fire (flame), and to interlink with auto-startup and auto-shutdown system. Results of this study has been highly recognized by industries and has been accepted for new station construction. We are looking forward to having these research outputs incorporated in the safety design guideline of the NG station to further upgrade its safety protection and risk management so that the potential risk of the NG station can be further reduced and to prevent accident from happening.