安全釋壓閥定徑設計規範比較研究

Comparative Study of Regulation on the Sizing of Safety Relief Valves

傳統上，安全釋壓閥之標準（包括由Bernoulli 方程式所推導之定徑公式）可由相關規章與標準獲得，例如：ASME （American Society of Mechanical Engineers）、API（American Petroleum Institute） 與BS （British Standard） 等。但其中或有些許差異，甚至相左之情況。本研究欲藉由各規章與標準之定徑方程式，計算同一事故條件與系統下所需設置之安全釋壓閥口徑。經比較發現：各國於制定標準規章時，主要之學理依據係源自Bernoulli 方程式，而此最大缺點為當釋壓行為發生時，便無法估計真正所需的噴出量；而且只考慮定點之數值，無法獲得釋壓過程的動態行為。因之，以目前現有之安全釋壓閥相關標準規章而言，仍不適用於反應與兩相行為發生時之安全釋壓閥定徑。建議必須加上對流體之動態過程、化學物質之熱／動力學性質、質量均衡及能量均衡作探討，才能針對此現象作合理的定徑計算。

In convention, the related Codes and Standards for safety relief valve (SRV), including sizing equations derived from Bernoulli equation, can be obtained from various organizations, such as ASME (American Society of Mechanical Engineers), API (American Petroleum Institute), BS (British Standard) and so on. There are, however, certain discrepancies or even contradiction among Codes and Standards. The purpose of this study is to use various sizing equations from Codes and Standards to compute the required SRV, under the same scenario and system. After comparing differences among Codes and Standards, it is found that acturalrequired flow can’t be estimated for such a dynamic system while venting. The so-called onepoint sizing equation could not currently calculate such a dynamic behavior for a relieving process. Therefore, the current Codes and Standards are not suitable on emergency relief sizing for reaction systems. It is recommended that, while sizing SRV for a dynamic system, two-phase flow behavior, thermodynamic/dynaimc properties of chemical compounds, mass/energy balanced should be included so that an adequate & duly vent size can be obtained.