Consequence Analysis of LNG Leaks During Offloading Operations: Effects of Substrate Types, Atmospheric Conditions, and Basic Process Control System Intervention

Abstract

With the increasing demands for liquefied natural gas (LNG), more and more LNG terminals are being constructed, and the risk of leakage during LNG off-loading processes has been given increasing amounts of attention. In the case of leakage accident during unloading, the control system is still running when the emergency stop condition is not reached. The adjustment of the control system to unloading parameters will affect the size of the leakage amount. However, the consequences of hazardous material leakage accidents predicted by correlation models depend on the amount of leakage. For precisely calculating the leakage amount and analyzing the leakage consequence, an HYSYS model and a flame acceleration simulator (FLACS) model were presented. This paper consists of two main parts: 1) an HYSYS model to calculate the spill flow rate according to various operating conditions that are with and without basic process control system (BPCS) intervention and 2) a FLACS model that estimates the consequences of vapor explosions and pool fires. This paper presents the conventional estimation method and compares it with a new method that estimates the risk according to spill flow rate, meteorological conditions, and substrate type (solid or grated) on pool spreading and vapor cloud dispersion. Using six scenarios, simulations are used to demonstrate that the HYSYS-FLACS model calculates the equivalent stoichiometric clouds (Q9) and pooling areas as being much larger than those calculated by the conventional model. During an emergency, the HYSYS-FLACS model can be used to estimate the consequences of an unplanned LNG release.