FPSO 압력배출 및 감압시스템의 동적해석

Abstract

Since the 1950’s, pressure relief and depressurization system has been exercised by the steady-state modeling method as per API standards. However, API standards was based on a few empirical test data available in the 1940’s. The figures produced by the steady-state model was quite different from the real ones mainly because of large design margin given in fear of any failure. It sometimes caused the increase in cost and weight and execution schedule and sometimes project failure, which made HSE group have concerns about the safety and integrity of the systems or plants. Many experienced authors reported the superiority of dynamic modeling to the steady-state model in contribution to the enhancing of the integrity and the reducing of the capital cost. This paper discusses what benefits expected in case of using the dynamic model in assessing the pressure relief and depressurization system of a FPSO installed with a comparison of the two models. For this the HYSYS Dynamic Depressuring Module (depressurization utility tool) and the Flare System Analyzer (Flarenet) were used for analyzing the steady-state model while the gFLARE, developed by PSE (process system entertainment Ltd), for the dynamic model. gFLARE is quite specialized for flare capacity, flare network size and low temperature study as a comprehensive dynamic analysis with fully coupled process and flare system model. A specific FPSO operated in the oil field is selected in order to optimize flare network and evaluate the economic benefits with gFLARE. The HP flare system is the main scope of this paper and defined as the design pressure is larger than 14 barg. It is composed of three sub-headers, main header, KO drum and flare tip. Dynamic analysis showed the design discharge flow rate in the header could be reduced by 10 percent. The size of the warm header is also reduced from 32 inch to 24 inch and the cold wet header from 16” to 10”. The length and sizing of flare stack mainly depending on the maximum flow rate is not discussed herein. It is believed that the dynamic analysis for the pressure relief and depressurization system minimizes the opportunities in oversizing the flare header, flare stack and flare tip. It showed the saving in the capital expenditure by about 23.4 ton, or US$70,000 in value per unit and the improvement in the integrity and safety of the plant.