De-Bottlenecking of Existing Flare System for Facility Up-Gradation using Dynamic Simulation Approach - Case Study

In today's oil prices scenario, industry's focus is shifting towards Brownfield projects having low CAPEX utilizing existing Oil & Gas assets. Towards this objective, de-bottlenecking of existing flare system becomes inevitable for facilities up-gradation. The spare capacity of existing flare is utilized to accommodate additional relief loads from new facility, thus avoiding installation of new flare. Dynamic simulation approach provides significant advantages over conventional approach in terms of realistic estimation of flare capacity and optimal use of existing plant assets. The conventional steady state approach assumptions provide conservative relief loads considering sum of instantaneous peak flows of relieving devices irrespective of their opening time. Flare operations are inherently dynamic in nature and dynamic simulations provide more realistic relief loads and presents optimal approach to de-bottlenecking of existing flare system. Latest API approach to determine relief rate based on Fire Response Analysis using vessel rupture acceptance criteria also provides additional benefits in terms of relief load optimization as compared to conventional API approach to reduce the system pressure to 50% or 100 Psig in 15 minutes. Dynamic approach also accounts for the packing effect in flare network, system operating pressure at which blow down will initiate and sequential opening of blow down valves for each isolatable section. Thus, dynamic approach provides better understanding of the dynamic behavior during blow down scenario. The flare system of offshore gas processing platform was originally designed based on steady state approach, commonly used being a conservative design which is more appropriate for green-field projects. In this approach, the total flare design load is established by adding all individual loads; assuming that peak flow from all sources will occur at the same time resulting in overdesign of flare system. A dynamic simulation model was developed to analyze the behavior of flare system during emergency relief scenario incorporating the actual volumes of Flare KOD, sub/main flare header and actual opening time of blowdown valves. The dynamic approach accounts for the packing phenomena in the overall flare system network which significantly optimizes the design of flare system and associated equipment. The results of dynamic approach are compared with conservative conventional approach. The study concludes that dynamic approach for flare system design provides more accurate estimation of peak flare load.