Cargo Oil Heating Requirements for an FSO Vessel Conversion

Abstract

Highly viscous crude oil stored in a floating-storage-and-offloading (FSO) vessel can provoke cargo pumping and remain-on-board (ROB) problems. Cargo oil heating in the vessel to reduce the viscosity and minimize the problems is studied in this paper as well as heating requirements. An operating scenario is introduced for a vessel of 300 kdwt with assumed data. Heat dissipation from warm cargo to ambient, heat addition to incoming cold cargo, and heat depletion during cargo offloading are analyzed for the vessel. A simplified but robust heat loss analysis for the vessel is presented. Using the readily available product crude as the boiler fuel to heat cargo is a logical decision. Fuel consumption is estimated for the vessel. Boiler loads for heating steam generation and heating devices are discussed. The cargo offloading configurations between the vessel and shuttle tanker are investigated for heated and unheated cargo to determine its deliverability. The configuration dictates the length of offloading hoses from the vessel to the tanker. High pressure losses within long hoses may prevent unheated cargo from being delivered at the design rate to the tanker. Alternatives to cargo heating are postulated. Addition of heating coils to an ultra-large crude carrier (ULCC) built in the 1970's or 1980's is considered during the vessel conversion. The cost estimates of addition and conversion for cargo heating are assessed. The transportational considerations are discussed. Conclusions and recommendations are presented.