FPSO crude oil storage tanks require a blanketing on top of the stored crude and FPSO Cargo Tank operations are characterized (for the purpose of current paper) by the displacement of the tank vapor during the loading cycle by produced oil and, reversibly by the vapor re-filling of the tank volume during the offloading operations.
In cargo oil tanks during offloading operations the tank is "topped-up" with blanketing gas to replace the displaced liquid volume and, during loading cycles the vapor is displaced so that the liquid can occupy the volume. Traditionally, the vapor ullage in the tank is composed of inert gas and, during the loading cycle until the start of the offloading, the gas is in equilibrium with the crude oil, so its composition changes through time due to the vaporization of hydrocarbons. Consequently, its calorific power is not constant so it cannot be reused in the process stream. For this reason, at every loading cycle the vapor phase of the cargo oil tank is vented, contributing to greenhouse gases emissions.
There are several possible methods to decarbonize offshore operations of FPSOs, as shown in Figure 1. Hydrocarbon Blanketing is one of these several alternatives and it allows for the recovery of volatile components otherwise released to atmosphere. As will be demonstrated in the paper, it has a considerable positive environmental impact, reduction in corrosion and safety benefits and is relatively simple to implement ("low hanging fruit").
