Reducing Emissions From Oil & Gas Facilities By Use Of Field Proven VOC Tecnology

Abstract

Abstract The focus has been to reduce or remove the need for flaring, but very little attention is given to another major cause of greenhouse emission; the venting of pure hydrocarbons from Oil & Gas Facilities especially from FPSO, FSO and trading tankers. Floating Production Storage and Offloading (FPSO) and Floating Storage and Offloading (FSO) units commonly use inert gas as a blanket gas of the crude oil during offloading of the storage tanks. The inert gas is generated by burning fuel oil or diesel and consists mainly of CO2 and N2 while CO and NOx are side products. During offloading of oil, the displaced volume of liquid is replaced by the generated inert gas to avoid ingress of air (Oxygen) and to keep a slight overpressure inside the storage tanks. When producing or transferring the crude oil, the oil displaces this gas, which is normally vented, resulting in a direct release of hydrocarbon gas to the atmosphere. During these operations, the inert gas is in contact with crude oil. Due to the difference in composition between the gas and the liquid phase, hydrocarbons flash into the inert gas atmosphere. The result is a gas mixture containing up to 80% hydrocarbon gases (methane and heavier components) at the end of a loading cycle. This mixture made of VOC, CO2 and N2 is normally vented directly into the atmosphere. The main component of the VOC is methane, which is a greenhouse gas with Global Warming Potential (GWP) 20 times higher than CO2. Routine flaring releases CO2, NOx and CO, which are precursors of the ground-level ozone. The ozone at the higher altitude of the Earth's atmosphere (Stratosphere) creates a layer which absorbs the ultraviolet radiations. However, the so-called ground-level ozone (Troposphere area) is toxic and dangerous for health and environment. Routine flaring and venting form personnel health hazard in addition to cause gas alarm trips with likelihood of subsequent production upsets/shutdowns. The technology to recovery these emissions has been in use since 1994 on the Norwegian continental shelf. It is also used on shuttle tankers and onshore plants. Recovery of VOC emissions can easily be combined with the recovery of routine Flaring Gas, re-routed into the process and utilized further. The technology has contributed to substantial reductions of VOC emissions on the Norwegian continental shelf over the last 20 years. Today, an increasing number of oil majors and governments require introduction of both VOC and Flare Gas Recovery, recognizing the major importance of emission reductions both from an environmental and from an economic point of view.