Fugitive emissions are accidental, diffusive or unproductive emissions that can come from a number of sources including leaking pipework, valves, flanges and seals.
In 2020, Tullow worked to mature its understanding of fugitive emissions from leaks, seeps and weeps from piping and valves from weekly inspections using Forward Looking InfraRed (FLIR) cameras and keeping our Leaks and Weeps register up to date with associated work orders for appropriate corrective maintenance on our floating production storage and offloading vessels (FPSOs).
Fugitive emissions from Piping Leaks
Tullow over the years has been using FLIR cameras to detect and fix fugitive emissions leaks from piping, flanges and valves in line with the Best Available Techniques (BAT). The methods used to fix (reduce/eliminate) the leak include the use of wraps, proper torquing of nuts/bolts on flanges, gasket change or seal changeout as dictated by the corrective work order specified to be executed. Tullow also intend to procure instruments to measure the concentration of components and gas composition in the immediate vicinity of the leak and to then apply the appropriate emission factors to each component within each leak found (depending on the FLIR’s camera detection limit) to estimate the total leak of green house gas (GHG) emissions.
“Volatile organic compounds from fugitive emissions could have costly consequences on health and safety of personal on board and operation safety in addition to their contribution to GHG emissions. These are the main drivers behind our effort in taking control of our fugitive emissions on the FPSOs” – Bismark Osei Bimpong, Senior Facilities Engineer.
GHG Emissions from Cargo Tanks
A significant source of unignited methane release is from emissions in vented gas from the KNK FPSO crude oil storage tanks. This vent gas stream composition consists of a mixture of inert gas and a rich hydrocarbon gas present within the FPSO’s cargo tanks that is continuously being displaced as these tanks are being filled with stabilised crude oil from the FPSO oil production train. Tullow Ghana are evaluating a number of vent gas displacement designs to improve gas dispersion from the vent.
Previously, for GHG emissions calculations, the company assumed that 100 per cent of vent gas was composed of methane. This resulted in an overstatement of GHG from cargo vent source. The vent gas stream is composed of propane, butane, nitrogen and other heavier hydrocarbon gases which have an indirect but uncertain effect on global warming, due to their short lifetimes and the nonlinear chemistry involved in ozone and hydroxyl chemistry. From 2021 onwards vent gas GHG emissions will be calculated based on methane content. Tullow will also be recalculating (and restating) its GHG emissions from the period 2015-2020.