Managing Greenhouse gases emission through minimizing the usage of blanketing gas on storage tanks – The Bonny Oil and Gas Terminal Case Study

摘要

Greenhouse gas emissions are primarily responsible for the greenhouse effect, which occurs when thermal radiation from the earth surface is absorbed by these greenhouse gases and radiated back to the earth surface. The consequence of this phenomenon is a rise in the average earth surface temperature. It is established that the earth’s natural greenhouse effect makes living on earth possible and comfortable for humans but the activities of humans such as burning of fossil fuels(hydrocarbons) over time has intensified the natural greenhouse effect by significantly increasing the atmospheric concentration of carbon dioxide resulting in global warming. Global warming has resulted in widespread melting of snow and ice, sea level rise, increased humidity, and increased heat content of the oceans. The Bonny Oil and Gas terminal receives, dehydrates, stabilizes, stores and exports all crude oil produced in SPDC Eastern operations and the processed crude oil is exported by pipeline to tankers and to the nearby NNPC refinery. In the Terminal, LP fuel gas (composed mainly of methane) is used as blanketing gas and is introduced into storage tanks and vessels to prevent a vacuum from developing when liquid is removed from a tank to maintain the desired blanket pressure and prevent outside air from contaminating the tank or creating a flammable or explosive environment. It also ensures that a constant gas pressure is maintained in the vapour space of a storage tank. Efficient blanketing gas demand would ensure that pressure relief from tanks and vessels which ultimately result in greenhouse gas emissions are minimized. This is implemented through the use of split range control scheme for blanketing gas on fixed roof storage tanks in the Export Terminal. In a split range control scheme, the output of the controller is split and sent to two final control elements (pressure control valves).The splitter is configured to define how each pressure control valve will open. The first valve which allows inflow of blanket gas to the tank opens when the output is of the range 0-45% while the second pressure control valve to the flare opens at an output range of 55%-100%. The deployment of this control scheme of blanketing gas on fixed roof storage tanks in Bonny Terminal has resulted in the lowering of greenhouse gas emissions, combating climate change, process optimization, and significant energy savings.