Pavel Spirov

3D Model of extraction of oil from north sea fields by supercritical carbon dioxide

The extraction of North Sea oil from the oil saturated chalk samples by supercritical carbon dioxide was investigated to determine the pressure value, at which the highest amount of oil can be extracted. The pressure of extraction was gradually increased at every next test to check out how the extraction of lighter hydrocarbon fractions at lower pressure affect the oil recovery rate at higher pressure. The first serial test was conducted with three core chalk samples of equal size and each of a weight of 9 g. The samples were naturally saturated with oil at three values of temperature of 50 o , 60 o and 70C. For comparison, the second serial test was conducted with three pure chalk samples of equal size and weight of 26 g saturated with the North Sea oil under vacuum in the laboratory at the same values of temperature. The results of experiments were represented as the surfaces in the coordinates of (Pressure, Amount of extracted oil, Temperature). 3D models revealed that the deviations in the graphs are not occasional. They form wavy surfaces where the folds of waves correspond to hydrocarbon fraction of certain compositions. The highest amounts of oil at all three temperature values in both tests were extracted at 18 MPa in average, where the graphs formed peaks, but the oil was very light, which means that the heavier hydrocarbon fractions were not extracted at such pressure value.

Removal of Grease from Wind Turbine Bearings by Supercritical Carbon Dioxide

This work aims to test the ability of liquid carbon dioxide to remove grease from bearings in wind turbines. Currently, the removal of grease from wind turbines offshore in the North Sea is done by dismantling the bearing covers and scraping off the grease. This procedure is long, labour intensive and raises maintenance cost. Another issue is the environmental policy, the approval for newly introduced chemicals for flushing purposes are procedurally long. If the problems with grease removal could be solved in a different way other than manual removal or using chemicals, it will open many new market opportunities and would carved out a niche for the wind turbine maintenance industry. The solution of flushing grease could lower cost, time and reduce environmental impact by applying Supercritical Carbon Dioxide. The oil based grease SKF LGWM 1 was designed to handle extreme pressure and low temperature conditions. The grease covered the main bearing for 4 - 5 y in a wind turbine at Horns Rev 1 Offshore Wind Farm in the North Sea, 14 km from the west coast of Denmark. The series of experiments focused on higher pressures and temperatures as well as the use of some co-solvents. The highest recovery by pure carbon dioxide is 26 % and was achieved at 60 MPa and 80 ˚C while the addition of Kirasol-318SC improved the recovery by 8 % at the same conditions. Outgassing losses increase with the addition of kirasol. The low recoveries and high pressures obtained by the experiment do not provide an applicable method for grease removal; however it can be implemented for the removal of the contaminants from grease wastes.

The bitumen extraction from Nigerian tar sand using dense carbon dioxide

The need for alternative sources of energy has become even more acute in light of the recognition of the dwindling conventional world oil reserves. The interest in exploring other avenues of complimenting and/or eventually replacing this resource is growing quite rapidly. A ready alternative to conventional crude oil is oil sands which are abundant and vastly unexplored. The huge deposits of tar sand found in SouthWestern Nigeria remain untapped due to concerns about the environmental impact. The consequences of the methods in processing tar sand, ranging from water pollution to emission of greenhouse gases, especially in Canada bring in to sharp focus the urgent need for an alternative means of extracting oil from tar sand. A more effective and less environmentally damaging procedure could be the break through needed to open a new chapter in the exploitation of oil sands. The alternative recovery procedure is supercritical carbon dioxide extraction. Recent supercritical extractions use high temperatures and pressures. The upgrade in this research involves using high pressures and lower temperatures which saves energy and improves the process. The experimental study of the bitumen extraction from Nigerian tar sand by dense CO2 was carried out by high pressure extractor. The samples of tar sand were first heated in an oven at 120 °C to melt. A 50 g sample of melted tar sand with addition of 3 g of ethanol was placed into an extractor and heated to 80 °C to initiate the experiment. Carbon dioxide was injected in to the extractor to create 50 MPa of pressure in static mode for 20 min after which the extract was collected. In the presence of ethanol, the extract had a lighter colour than the usual black. Nigerian tar sand is known to be composed of 84 % sand, 17 % bitumen, 4 % water and 2 % mineral clay. Using this data, an extract of 19.47 % was calculated which makes the recovery achieved very encouraging. The experiment shows that recovery of bitumen from tar sand is possible under relatively low temperatures and can be possibly economically profitable.