Tadashi Sano(1), Hisashi Isogami(2), Akira Mochizuki(2) and Norihide Saho(1)
(1)Mechanical Engineering Research Laboratory, Hitachi, Ltd., Japan
(2)Hitachi Plant Technologies, Ltd., Japan
In a process of extracting bitumen from oil sand, a large amount of sewage water is discharged since a large amount of hot water is added to the oil sand to reduce viscosity. Also, at various conventional oil production sites, a large amount of sewage water is produced along with crude oil since water infusion is required in the oil production process.
That sewage water includes silt, clay (SS: suspended solids), and oil emulsion. However, the sewage is currently being directly discarded without retrieving oil. Therefore we are developing a system that separates SS, oil and clarified water from sewage to reuse the water and reduce the environmental load. Our system employs a technique for coagulation and magnetic separation. This technique is enhanced from coagulation sedimentation used in water treatment plants. In this technique, first, a flocculating agent and magnetic powder are mixed into sewage and stirred. Moments later, flocs of impurities and magnetic powder form. The flocs are then removed from the sewage by a magnet, and clarified water and sludge are produced.
The amount of magnetic powder used in this system increases in proportion to the amount of sewage being treated. As there is a large amount of target sewage, the large amount of magnetic powder is drained with the sewage in the case the magnetic powder is not recoverable. Therefore, retrieving the magnetic powder from sludge is important.
In this study, we investigated the effectiveness of hydrothermal treatment on decomposing sludge that contains magnetic powder. There is a fear that when the treatment temperature increases, not only the flocculating agent but also the magnetic powder changes due to a chemical reaction. Therefore, we examined the decomposition temperature of the flocculating agent and the phase-change temperature of the magnetic powder and optimized the magnetic powder recycling system.