Silica removal from SAGD boiler blowdown by electrocoagulation

点击翻译按钮获取中文摘要

Heavy oil production of steam assisted gravity drainage (SAGD) is the largest in-situ production process in theCanadian oil-sands. This production process generates large quantities of produced water, typically 3 to 4 timesthe volume of oil, which must be treated and recycled to ensure that the process is viable and to meet regulatoryrequirements. The produced water must be treated before being fed to the steam generator (boiler) for injectioninto the reservoir as steam. To avoid fouling of the boilers, the water is usually treated by a process of warm orhot lime softening to remove hardness and silica which can scale the boilers. This process is high cost andgenerates significant volumes of sludge. An alternative process, so-called zero lime softening is beingdeveloped by the industry partner, Eco-Tech, which is lower cost and more environmentally freindly.Eco-Tech have shown that if the produced water is treated to remove hardness, the silica can be at a relativelyhigh concentration (>200 mg/L), without causing significant scaling of the boilers. However, the concentratestream from the boilers contains greater than 1200 mg/L silica, and must be treated prior to recycle or disposal.Conventional chemical processes (acidification) lead to a silica gel sludge which is difficult o separate from thewater. Electrocoagulation (EC), has been identified as a potential treatment process for the blowdownconcentrate. In previous work, we have been found that EC can effectively remove silica from SAGD producedwater. This project will investigate EC for the treatment of blowdown concentrate generated by the zero-limesoftening process. The treatment performance and filterability of the sludge will be investigated as a function ofthe operating conditions and design of the EC system.