Abstract
The recovery of bitumen through steam-assisted gravity drainage in Alberta produces about 2.7 m3 of water per one m3 of bitumen, resulting in about 118 million m3 of water per year having high levels of organic compounds. When this water is recycled to the boilers, the organic compounds contribute to fouling and corrosion, thus, the energy companies are interested in finding a cost-effective strategy to remove the organics before recycling the water. In mining operations, approximately 3 m3 of water are produced per one m3 of bitumen, resulting in 148 million m3 of water per year flowing into tailings ponds. While the majority of this water is reused, the organics in water can be metabolized and produce methane, a potent greenhouse gas.
Laboratory studies have shown that activated carbon from forestry residues (aspen wood) could remove the organics, create a carbon sink, reduce emissions from tailings and provide a new market for the residual biomass from the local forestry industry. This study compares the cost, energy requirement, and greenhouse gas (GHG) emissions associated with four scenarios: two scenarios for activated carbon production, pyrolysis and activation of biomass in mobile units in the field or transporting the residual biomass to a central location where it is both pyrolyzed and activated, and two scenarios for using the produced activated carbon for removal of organics from the produced water in either SAGD operations or tailings ponds in mining operations.
Field pyrolysis of biomass for both SAGD and mining operations was calculated to have lower emissions (approximately 75% lower GHG emissions), but higher economic costs (approximately 20% higher cost) compared to the centralized processing. The net emissions of the systems were calculated to be between 0 to 16 kgCO2e/m3. Furthermore, at 75% removal level, the maximum feasible amount for the systems used in this study, the net emissions range between -55 to -76 kgCO2e/m3. Hence, the ultimate GHG emissions range achievable by these systems is 16 to -76 kgCO2e/m3. The sensitivity analysis showed pyrolysis and activation yields as well as removal level are the main parameters that should be the focus of future research in order to reduce energy requirements, emissions, and cost of the entire process.
