High Pressure Oxy-fired (HiPrOx) Direct Contact Steam Generation (DCSG) for Steam Assisted Gravity Drainage (SAGD) Application (2013)

Production in Canada’s oil sands has been increasing, with a projected rate of 4.5 million barrels per day by 2025. Two production techniques are currently used, mining and in-situ, with the latter projected to constitute ~57% of all production by that time. Although in-situ extraction methods such as Steam Assisted Gravity Drainage (SAGD) are less invasive than mining, they result in more greenhouse gas (GHG) emissions per barrel and require large amounts of water that must be treated and recycled with a make-up water requirement of about 10%. CanmetENERGY is developing a steam generation technology called the High Pressure Oxy-fired Direct Contact Steam Generator (HiPrOx/DCSG, or DCSG for short) that will reduce these water requirements and sequester GHGs. This study evaluates the technical feasibility of this technology using process simulations, bench-scale testing, and pilot-scale testing. At first, a method in which to integrate the DCSG into the SAGD process was presented and process modeling of expected system performance was undertaken. The process simulations indicated that DCSG decreased the energy intensity of SAGD by up to 7.6% compared to the base SAGD case without carbon capture and storage (CCS), and up to 12.0% compared to the base SAGD case with CCS. Bench-scale testing was then performed using a pressurized thermogravimetric analyzer (PTGA) in order to investigate the effects of increased pressure and high moisture environments on a Canadian lignite coal char’s reactivity. It was found that under reaction kinetic-controlled conditions at atmospheric pressure, the increased addition of steam led to a reduction in burning time. The findings may have resulted from the lower heat capacity and higher thermal conductivity of steam compared to CO2. At increased pressures, CO2 inhibited burnout due to its higher heat capacity, lower thermal conductivity, and its effect on C(O) concentrations on the particle surface. When steam was added, the inhibiting effects of CO2 were counteracted, resulting in burnout rates similar to pressurized O2/N2 environments. These preliminary results suggested that the technology was feasible at a bench-scale level. Conflicting literature between bench-scale and pilot-scale studies indicated that pilot-scale testing would be advantageous as a next step. At the pilot-scale, testing was performed using n-butanol, graphite slurry, and n-butanol/graphite slurry mixtures covering lower and upper ends in fuel reactivity. It was found that stable combustion was attainable, with high conversion efficiencies in all cases. With the n-butanol, it was possible to achieve low excess oxygen requirements, which minimizes corrosion issues and reduce energy requirements associated with oxygen generation. With graphite slurry, it was found that it was possible to sustain combustion in these high moisture environments and that high conversion was achieved as indicated by the undetectable levels of carbonaceous materials observed in downstream equipment. Overall, these studies indicate that DCSG is technically feasible from the perspectives of energy and combustion efficiencies as well as from a steam generation point of view. Future work includes the investigation of possible corrosion associated with the product gas, the effect of CO2 on bitumen production, the nature of the mineral melt formed by the deposition of the dissolved and suspended solids from the water in the combustor, and possible scaling issues in the steam generator and piping associated with mineral deposits from the dissolved and suspended solids in the produced water is recommended.