This is an excerpt from Canada’s Oil Sands Innovation Alliance (COSIA) newsletter. The full-length version can be found on COSIA’s website.
Canadian Natural Resources Limited, along with COSIA Joint Industry Project participants Imperial, Shell Canada, Suncor Energy, Syncrude Canada and Teck are working with SRC to provide practical insight on operating and transporting thickened tailings slurries. Paterson and Cooke, global specialists on slurry handling and transportation will also be participating in the project as a contributor and an advisor. The research will be conducted by SRC at their Pipe Flow Technology Centre™.
Developing a reliable model for laminar operation
In order to extract bitumen from mined oil sands, it is mixed with warm water. Once the bitumen has been removed, a mixture of water, sand, silt, clay and residual bitumen is left over. This mixture is referred to as tailings. The tailings mixture is stored in tailings ponds where the majority of the solids settle to the bottom and the water is recycled through the bitumen extraction process.
The portion of tailings that does not quickly settle forms a layer in the middle of the pond. This mixture, called fluid fine tailings (FFT) can take decades to form a solid, if left on its own. The members of COSIA’s Tailings Environmental Priority Area (EPA) have developed a suite of technologies to accelerate the pace at which water is removed from FFT, in order to reduce the foot print of tailings ponds and accelerate the pace of reclamation. Tailings thickeners are being used by a number of operators to reduce FFT and speed reclamation.
Thickened tailings have a consistency of thick mud. Due to the viscous nature of the material, relatively high velocities are required to achieve turbulent flow. Operating slurry pipelines at high velocities requires significant energy and the pipelines are subject to accelerated wear. Consequently there is significant interest in operating slurry pipelines in laminar flow due to potential energy and wear related cost savings.
Technology and Innovation
Researching how slurry pipelines behave while operating in laminar flow will help improve the understanding of laminar flow and also lay the foundation for developing a reliable model for laminar operation of slurry pipelines that could be used to design pipelines that can effectively transport thickened tailings. This tool would improve pipeline design and operation, making them more energy efficient, more reliable and reduce costs.
“Currently there is no proven reliable model available to determine the conditions required to successfully operate large diameter slurry pipelines in laminar flow,” says Aref Najafi, Canadian Natural’s Continuous Improvement Engineer. “This could cause sand to settle in the pipeline, leading to blockages.”
In order to develop a more reliable pipeline design method, COSIA members need to have a thorough understanding of the mechanisms which allow for coarse particle transport in laminar flows.
"The SRC Pipe Flow Model which was developed over decades of research and recently improved through a multi-client project, is focused on the transport of slurries in the turbulent flow regime," says Lesley McGilp, Manager of SRC's PFTC. "This new study will contribute to the development of a model that oil sands operators can apply to systems involving laminar flows, including the transport of thickened tailings."
In the upcoming study, an in-depth matrix of pipe loop tests will be conducted with concentrated model slurries over a broad range of conditions comparable to oil sands thickened tailings operations.
- 2014 Laminar Flow research begins at the SRC’s Pipe Flow Technology Centre™
- 2015 Canadian Natural’s Thickened Tailings facilities will be operational in Q3
- 2016 Laminar Flow Experimental research complete
- 2017 Results will be used to develop a laminar model for slurry design
“This project is an ambitious undertaking,” says Aref. “Historical work on laminar flow is still limited and the end result may be that further work is required to complete the model development.”
But he thinks it’s worth it. No model of this kind currently exists, but once developed; it will be used alongside the existing SRC Pipe Flow Model, to increase the efficiency of tailings management operations by increasing the energy efficiency of thickened tailings transport. Ultimately, these improvements will contribute to the long-term aim of reducing the size of tailings ponds. The model will also be applicable to other industries transporting thick slurries via pipeline.
“The costs of this project have been divided between seven participants so costs and risks are mitigated while benefits to each participant are realized,” says Jonathan Matthews, COSIA Tailings EPA Director. “Sharing project costs and pooling resources and expertise provides a platform for innovative approaches and ideas to grow with minimum cost, maximum speed and efficiency.”
For more information about SRC's Pipe Flow Technology Centre™, check out these resources: