The ability to recycle byproducts as feedstocks rather than discard them as wastes helps to optimize refining efficiency and presents the potential for substantial environmental and economic benefits. Robust recycling solutions, particularly in the face of diversified crude slates, can help refineries keep pace with shifting production and refining requirements associated with the unconventional energy boom in North America.
While most refinery process designs offer significant latitude in the handling of crude, they can be negatively impacted by the production of oil-bearing secondary materials. Every refinery generates oil-bearing residuals as part of normal operations. Regardless of source or composition, operators must generally take one of two actions: process them into the refining process or dispose of them as costly hazardous wastes, imposing long-term risks and responsibilities on the refinery.
Sustainable solutions that maximize resource recovery within a refinery’s ongoing production processes, while minimizing cost and environmental impact, have become a key value proposition for refinery industry leaders.
Recovery approaches
The most fundamental level of available alternatives involves simple filtration/dewatering. This process can be applied to reduce the stream volume, typically leaving an oily cake (which, if not recycled into the refining process, must be disposed as a hazardous waste) and a water phase, which is transferred to the refinery’s wastewater treatment unit. The efficacy of this approach is largely contingent upon the oil and solids content and total composition of the material stream. Unfortunately, it is often inefficient, operator intensive and susceptible to changes in feed composition.
Moving to the next level, a three-phase, high-speed decanter centrifuge can be used. Indeed, the three-phase decanter is at the heart of most robust oil-bearing material recycling processes. This will generally afford relatively clean oil that is suitable for introduction into the ongoing refinery production processes and water streams that are suitable for transfer to the refinery’s wastewater treatment plant. When conducted with the proper process, this approach will also generate an oil-bearing solids phase conducive to further processing. These solids can be re-blended with oil and/or water to a spec appropriate for coker injection (quench side or fuel side), or transported to a cement kiln for reuse as waste-derived fuel.
The most aggressive approach is to forcibly desorb the volatile phases at a high temperature, recovering all water and oil — and leaving a dry solid phase — after the centrifuge stage. The oil and water phases are then condensed with the oil being returned to the refinery’s ongoing production processes. There’s also potential for the water to be beneficially reused within the refinery’s processes.
Comparison
General end results associated with the recycling of oil-bearing secondary materials can be illustrated by a hypothetical comparison (Table 1), which assumes a refinery produces 1,000 barrels of an oil-bearing material stream (comprised of 5-percent solids, 15-percent oil and 80-percent water) that is recycled, as well as cake that is 40-percent solids, 10-percent oil and 50-percent water. As refiners continue to face financial pressures from the downward trend in oil prices, the technologies and services applied to enhance recovery and improve operational efficiency become increasingly important. Successful partnerships that leverage integrated, holistic solutions are a key to success.
For more information, contact Miranda Schield at miranda.schield@veolia.com or (312) 552-2800.