PTQ Q1 2024 Issue

Overcoming wastewater challenges of opportunity crude processing

Refinery wastewater facilities need new practices and solutions for efficient and sustainable operation with heavy opportunity crudes

Shane Lund Veolia Water Technologies & Solutions

T he challenges associated with processing opportu- nity crudes have been well-documented over recent years. Their high content of small, suspended solids, tramp amines, asphaltenes, naphthenic acids, and many other problematic substances combined with high variabil- ity can make these crudes difficult to treat from beginning to end in a refinery. Increased difficulty desalting these crudes can lead to brine effluent heavily contaminated with hydrocarbons sent to the wastewater treatment plant. Even when the desalting operation is working well, the increased loading can overwhelm some wastewater plants, forcing production to be curtailed. When faced with this higher loading, many wastewater assets can become overburdened and more likely to push past the breaking point into upset conditions. Symptoms of these upset conditions can include foaming, poor sludge settling and compaction, internal or external toxicity, reduced nitrification rates, and reduced chemical oxygen demand (COD) removal. Identification and treatment of the symptoms and root causes are important to maintain compliance with increas- ingly tight water discharge limits. This article discusses com- mon wastewater management problems associated with processing opportunity crudes, holistic monitoring strategies to identify potential upsets early, and operation strategies and treatment techniques used to maintain effluent discharge compliance while processing opportunity crudes reliably. Opportunity crude contaminants The blending of tight oils and heavy ‘opportunity’ crude oils is now a common practice for many industry players. This practice certainly benefits operators by sourcing crudes based on availability and price. However, it does present a risk to the performance and reliability of the various pro- cess units within the refinery. The resulting blend sent to the crude unit can exhibit less-than-ideal properties that vary daily, even hourly, making it very hard to maintain the unit’s production quality. Increased use of ‘opportunity’ crudes has been shown to create challenging conditions in wastewater treatment as the crude unit struggles to separate water and oil efficiently. Working upstream by optimising crude blending strategies and desalter operations should certainly be part of a holistic

plan to manage heavy crudes. However, conditions should also be in place downstream to address potential desalter upsets. If a comprehensive plan to prevent and address wastewater systems’ contaminations and upsets is not put into place, there is a real risk that production may need to be curtailed as contaminants in the effluent discharge get too close to allowable limits. Much has been written about the connection between opportunity crudes and wastewater difficulties, such as foaming, poor sludge settling and compaction, internal or external toxicity, reduced nitrification rates, and reduced COD removal. Problematic features associated with the opportunity crudes that have been blamed for the waste- water difficulties include increased quantity of solids that are smaller in size, increased amine loading, more naph- thenic acids, and high variability in the crudes. The use of opportunity crudes in a refinery’s crude diet is expected to lead to a higher potential for desalter upsets due to variability, emulsions, pH, viscosity, stability, and asphaltene precipitation. These contaminations and fluctuations would provoke more frequent primary waste - water treatment problems as the desalter effluent brine undercarries process compounds such as asphaltenes, small, suspended solids and oil, all in variable quantities. In the secondary wastewater system, we expect to see potential problems due to elevated biochemical oxygen demand (BOD) and COD, elevated levels of both long- and short-chain organic acids, more tramp amines, higher sur- factant loads, and inhibitory substances. While it is true that any one of these properties can det- rimentally impact wastewater treatment, a single bad actor is not usually identified, as multiple parameters typically act together during an upset event. These combined properties push refinery wastewater treatment assets ever closer to the edge, and contingency plans cannot contain these con- ditions indefinitely. Each refinery wastewater treatment plant has its own unique set of potential constraints based on its system’s design and level of contingencies. However, the lack of a plan to predict and address upsets takes the system ever closer to the breaking point. Once the breaking point is hit, several things can occur, including foaming of aeration basins and clarifiers, floating solids on clarifiers, poor sludge settling and

PTQ Q1 2024