PTQ Q3 2025 Issue

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Figure 5 Turbidity reduction

QW emulsion, DSG corrosion and fouling 3 For any QW loop, the usual concerns observed are emul- sion, corrosion, and fouling. Key reasons and effects include: • QW emulsion: This refers to the difficulty separating hydrocarbon and water, which is governed by Stokes’ law. In an ethylene unit, two types of emulsion are commonly observed: oil-in-water and water-in-oil. Factors such as the presence of surfactants and pH control issues contribute to emulsion formation. • Hydrocarbons to process water stripper (PWS): The hydrocarbon/water separation is expected to be removed in the dispersed oil extraction (DOX) unit, which includes filters, coalescers, and oil and water settlers, before the stream enters the PWS and subsequently the DSG. The PWS can only strip the lighter hydrocarbons, and an increase in hydrocarbon loading would require higher steam consumption, leading to a higher fouling tendency at elevated temperatures. Though the fouling here is not as severe as in DSG, it can still take place and reduce stripping efficiency. • DSG fouling: The DSG is responsible for producing high-quality steam used to dilute feedstock before crack- ing. However, if monomers or oligomers bypass the DOX and PWS units, they can deposit in the DSG reboilers, lead- ing to hard fouling and corrosion, including:  Polymerisation of monomers/oligomers at high tempera- tures, forming sticky deposits. v Under-deposit corrosion, where trapped ions beneath the fouling layer create a localised low pH environment. w Presence of dissolved oxygen, which accelerates corrosion by promoting oxidation-reduction reactions on metal surfaces. Strategic priorities Emulsions in quench water are a hidden threat to sustain- able steam cracker operation. In fact, QWT-PWS-DSG is crucial in the ethylene plant due to the following factors:  Energy efficiency and heat recovery: • The quench system recovers huge amounts of heat from cracked gas. • This heat is used to generate dilution steam for the furnace. • Efficient steam generation reduces fuel consumption in boilers, lowering CO₂ emissions. v Water resource management: • Quench water is recycled, but losses happen via blow- down and evaporation.

• Sustainable operations ensure minimum water wastage, with treatment and reuse. • In areas with water scarcity, this is a critical environmental and cost factor. In the drive towards greener and more efficient steam cracker operations, sustainability is no longer optional; it is a strategic priority. While big picture initiatives often get the spotlight, small process inefficiencies, such as the formation of emulsions in quench water, can quietly erode sustainability efforts. These stable mixtures of hydrocar- bons and water directly compromise PWS and DSG per- formance, two units essential to resource recovery and emissions control. This usually results in reduced reliability and increased maintenance owing to: • Increased upstream turbidity from poor emulsion reso- lutions, resulting in fouling of DSG heat exchangers and reboilers. • Factors contributing to the carbon footprint of main- tenance activities (such as materials, energy, and waste disposal). Recommended solution Emulsion breaker selection was a key factor in managing the lower-density wash oil. Lab screening was conducted to identify the most suitable emulsion breaker (EB) that could act quickly. During the screening process, approximately 10 different emulsion breakers were tested at various dos- age ranges to determine their effectiveness in breaking the emulsion efficiently. Key benefits from the changes include: • Turbidity reduction: One of the most notable outcomes of the change in emulsion breaker is the reduction in turbidity levels (see Figure 5 ). • Lesser frequency of filter element replacements: With the significant reduction in turbidity levels, there has been a corresponding decrease in the amount of hydrocarbons entering the QW system. As a result, the filter elements in the DOX unit experience less strain and contamination (see Figure 6 ). This leads to a notable reduction in the frequency of filter element replacements. On average, the run length of these filter elements has increased by approximately 30%, leading to reduced maintenance costs and a more efficient filtration process. • Improved DSG reboiler performance: The EB dosing strategy has also proven beneficial for the DSG reboilers. By improving hydrocarbon control in the upstream, the EB dosing strategy has significantly extended the run length

PTQ Q3 2025