Desalter optimisation strategies: Part I Analysis and optimisation strategies implemented for a two-stage desalter processing light to medium API crude blends at a Southeast Asian refinery
Venkatesan Mani Veolia Water Technologies and Solutions
C rude oil desalting plays a pivotal role in refinery opera - tions by removing salts and impurities that can wreak havoc on downstream equipment through corrosion, fouling, catalyst poisoning, and product quality degradation. Despite significant technological advancements in desalter design, optimising desalter performance remains an intricate challenge due to the complex interplay of multiple factors, including crude oil composition, operational conditions, equipment design, and chemical treatment. This interde- pendence among factors often hinders achieving overall performance goals through isolated optimisation efforts. Insights gained from a Southeast Asian refinery desalter optimisation detail how the interdependence of key param- eters was validated and addressed at each step of the optimisation process, enabling the refinery to consistently achieve and sustain desalter performance indicators, includ- ing desalted crude salt levels below 0.5 pound per thousand barrels (PTB), overhead chloride levels below 30 ppm with- out caustic dosage, and sodium levels in atmospheric resi- due below 1 ppm to prevent downstream catalyst poisoning. Interdependent factors Electrostatic desalter technology gained traction in the oil refining industry during the mid-20th century for oil-water separation processes. Despite significant advancements in desalter design and technology, as well as the introduction of novel demulsifiers and best practice strategies for opti - misation, crude oil desalting remains a formidable challenge even in the 21st century. This complexity stems from the
multitude of interdependent factors, perpetuating the belief that desalter optimisation is more an art than a science. Inconsistencies in crude oil quality and associated impuri- ties impact on refinery units, as captured in NACE Technical Committee Publication 21415-SG,1 , ² coupled with variability in oil field additives during production, often necessitate desalter optimisation even within the same crude supply. Tracking the quality of each crude oil parcel is an intense and often daily challenge for refineries, prompting many to relinquish desalter optimisation responsibilities to local process additive suppli- ers. These suppliers not only provide desalting chemicals but also monitor most other aspects of desalter operations. While unit operators and refinery laboratories still carry out routine analytical tests and adjust desalter operations on a shift or daily basis as needed, major changes are often based on prior testing and recommendations provided by the process additive supplier. While relying on process addi- tive suppliers can make sense, failures in desalter optimisa- tion often stem from selecting suppliers solely based on the lowest-cost chemical supply, without expertise in desalter optimisation, lack of periodic review, narrow focus on key performance indicators (KPIs) with deviation action plans, lack of long-term optimisation goals, and the mindset that a single demulsifier chemistry will work for all crude types, even with operational limits on temperature, residence time, and electric grid. These factors often relegate desalters to the proverbial stepchild of crude unit operations. A poor desalting operation incurs significant expenses (see Figure 1 ). It is crucial for each refinery to benchmark the
Every 20 ptb doubles fouling rate
Corrosion $30-60 for 1 PTB as NaCl
Overhead
HDT, FCCU, RFCCU
Hot preheat train
Desalter
Catalyst poisoning ( C a, Na, Fe, Si, Pb), $15-20 million/year for fresh catalyst make up
CDU
1 bbl of water backs out 6-8 bbl of crude
Reprocessing $3 per bbl
ETP & slop management
Fouling/product quality (Ca, Na, Fe, Si, Pb)
Coker
$1 per bbl of slop oil
Figure 1 Cost of poor desalting
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PTQ Q4 2024
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