Controllable variables
Wash water rate
Mix valve dp
Mud wash practices Mud wash design
Temperature
Wash water location
Unit charge rate
Blend practices
Viscosity
Pressure
Vessel size / residence time
Grids
Slop oil injection
Asphaltene precipitation RIX / CPI
Solids TIS / TSS
Solids wetters
Operational
SARA
Chemical injection location
Level controller
Mix valve type
Inlet header
Crude stabili s er
Wash water quality
Brine pH control
Mud wash aids
Mechanical
Fluid quality
Emulsion breakers
Tank pretreatment
Chemical
Figure 2 Desalter performance influencing factors
cost of desalting, as monitoring overall costs and reporting regularly will drive intense optimisation plans. While refin - eries often desire to build large desalter vessels capable of processing all types of crude oil, capital expenditure (Capex) and operational expenditure (Opex) limitations hinder the existence of such universally effective designs. Even large, long-residence desalters with double-stage desalting may fail to meet KPIs due to variability in crude qual- ity, poor control over performance chemical management,
and lack of a holistic optimisation approach. Thus, under- standing the design and operation of desalters is the first step in troubleshooting, followed by analysing data on inter- dependent factors, debottlenecking operational limits if nec- essary, and finally establishing a desired optimisation range for each influencing parameter, which will help work towards achieving the desired performance indicator goals. Desalter performance optimisation For effective electrostatic desalter performance optimisation, it is essential to recap and understand the following steps: Desalter performance influencing factors v Data analysis and troubleshooting discrepancy parameters w Optimisation of key parameters – Southeast Asian refin - ery case study x Desalter performance influencing factors. The four key factors that drive desalter performance are fluid quality, operational parameters, chemicals, and mechanical aspects (see Figure 2 ). These factors govern emulsion formation and water-oil separation phenomena in desalters, with operational and chemical factors being critical and primary control parameters, while mechanical and crude oil fluid quality are independent and fixed variables. From the desalter survey (see Figure 3 ), it is evident that mix valve differential pressure (DP) and demulsifier feed rates are the top variables influencing desalter performance. The survey also identifies common causes of desalter upsets, including crude tank switching, crude quality changes, slop reprocessing, wash water quality, demulsifier and adjunct chemical feed rates, and interface level control, which are the most common and practical control parameters to focus on for any desalter optimisation exercise. Typically, a single-stage desalter achieves 85-90% desalt- ing efficiency and 90-95% dehydration efficiency. A double- stage desalting process can achieve 90-98% desalting efficiency and 95-99.5% dehydration efficiency in the long- term optimisation, with an increasing number of desalting stages increasing desalter performance efficiency. Generally, a desalter achieving less than 1 PTB salt with basic sediment
Common causes of desalter upsets
10% 5% 15% 20% 25% 30% 35%
31%
17% 16%
16%
14% 14%
9%
0%
Parameters in uences desalter performance
30%
26%
10% 5% 15% 20% 25%
20% 20%
12% 12% 11% 11%
9% 9%
0%
Figure 3 Desalter survey
90
PTQ Q4 2024
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