PED study with 8% wash water @ 3 KVA
PED study with 5% wash water @ 3 KVA
8.0
5.0
Blank Embreak 2W157i (9) Embreak 2W157i (9) + Embreak 2163 (3.5)
Blank Embreak 2W157i ( 3) Embreak 2W157i (9) Embreak 2W157i (9) + Embreak 2163 (3.5)
7.0
4.0
6.0
5.0
3.0
4.0
2.0
3.0
2.0
1.0
1.0
0.0
0.0
0
1
2
4
6
8
16
32
0
1
2
4
6
8
16
32
Residence time (minutes)
Residence time (minutes)
Figure 8 PED study with emulsion breaker, wetting agent, and wash water per cent change
emulsion layer growth. Mostly, split dosage of demulsifi - ers into the battery limit and at the mix valve is of prime importance for desalter optimisation. Figure 8 explains how the emulsion separation study helps to understand the emulsion’s stability without chem- icals. The emulsion stability reduces with chemical optimi- sation, with an increase in 5-8% wash water. An increase in dosage with solids wetter helped resolve the emulsion 100% within the given residence time of the desalter. Electric grid Electric grid = f {crude conductivity, brine conductivity, interface level, water solubility in crude, temperature} The electric grid is responsible for inducing dipole moments in water droplets dispersed in the crude oil, promoting the coalescence of small water droplets into larger droplets, which can then settle out of the oil due to gravity. The elec- tric grid acts as the heart of electrostatic desalter operation. High voltage is necessary to create a strong electrostatic field. The voltage should be maintained at the design spec - ifications to ensure effective coalescence, and monitoring amperage is equally important. Excessive amperage can indicate issues such as short-circuiting, which can damage the grid and reduce its effectiveness. Also, high operating temperatures can affect the perfor- mance of the electric grid and the dielectric properties of the crude oil. Hence, optimal temperature is crucial to ensure the grid operates within safe limits. In the desalter operation, the emulsion produced by the mix valve is distributed via the crude distributor between the electric grids. Between 70% and 90% of primary water coalescence occurs within a few seconds under the applied electric field. Secondary coalescence occurs beyond the electric grid, where larger coalesced water droplets continue to settle due to gravity, contributing significantly to overall water removal. Hence, emulsion growth control, specifically interface monitoring, is critical to control desalter upsets. The applied electric field for light to medium API crudes will be ~1-3 KVA/m². For the desalter in the Southeast
Asian refinery, the applied power from the transformer is 150 KVA with a designed applied voltage of 400 volts and a frequency of 50 Hz. The surface area under the grid is 60 m². Hence, the applied electric field will be 2.5 KVA/m². Since the applied electric field is within the recommended range of best practice windows, with brine conductivity (water droplets in the crude) in the range of 2,000-5,000 micro Siemens (discussed in detail in the wash water sec - tion), good desalting efficacy could be achieved for light to medium API crude blends operation periods without many challenges. Based on monitoring, the desalter could oper- ate at the recommended voltage of 400-380 volts and an amperage of 80-100 amps. For more than two years, the desalter targeted perfor- mance has been consistently achieved and sustained, with >90% performance indicators. Specifically, the desalted crude salt has consistently remained <0.5 PTB, the over - head chloride levels have been limited to <30 ppm without caustic dosage in the desalted crude, and controlled sodium levels in the atmospheric residue have been controlled to <1 ppm to prevent downstream ARHDT catalyst poisoning. To recap briefly, following a systematic optimisation strategy is crucial. More importantly, focusing on day-to- day monitoring, validating the desalter performance during each blend change and crude tank farm change operation, and slop oil management will lead to proactive optimisation towards operational and chemical factors. Also, do not for- get to conduct periodic data analysis with basic statistical or desalter benchmarking tools, which will be key to identi- fying the influencing parameters. Conclusion The cost of poor desalting is significantly high. From the desalter survey, it is evident that crude blend quality varia- tions drive the day-to-day desalter key parameter optimisa- tion using basic data analysis tools. The brief overview and key performance factor optimisation strategies followed in this real-time refinery case study exemplify the critical role of strategic parameter management in refining operations.
38
PTQ Q1 2025
www.digitalrefining.com
Powered by FlippingBook