Emulsion breakers screening (8% wash water)
Emulsion breakers screening (5% wash water)
100
100
Embreak 2W157i 5 ppm Embreak 2W197i 9 ppm + Embreak 2163 3.5 ppm Embreak 2W157i 9 ppm
Embreak 2W157i 5 ppm Embreak 2W197i 9 ppm + Embreak 2163 3.5 ppm Embreak 2W157i 9 ppm
60 70 90 80
60 70 90 80
50
50
30 40
30 40
20
20
0 10
0 10
BLANK
Embreak 2W157i
BLANK
Embreak 2W157i
Figure 3 Emulsion stability test study using portable electric desalter
(PED) to validate process operating conditions and opti- mise chemical dosages for the emulsion breaker and solids wetting agents. The impacts of wash water quality, pH, and chlorides were also assessed. Additionally, desalter emul- sion layer samples were analysed when there was growth in the desalter emulsion layer. The brief test results are summarised in Table 1 . Crude samples were subjected to compatibility and foul- ing assessments using field-proven technologies, such as the proprietary CrudePlus tools (see Figure 2 ). The emulsification tendency of the crude was evaluated in the PED. The crude was confirmed to have high emulsion potential based on poor water separation with no chemi- cal treatment. With the right emulsion breaker dosage, the emulsion broke down, and water separation was observed with treatments using solids wetting agents. These results were used for desalter optimisation, as shown in Figure 3 . Desalter temperature Desalter temperature = f {crude oil viscosity and density, water solubility in the crude} To achieve maximum desalting efficacy, a widely followed approach is to increase the desalter temperature, which can enhance salt removal efficiency. However, this method typ - ically adopted and pushed the desalter’s maximum oper- ating temperature limit (typically 155°C) or the limit based on the transformer bushing design temperature and some- times corrosion risk limits. While higher temperatures can reduce crude oil viscosity and aid water separation, beyond certain temperature increases, water yield diminishes the returns in separation efficiency. Hence, increasing to the maximum desalter temperature is not a cure-all and comes with limitations and risks. Temperature optimisation often starts based on the rec- ommended operating viscosity of the desalter. Even though there are no well-defined design limits for desalter operat - ing viscosity, the desalter is targeted to operate at a viscos- ity <2 cSt based on best practices guidelines for effective desalting. Hence, with the analysis of crude blend viscosity and API, the temperature required to achieve the desired operating viscosity can be estimated from the ASTM
standard viscosity temperature charts for liquid petroleum products (D341 Chart VII). It is important to remember that emulsion viscosity increases exponentially with lower temperatures, particu- larly in oil-water emulsions with varying water-to-oil ratios, as referenced in emulsion journals. Typically, emulsion vis- cosity >100 centipoise will lead to a stable emulsion layer in the desalter. Increasing the emulsion breaker dosage can help resolve short-term issues. However, with intense sol- ids and destabilised asphaltenes stabilisation conditions, increasing temperature will be the best approach for long- term sustainable operations. Hence, without temperature optimisation based on crude viscosity, optimisation of other parameters will not help achieve consistent KPIs. Another limitation of high desalter temperature operation will be an increase in water solubility in the desalted crude oil. To retain the BS&W <0.3 vol% in the desalted crude and keep the viscosity in control, the desired desalter oper- ating temperature target was >138-145°C, where Figure 4 shows the results achieved after temperature optimisation. Predominantly, refineries often report total BS&W <0.05 vol% in desalted crude, even at high desalting tempera- tures. The low BS&W is subject to debate based on the fact that 60% is due to sampling errors (such as hot sampling of desalted crude without proper cooling), 30% is due to the lack of water solubility at the desalter operating tempera- ture, and 10% is due to other analytical factors. Therefore, it is important to validate the BS&W in desalted crude with the water yield in the overhead based on different sources rather than solely relying on BS&W analytical results, as shown in the following example: BS&W in desalted crude = Water yield in CDU overhead boot – CDU column stripping steam – CDU side cuts steam – Overhead wash water before coolers . Mix valve DP Mix valve ΔP = f {crude characteristics, temperature, wash water, electric grid, interface level} The function of the mix valve extends beyond simply mix- ing crude oil and water. It is designed to control the water population, droplet size, and distribution within the crude
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PTQ Q1 2025
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