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Desalter Optimisation

Background

Jorin's client had experienced a period of poor desalter performance where high oil in water concentrations had been recorded leaving the vessel. It was not understood if this was a function of a change in process fluids or a lack of optimisation of operating conditions.

Aim

Jorin were to monitor the desalter's performance under a range of interface levels and ΔP to determine if water quality could be improved without affecting export oil quality.

Results

The site data was primarily collected using Jorin's mobile ViPA technology which is designed and constructed to operate in hazardous environments.

Graphs of oil in water concentrations are shown in Figure 1 and mean oil droplet sizes in Figure 2. The interface level of the desalter was set to 70% with a ΔP of 0.56 Barg across the mixing valve; under these conditions data was recorded for 5 hours. During this period the oil in water concentration fluctuated between 60 and 142 ppm with a corresponding mean oil drop size of 14 microns.

At 13:30 the ΔP was maintained at 0.56 Barg while the interface level was decreased to 50%. For the 3 hours that these conditions were monitored, the oil in water concentration varied from 73 to 118 ppm with a corresponding mean oil drop size of 13 microns. At 16:30 the ΔP was reduced to 0.47 Barg while the interface level remained the same at 50%. At 17:30, the ΔP was then increased to 0.7 Bar. With an interface level of 50% and a ΔP of 0.47 Barg, the mean oil drop size was 12 microns, whereas, when the ΔP was increased to 0.7 Barg, the mean oil drop size reported had reduced to 11 microns.

Figure 1: Oil in water concentrations downstream of the desalter.

Figure 2: Mean oil in water droplet size distribution downstream of the desalter.

Conclusions

Based on the two interface levels tested; 50% & 70%; it was concluded that there was a marginal improvement in water quality when the desalter is operated at an interface level of 50%. Additionally, it was noted that with the ΔP of 0.56 Barg the oil droplet sizes were in a better size range for the downstream oily water separation plant enhancing separability. These results clearly show the benefit of installed ViPA technology for the monitoring and management of a desalter; providing an early warning of process changes that could lead to decreased performance and subsequent effects on downstream process plant.