Mobile Oil Treaters (MOT) are oil treaters with moderate crude handling capacities of approximately 5000 BOPD. Designing MOTs is challenging due to severe space constraints, as the vessels are mounted on trailers. Here, a complete design for a 5000 BOPD, two-stage desalter featuring a unique partitioned vessel has been presented. The design addresses several key aspects, including salt and material balances over oil and water streams and dehydration efficiencies. Additionally, detailed specifications for the vessel design and electrode configuration are provided. This work aims to establish a systematic calculation procedure for desalters in Mobile Oil Treaters.
Figure 1. Process flow sheet of two stage desalter
Salt present in crude oil, from oil wells, poses significant issues in the downstream refinery process, such as catalyst deactivation and corrosion, which reduce efficiency and increase operational costs. Therefore, a Mobile Oil Treater (MOT) is essential. However, designing an MOT is challenging due to severe space constraints on the trailers, necessitating a compact process flowsheet and design. Incorporating two vessels for the two stage desalter (an important component of the MOT) is often particularly difficult.
- The effective crude oil emulsion residence time (τo) is approximately 38 min for the 5000 BOPD.
- Desalter can be used with a further increase in flowrate up to 7000-8000 BOPD, if the effective oil residence time that reduces to 20 min is sufficient.
- Overall 20 cm clearance is provided to prevent chain formation between the electrode and the vessel.
- Recycling water from the outlet of the second separator stage to mix with the crude oil before entering the first separator stage offers the advantage of reducing the amount of water needed from an external supply.
- Partitioned vessel design removes fabrication and space issues associated with two separate units (vessels) as in conventional two stage desalters.
- This innovation offers several advantages such as simplicity, ease of operation, controllability, and significant process intensification.
An electrode configuration consisting of three layers of rod electrodes has been proposed. The top and bottom electrodes are connected to the same live potential, while the middle electrode is grounded. In practical application, the vessel is also grounded. The separation between consecutive electrodes is determined by the distance at which typical chains of water droplets form when an electric field is applied, varying with the strength of the electric field. These electrodes are designed in an "antennae kind" manner, comprising a central long rod with smaller rods welded parallel to it.
The process and design parameters along with the material and salt balance have been identified and explained.
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This invention can be used for the efficient treatment of crude oil recovered from oil wells in both off shore and on shore oil fields.
Oil industry
202121030131
500497