Recently customers have been asking about what technologies are used to measure interface levels in a desalter.
How a Desalter works: Raw crude oil contains a lot of salt contaminants and water. If the salts are not removed, then they can cause significant corrosion of downstream refinery equipment due to high operating temperatures. To remove the salts, emulsifying chemicals and additional water are mixed with the oil to wash the salts out of the oil. This emulsified oil water mixture then needs to be separated quickly and efficiently. An electrostatic grid causes the dispersed water droplets and salts to coalesce and drop. This electro-static field operates at maximum efficiency when the water and oil interface is maintained at a level just below the electrostatic grid.
Guided Wave Radar Solution: Emerson does have experience with using guided wave radar on these applications. The vessel is typically entirely filled with liquid with hydrocarbons on top of the water. The important matter is to keep the water out from the grid area, so you need to keep track of the interface between the oil and the water – and thus the 5300 Guided Wave Radar provides a good solution. For optimum performance, they want to keep the water level as close to the grid as possible – without touching the grid. By adjusting the threshold of the 5300 to sense the emulsion – or by sensing the water layer, it is possible to control the vessel to its maximum performance. As the vessel typically is fully immersed, you can use either a Rosemount 5301 or a 5302.
The guided wave radar can be installed in an external chamber or direct Nozzle mount. Emulsion is always a challenge. However, if GWR is installed in a chamber, the emulsion will be less than the vessel. Emerson installations of GWR for Desalter Interface level measurement include IRAQ, Kuwait, Saudi and USA
Desalter Interface Measurement with Guided Wave Radar white paper (link)Reliable Desalter Interface Measurement Proven Result (link)
Displacer Option: There are also customers that use the Fisher DLC3010 displacers in still pipes, and others that still have the older Fisher pneumatic controllers. Displacers are mechanical devices, so often people think about using a technology with less maintenance, but others choose to continue using the displacer technology especially if it is currently meeting their needs.