Can anyone suggest/advise the procedure to reduce upsets during a water shot problem in the CDU during tank changeover or slop processing? Either design changes in the desalter or any equipment internals, modification etc.
Answers
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18/04/2021
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Sudhakara Babu Marpudi, Dangote Oil Refinery Company, m_sudhakarababu@yahoo.com
While there is no “this is it" solution Agar probe technologies promise that the probe installed near the tank can detect the water cut, reduce desalting water and optimise the de-emusifer injection rates etc., The probes installed on the desalter detect the solid build-up in the desalters and can probably optimise the mud wash cycles too.
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18/03/2021
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Jake Gotham, InSite Technical Services, jake.gotham@insitetechnical.com
I am not aware of any practical ways to eliminate this problem by design changes in the CDU. Prevention by good tank management is the key. Your procedures should include:
• Adequate settling time after import before putting a tank on feed. How long is adequate is something most sites learn by experience, and can be different for different crudes due to density, viscosity and water content variation. 24-48 hours is typical.
• Frequent water drawing during the settling period.
• Pre-feed checks for water at the water-draw nozzle and oil nozzle elevation.
• Introduce the tank to the crude unit at low rates, then increase up to the target percentage after a couple of hours if everything is stable. If the crude is a problem crude or there has been pressure to feed the crude before the usual settling time, the tank should be introduced at an even lower percentage initially.
• Management of the build-up of solids at the bottom of the crude tanks. If wax-banks or sediment are allowed to accumulate, they can hold water back and prevent it reaching the water-draw. If the tanks have a long inspection interval, it may be necessary to take intermediate tank shut-downs to clean the tank. Specialist companies can scan a tank to draw a profile of wax-banks with the tank still in service.
• Slop segregation to minimise slop water in the slop oil tank and vice versa.
• Continuous pressure on slop production and slop processing to minimise the requirement to transfer slop to a crude tank.
• If water does reach the CDU, the operator would usually reduce the furnace temperature rapidly but it may be too late to prevent damage. Signs of wet crude include:
o Sudden spike in atmospheric tower pressure.
o Erratic readings of furnace pass-flow meters.
o Changes in crude or product temperatures in the pre-heat train.
I hope that is helpful.
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