Weird Vacuum Tower dP problem
Weird Vacuum Tower dP problem
(OP)
Has anyone out there experienced salt built up in the Vacuum tower? During "normal" operations our LVGO section pressure drop is ~ 8mmHg. Over time, however, the dP increases! When it reaches 14mmHg, the unit goes thru a salt sublimation process. The temperature in the LVGO section is increased to ~400F for ~24 hours (naturally all vacuum is lost). At the end of the procedure the dP is back to "normal". Needless to say, this is costly (and at minimum irritating). I can't think of any reason why there are ammonium chloride salts in this section. Has anyone experienced something similar?
RE: Weird Vacuum Tower dP problem
RE: Weird Vacuum Tower dP problem
RE: Weird Vacuum Tower dP problem
We have been relying on our vendors to test for whatever is attached to the chlorides. They said it was ammonia coming from amine...As the matter of fact, during the "heat up procedure" we collected samples of the hotwell sour water every two hours. The vendor found a bunch of amines that spiked-up and died-down during the process. These amines were different from one we add for corrosion control at the top of the vacuum tower.
I am still at AWE as to how these amines survive my desalter, a heater, a crude tower, a vacuum heater and come up "alive" at the top of the vacuum tower. I mean is this possible? How come they don't degrade or crack? The boilint point of DEA is 516F, TEA is 680F but shouldn't they stay in the water?
Part of the problem is that we can't come up with how much salts are we taking about. Therefore I do not know the level of amine that I am looking for in the HC. (PPMs, wt%?)
Your suggestion is great. Somehow we will find a way to check for FeCl3.
Thank you!
RE: Weird Vacuum Tower dP problem
RE: Weird Vacuum Tower dP problem
There are refiners that add chlorinated hydrocarbons to the crude oil. For example, slop streams often injected to the crude oil stream contain:
-spent (additive-rich) lubes;
-chlorinated solvents used for equipment degreasing, or for "dewaxing" of storage tanks and other equipment, when handling "waxy" crudes.
Chlorinated hydrocarbons aren't removed in the desalters and may even reach the vacuum system. They may decompose, releasing chlorine gas, as Ca and Mg chlorides do. Ca and Mg chlorides are remnants of a non-effective desalter operation. Steam or water may help in turning Cl into HCl.
Chlorine can find its way to the vacuum tower also by leaks of saline (cooling) water as in heat exchangers and pumps, or when not using chlorine-free steam condensate to dilute chemicals.
One should strive to find the sources of chlorine, don't you think ?
By the way, it is apparent that amines are succeeding in neutralizing HCl, considered a strongly corrosive agent in crude units.
Good luck !
RE: Weird Vacuum Tower dP problem
I did not know about chlorinated hydrocarbons. Where else can I find information about the chlorinated hydrocarbons? Why aren't they removed in the desalters? Our vendor has not even mention this possibility.
This is a good suggestion. I will keep you posted. FYI our dP in the LVGO section is back to 14 mmHg and holding. Good grief, I need some success with this problem!
RE: Weird Vacuum Tower dP problem
One "good practice" approach is to take care that the injection of slops into crude oil streams be done in measured and small doses.
I hope you continue enjoying the VDU good performance of late.
RE: Weird Vacuum Tower dP problem
It turned out that it came from the crude via the topcondensate. The source in this case was the the crude producer added an amine (that decomposed in the heater). The additive (amine) was to prevent the crude to release H2S. The crude used was not new, we had been processing this amongst others for years without this problem and suddenly we got this effluent problem. It is appearent that the desalter doesnt remove these amines so the problem will either show up in the CDU or VDU section.
RE: Weird Vacuum Tower dP problem