5 replies to this topic

[Alawi]

Dear Experts,
It is a normal practice to use various types of neutralizing amines in atmospheric distillation columns to protect the over head system from corrosion , I am
studying the possibility of applying this practice to Vacuum distillation columns for the same purpose and was wondering if any of you have actually experienced such practice in there own refineries and plants, the major point of focus is the fact that the temperature in Vacuum distillation is significantly lower (Also the pressure ) will this have an effect on the quality of mixing of the amine with the over head products at the point of injection?
Any questions and comments are more then welcome.

Kind regards

[indy]

In crude distillation unit we have a neutralizing Amine injection. We have two vacuum units and here we have no chemical treatment inhibitor or amine neutralizing, but I have heard that others have done it.

My advice is that you should contact Nalco Ondeo or Baker Hughes, they have good know how on this matters and they can assess you with good knowledge on the subject.


Regards

Luis Marques

[Alawi]

Hello Mr.Luis

As you have suggested we have actually already asked several companies including Nalco & Baker Petrolite on this subject. They all advised to use neutralizing amines for this purpose, It was not surprising they well suggest to do so. We currently use Ammonia injection to neutralize our Vacuum O/H system and a certain company (A very big one) specialized in the oil and gas sector suggested to stick with the ammonia.
I cant stop my self from asking you about your Vacuum distillation column, you have mentioned that you do not use any type of chemical treatment for the column, what about the PH and corrosion control, what type of crude in processed upstream? Do you have a desalter ? We process a sour crude (Arab light) and we have no desalter both facts do contribute in increasing corrosion rates.

Kind regards

[indy]

Hi Alawi

Ammonia as a neutralizing agent is not good because it doesn’t answer smoothly to ph variations. If you inject ammonia when you have low ph, the ph quickly goes as high as 8 or 9, if you stop ammonia injection the ph quickly goes as low as 4 or 3, everything depends on the feed you process. In other words controlling ph with ammonia is hard to stabilize the ph in between the required interval of 5.5 or 6.5. This control is better achieved with amine neutralizing agents.

In cold overhead corrosion of our vacuum we don’t have any chemical corrosion inhibitor because from our history we don’t have so much corrosion on the system which is controlled through TML ultrasonic readings.

On the vacuum column we control hot naphtenic corrosion through napthenic corrosion inhibitor and on line ER corrosion probes to monitor naphtenic corrosion of column cuts between 190ºC and 350ºC. This is because from times to times our diet mix is blended with naphtenic crude such as Marlin, Kuito and other naphtenic crude. At the inlet of our CDU unit we have two dessalters in parallel. To fight against corrosion in an oil refinery is imperious to have a good dessalification. If you don’t have them all your down stream units will suffer the consequences.

Regards

Luis Marques

[Zauberberg]

Hi Alawi,

My contribution for this topic is: don't believe chemical vendors by default. They will tell you that you need corrosion protection, and it is going to be achieved if you buy their specific product(s). And remember this rule of thumb: injecting wrong chemicals or having overdosage is just as bas as there is no corrosion protection at all.

The best you can do, for the beginning, is to analyse your system and determine the origin of contamination species and the way they interract in the specific environment. Sometimes, the main cause of the problem can be in the upstream facilities, or perhaps, inappropriate laboratory methods have been selected for corrosion monitoring.

Long time ago, I read somewhere (maybe it was PTQ or Hydrocarbon Processing magazine, I'm not sure) that neutralizing amines are not good solution for Vacuum units, but I do not remember why.

Regards,

[smalawi]

Hi,

ammonia has been used for protection of the overhead system where ph control was required. sometimes the protection its not required.

the problem with ammonia is it formes salts that deposits on the vapour line of the overhead system and following vac system. as a result of the salts we have underdeposite corrosion of the line and subsequesnt failure of the line or high pressure drop.. these salts form in the vapour phase so they stay. ammonia also has other vices but some times it works fine, only by experiment that you could know about it.

nutralizing amines vary in thier effective nature, they might form salts but after water dew point and thus its washed by the water. there are other benifits that vary from case to case.

nutralizing amines are expensive and serious helth hazards, one needs to take care of that part as well.

we have switched from ammonia to nutralizing amines but still its on trial basis. if your vedors are confedent you can ask for a trail or demostration. they supply the injcetion facilty and containers and you pay for the chemical or reduced price. tallk to them and see what you can get.

GE water (betz in the past) also have some offers.

dont forget to have a cloase look at the control loop, its vitel to mantainining the ph.

cheers,

sm