High Inorganic Chloride salt n LVGO 1

[DDSpetro]

Hello…Experts !! Happy New Year to all of you !!

LVGO –Light Vaccum gas oil is one of the product from Vacuum crude distillation column , high Total chloride especially inorganic chloride is reported , while checking at overhead receiver boot water chloride it remains only 1 or 2 ppm , while LVGO chloride data shows total chloride 15 ppm ,20 ppm some times 23 ppm , it varies from 5 ppm to 25 ppm ; out of which organic chloride is very less say , e.g. out of 20 ppm , 16 ppm is inorganic and rest is organic , desalter efficiency remains ~ 98 % ,LVGO draw temperature is 130 to 140 C; LVGO Return temp. is ~ 40 C ; NH4Cl Desublimation temp. delta online monitoring is there but it shows more than 20 C delta difference, lab analysis shows no presence of Fe,Zn,Al metals & absence of amine,ammonia chloride or not even Na,Ca ; It sounds to be HCl.Caustic dosing in upstream crude unit is ~ 200 to 300 lph.One thing which was observed that , whenever NH3 demands goes up in VDU Column ovhd (Dosing as per Overhead reciver boot water pH), chloride in LVGO goes down ;

What are the potential cause of this chloride ? It is very critical point of concern because this LVGO goes to VGO hydrotreater and it can cause sever corrosion in the downstream.


Thanks in advance to all of you.

 

[25362]

Please consider that iron [sup](III)[/sup] chloride, formed as a result of corrosion, is a salt that boils (!) at around 315[sup]o[/sup]C.

 

[whammett]

I agree with 25362. How old is the system and how long has this been a problem? Is there anyway to check CS piping(if this is in fact the source of the problem) upstream for corrosion while the system is still in operation?


Will Chevron Corp.

 

[DDSpetro]

Thanks 25362 & whammett for your prompt reply.

The Unit is recently commissoned ~ 1 year of operation.

During Lab analysis No traces of Fe is found.If FeCl3 is formed ,I suppose it could have found as "Fe presence" during lab analysis of LVGO sample , but it is not the case ,however let me dig out one more time for sample.

Certain crudes type which is processed in the blend e.g. Merry 16 etc. Some prsence of Arsenic (As) is there as per Crude Assay data in VGO cut i.e. 0.5 ppm ,Is there any chance of AsCl3 at column overhead ?

 

[25362]

I'm not acquainted with that particular crude oil, but AsCl[sub]3[/sub] boils at about 130[sup]o[/sup]C. Therefore, depending on its partial pressure, if present, it may appear with distillates.

 

[whammett]

Has this been a problem since the unit started? If not, have you changed types of crude?

The reason I am asking is because if it is a recent development, and has not been present since the start, it could be stemming from corroded piping upstream of the vaccum distillation column.


Will Chevron Corp.

 

[DDSpetro]

Yes, this is the problem since allmost after unit start up.data is attached for reference.Crude blend diet keeps on changing;Merry is suspected crude where good correlation was found but again not all the time.

http://files.engineering.com/getfil...40e8-9ab1-e90af8eb8500&file=LVGO_Chloride.xls

http://files.engineering.com/getfil...-291fa45ffb29&file=LVGO_Chloride_analysis.ppt

 

[whammett]

Is there any way you could use a crude blend that does not require/include "merry", and then test those results?

If not, can you post the makeup of this merry?


Will Chevron Corp.

 

[DDSpetro]

The attached box plot analysis in ppt shows that when Merry crude was not there at that time, LVGO Chloride mean remains 12 ppm and when Merry was there in the blend at that time mean LVGO chloride remains ~ 20 ppm. Merry in the blend typically remains 10 to 30 % in the blend when it is processed.

The mystry here is that VDU Column overhead reciever boot water only 1 or 2 ppm while LVGO chloride , suspecting is it possible that HCL gets condensed and report along with LVGO instead of overhead

 

[DDSpetro]

LVGO Pump around return temp. remains 46 C in the unit, where LVGO High chloride observed; LVGO Draw temp. is ~ 120 C; VDU Column top temp remains ~ 40 C;

During Day time & night time difference of LVGO chloride is found 1.2 ppm to 3 ppm to see that whether HCl is getting condensed or what , because in other units where LVGO High chloride is not observed – LVGO Pump around return temp. remains 57 C ; is it possible for HCl condensation phenomena ?


Other problem since unit commissioning is that HRCO (Slop wax ) section is facing high corrosion rate as per corrosion coupon installed ( ~ 0.20 mpy/year – Metal Loss) the MOC is P5 material, 5% Cr,1/-Mo,rest Fe & this HRCO goes to Crude main fractionator for quenching media ~ 70 m3/hr , whether is it possible that CrCl3 / MoCl3 or similar compounds gets reported at LVGO through corrosion reaction at VDU Furnace at higher temperature ?

http://files.engineering.com/getfil...416f-b08b-4e90b6db5715&file=Chloride_LVGO.doc

 

[25362]

Has external contamination by ingress (in-leakage) of cooling (salt-containing) water been considered ?

 

[DDSpetro]

There is no as such cooling water exchangers in between or no any leaky exchangers so, doubt can be ruled out.

 

[DDSpetro]

After LVGO/Crude PA exchanger, one Fine fan cooler followed by C.W.HE is there but cooling tower performance in terms of ORP , monitoring parameters no any tale tale indication found of HE leakage.

 

[whammett]

Well it looks like the levels were still high before merry was introduced. However, merry made it worse. This is a tough problem because it's hard to tell if the problem stemmed from the crude blend having merry or not.

The feedstock comes straight from atmospheric distillation before it gets to the VDU?

Is there any way to slow the feed through the furnace to change the incoming feedstock temperture and see if that has an affect on the HCL without significant changes to your product cuts?


Will Chevron Corp.

 

[DDSpetro]

Yes, Before Merry,problem was there but with Merry problem has become worst , as may be it has got higher Ni,V metals any impact ?

Yes, RCO feed goes directly to VDU with ~ 365 C, slow down the feed through VDU furnace is cutting down the throughput may be difficult option ,

One another thing was observed that VDU Furnace transfer line Corrosion rate is high i.e. more than 0.35 mpy in both the units which is having MOC P-5 ,Cr,Mo.

What is the opinion about HCl condensation at vaccum condition i.e. 20 -24 mmhg pressure of VDU column at PA return temp. of 46 C against 57 C ; because boot water reciver is having only constant daily 1 or 2 ppm max.

 

[25362]

Corrosion on transfer lines may also be due to naphthenic acidity.

 

[whammett]

I agree with 25362. What is the TAN of the crude blend? Or do you have a TAN of the feedstock going into the VDU?

I have heard of Ni and V causing problems during FCC, but at the tempertures you mentioned, I do not think that they would pose a problem. However, antimony is a widely used heavy metal passivation additive if you were up for trying that.

If I were to have to try and guess where the chloride problems were coming from, I would suspect that it was from the transfer line corrosion. What is the piping material? CS? There is no quick fix to that problem except changing out the piping.


Will Chevron Corp.

 

[DDSpetro]

THE MOC Of transfer line is P5 MATERIAL.cromium 5%,1/2% moly rest FE, TO cater napthenic acid corrosivity,in VDU COL Feedstock pump circuit,phosphate based inhibitor is in place of well know vendor.

 

[25362]

It has been shown that stainless steels with up to 12% Cr have no advantage over carbon steel vis a vis naphthenic acid corrosion. In addition, naphthenic acids appear to accelerate high-temp sulfidic corrosion in heaters.
See, for example, thread124-214862 and thread338-177729.

 

[DDSpetro]

on an avg. crude blend TAN Value remains 0.6 Mg KOH/G OF oil sometime it goes up to 1.0 in the crude blend.