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.

 

[DDSpetro]

OK,

On internet, I have found out some Pxy,Txy graph as well as Azeo at low pressure @ Vaccum colum pressure i.e.24 mmHg top pressure as attached.

http://www.me.gatech.edu/energy/andy_phd/two.htm#f210

Can you pl. guide if it will helpful to control chloride in LVGO.

http://files.engineering.com/getfil...9687-42fd-a832-cc93bfcfc841&file=IMG00104.gif

http://files.engineering.com/getfil...652c-43d5-aad9-28947ae74598&file=IMG00110.gif

http://files.engineering.com/getfil...-03d4-408c-b05c-cf53f5979f27&file=Abb15_e.gif

 

[DDSpetro]

25362,

Chloride was analysed in 6.6 % caustic but it was 8 ppm only; if we consider 350 liter/hr dilute caustic of 3 % concentration then based on 1090 kg/m3 density;pure Caustic flow will be ~ 11 kg/hr & desalter outlet salt which remains 0.6 to 0.8 ptb max. ( 1 ptb = 3 wtppm salt) ; assuming 1.8 to 1.98 Kiloton/hr of crude flow ; stochiometric wise caustic injection seems to be allright , i.e. ~5.94 kg/hr of pure salt, 11 kg/hr caustic is available.

Meanwhile,attached are various parameters analysis including brine Mg & ca.In Vaccum residue chloride was analysed and found 9 to 13 wtppm.RCO sample is also given for Chloride analysis for chloride balance.

http://files.engineering.com/getfil...318-457c-b259-f7c0525ae300&file=Chloride1.xls

 

[25362]

It appears to me that liberated HCl is the culprit.

BTW, a 3% mass soda solution would have a density of 1031.8 kg/m[sup]3[/sup] at 20[sup]o[/sup]C; it still gives about 11 kg/h, which is above stoichiometric.

Therefore, the following things come to mind in line with your posting dd Jan 27th.:

[•] Check personally the caustic dosing pumps for true mechanical performance.
[•] Try to increase the caustic dosage to improve mass transfer and see whether chlorides in LVGO drops.
[•] Verify the chloride content of the HVGO, it should be similar to the contents found in the VR and the LVGO.
[•] Find what are the operating conditions that result in a low pH in the boot water that requires automatic injection of ammonia, since as you tell us under these conditions the chloride content of LVGO drops.

 

[786392]

Dear DDSpetro
I feel that 25362 estimation seems pertinent to have a try and give feedback,but do not ignore the word of caution 'physically'

as occassionally the flow does not finds its way for which it is destined and

either recycles back or

unknowingly goes to some other area.

That must carefully checked,ensured for the caustic flow here.
Good luck for successful way forward.

Best Regards
Qalander(Chem)

 

[DDSpetro]

i wil post physical observation soon on caustic injection,meanwhile today it was observed surprisingly,unit 1 where lvgo PA return temp was 48 c,col top temp 41 c,lvgo total chloride was observed 2.7 wtppm ,unit 2 lvgo PA return temp 39 c,top temp 33 c,lvgo total chloride 3.4 wtppm,unit 2,boot water chloride 3.5 ppm which was usually 1 ppm,even mery crude was present in the blend 20 %,caustic flow 270 lph,5.7 M3 dosing tank capacity,thrugh screw pump caustic is injected.

 

[786392]

Dear Somehow I feel as if you indicated mercury in crude is this correct? or what

Best Regards
Qalander(Chem)

 

[25362]

[•] Modern "dry" vacuum distillation units handling topped crudes operate at 3-5 mm Hg at the top of the vacuum tower and about 25-30 mm Hg in the flash zone.

[•] Please note that of both salts, MgCl[sub]2[/sub] hydrolyzes easily (although not completely, say 90%) at topping temperatures, while CaCl[sub]2[/sub] is more resistant (less than about 15% decomposes). H[sub]2[/sub]S also helps in liberating HCl. This is seen in the submitted (vacuum) brine analyses. BTW, calcium chloride is used in oil well drilling and completion operation.

[•] This fact implies that NaOH might not neutralize all the "potential" HCl from the 0.6-0.8 PTB of salts in the desalted crude oil at the topper. The remaining Mg and Ca chlorides apparently decompose/hydrolyze at the vacuum unit where steam catches and brings the HCl to the column top and eventually to boot water, as well as to the LVGO drawoff section.

 

[25362]

Besides, Ca and Mg chlorides readily absorb water. The hydrates decompose at the operating temperatures releasing HCl.

If there are solid particles in the crude, such as clay, the added "surface" may increase the extent of reactions between steam and chlorides.

 

[DDSpetro]

786392- It is Merry Crude type ( 20 wt % in the blend) it is venezulen crude - High Metal crude with As is also there in it.

25362,

Caustic dossing vessel is having gear pumps with one standby pump, its discharge goes to booster pump suction / slip stream of desalter downstream section : Two exchanger where quill is located , pressure remains 25 kg/cm2g with once in a day caustic batch making frequency with 40 % Low alaram & 75 % high alaram, one vessel is stand by; as V-12 chloride gets monitored every 2 hour so, with 300-400 liter/hr caustic injection ,so, mechanical performance wise caustic injection pump seems to be ok and NRV,pressure indication,flow indicator is also there in the line.

Meanwhile Chloride analysis in lab is through ASTM D-4929 ; Culometry ( Silver test) ; Once Desalter downstream salt Ca metal was analyzed and found 0.43 ppm while Na & Mg was < 0.1 ppm ; so, it seems that CaCl2 gets sliped froM Desalter downstream.So, CaCl2 decomposition theory seems intresting because we have seen High Potential H2S crude like Eocene when processed ,it is also coorelating with LVGO chloride.So, H2S helps in liberating HCl - if you can elaborate pl.

Thanks

PS : Earlier posted Brine analysis is of Desalter Brine water analysis.

 

[DDSpetro]

In previous post V-12 is Crude atmospheric column overhead reciver boot water ; caustic batch is prepared once in a day.

 

[786392]

Undoubtedly Magnesium Chloride is the worst culprit salt if not handled/got removed and drained at de-salter stage

since this most usually gets decomposed generating HCl(Hydrogen Chloride)which is main source of internal corrosion of overhead systems and certain chlorides generated thereby are found as being experienced in your case as pointed out accurately by "25362".

I believe it is desalting which needs to be focused since caustic is not showing satisfactory due impact its injection point(s) might need review for positioning further upstream.

Additionally each Crude storage feed tank's adequate settling and aqueous salt& sediments layer's thorough/careful draining may prove greatly useful.(Just an out of box idea)

Hope this proves helpful,ensures trouble shooting succes!

Best Regards
Qalander(Chem)

 

[25362]

[&bull;] A typical salt composition in crude oils would be 75% NaCl, 15% MgCl[sub]2[/sub] and 10% CaCl[sub]2[/sub].

[&bull;] It is commonly accepted that the NaOH injection can be increased and tolerated to a maximum of 3 lb/1000 bbl (~10 ppm) of crude oil without causing downstream problems.
Therefore, you could try to increase the soda dosage in cases where heavy and viscous crudes can not be effectively desalted.

[&bull;] The effect of H[sub]2[/sub]S is, apparently, via a corrosion intermediate at the top cooler column and condenser sections. The accepted mechanism is: wet HCl forms ferric chloride by corrosion, which in the presence of H[sub]2[/sub]S deposits gray/black iron sulfide on the metallic surfaces while, at the same time, regenerating HCl.

I hope you succeed in your troubleshooting efforts.

 

[786392]

Thanks! 25362,
the adequately/appropriately highlighting H2S(Hydrogen Sulfide)issue,I incidentally forgotten.

Best Regards
Qalander(Chem)

 

[25362]

DDSpetro, have you tried to correlate the HCl content of the LVGO with the temperature of the returning PA? It seems that higher temperatures reduce the HCl content. Please comment.

 

[DDSpetro]

no correlation found as posted earlier,pa return flow has correlation as since last two days without doing lvgo chloride has come down with pa return temp of 39 c ,chloride is 3 ppm in both units.if we put higher caustic then stochiometry,is it possible it can carry foreword and helps cacl2 decomposition.

 

[25362]

Let's summarize:

[&bull;] The desalter suceeds in bringing the salt content downto 0.6-0.8 ptb which is considered OK.

[&bull;] Now, apparently, the point is to avoid the further decomposition of the chlorides remaining in the reduced crude.

[&bull;] The naphthenic acidity of the crude mix can act in the vacuum hot sections by displacing chlorides producing HCl in the process. Apart from its possible action in the evolution of H[sub]2[/sub]S.

[&bull;] If this is so, one common procedure is to reduce this acidity by making crude blends with crudes having lower neutralization numbers. Try to correlate HCl in LVGO with the crude total acid numbers.

[&bull;] Otherwise, contact a chemical company who may help in providing an additive that neutralizers this acidity as encountered in venezuelan crudes, apparently "active" at the vacuum section operating conditions. There are some amines that can do the job.

 

[DDSpetro]

25362 ,Yes,

LVGO Chloride is very well correlating with Crude TAN - 80 % positive correlation as attached.

Further in Lab , one more experiement is done without water wash as such there was 6 ppm chloride with no free water.

With 5 % water wash and centrifuge of LVGO sample further chloride analysis done and it was found 1.6 ppm.so, most of the chloride was water soluble,which was confirmed.

http://files.engineering.com/getfil...461c0337&file=LVGO_Chloride_Vz._Crude_TAN.ppt

 

[DDSpetro]

With 10 % distill of LVGO sample, Out of total 6 ppm of LVGO Chloride sample, 4 ppm has come in to that 10 % recovery.

 

[786392]

Dear DDSpetro Hello/Good Evening,

All what you indicate in above two posts nothing but Confirms;

good initial upstream handling/treatment needs

And there is a definite need for desalter wash water flow rate and quality reviews to get rid of Chlorides at this stage.

at upstream stage ensuring thorough mixing of NaOH (i.e. caustic stream)with Crude Oil Suction pipeline through some in-line static or other mixer prior to landing into de-salter.

Sometime De-emulcifiers are helpful(if not in use,or might need replacement) or

even desalting electrodes and High potential difference ensuring mechanism may need overhauling etc.

Hope this helps in way forward for your problem resolution soon.

Best Regards
Qalander(Chem)

 

[25362]

The lab distillation seems to confirm the presence of volatile wet HCl.