SR naphtha reforming

[Milutin]

Hi all,

Is it possible describe clear symptoms for following reformer problems:

- metal poisoning
- overchlorinated catalyst
- underchlorinated catalyst
- catalyst end of life
- problems caused by poor regeneration

Our reformer has following deviations from normal operations:
- low dT on first two reactors
- low H2 content in recycle gas (below 50%)
- low H2 production
- low reformate production, 10% lower than expected
- slightly higher then expected LEP factor (C1+C2)/(C3+C4)
- RON below 90(after last start up)
- and after last start up no response of naphta RON after reactor temperature increase

Catalyst is regenerated and 10 days after start up we had emergency shutdown, after start up we have slight but continuous loss of reforming performance.
After that we had three more shoot downs and faster loss of performance after every start up. All shoot downs are performed according user manual. Cycle length is five months and this is seventh cycle.
Chloride and water content in recycle gas are within expected values. Sulfur level in hydrotreated naphtha is 0.5ppm. Inlet reactor temperatures are 500degC.

What can cause such behavior?

 

[blacksmith37]

Not my business; but do you mean the feed going into the reformer is 0.5 S ? The comical engineers were always concerned about S deactivating the catalyst (in Ultraformers which have a cycle time of only about 2 weeks).

 

[Milutin]

Yes, sulfur can deactivate reformer catalyst, this value 0.5ppm is design value for sulfur level. Sulfur is also easily detected by increased H2S concentration in recycle gas, this value is normal.

 

[25362]

Milutin,

I have some questions:

Are these new processing problems?

What are the concentrations of nitrogen and metals in the feed? Feed metal content is, sometimes, high, since there comes a time when naphtha hydrotreaters stop in retaining them.

What is the moisture content in the feed and the recycle gas?

Moisture in excess could be a cause for: underchlorination, loss of reformate yield, loss of hydrogen production, low concentration of hydrogen in the recycle gas, a greater production of C[sub]1[/sub]-C[sub]4[/sub] HC's, a shorter catalyst life.

Although the S normal level is [≤] 0.5 ppm, it has been claimed that bringing it down to 0.1 ppm lengthens the life of the catalyst while improving reformate yields.

Have you tried to change a bit the feed temperature by 10 to 20[sup]o[/sup]C?

 

[Milutin]

25362,

As wrote previously,after first emergency shut down recycle gas H2 content and reformate yield started to decline,after evry next SD this trend accelerated, yes in may opinion this is problem from beginning of cycle.

Nitrogen content in hydrotreated feed is very low about 0.1ppm, in previous cycle we had nitrogen problem but it was controllable by adding more chlorides.
Unfortunately till now we didn't have possibility to analyse metal content in feed, we will have results next week. According Donald Litlle book, metal poisoning has characteristic pattern, at begging first reactor is affected and his dT decrease, but as result in second reactor dT increase. We didn't have such pattern.
So metal poisoning, in my opinion, is possible but I am not assured.

Moisture content in recycle gas around 30ppmw.
0.5 ppm sulfur for as is normal value we had cycle length with this value more than 20 months.

 

[25362]

What is the water content in the feed?
What is the chloride content in the feed?

 

[Milutin]

We don’t do water and chloride content in reformer feed as regular analysis. I have two recent values for water in reformer feed 7 and 12 ppmw. Method is by coulometry.

We also inject 5 ppmw of methanol for water control.

 

[25362]

Do you inject sufficient organic chloride?

Have you tried to drop the first reactor temperature -after regeneration- to, say, 480[sup]o[/sup]C, to see whether results improve somewhat on straight run naphtha?

I assume the best approach to solving the problems is to forward your queries to the process supplier, who would surely give you useful advice.

 

[muhammadarshad]

hi.
my opinion is that is problem you are facing is due to sulphar concentration in naphtha feed.
before 3 or4 mounts in my refinery we are facing same like your problem but i identify initially acecully in my refinery we are introducing new crude blend and i know the crude blend high sulphar(in crude eassy)so we reduce the RITs and incereace hydrotreater reator temperature 10c.
so unit was normalize after 3 or 4 days

 

[Milutin]

Yes, according to content in recycle gas, chlorides are ok, but anyway we increased dosing rate from 0,6 to 2 ppm, but no response from reactors.
At thist stage there are no response on octane nuber even if we increase reactor temperatures it seems to me that catalist is complitely deactivated, delta T for reactors are 18, 12 and 7degC.

 

[10815L]

Hi,
Check about feed distillation range, this be 95-170. 0.5ppm sulphur is not hi.
and chloride must be 5ml/min, not 2 ppm.
Bring down RIT to 480^0C and feed to 50% of 100%,after this wait until H2% is improved and DT increased.once your H2 % increased and total H2 production come in the normal range then increase RIT step wise and also increase feed accordingly.
to jack up the reaction initially increase chloride more, you can go up to 25 ml/min even.
Don't be afraid of by injecting chloride nothing will happen. once reaction started and you get good H2 % then reduce the chloride injection level.
Cheers
10815l

 

[Milutin]

We tried hydrogen stripping but with no effect. I am attached several diagrams for better understanding.

http://files.engineering.com/getfil...570-40e9-81a5-66b1d4c23706&file=R-Delta_T.png

http://files.engineering.com/getfile.aspx?folder=e17a0424-e5c6-4b57-800d-1d906027960a&file=R-H2.png

http://files.engineering.com/getfil...-52c6-44e7-b7c4-ca2d25077fec&file=R-nap_S.png

http://files.engineering.com/getfil...7100-4566-a521-b20d562a2d43&file=R-rc_H2S.png

http://files.engineering.com/getfile.aspx?folder=3ff7a187-2871-45c9-a145-d03a8b748207&file=R-wcl.png

 

[10815L]

Hi,
Water and cocke is the main culpert for low DP.This looks after S/D, water was there in your feed and reactor not is perform well.
You need to keep temp on at 480^0C and feed 50% and keep your cl injection more.
Thanks
10815L

 

[786392]

Dear
Just a wild thought

have you checked the possibility of Hydrogen Sulfide or low molecular weight mercaptanes Slippage along with SRN stream unknowingly?

Have a SRN GC run to investigate/exclude the possibility.

At times it may have disastrous affect on reformer efficient operations!
Moreover the slightly excess cracking reactions indicated in post,could have been

as a result of some hydrogen chloride carry over if the SRN is not stabilized sufficiently with rejection of Off-gases.

Hope this could help in problem recognition/consequential resolution.

Best Regards
Qalander(Chem)