HNUU Reactor Detla P 1

[Petro0707]

Hi...All ..!! Warm good morning to you..

Currently we are facing sever problem on following :

1.Heavy Naptha Unionfining reactor (HNUU) Pressure drop is increasing since last couple of months from 1.8 to 3.6 kg/cm2g (existing),still increasing trend.

We process naptha from Crude units/VGOHT /DHT units as well as imported naptha from Tank farm :

Total processing throughput of reactor : 660 m3/hr with FBP of 165- 168 C.We are now analyzing root cause of the problem.

Feed to the HNUU reactor which is single bed reactor with around 120 MT CO/MO Catalyst bed.Feed to the reactor is from Naptha spiltter bottom and out of 660 m3/hr majority around 240 m3/hr is from CDU unit itself.

Generally, we don't carry out regular daily testing of contaminatns in the Naptha from CDU/VGOHT/DHTs like Fe,Chloride etc.but we have carried out test of Particulate matters in all naptha of all units during last 3 days in naptha including Imported naptha too mostly they fall in the range of avg. 10 - 30 ppm.Imported naptha (avg.8.7 ppm).

We have also analysed the Boot water PH,Fe analysis of CDU o/h reciver ,VGOHT fractionator,stripper o/h,DHT stripper o/h & from those datas also it is very difficult to get the clue about that what is that causing fouling in the HNUU reactor/from where particulate matters /Fe etc. takes place.

Increasing Detla P in HNUU Rx otherwise will lead Unit shutdown.

I request you to give your opinions on this.

Regret for long description.

Thanks to all of you...!!!

 

[KazakhJeff]

Hello Petro0707. More questions I am afraid, but no answer yet. Have you looked at ther delta T, or hydrogen concentration, to see if you have anything else unusual happening, or catalyst activity changing? How about the pressure taps? Are the readings genuine? Have you verified the results? Has chlorine injection changed in the reformer (or the crude unit), bringing back more with the hydrogen (more corrosion)? Was the change sudden, or over time?

We'll be interested to hear what you find.

 

[Milutin]

Hi Petro0707,

You should pay attention more on imported naphtha, every batch should be analyzed in details, because of possibility of contamination during production/transport. Increased quantity of particles can cause increase in dP.
You should also check if you have blanketing gas on naphtha tanks working properly.

Regards,

Milutin

 

[Petro0707]

Dear KazakhJeff & Milutin,

Delta T across reactor is alomst constant since last couple of months that is between 21 to 24 °C,Hydrogen purity almost we maintain 95-96 % along with other contaminants within limit , we have checked pressure taps , the reading is reliable ,there is no any change in chlorine injection or there is also no any change in chemical dozing in CDU units also since last 7-8 months , but when Platformer was in shut down , we have injected chloride in the feed line of platformer that is upstream of Packinox ,HE train but upstream NRVs are there and drain valves are also there,this pressure drop increment is over time of last 6 to 7 months,

we don't have N2 blanketing in floating roof tank of imported naptha,( we have got total two similar trains of CDU/DHT/VGOHT )but we have done monthwise analysis of boot water Fe and pH datas of CDU column overhead reciver , DHT stripper o/h reciver,VGOHT fractionator o/h reciver and found one significant observation from the analysis of last 8 months data that CDU train-1 has got signficant variation in pH & Fe ( i.e.increasing trends during last months in compare to 2nd train),we have also observed Fe in upstream filter in HNUU Plant B/L.now the question is from where Fe is coming whether it is from CDU train 1 or any thing else in HNUU reactor itself .

Can Oxygen/ingress happen ? one another signficant observation is that paticulate matters are high in all train -1 i.e. CDU/DHT/VGOHT compare to train2 of all and in imported naptha there is no higher particulate matter comparatively.

Still it is very toughest job to find what went wrong or what is creating HNUU reactor fouling ,pressure drop increament...??

 

[soumya1478]

What is the operating temp of the reactor now?If you operate at very high operating temp the dienes present in the feed may polymerise and lay down on top of catatalys.Check the diene no

 

[25362]

You may find some interesting notes in

thread483-101342 and thread483-147396

 

[Petro0707]

Dear Soumya1478 & 25362,

We don't have major dienes in the feed, infact we have got basket filters ( 50 Micron and followed by 20 Micron) at B/L of HNUU Plant i.e. upstream of Feed surge drum , where we find Fe particles too ,I have gone through the threads mentioned by 25362,good to go through it, We have got total 24 bundels in our CDU Column Ovehead fin fan cooler & we inject liquid & gaseous NH3 for pH control along with Corrosion inhibitor tour current wash water rate is 36 m3/hr & we have made survey also to ensure uniform distribution and almost in each bundle 10 lit/min we have found equal also..

We don't monitor Wash water quality in terms of NH4HS ,Chloride,Hardness etc. but we use non phenolic water from Sour water stripper,SRU unit as Wash water for CDU OH Condensers upstreams and usually pH & NH3 is being monitored that is around 8 -10 pH with 16-20 ppm NH3 in wash water.We have not found any major corrosion in bundels since last couple of years but looking to this issue and thread which is mentioned by 25362 , i am having doubt that whether to stop NH3 injection in CDU OH for pH control & to start neutralizing inhibitors to avoid NH4Cl sublimation or should we monitor hardness,chloride,NH4HS etc. in our non phenolic wash water ?,One of the intresting thing is that we able to control our CDU Overhead reciver Boot water pH range from 5.5 to 6.5 ( looking to the datas - Only 10 to 12 times it has gone between 6.8 to 7.0 since last 8 months )

Request to advise..

 

[RogerH]

Petro0707
I can come to think about three possible causes for your problem. One is Iron (FeS), oxygen and particulates.
FeS from corrosion upstream that forms a cake/crust on top of the reactor. This should be easily seen when you open the reactor and see the crust layer on the top first feet in the bed.
This one can be counteracted to some extent with size and activity grading on top of the bed. Look into

http://www.topsoe.com

and I guess you can find some info there.Filtering to 5 or 10 um will help but not solve the problem completely since the soluble iron isnt filterable.

The other is oxygen, you mention imported naphtha. this will most likely be saturated with oxygen. A floating roof will not be a full-proof safeguard agains oxygen ingress either. The best way is to have a domeroof tank with blanketting. Have experienced myself a major problem by just loosing the proper gas blanket on an intermediate tank. That shorten run lengths from 3 years down to 4-6 months just by not having the gas blanketting working on the tank. If this is the problem you shold also see a fouling problem on yur feed/effluent exchanger. If you can see a fouling on the hottest HX is is most likely due to oxygen. During next T/A check the fouling on the F/E HX, particularly the hottest ones on the feed side. This fouling will move during the run and can also cause deposits to be "blown" into the reactor.
An oxygen stripper on the feed will help getting rid of this problem. However this is quite costly. The problem hre is to motivate the investment and measruing soluble oxygen in a liquid and avoid contamination is tricky to say the least.
Particulates is an interesting phenomena. The reactor is acting like a large filter, if the particulates are fine enough they will/can penetrate the bed and be dispersed through a large proportion of the bed. Did see this in one application when a recontacing section in the CDU trapped the particulates out of the CDU off-gas into the liquid, these particulates were finally trapped in the reactor fairly deep down the bed and skimming of the top section didnt solve the delta-P problem. An adjacent CDU+hydrotreater unit did not have the same problem simply because in did lack the recontactor. Thats the way we figured out the source. After emptying the reactor we could monitor the dust content in the reactor and we could see that these fines had penetrated the bed quite a way through the bed.Here it is easy to be fooled since during the skimming the fines content go down drastically after 1/2-1 meter and one thinks that the problem area ha been removed. This wasnt the case as we realised after starting up again.
I hope this gives you some more "meat on the bone"
Roger

 

[Petro0707]

Thanks to all of you for your efforts.Fine..That is alright.As we did analysis and investigation for this issue and last T/A also,it is found that upper portion of HNUU Rx bed was almost FeS & Fe2O3..Mostly 70 % FeS.Though we have got PM problem in various Napthas streams as mentioned earlier,we suspect FeS and that too I suspect it should form in CDU overhead circuit which can carry over up to HNUU..that can be the probable causes..though we have taken gaseous+liquid NH3 for pH control,CI,sufficient quantity of Wash water precautions in CDU overhead,still something is missing as far as corrosion is concerned,and what do u think for my another post that is carbon disulfide in Naptha splitter overhead that is inside B/l of HNUU Plant ...since last almost 6-8 months CS2 gets started reporting in N/S overhead (PCN)(from 0.5 ppm to 20 max.)and same N/S out of 4 parallel reboilers -One gets fouled ,so, Is it FeS/Corrosion scales that can come from CDU overhead through Sat GASCON unit and end up in HNUU N/S O/H..or H2S,FeS,CO2,H2O (any reaction with piping or with each other) can form CS2 (carbon disulfide)somewhere...?Can it be linked with this issue...?

Any advise/help is appreciated...