5 replies to this topic

[rd20]

Dear all,

Good afternoon! I am currently troubleshooting a problem here at our plant regarding our diesel HDS.

We have experienced a recurring valve fouling of the suction and discharge valves of our recycle gas compressors due to sludge deposition. The content of this sludge was analyzed and was found to be mostly Carbon and Sulfur.

I think that there is no hydrocarbon (diesel) carryover and condensation in the recycle gas as there is no observed increase in differential pressure across the tail gas scrubber as a sign of foaming. I have also reviewed the design/sizing of KO pot and have found out that it is within the design limits. Several inspections were already done by the reliability engineers and they reported that the demister in the KO pot is well intact and in good condition (although they found some minimal dirt accumulation).

With this, I am suspecting that the sludge is formed by minute DEA carryover contacting with mist of lube oil from the valves which enhances foaming and then accumulates to form these deposits through time. However, I have no means of verifying this hypothesis.

Kindly post your comment regarding this matter. I am looking forward for your timely response.

[CCR]

hi dear
we have experinced a case near to what u mentioned in our gasoline+diesel HDT, we had a leaks of H2 in the make-up compressor's discharge valve, when we stop that compressor and remove the affected valve we foun black stuff around the valve rings it had been analyzed as carbon (coke) carried over with CCR H2 also this stuffs found in an electrical heater upstream to CCR reduction chamber which lead to short circutes and twice trip of that heater, when we opened the heater we found this black stuff in between the elec. heater tubes.

[Zauberberg]

One thing that is worth to be checked is olefin and diolefin content in your recycle gas system.
I have seen severe fouling in Reformer plant LPG vaporizer circuit (fuel gas make-up), with equipment filled with blackish and foamy stuff (low density resin - something looking like Alien). I don't recall the results of analyses in terms of ingredients percentage, but it was mostly carbon. Fouling was caused by olefin and diolefin polymerization reactions at elevated temperatures.

[rd20]

actually, we have two diesel hydrotreaters. i am wondering why this occur only in this particular hydrotreater whereas both of them are of the same feed and hydrogen quality.

I am thinking that high Cl- composition in the gas might be a factor. However, why does gum form?
Whay was it not knocked out at the suction drum? If it is due to olefin and diolefins, why are we not experiencing it in the other hydrotreater?

Thanks.

[rd20]

sirs, any updates regarding my question? thanks.

[Zauberberg]

Well there is a lot of other data missing, for example:

1. What are the relative flowrates of diesel in each HT reactor, and corresponding pressure drops?
2. Is the catalyst used in both reactors the same, with same bed geometry and performance?
3. What is the age of catalyst in both reactors?
4. Do you occasionaly process some other type of feed, apart from diesel? I remember we had problems when processing pygas from petrochemical plant, containing diolefins above maximum allowed concentration.
5. How do you know the same rate of hydrogen is distributed in both reactors? Sometimes, this phenomenon can occur due to so-called "hydrogen starvation" in the catalyst bed.

I'd suggest you to look for more information at Criterion website (online library) and look for possible explanations. And visit the unit, get some fresh data from the field. These things never happen out of nothing.
Sometimes, a procedure called Hot Hydrogen Stripping can be performed in order to restore catalyst activity and remove gums which have formed on the catalyst bed(s).

http://www.criterion...c_techpaper.htm

Troubleshooting hydrotreating units: http://www.criterion.../PDF/ht_bro.pdf
Hydrogen stripping: http://www.criterion...PDF/HYSTRIP.PDF


Best of luck,