Increased nitrogen content

[Milutin]

Hi all,

If nitrogen content is increased in naphtha reformer feed, hydrogen content in reformer recycle gas will be increased.
One of negative effects will be deposition of NH4Cl on reformer equipment.

What is reaction mechanism which cause increased hydrogen content in recycle gas and how it going to impact reformate properties?


Regards,

Milutin

 

[25362]

Just thinking aloud,

Increased hydrogen in the recycle gas: one reason could be that the neutralization by ammonia of the catalyst acid sites depresses more hydrocracking reactions than it does to isomerizing and dehydrocyclization reactions. As a result less hydrogen-diluting gases are produced.

Hydrogen-hydrocarbon ratio: a higher ratio may adversely affect the equilibrium aromatic formation. It also affects the reactants residence time. Economics, ie, costs of circulating and heating the gas to reaction temperatures dictate to minimize this ratio without jeopardizing catalyst life.

Specifications call for nitrogen to be below 0.5 ppm in the reformer feed.

Please correct me if I'm wrong.

 

[Milutin]

Hi 25362,

You are right, nitrogen specification for reformer feed is 0.5ppm, but we had 4-5ppm.
Our naphtha HDS is very limited in denitrification. Usual nitrogen content in HDS feed is around 1-2ppm, in such case we have 0.5ppm in naphtha for reformer, but recently HDS feed nitrogen content was 8-5ppm and outlet was 4-5ppm.

In this case with higher nitrogen content in reformer feed hydrogen content in recycle gas jumped significantly, from 72vol% to 81vol%.
Your explanation for increased H2 content seems logical.

What would be effect on reformer yields and catalyst if from some reasons water (moisture) content in recycle gas is increased?

Regards,

Milutin

 

[25362]

Could you tell me why should water content in the recycle gas increase ?

In general, increased water contents, beyond a minimum quantity (10 to 30 ppm) to avoid excessive demethylation, will affect differently in the short and in the long term.

An immediate effect would be to reduce reformate yields, and at the same time also reduce the hydrogen content of the recycle gas from the increased production of C1-C4 hydrocarbons due to the intensification of the catalysts' hydrocracking activity.

But in the long run it will act in the opposite way, ie, reducing the acidity of the catalyst by removing the organic chlorides added to compensate should there be too little natural chloride in the feed.

Sometimes water is added to a feed that contains too much chlorides, namely to reduce the excess from the catalyst. This operation is done simultaneously with a drop in reaction temperatures.

Typical feed chloride levels are about 0.5 to 2 ppm wt., and the water content in the recycle gas should be optimized for a particular catalyst.

 

[Milutin]

I will try to tell you whole story.
First we have problem with increased water content in recycle gas, as explained to much methanol is added. Methanol dosing is decreased and water content started to decrease.

Few day after that nitrogen content increased in HDS/reformer feed.
We immediately checked crude unit dosing neutralizers and inhibitors, but crude unit was not source, and no slop is added to crude oil.
To check crude oil we cut from crude fraction 60-180degC, and nitrogen content was also increased.
To check if crude oil is contaminated in pipeline, crude oil is tested from samples taken from tanker, an same results obtained.
Crude oil from different supplier (also different crude oil type), with different route of supply also has increased nitrogen content.

In this period of testing we have this increase of hydrogen content in recycle gas.
To cope with this situation we increased chloride injection and decrease temperatures in reactors.

Ten days after that all samples in same moment has "normal" nitrogen content (naphtha from crude unit, HDS and reformer feed), what is my opinion impossible because naphtha go first to two tanks and from tanks it is routed to naphtha HDS. It is necessary some time, if naphtha in tanks has increased nitrogen content, to be replaced with fresh low content nitrogen naphtha.

We increased reactor temperatures and all went to normal, hydrogen content in recycle gas, octanes etc..

This suggested me that lab testing was not so accurate and can be source for confusion.

But yet not sure what caused jump in hydrogen content in recycle gas, nitrogen or water.

Regards,


Milutin

 

[JJPellin]

I will apologize in advance as a mechanical engineer wandering into the chemical realm. But, a few years ago we had a problem with salt development in a Platformer recycle compressor. It was associated with nitrogen. The source of the nitrogen was found to be a wash water stream. Someone had changed from boiler feed water to stripped sour water to reduce the cost of the wash water. The sour water contained nitrogen. We had to revisit our source of wash water to several units to be sure this would not happen again. This may not be relevant to your situation. But I know it was very difficult for our process engineers to find this tricky source of nitrogen.

Johnny Pellin

 

[Milutin]

Dear Mr. JJPellin,

Thank you for shearing your experience with us.
Nitrogen in reformer feed going to convert to ammonia, and react with chlorides to form ammonium chloride. Reforming is "dry" process and no liquid water exist to wash ammonia chloride deposited salts. Salts will usually accumulate on compressor valves and column trays.

As you guess it was not our case, but thank you for your reply which is also useful for all interested in this subject.

Regards,

Milutin

 

[RogerH]

Gents
The nitrogen do affect the water-chloride balance on the catalyst so it will be a "cat on the rat, raot on the on the rope" effect. When (this is a few years back) we got higher nitrogen content in the feed, we added some extra chloride to counter balance the distorted Cl-H2O balance on the catalyst. Out of the catalyst system towards separator/compressor etc one can get deposits. Prolonged periods running like this one might have to do a compressor wash (with condensate)