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I am currently working on fixed bed platforming unit. The unit is Semi-regenrative catalytic reforming. The unit was commissioned on 1989. The unit is designed for Arabian light crude heavy naphtha. We have processed, Iranian light naphtha, Murban naphtha. Currently we are processing Arabian super light naphtha. I see that, the reactor delta T's are high enough (more than the one when process arabian light), but gases production increased, hydrogen purity is between 70 to 43% and reformate yield is OK but RON decreases. The water chloride management is in range. With this, recycle gas compressor discharge temperature and pressure increases as gas production increases. The discharge temperature are so high (200-230F). Common discharge header pressure also increases. As recycle gas flow increases, reactor effluent trim cooler which is before HP separator temperature increases. The temperature must be in range of 100-105F. The current temperatures ranges between 120-140F.

What could the reason's of above query. What action should we take to resolve these problems.

Dec-2023

Answers

Hamza Ali Rajput, NFC IET, Multan, cenfcu.1998@gmail.com

I am the same person who asked above question. Sorry there is mistake, the gases production decreases and hydrogen purity also decreases. While sulphur and nitrogen are in limit and moisture and HCL is also in limit.

Dec-2023
Marcio Wagner da Silva, Petrobras, marciows@petrobras.com.br

This is a relatively common situation faced by refiners which operate with semi-regenerative catalytic reforming processing units. To describe the phenomena that is occurring in this processing unit it's important to remember some concepts of the naphtha catalytic reforming process. In my response I'm considering that the both naphtha are free of contaminants which can reduce the activity of the catalytic beds, especially considering which is a semi-regenerative processing unit.

One of the most relevant reactions which is carried out in the catalytic reforming of naphtha is the paraffin dehydrocyclization which involves the conversion of paraffin's in aromatics which contributes significantly to the octane index of the reformed naphtha. Unfortunately, these reactions are extremely slow and it is necessary to offer adequate residence time to ensure that the paraffin dehydrocyclization reactions occur.

Considering the scenario presented in your question, I understand that the change of naphtha from AL (Arabian Light Crude) for ASL (Arabian Super Light Crude) is raising the paraffin's content in the feed of the catalytic reforming unit and a highly paraffinic feed is very hard to processing, especially in a semi-regenerative unit.

Long chain paraffins (as tends to be the case of ASL crude naphtha) tends to suffer hydrocracking which involves the reaction of the paraffins with hydrogen to produce methane, ethane, and propane. These side reactions can be responsible for the reduction in the octane index and hydrogen purity which is mentioned in your question, especially considering that paraffin hydrocracking is a quick reaction in comparison with paraffin dehydrocyclization.

To minimize this problem, it's possible to consider use a blend of naphthas in order to control the paraffins content the catalytic reforming feed, a very good factor to control the quality of the feed is the N + 2 A (Naftenics (%Vol) and Aromatics (% Vol)) parameter which should be controlled in the range required by the processing unit licensor.
Another key factor is the initial boiling point of the naphtha feed, the IBP upper to 160 F is recommend for semi-regenerative catalytic reforming units once avoid the paraffin's hydrocracking which normally is favoured in high-pressure naphtha reforming which is a characteristic of semi-regenerative processing units.

My suggestion is to carry out a complete characterization of the naphtha feed from ASL crude to determine the paraffin content, IBP and N + 2 A parameters which should help to understand what is occurring in your processing unit. As mentioned above, a naphtha blending with a heavier naphtha can help to solve this situation.

Dec-2023