COS LPG Coker

[Hedewandro Lucredi]

We are sending the coker LPG to propylene unit. The COS in the Coker LPG is increasing.
What is it the experience with coker LPG to produce propylene ? How can I reduce COS production in the DCU ? What is it the COS level in the coker LPG ? We have only amine treatment to coker LPG.

[Rene Gonzalez]

You may find the following paper useful, as it discusses DCLN increasing COS content of the LPG product.

Petroleum & Coal 51 (2) 80-90, 2009
UPGRADING OF DELAYED COKER LIGHT NAPHTHA IN A CRUDE
OIL REFINERY
Attila Lengyel1
, Szabolcs Magyar1
, Jen? Hancsók2*

[Hedewandro Lucredi]

Regards. If have more information I will appreciate

[evan]

Hello

I believe the source of most of the COS is derived from the oxygen and sulfur species in the feed. Has something changed in the feed?

Other sources may include
+ O2 from the open drum. This can be reduced by increasing your purge duration, minimum 6 drum volumes.
+ PDMS from antifoam has oxygen species that can be converted into COS. Antifoam injection practices can be optimized to use less and higher MW antifoam can be used to use less as well.

[Hedewandro Lucredi]

The feed is the same quality. The drum purge durations is +/- 4 volumes. The PDMS is 100,000.00 cSt and the rate is 3 ppm based on the feed. What is your experience with the feed quality ? How can I measure it? And our purge duration ? Any suggestion ?

[evan]

Determining oxygen in resid is tricky. I’m not aware of any simple tests but FTIR and neutron activation analysis have been used in labs in research papers that I have read about ashphaltene molecules.

Regarding AF, 100k cSt is middle of the road in terms of MW. You might consider 300k or 600k cSt.

Purge, 6 volumes may help but I would sample to check and determine if the direction change is effective. Come to think of it, I would sample before and after any change to measure its effectiveness.

If you make a change, please let us know on the thread if it works!

[Hedewandro Lucredi]

Thanks Evan. We are finding numbers of COS at non treated Coker LPG of 200,000 ppb up 1,800,000. We are processing a lot of by products in the DCU, like API sludge in the blowdown, flare condensate and Fuel gás from gasoline hydrotreater in the main tower vessel. Also, in the distillation unit we are processing residue from of shore tanks (heavy and light products).

[evan]

Additional comments from Chris Dean…..

Thanks Hedewandro for a very good question,

As previously mention the amount of COS produced is based on the feedstock. With only amine treatment for the LPG stream and/or PP Stream, it is difficult to reduce COS levels significantly or even at all. This could be confirmed by a SRU SME or from an amine supplier or treating licensor. To reduce COS significantly, catalytic treatment beds are used to produce polymer grade propylene as feedstock to polypropylene units.

You mention in the question that Coker LPG is sent to a propylene unit. Is this unit a PP splitter or does it have other treating facilities to produce polymer grade propylene? Most refineries will produce refinery grade propylene and some depending on location will produce chemical grade.

Just for information the typical COS spec is 0.5-1ppm for polymer grade propylene. Chemical and Refinery grades are negotiable due to the customer but COS does affect total sulfur.
Hope this helps

[Hedewandro Lucredi]

Thanks Even
Our propylene unit has a splitter and a final poliment reactor. We produce chemical grade propylene with purity above 99.5 % and the spec is less than 20 ppt of COS. In the final poliment reactor the design was made to treat less than 570 ppt. We have only amine (DEA) and regenerative caustic treatment for coker LPG. Our feedstock (crude oil) change a lot, but we do not observe any reduction in the COS coker LPG yet. What do we need to reduce the COS in the feedstock ? Is it not change the crude oil or even stop to inject offshore residue in the distillation unit ?

[evan]

It is hard to say where the COS is coming from without seeing the lab analysis of the various streams and know exactly where, when, and it what rates is is injected……have you tried sampling the LPG at various points to see where the COS is coming from or where it maybe removed to gauge the effectiveness of the LPG treating?

[Hedewandro Lucredi]

Evan

We do not have methodology to measure COS in liquid stream . Do you have ? Probably the best solution is what you have told before, remove the stream (like residue) and analyse the LPG COS.

[evan]

I do not know of a COS test for liquids but I was referring to measuring the Oxygen and Sulfur species in the liquid feed streams using FTIR and neutron activation.

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