Managing Coke Drum Foam with Chemicals

[Fernando]

Hello

[Fernando]

– Toxie: Do you know of any refinery that applies back pressure to drum to prevent or mitigate foam rises? Especially while switching to blowdown?

[Fernando]

– Reply, G.L.: Yes, if the facilities are available to apply back-pressure. This can be done to combat aggressive re-foams.

[Fernando]

– Reply, David Williams: The one slide that Evan showed the foam up after switch, the blue trend line is drum pressure. You can see that the pinch valve were closed a bit TI increase the drum pressure to help “push” the foam level back down.

[evan]

Yes, this is a good emergency strategy to reduce foam quickly but you have to be very careful when opening the system back up as the foam can re-appear just as quickly as it goes….

[Fernando]

– Raul Romero: What is your practice for carrier injection: continue or when antifoam application start?

[evan]

Not sure I fully understand your question, please clarify.

Carrier+AF can be injected intermittently based on level provided you are getting good knock down results. However, if the foam is tenacious and not responding the injection, generally people leave it in once started. If the foam layer is growing faster than ‘normal’ then multiple dosing pumps are started.

[Fernando]

– G.L. Says: Has the industry seen scenarios where injected antifoam actually promotes the occurrence of foaming after a drum switch (or “refoam”) via reduction in drum temperature with the carrier flashing?

[evan]

I do not think this is common but could be possible only at a very high flow rates of anti foam. I have never seen it happen but it seems plausible

[Fernando]

– Rajesh: What is the frequency for injection of Amit foam chemical ? And what flowmeter is best ? Should we use mass flow meter like coriolis

[evan]

The flow of AF is done generally with a metering pump and no direct flow measurement. This is most common in older style units. With newer units and more automation, corriolis and direct flow control is a good idea but still less common.

[Fernando]

– Maxi: Its common to use some flow/pressure indications to determine if you are not injecting for some reason (ie: pump stopped accidentally) besides operator check?

[evan]

Because the system is used intermittently, I think it would be hard to put a alarm on pressure or flow because the alarm would be in state when the system is turned off. But if you have a system that would allow you to make the alarm smart and only active when Diane iPhone should be going or at certain points on the cycle then this could be possible. Otherwise the operator can just watch it

[Fernando]

– S.G.: Can AF skid be placed on the top platform to minimize carrier?

[evan]

I’ve only see the skid on the ground. I have seen a emergency injection tank on the cutting deck

[Fernando]

– Parag Soni: Can carrier suppress foam over?

[Fernando]

– Reply, S.G.: No it can’t

[Fernando]

– Reply, Parag Soni: Thank you for the reply. It may be suppress upto some extend.

[evan]

If you are in a true form over situation, the carrier probably will not help. But if you are trying to suppress the phone before the carryover is massive, it might help. But anti-foam in large doses, running multiple pumps simultaneously, is the best that

[Fernando]

– Mayur Vaidya: What is the typical Antifoam dosage used with 60,000 cst PDMS Silicone?

[evan]

60k is relatively low on the scale as you learned in the webinar. Therefore, it is generally injected for longer and higher concentrations relative to carrier. Typically 20-50:1 for 4-6h in the cycle in plants that are using this type of material. What is your dosage and duration? Please share if you can.

[Fernando]

– Mayur Vaidya: What is the impact of 600,000 cst Hi Mol weight injection? Does it have a better performance over 60,000 cst?

[evan]

Generally speaking, higherMW (cSt) antifoam does have better performance. You have to weigh the additional cost vs the additional performance vs your foam needs to come up with the optimum for your site.

[Fernando]

– Freddys: Best location where AF + Carryover mixes should be occur? ground or grade location or cutting deck? and Why?

[evan]

This is a very interesting question and it has come up in one of our most recent projects. Almost all the cokers we have worked with, the carrier+AF is mixed near grade. Then there is a lag between this point and the actual injection point. Moving the mix point to the cutting deck seems like a smart option. Then you could very quickly adjust the dosage ratio.

Has FW done this? Results?

[Fernando]

– Gisela Palmero: From what moment is the antifoam injection recommended and until when? – What is wrong with the fine entrainment fractionator, is it recommended to add a higher flow rate of antifoam until the cause of the fine entrainment is found?

[evan]

There is no simple answer to this question as it was presented. There are various strategies from time to Level based to start injection. But consensus is generally to keep it going after switch until the steam to blowdown has started.

There is always some fines entrainment to the fractionator at the end of filling. Managing over time is the key to long term reliability. But if entrainment for 1 cycle is higher than normal, yes additional AF injection would be a good idea.

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