5 replies to this topic

[wojtar]

Dear all,

Could anyone kindly advice me about the following problem:

We have to design storage of liquid butadiene in spherical tanks. The tanks will be filled from railcars unloading station. Butadiene will be pushed to the spheres by means of vaporized butadiene from another section. Liquid butadien from spheres will go to the production unit. Liquid butadiene with required purity will be delivered in railcars.
The problem is that butadiene used in vaporizer contains much more impurities than it is required by the process. Additionaly -> railcars unloading station already exist. The Client is using it for unloading "dirty" butadiene to another part of their plant. Now they want to use the same unloading station and the same pipes for railcars with "clean" butadiene. According to them new pipeline going to the spheres should be connected with their existing system which is now used for unloading "dirty" butadiene and will be still used.

They want me to prove them by some kind of calculation that impurities from pipes and dirty gaseous butadiene will not affect their "clean" butadiene for production. The requirements for the "clean" butadiene are in ppm. Also impurities in "dirty" butadien are specified in ppm. The test methods specified by the process owner are based on chromatography.

Is it reasonable to do any kind of calculation or simulation?
Could the purity of such mixed butadiene be cofirmed for sure even if one could build detailed model taking into consideration volumes of such system?

Regards.

Edited by wojtar, 14 December 2012 - 08:03 AM.

[Rodscott]

Wojtar,

i am doing a project of a new plant that uses Butadiene (BD) to produce rubber. I had the "same problem" that you are having.

To guarantee that our purified BD will has no impurities, i had to separate completely these two system, one for "dirty" BD and another for "clean" or purified BD.

I think that none of the available simulation software can show you if using the same piping that you are using for "dirty" BD will contaminate the "clean" BD.

In some cases you can create a standard operational procedure to clean up the piping before using it to clean BD. But even doing that, you cannot guaratee that your clean BD will be free of impurities.

The only way to guarantee that purified BD is free of impurities would be sending a sample to analysis (chromatography, etc).

Hope this helps you and the others members can show the way to figure out your problem.

Rodscott

[wojtar]

Thanks a lot. This is exactly my opinion but highly experienced production people are arguing with me. They see costs of new separate "clean" system but cannot see the future problems with final product quality.

[Rodscott]

Wojtar,

you´re welcome.

In situations like that, they cannot only think about the maney spent to adapt the system (separate). They have to think about the money that the company could lost if it has "dirty" BD in production (production losts).

Anyway, another way to try knowing the level of contamination on purified BD would be to use the same pipes you are using for "dirty BD" once for purified BD and then take a sample and analyse it (probably the cost of used BD in this operation will be less than the cost of separating the whole system). Whatever the result you found, acceptable or unacceptable impurities, you will have real informations about this issue and you can discuss with everyone involved.

But keep in mind that even if the analysis of purified BD after that shows that is everything okay, you cannot guarantee that in some time later you will not have contaminated BD on your production!

Regards,

Rodscott

Edited by Rodscott, 14 December 2012 - 01:10 PM.

[Dazzler]

G'day wojtar,
A couple of additional points that come to mind that might assist with deciding on best course of action:

A. It is important to understand the type of contaminants, not just dissolved organics, but also possible aqueous phases and solid phases. These other phases can settle in low points and crevices in piping components and my be difficult to flush through totally. Sometimes BD is inhibited and the inhibitors or polymer residues may settle. Inhibitor removal typically involves washing with caustic water solution.

B. If unloading system and lines for products are not separated, then I wonder how much waste flushings will be created (clean BD gets flushed through to dirty BD system) on preparaton of the system for clean BD unloading. It could be a whole rail car, so for this to be a small percent, the total number of rail cars in a clean delivery needs to be many more than this flush amount.

C. If lines and fittings are suitable perhaps pigging could be used to help push through the dirty BD prior to a smaller flush. Would need pig launcher and receivers.

D. Lines could be blown through with nitrogen perhaps, but that can be hazardous particularly when the gas breaks through into the storage tanks.

E. Dual prupose lines is likely to need more automation to prevent stuff ups.

Dazzler

[wojtar]

Thanks Dazzler for your valuable comment.

I don't think my Client would be happy with all those flushing and even pigging proposal. Anyway -> that is an option.
I prefer option "E". Automation, interlocks etc. -> for sure. Railcars would have different nozzles. Since we have separate lines staff mistake would be minimized. But it is only my opinion. Their opinion is different. They want me to prove somehow that after mixing two different butadienes the level of contaminants will be below the limits specified by the process deliverer (consumer of our butadiene).
Both dirty and clean btadiene have the contaminants content specified in ppm. For example:

Acetylene, as vinyl acetylene: 80 ppm (dirty) 20 ppm (clean).
Taking into consideration that thermodynamic models, equations of state etc. are not so accurate, in my opinion we cannot trust the calculations. In other words -> any calculation can't be taken as a guarantee.

Regards.