Cold Box HE

[liberoSimulation]

Can any one give his experience or opinion of having a filter (or strainer) on all entering streams to a Cold Box HE made of Brazed Al material.
If having filter (or strainer) is very important, do you strongly recommend of having a spare one
The application I have is a big cold box to b installed in an ethylene plant.

Cheers

 

[cryotechnic]

I don't think you need one, but it depends ofcourse of the (pre)purification of your feed gas.
In our ASU, we only have filters in the air inlet from the aircompressor.
After that, the air passes a molsieve. No filter/strainer is installed after the molsieve.
At normal operation, the molsieve mass will not give much dust/particals who will be transferred to our coldbox.
We have Aluminum plate-fin heat exchangers, and never have problems.

Ofcourse you can also consult Linde Engineering, they are designing also Ethylene plants.

Good Luck
Cryotechnic

"Math is the ruler of your potential succes...."

 

[Montemayor]

liberoSimulation:

cryotechnic is correct; it all depends on your type of process and what upstream unit operations you are employing prior to entering your cold box. I've operated, modified, installed, and upgraded quite a few cryogenic operations in my time and I would never accept an adsorption unit (such as a mol sieve) without a carefully engineered filtering system on the outlet, prior to entering the ASU. In fact, the filtering system should be spared. No one - no matter how careful the operation is - can garantee that there will never be any adsorbent dusting or attrition. It it just blue sky engineering and pipe dreams. All adsorbents will dust - to some degree. The best policy is to be aware and prepare for it by proper design.

You should evaluate and analyze your upstream purification and other processes for possible solids, liquids, or other impurities possibly getting through. Filters won't do a thing for liquids or gaseous impurities (like CO2), but they can protect against solids - especially dusts. Take it from someone who's had to shut down a cold box, defrost for days and then have to open the cold box up and try to locate the suspected pluggage: don't leave home without a filtering system before your cold box!

Art Montemayor

 

[liberoSimulation]

Thank you guys for your replies

The cold box in current plant that is under basic design, is located at an ethylene plant, where many streams (process gas, refrigerant ethylene, refrigerant propylene, and other internal streams) entering and leaving the cold box that is brazed aluminum heat exchanger.

Now, we have got a filter with spare after the process gas being dried with a single strainer for this stream at inlet of Cold Box.
Other streams from refrigerant ethylene and refrigerant propylene are coming from a closed refrigeration loops and have single strainer at their inlets to the Cold Box.
Other internal streams are without strainer.

I'm still wondering if all streams to the Cold Box shall be provided with a strainer. If so, shall we provide a spare or a bypass for these strainers?

I heard that not only the process feed or quality causes the pluggage but also carbon steel piping can generate pluggage stuff during plant upset or after long time of piping life.

Any added explanation is appreciated

Cheers

 

[Montemayor]

Libero:

I don’t understand your wondering (questioning) the lack of a filter/strainer on a recycle or internal stream. Once the outside stream are filtered and free of any foreign substance, there should be no more concern for pluggage occurring in the system – especially the brazed aluminum heat exchanger. The only way a recycle or internal stream could present a plugging threat would be if the system inside of the cold box can contribute the subject contamination. I don’t think this is a feasible or credible scenario if your cold box components are made of stainless or other exotic material – as I believe it would be.

I’m going to take your comments based on your title of Chemical Engineer and say that it would be difficult –if not impossible – for you or any other ChemE to explain how a carbon steel line that only transports a pure hydrocarbon can undergo corrosion or other decomposition due to “piping life”. Here, I’m defining the pure hydrocarbons as those you identified: ethylene, propylene, methane, propane, etc., etc. It just is not credible. There is nothing magical about what hydrocarbons can do to carbon steel: essentially nothing – IF THEY ARE PURE. If they are contaminated with water, H2S, CO2, etc., etc., then that is out of your basic scope and doesn’t apply to this thread.

My main point is: concentrate on the real issue of protecting the brazed aluminum heat exchanger and the rest of the components inside of the cold box under the conditions of credible process operations. Do this by concentrating on operating an efficient purification train (this includes adsorbers) and installing TWO (one as a standby spare) efficient and proven filter/strainers before the cold box. You should operate the filters with a dP alarm/switch that allows for manual inspection and switching. Never put a by-pass on this type of important filter system. This is analogous to being a "little" pregnant. You either filter 100% of the time or you don't filter at all.

You haven’t stated if you represent the designer/constructor of the unit or if you are on the client’s/end-user’s staff. If you work for the contractor, you should be lobbying the client to kick in enough money and effort to ensure that a proper safeguarding of the cold box is done at the final design – for his/her benefit and profit. If on the client’s staff, you should be championing all efforts to ensure that the cold box will never be invaded by any substance foreign to the process because it poses a serious threat to the success of the unit. But the envisioned hazards should be credible; otherwise, people will get the impression that you’re pushing “Chicken Little” politics and they will disregard you.
Good luck and safe engineering.

 

[liberoSimulation]

The situation I am evaluating needs ethylene expertise not any one can give long speech with no end results.

I'm still looking for better answers.

Anyway, thanks for the effort you exerted in writing your reply

Cheers

 

[sshep]

liberoSim,

We don't filter these other streams (hydrogen, methane, C2R, C3R, etc) in our cold boxes. The benifits are not felt to be worth the filters, valving, venting and (possibly) relief requirements to have a filtration of these cryogenic streams. Most plugging problems seem to be on the charge gas side anyway, and are usually related to components which freeze in the process. The "cold" streams won't usually suffer from freezing problems because freeze outs are are generally a "hot" stream issue (note hot and cold definitions are relative to cooling and heating respectively). Freezing problems are usually start-up or upset related (like acetylene converter and drier problems) and cannot always be filter out upstream- they are typically remediated with methanol or other suitable antifreeze. I think if your feed treatment is good then you are following typical practice not to filter the other streams in the feed chilling area. This is just my opinion.

I am curious where your acetylene converters, acid gas treatment (CO2 scubber), and driers are located in the process, and what streams are being cross exchanged in your cold boxes.

best wishes,
sshep

 

[liberoSimulation]

sshep
sshep
I agree with you that having strainers (with bypass or spare one) makes life difficult due to the implications you mentioned.
I can understand from you that your experience for cold box in ethylene plants doesn't have strainers for entering streams and there is no need to install such strainer for these streams.
But in start up, we have got one strainer crashed and many were plugged in previous experience.
One strong justification of having strainer for all entering streams is that during the start up of the plant or sometimes in events of upsets.
The cold box is located downstream of dryer, caustic tower and a filter. Methanol is provided for some straimes to do anti-freezing.
Thank you for the feedback

Cheers

 

[Zoobie]

Our coldboxes were installed with screens on all the inlets (30 yrs ago). This was primarily a start-up concern and I think most were removed after start-up. I would agree that this is a necessity as aluminim plate fin exchangers will not fair well against any sort of junk in your stream. We however do not have by-passes installed and I probably wouldn't put them in if I was building the plant again...but that may not apply to your process. One other thing that was specified was MSF (mill scale free) carbon steel pipe. It wouldn't take much to block a channel in one of those exchangers.

 

[Samiran]

liberosim,

We operate one of the largest LNG Trains in the world. And, our situation is similar to yours. We do have strainer on the feed and refrigerant side going into the cold box.

Having the strainers is often the manufacturer of the cold box prerogative. Understand that cold box is one of the expensive equipment in your plant and very difficult to repair.

Spare strainers (never any bypass) are not justified - because typically of the size & frequency of plugging. Typically, you monitor the dp across the strainer and if it reaches alarm you may wish to "defrost" the strainer to remove the HC/CO2/Water plug.

In general "sparing" is a philosophy a company adopts based on economics. Ever think of why we have 2 kidneys but 1 heart (with no filter at suction) - need to understand God's philosophy!

Samiran

 

[Montemayor]

Samiran:

Excellent kidney analogy! My philosophy and feelings comply with this example of the ultimate in all engineering.

 

[liberoSimulation]

Thank you all guys for the contribution in this interesting subject.
I will let you know when we decide on the situation we are currently evaluating.

Cheers

 

[sshep]

An inline (i.e. cone style) start-up strainer seems a reasonable precaution -sshep

 

[jalvarez]

Libero:
Brazed HE's use to have mechanical problems at high defferential pressures between their streams. And this problem could be serious during startups, if the plugging of the filters are combined unfavorably. You may have already taken this into account, but I mentioned just in case... specially if having different suppliers for the design...
Good luck
J. Alvarez

 

[hazel]

I'm abloulately agree to Montemayor, you should have a strainer before Cold Box.
You can not image how the operator will do it during operation. After the turnover, the carbon steel will some rust from pressure test, it is the exprience I has. If these dust go to the Brazed HE's , it is difficult to blow them out.