6 replies to this topic

[ROGOR]

 Expansion Tank.PNG   34.26KB   3 downloads

 

I am designing the system described in the attached schematic. I need help sizing the Bladder Tank and the appropriate startup procedure  - pressurizing the bladder tank.  I have not had much luck working with the Bladder Tank suppliers.  Can someone provide me with direction to a knowledgeable (experienced) source?   

[Chemitofreak]

Hope this is helpful.

Attached Files

•  ASHRAE_Journal___Understanding_Expansion_Tanks_Taylor_Proof.pdf   806.51KB   33 downloads

[Art Montemayor]

Rogor:

 

I don’t believe anyone can furnish you with an operating, startup or shutdown procedure without having a detailed, as-built, P&ID (Piping & Instrumentation Diagram) and the ability to discuss a detailed Hazop.  Your PFD (Process Flow Diagram) is too simplified for technical or operational discussion.  We are unable to accurately interpret what is the intent, design, and scope of the system you show.

 

For example, you show something that cannot be a steady-state process: a steam-heated exchanger followed by a chilled water cooler.  No one does this in real-life steady state.  You either heat the circulated water or the chill the circulated water.  You don’t do both operations simultaneously under steady state operation.  Correct me if I am wrong, but I think your operation involves either / or operation of the heating or chilling exchangers.  If that is the case, it is important to indicate this on a P&ID and subject it to a Hazop review prior to final design.

 

I am attaching a copy of the subject ASME article that I converted to a Word document for better reading.  I have used this document in prior designs and I consider it a good outline and general technical description of an expansion (or “bladder”) tank.  Please note the importance of identifying the proper and safe design pressure.  Each expansion tank application is a unique one and should be designed individually.  You cannot logically design or describe your specific system using generalized equations or descriptions.  That is why a P&ID and a Hazop are required for proper, safe design, installation, and operation.  Startup, shutdown, and operating instructions should incorporate Hazop findings.  I am not familiar with Pharmaceutical industry design procedures, but I would certainly apply OSHA and standard engineering procedures and practices.  For example, consider the worst case scenario for each of the exchanger operations.  What is the maximum pressure (and vacuum) possible in each operating case?  You certainly should protect the expansion tank (and the closed system) with a pressure relief valve.  And this is normally not shown on a PFD such as yours, but on a P&ID.  And, as explained, this depends on how you are operating the system and how it is protected.

 

 Understanding Expansion Tanks2.docx   491.7KB   24 downloads

[ROGOR]

Art

Thank you for the feedback.  I appreciate you taking the time to respond and to send the article "Understanding Expansion Tanks", to me.  You are correct in thinking the heating and cooling are either / or type operations.  The transfer water is heated with steam (5barg) and in-turn the transfer water heats the product slurry to 130C.  The transfer water temperature is controlled such that the product slurry temperature is held at 130C for approximately 1 hour.  After the holding time, the transfer water is cooled with chilled water (8C) and the transfer water in-turn cools the product slurry to 30C. I was looking for direction to a knowledgeable source to work with.  I just included maximum and minimum temperatures in my simplified schematic. The pressures in the system are what I am not sure of.  I understand the bladder tank must be pressurized in order to keep the water from boiling during the heat-up process.  Is the air side of the bladder tank pressurized to say 10% higher pressure than the vapor pressure of water at the highest temperature?  Is the water side pressurized at all after being charged with water and prior to turning-on the pump?  Not too worried about the cool-down process.  I understand we will require a pressure relief valve on the system.  The large HX 1 is disassembled biweekly (to be cleaned) and the transfer water loop is drained during this time.  I want to make sure the transfer water loop is started-up safely and properly each time.

[Bobby Strain]

With the requirements you describe, you might consider something other than water as a circulating medium. To keep from losing water during the hot cycle, the pressure should be maintained to keep from venting whatever blanked gas used to maintain a minimum pressure during the cold cycle. In any event, with the closed cycle will want to use a glycol and water solution with appropriate inhibitors. Maybe pure ethylene glycol would be more applicable to avoid high pressure during the hot cycle or losing water.

 

Bobby

[Art Montemayor]

Rogor:

 

Bobby's tips are very good advice and the only thing I could add would be to use Propylene Glycol in the event you are concerned with any leakage and possible slurry contamination pertaining to food-grade contamination (since this is, I believe, a pharmaceutical application).  Propylene glycol is approved for consumable products.

 

Attached is an Excel sketch of what I envision is a more accurate depiction of your setup.  If the setup is accurate, you should have no problem in sizing the proper and safe expansion tank.  Designing the closed system for a maximum pressure equal to 5 barg should not be a big deal and, depending on the physical size, might be done with conventional piping and steel materials. safely containing 5 barg in a 12 inch diameter drum does not require a big tank wall thickness and I would normally use a seamless pipe with two ellipsoidal pipe caps for the tank.  The nitrogen charge you use is not going to be anything but a small amount of pressure - enough to allow for the inerting and for the expansion of the thermal liquid fluid when it gets hot.  You can easily calculate the amount of liquid expansion volume between the lowest and highest temperature achievable.

 

I show a 3-way control valve, but you can use manual block valves.  I don't show any necessary drain valves and by-passes as well as other details.  I think that is your job.

 

If the Excel drawing is not an accurate depiction of what you intend or if there are mistakes, then use flags and Excel call-outs to show what is different or draw your own sketch that can be edited or commented on by our members.  That way, one document is used for the duration of the thread and every member that can contribute is free to generate a revision (as long as it is tagged appropriately).

 

I hope this helps you.

 

 Expansion Tank Application.xlsx   216.41KB   26 downloads

[ROGOR]

Art

Thank you for the help.  The article you sent was very helpful and I have my answer.  Also, the reason I must use plain water is because the large HX1 is disassembled each week for cleaning - fluid contained therein is lost to drain.  The system is then re-charged with water and away we go.