5 replies to this topic

[shem]

Hi, my first post

What is the practice in storage of Ammonium Hydroxide 28-30% indoors in a temp controlled room at 65-70F? Tank has not been built so mawp and mawv can be made to suit. Location is California. Tank is under 2000 gallons.

Tank will be closed with p-v venting to contain vapors and vent any p vent discharge to pipe away system. Filling will be by a vapor displacement back to tanker.

In particular, what is the recommended p-v vent settings for such an application?

What about provisions for worst case scenario:

Tank rupture and spill?

Fire in room and use and setting for emergency vent?

Pressure rise if temp reaches bp?

Thanks!!

[Art Montemayor]

Shem:

I can’t cite specific national or local regulations on storage of Ammonium Hydroxide at this moment – although, with enough time I could come up with some documentation. However, I have done this in the past and I have some recommendations that I can recall:

1) Quickly and expeditiously, obtain all your local regulations on this storage – specifically for hazardous chemicals;

2) If you are trying to keep the hydroxide from absorbing CO₂ and atmospheric moisture, you will probably have to blanket the tank with something like dry nitrogen. If so, then take that into consideration and mechanically design enough MAWP and MAWV to give you a decent and ample dead band for your instrumentation on the tank levels and pressures.

3) Raise the tank on legs – well above the floor level. This will be expensive – but it is safer and gives you the ability to ensure that any bottom leaks or seepage is caught in time. Local Regs may already have taken this into consideration.

4) Try to avoid any indoors storage of this hazardous chemical. I know that this may be impossible to avoid for your application – but always bear in mind that the basic decision to take a hazardous bulk, liquid chemical like this one and store in indoors carries a heavy trade-off --- and it doesn’t necessarily mean just capital expenditures.

5) Construct heavy, traffic controlling barriers around the tank. Do not allow any fork lifts (similar heavy equipment) near the tank. Any threat to rupturing the tank walls or bottom is a potential for disaster because one can never guarantee that there will never be human beings present indoors during such a catastrophe. Not enough can be said about this subject. The storage building should be totally controlled in access and in quality and quantity of human beings at any one time.

6) Build a porcelain dike around the tank to contain any spills or leakage – with a positive, gravity chemical drain to a chemical sump outside. You cannot afford to be lax about caustic spills. This stuff will cause severe damage to human tissue and some of the damage is irreversible. Complete chemical suits and hoods should always be available around the tank. Safety showers and eye wash stations should be always available about a maximum of 10 feet away – and fully maintained and certified to be 100% operable, 100% of the time.

7) The tank and all interconnecting piping, pump(s) and other related equipment should be inspected and mechanically rated as 100% operable on a timely schedule – I would recommend no more than 3 years apart.

8) The area should be fully and safely lit with safe lighting;

9) The area should be fully ventilated 100% of the time and equipped to capture any ammonia fumes that may be evolved due to spills or leaks.

10) Fully leak-proof valves should be used to ensure no stem packing leakage.

11) The pressure-vacuum vent settings for such an application will depend on what you specify for your tank as fabrication specifications. Be conservative and allow sufficient metal thickness for corrosion as well as mechanical integrity and a wide dead bank for your instrumentation. Refer to my spreadsheet for tank pressure settings that I have posted for downloading on other threads.

12) The worse scenario you can have for this situation is not a fire. It is a sudden and catastrophic spill of hydroxide unto the floor and the surroundings within the building. To protect humans within this situation, it is not enough to equip them with chem suits and boots. One positive step to take to give a human a decent chance at survival under the worse scenario is to dike the area under the tank and construct structural steel elevated walkways with grating and safety rails. Your personnel are kept at least five feet above the floor level during normal operating checks and procedures. All electrical equipment should be also installed in an elevated position. Vertical, extended shaft, line pumps are desirable for this.

13) Use only instrumentation that avoids any need for human entry into the tank - such as radar (or microwave) level indicators and controllers. Do not use any glassware for level detection. Try to maximize all your nozzles (except the one drain, of course) to enter and exit through the top. This avoids any nozzle and valve leaks. This may involve a submerged vertical pump - but it may be worth the investment to avoid leaks and exposure to caustic during normal operations. Ensure you have redundent level detection at all times and that you will NEVER OVERFILL the tank.

There you have just some things that immediately come to mind that I have employed in the past. Do not under-estimate this common, easily obtained chemical. It can cause grave and deadly results if not designed and handled appropriately and safely.

Good Luck and take care of your personnel!

[shem]

Art, thank you for your timely reply.

I understand what you have said. Blanketing is not required. The tank will be buttoned up to prevent vapors in the area. Pressure venting will be to a vent system. Vacuum vent will be set low to respond to pump off, etc.

Can you tell me what the pressure would rise to should the bp be reached? (To size venting.)

I was not able to find any regulations for this material other than the MSDS. It is not classified as hazardous nor flammable/combustible. So I was going to size venting by API 2000 which will oversize but with small tanks, that is not a big issue anyway.

[Art Montemayor]

Shem:

Your conservation vent (PVSV) is probably going to have to handle the Fire Case – if that is a credible and realistic scenario in your application. If that is the case, then plan on working with a reliable and experienced PVSV vendor – such as ProtectoSeal. Meet or discuss with them your application and the fact that you both know that in the event of a fire, the water portion will generate steam but some ammonia vapor will also be generated. Find out if you can obtain an idea of the decomposition rate of the hydroxide into a combined steam + ammonia gas mixture. ProtectoSeal may have done this one before and have the answer or may be of help in obtaining data. In any event, we both know that your tank is relatively small (thank goodness) and that PVSVs are very relatively cheap equipment in the sizes you will be looking at. You are correct in your assessment of using API 2000 (which is what you should be using as your design guideline for the tank) and that the oversizing of the PVSV is a small issue. You should target a conservative sizing for the PVSV and associated piping as your goal. I would estimate a 100% oversizing as reasonable in consideration of what we know about the fluid in question and the associated decomposition product. You may also opt for a separate, emergency vent when you discuss your application with the supplier. In similar cases I have applied the emergency vent as an independent, additional safety device on such tanks. This is the type of redundancy that I was referring to. This is not simply “ass-covering” type of design; this is to ensure that you and everyone else remains safe and protected up to and including the worse scenario.

In the event of a fire that raises the fluid to the boiling point, the pressure in the tank should remain stable and equal to the setting on the PVSV. In other words, that is the condition for the sizing of the PVSV – it should handle all the vapors generated during a fire and allow them to vent out safely without raising the pressure in the tank above the set point. There is something good about having a liquid fluid in the tank during a fire: it buys you time to get out of harm’s way. The liquid (water, in this case) serves as the heat sink that absorbs the heat from the fire and thereby keeps the tank walls relatively cool by consuming the heat and converting the liquid to vapor (steam). It is when the liquid has all boiled out that the tank is in danger of mechanical collapse and failure – not when it is filled with liquid.

We both know that caustic is not classified as being hazardous. That is a political and not a chemical nor an engineering classification. You and I both know the real facts about human tissue exposure to caustics such as Ammonium Hydroxide and Sodium Hydroxide. Persons who have lost eyesight or have had to undergo serious and painful skin grafts in the past due to caustic spills know all too well the deadly consequences of such tragedies. We don’t want to go there – ever!

Do not forget to post clear and readable warning signs around the building stating that caustic is stored inside. In the event of a fire, outside firefighters need fair warning of what they face inside.

Good Luck.

[shem]

Art, I thank you so much for a thorough analysis of my issues. You have reinforced what I knew and added to that. I have always enjoyed your posts in the past and look forward to reading yours in the future.

I feel comfortable with the issue now and can proceed with confidence. I hope your "good luck" at the end was a social comment

[Art Montemayor]

Shem:

You are very welcome.