Need help to design an ammonia absorber

[saumian]

We have a 5000 US gal tank for aqua ammonia storage. We fill this tank from tanker truck by air compressor. Filling is finished in 30 minutes. The storage tank has a ball check valve, as a over-pressure release vent.

I want to design an exhaust for this tank with ammonia absorber. I have not been in touch with design aspects of this kind. I would appriciate your ideas for this need.

Saumian

 

[MortenA]

If you dont have in-house facilities you should get in contact with a consult. Stuff from these pages could hardly pass a normal QA review even though there are many competent ppl. around.

Best regards

Morten

 

[CraigTiras]

You shouldn't be filling the tank above 85% liquid level. You should have a level alarm high that stops the filling process. There should also be a tank pressure and tank level indicator at the unloading station.

 

[saumian]

CraigTiras,

Can you tell me why can't we fill more than 85 %, and what information I am going to get by reading the pressure inside the storage vessel.

Saumian

 

[CraigTiras]

ANSI K61.1 is a guideline for anhydous ammoina storage systems and we have adopted it for our aqueous ammonia systems.

It sounds like you are filling the tank so that it opens the relief valve and over flows with liquid. You should stop filling at the 85% level, per ANSI K61.1, and also display pressure at the unloading station so the operator can be sure not to open the pressure relief valve.

By doing this, you won't need an ammonia absorber.

 

[saumian]

CraigTiras,

I appriciate you for your information.

The situation is this: Our storage vessel is a closed one except the safety vent. i.e. in addition to inlet and outlet of the vessel, we have a duct with a ball check valve going from the roof of the tank through the roof of the facility to a small stack. The inlet and out are closed most of the time. For normal day to day operation, we do not need any exhaust at all.

Ammonia gassing occurs only during fill ups. The rating of the ball check valve says: "Maintain at least 30" of head pressure to prperly seat the ball". This means that anything less than 30" head pressure will keep the valve open at any time.

Literature says that we should have a safety valve in addition to a conservation valve. For normal procees-emptying the tank- we don't want any consevation valve because we do not have any concern like ammonia vapour or loosing the activity of aqua ammonia.

Will you suggest that we should have a pressure relief valve instead of a ball check valve?

It looks to me that using air compressor to tranfer AA causes for this gassing during fill ups.

Saumian

 

[CraigTiras]

Saumian,

I would go to this website:

http://www.ifsolutions.com/ifs/gp.n...ge=pnoxredprods;title=NOx Reduction Products;

and click on aqueous ammonia unloading station & storage/forwarding system. Then download the pdf file. That file has the P&ID that we use for these systems.

I'm not sure I understand your system completely. It sounds like the ball check valve is always open except when you fill the tank.

 

[jwalker2]

Aqueous Ammonia storage usually has a very small scrubber attached, made from a 300 mm NB pipe with about 2 m of 15 mm Pall Rings. The scrubbing solution is then a very small, say 1 m^3/h trickle of water. This scrubber only takes care of general tank breathing due to diurnal temperature swings.

For "Air Pad" discharges the gas flow from the displacement effect is low during the filling step but at the end there is usully a great surge of gas flow. If you use this approach the little scrubber described above will flood and the packing will very likely be pneumatically conveyed into the air. For such transfers a larger diameter is required just for this end of transfer surge. The liquid rate needed is then much higher and so a recirculation system is then required. For such systems a dilute acid would be appropriate to maintain a low ammonia vapour pressure over the solution.

Incidentally did you check if the explosive region is formed at any time between the air and ammonia?

An alternative transfer method is to use back venting. The tank vent is connected to the tanker top. The tanker's pump or your own is then used to pump across the liquid. The displaced gas then goes back into the tanker. You can then go back to using the little scrubber again.

Refer to scrubber vendors in your area (try

http://www.koch-glitsch.com)

and your ammonia supply company. Ensure that the installed equipment is properly designed and that a thorough hazard assesment is conducted.

Disclaimer - this is a personal posting only. This advice is given "Without Prejudice".

 

[saumian]

CraigTiras,

Thanks. Our installation is not a pressure storage installation , but it is a atmospheric pressure installation.

The ball check valve's arrow is pointing upwards in the vertical duct. This means that this valve is there for safety in case pressure builds up too much. This valve will be open if there is too much pressure inside the vessel. The valve always remains closed, or partially closed in normal operating times. This is why we dot have any ammonia vapours released or any loss in the strength of ammonia stored.

Therefore we are planning to have an exhaust blower connected to the spare opening locatd at roof of the tank, with a bubble chamber connected to clean the exhaust, dedicated only for fill up purpose. This secondary duct will be closed always, except during fill ups. We have to do this unless we change the bulk delivery method to our storage tank, to tranfer pump instead of air compressor.

Saumian

 

[CraigTiras]

Saumian,

I would follow jwalker2's advice.