3 replies to this topic

[victorvikram]

Dear All,

 

I am given a design task on unloading nitric acid 68 wt.% (NA 68) (SG = 1.405) from a tanker truck of capacity 33 m³ to a Nitric Acid storage tank of FRT type.  The content is to emptied via a pump to the nitric acid storage tank.

 

The concerns are:

 

a) Can I assume the tanker truck comes with a dedicated PD pump?

b) I have been told to consider a centrifugal pump to unload the NA 68 to storage tanks assuming PD pump is not attached to the tanker truck. Since the tanker truck is required to be emptied, a centrifugal pump may not be a good option.

c) If PD pump comes with the tanker truck, should I contact the tanker company to obtain the PD pump specs, i.e. pressure discharge, etc.?

 

Your opinion is highly appreciated. Also, could you please advise on reading materials that I can refer to when it comes to tanker truck loading and unloading design?  It would assist me in my design work.

 

Thank you.

 

Regards,

Victor

[Pilesar]

When you are paying for delivery, you can set the specifications which can include the unloading equipment. Contact the product and tanker vendors to coordinate in advance what are reasonable specifications. 

[Art Montemayor]

Victor:

 

You ask for our opinion and I will gladly furnish mine.  I’ve done this before and I recognize the installation as a potentially hazardous one and its serious design and implementation should be done at the highest level of safety and engineering.

 

Pilesar is absolutely correct.  YOU are the purchasing client and it is up to you to specify to the transporter whether a pump should be supplied on the tanker truck.  You should not be assuming anything on a project of this importance.  Your basic Project Scope of Work should clearly denote that in detail.  That is what a Scope of Work is supposed to do.

 

Who told you to “consider” a centrifugal pump?  Was it your boss or an authoritative supervisor?  What is meant by the term “consider”.  If you are going to design and implement a nitric acid unloading system, your Scope of Work should already be prepared, reviewed, and approved.  The type of pump should already be resolved and specified.

 

Please explain how you have arrived at the conclusion that a centrifugal pump will not “empty” the tanker truck - but a positive displacement one will.  Is this something that is also being assumed?  For your information, neither type of pump should be expected to fully deplete ALL the nitric acid out of the tanker truck and into the main storage tank.  There will always be residual nitric acid left in the suction, pump casing, discharge lines, etc..  Are you familiar with the operation of a liquid transfer system?

 

Additionally, are you familiar with the characteristics of a positive displacement pump and its operation?  What makes you think that there is a certain discharge pressure associated with the positive displacement pump?  Are you aware that regardless of the type of pump you use, the discharge pressure (as measured at the pump’s outlet nozzle will always be the same?  Pumps generate flow, not pressure.

 

What kind of PD pump are you referring to?  Is it a gear, piston, or paddle type?  Please be specific in your terms.  Don’t use acronyms without identifying them.  This leads to a lot of confusion and erroneous conclusions.  For example, what do you mean by “FRT type”?  Do you mean a Floating Roof Tank?  Or do you mean “FRP” (Fiberglass Reinforced Plastic) tank?  I would never use either of these types of tanks on nitric acid service.

 

There are a LOT of specification and safety issues involved with this proposed operation and I hope that you have had preliminary design, layout, and operating instructions already reviewed as well as a preliminary hazop.  I think the best way for our expert members to give you their best help is for you to inform us fully on what you are proposing, why, and at what stage of engineering you presently find yourself at.  Your experience in all this would also be of help to orient us all to your needs.  Please respond with as much detail as you have available.  Refer to the attached document.

 

 Transporting_Nitric_Acid_in_Tanks.pdf   2.99MB   44 downloads

[Mahdi1980]

Victor,

Following the correct comments of my friends, please note that Positive displacement might be an option. Anyhow, centrifugal pump can also be applied for your case and you can use some protection devices like an on-off valve or an inline level indicator to trip the pump and avoid cavitation through it.

positive displacement pumps may have the limitation of flow rate and in some cases low viscous liquids cannot be simply transferred by them.