Sizing mixers for a 98,500 cubic meter crude oil storage tank

[Amir Sedieqy]

I'm involved in purchasing a set of mixers for crude oil storage tank. The tank volume is around 98,500 cubic meter. The main purpose of the mixers is base Sediment & water control (cleaning). Deferent vendors offered different number of mixers with different required horsepower. I'm looking for some calculation or methods to size the mixers myself, so I'll be able to compare these offers.

 

[ChemAir]

I'd look at Penberthy for recommendations on this. They should have methods for calculating what you are doing.

 

[jrmichler]

My 5th Edition of the Chemical Engineers' Handbook by Perry and Chilton has an excellent section on mixing. This book is currently in the 9th Edition with a slightly different title: https://www.amazon.com/dp/0071834087/?tag=pfamazon01-20. Highly recommended.

There is a large difference in mixer size and power between "off bottom suspension" and "complete mixing". You will find that trying to calculate mixer size by theory alone cannot be done. Empirical knowledge is necessary. Mixer manufacturers normally have that knowledge, but even they sometimes learn something the hard way. As an example, I was involved in a project where the mixer manufacturer learned an expensive lesson on the difference between mixing precipitated calcium carbonate and ground calcium carbonate of the same particle size and concentration.

Your best approach is to first study mixing sufficiently to get a general knowledge of mixer theory, such as the section in Chemical Engineers' Handbook. Then go over the quotes with the sales engineers and discuss off bottom suspension vs complete mixing, and what assumptions they made in the quotes. Listen very carefully - are they quoting a large mixer that is larger than necessary, or a smaller mixer that will probably be sufficient.