Liquid-Liquid Static Mixer 1

[Brandon181]

I am evaluating two quotes on a Liquid-Liquid Statix Mixer. My conern is that one company is quoting a calculated pressure drop of 0.83 psi while the other is quoting a pressure drop of roughly 8 psi during normal flow. The first company (0.83 psi) has quoted one less element and is about half the price of the other. My company has had dealings with the second company so we feel confident we can trust their calcs. However, they are always a little pricy. My worry is that the first company is not providing adequate mixing which would explain the lesser pressure drop. If the first company CAN provide adequate mixing, I would like to go for their lower price. However, I am at a loss as to how to quantify the mixing. Is there a unit of measurement for this? Is there a comman way to quantify that the two fluids have been fully mixed so that I can get confirmation from the vendor that this is taking place? It simplay an efficiency rating? Any comments about what else could cause the differing pressure drops would be helpful as well!

Thank You in Advance!

 

[Latexman]

Theoretically, fully mixed is never achieved. We typically specify 80, 90, 95, 98, 99, or 99.99 % homogeneity. It depends on how important is it to the process. You can specify whatever you need. Pressure drop will depend on the element type and L/D you buy. Some companies market low dP elements pretty hard. Ask them what % homogeneity the quoted mixer is.

Good luck,
Latexman

 

[zdas04]

Latexman,
I've often wondered about how you measure homogeneity. I was thinking that you would take samples a fixed distance from the mixer and compare samples separated by a fixed time. Is there a better way? I'm assuming that for the percent number you are taking a specific parameter like SG or conductivity etc. and getting the delta from a theoretical 100% homogeneous.

David Simpson, PE
MuleShoe Engineering

"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.

 

[Latexman]

I am most familiar with how Chemineer does it on their Kenics mixers. They use a volume concentration of a component. They call it "coefficient of variation", or CoV. It is discussed on page 7 of Kenics Brochure Their normalized CoV = 1 - % Homogeneity/100. % Homogeneity makes more sense to me, and it's easier for me to remember.

Good luck,
Latexman

 

[Brandon181]

Latexman,

Thank you for your response. This is exactly what I needed. Now I can request homogeneity numbers from both companies and either disqualify the cheaper one or prove that it satisfies our specs. Like you said, the pressure drop should largely be determined by L/D, and both companies are quoting near the exact same dimensions. So it leads me to believe that the pressure drop difference is caused by the number of "baffles" in each element, ie the first company is not providing as many as the second. Perhaps this is an incorrect assumption but I think you have led me in the right direction for making a decision.

 

[jmw]

Interesting points raised here.
ISO 8217 2005E is a standard for marine fuels which says that the fuels shall be fully homogeneous.
Unfortunately they don't say what they mean by homogeneous, not a whisper, and no indication that true homogeneity is a pipe dream. (especially with marine fuels).
Nor do they indicate how this should be tested.
There are samples collected for lab evaluation but the essence of this is to assume that the fuel is not homogeneous across the pipe, as evidenced by the sample collection, nor from on end of a bunker to another since what they collect is a drip sample or flow proportional sample.
In other words, the test actually assumes the fuel is anything but homogeneous.
Typical sample collection equipment/procedures are here

I would hope one day to see a definition of homogeneity or marine fuels which looks at cross pipe homogeneity and end to end. That would mean, I guess, pipe wall and pipe centre samples and spot samples as the bunker is delivered.
Since this is virtually an instrument free industry I can't see it happening.
Oh, I can see how online measurements can get the data in real time but they don't seem that interested (yet) in fuel quality as it is, never mind worrying about homogeneity.

Ain't life wonderful?

Sorry to go off topic. I've had my moan and can be red flagged now.

JMW

http://www.ViscoAnalyser.com

 

[zdas04]

jmw,
That was kind of my reason for asking the follow-up question I asked--I've seen qualitative references to homogeneity, but never a quantitative one, Latexaman's post made me think that I was just missing something. The few times that this mattered to me, I stuck in a high-shear pump (like a centrifugal) and just pretended that heterogeneity could not survive that beating. I've rarely been able to afford the dP caused by a static mixer. I never found a good test instrument or procedure.

David

 

[jmw]

I can't find it now but there was a report I found on the internet that showed that water taken from two different lake sources, each with their own chemistry, were combined in a pipeline and yet some considerable distance down the pipe they were still found to be largely discreet flows.
Headloss is a big issue in bunkering.


JMW

http://www.ViscoAnalyser.com