Which is the best type of mixer to use prior to sampling? 1

[minty]

I am designing a sample point for an offshore platform and need to ensure a homogenous mixture (of produced water and condensate) is obtained prior to sampling. Assuming a liquid full section of pipework can be obtained, which would provide better mixing: an electric mixer or a static mixer?

Are there any inline electric mixers for pipelines available? I have managed to find plenty of mixers for vessels butvery few for pipework.

Would a static mixer be suitable for such an application?

Thanks!
Michelle

 

[epoisses]

I'm not sure about any specificities in offshore vs refining, but I would tend to avoid electric mixers for cost and maintenance reasons, and would tend to think that the cheapest solution is a "fast loop" i.e. a small bore recycle line across some delta P generator (a control valve or so). If flow rate is high, mixing should be sufficient. Not sure about static mixer prices, they could be competitive vs a fast loop depending on how long the fast loop would have to be. But I would gladly trade my opinion for a more informed one.

 

[SeanB]

We have inline static mixers on diesel rundown lines. These are 12" inline mixers with a design pressure drop of 2 psi at 2000 GPM flow. We have a sample point downstream of the mixers. We installed a restriction orifice to provide a pressure drop to sample around - this was "cheap and dirty" method. A true "fast loop" system has a pumped sample line running in parallel with the pipeline.

 

[dcasto]

there are a few static mixer vendors, I'm familiar with Koch Industries. All mixers tend to be pricey because its black magic (just like structured packing). I've had a weld shop (QBJOHNSON in OKC) make some up to mix natural gas and TEG and they worked just fine. The use of an orifice plate to drive a sample loop is fine or just an insertion pitot tube works nicely because you are drawing from the middle of the line. I bet an averaging annubar would be even better.

 

[minty]

Thanks for those tips. I haven't considered the use of a "fast loop" or parallel sample line as the area is quite congested already with pipework.

The use of a restriction orifice has also been suggested to me but I am dealing with very low operating pressures and so have limited liquid head available.

I am interested to know how DCASTO's pitot tube arrangement worked. Did you have any problems with blockages?

 

[Jason5000]

I believe Sulzer now owns and operates the business that was formerly part of Koch-Glitsch that designs static mixers. My experience with them is that they provide good mixing and low DP.

If you choose to install one make certain you have sufficient block valves, bleeds, bypass, etc. to roll it out online. Their design does make them prone to catching any large junk that comes down the line, and then you can throw low DP out the window.

 

[mixingbydesign]

Komax discovered the optimal approach by codeveloping a custody transfer mixer with two majors involved in a dispute over crude oil transactions in southern California. The CT mixer thoroughly disperses and then conditions the flow in prepartion for sampling. The unit will pass a solid up to 25% of the pipe ID. If you are planning to attend the upcoming ISHM (International School of Hydrocarbon Measurement) you will see their technology displayed.

 

[unclesyd]

Here is the information on the CT mixer posted by mixingbydesign. We have used a lot of their equipment and it all has done what was advertised.

http://www.komax.com/det-ogcustody.html