"Sparge" Mixing
"Sparge" Mixing
(OP)
For whatever reason, perhaps mostly historical, some terms come to be inappropriately applied.
So of all the operations described as "sparge mixing" the some may more accurately be described as " recirculation mixing."
As I am not overly familiar with mixing technology or processes I need some help with basic concepts in order to sort out what are the key problems in these applications.
I will be more than content with some definitions, basic pointers or guidelines, or references to some good web sites. I need a basic understanding to apreciate the problem areas, not to be able to design a system. A sort of "identikit" approach to appreciating what is good and bad about any system I come across would be helpful.
The process is commonly performed around the world but the equipment used appears to vary significantly.
Two liquids are being mixed by a process that is often described as "sparge mixing".
In this industry and in some plants this involves, as my limited knowledge would lead me to expect, using a sparge pipe at the bottom of the mixing tank to blow air through the liquids until the resultant mix is homogenous.
Undoubtedly this is how the process originally was used (even though my own concern would be the significant density and viscosity differences between the components i.e. is it the most suitable anyway?) but the term now seems to be applied to any arrangement of pipe work and as often as not it is simply a recirculation system (and probably not ideally designed for that process).
The two liquids are typified by:
90% is a 400-1000cst fluid at approx 50deg C
10% is a 1-5cst fluid at ambient
The two components often have significantly different densities.
Using air is a problem for many of the operations because (a) they don't have available adequate compressors
(b) because the air gives rise to what they call the "cappucino effect" and as the product is sold, as soon as mixed, and the volume determined by tank dipping, this leads to disputes over the amounts delivered
(c) density and viscosity are key target qualities measured at completion and entrained air gives false low density and false high viscosity (they do not have the facilities to centrifuge the samples nor an ultrasonic bath. Paradoxically, most quality disputes arise from false high density (around 6%; the product is sold by mass) and false low viscosity (around 7%; a better product but more expensive). Most quality disputes are not identified as a problem from the mixing process but from the pre-determined ratio of the components.
Hence many such "sparge mixing" operations are now based on pumped recirculation.
In these cases it is the discharge pumps that are used for recirculation. Pump capcities are usually sufficient to discharge the entire tank contents in around an hour. So even if the pumps are adequately sized, the time available and the pipe layout may not be. So far as I know most such installations do not have any special pump inlet piping arrangement, they just connect to a hole in the side/bottom of the tank.
The return might be via a sparge pipe in the bottom of the tank, it may be a stilling pipe returning the liquid back below the surface or it might be a "sparge" pipe (so called because the return pipe opening is above the liquid level in the mixing tank). One operator admitted they have problems because the return pipe is very close to the pump inlet.
One last feature is that time is often limited.
One of the major concerns would be that the mix is not homogenous especially as the mixing time is often not the time needed for mixing but simply the time available which can vary from one operation to another. It would be OK if the time available was always greater than the time needed but this is notthe case.
In almost all cases there is a reluctance to invest in special equipment and the systems that have evolved have exploited existing needed equipment as much as possible.
Any thoughts?
So of all the operations described as "sparge mixing" the some may more accurately be described as " recirculation mixing."
As I am not overly familiar with mixing technology or processes I need some help with basic concepts in order to sort out what are the key problems in these applications.
I will be more than content with some definitions, basic pointers or guidelines, or references to some good web sites. I need a basic understanding to apreciate the problem areas, not to be able to design a system. A sort of "identikit" approach to appreciating what is good and bad about any system I come across would be helpful.
The process is commonly performed around the world but the equipment used appears to vary significantly.
Two liquids are being mixed by a process that is often described as "sparge mixing".
In this industry and in some plants this involves, as my limited knowledge would lead me to expect, using a sparge pipe at the bottom of the mixing tank to blow air through the liquids until the resultant mix is homogenous.
Undoubtedly this is how the process originally was used (even though my own concern would be the significant density and viscosity differences between the components i.e. is it the most suitable anyway?) but the term now seems to be applied to any arrangement of pipe work and as often as not it is simply a recirculation system (and probably not ideally designed for that process).
The two liquids are typified by:
90% is a 400-1000cst fluid at approx 50deg C
10% is a 1-5cst fluid at ambient
The two components often have significantly different densities.
Using air is a problem for many of the operations because (a) they don't have available adequate compressors
(b) because the air gives rise to what they call the "cappucino effect" and as the product is sold, as soon as mixed, and the volume determined by tank dipping, this leads to disputes over the amounts delivered
(c) density and viscosity are key target qualities measured at completion and entrained air gives false low density and false high viscosity (they do not have the facilities to centrifuge the samples nor an ultrasonic bath. Paradoxically, most quality disputes arise from false high density (around 6%; the product is sold by mass) and false low viscosity (around 7%; a better product but more expensive). Most quality disputes are not identified as a problem from the mixing process but from the pre-determined ratio of the components.
Hence many such "sparge mixing" operations are now based on pumped recirculation.
In these cases it is the discharge pumps that are used for recirculation. Pump capcities are usually sufficient to discharge the entire tank contents in around an hour. So even if the pumps are adequately sized, the time available and the pipe layout may not be. So far as I know most such installations do not have any special pump inlet piping arrangement, they just connect to a hole in the side/bottom of the tank.
The return might be via a sparge pipe in the bottom of the tank, it may be a stilling pipe returning the liquid back below the surface or it might be a "sparge" pipe (so called because the return pipe opening is above the liquid level in the mixing tank). One operator admitted they have problems because the return pipe is very close to the pump inlet.
One last feature is that time is often limited.
One of the major concerns would be that the mix is not homogenous especially as the mixing time is often not the time needed for mixing but simply the time available which can vary from one operation to another. It would be OK if the time available was always greater than the time needed but this is notthe case.
In almost all cases there is a reluctance to invest in special equipment and the systems that have evolved have exploited existing needed equipment as much as possible.
Any thoughts?





RE: "Sparge" Mixing
So the air effectively reduced the local density, the aerated acid rose up, and the elbow imparted a horizontal velocity component, inducing a nice circulation in the tank, and the froth didn't get serious and there was no splashing because the pump's discharge remained submerged.
The air supply came via 1/4"od polypropylene tubing, from a regulator set to ~1 psi.
It didn't look real impressive, but it didn't take long to get a nice circulation going. Your mixture might require a little more pressure, but I think if you're making much froth you're just wasting air.
Mike Halloran
NOT speaking for
DeAngelo Marine Exhaust Inc.
Ft. Lauderdale, FL, USA
RE: "Sparge" Mixing
We tried to stay away from the single sparger type mixers, quill type mixer, and tee mixers instead we use the a reticulation system that has eductors, usually four to one, spaced on the bottom of the tank to insure blending as we make and take from a tank. We do several blending operations in molten polymer systems where we use the Kenics type mixers to mix low viscosity materials in the high viscosity polymers to minimize the concentration effects. Tee type mixers we do use have an inner pipe to insure we minimize the thermal gradients.
We didn’t have any product that we that we could inflate though we did catch a bulk oil vendor selling us a little air, actually had a valve on his pump.
In days gone by all local gasoline deliveries were corrected for density at they were dropped in the tanks. When a lot of gasoline tanks were above ground the best time to buy your gas was in the morning.
This type mixer does an excellent job of getting a liquid into a gas or in some cases vice versa.
http://www.komax.com/Default.htm
These type mixers do a very good job.
http://www.foxvalve.com/frameset-prod.html
Chemineer did have an excellent mixing booklet at one time.
http://www.chemineer.com/kenics_products.php
RE: "Sparge" Mixing
Unclesyd, very useful link to foxvalves where the tank mixing eductor should prove very valuable.
JMW
www.ViscoAnalyser.com
RE: "Sparge" Mixing
Similar to the Fox line
http://www.s-k.com/pr_jet.htm
In addition to the density control mentioned above we use a number of their level controls.
http://www.ohmartvega.com/
RE: "Sparge" Mixing
A rotating jet head is placed inside the tank which can be used for mixing liquid with liquid or dispersion of gas or powder. In addition the rotating jet head can be used as an automatic tank cleaning machine when the tank is empty.
RE: "Sparge" Mixing
I have added this to my list though I have to say it seems rather complex when compared with the eductor designs. For the applications I am looking at (Fuel oil homogenisation)I would have to suspect these might suffer from the usual problems of asphaltenes plus any catalytic fines not yet removed.
JMW
www.ViscoAnalyser.com