Boosters
There are many types of booster systems, and they do not all function the same. I will speak about the booster fittings offered by Dynamic Air.
The Dynamic Air boosters perform 2 basic tasks: 1) eliminate plugging, and 2) control velocity. This actually leads to lower air consumption. I'll explain why.
If a system without boosters is prone to plugging, the only remedy is to increase the air to material ratio (use more air). If the material to be conveyed has some variations in physical properties (moisture content, bulk density, particle size, etc…), the air to material ratio must be increased to work for the worst-case scenario material properties. Since the booster fitting is an automatic plug breaker, there is no need to increase the air to material ratio to keep the system from plugging. Also, the Dynamic Air booster system, by design, is constantly plugging and un-plugging the conveying system. This is a good thing because it reduces the air consumption by increasing the resistance of air passing through the material.
Finally, the booster allows the system to operate at a lower conveying velocity by introducing energy where the energy is needed...along the pipeline. Studies have proven that in most applications, a lower velocity system requires less energy to convey a given material. This is because the air velocities are lower (lower pressure drop due to air flow), less friction created in the bends, etc. The overall effect is lower air consumption.
The extra benefit from is that if you have a fragile or abrasive material, there is less damage to the material and the pipeline! ■
Bypass Vs. Boosters
Jack,
Your questions are right on the mark. The whole idea of “boosters” is an oxymoron. Boosters add gas to the conveying stream which is the last, I repeat, the last thing you want to do if you want to control velocity.
The correct terminology here is “bypass”. The idea of a “bypass” is, when a blockage forms in the conveying line, to bypass some of the conveying gas to an area of lower pressure to effectively break up the plug so conveying can resume.
There is a real need for bypass systems. Materials classified as Geldart Group B or Group C materials are candidates for bypass systems.
Kind regards,
Dennis Hauch ■
Boosters
Mr. Hauch,
You use the term “booster” in general. Reality is that there are several different “booster technologies”. Since you lump the Dynamic Air booster technology in with all “booster” systems, I must state that you are clearly misinformed as to the technical aspects of the Dynamic Air booster technology.
The Dynamic Air booster technology is also designed to automatically break a plug. However, unlike the “bypass” system you describe, the Dynamic Air booster technology directs the conveying gas to a point immediately upstream the plug to effectively break the plug. Also, you have made the naive assumption that just because there are booster fittings connected to the conveying line that the conveying velocity cannot be controlled. Nothing could be further from the truth.
Furthermore, in the bypass system you describe, the conveying gas is directed to the area of low pressure. In a plugged situation, the pressure immediately upstream the plug is at or near the same pressure as the pressure vessel pressure (high pressure). The pressure immediately downstream the plug is at or near the pressure of the receiving bin (low pressure). So, if you want to break a plug, you need the conveying gas upstream the plug in order to break the plug. In the situation you describe, the “bypassed” conveying gas has bypassed the plug entirely. ■
Booster Rebuttal
Jack Archer
Dynamic Air
I respectfully submit that the theories embraced by Dynamic Air regarding “boosters” ignore the laws of physics. I make two points:
1) It is an irrefutable fact that gas injected by a “booster” into a conveying line will increase the conveying velocity. This can hardly be construed as “velocity control” and it is entirely in the wrong direction if a minimum / optimum conveying velocity must be maintained. The Dynamic Air response was “Nothing could be further from the truth.”
2) The only effective way to accommodate an immovable, impermeable plug in the conveying line is to bypass conveying gas to “break off” the leading edge of the plug, in an area of lower pressure, to progressively reduce the length of the plug until conveying can again resume. The Dynamic Air approach would add “booster” gas at the trailing edge of the plug, which would only increase the strength of the plug.
The Dynamic Air respondent does not name himself and closes his responses with Dynamic Air Inc. so I assume he speaks for the company.
Dennis Hauch ■
Dynamic Air Booster Technology
Mr. Hauch has made some bad assumptions about the Dynamic Air booster technology. It is very clear he does not understand the Dynamic Air technology. I would ask, for the sake of the audience, that he refrains from comment on a system he is not an expert in!
1) The first bad assumption is that an increasing velocity is detrimental to velocity control and obtaining the minimum / optimal conveying velocity. The Dynamic Air booster technology allows the system to convey at lower velocities because of the ability to convey without the worry of plugging. That allows the system to operate at the minimum air to material ratio and minimum velocity. For example, a system starting at 100 ft/min increasing to 500 ft/min (500% increase) is certainly better in terms of wear and degradation than a system starting at 2000 ft/min increasing to 3000 ft/min (50% increase).
2) The second bad assumption is that the addition of conveying gas upstream a plug is a bad thing. A “plug” is at a specific location (point in space) in the convey line. The plug itself may be buried in a section of pipe filled with material, but the actual plug location is a fixed point. This being the case, introducing compressed air immediately upstream the plug is exactly what is required to break the plug. ■
Bypass / Booster Finis
Jack,
At this point I will conclude the dialog between myself and the Dynamic Air representative. My purpose was a spirited exchange between us that would provide answers to the questions that you posed in your original thread. I trust this has happened, but I must say that in the process I was disappointed in the professionalism exhibited by the respondent from Dynamic Air.
Please don’t hesitate should you have any questions.
Regards,
Dennis Hauch ■
Re: Boosters ? Do They Boost Anything ??
In my long career I have used Dynamic Air's booster systems to control the conveying velocity and thus reduce particle attrition. I have seen terminal velocities with these systems as low as a few meters/sec with solids to air ratios as high as 80 to 100. In my opinion, dense phase conveying lines with primary air, and injection of secondary air with "flow controlled line injectors, so called boosters" do have a place in pneumatic conveying.
Regards
Amrit Agarwal (Tim)
Pneumatic Conveying Consultants
polypcc@aol.com, or, pccsolt@enter.net ■
Boosters
It it nice that fundamental questions are being asked. The reason being that Pneumatic conveying is considered still as a state of art rather than science. I wonder if the doctor operating the patient or Missile scientist will consider their field as state of art not science!
Sorry! What am I driving at is that now a days, basic research in understanding fundamental principles of Pneumatic Conveying is not done at all. I thing it all stopped from 80s. May be due to PLCs, which take care of any adverse situations.
Why can not a Technical institute undertake this and let a PHD student give the solution, rather than discussing for next 20 years! ■
Re: Boosters ? Do They Boost Anything ??
From what I know, pneumatic conveying technology is today more science than art. A number of universities around the world now have PhD programs in pneumatic conveying. Since the early 80's dense phase conveying technology is much better understood and is being used effectively.
The word "booster" is not understood by many people. These should instead be called secondary air injectors. Several technical papers by well known institutes have been published on them.
Regards,
Tim Agarwal
Pneumatic Conveying Consultants ■
Re: Boosters ? Do They Boost Anything ??
Thanks for the spirited discussion regarding this important topic of secondary air injection in dense phase conveying systems. Forums, such as this, should be used to exchange our ideas and experiences freely.
As I understand, the boosters from Dynamic Air consist of a booster (primarily a check valve for gas-solid application) and a flow control valve upstream of the booster. The pressure difference between the booster header and the local pressure in the conveying line is the driving force for the gas injection into the conveying line through the booster assembly. The booster itself acts like a check valve while the gas flow rate is determined by the dP across & Cv of the flow control valve. The gas flow rate is pretty much constant if the dP between the booster header and the conveying line is greater than 15 psi. Otherwise, at constant setting - the gas flow rate is higher when line pressure is lower.
Other air-injection systems (from Gerricke, old Buhler) are functionally the same. The hardware is different but physics is the same.
In specific tests conducted on such systems, I have found that the gas injection rate from the booster is fairly constant. There is really no "modulation" going on. So what does the air injection do ? It simply reduces the local stresses in a plug and increases the local voidage for materials with low permeability and high deaeration characteristics. These are the most difficult to convey in dense phase conveying system since they do not have a natural tendency to form stable slugs. For plastic pellets, booster air injection is futile since there is sufficient permeability in the pellet slugs. For fine powders which do not have very high air retention times, the secondary injection helps to keep the material in fluidized mode, thereby reducing the specific pressure drop.
While it is true that secondary injection ( I will refrain from using specific brand names.. should it be misconstrued as accusatory) allows us to lower the minimum conveying velocity (esp. for coarse granular materials 200 - 1000 microns range), one must also be careful not to inject too much air along the conveying line. If one looks at the Zenz plot, it is easy to transition from good stable conveying to unstable conveying and on to dilute phase conveying by continuous air injection along the conveying line. Too much is not necessary good. Of course, the pressure fluctuations disappear at higher gas velocities due to transition from unstable dense phase flow to dilute phase flow. As long as the secondary injection systems are designed such that the end of the line velocity based on TOTAL gas consumption keeps the flow patterns on the LEFT hand side of the unstable region in a Zenz plot, it is acceptable.
By-pass systems have the distinct advantage of not adding any NEW gas into the system. However, it also assumes that the by-pass design is done properly and appropriate volume of gas is bypassed to locations along the conveying line where it is required.
I urge the vendors of "secondary air injection" type systems (Dynamic Air, Buhler/Coperion , Gerricke etc.) to publish their findings in peer reviewed technical journals (Powder Technology etc.) for the benefit of industrial users. By sharing their understanding of the fundamentals, they will enhance their marketing position.
Jack ■
Boosters
Dear friends .
I must agree with Dr. Armit.
Some universities have taken pneumatic conveying to the realm of science , very impressive work has been done by George Klinzing of the Pitts, as they call the University of Pitsburgh.
Roy Marcus from Southafrica made also significant contributions, as Dr Yang from Westinghowse.
Some 13 years ago I used his correlations as basis for a pneumatic conveying system matematical model and it worked very well , even considering heat transfer, and rarified atmospheres.
Recently I had the oportunity to see the results of an impresive simulation model used in the cement industry for the meal preheaters and certainly it is on the realm of science
But for the one that has no inside information , the most advanced of sciences will always be magic..
Just imagine , a flashlight or a lighter in the times of King Arthur , or an atomic bomb in biblical times, even a supersonic plane a television or a celular phone at the end of the 1800, and even matematics has had its magical times , remember the pentagram in Pithagoras times, experience is used with sucsess by many to substitute science, with modest extrapolations from those brave enough to live on the edge of . just like the alquimists, Pneumatic conveying in dense phase , with large polidisperse particles will still for some time will keep us in the realm of art , black art , magic.
Many times I have faced the dogs of incredulity before innovation, It will never fly, was said to the wrigth Brothers even when the flyer was on the air.
Friends from Dinamic air , do not be offended by honest comments, most of the time is just a question of semantics. I dont believe they were intended as detrimental to your product, just invite them to go and take a look.
Regards
Marco ■
Air Injection Solves Problems
A lot of time has elapsed since this discussion occured and yet I see some utility in furthering it for future readers. It has been my experience that dense phase transfer systems can plug and when this happens increasing the air pressure can result in considerable violence when the plug clears. This results in a phenomenon similar to water hammer in steam lines. The pressure surges involved can exceed design limits for explosion relief vents on surge hoppers and receivers. It can also result in an increase in fines.
There are also differences in the smoothness and quietness of dense phase convey systems attributable to the type of rail car delivering the raw material. Clearly the best convey system must be designed to compensate for externalities such as the weather or the delivery vehicle et cetera.
The addition of air injectors (or so called "boosters") can aid the smooth operation of dense phase systems. Summer operation involving higher humidity seems to be a time when air injection is most useful. The major objection to it has been higher velocities and an increase in fines. In my experience, the increase in fines is so slight as to be un-measurable in most cases. The difference in reliablility and quietness can be dramatic. There can be no question that if the bulk material being transported is subject to plugging or other misbehavior the judicious use of air injection is an important tool.
Regards,
Bill ■
Re: Boosters ? Do They Boost Anything ??
Jack,
What you need to ask is... Can the product be conveyed without boosters. I will bet that the answer is YES.. So why subject your self to the added initial capital cost and the added maintenance cost. I have installed applications for Cement, Gysum, CaCO3, Bauxite, dating back to 1995. Never have problems with plugging. My systems do not have boosters. Don't mind sharing with you my experiences on who to avoid and who to deal with. Call any time.
Joe Cacciola (617) 331-7974 ■
Re: Boosters ? Do They Boost Anything ??
Hello all,
Particularly this discussion has generated some bad remarks and bad feelings which is in no way healthy. I believe that this place been intended to be a thinking areana where people could do some exchange of ideas and constructive criticism!
I would just ask this question:
can anybody start trasnport of any powder(particulate material) at a velocity less than the minimum transport velocity !?
I belive that all pneumatic conveying professionals try their best to use the lowest possible conveying velocity at the start of conveying !!
Hence any additional air down the line would be expected to increase the air velocity !!!!!!
Just for information of bvsarma :
all over the world PhD students are working on pneumatic conveying of powders in universities and research institutions !
with best regard
Biplab K. Datta
Telemark Technological R & D Centre, Norway
biplab.k.datta@hit.no ■
Can The Material Be Transported W/O Boosters?
Joe,
I think you have put your finger on an extremely important point. If the material that is being transported is not susceptible to plugging then boosters are clearly not necessary. You cite examples from your experience that do not seem to plug and don't need boosters.
Sugar, artificial sweeteners, flavorings, dry milk, non-dairy creamers and the like do tend to be susceptible to plugging and do seem to transport more easily when boosters are employed.
You asked the key question. I think the need for boosters depends in large part on the nature of the material being transported.
Thanks,
Bill ■
Re: Boosters ? Do They Boost Anything ??
WHAT I FEEL THAT EVERY BODY IS TRYING SOMETHING AT THAT THEIR OWN, EARLIER BOOSTER WERE USED WITH MECHANICAL DIFFERENTIAL PRESSURES.
NOW IT CAN BE EASILY DONE BY INSTALING PRESSURE DIFFERENTIAL TRANSMITTERS IN MAIN PNUEAMATIC LINE AND IN BYPASS LINE(BOOSTER LINE, ACCELERATING LINE).
THESE PRESSURE DIFFERENTIAL TRANSMITTERS PLAYS A GREAT ROLE IN QUICK OPERATION OF REQUIRED BOOSTER VALVES.
PROBLEM LIES WITH ALL INDUSTRIALISTS, WHO DOES NOT ALLOW TO SHARE THE INFORMATIONS. ■
Boosters ? Do They Boost Anything ??
Fantastic! I love it when there is such heated debate.
Without adding fuel to the fire, I hope someone can answer the following.
1. When are boosters / bypass systems recommended? Surely with a well designed conveying system these would not be necessary from the start. Are these usually "add-ons" to uprate an existing system. or does it sometimes make sense to include these in the initial design?
2. If, in lean phase conveying, the system is subjected to increasing loads due to increasing production, it is possible that the conveying system could become over-loaded. This would move the system into the unstable zone. Can boosters / bypass systems be used here?
3. Does the extra air added enter the conveying line in front of the plug, behind the plug, or in the middle of the plug?
4. I would imagine that one whould want to break up the plug by injecting additional air into the plug itself. But how does the system know where the plug is, and therefore where to inject this additional air? Pressure switches?
5. Where can I get hold of comprehensive research data?
Thanks in anticipation,
Dave. ■
Does Booster Increase Delivery
Are boosters only for plug breaking or do they also help convey larger batches more frequently to increase delivery quantity or increase tons/hr of material conveyed( such as sand etc)? ■
Dense Phase Conveying
The Company I represent is in the process of uprating and de-bottlenecking our polyethylene production facility. We have a dense phase system conveying ca. 8 to 18 TPH, and need to uprate this to 25 TPH.
Conveying air is supplied at a pressure of 3 bar, via a single injector nozzel upstream of the Rotary feeder into the 130 meter conveying line. However this system has two shortfalls:
1. It is running at its limit. 2. At low rates, it operates to the left of the Zenz plot.ie lean phase.
Before installing the current system, we employed a dual pressure tank system.
Any suggestions? Is this the time to introduce secondary air, or to strip and replace with larger capacity equipment?
Thanks,
Dave.
P.S. Is there anyone out there who can help me with reports, procedures etc on previous uprating efforts in either dense or lean phase. I am trying to build up a knowledge base to help me better understand this "art-technology-science" of pneumatic conveying. Also some down-loadable software? ■
Re: Boosters ? Do They Boost Anything ??
Dave,
Secondary air is not the answer to your problem. It will only increase the solids velocity resulting in fines, dust, and streamers.
From your description, it looks like that you have a "pressure limit". i.e., you reach 3 bar pressure drop at 25 tons/hr. From what I have seen, conveying pressure is never constant when a single Laval nozzle is used for all conveying rates. It can pulse widely. You may be reaching the pressure limit due to these pulsations. The solution to this problem is to replace the Laval nozzle by a air control system that maintains flow depending upon the line pressure drop. These systems are available from several vendors.
If you need my help, please feel free to contact me.
Regards,
Amrit Agarwal
Pneumatic Conveying Consultants
polypcc@aol.com
www.powderandbulk.com/pcc
Fax: 304 346 5125 ■
Boosters ? Do they boost anything ??
I have seen a number of "booster systems" being sold during the past 20 years. Some injection additional compressed air into the line and some have bypass configuration.
The booster systems sold by Dynamic Air (&many others) inject additional air through booster valves.
Can someone enlighten me...
1. What exactly do these booster do ?
2. Why use them ? What material characteristics warrant using them?
3. Are we not increasing the gas velocity by adding more air to the line ?
It appears to me that we are buying a lot of hardware without much understanding of the basics. ■