Sounds like cement unloading on a mixing plant. Your second barge has the right size compressor for 6" pipe. Half your air flow and you will achieve 50 tph which is probably max rate you will achieve in a 6" pipe at 200m. if you want more rate then you will need to increase the pipe to 8". in this case your first barge compressor will be OK.

Dummies guide on pneumatic conveying is still being written and the first chapter is called "more air does not mean more conveying rate" ■

Dear Mantoo,

Your conclusion

is correct.

I calculated the installation (225m horizontal, 20 m vertical, 6 bends, 6”pipe diameter) for the 2 compressors.

35 m3/min at 2.2 barg gives approx. 55 tons/hr

19 m3/min at 2.2 barg gives approx. 49 tons/hr

That means that the installation is operating in dense phase.

(higher air flow gives higher capacity)

This statement does only apply when the pneumatic conveying system is operating in the dense phase region.

In the dilute conveying region, the statement is false.

Have a nice day ■

Originally Posted by inlandcementshipping

Hello to everybody,

at a specific client, with our inland silobarge, we cannot discharge faster than 45 tons/hour.

I want to know the raison why.

Barge has 3 pressure tanks of 150m each, 30 meter 6" conveying line (5m vertical, 25m horizontal and 2 bends D9 + D5 ) and compressorcapacity of 35m/min.

We discharge 1 tank at the time (tank per tank).

Piping on land also 6" and 200m horizontal and 15m vertical with 4 bends 3D and one divertervalve for different silos (350 tons/each).

Unloading is permitted at max 2.2 bar (usually we discharge at 3 bar WP).

At other locations with similar conditions, we can unload at rates up to 100 tons/hour. (at 3 bar WP)

With another barge with smaller pressuretanks (40m) and smaller compressor (19 m/min) we achieve better results!? (50 tons/hour)

In order to help our client modifying his installation, we want to give him scientific based advise.

We think dedusting capacity of the clients silos is not enough. Therefore with the bigger volume, it does not pass the filters quick enough, creating pressure in the silo of the client and at same time our discharging rates are lower than usual.

Therefor, what should be our maximum velocity (discharging capacity) and what should be the according dedusting capacity?

Is there an 'pneumatic conveying tool for dummies' available in .xls ?

Thx in advance,

Erik Pauwels

+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

Dear Eric,

You can run your own calculations for solving this problem by using the calculation method described in my article "Theory and Design of Dilute Phase Pneumatic Conveying Systems". This is an Excel based, easy to use, calculation method.

If needed, I will be glad to help you in these calculations.

Regards,

Amrit Agarwal

Pneumatic Conveying Consulting

Email: polypcc@aol.com ■

Originally Posted by inlandcementshipping

Dear Amrit,

may I request a copy of your article?

My e-mail : erik.pauwels@gitrashipping.be

Many thx in advance.

I'll probably need more advise, but your article would be a great start.

Best regards,

Erik.

+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

Dear Eric,

I have emailed a copy of my article to you. You may contact me for any questions. If your conveying rate is limited by the conveying pressure, you should find out your present pick up velocity, compare it with your other conveying systems, and reduce it if possible. Also look into improving the conveying line route by reducing number of bends.

Regards,

Amrit Agarwal

Pneumatic Conveying Consulting

+++++++++++++++++++++++++++++++++++++++++++++++++++ ■

Dear Amrit,

For the 35 m3/min compressor at 2.2 barg, the calculated pick up velocity is approx.. 10.5 m/sec.

The calculated continuous capacity is then 56.906 tons/hr.

Reducing the air flow to 30.m/sec, the calculation gives a pick up velocity of approx. 8.96 m/sec.

The calculated continuous capacity is then 55.791 tons/hr at 2.2 barg.

This indicates that the system is operating in dense phase.

Reducing the air flow in dense phase, increases the pressure drop or, at the same pressure drop, decreases the capacity.

Regarding the reduction of bends:

I calculated the installation for 6 bends:

capacity = 56.906 tons/hr

pneumatic conveying power = 70 kW

bend losses = 12.6 kw (18%)

I calculated the installation for 3 bends:

capacity = 57.774 tons/hr

pneumatic conveying power =69.9 kW

bend losses = 9.2 kw (13.1%)

The reason for the small difference between 6 and 3 bends is that the bends near the silo (at the end of the pipe line) consume more energy, because of the higher velocities at the end of the pipeline.

Have a nice day ■

==================================================================================================== ======

Dear Teus,

Thanks for your comments.

Pipe line thrust loads in a 50 tons/hr and a 6 inch dia line will be very high. They will require specially designed pipe supports, specially at the bends. From the given data, it seems that the system is running in low velocity dilute phase. Pick up velocity of 10.5 meters/sec is very high for a dense phase system.

If the system is indeed dense phase, available compressor should be more than 3 bars, and conveying capacity will not be limited by the available conveying pressure.

Regards,

Amrit Agarwal ■

Dear Amrit,

Thank you for your reply.

Here, the definition of dense phase and dilute phase is very important.

On this forum we had a discussion about this definition some years ago.

The common conclusion was then that dense or dilute is defined, using the Zenz diagram.

The Zenz diagram has a point, where, at constant capacity, the pressure drop is minimal at a certain air flow. (The Zenz point)

Left of this Zenz point is called dense phase and right of this Zenz point is called dilute phase.

This definition applies to any Zenz curve, whether at low pressure or high pressure.

In the Zenz curve, always for a defined installation, the Zenz point travels to the left at lower capacities.

The considered installation in this thread becomes dilute at lower pressures than the considered 2.2 barg.

I made the Zenz curve calculation for the question in this thread:

Air flow:------0.4------0.45-----0.5------0.55------0.5833------0.6------0.7------0.8-------0.9-------m3/sec

Pressure:----2.433----2.326----2.257----2.215-----2.2--------2.195----2.2-----2.252-----2.34-----barg

The Zenz point is at an air flow of approx. 0.6 m3/sec.

35 m3/min= 0.5833 m3/sec is left of the Zenz point, hence dense phase conveying, although close to the Zenz point.

At lower airflows, the system becomes more dense and the pick-up velocity will become lower. At the same time, the capacity will drop also at the same pressure of 2.2 barg.

( It can be proved that the Zenz point travels to the left at longer pipe lengths.)

The SLR at an air flow of 0.5833 m3/sec is 23 (kg/sec)/(kg/sec)

The impact force at a bend is calculated at approx. 3 kN.

Best regards ■

Dear Teus

Your calculations below are incorrect as it is already stated that the system only achieves 45 tph on site with this airflow.

"35 m3/min at 2.2 barg gives approx. 55 tons/hr"

My statement below is correct for lean phase also. As you have stated that lean phase is on the right side on Zenz diagram

and as the airflow in increases the dp/m also increases. If there was straight line on right side then my statement would be

incorrect.

"This statement does only apply when the pneumatic conveying system is operating in the dense phase region.

In the dilute conveying region, the statement is false."

Considering 35 m3/min air flow in 6" pipe dense phase is very debatable. It falls on the right side of the Zenz diagram not on left.

There will be no plugs flowing in the pipe with these velocities, it will be high SLR fully suspended flow.Again it goes into the

LP & DP definition.

It will be good if some feed back from site is left here after the system is modified.

Have a nice day ■

Dear Mantoo,

The calculation is based on the given (limited) data of the installation and performance.

The question was, whether the achieved capacity was the maximum or should that performance be more.

There was some doubt about the performance, because on other installations, higher capacities were achieved.

The “other installations” were not described and therefore hard to verify.

One remark made was that one of the other installations, the conveying pressure was 3.0 bar.

Anyway, maybe the calculated installation can perform a few tons more.

From the supplied information, it cannot be decided what the cause is.

[quote]Considering 35 m3/min air flow in 6" pipe dense phase is very debatable. It falls on the right side of the Zenz diagram not on left.{/quote]

I calculated the Zenz diagram:

Air flow:------0.4------0.45-----0.5------0.55------0.5833------0.6------0.7------0.8-------0.9-------m3/sec

Pressure:----2.433----2.326----2.257----2.215-----2.2--------2.195----2.2-----2.252-----2.34-----barg

How did you conclude that the system is operating in lean phase with the compressor of 35 m3/min = 0.5833 m3/sec?

Before I retired, I worked in the inland cement shipping stevedoring sector in Europe and have seen numerous installations using 35 m3/min at 6”pipelines.

Maybe not the most energetic efficient installation, but they worked properly and according the calculations.

Do we agree on the definition of LP & DP pneumatic conveying?

Have a nice day ■

Originally Posted by Teus Tuinenburg

Dear Amrit,

Thank you for your reply.

Here, the definition of dense phase and dilute phase is very important.

On this forum we had a discussion about this definition some years ago.

The common conclusion was then that dense or dilute is defined, using the Zenz diagram.

The Zenz diagram has a point, where, at constant capacity, the pressure drop is minimal at a certain air flow. (The Zenz point)

Left of this Zenz point is called dense phase and right of this Zenz point is called dilute phase.

This definition applies to any Zenz curve, whether at low pressure or high pressure.

In the Zenz curve, always for a defined installation, the Zenz point travels to the left at lower capacities.

The considered installation in this thread becomes dilute at lower pressures than the considered 2.2 barg.

I made the Zenz curve calculation for the question in this thread:

Air flow:------0.4------0.45-----0.5------0.55------0.5833------0.6------0.7------0.8-------0.9-------m3/sec

Pressure:----2.433----2.326----2.257----2.215-----2.2--------2.195----2.2-----2.252-----2.34-----barg

The Zenz point is at an air flow of approx. 0.6 m3/sec.

35 m3/min= 0.5833 m3/sec is left of the Zenz point, hence dense phase conveying, although close to the Zenz point.

At lower airflows, the system becomes more dense and the pick-up velocity will become lower. At the same time, the capacity will drop also at the same pressure of 2.2 barg.

( It can be proved that the Zenz point travels to the left at longer pipe lengths.)

The SLR at an air flow of 0.5833 m3/sec is 23 (kg/sec)/(kg/sec)

The impact force at a bend is calculated at approx. 3 kN.

Best regards

+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

Dear Teus,

Terminal velocity in this system will be well in dilute phase region. It will be about 72 ft/sec or higher.

A dense phase system at 50 tons/hr conveying rate will require sophisticated Air Control System to maintain system's operating stability.

From the data given, I think they have a dilute phase system that has not been designed properly.

Regards,

Amrit Agarwal

Pneumatic Conveying Consulting

++++++++++++++++++++++++++++++++++++++++++++ ■

Dear Teus

We have been on this forum for about 15 years and I think we have never agreed on LP& DP definition. In my

opinion this is due to your background which is from the FK pumps side. These companies have always maintained

that these pumps are DP and there definition is SLR above 10 and conveying pressure above 1 barg makes it

DP. if you go in cement or ash handling industry all the users will refer to these pumps as DP pumps. On the

contrary if you look at blow tanks they work at SLR normally above 50 up to 200 depending on the distance with

exit velocities of 15-18 m/s max are actually true DP.

My definition of DP is slightly different as it is based on my academic background and for me to have DP the material should

be in non-suspension flow. Pressure does not matter it could be below 1 barg. I have designed systems for pet food industry

running form blowers in DP you can actually see plugs of pet food biscuits moving in pipes as most of them have viewing windows.

There are hundreds of these systems.

Coming to this system with 35 Sm3/min doing 45 tph is SLR = 18 with exit velocity of 31m/s. I don't think it can be justified

as DP System on any classification and your Zenz calculations cannot be correct. . Again i will say more air does not mean

more rate. I have worked on a few of these big system in rail and barge unloading and they normally use slightly higher air flows

then normal standard blow tanks this is because these have aeration bases in the bottom and if they use less air they don't empty fully.

Dear Mr Amit

Indeed they have a very sophisticated control on these system and it is called the operator.A Man is normally standing on the

bypass valve and if the pressure goes aboves the desired pressure he opens the valve and vise versa. But actually once

the steady state is achieved the by pass valve does not need to be adjusted. ■

Dear Amrit,

I calculate the terminal velocity (including the influence of the present cement) at 33.5 m/sec (110 ft/sec.)

I worked in this branch for 17 years and can assure you that a butterfly valve as a kettle by-pass works fine, controlled by the conveying pressure.

From the calculations, the system is operating very close to the Zenz point, which means”: maximum capacity.

Reducing the air flow would mean a lower capacity, however more energetic efficient.

Highest capacity and highest energetic efficiency never coincide with the same airflow.

Again, if dense or dilute is determined by the operating point relative to the Zenz point, then this system is just dense.

If dense or dilute is defined by velocities and or pressures and or solid loading ratios, then the classification becomes very vague.

F.i.

A long pipeline requires lower SLR’s.

Can a long conveying line then be dense?

If a dense phase system is operating at partial low capacity with a lower pressure and a lower SLR than at full capacity, is this system then still dense phase?

How can we, without confusion, define dense and dilute phase conveying?

Have a nice day ■

[

Gentlemen,

The basis of Zenz diagram is saltation velocity. Higher than saltation velocity is dilute phase and lower than saltation velocity is dense phase.

Regards,

Amrit Agarwal

Pneumatic Conveying Consulting ■

Dear Dr. Mantoo,

I did one silo import- export cement terminal with FK pumps as a project manager and I operated that terminal as a “standby” operator when loading 2 bulk carriers of 35000 dwt each.

( I did the day shift from 06.00 to 20.00)

A FK pump is just a feeder and does not determine whether a pneumatic conveying system is DP or LP.

However, I did also many more installations with pressure tanks.

My background is much more versatile than just screw pump systems.

The perception of dense phase or dilute phase seems still very confusing.

If I understand you correctly, you also have your own definition.

However, using your definition (the material should be in non-suspension flow) implies that DP is on the left side of the Zenz point.

Above the Zenz point there is always suspended flow.

In a previous thread on this forum it was agreed to use the Zenz point as the boundary between DP and LP.

https://forum.bulk-online.com/showth...hase-Conveying

1)I appreciate your concern about my calculation of the Zenz point (Air flow where the pressure drop is the lowest for a given capacity)

It would be very interesting to know at what air flow you calculate the Zenz point for this installation.

2)Indeed, more air does not mean always more rate; when the operating point is right of the Zenz point. Your statement is correct for dilute systems.

3)Aeration bases in the bottom are only used in vessels with a dish head as bottom for maximum vessel volume. Kettles with cones used to have fluidizing pads, but that is the past.

In case of mobile barge unloaders, the pipe routing changes with the location (different pipeline), which requires adjusting the the by-pass valve for each location.

Therefore, the by-pass valve is controlled by the discharge pressure.

This automatic adjustment takes care, that the pipeline never chokes and that always the maximum rate is maintained.

Also the material pneumatic conveying properties are not always the same, which asks for extra adjustment.

And even on a fixed pipe line, this control is necessary because the out flow of the tank increases at the end of the content discharge, whereby the conveying pressure increases.

Take care ■

Dear Teus

Indeed FK pumps are feeders but are limited to 2-2.2 barg only on the other hand blow tanks work

up to 6 barg. My simple question is what is the effect if the higher air density at 2.0 barg on the

minimum suspension velocity ? will it be higher or lower ? will it change anything in your calcs?

It is also widely accepted that in true dense phase these equations do not work. All the properly designed

dense phase systems are based on empirical test data and the sizing is done on scaling of test data. The

reason for this is simple as the physics of individual particle in LP change to particles moving as single plug.

My definition which is probably very widely accepted by the academics and in industry and is very simple nothing

confusing about it. The material in non suspension flow is DP. MR Amit also has the same definition.

I will agree to disagree with you once again on the definition.

Coming back to this problem if it was up to me i would go with the 8" pipe this will get the unloading rate

up to approx 75 tph. ■

Dear Amrit and Dr Mantoo,

Amrit,

This is indeed what you stated in:

https://forum.bulk-online.com/showthr...hase-Conveying

And as the saltation velocity is below the Zenz point velocity, I will change my dense/dilute phase definition to your definition.

Dr. Mantoo,

According to the (now agreed) “saltation velocity” definition of DP & LP conveying, the installation is in dilute phase, as there is no saltation in the pipeline calculated.

High pressure systems above 4.5 barg are very sensitive to choking, because the capacity curve (capacity=function(pressure)) has a very flat slope above the 4.5 bar.

A small fluctuation in feeding creates a large fluctuation in pressure, causing a significant decrease in gas velocity, which can lead to saltation and choking.

These type of high pressure installations are widely used on Supply vessels and Oil rigs, where the conveying pressure is normally between 3.5 to 4.5 bar. (the applied compressors are made for 6 bar)

The local particle suspension velocity changes with the local gas pressure and becomes higher, proportionally with the square root of the absolute local pressure. Also in my calcs.

Saltation starts when the local wall velocity in the pipe becomes lower than the local suspension velocity of the particle and can be calculated.

Sedimentation starts and leaves a smaller diameter for the material/gas flow with a higher velocity.

Pneumatic conveying with sedimentation in the pipeline is well possible. Until choking occurs.

Plug conveying, close to the choking conditions, indeed, follow other physics, more like silo flow, because particles develop material stresses.

I calculate approx. 85 tons/hr to 90 tons/hr at 2.2 barg with no saltation, hence LP.

SLR = 37.8

Start velocity air = 6.4 m/sec

Start velocity cement = 5.15 m/sec

End velocity air = 19.5 m/sec

End velocity cement = 15.6 m/sec

I doubt, whether they are going to change 215 m of existing pipeline with valves.

Best regards,

Enjoy the discussion ■

Dear Amrit and Dr Mantoo,

I expected some response on my latest reply, regarding the discussion about the definition of dense- and dilute pneumatic conveying.

In the attached, calculated, Zenz diagram, I incorporated two lines:

1)The “Zenz line”, connecting the lowest pressure drops in the Zenz curve.

I used to define the dense-dilute boundary by this “Zenz” line.

2)The line where sedimentation along the pipe wall starts.

According to the “new” agreed dense-dilute definition, this line has to be considered as the boundary between dense and dilute pneumatic conveying.

Whether a pneumatic conveying installation is operating in dense phase- or dilute phase requires now to calculate the sedimentation line at the considered capacity.

Operating a pneumatic conveying system close to the sedimentation line is not recommended, as the chance of choking is eminent in this region.

A dense phase system, according to this definition, must be equipped with special features to break-up frequent blockages and will operate at least not smoothly.

I wonder how many pneumatic installations are really dense.

Have a nice day

Attachments

zenzdiagram (PDF)

■

Dear Teus

I thought you agreed with our definition of lean and dense phase so it was end

of discussion, hence no reply from my side.

Looking at the Zenz diagram you have produced using your method and where you

have got your sedimentation line if we move to left of it the pressure drop rise is almost

vertical on the X axis. This proves that your calculation is not capable of calculating the

dense phase plug flow side of conveying. I have mentioned this to you at a number of times that

you are using a calculation method which is based on suspended flow and not true dense

phase flow. But according to your previous definition it was dense phase.

For a true dense phase flow there is no theoretical calculations only models based on empirical

test results are available. They are normally scaled up to size bigger systems and scaling it self

is very interesting and it separates boys from men. The most comprehensive dense phase

published results are available in Dr D Mills book on PC. It will be a good idea if you compare

your model with the actual test data for cement given in DR D Mills book.

Once we have the comparison we can discuss this further. As always it will be my pleasure to

carry on the discussion

Have a nice day. ■

Dear Dr Mantoo,

Thank you for your reply.

I accepted the definition of lean and dense phase as proposed.

This definition limits the lean or dilute phase conveying region to the fully suspended flow.

As soon as the gas flow becomes so low that the material drops out of suspension, which starts at the pipe wall, where velocity is the lowest, the conveying regime gets the dense phase status.

In dense phase, there are 2 types of dense flow to be recognized.

1)Moving bed flow.

Here the material that drops out of suspension, forms a bed in the pipe, whereby the cross area that is left induces an increased gas velocity.

Hereby, the suspension flow is restored, although for a smaller pipe cross section.

I a way this condition can be considered as “dilute conveying” although there is sedimentation.

The developed algorithm still can be applied and that part is shown left of the sedimentation line in the Zenz diagram.

2)Left of the moving bed flow, the region where plug flow occurs exists.

In this way of conveying, the interaction between the moving gas and the particles are no longer based on transmitting impulse by drag forces.

Here, the material forces between the particles and between the particles and the wall are acting.

(This can be compared with silo flow with the influence of pressure gradients. Janssen silo theory)

The developed algorithm is based on impulse transfer and not on material stresses and therefore not applicable for the type of plug conveying.

If true dense phase is plug conveying, it has been clear from the beginning that the calculation is not developed for that. And never claimed to be.

Scaling up laboratory test to real installation is not necessary when the calculations are executed at the real scale directly. This eliminates a lot of difficulties with f.i. Reynolds numbers and the sudden change from laminar flow to turbulent flow.

In my career, I had the opportunity to measure, test, design, build, evaluate and to modify a large number of pneumatic unloaders (vacuum and pressure discharge) for a number of materials.

I even could detect malfunctioning equipment by assuming a defect and calculate the effects, after which I compared these calculated effects with the observed effects.

Take care ■

"......calculating the dense phase plug flow side of conveying."

I used to think plug flow was a reality until Shell's Den Haag office put me striaght. Plug flow is banned there because of tragic experience with a catalyst regenerator. In fact it is the first thing to be read in their specification preamble where it says something like "On no account is plug flow to be considered.". I imagine smaller firms will ignore this criticism at their petrochemical peril.

"It is also widely accepted that in true dense phase these equations do not work." You can say that again!...."these equations do not work." I once lashed out on a 1990(ish) textbook by Marcus et al. Most of the equations therein did not match the tabulated data therein: brackets and exponents in the wrong place; wrong units and so forth. Somwhere in the bowels of chapter 17 (thereabouts) it was clearly printed that "..despite all the theoretical hyptheses the practitioner is obliged to rely on empirical data."

"We only know what we can measure." Lord Kelvin. ■

prof. R D Marcus has a lot of contribution in the pneumatic conveying and he has a number ofpublications.

With all due repect to him personally I never had a chance to meet him. Once during my research days I quoted his work to my Prof.

and to this day I remember my professor's words,"do not believe in everything you read".

To this day I wonder why he said it. ■

Dear Dr Mantoo,

What is your point?

-You

?

-We should

?

-

in this forum?

I would say:” Science is not a matter of believe but the result of experiments, theory, research, discussion with arguments, intelligence and sometimes luck”

In my opinion: Not believing is not a valid argument.

Success ■

By definition belief is just an expression of ignorance. It is an unfortunate word and gives some people cause, often fanatical, to interfere with science, or knowledge as it could be called.

I was by no means criticising Markus; Leung; Klinzig & Rizk just their book presentation. My issue is about careless and incompetent proof reading which, is often as not, the publisher's fault. I bought the hardback: or rather my daughter went to the bookshop for me. Amazon now sell it for far less than I/she paid for it 25 years back. In her innocence she was shocked at the price of engineering texts. It got left behind somewhere because it wasn't worth the baggage cost. 'nuf said?

If I had accepted the contents of that texbook..believed what I read..and applied the formulae, the results would have been considerably off the mark.

My stance is the Muschelknautz (air bypass)system that was presented in the book. It impressed me. Very soon afterwards I was presented with a proposal for the system, in alumina, by Messrs. Johannes Muller, aus Hamburg and was able to discuss the sytem at length with their sales engineers. However I left Ferrostaal soon afterwards and heard no more until Clyde offered me a watered down version, again for alumina. I remembered and still liked the system, apart from a couple of reservations, but fortunately, for me, the Aerzen compressors did not match the installed Alcan piston jobs and the proposal was rejected. A decade later I was presented with Shell's document, referenced to a SABIC job, and my bacon was officially saved...by Saudi Arabian Basic Industries Corporaction...how's that for irony?

I am firmly in Mantoo's professor's camp. ■