Dear Carlos,

Does the fly ash has a moisture content?

An arragement sketch of the vessel could be helpful.

Conveying pressure depends on the design.

have a nice day

Teus ■

Typical Rathole scenario in the vessel. Flyash below 200 mic normally responds well to aeration. As suggested above the ash might be wet or could have high lime content. Probably your fluidisation pads are too close to the outlet valve and the material is forming a stable arch on the top.

Increasing the pre-pressurisation sometimes has adverse effect. If you are using air injection from the top of the vessel it can compress the material. Try pressurisation from the fluidising pads. But then it will take very long to pressurise the vessel depending on the vessel size. Do not leave the ash for long periods in the vessel; dump the ash and transfer as soon as the vessel fills do not let it de-aerate.

Other alternatives are to epoxy coat the internal of the vessel it will help by reducing wall friction.

If nothing works aeration lance from the top port towards one side of the vessel will help. ■

Originally Posted by Mantoo

Typical Rathole scenario in the vessel. Flyash below 200 mic normally responds well to aeration. As suggested above the ash might be wet or could have high lime content. Probably your fluidisation pads are too close to the outlet valve and the material is forming a stable arch on the top.

Increasing the pre-pressurisation sometimes has adverse effect. If you are using air injection from the top of the vessel it can compress the material. Try pressurisation from the fluidising pads. But then it will take very long to pressurise the vessel depending on the vessel size. Do not leave the ash for long periods in the vessel; dump the ash and transfer as soon as the vessel fills do not let it de-aerate.

Other alternatives are to epoxy coat the internal of the vessel it will help by reducing wall friction.

If nothing works aeration lance from the top port towards one side of the vessel will help.

Dear Mr Carlos

Following could be possible culprit for the witnessed problem

1)Presence of excess moisture , this could be due to online precipitator washing

2) I hope the ash you are referring is fly ash from precipitator and not from Air heater , where there could be leakege of condensated steam in air heater which will further clog the material . Though the fly ash is inherent , but without having comprehensive and conclusive evidence in context of chemical properies , this reason cannot be concluded

3) Fluidisation at conical shape of vessel in conjunction of pressurization from top of vessel works ok in india and we have no problem

4) Indeed incerase the kettle cycle will also patronage avoiding such problem

For futher assessment in efort to eradicate the obvious problem , i request you to pelase attach the general arrangement & p&i drawing of vessel and system

Dear Mr Montoo. My quiries to you

In india we have not experienced any problem with top vessel presurization , which will further incerase attrication rate of fly ash . But iam not wealth of information and indepth approach of the system , hence please justify the statment in context of practical expreience?. Have you ever face such problem ?, if so what was the problem ? , and how did you adress teh same? ■

Mr Guddu

If it was not a problem I wouldn't have known about it.

Yes I have come across this problem.

Fixing the problem is not generic, it is job specific. ■

Originally Posted by Mantoo

Mr Guddu

If it was not a problem I wouldn't have known about it.

Yes I have come across this problem.

Fixing the problem is not generic, it is job specific.

Mr Mantoo

Would you please specify in detail the nature of problem having top pressurization in vessel

Your reply will be very helpful for us ■

Dear Carlos,

Your conveying system is a kind of plug conveying system, whereby the plugs are assisted by air injection pulses along the pipeline. (Seems very hard to calculate)

In the pressure vessel, I notice the fluidizing pads, which are sticking into the cone.

These fluidizing pads are creating beautiful support points for arches. A smooth vessel cone would be much better for material flow.

I have used ordinary 1" membrane valves (as in filter pulse equipment) blowing into the cone through just a small hole. The silo cone wall stayed smooth with this solution. A clogging cement vacuum tank was made active again by this method.

The type of fluidizing pads in your system were also in a cement conveying system and were found to be not opening, due to the material pressure on the rubber pad and not sufficient opening pressure to overcome the material plus the internal pressure. And when a pad opened it was high in or above the material column, where the function was lost. We just took them all out to facilitate smooth flow and the system worked well.

I could make a calculation for your system as a normal pneumatic conveying system, but then I need as additional information, the capacity, conveying airflow (compressor displacement) and pipe diameter.

Take care

Teus ■

Dear Carlos,

Calculating your system as a dilute or dense phase system fails because the generated velocities are too low. (250 cfm # 0.118 m3/sec at a 6”pipe). The pipeline becomes blocked with sediment fly ash.

As an air assisted plug conveying system, I assume that the plug conveying pressure is about 6 bar (44 kW compressor).

This very low velocity could be far too less to fluidize the fly ash in the pressure vessel (more likely the high pressure compacts the fly ash after the fly ash was brought in under atmospheric pressure)

That could explain the rat holing in combination with the fluidizing pads obstructing the fly ash flow.

Calculating the pipeline for a standard dilute system with a blower of 0.4 m3/sec results in a capacity of 7.6 tons/hr at 0.15 bar conveying pressure. (Power 11 kW instead of 44 kW).

A bigger filter is then required.

What is the reaction and explanation of the supplier?

Take care

Teus

Attachments

flyash80106 (PDF)

■

6" pipe for conveying 6 tph of flyash at this distance with boosters very interesting. Must be a very good salesman. 6" pipe can do 60 tph in this set up without boosters provided it is a standard flyash.

But never the less you have a problem which needs solving and I think the problem is that most of the conveying air is passing through the boosters not leaving enough air going through the vessel hence the rathole scenario. I would suggest that you switch of the air supply to the boosters completely and put most of the air through the top of vessel and some air through the fluidisation pads.

Feedback after changes will be appreciated. ■

Originally Posted by Mantoo

6" pipe for conveying 6 tph of flyash at this distance with boosters very interesting. Must be a very good salesman. 6" pipe can do 60 tph in this set up without boosters provided it is a standard flyash.

But never the less you have a problem which needs solving and I think the problem is that most of the conveying air is passing through the boosters not leaving enough air going through the vessel hence the rathole scenario. I would suggest that you switch of the air supply to the boosters completely and put most of the air through the top of vessel and some air through the fluidisation pads.

Feedback after changes will be appreciated.

Dear all

Herer i want thrust out the approach we use in india

1) Firstly the the carlos problem was the piled up of fly ash in tank . There could be two cuase as depicted by all of you a) Moisture b) Fluidisation problem . The originator has concluded the negligible moisture on basis of conclusive evidence we dont know . But presuming the originator is right the second issue ie fluidisation in conical portion picks up . Now we in india , after filling the vessel fluidisie the vessel through conical fluidisation arrangement at conical portion of vessel upto 80% of deisred conveying pressure , followd by another 20% air for pressurzation from top of vessel , henec in this way idont think there could be any issue regardiung non-opening of fluidsation pad due to internal pressure . But i would llike comment from Mr teus in this regard . But eventually this way i think originator can address the issue.

2) Secondly performence parameter do not seems to be conveying regim of slug flow as the assuming the velocity mentioned is pickup velocity seems to be higher side & less SLR . Now if it is in lean phase then still the conveying velocity is lesser quite for given particle size of 200micron as in such case the fly ash will majorly fall in boundaly layer and tend to sediment in pipe thereby creating natural surge which leads to fly ash piles up in vessel

3) My quiry to respected Teus . He stated

. Sir would you please explain the same once broadly

Any comments is highly appreciated ■

Dear Mantoo,

Since the system is not working properly and severely underused, the salesman is probably good in selling, whether he has done a good job for the customer and for his company, I doubt that.

Your suggestion is to use the system not as a booster system anymore, but as an ordinary dense- or dilute system, which I second.

In this respect, I doubt that the 250 cfm (7 m3/min) compressor is enough as the particle size of the fly ash is rather coarse (100%< 200 micron). I assumed 100 micron, which is still above the normal particle size of approx. 40 – 50 microns.

Feedback is always appreciated.

Dear kj,

Check your fluidization pads on signs of wear, caused by passing air and fly ash along the rubber pads. When I removed abt 50 pads from 2 unloader tanks from a cement unloader, maybe 5 showed signs of being opened in operation.

There was a manual regulating valve installed to create the opening pressure of the pads. Even when we set the differential pressure over the pads at .25 bar (out of the available 2.5 bar) they did not open. Considering the 10% energy loss and approx. 15% of capacity loss, the only option was to remove them. After that everything worked well and without problems.

Pushing the rubber flap against the material column was almost impossible.

I am almost sure that when you remove the fluidizing pads and leave the remaining holes open, your system will function well.

Take care that, when there is a malfunction of the control system, all the valves are switched into the safe position.

A vessel with material, which is fed under low pressure and pressurized without proper fluidizing, will be compacted by the pressurizing air of (in this case) probably 5 to 6 bar.

Think of a pack of vacuumized coffee.

Have nice day

Teus ■

Dear sir

I checked up with the field operation but there is no sign of such trouble (non opening of fluidising pad) . Strong reason to support this answer could be the pre-pressurization of vessel via a fluidising pad taking motive air from convey air ( as a taping) pipeline up to 80% of conveyng pressure , there by 20% from top opening . In such case fluidising air pressure being higher than internal pressure of vessel will operatie smoothly . Secondly profile of fluidising pad (conical fluidising pad ) also contribute the smooth operation , i will forward you the GA drg for the same for reference

Please comment ■

Dear kj,

Not noticing any sign of fluidizing pads not opening, does not necessarily mean that they are opening.

A pressure kettle conveying system can operate with the fluidization pads closed, as long as there is a way to pressurize the kettle and mix the material with the conveying air.

In case of a poor material flow, the reached conveying pressure will not reach the designed pressure, but the system is still working, although underperforming. That is how we found out, that the pads stayed close, which was shown by some flow marks on some of them and the others were as brand-new after 50.000 tons of cement.

Removing them increased the discharge conveying kettle pressure from approx. 1.9 – 2.0 bar to approx. 2.3 - 2.4 bar, with the corresponding capacity increase.

It might well be that in your installation the pads stay closed and that you are still reaching the design pressure, due to sufficient material flow in combination with a low design capacity.

Use the supplier's data for estimating the opening pressure differential at kettle pressure and the related airflow per pad.

Keep in mind that the material on top of the pad also exerts material pressure, which can be quite high in case of arching. This material pressure is to be compensated by the air pressure differential.

You can test the situation in your case very easily, just remove the pads and monitor and evaluate the system before and aft the modification.

BR

Teus

By the way, this was my post Nu 1500 ■

Fine flyash is an easy material to convey. If you keep the air flow same and let all the air pass through the vessel instead of the boosters then it is highly unlikely that you will plug the line.

Conveying flyash in lean phase is never a good idea it is too abrasive and its cost a lot more to convey. ■

Dear carlos , would you specify the term rat hole being created and the location . Your response will help us to arrest the possible area of problem ■

Dear Carlos,

I live in the metric world.

1 ton =1000 kg

The calculation, I made, is for the existing pipeline and an assumed Aerzen compressor type GM025S at 4500 rpm (0.39 m3/sec at 1 bar).

The assumed fly ash is 100 microns.

The maximum capacity of such a system is approx. 48 tons/hr at 1 bar

At a capacity of 7.6 tons/hr, the conveying pressure is approx 0.15 bar. (close to the air only pressure).

Dilute or dense phase conveying is not related to the design pressure.

The definition of dense and dilute conveying is related to the lowest point in the so called Zenz diagram.

This observation shows that there is a cone flow problem.

The cone should be as smooth as possible and without any obstructions.

The cone angle must match the flow properties of the flyash (internal friction and cone wall friction).

Active flow enhancement by fluidizing or vibrators is only useful when there is enough conveying air passing through the vessel for material pick up.

For getting an indication of the flow properties, can you indicate:

-Poured density in kg/m3

-Tapped density in kg/m3

-Material density in kg/m3

-Particle size distribution

I assumed :

-Poured density 700 kg/m3

-Tapped density 1250 kg/m3

-Material density 2270 kg/m3

-Particle size 100 micron mean size

Resulting in:

Carr Index = 44 (Very poor flowing)

Geldart classification B (sandlike)

These results ask for more attention.

The 250 cfm air supply is likely to be too low for proper conveying through a 6”inch pipeline (assuming the just mentioned fly ash properties).

Choking the pipeline is indeed a real risk.

Executing the test with a bigger compressor is also an option, however, this requires a bigger filter.

A sketch, showing the kettle arrangement and how the conveying air is picking up the fly ash would be helpful.

How is the feedback of the supplier?

The used software is not available.

Have a nice day

Teus ■

Dear Mr Teus

Sir

1) What is difference between tappeed density & bulk density ?

2) Would you please forward the gildart classification chart you are referring to determine flowibility & carr index ?

thanks ■

Dear kj,

Geldart classification:

http://www.particles.org.uk/particle.../chapter7.pdf

http://www.gasification-freiberg.org...y-Mahinpey.pdf

Browse the web for Geldart classification

Hausner ratio:

http://en.wikipedia.org/wiki/Hausnerratio

Carr Index:

http://en.wikipedia.org/wiki/Carrindex

Flow-------------Hausner Ratio--------------Carr-Index

-----------------------1----------------------------0

Excellent-----------1,06------------------------5,66

---------------------1,07------------------------6,54

Fair-----------------1,19-----------------------15,97

----------------------1,22----------------------18,03

Passable------------1,23----------------------18,70

----------------------1,29----------------------22,48

Poor-----------------1,3----------------------23,08

----------------------1,54----------------------35,06

Very poor-----------1,55----------------------35,48

----------------------1,56----------------------35,90

----------------------1,57----------------------36,31

----------------------1,58----------------------36,71

----------------------1,82----------------------45,05

----------------------1,83----------------------45,36

----------------------1,84----------------------45,65

HRHausner Ratio =Tapped Density (TD) / Bulk Density (BD)

CICarr Index =(Tapped Density (TD) - Bulk Density (BD)) /Tapped Density (TD) * 100

see also:

http://en.wikipedia.org/wiki/User:So...Tappeddensity

Browse the web for Hausner ratio, Carr Index, Tapped density

Best regards

Teus ■

Dear kj,

The Carr Index is defined as = CI = [(Tapped density – Poured density) / Tapped density] * 100

The Hausner Ratio is defined as = HR = Tapped density / Poured density

For excellent flow:

1 < Hausner Ratio > 1.19

0 < Carr Index > 5.66

For fair flow:

1.19 < Hausner Ratio > 1.23

15.97 < Carr Index > 18.7

For passable flow:

1.23 < Hausner Ratio > 1.3

18.7 < Carr Index > 23.08

For poor flow:

1.3 < Hausner Ratio > 1.55

23.08 < Carr Index > 35.48

For very poor flow:

35.48 < Hausner Ratio > 2

35.48 < Carr Index > 50

Poured density is “as poured”

Tapped density is the density that remains after that a poured volume is densified by a standard procedure of densifying tapping.

Search the web for Geldart Classification.

Success

Teus ■

Originally Posted by Teus Tuinenburg

Dear kj,

The Carr Index is defined as = CI = [(Tapped density – Poured density) / Tapped density] * 100

The Hausner Ratio is defined as = HR = Tapped density / Poured density

For excellent flow:

1 < Hausner Ratio > 1.19

0 < Carr Index > 5.66

For fair flow:

1.19 < Hausner Ratio > 1.23

15.97 < Carr Index > 18.7

For passable flow:

1.23 < Hausner Ratio > 1.3

18.7 < Carr Index > 23.08

For poor flow:

1.3 < Hausner Ratio > 1.55

23.08 < Carr Index > 35.48

For very poor flow:

35.48 < Hausner Ratio > 2

35.48 < Carr Index > 50

Poured density is “as poured”

Tapped density is the density that remains after that a poured volume is densified by a standard procedure of densifying tapping.

Search the web for Geldart Classification.

Success

Teus

Dear sir

1) On being gone thru number of article and as per your explanation , i understand that , the value of carr index and Husner ratio are the indication of ease with which material can be induced to flow. For instance in our pneumatic flow world these co-relation is important in respect for fly ash flowing from precipitator hopper to conveying pipe line. But is these parameter (carr index, hausner ratio) has some influence on pneumatic conveying (from hopper outlet to silo top) ? If yes then , would you please explain ?

2) Secondly as explained by you ,

l. If iam correct with my understanding , then this parameter has something to do with fluidization of precipitator hopper (while unloading from hopper to vessel in pneumatic conveying system) . Other then this , is there any real significance of girdart classification in regard of pneumatic conveying ? . If yes then would you please explain ?

regards ■

Dear kj,

Your perception of the Carr Index, Hausner Ratio and Geldart classification are correct.

These characterizations are not considered in the pneumatic conveying process.

Success

Teus ■

Originally Posted by Teus Tuinenburg

Dear kj,

Your perception of the Carr Index, Hausner Ratio and Geldart classification are correct.

These characterizations are not considered in the pneumatic conveying process.

Success

Teus

Sir one of my client , using a system fly ash conveying below CFBC boiler . The fly ash primarily is constituent of lignite and limestone. Sysstem conveying parameter is

1)Fly ash conveying rate :- 50TPH

2)Fly ash temperature o/l of hopper :- 130 Deg c

3)Conveying sistance :- 150mtr

4)Bends:- 3

5)Compressed air :- 128 m3/hr @ 5 bar

6)Compressor type :- Reciprocating

7)Line size :- Unknown

Now client is facing a problem of frequent line chocking and he is of the opinion that the line chocking is primarily because of moisture after the compressor .

My opinion is that other moisture may not be issue as the combination of mixture temperature and pressure is well above the RH(relative humidity ) condition at both pickup and terminal location . Now my understanding is that , line chocking in this case is primarily because of high pressure . High pressure follows the slug flow regime , such flow without any bypass line pipe may tend to lead a severe chocking .

a)Would you please correct me with my understanding ?

b)Would you please also specify the potential reason of line chocking in such case ? ■

Dear kj,

The amount of conveying air is not clear.

It is unlikely that the compressor displacement is 128 m3/hr # 128*1.2 = 153 kg/hr.

With a capacity of 50000 kg/hr, this results in a SLR of 50000/153 = 326 (Seems very high, in fact too high)

Is the air volume given at an absolute pressure of (5+1)=6 bar?

If so, then the compressor displacement is 128 * 6 = 918 m3/hr # 0.2133 m3/sec

A 6” pipeline could correspond with this compressor.

Calculating this guessed system at 2.5 bar results in a conveying rate of approx 60 tons/hr.

Due to the high temperature of the fly ash, there is no condensation.

However, the gas velocity at the intake is rather low and the program indicates sedimentation.

At a pressure of approx. 2 bar (capacity = 55 tons/hr) there is no sedimentation.

For a better assessment of the installation, it is necessary to know the operational data (capacity and pressure) ad certainly the pipe diameter.

The system is probably operating close to overfeeding.

Is the choking taking place just after the intake?

Is the installation a pressure pot system or is there a rotary lock?

In case of a rotary lock, extra air losses have to be accounted for, worsening the sedimentation in the beginning of the pipeline.

Have a nice day

Teus ■