dear manthan,

Can you indicate the particle size of the fly ash?

This is necessary to estimate the conveyiing velocity.

BR

Teus ■

Dear manthan,

A particle that is free falling in a pipe in static air reaches a terminal velocity.

An upwards airflow with the same velocity as this terminal velocity keeps the particle floating.

Then, this velocity is called the floating velocity or the suspension velocity.

To accelerate and move the particle, a higher conveying air velocity than the suspension velocity must be maintained.

The pickup velocity is required to entrain the particles into the airstream and to convey, depending on the pickup mechanism.

The bed ash particles are rather big and heavy for a pneumatic conveying installation.

Assuming a particle density of 2000 kg/m3 (not bulk density) and an average particle size of 3000 micron, the suspension velocity is approx. 11 to 12 m/sec. (Comparable to f.i. soybeans)

The required air velocities are then approx 30 m/sec in the beginning of the pipeline to 50 m/sec at the end of the pipeline, at a pressure of approx. o.8 bar.

However, I do not have field data of this material and the material loss factor is unknown.

Due to the high velocities, a calculation is very sensitive to this material loss factor.

Therefore, it is advised to perform a conveying test with f.i. a bulk truck, to determine the material loss factor.

In addition, ask for existing installations, which convey this material at other locations.

I assume the bed ash is dry!

Success

Teus ■

Dear Manthan

Your bed ash could require a fairly high conveying velocity in suspension flow (in the order of approx 20-30 m/s) and this would call for a larger size compressor. Also, the 300 m distannce seems to be quite high, and with some bends in between and with such high velocity, their could be a significant pressure drop and chances of bend wear etc.

Have you looked into the dense-phase option? I know mill rejects in power plants are often conveyed in dense-phase (in many plants in India). The conveying air velocity at feed point is normally 3 m/s (approx). I have not physically seen the mode of flow, but I would suspect this could be single slug type.

I suggest you contact the suppliers who have such experience (dense-phase system with bed ash) and try to get info on some typical data on minimum conveying velocity, pressure drop/meter, mode of flow etc. You may not get all details and certain info may have some factor of safety, but this could be a starting point (and you could a feel of things).

Regards

SSMallick ■

6 - 0 mm bottom ash is never a good cantidate for true low velocity dense phase, nor a low pressure lean phase system. You should be looking at some thing in between the two. A blow pot system runnig at 2-3 barg at slightly higher velocities! ■

You are on the right track. The equipment you have described is the best suited for this job.

The difference from normal Dense Phase in this case will be higher air flows. This will reduce your loading ratios and increase the air velocities. ■

Dear manthan,

1)Start calculating your system with a 6”pipeline (Di=154 mm)

2)Terminal velocity approx. 64 m/sec. Pickup velocity approx. 27 m/sec at 1.5 bar

3)Air capacity 1.1 m3/sec (Blower displacement)

4)Air velocity in the conveying pipe above saltation velocity at every location.

5)Vessel volume approx. 75 cuft with a bed ash content of approx. 55 cuft.

The system pressure drop is mainly determined by the air only pressure drop due to the high velocities and the long length.

Ask your vendor to oversize the installation in order to cope with varying air conditions.

Ask for reference installations and inform yourself.

Do not design this system on your own without extensive experience.

Success

Teus ■

Ash handling is a very specialised field, there are a few companies which only do ash handling systems. They will be you best bet for a reliable conveying system. Majority coal fired power station these days use pneumatic conveying for ash handling as ash lagoons are not desired any more. Reputed vendors will have ample reference sites to show.

The pick up velocity is these system is around 18 m/s mark with stepped pipe line ending at about 30 m/s. Always remember ash is extremely abrasive and pipeline wear is directly related to the velocity. This size particles don't have to be above slatation velocity to convey as most of the time they are sliding on the pipe walls. ■

Originally Posted by Teus Tuinenburg

Dear manthan,

1)Start calculating your system with a 6”pipeline (Di=154 mm)

2)Terminal velocity approx. 64 m/sec. Pickup velocity approx. 27 m/sec at 1.5 bar

3)Air capacity 1.1 m3/sec (Blower displacement)

4)Air velocity in the conveying pipe above saltation velocity at every location.

5)Vessel volume approx. 75 cuft with a bed ash content of approx. 55 cuft.

The system pressure drop is mainly determined by the air only pressure drop due to the high velocities and the long length.

Ask your vendor to oversize the installation in order to cope with varying air conditions.

Ask for reference installations and inform yourself.

Do not design this system on your own without extensive experience.

Success

Teus

Dear sirs

I been tasked to work on the following mechacism and would like to be advised by you in attempt to approach the problem with optimum solution

Apparantly my client is using AFBC boiler , wher by he is getting the bed material from boiler as a waste

Now the waste material charecteristin in terms of particle size is 0 to 3mm

For a above given particle , clinet wants to use teh particle of 0.85 to 2.5mm which can be recycled to the boiler and ba;ance shall be dumped as a waste

This provision calls to have a screening process , but requesries more maintenence , moreover here there shall be three screening process ie

1) Bed material screened first 0 to 0.85 as a waste

2) Bed material screened second 0.85 to 2.5 recycled to boiler

3) Bed material screened third 2.5 to 3 waste

Now considerng the clinet consense over the heavy maintetence required in screening , i thought of to using the cyclone seperator thereby collecting in hopper and pneumatically conveying the desired particle size in to the furnace. But how will this approach stands the optimum solution is something i required your active consideration

Please suggest me ■

Dear Mantoo,

From the air velocities, you mentioned for the conveying of fly ash, it is possible to calculate the system pressure that relates to those velocities.

Assume the suspension velocity at the beginning of the pipeline as:

vsuspbegin and

the suspension velocity at the end of the pipeline as:

vsuspend.

Furthermore, assume the ratio:

vairbegin / vsuspbegin = vairend / vsuspend

or:

vsuspend / vsuspbegin = vairend / vairbegin

With:

vsusp –begin = Constant/SQRT(1/airdensitybegin)

and

vsusp –end = Constant/SQRT(1/airdensityend)

gives:

vsuspend / vsuspbegin = [Constant/SQRT(1/airdensityend)] / [Constant/SQRT(1/airdensitybegin)]

vsuspend / vsuspbegin = SQRT(airdensitybegin/ airdensityend)

With:

airdensitybegin = 1.293 * p(abs)begin

and

airdensityend = 1.293 * p(abs)end

becomes:

vsuspend / vsuspbegin = vairend / vairbegin = SQRT(p(abs)begin / p(abs)end)

p(abs)end = 1 (atmospheric)

results in:

vend / vbegin = SQRT(p(abs)begin / 1)

vend / vbegin = SQRT(p(abs)begin)

p(abs)begin = (vend / vbegin)^2

or conveying pressure: pconv = (vend / vbegin)^2 – 1

Substituted:

Pconv = (30/18)^2 -1 = 2.77 – 1 = 1.77 bar

For other pressures, the relationship vend/ vbegin for the same pipeline changes with the square root of the absolute conveying pressure.

Mentioning 2 values implicates at the same time that other value(s) are also set, due to the interrelation of the physical phenomena.

This makes the calculation of pneumatic conveying such a challenge.

To manthan,

For your academic purpose, ask Mr Agarwal for his article and spreadsheet on pneumatic conveying.

I also humbly recommend my own publications on the BulkBlog under the following links:

Pneumatic conveying, Performance and Calculations:

https://news.bulk-online.com/?p=65

Dense phase- or dilute phase pneumatic conveying:

https://news.bulk-online.com/?p=238

Pneumatic conveying, turbo- or positive displacement air mover:

https://news.bulk-online.com/?p=309

Energy consumption per ton of a pneumatic conveying system:

https://news.bulk-online.com/?p=331

Pneumatic conveying, an unexpected relationship.

https://news.bulk-online.com/?p=445

Pneumatic unloaders: Problems to avoid

https://news.bulk-online.com/?p=74

Influence of electro static charge on pneumatic conveying.

https://news.bulk-online.com/?author=15

Bacterial heating of cereals and meals.

https://news.bulk-online.com/?p=216

Success

Teus ■

Dear Teus

Indeed you are right you can very easily calculate the system pressure drops provided you have got some experience or the famous friction factors. These conveying conditions still fall under lean phase and one can use air velocity and suspension density relationship to calculate system pressure drops.

Have a good day ■

Originally Posted by manthan

I WANT calculation/hint/ for following problem

ASh with

density-600kg/m3

conveying dist-300mtr

height-20mtr

ash conveying rate--9tph

with help of pneumatic conveying system

(1)what should be the capacity of air required ?

(2)how we can calculate it?

(3)what sholde be the dia of pipe and how?

(4)what is the effect of change in density of ash in conveying?

typical system is as below

ash from hooper will be collected in ash vessel here with the help of pressurise airfrom compressor. ash will be conveyed to silo through pipe of suitable dia.(dense phase system)

Fuvale ceramic-lined valves.

Wear and corrosion resistance

The valve ball, valve seat and inner lining are all made of structural ceramics with hardness of HRA87 or above. So structural ceramic ball valves can withstand the impact of Hi-speed liquids and hard grains, displaying excellent performance on wear and corrosion resistance.

Corrosion resistance

The valve ball, valve seat and the inner lining are all made of structural ceramics. The structural ceramics have excellent corrosion-resistance, except to glass-liquor and hydrofluoric acid. ■

Dear Sirs,

Could any one guide me if a roots blower of 0.5 - 0.75 kg/cm2 pressure be used to achieve 50 tons per hour transfer rate for pumping dry fly ash into a hopper from the ground level with vertical elevation of the system as 35 m and horizontal distance of 5 m and 3 pipe bends of 90 degrees each. The material bulk density is 0.6 tons/m3 and size is 40 microns.

Regards

A Kaushik ■

Dear A Kaushik,

The answer to your question is: Yes, it can.

I calculated 2 installations.

1)Pipe size 154 mm (6”) and a blower of 18 m3/min: resulting in approx. 60 tons/hr at a conveying pressure of 1.5 bar. (comparable to a pneumatic bulk truck unloading)

2)Pipe size 203 mm (8”) and a blower of 30 m3/min: resulting in approx. 60 tons/hr at a conveying pressure of 0.65 bar.

Your silo must be equipped with a suitable filter and safety relief valve and level testers.

Success

Teus ■

Thank you for your prompt reply

Regards

A Kaushik ■

Dear Teus,

Shouldn't it be possible to bring down the pressure requirement of 1.5 bar to 0.6-0.75 bar for the 6" pipeline only, if the transfer rate of fly ash can be reduced to 35-40 tons per hour from 60 tons per hour.

Regards

A Kaushik ■

Dear A Kaushik,

I made 2 preliminary calculations for you.

1) with a screw compressor of 30 m3/min (instead of 18 m3/min) at a 6" pipe line

2) with a blower of 30 m3/min (instead of 18 m3/min) at a 6" pipe line

see attachment.

It is advised to consult a wellknown and experienced supp;ier instaed of designing a system on your own.

(Unless you are one yourself)

Have a nice day

Teus

Attachments

calculation for fly ash conveying (PDF)

■

Dear Teus,

Thanks a lot for your reply.

From your calculations, it seems that for a 6" pipeline, a blower of 30 m3/min and 0.685 bar (~0.7 bar) should be enough to achieve 40 tons per hour material tranfer rate. However, the bulk density of dry fly ash in your calculations seems to be 970 kg/m3 with particle size of 30 microns.

Shouldn't the system pressure and air volume requirement change for a coarser fly-ash of bulk density 700 kg/m3 and particle size of 65% material < 45 microns/ 35% material > 45 microns ( ~1-2 % material of at most 200 microns size).

Regards

A Kaushik ■

Dear A Kaushik,

I repeated the calculations for a particle size of 80 microns, with an Aerzen blower GM35S at 3150 rpm of 30 m3/min at a 6" pipe line

see attachment.

It is advised to consult a wellknown and experienced supplier instead of designing a system on your own.

(Unless you are one yourself)

Have a nice day

Teus

Attachments

calculation for flyash conveying 2 (PDF)

■

Dear Teus,

Thanks again for your help.

Regards

A Kaushik ■

Dear A Kaushik,

You are welcome.

Take care

Teus ■

Although the topic has been many years gone. Please help me if possible.

Fly ash (30-35 micron) with conveying dist-400mtr + height-20mtr with Number of bends 3; compressor 22 m3/min with P 2.2 bar; Pipeline size 6", . We test run Capacity about 65 tons/hr. But when there is a problem that has to be stopped, a blockage occurs, the fly ash does not fill the cross section of pipe. Please help me with the solution. I have a plan to arrange the injectors in  pipeline, will that solve the problem?

■