Dear sea-will,

As the pneumatic conveying properties of the magnesium chloride (mgcl2) is very important for the design, at least the following data are required:

-MgCl2 – material density (2320 kg/m3 – anhydrous or 1569 kg/m3 – hexahydrate)

-bulk density

-particle size(distribution)

-(if known, the suspension velocity in air at atmospheric conditions)

Furthermore:

-Altitude of operation

-Atmospheric conditions (Temperature and Relative Humidity)

Then a preliminary design calculation can be made.

In case that you have operating installations with the same product, it would help to have the installation- and operational data, in order to determine the Solid Loss Factor.

This would make the calculations more accurate.

Have a nice day

Teus ■

Originally Posted by sea-will

dense phase pneumatic conveying system for magnesium chloride (mgcl2)

Dear sir,

I want to know the Material/Air ratio when mgcl2 is conveyed in dense phase method, and the design condition as follows:

1. conveying distance: horizontal length:330m, vertical length: 30m, bends number:10;

2. discharge device: single blow tank ( bottom discharge type )

3. capacity: 60t/h(not include blow tank loading time)

thanks so much.

sea-will

As Teus has so kindly mentioned the two major problems are the seive size

of the material and the local atmosperic pressures.

Moving this material a thousand feet or more is going to consume a very large amount of energy.

Each and every bend consumes the available air energy to propel the material and

reduces the speed of flow of the material.

If you are filling a blowdown tank for a bagging line you should consider an elevator and a gravity system.

Is the Magnesium Chloride in question flaked or pelleted deicier?,

further are you bagging in form, fill and seal bags or super sacks or open mouth sacks

of triple wall paper construction? ■

Dear sea-will,

I preliminary calculated your installation for the following conditions:

horizontal length = 300 m

vertical length = 30 m

Number of bends = 10

Magnesium Chloride MgCl2 anhydrous

material density =2320 kg/m3

bulk density = 620 kg/m2

material temperature = 10 degrC

Ambient temp = 33 degr C

RH = 44 %

particle size = 1500 micron

suspension velocity = 8.15 m/sec under atmospheric conditions 1 bar and 0 degrC

As the flow properties are expected to be not fit for by pass feeding regulation, a rotary lock is probably required. This limits the conveying pressure to2 bar.

To prevent condensation in the pipeline, cooling of the conveying air is required.

To achieve the required 60 tons/hr, the following preliminary installation set up is determined.

At a Solid Loss Factor of 0.585 (high value compared to similar products) the calculation result is:

Pipe diameter =16”

4 screw compressors Aerzen VML150 at 4700 rpm

Air flow 8.3 m3/sec (490 m3/min – 29880 m3/hr) at 2 bar

Filter area at receiving silo = 800 m2

Begin velocity = 17 m/sec

End velocity = 72 m/sec

Solid Loading Ratio = 2.57

Power = 2172 kW

energy consumption = 35.5 kWh/ton

Capacity = 61.1 tons/hr at 2.0 bar

The same installation calculated with a Solid Loss Factor of 0.25 (average value compared to similar products) the calculation result is:

4 screw compressors Aerzen VML150 at 4700 rpm

Air flow 8.3 m3/sec (490 m3/min – 29880 m3/hr) at 2 bar

Filter area at receiving silo = 800 m2

Begin velocity = 17 m/sec

End velocity = 72 m/sec

SLR = 3.57

Power = 2172 kW

energy consumption = 25.7 kWh/ton

Capacity = 61 tons/hr at 1.7 bar

The conclusion is that a pneumatic conveying system for MgCl2 is technically possible, however, not a realistic feasible solution.

This is caused by the high suspension velocity of the MgCl2 and the thereby required high air velocities.

The long distance causes the low SLR values.

A 300 m long conveyor belt with bucket elevator seems a much more simpler, reliable and economical solution.

Have a nice day

Teus ■

The system calculations provided by Mr Teus are for a typical lean phase system starting at 17 m/s only difference is the system is running at 1.7 barg; so some people argue it is a dense phase system but in my opinion with a SLR of 3.57 it is a lean phase system.

Running a conveying system for 1.5 mm pellets at these velocities will pulverize the pellets and dust will come out of the other side. If degradation is not (which I know is) an issue then you will fine. Stepping the pipe at suitable intervals to keep the velocities in reasonable range will be required. This will reduce the conveying pressure and will have slight reduction degradation also.

If the material has no significant quantities of dust then 1.5mm pellets can easily be conveyed in dense phase at much lower velocities i.e 3 - 5 m/s pick up. For the given distance the conveying pressure is expected to be in 3-4 barg. You will need stepped conveying and at least a 5 barg compressor to run the system. ■

Dear Mr Mantoo,

I calculated the Zenz diagram of the installation assuming a Solid Loss Factor of 0.25 and for a capacity of 63 tons/hr.

(4 Screw compressors Aerzen VML 150 at xxxx rpm.

The Zenz table calculation resulted in:

3250 rpm --------- 1.460 bar -------- sedimentation -------- dense

3500 rpm --------- 1.419 bar -------- sedimentation -------- dense (lowest pressure drop)

3750 rpm --------- 1.427 bar -------- sedimentation -------- dilute

4000 rpm --------- 1.470 bar -------- sedimentation -------- dilute

4200 rpm --------- 1.538 bar -------- sedimentation-------- dilute

4500 rpm --------- 1.629 bar -------- -------- dilute

4700 rpm --------- 1.700 bar -------- -------- dilute

5000 rpm --------- 1.806 bar -------- -------- dilute

5500 rpm --------- 1.990 bar -------- -------- dilute

The calculated design (4700rpm) is indeed dilute or lean phase.

Stepping the pipeline will improve, however, the effect at lower conveying pressures is less than at higher conveying pressures.

Still the installation will be not economical.

I agree that the salt particles will degrade into much smaller particles during conveying.

(Experienced that with a pneumatic installation for 1.5” pebble lime)

Reducing the air velocities will cause saltation or sedimentation of material, beginning in the first part of the pipeline.

The chosen air velocity must be in relation to the suspension velocity of 8.15 m/sec at atmospheric pressure and 0 degrC

As the operating altitude is 2800 m (0.72 bar), the velocities must be higher anyway in order to carry the MgCl2.

A conveying pressure of 1.7 bar means an absolute pressure of 0.72 + 1.7 = 2.42 bar(a) instead of 2.7 bar(a) at sea level.

Assuming a pick up velocity of 5 m/sec at a conveying pressure of 4 bar, the local suspension velocity is 8.15 / SQRT(4.0+0.72) = 3.75 m/sec

The Reynolds number is then approx. 100.000 and the local wall velocity is approx. 0.442*5= 2.2 m/sec.(< 3.75 m/sec)

Along the pipe wall, the air velocity is too low to carry the material.

Reducing the air velocity too much will cause choking.

At least my program indicates choking.

Have a nice day

Teus ■

Dear Mr Teus

I think we have debated this issue many times before. You always keep the conveying system to the right side of the Zenz diagram in the lean phase side and so does your software. This is why you always end up with very high pick up velocities and any system with pick up velocity in single figures is a chocking scenario. Why don't you use the left side i.e dense phase side of the Zenz diagram? All proper dense system have a pick up velocity on single figures.

If you move on the left side of the Zenz diagram into the dense phase zone then conveying velocities are low but pressure drop/m increases substantially. In this zone the materiel is out of suspension and form plugs. Once the plugs are formed sedimentation of particles is not relevant as the material moves in plugs and single particle mechanics cannot be applied. The driving force of the plug is the pressure behind the plug less the air flow through the plug due to porosity.

Lastly I will not comparer this material with pebble lime. Lime's are considered specials dense phase conveying of pebble lime will never be a viable option !

Season Greetings! ■

Dear Mr Mantoo,

You are right that my software does not calculate plug conveying.

However the computer program does calculate from continuous dense conveying to dilute conveying.

Calculating a plug conveying system is based on friction forces and solid mechanics in the plug.

(Analog to silo calculations) as dense and the dilute conveying are based on the transfer of impulse between air and material at cost of the internal energy of the gas.

I agree with your remarks in your second alinea.

I normally design for a pneumatic conveying system, operating just above or with minor sedimentation in the pipeline.

Whether that turns out to be dense- or dilute phase conveying depends on the pneumatic conveying properties of the material.

(It is well-known that not all materials are conveyable in dense phase)

The cement conveying installations that I have designed and operated were almost always in the dense phase region.

Example:

Cement conveying installation:

122 m horizontal

30 m vertical

5 bends

pipe diameter 10” stepped to 12”

218 tons/hr

design: 1.4 m3/sec at 2.5 bar

Zenz diagram

0.6 m3/sec ---------- sedimentation------------- 3.97 bar ------------- 0.82 kWh/ton

0.7 m3/sec ---------- sedimentation------------- 2.98 bar ------------- 0.79 kWh/ton

0.8 m3/sec ---------- sedimentation] ------------- 2.87 bar ------------- 0.88 kWh/ton

0.9 m3/sec ---------- ------------- 2.78 bar

1.0 m3/sec ---------- ------------- 2.71 bar

1.1 m3/sec ---------- ------------- 2.65 bar

1.2 m3/sec ---------- ------------- 2.59 bar

1.3 m3/sec ---------- ------------- 2.55 bar

1.4 m3/sec ---------- ------------- 2.50 bar ------------- 1.43 kWh/ton --- DESIGN

1.6 m3/sec ---------- ------------- 2.43 bar

1.7 m3/sec ---------- ------------- 2.40bar

1.8 m3/sec ---------- ------------- 2.38 bar

1.9 m3/sec ---------- ------------- 2.36 bar

2.0 m3/sec ---------- ------------- 2.34 bar

2.2 m3/sec ---------- ------------- 2.30 bar

2.5 m3/sec ---------- ------------- 2.285 bar ------- DENSE

2.75 m3/sec ---------- ------------- 2.78 bar

2.85 m3/sec ---------- ------------- 2.281 bar --------- DILUTE

3.0 m3/sec ---------- ------------- 2.285 bar

In this example, the design is well in the dense region and still above the sedimentation point.

Whether the pickup velocity is a single figure depends on the local suspension velocity of the particle.

A particle with a high suspension velocity under atmospheric conditions might well result in a single number, in case the pickup pressure is high enough.

Pickup velocities in grain unloaders (suspension velocities up to 10-12 m/sec) are in the range of 28 to 35 m/sec.

My remark about the pebble lime was not intended to compare the pebble lime with MgCl2.

I meant to indicate that a friable material easily can degrade during pneumatic conveying, whereby the pneumatic conveying properties can change dramatically.

Resume,

Yes, you are right that I do not calculate plug conveying, however I do calculate dense phase conveying according to the definition and dilute phase conveying.

Whether the MgCL2 conveying installation can be a plug conveying system over 300 m + 30 m vertical, I have my doubts.

I do really appreciate your response.

Happy New Year

Teus ■

Originally Posted by Mantoo

The system calculations provided by Mr Teus are for a typical lean phase system starting at 17 m/s only difference is the system is running at 1.7 barg; so some people argue it is a dense phase system but in my opinion with a SLR of 3.57 it is a lean phase system.

Running a conveying system for 1.5 mm pellets at these velocities will pulverize the pellets and dust will come out of the other side. If degradation is not (which I know is) an issue then you will fine. Stepping the pipe at suitable intervals to keep the velocities in reasonable range will be required. This will reduce the conveying pressure and will have slight reduction degradation also.

If the material has no significant quantities of dust then 1.5mm pellets can easily be conveyed in dense phase at much lower velocities i.e 3 - 5 m/s pick up. For the given distance the conveying pressure is expected to be in 3-4 barg. You will need stepped conveying and at least a 5 barg compressor to run the system.

Dear Mantoo,

I agree with your objections in so far, as a rough estimation (and moderate extrapolation) on the basis of my own state diagram leads for instance to the following dataset for the beginning of the dense phase conveying state: bulk solid rate 60 t/h, pipe diameter 232 mm, aquivalent pipe length 400 m, gas temperature 30 °C, gas flow rate 2454 kg/h, pressure loss 2.5 bar. But for me remains the open question, whether such a system is really stable and how can this be proved.

Best regards, ManfredH ■

Dear Manfred,

Your SLR is 60000/2454 = 24.45

The begin velocity of the air is 2454/3600/1.2/(3.14/4)/0.232^2/3.5 = 3.85 m/sec

The end velocity of the air is 2454/3600/1.2/(3.14/4)/0.232^2 = 13.5 m/sec

The suspension velocity of the 1500 micron particles (particle density 2320 kg/m3) is approx. 8.5 m/sec at the end of the pipeline.

At the beginning of the pipeline, the suspension velocity is approx. 8.5/SQRT(3.5) = 4.54 m/sec

In the beginning of the pipeline, the local suspension velocity is higher than the local air velocity.

Particles cannot be kept in suspension and pneumatic conveying is not possible.

Unless you have calculated a plug conveying system, which I doubt, considering the airflow and pressure.

You also do not state that it is a plug conveying system.

Have a nice day

Teus ■

First of all if I had a choice for this system I would prefer a belt conveyor for this job. Simply on running costs " power is not cheap these days". Only if belt conveyors were not a option for what ever reason then I would look at a pneumatic conveyor.

For academic argument sake this system is also possible with a pneumatic conveyor but we have to look at material properties before designing. If there is substantial dust in the pellets then system will be problematic. If the pellets are friable then dust will be formed during conveying and will cause problems but these issues can be mitigated.

Assuming you are talking 60 tph average conveying rate and not instantaneous conveying rate next thing will be the vessel size. This will equate to conveying pressures, if you load 400m of 232mm pipe which is 17.5 m3 in total pipe volume with material, the system will never work and conveying pressure will keep on rising until it blocks. The air flows you have mentioned will give 3.8 m/s pick up velocity at the start which might be bit low for this distance.

As far as proving the design it can easily be tested in a test plant (which most of the reputed vendors have) then scale it up. If this was a proper enquiry you will get system quotes easily. ■

Dear Sirs,

I really do thank you both very much for your effort. Because of your explanation I am now in the position to interpret my own state diagram and its limits better. So, the measured values apply in the dense phase region only to fine Materals with particle diameters up to about 300 microns, possibly up to 700 microns. The maximum mass flow rate in these installations is 19,5 t/h. In contrast lie the operating data from systems with higher mass flow rates (35 t/h and 50 t/h) in the dilute phase area near the instable transition area. Bulk solids with particle diameters in the millimeter range lie always in the dilute phase area.

Thanks again,

Manfred Heyde ■