Dear Maurizio,

The particle density of salt (NaCl) is 2160 kg/m3

In combination with a particle size of 2400 micron to 4000 micron, the suspension velocity is approx. 13 m/sec .

That requires an air velocity of approx. 35 to 40 m/sec.

The pipeline diameter of 0.095 m and a velocity of approx. 40 m/sec leads to a compressor displacement of approx. 17 m3/min.

At these velocities, breakage will be a serious issue with this vulnerable commodity .

Review your design calculations or better; consult an experienced supplier.

Have a nice day

Teus ■

I worked in salt evaporation plants and a salt mine for more than 30 years and never had much success with pneumatic conveying of salt. I am not saying that it cant be done but as Teus has stated crystal breakage is going to be a very major concern as well as creating a high level of dust that you would need to contend with.

You would be much better off to install a bucket elevator to handle your product. Thats the way we always handled it and still doing it that way today. ■

2-4 mm Salt sounds more like dishwasher salt. Yes it can be conveyed in dense phase.

Since you have mentioned that it is off the sieve so it is safe to assume it is dust free.

Fine salt is much difficult to convey then than coarse.

Degradation will be the main issue. If it is granulated then the degradation will be less

than if it is angular. What is the acceptable limit of fines generation? The major cause

of degradation will be at the end of the cycle when the vessel will depressurise and

the end velocities will be much higher than 12 m/s. I would recommend that you use

a twin vessel arrangement and do not let the pipe de-pressurise (easier said then done).

If it is not possible then use a big blow tank and keep the cycling low. You might not

achieve 30 tph in 95mm id pipe you should be looking at around 125mm pipe. Airflows

are in the right ball park. Stepping the pipe at the end will also help. ■

To prevent particle wear and breakage, a dense phase system with line boosters should be considered because it can run at conveying velocities down to a maximum of 10 ft/sec. This is a system with conveying air divided into two parts, primary air and secondary air. Primary air is introduced at the start of the conveying line and secondary air is introduced every 4 or 5 ft intervals in the conveying line via flow control valves to minimize conveying air flow and hence the conveying velocity. This system can be designed in-house or purchased from any of several worldwide vendors.

Regards,

Amrit Agarwal

Pneumatic Conveying Consulting

Email: polypcc@aol.com ■

Dust free Granular salt will convey without Boosters. Since the conveying distance is relatively short the

conveying pressures will not be very high either. Adding boosters will also increase the total airflow which will not

help degradation. Generally Boosters are employed for fine powders or granular material with high fines content. ■

Dear Mr Teus

I have never understood why you keep on calculating suspension densities for a dense phase systems.

The dense phase is mostly plug flow and while material is moving in plug flow it is never in suspension it is

always sliding. Also in dense phase system the material flow rate is not consistent as there is always gaps

between plugs!

In my opinion the term suspension density for dense phase has no importance. If you could

kindly explain the rational for you dense phase calculations it will be very enlightening for me.

Regards ■

To prevent particle wear and breakage, a dense phase system with line boosters should be considered because it can run at conveying velocities down to a maximum of 10 ft/sec. This is a system with conveying air divided into two parts, primary air and secondary air. Primary air is introduced at the start of the conveying line and secondary air is introduced every 4 or 5 ft intervals in the conveying line via flow control valves to minimize conveying air flow and hence the conveying velocity. This system can be designed in-house or purchased from any of several worldwide vendors.

Dense phase system with line boosters minimizes conveying velocities because of operation in plug flow regime, to the far left of the Zenz Diagram. Primary air injected at the start of the conveying line can be as low as 10% of the total. The remaining 90% is injected via line boosters along the conveying line at about 5 ft intervals. Total air flow is, therefore, substantially reduced compared with injecting 100% at the start of the line, resulting in solids to air ratios of 50 or more. These systems are widely used for materials such as pelleted carbon black where particle attrition must be prevented.

Regards,

Amrit Agarwal

Pneumatic Conveying Consulting

Email: polypcc@aol.com ■

I would agree that for pelleted carbon back your proposed system will work well. But unfortunately

granulate salt is nothing like carbon black. Due to considerably higher bulk / particle density if you

put only 10% air in the vessel then you will struggle to push the material out of the vessel. Indeed

vessel geometry will have its influence on material discharge rates.

My comments were based actual granulated salt conveying experience and not on assumption if it

works for material it will work for that also. ■

Originally Posted by maurizio biscaro

Hello, I have read various opinions and the most relevant seems to me that Mr. Manitoo.

The plant may be made of dense phase pulsed air. The boosters could be used only if the transport is stopped due to lack of compressed air or electricity. For the diameter of the line to 30 t / h you could use a pipe DN125 (141.3 x3mm) or DN150 (168.3x3mm.). Do you think it is enough of a 1m3/min air X1T / h of salt? greetings M.Biscaro

No 1 m3/min is too low air flow as stated before size for 4m/s pick up velocity. ■