If you know Excel, please use my calculation method published in this month's issue of Powder Handling and Processing "Theory and Design of Pneumatic Conveying Systems" for solving your problem.

Let me know if you need any help from me.

Regards,

A. T. Agarwal

Consulting Engineer

Pneumatic Conveying Consulting Services LLC

polypcc@aol.com ■

Ahmed

63 m3/min of free air equates to about 1.3 kg/s and so if you are conveying 230 tonne/h the solids loading ratio comes to about 50 and this equates to dense phase conveying.

63 m3/min of free air in a 10 in bore pipeline at a conveying line inlet air pressure of 1.5 bar gauge gives a conveying line inlet air velocity of about 8 1/2 m/s and this also equates to dense phase conveying.

You include a "silo vertical length" of 74.1 m. Can this be assumed to be 7.41 m vertically up? The length of 10 inch bore pipeline is about 22 m, but the length of 12 inch bore pipeline is significantly longer, particularly with the 37.9 m horizontal section towards the end, and disregarding the 74.1 m, and so the balance between the two does not look too good.

Despite this imbalance the system should work OK with your air supply. Your best bet for an improvement to 250 tonne/h is probably to increase your air supply pressure if this is a possibility. Stepping the pipeline is usually suggested but yours is already stepped and I doubt if a further step to 14 inch bore could be recommended. ■

The previous reply from Dr. Mills is correct in that more air pressure would be needed to handle the rate you need. However, that raises a different set of concerns as well.

The motor BHP on a Screw Pump is a function of several parameters, through-put capacity is one BUT the discharge pressure the pump must work against is another and in many cases, it drives the BHP requirement exponentially higher.

Based on the line routing you gave, (which by the way, looks suspect because of the step point being so close to the start of the system), the line pressure will be significantly higher than the available 1.5 bar. I believe you may very well have a pump motor issue to contend with as well.

It has also been noted that you are in the "dense phase" mode. By many definitions, that is correct but I'd like to clarify that screw pumps work in the "slug flow" or "wave flow" of dene phase, not the "pulse / piston" flow.

I believe with the air volume you stated and the pressure anticipated, you are reaching the point where the slugs and waves are becoming too large and the air pressure is rising too much and you will have pipeline plugs. ■

If you increase the conveying air volume to the silo, you will need to either add another filter or install a new, larger one. If you add an additional filter, you need to add it in "parallel" to the existing filter, so they SHARE the load, not in "series".

If you mean to create a "suction" in the silo to help increase the pneumatic conveying rate, that is not recommended on a typical Cement silo as they are not usually designed to contain any internal negative pressure and it would be quite expensive to do so.

Actually, cooling the compressor discharge air will not help because I believe you are lacking Volume of air. As you increase the discharge temperature, the air density decreases so the actual volume increases because the total mass of air stays constant. You will have less ACFM on the compressor discharge because of cooling. ■

As that is no doubt a very minimal suction pressure, most likely only millimeters of water, that will not help you increase your conveying capacity and unless you have some form of vacuum relief valve on the silo roof, you could run the risk of a silo failure because of too much vacuum. ■

Ahmed

Please check your private messages as I have sent a message to you concerning this subject outside of the forum. ■

I stumbled, surfing “who is online”, this pneumatic conveying thread.

This thread is dated before I joined this forum.

Based on the given information of “grundfoss2004” I calculated the installation (as described in https://forum.bulk-online.com/showth...8469#post88469)

The calculation results are:

-conveying line inlet air velocity of 9.41 m/s (including the effect of present cement)

-Solids loading ratio = 35.4

A silo height of 7.41m is even more unlikely

-Capacity approx. 155 tons/hr at a conveying pressure 1.5 barg

-Capacity approx. 160 tons/hr at a conveying pressure 1.6 barg

-Capacity approx. 200 tons/hr at a conveying pressure 2.5 barg

These values are realistic considering the airflow (1.05 m3/sec), the conveying distance (161 m) and the energy consumption (1.1 kWh/ton).

“grundfoss2004” claims an existing capacity of 230 tons/hr.

This claim cannot be substantiated by the calculations.

Have a nice day ■

Dear Nevana,

I made a quick calculation of your described installation.

I believe it is unlikely that the burned lime has a moisture content of 2%, as the free water reacts immediately under the generation of heat.

The calculation, I made, corresponds roughly with yours.

Only the calculated pressure (3 barg) is far too high.

Probably a dimension error.

See for a description how to calculate a pneumatic conveying system on

www.yarca.nl

I calculated:

solid loading ratio = 15/3.6/0.11526=36

Pressure = 0.215 barg

Power = 3.1 kW

Air velocity = 11 m/sec to 14.5 m/sec

CaO velocity = 7.2 m/sec to 11 m/sec (after bends approx. 4.8 m/sec)

Attachments

quicklimecalc (PDF)

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