Carbon Black Conveying
A pressure regulator upstream of a sonic nozzle is the arrangement typically used to control the gas flow in blowtank conveying systems. As long as the ratio of the conveying pressure / regulated supply pressure is 0.528 or less, the total gas flow to the system can be adjusted by changing the regulator setting.
The gas flow to the blowtank system is normally split with a manual 3-way valve with a portion going directly to the conveying line and a portion going to the top of the blowtank. It is the flow to the top of the tank that determines the carbon black (solids) conveying rate.
So essentially two adjustments are needed to achieve ideal conveying conditions in blowtank systems.
Dennis Hauch, PE ■
Carbon Black Conveying
I would like to add the following to the very good response given above by Dennis.
Since a standard Laval nozzle has a fixed flow, depending upon the inlet pressure, this flow may result in too high (or too low) a velocity in the conveying line. It is desirable to use two or three Laval nozzles, in parallel, of different orifice sizes to allow variation of the flow, if needed. Another option is to use a Laval nozzle with a variable orifice opening. These options will give you more control on conveying velocities than a single fixed orifice Laval nozzle.
Regards,
Amrit Agarwal
Consulting Engineer
Pneumatic Conveying Consulting
Email: polypcc@aol.com
Ph and Fax: 304 346 5125 ■
Re: Carbon Black Pneumatic Conveying Problem
dear kevinjcg
I came accross the website :
www.aeromechanical-com/cs8102.html
dealing with carbon black conveying
success ■
Teus
Thanks
thank you for your reply
Dear Dennis Hauch
may you give me some advice about how can select the inlet pressure of laval nozzle , because different people have different idea, some researcher said using the pressure of regulator as inlet pressure of laval nozzle, but the others thought the stagnation pressure(the pressure of air vessel) is addmitted, so which should be selected as the inlet pressure of laval nozzle? thanks
Dear Amrit Agarwal
I browsed the website, may you give me some advice about selecting the inlet pressure of laval nozzle? thanks
thank you for your consideration
best regards
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Carbon Black Conveying
Dear All,
I found some missunderstandings in your discussion, so I give some comments:
- the mentioned relation 0,528 for back pressure/inlet pressure is valid for an orifice or a nozzle without diffusor, but not for a laval nozzle.
Because of the diffusor a laval nozzle has a critical pressure relation 0,85...0,9, depending on the shape quality.
- to find the right inlet pressure of the nozzle, which is positioned upstream the blowtank, you simply have to know the highest conveying pressure in the blowtank and the pressure losses of the piping, valves... between nozzle and tank.
Example:
pressure in blowtank <3bar abs
pressure loss for piping 0,5bar
-> back pressure at nozzle <3,5bar abs
-> minimum inlet pressure 3,5/0,85 = 4,1 bar abs
The diameter of the nozzle has to be designed for the required flowrate, depending on the calculated inlet pressure.
- high air flow at the end of blowtank discharge is not caused by the nozzle, because the massflow is strictly constant, also with low backpressure. The reason is expansion of the pressure in the blowtank. To avoid this, you have to shut the tank outlet by valve as soon as the tank is empty, but still on full conveying pressure. Then vent the tank via a vent valve on the top of the tank ■
Thank You
Dear Reinhard Ernst
thank you for your reply, the back pressure/ inlet pressure vary from 0.85~0.9 with the shape quality of laval, so the airflow is different for different shape qulaity of laval which have the same throat diameter, maybe the sutuation is complicated.
best regards
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Carbon Black
The shape quality only influences the critical pressure relation, but not the air flow. Flowrate is constant for any back pressure below the critical value.
Flowrate is only determined by inlet pressure and diameter ■
Carbon Black Beads
Carbon black beads breakup easily even at the low velocity of standard dense phase depending upon their crushing strength. Beads with low crushing strength will revert to their original form of "fluff", a very fine powder with a bulk density of about 4 lbs/cu ft. This powder has extremely poor flow properties. A proven solution to this problem is the use of primary and secondary air, with primary air injected at the pickup point and the secondary air along the conveying line at about 5 to 10 feet intervals. The ratio of these two is about 1 to 4. The goal is to attain a terminal velocity of about 3 meters/sec or less.
Regards,
Amrit Agarwal
Consulting Engineer
Pneumatic Conveying Consulting
Email: polypcc@aol.com
Ph and Fax: 304 346 5125 ■
Carbon black pneumatic conveying problem
we use laval nozzle and reductor to control air flowrate in carbon black pneumatic conveying,
but I am puzzled by the inlet pressure of laval nozzle , the back pressure/inlet pressure no less than 0.528,the air flowrate through laval
nozzle is constant, but how can i select the inlet pressure, and we convey barbon black using blow tank, that is inevitable in end of conveying,
the darg force is very small, so the back pressure decrease, the velocity of laval nozzle is becaming supersonic, that will create wave shock,
the disadvange of supersonic is it will impact pipe ,so how can I do ? and can I use stagnation pressure as inlet pressure?
thanks
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