Dennis Hauch - Freeport, TX, USA
(not verified)

Tanker Unloading

Posted on 25. Jun. 2003 - 03:42


Your questions are good, the answers are found in the design and operation of the bulk tanker.

Time is money so the drivers of bulk tankers always want to unload in the shortest possible time. That means unloading at or near the tanker maximum allowable working pressure (MAWP). The MAWP is 1 or 2 bar for US-built tankers and 2 bars minimum for European-built tankers.

The tanker operator manually adjusts a 3-way valve that splits the supply air, part of it going to the headspace above the material in the tanker, and part of it bypassing the tanker and going directly into the conveying line. This valve is adjusted until the operating pressure approaches the MAWP of the tanker (more air going to the headspace raises the conveying rate and the operating pressure).

The tanker air supply is from a truck-mounted PD blower arranged with a variable speed drive. The air supply must be capable of dilute-phase velocities because even slug flow (non-suspension) systems will see dilute-phase velocities in the clean out step. A blower curve is used to obtain the desired conveying flow (based on velocity and pipe size). I should think that a terminal gas velocity of 5 to 8 m/s (depending on the length of the system) would be a good starting point for cement.


Dennis Hauch


Posted on 25. Jun. 2003 - 11:18

Thank you for your information.

I have contacted the company that builds the cement trailers for the transport firm in question and it appears that the air flow is about 1000 m3/h (ambient conditions). I do not know whether this is typical for such trailers.

Pneumatic Cement Transport Air Flow

Posted on 25. Jun. 2003 - 12:37


I just saw your querries.

I would suggest to install PD Blower near the unloading station as it will reduce the number of PD Blowers. Otherwise, Youy need a PD Blower on each truck, it will increase your project cost.

The requiremetn of air depends upon the rate at which the truck mounrted Bin is to be unloaded.

The requirement for unloading of a tanker of capacity 30 tonnes in approximately 20-30 minutes upto a height of 35 meters, with a horizontal conveying of approximate 15 meters and 2 numbers of 90 degree bends is approximate 18-20 cu meter per minute at a pressure of 2 bar.

Hope it helps you.

In case you need the complete system, let me know, i have supplied such systems for unloading of fly ash in India.

My address is or

With Kind Regards.

HN Chhabra

Re: Pneumatic Cement Transport Air Flow

Posted on 25. Jun. 2003 - 01:33

These data correspond reasonably well with the unloading time of half an hour that I am dealing with. The horizontal section of the conveying piping will be much less in the case considered, the unloading point is right beneath the silo. From the information I have now, I think I can safely consider the air flow to be of the order of 1000 m3/h. Thnaks a lot for your kind offer to provide me with more details, but I do not think that that will be necessary.


Arne M Bollen.

(not verified)

Blower Volume

Posted on 21. Dec. 2005 - 12:57

Dear Mr. H N Chhabra sir

With reference your atricle in Web site forum of Areation Pad for Bin & Silo as well as using in the Air slide for cement & fly ash stronge & conveying by air slide.

Please send the Pressure & air volume (Blower capacity) calculation for cement & fly ash Stronge in Bin & silo. And also in case of air slide using for cement & fly ash conveying.

I hope & waiting your positive reply.

With regards,