I would not recommend a vertical screw elevator for this duty in view of its length, the abrasive nature of the material and its moisture content and tendency to form lumps. A bucket elevator would seem to be a more appropriate means to handle this material, perhaps with an inclined feed screw to control the input and provide a low loading hopper.

The diameter of the silo is not given, but it is suspected that it will not be of mass flow design, in which case some problems may be expected with the moisture content forming larger agglomerates than 3.5” diameter during indefinite storage. A mass flow construction would be taller than a non-mass flow silo of the same holding capacity, but a smaller volume may suffice if the contents move in live flow. The prospects of slow moving product sticking to the wall could be countered by using UHDPE liners on the walls to around 6 foot diameter. The lower region could then be transformed to a mass flow chisel shape for an outlet slot fitted with an inclined, progressive extraction discharge screw. This would offer a large, scoured flow channel to avoid discharge problems, but at low velocity to minimise wear. Wall friction tests should be conducted to provide design data.

The length of the discharge screw should be limited to a single span, as an intermediate bearing poses many difficulties. The screw diameter, length of inlet and flight construction requires a balance between operating speed, flow channel reliability, power consumption and wear. This is really the domain of a specialist as a crude solution may work, but could incur operational and maintenance difficulties that would far outweigh any saving on equipment cost. Perhaps Scorpio Conveyors of Bangladore may be able to assist in this project. ■

For elevating materials, vertical and inclined screw systems will be very high maintenance. Why not look at our DSI Snake-Sandwich High-Angle conveyors. These use all conventional conveyor equipment including smooth surface rubber belts that can be continuously scraped clean. Check these out at our web site.

Joseph A. Dos Santos, PE ■

Dear Mr. Y.R. Berde,

I take this opportunity to inform you that screw conveyor in any case is not a desired kind of equipment as it is a trouble some equipment.

Further you are asking for a vertical screw conveyor. In hindi it is said "Ek Karela doosare Neem Charaha". It implies it is more troublesome.

I strongly suggest you to opt for a Steel Cord Belt Bucket Elevator for the application. Ofcourse it is slightly expansive, but inthe long run it is not only ec0onomical but also is very much trouble free.

You may contact me at 00 91 11 2669 2847 or fax me 00 91 11 2669 1543.

Look forward to see You.

In case you are around Delhi, please drop in we will have a chat on the subject and may be are able to do some business, as we have already supplied more than 120 Steel Cord Belt Bucket Elevators in India and Abroad specifically for the Cement and Fly ash.

With Kind Regards.

for ENEXCO TEKNOLOGIES INDIA LIMITED

CHHABRA HN.

Sr. Manager-Marketing ■