If you are uncertain of you abilities to produce a 27 km long conveyor, why not issue enquiries to those companies with proven track records for such machines and let them provide a suitable machine for you. They can then select to offer a conventional or pipe conveyor. ■

Both can be designed to work. To date only the trough belt has reached this size at Curragh North mine in Australia.

The longest pipes to date, by my understanding is the 8 km in Peru and the 7 km in China. The technology exists today to make such a pipe conveyor.

The pipe conveyor will cost more than twice the price of the trough belt, based on your criteria, when you consider Total Life Cycle Cost of 10-15 years. ■

I have evaluated both concepts and conclude the pipe design is not possible by conventional pipe construction techniques. The power and belt strength will be very substantial and impractical for the pipe design. I would exceed known pipe construction in belt strength and power.

A conventional belt will not have this large penalty, and has been done before. ■

Power comparison:

Pipe will require about 10,000 kW more to move coal @ 1500 t/h over 21 km.

At $0.10 kW-hr. and 5000 hours per year @ full load = $ 5 million USD / year penalty for the pipe plus a large differential in capital cost. ■

Dear Sirs

In this case I submit that pipe conveyor is probably not the best option however with these perameters PC would require approx 1200 kW total installed power conventional trough approx 6000 kW and I believe the capital cost would be more but not twice that of conventional conveyor.

Yes in this case it is beyond the tensile limits of pipe conveyors which would probsaly require 3 off flights.

However depending on the requirement and geography the pipe conveyor can solve other problems but probably not in this case. ■

Dear Mr. Mallick, The better option is to go for Capsule Conveying Technology.Now,since you are from a consulting company to know more and feed it to the client you can request Mr.Leon. ■

Dear Associates:

I offer a following Q&A exchange from comments on the noted difference in power, belt details and idler count (reliability). I selected a large size pipe conveyor to compare with a typical, not optimized, trough conveyor. I wish to obtain counterclaims on the pipe design side to test the fair balance of those that design pipe conveyors for a living and/or trough belts:

His Questions, Notations & My Comments:

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Dear Lawrence,

Prima-facie, let me agree with what you have written. For instance the overall cost of the pipe is exorbitantly more than that of the conventional belt conveyor.

However there are a few points for you to please do a re-thinking about please. The difference in the consumed power is perhaps not so much, although the resulting tension in the pipe might not allow such a conveyor system at all. In that aspect, this is far less practical.

Further you wrote “5000 hours per year” – this is in fact far from reality. As far we are aware of the conditions in India, the company who is prepared to pay for such a system, will certainly have it functioning for as close to appr. 8000 hours per year. Thus presumably you can imagine, what an increased penalty for the pipe plus a large differential in capital cost will eventually result !

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Answer:

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Dear Sir,

Pipe conveyors, in general, will consume over twice the power of a conventional well designed trough conveyor. We know this because we measure the two concepts running in the field.

There are a number of reasons for the difference:

1. Pipe construction has tended to have higher construction stiffness modulii to maintain the pipe shape. This is dependent on the pipe diameter, belt tensions, curve radii and their orientations. The pipe stiffness is selected for the installation to keep the pipe from collapsing over + years of operation. The pipe stiffness will fall by 30% or more in the first few months and then taper in a gradual fashion. Higher stiffness means higher power to overcome the forming forces.

A special note on stiffness and seam orientation: First, You must have the seam near vertical as it approaches the head/drive pulley. If not you run the risk of the belt not unfolding and returning with material and half width. This problem has repeated itself multiple times. Second, you should have the belt track well at loading and discharge. If the belt is off at loading or at discharge, caused by seam orientation, the ore will track to one side and may induce spillage, excessive edge stress and mal-tracking which will lead to severe edge damage (very common with pipe installations). Operators will use their own corrective measures, not authorized by designers, to place belt closer to pulley centerline and not run the belt edge into the chute wall. Still we see pipe belts with one severely chewed edge. THis should not occur. Client is not given instructions, nor installer on how to make corrective action before damage.

2. Pipe contact stress with rollers is much higher than with trough conveyors. High forming pressures, smaller rolls although shorter spacing, poor belt construction, small horizontal and vertical radii. Most designers know not what these do to the design. They simply apply a friction factor over the conveyor length like DIN f = 0.045.

If this number were true, and it is in some installations, a well designed trough conveyor (no sharp radii) will have a DIN f =0.015 or lower. Given the conveyor has no elevation, the difference in power and belt selection is given as:

1. Assumed tonnage ................................................... 3000 t/h

2. Assumed speed ...................................................... 5 m/s

3. Material ................................................................. Coal @ 900 kg/m

4. Lump .................................................................... 100mm

5. Length x Lift ........................................................... 6000m x 0 lift

6. Idler drag with conventional design ............................ 9 x 6 N

7. DIN f for trough ........................................................ 0.015

8. DIN f for pipe .......................................................... 0.045

9. Belt cover thickness ............................................... 9 x 6 mm no rheology influence - only used DIN f values 0.015 for trough and 0.045 for pipe.

Results of the above .................................................... trough..................pipe

10. Power .................................................................... 1237 kW............. 4476 kW

11. Nameplate ............................................................ 3 x 450 kW ....... 3x1600 two head & one tail ( two electric stations)

12. Nameplate power summary ...................................... 1350 kW ........... 4800 kW 3.5 times greater for pipe

13. Belt Width ............................................................1524 mm........... 2150 mm..... 41% more

14. Belt Strength (ST-XXXX N/mm).................................1300 N/mm........ 2500 N/mm.. 92 % more

15. Belt mass (kg/m).................................................... 41.9 kg/m ........ 73.1 kg/m.... 74% more

16. Idler roll count......................................................... 6815..................36072.......... 530% more

For power, let us see your method to disprove the above. Also note we do not normally operate in the DIN f =0.015 range. We do operate much lower making the above a very conservative comparison. The pipe will be typically worse by a fair margin. I claim, based on the above, the pipe will cost about twice as much to build and 3 times as much to maintain. Tell me where you disagree. Provide backup -- as I have done above.

Your comment on 5000 hours vs. 8000 hours. I said the 5000 hours represents full design load. In fact there is a period where the belt operates empty (15-30%) and where it operates at nominal (65-80% of design), where it operates at full load ( 10-30%), and where it may operate for a short time at surges.

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Your Comments:

Looking for other knowledgable designers which will not only counter the above, but will offer details on why these numbers are exaggerated. Otherwise, the numbers are compelling and should be given due respect.

My last comment to the above: The pipe conveyor can be designed with values and techniques superior to the above DIN f=0.045 by using very modern techniques that:

a) control the top and bottom seam rotation - patented method to do so

b) reduce the forming force by using a patented belt construction by Veyance Technologies (Goodyear)

c) significantly reduce power and belt tension .

We look forward another voice on pipe stablizing techniques: Prof. Lodewijks presentation paper on seam rotates at the 2010 Mumbai conference.

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Dear Shri S S Mallick,

The earlier participants have already given adequate technical information. I would add few points and draw the attention about the other aspects.

Firstly, the pipe conveyor and belt conveyor have distinct areas of application. If material is powdery, if its concealed conveying is must and if there are sharp curves; then pipe conveyor would be a necessity as application requirement. But if the application is for conveying material like coal, limestone, iron ore, etc. then same do not have necessity for concealed conveying.

If it is simply transportation of material by 21 km, then belt conveyor is economical by very wide margin, with respect to initial investment as well as operational cost. For the given capacity mtph, the pipe conveyor needs wider belt and it has 6 rollers on carrying side and 6 rollers on return side (as against 3 rollers on carrying side and 2 rollers on return side for belt conveyor). This together with larger drive units results into more investment for pipe conveyor.

The pipe conveyor operational cost is more due to its higher power consumption and less easy maintenance work. For the belt conveyor replacement of certain length of belt is very simple, but not so for taking out and inserting such belt length in case of pipe conveyor. Also for belt conveyor the items to be attended are within 1.3 m height from walkway level, whereas for pipe conveyor the upper run is at higher level and its attendance is not within easy reach / handling by workman. All these aspects result into higher maintenance and operational cost and downtime for pipe conveyor.

As for the length of conveyor (whether it is pipe conveyor or trough belt conveyor), the decision about number of flights is purely economical in nature. The better way is to estimate / enquire the system price considering one flight or two flights, etc. The investor of the system would be seriously concerned about it rather then the focus on length of conveyor.

It is to be noted that the conveyor installation is not like overhead HT cable line where ‘install and forget’ is the rule. Nobody tries to steal anything, temper with it and remains away by tens of arm length.

In case of belt conveyor, it is operating installation wherein its components are in motion all the time. The belt conveyor (whether of trough type or pipe type) requires continuous check and attendance to see that everything is working all right. The conveying installation is prone to theft; pilferage and tempering (like some passerby pulling emergency pull cord and system comes to stop from beginning to end). So it requires round the clock general watch by the owners’ employees and security people. The installation also requires operational employees (engineers, workman, spare parts store setup, etc.). Adding one transfer house for two flights may hardly make difference in required employees.

Adding one transfer house makes the entire belt length of nearly half the strength, reduces the pulley sizes, but increases pulley quantity and certain increase in electricals, etc. Sometime extra ordinary long conveyor is provided with one or two fixed tripper type arrangement on carrying run to introduce tractive pull at intermediate points for economical design. In such conveyor long flight length (from head to tail end) is for name sake only, as it do have self-feed transfer houses.

The conveying installation needs service road along conveying route for regular monitoring of the system and movement of spare parts. The conveying route should also take care of animal and people movement across the conveying route.

The information draws attention that the conveying installation is of techno-commercial nature requiring comprehensive considerations irrespective of single flight or more flights. This will reduce the time lost from initial enquiry to order finalisation, changing requirement and consequently repetitive proposals from suppliers. The gradual knowing of all these issues at buyers end during project finalisation certainly take place, but with time loss and price for both sides.

Regards,

Ishwar G Mulani.

Author of Book : Engineering Science and Application Design for Belt Conveyors.

Author of Book : Belt Feeder Design and Hopper Bin Silo

Advisor / Consultant for Bulk Material Handling System & Issues.

Pune, India.

Tel.: 0091 (0)20 25871916 ■