Paulo

I moved your thread to a more appropriate forum.

Your question may sound simple but it cannot get a simple answer. Have you completed a design capacity check of your system? Is the ultimate goal to increase capacity? Just simply stating to increase speed creates many issues and lots of questions. The entire system will need to be investigated for suitability at the requested speed if the intention is to also increase capacity. For example: The trajectory into the chute will change and may create a poor flow through the transfer chute. All bearing loads will change and need to be looked at. Simply increasing the speed will not have a huge impact on the system other than the trajectory but an increase in capacity may have a huge impact on the system.

You need to state the end requirement of your manager. ■

Choice of speed is very important and if the speed is stepped up the design must accordingly match and this influences the upstream and downstream equipment.

Your own concerns are well founded.

Regarding practical test...

Once upon a time in a previous century I watched some not so clever mining consultants uprate a feed conveyor to the reverbatory furnace hall at a copper refinery in Zitwe. The original speed was the allowable speed of most Anglo American mines, painfully slow. The conveyor had been in operation since 1937 when the Empire had expanded to meet a foreseen demand for shell casings etc. In 1989 the speed of the belt was increased in line with modern practice. The idlers were rattling away nicely within a month of start up and the unforeseen spares were not easily available, especially since the plant was operating at run & repair to start with.

If your manager is really serous about speeding the belt up I suggest you manoeuvre him into providing written confirmation. Also point out to him that sugar dust can be explosive.

It becomes an extensive costing process, expensive in itself, where the idlers are selected in relation to the belt tensions, rotational speed, idler pitch and belt width. A design program can make the selection easier and faster. ■

Originally Posted by johngateley

Choice of speed is very important and if the speed is stepped up the design must accordingly match and this influences the upstream and downstream equipment.

Your own concerns are well founded.

Regarding practical test...

Once upon a time in a previous century I watched some not so clever mining consultants uprate a feed conveyor to the reverbatory furnace hall at a copper refinery in Zitwe. The original speed was the allowable speed of most Anglo American mines, painfully slow. The conveyor had been in operation since 1937 when the Empire had expanded to meet a foreseen demand for shell casings etc. In 1989 the speed of the belt was increased in line with modern practice. The idlers were rattling away nicely within a month of start up and the unforeseen spares were not easily available, especially since the plant was operating at run & repair to start with.

If your manager is really serous about speeding the belt up I suggest you manoeuvre him into providing written confirmation. Also point out to him that sugar dust can be explosive.

It becomes an extensive costing process, expensive in itself, where the idlers are selected in relation to the belt tensions, rotational speed, idler pitch and belt width. A design program can make the selection easier and faster.

I have come across such increase in speed.

The system was re-designed.

The drive system was changed to higher size.

Since the discharge profile changed, the transfer chute was modified.

The idler life is mainly of sealing system and bearing life : however take the idler manufacturer into confidence.

As suggested above there may be de-gradation of size of particle and increase in dust.

Rgds,

Narayanan Nalinakshan. ■

There are many examples of disasters caused by thinking you can simply increase capacity by increasing belt speed. I know of one example where very significant expenditure was made to increase system capacity to 5000 tph by simply increasing belt speeds and upgrading the stacker only to see the system capacity reduced by 20% instead of being increased by 30%. Why? Narayanan of all the those who replied focused on the real issue and that is the transfer chutes. If you do not modify all your transfers for the change in trajectory then build-up in the transfers is likely along with spillage and dust generation that can be a fire hazard. Other than transfers the process is relatively simple as the increased belt speed usually balances out the increased load for most components. Idler bearings may need to be checked just in case as will high tension pulleys. May need to check structural loads at the head end and this may require a bit of extra bracing. By looking at you current demand power at the current speed you can assess whether the current motor and gear boxes are adequate if you have VVVF drives otherwise you are up for new gear boxes and possibly motors.

Cheers

Colin Benjamin

Gulf Conveyor Systems Pty Ltd

www.conveyorsystemstechnology.com ■

Paulo,

Martin Engineering book, Foundations 4, can be downloaded from their website. Chapter 4 gives plenty of background but your increase in dust cannot be quantified from there.

Similarly, the dust control suppliers are understandably non-committal about the dust generated versus belt speed issue.

I would suggest that in the absence of test results you should stick to the figure given/applied in your industry. ■

Hello,

Mostly there is always the issue of belt speed for every project. So this topic is ever green.

In a lighter moment, this issue is something like car speed. Car will have capability for high speed, but speed being used at city centre, at city outskirt, on highway or on express way will be different. It will also depend upon road condition and traffic discipline (driving culture, etc.). In case of car, it is the issue of feasibility, safety and wisdom / madness.

Regarding belt conveyors, engineers have observed that it is ‘Better’ to have lower speeds for in-plant conveyors and higher speed for long distance conveyors. Here ‘Better’ implies:

- Economy (initial cost, operation cost, number of supply sources for spares / replacement, downtime for system). The cost to be inclusive of chute work, transfer house, etc.

- Reliability (equipment functional reliability, service life and number of supply sources i.e. if supply sources are very less, one may not get required item in time affecting the complete plant operation, etc.)

Theoretically designer is free to choose the speed he likes, and then design the conveyor system accordingly. In this context some practical restrictions are as below:

1) If material is light, fluffy or powdery, it can restrict the speed limit. 1 mps implies 3.6 km/hour, like walking medium speed. At 5 mps, it is 18 kmph (medium speed cycling). So judge if you are holding material open to such wind, whether it will suffer some loss (fly-off). Alternatively wind tunnel test.

2) Roller rpm. It seems for average good quality idlers, about 550 rpm speed could be limit. Although German design literature mentions upto 700 or 800 rpm.

3) Higher speed makes the chute and transfer house bigger. In case of long conveyors, this will have marginal influence on total cost, however for short conveyors its influence for plant price will be significant.

4) Speed limitation imposed by abrasiveness and lumpiness. Highly abrasive material will wear out the belt and idlers quickly if there is more speed. Sharp edged lumpy material like black stone (particularly for larger size lumps) necessitates slower speed of conveyor and also lower speed of incoming material at feed point; or else it can damage belt.

5) Conveyor speed for specialised situation, like space constraint in mines or boom conveyor of stacker-reclaimer machines, etc.

If you are not expert on belt conveyor design, then it is better to restrict your choice to conventionally used speeds which also have a speed range upto 5 mps for certain materials. The speed values mentioned in such tables do not have boundary limit. Suppose it is mentioned 3 mps, one can have + / - 10% without any reservation because it has been observed that sometime one gets 3.15 mps due to gear box ratio and pulley diameter and then it is not worth dispute / objection. The conventionally mentioned speed values are for in-plant conveyors. So for long distance conveyors, obviously the speed can be higher by say 35% or more depending upon the design and specific case.

If need be contact the expert designer who has first hand experience about the concerned application, or contact engineers at existing similar installation. There is nothing like modernism by using more speed.

Ishwar G. Mulani

Author of Book: ‘Engineering Science And Application Design For Belt Conveyors’. Conveyor design basis ISO (thereby book is helpful to design conveyors as per national standards of most of the countries across world). New print Nov., 2012.

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

Email: conveyor.ishwar.mulani@gmail.com

Website: www.conveyor.ishwarmulani.com ■

Mr.Paulo,

I am not a designer. 5m/3.5m = 1.43 .

Is your production rate expected to be increased to 1.43 times ? Belt speed depends on TPH ( Tonnes per hour) to be handled. What made to increase the belt speed?

Regards, ■

Originally Posted by sganesh

Mr.Paulo,

I am not a designer. 5m/3.5m = 1.43 .

Is your production rate expected to be increased to 1.43 times ? Belt speed depends on TPH ( Tonnes per hour) to be handled. What made to increase the belt speed?

Regards,

Good question.

Designers amongst us have assumed that in the 3rd line of the opener we must have been dealing with a newbuild: this because there is no mention of increased capacity. If we are dealing with a brownfield situation the conveyor must be completely reworked or else expect disaster.

In a life cycle world it would be quicker, safer and cheaper to build a new conveyor, space permitting, rather than mess around a site trying to make a conveyor do what it was not designed to do and therefore cannot do. Within the context of the opener there is uncertainty about the downstream equipment and/or conveyors which further reinforces the assumption that this is a newbuild.

However, sugar is a seasonal crop and, although the cane harvest season is very intensive, there are very long periods where maintenance of some very heavy machinery is prepared ready for the next harvest. Perhaps this was the case? It all depends on the commodity price and the insurers' explosion risk cover.

I know Paulo will advise. ■

Dear Mr.Paulo,

Having abnormal high belt speed may ask for frequent belt and rollers belt replacement. It may not be economical in the long run. Having correct designed conveyor's structure and drive is one time cost. But belt and rollers replacement will be repetitive in nature.

Kindly get expert designers advice before you go for final decision. Please mention at what TPH, you need them to be operated.

Regards, ■

Dear Mr.Paulo,

As per my experience, 1400 mm width conveyors with 2.7 to 3 mtr/sec belt speed can meet your required TPH. 159 mm diameter carrying rollers are used.

This is only my opinion. You may ask others advices also.

Regards, ■

This thread has become an example to us all.

We have reached the point where feedback is given and received in good spirit, conclusions are being reached and open discussions abound.

I, for one amongst many others, would like to congratulate the participants and hope, expect even, that this progresses into the New Year.

One worthwhile thread is worth dozens of some that come our way. ■

Originally Posted by johngateley

This thread has become an example to us all.

We have reached the point where feedback is given and received in good spirit, conclusions are being reached and open discussions abound.

I, for one amongst many others, would like to congratulate the participants and hope, expect even, that this progresses into the New Year.

One worthwhile thread is worth dozens of some that come our way.

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To your question of what limits belt speed aside from the typical idlers, chutes, ..., is the product particle size, shape, and mass.

There are conveyors operating at 15 m/s and have little dust. YEs, transfer stations must control flow and minimize expulsion of dust particles.

The main limiting features are particle size and density. Aside from the transfer station, the conveyor speed must not exceed the value where air flow turbulence at the product surface does not exceed the Reynolds number that supports your product suspension. This is a knowable values. Since you have not provided product size distribution, material density and shape (bagasse, crystals, ....), we cannot offer the belt speed number.

Belt speed = 5 m/s may be possible, depending on % of critical size in suspension you need to control, or it may be 2 m/s. However, as said it is knowable with the proper data.

However, as you note the wish to save money on belt selection, et. al., there are ways to run at 6 or 7 m/s with smaller width and not have dust emissions along the belt axis. This is done by enclosing the belt (i.e. pipe or other belt trough shapes) to contain the localized gas environment above the product from the ambient environment, or by a hood cover style that almost does the same. ■

Hi Paulo,

Dust is not an issue regardless of belt speed if you get the transfer chute design right, simple as that. You can create dust at 1 m/s or 6 m/s with a bad transfer as drop height can see the sugar accelerate significantly. The key to dust generation is flow control and key to this is intercepting the sugar at flow angles less than 20 degrees and then by design ensuring that it does not continue to accelerate.

Cheers

Colin Benjamin

Gulf Conveyor Systems Pty Ltd

www.conveyorsystemstechnology.com ■

I have seen the sugar silos at Liverpool and Durban which are arched sheds resembling overgrown railway stations. In the Liverpool silo a water spray was used. This could have only reached to the lower levels of the pile and dust must have been generated by the downfall through still air. Sugar was extracted through floor grids after having been severely moistened earlier. As if! This building has been listed as historic and cannot be demolished (even by ISIS) and another use must be found for it. The photograph shows that in the 1950's,and beyond, the dust from sugar falling at great heights was accepted.

href="https://forum.bulk-online.com/attachment.php?attachmentid=44992&d=1450781627" id="attachment44992" rel="Lightbox87155" target="blank">■

Originally Posted by Colin Benjamin

Hi Paulo,

Dust is not an issue regardless of belt speed if you get the transfer chute design right, simple as that. You can create dust at 1 m/s or 6 m/s with a bad transfer as drop height can see the sugar accelerate significantly. The key to dust generation is flow control and key to this is intercepting the sugar at flow angles less than 20 degrees and then by design ensuring that it does not continue to accelerate.

Cheers

Colin Benjamin

Gulf Conveyor Systems Pty Ltd

www.conveyorsystemstechnology.com

================================================================

Dear Paulo,

Dust control in chutes are not in dispute. Bad chutes can cause unwanted dust depending on particle distribution.

I disagree with Mr. Benjamin comment that "dust liberation is not an issue regardless of belt speed". He is entitled to his experience.

We see this differently. Often we design conveyor operation in tunnels where the dust is a concern and pass nearby villages with local concerns for health, et. al., and/or at higher speeds.

By example in tunnels, we ask is the tunnel ventilated and does the air flow concurrent or countercurrent to the conveyor motion. Even primary crushed rock can have sufficient dry dust size particles that contaminate the tunnel for personnel unless they used special respirators. Once the net speed exceeds 5m/s, some primary crushed ores will pollute in the tunnel.

Another example, a coal conveyor runs next to a village and the operator wishes to maintain a good relationship with the locals. If the conveyor had an open surface and cross winds were sufficient, the villagers would complain about their outdoor drying of cloths, children's health, and so forth.

How much dust is too much? I tried to give guidance in my prior posting to give a hint on how it is solved for various conditions and limitations of belt speeds. There are standards in some countries against such pollution. As such, you will need to evaluate the conditions in a scientific/engineered manner.

We run some conveyors far beyond 5 m/s where the conveyor transports enough dust to create a operating restriction. However, the conveyor is also designed for the occasion, such as Mundra and Dahej, India coal conveyors running at 7.5 m/s. At Dahej, the conveyor runs adjacent to a number of villages and is elevated. The villages are not at transfer stations, but, at this speed, the belt could liberate unwanted dust off the ore/product surface. A special belt hood cover prevents the potential for high dusting by isolating the transport plenum from the ambient environment. You will need to know the dust design criteria for your application. ■

Another example is fine cement where the belt speed is limited to at or below 2 m/s. Even at 2 m/s excess dust can be generated for operator health and well being. There are many such examples that do not consider the chute. Note here, the fine cement has most of the particle set, which limits the belt speed, to at or below 2 m/s.

Chutes can be a major dust pollutant with finer product sizes. This was never in dispute. Modern ore flow analysis codes can give good guidance on what level of dust is liberated and what chute geometry best minimizes excessive dust at the transfer as per the product in question. This is a special topic that, in part, also is impacted by higher belt speeds. ■