Dear Ton,

It is refreshing to hear interest in evaluating conveyor design from the Total Cost of Ownership. I believe this topic is one not often asked. To do the question justice, one needs knowledge of rubbers viscoelastic behavior. Few engineers are equipped to resolve the fundamentals of power consumption based on first principles.

Conveyor Dynamics, Inc. (CDI) competes for projects on the world market. Our target audience are long overland (curved or straight) and high lift/powered conveyors. We win jobs based on cost. We employ belt bottom cover (pulley cover) viscoelastic analysis of all major manufacturers. This is the analysis of belt rolling loss effieciencies. Although we win jobs based on bottom dollar. The true benefit is in the added value in power reduction. I give an example.

Two belt manufactures compete for a belt order.

Mfg No. 1 is prefer from historical performance

Mfg No. 2 is prefered from present support.

The conveyor operates from 1 deg C to 50 deg C.

We divided the 12 months into avg day and night temperatures to evaluate the sensitivity of power verses temperature.

The NPV operating cost penalty of mfgr 1 verses mfgr 2 in total kwhrs power for 15 years is $2 million.

The belt strength of mfgr 1 was lower due to its superior rolling resistance at zero deg. C

However, at elevated temperature mfgr 1 consumed far more power again due to the rubber's rolling effiency difference.

Motor sizes turn out to be the same. Without considering the operating cost of power mfgr 1 could have won the order. The total belt order is around $4 million. Most purchasing agent do not act on behalf of their client to secure the belt total life cylce cost. They do not have the tools and neither do most engineers.

To your specific question of optimized belt speed for best net life cycle cost, the real answer must have many qualifications. Which are too lengthy for this response. I did a brief analysis of two cases using coal to prove a point. Consider a conveyor either transports 2,000 t/h or 10,000 t/h of coal over 2000 m. The belt width is optimized to carry either of the two tonnages for 3 m/s or 6 m/s belt speed (ie what are the belt widths for 2000 t/h at 3 or 6 m/s and for 10,000 t/h at the two speeds). From this, derive the capital and operating cost over say 15 years to obtain the net total life cycle cost. In summary, the narrower and higher speed belt is the less total life cycle cost option unless the cost of power exceeded $0.10/kwhr. for both tonnages. Matereial density also plays a significant role. Coal will have a different optimization point from iron ore. For your information this review has the following belt specs.

2000 t/h: 1400 mm wide @ 3m/s; 1050 mm wide @ 6 m/s

10000t/h: 3000 mm wide @ 3m/s; 2200 mm wide @ 6 m/s

Some large users of conveyor systems are beginning to realize that substantial savings can be made if the more costly and superior rolling resistant rubber compound is specified. Here, 5% cost premium can return a NPV 50% belt cost benefit. On new conveyors the benefits are often far larger.

Thanks for asking the Question. I plan to do an article in a major publication on the many projects we have successfully completed using low rolling loss rubber compounds. A caveat to this is there are major pewrformance differences between manufacturers and compounds from one manufacturer. See our published papers in Bulk Solids Handling and other venues.

With Kind Regards,

Lawrence Nordell

President

Conveyor Dynamics, Inc.

1111 West Holly St.

Bellingham, Washington 98225

USA

ph 360-671-2200

fx 360-671-8450

email: nordell@conveyor-dynamics.com

web: www.conveyor-dynamics.com ■

Dear Ton,

Second comment. It is true that below $0.10/kwhr E-cost, we find, in general, higher speed, narrow belt, large idler spacing, lighter structure, and lower installation cost outweigh the incremental increase in drive assy equipment and NPV power cost. The E-cost savings is significant but not dominant. This assumes a constant speed system.

Capital cost savings usually dominate. Return on capital for many projects is very sensitive to initial cash flow and the level of a bank's assessment on IROR. The operating cost usually is incorrectly assessed, as stated in my initial commentary. We believe more projects would recieve funding if the true operating cost were made a part of the bankable feasibility study. This includes picking the best belt cover compound for the application and environmental conditions.

Varing motor speed to maintain a constant belt cross-sectional loading is becomming more common practice. How do constant volume belt feeders vary from their larger conveyor counter-parts? It certainly does offer a cost reward for reducing total kW-hrs. I am aware of a number of operators that do subscribe to the practice, even though they have the means. There are two main reasons:

1. Chute flow is altered and can cause greater wear not less if the design does not take this into consideration.

2. Operators are loath to stop a operating conveyor - most nusance problems occur during start-up, shutdown, or after the conveyor has be idled for a time. They look at the tariff of restarting weighed against producing on-demand and believe nusance outage or non-availablility is the greater evil.

Waiting to see the comments of others.

Regards,

Lawrence Nordell

Conveyor Dynamics, Inc. ■

There is a case study for such an application, you may review / print the paper at the following address:

www.saimh.co.za/beltcon/Beltcon8/paper89.html

Kind Regards ■