Considerations about the Cost of Conveyor Belting – Discussing re-evaluated Belt Safety Factors

Safety Factors for Conveyor Belts

Considerations about the Cost of Conveyor Belting – Discussing re-evaluated Belt Safety Factors

New conveyor belts and belt monitoring technologies reduce conveyor belt capital and operating costs by using lower belt strengths than previously thought possible. Key factors are improvements in splice performance, rubbers and real-time belt condition surveillance systems.
(ed. wgeisler - 01/2/2017)
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The following example illustrates these benefits:
An existing 2300 m long overland conveyor with 5.5 m lift transporting 4600 stph of coal at 5.1 mps was designed in 2007 using conventional CEMA design methodology. The belt is a 72” (1829 mm) ST2500. In Figs. 7 and 8, the original design is shown as the red line. Fig. 7 shows the required belt strength at different operating temperatures based on a 6.67 safety factor and Fig. 8 shows the power utilized at different temperatures.

For each chart, conveyor belt characteristic curves are shown for two different pulley cover rubber types:
a) Standard ARPM (formerly RMA) Grade I (blue line),
b) Energy Optimized Belt (EOB) LRR rubber (pink line).


Fig. 7: 6.67 SF belt rating vs. temperature (°F) 
 

Fig. 8: Required power vs. temperature (°F)

The charts show:
1. The significant temperature dependency of each pulley cover rubber.
2. That the new technology rubbers permit lower belt strengths
3. That the new technology rubbers use less power at all temperatures that the CEMA calculation

As a consequence of the analysis the required belt strengths can be summarized as follows:
1. ST2220 for a standard ARPM Grade I belt
2. ST2170 for a EOB LRR belt

The belt strength for each rubber type is dictated by the lowest operating temperature. In this case, the energy efficient EOB LRR rubber offers a small (2.2%) reduction in belt strength compared to a standard ARPM Grade I belt. As the additional cost of the EOB LRR rubber may be more than 2.2%, the belt’s operating energy cost savings must be calculated and considered in the choice.

In order to calculate the annual cost savings we determine the power requirement for each month considering the average day and night temperatures. Table 2 shows the monthly maximum and minimum temperatures for the conveyor location. 

Table 2: Average monthly max. and min. temperatures                                                                  

Based on the cost of power for the facility ($0.05/kW.h) and considering the total power requirement for the annual temperature profile, the annual operating cost for each option is:
1. ARPM Grade I:  $ 247,959
2. EOB LRR:         $ 184,213
Annual savings potential: $ 63 746

The cost savings for the EOB LRR of approximately $637,460 over 10 years, suitably adjusted for inflation, should be considered together with the initial belt capital cost of each belt option in order to properly evaluate the maximum potential cost savings.

As in the discussion on safety factors, if a lower strength belt is chosen, smaller and/or fewer steel cords are employed in the belt design and the belt is more vulnerable to damage from impact. In addition to 24/7 cord condition monitoring, another highly developed technology that should be considered to reduce potential impact damage and excessive belt wear is engineered chute design. This subject is discussed in Ref. 1.

References

[1] Minkin, A.: Cost Reduction in Belt Conveying - Cost-efficient and Application-oriented Design of Steel Cord Conveyor Belts for the Mining Industry; Bulk Solids Handling, Vol. 35 (2015), No. 2,  pp. 16-23.
[2] Jonkers, C.O.: The indentation Rolling Resistance of Belt Conveyors; Fördern und Heben, Vol. 30 (1980), pp. 312-318.
[3] Spaans, C.: The Calculation of the Main Resistance of Belt Conveyors; Bulk Solids Handling, Vol. 11 (1991), No. 4, pp. 809-826.
[4] Hager, M., and A. Hintz: The Energy Saving Design of Belts for Long Conveyor Systems; Bulk Solids Handling, Vol. 13 (1993) No. 4, pp. 749-758
[5] Lodewijks, G.: The Rolling Resistance of Conveyor Belts; Bulk Solids Handling, Vol 15 (1995) No. 1, pp. 15-22.
[6] Wheeler, C.: Design Considerations for Belt Conveyors; Australian Bulk Handling Review, May/June 2007.
[7] Steven, R.: Belting the World’s Longest Single Flight Conveyor; Bulk Solids Handling Vol. 28 (2008) No 3, pp. 172-181.
[8] Kropf-Eilers, A., L. Overmeyer and T. Wennekamp: Energy-Optimized Belt Conveyors – Develoment, Testing Methods and Field Measurements; Aufbereitungs Technik Vol. 49 (2008) No. 9, pp. 25-34.
[9] Wennekamp, T., A. Kropf-Eilers, and L. Overmeyer.: Energy-optimized Conveyor Belts; Bulk Solids Handling 29 (2009) Nr. 1, pp. 24-29.
[10] Wheeler, C.: Measurement of the Indentation Rolling Resistance of Conveyor Belts; Beltcon 16, Johannesburg, S. Africa, Aug 2011.
[11] Nordell, L.K.: The Channar 20 km Overland, A Flagship for Modern Belt Conveyor Technology; Bulk Solids Handling, Vol. 11 (1991) No. 4, pp. 781-792.
[12] Nordell, L.K.: The Power of Rubber – Part I; Bulk Solids Handling, Vol. 16 (1996) No. 3, p. 333 ff.

 

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