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The CEMA Horsepower Equation

Belt Conveyor Design

The CEMA Horsepower Equation

Development of a new Conveyor Power Prediction Methodology
The 7th edition of Belt Conveyors for Bulk Materials (known as “The Belt Book”) includes a new con­veyor power prediction methodology using “Large Sample Indentation Test” (LSIT) data. This article provides background and insight into how LSIT data is used to design conveyors, and describes the relation between this and the older conveyor power prediction methods. It also illustrates the use of LSIT data by using it to predict indentation losses in a recently commissioned conveyor system.
(ed. WoMaMarcel - 07/10/2015)
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The 61.7 N/set figure includes trampling losses, load dependent idler losses, and flexure losses. Using our proprietary flexure and trampling losses method, CDI predicts the 11% of the losses at Dahej resulted from trampling and flexure. If so the indentation losses were less than 55 N/set.

Further, the LRR belt data presented in CEMA is an LRR rubber compound made by an American manufacturer. The LRR rubber at Dahej is a different compound manufactured by a German company so the CEMA LSIT data does not really apply. The comparison is not perfect but these values are all in the right ballpark for an LRR belt.

Conclusions

Computing conveyor power using theoretical models involves a substantial amount of advanced mathematics, physics, and material science. Empirical methods like the classic CEMA method offer time tested simple methods of estimating a conveyor’s horsepower requirement as long as conventional rubbers are used in the belt. Large sample indentation tests allow designers to derive new empirical power consumption formulas and predict the behavior of modern rubbers with classical methods of conveyor design.

The indentation loss prediction using the method described in CEMA-7 is simple to implement in a spreadsheet and very similar to the classic CEMA horsepower equation. However, the derivation of CEMA-7’s formula for Cwd is not known to the author. Field measurements sug-gest that CEMA-7 works well in some scenarios, but without the derivation of Cwd, it is difficult for the author to determine the range of conditions for which CEMA-7 applies. The latest editions of CEMA are a step forward for the industry, and will allows designers to estimate the savings LRR rubbers can yield for operators.

Still, the methods presented in CEMA include a number of simplifications and approximations which impact their accuracy. CDI recommends that designer apply at least a 15% margin on top of any CEMA-7 based design. Internally, we do not plan to adopt the CEMA approach ourselves. We will continue to use the more detailed theoretical models we developed for Syncrude.

Acknowledgements

The author wishes to gratefully acknowledge Linda Musser, Head or the Earth and Mineral Sciences Library at Penn State for her assistance in locating documents associated with the work Penn State did with Hewitt-Robins.

References

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[14] Stevens, R.: Belting the Worlds’ Longest Single Flight Conventional Overland Belt Conveyor, Bulk Solids Handling, vol. 28, no. 3, pp. 172-181, 2008.

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[16] Grabner, K., Grimmer, K.-J. and Kess­ler, F.: Research into Normal-Forces between Belt and Idlers at critical Locations on the Belt Conveyor Track, Bulk Solids Handling, vol. 13, no. 4, pp. 727-734, 1993.

[17] Kropf-Eilers, A., Overmeyer, L. and Wennekamp, T.: Energy-Optimized Belt Conveyors _ Development, Testing Me­thods and Field Measurements, Aufbereitungs Technik, vol. 49, no. 9, pp. 25-34, 2008.

[18] Wheeler, C. and Munzenberger,  P.: Indentation Rolling Resistance Measurement, in Beltcon 16, Johannesburg, South Africa, 2011.

[19] Spaans, C.: The Calculation of the Main Resistance of Belt Conveyors, Bulk Solids Handling, vol. 11, no. 4, pp. 809-826, 1991.

[20] Tapp, T.: Energy Saving Trough Idler Technology, Bulk Solids Handling, vol. 20, no. 4, pp. 437-449, 2000.

[21] Jennings, A., Bhansari, J., and Shah, K.: India’s First Elevated, Triangulated Gallery Overland Conveyor, Bulk Solids Handling, vol. 33, no. 6, pp. 24-27, 2013.

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