Cost-efficient and Application-oriented Design of Steel Cord Conveyor Belts for the Mining Industry
Conveyor belts in the mining industry are facing ever higher demands as regards conveying capacity, conveyor length, service life and energy efficiency. In addition to designs according to various general standards manufacturers further develop their products for better economy.
Dr. Andrey Minkin
(ed. WoMaMarcel - 23/4/2015)
The OLC-2 long-distance conveyor at KPC in Indonesia transports 4000 metric t/hr (nominal) and 4500 metric t/hr (peak) of washed coal (bulk density of 0.9 metric t/m3) with a belt speed of 8.45 m/s. The conveying length is 12 589 m and the conveying height is 29.1 m. For this task, KPC as the user of the facility and PT RSSI as the EPC contractor selected the Contitech Stahlcord belt 1100 St2250 5.5:5.5 X/XLL with the extra low loss bottom cover. This selection is based on the successful application of the Contitech extra low loss belt with XLL-bottom cover in the existing OLC-1 back to 2002 and the expected improvements can be summarized as follows:
At the expected 15 year service life (assuming round the clock, i.e. 24 h/day and 365 days/year) for such a Contitech belt and the power difference of ΔPerf = 1751 kW, as well as the assumed electricity generation costs of ke = 0.05 €/kWh, the following capital savings K are achieved: K = 15 y∙365 d∙24 h∙0.05 €/kWh∙1751 kW
≈ €11.5 million
The belt amount ordered by KPC at 26 032 m with a belt weight difference of Δm‘G = 5.1 kg/m, yields weight savings G of: G = 26 032 m∙5.1 kg/m
≈ 133 metric tons
Thanks to the maximum belt tension being reduced by ΔTANmax = 114 kN (approx. 12 metric tons), the steel structure of the system, pulley shafts, bearings, etc. may be selected lighter and more economical.
Thanks to the reduction in the number of motors (1x2200 kW), smaller pulleys, a lighter steel structure, as well as a conveyor belt with reduced nominal breaking strength and mass per meter, the initial procurement costs (incl. logistics costs) for the OLC-2 long-distance conveyor with an XLL conveyor belt are lower than the standard commercially available conveyor belt. Subsequent maintenance costs are lower as well, because “light” spare parts are less expensive.
Steel Cord Conveyor Belt Design according to Version 1982 and 2011 of DIN 22101
In 2011, the old standard DIN 22101 version 1982 “Belt Conveyors for Bulk Material – Principles for Calculation and Design” was replaced by a new version. The calculation example shown below illustrates the advantages for belt design that the new standard DIN 22101 version 2011 brings to the table.
DIN 22101 version 1982
According to DIN 22101 version 1982 (DIN 22101-1982), the minimum nominal breaking strength kN,min of a belt is calculated according to Eq. (4):
where the safety factor for normal operation and favorable operating conditions is Ssta = 6.7 (Ssta = 9.5 for unfavorable operating conditions).
Breaking strength loss value rverb for steel cord conveyor belts is a function of the number of steps of a belt splice:
rverb = 0 for number of steps n ≤ 2 or
rverb = 0.05 for number of steps n ≥ 3
For example, for a steel cord conveyor belt of width B = 2100 mm and maximum belt tension Tmax = 1000 kN when in normal operation, the maximum belt tension ksta is resulting in:
According to Eq. (4), this yields the minimum nominal breaking strength of a belt:
For this numerical example, a standard steel cord conveyor belt St3500 is selected.
The breaking strength loss value is rverb = 0.05, because a steel cord conveyor belt St3500 has a three-step splice.