Reducing the Energy Consumption of Belt Conveyors

Reducing the Energy Consumption of Belt Conveyors by the Use of Intelligent Garlands André Katterfeld1, Christian Richter1, Adam Gladysiewicz2, Rolf Schwandtke2 1 University of Magdeburg, Chair of Conveying Technology, Universitätsplatz 2, 39106 Magdeburg, Germany 2 Artur Küpper GmbH & Co. KG, Bottrop, Germany ABSTRACT Idler garlands are often used in the high performance belt conveyors in the German open pit lignite mines. The hinged suspension of the idlers allows a better impact damping and more even load balancing than usual fixed idler stations. Garlands also allow an adaption of the troughing angle onto the load situation of the belt. Smaller troughing angles result in lower motion resistances than higher angles. This interrelation was the starting point for the development of so called Intelligent Garlands. An integrated spring in the garland suspension allows the elastic change of the troughing angle. The developed suspension can be used in the standard steel framework of the belt conveyor. Long time tests at a real belt conveyor plant in a German lignite mine were undertaken to validate the influence of the changing troughing angle on the overall energy consumption of the belt conveyor. The paper will give a brief introduction about the design of Intelligent Garlands and present the results of the field measurements. It could be proved that up to 13% energy could be saved if Intelligent Garlands are used. 1.

THE IDEA OF THE INTELLIGENT GARLANDS

The currently known measures to save energy in belt conveyors mostly aim at an optimal choice of the rollers and their fitting situation (idler spacing) or an optimization of the conveyor belt characteristics (so called energy saving belts) [1]. On the basis of long-term experience and theoretical analyses, the company Artur Küpper GmbH & Co. KG has developed an innovative concept for saving energy. It is based on a modified suspension of existing roller garlands, which allows an adjustment of the troughing angle according to the respective load situation. The basic idea of the Intelligent Garlands was already published in [2]. The basis of this development is the research published in [3], which indicates that with a smaller troughing angle less force is applied to the rollers, which also reduces the rolling resistances, especially the indentation rolling resistance above all. A variable troughing angle facilitates both, the originally high troughing angle for a design capacity and maximum load and a reduced troughing angle for smaller mass flow rates with correspondingly lower resistances. Both loading situations are presented in Figure 1. The changing of the trough is generated by springs acting on the garland. In case of maximum load, the garland geometry corresponds to a non-suspended standard garland. In case of idling or partial load, the tractive force of the springs causes a flatter troughing angle. By choosing the right spring parameters and type of the spring support, the adjustment of the trough can be optimally arranged and adapted to the characteristics of any belt conveyor.

Figure 1 Principle of the Intelligent Garland.

2.

REQUIRED TROUGHING ANGLE

The reduction of the troughing angle leads to a reduced energy consumption in case of idling or partial loading. The following condition must be met:

𝐴𝑡ℎ (𝜆) ⋅ 𝜌 ⋅ 𝑣 > 𝑄

(1)

In this context, Ath is the theoretical filling cross section according to DIN 22101 [4],  the bulk density of the bulk good, v the belt speed, λ the troughing angle, and Q. the mass flow rate. This implies that a reduction of the troughing angle is only possible when the mass flow rate is smaller than the nominal load. A second boundary condition refers to belt misalignment. The trough always has to be deep enough to be able to centre the belt through sufficiently strong lateral forces. Both in the CEMA [5] and DIN [6,7] standards, three-part roller sets with a troughing angle of a minimum of 20° are recommended. This value was chosen as the lower limit for the Intelligent Garland. 3.

PRACTICAL IMPLEMENTATION

A belt conveyor in the open-pit mine “Vereinigtes Schleenheim” of the MIBRAG GmbH with a length of 625 m was equipped with intelligent garlands and tested in long term field measurements. The conveyor has the following parameters:  Belt width: 2000 mm  Belt speed: 6.55 m/s  Nominal capacity: 14,500 t/h (average ca. 7000-8000 t/h)  Idler spacing: 2.5 m  Troughing angle 34° Taking into account the load data and the geometry, an Intelligent Garland was specifically designed for this plant. With the aid of especially developed calculation methods, the springs and spring supports were specifically designed for this system as well. The first prototypes were tested in the test laboratory of Artur Küpper GmbH & Co. KG on an original framework from the open-pit mine [8]. Figure 2 shows both the calculations and the simulations of the troughing angle depending on the mass flow rate. The standard garland shows a nearly constant troughing angle of 34°. The additional spring forces of the Intelligent Garland cause a variability of the troughing angle between 22° and 33°. The calculations made at the beginning were confirmed in practice by the measured troughing angles. The changing of the trough was within the specified limits. Subsequent to the laboratory tests, the Intelligent Garland was tested on a real conveyor belt.

Figure 2 Troughing angle of standard garland and Intelligent Garland.

Using different spring parameters and a modified geometry of the spring support, it becomes possible to obtain a dynamic changing of the trough relative to the current mass flow rate. Through this variability, the troughing angle continuously adapts to the given requirements. 4.

FIELD TESTS

Figure 3 shows the test installation before and after the fitting of the Intelligent Garlands. The conveyor belt GbF50 is in regular open-pit operation. In April 2012 it was fitted with adequate measuring technology in order to scientifically analyse the influence of the Intelligent Garlands on the energy consumption of the conveyor system. The following measurement data were taken and recorded continuously:  The electric drive capacity via the power input of the motors;  The drive torque of both drive pulleys (the drive shafts were fitted with strain gauges in connection with a miniaturized measuring amplifier with an integrated telemetry transmitter and an inductive power supply.);  The mass flow rate of the transported material through a belt weight;  Air temperature and humidity.

Figure 3 Top: Belt conveyor GBF50 before the equipment with Intelligent Garlands Bottom: GBF50 equipped with Intelligent Garlands. In June 2013, after a one-year field test with continuous measurements at the belt conveyor, all garlands were fitted with the elastic suspension of the Intelligent Garland. For the mounting and dismounting a special pretension device was developed, which allows a retrofitting within only two minutes per garland. It should be

underlined that the mounting can be affected without lifting and releasing the belt and without using heavy machinery. To obtain comparable measurement data for standard garlands and intelligent garlands, the time periods were examined at the same temperatures. For the analysis, the average loading condition on the belt was calculated. This condition was defined as the moving average of the belt weights signal. 5.

RESULTS

Figure 4 shows the comparison of the measurement and calculation results. The measurement values refer to the measured performance of the drive shafts. Here, the measurement points of standard garland and intelligent garland were chosen in a way that the environment temperature was the same for both. The gradient was determined by regression of several thousand points [9]. The calculations were carried out with the program QNK-AKT, taking into account all parameters of the conveyor system. The calculation method considers all components of the total rolling resistance:  indentation rolling resistance,  idler resistance,  belt flexure resistance,  bulk material flexure resistance,  extra resistances. In addition, the efficiency of the drive as a function of the load was taken into account.

Figure 4: Mechanical drive power: comparison between measured and calculated results.

In the calculation program QNK-AKT, no irregularities of the load distribution of the conveyor belt load was considered. Especially in shiftable conveyor belts, adjustment inaccuracies cause different roller/garland loads. These inaccuracies are leveled out when using Intelligent Garlands. Because of this leveling, the actual savings are significantly higher than the calculated ones. These calculated shares of energy consumption are presented in Figure 5. The losses marked with “drive” define the energy losses between the electrical power at the inlet and the mechanical performance at the drive shafts. The following components are regarded as secondary resistances:  friction resistance by belt cleaning;  inertial resistance of the conveyed bulk material and friction resistance between the bulk material and the belt in the area of a loading point;  friction resistance between the conveyed material and lateral chutes in the acceleration area of the loading point;

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belt flexure resistance on the pulleys During idling, the resistance on the carry side represents only 34.4 % of the total resistance. The Intelligent Garland only influences the resistance on the carry side. The reduction of the drive power during idling is relatively small because the resistance generated on the return side, secondary resistances, and energy losses in the drives remain unchanged. The highest reduction achieved by the Intelligent Garland was 12 % of mechanical drive power at a mass flow of approx. 4000 t/h. The positive effect was proved in a long-term test for mass flows ≤ 8000 t/h, which is the most frequent load. This statement is presented and evidenced in Figure 6. In the examined conveyor belt system, the mass flow is lower than 8,000 t/h in 85.6 % of all cases. In this chart the times with no load (idling) are not included

Figure 5 Calculated rates of the drive power

Figure 6 Distribution of the mass flowrates at the test belt conveyor

6.   

   

7. [1] [2] [3] [4] [5] [6] [7] [8] [9]

CONCLUSIONS By the use of Intelligent Garland, up to 13 % of mechanical drive power can be saved in a modified belt conveyor system. Because of the implied reduction of energy costs, a refitting will depreciate within a few months. Leveling-out of inaccuracies in the arrangement of the frames and thus an even distribution of the load on the garlands, with additional shock absorption in case of coarse-grain conveyed material is possible with the use of Intelligent Garlands. Through these positive side effects it can be assumed that the service lifetime of the rollers and the belt is increased. The measuring results from long-term field measurements match the calculation results very well. Regarding the tested conveyor system, energy saving could be achieved for mass flow rates ≤ 8000 t/h. Compared with other methods, the use of Intelligent Garlands is cost-effective and can quickly be implemented. The test belt conveyor system has a nominal troughing angle of 33°. For higher nominal troughing angles (e.g. 45°), the energy-saving potential of the Intelligent Garland is significantly higher. REFERENCES Gladysiewicz, A.: „Tragrollenoptimierung zur Effizienzsteigerung von Gurtförderern“. Fachtagung HdT Gurtförderer und ihre Elemente. 12-13. Juni 2013 Essen Katterfeld, A.; Gladvsiewcz, A.; Schwandtke, R.: Intelligent garland - conceptual design and first empirical results. In: BulkSolids Europe 2012. Würzburg: Vogel Business Media. 2012 Grabner, K.: „Untersuchungen zum Normalkraftverlauf zwischen Gurt und Tragrollen bei Gurtförderern“. Dissertation, Montanuniversität Leoben. 1990. DIN 22101: Stetigförderer - Gurtförderer für Schüttgüter - Grundlagen für die Berechnung und Auslegung. 12/2011 Belt Conveyors for Bulk Materials, 6th Ed., CEMA The Conveyor Equipment Manufacturers DIN 22111: Leichtes Traggerüst. 03/2000 DIN 22114: Schweres Traggerüst. 03/1993 Gladysiewicz, A.; Katterfeld, A.: „Intelligente Girlande Konzept und erste Praxiserfahrungen“. In:17. Fachtagung Schüttgutfördertechnik „Neues aus Wissenschaft und Praxis“. München 2012 Gladysiewicz, A.; Schwandtke, R.; Katterfeld, A.; Richter, C.: „Verifizierung der Intelligenten Girlande“. In: 18. Fachtagung Schüttgutfördertechnik 2013: „Treffpunkt für Forschung&Praxis” Magdeburg 2013