Overland Pipe Conveyor
Conveyor Belts: Save Energy by Minimising Belt Rolling Resistance
Application of Low Rolling Resistance Pipe Belts on Overland Pipe Conveyors
Low Rolling Resistance pipe belts have been implemented in several projects (Table 1). They serve as full scale tests to verify the aforementioned methodology.
Super Low Rolling Resistance Pipe Belt: Brazil Itaqui Pipe Conveyor System
The Itaqui pipe conveyor system is located near the Port of Itaqui, Brazil. The design capacity is 1000 metric tons coal per hour. There are two conveyors: a 4.3 km long first flight (PC1), using a 375 mm diameter Goodyear ST1400 pipe belt, and a 0.6 km long second flight (PC2), using 375 mm diameter Goodyear EP800 pipe belt. CDI designed the conveyor system, and partnered with Brazil Tecnometal Engenharia to implement the design. CDI also worked with the belt supplier Veyance Technologies, Inc. to design the pipe belts. The conveyor system was dry commissioned in August, 2012.
There are several highlights of this project:
- 1. The 375 mm diameter ST1400 pipe belt uses an improved LRR bottom cover. Its indentation rolling resistance is lower than typical LRR rubber, thus given a name Super Low Rolling Resistance (SLRR).
- 2. The PC1 conveyor replaces the conventional walkway with a self-powered maintenance trolley, which is shown in Fig. 4. This reduces the weight and cost of conveyor steel structure, and maintenance labour as well.
- 3. The pipe belt has a maximum speed of 5.2 m/s. It is the fastest belt speed for long overland pipe conveyor currently known to the author.
- 4. The PC1 conveyor has very difficult horizontal curves. The conveyor route in plan view is shown in Fig. 5
The 4.3 km PC1 conveyor has difficult horizontal curves, which were originally deemed as not suitable for steel cord pipe belt. There is one 300 m radius horizontal curve turning 78° degree, one 580 m radius horizontal curve turning 83° degree. Because of the difficult horizontal curves, a high stiffness pipe belt is designed. The high belt stiffness reduces the pipe belt deformation during horizontal curves and increases the belt stability against rotation. The high belt stiffness inevitably increases power consumption and belt tension. As a result, the design is an optimising process aiming to reach balanced belt stiffness. The pipe belt stiffness was analysed extensively through experimental testing and FEA, following the methodology outlined in Section 2.2. By adopting the SLRR belt, not only the power consumption is reduced, but the maximum belt tension is reduced as well. If using a conventional belt bottom cover, the high belt stiffness would cause excessive power consumption and belt tension. By using SLRR cover, the power consumption and belt tension is mitigated. The lower belt tension is beneficial in two aspects. First, a lower rating steel cord belt can be chosen, the lower modulus of which is helpful for negotiating horizontal curves. Second, the lower belt tension reduces the pipe belt deformation during horizontal curves.
After the conveyor is commissioned, CDI carried out data acquisition on the Itaqui PC1 conveyor to measure the torque on drive shafts, takeup tension and displacement, and belt speed. The measured torque values on drive shafts eliminate the uncertainties of drive efficiency. The results are summarized in Table 2. The measured value is very close to the initially predicted value for SLRR pipe belt. The predicted torque values for using LRR and conventional bottom cover on the same belt are also shown in the table. Due to the system characteristics, a conventional belt would not have worked for this conveyor.
Side by Side Comparison
The Kailin conveyor system has two identical, parallel pipe conveyors, with 6.2 km centre length and 103 m lift, commissioned in 2012 (Fig. 6). It is located in Guizhou province, China. The conveyors move through hilly regions, with multitude of horizontal and vertical curves. CDI audited the conveyor system design, and worked with Veyance Technologies, Inc. in designing a 375 mm diameter, ST2500 Goodyear Confine pipe belt with LRR bottom cover. The LRR Goodyear belt was installed on one conveyor. The other conveyor used a pipe belt from a different belt supplier, with the same pipe diameter and belt rating, but with conventional belt bottom cover. This parallel conveyor system provides the opportunity of side by side comparison between LRR and conventional pipe belt.
The torque values from the drive control PLC are shown in Fig. 7, for both the LRR pipe belt (blue) and the conventional pipe belt (red), for both empty and loaded condition. Fig. 7 is comparable to Fig. 2, only the vertical axis is torque ratio instead of horsepower. The reason is the Kailin conveyor uses variable speed drives. The belt speed changes with tonnage, so torque is a better measurement than power. Based on the torque data, the author estimated the other conventional belt’s stiffness and calculated the predicted curve of torque vs. tonnage.
Between the two belts, there is approx. 35 % difference in torque demand for full load condition, and approx. 30 % difference for empty condition. As is described, the pipe conveyor power consumption is very much affected by the belt stiffness. Similarly, the effect of using LRR bottom cover is also affected by the belt stiffness. The percentage in power and tension improvement from LRR bottom cover will vary, depending on the belt stiffness and belt construction. Nevertheless, the reduction in demand torque is very substantial. The Kailin conveyors were originally equipped with 4 × 800 kW drives. Because of the low power demand from the LRR pipe belt, the client was able to take one 800 kW drive off and store it as a spare.