Sasol Synthetic Fuels, based in Secunda, Republic of South Africa, is one of the largest manufacturers of synthetic oil in the world. Sasol was required to increase the demand coal throughput of the Secunda factory from 37 MTPA (million tons per annum) to 50 MTPA within six years. Eight coalmines were in operation in 1997. To meet the demand for the future, Sasol Mines needed to develop new mines. In 1997 the development of eleven new coalmines that were located within a 25 km radius of the Secunda factory was planned. All new mines were expected to have an annual capacity of 4 MTPA. Sasol wanted to investigate the feasibility of transporting coal from the mines to the factory by means of belt conveyors. The numbers of conveyors, the required capacities as well as the possible routes from the mines to the factory were unknown.
Sasol commissioned Prof. Lodewijks to head a team of transport and logistic engineers to determine the optimum design and route layout of a feasible belt conveyor system. The optimization problem was defined as follows:
Since each mine was expected to have a capacity of about 4 MTPA, the determination of the mine development timing was not too complicated. Taking the production forecast of the existing mines and the time it takes to develop a new mine into account it could easily be determined when coal from a new mine was required. The only complicating factor was that the quantity of coal (the coal reserve) varied from mine to mine, which implied that the mine life varied between the mines. Obviously, the mine development sequence affected the mine development timing in this respect.
The determination of the mine development timing and routing plan were far more complicated and could not be determined independently. With 11 new mines there were nearly 40 million different possible combinations of phasing in new mines. Although the vast majority of these combinations was not very realistic in practice, the number of rational combinations was still very large.
The first step towards the determination of the optimum mine development sequence and route layout was the physical determination of all different possible routes from the mines to the factory accounting for all relevant constraints. Constraints included the condition that the effect of the transport system on farms and villages (noise, number of road and power line crossings ect.) had to be minimized. Further conditions were that the amount of equipment had to be minimized and that all equipment had to be reused after the accompanying mine had been phased out.
The second step was the determination of all relevant mine and ambient parameters. Mine parameters included the available quantity, grade and quality of coal, the number of shifts a day, the number of working hours a day, the cost of labor, the cost of mine development and exploitation ect. Ambient conditions included the cost of utilities, the interest and inflation rates, temperature range, annual rainfall, relative humidity and altitude.
The third step towards the determination of the optimum (and feasible) mine development sequence and route layout was the design of new conveyor structures that were not only 25% lighter and could very easily be elevated, but that could have a considerable unsupported span width to ease the crossing of rivers, roads and power lines as well.
A numerical model was developed that, depending on a given selection criterion, found the optimum mine development timing, sequence and conveyor routing. Selection criteria included longest overall mine life, minimum cost, shortest conveyor routes from the new mines to the factory and the lowest net present value (NPV) of the coal storing, handling and transporting system in 1997 over a period of 43 years (until 2040). The lowest NPV scenario, which was adopted by Sasol, lead to an operationally acceptable mine development plan and an optimum conveyor system. With a net discount rate of 6 %, the minimum NPV of the total project, excluding the development of the mines, was about 500 million US dollars.
Western Power is a Western Australian supplier of electrical energy. Following the increase in the demand of electrical energy, Western Power decided in 1997 to open two new power stations. Considerable unused coal reserves exist around Collie, Western Australia. Therefore Western power opened two new coalmines in the Collie area and located the power stations in their near vicinity. To transport the coal from the mines to the power stations a system of long overland belt conveyors (13.5 km in total) was required. Because of the margins in the total project this system had to be as energy efficient as was technically possible. Another requirement was the minimization of the impact of the conveyor system on its environment (Australian bush land).
Prof. Lodewijks designed and developed the belt conveyors. One of the main challenges was the development of a new “low energy consumption” rubber compound for the conveyor belt covers. The physical development of this cover was done in close cooperation with Bridgestone of Japan. A difficulty in the development of the new rubber was the translation of the physical dynamic rubber parameters into reliable input parameters for a dynamic model of a long overland belt conveyor. This translation is essential because the results of the dynamic analysis are required to enable comparison of the energy consumption of the new developed compound with the energy consumption of existing compounds. This comparison is required to prove the necessity and the feasibility of the application of the new “low energy consumption” rubber. Besides the development of a new rubber compound, also a new conveyor structure was developed. This structure had a very low and slim profile and a minimum number of rotating components to reduce the noise levels around the conveyors.
After erection and commissioning it was found that the conveyor system had (and still has till date) the lowest reported energy consumption compared to any other belt conveyor system in the world. The system is frequently used as a reference and the specially developed rubber compound and conveyor structure have been successfully applied in other projects since then.
Nesher Israel Cement Enterprises Ltd., located in Ramla, Israel, is Israel’s largest producer of cement. The original capacity of the production facility in Ramla was 6,800 TPD (Tons Per Day). In 1999 Nesher decided to upgrade the plant and increase the capacity to 10,000 TPD. The source of limestone used for the production of cement was an open pit quarry located about 3.5 km from the plant. The existing belt conveyor system that transported the limestone from the quarry to the plant could handle the original capacity but not the increased capacity of 10,000 TPD. At the same time operational problems were reported for the belt conveyor system. To save costs Nesher wanted to increase the capacity of the current conveyor system, rather than adding a second conveyor line, and wanted to minimize the number of changes.
Nesher commissioned Prof. Lodewijks to inspect the belt conveyor system, to determine what the source of the operational problems was and to come up with a plan to upgrade the conveyor system. Besides that there were already operational problems that had to be solved, the geometry of the belt conveyor system was also very complex with many horizontal and vertical curves. This implied that a simple increase of the belt speed would not be sufficient to upgrade the system. To achieve a reliable upgraded conveyor system the total system had to be completely re-engineered.
The first action item was a throughout on site inspection of the conveyor system, including field measurements, to analyze and record the initial operational behavior of the system. The record of the operational behavior of the system was used to accurately determine the required input parameters for a dynamic simulation of the system. The dynamic simulation was used firstly to detect the source of the operational problems and secondly to determine the right course of action for the upgrade of the system to 10,000 TPD. Analysis of the results of the dynamic simulation showed that, provided that the start-up and stop procedures of the system were altered, increasing the belt speed could sufficiently increase the capacity of the system. The analysis of the results also showed that the belt’s supporting structure in all the horizontal curves and the drive and tensioning system of the belt had to be changed.
Second action item was the implementation of the recommended changes by Nesher. The third and final action item was a final on site inspection of the conveyor system, including field measurements, to analyze and record the operational behavior of the upgraded conveyor system. The field measurements were carried out not only to check the settings of the upgraded/changed conveyor components but also to prove the validity of the design assumptions and changes recommended to Nesher.
The second inspection of the system and analysis of the results of the field measurements showed that the upgrade had been successful. Till today there have been no reports of any operational problems and the conveyor system operates fully to Nesher’s satisfaction.
Dunlop-Enerka B.V., located in Drachten the Netherlands, is a large worldwide leading manufacturer of conveyor belting. To complete its product range, Dunlop Enerka wanted to develop a closed belt conveyor system. The most important component of any closed belt conveyor system is the belt. Therefore, Dunlop-Enerka, as a manufacturer of conveyor belts, participated in the development of the Enerka-Becker System (EBS) by developing a special rubber conveyor belt. The EBS was originally invented by FMW, located in Wilhelmshaven Germany, and the co-operation between FMW and Dunlop-Enerka was established in 1992. Today, the EBS is patented worldwide.
Dunlop-Enerka commissioned Prof. Lodewijks to scientifically support the development of the EBS. Since 1992 no real progress was made in optimizing the closed conveyor belt and the EBS drive system. The further development of the EBS therefore focused on the belt and the drive systems.
The heart of each EBS is the conveyor belt. The basis of the belt is a standard fabric belt with rubber covers. Solid rubber triangular profiles are vulcanized to both sides of the belt. The two triangular profiles form a larger triangle and the belt becomes a pouch when the belt is folded together. Special rollers installed in a gallery support the profiles. The triangular profiles play a critical role in the performance of the EBS because they support the belt and determine the belt’s tracking and resistance performance. Initially the profiles were straight triangles that, because of the wedge effect, jammed the belt in the support rollers. To solve this problem the support rollers were initially tilted, which unfortunately caused extra frictional resistances. The first action item was therefore to change the form of the profiles into curved triangles. This solved the “jam problem” and therefore tilting of the rollers was not longer necessary. Besides that the rolling resistance also decreased. A complex numerical model was developed accounting for the dimensions and the (visco-elastic) properties of both the rollers and the profiles to find the optimum curved triangular form of the profiles minimizing the rolling resistance and wear of the profiles.
Another feature of the EBS is the application of decentralized or multiple drive units. This keeps the belt tensions low, which enables the application of a lightweight conveyor belt and lightweight structure. Initially only 0.5 kW drive units (at 1 m/s) could be applied where, as far as the belt strength is concerned, 3 kW drive units should be possible. To keep the number of drive units for high tonnage or long overland systems down to a reasonable number, the standard drive size has to be increased from 0.5 kW to 3 kW. Therefore a very sophisticated model is being made to simulate the drive and power transmission phenomena accounting for the visco-elastic nature of the profiles and the exact dimensions and dynamic behavior of the drive units.
The rolling resistance of the EBS is lower than that of comparable closed belt conveyor systems thanks to the in-depth research into the phenomena that affect the rolling resistance including the development of the optimum profiles. It is to be expected that through ongoing research and development of the drive units, the EBS drive system will be feasible by the end of 2000. The current marketing forecast is that, due to the technical optimization, the annual sale of EBS belting for the next three years will be around the 10 million US dollars from only 2 million US dollars in total for the last eight years.