24.09.2008 | Author / Editor: Beumer
Maschinenfabrik / Wolfgang Geisler
A Chinese cement manufacturer needed to redesign its limestone supply chain, when the enlargement of a nearby dam flooded part of the originally designated railway.
Asia Cement Group, a major building material manufacturer headquartered in Taipeh (Taiwan), has built a new plant in the vicinity of Chengdu, the capital of Sichuan. Currently, a kiln with a capacity of 4200 tons per day is installed there. For moving the limestone from the quarry to the factory, located 30 km away, the Asia Cement Group has commissioned BEUMER with constructing a curved belt conveyor. The major order with a total volume of EUR 5 million includes design and installation of a 12.5-kilometre long system through rough mountainous terrain.
Chengdu has about 10 million inhabitants and is thus one of the largest markets building materials in China. That is why the Asia Cement Group decided in 2004 to set up a plant for mining limestone. During the development phase the company was given a permit by the Chinese government to use a closed railway line for transporting the limestone. When the plant was already half-finished the government decided to enlarge a nearby artificial lake to generate electricity and to flood the area intended for transport. Thus conditions changed for the cement manufacturer since now further use of the track was only possible for the last 15 kilometres. Inundation of the road and the resulting detour also made transport by truck more difficult. In addition the cement manufacturer is planning to install another two kiln lines at this site. Such a logistic challenge could not be adequately met with trucks in such rough terrain. The better alternative, from a time and cost perspective, turned out to be installation of a troughed belt conveyor.
For more than 20 years the Asia Cement Group and Beumer cooperate, and numerous Beumer conveyors and bucket elevators are in operation their sites. Due to the conditions of topography and the resulting logistical and engineering requirements, design, bridging and commissioning of the conveyor had to come from one source. The German machine system supplier earned a lot of know-how in the field of curved belt conveyors and has constantly provided proof of its pioneering role with a large number of patents as well as accomplishing even extremely difficult tasks. Besides its technological and innovative capabilities, the Beumer Group with its subsidiary in Shanghai is also situated close to the customer. The order for the 12.5-kilometre long troughed belt conveyor with a conveying capacity of 1500 tons per hour and a conveying speed of four metres per second was placed in May 2006.
The terrain to be conquered cfeatures mountains and bamboo forests. Since a good portion of the bamboo is under nature conservation, no approval was given for a service route, nor was any clear cutting allowed. Even the subsoil posed a serious challenge: on one hand it is unstable due to earlier coal mining, on the other it consists of granite that can only be removed to a certain extent. In addition, one segment along the line has to be routed through 1.5 kilometres of water. Such extreme outer constraints entail manual mounting of some 90 percent of the installation on site. Since transport by truck is partly impossible the structural elements have to be carried by mules, piece by piece. Therefore the entire facility was designed in such a way that all parts can be screwed together and no part extends three metres in length, ensuring optimum transport.
After the order was placed, BEUMER in consultation with the Asia Cement Group optimised the routing of the troughed belt conveyor on the spot. With eight horizontal curves featuring radii of some 1000 to 5000 metres, the machine manufacturer calculated the precise belt tensile forces in costly simulations. The routing selected by the engineers was examined for its feasibility on the spot. For this purpose, the entire 12.5 kilometres were gone over on foot through rough terrain in order to check the specified sites for the 460 supports for their suitability directly in the field and down to the millimetre. In doing so, it turned out that a 130 metre granite segment had to be tunnelled. Besides rough terrain, extreme altitude differences of up to 100 metres posed a particular challenge. In order to minimise total costs, Beumer uses horizontal curves and spans the mountains with bridges up to 55 metres in height.
In close collaboration with the customer, Beumer developed the entire design and computed the static prerequisites for the bridges and belt facilities. With two model conveyor sections, built on site and mounted and readjusted once again by the manufacturer, the design of the bridges could be tested with the conveyor. In addition, load tests were carried out with real-life loads and the model conveyor sections could serve as models for building bridges. Asia Cement is responsible for the steel construction of the bridge according to specifications by Beumer engineers and under the constant supervision of two technical instructors. Beumer designs, builds and delivers the core parts for the drive and take-up stations as well as all belting and drive technology.
The belt for the 12.5-kilometre long conveyor installation is 25 kilometres long – 56 segments need to be vulcanised. The width of the belt is 1200 mm and its rigidity is 2800 N/mm.
Besides the eight horizontal curves the installation has 28 vertical curves. In order to keep belt tensile forces under control through six declining and six inclining sections the installation is operated with special motors and with Beumer controls adapted to them. The installed drive power comes to six times 500 kW. Drive power is transmitted via two drive pulleys at each the conveyors’ head and tail, respectively. In this case, one pulley acts as a double drive for 1000 kW and one as a single drive for 500 kW. A movable take-up weight was dispensed, instead the take-up force is adjusted once and geometrically frozen with a take-up winch. The belt conveyor system should be installed and in operation by the end of 2008.
BEUMER Maschinenfabrik GmbH & Co. KG
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