Engineering and Mining Journal - Whether the market is copper, gold, nickel, iron ore, lead/zinc, PGM, diamonds or other commodities, E&MJ takes the lead in projecting trends, following development and reporting on the most efficient operating pr
Issue link: https://emj.epubxp.com/i/689616
SCREENS JUNE 2016 • E&MJ; 61 www.e-mj.com with two hydraulic needle gates. Under- neath each of the six bunker segments, a large Joest feeder discharges the material onto a vibrating screen. Overall, the screening plant measures 41 x 26 x 42 m (135 x 85 x 108 ft), and was constructed using more than 1,700 tons of steel. Each of the six double-deck vibrating screens is 3,000 mm wide and 9,200 mm long (10 x 30 ft). The screens are arranged in a back-to-back position for optimum material distribution. It was very important for the customer to be able to exchange screens separately for main- tenance purposes, so two removal posi- tions were set up for this purpose. Each screen has a maximum capacity of 1,500 t/h and has an effective screen- ing area of 27.6 m 2 (33 yd 2 ) per deck. This results in a total screening area of approximately 332 m 2 —comparable to the size of a lot for a single-family house with a small garden. The screens classify the input materi- als into pellets, fnes and larger material particles. The pellets are moved directly onto a belt for loading onto ships. The fn - er material, with a size range of 0–6 mm, reports to a fnes hopper for processing into pellets. The larger material, compris- ing about 2% or less of the feed and rang- ing from 20–50 mm in size, is conveyed to the oversize material handling facility, where it is reduced by a crusher and re- turned to the fne material belt conveyor. This allows all of the customer's material to remain within the process without loss of potential revenue. The entire plant contains 12 conveyor belts with a total length of 410 m. The belts, ranging in width from 800 to 2,000 mm, move material at up to 3 m/s. All conveyor belts are equipped with a hy- draulic tensioning device and longer in- clined belts also have a built-in brake to prevent a loaded belt from running back- ward and discharging its material. Optionally, incoming material can be sent directly for loading onto a ship via a 23-m bypass belt. The bypass also has the task of handling up to 11,000 t/h of fne ore, which does not need to be screened and can be moved directly to the ship. Among the facility's notable design elements is the attachment of moving components such as screens and hop- pers to a separate steel substructure that is not connected to the screening plant, thereby minimizing transmission of vibration. Screening equipment and bunker discharge feeders are also con- fgured with an isolation frame to reduce the remaining dynamic forces transmitted to the steel structure. This results in an optimized mass ratio between the vibrat- ing equipment and the isolation frame, with an effective degree of isolation ex- ceeding 90%. The large AC motors driving the screening equipment in the old plant use V-belts, which must be replaced at regular intervals. In order to keep the maintenance costs of the new plant as low as possible, the customer followed Joest's recommendations to power the new plant's screens by direct drive, with frequency converters. After an extensive I/O check to deter- mine, for example, whether all the cabling had been laid correctly and all electrical signals were correct, cold startup took place for each individual machine. To achieve this, each machine was activated and tested separately without load. These successful individual tests formed the ba- sis of cold startup of the entire equipment for automatic operations. Further checks also indicated whether the switch-off in- tervals between the machines were set correctly. Warm startup for the entire plant in early April was followed two days later by the frst ship arriving at the port, ready to take on cargo from the new facility. Some of the special challenges in- volved in this project, according to Joest, included meeting the customer's high level of requirements, especially in terms of the quality of the equipment, screen- ing effciency, durability, ease of main- tenance and automation. In addition, the outer shell of the screening plant had to be closed-in before the onset of the Scandinavian winter with its cold weather and short daylight periods. Information for this article was provided by Joest, part of the JÖST Group, which designs and develops system solutions for the processing of bulk materials. To reduce transmission of vibration, Joest mounted moving components such as screens and hoppers in a steel substructure isolated from the main plant structure. How It All Began A successful project in 2012 set the stage for Joest's involvement in the new expansion plant. Four years ago, the company delivered a large double-deck screen with movable hopper discharge feeder to LKAB, successfully designing and installing new, larger equipment in the existing, very narrow screening plant. This convinced the customer that Joest's technical expertise was equal to the chal- lenge of designing and equipping the new plant, and the company subsequently was selected as the supplier for the project.