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  • International Journal of Mineral Processing, 29 (1990) 249-265 Elsevier Science Publishers B.V., Amsterdam

    249

    Simulation - the modem cost-effective way to solve crusher circuit processing problems

    R.P. King Department of Metallurgy and Materials Engineering, University of Witwatersrand,

    1 Jan SmutsAvenue, Johannesburg (South Africa)

    (Received April 11, 1989; accepted after revision January 30, 1990)

    ABSTRACT

    King, R.P., 1990. Simulation- the modern cost-effective way to solve crusher circuit processing prob- lems. Int. J. Miner. Process., 29: 249-265.

    Simulation is an effective technique for the improvement of crusher plant performance, and it is now used routinely by some crusher manufacturers for both plant design and trouble shooting. MOD- SIM is probably the most versatile ore dressing-plant simulator in general use in the mineral-process- ing industry today. A case study using MODSIM applied to the crusher circuit of a major uranium producer is described in this paper. This study demonstrates the effectiveness of simulation to im- prove plant performance when reliable and effective models of the unit operations are available.

    The study was commissioned to investigate a 2000qon/h 4-stage crusher plant to identify a strategy to increase production at a finer product size. After an intensive technical audit on the plant, success- ful simulation was achieved for the existing operating conditions. The simulator was then used to identify the production bottlenecks and to establish plant modifications to meet the required produc- tion objectives in a cost-effective manner.

    INTRODUCTION

    Plant simulation techniques are becoming increasingly effective and there- fore more frequently used as tools to assess and improve plant performance. This is particularly so with crushing plants because the unit operations of crushing and screening can be described by reliable and accurate models. The study reported here was undertaken to establish cost-effective modifications to the fine crushing plant of Rossing Uranium Ltd., and the application of simulation to address some of the possibilities is described. The study was undertaken by a team consisting of personnel from Nordberg (Pty) Ltd., the Department of Metallurgy and Materials Engineering of the University of Witwatersrand, and Rossing Uranium Ltd.

    The objectives of the study were: ( 1 ) to investigate and establish all process and operating parameters under the current operating conditions; (2) to es-

    0301-7516/90/$03.50 1990-- Elsevier Science Publishers B.V.

  • 250 R.P KING

    tablish the complete mass balance and size distribution flowsheet for the pres- ent configuration and for the plant under various proposed alternative flow- sheet configurations; (3) to estimate energy, steel, and other cost reductions expected from any proposed plant modifications; and (4) to back up all pro- posals by basic engineering information and detailed flowsheet calculations.

    Simulation effectively addresses the second and fourth of these objectives and provides the necessary information to permit the calculation of energy and other cost savings to meet the third of the objectives. Nordberg Inc. of Milwaukee, have pioneered this approach and their Circuit Analysis Program (CAP) is now in use worldwide for the development and analysis of crusher circuits. Significant improvements in worker proouctivity and the quality of flowsheet design have been reported (O'Bryan, 1987). The application of simulation to crusher flowsheet design has been well described by Mage- rowksi and Karra (1982) and there is no doubt that simulation techniques will play an ever-increasing role in the future. This study afforded the oppor- tunity to use both MODSIM and CAP within the context of a real major plant analysis. The application of MODSIM to this problem is discussed in detail in this paper. The first objective was addressed by undertaking a detailed technical audit on the plant which included the measurement and recording of all relevant engineering parameters, together with tonnages and size distri- butions of key process streams.

    The most important plant improvement required from this study was the reduction of the final product size from 80% passing 10.5 mm as in the exist- ing circuit to 80% passing 7 mm.

    DATA COLLECTION

    The data collection was undertaken over a period of five days during which the plant was operated sunder conditions close to normal. Production was, however, interrupted to permit the necessary sampling to be undertaken. Great care was taken to ensure that all samples were representative of normal oper- ating conditions.

    The key process variables measured were the tonnages and size distribu- tions in those streams that were diagnostic of the operation of each of the units in the plant. The size distributions and tonnages were measured by stop- ping the appropriate conveyor belts in the plant in the plant and carefully cutting 1-m sections from the belt load. Total mass and size distributions of these samples were determined in the usual way.

    The existing plant flowsheet is shown in Fig. l, and the streams from which samples were taken are identified in Table I. When necessary, flow of material in portions of the plant was stoppexi to allow the sampling of only one of the parallel streams. For example, both east and west secondary crusher products

  • S IMULAT ION OF CRUSHER C IRCUIT PROCESSING PROBLEMS 251

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    TABLE I

    Stream identification and sample point location

    R,P. K ING

    Stream Identification Comments number

    1 2 3 4 5

    31 35 37 25 45 46 36 10 17 40

    Coarse ore reclaim conveyor Secondary crusher feed - west Secondary crusher feed - east Secondary crusher product - west Secondary crusher product - east Tertiary screen under size - west Tertiary screen under size - east Tertiary crusher product - west Tertiary crusher product - east Quaternary crusher product Quaternary screen underflow Final mill-feed product Tertiary screen top-deck overflow Tertiary screen lower-deck overflow Quaternary screen overflow

    No flow through east secondary No flow through west secondary No flow through east tertiary No flow through west tertiary

    TABLE 1I

    Important operating variables in existing plant

    Unit Type Operating parameters

    Secondary crushers

    Tertiary screens

    i

    Tertiary crusher

    Quaternary crushers

    Quaternary s~'eens

    7-ft standard Symons cone crushers

    Double-deck polyurethane

    7-ft short-head cone crushers

    7-It short-head cone crushers

    6 X single-deck polyurethane

    Closed-side settings: west 49.1 ram; east 51.7 mm

    Topdeck: 49-ram square opening 4 l-ram ribs 23.4% open area 5.486 m2.134 m 18 inclination

    Lower deck: 15.2-mm square opening 10.3-ram ribs 25.01% open area 6.094 m 2,134 m 18 inclination

    Closed-side settings west:No. 1 13.1 mm, No. 2 11.9ram east: No. 3 13.7 ram, No. 4 12.6 mm

    Closed-side settings No. 1 8.17 ram, No. 2 8.6 mm

    20.0-mm square opening 11.5-mm ribs 27.7% open area 5.48 m X 2.0 mm 18 inclination

  • SIMULATION OF CRUSHER CIRCUIT PROCESSING PROBLEMS

    TABLE III

    Measured size distributions (percent passing indicated size)

    253

    Size ( ram)

    Stream Stream Stream 1 Stream Stream Stream Stream Stream Stream Stream Stream Stream 2 3 reeonstr. 4 5 31 35 37 25 45 46 36

    from 2&3

    150 88.3 81.7 85.2 100.0 . . . . . . . 100 76.1 61.1 69.1 100.0 99.6 . . . . . . . 70 66.2 51.6 59.4 91.9 94.8 . . . . . . . 63 63.5 48.6 56.6 87.9 90.9 . . . . . . . 50 57.3 44.6 51.4 75.5 78.0 - - 100.0 . . . . 37.5 48.1 38.0 43.4 59.6 64.3 - - 99.7 100.0 100.0 100.0 - 25 40.5 33.0 37.0 48.9 52.3 100.0 - 93.6 94.4 99.5 99.0 - 19 35.1 29.8 32.6 42.9 47.3 99.6 100.0 80.7 81.4 95.2 96.5 100.0 12.7 29.4 25.6 27.6 35.6 40.0 97.5 99.3 55.7 53.5 70.4 79.6 88.3 6.4 23.1 22.3 22.7 26.9 30.7 80.1 82.1 37.2 30.0 39.4 50.0 58.0 4.7 20.8 20.0 20.4 24.2 27.5 71.2 73.2 29.4 25.6 33.1 43.0 50.6

    Flowrate 1071 933 2004 1150 970 366 366 856 724 677 1403 2270 (tons/ +352 +724

    h) 718 1580

    were sampled on the conveyor indicated as stream 35 in Fig. 1. Only one of the parallel crusher lines was operated while loading the belt for sampling.

    Crusher gaps were determined by leading, and when necessary, gaps were adjusted to ensure uniform operation during the entire the entire audit pe- riod. Current drawn by the crusher motors under operating load, as well as under no-load conditions, was determined from existing plant instrumentation.

    Screen dimensions and screen apertures were measured by direct observa- tion. Screen vibration amplitudes and motions were recorded for each screen. Samples of screen overflows were taken by the manual lunge method and are consequently less reliable than the belt samples taken.

    Conveyor belt speeds were determined from measurements of the drive drum diameters and rotational speed.

    The key operating variables that were measured are listed in Table II. The measured size distributions and tonnages are given in Table III.

    SIMULAT ION OF THE EX IST ING FLOWSHEET

    MODSIM is a modular simulator that can simulate any or dressing-plant flowsheet. Models are required for the description of the operation of each unit in the plant. For use within MODSIM, a model must be capable of ac- cepting as input the complete description of the feed to the unit and calculat- ing the nature of the product stream in detail sufficient for the needs of the simulation. The parameters that described the size and o