BULK MATERIALS HANDLING IN THE MINING …

1 BULK MATERIALS HANDLING IN THE MINING industry MADENC L K END STR S NDE MALZEME NAKL Roberts Keywords : Bulk HANDLING , Bins, Feeders, Stockpiles, Ore Passes, Wear ZET Bu makale, madencilik end strisinde malzeme naklinin baz konula r n incelemektedir. Silolar, serbest y mlar, yeralt depolama ve malzeme yollar gibi malzeme depolama sistemlerinin dizayn g zden ge irilmekte ve g venilir bo altma ak sa layacak besleyici dizayn ile ilgili hususlar verilmektedir.

2 Depolama silolar n n duvarlar nda, statik ve ak halindeki gerilim alanlar n n olu turdu u, y kleme anlat lmaktad r. Kullan lan ekip manda olu an a nma problemleri k saca anlat lmaktad r. ABSTRACT This paper reviews various aspects of bulk MATERIALS HANDLING in the MINING industry . An overview of bulk storage systems design, including bins and silos, gravity reclaim stockpiles, underground storage facilites and ore passes, is presented and aspects of feeder design for reliable discharge flow is given.

3 The loadings in wall of storage bins is discussed in relation to stress fields under both static and flow conditions. Problems of wear in HANDLING plant are briefly discussed. Professor and Director Senior Lecturer, Institute for Bulk MATERIALS HANDLING Research, School of Engineering, The University of Newcastlle, NSW, 2308, Australia. T RK YE XIII. MADENC L K KONGRES , 1993 9 1. INTRODUCTION Bulk MATERIALS HANDLING operations perform a key function in the MINING and mineral processing industries.

4 In such industries the relative costs of storing, HANDLING and transporting bulk MATERIALS are, in the majority of cases, very significant. It is important, therefore, that HANDLING systems be designed and operated with a view to achieving maximum efficiency and reliability. Over the past three decades much progress has been made in the theory and practice of bulk solids HANDLING . Reliable test procedures for determining the strength and flow properties of bulk solids have been developed and analytical methods have been established to aid the design of bulk solids storage and discharge equipment.

5 There has been wide acceptance by industry of this technology and, as a result, there are numerous examples throughout the world of modern industrial bulk solids HANDLING installations which reflect the technological developments that have taken place. The purpose of this paper is to briefly highlight the present state of knowledge associated with bulk HANDLING . 2. GRAVITY FLOW BIN DESIGN - BASIC CONCEPTS The general theory pertaining to gravity flow of bulk solids is fully documented.

6 The salient aspects are briefly reviewed. As is now well established, there are two basic modes of flow, namely, mass-flow and funnel-flow. These are illustrated in Figure 1. (a) Mass-Flow (b) Funnel-Flow Figure 1. Modes of Flow In mass-flow, the bulk solid is in motion at every point within the bin whenever material is drawn from the outlet. There is flow of bulk solid along the walls of the cylinder (the upper parallel section of the bin) and the hopper (the lower tapered section of the bin).

7 Mass-flow guarantees complete discharge of the bin contents at predictable flow rates. It is a 'first-in, first-out' flow pattern with the ability to re-mix the bulk solid during discharge should the solid become segregated upon filling of the bin. Mass-flow requires 10 steep, smooth hopper surfaces and no abrupt transitions or in-flowing valleys. Mass-flow bins are classified according to the hopper shape and associated flow pattern. The two main hopper types are conical hoppers which operate with axi-symmetric flow and wedged-shaped or chisel-shaped hoppers in which plane-flow occurs.

8 In plane-flow bins, the hopper half-angle a will usually be, on average, approximately 8 to 10 larger than the corresponding value for axi-symmetric bins with conical hoppers. Funnel-flow occurs when the hopper is not steeply sloped and the walls of the hopper are not sufficiently smooth. In this case, the bulk solid sloughs off the top surface and falls through the vertical flow channel that forms above the opening. Flow is generally erratic and gives rise to segregation problems.

9 Flow will continue until the level of the bulk solid in the bin drops an amount HD equal to the draw-down. At this level, the bulk strength of the contained material is sufficient to sustain a stable rathole of diameter Df as illustrated in Figure 1(b). Once the level defined by HD is reached, there is no further flow and the material below this level represents 'dead' storage. For complete discharge, the bin opening needs to be at least equal to the critical rathole dimension determined at the bottom of the bin corresponding to the bulk strength at this level.

10 However, for many cohesive bulk solids and for the normal consolidation heads occurring in practice, ratholes measuring several metres are often determined. This makes funnel-flow impracticable. Funnel-flow is a 'first-in last-out' flow pattern which is unsatisfactory for bulk solids that degrade with time. It is also unsatisfactory for fine bulk solids which may aerate, giving rise to flooding problems or uncontrolled discharge. Figure 2. Expanded Flow The disadvantages of funnel-flow are overcome by die use of expanded-flow, as illustrated in Figure 2.