Modern Mining September 2017

PRODUCT News

Rock intrusions a problem when specifying sizers/breakers

With coal miners moving into more dif- ficult geological conditions, a detailed characterisation of the orebody is increas- ingly vital when specifying feeder breakers or mineral sizers, according to PC Kruger, Capital Sales Manager at FLSmidth Buffalo. “Most of the ‘easy’ coal seams in the Witbank coalfields have been mined,” says Kruger,“and what remains tends to include a high level of hard rock intrusion as well as tramp material such as steel, wood and concrete.” In particular, strip mining of old under- ground bord-and-pillar mines often encounters a substantial portion of rock, which has a much higher ultimate com-

be reduced to about 300 mm in size in the primary phase,” he says. Similarly, in the secondary sizing stage, the ratio should be 3:1, which can reduce this 300 mm coal down to 100 mm. In the tertiary sizing stage, a ratio of 2:1 is the norm, breaking the material down further to the minus 50 mm size that the end-user usually requires. “Trying to operate outside the bound- aries of these reduction ratios invariably leads to increased wear and running costs,” he says. “Putting over-sized material – say, larger than 150 mm material – into a ter- tiary sizer designed for 100 mm material, prevents the positive ‘bite’ that breaks the product down. Instead, the size and geom- etry of the pieces means that they do not pass cleanly through the rotors, and cause undue wear on the rotor teeth and other components.” He emphasises that trying to reduce capital expenditure by having fewer sizing stages – and therefore less equipment – is usually false economy. With the capital cost of this equipment making up only 8 % to 10 % of its total cost of ownership over its lifespan, the operating cost normally outweighs any upfront saving by orders of magnitude. FLSmidth, tel (+27 10) 210-4820, website: www.flsmidth.com Becker’s advanced solutions prevent electromagnetic interference by transmit- ting data packets across the generated H field. Data received is recognised as a system tag and not an environmentally generated signal that could cause unneces- sary warnings. The tri-technology tag, which supports accident investigation and multi-mode operation, is compatible with Becker’s tagging systems and communications net- works. This tri-axis electromagnetic receiver ensures reliable detection by the system, regardless of the tag or miners’ position. Vehicle tags are self-powered RF devices that ensure the presence of a vehicle con- tinues to be broadcast, even if the ignition has been turned off or the battery has been isolated. Control tags transmit specific commands to PDS controllers and miner tags, also providing alerts when entering a restricted or hazardous area. Andrew Trentelman, Becker Mining South Africa, tel (+27 11) 617-6300

pressive strength (UCS) than the coal. While the UCS of coal ranges from about 40 MPa to about 60 MPa, tests in the Witbank region, over a number of decades, have found that some rock intrusions eas- ily measure up to 210 MPa in strength. Kruger says that feeder breakers are well suited to most underground mining conditions where the coal is relatively soft and homogenous. “However, they are not designed to deal with high strength material,” he says. “Where there are regular hard rock intru- sions, you will generally opt for mineral sizers.” Another critical consideration in speci-

fying equipment for coal processing is the principle of reduction ratios in each stage of sizing. Kruger says the ‘rules of the game’ require that, in the primary sizing stage, the ratio between the input size of coal and the out- put size should be about 4:1 or 5:1. “In other words, a large chunk of material with dimensions of 1 200 mm in two or three dimen- sions can realistically only

Typical underground feeder breaker being used by the bord-and- pillar mines.

Becker PDS solutions combine three technologies Becker Mining SouthAfrica provides turnkey proximity detection systems (PDS), tagging and tracking and related communication systems, which comply with stringent min- ing health and safety regulations.

technology point of detection system is the only system available globally that com- bines three technologies – UHF, Radar and Electromagnetic – into one scalable system.” Bi-directional notification and early warning messaging alert vehicle opera- tors and personnel to the presence of each other and to stationary or moving vehicles in close proximity, enhancing safety in ardu- ous conditions. Becker’s latest PDS controller, which is the interface between the vehicle operator and multiple detection sensors mounted around the vehicle, provides various alert mechanisms for operators. These include cabin lighting and alert tones which are selected to suit exact requirements. This system consists of a customisable caution zone, warning zone and critical zone. Detection zone threshold distances are set according to specific requirements, covering small and large vehicles.

The company has developed advanced proximity detection systems for nearly 20 years, which have reportedly significantly improved safety on the mines. Becker’s modular PDS solutions are designed to prevent potential collisions during the operation of vehicles in the proximity of personnel on the surface or underground. “The company’s latest patented tri- technology PDS solutions – which range from a simple, low-cost single technology system to integrated multi-technological solutions – encompass all aspects of the most advanced mining communications and technology,”states AndrewTrentelman, Senior General Manager: Electronics, Becker Mining South Africa. “Becker’s patented tri-

44  MODERN MINING  September 2017