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Transponder News

A news service reporting on developments regarding the use of radio based tagging transponder systems for commerce and scientific applications. Covering the RFID technologies, EAS technologies and magnetic coupled techniques.


RFID Coal Tracking Technology

By Deryck Lauf

This article discusses an interesting new application for RFID tagging of coal ore. The system was developed by Systems & Power engineering cc, Johannesburg and was commissioned at Hendrina Power Station, South Africa in May 2000. The system has been patented by Eskom and Systems & Power Engineering cc. The computer networking was developed by Meitron cc.

Most of Eskom's Coal-fired power stations receive coal from pit-head mining operations. The coal is generally of variable quality. The degree of variation has only been shown up with the introduction of a Prompt Gamma Neutron Activation Analysis, (PGNAA) technology on-line elemental coal analyser at the Hendrina Power Station / Optimum Colliery interface. This instrument produces the following coal analyses in near real time.

  • Proximate analysis
  • Ultimate analysis
  • Ash elemental analysis
  • Calorific value
  • (attempts have also been made to estimate ash fusion temperature with limited success).
  • Recent work at Eskom's Lethabo Power Station has shown that significant efficiency gains can be achieved if the "bandwidth" of the quality of coal being sent to a boiler can be minimised. The implication of this is that a boiler can be fine-tuned for a particular coal, and does not need to be set up to handle large variations in quality. (This is analogous to the gain in efficiency that can be achieved by setting up a motor car's engine to take for example unleaded petrol as opposed to the engine having to burn anything from petrol with an 87 octane rating to a 97 octane rating within short intervals).

    On-line analysers of this technology are very expensive and it cannot at this stage be justified to place them anywhere but at the interface between the mine and the Power Plant. The information is, however, available in real time and the potential of the analyser would be wasted if the information was only used for daily analysis purposes. In addition to this the residence time of coal in the Power Station system may be anything from a few hours to a few years. The challenge was to track the coal through the process in order that with one analyser, the quality of coal at the mill inlet could be known and potentially controlled. Previous efforts have been made to simulate coal flow in bunkers but were deemed to be unworkable due to the changing nature of the coal and the inability to measure on-line the critical parameters of the coal affecting flow. An alternative approach to track the coal was therefore developed. This involved the physical marking of the coal as described below.

    The Solution.
    Systems & Power Engineering cc developed a method of tracking the coal by using passive tags (transponders) and a set of reading coils strategically placed on conveyors around the plant. Each transponder has a unique number (48 bit binary code) programmed into the silicon chip. The chip design allows for many billions of unique numbers. The tag is passive, meaning it has no battery or power source, but receives its power from the fixed reader coils placed around the conveyor belt at various points in the coal handling system. The transponders are packaged in such a way that they approximate the average size of the coal. This ensures that, from a materials handling point of view, the packaged transponder will behave in a similar fashion to the coal.

    The transponders are dropped into the incoming coal stream at pre-determined mass intervals. The droppers are situated adjacent to the On-line analyser. The reader coils on the dropper determines the transponders unique code and transmits this information to a central computer. Here the code is associated with the coal quality of the lot that the transponder was dropped into in the coal management system's central database. Due to the packaging, the transponder should in general follow that batch of coal wherever and for however long it is stored.

    Transponder readers positioned as close as is reasonably possible to the mill bunkers, read the passing transponder's ID number. This number is passed on to the coal management computer system, which associates it with the stored data from the on-line coal analyser.. This data is then passed on to the plant Operators who can use the information to optimise their plant.

    At Hendrina power Station, Systems & Power Engineering have developed the technology in two ways. The transponder chip has been designed for long range reading in wet conditions and packaged into a robust container at low cost. Secondly S&PEcc have developed a reader to read the unique tag code when the Tag is transported on a fast-moving conveyor belt.

    A specially designed dropper/reader was built to release one transponder onto the incoming belts on command from a PLC, which is synchronised to the on-line analyser. Readers have been installed onto the head pulley end of each of the six incline belts feeding the mill bunkers.

    Alternative tagging methods
    Electronic tagging is important because other known methods of identification are not practical. e.g. bar code, VHF transponders etc. Some projects have tried colour tags, but this has many problems not including the problem of supplying and then identifying thousands of different coloured tags. This is particularly difficult in a dirty coal environment.

    Costs
    A typical RFID tagging system on a power station would utilise one on-line coal analyser, a minimum of one reader and dropper on the coal receiving belt, and one reader per belt on the feed belts to the mill bunkers.

    An imported on-line analyser installation would currently cost in the order of US$600 000. However, the cost of a locally manufactured S&PEcc system of one dropper, six readers, a radio data telemetry system, and seven thousand re-usable tags is only US$50 000

    Other Applications
    RFID tracking has applications to the tracking of any product which cannot be bar-coded. It can be used for tracking coal, cement, any metal ore including iron, gold, uranium, chrome, copper or diamonds, liquids like milk or petroleum, or agricultural products like grain, corn, wheat or coffee. It may also easily be applied to tracking boxes of bulk manufactured goods like clothing and textiles, airport baggage, food and any warehousing application.

    Systems & Power Engineering cc
    S&PEcc is a systems engineering house with graduate electrical engineers and computer science software engineers with many years experience in the design, manufacture, commissioning and guarantee of products for the communication, electrical utility, industrial control, and mining industries.

    Deryck Lauf may be contacted at laufdg@mweb.co.za

    RFID scanner

    Read-back readers at the top of the incline conveyors before the coal enters the power station mill. The blue piping is the reader 125 kHz antenna.



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