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This is a fine example of an industry working proactively and responsibly to ensure their waste is able to be recycled with the minimum amount of cost to the consumer or risk to the environment. As a result, future recycling technologies for primary batteries can concentrate on recycling for resource conservation, rather than toxic elimination. This has not been the case with most of the dedicated recycling processes operational today. Many of these recyclers have argued that the battery industry will never be able to guarantee that batteries being sent for recycling are indeed mercury free. This argument is used as justification for maintaining high costs because of the need to capture and treat mercury. It is very clear however that mercury within primary batteries is an historical problem and does not need to be a consideration for future, long-term, sustainable recycling options.

Battery Sorting

Battery recycling is undertaken in order to: either remove toxic material from the waste stream, as is the case with mercury, lead or cadmium containing batteries, to recover materials with high commercial value, including nickel, cobalt and metal hydrides found in rechargeable systems, or for resource conservation, as is the case with mercury-free primary batteries. Battery recycling operations which seek to process all batteries collectively are either unable to recover the value from the high value materials at all, as they concentrate on detoxification, or their resale value is diminished as a result of impurities introduced from the other battery systems also being processed. In the latter case, expensive and complex purification processes are often necessary in order to reclaim even a small percentage of the materials value.

It is therefore evident, that to maximise the benefits of both of these goals, some degree of pre-sorting is necessary before recycling. This is not a novel idea. Many commercial recycling processes operating today require sorting of the products before recycling. These include scrap metal for the steel industry as well as glass, paper and plastics recycling.

The degree of accuracy required of sorting operations will be dictated by the purity requirements of the recycling facility. Most recycling facilities available in Europe today require sorting to some degree. Typically for recycling of primary batteries, the contamination by rechargeable systems such as nickel cadmium or lead acid, should be less than 2%. However, one tonne of mixed consumer batteries can contain anything up to 40,000 individual battery units of perhaps 10 different battery chemistries. These can vary in size from button cells with a diameter less than 7 millimetres and weighing less than 0.3 grams, up to block batteries weighing a kilogram or more. With this in mind, one can clearly see that hand sorting of batteries, even on a small scale, is likely to be inaccurate and very time consuming. Consequently automated battery sorting technology has developed hand-in-hand with recycling technology.

Accurate sorting relies on the identification of a number of different properties of a battery. These include the physical size and shape, the weight, the electromagnet properties and any surface identifiers such as colour or unique markings. These properties can be analysed in a number of different combinations in order to sort batteries into nickel cadmium, nickel metal hydride, lithium, lead acid, mercuric oxide, alkaline and zinc carbon batteries. Due to an voluntary marking initiative introduced by the european battery industry, it is now also possible to separate the alkaline and zinc carbon cells further into mercury free and mercury containing streams.

With battery recycling operations ranging in size from 2,000 tonnes per year up to 20,000 tonnes per year and battery collection also increasing annually, it is also very evident that high speed is an essential requirement of a successful sorting facility. The third element for successful battery sorting is that the operation must be achievable at low cost. This means that large-scale facilities, in the order of 2 to 3,000 tonnes per shift, which have the added benefit of economies of scale, are preferred to smaller, more costly operations. Such facilities can be operated at a cost not exceeding $150 per tonne.

One example of such an operation is the Sortbat sorting facility, operated by AVR Holding, in Rotterdam, The Netherlands. The plant is capable of processing 3,000 tonne per shift per year of post consumer batteries at an accuracy exceeding 99% for critical battery streams.

Initially the machine was developed by the European Portable Battery Association to prove the concept of high speed battery sorting. However, around the same time, the need arose in The Netherlands to be able to recycle all battery types. Consequently, after discussions with dutch collection and recycling organisation - STIBAT, the EPBA agreed to build a prototype sorting installation which would provide enough capacity to satisfy this demand. The ownership of the machine throughout its development was to remain in the hands of the manufacturers and be leased by STIBAT. Consequently the battery manufacturers set up a non-profit making company, SORTBAT to oversee its development, installation and management.

The heart of the sorting line is an electromagnetic sensor which induces a magnetic field within each battery and measures either a voltage or a frequency response. The most successful electromagnet sensor technology available to date, and that used within this facility, is the Tri-Mag sensor developed and commercialised through a partnership between Titalyse S.A. of Geneva, Switzerland and Euro Bat Tri Sari based in Lyon, France.

Each battery is presented to the sensor by conveying it on two parallel polycord belts and transported directly through the centre of the sensor coils. This is illustrated in Figure 2. This transport method allows each battery to pass through the sensor in a very stable manner, thereby ensuring the accuracy of selection. The signal from the Tri-Mag is stored electronically and processed together with an accurate weight measurement. It is this combination of electromagnetic sensing and weighing which is responsible for the high purity levels achieved. Both measurements are carried out without the need to stop the battery. Consequently the operation is carried out at high speed. Today, each sensor is capable of measuring five cells every second, with mechanical handling being the rate limiting step. It is feasible that this speed could double in the future.

Epba Sortbat
Figure 2. Battery on polycord belt and direction of travel

The process can be considered to be divided into four main stages. Stage I, hand sorting of large battery packs and removal of non-battery waste. Stage II, the dust and button cell removal. Stage III, where batteries are sorted according to size and stage IV, where the batteries are sorted by chemistry.

Stage I

Batteries are first loaded via a bunker onto a band conveyor where block batteries, battery packs and non-battery waste are removed and sorted by hand. The batteries selected at this stage are those which are unable to be passed through the electromagnetic sensors in stage IV of the process. These include rechargeable battery packs and industrial batteries.

Stage II

The remaining batteries are fed into a charging hopper which feeds a pocketed belt conveyor. This in turn deposits the batteries onto a cascade of sieves which have been carefully selected to remove dust and button cells. The remaining batteries are then fed onto a wide band conveyor which passes beneath a magnetic over-band conveyor which separates the magnetic fraction from the paper jacketed zinc carbon cells and batteries.

Stage III

The over-band transfers all of the magnetic batteries onto a second pocketed belt conveyor and from there onto an additional hand sorting table. Here any remaining non-battery waste, rechargeable packs or damaged cells which evaded the initial hand sorting phase can be removed. They then pass onto a second series of cascading sieves which sort the batteries according to their physical dimensions. The main outputs from this section are the AAA, AA, C and D size cylindrical batteries most commonly used by the general public. These are deposited into individual bunker feeders which supply the batteries to stage IV on demand.

Prismatic batteries, such as those used in smoke alarms and alkaline flat-pack cycle lamp batteries are also removed at this stage.

StaselV

This is the most technical stage of the process. The size-sorted batteries are individually fed from a vibrating bowl feeder onto the polycord belts. The supplies to the belts are regulated to ensure an even distribution of batteries to the sensors. The installation is equipped with four sets of polycords and sensors. One for C and D cells combined, one for AA and AAA combined and two for AA size batteries only. This combination has been determined in order to balance the operation of the installation with the market mix of batteries sold in Europe. This balance is critical in ensuring the optimal operation to achieve the 3,000 tonne per shift throughput.

Each battery in turn passes through a series of sensors. Measurements are taken 'on-the-fly' and stored in a programmable logic controller, a PLC. Decisions on battery chemistry are made based on inputs from each of the sensors as shown in Figure 3.

Specialist batteries, which are generally shorter than general purpose batteries are selected by a simple size measurement. This is undertaken by the use of two through-beam detectors fitted approximately 50 millimetres apart. Only standard consumer size batteries are allowed to pass this point.

As the consumer size batteries continue along the polycords they pass beneath small magnetic over-band polycords which lift the battery off of the main line for a fraction of a second. These over-bands are connected to load cells which take up to 50 weight measurements of the battery as it passes across. These measurements are stored in the PLC, and used in conjunction with the information from the Tri-Mag sensors. All batteries over a set weight are rejected immediately, as these will be either lead acid or mercuric oxide.

Immediately after weighing, the batteries pass through the Tri-Mag sensor. Induction coils induce a magnetic field within the battery and detector coils measure a voltage response which is converted to a unique alphanumeric signature which is also fed to the PLC. Within the Sortbat machine, this sensor is specifically used to differentiate between alkaline, zinc carbon and nickel cadmium batteries. However due to the construction of the outer casings, some specific batteries of different chemistries provide identical signature responses from the Tri-Mag. Most of these conflicts however are eliminated by reference to the weight measurement taken previously.

UV Sensing

The fastest sensor by far in the sorting installation is the Ultra Violet, UV detector. Two detectors per line look for a UV marker on battery labels which has been added

Two stage Sieve

^Cylindrical is X YES

Reject

"Dust "Buttons

Paper

Dimensional Sort

Record Weight

^Cylindrical is X YES

Reject

90/30 PLC

Weighing Ï

Tri-Mag

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