Innovative sorting: an essential for economic improvements in waste handling

The more high-quality material recovered using advanced waste sorting systems, the more revenue achieved.

The more high-quality material recovered using advanced waste sorting systems, the more revenue achieved. Modern sorting technologies, like modern eddy current separators and magnets with high recovery rates for metal products, or optical sorting systems for plastics recovery, help counteract high raw material costs and any investment and operating costs

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The quantity of waste worldwide has been rising for decades. In 2006, the US population alone generated some 517 million tonnes (569 million US tons) of municipal solid waste (MSW). In Europe, it is around 250 million tonnes (275 million US tons) of MSW per year. Following trends from the last few years, estimations are that Italy will produce 540 kg/capita, France 570 kg, Germany 590 kg and Monaco 1300 kg/capita that’s an average of 516 kg/capital per year.

During the same period, the shortage of landfill sites has become obvious with a decrease in Europe and America of nearly 70%. Europe has introduced a strategic legislation to reduce the number of landfill sites, but not every country has realized the targets yet.

At the same time, a dramatic increase in raw material costs has gone hand-in-hand with the limitation of natural resources. At the end of 2008 prices were low, but all economic factors and parameters are telling us that prices will increase again, and will be higher than before.

As mentioned, the recent worldwide trend has been to close landfills this is to the continuous operation and maintenance needed at sites which translates into long-term costs for the economy. An additional trend from the last four years, has seen a dramatic increase in recycling due to high raw material prices.

All these factors together strengthen the need to use advanced technologies in waste management, as opposed to simple machinery. This means there is a need for more modern collecting and transport infrastructure, despite its high costs, and modern sorting technology which has become invaluable. Disposal technology, such as landfill and incineration, also has its cost.

The use of state-of-the-art sorting technology reduces the costs for disposal, increases the cost recovery potential and saves national and international resources. In mineral processing, operators are investigating loss of material and the technologies required to prevent it. In the case of waste sorting, awareness of these measures needs to increase. Using state-of-the-art magnetic separators and eddy current separators, or sensor-based sorting such as near-infrared (NIR), induction or x-ray sorting systems, a greater quantity and quality of material can be recovered. The production of refuse derived fuel (RDF) needs to be quality assured as well with no metal and no PVC content. Improved sorting technology allows for the collection of different waste fractions together.

Costs and incomes

Waste management has many different cost and profit implications.


Suspension magnets in a waste sorting plant STEINERT Click here to enlarge image

On the costs side are:

households reserving space for bins, collecting paper, packaging, compostables and waste separately requires around a 2 m² storage area collection and transport each waste fraction requires a different collection truck, between once a week and once every two weeks treatment plants need investment and have operating costs disposal preparing and operating the landfill; maintenance for gas and sewage treatment has to last 3050 years.

On the profit side:

materials recovery depending on the sorting success and the material prices, this process opens up opportunities to recover more than just its costs.

By treating the MSW more intensively with better technology, the costs for collection and transport and disposal will decrease. In addition, the income from selling recovered materials will increase.

Waste treatment processes and technologies

The flow of modern waste treatment is generally as follows: after delivery of the waste, it is fed into a crusher and then on to a sift and/or trommel to prepare the fractions into the ideal sizes for the sorting equipment. The coarse fractions are often sorted by hand; while both the middle and coarse sized fractions have a suspension magnet removing any ferrous components.

The first optical sorter recovers beverage containers using NIR technology. The non-ferrous metal separators often sift these containers in with the other metal products, so polluting the non-ferrous metal stream.

The eddy current separator (ECS) removes non-ferrous metals, such as beverage and food cans and other aluminium materials. In most countries, industry focuses on aluminium drinks cans, while other aluminium components such as foil, metal/plastic/paper compounds, disposable cups etc. remain in the waste stream. The final treatment and sorting of these materials has not been implemented until now.

Beyond the ECS, various optical sorters sort polymers using NIR technology; they analyse the specific spectrum of reflected NIR light the recovery of PET bottles is the main aim. PET bottles are valuable and technology exists in the industry for their reuse.

Any remaining material may be landfilled or sent to the incineration plant to generate electrical and thermal energy. The remaining ash after incineration is increasingly being treated by metal separation equipment. Iron, aluminium, copper and specific stainless steels are valuables worth recovering.

Another alternative product formed during the sorting process is the generation of refuse-derived fuel (RDF). RDF is used as an alternative to fossil fuel, specifically coal. It uses materials which are not otherwise possible to recycle. To make the use of RDF feasible in nearly every industrial incineration and energy generating plant, it is important to ensure the quality when it comes to heating values, ingredients, and contaminants like metals, stones and chemicals. Therefore, in some plants, induction sorting systems and x-ray sorting systems are installed to detect and remove these components.

It must be said that in energy recovery, the RDF, or residue, is competing with fossil fuel energy like coal, which has a price of around $30 (€21) per tonne. High quality polymers are worth between $300$1000 (€214€711) per tonne. This means, by removing as many plastics as possible and getting the best quality achievable, one can generate an economic advantage with prices more than ten times higher.

Sorting technologies

To measure the sorting success, a proper analysis of each material output is needed. To compare, the sample volumes need to be large enough corresponding with the sizes and volume typically found.

Iron recovery

Suspension magnets can be found in nearly every materials recovery facility (MRF). There is typically 5%10% iron in the waste stream. Its value is about $30$80 (€21€57) per tonne. Depending on the performance of the magnet, the recovery of ferrous is very high; infact more than 95% recovery rates are possible using this technique. The important point here is that due to the volume of material, the magnet suspension height must be high this means it must have a position in the line over the head pulley of the conveyor. This may be more expensive for installation, but is needed for maximum ferrous recovery.

In addition, long magnets with a deep magnetic field are needed to attract other kinds of ferrous particles, not only steel cans. These may also be more expensive, but the material value justifies this. Often an investment difference of a few thousand dollars is worth an additional few thousand dollars income a year.

Non-ferrous metal recovery

Non-ferrous metals in the waste stream are mainly aluminium-based and account for about 1%5% of the MSW. Copper, zinc and lead are rare. The value is about $500$1200 (€357€857) per tonne. But in spite of this, with a ten times higher value than iron, the non-ferrous metal recovery is often not recovered or is sometimes manually sorted. Drinks cans are the most common non-ferrous metals, but there are lot of other things made out of aluminium.


Eddy current separator in a MRF in Germany STEINERT Click here to enlarge image

This higher value means that if 10% ferrous metal is recovered then it must be worthwhile recovering even just 1% aluminium. Normally, manual sorting achieves just 40% recovery, this is measured based on all size fractions and all aluminium containing components. Modern ECSs, used for the aluminium recovery, achieve more than 95% recovery.

Sensor sorting systems

Sensor sorting systems use sensors to detect specific optical, chemical or physical properties of single particles. After they are detected and recognized, computer-controlled jets of compressed air eject the specific particles. These technologies are widely used in the chemical and food industry, and, for the last eight years, in waste treatment. With optical detection, plastics are sorted by examining near infrared light, others work with visible light; induction sorting systems measure the electrical and magnetic performance. X-ray sorting systems also work like optical systems but use the transmitted x-rays absorbed by chemical components to generate a picture. These machines are available with a maximum working width of three metres and may treat around 120 m³/h.

Technology drives the economical results

A balance sheet from a German RDF plant showing economic potential is illustrated in Table 1 on page 38. The in-feed material is the household residue. The packaging material was collected separately, as well as organic material, glass and paper. The plant is producing RDF as a by-product, as well as iron, non-ferrous metals and plastics.

Click here to enlarge image

One important point to note here is that it is not a mistake that the RDF sales are generating a negative profit - this is due to costs. The consumer of the RDF, e.g. concrete plants or power plants, are receiving money for using the high quality RDF. Due to the high prices for waste incineration (around $200$400 or €150€285 per tonne) the further sorting and production of RDF is in direct competition. Further treatments cost only $40$80 (€29€57) per tonne and generate additional revenues.

Table 1 shows that the main income is generated by non-ferrous metals. The other profit is in avoided waste incineration. That underlines that even the loss of 1% of non-ferrous metal will reduce the economical output.

Advanced sorting technology is good value for money. We often recognize, especially in waste management, that only the investment costs are investigated, and the life cycle costs of the equipment are neglected as well as the advantage of 1%3% more separation efficiency and availability which is not seen and calculated.

Non-ferrous metals can be separated from some 200 mm down, with a 1 mm particle size, using the eddy current separators. They are used to a large extent in metal recycling facilities. Others facilities, like bottom ash recycling plants and MRFs, are becoming more and more popular; in Germany, Austria and Scandinavia, they are widely used in solid waste treatment.

The pole system of an ECS generates a short, repulsing magnetic force on every electrical conductor which comes into the area of the changing magnetic field. Lightweight and good conductors like aluminium will jump out of the waste stream, whereas plastic, paper, wood or glass will fall down with the normal trajectory. In the case of iron, the attracting magnetic force is stronger than the repulsing one.

Eddy current separators are available with two technologies, these differ with regard to the position of the fast turning magnetic rotor, i.e. the ‘pole system’. The first system is a complex technology with an eccentric position of the pole system, and the second is a more simple concentric system. The eccentric pole system is the most widely used technology in western European waste treatment as well as in international metal recycling, due to the higher accuracy in separation (recovery and purity) and the much higher durability.

Table 2 on page 39 compares the two principals of eddy current separators. For the eccentric system, there are higher investment costs (e.g. another 21%) along with small increases of availability (+3%) and separation efficiency (recovery +2% and purity +1%). So a careful calculation of yearly additional profit versus investment and life cycle costs is needed.

Click here to enlarge image

In the concentric system, the magnetic force is all around the head pulley iron particles stick on the conveyor belt and the shell of the pulley, and will damage both. With the eccentric system the magnetic field is concentrated in a small area it is strong and short enough to make the non-ferrous (NF) particles jump. Beyond this area, magnetic particles have no magnetic field to stick to. This increases the durability of the process and its availability and the mass of material that can be treated.

In most eccentric eddy current systems the pole can be adjusted between ‘12 pm and 2 pm’ within the pulley, to maximize the area of impact precisely at the moment when the particles are in the perfect position to be ejected. This increases the recovery rate by 30% especially for finer particles. The comparison shows the difference in investment for the advanced technology is paid within three months.

Other examples of economical advantages through advanced technologies, include the introduction of sensor sorting systems to recover stainless steel or to remove stones and some PVCs excluded from RDF. Optical sorters with near-infrared technology can sort polymers very accurately and are worth investing in. Starting with bottles and beverage containers, they are now working with a particle size of around 5 mm, which allows for working with polymer flakes.

With current high raw material prices, both the waste industry and the government, are interested in recovering more and more. This allows, for example, for a smaller increase in waste collection fees in Germany, the Green Dot System is aiming for greater co-operation with the increased metal prices, and organizers are in the process of changing the contracts with the subcontractors who treat the collected waste material. In the past, metal prices and their related additional reimbursement was the only focus for (mostly private owned) waste management companies.

As mentioned before, it is also a question of economics and whether residues from waste will be used as fuel with a comparable market value of $30 (€21) per tonne or as a source for production with a market value up to $1000 (€711) per tonne.

The treatment of bottom ash or incineration slag is an already existing business, even in the US. The recovery of stainless steel from bottom ash has also a financial benefit, which can be achieved with most modern induction sorting systems. Industry in Germany prefers to work with the more advanced technologies like the eddy current with eccentric pole system for economic reasons.

Summary

For further efficiency in waste recovery, it is recommended that one considers using advanced and adapted technologies, for example, for non-ferrous metal recovery and/or for other material recoveries.

Material recovery should always be performed by maximizing the output due to increasing material prices and worldwide demand for raw materials. Recycling will strengthen its market position as a means of raw material supply, which further enforces the use of advanced sorting technology and processes.

Dr Ing Ulrich W. Kohaupt heads the department for business development and marketing at STEINERT Elektromagnetbau GmbH, Germany
e-mail: kohaupt@steinert.de

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