Screening In Waste Management
Are we the casualties of our own success? Do we really know what is happening or are we being forced to take note of the increasing need to reduce waste. Barely 20 years ago gardens were places where families grew fresh produce as a means to reduce cost, now they are transformed with decking, patios and barbecues to provide rest from the increasing pressure of business success, long hours and fast living.
Recycling has become necessary due to the massive demands that the human race, in the “booming metropolis countries” has put on the need to produce goods, which are pre packed and ready to use. Our actions now are rapidly becoming more important if we are to wake up to the reality of life at an accelerated rate.
Accepting that recycling is probably one of the most important issues on the modern agenda there is a need to understand how we can best make use of the millions of tonnes of waste that is produced each year. Systems are now either in place or being developed to allow these materials to be re-used in an eco-friendly manner. More and more products are being segregated and crushed to a form that is useable. The need therefore to separate products into specific categories/sizes helps and as such the need for screening is becoming an integral part of many recycling systems.
Screening in its simplistic form is the separation of products by size, either in a wet or dry form. When dry the nature of the recoverable product plays an important part in machine selection. Factors such as resale value, accuracy of product size, yield, and production timescales all play major roles. As such it is essential that machine selection is correct. Where larger sized granular products are required linear motion screens with large amplitude and high frequencies are usually sufficient. Woven mesh, finger or taper slot type screens are generally selected because of their robust nature and adequate capabilities within this band.
Where more accurate grades of product are required (usually sub 1.0mm) the selection of screening equipment and media is essential. The more accurate the requirement the more difficult it is to achieve high yields within specification. Flatbed screening provides an ideal platform to use mesh aperture with maximum efficiency. Large stroke and relatively low frequencies give maximum product movement and therefore allow stratification to be as effective as possible. Anti mesh blinding needs to be offered in most cases due to the problem of near size either pegging or blinding the mesh. Selection of screening media can be as important as any other factor.
Thin wire diameter may maximise screen area but can lead to a shorter life. Slotted mesh may be selected where product such a pellet needs to be sized with higher yields. Synthetic mesh such as nylon or polyester can in certain cases provide a better screening media than woven wire especially where product blinding of certain materials is prone.
ROTEX, for their part, have seen the trend in recycling and responded in areas where their equipment is best suited namely in the separation of dry granular materials. Because of the “in-house” testing facilities it has been beneficial to certain companies to use these facilities to prove the principle of screening before committing to actual projects. Depending on the specific needs of each screening project the material has to be evaluated to assess whether the screening needs to be coarse and simplistic, fine and accurate or difficult and uncomplimentary to traditional methods. The following are typical examples where success has been gained on the back of testing.
A few years ago ROTEX undertook a series of lab trials on a waste glass mixture that could include both float and container glass products. Once crushed the glass mixture was subjected to a range of tests on the Gyratory motion screener system to product fractions from 3mm down to 63 micron with high degrees of accuracy. This was due to the almost flat bed type screens and the unique motion of the Rotex system. Such was the success that the project was seen as viable and has been working successfully now for the last 2 years. Production from the system demanded high degrees of accuracy due to the specific industries that needed to be served. In addition due to the value of recycled products being generally low it was essential to achieve yields that were economically viable within an affordable budget. ROTEX was chosen not purely because of the ability to achieve specification but also because of the international reputation for longevity, simplistic and rapid screen change and recoverable costs due to yield and accuracy being consistently maximised.
Plastics
Since timber has become increasingly scarce, and an increasingly costly commodity, the use of plastics in the window industry has seen an unprecedented growth over the last 10 years. Production systems now have to cater for the public’s demand for double and triple glazing where accuracy of manufacture is essential in order to achieve the recognised brand of certification. Wastage from production system start-up and finish is enormous and needs to be controlled with regards to waste classification. One opportunity is to recycle the plastic product whilst it is clean thereby allowing it to be re-introducing it into the manufacturing process. As such certain companies have specifically set themselves up to take the waste products and grind the plastic into recyclable material. ROTEX have played a part in offering screening systems to cope with the demand for high accuracy fine ground products where oversize can potentially cause serious problems during extrusion procedures. In addition Rotex screens have been employed within the PET bottle recycling industries to separate larger items from caps and other foreign products by maximising the use of the large stroke screeners to effect fast and efficient separation.
Waste Management
Based on the needs within the aluminium industry to develop a screen to allow waste aluminium to be recovered from casting slag ROTEX provided Alcan with a specific screen deck to recover the pure aluminium with maximum efficiency and minimal screen blinding. The screen deck development was trial tested at the ROTEX manufacturing facility in conjunction with Alcan representatives and fully tested prior to machine shipment. As a result of this success the same principle has been introduced into the Bio-mass pellet production systems that are presently being developed for waste to energy production.
In other areas plasterboard demand has seen a massive increase due to the booming housing and industrial growth. Such are the costs for wastage disposal that the main producers are finding it necessary to guarantee that damaged board can be returned. Recycling of this board on a large scale has now had to be introduced at source and as such Rotex are presently looking at future success based on successful lab trials on crushed plaster/board coating separation.
For many years the aggregate industry has benefited from the natural resources of the countries where such products are in abundance. Indeed within the UK the aggregate and associate industries have, until recently, taken swathes of land on a continual basis to meet the demands of industrial growth. Legislation now means that recycling has to be increasingly used to achieve standards set by government. Once again glass is being seen as a major recyclable material for use as fillers in concrete etc. Sand (in its dry form) is being recycled from such industries as roofing production, Building materials are being crushed and recovered. ROTEX, through the development of its Gyratory motion screens and linear motion screens as well as its vibratory feeders in conscious of the industry needs and is continually striving to produce machines that are not only suitable for the industry needs but maximise the recoverable product by the implication of testing and machine selection.
ROTEX Europe is a subsidiary of ROTEX Inc. in Cincinnati, USA, one of the largest screening and bulk equipment manufacturers in the World. The company, with offices in Runcorn, UK, Wavre, Belgium, Germany and Japan provides processing solutions for a number of industries including bulk food, animal/pet food, chemicals, mining, quarrying, fertilizer, glass, plastic, recycling, rubber, salt, sugar and wood.
Andrea Nikolic, ROTEX Europe, Avenue Lavoisier 18b, B-1300 Wavre (Belgium)
Tel. +32 10 41 61 71 – Fax. +32 10 41 41 28 - E-Mail: a.nikolic@rotexeurope.be
