Let us first start with a short background story on material screening, which isn’t as new of a process as one could think. The screening or sieving, or winnowing was used by ancient cultures for the cleaning of cereals, separating the grain from the straw or sand, a process mainly used for barley and wheat crops. By 1737, the winnowing machine for corn, called the Fanner was developed and, with the first industrial revolution, the winnowing process was mechanized, and the fanning mills were invented. These machines would clean the grain and separate it from dust, weed seeds, and so on.
In 1926, begins the manufacturing of vibrating screens for the separation of materials. By the way, did you know that besides the material screening, the vibrant screens are also used for sifting green coffee (that is dried coffee after being harvested), to remove impurities before it is roasted?
Fast forward, other technologies are taking the screeners market and become the most common. And in 1997, Ecostar starts the development of a disc screening technology known today as DDS – Dynamic Disc Screening.
Now, this market developed on a need – that of treating and recovering as many materials as possible and stop disposing of waste in landfills, which unfortunately still happens on a large scale today. We are talking about food waste, wood, metals, plastics, paper, and cardboard, and so on, materials that with today’s technology could be easily returned to the market and reused by us all. One could argue that the material screening or the screening process is not that important in a recycling line, as it is a step that could be easily skipped, but if that were true, there wouldn’t be such a big screeners market today, would it? So, let’s see how the screener works and the value it brings to the recycling process, by answering three of the main questions we have been asked over the years.
The screening or the dimensional separation of waste is one of the pre-treatment operations that waste undergoes before it is sent to the actual treatment and consists of separating the materials in different sizes, as well as separating it from other waste (e.g., organic from plastics). This way, the materials can further be processed and turned into various finished products, depending of course on the type of waste to be treated and on the operator’s business objectives. To better understand the results of the screening process, at the end of the article you can read an application on wood, that after it’s been separated it is used to produce oriented strand boards.
So, you can see why the screening process increases the value of the material. Moreover, it reduces landfill costs for operators, as lots of waste can be treated and reused.
The screener is a machine that can work either by standing alone or in line with a shredder or a bag opener. And that, of course, also depends on the type of material to be screened.
A screener can work by itself when the waste is compact, such as compost, biomass, MSW, or aluminum cans, so there isn’t the need for a complex recycling line.
Instead, when working with organic waste that usually is brought to the recycling line in bags, the screener can work with a bag opener, that first opens the bags, without shredding or cutting the inside waste. For the screening of organic waste, in Ecostar, we often design an extra step to the screener, where the bag falls, and it is shaken so that the waste comes out easily and then spreads on the screening surface.
Finally, when operators are dealing with materials that need to be cut into pieces, such as waste wood, or tyers, or metals, they can use the screener in line with a shredder. And our machines are known to work in line with almost any kind of a shredder. Moreover, they prove to be very efficient and economical, especially for businesses that recover wood waste. For example, an 8-meter-long machine can screen up to 200 t/h of scrap wood, performs with wet material, and can work in line with the most powerful shredders on the market.
We have often heard this question and we would say that these machines are used for different purposes and materials, and the most important thing to take into consideration when this question arises is: what is the material that I want to treat, and what do I want to do with it? Simply put, the shredder cuts the material into pieces, while the screener separates the little parts of the material from the medium or the big ones (from 10mm to 200mm with the Ecostar screeners, depending on the type of the material) thus preparing them to be reutilized thanks to further recycling steps. So, this material, separated into different dimensions, can be reused for different purposes, and that is the real value of a screener, as it helps operators to have a calibrated and clean material ready to be fully recovered.
Waste wood screening, case study
This is a recycling line in Austria, where Ecostar’s client wanted to improve the screening of wood waste in an existing working line. Poplar wood is very difficult to process as it puts a strain on the shredding phase, which precedes the separation of the material by dimension, this resulted in lower production. In its original configuration the system used two shredders, the first one was used for the initial shredding and the second one was to produce the material in the desired size, but this also included the very fine fraction that was of little interest for the company. This resulted in a low quality of the screened material and high maintenance costs for the second shredder, which was receiving different lengths of material to be processed. After installing a HEXACT DDS into the system, the company was able to separate the material into three fractions: 0-10mm fine fraction; 10-100mm, which was the right dimension to send to the plant to produce oriented strand boards; and >100mm oversize that was to be shredded once again. The result? The system is now able to reach a higher production of 30 tonnes per hour while obtaining a clean fraction for the company’s business need.