18 ANDRITZ 3


of the available waste streams – amount of valuable waste compounds and heating values of the potential fuels – the existing equipment at the mill, and the desired final result. Let’s take a closer look at the individual process steps: Reject handling. With few


exceptions, practically all recycled paper rejects can be used as a fuel source. What ANDRITZ does is to separate out contaminants that cannot be readily converted into energy – part of them, however, can be recycled as valuable goods. An early step is to remove


coarse, iron-containing metals using a powerful magnet. With a ballistic separator (Figure 3) bulky material is removed from the reject stream: unwanted debris like stones, bricks, and other heavy items as well as valuable compounds, such as plastic bottles or cans. After mechanical dewatering, the rejects are reduced in size and made more homogeneous in a shredder (Figure 4) before further components, such as non-ferrous metals or PVC, are sorted out. The metals removed can be sold as scrap to the metals industry. After this, the material may have to be dried before being combusted or pyrolysed.


Sludge handling. After


pre-thickening using gravity, fibrous sludge is dewatered on mechanical presses applying very high pressures. Sludge from biological water treatment is somewhat more difficult to dewater mechanically. This is why flexible belt presses are typically used for this purpose. ANDRITZ technologies for sludge dewatering include screw and belt presses, gravity tables, thickening drums (Figure 5), and


May/June 2016


Pulp Paper & Logistics


Figure 5: ANDRITZ TD thickening drum, used for continuous sludge pre-thickening


other dewatering devices. Drying. Thermal drying is


required to remove more moisture from pre-dewatered sludges. ANDRITZ has a large portfolio of dryers. Quite often, belt dryer technology is used for rejects and sludge materials, and also for woody biomass. By drying in a closed system‘, the heat in the drying air can be recovered and utilized – reducing overall energy consumption. Pelleting. Due to their dense


form and low moisture content, pellets are very efficient to transport and store. Pelleting is therefore an excellent technique for preparing the waste fuel. The waste is pretreated and fed at a higher temperature into an ANDRITZ pelleting machine. The machine extrudes the material through a perforated die to form pellets of uniform diameter.


The pellets are cooled and conditioned to prevent them from sticking together. While wood pellets can be used in household heating systems, the pellets made from rejects and sludge materials need official permission for commercial waste combustion. Pyrolysis and combustion.


ANDRITZ offers innovative pyrolysis technology for full recycling of plastics rejects and laminates (plastics-aluminium films). The basic technical principle of pyrolysis is a chemical process, a technology for high-temperature heating of organic material in the absence of oxygen. For combustion, ANDRITZ provides proven power boiler technologies – well suited for biomass and alternative fuels – with high combustion efficiency. With both pyrolysis and combustion processes,


complex waste products can be converted back into resources, thus making substantial contributions towards protecting the environment. There is an old saying that


“one man’s trash is another man’s treasure”. Just as crafts people turn old metal and textile scraps into works of art, ANDRITZ technology is turning once- disposed-of waste materials into valuable energy sources and products. Perhaps the outcome is not as beautiful as a work of art, but it is important as a cost-saving and environmentally sound solution. So, don’t waste your waste!


• Michael Waupotitsch is VP, Sludge, Reject and Recycling, and Regina Puschnig is Marketing Manager, Pulping and Fiber Division, at ANDRITZ AG, Graz, Austria.


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