Glass Recycling with RHEWUM sorting machines
Recycling by efficient and energy-saving classification
Recycling is defined as a process which produces a secondary raw material from waste or residues. Since recycling means every recovery technique which produces products, materials or substances for the original or another purpose it is a very wide range of processes with varying requirements for separation technologies.
- Glass recycling is seen as the “prototype” of modern recycling economy. The production of glass using recycled material saves raw material and energy. The melting on of the base material mix after crushing and screening and optionally optical sorting need less time and lower temperatures.
- Reclaimed building materials are mixtures with varying characteristics regarding to their origin. Ashes of waste combustion are belonging to this group of material. Even if they are coming from the same waste combustion plant their characteristics are also varying by and by. This can be observed especially in the fine and fines fractions. Regarding to the area of application after recycling these ashes are separated in various particle size fractions.
- Fly ash is produced in the combustion process of hard coal in power plants using pulverised coal firing or grate firing. The particle size is fine as flour and they are consisting of 10 to 30% of sand particles and with largest particles of 0.5 mm (aluminosilicate glass with crystalline inclusions) and remains of unburnt coal.
- Slag tap granulate is produced in the combustion process of hard coal in power plants with slag tap firing. Mineral impurities are melted and then cooled by water quenching. This produces a glass-like mineral mixture with fissured single grains. By crushing and screening this mixture is improved in quality.
- Residues from quarries and secondary rock of hard coal are tailings from low-grade areas of the deposit. They have an irregular particle size distribution and therefore have to be screened to single particle size fractions. These materials are then relatively high-grade building materials.
- Waste rubber from tires resp. natural rubber (caoutchouc) can be applied for modification of bitumen. The bitumen-rubber-mixture can be used for the surface treatment of split for its improved cohesive properties. Furthermore this mixture is used as joint sealing compound or as tension absorbing interface layer of membranes at gasket seals of bridges and asphalt beton connections. Challenging in screening of waste rubber from tires are the required fine screen cuts and the elastic behaviour of rubber granules.
- Wood recycling means the crushing and screening of contaminant-free waste wood and the following thermal recycling or pressing to wood pellets for generation of energy. Feed materials are railway ties, waste wood, bulky waste after sorting as well as wood from forestry. One of RHEWUM´s machines screens up to 50 t/h wood dust and separates at 1mm to not affect the following conveyance negatively.
RHEWUM optical systems grade waste glass energy-efficiently
Recovered glass is packaging glass including glass bottles which is collected and recycelt. After the waste glass collection the material is processed to secondary raw material which can be added to the glass melt mixture in glass factories. Some glass factories operate own waste glass processing plants.
Using recovered glass plenty of energy and raw materials can be saved. Usually up to 65% of waste glass are used in the glass production process, for green glass it can be up to 95%. In the case of 65% waste glass the energy consumption is reduced by 20%.
The waste glass has to be separated mono-fraction as accurately as possible. First step to reach this is to collect it separately. Due to common impurities of approx. 7% in the collected glass before smelting an optical sorting process in fully automated optical sorting plants is necessary. These plants classify the broken glass by optical criteria (colours). The broken glass normally is produced by means of a crusher and should be as homogenous as possible regarding the particle size. To reduce the dust content which downgrades the efficiency of the sorting process the undersize particles are separated by screening.
Also after sorting single colour fractions may contain a certain amount of wrong colour particles to be melted together with the fresh raw materials. For green glass this can be up to 15%, for brown glass up to 8% but for clear glass maximum up to 0.5%. Glass with higher impurities is traded as olive green glass (mixture of green and brown) or natural white glass (white with colour impurities).
Glass is coloured by means of following materials and substances: ferric oxide, copper oxide, cobalt oxide, nickel oxide, manganese oxide (pyrolusite), selenium oxide, silver, indium oxide, neodymium, praseodymium, europium and at least gold (aqua regia). In the glass melt process problems are caused by ceramics, stone ware and porcelain, they produce imperfections in the glass structure. Furthermore window glass, mirror glass, laboratory glass, monitor glass and other kinds of special glass are not recyclable. The main important glass are quartz glass, float glass, crystalline glass and borosilicate glass.