Ecological effect of the glass waste recycling
Recycling of the waste flat and bottle glass significantly contributes to reduction of quantity of waste dumped on landfill, which is an important factor of prolonging the life of such a landfill.
The most effective way of recycling the glass waste, both flat and bottle waste, is melting cleaned glass waste once again in glass-furnace and using it once again for the production of glassware. Additional benefits from using the cullet as a raw material in the process of melting glass are:
- reduction of CO2 emission as a result of decreasing the use of fuel and carbonate materials: silica flour, soda, dolomite, which undergo decomposition with emission od carbon dioxide,
- reduction of SOx emission eg. Green glass can be melted without clarifying components (calcium sulfate, sodum sulfate),
- reduction of chlorine and fluorine emission,
- oreduction of dust emission, owing to decreasing the quantity of primary materials, which contain up to 25% of dusty parts of grain size below 0.10mm
- reduction of NOx emission through decreasing combustion in glass-furnaces
Generally it is estimated that 1kg of cullet equals 1.2 kg of primary materials, decreasing at the same time the cost of batch and giving a great environmental effect. According to data published by German Association of Glass Producers, cullet additives in glass production have influence on decreasing batch supply by:
- 0.72 tone of high silica sand, which main component is SiO2,
- 0.25 tone of soda ash (sodum carbonate Na2CO3),
- 0.18 tone of silica flour containing calcium carbonate CaCO3.
Hence using appropriately cleaned cullet let reduce significantly usage of natural materials, therefore decreasing environmental interference. Glass production containing cullet is much less energy-consuming, than glass production of primary materials, as every 10% of cullet reduces energy demand by 2.3%-2.8% You can save up to 25% of energy in glass production with cullet additives. Just 1% of cullet additive in glass batch causes reduction in energy consumption by approx. 8kJ/kg of glass. Energy consumption reduction results mainly from lowering the temperature of melting the batch containing the cullet. The temperature is respectively 1000C , in comparison to 1200-1300C when no cullet is used. The more cullet is used , the lower the temperature of batch, as the cullet turns faster into liquid phase, which facilitates and accelerates the course of reaction proceeding in glass malting process.
Lowering the temperature also has an impact on reducing the quantity of out-gassed substances, which are formed from primary materials. The presence of cullet in the batch reduces the corrosion of of the glass-furnace lining , which prolongs the period of tank furnace operating and reduces the draftage of the batch. The latter causes decreased emission of dust and steam of batch components, which escape together with waste gas. The cullet contains less chlorides and fluorides than primary materials, thus the emission of those is significantly reduced.
It is worth highlighting the fact that the emission of carbon dioxide is also significantly reduced. Not only is it because of decreasing the usage of materials releasing carbon dioxide during melting process, but also because of decreasing energy consumption (up to 25% depending on the quantity of cullet) used for heating the batch. It is known that reduction of CO2 emission is quite difficult to achieve, as it depends on fuel consumption and the kind of batch. That is why reducing energy consumption and at the same time maintaining effective production is the challenge. Owing to the waste glass usage in the glass melting process, the volume of the batch used for glassware production is much lowered as well as the temperature of melting the batch. The result is that the reduction of CO2 emission is estimated at the level of 220kg for the tone of recycled glass.
Nowadays, when all over the world there is a great attention paid to the CO2 emission reduction, such a possibility of lowering its emission to the atmosphere can be realized through enlarging the usage of cullet in glass batch. Nevertheless, realization of this task should be preceded by precise preparation of not only the quantity but also the quality of cullet. That is why collecting, cleaning, separation and fractionation of glass are very important stages of glass recycling.
Another very important aspect of is the realization of waste containers recycling duty according to environmental policy of the European Union. Taking into account the requirements of EU concerning the level of recycled waste containers, there is need to achieve the level of recycled waste containers at 600 thousand Mg annually.. It means additional investment in new glass waste recycling lines.
| Year | 2007 | 2008 | 2009 | 2010 | 2011 | 2012 | 2013 | 2014 |
|---|---|---|---|---|---|---|---|---|
| % | 40,0 | 39,0 | 41,0 | 43,0 | 46,0 | 49,0 | 55,0 | 60,0 |
Table 1. The level of glass containers waste to be recycled in 2007-2014
Attention: The above table is made according to the Decree of Minister of Environment, 14 June 2007, concerning annual levels of recovery and recycling of containers and after use waste (Dz.U. 2007 item 752)
It is worth paying attention to the level of cullet used in other European countries, reaching in some of German glassworks up to 80%, and in Switzerland up to 100% of batch.