Ben Eule looks at how glass quality and the recovery process can be improved in MRFs
The processing of commingled recyclables with glass has been practised across the UK for more than a decade, yet it is still surprising to see the variety in quality and quantity of glass from that commingled material.
The first stage in any glass recycling process is that the input material has to be reduced in size and then effectively separated from the more valuable commodities such as paper, card and rigid plastics.
This approach retains the value of the MRF products and, at the same time, reduces the wear and tear on the sorting and conveying equipment. The downside of this process is that it calls for more aggressive screening to separate the glass from the other recyclable commodities.
Paradoxically, this aggressive approach to maximise glass diversion increases the non-glass content in the isolated glass mix, which leads to increased challenges to clean up it up.
Research, carried out as part of my recent doctorate thesis at Aachen University of Technology in Germany confirms that the removal of standard contaminants of recovered MRF glass, such as organics, shredded paper and plastics, can be done with a combination of screening, air density separation and optical sorting.
The study involved collecting data through research and field work at UK MRFs and the results led to the development of a process for the improved processing of commingled recyclate with glass. This integrated treatment is capable of achieving glass purities in excess of 98%. It gives the processor the opportunity to focus on the production of a mixed glass cullet for the remelt market rather than having to downgrade it to glass sand to be used in the aggregate industry.
Given that glass is a fragile commodity and has a number of handling processes before it reaches the MRF, there will always be an element of glass sand produced and, while every effort should be made to keep this to a minimum, there is still a need to reduce its loss of ignition content in order to market it successfully.
The positive aspect of the research results is that any changes to the processing lines to achieve the improved glass recovery and purity rates can be implemented with very little disruption to the ongoing operation. In most cases, the equipment required can be installed as a separate line.
With the ongoing reduction of higher value recyclables, such as paper, in the fully commingled mix all other commodities will increase, by mass, over time and glass will become an even more important commodity which can, if treated properly, provide an increased income stream for processors and local authorities.
Ben Eule is global technical manager with sorting and waste treatment supplier Stadler Engineering. He recently obtained his doctorate from Aachen University for his research ‘Processing of Co-mingled Recyclate Material at UK Material Recycling Facilities (MRF’s)’.