Ardagh Group recently won a Sustainability Award for its method of producing remeltable briquettes. Brendan O’Meara* describes the process.

Once collected for recycling, glass contains certain contaminants which must be removed by processing at a glass recycling plant to ensure the maximum amount of glass collected is suitable for remelt.

These contaminants include:
Organics (paper, plastics, caps, rings, and labels);
Inorganics (ceramics, Stones, Porcelains or CSP);
Metals (ferrous and non-ferrous); and
Heat-resistant and lead glass.

During this processing, and as a result of breakages incurred in collection, around 10% of the recovered glass (cullet) will be broken into small particles, typically <4mm, also referred to as ‘fines’.

The fraction size of this material is too small to be sorted by current sorting equipment technology.

The fines cannot be remelted in the furnace as they contain high levels of loose organics and fine particle CSP which can cause defects in the containers, such as blistering and particle inclusions.

They also cause foaming in the furnaces which forms an insulation on the surface of the molten glass and requires additional energy to penetrate and continue the melting process.

For these reasons, in the UK market, around 10% of recovered cullet is diverted into aggregate or ends up in landfill: a cradle to grave scenario, as it can never be recovered.

Ardagh Group has embarked on a project to achieve full recyclability of collected glass containers, by developing a method to produce remeltable briquettes from the fines, which can be safely used in the furnace to make new glass bottles and jars.

Ardagh’s research and development has culminated in the design of a processing plant to close the recycling loop and use 100% of recycled glass containers recovered through the various collection systems across the UK.

The plant will be the first commercial type in the world.

For more than 12 years Ardagh has been at the forefront of initiatives to increase the percentage of cullet used in glass batch recipes for container glass.

Ardagh considers cullet to be the most important but also most volatile raw material.

Cullet has long been a component of the batch recipe for producing container glass, but the quality of the cullet is critical for container production.

To address all aspects of cullet, Ardagh took a decision to initiate a Cullet Team, responsible for all aspects of the procurement process for cullet with a focus on:

Improvement of the quality of the delivered cullet;

Defining specifications for allowed contaminant values to increase cullet use;

Engagement with cullet suppliers and equipment manufacturers in a partnership approach to improve the cullet quality.

The Cullet Team is given executive support by Ardagh’s Chief Sustainability Officer, emphasising the importance placed on sustainability and the Circular Economy.

Their endeavours have greatly improved the quality of the processed cullet procured through positive engagement with suppliers and cullet processing equipment manufacturers.

Recovery of the lost 10% represented the next challenge.

Fines Recovery Research and Development
The project to transform the fines into a briquette is driven by the known benefits of using cullet:

Reduced energy consumption. For every 10% of cullet used, energy costs are reduced by 2-3%.

For every 6 tonnes of cullet used, carbon dioxide is reduced by 1 tonne. A 10% increase in cullet reduces particulates by 8%, nitrogen oxide by 4%, and sulphur oxides by 10%1.

Reduced environmental impact of raw material quarrying.

Over a tonne of natural resources are conserved for every tonne of glass recycled, including 1,300 pounds of sand, 410 pounds of soda ash, 380 pounds of limestone, and 160 pounds of feldspar1.

In addition to these incremental increases, there are additional benefits:

For a plant processing 100,000 tonnes per annum of collected glass, 10,000 tonnes will be diverted away from landfill. Glass recycler, URM, forecasts its plants diverting 50,000 tonnes per annum away from aggregate and landfill into briquetting.

Reduced CO2 emissions and fuel consumption from transporting waste.

The additional cullet volumes available as briquettes will help to achieve the objective of 95% cullet and 5% raw materials within the glass batch.

During the initial concept and Research & Development phase, Ardagh engaged with CelSian Glass & Solar, located in The Netherlands, which carried out 18 laboratory experiments to determine the ideal Briquette recipe.

Wrights Engineering joined the project during the Plant Design and Product Improvement phase, working with Sheffield Hallam University to optimise the recipe, with the goal of reducing the percentage of binding agent required, as this constituted the most expensive part of the recipe and was essential to make the project viable.

Ardagh supported a successful application by Wrights and Sheffield Hallam University for grant support for their research and development.

This grant allowed Wrights to produce a rudimentary production line for a scaled trial of briquettes into an Ardagh furnace.

The line was able to produce 150 tonnes of briquettes which were successfully melted in a controlled trial in Ardagh’s Knottingley glass facility.

The success of the trial encouraged the project team to move to the final stage. The goal was to achieve a more robust briquette with the physical properties to be transported, handled and stored without deterioration.

The resulting briquettes were then subjected to various tests: immersion in water, compression testing, drop testing and High Temperature Melting Observation Studies (HTMOS) and performed excellently.

Following on from the success of the initial trial, Professor Paul A. Bingham of Sheffield Hallam University has published an article2 on the positive effects of using briquettes in the batch recipe.

Ardagh Group’s briquettes created from glass fines
Commercialisation of the briquetting process is the final step, and after extensive assessment of equipment, Wrights has designed a detailed plant to produce commercially viable briquettes.

Ardagh’s Cullet Process Engineer, Brendan O’Meara, said: “The ability to use 100% of recycled glass to make new glass containers is a significant achievement which will reduce the need for raw materials, reduce energy consumption and CO2 emissions, and improve the environmental impact of glass packaging.

“We are incredibly proud that this initiative has been recognised with a Sustainability Award and is a finalist in several other glass and recycling industry awards.”

2 Article in International Journal of Applied Glass Science 10(1) August 2018 This article is protected by copyright. All rights reserved.

* Cullet Process Engineer Glass-Europe, Ardagh Group