Topic of the month April

Benefits of Recycling to the Glass Manufacturer
(special focus on UK)

All glass manufacturers recycle their own internally generated scrap within the glass melting process and theoretically it would be possible for all glass makers to augment their own internal recycling with post-consumer recycled glass. However, using external cullet can result in lower quality and poorer yields for both container and flat glass manufacture. Balanced against the possible reduction in quality, the use of external cullet offers the glass maker other important benefits:

Raw Material Cost Reduction

The three principal raw materials used in glass manufacturing are:

• Sand – this is the major constituent of glass and it will typically have a minimum silica content of 99.6%.
• Soda ash – this is used to provide the sodium oxide in the glass, which acts as a strong fluxing agent.
• Limestone – this is used to provide the calcium oxide in the glass, although calcite and dolomite are sometimes used.

These principal ‘batch' materials are backed up by a wide range of minor constituents such as melting aids, refining aids, colorants and other materials that provide the glass with special properties. Depending upon the exact composition of the glass the total raw material cost will be in the region of £40-45/tonne.

Although cullet can be purchased at a lower cost there are collection, transport and processing costs to be taken into account. Some of these costs and the investment costs required for processing plant can be covered by the revenue from the sale of PRNs. With current PRN values of £15/tonne, the income is reported to be insufficient to cover the collection and processing costs and the net effect is that recycled glass can be more expensive compared to virgin raw materials.

Energy Savings

The theoretical energy requirement to produce soda lime glass from virgin raw materials is approximately 2.7 GJ/tonne. The energy requirements to simply melt glass are somewhat lower at 1.9 GJ/tonne. Therefore, using recycled glass as a raw material represents significant energy savings and in practice for every 10% increase in cullet into the melting furnace energy consumption will fall by approximately 2.5%.
Glass manufacture is a high-temperature energy-intensive process and depending upon the size and efficiency of the furnace the typical energy requirements range from around 4 GJ/tonne to 9 GJ/tonne.

The UK average energy requirement for container glass melting is 4.97 GJ/tonne11 with an average recycled content of the feedstock at 30%. At current energy prices this is equivalent to approximately £14/tonne. Extrapolating backwards and assuming no recycled glass in the feedstock gives a melting cost of £15.20/tonne. Therefore, it is estimated that overall the glass container sector saves some £2 million/year from the use of recycled glass.

In April 2001 the UK glass manufacturers became liable for ‘Climate Change Levy' (CCL) which is an energy tax equivalent to about a 15% increase in energy costs. However, the UK glass industry has obtained an 80% rebate on the CCL providing it can achieve year on year energy savings: between 2000 and 2010, it must reduce its energy consumption by approximately 10% and every two years it has to meet specified interim targets.

The CCL has a huge financial implication for the glass industry and if levied at its full rate would cost the glass container manufacturers an additional £9m/year. However with the rebate this cost is reduced to £1.8 million/year. Over the past 20 years the glass industry has made some dramatic increases in energy efficiency and further significant improvements will be difficult to achieve with current manufacturing technology. Therefore, the CCL targets are a challenge to the industry and an increase in the use of recycled glass has an important role to play in meeting the targets.

Environmental Benefits

There are reductions in carbon dioxide (CO2) emissions associated with the energy savings resulting from increased cullet use. There are also additional CO2 reductions through avoiding the use of soda ash, limestone and dolomite, all of which are carbonates and release CO2 during the glass-making process. For every tonne of glass produced from virgin raw materials approximately 200 kg of CO2 is released from the breakdown of carbonate raw materials. Increased cullet use will also reduce particulate and nitrogen oxide emissions from the glass furnace. With the introduction of the Integrated Pollution Prevention and Control (IPPC) Directive in 2004, glass companies will be required to reduce these emissions.

Furnace Life

Glass furnaces operate continuously for up to 10 years before the whole furnace will need to undergo a rebuild at a cost of £5-10 million. The life of the furnace is determined by the total glass throughput and the operating temperature. A furnace that is continuously operated at high ‘pull' rates will have a shorter life. Increasing the cullet content of the raw materials allows the furnace to be operated at slightly lower temperatures thus prolonging its life and enabling the rebuild to be deferred.

Disadvantages of Recycled Glass

There are some possible negative effects of recycling glass, all of which are related to impurities that may be introduced into the glass furnace. Small pieces of ceramic material derived from pottery or other contaminants may not melt in the furnace giving rise to ‘stone' defects in the finished product. Metals can react in the furnace, giving rise to gas bubbles in the glass melt, again ending up in the finished product and causing rejects. Even more problematic are ‘glass ceramic' materials and heat resistant borosilicate glasses (e.g. ‘Pyrex') which are difficult to detect in the raw cullet and cause defects in finished products and can block the liquid glass flow in the glass moulding machinery. Most processors are equipped with magnetic and eddy current separation for the removal of ferrous and non-ferrous metals. Investments have taken place in equipment for colour enhancement (to further improve the quality of a colour sorted stream) and colour separation (to sort a mixed coloured glass stream). Berryman has recently installed a pyro-ceramic detection system that can remove ‘Pyrex' type materials. All these systems are relatively high capital cost and are only financially viable on high throughput plants.

Future Prospects

In theory furnaces can operate using 100% cullet, and this level is claimed by some international operators of green glass furnaces such as Vetropack in Switzerland. However, 90% is probably a more reasonable figure if quality is to be maintained. In theory the same applies to flint and amber furnaces; however these colours are more sensitive to colour contamination. This applies especially to flint furnaces manufacturing ‘premium' high quality glass e.g. for spirit bottles where the maximum cullet levels are restricted to 50-60%. To achieve a consistent amber colour is also difficult and this restricts the maximum cullet levels to around 60-70%.

The UK container manufacturers have recently undertaken an exercise to determine the maximum quantities of recycled glass they could consume. With the current processing capacity and capability they estimate they could consume approximately 1.1 million tonnes/year of recycled glass. With UK green glass furnaces already operating at 73% cullet levels there is little scope for significantly increased green glass recycling. The increase will be mainly brought about through increased amber and flint glass recycling. This increase from 555,4000 tonnes (excluding flat glass) to 1.1 million tonnes would raise the average recycled glass content of containers from 28% to 66%. With investment in additional reprocessing capacity, principally aimed at improving the quality of amber and flint cullet, these recycling rates could be further increased and 1.3 million tonnes could probably be achieved.

Source: This text was generated by OGIS GmbH http://www.glassglobal.com with reference to material from British Website: http://www.wrap.org.uk