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Carbon Trust & GTS Study Proves the Benefits of Using Recycled Glass

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Tuesday 19 October 2004

Over a 12 month period (June 2002 to May 2003) energy consumption by the glass container industry was monitored, which resulted in findings collated by Glass Technology Services (GTS) Limited that the industry had consumed some 4.64 TWh (4.64 x 109  KWh) of delivered energy. Over 70% of this energy was used by the furnaces to melt glass. Fuel-related CO2 emissions from these furnaces amount to approximately 650,000 tonnes per year.

Glass manufacture is a high-temperature energy-intensive process. When using raw materials, glass is manufactured from sand, limestone and soda ash, all of which are abundant natural minerals. However, both limestone and soda ash are carbonates which liberate additional C02 during the melting process. For each tonne of glass produced from virgin raw materials this decomposition produces approximately 185 kg of CO2.

Industrial manufacturers employ large furnaces which operate on a continuous basis and are typically fossil fuel fired. The UK container sector currently operates 32 furnaces each melting an average of 207 tonnes per day of glass and consuming 304 MWh of energy.

One of the virtues of glass is that it can be endlessly remelted and recycled without any loss in quality. The glass industry has long since realised the benefits of using recycled glass (cullet) in its processes. If more recycled glass can be reprocessed into new bottles then fewer raw materials need be quarried. Each tonne of glass returned to the melting furnaces reduces our demand on raw materials by 1.2 tonnes. Using recycled glass to produce new items reduces CO2 emissions in two ways:

* it is easier to melt than the individual raw materials so uses less fuel; and
* it contains no carbonates so it does not release any CO2 during the melting process.

Increasing glass recycling therefore has the potential to deliver significant reductions in CO2 emissions. To maximise this energy-saving potential, furnace operating systems need to have the inbuilt sophistication to enable them to reduce the fuel consumption when melting loads containing higher levels of recycled glass. Glass Technology Services together with a group of leading glass container manufacturers and The Carbon Trust have undertaken a project to produce a model that can be used as a forecasting tool able to calculate current (optimum) furnace efficiency at any combination of production level and cullet ratio.

The first stage in the project was to develop a control strategy providing a fundamental understanding of the process and quantify the potential savings. Armed with this knowledge the second stage involved the development of algorithms or, put more simply, mathematical statements which would then allow process engineers to develop control routines to optimise furnace operation, ensuring that the furnace is always run in the most fuel efficient manner. As a result a model has been developed with funding and support from The Carbon Trust, a group of leading glass container manufacturers and the expertise of Glass Technology Services.

The study concluded that an improved furnace control regime, which is able to compensate for changes to cullet levels and moisture content, could produce an energy-saving of 2.1% of furnace energy consumption. Such a saving equates to a reduction in CO2 emissions of 13,650 tonnes per year.

Notes to Editors:

1. Glass Technology Services Ltd

Glass Technology Services, is a subsidiary of British Glass which operates independently and offers technical services and consultancy serving customers who manufacture, work with, or use glass.

The British Glass Manufacturers' Confederation represents the interests of all sectors of the glass industry in the UK. Its main activity is in representing the industry at European, national and local level on a wide range of topical legislative issues. It also conducts independent research into all aspects of glass production and technology.

2. Glass Melting Furnaces

A large-scale glass melting furnace is basically a refractory box-like structure, which operates at temperatures up to 1,600°C.  The furnace operates continuously providing glass 24 hours a day 7 days a week and all activities within the factory are entirely dependent upon its output. A furnace is designed to operate a "campaign" lasting typically 10 years before it is demolished and rebuilt. The cost of a furnace rebuild is obviously related to its size but a typical 300 tonne per day container furnace would cost around £6 million.

3. Glass Melting

The high temperatures required to melt the glass requires a lot of fuel and consequently the furnace is the main energy centre in any glass plant, accounting for around 70% of the total plant demand. Most furnaces are fired with natural gas but can also be fired on oil as a standby fuel. An efficient large furnace will require 1100 kWh of energy for each tonne of glass melted. Thus a furnace melting 300 tonnes per day consumes around 32,000 cubic meters of natural gas each day which will release some 62 tonnes per day of CO2.

4. CO2 emissions

Glass made entirely from virgin raw materials releases approximately 185kg of CO2 per tonne of glass produced whilst glass produced from cullet produces no (process) CO2.

5. The Mathematics

In simple mathematical terms the energy consumption of a furnace would be described by the following equation:

Furnace Energy   =   Holding Heat   +   Load x Constant

A plot of furnace energy vs glass melted should produce a straight line from which the fixed and variable elements of the energy/load relationship could be derived.

In practice the energy consumption of a furnace is influenced by several sometimes interdependent factors. The scatter of data points is an indication of the influence of these factors on furnace energy consumption. The more important factors include:

Furnace design -  a well insulated and designed furnace will have  inherently lower  energy consumption
Cullet levels  -  higher cullet levels require less energy.
Electrical input   -  in addition to the fossil fuels, many furnaces use a
small amount of electrical heating energy to melt the glass. This electrical energy is utilised more efficiently by the furnace than that from the fossil fuels.
Furnace Age  -  furnaces become less efficient with time.

Further information can be obtained from:

Andy Hartley
Glass Technology Services
9 Churchill Way
Chapeltown, Sheffield
S35 2PY
Tel: 0114 290 1801
Fax: 0114 290 1851
E-mail:  a.hartley@glass-ts.com
Web:  www.glass-ts.com

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