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Evaluation of the possibilities of substituting potent greenhouse gases (HFCs, PFCs and SF₆)

5 Application of SF₆ and its substitution possibilities

Danish consumption

SF₆ (sulphur hexafluoride) is a heavy gas. According to the analysis of the Danish Environmental Protection Agency, 12 tons of SF₆ was used in the Danish industry in 1999. It is corresponding to the levels of previous years. The glass industry (sound insulating windows) is the largest area of application, then comes the industry of distribution of electrical energy and metalworking factories.

In addition to this, there are some very small areas of application. The Danish Technological Institute is informed that the substance is used for production of electronic and optical microchips and as a tracer gas. There are probably also other areas of application, e.g. laboratory use and medical applications.

Global consumption

The global consumption of SF₆ is approx. 7,500 tons per year and it is increasing. The vast majority (approx. 6,000 tons per year) is used as dielectric material in high-voltage installations in connection with the rapid expansion of the electricity supply in new growth areas, i.a. in Asia. In the "old" industrialised countries, this expansion took place some years ago, and the use of SF₆ for electric installations is relatively low due to recycling of the substance.

Magnesium production is the second largest area of application worldwide (approx. 500 tons per year). Other areas of application are degassing of aluminium and cleansing of electronic components.

5.1 Sound insulating windows

SF₆ (sulphur hexafluoride) is a gas at normal temperatures and atmospheric pressures. SF₆ is used in some sound insulating windows, where SF₆ is used in a mixture of i.a. argon to fill the space between the glass panes. The purpose of this is to damp acoustic pressure waves and thus protect against noise from the outside.

7.2 tons of SF₆

According to the analysis of the Danish Environmental Protection Agency, 7.2 tons of SF₆ was used for this purpose in 1999. The use of SF₆ for this purpose is decreasing and was approx. twice as high in the mid-1990s.

A large part of this production is sold in Denmark. There are approx. 10 producers of this type of sound insulating windows in the country.

According to the analysis of the Danish Environmental Protection Agency, there is a direct emission of SF₆ in connection with charge of the panes, and this loss varies between 10 and 20% depending on the equipment and procedures used. Previously this emission was much larger.

The charged SF₆ is first accumulated in the windows, but the substance will escape to the atmosphere, when the panes puncture.

As there are no schemes for collection or recovery arrangements (which would be difficult to establish), it is expected that all SF₆ will end up in the atmosphere. As this type of windows has been produced for many years (15-20 years), it is expected that there is emission constantly from old with SF₆ in connection with puncturing or scrapping. If it is assumed that the average life for these windows are 20 years, we are reaching the stage where the real emission is equal to the raw materials consumption.

SF₆ adds only a little to noise reduction. The other contributions come from the structure of the window, the thickness of windows and lamination with different materials. Besides, the thermal insulating properties of SF₆ are not very good.

Cleaner Technology effort

In accordance with recommendations in the report from 1999, a Cleaner Technology project was initiated in which Delta Akustik og Vibration carries out a more precise analysis of the production of sound insulating windows (which panes and types of windows, number, areas of application with regard to types of traffic noise, expected life, etc.). Laboratory measurements are carried out on a number of windows (with SF₆). Parallel measurements are carried out on the same windows without SF₆. The project should conclude on the significance of SF₆ for the sound insulating.

There are certain indications that SF₆ is being phased-out. Energy marking of windows has been introduced, and one of the criteria for becoming an energy class A window is that SF₆ must not be used in the production. In addition, a tax of 400 DKK per kg of SF₆ in the production has been introduced.

5.2 Gas protection in light-alloy metal foundries

According to the analysis of the Danish Environmental Protection Agency, 0.7 tons of SF₆ was used in 1999 as gas protection for production of light alloy. The consumption has now been stopped.

Magnesium

Casting of magnesium parts takes place at the company Metallic A/S. SF₆ was used in a mixture of other gases (CO₂ and atmospheric air) for protecting liquid magnesium from catching fire, when the metal is cast into machine parts.

Liquid magnesium is very flammable and will catch fire if it get in contact with the oxygen of the air.

Metallic also casts pieces in aluminium, zinc and brass, but SF₆ is only used in connection with magnesium.

Magnesium is a very light and strong metal. Thus, the car industry has started to use magnesium parts in cars to a greater extent.

SO₂

Metallic has built a new production facility for casting of magnesium parts and closed down the old facility. SO₂ is used in closed machines instead. This new technology is developed in co-operation with Norsk Hydro.

Aluminium production

Degassing of aluminium

According to the company DISA, SF₆ is used for degassing of aluminium melter before casting. Previously "chlorine gases" were used for this purpose and it was quite problematic due to the working environment.

SF₆ is introduced into the liquid metal in small bubbles, and gas (i.a. hydrogen) diffuses into the bubbles, which then rise to the surface and are released to the atmosphere.

Worldwide, there are more than 20 Disamatic casting machines for aluminium production. This market is increasing steadily as aluminium is used for machine parts, i.a. in the car industry to a greater extent.

DISA has earlier tested this technique at its test foundry, but does not at the moment use SF₆ for this purpose.

5.3 Insulating gas in electric power switches

According to the analysis of the Danish Environmental Protection Agency, the consumption of new SF₆ for these purposes was approx. 4.8 tons in 1999. The installed amount is approx. 56 tons (T. S. Poulsen, COWI). The substance is in closed containers, which is collected and recycled in connection with maintenance or taking down of the equipment. The emission occurs thus by accident or unforeseen leakages.

There are no Danish producers of this equipment. But large international companies such as ABB, Siemens, Group Schneider, Ahlstrom and Ormazabal sell the equipment. The switches are charged with SF₆, when they are imported to Denmark.

There are approx. 600 transformer stations of the 10-20 kV level in Denmark, and these can be equipped with either SF₆ or vacuum switches.

The price is more or less the same, and there is a keen competition between the producers. It is thus possible to purchase SF₆ free switches for 10-20 kV transformer stations. Spacial problems can be associated with this and it may require a replacement of the entire station.

In addition, there are approx. 60,000 10 kV/400 V distribution substations. The equipment can be based on SF₆ both as switches and isolator, but there are also other SF₆ free solutions. Due to the large number, the reliability, maintenance and small dimensions play a decisive part.

Alternatives are on the other hand not available in the high-voltage area, i.e. from approx. 60 kV and higher.

According to Henrik Weldingh of DEFU (Research Institute for Danish Electric Utilities), a new technology does not appear to be on its way. New semiconductors may however be available on the market in the future, but this requires a technological breakthrough, as there are too large losses in the technology known today.

The other application within the high-voltage area is as insulating gas in compact transmission cables. E.g. high-voltage cables of 400 kV from the generator and out of power plant buildings are carried in pipes of 20 metres filled with SF₆. This prevents flashover to the pipe material and thus also short-circuiting of the high-voltage cables. The alternative is that the cables are placed with larger distance between them, where atmospheric air is the isolator.

As there are no Danish producers of the equipment, it does not seem reasonable to commence a development project in this area. It can be chosen to install a SF₆ free switch in the 10 kV system, if it is desired to use technology, which does not contain potent greenhouse gases.

Recycle

COWI has carried out a project with subsidy from the Danish Environmental Protection Agency with the purpose of describing a method for reducing the emission of SF₆ in this sector (Miljøprojekt no. 592, 2001). In the project, an analysis of the problem has been carried out, and the investigation demonstrates that most electricity companies do not collect SF₆. The project has moreover demonstrated that cleaning equipment is available, which can clean SF₆ to the desired cleaning degree (> 99.9%). Finally, an entire recycling system is described based on collection of return bottles, cleaning and recycling.

It is expected that this system will be commenced by the industry of distribution of electric energy, if possible, with an initial subsidy from the authorities.

5.4 Tracer gas and other laboratory purposes

According to the analysis of the Danish Environmental Protection Agency, there has been an insignificant use in Denmark in 1999 by "Research institutes". Previously approx. 0.5 tons was used for this purpose, but an increased focussing on the environmental impact of the substance has probably resulted in a reduced consumption and the use of alternatives.

Tracer gas

DMU (National Environmental Research Institute) uses a small amount of SF₆ as tracer gas in connection with testing dispersal in the atmosphere. These tests are carried out in order to test mathematical models for dispersal, and this type of tests make up the basis for i.a. standards for chimney heights, etc.

The consumption is very low. The application of SF₆ as tracer gas is due to a number of special properties of the substance, which make it difficult to replace, including that it is precise and traceable in very low concentrations, and it has a very low occurrence in the atmosphere. Tests have been carried out abroad with a PFC substance, but it is also environmental problematic.

DMU assesses that there is no usable alternative, but that the amount used should still be limited and monitored in connection with tests.

There are approx. five Danish laboratories, which carry out ventilation tests. Small amounts of SF₆ are used as tracer gas for indoor tests. The measurements are used for assessing the dispersal of pollution, leakage from heat exchangers and assessment of short-circuiting between airflows, etc.

The Danish Technological Institute has earlier used approx. 2 kg per year for these tests, but has started to use nitrous oxide (N₂O) to a greater extent.

5.5 Microchips

A number of companies have developed microprocessing technologies and optical components, which are the technological basis for production of semiconductor components, biochips and optical fibres. This applies to IONAS A/S, which produces microchips, Grundfos (former ADC), which i.a. produced sensors for pumps and boiler systems and Lucent Technologies Denmark, which produces optical fibres.

The characteristic feature of these processes is that they by means of the industrial greenhouse gases HFC, PFC and/or SF₆ substitute the use of other chemicals, e.g. SiF₄, which is problematic with regard to the working environment.

In the production process of optical fibres, microchips and sensors, no relevant alternatives are available now or in the very near future for substituting the use of greenhouse gases.

Another characteristic feature of the use of these processes for production of e.g. optical fibres for optical cables, etc., microchips and sensors for pumps, etc. is that they contribute to positive environmental benefits.

Generally speaking, it applies to the production of products using these gases that the greenhouse gases are broken down completely or partially during the production process itself.

Microchips

Microchips can increase the communication through fibreoptic cables by a factor 10. Common to Danish companies like IONAS, which produces these chips, are that they use production technologies, which are implemented from the Micro- and Nanotechnology Research Center (MIC) at DTU. It is a technology, which is used worldwide (with small variants).

Small amounts of SF₆, HFC-23, PFCs (especially CF₄, but also a little C₂F₆ and C₂F₆) are used in the process. The consumption in Denmark is assessed at the moment to be a few hundred kg, and it is moreover assessed that the consumption will be in the order of 1 ton per year, when the companies, which are in the melting pot, come into production.

Microchips are produced by IONAS A/S during a process where the chips are corroded with the greenhouse gas, so that the end product does not contain these gases. MIC informs that the majority of the gases are destroyed during the processes. This applies both to SF₆ and other substances in the processes.

Sensors

Grundfos also uses small amounts of SF₆ for producing a type of sensors with the purpose of reducing the energy consumption in pumps. The environmental department of Grundfos has carried out life cycle calculations on how many CO₂ equivalents the energy saving corresponds to by use of sensors compared to the SF₆ consumption used for producing the sensors. The calculations show that the energy saving in the pumps quickly compensates the additional emissions of SF₆.

Fibreoptic cable

Lucent Technologies Denmark produces optic fibres for use in the production of fibreoptic cables.

For production of optic fibres, fluoride compounds have been used worldwide during the past 20 years. After the phase-out of CFC-12, C₂F₆ has been used and lately SF₆. The gases are broken down in the process at temperatures of 2000 degrees Celsius, and fluoride is bound in the glass and becomes to optic fibres.

The reaction products are subsequently cleaned. Due to the extremely high heat development during the process, there is no emission from here. Thus, there is not contributed to the greenhouse effect.

The substitution of SF₆ for production of optic fibres has not yet been found, as the properties of fluoride compound have to be used in the glass. Fluoride compounds from other and more degradable chemicals are not desired for working environmental reasons. The alternative SiF₄ is e.g. toxic. It is moreover in case of errors that a gas emission during production of optic fibres will occur.

Project proposal

5.6 Other applications of SF₆

The Danish Technological Institute does not at the moment have knowledge of other uses of SF₆ in the Danish industry than the above-mentioned.

Reportedly, large amounts of SF₆ (of the size of 100 tons per year) are used in Germany as blowing agent of car tyres, but this application is not known in Denmark.

Nike sports shoe

The Danish Technological Institute is also informed that SF₆ is used in soles of Nike sports shoe. According to a letter from Sarah Severn, Director for Nike Environmental Action Team to Greenpeace Danmark (dated 12 September 1997), approx. 288 tons was used in the year 1 April 1996 to 31 March 1997. The substance is used in Nike's air models, and all soles are produced in the United States.

Nike informs in September 2001 to Greenpeace Danmark that it has started to phase-out the use of SF₆ in its products, and at the end of 2002, no sports shoe or other Nike products will be produced with SF₆. From 1 July 2003, there will no longer be sent products containing SF₆ on the market. Nike expects that the consumption in 2001 will be reduced by 80% compared to the consumption in 1997.