What is Float Glass?

Float glass is a specialized type of glass with an extremely smooth and uniform structure, with superb optical properties. For this reason, it is used in a wide variety of different applications including windows, solar panels, LCD displays, and automotive windscreens.

Float gas is produced via the float glass process, which involves floating the molten glass on a bed of molten metal and then allowing the glass to set. The method means large panes can be produced easily, and thickness can also be controlled. The float glass process has significantly reduced the cost of producing glass that is flat and smooth.

The Float Glass Process

Modern glass is produced from several different materials including sand, dolomite, limestone, carbonate, sodium sulfate and also scrap glass. All of these materials are heated to extreme temperatures (2,800 °F) to form molten glass. This glassy liquid is then poured onto a ‘tin bath’ consisting of molten tin, which acts as a level template for the glass to distribute over and then harden.

As the glass hardens the tin template ensures the glass has flat top and bottom surfaces. Once it has cooled and completely solidified the monolithic sheet of glass can be cut into smaller sections.

The molten tin is prone to oxidizing – this is prevented by keeping the tin bath in an atmosphere of 90% hydrogen and 10% nitrogen.

The Importance of Nitrogen and Hydrogen in Float Gas Manufacturing

The oxidation of tin introduces flaws in the tin’s structure, which in turn will create flaws in the surface of the glass itself. To stop oxidation from happening the tin bath chamber is filled with an atmosphere of 90% nitrogen and 10% hydrogen. The hydrogen that is pumped into the system will react with any oxygen present, which stops oxygen from being able to oxidize the tin.

To ensure that the oxidation of the tin does not occur a huge volume of gas is required with some plants using as much as 85 NM3 per hour of hydrogen and 765 NM3 per hour of Nitrogen. As float glass manufacturers tend to operate around the clock, every day of the year, this is a huge amount of nitrogen and hydrogen.

Sourcing the Gas

Liquid Gas

Conventionally, industries that require high gas volumes for production purposes have used liquid (i.e. compressed) forms of nitrogen and hydrogen, which are supplied in cylinders. However, this is not without its problems.

Liquid hydrogen is produced via steam methane reforming (SMR), which uses fossil fuels and creates carbon dioxide emissions. In addition, liquid hydrogen is very explosive which means it must be handled and stored very carefully.

Liquid nitrogen is produced using pressure swing absorption generators, following which it is cooled and compressed into containers. Liquid nitrogen is a dangerous gas to store. If it escapes into an enclosed space, there is a high risk of asphyxiation or if pressure builds up there is a high risk of explosion.

On-Site Gas Generation

Storage of liquid hydrogen and nitrogen is not always essential – the gases can be generated as and when required using an on-site gas generator. This removes the need for on-site storage, improves safety, simplifies logistics and means operations are not influenced by market values of nitrogen and hydrogen.

Electrolyzers

In the early 1900’s, large-scale electrolyzer plants were driven using cheap hydroelectric power. As renewable energy has become increasingly prevalent, under increasing environmental pressure, the use of industrial electrolyzers is becoming popular again.

Industrial electrolyzers are a cleaner method of producing hydrogen than SMR – electrolysis produces no greenhouse gases in the production of hydrogen (providing a renewable energy source is used), whereas SMR produces between 10 -17 T of carbon dioxide per 1 T of hydrogen.

Nel Hydrogen is an industry leader in the supply of industrial-scale electrolyzers. Their Proton OnSite M Series of electrolyzers are capable of economically generating between 100 NM3 to 400 NM3 of hydrogen per hour. In addition, Nel Hydrogen can also provide turnkey PEM or Alkaline containerized solutions, which can generate 50-300 NM3 per hour and alkaline electrolyzer solutions which can generate 50 NM3 per hour, as well as multi-electrolyzer systems.

This information has been sourced, reviewed and adapted from materials provided by Proton OnSite.

For more information on this source, please visit Proton OnSite.

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