Burner Innovation for Glass Melting

View of a glass melting tank
Picture: Glaverbel

The use of flameless burners in glass melting can make energy savings and considerably reduce nitrogen oxide emissions. This was proven in a current practice project researching burners that was conducted by the Gaswärme-Institut (Gas-Fired Thermal Energy Institute) in Essen.

In glass production very high temperatures of more than 1,500° Celsius are required in the melter to melt the glass batch. Maintaining this temperature level over a long period of time entails considerable energy consumption and furthermore the high temperatures cause increased formation of nitrogen oxide. In view of rising oil and gas prices and the strict laws on emissions there is an onus on the glass industry to further increase the efficiency of its high-tech melting tanks/furnaces.

Successful Project

In order to find solutions to reduce energy consumption and nitrogen oxide emissions the Gaswärme-Institut in Essen joined forces with partners in the industry to test flameless burners (FLOXÒ burners) in a project especially focused on the needs of glass production, which was sponsored by the German Federal Ministry for Economics. The results of this project concluded in April 2008 are promising. By using the burner technology already deployed in the metal industry the Essen researchers were able to prove that energy consumption in glass melters could be reduced and nitrogen oxide emissions could by cut by almost half.

Innovative Burner Technology

Working on the flameless oxidation principle, gas FLOXÒ burners use exhaust gas heat to pre-heat the combustion air, which makes them very efficient. Unlike conventional burners they achieve an even spread of temperature in the combustion chamber. This causes the nitrogen oxide emissions to drop while a higher average combustion chamber temperature can be maintained. With flameless burners combustion gas and combustion air flow unmixed at a high flow rate into the combustion chamber.

The main difference compared to burners previously used is the strong internal recirculation of exhaust gases in the combustion chamber and the mixing of these gases with the combustion air. This and the delayed mixing of air and combustion gas “burns” the mix of gases throughout the entire volume of the combustion chamber at at least 800° Celsius without a visible flame front forming. By contrast to this with the melt technology hitherto deployed the combustion of oil or gas in the melting chamber caused strong bright flames whose energy penetrates deep into the molten glass. Peak temperatures, particularly at flame tips, cause increased formation of nitrogen oxide here.

Positive Practical Test

In the practical test operation with a glass melter completely refitted with the flameless burners proved largely problem free. Compared with conventional firing, nitrogen oxide emissions were virtually halved and energy consumption dropped slightly. Air preheat temperature rose by nearly 80°C. For cost reasons in the practice test the flameless burners were installed in the melting tank at the points where the old burners had been. Despite slight twisting it was not possible to achieve perfect coverage of the glass bath.

Neverthless, researchers at the Gaswärme-Institut are convinced that with future glass tank constructions a comb-like arrangement of burners will improve the coverage of the glass bath and achieve an even more homogenous temperature flow. This would increase efficiency even more and further reduce energy consumption. Another advantage is the lower carriage of dust by the exhaust gases. The less frequent need for cleaning of the heat exchange surfaces resulting from this also contributes to cost reduction.
The burners have already been in operation for over a year now with no signs of excessive wear. Fears that the lack of flame might have a negative impact on production proved unfounded.

Burners Available on the Market

Glass producers using flameless burners can, in the eyes of the researchers, now face stricter emission levels with composure. The use of this technology is not just restricted to unit-melters. The flameless burners are also suited to oxy-fuel melters where natural gas is replaced with pure oxygen. Burner manufacturer Hotwork International GmbH is now offering the products on the market. Operators and manufacturers of glass melters interested in innovative burner technology can access the research results of the Essen Gaswärme-Institut.


Flameless burner in flame operation and with flameless oxidation
Picture: BINE Information Service


Transverse section of the flow pattern in the tank with conventional burners (left) and with flameless burners (right)
Picture: Gaswärme-Institut e.V

Detailed information on the project can also be found at BINE, an information service by FIZ Karlsruhe promoted by the German Federal Ministry of Economics and Technology. In its projektinfo 05/08 the BINE information service takes a look at the technology and sums up the stages of the project and its research results over just a few pages in a file entitled “Glas herstellen – energieeffizient und schadstoffarm” (Glass Production – Energy-Efficient and Low-Polluting). The information file can be downloaded free of charge from the Internet at www.bine.info /„Industrie und Gewerbe“ / „Prozesswärme“ / as a PDF file.

Comprehensive Information at glasstec 2008

From 21 to 25 October 2008 the international glass sector will be presenting its latest innovations at the most important glass trade fair in the world. In focus here will be the latest glass production and finishing technologies.