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Gas system reduces nitrous oxide emissions

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FURNACE heating specialist Kanthal has launched Ecothal, a new gas treatment system with the potential for reducing nitrous oxide (NOx) emissions from gas fired radiant tube heaters by more than 75 per cent.

Ecothal comprises a catalyst package located in the burner to reduce nitrous oxide emissions and another oxidation catalyst to reduce carbon monoxide (CO) and unburned hydrocarbons.

The first catalyst is positioned in the furnace wall region of the recuperator and is set to provide reducing conditions. NOx formed in combustion is reduced by this first catalyst.

In order to ensure that no CO leaves the system, the second catalyst is positioned after the burner, in the exhaust pipe. By adding a small quantity of 'secondary air' just before the flue gases, any CO is burned.

Following extensive testing both in the laboratory and on an industrial scale, results show that a nitrous oxide level of less than 50ppm is achieved as standard compared to about 200ppm with conventional systems.

Kanthal's NOx reducing technology has been tested on a number of commercially available radiant tube burners of both traditional design and the newer low NOx burners.

At the same time as reduced emissions, there is an increase in thermal efficiency. Combustion takes place with a lower air/gas mixture than is normal.

By using special mixture tubes, there is an increase in thermal efficiency to around 75-80 per cent compared to 60-70 per cent or worse for conventional systems.

Ecothal is made with Kanthal APM tubes - a FeCrAl material with outstanding properties of corrosion resistance at high temperature.

Rather than producing complete burners, Kanthal is using existing commercially available burners and modifying them with the new technology.

Ecothal has the same basic design as single ended recuperative tube systems. The tubes are standard size and the air and gas supply does not require special reconstruction. Upgrading to the new Kanthal system is therefore straightforward.

An additional benefit of using APM tubes is the ability to run each heating position at 30-40 per cent higher power compared with conventional nickel chromium tubes.

Ongoing testing has shown that the Ecothal is reliable, has good reproducibility and that no major degradation can be found after more than 12,000 hours operation.

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