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Regenerative thermal oxidizers based on the pebble-heater technology

Regenerative thermal oxidizers are used for cleaning the exhaust gas of different industrial furnaces. They are more and more demanded as the environmental regulations become more strict. On the other hand, there is a steady effort to develop systems with lower investment and especially operational costs.

The new Pebble-Heater technology with annular beds and radial fluid flows has been used as a basis for developing a system of a regenerative thermal oxidizer which can meet the market requirements. Theoretical studies and numerical simulations have shown that an extremely effective heat transfer at Péclet numbers around Pe=30 in granular beds of natural materials/minerals (like quartz-gravels, volcanic stones or fire-clay) is possible. Temperature gradients of more than 20 K/cm have been realized, so that the required bed thickness may be as low as 35 cm. That also results in a lower pressure drop. Those studies have shown that under optimized conditions the natural materials/minerals are much more effective than artificial forms (ceramic rings, saddles, honeycombs...) developed especially for heat regenerators. The price ratio between the two is more than 1:100. The realized facilities have justified the expectations. A heat recovery degree of more than 98% has been achieved, with a total pressure drop of about 18 mbar. The next best system on the market has at least a 100% higher energy (gas/oil) consumption and a 50% higher fan power consumption. Some other characteristics of the new system have also shown important improvements for the process. The bigger volume of the hot chamber (reaction zone at 800°C) results in a longer residence time (1,5 - 1,7 seconds), so that the destruction of different pollutants (aldehyds, benzols, phenols...) and carbon-monoxide is more effective. The measured emission values are far beyond the limits set by the regulation authorities. The realized facilities have capacities in the range of 15.000 - 45.000 m3 STP/h. The next development stages are a scale-down (1.000 - 5.000 m3 STP/h) and a scale-up (over 100.000 m3 STP/h) of the existing technology. It is intended to substitute some very expensive catalytic facilities with the new system. With the extremely high heat recovery degree, the reaction zones at 800°C - 1000°C do not cause high operational costs any more. Lowering the reaction temperature (the main advantage of the catalytic facilities) is no longer a decisive parameter for the facility design.

Veröffentlicht in: Umweltpraxis No. 5/2001, GWV Fachverlage GmbH, Wiesbaden 2001

Copyright:	© OTH Amberg-Weiden
Quelle:	Veröffentlichungen 2003 und ältere (August 2005)
Seiten:	10
Preis:	€ 5,00
Autor:	Dr. Dragan Stevanovic
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