DE19724813A1 - Catalytic burner with mixture space and catalyst on grid - Google Patents

Abstract

The catalyst bed (5) is covered by a finely perforated radiation burner (6) in the form of a metal grid. The catalyst bed is made up of cylinders, hemispheres or planar polyhedra, all with catalytically coated surfaces. Additional components of the specified burner (1) include a mixing space (2) and perforated sheet (4) carrying the catalyst bed. In service, most of the gas mixture is catalytically converted to produce gases which pass through the burner along with the hitherto unconverted mixture only to burn with small flame on the surface of the catalyst bed. On light-up, the catalyst bed is radiantly heated to progressively bring the catalyst into effect.

Description

The invention relates to a catalytic burner according to the preamble of the An saying 1.

In known burners of this type, the mixture space is usually catalytically be layered perforated plate, for example an expanded material, or a wire mesh covered.

With such burners, stable operation has the advantage of only a small one Nitrogen oxide and carbon monoxide emissions. However, such burners result different problems. So when starting such a burner, it is necessary provide appropriate preheating to the catalyst to its operating temperature bring to. Furthermore, during the operation of the burner for a corresponding Heat dissipation can be taken care of on the one hand overheating of the catalyst, which leads to the could lead to destruction, and on the other hand, the temperature of the Prevent catalyst below the reaction temperature. It can also change over time a decrease in the reactivity of the catalyst occurs, causing it to increase Emission of unburned hydrocarbons can occur.

The aim of the invention is to avoid these disadvantages and a burner at the beginning mentioned type to propose, even during the start-up of a burner result in only low start-up emissions and it is ensured that there are none significant emissions of unburned hydrocarbons can come.  

According to the invention this is in a burner of the type mentioned by the kenn drawing features of claim 1 achieved.

The proposed measures achieve a combination of a catalytic burner with a radiant surface burner. In stationary operation, part of the fuel-air mixture is converted catalytically and the rest is burned using the radiant burner. With this mode of operation and sufficient surface loading of the radiant burner of approx. 10 W / cm, no unburned hydrocarbons are formed and the emission of NO _x and CO is largely reduced due to the catalytic conversion.

Should the catalyst lose its activity over time, the entire fuel gas-air mixture is nevertheless completely converted in a burner according to the invention, only the conversion takes place in an increasing amount by combustion in flames above the radiant burner, which, however, does leads to an increase in NO _x emissions.

During the start of a burner according to the invention, a separate heating of the Catalyst not required, because the Benngas-air mixture during the start phase Flows through the bed and is burned via the radiant burner. Through the first radiant heat heats up the bed, and an ever larger part of the Bed reaches the reaction temperature, so that the fuel gas-air mixture more and is implemented more catalytically.

To avoid overheating of the catalyst, the height of the bed may be a Do not exceed the correct level to the heat generated in the bed in one to be able to decouple sufficient extent by heat radiation.  

Due to the features of claim 2, there is the advantage that, especially in the start-up phase, a large number of small flames are formed, so that a carpet of flames practically arises, which means that compared to burners with a few large flames, a low rer NO _x emission results.

The features of claim 3 ensure that there is between the individual Bodies of the fill provide sufficient free spaces over which the fuel gas-air Ge flow through the mix and implement it on the catalytically coated surfaces that can.

The invention will now be explained in more detail with reference to the drawing, which schematically invented one according burner shows.

A burner 1 according to the invention has a mixture chamber 2 , into which a mixture line 3 opens.

The mixture chamber 2 is covered with a perforated plate 4 . On this perforated plate 4 there is a bed 5 of catalytically coated bodies, for example cylinders, hemispheres or planar surfaces. The bed 5 is covered by a radiant burner 6 which has finely divided openings. This radiation burner 6 can be formed by a wire mesh.

The burner 1 is arranged in a combustion chamber 7 , in which a primary heat exchanger 8 is arranged.

In operation, the largest part of a fuel gas-air mixture is catalytically converted in the region of the bed 5 . The resulting hot exhaust gases flow through the unreacted rest of the mixture, the radiant burner 6 and are burned on its upper side in small flames.

The hot exhaust gases act on the primary heat exchanger 8 and largely give off their heat.

At the start of the burner 1 , the mixture flows through the bed 5 and is burned on the upper side of the radiant burner 6 . The resulting radiant heat heats the bed 5 . As a result, the area of the bed 5 , in which the catalyst has reached its operating temperature, is enlarged more and more by the radiant burner 6 until the entire bed 5 has reached its operating temperature and the fuel gas-air mixture is converted almost entirely catalytically and the proportion of the mixture that is burned in flames drops accordingly.

Claims (1)

Catalytic burner ( 1 ), in which a mixture chamber ( 2 ) to which a fuel gas-air mixture can be applied is covered by a perforated plate ( 4 ) on which a bed ( 5 ) of bodies coated with a catalyst is covered, characterized in that in that the bed (5) is covered lattice perforations provided radiant burner (6) by a metal of a distributed finely and in that the bed (5) is formed in a known per se from cylinders, hemispheres or Ebenflächnern with catalytically coated surfaces.