Chemical apparatus and process disinfecting – deodorizing – preser – Chemical reactor – Waste gas purifier
Reexamination Certificate
2000-09-20
2003-09-02
Tran, Hien (Department: 1764)
Chemical apparatus and process disinfecting, deodorizing, preser
Chemical reactor
Waste gas purifier
C422S171000, C422S177000, C422S222000
Reexamination Certificate
active
06613297
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a catalyst body with an inlet side, an outlet side and a multiplicity of longitudinal passages through which a medium can flow from the inlet side to the outlet side.
A catalyst body is used for cleaning off-gas (exhaust gas) from a combustion plant, for example for removing nitrogen oxides using the selective catalytic reaction (SCR) process, hydrocarbons, carbon monoxide and/or dioxins from the off-gas. A combustion plant is, for example, a boiler plant, a coal-fired, oil-fired or gas-fired fossil power plant, a gas turbine or an internal combustion engine, in particular a diesel engine. A refuse incineration plant also emits pollutants. The reactants that are to be reacted with one another flow through longitudinal passages from the inlet side to the outlet side of the catalyst body, through the latter. The catalyzed reaction proceeds when the reactants come into contact with the wall surface. In this context, a catalyst body is understood as meaning a compact catalytic element or a module composed of a plurality of catalytic elements.
The so-called AP value represents a measure of the catalytic activity of a catalyst body. This value is defined as the ratio of a geometric surface area of the catalyst body to its volume (m
2
/m
3
). To achieve the maximum possible AP value for the catalyst body—and therefore the smallest possible volume of the catalyst body—it is attempted to shape the catalyst body in such a way that it has the largest possible surface area. One possibility of achieving this is to make the cross sections of the individual longitudinal passages small in combination with walls between the longitudinal passages which are configured to be as thin as possible.
However, the size of the cross section of the longitudinal passages must depend on an installation location of the catalyst body. The use of a catalyst body with longitudinal passages of small cross section for lowering the nitrogen oxide or dioxin levels in an off-gas from a combustion plant causes problems if the off-gas at the same time has a very high dust content. In a plant of this nature, a so-called high-dust plant, it is preferable to use catalyst bodies with longitudinal passages of large cross section, since these are less susceptible to blockages. However, given the same catalytic activity of the overall catalyst body, the volume of a catalyst body with longitudinal passages of large cross section is greater than that of a catalyst body with longitudinal passages of small cross section. If a catalyst body with longitudinal passages of small cross section is used in a high-dust plant, for example because there is not sufficient space in the off-gas duct of the plant for a large catalyst body, the operating risk is correspondingly high. In some cases, catalyst bodies in plants of this nature become blocked.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a catalyst body which overcomes the above-mentioned disadvantages of the prior art devices and methods of this general type, which combines the advantage of a high AP value with longitudinal passages of small cross section with a low risk of blockages even in dust-containing off-gases.
With the foregoing and other objects in view there is provided, in accordance with the invention,a catalytic converter. The catalytic converter contains a catalyst body, including: an inlet side having at least one recess formed therein; an outlet side; and a multiplicity of first longitudinal passages formed in the catalyst body and extending from the inlet side to the outlet side. Each of the first longitudinal passages has a passage cross-section through which a medium can flow from the inlet side toward the outlet side. A plurality of second longitudinal passages are formed in the catalyst body and extend from the inlet side to the outlet side. Each of the second longitudinal passages are disposed substantially in a region of the recess and has a passage cross section being larger than the passage cross section of the first longitudinal passages. Additionally, the number of the second longitudinal passages is less than the number of the first longitudinal passages.
The object is achieved by a catalyst body that contains a multiplicity of first longitudinal passages and, according to the invention, additionally a smaller number of second longitudinal passages. A passage cross section of the second longitudinal passages is larger than a passage cross section of the first longitudinal passages.
The invention is based on the consideration that longitudinal passages become blocked in particular if large individual particles—such as so-called popcorn ash, which forms, for example, through the coal burner of a coal-fired power plant functioning incorrectly, or melt beads which are entrained by the off-gas and are formed during so-called slag tap firing—occur, which are unable to fit through the first longitudinal passages. Starting from these blocked longitudinal passages, the increased depositing of ash results in that further blockage of adjacent regions can easily occur. Therefore, a relatively small number of large individual particles leads to a large part of the catalyst body becoming blocked. The fact that only a few second longitudinal passages of large cross section are provided results in that first the advantage of the high AP value is scarcely detracted from, and second a free passage is created even for oversized individual particles, so that blockage is reliably avoided. The number of second longitudinal passages, as well as their size and configuration in the honeycomb structure, can be adapted to the specific operating conditions.
In an advantageous configuration of the invention, the openings to the second longitudinal passages are distributed over the inlet side of the catalyst body and are each spaced apart by regions with regularly disposed first longitudinal passages. Large individual particles from the off-gas which do not fit through the first longitudinal passages are moved to and fro by the gas flow over the openings to the first longitudinal passages, which are disposed regularly over the inlet side of the catalyst body, and, in the above configuration of the invention, find an opening to a second longitudinal passage in the vicinity, through which they fit and can leave the inlet side in this way.
In catalyst bodies of standard construction, the passage cross section of the first longitudinal passages is between 4 mm
2
and 70 mm
2
. This enables a favorable AP value of up to more than 900 m
2
/m
3
to be achieved. The passage cross section of the second longitudinal passages is expediently selected in such a way that individual particles of standard size which are entrained in the gas flow can pass through the second longitudinal passages. Definitive determination of the cross section may, but does not necessarily have to, be preceded by a dust analysis carried out on the off-gas. The dust analysis gives information on the grain size distribution in the off-gas and on the presence of individual particles of excess size (popcorn ash, slag tap beads). The passage cross section of the second longitudinal passages is expediently between 9 mm
2
and 200 mm
2
. If a cross section that is not a multiple larger than that of the first longitudinal passages is selected, the AP value of the catalyst body is reduced only slightly.
Likewise in order to ensure that the AP value of the catalyst body is reduced only slightly, the number of second longitudinal passages is selected to be as low as possible. Depending on the dust and particle content of the off-gas, the number of second longitudinal passages is expediently between 10 and 500 per m
2
of inflow area. The inflow area is intended to mean the inlet side of the catalyst body lying perpendicular to the inlet direction of an off-gas.
In a further advantageous configuration of the invention, the inlet side of the catalyst body has at least one recess and the second longitudinal passages are
Greenberg Laurence A.
Locher Ralph E.
Siemens Aktiengesellschaft
Stemer Werner H.
Tran Hien
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