Gas separation – With nonliquid cleaning means for separating media – Cohesive filter media cleaning
Reexamination Certificate
2000-04-04
2001-11-20
Simmons, David A. (Department: 1724)
Gas separation
With nonliquid cleaning means for separating media
Cohesive filter media cleaning
C055S283000, C055S303000, C095S278000, C095S280000
Reexamination Certificate
active
06319295
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method of cleaning a dust separator which has a raw gas shaft, through which raw gas flows from the top to the bottom, and filter elements protruding into the raw gas shaft transverse to the raw gas flow, by which filter elements the raw gas is deflected into a clean gas shaft under a corresponding separation of dust, and which filter elements are briefly subjected to compressed air one after the other for blowing off the dust particles deposited thereon into the raw gas shaft, where during the application of compressed air onto the filter elements their flow connection to the clean gas shaft is interrupted, as well as to an apparatus for performing the method.
2. Description of the Prior Art
In dust separators with a raw gas shaft, which accommodates filter elements, usually filter cartridges, that are connected to a clean gas shaft, the dust-laden raw gas introduced into the raw gas shaft flows through the filter surfaces into the filter elements, from where they are sucked off as clean gas via the common clean gas shaft. To be able to remove the dust particles retained during the passage of raw gas from the filter surfaces during the operation of the filter, it is known to briefly subject the clean gas shaft to compressed air in certain intervals, so that by means of the pulses of compressed air in the individual filter elements the dust particles are blown off from the filter surfaces of the filter elements into the raw gas shaft. To prevent in this connection that the dust particles blown off from the filter elements have to be discharged from the raw gas shaft in downward direction against the raw gas stream usually passed through the raw gas shaft from the bottom to the top, the filter elements of a known dust separator are arranged in groups one above the other in a horizontal orientation, so that in the case of a raw gas flow inside the raw gas shaft from the top to the bottom the coarse-grained fraction of the dust that has been blown off can be moved downwards by the raw gas stream. This is possible because the coarse-grained fraction of the dust is accelerated when it is blown off and due to its inertia is moved away from the filter surface so far that in the case of a flow reversal by the raw gas fraction again flowing through the filter surface after the pulse of compressed air, it is no longer attached to the cleaned filter surface. Due to the friction behavior relevant for the movement of the fine fraction of the dust, which is characterized by a small Reynolds number (e.g. Re
particle
<30), the movement of the fine dust particles is substantially determined by the gas flow. This means that the fine dust particles, which were blown off from the filter surfaces by the pulse of compressed air only to a comparatively small extent, are again attached to the filter surfaces of the filter elements by means of the raw gas stream directly subsequent to the pulses of compressed air, which leads to an increasing pressure loss and thus to a decreasing filter performance with the result that after certain operating periods the dust separator must be shut off for cleaning the filter elements. By means of a scavenging air flow through the filter elements against the raw gas flow the fine dust fraction can naturally be blown off from the filter surfaces of the filter elements and be discharged from the raw gas shaft without raw gas flow, but not during the operation of the filter.
Moreover, it is known (DE 31 11 502 A1, DE 43 34 699 C1) to block the filter elements against the clean gas shaft during the application of compressed air. Filter elements vertically lying one above the other are combined to groups, so that in the vicinity of such vertical group of filter elements there cannot be formed a raw gas flow from the top to the bottom. To make things worse, the filter elements which are disposed laterally beside the filter elements vertically lying one above the other and subjected to compressed air are likewise separated from the clean gas shaft during the application of compressed air onto the filter elements lying therebetween, which prevents the formation of a suction flow in the vicinity of these filter elements disposed one beside the other. This means that merely the coarse-grained fraction of the dust blown off can be discharged downwards due to a corresponding sinking speed, but not the fine-grained fraction, which during the subsequent connection of the filter elements to the suction of the clean gas shaft is again sucked towards the filter elements.
SUMMARY OF THE INVENTION
It is therefore the object underlying the invention to eliminate these deficiencies and provide a method of cleaning a dust separator as described above such that also the fine dust fraction can largely be removed from the filter elements during the operation of the filter.
This object is solved by the invention in that during the interruption of the flow connection between the filter elements and the clean gas shaft a raw gas stream having a flow component directed from the top to the bottom flows around the filter elements blocked against the clean gas shaft.
Since as a result of these measures the filter elements blocked against the clean gas shaft remain in a raw gas stream directed from the top to the bottom, not only the coarse dust particles flung off at a larger distance due to their greater inertia, but also the fine dust particles in the direct vicinity of the filter surfaces are downwardly entrained by the raw gas stream, which ensures the desired cleaning of the filter elements, because the fine dust particles are no longer sucked towards the filter elements during the connection of the cleaned filter elements to the clean gas shaft.
When the filter elements are at least arranged in groups one above the other, it is therefore recommended to apply compressed air onto the filter elements one after the other from the top to the bottom, so that the filter elements are progressively cleaned from the top to the bottom during the operation of the filter. Because of the downward flow of the raw gas decreasing in the vicinity of the bottommost filter elements, the cleaning effect described above can develop only incompletely in the bottommost filter elements. In these bottommost filter elements a higher dust loading must therefore be expected, which influences, however, the entire filter performance only to a comparatively small extent.
As has already been explained above, it is of decisive importance for the invention that the raw gas flow carries away the dust particles blown off during the pressurization of the filter elements from the cleaned filter surface, so that when the flow connection between the clean gas shaft and the filter elements blocked for the application of compressed air is opened, the raw gas fractions again flowing through the open filter elements can no longer deposit the dust particles blown off at the cleaned filter surfaces. To be able to satisfy this request even when the filter elements are disposed one beside the other, the raw gas stream is divided by means of partitions between the filter elements into partial streams associated to the filter elements at least in groups, which partial streams ensure a further downward movement of the dust particles blown off from the filter elements. In this connection it should be considered that despite the blocking of a filter element, a raw gas flow will be produced between the partitions fluidically delimiting this filter element against the filter elements disposed one beside the other, when the partitions form downwardly open flow passages, as this is absolutely necessary for discharging the dust particles blown off. In the vicinity of the flow passages having a flow connection at their lower end a negative pressure is produced as compared to the upper inflow side of these passages, which negative pressure effects a raw gas flow from the top to the bottom in the vicinity of the blocked filter element.
To improve the cleaning effect by
Collard & Roe P.C.
Kappa Arbeitsschutz & Umwelttechnik GmbH
Pham Minh-Chau T.
Simmons David A.
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