Gas separation – Means within gas stream for conducting concentrate to collector
Patent
1989-01-27
1992-03-10
Hart, Charles
Gas separation
Means within gas stream for conducting concentrate to collector
55 96, 55302, B01D 4604
Patent
active
050946757
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a method of removing dust from a dust-laden gas using gas-permeable filter elements that are disposed in at least one tank, with the gas flowing through the filter elements from the outside to the inside thereof and depositing the dust on the outer surfaces of the filter elements, and with the deposited dust being removed from the filter elements by compressed or pressurized gas pulses that are applied to the interior of the filter elements, whereby the gas pulses are released at least as a function of a pressure differential that is measured across the filter elements.
Such a method is used, for example, for cleaning dust-laden flue gases from pressurized or atmospheric fluidized bed reactors. In this connection, customarily a plurality of tanks are supplied in parallel with the flue gas that is to be cleaned. Since only the pressure differential across the filter cartridges is determined and the cleaning pulses are released by the pressure differential as a function of reaching a prescribed limiting value, a cleaning or dust-removal is also effected at pressure differentials that are not based upon the formation of a sufficiently thick layer upon the filter elements, but rather upon changes in the flow rate. Thus, the cleaning pulses are also released when no layer is present or where the layer is to thin.
It is an object of the present invention to provide a method with which the release of the cleaning pressure pulses is essentially effected only as a function of the formed dust layers.
SUMMARY OF THE INVENTION
This object is realized in that for the tank, in addition to the pressure differential over the filter elements, the flow rate of the gas that is to be cleaned is determined, and the cleaning pulse is released when the ratio of the pressure differential to the flow rate, which ratio increases with time during the formation of the dust layer, reaches t least one experimentally determined lower limiting value.
The pressure drop caused by the gas flowing over the filter elements can be determined in conformity with the following Darcy formula: ##EQU1## where: V is the flow rate of the gas that is to be cleaned,
This equation can be found, for example, in "Chemical Engineers' Handbook", 5th Ed. (Intern. Students Ed.), McGraw-Hill (1973) pages 5-54.
The flow rate can be measured, for example, by introducing a restrictor in the cleaned gas stream and by determining the pressure differential across the restrictor. In a manner known per se, the flow rate is proportional to the square root of the pressure differential measured across the restrictor.
Thus, from equation (1) the ratio ##EQU2## can be determined, and can be compared with an experimentally determined fixed value.
This ratio increases during the cleaning operation, and it is possible to experimentally determine the limiting value at which it is expedient to release the cleaning pulse. The method of the present invention prevents cleaning pulses from being released merely by changes in flow rate, or where the thickness of the layer is still too small.
The intensity of the cleaning pulse is essentially determined by the cohesive force of the dust particles that form the layer, and by the pressure differential that is formed across the filter elements and is directed from the outside toward the inside. In this connection, it is advantageous if as a function of the pressure differential that is obtained across the filter elements, the pressure of the supplied cleaning gas be set in such a way that the intensity of the cleaning pulses is adequate for cleaning or dust removal. The ratio, and hence the intensity, are experimentally determined.
If the quantity of the dust-laden gas that is to be cleaned makes it necessary to use a plurality of tanks, it is advantageous that with this plurality of tanks, which are supplied in parallel with partial streams of the gas that is to be cleaned, the ratios of the pressure differentials across the filter elements of the individual tanks to the f
REFERENCES:
patent: 2892512 (1959-06-01), Watts et al.
patent: 4500326 (1985-02-01), Sunter
patent: 4507130 (1985-03-01), Roth
patent: 4624689 (1986-11-01), Volk et al.
patent: 4718924 (1988-01-01), DeMarco
Pitt Reinhold U.
Steven Hubert
Hart Charles
L. & C. Steinmuller GmbH
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