Gas separation: processes – Liquid contacting – And recycle or reuse of contact liquid for further contact
Reexamination Certificate
1999-04-22
2001-03-06
Spitzer, Robert H. (Department: 1724)
Gas separation: processes
Liquid contacting
And recycle or reuse of contact liquid for further contact
C095S200000, C095S205000, C095S211000, C095S224000, C095S228000, C096S273000, C096S290000, C096S361000, C210S618000, C210S626000, C210S188000
Reexamination Certificate
active
06197093
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for the purification of waste gas of an apparatus for drying biological matter. It furthermore relates to an apparatus for the purification of waste gas of an apparatus for drying biological masses.
2. Description of the Prior Art
In industrial plants, in which for instance wood or feed stock is dried, three groups of air contaminating matter is released, which groups depend from the kind of the biological mass being processed, from the design of the drying apparatuses present, and from the temperature level of the drying process. These three groups of air contaminants are a) dust, b) resin aerosols which the art also defines as blue smoke, and c) organic gases such as formaldehyde, pinenes, terpenes and organic acids.
These contaminants must be removed from the waste gas of drying apparatuses before the waste gas is released into the environment.
The purification treatment necessary for this task substantially depends from the differing portions of the above named groups of contaminants and, therefore, is to be made to suit the respective conditions encountered.
For the purification of the waste gases of drying apparatuses of wood drying plants, specifically three kinds of purifying methods and purifying apparatuses, respectively, have become known such as follows.
a) Wet-washing apparatuses with or without an addition of chemicals and with a discharge of waste water. These known apparatuses are designed as a Venturi-apparatus, a counter-current jet apparatus or also as a wet electro-filter apparatus. These apparatuses are in a position to remove dust at degrees of efficiency of 80-90%. However, regarding organic gases (e.g. formaldehyde) they are restricted to a range of 10-20% regarding the removal efficiency.
b) Regenerative thermal after-burning apparatuses including pre-washing. By means of such apparatuses it is indeed possible to remove dust and also organic gases with an efficiency of more than 90%; such after-burning apparatuses are, however, extremely expensive regarding investment as well as operation.
c) Apparatuses having a combined purification process, including a pre-washing apparatus and a bio-washing apparatus. Such apparatuses, however, specifically due to the problems regarding the removal of resin aerosols and the high points of condensation of the waste gas, have been installed rather seldom. Generally, it is indeed possible to achieve removal efficiency of dust of 80-90%, however only in case that no resin aerosols are present, and regarding organic gases a removing efficiency of not more than 50-60% can be reached.
SUMMARY OF THE INVENTION
Hence, it is a general object of the present invention to provide a method and an apparatus by means of which the drawbacks described above may be eliminated and by means of which an additional burdening of the waste water can be avoided.
A further object is to provide a method wherein during a first process step the waste gas is pre-washed in a washing apparatus having a first washing water circuit such to remove predominantly solid matter particles, whereafter during a second process step the pre-washed waste gas is subjected to an activated sludge treatment including a second washing water circuit such to remove gaseous contaminants, and wherein the temperature of the waste gas is reduced for the activated sludge treatment such to reduce its point of condensation by a reduction of the absolute humidity.
A still further object is to provide an apparatus for the purification of waste gas comprising a first washing water circuit which includes a washing apparatus, followed in the direction of the washing water flow by a pumping device and a solid matter removing apparatus, and further comprising a second washing water circuit which includes a stationary trickling filter device, followed in the direction of the washing water flow by an activated sludge basin and a second solid matter removing apparatus, which washing apparatus communicates at its waste gas exit side with the trickling filter device; and comprising an apparatus operative to reduce the temperature of the waste gas led to the trickling filter device.
The advantages gained by the invention are to be specifically seen in that the range of application for the microbiological purification of waste gas at the drying of biological masses is considerably broadened. Accordingly, higher economics are achieved. Furthermore, the availability and stability of the process are increased, whereby the investment and operation costs can be considerably reduced.
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Alois Sceuch GmbH
Ladas & Parry
Spitzer Robert H.
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