Liquid purification or separation – Processes – Making an insoluble substance or accreting suspended...
Patent
1999-04-27
2000-08-15
Lithgow, Thomas M.
Liquid purification or separation
Processes
Making an insoluble substance or accreting suspended...
210219, 210220, 2102212, 261 28, 261 93, 96216, 96217, 162 4, 209164, 209170, 95261, B01F 304, B01F 512, C02F 124, B03D 114, D21C 502
Patent
active
061031283
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND AND SUMMARY OF THE INVENTION
The present invention relates to a method and apparatus for adding a treating agent/treating agents to a liquid. More particularly, it relates to a method and apparatus for mixing gas, usually air, with a liquid, e.g, effluent, and dissolving the gas in the liquid.
Many different methods and apparatus are known which are used for this purpose. However, reference is here made to one prior art apparatus only. It is disclosed in Finnish patent 86381. Reference is here also made to a theory disclosed in that patent publication, for dissolving gas in a liquid. It is taught, among other things, in the publication that the solubility of a gas in water is directly proportional to the pressure of the gas and inversely proportional to the temperature, with certain coefficients. Thus, it can be established that, by raising e.g. the pressure of the liquid several atmospheres, the volume of dissolving gas may be correspondingly increased, in comparison with normal atmospheric pressure conditions. An increase in the temperature lowers the solubility to correspond 0.degree. C. (Kelvin temperature +273.degree. K), which is correspondingly revised with the prevailing temperature ratio, i.e., if the conditions are +20.degree. C., the solubility has lowered from the 0-degree condition by a ratio 273/293, i.e., to a 0.9317406-fold value. Each gas has a coefficient of its own, readable from technical tables, which coefficient also influences the solubility value. Solubility may be given in volume units of gas per volume unit of liquid (Ncm.sup.3 /cm.sup.3) or in volume units of gas per weight unit of liquid (Ncm.sup.3 /g).
In practice, the most usual uses are related to, e.g., dissolving of air in water, for example in connection with effluent treatment or in aerating lake and pond waters. An essential role is played here by the oxygen of air, about 20% of the air being oxygen. Oxygen provides, e.g., living conditions of fish in water, and the oxygen content of water should be at least 4 to 5 mg/l. Usually the oxygen content is and it should be over 6 mg/l. Oxygen is consumed by organic compounds which have ended up in water and which oxydate and decompose, causing water-courses to overgrow and become eutrophic. To prevent such a course of events, effluents are normally handled in water purification plants where solids are removed as completely as possible and, finally, organic residuals are oxydated, i.e., treated biologically. This procedure often requires plenty of oxygen to be dissolved in water.
Many different methods exist, which may be used for this purpose. The most usual method is to use pressurized air produced by a compressor and to blow it to the bottom part of a waste water basin, through shattering nozzles arranged in connection with the bottom. The smaller the bubbles are, the faster the solubility of air. Therefore, production of extremely small air bubbles with the shattering nozzles is aimed at. This requires extra pressure in air blowing. This pressure is in principle wasted for breaking up the air in water, since the solubility is only influenced by how deep down below the liquid level the shattering nozzles are disposed. The method is therefore not economical, even though it is widely used as it is technically easy to realize. Besides being uneconomical, it also has a further drawback, i.e., nozzles becoming clogged by impurities in compressed air.
Another way of mixing oxygen with water is to use various, large mixers. In these devices, water is lifted to fly in large quantities, in the form of drops, in the air, whereby the airdraft being simultaneously formed comes into contact with the drops. As a result, oxygen dissolves in the treated water. This method is used, for example, for treating effluents in the wood processing industry. However, in spite of large quantities of treated liquid, it cannot be considered an efficient method in terms of energy economy.
One way is to use a swiftly rotatable rotor within the liquid and supply pressurized air to the rotor, ei
REFERENCES:
patent: 5240621 (1993-08-01), Elonen et al.
Koso Arto
Manninen Heikki
Lithgow Thomas M.
Sulzer Pumpen AG
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