Liquid purification or separation – Processes – Making an insoluble substance or accreting suspended...
Patent
1996-11-27
1998-06-02
Lithgow, Thomas M.
Liquid purification or separation
Processes
Making an insoluble substance or accreting suspended...
2102212, 261 361, 261 93, 261123, C02F 124, B01F 304
Patent
active
057594082
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention concerns a method for treatment of a liquid flow to be cleaned and passed into a flotation plant or equivalent.
Further, the invention concerns an equipment for treatment of a liquid flow to be cleaned and passed into a flotation plant or equivalent.
Flotation is a commonly known mode of removing solid materials from liquids. In particular a solid matter that is present as dispersed, which often contains static electric particles of solid matter, can be cleaned by means of flotation. In flotation, small gas bubbles are formed into the liquid to be cleaned. In studies carried out in this field, it has been ascertained commonly that a removal of particles larger than 10 .mu. can be achieved readily by means of flotation. However, it should be ascertained that absolute cleaning of water cannot be achieved by means of flotation. The size of the air or gas bubble is likely to have a substantial significance for how large/small particles can be removed. The composition of the gas dissolved in flotation and the pressure that is employed play an essential part, because the solubility of a gas into a liquid is directly proportional to the pressure. It is a substantial factor in dissolving of gas into liquid how to bring the liquid and the gas into contact with each other.
Currently, the commonest mode of dissolving air or gas into water/liquid is dissolution taking place in a pressure vessel. In the pressure vessel, the top portion is provided for the gas to be dissolved, and the liquid is placed in the bottom portion of the pressure vessel, the gas having been dissolved into said liquid or attempts being made to dissolve the gas into said liquid. As a rule, a separate pump circuit takes liquid from the bottom portion of the pressure vessel and sprays the liquid into the gas phase placed in the top portion of the pressure vessel, either through an ejector nozzle or by otherwise atomizing the liquid into the gas space. From the bottom portion of the pressure vessel, the liquid that contains dissolved gas is taken out, for example, through a suitable nozzle into the liquid to be treated. Thus, in this commonly known method, a pressure vessel, a pressurized feed of new liquid, and a feed of gas under pressure are needed. The cost of investment of such a solution is high, and it requires precise control, for example, to monitor the boundary between the liquid phase and the gas phase. It is a substantial drawback of this prior-art solution that when, for example, compressed air is used as the gas to be dissolved, for example, into water, it is the final result that the dissolved gas mainly consists of nitrogen, i.e., at an equilibrium, the proportion of oxygen in the gas phase is just about 8 % by weight, which is substantially less than in the free atmosphere, in which the proportion of oxygen is about 21 % by volume. This phenomenon comes from the fact that the solubility of oxygen in water is about twice as high as that of nitrogen. This is why, out of the gas present in the top portion of the pressure vessel, oxygen is dissolved first, and after refilling the oxygen is dissolved again, and finally the state of equilibrium of 8 %-wt. described above is reached. This is why a water that floats by means of pressure-vessel flotation is almost free from oxygen, i.e., in any case, non-oxidative. It is a consequence that this prior-art method has its drawbacks.
In order to solve the problem described above, a solution has been looked for by whose means a more oxidative flotation liquid could be obtained, i.e. a water rich in oxygen could be achieved. The activity of such a water towards chemical impurities is totally different from that of a water that contains inactive gas, such as nitrogen. It is only in cases in which it is desirable to exclude oxidation that dissolved oxygen is, of course, not favourable. Anyway, ionization and the activity of ions depend on the oxygen potential of the water/liquid. Thus, when a gas is dissolved into a liquid, it can be considered to be advant
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Ellis et al, "Clarifying Oilfield and Refinery Waste Water by Gas Flotation", Journal of Petroleum Technology (Apr. 1973), pp. 426-430.
B. Eppler, "Flotation als Modernes Verfahren in Industriellen und Kommvnalen Klaranlagen" 3R International, Apr. 1993. pp. 210-215.
G. Rohlich; "Application of Air Flotation to Refinery Waste Waters" Industrial and Engineering Chemistry, Feb. 1954, vol. 46, #2, pp. 304-308.
"Die Flotation-ein modernes Verfahren der Abwassraufbereitung", H. Richter, Chem-Ing-Tech., vol. 48, No. 1, Jan. 1976, pp. 21-26.
Lithgow Thomas M.
Wiser Oy
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