DEAERATION VESSEL

Abstract: The present invention relates to a deaeration vessel used in the paper and pulp industry. Especially it relates to an improved double-acting deaeration vessel. As implied by their name, these vessels are purposed for removing gas from a fiber suspension (a first medium). Deaeration vessels are large vessels, into which a fiber suspension to be fed into a paper machine is led as a dilute mixture. It is previously known that the final consistency of the stock to be fed from the headbox to the wire section is preferably fine-adjusted just before the headbox or in connection therewith. This fine adjustment requires deaerated fresh water or equivalent (a second medium). It is characteristic of the deaeration vessel in accordance with the invention that the same gas space (17) where the first medium is treated in the vessel (2), is provided with a second partition wall (13) forming a second weir K2 and that the vessel jacket is provided with an inlet/inlets (11) for a second medium to be introduced into the vessel and with an outlet (14) for a substantially gas-free second medium, and that the common gas space (17) is provided with an outlet (7) known per se, which outlet is intended for the gas separated from both the first and the second medium, and with an outlet (8, 15) for the surface flow/fraction (19) of the second medium separated by weir K2.

Description: DEAERATION VESSEL The present invention relates to a deaeration vessel used in the paper and pulp industry. Especially, it relates to a deaeration vessel comprising the vessel itself, a par¬ tition wall arranged therein and forming a weir Kl and, arranged in the vessel jacket, inlets for a first medium to be introduced into the vessel, outlets for a substan¬ tially gas-free first medium, an outlet for separated gas, and an outlet for a surface flow/fraction of the first medium, which surface flow/fraction has been separ¬ ated by weir Kl. Experts of the field know these deaeration vessels best by the trademark DECULATOR® (A. Ahlstrom Corporation) . These deaeration vessels are used especially in the paper and pulp industry. As implied by their name, these vessels are purposed for removing gas, e.g. , from a fiber suspension. Deaeration vessels are large vessels, into which the fiber suspension to be fed to the papermaking machine is introduced as a dilute mixture. The operating principle of the vessel is to boil the fiber suspension in sub- atmospheric pressure and thus separate the gas into a so- called gas space and discharge it from the vessel, and to allow other light impurities to be separated onto the liquid surface in the vessel because of their lightness and then discharge them along with the surface flow/fraction from the vessel. The suspension directed to the papermaking machine is withdrawn through an opening in the bottom of the vessel, the idea naturally being to withdraw fiber suspension in as gas-free a state as poss¬ ible from the vessel. In order to maximize the deaeration capability of the vessel, it is evacuated by means of a vacuum pump, whereby the gas is withdrawn from the vessel via the vacuum pump. The deaeration capability is further enhanced by introducing liquid via nozzles above the level of liquid in the vessel and by causing the intro¬ duced liquid to hit, e.g., the ceiling of the deaeration vessel, whereby the gas, if any, present in the liquid in the form of bubbles is separated prior to the liquid becoming into contact with the liquid in the vessel. Equipment in accordance with a so-called DECULATOR® Fly¬ ing Wing process disclosed in, e.g., Finnish patent 47795 (US 3,538,680) is used for cleaning of papermaking stock and removing of air/gas therefrom. It is previously known that the final consistency of the stock to be fed from the headbox to the wire section is preferably fine-adjusted just before the headbox or in connection therewith. This fine adjustment requires de¬ aerated fresh water or equivalent. The medium being introduced into the papermaking machine and substantially comprising stock is hereinafter referred to as a first medium. The white water, fresh water, or equivalent needed for the fine adjustment of the stock consistency is hereinafter referred to as a second medium. The second medium is deaerated in a separ¬ ate deaeration means, in accordance with prior art. Our invention relates to an improved apparatus for pre¬ paring the gas-free or substantially gas-free second medium, required for the fine-adjustment of the stock consistency. It is a characteristic feature of the deaeration vessel according to the invention that the same gas space where the first medium is treated in the vessel, is provided with a second partition wall forming a second weir K2 and that the vessel jacket is provided with an inlet/inlets for a second medium to be introduced into the vessel and with an outlet for a substantially gas-free second medium, and that the common gas space is provided with an outlet known per se, which outlet is intended for the gas separated from both the first and the second medium, and with an outlet for the surface flow/fraction of the sec- ond medium separated by weir K2. Other characteristic features of the deaeration vessel will become apparent from the accompanying claims. In accordance with the arrangement of the invention, the deaeration of the second medium employs the same equip¬ ment as the deaeration of stock to be introduced into the headbox. Thus the water, preferably white water, used for adjusting the final stock consistency is preferably taken from the wire pit and conveyed to a deaeration vessel, which may be of, e.g., the same type as DECULATOR® deaer¬ ation vessels and in which the water is deaerated. The equipment in accordance with the invention is easy to connect with prior art deaeration vessels. For example an end of a cylindrical deaeration vessel is readily pro¬ vided with means, such as necessary conduits and weir, needed for deaeration of dilution water, i.e., the second medium, by extending the vessel. The arrangement of the present invention utilizes means existing in the deaera- tion vessel, for removal of gas. Deaeration of the first and the second medium in one and the same gas space, i.e., in one vessel, brings an obvious space saving. The equipment also forms a whole. If the so-called Flying Wing type deaeration means is used, it is easy to add deaeration means for the second medium in accordance with our invention to an end of this structure. The surface flow/fraction of the second medium, separated by a weir, may be discharged from the vessel through a separate outlet. In that case, weirs Kl and K2 have a partition wall between them, to separate the surface flows/fractions, separated by a weir, of the first and the second medium from each other. When the second medium has been deaerated, this second medium, which is e.g. water removed from the wire of the papermaking machine, fresh water, or a mixture of these, is conveyed via a pump and appropriate screens to the headbox, where the ultimate fine-adjustment of the con¬ sistency of the stock to be fed to the wire is effected. By white water is meant water discharged from the wire of the papermaking machine. The deaeration vessel according to the invention will be described more in detail in the following, by way of example, with reference to the enclosed drawings, in which Fig. 1 is a schematic illustration, showing a sectional side view of a deaeration vessel in accordance with the invention, and Fig. 2 a schematic illustration, showing a sectional side view of a second deaeration vessel in accordance with the invention. In accordance with Fig. 1, the deaeration vessel 1 ac¬ cording to the invention comprises a jacket 2, an inlet header 3 for a first medium, such as e.g. a suspension, to be handled, feed pipes or inlets 4, an outlet 6 for the deaerated first medium, such as a suspension, gas evacuation/vacuum duct 7, a plate 9 forming a weir Kl, and an outlet 8 for a fraction or a surface flow of the first medium separated by a weir Kl. The surface of the first medium in the deaeration vessel 1 is denoted with reference numeral 5. At the other end of the deaeration vessel 1 is disposed an inlet header 10 for the second medium, such as white water (= water discharged from the wire of the papermaking machine) , and a feed pipe/feed pipes or inlets 11 for the second medium, an outlet 14 for the gas-free second medium, such as white water, and a gas evacuation/vacuum duct 7. The surface of the second medium in the deaeration vessel l is denoted with refer- ence numeral 12. Thus, the deaerating means of the first and the second mediums are common, which is only natural and advantageous, because both the first and the second medium are treated in the same gas space. A plate 13 forms a weir K2. The outlet for the fraction 19 or sur- face flow of the second medium, separated by weir K2, is denoted with reference numeral 8 in Fig. 1. In this ar¬ rangement of our invention, the surface flows separated by weirs Kl and K2 are conveyed to one and the same space, wherefrom they are discharged via outlet 8 from the deaeration vessel 1. Leading the surface flows (frac¬ tions) separated by weirs Kl and K2 into one and the same space, wherefrom they are discharged from the deaeration vessel 1 via a common outlet 8, makes it possible to make the construction of the deaeration vessel as simple as possible. A maintenance hatch is denoted with reference numeral 18. The arrangement shown in Fig. 2 is otherwise identical with that shown in Fig. 1, except that the surface flows (fractions) of both mediums, which surface flows have been separated by weirs Kl and K2, are conveyed to spaces of their own, which spaces are separated by a partition wall 16, and therefrom they are discharged via separate outlets 8' and 15 from the deaeration tank 1 for further treatment. As described above, the deaeration vessel may be, e.g., of Multi-Retention type or of the so-called Flying Wing type. The arrangement of our invention is applicable to deaeration vessels of other types also. When the deaerat¬ ion means of the second medium, which is most usually a mixture of white water and/or white water and fresh water, is constructed to form an extension to a prior art deaeration vessel, we receive a construction which is compact and readily implemented. Hereby, it is advan¬ tageous to arrange discharging of the surface flow (frac¬ tion) of both mediums via one and the same space and outlet. If each fraction is to be discharged separately, a partition wall may be constructed between these two surface flows (fractions) and both fractions be dis¬ charged via a separate outlet from the deaeration vessel. The apparatus according to our invention is easy to attach to prior art deaeration tanks, such as so-called Multi-Retention type or so-called Flying Wing type, to form an extension thereto. The apparatus according to our invention is readily connected also afterwards with an existing deaeration vessel of a fiber suspension. When the inlets (4, 11) introducing the mediums to be treated into the deaeration vessel are so arranged that each of them starts from or is in connection with essen¬ tially opposite sides of the vessel, and the outlet/out¬ lets (8; 8', 15) of the fractions (18,19) of the first and the second mediums, which fractions have been separ¬ ated by weirs Kl and K2, are arranged in connection with that part of vessel (2) which is between the inlets (4, 11) of the first and the second mediums, the arrangement according to the invention may be implemented so that the total space consumption and the layout of the various components is well controlled. When the means for processing deaeration of the first and the second mediums are each arranged to start from or to be in connection with essentially opposite ends of the vessel, it is possible, in a simple manner, to extend the deaeration equipment from the original, which was intended for deaeration of fiber suspension only, so that it is applicable to deaeration of a second medium also. This second medium is, for example, water discharged from the wire of the papermaking machine, i.e., so-called white water, fresh water, or a mixture of these, which is then conveyed via a pump and appropriate screens to the headbox, where the ultimate fine-adjustment of the con¬ sistency of the stock to be fed to the wire is effected. When the inlets (4, 11) for introducing the mediums to be treated into the deaeration vessel are each arranged to start from or to be in connection with essentially oppo- site ends of the vessel, the fractions (18, 19) of the first and the second mediums, which fractions have been separated by weirs Kl and K2, may have a common outlet (8) . If the fraction (19) separated by weir K2 from the second medium, e.g., white water, is to be further treated separately from the fraction (19) separated by weir Kl, it is possible to construct a partition wall 16 between these fractions and to arrange outlets (8', 15) in the immediate vicinity of each other. These arrange¬ ments enable the deaeration equipment of the second medium to be readily constructed in connection with an existing deaeration vessel and, on the other hand, the new arrangement of the invention, intended especially for deaeration of two mediums, is very compact. As can be seen from the embodiments described herein- above, a deaeration vessel has been developed which is clearly different from the prior art equipment and in which a gas-free or substantially gas-free second medium, needed for fine-adjustment of stock consistency, is pre- pared. Only a few different embodiments of the arrange¬ ments according to our invention have been presented hereinabove, and they are by no means intended to limit the extent and scope of the invention from what is dis¬ closed in the accompanying claims, which alone define the extent of the invention.

Claims: CLAIMS 1. A deaeration vessel (1), comprising the vessel itself (2) , a partition wall (9) arranged therein and forming a weir Kl and, arranged in the vessel jacket, inlets (4) for a first medium to be introduced into the vessel, outlets (6) for a substantially gas-free first medium, an outlet (7) for separated gas, and an outlet (8, 8') for the fraction (18) of the first medium, which fraction has been separated by weir Kl, characterized in that the same gas space (17) where the first medium is treated in the vessel (2), is provided with a second partition wall (13) forming a second weir K2 and that the vessel jacket is provided with an inlet/inlets (11) for a second medium to be introduced into the vessel and with an outlet (14) for a substantially gas-free second medium, and that the common gas space (17) is provided with an outlet (7) known per se, which outlet is intended for the gas separ¬ ated from both the first and the second medium, and with an outlet (8, 15) for the fraction (19) of the second medium separated by weir K2. 2. A deaeration vessel in accordance with claim 1, char¬ acterized in that the vessel is provided with a separate outlet (15) for the second medium separated by weir K2. 3. A deaeration vessel (1) in accordance with claim 1 or 2, characterized in that the inlets (4, 11) for introduc¬ ing the mediums to be treated into the deaeration vessel are each arranged to start from or to be in connection with essentially opposite ends of the vessel and that the outlet/outlets (8; 8', 15) for the fractions (18, 19) of the first and the second mediums, which fractions have been separated by weirs Kl and K2, are arranged in con- nection with that part of the vessel (2) which is between the inlets (4, 11) of the first and the second mediums to be treated. 4. A deaeration vessel in accordance with claim 1, 2, or 3, characterized in that the second medium is essentially water discharged from the wire of the papermaking machine. 5. A deaeration vessel in accordance with claim 1, 2, or 3, characterized in that the second medium is essentially fresh water.

Inventors: ERLUND HARRY, LUQMANI HAMID, ERLUND, HARRY, LUQMANI, HAMID
Applicants: AHLSTROM MACHINERY OY, ERLUND HARRY, LUQMANI HAMID, ERLUND, HARRY, LUQMANI, HAMID
Application year: 1996
Main classification: D21D5
IPC codes: B01D19, D21D5, D21F1