专利汇可以提供Method and Apparatus for Feeding Gaseous or Liquid Fluid into a Medium专利检索,专利查询,专利分析的服务。并且The present invention relates to a method of and an apparatus for feeding gaseous or liquid fluid into a medium. The method and apparatus in accordance with the present invention are especially suitable in various fields of industry for mixing gaseous and liquid chemicals and steams into a flow containing at least liquid. The method and apparatus in accordance with the present invention are most preferably suitable for feeding steam into the fiber suspensions of wood processing industry. Most preferably the method and apparatus in accordance with the present invention is used, for example, in such a way that a side flow is taken from a first medium flowing along a suction duct (16) of a centrifugal pump (10), which side flow is recirculated by means of a conduit (18) and into which second medium is fed via a duct (24) in such a way that said side flow and second medium are fed into said first medium flowing in the suction duct (16) prior to taking said side flow from said first medium in view of the main flow direction of said first medium.,下面是Method and Apparatus for Feeding Gaseous or Liquid Fluid into a Medium专利的具体信息内容。
The present invention relates to a method of and an apparatus for feeding gaseous or liquid fluid into a medium. The method and apparatus in accordance with the present invention are suitable in various fields of industry for mixing gaseous and liquid chemicals and steams into a flow containing at least liquid. The method and apparatus in accordance with the present invention are especially suitable for feeding steam into the fiber suspensions of wood processing industry.
There are a large number of different known methods and apparatuses for feeding chemicals to liquid flow. The apparatuses are divided into two basic types: static and dynamic. In static apparatuses, at its simplest chemical is allowed to be discharged through an opening in a wall of a flow duct to the flow, to which the chemical mixes in the course of time due to turbulence. In static mixers, various perforated plates or porous rings are used, too, through which especially gaseous chemicals, such as oxygen or ozone, are fed into the flow. The idea is thereby to feed the chemical in as small droplets to the flow as possible, whereby it would mix into the flow more rapidly and more homogeneously. Furthermore, with static mixers, it is possible to use also flow restrictors arranged inside the flow channel, by means of which turbulence greater than the usual duct flow is caused in the flow, which naturally facilitates the mixing of chemicals leading to a quicker and more homogeneous mixing.
With dynamic mixers, the mixing generally takes place by means of some kind of a rotary apparatus. Said apparatus is located in the flow duct and the chemical is supplied either via the rotary apparatus or upstream thereof into the flowing medium. Rotary mixers are exemplified, for example, by apparatuses in accordance with the following patents: U.S. Pat. No. 5,279,709, U.S. Pat. No. 5,536,368, U.S. Pat. No. 5,378,321, and U.S. Pat. No. 6,791,778. All disclosed apparatuses are designed especially for mixing, which can be understandable as such, because at the time the apparatuses were developed, ozone was becoming a popular bleaching chemical in bleaching pulps of wood processing industry and mixers were developed especially keeping the special features of ozone in mind.
It has, however, been noticed now that as for the mixing speed, the majority of the chemicals or like materials to be mixed are not so demanding. In other words, it has been noticed that it is not necessary to use separate apparatuses especially designed for the mixing, but mixing of most of the chemicals can be performed by a centrifugal pump so that the centrifugal pump as such acts as mixer.
At least some of the patents or patent applications suggest the centrifugal pump to be used for mixing chemicals or like. The suggestions have not, however, always led to practical applications. One of the patents suggesting the use of pump for mixing is U.S. Pat. No. 4,834,547, in which the volute of the pump is extended to the rear side of the impeller in such a way that the chemical to be added can be supplied to the rear side of the impeller and be mixed there with the medium circulating in the volute by means of specific rear vanes arranged into communication with the impeller. Said patent is especially concerned about adding chemical into a medium consistency pulp.
Patent application F1 823279 also discusses adding chemical into a medium consistency pulp in a pump. In this arrangement, chemical is added through a conduit in a wall of a suction duct of a fluidizing centrifugal pump into the pulp flowing in said suction duct. The solution in accordance with said patent application is used when the chemical to be mixed is liquid, whereby it does not affect the pumping.
The pump structure discussed in the first mentioned publication is unnecessarily complicated to be competitively manufactured. On the other hand, also the feeding point of the chemical relative to the mixing vanes is not at all ideal. It can even be doubted, whether the disclosed structure allows proper mixing at all; at least not with simple structural changes.
Neither of the structures in the disclosed publications works when mixing, for example, steam into pulp, because in both cases steam would heavily disturb the pumping of the pulp. The main reason for the steam disturbing the pumping is that the steam does not have time to condense before it enters into contact with the impeller of the pump. In other words, the steam gathers into the eye of the impeller of the pump and either forces the impeller to work at least partially in a gas bubble or exits through the gas discharge of the pump, if such exists in the pump, or causes cavitation in the pump.
A purpose of the present invention is to eliminate drawbacks of the prior art solutions by a very simple apparatus, which is inexpensive to manufacture, and by means of which, for example, following advantages may be achieved:
In accordance with the present invention, it is typical of a method of mixing a second medium into a first medium, in which method said first medium is allowed to flow along a suction duct into a centrifugal pump, where the pressure of the medium is raised and the medium is discharged from the pump, that a side flow is taken from said first medium, which side flow is recirculated and into which second medium is fed in such a manner that said side flow and second medium are fed into said first medium prior to taking said side flow from said first medium in view of the main flow direction of said first medium.
In accordance with the present invention, it is typical of an apparatus for feeding a second medium into a first medium, said apparatus comprising a centrifugal pump with an impeller, a volute and a suction duct as well as an inlet conduit for said second medium, that a recirculation duct for a first medium is arranged into communication with said suction duct or with a front wall of said volute, in which recirculation duct said inlet conduit is located.
Other characterizing features of the method and apparatus in accordance with the invention become apparent in the accompanying claims.
The method and apparatus in accordance with the present invention are discussed more in detail by way of example with reference to the accompanying drawings, in which
The operation of an apparatus in accordance with the invention is based on the feature already typical of the conventional centrifugal pumps that at least for a large part of their operational area the flow on the surface of the suction duct runs away from the pump. Now, the flow is facilitated by arranging a recirculation duct 18 into communication with the suction duct 16, the inlet opening 20 of which recirculation duct while being positioned closer to the impeller 12 is positioned to the area of higher pressure than the outlet opening 22 of the duct, whereby backflow takes place by itself. At least one reason for the higher pressure of the opening 20 closer the impeller 12, or the volute 14, is the stronger centrifugal force, which again results from the effect of the impeller 12 of the pump, which causes whirling of the first medium flowing towards the pump in the suction duct 16. Said whirling is the faster, the closer the impeller it is. In other words, the centrifugal force and thereby also the pressure is higher right in front of the impeller 12.
Now, when a second medium, such as steam, peroxide, water, oxygen, etc. is supplied from conduit 24 into a first medium (to be exact it is already a medium containing some of the second medium, but for the sake of clarity it is referred to merely as a first medium) back-flowing in channel 18, said second medium flows to the inlet end of the suction duct 16, or at least closer to it, and begins there to rotate/whirl at an increasing velocity with the first medium ending finally to the pump 10, where eventually the turbulence caused by the vanes of the impeller 12 of the pump mixes the second medium evenly into the first medium.
The apparatus in accordance with the invention is especially suitable for mixing steam into a first medium, which may preferably be a low consistency (consistency 0-6%) or medium consistency (6-25%) fiber suspension of wood processing industry, because steam, as known, requires some time to condense and the disclosed mixer allows the steam time to condense. Moreover, the steam is mixed into a medium in a rotating, but at the same time in a turbulent state, whereby the steam mixes well already because of the mere turbulence. Further, since the steam is supplied to the outer rim of the rotating medium, the steam tends to move towards the center of the flow owing to the centrifugal force affecting the pulp with a higher specific gravity, which also facilitates the mixing of the steam throughout the medium.
Naturally it is also possible to use in connection with the embodiment illustrated in
The apparatus in accordance with
Moreover, it is clear that if so desired, it is possible to arrange in the rotor in the suction duct of the structures shown in
The above disclosed and also other recirculation ducts within the scope of the invention are preferably located directly as a part of the suction duct, especially when the suction duct is manufactured as a cast unit. The recirculation duct(s) may, when so desired, be arranged more or less winding round the suction duct, whereby the length of the duct/ducts can be used to control the time the first medium remains in the channel. For example, when mixing steam it would be preferable that the steam would have as much time as possible to condense already in the recirculation duct. In fact when fiber suspension is concerned, it must be taken into consideration that the higher the consistency of the pulp to be recirculated is the more straight and better designed the recirculation duct should be so that the thick pulp will not clog the duct.
In addition to the above-disclosed alternative it is naturally possible to arrange one or more recirculation ducts also as a member separate from the suction duct, which members are merely connected with the conduits in the suction duct or in the suction duct and the pump volute.
Further, it is worth noting that when the second medium to be mixed is steam, it is advantageous to feed the steam as close to the inlet flow opening of the recirculation duct as possible so that time remains for the steam to condense to the first medium already prior to the discharge of the mixture of the recirculated medium and steam into the first medium. Similarly it is possible to arrange more feed points of the second medium over the length of the recirculation duct, whereby in some cases it is possible to feed to some extent more second medium into the first medium.
Finally it is worth noting that the impeller of the pump is illustrated in the drawing figures either without a so-called fluidizing rotor or with it. The figures do not, however, illustrate any specific structure of the fluidizing rotor, because a rotor structure may be chosen for each application according to the need in question, whereby the rotor structures can vary considerably from each other. Thus it is clear that in some applications it is advantageous that the rotor extends outside the suction duct in the longitudinal direction thereof, in some cases the fluidization within the suction duct is sufficient. Correspondingly, in some cases it is necessary to arrange fluidization over the entire length of the suction duct, in some cases only over a part thereof. Thus, in some cases an area may remain between the rotor and the impeller, which is pierced only by the shaft of the rotor. Thereby, also the inlet opening of the recirculation duct may in some applications be located at said shaft.
As can be seen from the above description, a new kind of apparatus has been developed replacing in many situations the prior art mixers, which apparatus replaces the prior pump-mixer combinations. With reference to the above description it should be understood that although only some of the preferred embodiments and in fact only one application are disclosed above, it is possible to use the construction also for other applications suitable for the feeding apparatus and modify both the field of use and the structure of the invention so that the accompanying patent claims alone define the scope of the present invention.
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