WO1997038788A1

WO1997038788A1 - Apparatus for mixing of media

Info

Publication number: WO1997038788A1
Application number: PCT/SE1996/000488
Authority: WO
Inventors: Kjell Nilsson
Original assignee: Regalco Engineering Ab
Priority date: 1994-10-21
Filing date: 1996-04-16
Publication date: 1997-10-23
Also published as: SE503500C2; SE9403617D0; SE9403617L

Abstract

The present invention relates to a device for mixing of two or several media fed into the device, like exceptional highly viscous suspensions of lignocellulosic fibres in water, for example at hydrolysis of cellulose. This is achieved, according to the invention, in a straight, cylindrical, at one side open, mixing house (1) in which the media are fed in through an opening (5) in the cylindrical wall of the housing (6) whereafter they are fed sideways through the housing against the outlet opening (9). In the housing (1) a coaxial rotor (7) is arragned which has two rotor crosses, with radial arms, driven by a motor. The first rotor cross (10) is located at the gable (12) and the second rotor cross (8) at the outlet opening (9), both with radial arms, which are connected to each other by means of axial bars (15) between the two crosses, which sweep along the inside of the cylindrical housing (1) and the inlet opening (5). The bars (15) of the rotor and the second rotor cross (8) will thereby treat the media at the inlet opening (5) and at the outlet opening (9), respectively, in two directions perpendicular to each other.

Description

APPARATUS FOR MIXING OF MEDIA

The present invention relates to a device for mixing of two or several media.

Generally these kinds of devices are made as a type of vessel into which different media are fed and exposed to agitation by means of rotating or revolving stirrers. Usually the media are fed in continuously and the mixture is also discharged continuously. If the mixing takes place under high pressures the vessel has to be made as a pressure vessel and if the media are highly corrosive all parts, in contact with or exposed to the media, have to be made of materials resistive to corrosion.

Conventional mixers normally function satisfactorily, but are restricted to media which are relatively easy to mix. This is a disadvantage as a wide range of use would be preferable for the often very big and expensive mixers that are used, in the first place, within the process industry. When these mixers are made to resist highly corrosive media they tend to be even more expensive.

The type of mixer, according to the invention, is intended for use in ordinary mixing applications, when only a very effective degree of mixing is to be obtained, and also for very difficult applications in continuous processes with lignocellulosic material as media. The mixer will be able to operate highly viscosic media, such as suspensions of lignocellulosic fibres in water, with a concentration of dry substance as high as approximately 35 %. When required, the mixing in such applications will be possible to execute with such high power and energy input that the media will be fluidized.

It is well known, that cellulosic fibres have the ability to form a network unaided, a so called network of fibre, at relatively low consistencies. This leads to a rapid decrease in the mixtures ability to flow, like a "Newtonian hquid". If this phenomena cannot be overcome or eliminated it will strongly effect the result in a negative way when mixing additives like, bleaching chemicals, oxygen, acids, etc.

Acid hydrolysis of lignocellulosic materials can be used as an example. If a strong network of fibre exists, the added acid will not be distributed to the medium in an satisfactory way for this process. To arrange the condition for a proper admixture ofthe acid, and in this case not only to achieve a well defined start ofthe hydrolysis reaction, which is catalyzed by the acid, but also to achieve a proper result of hydrolysis, the network of fibre should be broken so that all the individual fibres can be reached rapidly by the acid. This can be achieved by an agitation ofthe fibre suspension strong enough to fluidize the mixture. The mixture will than start to behave like a "Newtonian liquid", which will allow a proper and homogeneous addition ofthe acid. The transport ofthe mixture through the mixer will also be facilitated. The mixer will also be constructed so that it can be equipped with an internal cover of special material, as a protection from corrosion, without being too complicated or in any other way leading to unreasonable costs.

The purpose ofthe invention is to achieve a mixer which is unsophisticated, effective and easy to facilitate, and which also complies with above mentioned requirements.

This has, according to the invention, been reached by giving the mixer the distinctive features listed in the following claims. The housing ofthe mixer has a straight cylindrical form and the media, that should be mixed, are fed in through an opening in the mantle surface, essentially radial to the housing, where the media immediately in the opening are subject to a first mixing, or agitation, by the axial bars that sweep close to the inner wall ofthe cylindrical mixing housing. Inside the mixing housing, the media are transported perpendicular to the intake direction and are subject to at least one more mixing or agitation, but now perpendicular to the first mixing, by a rotating rotor cross with radial arms located in the open -end ofthe mixing housing, coaxial with the housing. This especially contributes to a strong turbulence ofthe media mixture.

As an alternative the media could also be fed, through the mixing housing, in the other direction.

The invention is explained more clearly in the following text with reference to enclosed drawing which in a schematic way shows one example of design of a device according to the invention in which figure 1 is a side view ofthe device, partly in section, and figure 2 is an end view ofthe device.

It can be seen from the drawing that the device consists of three main parts, namely one straight cylindrical mixing housing 1, one straight cylindrical bearing housing 2 and one electrical motor 3, positioned at the end ofthe bearing housing. These three parts are connected to each other by flanges. At the mixing housing 1 a feed pipe 4 is welded at an opening 5 through the cylindrical wall 6 ofthe mixing housing. Inside the mixing housing 1 a revolvable rotor 7 is arranged. The rotor has one rotor cross, with radial arms 8, at the outlet opening 9 ofthe housing 1 and a similar rotor cross 10 at the other end ofthe housing 1, and the ends ofthe arms 8 are connected to the ends ofthe arms ofthe rotor cross 10 by four axial bars 15 which sweep along the inside ofthe housing 1 when the rotor is rotating. The rotor cross 10 is fixed to a shaft 11 which goes through an opening in the end wall 12 ofthe bearing housing 2. End wall 12 is also, at the same time, the end wall ofthe mixing housing 1. The shaft 11 is supported by the bearings 13 in the bearing housing 2 and is connected to the motor 3 by a coupling 14. The passage ofthe shaft, through the opening ofthe end wall 12, is thoroughly sealed to resist high pressures as well as the effect of strongly corrosive media. It is then obvious that the bearing housing 2 and the motor 3, as a unit together with the rotor 7, which is introduced in the housing 1, can be mounted against the end flange ofthe housing 1 when assembling the device.

The rotor cross 10 has arms which are somewhat inclined to feed the media from the end wall 12, as are the bars 15, to feed the media from the inside ofthe wall 6 against the centre ofthe housing 1. Furthermore the axial bars 15 can be designed slightly curved to support the feed ofthe media through the housing 1 forwards the outlet opening 9. The arms 8, ofthe rotor cross in the outlet opening 9, are twisted and/or curved causing a strong turbulence when the media is passing.

If desired, one or several more rotor crosses can be arranged at the rotor 7 between the two which are shown in the drawing.

As a result ofthe described design ofthe mixing housing 1 and the inlet pipe 4 the possibility for the housing to handle high pressures will be very favourable. The axial part ofthe housing has a diameter of 350 mm and a length of 600 mm. The inlet pipe 4 has a diameter of 325 mm. The housing 1 and the inlet pipe 4 are made of stainless steel and the inside are lined with a 4 mm thick plate of Zirconium 16.

The rotor 7 is manufactured of solid Zirconium and the design gives the suitable stability and strength to take the full torque that the motor 3 can give. This motor has an effect of 75 kW and a speed of 750 rpm, which gives the rotor a circumferential speed of 13,5 m/s.

The invention is naturally not restricted to the example shown and described here above. On the contrary, a number of modifications and variations are possible within the frame ofthe idea ofthe invention presented in the claims. As an example, the arms of the rotor crosses can be more or less than four. Furthermore the ends ofthe arms can be connected by a circular reinforcement if increased rigidity ofthe rotor is desired.

When the media are fed in the opposite direction to that shown in the example, the arms ofthe rotor crosses and the bars between the rotors naturally should be inclined with respect to the different direction of feed.

Claims

1. Device for mixing of two or several media, fed to the device, characterized by, the fact that the rnixing takes place in a straight cylindrical mixing housing ( 1 ) in which a rotor ( 7 ) is geared by means of a bearing housing ( 2 ) mounted to one end of the mixing housing, which at the other end has an axial directed inlet or outlet opening ( 9 ). The rotor, driven by a drive shaft ( 11 ), is equipped with a first rotor cross ( 10 ), positioned close to the bearing housing, and a second rotor cross ( 8 ), positioned at the outlet or inlet opening ( 9 ). Those rotor crosses have radial arms ( 8 ) and the ends ofthe first rotor cross ( 10 ) are connected with the corresponding ends ofthe second rotor cross by means of axial bars ( 15 ), which are arranged to sweep along the inside ofthe cylindrical part ofthe mixing housing ( 1) and an inlet or outlet opening, ( 5 ) for the media, which is arranged at the cylindrical wall ( 6 ) of the rnixing housing.

2. Device according to claim no.1 characterized in, that the radial arms ( 8 ) ofthe rotor crosses are inclined so that the media are fed against the outlet opening ( 9 ) by the arms ofthe first rotor cross ( 10 ) and are given a strong turbulence by the arms of the second rotor cross ( 8 ).

3. Device according to claims no. 1 or 2, characterized in, that the bearing housing ( 2 ) has an end wall ( 12 ) that at the same time is an end wall ofthe mixing housing ( 1 ).

4. Device according to any ofthe claims no. 1 - 3, characterized in, that the axial bars ( 15 ) are fixed somewhat inclined to keep the inside ofthe cylindrical part ofthe mixing housing ( 1 ) clean.

5. Device according to any ofthe claims no.1 - 4, characterized in, that the axial bars ( 15 ) are slightly curved to feed the peripheral parts ofthe media forward, along the cylindrical inside ofthe mixing housing ( 1 ).