Agitating – Stirrer within stationary mixing chamber – Pump type
Patent
1989-07-13
1992-01-07
Hornsby, Harvey C.
Agitating
Stirrer within stationary mixing chamber
Pump type
366263, 366272, B01F 716
Patent
active
050785052
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method for mixing liquids together or mixing different phases into liquid by using the double loop flow created below the surface zone of the reactor in order to maintain intensive mixing. It is a characteristic feature of this "Bottom Toroidal Roll" or BTR principle that the employed mixer has a strong draft from beneath and presses obliquely downwards, and that the said mixer is installed according to the mixing method of this invention and its flow pattern is controlled in a strictly determined fashion. According to this method, the mixer jet hits the cylinder surface of the reactor, whereafter the jet is divided into two nearly equal parts, and the division is adjusted by means of a back-flow guiding member according to the invention, which guiding member is located above the mixer. The circular flow taking place within the reactor is controlled by means of special baffles.
Generally the reactor is mixed by applying the so-called backmixed principle, which means that all of the different phases are continuously mixed to each other. A typical feature of the mixer arrangement of the present invention is that the mixing space is divided into two zones. The zone below the back-flow guiding member is intensively mixed, whereas the zone above the back-flow guiding member is calmed down in a controlled manner. The flow pattern of the upper zone is adjusted in accordance with the corresponding flow pattern of the lower zone, as is explained in more detail below. When the mixing space is not mixed in a totally uniform fashion but is composed of two toroidal zones below the back-flow guiding member and of the pacified zone above the back-flow guiding member, it is possible to affect the delay time distribution of the material fed into the mixing space. The material fed close to the bottom of the reactor is seized along in the bottom toroid, wherefrom it is only gradually, against the rolling motion captured by the toroid, shifted into the upper toroid and correspondingly, when released therefrom, into the top space of the reactor. From a continuously run BTR reactor, the outlet is arranged as an overflow through the top space or from below the surface. In the latter case, the volume of the reactor contents is controlled by using a separate surface adjustment.
The BTR principle is viable in many fields of the process industry, where a mixing stronger than the normal backmixed type is needed in order to bring some degree of mixing or some chemical reaction nearer to the final state or to the equilibrium. By applying the principle of the present invention, it is possible to construct a number of reactors for various fields of technique.
Among the practical advantages achieved with the BTR principle, let us point out that the location of the mixing member can be arranged remarkably higher than in standard installations. Generally it is recommended that the diameter of the mixing member should be 0.33.times. the diameter of the reactor, and that the mixer is placed at a distance equal to its own diameter with respect to the bottom. While applying the BTR principle, these rules can be ignored and larger mixers employed, which mixers may have diameters of 0.33-0.50.times. the reactor diameter, and may be located at a distance of 0.5-1.5.times. the mixer diameter with respect to the bottom. According to this new dimensioning system, the drive shaft of the mixer becomes shorter, which brings about a remarkable advantage as for the strength of materials, when large reactors are constructed.
Another essential advantage is that the major part of the shaft power is distributed into the reactor space located below the back-flow guiding member. Thus the shaft power per volume is increased in the mixing zone of the reactor, without having to increase the total power demand of the reactor respectively. If the reactor contains some solid material in addition to the liquid, the fluidization of the solid material in the bottom part of the reactor is improved, and simultaneously the reactor bottom
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Jounel Seppo S.
Lilja Launo L.
Makitalo Valto J.
Nyman Bror G.
Brinson Patrick F.
Hornsby Harvey C.
Outokumpu Oy
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