DE2820077A1 - Fluidisation of bulk materials normally difficult to handle - using very intense local aeration with jets on arms rotating round the base of the bed (NL 14.11.78) - Google Patents

Abstract

Bulk materials which are otherwise difficult to handle are fluidised by a mechanism in which the fluidising medium esp. air is introduced by a rotating distributor mechanism. The distributed air is momentarily and locally concentrated in the bulk material. By this means the fluidised material temporarily and locally overflows. In a horizontal plane a number of changing beds are created with intense local fluidisation. The momentary effective zones do not interact. The outlet air velocities have a value which is 5-200 times the suspension velocity of individual particles. The circles of rotation of the various outlet jets for the air can be arranged with geometrical regularity or without it. The spacing of the jets lies between. K square root of (4A/pi n) and 0.5 d (where k is the air jet divergence constant, A is the total area of the air outlet opening in m2; n is the number of air jets and d is the dia. of the fluid bed vessel).

Description

Method and device for the fluidized bed treatment of

Piles unwilling to flow Field of application of the invention The invention relates to a method and a device for fluidized bed treatment of those who are unwilling to flow Piles, especially of powdery and / or surface-moist bulk materials. With the invention, a variety of procedural tasks, such as e.g. realize cooling, drying, mixing processes, reactions.

Characteristics of the known technical solution One method is known and a device in which air inlet openings opening near the floor air is blown discontinuously into a pile (L. SELIK, Chem.-Äng.-techn. 32, 1960, 4, 253-257). The disadvantage here is the relatively complicated device for the discontinuous air supply, which is also always in the same place entry. If one wants to achieve higher empty space speeds, the system will the air supply and distribution even more complex.

Devices are known in which the vortex medium over the edge, For the leg distribution of the vortex medium with a large number of individual openings or elongated holes or slots provided distribution pipes of a rotating on the bottom part Hollow stirrer is entered into the pile (US-PS 2,336,018, DL-PS 69507 and DL-PS 103460).

In these devices forms, regardless of the speed of the hollow stirrer, a stationary one that revolves with a vertical main exchange direction Fluidized bed. Due to geometrical relationships, there is a surrounding The vertebral layer is a heavily material-thinned zone with an upward direction of flow and at the periphery a downward current with a very high load. These devices have limited effectiveness.

If in a device with the air distribution described, the Increased vortex speed, another occurs in the center of the orbital layer strong diohtea decrease and it forms a typical fizzy layer with a pneumatically conveying discharge channel. At the transition from the rotating layer increases the discharge starts by leaps and bounds and the increase in the vortex speed does not lead to any equivalent increase in heat transfer between the wall and the fluidized bed. Internal Heating or cooling surfaces can disrupt the effervescent layer in such a way that they partially or comes to a complete standstill. Temperature-sensitive substances know qualitatively be significantly damaged.

OBJECT OF THE INVENTION The invention has the object of using little apparatus and energy expenditure while avoiding high dust emissions at the same time Improvement of the effectiveness of the heat exchange through peripheral or internal or cooling surfaces, unwilling to flow and temperature-unstable substances of a gentle fluidized bed treatment to undergo.

Statement of the essence of the invention The object of the invention is that known feeding and Distribution devices for the fluidizing medium, the either discontinuous and locally constant air supply or Avoid stationary layers of circulation or fizzy drinks by a novel entry and distribution of the vortex medium is created.

According to the invention, the object is achieved that the partial air quantities be entered momentarily and locally concentrated. They overflow in time and eddy limits the eddy material.

This results in a number corresponding to the number of partial air quantities generated discrete circulation layers. These exist through the rotary movement of the air distributor, based on a fixed point on the base area of the vortex apparatus, only for a short time, d. ho finds on each radius assigned to the outlet opening of the air distributor a permanent new formation of discrete circulation layers takes place. The one on the respective Discrete circumferential slips that arise in a radius form in a vertical extent a hollow cylinder, the wall thickness of which is approximately the current zone of action of the Partial air outlet opening near the bottom corresponds to 0 Since the inventive momentary zones of action of the partial air volumes do not mutually penetrate each other, forms Starting from each partial air outlet point, a discrete one for the circulation layer typical density gradient.

Duroh this is a circumferential within the discrete Umlaufschioht Movement developed. As a result of the change in location along the partial air outlet point the circumference of the partial radius assigned to the partial air outlet opening becomes the discrete Umlaufsohioht in the partial circle of action constantly newly formed. The vortex air therefore always acts on areas with a downward tendency a. The acceleration forces emanating from the locally exiting eddy air are in the direction of movement of the partial air outlet points from the downward Product flow compensates for the downward tendency of the product flow the period of effect of the vortex air is converted into an upward direction and an intensive fluidization with a constantly changing main exchange direction reached 0 The currently locally concentrated entry of the partial air quantities takes place in that the vortex air in a sharp jet at right angles or in a An angle of up to 300 is blown against the container bottom0 when the air jet hits on the container bottom this is diversified, reflected and based on the diverted hydrostatic conditions. Here it mixes with that in the Vortex apparatus located bulk material and forms the vertical extension already described discrete rotating layer. The effective zone of the air jet is almost identical to the reflection zone. The above-described entry of the Vortex medium and the decomposition of the total amount of air into the limited number of Partial amounts of air take place in the device according to the invention by a special trained, rotating air distribution device.

At the air distributor according to the invention, the outlet points for the vortex air are arranged in such a way that the following relationship applies to the distance a between the partial air outlet points: where a distance between two individual air outlet openings in mk factor for the air jet broadening A total area of the air outlet opening in m2 n number of air outlet openings or

of the air distribution pipes d diameter of the base of the fluidized bed apparatus in m mean. The factor k varies between five and 16 and is among others depending on the air outlet speed of the partial air volume, the fluidized bed height and the hydrodynamics of the vertebrae. The arrangement of all air outlet openings of the air distribution elements is further characterized by the equivalent radius räqu.

This is defined as follows: the sum of the distances between the air outlet openings from the center divided by the number of air distribution elements.

The equivalent radius of an Archimedes spiral arrangement of the air distribution elements is approximately 0.5 r and approximately represents the lower limit according to the invention the mean distance of all air outlet openings from the pivot point of the air distribution device represent.

The upper limit for the equivalent radius is <1 r, preferably 0 * 6 to 0.9 r.

The length of the air distribution elements is determined by the distance between the air outlet openings determined by the pivot point of the air distribution device. The number of air outlets is approximately inversely proportional to the radius of the belt distributor and is 4 to 55 per square meter that of the air distribution device Swept areas of the vortex apparatus.

In the device according to the invention, the total area is Partial air outlet points between 0.005 m2 / m2 and 0 * 04 m2 / m2. That corresponds to a "Free sieve area" of only 0.5 to 4% thereby distributing the required air volumes Compared to previously used vertebral slicing devices, this is considerably easier will.

Since the method according to the invention and the device according to the invention If you are more flexible, you can use the suggested solution to do a wide variety be solved by procedural tasks. The great flexibility is due to the choice of the peripheral speed of the air distribution device, through the dimensioning the partial air inlet points and the air outlet speed is reached.

Depending on how the peripheral speed of the air distributor, the Arrangement of the air outlet points to one another as well as the dimensioning of the air outlet points has been selected on the air distribution elements, a characteristic design is obtained the Virbelschioht, so it is z.3. possible by changing the peripheral speed the air distribution device to influence the formation of the fluidized bed.

When the peripheral speed is low, they come from the air outlet openings outgoing discrete circulating layers through to the layer surface. The vortex layer is characterized by strong vertical mixing movements.

At higher peripheral speeds, the acceleration forces the one emerging from the individual openings Vortex air already in compensated for deeper zones of the fluidized bed, so that the fluidized bed below otherwise The invention assumes a calm boiling character under the same conditions The device is operated with speeds of 0.3 räqu per second to 6 ruqU operated per second.

For many fluidized bed treatments has a peripheral speed of 1 raqU per second proved to be beneficial.

There were air exit velocities from the partial air exit points used between 20 m per second and 100 m per second. For a large number For piles that are unwilling to flow, a rate of 35 to 80 m per second is required. This corresponds to an air speed in the starting point of the air jet, which 3 to 200 times higher than the floating speed of the single grain.

Are in the fluidization of extremely fine powdery heaps of If certain limits are set at the air outlet speed, such acceleration forces are created that a homogeneous fluidization of extremely fine powdery heaps while avoiding high dust discharge.

In this case, the upper limit of the air outlet speed becomes used.

With the solution according to the invention, a large number of process engineering can be achieved Tasks like æ.B. Perform drying tasks, reactions, mixing processes, Da it is possible with the solution according to the invention, finely powdered and / or surface moist To fluidize materials homogeneously even in the presence of internal heating and cooling surfaces, the very large specific surface of the finely powdered materials fully available, so that heat and mass transfer processes at high speed can expire.

The invention is explained in more detail below using 3 exemplary embodiments will. For this purpose, it will be expedient for expedient embodiments of the invention Device for the implementation of certain procedural tasks described.

FIG. 1 shows partially a sectioned fluidized bed apparatus with a cylindrical shell 1 the lower part with base plate 2 and air distributor. The main details of the air distributor are the shaft 3, which is supported by two bearings the distributor head 4 and distributor elements 5. The distributor elements each have an air outlet point 6 at the end of the tube. The vortex air A is over the Air box 7, the distributor head 4 and the distributor elements pressing and sucking promoted. The eddy air blows, emerging from the Ittft outlet points, against the floor panel.

The vortex air mixes with the pile, whereby the action zone with the diameter D on a circular ring corresponding to the width B in the direction of rotation is constantly being re-formed.

Figure 2 shows the top view of a complete base part with a Air distributor and six air distributor elements, the arrangement of the air outlet points is approximately equivalent to the length of the individual tubes and forms a left-handed one Spiral with räqu equals 0.75 r.

The device described in Figures 1 and 2 makes the application high whirling speeds especially at very fine material possible. As a result of the change in location of the air outlet points, a Canal formation with its negative consequences is permanently prevented and congestion kept out of the layer within minimal limits.

Example 1 - Mixing ground dry potatoes with potato starch and table salt It is in a fluidized bed apparatus with 1.2 m diameter at the same time 962 kg of ground dry potato, 273 kg of commercial potato starch and 65 kg of table salt were fed. Vortex air is already generated during feed-in via an air distributor rotating at 60 rpm with eight individual tubes as shown in the figure 2 registered.

The void velocity is 0.32 n / s. The mix is convenient homogeneous at the end of the feed. With a safety margin of 20 5 the mixing process ends.

The treatment of surface-dampened material also prepares no difficulties. Solid compositions are based on a circular path Circumferential discrete layers dissolved very quickly and the surface moist Material mixed intensively with the material presented.

Such a treatment is described in the following example.

Example 2 describes the production of extraction urea chips In a fluidized bed apparatus according to Example 1 is carried out at an empty space velocity of 1 m / s fluidized sugar beet extraction chips, based on the presented Lot, Entered 2% aqueous urea solution. The particle diameter of the extraction chips is between 0.1 and 4 mm. Despite large particle differences and a relative the layer does not come to a standstill with a high water content.

It is also possible to use complicated built-in components, e.g.

Pipes etc. to install in the fluidized bed without affecting the fluidized bed quality suffer from. In drying processes, the ratio of more concrete Heat can be shifted to contact heat in favor of contact heat. The vortex air in this case has, in addition to achieving the desired hydrodynamics, only the task of to transport away the dried water. The heat losses are thus reduced. The reduction of the tasks of the fluidization proves to be particularly advantageous, when working with inert gases or superheated solvent vapors.

Figure 3 shows the top view of a complete base part with a irregular arrangement of the air outlet points and räqu equal to 0.7 r.

Further arrangements are mdgliah.

Figure 4 shows a fluidized bed dryer. Essential elements of this Dryer are the bottom part according to Figure 3, the heated double jacket the heatable inner heat exchanger, the product feed above the vortex layer as well as the product discharge located above the fluidized bed. the Vortex air is dedusted via a cyclone and the material to be returned is removed a cell lock or an equivalent closing organ returned.

Example 3 - Drying commercial potato starch in a hygroscopic Area The embodiment of the invention described by FIGS. 3 and 4 Device can be used for drying commercial potato starch in a hygroscopic manner Use area.

In addition, 5625 kh / h of commercial potato starch is continuously fed with an initial water content of Xa a 0.25 kg H2O / kg starch and an initial temperature of 800 C. The vortex air flow is driven by the rotating at 40 rpm Air distributor according to FIG. 3 roughly divided into six individual air flows. The void speed is 0.73 m / s, the free space above the fluidized bed (separation space) 1.1 x height of the fluidized bed. Steam with t = 1950 C, the sum of all, is used as the heating medium peripheral and internal heating surfaces directly in contact with the fluidized bed 18.7 m2.

The fed-in pile leaves the apparatus at one temperature of 1000 C and is practically anhydrous. The realized heat flow is through Heat transfer coefficient k = 667 koal / m2 h ° C. Per kg of evaporated water 887 koal are consumed.

Claims (4)

Patent claims Process for the fluidized bed treatment of unwilling to flow Piles in which the fluidizing medium, preferably air, with a rotating Distribution device is broken down into partial air quantities characterized in that the partial air quantities entered into the pile at the moment and in a locally concentrated manner be, with the eddy material temporarily and locally flooded and an intense Fluidization through the emerging two or more discrete, in horizontal Level on a partial circular ring in the direction of rotation movable layers of rotation, their partial circles of action / betw. Hollow cylinders overlap, the momentary zones of action of which do not penetrate each other and the air velocities at the starting point of the exiting air jets are 5 to 200 times higher than the floating velocity of the single grain The vortex air is introduced into the pile by means of a limited number of partial air outlet openings, which are arranged so that they sweep over different partial circles which form geometrically regular or geometrically irregular figures in their arrangement to one another, the distance a of the partial air outlet points of the relationship follows and the equivalent radius <1 r, preferably 0.6 to 0.9 r. 30 Apparatus according to claim 2, characterized in that the number the partial air outlet points per m2 of floor space is between 4 and 55, 4. Device according to claims 2 and 3, characterized in that the total area of the partial air outlet points is between 0.005 m2 per m2 and 0.04 m2 per m2 of floor space. So device according to claim 2, 3 and 4, characterized in that the number of partial air outlet points approximately inversely proportional to the radius the air distribution device is. 60 device according to claim 2, 3, 4 and 5, characterized in that that the air exit speed from the partial air exit points between 20 and 100 meters per second, preferably 35 to 80 meters per second. 7O device according to claim 2, 3, 4, 5 and 6, characterized in that that the peripheral speed of the rotating air distributor of 0.3 räqU per second to 6 räqu per second.