DE3519979A1 - Process for the continuous production of granules of a solid - Google Patents

Abstract

The invention relates to a process for the continuous production of granules of a solid by drying and simultaneous granulation in a fluidised bed. In the process, the solid to be granulated is sprayed in the form of a solution or suspension into the material bed which consists of pregranulated solid and is fluidised by an injected drying gas of a suitable temperature, a corresponding amount of granular material is discharged from the material bed, and the drying gas, together with the water vapour produced, is drawn off separately. So that the process can be operated independently of the grain size distribution in the fluidised material bed, the mass of the material forming the fluidised bed, while keeping constant over time the amount of the solid introduced as a solution or suspension, is kept constant over time by controlled discharge and controlled infeed of granular material grains which have not yet attained the grain size of the finished product.

Description

description

The invention relates to a method for continuous Production of solid granules by drying and granulating at the same time in the fluid bed.

The main features of such a procedure are: that the solid to be granulated in the form of a solution or suspension in the from existing pre-granulated solid, suitable by an introduced drying gas Temperature fluidized bed of material is sprayed, with a corresponding amount of granules discharged from the bed of material and separated from it the drying gas together with the resulting water vapor is drawn off. A detailed description of this procedure is found, for example, in US Pat. No. 3,231,413. There is also among other things provided that the discharged granulate is separated into three grain size fractions the middle fraction is discharged as a finished product, and the oversize after it has been crushed back into the with the unchanged undersized grain Fluidized bed is returned.

Tests have shown, however, that the process in most Cases can not lead stably. Obviously, it's only useful if - as can also be seen from the cited publication - the amount of oversized grain and undersize together is relatively small in relation to the finished product. As has shown that stable operation can only be achieved if both the amount and the grain distribution of the discharged granulate are constant can be held. The amount could be regulated in a simple manner Discharge can be kept constant, yet it is practically impossible to control the grain distribution to keep constant, as this depends on the grain distribution of the introduced seed particles depends. However, the crushed upper grain and the lower grain are used here as germ particles of the discharged granulate is used, so that every slight change in its grain distribution causes that this will continue to change. Usually it looks like the amount of the undersized grain increases steadily and the amount of the finished product decreases accordingly until finally no finished product is produced at all.

The object of the invention is to improve the known method in such a way that that a continuous production of a solid granulate independently of the Grain distribution in the fluidized bed is made possible and can be carried out in a simple manner. To solve this problem it is proposed that the mass of the fluidized bed forming To keep good things constant over time, e.g. by taking a certain amount of granules from the fluidized bed and at the same time regulated supply of granules coming from the previously removed amount of granules obtained after separating the finished product that have not yet reached the grain size of the finished product. Included the amount of solid introduced as a solution or suspension is also temporal kept constant; it corresponds to the amount of the withdrawn finished product.

In order to ensure a continuous process flow, further proposed that discharged from the fluidized bed and after separation of the finished product remaining granules in a collecting container and then to take them therefrom for the regulated supply to the fluidized bed.

Although the granulation process itself takes place here in exactly the same way as with known method, is through the division of the solids involved into an actively participating mass, which forms the fluidized bed, and a passive mass, in the collecting container temporarily stored mass and by forcibly keeping the fluidized bed constant a constant, easy-to-control operating sequence is achieved.

Is z. B. the grain size of the finished product is not reached quickly enough, this increases the number of granules whose grain size is only slightly smaller is than that of the finished product. The associated increase in mass is according to the invention countered by the fact that so much granulate is removed that the mass of the fluidized bed remains constant. This has the consequence that the number of granules that the grain size of the finished product have not yet reached, becomes smaller, with the remaining The remainder can now grow very quickly to the grain size of the finished product (because of the constant amount of the solids supplied as a solution or suspension), which is followed by a phase of increased discharge. The fluidized bed mass decreases and is now brought back to its initial value with granules from the collecting container.

By forcibly keeping the fluidized bed mass constant, achieve a very stable process flow in which the finished product in continuous Electricity is generated. In many cases, a special addition of granulation germs is unnecessary. If it is nevertheless necessary to increase the number of granules in the fluidized bed, so this can be done in a simple manner that some of the from the fluidized bed discharged granules are crushed and then returned to the fluidized bed as germs is introduced.

It is not necessary to keep the fluidized bed mass constant to know absolute size; for the process according to the invention it is sufficient if the fluctuations are determined around a mean value that has been set once. As a measured variable to determine the rise or fall of the fluidized bed The material mass can advantageously be controlled by the pressure drop that occurs across the fluidized bed of the drying gas, which is directly proportional to the mass of the fluidized bed and can be determined with simple means.

In one embodiment, the application of the invention Procedure are shown. In the figure is a system for continuous Production of solid granules by drying and granulating at the same time shown in the fluidized bed, the mode of operation of which is described below.

The amount pumped in through line 4 in a constant amount over time The solution or suspension is fed through the two-fluid nozzle with the aid of compressed air from line 5 7 is sprayed upwards into the fluidized bed by a stream of hot air flowing through Fan 1 and heater 2 generated and through the distributor ring 3 and the conical Sieve bottom 6 is supplied, flowed through from bottom to top and fluidized in the process will. Due to the high exit speed of the compressed air from the nozzle 7, the fluidized bed broken up, so that a strongly pronounced fountain is created, which transports the sprayed, moist granules in a straight line upwards, until they have reached their respective final climbing height. After reversing direction at the vertex the granules now fall against the upward stream of hot air on the outside Scope of the apparatus back into the fluidized bed, with it already at this point must be dried to such an extent that they come into contact with other granules do not clump together. The air cooled by the absorption of water vapor leaves the apparatus Dust is removed from the filter 10 via the suction spiral 9 and blown out via the fan 11. In order to prevent the smallest grains of granulate, which rise very high with the current, are carried out, there is a centrifugal force principle in the upper part of the device Acting diverter classifier 8.

Just above the conical sieve bottom 6 is located at one point the circumference a discharge chute 12, from which each part of the falling back Granulate flow through a cell lock on the sieving machine 13 with the sieve mesh size the grain size of the finished product is conveyed. The sieve overflow 14 is a finished product and is discharged, the sieve passage is either directly via conveying line 15 returned to the fluidized bed, or over Delivery line 16 to the collecting container 17 directed when the fluidized bed mass grows above a predetermined size. Falls the fluidized bed material below this size is temporarily stored with the aid of the metering device 18 Granules are withdrawn from the collecting container 17 and transferred to the fluidized bed via the conveying line 15 supplied again until it has reached its specified size. Through regulated discharge and regulated supply of granules that still match the grain size of the finished product have not reached, the mass of the material forming the fluidized bed is therefore temporal kept constant.

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Claims (4)

relating to a method for continuously producing a solid granule ats claims 1. Process for the continuous production of solid granules by drying and simultaneous granulating in a fluidized bed, the granulating to be Solid in the form of a solution or suspension in the pre-granulated solid existing fluidized by an introduced drying gas of a suitable temperature Good bed sprayed, a corresponding amount of granules discharged from the good bed and separately therefrom, the drying gas is withdrawn together with the resulting water vapor is, as a result, that the amount is kept constant over time of the solid introduced as a solution or suspension is the mass of the fluidized bed forming goods through regulated discharge or regulated supply of granulate grains, which have not yet reached the grain size of the finished product, constant over time is held. 2. The method according to claim 1, characterized in that g e k e n n z e i c h -n e t that the granules discharged from the fluidized bed after separation of the finished product be stored in a collecting container, from which the regulated Zafuhr granules serving to the fluidized bed are removed again. 3. The method according to claim 1 or 2, characterized in that g e k e n n -z e i c This means that some of the granules discharged from the fluidized bed are comminuted and then reintroduced into the fluidized bed as germs. 4. The method according to any one of claims 1 to 3, characterized in that g e -k e n n z e i c h n e t that as a measured variable to determine the rise or fall of the the material mass forming the fluidized bed is the pressure drop across the fluidized bed of the drying gas is used.