Abstract:
The invention relates to a process and an apparatus for the granulation of granulatable and/or pelletizable substances in which the substance to be granulated is introduced in the form of a closed jet into a rapidly flowing refrigerant--preferably liquid nitrogen. This purpose is served by a vertically arranged reaction tube (2) into the upper part of which the jet enters and through which the refrigerant circulates by means of a transport element (7).

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a process for the granulation of granulatable and/or pelletizable substances. 
     In German Application P 43 29 110 of the applicant a process and an apparatus suitable for carrying out the process are described, in which pelletizable liquids are pelletized by being introduced into a waterfall-like stream of a refrigerant. When droplets impact onto the surface of the refrigerant flowing in the manner of a waterfall, the droplets, which preferably have a lower dripping velocity than the flow velocity of the refrigerant, are entrained and thus isolated. Agglomerization of the particles on introduction can thus be prevented. The process is particularly advantageous if small pellets are to be generated, since high throughputs can be achieved with low space requirement. 
     U.S. Pat. No. 4,843,840 shows an apparatus for the production of frozen solid particles in which the liquids to be frozen are transported into a discharge apparatus by a refrigerant through pipes which are adjustable in height at the upper end. 
     By means of the process according to the application P 43 29 110, pellet products can be produced, for the starting materials of which certain boundary conditions must be established with respect to surface tension and viscosity. Thus not all customer requirements can be covered. 
     SUMMARY OF THE INVENTION 
     The object therefore underlying the invention is to provide a process and an apparatus by which granules can be generated substantially independently of the viscosity and surface tension of the starting materials. By means of the process, substances are also to be able to be processed which are not pelletizable and which have a very high solids or particle content. 
     Surprisingly it has now been found that starting materials can be granulated substantially independently of their viscosity and surface tension if they are allowed to enter in a closed jet into the moving volume of a refrigerant. In this case, the jet which is still closed on entry into the, for example, waterfall-like volume stream of the refrigerant is broken up to form granules as a result of the high velocity of the refrigerant stream and the forces occurring as a result. In the course of this as a result of the coldness of the refrigerant, for example liquid nitrogen, the said jet is fixed in its shaping and is frozen out. 
     By means of the process according to the invention, independently of viscosity and surface tension, a much higher throughput can be achieved than in the above-described prior art. As a result of penetration of the jet into a volume, in comparison to impacting on a surface, a significantly greater heat exchange capacity is made available in a small space. Disintegration into granule particles does not occur by atomization at a nozzle sheet but as a result of the refrigerant. Thus complex feed apparatuses such as nozzle sheet plates which, depending on the product to be processed, can even block, can be dispensed with. Cleaning operations are largely dispensed with; rather the product feed apparatus can be cleaned by flushing a wash medium through a feed tube. Change of nozzle when there is change of production is dispensed with, since nozzle sheets specially adapted for the product to be granulated do not need to be used. Solid particles can be introduced without problem with a liquid jet and any liquid which may be pumped can he processed. By means of the process according to the invention, instant granules of foods can also be produced which would not be acceptable to the consumer in pellet form. A process has thus been created which also satisfies optical product requirements. A further advantage of the process according to the invention is that pasty, pumpable and extrudable masses and substances having a particle or very high solids content and non-pelletizable substances such as piece goods can also be processed to form granules with high production throughput. 
     THE DRAWING 
     Two exemplary embodiments of the invention are described with reference to the accompanying drawings. 
    
    
     In the drawings: 
     FIG. 1 shows an apparatus for carrying out the process according to the invention in diagrammatic form. 
     FIG. 2 shows a modification of the apparatus in FIG. 1. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 shows an apparatus in which a reaction tube 2 is situated in an insulated vessel 1. The reaction tube 2 is vertically arranged and at the lower end converts laterally into a transport tube 3 which opens out by its upper end into a separation apparatus 4. The separation apparatus is essentially composed of a ribbon screw 5 having screen holes. Below the ribbon screw 5 is situated a discharge channel 6 which opens out into the reaction tube 2. At the bottom of the reaction tube 2 is situated a transport element 7, for example a propeller screw, which is driven via a motor 8. Above the reaction tube 2 is situated a product entry 9 having a feed pump 10. In the insulated vessel 1 is situated a liquid nitrogen bath 11. The filling height of the bath can be controlled by a level controller 12 and a liquid nitrogen feed 13. The liquid nitrogen bath 11 is connected via orifices 14 to the interior of the reaction tube 2 so that the interior of the reaction tube is supplied with liquid nitrogen. 
     FIG. 2 shows an apparatus in which control of the amount of refrigerant in the reaction tube 2 and thus in the refrigerant circulation is ensured by a compensation vessel 15 having a connection 16 to the reaction tube 2. The compensation vessel has a level controller 12 and a liquid nitrogen feed 13. The filling of the reaction tube 2 results from the level controller 12 in combination with various crosssections of the orifice 14 of the connection 16. The crosssection can be varied by various inserts. The granulated product is transported into a collection vessel 17. The separation apparatus used in this embodiment is a conveyor screw 18 having a screen drum 19. 
     In operation, the product to be processed, for example a pasty mass, such as bread starter, is then transported by a monopump 10 through the product entry 9 in the form of a closed jet into the reaction tube 2. By pressurizing the jet, high feed rates are possible. The liquid nitrogen situated in the reaction tube 2 is agitated by the propeller in such a way that a flow directed downwards with high velocity of the liquefied gas is formed which is led off through the transport tube 3 into the separation apparatus 4. The liquid nitrogen can flow to the discharge channel 6 Through the screen holes of the ribbon screw 5 or the screen drum 19 of the conveyor screw 18. This arrangement recirculates the liquid nitrogen back to the reaction tube 2. The bread starter introduced in a closed jet according to the invention is broken up into granule particles as a result of the turbulences and the high velocity of the liquid nitrogen and is frozen by the cold and fixed in shape. The granule particles thus formed are introduced by this flow through the transport tube 3 into the ribbon screw 5 or into the conveyor screw 18 having the screen drum 19 and transported into the collection vessel 17. The excess liquid nitrogen flows according to the invention through the discharge channel 6 back into the reaction tube 2 and is fed back to the refrigerant circulation. The flow velocity of the liquid nitrogen volume can be varied by the speed of rotation of the propeller. In a preferred use form, the velocity of the moving liquid nitrogen volume is greater than the penetration velocity of the substance to be granulated substance. A refrigerant velocity is preferred which is greater by a factor of 1.5 to 4 than that of the introduced substance to be granulated. If the entry velocity of the substance to be granulated and the flow velocity of the liquid nitrogen are equal, only the turbulences of the refrigerant flow still contribute to the granulation. Thus results which are likewise still useful are achieved at any rate. The filling height of the insulated vessel 1 can be controlled and the interior of the reaction tube 2 is connected via orifices 14 to the insulated vessel 1, or in the embodiment according to FIG. 2 is fed with refrigerant by the compensation vessel 15 through the connection 16. Accordingly at a given flow velocity, over different filling levels, a different flow path length and thus a different residence time can be achieved. The insulated vessel 1 thus functions exactly as a compensation vessel, as does the condensation vessel 15 in FIG. 2, with respect to the amount of refrigerant which is in circulation. Obviously, apart from liquid nitrogen, other refrigerants can also be used. Depending on the production rate, the jet of the product introduced can be made to be as strong as desired. Optionally, a plurality of product jets can also be introduced into the moving liquid volume. In the case of granulation of substances which have pasty properties, the exiting jet has the form of a rope. 
     The moving refrigerant liquid volume must not be orientated with its flow parallel to the direction of the influx or injection of the product to be processed. And arrangement is alternatively practicable in which a refrigerant flow is present at an angle to the inflow direction of the substance to be granulated. Likewise, the substance to be granulated can be introduced into a refrigerant vortex or into a flow which has rotating directional components. 
     Furthermore, by means of the process according to the invention, for example, the following products can also be processed to give granules: 
     biological solutions containing living microorganisms 
     starter cultures (solutions having an approx. 20% solids content) 
     egg yolk (approx. 30% solids) 
     protein 
     whole egg 
     sewage sludge for reactivating sedimentation tanks after erroneous introductions (containing solid particles 1-2 mm φ) 
     Bolognaise sauce (minced meat portion) 
     goulash soup (containing meat having an edge length of approx. 1.5 cm) 
     pea soup 
     lentil soup 
     mushroom soup containing sliced mushrooms 
     isopropanol 
     peroxide 
     liquid flavorings 
     fruit pulp 
     fruit preparations 
     extrudable masses, such as thickened bacterial cultures, e.g. yeasts 
     pasty masses of rye flour, water and yeasts, such as bread starter 
     extracts, e.g. cough syrup extract 
     plastic melts which are used for example for producing granules as a support for catalysts 
     coffee concentrate.