A METHOD AND A MEANS FOR CONTINUOUS, STATIC MIXING OF THIN LAYERS

Abstract: A method and a means for controlling the volume or quantity of components being fed into a continuous, static mixing head are based upon the phenomenon of concentric, thin layers meeting with high velocities in a circular and free-flowing mixing zone (14). The regulating method can be adapted to various embodiments of mixing heads, and can be used for raw material combinations comprising powders, liquids, gas, vapour or air, as well as a small quantity into a large quantity. The thin layers are formed and controlled in conical, annular nozzles between fixed cone surfaces (12, 25, 27) and axially movable cone surfaces (11, 28, 29) where the movements are transferred from displacement members (15, 34) on the outside of the mixing head which regulate nozzle orifices and amounts or volumes. The drawing shows a situation with regulating a mixing head where a downward directed powder layer in the mixing zone meets with obliquely downward directed liquid layers from the inside and the outside. In the mixing zone, mixing and discharge occurs instantaneously. There is disclosed a mixing process for cement related products, using three mixing heads connected in series, with different products after each respective step. The mixing heads in accordance with the invention are compact. For example, capacities of up to 150 m<3>/hour can be achieved with a mixing zone diameter smaller than 200 mm.

Description: A METHOD AND A MEANS FOR CONTINUOUS, STATIC MIXING OF THIN LAYERS The present invention relates to a method and a means for controlling the amounts (quantities; volumes; proportions) of components being fed into a continuous, static mixer of the thin layer type. Said means controls directly the slit of the annular nozzles which convert the component flows into thin layers in the mixing apparatus, so as to be able to control the layer thicknesses and hence the through-put quantity. Continuous static mixing is generally characterized by the feature that the components are fed continuously and at a high speed into a mixing apparatus without moving parts, where only the kinetic energy is used for mixing. This in contrast to a batch mixing process with charge feeding, and where mixing is effected by means of agitators or overturning the compoun . Today, mixing processes are part of almost all process industry. In order to save energy, investments, labour, etc. there is an increasing tendency to avoid batch mixing and turn to a continuous mixing procedure. The present method and control means increases the range of use for thin layer mixing, so that this mixing system will be used increasingly with raw material combinations like: powder/powder, powder/liquid, liquid/liquid and powder or liquid/gas, vapour or air and in special cases: large quantity/small quantity. In continuous, static thin layer mixing, the mixing process takes place inside a mixing head where preferably a fluidized powder component or suspension is fed in axially from above, and where a liquid or gas component has a radial inlet. The raw materials are subject to a moderate excess pressure before being led through off/on valves into the mixing head nozzles where static pressure is converted to kinetic energy. Thin layers are formed by the axial component flow out of the nozzle when the flow is spread out on an underlying cone surface while thin layers of the radially introduced component are formed in annular nozzles. When the thin layers meet in a freely flowing circular mixing zone, an instantaneous mixing effect is achieved with an instantaneous further transport of the mixed product out of the mixing zone. The best mixing result is achieved in a mixing zone where a downwards directed layer of axially introduced raw material meets one layer from the outside and one layer from the inside, both containing the radially introduced raw material. This means that the radial raw material flow is distributed to an annular nozzle on the outside and an annular nozzle on the inside of the mixing zone. So far, the thin layer mixing method has not gained any substantial ground. This is due to the fact that this method has not included an effective method and means for adjusting the amount of raw material before the mixing process is started, nor a possibility to be able to adjust the quantities during mixing. With normal pressure/quantity control valves in front of the mixing head, it will certainly be possible to regulate quantities, however then the exit velocity from the nozzles will be different with unchanged nozzle cross section. Besides, the available pressure convertible to velocity in the nozzle, will be reduced in said valve system. In the present invention, quantity control takes place in the annular nozzles in such a manner that the exit velocity is maintained approximately constant even if the through-put amount is regulated. In accordance with the construction, quantities are regulated by means of movable nozzle surfaces inside the mixing head, and by transferring the movements to operating elements on the outside of the mixing head. By pre- adjusting the operating elements, the proportions can be determined before start of the mixing process, and furthermore, adjustment can be executed during the mixing procedure. Normally, also each separate raw material supply will be provided with its respective outside off/on valve. These valves will in this system preferably be used for starting/ stopping the mixing process. The above mentioned advantages of this quantity regulating method are achieved by the feature that the nozzles have one fixed and one coaxially movable cone surface. By displacing axially the movable cone surfaces in relation to the fixed ones by means of e.g. threaded joints, the circular nozzle orifices are changed. Thereby the thickness of the layers flowing out, and hence the amounts are changed. This means that with a constant pressure drop through the nozzle and a constant exit velocity the mixing ratio can be regulated. With said threaded joint a certain angular setting will correspond to a certain nozzle orifice. It will be possible to read the associated quantity on scales on the outside of the mixing head. For industrial use the quantity determination of the components is more difficult in a continuous process than in batch processes where exact weighing is undertaken for each raw material. In a continuous mixing process there are continuous measuring methods for the raw materials before mixing, however these methods do not provide the desired accuracy and practical usefulness. Therefore, in the present mixing method the direct control in accordance with the invention is an alternative or a supplement in a continuous mixing process. One regulating problem in other continuous mixing processes is a correct mixing ratio in the start/stop phases. In contrast, the present mixing and regulating method comprising short and approximately the same run-through time for the raw materials as w'ell as instantaneous mixing, which features are combined with pre-adjustment of the mixing ratio, provides correct mixing conditions also when starting/ stopping. The method and control means in accordance with the invention appear from the drawings which together with the description refer to a mixing head in two embodiments, particularly for mixing of powder/liquid: Fig. 1 shows a section through a mixing head with supply to an inner liquid nozzle through pipe ribs laid through the outflowing finished mixture. Fig. 2 shows a section through a mixing head with supply to the inner liquid nozzle through pipe ribs laid through the inflowing powder. Fig. 3 shows schematically a mixing process comprising several mixing heads. Fig. 1 represents a view of the lower part of exit funnel 2 in a pressure hopper containing fluidized powder 1, which lower part opens for axial powder introduction to the mixing head when an on/off valve 3 is opened. Correspondingly, the on/off valve 23 simultaneously opens for radial introduction of a liquid component 21 which is subject to a corresponding pressure. The main part of the mixing head is a housing 4 with internal nozzles and distribution channels. The upper part 5 of the house has an inwardly directed, radial rib system 6 with a hold for central member 7. Concentrically and externally thereto is an axially sliding control member 8. Members 7 and 8 constitute at the top the powder nozzle with fixed cone surface 10 and an adjustable cone surface 11. Member 8 has on its outside a cylindrical upper surface in sliding engagement with the inner surface of part 5. The outer lower surface of member 8 has external threads 9 in engagement with the threads of housing 4. Beneath the nozzle member 7 has a spreading surface 12 where the thin layer is formed. Quantity control takes place where the cone surface 11 by an axial displacement regulates layer thickness against the spreading surface 12 where the layer has its greatest thickness, so that lumps as large as possible may pass. The cone surface 13 has a clearance volume toward the powder layer which provides a possibility for ventilating or introducing a third raw material by means of hole 17 in member 8. At the lower end of cone surface 12 where the powder layer has reached its smallest thickness, the layer is directed downwards when meeting with cone surface 13 prior to entering the mixing zone 14. The radially introduced amount of liquid 21 is led into the house 4 and to an annular chamber 24 wherefrom half the amount exits through an inwardly directed annular nozzle with a fixed cone surface 25. The rest of the liquid passes from the annular chamber through a number of radially inwardly directed pipe ribs 26 to a central distribution chamber 32 with an outwardly directed annular nozzle with a fixed cone surface 27. The thin layers from the outer and inner annular nozzles hit the downwardly directed powder layer both from an outward and inward direction in the mixing zone 14. The pipe ribs also connect member 30 to member 31, forming a slab where a rotation of threads 33 regulates the nozzle orifices in parallel between the fixed cone surfaces 25 and 27 and the adjustable cone surfaces 28 and 29. The finished mixture from the mixing zone passes through the openings between the pipe ribs. The slab is rotated by means of handle 34 with a pointer 35 against a fixed scale which indicates layer thickness and quantity from given operation conditions. Correspondingly, the powder amount is controlled by means of handle 15 with a pointer 16 againt corresponding scales. When operating by means of a remote control, cylinders, step motors or similar well known components are used. In fig. 2 a corresponding regulating scheme is shown for a mixing head for a sticky mix product. In this case the pipe ribs have been placed above the powder nozzles, and a rib system 48 which is as thin as possible, is used after the mixing zone. In such a manner larger exit openings are achieved for the mixed product, as well as an improved self- cleaning of the ribs. The mixing head has a split inlet pipe 43, with half the liquid supply to annular channel 44 and further on through pipe ribs 45 to member 46 which has a central pipe connection to the inner annular nozzle 47. The rest of the amount of liquid introduced passes directly to the outer annular nozzle 49. Control of powder amount and liquid amount is effected in the same manner as in fig. 1, by varying the layer thicknesses between the fixed and the adjustable cone surfaces of the three nozzles. In fig. 3 there is shown, in a schematical fashion, a process solution constructed of serveral mixing heads in a series configuration. A tangible example is a manufacturing process for cement related products where each step actually delivers a ready-made product, but where this product also may enter successive steps as a raw material. For steps I, II and III the sketch shows associated mixing heads where: Al indicates cement with optional additives. βl II II II II Cl, Dl and B2 indicate cement slurry for respectively molding purposes in oil drilling, building and construction and as a raw material for step II. A2 and A3 indicate sand and gravel of various grading. C2, D2 and B3 indicate respectively plaster cement, spray concrete and a raw material for step III. C3 indicates pre-mixed concrete with C4 as finished concrete after additional mixing in e.g. screw/pump equipment. RA1, RBI - RA3, RB3 indicate means for controlling or regulating of quantity. Optionally also the shown intermediate containers, pressure pumps and pipe/hose transport means are included. A method and regulating means following the same principles will also apply to special embodiments of mixing heads where more than two raw materials are introduced into the same mixing head. Such extra raw materials will preferably be based upon unilateral introduction into existing layers in order not to make the mixing head too complex. Finally some data from finished mixing heads with regulating means in accordance with the invention: Pressure range for incoming raw materials for powders and liquids 1-3 Bar, which corresponds to thin layer velocities of 10-15 m/s. Thickness of powder layer 1-3 mm and liquid layer 0,1-1 mm. The mixing head capacity will be a product of velocity, layer thickness and mixing zone circumference. For a selected mixing zone diameter of about 30-200 mm it is possible to obtain capacities in the range 5-150 m 3 /hour.

Claims: P A T E N T C L A I M S 1. A method for controlling the amount of the respective components (1, 21) of liquid and/or powdery and/or gaseous material being fed through a static mixing head, where thin coaxial layers of the components are formed in coaxial annular nozzles and brought together in a common circular mixing zone (14) , the number of components being at least two, c h a r a c t e r i z e d i n that the thickness of the layers and thereby the amount passing through the nozzles are controlled by varying the nozzle orifices, the variation of the orifices being transferred from displacement mechanisms on the outside of the mixing head. 2. A method in accordance with claim 1, where at least one of the coaxial annular nozzles has a fixed inner cone surface (10, 12, 25, 27) and a movable outer cone surface (11, 28, 29), c h a r a c t e r i z e d i n that the movable outer cone surface (11, 28, 29) is displaced axially to control the nozzle orifice. 3. A method in accordance with claim 2, c h a r a c t e r i z e d i n that the movable outer cone surface (11, 28, 29) is displaced by operating a coaxial threaded joint (9, 33) or a movable and coaxial, telescopic or similar system for providing movement in relation to a fixed part of the mixing head, optionally by remote controlled operation with mechanical, electric, pneumatic or hydraulic transfer to operating members (15, 34) on the mixing head. 4. A method in accordance with claim 2 or 3, c h a r a c t e r i z e d b y simultaneous control of at least two nozzles, the movable nozzle surfaces belonging to nozzle parts (31) connected by pipes (26) or ribs (48) between which pipes or ribs the finished mixture passes, said pipes (26) optionally being used for rigid connection between said nozzle parts (31) and material transport of components between the co-controlled nozzles, and said ribs (48) optionally being used for rigid connection between said nozzle parts when the material transport of components to co-controlled nozzles takes place via fixed, separate piping connections. 5. A means for controlling the amount of the respective components (1, 21) of liquid and/or powdery material being fed through a static mixing head, where thin coaxial layers of components (l, 21) are formed in coaxial annular nozzles and brought together in a common circular mixing zone (14) , c h a r a c t e r i z e d i n that the orifices of the nozzles are controllable, and that displacement mechanisms are provided on the outside of the mixing head for by operation thereof causing variation of the orifices and thereby control of the thickness of the layers. 6. A means in accordance with claim 5, c h a r a c t e r i z e d i n that at least one of the coaxial annular nozzles has a fixed inner cone surface (10, 12, 25, 27) and a movable outer cone surface (11, 28, 29), said movable outer cone surface (11, 28, 29) being axially and adjustably shiftable so that the nozzle orifice can be controlled. 7. A means in accordance with claim 6, c h a r a c t e r i z e d i n that the movable outer cone surface (11, 28, 29) is adjustably shiftable through a coaxial threaded joint (9, 33) or through a movable and coaxial telescopic or similar system for providing movement in relation to a fixed part of the mixing head, there being optionally provided remote control means for operating the shifting mechanisms, with mechanical, electric, pneumatic or hydraulic transmission line to operating members (15, 24) on the mixing head. 8. A means in accordance with claim 6 or 7, c h a r a c t e r i z e d i n that the movable nozzle surfaces of at least two of said nozzles belong to parts connected by pipes (26) or ribs (48) between which pipes or ribs the finished mixture passes. 9. A means in accordance with one of claims 5-8, c h a r a c t e r i z e d i n that the mixing head comprises a number N > 2 coaxial and adjustable annular nozzles as well as associated control means therefor, for mixing N components. 10. Use of one or several mixing heads in accordance with one of claims 5-9, as elements in a process plant, optionally in combination with some other set of apparatus.

Inventors: HIORTH HANS, HIORTH, HANS
Applicants: HIORTH HANS, HIORTH, HANS
Application year: 1992
Main classification: B01F3
IPC codes: B01F5