Mixing and processing apparatus

Abstract

A rotating drum apparatus for the mixing and processing of materials, the rotating drum apparatus comprising: a rotating drum (12) arranged with the length of the drum and the axis of rotation of the drum extending along the horizontal; an inlet at a first point on the drum (12) for receiving materials prior to mixing and/or processing; a screw (14) within the drum (12) for mixing the materials whilst conveying them lengthwise along the drum (12), wherein the screw (14) includes a helical blade extending along the length of the drum (12) with the outer edge of the helical blade being fixed to the inner surface of the drum (12) such that material can be conveyed and mixed in separated volumes (16) between each turn of the screw blade (14); an outlet at a second point along the drum for discharge of materials after mixing and/or processing; and a plurality mixing devices (18) for promoting mixing of the material in each of the separated volumes (16) of material as the material is conveyed along the screw (14), wherein the plurality of mixing devices (18) are spaced apart along the blade of the screw (14), and wherein there is at least one mixing device (18) for each turn of the screw blade (14).

Claims

1. A rotating drum apparatus for the mixing and processing of materials, the rotating drum apparatus comprising: a rotating drum arranged with a length of the drum and an axis of rotation of the drum extending horizontally; an inlet at a first point on the drum for receiving materials prior to mixing and/or processing; a screw within the drum for mixing the materials while conveying the materials lengthwise along the drum, wherein the screw includes a helical blade extending along the length of the drum with an outer edge of the helical blade being fixed to an inner surface of the drum such that the materials can be conveyed and mixed in separated volumes between each 360 degree turn of the helical blade of the screw; an outlet at a second point along the drum for discharge of the materials after mixing and/or processing of the materials; and a plurality of mixing devices for promoting mixing of the materials in each of the separated volumes of the materials as the materials are conveyed along the screw, wherein mixing devices of the plurality of mixing devices are spaced apart along the helical blade of the screw, wherein at least one mixing device of the plurality of mixing devices is provided for each 360 degree turn of the helical blade of the screw, and wherein the mixing devices comprise fluid inlets for the addition of fluid to the mixture within each volume between 360 degree turns of the helical blade of the screw.

2. The rotating drum apparatus as claimed in claim 1, comprising multiple mixing devices for each 360 degree turn of the helical blade of the screw.

3. The rotating drum apparatus as claimed claim 1, wherein the plurality of mixing devices comprises mixing vanes spaced apart along the screw with multiple vanes for each 360 degree turn of the helical blade of the screw, the mixing vanes being arranged to promote mixing of the materials in the rotating drum.

4. The rotating drum apparatus as claimed in claim 3, comprising at least one of the following features (a) or (b): (a) the mixing vanes comprise an element mounted to the helical blade of the screw with a ramp surface having a greater angle of attack than a surface of the helical blade of the screw, or (b) the mixing vanes are mounted at an outer part of the surface of the helical blade of the screw adjacent to the inner surface of the drum and extend from the inner surface of the drum along the surface of the helical blade of the screw toward the axis of rotation of the drum.

5. The rotating drum apparatus as claimed in claim 3, wherein a height of the mixing vanes is at least 20% of a height of the helical blade of the screw.

6. The rotating drum apparatus as claimed in claim 1, wherein the mixing devices comprise fluid inlets opening into the drum at a trailing edge of the mixing vanes.

7. The rotating drum apparatus as claimed in claim 1, wherein the fluids introduced by the fluid inlets are at an elevated or lowered temperature compared to the temperature of the materials within the drum.

8. The rotating drum apparatus as claimed in claim 1, comprising fluid flow control devices for controlling the rate of flow of fluid through the fluid inlets.

9. The rotating drum apparatus as claimed in claim 8, comprising a controller arranged to permit flow through fluid inlets that are immersed within the material that is being mixed, and to prevent flow when the fluid inlets are not within the material that is being mixed.

10. The rotating drum apparatus as claimed in claim 9, wherein the controller comprises switching devices located adjacent to an expected level of the materials within the drum, such that individual fluid inlets are activated and deactivated in accordance with the state of the switching devices as the switching devices cause the materials to enter into or exit from the material at a base of the drum.

11. The rotating drum apparatus as claimed in claim 1, wherein the helical blade of the screw has a change in pitch between the inlet and the outlet.

12. The rotating drum apparatus as claimed in claim 1, further comprising one of the following features (i) or (ii): (i) the separated volumes formed between adjacent turns of the helical blade of the screw are open to a hole at a center of the drum, or (ii) the separated volumes formed between adjacent turns of the helical blade of the screw are closed by a cylindrical body along the center of the drum and that is fixed to an inner edge of the helical blade of the screw.

13. The rotating drum apparatus as claimed in claim 1, wherein the drum and/or the helical blade of the screw are provided with outlet features during a final turn of the helical blade of the screw in order to provide a more even flow rate from the outlet of the drum, wherein the outlet features include holes in the wall of the drum and/or holes in the surface of the helical blade of the screw during the final turn of the helical blade of the screw.

14. The rotating drum apparatus as claimed in claim 13, wherein holes are provided with openings through the final turn of the helical blade of the screw in order to provide for fluid communication between (i) a separated volume formed between the final turn and a penultimate turn of the helical blade of the screw and (ii) an outlet end of the rotating drum.

15. The rotating drum apparatus as claimed in claim 13, wherein a total area of holes is sufficient to allow for all of the materials within the separated volume formed between the final turn and a penultimate turn of the screw to flow out toward the outlet end of the drum through the final turn of the helical blade of the screw during one turn of the drum.

16. The rotating drum apparatus as claimed in claim 13, further comprising at least one of the following features (a) to (c): (a) a total area of the holes beneath the expected level of materials in the drum is in the range of 40-200 cm.sup.2; (b) a total area of all of the holes is 180-850 cm.sup.2 with the holes spaced about a circumference of the final turn of the helical blade of the screw; or (c) the holes are of adjustable size.

17. The rotating drum apparatus as claimed in claim 1, further comprising at least one of the following features (a) or (b): (a) a diameter of the drum is at least 2 m, or (b) the length of the drum between the inlet and the outlet is at least 3 m.

18. An enzymatic processing plant configured for hydrolysis of protein, triglycerides, cellulose, or chitin, the processing plant comprising a rotating drum apparatus as claimed in claim 1.

19. An enzymatic processing plant configured for enzymatic processing of organic molecules, the enzymatic processing plant comprising: at least one enzymatic processing area that comprises a rotating drum apparatus as claimed in claim 1 configured to mix a reaction mixture flowing through the enzymatic processing area, wherein the enzymatic processing plant and the enzymatic processing area are arranged such that the reaction mixture is subjected to turbulence and/or mixing within the enzymatic processing area of the rotating drum for a reaction time of at least 15 minutes.

20. A kit of parts for making an enzymatic processing plant for enzymatic processing of organic compounds in a reaction mixture, the kit of parts comprising: a pump for pumping the reaction mixture through the enzymatic processing plant; a first enzymatic processing area for performing a first stage of enzymatic processing; and a separator system comprising a decanter for separating a flow of water soluble components, oil-soluble components and solid components; and the kit of parts further comprising one or more of: a filter; a second enzymatic processing area; a third enzymatic processing area; a flow division stage; a flow combining stage; an injection point; a mixing chamber; a heat inactivation stage; a polisher; and a drier; wherein at least one enzymatic processing area of the first, second, and third enzymatic processing areas comprises a rotating drum apparatus as claimed in claim 1.

21. A method of mixing and/or processing materials, the method comprising: feeding materials requiring mixing and/or processing into a rotating drum apparatus as claimed in claim 1 via an inlet at a first point on the drum; rotating the drum and thereby mixing the materials while conveying the materials lengthwise along the drum using a screw within the drum, wherein the screw includes a helical blade extending along the length of the drum with an outer edge of the helical blade being fixed to an inner surface of the drum such that the materials can be conveyed and mixed in separated volumes between each 360 degree turn of the helical blade of the screw; and discharging materials after mixing and/or processing from an outlet at a second point along the drum.

22. A method of manufacturing a modular enzymatic processing plant for enzymatic processing of a reaction mixture, the method comprising determining a required enzymatic processing process and manufacturing a suitable enzymatic processing plant from a kit of modular parts by providing: a pump for pumping the reaction mixture through the enzymatic processing plant; a first enzymatic processing area for performing a first stage of enzymatic processing, the first enzymatic processing area including a rotating drum apparatus as claimed in claim 1; and a separator system comprising a decanter for separating a flow of water soluble components, oil-soluble components and solid components.

Description

(1) Certain preferred embodiments will now be described in greater detail by way of example only with reference to the drawings, in which:

(2) FIG. 1A shows a part of a corrugated turbulence-generating pipe;

(3) FIG. 1B shows a part of a helical turbulence-generating pipe;

(4) FIG. 1C shows a part of a turbulence-generating pipe having bends;

(5) FIG. 1D shows a part of a turbulence-generating pipe having a changing cross-sectional shape;

(6) FIG. 1E is a cross-sectional view of a pipe with a helical corrugation pattern;

(7) FIG. 2 shows the parameters of depth and width for a corrugated pipe;

(8) FIG. 3 shows a modular plant for enzymatic processing;

(9) FIG. 4 illustrates a drum for rotation to mix material within the drum and convey the mixture along the length of the drum;

(10) FIG. 5 shows a screw blade with mixing devices as used in the drum of FIG. 4;

(11) FIG. 6 is a close up view of a part of the screw blade of FIG. 5; and

(12) FIG. 7 is a further close up of a part of FIG. 6.

(13) FIG. 1A shows a part of a corrugated turbulence-generating pipe. The pipe has a diameter of about 60 mm, corrugation depth e of about 6 mm, and p/e of about 13. In such a pipe, turbulence occurs at Reynolds number above approximately 800.

(14) FIG. 1B shows a part of a helical turbulence-generating pipe. The pipe has a diameter of about 60 mm. The pitch of the helical centre-line is 20 mm, and the radius of curvature of the helical centre-line is 1.5 mm.

(15) FIG. 1C shows a part of a turbulence-generating pipe having bends. The pipe has a cross-section that is square with sides of about 60 mm. The bends are at an angle in the range of 15° to 30°

(16) FIG. 1D shows a part of a turbulence-generating pipe having a changing cross-sectional shape. The pipe changes from a circular cross-section to an elliptical cross-section. The cross-sectional area is about 2800 mm.sup.2.

(17) FIG. 1E is a cross-sectional view of a pipe with a helical corrugation pattern, the helix having a single start.

(18) FIG. 2 shows the pitch (width) p and depth e of corrugations on a corrugated pipe.

(19) FIG. 3 shows a modular plant for enzymatic processing of organic molecules. In this case, the plant is for hydrolysis of protein in a protein-lipid mixture. The use of the plant for hydrolysis is exemplary and not limiting on the invention; it will be apparent that a similar apparatus could be used for any multi-stage enzymatic process. Further, in this case, the raw material processed by the system is fish. However, the use of the plant for processing fish is exemplary and not limiting on the invention; it will be apparent that a similar apparatus could be used with a different raw material. Further examples of processes making use of the proposed device are set out below. It should further be noted that although use of the rotating drum of FIGS. 4 to 7 within the plant of FIG. 3 is an advantageous use, the rotating drum may also be used for other types of processing as described earlier.

(20) The particular enzyme (and hence reaction conditions) used in each stage will depend on the raw material and the products to be obtained, and can be chosen accordingly.

(21) The plant of FIG. 3 may use only the rotating drum of FIGS. 4 to 7 as the apparatus for carrying out the various hydrolysis stages. Alternatively the turbulence generating pipe may be used. The rotating drum could instead or additionally be used as the mixing chamber for pre-mixing of the materials, either prior to hydrolysis in another rotating drum, or prior to hydrolysis in a turbulence generating pipe (or indeed hydrolysis in any known hydrolysis apparatus).

(22) The plant in one example comprises a rotating drum as described below for pre-mixing the reaction mixture prior to injection into the first hydrolysis stage. Aside from an input for receiving the raw materials and an output for connection to the next section of the hydrolysis plant, the mixing chamber is sealed and preferably has an oxygen depleted headspace, for example an atmosphere of an inert gas such as nitrogen gas, so as to reduce the amount of oxygen which is brought into contact with the reaction mixture. This reduces oxidation of oils present in the feedstock. The rotating drum is heated by a heat exchanger, or alternatively the reaction mixture is heated after it exits the rotating drum in order to bring the reaction mixture to a temperature suitable for optimal enzymatic action in the first hydrolysis stage.

(23) The fish material, water, and a protease are mixed and heated in the mixing chamber. After mixing, the reaction mixture is pumped by a pump into the first hydrolysis stage. Here, protein in the reaction mixture is hydrolysed to form high-molecular weight peptides. The first hydrolysis stage is a corrugated pipe having a mean diameter of 46 mm, with a plurality of 180° bends, with radius of curvature of 200 mm.

(24) In the first hydrolysis stage, the reaction mixture has the following properties:

(25) Density μ=1000 kg/m.sup.3

(26) Viscosity ρ=0.02 Ns

(27) Reynolds number Re=800

(28) Mean velocity ν=0.35 m/s

(29) The volume flow rate for a given diameter is given by:

(30) $\begin{array}{cc}\stackrel{.}{V}=\frac{\pi }{4}*D^2*v& \mathrm{Equation}3\end{array}$
For the parameter values given above, this gives a volume flow rate of 2.1 m.sup.3/h. The total length of the first hydrolysis stage is of the order of 1 km, and the processing time is of the order of 1 hour.

(31) Towards the end of the first hydrolysis stage, the corrugated pipe is heated to a temperature hot enough to deactivate (denature) the protease.

(32) The flow from the first hydrolysis stage is pumped using a pump to a separator system. The separator system comprises a three-phase decanter operable to output a flow of oil (lipids, and oil-soluble components), a flow of water-soluble components, and solid components.

(33) The solid components from the separator system (primarily bone) are treated in two separate ways. A portion of the solids is passed to a drier (for example by a conveyor, not shown) and is dried to form fishmeal. The fishmeal is output as a product of the system (useful outputs of the system are shown as shaded arrows). A second portion of the solids is passed (for example by a conveyor, not shown) to a further enzymatic treatment stage for further treatment.

(34) The further enzymatic treatment stage includes an input means for modifying the pH or ionic properties of the reaction mixture to suit the optimal operating conditions of the enzyme (shown as a hatched arrow). The product of the further enzymatic processing is output as a product of the system, after drying in a further drier (not shown).

(35) The oil-soluble components from the separator system are also treated in two separate ways. A portion of the oil-soluble components is passed to a polisher (using a pump, not shown) which cleans the oil. The cleaned oil is separated into component parts using a centrifuge and filter (not shown) and the resultant components are output as products of the system. A second portion of the oil-soluble components is passed to a lipid hydrolysis stage (using a pump, not shown) and is treated with lipases. The lipid hydrolysis stage includes an input means (shown as a hatched arrow) for modifying the pH or ionic properties of the reaction mixture to suit the optimal operating conditions of the lipase. In addition, the input means allows for the introduction of water. This is necessary since lipases are water soluble (not oil-soluble). Thus, for the lipase to act on the lipids, a suspension may be formed, allowing contact between the lipase and lipids. Provision of a turbulence generation pipe which mixes efficiently but minimizes the formation of emulsions is useful in such a process. The option of providing a low-oxygen atmosphere in the headspace is a further advantage. The product of the lipase processing is output as a product of the system.

(36) The water-soluble components from the separator system are also treated in two separate ways. A portion of the high-molecular weight peptide components are filtered out (using a filter, not shown) and are output from the system as a product. The remaining portion is input into a second hydrolysis stage.

(37) The second hydrolysis stage includes an input means (shown as a hatched arrow) for modifying the pH or ionic properties of the reaction mixture to suit the optimal operating conditions of the second protease. The protease hydrolyses high-molecular weight peptide components to form medium-molecular weight peptide components. Towards the end of the second hydrolysis stage, the second hydrolysis stage is heated to a temperature hot enough to deactivate the protease.

(38) From the second hydrolysis stage, a portion of the medium-molecular weight peptide components are filtered out using a filter and are output from the system as a product. The remaining portion is input into a third hydrolysis stage.

(39) The third hydrolysis stage includes an input means for modifying the pH or ionic properties of the reaction mixture to suit the optimal operating conditions of the third protease (shown as a hatched arrow). The protease hydrolyses medium molecular weight peptide components to form low-molecular weight peptide components.

(40) Towards the end of the third hydrolysis stage, the third hydrolysis stage may, if needed, be heated to a temperature hot enough to deactivate (denature) the protease.

(41) From the third hydrolysis stage, the reaction mixture is passed to a separator system, which separates low-molecular weight peptide components from any remaining solids or oil soluble components. Any solid components are passed back to the drier (or the enzymatic bone treatment stage) and any oil components are passed back to the lipid hydrolysis stage (or the polisher). The low-molecular weight peptide components are output from the system.

(42) The skilled person will appreciate that not all of these components are essential, and depending on the raw materials and desired end products, a combination of the elements of this system will be employed. In particular, the rotating drum could be used as an apparatus for handling one or more of the hydrolysis stages as well as for the mixing chamber.

(43) FIGS. 4 to 7 show a rotatable drum that can be used in a rotating drum apparatus for mixing and conveying raw materials, such as for mixing raw materials for hydrolysis as explained above. As can be seen in FIG. 4 the rotatable drum has a cylindrical shape with an outer wall formed as a cylindrical tube 12. A screw blade 14 taking the shape of a helix is provided within the cylindrical tube 12 with the outer edge of the screw blade 14 being fixed to the inner wall of the cylindrical tube 12. This may be done, for example, by welding. It is beneficial to ensure that a watertight seal is formed between the outer edge of the screw blade 14 and the inner wall of the cylindrical tube 12, since this means that multiple chambers 16 can be formed, with a chamber 16 in between each 360 degree turn of the screw blade 14. A plurality of mixing devices 18 are provided on the surface of the screw blade 14 at the outer edge thereof. There are multiple mixing devices 18 for each 360 degree turn of the screw blade 14, and as shown in this example there can be eight for each 360 degree turn of the screw blade 14.

(44) The mixing devices 18 and the screw blade 14 can be seen more clearly in FIG. 5 where the cylindrical tube 12 is removed for clarity. FIG. 5 also shows pipework used to supply fluid to the mixing device 18, including central supply pipes 20 and branch pipes 22 extending to each individual mixing device 18. In this example the material within the rotating drum, which may for example be a mixture of solid and liquid elements forming a slurry or the like, would sit in each chamber 16 between adjacent turns of the screw blade 14 and extend up the screw blade toward the centre of the rotating drum by about 50% of the height of the screw blade 14, for example.

(45) The mixing devices 18 will now be described in greater detail with reference to FIG. 6 and FIG. 7. FIG. 6 shows a part of two turns of the screw blade 14 in enlarged view with one of the mixing devices 18 at the top of the figure shown in partial section view. FIG. 7 shows a close-up of the top of FIG. 6 so that further detail can be seen. Each of the mixing devices 18 comprises a wedge shaped mixing vane and fluid inlets. The mixing vane in this example has a side profile of the shape of a right-angled triangle with one surface of the triangle being coupled to the surface of the screw blade 14, a vertical surface of the triangle extending at right angles from the surface of the screw blade 14 and a ramp surface of the triangle providing the mixing vane surface 18a. The ramp surface of the triangle extends from a leading edge 18b at the narrow point of the triangle to a trailing edge 18c at the apex of the triangle that is furthest from the screw blade 14. The trailing edge of the mixing vane is provided with fluid inlets 24 which convey fluid supplied via the pipes 20 and branch pipes 22 through the mixing device 18 and out of the inlets 24 into the rotating drum.

(46) The processing plant of FIG. 3 and/or the rotating drum of FIGS. 4 to 7 may be used for other processes as well, and provide advantages for any process requiring constant mixing and/or relatively long reaction times. Various possible processes are set out in the examples below:

EXAMPLE

Hydrolysis Process 1

(47) The process uses a corrugated pipe with whole sardines (anchovy) with Alcalase (Novozymes), ground through 6 mm dyes, a raw material/water ratio 50/50 (w/w), which may be mixed using the rotating drum, and a reaction temperature 60° C. Targeted % DH=17 (% DH=number of peptide bonds cleaved/total number of peptide bonds), estimated reaction time 45 minutes based on info from the enzyme manufacturer. The enzyme added is 0.1% (d.Math.w) of raw material (w.Math.w) excluding added water. The plant is operated with a capacity 7 MT per hour, of which 3.5 MT of fish and 3.5 MT of water. The tube length will be 863 m when a corrugated pipe is used for the hydrolysis stage. It will be appreciated that a suitably sized rotating drum with an appropriate speed of rotation might be used as an alternative apparatus for the hydrolysis stage.

(48) Supplementary Information:

(49) In this case no large bone particles are present, and thus the risk of clogging due to sedimentation of hard particles is low. The whole length of the tube is of similar shape and diameter throughout, although viscosity decreases down the line. A boost pump is fitted in ⅓ the length from the inlet as a safety guard towards clogging. The concentration of peptides increases with time as protein hydrolysis goes on. Peptides can act as emulgators, and a key point is to avoid the formation of emulsions along the tube.

(50) Reaction Mixture Properties: Density μ=1000 kg/m.sup.3 Viscosity ρ=25 cP (inlet)

(51) Selected Properties of the Flow: Reynolds number Re=1125 Mean velocity ν=0.32 m/s

(52) Using these parameters gives the diameter D=88 mm. For the parameter values given above, this example has a volume flow rate of 7 m.sup.3/h.

EXAMPLE

Hydrolysis Process 2

(53) This example uses a corrugated pipe with raw material (heads and backbones from salmon or chicken frames) to be hydrolysed using Protamex (Novozymes). The enzyme concentration is 0.1% (d.Math.w) of raw material (w.Math.w). The raw material undergoes grinding through 6 mm dyes, and is mixed in a ratio of raw material/water 50/50 (w/w) optionally via the rotating drum, before being processed at a reaction temperature of 50° C. The targeted degree of hydrolysis % DH=10 (% DH=number of peptide bonds cleaved/total number of peptide bonds), and the estimated reaction time 30 minutes based on information from the enzyme manufacturer. Again, a rotating drum with suitable dimensions and an appropriate rotation speed could be substituted for the corrugated pipe.

(54) Supplementary Information:

(55) In this case where large bone particles are present the optimal configuration of the hydrolysis unit is a first part (⅓) where there is less risk of sedimentation of the bone particles resulting in a clogged tube—due to relative high viscosity. As process runs then the viscosity declines increasing the risk of clogging. Therefore, in this embodiment the hydrolysis unit is constructed by means of three different tube diameters linked together. Optionally there may be a filtering system after mixing in order to remove larger bone particles.

(56) The hydrolysis unit parameters are given below for the pipe inlet, at the mid-length and at the pipe outlet.

(57) Reaction Mixture Properties: Density μ=1000 kg/m.sup.3 Viscosity ρ=33 cP, 25 cP and 20 cP

(58) Selected Properties of the Flow: Reynolds number Re=853, 1415, 1956 Mean velocity ν=0.32 m/s, 0.51 m/s and 0.62 m/s

(59) Using these parameters gives diameters of D=88 mm start, 70 mm in mid-section and 63.2 mm the last part. The total tube length is 866 m, distributed into 192 m first part, 303 m mid part and 371 m last part. There will be a boost pump before section 2 and before section 3. The volume flow rate for this example would be 7 m.sup.3/h.

EXAMPLE

Hydrolysis Process 3

(60) In this case hydrolysate processed from salmon frames and heads by means of Alcalase (Novozymes) is further processed through a secondary hydrolysis using Flavourzyme (Novozymes) which is an exopeptidase/endopeptidase complex specially designed to optimize taste and reduce bitterness. The hydrolysate was diluted to contain 10% dry matter, of which protein is the major part (approx. 90%). The substrate contains virtually no lipids. The reaction time is 20 minutes and the reaction temperature 55° C. The enzyme concentration is 0.1% (d.Math.w) of raw material (w.Math.w).

(61) Supplementary Information:

(62) In this case the substrate is a free-flowing liquid with no particles nor lipids are present, and thus there is no risk of clogging or formation of emulsions. Viscosity is low throughout the process tube, which is of similar construction throughout.

(63) The following exemplary calculation uses values for the parameters which may be typical of a working system:

(64) Reaction Mixture Properties: Density μ=1040 kg/m.sup.3 Viscosity ρ=6.5 cP

(65) Selected Properties of the Flow: Reynolds number Re=1811 Mean velocity ν=0.09 m/s
Using these parameters gives the pipe diameter D=125 mm. The tube length is 109 m. For the parameter values given above, the volume flow rate is 4 m.sup.3/h.

EXAMPLE

Rotating Drum 1

(66) Basic Example Data:

(67) Capacity: Approx 30 m.sup.3 per hour (15 tons raw material and 15 tons of water)

(68) Processing time: 1 hour

(69) Density: 1000 kg/m.sup.3

(70) Drum diameter: 3.5 m

(71) Drum diameter inner opening: 1 meter

(72) Drum length: 11.75 m

(73) Comments: Calculation by means of «Solidworks» show that an outer diameter of 3.5 m, length 11.75 m, inner opening 1 m and 15 cm between liquid level and top of the screw blades—exclusive of the volume of screw blades and mixing vanes—gives a total liquid volume of 30,421 litre.

(74) The incline of the screw is linked to the rotational speed of the drum. High incline gives few “chambers” resulting in a more “batchlike” process. An example configuration (present example) with 750 mm between the vanes with a rotation of ¼ revolution/min gives a periphery speed of 0.0458 m/s.

(75) Nozzles are integrated within each vane as fluid inlets to supply fluid to the rotating drum during mixing. The angled vane propels particles away from the surface of the screw blade, the screw blade continues to rotate and the particles are “launched” from the trailing edge of the vane, whereafter there is turbulent mixing. When the next vane meets the material in the drum the particles in the material would be close to the screw blade again (to be calculated depending on space between screw blade and vane size in each case). By having nozzles along the edge of the vane a very effective mixing is promoted, since the fluid is injected into the zone of turbulent mixing

(76) The vanes in this example could have a height of 500 mm with nozzles mounted 50, 150, 250, 350 and 450 mm from the outer wall of the drum. The maximum height of liquid in the drum will be 1.1 m, but the vane height is 500 mm rather than the full extent of the screw blade or the liquid level since particles will aggregate near the bottom of the rotating drum.

(77) One nozzle typically delivers 10 litre per hour. Having 8 vanes with 5 nozzles each per revolution give a total of (8×15×10)=600 nozzles. Active nozzles (activated when submerged only) will constitute 38% —that is 600×0.38=228 active nozzles a run of one hour.

(78) If we anticipate nozzles ejecting 10 l/hour, which means that the addition of water will be 228×10=2280 l/hour. This gives a volume increase of 7.6% —or increase in liquid level of approximately 6 cm for the chambers at the outlet end of the drum compared to at the inlet end. While this may not be a problem, a steady level could be obtained either by a slight and steady increase of the pitch/angle of attack of the screw blade along the length of the drum or a slight downwards tilt of the drum.

EXAMPLE

Rotating Drum 2

(79) A drum of 2.5 m diameter, 75 cm inner opening and 5.5 m length would have a capacity of 7.13 m.sup.3 (liquid level 10 cm below top of the screw blade, calculated without volume of the screw blade and the vanes). This could be mixed with a screw blade of similar characteristics to that shown in the Figures, but with a reduced number of vanes (for example five vanes for each turn of the screw blade) to allow for an increased mixing volume.

EXAMPLE

Outlet Arrangement for Rotating Drum 1

(80) The first example drum discussed above has a rotational speed of ¼ rotations per minute, that is 240 seconds per revolution. The final chamber has a liquid volume of about 2000 litres. Having an even flow rate out from the drum will make it easier to handle the material from the drum during the next processing steps. In addition, it is an advantage to drain from the bottom of the chamber to avoid separating the liquid from the solid, otherwise all the solid material will be discharged at the end. An even flow rate with a mixture of solid and liquid can be provided by having small holes/openings in the final turn of the screw blade, thereby distributing the discharge flow over the entire revolution of the drum. The openings can be distributed along the entire outer diameter and/or distributed along the blade with different distances from the centre of the drum. To describe this mathematically is quite complex, but it is theoretically possible to obtain a flow out of the drum of less than 12 litre/second.

(81) The openings can be constructed with adjustable sizes, including the possibility to block some of the openings. Having an adjustable total area for the openings allows the flow rate to be adapted for differing volumes of material and/or for differing mixtures of liquid and solid materials. The adjustable openings can be implemented by sliding plates or exchangeable plates connected to the surface of the screw blade.

(82) Calculations based on a variant of Bernouillis equation called Toricellis law, which describes the flow from a tank, can be made to determine the flow rate, with approximations allowing for friction of the liquid/solid material and the design of the outlet, as well as assumptions regarding the effect on the flow rate of the rotation of the drum. To set an opening size that will fully empty the chamber within one revolution then the calculations can be based on emptying during three quarters of a revolution. Fine tuning of the opening time can be done via experiments and/or during first operation, for example by blocking some of the openings if the flow rate is too high.

(83) In this case the calculation shows that it is necessary to have openings under the surface of the material in the drum with a total area of about 72 cm.sup.2. To avoid that hard particles (crab shells, larger sized bones etc.) will clog the openings then they need to have a certain minimum size. In this example we use openings of 25×40 mm, so that each opening has an area of 10 cm.sup.2. This means that about 7 openings are needed under the surface of the material of the drum. Assuming that the material of the drum has a level that is similar to a chord subtending an arc of 60°, and the screw blade is open for 90° of perimeter of the final turn then in total around 32 openings are needed spaced apart over the final 270° of the screw blade. Even if this calculation is very simplified, it shows that due to the low rotational speed only relatively few openings that are relatively small compared to the drum size are needed to empty the last chamber. Thus, such openings can easily be placed and designed in a way resulting in an even and controlled flow rate out of the drum.