GB2070750A - Fluidised-bed drying of loose bulk materials in coarse pieces - Google Patents
Fluidised-bed drying of loose bulk materials in coarse pieces Download PDFInfo
- Publication number
- GB2070750A GB2070750A GB8039780A GB8039780A GB2070750A GB 2070750 A GB2070750 A GB 2070750A GB 8039780 A GB8039780 A GB 8039780A GB 8039780 A GB8039780 A GB 8039780A GB 2070750 A GB2070750 A GB 2070750A
- Authority
- GB
- United Kingdom
- Prior art keywords
- fluidised
- drying
- bed
- coarse pieces
- bulk materials
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Withdrawn
Links
Classifications
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F26—DRYING
- F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
- F26B3/00—Drying solid materials or objects by processes involving the application of heat
- F26B3/02—Drying solid materials or objects by processes involving the application of heat by convection, i.e. heat being conveyed from a heat source to the materials or objects to be dried by a gas or vapour, e.g. air
- F26B3/06—Drying solid materials or objects by processes involving the application of heat by convection, i.e. heat being conveyed from a heat source to the materials or objects to be dried by a gas or vapour, e.g. air the gas or vapour flowing through the materials or objects to be dried
- F26B3/08—Drying solid materials or objects by processes involving the application of heat by convection, i.e. heat being conveyed from a heat source to the materials or objects to be dried by a gas or vapour, e.g. air the gas or vapour flowing through the materials or objects to be dried so as to loosen them, e.g. to form a fluidised bed
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F26—DRYING
- F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
- F26B3/00—Drying solid materials or objects by processes involving the application of heat
- F26B3/02—Drying solid materials or objects by processes involving the application of heat by convection, i.e. heat being conveyed from a heat source to the materials or objects to be dried by a gas or vapour, e.g. air
- F26B3/06—Drying solid materials or objects by processes involving the application of heat by convection, i.e. heat being conveyed from a heat source to the materials or objects to be dried by a gas or vapour, e.g. air the gas or vapour flowing through the materials or objects to be dried
- F26B3/08—Drying solid materials or objects by processes involving the application of heat by convection, i.e. heat being conveyed from a heat source to the materials or objects to be dried by a gas or vapour, e.g. air the gas or vapour flowing through the materials or objects to be dried so as to loosen them, e.g. to form a fluidised bed
- F26B3/092—Drying solid materials or objects by processes involving the application of heat by convection, i.e. heat being conveyed from a heat source to the materials or objects to be dried by a gas or vapour, e.g. air the gas or vapour flowing through the materials or objects to be dried so as to loosen them, e.g. to form a fluidised bed agitating the fluidised bed, e.g. by vibrating or pulsating
- F26B3/0923—Drying solid materials or objects by processes involving the application of heat by convection, i.e. heat being conveyed from a heat source to the materials or objects to be dried by a gas or vapour, e.g. air the gas or vapour flowing through the materials or objects to be dried so as to loosen them, e.g. to form a fluidised bed agitating the fluidised bed, e.g. by vibrating or pulsating by mechanical means, e.g. vibrated plate, stirrer
Landscapes
- Engineering & Computer Science (AREA)
- Life Sciences & Earth Sciences (AREA)
- Microbiology (AREA)
- Mechanical Engineering (AREA)
- General Engineering & Computer Science (AREA)
- Drying Of Solid Materials (AREA)
- Crystals, And After-Treatments Of Crystals (AREA)
Abstract
A method and an apparatus for the fluidised-bed drying of loose bulk materials in coarse pieces, especially products of agriculture and the foodstuffs industry, comprises charging the material in coarse pieces into a fluidised bed, where it is fluidised and superficially pre- dried with application of high drying agent temperatures and speeds, comminuting the material by cutting, discharging from the fluidised bed the loose material in coarse pieces, and finally drying the material above this fluidised bed in a suspension layer, with reduced drying agent speed and temperature. <IMAGE>
Description
SPECIFICATION
Method and apparatus for fluidised-bed drying of loose bulk materials in coarse pieces
The present invention relates to a method and an apparatus for the fluidised-bed drying of soft to medium-hard loose bulk materials in coarse pieces, especially products of agriculture and the foodstuffs industry, the moisture of which is bound predominantly as swelling liquid.
Loose bulk materials in coarse pieces, especially if their moisture is present as swelling liquid, are for various reasons not well adapted for dyring in the fluidised bed. The application of the fluidised-bed technique necessitates, by reason of the physical nature of the moist material, a minimum speed for the flowing medium. The application of high drying agent temperatures mostly leads to irreversible product damage, because sufficient moisture can no longer penetrate from the mass of the material to the surface of the material.
Loose bulk materials having the stated material properties are therefore regarded as typical subjects for long-term drying. If such loose bulk materials are to be dried in a fluidised bed, then by reason of the compulsorily prescribed minimum speed for the flowing medium and of the necessity of reduction of the drying agent temperatures, low efficiency of the drying apparatus and high specific energy consumption occur.
To avoid irreversible damage to thermolabile materials and to reduce the specific energy consumption, various solutions have already become known.
By way of example apparatuses for drying loose bulk materials in coarse pieces in the fluidised bed are known where the inflow floor or the entire drier vibrates vertically or horizontally with a specific amplitude and frequency. Thus the working speed for the drying medium can be reduced and higher drying agent temperatures can be applied. The effective heat flow is not however thereby increased, so that in the final effect no reduction of the drying time occurs. The stated solutions are also extraordinarily expensive as regards apparatus. A uniform final degree of drying for the dried material is achievable only in intermittent operation by reason of the known conditions of time of sojourn in a single-stage fluidised bed.
Methods for drying loose bulk materials in coarse pieces in the fluidised bed are also known where the loose bulk material is intermittently dried and cooled. In this case it is possible to use higher drying agent temperatures and speeds at times. Here the long drying times and the high specific energy requirement as a result of the long times of sojourn are likewise disadvantageous. The known methods work by batches.
The aim of the invention consists in developing a method and an apparatus for tie fluidisedbed drying of loose bulk materials in coarse pieces so that with reduced expense for apparatus and energy consumption an increase of the working productivity and an improvement of the quality of the end product are achievable.
The invention is based upon the problem of producing a method and an apparatus for the fluidised-bed drying of loose bulk materials in coarse pieces by means of which an improvement of effectiveness is achievable by shortening of the drying duration and reduction of the specific energy consumption, while irreversible damage to thermolabile materials is avoided and a uniform degree of drying is guaranteed with a continuous conducting of the method.
In accordance with the invention the problem is solved in that the material in coarse pieces is charged into a fluidised bed, fluidised and superficially pre-dried by the application of high drying agent temperatures and speeds, the superficially pre-dried material is comminuted by cutting, the comminuted material is discharged from the fluidised bed of loose bulk materials in coarse pieces, completely dried to the desired final drying degre above this fluidised bed by the application of reduced drying agent speeds and temperatures in a suspended layer, and the finally dried material is discharged with the waste air current into a material separator. The drying is preferably carried out predominantly as co-current drying.
For carrying out the method in accordance with the invention an apparatus is also provided which comprises, adjoining a cylindrical suspension chamber, a conically narrow fluidised-bed chamber, an inflow floor with an air chest and a comminuting apparatus consisting of a double shaft and at least one two-member, contrarily movable cutting element, the suspension chamber being arranged to open with an overflow into a subsequently placed material separator.
The double shaft and the cutter devices secured thereon are driven contrarily. They then rotate in the fluidised loose bulk material in coarse pieces and comminute the coarse pieces of loose material by cutting. Shear effect is precluded so that a considerably proportion of pulp and fines is avoided which leads to a soiling of the comminuting apparatus and structural damage.
The cutter apparatus can be made with equal or unequal pairs. For example a three-member upper cutter and a two-member lower cutter are possible. The rotation rates for the upper and lower cutters can be equal or different. If work is carried on with an odd-number ratio of upper and lower cutters, then rotation rates in approximate inverse proportion are necessary.
The cutter blades are advantageously arranged at an angle to the radial of up to 40"C. against the direction of movement. Thus the effective cutting performance is increased, the blades run sliding on one another and in self-re-sharpening manner, and the energy for comminution is consumed more uniformly.
To achieve jolt-free cutting work it is further expedient to arrange the cutter blades so that the cutting edges do not pass through the centre of rotation of the cutter apparatus but are tangential thereof. Thus a "shear effect" occurs which prevents the blades from colliding and breaking. Moreover continuous cutting work takes place.
Due to the cutting manner of operation of the comminuting apparatus new surfaces are constantly exposed in structure-preserving manner so that the product moisture no longer has to diffuse from the interior to the surface of the material. Thus the prerequisities for the heat and substance transference are substantially improved, the drying itself is carried out substantially in the first drying section and effective exploitation of the supplied heat and a reduction of the specific heat consumption per kg of evaporated water are achieved.
According to an advantageous form of embodiment the mean speed of revolution of the contrarily rotating cutter elements amounts to 1.0 to 25 m/sec., preferably 6 to 1 5 m/sec.
The drying agent speeds are set so that the loose bulk material in coarse pieces is fluidised in the conical fluidised-bed chamber at speeds of 6 to 1 5 times UKr (critical fluidisation speed of a vibratory fluidised bed), so that the comminuted but substantially still moist small parts are discharged from the fluidised bed of loose material in coarse pieces, eddy above the loose material in coarse pieces and form a graded fluidised bed, remain eddying in the cylindrical suspension chamber until they have reached the desired uniform drying degree and are conveyed by the waste air into the subsequently placed material separator, so that the drying agent and the dried material are situated substantially in co-current.
It is expedient if the inflow floor has a reducing permeability for the drying agent from the centre to the periphery.
The free sieve area for the fluidised-bed floor can lie between 50% and 80%. However it should preferably be above 70%. It is advantageous if the free sieve area lies higher in the middle of the fluidised-bed floor than at the periphery. This favours the comminution work and contributes to pulp-free comminution of the loose materials in coarse pieces.
The invention shortens the paths for the transport of moisture to the surface of the material and effectively avoids irreversible damage to thermolabile goods.
Moreover a selective discharge of the dried goods is achived with regard to uniform degree of drying as far as continuous conducting of the process.
By the avoidance of intermittent operation the specific energy consumption is reduced and the drying duration is shorted.
The expense for apparatus is also reduced.
Example of embodiment
The invention is to be explained in greater detail below by reference to an example of embodiment. In the accompanying drawing:
Figure 1 shows a diagrammatic representation of the apparatus according to the invention;
Figure 2 shows a plan view of the inflow floor.
The apparatus as illustrated in Fig. 1 comprises a conical fluidised-bed chamber 1, a cylindrical suspension chamber 2, an inflow floor 3 with an air chest 4 and a motor-driven comminuting device 5. The comminuting device 5 is formed from a double shaft 6 and contrarily rotating cutter elements 7. The suspension chamber 2 is followed by a material separator 8 with a discharge device 9 for the dried material. The feed of the moist material takes place by way of a conveyor worm 10. The current of drying agent is generated by a fan 11 and conducted through a heat exchanger 1 2.
In Fig. 2 a plan view is shown of an inflow floor 3 with two-member cutter elements 7 in even pairs and free sieve area indicated. By this there is understood the total area of passage cross-sections in the inflow floor 3. The cutting edges of the cutter elements 7 are arranged not extending through the centre of rotation of the hollow shaft 6 but tangential thereto.
The apparatus as described in greater detail in Figs. 1 and 2 permits of solving a plurality of processing problems.
The invention is to be explained by the following example of application in the drying of blanched edible potato squares with an edge length of 8 x 8 x 4 mm. Blanched potato squares form no micro-cracks during drying from which moisture can evaporate from the inner strata.
Rather the surface consists of a glassy skin consisting of gelatinised starch, with a high diffusion resistance. This phenomenon is generally known as cornification.
The most important dimensions of the apparatus as used in the example and as represented diagrammatically in Figs. 1 and 2 are:
Floor area of the inflow floor 0.785 sq.m.
Free sieve area 75%
Diameter of the cylindrical suspension chamber 2.3 m.
Rotation rate of the cutter 250 rpm.
850 kg. of edible potatoes cut into squares and blanched are charged per hour into the apparatus according to the Example. The drying air quantity of 28,000 cu.m/h has a temperature of 1 60 C. In the vicinity of the floor a great turbulence and a relatively low loading prevail. Thus no overloading of the drive motors of the comminuting apparatus occurs. After superficial drying the potatoes are taken and cut to pieces by the comminuting apparatus. The irregularly formed cut granulates are discharged from the fluidised bed and finally dried at about 80"C. above the fluidised bed in a collecting fluidised bed.
In this drying they shrink further with emission of moisture so that under the stated flow conditions after reaching the final degree of drying they are discharged with the waste air current from the apparatus. The dried product is a fine granulate and free from foreign smell and charring. Using the dried edible potato product produced in accordance with the invention it is possible for example with the addition of the usual ingredients to manufacture tasty potato dumplings.
Using the solution in accordance with the invention it is possible to dry a plurality of products of the agricultural and foodstuffs industry, for example potatoes, carrots, peas, beans, celery, kohlrabi, red and white cabbage, apples, sugar beet, beetroot, onions, etc. in a productpreserving manner.
Claims (9)
1. A method for the fluidised-bed drying of soft to medium hard loose bulk materials in coarse pieces, the moisture of which is bound predominantly as swelling liquid, characterised in that the material in coarse pieces is charged into a fluidised bed, fluidised and superficially predried by the application of high-drying agent temperatures and speeds, the superficially predried material is comminuted by cutting, the comminuted material is discharged from the fluidised bed of loose materials in coarse pieces, completely dried to the desired final degree of drying above this fluidised bed by the application of reduced drying agent speeds and temperatures in a suspension layer, and the finally dried material is discharged with the waste air current into a material separator.
2. A method as claimed in claim 1, wherein the drying is carried out predominantly as cocurrent drying.
3. An apparatus for carrying out the method as claimed in claim 1 or 2, wherein it comprises a cylindrical suspension chamber, adjoining this a conically narrowed fluidised-bed chamber, an inflow floor with an air chest and a comminuting device, arranged on the bottom of the fluidised-bed chamber, consisting of a double shaft and at least one two-member contrarily movable cutting element, the suspension chamber being formed to open with an overflow into a subsequently placed material separator.
4. An apparatus as claimed in claim 3, wherein the cutter blades of the cutting elements are arranged contrarily of the direction of movement in each case at an angle up to 40 to the radial.
5. An apparatus as claimed in claim 3 or 4, wherein the cutting edges of the cutting elements are tangential to the centre of rotation of the comminuting apparatus.
6. An apparatus as claimed in claim 3, 4 or 5, wherein the mean speed of revolution of the contrarily rotating cutter elements amounts to 1.0 to 25 m/sec., preferably 6 to 1 5 m/sec.
7. An apparatus as claimed in claim 3, wherein the inflow floor has a reduced permeability for the drying agent from the centre to the periphery.
8. A method for the fluidised-bed drying of soft to medium-hard loose bulk materials in coarse pieces substantially as described.
9. An apparatus for carrying out the method of claim 1, substantially as described with reference to the accompanying drawings.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DD21797679A DD154874A3 (en) | 1979-12-21 | 1979-12-21 | DEVICE FOR DRY LAYER DRYING OF GROOVED WORKS |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| GB2070750A true GB2070750A (en) | 1981-09-09 |
Family
ID=5521866
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB8039780A Withdrawn GB2070750A (en) | 1979-12-21 | 1980-12-11 | Fluidised-bed drying of loose bulk materials in coarse pieces |
Country Status (4)
| Country | Link |
|---|---|
| CS (1) | CS239305B1 (en) |
| DD (1) | DD154874A3 (en) |
| DE (1) | DE3043722A1 (en) |
| GB (1) | GB2070750A (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5580002A (en) * | 1993-08-27 | 1996-12-03 | Bpb Industries Public Limited Company | Method and apparatus for heating and grinding materials |
| CN112696878A (en) * | 2020-12-16 | 2021-04-23 | 浙江丰宇海洋生物制品有限公司 | Fish meal flash drying device |
| CN114308659A (en) * | 2022-01-11 | 2022-04-12 | 中国矿业大学 | Magnetic auxiliary gas-solid interference fluidized bed sorting device |
-
1979
- 1979-12-21 DD DD21797679A patent/DD154874A3/en not_active IP Right Cessation
-
1980
- 1980-11-20 CS CS807948A patent/CS239305B1/en unknown
- 1980-11-20 DE DE19803043722 patent/DE3043722A1/en not_active Withdrawn
- 1980-12-11 GB GB8039780A patent/GB2070750A/en not_active Withdrawn
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5580002A (en) * | 1993-08-27 | 1996-12-03 | Bpb Industries Public Limited Company | Method and apparatus for heating and grinding materials |
| CN112696878A (en) * | 2020-12-16 | 2021-04-23 | 浙江丰宇海洋生物制品有限公司 | Fish meal flash drying device |
| CN114308659A (en) * | 2022-01-11 | 2022-04-12 | 中国矿业大学 | Magnetic auxiliary gas-solid interference fluidized bed sorting device |
| CN114308659B (en) * | 2022-01-11 | 2022-11-29 | 中国矿业大学 | Magnetic auxiliary gas-solid interference fluidized bed sorting device |
Also Published As
| Publication number | Publication date |
|---|---|
| DE3043722A1 (en) | 1981-08-20 |
| CS794880A1 (en) | 1985-05-15 |
| CS239305B1 (en) | 1986-01-16 |
| DD154874A3 (en) | 1982-04-28 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| WAP | Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1) |