WO2003091644A1

WO2003091644A1 - Method and apparatus for drying loose materials in fluidised bed

Info

Publication number: WO2003091644A1
Application number: PCT/LV2003/000004
Authority: WO
Inventors: Anatoly Engelbreht; Mihail Dobrodushin; Oleg Gerdt; Rolands Petersons
Original assignee: Endo Impulss, Sia
Priority date: 2002-04-25
Filing date: 2003-04-25
Publication date: 2003-11-06
Also published as: LV12929B; AU2003224492A1

Abstract

The invention relates to a method and apparatus for drying loose materials, mainly agricultural products, in a fluidised bed. According to the invention, the material is processed simultaneously by two heat carrier flows, by a constant heat carrier flow having a velocity of 0.2-0.5 mps and by a pulsating flow in the form of fluid shock wave with a pulsating frequency of 4-20 Hz and at duration of an impulse of not more than 0.02 sec, at a relative pressure difference between the flows of 1500-2000 Pa, thereby a fluid shock wave being created. Application of the invention provides enlarging the variety of materials, which can be dried, reducing the power inputs and simplifying the construction of drying equipment.

Description

METHOD AND APPARATUS FOR DRYING LOOSE MATERIALS IN

FLUIDISED BED

Description

The present invention relates to drying machinery and can find application in drying agricultural products.

The method for drying medical ascorbic acid is known (Patent RU 2131567, 10.06.1999) according to which a hot air is blown through it in pulsating mode at a frequency of 0.5 - 5.0 Hz, on-off time ratio of 0.5 - 0.7 and a velocity of 0.4 - 0.6 mps, at a temperature in the layer of 60 - 65 °C. However, the batch of humid product should be mixed with a portion of preheated dry product before the drying that complicates the process and makes it impossible to operate in continuous mode.

The process and apparatus for treatment of loose solid materials in pulsed gas fluidised bed is also known (US Patent 5,918,569, 07.06.1999). According to this method, the layer of the treatable material is exposed to two independent pulsating gas flows. One of them has a low velocity, which is sufficient to keep the layer in an "bloated" state, but the other one has a high velocity intended to create the fluidised bed. Both flows are created by the system of valves consisting of two pairs of discs with openings of a shape of circular sector, wherein, in each pair of the discs, one disc is fixed and the other one is movable. The fixed disc forms a clearance either with the movable disc or with a chamber body to provide that a portion of the gas flow is being fed in the gas chamber at the moment of the overlapping of circular sectors. Variation of the rotation speed of valves allows to change the pulsing rate of gas flow within the range of from 1 to 50 Hz. The main limitation of the known method and apparatus consists in the high consumption of heat carrier for creation of two pulsating flows of heat carriers and in complexity of the apparatus for realisation of the process.

The objects of the present invention are reduction of the power inputs b y decreasing the consumption of energy carrier and simplifying the construction of apparatus. The stated objects can be achieved by a method for drying loose materials in a fluidised bed according to the present invention. The method including simultaneous processing the material by two heat carrier flows, is characterised in that the material is processed simultaneously by a constant heat carrier flow having a velocity of 0.2- 0.5 mps and by a pulsating flow with a pulsating frequency of 4-20 Hz which creates fluid shock waves directed along the heat carrier flow, at a relative pressure difference between the flows of 1500-2000 Pa (Claim 1). The stated objects are also achieved in such a way that, in the apparatus for drying loose materials in the fluidised bed comprising sequentially disposed a forcing fan, a heat generator, a chamber with fluid shock wave generator (Claim 9), an aerodynamic chamber disposed above a drying chamber with internal cavities separated by grate having a net, and handling facilities, according to the invention (Claim 13), the internal cavity of aerodynamic chamber is joined with the chamber of the shock wave generator through openings controllable by the chokes, and is joined with an inner cavity of a cylinder of the generator through a rectangular slot having a long axis directed along the cylinder, the slot in the wall of the aerodynamic chamber and the slots on the surface of the cylinder being equal to each other and coincide when being in register during rotation.

The following implementation variants of the method for drying loose materials are provided (Claims 2-8), in which:

the pulsating flow is created by rotating of a straight circular cylinder of an impulse generator, a side wall of the cylinder carrying at least one rectangular slot having a long axis directed along the cylinder, the fluid shock waves being generated only in case the slot located on a surface of the cylinder coincides with the slot of the same geometry and dimensions located in a wall of an aerodynamic chamber; and the constant flow is created by connecting the impulse generator chamber directly with the aerodynamic chamber through the openings, which are uniform by shape and dimensions with each other and are controllable by a choke; the required frequency and duration of impulses are adjusted by varying a rotation speed of said cylinder, and the velocity of the constant flow is controlled by means of the chokes, connecting the inner cavity of the aerodynamic chamber with the chamber of the fluid shock wave generator; the rotation speed of the cylinder and/or the position of the chokes are controlled automatically, according to the measured flow rate and/or the relative pressure difference between the flows; a monitoring of the process and a registration of operating parameters of the apparatus during the whole drying process are carried out simultaneously over a temperature channel, where the temperature of the heat carrier is determined, over a humidity channel, where a humidity of the loose material is determined, over a tachometric channel, where the rotation speed of the cylinder of the fluid shock wave generator is determined, and over a channel of pressure difference, where the pressure difference between the constant and pulsating flows is determined, wherein the measuring, conversion, recording and data output for each of said channels are carried out by any of known technical measuring means, for example, by multi-channel potentiometer, and the processing of the recorded data is carried out using the methods of applied analysis employed for the real time monitoring and control of complex technological processes, considering a priori the obtained information about the progress of the drying process for the particular material; - the frequency of generated impulses is determined over the tachometric channel, instead of the rotation speed of the cylinder; the monitoring and the control of the process are carried out by means of a microprocessor, comparing the determined parameter values with the predetermined ones.

Further, the following solutions are proposed for the shock wave generator (Claims 10-12), in which:

during the rotation of the circular cylinder with given speed, the pulsating flow of heat carrier is fed into the aerodynamic chamber with pulsating frequency of 4-20 Hz and duration of an impulse not more than 0.02 sec; the diameter of the circular cylinder is not less than 2/3 of the height of the aerodynamic chamber; and the length of the circular cylinder does not exceed 3/4 of the width of the aerodynamic chamber. The following embodiment variants are also proposed for the apparatus for drying loose materials in the fluidised bed (claims 14-17), in which:

the length and width of the slot of the cylinder of the shock wave generator are approximately equal to 1/3 of the height and 3/4 of the width of the aerodynamic chamber respectively; the air distributing grate has deflector blades, set up at an angle not less than 45 degrees to the plane of grate and to the direction of heat carrier flow; - the aerodynamic chamber is made convergent, the ratio of the cross sections of passage at the beginning and the end of the chamber being 5:1 ; the apparatus is provided with technical means for simultaneous monitoring and controlling the drying process of material over a temperature channel, where the temperature of the heat carrier is determined, over a humidity channel, where a humidity of the material is determined, over a tachometric channel, where the rotation speed of the cylinder of the fluid shock wave generator is determined, and over a channel of pressure difference, where the pressure difference between the constant and pulsating flows is determined, wherein the control of means for measuring, conversion, recording and data output over each of said channels, executed by, e.g., multi-channel potentiometer, as well as processing of the results of measurement and the real time adaptive control of the technological process are effected by a microprocessor.

The basic principles applied also for the monitoring and the control of the technological process of drying loose material in the fluidised bed are described in the publications /1 , 2, 3/:

- the procedure used for the single as well as multiple measuring physical values is described in the publication /1/, including consideration of the a priori known information, which significantly facilitates the control of the process; the control systems, which automatically adjust to the extremes of several given functions depending on several variables or parameters are described in the publication 121; the methods for calculation of the best models by the statistical methods to present the a priori obtained experimental data of progress of the process are described in the publication 131.

Just the consideration of the a priori obtained experimental data allows carrying out the monitoring and the control of the process with minimal expenses and technical supply, considering the specific character of the progress of the drying process in the fluidised bed for the particular material.

The following cause-and-effect relation between achievable technical result and the scope of the essential features is found by the applicant. The drying of the material in the fluidised bed, caused by processing the material by fluid shock waves, changes the molecular pattern of the humidity evaporation from the material, namely, in state of equilibrium the upper molecular layer of the humidity to be evaporated removes intensively from the material surface by the exposition to the leading edge of the fluid shock wave impulse (Fig. 4, phase A), and b y overcoming the intermolecular cohesion, and the phase B of sharp relative pressure reduction which follows the leading edge will cause intense moisture evaporation. Thus, the function of the fluid shock waves can be compared to the function of a pump, in which in the phase A of the jump of pressure and velocity removing of moisture from the surface of the material occurs, but in the second phase B the intense moisture evaporation takes place. This process is repeated by the passage of the each fluid shock wave impulse.

To create the fluid shock wave, square-shaped impulses with steep leading edge and duration not longer than 0.02 sec have to be introduced in the aerodynamic chamber at a pressure difference in the inner cavity of the cylinder and in the cavity of the aerodynamic chamber not less than 1500-2000 Pa. To realise this condition, a side wall of the cylinder of the fluid shock wave impulse generator has to carry longitudinal rectangular slots. In the known apparatus the heat carrier flow is affected by impulses, formed by circular sectors. It is easy to find, that such solution cannot generate an impulse with steep leading edge due to the different resistance of the heat carrier flow in the rotation centre and in the periphery of the sector, as well as the different velocity of the increment of the section area of the opening. Thus the impulse will be "spread over" by shape and by density and the necessary fluid shock wave cannot be formed (see Fig. 4). Owing to the high physical and mechanical properties of the fluid shock wave the processes of the extraction of moisture are accelerated and the combined effect on the material by a constant flow and a pulsating flow creates the fluidised bed with minor power inputs, in shorter time and more stable across the whole surface of the fluidised bed.

The essence of the present invention is illustrated by the following drawings where:

Fig. 1 represents general view of the apparatus; Fig. 2 represents general view of the fluid shock wave generator, Fig. 3 represents the cylinder of fluid shock wave generator, Fig. 4 represents the diagram of the fluid shock wave impulse, where P is the pressure.

The apparatus for drying loose material in the fluidised bed according to the invention (Claims 13-17) comprises a forcing fan 1 , a heat generator 2, a chamber of the fluid shock wave generator 3 having an impulse generator inside it, an aerodynamic chamber 4 and a drying chamber 5 disposed above it. The drying chamber 5 is separated from the aerodynamic chamber 4 by an air distributing grate 6 having a net and deflector blades 13, set up at an angle not less than 45 degrees to the direction of heat carrier flow. A charging hopper 7 is situated above the drying chamber 5 and a chute 8 for discharging dry product is arranged in the opposite end of the chamber.

The impulse generator (Claims 9-12) comprises a straight circular cylinder 9 with longitudinal rectangular slots 14 and openings 15 in the ends of the cylinder, a drive 10 for rotation of the cylinder, controllable chokes 11 and a diffuser 12 for connecting the chamber of fluid shock wave generator 3 with the aerodynamic chamber 4.

The apparatus for drying loose material in the fluidised bed operates in the following manner. The forcing fan 1 feeds air in the heat generator 2 and heated air enters the chamber 3 of the fluid shock wave generator, in which one part of the flow enters the cylinder 9 of the fluid shock wave generator through the openings 15 in the ends of the cylinder, but the other part of the flow enters directly the aerodynamic chamber 4 through the chokes 11. During the rotation of the cylinder 9 of the impulse generator the inner cavity of the cylinder 9 of the impulse generator communicates periodically with the inner cavity of the aerodynamic chamber 4 through the rectangular slot 14 of the cylinder 9 and the same slot (not presented in the drawing) in the aerodynamic chamber 4 for the time not more than 0.02 sec. When the slot of the cylinder and the slot of the chamber do not coincide with each other, the pressure in the cylinder 9 jumps and becomes higher than in the aerodynamic chamber 4, due to the retardation of the air flow. When pressure difference reaches 1500-2000 Pa, the fluid shock wave is formed at the next coinciding of the slots. The extraction processes of the moisture from the material during passage of the fluid shock wave in the aerodynamic chamber and interaction between them are described above. During the passage of the trailing edge of the fluid shock wave impulse the velocity of the heat carrier flow can be insufficient to maintain the bed in a "bloated" state and the process of the fluidising the bed can be terminated. To prevent such condition, the chokes 11 are made with the possibility of controlling the section of their passages. During the moving the fluid shock wave along the chamber 4 its intensity decreases and the uniformity of air flow distribution vary. To maintain the uniformity of air flow distribution, the aerodynamic chamber 4 is made convergent and the deflector blades 13 of air distributing grate 6 are positioned at an angle not less than 45 degrees to the direction of air flow to deflect it to the direction of the air distributing grate 6 with the net. The ratio of the cross sections of passage at the beginning and the end of the chamber is 5:1.

Geometrical dimensions of the slot 14 of the cylinder 9 and the area of the opening of the choke 11 are selected taking into account the following considerations. As for drying of different materials it is necessary to change either the impulse frequency or the number of slots, in the same time maintaining the same relative pressure difference of about 1500-2000 Pa, the forming conditions of the fluid shock waves are kept out in the apparatus according to the invention by varying the velocity of constant flow by means of the chokes, the number of slots 14 and their dimensions being constant. The slot in the side wall of the cylinder has the following proportions to the dimensions of the front part of the aerodynamic chamber, namely: the length of the slot of the cylinder is at least 2/3 of the width of aerodynamic chamber and the width of the slot of the cylinder is at least 1/3 of the height of aerodynamic chamber. To control the velocity of entering of the constant flow into the aerodynamic chamber, the sections of the passages of the openings of chokes 11 are taken as at least 1/10 of the area of the rectangular slot 14 of the cylinder 9.

The boundary values of the velocity of the heat carrier flow, the frequency and the duration of the impulses, the relative pressure difference between the two heat carrier flows, which provide considerable reduction of power inputs due to the reduction of the drying time and reduction of heat carrier consumption, were determined experimentally and correspond to the optimal parameters of drying process when material is processed by fluid shock waves. The velocity of the heat carrier flows and the parameters of the shock wave were measured by probes DMI-1000 and registered by the oscillograph.

The possibility of achieving the stated objects by the method according to the invention was examined on the pilot apparatus for drying rye grain under the laboratory conditions. The technical results are presented below.

Table 1

Parameters of the drying process:

Treated material rye grain

Impulse frequency, imp/sec 4

Relative pressure difference between flows, Pa 2000

Average flow velocity, mps 0.5

Temperature of the heat carrier, °C 55

Batch weight, kg 10

Initial humidity of the sample, % 20.8

Final humidity of the sample after 30 min drying, % 13.1

Total extraction of the moisture in 30 min treatment, % 7.7

The obtained results demonstrate considerable exceeding of previously known values for drying velocity and for moisture extraction with the same power inputs. Thus, when the drying seed grain is carried out by known methods, the humidity of 13% can be reached in 1 hour at a temperature of 70 °C, but for drying food grain at a temperature 130-143 °C during 30 min the moisture extraction is only 4% instead of 7,7% according to the method of this invention. Low temperatures of the drying process according to the method of this invention allows not only reducing the drying time, but also preserves natural biological, physical and mechanical properties of the materials to be processed.

The variants of the implementation of the method according to the present invention 5 (Claims 1-8), especially for monitoring and controlling automatically the drying process, and embodiments of the drying apparatus in whole (Claims 13-17) and of fluid shock wave generator (Claims 9-12) are not limited by the solutions, presented in the Claims 18 and 19. The skilled person in the art can apply, without any further inventive activity, the principles of drying method according to the o invention, namely the drying by fluid shock wave of extra short effect, also in other modes of realisation for drying loose materials or other materials, such as fabric, wood, etc.

5 References:

1. I.F. Shishkin. Fundamentals of metrology, standardisation and quality control. M., Standards Publishers, 1988, p.p. 72-183.

2. F. Chaky. Modern theory of control. Non-linear optimal and adaptive 0 systems. M., MIR Publishers, 1975, p.p. 256-259.

3. D. Hymmelblau. Statistical methods for process analysis. M., MIR Publishers, 1973, p.p.384-394.

Claims

1. A method for drying loose materials, mainly agricultural products, in a fluidised bed, including simultaneous processing the material by two heat carrier flows, characterised in that the material is processed simultaneously by a constant heat carrier flow having a velocity of 0.2-0.5 mps and by a pulsating flow in the form of fluid shock wave with a pulsating frequency of 4-20 Hz and at duration of an impulse of not more than 0.02 sec, at a relative pressure difference between the flows of 1500-2000 Pa.

2. The method according to claim 1 , characterised in that the pulsating flow (the sequence of the fluid shock wave impulses) is created by rotating of a straight circular cylinder of an impulse generator, a side wall surface of the cylinder carrying at least one rectangular slot having a long axis directed along the cylinder, the fluid shock waves being generated only in case the slot located on a surface of the cylinder coincides with the slot of the same geometry and dimensions located in a wall of an aerodynamic chamber.

3. The method according to claim 2, characterised in that the constant flow is created by connecting the impulse generator chamber directly with the aerodynamic chamber through the openings, which are uniform by shape and dimensions with each other and are controllable by a choke.

4. The method according to claim 2 or 3, characterised in that the required impulse frequency and duration are adjusted by varying a rotation speed of said cylinder, and the velocity of the constant flow is controlled by means of the chokes, connecting the inner cavity of the aerodynamic chamber with the chamber of the fluid shock wave generator.

5. The method according to claim 4, characterised in that the rotation speed of the cylinder and/or the position of the chokes are controlled automatically, according to the measured flow rate and/or the relative pressure difference between the flows.

6. The method according to any of claims 1-3, characterised in that a monitoring of the process and a registration of operating parameters of the apparatus during the whole drying process are carried out simultaneously over a temperature channel, where the temperature of the heat carrier is determined, over a humidity channel, where a humidity of the loose material is determined, over a tachometric channel, where the rotation speed of the cylinder of the fluid shock wave generator is determined, and over a channel of pressure difference, where the pressure difference between the constant and pulsating flows is determined, wherein the measuring, conversion, recording and data output for each of said channels are carried out by any of known technical measuring means, for example, by multi-channel potentiometer, and the processing of the recorded data is carried out using the methods of applied analysis employed for the real time monitoring and control of complex technological processes, considering a priori the obtained information about the progress of the drying process for the particular material.

7. The method according to claim 6, characterised in that the frequency of generated impulses is determined over the tachometric channel, instead of the rotation speed of the cylinder.

8. The method according to any of claims 5-7, characterised in that the monitoring and the control of the process are carried out by means of a microprocessor, comparing the determined parameter values with the predetermined ones.

9. A shock wave generator for realising the method according to any of preceding claims, characterised in that it comprises a straight circular cylinder, a side wall of the cylinder carrying at least one rectangular slot having a long axis directed along the cylinder, and each end of the cylinder having at least one opening, the sum of areas of said openings being not less than the sum of the areas of said rectangular slots carried by said side wall of the cylinder.

10. The shock wave generator according to claim 9, characterised in that, during the rotation of the cylinder with given speed, the pulsating flow of heat carrier is fed into the aerodynamic chamber with pulsating frequency of 4-20 Hz and duration of an impulse not more than 0.02 sec.

11. The shock wave generator according to claims 9 or 10, characterised in that the diameter of said cylinder is not less than 2/3 of the height of the aerodynamic chamber.

5 12. The shock wave generator according to claims 9, 10 or 11 , characterised in that the length of said cylinder does not exceed 3/4 of the width of the aerodynamic chamber.

13. An apparatus for realising the method according to any of claims 1 -8 o comprising a forcing fan drive, a heat generator, a chamber with the shock wave generator according to any of claims 9-12, an aerodynamic chamber with a drying chamber with inner cavities separated by an air distributing grate having a net, characterised in that an inner cavity of the aerodynamic chamber is joined with the chamber of the shock wave generator through 5 openings controllable by the choke, and is joined with an inner cavity of a cylinder of the generator through a rectangular slot having a long axis directed along the cylinder, the slot in the wall of the aerodynamic chamber and the slots on the surface of the cylinder being equal to each other and coincide when being in register during rotation. 0

14. The apparatus according to claim 13, characterised in that the length and width of the slot of said cylinder of said shock wave generator are approximately equal to 1/3 of the height and 3/4 of the width of the aerodynamic chamber respectively. 5

15. The apparatus according to claim 13 or 14, characterised in that the air distributing grate has deflector blades, set up at an angle not less than 45 degrees to the plane of grate and to the direction of heat carrier flow.

0 16. The apparatus according to any of claims 13-15, characterised in that the aerodynamic chamber is made convergent, the ratio of the cross sections of passage at the beginning and the end of the chamber being 5:1.

17. The apparatus according to any of claims 13-16, characterised in that it is 5 provided with technical means for simultaneous monitoring and controlling the drying process of material over a temperature channel, where the temperature of the heat carrier is determined, over a humidity channel, where a humidity of the material is determined, over a tachometric channel, where the rotation speed of the cylinder of the fluid shock wave generator is determined, and over a channel of pressure difference, where the pressure difference between the constant and pulsating flows is determined, wherein the control of means for measuring, conversion, recording and data output over each of said channels, executed by, e.g., multi-channel potentiometer, as well as processing of the results of measurement and the real time adaptive control of the technological process are effected by a microprocessor.

18. Use of an apparatus according to any of claims 13-17 as an individual module for assembling the multi-deck arrangements of continuous operation mode for drying loose materials in a fluidised bed.

19. Use of the shock wave generator according to any of claims 9-12 as an individual module for assembling continuously operating arrangements for drying various loose materials, optionally in a fluidised bed.