Title of Invention

"AN IMPROVED DRIER USEFUL FOR PROCESSING AGRICULTURAL PRODUCTS"

Abstract

An improved drier useful for processing agricultural products, which comprises a top open storage chamber (20) having a material discharge outlet door (22) at its bottom portion; characterized in that the said storage chamber (20) being provided with an inlet (21) which is suitable for connected to a controllable hot air source; the open top of the said storage chamber being provided with fixing flanges (2) for mounting a top and bottom open mechanically stirred drier unit, the said drier unit essentially consisting of a chamber (1) having a perforated (4) distributor plate (3) covering the total cross section of the said chamber (1); the said distributor plate (3) being provided with a bottom door opening (5) having means (6,7,8) for opening/closing; the said chamber (1) being provided above the said perforated distributor plate (3) with a horizontal shaft (9) rotatably fixed on to the chamber (1) by bearings (13,14); the said shaft (9) being provided with one or more fixed sleeves (10) having one or more fixed flats (11) capable of holding by means variable sweep-length stirring-cum-mixing blades (12); the chambers (1,20) being also provided with suitably placed inspection/observation windows (19); the said horizontal shaft (9) being provided at one or both ends with conventional means (15,16) capable of transmitting rotatory power from a variable speed (18) prime mover (17); the open top of the said mechanically stirred drier unit being provided with fixing by means of flanges (2) or serial mounting of one or more said drier unit; the upper most drier unit being provided with an openable top cover.

Full Text

This invention relates to an improved drier for processing agricultural products. The improved drier of the present invention particularly relates to improved mechanically stirred drier having one or more stages for drying materials, which are difficult lluidi/e. at a faster rate by virtue of the good mixing of solids and the resultant good contact: between solids and hot air stream through the action of mechanical scooping cum mixing blades. Some materials due to its highly irregular shape, softness, stickyncss or materials having bigger particle si/e are difficult to lluidi/e. The drier of the present invention is designed to be operated under countcrcurrcnt mode by mulli-slagiug wilh a]l the stages identical, placed one above the other and each stage provided with mechanical mixing system. The counlcrcurrent operation makes the drying process more efficient with respect to time of drying and energy saving. The improved drier of the present invention can be used to dry granular materials wilh all the particles to have only the desired moisture content. In continuous systems, especially in tluidized bed system, there will be variations in residence times of particles in the drier. This residence time distribution of particles causes the particles to have different level of moisture content. In certain agricultural products and food materials the variation can cause mould growth or spoilage to particles with low residence lime in the drier wilh the result that moisture content in those particles may be higher than the safe level for storage. Most of the agricultural and plantation products require comparatively longer lime for drying. This is mainly due to three reasons. The first being the drying is dillusion controlled, i.e. the moisture irom the centre of the particle has to diffuse to the surface of the particle. The second being the initial moisture content is high and in some cases as high as 80%. The third being there if; an upper limit for the temperature of drying due to possible degradation, discolouration and denaturation of the material being dried. The method known from time immemorial is sun-drying which is although very cheap is cumbersome and highly labour oriented. Cross How driers, also called as cabinet (tray driers), are also used in certain cases. The disadvantages with this type of driers arc that the capacity is low, non-uniformity of moisture content, labour intensive, batch operation, stagnant air pocket etc. Reference may be made to Robert E. Treybal, 'Mass Transfer Operations'. .Vd Kdition, McGraw Hill Int., 1980, p. 661 -666. Rotary driers are very rarely used for drying as the initial investment is high and due to lack of controllability of drying. Another disadvantage of the rotary drier is that the material to be dried must be reasonably free flowing. Reference may be made to A. Williams Gardner, 'Industrial Drying', George Godwin Ltd., 1.971, p.116. Another commonly used form of drier is the bin drier or through-flow drier. In this type of drier the granular material to be dried is loaded in the bins and hot air is admitted from the bottom. The material starts drying from the bottom. A moisture gradient develops from the bottom layer in the bin to tiie top layer. The time taken for total uniform drying is enormous. Also due lo channelling (here exists isolated pockets wherein the moisture content differs considerably from uniformity.. For the drying of materials like grated coconut a description of the drier is given by Brain E. Grimvvood of Tropical Products Institute in his book Coconut Palm Products' published by FAG London (1975), p. 172. A drier originally used for tea industry was adopted for coconut gratings. The drier consisted of a tier of seven or eight trays made of strips of perforated metal about 8 cm wide. The disintegrated meal is loaded on to the top tray and subsequently dropped down slowly to the tray beneath by means of a tipping mechanism, and the process is continued until it reaches the bottom Iray and is removed. The major disadvantage of this drier is that there is no good mixing of the material in each tray causing non-uniformities, lumplormation, channelling of hot air resulting in inefficient air-solid contact. The depth of material loading in each tray is highly limited. Tunnel driers also require pretty longer time and lack of controllability, non-uniformity etc also exists. When comparatively small batches of material are produced which do not lend themselves to batch lluidi/ed bed drying and particularly if they tend to suffer from surface 'case hardening' when dried on trays, drying can be earned out in agitated pan drier.Reference may be made to A. Williams-Gardner, 'Industrial Drying', George Goodwin Ltd., 1971, p.243-246. Basically these driers consists of a shallow cylindrical pan provided with a mechanically driven vertical shaft which carries radial arms supporting scraper blades or ploughs bearing on or just clearing the Hat base of the pan. The shaft is designed for top or bottom drive. The pan ilseli' may be open-lopped or, more usually, covered for atmospheric operation or fitted with a vacuum tight domed cover for vacuum or reduced pressure operation. This type of drier is noted for its low thermal efficiency, can handle only small batches, heat transfer by conduction through the walls of the vessel and non-uniformity in drying. Huidized bed driers especially batch type of driers are also used in some cases. Here the batch operation ensures uniformity in final moisture content but has several disadvantages. The capacity per batch is limited. In most of the agricultural and plantation produce the lluidization characteristics are poor. Some of the raw materials are cohesive in character making it difficult to fluidizc. In some cases the particle size is larger and hence requires high volumetric How rate of hot air for tHiidizalkm.and often slugging and other related problems associated to poor quality fluidization arises. The materials requiring longer residence time for drying requires enormous amount of energy for heating the fluidizing gas. A lot of energy is wasted as only a small amount of the input energy is utilized tor healing the solids and the remaining energy is lost as sensible heat of the outgoing air. To overcome the drawback of low capacity, continuous lluidized bed driers were employed. Here the geometrical configuration is essentially as that of batch but provision is made for the continuous feeding of raw material and dischaige of the diied material. For agricultural products this type of drying has only limiled applications due to the variation in residence times of the particles in the drier. The residence time distribution leads to unacceptable non-uniformity in the dried product. To over come the draw-back of low thermal efficiency associated with batch system of drying multistage driers were used in certain cases. Reference may be made to Diazo Kunii and Octave Leven Spiel in rluidi/alion Engineering, Pub. Robert E. Krieger Pub. Coy., 1977, p.428-431 Here, required number of stages are provided one above the other. Material is fed at the top stage continuously and passes from one stage to another. Hot air enters at the bottom stage and passes upwards after contacting the solids in deferent stages and finally escapes from the top stage to the atmosphere. The hot air percolates upwards through the perforated holes of the distributor plate. The distributor plate of each stage has dual function. It has to support the solid material conlained in that particular stage and has to allow the passage of air through the holes to tluidize the solids. The solids arc continuously transferred from one stage to the stage below by means of down-comers. The down-comer is pipe of appropriate diameter fixed on to the distributor plate and length sufficient to dip in the lluidi/ed bed in the stage bciow. The diameter of the down-comer pipe should be such that it should allow the uninterrupted flow of solids from one stage to the stage below it. In another arrangement the solids are allowed to fall down to the stage below by providing sufficiently bigger holes in the distributor plate. Here the solids as well as the air passes through the same holes simultaneously. In this type of multistage fluidized bed driers if the solids do not have good fhiidizing and flow property choking may take place aifecting the operation of the drier. Besides, here afso the distribution in residence times causes the non-uniformity in drying of particles. Drying of agricultural products is very much important as the dried material has to be stored for several months. Some material has to be dried immediately after harvest to prevent germination and spoilage. These are materials which require longer hours for drying as the moisture has to diffuse from the centre of the panicle to the outer surface of the particle by diffusion. Fluidi/ed beds are generally used to dry free moisture content. Moreover, certain food materials which are cohesive in nature do not oiler good riuidi/ation characteristics. Continuous fluidixcd beds offers the disadvantages of residence time distribution and non-uniformily in drying of particles. However, it is always desirable to use the advantages of fluidized beds to di"y granular agricultural and food products. Good mixing of solids and intimate contact between solids and hot air is a good feature of fluidized beds. CounlereuiTent How of solids and hot air as in multistage Huidi/,ed beds is good for high thermal efficiency. In batch lluidizcd bed, the drawback associated with continuous lluidi/ed bed, i.e. residence time distribution of solids is non-existent. It may also be noted, as explained earlier, lluidi/ed bed system is not ideally suited for the drying of agricultural produce. In order to overcome the disadvantages of fluidized bed drying system and at the same time incorporating the advantages of lluidiscd bed system research work was carried out by us for the development of a suitable drying system which resulted in the development of the improved drier of olhe present invention. The main object of the present invention is to provide an improved drier which obviates the above noted drawbacks. Another objective of the present invention is to provide a mechanically jiiiiiejL-djiuLlluviug..i>ue. or ni«vro sloges for the drying of granular materials which require longer residence time for drying. Yet another objective of the invention is to avoid the residence time distribution of particles as encountered in continuous driers. Still another objective of the invention is to provide good mixing and contact with solids and hot air to result in good heat and mass transfer even for materials that are difficult to iluidi/c. Yet another objective of the invention is to provide maximum thermal efficiency by providing countercurrenl How of solids and hot air stream. The principle on which the development of the improved drier of the present invention is based on as follows: Increased rate of drying is achieved by mechanical stirring and mixing of solids and hot air; Increased thermal efficiency is achieved by muItistaging and countcrcurrent flow of solids and hot air; Residence time distribution is avoided by the transfer of solid material from one stage to the stage below at a stretch by opening the dour fixed to Ilie distributor plate An embodiment of the improved drier of the present invention is shown in the drawings accompanying this specification. In the drawings: Fig. 1 represents the front view of the improved drier depicting a multistage mechanically stirred drier. Fig.2 represents the side view of the improved drier depicting a multistage mechanically stirred drier. Fig.3 represents the back view of the improved drier depicting a multistage mechanically stirred drier. Fig.4 represents the sectional view of a stage of The improved drier. Fig. 5 represents the top view of a stage of the improved drier. Accordingly the present invention provides an improved drier useful for processing agricultural products, which comprises a top open storage chamber (20) having a material discharge outlet door (22) at its bottom portion; characterized in that the said storage chamber (20) being provided with an inlet (21) which is suitable for connected to a controllable hot air source; the open top of the said storage chamber being provided with fixing flanges (2) for mounting a top and bottom open mechanically stirred drier unit, the said drier unit essentially consisting of a chamber (1) having a perforated (4) distributor plate (3) covering the total cross section of the said chamber (1); the said distributor plate (3) being provided with a bottom door opening (5) having means (6,7,8) for opening/closing; the said chamber (1) being provided above the said perforated distributor plate (3) with a horizontal shaft (9) rotatably fixed on to the chamber (1) by bearings (13,14); the said shaft (9) being provided with one or more fixed sleeves (10) having one or more fixed flats (11) capable of holding by means variable sweep-length stirring-cum-mixing blades (12); the chambers (1,20) being also provided with suitably placed inspection/observation windows (19); the said horizontal shaft (9) being provided at one or both ends with conventional means (15,16) capable of transmitting rotatory power from a variable speed (18) prime mover (17); the open top of the said mechanically stirred drier unit being provided with fixing by means of flanges (2) or serial mounting of one or more said drier unit; the upper most drier unit being provided with an openable top cover. The controllable hot air source used may be such as having variable air How and air temperature. The perforations (4) on the distributor plate (3) may be such as capable of supporting the material to be dried and allowing the passage of air to fluidizc the said material. The perforated distributor plate door opening (5) may be opened/closed by means such as mechanically, hydraulically, electrically actuated systems. The rotary power transmission means (15,16) used may be such as sprocket and chain, pulley and belt, gear-train. The variable speed prime mover used may be such as a gear unit, electronic control unit coupled to a diesel motor, an electric motor. Fig. I of the drawings shows the front elevation of an embodiment of the assembled multistage mechanically stirred drier incorporating typically three idenlieal stages. The three stages (1) are mounted one above the other by using flanges (2). The stages are rectangular in construction as can be seen in Fig.5. The distributor plate (3) covering the total cross section of the rectangular stage is given perforations (4) on the complete area. The hole size of the perforations should be such that it should allow the passage of air and at the same time should not allow the passage of solid particles downwards. A door (5) is provided by segmenting the distributor perforated sheet to transfer the material from that stage to the stage below. The opening and closing of the door (5) is done by using the lever arrangement (6). The lever is actuated by a. handle (7) through the threaded connecting rod (8). The door can be closed and opened by operating the handle (7) from outside. The stirrer blades are incorporated on to the shaft (9) by means of sleeves ( 10). The sleeve is firmly fixed on to the shaft by means of locking screws. Hach sleeve has two or more Hats (11) welded on to it. Two or three holes are provided on the Hal. This is to enable the fixing of suitable stirring cum mixing blades (12) and also lo vary the length of sweep by the blades. One end of the shaft ends in the bearing housing (13) and the other end passes through bearing housing (14) and lo this end is connected sprokct wheels (.15) of desired diameter. The sprokct gears are interconnected through chains for power transmission and for rotating the mixing blades. The sproket in the bottom most stage is connected to the motor (17) and gear unit (18) through chain drive (16). Light and sight glasses (19) are provided on opposite side in each stage. To the bottom chamber (20) hot air is admitted through the inlet connection (21). The dried material discharged from Ihe bottom stage can be temporarily stored in the chamber (20) and can be taken out through the door (22) when desired. The use of the improved drier of the present invention is detailed below: Sufficient quantity of hot air is to be sent from the bottom inlet connection (21). The slirrer is also to be started. The material lo.be dried is lo be changed into the lop stage. After the desired lenglh of drying the door (5) has lo be opened by operating Ihe handle to discharge the material to the stage below. Again fresh material is to be charged into the top stage. Again after the desired time of drying material has to be discharged from stage to stage, starting from the bottom to top. Fresh material has always to be fed to lop stage. From the bottom most stage, the material is to be discharged into the base (20) for temporary storage and can be taken out by opening the door (22) when desired. Alter few operations steady state conditions will prevail. The moisture content will attain a steady value in each stage. The r.p.m. of the slirrer blades can be fixed depending upon the degree of stirring needed and the nature of particle. The air velocity can be set to any value. Here again it depends to a large extent on the nature of the material to be dried. In each stage, all the material contained in that stage undergoes the same extent of drying till it is transferred to the next stage below. There is no distribution of residence time to particles. The transfer of material from one stage to the stage below can be made fully automatic and the sequence of drying operation can be programmed. The door (5) fixed to the distributor plate can be opened and closed manually by using the handle (7) as shown in Fig.l. It can also be made automatic by using hydraulic system to actuate the lever mechanism or by coupling to electric motor system. The number of stages to be incorporated depends upon the overall drying requirements, nature of material to be dried, air temperature and air flow rate. More number of blades can be incorporated, if necessary, and depends on the extent of stirring and mixing needed. The drier can handle a wide range of materials for good and uniform drying. If necessary, the degree of stirring and mixing can be varied from stage to stage. The equipment can also be used as a multistage lluidized bed drier if sufficient quantity of air can be admitted to fluidize the material with or without the stirrer in operation. The use of the improved drier of the present invention is described in detail in the following examples which are provided by way of illustrations only and therefore should not be construed to limit the scope of the invention. Kxamplc 1: Drying of Cohesive and difficult to fluidize material Wet coconut gratings come under the above category of cohesive and difficult to lluidizc material. Coconut kernel or coconut meat was separated from the shell of the coconut and grated using pin mill as is followed in industry. A rectangular type of multistage mechanically stirred drier was used for the drying of grated coconut. The initial moisture content of the samples varied from 40 percent to as high as 48 percent. It was seen that moisture content of the coconut meat varied with the maturity of the nuts. A mixer/stirrer configuration as shown in the accompanying drawings was used for the stirring and mixing operation. The rpm of the stirrer blades was maintained in the range 5 to 20 to provide sufficient mixing. It was seen that a maximum of three identical stages were sufficient for the drying of the wet coconut gratings. A temperature in the range of 7()°C tol 10°C was employed. For lower temperatures, i.e. up to 85°C the use of two stages was sufficient. The use of third stage at higher temperatures improved the heat utility. The holding time for drying before the transfer of material from that stage to the stage below was varied between 15 minutes to 45 minutes to give a linal moisture content of less than 5 percent. Fresh feed was always admitted at the lop stage and dried material withdrawn from the bottom chamber. Example 2: Drying of granular agricultural product Mustard seeds (Brassica Napus Linn) comes under this category. The particle si/e used was in the range from 2.5 to 4 mm. In these types of agricultural produce the intra-paiticlc movement of moisture is diffusion controlled and hence require longer times for drying. The initial moisture content varied from 30 percent to 35 percent. Three stages were found to be sufficient for carrying out the drying operation. The time of holding was varied from 20 minutes to 60 minutes. The temperature employed varied between 60"C to l00l'C. An rpm of the stirring blades in the range of 10 to 40 gave sufficient degree of mixing of the material. The fresh material was always led to I he top stage and dried material discharged from the bottom stage and taken out from the collection chamber. The final moisture content varied between 4 percent to 10 percent. The main advantages of the improved drier of the present invention are: I. The stirring and mixing imparted to the particles lo be dried results in good and intimate contact with the dry air resulting in good heat and mass transfer and thereby increasing the rales of drying when compared to non-stirred systems of conventional drying. 2. The velocity of air flow and temperature can be adjusted from very low value to the desired high value suiting to the needs of the material to be dried. 3. The stirring effect and thereby the turbulence can be varied by changing the. rotary speed. 4. The drier can be used to handle granular, irregular shaped material and produce scini-lluidi/ed state even for cohesive and dillicull to fluidi/e materials. 5. Since solid material is fed and removed as single lot from each stage there is no residence lime distribution of solids and the solids will have uniform moisture content. d. The drying system is very useful for the drying of particles which are diffusion controlled. 7. The system can be operated in a continuous eounlercurrent manner thereby increasing the thermal efficiency of drying. 8. The processing can be made continuous and fully automatic. 9. The stirring configuration can be avoided in certain stages, if necessary depending upon the type of material being dried. We Claim: 1. An improved drier useful for processing agricultural products, which comprises a top open storage chamber (20) having a material discharge outlet door (22) at its bottom portion; characterized in that the said storage chamber (20) being provided with an inlet (21) which is suitable for connected to a controllable hot air source; the open top of the said storage chamber being provided with fixing flanges (2) for mounting a top and bottom open mechanically stirred drier unit, the said drier unit essentially consisting of a chamber (1) having a perforated (4) distributor plate (3) covering the total cross section of the said chamber (1); the said distributor plate (3) being provided with a bottom door opening (5) having means (6,7,8) for opening/closing; the said chamber (1) being provided above the said perforated distributor plate (3) with a horizontal shaft (9) rotatably fixed on to the chamber (1) by bearings (13,14); the said shaft (9) being provided with one or more fixed sleeves (10) having one or more fixed flats (11) capable of holding by means variable sweep-length stirring-cum-mixing blades (12); the chambers (1,20) being also provided with suitably placed inspection/observation windows (19); the said horizontal shaft (9) being provided at one or both ends with conventional means (15,16) capable of transmitting rotatory power from a variable speed (18) prime mover (17); the open top of the said mechanically stirred drier unit being provided with fixing by means of flanges (2) or serial mounting of one or more said drier unit; the upper most drier unit being provided with an openable top cover. 2. An improved drier as claimed in claim 1 wherein the perforations (4) on the distributor plate (3) are capable of supporting the material to be dried and allowing the passage of air to fluidize the said material. 3. An improved drier as claimed in claims 1 to 2 wherein the perforated distributor plate door opening (5) is opened/closed by means selected from mechanically, hydrau'^Hy, electrically actuated systems. 4. An improved drier as claimed in claims 1 to 3 wherein the conventional means (15,16) for rotary power transmission used is selected from sprocket and chain, pulley and belt, or Gear-train. 5. An improved drier as claimed in claims 1 to 4 wherein the variable speed prime mover used is selected from a gear unit, electronic control unit coupled to a diesei motor, an electric motor. 6. An improved drier useful for processing agricultural products substantially as herein described with reference to the drawings accompanying this specification.

Documents:

3385-del-1998-abstract.pdf

3385-del-1998-claims.pdf

3385-del-1998-correspondence-others.pdf

3385-del-1998-correspondence-po.pdf

3385-del-1998-description (complete).pdf

3385-del-1998-drawings.pdf

3385-del-1998-form-1.pdf

3385-DEL-1998-Form-19.pdf

3385-del-1998-form-2.pdf