MXPA06001899A

MXPA06001899A - Method and device for the continuous drying of rice.

Info

Publication number: MXPA06001899A
Application number: MXPA06001899A
Authority: MX
Inventors: Saswato Mitra
Original assignee: Buehler Ag Geb
Priority date: 2003-08-19
Filing date: 2003-08-19
Publication date: 2006-05-31
Also published as: CN1823250A; AU2003250717A1; WO2005017431A1; JP2007533939A

Abstract

The invention relates to a method and a device for continuously drying rice, especially paddy. The aim of the invention is to significantly shorten the treatment time while substantially reducing breaking of the grains. Said aim is achieved by performing a drying process in a fluidized bed following preliminary cleaning of the paddy, the paddy being tempered or cooled only in a subsequent process.

Description

METHOD AND DEVICE FOR DRYING RICE CONTINUOUSLY FIELD OF THE INVENTION The invention relates to a device for continuously drying rice, especially paddy rice (Paddy type rice) as well as a device for continuously drying rice. BACKGROUND OF THE INVENTION Freshly harvested rice has an initial humidity greater than 20%, which must be reduced to a storage humidity of approximately 14%. Previously cleaned raw rice (Paddy) is first placed in cells prior to a dryer, and subsequently dried by means of a mechanical dryer. The drying takes place mainly in several steps in a plate dryer to which hot air is applied at 50-60 ° C (for example according to WO 98/45656). Between each step there is a resting time of up to 12 hours. Even in the case of drying towers, only a limited degree of drying of up to 2% is possible. Between the individual steps, a rest period of at least 2 hours is required to achieve a compensation of the temperature between the grain and the husk. The necessary mechanical transport processes increase the breakdown of the grain.

In the case of static drying in silos or granaries, large areas are required since the thickness of the layer of the rice to be dried is limited (approximately 80 to 100 cm). Drying takes place unevenly from the inside out due to the placement of ventilation devices, and is difficult to control, since a true uniform distribution of air is not obtained. Also the process is very slow. According to DE-A-2926256 for the grain drying process fresh air is heated and conducted on the grain, previously cooling the fresh air to reduce its moisture content. A similar solution is presented in DE-A-294759. DE-A-2938620 shows a through dryer with a cylindrical drying zone having perforated sheets. This is followed by a cooling zone of similar shape. DE-A-4119787 shows a packaging device for bulk vegetable products, with a tunnel-like closed conditioning station having a transport track on which the product is conveyed in bulk. Here the product is subjected to a heat carrier in the form of a gas. These conveyors may have porous surfaces through which hot or cold gas streams can flow, to cool or heat the grains and reduce their moisture content (WO 01/02786). DE-A-19806951 presents a method for sponging grain products, for which the product is heated by fillers in a fluidized bed chamber. EP-A-1099380 discloses a process for producing heat-treated grains, the heat treatment being carried out by means of a gas stream in an annular fluidized bed. The gas stream has different velocity components. According to JP-A-58056650, the raw rice with a content of about 18% moisture is heated with hot air at about 140 ° C for 30 minutes. The drying can be carried out both in a drum dryer and in a fluidized bed, in which the intensity is thermally influenced. The dry raw rice is directly peeled or peeled and cooled, in case an unpolished and easily cooked rice is required. The dry and clean rice can be stored until processing in the same way as any other grain. SUMMARY OF THE INVENTION The invention proposes the task of overcoming the disadvantages of the state of the art at least partially and developing a process to continuously dry the rice, especially rice with paddy shell. The solution of the task obtains with the features of claim 1 and the advantageous embodiments are presented in the dependent claims. The invention is based on the assumption that under certain conditions of humidity and temperature the rice (Paddy) behaves in a similar manner to a polymer, since depending on a series of conditions it is possible that it presents a more crystalline or more gummy state. At a lower temperature (approximately up to room temperature) and an initial humidity of 20% Paddy rice is crystalline, but as the temperature increases it changes to a rubber-like state. This state can only be obtained by maintaining the temperature and simultaneously removing the moisture. When the Paddy rice cools it regains a crystalline state. This knowledge can now be used to dry the Paddy in a continuous drying process and thus prevent the grain from breaking. Paddy rice is heated to this at about 50 to 55 ° C, dried to a moisture content of about 14% and subsequently dried at room temperature. Heating and drying are preferably carried out in a fluidized bed. In the fluidized bed the internal pressure in the rice grains increases by evaporation of the water. The moisture in the grain can be eliminated by compensating the pressure between the grain and the environment. The treatment in the fluidized bed can be carried out in one, two or more stages. In the case of drying in two stages, no intermediate rest is required and the second stage is preferably a combined drying / cooling process. By introducing hot steam it is possible to start the drying of Paddy rice with a high moisture content at a higher temperature (approximately 120 ° C). Another task consists in the production of a device for drying rice continuously, especially that it is suitable for carrying out the process according to the invention. Here, separating and sorting machines are used for pre-cleaning and at least one fluidized bed apparatus for drying. In a variant, two fluidized bed apparatuses can be sequentially placed, the second device serving in addition to drying also for cooling. BRIEF DESCRIPTION OF THE FIGURES The invention will be described in detail in two examples of embodiment with the help of a drawing. The only figure 1 shows a drawing of a simplified diagram. DESCRIPTION OF THE INVENTION The raw rice arrives from a tank 1 to a drum screen 2, where very large impurities are removed. A 'This follows another cleaning in a separator / classifier 3, to remove stones, sand and other light impurities such as paper, straw or loose husks. The conformation of the previous cleaning depends on the degree of impurities in the raw rice used. It is advantageous to separate the impurities and other products from the rice before the subsequent treatment. After the preliminary cleaning and a short intermediate storage in another tank 4 the rice is tported to a first fluidized bed apparatus 5, in which hot air flows through a layer of rice, which is heated to approximately 50 ° C and it dries, removing approximately 3-4% moisture. Then the rice arrives directly to a second fluidized bed apparatus 6, in which a temperature of about 50 ° C is maintained and another 3-4% of the moisture is removed. In the third third of the second fluidized bed apparatus 6 the rice is cooled to about 40 ° C. Paddy rice then arrives in a resting vessel 7, where it is slowly cooled (approximately 20 hours) to room temperature and there still loses 1% humidity. The tempering / rest time can be reduced by means of suitable methods. Alternatively to quenching, the cooling of the rice (with or without pre-cooling in the second fluidized-bed apparatus 6) can also be carried out more quickly in a countercurrent cooler, for example in the course of 15 minutes. Compared with conventional methods, a clear reduction in grain breakage was obtained with drastically reduced drying times. It is also less expensive to maintain the facilities Due to the reduced drying times, raw rice can be stored faster or more rice can be purchased during the harvest season. In another embodiment, the very moist raw rice (for example with an initial moisture content of about 37%) is dried in several stages in a fluidized bed plate dryer. In the first stage it can be carried out with hot steam at approximately 120 ° C for 3 hours. The humidity is reduced here to approximately 20-22%. In other steps of 1 hour each one is continued with the drying by means of the steam supply reduced in a stepped way, with which the temperature of the air or steam is also reduced stepwise to 50 ° C. A moisture content of approximately 13% is obtained. In the last stage the rice is cooled to room temperature in the course of half an hour, in which steam is no longer fed. A moisture content of approximately 12.5% can be obtained.

Reference list 1 Tank 2 Drum screen 3 Separator 4 Tank 5 Fluidized bed apparatus 6 Fluidized bed apparatus 7 Resting vessel

Claims

10 NOVELTY OF THE INVENTION Having described the invention as above, property is claimed as contained in the following: CLAIMS 1. A process for continuously drying rice in particular rice with paddy or paddy type, characterized because the rice after a previous cleaning dries in a fluidized bed at a temperature of about 50-55 ° C to a moisture content of about 13% and after drying, the rice is slowly cooled / warmed to room temperature. 2. The process according to claim 1, characterized in that the drying in the fluidized bed is carried out in a single step. 3. The process according to claim 1, characterized in that the drying in the fluidized bed comprises two stages. 4. The process according to claim 1, characterized in that the drying in the fluidized bed comprises more than two stages. 5. The method according to claim 3, characterized in that the bed 11 The second stage fluidized process includes drying and pre-cooling. The method according to claim 5, characterized in that the pre-cooling is carried out in the last third of the second stage. The process according to claims 1 to 6, characterized in that the rice is dried at a temperature of about 50-55 ° C to a moisture content of about 13% and after cooling is cooled countercurrent to room temperature . The process according to claim 1 or 4, characterized in that the drying is carried out in several temperature stages by feeding hot steam. The method according to claim 8, characterized in that in the first stage hot steam is fed at approximately 120 ° C, a temperature which in the other steps is reduced stepwise to approximately 50 ° C. 10. The procedure according to Claim 9, characterized in that the steam supply is reduced stepwise. 12 11. A device for continuously drying rice, especially paddy-type rice, characterized in that it includes a preliminary cleaning of rice and a means for closing the rice by means of hot air to carry out a process according to claims 1 to 10, characterized in that the means for drying includes at least one fluidized bed apparatus. 12. The device according to claim 11, characterized in that two fluidized bed apparatuses are placed one after the other. The device according to claim 12, characterized in that the second fluidized bed apparatus has a drying zone and a cooling zone. 1 . The device according to one of claims 11 to 13, characterized in that after the at least one fluidized bed apparatus, a cooling stage is placed. 15. The device according to claim 14, characterized in that a cooling stage is integrated in the fluidized bed apparatus. 13 16. The device according to one of claims 11 to 15, characterized in that the fluidized bed apparatus is a plate dryer.