JP2007533939A - Method and apparatus for continuous drying of rice - Google Patents

Abstract

  The present invention relates to a method and apparatus for continuously drying rice, particularly paddy rice. The object of the present invention is to clearly reduce the processing time and kernel destruction. This was achieved according to the invention by preliminarily purifying the paddy rice, followed by drying in the vortex bed and then conditioning or cooling the paddy rice for the first time.

Description

  The present invention relates to a method for continuously drying rice, particularly paddy rice, and an apparatus for continuously drying rice.

  Freshly harvested rice has an initial humidity greater than 20%, which must be reduced to a storage humidity of about 14%. The coarsely prepurified rice (paddy rice) is first stored in the front chamber of the dryer and then dried by a mechanical dryer. This drying is often carried out in a roof dryer (eg WO 98/45656) loaded with hot air of 50-60 ° C. in a plurality of steps. There is a standing time of 12 hours between the individual steps. In this case, only a limited dryness of up to 2% is possible, as in the case of tower dryers. In order to achieve temperature compensation between the kernel and the shell, it is required to leave at least 2 hours between the individual steps. The necessary mechanical transport process increases debris formation.

  In the case of static drying in a silo or hall, a large area is required because the layer thickness of the rice to be dried is limited (from about 80 to 100 cm). Drying progresses unevenly from inside to outside based on the arrangement of the ventilator and is not possible to control well because it does not give a truly even air distribution. The consumption time is also long.

  According to DE-A-2926256, in a grain drying process, fresh air is heated and directed onto the grain. In this case, fresh air is cooled prior to reducing humidity. A similar solution is also disclosed in DE-A-2947759.

  DE-A-29386620 discloses a through dryer having a cylindrical drying zone with a perforated sheet. DE-A-4119787 discloses an air conditioner for plant-type bulk cargo, which has a closed tunnel-like air conditioning station through which a conveyor belt is guided, An air conditioner in which bulk goods are conveyed on a belt is disclosed. In this case, the bulk is exposed to a gaseous heat carrier.

  The conveyor has a porous surface and hot or cold gas is flowed through the porous surface to heat or cool the grains and reduce the moisture content (WO 01/02786). ).

  DE-A-19806951 discloses an apparatus for popping granular objects, in which the objects are heated in a batch fashion in a vortex bed chamber. EP-A-1099380 discloses a method for producing heat-treated grains. In this case, the heat treatment is performed in a ring-shaped vortex bed with a gas flow. The gas stream has various velocity components.

  According to JP-A-580565650, untreated rice having a humidity of about 18% is heated with hot air of about 140 ° C. for about 30 minutes. Drying takes place in a drum dryer or in a vortex bed. In this case, the strength is thermally affected. The dried rice is then directly shelled or shelled and cooled as needed to obtain easy to cook, unpolished rice.

  Dried and pre-purified rice can be stored until processing like other grains.

  The object of the present invention is to at least partly eliminate the enumerated drawbacks of the prior art and to develop a method for continuously drying rice, especially paddy rice. This problem has been solved by the features of claim 1. Advantageous embodiments are disclosed in the dependent claims.

  The present invention is based on the recognition that rice (paddy rice) exhibits dynamics similar to polymers under predetermined humidity and temperature conditions. This is because rice can be in a glassy or rubbery state depending on the conditions of the above conditions. When the temperature is low (up to room temperature) and the initial humidity is 20% or more, the rice is in a glass state, but when the temperature rises, it shifts to a rubber state. This rubbery state maintains temperature and is maintained when dehumidified. When cooled, the paddy rice becomes glass again. This recognition can be used to dry paddy rice in a continuous manner and nevertheless avoid the destruction of kernels. For this purpose, paddy rice is heated to about 50-55 ° C., dried to a humidity of about 14%, and then cooled to ambient temperature.

  Drying with heating is preferably carried out in a vortex bed. In the hot vortex layer, the internal pressure of rice kernels increases due to water evaporation. Humidity oozes out of the kernel by pressure compensation between the kernel and the surroundings.

  The treatment in the vortex layer can be performed in one step, two steps, or three or more steps. In the case of two-stage drying, there is no intermediate standing, and the second stage is preferably combined drying / cooling.

  When the moisture content of paddy rice is high by supplying heated steam, drying can be started at a relatively high temperature (up to about 120 ° C.).

  Another object of the present invention is to provide an apparatus for continuously drying rice, in particular suitable for carrying out the process of the present invention. In this case, a separator and a sorter known per se are used for preliminary purification, and at least one vortex bed apparatus is used for drying. In an alternative embodiment, two vortex bed devices can be arranged in sequence. In this case, the second device can include cooling (pre-cooling) in addition to drying.

Hereinafter, two embodiments of the present invention will be described in detail with reference to the drawings. The drawings show a schematic diagram in only one figure.
The untreated rice that has been sent reaches the drum-shaped sheave 2 from the depot 1, and extremely coarse impurities are removed by the drum-shaped sheave 2. Then another precleaning is performed in the separator / classifier 3 to separate not only stones, sand but also light impurities such as paper, straw or free shells. The form of precleaning is related to the degree of contamination of the raw rice that has been sent. It is advantageous to separate as much as possible impurities and contaminants from untreated rice before further processing.

  After pre-cleaning and short-term intermediate storage in another depot, the rice is heated to about 50 ° C. in the first vortex bed apparatus 5 where hot air flows through the rice layer from below and the moisture at 3-4 ° C. is dried. Is done. The rice then reaches the second vortex bed apparatus 6 directly. The temperature of about 50 ° C. is maintained in the vortex bed apparatus 6, and the moisture is dried at 3-4 ° C. In the last third of this second vortex bed apparatus 6, the rice is cooled to about 40 ° C.

  The paddy rice then reaches the container 7 where it is slowly cooled (to about 20 hours) to ambient temperature, with a further loss of 1% moisture. The tempering / leaving time can be reduced by appropriate means.

  As an alternative to tempering, the rice can be cooled more quickly (for example within about 15 minutes) with a countercurrent cooler (with or without preliminary cooling in the second vortex bed apparatus 6).

  Unlike the general method, the drying time has been significantly shortened and grain destruction has been clearly reduced. Also, due to low equipment maintenance costs and short drying times, untreated rice can be stored more quickly or more rice can be obtained at harvest time.

  In another embodiment, untreated rice with very high moisture content (eg, about 37% initial humidity) is dried in multiple stages in a roof dryer with a fluidized bed. The first stage is already carried out with heated steam at about 120 ° C. for more than 3 hours. In this case, the humidity is reduced to about 20-22%. In separate stages, each exceeding one hour, drying continues with a progressively reduced steam supply. In this case, the air or steam temperature is similarly stepped down to 50 ° C. As a result, a humidity of about 13% is obtained. In the last stage, the rice is cooled to ambient temperature within half an hour. In this case, steam is no longer supplied. The achievable humidity is about 12.5%.

Schematic which showed the Example of this invention.

Explanation of symbols

  1 depot, 2 drum-shaped sheave, 3 separator, 4 depot, 5 vortex bed apparatus, 6 vortex bed apparatus, 7 stand container

Claims (17)

  A method for continuously drying rice, particularly paddy rice, in a type that includes preliminary purification of rice and drying using hot air, and drying rice in a vortex layer after preliminary purification. A method for continuously drying rice, especially paddy rice.   The process according to claim 1, wherein the drying in the vortex bed is carried out in one stage.   The process according to claim 1, wherein the drying in the vortex layer is carried out in two stages.   The method according to claim 1, wherein drying in the vortex bed is performed in three or more stages.   4. The method of claim 3, wherein the second stage includes drying and precooling.   6. A process according to any one of the preceding claims, wherein the rice is dried at a temperature of about 50-55 [deg.] C to a moisture content of about 13%, and after drying slowly cooled / tempered to ambient temperature.   6. A method according to claim 5, wherein the precooling is performed in the last third of the second stage.   8. A method according to any one of claims 1 to 5 or claim 7, wherein the rice is dried at a temperature of about 50-55 [deg.] C to a moisture content of about 13% and, after drying, cooled to ambient temperature in countercurrent. .   The method according to claim 1 or 4, wherein the drying is performed at a plurality of temperature stages by supplying heated steam.   The method of claim 9, wherein heated steam at about 120 ° C. is supplied in a first temperature stage and the temperature is reduced stepwise to about 50 ° C. in another temperature stage.   The method according to claim 10, wherein the supply of steam is gradually reduced.   An apparatus for continuously drying rice, particularly paddy rice, which has a device for preliminarily purifying rice and means for drying rice with heated air, wherein said means for drying is at least one An apparatus for continuously drying rice, particularly paddy rice, characterized by having a vortex bed apparatus (5, 6).   13. The device according to claim 12, wherein two vortex bed devices (5, 6) are provided in sequence.   14. The device according to claim 13, wherein the second vortex bed device (6) has a drying zone and a cooling zone.   15. The device as claimed in claim 12, wherein a cooling stage is arranged behind the at least one vortex bed device (5, 6).   16. The device according to claim 15, wherein the cooling stage is integrated in a vortex bed device (5, 6).   17. A device according to any one of claims 12 to 16, wherein the vortex bed device is a roof dryer.

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