RU2302740C1 - Plant material drying apparatus - Google Patents

Abstract

FIELD: food-processing industry, in particular, plant product drying technique, more particular, vegetables, mushrooms, fruits, greens and spices.

SUBSTANCE: apparatus has two drying chambers, receiver, heat-exchanger, sluice chamber, vacuum and air pumps, fan and air heater. Apparatus is further equipped with two heat-exchangers-condensers. Each of drying chambers is connected with one of heat-exchangers-condensers, and also with receiver to which vacuum pump is connected. Apparatus of such construction allows existing equipment to be used.

EFFECT: simplified construction and operation, elimination of possible expenses for manufacture of costly and massive technique.

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Description

The invention relates to the field of drying of plant materials, in particular to chamber vacuum dryers of periodic action, and can be used for drying food products, namely vegetables, mushrooms, fruits, herbs, spices, etc.

A device is known for drying fruits and berries of universal combined action, comprising a vertically mounted cylindrical body located inside the carousel, which is a shaft with a rotary drive, a frame fixed to the shaft and mesh pallets belt-mounted on the frame to accommodate the processed material, means for supplying and removing drying agent, means for supplying energy. The frame is made in the shape of a cone, and the mesh pallets have funnels and are mounted on the frame with an inclination towards the shaft, and the means for supplying energy is a microwave energy generator, the emitters of which are located in one of the sectors of the body above each tier of pallets (see RF patent No. 2051588, M. cl. A23B 7/02).

The disadvantages of the known device include the complexity of the design and the use of a hazardous to human health source of microwave energy.

Known universal drying unit of combined action, comprising a working chamber, loading and unloading devices, a microwave energy emitter and a drying agent input device. The side walls of the working chamber are made conical, the drying agent in the lower part of the working chamber is connected tangentially to the side walls together with the energy supplied from above and provides separation by a stream rotating in the form of a tornado and its removal through openings in the upper part of the chamber. The versatility of the camera is ensured by the loading table, which is installed on the axis of the loading screw mechanism located at the bottom of the camera (see RF patent No. 2078522, M. class. A23B 12/08, A23B 7/02).

The disadvantages of the well-known universal installation for drying vegetable products of combined action include - even higher design complexity and high energy intensity.

Known for a more advanced radiation dryer for plant foods according to the patent of the Russian Federation No. 2034489, M. cl. А23В 7/02, А26В 3/30, including a drying chamber, product trays that are located in the chamber along a horizontal axis, means for introducing and discharging a drying agent, mid-spectrum IR emitters. The processed food product is heated by direct, reflected infrared radiation and convective upward air flow. The heating mode is determined by the type of processed product. Through the side slots and the lower cut-out, external air enters the lower part of the drying chamber. Air heating is mainly carried out by emitters, partly reflective ducts and ducts. When the product is heated, its moisture evaporates, diffuses into the air stream and with it is removed through the open chamber lid. After the drying process of the product is completed, the dryer is disconnected from the network, the top cover is closed, the trays with the dried product and the tray with a fine fraction are removed from the drying chamber.

The installation allows you to implement a method of drying food products, which significantly improves the quality of the dry product, increases the drying performance, ensures safety and ease of operation compared to existing analogues. All of these known installations have a number of unsatisfactory performance:

- high specific energy consumption due to the complete transfer of product moisture to a vapor state,

- long duration of the drying process,

- lack of guarantee of partial, local burning of the product,

- the air-vapor mixture after the drying chamber is not captured, but enters the atmosphere.

The closest solution in technical essence - the prototype - is a plant for drying plant materials according to the patent of the Russian Federation No. 2232955, M. cl. 7 F26B 5/04. The installation is equipped with a receiver and a second drying chamber, connected, like the first, by means of a pipeline with a quick-acting valve mounted on it with a receiver, which is equal in volume to the free volume of the drying chamber, and the installation is equipped with a heat exchanger, means for heating the drying agent, and a refrigerating machine for cooling the heat exchanger, with a vacuum pump and a lock chamber for collecting liquid from the receiver, drying chambers and heat exchanger. The pipelines connecting the drying chambers to the receiver are installed tangentially with respect to the receiver, and the diameter of the piping connecting the drying chamber to the receiver is calculated according to the formula specified in the description. Alternating pulses of vacuum exposure with periodic exposures under the residual vacuum of plant material in combination with vacuum and temperature conditions allow for a short time 60-75 minutes to dry carrots, potatoes, onions, peppers and other food products.

The known installation - the prototype - has some unsatisfactory performance properties:

- heating of plant materials in a hermetically sealed chamber is carried out with saturated juice vapor of plant materials and this drastically slows down the drying process,

- heating of plant materials in an atmosphere of saturated steam translates the drying process into steaming - cooking,

- increased specific energy consumption due to a decrease in the drying efficiency when heated with saturated juice vapor.

The objective of the present invention is to eliminate the disadvantages of the prototype, in particular the creation of a plant with high performance properties in terms of reducing capital specific energy consumption, increasing the drying productivity of plant materials, ensuring their quality characteristics and environmental parameters of the process.

The task is achieved in that each drying chamber of the installation is equipped with a heat exchanger-condenser, the input and output of which is looped with the cavity of the chamber in accordance with the path of the coolant, while the input of the heat exchanger-condenser is additionally connected to the receiver, and the output of the heat exchanger-condenser is connected to the lock chamber .

The heat exchanger-condenser is made in the form of a cylindrical tank, in the cavity of which a tubular radiator is mounted for the passage of water in it for cooling and condensation on its outer walls of the coolant.

Signs of the invention, expressed in that each drying chamber of the installation is equipped with a heat exchanger-condenser, the input and output of which is looped with the cavity of the chamber in accordance with the path of the coolant, while the input of the heat exchanger-condenser is additionally connected to the receiver, and the output of the heat exchanger-condenser is connected to the lock camera, are signs of new, non-obvious, exceeding the prior art, unexpected, have an inventive step and are aimed at achieving the set of the acquisition of the task of reducing drying time, improving quality and lower capital unit costs. So, the equipment of each drying chamber with a heat exchanger-condenser allows you to cool the coolant circulating through it to a temperature below the dew point, which leads to moisture condensation on the outer walls of the heat exchanger-condenser. Its connection with the lock chamber allows you to remove condensed moisture from the coolant, which is formed during the heating of plant materials after a vacuum pulse. The presence of a heat exchanger-condenser for each drying chamber and its connection with the lock chamber allows the continuous removal of condensed moisture in each drying chamber during the heating process and thereby allows to obtain an unexpected positive result using the same equipment (receiver, lock chamber, vacuum pump) to improve the quality drying of plant materials, avoid steaming of dried plant materials, increase plant productivity by combining removal processes I moisture and heat plant materials.

The sign of the connection of the heat exchanger-condenser with the receiver using pipelines and valves mounted on them, as well as a sign that the inlet and outlet are looped with the chamber cavity in accordance with the path of the drying agent, constantly ensure that dry dehydrated coolant enters the drying chamber, on which performance depends , quality and the whole drying process.

The sign of the heat exchanger-condenser in the form of a cylindrical tank, in the cavity of which a tubular radiator is mounted to pass water in it for cooling and condensation of the coolant, is an additional feature aimed at achieving the objective of the invention to improve the drying quality of plant materials by reducing the coolant humidity and, as a result prevent steaming of plant material.

The drawing schematically shows the proposed installation for drying plant materials.

The proposed installation for drying plant materials (product) consists of drying chambers 1 and 2, each of which is equipped with guides 3 for uniform distribution of the coolant, heaters 4 for heating the coolant and fans 5 for supplying the coolant throughout the volume of the drying chamber and circulating it through the heat exchanger capacitor. Pipelines 6 with quick-acting pneumatic valves 7 and 8 integrated in them connect the drying chambers 1 and 2 to the receiver 9. Each drying chamber 1 and 2 has a valve 10 for connecting the chamber to the atmosphere and a valve 11 for draining moisture from the chamber that accumulated during the drying of the product. Sealed doors 12 provide loading and unloading carts with plant material. The vacuum pump 13 provides a predetermined vacuum in the receiver 9. The lock chamber 14 is designed to collect and remove condensate from the receiver 9 and the heat exchanger-condenser 15, which is cooled, for example, by water. To drain the fluid from the lock chamber 14, without depressurizing the entire installation, use valves 16, 17, 18. To drain the condensate from the heat exchanger-condenser 15, without depressurizing the installation, use valves 19 and 20. The operation of the pneumatic valves 7 and 8 is provided by the compressor 21, which through the control panel provides high-speed valves with compressed air. In the cavity of the drying chambers, temperature sensors 22 of the plant material and coolant are installed. The heat exchanger-condenser 15 is connected to the drying chamber 1 as follows: on the one hand with the inlet 23 into the drying chamber located at the rear end of the chamber, and on the other hand with the outlet 24 located near the doors of the drying chamber 1. In the cavity of the heat exchanger-condenser 15 mounted radiator 25 for cooling and condensation of moisture of the coolant, which is constantly supplied with cold water. The cart 26 with mesh pallets rolls into the cavity of the drying chamber 1.

Installation for drying plant materials works as follows.

The plant material intended for drying, pre-washed, peeled and cut, according to the requirements of the standard, is uniformly laid on mesh pallets by the thickness of the layer, which are then installed on a trolley 26, which is rolled into the drying chamber 1, after which the doors 12 are hermetically closed, turn on heating heater 4, include a fan 5 and at atmospheric pressure heat the air in the drying chamber. In this case, the drying chamber 1 is isolated from the receiver 9 by closing the high-speed valve 7 and the valve 16 from the external environment using the valves 10, 11, 17, 18. At the same time, the valve 19 for draining the condensate from the heat exchanger-condenser 15 is open. At the same time, flowing industrial process water is turned on for cooling the heat exchanger 25 and a vacuum pump 13 to create a pressure of 30-40 mm Hg in the receiver. Simultaneously with the vacuum pump 13, a compressor 21 is turned on. The plant material in the drying chamber 1 is heated to a volume average temperature that does not cause its denaturation. Heating leads to a decrease in the surface tension of water in the cells and the intercellular space of the plant material and to an increase in the water vapor pressure to values equal to the equilibrium vapor pressure at a given temperature. In the process of heating the plant material to a predetermined temperature, the air-vapor mixture through the outlet 24 enters the heat exchanger-condenser 15, where, in contact with the cooled pipes of the radiator 25, it is cooled to a temperature below the dew point. The dehydrated coolant through the inlet 23 again enters the drying chamber 1. In this case, the moisture of the coolant condenses on the cooled radiator of the heat exchanger-condenser 15 and flows through the pipeline through the open valve 19 to the lock chamber 14. The partially dehydrated coolant is again heated by heaters 4 and fed to the heating of the plant material . When the desired temperature of the plant material is reached, the valve 19 is closed and, using the high-speed valve 7, for a time equal to 0.1-0.5 s, the drying chamber 1 is connected to the receiver 9, in which a pressure of 30-40 mm Hg is previously created, thereby creating a vacuum in the drying chamber 1, under which the plant material is kept for a predetermined time, depending on the type of plant material, for example, for carrots - one minute. Next, the drying chamber 1 is isolated from the vacuum by closing the high-speed valve 7. With a quick, sharp effect of the vacuum on the plant material, its temperature decreases by 10-15 ° C. In this case, free moisture under the action of a deeper vacuum starts to leave the plant material and accumulate at the bottom of the drying chamber 1, which is then drained. Then, the valve 19 is opened and the plant material is heated to a predetermined temperature, for example, for 7 minutes for carrots, with the valves 17 and 18 closed. In this case, the heating coolant constantly circulates through the heat exchanger-condenser 15, and the moisture released in the heat exchanger-condenser 15 flows into the airlock 14. A uniform supply of coolant during purging, heating, repeated alternating evacuation and holding the plant material throughout the entire volume of the insulated drying chamber is carried out by heat flows ositelya using adjustable guide 3.

Heating of the plant material with circulation of the coolant through the heat exchanger-condenser 15, high-speed evacuation with heating, holding under the residual vacuum with heating of the plant material throughout the volume and circulation of the coolant through the heat exchanger-condenser comprise one drying cycle. Depending on the properties of the plant material: - density, thickness, and other parameters - the number of cycles can be at least more than two, i.e. the number of cycles can be increased many times to achieve the residual desired humidity.

After holding the plant product under residual vacuum, heating it with a coolant with circulation through the heat exchanger-condenser 15 and reaching the desired temperature of the plant material after the vacuum pulse, close valve 19, the pressure in the drying chamber 1 is released for 0.5-5 s by connecting the drying chamber 1 s receiver 9 to a pressure below the equilibrium pressure of saturated steam for a given temperature and again make exposure of the plant material in the deeper vacuum created in the drying chamber. During this exposure of the plant material under vacuum through the valve 16 without depressurization of the installation, the resulting water is removed from the plant material — water and condensate trapped in the airlock 14. The drying chamber 1 is isolated from the receiver by shutting off the quick-acting valve 7. 9. In this case, the coolant is continuously circulating through the heat exchanger-condenser 15, and the plant material is heated under residual pressure to medium volumetric temperature that does not cause denaturation of plant material.

Water in plant materials is found in two main structural elements, free moisture in the cavities of cells and capillaries, and bound moisture in the walls of cell walls. Cell pore sizes are between 100A and 10A. The maximum amount of bound moisture that can be present in plant materials is approximately the same for all plant materials and is about 30 wt.% At 20 ° C. All other moisture is free. When drying products with a moisture content of more than 30%, first of all, free moisture is removed, and then bound.

When heating plant materials, hygroscopicity decreases and part of the bound moisture goes into free moisture. Drying of plant materials in the proposed installation includes two stages. At the first stage, free moisture is removed when moisture from the capillaries and intercapillary space is removed by quickly creating a pressure of saturated water vapor in the volume of the drying chamber and the plant materials contained in it at a given temperature and moisture is expelled from the capillaries by expanding dissolved and trapped in the plant gas materials and partially occurring vaporization process.

Unlike the prototype, where heating is performed with saturated steam and drying does not occur, in the proposed design of the installation at the first stage, additional water is removed due to the heat exchanger-condenser through which the saturated air-air mixture circulates during the heating process.

In the second stage, the bound moisture is removed only due to intensive vaporization and its subsequent removal from the pore volume of the plant material. This is achieved in that the preheated plant material at a pressure equal to the equilibrium pressure of saturated vapors at a given temperature is subjected to quick coupling with the receiver vacuum and briefly creating a pressure in the drying chamber below the equilibrium vapor pressure, i.e. they start a second vacuum-pulsed effect on the plant material, but already to remove bound moisture.

The creation of pressure in the drying chamber 1 below the equilibrium pressure of saturated vapors leads them to an unsaturated state, similar to superheated steam, and a sharp transformation of moisture on the surface of the plant material into steam. This leads to cooling of the liquid on the surface of the plant material below its boiling point at a given pressure. Due to the low thermal conductivity of plant materials, steam located in the entire volume and inside the capillaries does not have time to cool to a temperature below the boiling point and, due to its increased pressure with respect to the outer surface, squeezes moisture out of the capillaries. The creation of a pressure below the equilibrium pressure in the drying chamber 1 also leads to a sharp expansion of the gases trapped and dissolved in the capillary liquid. A sharp increase in gas volume pushes the liquid from the capillaries into the volume of the drying chamber in the form of a finely divided phase.

In the second stage of drying of plant materials, in contrast to the prototype method, the efficiency of the action on the drying process of the heat exchanger-condenser increases even more, since all moisture of the plant material goes into a vapor state, circulates through the heat exchanger-condenser, condenses and continuously flows into the lock chamber 14.

A specific example of the drying of plant material.

The drying process of plant materials was experimentally implemented in a pilot plant, the technological scheme of which is shown in the drawing.

In two drying chambers 1 and 2 with a volume of 4 m ^{3, the} plant material that is prepared for drying is loaded — washed, cut and distributed in an even layer on mesh pallets.

Example 1. Drying was subjected to table carrots with an initial mass moisture content of 83%. Pre-washed, peeled and cut into cubes with sizes from 5 to 10 mm, carrots were laid out on mesh pallets with a layer 30 mm thick. The required final humidity according to GOST 12326-66 "Dried table carrots for export" should be no more than 8%. In each drying chamber 1, 2 on carts, 8 pallets with cubes of carrots were installed. A needle-type TSM-50M thermal sensor was installed in one of the carrot cubes. In each drying chamber for carrying out the drying process, finned electric heating elements with a capacity of 0.37 kW in the amount of 45 pcs were installed. and axial fan No. 5 with a capacity of 6000 m ³ / h, under normal conditions, providing a pressure of at least 50 mm of water st. at 3000 rpm To create a vacuum in receiver 9, a VVN-3 vacuum pump was used, which ensured the creation of a working vacuum in receiver 9 and the suction of ballast gases from it. High-speed evacuation was carried out using a receiver with a volume of 4 m ³ and pneumatic valves 7 and 8 of Du-150. The heat exchanger 15 was cooled with cold running water.

The drying chamber 1 was hermetically sealed and water was turned on to cool the heat exchanger-condenser 15, the heaters 4 and fans 5 were turned on to heat the air and carrots in the drying chamber 1. The air exited the heater at a temperature of 90 ° C at atmospheric pressure in the drying chamber 1, which was isolated from the receiver 9 and from the external environment by blocking the high-speed valves 7 and valves 10, 11, 16, 17, 18. Valve 19 was in the open state. Simultaneously with the inclusion of heating, a vacuum pump 13 was turned on to create a pressure of 30-40 mm Hg in the receiver 9. after reaching an average volume temperature of carrots of 60 ° C (heating time was 12 minutes), they closed valve 19 and turned on the high-speed valve 7 connecting the drying chamber 1 to receiver 9 and kept the carrots under vacuum for 1 minute. Then, the quick-acting valve 7 of the drying chamber 1 was closed, thus isolating the drying chamber 1 from the receiver 9, the valve 19 was opened, and the carrots were aged while it was heated under a residual vacuum for 10 minutes. At the same time, the air heater worked without shutting down and the temperature in the drying chamber reached 90 ° C, and the temperature of the carrots during aging under residual vacuum again reached 60 ° C. High-speed valves 8 of the drying chamber 2 at this time were in the "closed" position.

These operations were repeated three times, and the total time it took to remove free moisture was 30 minutes. Free moisture released from carrots in a state of steam and condensed in the heat exchanger-condenser 15 was removed by opening the valve 19.

During exposure of carrots under a residual vacuum in the first drying chamber, heating was started in the second drying chamber 2 with the same sequence of drying operations carried out therein.

Bound moisture was removed to a residual moisture content of 8% by performing high-speed vacuum operations with heating and holding carrots under vacuum for 1 minute, heating carrots in a drying chamber under residual vacuum while circulating the coolant to a temperature of 60 ° C for 3 minutes. The number of cycles above was five.

The total drying time of carrots was:

- 30 minutes removal of free moisture;

- 15 minutes removal of bound moisture.

Only 45 minutes. The resulting product in terms of quality met the GOST 12326-66.

The decrease in installed electrical power compared to the prototype was 50%, the reduction in energy consumption for drying 1 kg of finished products was 80%.

The proposed plant drying plant materials, in particular food products, successfully passed experimental tests in the conditions of an industrial enterprise for drying vegetables in the city of Barnaul and gave good, stable results in the quality of drying. The drying quality of plant materials (potatoes, onions, carrots, bell peppers, etc.) obtained at this installation complies with the requirements of Russian standards.

The proposed installation for drying plant materials does not cause difficulties in its manufacture and operation, allows the use of existing equipment and prevents possible costs for the manufacture of expensive and bulky equipment.

Currently, the authors are working on a wider use of the proposed installation.

Claims (1)

Installation for drying plant material, containing two drying chambers with hermetically sealed doors, a receiver, a heat exchanger, airlock, vacuum and air pumps, and in each drying chamber there is a fan and air heater, characterized in that it additionally contains two heat exchangers-condensers, In this case, each drying chamber is connected by pipelines to one of the heat exchangers-condensers, as well as to the receiver to which the vacuum pump is connected, to the pipelines connecting the drying chambers s and receiver, by means of valves connected air pump outputs, the inputs of heat exchangers, condensers conduits additionally connected to the receiver, and outputs capacitors heat exchanger by means of valves and piping connected to the lock chamber.