RU2489657C1 - Drier for bulk temperature-sensitive materials - Google Patents

Abstract

FIELD: heating.

SUBSTANCE: drier for bulk temperature-sensitive materials includes a housing, a loading mechanism in the form of a belt conveyor and a movable carriage, a drying chamber, with inwardly located drying surfaces in the form of horizontal flanges of the plates installed so that they can be rotated from a turning mechanism of plates with pushers on a traction device, a ventilation and calorific system with supply air ducts of prepared drying agent to the space between horizontal flanges with creation of different drying zones, and an unloading device. The loading mechanism is made in the form of one belt conveyor installed on a movable carriage with possibility of performing back-and-forth movement from the wall of the drying chamber to the opposite none along the horizontal flange; at that, linear speed of the conveyor is higher than that of the carriage due to the fact that the carriage wheels and the conveyor drum have different diameters and located on one and the same shaft with overall rotation speed; the plate turning mechanism includes two opposite pushers, one of which is made in the form of a non-isosceles trapezium, the other one is made in the form of two non-isosceles trapezia, and the ventilation and calorific system with air ducts is arranged inside the housing and includes two air ducts with a recuperator, which are installed on one side, with possibility of creating the first drying zone, and on opposite side of the drying chamber there additionally installed is an air duct with possibility of creating the second drying zone; at that, drying zones are restricted with air gates formed with horizontal flanges preventing air flows between the drying zones.

EFFECT: invention shall improve the drier efficiency, reduce overall dimensions, improve its reliability and effectiveness.

5 dwg

Description

The invention relates to the drying of bulk solids and can be used for drying short-cut pasta.

Known dryer for bulk thermosensitive materials of mine type VIS-42D, containing a loading mechanism, a drying chamber, a ventilation-air heater, a mechanism for turning plates in a drying chamber with a pusher and an unloading device. It is used for drying bulk products - grain, cereals, tomato seeds, etc. The loading mechanism for placing the product in the drying chamber consists of a loading hole, a movable carriage and two belt conveyors. The drying chamber has an iron profile body with an insulating layer on the outside and drying surfaces located inside in the form of horizontal shelves.Each shelf consists of 16 plates, with the possibility of rotation of the plates 90 ° from the rotation mechanism, the even and odd rows of plates of the shelves of rotation Return to the horizontal position is provided by springs.The rotation mechanism consists of a vertically traction device, a system of levers and rods, a pusher in the form of a finger is installed on the chain of the traction device, which, when it moves, presses the levers of the plate turning mechanism. Designed to prepare air as a drying agent, it consists of fans, air heaters, ducts and cyclones. For unloading the product there is an unloading device [1].

The main disadvantage of the described dryer for bulk thermosensitive materials is the inefficiency of the drying process of bulk materials due to the mixing of a drying agent with various thermophysical properties and its partial breakthrough (entering the dryer under high pressure) through the upper and lower horizontal shelves.

In terms of the essential features, the closest to the claimed invention (prototype) is a dryer for bulk thermosensitive materials such as VIS-2 shaft type, designed for drying pasta: horns, noodles, noodles and others, which contains a loading mechanism, a drying chamber with horizontal shelves, made of plates, the mechanism of rotation of the plates with a pusher, ventilation and air-heating system with air ducts and an unloading device. The loading mechanism is designed to feed the product into the dryer from the loading opening and consists of a movable carriage and two belt conveyors located one above the other and extending beyond the housing. The carriage, and with it the conveyor belts, can move back and forth along the guides forward and backward. The free end of the lower conveyor at the same time as the reciprocating can swing in the horizontal plane at a distance equal to the width of the shelf. The shaft-type drying chamber has a housing which is made of a standard profile sheathed with sheet iron and coated on the outside with a heat-insulating layer. All the mechanisms of the dryer are mounted in the camera body. In the chamber, as drying surfaces, there are twenty horizontal shelves located at an equal distance from one another in height. There are side channels at the ends of the drying chamber, inside of which there are partitions forming three zones. Each shelf is assembled from 16 plates mounted on axles in bearing units with the possibility of rotation by 90 ° and is held in horizontal position by springs. The mechanism of rotation of the plates is installed on the front wall of the drying chamber relative to the axis of rotation of the plates. At one end of the axis at an angle of 45 ° to the plane of the plate, a lever is mounted, at the end of which there is a finger. The axis of the finger is located at a distance of 70 mm from the axis of the plate. The fingers of all sixteen plates are inserted into the holes of a single link attached to the lever. All levers are located on a vertical guide in two rows, between them passes the chain of the traction device with a pusher in the form of a roller, which deflects the lever and thereby pulls the rod. To prepare the air and supply it as a drying agent into the channels, there is a ventilation-air-heating installation located on the outer surface of the drying chamber body. It consists of a centrifugal fan and two plate heaters. An unloading device is installed in the lower part of the drying chamber. The described dryer operates as follows: the initial product enters through the loading opening of the drying chamber to the upper conveyor of the loading mechanism, then it is poured onto the lower conveyor, which makes oscillating movements. The carriage, and with it the conveyor belts, move back and forth along the guides forward and backward along the longitudinal axis of the dryer and evenly distribute the product on the surface of the upper shelf. The speed of movement of the conveyors is consistent with the movement of the traction device - the vertical chain, the rotation of the plates, since the plates of the upper shelf open after it is fully loaded, i.e. when the free swinging end of the lower conveyor is in one of its final positions along the length of the shelf, while the product is poured onto the second shelf, which is at that time in a horizontal position, in the same way they fall from the second to the third shelf, etc. The rotation of the plates is carried out automatically by the mechanism of rotation of the plates, when the chain of the traction device is moving up, the roller hooks the rotary levers from bottom to top, turning them 90 ° even rows of plates in one direction, and odd rows in the other, this way of dropping the dried product from shelf to shelf prevents displacement it to one side of the drying chamber. The drying agent is prepared in a ventilation-air heater as follows. Atmospheric air is pumped by a fan through heaters into the side channel and, as a drying agent, it enters the lower zone of the horizontal channels of the drying chamber. The drying agent moves in horizontal channels along the dryer, so the product lying on the drying surfaces is blown during the transverse countercurrent movement of the drying agent. Having gone through all three zones of the dryer in series with 180 ° rotation, the spent drying agent is thrown out through the cyclone. The dried product from the last shelf is poured into the unloading device automatically at strictly defined time intervals [2].

The main disadvantages of the described dryer is the complexity of the design of the loading mechanism, which during operation extends beyond the drying chamber body, which ultimately significantly increases the overall dimensions of the dryer, and the inefficiency of the drying process of heat-sensitive bulk materials, due to the application of the most severe drying conditions to an already dried product, which leads to microcracks due to the difference in the gradient of the rate of moisture removal from the surface of the dried material and the supply of moisture from sulfur dynes material to be dried to the surface. Passing sequentially from the bottom up, the air loses its drying ability, and as a result, in the upper part of the dryer, when more stringent conditions are needed to blow wet products, the possibility of adhesion of the material due to uneven removal of moisture increases. Uneven drying of the product, obtaining both over-dried and under-dried products, leads to a decrease in the productivity of dryers and consumer qualities of the products due to adhesion, cracking and a decrease in glassiness. In addition, at the time of loading the initial product for drying and unloading the dried product, a partial release of the coolant occurs through the upper and lower shelves in the workshop. As a result, the heat transfer from the dryer to the room increases, which increases the energy consumption for drying.

The task set by the developers of the new dryer for bulk thermosensitive materials was to create such a dryer that would increase the productivity of the dryer for bulk thermosensitive materials, in particular short-cut pasta, reduce overall dimensions and increase its reliability and efficiency.

The problem is solved in that in a dryer for bulk thermosensitive materials, comprising a housing, a loading mechanism in the form of a conveyor belt and a movable carriage, a drying chamber, with drying surfaces located inside them in the form of horizontal shelves of plates mounted rotatably from the plate turning mechanism with pushers on the traction device, a ventilation-calorifer system with air ducts for supplying the prepared drying agent to the space between horizontal shelves with by creating various drying zones, the unloading device, the loading mechanism is made in the form of one belt conveyor mounted on a movable carriage with the possibility of reciprocating movement from the wall of the drying chamber to the opposite along the horizontal shelf, and the linear speed of the conveyor belt is greater than the linear speed of the carriage due to that the running wheels of the carriage and the conveyor drum have different diameters and are located on the same shaft with a common rotation speed; the rotation mechanism of the plates contains two opposing pushers, one of which is made in the form of an isosceles trapezoid, the second in the form of two isosceles trapezoid; a ventilation-air-heating system with air ducts is located inside the housing and contains two air ducts with a recuperator installed on one side of the drying chamber with the possibility of creating a first drying zone and an air duct with the possibility of creating a second drying zone additionally installed on the opposite side of the drying chamber, and the drying zones are limited by air gates, formed by horizontal shelves and preventing air flow between the drying zones.

Figure 1 presents a General view of the dryer for bulk thermosensitive materials;

figure 2 shows a diagram of the loading mechanism;

figure 3 shows a diagram of a drying chamber with a ventilation-calorifer system;

figure 4 is a diagram of the mechanism of rotation of the plates of the horizontal shelf;

figure 5 is a graph of the moisture content of the dried material from the drying time.

A device for drying pasta consists of a housing 1, a loading hole 2, a loading mechanism 3 mounted inside the drying chamber 4, a rotation mechanism of the plates with pushers 5, a ventilation-air-heating system with air ducts 6, 7 and 8, a recuperator 9 and a discharge device in the form of bins stabilizers 10.

Case 1 is made of a standard profile, sheathed on the outside with heat-insulating panels. In the case, all mechanisms and systems of a dryer 4 of a shaft type are mounted.

The conveyor belt 11 of the loading mechanism is mounted on a movable carriage 12. They have a common own drive 13. The linear speed of the conveyor belt 11 is greater than the speed of the carriage due to the increase in the diameter of the drum 14 relative to the diameter of the running wheels 15 of the carriage 12 at a total rotation speed, which when changing the direction of movement of the carriage 12 to completely free the surface of the belt of the conveyor 11 from the incoming products from the loading hole 2.

The drying chamber 4 comprises horizontal shelves formed by steel plates 16. In the upper part of the drying chamber 4, the air lock is formed by the shelves 17 and 18. In the middle part of the drying chamber, the air lock is formed by the shelves 19 and 20. In the lower part, the air lock is formed by the shelves 21 and 22. These gates limit the preliminary zone and the basis of the drying zone.

Ventilation-air-heating system with air ducts 6, 7 and 8 provides air preparation as a drying agent with specified parameters (temperature and relative humidity). The system includes medium-pressure centrifugal fans 22, 23, air heaters 24, 25, valves 26, 27 and 28 for supplying fresh air and exhaust exhaust drying agent, diffusers 29, 30, confusers 31, 32 and a heat exchanger 9.

A mechanism for turning the plates 5 is fixed on the front wall of the drying chamber 4. Steel plates 16 on the axes 33 are fixed in the wall 34 of the housing 1. On the axes 33 levers 35 are mounted. The levers of one shelf of the plates are connected to the rod 36. To hold the plates 16 in a horizontal position, one end traction 36 is connected to the spring 37 and the other to the lever 38. On the levers 38 on the axes of different lengths 39 and 40, bushings 41 are installed, which allows you to move the drive bushings 41 of the plates of the first eight shelves from the bushings of the plates of the remaining shelves. For opposing the levers 38 up to a 90 ° angle, two opposing pushers 42 and 43 mounted on the traction device 44 are used. The pusher 42 is made in the form of a single isosceles trapezoid, and the pusher 43 is in the form of two parallel non-isosceles trapeziums providing smooth opening and sharp closing of the plates 16 in different drying zones.

The linear dimensions of the zones of preliminary and main drying are proportional to the drying time of the material, which is determined by the graph of the dependence of the humidity of the dried material on the drying time (figure 5). The schedule was obtained by the method of determining the moisture content of material samples in accordance with GOST 14849-69 "Methods of quality control of flour products". The material was dried in a laboratory oven with optimal values of temperature, humidity and coolant speed. The graph shows the region of linear moisture change in time of plastic samples from 32 to 22% for 0.5 hours, which corresponds to the time the material was in the zone of intensive preliminary drying of the claimed device. In order to uniformly partially redistribute the moisture over the product volume and reduce the critical values of the moisture gradient of the material, in accordance with the schedule, the material to be dried was partially cured for 6 minutes, equal to the time the material was in the second air lock. The dimensions of the main drying zone are determined by the need to dry the material under appropriate conditions to standard values of 13-14%. In the intensive drying mode, the material has a specific gravity of 516 kg / m ³ and a moisture content of about 30-32% for 1 hour in accordance with the schedule for short-cut pasta with a diameter of 1.5 mm from premium flour reduces its moisture content to 13%. The dimensions of the dryer are designed to ensure uniform heat transfer of the material and the coolant [3]. Preliminary drying occurs at t = 70-75 ° C and φ = 45-50%, the main one at t = 45-55 ° C and φ = 75-80%. We determine the drying time by the formula (1):

$${\tau }_{\mathrm{one}}=\frac{(W_{\mathrm{one}}-W_2)}{\nu },(\mathrm{one})$$

where W ₁ - the initial moisture content of the products,%;

W ₂ - the final humidity of the products,%;

ν is the drying rate in the period of constant drying speed according to the formula (2),% / hour:

$$\nu =\mathrm{one}00\cdot q_m/(R\cdot {\rho }_0),(2)$$

where q _m is the amount of moisture transferred from the surface of the layer to the environment, q _m = 0.765 kg / (m ² · h);

R = 0.01 m = 10 mm — half the thickness of the layer on the shelf (based on literature data, the recommended layer thickness is ≈20 mm);

ρ ₀ - the density of the layer of dry material (346 kg / m ³ ).

Then ν = 100 · 0.765 / (0.01 · 346) = 22.1% / hour and, accordingly,

$${\tau }_{\mathrm{one}}=\frac{(32-22)}{22.\mathrm{one}}=0.\mathrm{four}5h=27m\mathrm{and}n.$$

We determine the time of the main drying by the formulas (3) and (4):

$${\tau }_2=\left(\frac{\mathrm{one}}{K}\right)ln\left[\left(W_n-W_R\right)\left(W_{\mathrm{to}}-W_R\right)\right],(3)$$

$$K=\nu /(W_n-W_{\mathrm{to}}),(\mathrm{four})$$

where W _n - the initial moisture content of the products,%;

W _p - equilibrium humidity,% (according to [3] 11.5%).

Then K = 22.1 / (22-11.5) = 2.1.1 / h, and

$${\tau }_2=\left(\frac{\mathrm{one}}{2.\mathrm{one}}\right)ln\left[\left(22-\mathrm{one}\mathrm{one}.5\right)\left(\mathrm{one}3-\mathrm{one}\mathrm{one}.5\right)\right]=0.93h\approx 56m\mathrm{and}n.$$

The total drying time τ = τ ₁ + τ ₂ = 27 + 56-83 min, take 90 minutes or 1.5 hours.

For example, for a line with a capacity of 400 kg / h on dry products and a recommended product layer thickness of up to 20-25 mm, the loading time of the first shelf is 3 minutes.

=3 мин по формуле (5)We determine the number of drying shelves in the pre-drying zone n ₁ , having the drying time on one shelf $${\tau }^{\prime }$$

= 3 min by the formula (5)

$$n_{\mathrm{one}}={\tau }_{\mathrm{one}}/{\tau }^{\prime }=27/3=9wt\mathrm{.,}(5)$$

including air shutter shelves.

=6 мин по формуле (6)We determine the number of shelves in the main drying zone, based on the fact that the thickness of the product layer on the shelves of the main drying in order to optimize the drying process doubles to 40-50 mm and, accordingly, the drying time on one shelf also doubles and amounts to $${\tau }^{″}$$

= 6 min by the formula (6)

$$n_2={\tau }_2/{\tau }^{″}=56/6\approx \mathrm{one}0wt\mathrm{.,}(6)$$

we accept 11 shelves taking into account the air lock.

From the formula for determining the productivity of the dryer, we determine the area of the drying surface according to the formula (7):

$$F=\frac{Q\cdot \tau }{(h_{\mathrm{one}}\cdot n_{\mathrm{one}}\cdot \rho +h_2\cdot n_2\cdot \rho )},m^2(7)$$

where Q is the productivity of the dryer, kg / h (for example, the productivity of the prototype);

h ₁ - layer thickness in the zone of preliminary drying, m;

n ₁ is the number of shelves in the pre-drying zone;

h ₂ - layer thickness in the zone of the main drying, m;

n ₂ is the number of shelves in the zone of basic drying;

$$F=\frac{\mathrm{four}00\cdot \mathrm{one}.5}{(0.02\cdot 9\cdot 5\mathrm{one}6+0.0\mathrm{four}\cdot \mathrm{one}\mathrm{one}\cdot 5\mathrm{one}6)}=\mathrm{one}.875,m^2.$$

We take the width of the shelf B = 1.1 m, then the length of the shelf A is determined by the formula (8)

$$A=F/B=\mathrm{one}.785/\mathrm{one}.\mathrm{one}=\mathrm{one}.7m.(8)$$

The total area of the drying surface is found by the formula (9)

$$F_{\mathrm{from}\mathrm{at}w}=n\cdot F=20\cdot \mathrm{one}.875=37.5m^2,(9)$$

where n = n ₁ + n ₂ = 9 + 11 = 20 pcs. - total number of shelves in the dryer.

We determine the specific productivity of the dryer by the formula (10)

$$q=Q/F_{\mathrm{from}\mathrm{at}w},\mathrm{to}g/(h\cdot m^2).(\mathrm{one}0)$$

Thus, in comparison with the prototype, in which the drying surface area is 42.2 m ² and the specific productivity q = Q / F _sush = 400 / 42.2 = 9.48 kg / (h · m ² ), in the dryer proposed as an example of the invention, the specific productivity is q = Q / F _sushi = 400 / 37.5 = 10.7 kg / (h · m ² ). Thus, as a result of an increase in the specific productivity of the proposed dryer, our conclusions about reducing the overall dimensions of the installation and reducing energy costs are confirmed.

A dryer for short pasta, cited as an example of the use of the invention, operates as follows. After hydrothermal treatment, the product by pneumatic transport (not shown in Fig.) Is fed through the loading hole 2 and falls onto the belt of the conveyor 11 of the loading mechanism 3. The carriage 12 with the conveyor 11 moves back and forth along the drying chamber from one wall to another. Products from the conveyor belt 11 are poured onto the upper shelf 17 and scattered evenly over the entire surface due to the fact that the linear speed of the conveyor belt 11 is greater than the linear speed of the carriage 12 with the total speed of the drive 13. After the time specified by the technological process, the mechanism is activated the rotation of the plates 5. Installed on the traction device 44 of the rotation mechanism 5, two pushers 42 and 43 move clockwise and rotate the plates 16 of the first eight shelves with each passage of both pushers 42 and 43. The plates of the remaining rows of shelves rotate due to the movement of the pusher 42 in the form of a single trapezoid and the displacement of the bushings 41 mounted on the axes 39 and 40 at the ends of the levers 38, which allows you to stack, starting from the ninth row of shelves, a double portion of the dried product and, accordingly, increase product layer thickness. The product, located on the first shelf 17, is poured onto the second shelf 18, falling into the air lock, where the parameters of the dried product are partially stabilized. The next time the rotation mechanism 5 is activated, the product to be dried falls onto the next shelf, etc. Six horizontal shelves pass in succession, where preliminary drying is carried out. Upon further activation of the rotation mechanism 4, the product falls on the shelf 20 of the second air lock, where the secondary partial stabilization of the product is carried out. Moreover, the supply of the product to the shelf 20 is carried out twice, while the thickness of the product layer increases. The next actuation of the rotation mechanism 5 moves the product to the shelf of the main drying zone. Then, when turning the plates, the product passes successively the remaining horizontal shelves and falls on the shelf 22 of the third air lock. It should be noted that the air gates prevent air flow between the preliminary and main drying zones, as well as the release of air into the workshop room at the time of loading and unloading the product. At the next turn of the plates of the shelf 22, the product enters the unloading device 10. The time for turning on the mechanism can vary and is selected depending on the type of product. The movement of air is as follows. The fan 22 through the valve 26, the recuperator 9 and the duct 6 draws in atmospheric air. After passing through the heater 24, it as a drying agent with a temperature of 70-80 ° C and a relative humidity of 45-50% through the diffuser 29 enters the pre-drying zone, where the dried product is on horizontal shelves. When blowing the product as a result of the heat exchange process, the temperature of the drying agent decreases. Thus, having passed the pre-drying zone, the drying agent enters the confuser 31 and then there is partial mixing with atmospheric air, which is sucked in by the fan 23 through the valve 27 and the air duct 7. After heating in the heater 25, having a temperature of 45-55 ° С and relative humidity 75-80%, the drying agent is sent to the main drying zone. Here he gives up part of the thermal energy and its temperature decreases. Next, the spent drying agent through the confuser 33 and the duct 8 enters the recuperator 9, where it gives up another part of the thermal energy to the fresh newly incoming air, and then is discharged into the atmosphere. It should be noted that the drying zones are separated from each other and from the premises of the workshop with air locks, where the drying agent does not move.

Due to this design, the drying agent has strictly specified parameters, i.e. there is no mixing of the drying agent of different zones, due to which the drying process is increased and there is no emission of the drying agent into the premises of the workshop, which allows to increase the drying efficiency. The proposed dryer allows for drying the product to produce drying with maximum use of thermal energy. When using a dryer, heat recovery is achieved, and this increases the drying efficiency. Due to the proposed design of a dryer for bulk thermosensitive materials, the specific drying capacity increases. Placing structurally local drying zones in a single casing of the drying chamber, which are calculated taking into account the technological process and the moisture content of the dried material over time, reduced drying time and improved the quality of dried pasta (color and cooking properties) and their microbiological condition, reduced energy consumption and reduce weight and size parameters per unit of produced products. Improving the drying efficiency is achieved by organizing directed intense contact of the coolant with the material to be dried and eliminating mechanical damage to the surface and shape of the products when moving the material in the dryer during pouring.

Information sources

1. Equipment for drying food / Chagin OV, Kokina NR, Pastin VV: Ivan. chemical technol. University: Ivanovo. 2007 - C.117.

2. Polyakov E.S. Technology and equipment of pasta production. - M .: Food industry, 1968 - P.188.

3. Ginzburg A.S. Calculation and design of drying plants for the food industry. - M .: Agropromizdat, 1985 .-- 336 p.

Claims (1)

A dryer for bulk thermosensitive materials, comprising a housing, a loading mechanism in the form of a conveyor belt and a movable carriage, a drying chamber with drying surfaces located inside in the form of horizontal shelves of plates mounted rotatably from the plate turning mechanism with pushers on a traction device, a ventilation-calorifer a system with air ducts for supplying a prepared drying agent to the space between horizontal shelves with the creation of various drying zones, unloaded A device, characterized in that the loading mechanism is made in the form of one belt conveyor mounted on a movable carriage with the possibility of reciprocating movement from the wall of the drying chamber to the opposite along the horizontal shelf, and the linear speed of the conveyor belt is greater than the linear speed of the carriage due to that the carriage wheels and the conveyor drum have different diameters and are located on the same shaft with a common rotation speed; the plate turning mechanism contains two opposing pushers, one of which is made in the form of an isosceles trapezoid, the second in the form of two isosceles trapezoids, and a ventilation-air heater with air ducts is placed inside the housing and contains two air ducts with a recuperator installed on one side of the drying chamber with the possibility of creating the first the drying zone and on the opposite side of the drying chamber an additional duct is installed with the possibility of creating a second drying zone, and the drying zone is limited to stuffy closures formed by horizontal flanges which prevent cross-flows of air between the drying zones.

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