RU1815566C - Device for processing friable materials - Google Patents

Abstract

Usage: heat power, heat and mass transfer, heating and cooling of bulk materials with a gaseous coolant. SUMMARY OF THE INVENTION: bulk material through a loading unit 2 enters the shelves 4 located in the housing and, pouring over the latter, is washed by incoming. meeting gaseous coolant. There are two parallel passages in the shaft for bulk material, each of which is formed by two rows of parallel shelves, the latter in rows arranged offset in height and at an angle to one another. The angle of inclination of the shelves 4 is 25-45 °. The width of the shelf is 2-10 times greater than the shortest distance between adjacent shelves in the running range, 2-3.3 times greater than the part of the width of the shelf 4, located above the conditional line of intersection of the planes of the neighboring rows of shelves 4, by 3.3- 10 times the shortest distance between the shelves in adjacent rows of different moves, as well as 3.3-10 times the distance from the shelves of the series closest to the shaft wall to the last. 1 ill. ate with

Description

FIELD OF THE INVENTION This invention relates to heat exchangers for direct contact between a gas and a solid bulk finely divided material moving by gravity. The heat exchanger is intended for heating (cooling) of bulk materials by a gaseous heat carrier, the temperature of which is higher (lower) than the permissible temperature for the processed materials. The heat exchanger can be used in the building materials industry, in the chemical, food and other industries of the national economy; for example: as a waste gas heat exchanger for preheating a charge before loading it into a glass melting furnace, into a furnace for melting basalt or other silicate materials; during heat treatment of granular polymeric materials, cereals, etc.

An object of the invention is to increase heat exchange efficiency.

The problem is solved in that in a device for processing bulk materials containing a vertical shaft formed by the walls with loading and unloading units, respectively, in the upper and lower parts, located between the last, at least two parallel passages for bulk material, each of which is formed two rows of parallel shelves, the latter in the rows placed with an offset in height and below: angular one relative to the other, according to the invention, the angle of inclination of the shelves (a.) is 25 a 45 °, and the width and the shelves are 2-10 times greater than the shortest distance between adjacent shelves in the running range, 2-3.3 times greater than the portion of the width of the shelf located above the conditional line of intersection of the planes of the neighboring shelves in the rows, exceeds 3.3-10 times the shortest distance between the shelves in adjacent rows of different passages, and also 3.3-10 times - the distance from the shelves closest to the shaft wall of the row to the last.

The residence time of particles in the heat-exchange chamber (contact time) leads to an increase in the efficiency of the heat exchanger due to heating of the material to higher temperatures by the gas coolant without increasing the height of the shaft of the heat exchanger, or, ceteris paribus, reducing the height of the heat exchanger, or other conditions being equal reduction of the height of the heat exchanger of the claimed design in comparison with others. This ensures high uniformity of heat treatment of bulk materials

with a deviation of the residence time of individual particles in the heat exchanger shaft of not more than 6.5% ...

The second, no less significant effect is an increase in the amount of heat transferred, which leads to an increase in the efficiency of the heat exchanger due to the intensification of heat transfer between the solid and gaseous coolant when installing shelves with

the optimal gap between adjacent pairs of rows and between the shelves and side walls of the chamber-shaft.

In addition., A comparison of the claimed design of the heat exchanger with the prototype

in two-stream schemes (with two pairs of vertical rows of shelves) with the angles of inclination of the shelves a 30 °, the ratio of the width of the shelves and the shortest distance between adjacent shelves in the range of 3.3; width

shelves and part of the width of the shelf located above the conditional line of intersection of the planes of the shelves adjacent in the rows of travel 2.5: 1, the width of the shelves and the shortest distance between the shelves in adjacent rows of different

5: 1 moves; the width of the shelves and the distance from the shelves closest to the wall of the mine row to the last 5: 1 showed an excess of more than 17% in the efficiency of using the total volume of the heat exchange chamber for

due to more compact placement of adjacent pairs of rows,

The proposed design of a device for processing bulk materials is shown in the drawing, which shows a heat exchanger with two pairs of vertical rows of shelves providing two parallel particle flows.

The device comprises a shaft 1 formed by vertical walls. In the upper and lower parts, loading units 2 and unloading units 3 for bulk material are installed. At least two parallel passages for bulk material are located between them, each of which is formed by two rows of parallel shelves 4. At the bottom there is a gaseous coolant supply device 5. The shelves in the rows are arranged with a height offset of one relative to

other. They are located with an inclination angle of 25 a 45 °. The width of the shelf (B) is 2-10 times greater than the shortest distance between adjacent shelves in the travel ranges (C). In addition, the width of the shelf (B) is 2-3.3 times greater than the part of the width of the shelf located above the conditional line of intersection of the planes of the adjacent shelves (b). Moreover, it is 3.3-10 times higher than the shortest distance between the shelves in neighboring

in rows of different passages (d) and 3.3 to 10 times the distance from the shelves of the row nearest to the shaft wall to the last (d).

The heat exchanger operates as follows. From below, a gaseous coolant, for example, high-temperature products coming from a furnace or furnace in the case of heating of a dispersed material, is supplied through a shaft 1 through a gaseous coolant supply device. When it is necessary to cool hot particles, cold air, nitrogen, steam or another gas is supplied depending on the requirements of the technology. From above, using a loading unit (loading device) 2, dispersed material is continuously fed to separate streams. Particles of material enter the first shelves along the material. Along the inclined surface of the first shelf 4, particles of material roll up if their shape is close to the ball, or slip down in the case of another shape. Acceleration by gravity over the surface of the shelf 4 particles then fly about a straight distance between the first and second shelves, hit the surface of the underlying shelf, jump up, again fall to the surface above the point of impact (the intersection of adjacent planes shelves) and then slide down to collide with the third shelf along the movement of particles. Further, the particle path is repeated many times. When particles move in the heat exchanger shaft, they are heated directly from the gases, as well as from the surface of the shelves 4 in contact with them. The shelves 4 themselves are heated by flushing them with a stream of gases. From the last during the movement of the material, the shelves 4 particles are poured into the hopper of the unloading unit (device for unloading bulk material) 3.

The experimental bench, which determined the optimal geometric parameters for the movement of bulk material nd to the shelves of the heat exchanger, consisted of two vertically arranged parallel walls of transparent plexiglass. Wall dimensions: height 2000 mm, width 300 mm, distance between them 50 mm. Inside the walls, plates were mounted perpendicular to their surfaces, which imitated the shelves of a heat exchanger. The walls along the edges were fastened together by stitches and thus fixed the shelves in the required position. Such a design made it possible, if necessary, to easily change the shelves, their angle of inclination and the gaps between them.

A small hopper with a feeder equipped with an electromagnetic shutter was installed in the upper part of the stand. The feeder hole was located at the top of the first shelf along the movement of particles. A photosensor was installed at the bottom of the last along the movement of 5 particles of the shelf from the outside of one of the walls. Opposite the other wall was a point source of light, whose sharp beam was directed to the photosensor. The optical system was tuned so that particles gliding along the shelf interrupted the flow of light. When the electric shutter was turned on to open the hopper, an electric pulse was recorded on the tape of the recorder, which was moving at a constant speed. A photosensor was connected to the same recorder.

The tests were carried out as follows. A fixed and constant portion of particles with a volume of 23 cm3 was poured into the hopper with the shutter closed. Then, by pressing the button, they opened the shutter, which was fixed on

5 diagram tape, and a portion of particles 0.2-0.3 poured onto the first shelf. Further, the particles continued to move, according to the accepted scheme, along the shelves and during the passage of the last shelf they interrupted the light

0 thread. EMF surges were visible on the tape of the recorder. The distance between the EMF peaks on the diagram tape from the start of the relay on and the first particle passed by the photocell corresponded to the time the particles spent in the shaft for this shelf arrangement. In addition, on the chart tape, it was possible to determine the spread in the travel time along a:

5 particles. If all particles moved according to a certain law, then the scatter between the initial peak indicated by the photocell and the last was Dt 0.2-0.5 s. When

5 particles moved randomly, strongly colliding and jumping over the top of the shelves - the time spread was from 0.5 to 5 s.

The studies were performed on a single stream and for two wavelengths, - 60 mm and 120

0 mm, and, accordingly, the number of shelves, n - 32 and 16 pieces. The geometric I / O ratios ranged from 2 to 5; B / C- from 1.58 to 2 ,; the angle of the shelves and from 25 to 47 °. Accordingly, the height between the beginning

5 of the first shelf and the end of the last changed from 446 to 1965 mm. Three types of particles were used; from crushed separated basalt (grains) of two fractions, di 3-5 mm in size, as well as pellets from high alumina ceramics with a di di 3-4 mm in diameter. The laws of particle motion and the optimum geometric parameters are verified

on various materials of shelves - ceramics made of rough chamotte, rolled steel with an oxidized surface and smooth organic glass.

In order to compare different types of heat exchangers, studies were carried out both for the claimed scheme and for the prototype, as well as for a heat exchanger with horizontal shelves, for free fall of particles and sliding-rolling along one inclined plane located along the entire height of the compared heat exchangers. The main parameters of the claimed heat exchanger and prototype were taken equal, i.e. they had an equal height of H 864 mm, the same number of shelves n 32 pieces and the same length B 60 MM; The inventive design and prototype shelves were installed at an angle a. 30 ° with a ratio of geometric parameters B / C 3.3; I / O 2.5. According to the operation scheme of the heat exchanger with horizontally located shelves bounded by a wall on one side, the disperse material under investigation was poured onto them until an angle of repose was formed. The scheme and the ratio of geometric parameters for which the transit time of particles r through the shelves was maximum with a minimum scatter Дг were best accepted.

Initially, the angle of the beginning of rolling (sliding) of the test particles on the flat surface of steel, ceramic and plexiglass plates was determined experimentally. To do this, a stop was placed on one side of the plate located on the table surface, and the other side, on which the particles were located, was slowly lifted until the particles started to slide down. In this position, the angle between the planes of the table and plate was measured. For the listed materials of particles and shelves, the angles of the beginning of rolling (sliding) were obtained in the range from 16 to 25 °.

All tests of the design of the heat exchanger were carried out, starting with an angle of inclination of the shelves of 25 °, since at smaller angles, as can be seen from previous studies, the heat exchanger is inoperative due to the fact that the material simply will not move along it.

The longest passage time of particles r through the heat exchanger shaft was obtained at an angle of inclination of the shelves of a to 45 °. At an angle a exceeding 45 °, a sharp approximately 3-5 times decrease in the time r is observed, while the transit time of the particles within the tilt of the shelves from 25 to 44 ° varies slightly, by about 20-30%.

The large spread at 45 ° is explained by the shelf installation error, which is ± 0.5 °.

The longest particle transit times were obtained for I / O 2-3.3; B / C 2-10, which corresponds to the claimed ratio. It is characteristic that

ratios of parameters were in the range of 0.3-0.8 s. At B / C greater than 10, there was a strong spread in particle transit time, Dg 3-5 s. In the case of B / C less than 2, the time g markedly decreased.

Exceeding the optimal I / O values led to the emission of particles through the upper part of the shelves, and underestimation led to an abrupt decrease.

Note that the hopping character

changes when exceeding the declared geometric ratios are maintained even with an increase in the length of the shelves from 60 to 120 mm and a decrease in their number from 32 to 16 pieces at the same heights, although

there is a reduction in time g by about 20-30%.

In experiments with different sizes and shapes of the dispersed material (grains and pellets), the jump-like nature of the time change r also remains with the parameters passing over the claimed range of values.

The material of the shelves does not affect the measurement error over time

g and its scatter Дг. Therefore, the averaged experimental data were considered. The accuracy of the determination is ± 10%. The results of a comparison of different heat exchanger circuits showed that

particle transit time obtained

for the claimed design, t - 7.70 s. and with a minimum spread of Dg of 0.5 s. The time g for the heat exchanger with horizontal shelves was 3.63 s and the spread of Dg was 4.2 s. For comparison, the falling time of particles from the same height is 0.43 s and when the particle moves on an inclined plane g 0.62 s at a 30 °.

An experimental bench was made to conduct thermotechnical studies to determine the optimal arrangement of pairs of vertical rows of shelves in a heat exchange chamber. It included; metal model of the heat exchanger and gaseous coolant supply system.

The heat exchanger model contained end walls with a height of 2000 mm and a width of 400 mm, to which 32 inclined panels 50 mm long and 60 mm wide were attached. The shelves are mounted in the form of one pair of vertical rows with relative positioning parameters optimal for the movement of solid particles (a 30 °; I / O 2.5; I / O 3.3). The design of the model allows the side walls of the model to be installed at various distances from the vertical rows of shelves with a width of 50 mm and a height of 2000 mm.

 The gaseous coolant supply system is made up of air ducts, a gate to control air flow, a flow diaphragm with a differential pressure gauge, a chromel-kopel thermocouple for measuring the air heating temperature, a fan and an electric heater with a stepless control of the level of air heating used as the gaseous heat transfer medium. As a bulk coolant, basalt grains of di 2-43 mm in size were chosen. The amount of heat transferred in the heat exchanger from the heated air to the bulk material was determined by the calorie-1 metric method. The basalt particles subjected to heating were collected by means of a funnel into a thermally insulated vessel filled with water. The amount of heat transferred in the heat exchanger brought with the material heated in the heat exchanger was determined by changing the temperature of a known amount of water in the vessel. Measurements were made using a chromel-kopel thermocouple.

During the study, the air flow rate QB was set at 7.5 m3 / h with a temperature at the inlet to the heat exchanger tMi 350 ° C. bulk material was loaded into the heat exchanger with 4, g samples each. The initial temperature of the material and water in the insulated vessel was tMi 18.3 ° C.

In each experiment, 200 ml of water was poured into a vessel from a separate container and its temperature was monitored. Then the material was loaded into the heat exchanger and the change in water temperature was recorded after the heated material entered the vessel.

Measurements were made at distances from shelves to side walls, varying from 0 to 21 mm in increments of 3 mm.

As can be seen from the experimental results, the maximum amount of heat transferred from the gaseous coolant to the bulk material takes place at B / d values of 3.3-10. At high values, the resulting stagnant zones

Claims (1)

between the side walls and shelves reduce the heat transfer efficiency, and at lower - the relative speed of the heat carrier is reduced. The claims A device for processing bulk materials, comprising a vertical shaft formed by the walls with loading and unloading units, respectively, in the upper and lower parts, located between the last at least two parallel passages for bulk material, each of which is formed by two rows of parallel shelves, the latter are placed in rows with an offset in height and under one relative to the other, characterized in that, in order to increase the efficiency of heat transfer, the angle of inclination of the shelves is 25-45 °, and the width of the shelf is 2-10 times the shortest the distance between adjacent shelves in the rows of travel is 2-3 times greater than the part of the width of the shelf located above the conditional line of intersection of the planes of the shelves adjacent in the rows of travel is 3.3-10 times the shortest distance between the shelves in adjacent rows of different passages, as well as 3.3-10 times - the distance from the shelves closest to the shaft wall of the row to the last.