RU2851240C1 - Installation for drying bulk materials with boiling layer - Google Patents

Abstract

FIELD: drying devices.

SUBSTANCE: invention is intended for drying bulk materials, such as grain crops and other granular materials. In a fluidised bed drying plant for bulk materials, the bulk material to be dried is suspended in a state of suspension and blown with a heated air stream. A distinctive feature of the plant is that it is designed in the form of a vertically arranged cylinder divided by horizontal partitions containing through holes into several drying chambers, connected in series by pipelines located alternately on opposite sides, with conical projections installed on each horizontal partition between the through holes, the base diameter of which is determined depending on the diameter of the partition hole, the outlet pipes are located at an angle of α = 5°, the length of which is determined depending on the diameter of the drying section, the height of the outlet pipe above the partitions, from the lower section to the upper section, is determined depending on the height of the outlet pipe above the partition of the first section.

EFFECT: increased efficiency of heat and mass transfer between the drying agent and the material being dried by maximising the volume of each drying chamber.

1 cl, 3 dwg

Description

The proposed invention relates to drying devices and is intended for drying bulk materials, such as grain crops and other granular materials.

Devices for drying bulk materials are known, comprising a drying chamber in which the material to be dried is blown with a stream of heated air or other heated gas. In particular, a shaft drying unit for bulk materials is known, comprising a loading bin, a vertical drying chamber, a blower fan, and bulk material feeders (Utility Model Patent No. 105726 IPC 7 F26B 17/12, IPC 7 F26B 3/347, published 06.20.2011). Shaft drying units have a relatively low productivity due to the low throughput of the drying chamber.

The process of drying bulk material occurs most intensively in the so-called fluidized or boiling bed, in which the particles of bulk material are in a suspended state and are intensively flown by a gas stream (Kavetsky G.R., Vasiliev B.V. Processes and equipment for food technology. - M.: Kolos S, 2000. - P. 171).

A fluidized bed drying unit is known, containing a drying chamber in which the bulk material to be dried is suspended and blown by a heated air stream. (Plaksin Yu.M., Malakhov N.N., Larin B.A. Processes and equipment for food production. - Moscow: Kolos S, 2005. - P. 543). In this unit, particles of the bulk material are washed on all sides by a heated air stream, which creates favorable conditions for heat exchange and thereby ensures a high-intensity drying process.

This drying system has the following drawback. The contact time between the airflow and the material being dried is excessively short due to the low height of the granular material layer through which the airflow passes. Therefore, the potential drying capacity of the airflow is not utilized effectively, meaning it is not fully utilized, resulting in increased consumption of heated airflow.

The closest technical solution in terms of the set of features to the claimed object and adopted as a prototype is an installation for drying bulk materials with a fluidized bed, in which the bulk material to be dried is blown with a heated air flow and is in a boiling state, which is made in the form of a vertically located cylinder, divided by horizontal partitions containing through openings, into several drying chambers, sequentially connected to each other by pipelines located alternately on opposite sides of the cylinder, wherein the through openings located in the circular segments of the partitions adjacent to the inlet openings of the pipelines have a diameter 1.5 ... 2 times smaller than the diameter of the remaining openings of the partitions, and the height of these segments is 1.2 ... 1.5 times greater than the width of the inlet openings of the pipelines. [PM RF No. 218097, IPC F26B 17/10, published. [05.11.2023].

The disadvantages of this design include the inability to create a uniform fluidized bed in each section due to the adhesion of bulk material particles to the non-perforated surface of the baffle, the formation of complete or partial channeling within the bed, and stagnant zones between the baffle perforations. Particle entrainment is also possible in the area where material flows through the pipeline into the next section, due to the high apparent velocity of heated air in the baffle perforations with a smaller flow area, compared to the much lower apparent velocity in perforations with a larger flow area. All of the above indicates low efficiency of heat and mass transfer between the drying agent and the material being dried, and, consequently, of the entire drying system.

The technical result consists in increasing the efficiency of heat and mass transfer between the drying agent and the material being dried by maximizing the use of the volume of each drying chamber.

The stated technical result is achieved in an installation for drying bulk materials, which is made in the form of a vertically located cylinder, divided by horizontal partitions containing through holes, into several drying chambers, successively connected to each other by pipelines located alternately on opposite sides, and on each horizontal partition between the through holes conical protrusions are installed, the base diameter of which is determined by the expression

d ₁ = 0.9⋅d,

where d ₁ is the diameter of the protrusion, m,

d - diameter of the partition opening, M,

and the outlet pipes are located AT an angle of α=5°, the length of which is determined by the ratio

l=0.33⋅D,

where l is the length of the outlet pipe, m,

D - diameter of the drying section, m,

and the height of the outlet pipe above the partitions, from the lower section to the upper section, is determined by the expression

h _i =(0.935 ^[i-1] )⋅h ₁ ,

where h ⁱ is the height of the outlet pipeline above the partition of the i-th section, m,

h ₁ - height of the outlet pipeline above the partition of the first section, m,

i=2,3…n - section number,

n is the number of sections.

Installing conical protrusions between the through-holes on the baffle will create a uniform fluidized bed within the working volume of the section and prevent the adhesion of particles of the drying material to the baffle surface by preventing continuous contact between the particles of the drying material and the heated surface of the baffle. The installation of the protrusions will also allow particles of the drying material within the bed to move freely (due to the streamlined shape of the protrusion) from the entrance to the exit of the working zone, which will collectively improve the efficiency of heat and mass transfer between the drying agent and the material being dried.

The diameter of the base of the conical protrusion, determined by formula (1), will eliminate the creation of a layer of material on the non-perforated part of the horizontal partition, which will thereby prevent contact of particles of the material being dried with the surface of the partition and, as a result, eliminate sticking, which in total will allow the most efficient heat and mass transfer between the drying agent and the material being dried.

The execution of the outlet pipe at an angle of α=5° and a length determined by the ratio (2) will allow the particles of the material being dried to move spontaneously from one section to another, which will eliminate overdrying of the particles in one section, and as a consequence will allow the most efficient heat and mass transfer between the drying agent and the material being dried.

The height of the discharge pipe above the baffles, starting from the lower section and ending at the upper section, determined by expression (3), allows for the efficient removal of dried material from each section, preventing overheating and excessive moisture removal (overdrying). The difference in height is due to the various process parameters in each section (drying capacity, air moisture content, bulk material layer porosity), which collectively alter the height of the dehydrating bed and, consequently, the height of the drying material layer and the discharge height of the finished dried material. All of the above, taken together, allows for the process to be carried out under specified process conditions and, consequently, for the most efficient heat and mass transfer between the drying agent and the material being dried.

Fig. 1 shows a general view of the installation, Fig. 2 shows an enlarged fragment A, and Fig. 3 shows a section along section A-A.

The installation for drying bulk materials is made of a housing 1, a conical bottom 2 installed on a conical bottom 3, a cover 4 with a branch pipe 5 for removing the drying agent, on which a hopper 6 for loading the material to be dried with a slide valve 7 is installed. The housing 1 is divided into sections by horizontal partitions 8, 9, 10, the flow between which occurs through pipelines 11 and 12, and unloading - through a branch pipe 13, which are equipped with transfer pipes 14, 15 and 16 located at an angle of α = 5° to the horizon, at a height relative to the horizontal partitions 8, 9 and 10 determined by expression (3), and a length determined by expression (2). Horizontal partitions 8, 9, 10 contain openings 17 and conical projections 18, the diameter of which is determined by expression (1).

The unit operates as follows. The drying agent is fed through conical bottom 2 into body 1 and passes through the entire apparatus, leaving it through drying agent outlet pipe 5. The material to be dried is fed after the gate valve 7 is opened from the hopper 6 into the body 1 into the first section, which is formed by the horizontal partition 8. In the section itself, the material begins to contact with the drying agent, passing into the state of a fluidized bed and in the absence of contact of the material with the surface of the partition 8 under conditions of creating a fictitious entrainment velocity in the lower part of the section due to the installation of conical projections 18 between the openings 17 of the partition 8. When drying the material in the section, the removed moisture will leave together with the drying agent through the branch pipe 5, and the dried particles of the material will rise along the height of the layer and enter the transfer pipe 14, the location of which at an angle of α=5° to the horizon allows the particles to move arbitrarily into the pipeline 11 and enter the next section, limited by the partitions 8 and 9. When the material to be dried reaches the third section, the dried particles are unloaded from the apparatus through the branch pipe 13.

An example of calculating the geometry of the device.

The density of the material particles is ρ _h = 1370 kg/m ³ , and the diameter of the particles is d _h = 3 mm. The diameter of the housing 1 (drying section) is D = 1 m.

For bed particles, the onset velocity of fluidization will be

Where - Reynolds criterion for the onset of fluidization;

- Archimedes criterion;

μ - viscosity of the drying agent (air), Pa⋅s;

d _h - diameter of particles of the material being dried, m;

ρ _c - density of drying agent (air), kg/m ³ ;

ρ _h - density of material particles, kg/m ³ ;

g=9.81 – acceleration of gravity, m/ ^s2 .

Then the Archimedes criterion is equal to

Then the Reynolds criterion is equal to

And the speed of the onset of fluidization

Speed of the beginning of the carryover

Where - Reynolds criterion for particle entrainment.

Then the Reynolds criterion for particle entrainment is

and the speed of carryover

Since the operating air velocity in the dryer must be between the initial fluidization velocity and the entrainment velocity, we will take the operating air velocity to be u = 9 m/s. Then the volumetric flow rate of the drying agent will be

The number of protrusions corresponds to the number of holes, and the area of the holes on the partition is 22% of the section area and is equal _to S = 0.1727 m ² . Let the diameter of the hole be equal _to d = 5 mm, then the number of holes on each partition will be equal to

And the area of the lower edge of the protrusions

S _height =n⋅(0.9⋅d _from ) ² ⋅0.785=8800⋅(0.9⋅0.005) ² ⋅0.785=0.139 m ² .

Let us assume a 5% reduction in the area of the protrusion relative to the base, then the flow rate of the drying agent at a given height will be equal to

Consequently, the particles will not come into contact with the surface of the partition and will float freely in the volume.

G = 1000 kg/h of material to be dried is fed to the drying unit. The moisture intensity of the fluidized bed apparatus will be A _v = 44 [kg moisture/(m ³ ⋅h)]. Moisture is removed from the material with an initial moisture content w _n = 52% to a final moisture content w _k = T3%. In the upper section, 7.8% of moisture is removed, in the subsequent sections, 11.7% and 19.5%, respectively. Then G ₁ = G = 1000 kg/h will be fed to the upper section and G _w1 = 139.8 kg/h of moisture will be removed from the material. In the subsequent section, G ₂ = G ₁ - G _w1 = 860.2 kg/h of wet material will be fed, and the moisture removed will be G _w2 = 149.1 kg/h. The last section will be supplied with G ₃ = G ₂ - _{G w2} = 711.1 kg/hour, and the moisture removed will be G _w3 = 159.4 kg/hour.

Then the height of the layer in the lower section will be

Similarly for subsequent sections: h ₂ = 4.32 m, h ₃ = 4.05 m.

According to equation (3) h ₂ = 4.31 m, h ₃ = 4.03 m. The height differences allow for the removal of a sufficient amount of material from the layer to ensure the specified productivity.

Thus, a unit for drying bulk materials, made in the form of a vertically located cylinder, divided by horizontal partitions containing through holes, into several drying chambers, sequentially connected to each other by pipelines located alternately on opposite sides, where on each horizontal partition between the through holes conical protrusions are installed, allows for an increase in the efficiency of heat and mass transfer between the drying agent and the material being dried.

Claims (14)

An installation for drying bulk materials, which is made in the form of a vertically located cylinder, divided by horizontal partitions containing through holes, into several drying chambers, successively connected to each other by pipelines located alternately on opposite sides, characterized in that on each horizontal partition between the through holes conical protrusions are installed, the diameter of the base of which is determined by the expression d ₁ = 0.9d, where d ₁ is the diameter of the protrusion, m, d - diameter of the partition opening, m, and the outlet pipes are located at an angle of α=5°, the length of which is determined by the ratio l=0.33⋅D, where l is the length of the outlet pipe, m, D - diameter of the drying section, m, and the height of the outlet pipe above the partitions, from the lower section to the upper section, is determined by the expression h _i =(0.935 ^[i-1] )-h ₁ , where h _i is the height of the outlet pipeline above the partition of the i-th section, m, h ₁ - height of the outlet pipeline above the partition of the first section, m, i=2,3,…n - section number, n is the number of sections.