SU748102A1 - Fluidised-bed drying chamber - Google Patents

Description

I

The invention relates to the drying of bulk materials, for example, table salt, in a fluidized bed.

Apparatuses for drying bulk materials in a fluidized bed are known, comprising a housing with a gas distribution grid, a subgrid gas chamber, and a device for introducing and withdrawing material (I.

The disadvantage of these apparatuses is that the supply of wet material to the bed is carried out in a concentrated flow.

Fluid bed chambers are also known, containing an upwardly expanding body, equipped with a gas distribution grid, loading and unloading devices, and a rotary spreader, located under the loading device 2.

These cameras have the following disadvantages:

- high specific costs for drying, due to the need to heat cold air entering the drying chamber through a pneumatic spreader in order to avoid the occurrence of a dew point in the dust collection means;

- the intensity of the process of the drying process is not sufficiently high due to the very rapid growth of the nozzle of the pneumatic spreader solk1; a curtain of wet material is not created above the layer, and this leads to the need for

from reducing the operating speed of the fluidizing agent in order to avoid large entrainment of the material and, consequently, to reduce the intensity of the process of the substance;

- low reliability, since due to the formation of build-up of salt on the wall of the drying chamber under the spreader and the collapse of these build-ups on the gas distribution grid, non-working zones appear on the latter, which eventually leads to device malfunction; for cleaning the walls and the grate from salt build-ups requires-,

15 n every shift stop of the device for at least 1 hour;

- relatively high energy costs due to the need to maintain a high layer, which is a consequence of the unsuccessful layout of the spreader (outside the drying chamber) and low reliability of the pneumatic spreader: after the failure of the pneumatic spreader, the salt slips into the layer in a concentrated flow along the wall of the drying chamber and in order to avoid stagnation zones on the grid layer must be kept high. The purpose of the invention is to intensify the drying process and reduce energy consumption. This is achieved by the fact that the spreader is inserted into the body, and over the entire width of the wall of the latter under the spreader, a three-dimensional guide is fixed, having a triangle shape with cross-section with concave sides tangential to the wall of the body. The drawing schematically shows the described chamber of the fluidized bed. The chamber includes a housing 1 with an inclined gas distribution grid 2 with gas supply box 3 under it and a rotary thrower 4 placed under the loading device 5 and inserted into the housing I. Under the thrower 4, along the body wall 1, a volume guide 6 is reinforced, having the cross section is a triangle shape with concave sides 7 and 8, tangent to the wall of the housing. To unload the dried material, a discharge device 9 is provided, for the supply of fresh coolant - nozzle 10, for withdrawal of spent coolant - nozzle 11. The chamber works as follows. The coolant comes from the duct 3 and leads to a fluidized state located on the inclined gas distribution grid 2 a layer of salt, transfers part of its heat to the layer (at the same time heat and mass transfer processes occur between the coolant and salt) and is discharged through pipe 11. In the duct 3 an overpressure is maintained, and a slight vacuum is maintained above the layer (up to 3 mm water. Art.). Wet salt is loaded into the drying chamber by the loading device 5. Using the spreader 4 and side 7 of the triangular guide 6, the concentrated flow of the initial salt is pre-destroyed, and with the help of a jet of heat-transfer agent that slides along the side 8 of the guide 6 and acquires horizontal direction, the final distribution of salt over the front layer. The dried salt is unloaded from the lattice level by the unloading device 9. The layer moves along the chamber from the point where the wet salt is loaded to the point of discharge of the neck salt. The direction of movement of the coolant through the layer and the layer itself is a cross. Due to the inclination of the grate 2 and the presence of the unloading device 9, the boiling layer is ravi-high along the length of the apparatus, the layer has a minimum height under the spreader 4, and the maximum height for the discharging device 9. Since the living section of the grid 2 along the chamber is constant, and the layer height at the beginning of the chamber is less than at the end of it, the coolant passes through the layer at different speeds at different points along the chamber: the velocity of the coolant at the beginning of the chamber is greater, at the end - less. Because of this gassing, the porosity of the fluidized bed is variable along the length of the chamber: at the beginning of the chamber, the porosity of the layer is greatest, at the end - the smallest, as a result of which, in addition to the usual chaotic movement of particles, there is an additional directional movement of particles. In a vertical longitudinal section of a layer with respect to any of its points, a mixture of nearby particles makes a circular motion clockwise. Because of this, the resultant additional particle motion at the level of the lattice 2 is directed against the motion of the layer, and in the upper part of the layer coincides with the direction of its movement along the chamber. Such a character of the additional movement of particles eliminates the possibility of local stagnation zones on the lattice 2 and, therefore, eliminates the possibility of long-term stay of particles in this zone (for example, in the zone under side 8 of guide 6). The passage of the coolant with the highest velocities through that part of the layer, which is located under side 8, contributes to the emergence of large horizontal velocities at the exit from it and, consequently, the effective distribution of wet salt particles over the front of the layer along the length of the chamber, and the scattering distance of particles of various sizes below The effect of the horizontal jet of the treated coolant is unequal: the range of throwing of large particles is less than that of small particles. This has a beneficial effect on the drying process. Large particles remain in the layer longer than small ones, and this contributes to the uniform substance of particles of various sizes. Due to the fact that the gas distribution grid 2 and the layer have a certain hydraulic resistance, the velocities of the exhaust heat transfer medium over the entire width of the chamber at the exit of the layer 3 and, consequently, at the outlet from side 8 of guide 6 are almost equal. This contributes to a uniform distribution of particles above the layer in the cross section of the chamber. Thus, in the chamber described above, the creation of a curtain of moist material over the front of the layer is carried out by the spent heat carrier, and not by cold air, as it happens in the known chambers. The use of spent heat carrier to create a curtain not only eliminates the need for additional heat loss, but on the contrary, leads to an additional use of heat due to the flow of heat and mass exchange processes between the spent heat carrier and the scattered wet salt. Moreover, the associated use of the properties of the gas distribution grid 2 and the layer as averagers of gas flow rates in the cross section of the chamber in combination with the influence of the side 8 of the guide 6 allows to solve the problem of providing a stable and highly-proportional distribution of wet salt over the layer front, and this, in its the turn allows to increase the flow rate of the coolant without increasing the entrainment of salt from the chamber {thereby intensifying the drying process) and reducing the hydraulic resistance of the layer (energy consumption) by reducing its height, while the loaded salt e punches the thickness of the fluidized bed and sticks to the grid.

Claims (2)

1. Romankov P. G., Raschkovska N. B. Drying in a suspended state. L., “Himi, 1968, p. 102 2. USSR author's certificate NS 163534, t. F 26 V .17 / 10. 1963.