RU2463536C2 - Counterflow spray dryer - Google Patents

Abstract

FIELD: power engineering.

SUBSTANCE: counterflow spray dryer comprises a cylindrical drying chamber with nozzles arranged on the upper level of the drying chamber, covering the lower level of the drying chamber from the outside, a gas duct in the form of a box with permanent cross section, separated into two compartments by a helical partition, the pitch of which is equal to the height of the box, a divider of a coolant flow arriving into the box into two flows sent into compartments into mutually opposite directions, gas-distribution grids at the coolant inlet into compartments, nozzles to supply coolant from compartments into a drying chamber arranged evenly on the upper and lower surfaces of the box. The helical partition comprises gas permeable parts that separate compartment sections that are initial and final along the coolant flow, every of which comprises at least one nozzle. Nozzles arranged on the upper surface of the box are displaced relative to the nozzles arranged on the lower surface of the box by half of the distance between neighbouring nozzles, and a part of the surface of the divider entering the box is perforated. Nozzles are arranged in plan at the angle of not more than 12° to conventional radii stretching in the drying chamber.

EFFECT: invention shall intensify drying process as a result of higher evenness of coolant distribution in a drying chamber and elimination of chamber walls overheating at coolant entry level.

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Description

The invention relates to techniques for spray drying and can be used in the production of powdered products, mainly synthetic detergents (CMC). These productions are equipped with counter-current spray nozzle dryers. The economical operation of dryers, product quality, and fire safety are due, in particular, to the uniform distribution of the coolant over the cross section of the drying chamber.

Known spray dryer [1], containing a cylindrical drying chamber with nozzles located at the upper level of the chamber, and covering the outside of the lower part of the chamber gas supply, made in the form of a duct with pipes for entering the coolant into the chamber. The box has a uniformly variable section, decreasing in the direction of the coolant. It is assumed that the gas flow velocity in the duct is constant, since the cross-sectional area decreases in proportion to the amount of gas discharged. The dynamic gas pressure is also constant, so the flow rate from each nozzle must be the same. With equal flow sections, this should ensure equal costs through each pipe. However, it was shown in [2] that collectors with uniformly variable cross-section have a common drawback: reduced flow rate through the first and last and increased flow rate through the middle pipes along the gas pipe. The authors experimentally found that the alignment of the velocity profile at the inlet to the manifold, for example, using a gas distribution grid, helps to increase the uniformity of flow rates through the nozzles. At the same time, through the first pipes along the gas flow, the flow rate becomes higher than the average, and a reduced flow rate through the last pipes along the gas flow is preserved [2, Fig. 2, curves 2 and 3].

The closest set of essential features to the proposed technical solution, adopted as a prototype, is a countercurrent spray dryer according to the patent [3]. The gas supply of the dryer is made in the form of a duct with a constant cross section and is divided into two isolated compartments by a screw partition with a step equal to the height of the duct. Gas is introduced into the drying chamber through nozzles that are evenly located on the upper and lower surfaces of the duct. To swirl the coolant flow entering the dryer, the nozzles are installed at an angle to the radial direction. The compartments of the box are collectors of uniformly variable cross-section; therefore, the design has a drawback characteristic of the dryer gas supply [1], i.e. the difference in flow in the nozzles. This entails uneven distribution of the coolant over the cross section of the drying chamber. A design drawback is also an overestimated angle of the nozzles relative to the radial direction. With this solution, cases of overheating of the chamber walls and fire of the product settled on the walls near the nozzles are possible. Fire hazard forces to lower the initial temperature of the coolant, which complicates the intensification of the process.

The aim of the invention is to intensify the drying process by increasing the uniformity of the distribution of the coolant in the drying chamber and eliminating overheating of the walls of the chamber at the input level of the coolant.

This goal is achieved in that a counter-current spray dryer containing a cylindrical drying chamber with nozzles located at the upper level of the drying chamber, covering the outside of the lower level of the drying chamber with a gas supply in the form of a duct of constant cross-section, divided into two compartments by a screw partition, the step of which is equal to the height of the duct, divider of the heat carrier entering the duct into two flows directed to the duct compartments in mutually opposite directions, gas distribution grids at the inlet are warm the carrier in compartments, nozzles for introducing the coolant from the compartments into the drying chamber, located uniformly on the upper and lower surfaces of the duct, the screw partition containing gas-permeable parts separating the sections of the compartments, beginning and ending along the coolant, each of which contains at least one nozzle. The nozzles located on the upper surface of the duct are offset from the nozzles located on the lower surface of the duct half the distance between adjacent nozzles, and part of the surface of the divider of the coolant entering the duct has perforation. The nozzles are located in the plan at an angle of no more than 12 ° to the conditional radii held in the drying chamber.

The invention is illustrated by the accompanying figures, where figure 1 shows the proposed dryer; figure 2 is a section aa in figure 1; figure 3 is a section bB in figure 2; figure 4 - scan section of the duct gas supply on the average diameter.

The counter-current spray dryer, shown in figure 1, contains a cylindrical drying chamber 1 with nozzles 2, which are combined by a collector 3. For input and distribution of the coolant is a gas supply 4. The gas supply duct 5 is divided by a screw partition 6 into two compartments 7 and 8. Pipes 9 and 10 with equal flow sections connect the gas supply to the drying chamber and are located on the upper and lower surfaces of the duct 5. To collect and unload the dry product, use a conical bottom 11 and a pipe 12. A pipe 13 is designed to remove heat ositelya.

In Fig.2 shows a top view of the gas supply (section aa, Fig.1). The nozzles 9 and 10 are installed at an angle to the radial direction. Inlet 14 has an inlet coolant divider 15. The bottom row of nozzles is offset from the top by half the distance between adjacent nozzles.

Figure 3 shows a section bB in figure 2. To supply the coolant to the pipe 10 *, located on the axis of the pipe 14 (see figure 2), part of the surface of the divider 15 has a perforation 16. At the inlet of the coolant in the compartments 7 and 8, into which the duct 5 is divided by a screw partition 6, gas distribution grilles are installed 17 and 18. The arrows indicate the direction of movement of the coolant.

Figure 4 shows the scan section of the duct 5 gas supply along the average diameter. The partition 6 divides the box into two adjacent compartments of uniformly variable sections 7 and 8. The gas-permeable parts of the partition 19 and 20 separate the initial and final sections of both compartments along the coolant. Gas permeability can be provided, for example, by perforation.

The dryer operates as follows.

The initial product in the form of a flowable composition CMC is supplied under pressure to the manifold 3, sprayed with nozzles 2, dehydrated in countercurrent mode with the coolant in the drying chamber 1. The powdery product is discharged from the conical bottom 11 through the pipe 12.

The coolant enters the gas supply 4 through the nozzle 14. By the divider 15, the incoming coolant is divided into two flows, which, after a 90 ° smooth turn, enter the compartments 8 and 7 and move in mutually opposite directions (see Figs. 2, 3). To the pipe 10 *, located on the axis of the incoming stream, the coolant is supplied through the holes in the perforation 16 in the splitter 15. The gas distribution grids 17 and 18 form a uniform distribution of the flow velocity over the input sections of the compartments (see Figs. 3, 4). As you move through the compartments, the coolant is evenly discharged into the drying chamber through the nozzles 9 and 10. The spent coolant is discharged from the top of the dryer through the nozzle 13.

Since the pressure in the drying chamber is constant, or fluctuates in a very small interval, the flow rate of the coolant from the nozzles and the flow through the nozzles are determined only by the sum of the static pressure in the gas supply and the dynamic pressure of the flows in the compartments. In the sections of the compartments that are final along the coolant, the dynamic pressure decreases due to losses caused by hydraulic resistance. The gas-permeable parts of the screw baffle compensate for these losses by equalizing the pressures between the initial and final sections of the compartments. Part of the coolant flows from the initial sections of the compartments to the final ones, smoothing out the uneven flow through the pipes (see Fig. 4). In this case, symmetry is achieved with respect to the axis of the drying chamber of the speeds and costs of the coolant introduced into the dryer. Accordingly, a uniform distribution of the coolant is formed in the cross section of the chamber, which is a necessary condition for optimal heat treatment of the sprayed product and intensification of the drying process.

For a more uniform distribution of the coolant around the perimeter of the chamber at the input level, the upper row of nozzles (nozzles 9) is offset from the lower row (nozzles 10) by half the distance between adjacent nozzles. The offset of the axes of the nozzles relative to the radial direction creates the initial swirl of the flow, which contributes to the uniform distribution of the coolant over the cross section of the chamber. The angle in the plan of the axes of the nozzles to the conditional radii held in the drying chamber is limited to 12 °, which protects the chamber walls from overheating.

Literature

1. Lykov M.V., Leonchik B.I. Spray Dryers. Moscow, Mechanical Engineering, 1966, p. 167, Fig. 82∂.

2. Idelchik I.E., Alexandrov V.P. Investigation of the distribution of dust and gas flow in distributing collectors of uniformly variable cross-section. Thermal Engineering, No. 2, 1979, p. 55-58.

3. RF patent No. 1032293, F26В 3/12, 03/09/1982.

Claims (3)

1. Countercurrent spray dryer containing a cylindrical drying chamber with nozzles located at the upper level of the drying chamber, covering the outside of the lower level of the drying chamber with a gas supply in the form of a duct of constant cross-section, divided into two compartments by a screw partition, the step of which is equal to the height of the duct, divider included in the duct coolant into two flows directed to the compartments of the duct in mutually opposite directions, gas distribution grilles at the coolant inlet to the compartments, nozzles for input coolant from the compartments into the drying chamber arranged uniformly on the upper and lower surfaces of the box, characterized in that the helical partition portion comprises a gas-permeable separating the leading and trailing portions of the coolant along the compartments, each of which comprises at least one nozzle. 2. The dryer according to claim 1, characterized in that the nozzles located on the upper surface of the duct are offset from the nozzles located on the lower surface of the duct by half the distance between adjacent nozzles, and part of the surface of the divider of the coolant entering the duct has perforation. 3. A dryer according to any one of claims 1 and 2, characterized in that the nozzles are located in plan at an angle of not more than 12 ° to the conditional radii held in the drying chamber.

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