RU2267066C1 - Drying plant to obtain powder from liquid product and liquid product drying method - Google Patents

Abstract

FIELD: machines or apparatus for drying materials in loose, plastic, or fluidized form, particularly spray driers adapted to be used in different industries.

SUBSTANCE: drying plant has drying chamber with side surface composed of plates arranged so that slots are created between adjacent plates. The slots are adapted to spray drying agent into the chamber. The plant also has liquid product sprayers. Tangent of angle ψ of drying agent spray inside the chamber through each slot is selected from equation. The angle ψ provides elimination of sticking of particles obtained from dried liquid product to plates. Necessary number of plates and height of slots defined between adjacent plates are determined from angle ψ tangent with taking into consideration drying chamber perimeter. Angle ψ is defined between velocity vector of drying agent entering into the chamber through the slot and tangent of drying chamber surface generator at flow inlet area. In disclosed drying method radial component of drying agent flow velocity acts on particle with force, which is not less than sum of centrifugal force and gravity force.

EFFECT: possibility to perform drying under atmospheric air temperature.

2 cl, 4 dwg

Description

The invention relates to spray drying plants for the production of dry solid materials in the form of a powder from such liquid starting materials as solutions, emulsions and suspensions. The invention can find application in various industries, for example, chemical, food.

Known drying chamber for conducting the process of heat and mass transfer between dispersed liquid particles and a gaseous medium. A drying chamber with porous walls is enclosed to form a gap in a vertical cylindrical body having a nozzle for introducing a coolant, and is equipped with an atomizer of a liquid source substance introduced inside. In the housing there is a hole in the base for removing powder and a hole for removing exhaust gas with products of evaporation of the liquid base of the solution or suspension. The coolant with the specified temperature and humidity enters through the pipe into the free space between the walls of the housing and the drying chamber with porous walls. Under the pressure created by the fan, the coolant penetrates through the pores of the drying chamber inward, where heat and mass transfer occurs between the coolant and atomized droplets or particles [1].

A dryer is also known that contains a vertical cylinder-conical housing with a disk sprayer in the upper part and simultaneously supplying a high-temperature drying agent (170 ° C) for the drying process, followed by drying with air at a temperature of 90 ° C. For drying milk in this dryer, it is necessary to pre-thicken it before spraying [2].

A known method of drying and granulating materials in the counter, swirling in one direction of the primary and secondary flows of the drying agent, between which a gas suspension is supplied in the form of a vortex ring flow and twisted in the same direction [3].

There are various designs of drying chambers and methods of supplying air to the chamber, providing the initial interaction of droplets of atomized liquid and drying air, which determines the evaporation rate and temperature in the dryer. There are three main modes of this interaction: forward flow (the drying agent and particles move in the same direction through the drying chamber), counterflow (the drying agent and particles move in the opposite direction through the drying chamber), mixed flows (the movement of particles through the drying chamber experiences as direct-flow and countercurrent phases).

Drying methods usually consist in the fact that in the chamber there is a spraying of liquid raw materials to obtain a droplet stream and contact of the droplets with a hot agent. The disadvantages of the known drying chambers and methods of drying in them are the high temperature of the supplied agent 120-240 ° C, which is due to the short residence time of the particles of the atomized liquid in the coolant flow until the moment of deposition in the chamber. Such a temperature regime of drying affects the quality of the resulting product (heat-sensitive) and is the reason for the high energy consumption, which is also a disadvantage of these plants. Also, in these drying plants, preliminary thickening of the initial product in the evaporator is used (for example, when drying milk), which complicates this design and also increases the energy consumption for drying.

The closest technical solution, selected as a prototype, to the proposed drying installation and drying method is a spray drying installation for solutions, suspensions and pastes, containing enclosed in a casing with the formation of an annular cavity drying chamber with a side surface of plates installed with a gap relative to each other for introducing the drying agent into the chamber, and a spray device inside, as well as tangential nozzles for introducing the drying agent into the chamber cavity through the plates and the outlet gas suspension in the separation system for separation of the finished powder [4].

In this spray dryer, a method of drying solutions and suspensions by spraying them in the cavity of the drying chamber, bringing the particles of the material to be dried into suspension by multi-channel input of the drying agent into the cavity of the drying chamber, subsequent removal of the gas suspension from the chamber and separation into powder and spent agent [4] .

The disadvantages of the prototype — the spray dryer and the drying method therein — are the high manufacturing and operating costs, low manufacturability of the powder by this drying method, due to the high drying temperature, leading to a loss in the quality of the finished product, and preliminary thickening, as well as sticking of the dried product to the walls cameras.

The technical problem to which the present invention is directed is to provide a process for drying a liquid product at a low temperature of the supplied drying agent (air) without preheating at atmospheric air, spraying in a drying chamber a liquid source product without preliminary thickening (drying of condensed liquids is possible , but this is an optional condition for the process), as well as the exclusion of sticking and contacting of sprayed droplets or particles n odukta chamber walls.

To solve this problem, in a drying plant for producing powders from liquid products, containing a drying chamber with a side surface made of plates installed with a gap between adjacent plates for introducing a drying agent into the chamber, liquid product sprays in the chamber interior and a gas suspension outlet connected to the separation system for separating the finished powder, the chamber is enclosed in a housing with the formation of an annular gap for introducing into the chamber a drying agent connected to the tangential a pipe for feeding it, and the tangent of the angle ψ of the agent’s entry into the chamber cavity through each slot gap, which affects the exclusion of particles of the dried liquid product from sticking to the plates, is selected based on the following relation

where ρ _to the particle density [kg / m ³ ];

D _max - diameter of the sprayed particle [m];

μ _g = 1.7 · 10 ^-5 is the dynamic viscosity of the drying agent [kg / (m · s)];

g = 9.8 - acceleration of gravity [m / s ² ];

R is the radius of the side surface of the camera [m],

and the tangent of the angle ψ, taking into account the perimeter of the drying chamber, determines the required number of plates located on the lateral surface of the drying chamber and the height of the gap between adjacent plates, while the angle ψ is located between the velocity vector of the flow of the drying agent entering the gap and tangent to the generatrix lateral surface of the drying chamber at the place of flow inlet.

The dryer can be equipped with an additional gas suspension outlet pipe and both pipes are located on opposite end walls of the drying chamber.

To solve the technical problem in the method of drying liquid products by spraying them in the cavity of the drying chamber, bringing the product particles into suspension by multi-channel input of the drying agent into the cavity of the drying chamber, subsequent removal of the gas suspension from the chamber and separation into powder and spent agent, the radial component of the vector the speed of the flow of the drying agent introduced into the internal cavity of the drying chamber has an effect on the particle of the dried product with a force not less than the sum of the centrifugal and gravity forces, and under the influence of the agent during drying to the final moisture of the product particles, they are moved by the agent in the chamber cavity along a circular path with the subsequent withdrawal of the gas suspension along a spiral path in mutually opposite directions perpendicular to the plane of movement of the product particles along a circular path, or in one perpendicular direction relative to the plane of movement of the particles along a circular path.

The insufficient time the particles are in suspension in similar devices is compensated by the significant temperature difference of the product particles in the form of a droplet and drained air. As a result of this, the task was set to create a condition for keeping in suspension the sprayed liquid product in the drying chamber and to ensure the conditions of non-adhesion of particles to the walls of the chamber. It is based on the idea of spraying a substance into a swirling drying agent, which is used as an air stream. The velocity field in the chamber is determined by the air supply conditions at the periphery. Consider the installation element (figure 1), forming the flow of the drying agent entering the internal cavity of the drying chamber through plates installed with a gap gap relative to each other, shown in figure 2.

To do this, we accept the following conventions

R is the radius of the side surface of the drying chamber [m];

m is the mass of the particle (drop) of the atomized product [kg];

D is the diameter of this particle [m];

h is the height of the slit [m];

n is the number of plates

l - installation depth [m];

Q is the flow rate of the incoming drying agent [m ³ / s].

Consider the surface areas S _r and S _φ , forming the radial U and tangential υ _φ component of the velocity vector of the drying agent passing through the plates.

We introduce the quantity

where the angle ψ is the angle between the velocity vector of the flow of the drying agent entering the slotted gap and the tangent to the generatrix of the side surface of the drying chamber at the place of flow inlet (Fig. 1).

From the necessary condition for the particle not to touch the walls (centrifugal forces should not exceed centripetal forces), an expression was obtained from the ratio of the forces acting on the particle.

Differentiating this expression, we obtain that for

D takes the maximum value:

Accordingly, it follows from (1) and (4) that in order to keep particles with the maximum possible diameter in suspension and to ensure the conditions of non-adherence of particles to the chamber walls, the flow rate of the incoming agent is equal to:

Knowing the height of the room, we select respectively R (radius of the drying chamber), and knowing the maximum diameter D _{max of the} sprayed particle, tgψ is selected, not less than

Accordingly, from (5), the flow rate of the incoming agent for this installation is selected.

Thus, in the proposed method of drying a liquid product, it is sprayed in the cavity of the drying chamber, the particles of the product are brought into suspension by multi-channel introduction of a drying agent into the cavity of the drying chamber, subsequent removal of the gas suspension from the chamber and separation into powder and spent agent. To avoid sticking and contacting the sprayed droplets or particles of the product with the side surface of the chamber formed by the plates, it is necessary that under the influence of all forces acting on the particle of the sprayed substance, it moves in the chamber without moving away from the center by a distance exceeding the radius of the side surface of the chamber. Thus, along the segment connecting the particle with the center of the chamber, the resulting force acting on the particle should be directed toward the center of the chamber. The resulting force in this case is the sum of the projections of forces in a given direction, that is, the centrifugal force, the projection of gravity and the force acting on the particle under the influence of the radial component of the velocity vector of the drying agent stream introduced into the internal cavity of the drying chamber. Knowing the maximum particle diameter, installation dimensions, choosing tgψ, we determine the required flow rate from dependence (5) in order to ensure that the radial component of the velocity vector entering the working cavity of the agent on the particle of the product being dried with a force not less than the sum of centrifugal and gravity forces.

An increase in the angular velocity of rotation of the flow of the drying agent in the vicinity of the outlet increases the centrifugal force acting on the under-dried particle, holding it on a circular path in the vicinity of the outlet, until it is completely drained and then withdrawn through the outlet.

Figure 1 shows the installation element, showing the input of the drying agent into the inner cavity of the chamber through the gaps between the plates of the side surface of the chamber, figure 2 shows a cross section of the drying chamber; figure 3 shows a General view of one of the options for the drying installation, figure 4 is a functional diagram of the drying process.

The dryer for the production of powders from liquid products contains a drying chamber 1 with a lateral surface of plates 2 installed with a slit gap 3 between adjacent plates to provide multi-channel input of the flow of the drying agent into the chamber 1 through the tangential nozzle 4 by sprayers 5 (for example, nozzles ) a liquid product located in the inner cavity 6 of the chamber 1, and the main and additional nozzles 7 (not shown) for discharging a gas suspension into a separation system (dust collecting device) (Fig. 4) for isolating the finished powder, for example, made in the form of a cyclone (not shown). In this case, one of the nozzles 7, if necessary, can be plugged and the discharge of the gas suspension will be carried out in this case through another nozzle. Both nozzles 7 are located on opposite end walls 8 of the drying chamber 1. The drying chamber is enclosed in the housing 9 with the formation of an annular gap 10 for introducing a drying agent connected to the tangential nozzle 4 for its supply.

The angle ψ is formed between the velocity vector of the drying agent stream entering the slotted gap and the tangent to the forming side surface of the drying chamber at the inlet of the flow and determines the size of the gap gap 3 for introducing the drying agent into the chamber cavity, namely, the height h and the length of the gap, and the value the tangent of the angle ψ of each gap for introducing the agent into the cavity 6 of the chamber 1 affects the exclusion of adhesion of particles of the dried liquid product to the plate 2. This value is selected based on the size of the installation, the diameter of the sprayed particles, and also depends on its density, the dynamic viscosity of the drying agent and the gravitational acceleration.

The tangent of the angle ψ is selected no less in value than

Using the tangent of the angle ψ, taking into account the perimeter of the drying chamber, determine the required number of plates 2 (n) located on the side surface of the drying chamber 1, and the height (h) of the gap between adjacent plates 2 according to the following dependence: tgψ · 2πR is equal to the product (n) on (h). Next, carry out the selection of the values (n) and (h).

In the chamber, the drying agent coming from the nozzle 4 into the annular gap 11 passes between the slotted gaps 3 of the plates 2, which provide a multi-channel input, the necessary speed and direction of the flow of the drying agent into the internal cavity 6 of the chamber 1. The plates 2 can have a different profile: both straight and curved (Fig. 1), which is convenient for their fastening and for ensuring the formation of a flow between adjacent plates attached overlapping to each other. Due to the fact that the profile of the plates can be different, the determination of the angle ψ is possible through the velocity vector and tangent to the forming surface of the drying chamber 1 due to the complexity of the shape of the gap gap. The tangent of the angle ψ essentially determines the dimensions of the gap gap 3, namely its length and height h, since tgψ is the ratio of the height of the gap 3 (h) to the length of the gap 3 between adjacent plates 2. In the chamber, the initial liquid is sprayed with spray guns 5 and through nozzles 7 located in opposite end walls 8, the spent agent comes out with suspended powder particles to a dust collector (for example, to a cyclone). The unit is equipped with a fan, providing the supply of the required amount of a drying agent (not shown).

A drying apparatus for producing powders from liquid products operates as follows and a method of drying in a chamber of liquid products is as follows.

The flow of the drying agent coming from the fan passes through the plates 2 forming the internal cavity 6 of the drying chamber 1, in which the liquid is sprayed with atomizers 5. Under the influence of the swirling flow of the drying agent supplied with the necessary flow rate Q coming out of the gap gaps 3, the particles of the atomized liquid make movement along a circular trajectory in suspension during the drying period to final moisture. And due to the fact that the influx of the agent into the drying chamber 1 is carried out along the entire perimeter of the side surface of the working chamber 1 through slotted gaps 3 of a certain height h (by choosing the tangent of the angle ψ) multichannel with a certain flow rate and speed, the radial component of the drying agent's flow velocity vector has the particle of the product to be dried is exposed to a force not less than the sum of the centrifugal and gravity forces, which allows the particle in suspension to be in the chamber without contact with its walls and to achieve high Shivani liquid products without prior condensation. Such a time of particle wandering in the chamber along a circular path with constant blowing of the drying agent allows to significantly reduce the temperature of the supplied drying agent. As the particle is drained, it also loses mass along a spiral-shaped trajectory in mutually opposite directions, perpendicular to the plane of movement of the gas suspension along a circular path, or in one perpendicular direction relative to the plane of movement of the gas suspension along a circular path, rushes with the agent flow to one of the nozzles 7 or the outlets of the gas suspension, from where the spent drying agent with a suspension of dried particles is fed to a dust collector (cyclone), where the spent waste is separated og agent from dry powder, the precipitation of the resulting product (powder) and its conclusion from the installation. 4, for illustration, a functional diagram of a drying process is shown.

The installation in different technological conditions is illustrated by examples.

Example 1. A solution of technical calcium chloride (with a mass fraction of calcium chloride of at least 32.0%) is sprayed with nozzles to a particle size (drop) of not more than D _max = 150 μm. The dimensions of the room made it possible to ensure the installation of equipment no more than 6.5 m high.

Installation Parameters:

H = 5.8 m total installation height; R = 2.5 m distance from the center to the plates; l = 1.5 m installation depth.

Using expression (6), the quantity tgψ is selected, and using expression (2), (n) and (h) are selected

n = 130, h = 0.04 m,

Accordingly, this requires a flow rate of incoming air Q = 140,000 m ³ / h. The temperature of the incoming air did not exceed 20 ° C.

Example 2. A liquid extract of chicken pepsin with a solids concentration of 13% and with the addition of 10% salt is sprayed with nozzles to a size not exceeding D _max = 70 μm. The dimensions of the room made it possible to install equipment not exceeding 3 m high.

Installation Parameters:

N = 2.5 m total installation height; R = 1 m distance from the center to the plates; l = 0.5 m installation depth.

Analogously to example 1 we determine that

n = 104, h = 0.01 m,

Accordingly, this requires a flow rate of incoming air Q = 5900 m ³ / h. The temperature of the incoming air did not exceed 20 ° C.

Example 3. Milk with a solids concentration of 13% and a fat content of 3.2% in an uncondensed form is sprayed with nozzles to a size not exceeding D _max = 100 μm. The dimensions of the room made it possible to install equipment not exceeding 3 m high.

Installation Parameters:

N = 2.5 m total installation height; R = 1 m distance from the center to the plates; l = 0.6 m installation depth.

Analogously to example 1 we determine that

n = 104, h = 0.015 m,

Accordingly, this requires a flow rate of incoming air Q = 10600 m ³ / h. The temperature of the incoming air did not exceed 20 ° C.

Example 4. Freshly squeezed carrot juice with a solids concentration of 15% is sprayed with nozzles to a size not exceeding D _max = 70 microns. The dimensions of the room made it possible to ensure the installation of equipment not exceeding 5 m in height.

Installation Parameters:

N = 4.8 m total installation height; R = 2 m distance from the center to the plates; l = 1 m installation depth.

Analogously to example 1 we determine that

n = 104, h = 0.01 m,

Accordingly, this requires a flow rate of incoming air Q = 16700 m ³ / h. The temperature of the incoming air did not exceed 20 ° C.

Reducing the drying temperature allows you to dry heat-sensitive products without loss of quality in a short time. Also, the advantages of the invention include: simplicity of design, low production costs, low energy consumption during operation and the possibility of using this device on a moving platform of a vehicle. This invention allows to solve the problem of drying liquids without preheating the air flow entering the chamber, that is, when the temperature of the incoming air does not exceed the ambient temperature.

Sources of information

1. USSR author's certificate No. 840629, F 26 B 3/12, 17/10, 06/23/1981.

2. USSR Author's Certificate No. 827006, F 26 B 3/12, 05/07/1981.

3. USSR author's certificate No. 1164526, F 26 B 3/10, 17/10, 06/30/1985.

4. Copyright certificate of the USSR No. 881484, F 26 B 3/12, 11/15/1981.

Claims (3)

1. A drying apparatus for producing powders from liquid products, comprising a drying chamber with a side surface of plates installed with a gap between adjacent plates for introducing a drying agent into the chamber, liquid product sprays in the internal cavity of the drying chamber and a gas suspension outlet connected to the separation system for separating the finished powder, while the camera is enclosed in a housing with the formation of an annular gap for introducing into the chamber a drying agent connected to a tangential cartridge SCU for supplying it, characterized in that the value of the tangent of the angle ψ input agent in chamber cavity through each slit gap, affecting the adhesion of the particles to be dried exclusion liquid product on the plate is selected according to the following relation:

and according to the tangent of the angle ψ, taking into account the perimeter of the drying chamber, the required number of plates located on the lateral surface of the drying chamber and the height of the gap between adjacent plates are determined, the angle ψ being located between the velocity vector of the flow of the drying agent entering the slot and tangent to the generatrix the side surface of the drying chamber at the inlet of the stream, where ρ _k is the particle density, kg / m ³ ; D _max - particle diameter, m; μ _g , = 1.7 · 10 ^-5 - dynamic viscosity of the drying agent, kg / (m · s);

- acceleration of gravity, m / s ² ; R is the radius of the side surface of the camera, m 2. The dryer according to claim 1, characterized in that it is equipped with an additional outlet for gas suspension and both nozzles are located on opposite end walls of the drying chamber. 3. The method of drying liquid products by spraying them in the cavity of the drying chamber, bringing the particles of the product into suspension by multi-channel input of a drying agent into the cavity of the drying chamber, subsequent withdrawal of the gas suspension from the chamber and separation into powder and spent agent, characterized in that the radial component of the vector of the velocity introduced into the internal cavity of the drying chamber of the flow of the drying agent has an effect on the particle of the dried product with a force not less than the sum of the centrifugal forces and the severity and under the influence of the agent during the drying to the final moisture of the product particles, they are carried out by the agent in the chamber cavity along a circular path with the subsequent withdrawal of the gas suspension along a spiral-shaped path in mutually opposite directions, perpendicular to the plane of movement of the product particles along a circular path, or in one perpendicular direction relative to the plane of movement of the particles along a circular path.

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