RU2306502C1 - Spraying drier - Google Patents

Abstract

FIELD: drying of dispersed materials; microbiological, food-processing, chemical and other industries.

SUBSTANCE: proposed spraying drier has moist material loading bin with screw feeder, drying chamber with injector for feeding the material, furnace with mixing chamber, turbo-gas-blower and used air cleaning system. Drying agent from furnace is delivered by fan together with material being sprayed in parallel flow. Fine solid particles of dried material settle on bottom of chamber and are removed by screw conveyer; used dust-laden gases are subjected to preliminary acoustic treatment in dust entrapping acoustic plant.

EFFECT: increased productivity.

3 cl, 1 dwg

Description

The invention relates to techniques for drying dispersed materials and can be used in microbiological, food, chemical and other industries.

The closest technical solution to the claimed object is a dryer by.with. USSR No. 553424, F26В 17/10, 1975, containing a wet material hopper with a screw feeder, a drying chamber with a support grill, a furnace with a mixing chamber, a gas turbine and an exhaust air purification system (prototype).

The disadvantage of the prototype is the relatively low productivity of drying the final product.

The technical result is an increase in drying performance.

This is achieved by the fact that in a spray dryer containing a drying chamber with a nozzle for supplying material, a furnace with a mixing chamber, a gas turbine and a cleaning system for a drying agent, a drying agent from the furnace is turbo-gas blowed by a parallel current with the sprayed material, and small solid particles of the dried material are deposited on the bottom of the chamber and are discharged by the screw, while the spent drying agent is subjected to preliminary acoustic treatment in an acoustic installation for dust collection.

The drawing shows a spray dryer.

The spray dryer contains a chamber 1 into which material is fed through the nozzle 2. The drying agent from the furnace 7 by the fan 6 is pumped in parallel with the sprayed material. Small solid particles of dried material (up to several microns in size) are deposited on the bottom of the chamber and discharged by a screw 3.

The spent drying agent is subjected to preliminary acoustic treatment in an acoustic installation 8 for dust collection. Then, the flow of the drying agent is directed to the cyclone 4 with a hopper, where the main part of the dry material carried away by the drying agent is released, and its final cleaning takes place in the bag filter 5. In the exhaust tract of the bag filter 5, a recirculation valve 9 is installed, which is commanded by the microprocessor (in the drawing not shown), which controls the drying optimization process depending on the parameters of the material being processed, can switch the flow of spent and purified drying agent to the inlet of the mixing chamber (on the furnace is not shown in the drawing) 7. The microprocessor is connected to the sensors of pressure, temperature, humidity, and the speed of the drying agent flow (not shown in the drawing) installed in the elements of the drying circuit and to executive bodies (not shown in the drawing) that regulate the parameters of all the circuit elements drying. The microprocessor analyzes the parameters of the drying process and sets the optimal mode by applying control signals to the actuators of the drying circuit elements.

Spray dryer operates as follows.

A high evaporation rate of moisture is achieved in the dryer due to fine atomization of the dried material in the drying chamber through which the drying agent (heated air or flue gases) moves. When spray drying, the specific evaporation surface becomes so large that the drying process is completed extremely quickly (in about 15 ... 30 sec).

In a spray dryer, the material is fed into the chamber 1 through the nozzle 2. The drying agent moves in parallel with the material. Small solid particles of dried material (up to several microns in size) are deposited on the bottom of the chamber and discharged by the screw 3. The spent drying agent, after cleaning from dust in a cyclone 4 and a bag filter 5, is released into the atmosphere. Before the cyclone, the drying agent (coolant - heated air or flue gases), together with small particles of the product, enters the acoustic installation, the sound vibration parameters of which are adjusted from the control unit. In an acoustic installation, dust particles are separated from the coolant, since under the influence of the sound field and the associated oscillatory processes occurring in the medium of the spent coolant, the dust particles stick together, that is, coagulate, forming large aggregates, which greatly facilitates the subsequent cleaning of the coolant in gas cleaning devices . The following main factors act on suspended particles under the influence of acoustic vibrations: joint oscillation of particles and a gas medium, dynamic forces between neighboring particles. Large particles settle down either in an acoustic installation or enter a cavity associated with an inertial dust separator.

The optimal parameters for sound processing of medium-sized dust are: sound pressure level of 140 dB or more, vibrational frequency of 900 Hz, dust concentration in the flow of the drying agent is at least 2 g / m, sounding time is 1.5 ... 2 s. These parameters are due to the fact that, depending on their size, the suspended particle either participates in the oscillations of the medium (fully or partially), or does not participate, since the Stokes forces act on the particle and the medium. Moreover, when sound waves are transmitted through the volume of a gas located in a closed vessel, standing sound waves are established in the latter with the formation of nodes (the oscillation velocity is zero) and antinodes in which the amplitude of the velocity oscillations is maximum. The frequency of the oscillatory process, equal to 900 Hz, creates for the dust concentration in the coolant flow equal to at least 2 g / m ³ such an amplitude of the sound wave at which the amplitude of the velocity of the gas particle, determined by the ratio of sound intensity (sound pressure level 140 dB or more) to the speed of sound in the medium, will be in the antinode region of standing sound waves in a given closed vessel (acoustic installation), which ultimately determines the intensity of acoustic coagulation, that is, the rate of formation of large parts its. The scoring time of 1.5 ... 2 s is assigned from the condition of formation of an antinode of standing sound waves in a given closed vessel. If the scoring time is outside the range of 1.5 ... 2 s, then this will lead to the formation of nodes in standing waves (the oscillation speed is zero) and, as a result, to weaken the effect of acoustic coagulation.

Spray dryers also work according to the principles of counterflow and mixed current. However, direct flow is especially common, as it allows drying at high temperatures without overheating of the material, and the rate of deposition of particles in this case is the sum of their speed and the speed of the drying agent.

In counterflow, the deposition rate is less and, accordingly, the residence time of particles in the chamber is longer. This allows you to get dried material with a higher density.

For the deposition of small particles (the average droplet size is usually 20 ... 60 microns) and to reduce entrainment, the speed of the drying agent in the chamber, considering its full cross section, usually does not exceed 0.3 ... 0.5 m / s. But even at these speeds, entrainment is significant and requires good dedusting of the spent agent. For a more uniform distribution of the drying agent over the cross section of the chamber and good mixing with drops of the liquid to be dried, a gas inlet is used through a nozzle located tangentially to the chamber body, or through a series of slots, around its circumference.

In conditions of almost instantaneous drying, the surface temperature of the particles of the material, despite the high temperature of the drying agent, is only slightly higher than the temperature of adiabatic evaporation of a pure liquid. Thus, quick drying is achieved under mild temperature conditions, which allows to obtain a high-quality powdery product that is highly soluble and does not require further grinding. Drying is also possible with coolant when the sprayed material is preheated.

Spraying is carried out by mechanical and pneumatic nozzles, as well as using centrifugal discs, the rotation speed of which is 4000 ... 20,000 rpm.

Claims (3)

1. A spray dryer containing a drying chamber with a nozzle for supplying material, a furnace with a mixing chamber, a turbo-gas blower and a cleaning system for a drying agent, characterized in that the drying agent is blown from the furnace by a turbo-gas blowing in parallel current with the sprayed material, and small solid particles of the dried material are deposited on the bottom of the chamber and are discharged by the screw, while the spent drying agent is subjected to preliminary acoustic treatment in an acoustic installation for dust collection. 2. The spray dryer according to claim 1, characterized in that the spent drying agent is subjected to preliminary acoustic treatment in an acoustic installation, the optimal parameters of which for sound processing of medium-fine dust are the sound pressure level of 140 dB or more, the oscillation frequency of 900 Hz, the dust concentration in a flow of at least 2 g / m, sonication time 1.5 ... 2 s, after which the drying agent is sent to a cyclone with a hopper, where the bulk of the dry material carried away by gases is released, and the final the drying agent is cleaned in a bag filter, in the exhaust duct of which a recirculation valve is installed, which switches the flow of spent and purified drying agent to the inlet of the furnace combustion chamber. 3. The spray dryer according to claim 1, characterized in that the microprocessor is introduced into the circuit, which is connected to pressure sensors, temperature, humidity, flow rates installed in the elements of the drying circuit, and with executive bodies that regulate the parameters of all elements of the drying circuit, which analyzes the parameters of the drying process and sets the optimal mode through the action of control signals on the actuators of the drying circuit elements.