Aerosol precipitor

[57] ABSTRACT

An apparatus for precipitating aerosol particles comprises at least one pair of tubular elements placed one inside the other and forming an annular working space. The inner tubular element is connected to a source of steam or liquid to be evaporated and is made porous to enable penetration therethrough of the steam or liquid to be evaporated into the working space. The outer tubular element is maintained at a temperature below that of the inner tubular element and rotary motion is imparted to the aerosol flow in the annular working space by means of rotary blades.

Claims, 4 Drawing Figures

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PATENTED 02 21973

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AEROSOL PRECIPITOR

This application is a continuation of applicant’s copending application Ser. No. 764,803, filed Oct. 3, 1968, now abandoned.

The invention relates to devices for precipitating aerosol particles, i.e. high-dispersing solid and/or liquid particles suspended in gas, and may be utilized in many industrial branches, specifically, for dust catching, gas cleaning, air sterilization, etc.

Commonly known is a dust precipitator, wherein a flow of dusty air passes between wet surfaces of differing temperatures. The precipitator is made as a chamber divided in height into three compartments by means of horizontal heat-conducting partitions. The lower compartment serves to house the heating means, while the upper one accommodates the cooling means. The middle compartment thus has a lower, heated, wall and an upper, cooled, wall. Fed to the middle compartment through pipe connections is water which fills partially the middle compartment and is evaporated under the effect of heat radiated by the lower heated wall. Also fed to the same middle compartment is dusty air subject to cleaning, which, mixing with water vapor and coming into contact with the upper cooled wall, is supersaturated with vapors, which leads to an increased condensation of dust particles present in the air. The thus formed drops of the condensation fog are precipitated in a coil provided in the upper compartment of the installation under the action of the forces of inertia developing when the flow turns in the coil ducts.

The known precipitator is bulky and does not permit intensification of the condensation growth of lowactive particles. This latter disadvantage is due to the fact that because of the lack of uniformity in the vapor condensation of particles suspended in gas, which, as a rule, are of varying sizes (varied dispersion composition) and of differing physical and chemical activity (different moisture-imbibing capacity, solubility etc.), the condensation involves larger and physically and chemically more active particles imbibing most of the excess moisture, which fact results in a reduced supersaturation of the flow on these portions and the absence of condensation on smaller and little-active particles. As a result, the growth of the latter is slowed down or discontinued altogether, and they freely “fall through” precipitation devices provided behind the supersaturation chamber, without being caught in said devices.

It is an object of the present invention to provide an aerosol precipitator permitting increase of the condensation growth of low-active particles, and rather inexpensive and simple in construction, easy to mount and service, as well as allowing automatic control of the intensity of the supersaturation of the flow depending upon the values of the forces of interia, developed by the moving flow.

According to the above-mentioned and other objects, the aerosol precipitator, in which the aerosol flow proceeds in a working space limited by walls having different temperature at a simultaneous feed of vapor to said working space from the side of a wall heated to a higher temperature so as to insure supersaturation of the flow with vapor and the condensation growth of aerosol particles to facilitate their separation from the flow under the action of the forces of inertia, according to the invention, comprises at least one pair of tubular elements inserted one into the other and forming an an nular working space, the inner of said tubular elements being penetrable to a vapor or a liquid subject to vaporation and fed inside said inner element, whereas the outer tubular element is provided with a means for maintaining its temperature lower than that of the inner element; in addition, the precipitator is fitted with a means for imparting rotary motion to the aerosol flow in the above-said annular working space.

Rotary motion may be imparted to the aerosol flow with the aid of a screw-type eddy-producing device installed preferably in the annular working space of the precipitator.

The tubular elements inserted one into the other may be made tapered and arranged with the possibility of axial displacement of one about the other.

The inner tapered tubular element is preferably made such as to expand with its wider section toward the top of the precipitator, said element being immovably connected with the top eddy-producing device at the place of this wider section, said eddy-producing device freely resting against the top end of the outer tubular element to insure unimpeded axial displacement of the inner tapered tubular element under the action of the ascending aerosol flow.

The invention will be more apparent from the description of an exemplary embodiment thereof and appended drawings, wherein:

FIG. 1 shows an aerosol precipitator, according to the invention, in a longitudinal section with tubular elements made cylindrical;

FIG. 2 is a section taken on line II—II as in FIG. 1;

FIG. 3 is the same precipitator with several pairs of parallel tubular elements which are made tapered and expanding with their wider section toward the precipitator bottom; and

FIG. 4 is the same precipitator with tubular elements made tapered and expanding with their wider section toward the precipitator top.

FIGS. 1 and 2 show an exemplary embodiment of the apparatus wherein the working area is formed by two coaxial cylindrical tubes, i.e. the outer tube 1 and the inner tube 2. In the annular space between said tubes there are arranged screw-type eddy-producing devices 3 imparting rotary motion to the aerosol flow, either of them being a cut portion of a multithread worm.

These also serve as a means for centering the tube 2 along the axis of the tube 1.

The outer tube 1 is provided with a jacket 4 in which a cooling liquid fed through branch pipes 5 is circulating, while the inner tube 2 is made porous to receive vapor or a liquid liable to vaporization, through branch pipes 6, and heated either prior to its feed to the porous tube 2 or right inside this tube.

Heating of the liquid right inside the tube 2 is effected, by passing through said tube electric current supplied to the inlet and outlet branch pipes 6. In this case, the tube 2 and the pipes 6 should be isolated from the outer tube 1, for which purpose the eddy-producing devices 3 are manufactured from plastic or other electric-insulating material, while the branch pipes 6 are separated from the tube 1 by electric-insulating bushes.

Thus, in the course of the precipitator operation, different temperatures are maintained in the tubes 1 and 2, the temperature of the outer tube 1 being lower than that of the tube 2. In the annular working space limited by differently heated walls of the tubes 1 and 2, with a simultaneous feed into the working space of vapor from

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Yet, the temperature difference is preferably increased not by raising the vapor temperature but by decreasing the temperature of the cooled tube 1. In addition to making use of the cooling jacket, the cooling of the tube 2 may be achieved, e.g., with the aid of coils when coolants from cooling installations are utilized, as well as by means of any other cooling means.

The means for imparting rotary motion to the aerosol flow may also be fashioned as inlet and outlet branch pipes tangentially attached to the tube 1 and serving to introduce aerosol and discharge purified gas, as is the case in common cyclones (not shown in Figs), or may have some other embodiment, preferably such as would permit transformation of the axial gas flow into a rotary flow, with minimum losses of kinetic energy of the moving aerosol.

In the proposed precipitator, the tube 1 may be made both stationary or rotary. The eddy-producing devices 3 may also be stationary or rotary.

The proposed apparatus may be made as separate interchangeable sections shown in FIG. 1, which can be then attached one to another successively on the flanges with sealing gaskets. The height of each section, as well as their required number, is established through calculations or experimentally depending upon the amount of the aerosol passing through the precipitator, initial moisture and temperature of the aerosol, dispersion ability and fractional composition of suspended particles and their moisture-imbibing capacity, required degree of precipitation of aerosol particles, etc.

In case the vapor tube 2 and the cooled tube 1 are made of similar length, the gas freed from aerosol particles or air at the outlet from the precipitator top mouth will have approximately 100 percent moisture content.

If it is necessary to have the exhaust gas or air of a predetermined moisture and temperature, the porous tube 2 should be made shorter than the outer tube 1. In this case, the upper portion of the cooled tube 1 will be used as a gas cooler. The gas being cooled, its moisture is also decreased.

An additional cooling surface for the exhaust gas may be obtained by attaching one more section having no inner vapor tube 2 to the top portion of the precipitator.

To insure treatment in the precipitator of large volumes of aerosol, the apparatus may comprise several parallel pairs of the tubes 1 and 2, the outer tubes 1 possibly having both cooling means individual for each of the tubes 1 a cooling device common to all of the parallel tubes. Said cooling device may be fashioned as a common cooling jacket (as shown in FIG. 3) fitted with branch pipes for the supply of the cooling liquid.

If it is necessary to regulate the intensity of supersaturation created in the annular working space of the precipitator without varying the established difference in the temperatures of the walls of the tubular elements, both the outer and inner tubular elements should be made tapered.

FIG. 3 shows such tapered tubular elements I¹ and 2¹expanding with their wider sections toward the bottom of the precipitator. Hereafter, the tapered tubular elements are referred to as tapered tubes.

The outer tapered tubes 1¹ of the precipitator shown in FIG. 3 have a common cooling device made as a res5 ervoir jacket 4 fitted with branch pipes 5 to feed and discharge the cooling liquid.

The eddy-producing devices 3* of the aerosol flow are provided at the inlet of the aerosol flow and at its outlet from the annular working space in cylindrical 10 pipe sockets 7 attached to the ends of the outer tapered tube I*. The branch pipes 6* for feeding and removing the vapor or a liquid liable to evaporation are made as flexible hoses in the precipitator bottom and as cut portions of metal pipes in the top of the apparatus, said cut 15 portions being attached to a metal tube, 8 closed in its ends and connected, in its turn, with a flexible hose.

The metal tube 8 is at the same time a crosspiece intended for lifting and lowering the tapered tubes 2¹. Attached to both ends of the tube 8 are ropes 9 wound on drums 10 and unwound from them when varying the direction of rotation of axle 11. By displacing the inner vapor tubes 2¹ about the cooled tubes I¹, it is possible to vary the annular gap between the tubes and, consequently, the intensity of supersaturation in the working space of the precipitator.

A relative displacement of the tapered tubes 1* and 2* may be effected in other ways, too, e.g. with the aid of an electromagnet (not shown in the drawing) whose core can be linked with the inner tubes 2¹. By varying the strength of the electric current supplied to the electromagnet coil, the inner tubes 2¹ may be lifted and lowered.

To make possible automatic control of the intensity of the flow supersaturation depending upon the value of centrifugal forces developed by the moving flow, the tapered tubes I¹ and 2* (FIG. 4) should be installed with their wider section above. Besides, each inner tapered tube 2¹ with the eddy-producing devices 3* attached to it should be so positioned in the precipitator that, when being out of operation, it should freely rest against the upper end of the outer tube I¹ with the upper eddy-producing device 3¹ and, when in operation and with the aerosol flowing through the apparatus, it should freely soar in the ascending flow of the latter. The higher the speed of the aerosol motion and, consequently, the centrifugal forces developed in the course of its eddying, the greater the gap between the tubes. This permits automatic control of the intensity of the supersaturation created in the precipitator, depending upon variations in the value of the centrifugal forces.

To prevent spontaneous rotation of the inner tube 2¹(FIG. 4) as a result of the pressure of the ascending gas flow on the blades of the eddy-producing devices 3‘, a plank 12 resting against a stop 13 may be attached to one of said eddy-producing devices.

The general operational principle of the proposed precipitator is described hereinbelow only for the first embodiment, since the operational principle in the other cases is analogous.

Vapor or a hot liquid is brought to the porous tube 2, which is evaporated from the tube outer surface into the annular space between it and the outer cooled tube 1 in whose water jacket cold water or other cooling liq₆₅ uid is circulating. Thus, in the course of the precipitator ³ operation, the tube 1 and the tube 2 are maintained at diffeferent temperatures. The greater the temperature difference, the higher the supersaturation of the flow.

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The aerosol flow is fed to the apparatus mostly from the bottom upwards; eddying at the inlet and rotating in the annular gap between the differently heated surfaces of the tubes 1 and 2, the flow is supersaturated with vapor. Owing to the uniform distribution of the 5 vapor throughout the height of the annular gap, made possibile by the use of the porous tube 2, the supersaturation of the flow is also uniform throughout all of its path in the annular working space of the precipitator.

Aerosol particles suspended in the flow, in the course i of their condensation growth, are incessantly deposited on the precipitator walls under the action of centrifugal forces developing in the course of the flow rotation, owing to which conditions are created for involving less active particles into the process of condensation growth. As a result, all suspended particles are separated from gas directly in the annular space between the tubes 1 and 2.

Drops of the emerging condensation fog, thrown back onto the inner wall of the cooled tube 1, merge 20 into a fluid film which runs down the walls, carrying with it the trapped particles into the bottom portion of the precipitator, predominantly into a hopper provided with a gate (not shown in the drawing).

In the course of the apparatus operation, the differ- 25 ence of the temperatures on the walls of the tubes 1 and 2 should be maintained so that the temperature of the tube 2 penetrable for vapor or a liquid liable to evaporation be enough to insure uniform supply of the vapor into the working space of the precipitator, while the ³⁰temperature of the cooler tube 1 should be sufficient to insure a required intensity of supersaturation of the aerosol flow being treated in said precipitator.

In practice, when using different liquids for vapor generation, the temperature of the tube 2 penetrable ³⁵for a particular liquid should be maintained on the level of the boiling point of a selected liquid or 5° to 10° C lower than this point. In case vapor is used, the temperature of the tube 2 penetrable for a selected vapor should be kept higher than its condensation point. ⁴θ When using water vapor or the vapor of other liquids with a higher boiling point (higher than 100° C), the temperature of the both tubes 1 and 2 may be above zero, e.g. the temperature of the tube may be 145° C and of the tube 1, 20° C. ⁴⁵

When using the vapors of low-boiling liquids, the temperature of the tube 2 may be above zero, e.g. 60° C, and the temperature of the tube 1 - subzero, e.g. —30° C. In the case of using liquefiable gases, the temperature of both tubes may be subzero, e.g. when using propane whose condensation point is —42.1° C, the temperature of the tube 2 may be —20° C, while that of the tube 1 —100° C.

Liquefiable gases and, correspondingly, the subzero temperatures of the tubes 1 and 2 are most suitable when effecting the process of condensation or freezing vapors from gas or air with a simultaneous separation of emerging drops or crystalls. Liquefiable gases, condensing on the particles of a newly emerging phase, make these particles heavier and facilitate their separation from the flow under the action of centrifugal forces.

Used as vapor brought into the tube 2 penetrable for them may be various chemically generated secondary vapor, e.g. volatile solvents removed from solutions by evaporation. The proposed apparatus permits the use of these solvents for condensation precipitation of the aerosol particles with a simultaneous regeneration of these solvents for their further utilization. Utilized analogously may be waste vapors from various plants as well as hot discharge (drain) liquids.

Furthermore, the precipitator may also be used for different combined processes. Thus, in addition to the process of precipitation of aerosol particles, the apparatus may also be employed for evaporative cooling of hot liquid and (or) heating of cold liquid by regulating the temperature of outgoing liquids through variations in the speed of their travel inside the porous tube 2 and (or) in the cooled jacket 4.

The proposed precipitator may also be used as a distillation apparatus wherein it is possible to effect the condensation trapping of bacteria and other particles suspended in the air along with the evaporation of volatile solvents from a complex solution and the regeneration of these solvents.

The precipitator is particularly suitable for such combined processes of heat- or mass-exchange which are most effective in conditions of phase transformations and in temperature spheres close to evaporation (condensation) points of substances involved in the abovesaid processes.