US3839802A

US3839802A - Desiccator for wet powder particles

Info

Publication number: US3839802A
Application number: US00280205A
Authority: US
Inventors: S Saito; H Nakamura; T Watanabe; H Wakamori
Original assignee: Kureha Corp
Current assignee: Kureha Corp
Priority date: 1971-08-18
Filing date: 1972-08-14
Publication date: 1974-10-08
Anticipated expiration: 1991-10-08
Also published as: JPS4828557A; GB1379833A; FR2151878A5; DE2240524A1; IT964093B; NL158608B; JPS5551723B2; BE787784A; NL7211246A

Abstract

A desiccator for wet powder particles of synthetic high polymer substance, the main construction of which is a long vertical cylinder having a material feeding inlet at a lower part on the peripheral wall thereof and an inverse conical section forming the bottom part of the cylinder, a high speed hot gas current inlet being provided at the vertical angle of the inverse conical section, and the top end of the cylinder being communicated to a cyclone for collecting the dried product through a conveying tube.

Description

United States Patent Saito et al.

[ 1 Oct. 8, 1974 DESICCATOR FOR WET POWDER PARTICLES Inventors: Shigeru Saito; Tetsuya Watanabe;

Hideki Wakamori; Hideo Nakamura, all of Iwaki, Japan Kureha Kagaku Kogyo Kabushiki Kaisha, Tokyo-to, Japan Filed: Aug. 14, 1972 Appl. No.: 280,205

Assignee:

Foreign Application Priority Data Aug. 18, 1971 Japan 46-62314 US. Cl 34/10, 34/57 A, 432/15 Int. Cl. F26b 3/08 Field of Search 34/10, 57 A, 57 R; 432/15,

References Cited UNITED STATES PATENTS 10/1949 Wachs 34/57 R Gishler et al. 34/10 2,903,800 9/1959 Skoglund 34/57 A X 3,066,017 11/1962 Jahnig 3,263,338 8/1966 Gordon 3,273,257 9/1966 Johnson et al 3,399,462 9/1968 Koch et al. 34/57 A Primary ExaminerWilliam F. ODea Assistant Examiner-William C. Anderson Attorney, Agent, or FirmWenderoth, Lind & Ponack [5 7 ABSTRACT A desiccator for wet powder particles of synthetic high polymer substance, the main construction of which is a long vertical cylinder having a material feeding inlet at a lower part on the peripheral wall thereof and an inverse conical section forming the bottom part of the cylinder, a high speed hot gas current inlet being provided at the vertical angle of the inverse conical section, and the top end of the cylinder being communicated to a cyclone for collecting the dried product through a conveying tube.

2 Claims, 1 Drawing Figure DESICCATOR FOR WET POWDER PARTICLES This invention relates to a desiccator, or a drying apparatus. More particularly, it is concerned with a desiccator for wet powder particles of synthetic high polymer substances.

lmportant problems in drying wet powder particles are the sufficient breaking or division of agglomerated masses of wet powder particles into individual fine particles for enhancing the effect of the drying, and dispersion of these individual fine particles into a hot gas current for desiccation. To meet both requirements, various proposals have heretofore been made and put into practice. All these proposed devices to solve the problem, however, are just a combination of a drying machine and a special device for crushing the mass of wet powder particles and for dispersing individual fine powder particles into a gas current.

As one example, there has been employed a desiccating device, in which a dryer is combined with mechanical means for dividing the mass of wet powder particles such as, for instance, a cage mill, or other mechanical expedientprovided with a rotary body. While a remarkable effect of division can be obtained from this type of apparatus, if the mass to be divided is one that is highly agglomerative, there inevitably occur various problems such as notorious adherence of the wet, massive powder particles to the crusher main body or to the inner peripheral portion thereof. Particularly, in the desiccation of synthetic high polymer, such adhered material not only mixes into the final product later on to lower the quality of the product, but also causes inflammation and fire, when the adhered material is exposed in a high temperature circumstance for a long period of time, which is serious from the standpoint of operation and maintenance of the installation.

With a view to eliminating such defects and disadvantages in the conventional apparatus as mentioned in the foregoing, the present inventors conducted a long series of studies and experiments, as the result of which they have succeeded in building an improved desiccating apparatus free from these disadvanges.

It is therefore the primary object of the present invention to provide an improved type of desiccating apparatus useful for drying wet powder particles of synthetic high polymer substance.

It is another object of the present invention to provide a desiccator for wet powder particles of synthetic high polymer, which is so constructed that breaking up of agglomerated wet powder particles of synthetic high polymer substance as well as drying of individual wet powder particles as crushed can be accomplished at a single step by utilizing high speed hot gas current.

It is still another object of the present invention to provide a method for drying wet powder particles of synthetic high polymer substance.

The foregoing objects and other objects of the present invention will become more apparent and understandable from the following description of the invention, when read in conjunction with the accompanying drawing.

ln the drawing, the single FIGURE is a schematic structural diagram of an embodiment of the present invention.

As seen from the FIGURE of the drawing, the desiccator according to the present invention is much simpler in its construction than that of the known apparatus.

That is, the main part of the apparatus according to the present invention is a vertical cylinder 3, the bottom part 1 of which is in an inverse conical shape with an inlet 2 for high speed hot gas current at the bottom center part thereof, and the upper part of which is connected with a conveying tube 5 for the desiccated product, which further communicates to a cyclone 6 for collecting the dried product therein and a gas exhaust tube 7. The cylinder 3 is also provided at one position on its peripheral wall in the vicinity of the bottom part 1 with an inlet 4 for feeding raw material to be desiccated.

Specifically, the cross-sectional area of the cylinder is necessarily from 10 to times as large as that of the inlet 2 for high speed hot gas current, and the total length (or height) of the cylinder 3 should be from 5 to 10 m long at least. The interior of the cylinder 3 need not be provided with any special devices such as a crusher for agglomerated masses of wet powder particles or a sieve for screening such crushed powder particles.

In the actual operation of the desiccator of the abovedescribed construction according to the present invention, air which has been heated to and maintained at a temperature range of from 70 to 200C is blown into the cylinder 3 through the inlet 2 at the bottommost and of the cylinder as a high speed hot gas current of from 40 to m/sec.. By this high speed hot air current, agglomerates of the wet powder particles of synthetic high polymer substance which is being fed continuously from the inlet 4 for feeding material are break up into individual fine particles, and these fine particles are perfectly dried in the course of their travel up through the cylinder 3 to the top thereof. The dried powder particles as the final product are then transferred to the cyclone 6 through the conveying tube 5.

For the purpose of dividing and dispersing the wet powder particles of synthetic high polymer substance containing agglomerated particles within the cylinder, it is necessary to have a speed of the hot gas current through the outlet sufficient to blow the agglomerates upwardly, in other words, a speed of the hot gas current higher than the end speed of the agglomerates.

In practice, the size of the agglomerates is reduced to a certain extent within a feeding apparatus before the desiccator, and an average diameter thereof is about 5 cm or less. The required speed of the hot gas current to blow this size of the particles upwardly is at least 30- m/sec..

Although it is desirable for the hot gas current to be the highest possible in speed to exert much more breaking force against the agglomerates of the wet powder particles, most of the masses of powder particles of synthetic high polymer can be sufficiently divided into individual particles at a current speed of 150 m/sec.. The hot gas current having an extremely high speed is obtained by an increased outlet pressure for a blower, and it is difficult to maintain constant the current speed within the cylinder. A preferable speed of the hot gas current is therefore from 30 to 150 m/sec..

Moreover, the average speed of the hot gas current within the cylinder is determined by the particle size, specific gravity and shape of the material to be desiccated. It is necessary that the average current speed be chosen within a range between the end speed of the largest powder particles in the material to be dried and the end speed plus 2 m/sec.. If a current speed lower than this range is selected, any powder particles having higher end speed than the current speed within the cylinder remain in the cylinder without being discharged therefrom. On the contrary, when a current speed higher than this range is selected, thepowder particles are discharged out of the cylinder without sufficiently dcssicated and without masses of powder particles being completely broken up. Generally, in the case of synthetic high polymer particles, effective dividing and drying of the powder particles can be attained at the selected current speed of from 1.5 to 5 m/sec..

Another important point in carrying out the present invention is that the cylinder should have a sharp expansion of the space at the apex of the inverse conical section constituting the inlet for high speed hot gas current into the cylinder main body where the current speed somewhat slows down, whereby violent turbulence occurs at the expanded portion of the cylinder to flush the inner surface of the inverse conical section so as to prevent the wet powder particles from adhering thereonto.

In this case, however, if the apex angle of the inverse conical section is too large, the wet powder particles fed from the material feeding inlet accumulate on this sloped bottom part and are difficult to flush by the turbulence caused by the high speed hot gas current passing through the center part of the cylinder with the consequence that the intended division of the masses of powder particles becomes difficult, hence continuous operation is impossible.

On the contrary, if the apex angle of the inverse conical section is too small, the defect of accumulation of the raw material on the sloped bottom part of the inverse conical section can be eliminated. However, there is caused another defect, namely that, since the expansion of the cylinder space from the apex angle of the inverse conical section, i.e., the slope of the inverse conical section at its apex angle, is gentle, no turbulence occurs with the result that highly adhesive and agglomerative material will stick to this inclined surface of the inverse conical section.

As the result of various studies and experiments, it has been found out that the apex angle of the inverse conical section is preferably in the range of 60 Next, for the wet powder particles of synthetic high polymer substance to be effectively divided, dispersed and desiccated by the high speed hot gas current blown into the cylinder from the bottom thereof, the total length of the cylinder constitutes the third important point.

That is, when the powder particles including masses of particles are blown upwardly by the high speed hot gas current, it is necessary that perfectly divided and dispersed particles are carried upward through the cylinder, while undivided masses lose their speed to drop downward. In this case, if the total length of the cylinder is too short, the masses of powder particles are also discharged from the cylinder by their own inertia imparted by high speed hot gas current before they lose their speed, and mix into the dried final product.

The height at which the blown-up masses lose their speed and drop downward depends on the flow-rate of the high speed hot gas current, and size, shape and weight of the agglomerated mass. As the result of study,

it has been found that, in order that there not be any agglomerated masses of the wet powder particles in the dried product, the total length of the cylinder should be made greater than a value represented by a relationship of(0.05V 3m), where V is from to 150 meters and the numerical value thereof corresponds to the numerical value of the distance of the flow of the high speed hot gas current per second.

Furthermore, when the inlet for feeding the material to be dried is at a very high position on the cylinder, those particles having a lower end speed than that of the current flow rate within the cylinder are blown upward as they are fed in from the position of the inlet, so that the space below the feed inlet does not contribute to the drying operation, and the powder particles are discharged from the top of the cylinder while incompletely dried.

More concretely, length of the cylinder portion from the material feeding inlet to the outlet at the top thereof should be at least 3 meters, and the position of the material feeding inlet on the peripheral wall of the cylinder should preferably be at a distance of from k to l/20 of the diameter of the cylinder but not exceeding l/ 10 of the total length of the cylinder from the bottom end thereof.

In the following, explanations are made as to continuously drying wet powder particles of synthetic high polymer substance using the desiccator according to the present invention.

First, hot air is blown into the cylinder 3 constituting the dryer main body from the hot gas current inlet 2 at the bottom thereof at a high speed hot gas current of from to 150 m/sec.. Simultaneously, wet powder particles of synthetic high polymer are continuously fed from the material feeding inlet 4. The powder particles thus fed into the cylinder 3 are dispersed and dried in the cylinder by the high speed hot gas current from the inlet 2. During the drying operation, agglomerated masses in the wet powder particles are also divided by this high speed hot gas current into individual fine particles.

Even among the masses of powder particles which have once been separated and blown upwardly by-the high speed current, those masses which are insufficiently divided and insufficiently dried drop downward again to be repeatedly divided and dried by the hot gas current moving at an average speed of 1.5 to 5 m/sec. within the cylinder whereby only the finely divided and dried powder particles are collected in the cyclone 6 through the product conveying tube 5, and the desiccated product can be taken out therefrom as the final product.

The entrance speed of the high speed hot gas current as well as the average speed of the same within the cylinder according to the present invention may be varied. For the purpose of drying powder particles of synthetic high polymer, high speed hot gas current of 40 to 150 m/sec. and an average speed within the cylinder of 1.5 to 5 m/sec. can effectively carry out the drying.

In order to enable skilled persons in the art to reduce the present invention to practice, the following actual examples are presented. It should be noted that these examples are illustrative only and are not intended to restrict the scope of the present invention.

EXAMPLE 1 M resin having a particle size range of from 44 to 1,000 microns and a moisture content of 50% was fed at a rate of 18 kg/hr. into a desiccator constructed with a cylinder main body of 30 cm in diameter and 800 cm in height, the bottom part of which forms an inverse conical section having an apex angle of 60. The bottom center of the inverse conical section is provided with a high speed hot gas current inlet of 5.5 cm in diameter. A material feeding inlet of 8 cm in diameter is provided at a position 10 cm away from the bottom end of the cylinder main body.

The drying operation was conducted under the following conditions.

ABS resin having particle size range of from 44 to 500 microns and a moisture content of 40% was fed at a rate of 40 kg/hr. into a desiccator constructed with a cylinder main body of 30 cm in diameter and 600 cm in height, the bottom part of which forms an inverse conical section having a the vertical angle of 60. The bottom center of the inverse conical section is provided with a high speed hot gas current inlet of 10 cm in diameter. A material feeding inlet of 8 cm in diameter is provided at a position 10 cm away from an bottom end of the cylinder main body.

The drying operation was conducted under the following conditions.

Humidity of Air High Speed Hot 0.018 kg H O/kg D-air within Cylinder What is claimed is:

1. A method for desiccating wet powder particles of synthetic high polymer substance which comprises the steps of:

a. continuously feeding wet powder particles of synthetic high polymer substance in a lateral direction into the lower portion of a defined drying zone having a cylindrical cross section and a length in meters of at least 0.05V 3, where V is from 30 to 150, and having an inverse conical section having an apex angle of from 50 to b. blowing into the defined drying zone through the apex of the conical section a stream of high speed hot gas at a temperature of from 70 to 200C at a flow rate of from 30 to 150 m/sec., the value V being equal to the numerical value of said flow rate, said stream further having a cross-section of from l/10 to H the cross-sectional area of the cylindrical portion of the defined drying zone for maintaining the average speed of the hot gas through the cylindrical portion at 1.5 to 5.0 m/sec.; and

c. withdrawing the dried particles and gas from the top of the defined drying zone for sending them to a product collecting cyclone.

2. A method for desiccating wet powder particles of synthetic high polymer substance which comprises the steps of:

a. continuously feeding wet powder particles containing agglomerated masses of the wet powder parti cles into a defined zone for drying; and

b. blowing into the defined drying zone a stream of high speed hot gas at a temperature of from 70 to 200C at a flowrate of 30 to m/sec. and having a cross-section from l/lO to l/ 100 the crosssectional area of the defined zone to cause fluidization of said powder particles within the defined drying zone for dividing the agglomerated masses into individual fine particles, dispersing and sufficiently drying the fine particles within the drying zone;

the speed of the hot gas stream being sufficient to maintain the average speed of the hot gas through the defined drying zone at 1.5 to 5.0 m/sec.

Claims

1. A method for desiccating wet powder particles of synthetic high polymer substance which comprises the steps of: a. continuously feeding wet powder particles of synthetic high polymer substance in a lateral direction into the lower portion of a defined drying zone having a cylindrical cross section and a length in meters of at least 0.05V + 3, where V is from 30 to 150, and having an inverse conical section having an apex angle of from 50 to 70*; b. blowing into the defined drying zone through the apex of the conical section a stream of high speed hot gas at a temperature of from 70 to 200*C at a flow rate of from 30 to 150 m/sec., the value V being equal to the numerical value of said flow rate, said stream further having a cross-section of from 1/10 to 1/100 the cross-sectional area of the cylindrical portion of the defined drying zone for maintaining the average speed of the hot gas through the cylindrical portion at 1.5 to 5.0 m/sec.; and c. withdrawing the dried particles and gas from the top of the defined drying zone for sending them to a product collecting cyclone.

2. A method for desiccating wet powder particles of synthetic high polymer substance which comprises the steps of: a. continuously feeding wet powder particles containing agglomerated masses of the wet powder particles into a defined zone for drying; and b. blowing into the defined drying zone a stream of high speed hot gas at a temperature of from 70 to 200*C at a flowrate of 30 to 150 m/sec. and having a cross-section from 1/10 to 1/100 the cross-sectional area of the defined zone to cause fluidization of said powder particles within the defined drying zone for dividing the agglomerated masses into individual fine particles, dispersing and sufficiently drying the fine particles within the drying zone; the speed of the hot gas stream being sufficient to maintain the average speed of the hot gas through the defined drying zone at 1.5 to 5.0 m/sec.