US3918170A

US3918170A - Discharge means in a centrifugal drier

Info

Publication number: US3918170A
Application number: US509914A
Authority: US
Inventors: Andre Mercier
Original assignee: Fives Cail Babcock SA
Current assignee: Fives Cail Babcock SA
Priority date: 1973-09-27
Filing date: 1974-09-27
Publication date: 1975-11-11
Anticipated expiration: 1992-11-11
Also published as: BR7408062D0; AU7375274A; IN141162B; BE820454R; ZA746164B; FR2245417B2; ES430346A2; FR2245417A2; GB1468300A; IT1022129B; DE2446343A1

Abstract

The discharge means for a centrifugal drier comprises a vibratory hopper fluid-tightly connected at one end thereof to the outlet of the drier casing which received the dried particles and is filled with a gaseous fluid under a pressure exceeding that of the ambient atmosphere. A vertical discharge conduit is fluid-tightly connected to the opposite end of the vibratory hopper and holds a column of the removed dried particles. The length of the conduit is such that the loss of pressure of the gaseous fluid passing from the casing through the column of dried particles is substantially equal to the pressure differential between the gaseous fluid in the casing and the ambient atmosphere. A control valve at the lower end of the discharge conduit is so regulated that the output of the particles from the conduit maintains the level of the dried particles in the hopper above a set minimum level.

Description

United States Patent [191 Mercier Nov. 11, 1975 [75] Inventor: Andr Mercier, La Madelaine,

France [73] Assignee: Fives-Cail Babcock, Paris, France [22] Filed: Sept. 27, 1974 [21] Appl. No.: 509,914

[30] Foreign Application Priority Data Sept. 27, 1973 France 73.34614 [52] US. Cl. 34/58; 34/56; 34/164 [51] Int. Cl. F2613 17/24 [58] Field of Search 34/43, 52, 55, 56, 58, 34/164, 176, 170; 198/57; 210/360 R [56] References Cited UNITED STATES PATENTS 2,834,658 5/1958 Lieffers et a1 34/56 2,880,519 4/1959 Pollock 34/58 3,553,846 1/1971 McKenzie et al 34/56 3,618,227 11/1971 Breakell et al 34/164 FOREIGN PATENTS OR APPLICATIONS 618,502 8/1935 Germany 34/34 Primary Examiner-Kenneth W. Sprague Assistant Examiner.lames C. Yeung Attorney, Agent, or FirmKurt Kelman [57] ABSTRACT The discharge means for a centrifugal drier comprises a vibratory hopper fluid-tightly connected at one end thereof to the outlet of the drier casing which received the dried particles and is filled with a gaseous fluid under a pressure exceeding that of the ambient atmosphere. A vertical discharge conduit is fluid-tightly connected to the opposite end of the vibratory hopper and holds a column of the removed dried particles. The length of the conduit is such that the loss of pressure of the gaseous fluid passing from the casing through the column of dried particles is substantially equal to the pressure differential between the gaseous fluid in the casing and the ambient atmosphere. A control valve at the lower end of the discharge conduit is so regulated that the output of the particles from the conduit maintains the level of the dried particles in the hopper above a set minimum level.

4 Claims, 1 Drawing Figure US. Patent Nov. 11, 1975 3,918,170

DISCHARGE MEANS IN A CENTRIFUGAL DRIER The present invention relates to improvements in the continuous drying of liquid-solid mixture, such as sugar juice, and more particularly to a type of centrifugal drier for the continuous production of dried solid particles, which comprises a rotary drying basket, a fluidtight casing defining a chamber arranged to receive the solid particles centrifugally ejected from the basket and filled with a gaseous fluid under a pressure exceeding that of the ambient air outside the casing to increase the drag on the particles along their trajectory in the chamber, the casing having an outlet for removing the dried particles therefrom, and a discharge means fluidtightly connected to the outlet. I have disclosed and claimed a centrifugal drier of this type in my US. Pat. No. 3,821,857, dated July 2, 1974, whose entire disclosure is herewith incorporated by reference.

In my patent, the disclosed discharge means is a gastight rotary gate. This, however, has been found notalways to give satisfactory results, particularly when the dired material is sticky, such as sugar. It also is unsatisfactory when the pressure differential between the inte rior of the casing and the ambient atmosphere is too great. If a lock chamber is used, the-particle discharge is discontinuous and dried particles are accumulated from time to time at the outlet of the casing. This would make the device inoperative for the treatment of sugar, for instance, since the accumulated sugar particles would block the outlet. Therefore, a double lock chamber would have to be used and controlled automatically for cycles of alternative openings to assure a continuous discharge. Such an automatic system is complicated and expensive.

It is the primary object of this invention to provide a simple discharge means for a centrifugal drier of the indicated type, which assure a regular continuous output, functions with considerable pressure differentials between the interior of the casing and the ambient atmosphere, and comprises no mobile parts whose movements may be impeded by deposits of solid particles.

The above and other objects are accomplished in accordance with the invention with a discharge means including a vibratory hopper fluid-tightly connected at one-end thereof to the outlet of the casing and a vertical discharge conduit fluid-tightly connected to the opposite end of the vibratory hopper. The discharge conduit holds a column of the removed dried particles and the length of the discharge conduit is such that any escape of the gaseous fluid passing from the casing through the column of removed dried particles is minor, i.e. has a small value. A control valve at the lower end of the discharge conduit controls the output of dried particles from the discharge conduit and means 1 Referring now to the drawing, the conical outlet bottom 10 is part of a centrifugal drier casing such as fully shown and described in my above-mentioned U.S. patent. This casing is filled with a gaseous fluid under pressure and the dried particles received therein must be continuously removed through the outlet without permitting the compressed air in the casing to escape to the atmosphere. The discharge means of this invention is designed to accomplish this purpose. It includes vibratory hopper 12 fluid-tightly connected at one end thereof to outlet 10 of the casing my means of flexible sleeve 14. The flexible sleeve may be of natural or synthetic rubber, for instance, and its ends are affixed to connecting flanges on the casing and hopper, respectively. Vertical discharge conduit 16 is fluid-tightly connected to the opposite end of vibratory hooper 12.

The vibratory hopper comprises a cylindrical upper portion and a frusto-conical lower portion, and valve 18 for stopping the flow of particles is arranged between the lower portion of the hopper and the upper end of vertical discharge conduit 16. In the illustrated embodiment, valve 18 comprises a deformable cylindn'cal sleeve interconnectingrespective flanges at the opposite end of hopper l2 and the upper end of discharge conduit 16, and a housing surrounding the deformable sleeve. A fluid may be introduced into the space between the housing and the deformable sleeve to constrict the latter so as to restrict or close communication between the hopper and the discharge. conduit whereby the flow of particles may be restricted or stopped.

A suitable vibrator 20 of any known design is attached to hopper 12 for subjecting the same to suitable vibrations of a low amplitude; Flexible connecting sleeve 14 prevents these vibrations from being transmitt'ed to the casing of the centrifugal drier. If desired, a similar flexible connecting sleeve may be arranged between the hopper and the discharge conduit to accomplish alike purpose, thus isolating the vibrations of the hopper from all other parts of the drier.

Control valve 22 is mounted at the lower end of discharge conduit 16 for controlling the output of dried particles from the discharge conduit, this output determining the level of the dried particles in the hopper which receives the particles from the casing by gravity feed, and the particles being gravity fed from the hopper into the discharge conduit according to the setting of valve 18.

Automatic control 24 constitute means for regulating control valve 22 so that the output of the particles from the conduit maintains the level of the dried particles in the hopper above set minimum M. In the disclosed embodiment the control is so set that it maintains the level of the dried particles in the hopper at a level between set maximum level M and minimum level M. For this purpose, sensors are mounted in the hopper at the set minimum and maximum levels to. sense the column of particles in the hopper. On sensing particles at that level, the sensors produce respective control signals electrically transmitted to control 24 and an electric control circuit 25 connects the control to valve 22 for regulating the same in response to the control signals.

An alarm system 26, incorporating a sensor at a set maximum level M warns tthe operator by a visible and/or audible signal if the particles in the hopper reach this upper limit. Alternatively, this alarm system may be connected directly to a control system which regulates the feed to the drier so as to control this feed in response to this upper level limit in the discharge hopper.

An arcuate deflecting guide or baffle 28 is pivotally mounted at the lower output end of discharge conduit 16 to permit the discharged particles to be directed to a desired location, such as endless conveyor band 29 mounted below the discharge conduit to convey the discharged solid particles away from the drier.

The particles are conveyed through the discharge means by the pressure of the gaseous fluid in the casing.

In accordance with the present invention, the length of discharge conduit 16 is so selected that any escape of the gaseous fluid passing from the casing through the column of removed dried particles in the discharge conduit is minor. Any such loss of gaseous fluid is produced by the flow of the gaseous fluid through the col umn of particles in discharge conduit 16 and in hopper 12 when the level of the particles in the hopper is between minimum level M and maximum level M Under this condition, the escape of air from the casing into the atmosphere through the discharge means is to]- erable.

Control 24 maintains the level of the particles in the hopper between levels M and M by regulating the opening of valve 22. Since the surface of the column of particles in the hopper is not plane, a mean level between M and M is maintained. The level sensors for the control may comprise a radioactive source emitting gamma radiation and a detector measuring the intensity of the emitted radiation across the hopper.

To make the control responsive in sufficient time to effectuate the valve regulation, the level control must be effected in a zone where the particles move relatively slowly. For this reason, the control is effectuated in hopper 12 rather than in discharge conduit 16 because the particles move much more slowly down the frusto-conical hopper than the conduit.

When the output of solid particles is small, for instance towards the end of the drying procedure, and control 24 must close valve 22 to maintain the level of particles above set minimum level M, the control circuit is de-energized to permit automatic evacuation of the hopper and the discharge conduit. The discharge means then functions like a lock chamber, with valve 18 closed and valve 22 open, or vice versa. This prevents clogging of the discharge means.

Throughout the specification and claims, the term minor escape of the gaseous fluid passing from the casing through the column of removed dried particles is meant to designate an amount of gaseous fluid escape of such magnitude that the power necessary for compensating for such escape and to maintain the pressure in the casing at the set value is negligible in relation to the total power consumed by the drier.

I claim:

1. In a centrifugal drier for the continuous production of dried solid particles, which comprises a fluidtight, closed casing arranged to receive the dried parti cles and filled with a gaseous fluid under a pressure exceeding that of the ambient air outside the casing, the casing having an outlet for removing the dried particles therefrom: a discharge means fluid-tightly connected to the outlet, the discharge means including 1. a vibratory hopper fluid-tightly connected at one end thereof to the outlet of the casing,

2. a vertical discharge conduit fluid-tightly connected to the opposite end of the vibratory hopper,

a. the discharge conduit holding a column of the removed dried particles and b. the length of the discharge conduit being such that any escape of the gaseous fluid passing from the casing through the column of removed dried particles is minor,

3. a valve between the opposite end of the hopper and the discharge conduit for controlling the flow of particles from the hopper into the discharge conduit,

4. a control valve at the lower end of the discharge conduit for controlling the output of dried particles from the discharge conduit, and

5. means for regulating the control valve so that the output of the particles from the conduit maintains the level of the dried particles in the hopper above a set miniumum level.

2. In the centrifugal drier of claim 1, a flexible sleeve fluid-tightly connecting the outlet of the casing to the one end of the hopper.

3. In the centrifugal drier of claim 1, the regulating means comprising an automatic control maintaining the level of the dried particles in the hopper at a level between set maximum and minimum levels.

4. In the centrifugal drier of claim 1, an alarm system responsive to a set maximum level of the dried particles in the hopper.

Claims

1. In a centrifugal drier for the continuous production of dried solid particles, which comprises a fluid-tight, closed casing arranged to receive the dried particles and filled with a gaseous fluid under a pressure exceeding that of the ambient air outside the casing, the casing having an outlet for removing the dried particles therefrom: a discharge means fluid-tightly connected to the outlet, the discharge means including 1. a vibratory hopper fluid-tightly connected at one end thereof to the outlet of the casing, 2. a vertical discharge conduit fluid-tightly connected to the opposite end of the vibratory hopper, a. the discharge conduit holding a column of the removed dried particles and b. the length of the discharge conduit being such that any escape of the gaseous fluid passing from the casing through the column of removed dried particles is minor, 3. a valve between the opposite end of the hopper and the discharge conduit for controlling the flow of particles from the hopper into the discharge conduit, 4. a control valve at the lower end of the discharge conduit for controlling the output of dried particles from the discharge conduit, and 5. means for regulating the control valve so that the output of the particles from the conduit maintains the level of the dried particles in the hopper above a set miniumum level.

2. a vertical discharge conduit fluid-tightly connected to the opposite end of the vibratory hopper, a. the discharge conduit holding a column of the removed dried particles and b. the length of the discharge conduit being such that any escape of the gaseous fluid passing from the casing through the column of removed dried particles is minor,