GB2198510A

GB2198510A - Apparatus for evaporating and drying a slurry based on water or other solvent

Info

Publication number: GB2198510A
Application number: GB08725998A
Authority: GB
Inventors: Andras Czeiler; Jozsef Scholtz; Miklos Keri; Laszlo Meszaros; Tibor Lakatos; Tibor Egyhazy; Jozsef Kovacs
Original assignee: Tungsram Rt
Current assignee: Tungsram Rt
Priority date: 1986-11-11
Filing date: 1987-11-05
Publication date: 1988-06-15
Also published as: GB8725998D0; DE3735655A1; HUT45906A; HU198265B; NL8702541A

Description

2198510 e_ APPARATUS FOR EVAPORATING AND DRYING A SLURRY BASED ON WATER OR

OTHER SOLVENT

BACKGROUND OF THE INVENTION

The present invention relates to an apparatus for evaporating and drying a slurry based on water or other solvent, especially for producing a grainy material as a luminophore. The proposed apparatus is capable of evaporating, drying a slurry and subsequently comminuting the dried material. It is possible to recover the solvent, if necessary.

The methods of pleparing coating by mans of electrostatic forces from white or coloured pigments, especially from luminophores require applying surface treatments. The pulverized grainy materials can by applied for coating the vessels of the light sources after surface treatment only. The surface treatment results in a grainy material which has the required surface resistance, degree of hydrophobia and can be pulverized by simple means. The pulverized grainy material adheres to the vessel during the electrostatic coating process and the subsequent heat treatment, and by a sintering processforms a coating of therequired quality and homogeneity. The luminophores applied in these processes should be capable of forming a coating of perfectl uniform thickness. The inhaTogene-'tty of the concentration may result in big differences in the pulverizability, chargeability of the coating material, in its adherence to the walls of the vessel and to the other lurninophore particles. The effects mentioned cause a high rate of products of unacceptable quality.

The features mentioned above have determined an important demand of the industral branches related to the light sources: it is important to create an apparatus where- by the active ingredients dissolved in an aqueous, other inorganic or an organic solvent can be dried on the surface of a pigmented material or a luminophore so as to assure the conditions of a chemical reaction to be developed during a heat treatment process. The recovery of the solvent should be also considered as an important task.

The manufacturing processes applied to the light sources require a dried product of such grain sizes that the grains be comminutable to a desired small grain size by means of a jet mill without ellutriation.

The requirements cannot simply be met by the distillation process because of stratification resulting in inhomogeneous distribution of the active ingredients: they will be present at higher rate in the upper strata.The distillation apparatus can be equipped with a mixer, however, this solution cannot be considered to be advantageous be cause of intensive friction forces resulting in breaking of the constructional elements. If applying a drying method by pul verizing, uniform concentration cannot be assured, and the recover of the sGI,.ent requires expensive refrigerator il apparatuses.

It has become clear that to solve the problem it is necess2ry to create an apparatus for continuous treatment of a pigment powder. The apparatus should ensure the oonditions of treatment of a suspension in a continuous manner, in a closed vessel, by applying a steady mixing during evaporating the solvent. The apparatus should continuously supply a suspension to the input of a vessel, comminute the dried suspension on the output of the vessel, ensure a required temperature range of drying, and ensure the continuous process of manufacture of the solid material and the recovery of the solve-rit.

The most important apparatuses for continuous heat trestrtent of solid pigmented and grainy materials are shown in different publications (see e.g. the Chemical Engineers' H2ndbook, 4 th edition, edited by R. H. Perry, C. H. Chilton and S. 0. Kirkpatrick, McGraw-Hill, Inc., New-York, 1966, part 11-5Z-). Figs. 11-36 of the mentioned publication shos an apparatus for melting solid state materials which can be applied to drying grainy materials, too. The apparatus comprisesa tubular double-walled vessel and two spiral mixing elements, an inlet for supplying a material to be dried into the interior of the vessel and output for delivering the dry material. The apparatus depicted in the Fig. mentioned is not capable of offering a solution to all problems of the production of luminophores.

SURIARY OF THE INVENTION An object of the invention is.to create an apparatus far evaporating and drying a slurry based on water or other solvent W- iich can be applied to manufacture of luminophores of required high quality and generally to production of grainy materials by drying an active material dissolved in slurry.

The invention is based on the recognition that the apparatus shown in the publication cited can be considered as a basis of an apparatus created for solving the problem of the present invention if it is equipped with appropriate inlet and outlet means. It has been recognized that the slurry should by supplied into a double-walled vessel by means of a valve of flexibly regulatable cross-section as snown e.g. in the US Letters Patent No. 1 872 792 granted to H. M. Neorr. It is also a part of the recognition that the valve of Neorr. is not satisfactory.

The object of the invention is an apparatus for eaporating and drying a slurry based on water or other solvent, especially for preparing a grainy material, comprising a tubular double-walled vessel and two spiral mixing ele- ments arranged therein,aninlet for supplying the slurry into the interior of the double-walled vessel and an outlet for delivering dry material, the improvement of which is that the inlet is connected with a tubular element for supplying the slurry from a container to the double-walled vessel, the tubular element surrounds a mixing shaft reaching the interior of the container and includes a tubular part made of flexible material, and the double-walled vessel is connected by means of its outlet to a unit for co.,TY-,inuting the dry material.

1 The tubular part is advantageously connected to a regulator unit for adjusting its cross-section and the unit for conTninuting includes a beater mill arranged over a sieve.

The doUble-walled vessel is in a further advanta geous embodiment equipped with a flange fcr recovery of the solvent. It is also proposed to divide the interior of the walls of the double-walled vessel into more sections.

Sum,.iarizing, the apparatus of the invention is equipped with an inlet for regulated supply of a slurry and a unit foc comminuting the dried slurry, in order to obtain a product of required grainy sizes by drying on the surface of particles an active material solved in the slurry. By means of the proposed apparatus the pigmented material of high quality can bje produced for meeting the requirements to be filled in the production of the light sources.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in more detail by way of example and with reference to a preferred embodiment illustrated in the accompanying drawings, wherein: Figure 1 is a vertical cross-section of the apparatus proposed by the invention, and Figure 2 shows a cross-section of the apparatus of Fig. 1 in a plane A - A.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The apparatus as proposed by the invention (Figure 1) comprise a doblewalled vessel 1 - preferably with the r, the annular interior of the walls divided inte more cylindrical sections - with spiral mixing elements 2, 6 acting L against one another in the tubular inner space of the double-walled vessel 1 divided into an inlet part 14, a drying part 15 and an outlet part 16. Between the inlet part 14 and the drying part 15 there is a barrier 5. The outlet part 16 is connected with a comminuting unit corrprising a beater mill 3 arranged cver a sieve 4 covering a vessel 13 for receiving the comminuted material. This vessel 13 is connected 10 with an inlet 11 for introducing gaseous media. The comminuting unit is covered by a window 12 wfiereby the grainy material produced by the beater mill 3 can be observed.

The double-walled vessel 1 is equipped also with a recovery flange 10 for taking away the evaporized solvent 15 from the inner space.

The mixing elements 2, 6 and the grounding elements of the beater mill 3 are arranged on respective shafts 20. The apparatus may include a higher number of shafts 20, and in this case the double-walled vessel 1 can have a non-cir20 cular cross-section.

The inlet part 14 of the double-walled vessel 1 is connected with a container 7 receiving a slurry. Between the container 7 and the doublewalled vessel 1 there is an inlet 19 for introducing the slurry from the container 7 into double-walled vessel 1. This inlet 19 surrounds a mixing shaft 9 reaching the interior of the container 7 in form of a mixing blade 17. It includes also a tubular part 18 made of a flexible material, e.g. rubber and connected to a regulator means 0 for the control of the cross-section between -4 mixing shaft 9 and the tubular part 18 of the inlet 19 which is generally a tubular element, too.

The apparatus of the invention operates as folloAs.

The slurry of a pigmented material, a luminophore is continuously homogenized by the mixing blade 17 and in this time it is introduced into the double-walled vessel 1 over the tubular element 18 made of flexible material. In the interior of the double-walled vessel 1 there are two pairs of the mixing elements 2, 6 rotated in opposite directions.

The sections of the double-wall of the vessel 1 are heated up -to required temperature by introducing overheated vapour or oil. The slurry is introduced at regulated rate by means of the regulator unit 8 into the double-walled vessel wherein the slurry reaching the barrier 5 is taken into a region with temperature lying over the boiling point of the solvent applied in the slurry (water or other organic or inorganic solvent). The evaporized solvent - together with a carrier and/or protective gas introduced by means of the inlet 11 can be recovered by the flange 10 and transported by app- ropriate means to a heat exchange unit. The slurry is dried on the way from the inlet part 14 to the outlet part 16. The dried material is coffninuted into grains with size smaller than I mm by the beater mill 3 and the comminuted material falls down through the sieve 4. 25 The regulator unit 6 is applied to control the cross-section of the inlet 19 on the basis of the process parameters. It can be an automatic pneumatic or a hand-controlled regulator or based on other principles.

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Claims

1. Apparatus for evaporating and drying a slurry based on water or other solvent, especially for preparing a grainy material, comprising a tubular double-walled vessel and two spiral mixing elements arranged therein, an inlet for supplying the slurry into the double-walled vessel and an outlet for delivering dry material, wherein the inlet is connected with a tubular element for supplying the slurry from a container to the double- walled vessel, the tubular element surrounding a mixing shaft reaching the interior of the container and including a tubular part made of a flexible material, and the outlet of the double-walled vessel is connected with a unit for comminuting the dry material produced in the double-walled vessel.

2. An apparatus according to claim 1, wherein the tubular part made of flexible material is connected to a regulator unit for adjusting the cross-section of the tubular part when supplying the slurry into the double-walled vessel.

3. An apparatus according to claim 1 or 2, wherein the unit for comminuting includes a beater mill arranged over a sieve.

4. An apparatus according to any of claims 1 to 3, wherein the doublewalled vessel is equipped with a flange for leading away the vapour of the solvent.

5. An apparatus according to any of claims 1 to 4, wherein the interior of the walls of the double-walled vessel is divided into more sections.

6. An apparatus for evaporating and drying a slurry based on water or other solvent as herein described with reference to and as shown in the accompanying drawings.

7. An apparatus for preparing grainy luminophores as herein deoscribed with reference and as shown in the accompanying drawings.

1 Published 1988 at The Patent Office, State House, 66171 High Holborn, London WClR 4TP. Further copies may be obtained from The Patent Office, Saaes Branch, St Mary Cray, Orpington, Kent BR5 3RD. Printed by Multiplex ter,,bniqueS Itd, St Mary Cray, Kent. Con. 1/87.