US3607116A

US3607116A - Furnace for continuous firing of phosphors

Info

Publication number: US3607116A
Application number: US258A
Authority: US
Inventors: Martha J B Thomas; Ernest A Dale; William A Finch
Original assignee: Sylvania Electric Products Inc
Current assignee: GTE Sylvania Inc
Priority date: 1970-01-02
Filing date: 1970-01-02
Publication date: 1971-09-21
Anticipated expiration: 1988-09-21

Abstract

A furnace for continuous firing and recovery of fluorescent material including a rotating burner which generates a flame into which the fluorescent material is introduced. The fluorescent material is transported by gaseous stream into a chamber where it is mixed with a fuel, and the mixture is then forced through rotating nozzles, located at the top of the furnace, where the fuel burns and fires the fluorescent material.

Description

United States Patent Martha J. B. Thomas Winchester; Ernest A. Dale, Hamilton; William A. Flnch, Mlrblehead, all 01 Mass. Appl. No. 258 Filed Jan. 2, 1970 Patented Sept. 21, 1971 Assignee Sylvania Electric Products Inc.

[72] inventors FURNACE FOR CONTINUOUS FIRING 0F PHOSPIIORS 4 Claims, 3 Drawing Figs.

US. Cl 23/277 R, 431/182, 431/185, 252/30l.4, 239/406, 23/284 Int. CL... ..F27b 15/10,

[50] Field ofSearch 23/277, 252, 284; 252/3014; 75/21 1, 84.5; 266/34. I, 34.2; ll7/l05.2,9l.5; ll8/47;431/4, 9,185,182;

[56] References Cited UNITED STATES PATENTS 836,219 11/1906 Schultz 431/9 Primary Examiner-James I-I. Tayman, Jr. AnorneysNorman J. O'Malley and Owen J. Meegan S s s FURNACE FOR CONTINUOUS FIRING OF PI-IOSPIIORS BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to furnaces and particularly to those which can be used for the manufacture of phosphors. Continuous firing of materials can be provided through the use of the present furnace.

2. Description Of The Prior Art US. Fat. to Butler, No. 2,755,254 discloses a method of making a halophosphates phosphor in a continuous manner in a furnace. The raw materials necessary to form the phosphor were blended in the proper proportions and then placed in open silica boats. These boats were then placed in an elongated furnace and moved in a semicontinuous manner form one end of the furnace to the other. A blanket of inert gas flowed through the furnace in a direction opposite to the direction in which the boats were moved.

In a US. Pat. to Homer et al., No. 3,093,594, an improvement on the method of firing is disclosed in which the furnace was divided into zones. Inert gas flowed counter to the direction of the boats in the first zone and then in the same direction in the second zone. In a third zone the inert gas then flowed in a direction counter to the direction in which the boats were traveling. In the last zone, the gas flowed in the same direction as the boats. Between each of the zones, interlocks were provided which allow different firing temperatures and changes in the direction of flow of the inert gas.

These furnaces have been the core of the processing equipment for full scale production of fluorescent materials. They have worked well and provided a superior phosphor which has been used in the manufacture of fluorescent lamps.

Many other improvements have been made in the processing techniques which were used during the firing. For example, the US. Pat. to Homer, No. 3,002,933, discloses an important technique to prevent traces of manganese from boiling out of the raw material blend and depositing on the surface of the blend as a pink-top." Through the relatively uncomplicated step of not filling the boats to the brim, the volatilization of the manganese is inhibited.

Other techniques and modifications have been made in the semicontinuous firing approach discussed above but the fundamental concept of firing has not been changed. For example, the US. Pat. to Vodoklys, No. 3,023,339 discloses a post firing treatment of a phosphor in which the phosphor was slurried in water and dispersed through an atomizer into heated gas. According to patentee, the treatment can improve the finished phosphor through the elimination of milling steps.

DESCRIPTION OF THE DRAWING FIG. 1 is an elevational cross-sectional view of the furnace for preparing phosphors according to the present invention.

FIG. 2 is a cross-sectional view of the burner assembly which is disposed on the top of the furnace.

FIG. 3 is a view of the lower surface, taken along the line 33 of the burner assembly shown in FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. I, the furnace includes a lining 1, preferably formed of a refractory material in an elongated tubular shape with the upper end and

lower end

3 and 5, respectively, converging upon the axis of the tube.

Surrounding the lining is a refractory insulator 8, preferably in the form of blocks, to retain the heat within the furnace. The thickness of the insulator 8 should be sufficient to prevent the formation of any localized cold spots.

A burner assembly is disposed at the upper end of the furnace and the flow path is directed along the axis of the lining. Details of the burner are more specifically shown in FIG. 2. Raw materials for the process can be formed as disclosed in the application of Dale et al., Ser. No. 606,159, filed Dec. 30, I966, now abandoned, and continuation application Ser. No. 56,l63 filed July 8, 1970, entitled Process Of Forming Phosphors and assigned to the same assignee as the present invention.

These phosphor-forming materials are transferred, preferably by air, from a central conduit 7 into the interior of the furnace. Combustible gas, natural gas for example, is introduced through conduit 9 into an annular mixing chamber 11 wherein the gas and the phosphor are intermixed. A secondary supply of combustion supporting gas, preferably air, is introduced through conduit 10 and enters into casing 15 which serves as a manifold to supply secondary air to the nozzles 17. Nozzles 17 are preferably an'anged about the annular mixing chamber 11 and rotate to facilitate mixing of the burning gases and the phosphor-forming particles which are passing therethrough.

A tube 19 of ceramic material surrounds the nozzles 17 to promote turbulent flow of the gas and powder suspended therein and therefore, insure mixing. Such turbulence also reduces the likelihood of agglomeration of the particles. Buildup of particles upon the walls of the ceramic tube 19 is also inhibited by the rotation of nozzles 17.

The specific details of the burner assembly are shown in FIG. 2. The particles of phosphor-forming material are transported by air through conduit 7 which terminates below the entrance port 21 for the natural gas from conduit 9. The phosphor and air mix with the natural gas in annular mixing chamber 11 and vent through port 23 into tube 19.

Annular mixing chamber 11 is divided into two parts, the

upper part of which is fixedly disposed upon the burner. Bolts 24 attach to annular cover plate 25. Disposed beneath the upper part is a lower part which is formed by tube 31. Worm drive gear 27 is attached to a motor (not shown) and mating worm drive gear 29 is attached to tube 33 to rotate concentric conduit 33. Tube 31 remains stationary. Attached to the lower end of conduit 33 is an annular flange 35 through which a plurality (preferably eight) of holes are formed. The peripheral edge of the annular flange 35 rests upon a fixed ledge 37 which provides support for the lower part of the annular mixing chamber and also prevents air from leaking into the furnace. Nozzles 17 are radially disposed in the annular flange and will rotate at the desired speed (r.p.m.) which conduit 33 rotates. Peripheral cavity 18 provides a space for the flow of cooling media around flange 37 to prevent overheating. Bearings 28 provide support for the rotation of conduit 33 around tube 31.

Secondary air from conduit 10 enters into casing 15 which forms a manifold for the distribution of air through nozzles 17 and thence into the furnace. The ends of the nozzles 17 in the furnace should be beneath the mouth of the tube 31 which forms the annular mixing chamber so as to provide a flame front which begins wholly within tube 19.

As seen in FIG. 3, the nozzles are radially disposed about annular flange 35 which in turn surrounds mixing chamber 11. A refractory heat shield 39 with peripheral recesses, cut out to accommodate the nozzles 17 is attached to the bottom of flange 35. Surrounding the periphery of the burner is tube 19.

Referring again to FIG. 1, the lower portion 5 of the furnace is reduced in diameter to form an exit outlet 2 which terminates in a water zone 4. Cooling water for the manufactured phosphor is introduced through spray nonle 6. A suspension of phosphor and water is withdrawn from water zone 4 for drying and elimination of the water.

In operation, the particles of powder are introduced into the upper end of the furnace through the innermost tube 7, the diameter of which is three-fourths inch, at a rate of 40 lbs/hour with a transport gas (air) rate of 625 cubic feet/hour. Natural gas is introduced through the intermediate tube 9, the diameter of which is one and five-eighths inches. Secondary air is introduced through the conduit 10 and flows into the manifold formed by casing 15. The air is introduced into conduit 10 at the rate of 2,000 cubic feet/hour. From the manifold, the air flows through eight nozzles 17 which extend three inches below the annular mixing chamber 11. With the three inch extension, together with the close-proximity of the powder and natural gas inlets, the phosphor mixes thoroughly with the gases before entering the furnace and before being effected by a flame front which begins within the tube 19. The flame can be initiated by an electric arc, such as a spark plug, which is disposed within the tube 19.

The flame front starts slightly below the nozzles 19 and extends downward about 2 to 3 feet, filling substantially the entire cross-sectional area of the chamber, thereby effecting substantially all the particles in the path downward through the chamber.

A heat resistant ceramic tube 19 surrounds the nozzles 17 and is 5 inches in diameter and 9 inches long. The tube promotes turbulence in the gas stream and enhances mixing and prevents agglomeration of the individual particles. The furnace is a ceramic cylinder 1, 16 inches in diameter and 16 feet high.

In order to further improve the mixing of the natural gas and air and for improving uniformity in the flame temperature, the nozzles are rotated at a rate of 10 rpm. This rotation also helps prevent sticking and building of hot particles on the walls of the hot ceramic tube.

As the converted particles drop to the bottom of the chamber, they are collected in a container 4 of water in order to separate them from the exhaust gases. In addition, the exhaust gases are passed through a cyclone separator (not shown) to recover particles carried out with the gases. The collected particles are then centrifuged to separate them from the water and subsequently dried to yield a free flowing powder.

It is apparent that modifications and changes may be made within the scope of the instant invention. it is our intention however only to be limited by the scope of the appended.

claims.

As our invention, we claim:

1. A furnace for continuous manufacture of phosphors comprising: an elongated tubular furnace having an enlarged central portion; a burner disposed at the upper end of said furnace, said burner being adapted to empty the products thereof into said furnace; said burner including feeding means disposed within an outer casing and adapted to feed a gaseous suspension of unfired phosphor into the furnace; means to introduce a fuel into a mixing tube concentrically disposed about the length of said feeding means and extending therebeyond, whereby the fuel will mix with the gaseous suspension of unfired phosphor; a plurality of nozzle means radially disposed about said mixing tube; the egress of said nozzles being disposed beneath the egress of said mixing tube; the egress of said nozzles being disposed beneath the egress of said mixing tube; a second tube disposed about the nozzles, said second tube being coaxially disposed about said mixing tube and extending into the body of said furnace; a manifold disposed in gas flow relationship with said nozzles and adapted to serve as a supply of secondary air for the combustible gases in said mixing tube; means to rotate said nozzles whereby tur bulence is produced in the mixture of gases and phosphor; means to remove the phosphor from said furnace.

2. The furnace according to claim 1 wherein said casing serves as said manifold for the supply of secondary gas into said nozzles.

3. The furnace according to claim 1 wherein the means to rotate the nozzles includes a conduit which is disposed about the mixing tube and which is attached to a flange in which the nozzles are disposed, said flange resting upon a lip which is disposed upon the outer casing.

4. The furnace according to claim 3 wherein a heat shield is disposed beneath said flange to insulate the flange from the heat in the furnace.

Claims

2. The furnace according to claim 1 wherein said casing serves as said manifold for the supply of secondary gas into said nozzles.
3. The furnace according to claim 1 wherein the means to rotate the nozzles includes a conduit which is disposed about the mixing tube and which is attached to a flange in which the nozzles are disposed, said flange resting upon a lip which is disposed upon the outer casing.
4. The furnace according to claim 3 wherein a heat shield is disposed beneath said flange to insulate the flange from the heat in the furnace.