US2170745A - Method of heat treatment - Google Patents

Description

2, 1939. J. G. BRUSH METHOD OF HEAT TREATMENT Filed Dec. 28, 1936 s Sheets-Sheet 1 c/omv ATTORNEY.

Aug. 22, 1939. J. G. BRUSH 2,170,745

- METHOD OF HEAT TREATMENT Filed Dec. 28, 1936 3 Sheets-Sheet 2 'INVENTOR. Joly/v 6: Biz/3H, 1$ "1W ATTORNEY.

Aug. 22, 1939. 4 G RU 2,170,745

METHODOF HEAT TREATMENT I Filed Dec. 28, 1956 3 Sheets-Sheet 5 Cu; A

. ATTORNEY.

. methods, the olderbeing into a vertically arranged Patented 1939 PATENT omen 2.11am much or near rnasmn'r John Goyer Brush,

Westiield, r1. 1., assignor to' American Gyanamid & Chemical Corporation, NewYork, N. Ya a corporation of Delaware Application December as. an, Serial No. nus:

' 40mins. (c1. sea-s3) elongated heating zone also as a curtain through- The present invention relates to a method and apparatus for heat treatingvmaterials primarily for the purpose 'of removing water therefrom, whether free or combined. The invention has particular. reference to the calcination of gypsumof either the natural or by-product type starting either with a dry material or material containing some free water. This application is related to my copendingfapplication Serial No. 247,147,

filed December 22.1938.

Gypsumis ordinarily calcined by two-general stirrers, heat being applied to the bottom'thereof, suitable heat flues extending up into the body of gypsum being treated. The material is heated in the'kettles until its temperature is about400 F., at which time the desired degree of water removal or calcination is effected. At that time,

the kettle "is discharged.- The chief disadvantsges of the kettle process are'that ,,'f irst,.it is discontinuous in operation; second, the power costs are high; and. third, maintenance costs are high owing to wear on'the agitators'and cracking of the kettle bottoms due to heat.

A second common method of calcining gypsum.

interiorly fired rotating inclined tube'provided withbaiiies and. the like, the material tumbling-on itself until is to feed the material intoan discharged at-th'e proper degree of calcination. The disadvantages of such'a process are that the power costs are hi h, maintenance costs are high due to wear and tear on the-parts and a rather inefllcient contact of the heated gas with the material to be calcined is obtained.

The principal object ofthe present invention,

therefore, is to devise a method andv apparatus 1 which may be used to heat treat materials even to the point of calcination havinga minimum number of moving parts, which will entail an enicient heat transfer relationship, whichwill require a 'minimum number of workmen to oper- Z 'ate, which will be more or less automatic in its action and which will be proyidedwith readily replaceable in case of failure. making unnecessary the utting' down-of the'equipment for long periods of time such repair or replacement.- I I with this and other objects in view, the invention comprisesin its broadest aspect the feeding of the material to be beat treated'in a thin c tain through a flame, followed 1 by movement through, an elongated heating zone either under the action of'mvity or under m moirs: of the name and/or the hot gases therefrom. During the e oif'thematerial-tlirough this elongated chamber, subiected to contact with the hot the-material will. of course, be

to place the gypsum.

kettle equipped with ual crystals into feed funnel of 7% inches per foot.

walis'thereof .which .will materiallyxassist'in such treatment. Itisproposedtodischa'rgethematcrialfromthewhich the hot gases from the reaction zone pass.

.The thus treated materials then pass into an area of the exhaust gases from the apparatus using the sensible heat tome-conditionthe material to be'treated prior to its entrance into the elongated heating chamber.

The invention further consists "in the novel arrangement, combination and construction of parts more fully hereinafter described and shown in the accompanying drawings.

In the drawings: 4 Fig. l is a side elevation bodying the invention;

Fig. 21s a front-view assembly of Fig. 1; 1

Rig. 3 is a sectional elevation through the heat? ing chamber and associated parts;

- Fig. 4 is an enlarged detail partly in section showing the construction of the heating chamber. The invention may be described with reference tothe embodiments shown in the drawings which of an assembly em harm in section of the are particularly adapted for the treatment of gypsum to produce therefrom calcium sulfate hemihydrate or plaster of In these drawings, i into which the, gypsum to be treated is fed and discharged onto a distributor 2. This distributor may be preferably of a vibratory type so as to -tend to break up any loose agglomerates and feed the material uniformly-to a vibrating screen 3 -.where the material is further broken up and evenly distributed as near as possible as individof the funnel l is arran ed 5 so located as to therefrom as' a thin curtain having a substantial lateral dimension.

A burner tis arranged to projectits flame through the curtain spilling from the chute 5 i into the upper end of-an elongated 'heating cham her 'I.

It has been found satisfactory tov use for this'purpose a cast iron pipe for instance, 8 inches in diameter and Means are also provided to raise or lower one end of the pipe and, hence, its pitch is adjustable. It is also preferable to insulate the pipe, such for instance, as with one inch of 85% magnesiashown at "la.

The fuel 101 17110 u may be. gas admixed with compressed air as this has been found to give a good s'wtem of control, although obviously an oil or other burner may s ply the necessary a feed hopper is shown at l.- The lower end with a flat portion permit the material to drop,

The material treated. is discharged from thelowerend of the pipe I onto the inclinediiottom portion Q ofa bane "aside-a dust chamber 7 v I i I I. g

16 feet long with a pitch major portion of any entrained dust in the.

settling chamber l3, passes downwardly, around and under the lower edge of the baflie 8 and throughthe curtain of falling material and finally upwardly and out through exhaust port H. An exhaust fan l5 may be. used to assist the removal of the gas.-

In cases where there is still a quantity of usable heat in the exhaust gases and such gas is not completely saturated with moisture, they may be conveniently led into an inlet IS in a predrying. chamber l1 and exhausted through the stack I8. 'I his predrying unit may conveniently be provided with an endless belt l9 receiving the material to be preheated from the hopper 20 and discharging it at the other end of the conveyor l9 into hopper I.

The predrying unit has been found to be particularlrefiective when calcining by-product gypsum inasmuch as this material is usually delivered to the calciner in a moist condition and containing usually from 8 to 15% of free water. It has been ,found that under such circumstances,- if the moist material containing the higher percentages of water is first passed through the predrier, the free moisture content may be reduced to from 10 to 12% or even lower and that with this range of free moisture, it is then most u suitable to be moved uniformly into the upper end of the heating zone -'1==-with eflicient results. It has been found that with more than 12% moisture the material entering the upper end of the chamber I requires either a higher temperature or a. longer interval of time in the heating zone to accomplish the result obtainable by treating a material containing less moisture. The degree of heat secured may be readily adjusted through'manipulation of the burner 6 or reducing the amount of material delivered from the distributor 2. The interval of time to which the material is subjected to heat may be varied by adjusting the inclination of the pipe I through adjustable rod 2|.

It is to be noted that a flash removal of a large part of the water contained in the material being treated is first obtained as the material passes through the flame issuing from the burner 6.

This has been found to be a very eflicient method for quickly raising the temperature of the material being treated to the desired point. As the material slides-down the pipe I either under the action of gravity orunder the impetus of the flame or the gases therefrom or both,'it is additionally heated both by the gases themselves and by contact with the walls of the hot'pipe. A further intimate contact of the hot .gases with the material being treated is obtained at the end 8 of -the baflle 9 where the gases pass through or in contact with the curtain of falling material. Any dust entrained in the exhaustgases prior to removal of the gases from the chamber l0 finds its way into the compartment II by reason of the inclinedbottom walls of the cham- 0 ber.

calcination of gypsum are obtained where the particle size of the material being treated is such that approximately will pass a mesh sieve. Of course, the dryer the material entering the upper end of the pipe I, the more efllcient the calcining operation will be, withrminimum fuel requirements.

Typical data on a semi-commercial plant run are as follows:

One of the real advantages of the above equipment is that it may be operated in batteries of any number of tubes to step up the production to any desired point. The tubes or pipes are subjected to minimum wear and tear but in caseof a desired replacement, this may be done with ease and speed by merely shutting down the burner for that particular pipe and making the replacement without disturbing the rest of the battery.

While the invention has been described with particular reference to the calcination of gypsum,

yet obviously it is not to be restricted thereto but the invention is to be construed as applicable to any situation where these steps and apparatus described will be found useful.

I claim:

1. A method of calcining gypsum: which includes continuously feeding the material in a stream through a flame at greater than a calciningtemperature.

. 2. A method of calcining gypsum which in-- cludes continuously feeding the material in a stream through a flame at greater than a calcin ing temperature and then through a stationary elongated heating chamber cocurrently with hot gases from said flame.

3. A method of calcining gypsum which includes continuously feeding the material in a stream through a. flame at greater than a calcining temperature and then through a stationary elongated heating chamber cocurrently with hot gases from said flame and discharging the calcined material from the end of said chamber, at least a part of the hot gases from said chamber passing through the discharging calcined material.

4. A method of calcining gypsum which includes continuously feeding the material in a stream through a flame at greaterthan a calcining temperature and then through a stationary elongated heating chamber cocurrently with hot gases from said flame and conducting the exhaust gases from the chamber in direct heat exchange relation with fresh oncoming ypsum prior to its entry into the flame.

a JOHN GOYER BRUSH.

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