US1840857A - Drying device - Google Patents

Description

Jan. l2, 1932.- N; TESTRUP E1' AL 1,840,857

DRYING DEVICE U Filed Feb. 27. 1929 2 Sheets-Sheet l Jan. 12, 1932. N. TEsTRUP ET AL' l 1,840,857

nanna DEvI'cE Filed Feb. 27. 1929 2 sheets-sheet 2 15 ly high Patented Jian. 1.2, .1932

UNITED STATES PATENT OFFICE NILS TESTRUP, OLOF SODERLUND, AND THOMAS GRAM, OF LONDON, ENGLAND, AS- SIGNORS T TECHNO-CHEMICAL LABORATORIES, LIMITED, LONDON, ENGLAND DRYING Application led. February 27, 1929, Serial No.

This invention relates to the drying of materials which are. wholly 'carried in or by gaseous medium and to which heat is imparted from partition surfaces in proximity to which the material is moved.

In drying devices thus employing heating surfaces through which the heat for the drying is transmitted the economy of the drier depends largely upon the cost of the heat- 1o ing surface per unit output and in driers which are employed for example in the lignite industry the cost of the heating surface per unit output is so high that the driers cannot be worked economically unless a relativetemperature difference is employed say 1n the neighbourhood of 40o C. or upwards.

In the British Patent No. 286,743, there is described a drier where the cost of heating surface per unit output is considerably reduced and lower temperature dierences say about 20 C. become economical and in the British Patent No. 294,289 there is described how as a consequence multiple effect drying can be obtained.

The object of the present invention is to provide drying devices in which the heating surface per unit of output will represent a,

much lower cost and in which for example lower temperature differences, say of about 5 to 10 C., become realizable economically,

the cost of single effect driers can be greatly reduced, multiple eect drying becomes even more advantageous, and it becomes practica- 85 ble to employ the thermo-compressor in driv ers for obtaining high thermal efficiency.

When drying fine coal, powdered lignite,

peat powder and other materials in the above manner by carrying them by and suspended 0 in a gaseous medium through tubes heated on the outside, we discovered that by increasing the weight of material carried per unit of gaseous medium we could increase the rateV of evaporation per unit of heating surface and when investigating the cause of this increase we found that when blowing the material through the tubes'the bulk of the mai terial would travel in the centre of the tube and that bymcreasing the quantity of material present we increased the number of DEVICE 343,097, and in Great Britain March 1, 1928.

particles travelling in closeproximity to the heating surface. We also found that the larger particles, which take a longer time to drythan the smaller-ones, were travelling near the centre and therefore were at the longest distance from the heating surface.

vThe invent-ion consists in a drying device employing the gaseous medium suspension method for transmitting heat to the material to be dried'in which the particles of material are subjected to forces which cause them to maintain a close relationship with the heattransmitting surfaces.

The invention further consists in giving to the gaseous medium in which the material to be dried is carried,'an impulsecausing the material to travel along or closely adjacent to the heating surface and not in the centre -of the tube.

The invention further consists in carrying out drying processes in accordance with either of the preceding paragraphs and in arranging for the material and the gaseous medium to have a rotating movement while travelling through the tubes, so as to keep the material closely adjacent to the heating surfaces.

The invention further consists in carrying out drying processes-in accordance withany of the preceding paragraphs and in arranging for example by using spirally rifled tubes for the heating surface to subject the particles of material to centrifugal force and keep j them in contact with or close proximity to the tube Walls while travelling therein.

The invention also consists in improvements in or relating to drying devices and processes carried out therein as hereinafter described. v Referring now to the accompanying drawings l Figure 1 shows a drying apparatus containing a drier having tubes in accordance rwith the invention;

Figure 2 shows to a larger scale a short.5l length of one tube;

Figures 3, 4, 5, 6 and 7 show alternative forms of the cross section of drying tubes in accordance with the invention.

In carrying the present invention into effect in one way we employ instead of ordinary cylindrical tubes tubes which have spiral grooves extending all or the greater part of the length for example in the manner in which they are disposed in a ride barrel. rlhis, due to the action of the centrifugal forces set up, causes the material to travel along in contact with or closely adjacent to the interior surfaces of the tubes and considerably increases the evaporation per unit of heating surface.

in the drying apparatus shown in Figure l a is a fan which. is driven by the pulley a and draws a current of air through pipe b into which disintegrated material which is to be dried is delivered. through the branch connection b by means of a feed screw b2.

The fan a delivers the current of air in which the material to be dried is carried to y the tubes l: of the drier c, a flaring :mouth piece c2 being provided at the outlet of the fan so that the material-laden current of air may be uniformly divided up between all the tubes of the drier.

The drier consists of a cylindrical or other casing oin which is provided a plurality of tubes hereinafter more fully described and the space surrounding the tubes in the casing is fed with heating medium as for example steam, water or the like which enters at the pipe Z and leaves by the pipe d.

The tubes 0 although shown. of limited length in the drawing are of any length which may be desirable to perform the drying operation and the current of air carrying the dried material leaves the drier by the pipe reducing outlet e and bend by which. it is led into the cyclone separator g from which the separated dried material is collected from the outlet la while the current of air freed from the material leaves by the outlet j'.

The tubes c of which a short length is shown to a larger scale in Figure 2 are provided with spiral grooves it or equivalent means for maintaining a spiral motion of the material-laden air throughout the full length of the tubes and the grooves or their equivalent may be formed in a variety of different ways.

Figure 3 shows a tube formed from two half sections Z, Z each. of which represents a D shape with the central portion of the straight part Iof the outline cutaway and the faces of the vremaining parts Z2, Z3 of the straight portions joined together as by brazing or other suitable treatment, the two sections being helical so that when joined as described there is formed a cylindrical tube with the internal fins Z2, Zs extending in a helical direction throughout the length of the tubes.

Figure 4 shows a tube m having longitudinal indentations m', m2 upon opposite sides thereof, the indentations running the full Leanser length of the tubes and being helically or spirally disposed throughout the length in the same manner as the fins in the tube last described.

Figure 5 shows a square or rectangular section tube n in which the corners n, n2, n3 and n4 are slightly rounded and the tube is given a helical twist as in the other cases.

Figure 6 shows another tubular section 0 somewhat similar to the tube m but with the l indentations less pronounced and taking more the form of flattened 4sides o', o2.

Figure 'i' shows a tube p having six indentations p which are as in the other tubes disposed in a helical or spiral direction throughout the length of the tubes.

The spirally grooved or riiied tubes may be produced in any convenient manner which will provide the grooving preferably without alteration in the normal thickness of the walls of the tubes or the like employed; for instance tubes might be drawn with spirally disposed grooves or projections upon the walls thereof or such grooves or projections might be produced by rolling or other convenient processes. Multi-sided tubular elements having a twisted or spiral configuration may also be employed and suitably modified at the ends for conveniently fastening in tube plates or the like.,

rlhe foregoing arrangement also ensures that the larger particles make the greatest amount of contact with or are maintained in closest proximity to the heating surfaces and thus they obtain the greater supply of heat necessary for their drying and a .more uniform drying of the whole of the material is edected.

When divided material is carried in suspension along a tube by a current of ,fluid the friction with the walls creates eddy currents or whirls which result in a greater proportion of the material being in the centre part of the iiuid than in the surroundingportion and the object of the helical distortions is to create by a spiral motion of the fluid suf;-

ficient centrifugal force to overcome this centre seeking effect on the particles. helices must, therefore, be so proportioned that a sufficient centrifugal action isobtained without undesirably adding to the wall friction effect.

A s shown in the drawings the pitch of the helix is about eight times the tube diameter which is substantially correct for some materials. ln other cases, however, somewhat shorter pitches may be employed provided the foregoing requirementsI are complied' with. l.

An impulse can be given to the particles or a force may be imposed upon them lby any other suitable means having regard to the nature of the material tol be dried and to the circumstances of each case; for example baf- The i es or other deformations of the tubes and similar means may be employed.

With the low temperature differences made possible when Working in accordance with this invention it may be desirable to employ the thermo-compressor in connection with such drying devices and to raise the temperature of the evolved vapours suiiciently by .compression to employ them upon the other side of the heat-transmitting partitions as the heating medium.

It is to be understood that the constructions hereinbefore described are given by Way of. example only and the arrangement showing the passage ov air and material through the drier may ent ways. V

Modications and additions of other kinds may also be introduced Without in any Way departing from the spirit of this invention.

We claim:

1. Apparatus for drying nely divided material comprising means for inducing a streamv of fluid charged with the material to be dried, means directing said charged stream into a plurality of extended conduits, helical distortions in the entire length of the Walls of said conduits making an angle of more than 45 with a circumferential line on ity of extended conduits, yhelical distortions in the entire length of the walls of said conduits of a pitch at least exceeding four diameters or creating rotation without transverse eddy movement of the fluid in each condult and tovobtain by centrifugal action close contact of the suspended material with the walls thereof, and means for heating the Walls of said conduits from' the exterior.

In testimony whereof We have signed our names to this specification.

NILS TESTRUP. OLOF SODERLUND. THOMAS GRAM.

be modified in ldiffer- .the conduit Walls, and means for heating the Walls of said conduits-from the exterior.

2. Apparatus for drying finely divided material comprising means for inducing a stream of luid charged With the material to be dried carried in suspension therein, means directing said charged stream by gradual increases of cross-sectional area into a plural.- ity of tubular conduits, twoihelical distortions diametrically opposed in the entire length of the Walls of said conduits making an angle of more than 45 with a circumferential line on the conduit Walls, and means for heating the walls of said conduits from the exterior.

3. Apparatus for drying finely divided material comprising means for inducing a stream of fluid charged with the material to be dried carried in suspension therein, means directing said charged stream by gradual increases of cross-sectional area into a plurality of tubular conduits, helical distortions in the entire length of the walls of said conduits disposed at a smaller angle to a plane containing a tubev axis than to a plane at right angles thereto for creating rotation without transverse eddy movement of the fluid in each conduit, and means for heating the walls of said conduits from the exterior.

4. Apparatus for drying finely divided material comprising means for inducing a stream of fluid charged with the material to be dried carried in suspension therein, means directing said charged stream by gradual increases of cross-sectional area into a plural-

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