US2284623A - Vaporizer - Google Patents

Description

June 2, 1942. w. sAMANs '2,284,623

VAPORIZER v Filed oct. 13, 19:59 :s Shasta-sheet 1 47 49 03 arams/e 9 Sm f June 2, 1942.

I W, SAMANS VAPORIZERl FiledDct. 13,' 1939 3 SheeftsuSheell 3 fwn/Ars.:

Patented June 2, 1942 i VAPORIZER Walter Samans, Philadelphia, Pa., assigner to Sun Oil Company, Philadelphia, Pa., a corporation of New Jersey Application October 13, 1939, Serial No. 299,288

(Cl. 19d- 128) 9 Claims.

This invention relates to vaporizers and more particularly to that type of Vaporizer in which a liquid is vaporized by being conducted in a shallow stream over a heated surface.

In particular this invention is adapted for use in the distillation or fractionation of high boiling petroleum cuts to product lubricating oils, where the oil to be distilled is passed in a thin or shallow stream over surfaces heated indirectly, as by mercury or diphenyl vapor, to the desired temperature, under a vacuum sufficient to effect volatilization of the desired fraction.

In installations of this character, it is important in order to secure uniformity in the distillate that the heat transfer from the mercury vapor, for example, to the flowing oil be as nearly uniform as possible over all portions of the oil stream in any one section or unit of Vaporizing surface. Because the critical rate of heat transfer between the mercury vapor on the hot surface of the partition and the liquid oil of which a fraction only is to be evaporated, flowing over the other side of the partition, is on the mercury side, the change in velocity in the radial flow of the oil over the trays does not materially affect the rate of heat transfer obtainable. However, since the depth of the liquid stream in vaporizers of this type is usually of the order of 1/8 to 1/4", it is apparent that changes in the stream thickness would cause a material difference in the amount of evaporation that takes place.

Consequently, vaporizers of this general type heretofore designed cannot operate with a sufli ciently uniform liquid thickness over the vaporizing surface, with resultant non-optirnum uniformity in vaporization rate and in the distillate produced,

It is an object of the present invention to provide a vaporizer so designed that the thickness of the flowing liquid stream on any vaporizing surface will be substantially uniform over the entire surface.

It is a further object of this invention to pro- Vide means for cleaning or scraping the vaporiz ing surfaces during operation so that no deposits may tend to accumulate thereon.

An additional object of this invention is to provide a compact unit with maximum vaporizing surface and designed for easy accessibility.

Other and further objects of this invention will appear from the following description of a preferred embodiment of the invention as shown in the accompanying drawings, in which:

Figure l is an elevation, somewhat diagramcating oil stock. Vaporizing unit B is supported Y on platform 5 with its bottom adjacent the top of vaporizer A, as shown.

Each vaporizer comprises a lower shell 9 and an upper shell 'I secured together at .Il by a vacuum-tight joint. Withinl the shell are arranged, one above the other, a plurality of annular Vaporizing pans or trays !3a, 13b, the upper or vaporizing surfaces 15a, I5b, of which slope alternately inwardly and outwardly, so that the oil to be distilled, entering at the top of the vaporizer passes downwardly in a zig-zag course over the surfaces I5a, 15b.

Each of the pans or trays 13a is supported on brackets l1 secured to uprights I9, which are in turn supported on and secured to brackets 2l ailixed to the lower shell 1 adjacent its upper edge. Each of the pans or trays 13b is supported from the tray i3d immediately beneath it by means of rods 23 resting in sockets 25; Mercury vapor is conducted into the sealed interior 2l of pans 43a, i313, where it delivers heat to the vaporizing surfaces |5a, 552i, through conduit .29 and branch conduits 3|, and removed therefrom through branch conduits 33 and conduit 35.

In Figure 2 oil'to be vaporized is admitted ythrough conduit 3'! and is fed into distributing trough 39a, surrounding the uppermost pan 13a, whence it flows over the Weir Ma and down the first vaporizing surface lia.

In Figure 3 (which shows a somewhat modified form of construction) oil to be vaporized is admitted through conduit 3l and is fed through distributor head 43 onto the surface of cap 45 and then into distributing trough 39h formed at the inner edge of pan ISD, whence it flows over the weir Mb and down the first vaporizing surface |517.

In either case the oil stream flows downwardly through the vaporizer, flowing over the outer edge of each surface 51; into the distributing trough 39a of the `next lower pan |3a, and over the inner -edge of each surface |5a into the distributing trough 3917 of the next lower pan |311. Caps 45 act to prevent any splashing of oil out of the troughs 391).

Vapors formed as the oil flows over the surfaces |5a, |517, heated by the circulating mercury vapor in the spaces 21, leave the vaporizer through outlet 41 and pass to a fractionating tower, not shown. An inspection manhole 49 is provided adjacent the outlet 41 (in Figure 3, 41 and 49', respectively). Oil not vaporized in its passage over the vaporizing surfaces ows from the lowermost pan |31) into an annular trough 5|, from which it leaves the vaporizer through conduit 53. Insulation 55, secured to the lower faces l of pans I 3a, |31), protects the vapors formed from radiant heat emanating from the pans.

Of particular importance in accordance with this invention is the character of the flow surfaces l5a, |511. These are so designed that, for lm depths of the order of 1A", the lm depth or thickness of the fluid layer will be uniform over the entire flow surface.

This result is accomplished, in accordance with this invention, by having the slope s,

h r tan of the flow surface, at any horizontal distance, r, from the axis, inversely proportional to the square of the distance r. Or, stated in the form of an equation:

Where K is a constant for any particular apparatus, having a value depending, inter alia, on the desired flow, velocity of flow, and film thickness.

This relationship is true for both surfaces |a and |511. Indeed, surface |519 is formed merely by rotating the plane 180.

That, for a given flow, which is of course determined by the flow through conduit 31, 31', the lm depth on suchV a flow surface will be uniform can be seen from the following considerations The velocity of flow of hot oil over the flow surfaces in question may be considered as related to the slope of the surface and the depth or thickness of the flowing layer as set out in the Kutter modification of the Chezy formula for flow of water in open channels, since the viscosity of the hot oil, at operating temperatures, is of the same order as that of Water.

This formula is as follows:

l.811+41'6+0.0028l 1': n o 00281S n Wg (l) 1+(41-6-is. where s is the slope; t the mean hydraulic depth, in this case the film thickness; and n, a coeflcient of surface roughness, experimentally determinable and constant for any given apparatus.

Since the term is negligible and may be disregarded for slopes of 1 in 1000 `or greater, it is apparent from this formula that if t, the lm depth, is to be kept constant, then the relationship must be maintained, where C is the constant of proportionality.

However, the total flow, q, is constant, by hypothesis, and may be represented, at any line on the flow surface, by the equation:

where r is the radius, or horizontal distance from the axis, of such line; tis the film depth or thickness; and v the velocity of flow.

Substituting in (3) the value of 1J from Equation 2, we obtain (Farrow/s- 4) from which it follows that if t is to be kept constant the relationship between 1' and s must be:

""/=21rqt0 (5) T2s= q 2=k (t) K .sf-

which is the equation of the flow surfaces in question.

In the structure shown in Figures l and 2 means are provided for scraping the flow surfaces I5a, |5b to prevent the accumulation of any deposit on such surfaces. These means comprise a shaft 6| extending centrally through the vaporizer and journalled in bearings 63, 65. To the shaft 5| are secured 'a plurality of collars E1 in each of which are secured a plurality of scraper arms 69, from the outer portions of which hang chains 1| of sucient length to reach the heating surfaces |5a, |511. As shaft 5| revolves slowly the chains 1| are dragged across and around the heating surfaces, clearing them of any accumulations, A casing 13 provided with openings 15 for the arms 69 is secured to the shaft 6| by cap 11 and collar 19, and serves to aid in directing the liquid flow and to block off the central shaftcontaining portion of the vaporizer.

Exteriorly of the vaporizer, shaft 6| extends through casing 8|, terminating in a stuing box 83, to bevel gearing 85, through which it is driven from shaft 81. Casing 9| is provided adjacent its lower end with an oil inlet 89, through which oil stock similar to that being distilled in the vaporizer may be admitted to the interior of the casing. Since, as previously stated, the platform is at least 40 feet above the ground level 3, casing 8| forms a barometric column and enables the stuing box 83 to have substantially atmospheric pressure on both sideswhen the vaporizer is, as is usual, under high vacuum; while'bearing 55 need not be liquid tight.

Each vaporizing unit in accordance with this invention is designed to be used separately, or in series with other like vaporizers. Thus, in Figure 1, charging stock to be distilled may be pumped by pump 9| through conduits 93 and 95 to vaporizer A, the unvaporized portion issuing from outlet 53 being recirculated or otherwise used. Or the charging stock may be pumped through conduits 93 and 91 to vaporizer B, and the unvaporized portion leaving unit B fed into vaporizer A as charging stock, through conduit 99 which forms a liquid seal against the absolute pressure difference usually obtaining between two successive vaporizers in a series arrangement.

The vaporizing units are designed in accordance with this invention with the vaporizing pans, connecting piping. etc. substantially al1 secured to the lower shell 9 only, s0 that upon unaasaaa .ealing the joint Il, separating the unions IDI an the inlet conduit 31, and unbolting the flange )f the vapor outlet 41, the entire upper shell 'l nay be lifted off, using eyebolt |03, and complete lccess to the interior structure obtained.

While the vaporizing pans 13a, [3b shown are '.ruly annular, it will be appreciated that pans of my generally annular shape may be used, as varous polygonal forms, etc.

What I claim and desire to protect by Letters .Datent is:

1. In a vaporizer in which liquid to be vaporized is flowed in a thin stream over a heated /aporizing surface, the improvement which comvarises a vaporizing surface positioned symmetri- :ally about a vertical axis within said vaporizer, ;aid surface having a slope, at any horizontal iistance from said axis, substantially inversely proportional to the square of said distance.

2. In a vaporizer, a generally annular vaporizing pan positioned symmetrically about a vertical axis, the flow surface of said pan being characterized by a slope, at any horizontal distance from said axis, substantially inversely proportional to the square cf said distance, and means for heating the ow surface of said pan.

3. A vaporizer comprising a shell, a vapor outlet therefrom, a plurality of generally annular vaporizing pans positioned vertically one above the other within said shell, the flow surfaces of said pans sloping radially alternately inwardly and outwardly, whereby liquid to be vaporized may flow downwardly over the flow surface of each pan to the flow surface of the next lower pan, following a zig-zag course, means for feeding liquid to be vaporized to the flow surface of the uppermost of said pans, means for withdrawing unvaporized liquid leaving the lowermost of said pans, and means for heating the flow surfaces of each pan; the said vaporizer being additionally characterized by the fact that the slope of the flow surface of each vaporizing pan at any horizontal distance from the vertical axis thereof is substantially inversely proportional to the square of said horizontal distance.

4. A vaporizer comprising a shell, a vapor outlet therefrom, a plurality of generally annular vaporizing pans positioned vertically one above the other within said shell, the flow surfaces of said pans sloping radially alternately inwardly and outwardly, whereby liquid to be vaporized may flow downwardly over the flow surface of each pan to the flow surface of the next lower pan, following a zig-zag course, a generally annular distributing trough surrounding the upper edge of the flow surface of each pan, a weir between said trough and said flow surface over which liquid ows onto the flow surface, means for feeding liquid to be vaporized into the distributing trough associated with the uppermost of said pans, means for withdrawing unvaporized liquid leaving the lowermost of said pans, and means for heating the now surfaces of each pan; the said vaporizer being additionally characterized by the fact that the slope of the flow surface of each vaporizing pan at any horizontal distance from the vertical axis thereof is substantially inversely proportional to the square of said horizontal distance.

5. A vaporizer comprising a shell, a vapor outlet therefrom, a plurality of generally annular vaporizing pans positioned vertically one above the other within said shell, the flow surfaces of said pans sloping radially alternately inwardly and outwardly, whereby liquid to be vaporized between said trough and said flow surface over which liquid flows onto the now surface, means for feeding liquid to be vaporized into the distributing `trough associated with the uppermost of said pans, means for withdrawing unvaporized liquid leaving the lowermost of said pans, and means for heating the flow surfaces of each pan the said vaporizer being additionally characterized by the fact that the slope of the flow surface of each vaporizing pan at any horizontal distance from the vertical axis thereof is substantially inversely proportional to the square of said horizontal distance.

6. A vaporizer comprising a shell, a vapor outlet therefrom, a plurality of generally annular, double-walled vaporizing pans positioned vertically one above the other within said shell, the flow surfaces of said pans sloping radially alternately inwardly and outwardly, whereby liquid to be vaporized may flow downwardly over the flow surface of each pan to the flow surface of the next lower pan, following a zig-zag course, means for feeding liquid to be vaporized to the flow surface of the uppermost of said pans, means for withdrawing unvaporized liquid leaving the lowermost of said pans, and means for circulating a heating fluid through the interior space defined by the double walls of said pans; the said vaporizer being additionally characterized by the fact that the slope of the flow surface of each vaporizing pan at any horizontal distance from the vertical axis thereof is substantially inversely proportional to the square of said horizontal distance.

7. A vaporizer comprising a shell, a vapor outlet therefrom, a plurality of generally annular vaporizing pans positioned vertically one above the other within said shell, the flow surfaces of said pans sloping radially alternately inwardly and outwardly, whereby liquid to be vaporized may flow downwardly over the flow surface of each pan to the now surface of the next lower pan, following a zig-zag course, means for feeding liquid to be vaporized to the flow surface of the uppermost of said pans, means for withdrawing unvaporized liquid leaving the lowermost of said pans, means for heating the flow surfaces of each pan, and insulation covering substantially all surfaces except the flow surface of said pans.

8. A vaporizer as claimed in claim '7 additionally characterized by the fact that the slope of the flow surface of each vaporizing pan at any horizontal distance from the axis is substantially inversely proportional to the square of said horizontal distance.

9. A vaporizer comprising a shell, a vapor outlet therefrom, a plurality of generally annular vaporizing pans positioned vertically one above the other within said shell, the flow surfaces of said pans sloping radially alternately inwardly and outwardly, whereby liquid to be vaporized may flow downwardly over the flow surface of each pan to the flow surface of the next lower pan, following a zig-zag course, means for feeding liquid to be vaporized to the flow surface of the uppermost of said pans, means for withdrawing unvaporized liquid leaving the lowermost of said pans, and means for heating the ow surfaces of each pan; said Vaporizer being additionally characterized by means for scraping the iiow surfaces of the several pans during opera'- tion, said means comprising a central shaft extending through said shell, a plurality of radial arms secured to said shaft within the shell at different` heights and rotatable therewith, the outer ends of Vsaid arms defining, when rotated, surfaces substantially parallel to and spaced above those of the several flow surfaces, a plurality of linked chains secured to the outer ends of said arms and of just suiiicient length to extend to the flow surface immediately below the respective arm, a tube surrounding that portion of said shaft outside said shell, said tube being secured at its upper end to said shell and extending downwardly at least 40 feet, a stuffing box at the lower end of said tube sealing said shaft, means for introducing liquid substantially identical with that to be vaporized into said tube to ll the space between shaft and tube, whereby when said shell is under vacuum said stulng box is exposed to substantially the same pressure on both sides, and means located beyond said stufng box for rotating said shaft.

WALTER SAMANS.

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