US2924292A

US2924292A - Apparatus for pumping

Info

Publication number: US2924292A
Application number: US565811A
Authority: US
Inventors: Kenneth C D Hickman
Original assignee: Consolidated Electrodynamics Corp
Current assignee: Consolidated Electrodynamics Corp
Priority date: 1956-02-16
Filing date: 1956-02-16
Publication date: 1960-02-09
Anticipated expiration: 1977-02-09

Description

Feb. 9, 1960 K. c. D. HICKMAN APPARATUS FOR PUMPING 3 Sheets-Sheet 1 Filed Feb. 16, 1956 ON kv Q\ INVEN TOR. KENNETH c. 0. H/CKMAN BY 8411 5421, M4: 79 -4 A TTOR/VEVS Feb. 9, 1960 K. c. D. HICKMAN APPARATUS FOR PUMPING 3 Sheets-Sheet 2 Filed Feb. 16, 1956 FIG. 2.

INVENTOR. KENNETH c. D, H/CKMAN A TTORNEKS" Feb. 9, 1960 K. c. D. HICKMAN APPARATUS FOR PUMPING Filed Feb. 16, 1956 FIG. 3.

3 Sheets-Sheet 3 w B WMU m M w? AV. v L W m/ W/ 37 of WW7 AY/ W1 @MMN/ MW W 0 Q/ m m m n m w M 2 n m 9 a 7 6 5 4 a 2 7 AIR LEAK RATE INTO PUMP INLET-CCS/SEC.

A TTORNEVS APPARATUS FOR PUMPING Application February 16, 1956, Serial No. 565,811

3 Claims. (cuss-2 This invention relates to improvements in fan-type pumps or blowers used to pump gases or'vapors.

Fan-type pumps are generally divided into two main classes, namely, centrifugal fans and axial-flow fans. The centrifugal fans use rotating impellers to drive the pumped gas or vapor by centrifugal force in a direction radial to that of the impeller axis of rotation, while the axialfiow fans use propellers to drive thepumped material in a direction along the propeller axis of rotation. For -thetpurpose of describing this invention, the terms vapor and fgas are used interchangeably, and the term fan isjused to include both centrifugal and propeller fans. Both types of fans have long been used for transporting vapors. or gases under relatively low pressure differentials. However, one of the disadvantages, of these fans in pumping vapors or gases of relatively low average density or average molecular weight is that the force that can be developedby the rotation of .the fan impeller on the gas molecules is small, and therefore the pressures that .can be-produced are relatively low. I

This invention provides apparatus for enabling'fans to pump a gas of a given average molecular weight to a pressure head greater than canuordinarily be produced -by conventional fans of comparable size andoperating at the same speed of rotation. The operation of fans 'designed; for pumping gases .or. vapors of. a .given. average molecular weight is improved by vaporloading: the fans, that is,,introducing into the fan inlet :a vapor having. a molecular weight greater than. that of the. gas or vapor .being pumped. The fan imparts more momentum to the molecules 0f heavier vapor. than it imparts to the molecules of the lighter-vapon-and theheavy molecules entrain the'lighter molecules. to provide a more elfective pumping action than can be achieved on the light molecules alone. This improvement permits fans to produce .va'cuuacomparable to those produced by vapor-operated -vacuum.pumps,'such as the well known oil'ejector pumps.

-. :In:; terms of apparatus the invention contemplates a .vapor pump comprising a casing having an inlet and an outlet. A rotatable impeller is mounted in the-casing .forforcing vapor from the inletto the outlet, and means are provided for introducing a relatively high molecular The invention contemplatespumping a first vapor con- -stit uent of a given average molecular weight with a ,fan having an outlet and an inlet The first vapor constituent is.-. admitted into the fan inlet 'and'a second, vapor constituent of a greater molecular weight than'thatof the y first is also introduced into the fan inletso that the mixture of the vapor constituents is pumped to the fan outlet at apressure greater than would beproduced ifthe fan jwere pumpingonly the first vapor constituent,

,. This invention also includes the feature of. achieving 'with'a fan fractional separation bf a vapor having a 1 I Patented Feb. 9,1960

plurality of constituents of different vapor pressures, along. with improved. pumping by the fan of the light vapor constituents. For example, a fan used in a still in accordance with this invention to pump and fractionate a vapor having various constituents of ditferent vapor pressures is operated to compress the vapor toa pressure sufiicient to condense at least the less volatile constituents from the vapor. All of the condensed constituents may either be removed from the pump as a product, or else in part be recirculated through the fan to improve the efiiciency of the fan, in pumping the lighter and more volatile constituents in the vapor.

Use of the fan of this invention in a still to obtain fractional separation of a vapor of various constituents provides some important advantages over conventional stills. One advantage is that it permits the purification of high molecular weight, low volatility compounds at a low pressure and low temperature, and reduces the tendency for such compounds to decompose as when separated in conventional stills at higher pressures and temperatures. Another advantage is that the fan used in a still provides a negative pressure'drop, that is, the pressure in the still increases in the direction of vapor flow rather than decreases as occurs in conventional stills. As applied to the petroleum industry, for instance, molecular high vacuum distillation with the fan of this invention is obtained at the low pressure end of the still, 'while relatively high pressure separation is securedat the other end ofthis still. Moreover, because of the internal pumping action of the fan, such operation is achieved at a high throughput with, low thermal hazard. This permits commercial separation not heretofore possible for the high boiling, high molecular weight constituents of petroleum.

The invention will be more, completely understood from the following detailed description, taken in conjunction with the accompanying drawings, in which:

Fig. 1 is a sectional elevation of a fan made in accordance with the present invention and using both the axialflow and centrifugal flow principles;

Fig. 2 is a vertical section taken on line 22, partially broken away, showing a centrifugal impeller and an associated stator deflector; and

Fig. 3. is a' graph of data showing how the vapor loading principle of this invention improves the operation of a fan.

' Referring to the drawings, the vapor loaded pump comprises a horizontal, generally cylindricalcasing 10 secured at its righthandfend (as viewed in Fig. l) by means of bolts '12 to an end plate 14. Au annular gasket 16 dis-.

posed in an annular groove 18 in the end plate, effects a. gas-tight seal between the casing and the end plate. fThecasing is integrally formed in three sections of stepped diametersgincreasing from left to right. (as. viewed in Fig. 1),the smallest being a'discharge section 20, which forms the outlet end of. the casing, the intermediate size beingan intermediatesection 21, and the largest being an inlet ,section 22, .Which forms the inlet end of the casing, An inwardly extending lip 23 is formed integrally at the-inlet endof the casing. An inlet spider 24 mounted 'in the inlet end of thecasing by means of radially extend- .ing inlet guide vanes 25 supports a ball bearing 26 in the center of the casing-inlet, and an outlet spider 28 mounted in theoutlet end of the casing supports a second ball bearing 30 in the center of the outlet end of-the casing.

A shaft 32 rotatably sealed by a packing gasket 34 extends through an outwardly projecting boss 36 on the outside z ps! is's ealed'throughihehousing qandconnected to An axial flow compressor stage is mountedin the inlet section of the pump'casing and is, of the type described in the text book entitled Internal Combustion 7 Engines Analysis and Practice, second edition, byEdward F. Obert, published by International Textbook Company of Scranton, Pennsylvania. Two longitudinally spaced rotor plates 37 are secured to the shaft by keys stream side 'of each set of rotor blades.' The stator vanes terminate adjacent thehub ringor the periphery of the hub cap. The rotor blades and stator vanes are rate 'valve 58 in each withdrawal. tapexterior of the housing permits liquid to be withdrawn or added to the individual receptacles as desired..

An inlet conduit 59 in the end of the bell jar housing each respective receptacle within the casing. A separemote from the end plate is adapted to be connected to either a ;source of-vappr'pr, a system to be evacuated.

"An outlet conduit60in the portion of the end plate within the pump casing extends through a cold trap 61 where itis connected to an upwardly extending discharge line 62, [A downwardly extending condensate returnconduit 63 isconnected to ,the' lower portion of Set in. the conventional manner at opposite angles to the longitudinal axisiof the pump casing so that vapor may be forced from the pump inlet toward the'outlet with an accompanying increase in pressure. 3

In the intermediate section of. the pump casing,fa plurality of disc rotors 43 are rigidly attached, welded for example, to the shaft and extend perpendicular thereto almost to the casing. Each rotor is provided with a plurality of radially extending vanes or impellers 44, mounted on the inlet side of each rotor and ex tending from the periphery ofeach rotor to an intermediate location thereon. l

A plurality of annular stator plates 46 are attached at their outer peripheries to the casing'interior at spaced intervals and extend radially between adjacent rotors. Each stator plate is provided on its inlet side'with'a plurality of perpendicularly extending diffusers 47. Each dilfuser extends from the outer periphery to the inner periphery of its respective. stator plate and is curved to present a concave surface: to the gas or vapor being discharged from the. preceding rotor so that the gas is defiected in towardthe center of the following rotor. Rotors, impellers, stators and dilfusers are similarly mounted in the outletsection of the pump. casing, and are assigned the same reference characters as indicated for the intermediate section of the pump. A' final stator plate 48 with its associated diffusers 49 is mountedlwithin the outlet sectionof the casingon the outlet side i of the final rotor and adjacentthe inletsideof the y outlet spider.

A separatedeflecting and spacing spool 5 0'having a concave surface around. its periphery is rigidly. attached,

as by welding, to the shaft between adjacent rotors to the outlet conduit ,GOwithin the cold trapso that vapors, whicli'may be condensed in the cold trap, may be returned through'a' vapor loading line.64, to :which the lower end of condensate return conduit 63 is connected, to an intermediate point in the. pump casing: A valve 65 'in condensate return conduit 63is used to control the --re turn.of;condensate frorri'the cold trap, t i

A reser-voi'rfl66, containing. a vapor loading 1i uid 67 l is connected by a supply line .68 to thevapor loading line 64, and a valve 69 in the .sup'plyline controls the admission] of the vapor loading. liquid into the vapor loadingline- 64. The' vapor loading materialmayhe introduced at any point. within the pump casing, however, whentusing the pump to "produce Ia vacuum, it is often advantageous to admit the material to one of the intermediate. impellers, andfope'rate-the impellers nearest the casing' inletsubstantially dry to produce ;a-.vac- .uum whichis virtually free of the vapor loading material, a condition which is not: practical with conventional H vacuum "pumps using thevapors of aboilingliquid to i "produce a vacuum. For example, the openingin the statorplate' nearest the casing inlet, may be plugged so thatnd liquid fiowsinto the receptacle nearest the casing i inlet. Withthis airiangement the propellers (axial-flow .stages) and the r-otor nearestuthe casing inlet are not directly vapor loaded,andby their-pumping action preventthe .hackstreaming of vapor loading material into the-volume being evacuated. 3

.An up'rightq'cooling coil70 having an. inlet 71 and an outlet 72 sealed-through the end plate is' disposed ad- "jacent the outlet sideof the last stator plate. A first pressure gauge 74: is connected through the end plate to .thel annular space between the housing and the pump casing'to measure pressure at the inlet'end' of the pump. A second pressuregauge 76 is connected through the end,

- ,platetomeasure pressure at the outlet endof the pump.

aid in deflecting the pumped. gases in'the direction as indicated by the arrows in Fig. 1. A separte .liquid receptacle 51 is formed in the bote tom of the casing between each of'the stator plates, and each stator plate is provided with an opening Slat its lower edge and between two difiusers so that there is a t communication between the successive receptacles of the pump to permit liquid to flow therebetween as described more fully below. The lip at the inlet endof the casing and the shoulder formed 'betweenxtheinlet andintermediate sections of the casing form the receptacle nearest the casing inlet. The outlet spider and the end stator plate 48 form the receptacle nearest the casingioutlet, the outlet spider andstator plate 48' both havingopenings 52 to permit liquid to flow from the receptacle at '1 the outlet toward the pump inlet. i is I A bell jar housing 53'is disposed'around the purnp. casing and secured at its open end to the end plate by means oi bolts 54. An annular gasket in an annular groove 56 the end plate effects a gas-tight sealbetween the housing and the end plate. Alseparate withdrawal platesxtoward the. inlet end or the pump casing due to "the pressureditference betweenthe various stages l the pump. Eventually, theliquid reaches a stage which In the operation of the vapor loaded pump shown in Figs; 1 and; 2, to: pumpa relatively light 'gas such as air :(Which: hasianaverage molecular weight-oi 29), the

shaft "isrotated counterclockwiseaswiewed in Fig. 2

rata.suitable'speed' (say;5000 r.p.m. causing the air to i be forced fromthe inletto the outlet in the direction The decrease in thecross-sec- -tion' areaoffi theqpump casing from the. inlet to the oufl .shownbythe. arrows.

ietjaccommodates thedecrease infvolume of the air as llE"1S compressed... f

Asythe pumping proceeds, the vapor" loading liquid, whichqis, preferably of a, molecular weight or at" least.

several times; the average molecular weight of air, is 'adrnittedfr'om the reservoir into the vapor-loading line 64 where. it is.'thenudelivered'linto the pump casing' interior'. I The fiuid fills the receptacle. into which it' is introduced and flows through the openings 'in the stator "is ofa*sufl'iciently low-*psessure that the liquid either boils or. atfleast volatilizes at a substantial rate. The

heavywaporl oadihg molecules are then picked upby theimpellers either the opelle'r or centrifugal type," and.

, I l e i s he l hte air molecules; Due. to the'jg reater mass of the vapor pump oward? h wpni Patties ma s efis erme a e avslqasd i ms stage than would be possible if the relatively-light air molecules were pumped alone. As the heavy molecules move towardthe pump outlet into stages of increasing pressure, they are condensed into the receptacles and flow back toward the pump inlet where they are again vaporizedrfi The coolingcoil and the cold trap at the pump outlet are operated at properly selected temperatures to prevent any undue loss of the vapor loading material.

The vapor loadingmaterial may either be a single compound, or it may be a mixture of compounds having constituents of various vapor pressures. If the latter is used, the various constituents automatically fractionate within the pump, that is, the less volatile constituents find an equilibrium position in the low pressure or inlet. end of the. pump and are cyclically evaporated from one receptacle, condensed in a succeeding receptacle, and returned, to a preceding receptacle. .The more volatile constituents behave in a-like manner in stages of higher pressure;

The pump shown in'Figs. 1 through 2 may be used in numerous different ways. For example, the pump is well adapted for rapidly evacuating a large volume of gas :or vapor, and may be operatedeither against atmospheric pressure or be provided with a mechanical backing pump at the outlet end.

The curves of Fig. 3 illustrate the effect of vapor loading a pump of the type shown in Figs. 1 and 2, in which a mechanical backing pump was connected to the discharge line 62 at the outlet end of the pump. A cyclic ether having a molecular weight of 416 and a vapor pressure of 31 millimeters of mercury at 25 C. (sold under the trade name of Fluorochemical -75) was used as the vapor loading material. The mechanical pump was operated at a constant speed and a flow rate meter was connected to the inlet conduit 59 so that a variable and measurable amount of air was admitted to the pump inlet.

Curve A of Fig. 3 shows how the pressure varied at the pump inlet as air was permitted to leak into inlet conduit of the housing at various rates, the pump shaft being stationary, and no vapor loading material being introduced into the pump. Curve B of Fig. 3 shows how the pressure varied at the pump inlet with various air leak rates while the pump shaft was rotated at 6400 r.p.m. The difference between curves A and B shows the capacity of the pump at 6400 r.p.m. when it was not vapor loaded. Curve C shows how the pressure varied at the pump inlet with leak rate, the vapor loading material being introduced into the pump casing, but the pump shaft being stationary. Curve C shows that the vapor pressure of the vapor loading material with the pump shaft stationary caused the pressure at the pump inlet to be slightly greater than when the vapor loading material is not present. Curve D shows the pumping capacity of the pump when the pump was operated vapor loaded with the shaft turning at 5800 r.p.m. Curve D demonstrates that vapor loading increased the pumping capacity of the pump by several fold, even though the pump was operated at a slower speed (5800 r.p.m. vapor loaded, as compared to 6400 r.p.m. not vapor loaded).

Although the vapor loading material used in the example given above was a chemically pure compound, the invention is not limited to the use of vapor loading materials of a single constituent with a single vapor pressure. In fact, it is preferable to use a material having fractions of several vapor pressures, the .constituents making up the vapor loading material being selected to fit the pressure range in which the vapor loaded pump is to be operated. An advantage of the vapor loaded pump is that even if the vapor loading material is made up of constituents of different vapor pressures, and is introduced in the inlet end of the pump, the various fractions of the vapor loading material will automatically seek an equilibrium position. For example, as the mixture of constitutents is driven rrbm the'pump inletto t tl entraining lighter vapors as it is so driven, thelessvolatile constituents soon reach a pressure range withinthe pump where at least a portion of them condenseandfill the proximate receptacle. The slightly more 'volatile' con stituents are condensed as they reach zones of *higher pressures within the pump, until eventually each receptacle contains condensed constituents, the volatility of the condensed constituents increasing from the pump inlet to the-pump outlet. The condensed fluids flow through the openings in the stators toward the pump inlet-until they reach a stageof sufiiciently low pressure where they are again volatilized and vapor load the pump. The noncondensables or'constituents which are not readily condensed by the pressures and temperatures encountered within the pump, are discharged from the pump outlet, and are. either condensed by the cooling coil or the cold trap, or are discharged through conduit 60.

his the inherent fractionating property of the pump of this invention which makes it well suited to serve in a fractionating still. For example, theinlet of the pump -is.-adapted to'be connected to a sourceof vapor having constituents of various vaporpressures, say. a boiler containing a mixture of liquid petroleum hydrocarbons. The pump is operated to reduce the pressure on the liquid hydrocarbons to a point where boiling or substantial evaporation occurs. The more volatile and lower molecular weight constituents are removed first by the pump, and are either condensed in the outlet stage of the pump, or are pumped out of the discharge line. As pumping proceeds, increasing amounts of the lower boiling and higher molecular weight constituents are evaporated from the hydrocarbon liquid mixture by the pump and pumped therethrough. The higher molecular weight constituents serve to drive the lower molecular weight compounds to effect an efiicient pumping action on the lower molecular weight constituents. The higher molecular weight constituents are condensed in the various receptacles within the pump, the order of deposition from the pump inlet to the outlet being in the inverse order of the volatility of the constituents. The condensed constituents reflux from receptacle to receptacle until an approximately equilibrium composition is reached in each receptacle. The liquid product in each receptacle is then separately removed from the pump by means ofthe withdrawal taps.

This type of fractionation is ideal for separating and purifying low boiling, high molecular weight compounds which are ordinarily not recoverable since they are usually decomposed by the pressures and temperatures encountered in conventional still operations. The reason for the improved separation resulting in a fan-type still is that the pressure in the still increases in the direction of the flow of the vapor within the still, permitting molecular high vacuum evaporation of the low boiling constituents at the still inlet, and relatively high pressure separation of the more volatile and less easily damaged constituents at the pump outlet.

I claim:

1. Apparatus for fractionally separating a vapor having constituents of different vapor pressures, the apparatus comprising a casing having an inlet and an outlet, a plurality of rotatable impellers serially disposed in the casing for progressively increasing pressure in the casing from the inlet toward the outlet to cause vapor constituents to condense in the casing in accordance with their vapor pressures, and means for transferring condensed vapor from one point at one pressure in the casing to another point in the casing at a lower pressure.

2. Apparatus for fractionally separatinglow boiling, high molecular weight liquids having constituents of different vapor pressures comprising a casing having a plurality of pumping stages arranged intermediate an inlet and an outlet with said pumping stages disposed for progressively increasing pressure from the inlet toward sutlet, means CfQI :intttodueiug a low boiling; high mole ula weight "liquid having constituents of difierent yams-pressures into said. casing adjacent said outlet, said asingbeing defined to allowwthediquid tobe fracr tti onatedto flowtowaxd' saidinlet to therebyallow each oi aid-constitueuts to vaporize at a different pumping stage whereby the vapors are pumped to ',a :stage. of a constituents of said liquid vaporize'in the various pump- 20 casing being definedto allow said liquidto flow th'r ough ,said. pumping stages towards said inlet while the various ihg sta'gjesj'theztesultingwepdmemixing' svith m w asm be 'pumped andent'raining same into a pumping stage :of

highera'zpressure, .said vapors being pumped 'itowardsfisaid outletauntil ta (pumping stage. is 1 xeached that caus'es the condensation :of the vapors whereby the compression of the t apparatusqaetingt; on the 10w molecular weight 1 gas is increased 1 7' t 1 1;; t.

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