CA1098026A - Vapor compression liquid treating system - Google Patents

Abstract

APPLICATION OF: RALPH P. HORAN

FOR: VAPOR COMPRESSION LIQUID TREATING SYSTEM

A B S T R A C T

A liquid containing a solvent to be evaporated is fed to a concentration chamber which is fluidly connected to an evaporation chamber maintained at a reduced pressure. A vapor compression means withdraws solvent vapor from the evaporation chamber, compresses the vapor and forces the compressed vapor to a liquification chamber. Regulator means responsive to the density of the liquid remaining within the concentration chamber will regulate the rate of solvent evaporation to provide a concentrate suitable for recycling.
In one form of the invention, a variable capacity heat exchanger can be used to control the rate of solvent removal The heat exchanger has a liquification chamber to receive com-pressed vapor which surrounds an evaporation surface in fluid communication with the concentration chamber. A portion of the liquification chamber is filled with liquid. The amount of evaporation surface being contacted by liquid or vapor can be varied thereby varying the amount of heat which is transferred from the compressing vapor to the solvent to be evaporated. Since the vapor and liquid normally have different rates of heat transfer, the amount of heat given to the evaporation surface also varies.

Description

In one aspect, this invention relates to vacuum distillation sys-tems. In another aspec-t, this invention relates to closed loop waste treating systems. In yet a further aspect, this invention relates to heat exchangers.
One example o~ a prior art distillation system is shown in United States Patent 3,190,817 issued to Neugebauer, et al. Neugebauer discloses a compression distillation apparatus where a distilland is placed on the upper portion of a cylindrical, wiped falling film evaporation tube and falls along the tube's inner surface under the force of gravity to a collection reservoir which is below the evaporation tube. Vapor generated on the inner surface is compressed and brought into con-tact with the outer sur:Eace of the evaporation ~ube where the vapor condenses giving off its latent heat of condensation to the falling film.
The inner surface is constantly wiped by a wiper to distribute the distilland.
The prior art systems generally provide for a simple once through flow of distilland with a resulting variation in the concentrate formed by t~e system.
Further, prior art vapor compression systems have used condensation systems where the compressed vapors are condensed and their heat given off. There are no variable capacity heat exchangers shown in the art which would allow the production of vapor from a distalland to be controlled by -the amount o:~ heat transferred from the condensing vapor to the distalland.
According to the present inven-tion there is provided a vapor distillation system for concentrating a liquid by extracting one component thereof r this system havin~ a housing containing an evacuation evaporation chamber, the chamber being maintained at a reduced pressure to Eacilitate , ~ .

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Eormation o:E a vapor. ~ concentration chamber is adapted to hold the liquid to be concen-trated. An evapora-tion surEace Eluidly connects the concentration chamber to -the evaporation chamber, and a compressor is adapted to receive vapor ~ormed on the evaporated surface and compress the vapor so formed. Means receives the compressed vapor and condenses the vapor ~hereby heat is transferred Erom the compressed vapor to the liquid. Means removes the con-centrated liquid :Erom the concen-tration chamber when the liquid has reached the desired concentration.
More specifically, there may be provided a variable capaeity heat exchanger adapted to recèive com-pressed vapor from the compressor and condense the vapor liberating the latent heat vaporization and conduet the heat liberated to the liqu:id to form vapor.
I'here may be provided means to sense the density oE liquid remaining in the concentration ehamber and generate a signa:l. propor-tional to the coneentration with means being provided responsive to the signal generated by the sensing means to control the withdrawal of eoncentrate ~rom the concentration chamber.
The variable eapacity heat exehanger allows vaporization rate to be varied without changing the com-pressor if so desired but the heat exehanger and compressor capacity are matched.

cbr/!l.r 0~6 . 76-RE5-~13 BRIEF DESCRI PTION OF THE DRAWINGS
~ In the accompanying drawingo I !
FIGURE 1 is a schematic drawing of a plating line l which includes a vapor compression unit of this invention and is l~adapted for closed loop operation;
FIGURE 2 is a side elevation view in partial section ~of a vapor compression unit incorporating features of this l invention; and ¦1 - FIGURE 3 is a top view of a second embodLment.

~' 10 ~ DETAILED DESCRIPTIOl!~ OF THE PREEERRED EMBODIMENTS
i A typical plating schematic using a vapor compression still is shown in FIGURE 1. Parts to be plated are placed in ' a plating tank 12 which contains a solution of ions to be depositad ~ on the parts as a metal layer. After a metal layer has been I deposited on the parts, the plated parts are moved successively to rinse tanks 14, 16, 18 where any plating solution clinging to the plated part is rinsed off.
A substantial amount of plating solution, containing l valuable metal ions and organic additives; is carried into the 1 rinse tanks. Also, some water is caxried from tank to tank by ¦ the parts as they are rinsed. The carry o~er and evaporatio ¦ from the rinse tanks dapletes the water in the rinse tanks and ¦ the concentration of plating solution will steadily rise, espec-ially in the first rinse tank 14.
25 11 A portion of the wat~r in the first rinse tank 14 is periodically wi=hdrawn from the bottom of the tank and sufficient

-3-~ 0~ 7~~RE~ 413 water frcm the secolld tank 16 is transferred via line lS to refill tank 14~ The tank 16 is refilled from tank 18 via line 17 and tank 18 is in turn filled by purlfied water from a vapor ~ compression still 20 via line 19. Additional water can be added from an outside source of fresh water 21 when needed.
As shown, the rinse water or distilland from the first rinse tank 14 is withdrawn at outlet 22 by opening valve 24.
' The contaminated rinse water is conveyed by a pipe 26 to a heat exchanger 28 where the rinse water extracts some heat from purified water condensed in the vapor compresslon still 20. The llpreheated ri.nse water passes thxough a three-way valve 30 and is i fed to the vapor compression still 20 where pure water is llevaporated and condensed from the rinse water. The rinse water ¦~is concentrated to a density suitable for return to the plating 'Itank 12. The concentrated solution is withdrawn from the ~concentxation chamber through a valve 32 and pumped to the plating ¦~tank 12 via a line 34.
The pure water resulting from the vapor compression cycle I ! is withdrawn through valve 36 into the heat exchanger 28 via 20 ,`line 38 and then is returned to rinsP tank 18 by line 19.
! If desired, the vapor compression system can be used to ~purify fresh water before it enters the plating cycle. Tr~atment of the water before it entexs the system removes the calcium, limagnesium~ and other undesired metal ions which are present in 'every source of water. These metal ions will concentrate in the i, ,~plating bath as water is lost and settle out as solid salts to 2~ 1 . 76-RES-413 form a sludge at the bottom of the tank 12 or remain in the plating solution. In either case, the increasing concentration of undesired metal ions reduces plating e~ficiency. Eventually i the plating solution must ~e di~carded, resulting in a loss of ; valuable metal ions in the solution discarded, or the sludge must be removed from the plating tank requiring that plating operations be suspended. Accumulation of this sludge would be particularly pronounced where the process cycle is a closed loop as sh~wn.
' Purification of the ~ncoming fresh water would lessen or eliminate this problem.
Il FIGURE 2 shows a detailed view of one vapor compression j apparatus useful in the practice of this inven~ion. The operation ¦¦ of this unit is described with reflerence to plating rinse water.
Il The system could also be used to treat other liquids such as ¦ fruit juices, organic solvents or sea water. A generally jlcylindrical, vertically oriented housing 39 defines an evaporation ~¦ chamber 40 which collects vaporized water from the inside of the ¦ tubes 54 located at one end o~ the housing near a compressor 42.
~ The compressor 42 comprises generally a compressor wheel 43, ~ volute 45 and driving means 46. ~s shown; the driving means is ¦¦an electrlc motor 47 mounted on a bracket 48 attached to the ~li housing 39. The motor 47 drives a v-bel~ drive 49 which in turn ¦Irotates the compressor wheel 43. The compressor wheel 43 ~¦withdraws vapor from the evaporation chamber maintaining the l evaporation chamber at a reduced pressure e.g., 0.5 to 1.5 pisa.
~As shown, cross-tubes 50 transport compresseù vapor from the _5_ . .

~ . 76-RES-413 volute 45 to a condensation-heat exchanger chamber 52.
At the lower end of the housing 39, distal the compressor 42, are a number of concentration chambers (three being shown) , 44a, 44b, 44c which are filled with rinse water to be concentrated or incoming fresh water to be purified. Each concentration chamber is fluidly connected to the evaporation chamber 40 by an l e~aporation surface. As shown, the fluid connection is by means ,l of capillary tubes 54 which extend from the lower portion of their 1 respective concentration chambers and terminate in a plate 56 which forms the floor of the evaporation chamber 40. In general ,l there wlll be a plurality of tubes extending from each concen-tration chamber into the evaporation chamber, only one tube per concentration chamber being shown for clarity. The interior walls of the capillary tubes 36 are wet by the liquid being llconcentrated and provide a lar~e surface area fox the formation ~of water vapor which passes into the evaporation chamber 40, ¦I Sensing means 58a, 58b, and 58c are installed in each ¦¦concentration chamber to measure the concentration of the Iremaining liquid. As sho~n, the various sensing means generate an electrical signal which is fed to a control means 60. rrhe ! control means 60 activates the three-way valve 32 so that the concentration chambers can be emptied when the liquid in the jich,~mbers reaches the desired concentration. One means of lidetermining the concentratiorl of the remaining liquid is by l measuring its densii~y. Suitable density measuring devices are i~kni~wn in the liquid processing art. One general method of Ii !

!i , !~ density measuremen-t, which could be used i~ practicing this 1~ iMVelltiOn, i5 displacemen~ m~asurement using a float. Such l~ devices operate submerged in a liquid and generate a continuously ~ variable si~nal proportional to the densit~ of the surrounding ~ liquid. ~urther information can be found in Chemical Enqineexs ,' ~andbook, 5th Ed., McGraw-~ill, New York 1973, especially pages i .
22-48, and 49.

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ll In genexal, pumps (not shown) wou~d be associated with the , various valves to move the liquid within the s~stem as needed.
i The chamber would be replenished via valve 30 with more liquid ~ to be concentrated as needed.
¦ A large diameter vertically oriented duct 51 extends longitudinally along the midline of housing 39. Overflow liquid from tubes 54 flows into the duct and down into a reservoir 65.
~¦ The liquid in reservoir 6~ can in turn be pumped by a pu~p 66 through a valve 68 to the inlet of valva 30, returning the over~lcw liquid into the concentration chambers.
FIGURE 3 shows an alternate arrangement of capillary ~ tubes 54. In this arrangement, tubes 54 are arranged so that all the tubes for a particular concentration chamber terminate in the same general area. A baf~le 70 projecting from the plate 56 divides the area Lmmediately above the plate into three ~ equal sections~ Liquid overfl~ing from the tubes 54 will be j confined within the axea defined b~ the baffle 70 and the housing ¦~ 39. An o~erflGw tube 7~ is provided for each section and returns 7~

76 R~S-413 I an overflow liquid directly to the concentration chamber serviced i by the capillary tuhes.

~ OPERATIQN
i, In general, as with stills of this type, vapor from the , liquid being treated will be generated on an evaporation surface.
The vapor generated will be drawn into a compressor, compressed, I,and the compressed vapor is condensed. Generally the vapor is j condensed so that the latent heat of condensation is transferred ¦Ito the liquid being treated thereby creating more vapor to be I compressed.
¦ In greater detail, vapor exiting from the upper end of ~t~bes 54 will enter the evaporation ch,~mber 40, passing over the i! . ` i cross tubes 50. As the vapor passes the cross tubes 50, it will ¦remove some heat rom the cross tuhes which super heats the vapor and lowexs the heat in the compressed vapor. A ris~lg vapor enters a liquid barrier 74 which will remove any remaining liquid droplets entrained in~the vapor stream~ The barrier is sh~wn as a screen jbut can be other materials kno~nin the art, one barrier mat~rial !be~ng porous agglomerated plateO
1 The vapor, free ~rom liquidi enters the housing surrounding the rota~ing compressox wheel 43, is accelerated by the wheel and I is pushed into the volute 45 where the vapor 9 S velocity decreases ¦'and the pressure increases.
¦i ~he vapor from volute 45 enters the cross tubes 50 and i passes through the tubes to a plenum 76 located within the housing~

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!. I t ~ 76-RES-413 - !
From the plenum, the compressed vapor enters a variable capacity . heat exchange chamber. The heat exchange chambex comprises the l.chamber 52 defined by the plate 56, the upper surface of concen-tration chamber 44a, and the housing 39. Vapor entering the , chamber 52 will be exposed to the exterior walls of th~ tubes 54 l and~ being at a higher temperature and pressure than the liquid I~Lnside the tubes, will condense to form a liquid. As shown, the chamber 52 contains a quantity of l~quid and a vapor filled space jl66 above the liquid. The heat transfer to the capillary tubes is o ! different for the vapor filled phase and the liquid phase. By varying the liquid level within the heat exchange chamber 52, ¦~the amount of heat transferred to the liquid within the tubes 36 ~and thus the zmount of additional vapor created can be cont.rolled. .
~ The heat transfer and thereby the amount of vapor can also be Icontxolled by varying the height c~f solvent within the tubes, a ¦lower liquid level resulting in a lower heat transfer.
Of course, control of the vapor compression still involves several variables in addition to the liquid level in the chamber 52 or tubes 54. With a given compressor wheel, the amount o lliquid withdrawn from the concentration chambers will vary as a unction of: compressor wheel speed, inlet geometry and guide vane angle. In general, if the liquid level in the heat exchange chamber is increased, the amount of heat available to evaporate l,solvent and concentrate liquid is decreased.
1! The inlet geometry can be changed to vary the compressor's operating capacity Such variable in}et geometries are well Il _g_ ' `
~.

~9 ~ ~ 2~D . 76-RES-413 known in the art and a further description is omitted in the interest of brevity.
One method of operating the compressor of this system is ~ to increase the compressor capacity, such as by increasing ~compressor wheel speed until the compressor crosses the surge ~line and begins to surge. The compressor capacity could then be ,,reduced by a fixed amount to bring the capacity to the desired ,operating efficiency. The operating efficiency curves are deter-mined by the variables present in the system. Such charts showing eficiency islands as a function of pressure ratio versus flow ¦ at a constant impeller tip speedare so well known that a detailed lexample is omitted. One example oE a centrifugal compressor ¦perfo~mance chart can be found in Gas Turbines, Sorenson~ Ronald IPress Co., ~ew ~ork 1951, especially page 267.
I Ordinarily causing a centriEugal compressor wheel to surge ' ~ould not be a viable means of controlling a process. However, jbecause the compressor wheel is operating at a reduced pressure, ¦the amount of energy applied to the wheel during surge is minimal.
~¦Using the surge point of the compressor as a control measurement 20 il provides a quick and easy method of determining the operating conditions at a given time since the pressure ratio changes l,~markedly when the compressor surges. Pressure sensing devices - ~iare well known in the art and a detailed description is omitted l¦in the interest o~ brevity.
The operating steps detailed above could be performed by I a microprocessor which would receive reLevant data and determine !l I

' the operating condition of the system by comparison with a predetermined performance chart. If the system needed correction, the microprocessor would be programmed to drive the system into the surge condition and adjust the compressor capacity as discussed hereinbefore.
Where the liquid in one of the ~oncentration chambers 4~a t ~4b, and 44c reaches the desired concentration, the sensing means ' in the associated chamber will activate the control means 60 , which in turn activates the valve 32 to empty the concentration i chambers. The emptiea chamber is refilled and the process 1 continues.
¦, Various modifications and alterations of this invention ¦ will become obvious to those skilled in the art without departing 1 from the scope. and spirit o this inventionO For example, the ~` i I still of this invention can be used to concentrate ruit juice and for disalinization of water in addLtion to treating plating rinse water.

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Claims (6)

C L A I M S
WHAT IS CLAIMED IS:

1. A mechanical system for treating a liquid to form a concentrate comprising:
a closed housing having therein an evaporation chamber maintained at a reduced pressure, at least one concentration chamber located within the closed housing for holding said liquid;
fluid connecting means which connect the evaporation chamber and the concentration chamber, the fluid connecting means providing an evaporation surface for the evaporation of vapor from said liquid;
a vapor compression means located at the end of said housing adjacent said evaporation chamber, and operated to maintain said evaporation chamber at a reduced pressure and compress vapor withdrawn from said liquid and force it into contact with the surface of said fluid connecting means not in contact with said liquid thereby transferring heat from the compressed vapor to the liquid;
means to sense the density of the liquid remaining in the concentration chamber and generate a signal proportional *o said concentration; and means responsive to the signal generated by said sensing means to control the withdrawal of concentrate from the concentration chamber.

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2. The mechanical system of Claim 1 further comprising:
cross tubes extending across the evaporation chamber said tubes carrying compressed vapor from the vapor compression means to a location near the fluid connection means.

3. The mechanical system of Claim l wherein said fluid connecting means comprises, a plurality of capillary tubes having a first end terminating in a wall of the evaporation chamber and a second end passing through the wall of the concentration chamber, the interior surface of said tubes forming an evaporation surface and the exterior of said tubes a condensation surface, the wall of said evaporation chamber, the wall of said concentration chamber and a portion of the housing forming a heat exchange chamber to receive compressed vapor which can contact the condensation surface of the capillary tubes, condense to a liquid and transfer latent heat of condensation to the liquid in the interior of the tubes thereby creating additional vapor.

4. The system of Claim 3 having means for controlling the liquid level in said heat exchange chamber to control the amount of surface area available for condensation and thereby control the amount of vapor produced.

5. A vapor distillation system for concentrating a liquid by extracting one component thereof comprising:
a housing containing an evacuated evaporation chamber said evaporation chamber being maintained at a reduced pressure to facilitate formation of vapor;
a concentration chamber adapted to hold the liquid to be concentrated;
an evaporation surface fluidly connecting the concentration chamber to the evaporation chamber;
a compressor adapted to receive vapor formed on the evaporation surface and compress the vapor so formed;
means operative to receive compressed vapor from the compressor and condense the vapor liberating the latent heat of vaporization and conducting the heat liberated to said liquid to form vapor; and means for removing the concentrated liquid from the concentration chamber when the liquid has reached the desired concentration

6. The mechanical system of Claim 5 wherein said evaporation surfaces comprise, a plurality of capillary tubes having a first end terminating in a wall of the evaporation chamber and a second end passing through the wall of the concentration chamber and terminating in the concentration chamber, the interior surface of said tubes forming an evaporation surface and the exterior of said tubes forming a condensation surface, the wall of said evaporation chamber, the wall of said concentration chamber and a portion of the housing form a heat exchange chamber to receive compressed vapor which can contact the exterior surface of the capillary tubes, condensing to a liquid and transferring latent heat of condensation to the liquid in the interior of the tubes thereby creating additional vapor, the level of the condensed liquid within the heat exchange chamber being controlled to vary the amount of liquid condensing and thereby the amount of vapor generated.