US3455791A

US3455791A - Vapor compression distillation with lobe ring compressor

Info

Publication number: US3455791A
Application number: US599625A
Authority: US
Inventors: Benjamin C Nash; James B Fitch
Original assignee: Nash Engineering Co
Current assignee: Nash Engineering Co
Priority date: 1966-12-06
Filing date: 1966-12-06
Publication date: 1969-07-15
Anticipated expiration: 1986-07-15
Also published as: NL6716452A; BE707550A; GB1211237A; FI51767B; GB1211236A; FR1583667A; FI51767C

Description

July 15, 1969 a. c. NASH ET AL 3,455,791

VAPOR COMPRESSION DISTILLATION WITH LOBE RING COMPRESSOR Filed Dec. 6, 1966 TECH- 2 Sheets-Sheet l WA 7m JACA/fr 75A 46;

July 15, 1969 a. c. NASH ETAL 3,455,791

VAPOR COMPRESSION DISTILLATION WITH LOBE RING COMPRESSOR Filed Dec. 6, 1966 2 Sheets-Sheet 2 T'uzi. 2 1.

United States Patent O 3,455,791 VAPOR COMPRESSION DISTILLATION WITH LOBE RING COMPRESSOR Benjamin C. Nash, Noroton, and James B. Fitch,`Strat ford, Conn., a'ssignors to The Nash Engineering Company, South Norwalk, Conn., a corporation of Connecticut Filed Dec. 6, 1966, Ser. No. 599,625 Int. Cl. B01d 3/00, 5/00; F28c 3/06 U.S. Cl. 203-24 10 Claims ABSTRACT OF THE DISCLOSURE Vapor compression distillation apparatus utilizing a circular lobe liquid ring compressor capable of receiving a liquid and discharging a vapor in a nearly saturated condition, thereby effecting a very efficient heat transfer in a series of heat exchangers which receive said Vapor. The cooled distillate is used for cooling parts of the system, such as the compressor.

The present invention relates to a method and apparatus for the compression distillation of vapors.

The invention may be used, for example, in the distillation of sea water.

One of the objects of the present invention is to provide an extremely eticient vapor compressor.

In particular, it is an object of the present invention to provide a compressor which will have minimum contact with the vapor and which will operate at an efficiency higher than could have heretofore been achieved.

Thus, the objects of the present invention include the provision of a liquid ring type of compressor which will operate with greater efliciency than has heretofore been possible with compressors of this type.

A further object of the present invention is to provide a compressor of this type which is capable of discharging a vapor in a nearly saturated condition so as to produce a very efiicient heat transfer in heat exchangers which receive the nearly saturated vapor.

Furthermore, it is an object of the present invention to provide a distillation system utilizing a compressor of the above type and providing an extremely efficient ow of liquid and vapor, deriving the maximum possible heat from the system to be applied to the liquid introduced into this system so as to achieve a high eiciency.

In particular, it is an object of the invention to provide not only highly eicient heat exchanging relationships between the incoming liquid and the outowing vapor and distillate, but also to make highly efficient use of the cooled distillate, for the purpose of cooling parts of the system, as well as to make highly eiiicient use of overow liquid for preheating purposes. Y

It is an object of the invention to provide a system which is particularly suited for the distillation of sea water.

The compressor of the invention is of the circular lobe liquid ring type which has potential advantages over the double lobe type which has been so far thought to have a greater volumetric capacity at a given structure and at a given speed by having the pumping action take place twice in one revolution with the added benefit that the radial pressure against the rotor was balanced because the compression cycles take place simultaneously on opposite sides of the rotor.

Under the conditions that minimum heat transfer should take place between the liquid ring and the vapors being compressed, a double lobe liquid ring compressor would not be able to meet such requirements since in it the liquid ring surfaces are disturbed during transition 3,455,791 Patented July 15, 1969 Fice between the two lobes, whereupon a turbulent interface between the cool ring and the hot vapors is created which circumstance leads to undesired changes in the vaporpressure characteristics of the vapors being compressed.

In contrast to this, in a circular lobe or single lobe pump, because a single compression cycle takes place only once per revolution, there is more time for the water to enter and leave the displacement chambers and because the water has a smoother passage around the casing a smooth liquid-vapor interface is provided with minimum interaction between liquid and vapor along with minimum heat transfer between them with resultant improvement in the net vapor capacity. The vapor compressor may be run at a considerably higher r.p.m. and with considerably greater stroke whereby capacity at least equal to that of a double lobe construction of the same size may be attained in addition to the above-mentioned advantages of minimum interface between the liquid ring and the vapors.

The vapor capacity per unit of work input in the case ofthe single lobe compressor is considerably greater than that of the double lobe compressor. Higher speed, work etliciency and the mentioned increase in net vapor capacity is attained because of minimum interaction between the vapor and the smooth liquid ring. The vapor capacity of the single lobe compressor will vary between 106 and 200% of the double lobe compressor with the same basic displacement and power input.

In addition, the efficient vapor compressor includes conical inlet and discharge manifolds which together with the minimum disturbance of the liquid ring make a highly etlicient vapor compressor. The conical inlet and discharge manifold which communicate with the eye of the rotor of the compressor of the invention provide signicantly better vapor compression than conventional liquid ring compressor designs, and in addition recirculated relatively cool condensed vapor in the form of a distillate is directed to selected locations within the liquid ring cornpressor so as to increase the performance and eiiiciency thereof. The capability of the compressor of the invention to provide a nearly saturated vapor which is discharged from the liquid ring compressor provides a more etiicient heat transfer in the condenser tubes of the distillation system than, for example, dry superheated vapor discharged by other types of vapor compressors, so that in this way also the performance of the distillation appa- -ratus is improved. It is to be noted tha this latter result is achieved without the use of any special accessories since the nearly saturated vapor is derived directly from the compressor itself.

The distillation method and apparatus of the invention include not only a circular lobe liquid ring compressor of the above type, lbut in addition a iirst or main heat exchanger in which preheated feed water, such as a Sea water feed, is placed inheat exchanging relation with the nearly saturated vapor to condense the latter while receiving sensible heat therefrom, after which the preheated feed water is evaporated in a low pressure flash q heat from the source of power. The distillate is then directed'from the water jacket to the compressor to cool stuing boxes thereof as well as to receive heat resulting from the friction of the operation of, the compression produced by the compressor, this latter liquid then being used as makeup liquid for the liquid ring. Part of the liquid from the flash evaporator is directed from an over flow conduit to the liq-uid which flows to the main heat exchanger so as to mix with the latter, and the remaining part of the overflow liquid passes through an additional heat exchanger for additionally preheating the feed water as it ows from the distillate heat exchanger to the main heat exchanger.

The invention is illustrated by way of example in the accompanying drawings which form part of this application and in which:

FIG. l is a schematic illustration of a vapor compression distillate apparatus and method according to the preS- ent invention;

FIG. 2 is a sectional elevation of a circular lobe liquid ring compressor of the invention;

FIG. 3 is a sectional elevation perpendicular to FIG. 2 showing further features of the compressor illustrated therein; and

FIG. 4 shows a variation of FIG. 1.

Referring to FIG. 1, a sea water feed conduit feeds liquid, such as sea water, through a distillate heat exchanger means 12 in which the feed Water is preheated as it recovers Waste heat while owing through the distillate heat exchanger 12. A conduit means 14 directs the feed water from the distillate heat exchanger means 12 through a blow down heat exchanger means 16 from where the preheated feed water is received by an additional conduit means 18 which directs the liquid to a main heat exchanger 20.

A circular lobe liquid ring compressor 22, the details of which are described below in connection with FIGS. 2 and 3, has an inlet communicating with an inlet conduit means 24 for receiving a vapor which is compressed to a nearly saturated state in the compressor 22. A discharge conduit means 26 receives the nearly saturated vapor and directs it through the main heat exchanger means 20 so as to heat the feed water delivered to the main heat exchanger means 20, after passing through the preheater

heat exchanging means

12 and 16. In this way the vapor flowing through the discharge conduit 26 is condensed in the main heat exchanger means 20, to form a distillate flowing along the discharge conduit means 26 through Athe distillate heat exchanger 12, and thus sensible heat is given up to the liquid in the main heat exchanger 20. A heating unit 28 may be provided for producing a minimum amount of heat to be added to the liquid in the main heat exchanger 20 so as -to make up for heat losses, although usually the heat derived from a source of power 30 lfor the compressor 22 and from the compressor 22 itself will suice.

The heated liquid mixture in the main heat exchanger 20 is delivered through a conduit 32, which may optionally be provided with a pressure diierential valve 34, to a low pressure flash evaporator means 36. The vapor which results from the evaporation in the evaporator means 36 flows through the inlet conduit means 24 to the inlet of the compressor 22.

An overflow conduit means 38 receives overflow brine from the evaporator means 36 and part of this overflow liquid is directed through a conduit 40 to the conduit 18 to mix with the liquid therein before the latter liquid reaches the main heat exchanger means 20. A recirculating brine pump 42 is carried by the conduit 40 for directing part of the overflow liquid into the conduit 18 so as to mix therein with the preheated liquid derived from the blow down heat exchanger means 16.

The remaining overflow continues to flow through the conduit 38 which passes ythrough the blow down heat exchanger means 16 so as to reject its sensible heat to the sea Water feed which flows through the heat exchanger means 16 from the portion 14 and to the portion 18 of the conduit means which directs preheated liquid from the distillate preheater means 12 -to the main preheater means 20. The flashed vapor which ows through the conduit means 24 to the compressor 22 was raised to a higher pressure and temperature by the circular lobe liquid ring compressor 22 of the invention. The hotter, nearly saturated vapor is then discharged through the discharge conduit 26 into the main vapor heat exchanger means 20 as the latent heat of the vapor is transferred to the brine mixture situated in vthe main heat exchanger means 20. l

The distillate flowing through the discharge conduit 26 downstream of the main` heatexchanger means 20 rejects its sensible heat to the sea water feed in the distillate heat exchanger 12, and the cooled distillate continues to flow from the distillate heat. exchanger means 12 Ithrough an optional pressure reducing valve 44 to the distillate receiver 46.

A coolant conduit means 48 communicates with the discharge conduit 26 downstream of the distillate heat exchanger 12 to receive a part of the cooled distillate therefrom, and the coolant conduit means 48 directs this part of the distillate to a water jacket 50 of lthe power source 30 which may be in the form of a water-jacketed motor. From the Water jacket 50 a conduit 52 directs the heated distillate to the compressor 22, so that in this Way heat losses are received from the power source 30 and in addition the liquid from the cond-uit 52 is used to lubricate and cool the compressor stuffing boxes, yto provide makeup for the compressor liquid ring and to absorb most of the heat of compression and friction of the compressor.

If desired, the sea water feed may be circulated in place of the cooled distillate through the water jacket of the compressor power source 30.

Referring to FIGS. 2 and 3, the circular lobe liquid ring compressor 22 illustrated therein includes a cylindrical or other shaped single lobed casing member 60 which at its ends is closed by enclosing heads 61. A main drive shaft 62 rotationally mounted in a pair of bearings 63 of which only one is shown, since FIG. 3 is showing only half of the compressor the other half being broken away. The shaft 62 supports a rotor 64 which is suitably secured, such as by keys, thereto. Shaft 62 is situated at an elevation lower than and to one side of the `axis of the casing 60 while being parallel to the latter axis, so that the shaft 62 is excentrically situated with respect to the casing 60.

In order to prevent liquid seepage about the rotating shaft, liquid sealing packing and gland assemblies 96' are fitted into the heads 61 at both ends of the compressor.

The rotor 64 is of the duplex variety containing a plurality of radially extending pumping chambers 65 defined therein by blades 66, side shrouds 67 and a central partition wall 68, which is in line with a corresponding partition wall 69, in the casing 60 to form adjacent crescent shaped lobed pumping chambers 68'. Disposed at each end of the pump are a pair of frustoconical inlet passages 74 (of which only one is shown) formed in the heads 61 and which direct inlet air or gas to right and left hand port members 76. Inlet passages 74 communicate with conduit 24. The port members include inlet passages 78 in communication with the pumping chambers 65 within the rotor and discharge ports 80 `also in communication therewith. The discharge ports -80 through a frustoconical discharge passage communicate with a header chamber 81 formed in each head 61 to provide access to several alternate discharge port anges 82 located on the lower sides and bottom of the head.

The compressor is mounted such that its inlet chamber y84 land its outlet chamber y86 are separated by a. partition 96 situated in .a plane located between a horizontal plane including the shaft axis and between a vertical plane which includes the axis of shaft 62, as seen in FIG. 2, with the compressor band being situated in the plane of the partition 96. An illustrative location of the partition 96 is shown as being about 45 from the horizontal plane.

-In operation, the receding of liquid within chambers 65 in the area of the intake port 78 creates a void :thereby a suction in passage 74, and when forced back toward the center of the rotor, produces compression through port 80.

The cooled recirculated distillate delivered by the conduit 52 to the compressor 22 is delivered to the location 94 (FIG. 3) where it will cool and lubricate the gland assemblies 96 and provide makeup for the liquid ring 68 as well as absorb part of the heat input due to the work of compression and friction.

lt will be noted that with this construction the liquid ring 68 rotates in a very smooth manner so that there will be a minimum of heat transfer ibetween the relatively hot compressed vapor and `the liquid ring, and minimum vapor capacity loss due to vapor ashing as the liquid ring passes through the low pressure inlet portion of the cycle.

The above-described compressor conliguration, with the described features such as the attitude of the inlet and outlet ports and the frustoconical manifold portions effect an eicient movement of vapor through the compressor with minimum contact between the hot discharge vapor and the relatively cool liquid ring 68. The large vapor capacity and higher temperature compression differentials are achieved with relatively less power than can be achieved with other compressors, and a significant improvement in performance of the vapor compression distillation is achieved from the compressor 22.

In particular, Ithe nearly saturated vapor which can be discharged directly from the compressor 22 makes for a more eicient heat transfer in the condenser tubes of the distillation system used in accordance with the method of the invention.

In the variation shown in FIG. 4, additional heat exchanging can be provided so as to achieve -additional preheating of the feed water. For this purpose, the feed water is introduced through a conduit 100 which has a pair of branches 102 and 104 respectively leading to the

further heat exchangers

106 and 110. The heat exchanger 106 receives the conduit 38 which passes through the heat exchanger 106 so as to give up heat to the feed water introduced through the branch 102, and this latter feed water than issues from the heat exchanger 106 through the conduit 108 so as yto flow into the supply conduit 10 referred to above.

The distillate which ows through the conduit 26 passes through the other heat exchanger 110 so as to give up additional heat to the feed watei flowing into the heat exchanger 110 through the conduit 104, and this latter feed water Ithen `tiows out of the heat exchanger 110 through the conduit 112 to also be received by the conduit referred to above and shown in FIG. 1. From the conduit 10 the feed Water, which now has been additionally preheated, ows in the manner described above in connection with FIG. 1. Except for these differences lthe embodiment of FIG. 4 is precisely the same as that of FIG. 1.

What is claimed is:

1. Vapor compression distillation apparatus comprising a circular lobe liquid ring compressor means having an inlet and an outlet, a low pressure ash evaporator means, conduit means communicating with said evaporator for supplying vapor to said compressor means to be compressed therein, said compressor means discharging the vapor at said outlet thereof in an almost saturated state, discharge conduit means communicating with said outlet of said compressor means for receiving the compressed vapor therefrom, a first heat exchanger means through which said discharge conduit means passes, a distillate heat exchanger disposed adjacent said rst heat exchanger means and having said discharge conduit means extending therethrough supply conduit means communicating with said distillate heat exchanger for supplying liquid feed to be placed in heat exchanging relationship with said discharge conduit means in said distillate heat exchanger means for preheating said liquid, a blow down heat exchanger means in communication with said distillate heat exchanger means and additional conduit means communicating with said blow down heat exchanger means and said rst heat exchanger means for directing said preheated liquid from said blow down distillate heat exchanger means to said iirst heat exchanger means and in heat exchanging relationship with said discharge conduit means in said rst heat exchanger before said liquid is received by said flash evaporator, said first heat exchanger means placing said liquid in heat exchanging relationship with said discharge conduit means so that the liquid in said first heat exchanger means is heated by the vapor in said discharge conduit means condensing the vapor therein and receiving latent heat therefrom, said low pressure ash evaporator means communicating with said iirst heat exchanger means to receive the heated liquid therefrom and to flash the liquid into a vapor, and said inlet conduit means of said compressor communicating with said evaporator means for receiving the vapor therefrom and directing it to said compressor.

2. The combination of claim 1 and wherein a drive means is operatively connected with said compressor means for driving the latter, said drive means having a water jacket, coolant conduit means communicating with said discharge conduit means at a part thereof situated downstream of said distillate heat exchanger means and with said water jacket for directing part of the distillate from said discharge conduit means to said water jacket to receive heat from said drive means, said coolant conduit means having a portion extending from said water jacket to said compressor means for cooling stuing boxes thereof, for receiving heat therefrom, and for providing makeup liquid for a liquid ring in said compressor means.

3. The combination of claim 2 and wherein an overflow conduit means communicates with said evaporator means for directing overflow liquid away from the latter, and recirculating conduit means communicating with said overow conduit means and with said additional conduit means for recirculating part of the overow liquid to the liquid which tlows through said additional conduit means from said distillate heat exchanger means to said rst heat exchanger means.

4. The combination of claim 3 and wherein a blow down heat exchanger means is interposed in said additional conduit means so that the liquid ows through said blow down heat exchanger means after leaving said distillate heat exchanger means and before reaching said rst heat exchanger means, as well as before mixing with overow from said evaporator means, said overow conduit means passing through said -blow down heat exchanger means whereby the liquid supplied to said flash evaporator means is iirst preheated in said distillate heat exchanger means and then in said blow down heat exchanger means before reaching said lirst heat exchanger means in a condition mixed with recirculated liquid from said evaporator means.

5. The combination of claim 4 and wherein a further heat exchanger means is situated upstream of said blow down heat exchanger means and receiving said overflow conduit means, and further conduit means directing liquid in heat exchanging relation with that part of said overflow conduit means which passes through said further heat exchanger means, said further conduit means directing the liquid after passing through said further heat exchanger means to said supply conduit means, so that the liquid is preheated before reaching said supply conduit means.

6. A method of distilling sea water to recover distillate water comprising the steps of preheating the sea water and passing the heated sea water to a flash evaporator zone to evaporate the sea water producing water vapor, compressing the water vapor in a circular lobe liquid ring compressor driven by a power source having a water jacket, discharging the resultant compressed vapor from the compressor in a nearly saturated state and directing the vapor through a heat exchange zone in indirect heat exchange with sea water feed immediately prior to its passage into the evaporator zone t-o bring about condensation of the vapor forming distillate and heating of the sea water feed, conducting the distillate from the heat exchange zone through an additonal heat exchange zone in indirect contact with the sea water feed upstream of the rst mentioned heat exchange zone, and withdrawing part of the distillate which has been further cooled in the additional heat exchange zone and directing it to the Water jacket of the power source to cool the same and provide make up liquid for the liquid ring of the compressor.

7. The method of claim 6 and wherein said evaporator step is carried out by a low pressure flash evaporator, the step of directing overflow liquid away from said evaporator, and recirculating part of the overow liquid with liquid owing from said additional heat exchanger to said iirst-mentioned heat exchanger.

8. The method of claim 7 and including the step of providing an additional heat exchanging `transfer between the overflow liquid and the liquid flowing from the additional heat exchanger to the first-mentioned heat exchanger.

9. The method of claim 8 and wherein the third, additional heat exchanging relationship is provided in the liquid flowing -to the first-mentioned heat exchanger before the latter liquid mixes with recirculated overflow liquid.

10. Vapor compression distillation apparatus comprising a circular lobe liquid ring compressor means having an inlet and an outlet, conduit means communicating with said inlet for supplying to said compressor means vapor to be compressed therein, said compressor means discharging the vapor at said outlet thereof in an almost saturated state, discharge conduit means communicating with said outlet of said compressor means for receiving the compressed vapor therefrom, a first heat exchanger means through which said discharge conduit means passes, said rst heat exchanger means placing said liquid in heat exchanging relationship with said discharge conduit means so that the liquid in said rst heat exchanger means is heated by the vapor in said discharge conduit means condensing the vapor therein and receiving latent heat therefrom, and low pressure flash evaporator means communieating with said rst heat exchanger means to receive the heated liquid therefrom and to ash the liquid into a vapor, said inlet conduit means communicating with said evaporator means for receiving the vapor therefrom and directing it to said inlet of said compressor, overow conduit means communicating with said flash evaporator means, a distillate heat exchanger means disposed adjacent said first heat exchanger means, supply conduit means communicating with said distillate heat exchanger means for supplying liquid feed thereto, a blow down heat eX- changer means interposed in said overflow conduit means so that the liquid flows from said evaporator through said blow down heat exchanger means, conduit means connected with said overflow conduit means at a point intermediate said evaporator and said blow down heat exchanger means, said last mentioned conduit means being connected to said rst heat exchanger means, additional conduit means connecting said blow down heat exchanger -means and said intermediate overow conduit means whereby the liquid supplied to said ash evaporator means is first preheated in said distillate heat exchanger means and then in said blow down heat exchanger means before reaching said i'rst heat exchanger means in a condition mixed with recirculated liquid flowing through said intermediate overflow conduit from said evaporator means, a pair of further heat exchanger means being provided for preheating liquid before the liquid reaches said supply conduit means, a distillate receiver communicating with said distillate heat exchanger, one of said further heat exchanger means being situated downstream of said distillate receiver, said other `of said pair of heat exchanger means being situated downstream of said blow down heat exchanger means and receiving the overflow conduit means after the latter passes through said blow down heat exchanger means, and further conduit means having branches directing liquid through both of said further heat exchanger means, and including conduit portions leading from the latter to said supply conduit means for passing the liquid, which has thus been preheated, to said supply conduit means to reach the latter in an initially preheated condition.

References Cited UNITED STATES PATENTS 2,280,093 4/ 1942 Kleinschmidt 202-177 X 2,389,789 ll/ 1945 Latham 203-24 X 2,515,013 7/ 1950 Kruhmin 202-180 2,537,259 1/1951 Cleaver et al 202-177 2,619,453 11/1952 Andersen 203-24 X 2,637,684 5/ 1953 Bufum 203-24 X 3,312,600 4/`1967 vMorton 202-160 FOREIGN PATENTS 1,359,062 4/1961 France.

OTHER REFERENCES German application K24930, Knur, December 1956, Cl. 202-236.

NORMAN Y'UDKOFF, Primary Examiner F. E. DRUMMOND, Assistant Examiner U.S. Cl. X.R.