This invention relates to distillation apparatus. This invention has particular but not exclusive applicatio to vacuum distillation, and for illustrative purposes referenc will be made to such application. However, it is to b understood that this invention could be used in othe applications, such as solvent refining, liquid recovery, liqui purification and the like.

The purification of liquids such as water by distillatio has been a well-known process for many years. Where such process is operated at normal pressure, substantial heat inpu at high temperature is necessary, and due to inter alia th relatively high heat capacity of water the process is generall quite wasteful of energy. If the pressure within the evaporating vessel is reduced, the boiling point of the liquid falls substantially. This ha two beneficial effects - the heat losses are reduced, and i becomes possible to operate the apparatus from a low-temperatur source of heat such as waste heat. One particularly usefu application of reduced-pressure, or vacuum distillation is th production of drinking water from sea water on a power boat b using the waste heat from the engine cooling water. Suc distillation apparatus typically comprises a distillation vesse containing a vapourising portion into which sea water may b fed, heated and evaporated, and a condensing portion in whic water vapour may be condensed to produce potable water. Air an non-condensed vapour is drawn off the top of the distillatio vessel by a vacuum pump to maintain the desired reduction i internal pressure, and water is constantly bled from th vapourising portion to maintain a low concentration of salts i the water therein.

Hitherto, such vacuum distillation apparatus has require multiple vacuum pumps or ejectors in order to remove both non condensible gases and concentrated liquids from the distillatio vessel. For example, a vacuum distillation apparatus disclose in United States Patent No. 4,664,751 uses a vacuum still wit

an evaporation chamber and a condensation chamber, and sprays the incoming brackish or saline water into the evaporation chamber after passing it through a coil in the condensation chamber. The vacuum is established and maintained by using an eduσtor having one inlet line branching from two inlet lines from the evaporation chamber, one from below the liquid surface, and another at the liquid surface, the latter one being used to maintain the level in the evaporation chamber. The two inlet lines have control valves, and the system is difficult to operate because the valves on the inlet lines need to be finely adjusted. This has complicated the construction •of such apparatus, and made it difficult to maintain the correct operating relationship between liquid and gas flowrates exiting the system. The eductor used in that patent is a Herschel venturi having a modified throat tap in that the throat tap projects into the throat and has a cut away section down stream within the throat.

In another example, Soviet Union Patent No. 837,916 discloses a vacuum distillation apparatus having liquid sprayed into an evaporation chamber, the liquid having a vortex induced therein by an agitator in the base thereof. The water vapour is recovered by recompression using a lobe pump, the lobe pump also being used to generate the reduced pressure in the still. This disclosure also makes use of three extraction pumps for removal of brine, vapour and distilled water from the still. The vacuum distillation apparatus described in that patent is complex to build.and to operate, and inefficient in use.

The present invention aims to alleviate the above disadvantages and to provide suction apparatus which will be reliable and efficient in use. Other objects and advantages of this invention will hereinafter become apparent.

With the foregoing and other objects in view, this invention in one aspect resides broadly in suction apparatus of the type having a throat formed in a fluid flow passage and a throat tap through which fluid is induced into the fluid flow passage during flow of fluid through the passage wherein:-

the fluid flow passage has a substantially constant cross- sectional area; the throat is a reduced section of the fluid flow passage _/ and the flow passage includes a flow restriction upstream of the throat.

In a preferred form, the flow restriction is an orifice plate and the reduction in section is an abrupt change in section. In a further preferred form, there are provided a plurality of throat taps formed in the throat portion of the reduced section in the flow passage.

In another aspect, this invention resides broadly in distillation apparatus of the type having an evaporation chamber and a condensing chamber which operate at a substantially common reduced pressure, characterised in that:- liquid to be distilled is introduced into the evaporation chamber through degassing apparatus and control means are provided for selectively maintaining the level of degassed liquid in the evaporation chamber. Preferably, the distillation apparatus has provided a suction means to draw concentrated liquid from the evaporation chamber and for maintaining the reduced pressure. In a further preferred embodiment, the distillation apparatus uses common suction means for removing the concentrated liquid from the evaporation chamber and for maintaining the reduced pressure.

In a preferred embodiment, the distillation apparatus uses as common suction means a suction apparatus of the type having ^" a throat formed in a fluid flow passage and a throat tap through which fluid is induced "into the fluid flow passage during flow of fluid through the passage wherein the fluid flow passage has a substantially constant cross-sectional area, the throat is a reduced section of the fluid flow passage and the flow passage includes a flow restriction upstream of the throat.

In a preferred form, the flow restriction is an orifice plate and the reduction in . section is an abrupt change in section. In a further preferred form, there are provided a

plurality of throat taps formed in the throat portion of the reduced section in the flow passage.

Preferably, the degassing apparatus is a chamber maintained at a reduced pressure, and preferably includes an inlet passage, a separation chamber connected to the inlet passage, a gas and liquid outlet connected to an upper portion of the chamber and a liquid outlet connected to a lower portion of the chamber wherein substantially all dissolved gas is removed from liquid passing through the degassing apparatus.

In another aspect, the distillation apparatus of this invention is of the type having an evaporation chamber and a condensing chamber which operate at a substantially common reduced pressure, wherein the suction means provided to draw concentrated liquid from the evaporation chamber and for maintaining the reduced pressure . is a suction apparatus as hereinbefore defined.

In a preferred form, the distillation apparatus includes:- a liquid flow passage passing through:- the condensation chamber; the suction apparatus; the degassing means and a pump; a first throat tap connecting the suction apparatus to a gas outlet on the condensation chamber; a second throat tap connecting the suction apparatus to a liquid outlet on the evaporation chamber; a liquid feed line connecting the degassing chamber with the evaporation chamber through a valve controlled by the level of liquid in the evaporation chamber; a heating means disposed within the evaporation chamber, and a fluid pump having its suction connected to a liquid outlet in the condensation chamber. Preferably, liquid is drawn from the evaporation chamber of the distillation apparatus as concentrated brine, and non-

condensible gas is drawn from the condensation chamber.

In a still further aspect, this invention resides broadly in a method of distilling liquid at reduced pressure, the method including:- passing liquid feedstock through a flow passage which passes through the condensation chamber of a distillation apparatus and into a suction apparatus and a degassing apparatus; passing some of the degassed liquid from the degassing apparatus into the evaporation chamber of the distillation apparatus wherein some of the liquid evaporates to form a vapour and the remainder of the liquid is drawn from the evaporation chamber as concentrate; passing the vapour into the condensation chamber and condensing substantially all of the vapour therein as purified liquid; removing the purified liquid from the condensation chamber; passing the concentrate into the suction means to combine with the feedstock; connecting the condensation chamber to the suction means to maintain the reduced pressure therein, and passing the remainder of the feedstock, the concentrate, and non-condensible gas through a pump.

Research has found that a reduced section used in accordance with this invention is preferably formed with the entrance to the throat being a sudden reduction in cross sectional area rather than the contoured reduction in cross sectional area usually taught in Herschel-type venturi devices.

In addition, it has been found that the suction apparatus of this invention is suitable for two-phase flow whereby the liquid phase portion i's drawn from the evaporator portion of a distillation apparatus as concentrated brine, and the gas phase portion is drawn from the condenser portion of a distillation apparatus as vapour and/or non-consensible gas. In order that this invention may be more easily understood and put into practical effect, reference will now be made to the

accompanying drawings which illustrate a preferred embodiment of the invention, wherein:-

FIG. 1 is a schematic diagram of a reduced-pressure distillation apparatus including suction apparatus according to the invention;

FIG. 2 is a cross-sectional view of the suction apparatus shown in FIG. 1;

FIG. 3 is a cross-sectional view of the de-aeration apparatus shown in FIG. 1; FIG. 4 is a cross-sectional view of the combined suction apparatus and de-aeration chamber shown in FIG. 1, and FIG. 5 shows the raw liquid level control assembly illustrated in FIG. 1.

The distillation apparatus 10 shown in FIGS. 1 to 4 includes a distillation vessel 11 having a lower vapourising portion 12 and an upper condensing portion 13, separated by a vapour flow vent 14 filled with mesh 15. A heating coil 16 is disposed within the vapourising portion 12, while a condensing coil 17 passes through the condensing portion 13. The outlet from the condensing coil 17 is connected to the inlet 20 of the suction apparatus 21, while the outlet from the latter is connected in turn to the inlet 22 of the de-aeration apparatus

23. The liquid outlet 24 from the latter is joined to the vapourising portion 12 through an electric solenoid 25 which is controlled by a mini-float switch 26, the latter being arranged for operation at a desired liquid level within the vapourising portion 12.

The first auxiliary inlet, 27 to the suction apparatus 21 is joined to a gas outlet 30- within the condensing portion 13, and the second auxiliary inlet 32 to the suction apparatus 21 is joined to a lower portion of the vapourising portion 12. The lower section of the condensing portion 13 is connected to a purified liquid pump 34.

The inlet 22 of the de-aeration apparatus 23 leads to a de- aeration chamber 36, to the base of which the liquid outlet 24 is joined, while a gas and liquid outlet 37 exits from the top

of the de-aeration chamber 36 and is connected to the inlet of a pump 40.

The suction apparatus 21 comprises an inlet restriction or orifice plate 41 in series with a reduced section 42, the first and second auxiliary inlets 27 and 32 being connected to the throat 43 of the reduced section 42.

In use, a source of impure liquid is connected to the inlet of the condensing coil 17, and this liquid flows through the suction apparatus 21, inducing a reduced pressure in the auxiliary inlets 27 and 32. This action draws liquid from the vapourising portion 12 and gas from the condensing portion 13. The mixture thus produced passes into the de-aeration apparatus 23, where the reduced pressure produced by the orifice plate 41 assists in the separation of gases from the liquid. The former are drawn off by the pump 40, while the latter passes into the vapourising portion 12 through the solenoid 25. Heat is applied to the liquid in the vapourising portion 12 through the heating coil 16, and the liquid boils at reduced temperature as a result of the reduced pressure induced by the action of the suction apparatus 21.

The vapour so formed rises through the vent 14 into the condensing portion 13, where it condenses on the condensing coil 17 and is pumped away by the liquid pump 34. Droplets of impure liquid rising into the vent 14 are trapped on the mesh 15 and returned to the vapourising portion 12.

It will be appreciated that the mesh may be a hydrophobic membrane which would allow vapours, but not liquids, to pass therethrough. Thus if the boiling raw water foams, the foam will not pass through the membrane. The use of a hydrophobic membrane prevents any foam from reaching the condensation chamber thereby contaminating the condensed liquid. The use of a hydrophobic membrane will also prevent contamination of the condensed liquid due to splashing or other movement of the raw water. It will of course be realised that while the above has been given by way of illustrative example of this invention, all such

and other modifications and variations thereto as would, be apparent to persons skilled in the art are deemed to fall within the broad scope and ambit of this invention as defined in the claims hereinafter.