GB2028149A - An apparatus and method for separating entrained vapour from a gas - Google Patents

Abstract

An apparatus and method for separating entrained vapour from a gas provides casing 1 enveloping a finned primary heat exchanger 2 and a coaxial vortex tube 4. Compressed gas passes into the casing and down a cooling heat exchange passage A. A portion of the gas is then fed in a tangential stream into the vortex tube 4 where it separates into an outer hot layer which rises and an inner axial cold layer which falls and is removed by passages h and f to become a cooling medium for the primary heat exchanger. The hot gases in the vortex tube heat the tube wall and form a secondary heat exchanger which reheats the cooled gas from the primary heat exchanger in passage D. Condensed vapour falls into an automatic cistern which intermittently ejects a batch of this liquid to the exterior. The cistern includes a float-operated valve 31,36 which is held in its open position by a magnet 34. <IMAGE>

Description

SPECIFICATION An apparatus and method for separating entrained vapour from a gas This invention relates to an apparatus for the separation of an entrained vapour from a gas, and particularly to a dehumidifier for removing water vapour from compressed gas such as air.

Recently compressed air has become frequently used for various purposes in many industries. For example, it is extensively used for paint spraying, for the operation of pneumatic automatic control systems and for pneumatic tools for machines. In these cases it is most desirable that the air has a comparatively low dew-point and is dry enough since when it is used in paint spraying irregularities occur on a resultant painted surface and pneumatic tools with metal parts get rusty.

Many kinds of the dehumidifiers have been described and these generally comprise two heat exchangers. They need the first heat exchanger to cool the compressed air to lower than the saturated vapour pressure and condense the vapour and the second heat exchanger to heat the treated gas to an adequate temperature for use.

There are different kinds of dehumidifiers based on the principles of refrigeration, adhesion, absorption or compression. Many of them need cooling media or adhesive materials which are most complex and hence the operating costs are high, and adjustments are rather difficult. The apparatus and method of this invention separates the compressed gas itself which is to be dehumidified into a cooling medium and a heating medium.

According to the present invention there is provided apparatus for separating an entrained vapour from a gas which comprises a casing, compressed gas supply means, primary heat exchange means, means for separating said compressed gas into relatively hot and cold portions, and means for applying said cold portion of gas as a heat exchange medium to said primary heat exchange means.

According to a further feature of the invention there is provided a process for separating entrained vapour from a gas which comprises, compressing the gas and cooling the same with a primary heat exchanger to separate said vapour; supplying a portion of said cooled gas to a vortex separator; selecting a colder separated portion of said cooled gas and utilising the same as a cooling medium for said primary heat exchanger.

Thus, in the vortex tube the outer rapid vortex flow becomes hotter and the inner slower flow cooler by the action of the vortex flow. So the cool gas gathered along the inner axial part of the tube can be available as a cooling medium of the primary heat exchanger and the hot gas separated in the outer part of it can be used as a heating medium of a secondary heat exchanger.

In another feature of the invention there is provided an automatic cistern which comprises first and second chambers interconnected by a channel, having a valve operated by a float in said first chamber, Latching means adapted to retain said valve in the open position, unlatching means adapted to cause the valve to close, and means for maintaining said first chamber at an elevated pressure relative to said second chamber; whereby in use liquid entering the first chamber causes the float to rise until the valve becomes latched in the open position and whereby emptying of the liquid from the first chamber into the second chamber causes a temporary equalisation of pressure which causes the valve to be unlatched and hence closed.

A detailed description of one embodiment of this invention is given hereinafter referring to the accompanying drawings wherein:~ Figure 1 is a vertical sectional front view of dehumidifier of this invention Figure 2 is a vertical sectional side view of it.

Figure 3 is a vertical sectional view of the automatic drain trap, with the float raised.

Figure 4 is a vertical sectional view of the trap of Fig. 3 wherein the pistons have pushed down the float.

A cylindrical container 1 is made of either a metal or a plastics material. Cold worked nylon is particularly suitable, because it is highly resistant to pressure and acids. Disposed within said container 1 is a heat exchanger tube 2 which has on its outer and inner surfaces spirally disposed fins. A flange portion on the upper part of the heat exchanger tube 2 has a radially disposed gas inlet 11 and a gas outlet 12 which are disposed substantially along a common axis.

The upper part of the container 1 terminates in a flange which is use abuts the flanges of the heat exchanger tube 2, a union nut 14 urges said flanges into sealed abutment, which is assisted by an O-ring 51, disposed therebetween. Hence between the inner surface of the container 1 and the outer spiral fin of the heat exchanger tube 2 a spiral cooling passage A is formed. The cooling passage A extends from said aforementioned gas inlet 11 toward the top of the device to a drain receptacle E at the bottom thereof.

An insulating tube 7 is disposed to contact the inner fins of the heat exchanger tube 2 thereby to form a spiral cool gas passage B between the inner fins of the heat exchanger tube 2 and the inner surface of the insulating tube 7. The cool gas passage B extends from a cool gas outlet 17 disposed at the top of the exchanger tube 2. The cool gas outlets 17 discharge gas along line perpendicular to a line connecting the gas inlet 11 and the gas outlet 12, and fitted with a silencer 16'.

Toward the upper end of the insulating tube 7 a gas exhaust port 20 interconnects with the gas outlet 12. In order to ensure a gas-tight seal above and below the gas exhaust port 20 O-ring 52 and O-ring 53 are disposed respectively between the tube 7 and the exhaust port 20.

It is desirable that the insulating tube 7 be thick enough to prevent thermal diffusion. As will be described in more detail later, the outer surface of the insulating tube 7 effectively forms a first heat exchanger and the inner surface thereof forms a second heat exchanger. So the diffusion of thermal energy between them must be suppressed as far as possible. A thin vortex tube 4 is also inserted into the insulating tube 7. Thus four tubes; the container 1, the heat exchanger tube 2 the insulating tube 7 and the vortex tube 4~are all coaxially disposed, the former three tubes 1, 2 and 7 are each in contact with an adjacent tube, but the vortex tube 4 is isolated except at either end.

The inner space of the vortex tube 4 forms a vortex passage C where a rapidly rotating vortex flows gradually upward. The space between the vortex tube 4 and the insulating tube 7 forms a heating passage D.

A junction body 5 is fixed to the bottom end of the heat exchanger tube 2 thereby to interconnect the drain receptacle E and the three passages B, C or D.

A filter 13 covers the bottom of the junction body 5. The filter 13 is fixed to the outer surface of the heat exchanger tube 2 with a filter band 22, and is secured to the junction body 5 with screws at its lower-most extremity. The junction body 5 forms a sealed abutment with the lower horizontal and inner cylindrical surface of the heat exchanger tube 2, by means of an O-ring 55 and an O-ring respectively. The junction body 5 incorporates two jets g, two ascending passages k, a descending passage f, and bifurcate passages h.

The jets g are tangentially disposed at the lowest part in the vortex tube 4 and discharge into the vortex passage C. Gas is thus tangentially supplied to the vortex passage C from the jets g and forms a rapid vortex flow which ascends the vortex tube 4 in vigourous rotation. The ascending passages k are connected with the lowest end of the heating passage D.

Gas rising from the ascending passages k into the heating passage D receives heat for the vortex tube 4 and the temperature thereof rises during ascent of the said passage.

The descending passage fconnects the lowermost end of the vortex passage C to the bifurcate passages h. It will be appreciated that in general rapid vortex flow is formed in the vortex passage C. Thus the cooler gas in said passage C tends to move, by virtue of the vortex, to the axis of the passage C and hotter gas is separated toward the outer surface thereof. The hotter gas in the outer part will continue to rise, but the cooler gas near the centre begins to descend by reason of its higher specific gravity. The cooler gas therefore enters the descending passage f, rises through the bifurcate passage h and rises up to the cool gas passage B.

A cylindrical screw threaded body 16 connecting the lowest end of the vortex tube 4 and the upper face of the junction body 5. A cap 24 is disposed upon the upper end of the vortex tube 4, which cap has a narrow bore j in the upper thickness thereof.

Above the cap 24 an outlet 25 for hot gases is provided. This comprises an exahust valve 6 for the hot gases. The exhaust valve 6 is fitted about the male screw at the top of the insulating tube 7 and secured by locking nut 23. The valve body 19 acts to open or shut the outlet 25 as desired. Fig. 1 shows the valve 6 in the open state and Fig. 2 shows the exhaust valve 6 in the closed state.

The exhaust valve 6 terminates in a silencer 18. The reason that silencers 16' and 18 are fitted upon the cool gas outlet 17 and hot gas exhaust valve 6 is both to maintain the high pressure state in the respective tubes and to suppress noise. The pressure loss caused by both silencers must be carefully adjusted to allow the rapid flow of gas in the vortex tube 4.

The automatic drain trap 3 will now be explained, with particular reference to Figs. 3 and 4 of the drawings. A drain hole 29 is formed at the bottom of the container 1 of the dehumidifier. Of course it is possible to fit it with a drain valve and to open the valve occasionally to empty liquid from receptacle E. However, in this example an automatic drain trap is furnished which stores liquid and can exhaust it automatically when it exceeds a predetermined level. The drain hole 29 is contiguous with an inlet bore 33 and an opening 39 which allows access to the first drain chamber M, which contains a light float 31. Between the exterior casing of the trap 3 and the interior casing 40 a second drain chamber N is formed. At the centre of the base portion of the interior casing 40 an outlet is disposed, into which a valve base section 41 which is an upper part of a sleeve 37, is inserted. The valve base section 41 is cylindrical and a valve bore 42 is bored through a side surface.

A valve body 36 is fitted into the valve base section 41 and acts to open or shut the valve bore 42. The top of the valve body 36 is held loosely in an axial recess of the float 31.

When the float 31 falls, the valve body 36 is pushed down. However when the float 31 goes up beyond a certain level, the valve body 36 is pulled up by a rim 43 of the float 31. Thus, the valve body 36 accompanies the float 31 with some hysteresis, by virtue, inter alia, of a magnet 34 which attracts a ferromagnetic material 35 fixed upon the top surface of the float 31. Pistons 32 are also provided, and these are free to move axially up or down. Ordinarily the first drain chamber M is at high pressure and the second drain chamber N is under atmospheric pressure. In this instance the pistons 32 are pushed up as shown in Fig. 3, because the space above the piston 32 interconnects with the second drain chamber N through a narrow passage S.

At first, in use, the float 31 is at its lowest level and the valve body 36 shuts the valve hole 42. The pistons 32 are set at their highest level by the pressure difference.

Liquid drains from the dehumidifier through the drain hole 29 and opening 39 into the first drain chamber M and is stored there. As the stored quantity of the liquid increases, the float 31 rises slowly by virtue of its buoyancy.

When the ferromagnetic material 35 approaches the magnet 34 nearer than a predetermined distance, the magnetic force becomes stronger than gravity and the float 31 attracted by the magnet 34 suddenly rises momentarily. Fig. 3 shows such state. Now the rim 43 of the float 31 pulls up the head of the valve body 36 and the valve holes 42 opens. The liquid flows from the first drain chamber M into the second drain chamber N and is exhausted from the exit 45 of the sleeve 37.

When the first liquid chamber M is evacuated, the first and the second drain chamber M and N become effectively continuations of each other and their pressures are therefore equalized. Thus the force holding up the pistons 32 vanishes, and the pistons 32 fall by their own gravity and pushes down the float 32, Fig. 4 shows such a transient state. The float 31 falls and the valve 36 shuts the valve hole 42. When the liquid from the second chamber N is almost evacuated air from the second chamber N escapes into the atmosphere, thereby equalizing the pressure of the second chamber N with atmospheric pressure.

Then the pistons 32 begin to rise acted upon by a larger pressure from the first chamber M.

In use of the whole device compressed gas is introduced into the gas inlet 11. The compressed gas entering the inlet 11 under pressure enters the spiral cooling passage A and is gradually cooled going spirally down the passage A. In this instance the cooling medium is the cool air in the cool gas passage B. As the gas under a normal atmospheric pressure is compressed, the partial pressure of aqueous vapour increases in proportion to the compression rate and approximates to the saturated aqueous vapour pressure at this temperature.

The gas in the semi-saturated condition is cooled, so the saturated aqueous vapour pressure decreases to a value lower than the partial aqueous vapour pressure of the gas.

The quantity of aqueous vapour which corresponds to the difference of the saturating pressure and the real partial vapour pressure at this temperature condenses and flows into the receptacle E from which it drops, and is stored in the chamber M. The gas then enters the filter 13 and a part thereof is forced at pressure through the jets gtangentially into the vortex passage C and begins a vigorous vortex motion.

As mentioned before, the hotter gas molecules tend to move to the outer surface of the vortex and coller gas molecules tend to gather at the axis by the action of the vortex motion.

The hot gas therefore rises, heating the gas in the heating passage D by raising the temperature of the outer walls of the vortex tube 4, the gas in the tube 4 then enters the silencer 18 of the hot gas exhaust valve 6 through the opening j.

The cool gas generated at the axis of the vortex passage C flows through the bifurcate passages h to reach the cool gas passage B.

Here the cool gas passes through the spiral cool gas passage B, cooling the gas introduced into the cooling passage A by agency of the heat exchanger tube 2. Finally at the silencer 16' its pressure is reduced and the cool gas ejected from the cool gas outlet 17.

Residual gas which does not pass into the jets g goes into the heating passage D through the ascending passage k The gas rises there, is heated by the vortex tube 4 up to higher enough temperature than that of its dew-point and is exhausted from the gas outlet 12.

The exhausted compressed gas can be utilized for spray painting applications, for pneumatic tools and machines. As the gas has most water eliminated therefore it has a low dew-point and contains little aqueous vapour.

By this invention substantially dry compressed gas can easily be made. Thus, no special cooling heating mediums are necessary, cool and hot gases separated from the compressed gas itself are utilized as such media. So its composition is simple, its heat efficiency is high and its operation is easy.

Moreover the dehumidifer of this invention can be small and handy because the first and the second heat exchangers are disposed coaxially. Finally it is convenient for piping as the gas inlet 11 and the gas outlet 12 is set on a common axis.

Claims (27)

1. Apparatus for separating an entrained vapour from a gas which comprises a casing, compressed gas supply means, primary heat exchange means, means for separating said compressed gas into relatively hot and cold portions, and means for applying said cold portion of gas as a heat exchange medium to said primary heat exchange means.

2. An apparatus according to claim 1 including a secondary heat exchange means and means whereby the hot portion of the gas may be utilized as an exchange medium therefor.

3. Apparatus according to either of claims 1 or 2 wherein the means for separating said compressed gas is a substantially vertically disposed vortex tube including towards its lower most end at least one jet adapted to supply the compressed gas tangential to the axis of the vortex tube thereby to form a vortex therein.

4. An apparatus according to claim 3 wherein said casing, primary and secondary heat exchange means, and said vortex tube are all coaxial.

5. An apparatus according to either of claims 3 or 4 wherein the primary heat exchanger is a substantially cylindrical finned body.

6. An apparatus according to any one of claims 3 to 5 wherein a minor portion only of the pressed gas enters said jet.

7. An apparatus according to any one of claims 3 to 6 wherein the secondary heat exchange surface is constituted by an outer surface of the vortex tube.

8. An apparatus according to any one of claims 3 to 7 wherein the means for separating said cold portion of gas includes a cold gas outlet disposed axially at the lower most point of the vortex tube.

9. An apparatus according to any one of the preceding claims wherein said hot and cold portions are vented to the atmosphere and wherein adjustment means are provided to regulate the flow of the vented gas.

10. An apparatus according to any one of the preceding claims including means for collecting condensed vapour.

11. An apparatus substantially as hereinbefore set forth with reference to, and as illustrated in Figs. 1 and 2 of the accompanying drawings.

12. A compressed air utilising device incorporating an apparatus as claimed in any one of claims 1 to 11.

13. A process for separating entrained vapour from a gas, which comprises, compressing the gas and cooling the same with a primary heat exchanger to separate said vapour; supplying a portion of said cooled gas to a vortex separator; selecting a colder separated portion of said cooled gas and utilising the same as a cooling medium for said primary heat exchanger.

14. A process according to claim 14 wherein a hotter portion of said cooled gas from said separator is utilised to reheat the gas cooled by the primary heat exchanger.

15. A process according to either of claims 13 or 14 wherein said vortex formed in said separator by supplying the compressed gas from a jet in a stream tangential to the axis of the separator.

16. A process according to any one of claims 13 to 15 wherein a minor part only of said cooled gas stream enters the separator.

17. A process according to any one of the claims 13 to 16 wherein the colder cooled gas is withdrawn from the separator at the lower most point of the axis of the vortex formed.

18. A process according to any one of claims 13 to 17 wherein the hotter and the colder portions of the gas from the separator are vented to the atmosphere and wherein the pressure at which said portions vent is adjusted for optimum operation of the process.

19. A process according to any one of claims 13 to 18 wherein the separated vapour is collected in a reservoir.

20. A process substantially as hereinbefore set forth with reference to and as illustrated in Figs. 1 and 2 of the accompanying drawings.

21. An automatic cistern which compriese first and second chambers interconnected by a channel, having a valve operated by a float in said first chamber, latching means adapted to retain said valve in the open position, unlatching means adapted to cause the valve to close, and means for maintaining said first chamber at an elevated pressure relative to said second chamber; whereby in use liquid entering the first chamber causes the float to rise until the valve becomes latched in the open position and whereby emptying of the liquid from the first chamber into the second chamber causes a a temporary equalisation of pressure which causes the valve to be unlatched and hence closed.

22. A cistern according to claim 21 wherein said valve comprises a stem having an upper engagement portion for engagement in a corresponding recess in the float, whereby only when the float moves axially upwardly beyond a predetermined point will the engagement portion engage the float and hence cause the valve to open.

23. A cistern according to either of claims 21 or 22 wherein the latching means is magnetic.

24. A cistern according to either of claims 22 or 23 wherein the float has an upper magnetisable surface and the first chamber includes a magnet to latch the same.

25. A cistern according to any one of the preceding claims 21 to 24 wherein said unlatching means includes a piston axially movable on equalisation of pressure to unlatch said valve.

26. An apparatus including a system as claimed in any one of the preceding claims 21 to 25.

27. An apparatus substantially as hereinbefore set forth with reference to and as illustrated in Figs. 3 and 4 of the accompanying drawings.