GB2050182A - Method of and apparatus for drying liquid suspensions or solution - Google Patents

Abstract

Carrier bodies 20, in the form of balls or polyhedrons wetted with or coated with a liquid containing a solid which is desired to be recovered, are supplied to and move down within a bed inside a treatment chamber 11. Hot air supplied by way of a plenum 21 passes up through the bed and evaporates off the moisture, leaving the solid on the carrier bodies 20 which then roll onto separator plate 29 whereat loosened solid material falls into chute 28. To simplify recoating of the bodies 20 and to return them to the top of the bed in the chamber 11, the bodies 20 are entrained by the liquid which is forced up duct 38 by a pump 41. Liquid and bodies emerging at the top of the duct 38 are separated by a screen 45 which provides for the bodies to roll back to the top of container 10. Any excess liquid entering the container 10 with the bodies is conducted back to tank 43 by a catcher box 25 having a mesh cover 26. <IMAGE>

Description

SPECIFICATION Method of and apparatus for drying or concentrating liquid suspensions or solutions This invention concerns a method of and apparatus for drying or concentrating liquid suspensions or solutions.

More particularly, the invention pertains to a method and apparatus for continuously treating a liquid, in the form of a suspension or solution of a solid, by applying the liquid to the surfaces of a large number of carrier bodies, which may be spheres or polyhedrons, by wetting said bodies, blowing a gas, such as hot air, through a bed of the wetted bodies so as to cause evaporation of some or all of the moisture from the liquid to leave a film or layer of dry or substantially dry solid on the carrier bodies, which solid is then recovered by separating it from the bodies, which move down through the bed and, after emerging at the bottom thereof, are transferred to the top thereof.

Apparatus of this type is already known for example in United Kingdom Patent Specifications Nos. 423934 and 1265719. In the arrangement of Specification No. 423934, raising of the carrier bodies to supply them into a treatment chamber is effected mechanically (e.g. by a bucket elevator) and application of the liquid thereof is effected separately, for example by causing the elevator to discharge the bodies into a preliminary coating device from which they then pass into the treatment chamber, or by spraying the liquid onto the bodies after they have been transferred into the treatment chamber.In the proposal of Specification No. 1265719, a central screw, within the treatment chamber, serves to raise the bodies up through the centre of the bed of said bodies as contained in the chamber, and the liquid is applied to the bodies as they emerge at the top end of the screw and join the bed of bodies, in the upper part of the chamber.

An object of the present invention is to provide a method of and form of apparatus as above discussed in which the mechanical raising of the carrier bodies is eliminated, use being made of the liquid under treatment for raising the carrier bodies, thereby obtaining the advantages of combining and simplifying the two steps involved, namely the wetting and the raising of the bodies, with consequential improvement in the efficiency and economy of the method. In relation to the apparatus of Specification No. 1265719, the proposal of the invention is to provide the further advantage that no screw or other mechanical body-raising means needs to be present within the treatment chamber, so that much higher temperatures may be used therein as compared with the prior proposal.

With these objects in view, the present invention provides a method of continuously treating a liquid, in the form of suspension or solution of a solid, by applying the liquid to the surfaces of a large number of carrier bodies, by wetting said bodies, blowing a gas through a bed of the bodies within a treatment chamber, so as to cause evaporation of some or all of the moisture from the liquid to leave a film or layer of dry or substantially dry solid on the carrier bodies which solid is then recovered by separating it from the bodies, which move down through the bed and, after emerging at the bottom of the bed, are transferred to the top of the latter characterised in that the bodies, after emerging from the bed and solid separation, pass to a liquid application system including a rising duct up through which the bodies are entrained by the liquid being caused to flow therethrough, said bodies, upon emerging at the top of said duct.

being separated from the liquid and passing back to the upper part of the treatment chamber.

The invention further provides apparatus for continuously treating a liquid, in the form of a suspension or solution of a solid, comprising means for applying the liquid to the surfaces of a large number of carrier bodies, by wetting said bodies, a treatment chamber accommodating a bed of said bodies and having means for blowing a gas through the bed of the bodies so as to cause evaporation of some or all of the moisture from the liquid to leave a film or layer of dry or substantially dry solid on the carrier bodies, means for recovering the dry or substantially dry solid by separating from the bodies which move down through the bed, and transfer means for transferring said bodies, emerging at the bottom of the bed, back to the top of the latter, characterised in that the transfer means comprises a liquid application system to which the bodies pass after emerging from the bed and solid separation, said liquid application system comprising a rising duct and means for causing the liquid to flow upward therethrough whilst simultaneously entraining the bodies, and separator means at the top of said duct for separating the bodies from the liquid and passing them back to the upper part of the treatment chamber.

The invention will be described further, by way of example, with reference to the accompanying diagrammatic drawings, in which:~ Figure 1 is a sectional side elevation illustrating a first practial embodiment of the apparatus of the invention; Figure 2 is a fragmentary view illustrating a modification of the apparatus of Fig. 1, to form a second embodiment; and Figure 3 is a view comparable with Fig. 2 illustrating another modification, providing a third embodiment of the apparatus.

Referring firstly to Fig. 1, a first practical embodiment of the apparatus of the invention, which is for continuously treating a liquid, in the form of a suspension or solution of a solid, so as to evaporate the moisture from the liquid to leave the dry or nearly-dry solid comprises a cylindrical tower or container 10 arranged with its axis substantially vertical and defining a treatment chamber 11 the bottom of which is defined by a substantially frusto-conical deflector 12 the open bottom of which is occupied by a rotatable discharge disc 13 provided at the upper end of a substantially vertical shaft 14 which extends through a bearing housing 15 set into an oblique discharge plenum 16 at the bottom of the tower or container 10. The shaft 14 is driven, through a gearbox 17 from an electric motor 18, and attached to discharge disc 13 is a conical centre piece 19.

The treatment chamber 11 is occupied by a bed consisting of many thousands of material carrier bodies 20. These bodies 20 may, for example, be in the form of spheres (e.g. of a ceramic or metallic material) or polyhedrons, the bottom of this bed being supported by the deflector 12 and the discharge disc 13.

At a level corresponding to the upper part of the deflector 12, a gas inlet plenum 21 surrounds the tower or container 10 in register with gas inlet openings 22 through the wall of the tower or container 10. This plenum 21 is connected to a source of hot gases which may, for instance, be from combustion equipment or be waste gases from another industrial processing plant (not shown), and enables the hot gases to be fed to the bed of carrier bodies 20 and to flow upwards therethrough to an exhaust gas outlet 23 connecting to the tower or container 10 near the top thereof. Centrally disposed within the container 10, beneath an axiallydisposed material carrier body inlet 24, is an excess liquid catcher box 25 the top of which is covered by a perforate or mesh cover 26 which can be convex when viewed from the side and the bottom of which runs to a surplus liquid outlet 27.

The oblique discharge plenum 16 opens to a solid separator comprising a solid materialreceiving chute 28 the top of which is in an inclined plane contiguous with the incline of the plenum 16 and is covered by a respective perforate plate or mesh cover 29 which is substantially planar and has an off-flow edge 30 disposed so that when carrier bodies 20 roll across the cover 20 (as will later be described) they roll off said edge 30 and fall into a hopper 31 having respective entries 32, controlled by respective top receiver valves 33, for two carrier body receiver vessels 34, of which one only is shown in the drawing. If desired the cover 29 may be fitted with means for vibrating it.

Respective flap valves 35 are provided at the bottom of each of the receiver vessels 34, and the arrangement is such (as will later be explained further) that when the top receiver valve 33 of either vessel 34 is open its flap valve 35 is closed and vice versa and that when the top receiver valve 33 of the one vessel 34 is open to permit carrier bodies 20 to drop into said one vessel 34 the top receiver valve 33 of the other of the vessels 34 is closed and vice versa.Accordingly, the filling and emptying of the two vessels 34 alternates; when the one of the vessels 34 is being filled with carrier bodies 20 through its top entry 32, discharge of these same bodies 20 at the bottom of that vessel 34 is prevented by the respective flap valve 35; however, simultaneously at the other vessel 34 the respective entry 32 is closed and the flap valve 35 opened to permit said other vessel 34 to empty.

The flap valves 35 are located at the upper ends of respective carrier supply ducts 36 which converge and together join with a horizontal lower duct section 37 connecting with a rising duct 38 which extends up to and terminates within a high level separator vessel 39. Projecting into the horizontal lower duct section 37 is a nozzle 40 provided on the outlet of a pump 41 which serves to draw liquid 42 from a feed tank 43, through a valve 44 and forward it as a jet through the nozzle 40, thereby simultaneously to cause the liquid flow up the rising duct 38 to the separator vessel 39 and to cause reliable entrainment by the liquid of carrier bodies 20 reaching the lower duct section 37 by way of the supply ducts 36.

As can be seen from the figure, the rising duct 38 terminates, within the vessel 39, at an inclined perforate separator screen 45 which slopes towards and connects with an inclined carrier body return chute 46 extending to and connecting with the carrier body inlet 24 of the tower or container 10. The lower part of the separator vessel 39 has an outlet 47 connecting with a liquid return pipe 48 which in turn is connected back to the feed tank 43; it also optionally has a second or alternative outlet 49 which is similarly connected back to the feed tank 43 by way of entry 50, as has been indicated by dot-dash lines in the drawing, as also is the surplus liquid outlet 27. The entry 50 may, additionally, be connected to a fresh liquid supply arrangement (not shown).

The mode of operation of the apparatus will readily be understood from the foregoing.

Hot gases enter the container or tower 10 by way of the plenum chamber 21 and through the gas inlet openings 22 around the wall of the container or tower 10 near to its bottom. These gases pass upwards through the bed of carrier bodies 20 and are discharged near the top of the chamber through the exhaust gas outlet 23. As previously mentioned, these gases might consist of hot air or hot waste gases from some other process. The exhaust gases emerging at the outlet 23 are reduced in temperature as compared with their temperature when entering via the plenum 21, and contain moisture evaporated from the surfaces of the carrier bodies 20.

The carrier bodies 20 joining the bed in the chamber 11, at the top of said bed, are all wet on their surfaces with a liquid, in the form of a solution or suspension of a solid, of which the solid is required to be recovered.

These carrier bodies 20 pass vertically downwards through the treatment chamber 11 by gravity, the arrangement of the deflector 12, the conical centre piece 19, and the discharge disc 13 providing for the bodies 20 to move downwards at approximately equal velocities through the bed. The disc 13 contains a number of holes for the bodies 20 to pass therethrough and the arrangement may be such that the areas of these holes can be adjusted whereby the rate at which the carrier bodies 20 pass out of the chamber 11 is controlled. Typical speeds of rotation for the disc 13 are from 5 rpm to 20 rpm, but of course an appropriate speed will be chosen to ensure an even flow of the carrier bodies 20 through the chamber.

After passing through the discharge disc 13 the carrier bodies 20 run down the inclined base of the oblique discharge plenum 16 and from the latter onto the cover 29 of the material-receiving chute 28. This cover 29 may be vibrated, and the carrier bodies 20 roll over the top of the cover 29 whilst dried solid from the surfaces thereof passes through the perforations in the cover 29 to fall into the chute 28 from which it can be directed for further processing or can be bagged.

A feature of this method of discharging the carrier bodies 20 from the bottom of the treatment chamber 11 is that, depending on the nature of the liquid material being treated and of the solid content thereof to be recovered, a proportion of the dry solid material on the bodies moving down the bed will already be separated from the bodies 20 by the time they pass through the disc 13. The bodies 20 in immediate contact with the disc 13 rotate with the latter and impart a rotating action to the balls immediately above. The resultant relative movement of the bodies 20 involves them in rubbing against one another, loosening dry product from their surfaces and reducing the efficiency required of the subsequent separator constituted by the mesh cover 29.

Either all, or a proportion, of the dried solid material having been removed from the bodies 20 passing over the cover 29 it is necessary to wet them or coat them with a fresh quantity of liquid material and to raise them to the top of the treatment chamber 11.

As has already been described, these bodies 20 passing over the cover 29 roll into the one or the other of the receiver vessels 34. The arrangement of the receiving vessels 34 is such as to enable the bodies 20 to be introduced into liquid present in the horizontal duct section against the pressure of liquid in the rising duct 38. The receiving vessel being filled has its top receiver valve 33 open to allow the bodies 20 to enter. The other vessel 34, already containing a quantity of the bodies 20 has its top receiver valve 33 closed and its bottom flap valve 21 open, thus allowing its bodies 20 to enter the horizontal duct section 37 whilst the closed top receiver valve 33 prevents loss of liquid out of the top of the receiver 34.When the bodies 20 have emptied out for the respective receiver 34 its bottom flap valve 35 closes and its top receiver valve 33 is opened to admit a fresh charge of the bodies. Simultaneously with these latter operations, the valves 33 and 35 of the other receiver vessel 34 are actuated to' permit their bodies to enter the horizontal duct section 37. The valve operation can be effected by pneumatic means under control of timers.

Having passed out of the respective receiving vessel 34, the bodies 20 enter the duct section 37 and are conveyed, by the liquid being pumped up the rising duct 38, into the separator vessel 39. The valve 25 enables the liquid velocity to be adjusted until it is in excess of the minimum required to convey the bodies 20 up the rising duct 38. For example with a dilute cold water solution and ceramic type carrier bodies of 19 mm diameter it might be necessary to have a velocity in the rising duct section 38 in excess of about 3 feet per second. Other liquids, solutions or slurries will have different minimum velocity requirements.

Separation of the bodies 20 from the liquid after being carried to the top of the duct 38 is carried out at the separating vessel 26 where the liquid and the bodies 20 entrained thereby emerge at the open top end of duct 38 and flow over the inclined perforate separator scree 45. Surplus liquid passes through the perforate screen 45 and flows down into the bottom part of the separator vessel 39.

and is returned through the return pipe 48 back to the feed tank 43. Depending on the location of the feed tank 43 and the liquid velocities employed in the system, it may be necessary to incorporate one or more mesh sheets 51 or to employ some other recognised means e.g. in the feed tank 43, for removing entrained air or gases from the returned liquid and prevent such air or gas from being circulated around the liquid system. Fresh liquid is added to the feed tank 43, by way of the entry 50, as the contents thereof become depleted.

The bodies coated with or wetted with the liquid material pass over the perforate separator screen 45 and are then fed back into the top of the chamber 11 by way of the return chute 46 and inlet 24.

The bodies 20 entering by the inlet 24 impinge on the mesh cover 26 of the excess liquid catcher box 25, and any excess liquid from said bodies passes through the cover 26 to flow back to the feed tank 43 by way of the surplus liquid outlet 27. The bodies 20, themselves, roll down the cover 26 and into the chamber 11.

A particular feature of the method as described lies in the fact that the raising of the carrier bodies 20 from the solid separator 28, 29 back to the top of the treatment chamber 11, to rejoin the bed therein, is carried out using the liquid to be treated, thus eliminating the need for any separate coating system either situated in the top of the chamber 11 or external to the container or tower 10.

Another important feature of the method resides in the fact that by use a suitable liquid velocity through the nozzle 40, only a single receiver vessel 34 needs to be provided, and this can be used with the valves 33 and 35 both in the open position, the entraining effect of the nozzle 40 being such as to prevent liquid backflow through the vessel 34 and to maintain the liquid column in the rising duct 38. Alternatively, the feed tank 43 can be positioned below the level of the receiver vessel 34 and with sufficient free volume in the top of it, the valves 33, 35 need not be incorporated.If the nozzle 40 is made of suitable dimensions, for example its throat being about half the diameter of the horizontal duct section 37, then with a suitable liquid velocity (which depends on the physical properties of the liquid) sufficient suction can be created in the region of the outlet of the nozzle 40 to hold the liquid level in the receiver vessel 34 below the top of said receiver vessel 34 so that any valve incorporated in the latter may be left open, when the pump 41 is running.

Referring now to Fig. 2, as a modification of the apparatus of Fig. 1, the separate receiver vessel 34 and feed tank 43 may be replaced by a single tank 60. The carrier bodies may be fed into the tank 60 from the solid separator 28, 29 and directed down to an outlet 61, for example by the shape of the tank 60 and a perforated mesh sheet 62 adjacent one end thereof. The nozzle 40, previously described, is situated below the outlet 61 and the carrier bodies move under the influence of gravity and the suction effect produced by the nozzle 40, as previously described, into the rising duct 38. The return pipe 48 returns surplus liquid from the separator vessel 39 back to the feed tank 60.The capacity of the tank 60 can be made sufficient to hold all the liquid in the system, so that then there is no requirement to incorporate any valves such as might be the case with the receiver vessel 34. To remove entrained air or gas from the liquid system one or more baffle plates 63 or meshes 64 may be incorporated in the feed tank 60 or the return pipe 48 may pass into a further tank (not shown) the liquid then flowing from the further tank into the tank 60. The mesh sheet 62 prevents the bodies 20 from being drawn through liquid outlet 64 and into the pump 41.

In the alternative modification illustrated in Fig. 3, liquid feed tank 70 is connected, via an outlet 71, directly to inlet 72 of a pump 73 which is one of several centrifugal pumps which are commercially available and are capable of handling a liquid containing solid bodies, for example of 10 mm diameter or larger, without damaging them.

Since this arrangement does not lend itself to incorporation of a valve 44 (Fig. 1) to control the liquid flow rate, this control is achieved by varying the speed of the pump's impeller. For example if the impeller is carried on shaft 75 and supported by bearings 76, driven by pulleys 77, driving belt 78 and electric motor 79, then the speed of the pump impeller may be varied by changing the ratios of the pulleys 77. Alternatively, the pump 73 may be driven through a variable speed gearbox (not illustrated) or directly coupled to a variable speed motor. The outlet of the pump 73 is connected to the rising duct 38 which takes the liquid and carrier bodies to the separator vessel 39 as previously described.

The features described for tank 60 may also be applied to the tank 70.

Claims (15)

1. A method of continuously treating a liquid, in the form of a suspension or solution of a solid, by applying the liquid to the surfaces of a large number of carrier bodies, by wetting said bodies, blowing a gas through a bed of the bodies, within a treatment chamber, so as to cause evaporation of some or all of the moisture from the liquid to leave a film or layer of dry or substantially dry solid on the carrier bodies, which solid is then recovered by separating it from the bodies, which move down through the bed and, after emerging at the bottom of the bed, are transferred to the top of the latter characterised in that the bodies, after emerging from the bed and solid separation, pass to a liquid application system including a rising duct up through which the bodies are entrained by the liquid being caused to flow therethrough, said bodies, upon emerging at the top of said duct, being separated from the liquid and passing back to the upper part of the treatment chamber.

2. A method as claimed in claim 1 wherein the bodies, after solid separation, pass alternately to the one and the other of two receiver vessels, the one said receiver vessel supplying bodies to the liquid application system whilst the other is isolated therefrom and is receiving bodies, and vice versa.

3. A method as claimed in claim 1 wherein a pump, which causes the flow up the rising duct, pumps the liquid through a nozzle which serves to cause the# bodies to be entrained with the liquid.

4. A method as claimed in claim 3 wherein the bodies, after solid separation, pass to receiver vessel and from hence into the rising duct, the nozzle creating a suction sufficient to maintain a liquid level in said vessel but to avoid entraining air with the liquid.

5. A method as claimed in claim 1 wherein a pump, which causes the flow up the rising duct, is disposed for the bodies to pass therethrough.

6. A method as claimed in any preceding claim wherein the liquid and bodies emerging at the top of the rising duct are separated by flowing over a perforate screen.

7. A method of continuously treating a liquid, in the form of a suspension or solution of a solid, substantially as hereinbefore described with reference to Fig. 1, Fig. 2 or Fig.

3 of the accompanying drawings.

8. Apparatus for continuously treating a liquid, in the form of a suspension or solution of a solid, comprising means for applying the liquid to the surfaces of a large number of carrier bodies, by wetting said bodies, a treatment chamber accommodating a bed of said bodies and having means for blowing a gas through the bed of the bodies so as to cause evaporation of some or all of the moisture from the liquid to leave a film or layer of dry or substantially dry solid on the carrier bodies, means or recovering the dry or substantially dry solid by separating from the bodies which move down through the bed, and transfer means for transferring said bodies, emerging at the bottom of the bed, back to the top of the latter, characterised in that the transfer means comprises a liquid application system to which the bodies pass after emerging from the bed and solid separation, said liquid application system comprising a rising duct and means for causing the liquid to flow upward therethrough whilst simultaneously entraining the bodies, and separator means at the top of said duct for separating the bodies from the liquid and passing them back to the upper part of the treatment chamber.

9. Apparatus as claimed in claim 8 wherein the bodies are spheres or polyhedrons.

10. Apparatus as claimed in claim 8 or 9 wherein two receiver vessels are provided for the bodies to pass alternately thereto after solid separation, said vessels being adapted for the one vessel to supply carrier bodies to the liquid system whilst the other is isolated from said system and is receiving bodies, and vice versa.

11. Apparatus as claimed in claim 8 or 9 including a pump which serves to cause the liquid to flow up the rising duct and pumps the liquid through a nozzle so disposed as to cause the bodies to be entrained with the liquid.

12. Apparatus as claimed in claim 11 including a receiver vessel disposed to receive liquid emerging from the top of the rising duct and from which the bodies have been separated, the nozzle being adapted to create a suction sufficient to maintain a liquid level in said vessel, whilst avoiding entraining of air with the liquid.

13. Apparatus as claimed in claim 8 or 9 including a pump adapted to cause the liquid flow up the rising duct and disposed for the bodies to pass therethrough.

14. Apparatus as claimed in any of claims 8 to 13 including a separator, at the top end of the rising duct, for separating the bodies from the liquid, and comprising an inclined perforate screen.

15. Apparatus for continuously treating a liquid, in the form of a suspension or solution of a solid substantially as hereinbefore described with reference to and as illustrated in Fig. 1, or in Fig. 2, or in Fig. 3 of the accompanying drawings.