GB2050181A - Apparatus for drying liquid suspensions or solutions - Google Patents

Abstract

Carriers bodies 21, in the form of balls or polyhedrons, wetted with or coated with a liquid 53 containing a solid which is desired to be recovered, are supplied, by way of a riser duct 49 up which the liquid 53 is propelled by a pump 52, to and move down within a bed inside a treatment chamber 11. Hot air from a plenum 32 passes up through the the bed and evaporates off the moisture, leaving the solid on the carrier bodies 21 which then roll across separator plate 40 whereat loosened solid material falls into chute 39, and return to the bottom of the riser duct 49. The bed is supported from below by a rotatable discharge disc 13 having therethrough holes whose open areas can be adjusted according to the desired discharge rate as by a banking plate beneath the disc 13 which can be adjusted in its orientation by means of a screw. Further optional through-holes, closed by removable masking plates, may be provided in the disc 13. <IMAGE>

Description

SPECIFICATION Apparatus for drying or concentrating liquid suspensions or solutions This invention concerns apparatus for drying or concentrating liquid suspensions or solu tions.

More particularly, the invention pertains to a apparatus for continuously treating a liquid, in the form of a suspension or solution of a solid, comprising means for applying the liq uid to the surfaces of a large number of carrier bodies, which may be spheres or poly hedrons, by wetting said bodies, a treatment chamber for receiving a plurality of said bod ies and holding them as a bed, and means for blowing a gas, such as hot air, through the 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 back to the top thereof.

Apparatus of this type is already known for example in United Kingdom Patent Specifica tions 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 mechani cally (e.g. by a bucket elevator) and applica tion of the liquid thereof is effected separ ately, for example by causing the elevator to discharge the bodies into a preliminary coat ing device from which they then pass into the treatment chamber, or by spraying the liquid onto the bodies after they have been trans ferred 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 form of apparatus as aforesaid hav ing means controlling the rate at which the bodies are able to leave the bed, at the bottom thereof, thereby to provide for control of the dwell of the bodies within the bed to ' achieve proper evaporation of the moisture from the liquid, to ensure a constant flow rate for the bodies, and furthermore to achieve relative rotation or movement of the bodies in the lower part of the bed, thereby to loosen dry material on the surface thereof so that said material can more easily be separated from the bodies upon emergace from the bed.

With this object in view, the present inven tion 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 for receiving a plurality of said bodies and holding them as a bed, and means for blowing a gas through the bed of the bodies, within the 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 back to the top of the latter characterised by the provision, in the treatment chamber, of a discharge disc which supports the bed from below, said discharge disc being rotatable and" having therethrough holes for the controlled passage therethrough of the carrier bodies.

With such an arrangement, in addition to controlling the discharge of carrier bodies at the bottom of the bed within the treatment chamber, the rotation of the discharge plate serves to cause corresponding rotation of those bodies which are in immediate contact with it, and these in turn impart a lesser rotational effect upon the bodies immediately above. Likewise, the bodies above these will rotate a lesser amount, until at a distance above the discharge plate do not perform any significant rotation but follow only a general downward movement in the bed.The relative movement resulting from this differential rotation of the carrier bodies in the lower part of the bed causes the bodies to rub against one another, thereby loosening the dry product on the surfaces of said carrier bodies, so that at the bottom of the bed a proportion, at least, of the dry solid will emerge from the bed as loose powder, with corresponding lesser demands being involved in any following separator apparatus for separating the dried solid material from the carrier bodies.

Preferably the discharge disc has means enabling the open areas of the holes through said disc to be adjusted. Said means may comprise a blanking plate located by a screw which permits said adjustment.

The invention will be described further, by way of example, with reference to the accompanying drawings, in which:~ Figure 1 is a diagrammatic sectional side elevation illustrating a first practical embodiment of the apparatus incorporating the present invention; Figure 2 is a detached sectional elevation illustrating details of the discharge disc of the apparatus of Fig. 1, the section corresponding to the line Il-Il of Fig. 3; and Figure 3 is an underneath plan view of the discharge disc shown in Fig. 2.

Referring firstly to Fig. 1, a 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 (see also Figs. 2 and 3) 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 is protected at its upper end by a conical centre piece 19 above the discharge disc 13.

It will be seen from Figs. 2 and 3 that the discharge disc 13 has therethrough, at two diametrically-opposed locations, discharge holes 20. The diameters of these holes 20 are somewhat larger than the diameters or largest dimensions of carrier bodies 21 of which there are many thousands in a bed occupying the treatment chamber 11 and supported from below by the discharge disc 13. Adjustment of the open areas of the holes 20 can be effected by adjusting the angular orientation of a diametrically extending blanking plate 22 which is located, so as to be angularly adjustable relative to the discharge disc 13, between a central boss 23 of the disc 13 and a collar 24 bolted thereto.An adjustment bolt 25, extending through a swivel boss 26 located in a bracket 27 secured to the underside of the discharge disc 13, is located so as to be rotatable in the boss 26 but is prevented from moving axially relative thereto.

This bolt 25 engages threadedly in a swivel nut 28 located in a respective bracket 29 secured to the blanking plate 22. It will, accordingly, be understood that the blanking plate 22 can be adjusted in its position by turning the bolt 25, by means of an appropriate tool (not shown), an access door (not shown) being provided in the wall of the discharge plenum 16 for this purpose.

Fig. 3 shows, additionally, the presence of two further discharge holes 30, 30 through the discharge disc 13, these being blanked off by respective masking plates 31. It will readily be understood that these further holes 30 are optional, and they can be used, or not, as may be required, according to how fast it is required to permit carrier bodies 21 to discharge at the bottom of the bed, as will later be described.

As already mentioned, the treatment chamber 11 is occupied by a bed consisting of many thousands of the material carrier bodies 21. These bodies 21 may, for example, be in the form of spheres (e.g. of a ceramic material) or polyhedrons and the bottom of the bed is supported by the deflector 12 and the discharge disc 13.

At a'level corresponding to the upper part of the deflector 1 2, a gas inlet plenum 32 surrounds the tower or container 10 in register with gas inlet openings 33 through the wall of the tower or container 10. This plenum 32 is connected to a source of hot gases which may, for instance, be waste gases from another industrial processing plant (not shown), and enables the hot gases to by fed to the bed of carrier bodies 21 and to flow upwards therethrough to an exhaust gas outlet 34 connecting to the tower or container, 10 near the top thereof. Centrally disposed within the container 10, beneath an axiallydisposed material carrier body inlet 35, is an excess liquid catcher box 36 the top of which is covered by a perforate or mesh cover 37 which is convex when viewed from above and the bottom of which runs to a surplus liquid outlet 38.

The oblique discharge plenum 16 opens to a solid separator comprising a solid materialreceiving chute 39 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 40 which is substantially planar and has an off-flow edge 41 disposed so that when carrier bodies 21 roll across the cover 40 (as will later be described) they roll off said edge 41 and fall into a hopper 42 having respective entries 43, controlled by respective top receiver valves 44, for two carrier body receiver vessels 45, of which one only is shown in the drawing. If desired the cover 40 may be fitted with means (not shown) for vibrating it.

Respective flap valves 46 are provided at the.bottom of each of the receiver vessels 45, and the arrangement is such (as will later be explained further) that when the top receiver valve 44 of either vessel 45 is open its flap valve 46 is closed and vice versa and that when the top receiver valve 44 of the one vessel 45 is open to permit carrier bodies 21 to drop into said one vessel 45 the top receiver valve 44 of the other of the vessles 45 is closed and vice versa. Accordingly, the filling and emptying of the two vessels 45 alternates; when the one of the vessels 45 is being filled with carrier bodies 21 through its top entry 43, discharge of these same bodies 21 at the bottom of that vessel 45 is prevented by the respective flap valve 46; however, simultaneously at the other vessel 45 the respective entry 43 is closed and the flap valve 46 thereof is open to permit said other vessel 45 to empty.

The flap valves 46 are located at the upper ends of respective carrier supply ducts 47 which converge and together join with a horizontal lower duct section 48 connecting with a risi#ng duct 49 which extends up to an terminates within a high level separator vessel 50. Projecting into the horizontal lower duct section 48 is a nozzle 51 provided on the outlet of a pump 52 which serves to draw liquid 53 from a feed tank 54, through a valve 55 and forward it as a jet through the nozzle 51, thereby simultaneously to cause the liquid 53 to flow up the rising duct 49 to the spearator vessel 50 and to cause reliable entrainment by the liquid 53 of carrier bodies 21 reaching the lower duct section 48 by way of the supply ducts 47.

As can be seen from Fig. 1 the rising duct 49 terminates, within the vessel 50, at an inclined perforate separator screen 56 which slopes towards and connects with an inclined carrier body return chute 57 extending to and connecting with the carrier body inlet 35 of the tower or container 10. The lower part of the separator vessel 50 has an outlet 58 connecting with a liquid return pipe 59 which in turn is connected back to the feed tank 54; it also optionally has a second or alternative outlet 60 which is similarly connected back to the feed tank 43 by way of entry 61, as has been indicated by dot-dash lines in the draw ing, as also is the surplus liquid outlet 38.

The entry 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 32 and through the gas inlet openings 33 around the wall of the container or tower 10 near to its bottom. These gases pass upwards through the bed of carrier bodies 21 and are dis charged near the top of the chamber through the exhaust gas outlet 34. As previously men tioned, these gases might consist of hot air or hot waste gases from some other process. The exhaust gases emerging at the outlet 34 are reduced in temperature as compared with their temperature when entering via the plenum 32, and contain moisture evaporated from the surface of the carrier bodies 21.

The carrier bodies 21 joining the bed in the treatment chamber 11, at the top of said bed, are all wet on their surfaces with liquid, originating at the feed tank 54, in the form of a solution or suspension of a solid, of which the solid is required to be recovered. These carrier bodies 21 pass vertically downwards through the treatment chamber 11 by gravity, the arrangement of the deflector 12, the coni cal centre piece 19, and the discharge disc 1 3 providing for the bodies 20 to move downwards at approximately equal velocities through the bed. The holes 20 in the disc 13 permit controlled passage of the bodies 21 to pass through the disc 13 and as described the areas of these holes 20 can be adjusted whereby the rate at which the carrier bodies 20 pass out of the chamber 11 is controlled.

If the discharge rate is not high enough when both holes 20 are open, one or both of the holes 30 may also be opened, with corresponding additional adjustment of the blanking plate 22, if necessary, to reduce the open areas of the holes 20. Typical speeds of rotation of the discharge 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 21 through the chamber.

After passing through the discharge disc 13 the carrier bodies 21 run down the inclined base of the oblique discharge plenum 16 and from the latter onto the cover 40 of the material-receiving chute 39. This cover 40 may be vibrated, and the carrier bodies 21 roll over the top of the cover 40 whilst dried solid from the surfaces thereof passes through the perforations in the cover 40 to fall into the chute 39 from which it can be directed for further processing or can be bagged.

A feature of this method of discharging the carrier bodies 21 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 21 by the time they pass through the disc 13. The bodies 21 in immediate contact with the disc 13 rotate with the latter and impart a rotating action to the bodies immediately above. Likewise the bodies 21 above these will rotate a lesser amount until at some distance above the discharge disc 13 there is no more rotation but only general downwards movement of the bodies 21.The resultant relative movement of the bodies 21 in the lower portion of the bed involves the bodies 21 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 40.

Either all, or a proportion, of the dried solid material having been removed from the bodies 21 passing over the cover 40, 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 21 passing over the cover 40 roll into the one or the other of the receiver vessels 45. The arrangement of the receiving vessels 45, as described, is such as to enable the bodies 21 to be introduced into liquid present in the horizontal duct section against the pressure of liquid in the rising duct 49. The receiving vessel 45 being filled with bodies 21 has its top receiver valve 44 open to allow these bodies 21 to enter. The other vessel 45, already containing a quantity of the bodies 21 has its top receiver valve 44 closed and its bottom flap valve 46 open, thus allowing its bodies 21 to enter the horizontal duct section 48 whilst the closed top receiver valve 44 prevents loss of liquid out of the top of the receiver 45.When the bodies 21 have emptied out of the respective receiver 45 its bottom flap valve 46 closes and its top receiver valve 44 is opened to admit a fresh charge of the bodies 21. Simultaneously with these latter operations, the valves 44 and 46 of the other receiver vessel 45 are actuated to permit their bodies 21 to enter the horizontal duct section 48. The valve operation can be effected by pneumatic means under control of timers.

Having passed out of the respective receiving vessel 45, the bodies 21 enter the duct section 48 and are conveyed, by the liquid being pumped up the rising duct 49, into the separator vessel 50. The valve 55 enables the liquid velocity to be adjusted until it is in excess of the minimum required to convey the bodies 21 up the rising duct 49. For example with a dilute water solution and ceramic type carrier bodies of 19 mm diameter it might be necessary to have a velocity in the duct section 48 in excess of about 3 feet per second.

Other liquids, solutions or slurries will have different minimum velocity requirements.

Separation of the bodies 21 from the liquid after being carried to the top of the duct 49 is carried out at the separating vessel 50 where the liquid and the bodies 21 entrained thereby emerge at the open top end of duct 49 and flow over the inclined perforate separator screen 56. Surplus liquid passes through the perforate screen 56 and flows down into a bottom part of the separator vessel 50 and is returned through the return pipe 59 back to the feed tank 54. Depending on the location of the feed tank 54 and the liquid velocities employed in the system, it may be necessary to incorporate one or more mesh sheets 62 or to empliy some other recognised means e.g.

in the feed tank 54, for removing entrained air or gases from the returned liquid and preventing such air or gas from being circulated around the liquid system. Fresh liquid is added to the feed tank 54, by way of the entry 61, as the contents thereof become depleted.

The bodies 21 coated with or wetted with the liquid material pass over the perforate separator screen 56 and are then fed back into the top of the chamber 11 by way of the return chute 57 and inlet 35.

The bodies 21 entering by the inlet 35 impinge on the mesh cover 37 of the excess liquid catcher box 36, and any excess liquid from said bodies passes through the cover 37 to flow back to the feed tank 54 by way of the surplus liquid outlet 38. The bodies 21, themselves, roll down the cover 37 and into the chamber 11.

A particular feature of the method as described lies in the fact that the raising of the carrier bodies 21 from the solid separator 39, 40 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 feature of the method resides in the fact that by use a suitable liquid velocity through the nozzle 51, only a single receiver vessel 45 needs to be provided, and this can be used with the valves 44 and 46 both in the open position, the entraining effect of the nozzle 51 being such as to prevent liquid backflow into the vessel 45 and to maintain the liquid column in the rising duct 49. Alternatively, the feed tank 54 can be re-posi- tioned to replace the receiver vessel 45, when the valves 44, 46 need not be incorporated.If the nozzle 51 is made of suitable dimensions, for example its throat being about half the diameter of the horizontal duct section 48, then with a suitable liquid velocity (which depends on the physical properties of the liquid) suficient suction can be created in the region of the outlet of the nozzle 51 to hold the liquid level in the receiver vessel 45 below the top said receiver vessel 45 so that any valve incorporated in the latter may be left open.

What is particularly important in the described arrangement is the fact of the rotation of the discharge disc 13 causing corresponding rotation of the carrier bodies in the bottom of the bed, with differentially reducing rotational speed with increase in the distance of the bodies from the discharge plate 13. As described, this rotation of the bodies causes loosening of the dried solid material on the surfaces of the bodies 21 as they move down towards the bottom of the bed, facilitating and rendering more efficient the separation of the solid material from the bodies.

Claims (7)

1. 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 for receiving a plurality of said bodies and holding them as a bed, and means for blowing a gas through the bed of the bodies, within the 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 back to the top of the latter characterised by the provision, in the treatment chamber, of a discharge disc which supports the bed from below, said discharge disc being rotatable and having therethrough holes for the controlled passage therethrough of the carrier bodies.

2. Apparatus as claimed in claim 1 wherein the discharge disc has means enabling the open areas of the holes through the disc to be adjusted.

3. Apparatus as claimed in claim 2 wherein the means enabling the open areas of the holes to be adjusted comprise a blanking plate located by a screw which permits said adjustment.

4. Apparatus as claimed in claim 1, 2 or 3 wherein further holes, having respective removable masking plates are provided through the discharge disc.

5. Apparatus as claimed in any preceding claim wherein the discharge disc occupies the open bottom of a frusto-conical deflector at the bottom of the bed.

6. Apparatus as claimed in any preceding claim wherein a conical centre piece is provided on the upper surface of the discharge disc.

7. Apparatus for continuously treating a liquid, in the form of a suspension or solution of a solid, substantially as hereinbefore described with reference to the accompanying drawings.