GB2219523A

GB2219523A - Contacting particulate solid materials with a liquid

Info

Publication number: GB2219523A
Application number: GB8908658A
Authority: GB
Inventors: Lajos Horvath; Laszlo Szommer; Arpadne Erdelyi; Laszlo Horvath; Istvan Szigeti; Peter Arva; Aba Boros; Bela Csukas; Andras Koroknai; Dezsoe Nagy; Jozsef Vass
Original assignee: Nitrokaelepek
Current assignee: Nitrokaelepek
Priority date: 1988-04-18
Filing date: 1989-04-17
Publication date: 1989-12-13
Also published as: IT1230185B; GB8908658D0; IT8920179A0; JPH0263546A; DE3912612A1; HUT52999A; FR2630024A1

Description

A PROCESS AND APPARATUS FOR THE INTENSIVE COUNTERCURRENT CORRACTING OF

PAWIaR^ SOLID MATERJAW WITH A S QUAN= OF ILIQUID The invention concerns a process and apparatus for the intensive countercurrent contacting of particulate solid materials with a small quantity of liquid, in a loose bed.

Three known processes may be utilised for the contacting of solid materials and liquids in a dense bed: processes based on a stationary bed, a sliding bed and fluidisation. In a stationary bed the liquid passes mainly through channels (preferred flow paths), and therefore this process does not make it possible for the phases to be intensively contacted with each other. In addition the intermittent emptying of the bed also causes problems. The sliding bed process assures adequate countercurrent contacting; however, as the bed diameter increases a uniform flow across the whole cross-section is less and less assurable. Fluidisation makes intensive phase contacting possible, but one requires a high velocity of the solution for its formation, and as a result of the significant amount of axial cross-mixing, countercurrent contacting can be assured only at the price of complicated constructional arrangements, e.g. dividing the bed up into sections and mounting special disks. Prom a theoretical point of view, an overview of the problems of dispersing slow liquid streams is readily available, see e.g. the article by Crine, M., Asua, J.M., and L1Homme, G. (Chem. Eng. Journal 25, 183-190 (1982)). Prom a practical point of view the state of the art relating to solid liquid processes can be surveyed e.g. from published Hungarian Patent Application No. 81/1985.

To assure the temporary state of movement between the stationary or sliding bed and a fluidised bed the process known as the pulsating disc process has been developed. Most frequently one uses perforated discs divided into segments and having inclined plates (e.g. Soviet Patent Specification No. 816478) and regular pulsation of small amplitude by mechanical or

2 pneumatic means (e.g. Soviet Patent Specification No. 56603.1). In the case of processing hetero-disperse solid materials the discs promote the fractionation of articles of differing sizes and so this method is also suitable for separation according to particle size. Of course, this separation sorting may also be disadvantageous in the event that the aim is to contact the whole mass of a solid phase with a liquid.

Frequently there is a need for the fluidised or at least expanded bed to be formed at low liquid velocity. This is the aim, for instance, where the task is to produce a concentrated solution or to reduce the amount of waste solution. Conventionally, smaller liquid flows are achieved by some sort of energy transfer, e.g. mechanical mixing or vibration. Supplementary energy transfer is rendered possible by liquid flow circulations in alternating directions or by pulsation; however, in this case, especially when the ratio of bed height to bed diameter is relatively high, one must generally provide for redispersing or redistributing the liquid flows along the height of the bed. All of the above leads to the solutions similar to the above-mentioned pulsating disc columns, together with all their advantages and disadvantages.

The aim of this invention is to eliminate the drawbacks of known solutions and to provide a process and apparatus with the aid of which intensive contacting of solid materials and liquids is rendered possible in an expanded bed without the use of complicated mechanisms and at an average flow velocity which is significantly lower than the minimum fluidisation velocity.

The basis of the invention is the recognition that complicated spatial constructions may be obviated by performing the operation in a 'time-structured' manner. This is made possible by the fact that for liquids flowing through a bed of solid materials the functional relationships of pressure drop and flow velocity, on the one hand, and of free volume fraction and flow velocity on the other hand are strongly non-linear and assymetrical. By taking this into account and by suitably forming the velocity-time function of the liquid flowing upwardly 3 and with a small resultant liquid consumption a suitably expanded bed may be assured. At the same time by the use of pneumatic pulsators controlled by a microcomputer one can achieve the 'structuring', practically as desired, of the velocity-time function of the liquid flowing in the bed upwardly and downwardly. In this way (especially in the case of solid materials which can be readily fluidised) the possibility is afforded of achieving a fluidised state of movement in a high bed without a disc mechanism. In the continuous, column-like fluidised bed the resultant throughf low of liquid, which is as small as desired and may even be zero, permits the formation of suitable bed expansion and periodic or irregular particle movement while a limited amount of axial mixing of solid material takes place. At the same time, as a consequence of the intermittently occurring reorganisation of the structure of the bed the channelling phenomenon may also be obviated.

The aim sought to be attained is achieved according to the invention by means of a process in which an amount of liquid less than that required for ensuring the minimum rate of fluidisation, is caused to flow from below upwardly through a bed of a particulate solid which is either continuously or intermittently fed and discharged. The liquid is passed through the bed of particulate solid material by a flow which is of varying direction and/or which is 'broken down' or divided into pulselike doses or increments. During this time the maximum velocity of the upwardly flowing liquid from time to time exceeds the minimum fluidisation velocity. The average volume flow rate of the liquid flowing upwardly in the bed exceeds the average volume flow-rate of the liquid flowing downwardly by the amount of liquid fed in. The liquid is finally discharged by overflow above the bed. The extent of bed expansion is controlled by changing the velocity of the upwardly or downwardly flowing liquid over time.

Thus in the use of the process the instantaneous and mean velocities of the downward f low are smaller than the instantaneous and mean velocity, respectively, of the upward 4 flow. Having regard to the non-linear characteristic of the pressure drop- f low velocity f unction and the f ree volume rateflow velocity function a permanent bed expansion results thereby.

In carrying the process according to the invention into practice it frequently occurs that the liquid, or a component thereof, passed into the expanded or loosened layer physically and/or chemically affects the solid material, or a component thereof, in the layer. The physical reaction may, for instance, be dissolving or leaching, while the chemical ef f ect may be a catalytic or heterogeneous chemical reaction.

Expediently, the liquid is fed into an auxiliary space connected in the manner of communicating vessels with the bed of particulate solid material and the liquid flow of alternating directions or pulsating flow is achieved by displacing the level of the liquid in the auxiliary space in an alternating downward and upward manner.

According to a preferred embodiment of the process according to the invention the alternating downward or upward displacement of the liquid level in the auxiliary space takes place by periodic cycling. Within that concept, of course, the duration of the upward displacement may significantly differ from the period of downward displacement; moreover, within one cycle there may be several strokes or phases of cycle of differing length to assure the upward or downward displacement.

In another embodiment of the process according to the invention the varying downward or upward displacement of the liquid level in the auxiliary space may take place by means of an irregular or pseudo-random cycling. By a pseudo-random period we mean a period having a given time interval of irregularly changing characteristics and another given interval of uniform characteristics.

Expediently the duration of upward or downward f low formed in the bed is 10-4 - 10-1 hour and the volume of liquid f lowing upwardly or downwardly in one cycle is 0.2 to 10% of the total bed volume. Advantageously in the auxiliary space above the liquid a gas space sealed from the external atmosphere is formed and the level of the liquid is displaced by changing the pressure of the gas space. The gas may expediently be air, but in the event of using liquids which react with air or which are explosive, inert gases may for instance also be utilised.

Changing the liquid level by means of gas pressure is not only simple but also has favourable dynamic properties. Naturally we do not exclude changing the liquid level by mechanical means, e.g. a piston or by a combined pneumatic-mechanical means, e.g. a gas space divided by a flexible diaphragm.

The process according to the invention may be realised by various constructional solutions, but from a practical point of view problems may arise if the level changes causing the upward and downward flows are achieved by elements which perform mechanical displacerr,-_nts or resilient deformations. Although the scope of the invention extends to embodiments operated by means of mechanically displaced or resiliently deformed elements also, pneumatic operation seems the most expedient.

The apparatus according to the invention includes a container for the bed for the particulate solid material flooded with liquid, a liquid discharge outlet connected to the container, a solid material -nlet and a solid material outlet. A closed auxiliary space is connected with the bottom part of the container in the manner of communicating vessels. At the top of the auxiliary space there is a liquid inlet coupling and a coupling for gas (expediently air) inlet and discharge, which is connected by ducting to a control unit, expediently a shut-off fitting provided with a programmable timer. The shut-off device is connected with a higher pressure manostat (a term used herein for a pressure source, usually of constant value) as well as with a lower pressure manostat, expediently with the ambient atmosphere. The higher pressure manostat may, for instance, include a pressure regulator (pressure reducer) coupled to a compressed air mains.

Expediently the shut-off fitting is realised by a three-way valve or two two-way valves. Throttles are mounted between the shut-off fitting and the manostats.

6 The fittings need not be simple two-state (opening-closing) elements but their opening or closing characteristics may be predetermined or they may be supplemented by controllable throttles.

In the preferred embodiment of the invention described above the shut-off fittings are frequently operated by means of a programmable timer, expediently by way of a microprocessor-based control unit. In this solution the velocity-time function is essentially set by the programme of the timer or microprocessor- based control unit.

According to a preferred embodiment of the apparatus the auxiliary space is connected from the outside to the bottom part of the container in a horizontal or inclined manner. In the case of containers of smaller crosssection this embodiment provides a well utilisable, simple constructional solution.

In the case of larger cross-section containers or those with a smaller height:diameter ratio it is expedient to use a preferred embodiment in which the auxiliary space is internally vertically connected to the bottom portion of the container.

Such a solution may for instance be a concentrically arranged construction wherein the auxiliary space projects from above into the interior of the container. The container and/or the auxiliary space may each be of circular or rectangular cross-section. 25 It is a characteristic of an advantageous preferred embodiment of the apparatus, especially for large cross-sections, that the internal space of the container is divided by expediently vertical partitions into compartments. These compartments may also be connected to the same auxiliary space. 30 According to another preferred embodiment of the apparatus the liquid is discharged from the closed bottom of a jacket surrounding the upper portion of the container. In general the cross-section of the auxiliary space may amount of 10-50% of the cross-section of the container and the rctio of the height and hydraulic diameter of the layer in the container may vary between 1 to 50.

7 It is part of the essence of our apparatus that the connection of the auxiliary space and the vessel replaces the' function of the bed support and the liquid-distributing support, in that the bottom part of the vessel containing the solid material is connected to closed auxiliary space in the manner of communicating vessels and in that a timing unit assuring the inlet and discharge of a gas (air) into or from the auxiliary space according to a prescribed programme is connected to shutoff fittings. As a result, by providing the auxiliary space with a liquid inlet coupling the state of fluidisational movement may be maintained in the thus formed apparatus without a separate bed support and liquid-distributing component. The invention is described below by way of preferred embodiments illustrated in the drawings, wherein: 15 Figure 1 is a diagrammatic view of a preferred embodiment of apparatus according to.the invention; Figure 2 illustrates the process or apparatus according to the invention realised in a preferred embodiment utilising operation with alternating flow; 20 Figure 3 is a diagram of the process and apparatus in another operative condition with intermittent flow; Figure 4 is a side view of a preferred embodiment of apparatus according to the invention; Figure 5 -is a plan view of the apparatus according to Figure 4; Figure 6 is a further embodiment in side view of apparatus according to the invention; Figure 7 is a plan view of the apparatus according to Figure 6; Figure 8 is a side view of an embodiment of the apparatus of concentric form; Figure 9 is a plan view of apparatus according to Figure 8; Figure 10 is a side view in greater detail of the embodiment according to Figures 4 and 5; and Figure 11 is a side view in greater detail of the embodiment 8 according to Figures 8 and 9.

The most important basic components of the process and of the apparatus for realising the process may be seen in Figure 1.

A vessel 1 has a bottom part 2 which is connected via a duct 3 with a closed auxiliary space 4 in the manner of communicating vessels. An overflow jacket 21 surrounding the upper part of the vessel 1 has a bottom to which a liquid discharge duct 20 is connected. An inlet for the solid material is provided at the top of the vessel 1 while at its bottom there is an outlet for the solid material. At the top 5 of the auxiliary space 4 are a liquid inlet coupling 6 and a coupling 7 for the inlet and discharge of a gas, advantageously air. The coupling 7 is connected via a duct 8 to a shut-of f device 9 constituted by valves 9a and 9b which are connected via throttles 22, 23 to a manostat 10 of higher pressure and a manostat 11 of lower pressure, the latter being expediently connected with the ambient atmosphere.

The solid material is charged in at the top of the vessel 1 and is discharged from its bottom. The liquid is charged in at the top 5 of the auxiliary space 4 through the liquid inlet coupling 6. The inflow and discharge of air takes place via the duct 8 and valve 9a, 9b connected to the coupling 7. The liquid is removed from the overflow jacket 21 via the liquid discharge outlet 20. The pressure of the closed gas space above the liquid in the auxiliary space 4 is varied according to a predetermined programme with the aid of the valves 9a, 9b. In a compression stroke the valve 9a is open and the valve 9b is closed and air flows into the auxiliary space 4 from a mains via the throttle 11 and the manostat 10 which latter is in the f orm of a pressure reducer. The liquid level is lowered in the auxiliary space 4 from the level hf to the level ha while in the container the level rises from height Ha to Hf. The level of the solid material in the auxiliary space is lowered from level hf to level A Ra while at the same time it rises in the container from Ha to A He In the so-called blow-off stroke the valve 9a is shut and the valve 9b is opened towards the manostat 11, i.e. towards the 9 ambient atmosphere. The levels of solution and the level of the bed are then displaced in opposite directions by an amount which is functionally related to the available time while at the same time the introduction of liquid into the auxiliary space 4 also causes a rise in the level.

What is essential is that as a consequence of the assymetric pressure drop-velocity characteristic arising during the charging in of the liquid and its upward or downward f low - the bed continuously expands to a certain degree (the free volume fraction oscillates around an increased mean value), - and in the auxiliary space the level of the solid material is appreciably lower than in the container (usually in the auxiliary space there is no solid material at all) and at the bottom of the container repeatedly an intensively fluidised zone is formed. The solution is dispersed by this zone and there is no need for separate dispersing supports. The throttles 22, 23 built into the gas inlet and discharge ducting have an important role because it is with their aid that the rate of pressure change and thus the rate of changes in the level may be regulated. By forming the auxiliary space 4 at the same height as the container 1 the appropriate state or condition of displacement may be maintained by a pressure of only a few tenths of bar.

Amongst the geometrical characteristics of the process 25 fundamental importance attaches to the ratio of the cross- sections of the container and of the auxiliary space. According to our experience this ratio should be chosen to lie expediently between 2 and 10. On the other hand the height of the column may be 1 to 50 times the hydraulic diameter.

Depending on the manner of operation of the valves controlling the inlet and discharge of the gas f low two fundamentally different operating conditions maybe formed and these are illustrated by way of example in Figures 2 and 3, respectively. In the drawings we have shown the change with time of the operation of the valves 9a and 9b and of the velocity of the liquid. In the diagrams illustrating the operation of the valves 'l' designates the open condition while 101 the closed condition. The velocity of the liquid is illustrated with a prefixed sign, u. designates the mean velocity over time and umf indicates the minimum fluidisation velocity.

In the operating condition (a) (Figure 2) the velocity of upward and downward displacement can be combined, hence an alternating flow is formed in the layer. The length of the compression and blow-off strokes generally differs: the duration of the blow-of f periods is longer. As a result of this and of the constant liquid infeed, liquid passes through the bed but the velocity of the through flowing liquid may be significantly lower than the minimal fluidisation velocity. At the same time, velocities higher than the minimal fluidisation velocity may from time to time also be formed in the layer. The relationships of pressure drop and liquid velocity and of the free volume fraction and the liquid velocity are non-linear and as a result of their assymetrical characteristic the resultant dead expansion and fluidisational movement are on average positive, despite the alternating displacement In the condition of operation (b) shown in Figure 3 the lengths of the compression and blow-off strokes differ significantly from each other and appreciable throttling is used in the blow-off branch. Consequently the mean velocity of upward flow differs appreciably from that of the downward flow but in this case also liquid passes through the bed. In the limiting case there is no downward flow at all because the amount of liquid charged into the auxiliary space just equalises the difference in level.

Summarising, the two operating states may be characterised in that case a) produces alternating flow while in case b) a small amount of liquid is charged in, and is divided into pulse like doses or increments in such a manner that from time to time a flow velocity higher than the minimum fluidisation velocity should be formed. The technological parameters determining the manner of operation are the following:

the pressure of the air passed into the auxiliary space the timing of operation of the compression and blow-off valves, and the adjustable resistance of the air inlet and outlet couplings.

In Figures 4 to 9 various possible preferred embodiments of the apparatus according to the invention are shown. In the variants shown in Figures 4 and 5 the auxiliary space 4 of circular cross-section is connected at the bottom with a horizontal pipe section 3 and through it to the vessel or container 1 of similarly circular cross-section.

In Figures 6 and 7 both the vessel 1 and auxiliary space 4 are of rectangular cross-section. The vessel 1 is divided into compartments by vertical partitioning walls 19. The bottom of the auxiliary space 4 is connected via a horizontal pipe section 3 to the vessel 1.

In Figures 8 and 9 the auxiliary space 4 of circular crosssection is vertically coupled to the vessel 1.

In Figure 10 there is shown an enlarged detail of the embodiment according to Figures 4 and 5. The vessel 1 contains a bed of solid material flooded with a liquid and the inlet 24 for the solid material is located at the top of the vessel. The liquid discharge duct 20 is coupled to an overflow jacket 21 surrounding the top of the vessel 1. The solid material discharge outlet is at the bottom portion 2 of the vessel 1, and furthermore the auxiliary space 4 is coupled via a horizontal pipe section 3 to the bottom portion 2. The top 5 of the auxiliary space 4 is closed and is formed with a liquid inlet coupling 6 and an air inlet and outlet coupling 7. The coupling 7 is connected by way of ducting 8 and valves 9a and 9b to manostats 10 and 11, respectively. The operation of this apparatus corresponds to that shown in Figure 1.

Figure 11 shows in enlarged detail the apparatus according to the preferred embodiment of Figures 8 and 9. In this embodiment the auxiliary space 4 is cylindrical and mounted concentrically within the equally cylindrical vessel 1. The 12 bottom end 13 of the auxiliary space 4 opens into the interior of the vessel 1. The elements coupled to the top 5 of the auxiliary space 4 are formed as described above. A programmable timer 12 is connected to the valves 9a and 9b. Advantageously the timer 12 is a microprocessor-based unit which controls the valves 9a and 9b, and thus also the liquid level in the auxiliary container 4, according to a predetermined programme.

Two examples of the utilisation of the invention are described below.

Example 1

The process was carried out in the apparatus according to Figure 10 wherein the container 1 had a diameter of 138 mm. and a height of 6000 mm, to the bottom of which an equally cylindrical auxiliary space 4 of a diameter of 63 mm and height of 6000 mm was coupled. 15 1/h synthetic resin having a particle size of 0.315 - 1.2 mm and contaminated with the residue of reagents were passed through the container 1 while 45 1/h water was fed into the auxiliary space 4. The overpressure of the higher pressure manostat 10 connected to the gas space above the liquid in the auxiliary space 4 was 0.2 bar while the lower pressure manostat 11 was in fact at ambient atmosphere. The programmed operation for periodically changing the air inlet and outlet was as follows:

Cycle Air Discharge (s) Air Inlet (s) 1 10 2 2 10 4 3 10 2 4 5 1 1 1 6 1 1 7 2 1 8 10 0 In the course of washing the'contaminatlion of the synthetic resin having a value of 75 milli-equivalent/ml oxygen consumption 13 (measured by oxidation with potassium permanganate) was reduced to 0.2 mill i-equivalent/ml In the expanded bed utilised without liquid distributing inserts and disc constructions we succeeded in avoiding the formation of channels. The average bed expansion was about 500 mm. In the case of stationary operation at such flow velocity no significant bed expansion was experienced and because of the channel formation the remaining contamination of the solid material was greater by an order of magnitude. In the case of conventional fluidisation the required washing liquid flow was 230 1/h which is five times greater than the liquid flow in the process according to the invention. Despite the greater consumption of water and increasing quantity of contaminated water the efficiency of the washing was worse because of the axial mixing, the oxygen consumption being approximately 1-1.5 milli-equivalent/ml.

Example 2

The process and apparatus according to the invention were used in the second stage of the aqueous washing of sulphonated ion exchange resin. The washing was carried out in two vessels of the size described in Example 1 connected in countercurrent flow. 10 1/h ion- exchange resin and 8 kg/h ion-exchange resin containing 35-36 weight percent of sulphuric acid were charged into the first vessel. 16 kg/h water was fed into the auxiliary space of the second vessel and from its top the solution containing 8-9 weight percent of sulphuric acid was fed to the auxiliary space of the f irst vessel. The washed resin was in practice free of sulphuric acid while the 11.7 kg/h solution discharged from the first vessel had a sulphuric acid concentration of 24-25 weight percent.

Air at an overpressure of 0.3 bar was introduced into the gas space above the liquid in the auxiliary space of the first vessel and this was blown off to the atmosphere. The overpressure of the air fed into the auxiliary space of the second vessel was 0.35 bar. The vessels were operated with a compression cycle of one second and a blow-off cycle of 10 14 seconds. When using this quantity of washing water in a washihg process carried out with a stationary bed the product was contaminated by approximately 3% sulphuric acid. For fluidisation, on the other hand, much more washing liquid would be necessary and at the same time it would not be possible to assure the prescribed approximately 25% sulphuric acid content of the solution discharged from the first vessel.

An advantage of the process and apparatus according to the invention is that in the countercurrent contacting of solid materials and liquids at low liquid velocities (significantly lower than the minimum fluidisation velocity), on an expanded bed, intensive contacting conditions may be formed. A further advantage of the invention is that for the uiform distribution along the cross-section of the liquid there is no need for any kind of liquid distributing insert or support. Similarly there is no need to use flow-redistributing discs along the height of the bed and thus the column-like high beds may be formed without complicated constructional solutions. It is an advantage in the utilisation of the invention that there is no need for constructional elements such as mixers and vibrators performing mechanical movement. only the valves controlling the inflow and outflow of the gas (air) operate with mechanical components. The operation of the apparatus according to the invention may be varied in a flexible manner and thereby the special requirements made by given materials may be taken into account in every system.

In the annexed claims reference numbers have been used purely by way of example in order to facilitate comprehension, but it is hereby declared that absolutely no limitation of scope whatsoever is intended thereby.

Claims

1. A process for the intensive countercurrent contacting of particulate solid materials with a small amount of liquid on an expanded bed of particulate solid material which is charged in and removed continuously or intermittently, wherein liquid is caused to flow from below upwardly through the bed in an amount less than that required to assure the minimum fluidisation velocity and the liquid is discharged by overflow above the bee], characterised in that the liquid is passed through the bed of particulate solid material by alternating flow and/or by the flow of the liquid being broken up into pulse-like increments or doses, while the maximum velocity of the upwardly flowing liquid from time to time exceeds the minimum fluidisation velocity and the average of the volume flow of the liquid flowing upwardly in the bed per unit of time is greater by the amount of liquid fed in than the average of the volume flow of the liquid flowing downwardly per unit of time and further that the extent of bed expansion is controlled by changing the velocity over time of the upwardly or downwardly flowing liquid.

2. A process according to claim 1 characterised in that the liquid is fed into an auxiliary space connected with the bed of particulate solid material in the manner of communicating vessels and the alternating or pulse-like flow of the liquid is generated by alternatingly downwardly and upwardly displacing the level of liquid in the auxiliary space.

3. A process according to claim 2 characterised in that the alternating downward and upward displacement of the liquid level in the auxiliary space is achieved by periodic cycling. 30

4. A process according to claim 2 characterised in that the downward or upward displacement of the liquid level in the auxiliary space is achieved by irregular or pseudo-random cycling.

5. A process according to any of claims 1 to 4 characterised in that the duration of the upward or downward f low in the bed is 10-4 10-1 hour, and the volume of liquid flowing 16 in one cycle in an upward or downward direction is 0.2 - 10% of the complete bed volume.

6. A process according to any of claims 3 to 5 characterised in that a gas space sealed from the ambient atmosphere is formed above the liquid in the auxiliary space and the liquid level is displaced by changing the pressure in the gas space.

7. Apparatus for the intensive countercurrent contacting of particulate solid materials with a small amount of liquid, primarily for carrying out the process according to any of claims 1 to 6, which apparatus contains a vessel for a bed of particulate solid material flooded with the liquid, a liquid discharge duct connected to the vessel, an inlet and an outlet for the solid material, characterised in that an auxiliary space (4) is connected to the bottom part (2) of the vessel (1) in the manner of communicating vessels, the top (5) of the auxiliary space (4) being provided with a liquid inlet coupling (6) and a coupling (7) for the inlet and outlet of gas, expediently air, the coupling (7) being connected via a duct (8) with a shut-of f fitting (9) provided with a control unit, expediently a programmable timer, and the shut-off fitting is provided with a manostat (10) at high pressure and a high manostat (11) at lower pressure, expediently the ambient atmosphere.

8. Apparatus according to claim 7 characterised in that the shut-off fitting (9) is formed either as one three way valve or two two-way valves (9a 9b).

=91 -

9. Apparatus according to claims 7 or 8 characterised in that throttles (22, 23) are mounted between the shut-off fitting (9) and the manostats (10, 11).

10. Apparatus according to any of claims 7 to 9 characterised in that the auxiliary space (4) is connected to the bottom portion (2) of the vessel (1) f rom the outside by an essentially horizontal pipe section (3).

11. Apparatus according to any of claims 7 to 9 caracterised in that the auxiliary space (4) is connected to the 41 bottom portion (2) of the vessel (1) internally and vertically.

17

12. Apparatus according to any of claims 7 to 11 characterised in that the vessel (1) is of circular or rectangular cross-section.

13. Apparatus according to any of claims 7 to 1.2 characterised in that the auxiliary space (4) is of circular o. rectangular cross-section.

14. Apparatus according to any of claims 7 to 13 characterised in that the vessel (1) is divided into compartments by vertical partitioning walls (19).

15. Apparatus according to any of claims 7 to 14 characterised in that the liquid discharge outlet (20) is connected to the bottom of an overflow jacket (21) surrounding the upper portion of the vessel (1).

16. Apparatus according to any of claims 7 to 15 characterised in that the cross-section of the auxiliary space (4) is 10- 50% of the cross-section of vessel (1).

17. Apparatus according to any of claims 7 to 16 characterised in that the ratio of the bed height in the vessel (1) and the hydraulic diameter of the vessel (1) is between 1 and 50.

18. A process according to claim 1, substantially as herein described with reference to and as shown in the accompanying drawings and/or in either of the Examples.

19. Apparatus according to claim 7, substantially as herein described with reference to and as shown in the accompanying drawings and/or in either of the Examples.

Published 1989 at The Patent Office. state House, 66,171 High Holborn, London WClR 4TP- Further oopiesmaybe obtalned from The Patent Offi0e. Sales Branch, St Mary Cray, Orpington, Kent BR5 ZRD. Printed by Multiplex techluclues ltd, st Mary Cray, Kent, Con. 1/87