Patent Application
20100220549
The present invention relates to an apparatus in which water soluble or water swellable particulate material is conveyed to a make up unit for hydration or dissolution. The invention also relates to a method in which the apparatus is used to prepare an aqueous dilution or an aqueous solution of said particulate material.
Water-soluble or water swellable particulate materials, including polyelectrolyte powder and other similar granular powders of a hygroscopic nature are notoriously difficult to add to water in order to mix into homogenous aqueous solutions or aqueous dilutions. Such particulate materials if incorrectly added to water can stick to the make-up equipment and/or form lumps or agglomerates in the aqueous dilution or solution which do not dissolve. It is normally important that the solutions or dilutions are substantially homogenous since otherwise in various chemical treatment applications to which these solutions or dilutions are applied, the dosing equipment may become blocked or lumps/agglomerates may adversely affect the particular process.
Typically the water-soluble or water swellable materials will be hydrophilic polymers, especially high molecular weight polymers of ethylenically unsaturated monomers.
Since hydrophilic particulate material readily absorbs water and becomes sticky care has to be taken in the transfer of the material and also in the material wetting and make-up equipment. Desirably the particles of the material should remain as individual entities and hydrate separately. However, material wetting and make-up equipment can become blocked because the particulate material becomes hydrated prematurely. This can happen if particles stick to damp surfaces. Frequently this can happen in the proximity of the wetting equipment where water is combined with the particulate material, for instance where too much particulate material or agglomerated material is fed into the mixing equipment. This often results in this part of the equipment becoming blocked with gel or with layers of concretions which can stop the process and/or cause spillage of particulate material. Consequently, the operation will require regular maintenance.
Most commercially available powder make up systems employ a screw feeder to meter the powder to the powder/water mixing process. This consists of an Archimedes Screw type auger or scroll connected to a drive motor as shown in
Some systems feed the powder by a screw action at a controlled rate directly into a wetting apparatus positioned directly below the screw feeder outlet tube. This type of system is described in U.S. Pat. No. 4,531,673, U.S. Pat. No. 5,344,619 and U.S. Pat. No. 5,660,466.
WO 2004/007894 describes a process for hydrating polymer to form a high concentration polymer gel or slurry for oil well applications. The polymer is screw fed into a venturi cyclone pre-wetting device and the wetted powder water mixture is passed through a high shear mixer and then into a blender. This system will tend to produce a very high viscosity polymer gel which is not fully hydrated.
In general where powder is fed by screw action directly into a wetting apparatus a controlled flow of water introduced into the wetting apparatus forms swirls and the powder falls on to the swirling water. The mixture of powder and water then fall by gravity into a mixing vessel. In some cases the powder/water mixture is pumped from the outlet of the apparatus into a mixing vessel. Such systems are prone to blockage in the apparatus and also prone to a build up of powder at the end of the scroll. Consequently the resulting aqueous solution or dilution is of poor quality since it can contain lumps or fish eyes. This will inevitably lead to inefficient use of the product and can adversely affect the efficiency of the process in which the solution or dilution is applied. This is especially so when the powder is a hydrophilic polymer, for instance a flocculant used in a flocculation type process.
U.S. Pat. No. 5,344,619 describes an apparatus for dissolving polymer into water in which polymer is fed by means of a screw feeder from a storage hopper directly into the inlet of a wetting cone positioned vertically below the screw feeder outlet. This wetting device will typically be conical in shape or bowl shaped. Water is fed into the top of the cone in a way such that a swirl effect is achieved around the surfaces of the cone. Polymer falls onto the liquid surface and is carried to the bottom outlet of the cone, from where it is sucked into a liquid conveying line by the action of a water venturi. The water/polymer mix is conveyed by the momentum of the conveying water into a mixing tank, where it is mixed and aged before being transferred to a holding tank ready for dosing to the process. With this equipment, the polymer storage hopper and screw feeder are in very close proximity to the water interface. Polymer is extremely hygroscopic, and such systems are prone to problems of caking of product, build up of sticky coatings on the feeder, build ups and blockages at the wetting cone. This particular reference attempts to address this by addition of a compressed air line directed past the screw feeder outlet to keep the outlet clean. Since compressed air produces a chill effect, in humid atmospheres this could facilitate condensation forming on metal surfaces with the consequence that the polymer would absorb the water and produce sticky agglomerates.
Some systems overcome the problems resulting from screw feeding hygroscopic powder directly into the wetting apparatus by locating the screw feeder remotely such that the screw feeder remains dry. This can be achieved by delivering the particulate material from the screw feeder into an air transfer line in which the particulate material is conveyed to the wetting device pneumatically. In this case the screw feeder can be positioned above a small intermediate hopper. In one instance hopper outlet leads to a venturi eductor and conveying line. An air blower injects atmospheric air through the venturi and this creates suction at the hopper outlet. Since the powder falls into the hopper by the action of gravity it is sucked into the air conveying line and transported to the wetting device where it is hydrated before falling into an agitated vessel.
However, although use of a venturi eductor with an air conveying line avoids the aforementioned problems associated with screw feeding directly into the wetting apparatus, there are nonetheless disadvantages with this type of system.
It is also known to use a blowing valve (rotary valve) in place of a venturi system. However, such a system can also present disadvantages. In particular blowing valves are difficult to obtain for smaller powder feeding units and in any case are expensive. Furthermore, it is often difficult to calibrate the powder feed rate and there can be a variation in the powder feed rate which is dependent on the pressure in the conveying line. An additional problem with such a system is that large volumes of conveying air can bleed back through the blowing valve into the powder storage hopper which can reduce conveying efficiency and create dust which would necessitate employing an air filter system on the hopper.
An objective of the present invention is to provide an apparatus in which water soluble or water swellable particulate material, in particular polymeric material, is hydrated or dissolved in water form and aqueous dilution or aqueous solution and avoiding any of the aforementioned disadvantages. In particular, it is desirable to provide an apparatus which avoids blockages and provides homogenous solutions or dilutions substantially without lumps, agglomerates or fish eyes. A particularly preferred objective is that this is all achieved cost effectively and without creating any dusting problems.
The present invention relates to an apparatus for conveying a water-soluble or water swellable particulate material to a make up unit used in the hydration or dissolution of said material comprising:
We have found that the apparatus allows the metering of hygroscopic granular powders, such as water-soluble or water swellable polymers, into an air conveying line to a wetting apparatus where the hygroscopic powders can be wetted out and combined with water form a homogenous solution or dilution.
A further aspect of the invention relates to a method of forming an aqueous dilution or aqueous solution of a water soluble or swellable material comprising:
The scroll conveying line outlet may open directly into the air conveying line.
However, in one form of invention it is preferred if the scroll conveying air outlet opens into a shaft which connects with the air conveying line. More preferably the shaft is orientated such that the material can flow downwards and into the air conveying line. More preferably still the shaft is substantially vertical. In general the shaft will only contain two openings, namely the scroll conveying line outlet and the opening where the lower end of the shaft connected to the air conveying line. In this regard the shaft may be regarded as a closed system.
The scroll conveying line may be located in any orientation about a vertical axis with regard to the air conveying line. In one form the scroll conveying line is in line with the air conveying line. In an alternative form the scroll conveying line may be conveniently arranged such that it is substantially 90 degrees about a vertical axis in relation to the air conveying line.
The means for ensuring that the particulate material substantially fills the space between the scroll conveyer and the wall of the duct at least at the outlet end of the conveying line may be any suitable means selected from either (a) employing an element which is in communication with the scroll conveying line (6) or the outlet (6C) and restricts the flow of the material or (b) mounting the scroll conveying line at a gradient or in a substantially vertical orientation, such that the outlet (6C) is positioned higher than the inlet (6A).
The means for restricting the flow of material will normally be a constricting member which provides the scroll conveying line or outlet with a cross-sectional area less than the cross-sectional area of the scroll conveying line or outlet without the constricting member. The constricting member may reduce the cross-sectional area by a significant amount. Generally this concentrating member will obstruction at least 5 or 10% of the cross-sectional area and usually more. The constricting member may cover as much as 80 or 85% or more of the area of the scroll conveying line or outlet. Typically this can be between 15 and 75%, for instance between 20 and 70%.
This means tends to prevent air from the air conveying line to escape through the scroll conveying line and out through the inlet. Furthermore, it appears that this means also induces compression of an action of the particulate material within at least at outlet end of scroll conveying line.
This appears to have the advantage that the material is more efficiently conveyed to the wetting apparatus without any loss of air pressure and furthermore material, for instance material fines, is not blown from the inlet to the scroll conveying line and where fitted a material supply container (for instance a hopper) which would create a dusting problem and tend to blow even larger size material out of the apparatus. Furthermore, the hygroscopic material is successfully conveyed to the wetting apparatus without suffering the problems of agglomeration formation and/or blockage of the apparatus. The apparatus also enables the formation of aqueous solutions or dilutions that are substantially homogenous and substantially free from lumps, agglomerates or fish eyes.
The air conveying line will desirably be provided with an air flow rate and pressure rated suit the particular application. In general this will be sufficient flow rate and pressure to carry the particulate material to the make up unit. Normally the rate will be at least 10 m3/h, for instance up to 300 m3/h or more, but usually not more than 400 m3/h. Often the rate will be at least 100 or 200 m3/h. In general the air pressure will be at least 20 milli-Bar (2,000 pascals), frequently at least 50 milli-Bar (5,000 pascals) but usually not more than 500 milli-Bar (50,000 pascals). Preferably the air pressure will be up to 200 milli-Bar (20,000 pascals) and more preferably up to 150 milli-Bar (15,000 pascals).
Preferably the air conveying line will comprise a conduit that has an inner surface which has antistatic properties. This may be achieved by constructing the air conveying line from an antistatic material or alternatively by applying an antistatic surface covering to the inner wall of the air conveying conduit. The antistatic inner surface prevents static discharge sparks and also prevents particles of the material being conveyed sticking to the inner surface. Suitable antistatic surface coverings are commercially available.
Typically the air conveying line will comprise a conduit suitable for transporting the particles to the make up unit. Typically such a conduit will have an inner diameter of at least 30 or 40 mm or 50 mm and is some cases as much as 80 mm or even 100 mm. Usually the inner diameter will be in the range of the between 50 mm or 55 mm to 75 mm or 80 mm. The air conveying line may be constructed from a flexible or rigid material. This can for instance be plastic, rubber or metal etc.
The choice of air pump and air conveying line will be chosen to give a suitable flow of the particulate material. Generally this will be chosen to provide a flow rate of between 1 and 70 m/s. Typically this will be in the range of 5 to 45 m/s, especially for particulate water-soluble or water swellable polymers, including polyelectrolytes. In some cases it may be desirable for this to be below 25 m/s.
In some cases, typically when the air conveying line has a diameter of below 50 mm and the airflow exceeds 25 m/s, a small proportion of air passes into the shaft (8) and creates an air vortex within the shaft chamber. This is illustrated in
Therefore where the air conveying line (3) has a diameter of below 50 mm it is generally desirable to maintain an air flow of below 25 m/s, or at least adjusting the airflow accordingly when the conveying of particulate material stops.
Furthermore, in some cases when the diameter of the air conveying line is around 80 mm or greater it is also possible that an air vortex develops in the shaft (see
Unexpectedly we have found that when the air conveying line is around 80 mm or greater in diameter the inclusion of a deflector (25) located at the base of the shaft on the shaft wall opposite to the direction of the flow of the air and the airflow is maintained below 25 m/s and air vortex is prevented from developing in the shaft. This is illustrated in
The deflector may be formed by the addition of a machined component which fits into the base of the shaft onto the shaft wall opposite to the direction of the air flow in the air conveying line. Alternatively the deflector may be built into the design of the shaft (8) by shaping, or angling or curving of the wall. When the deflector is a machined component it can for instance be a plate, baffle or a prism which has a base that fits into the cylindrical wall of the shaft.
Typically the deflector may be constructed from the same or similar material as the shaft or scroll conveying line. In any case it is generally constructed from a hard durable material such as metal or metal alloy.
Preferably the deflector will extend across the diameter of the shaft such that at least 5% and as much as 60%, frequently between 10 and 50%, preferably between 15 and 30% of the cross-sectional area is covered by the deflector. Alternatively the deflector extends across shaft such that the cross-section distance between the shaft wall closest to the direction of airflow in the air conveying line and the deflector may be at least 10 mm and can be as much as 100 mm or more but usually between 50 and 80 mm, preferably between 55 and 75 mm.
Where the means is an element which is in communication with the scroll conveying line (6) or the outlet (6C) it may for instance be an element that partially obstructs said outlet or said scroll conveying line after the end of the scroll thereby restricting the flow of material or alternatively a flexible member that fits substantially over the outlet thereby restricting the flow of material.
In one particularly preferred form of the invention the scroll conveying line (6) or the outlet (6C) is in communication with a weir (19) over which the material must pass. The weir may be an annular member with an orifice of diameter less than the diameter of the scroll conveying line in which the annular member sits within the scroll conveying line after the end of the scroll or could be fitted to the end of the scroll conveying line at the outlet. The orifice would normally be concentric with the scroll conveying line although alternatively it may be the annular member may be fitted with an orifice in an eccentric position.
Alternatively the weir may be in the form of a wall or dam which fits across a portion of the scroll conveying line after the scroll or the outlet. Usually this type of weir will be located across the lower part of the scroll conveying line after the scroll or across the lower part of the outlet. The weir may be in the form of a substantially vertical wall which is located across the scroll conveying line or outlet. Alternatively the weir could be in the form of a wall that is angled such that the face of a wall facing the scroll forms an angle with the base of the scroll conveying line or outlet greater than 90 degrees and less than 180 degrees, usually between 90 and 135 degrees. In another form the weir may be a wall which has an angled face facing the scroll and a substantially vertical face facing the opposite direction. In one form the weir may be a prism shape.
A suitable representation is shown in
Alternatively, the weir may be located in a position extended from the end of the scroll or scroll conveying line. When the weir is located as such it may be connected to the scroll conveying line by means of a connecting element (20). The position of the weir from the end of the scroll or scroll conveying line may vary depending on the material that is being conveyed and also the conveying rate. It will also depend upon the diameter of the scroll conveying line. For instance the distance of the weir from the end of the scroll all the scroll conveying line will typically be between 0 and 500 mm for a scroll conveying line diameter of up to 51 mm.
Typically the weir, and the connecting element where included, would be made of a suitable material that is preferably rigid. Usually this will be metallic, for instance iron or steel. In general the weir and connecting element would have a thickness of at least 3 mm and usually not more than 10 mm.
In another preferred form of the invention the outlet (6C) is in communication with a compression element (21). A suitable representation is shown in
The compression member (22) should provide sufficient force to hold the compression element substantially over the outlet (6C), but to allow sufficient movement of the compression element (21) to allow restricted flow of the particulate material from the outlet. The compression member may allow movement in any dimension, for instance lateral, upward or downward movement in relation to the axis of the scroll. However, it is preferred that the movement of the compression element is substantially in line with the axis of the scroll. Suitably the compression member is selected from any of the group consisting of a spring action, pneumatic action, hydraulic action and electrically generated action, provided that it exerts sufficient force on the compression element to enable restricted flow as specified above. Preferably, the compression member comprises a spring action. Suitably the compression member will provide an axial force in the range of between 2 Newtons and 20 Newtons Force.
In a further preferred embodiment of the present invention the outlet (6C) is in communication with a flexible element (23). An example of this is shown in
In a still further preferred form of the invention the outlet (6C) is in communication with a hinged flap (24). An exemplification of this can be found in
As an alternative to gravity weighting in the hinged flap may be mechanically operated by use of a compression member. In this form the flap may be hinged from any position around the outlet, for instance above, below or to the side of the outlet. Suitably the compression member is selected from any of the group consisting of a spring action, pneumatic action, hydraulic action and electrically generated action, provided that it exerts sufficient force on the compression element to enable restricted flow as specified above. Preferably, the compression member comprises a spring action. The compression member may be as defined above in regard to the compression element.
In yet another preferred embodiment the means provided for ensuring that the material substantially fills space between the scroll conveyor and the wall of the duct comprises mounting scroll conveying line (6) as a gradient or a substantially vertical orientation, such that the outlet (6C) is positioned higher than the inlet which feeds the particulate material into the scroll conveying line inlet (6A). An example of this is embodiment is given in
The scroll conveying line may be orientated at any suitable angle from horizontal in order to facilitate the particulate material to fill the void between the scroll conveyor and the duct. Typically this will be an angle of 20° to 60° and preferably between 25° and 50°.
In a further form of the invention the means for ensuring the material substantially fills the space between the scroll conveyor and the wall of the duct at least at the outlet end of the conveying line comprises both
Thus any of the aforementioned forms of the invention in which an element that restricts the flow of material is included may be used in combination with mounting the scroll conveying line at a gradient or a substantially vertical orientation.
In a still further form of the invention the means for ensuring the material substantially fills the space between the scroll conveyor and the wall of the duct is at least two of the aforementioned elements that restrict the flow of material from the outlet. One particularly preferred combination is where the means incorporates providing the scroll conveying line or outlet with a weir (19) in addition to the outlet (6C) being in communication with a hinged flap (24).
In any of form of the invention the scroll conveyor is often a screw feeding mechanism typically consisting of a single feed scroll. Nevertheless, it may be desirable to employ multiple scrolls especially for particulate material which is difficult to convey using a single scroll.
In order to assist the flow of the particulate material from the storage and feeder through to the make up unit it may be desirable to install bridge breakers and/or vibrator devices. Control and alarm sensors may be incorporated, including but not limited to level sensors in the storage hopper (4), feeder box (5), and shaft (8). It may also be desirable to include pressure or flow sensors in the air conveying line (3).
It is particularly desirable that the scroll conveying line is substantially entirely full of particulate material during the operation of the apparatus. It is also particularly preferred that the powder is compressed sufficiently to create an air seal. Nevertheless, the means for inducing filling of the space between the scroll conveyor and inner wall of the duct should be adjusted in such a way so as not to overcompress the particulate material since this would cause friction and overheating or jamming of the scroll conveyor.
Preferably scroll conveyor should be of a solid construction containing a solid member through the central axis since this is more likely to allow filling and appropriate compaction within the scroll conveying line. A scroll conveyor constructed in an open helix (coil spring like) may not be as desirable as the scroll of solid construction since it may not provide the ability to allow filling and compaction of the particulate material to the same extent.
In any of the forms of the apparatus defined above it may be desirable for the pitch of the scroll conveyor (6B) to reduce from the inlet to the outlet.
Preferably, the pitch of the scroll will gradually reduce from the drive end, closest to the inlet, to the outlet end. We have found that this has the effect of compressing the powder as it is being screwed towards the outlet. This assists in preventing escape of air through the scroll contain line which also prevents loss of pressure in the air conveying line. Although this decreasing in pitch may be applied to any of the aforementioned forms of the apparatus, it is preferred that it is applied to the aforementioned form of the invention in which the scroll conveying line is mounted at a gradient or vertically.
The make up unit can be any piece of equipment in which the material is hydrated or dissolved the form an aqueous dilution or aqueous solution.
Generally the make up unit will incorporate equipment that brings about wetting of the polymer particles and then mixing to hydrate the polymer such that it either dissolves or at least forms an aqueous dilution. Such make up units may also be termed making down units or hydration module.
Suitably the make up unit will comprise a material wetting head (9) which is for contacting the water-soluble or water swellable particulate material with water, and a mixing vessel (14). The particulate material is hydrated or dissolved should be hydrated or dissolved to form a uniform aqueous dilution or aqueous solution. In general water-soluble particulate material will dissolve to form an aqueous solution whereas water swellable particulate material which is water insoluble will hydrated to form a uniform aqueous dilution.
More preferably the make up unit of the apparatus will have a material wetting head (9) which comprises:
In this preferred form the particulate material is supplied to the to the duct inlet from the air conveying line (3). Water spray orifices may be positioned within the upper part of the wetting duct radially outwards of the duct inlet and arranged in such a way so as to direct sprays of water downwardly in the wetting duct in order to wet the particulate material. Furthermore, in this preferred form there is a means for providing a supply of water to the water spray orifices.
Suitable material make up units are available commercially and may be used in conjunction with the present invention. In general these will all include material wetting heads. Suitable wetting heads are for instance described in U.S. Pat. No. 4,086,663 and U.S. Pat. No. 5,660,466. Another example of a make up unit is described in WO 02/092206.
The water-soluble or water swellable particulate material may be any material that is normally combined with water to make an aqueous solution or an aqueous dilution. Preferably this will be a water-soluble or water swellable polymer. Typically the polymer may be a synthetic polymer or a natural polymer. Natural polymers will include polysaccharides, for instance particulate starch, Guar gum, dextran and xanthan gum etc. Preferably the polymer will be synthetic and usually formed from ethylenically unsaturated monomers and usually will have a relatively high molecular weight. Suitable polymers include acrylamide polymers including homopolymers and copolymers of acrylamide with anionic monomers such as acrylic acid, methacrylic acid, 2-acrylamido-2-propane sulphonic acid and the like and copolymers of acrylamide with cationic monomers such as di alkyl amino alkyl (meth) acrylate, di alkyl amino alkyl (meth) acrylamide including quaternary ammonium salts etc.
The polymers may be in the form of beads or powder. Typically the particle size distribution within the polymer may range from 20 microns to 2000 microns and often between 15 microns and 1500 microns. Often the weight average particle size distribution will be no higher than 2000 microns and often be between 800 microns and 1500 microns.
One typical apparatus for providing an aqueous solution or dilution of a water-soluble or water swellable particulate material contains a powder storage hopper (4) mounted above a screw feeder box (5) onto the inlet (6D) of a scroll conveying line (6). The scroll conveying line contains a scroll conveyor (6B) which is powered by a drive motor (7). The scroll conveyor is located within a duct (6A) defined by a wall and an outlet (6C) through which particulate material exits the scroll conveying line. The scroll conveying line opens into a shaft (8) down which the particulate material can fall by gravity into an air conveying line (3) through which air is pumped by means of a blower (1) into which air is fed through an air inlet (2). The inlet can be adapted in such a way to prevent the ingress of damp air and tramp material. The air conveying line transports the particulate material to a material make up unit (18). The material make up unit has a wetting head (9) into which the air conveying line feeds particulate material through the other end centrally. The wetting head is supplied water through water feed line (10) by means of water pump (11). The particulate material and water are combined within the wetting head and the wetted particles and water fall by means of gravity into a tank (14) which is mixed by means of agitator (12) powered by drive motor (13). The make up unit may also contain an additional water feed (17). An aqueous solution or dilution of the particulate material can be removed from the tank (14) through an aqueous product feed line by means of pump (16).
The process employing said apparatus of the present invention may also be automated. This can be for instance controlled by level sensors (15) in the tank. This may be a series of conductive level probes, or a pressure sensor at the bottom of the vessel, or ultrasonic/radar device, or by various pressures which is mounted in the vessel. This may be operated such that when the particulate material is correctly dispersed or dissolved, a pump (16) would transfer the solution or dilution to a holding vessel. Typically the pump (16) may be substituted by an actuated valve in the case where gravity transfer is used. In the case of a continuous process the pump (16) may be a pump that doses the solution to a process.
In one typical method of employing the invention in a batch type process and starting with an empty mixing vessel (tank) (14), the blower (1) will start and the water valve (11) will open allowing a water flow through the water line (10) and wetting head (9). If required, a rapid fill water supply (17) will also start to fill the vessel. The blower (1) will preferably run at this stage in order to prevent the tendency of conveying line to otherwise become damp.
The liquid level in the vessel (14) is monitored by the level controls (15) and when the liquid level in the vessel covers the agitator (12), if employed, the rapid fill system (17) will shut down, screw conveying line drive pump (7) will start and drive the scroll conveyor (6B) will start to feed the particulate material into the conveying line (3), and the agitator (12) will start. The strength of the aqueous solution or dilution will depend on volume of water added to the vessel and the weight of the particulate material fed to the vessel. The water volume is controlled by the level controls (15) and the amount of powder may be controlled by a feed timer or may be controlled by a loss of weight in the powder storage hopper. A loss of weight system normally employs mounting the powder storage hopper on load cells.
The particulate material and water will continue to be fed to the vessel until the prescribed quantity of the powder has been added, at which point the scroll conveyor (6B) will stop. At this point, if employed, the rapid fill (17) will restart. When the liquid level in the vessel reaches a predetermined high level, the water valve (11) and if employed, the rapid fill (17) will shut off, and the blower (1) will stop. After a preset time sufficient to allow the solution or dilution to homogenise or age the agitator (12) will stop. If the storage vessel is empty, the mixed and age solution will be transferred by pump (16) to the storage vessel. The above cycle will then repeat.
In another typical process of operating the apparatus a continuous mixing system may be employed. Such a continuous mixing system, particulate material will be drawn from the mixing vessel (14) by the pump (16), and the level in the vessel will fall. Typically for this type of process, the blower (1) and agitator (12) will run continuously, or these may have a cut out timer to stop them in the event of a fill cycle not happening for a preset time. When the liquid level reaches a predetermined point, the water valve (11), and if employed, the rapid fill (17) will start, and after a preset delay (e.g. 1 to 10 seconds), the scroll conveyor (6B) will start, & powder will be transported via the conveying line (3) to be wetted out by the wetting head (9) before falling into the mixing vessel. For the continuous process, total water flow and powder feed rate are fixed values.
When the liquid reaches a predetermined high level, the scroll conveyor (6B) stops, and after a preset delay time (seconds), the water valve (11), and if employed, the rapid fill (17) closes. The above cycle repeats.
The following example further illustrates the invention.
For the following example, item part numbers refer to schematic
40 m3 mixing tank (14) complete with an agitator (12 & 13)
50 m3/h rated transfer pump (16).
500 lpm water feed (10 & 11) to the wetting head (9)
1000 l/m rapid fill line (17).
Blower (1) 7.5 kW
50 mm NB feeder (6)—maximum feed due to conveying constraints 3.5 kg/min.
3″ NB (76 mm), maximum conveying line distance 15 m.
Assuming the above specifications, the batch cycle time to mix and transfer a 0.5% solution of polyelectrolyte for this system is nominally 176.6 minutes, giving an average throughput capacity of 68 kg/h of powder. This is based on an ageing time of 60 minutes after the level in the mixing tank reaches high level. The rapid fill only runs when powder is not being fed. Typically, the noise of this system measured at 1 m distance is >=84 dB(A).
If we use the same basic equipment and parameters as (1a) above and modify to the new screw feeder:
The transition piece (8), the venturi eductor is removed & replaced by a plain connection passage.
The blower (1) is replaced by a 1.3 kw blower.
The conveying line (3) is replaced by 2″ NB (51 mm NB) pipe.
With this set up, the screw feeder rate can be raised to >=5 kg/min, the conveying distance can be raised to 30 m.
The batch cycle time to mix and transfer a 0.5% solution of polyelectrolyte for this system is now nominally 168 minutes, giving an average throughput capacity of 71.4 kg/h of powder. This is based on an ageing time of 60 minutes after the level in the mixing tank reaches high level. The rapid fill only runs when powder is not being fed.
The noise of this feeder system measured at 1 m distance is <=74 dB(A).
smaller blower gives 82% reduction in power consumption (kWh) for this item.
smaller blower gives 86% cost saving on this item
smaller diameter conveying line gives 35% cost saving per metre on this item.
Conveying line limit can be increased by 100% in length.
Noise reduced from 84 to 74 dB(A)
Average throughput of powder is increased by 4.8%
Removal of venturi assembly cf. increased cost of feeder modifications cost neutral.
| Number | Date | Country | Kind |
|---|---|---|---|
| 0720368.0 | Oct 2007 | GB | national |
| 0803454.8 | Feb 2008 | GB | national |
| 0810549.6 | Jun 2008 | GB | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP08/63178 | 10/1/2008 | WO | 00 | 3/31/2010 |
