GB2192805A

GB2192805A - Mixer

Info

Publication number: GB2192805A
Application number: GB08616905A
Authority: GB
Inventors: Allon Charles Day; Peter Alexander Young
Original assignee: LONGCLIFFE QUARRIES Ltd
Current assignee: LONGCLIFFE QUARRIES Ltd
Priority date: 1986-05-09
Filing date: 1986-07-11
Publication date: 1988-01-27
Also published as: GB8616905D0; GB8611331D0; GB2192388A; GB2192805B

Abstract

A mixer, which is suitable for use in a silica sand acid-leaching process, comprises a rotatable vessel (6), at least one agitator assembly (11,12) mounted for rotational movement within the vessel, means (14) for discharging material from the vessel, a receptacle (15) for receiving the discharged material and a plough (16) for removing the material from the receptacle. The vessel, agitator assembly or assemblies, discharge means and receptacle are at least partially coated with an erosion and corrosion resistant coating. <IMAGE>

Description

GB2192805A 1 SPECIFICATION tice as regards the apparatus in which the

reaction takes place. Moreover, for satisfac Intensive mixer tory reaction, the preferred intensity of mixing requires an energy input typically in the range This invention relates to an intensive mixer 70 of 8-80 W/m3 working volume.

and, in particular, to an intensive mixer which It is thus an object of the present invention can be used in the processing of silica sand to provide a mixer which is capable of with to reduce the iron content thereof. The mixer standing the erosive and corrosive conditions of the present invention is particularly suitable created during the reaction and capable of for use in the silica sand leaching process de- 75 providing a suitably intensive mixing action.

scribed in our copending application No. According to the present invention there is 8611331. therefore provided an intensive mixer for use In order to produce silica from sand or in a silica sand acid-leaching process compris sandstone of sufficiently high grade for the ing a rotatable vessel, at least one agitator manufacture of glass, it is necessary rigo- 80 assembly mounted for rotational movement rously to control the levels of, inter alia, iron, within the vessel, means for discharging ma chromium and aluminium in the silica. In this terial from the vessel, a receptacle for receiv respect, it is particularly important to be able ing material discharged from the vessel and to control the quantity of iron present in a means for removing the material from the re sample of silica since the level of iron dictates 85 ceptacle; wherein the vessel, the or each agi the quality of the glass which may be ob- tator assembly, the discharge means and the tained from that silica. Generally, the higher receptacle are at least partially coated with an the level of iron present, the lower the quality erosion and corrosion- resistant coating and will be of the glass produced. Thus, if high the or each agitator assembly is so shaped quality glass is to be produced, it is frequently 90 and rotates at such a speed that it vigorously necessary to treat the sand to reduce its iron mixes material within the vessel.

content. Preferably, the vessel is a rigid pan of circu The level of iron present in a given sample lar cross-section and the receptacle is a rota of silica may be reduced in a variety of ways ble disc which is preferably provided with a depending on the physical nature of the iron 95 fence around its perimeter to retain the dis constituent. However, if the iron content is to charged material.

be reduced to a very low level, it will usually It is preferred that the or each agitator as be necessary to employ an acid-leaching pro- sembly comprises at least one blade assembly cess which generally involves reacting a sus- mounted on a shaft and that the or each pension of sand and water with an excess of 100 blade assembly comprises two diametrically sulphuric acid. opposed blades mounted on a central hub.

A particularly efficient acid-leaching process Preferably each blade has a metal core which is described in our co-pending application No. is shaped along its longitudinal axis as a slow 8611331. In this process, the amount of sul- taper pyramid and which has a vertical cross- phuric acid generally required in acid-leaching 105 section which is inclined at 20o to the direc processes is considerably reduced by vigorous tion of motion of the blade. The metal core mixing of the reagents which promotes mass may be completely encapsulated by a ceramic transfer processes whereby fresh acid is sleeve which consists of 90% alumina and brought into contact with the ion oxide sur- which is shaped so as to provide each blade faces on the sand grains and the product of 110 with pre-determined external contouri.

the reaction, that is, iron sulphates and basic Preferably, the or each agitator assembly iron sulphates, are removed from the reaction will be provided with four blade assemblies site, thus reducing the retention time required mounted on a shaft in such a way that adja and further increasing the efficiency of the re- cent blade assemblies will lie at right angles action. More specifically the process corn- 115 to one another.

prises the steps of drying-preheating the sand; It is also preferred that the or each agitator vigorously mixing the preheated sand in an assembly be removably mounted on an exter intensive mixer with a pre-determined quantity nal support to facilitate removal for mainte of sulphuric acid, typically 7.5kg 100% sul- nance and cleaning purposes.

phuric acid per tonne of sand, sufficient to 120 In a particularly preferred arrangement the keep the surface of each grain of said coated mixer is provided with two agitator assemblies with a thin film of sulphuric acid during mix- both of which are off-set from the centre of ing, and retaining the sulphuric acid in contact the vessel.

with the sand for a pre-determined retention Preferably, the vessel and receptacle rotate time, typically 5 to 10 minutes, sufficient for 125 in the same direction, preferably both at a reaction to occur. speed of 3 r.p.m., and the or each agitator It is clear that severe abrasive and corrosive assembly rotates in the opposite direction, conditions will exist during the above reaction preferably at a speed of 120 r.p.m.

and these severe conditions create consider- It is preferred that the vessel, the or each able wear and maintenance problems in pracagitator assembly and the receptacle are 2 GB2192805A 2 coated with a ceramic coating which may heater 2 and a mixer 3 which is located be comprise a plurality of suitably shaped tiles neath the sand heater 2. The chassis of the which consist of 90% alumina. mixer 3 rests on two stout steel trestles 4, 5 Preferably the discharge means comprises a which stand on the floor. Coal combuster 1 is conical frustum which is located below an 76 used to burn coal to generate-hot gases aperture in the vessel and diverges away from which are in turn used to heat sand in rotary the vessel. This may consist of metal lined sand heater 2.

with rubber and may include a rubber skirt The mixer 3 is shown in more detail in Fig located at the end of the cone furthest from ures 2, 3 and 7 and essentially comprises a the vessel. 75 cylindrical pan 6 having a circular base 7, It is preferred that the means for removing which is provided with a centrally located cir material from the receptacle is designed to cular hole 8 of 80Omm diameter through extend into and retract from the receptacle which sand may be discharged, and a circular and, preferably, comprises a plough whose lid 9, which is supported by a bridge 10. The position is controlled by means of a screw 80 pan 6 is also provided with a main bearing or driven by a worm-geared motor. slewing ring 35 which is driven by means of Preferably, the mixer also includes means two motors 36, 37 connected via belt drives for continuously weighing the mixer and ma- 38 and 39 respectively with gear boxes 40 terial contained within the mixer and it is fur- and 41 respectively which in turn drive slew- ther preferred that the vessel is provided with 85 ing ring 35 via pinions 42 and 43 respec -a scraper blade assembly to displace material tively. Two agitator assemblies 11, 12 and a in the region of the periphery of the vessel. scraper blade assembly 13 are also provided.

Preferably, the vessel has a lid which in- A discharge cone 14 is attached to the rim of cludes a contained fume system. discharge hole 8 so that it hangs below the According to a second aspect of the inven- 90 base 7 of pan 6 and diverges away from the tion there is also provided a method of pro- discharge hole. Most of the discharge cone 14 cessing sand in an intensive mixer as de- is rubber covered metal but the bottom third scribed above which process comprises the consist of a flexible rubber skirt. A discharge steps of causing the vessel, the or each agita- disc 15 is located beneath discharge cone 14 tor assembly and the receptacle to rotate; in- 95 and a plouth 16 is provided for removing sand troducing sulphuric acid and heated sand into from discharge disc 15.

the vessel; allowing the or each agitator. as- The easing of the pan 6 is constructed from sembly to mix the acid and sand vigorously in 20mm thick steel plate which is stiffened both the vessel for a pre-determined length of time; circumferentially and over the base 7 to sup discharging acid and sand from the vessel into 100 port a ceramic lining. The ceramic lining is the receptacle via the discharge means; re- made out of tiles which are 25mm thick and moving sand from the receptacle; and quench- consist of 90% alumina. These tiles are ar ing the sand in a quench tank. ranged over the interior surface of pan 6 and A preferred embodiment of the mixer acbedded on a complete covering of 2mm thick cording to the present invention will now be 105 room temperature vulcanising (R.T.V.) sealant described with reference to the accompanying cement to form the lining. The tiles which drawings in which: cover the walls of pan 6 are generally rectan Figure 1 is a side elevation of a complete gular whereas the tiles which cover the base sand-processing plant including a mixer ac- 7 of the pan are arranged, in concentric rings cording to the present invention; 110 and each form a section of a ring. To assist Figure 2 is a plan view of a mixer according in the formation of a continuous lining, each to the present invention; tile is provided with a tongue on one of its Figure 3 is a vertipal longitudinal section sides and a corresponding groove on the op through the mixer taken along the line X-X of posing side which, when joined together, form Figure 2 with the agitators omitted for clarity; 115 vertical joints on the walls of pan 6 and radial Figure 4 is a vertical longitudinal section joints on the base 7 of the pan. In addition, through the agitator blade assembly of the every other tile is secured in position by a mixer; mild steel ferrule located in a conical hole at Figure 5 is a vertical cross-section through the centre of the tile. This ferrule is welded to the agitator blade assembly taken along the 120 the steel pan casing and a plug of the same line Y-Y of Figure 4; ceramic material as is used to form the tile is Figure 6 is an enlarged horizontal section cemented into position over the ferrule to give through part of the mixer showing the rela- a smooth surface to the pan lining and to tionship of the scraper blade assembly to the protect the ferrule against corrosion.

wall of the mixer; and 125 The pan lid 9 is constructed from 4mm Figure 7 is a plan view of the discharge disc thick polyvinylidene fluoride (P.D.V.F.) rein and plough of the mixer. forced with glass fibre reinforced plastic Referring to the drawings, Figure 1 shows a (G.R.P.) and is acid resistant. This lid 9 is sand-processing plant comprising essentially a mounted on bridge 10 so that it remains in a coal combuster 1, an overhead rotary sand 130 stationary position throughout the operation of 3 GB2192805A, 3 the mixer. The lid 9 is also provided with a shaped to fit the contour of the blade whilst port 17, through which heated sand may be 11 green", that is, before firing. After firing, ad fed into pan 6 from overhead sand heater 2 hesive may be applied to the tiles and each via a chute, and an access door 18 to provide tile placed in the appropriate position on the access to pan 6 for, eg. maintenance person70 metal core.

nel. Acid may be fed into pan 6 by means of Whichever form of ceramic coating is used, a vertical pipe 18a. A contained fume system the blade assembly is small enough to be eas comprising a series of ducts and at least one ily handled and it is therefore particularly easy fan is also provided and this is attached to to apply the sleeves and/or tiles to the metal fume off-take vents 55 and 56 in pan lid 9. 75 core and then put these pieces into an oven Agitator assemblies 11 and 12 each com- in order to heat cure the adhesive. The blade prise an agitator shaft, 19 and 20 respec- assemblies 25 may then be built up into com tively, carried in a massive housing, 21 and plete agitators.

22 respectively, which is supported by bridge The scraper blade assembly 13 is illustrated 10 and each agitator assembly is also pro- 80 in Figure 6 and comprises a blade 31 having vided with a motor drive unit, 23 and 24 re- an alumina tile working face which is carried spectively. The agitators are arranged so that on the lower end of a massive vertical shaft the whole agitators plus housings can be 32 which is mounted on bridge 10 and de readily lifted vertically off the mixer to facili- pends from pan lid 9. The scraper blade 31 is tate servicing. 85 positioned so that it does not touch the cera Eight agitator blade assemblies 25, each mic tiles 33 lining the walls of pan 6 but is carrying two agitator blades 26, are mounted set off from the lining by a distance which on two vertical keyed shafts (not shown) so can be controlled by an external stop. This that four assemblies are carried on each verti- allows a "semipermanent" lining of sand 34 cal shaft and the eight blades on each shaft 90 to be built up over the tile lining 33 which are located at right angles to one another, as helps to protect the tile lining against wear shown in Figure 2. Ceramic coated distance and chemical action. It is thought that the pieces may be provided on each vertical shaft scraper blade assembly 13 acts as a deflector to ensure the correct vertical height settings which displaces and thereby keeps alive the for the blades. Each vertical shaft is attached 95 material in contact with or in the region of the to an agitator shaft 19, 20 via a heavy flange. periphery of the pan 6.

A single agitator blade assembly 25 is The discharge disc 15 is 2.1 metres in dia shown in detail in Figures 4 and 5. This as- meter and is tiled on its upper surface with sembly comprises two diametrically opposed 90% alumina tiles in a manner similar to that blades 26 attached to a central hub 27 of 100 of the base 7 of pan 6. The discharge disc generally cylindrical cross-section. Each blade 15 is driven separately from pan 6 by means 26 has a vertical cross-section which is in- of a slewing ring 44 driven by a motor 45 clined at 20' to the direction of motion so as connected via a belt drive 46 with a gear box to impart a lift to the sand/acid mixture in the 47 which in turn drives slewing ring 44 via pan 6 and to enhance the relative movement 105 pinion 48. A fence 49 around the perimeter of of the particles and liquid in order to promote discharge disc 15 keeps the sand on the disc chemical reaction. The blade assembly 25 has and a gap 50 in fence 49 on one side permits a metal core 28 and each blade 26 is shaped the entry of plough 16 which can be extended along its longitudinal axis as a slow taper into or retracted from the disc 15 by means pyramid. The inclination and shape of each 110 of a screw driven by a worm-geared motor blade 26 is best illustrated in Figure 5. A 51.

number of 90% alumina sleeves are located In operation, the mixer 3 is started so that over each pyramidal metal blade core to form pan 6 rotates in an anticlockwise direction at a ceramic coating and these sleeves have an a speed of 3 r.p.m. and the agitator assem- external shape and contours which are de- 115 blies 11, 12 each rotate in a clockwise direc signed to give the rpquired cross-section to tion at a speed of 120 r.p.m. Discharge disc each blade 26. The innermost sleeve 29 is 15 is set to rotate in the same direction and shaped to blend in with hub 27 and the outer- at the same speed as pan 6. Sand, which has most sleeve 30 is closed at the end so as to been heated in-overhead rotary sand heater 2 completely encase the metal core 28. The re- 120 by the counter current flow of hot gases pro mainder of the hub periphery is coated with duced by coal combuster 1, is then introduced segmented 90% alumina tiles. The ceramic into pan 6 via inlet port 17 and the equivalent sleeves and tiles are held in position by of 7.5 kg 100% sulphuric acid is also fed into means of a high temperature epoxy resin. pan 6 via pipe 18a. From the pan 6, the sand As an alternative to the ceramic sleeves de- 125 passes through discharge hole 8 onto dis scribed above, which completely encapsulate charge disc 15 via discharge cone 14. Plough the metal cores of the blades, a considerable 16 is then used to remove sand from dis number of flat ceramic tiles may be used charge disc 15 at any desired rate so that the which can be stuck on to the metal core so sand falls into a quench tank (not shown) as to cover the metal and may be externally 130 which stands on the floor.

4 GB2192805A 4 The whole machine and its sand content is plates then attached to the vessel or recepta- continuously weighed to ensure that the mass cle.

of sand being processed is kept constant, that

Claims

is, that sand is withdrawn from the mixer at CLAIMS the same rate as it is

supplied to the mixer. 70 1. An intensive mixer for use in a silica The machine is weighed by supporting one sand acid-leaching process comprising a rota end of its chassis on a pair of pivots or plum- table vessel, at least one agitator assembly mer blocks 52, 53 and the other end of its mounted for rotational movement within the chassis by two load cells (not shown) which vessel, means for discharging material from produce an electrical output which varies ac- 75 the vessel, a receptacle for receiving material cording to the weight which they carry. discharged from the vessel and means for re The design of the mixer according to. the moving the material from the receptacle; present invention has many advantages over wherein the vessel, the or each agitator as known mixers designed for similar purposes. sembly, the discharge means and the recepta For instance, the provision of a discharge 80 cle are at least partially coated with an ero cone and discharge disc lengthens the acid/- sion and corrosion resistant coating and the sand contact time because the sand is not or each agitator assembly is so shaped and quenched immediately it leaves the mixing rotates at such a speed that it vigorously pan. This permits a more complete reaction to mixes material within the vessel.

be obtained whilst at the same time reducing 85
2. An intensive mixer according to claim 1 the retention time in the mixing pan itself. in which the vessel comprises a rigid pan of Moreover, since each agitator assembly is circular cross-section.

constructed from a number of smaller items, it
3. An intensive mixer according to claim 1 is easy to service as any component which or claim 2 in which the receptacle is a rotable fails can be easily replaced. Also, since the 90 disc.

individual components are relatively small, any
4. An intensive mixer according to any one component to be repaired can simply be of claims 1, 2 and 3 in which the receptacle soaked in a small tank containing the appropri- is provided with a fence around its perimeter ate chemicals to dissolve the adhesive and to retain the discharged material.

thus remove the ceramic coating ready for re- 95
5. An intensive mixer according to any pre pair. Spare parts can also be manufactured in ceding claim in which the or each agitator as advance by heating them in small ovens to sembly comprises at least one blade assembly cure the adhesive and then storing them until mounted on a shaft.

they are required. These factors, together with
6. An intensive mixer according to claim 5 the easy removal of the agitator assemblies 100 in which the or each blade assembly corn from the mixer discussed earlier, clearly facili- prises two diametrically opposed blades tate servicing of the mixer and thus minimise mounted on a central hub.

down-time.
7. An intensive mixer according to claim 5 The provision of a continuous weighting or claim 6 in which each blade has a metal system linked to the operation of the plough 105 core which is shaped along its longitudinal is also important in that it allows the mixer to axis as a slow taper pyramid and which has a be operated on a continuous basis whilst still vertical cross-secti-on which is inclined at 20' ensuring that the sand is retained in the mixer to the direction of motion of the blade.

for a sufficient length of time.
8. An intensive mixer according to claim 7 A further advantage is the provision of a 110 in which the metal core is completely encap- contained fume system connected to the lid of sulated by a ceramic sleeve which consists of the vessel which prevents the escape of noxi- 90% alumina and is shaped so as to provide ous fumes to the immediate working environ- each blade with pre- determined external con ment and enables acid vapour to be con- tours.

densed and re-cycled, if desired. 115
9. An intensive mixer according to any one It will of course bp understood that the pre- of claims 5 to 8 in which the or each agitator sent invention has been described above assembly is provided with four blade assem purely by way of example and modifications blies mounted on a shaft in such a way that of detail can be made within the scope of the adjacent blade assemblies lie at right angles to invention. For instance, the number of sleeves 120 one another.

covering the metal core of each agitator blade
10. An intensive mixer according to any may be reduced to two, that is, an inner preceding claim in which the or each agitator sleeve and an outer sleeve. In this case, the assemby is removably mounted on an external inner sleeve may be very short along the long- support.

itudinal axis of the blade and the outer sleeve 125
11. An intensive mixer according to any may cover the full length of the blade. Also, preceding claim in which the mixer is provided instead of attaching the ceramic tiles directly with two agitator assemblies.

to the metal of the vessel or receptacle by
12. An intensive mixer according to any means of adhesive, the tiles could be sup- preceding claim in which the vessel and recep- ported on sectional backing plates and these 130 tacle rotate in the same direction and the or GB2192805A 5 each agitator assembly rotates in the opposite the accompanying drawings.

direction. 26. A method of processing sand in an in
13. An intensive mixer according to any tensive mixer substantially as hereinbefore de preceding claim in which the vessel and recep- scribed and with reference to the accompany tacle rotate at a speed of 3 r.p.m. and the or 70 ing drawings.

each agitator assembly rotates at a speed of Published 1988atThe Patent Office, State House, 66/71 High Holborn, r.p.m. London WC 1 R 4TP. Further copies may be obtained from
14. An intensive mixer according to any The Patent Office, Sales Branch, St Mary Cray, Orpington, Kent BR5 3RD.

preceding claim in which the vessel, the or Printed by Burgess & Son (Abingdon) Ltd. Con. 1/87.

each agitator assembly and the receptacle are coated with a ceramic coating.
15. An intensive mixer according to claim 14 in which the ceramic coating comprises a plurality of tiles which consist of'90% alumina.
16. An intensive mixer according to any preceding claim in which the discharge means comprises a conical frustum which is located below an aperture in the-vessel and diverges away from the vessel.
17. An intensive mixer according to any preceding claim in which the discharge means is coated with rubber. -
18. An intensive mixer according to claim 16 or claim 17 in which the discharge means includes a rubber skirt located at the end of the cone furthest from the vessel.
19. An intensive mixer according to any preceding claim in which the means for removing material from the receptacle can ex- tend into and retract from the receptacle.
20. An intensive mixer according to claim 19 in which the material removing means comprises a plough which can be extended and retracted by means of a screw driven by a worm-geared motor.
21. An intensive mixer according to any preceding claim which includes means for continuously weighing the mixer and material contained within the mixer.
22. An intensive mixer according to any preceding claim in which the vessel is provided with a scraper blade assembly to displace material in the region of the periphery of the vessel.
23. An intensive mixer according to any preceding claim in which the vessel has a lid which includes a contained fume system.
24. A method of processing sand in an intensive mixer according to any preceding claim which comprises the steps of:

(a) causing the vessel, the or each agitator assembly and the receptacle to rotate; (b) introducing sulphuric acid and heated sand into the vessel; (c) allowing the or each agitator assembly to mix the acid and sand vigorously in the vessel for a predetermined length of time; (d) discharging acid and sand from the vessel into thereceptacle via the discharge means; (e) removing sand from the receptacle; and (f) quenching the sand in a quench tank.
25. An intensive mixer for use in a silica sand acid-leaching process substantially as hereinbefore described and with reference to