GB1586895A

GB1586895A - Apparatus and method for mixing loose particulate material

Info

Publication number: GB1586895A
Application number: GB36845/77A
Authority: GB
Original assignee: Claudius Peters AG
Current assignee: Claudius Peters AG
Priority date: 1976-09-10
Filing date: 1977-09-02
Publication date: 1981-03-25
Also published as: DE2640714C2; FR2364597A7; DE2640714A1; AT355994B; ATA650377A

Description

(54) APPARATUS AND METHOD FOR MIXING LOOSE PARTICULATE MATERIAL (71) We, CLAUDIUS PETERS AG, a corporation organized and existing under the laws of the State of Germany, of Kapstadtring 1, 2000 Hamburg 60, German Federal Republic, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:: The present invention relates to an apparatus and method for mixing loose particulate material, the apparatus including a silo having in the upper part thereof a device for admission of material and having a floor provided in different regions thereof with pneumatic conveyors which can be supplied with air at different pressures and which lead to a centrally disposed mixing chamber whose volume is small in relation to the silo space and is provided with inlet apertures for the material, the bottom of the mixing chamber being adapted to receive a relatively large supply of air.

In one known apparatus of this kind the mixing action is based not only on homogenisation of relatively small amounts of material in the mixing chamber but also premixing of the material in the silo. This premixing is primarily effected by supplying air to individual regions of the floor of the silo to force material out of these regions into the mixing chamber above these regions thereby creating movement of material from top to bottom which is not only accompanied by a displacement of the layers deposited above this region in relation to neighbouring layers, but also by an interflow of material within the descending column of material and in the region of its edges and also in the region of the funnel forming on the surface. A movement of the material of this kind is called "funneling".

By shifting the region at which air is supplied to the silo floor it is possible to cause a funnel to travel gradually through all regions of the silo so that an effective mixing funnel action is achieved which can be controlled in order to achieve an optimum mixing effect. After this premixing the loose material which has flowed into the mixing chamber is homogenised by a powerful and optionally controlled supply of air to the floor.

In this known apparatus there are therefore two mixing operations. The purpose of the mixing operation in the main silo space is to effect at least partial compensation for differences in the mixture proportions of the loose material introduced to the extent required by the desired value prescribed for the operation. In the mixing chamber itself intensive homogenisation is then effected.

From the construction of this known apparatus and from the way in which the mixing process is carried out it can be seen that it is difficult to modify the composition of the material during the mixing process.

The purpose of the present invention is to provide apparatus for mixing loose material after the style of the known installation comprising a mixing chamber and a silo, wherein it is possible to add one or more additional components during the mixing process in such a manner that proper mixing of these added portions, which are generally small in amount, with the main components of the loose material introduced into the main silo space is ensured.

Therefore we provide apparatus for mixing particulate material comprising a silo having disposed therein a circular mixing chamber whose internal volume is less than that of the silo, the chamber having vertical walls, the ratio of the diameter to the height of the internal space of the mixing chamber being in the range from 1:1 to 1:2; means for supplying material to the upper part of the silo, one or more pipes to convey particulate material into the upper region of the mixing chamber from outside the silo, and pneumatic conveyors in the floor of the silo and mixing chamber to pre mix the material in the silo supplied thereto by said supplying means and flow the pre mixed material into the mixing chamber and homo genise in the mixing chamber the materials fed thereto from the silo and the pipe or pipes.

While the basic arrangement of the mixing chamber is retained the volume of the chamber is enlarged by constructing it with vertical walls. By increasing the volume of the chamber the loose material remains in the chamber for a longer time, so that for some components which are difficult to mix a good mix is ensured. Through the intensive supply of air to the floor the fluidised bed which is formed can extend uniformly upwards over the entire area of the mixing chamber floor.

The simpler construction of the apparatus of the invention in comparison with the known mixing chamber, in which the walls are vertical only in the bottom region and thereafter extend upwards in the form of an acute-angled cone, also provides the advantage of less expensive erection.

With the aid of the conveyor pipe or pipes leading into the upper region of the interior of the mixing chamber it is possible according to the invention to operate this mixing apparatus in such a manner that one or more added components can be introduced either continuously or discontinuously into the second mixing process, that is to say the in tensile homogenisation.

The conveyor pipe may for example be a conveyor tube in which pneumatic flying or optionally also plug conveying is effected.

The conveyor pipe may however also be a tube in which conveying is effected for example with the aid of a conveyor screw.

Also, the conveyor pipe may be a pneumatic conveyor trough.

With the aid of conveyor pipes of this kind it is possible for added substances to be introduced directly, that is to say without having to pass through the main silo space into the space in which the final mixing of the loose material is effected.

In the embodiment described the conveyor pipe or pipes enters or enter the interior of the mixing chamber above the outlet aperture of the mixing chamber. This arrangement ensures that the flow of components passing out of the conveyor pipe under pressure will be delivered to the opposite side of the mixing chamber to that where the inlet mouth of the conveyor pipe and the outlet opening of the mixing chamber are situated, so that a bypass flow to the mixing chamber outlet, and thus the direct discharge of unmixed material, is prevented.

A by-pass flow can also be avoided if according to another feature of the invention the outlet aperture of the mixing chamber is disposed above the air admission floor of the chamber, but below the conveyor pipe or pipes leading into the mixing chamber. The time during which the added components remain inside the mixing chamber is lengthened by this means so that the material is prevented from selecting the shortest path directly to the outlet.

According to another feature of the invention a swinging flap is disposed at the mouth of the conveyor pipe or pipes. The dead weight of this swinging flap closes the conveyor pipe mouth projecting into the interior of the mixing chamber as long as no material is being conveyed in the pipe. A back-flow of dust-laden air in the opposite direction, which could lead to caking and clogging of the added material the swinging flap is held open by the conveying pressure.

Swinging flaps can be used both for pneumatic pipe conveying and for conveying by means of a conveyor screw.

The increase in chamber volume resulting from the construction of the mixing chamber is found particularly advantageous if extremely fine ducts are to be introduced as added components. Thus, for example in the cement industry the return of furnace filter dust for re-use constitutes a particular problem. This dust is very fine and at a high temperature. Because of the high temperature the dust cannot be immediately added to the raw powder, but must usually first be separately stored in containers capable of withstanding such high temperatures.Apparatus in accordance with the invention can be used to receive ducts of this kind, firstly because the dust is rapidly separated on introduction into the upper space of the mixing chamber because of its increased volume, and secondly because the hot furnace filter dust is intensively mixed within a very short time with raw powder at a low temperature.

There is no need to use special intermediate conveyor equipment, when added components at high temperature are used with the apparatus described above it is merely necessary to adjust the air supply to the floor of the mixing chamber to a temperature approximating to that of the added components for which purpose known means are used. A preferred embodiment of the invention is explained more fully below with reference to the single drawing which is a vertical section through a silo and mixing chamber.

The walls, roof and base of the silo 1 are shown diagrammatically by thick lines. On ;the roof of the silo are disposed known supply devices for feeding the main silo space with loose material and also a filter which are here not shown in the drawing since they have no direct connection with the invention.

The floor 2 of the silo extends at a slight angle towards the centre where the mixing chamber 3 is situated, the diameter of the mixing chamber being in the ratio of about 1:2 to its height in this embodiment. The walls 4 of the mixing chamber are vertical and the ceiling is horizontal. The roof 5 of the mixing chamber is conical.

Air supply elements 6 (for example pneumatic conveyor troughs) are provided on the floor 2 of the silo. Air supply elements 7 are also situated on the floor inside the mixing chamber 3. -Compressed air pipes and fittings for the supply of air are not shown in the drawing.

The vertical walls 4 of the mixing chamber are provided with inlet apertures 8. An outlet 9 from the mixing chamber leads into an outlet tunnel 10. This outlet tunnel, which is also provided with air supply elements, leads downwards to the silo outlet aperture 11 to which is connected an air conveyor trough provided with a shut-off device. Air is discharged from the mixing chamber and outlet tunnel by way of an air outlet pipe 12 which has a side aperture just below the silo roof. Air is discharged from the silo through a filter (not shown).

From outside the silo a pipe 13, which is provided with a swinging flap 14 and a shutoff device 15, leads into the upper space in the mixing chamber 3. In this example the pipe is a tube for pneumatically conveying added components. The pipe 13 can be inspected or cleaned through a short pipe 16.

The mixing apparatus is operated by first filling the main silo space completely or at least to a substantial extent with the main components of the loose material which are to be mixed. Even during filling the supply of air to the floor can be varied so that premixing of the admitted components can start. This premixing can also be effected by introducing air at predetermined time intervals.

When the main silo space is adequately filled, the homogenisation commences in the mixing chamber 3, this being effected by the intensive admission of air. The known quadrant air supply system can be used as air supply rhythm.

During homogenisation within the mixing chamber 3 added components of loose material can be introduced through the pipe 13 into the upper space of the mixing chamber. They may be introduced either continuously or discontinuously. The swinging flap 14 closes automatically when no material is flowing through the pipe 13. The shut-off device 15 can additionally be closed.

In the example illustrated only one conveyor pipe 13 is shown. It is also possible for a plurality of pipes to lead into the interior of the mixing chamber so that different added components can be introduced simultaneously into the intensive mixing region.

The conveyor pipe 13 has its outlet above the mixing chamber outlet 9, so that the added loose material component delivered under pressure into the mixing chamber flows in the direction of the opposite mixing chamber wall and does not pass unmixed in a by-pass flow to the mixing chamber outlet.

WHAT WE CLAIM IS:- 1. Apparatus for mixing particulate material comprising a silo 'having disposed therein a circular mixing chamber whose internal volume is less than that of the silo, the chamber having vertical walls, the ratio of the diameter to the height of the internal space of the mixing chamber being in the range from 1:1 to 1:2; means for supplying material to the upper part of the silo, one or more pipes to convey particulate material into the upper region of the mixing chamber from outside the silo, and pneumatic conveyors in the floor of the silo and mixing chamber to pre mix the material in the silo supplied thereto by said supplying means and flow the pre mixed material into the mixing chamber and homogenise in the mixing chamber the materials fed thereto from the silo and the pipe or pipes.

2. Apparatus as claimed in Claim 1, wherein the outlet of the conveyor pipe or pipes in the internal space of the mixing chamber is situated above the outlet aperture of the mixing chamber.

3. Apparatus as claimed in Claim 1, wherein the outlet aperture of the mixing chamber is situated at the height of the air supply floor of the chamber.

4. Apparatus as claimed in Claim 1, wherein the outlet aperture of the mixing chamber is situated above the air supply floor of the mixing chamber, but below the conveyor pipe or pipes leading into the mixing chamber.

5. Apparatus according to any one of the preceding claims, including a swing flap or flaps disposed at the outlet of the conveyor pipe or pipes.

6. A method of operating the apparatus claimed in Claim 1 comprising introducing particulate material into the silo, supplying air through said pneumatic conveyors to pre mix the material fed to the silo, continuously introducing material into the mixing chamber through the pipe or pipes and supplying air through the floor of the mixing chamber to homogenise the material fed thereto from the silo and pipe or pipes.

7. A method of operating the apparatus claimed in Claim 1 comprising introducing particulate material into the silo, supplying air through said pneumatic conveyors to pre mix the material fed to the silo, discontinuously introducing material into the mixing chamber through the pipe or pipes and supplying air through the flow of the mixing

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. and the ceiling is horizontal. The roof 5 of the mixing chamber is conical. Air supply elements 6 (for example pneumatic conveyor troughs) are provided on the floor 2 of the silo. Air supply elements 7 are also situated on the floor inside the mixing chamber 3. -Compressed air pipes and fittings for the supply of air are not shown in the drawing. The vertical walls 4 of the mixing chamber are provided with inlet apertures 8. An outlet 9 from the mixing chamber leads into an outlet tunnel 10. This outlet tunnel, which is also provided with air supply elements, leads downwards to the silo outlet aperture 11 to which is connected an air conveyor trough provided with a shut-off device. Air is discharged from the mixing chamber and outlet tunnel by way of an air outlet pipe 12 which has a side aperture just below the silo roof. Air is discharged from the silo through a filter (not shown). From outside the silo a pipe 13, which is provided with a swinging flap 14 and a shutoff device 15, leads into the upper space in the mixing chamber 3. In this example the pipe is a tube for pneumatically conveying added components. The pipe 13 can be inspected or cleaned through a short pipe 16. The mixing apparatus is operated by first filling the main silo space completely or at least to a substantial extent with the main components of the loose material which are to be mixed. Even during filling the supply of air to the floor can be varied so that premixing of the admitted components can start. This premixing can also be effected by introducing air at predetermined time intervals. When the main silo space is adequately filled, the homogenisation commences in the mixing chamber 3, this being effected by the intensive admission of air. The known quadrant air supply system can be used as air supply rhythm. During homogenisation within the mixing chamber 3 added components of loose material can be introduced through the pipe 13 into the upper space of the mixing chamber. They may be introduced either continuously or discontinuously. The swinging flap 14 closes automatically when no material is flowing through the pipe 13. The shut-off device 15 can additionally be closed. In the example illustrated only one conveyor pipe 13 is shown. It is also possible for a plurality of pipes to lead into the interior of the mixing chamber so that different added components can be introduced simultaneously into the intensive mixing region. The conveyor pipe 13 has its outlet above the mixing chamber outlet 9, so that the added loose material component delivered under pressure into the mixing chamber flows in the direction of the opposite mixing chamber wall and does not pass unmixed in a by-pass flow to the mixing chamber outlet. WHAT WE CLAIM IS:-

1. Apparatus for mixing particulate material comprising a silo 'having disposed therein a circular mixing chamber whose internal volume is less than that of the silo, the chamber having vertical walls, the ratio of the diameter to the height of the internal space of the mixing chamber being in the range from 1:1 to 1:2; means for supplying material to the upper part of the silo, one or more pipes to convey particulate material into the upper region of the mixing chamber from outside the silo, and pneumatic conveyors in the floor of the silo and mixing chamber to pre mix the material in the silo supplied thereto by said supplying means and flow the pre mixed material into the mixing chamber and homogenise in the mixing chamber the materials fed thereto from the silo and the pipe or pipes.

chamber to homogenise the material fed thereto from the silo and pipe or pipes.

8. Apparatus substantially as herein described with reference to the accompanying drawing.

9. A method of operating the apparatus claimed in Claim 8 substantially as herein described with reference to the accompanying drawing.