WO1982004033A1

WO1982004033A1 - Method and device for sucking air from silo compartments

Info

Publication number: WO1982004033A1
Application number: PCT/EP1982/000099
Authority: WO
Inventors: Gebr Ag Buehler
Original assignee: Oetiker Hans
Priority date: 1981-05-13
Filing date: 1982-05-12
Publication date: 1982-11-25
Also published as: SU1149867A3; IT8267619A0; IT1155344B; DE3118993A1; JPS58500710A; EP0073833A1; DE3118993C2

Abstract

The method allows for the suction of air from silo compartments (8, 9, 10, 11) filled with pulverulent products, wherein the supply of the products is effected pneumatically. From the delivery air a signal is obtained, preferably a mechanical-pneumatic signal, which controls the air suction by means of servo controls (33, 34, 35). A suction flap (42) is connected to a common vacuum source and is controlled by a pneumatic device (3) for admission of air which may be set on by a tubular switching (4-7) or similar. This suction flap (42) is controlled by servo controls (33, 35) and at the same time it is capable of operating as a security flap for the pressure (43-47) for the silo compartment (8; 9; 10; 11) concerned.

Description

Method and device for securing air extraction from silo cells

Technical field

The invention relates to a method for securing the air extraction from silo cells with mill products or other pourable foodstuffs or animal feed, with pneumatic product feed, and to an aspiration flap for silo cells which are particularly suitable for carrying out such a method is.

Underlying state of the art

Recently, the interest of experts has turned increasingly to the problems with the storage of mill products in large storage silos or storage cells. This is particularly true after various explosions have occurred in the USA (but also recently in Europe). like accidents have occurred in this area. It is sometimes believed that only small cells should be built, especially for Xühlen products, because the

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S \ / IP Is of the opinion that it can also keep the corresponding problems small. However, the use of small storage cells would force them to process in inefficient small batches _/ which would have to result in an uninterrupted change of products, machine settings, etc., which in turn would lead to other negative consequences in the case of large-volume production units. For many years now, attempts have been made to find weak spots in the area of the storage units, with the aspect of achieving greater operational safety being particularly important. A decisive step in this direction was achieved with a new concept for dimensioning the entire cell body *, but especially the outlet section, the so-called "mass flow silo" according to Jenike's suggestions. With this solution, in the majority of cases, a uniform, trouble-free emptying of the silo content can be achieved and external disturbances can be reduced. With correct dimensioning, reworking in the area of the silo body is then only rarely required, so that the corresponding source for dust explosions has so far been partially eliminated.

Experience has shown that one of the weak points in silo systems is aspiration. The aspiration should ensure the air intake from the interior of the silo as economically as possible, with the aim being to prevent a fire in one silo cell from being spread from there to another.

The experience of the past few years seems to indicate that mills in which the material is mainly transported with pneumatics are less susceptible to fires and dust explosions than mills with others

W - ^{• •} Material transport. Pneumatic material transport therefore dominates today in mill operations, although care must be taken to ensure suitable extraction of the conveying air from the cells. Such a solution is described, for example, in DE-C-1 150 622: there, the goods are conveyed into a silo cell by means of a pneumatic transport, after selection via a corresponding pipe switch. The end of the pneumatic delivery line is closed by a spring-loaded cone ^* . When it comes to product promotion, the mixture of

Flour and air on the central cone and brings this in an open position. At the same time, a second cone, which surrounds the first, is also moved, as a result of which a corresponding opening for the air suction for the aspiration is cleared.

Depending on the force of the flour-air mixture, that of the retaining spring and the structural resistance of the conical valve body, the air inlet and the air suction are regulated automatically at the same time. * Be ^"lung entschärf with this construction to - At the very least to ^'the paper seems to be the beginning Problemst described **; in practice, however, the solution according to DE-C has not proven one ι50 622 Sun turns out!. this solution is not functional when the pneumatics are idling, although it is known that the largest amounts of air are conveyed and dust blows are generated during idling: because when idling, the "force" of the rapidly moving product mass in the pneumatic conveying means that a corresponding silo valve is opened The pneumatic conveying air inevitably builds up overpressure in the silo cell in the arrangement from DE-C-1 150 622. Furthermore, with this purely mechanical design, even after a long period of operation, still uncontrollable friction problems l occur that often shut down the whole device.

In another known embodiment, a position signal is emitted to an aspiration flap based on the position of the pipe switch. By appropriate locking under all pipe switches and the aspiration flaps it can be ensured that the aspiration flap via which the pneumatic trans-

- _[ _Q port is done, is open. In this way, the aspriation problem is solved satisfactorily for most cases, but for this - depending on the number of selectable silo cells - a considerable electrical control effort has to be carried out. Real problems came up

15, however, in cases in which products from silo cells are directly weighed, e.g. for bagging, were poured. In such systems, several pipelines lead into the area of the scales via common transport screws. The one in a single silo cell from the

20 generated aspiration vacuum can lead to failure of the weighing result, when the silo is empty and he U ⁿ terdrück can propagate through the transport screw '. This can be done by additionally locking the pneumatics with the aspiration and the weighing system

25 between. unpopular, which makes the concept of total plant control

«However, is becoming considerably more complicated.

Disclosure of the invention

Proceeding from this, the object of the invention is

30 reasons, largely avoiding the shown

Disadvantages of this prior art to achieve the most economical possible operation and, in particular, to achieve an improvement in the safety of such systems, insofar as the silo ventilation is the cause.

35 is connected. According to the invention, this object is achieved in that a (preferably mechanical-pneumatic) control signal is derived from the air flow of the pneumatic conveying air and is used to control the air suction via servo means.

The solution according to the invention is surprisingly simple, explosion-proof (insofar as the elements directly required for it are concerned) and can be used autonomously even when using a large number of corresponding aspiration flaps; it also brings about a noticeable increase in operational safety. It is essential that a signal is derived from the flow of the conveying air: "^" ύϊfc. ^"" this is increasingly used to control the air extraction via servo means. In the solution according to the invention, in contrast to the prior art, the air extraction can be controlled as desired even at the start of the air flow. The aspiration flaps can already be fully opened even when idling, which, in contrast to the prior art from DE-C-1 150 622, already gives full functionality even when idling.

The invention allows a large number of advantageous configurations: the control signal can advantageously be derived from the conveying air flow by means of a sensor plate and into a corresponding pneumatic one

Control signal for controlling the air extraction can be implemented. Both the opening and the closing of the air extraction are preferably carried out using small, but previously defined (adjustable) servo forces. The invention enables a valuable additional contribution to the safety of silo systems due to a completely unexpected, new mode of operation. Advantageously, the control means for the air extraction are also designed to act as safety elements (safety valves) which open and close again automatically in the event of pressure deviations in both directions: if an unforeseen reduction in pressure occurs in the silo cell concerned, both Development of an undesirable negative pressure, as well as an undesirable excess pressure in the cell, the corresponding pressure equalization can be easily established via the aspiration.

Apart from explosions which are triggered directly inside the silo (e.g. by welding), a whole chain of weaker individual explosions is frequently also found in known silo systems, which are to be seen as a precursor to actual large explosions in large cells. These weaker individual explosions in turn find their nutrient medium vial in the dust lying around and whirled up by the first pressure wave. It is precisely here that the invention leads to the fact that at least some of the dust sources are removed, in that the control means in the air suction are simultaneously effective in that both negative pressure and positive pressure in the cell can be reduced via the aspiration. For example, by means of suitable constructive training, e.g. in the manner of a "swing door" that can be opened on both sides, the way between the inside of the silo and the aspiration can be cleared easily and quickly.

The way for the dusty air is in this way both during the operation of the pneumatic conveyor tion, as well as during the breaks in operation, namely directly from the cell into the aspiration and into a filter system, where the air is freed of dust.

In prior art processes, a pressure flow caused by rapid product movements often did that

Escape of a noticeable amount of dust air by lifting the cell access cover or through other leaks. However, it is precisely these faults that can be eliminated with the invention, so that the space outside the silo cell always remains clean. The invention also leads to the fact that the risk of incorrect manipulation with the manual control is lower in the case of service work.

Compared to previously used principles, namely not to save on aspiration or ventilation of the silo cells, in order to achieve a more complete elimination of the dust air and an increase in safety in this way with somewhat oversized aspiration or with a lot of false air, the new invention brings a considerable advantage increased economy. When using the method according to the invention, it is possible, without further ado, to reduce the false air of the cells, in which no product is pneumatically fed in at the given time, to 10 to 50% of the values without control in an extreme case, without any loss of Operational safety occurs. The method according to the invention can preferably be used with a group of silo cells, at least for larger pneumatic conveying capacities, the silo being fed via pipe switches from a pneumatic conveying system optionally to a silo cell from a group of silo cells and each of the silo cells in question via controllable aspiration flaps with a common one Aspiration is connectable: Advantageously, the (pre- preferably pneumatic) control signal via servo means or via the aspiration flap to connect or interrupt the connection of the silo cell with the aspiration, the entire control system for air extraction of each silo cell working autonomously. In this embodiment, the connection between all silo cells and the aspiration is interrupted as soon as the pneumatic system is out of operation. However, since the aspiration flaps are simultaneously active as a safety system, safety is also provided for the aspiration and the ventilator. Regardless of the operating state, fires, glowing parts etc. can be prevented from being transmitted from cell to cell via the aspiration.

The invention further relates to an aspiration flap which is particularly suitable for carrying out a method according to the invention, preferably assigned to each silo cell from a group of silo cells and connected to a common aspiration and depending on either via pipe switches or the ¬ same switchable feed pneumatics is controllable. According to the invention, the aspiration flap can be controlled via servo means and at the same time is designed as a pressure safety flap for the associated silo cell. So far, the structural design of the aspiration flaps has been particularly unsatisfactory, be it that mechanical faults continuously occurred or that an overly complex control system became necessary. In the area of silo systems for mill products or other food or feedstuffs, there was even a tendency to avoid electrically operated elements and lines for electric current as far as possible, which in turn resulted in the concept of known aspiration controls, for example from the relevant pipe switches , not a satisfactory solution

allowed.

Surprisingly, it was found that the formation of an aspiration flap according to the invention made it possible to make significant progress in solving the entire problem area ⁿ silo ventilation ^π shown.

The aspiration flap according to the invention thus becomes a central element of the entire air system of a silo system. A particularly functionally reliable embodiment of the device according to the invention is obtained if a sensing plate associated with the supply pneumatics is provided for sensing the conveying air and for generating a corresponding control signal for the servo means. In this case, the sensing plate is expediently designed to be pivotable via a swivel arm and assigned to a pipe end leading into the silo cell of the supply pneumatics, so that the opening of the pipe end is released or closed by the swiveling movement and the sensing plate is thereby released by a low restoring force, e.g. by a spring, is pressed into the closed position.

The pneumatic servo means advantageously have a pneumatic valve which can be actuated by the swivel arm of the sensing plate. A very simple construction is obtained if the pneumatic servo means have a logic element, preferably a negation element, and a double-acting pneumatic cylinder, so that the aspiration flap which can be actuated by the pneumatic cylinder can be moved with compressed air in both directions.

The play of forces that acts on the aspiration valve is manageable, so that the entire device Specific states (overpressure or underpressure in the silo) can be set and can thus be easily adapted to the respective requirements of each specific system.

The switching point of the pneumatic valve is preferably set to only a small path of the swivel arm, which is of the order of mm, in order to trigger the full opening of the aspiration flap even with only a small air flow in the pneumatic delivery line.

Advantageously, the closing pressure for the aspiration flap can also be preselected to a certain value such that when a corresponding overpressure in the interior of the silo or a corresponding force on the aspiration flap is exceeded, the latter opens automatically. It has also proven to be very expedient if the aspiration flap is assigned a pressure safety plate that opens against its own weight. With regard to simple manufacture and assembly, it is very expedient if all elements of the aspiration flap, the control and the pressure safety flap are combined as a construction ji-ippe on a common support plate. It is also advantageous if the assembly is combined with a cell entry cover. It is advisable to fasten the manhole cover so that it is airtight and dust-tight, so that if only a slight excess pressure occurs, the lid is not immediately lifted and dust can escape from the cell in question, so that the aspiration actually does flap fully functional -

The pressure safety flap can advantageously also be controlled via signals other than those described. l, for example via a limit switch in the area of a pipe switch or via an elevator which automatically emits the signal for opening the aspiration flap when it is started up. This can be particularly important for existing systems, since elevators require very little energy, but produce a lot of dust-laden air and are relatively often the source of interference for fires. The solution according to the invention therefore proves to be particularly useful here, as it generally prevents a fire from spreading into other cells. Several aspiration flaps according to the invention can also be easily attached to a silo cell into which several pneumatics open.

5 Brief description of the drawing

The invention is explained in more detail below in principle on the basis of the drawing. Show it:

FIG. 1 shows a section through an aspiration device according to the invention;

Figure 2 shows the circuit diagram for the device of Figure 1;

5 Figure 3 is a schematic representation of a silo with pneumatic Prou.u _-. T conveying and air extraction according to the invention.

In the illustration in FIG. 3, the product from 0 manufacturing containers 1 is fed into silo cells 8, 9, 10 and 11 via locks 2, a pneumatic conveying line 3 and also via pipe switches 4, 5, 6 and 7. These silo cells are then transformed into a suitable conveyor,

n. ^J 'fl for example, a chain conveyor 12 or a tubular screw, weighing or other treatment. Each silo cell has an aspiration flap, which is connected as a unit 13, 14, 15 or 16 directly to a common aspiration or aspiration line 17, which in turn cleans the central filter system 19 via a fan 18 * Releases air back into the open.

The details of the assemblies 13, 14, 15 and 16 and the aspiration flaps are shown in FIG. 1 and the pneumatic circuit diagram used for this is shown in FIG. 2: In FIG. 1 and FIG. 2, only the end of the delivery line 20 is shown, that directly into the interior of the respective silo cell 8, 9, 10 or 11 (Figure 1, Figure 3) opens. This delivery line end 20 is closed in the position shown in FIGS. 1 and 2 by a sensor plate 21, so that no product delivery can take place. The sensing plate 21 is fixedly attached to a swivel arm 22 with bolts 23 (FIG. 1). The swivel arm 22, which works with the sensing plate 21 in the dust air, is guided by a rubber membrane 24 (FIG. 1) into a housing 25, in which it is pivotably articulated with a ball bearing 26 in a bushing 27 on the housing 25. The swivel arm 22 is extended beyond the ball bearing 26 by means of a shift lever 28, at the outer end of which a tension spring 29 engages, which is also fastened to the housing 25 via an adjusting screw 30 and a bracket 31. The closing force of the sensing plate 21 can be adjusted by a suitable choice of the tension spring 29 and the tension of the adjusting screw 30, depending on the specific operating conditions. The force of the tension spring 29 must be so great that it compensates for the weight of the sensing plate 21 and a small one Residual contact pressure remains in order to really keep the sensing plate 21 closed when there is no pneumatic transport. The movement of the sensing plate 21 is controlled by the air flow of the conveying air. Even if the sensing plate 21 supports the function of the pipe switches 4, 5, 6 and 7, since the unused delivery line end 20 is additionally closed by means of the sensing plate 21, the central importance of the device lies in the fact that the air flow is pneumatic Signal is derived, which controls the air extraction via servo means. The mechanical-pneumatic control signal is generated by the sensor plate 21, the swivel arm 22, a switch contact 32 and a pneumatic valve 33 and controls a pneumatic cylinder 35 together with a negation element 34. The switch contact 32 is in the closed position of the sensor plate 21 in the pressed-in position and gives compressed air via a pressure line 36 and 37 to a control connection 38 of the negation element 34 and to the lower side of the pneumatic cylinder 35 _. * so that the piston rod 39 of the pneumatic cylinder 35 remains in the raised position. A second connecting line 40 leads from the compressed air line 37 to a second control connection 40 'of the negation element 34. The pneumatic valve 33 is set in such a way that the valve 33 is switched over a short distance (in the order of magnitude of mm). The setting is normally carried out in such a way that the pressure in the control line 38 is interrupted at a gap "A" (point 1) of a few mm, so that the pressure drops both at the negation element 34 and at the lower pressure connection 38 '. The negation element 34 is switched over simultaneously. The desired displacement pressure is immediately set at the pressure connection and the piston rod 39 moves together with an aspirator. tion flap 42 down (arrow B-Figure 1) in the open position. In this way, with a minimal air movement in the delivery line end 20, an arbitrarily large or adjustable force is delivered to the aspiration flap via the pneumatic cylinder ^* 35. Because the piston rod 39 is clamped between two defined forces, when the pressure falls below a certain pressure inside the silo cell 8 or 9 or 10 or 1.1, the aspiration flap 42 can be pulled down and opened even when the sensor flap 21 is closed, if, for example large quantities of product collapse inside the silo.

The aspiration flap 42 (FIG. 1) consists of a support ring 43, a rubber seal 44 and a fastening ring 45, which together form the main body of the aspiration flap 42. These four individual parts (piston rod 39, support ring 43, rubber seal 44 and fastening ring 45) are screwed together rigidly. The overpressure safety device 46, on the other hand, is freely displaceable relative to the piston rod 39 and rests on the rubber seal 44. The support ring 43 is connected to the piston rod by four spokes 47, so that essentially the entire inner annular surface of the support ring 43 or the rubber seal 44 is closed only by the overpressure protection. If a pressure deviation of a predetermined amount now occurs in the interior of the silo body 8 or 9 or 10 or 11, the overpressure protection device 46, which rests on the rubber seal 44 only by its own weight, is lifted off and thus the Released from the interior of the silo through the aspiration line 17.

With the shown, surprisingly simple solution according to the invention, it has been possible to create a completely autonomous unit with additionally autonomously functioning basic elements (sensing plate, low pressure safety, high pressure safety). unit), which is also robust and can be created with only small investment costs. Only compressed air has to be connected as the only energy source, after which the aspiration flap is immediately ready for operation. The whole is expediently screwed tightly as a closed structural unit, for example onto a cell entry grate 50, which at the same time also carries the manhole cover.

In individual cases, e.g. if the product feed via an elevator instead of pneumatic conveying 3 __. is given, however, the pneumatic control signal can also be taken off directly by corresponding switch contacts on the elec- tor. The aspiration flap then maintains at least a partially autonomous function. It is advantageous if the conversion of the electrical signal into a pneumatic signal is carried out at a point that lies outside each danger zone.

Claims

1. Method for securing the air extraction from silo cells (8-11) with mill products or other pourable foods, with pneumatic

15 sher product feed, thereby ensuring that a control signal is derived from the air flow of the conveying air and is used via servo means (33-35) to control the air extraction.

20th

2. The method according to claim 1, characterized gekenn¬ characterized in that the control signal is formed as a mechanical-pneumatic signal.

25 3. The method according to claim 1 or 2, characterized ^ that the control signal is derived from the För¬ derluft via a sensing plate (21).

4. The method according to any one of claims 1 to

30 3, characterized in that the opening and closing of the air suction using small preselectable

35 Servo forces is made.

5. The method according to any one of claims 1 to 4, da¬ characterized in that the control means for air suction open or close again in both directions when a predetermined pressure deviation to the internal silo pressure in the relevant silo cell occurs.

6. The method according to claim 1, in which the silo is fed via pipe switches from a pneumatic conveying system either to a silo cell from a group of silo cells and each silo cell can be connected to a common aspiration via controllable aspiration flaps, characterized in that the control ¬ signal via servo means (33-35) or via the aspiration flap (42) establishes or interrupts the connection of the respective silo cell (8; 9; 10; 11) to the aspiration (17), the entire control system of the Air extraction of each individual silo cell (8; 9; 1 * 0; 11) works on its own.

7. Aspiration flap, in particular for performing a method according to one of claims 1 to 6, which is connected to a common aspiration and can be controlled via a feed pneumatics which can be optionally switched on via pipe switches or the like, characterized in that the aspiration flap (42) Controllable via servo means (33-35) and at the same time designed as a pressure safety flap (43-47) for the silo cell (8; 9; 10; 11) in question.

8. Aspiration flap according to claim 7, characterized in that the servo means (33-35) are designed as pneumatically active servo means. - 16 -

9. Aspiration flap according to claim 7 or 8, da¬ characterized in that a sensing plate (21) is provided for sensing the conveying air and for generating a corresponding control signal for the servo means (33-35).

10. Aspiration flap according to claim 9, characterized ge indicates that the sensing plate (21) via a swivel arm (22) is designed to be pivotable and a pipe end (20) of the supply pneumatics (3) leading into the respective silo cell (8, 9, 10, 11) ) is assigned, whereby the opening of the tube end (2) can be released or closed by the pivoting movement, and that the sensing plate (21) is pressed into its closed position by a slight restoring force.

11. Aspiration flap according to claim 10, characterized ge indicates that the pneumatic servo means (33-35) have a through the swivel arm (22) of the sensing plate (21) be¬ operable pneumatic valve (33).

12. Aspiration flap according to claim 11, characterized in that the pneumatic servo means (33-35) have a logic element (34) and a double-acting pneumatic cylinder (35), the aspiration flap (42) which can be actuated by the pneumatic cylinder (35) ) can be moved in both directions with compressed air.

13. Aspiration flap according to claim 12, characterized in that the logical element (34) is designed as a negative element.

14. Aspiration flap according to one of claims 11 to 13, characterized in that the switching point of the pneumatic valves (33) can be adjusted in the order of mm on a short path of the swivel arm (22), so that even a small air flow in the pneumatic delivery line (20) already causes the aspiration flap (42) to open fully.

15. Aspiration flap according to one of claims 7 to 14, characterized in that the closing pressure for the aspiration flap (42) can be preset such that when a preselectable vacuum in the interior of the silo or a corresponding force on the aspiration flap (42) is exceeded opens automatically.

16. Aspiration flap according to one of claims 7 to 15, characterized in that the aspiration flap (42) is assigned a pressure safety plate (46) which opens against its own weight.

17. Aspiration flap according to one of claims 7 to 16, characterized in that all parts of the aspiration flap (42), the control and the pressure safety plate are designed as an assembly.

18. Aspiration flap according to claim 17, characterized in that the assembly is combined with a cell entry grate (50).

.