NO149761B - FILTERING DEVICE WITH A CONTINUOUS UNDER PRESSURE AND PRESSURE WORKING FILTERING DEVICE - Google Patents

Abstract

1. A filtering apparatus having a filtering device operating under gage pressure and vacuum, comprising a layer of filtering material e.g. a filter cloth for extracting solid particles from liquids, characterized in that the filtering device is a vacuum-filtering device (10, 20, 40), and in that the whole vacuum-filtering device (10, 20, 40) including the bearings, the driving system, the controls and the like is placed in a gage pressure space (11) to which the operators have access, which is under gage pressure and which is shut off from the outside atmosphere.

Description

The invention relates to a filtering arrangement

of the kind specified in the introduction to patent claim 1.

It is common knowledge that the residual moisture value that is possible to achieve by vacuum filtration depends

ig of the pressure difference between the atmospheric pressure and the relevant vapor pressure in the liquid from which the solid material or materials are to be separated. Even by extending the suction time under conditions of maximum pressure difference, only such an insignificant reduction in residual moisture can be achieved that the costs for the necessary extra energy consumption become disproportionately high. The flowing air must constantly suck

es out using vacuum pumps. In addition, the throughput decreases with increasing suction time. It would there-

because there would have been a need for a very expensive apparatus-technical device if the vacuum filter should have been operated with very long suction periods.

Attempts have already been made to implement

a further dewatering of the separated solid material(s) by using pressure filters. With such a device, one or more of the filter's structural parts, e.g.

a drum or disc, which carries the filter medium, placed in a pressure vessel. Thereby, the achievable differential pressure can be set to the maximum container pressure. However-

over time, this construction has the palpable disadvantage that the costs for the equipment technical consumption when switching to a pressure vessel construction rises to many times what pure vacuum filtration costs. As a guide value for sli-

ke pressure vessel constructions, a cost increase is indicated

at three or four times the normal.

It is admittedly possible with pressure filtration and likewise with combined filtration to achieve significantly lower residual moisture values than with pure vacuum filtration. However, the necessary equipment consumption and the accompanying high costs are unacceptable. In addition, for many purposes, e.g. in the filtration of ore, coal, etc., only a rather small improvement in the residual moisture value would have been fully sufficient to meet the necessary conditions for the further processing of the separated solid material. Such a reduction of the residual moisture just opposite the value which is in itself limited by the pressure difference between the atmospheric pressure and the vapor pressure of the liquid, would thus represent a significant economic advantage.

The invention therefore aims to create a filtration device of the kind indicated at the outset, where without the technical consumption required for pressure filtration, a significant reduction of the residual moisture can be achieved beyond the value, which in and of itself is limited by vacuum filtration through the difference in pressure between the atmospheric pressure and the current vapor pressure.

According to the invention, this can be achieved by the filtering device being designed in accordance with the characterizing part of patent claim 1. The positive pressure chamber can be advantageously over a sluice device. connected to a discharge chamber, which is preferably arranged to be able to maintain a pressure higher or lower than the atmospheric pressure, in which discharge chamber the filter cake can be taken out of the overpressure chamber. However, the discharge chamber can also be kept at atmospheric pressure. Appropriate measures can then be taken to ensure that the differential pressure between the overpressure chamber and the discharge chamber is ii. the area from approx. 1 to 2 bars. For many applications, a differential pressure between the overpressure chamber and the discharge chamber of approx. 1.5 to 1.8 bar. Such an increase in the differential pressure will, especially in the case of a large number of high-tech application possibilities, lead to perfectly satisfactory results, respectively products.

In the case of similarly large filter systems, the over-pressure room can preferably be an occupied room in a mine.

In connection with such an advantageous embodiment of the invention, it is expedient that the overpressure room against the free atmosphere has a sluice chamber with a pressure equalization device and intended to be used by operating and control personnel, also when the vacuum filter is in operation. If, in order to clarify the relationship, one takes into account that a pressure of 1.5 bar absolutely corresponds to an immersion depth of approx. 5 metres, it should be clear that at least a temporary stay in the pressurized room during any maintenance or control work should not expose the operating staff to health problems.

Depending on the technical design of the device and the size of the vacuum filter in question, it may also be advantageous for the overpressure chamber to be designed as a cell that encloses the vacuum filter with little clearance. In order to ensure easy access to the filter device, such a device may preferably have an opening, which can be closed pressure-tight with a lid, above the vacuum filter.

The lid over the filter can, for example, consist of a steel or tin dome, while the walls are made of steel or reinforced concrete.

With the device according to the invention, the feeding of the filter can be done without difficulty by means of pumps, which are dimensioned in such a way with respect to transport height that the overpressure in the overpressure room is taken into account.

A continuous discharge of the solid material can be carried out using ordinary devices such as a discharge screw, a cell wheel sluice etc. 1..

The device according to the invention can in principle and with advantage also be operated without an overpressure being produced, namely in cases when elevated residual moisture values can be tolerated. Alternatively, the filter can also be temporarily or continuously operated only with excess pressure, i.e.

without suction effect.

According to the invention, the significant advantage can be achieved that a significant reduction of the residual moisture in the solid material can be achieved with only a relatively insignificant increase in supply beyond the classic vacuum filtration. The reduced residual moisture value, which can be achieved according to the invention, can also be achieved by using relatively short suction periods.

In accordance with a further advantageous further development of the invention, measures have been taken to ensure that the discharge space is kept at a higher pressure than atmospheric. A device can then preferably be used, which is characterized by the fact that the pressure difference between the overpressure chamber and the discharge chamber in a mine tunnel under the ground can be set just up to a maximum value, which can be selected exclusively on the basis of the requirements the current filtration problem may have. A particularly preferred embodiment in this context involves the filter, which is structurally designed as a vacuum filter, during coal or ore extraction and processing being arranged in a cavity, which is located underground inside an extraction shaft. Belt filters are particularly suitable for such applications.

An alternative preferred embodiment of the invention consists in the discharge space being kept at a lower pressure than atmospheric.

Thus, in accordance with the most essential principle of the invention, with the intention of achieving a significantly simpler construction method and thereby a significantly more economical device than with classic filtering devices, the entire filtering device, including the bearings, which are common with rotary filters, and operation, placed in an overpressure chamber, the available discharge chamber being optionally kept at either atmospheric pressure or a pressure above or below atmospheric.

In the case of a filtering device, which is, for example, placed underground in a mine tunnel, stable walls are thus available, so that the overpressure is practically neither limited to cake formation nor to drying suction.

With such a device, especially in ore and coal extraction as well as in the processing of such raw materials, extremely strong economic advantages will be achieved precisely because the filtering process can be carried out at the extraction site, so that one does not have to pump large quantities of material up to the earth's surface, i.e. often over significant altitude distances. The majority of the mentioned quantities of material often have to be brought back underground at a later stage. For example, in the case of ore extraction, particularly when extracting precious metals, a large part of the processing process can be carried out underground at the extraction site. In this way, extremely large savings opportunities arise, as the unproductive transport of waste materials is eliminated to the greatest extent possible.

Furthermore, the invention can also be used, for example, in paper production, respectively in the processing of starting materials, which will entail major advantages.

While in the past filtering devices were used to a large extent, where a downpipe system or a so-called "barometer foot" was connected, the problems that used to arise with such facilities can now be overcome to a large extent with the help of the invention under a strong apparatus-technical simplification. With a device according to the invention, in particular, the achievable negative pressure for cake formation and for drying suction is no longer absolutely limited by the steam pressure. In contrast, the excess pressure can be set in accordance with

the prevailing requirements.

Furthermore, with such installations, it has proven disruptive that the drying suction air is carried away with the filtrate and thus reduces the apparent specific weight of the filtrate due to entrained and trapped air. This was the reason why the usable negative pressure at such facilities was often reduced to a few meters of water column. By using the invention, however, drying suction air and filtrate can be removed and collected separately.

According to the invention, the desired pressure differences can be set independently of each other.

According to the invention, the previously constantly occurring problem when starting the filter also disappears.

While in previous installations it was highly problematic to "dimension the downpipe", as there existed a relationship of dependence between this and the filtering properties of the fiber mat, according to the invention, correspondingly large filtrate and air discharge pipes can be used, which thereby show little play. Furthermore, the arrangement can -g the invention takes place at a desired level, as it is no longer necessary to set up at a relatively high height above the ground as was required with the classic set-up. The previously existing problems with the high-lying set-up disappear according to the invention, because it here no downpipe must be used as a "barometric foot".

The invention is described in more detail in the following in connection with embodiments shown in the drawings, where: Fig. 1 shows a schematic perspective view of the filtering device according to the invention in connection with an overpressure chamber, which can be moved, and various additional devices. Fig. 2 shows a preferred embodiment of the invention, where a band filter is used in a mine passage. Fig. 3 shows as a comparison a traditional filtering device with downpipe, and

fig. 4 schematically shows a filtering device for the same purpose of use as the one in fig. 3 shown, traditional filtering device.

In accordance with the drawings there is

an overpressure room 11, which can be occupied by operating and supervisory personnel. A vacuum filter 10 is arranged in the overpressure chamber, which is illustrated purely schematically in the form of a disc filter. However, it should be noted that, in principle, another rotating filter or a vacuum filter of any other kind can also be used.

The supply of the 'sludge' can take place in the usual way and is therefore not shown in detail on the drawings. Nor do the further technical details of the vacuum filter 10 require further illustration or explanation, as all well-known constructions are suitable for use with the device according to the invention.

A sluice device 12, which is schematically shown in the drawings in the form of a cell wheel sluice, serves to lead the solid material separated by the disc filter out of the overpressure chamber 11 into the free atmosphere in the direction of the arrows. Instead of the cell wheel lock shown, a transport auger or another similar device could of course also have been used.

The overpressure chamber 11 can be accessed by operating and/or supervisory personnel via a sluice chamber 13, which thus forms both an entrance and exit for the overpressure chamber 11. A (not shown) pressure equalization device is suitably arranged in the sluice chamber 13.

In order to produce the desired overpressure in the overpressure chamber 11, an air compressor 14 is arranged, which is also shown purely schematically. According to fig. 1, compressed air is blown through the air compressor 14 into the overpressure chamber 11 in the direction of the arrow, until the desired overpressure for the relevant use case is reached. With the aid of the air compressor 14, equalization must of course also be carried out for pressure loss, which occurs in the area of the sluice device 12 during the discharge of the solid material and when using the sluice chamber 13.

In many application cases, it may be appropriate to design the overpressure room 11 in the form of a mine with the walls made of reinforced concrete. Especially in large-scale technical applications such as processing of ore or coal, etc., the shown embodiment of the device according to the invention has proven particularly advantageous, as the device technical savings made possible according to the invention in such cases can be extremely large.

Fig. 2 shows a case of use for the device according to the invention, where between two stone layers 29

in an underground mine passage, a belt filter 20 is arranged. With the help of a pressure-resistant wall 29' between the two mentioned rock layers 29, a closed pressure chamber is formed, which with the help of

a compressed air supply'- 26 can easily • be put under a pre-extension; - adjusted or desired overpressure: ' '■ In the 'pressure-resistant wall 29', a double lock 27: is preferably placed. Through the pressure-resistant wall 29, not only pressure air is blown into the pressure chamber, but also the sludge or suspension 25 s'k'j is through the wall', namely for the delivery of suspension ions on top of the band filter: 20 .' The filter cake 21, which forms on the band filter, is shown in Fig. 2 is thrown by the filter belt in the right part of the band filter 20 and ends up on a conveyor belt 22, which is preferably adjustable both in the lateral direction and with regard to the slope. From" the conveyor belt.;

22, the solid materials end up in a pile 24 in the right part of fig. 2. •' - - ' ' '

From a filter collection box' 23, which is "placed above the filter belt, air and filtrate are led through a common discharge pipe '28 away from the belt filter 20 and out through the pressure-resistant wall' 29'. '■" -<:>

Using the device shown in fig.

2, relatively large quantities of starting material can be processed without transport up to the earth's surface and back to the site itself, so that only an almost negligible part of the material quantities must be transported up to the earth's surface, namely the proportion of the output material that e r bé-free from waste substances and which is already highly enriched • ■■ with one' noble metal 1 e . 1.. - - •■ " '• ■'•, -'•••-"'■ -' In order to highlight the advantages that can be achieved with innovation, in fig. 3 a t-radius is shown j;o'nelt filter plant for comparison".--The-t: kjéntev plant- includes"-' supports: 37', s ' 37 ' , - which- in' 'a considerable' height above the ground carries: a platform 36 on which a vacuum filter 30 rests. The high height of the vacuum filter ~ 30;- installation- skyidé- a-t f il- ":" funnel tube -31- above etj control head 32- and especially above' a down pipe.'- < - 33 is led down into a filtrate collection basin 35. The down pipe "33", which is also referred to as "barometric foot", serves to produce an equivalent negative pressure in the filter tubes 31 for the vacuum filter 30. The liquid mirror in the f-iitertraugét■ 34f- ;is in ' -''''- '<: >fig.' 3 denoted by 3 8. • ' It should be' obvious that; a;;siik high lying-

the arrangement of the vacuum filter' 30 entails 'one row - koh-:; ~ ■-' structive problems. In addition, as explained above, significant problems will arise when starting the filter

in such facilities. In addition, the dimensioning of the down pipe is problematic, as there is a dependency between this and the filtering properties of the fiber fleece. As the dry suction air is also carried away together with the filtrate, the apparent specific weight of the filtrate decreases due to the trapped and entrained air in the filtrate. This necessarily leads to a reduction in the practically usable negative pressure. <;>i

With such a device, it is finally under<1>

pressure, which the overhead can 'achieve':tif'caking formation , ' abso-!

lye limited by the vapor pressure.

The significant disadvantages associated with the plant according to fig. 3 and which, for some of the most important parts, is discussed in the foregoing, can practically be completely remedied by means of a filtering device according to the invention, which is schematically shown in fig. 4<:>.

According to fig. 4 is the entire filtering device',

which is constructively built up as a vacuum filter and which is designated in its entirety by 40, arranged in an overpressure

room. The schematically illustrated overpressure chamber is denoted

net with 46. Filtrate pipe 41 is connected above a control head 42 - to two outlet lines. Above one control valve 48 for

air, the one outlet line is connected to one gas cyclone 47, which is located outside the overpressure chamber 46 and exhibits --<?>

is a iuft outlet 47'. The other outlet line, which is equipped with a regulating valve 49 for filtrate, is likewise connected outside the overpressure chamber 46 to a collection basin 45 for filtrate. i ■ ■■ ■ l-The solid materials can be carried away :f;ra"''bvér-pressure chamber 46 through a filtrate outlet 43. A filter trough 44, like the other structural parts, is shown -purely schematically'in Fig. 4. , .. • .•• i v - ' j- r.

Overpressure to! kakadahnélse på'vacuumf ilteret-

40 can according to the schematic visté^^-noTdrtin-g-^i^f-ig'-. 4 is set in the desired way by a (not shown) ■ Itff-tförsél and is neither limited to cake formation nor to dry suction. The dry suction air and the filtrate can advantageously be removed and collected separately, as already explained above.

The pressure differences are set completely independently of each other.

It should be obvious from fig. 4 that the set-up of the entire device can take place at any desired level, namely what suits everyone best for the relevant requirements for the application.

Correspondingly dimensioned and thereby largely loss-free filtrate and air discharge pipes can also be used without practical limitations with the device according to the invention.

Naturally, the device according to the invention as shown in fig. does not exist either. 4 any difficulties in connection with starting the filter, as is the case, however, with the traditional device according to fig. 3, where a complete column of liquid must first build up in the downpipe before the desired function can be achieved. However, due to trapped air or other disturbing factors, interruptions in the liquid column can easily occur with such a known device, so that the intended suction or extraction effect is cancelled.

In the case of a cellulose filter of the kind, as fig. 4 in schematic form shows an exemplary embodiment of, not only is the advantage achieved that the passages of air and filtrate can be made largely independent of each other, as it also makes it possible that additional air with the desired pressure can be blown through the filtering device. In addition, the solid material in such an embodiment of the device according to the invention is also particularly easy to wash out.

The invention is also in principle suitable for, in the case of a vacuum filter which is for example designed as a rotary filter, to run only a specific zone with the intended overpressure, for example the wet zone, so that a particularly strong cake formation can be achieved. In an alternative embodiment, it is also possible to expose the dry suction zone to the desired excess pressure, so that a particularly low residual moisture is ensured with correspondingly small cake formation. With such devices according to the invention, the achieved effect can only be used in partial areas.

Claims (5)

1. Filtration device with a filter arrangement working continuously under negative and positive pressure, which exhibits a porous material serving as filter material, in particular a filter cloth, for separating solid material from a liquid, characterized in that the filter device is a vacuum filter device (10, 20, 40) and that the entire vacuum filter device (10, 20,40) possibly including storage, drive, control devices etc. is placed in a closed overpressure room (11) - which is accessible to the operating and supervisory staff and which is under overpressure relative to the free atmosphere. 2. Filtration device in accordance with claim 1, characterized in that the overpressure chamber (11) above a sluice device (12) is connected to a discharge chamber, which is preferably arranged to be able to maintain a pressure higher or lower than the atmospheric pressure, in which discharge chamber the filter cake can be taken out of the overpressure chamber (11). 3. Filtration device in accordance with claim 1 or 2, characterized in that the overpressure chamber (Jl) in the direction towards the free atmosphere has a sluice chamber (13) with a pressure equalization device and intended for use by the operating and supervisory staff also when the vacuum filter device (10) is in operation. 4. Filtration device in accordance with one of the claims characterized in that the pressure difference between the overpressure chamber (11) and the discharge chamber is adjustable. 5. Filtration device in accordance with one of the preceding claims, characterized in that the vacuum filter device is designed as a belt filter.