The present invention concerns a filter con¬ struction as defined in the preamble to Claim 1. Powdery and granular substances are mainly transported with the aid of a carrying gas, such as air, in various industrial branches. The mass is trans¬ ported at comparatively high velocity, between 5 and 40 m/s, whereby the gas content of the mixture that is being moved can be kept fairly low and mass is trans¬ ported with good efficiency. At the end of transporta¬ tion the mass and the gas which transported it are separated, employing a filter structure in which the gas flows through the filter while the mass remains e.g. in a container under the filter, such as a storage silo.

Sine one filter construction is required in conjunction with every intermediate storage container, small though it be, endeavors are to make the filters as small in size as possible and occupying a minimum of space. However, filtration takes place with greater efficiency the larger that area which the gas traverses without letting any mass pass through. For this reason, a great number of filtering elements closely adjacent to each other are used, such as fabrics, which are shaken time and again to clean them. Owing to the nar¬ row gaps, however, the filters tend to become clogged, since in existing filter constructions the mass which is being transported, together with its transporting gas, discharges at the high transport velocity direct¬ ly from the input duct into the vicinity of the filter¬ ing surfaces, and this causes powerful dusting and turbulence of the mass in the vicinity of the filtering surfaces and in the narrow spaces therebetween. More- over, such turbulence frequently raises into the filter such mass which was already deposited in the storage container, thereby increasing the need of filter

cleaning. Also as a result of powerful turbulence the storage containers fill up non-uniformly and therefore their full volumetric capacity cannot be utilized in every instance. The object of the invention is to eliminate the drawbacks mentioned. Specifically, the object of the invention is to disclose a novel filter construc¬ tion in which the mass flow can be made to go substan¬ tially straight from the input duct to the storage con- tainer so that it cannot clog the narrow-spaced struc¬ tures of the filter.

Regarding the features which are characterist¬ ic of the invention, reference is made to the claims section. The filter construction of the invention for separating the mass being transported from the gas transporting it comprises an inlet passage, a gas ex¬ haust passage and a filter placed in the gas flow be¬ tween said passages, and a preseparation chamber having a flow cross section area substantially greater than that of the inlet passage, and into which the inlet passage opens. As taught by the invention, the filter and the preseparation chamber constitute an upright one-within-the-other structure presenting around a tub- ular preseparation chamber, a vertical annular filter, the inlet passage opening into said preseparation cham¬ ber in the region of the filter's upper part, and the mass and gas flowing downward in the preseparation chamber down to the level of the filter's initial, or lower, end, where they separate into a substantially downward directed mass flow and a gas flow directed upward and through the filter.

Since the preseparation chamber terminates close to the lower end of the filter, the mixture that has run down from the preseparation chamber becomes divided into two parts, the mass being transported con¬ tinuing its downward course into the storage volume and

the transporting gas turning upward to go out through the filter. In this way, the preseparation chamber and the filter constitute a one-in-the-other, compact con¬ struction which, consuming little space, is easy to place in any location where it has to be used. Advan¬ tageously, when the annular filter is encircling the preseparation chamber, i.e., when the two are concen¬ tric and symmetrical with reference to their common vertical central axis, the flows from the preseparation chamber will distribute uniformly over the entire areas of the filter's filtering surfaces. Likewise, one achieves in this instance uniform flow of the mass into the centre of the storage volume, whereby this volume can be filled to full capacity. Advantageously, a preseparation cyclone is provided in the preseparation chamber, the inlet pas¬ sage being connected thereto tangentially so that the mass and gas flow will rotate strongly owing to the powerful flow, and the centrifugal force thus produced will separate the mass and the gas. Thus, a large frac¬ tion of the mass will flow rather placidly through the cyclone into the storage container, while the gas moves through the filters and out of the system.

Various types of filter known in themselves from various connections can be used in the filter con¬ struction. There may for instance be several tubular filter cassettes, plate-like filter constructions, or gas-permeable surfaces disposed in some other way which inhibit the passage through them of powdery and granu- lar masses.

Advantageously, the preseparation chamber ex¬ tends in the centre of the filter to greater height than the filters, in which case the inlet passage com¬ municates with the preseparation chamber above the fil- ters. It is also conceivable that the preseparation chamber and the filters have the same height, in which case the inlet passage may pass through the upper part

of the filters to the preseparation chamber. In this way the overall height of the filter construction can be minimized.

The advantage of the filter construction of the invention over the state of art is that the mass which is being transported does not raise dust nor is it turbulent, and it will not clog the filtering sur¬ faces in such degree as is encountered in existing filter constructions, and therefore the construction of the invention operates more positively and more effi¬ ciently, having a greater life span and requiring less maintenance. With its aid is also prevented the ascent of mass from the storage silo back to the filter, and filling of the storage silo to full capacity is render- ed possible. Furthermore, the construction of the in¬ vention enables an exceedingly small and compact filter to be built and which can be disposed in small and cramped spaces on top of the storage silos and equival¬ ent, thus reducing the required height of any surround- ing protective buildings.

In the following the invention is described in detail with reference to the attached drawings, wherein Fig. 1 presents, partly sectioned, a filter construc¬ tion according to the invention, and Fig. 2 presents, partly sectioned, another filter con¬ struction according to the invention.

In the embodiment depicted in Fig. 1 the fil¬ ter construction is located above the container 9, into which one intends to transport mass. The filter con- struction comprises an inlet passage 1 terminating in the upper part of the filter construction, where it joins the vertical, tubular preseparation chamber 4, which has a flow cross section area substantially larg¬ er than that of the inlet passage 1. Encircling the preseparation chamber 4, a space having annular cross section is provided, in which a plurality of tubular filter cassettes 3 have

been disposed. These are open on their underside, that is at the initial end 8 of the filter, and they come together at the upper end of the filter construction to form the exhaust passage 2. The filter construction of Fig. 1 operates as follows. A mixture of gas and mass to be transported is blown in through the inlet passage 1 at high velocity. Usually air is used to serve as transporting gas. The mixture is discharged into the preseparation chamber 4, and since the flow cross section of the preseparation chamber is substantially superior to that of the inlet passage, the flow velocity of the mixture is consider¬ ably reduced. Since the inlet passage opens substan¬ tially at right angles onto the upper end of the pre- separation chamber 4, the flowing mixture will not dis¬ charge downward with high speed: after hitting the wall of the chamber, it becomes turbulent and comes to rest at the upper end of the chamber.

Hereby the mass which is being transported, and the air transporting it, running down in the pre¬ separation chamber 4 mainly by effect of gravity, are pacified and move in a downward direction. At the bot¬ tom end of the preseparation chamber the mass, for the greater part, continues to travel in the same direction and runs into the container 9, while only part of the mass will go along with the air flow to the initial end 8 of the filter, and thence to the filters 3.

Since the filters 3 pass air exclusively, the air that has served as carrier gets out through the exhaust passage 2, while the mass which followed along is retained in the filters 3, from which it can be shaken down into the container 9 time and again by means of apparatus and procedures previously known in themselves, which are not more closely described in this context.

Fig. 2 shows another embodiment of the inven¬ tion, this embodiment being otherwise like that of

Fig. 1, except that to the preseparation chamber 4 a preseparation cyclone 5 has been added.

The preseparation cyclone 5 consists of a tub¬ ular construction of substantially equal height as the preseparation chamber 4 and having a cylindrical upper part 10 and a downward tapering, conical lower part 11. In addition, to the upper rim of the cylindrical upper part has been attached an inward extending guide cone 12 and an inner cylinder 13, the latter extending down- ward from the lower rim of the guide cone. Hereby, an intermediate space 6 is defined between the cylindrical upper part 10 and the inner cylinder 13, the inlet pas¬ sage 1 opening tangentially into this space. Further¬ more, a flow passage 7 is defined between the shell of the preseparation chamber 4 and the shell of the pre¬ separation cyclone 5.

The filter construction of Fig. 2 operates as follows. As the mass/air mixture discharges from the inlet passage 1 with high velocity tangentially into the annular intermediate space, the mixture rotates in the intermediate space, beginning at the same time to descend under gravity effect. Owing to the centrifugal force, mass and air are substantially separated, i.e., the mass closer to the shell runs downward and the air, finding itself in the centre of the separation cyclone, is free to flow upward inside the inner cylinder 13. Thus while the mass runs freely and placidly down and through the conical lower part 11 into the container 9, the air which served as carrier fluid flows through the inner cylinder 13 and through the guide cone 12 and down along the flow passage 7, towards the initial end 8 of the filter. Here, the air flow can turn without obstruction into the filters 3, while the mass runs down into the container 9, through the centre of the air flow. Cross flows of mass and air flow are thus avoided at the lower end of the filter, which would occur if mass and air were to flow together downward

in one cyclone, although such a construction is still conceivable within the scope of the inventive idea of the present invention, and which construction also represents a significant improvement over any filter constructions known in the art.

In the foregoing the invention has been de¬ scribed by way of example with the aid of the attached drawings, while different embodiments of the invention are feasible within the scope of the inventive idea delimited by the claims.