This invention relates to a treatment tank with a horizontal candle filter tray for cleaning liquids and/or gases, in particular in a sulfuric acid tower.

In the production of sulfuric acid, the sulfuric acid is guided in counterflow to a gas stream containing sulfur trioxide through a spray tower (absorber) in which part of the sulfur trioxide is absorbed by the sulfuric acid and thereby increases its concentration. Due to the intensive contact with the acid, the gas velocity and the spray density, the gas absorbs a small amount of acid in the form of fine droplets or mist. For protecting the equipment following the absorber against corrosion and condensate and, in the case of the final absorber, to avoid sulfuric acid emissions, these droplets must be separated as far as possible. For this purpose, filters are installed in the gas outlet of the absorber. Very good separation efficiencies are offered by so-called candle filters, which consist for example of a two-layer, hollow-cylindrical wire mesh with interposed glass wool or the like. The candles are inserted in a candle tray of the filter housing installed on the tower, wherein the candles can be arranged both hanging and also upright. The acid separated flows off along the inner or outer candle wall. It gets back into the tower or can be discharged separately.

In known constructions of candle filter trays, which are fixed at the tower wall along their periphery, high vertical deformations frequently occur in the center of the tray. This is disadvantageous, because the filter candles then are no longer upright. It has been attempted to eliminate this disadvantage by stiffening elements of the tray. However, this requires a considerable expenditure of material. With a tower diameter of about 7 to 10 meters, very strong stiffening elements would be required, for example by a system of main and secondary beams.

From DE-PS 974 661 , for example, a nozzle filter tray for potable and industrial water filtration is known, which consists of perforated and reinforced concrete plates arranged in parallel one beside the other. For stiffening purposes, closely spaced beams of prestressed concrete of single or multiple T cross-section are used, which extend over the entire filter basin and only are supported on the opposite walls thereof and in whose horizontal part uniformly distributed filter nozzles are inserted on both sides of the perpendicular web or webs.

From DE-PS 1 153 346 a filter tray with a closed or open construction is known for cleaning liquids, in particular for rapid and pressure filters, in which to avoid deflections the filter tray consists of at least two horizontal base plates lying one above the other at a distance and provided with through holes, which are frictionally and rigidly connected with each other by filter elements extending between the same.

From DE 23 05 564 C2, a column for contacting liquids and steam with column trays is known, which along their periphery are held by one peripheral bracket each, which in turn is attached to the column wall, wherein each tray includes steam through holes and elongated pans which partly extend above and partly below the active tray surface, are open towards the top and include liquid discharge openings at the pan base. To create a column with trays constructed lighter in weight, it is provided that each tray includes one or more support brackets which extend along a tray diameter and/or along tray chords, and that the pans extend from the peripheral bracket to a support bracket and, in the case of a plurality of support brackets, between the support brackets.

From DE 197 49 617 A1 , a supporting structure for buildings is known, which should provide possibilities for variations and modifications of the division of ceilings and walls during the construction and/or at a later date, in order to be able to realize expansions or reconfigurations in the case of an increased or changed demand of living space or usable space, for which purpose vertical supports are provided, which are connected with each other by means of at least one frame and for which purpose the supporting structure, the roof of the building as well as ceilings and walls are at least partly of the load-bearing type, and for which purpose the supporting structure is configured to absorb tensile forces caused by roof and/or walls and/or ceilings.

It is the object of the present invention to propose a treatment tank as mentioned above, in which a deflection of the candle filter tray is effectively avoided with little effort. This object is solved with the invention by the features of claim 1 , in particular by a vertical central beam, to which the tray, in particular a candle filter tray for holding candle filters, is centrally attached, and by one or more prestressed tension bars ar- ranged below the tray, which extend from the central beam upward-outside at an angle in the direction of the tank wall and are fixed, in particular welded or screwed thereto.

By means of the adjustable prestress of the tension bars, the movement of the central region of the candle filter tray fixed at the outer periphery of the tank wall virtually can be brought to zero, independent of the load. At the same time, relatively little material is required for the candle filter tray construction, so that a proper positioning of the filter candles can be ensured with lower costs.

Preferably, the tension bars are guided up to the tank wall and are fixed thereto.

It is also possible that the tension bars are guided upward-outside at an angle from the central beam in the direction of the tank wall over more than half of the tank radius up to the candle filter tray and are attached to the same.

In a particular configuration, the tension bars can extend upward-outside from the central beam over more than 2/3 of the tank radius in the direction of the tank wall up to the candle filter tray and can be fixed thereto.

For simplicity, the central beam can for example be a commercially available tube.

In accordance with the invention, a plurality of receiving openings are provided in the candle filter tray, in order to receive the candle filters.

In accordance with a development of the invention, the receiving openings are formed by tube sections, wherein ribs preferably are provided between the tube sections, in order to increase the rigidity of the candle filter tray. - A -

Further developments, advantages and possible applications of the invention can be taken from the following description of embodiments and the drawing. All features described and/or illustrated form the subject-matter of the invention per se or in any combination, also independent of their inclusion in the claims or their back-reference.

In the drawing:

Fig. 1 schematically shows an oblique view of a circular sector of a candle filter tray construction including the invention,

Fig. 2 shows a top view of a candle filter tray in accordance with the invention, and

Fig. 3 shows a partial section through the candle filter tray of Fig. 2.

In the candle filter tray construction shown in Fig. 1 , the filter tray 3 is centrally attached to a vertical central beam 1 formed e.g. as tube. One or more prestressed tension bars 2 extend upward-outside at an angle from a point of the central beam 1 located below the candle filter tray 3 in the direction of the tank wall 4 and are attached, e.g. welded or screwed thereto.

Since the candle filter tray itself is fixed to the tank wall 4 along its outer periphery, the tension bars 2 need not be mounted directly to the tank wall 4, but can also extend from the central beam 1 over only more than half or up to more than 2/3 of the tank radius upward-outside in the direction of the tank wall 4 up to the candle filter tray 3 and be attached thereto. In the illustrated case, the only tension bar 2 visible is guided up to the tank wall 4 and fixed thereto. The number of tension bars 2 used altogether can be adapted to the respective load conditions. Preferably, 3 or 6 tension bars 2 uniformly distributed over the periphery of the central beam 1 are provided.

The candle filters not shown here are hung into receiving openings 5, wherein they can either hang downwards through the candle filter tray 3 or protrude upwards from the same. Below the candle filter tray 3, reinforcing ribs 6 are provided, in order to increase the stiffness of the tray 3. The tension bars 2 previously are mounted on the candle filter tray 3, wherein the candle filter tray 3 is turned upside down for this purpose and the tension bars 2 are mounted. Due to a corresponding prestress of the tension bars 2 it is ensured that no vertical displacement occurs in the center of the tray during insertion of the candle filter tray 3 into the sulfuric acid tower.

As can be taken from Fig. 2, a multitude of receiving openings 5 can be provided by maximally utilizing the surface area of the candle filter tray 3. If a corresponding num- ber of candle filters is not required in a specific case of application, individual receiving openings 5 can be closed by blind covers 7 or the like. The tension bars 2 indicated in broken lines are attached to a central tube 8, which serves as central beam 1.

In the embodiment shown in Fig. 3, the receiving openings 5 are formed as tube sec- tions 9 which are pushed through the candle filter tray 3 and for example welded to the same. The additional reinforcing ribs 6 at the bottom surface of the candle filter tray 3 can be omitted in this case. It has turned out that when using the tension bars 2 to prevent the deflection, it is sufficient to connect the tube sections 9 by correspondingly short ribs 10. In this way, the weight of the candle filter tray 3 and hence the costs can be reduced considerably.

List of Reference Numerals:

1 central beam

2 tension bars

3 candle filter tray

4 tank wall

5 receiving openings

6 reinforcing ribs

7 blind cover

8 tube

9 tube sections

10 ribs