US3810740A - Apparatus for the production of phosphoric acid - Google Patents

Abstract

THE APPARATUS COMPRISES A DOUBLE-WALLED COMBUSTION TOWER PROVIDED WITH A COVER AND BOUNDED BY AN INSIDE WALL AND AN OUTSIDE WALL SPACED APART FROM ONE ANOTHER. THE INSIDE WALL HAS A BOTTOM SECTION SHAPED AS AND TERMINATING IN A TRUNCATED CONE AND A COMBUSTION NOZZLE OPENING INTO THE COMBUSTION TOWER IS PASED THROUGH THE COVER. AN ACID COLLECTING TANK IS DISPOSED DOWNSTREAM OF THE COMBUSTION TOWER; AND AN IMMERSION TUBE WHICH IS OPEN AT ITS LOWER END IS ARRANGED SO AS TO OPEN INTO THE TRUNCATED COME SECRION OF THE COMBUSTION TOWER.

Description

May 14, 1974 BERG ErAL 3,810,740

APPARATUS FOR THE PRODUCTION OF PHOSPHORIC ACID Filed Dec. 7, 1971 United States Patent US. Cl. 23-277 R 6 Claims ABSTRACT OF THE DISCLOSURE The apparatus comprises a double-walled combustion tower provided with a cover and bounded by an inside wall and an outside wall spaced apart from one another. The inside wall has a bottom section shaped as and terminating in a truncated cone and a combustion nozzle opening into the combustion tower is passed through the cover. An acid collecting tank is disposed downstream of the combustion tower; and an immersion tube which is open at its lower end is arranged so as to open into the truncated cone section of the combustion tower.

The present invention relates to an apparatus of acidproof metallic material for the production of phosphoric acid by burning yellow phosphorus.

It has been reported earlier that phosphoric acid can be produced in an apparatus of acid-proof steel which substantially comprises, as a combination of a combustion tower with an acid collector, a cylindrical container closed by means of flanged dished heads, and an off-gas outlet that is disposed laterally with respect thereto. With reference to this apparatus, it should be noted that the supporting structure, in which the container is hooked, has to support not only the containers weight but also the weight of the phosphoric acid accumulating therein, which is disadvantageous. Furthermore, the container is subject to thermal expansion and it is accordingly necessary for the acid outlet projecting outwardly from the containers bottom portion to be provided with compensators which, however, are susceptible to disturbances. The step of cooling the container from the outside by spraying water onto it also is not fully satisfactory. This in view of the fact that it is customary for a phosphorus combustion facility to be erected in the open air. As a result, the container may often be found to be cooled unilaterally only as the film of water sprayed onto it may fail to be effective on the side before the wind. The partial evaporation of cooling water on the containers outside wall may effect deposition of boiler scale and handicap the heat exchange through the wall of the container. In addition thereto, vapor damp or cooling water may cause inconvenience to the neighborhood of the combustion means. Still, further, the off-gas outlet is disposed laterally with respect to the container and the stream of gas is accordingly caused to travel through the combustion and reaction chambers in a direction inclined with respect thereto. As a result, the off-gas in the lower section of the reaction chamber is sprayed irregularly with recycle acid whereby the absorption of P 0 in the recycle acid is impaired.

It is an object of the present invention to provide a fully satisfactory apparatus for the production of phosphoric acid by burning yellow phosphorus, the apparatus being designed so as to permit the structure supporting the container to be released from the weight of the phosphoric acid accumulating downstream of a combustion tower and to permit the outside wall of the combustion tower to be cooled uniformly by forcing the cooling 'ice water to flow in a predetermined manner. To achieve this, the invention provides an apparatus which substantially comprises a double-walled combustion tower provided with a cover and bounded by an inside wall and an outside wall spaced apart from one another, the said inside wall having a bottom section shaped as and terminating in a truncated cone; a combustion nozzle opening into the combustion tower through said cover; an acid collecting tank disposed downstream of the said combustion tower; and an immersion tube open at its lower end and opening into the said truncated cone section of the combustion tower.

Further preferred embodiments of the apparatus of the present invention, which can be used singly or in combination, provide (a) for the upper end of the combustion tower to be booked in a steel structure supporting it;

(b) for the lower section of the combustion tower to be provided with a bevelled off-gas conduit opening deeply into the center portion of the tower and projecting outwardly through, and upwardly with respect to, the towers inside and outside walls;

(c) for the acid collecting tank to be provided with an immersion pump and conduits connecting the pump to an orthodox annular acid-receiving cup in the head portion of the combustion tower, and connecting it to conventional nozzles disposed in the center portion of the combustion tower;

(d) for the immersion tube to be arranged so as to project freely into the acid collecting tank;

(e) for screw threads to be welded onto the inside wall of the combustion tower so as to uniformly distribute cooling water in, and fill with cooling water, the space left between the combustion towers inside and outside walls;

(f) for the outside wall to be welded with merely its lower end to the combustion towers inside wall;

(g) for the outside wall to be comprised of a plurality of,

preferably two, cylindrical jacket sections;

(h) for the jacket sections to be welded with merely their lower ends to the combustion towers inside wall;

(i) for the off-gas conduit projecting into the center portion of the combustion tower to be cut off so as to be bevelled downwardly.

By the separate arrangement of the phosphorus combustion chamber and the acid collecting tank, the supporting structure merely has to bear the combustion tower, which is hooked therein, whilst the acid collecting tank with the phosphoric acid contained therein rests on the floor. Reliable functioning of the combustion tower, which is subject to considerable variations in length during the operation and standstill periods, is ensured firstly by the non-rigid connection existing between the combustion tower and acid collecting tank and secondly by the fact that merely the upper end of the tower is secured to the structure supporting it. In addition to this, the use of compensators in the acid conduit system is rendered unnecessary by positioning the immersion pump, which is used to circulate the acid, on the acid collecting tank.

To avoid partial evaporation of cooling water and the consequential deposition of boiler scale on the walls of the combustion tower, it is necessary for the space left between the towers inside and outside walls to be continually and completely filled with water. Screw threads may advantageously be placed between, and welded to the towers inside and outside walls, to ensure the uniform supply of all tower sections with fresh cooling water.

The load exerted against the towers inside wall by the outside pressure which results from the static height of the cooling water column can be kept low by subdividing the towers outside wall into a plurality of, preferably two, jacket sections. As a result, the inside wall can be made thinner which means less expensive of structural materials and simultaneously means improved abstraction of heat from the interior of the tower.

While the towers inside and outside walls are subject to inconsistent thermal expansion, the fact remains that this is no problem if merely the lower ends of the jacket sections forming the outside wall are welded to the towers inside wall. By means of the bevelled off-gas conduitthis element is disposed in the lower section of the combustion tower, projects deeply into the towers center portion and is cut off downwardlyit is possible to render the flow of gas in the combustion and reaction chambers more uniform and thereby to also improve the reaction conditions considerably. Still further, the separation of off-gas from acid droplets is beneficially influenced -'by breaking turbulence which is produced upon the introduction of the gas stream into the off-gas conduit and which causes the direction of flow of the gas stream to be sharply deflected.

The present invention will now be described with reference to the accompanying drawing showing a diagrammatic and exemplary form of apparatus.

As can be seen from the drawing, a combustion tower 2 is hooked in a steel structure supporting it. The combustion tower 2 is bounded by an inside wall 3 provided with a bottom 4, which has the shape of a truncated cone and terminates in an immersion tube 5 having an open lower end, and by an outside wall comprising two jacket sections 6 and 7, respectively. Between jacket section 6 and jacket section 7, the inside wall 3 is provided with passageways 8 receiving nozzles which open into the towers interior. In its base portion, the combustion tower 2 is provided with an olT-gas conduit 9 which is inclined with respect thereto, projects outwardly through the inside wall 3 and jacket section 7 and opens deeply into the center portion of tower 2, where it is cut off downwardly. An immersion tube 5 opens freely into an acid collecting tank 10 which has an immersion pump 11 mounted thereon.

The upper end of inside wall 3 terminates in a semicircular rounded overflow edge 12. Disposed around the upper end of inside wall 3 and spaced therefrom is an outer collar 13 the lower end of which is secured by means of a circular ring 14 to the inside wall 3 so as to form an acid cup 20. The upper rim portion of outer collar 13 is fast with a conically shaped tower cover 5 having a passageway 16 centrally placed therein. Passageway 16 supplies fresh air and receives a phosphorus supply line 17 opening into the tower and having a nozzle 18 secured to its lower end. Cover is water-cooled by means of an annular conduit 19 which is disposed thereabove and has apertures in its underside. The cooling water travels via an orifice plate 21 to collecting groove 22, this latter being connected by means of conduit 23 to the towers cooling system. The tower is cooled with water which enters the system through inlet 24 and is forced to flow helically through screw threads 25 which are disposed between, and welded to, inside wall 3 and jacket section 6. Jacket section 6 has a widened upper end shaped as an annular cup 26 delivering water through socket 27 and a conduit 28 to the towers base portion. In analogous manner, water is forced to flow in the towers base portion through screw threads 25 disposed between, and welded to, inside wall 3 and jacket section 7, and delivered to an annular cup 29, from where it is removed through an outlet 30.

The acid-receiving cup and the nozzles opening into the towers interior through passageways 8 are supplied with phosphoric acid circulated by means of immersion pump 11 causing the acid to flow through conduits 31, 33 and 34, and a heat exchanger 32. Acid cup 20 is coutinually filled with acid. To ensure this, conduit 34 is provided with a gooseneck 35 and a vent pipe 36. To avoid the escape of splashes of acid, vent pipe 36 is connected to a conduit 37 terminating in cover 15.

The claims:

1. An apparatus for the production of phosphoric acid by burning yellow phosphorus by means of a combustion nozzle in an acid-proof metal combustion tower having an acid collecting tank associated therewith, the apparatus comprising a combustion tower having a doublewalled upper section and middle section bounded by an inside wall and an outside wall, the walls being spaced apart, and a single-walled lower section bounded by the inside wall having a lower portion terminating in a truncated cone which in turn terminates in an immersion tube, the immersion tube being open at its lower end and projecting freely into the acid collecting tank bounded by a top wall, being disposed and being supported separately from, and downstream of the combustion tower; seals between the immersion tube and the top wall of the acid collecting tank; the combustion tower being hooked near its upper end in a steel supporting structure to provide a non-rigid connection with the acid collecting tank to release the steel supporting structure from the Weight of the phosphoric acid in the acid collecting tank; an immersion pump being freely mounted on the acid collecting tank so as to project thereinto; seals between the immersion pump and the top wall of the acid collecting tank; the upper section of the combustion tower having an annular acid-receiving cup, nozzles disposed in the middle section of the combustion tower, an acid conduit system free from compensators connecting the immersion pump to the annular acid-receiving cup disposed in the upper section of the said combustion tower, and further connecting the said pump to the nozzles disposed in the middle section of the combustion tower; and an off-gas conduit inclined with respect to the combustion tower projecting through the inside wall and the outside wall of the combustion tower so as to deeply and centrally reach thereinto, the off-gas conduit having an inclined end and bevelled downwardly.

2. The apparatus as claimed in claim 1, wherein screw threads are welded to the inside wall of the combustion tower so as to uniformly distribute cooling water in, and fill with cooling water, the space left between the combustion towers inside and outside walls.

3. The apparatus as claimed in claim 1, wherein the outside wall is welded with merely its lower end to the combustion towers inside wall.

4. The apparatus as claimed in claim 1, wherein the outside wall is comprised of a plurality of cylindrical jacket sections.

5. The apparatus as claimed in claim 4, wherein the outside wall is comprised of two cylindrical jacket sections.

6. The apparatus as claimed in claim 4, wherein the jacket sections are welded with merely their lower ends to the combustion towers inside wall.

References Cited UNITED STATES PATENTS 3,526,482 9/1970 Beltz ct a1. 23--283 3,064,408 11/1962 Erga et a1. 26l-115 X 2,708,620 5/1955 Winnicki 23262 X 858,062 6/1907 Day 23-262 JAMES H. TAYMAN, 111., Primary Examiner U.S. C1. X.R.

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