US3408168A - Phosphoric acid concentration - Google Patents

Description

Oct. 29, 1968 c, o wm 3,408,168

PHOSPHORIC ACID CONCENTRATION Filed July 16, 1965 2 Sheets-Sheet l INVENTOR.

' M/LLA/PD a. GODWl/V Oct. 29, 1968 M. c. GODWIN 3,408,168

PHOSPHORIC ACID CONCENTRATION Filed July 16, 1965 2 Sheets-Sheet 2 m vsrv r01? M/LLARD 6. GODW/N United States Patent 3,408,168 PHOSPHORIC ACID CONCENTRATION Millard C. Godwin, Lakeland, Fla., assignor, by mesne assignments, to Armour Agricultural Chemical Company, a corporation of Delaware Filed July 16, 1965, Ser. No. 472,410 3 Claims. (Cl. 23-307) ABSTRACT OF THE DISCLOSURE Submerged combustion concentration of phosphoric acid wherein water instead of phosphoric acid is introduced into the dehydrator vessel in starting up the process. When operating conditions are reached addition of water is stopped and phosphoric acid introduced into the vessel while withdrawing the water.

This invention relates to phosphoric acid concentration, and more particularly to method and apparatus for the concentration of wet process phosphoric acid in which hot combustion gases are employed as the heating medium.

In the dehydration of wet process phosphoric acid in which combustion gases are discharged through a dip pipe into a pool of phosphoric acid held within a bricklined dehydrator vessel, it is found that in the start-up stage an oft-condition product caused by trying of the aci is produced, and also there is a tendency for metal salt deposits to build up on the dip pipe.

I have discovered that water, instead of acid, can be utilized during the start-up period, and thereby the startup time is shortened, the amount of cit-condition product is greatly reduced, while at the same time the salt deposit build-up on the evaporator surfaces is substantially eliminated for this period. By using the water technique, it is found that there is no plugging during the start-up period.

A primary object, therefore, is to provide a process for overcoming the above described difliculties in the start-up of the dehydration of wet process phosphoric acid. Another object is to provide a process in which water is utilized in the start-up of the dehydration operation to reduce start-up time, production of off-condition product, and build-up of salt deposits on evaporator surfaces. Other specific objects and advantages will appear as the specification proceeds.

The invention is shown in an illustrative embodiment by the accompanying drawings, in Which- FIGURE 1 is a diagrammatic and part-sectional view of apparatus which may be employed in the practice of the invention; FIG. 2, a top plan view on an enlarged scale of the evaporator vessel with the upper top portion of the vessel removed; and FIG. 3, a vertical sectional view of the structure shown in FIG. 2.

In the illustration given, particularly in FIG. 1, designates a furnace or combustion chamber. A suitable fuel gas, such as propane, is introduced from a source of supply through pipe 11, and air is introduced through pipe 12 from a blower. The gases enter a vortex burner 13 and are discharged into the combustion chamber through pipe 14.

15 designates a dehydration vessel which, like combustion chamber 10, is provided with an inner carbon brick lining. On one side is provided a manhole opening 16 closed by a manhole cover 16a. The insulation within the dehydrator provides a dehydrator well 17, and in line with the upper portion of the Well 17 is a drawofi pipe 18 from which the dehydrated phosphoric acid is recovered. In the upper portion of the dehydrator vessel is a vapor pipe 19. The moisture-laden gases which dis- "ice engage from the acid in the space above the evaporator bottom are removed by the duct 19 to a separator 20 Where entrained acid droplets are removed and may be returned through pipe 21 to the product receiver. The gases continue on to the floating bed scrubber 22 where condensable and water-soluble pollutants are removed.

In the evaporator 15, the well 17 is in the form of an arc, and a series of four dip pipes 23 depend from the elongated combustion chamber 10 and are provided with end pipes 24 extending downwardly into the well 17, as seen best in FIG. 2.

If desired, the metal sleeve 25 of each dip pipe may be provided on the interior thereof with a ceramic lining 26. The upper end of each metal strip 25 may be embedded within a top layer 27 of ceramic material. Thus, the metal of the dip pipe may be protected with a thick layer of ceramic on the interior thereof. The lower short length of pipe 24 is kept cool because of its proximity to the liquid in the well, being washed and cooled by the liquid during the dehydration operation. The present process, however, may be operated with or without the ceramic linings.

In the specific structure shown, wet process phosphoric acid to be dehydrated is fed into the well 17 through inlet pipes 28, and between the acid inlet pipes are water withdrawal pipes 29 (three in number) as seen best in FIG. 2. Pipe 30 may be employed as a thermocouple tube.

OPERATION In the operation of the process, I introduce water through the inlet pipes 28 into the arcuate well 17 while at the same time bringing about a combustion of the fuel gases with air and discharging the heated gases through the four dip pipes 23 into the arcuate well 17. The operation is continued, putting in enough water to have some overflow, to bring the gas heater to proper on-stream condition, while protecting the brick lining. The water serves the function of keeping the evaporator cool during the period in which the furnace or combustion chamber is brought to full flow rates of gas and air and to a water temperature of about 200 F. When such conditions have been attained, feed phosphoric acid is then introduced through the pipes 28 at full feed rate, and simultaneously the water is drained through pipes 29 and equilibrium is thus quickly attained. The operator can observe the liquid being withdrawn and can detect the point at which acid is beginning to flow from the vessel and can then terminate the withdrawal of water. The process is then continued in the usual way. Moisture-laden gases disengage from the liquid within the dehydrator and are carried off through the pipe 19, while dehydrated or concentrated phosphoric acid is drawn oif through pipe 18 to a product receiver.

Specific examples illustrative of the apparatus and process may be set out as follows:

Example I The process was carried out in apparatus as shown in the drawings but instead of starting up the apparatus with Wet process phosphoric acid, water was introduced through a period of about 2 hours, and with a constant overflow. The water was introduced through pipes 28, and the gas heater or furnace 10 was brought up gradually until the air-diluted gases from the furnace were about 1900 F. and with full flow rates of gas and air. The temperature of the water was about 200 F. and steam passed through the vapor lines. After full operating on-stream conditions for gas and air were reached, the fiow of water was discontinued and Wet process phosphoric acid analyzing 55.4 percent P 0 and 4.8 percent solids was introduced at full rate through the pipes 28.

Waterwas withdrawn through pipes 29 until the acid filled the Well and equilibrium was then quickly reached. The lining brick suffered no damage. The acid was dehydrated at a pool temperature of around 600 F. and an excellent product was obtained with substantially no oil-condition product. There were no metal salt deposits during the start-up period.

Example II The above process was repeated in apparatus similar to that shown in the drawings except that the ceramic liner was omitted. By the use of the water feed, build-up of deposits was avoided during the start-up period, and the build-up of deposit did not begin until after the acid at full flow rate was introduced into the dehydrator. There was substantially no off-condition product and no build-up of salt deposits during the start-up operation.

While in the foregoing specification I have set forth specific structure and procedure in considerable detail for the purpose of illustrating embodiments of my invention, it will be understood that such details may be varied widely by those skilled in the art without departing from the spirit of my invention.

I claim:

1. In the dehydration of Wet process phosphoric acid in which hot combustion gases are discharged through a dip pipe into a dehydrator vessel containing wet process phosphoric acid, the improvement comprising starting up the process using water in said dehydrator vessel instead of phosphoric acid, continuing the operation until combustion operating temperatures and gas flow rates are reached, discontinuing the feeding of water to said vessel,

and feeding Wet process phosphoric acid to said vessel while draining water from the vessel.

2. The process of claim 1 in which the wet process phosphoric acid is fed at full flow rate into the vessel While draining the water.

3. In the dehydrationof wet process phosphoric acid in which hot combustion gases are discharged through a dip pipe into a dehydrator vessel containing wet process phosphoric acid, the improvements comprising starting up the process by introducing water into the dehydrator vessel in contact with said hot combustion gases, maintaining an overflow of Water from said vessel until the gas and air mixture forming said combustion gases are brought to about operating flow rates and temperatures, discontinuing the feeding of water, and feeding wet process phosphoric acid into said vessel while draining water from the vessel.

References Cited UNITED STATES PATENTS 3,073,683 1/1963 Switzer 23307 X 3,104,947 9/1963 Switzer 23307 X 3,276,510 10/1966 Austin 23165 X OTHER REFERENCES Young et a1.: Wet-Process Phosphoric Acid, Chemical Engineering Progress, vol. 59, #12, December 1963, pp. to 84.

NORMAN YUDKOFF, Primary Examiner. S. EMERY, Assistant Examiner.

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