US3073683A - Apparatus for submerged combustion heating of liquids - Google Patents

Description

Jan. 15, 1963 R. SWITZER ETAI. 3, 8

APPARATUS FOR SUBMERGED COMBUSTION HEATING OF LIQUIDS Filed Aug. 25, 1959 2 Sheets-Sheet 1 F550 A/QU/D Jall- 1963 R. L. SWITZER ElAl. 3,073,683

APPARATUS FOR SUBMERGED COMBUSTION HEATING OF LIQUIDS Filed Aug. 25, 1959 2 Sheets-Sheet 2 R. 4. smrzsx? E 4 we. LIEFFEIQS CLYD ERG 4rr mewe United States Patent 3,073,683 APPARATUS FOR SUBMERGED COMBUfiTlG HEATING 0F LIQUIDS Robert L. Switzer, Long Beach, William C. Liefiers, Garden Grove, and Clyde H. 0. Berg, Long Beach, Calif, assignors, by mesne assignments, to Collier Carbon and Chemical Corporation, a corporation of California Filed Aug. 25, 1959, Ser. No. 835,946 13 Claims. (Cl. 23-275) 1 formation of stable phosphoric acid aerosols in the combus gases.

Submerged combustion heating is a process wherein a fuel is burned within a chamber and the resultant hot combustion gases are discharged beneath the surface of a body of liquid being heated, transferring their heat to the cooler liquid by direct contact. After passage through the liquid the gases are usually discharged to the atmosphere as exhaust gases. The flame within the burning chamber, which in most, but not all instances is partially or wholly submerged in the liquid, is usually prevented from impinging upon the liquid by extending the burning chamber walls or by attaching an extended conduit, usually referred to as a dip tube, to the burning chamber. To maintain proper burning conditions within the chamber, it has been customary to constrict the outlet of the burner wall extension or dip tube.

From the preceding discussion, it is apparent that submerged combustion heating requires fewer heat transfer steps than do the more conventional indirect heat I transfer methods, and that, therefore, submerged combustion is more eflicient than the commonly employed heating techniques. Despite this, submerged combustion has found only limited acceptance since its introduction in the latter years of the last century; its use generally confined to heating corrosive or scale depositing liquids which can not be satisfactorily heated by conventional indirect heat transfer methods.

Despite prior limited acceptance of submerged combustion heating, this improvement thereof is applicable for the heating of any liquid, solution, or slurry, however, it is particularly suited for the heating of those liquids which tend to deposit excessive amounts of solids on the heating equipment during the heating step. Examples'of such liquids are aqueous salt solutions, for instance, aqueous solutions of the carbonates, sulfates, sulfites, nitrates, phosphates and halogen salts of sodium, potassium, calcium, magnesium, iron, aluminum, ammonium, etc. Acids, such as sulfuric and phosphoric, can also be heated in accordance with the invention. Solutions of organic compounds, such as sugar, starch, and rubber solutions, can also be heated, as well as slurries of solids, such as slurries of waste citrus products or the liquor slurries of wood chips encountered in the paper industry. The heating of the solutions can be for any purpose, for instance, to raise the liquid temperature, to supply reaction heat or to supply the latent heat of vaporization of a solvent to concentrate the solution. This invention is particularly suited for supplying heat to evaporating solutions, since it is in this type of operation that scale and deposit formation frequently occurs.

Submerged combustion has previously been used to heat scaleforming liquids; however, its use in this service re quires frequent interruption to remove solid deposits "Ice The use of submerged combustion to supply heat in I the evaporative concentration of phosphoric acid has also been suggested; however, previous investigators have reported that its use in this service is not satisfactory since phosphoric acid aerosols are formed in the exhaust gases. These aerosols are exteremely minute particles of phosphoric acid, 0.2 to 2 microns in diameter, which cannot be removed by conventional absorption or scrubbing steps. Since the aerosol comprises corrosive phosphoric acid and since it forms a visible White fume, the venting of the exhaust gases to the atmosphere is objectionable and expensive aerosol removal steps must be taken. When wet process phosphoric acid, i.e., that produced by leaching phosphate rock with sulfuric acid, is heated, the fluorine compounds which are present as impurities in the acid are violatilized and are absorbed by the phosphoric acid aerosol thereby increasing its corrosivity. Other impurities in the crude acid, e.g., organic matter and salts of aluminum, iron, magnesium, as well as residual calcium sulfate, cause frothing and foaming of the acid during heating and in part cause solid deposition on heating surfaces. Accordingly, submerged combustion has not been widely accepted as a method for supplying heat to the evaporative concentration of phosphoric acid.

It is a purpose of this invention to provide a submerged combustion heating apparatus which, when used to heat a deposit-forming liquid, does not require frequent clean- It is also a purpose of this invention to provide a method and apparatus to concentrate dilute phosphoric acid by evaporation while supplying the necessary heat with an improved submerged combustion technique which prevents formation of objectionable amounts of phosphoric acid aerosols in the exhaust gases.

The aforementioned purposes are achieved by use of an improved submerged combustion apparatus described as follows:

A submerged combustion burner consisting of a com bustible gas supply conduit, suitable ignition means, and a burning chamber, is concentrically disposed within a surrounding conduit, hereafter referred to as a dip tube,

' which extends a substantial distance below the burning substantially greater diameter which also concentrically surrounds the dip tube.

In operation, a pre-mixed stream of combustible fluid with an oxidant, preferably natural gas and air, are supplied to the burning chamber, ignited, and the resultant hot combustion gases flow from the burning chamber into the surrounding dip tube. These hot gases fiow downwardly through the dip tube and pass through a special nozzle into contact with the cold liquid. The mixed liquid and gas stream reverses the direction and flows upwardly through the annulus between the dip tube and the surrounding subjacent conduit. This annulus is sized sufiiciently small in area in relation to the gas and liquid flow rates so that the gas exerts a. lifting effect on the liquid. The mixed gas and liquid stream discharges from the upper open end of the subjacent conduit into the larger diameter superimposed conduit. In this latter conduit the gas and liquid separate. The gas is removed overhead and the liquid flows back into the mixed gas-liquid stream within the annulus. A continuous bleed stream of liquid is removed as product from the upper region of the annulus. The apparatus thus permits repeated contact between the liquid and hot gas and thereby insures a high rate of heat transfer.

The specially designed nozzles of this invention constrict the lower end of the dip tube and are provided with means to remove or prevent the formation of solid deposits across the constriction orifice. These nozzles are essential to the proper functioning of the apparatus since the use of an open-ended dip tube, i.e., without a nozzle, results in liquid surging which interferes with good flame conditions and which splashes liquid .on the hot inside surfaces of the dip tube. This liquid is dried in place by the hot gases to form a ,hard hygroscopic solid, while the volatilized fraction collects in the upper portion of the dip tube. When Wet process phosphoric acid is being heated, the volatilized fraction contains fluorine and phosphorous compounds which create a serious corrosion problem. The use of a nozzle avoids this difficulty; however, if the nozzle does not have means to remove or prevent the accumulations of solid deposits, it is not satisfactory because deposits form on the constricted flow area of the nozzle and greatly disturb the flow pattern, creating excessive turbulence and eddy currents which cause the dispersion of phosphoric acid aerosols in the combustion gases.

The nozzles suitable for this invention can have single or plural passageways for the hot gases. These passageways may simply be holes bored through an end plate on the dip tube, but preferably their shape approaches that of a venturi, with a smoothly converging entrance, a narrow throat and a smoothly diverging exit, so that eddy currents and high turbulence which contribute to aerosol formation are avoided. When thus shaped, the entrance and exist passageways can suitably take a trumpet, conical or conoidal shape. If conical in shape, the total angle between the entrance walls is not greater than 40 to 50 degrees and preferably between about 25 to 30 degrees. The angle between the exit passageway walls, also if conical, is no greater than 30 to 40 degrees and preferably less than about degrees. Regardless of the specific shape of the passageways, the convergence and divergence of the passageway is gradual, with a smooth transition through the throat so as to avoid the formation of a vena contracta, i.e., the maximum contraction of a stream, normally formed downstream from a sharp edge orifice or an improperly designed nozzle.

The removal and/ or prevention of solids accumulation on the nozzle flow passageways is essential to avoid excessive turbulence with resulting aerosol formation. Following is a brief discussion of nozzle embodiments of this invention which achieve this goal:

To prevent the liquid from adhering to the nozzle surfaces and evaporating to. dryness in place, the nozzle can be coated with a repellant for. the liquid being heated. For aqueous solutions, this coating can be of any suitable water-repellant material, such as polymers of tetrafluoroethylene, trifiuorochloroethylene, or vinyl chloride, or copolymers of vinyl chloride with vinyl acetate or vinylidene chloride. The first of the aforementioned coatings is available under the trade name Teflon from E. I. du Pont de Nemours & Co. These coatings can be employed alone, or can be combined with any of the following nozzle modifications to avoid solid deposition.

Cooling the nozzle keeps the latter free of deposits and this cooling is achieved in this invention by thecirculation of a gaseous or liquid cooling medium in indirect contact with the fouling surfaces. Indirect contact is achieved by circulating the cooling medium through a chamber hollowed in the nozzle body to form an annulus perpendicular to and surrounding the single or plural longitudinal gas flow passageways through the nozzle. Heat insulation is provided between the cooling fluid and those walls of the nozzle which do not normally in cur solid deposition and which, therefore, do not need to be cooled.

Direct contact between a cooling liquid and the fouling surface of the nozzle can be achieved with the same nozzle construction as described above, if the nozzle body is constructed of a material which is permeable to the flow of the fluid. Permeation of the cooling fluid to parts of the nozzle other than the fouling surfaces, i.e., those which normally incur solid deposition, can be prevented by sealing the appropriate walls of the cooling fluid annulus with a non-permeable resinous sealing material. When a liquid is chosen as the cooling medium, additional cooling of the surface is achieved by evaporation of the liquid from the surface into the hot combustion gas stream. When the cooling liquid is also a solventfo r thedeposits, loosening and removal of the de posits is augmented by the dissolving power of the liquid.

Rather than constructing the nozzle with a hollowed interior for the flow of wash or cooling fluids, the nozzle can be solid and scraping means can be provided to remove solids from the surfaces of the longitudinal passageways. In this embodiment a bob with an inverted truncated cone shape is placed with its small diameter end within each longitudinal passageway and a bob stop is placed beneath each bob. The bob can be mechan ically operated up or down or can float within the passageway so that normal pressure fluctuations will move it up and down, against the surfaces of the passageways, scraping away any deposits. To prevent undue turbulence, the bob can be egg-shaped and can have a spiral groove or a raised spiral thread on its surface to spin it and obtain a good scraping action.

The invention is more completely described by reference to the drawings of which:

FIGURE 1 shows the submerged combustion heating assembly of this invention;

FIGURES 2 to 4 show the dip tube nozzle cooling and/or washing embodiments of this invention; and

FIGURE 5 shows the scraping embodiment of this invention.

Referring now to FIGURE 1, the heating apparatus consists of an upper metal vessel 6 closed at its upper end by plate 4 and fitted at its lower end with an inclined bottom plate assembly 13, which supports concentrically disposed, subjacent vessel 15. Vessel 15 is closed at its lower end with plate 19 and is fitted with graphite liner 16 and graphite plate 17. The graphite liner 16 at its upper end is threaded into the tapered bottom of a second graphite liner 8 having a greater diameter than liner 16 and extending a substantial distance up the length of vessel 6, but terminating below the entrance of conduit 5 into vessel 6. A concentric graphite dip tube 7 extends the length of vessel 6, into graphite liner 16 and is provided with a special discharge nozzle 14, discussed in detail below, at its lower end which lies slightly above plate 17. A burner 9, comprising spark discharge igniting means, not shown, and a fuel supply conduit 3 is positioned within dip tube 7 and is sufficiently spaced above the latters lower end that the flame from the burner does not extend to nozzle 14. A liquid feed inlet 18 extends into vessel 15 through base plates 19 and 17, and a liquid product outlet 10 is tapped through vessel 15 and liner 16 at an angle inclined about 15 degrees from the horizontal. A Teflon tube 11, attached to outlet 10, passes to the exterior of the heating assembly through conduit 12 in bottom plate assembly 13 to permit withdrawal of the heated product.

In the discussion of this apparatus, reference has been made to graphite liners and plates. Graphite is suitably employed in this invention when wet phosphoric acid is concentrated because it has sufficient corrosion resistance to the phosphorus and fluorine compounds present in this acid. It is, of course, obvious that other-materials of construction may be employed which are also inert to the liquid being heated. When possible, with less-corrosive liquids, it is preferred to dispense with graphite liner 16 and plate 18 and to construct liner 8 of metal. In such an embodiment, metal liner 8 has a tapered or inclined bottom which is attached to and in open communication with the upper end of subjacent vessel 15. The corrosion resistant plastic tube 11 is also eliminated and the heated liquid allowed to drain into vessel 6 through outlet tap 10. It is also apparent that clip tube 7 may suitably be constructed from any material which is resistant to the liquid being heated. Although the use of a dip tube is preferred, it is of course apparent that the function of the dip tube could also be accomplished by extending the walls of burner 9. Alternatively, dip tube 7 need not extend the length of vessel 6, but can be attached directly to the lower end of burner 9.

In operation, a pre-mixed stream of natural gas and air is supplied to the flame within burner 9, and the resulting hot combustion gases flow downwardly through dip tube 7 and nozzle 14 into zone A where they come in direct contact with cold feed liquid supplied through conduit 18. The combustion gases reverse their flow and pass upwardly through annulus B into enlarged zone C from whence they are removed via conduit 5. As the gases pass upwardly through annulus B they exert a lifting effect on the liquid and carry large amounts of the same up into the annulus, thereby prolonging the contact time between the liquid and gases and resulting in a high rate of heat transfer. In zone C, the liquid disengages from the gases and flows down the inclined bottom of liner 8 and down the interior surface of liner 16. As the liquid passes outlet It), some of it is removed asproduot and the remainder flows into repeated contact with the hot combustion gases. Because of the turbulence within the annulus, some liquid is also thrown directly into outlet 10 and is removed.

The positioning of outlet 16 in the upper portion of vessel I5 provides for adequate contacting of the hot gases and the liquid. In addition, sizing the outlet sufficiently small provides adequate residence time of the liquid within the heating zone without the need of a level control system which would be extremely difficult to use on the highly turbulent mixed gas-liquid phase in the annulus.

FIGURE 2 illustrates the construction of a burner nozzle modification which successfully prevents the formation of solid deposits in the area of restricted flow. In this modification, the lower end of clip tube 7 is threaded on its inside surface and a doughnut shaped graphite plug 23 is constructed to thread into the end of the dip tube. Plug 23 is threaded at its lower end to receive a nozzle liner such as shown by 25, the interior surface of which comprises a longitudinal flow passageway for the hot combustion gases. The lower half of plug 23 has a greater internal diameter 36 than its internal diameter 27 in its upper portion so as to provide recessed surface 24. A groove 28 is cut into the upper end of enlarged diameter section 36 to provide shoulder 29. Flow passageways 21 and 22 are bored as shown into opposite sides of plug 23. Bore 22 can, if desired, be tapped to receive the threaded end of conduit Zll, or if desired, the bore diameter 22 can be chosen so as to permit a swedge fit of conduit within the hole. A ring 33 constructed from a suitable heat insulation ma erial, for instance Teflon, is inserted into plug 23 and held in place by the lower flared end of nozzle liner 25 when the latter is threaded into the lower end of plug 23. The upper edge of ring 33 is of slightly smaller diameter than groove 28 into which it fits to allow for the dissimilar thermal expansion of the ring and plug during use. The exterior surface of nozzle liner 25 is recessed along a portion of its length as shown by 32 to provide an enlarged annular chamber in the nozzle assembly. A shoulder 31 is provided at approximately the central portion of the liner to support an O-ring seal which is compressed against shoulder 29 of plug 23 when liner 25 is threaded into the plug, thereby sealing the annular space between liner 25 and plug 23. When the assembly is complete, recessed surface 32 of the liner and the interior surface of ring 33 form an annular chamber D which surrounds the longitudinal gas passageway through the nozzle so that the circulation of a cooling fluid through conduits 20 will remove heat from the non-insulated surfaces 32 and 35 of the nozzle liner. Recessed surface 32 is shown to extend upwardly to only approximately the middle of the liner, for it is in this region that sol-id deposition is found to occur on the gas passageway surface in an uncooled nozzle. However, it is clear that, if desired, a greater height of the liner could be cooled merely by extending the height of enlarged diameter section 36, ring 33 and recessed surface 32. Preferably, the interior longitudinal gas passageway surface is coated with a nonwetting material, for instance Teflon, to decrease the tendcncy for solids to deposit on this surface.

The embodiment of FIGURE 2 may also be used when it is desired to wash the surface of liner 25. In this modification, liner 25 is constructed of a material which is permeable to the wash fluid, such as air or water, which is circulated through chamber D. Suitable permeable materials may be selected from permeable ceramics, or permeable metals and glass which are made by sintering of metal or glass powders. Where an extremely corrosive liquid, such as wet process phosphoric acid, is heated, the aforementioned materials are not suitable, and permeable graphite should be employed. If it is desired to use only the indirect cooling feature with a graphite liner, surfaces 32 and 35 can be made impervious to the cooling fluid by coating with plastic or resinous material. Since graphite has a high thermal conductivity, the longitudinal gas passageway surface is readily cooled by this modification.

FIGURES 3 and 4 depict a nozzle liner having a plurality of longitudinal gas passageways and provision for circulation of a cooling and/or washing fluid. The elevation view, FIGURE 3, shows the liner/I2 to be a solid plug with a plurality of longitudinal venturi-shaped gas passageways 43. The upper end of liner 42 is slightly less than diameter 27 of plug 23 shown in FIGURE 2,

and the base of liner 42 is provided with a threaded edge 39 which fits into the threaded socket base of plug 23 to permit the liner to be securely fastened within this plug. Shoulder 38 is provided on liner 42 to support a sealing ring against shoulder 29 of plug 23 to seal the annular chamber formed between wall 40 of liner 42 and insulation ring 33. During use, a fluid is circulated through 20, 22 and 21 shown in FIGURE 2 and into the annular chamber surrounding the liner.- To increase the cooling surface, radial chambers 41 can be provided within the liner 42. FIGURE 4 shows these chambers 41 and longitudinal passageways 43 as they are disposed within the liner. If desired, particularly when liner 42 is constructed from a material with a high heat conductivity, chambers 41 can be omitted, whereby the central longitudinal passageway is cooled by conduction through the body of liner 42. Although this embodiment is illustrated with seven longitudinal passageways it is, of course, apparent that the number as well as the geometrical arrangement of these passageways can be varied as desired.

The embodiment shown in FIGURES 3 and 4 can also be constructed of fluid permeable metal, glass, ceramic or graphite, the latter being preferred when heating solutions containing fluorine and phosphorous compounds. Circulation of a fluid through the annular chamber will then result in permeation of the fluid through the liner body into the longitudinal gas passageways 43 in the same manner as discussed in the embodiment of FIGURE 2.

FIGURE 5 illustrates the embodiment of the invention which provides scraping means to remove solid deposits. This modification greatly simplifies the nozzle construction since no internal fluid chambers are needed for circulation of'a cooling or washing fluid. Instead the nozzle comprises a simple solid member provided with a longitudinal flow passage and adapted to fit on the end of the dip tube. A bob 46, which is shown as a truncated cone in FIGURE 5, is placed upright within the nozzle flow passage, shown by the broken lines. A circular plate 45, which has a diameter greaterthan the nozzle discharge diameter, is attached to the base of cone 46 to prevent the bob from passing upwardly through the nozzle or from becoming wedged within the flow passage. Beneath the bob and attached to base plate 17 is placed a bob stop 44 which restricts the downward movement of the bob. When in use, the normal pressure fluctuations in the heater cause bob 46 to move up and down against the nozzle surfaces, scraping off any deposits which may form on this surface. In order to reduce eddy formation, the bob can be egg-shaped, i.e., having conoidal-shaped ends with the upper end sufiiciently small to permit entry of the bob into the nozzle flow passage and the lower end sufficiently large to prevent the bob from passing upwardly through the nozzle. Spiral grooves or a raised spiral thread can also be provided on the bob, whether it be egg or cone-shaped, so as to spin the bob and increase its scraping effect.

Bob 46 can also be mechanically moved up and down or about its axis within the nozzle flow passageway. To accomplish this, a shaft connected at its upper end to plate 45 can extend downwardly through base plate 17 and the bottom of vessel 15. This shaft can then be reciprocated or rotated to impart a suitable movement to plug 46. Bob 46 can also be moved by installing an electromagnet within bob stop 44 and constructing the bob of a magnetic material. A compression spring is then placed beneath bob 46 to hold the latter against the nozzle flow passageway when the spring is in its extended position. When an electric current is supplied to the electromagnet within stop 44 it will pull bob 46 down, compressing the spring. Stopping the current flow will release the bob and the spring will force it up against the flow passageway, knocking ofi any deposits on the surface of the passageway.

The apparatus shown in FIGURE 1 was employed to concentrate wet" process phosphoric acid. A ceramic burner encased in a stainless steel shell was supported on the end of a gas supply conduit, which Was sufiiciently small inch in diameter) that the flame was prevented from moving up into the supply conduit. The clip tube surrounding the burner was of one inch thick graphite having an internal diameter of about five inches and extending downwardly into the subjacent contacting vessel about 2 feet. The internal diameter of the subjacent contacting vessel was about seven inches, and the internal diameter of the upper disengaging vessel 8 was about twelve and one-half inches. During operation, a pre-mixed stream of natural gas and air was supplied to the burner at a constant rate to provide a constant heat release to the acid, and the acid feed rate was controlled to maintain a constant acid temperature. The acid temperature and residence time were chosen to produce a concentrated acid having between about 67 and 73 percent P The stack gases from conduit 5 were scrubbed with a single countercurrent spray of water, and then vented to the atmosphere. The gas was sampled after the water spray and the P 0 content of this sample was found to be a reliable indication of the amount of phosphoric acid aerosols in the stack gases. The pressure differential between a point within the dip tube slightly above the burner and a point in the exhaust gas stream was recorded to indicate changes in flow conditions through the system. The following examples will illustrate the invention:

EXAMPLE 1 The apparatus described above was employed without run period of five hours, the dip tube was removed and found to be heavily coated with solid deposits in the vicinity of the burner. These deposits, formed when the acid splashed up into the dip tube and dried in place by the hot gases, completely covered the narrow annulus between the outer stainless steel shield of the burner and the dip tube. The deposits adhered so tenaciously to the ceramic burner tip and steel shield that they had to be ground off.

EXAMPLE 2 To prevent acid from splashing up into the dip tube, a plug with a single longitudinal passageway having a throat diameter of one and five-sixteenths inches and smooth entrance and exit sections, similar to that shown in FIG- URE 2, was employed. No provisions were made to wash or cool the plug, nor was the gas passageway sur face coated with a water repellant material. The apparatus performed satisfactorily at the start of the run, but after four and one-half hours, the pressure drop across the dip tube and nozzle had increased from 17 to more than 50 inches of water indicating the formation of solid deposits in the gas flow path, and a white fume, which was not removed by the water spray, was visible in the exhaust gases, indicating excessive aerosol formation. After the run, the dip tube and nozzle were inspected and, although the dip tube was free from deposits, the exit portion of the nozzle, immediately below the nozzle throat, was covered with an annular layer of solids which reduced the flow area through the nozzle to approximately one half its original value. Other operating data are reported in Table 1. The high aerosol content and visible fume of the exhaust gas was due to the extreme turbulence and eddy currents caused by the solid deposits which protruded into the gas stream.

EXAMPLE 3 During a six hour run, the pressure drop across the lower end of the dip tube and nozzle remained constant at 31 inches of water and at the termination of the run, no deposits were found on the nozzle or dip leg surfaces. The operating data are shown in Table 1.

EXAMPLE 4 The nozzle embodiment shown in FIGURE 2 was again employed, but unlike Example 3, surfaces 32 and 35 were not sealed and water was permitted to permeate through the liner to wash the surface of the longitudinal gas passageway. After seven hours of use, the pressure drop through the lower portion of the dip tube and the nozzle had remained at its original value of thirty-one inches of water, and no deposits were found on the dip tube or nozzle. Other data are shown in Table 1.

EXAMPLE 5 A nozzle was constructed from a circular graphite plate by boring twelve holes, one-fourth inch in diameter, through the plate, arranged in a circular pattern. The holes were bored at a slight angle from the perpendicular so that when the plate was fitted onto the end of the dip tube, they were directed downwardly and outwardly from the centerline of the tube. This nozzle was employed to concentrate phosphoric acid under comparable conditions to those of Examples 1 to 4, as shown in Table 1. At the start of the run, the pressure drop through the lower portion of the dip tube and nozzle was three inches of water, and at the end of a two and one-half hour run, the pressure had increased to one hundred twenty inches.

Table 1 6. The apparatus of claim 1 wherein said longitudinal passageway has a smoothly converging entrance, a narrow throat and a smoothly diverging exit.

Example 1 2 3 4 5 Fed Acid Concentration, Percent 5 s4 54 30.

z 5- v Type of Constrietion N one Single Passage Single Passage Single Passage Plug with 12 Nozzle. Cooled, Coated Cooled, Washed I.D. Holes.

. Nozzle. Nozzle. Firing Rate, B.t.u./Hr 78,600-.. 200,000 189,000 185,000 200,000. Acid Temperature, F 450 450. 41 Min 398. P105 Aerosols in Exhaust Gas, p.p.m l2 3,400 W4 372 4,750. Pressure Drop, Dip Tube and Nozzle,

Inches Water;

Start 25 17- 31 31 3 Finish 27 50 ll 31 120. Run Duration, Hour 4% ti 7 2%.

From the above examples it is apparent that the lower end of the dip tube must be constricted to prevent liquid surging and splashing within the dip tube. To avoid the formation of objectionable amounts of aerosols, this constriction must take a relatively low pressure drop, and when used to heat liquids which tend to deposit solids, means must be provided to remove these solids from or to prevent their accumulation on the flow constricting surface of the nozzle.

These needs are successfully provided by the nozzles of this invention which are preferably trumpet, conoidal or conical in shape, and which must be provided with either a liquid repellant coating, washing, cooling or scraping means or any combination thereof to prevent solid accumulation on the nozzle surface exposed to the hot combustion gas flow.

Having clearly and completely described the invention, we therefore claim:

1. An apparatus for the submerged combustion heating of liquids which comprises a vessel with liquid feed means and liquid withdrawal means connected thereto and means to remove products of combustion therefrom, a conduit extending vertically into said vessel, a burner having fuel and oxidant supply means to produce a flame and generate combustion gases, said burnerbeing positioned within said conduit to discharge said combustion gases thereto, said conduit extending downwardly from said burner a substantial distance, said distance being greater than the length of said flame normally produced by said burner so as to prevent the flame produced by said burner from impinging onto said nozzle, the end of said conduit terminating within said vessel, beneath said liquid withdrawal means, and having a.- discharge gas passageway comprising a throat of constricted cross-section and an exit section immediately beneath said throat, said exit section having asmoothly divergent cross-section so as to expand gases flowing therethrough and into said vessel, an annular chamber surrounding said discharge gas passageway, said chamber positioned beneath said throat so as to surround only said exit section of said nozzle and means to circulate a heat exchange fluid through said annular chamber to cool the surface of said exit section of said discharge gas passageway.

2. The apparatus of claim 1 wherein said annular chamber is separated from said longitudinal gas passageway by a common Wall of a material which is permeable to fluids.

3. The apparatus of claim 1 wherein said discharge gas passageway comprises a nozzle having a removable liner sleeve, said sleeve forming said longitudinal gas passageway.

4. The apparatus of claim 1 wherein said longitudinal passageway is coated with a water repellant coating.

5. The apparatus of claim 1 wherein said nozzle contains a plurality of longitudinal passageways.

7. The apparatus of claim 6 wherein said entrance has a maximum angle of convergence no greater than about 50 degrees and said exit has a maximum angle of divergence no greater than about 40 degrees.

8. An apparatus for heating liquids comprising a first conduit having a closed upper end and a nozzle at its lower end, said nozzle having a centrally disposed longitudinal passageway having a lesser diameter than said first conduit and a smoothly diverging exit portion with an interior annular chamber surrounding said exit portion of said passageway along a substantial portion of its length, said chamber being separated from said passageway by a common wall, a gas burner disposed within said first conduit and positioned above said nozzle a distance greater than the length of flame normally produced by said burner so as to avoid flame impingement on said nozzle, gas supply line to said burner, a first vessel having a closed upper end concentrically surrounding the lower portion of said first conduit; said firstvessel having a substantially greater internal diameter than the outside diameter of said first conduit to form a first annular space therebetween; a second vessel closed at its lower end and having a lesser diameter than said first vessel, said second vessel concentrically surrounding said first conduit, disposed beneath and in open communication with said first vessel and having a slightly greater internal diameter than said outside diameter of said first conduit to form a second, narrow annular space therebetween, means sealing the outer upper periphery of said second vessel to the inner periphery of said first vessel; means to circulate a heat exchange fluid through said interior annular chamber, liquid feed means extending through the closed lower end of said second vessel, liquid withdrawal means in the lower portion of said first annular space and vapor withdrawal means from the upper portion of said first annular space.

9. The apparatus of claim 8 wherein said longitudinal passageway has a smoothly converging entrance, a narrow throat and a smoothly diverging exit.

10. The apparatus of claim 9 wherein said entrance has a maximum angle of convergence no greater than about 50 degrees and said exit has a maximum angle of divergence no greater than about 40 degrees.

11. The apparatus of claim 8 wherein said common wall is composed of a fluid-permeable material.

;12. The apparatus of claim 8 wherein said constricted lower end of said first conduit comprises a short section having a plurality of longitudinal passageways of lesser diameter than said first conduit, said section containing an annular chamber surrounding said passageways along a substantial portion of their length, but separated therefrom, and fluid supply and withdrawal conduits communicating with said chamber.

13. The apparatus of claim 12 wherein said chamber 1 1 1 2 is separated from said longitudinal passageways by a flu 2,772,729 Mayhew Dec. 4, 1956 permeable i l, 2,893,900 Machlin July 7, 1959 2,902,029 Hill Sept. 1, 1959 References Cited in t11fil6 Of t Paffiflt 2,962,221 Kunz Nov, 29, 1960 UNITED STATES PATENTS FOREIGN PATENTS 1,730,440 Smith Oct 8, 1929 759,062 Great Britain Oct. 10, 1956

Claims (1)

1. AN APPARATUS FOR THE SUBMERGED COMBUSTION HEATING OF LIQUIDS WHICH COMPRISES A VESSEL WITH LIQUID FEED MEANS AND LIQUID WITHDRAWAL MEANS CONNECTED THERETO AND MEANS TO REMOVE PRODUCTS OF COMBUSTION THEREFROM, A CONDUIT EXTENDING VERTICALLY INTO SAID VESSEL, A BURNER HAVING FUEL AND OXIDANT SUPPLY MEANS TO PRODUCE A FLAME AND GENERATE COMBUSTION GASES, SAID BURNER BEING POSITIONED WITHIN SAID CONDUIT TO DISCHARGE SAID COMBUSTION GASES THERETO, SAID CONDUIT EXTENDING DOWNWARDLY FROM SAID BURNER A SUBSTANTIAL DISTANCE, SAID DISTANCE BEING GREATER THAN THE LENGTH OF SAID FLAME NORMALLY PRODUCED BY SAID BURNER SO AS TO PREVENT THE FLAME PRODUCED BY SAID BURNER FROM IMPINGING ONTO SAID NOZZLE, THE END OF SAID CONDUIT TERMINATING WITHIN SAID VESSEL, BENEATH SAID LIQUID WITHDRAWAL MEANS, AND HAVING A DISCHARGE GAS PASSAGEWAY COMPRISING A THROAT OF CONSTRICTED CROSS-SECTION AND AN EXIT SECTION IMMEDIATLEY BENEATH SAID THROAT, SAID EXIT SECTION HAVING A SMOOTHLY DIVERGENT CROSS-SECTION SO AS TO EXPAND GASSES FLOWING THERETHROUGH AND INTO SAID VESSEL, AN ANNULAR CHAMBER SURROUNDING SAID DISCHARGE GAS PASSAGEWAY, SAID CHAMBER POSITIONED BENEATH SAID THROAT SO AS TO SURROUND ONLY SAID EXIT SECTION OF SAID NOZZLE AND MEANS TO CIRCULATE A HEAT EXCHANGE FLUID THROUGH SAID ANNULAR CHAMBER TO COOL THE SURFACE OF SAID EXIT SECTION OF SAID DISCHARGE GAS PASSAGEWAY.

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