Immersion-heater dip tube

[57] ABSTRACT

A heater comprises two concentric vertical tubes having a flame projecting down in the inner tube with the lower end of at least one of the tubes immersed in a tank of liquid, as a salt solution or an acid solution to be evaporated, condensed, and recirculated in the annulus between the tubes. Helical spiral vanes are formed in the annulus for delaying and spinning a thin, consistent film of the liquid over the contiguous surfaces of the tubes for producing considerably decreased operating temperatures of the tubes resulting in greatly decreased corrosion of and deposit formation on the heater.

Claims, 2 Drawing Figures

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PATENTED FEB 2 61974

3,794,015

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3,794,015

IMMERSION-HEATER DIP TUBE DESCRIPTION OF THE PRIOR ART

The present invention relates to an immersion-heater dip tube for immersion-heater installations which bum a fuel and air mixture for evaporating salt solutions or more particularly acid solutions.

It is common to use immersion-heater installations to evaporate and concentrate dilute aqueous salt or acid solutions. Basically, such installations include a furnace chamber partly filled with the liquid to be evaporated and communicating with a flue or vapor outlet for the flue gas. At least one immersion-heater dip tube protrudes into the liquid so that the hot fuel gases are discharged into the liquid at the tube outer opening where the heat is released and finally passes up through a flue or vapor outlet.

Conventional immersion-heater dip tubes have an upper section extending at least partially beyond the furnace chamber of the immersion-heater installation and serve as an intake for the gaseous or liquid fuel, e.g., natural gas, lighting gas, coke oven gas, or fuel oil, or similar fuels, and air. In different design of the immersion-heater, fuel and air may be introduced either separately into the upper section or intake of the immersion-heater dip tube and mixed there, or they may be introduced as a combustible mixture. The immersion-heater dip tube upper section or intake communicates downwardly with a combustion unit or section, which usually has an enlarged cross-section The fuel and air mixture applied via the intake is ignited in the combustion chamber section and burns with an open flame. It is known to be useful to build the combustion chamber long enough to permit only the hot fuel gases, but not the flame itself, to touch the urface of the liquid to be evaporated. Otherwise a larger quantity of liquid droplets will be entrained by the fuel gases and pass an aerosol into the flue.

A very difficult problem encountered in immersionheater installations of the above described design is the formation of a deposit on and corrosion of the combustion chamber section lower end extending into the liquid. Salt solutions very often leave a deposit, particularly on the hot combustion chamber walls, thus narrowing the free cross-section of the combustion chamber normally available for the flue gases and necessitating the heater to be closed down. The concentration of dilute acid solutions such as phosphoric or sulfuric acid requires additional efficient corrosion-inhibiting measures regarding the immersion-heater dip tube. It is therefore customary to manufacture all or at least the most severely stressed parts of an immersion-heater dip tube from materials that are sufficiently temperatureresistant and acid-resistant, as for example, graphite, ferro-silicon, and the like. Owing to the high cost of these materials it is also common to use a cheaper material, e.g., grey cast iron which is only temperatureresistant for the inner wall of the combustion chamber section and protect this immersion-heater dip tube inner part with a jacket tube made of, for example, ferro-silicon, which is corrosion-resistant but less resistant to thermal and mechanical stresses. It is further known to insert thermal insulating material between the two tubes.

German Offenlegungsschrift 1,519,685 discloses an immersion-heater dip tube, with the jacket tube being fitted at a radial distance from the internal combustion tube, leaving a space between the combustion tube and the jacket tube, into which inert gas is injected and maintained at a pressure suficent to prevent the acid solution from penetrating therein. In this conventional 5 installation the jacket tube, having a higher resistance to corrosion, is thermally relieved by the annular space filled with inert gas. But even with this type of heater neither the combustion tube nor the jacket tube can be prevented from corroding after a relatively short run10 ning time, so that both have to be exchanged or at least overhauled and reconditioned.

OBJECTS OF THE INVENTION

Accordingly, a primary object of this invention is to 15 provide a heater that is not susceptible to corrosion and thus has a longer life.

Another primary object of this invention is to form the walls of an immersion-heater dip tube of an inexpensive material as glass or a synthetic material and to 20 maintain the walls cool by evaporation of the liquid there-between.

Yet another object of this invention is to provide an immersion-heater dip tube with concentric tubular walls with a liquid circulating around the walls for cool25 ing thereof.

A further object of this invention is to provide an immersion-heater dip tube which spreads a thin film of liquid to be concentrated over a greater portion of the walls of the heater for achieving greater evaporation.

³⁰ A still futher object of this invention is to provide an immersion-heater dip tube that is easy to operate, is of simple configuration, and is formed of economical inexpensive materials.

Other objects and various advantages of the disclosed ³³ immersion-heater dip tube will be apparent from the following detailed description, together with the accompanying drawing, submitted for purposes of illustration only, and not intended to define the scope of the invention, reference being had for that purpose to the ⁴⁰ subjoined claims.

BRIEF DESCRIPTION OF THE DRAWING

The drawing diagrammatically illustrates by way of example not by way of limitation, two forms of the in⁴³ vention wherein like reference numerals have been employed to indicate similar parts.

FIG. 1 is a schematic elevation of the immersionheater dip tube with parts in section; and

FIG. 2 is a modification of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

The invention disclosed herein, the scope of which being defined in the appended claims is not limited in its application to the details of construction and arrangement of parts shown and described, since the invention is capable of other embodiments and of being practiced or carried out in various other ways. Also, it is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation.

The present invention achieves the above objects by providing an immersion-heater dip tube for an immersion-heater installation heated with a fuel-air mixture, for use in evaporating salt solutions or more particularly acid solutions. This heater comprises at least one intake means for the fuel and/or air mixture, an ignition

3,794,015 ⁴ device for the fuel gas, a combustion chamber having an open end protruding vertically downwardly and at least one tube extending below the level of a liquid to be evaporated by the immersion-heater, and a protecting shield or second tube which is spaced from the first tube but which is fixed relative thereto and concentric therewith. One feature of this immersion-heater dip tube is that at least one of the tubes is covered with a continuously renewed, relatively thin, consistent film of the liquid to be evaporated.

FIG. 1 illustrates schametically one embodiment of the invention, an immersion-heater dip tube 10 comprising two concentric tubes 11 and 12 having fixed at the top thereof a suitable furnace, such as but not limited to, a gas-air furnace 13 wherein a fuel and air mixture is injected at the top thereof. This fuel-air mixture is injected downwardly in the first or inner tube, the upper portion of which forms an intake conduit 14, ignition taking place at the mid-portion 15 of the tube where the inside diameter of the tube increases to form a combustion chamber 16. The second or outer tube 12 is concentric with the first tube 11 and extends in this modification down to the bottom of the first tube, the lower end of both tubes extending down into a container of liquid 17 such as the salt or acid solutions. This liquid to be evaporated is circulated by a suitable hydraulic pump 21 for pumping the liquid 17 from the tank at the bottom up through pipe 22, the pump 21, and pipe 23 into the liquid intake 18 at the top portion of the heater and down in the annular space or chamber between the two tubes 11 and 16. Thus as it passes down the annular chamber, a film of coolant liquid is formed on the contiguous surfaces of the tubes and the liquid is evaporated as it circulated downwardly to raise the density of the remaining liquid below. Helical spiral cooling vanes 19 are formed on the external surface of the inner tube 11 for causing the liquid to spiral and circulate around the inner tube as it returns to the tank at the bottom. In addition to the helical spiral vanes is a helical spiral packing cord 20, or the like, which is circular in cross-section and likewise encircles the inner tube in a helical spiral configuration, but with increased pitch for causing the fluid to spiral around the inner tube and between the two tubes as it flows around and downwardly. Thus, the annular space or annulus between the two tubes is formed in which the liquid to be evaporated is continuously circulated so that the inner parts of the immersion-heater dip tube or surfaces of the two tubes are continuously covered with a relatively thin film of liquid. With the annulus being open at the lower end of the tubes, the circulating liquid ultimately passes into the liquid container or furnace bottom where it combines with the liquid 17 stored there. The fins 19 and spiral cord 20 all forming a continuous spiral surface which will greatly improve the heat transfer from the walls of the tubes where combustion takes place to the thin film of liquid on the tube surfaces.

FIG. 2 illustrates a second embodiment of the immersion-heater dip tube 10α wherein the air-gas mixture is injected from the heater 13α which is connected to the tops of the two tubes 11α and 12α. and passes down internally of the inner tube 11α. The inner tube ends where the combustion chamber 16α begins. The outer tube 12α which is concentric with and spaced radially from the inner tube forms the outer wall of a helical conduit therein the liquid 17α from the tank is pumped by a suitable hydraulic pump 21α up through pipes 22α and 23α into the top of the tube at intake 18α and passes down this annular space. Helical, radial and spiral vanes, or a continuous spiral surface 19α is secured to the outer surface of the inner tube 11α in this annu5 lar space whereby as the liquid passes down through the annular space it is given a centrifugal whirl so that when the liquid passes down and out of this annular space into the combustion chamber formed by only the outer tube, centrifugal force holds the fluid pressed 10 against the wall in a spiralling condition as it flows down the inner surface of the wall to the liquid 17α below. As seen in FIG. 2, the outer tube forms the wall of the combustion chamber 16α. As the liquid flows down the inner surface of the outer tube 12α it is evap15 orated and results in concentration of the liquid in the tank. Thus, the annular vanes 19α impart a spin to the liquid as it leaves the annular space and is distributed in a thin film over the inside surface of the outer tube.

Further, as long as the liquid film contains water the 20 temperature of the liquid film will not exceed substantially 100° C., irrespective of the temperature of the fuel gases. The walls of this area where combustion takes place are thus kept at a relatively low temperature due to liquid evaporation cooling. At this tempera25 ture, corrosion is not accelerated and the risk of deposit formation is small. With such intensive cooling of the tube where combustion takes place, there is not even need for double walls for this area of the immersion-heater dip tube. In the simplest case the hitherto ³⁰ necessary combustion chamber may be deleted and the outer tube act as the fuel gas conduit and combustion chamber. Another advantage offered by this embodiment of the invention is the use of inexpensive materials such as synthetics or silica glass for the manufacture ³⁵ of the jacket or outer tube.

In operation, the liquid is pumped up and injected into the liquid intake at the top of the heater from where it flows down the annular space between the two tubes. As the liquid is guided by the radial helical spiral ⁴θ vanes a whirling action is imparted to the liquid as it leaves the guiding vanes where it is whirled around an pressed by centrifugal force against the internal surface of the hot outer tube on its route to the tank of liquid below. Thus, it has been shown that the liquid can be ⁴⁵ distributed as a thin layer of film over the inner surface of the outer tube in the combustion area by using the guide vanes, the pitch of the guide vanes being formed to provide the proper flow rate of liquid through the annular space and over the cylindrical surface of the ⁵⁰ outer tube.

Thus, it will be seen that the instant immersionheater dip tube provides an evaporating heater for condensing liquid in a manner which meets each of the objects set forth above.

⁵⁵ While two portions of an immersion-heater dip tube have been disclosed in the accompanying specification and drawing, it will be evident that various other modifications are possible in the arrangement and construction of the disclosed immersion-heater dip tube without ⁶⁰ departing from the scope of the invention, and it is accordingly desired to comprehend within the purview of the invention such modifications as may be considered to fall within the scope of the appended claims.