US2556984A - Immersion heater - Google Patents

Description

June 12, 1951 sMlTH 2,556,984

IMMERSION HEATER Filed Feb. 14, 1946 INVEN TOR. FRANK E. SMITH AGENT Patented June 12, 1951 i IMIWERSION HEATER Frank E. Smith, Niagara Falls, N. Y., assignor to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware Application February 14, 1946, Serial No. 647,522

2 Claims.

This invention relates to gas or oil heaters particularly heaters of the immersion type adapted to be partially immersed in liquid to be heated.

Immersion heaters are known which are constructed in the form of a U or hairpin. Gas or oil with suflicient air is delivered to the end of one leg of the U so that combustion occurs as the gaseous products travel through the U and out of the second leg to a stack. The heater is employed by immersing the lower part of the U into the liquid to be heated with the legs extending above the liquid. When used for heating liquids at high temperatures, e. g. fused salt mixtures at temperatures around 800900 C., delivery of heat is generally inadequate especially when the liquid being heated is employed as a reaction medium for carrying out a chemical reaction requiring a large heat input. Attempts have been made to increase the heating capacity by delivering fuel premixed with sufficient air to support complete combustion to the lower part of the U. Such a practice, while successful in supplying large amounts of heat due to the almost instantaneous type of combustion resulting from igniting fuel premixed with air, rapidly burns out the heater in the vicinity of the bend of the U. If fuel and air are supplied separately to the bend of the U, the maximum heat obtainable from the fuel is not developed before the gases escape to the stack.

It is an object of my invention to provide an immersion type heater of such construction that those parts thereof which are immersed in the liquid to be heated will be the parts in which maximum evolution of heat is attained. A further object is to provide an immersion type heater capable of supplying to the liquid being heated a large amount of heat at high temperatures, the heater being so constructed that maximum heat is generated only inthose parts immersed I in the liquid and the danger of structural failure of the heater parts will be substantially minimized. A still further object is an improved method of heating a liquid utilizing the improved heater of this invention. These and further objects will be apparent from the following description of the invention.

The above objects may be accomplished in accordance with my invention by partially burning a gaseous or liquid fuel in an upper chamber, passing the partially burned gases to a lower vertical shell immersed in the liquid being heated, and supplying sufiicient air to the partially burned gases in the lower shell so as to complete the combustion and develop maximum heat ina zone 2 within the shell where maximum transfer of heat to the liquid being heated occurs.

The invention will be better understood by reference to the attached drawing which is a vertical view, shown partly in section and partly in elevation, of one modification of the invention.

In the drawing, upper combustion chamber I, which is positioned horizontally, has an inner lining of refractory material 2 and an outer protective metal plate covering 3. Chamber I is provided with an inspection door 4, a clean-out door 5 and a burner 6 having a fuel inlet 1 and an air inlet 8. Positioned below the forward portion of chamber I is a vertical, cylindrical shell '9 whose lower end is closed. An inner conduit Ill functions to conduct the products of partial combustion from the forward end of chamber I to the lower-end of shell 9. Between conduit I0 and the walls of shell 9 is an intermediate tube II which is of substantially equal length with tube I0 and is annular with respect thereto. Conduit l9 and tube II together form an annular air chamber I2, since the bottom ends of those two members are closed off from the remaining space in shell 9 by circular member I3. Intermediate tube II forms together with the walls of shell 9 a relatively narrow annular space I4.

Tube I5 serves to deliver air to annular air chamber l2 and such air is admitted to the stream of partially combusted gases as they flow through the burner by way of holes IS in the lower end of inner conduit I0. These holes are shown spaced around the circumference of inner tube II) in two rows. Annular space I4 adjacent the walls of shell 9 opens into stack II. The heater is shown partially immersed in a liquid bath I9 provided with a cover I8 through which shell 9 passes. The heater is supported on cover I8 by means of flange 20 around shell 9. At'the point at which tube I5 enters shell 9, there is provided a packing material 2| which may be an insulating cement or any other suitable material.

' In operation, a mixture of fuel and a deficiency of air is injected from burner 6 into chamber I where partial combustion occurs. The products of that partial combustion are delivered by inner conduit III to the bottom of shell 9. Suflicient air to complete combustion is supplied to the gas stream near the bottom of shell 9 through holes I6 of conduit III by way of air chamber I2 and tube I5. Complete combustion occurs at the bottom of shell 9 and in the annular space, I l

adjacent the side walls thereof. It will be noted that the portion of the heater wherein complete combustion occurs, i. e. that portion in which maximum heat is evolved, is the part which is immersed in the liquid being heated. The combustion gases pass from annular space [4 into stack I1.

I have found that satisfactory operation of the heater described may be accomplished by supplying sufiicient air with the fuel in the upper combustion chamber to burn the fuel to the water and carbon monoxide stage. I prefer, when using fuel oil, to supply about 70% of the air required to support complete combustion along with the fuel to the upper combustion chamber. That amount of air will cause the release of about 60% of the heat value of fuel oil and will result in the gases passing from the upper combustion chamber having a temperature in the range of around 900-1000 C. About 30% of the air required for complete combustion is admitted to the gas stream by way of holes l6. Ihe temperatures of the gases in the zone where complete combustion occurs will, of course, vary depending upon the temperature of the liquid surrounding the immersed part of the shell. With liquid being heated at a temperature in the range of 8504300 C., I have operated the heater with temperatures in the zone of complete combustion around 950-l000 C., or not more than about 100 C. higher than the temperature of the liquid surrounding the immersed part of the heater. Without rapid transfer of heat to the bath being heated, the temperature in the zone of complete combustion would, of course, be much higher, e. g. in the range 1500-1600 C.

The distribution of the air required to complete combustion between the upper and lower zones of combustion may be varied considerably and will depend largely upon the particular fuel being used. Generally, from 60 to 70% of the air should be supplied with the fuel to the upper chamber with the balance of the air being injected into the products of partial combustion by way of holes I6 as described above. The quantity of air to be supplied with the fuel to the upper chamber should be sufiicient to liberate from 55 to 65% of the total heat value of the fuel. Any fluid fuel, for example, any of the natural or artificial gaseous fuels, may be used, but the invention is especially well suited for the use of fuel oil.

I have found it very advantageous to supply the supplemental air from an annular chamber surrounding inner conduit 9 over its entire length, even though the injection of such air into the products of partial combustion is to be made only at the lower portion of the heater. This is because air supplied as indicated serves to cool inner tube l and also intermediate tube ll and maintains those tubes at temperatures sufilciently low to prevent their failure. An additional advantage is that air so delivered becomes thoroughly preheated before actual injection.

As will be apparent from the foregoing description, the parts of the heater which are subjected to the greatest degree of heat are that part of shell 9 below the stack, the corresponding part of tube I l, and the lower part of inner conduit 1 0. The manner of burning and of supplying supplemental air operate to keep the temperatures of those parts as low as possible. Thus, those parts of shell 9 which are subjected to the highest temperatures are in direct contact with the bath being heated which removes heat therefrom while the parts of the inner tubes of the heater subjected to the greater heat are cooled by means of .the stream of air in annular air chamber l2. The heater therefore is admirably well constructed for delivering large quantities of heat to a surrounding liquid medium while insuring maximum cooling of burner parts.

When using the heater for heating liquid baths at very high temperatures, it will, of course, be desirable to construct the burner parts of materials designed to withstand high temperatures, thus the various high temperature heat-resisting stainless steels may be used to construct those parts which cannot be advantageously lined with refractory material. The choice of structural materials will, of course, depend upon the intended use of the heater and shell 9 should be constructed of material which will be chemically resistant to the ingredients of the bath being heated.

The immersion heater of my invention is particularly well-suited for heating liquid reaction mixtures wherein the production of cyanides is effected. Such reactions require high temperatures and. an unusually high heat input as a result of which immersion heaters heretofore known, e. g. heaters of the U type, have not been satisfactory.

Various modifications may be made in the details of the heater. For example, the gaseous products of combustion may be withdrawn by way of a flue in the form of an annular passage around the vertical shell instead of from one side .as illustrated in the drawing. Furthermore, the holes for admitting air into the products of partial combustion need not be arranged in two rows as indicated but may be distributed around the end of the inner conduit in a variety of ways. It is important, however, for satisfactory operation that such holes be in the lower end of the inner tube If! so that maximum heat evolution will occur outside of tube E0 in a zone adjacent the walls of shell 9 where rapid transfer of heat to the Surrounding liquid bath results. Holes 16 are preferably spaced around tube H1 so that the jets of air delivered to the gas stream will oppose each other. Positioning of the holes so that jets of air will impinge directly upon the surface of tube 10 or shell 9 should be avoided.

Since many changes may be made in the details of the invention as set forth above without departing from the spirit and scope thereof, it is to be understood that the invention is not restricted to such details except as indicated in the appended claims.

I claim:

1. A heater of the type adapted for use by immersion in liquid to be heated which comprises an upper horizontal combustion chamber and a lower vertical cylindrical shell having a closed lower end adapted to be immersed in the liquid being heated, a cylindrical concentric conduit Within said shell adapted to lead products of partial combustion from the forward end of said upper chamber to the bottom of said shell, the walls of said conduit being provided near its lower end with a plurality of holes spaced around .said walls, an annular member between said shell and said conduit, said annular member being of substantially the same length as said conduit and forming therewith an annular air chamberwithin said shell, means for delivering air into the upper portion of said air chamber, and means for exhausting combustion gases from the upper portion of said shell.

2. A heater of the type adapted for use by iminersion in a liquid to be heated which comprises an upper horizontal combustion chamber and a lower vertical cylindrical shell having a closed lower end and adapted to be immersed in the liquid being heated, two concentric cylindrical conduits of substantially equal length positioned 5 within said shell so as to provide an annular air chamber within said shell, the inner-most of said conduits being adapted to lead products of partial combustion from the forward end of said upper chamber to the bottom of said shell, the walls of the lower portion of said inner-most conduit being provided with a plurality of holes spaced around said walls, the outer-most of said conduits forming with said shell an annular space leading to a stack and a tube for supplying air 15 to said annular air chamber.

FRANK E. SMITH.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,923,614 Clarkson Aug. 22, 1933 2,059,523 Hepburn et a1. Nov. 3, 1936 2,118,479 See et al. May 24, 1938 10 2,200,731 Woodson May 14, 1940 FOREIGN PATENTS Number Country Date 502,112 Great Britain Mar. 13, 1939

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