US3385269A - Tube heating furnace - Google Patents

Description

May 28, 1968 R. M. BRECKENRIDGE 3,385,269

TUBE HEATING FURNACE Filed Jan. 26, 1967 FIG INVENTOR. R. M. BRECKENRIDGE ATTORNEY.

United States Patent O 3,385,269 TUBE HEATING FURNACE Robert M. Breckenridge, Maple Glen, Pa., assignor to Selas Corporation of America, Dresher, Pa., a corporation of Pennsylvania Filed Jan. 26, 1967, Ser. No. 611,856 7 Claims. (Cl. 122-240) ABSTRACT F THE DISCLOSURE A lmultiple cell tube heater in which one cell is used to bring the tiulid being heated almost to iinal temperature and a second :cell is used to finish the heating. Said one cell Lis fired primarily with oil as a fuel with gas fuel being used to supplement the oil. The second cell is fired entirely by gas as a fuel to `get accurate temperature control.

Background of invention In the heating of various uids in the petrochemical industry, it is customary to pass the fluid through an elon gated, serpentine coil, the passes of which may be either horizontal or vertical. In heating the liuid as it flows through the coil it is desirable, if not necessary, to raise the temperature at Ia predetermined rate and to control accurately the final or exit temperature of the uid. Furnaces of this type are usually red with either oil or gas as the fuel. Generally speaking more accurate control of the temperature along the coil ycan be obtained with gas as a fuel, and for this reason it is often used even though it is more expensive than oil. In some places, however, even though `accurate control is needed, gas is not available in sufficient quantities and/or its cost is too high to be used in the quantities necessary to tire a large tube heater.

Summary ofthe invention The furnace or heater of the present invention is provided with a plurality of chambers that are substantially separated from each other. An elongated, serpentine coil with vertically extending tube passes is suspended in the furnace with one group of tube passes in one chamber |and -other passes in another chamber. The chamber containing that portion of the coil forming the first passes through which the fluid to be heated flows, is ired primarily with oil as a fuel. Gas supplementary heating is used in this chamber to even out the temperature of the tube passes lengthwise. The chamber containing the last Ifew tube passes through which the fluid being heated travels, is heated by gas burners which may be adjusted to control accurately the final temperature of the uid. If desired, the heater rnay be so constructed that it contains more than one heating coil.

It is an object of the invention to provide a tube heater in which oil is the fuel use-d for the bulk of the Iheating Iand |in which gas is used to even the heating and produce the nal desired temperature of the material being heated.

It is la further object of the invention to provide a tube heater in which different sections of the coil are segregated so that they may be heated at different rates. Another object of the invention is to provide an oil red tube heater having supplementary gas firing for accurate temperature control.

The various features of novelty which characterize my invention are pointed out with particularity in the claims annexed to land forming a part of this specification. For a better understanding of the invention, however, its yadvantages and specific objects attained with its use, reference should be had to the accompanying drawings ice and descriptive matter in which I have illustrated and described Ka preferred embodiment of the invention.

In the drawings:

FIG. 1 is an elevation in section of the furnace taken on line 1-1 of FIG. 2; and

FIG. 2 is a section with a portion taken on the upper line of 2-2 of FIG. 1 and a portion taken on the lower line of 2 2 of FIG. l.

Referring to the drawings, it will be seen that while the he-ater may be built in two sections, it is shown herein las being built in three sections including end chambers 1 and 2 and a center chamber 3. The end chambers are identical in construction and same reference numerals will be used for the similar parts of these chambers. Each chamber includes an end wall 4 with lower side walls 5 and 6 joined by sloping walls 7 and S to upper side walls 9 and 11. A floor 12 extends between the lower ends of lside walls S and 6 and beneath the center chamber. It wiill be seen that the lower portion of the chamber 1 is considerably wider than the upper portion. This is because the lower portion 'is fired with oil Whereas the upper portion is fired with gas.

Floor 12 is provided with a plurality of openings 14 on each side thereof into which exten-d oil burners 15. These burners are supplied by a pipe 16 having a valve 17 therein. Supplemental -heat `for the upper, narrow p0rtion of the chamber is provided by Ia plurality of vertically extending rows of gas burners 18, each row of which is supplied with fuel by a manifold 19. Valves 21 are provided so that each burner can be adjusted individually and each manifold has in it a valve 22 so that the manifolds can be adjusted individually after the burners have been adjusted. lilii Central chamber 3, between the two end chambers, is of a width throughout its height substantially equal to the width of the upper narrow portion of the end chambers. This central chamber is provided with side walls 23 and 24 that extend vertically and are parallel to each other. There may also be provided, pairs of bafes 25 which extend inwardly from the side walls between the end chambers and the central chamber. These baies reduce the flow of combustion gases between the chambers but do not close the chambers off completely from each other.

The central chamber 3 is heated by gas burners 26 which are placed in vertical rows in the side walls. Each vertical row of burners is supplied with fuel from a manifold 27 and there are provided valves 28 between the manifold and each burner. Suitable valves are also provided for each manifold. It is noted that the gas burners in the upper portions of the side walls of the end chambers, as well as those in the walls of the central chamber, are preferably of the radiant cup type.

The products are combustion produced by the burners in the various chambers are carried off to a stack through an opening 31 that extends from one side of the roof 29 from all three of the chambers. The roof is provided with a vertically disposed and horizontally extending slot 32 through which the coils to be heated are placed and are supported. The heater of the present application is shown as being provided with two tube coils 33 and 34. One of these coils is in chamber 1 with its last few tube lengths in chamber 3 while the other coil 35 is located mainly in chamber 2 with the last few tube lengths in chamber 3. Each of the coils is a serpentine, endless coil consisting of vertically extending tube passes that are joined at each end by return bends. In mounting the coils in the furnace they are moved in a vertical position by a suitable crane downwardly through slot 32. The lower retu-rn bends 36 are provided with a threaded bolt 37 that extends through the iloor and is held in position by nuts 38. Thus, the tube passes are definitely located in the furnace with respect to the burners and are held in position. The upper ends of the coil are mounted so that, as the furnace is heated, expansion of the tubes may take place. To this end, each of the upper return bends is provided with a bracket 39 through which extends a ring 41. This ring has attached to it a cable 42 passing over pulleys 43 to a suitable counterweight 44. The counterweight is preferably of a weight sufficient to equal about 60% of the weight of the pair of vertical tubes to which it is attached. In this manner, the tubes are held straight as they expand when the furnace is heated. There are provided bricks 45 which surround the tubes in slot `32 in order to close this slot and prevent loss of heat therethrough. The space above the bricks 45 around the upper return bends and between beams 45 is preferably filled with a fibrous insulation in order to insulate the root of the heater.

ln operating the heater, the fluid to be heated, which can be naphtha or some other hydrocarbon, is introduced at the bottom, fixed ends of coils 33 and 34 in the last tube adjacent to the end walls 4 of chambers 1 and 2 as indicated by the arrows. The flow is toward the center of the heater to be discharged at the fixed lower end of the last tube of each coil in the center of chamber 3, as indicated by the arrows.

Oil burners 1S are red in the lower portions of chambers 1 and 3 to -heat the side walls of those chambers to incandescence and thereby radiate heat to the lower ends of the tubes therein. The burners are so fired that the tubes are heated as evenly as possible. The hot products of combustion owing upwardly through the narrow portions of these chambers -heat the upper ends of these tubes, but not as much as the lower ends are heated. Supplemental heat to even out the temperature of the upper ends of the tubes is supplied by gas burners 18. Generally the lower burners will be supplied with less fuel than the upper burners of each row since the combustion gases passing through the lower part of the narrow section are hotter than those passing through the upper part. Individual burners and rows of burners can be adjusted as necessary.

By the time the fluid in the coils has reached the last few tubes in center chamber 3 it has almost reached its final temperature, which must be accurately controlled. These tubes are in narrow chamber 3 between the vertical rows of burners 26. The plurality of burners in each row and the plurality of rows of burners can be adjusted -to regulate accurately the nal temperature of the tubes and the fluid flowing through them.

Many tube heaters are fired entirely by oil, and adequate temperature control can be obtained for many noncritical processes. It is well known, however, that multiple radiant gas burners are capable of heating a tube more uniformly and more accurately than is possible with oil. The furnace construction disclosed herein uses oil fuel to provide most of the heat and uses gas to supplement the oil in order to even out the tube temperatures and to control accurately the final temperature. Generally about 60% of the required heat is produced by the oil, although this percentage may be reduced somewhat Where the lrequirements for accurate control of the temperature of the tubes is increased.

While in accordance with the provisions of the statutes I have illustrated and described the best form of embodirnent of my invention now known to me, it will be apparent to those skilled in the art that changes may be made in the form of the apparatus disclosed without departing from the spirit and scope of the invention set forth in t-he appended claims, and that in some cases certain features of my invention may be used to advantage without a corresponding use of other features.

What is claimed is:

1. In a tube heater the combination of structure forming a plurality of vertically extending chambers communicating with each other, a first of said chambers having a wide portion and a vertically displaced narrow portion, a plurality of oil burners tiring into said wide portion with the products of combustion tiowing through said narrow portion, a plurality of gas burners firing into said narrow portion, means individually to adjust said gas burners, a second of said chambers being of a width substantially equal to the width of the narrow portion of said first chamber, a plurality of vertically extending rows of gas burners firing into said second chamber, 4an elongated serpentine coil comprising a plurality of tubes connected by upper and lower return bends, means to mount said coil with the tube passes extending vertically through the center of said chambers with some of the tube passes in said first chamber and some of the tube passes in said second chamber.

2. The combination of claim 1 in which said structure includes a door and a roof for said chambers, said roof being provided with a :slot extending above said chambers, said lower return bends being fastened to said door in spaced relation thereto, said upper return bends extending through said slot, and means to bias said upper return ybends in an upwardly direction.

3. The combination of claim 1 in which said oil burners fire through said door generally toward the portion of said structure forming side walls of the wide portion of said first chamber thereby to heat the length of said tubes in said portion, the products of combustion -iiowing througs said narrow portion to heat the length of tubes therein.

4. The combustion of claim 3 including means to adjust the supply of fuel t-o the gas burners in the walls of the narrow portion of said first chamber to supplement the heating of the length of tubes therein whereby to even the heating of the entire lengths of the tube passes in said first chamber.

`5. The combination lof claim 1 in which said gas burners firing into the narrow portion of said first chamber are located in vertically spaced rows, parallel to said tubes, in the structure forming the side walls of said narrow portion.

`6. The combination of claim 5 including means to adjust separately the supply of gas to the rows of burners firing into said narrow portion of said first chamber, and means to adjust individually the burners in each `now.

l. The combination of claim 1 in which the tube passes in said first chamber form the entrance end of said coil and the tube passes in said second chamber form the exit end of said coil, said vertical rows of burners firing into said second chamber being parallel to and on opposite sides of the tube passes therein, and means individually to adjust said rows of burners.

References Cited UNITED STATES PATENTS 2,638,879 5/1953 Hess 122-356 `3,066,656 12/ 1962 Hensel 122-240 3,182,638 5/ 1965 Lee et al. 122-240 3,240,204 3/ 1966 Von Wiesenthal 122-240X CHARLES I. MYHRE, Primary Examiner.

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