US2224917A - Method of heating fluids - Google Patents

Description

Dec. 17,1940. L. A.

METHOD OF MEKLER 2,224,917

.HEAT ING FLUIDS Original Fi led Dec. 26; 1931 I 0 7 lo O v 0000 n 1 1 l5 l7 4/ 0000d000 FIG. I

TEMPERATURE OF FLUID PERCENTAGE OF HEATING SURFACE FIG. 3

INVENTOR LEV A. MEKLER ATTORNE Patented Dec. 17, 1940 PATENT OFFICE METHOD OF HEATING FLUIDS Lev A. Mekler, Chicago, 111., assignor, by mesne assignments, to Universal vOil Products Com pany, Chicago, 111., a corporation of Delaware Application December 26, 1931," Serial No. 583,341

' Renewed November 10, 1938 1 Claim.

many of these furnaces may be easily converted into more eflicient heating units, employing the more modern methods of combination radiant and convection heating, by adding, inaddition to the existing bank of convection tubes, a row of radiant tubes in the upper portion of the furnace along the roof and along a portion ,of the Walls and by adding a row .of radiant floor tubes along the floor of the combustion zone of the furnace. Preferably the old firing arrangement is changed and the improved furnace is fired throughoneor a-plurality of firing tunnels extending into a side of the furnace and having air inlet ducts substantially surrounding or adjacent the firing compartment thereof.

In its specific embodiment the present invention comprises an improved form of furnace for heating fluids having a combustion zone, means for supplying combustible materials to said combustion zone, a convection heating zone, a bridge wall separating said combustion zone from said convection heating zone, fluid conduits disposed along the floor of said combustion zone receiving substantially radiant heat, fluid conduits disposed along'the roof and upper portion of the walls of the furnace to receive substantially radiant heat and fluid conduits disposed within said convection heating zone to receive substantially convection heat.

The arrangement of the heating element, i.- e., the conduit through which the fluid is passed during heating, as provided by the apparatus of the invention, is especially well adapted to a flow of fluid which results in an improved heating method and which is especially advantageous in heating hydrocarbon oil to the relatively high temperatures utilized in their conversion or cracking. Ihis method comprises subjecting the oil, during the initial stages of its heating, toa relatively high rate of heating to bring it quickly to a conversion temperature, thence subjecting it to continued heating at a somewhat slower rate and finally again subjecting the oil to a relatively rapid rate of heating to bring it to the maximum temperature employed substantially at the outlet from the heating element. This may be accomplished in the apparatus of the present inventionby passing the oil first through the floor bank of I radiant tubes, thence through the convection bank of tubes preferabIy countercurrent 5 to' the flow of combustion gases and finally through the radiant bank of tubes disposed along thereof and sides of the furnace.

The attached diagrammatic drawing illustrates one formof apparatus for carrying out the 10 method of the present invention. Figure l is a cross-sectional elevation of the furnace. Figure 2- illustrates diagrammatically the preferred flow of fluid through the heating element of the furnace illustrated in Figure 1,. Figure 3 illustrates the generalform of heating curve obtainable by employment of the improved heating means illustrated in Figures 1 and 2.

Referring nowipar'ticularly to Figure 1, the side walls are indicated at I and 2, the roof is indi- 20- cated at 3 and the floor of the combustion zone 4 is indicated at5. "A'bridge wall6 separates combustionzone 4 from convection heating zone 1.

One or a plurality of firing tunnels 8, disposed along side wall I of the furnace, furnish means of supplying combustible materials to combustionzone 4'; Any suitable fuel such as, for ex-v ample, 'o'il, pulverized solid fuel, gas or the like, may be introduced through any suitable burner arrangement, not shown, to firing compartment 30 9, of tunnel 8. 'Ducts l0 and H, adjacent firing compartment 9, serve as a means of introducing air, steam or both to the combustion zone of the furnace, the admission of such materials being regulated by dampers l2.

The combustion gases pass upward through combustion zone l over bride-wall 6, downward throughjconvectionheating zone I and out of the furnace to'a stack, not shown,through flue l3. i

A row or bank ll of tubes I5, preferably connected at their ends in series by suitable return bends, headers or other well known means not illustrated, is disposed along the floor 5 of combustion zone 4. Preferably radiant bank I4 is depressed below the level of firing compartment 9 sufliciently to prevent any substantial direct impingement of flame upon the tubes. A radiant bank or row l6 of tubes I5 is disposed along the upper portion of the furnace, adjacent roof 3 and walls I and 2. That portion of bank I6 adjacent wall I of the furnace may, if desired, be recessed, as illustrated in the drawing, to substantially prevent flame impingement against the tubes. A convection bank I! of tubes I5 is disposed within 55,

" conversion temperature and, second, by virtue of ture, by having first passed through another porconvection heating zone 1 of the furnace, being separated from combustion zone 4 by bridge wall 6. The tubes of radiant bank I6 and convection bank I! are also preferably connected in series, as already mentioned in connection with radiant bank I4. Radiant heating banks I4 and 16 receives substantially radiant heat from the hot combustion gases and-from the heated refractory walls of the furnace while convection bank I'I receives substantially convection heat from the somewhat cooler combustion gases passing downward through convection zone 1 around the tubes of said convection bank.

It will be apparent from the drawing, that'the tubes of the radiant floor bank [4 aresubjected to more severe conditions than thetubes of theother heating banks in the furnace and unless fluid to be heated, first into the radiant floor bank l4, serves a two-fold purpose. First it provides a means of rapidly bringing the oil to a the relatively cool condition of the oil entering this bank of tubes, said tubes are protected against such overheating as might result if the oil were introduced thereto at a higher temperation of the heating element.

Referring now to Figure 2 which diagrammatically illustrates the preferred flow of fluid through the heating elements of a furnace such as illustrated in Figure 1. The radiant bank of floor tubes is again indicated at l4, the convection bank is indicated at IT and the radiant roof and wall bank at It. Theoil to be treated is 40? introduced through line [8 into the first tube of radiant floor bank I4, passing through the sucsucceeding tubes of this bank in series, transdicated in Figure 1) of the furnace, j passing "the upper portion of wall I (indicated in Figure ferring thence through line 20, which is also preferably located outside the heating zone, to the lower tube of that portion of radiant bank IS, located along the upper portion of wall 2 (inthence through the succeeding tubes of radiant bank 16 in series and out of the furnace through line 2|, being dischargedfrom the lower tube of that portion of radiant bank I6, located along 1) of the furnace.

Figure 3, as already stated, indicates the gene eral type of heating curve which may be obtained by utilizing the form of furnace illustrated in,

Figure 1 and a flow of fluid through the fluid conduit of this furnace, as illustrated in Figure 2. It will be noted from the heating curve and by comparison of this curve with the flow diagram of Figure 2 that the oil is first heated in the radiant floor bank M at a relatively high rate, that the temperature obtained in this zone is gradually increased at a slower rate of heating in convection bank l1 and is thence again subjected to a relatively rapid rate of heating in radiant bank l6, discharging from this zone at the maximum temperature attained in the furnace. Those conversant with the cracking art will, appreciate the advantages of this type of heating curve in the conversion of many types of oils. Its primary advantages reside in the fact that the oil may be first rapidly raised to a relatively mild conversion temperature, may be thence maintained at a gradually increasing but relatively mild conversion temperature for an eX- tended period of time and may be thence rapidly brought to the maximum conversion temperature desired. This procedure not only minimizes local overheating of the oil with consequent excessive gas and coke formation but also serves as a means of protecting that portion of the fluid conduit which is subjected to the most severe heating conditions by feeding the oil therethrough while said oil is still relatively cool.

It will be understood that the invention is not limited to the particular flow of fluid illustrated in Figure 2, nor to the specific form of furnace illustrated in Figure 1, nor to the type of heating curve indicated in Figure 3, as the principles involved may be accomplished in modified forms of apparatus and under different heating conditions whichv do not depart from the scope of the invention. v

I claim as my invention:

In the heating of hydrocarbon oils to cracking temperature in furnaces having a pair of side walls, a floor and a roof and, av bridge wall dividing the furnace into a, convection heating zone and aradiant heating zone, the method which comprises firing the furnace adjacent the lower portion of the radiant zone and passing resultant combustion gases through the convection zone, passing the ,oil initially through tubes adjacent the floor to raise it quickly to mild cracking temperature. at a relatively high rate of heating, thence passing, the oil through the convection zone tosubject itto continued heating at a lower rate of heating, and .then raising theoil to maximum cracking temperature under a relatively high rate of heating by passing it through tubes adjacent the side wall nearer the convection zone, then through tubes adjacent the roof and finally through wall tubes on the firingside of-the furnace.

LEV A. MEKLER.

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