US2752897A - Multi-coil heater - Google Patents

Description

July 3, 1956 A. MEKLER MULTI-COIL HEATER 5 Sheets-Sheet l Filed Feb. 3, 1953 INVENTOR. Lev ,4. Me/er JJMM;

ATTORNEYS July 3, 1956 L. A. MEKLER MULTI-com HEATER 5 Sheets-Sheet 2 Filed Feb. 3, 1953 P' `[E E nrdfffgm INVENTOR. ez/ f4. Me/er Arrow/5v5 July 3 1956 L. A. MEKLER 2,752,897

MULTI-COIL HEATER Filed Feb. 3, 1953 5 Sheets-Sheet 3 INVENTOR. 1 Lev A. Me/6r 5 Sheets-Sheet 4 Q 'ajron R .i Convedion M DimmL Qadiaron m erad erad L.. A. MEKLER fRadainq Plane JNVENTOR. Lev. /l//e/a/@r ATmQA/Evs Plane MULTI-COIL HEATER Tube Number f El July 3, 1956 Filed Feb. 3, 1953 My 1956 L.. A. MEKLER MULTI-COIL HEATER 5 Sheets-Sheet 5 Filed Feb. 3, 1953 INVENTOR., ev ,4. /We ,4f/ef BY vida.,

ATTORNEYS United States Patent O MULTI-COIL HEATER Lev A. Mekler, Palo Alto, Calif.

Application February 3, 1953, Serial No. 334,793

3 Claims. (Cl. 122-262) This invention relates to an apparatus for heating fluids and more particularly to an apparatus for effectively regulating the amount of heat absorbed by the uid in the various stages of the heating process.

At present tubular heaters supply most of the heat requirements by radiation to heat absorbing surfaces normally located out of the path ofthe main flow of the products of combustion. The surfaces receive the radiant heat, at least theoretically, at substantially uniform average rates to the different tubes, but each tube absorbs approximately Athree times as much heat on the exposed half of the circumference as it does from the shielded half of the circumference. This is on the assumption that there is normal spacing between the tubes and the refractories behind them. By the exposed half of the circumference, I mean the half which faces the flame and the gases, and by the shielded half, the half which faces the refractory behind the tubes. n

It is an object of my invention to provide, Within a single structure, a multi-coil heater with separately red coils in which the heat input rates into each coil may be regulated to meet predetermined process requirements.

lt is another object of my invention to provide a means whereby the heat input rate may be changed between runs to meet changed requirements caused by changes in capacity or in processing.

It is another object of my invention to provide a means for increasing heat absorption my the shielded half of the circumference of the tubes.

It is another object of my invention to provide a means for varying the amount of additional heat supplied to the shielded half of the tubes.

It is another object of my invention to provide a` means for varying the heat input to the iluid to correspond to the heat requirements of this fluid as it passes through the heating coils.

lt is another object of this invention to prevent the imposition of strain on the baiiies by warping or expansion of the tubes. t

It is another object of this invention to allow portions of the baffles to follow the warping of a section of a tube without aifecting the spacing at the less Warped or straight sections of the tube or other tubes.

It is another object of this invention to allow installation or removal of the batlies without disturbing the tubes.

Other objects and advantages of this invention will appear from the following specifications taken in conjunction with the accompanying drawings in which:

Figure l illustrates, in cross section, a multi-coil heater, incorporating my invention;

Figure 2 is a cross-sectional view of the heater taken along the line 2-2 of Figure l;

Figure 3 is an enlarged detail ofthe tube and battle arrangement illustrating the means for connecting the tubes;

Figure 4 is an enlarged detail of the tube and bae arrangement where the clearance between the baies` and suitable means such as welding.

2,752,897 latented July 3, 1956 the tubes has been reduced to prevent the passageof combustion gases between the tubes and the bales.

Figure 5 illustrates typical heating curves for various sections of the heater incorporating my invention;

Figure 6 is a graph illustrating the diierence between using a plane and a baffle as a reradiating surface and it also illustrates the additional heat input obtained by using my invention.

Figure 7 is a cross sectional 7-7 of Figure 3.

Figure 8 is a cross sectional view taken along the line 8--8 of Figure 3.

Referring to Figure l, my heater consists of a shell 1l) adapted to besupported by member 11. Shell `10 may be made of any conventional material and of any size and shape desired, e. g. rectangular as shown in Figure 2. At the upper extremity of shell 10 I have provided a truncated rectangular section 12 which extends into a rectangular convection section 13 which in turn extends into exhaust stack 14.

I have provided by heater with two compartments 15 and 16. Each compartment may be adapted to receive one or more burners 17 of any conventional type adaptable to receive and burn any suitable fuel and to dis view taken along the line charge the products of combustion into the interior of n their respective compartments.

Compartment 15 has been formed `by the horizontal arrangement of heating tubes 18 in two vertical sections 19 and 2) and two inclined roof sections 21 and 22. The vertical section 19 is mounted next to the shell 10 whereas the vertical section 2t) serves to partition compartment 15 from compartment 16. lnclined roof sections 21 and 22 serve to separate the radiant section 25 of my heater from the convection section 13.

Section 16 is formed similar to section 15 whereby horizontal heating tubes 18 form the vertical sections 28 and 29 and the inclined roof sections 30 .and 31. The inclined roof sections 30 and 31 again separate the radiant section 35 from the convection section. 13. n

The convection section 13 is also supplied with horizontal heating tubes 36.

As shown in Figure 2, tubes 18 are provided at the ends with elbows 23 which can be tted with removable plugs 24 so that the tubes 18 can be cleaned. Compartments 27 `with doors 32 are provided to iit over the elbows 23.

The heating tubes 18 of the compartments 15 and 16 are backed by 'battles 37. Figure 3 shows one method of arranging the baiies when the tubes they face are located along the refractory of a wall, roof or lloor of the heater. Substantially the same arrangement can be used for tubes located in a double row away from the outer wall of the heater, that is by rows 2t) and 29. In the embodiment of my invention shown vin Figures l and 2, it would not be possible to use floor tubes because of` the oor tiring butin side or end wall tired heaters, use of floor tubes would be possible. of the type herein disclosed could be used.

Each battle 37 is preferably made of hightemperature alloy metal with `a curvilinear front 38 and tlat back 39. The lat back 39 is bent at the ends to form `the end clo sure 40 to retain the granular insulation 41 which nor mally llls the baffles. The end closures 40 are secured to the curvilinear front 38 by clips 41a which are lixed to the curvilinear fronts 38 and the end closures`40 by vEach baille is connected toonly one of the two tubes which it serves by replaceable links 42 which have one end pivotally connected in holes `43 in the end closures 40 and the other end pivotally connected in holes 44 in lugs 45 fixed to the tubes. In this manner any movements of the tubes dueto expansion or warping of the tubes Baies n will not impose any strain on the baftles and will not materially disturb the spacing between the bailles and the tubes. I have found it suitable to make the baflles in relatively small sections, e. g. three to four feet long, so that warping of a section of a tube can be followed by the short sections of the 'bales without all'ecting the spacing at the less warped or straight sections of the tube. Also, I have made the tube and baille arrangements in such a manner that the bailles can be installed or removed without disturbing the tubes.

'Another type of articulate construction is disclosed in my copending application for a Petroleum Heater, Serial No. 188,187, tiled October 3, 1950 now abandoned.

Clearance between the curved faces of the bailles 37 Iand the backs of the tubes 18 is determined by the height `of the end closure plates 48 above the curvilinear surfaces 38. This clearance may be varied when it is desired to pass more or less combustion gases between the shielded half of the tube surface and the baille and thereby to vary the relative amount of additional heat lsupplied to the shielded halt` of the tubes by reradiation from the baille and by direct convection from the gases. This variation may be obtained by using end plates and links of various sizes Aand then shifting them in the heater to meet the various heat input requirements in the different sections of the heater.

Figure 4 illustrates the positions of the tubes and the batlles when it is desired to prevent a ilow of the combustion gases. End closure plates of reduced height and links of decreased length have been used to obtain such positions.

Operation of the device may be briefly described as follows: Let it be assumed that heat is generated within the burners 17 with the result that combustion gases are distributed in the area within the compartments 15 and 16. Normally the combustion gases would proceed directly to the convection section 13, primarily through the inclined roof sections 21, 22, and 31, and especially through sections 21 and 30. Also, normally, there is more space between the tubes of the inclined roof sections than is required for passage of the gases from the burners so that the outgoing gases would till only a .portion of the spaces between all of these tubes or all of the space between only a few of the tubes. This would create relatively hotter and colder zones along the length of the individual tubes or in groups of tubes, with the locations of the zones changing with a change of draft of an unintended change of iring of individual burners which often occurs in actual operation. The bailles in my invention restrict the passage of gases between the tubes and will distribute the gases substantially in even proportions around those tubes over which 19 and leave through tube 55. If the process requires high input rates towards the end of the coil, the baffles 37 behind the lower half of the vertical section 19 will have little or no clearance between them and tubes 18 as is illustrated in Figure 4. No gases will therefore pass between the bailles and the tubes and the baflle will act only as a reradiator at its equilibrium temperature. The increase in heat input to the shielded half of the tube 18 will be by radiation only and the total increase may be in the order of 10% for the average along the whole circumference. This increase is shown schematically by the area between the lines c and d on the left hand side of Figure 6.

The right hand side of Figure 6 shows the type of heat input with a plane as a reradiating surface. Line a represents heat input by direct radiation, line b the heat input by reradiation from a plane, and line c represents total heat input obtained by the addition of lines a and b.

The left hand side of Figure 6 represents the types of heat input with a baille as a reradiating surface. Line d represents heat input by direct radiation, line e, the heat input by reradiation from a baille, and line f represents the total heat input obtained by addition of lines d and e. Line g represents the additional heat input obtained by reradiation and convection as is hereinafter explained.

As the lluid progresses upward in the vertical section 19, the clearance between the tubes 18 and bailles 37 will be increased. This increase in the ilow of gases will increase the temperature of the bailles which in turn will increase the re-radiation from them and will also impart convection heat to the shielded one-half of the tubes so that the overall increase in heat input rates will be in the order of 20 to 30% above that imparted to the tubes in the lower part of vertical section 19 where the clearance has been reduced to a minimum. This increase is shown schematically by line g of Figure 6. However, the increase in heat input rates will depend upon the number of tubes over which the total gases are made to ilow. The smaller the number of tubes over which the total gases flow, the higher will be the velocity of the gases over those tubes and the greater will be the heat input rate to the fluid in those tubes. This is in comparison to the heat input rates in the tubes where the clearance between the bafes and the tubes has been reduced to a minimum so that substantially no flow of combustion gases occurs.

Various combinations of iluid llow can be Worked out.

` By splitting the flow through the convection section from the baflles permit passage of gases so that the ilow of gases is deiinitely around the tubes selected and is not materially affected by changes of draft or operation of individual burners.

Combustion gases in addition to primarily passing through the roof sections, will also escape through the vertical wall sections 19, 20, 28 and 29, the amount being dependent upon the positions of the baflles with respect to the tubes in the various sections. 'The gases escaping through these vertical sections will then travel to the convection section 13 through the space formed by the'vertical sectionsand the shell 10 or through the space formed between the vertical sections 20 and 29.

The use of baffles to vary the relative values of heat input into tubes 18`inv chamber 15 can be best explained by referring to Figure l and using the llow of fluids inlet-50 to outlet 52 into two parallel streams and arrangingkthe ilow and the baflling of the vertical section 20 and inclined section 21 in the same manner as in the sections 19 and 22, it would be possible to have two parallel streams of iluid in each compartment, and four parallel streams through the heater by using both compartments 15 and 16 which will receive identical thermal treatment. Also each of the parallel streams in one compartment can be sent into two parallel streams through the next compartment, where wide variation of rates of heat input through the portions of two parallel streams can be obtained by varying the llow arrangement, bafile spacing and tiring rates.

Normally, the burners in each compartment are fired as nearly as possible at the same rate, but the compartments can be fired at different rates as long as uniform tiring is obtained from the burners in each individual compartment.

The right hand side of Figure l shows a series ilow through all of the tubes in compartment 16 and half of the convection section 13. Identical treatment to two streams passing through the heater can be obtained by this type of ilow by using both compartments 15 and 16.

Typical heating curves for one embodiment of my heater are shown in Figure 5. Curve No. 1 represents the temperature, ofthe fluidas .it risesthrough the .vertical section 19 when all of the combustion gases are flowing over all these tubes at a uniform rate. Curve No. 2 represents the temperature of the fluid as it is rising when combustion gases are owing only over section BC. Curve No. 3 represents the temperature of the fluid when the combustion gases are flowing only over a section AB.

In using two parallel series streams, compartment 15 can be made to give a heating curve like No. 2 in Figure 5, which curve is normally used for the heavy oil coil of a two-coil cracking unit while the other compartment 16 can be arranged to give a heating curve link No. l, which is normally used for the light oil coil of a two-coil unit. This permits both coils to be in the same structure, which is dificult to do in another type of heater.

With the two-compartment heater the same elfects can be obtained with four parallel streams through the two compartments, two for heavy oil coils in compartment 15, and two for light oil coils in compartment 16. With longer tubes and operating near the top capacity of a two-compartment heater (e. g. 60,000,000 B. t. u. per hour applied to the oil), splitting the oil into two parallel streams may be highly desirable both from the pressure drop and the time-temperature requirements of the oil in the coils.

In most processes where fluids are heated in a tubular heater, the heat requirements per degree temperature rise varies from the inlet to the outlet of the heater. For example, in thermal cracking these heat requirements increase due to increased temperatures and decomposition ot' the nid toward the outlet. In other processes substantially constant soaking temperature in the reaction zone of the coil is necessary, but the heat requirements may decrease towards the end of the coil due to the decrease in the reaction rate as the equilibrium condition is approached and the reactants already formed retard the rate of reaction. My heater has been designed to meet the requirements of such processes.

While Figures 1 and 2 show an embodiment of my heater with two compartments, my invention also embodies heaters with one compartment or withv two or more compartments.

The elect of varying the quantity of combustion gases passing over the tubes, which may be done in my invention, can be shown in relative numerical values. In most formulae for convection heat transfer, the rates vary as the mass velocity is raised to a fractional power, usually two-thirds. If we assume that we have a certain rate of firing of my heater and with gases permitted to ow between all tubes and baffles, the mass velocity is 0.2 and the mass velocity factor in the formula will be 0.34. However if the gases are permitted to leave only onefourth of the tubes with a mass velocity of 0.8, the factor Will be 0.86 or approximately 2.5 times as high. If, under existing temperatures of gases and tubes, the convection heat input into the tubes is 1,000 B. t. u. per square foot with all bales open, it will be 2,500 B. t. u. per square foot with only one-fourth of thetubes having gases flowing over them. Also, the temperature of the baflles in the second example may be 150 to 200 F. higher than the lirst example. This additional increase in temperature may contribute 1,000 to 3,000 B. t. u. per square foot of tubing.

In this manner by varying the spacing between the bafes and the tubes, as may be done in my invention, the overall heat input rates may be varied from 30 to 40% of the basic rate of a heater with no baffles, or from 22 to 30% of the basic rates of a heater with baffles but with no combustion gases flowing between the bales and the tubes. Normally, the heat input rates for a heater with baes but with no combustion gases flowing between the baes and the tubes are from to 15% higher than the heat input rates for a heater without bafes.

The same principle would apply whether or not the tubes in each compartment were used as parallel vertical sections or as one series section or, whether the tubes in both compartments were used in parallel or series. In the latter case, four points of temperature control can be obtained by firing the two compartments at different rates and by making the gases pass over some particular portion of the tubes in each compartment. Additional points of temperature control can be obtained by adding more compartments.

It is apparent from the foregoing that: I have invented a heater which can be used for many processes, especially for the type that require a different heat input rate during the various stages of the heating process.

l claim:

l. In a heater, a vertical shell, a source of hot combustion gases within said shell and located at one end thereof, a plurality of tubes mounted in vertical sections, a plurality of tubes mounted in inclined roof sections, a plurality of articulated removable baffles having curvilinear surfaces andforming passageways between said baies and said tubes for the discharge of said combustions gases, and means for positioning said bales on the side of said tubes away from said source.` and for varying the size of said passageways, said means` comprising end closure plates of various sizes rigidly fixed to said balles, lugs rigidly fixed to said tubes, retaining holes in said plates and lugs, and links inserted in said holes..

2. In a uid heater, burner means for conducting combustion, a plurality of fluid conducting tubes mounted in sections spaced from said burner means to form substantially vertical walls about said burner means, a plurality of articulated replaceable heat reflecting baffles interposed between said tubes on the sides of said tubes opposite the source of heat, each of `said tubes having two heat reflecting surfaces for reflecting heat towards two adjacent tubes whereby each tube receives heat reflections from each of two of said surfaces formed on adjacent baffles, said heat reflecting surfaces in section having radii considerably greater than the radii of said tubes to increase the proportion of radiant heat supplied by reradiation and reflection to the sides of the tubes opposite the source of heat, and means for spacing the battles from said tubes to predetermine the size of the passages between the tubes and the baifles, said last named means comprising spacing members fixed to said baiiles and removable members connecting said spacing members to said tubes, said removable members permitting the interchange of baffles `whereby the flow of gases over the tubes may be varied t0 determine the relative amount of heat input to predeterminedtubes.

3. In a fluid heater, burner means for conducting combustion, a plurality of horizontal uid heating tubes grouped in sections to form substantially vertical side walls about said burner means, a plurality of articulated heat reflecting baffles, and means for suspending said baffles horizontally from said tubes on the sides of said tubes oppose the source of heat in such a manner that the weight of the bafes urges said balfles towards said tubes, ,lsaid last named means comprising spacing members mounted on said baiiles and removable links pivotally connecting said spacing members to said tubes, each of said baies being connected only to the tube immediately above it, the spacing members being of various sizes and the links being of various lengths whereby the baffles may be interchanged to vary the ow of combustion gases over the tubes to determine the heat input into certain predetermined tubes.

References Cited in the tile of this patent UNITED STATES PATENTS 2,121,537 Coghill .Tune 2l, 1938 2,380,464 Primrose et al. July 3l, 1945 2,479,544 Schauble Aug. 16, 1949 FOREIGN PATENTS 242,198 Great Britain Nov. 5, 1925

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