US2326492A - Petroleum heater - Google Patents

Description

Augu l0, w43. F. H. PRAEGER PETROLEUM HEATER Filed sept: 22, 1941 l lNvENToR. BY fv/QNX /Qe/Qf'e ATTORNEY.

Patentecl Aug. 10, 1943 UNITED STATES PATENT OFFICE PETROLEUM HEATER Frank H. Praeger, Merton, Pa., assigner to Alcorn Combustion Company, Philadelphia, Pa., a corporation o! Delaware Application september 22, 1941, serial No. 411,890

. 7 claims. (ci. 122-356) My invention relates to heating systems, more particularly to heaters especially designed for the heating of petroleum and its components and has for an object the Provision of a heater of high efliciency and of relatively low cost.

It is a. further object of my invention materially and substantially to increase the heat absorption in that zone of the heater generally known as the convection chamber.

It is a further object of my invention to so increase the transfer of heat within the convection chamber to the oil A:flowing through the tubes therein that the present normal size of the convection chamber may be decreased to a substantial degree without loss in heater eflifciency; or. with the present, normal size of convection chamber materially and substantially to increase the efficiency of the heater byproviding for a greater absorption of heat in the con vection section.

In many petroleum heatershot gases or the l products of combustion ilow from a nre chamber into a convection section where the transfer oi! heat from the hot gases to the oil is largely by convection. Usually the convection section consists of a relatively large number of tubes intimately washed by the gases and through which tubes heat is conducted to the oil iiowing therein. In general, the spacing of the tubes one from the other is limited by the temperature and pressure conditions within the convection section and while a closer spacing may sometimes be desired, the return bends, headers, or fittings are not available for such-closer spacing of the tubes- Moreover, tubes in the convection section are located equal distances one from the other because with this arrangement maximum room for the headers is provided for the minimum spacing between tubes. Nevertheless the gases passing between adjacent tubes divide around the next tube so that the gas velocity is reduced as much as fty per cent in the region where the divided flow occurs.

It is a further object of my invention to provide means for maintaining throughout the convection bank and ,in the regions of divided ow, substantially constant and relatively high, the velocity of the hot gases for the more effective heating of the convection tubes.

In the past there have been many proposals for increasing the transfer of heat in the convection section. YFor example, it has been proposed to encircle :the oil conducting tubes with gill rings or especially made castings. Hairpinlike members and refractories secured to the tubes have been suggested to increase the absorption of heat. These schemes all include the disadvantage of the interposition of a substantial amount of heat insulation between 'the gases and the tubes.

In carrying out my invention in one form thereof, I provide means spaced from the convection tubes for directing and controlling the ow of gases thereover to insure a high velocity of the gases over the tube surfaces and to overcome and prevent large decreases in the velocity of the combustion gases passing through the convection section. More speciically, I provide members extending lengthwise or longitudinally of the convection tubes and in spaced relation therewith and so positioned as to provide narrow passages between each member and two adjacent tubes so that upon division of the gases between a pair ofl tubes the area of the ow passages will be reduced by one-half, thereby to prevent material reduction in the velocity oi the gases.

For a more complete understanding of my invention, reference should be made to the accompanying drawing wherein I have shown in Fig. 1 a sectional elevation of a heater embodying my invention;

Fig. 2 is an enlarged fractional elevation of a pat of one of the convection sections of Fig. 1; an

Fig. 3 is a fractional side elevation showing the tube sheets in the left hand convection section of Fig. 1.

Referring to the drawing, I have shown my invention in one form as applied to a petroleum heater of the type which forms the subject matter of a copending application, Case No. AC23, Serial Number 411,891, filed concurrently herewith by Roy S. Lyster and assigned -to the same assi-gnee as the present invention and comprising three fire chambers I0, vI I, and I2. Suitable fuel, such as oil or gas, is burned within the respective re chambers. By means of a pluralit'yoi burners I4, each directing oil or gas within muilles I5. spaced along a front wall I6 of the-heater, burning gases are projected generally horizontally across the lire chamber I0 and intermediate a bank of floor tubes I1 and a bank of roof tubes I8. 'I'he door tubes are located adjacent the iioor I9 while the bank of roof tubes I8 slopes upwardly along the upwardly sloping roof' 2li of lire chamber I0. The hot gases and products of combustion -rise through a convection section 2| of the heater and then pass into a second convection section 22. The rows of tubes in each convection section are in staggered relation to each other.

The ilre chamber I2 is of the same construcnected in parallel with each other by means of large headers (not shown) Fuel is burned above the oor tubes 26 and is preferably directed inwardly from opposite ends of the heater and lengthwise of the door tubes 26, three of such burners 23 being shownv in the drawing, the outer two burners being for gas and the center burner for oil.

The combined gases and products of combustion from the fire chambers I0, II,and I2 unite within the common convection section 22 and after passage therethrough flow to the stack (not shown).

My invention, applicable to any kind of a convection section whether up-draft or downdraft, may be readily understood by reference to the enlarged fractional view of the convection section 2|,y shown in Fig. 2. More particularly, the hot gases `or products of combustion from burners I4 pass through the lowermost row of four tubes which are, of course, subjected to radiant heat fromthe lire chamber I0 and to convection heating by the gases contacting them. There are three openings between the tubes, not counting the opening to the left of the tube 29 and the opening to the right of the tube 30. Since the tubes in the rst row including tubes 29 and 30 are subjected to both radiant and convection heat,'no provisions are made to increase the rate of convective transfer in the regions of divided flow of the gases. Some heat by, direct radiation is also received by the second row of tubes, 3I-34, and no provision has been made to increase the convective transfer thereto in the regions of divided gas flow.

My invention is shown applied intermediate the second row of'tubes 3I-34 and the third row of tubes 35--3'I, in the manner now to be explained. The gases rising between the adjacent tubes 3I-32 divide, one part flowing to the left around tube 35, and the other part flowing to the right thereof. As a result of this division, the velocity normally would be 'reduced one-half in the regions of divided flow and heat would be transferred at low rate to the heat-absorbing tubes 3I, 32, and 35. `However, by interposing suitable means, such for example as flow controlling elements 38 and 33 in the regions of divided flow, the gas passagesmay be reduced in area to prevent reduction in the rate of flow of the gases. The rate of heat transfer is maintained at a higher rate due to the continued high velocity of the convection gases. Similarly, the gases flowing between the tubes 32--33 divide, one-half going to the left of tube 36 and Vone-half to the right. of it. The flow-controlling elements 39 v and 40 reduce the now areas to prevent decreased velocity of the gases in contact with the tubes 32, 33, and 36, and the elements 40-43 perform like functions for the tubes 32-34 and 36-31. The gases which flow between the tubes 35 and 33 are about the same in quantity as the gases which flow between tubes 3l and 32, or as between tubes 32 and 33. In consequence, the means for controlling the flow of the gases are omitted from between tubes 3I-34 and 35-31 but they are included, 44-48, in the regions of divided ow just above tubes 35-3`L The additional ow controlling means 52--55 are likewise disposed in the regions of divided ow just below tubes 56 and 51 and above tubes 49-5I.- All of the tubes in the convection section 2| are in staggered relation. They are equidistant one from the other and lines drawn between the respective centers form equilateral triangles, as shown by the broken-line triangle between the centers of tubes 32, 33 and 36.

In the preferred form of my invention, the iiow controllingmeans is disposed intermediate the sides of such equilateral triangles, the elements 40 and 4I having such positions. While neither the shape nor the material of which the flow controlling means is made is deemed an essential part of my invention, I prefer to use cast iron tubes or steel pipe of the requisite size, although it is again emphasized solid bars of heat-refractory material, either circular, polygonal, or angular in shape, may be used. In the drawing solid bars are shown. When there is substantial spacing of certain tubes from an adjacent wall, it is desirable to provide a projection such as the projection 24a, which extends outwardly from the bridge wall 24, to prevent by-pass of the gases through the opening between tube 3l and the plane of the bridge wall 24.

Again referring to tubes 32 and 33, it is, to be observed the elements 40 and 4I not only reduce the area of the iiow passages in the regions of divided flow but they also'direct the gases against the adjacent heat-absorbing surfaces of tubes 32, 33, and 36 in contrast with the heat-insulating material which has in the past encircled convection tubes. By maintaining the velocity of the gases over the tube surfaces and over a greater area thereof the rate of heat absorption by convection is increased materially. l

The initial spacing of the tubes in the convection section is ordinarily determined by the design of the headers. The manufacturers of such headers have adopted standard designs with predetermined distances between tubes, although such distances vary with the temperature and pressure of the oil being heated. For low pressure, low temperature operation, the tubes may be spaced closer together than for the higher temperatures and pressures. The greater spacings are required to allow for increased thickness of the metal in the headers or return bends for the higher temperatures and pressures. That is, the headers are made for as close aspacing as each design permits (about one-half a tube diameter) and for higher temperatures the tube spacing must be increased for the heavier headers which must be used.

It will be seen that regardless of tube spacing,

there will always be a substantial decrease in the velocity of the gases in the regions of divided flow and that the flow-controlling means will maintain the velocity of the gases and prevent decrease in the rate of heat transfer.

Moreover the gases are directed by the elements against the convection tube surface. This directing effect is important as will be seen by considering the flow of gases around a typical tube, the tube 32. Since the rising gases pass to the right and the left of tube 32 the intermediate portion is not as thoroughly washed by the gases and the heat transfer thereto is materially less than to the lower side portions. Since a greater quantity of gases, about twice, ows between tubes 3I and 32 the maximum transfer rate is along the side portions of tube 32. By reaaround tube 35 are directed against the upper side of tube 32. That is, they must pass between ele- J ment 39 and tube 32; and between element l0 and tube 32, the two subdivided streams Joining to.- gether between elements 33 and 40. Thus the gases to substantial degree encircle tube 32.

The encircling effect is even more pronounced in connection with another typical tube 36. In this case,A the gases ow between the respective elements 40 and 4| and then divide one part passing between element 40 and tube 36 and the other between element 4| and tube 33; in contrast with the undirected gases which do not so eiectively wash the lower portion of tube 32. Both sides of .tube 36 are then thoroughly washed by the gases inthe regions of united iiow of the gases. In the subsequent regions of divided flow, the gases are again directed against the upper half of tube 33 because they must pass between element 45 and'tube 36 and between element 46 and tube 36. Besides decreasing the area of the ow passages to prevent decrease in both gas velocity and rate of heating, each element directs the gases against two convection tubes. Adjacent elements such as lil-4|, and. 45-46, by their location extend the effective heat absorbing surface of their associated tubes by substantial elimination of the previously relatively low rate areas of each tube comprising the upper and lower half of each tube, or the sides of each tube normal to the flow of gases through the convection section.

While flow controlling elements which maintain the velocity of the gases are preferred, it is of course apparent that elements which decrease the cross-sectional area of the gas passages inthe regions of divided flow are highly benecial because of their gas directing functions even though the original velocity ofthe gases is not maintained. Also if the flow areas are proportionately smaller, the gas velocity may actually exceed the velocity between adjacent tubes preceding the regions of divided flow. In each form of my invention the heat transfer rate is maintained high in those regions where it formerly has been exceedingly low. In consequence, the convection bank has a high overall eiilciency. l

As above indicated, the temperature and pressure requirements on a six inch outside diameter tube may require a spacing from the center of one tube to the center of an adjacent tube of from 9 inches to 11 inches or more, with the result the convective transfer is greatly decreased 'with an eleven inch spacing over what it would be with between tubes 3| and 32 but as above explained the now controlling element 38 directs or localizes the flow of gases against a greater proportion of the heat-absorbing surfaces of tubes 3| and 35.

In calculating the heat absorbed in a convection section determination is first made of the K factor defined as the British thermal units per square foot of heat absorption surface per hour per degreeof temperature difference (F.) between the convection gases and the liquid being heated. In accord with my invention the K factor is increased from thirty to fifty per cent, which means more heat may be absorbed per square foot of heat absorption surface. The convection bank is more efllcient. It may be correspondingly smaller for a given heating duty.

The convection section 2 la, as above stated, including the now controlling elements, is identical with the convection section 2| and need not be further described.

M y invention has also been applied to the central convection section 22 and there are shown rows 60-61 of ow controlling means for the. combustion gases passing therethrough. Though the tubes may be connected for any desired sequence of flow, I have shown inlets 69 and 10 for entry of two streams of oil to the convection section 22 from which one stream ows through the tubes 2|a, |8a and Ila of fire chamber I2; and the other-stream nows through tubes 2|, I8', and |1 of fire chamber |0.- From the respective outlets 1| and 12 the streams may be conducted to vaporizing drums and the oil vapors therefrom may pass throughthe floo'r tubes 26 in flre chamfactor is thirty to fifty per cent greater by reason of the flow-controlling elements, an increase over the K factor of convection sections of the prior my invention, it is to be understood that I do not a closer spacing. As a specic example, and not to be taken as limitative in any way with respect to my invention, a 51/2 inch outside diameter tube maybe spaced 81/2 inches center to center, which leaves between adjacent tubes an opening of 3 inches. To maintain the same velocity of the gases in the regions of divided ow, the ow controlling means should, therefore, if in circular form, have a diameter of 11/2 inches, which leaves on each side thereof a 3A, inch opening between it and the nearest tube; or stated differently, with each of elements 38-43, 1%/2 inches in diameter, the area of each of the gas passages such as between the element 38 and the tubes 3| and 35 is one-quarter that between tubes 3| and 32. Since half the gases flow to the left or intermediate tubes 3| and35, the velocity thereof in the regions of divided ilow and in convective contact with tubes 3|-35 remains not only about the same as limit myself thereto, since many modifications may be made, and I, therefore, contemplate by` tion gases to the tubes of the next row, each tube thereof disposed intermediate one of said inlet passages for divided flow of gases around it, and means comprising elongated elements disposed in the regions where the gases divide and each of a size which decreases the areas of the flow-passages an amount adequate to prevent tubes.

rows coinciding with the apices of equilateral triangles, the region corresponding with the base of each said triangle forming an inlet passage for now of gases between adjacent tubes of one row, and means disposed in spaced relation with said tubes and intermediate the two remaining sides of each said equilateral triangle for reducing the area of the ow passage between adjacent tubes and for preventing substantial decrease in the velocity of the gases in convective contact with said last-named tubes.

3. The combination With a heater, of a convection section comprising a plurality of tubes the centers of adjacent groups of three of which .coincide with equilateral triangles, and means interposed intermediate each row of tubes and intermediate the legs of each said triangle for defining narrow passages for the ow of combustion gases throughout a substantial part of the circumference of two of said tubes.

4. In a heater having a convection section consisting of rows of tubes with the tubes of each row disposed in staggered relation with the tubes of each adjacent row, said staggered arrangement producing divided iicw of gases about a tube in one row after unitedy flow of gases between adjacent tubes of the preceding row, means for preventing substantial decrease in the velocity of iiow of the convection gases within the regions of divided flow comprising elongated elements so disposed as to decrease the area of 1 the ow passages within said regions, and each of a size so as to produce undiminished flow of the divided gases in the passages of decreased area and against and in intimate convection heat transfer with the tube surfaces therein.

5. The combination with a heater, of a convection section having a plurality of rows of tubes adjacent groups of three of said tubes substantially coinciding with the aplces of equilateral triangles, elongated elements disposed intermediate' the legs of said triangles and extending parallel to said tubes and deiining narrow passages for the now of combustion gases throughout a substantial part of the circumference of the adjacent tubes, and tube sheets for supporting said tubes and said elongated elements.

7. The combination with a heater, of a convection section having a plurality of rows of tubes in staggered relation and disposed with the axes of the tubes of adjacent rows substantially coinciding with the apices of equilateral triangles, the region between adjacent tubes of one row corresponding with one side of one of said triangles for undivided ow of gases therethrough, and the regions corresponding with the other two sides of said one of said triangles providing for divided flow of gases therethrough, and elongated elements extending parallel to the tubes disposed midway of the regions of divided iiow for reducing the area of the flow passages between adjacent tubes, thereby to prevent substantial decrease in the velocity of the gases in said regions of divided iiow.

FRANK H. PRAEGER.

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