US2072535A - Method of and radiant heat stills for distilling hydrocarbon oils - Google Patents

Description

March 2, 1937. D. L. THOMAS METHOD OF AND RADIANT HEAT STILLIS FOR DISTILLING HYDROCARBON OILS 4 Sheets-Shea?l l NNE uw n ..--..-..H..--.|....|:. --.-.|...|...1...lw-\ .um w m z .N w ...H b u., 0000000000000 oooooouoooo 0.0.0@000000 A .m 0.0.0000 0 ooooonx Y.. .0.0.0.0. 0 000000000. .m ...5 wh: f .w \ml\ s w. n HW s u w. m n dw M A o w v w u M..`..i.;..-.%n 0. m n n a 1N VEN TOR.'

A TTORNEY METHOD OF-AND RADIANT HEAT STILLS FOR DISTILLING HYDROCARBONVOILS Filed Nov. 2l, 1951 4 Sheets-Sheet 2 L\ l @n L'L Fis BY 0s/MME @S4/A TTORNEY MarchZ, 1937. D. 1 THoMAs 2,072,535

METHOD OF AND RADIANT HEAT STILLS FOR DISTILLING HYDROCARBON OILS Filed Nov. 21, 1931 4 sheets-sheet s L ,v 1 ATTORNEY March 2, 1937. D. THOMAS 2,072,535

METHOD OF AND RADIANT HEAT STILL'S FOR DISTILLING HYDROCARBON OILS Filed Nov. 2l, 1931 4 Sheets-Sheet 4 Tok.'

'\ MA TTORNEY,

' mensa M. z. .1937

METHOD oF'ANn RADIANT HEAT s'riLLs Foanisrnmcnvnnocaanon oms Donald L. Thomas, New' York, N. Y.. 'assignonby' mesne assignments, to Gasoline Products Com- Dany, Inc., Newark, N.

Delaware f J., a. coi-poration'v of Application November 21, `1931, Serial" No. 576.518

,.16 claims. (ci. 19e-iis) t This invention relates to improvements in oil stills, particularly of -oil cracking stills of the radiant .heat type, and involves an improved -method of arranging and distributing the heating surfaces vof such stills whereby danger of.over heating the oil is avoided, and a more 'uniform heating action is obtained with "lower heating surface requirements.

I'he tendency in conventional tubular Vheaterdesign has been the application of both radiant and convection heat transfer in a furnace, with two distinctY heating lzones. The rstsection of such a furnace consisted of tubes 'in view of the-` flame absorbing heat by radiation, while the secondary bank shielded-from the flame, absorbed heat byconvection from the somewhat cooled flue gases flowing over the tubes. To insure mild furnace conditions and to protect the tubes nearest the flame', excess air ranging from fifty `2n per cent to one `hundred per cent of that necessary for combustion has been employed. As a further effort to obtain mild heating conditions in some cracking, furnaces where the oil is heated to temperatures of900 F. or more, the flue gasesv have been recirculated in order to cool the products of combustion and relievev the tubes nearest j-the fire of too. great a burden. Flue gas' recirculation is indeed an effective control particularly on cracking furnaces of the o two-zonev type, in that the distributionof heat pickup between 'the two banks, may readily be varied by an increase ordecrease in percentage of gases returned to the .combustionzone 1 However, in such furnaces the`:rat e of heat transfer may be as high as '12,0001B. t. u. per

'square foot per hour in the tubes near the flame, while in the coolerj Portion of lthe v'convection bank the rate may be as low as 1000 B. t. u. per square foot per hour.' Also in 'suchffurnaces from I .1o/fifty per cent to sixty per cent of the total heat absorbed bytheI oil is picked up in' the radiant section. I Recent developments have shown that amuch greater portion of the total heat absorbedby 45 the oil can be transferred by radiation with the same overall eiciency, but' with much less sur# face.

I per cent of thetotal heat absorbed by the cil 5o`was radiant energy, now eighty per cent or more of theheat picked up may be radiant energy. vTubular heaters are now being designe'dbf the two-zone box type, with more than four-fifths of the heat absorbed by the oil in tubes in view of 66 the flame. j

` dimensions.

Experiments on existing two-zone furnaces, clearly indicate that, where formerly fifty to sixty' of conventional furnaces are often accompanied f I The usual designsof heat absorbing surfaces I by inconsistency between the volume and the surl face of furnace since the achievement of complete combustion independently determines the volume of the furnace according to its rate of heat liberation, thus determining the furnace The surface of furnace walls thus obtainedloften presents an insufficient area for the-distribution of the absorbing surfaces, necessary'for reducing the gas temperatures to a I desirable degree.. Yet, the usual gas velocities in the frst'rows of tubes render the coefficients of heat transmission through 4ccnvection com paratively small. The question 'arises as tothe most adequate temperature at which the heat` transmission through convection should be preferred to that taking place through radiation.

The drop in the gas temperature'reduces the,y intensity of the heat. transferred through radia' tion so that at a certain temperature, the limit is reached when it becomes profitable to' adopt the transmission of heat through convection.;, Calculations show, this limit usually fluctuatesjf.`

between 1,400 F. and 1,800* F. i. e. theoretically it appears profitable to cool gases in the furnace down to 1,400 F. to 1,800? F. 'and after thatA only let them enter the nest of tubes inthe convection bank where the heat transmission through" convection will take place.

It is manifest that such a drop in temperature at the end ofthe furnace cannot affect the com' pleteness of combustion 'unless tle combustion chamber is incorrectlyvdesigned. Certain tem peratures are required for the completeness of combustion at those points only where the coml bustion as such takes place; as soon as combustion is' complete it becomes :the object of the `designer to attain 'maximum .intensity of gas cooling by whatever 'm'eanshel may choose.

vPursuing-the above process of reasoning I may state that, from the standpoint of minimum use of heating surfaces, the most expedient principle consists in maintaining suiliciently high temperatures in the initial portions of the flame in which the combustion takes place and, on the other hand, very intense cooling furnace temperatures r down to 1,4oo to 1,oo 'r'. through radiation by the end of the flame wheregthe combustion is already complete. However, .fori such intense cooling, the surface of the furnace wall is usually insufficient to comprise .the requisite heit-absorbing area, especially when turbulent atomzers are provided as well as other arrangements securing such increase ofrates of heat liberation per unit furnace volume as to reduce both the volume and the surface of the furnace.

In order to obviate vthese diiiiculties, as well as to give the designer full liberty in distributing the requisite ray absorbing surfaces, I have elaborated a novel principle of furnace cooling as applied to oil stills which is illustrated in the accompanying drawings, wherein Figure l is a vertical cross-section of a tube still embodying in its design the principies set forth above;

Fig. 2 is a vertical longitudinal section of the still shown `in Fig. l, the view being taken along the line A-A of Fig. 1;

Fig. 3 is a vertical cross-section of a modied type of still which utilizes the same principles;

' Fig. 4 is an outside elevation of these types of still. 'Ihis figure corresponds to Fig. 2, being an outside view thereof, showing the buckstays and tube supports used with this kind of still;

Fig. 5 is a verticalcross-sectional View of a type of steam controller for the steam turbines employed in driving the centrifugal pumps which feed oil to these stills;

Fig. 6 is a type of protective sheath shown on a tube which may be'used in connection with the radiant heat tubes of these stills to protect them from any tendency to overheating, should it develop;

Fig.-f7 is a cross-section of a stillv tube with one of these sheaths in place thereon;

Fig. 8 is a cross-section of a still tube similar to Fig. 7, except that two sheaths, one over the other, are employed;

Figs. 9, l0, 11 represent'tube supports for these still tubes in the free space of`the still, the supports being attached to steel beams that usually support the refractory blocks constituting the roof of the furnace;

Fig. 12 is a vertical cross-section of a portion of the still'wall, say on the line B-B of Fig. 4, and is designed to show how the ends of the roof tubes where they pass through the side wall, are

' supported;

Fig. 13 is an enlarged cross-section of some of the supporting members shown in'Fig. l2;

Fig. 14 is a transverse cross-section of the top horizontal buckstay support for the roof tubes, as shown in Figs. 4 and 12;

Fig. 15 is a polar diagram illustrating the radiant heat absorption of one row-of still tubes.

located near a wall surface and receiving heat from one side;

Fig. 16 is a polardiagram illustrating the radiant heat absorption of one row of still-tubes supported in free space and receiving heat from both sides; A

Fig. 17 is a vertical longitudinal cross-section of a horizontal tube two-zone box type radiant heat. still designed according to this invention,

and having in addition a digestion coil in the roof thereof; Y

Fig. 18 is a horizontal cross-section of a modied form of vertical tube radiant heat still, (De Florez type) designed according to the principles of this invention and having in addition a digestion coil adgacent the still walls.

' As may be seen from Fig. 2 the usual roof tubes y3 have depending portions 31 to 312 extending downward to a distance equivalent to about 1,/3

to 1/2 the furnace height, thedepending rows bel formed. is usually sufficient, as such intervals yield suiiiciently thick gas layers possessed of intense radiation. Due to the fact that gas layers of 20 inches thickness are capable of absorbing at least 92 percent of the total radiant heat falling on them, such layers, by reradiating this ,absorbed heat act as secondary radiant heat tial transmission of heat rays occurs Abetween the spaced tubes of the opposite row. In this latter case, however, the heat transmission from the back averages only about 1A of that received by the front tube surface. With single rows, calculations show that such spaced tube sections form much more eflicient heat absorbers than the first rows of tubes adjacent a furnace wall as employed in the usual type of radiant heat still. The polar diagrams of Figs. l5 and 16, bring out clearly the advantages of the double exposedv single row of tubes over the double row, as used f in Fig. 2.

A similar principle of construction of ray absorbing surfaces may also be applied to cylindrical vertical placed tube stills of the De Florez type, (See Fig. 18). In this case, it also is expedient to space the nest of tubes of the first row so that only separate rows of tubes remain located on the inner arcs of the furnace center.

In its actual idea the new principle of ray absorption ymeans the use of ribbed surfaces,-

though the ribs should not form continuous plates, butl rows of tubes of which the fundamental plane of the axes of the tubes is perpem1 dicular either to the fundamental surface of the furnace wall, or to the plane of the first row orl rows of walltubes.

Referring to Figs. 1 and 2, tion chamber of a. tube still of the two-zone box type, 2 and 21 are the burners therefor, arranged for gas, pulverized coal or oil firing, as desired;

3 to 312 are the tube banks forming the -radiant heat section of the still, 4 is the convection bank i is the,Y combus.

forming the economizer section which in thisv still is -of comparatively small dimensions as its main function is simply that of ai heat bale ancing coil to aid in controlling the still temperatures of the oil being treated; it may for instance be 5 rows wide and VIl) tube rows high and is designed to pick up from 10 to 20 percent of the total heat to be transferred. The heatA remaining in the iiue gases after passing this coil is recovered in an air heater 5, located be- Ineath the coil, the iiue gases passing. the air. heater escaping by the opening 6, to the custom-- ary underground flue leading to the tube stack.

Most stills`of the type illustrated employ only a single series oil circuit, but in the still illustrated a two-circuit series -type is shown, that is to say, there are two separate and distinct series of connected oil circuits extending throughout the furnace heating space, which circuits are fed with charging stock by means of a steam driven centrifugal pump.

Referring to Fig. 2, the centrifugal pump which in this instance` consists of two separate `centrifugal pumps placed end to end'on the same drlve'shaft, so as to be driven by' one andthe l 2m72.591s" same motor. 'Ihese'puinps have their discharges sure'differential existing between the pump outlocated at the near center and adjacent to'each other, which arrangement does away with the necessity for shaft stuffing boxes at this point asthe oil pressures in the-,two circuits is the Asame throughout. This is important point in a pump intended to handlehot'oils. as" this one is, and avoids much complication., the inlets are under more or less internal suction, shaft packing diiilculties do not present themselves atthis point. 91 is' the inlet tothe pumps and is branchedV into two mains .91, 93 leadingto the pump inlets asshown; The-pump outlets connect to mains 94,' 95 which deliver the charging stock for each coil to the coil inlets I3, 44 (Figs. 1 and 2) `oi the convection bank of tubes 4, the tubes',l forming the two circuits. of which are connected together as indicated by the chained lined tube circuits of Fig. 1. After passing Athrough the convection bank the oil leaves by way of the transfer lines 41 and 42 of Figs. 1 and 2 each leading to a. radiant heat circuit, of the type described above, located-in the upper part of the combustion chamber.

These lradiant heat circuits, as previously ex plained, are made upv of'la series of .ribbed surfaces consisting of downwardly depending rows of horizontally disposed tubes, the rows spaced from one another a distance oill from 20 to 24 inches. The latter distance is preferred forgeneral use. :It/ is to be clearly understood that while -the tube rows may extend downward nearly to one-half--the furnace height, nevertheless the furnace dimensions and the positions ofthe burners `inl reference thereto are to be so\ correlated to one another that combustion ofall fuel is to be entirely completed'before any part 'of the combustion gases contact with these tubes.- This, of course, implies the use of comparatively large furnace volumes, although the' fact remains that a furnace with this type of cooling surface voperates with little .or no excess air and tends to small volumetric capacity as practically all of the heat absorbing surface is-of`` the radiant heat type and works at high ratings.:

In the lfurnace design shown in Fig. 52, the

tubes making up the ribbed surface are in the form of double rows.' It is however, preferable wherever possible to employ single rows of tubes 'as indicated in Figs. 4 andv 17; as this permits of full two-sided application of radiant heat`from the gases, to. both sides of the tubes ofeach @to alter the turbine speed.v

' row which, as

pointedout above, is of special advantage. 'Ihere are, as stated, two radiant heat circuits, one consisting'of tuberows from 31 toA 9 inclusive, which is connected to transfer line 41. 'I'he other radiant heat circuit is majde up of tube rows from 3fl to 31 inclusive, and' connects to the other transfer line 41.' The'oil after passing through thesecircuits escapes bythe flanged 1- outlets I0. and 'il leading from'the stillfl The centrifugal pump 9 that deliversv charging stock to the still is usually driven by- 8. steam. turbine 1. A notable feature infconn'ection with y this turbine isfthel'mann'erffof controlling its speed. As the rotary'spe'edoi: theturbinegoverns the delivery pressures o; 'thefcentriiugal pumps, it is self-evident that'where we want to alter this delivery pressureI it'will bevneces'sary In order to do this andat the same-time keep the tur'binev speed steadyfthere .isf provided a.

pressure actuated controller 8, which controls baille wall 54 and attached to tube sheets forming the steam ilow in correspondence withth pres- -terior is provided by the'pipe connection 81.

thoutlet openings I8 and Il of a double seated balanced poppet steam throttle valve 8 located in the casing 8. The valve v'rod 81z is connected at top and bottom to two similar 'sized expansibletype metallic bellows 85 and 8.

The topof the valve rod 81 is connected-to one end of the metallic bellows 85,.this end being her metically sealed against entrance of steam into ythe bellows interior.

T'he other end of the bel-v lows is also hermetically sealed to the upperchamber wall of the casing 8, as shown. Thus while the valve rodis movably supported by the bellows, yet no steam can directly enter the bellows interior. However an opening to said in- A -similar arrangement is providedA in connection with. bellows 86 to which the lower `end of the valve rod is attached Ias shown, and which has an inlet 811 as above specified. In additionto the above, the lower portion of the valve rod carries a spring 8", one end of which bears against,

the upper end of bellows 86tending to collapse it. The other end of the spring bears against a movable member 813 carried by a rotatable threaded rod 8a by which the tension of spring 8T can be matcally indicated in Fig. 2. From this 'it will to the oil circuits, of the still about as diagrambe seen that the bellows inlet pipe 81 is connected to the inlet mains leading to the still, a small v bore pipe 96 connected to each main and. to the controller conduit being used for this purpose.,

In a similar manner the pipe 811 of bellows 86 is connected to each of the outlets 'I8 and Il of@v the still proper. `As both bellows have the same dimensions and Work in opposition to each other,

it is self-evident that whatever movement of the valv e takes' place will be due to the" difference irr pressure between the inlets and outlets ofthe "still so that variations in these pressures will afi''ct the steam flow to the turbine andthuscon- I,

trol the pump speed in conformitytherewith.

-However. the actual rate of "steam l'ilow due to the normal opening'of the valve `is controlled by tension of the spring 8'I which is adjustable-by means of the threaded 'rodil3 and this adjustment, ofcourse, controls the'turbine speed and consequently the pump pressure.

From the above description it can' be seen how oil drawn Vin through the inlet 91 of the pump and driventhrough the still Icircuits reacts on the steam controller lofthe turbine to regulate they of the oiljcircuits at any Vpoint fixed bythe operatr'.

An air prelieater located below the convection .speedand keep constant the pressure differential bank oiI tubes. as shown in Fig. I, preheats the `in- :f

coming air to the unusual high temperature of yabout 800 F. with the ilue gases entering the convection bank' from 'above at 14`0OF. to 1500* F. As shown clearly in Figs. 1 and 2, this preheater consists of a, two-pass box vlike tubular structure formed o f a series of horizontal tubes in two banks separated from each other by the` the inside vertical sides of the preheater casing. This steel casing vwhich has the form shown in Figs'. 1 and 2, has openings at top and bottom as shown at 53 of Fig. 2 so that combustion gases from above -can pass downward therethrough over the outside of the horizontal tubes of the preheater to the still outlet ti.

In practice, air for combustion purposes is drawn in through damper controlled openings |21 in' the side walls of the still shown in Fig. l. These side openings lead in to the upper part of the air space |22 in the curtainwall l2. From the upper air passage the air flows into the upper header 51 of the-air preheater above the bale 54,

thence through the upper bank of tubes to the en- `closed space E, having a removable door which space communicates with the lower bank through which the air then ows into the lower header 52, from which it passes into the lower air space |2.3 of the curtain wall and thence into the air space |21 of the still iloor to escape finallyA by way of side openings |25 to I26 (see Fig. 2) to the burners 2, 21 where it is used for burning fuel in the well-known manner. Y

In the still design shown in Fig. 3, which corresponds in section to Fig.' 1, there are twoY circuits as before stated but in this case, there are two separate economizer convection banks which are located on opposite sides oi the combustion chamber behind air cooled curtain walls, as shown in the gure. These economlzer sections give to `the stiil greater overall eiilciency with greater'. flexibility and ease of control, than is obtainable with an all radiant furnace. Moreover, such a bank will absorb a great deal. of radiant energy from the incandescent gases above it, as well as convection heat from the stream oi gas coming in contact with the tubes. Below each bank there is located an air preheater of the same type and arrangement as the one already described in connection with Fig. 2.v

The radiant heat section of the still is arranged similarly to the stills just described with depending tubes 'forming rib-like roof surfaces; thertube rows whichv may be of either single or double formation being spaced from one another a distance corresponding to 20 to 24 inches between centers of the rows. In the free space of the still the tubes in these rows are sup` ported at two or more points by hanger bars I3, |31 which extend through the roof and are att'ached to I-beams (not shown in this ligure) that support the refractory blocks forming the still roof. Types of these hangers are shown in Figs. 9, 10, and 11, Fig. 10 being for single row tubes, while Fig. 11 is intended for double row tubes as in Fig. 2. There are usually two extra roof tubes between the rows, as shown in Fig. 2, and Fig. 9 shows means for providingva'support for these extra tubes. r

As the combustion chamber of this type of still usually has two ue openings 6 and 61V through which combustion gases are discharged to the central flue 63,;1 control the ow of these gases by means of dampers liA1 and 65 in the flues, the adjustment of which permits of -regulating the relative temperatures of the com bustion bank l pages33-39, wherein crude charging stock pr e` distilled before cracking by means of hot cracked crude oil.

' leading to the strippers.

i the main crude oil stock can be carried out without passing said crude oil directly through the still. In this case, the crude stock is charged direct to the column still and is distilled and fractionated therein by means of the hot cracked oil vapors from this tube still which are led into the base of the column to supply the necessary heat for the operation. Different fractions will be drawn from the side of the column still in known manner and one of these fractions, usually the gas oil cut is used as the primary charging stock for the tube still. In this way the unit will operate as a combined topping, iractionating and cracking apparatus, thus avoiding the necessity 0f separately distilling and fractionating the In such an operation wherein separate fractions are withdrawn from the side of the tower, it is customary to strip undesired light constituents from these fractions by means of superheated steam introduced along with the fraction into a small supplementary column termed a stripper. In order to supply this superheatecl steam,4the still shown in Fig. 3 is provided with a' radiant heat type or" superheater which consists of a series lof horizontal tubes located in recesses in the front faces of the two curtain walls which separate the convection tube banks from the combustion chamber. An inlet main I4 is joined to an inlet-header I42 which is common to a number of horizontal tubes connected upin parallel through which the steam from main Hi passes.

The steam. after passing through the tubes connected to this header enters a transfer header M4 in order to reach a lower set of parallel tubes wherein it again, makes a reverse pass through the combustion chamber and enters header |46, which is connected by way of transfer line |48 to header |41 which in turn serves a lower set of parallel tubes set in the face of the opposite curtain wall. After passing through these tubes the steam enters transfer header lsfwhich conveys it to the upper set of parallel tubes through which it travels vto reach the outlet header |43, which in turn connects with the outlet main |51 From this point on the steam is handled in the customary manner and needs no further description herein.

Instead of arranging the steam superheater as described'above, it may be constituted by a series of parallel horizontally aligned tubes in front of the bridge walls which are placed in Valternate relation with a similar series of radiant heat oil tubes intercalated with the steam superheater tubes and overhanging these latter in order to cool and protect these tubes from danger of overheating. Thiscan be done by arranging the oil tubes in a plane parallel to and in advance of the superheater tubes, the alternate rows of course being placed in staggered relation to one another so that radiant heat by passing between the rows of oil tubes can readily reach the superheater tubes, the latter being protected from destructive heat effects by the near presence of the oil tubes.

Fig. 4 is intended to show how the radiantheat tubes are distributed and' supported in the furnace wall. 'I'hls shows the outside surface of one of the still walls, 'the view corresponding in elevation toFig'. 2, except that single vertical rows of radiant h eat tubes are shown insteafipf double rowsasinthatfigure. Referring to Fig. 4, I is a hea\vy I-beam restingon a concrete foundation, l and 'supports the main buckstays I6, |61., |62, I 63, the lower ends of which restl onthe I-beam and are welded thereto. -Y

l The construction of these. buckstaysis shown in ing plates 16, I5".

' I-beam sections I9, |91, |82, which are welded t0 Fig. 14, Awherein it can be seen they are formed of two channeled' members |64, 1 65, placed face to face and welded together as shown and to backconstrution and rests on top of the twocenter buckstays |61v and I 62 to which it is welded and itis also welded to the sides of the corner buckstays I6,'YI53` as shown in Fi'g. 4. These corner the sides of the main buckstays and serve as sup- I- ports for short auxiliary buckstay sections20, 201, 201, 203, 204, 205, 20, 20", 20", 20, 201, 2011 connecting to the member I'I at the top and to the horizontal I-beam sections I9, |91, I92- at the bottom. I'he auxiliary buckstays serve as tube supports for the ends of 'the depending radiant heat tube sections, which connected together correspond to the ribbed surfaces referred to above.

`The openings for, the radiant heat .tubes are clearly shown in Fig. A4,-and in the section at Fig, 14. The member l1 shown, which is similar 'in section to Fig- 14, supports a series of roof tubes which formpart of the radiant heat circuit. 'I'he way in which the still wall is constructed -and jsupported at this point is shown in Figs. 1 2 and 13. Thestill wall 26 isbuilt up inside"the'paral.

lelogram outlined by the buckstays so that they .rest against the outside surfaces `of the wall' and act as 'supports therefor. The buckstays are bound together in parallelogramfform by a series of members I8 andI5 bindingtheir tops and bottoms together to form a single unitary box-like skeleton structure' surroundingA the walls.

rn Fig. V12,21; is' the stm wan which is carried up to the member I1 of Fig. 4. At this point it is necessary to provide means for supporting the roof tubes and passingthem through the side wall. 'Thisis accomplished by supporting the upper part of the wallIi1 onv a'horizontal girderlike member formed as shown in full llines in Fig. 1a and which member is bunt into the furnace wall as shown in Fig. 12. f

The girder ismade. up of a broad, flat top plate 22 which is welded'to. an outside channelsection "te Fig. 13itwi1ibe seen that the end 221 of the girder projects outward -to a distance approxi- 24, andan inside I-beam section'25, these members beingl pierced at 241 and 251 for the passage of the tubes. A lower plate 23 welded tothese e, which .when in' members completes the struc use is positioned in thewall a shown in Fig. 12.

From this latter figure it' will be seen that the inner edges of the top yand bottom plates of the girder reach within about A2 to '3 inches of the inner face of the wall, the open space 28 being lled in with plastic furnace cement as soon as the radiant heat tubes- 2l are put in place. Referring The member Il is of similar` mately equivalent to ehe-half the thickness ofthe 'member'fll of Fig. 4. With the`horizontal girder in position-in thewall this flange-like projection of the plate 22 rests on top of memberV I1 as .shown in Fig. 12 andl also in Fig.4 and is welded thereto. By studying the figures it will be seen how the upper section 261 of the wall is supported on the girder which in turn rests on the lower wall section 26 and partly. on the. member Il by meansl of `the flanged extension 221, all of the lparts being thus firmly bound together, while the openings in the girder and in member I1 provid for support of the roof tubes.

A "A similar type ofvertically placed girder memberformed with both plates 22 and 23 o f Fig. 13

arranged with overhanging edges 221 and- 231 is used in connection with the auxiliaryfbuckstays 20 to 2011 in building up the side walls of the still, one suchgirder being placed in front of .each buckstay, the sides of the buckstays vbeing embraced between the .overhanging flanges of 'th'e.

two plates as shown in dotted outlines in Fig. 13 which arrangement `prevents lateral displace' ment of the short girder sections from in front of the buckstays. 'I 'hese girders embedded in the wall in front of each auxiliarybuckstay provide the uprightsupports forthe depending radiant tube sections which are ofcourse spaced on V2) to 24 inch centers. The open Vsigamos-.,262 (see Fig. `4) between these buckstays is lledwlth brickwork, thus completing the furnace wall. Observation peepholes can be' arranged in these brick'- Work sections as desired.

The manner in which theradiant heat tubes are connected together can be traced by the lines ljoining the tubes, as shown in Figs. 4. It will be noted that certain sections, notably '29, 291, 291, 293 are joined together by lengthened junction -boirsections 'provided with clean-ouil plugs on the rsides as well as in front, as is visible in Fig. 4. The central tube rows 205. and 208 are in this figure shown as double rows contained in a single support, but in practice they should be separated from each other the usual distance l20 -to "24 inches in order to take advantage of the radiant -heat impingement on both sdes'of single'row tubesf I0 and 'II are the nal outlets leading from the radiant heat section of the still, while `:so

35 and 351 are the inlets thereto.

Referring again to'the vertical tube supports,

,the constructional detailsof which are shown partly in Iull and partly in dotted outline in Fig. f

13, 22 is one of the girder side plates which has a projecting flange end 221., and 23 is the other e girder sider plate likewise formed with ailange extension 231; The buckstay 20 is embraced between these two flanges and rest against the outer" surface of the co-operating channel member 24, which latterI is ush with the outer surface 26,4 of the still wall 25. The I-beam 25 forms the inner surface of the girder, and the open channe1 like space left in front of it, when the girder is in position in the wall, is intended to be filled inv with plastic furnace cement, up to and flush with the inner wall surface 263 of the furnace, it being understood that the radiant heat tubes are first. putin position before lfilling up this "channel,

'In the type of ltube still illustrated the lower radiant heat tubes are sometimes exposedto lgreat extremes of temperature and it may be advisable in some'cases to protect these tubes from danger of injury by enclosing them in metallic casings -or sheaths. Av type of metallic sheath suitable for this purpose vis shown in Figs.

"external diameter of the tube to be protected.

The alloy tube is slit throughout its length as shown in Fig. 6 and is forced over the outside of when heated be perhaps in liquid form, but it will not drain out no matter wh't be the temperathe furnace tube, the slot permittingsuilicient expansion of the alloy tube for this purpose. The furnace tube is thus tightly gripped by its protective sheath, as shown inFig. '7, the only partl remaining uncovered being the narrow slot 'Whose width at no time should exceed 116". If the unitary structure described above be dipped into a molten metal, such as tin, brass, bronze, aluminum, etc., the molten metal will be drawn into the capillary spaces between the two tubes and will be retained therein by capillary forces as occurs instandard dip brazing. This provides an all metal contact between the tubes to aid the heat transfer therein. The metal so retained will ture to which it is exposed. Y

Fig. 8 shows a case wherein twol protective sheaths, one over the other are employed to guard the furnacetube. Any number of sheaths desired may be so used, and itis self evident that replacements can easily and quickly be made whenever necessary by forcing open the slot and withdrawing the inner tube as required.

With cracking stills in order to secure the best returns from any unit, it is important that the initial process of heating the oil to the temperature desired, under the pressure prevailing in the system, be given careful consideration. The illustrations shown in Figs. 1'7 and 18'show two distinct arrangements of tube stills, embracing the features of this invention, as arranged for high temperature and pressure. The diiference in design of the two is intended to show the versatility convection bank is usually arranged 5 tubes wide and 10 tubes high, as explained, in connection with Figs. 1, 2, and 3. It is also provided with an air preheater located below the convection bank for preheating the secondary air for combustion as in the previous designs.V Directly over the furnace a Vseries of rows 'of radiant heat tubes are arranged in-widely spaced relation in accordance with the basic features of this invention. Usually these tubes run in a 'direction at right angles to the tubes of the convection bank, although this particular arrangement is not an absolute necessity, as under certain circumstances they may run in the same direction. The first arrangement however, isfto be preferred because the. open spaces between the tube rows provide a series of open-tunnels into which the combustion gases rise and ilow without obstructionA over the bridge.-wa l l s into the convection-bank of spaced tube rows, there is a series of horizontally placed rows of tubes, live suchf rows altogether, being shown in this figure. It will be noticed that the upper three rows shown, are of some-Q what larger diameter than the rst two lower rows,- and that the upper rows of tubes in this sectign are partially shielded from .the furnace by the lower two rows, all of the tubes inthis section being staggered and their center-to-center relationship determined definitely to lessen the heat absorption of the upper rows. This provides for holding the oil in the tube stills for an appreciable period of time dependingon the flow rate, without materiallyabsorbing more heat. This is a most Aimportant -feature in tube still construction as it permits of introducing the time element into oil cracking without resorting tothe use of heavy expensive expansion chambersfor this purpose such as are commonly employed with most high pressure oil cracking` processes. The digestion period of the cracking operation is thus completed in the still itself, all that is required to complete the operation being to flash the cracked stock into an expansion chamber, at substantially atmospheric pressure. By cooling the oil at the instant of ashing, substantially no heavy tar or coke-will be precipitated, but a saleable residual fuel oil will result; while if this cooling be omitted, the distillation will be so complete, that practically only residual coke of 'small amount will be left in'the flash chamber.

In such a system the pressure control valve for the process will .be located between the still and the low pressure flash chamber, so that by manipulating thi's valve any amount of pressure from normal atmospheric up can be put on the cracking still as required. In this way it is pospressure vapor phase method, or as a high pressure liquid phase oilcracking process; all gradationsbetween the two being available by lvariation in operating pressure, oil ilw and furnace temperatures. The flexibility of such a method is very great indeed as it permits a renner to adapt his product to market requirements and to change the character thereof at any time it may be necessary to do so.

In the type of still shown in Fig. 17, the bridge wall I2, is provided on its front face with a series ofradiant heat tubes 30, set in recesses 301 in the front of the bridge wall as in Fig. 3. These tubes are connected into theL oil circuit in such manner that the oil after passing through the convection bank of tubes enters this radiant heat section at the bottom-by way of transfer lines 3| (Where two convection banks are employed as in Fig. 3).

After owing through these tubes the oil passes by transfer lines 311 to the radiant heat section in the upper part of the furnace chamber. The broken line of tubes in Fig. 1'7 shows the direction of ow in the two oil circuits, which direc- 'to'further here.

In Fig. 18 there is shown an application of theseprinciples to an all radiant heat circular still of the De Florez type. This form of still comprises a vertical cylindrical shell with tubes arranged in a circle against the inner wall. In the still illustrated there are provided four such rows; the two outermost rows forming the digestion timefelement being constituted oftubes of larger diameter thanthe radiant heat section. The radiant heat section is provided with inwardly projecting vwidely spaced rows of tubes, the `fundamental plane of `the tube axes in eachl row is, in this still, arranged perpendicular to the fundamental surface ofthe furnace wall.

The rows thus present a ribbed-like form to the furnace center wherein combustion takes place by means oi burner 3,2. Caremust be taken .to designl the furnace of suillcient diameter to prevent direct impingement of flame on any of these Atube rows, a matter not dilcult of accomplish* ment with 4upshot furnaces of this type. 33 and 331 are the inlets to the two oil circuits, since this still is herein designed as a double circuit type.

34 and 341 are the outlets from the still; all ofl these openings are located leither above or be- Ilow the. furnace chamber as' may be most convenient and they may be given any form most suitable for the purpose in hand. The 'direction of o'il flow in the circuits is easily traceable from the lines of the flgure, and it will be noted therefrom 'that this flow is mainly outwards toward -an increasing diameter so that the oil in passing through the larger tubes of the two outer rows is given sumcient time to complete the cracking ,reactionv without danger of overheating as theselargertubes are shielded more or less from the radiant heat bythe smaller lized innerrows..

The advantages of `the arrangement are self evident as it provides for intensive cracking and digestion of the oil in a single unit,"as in the design just previously discussed.

In Figs.15' and 16 are shown polar diagrams which give a clear idea of the intensity of heat absorption at different points of a' radiant heat tube located inV a front tube bank directly exposed to an open flame-or other source of radiant` heat. Fig. 15 shows the absorption by,a tube exposed on one side only, while Fig. 16 shows the absorption when the tube has both sides exposed, It willA be noted that time element digestion tubes are arranged in rising tiers in the ,furnace roof on the box type still or adjacent the wall surface of the circular De Florez type'in s such manner that the oil first flows through the tube rows nearest the radiant heat source and then progressively through the rows further and further away from this source, which arrangement, vof course `provides diminishing heat ab' sorption for the. final passes of 'the oil stream, in `t5 order to avoid overcracking.

process wherein. an enort at increased eiliciency y is attempted in oil cracking processes. Stills such 'f of horizontally disposed rows of radiant heat',-

heating surface of the furnace lis ofthe utmost necessity and importance. Having thus described my invention, what I claim and desire to obtain by United States Let- ,ters Patent isz- 1. An oil heatercomp'ising a combustion chamber, a source of heat for the' combustion-chambei',` a heatingcliamber.v having a flue gas exit, anair-cooled vertical bridge wall vseparating the combustion chamber from the heating chamber,'

a convection heated bank of economizer tubes located in said heating chamber and extending Y transversely to the ,general direction of flow of the heating gases in the heating chamber, a series tubes' in the upper part of the combustion chamber adjacent the roof thereof, said rows having ,ovasas y such manner as to form two separate circuits,

portions in the form of widely spaced depending loops hanging in the free space substantially enl tirely above the bridge wall and in the combus- 1 tion chamber above the source of heat and freely exposed thereto in heat transferring relation and heated preponderantly by radiant heat, means for supporting thev radiant heat tubes in the still walls and in the free space of the still, means for joining the radiant heat tubes together in series, means for joining the economizer bank 'of tubes together, in series, and means forsconnecting the economizer bank of tubes in series -to the radiant heat tubes in such manner that -the oil flow therein is first through the economizer bank of tubes and then through the radiant heatrows to the outlet of the still.

2. A-.d ual circuit oil still comprising a central combustion Nchamber, a source of heat, for the l combustion chamber, two separate heating chambers located one on each side ofA the combustion lchamber oppositethe other,y air-cooled bridge walls separating the combustion chamber from the heating chambers, a-convection heated bank of economizer tubes located in each heatingy chamber 'and extending transversely tothe gen- .eral directionof flow of the Aheating gases in the heating chambers, dual oil circuits in the form of a series of horizontally disposed. rows -of radiant heattubes in the upper partr of the combustion chamber adjacent the roof thereof, said rows lhaving portions in the form of widely spacedfdepending loops hanging in the free spaceof the upper part of the combustion chamber above the source of heat and freely exposed there- .to in heat transferring relation and heated pre.

ponderantly by radiant heat, means for support'- ing the radiant heat tubes m the son walls and in the free space of thestill, means for .joining the radiant heat tubes 4together in series, means for joining the economizer bank of tubes together in series, and means for connecting the economizer bank vof tubes in series to theradiant heat tubes in such manner that the oil flow thereyin is first through the economizer bank of tubes and then through the radiant heat rows tothe- The above completes theI description of this m Outlet 0f the stm- 3. A dual circuit oil still comprising a central combustion chamber, a source of heat for the combustion chamber, two separate heating chambers located on opposite sides of the combustion chamber, aircooled bridge walls separating the combustion chamber from the heatigl'g chambers, a convection heated bank of econdmizer tubes located in each heatingchamber and extending transversely vto .the general direction of flow of the heating gases'in the heating chambers, two

separate radiant heat banks of tubesfeach bank consisting of a series of horizontal tubes located in recesses in the frontv face of a bridge wall facing the combustion chamber and fully ex-I posed to radiation' from the heat source therein, dual oil-circuits'in theform of a series of hori,v zontallyl disposed rows of radiant heat tubes in the upper part. of the combustion chamber adjacent -the roof thereof, said rows having portions in the form of widelyjspaced depending loops hanging in the free space of the upper part of` the combustion chamber' above the source of heat `and freely exposed thereto in heat transferring relation and yheated preponderantly by'radiant heat,means for supporting the radiant heat tubes in the still walls and in the free space of the still, means for joining the radiant heat tubes in the upper part of the still together in series in l bank .of tubes to the lower end of one of the radiant heat circuits located in front of a bridge wall, and means for connecting the upper ends of these bridge wall radiant heat circuits to the radiant heat circuits located in the upper part `of the combustion-chamber in such manner that the oil iiow is vfirst upward through the econo- "mizer bank of tubes then to the bottom of the bridge .wall circuits and upward therein and` thence through the radiant heat circuits in the upper part of the combustion chamber to the youtlet of the still.

4. Radiant heat stills in accordance with claim 1 as characterized by having a two-pass double bank air preheater provided with horizontal heat interchanging tubes located in the exit flue gas passage of the still below the economizer bank of tubes, means connecting the air-space of the ventilated bridge wall to said air preheater so that-air drawn into the upper part of this space will pass through the upper bank of preheater tubes into a transfer space of the air-heater and thence through the lower bank of tubes belonging thereto into a lower separated part of the bridge-wall air-space, passing transversely to the flow of heating gases over the outside of the the heating gases' thru said chamber, dual oil` circuits in the form of a series of horizontally disposed rows of radiant heat tubes in the combustion chamber adjacent the roof thereof, saidrows having portions thereof in the form of widely spaced loops depending in the free space of the upper portion of the combustion chamber above its said source of heat and freely exposed there-- to in heat transferring relation therewithand heated preponderantly by radiant heat, and means for connecting the economizer bank of tubes in series with the radiant heat tubes in such a manner that the oil ow is first through the economizer bank and thence through the radiant heat tubes to the still outlet. A

6. In a furnace for heating hydrocarbon fluids to cracking temperature, a heating chamber divided into radiant and convectionheating chambers by a vertical bridge wall, means vfor producing hot products of combustion for passage through the radiant and convection heating chambers yin `the order una "ed, interconnected heat absorbing tubes ineac heating chamber for conducting a hydrocarbon fluid therethrough, at least a portion of the tubes in the radiant heating chamber being disposed above the bridge wall `and arranged in a plurality of interconnected spaced parallel banks of several tubes each disposed in'vertical planes parallel to the-ow of hot products of combustion toward the vconvection section to expose the tubes thereof to radiant heat on both sides from the hot products of combustion and the tubes in the convection heating chamber, by convection heat therefrom.

7. In a furnace for heating hydrocarbon fluids to cracking temperature, a heating chamber divided into radiant and convection heating chambers by a vertical bridge wall, means for producing hotl products of combustion for said furnace, a plurality of interconnected parallel banks of radiant heat absorbing tubes for conveying hydrocarbon uid being heated from one bank to another disposed above the bridge wall and de'- pending fromv the roof of the radiant heating chamber in vertical planes parallel to the flow of hot products of combustion toward the convection section and spaced apart to expose the tubes thereof to radiant heat cn both sides from the hot products of combustion and heat absorbing tubes in the convection heating chamber for receiving heat from said combustion products preponderantly by convection.

8. In a furnace for heating hydrocarbon fluids to cracking temperature, a heating chamber' divided into radiant andconvection heating chambers by a vertical bridge wall, means for producing hot products of combustion for said furnace, a plurality of interconnected parallel banks of radiant heat absorbing tubes for conveying hydrocarbon fluid being heated from one bank to another disposed above the bridge wall and depending from the roof of the radiant heating chamber in vertical planes parallel to the i'iow ofhot products of combustion toward the convection section and spaced apart to expose the tubes thereof to radiant heat on'both sides from the h ot products of combustion,y other radiant heating tubes disposed immediately adjacent the walls of the radiant. heating chamber and heat .absorbing tubes in the convection heating chamconduit composed of series of widely spaced parallel rows of several depending tubes while subjecting the exterior of such tubes to radiant heat from an adjacent zone of combustion to heat said tubes preponderantly by radiant heat, the planes in which thedifferent series of tubes are disposed being spaced sufliciently from each other to insure that sub-divided masses of radiant heat from said combustion zone passing between such planes of tubes will approximate from 20 to 24) inches in thickness and thereby insure a maxi` mum radlatlve'capacity to heat th'e oil lto the desired elevated temperature.

10'1na furnace for heating hydrocarbon fluids to a cracking temperature, a radiant heating chamber, means for producing hot products of combustion for heating said chamber, a plurality of heat absorbing tubes in said chamber, meansv j disposed in verticalplanes adapted to be heated preponderantly by radiant heat from hot products of combustion to expose the tubes of each bank to intense radiant heaton both sides therefrom for substantially their entire length to heat .aorasssthe hydrocarbon uuid passing 'through manescing coil to an elevated temperature.'

l1. In a furnace forheating hydrocarbon fluids to'a cracking temperature, a radiant heating" chamber, means .for producing hotproduc'ts `of l0 to convey a separate stream of hydrocarbon uid combustion for heating said chamber', a plurality@ 'of heat absorbing tubes in said chamber, means for interconnecting. said tubes to form a plurality of separate heating coils, each of which is adapted therethrough, at leastv a portion of the tubes'of each heating coil being arranged in a plurality of spaced parallel banks' ofv severaltubes each disposed in vertical planes adapted to be heated preponderantly by radiant heat from hot products of combustion to expose the tubes of `each bank to intense radiant heat on both sides therefrom for substantially their entire length. toI heat the-'hy- ,droc'arbon uid passing through each heating 'coil to an elevated temperature, a convectionheating chamber receiving combustion products from said radiant heating chamber, heat absorbing tubes in said convection -heating chamber for conveying hydrocarbon fiuid'to b`.e heated andmeans for .2K5 connecting tubes in said convection heating ber, me ans for producing' hot products of 'comchamber to atA least one of the .heating ',coils in said radiant heating chamber.

' .12. IIn afurnace forfheating hydrocarbon fluids to cracking temperature, a radiant heating chambustion for heating said, chamber, a vertical bridgel wall over which' the exit furnace Vgases `ow, a'

`plurality of heat absorbing tubes in said chamber,

-i a portion bf -said tubes being disposed alongside 35, of the walls of theradiant heating chamber and heatedpreponderantly by radiant heat,`another .portion oi saidv tubes being disposed above said bridge walland arranged in a plurality of spaced y parallel `banks of several tubes each-disposed in vertical. planes parallel to the flowof hot prod- Vtubesto each other for conveyinga stream of hy- .A

ucts of combustion toward thebridge wall t exlpose 'the tubesbf 'each bank-to intense radiant heat on both sides from the hot products of combustion and means for connecting the portions of drocarbon `fluid therethrough. Y

' 13. In a furnace for heating hydrocarbon fluids to cracking temperature, a radiant heating chamber, ,means for producinghot products of combustion for heating said' chamber, avertical bridge wall over which-the ent'furnace gases ow, a. plurality of heat absorbing tubes i-n said chamber,

a portion of said tubes being disposed alongside-of thewalls of the radiant heating' chamber and' 55 heated preponderantly byradiant heat, another portion of said tubes being arranged above said first `mentioned portion and"above said bridge 1 wall disposed alongside of the walls of the radiant heating chamber and'in afplurality of'spaced 60 parallel-banks. of! several tubes each disposed in verticar planes parallelto the flow oLhot products of lcombustion toward the bridge wall to ex'- thejubesof each toiintenseradiant heat on both "sides from thehot products of combustion and means for connecting theportions of tubes. to leach other for conveying a4 stream of hydrocarbon uid therethrough. Y

. 14).In a furnace for heating hydrocarbon fluids y to a cracking temperature, a radiant heating .a chamber,-means ,for producing hot products of 1 l combustion for heating said chamber, intercon conducting a continuous stream of hydrocarbon /fluid therethrough, said tubes being arranged in nected heat absorbing tubes in said chamber for a plurality of spaced parallel banks of several tubes each disposed in vertical planes adapted to be heated preponderantly by radiant heat'to expose the tubes of each bank'to intense radiant heat on both sides therefrom for substantially" their entirelength to heat the uid passing there' through to an elevated temperature and means for protecting the tubes of the parallel rows nearest the means for producing hot products of comvbu'stion from excessive heat.

15`. In a furnace for heating hydrocarbon fluids `to cracking temperature, a combustion chamber. means for producing hot products of combustion for said combustion'chamber, a plurality of heating chambers'separated from said combustion chamber by bridge walls in communication' with 'f posed in vertical lanes parallel to the flow of hot products of com ustion toward the heating cham" bers to exposesaid tubes to radiant heat on both sides-from the hot products of' combustion, and

l heat absrbingtubes in each heating chamber for receiving heat from said combustion products by convection.

to cracking temperature, a radiant heating chamber, means for producing hot products ofcqmbusltion in the lower part of said radiant heating chamber, means forming a passage for withdraw-v ing the products of combustion from the radiant heating chamber, a plurality of interconnected `parallel rows of radiant heat absorbing tubes-in .the upper part` of the combustion chamber for Y conveying hydrocarbon fluid being heated from one-row to another, said rows having portions of several tubes each substantially entirely above the lower partof said radiant heating chamber wherein the hot products of combustion are generated and depending in a plurality of spaced parallel .vertical planes parallel to the iiow of hot 16. In a furnace for heating hydrocarbon fluids productsfof combustion .towards said passage in the ncombustion chamber and spaced apart to expose the tubes thereof to radiant heat on both sides from the:hoi'mproductsof` combustion after generation thereof.- g

l. -s noNALnL. THOMAS.

CERTIFICATE OF CORRECTION.

Patent No. 2,072,535.

DONALD L. THOMAS.

It is hereby Certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 9, second Column, line 27, Claim l5, .before the Word "bridge insert the wordl vertical; and that thesaicl Letters Patentshould be read Withthis correction therein that the same may conform to the record o the Case in the Patent Office. l

-Signed and sealed this 11th day of May, A. D. 1937.

Henry Van Arsdale (Seal) Acting Commissioner of Patents March 2, 1937'.

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