US1779405A - Flue-gas-recirculation system for shell stills - Google Patents

Description

Oct. 28, 1930. ATWATER 1,779,405

FLUE GAS RECIRCULA'PION SYSTEM FOR SHELL STILLS Filed Feb. 16, 1928 2 Sheets-Sheet l (r -Tw- /0 50 i: w I

INVENTOR BY Harry 14.19

M QQUQJ ATTORNE Oct. 28, 1930. H. A. ATWATER 1,779,405

FLUE GAS RECIRCULATION SYSTEM FOR SHELL STILLS Filed Feb. 16, 1928 2 Sheets-Sheet 2 ATTORNEI} Patentecl' Oct. 28, 19

UNITED'STATES HARRY A; ATWATER, or' xans'ns CITY, MIssoURr FLUE-GAS-RECIRCULATION SYSTEM FOR SHELL STILLS Application filed February 16,1928. Serial m.-254,79a.

The present invention relates to oil refining apparatus, and particularly torefining or toppingstills of the shell type, and aims to improve the efficiency of such apparatus c by providingffor the recirculationof a 'portion of the flue gases in suchwa manner as to not only increase the area of the'heat exchange surfaces but also the refining capacity of apparatus of this type. It is also sought to devise a still construc tion of this character in which this increased efficiency is efiected along with an increase in fuel-economy due to the recirculation feature, and'at the same time the danger'o'f'injury to the still structureon account of socalled.hot spots is practically eliminated.

- In carrying out theseobjects of the invention, it is further sought to provide apparatus of such character as to improve gen- 2 erally shelll still constructions. for which the invention is especially. adapted.

With the foregoing general objects in view, the invention will now be described by reference-to the accompanying drawings il- M lustrating one form of furnace and shell still construction which is adapted forthe em bodiment of my improvements, afterwhich those'features and combinations deemed to be novel will be set forthand claimed.

In the drawings 1 i -.:Figure 1 is a plan view; showing a portion of a stillbattery embodying the herein de-V scribedflue gas-recirculating system; 7 c

Figure 2 is a side-elevation, partly broken away :and in vertical section; J

- Figures 3 and 4 are views inrear and front elevation, respectively; l Figure 5 is, an enlarged: detail view illusi V a .t

Figuresi6 and 7 are end views of one of the recirculating flues, showing twodifierflow of flue gas.' I c In the drawings .is illustrated a common form of shell stillunit 10,.usually'arranged ent forms of ribs orfins for dividing the in battery form with "each unit 10 overlying :a" furnace or combustion. chamber '11 using either a'solid fuel, .or oil or gas, as in the illustrated apparatus, this fuel being trating' the interior ofone of the recirculatsupplied-by way of aburner opening '12. lhe'air for supporting combustion in the illustrated construction is admitted through an intake opening 14 into a bottom chamber 15,, and thence through checker openings 16 into the combustionchamber 11, from whichv the waste flue gases are conducted outv through a furnace flue passage 17 to a tunnel 18, and thence to a stack (not shown),

WVhere a series of suchstills are operated asa continuous'battery,.those still units in which the finalfractions aretaken oiffrom thecrude oil must be operated at a comparatively high temperature, resulting in flue gas temperatures of around nine hundred degrees Fahrenheit whereas, in the stills at spotswhich alwaysfollow rapidly the-ace V cumulation or" deposit of carbon, at low temperature nact the battery especially; But thls excess air must beheated, and hence the i excessiv'efiring and fuel consumption for'tha-t purposeat low temperature end of 1 the battery Even so, the firing can only be carried on within certain limits, because of this dangerof hot spots, and such limitation in firingtemperature likewise limits the ca-i pacity of the? still. I

These inefficient characteristics inherent in the operation of shell stills have long been 'recognized andrhave resulted in the gradual abandonment of this type in favor of the more efficient tube still, wherever new installations n a are being made .However, a vast number 'of shell still installations are yet being opoperated, as they represent an enormous investment, too great either to abandon or! to convertiover into thetube form of still. It isthe purpose 'of the present inventionzto r' surface alone.

render these shell types of installations very much more elficient, and this I have found to be possible by the simple expedient of sub stituting for the excess air employed in the combustion chamber a certain amount of recirculated flue gases, for the reason that the recirculation of such gases is practicable and feasible Where provision can be made to efr feet a greater percentage of heat transfer from the combustion gases to the contents of the still by convection or rubbing contact with the heat exchange surfaces than ordinarily takes place in the usual shell still construction through the medium of its bottom If the necessary additional heat exchange surface can be incorporated into this old shell type, and a further safety factor introduced for. blanketing and temperingthe hot combustion gases directly be neath the still bottom, it Will beunderstood that the results sought after in this connection may be accomplished.

lVith this end in view, each flue passage 17 is provided with a gate damper 20, and at some point along the flue gas tunnel 18 connection is made for each battery, as by a.

bendio'r elbow 22, with a suction fan 2 f for pullingia certain volume of the hot flue gases.

from the tunnel 18 and discharging the same into a header conduit 26, as clearly. shown in Figures 1 to 3. From the header 26 connection is made by means ofibranchconduits ori pipes 28 with a series ofuflue pipes 30, preferably two pairs of such flue pipes for each still unit 10, these fiues 30 extending longitudinally through the still, and at points not interfering with the manholes 31 and at some distance above the bottom of the still so as to afford access thereto for cleaning purposes. At the front end of each still, return bends 32 are connected with the ends of the flue pipes 30 for reconducting the fiuegases to the combustion chamber 11 into which the recirculated gasis discharged through a pass sage 34 located near the top ofthe chamber 11 and above the peephole 35 usually provided at the front of the furnace.

A suitable damper 36 is provided in the elbow 22 of each battery, and a damper 37 is located in. each of the branch pipes 28, for facilitating the proper regulation of the flow of the gases; and a cable 38 and suitable coun-' terwcight 39 may also be provided for facilitating the regulation of each of the dampers 20 above referred to (see Figure lVith such an arrangement, it willbe seen that each still unit has a dampered communication with the flue gas passages 1718, and by control of the dampers the flue gasescan be recirculated through .any one or more of the still units at will, and the extent or volnine of the flow conveniently regulated to any desired degree.

On account of the length of the stills,rang-. ing from thirty toforty feet, thetubes 30 will ordinarily be of comparatively large diameter, or from six to twelve inches, hence with flues of this size, without other provision, there would probably be a loss in efiiciency of heat transfer on account of the large core of gases traveling axially through the fine without coming in-contact with the interior surfacethereof; I therefore contemplate using ahollowhcore tube 40 (Figure 5) closed at each end by the preferably tapered terminals 41, each core tube being of smaller diameter than the flue, whereby the recirculated flue gases are caused to travel through the annular space between ,the flue and its core. Each core is maintained properly spaced centrally within the flue by means of longitudinal ribs or fins 42- (Figure 6). by which the flow of gases is. split or divided, and. these may be obliged to follow a still longer course through the flue by substituting ribs or fins of helical outline asillustrated at LE/in Figure 7.

By means of the above described recirculatingv arrangement, it will be seen that the flue gases which are returned to the combustion chamber 11through the passages 34 are utilized in place of the excess air ordinarily used, and sincethese gases are still relatively iot their use representsa clear gain in fuel economy as represented by the difference in temperature of such gasesand that of the atmospheric air it replaces. The discharge of the iecirculatedgases into the upper portion of the combustion chamber produces a tempering orblanketing eifectiupon the combustion gases, and thus protects the bottom of the still to such an extent as to practically eliminate .the dangerof. hotv spots, and the rate offiring can be increased without danger to the still bottom. This increased firing rate is ,ofcourse desirablein the interest of greater still capacity, and. furthermore is made practicable and feasible by the increased heat transferring 1 capacity afforded by the convective: heating surface. of the flues 30. Ihe displacement of excess air by the recirculated flue gases also works outin the interest of increased firing rate because of the higher percentage of CO in the fresh combustion gases and resultant highervfiame temperatures. amount of heatevolved is ofisetby the increase in the rate of heat transfer through the medium .ofthe flues 30. and the extensive area of convective heating surfaces there provided, this means an increase instill capacity whichdoes not impose any increased or excess burden upon the bottom heating surface of the still;

An additional advantage in theimproved construction resides in its adaptability to continuous battery, stills in, rerun'operations, in which the necessity of direct firing can be dispensed with in connection with thoseunits whichare fired only. very lightly, since the fairly hot recirculated.fluegases will afford But as. the increase. in the,

the requisite heating capacity in lieu of such direct firing. This is a distinct economical gain, especially since it is well known that direct firing is always a comparatively inefficient process where the rateof firinghas to be kept low. The selective regulation provided in the apparatus herein described not only makes such indirect firing operation possible, but permits such convenient adjustment of the operation of the different stills of the same battery as may be desirable. Again Where the particular stills of the same battery all require to be fired at the same rate, the increase in the heat transfer capacity by means of the flue structure herein described makes possible a lower firing rate for the same still capacity, or if the former firing rate be maintained the still capacity will be increased; hence, if the former rate of firing is injurious to the still, the improved flue gas recirculating system will provide the.

means for eliminating such injury Without any loss of capacity.

It Will thus be apparent that I have devised a practical and efiicient arrangement and construction for fulfilling all the desired objects of the invention, and it is equally apparent that the construction or arrangement of the system can be altered in any desired or required way to meet varying conditions of operation, and is in no sense tobe limited to details herein illustrated; accordingly, I desire to reserve the right to make all such changes or modifications as may fairly fallwithin the scope of the appended claims.

Having thus described my invention, what I claim and desire to secure by Letters Patent 1s 1. Flue gas recirculating apparatus for oil refining shell stills comprising, in combination with a furnace combustion chamber and an oil refining still of the tubeless shell type type overlying said chamber, one or more flues extending through saidstill, and means for conducting a portion'o-f the waste flue gases from the combustion chamber, through said fines and thereafter discharging the same into the space Within said combustion chamber directly underlying the bottom of the still. i V

3. Flue gas recirculating apparatus for oil refining shell stills comprising, in combibers, a flue gas header provided with means for diverting a portion of the combustion gases issuing fromsaid chambers, one or more fiues extending from said header through each of said stills, means communicating with said fines for reconducting gases from said flues to the combustlon chambers, and damper means for selectively regulating the recirculating flow of said gases through the 4;. Flue gas recirculating apparatus for oil 'r efiningshell stills comprising, in combination with the combustion chamber and a still overlying sa1d chamber, a tube extending through the still, a core structure in said tube and forming an annular passage there H through, and means for conductlng a portion of the Waste combustion flue gases from the combustion chamber into said flue passage and thence back into the combustion chamber.

5. Flue gas recirculating apparatus for oil refining shell stills comprising, in combination With the combustion chamber and a still overlying said chamber, a tube extending through the still, a core extendlng axially nature.

HARRY A. A'IWVATER,

nation with a series of furnace combustion chambers, an oil refining still of the tubeless shell type overlying each of said cham-

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