US2761496A - Flare stack apparatus for burning waste gases - Google Patents

Description

Sept. 4, 1956 R. A. vERNl-:R ETAL FLARE STACK APPARATUS FOR BURNING WASTE GASES 2 sheets-sheet 1 Filed June 29, 1951 Qrzverzbors Sept. 4, 1956 R. A. VERNER ErAL 2,761,496

FLARE STACK APPARATUS FOR BURNING WASTE GASES b t CLU Qfb. Longgg @www5 United States Patent FLARE STACK APPARATUS FOR BURNING WASTE GASES Robert A. Verner, Linden, and John P. Longwell, Scotch Plains, N. J., assignors to Esso Research and-Engineering Company, a corporation of Delaware Application June 29, 1951, Serial No. 234,398

2 Claims. (Cl. 158-109) The present invention relates to an improved apparatus for effecting substantially smokeless combustion of gaseous, combustible materials, and more particularly, gaseous hydrocarbon materials. The invention relates especially to a method and means for burning waste refinery gases by the use of are stacks, and includes means for modifying conventional are stack apparatus.

In many industrial operations, and particularly in the refining of petroleum oils, large volumes of combustible gaseous materials are produced which have no real economic value either as fuel or otherwise. In addition, in venting safety valves and other similar devices, the exhausted gases must be safely disposed of. The volume of such gases and their hazardous nature makes it impossible for them to be exhausted directly into the atmosphere. Normally, they are burned as discharged from exhaust or flare stacks at a considerable distance above the ground, although on occasion relatively low, large diameter flare structures may be employed.

In burning such gases in the conventional manner, diculty is experienced in providing sut`n`cient quantities of air to accomplish complete combustion at the stack discharge. As a result, large quantities of heavy, sooty smoke are produced to create undesirable atmospheric pollution in the vicinity of the operation. An additional objection to present burning methods and means is to be found in the luminosity of the ame produced. Primarily, this is due to the fact that the flame of the ordinary are contains large quantities of incandescent carbon particles. These particles may form dense, sooty smoke upon cooling.

In the conventional operation, the gases are discharged from the open upper end of a tlare stack without substantial premixing of air therewith and are ignited, as discharged, by a continuous pilot ame. Combustion of the gas thus takes place in air rather than as a combustible mixture of gas and a'ir. The flame thus produced is known as a diffusion type flame. Although a portion of the gas may burn immediately, the oxygen deficiency induces carbon formation, and especially where oletinic materials are present. In addition, it has been found that the heat generated by combustion of a portion of the gas stream may cause cracking of the unburned portions to form additional oleiinic and parainic materials and, under severe conditions, carbon and hydrogen. At the same time, some molecules may polymerize to form long chain hydrocarbons. The combustion or partial combustion of such compounds increases carbon formation particularly Ain the presence of hydrogen and a reducing atmosphere.

Patented sept. 4, e

ICC

Various attempts have been made to overcome the defects of the conventional are stack operation but without substantial success.` These efforts have ranged from attempts to adapt the principles of Bunsen, and other similar gas burners, to llare stack operation, to those according to which the required combustion air is supplied directly by means of blowers, or otherwise induced dilution of the gas stream with air, prior to ignition.

The use of are stacks operated in a fashion similar to a Bunsen type burner has been largely unsuccessful for the reason that such type of operation requires that the gas be supplied to the burner at a substantially constant rate and high ow velocity in order to prevent reverse ow of the combustible gas through the air induction inlets. Furthermore, as the gases to be burned are usually exhaust gases from process equipment which must be released without substantial back pressure, they are usually discharged at pressures close to atmospheric pressure, and it would be impractical and uneconomic to repressurize such gases once they had been released from the process pressures. Where air dilution or prem-ixing of the gas stream with a forced air supply has been attempted, it has been found that the volume of air required plus the volume of combustible gas to be burned would necessitate employment of are stacks of excessively large diameter. For example, whereas a conduit six inches in diameter would be adequate as a flare stack according to conventional procedures, to obtain an optimum ame condition by dilution of the gas with air prior to discharge of the gas from the stack, in the burning of each 1000 cubic feet of gas, provision would have to be made for the stack to handle about 6000 cubic feet of air per minute in addition. With such volumes of air and gas, the stack would have to be about sixteen inches in diameter. Considering the large volumes of gas required to be disposed of, the size of the stacks needed would present a considerable problem, and the cost of construction, including means for providing such large quantities of air, would be excessive.

As compared with previous solutions for the problem involved, it is an object of the present invention to provide a means for substantially complete combustion of the gaseous waste materials without inspiration or forced feeding of the required combustion air through the burner means employed. It is also an object of the invention to provide for substantially complete combustion of these gaseous materials under circumstances -in which the materials are burned by producing turbulent diffusion of combustion air into a stream of combustible gas discharged from a generally conventional ilare stack structure, with the required air being derived directly from the surrounding atmosphere. It is also an object of the invention to prevent thermal cracking and polymerization reactions in a burning stream of gas, tending to form undesired combustion products. A further object of the invention is to provide simple and economical means for carrying out a method according to this invention, and which means may be readily adapted for use with existing are stack structures for .the purpose contemplated. v

The invention and its' objects may be more fully underst'ood fron the following description when read in jiti with the accompanying dr'awings in which:

Fig. 1 is a diagrammatic view, partly in vertical section, of a typical ilare stack installation according to the present invention;

Fig. 2 is an enlarged vertical section of the upper end of the stack illustrated in Fig. 1;

Fig. 3 is a similar view of an adapter as applied to an existing stack structure and suitable for conversion thereof for operation as now contemplated;

Fig. 4 is a similar view of a modified form of apparatus according to tlie present invention;

Fig. 5 .is atljrorizontal section through the vapparatus of Fig: 4, takenv along the line VAV thereof.

Referring to the' drawings in greater detail,l the numeral 1 designates a typical flare stack structure. As shown in Fig. l; the stack is mounted on a base portion 1a and has discharg'eontlet end 1b', a conduit 2 opening into the lower end 'of the stack provides for' the introduction of combustible waste gases.l As shown', the conduit 2 ccmmunicates willi a water vseal drum 3 provided with an inlet 'conduit 4 whichv extends inte" thedruin by extension 421' to open below the' surface of body of water 5 maintained inthe drinn as by means of water inlet line 5a'. The line 5b provides for drainage of the drum. The inlet conduit 4 is connected to and communicates with a suitable source of exhaust gases which are to be disposed of by burning upon discharge from the stack 1. Suitable ignition and pilot llame means, not shown,- are provided for initialand subsequent ignition of theA gases issuing from the discharge end'lb of the ilarehstack.

In addition, and as shown in l, a conduit means 6 provides for the injection of a stream of a vaporized or gasous, substantially hon-combustible, diluent material, such as stearii, into 'the' upper end of the flare stack The conduit 6 enters the stclt through a side wall thereof, and terminates therein in an injection end portion 7 disposed oaxially with the stackv and opening upwardly toward the open end 1b thereof. The disposition of the injection end portion 7 within the 'stack eiid portion b is more clearly illustrated in the enlarged view provided by Fig. 2.

As shown in Fig; 2, the center line x-x of the stack 1 and end portion 1b is common to the injection end portion 7 of the conduit 6. The portion 7, While illustrated as a simple jet as provided by an open-end, pipe fitting or nipple, may be replaced by a constricted jet discharge nozzle element as desired. In any event, however, the outlet of the nipple or nozzle 7 should be located in vertically spaced relation to the open vorl outlet end of stack portion lbso( that with a substantially cone-shaped pattern imparted to a diluent iluid discharged from the nozzle 7, the surface thereof will be -substantially coincident with a conical* surface including a line .y-y drawn throughthe periphjeral 'edges of thiiozzle 7 and theopen end of the s 't'ck portion 1v1?. Furthermore, the location of the nozzle 7 should be such tli'atu'rider any 'git/en `conditions of operation, a fluid material discharged from the nozzle 7 will be substantially completely mixed, with the gaseous matferial passing through the stack prior to discharge of 'the combined materials therefrom, While imparting gross turbulence to the combined stream of materials issuing from the stack, and With a minimum condensation 'effect where steam is the huid material employed.

When a simple jet discharge element, such as the pipe nipple 7 illustrated, is employed, the location of the outlet thereof with respect tothe outlet of the stack .portion will be generally determinable as that level at which the inner peripheral edges of thedischange element outletintersect the surface of an inverted right conical surface based on the inner peripheral edge of the stack portion 1b, and having an apex angle of about 32. Expressed otherwise, this lei/el will be'th' l at which r-the line y-y drawn vbetween said edges, and extended V"to intersect the center line 'x-x will form an angle of 162C. with `said center line. lSpeciiical'lyillstfting su'ch disposition of 'the nozzle 7, Vin a stack having an internal diameter of twenty inches, the outlet of three inch pipe nipple discharge nozzle will be spaced from the outlet end of the stack by a distance of about twenty-eight inches. In another such installation, a simple jet nozzle consisting of a pipe nipple of one inch internal diameter was disposed within an eight inch stack spaced from the open end thereof by a distance of about twelve and one-tenth inches.

As illustrated in Fig. l, the conduit 6 is provided with a trap 6a at the lower end of.. the vertical portion thereof, and also with a liow control valve 8; a valve by-pass line 9; and suitable by-pass valves 9a, 9b, and 9c. The ow control valve 8 may be operated by means of a flow controller instrument 1i) connected to the conduit 4 and actuated by the registered how of combustible gases therethrough. v

The method and apparatus is equally suited for use in conjunction with existing hare stack structures, and in Fig. 3, atypical means* fo'r' such niodiication is illustrated. In this drawing, the numeral ZI designates the upper end of existing flare stack having an open discharge end provided with a collar portion 21a. An adapter element 22 forms an' extension of the stack conduits. This adapter element is of the same inside diameter as the stack conduit for the greater portion of its length but is flared outwardly at its lower end, as at 22a, to accommodate the tmtsidev dimension of the stack, or the collar 21a. This enlarged portion of the adapter element is of sufcient length to accommodate an annular clamp member 233 and slotted portions 22b extended into the body of the enlarged portion longitudinally from the lower peripheral edge portion 22C. Pressure exerted by means of the clamp and clamp bolts 23a compresses the enlarged portion to engage the collar 21a or stack 21 and to establish the adapter in fixed relation thereto. The adapter element 22 is also provided with an injector means, including an exterio'rly disposed 'section 26 adapted for connection to a conduit line such as the line 6 of Figs. l and 2, and an in jection 'end portion 2'7 comparable in nature and disposition to the portion 7 of Figs. l and 2.

ln operation of the apparatus described, combustible exhaust gases are exhausted by way of the hare stack 1 and ignited at the discharge end thereof. A substantially inert, huid diluent material is supplied to the upper end of the stack 1, as by means of the conduit 6, and discharged into the sa'ck, by Way of the nipple or jet nozzle member 7, in such fashion as to' be thoroughly and substantially completely mixed with the gases passed through the stack at about the outlet therefrom. The velocity of discharge from the nozzle 7 is also regulated to produce a high degree of turbulence in the combined stream of materials issuing from the stack, whereby such turbulence increases normal inspiration and diffusion of atmospheric air through 4the issuing stream. Turbulence in the stream of combustible 'gases i's further increased by rapid expan; sion of the gaseous diluent material upon ignition of the combustible gases with which combined. Normally the how of dil'uent material through line 6 is controlled automatically by the valve S in proportion to the liow of com bustible gas through line 4, but if necessary or desired, with valves 9a and 9c closed, the flow may be diverted through line 9 and controlled manually by means of valve 9b.

Al't'houghmany types of dilueut ,materials may be ernp'loyed discharge in the manner described, including air and even nitrogen, steam has been found to be exceptionally eifective yfor the purpose contemplated. Satisfactory results were obtained when operating bythe injection of steam using steam, at ll() pounds gauge pressure, injected at rates of from about 0.2 to about 0.7 pound per `pound of 'combustible material in the gas Ito be burned. Exhaust steam at .lowerpressures 4may `also `be employed with generally equivalent results. These results, classified by the character of the ilame obtained, are listed in the following tables;

TABLE I Gas Ratio Steam, Flame Condition om Combustible LbJHr. Lb. steam Average SCFH Lb. Comb.

SCFH LiL/Hr.

19,700 14,870 1,730 400 0.231 No Trailing Smoke,--- 13,300 10,020 1, 170 330 0. m2 0.27

7, 700 5, 800 075 200 0. 296 19, 700 14, S70 1, 730 63o 0. 364 No smoke 13,400 10,100 1,180 380 0.322 0. 37 7, 600 5, 740 670 285 0. 425 am a, 1i; as 1' as its te i .58

TABLE II Gas Ratio Steam, Conditions Total Combustible Lb./Hr. Lb* Steam Average SCFH Lb. Comb.

SCFH Lb./Hi.

NTfai1mgSmke-{ t 13:33 2 Si 151. No Smoke i asia 1s; ai ai te m The same waste gas materials burned without steam inburned, it is evident that the quantity of steam required jection produced a long trailing ame of intense lumito obtain a ame of any desired character, will vary with nosity, and large amounts of dense, sooty smoke. both the quantity and qualityof the gas being burned.

The exhaust gases burned as recorded respectively in With particular reference to the relative degree of un- Tables I and II; each had a composition as indicated by saturation it is indicated that steam requirements increase the following analyses: in direct relation to the degree of unsaturation.

Operations according to the present invention are in- Table Number dicated to be eiective in several ways to suppress the COI'JIJODHIIt v formation of carbon and other undesired products of 1 H ordinary combustion. First by mixing an inert diluent, and steam particularly, with the combustible gas prior C0, voipernt 0.6 46 to ignition, the molecules of the combustible material )gis gg-m fg 40 are separated by the diluent material. Secondly, the N7." an 224 1110 presence of the diluent, and particularly steam, tends to C0 d a0 7-9 reduce the combustion temperature. Where hydrocarrr, do 0.8 27.0 bon gases are burned, separation of the molecules tends gam g 131g to minimize polymerization with its consequence of in- C, an 0.4 22.8 creased carbon formation. At the same time, reduction Ca: n 3.3 4.3 of combustion rate and temperature tend to reduce the ca do- 22.0 1.5 eiects of cracking unburned gases to produce undesired ggd 22"-- l 0 4 oleiinic and parainic materials. Further, the reduc- C,= do-- 2.2 tion of combustion temperatures, and the substantial ,C5 n 2 3 o 2 50 elimination of incandescence increases the normal life not dem- 1.1 of the are stack at the discharge end. lAlso when steam g: "jg: 31% gj?, is employed as a diluent material, a'water gas reaction v A is promoted, wherein the gases to be consumed are cargxlggqgglfpemem of Comb d 7gg g1g bon monoxide and hydrogen, producing a non-luminous, Avg.Mo1.wt.ofcomb 445% (2)0.77 55 substantially sootless ame in contrast to that of burnclea: 1:37 0:72 me hyfifocarbons- `In Figs. 4 and 5, the concept of this invention 1s shown As indicated in the test reported according to Table II, is apphed to pparams fol-.bulgmg combustlble ex the combustible gas contained a considerably larger V01- aus, gases W 1c apparatus 1s own as .a .grolm are. The Hare as represented in the drawing is cornume percent of unsaturate material. d f tht d. u d l. dri al l Atmospheric conditions which existed at the time the pose o ree comen nc ra la .y Space cy m c e e" results according to Tables I and l1 were obtained, are ments 31 32 and 33' In a typlc'fl strucmfe the opter' indicated by the following table: v most element 31 may be about thirty feet 1n height, and

have an inside dlameter of about fourteen feet; the 1n- AfmOSPhefiC OndiIl'Ofl-SA 65 nermost element 33 a height of about-four feet and an v inside diameter of about thirty inches; and the inter- Tabie'Number mediate element 32 a height of about twelve feet and Condition an inside diameter of about six feet. Normally, each IA II of the elements 31, 32 and 33 will be constructed of reim inforced re brick, the outermost element 31 being con- Temperamre -.F. 78 42 structed so as to provide a substantially annular due-like Pre :irre in Hg 29.9 30.3 Wma velocity RH.-- 10 10 space 31a between inner and outer surface portions of the wall thereof. Each of the elements 31, 32 and 33 By comparison of the results reported by Tables I iS PIOVded With a plurality 0f Open POI'S 315 325, and l1, and in conjunction with the analyses of the gases and 331i' adjacent the bottom thereof, permitting entrance ments under the influence of the thermal draft created byv burning of exhaust gases. The upper end of element 133- is preferably chamfered inwardly as shown at 33a, with a plurality of cooling passageways or ports 33t` opening angularly from the outer wall surface through the chamfer surface.

The innermost element 33 serves as the discharge outlet for the combustible exhaust gases to be burned. These gases are supplied thereto by means of an exhaust gas conduit 34 extended through the respective concentric elements and having an outlet end 34a opening into the bottom portion of the cylindrical element 33. As shown, the outlet 34a is provided with a helically vaned interior surface designed to impart some degree of swirling motion to the exhaust gases as discharged therefrom. Means for ignition of the Combustible gases discharged from the upper end of the element 33 is provided as by a pilot gas ame from the discharge end of a supply conduit 35. Any suitable means, not shown, may be provided for ignition and maintenance of the pilot dame as desired.

According to the present invention, the center element 33 of the ground flare structure as set forth above is additionally provided with means for injecting a stream of vaporous fluid diluent material into the stream of combustible exhaust gas discharged from the element 33, immediately prior to discharge into the surrounding at. mosphere, at an initial velocity greater than that of the strearn, so as to dilute the gaseous stream and induce gross turbulence therein substantially at and beyond the point of discharge from the element, the exhausted gaseous material then being burned in the presence of the diluent. The injection means, as shown, includes a supply conduit 3 6- communicating at one end with a source of a vaporous diluent material, such as steam, and at the other end extended through the sidewalls of elements 31, 32 and 33, and concentrically upward within the latter into vertically 'spaced relation -to the .Upper end thereof. The conduit 36 terminates within the element 33 in a discharge nozzle portion 37, in a manner similar to that illustrated and described with reference to Figs. 1 to 3, inclusive, and for the -sarne purpose. The outlet of nozzle 3.7 also is spaced from the upper end of the element 33 by a distance such that the inner peripheral edges of the nozzle outlet intersect the surface of an inverted right conical surface based on the lower peripheral edge .of the chamfered portion 33a.

As compared with the 'aparatus illustrated in Figs. '1 to 3, inclusive, where the combustible gases are discharged directly into the atmosphere, and combustion air derived therefrom, entirely by :the inspiradas effect 0f turbulence in the burning gases .as induced by injection .of `the diluent material, and lthe expansion thereof -by the heat of combastion, ,in the apparatus according Vto Figs. -4 and `5, combustion yis initiated in a .conined'combu-stion zone as provided by the intermediate and outermost elements I32 and 31. vCombustion air, while inspirated ,and diffused into the burning-stream of gases in the same fashion as in the apparatus according to Figs. l to 3, inclusive, primarily is derivedbytherma-l draft induction through the passageways or ports 31-b, 32b, and 33b. The tiow of air through ports 33h is partly due to the inspiratingfeffect yof the jet of ydiluent material ydischarged lfrom Ythe -jet discharge nozzle 37. krOperation of the apparatus according to Figs. 4 and f5, is generally comparable to the operation of the apparatus illustrated 'by Figs. 4l to 3, inclusive, and 'as described wit-h reference thereto.

What' is claimed is:

V1. fln `'a lhare Ystack structure, 'including a vertically elongated iflare Vstack conduit, means 1forming an inlet for combustible gaseousm'aterials opening into said stack conduit adjacent the lower end thereof, conduit meansl connecting said inlet means to a source of said combustible gaseous materials, and wherein said conduit stack terminates at the upper end thereof in a discharge end opening into substantially unrestricted communication with the atmosphere surrounding the stack and is adapted to discharge a stream ofl gaseous material into said atmosphere, a means for inducing gross turbulence in said stream of gaseous materials and for diluting said stream with steam immediately before and after discharge thereof into the atmosphere, comprising a steam supply conduit extended upwardly into said stack conduit, a discharge nozzle at the terminal end of said supply conduit Within the discharge end of said stack conduit disposed in substantially concentric relation to said stack conduit, said nozzle having a discharge outlet of a radius substantially equal to from about one-seventh to about one-eighth the radius of said flare stack conduit, said nozzle opening toward the discharge end of said stack conduit aud disposed in vertically spaced relation thereto by a distance substantially equal to the product ,of the natural cotangent of an angle of- 16 multiplied by the diierence between the radius of said stack and the radius of said nozzle discharge outlet, and wherein said nozzle is adapted to provide a steam discharge pattern having a substantially inverted conical contour with an apex angle of about 2. An apparatus according to claim l wherein said flare stack conduit comprises a lower conduit section having an upper end, an annular collar secured to said upper end circumferentially thereof, and an upper Conduit section constituting said stack conduit discharge end, said upper conduit-section including .a body portion, having an upper end and a lower end, said body portion having a radius between said ends substantially equal to the radius of said lower conduit section, and a radially enlarged portion extending from and beyoru the lower end of said body portion, said enlarged portion being adapted to ref ccive the yupper. end of said lower conduit section telescopically, and frictionally to engage said collar thereon, said enlarged portion being provided with a series of vertical slots extending upwardly through the lower peripheral edge thereof and disposed in parallel spaced relation one to another circumferentially of said enlarged por.- tion, and an annular clamp encircling the slotted end of said enlarged portion, said clamp adapted to compress said slotted end of the enlarged portion into rigid Yengagement with said collar and the upper end of said lower conduit section, and wherein said steam discharge nozzle is disposed concentrically of said upper conduit section body portion.

References .Cited inthe Jile of this patent UNITED STATES PATENTS France Mar. r20,

Claims (1)

1. IN A FLARE STACK STRUCTURE, INCLUDING A VERTICALLY ELONGATED FLARE STACK CONDUIT, MEANS FORMING AN INLET FOR COMBUSTIBLE GASEOUS MATERIALS OPENING INTO SAID STACK CONDUIT ADJACENT THE LOWER END THEREOF, CONDUIT MEANS CONNECTING SAID THE INLET MEANS TO A SOURCE OF SAID COMBUSTIBLE GASEOUS MATERIALS, AND WHEREIN SAID CONDUIT STACK TERMINATES AT THE UPPER END THEREOF IN A DISCHARGE END OPENING INTO SUBSTANTIALLY UNRESTRICTED COMMUNICATION WITH THE ATMOSPHERE SURROUNDING THE STACK AND IS ADAPTED TO DISCHARGE A STREAM OF GASEOUS MATERIAL INTO SAID ATMOSPHERE, A MEANS FOR INDUCING GROSS TURBULENCE IN SAID STREAM OF A GASEOUS MATERIALS AND FOR DILUTING SAID STREAM WITH STEAM IMMEDIATELY BEFORE AND AFTER DISCHARGE THEREOF INTO THE ATMOSPHERE, COMPRISING A STEAM SUPPLY CONDIUT EXTENDED UPWARDLY INTO SAID STACK CONDUIT, A DISCHARGE NOZZLE AT THE TERMINAL END OF SAID SUPPLY CONDUIT

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