US3925001A

US3925001A - Placement of catalytically active materials in combustion flames

Info

Publication number: US3925001A
Application number: US098338A
Authority: US
Inventors: Kailish Chander Salooja
Original assignee: Exxon Research and Engineering Co
Current assignee: ExxonMobil Technology and Engineering Co
Priority date: 1969-12-19
Filing date: 1970-12-15
Publication date: 1975-12-09
Anticipated expiration: 1992-12-09
Also published as: FR2074025A5; CA933461A; NL7018509A; DE2062225A1

Abstract

Combustion of a carbonaceous fuel in a flame is improved by placing a catalyst comprising a metal or metal oxide in the primary reaction zone and thereby reducing smoke formation.

Description

United States Patent [1 1 [111 3,925,001 Salooja Dec. 9, 1975 PLACEMENT OF CATALYTICALLY [56] References Cited ACTIVE MATERIALS IN COMBUSTION UNITED STATES PATENTS FLAMES 2,014,686 9/ 1935 Lubovitch et al 44/4 Inventor: Chander salooja Reading Taylor X England 2,828,814 4/1958 Larkin, Jr. 2,855,770 10/1958 Grube 431/347 [73] Assgnea and Engneermg FOREIGN PATENTS OR APPLICATIONS Company, Linden, NJ. 1,067,642 5/1967 United Kingdom 431/350 [22] Filed: Dec. 15, 1970 21 APPL 9 33 Primary Examiner-Charles J. Myhre Assistant ExaminerW1lliam C. Anderson Attorney, Agent, or Firm-Harold N. Wells; F. Donald [30] Foreign Appllcatlon Priority Data Paris Dec. 19, 1969 United Kingdom 61916/69 July 29, 1970 United Kingdom 86707/70 [57] ABSTRACT Combustion of a carbonaceous fuel in a flame is img 431/4 431/347 proved by placing a catalyst comprising a metal or I n n u u u u e s s n l u I n e n l l I o e e s l l I u I e I l I I on t l I Field of ch IIIII u 326, 50, 351; me al oxide in the prlmary reaction zone and thereby reducing smoke formation.

7 Claims, 1 1 Drawing Figures US. Patent Dec. 9, 1975 Sheet 1 of 6 3,925,001

FIG. 7. P23 21 22 US. Patent Dec. 9, 1975 Sheet 2 of6 3,925,001

.ll ll :rir:

US. Patent Dec. 9, 1975 Sheet 3 of6 3,925,001

US. Patent Dec. 9, 1975 Sheet 4 of 6 3,925,001

US. Patent Dec. 9, 1975 shw 5 of6 3,925,001

US. Patent Dec. 9, 1975 Sheet 6 of6 PLACEMENT OF CATALYTICALLY ACTIVE MATERIALS IN COMBUSTION FLAMES (all hereinafter termed smoke for brevity) produced during combustion.

Carbon-containing materials such as natural gas, liquid petroleum hydrocarbons and solid carbonaceous fuels are combusted with air or oxygen to provide heat and/or power. In most instances of such combustion, efforts are made to derive thehighest combustion temperatures by employing the minimum quantities of air (or oxygen) but in the interests of efficient utilization of the heat value of the fuel, it is necessary to provide an excess of air or oxygen over the stoichiometric requirement. The excess air lowers the temperature of the combustion gases but ensures that the overall heat output is increased and that the amount of non-combusted material which appears as smoke is reduced.

The smoke represents a wasted resource, is a potential ficult it is to effect heat transfer from the combustion gases, in the case of boilers and furnaces, while in the case of heat engines, the thermodynamic efficiency is reduced. Among the proposals to reduce smoke, there may be mentioned the use of additives in the fuel which pass with the fuel into the flame, and pass through the flame: the additives or derivatives of the additivescan be detected in the resulting combustion gases, and in some cases contribute to the polluting nature of the combustion gases.

It is known in the art that all flames have a structure which can be characterised as follows:

1. A cool zone at the base of the flame in which admixture of air and the fuel takes place without substantial combustion of the fuel.

2. A very hot zone, termed the primary reaction zone, adjacent the base of the flame in which combustion proceeds vigourously and in which the concentration of ions is at a maximum in the flame.

3. A secondary reaction zone downstream of the primary reaction zone which contains the most luminous part of the flame.

Towards the downstream-end of the secondary reaction zone, smoketends to be apparent especially when there is insufficient excess air.

It has now been surprisingly discovered, in accor materials will for convenience hereinafter be termed catalysts.

Among the catalysts which are found to be useful are metals,- metal oxides and compounds which decompose under heat to metals and metal oxides, and metal salts which are substantially stable at high temperatures. Specific examples of catalysts are barium, magnesium, iron, tin, aluminium, vanadium, manganese, sodium, calcium, zirconium, platinum, yttrium, lanthanum, erbium, gallium,.titanium, chromium, cobalt, nickel, palladium, rare earth metals other than those hereinbefore specified, oxides of any of .the foregoing metals, compounds which decompose to oxides of the foregoing metals under the action of heat, and heat stable compounds of said metals. It will be appreciated from the foregoing that many other metal compounds may be employed.

It has also been discovered that materials which are in themselves catalysts, in the sense herein intended, either having a weak or strong smoke reducing effect, interact synergistically in a surprising and effective way to enhance the reduction in smoke formation. Specific examples of such synergistically effective combinations are the metals, oxides or heat stable compounds of: barium and sodium, barium and yttrium, barium and erbium, barium and zirconium, aluminium and sodium, aluminium and yttrium, aluminium and lanthanum, aluminium and erbium, aluminium and platinum, gallium and sodium, zirconium and yttrium, zirconium and erbium, zirconium and chromium, zirconium and manganese, zirconium and iron, zirconium and platinum, manganese and sodium, manganese and yttrium, manganese and titanium, manganese and chromium, manganese and iron,-manganese and nickel and palladium and iron. The foregoing is not an exhaustive list.

The invention is distinguished from prior expedients to mitigate smoke formation in that substantially none of the catalyst is found in the combustion gases. Moreover, the combustion of flames in contact with materials which are catalytically active for reducing smoke has previously been carried out with the said materials contacting either the whole flame or the secondary zon'e thereof, but it has not previously been proposed that contact between the flame and any particular material or materials shouldbe confined to the primary reaction zone of the flame.

It is preferred that the catalyst be located within the primary reaction zone as far as possible upstream from the secondary reaction zone, and near to, but within the base of the flame, so that the risk of contact of the secondary zone withthe catalyst is minimized.

Depending on the physical nature of the catalyst, and the type of equipment with which it is to be used, the catalyst may be provided in the form of wires or a planar mesh or grid, or a flat spiral, or cylindrical coil, of wires or a perforated screen, the wires or screen being either of the catalyst itself or of a supporting material which is composited with or on which is coated the catalyst. Alternatively the catalyst may be impregnated onto asbestos or like flame resisting porous material. A convenient method'of making the supported form of catalyst is to impregnate the support with a solution of a suitable metal compound, dry the impregnated support of solvent and to heat the support until the metal compound or a heat stable derivative thereof is effectively bound to the support.

However, it is-preferred wherever'possible that the form in which the catalyst is provided should be such 3 that it causes a minimum of disturbance to the flow of fuel and air and to the general aerodynamics of the flame.

The benefits arising from the invention include, as a result of the use of less excess air than would otherwise necessarily be the case, not only a higher thermodynamic efficiency, but also the possibility of burning fuel at greater rates without producing smoke in a given volume, and thereby increasing the maximum power output from a boiler, furnace or engine. In addition, when the fuel employed contains sulphur (which is usually the case), the reduced excess air reduces the proportion of corrosive sulphur trioxide in the combustion gases which is produced by oxidation of sulphur dioxide: similarly, because there is less excess air, the proportion of undesirable oxides or nitrogen tends to be reduced.

The invention will now be illustrated by reference to the accompanying drawings in which:

FIG. 1 illustrates diagrammatically a method of locating the various reaction zones of a flame.

FIG. 2 illustrates schematically an apparatus employed for investigations in connection with the present invention.

FIG. 3 shows an investigation in connection with this invention being effected using the apparatus of FIG. 2.

FIG. 4 is a cross-sectional elevational view of the principal parts of a domestic central heating burner.

FIG. 5 is a perspective view ofa flame plate assembly forming part of the burner of FIG. 4.

FIG. 6 shows perspectively a mesh or grid of catalytically active material for use with the burner of FIG. 4.

FIG. 7 shows the lower part of the burner of FIG. 4 and the general structure of a typical flame therefrom.

FIG. 8 shows a conventional refinery flare stack.

FIG. 9 is a perspective view of a form of catalyst for use with refinery flares.

FIG. 10 depicts perspectively the embodiment of FIG. 9 mounted on a refinery ground flare or stack, and

FIG. 11 illustrates the mode of action of the embodiment of FIG. 10.

Referring first to FIG. 1, there is shown a burner tube through which a fuel, such as an inflammable gas, is passed. The gas is combusted to form a flame 23 and

electrodes

21, 22 are located with their free ends in diametrically opposed parts of the visible edge of the flame 23.

The ends of the

electrodes

21, 22 are rounded to a known radius so that the area of electrode available for ion collection is known: a suitable radius is 0.5 mms. for electrodes I mm. diameter. A voltage is applied across the flame 23 from the

electrodes

21, 22, the voltage being supplied from a battery 24 and regulated by a tapping 25 of a potentiometer 26. The voltage is measured by a voltmeter 27 and the current passing through the flame by a micro-ammeter 28.

The voltage applied across the flame 23 is progressively increased for each location of the flame until a saturation current is reached indicating that for that location, the maximum current for the ionic concentration has been reached. The current direction is reversed by a switching device (not shown) to compensate for any assymmetry in the flame, and the procedure repeated. The whole procedure so far described is repeated for a number of positions of the

electrodes

21, 22 in the flame 23 until a profile of the ion concentration for the flame can be constructed.

It is found that the region of the flame nearest to the burner tube 20, apart from a cool fuel and air mixing zone 29 has the highest ion concentration, this being the so-called primary reaction zone. The primary reaction zone is always adjacent to the base of the flame 23, and terminates fairly abruptly at locations distal from the base of the flame: the region of the flame which is furthest from the base of the flame is found to be of low conductivity, and contains the most luminous part of the flame.

Referring now to FIG. 2, tests were performed using an upright laboratory burner 30 which burned ethylene in air. Ethylene from a cylinder (not shown) was supplied via line 31 and a regulating valve 32 to a flow measuring device 33 of the type known as a rotameter, and then to a mixing line 34 wherein was mixed with a small proportion of air supplied from line 35, valve 36 and rotameter 37. The rate of flow of air was kept constant, while the rate of flow of ethylene-air mixture was regulated by valve 38 and measured by a rotameter 39. The mixture was burned in a flame 40 at the top of the burner 30 with a known amount of secondary combustion air supplied to a glass tube 41 surrounding the burner 30 from a line 42. The secondary combustion air flow rate was regulated by a valve-43 and monitored by a rotameter 44. A glass tube 45 surrounded the tube 41 and extended a considerable distance above the flame 40 to shield the flame 40 from draughts.

In the flame 40, the various zones found by the method described in relation to FIG. 1 are indicated by I which is the primary reaction zone extending from the cool base of the flame at the top of the burner 30, II which is the secondary reaction zone which, with the cool zone, sandwiches the primary reaction zone, and III a cooler tertiary zone wherein smoke (if any) tends to be visible to the eye. The various zones of the flame 40 are not intended to be shown in the correct relative sizes in FIG. 2.

FIG. 3 shows a test for smoke mitigation in accordance with the invention using the apparatus of FIG. 2. The test procedure is as follows in a typical case, given by way of Example.

EXAMPLE 1 Test (a) Ethylene gas from the cylinder (not shown) was passed through the rotameter 33 of FIG. 3, premixed with a small known fixed flow rate of air measured by the rotameter 37 of FIG. 2 and passed to the barrel of the upright tubular burner 30. A measured fixed flow rate of secondary combustion air was passed into the annular space between the burner 30 and the glass tube 41, and maintained throughout the tests at 400 cc s/minute.

The ethylene-air mixture'was ignited at the top of the burner and it was found that with 21.5 ccs per minute of air, about 94 ccs per minute of ethylene in the ethylene-air mixture could be burned before smoke was just visually detectable at the top of the flame (zone III of FIG. 2).

The effect of a catalyst in accordance with the invention was now investigated. The chosen catalyst was barium oxide coated onto a circular filament of quartz at one end of a quartz rod, as depicted in FIG. 3.

Test (b) The quartz rod 46 with the filament 47 at its end was so located that the coated filament was within the yellow luminous secondary reaction zone (zone II of FIG. 2) of the flame 40. The flame began to smoke copiously and the flow-rate of ethylene was reduced gradually (using the control valve 32 of FIG. 2) until the smoking had virtually ceased. It was found that the flow-rate of ethylene was now about 64 ccs per minute as measured by the rotameter 33 of FIG. 2.

When the coated filament 47 was removed from the flame, the smoking disappeared, and the flow-rate of ethylene could be increased to about 94 ccs per minute before smoking was once again just detectable.

Test (c) The coated filament 47 was positioned within the flame just above the barrel of the burner tube 30 and in the bluish-coloured primary reaction zone (zone I of FIG. 2).

No smoke was at all discernible at the ethylene flowrate of 94 ccs per minute, and the ethylene flow-rate was gradually increased by opening the valve 32 of FIG. 2 until smoke was just detectable: the flow-rate was then about 137 ccs per minute.

When the coated filament 47 was removed from the flame, smoking was very marked and did not substantially cease until the ethylene flow-rate had been reduced once again to 94 ccs per minute.

Test ((1) The coated filament 47 was located at the top (zone III of FIG. 2) of the visible flame with an ethylene-air flow rate of 94 ccs per minute. No effect on the amount of smoke was observed, and an increase in the ethylene flow rate increased the amount of smoke in the same way as in the absence of the filament 47.

The tests (a) (d) demonstrate that to attain the limit of smoke formation, the combustible fuel could be increased by about 37% by the embodiment of the invention relative to the premixed ethylene-air flow-rate which gave a flame just at the limit of smoke productron.

The tests (a), (b), (c) and (d) illustrate the criticality of the location of the catalyst in the flame. The tests also demonstrate in a simple way that by the practice of the invention, the proportion of excess air in relation to the fuel consumed necessary for the satisfactory combustion of a fuel can be reduced thus improving the efficiency of combustion.

Results which were qualitatively similar to those of tests (a), (b), (c) and (d) were obtained in tests employing all the isomers of butene, isoand nbutanes, kerosine, gas oil and petroleum gases, and the benefits of the invention were realized both with diffusion and premixed flames, and partially premixed and diffusion flames. In every case, it was found that the practice of the invention enabled 30-60% more fuel to be burned without any increase in smoke or in secondary air.

EXAMPLE 2 The test of Example 1 were performed again but with ethylene premixed with a fixed quantity of air (from line 35 in FIG. 2), the air flow rate being again 21.5 ccs/minutes, and the amount of secondary air again being fixed at a flow-rate of 400 ccs/minute.

The filament 37 of FIG. 3 was coated with different metal oxides in each test, and starting with an ethylene flow-rate of 94 ccs/minute to give a flame in which smoke formation was about to occur at the top, the percentage increase in the rate of ethylene flow with each coated filament located in the primary reaction zone of the flame, relative to the fuel flow rate in the absence of the coated filaments, being noted.

The results are summarized in Table 1.

The results given in Table 1 show gallium oxide to be the best filament coating followed closely by the noble metals platinum and palladium.

The same pattern of results was obtained in other experiments using diffusion, pre-mixed and partially premixed flames with other hydrocarbon gases as fuels, although the actual percentage increase in smoke-limited fuel flow-rate was not in each case the same.

From the point of view of cost, availability and effectiveness, the metal oxides which prima facie appear to be of greatest potential for ordinary or commercial usage are barium and sodium. However, since sodium oxide is relatively more volatile than barium oxide (although the actual volatility is very small), further experiments, as hereinafter described, were performed using barium.

EXAMPLE 3 A number of tests were performed employing the burner of a commercially available high efficiency domestic boiler consuming light fuel oil.

The burner is shown in FIG. 4 and was of the downwardly-firing type that is to say, the flame extended downwards from the burner. The burner 50 comprised a fuel pump 51, a central tube 52 for the fuel which terminated at its lower-most end in a nozzle 53 having number of fine orifices for atomising the fuel, a centrifugal fan 54 for supplying primary combustion air and a concentric tube 55 for primary combustion air surrounding the fuel tube 52. The concentric tube 55 extended slightly lower than the central fuel tube 52, and a flame plate extended across the bottom of the air and

fuel tubes

55, 52 respectively. Ignition of the mixture of air and atomized fuel was effected by means of an electrode 56 carried by an insulated support. The flame plate is shown in more detail in FIG. 5 and comprises an outer support ring 57, which is a close fit in the end of the air tube 55, and a number of inwardly extending blades 61 which are generally radial but which do not meet at the axis of the support ring 57. The blades 61 are slightly curved in cross-section so that they impart a swirling motion to the air passing through the flame plate and thereby promote good mixing of the fuel and air. The flame plate is supported by a number of struts 64 which extend from the upper side of the support ring 57 to a fixed ring located around the fuel tube 52.

The burner 50 is set into a refractory wall 58 at its downstream side, and a stout strut 59 attached to the outside of the air tube 55 provides lateral support for the burner 55.

A catalytically active grid 66, shown in FIG. 6, was made up by forming in a ring 60 of 4% inches diameter a refractory mesh or network of 1/16 inch thick wire like members forming individual rectangles of 1 inch by 72 inch. A layer of barium oxide was coated on the wires of the grid to bring the thickness of the wires to about 7% inch. On diametrically opposite outer sides of the ring 66 were provided supporting lugs having internally threaded holes for the receipt of locating screws.

The burner was ignited in the normal way and the air flow rate was monitored. During normal operation, the excess air was found to be about 20% for the selected fuel flow-rate.

Flg. 7 shows the general form of flame produced below the burner. The flame base was located about Vs inch below the flame plate, and the flame itself extended about -12 inches below the flame plate and was 3% to 4 inches in diameter, In contrast to the ethylene flame of Examples 1 and 2, the relatively high velocity of the swirling fuel and air mixture passing from the flame plate made the primary reaction zone boundaries somewhat indeterminate by visual observation, but it was expected that the primary reaction zone would not extend much more than about 1% 1% inches from the flame plate, the secondary reaction zone accounting for most of the rest of the flame. These expectations were confirmed to a satisfactory degree by electrical conductivity determinations along the lines discussed in relation to FIG. 1.

Without changing the fuel or air flow-rates, the catalyst grid 66 of FIG. 6 was disposed in the flame at various distances from the flame plate, which was used as a reference for distance. As will be seen from FIG. 7, the burner support wall 58 is provided with apertures through which depend captive screws 69 held in position by washers 70 around a neck of the screws 69. The captive screws 69 are so arranged that they can engage with the threaded holes in the lugs 68 of the grid 66 and by rotation of the screws 69, the distance between the plane of the mesh or network of coated wires 67 and the flame plate can be adjusted.

The amount of smoke generated by the flame was determined by the Standard Bacharach test.

The results of the test are summarized in the following table, in which the column headed distance refers to the distance from the flame plate.

The results in the table demonstrate that a marked reduction in smoke and hence an improvement in fuel utilization is obtained by disposing the catalyst near the base of the flame (i.e., near the flame plate), and in the region of the primary reaction zone of the flame.

When test No. 2 of the table was repeated with varying quantities of air, it was found that the excess air requirement could be reduced from the normal value of 20% to 1 1% before a Bacharach smoke No. 3, equal to the normal smoking tendency of the burner, was obtained.

Apart from the increase in thermal and thermodynamic efficiency provided by the decrease in excess air from 20% to 11%, it would be expected that there would also be areduction in the concentration of sulphur trioxide in the combustion gases of nearly 60%, and a reduction in the concentration of nitrogen oxides of about 13%.

Although the above tests of Example 3 were performed on a domestic boiler, it will be appreciated that the benefits of the invention can be realized on larger boilers, and that due to the lower excess air requirements, benefits such as smaller air fans, pipes and combustion chambers can be realized with considerable savings in cost. The reduction in SO concentration would be beneficial in respect of less corrosion, and in nitrogen oxides in less atmospheric pollution. In addition, the decrease in smoke would of course lead to less frequent shut-downs of industrial plant for cleaning.

There are some instances in the combustion of carbon-containing materials in which it is not necessary to attempt to attain the highest combustion temperatures but it is desirable to mitigate the amount of smoke formed during combustion. Among these instances may be cited by way of example the combustion of waste hydrocarbon or fuel gases from petroleum refinery and blast furnace operations and the combustion of hydrocarbons or fuel gases in the firing of lime and in some ceramic and brick production processes.

A particularly useful application of the invention is to the mitigation of smoke formation in the burning of petroleum refinery waste hydrocarbon gases. These gases are of variable composition and their quantity often varies: accordingly, they have little value and their disposal is most simply accomplished by burning them in flares which are commonly at the top of tall flare stacks, and sometimes nearer to the ground on socalled ground stacks.

There is a marked tendency for the burning of refinery gases in flares to cause serious smoke formation. I-Ieretofore, the smoke formation has been mitigated at least to some extent by injecting steam into the flare. For a satisfactory degree of effectiveness, relatively large quantities of steam are required for example, from 1 to 3 lbs. of steam for each 1 lb. of refinery gas, and it will be appreciated that the mitigation of smoke formation by this expedient is expensive. In addition, steam injection is very noisy.

FIG. 8 shows the essential features of a conventional flare stack arrangement wherein the stack 81 is supplied with waste refinery gases by a trunking 82, and the gases are burned in a flame 84 at the top of the stack 81. The flame may be 60 feet in length, sometimes more, any may produce large quantities of smoke, depending on the composition of the gases. For steam injection, steam is injected into the stack 81 through a trunking 83.

One form of catalyst for refinery flare use in accordance with the invention is a cylindrical coil of alumina-silica material previously impregnated with a mixture of barium and sodium compounds such as barium nitrate and sodium hydroxide and fired to convert the barium nitrate to barium oxide and to dehydrate to some extent, the sodium hydroxide to sodium oxide which combines with the ceramic. It has been found that the cylindrical coil stablized flames, and promoted the induction into the flare flame of secondary air which enhanced the smoke reducing activity of the barium, sodium and alumina containing coil.

A suitable cylindrical coil 90 is shown in FIG. 9.

Preferably, the coil has a mean diameter slightly exceeding the diameter of the flare exit, and a length preferably no greater than 20% of that of the expected mean length of the flame and more preferably, up to of the flame length.

EXAMPLE 4 In a qualitative experimental simulation of the application of the invention to flare stack operation, a tube of approximately 1% inches internal diameter represented the flare stack, and the fuel was a mixture of saturated hydrocarbon gases known in the art as LPG (liquified petroleum gas) enriched with propene to cause smoke formation. The rate of gas flow was so adjusted that a smokey flame having a height of 4 to 5 feet was obtained.

A cylindrical barium/sodium/silica-alumina coil made as described above having the form shown in FIG. 9 with dimensions of about 1% inches internal diameter and about 9 inches long was inserted into the base of the flame. A number of human observers subjectively estimated that smoke intensity was almost halved. Additionally, it was noted that the flame was considerably more stable with the coil in the flame than before the coil was disposed in the flame. When the coil was removed from the flame, the smoke intensity was estimated to be about the same as before the insertion of the coil.

Although the experimental simulation described above was effected in still air conditions, the invention is useful in windy conditions when the axis of the flame is inclined to the vertical or even substantially horizontal. For the most advantageous effect, it is preferred that the catalyst coil be mounted, e.g., on gimbals, for rotational movement about a vertical axis and rotational movement about a horizontal axis, there being at least one wind vane device attached directly or indirectly to the catalyst coil to maintain the catalyst coil within the primary reaction zone of the flame and with the axis of the coil and the flame substantially coincident.

It is preferred that the bearings of the gimbals or other mounting be located well clear of the flame, and it is advantageous to provide one wind vane device responsive to horizontal directional changes in wind motion and one wind vane device responsive to vertical directional changes in wind motion. It is preferred that the wind vane devices be so located that they will be clear of the flame at substantially all time. FIG. 9 illustrates a way of applying the practice of the invention to refinery flares, and the stack 81 may be of the type shown in FIG. 8 or it may be of the ground flare type.

Attached near the top of the stack 81 is a collar 91 on which is rotatably mounted a ring 92 which is suitably separated from the collar 91 by bearings, diagrammatically shown as rollers 93. It is also preferred to provide bearings (not shown) between the ring 92 and the stack 81. The form of the appropriate bearings will be clear to those skilled in the art.

A wind vane 94 responsive to changes in the horizontal component of wind direction is attached to the ring 92 so that changes in wind direction in horizontal planes cause rotation of the ring 92. At right angles to the direction of the vane 94, there are provided stub axles 95 which project outwardly from the ring on diametrically opposed sides thereof. Each stub axle 95 serves to support in a recessed journal-bearing a rod 96 having a bearing collar 97. At the bottom end of each rod 96 is a counterweight 98 which serves to maintain the rod 96 in the position illustrated. A wind vane 99 is formed in each rod 96 above the collar 97, the vanes 99 being at right angles to the vane 94 and responsive to changes in the vertical components of wind direction.

A coil 90, of the type illustrated in FIG. 9, is located relative to the stack 81 by horizontal rods extending inwardly from the tops of rods 96, the rods 100 being attached to the coil 90.

In the absence of wind, the flare flame encloses the coil 90 and burns vertically, the coil 90 helping to diffuse air into the flame and additionally stabilizing the flame. The mitigation of smoke may be so great that steam injection may be dispensed with entirely.

In the presence of wind tending to tilt the flare flame, as shown in FIG. 11, the vane 94 causes the ring 92 to rotate to a position in which the vanes 99 are substantially perpendicular to the wind direction, and the wind, then acting on the vanes 99 against the action of the counterweights 98, causes the coil 90 to be tilted substantially into the flame 101. To a substantial extent, the flame stabilizes around the coil, and, by the principles of the present invention, smoke produced by the flame is substantially reduced or eliminated.

Although the invention has been most specifically described by reference to FIGS. 8-10 in relation to petroleum refinery flare stack flames, it will be appreciated that it may be applied to other flames where smoke formation is to be mitigated.

EXAMPLE 5 The experiments described in examples 1 and 2 and illustrated diagrammatically in FIGS. 2 and 3 were performed with mixtures of metal oxides coated on the quartz filament 47. The fuel was again ethylene premixed with a fixed flow-rate of air (21.5 ccs per minute) and with a fixed flow-rate of secondary air (400 ccs per minute). i

The percentage fuel flow increase for a number of mixed metal oxide coatings on the filament 47 before smoke was discernable was noted, and the results are summarized in Table 2.

TABLE 2-continued When the results of Tables 1 and 2 are compared, it is clear that the mixtures of metal oxides give superior results to the use of single metal oxides alone and that a synergistic interaction takes place in the case of mixed metal oxides.

Accordingly, it is yet another aspect of this invention that a mixture of metal oxides, such as the mixtures disclosed in table 2, are located in the primary reaction zone of the flame of a domestic or industrial burner, or in the flame of a refinery gas flare, or in the flames from blast furnace gases or flames for the firing of limestone, ceramics and bricks.

The invention is also useful in engines wherein there is a reasonable degree of definition of the primary reaction zone of the flame e.g., in external combustion engines and in the cans of the combustion chambers of gas-turbine engines. The invention may also be useful in certain types of diesel engine wherein the initial combustion of the fuel is effected in a cell which is separated from the main combustion chamber.

What is claimed is:

1. A method of improving the combustion of a carbon-containing fuel in a flame, comprising fixedly disposing in the primary reaction zone characterized by the flame having its highest ion concentration, a solid material which is catalytically active for reducing smoke and which is substantially involatile at the temperature of the primary reaction zone, wherein the catalytically active material is selected from the combination of compounds of barium and sodium, barium and yttrium, barium and erbium, barium and zirconium, aluminium and sodium, aluminium and yttrium, aluminium and lanthanum, aluminium and erbium, aluminium and platinum, gallium and sodium, zirconium and yttrium, zirconium and erbium, zirconium and chromium, zirconium and manganese, zirconium and iron, zirconium and platinum, manganese and sodium, manganese and yttrium, manganese and titanium, manganese and chromium, manganese and iron, manganese and nickel and palladium and iron.

2. A method according to claim 1 in which the catalytically active material is selected from the following metal and metal compounds: barium, magnesium, iron, tin, aluminium, vanadium, manganese, sodium, calcium, zirconium, platinum, yttrium, lanthanum, erbium, gallium, titanium, chromium, cobalt, nickel, palladium, a rare earth metal, oxides of any of said metals, compounds of said metals which decompose to oxides 12 under the action of heat, and heat stable compounds of said metals.

3. Apparatus for burning a carboncontaining fuel comprising means for the supply of a carboncontaining fuel to a combustion zone wherein the fuel is burned in a flame having a primary reaction zone characterized by the flame having its highest ion concentration and a secondary reaction zone having low ion concentration relative to said primary zone, and a solid catalytically active material located in the primary reaction zone of the flame, said solid material being active for reducing smoke and being substantially involatile at the temperature of the primary reaction zone, wherein the catalytically active material is a compound selected from compounds of barium and sodium, barium and yttrium, barium and erbium, barium and zirconium, aluminium and sodium, aluminium and yttrium, aluminium and lanthanum, aluminium and erbium, aluminium and platinum, gallium and sodium, zirconium and yttrium, zirconium and erbium, zirconium and chromium, zirconium and manganese, zirconium and iron, zirconium and platinum, manganese and sodium, manganese and yttrium, manganese and titanium, manganese and chromium, manganese and iron, manganese and nickel and palladium and iron.

4. Apparatus according to claim 3 in which the catalytically active material is selected from the following metal and metal compounds: barium, magnesium, iron, tin, aluminium, vanadium, manganese, sodium, calcium, zirconium, platinum, yttrium, lanthanum, erbium, gallium,'titanium, chromium, cobalt, nickel, palladium, oxides of any of said metals which decompose under the action of heat to the oxide.

5. Apparatus for burning a carboncontaining fuel comprising means for the supply of a carboncontaining fuel to a combustion zone wherein the fuel is burned in a flame having a primary reaction zone and a secondary reaction zone, and a solid material having at least part located in the flame, at least a major portion of said part being located in the primary reaction zone of the flame, the said solid material being catalytically active for reducing smoke and being substantially involatile at the temperature of the primary reaction zone, said catalytically active material being in the form of a substantially cylindrical spiral having a mean diameter slightly smaller than the mean diameter of the primary reaction zone.

6. Apparatus according to claim 5 in which the fuel is a gaseous fuel and the said means for the supply of fuel to the combustion zone comprises an upstanding tube having an outlet for gaseous fuel at the top, the said substantially cylindrical spiral being mounted relative to the tube on supports permitting movement of the spiral in three dimensions, and there being means responsive to the wind direction in the vicinity of the top of the tube for causing movement of the spiral relative to the top of the tube whereby the axis of the tube is substantially maintained coaxial with the axis of the flame formed by combustion of the fuel at the top of the tube.

7. Apparatus according to claim 6 in which the said means responsive to the wind direction comprise vanes

Claims

1. A METHOD IF IMPROVING THE COMBUSTION OF A CARBON-CON TAINING FUEL IN A FLAME, COMPRISING FIXEDLY DISPOSING IN THE PRIMARY REACTION ZONE CHARACTERIZED BY THE FLAME HAVING ITS HIGHEST ION CONCENTRATION, A SOLID MATERIAL WHICH IS CATALYTICALLY ACTIVE FOR REDUCING SMOKE AND WHICH IS SUBSTANTIALLY INVOLATILE AT THE TEMPERATURE OF THE PRIMARY REACTION ZONE, WHEREIN THE CATALYTICALLY ACTIVE MATERIAL IS SELECTED FROM THE COMBINATION OF COMPOUNDS OF BARIUM AND SODIUM, BARIUM AND YTTRIUM, BARIUM AND ERBIUM, BARIUM AND ZIRCONIUM, ALUMINIUM AND SODIUM, ALUMINUM AND YTRIUM, ALUMINUM AND LANTHANUM, ALUMINUM AND ERBIUM, ALUMINUM AND LATINUM, GALLIUM AND SODIUM, ZIRCONIUM AND YTTRIUM, ZIRCONIUM AND ERBIUM, ZIRCONIUM AND CHROMIUM, ZIRCONIUM AND PLATINUM, MANGANESE ZIRCONIUM AND IRON. ZIRCONIUM AND PLATINUM, MANGANESC AND SODIUM, MANGANESE AND YTTRIUM, MANGANESE AND IRON, MANGANESE MANGANESE AND CHROMIUM, MANGANESE AND IRON, MANGANESE AND NICKEL AND PALLADIUM AND IRON.

2. A method according to claim 1 in which the catalytically active material is selected from the following metal and metal compounds: barium, magnesium, iron, tin, aluminium, vanadium, manganese, sodium, calcium, zirconium, platinum, yttrium, lanthanum, erbium, gallium, titanium, chromium, cobalt, nickel, palladium, a rare earth metal, oxides of any of said metals, compounds of said metals which decompose to oxides under the action of heat, and heat stable compounds of said metals.

4. Apparatus according to claim 3 in which the catalytically active material is selected from the following metal and metal compounds: barium, magnesium, iron, tin, aluminium, vanadium, manganese, sodium, calcium, zirconium, platinum, yttrium, lanthanum, erbium, gallium, titanium, chromium, cobalt, nickel, palladium, oxides of any of said metals which decompose under the action of heat to the oxide.

7. Apparatus according to claim 6 in which the said means responsive to the wind direction comprise vanes attached to the said supports.