GB2185097A - Burning viscous liquid fuels - Google Patents

Abstract

In a method of burning a viscous liquid fuel, the fuel is fed to the inlet (4) of a pipe 2 and mixed with a gas to obtain an atomized fuel, the gas being an air-steam mixture produced by mixing a superheated water steam with air. The mixture is fed from a pipe 8 to an apertured chamber (6) and into the flow of fuel to produce gas bubbles. The atomized fuel is then mixed at the outlet (5) of pipe (2) with a swirled flow of oxidant initially fed into pipe (9). <IMAGE>

Description

SPECIFICATION Method of burning viscous liquid fuels and apparatus for carrying out the method This invention relates generally to heat power engineering, and more particularly to a method of burning a viscous liquid fuel and an apparatus for carrying out the method.

The invention can be utilized to the utmost advantage in burning heavy viscous wastes resulting from pyrolysisofoil and shale.

In addition, the proposed method of burning a viscous liquid fuel and the apparatus for carrying out the method can find application for burning water-coal and mazut-coal suspensions, sludge, industrial sewage containing organic solids, liquid and toxic substances of organic origin, liquid domestic and municipal wastes, liquid farm wastes, and the like.

There is known a method of burning a liquid fuel (cf. e.g., West German Patent No. 1,233,082, Int.CI. F 23 D, published 1967) which includes mixing the fuel with a gas under a pressure substantially higherthan the pressure of the fuel to result in an atomized fuel.

The atomized fuel is then mixed with a flow of oxidanttotheformation ofa fuel mixture. Thefuel mixture is then heated to the flare point.

The method employs air as the gasforatomizing the fuel and as the oxidant.

This known method can be effectively used for burning a heavy oil fuels, such as mazut.

However, the shortage of such fuel resources as mazut and other oil fuels necessitated utilization of production wastes, for example, heavy wastes resulting from pyrolysis of oil, shale, coal and other organic matter not amenable to burning by using the prior art methods because oftheir high viscosity exceeding that of mazut, low heat of combustion, and fluctuating content or organic matter in the flow offuel, and also because such liquidfuelscontain solid matter, which prevents efficient atomization priorto burning.

Experiments have shown that such viscous liquid fuels, when burned by the known method, fail to exhibit stable ignition and burning due to high viscosity, low temperature of flame, and incomplete burn-out of organic matter.

The reason is that drops of the liquid fuel burn well, whereas particles of solid fuel burn incompletely, since most of the oxygen carried by the oxidant is expended for burning the drops ofthe viscous liquid fuel,which is morecombustiblethan the solid components ofthefuel.

Also, the known method offers low ignitability of highly viscous liquid fuels duetothatthe flow of oxidant is not swirled.

In consequence, this results in insufficient flame coneforefficientlyburning highlyviscousfuels, particularly two-component fuel mixtures fed at differentflow rates.

There is known an apparatus for carrying outthe known method of burning a liquid fuel (cf., e.g., the same West German Paterit No. 1,233,082, Int. CI. F 23 D, published 1967) comprising a housing and afuel feeding pipe arranged coaxial Iy inside the housing.

The apparatus is also provided with a gas feeding pipe, a meansforfeeding the gasto thefuel for atomizing the fuel, and a pipeforfeeding an oxidant to produce a fuel mixture.

The means forfeeding the gas to the fuel is fashioned as a nozzle made integral with the gas feeding pipe, flared relative to this pipe, and arranged coaxiallywith the fuel feeding pipe downstream of its outlet end. The sidewall ofthe nozzle has holesforthe passage therethrough ofthe gas delivered by the gas feeding pipe to the interior ofthe nozzle. The interior ofthe nozzle has a cross-sectional diameter substantially greaterthan the inside diameterofthe pipeto serve as a mixing chamberforthe diverging flow of fuel to form a jet of such fuel escaping from the fuel feeding pipe and mix with the gas to produce an atomized fuel.

The gas feeding pipe communicates with the interior of the nozzle ofthe gas feeding means through an annular passage defined between the outer surface ofthefuel feeding pipe and the inner surface ofthe annularwall of the nozzle spaced therefrom, and through said holes made in the section ofthe nozzlewall adjacentto the wall ofthe fuel feeding pipe.

Formed between the outer surface ofthe nozzle and inner surface of the housing is an annular passage also communicating with the gas feeding pipe and extending down-stream ofthe flow of atomized fuel and gas to form an axial passage or confuser, which is a continuation ofthe interior of the fuel feeding pipe, having atthe outlet afirst diverging tube, and communicating downstream of the flow with the combustion chamber.

There is also provided a pipe forfeeding an oxidant arranged radially relative to the longitudinal geometrical axis ofthefuel feeding pipe.

A second confuser is further provided, which communicates the oxidant feeding pipe with a second diverging tube arranged atthe outlet ofthe housing, facing the combustion chamber, and communicable with the first diverging tube at the side ofthefuel feeding pipe.

This prior art apparatus is inherently disadvantageousforburning highlyviscousheavy liquid fuels, two-componentortwo-phase fuels containing much solids suspended in the liquid phase, and fuelsfeaturing a heatofcombustion substantially below the heat ofcombustion of mazut, as well as otherfuelstending to exhibit reduced heat of combustion.

This disadvantage is accounted for bythatsince the holesforfeeding gas are provided in the nozzle at the outlet from the fuel feeding pipe, and mixing is effected in the diverging portion of the nozzle, the fuel flow is broken into drops, whereby thorough atomized mixing ofthe fuel with the oxidant is impossible.

Also, the aforedescribed arrangement of holes in the wall ofthe nozzle fails to assure reliable atomization of the fuel as its composition, viscosity and flow rate vary.

Further,the radial arrangement ofthe pipe for feeding the oxidant, and the coaxial arrangement of the annular space extending from this pipe to the second diverging tube fail to ensure reliable ignition ofthefuel.

The present invention is therefore aimed at providing a method for burning a viscous liquid fuel and an apparatusforcarrying outthe method, which would ensure sufficientlythorough atomized mixing ofthe highly viscous liquid fuel with an oxidant and reliable ignition ofthe mixtureforcarrying out efficient burning thereof.

The aims ofthe invention are attained by that in a method of burning a viscous liquid fuel residing in that the fuel is mixed with a gas under a pressure higher than the pressure ofthefuel tothus obtain an atomized fuel subsequently mixed with a flow of oxidant to the formation of a combustible mixture, after which the combustible mixture is heated to the fire point, according to the invention, used as the gas is an air-vapour mixture obtained by mixing a superheated steam with air and introduced directly to the flow of fuel fortheformation of gas bubbles in the flow of fuel, whereas the flow of oxidant is preliminarily swirled and admitted to the periphery ofthe flow of fuel carrying the gas bubbles.

Utilizing an air-vapour mixture as the gas allows to make use ofthe inherent capacity of the superheated steam to vaporize light fractions from heavy highly viscous fuels, these light fractions producing a homogeneous mixturewith the air present in the air-vapour mixture. In addition, the superheated steam acts to increase the temperature and fluidity of highlyviscousfuels, and also reduces the surface tension of such fuels.

The introduction ofthe air-vapour mixture directly to the flow of fuel before it expands at the outlet from the fuel feeding pipe is accompanied by the formation of gas bubbles containing a homogeneous mixture of air and vaporized fractions ofthe heavyfuel,thefine shells ofthe gas bubbles containing the heaviest fuel fractions, such as resins, when burning two-phase mixtures of heavy liquid and solid fuel, the shell of each gas bubble also accumulates particles of the solid fuel. The presence of easily ignitable homogeneous mixture of vaporized fuel fractions with oxygen in a gas bubble facilitates ignition and burning of the heavy fractions and solid phase ofthefuel.

Preliminary swirling ofthe oxidant provides mixing of gas bubbles with the high temperature combustion products,which are sucked in bythe flow of oxidant from the flame zone to occupythe volume oftheflame cone. This ensures reliable ignition ofthe homogeneous mixture inside the gas bubbles and subsequent burning of the shell of the gas bubble and solid particles present in the bubble shell. Feeding the swirled flow of oxidantto the periphery ofthe fuel ensures the greatest surface contact and mixing ofthefuel flow with the gas bubbles and flow of oxidant.

It is recommended that the mass flow rate ofthe air-vapour mixture be maintained within a range of between 0.9 and 5.0 parts by weight of the mass flow rate ofthefuel.

Maintaining the above relationship between the mass flows rates of air-vapour mixture and viscous liquid fuel affords reliable ignition and ensures complete combustion ofthefuel.

If this ratio is reduced to below 0,9, the amount of air in the air-vapour mixture is rendered insufficient for reliably igniting the fuel.

An increase in this relationship to over 5.0 results in thatthetemperature oftheflame of burning fuel tends to drop to belowthe optimum duetothe excess of air in the fuel.

Preferably, the swirled flow of oxidant is admitted so that the cone angle oftheflow of oxidant to the geometrical axis of the flow of fuel would range from 100to 20 .

The flow cone angle is understood to express an angle between the vector of maximum velocity of the swirled flows of oxidant and viscous liquid fuel and the axis ofthe straight flow of fuel.

It has been determined experimentally that the cone angle oftheflow of oxidantand theflareangle oftheflame are equal in magnitude.

Maintaining the cone angle ofthe swirled flow of oxidantwithin the above range allows two reliably ignite and completely burn heavyfuels.

Areduction inthe cone angle ofthefuel flameto below 10 causes less efficient ignition and burning duet a decrease in orcomplete loss of high-temperature products of combustion being sucked-in bytheflow of oxidantfrom the flame zone and initiating ignition ofthe gas bubbles.

Conversely, an increase in the cone angle ofthe flame to over 20 results in a tendency of the volume producedbytheflameconetosuck-in notonlythe products of combustion but also the oxidant, which acts to sharply reduce the tem peratu re of the products of combustion and consequently affects theircapacityto ignite, The aims ofthe present invention are also attained by that in an apparatus for burning a viscous liquid fuel comprising a housing with a pipeforfeeding an oxidant and accommodating a coaxial fuel feeding pipe and having a meansforfeeding the gas to the fuel for atomization, according to the invention, the gas feeding means has the form of a part of a circular cylinder partially embracing the fuel feeding pipe at the under side thereof, the interior of the gas feeding means communicating with the fuel feeding pipe through a plurality of holes made in its wall, whereas theoxidantfeeding pipe is adaptedto swirl theflow of oxidant and is arranged so that the oxidant isfed downstream of an inlet hole ofthe fuel feeding pipe.

The arrangement of the gas feeding means in the form of a parts a circularcylinderpartially embracing thefuel feeding pipe atthe underside thereof makes it possible to reliably,thatis irrespective ofthe fluctuations in the level ofthefuel in the fuel feeding pipe, introducethe required quantity of gasto the flow of fuel and enhance interaction between the gas and fuel, which improves their mixing. Such interaction remains as efficient, when the fuel flow rate is reduced.

The provision of a plurality of holes in the wall of the fuel feeding pipe communicating the interior of the gas feeding means with thefuel feeding pipe promotes interface between the gas and viscous liquid fuel and enablesto deliverthe gas in theform of a plurality of jets, whereby the total interface between the gas and fuel is substantially increased to result in a more vigorous generation of gas bubbles.

The presence in the viscous liquid fuel of solid particles, that is with the loss of calorific power of the fuel, the generation of gas bubbles is not reduced.

Such an arrangementoftheoxidantfeeding pipe ensures a swirled flow of oxidant centrifugally accelerated at the periphery of the flow of viscous liquid fuel with gas bubbles. The centrifugal acceleration is uniformly distributed aboutthe periphery ofthe flow of liquid viscous fuel.

It is advisablethatthe oxidantfeeding pipe be arranged so that its geometrical longitudinal axis would be offset relative to the geometrical longitudinal axis ofthe housing and inclined thereto for swirling the flow of oxidant.

The thus offset arrangement of the axis of the oxidant feeding pipe and the axis of the housing, as well as the provision ofthe inclination ensure that theflowofoxidantisswirled in a mostsimple manner.

Preferably, the distance between the outlet hole of the fuel feeding pipe and the nearest hole ofthe plurality of holes provided in its wall is three to six times the diameter of the fuel feeding pipe.

This distance between the outlet hole ofthefuel feeding pipe and the nearest hole of said plurality of holes makes it possible to equalize the velocity ofthe flow of viscous liquid fuel at the outlet from the fuel feeding pipe and ensure uniform distribution ofgas bubbles throughout the volume of the fuel, whereby the flow of viscous liquid fuel is caused to ignite spontaenously and uniformly about its periphery.

Advisably, the gas feeding means has in cross-section the form of a sector of a circle corresponding to the central angle of 90"to 1200.

This cross-section of the gas feeding means ensures that the entire volume of gas is admitted to the lower part ofthefuel feeding pipe replete with the viscous liquid fuel. In addition, when feeding a viscous liquid fuel containing solid particles, such a shape of the gas feeding means prevents the solid particles from being settled and accumulated in the fuel feeding pipe. As a result, mixing conditions become morefavourable,and ignition oftheflowof viscous liquid fuel is intensified.

The above range ofthe central angles provides uniform distribution of the flow of gas in the volume oftheviscous liquid fuel atdifferentflow rates ofthe fuel and various degreestowhich thefuel feeding pipe is filled therewith.

When this angle is less than 90", the hydraulic resistance of the gas feeding means grows sharplyto cause non-uniform distribution of the gas through the volume ofthe viscous liquid fuel and result in less efficient mixing thereof with the gas and incomplete combustion.

Conversely, when this angle is more than 1200, the upper rows of holes wherethrough the gas is admitted to the flow of viscous liquid fuel resttoo close to the level of the flow of viscous liquid fuel at the outer su rface of the fuel feeding pipe, as the fuel isfed non-uniformlyto the interior ofthefuel feeding pipe. Part ofthe gasfailsto enterthevolume ofthe viscous liquid fuel to resultin less vigorous generation of gas bubbles, less uniform distribution ofthe bubbles through the volume of the fuel, and incomplete combustion.

Favourably, the radial height ofthe circular cylinder ofthe gas feeding means is 0.3 to 0.5the inside diameter of the fuel feeding pipe.

Experiments have shown that such an arrangement provides uniform distribution ofthe gas through the volume of the viscous liquid fuel, vigorous generation of gas bubbles, and uniform distribution thereof in the volume ofthe viscous liquid fuel resulting in improved combustion.

A decrease in this ratio to less than 0.3 causes a greater hydraulic resistance ofthe gas feeding pipe, as well as less uniform distribution of gas bubbles and less complete combustion.

Conversely, increasing this ratio to over 0.5 results in thatthe hydraulic resistance ofthe holes becomes less than the hydraulic resistance ofthe gas feeding means, which also affects the uniform distribution of gas through the volume of the viscous liquid fuel to impair combustion.

Preferably,the diameterof each ofthe plurality of holes is 0.2 to 0.3 the radial height ofthe circular cylinder of the gas feeding means.

The gas is therefore uniformly distributed through the volume of the viscous liquid fuel, whereas gas bubbles of approximately equal size are generated, which results in improved ignition and combustion.

If this ratio is less than 0.2, the gas is fed less uniformly to the volume ofthe viscous liquid fuel due to increased hydraulic resistance ofthe holes relative to the hydraulic resistance of the gas feeding means.

When this ratio is greaterthan 0.5, the gas is fed less uniformly because of the discrepancy in the hydraulic resistance ofthe holes and gasfeeding meansto result in lessefficientcombustion.

In view of the aforedescribed, the proposed method and apparatus for burning viscous liquid fuels are simple and reliable to ensure sufficient atomized mixing of the viscous liquid fuel with an oxidant for reliable ignition and complete combustion.

The method is especially advantageous for burning a mixture of viscous liquid and solid fuels with the aim of replacing the liquid fuels with such mixtures.

These and other advantages of the present invention will become more fully apparent from a detailed description of a specific embodiment thereof taken in conjunction with the accompanying drawings, in which: Figure lisa partial sectional view of an apparatus for carrying outthe method of burning viscous liquid fuels according to the invention; and Figure2 is a section taken along the line Il-Il in Figure 1.

The proposed method of burning viscous liquid fuels and apparatus for carrying outthe method will be hereinafter referred to as "thq proposed method" and "the proposed apparatus" for brevity.

The method involves feeding a viscous liquid fuel and mixing itwith a gas under a pressure higherthan the pressure of such fuel. Used as the gas is an air-steam mixture obtained by mixing a superheated water steam with air, particularlythrough ejection of the atmospheric air by superheated steam.

The air-steam mixture is introduced in the form of jets directlyto the flow offuel, which is accompanied bythegeneration of gasbubblesinsidetheflowof fuel.

The gas bubbles are generated because the temperature ofthe air-steam mixture containing superheated steam is higherthan the temperature of the viscous liquid fuel, whereby the surface tension ofthefuel is caused to reduce. This results in the formation of gas bubbles containing a mixture of steam and air, as the air-steam mixture is introduced directlyto the flow offuel. The air-steam mixture is fed to the flow of fuel until the entire fuel flow is replete with the gas bubbles.

Thefroth-like mixtureoffuel and gas bubbles is mixed with a preliminarily swirled flow of oxidantto the formation of a combustible mixture which is thereafter admitted to the periphery ofthe fuel flow with the gas bubbles. The centrifugal forces of the swirled flow of oxidant act on the flow of viscous fuel with gas to swirl it and produce a diverging cone of the flow ofoxidantand viscous liquid fuel with gas bubbles therein.

The mass flow rate of the air-steam mixture is maintained within the range of 0.9to 5.0 parts by weight ofthe mass flow rate ofthe viscous liquid fluid; for example, for heavy resin wastes resulting from pyrolysis of solid fuel this ratio is 3 parts by weight.

The swirled flow of oxidant is admitted so that the cone angle of the flow of oxidant is 1 O"to 20" to the geometrical longitudinal axis of the flow of liquid fuel; forthe above type offuel it is 150. Thethus obtained combustible mixture is then heated to the fire point.

The proposed method will be understood more fully with reference to an apparatusfore carrying out this method as disclosed hereinbelow.

The proposed apparatus comprises a housing 1 (Figure 1) of cylindrical shape with an open end face at the left side as seen in Figure 1. Secured coaxially insidethehousing 1 isafuelfeeding pipe2.An annularspace 3 is formed between the inner surface ofthe housing 1 and outer surface ofthe pipe 2. An inlet end 4 (to the right in Figure 1 ) ofthe pipe 2 communicates with a source (not shown) of viscous liquid fuel, whereas an outlet hole 5' (to the left in Figure 1) ofthe pipe 2 lies in one plane with the respectiveendfaceofthehousing 1 and communicates with a combustion chamber(not shown) of any known suitable construction.

Secured on the pipe 2 is a means 6forfeeding gas fashioned as a section of a circular cylinder partially embracing the pipe 2 atthe underside thereof, as seen best in Figures 1 and 2. The part of the cylindrical wall of the pipe 2 embraced by the gas feeding means 6 has a plurality of holes 7 serving to communicate the interior of the gas feeding means 6 with the pipe 2.

A pipe 8 is further providedforadmitting the gas to the interior ofthe gas feeding means 6, this pipe 8 being connected to a source (not shown) of gas, in this case an air-steam mixture.

There is also provided a pipe 9 forfeeding an oxidant made integral with the housing 1 and communicating with a source (notshown) of oxidant. The pipe 9 serves to feed a flow of oxidantto the periphery of the flow of fuel, and is arranged so that the oxidant is admitted downstream of the outlet hole 5' of the pipe 2.

The pipe 9 actsto swirl theflowof oxidant,for which purpose this pipe 9 is arranged so that its geometrical longitudinal axis 9' is offsetto about half diameter of the housing 1 relative to the geometrical longitudinal axis 1' thereof as seen in Figure 2, and is inclined to the axis 1 ' atthe angle oi (Figure 1 of about 60".

The distance f between the outlet hole 5' ofthe pipe 2 and the closestofthe plurality holes7 is 3to 6timesthe inside diameters ofthe pipe 2,viz.,four times this diameters in the case under discussion.

The gas feeding means 6 having the form of a part of an circular cylinder looks in cross-section (Figure 2) as a sector of a circle.

The sector of a circle corresponds to a central angle of 90to 1200, in this case t3 = 105 . An annular clearance is provided between the underside ofthe circularcylinderofthegasfeeding means6and inner surface ofthewall ofthe housing 1 .The circularcylinderofthegasfeeding means 6 has a radial height h (Figure 1 ) of 0.3 to 0.5the inside diameter ofthe pipe 2; in the instance under discussion 0.4that diameter.

The diameter of each ofthe plurality of holes 7 is 0.2to 0.3 the radial height h ofthe circularcylinderof the gas feeding means 6; in this case 0.25 the radial heighth.

The apparatus for carrying out the method according to the invention operates in thefollowing manner.

The operation ofthe proposed apparatus will be now described, when it is used with such fuels as highly viscous resins, viz., wastes resulting fram the thermaltreatmentoflow-calorie solid fuels. Such resins are conveyed by a pump (not shown) of any known suitable construction from a source, in this case from a storagetank,tothefuel feeding pipe 2, particularly to its inlet end 4, to flow therealong to the outlet end 5.

Simultaneously, a gas, in this case a mixture of superheated steam with air, is admitted under pressurethroughthe gas feeding pipe 8tothe interior of the gas feeding means 6 in any known suitable manner. From the interior of the gas feeding means 6 the mixture ofsuperheated steam and air escapes through the plurality ofholes7tothe interior of the fuel feeding pipe 2 between its inlet end 4 and outlet end 5.

The jets of superheated steam and air are mixed with the flow of highly viscous resin intheinteriorof the fuel feeding pipe 2 in the area ofthe holes 7 and to the outlet end 5. The resin is heated by the superheated steam, which results in a reduced surface tension thereof. Vigorous mixing of the flow of resin with the jets ofsuperheated steam and air, as well as heating of the resin and reduction in the surface tension thereof give rise to the formation of bubblesintheflowofthe highlyviscousresin.

Each gas bubble includes a shell of highly viscous resin, whereas the inside of the shell contains a mixture of steam and air.

Underthe action ofthe temperature ofthe superheated steam and dipole electrostatic moment of its molecules the lightestfractions ofthe highly viscous resin departto the inside ofthe gas bubbles to form a homogeneous combustible mixture.

In the course oftravel along the pipe 2 through the distancetto its outlet end 5 a maximum amount of gas bubbles tends to be formed in the flow of the highly viscous resin.

Simultaneouslywithfeedingthefuel and air-steam mixture a forced-draught fan (not shown) ofany known suitable design is actuated to force the oxidant, in this case air, to the pipe9forfeedingthe oxidant. While travelling along the pipe 9, the flow of air is swirled thanks to angular acceleration ofthe flow of oxidant relative to the axis 1 ' of the housing 1.

Swirling the flow of oxidant ensures that the oxidant escapes from the outlet ofthe housing 1 in the form of a cone diverging toward the combustion chamber.

The inside of the cone includes recirculating hot products of combustion mainly responsible for igniting the gas bubbles present in the flow ofhighly viscous resin discharged to the combustion chamber adjacent to the outlet end 5 of the fuel feeding pipe 2.

This sequence of preparation ofthehighlyviscous resin to burning and mixing ofthe resin with the oxidant affords efficient and complete combustion ofthe resin (i.e., wastes resulting from processing solid fuels).

When making use of a mixture of resin and solid particles asthefuel, the proposed apparatus ensures uniform distribution of solids through the volume of the fuel and in the shells of gas bubbles.

The proposed apparatus is started byan ignition device (not shown) of conventional design provided insidethe combustion chamber in close proximity to the outlet end 5 of the fuel feeding pipe 2.

Operation of the apparatus according to the invention is terminated by stopping the fuel feeding pump, cutting offthe delivery ofthe mixture of superheated steam and air, and deenergizing the forced-draughtfanforfeeding air.

Laboratory research and test burning of highly viscous liquid fuels have shown that the proposed method and apparatus are highly efficient for burning fuels having a viscosity 350 - 380 centistokes.

In addition, when burning a mixture of viscous liquid fuel with solid fuel, it is possible to replace up to 25% ofthe liquid fuel with solid without reducing the efficiency of combustion.

Itisto be notedthatduring burning highlyviscous liquid fuels having a low specific heat of combustion of, for example, 3000-5000 kcal/kg the highest flame temperature is close to the combustion temperature of ordinary mazutwith abputtwice as pronounced heat of combustion.

The apparatus for effecting the method according to the invention is simple to fabricate and serve, and is amenable to mounting on boilers of various types.

Claims (11)

1. A method of burning a viscous liquid fuel residing in that the fuel is mixed with a gas under a pressure higherthan the pressure of fuel to obtain an atomizedfuel,which is then mixed with aflowof oxidant until a combustible mixture isformed, after which the thus obtained combustible mixture is heated tothefire point; used as the gas is an air-steam mixture produced by mixing a superheated water steam with air and introduced directlytothefuel flowto generate gas bubbles insidetheflow, the flow of oxidant being preliminarily swirled and fed to the periphery ofthe fuel flow with the gas bubbles.

2. A method as claimed in claim 1, in which the mass flow rate of the air-steam mixture is maintained within a range of 0.9 to 5.0 parts by weight of the mass flow rate of the fuel.

3. A method as claimed in claims 1 or2, in which the swirled flow of oxidant is fed so that the cone angle of this flow is within 1 0 to 20 to the geometrical axis of the flow of liquid fuel.

4. An apparatusforcarrying out the method as claimed in claim 1 comprising a housing having an oxidant feeding pipe and accommodating a coaxial fuel feeding pipe communicating with a source of fuel, and a means for feeding the gas to the fuel for atomization communicating with a source of gas, the gasfeeding means having the form of a part a circularcylinder partially embracillg thefuel feeding pipe at the underside thereof, the interior of the gas feeding means communicating with the fuel feeding pipe through a plurality of holes made in its wall, the oxidant feeding pipe being adapted to swirl the flow ofoxidantand arranged sothatthe oxidant is fed downstream of an outlet hole ofthe fuel feeding pipe.

5. An apparatus as claimed in claim 4, in which theoxidantfeeding pipe is arranged sothat its geometrical longitudinal axis is offset relative to the geometrical longitudinal axis ofthe housing and is inclined thereto.

6. An apparatus as claimed in claims 4 or 5, in which the distance between the outlet hole ofthefuel feeding pipe and the nearest hole ofthe plurality of holes in its wall is three to six times the inside diameter of the fuel feeding pipe.

7. An apparatus as claimed in claim 4, in which the gas feeding means has in cross-section the form of a sector of a circle corresponding to a central angle of 90 to 120'.

8. An apparatus as claimed in claim 4, in which the radial height ofthe circular cylinder of the gas feeding means is 0.3to O.5theinsidediameterofthe fuel feeding pipe.

9. An apparatus as claimed in claim 4, in which the diameter of each of the plurality of holes in the wall ofthe gas feeding means is 0.2 to 0.3 the radial height ofthe circular cylinder of the gas feeding means.

10. A method of burning a viscous liquid fuel as claimed in any of the claims 1 to 3 substantially as described in the description.

11. An apparatus for carrying out the method of burning aviscous liquid fuel as claimed in anyofthe claims 4to 9 substantially as described in the description and represented in the drawings.