GB2482863A

GB2482863A - Method And Apparatus For Atomising Oils Or Liquid Fats

Info

Publication number: GB2482863A
Application number: GB1013643.0A
Authority: GB
Inventors: Keven Chappell
Original assignee: Individual
Current assignee: Individual
Priority date: 2010-08-16
Filing date: 2010-08-16
Publication date: 2012-02-22
Also published as: GB201013643D0

Abstract

An invention 5 for atomising oil or liquid fat has a pressure chamber 10 with a first inlet 13 for receiving at least a supply of oil or liquid fat and a first outlet 16 for emitting a pressurised flow of oil or liquid fat. The chamber also has a second outlet 18 for emitting a pressurised flow of steam. An associated nozzle 30 has a first inlet 31 connected to the first outlet from the chamber and a second inlet 32 connected to the second chamber outlet. The nozzle has an outlet 37, and in use combines the pressurised flow of oil or liquid fat and the pressurised flow of steam to form an atomised flow of oil or liquid fat and steam at the nozzle outlet. The pressure chamber can include a second inlet 14 for receiving a supply of water, and may also include a porous medium 15 positioned within the chamber and which divides the chamber into a first region 11 and a second region 12. The invention may find use in a burner within a combustion zone 50, and the invention may include means to circulate (26 fig 2) the oil or liquid fat for heating in the burner combustion zone or through a heater (25 fig 2).

Description

APPARATUS FOR ATOMISING OILS OR LIQUID FATS

FIELD OF THE INVENTION

This invention relates to apparatus for atomising oils or liquid fats, such as oil and/or fat based liquid fuels. The apparatus can be used as a fuel conditioning unit for a burning device.

BACKGROUND TO THE INVENTION

An oil burner is a heating device which typically bums fuel oil. Atomisation is a process used in connection with fuel injectors for oil burning devices. Forming an atomised flow of a liquid fuel aids combustion, thereby improving efficiency of the burning device.

Various techniques are known to form an atomised flow of fuel. In a pressure jet technique, the fuel oil is atomised into a fine spray, usually by forcing the fuel oil under high pressure through a nozzle. This spray is usually ignited by an electric spark within a combustion chamber, where an electric fan feeds excess air to aid combustion.

In an air/steam atomiser, a supply of fuel oil is fed to a vertical orifice where a jet of compressed air is directed across the surface of the oil. This causes the pressure upon the oil to be reduced and the oil is subsequently atomised and sprayed into a combustion chamber whereupon it is ignited. The steam versions are similar but may employ a concentric aperture steamloil nozzle where the oil is drawn through the central orifice by the velocity of the steam.

In an effervescent atomiser, or effervescent nozzle, the supply of fuel oil is mixed in a chamber with a gas supplied at the same pressure. The gas is partially dissolved within the oil due to the pressure, but typically is defined as a bubbly flow within the chamber. The mixture is directed by a pump to an orifice. Upon exiting the device, the gas is allowed to expand out of the oil, atomising the oil into droplets.

The above techniques can be used with refined, uncontaminated, fuels. For contaminated fuels, such as vegetable oil and used oils, a vaporising technique can be used. A supply of fuel oil is fed, typically by gravity, to a heated receptacle where it vaporises on contact with the receptacle. The vapour is ignited and exits through a carefully designed flue causing a natural draught to maintain the supply of combustion air to the burner receptacle and maintain steady combustion.

GB 2,085,758A describes a nozzle for atomizing a liquid. The nozzle has tangential inlets for receiving a supply of liquid fuel and a supply of gas (steam). The liquid and steam are mixed at the nozzle. This atomiser is of the air assist or air blast type, where the kinetic energy of the gas is used to break up the oil. This typically uses large quantities of gas in operation.

US 3,921,901 describes atomisation of liquid fuels. A pressurised liquid fuel supply and a pressurised water supply are combined in an emulsifier and then heated and discharged through a nozzle. Apparatus of this kind requires a single refined fuel and requires complex control and feedback loops.

SUMMARY OF THE INVENTION

An aspect of the invention provides an apparatus according to claim 1.

The apparatus is capable of atomising oil, liquid fat, or a combination of oils and/or liquid fats. An application of the apparatus is as a fuel conditioner for a burner.

The term "liquid fuel" will be used throughout the description to refer to oil, liquid fat or a combination of oils and/or liquid fats supplied to the apparatus.

Apparatus according to an embodiment of the invention has an advantage of using the phase change of water into steam as a motive force to drive liquid fuel to the nozzle where atomisation occurs.

An apparatus according to an embodiment of the invention has an advantage of being a self-contained liquid fuel atomising unit that does not require an external compressed air supply, separate steam raising plant or a high pressure oil pump with fine filtration. An apparatus according to an embodiment of the invention has an advantage of working with a wide range of fuels. An apparatus according to an embodiment of the invention has an advantage of reliably producing a finely atomised spray which promotes clean burning. An apparatus according to an embodiment of the invention has an advantage of utilising steam to atomise the fuel, thereby promoting lower levels of flue gas contaminants. The apparatus can be assembled and maintained at low cost.

Apparatus according to embodiments of the invention can be used with a wide range of liquid fuels, such as oil or fat based liquid fuels. The oil can be a petrochemical oil, an organic oil (e.g. vegetable oil) or a mineral oil. The fat based liquid fuel can be rendered animal fat or full fat milk. The liquid fuel can be obtained by a refining process, or it can be a reclaimed fuel or a fuel obtained from a renewable source. The apparatus can be used with mixed fuels and fuels of unknown calorific value. Further, the apparatus can tolerate fuels with high levels of contamination, both water and particulate.

When compared with a conventional effervescent nozzle oil burning equipment, embodiments of the invention have advantages of not requiring at least one of: a separate compressor or stored pressure cylinder for a gas supply; a feedback system for balancing the gas and oil pressures; an elongated combustion chamber typically associated with these nozzles. The elongate combustion chamber is required because the included angle of the spray cone from a typical effervescent nozzle using compressed air as the gas has been found to be around 20 degrees on average (Chen & Lefebvre -Spray Cone Angles of Effervescent Atomizers 1993), so a long combustion chamber is usually required to ensure full combustion is able to take place. In contrast, the steam used in embodiments of the invention expands more rapidly than compressed air and the resultant spray cone has proved to be much shorter and wider than could be expected with compressed air.

When compared with a conventional pressure jet oil burning equipment, embodiments of the invention have advantages of not requiring at least one of: a high pressure pump for the fuel oil supply; a micron level fuel oil filter to prevent blockages; selected refined fuels of the same viscosity and calorific value.

When compared with a conventional air or steam atomised oil burning equipment (sometimes called Air Assist) using either compressed air or steam as the atomising propellant, embodiments of the invention have advantages of not requiring at least one of: selected refined fuels of the same viscosity and calorific value; separate steam raising plant for the steam supply; condensate and water management systems.

When compared with a conventional vaporising oil burning equipment, embodiments of the invention have advantages of not requiring at least one of: the fuel oil to be fed by gravity; constant adjustment of fuel flow to maintain combustion; application of a more volatile fuel to bring it up to its working temperature; removal of post combustion "concretions" typical of this type of burner; flue gas treatment and smoke reducing measures due to poor combustion.

The pressure chamber of the apparatus can be heated in various ways. Heat can be purposely applied to the external surface of the pressure chamber, or the pressure chamber can make use of waste heat from an external heat source.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 shows an embodiment of apparatus for atomising oils or liquid fats; Figure 2 shows an alternative form of the apparatus of Figure 1 with circulation of liquid fuel through the combustion zone; Figure 3 shows a nozzle for use in the apparatus of Figures 1 and 2; Figure 4 shows another nozzle for use in the apparatus of Figures 1 and 2; Figure 5 shows an embodiment of the apparatus of Figure 1 with circulation of steam through the combustion zone; Figure 6 shows a nozzle with a thermal transfer member; Figure 7 shows a heater unit using the atomising apparatus; Figure 8 shows a hob/griddle using the atomising apparatus; Figure 9 shows a vertical grill using the atomising apparatus; Figure 10 shows a fryer unit using the atomising apparatus; Figure 11 shows a fuel injection nozzle using the nozzle of Figure 3 or 4; Figure 12 shows a gas turbine nozzle using the nozzle of Figure 3 or 4; Figure 13 shows a method of atomising oils or liquid fats.

DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention will be described with respect to particular embodiments and with reference to certain drawings but the invention is not limited thereto but only by the claims. The drawings described are only schematic and are non-limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn on scale for illustrative purposes. Where the term "comprising" is used in the present description and claims, it does not exclude other elements or steps. Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein.

Figure 1 schematically shows a liquid atomiser/fuel conditioner 5 according to an embodiment of the invention. In Figure 1 the liquid atomiser is shown as part of a burner with a combustion zone 50. The unit 5 comprises a pressure chamber 10. The pressure chamber 10 has at least a first inlet 13 for receiving a supply of liquid fuel and a first outlet 16 for emitting a supply of pressurised liquid fuel. The pressure chamber also has a second outlet 18 for emitting a supply of steam.

Depending on the type of liquid fuel, the pressure chamber 10 can have a single inlet 13 or two separate inlets 13, 14 as shown in Figure 1. The single inlet 13 is sufficient when the liquid fuel comprises a mix of water and liquid fuel, such as water contaminated with oil. When two inlets 13, 14 are provided, the first inlet 13 is for receiving a supply of liquid fuel and the second inlet 14 is for receiving a supply of water. The first inlet 13 and first outlet 16 are positioned on different parts of the pressure chamber to the second inlet 14 and second outlet 18. Advantageously, the first inlet 13 and first outlet 16 are positioned on a different side, or end, of the pressure chamber 10 to the second inlet 14 and second outlet 18. Advantageously, the pressure chamber 10 is oriented with a part of the pressure chamber 10 having the first inlet 13 and outlet 16 positioned beneath a part of the pressure chamber 10 having the second inlet 14 and outlet 18. In use, liquid fuel will occupy a first region 11 of the pressure chamber 10 and water/steam will occupy a second region 12 of the pressure chamber positioned above the first region due to the immiscible nature of oil-based liquid fuels and water. At a boundary layer between the first region 11 and second region 12, the liquid fuel will contact the water.

The pressure chamber 10 is shown in Figure 1 as a spherically-shaped chamber.

Other shapes of chamber can be used, such as a cylindrical or box shaped chamber or any other regular or irregular shape of chamber that allows the water to come into contact with the liquid fuel. The pressure chamber 10 can be formed of metal, high-temperature tolerant synthetic fibres or plastics.

A first supply line 17 connects the first outlet 16 to a nozzle 30. A second supply line 19 connects the second outlet 18 to the nozzle 30. A metering valve 21, 22 can be located in each of the supply lines 17, 19.

The pressure chamber can be heated in various ways. Heat can be purposely applied to the external surface of the pressure chamber 10, or the pressure chamber 10 can make use of waste heat from an external heat source. In an embodiment shown in Figure 2, liquid fuel is heated by heat energy from the combustion zone 50. A supply line 24 circulates liquid fuel between the pressure chamber 10 and combustion zone 50 to heat the liquid fuel. Supply line 24 has an inlet 23 and an outlet 27 located in the second region 12 of the pressure chamber 10. Advantageously, the inlet 23 is positioned near the base of the second region 12 and the outlet 27 is positioned higher in the second region 12. A portion of the supply line 24 passes through the combustion zone 50. Alternatively, a portion of the supply line 24 can pass sufficiently near to the combustion zone 50 to heat the liquid fuel a required amount or a heat transfer medium can be used to transfer heat from the combustion zone 50 to the supply line 24. A circulation pump 26 is provided for circulating liquid fuel along supply line 24. This embodiment has an advantage of not requiring a separate heat source for the pressure chamber, once combustion has started. A heater 25, such as an electrical heating element, can be provided for heating the liquid fuel during a starting phase of operation, before combustion has started. A further feature, which can be used in conjunction with the circulation of liquid fuel in the manner of Figure 2, or as an alternative to the circulation of liquid fuel, is to thermally conduct heat from the combustion zone 50 to the pressure chamber 10.

Advantageously, a porous medium 15 is provided within the pressure chamber and divides the pressure chamber 10 into the two regions 11, 12. The porous medium 15 has an advantage of promoting nucleation of steam at the boundary found at the surface of the oil. The porous medium 15 also has the effect of promoting a steady gasification, reducing pulses within the system. Examples of suitable materials for the porous medium 15 are: a cast ceramic or metal, engineered plastic or a naturally occurring material. The porous medium 15 can be a rigid material or a flexible material. The porous medium 15 can be mounted at a fixed position within the chamber 10, it can be mounted within the chamber 10 such that it can move within the chamber. Tn one embodiment, the porous medium 15 is mounted so that it can "follow" or "float" along the boundary level of the water/oil.

A further way of causing turbulence within the chamber is to position the water inlet 14 and the inlet 23 and outlet 27 of the circulating supply line 24 within the chamber 10 so that they work together to promote a rotor of convection currents. This helps to promote active mixing of fuels and breaking down of any coagulation. It is also possible to introduce the water directly into the hot oil portion of the chamber 11 within the last section of the line 24, prior to outlet 27. This works by the creation of a gas bubble in the last section of the line 24, causing an imbalance of the oil levels within that system and the oil is caused to flow.

Operation of the apparatus 5 will now be described. In use, the liquid fuel within the first region of the pressure chamber 10 is heated to a temperature which is in excess of the point where water changes phase to a gas, i.e. its saturation temperature.

Small quantities of water are allowed to contact the surface of the heated fuel oil. The amount of contact between the water and fuel oil is restricted by the inherent immiscible nature of water and oil. Typically, water and liquid fuel, with few exceptions, are immiscible and have very different specific heat capacities (see Appendix) but similar viscosities at elevated temperatures thus causing a predictable and controllable interaction between them at various temperatures. The water quickly undergoes a change of phase (liquid to gas) resulting in the generation of super heated steam. The steam acts as a propellant. As the expanding steam increases the pressure within the chamber 10, both the saturation temperature and the saturation pressure of the water are raised thus creating a store of energy enabling the system to do useful work with the rapid expansion of the super heated steam upon the reduction of the pressure. The increase in pressure from the expanding steam acts upon the surface of the oil. This pressure is used to drive the heated liquid fuel along supply line 17 to nozzle 30. Similarly, steam is supplied to the nozzle 30 via supply line 19. A metering valve 21 controls the delivery of liquid fuel along line 17 and a metering valve 22 controls the delivery of steam along line 19.

The device is regulated by the natural link between the (absolute) temperature and pressure in a system (the combined gas law) -as the temperature rises within a given volume, the steam pressure is increased proportionally. The elevated steam pressure is harnessed to provide the motive force within the nozzle, but it is also employed via metering valves to regulate the amount of water being issued into the hot oil to form more steam and so actively controls the system pressure. As the temperature and pressure within the system rise due to the application of an external heat source, the temperature and pressure at which the water enters a phase change and "boils off' is increased, enabling it to remain as a liquid for longer and with significantly higher energy content (enthalpy) than would be normally attributable to water at atmospheric pressure and a temperature of one hundred degrees Celsius. As the pressure is reduced in the system (to do work) this store of water will tend to flash into its steam phase at a temperature that can perform this useful work, thus maintaining the pressure within the system subject to the continued provision of an external heat source. n addition to other roles a proportion of the steam is introduced into the nozzle arrangement where it can be said to "aerate" the hot fuel oil and cause atomisation of the said oil upon exiting the nozzle. The temperature and pressure are dynamically linked within the system i.e. reducing the steam pressure automatically lowers the force issuing the oil from within the nozzle, which in turn lowers the amount of oil being atomised and subsequently burned. It follows that this reduction will then lower the temperature of the oil within the chamber, thus reducing the energy within the steam being produced, which will ultimately lower the steam pressure. It can also be said that the reverse is true, so simply by controlling its internal pressure, one is able to adjust the rate of both water and oil replenishment and the thermal output of the device.

The atomisation unit 5 can be used as part of a burner, as shown in Figures 1 and 2. The burner comprises an ignition unit 40 for igniting the atomised spray. The ignition can be operated in response to a control signal, or in response to manual actuation. The ignition unit is optional and the spray can be ignited manually using a match, lighter or similar device, if required.

Two example embodiments of the nozzle 30 are shown in Figures 3 and 4.

Both embodiments have some features in common. The nozzle 30 comprises a housing 33 which defines a chamber. The nozzle has a fuel inlet 31 and a steamlgas inlet 32 at one end of the chamber. The fuel inlet is aligned with the longitudinal axis of the chamber and the steamlgas inlet is perpendicular or tangential to the longitudinal axis of the chamber 33. At the distal end of the nozzle 30 the cross-sectional area of the interior 34 of chamber 33 reduces and leads to a narrow outlet orifice 37.

The nozzle shown in Figure 3 is a conventional nozzle used in an effervescent atomiser. The liquid fuel inlet 31 is formed as a tubular pipe 35 aligned with the longitudinal axis of the chamber 33. The pipe 35 has holes 36 along its length.

The nozzle shown in Figure 4 has a porous medium 41 lining the wall of the chamber 33. Steamlgas must pass through the porous medium 41 to reach the region 34 within the chamber. The porous medium 41 can be any of a range of materials, such as a porous ceramic material, Sandal Wood, fine sand, wire wool, or any other material that remains porous while withstanding elevated temperatures.

In both embodiments of the nozzle, the nozzle 30 creates a partially aerated or "bubbly flow" phase cusp solution with the fuel. The porous medium 41 can improve transfer of steam into the "aerated" or "bubbly flow" realm within the nozzle. This increases the nucleation points for the steam and the subsequent aeration of the oil is increased by some magnitude over the typical single drilled pipe arrangement shown in Figure 3. The porous material can be a porous ceramic material. The Enthalpy within the steam can be further enhanced by passing the steam supply line 19 through the combustion zone 50, or thermally transferring heat energy from the combustion zone to the supply line 19. Figure 5 shows an embodiment in which the steam supply line 19 includes a portion 28 which passes into the combustion zone 50. A valve 29 can be provided for controlling flow of steam through portion 28 of the steam supply line.

Upon exiting the nozzle 30 through orifice 38, the steam comes out of solution with a particular violence, shattering the oil droplets to provide a readily combustible finely atomised spray. The rate of expansion of the atomised spray coupled to its velocity creates a wide angle spray pattern which in turn promotes good combustion.

Figure 6 shows a nozzle 30 with the addition of a heat transfer member 45 to improve transfer of heat to the nozzle 30. Member 45 is formed of a thermally conductive material and thermally connects to the housing 33 of the nozzle. The remote end 46 of the member 45 is located in the combustion zone 50.

Any impurities and minerals originally present in the water are dissolved out when the water evaporates and remain suspended within the fuel oil providing gas nucleation sites and are subsequently either passed through the device to the combustion chamber or can be removed via suitable filtration equipment (not shown), as required. Typically, any impurities present in the fuel, if not filtered out, will be carried through the nozzle 30 and into the combustion zone 50 where they would either be destroyed, with the remnants being carried away in the exhaust, or be deposited in a cleanable well within the combustion chamber 50/exhaust stack as in a typical combustor. Tn the case of the condensing version, any impurities or solids remaining after combustion can be collected within the condensate below the condensing unit and then disposed of During operation, and where required, the elevated pressure and the temperature of the device may be used to supply the pressure chamber with a continuous supply of fuel and water via simple low pressure reciprocating pumps.

These simple pumps can be made to supply the two fluids to the device drawing their energy from either the temperature differential of the water and oil or the pressure differential of the steam over ambient. This has a negative effect on the thermal efficiency of the device, but allows it to run independently of an external power source.

The apparatus shown in Figures 1 and 2 can be used in a range of different applications. Some example applications are shown in Figures 7 to 10. For clarity, in each application the liquid fuel atomiser/fuel conditioner 5, which has been described in detail in previous Figures, is shown as a single block.

Space heating device An embodiment is shown in Figure 7. The device 5 is used as part of a burner for heating air within a forced draught flue system for comfort heating of premises.

Figure 7 shows a fan 101 and a heat exchanger/condensing unit 102. Item 102 is an optional heat exchanger that can be added to the basic burner unit in Figure 7 if it is going to be used to heat water.

Water heating devices A simple heat exchange unit may be employed to provide hot water or domestic central heating.

Industrial incineration/kilns/ovens A number of the units may be installed together to elevate the temperature within a confined space for various industrial practices.

Cooking apparatus The unit may be used in various forms of cooking apparatus. Figures 8 to 10 show three example forms of cooking apparatus. Figure 8 shows a hob/griddle, Figure 9 shows a vertical grill and Figure 10 shows a food fryer. Tn general, the device 5 is used as part of a burner which directly, or indirectly, heats a surface where food is placed for the purpose of cooking, or heats a receptacle containing foodstuff for heating.

Figure 8 shows a hob or griddle 140 using the atomiser 5 as part of a burner unit. The liquid fuel inlet 13 to the pressure chamber 10 of the atomiser 5 is connected to a fuel supply line 141. The fuel can be cooking oil. Fuel inlet 13 is also connected to an oil catch tank 143 which catches oil from the cooking surface 141. A filter 142 filters debris at the inlet to the catch tank 143. A pump/valve 145 can be provided in line 144, if needed. A water supply 146 is connected to the water inlet 14 of the atomiser 5. A pump/valve 147 can be provided in line 146. The atomiser 5 is used as part of a burner for heating the cooking surface 141 to a temperature required for cooking. The hob also has an air inlet 148 for drawing fresh air to the burner and an exhaust 149 for expelling exhaust air. Tn use, the atomiser 5 receives a supply of fuel from supply 144 and the catch tank 143.

Figure 9 shows a vertical style grill 150 using the atomiser 5 as part of a burner unit. The liquid fuel inlet 13 to the pressure chamber 10 of the atomiser 5 is connected to a fuel supply line 154. The fuel can be cooking oil. Fuel inlet 13 is also connected to a drain port 160 of a receptacle 161 beneath the cooking area 151. A pump/valve can be provided in line 154, if needed. A water supply 156 is connected to the water inlet 14 of the atomiser 5. A pump/valve 157 can be provided in line 156. The atomiser 5 is used as part of a burner for heating a radiative panel 152 to a temperature required for cooking. The hob also has an air inlet 158 for drawing fresh air to the burner and an exhaust 159 for expelling exhaust air. In use, the atomiser 5 receives a supply of fuel from supply 154 and the drain port 160 of receptacle 161.

Figure 10 shows a self-contained food frying unit 110 using the atomiser 5 as part of a burner unit. The liquid fuel inlet 13 to the pressure chamber 10 of the atomiser 5 is connected to a line 111 which draws a supply of cooking oil 115 from a tank/reservoir 116 used for frying. A pump/valve 112 can be provided in line 111, if needed. A water supply 113 is connected to the water inlet 14 of the atomiser 5. A pump/valve 114 can be provided in line 113. The atomiser 5 is used as part of a burner for heating the reservoir 116 to a temperature required for cooking. A heat transfer unit 117 transfers heat from the burner to the reservoir 116. The fryer also has an air inlet 118 for drawing fresh air to the burner and an exhaust 119 for expelling exhaust air.

Internal combustion engine fuel injection An embodiment is shown in Figure 11, using a modified version of the nozzle previously shown in Figure 3 or 4, and like parts and numbered as before. The nozzle 30 includes a valve 121 in the orifice 37. The valve 121 is electrically operated by applying a control signal to a solenoid coil 122. A permanent magnet 123 is fitted to the valve 121. The valve is controlled to release atomised fuel at required times.

The device shown in Figure 11 can be installed as a fuel injector for a conventional internal combustion engine.

Gas turbine engine fuel injection An embodiment is shown in Figure 12, using a modified version of the nozzle previously shown in Figure 3 or 4, and like parts and numbered as before. The device lends itself to fitment within the fuel system of a gas turbine engine where the finely atomised fuels will promote reductions in exhaust emissions, while the steam within the spray increases the mass flow through the engine and its pressure ratio. The vanes 131 are swirl vanes. These are stationary vanes, and direct the flow of air.

Figure 13 shows steps of a method of atomising oil or liquid fat. The method comprises introducing a supply of oil or liquid fat to a pressure chamber and a supply of water to the pressure chamber (step 200) and applying heat to at least the oil or liquid fat (step 201). The method further comprises conveying a pressurised flow of oil or liquid fat from a first outlet of the pressure chamber to a first inlet of a nozzle (step 202). The method further comprises conveying a pressurised flow of steam from a second outlet of the pressure chamber to a second inlet of the nozzle (step 203). The method further comprises combining the pressurised flow of oil or liquid fat and the pressurised flow of steam in the nozzle to form an atomised flow of oil or liquid fat and steam at an outlet of the nozzle (step 204).

Appendix (1) Specific Heat Capacity (SHC) of: Fresh Water: c = 4.19 (kJ/kg.K) Vegetable Oil: c 1.67 (IJ/kg.K) Sesame Oil: c = 1.84 (kJ/kg.K) Olive Oil: c = 1.97 (kJ/kg.K) Mineral Oil: c = 1.67 (kJ/kg.K) @ 15°C and 101.325 kPa The Specific Heat Capacity (SHC) of water is roughly within two to two and a half times the SHC of the various oils that might be utilised and, at temperature, the viscosity of the oils is similar to water, thereby allowing a predictable egress. As long as a similarly predictable metered supply of water is introduced, randomly introduced oil types will be able to raise the temperature of the water to saturation point almost instantly, given that the volume of oil and its temperature are maintained within a set range.

The invention is not limited to the embodiments described herein, which may be modified or varied without departing from the scope of the invention.

Claims

Claims: 1. Apparatus for atomising oil or liquid fat comprising: a pressure chamber; a first inlet to the pressure chamber for receiving at least a supply of oil or liquid fat; a first outlet from the pressure chamber for emitting a pressurised flow of oil or liquid fat; a second outlet from the pressure chamber for emitting a pressurised flow of steam; a nozzle comprising a first nozzle inlet connected to the first outlet from the pressure chamber, a second nozzle inlet connected to the second outlet from the pressure chamber and a nozzle outlet, wherein the nozzle is arranged, in use, to combine the pressurised flow of oil or liquid fat and the pressurised flow of steam to form an atomised flow of oil or liquid fat and steam at the nozzle outlet.
2. Apparatus according to claim 1 further comprising a second inlet to the pressure chamber for receiving a supply of water.
3. Apparatus according to claim 1 or 2 further comprising a porous medium positioned within the pressure chamber, which divides the pressure chamber into a first region and a second region.
4. Apparatus according to claim 3 wherein the porous medium is a porous ceramic material.
5. Apparatus according to any one of the preceding claims wherein the nozzle comprises a chamber and wherein the first nozzle inlet is connected to an apertured tubular pipe mounted within the chamber.
6. Apparatus according to any one of claims 1 to 4 wherein the nozzle comprises a chamber and wherein the chamber has a lining of porous material, and wherein the second nozzle inlet is arranged to feed a supply of steam into the chamber through the porous material.
7. Apparatus according to claim 6 wherein the porous material is a porous ceramic material.
8. A burner comprising an apparatus according to any one of the preceding claims, the burner comprising a combustion zone adjacent the nozzle.
9. A burner according to claim 8 wherein the apparatus further comprises a supply line connected between an outlet of the pressure chamber and an inlet of the pressure chamber for circulating oil or liquid fat, the supply line having a portion located in, or thermally connected to, the combustion zone.
10. A burner according to claim 9 further comprising a pump for circulating oil or liquid fat along the supply line.
11. A burner according to claim 9 or 10 further comprising a heater for heating the supply line.
12. A burner according to any one of claims 8 to 11 and the apparatus further comprises a heat transfer member which thermally connects the combustion zone to the nozzle.
13. Apparatus according to any one of the preceding claims wherein the supply of oil or liquid fat is a liquid fuel.
14. A method of atomising oil or liquid fat comprising: introducing a supply of oil or liquid fat to a pressure chamber and a supply of water to the pressure chamber; applying heat to at least the oil or liquid fat; conveying a pressurised flow of oil or liquid fat from a first outlet of the pressure chamber to a first inlet of a nozzle; conveying a pressurised flow of steam from a second outlet of the pressure chamber to a second inlet of the nozzle; combining the pressurised flow of oil or liquid fat and the pressurised flow of steam in the nozzle to form an atomised flow of oil or liquid fat and steam at an outlet of the nozzle.
15. A method according to claim 14 further comprising: igniting the atomised flow of oil or liquid fat in a combustion zone adjacent the nozzle outlet.
16. A method according to claim 15 further comprising circulating oil or liquid fat between an outlet of the pressure chamber and an inlet of the pressure chamber via a supply line which passes within, or is thermally connected to, the combustion zone.