WO2013175466A1

WO2013175466A1 - Burner for combustion of heavy fuel oils

Info

Publication number: WO2013175466A1
Application number: PCT/IL2013/050429
Authority: WO
Inventors: Yinon FELDHEIM; Zafrir BLOCH-DAVID
Original assignee: Siete Technologies Ltd.
Priority date: 2012-05-22
Filing date: 2013-05-20
Publication date: 2013-11-28
Also published as: IL219929A0; US20150159862A1

Abstract

A combustion chamber for combustion of heavy fuel oil, enclosed by a wall extending longitudinally toward a gas outlet in a tapered manner, defining an elongated chamber. The chamber includes a pre-combustion region operative for mixing the fuel oil with air, a peak-combustion region, and a secondary-combustion region. An upstream group of confinement apertures, and a downstream group of confinement apertures, circumferentially disposed around the perimeter of the wall, allow pressurized air flow into the combustion chamber to form an air curtain barrier between the pre-combustion region and peak-combustion region and an air curtain barrier between the peak-combustion region and secondary-combustion region during the combustion of the air-fuel mixture, such that the air-fuel mixture is temporarily detained and confined within the peak-combustion region, prolonging the combustion within the peak-combustion region. A corresponding method for combustion of heavy fuel oil is also provided.

Description

BURNER FOR COMBUSTION OF HEAVY FUEL OILS

FIELD OF THE DISCLOSED TECHNIQUE

The disclosed technique generally relates to combustion chambers and burners for fuel combustion.

BACKGROUND OF THE DISCLOSED TECHNIQUE

Burners for fluid fuels include an igniter, a combustion chamber having a fuel inlet for spraying fluid fuel droplets into the combustion chamber and an air inlet through which air may be injected into the combustion chamber using a blower. The air and fluid fuel droplets provided into the combustion chamber create an air-fuel mixture that is ignitable by the igniter. Ignition of the air-fuel mixture and the continuous inflow of fluid fuel droplets results in a combustion process inside the combustion chamber. This combustion process generates hot gases, which exit the combustion chamber through a respective hot gas outlet. These hot gases can be used for heating. The amount of fluid fuel required to obtain a minimum temperature of the hot gases is related to the efficiency of the burner. Furthermore, the burner's efficiency impacts the quality of the output of hot gases in terms of the amount of pollutants and/or toxic gases leaving the hot gas outlet as a result of the combustion of the fluid fuel. More specifically, it is virtually impossible to ensure perfect (stoichiometric) combustion in practice, since it is extremely difficult to control and maintain a perfect relationship between the air and the fluid fuel in the combustion chamber. Accordingly, imperfect conditions prevail during the combustion process, resulting in the generation of gases and combustion byproducts that may adversely affect human health. In particular, during the combustion some of the oxygen molecules may combine with nitrogen molecules to form nitrogen oxides (NOx). In addition, if the ratio between the air and the fluid fuel being provided is below a certain amount, unburned fuel may be carried over to the combustion chamber's output and smoke may be produced.

In an attempt to address at least some of the aforementioned concerns, various types of fluid fuel burners have been proposed. U.S. Patent No. 4,1 13,425 to Von Linde et al., entitled "Burner for Fluid Fuels", discloses a combustion chamber in the shape of a double cone or frustrum having its largest diameter between its ends, a separation between the end of the double cone adjacent to the fuel supply means and the peripheral wall to form a prechamber comprising the fuel supply means and an ignition means, holes in the separation and in the wall of the double cone. The air supply passage is arranged in such a manner that its longitudinal axis includes an angle with a radial line passing through the center of the combustion chamber and the intersection between the longitudinal axis of the passage and the inner wall of the housing.

U.S. Patent No. 5,628,192 to Hayes-Bradley et al., entitled "Gas turbine engine combustion chamber", discloses a gas turbine engine combustion chamber which has primary, secondary and tertiary combustion zones in flow series having a secondary fuel and air mixing duct and a tertiary fuel and air mixing duct. The secondary mixing duct has a secondary air intake at its upstream end, and the tertiary mixing duct has a tertiary air intake at its upstream end. The tertiary air intake is arranged adjacent to the secondary air intake. A combined secondary and tertiary fuel system is provided to supply fuel to the secondary and tertiary mixing ducts. The fuel system comprises a manifold arranged adjacent to the secondary mixing duct but spaced from the tertiary mixing duct by the secondary mixing duct. The manifold has apertures to direct fuel towards the tertiary air intake across the secondary air intake. Variations in fuel pressure cause the fuel to flow into the secondary air intake or the tertiary air intake.

Japanese Patent Application No. 59001 91 7 to Ueshima et al., entitled "Burner for heating", discloses a burner that is provided with an outer tube having the rear end communicated to a blower, an inner tube, and an intermediate tube, and a secondary combustion part which is formed between the inner and the intermediate tubes. When ignition is performed by an igniting plug and with a blower actuated, primary air is fed through draft holes for the primary air, a primary combustion is conducted at the rear at the inside of an inner tube. A secondary air feed in the direction of the center of the inner tube through draft holes collides with the primary air to create turbulence. As a result, the adhesion of soot prevents a failure at an igniting plug from occurring, and the fuel oil and the air jetted through a jet nozzle are fed through the combustion holes into the intermediate tube for secondary combustion. Unburnt combustion oil is gasified as a result of the oil being heated by the secondary combustion.

GB Patent Application No. 2,035,538 to Robert Bosch GmbH, entitled "Oil atomisation burner", discloses a burner that comprises an oil- atom isation nozzle and a cup-shaped combustion chamber whose wall is provided with holes for the feeding of preheated combustion air. A tangential flow component of the air is introduced into a first, inner portion of the combustion chamber, where it forms a vortex which is constricted to form an axial potential vortex flow by a tangential flow component of the combustion air. The combustion air is introduced into a second portion of the combustion chamber, so that there ensues in this portion a rotary flow which is superimposed on the potential vortex flow, thereby resulting in complete combination of even the smallest quantities of fuel.

SUMMARY OF THE DISCLOSED TECHNIQUE

In accordance with one aspect of the disclosed technique, there is thus provided a combustion chamber for combustion of heavy fuel oil. The combustion chamber is enclosed by a wall extending longitudinally toward a gas outlet in a tapered manner, defining an elongated chamber having a longitudinal axis normal to the gas outlet. The chamber includes a pre-combustion region, a peak-combustion region, and a secondary-combustion region. The pre-combustion region is operative for mixing the fuel oil with air. The chamber further includes a plurality of apertures, for allowing air flow into the chamber. The apertures include an upstream group of confinement apertures, circumferentially disposed around the perimeter of the wall between the pre-combustion region and the peak-combustion region, and a downstream group of confinement apertures, circumferentially disposed around the perimeter of the wall between the peak-combustion region and the secondary-combustion region. The groups of confinement apertures allow pressurized air flow into the peak-combustion region, forming an air curtain barrier between the pre-combustion region and peak-combustion region and forming an air curtain barrier between the peak-combustion region and secondary-combustion region during the combustion of the air-fuel mixture, such that the air-fuel mixture is temporarily detained and confined within the peak-combustion region, prolonging the combustion within the peak-combustion region. The combustion chamber may further include a fuel atomizer nozzle for injecting a spray of fuel droplets into the pre-combustion region, a gas inlet for injecting ignition gas into the pre-combustion region, and an igniter for igniting the ignition gas to initiate combustion of an air-fuel mixture within the pre-combustion region. The plurality of apertures may further include a group of air mixture apertures, circumferentially disposed around the perimeter of the pre-combustion region upstream from the upstream group of confinement apertures. The air mixture apertures allow air flow into the pre-combustion region effecting the formation of an air-fuel mixture within the combustion chamber prior to the combustion process. The air mixture apertures may be arranged in at least two layers circumferentially disposed around the perimeter of the pre-combustion region, where the orthogonal axis of the air mixture apertures is directed to cause the intersection of air streams between apertures of different layers. The air mixture apertures may include three layers disposed on a convex portion of the wall, where the apertures of each layer extend orthogonally relative to the surface of the wall. The plurality of apertures may further include a group of secondary air feed apertures, circumferentially disposed around the perimeter of the secondary-combustion region downstream from the downstream group of confinement apertures. The secondary air feed apertures allow air flow into the secondary-combustion region, prior to the exiting of the generated gases from the chamber, allowing for the combustion of residual air-fuel mixture when delayed in the secondary-combustion region. The apertures of the upstream group of confinement apertures, the downstream group of confinement apertures, the group of air mixture apertures, or the group of secondary air feed apertures, may include: uniform apertures, round apertures, and/or apertures arranged equidistantly from one another. At least a portion of the wall enclosing the pre-combustion region may be convex immediately upstream of the upstream group of confinement apertures. An orthogonal axis of the apertures of the upstream group of confinement apertures or the downstream group of confinement apertures may be normal to the longitudinal axis. The combustion chamber may include a circular cross section profile perpendicular to the longitudinal axis, where the ratio between the diameter of the cross section located between the pre-combustion region and the peak-combustion region and the diameter of the cross section at the gas outlet, is substantially 3:2, or where the ratio between the diameter of the cross section located between the pre-combustion region and the peak-combustion region, and the length of the combustion chamber along the peak-combustion region and the secondary-combustion region is substantially 7:1 0. The pre- combustion region may include a dome-shaped cover. The combustion chamber may further include a shell enclosing at least a portion of the combustion chamber and defining an interspace therebetween, where air flows into the interspace via an air inlet of the shell, and continues into the combustion chamber via the plurality of apertures. The shell may include at least one exit aperture, for allowing air that entered the interspace to exit. The exit aperture may be located proximate to the gas outlet. The combustion chamber may resemble the shape of: a cylinder, a tube, a truncated cone, a frustum, a bifrustum, a truncated bipyramid and/or an urn. The combustion chamber may include a lateral cross-section of: a circle, an ellipse, and/or a polygon. The heavy fuel oil may be: diesel oil, kerosene, mazut, naphtha, asphalt, petroleum, bunker fuel, residual fuel oil, crude oil, synthetic crude oil, shale oil, heavy crude oil, extra heavy oil, any of the above mixed with light oil or fuel or liquid hydrocarbon and any combination of the above. The combustion chamber may be operative for the production of asphalt concrete, where the combustion efficiency of the combustion chamber is within the range of 2 to 3 liters of fuel oil per 1 ton of mineral aggregate. The combustion chamber may further include an air pump for enhancing air flow into the chamber. The combustion chamber may further include a turbofan, powered by the exhaust gases ejected from the combustion chamber, the turbofan operative for supplying mechanical energy to at least one component.

In accordance with another aspect of the disclosed technique, there is provided a method for combustion of heavy fuel oil. The method includes the procedures of providing the fuel oil in a combustion chamber, and mixing the fuel oil with air to produce a combustible air-fuel mixture applied into a pre-combustion region of the combustion chamber. The method further includes the procedures of forming an air curtain barrier between the pre-combustion region and a peak-combustion region of the combustion chamber, and forming an air curtain barrier between the peak-combustion region and a secondary-combustion region of the combustion chamber. The method further includes the procedure of initiating combustion of the air-fuel mixture, where the combustion is temporarily detained and confined within the peak-combustion region, prolonging the combustion within the peak-combustion region. The method may further include the procedures of allowing air flow into the secondary-combustion region to combust residual fuel therein.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosed technique will be understood and appreciated more fully from the following detailed description taken in conjunction with the drawings in which:

Figure 1 is a side view schematic illustration of a burner for fluid fuel combustion, constructed and operative in accordance with an embodiment of the disclosed technique;

Figure 2 is a perspective view schematic illustration of the burner of Figure 1 ;

Figure 3 is a cross-sectional side view schematic illustration of a section of the combustion chamber of Figure 1 showing the different groups of apertures;

Figure 4A is a side view schematic illustration of a burner with an air pump for displacing air into the combustion chamber, and a turbofan powered by the combustion chamber, constructed and operative in accordance with another embodiment of the disclosed technique;

Figure 4B is a side view schematic illustration of a burner with an air pump powered by a jet engine type turbofan, constructed and operative in accordance with a further embodiment of the disclosed technique;

Figure 5 is a cross-sectional view schematic illustration of the peak-combustion region of the combustion chamber of Figure 1 , constructed and operative in accordance with an embodiment of the disclosed technique; and Figure 6 is a flow chart for a method for combustion of heavy fuel oil, operative in accordance with an embodiment of the disclosed technique.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The disclosed technique overcomes the disadvantages of the prior art by providing a burner with a unique combustion chamber configured to efficiently convert chemical energy stored in the fluid fuel into thermal energy, which is provided as hot gases at the burner's output.

It should be noted that the usage of the indefinite articles "a" and "an" when introducing a feature should not be interpreted as there being only one of that feature. Accordingly, the indefinite articles "a" and "an" as used herein encompass the meaning of the phrase "at least one" of the same feature.

The terms "right", "left", "bottom", "below", "lowered", "low", "lower" "top", "above", "elevated", "upper" and "high" as well as grammatical variations thereof as used herein do not necessarily indicate that, for example, a "bottom" component is below a "top" component, or that a component that is "below" is indeed "below" another component or that a component that is "above" is indeed "above" another component as such directions, components or both may be flipped, rotated, moved in space, placed in a diagonal orientation or position, placed horizontally or vertically, or similarly modified. Accordingly, it will be appreciated that the terms "bottom", "below", "top" and "above" may be used herein for exemplary purposes only, to illustrate the relative positioning or placement of certain components, to indicate a first and a second component or to do both. Reference is now made to Figures 1 and 2. Figure 1 is a side view schematic illustration of a burner for fluid fuel combustion, generally referenced 1 00, constructed and operative in accordance with an embodiment of the disclosed technique. Figure 2 is a perspective view schematic illustration of the burner 1 00 of Figure 1 . Burner 1 00 includes a combustion chamber 1 1 0 formed by a wall 1 25 which extends longitudinally in a tapered manner toward a gas outlet 1 21 of combustion chamber 1 1 0. Wall 1 25 defines an elongated chamber having a longitudinal axis normal to the gas outlet 1 21 , a pre-combustion region 1 1 2, a peak-combustion region 1 1 4 and a secondary-combustion region 1 1 6. Pre-combustion region 1 1 2 includes an initiating mechanism operative for initiating a combustion process. The initiating mechanism includes a fuel atomizer nozzle 1 24 for injecting a spray of fuel droplets into combustion chamber 1 1 0, a gas inlet 1 22 for injecting ignition gas into combustion chamber 1 1 0, and an igniter 1 26 for igniting the ignition gas in order to initiate combustion of an air-fuel mixture within combustion chamber 1 1 0.

Preferably the fuel injected by fuel atomizer nozzle 1 24 is a heavy fuel oil, such as diesel oil, kerosene, mazut, naphtha, asphalt, petroleum, bunker fuel, residual fuel oil, crude oil, synthetic crude oil, shale oil, heavy crude oil, extra heavy oil, any of these heavy fuel oils mixed with light oil or fuel or liquid hydrocarbon, or any combination thereof. This list includes examples of heavy fuel oils, and should in no way be seen as a limitation. Heavy crude oil is defined by the American Petroleum Institute (API) as having an "API" gravity below 22.3 (920 to 1 000 kilograms per cubic meter) and extra heavy oil is defined with an API gravity below 1 0 API (greater than 1 000 kilograms per cubic meter). It should be noted for clarity the distinction between asphalt and asphalt concrete. Asphalt is a petroleum-derived pitch, also known as bitumen. Asphalt concrete is a composite material commonly used in construction projects and consists of asphalt (used as a binder) and mineral aggregate mixed together, then laid down in layers and compacted.

Combustion chamber 1 1 0 includes a plurality of apertures through which air flows inside. In particular, an upstream group of confinement apertures 1 38 are circumferentially disposed around the perimeter of wall 1 25 downstream of pre-combustion region 1 1 2 and upstream of peak-combustion region 1 1 4, and a downstream group of confinement apertures 1 40 are circumferentially disposed around the perimeter of wall 1 25 downstream of peak-combustion region 1 1 4 and upstream of secondary-combustion region 1 1 6. Furthermore, an optional group of air mixture apertures 1 36 are circumferentially disposed around the perimeter of pre-combustion region 1 1 2, upstream from confinement apertures 1 38. Air mixture apertures 1 36 are configured to allow air flow into pre-combustion region 1 1 2 in a manner which effects the formation of an air-fuel mixture within pre-combustion region 1 1 2 prior to the combustion process. For example, it is possible to achieve this effect by arranging multiple layers of air mixture apertures 1 36 such that there is an intersection of air streams between apertures of different layers.

Reference is now made to Figure 3, which is a cross-sectional side view schematic illustration of a section of combustion chamber of Figure 1 showing the different groups of apertures. Air mixture apertures 1 36A, 1 36B and 1 36C represent three layers of apertures 1 36 disposed on a convex portion of wall 1 25, where each layer is disposed along a respective perimeter of pre-combustion region 1 22 and where the apertures of each layer extends orthogonally relative to the surface of wall 1 25. As a result, when air is injected into pre-combustion region 1 1 2 through air-mixture apertures 1 36, intersecting streams of air are formed between apertures of the same layer and apertures of a different layer. Accordingly, a spray of fuel injected into pre-combustion region 1 1 2 via fuel atomizer nozzle 1 24 is mixed with air by the effect generated by apertures 1 36A, 1 36B and 1 36C. In contrast to air mixture apertures 1 36, the upstream group of confinement apertures 1 38 and downstream group of confinement apertures 1 40 are configured parallel to each other and in respect with base 1 20.

Combustion chamber 1 1 0 may further include a group of secondary air feed apertures 1 42 circumferentially disposed around the perimeter of secondary combustion region 1 1 6, downstream from the downstream group of confinement apertures 1 40. Secondary air feed apertures 1 42 are configured to allow air flow into secondary combustion region 1 1 6 prior to the exiting of generated gases out from combustion chamber 1 1 0, providing combustion of the residual air-fuel mixture in secondary combustion region 1 1 6. Secondary combustion region 1 1 6 may be elongated in a manner sufficient to ensure that the combustion of residual air-fuel mixture occurs substantially within the combustion chamber 1 1 0.

Downstream group of confinement apertures 1 40 and upstream group of confinement apertures 1 38 may be round apertures with a diameter of 1 2.5 millimetres (mm) with a tolerance of 5%. In The group of air mixture apertures 1 36 may be round apertures with a diameter of 4 mm with a tolerance of 5%. The group of secondary air feed apertures 1 42 may be round apertures with a diameter of 4 mm with a tolerance of 5%. In general, any of the groups of apertures 1 36, 1 38, 1 40, 1 42 may partially or fully include apertures of different shapes, sizes and/or patterns, such as: round apertures, uniform apertures, and apertures arranged equidistantly from one another.

It will be appreciated that the combustion chamber 1 1 0 of the disclosed technique may have a shape resembling, for example: a cylinder, a tube, a truncated cone, a frustum, a bifrustum, a truncated bipyramid or an urn. An urn shape may further include the shape of a sarcophagus or a traditional Russian nested doll known commonly as Matryoshka. Likewise, combustion chamber 1 1 0 may additionally include a lateral cross-section of a circle, ellipse or polygon, where the lateral cross-section is perpendicular to the longitudinal axis. Combustion chamber 110 may include a substantially circular cross section perpendicular to the longitudinal axis, where the ratio between the diameter of the aforementioned cross section, which is located between pre-combustion region 112 and peak-combustion region 114, and the diameter of a parallel cross-section at the gas outlet 121, is substantially 3:2 with a tolerance of 15%. Alternatively, combustion chamber 110 may include a substantially circular cross-section perpendicular to the longitudinal axis, where the ratio between the diameter of the aforementioned cross-section, which is located between pre-combustion region 112 and peak-combustion region 114, and the length of combustion chamber 110 along peak-combustion region 114 and secondary combustion region 116 is substantially 7:10 with a tolerance of 15%.

Combustion chamber 110 is at least partially enclosed by a shell 135 that includes a base 120 with at least one exit aperture 134. Wall 125 and shell 135 define together an interspace 180 in between, where air flows into the interspace 180 via an air inlet 115 of shell 135, and continues into combustion chamber 110 via the plurality of apertures (136, 138, 140, 142). Pre-combustion region 112 may include a dome-shaped cover 118, configured to accommodate fuel atomizer nozzle 124, gas inlet 122 and igniter 126. Dome-shaped cover 118 may be an aerodynamic structure which allows air to flow via air inlet 115 in a uniform manner around combustion chamber 110. Reference is now made to Figure 4A, which is a side view schematic illustration of a burner, generally referenced 1 70, with an air pump for displacing air into the combustion chamber, and a turbofan powered by the combustion chamber, constructed and operative in accordance with another embodiment of the disclosed technique. Burner 1 70 includes an air pump 1 44 which provides a continuous supply of air (or another combustible gas) into combustion chamber 1 1 0. Air 1 47 is displaced by pump 1 44 through piping 1 45 and then flows through air inlet 1 1 5 into the interspace 1 80 between outer wall 1 25 and shell 1 35, from where it continues into chamber 1 1 0 via the apertures (1 36, 1 38, 1 40, 1 42). Air pump 1 44 may be used in conjunction with other means for incoming air flow, thereby enhancing the overall supply of air into chamber 1 1 0. Air pump 1 44 may be powered by a turbofan (fanjet) 1 46, which itself may be powered by the energy generated by combustion chamber 1 1 0. Accordingly, the heated exhaust gases 1 49 ejected from outlet 1 21 is converted into mechanical energy by turbofan 1 46, at least part of which is then utilized to power air pump 1 44, in a continuous cycle. In this manner, the overall efficiency of burner 1 70 is increased. Alternatively, air pump 1 44 may be powered by electricity or other standard power sources. Turbofan 1 46 may also be used to power or provide mechanical energy to other components, instead of or addition to pump 1 44. Air pump 1 44 may include any suitable components configured for air displacement, including devices or mechanisms associated with various types of air compressors, as known in the art. Piping 1 45 may be embodied by any suitable passageway or means for conveying the displaced air into chamber 1 1 0. Similarly, turbofan 1 46 represents an exemplary type of reaction engine known in the art, for which other alternatives may also be employed. Turbofan 1 46 may resemble the structure of a jet engine turbofan used for powering various jet aircrafts. Reference is now made to Figure 4B, which is a side view schematic illustration of a burner, generally referenced 1 80, with an air pump powered by a jet engine type turbofan, constructed and operative in accordance with a further embodiment of the disclosed technique. The turbofan includes a fan 1 82 and a turbine 1 86, which are coupled to one another via a shaft 1 84. Hot gases ejected from gas outlet 1 21 may be used to propel turbine 1 86. Rotation of turbine 1 86 triggers the rotation of fan 1 82, which in turn results in the suction of air into combustion chamber 1 1 0.

Reference is now made to Figure 5, which is a cross-sectional view schematic illustration of the peak-combustion region 1 1 4 of the combustion chamber 1 1 0 of Figure 1 , constructed and operative in accordance with an embodiment of the disclosed technique. Upstream group of confinement apertures 1 38 allows air to flow into the peak-combustion region 1 1 4 at a sufficient intensity that results in the formation of an air curtain barrier, designated 1 50, between peak-combustion region 1 1 4 and pre-combustion region 1 1 2. Downstream group of confinement apertures 1 40 allows air to flow into the secondary-combustion region 1 16 at a sufficient intensity that results in the formation of an air curtain barrier, designated 152, between peak-combustion region 1 14 and secondary-combustion region 1 16. Consequently, the air-fuel mixture is temporarily detained and confined substantially within peak-combustion region 1 14. The hot gases in the central regions of combustion chamber 1 10 tend to drift at a velocity higher than the gases alongside the surrounding wall 125. The strong airflow that creates air curtains 150 and 152 begins to attenuate as air progresses towards the central longitudinal axis of combustion chamber 1 10. Accordingly, the general shape of air curtains 150 and 152 warps to form a funnel-like pattern, and the peak combustion 192 slightly drifts downstream toward secondary-combustion region 1 16, confined between air curtains 150 and 152. This confinement between air curtains 150 and 152 detains the combustion process within peak-combustion region 1 14 and ensures that peak combustion 192 is substantially thermally isolated from pre-combustion region 1 12 and secondary-combustion region 1 16. This configuration also prolongs the peak combustion 192, adding to the effective combustion, which is manifested by the high temperatures at the center of peak combustion 192, that can reach 1600°C and even 2000- 3000 °C in some cases.

Secondary combustion 194 occurs downstream of air curtain 152, and is prolonged and confined within combustion chamber 1 10, by the elongated secondary combustion region 1 16 of combustion chamber 1 1 0. Further prolonging of the secondary combustion may be effected by the air fed through the group of secondary air feed apertures 1 42 (as shown in Figures 1 and 2). Secondary air feed apertures 1 42 are densely spaced from one another to provide a detaining effect, which is generally weaker than the strong "curtain" effected by confinement apertures 1 38 and 1 40. Secondary air feed apertures 1 42 are also slightly distanced from downstream group of confinement apertures 1 40 to enhance the detaining effect. Secondary combustion 1 94 occurs at temperatures typically several hundred degrees centigrade lower than those at peak combustion 1 92. The confinement of secondary combustion 1 94 within secondary combustion region 1 1 6 ensures that substantially no further combustion continues beyond gas outlet 1 21 (i.e., no flame is present outside combustion chamber 1 1 0) such that only heated exhaust gases exit from combustion chamber 1 1 0. The high temperatures of peak combustion 1 92, and the completion of the secondary combustion 1 94, ensure that essentially no residual fuel particles remain unburned, adding to the efficiency of combustion chamber 1 1 0 and to the substantial elimination of pollutants from the ejected heated exhaust gases.

Reference is now made to Figure 6, which is a method for combustion of heavy fuel oil, operative in accordance with an embodiment of the disclosed technique. In procedure 202, fuel oil is provided in a combustion chamber. Referring to Figures 1 and 2, fuel atomizer nozzle 1 24 injects a spray of fuel droplets into pre-combustion region 1 1 2 of combustion chamber 1 1 0. In procedure 204, the fuel oil is mixed with air to produce a combustible air-fuel mixture applied into a pre-combustion region of the combustion chamber. Referring to Figures 1 and 2, air mixture apertures 1 36 allow air flow into pre-combustion region 1 1 2 in a manner which effects the formation of an air-fuel mixture within pre-combustion region 1 1 2 prior to the combustion process.

In procedure 206, an air curtain barrier is formed between the pre-combustion region and a peak-combustion region of the combustion chamber. Referring to Figures 1 and 5, upstream group of confinement apertures 1 38 allows air to flow into peak-combustion region 1 1 4 at an intensity that results in the formation of an air curtain barrier 1 50between peak-combustion region 1 1 4 and pre-combustion region 1 1 2.

In procedure 208, an air curtain barrier is formed between the peak-combustion region and a secondary-combustion region of the combustion chamber. Referring to Figures 1 and 5, downstream group of confinement apertures 1 40 allows air to flow into secondary-combustion region 1 1 6 at an intensity that results in the formation of an air curtain barrier 1 52 between peak-combustion region 1 1 4 and secondary-combustion region 1 1 6.

In procedure 21 0, combustion of the air-fuel mixture is initiated, where the combustion is temporarily detained and confined within the peak-combustion region, prolonging the combustion within the peak-combustion region. Referring to Figures 1 and 5, the air-fuel mixture undergoes peak combustion 1 92 within peak-combustion region 1 1 4, and subsequently undergoes secondary combustion 1 94 within secondary combustion region 1 1 6 The peak combustion 1 82 becomes confined between the funnel-like pattern formed by air curtains 1 50 and 1 52, which serves to detain the combustion process within peak combustion region 1 1 4 and ensures that peak combustion 1 82 is substantially thermally isolated from pre-combustion region 1 1 2 and secondary combustion region 1 1 6. The peak combustion 1 82 is thus prolonged, manifested by very high temperatures at the center of peak combustion 1 82.

A combustion chamber constructed and operative according to the disclosed technique has been successfully used in the manufacture of asphalt concrete, where bitumen is mixed under conditions of high heat, generated within a combustion chamber, with a mineral aggregate. In this field it is common to define a combustion efficiency of the combustion chamber by the liters of fuel required to bind 1 ton of mineral aggregate together with bitumen. Efficiencies known in the art are typically 6 to 7 liters of fuel per ton of mineral aggregate. In an experiment conducted with the combustion chamber of the disclosed technique, an efficiency of 2.5 liters of fuel per ton of mineral aggregate was achieved.

It will be appreciated by persons skilled in the art that the disclosed technique is not limited to what has been particularly shown and described hereinabove.

Claims

A combustion chamber for combustion of heavy fuel oil, the combustion chamber enclosed by a wall extending longitudinally toward a gas outlet in a tapered manner, defining an elongated chamber having a longitudinal axis normal to said gas outlet, said chamber comprising:

a pre-combustion region;

a peak-combustion region;

and a secondary-combustion region,

wherein said pre-combustion region is operative for mixing said fuel oil with air,

said chamber further comprising a plurality of apertures, operative for allowing air flow into said chamber, said apertures comprising:

an upstream group of confinement apertures, circumferentially disposed around the perimeter of said wall between said pre-combustion region and said peak-combustion region; and

a downstream group of confinement apertures, circumferentially disposed around the perimeter of said wall between said peak-combustion region and said secondary-combustion region,

wherein said groups of confinement apertures allow pressurized air flow into said combustion chamber, forming an air curtain barrier between said pre-combustion region and said peak-combustion region and forming an air curtain barrier between said peak-combustion region and said secondary-combustion region during the combustion of said air-fuel mixture, such that said air-fuel mixture is temporarily detained and confined within said peak-combustion region, prolonging said combustion within said peak-combustion region.

2. The combustion chamber of claim 1 , further comprising:

a fuel atomizer nozzle, operative for injecting a spray of fuel droplets into said pre-combustion region;

a gas inlet, operative for injecting ignition gas into said pre-combustion region; and

an igniter, operative for igniting said ignition gas to initiate combustion of an air-fuel mixture within said pre-combustion region.

3. The combustion chamber of claim 1 , wherein said plurality of apertures further comprises a group of air mixture apertures, circumferentially disposed around the perimeter of said pre-combustion region upstream from said upstream group of confinement apertures, said air mixture apertures allowing air flow into said pre-combustion region effecting the formation of an air-fuel mixture within said combustion chamber prior to the combustion process.

4. The combustion chamber of claim 3 wherein said air mixture apertures are arranged in at least two layers circumferentially disposed around the perimeter of said pre-combustion region, wherein the orthogonal axis of said air mixture apertures is directed to cause the intersection of air streams between apertures of different layers.

5. The combustion chamber of claim 4, wherein said air mixture apertures comprise three layers disposed on a convex portion of said wall, wherein the apertures of each layer extend orthogonally relative to the surface of the wall.

6. The combustion chamber of claim 1 , wherein said plurality of apertures further comprise a group of secondary air feed apertures, circumferentially disposed around the perimeter of said secondary-combustion region downstream from said downstream group of confinement apertures, said secondary air feed apertures allowing air flow into said secondary-combustion region, prior to the exiting of the generated gases from said chamber, allowing for the combustion of residual air-fuel mixture when delayed in said secondary-combustion region.

7. The combustion chamber of claim 3 or 6, wherein the apertures of at least one of: said upstream group of confinement apertures, said downstream group of confinement apertures, said group of air mixture apertures, or said group of secondary air feed apertures, comprise apertures selected from of the list consisting of:

uniform apertures;

round apertures; and

apertures arranged equidistantly from one another.

8. The combustion chamber of claim 1 , wherein at least a portion of said wall enclosing said pre-combustion region is convex immediately upstream of said upstream group of confinement apertures.

9. The combustion chamber of claim 1 , wherein an orthogonal axis of the apertures of at least one group of:

said upstream group of confinement apertures; and

said downstream group of confinement apertures,

is normal to said longitudinal axis.

1 0. The combustion chamber of claim 1 , comprising a circular cross section profile perpendicular to said longitudinal axis, wherein the ratio between the diameter of said cross section located between said pre-combustion region and said peak-combustion region and the diameter of said cross section at said gas outlet, is substantially 3:2. 1 . The combustion chamber of claim 1 , comprising a circular cross section profile perpendicular to said longitudinal axis, wherein the ratio between the diameter of said cross section located between said pre-combustion region and said peak-combustion region, and the length of said combustion chamber along said peak-combustion region and said secondary-combustion region is substantially 7:1 0. 2. The combustion chamber of claim 1 , wherein said pre-combustion region comprises a dome-shaped cover. 3. The combustion chamber of claim 1 , further comprising a shell enclosing at least a portion of said combustion chamber and defining an interspace therebetween, wherein air flows into said interspace via an air inlet of said shell, and continues into said combustion chamber via said plurality of apertures. 4. The combustion chamber of claim 1 3, wherein said shell comprises at least one exit aperture, for allowing air that entered said interspace to exit.

5. The combustion chamber of claim 1 4, wherein said at least one exit aperture is located proximate to said gas outlet. 6. The combustion chamber of claim 1 , wherein said combustion chamber resembles a shape selected from the list consisting of:

a cylinder;

a tube;

a truncated cone;

a frustum;

a bifrustum;

a truncated bipyramid; and

an urn. 7. The combustion chamber of claim 1 , wherein said combustion chamber comprises a lateral cross-section selected from the list consisting of:

a circle;

an ellipse; and

a polygon. 8. The combustion chamber of claim 1 , wherein said heavy fuel oil comprises at least one selected from the list consisting of:

diesel oil; kerosene;

mazut;

naphtha;

asphalt;

petroleum;

bunker fuel;

residual fuel oil;

crude oil;

synthetic crude oil;

shale oil;

heavy crude oil;

extra heavy oil;

any of the above mixed with light oil or fuel or liquid hydrocarbon; and

any combination of the above.

1 9. The combustion chamber of claim 1 , operative for the production of asphalt concrete, wherein the combustion efficiency of the combustion chamber is within the range of 2 to 3 liters of fuel oil per 1 ton of mineral aggregate.

20. The combustion chamber of claim 1 , further comprising an air pump, operative for enhancing air flow into said chamber.

21 . The combustion chamber of claim 1 , further comprising a turbofan, powered by the exhaust gases ejected from said combustion chamber, said turbofan operative for supplying mechanical energy to at least one component.

22. A method for combustion of heavy fuel oil, said method comprising the procedures of:

providing said fuel oil in a combustion chamber;

mixing said fuel oil with air to produce a combustible air-fuel mixture applied into a pre-combustion region of said combustion chamber;

forming an air curtain barrier between said pre-combustion region of said combustion chamber and a peak-combustion region of said combustion chamber;

forming an air curtain barrier between said peak-combustion region of said combustion chamber and a secondary-combustion region of said combustion chamber; and

initiating combustion of said air-fuel mixture, wherein the combustion is temporarily detained and confined within said peak-combustion region, prolonging said combustion within said peak-combustion region.

23. The method of claim 22, further comprising the procedure of allowing air flow into said secondary-combustion region to combust residual fuel therein.