OIL PREMIX BURNER

Abstract

An oil premix burner, having a burning element, a burner surface on the outer lateral surface, a distribution chamber below the burner surface, a central oil injection device, a combustion air duct connected to a fan situated upstream, and an air heat exchanger for preheating the combustion air in the area of the burner surface. The combustion quality and the robustness are optimized in an oil premix burner, in particular with respect to the modulation capability. It is provided that the air heat exchanger is composed of at least one double tube element including an inner tube, having inline throughflow, and an outer tube concentric to the inner tube. The air heat exchanger is situated above the burner surface and is composed of multiple parallel throughflow double tube elements symmetrically distributed over the circumference and which extend axis-parallel to the burning element at least over a portion of its length.

Description

THE FIELD OF THE INVENTION

The present invention relates to an oil premix burner.

BACKGROUND INFORMATION

These types of oil premix burners have a cylindrical burning element with a burner surface on the outer lateral surface. Generally, there is a central oil injection device around a distribution chamber for the generated oil mist so that this reaches the burner surface evenly from inside. Combustion air reaches the distribution chamber via at least one inlet opening in the area of the oil injection device which may be an injector or an oil nozzle, which is fastened to a nozzle fitting having an oil preheater. Upstream from the oil injection device is a combustion air duct having a connection to a fan.

The so-called premix burners have been accepted in particular for gas burners which are operated in a modulated manner, thus, in which the capacity range maybe controlled between a small portion of the maximum capacity and the maximum capacity. In these burners, the fuel and the combustion air required for its combustion are locally separated from the flame, mixed and then burned. For this purpose a cylindrical burning element is usually used as a flame holder which is permeable to the fuel/air mixture and which surrounds an inner space to which the fuel/air mixture is supplied. Using this technology, it is possible to implement small flames having good exhaust gas values, relatively small flame holders and large modulation ranges.

The basic principle of an oil premix burner is the mixing of finely atomized oil with preheated air. By using this principle it is possible that, for example, a so-called cold flame is formed so that the fuel maybe burned over a surface. However, surface burning is also possible without a cold flame. In general, the heating of air is relatively difficult due to the low heat capacity, because either an effective heat transfer via a wall to the air flow and/or high wall temperatures are necessary for this purpose.

For example, an oil premix burner is discussed in DE 10 2006 000 174 A1. Here, use is made of the fact that hot air vaporizes the oil and thus a gas mixture may be formed, which, as in the case of a gas premix burner, passes through the flame holder and burns away. By admixing exhaust gas to combustion air for air preheating, the formation of nitrogen oxides is additionally reduced and in this way the starting behavior should also be improved because the operating point is reached relatively quickly. For heat absorption, the combustion air is guided through a guiding system, which projects at least in sections over a burner surface, and is distanced from the burner flame and is accelerated in a nozzle in the guiding system so that the exhaust gas may be drawn from the combustion chamber and mixed with the air.

German patent document DE 26 43 293 A1 also discusses that such a duct for the combustion air which is situated as a cylinder around the rear area of a burning rod or burning element. Since a certain minimum burning element diameter is necessary for the mixing and the combustion reaction, this configuration may result in a relatively large combustion chamber in contrast to known configurations.

Furthermore, a system is discussed in DE 21 07 514 A for heating using infrared radiation, and from U.S. Pat. No. 1,082,576 A an oil burner is discussed having closed, continuous ducts situated flat below the burner surface for preheating the air. From these uninterrupted ducts, in both cases the preheated air is guided back to the center with the fuel supply and there mixed with fuel. From this center the mixture enters the combustion zone without again coming into the vicinity of the air flow path used for preheating.

SUMMARY OF THE INVENTION

An object of the exemplary embodiments and/or exemplary methods of the present invention is thus to optimize the combustion quality and robustness in an oil premix burner in particular in view of the modulation capability.

According to the exemplary embodiments and/or exemplary methods of the present invention, this is achieved with the features described herein. Further refinements may be derived from the further description herein.

The oil premix burner is characterized in that the air heat exchanger is composed of at least one double tube element including an inner tube having an inline throughflow and an outer tube concentric thereto. In this case, the air heat exchanger is situated above the burner surface and is composed of multiple parallel throughflow double tube elements symmetrically distributed over the circumference and extending axis-parallel to the burning element at least over a portion of its length.

Each double tube element has on the front side of the free end a deflection zone as a connection between the inner tube and an annular space formed between the inner tube and the outer tube.

Thus, each double tube element is advantageously connected at its entry end of the inner tube to the combustion air duct.

There the combustion air enters and, after leaving the inner tube, arrives in a deflection zone at the front side of the free end in the annular space formed between the inner tube and the outer tube. Here, the already preheated air flows back in the direction of the oil injection device near the front side and picks up additional heat. There it enters the distribution chamber in the area around the oil injection device as preheated combustion air.

In one specific embodiment, in a double tube element, the inner tube projects beyond the outer tube in the longitudinal direction at the end near the oil injection device, so that it passes through the outlet area of the annular gap (space) which is connected to the distribution chamber and reaches through a boundary wall up into the combustion air duct.

In one further specific embodiment, the inner tube and/or the outer tube has/have turbulence-generating surfaces, a profiling and/or surface-enlarging elements in order to improve the heat transfer and in particular to break up the flow near the walls. For this purpose, the inner tube and/or the outer tube is/are provided with profiles and/or beads for turbulence-generation, which may run spirally on the tube surface. It is particularly advantageous when at least the inner tube is provided on its outer side with means for influencing the flow in the surrounding annular gap (space).

The diameters of the inner tube and the outer tube may be dimensioned in such a way that the free cross section in the course of the flow path of the combustion air remains at least the same or increases. In this way an adaptation of the volume which increases with the air temperature is achieved. On the other hand, the flow velocity and thus the heat absorption capability and also the thermal load of the outer surface are influenceable in a targeted manner in the respective duct areas via the cross-section formation.

In one further specific embodiment, the inner tube may also be provided with multiple openings in its housing. These permit a direct flow into the surrounding annular gap (space), create local turbulences and cooling effects and, in cross section, may each be ten times smaller than the internal diameter of the inner tube.

In addition, the exemplary embodiments and/or exemplary methods of the present invention provide that the inner tube and the outer tube are mutually supported at least at selected points. This takes place in particular in the deflection zone at the front side of the free end and/or via fittings and/or a special configuration of the tube wall, in that the deflection zone, for example, is provided with web-like projections, bumps, small chamfers in the end area or local impressions.

Using the measures according to the exemplary embodiments and/or exemplary methods of the present invention, both the combustion quality and the robustness are improved for oil premix burners. The system according to the present invention having the integrated air heat exchanger is advantageous in particular for modulated operation. This applies to burners having a cylindrical burning element as well as to surface burners having a horizontal burner surface and the configuration according to the present invention. The flame burns on or in the burner surface so that above it energy is extracted from the flame and used for preheating the combustion air. In this way electrical preheating is dispensed with during the stationary burner operating state. This has a positive effect on the energy balance of the burner.

An important advantage of the integrated air preheating function according to the present invention is that with increasing burner surface, for example in the case of a burning element for larger capacity ranges, the heat exchanger surface is expandable to the same extent in that simply longer double tube elements are used. In this way the sought air temperature remains constant. Each tube is defined according to its specific capacity density and the number of tubes as a function of the overall capacity. Except at the double tube elements of the air heat exchanger, no structural modifications are necessary at the periphery or other burner components for demonstrating different burner performances. The other burner configuration thus remains just the same as are the demands on the surrounding combustion chamber.

Using the air heat exchanger according to the present invention, combustion air should be provided at all burner operating points having a minimum temperature of approximately 350° C. Here it must be noted that under observance of the maximum permissible surface temperature at the air heat exchanger, the length of tube elements of an available configuration, i.e., in the form of smooth, U-shaped heat exchanger coils, as well as the number of the tubes cannot be increased arbitrarily. In addition to the limits in the observance of the maximum bending radius, the material temperatures also continue to rise when longer conventional tubes are used, entailing the risk of deflection.

In contrast, according to the exemplary embodiments and/or exemplary methods of the present invention, a longitudinal expansion due to thermal loading is possible since each double tube element of the air heat exchanger is only fixed at one end. Longer lengths correspondingly adapted to a burning element or cantilevers of double tube elements may be implemented via mutual support of the inner tube and the outer tube.

The use of profiled tubes which favor the heat transfer and which ensure a low material-preserving surface temperature becomes possible only with the aid of the present invention.

In particular the inner tube may act as turbulence exciter or a flow breaker. In general, by using the double tube element according to the exemplary embodiments and/or exemplary methods of the present invention, a higher packing density on a pitch circle in the area of the burner surface may be achieved in contrast to the related art. In addition, these double tube elements have advantages with regard to pressure loss and scalability. In principle, according to the exemplary embodiments and/or exemplary methods of the present invention, a counter-flow heat exchanger is implemented by using a double tube element since the air flow in the two ducts moves in opposite directions.

The drawing shows an exemplary embodiment of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an oil premix burner in longitudinal section.

FIG. 2 shows a longitudinal section through a part of the air heat exchanger.

DETAILED DESCRIPTION

The oil premix burner is composed essentially of a cylindrical burning element 1 having a burner surface 2 on the outer lateral surface, a distribution chamber 3 below burner surface 2, a central oil injection device 4 and a combustion air duct 5 connected to a fan situated upstream.

For preheating the combustion air in the area above burner surface 2, burning element 1 has an air heat exchanger composed of multiple parallel throughflow double tube elements 6 symmetrically distributed over the circumference and including an inner tube 7, having an inline throughflow, and an outer tube 8 concentric thereto.

Each double tube element 6 is closed at the front side of the free end with a cap 9 so that a flow-advantageous deflection zone 10 is a connection between inner tube 7 and an annular space 11 formed between it and outer tube 8. From combustion air duct 5, combustion air enters inner tube 7 of each double tube element 6 and flows via deflection zone 10 into annular space 11. Herein it flows back in the direction of oil injection device 4 and enters distribution chamber 3.

Both inner and outer tubes 7 and 8 have turbulence generating surfaces and are equipped with a profiling 12 shown as spirally running beads on the tube surfaces.

Claims

1-11. (canceled)

12. An oil premix burner, comprising:

a burning element, a burner surface on the outer lateral surface, a distribution chamber below the burner surface;

a central oil injection device;

a combustion air duct connected to a fan situated upstream; and

an air heat exchanger for preheating the combustion air in the area of the burner surface, wherein the air heat exchanger includes at least one double tube element including an inner tube, having an inline throughflow, and an outer tube concentric thereto.

13. The oil premix burner of claim 11, wherein the air heat exchanger is situated above the burner surface and includes multiple parallel throughflow double tube elements symmetrically distributed over the circumference and extending axis-parallel to the burning element at least over a portion of its length.

14. The oil premix burner of claim 11, wherein each double tube element has a deflection zone on the front side of the free end as a connection between the inner tube and an annular space formed between the inner tube and the outer tube.

15. The oil premix burner of claim 11, wherein each double tube element is connected with the entry side of the inner tube to the combustion air duct, wherein the combustion air, after leaving the inner tube, arrives in a deflection zone on the front side of the free end and flows into the annular space formed between the inner tube and the outer tube and flows back in the direction of the front side near the oil injection device and there enters the distribution chamber in the area around the oil injection device as preheated combustion air.

16. The oil premix burner of claim 11, wherein in a double tube element, the inner tube projects at the end near the oil injection device beyond the outer tube in the longitudinal direction so that it passes through the outlet area of the annular space connected to the distribution chamber and reaches through a boundary wall up into the combustion air duct.

17. The oil premix burner of claim 11, wherein the inner tube and/or the outer tube has/have turbulence generating surfaces, a profiling and/or surface enlarging elements.

18. The oil premix burner of claim 11, wherein the inner tube and/or the outer tube are provided with profilings and/or beads for turbulence generation, which run spirally on the tube surface.

19. The oil premix burner of claim 11, wherein at least the inner tube on its outer side has an arrangement for influencing the flow in the surrounding annular space.

20. The oil premix burner of claim 11, wherein the diameters of the inner tube and the outer tube are dimensioned so that the free cross section in the course of the flow path of the combustion air remains at least the same or increases.

21. The oil premix burner of claim 11, wherein the inner tube has multiple openings in its housing which permit a direct flow into the surrounding annular space and generate local turbulences and cooling effects in the annular space and, in cross section, are at least ten times smaller than the internal diameter of the inner tube.

22. The oil premix burner of claim 11, wherein the inner tube and the outer tube are mutually supported at least at selected points, this taking place in particular in the deflection zone on the front side of the free end and/or via fittings and/or a special design of the tube wall.