Heating Burner

Abstract

The invention relates to a heating burner, in particular a heating burner for the combustion of long chain liquid fuel. The heating burner according to the invention comprises a control device which controls its actuators, namely an ignition device for igniting the fuel, an air delivery device for delivering combustion air and a fuel delivery device for delivering fuel to the ignition device, in such a way that the fuel is ignited at periodically recurring ignition intervals and burns for an adjustable combustion interval, wherein the heating capacity can be regulated at the interval concerned for the duration of the combustion interval by the control device.

Description

The present invention relates to a heating burner for a heating system.

Heating burners are used in a wide variety of applications. They are used for heating buildings, areas and liquids, either for day-to-day use or, for instance, for a swimming pool. Even if the requirements arising in the various fields of application do, in part, differ quite widely, one requirement on the burner is common to all applications. The problem is to achieve a specific required temperature in the system to be heated at any time, whereby the temperature can vary widely over time, but with the reaction time of the heating burner being short. A factor which makes this more difficult is that the system often reacts slowly to heating by the burner.

In order to meet this requirement, the majority of heating burners have an input that specifies the desired setpoint temperature, and at least one sensor that determines the actual temperature in the system. Internal control methods attempt to regulate the heating burner, or rather its combustion flame, so that the actual temperature corresponds as closely as possible to the setpoint temperature. It must be noted in respect of this control method that the reaction time of the full heating system is relatively slow, the requirements on the setpoint vary constantly and that efficient and maintenance-free heating is required. A high efficiency of the heating burner, and combustion producing little exhaust gas and no soot from the fuel used, is also a precondition for commercially available heating burners.

Essentially, two methods for the control of heating burners are distinguished; these may be used either individually or in combination:

• the intermittent method
• the modulating method

In intermittent control, a range is determined around the desired setpoint temperature. The heating burner knows only two states during combustion. In the burning state, fuel is burnt under no control, and thermal energy is produced. In the switched off state, no fuel is burnt, no additional thermal energy is passed to the heating system. If the actual value falls below the lower bound of the range for the setpoint value, the heating burner is ignited and burns until the actual value exceeds the upper bound of the range. The burner is then switched off and remains in this state until the actual value determines that ignition is necessary again. An actual value temperature graph, as is normally found for a heating burner with intermittent control, can be found in FIG. 4a. The intermittent control method has the disadvantage that the interval duration is chosen relatively generously in order to ensure combustion that is low in pollutants and fully exploits the calorific value of the fuel and hysteresis additionally arises as a result of what may be a long reaction time. The consequence of this is high over-control and under-control which impairs the quality and efficiency of the system. On the one hand it is only seldom that precisely that amount of thermal energy is supplied that is really desired, and on the other hand, the significant over-control of the actual performance increases the thermal loss in the piping and leads to wear (e.g. calcification).

The modulating method regulates the calorific output analogously to the actual value of the temperature in the system. For example, the fuel supply can be regulated within the framework of a control range. As the control range is, however, finite, it is necessary to change over to the intermittent control method if the value exceeds or falls short of the control range. The disadvantages described for this method apply in the same way, if not more so.

With this method it is also difficult to regulate the controlled variables (such as air supply and fuel supply) so that efficient, low pollutant combustion is given over the entire control range.

Proceeding from this prior art, the problem to be solved by the present invention is to provide a heating burner that will produce a desired calorific output in an efficient and low polluting fashion.

The problem is solved according to the invention by a heating burner according to the features of claim 1.

The problem is solved according to the invention by a heating burner for a heating system with a control device having at least one primary sensor for determining the calorific output from the heating burner and having actuators which comprise an ignition device for igniting fuel, an air delivery device for delivering combustion air and a fuel delivery device for delivering fuel to the ignition device, wherein the volume delivered by the fuel delivery device is essentially freely variable and the control device adjusts the actuators such that the fuel is ignited in periodically recurring ignition intervals and is burnt for a variable combustion interval wherein the calorific output is controllable by the control device by means of the duration of the combustion interval within each ignition interval.

The central idea behind the invention is, thus, that the control device ignites the fuel at regular intervals and allows a flame to burn at a predefined output. The calorific output produced by the heating burner is regulated solely by the duration of combustion, i.e. by the variable combustion interval. The control device essentially needs only distinguish between three phases within a combustion interval, an initialisation phase in which the combustion output is increased up to a predefined value, a constant combustion phase in which the combustion output is held at a constant value, and a stop phase in which the combustion output is reduced back down to practically zero.

The control device can thus be designed such that it operates the actuators so effectively for these three phases that efficient combustion of the fuel is guaranteed. The actuators in the control device are particularly concerned with the regulation of the fuel/air ratio and thus, according to the invention, at least the volume delivered by the fuel delivery device is freely adjustable. The thermal losses in the heating system overall, and in particular in the pipes, are less as a result of the precise regulation of the calorific output.

The ignition intervals are preferably less than or equal to 60 seconds. This ensures rapid reaction of the heating burner and the actual output of the heating burner adapts itself perfectly to the desired output. Overshoot and undershoot by the calorific output can be avoided.

Preferably the fuel is a liquid fuel, more particularly rapeseed oil or other natural oils.

It is advantageous if the actuators comprise a motor that sets a truncated cone in rotation around its own longitudinal access so that fuel introduced into the truncated cone via an inlet exits via an exit opening and is atomized by the centrifugal force. The truncated cone is thus a cylindrically formed tube through which fuel is introduced at the inlet opening where the tube has the lesser diameter; said fuel being driven towards the exit opening by the rotation. If the truncated cone is driven rapidly enough, the fuel exiting through the exit opening will be atomized because of the centrifugal forces acting on it. The molecule chains in long chain liquid fuels will be cracked.

The ignition device preferably comprises a heat recovery feature fabricated from a thermally conducting material and giving off heat arising on the combustion of the fuel to the fuel flowing in behind. The heat recovery feature may, for instance, be a rod, a pipe with internally mounted, motorized impeller or another design suited to leading off a part of the heat generated when the fuel is burnt. The heat is diverted to a fuel supply line. In this way, the incoming fuel can be heated to just below the ignition temperature without the need to provide additional preheating.

Alternatively, it is also conceivable that the incoming fuel is preheated to a temperature above the relevant ignition temperature so that the fuel ignites immediately air is supplied.

This heat recovery feature is preferably arranged at least in part inside the hollow cylinder described above and projecting from the outlet opening. Thus the heat occurring at the outlet opening of the truncated cone is transported away towards the inlet opening of the truncated cone. As there is a lack of oxygen inside the truncated cone, the fuel can be preheated to temperatures above the ignition point. Ignition only occurs when the fuel exits from the truncated cone through the outlet opening.

The ignition device preferably comprises preheating that heats the fuel to ignition temperature, in particular in order to ignite the fuel in the initialization interval or the initialization phase. As there is not sufficient combustion output outside the combustion interval to preheat the incoming fuel adequately in the initialization interval, it is helpful to provide an external preheating device. Preheating may be provided by resistance or inductance. The decisive factor is that the preheating is controllable from the control device and is regulated in accordance with the phases.

The preheating device preferably comprises a heating coil enclosing the truncated cone. In this way, the fuel is heated indirectly via the truncated cone.

The control device is preferably designed such that it controls the fuel delivery device and the air delivery device in such a way that an essentially constant air/fuel ratio is present at the ignition device during the combustion interval, preferably in an initialization interval or initialization phase and a stop interval or stop phase. The air/fuel ratio may be selected such that the combustion of the fuel is guaranteed to be as efficient as possible and more particularly soot-free. Because it uses this type of intelligent control device the heating burner need only rarely be serviced, yet despite frequent re-ignition guarantees efficient utilization of the fuel.

It is advantageous if the heating burner comprises an air flow sensor for determining the delivery rate from the air delivery device. This means that the control device is not only able to control the air needed for igniting and burning the fuel according to a preset mode, but can also regulate it as demanded. In addition to air flow sensors, various temperature sensors may be provided both for fuel and for air, and also flow sensors for the fuel delivery rate.

The control device preferably sets the actuators, more particularly the fuel pump or fuel delivery device and the air delivery device, in such a way that a pilot flame is present outside the combustion interval. Re-ignition of the fuel is thus not necessary and there is no need to provide a device sufficiently powerful to achieve this. Furthermore, because the pilot flame is present, it is possible to avoid explosive ignition of the fuel in the initialization phase. The pilot flame may also be used to provide heat for preheating the fuel and thus securing efficient combustion of the fuel beyond the ignition interval.

The control device is preferably designed such that it controls the fuel pump outside the combustion interval to supply the pilot flame so that less than one percent, preferably less than one pro mille, of the fuel pump's maximum delivery rate is delivered.

Preferred embodiments of the invention are described by the dependent claims.

Preferred embodiments of the invention are described below using the drawings. Where

FIG. 1a shows a block diagram of a control device for a heating burner according to the invention with the associated actuators and sensors;

FIG. 1b shows individual sensors on the control device from FIG. 1a;

FIG. 2 shows the functional arrangement of the individual components of a heating burner according to the invention;

FIG. 3 shows the structure of a heating burner according to the invention;

FIG. 4a is a time/temperature graph of a heating burner with intermittent control;

FIG. 4b is a time/temperature graph of a heating burner according to the invention;

FIG. 5a shows the combustion output of a heating burner according to the invention over several ignition intervals;

FIG. 5b shows the combustion output of a heating burner according to the invention over a first ignition interval; and

FIG. 5c shows the combustion output of a heating burner according to the invention over a second ignition interval.

The same reference numbers will be used for identical and identically acting parts in the description below.

A heating burner according to the invention can comprise the components illustrated in FIG. 1a. The central unit in the heating burner is the control device 10. This is connected with a plurality of actuators; in the present example these are an ignition device 50, an atomizer 70, an air delivery device 80, a fuel delivery device 20, a cracker device 30 and preheating 40. The control device 10 for the heating burner regulates or controls the actuators so as to guarantee that the fuel is efficiently burnt, ignited and regulated back or extinguished. In this case, efficiently means that the calorific value of the fuel is utilized as fully as possible, while ensuring a low polluting and soot free combustion, so that servicing of the heating burner according to the invention is rarely necessary. The control device 10 receives signals from a plurality of sensors 60 for controlling the actuators. These sensors 60 comprise at least one primary sensor by means of which the control device can determine the actual temperature of the system to be heated.

In the present heating burner this primary sensor is a hot water temperature sensor 65 that determines the temperature of a heating circuit heated by the burner. The control device is designed so that it can determine the difference between the actual temperature and a setpoint temperature and regulates the actuators so that this difference at any point in time is as small as possible.

Since the heating burner according to the invention has a very low number of states, that is to say ignition of fuel, combustion of fuel, extinguishing of the combustion flame or reduction of the combustion flame and operation without a combustion flame or with reduced combustion flame, preconfiguration of the control device 10 is conceivable. This preconfiguration determines optimum parameters for controlling the actuators for each of the states referred to. In the embodiment illustrated in FIGS. 1a and 1b the sensors 60 additionally comprise an air temperature sensor 61, an air flow sensor 62, a fuel temperature sensor 63 and a fuel flow sensor 64. The fuel flow sensor 64 and the air flow sensor 62 supply signals to the control device 10 which allow it to draw conclusions regarding the performance of the fuel delivery device 20 and the air delivery device 80. The air temperature sensor 61 and the fuel temperature sensor 63 help the control device 10 to regulate preheating 40 so that optimum combustion of the fuel is achieved. A combustion chamber according to the invention 1 comprises two supply lines as illustrated diagrammatically in FIG. 2. One, a fuel line 21, supplies fuel to the combustion chamber 1, the other, an air supply line 81, ensures a supply of the oxygen or the oxidization agent necessary for combustion. In the present embodiment, the fuel to be burnt is rapeseed oil. The fuel is stored in a fuel tank 24 and delivered through the fuel line 21 to the combustion chamber 1 by means of a fuel delivery device 20. The unprocessed oil here passes through preheating 40, which heats the fuel to make ignition easier, and a cracker device 30 which processes the fuel. A further functional unit, an atomizer 70, is provided directly on the combustion chamber 1 and mixes the fuel with the air supplied through the air line 81. An ignition device 50 ignites the air/fuel mixture in the combustion chamber 1.

It is possible to dispense with the separate ignition device 50 inside the combustion chamber 1 if preheating 40 heats the fuel above its specific ignition temperature. When the fuel is mixed with the air it will ignite spontaneously. The preheating device 40 thus assumes the functionality of the ignition device 50.

FIG. 3 shows the structure of the embodiment of the heating burner according to the invention illustrated diagrammatically in FIG. 2. The air line 81 is a generously proportioned pipe. At a point in the air line 81, the fuel line 21 passes through the external wall of the air line 81 and carries on inside the latter. The fuel line 21 and the air line 81 remain separate from one another.

A first opening in the fuel line 21 opens out in the fuel tank 24 from which the fuel is conveyed to a second opening in the fuel line 21. This second opening makes an air tight connection inside the air line 81 with an inlet opening 35 in a truncated cone 32. The truncated cone is driven by a motor 37, not illustrated, in such a way that the fuel entering through the inlet opening 35 is conveyed by the centrifugal force inside the hollow truncated cone 32 towards an outlet opening 36 on the opposite side to the inlet opening 35 but having a larger diameter because of the shape of the truncated cone 32. The centrifugal force applied by the motor 37 causes the unprocessed oil introduced into the truncated cone 32 to be both mechanically cracked on a trailing edge along the outlet opening 36 and mixed with the air surrounding the truncated cone 32 that has been introduced through the air line 81. The motor 37 and the truncated cone 32 thus make up the functional units of the atomizer 70 and the cracker device 30 illustrated in FIG. 1a. The truncated cone 32 is loosely enclosed by a heating coil 44. This heats both the air surrounding the truncated cone and also the truncated cone 32 itself. As the truncated cone 32 is manufactured from a thermally conducting material, the thermal energy from the heating coil 44 is passed to the fuel inside the truncated cone 32. The heating coil 44 hence has a dual functionality and preheats both the fuel and the air.

The preheated fuel ignites as soon as it is mixed with the air. The heat output generated here is not solely given off as the calorific output of the heating burner, but a small portion of the heat is passed to the following fuel flowing into the truncated cone 32 by way of a heat recovery feature 42 which extends into the interior of the truncated cone in the form of a metal rod.

A fuel delivery device 20 and an air delivery device 80 (cf. FIG. 1a) are not illustrated in FIG. 3 but may be provided in the fuel line 21 or the air line 81 respectively with no problems.

As illustrated in FIG. 1a, the actuators are connected with the control device 10 and, according to the invention, control the heating burner so that this increases the combustion flame at constant pre-set, ignition intervals t_Z to a pre-adjusted combustion output L and maintains this for the duration of combustion interval t_B (cf. FIG. 5a). The duration of the combustion interval t_B is determined by the control device 10 as a function of the calorific output to be provided by the heating burner. FIG. 5a shows a time/combustion output graph. It illustrates three ignition intervals t_Z. In the embodiment selected, an ignition interval has a duration of 100 seconds. The control device thus increases the combustion output L to a pre-set level every 100 seconds and maintains this higher combustion output L for the adjustable combustion interval t_B. The control device 10 (cf. FIG. 1a) is designed such that it determines the duration of the combustion interval t_B for the optimum heating performance required at the relevant time. In the graph in FIG. 5a the control device 10 determines that approximately 20% of the maximum calorific output is required in a first ignition interval t_Z. Accordingly, it increases the combustion output L to the pre-set level at time t=0 and maintains this level for approximately 20 seconds. For the remaining 80 seconds of the first ignition interval t_Z, the actuators are regulated by the control device 10 so that the combustion output L is practically zero. At time t=100 the control device 10 determines that approximately 60% of the maximum output is required for an optimum calorific output in a second ignition interval t_Z. Accordingly, the combustion interval t_B in this second ignition interval t_Z is approximately 60 seconds long. The same is true for a third ignition interval t_Z beginning at time t=200.

FIG. 5b shows a time/combustion output graph for the first time interval t_Z from FIG. 5a, the duration of the combustion interval t_B being 20 seconds, as already mentioned. The start and stop phases, i.e. the period in which the control device 10 increases the combustion output L to the preset high level or decreases it from this level respectively are known as the initialization interval t_I or the stop interval t_S. A constant fuel/oxygen ratio in these phases is particularly decisive for efficient and low pollution combustion in the heating burner according to the invention. The control device 10 regulates the actuators accordingly.

A detailed view of the second ignition interval t_Z from FIG. 5a may be found in the time/combustion output graph in FIG. 5c. An improved actual value setting, as is illustrated in FIG. 4b, may be achieved through this precise control of the heating output. In this graph, the abscissa plots the time, and the ordinate plots the actual temperature.

List of Reference Numbers

1 Combustion chamber

10 Control device

20 Fuel delivery device

21 Fuel line

24 Fuel tank

30 Cracker device

32 Truncated cone

35 Inlet opening

36 Outlet opening

37 Motor

40 Preheating

42 Heat recovery

44 Heating coil

50 Ignition device

60 Sensors

61 Air temperature sensor

62 Air flow sensor

63 Fuel temperature sensor

64 Fuel flow sensor

65 Hot water temperature sensor

70 Atomizer

80 Air delivery device

81 Air line

t_B Combustion interval

t_Z Ignition interval

t_I Initialization interval

t_S Stop interval

L Combustion output

Claims

1. Heating burner for a heating system

having a control device,

having at least one primary sensor for detecting the calorific output of the heating burner and

having actuators comprising an ignition device for igniting fuel, an air delivery device for delivering combustion air and a fuel delivery device for conveying fuel to the ignition device,

wherein the delivery volume from the fuel delivery device and/or air delivery device is essentially freely adjustable and the control device adjusts the actuators in such a way that the fuel is ignited in periodically recurring ignition intervals (tZ) and burns for an adjustable combustion interval (tB), wherein the calorific output may be regulated by the control device by way of the duration of the combustion interval (tB) in the ignition interval (tZ) concerned.

2. Heating burner in accordance with claim 1

characterized in that

the ignition intervals (tZ) are less than or equal to 60 seconds.

3. Heating burner in accordance with one of the preceding claim 1

characterized in that

the fuel is a liquid fuel, more particularly rapeseed oil.

4. Heating burner in accordance with claim 1

characterized in that

the actuators comprise a motor which sets a truncated cone in rotation around its longitudinal axis in such a way that fuel introduced via an inlet opening into the truncated cone exits from an outlet opening and is atomized because of the centrifugal forces generated.

5. Heating burner in accordance with claim 4

characterized in that

the ignition device comprises a heat recovery feature manufactured from a thermally conducting material and which passes the heat arising on combustion of the fuel to the fuel flowing into the burner.

6. Heating burner in accordance with claim 5

characterized in that

the heat recovery feature is arranged at least partially inside the truncated cone projecting beyond the outlet opening.

7. Heating burner in accordance with claim 4,

characterized in that

the ignition device comprises a preheater that heats the fuel to ignition temperature.

8. Heating burner in accordance with claim 7,

characterized in that

the preheater comprises a heating coil enclosing the truncated cone.

9. Heating burner in accordance with claim 1

characterized in that

the control device is designed such that it controls the fuel delivery device and the air delivery device in such a way that an essentially constant air/fuel ratio is present at the ignition device during the combustion interval (tB), preferably in an initialization interval (tI) and a stop interval (tS).

10. Heating burner in accordance with claim 9,

characterized in that

an air flow sensor is provided to determine the delivery volume from the air delivery device.

11. Heating burner in accordance with claim 1

characterized in that

the control device adjusts the actuators, more particularly the fuel delivery device and the air delivery device such that a pilot flame is present outside the combustion interval (tB).

12. Heating burner in accordance with claim 11,

characterized in that

the control device is designed such that it controls the fuel delivery device to supply the pilot flame outside the combustion interval (tB) such that less than 1%, preferably less than 1 pro mille, of the maximum delivery capacity of the fuel delivery device is delivered.