EP0017057B1 - Fuel oil preheating device - Google Patents

Description

The invention relates to a device for preheating heating oil in front of the nozzle of a burner with a current-carrying PTC element which is in heat-conducting contact with a line leading the heating oil to the nozzle.

Small and very small oil burners have considerable advantages for many applications. It is possible with such burners to adapt the heat output to a smaller requirement, as is the case, for example, with floor and room heating systems or the like. The small burner output enables a smaller and therefore cheaper and space-saving boiler. The thermal insulation of the boiler is cheaper and the boiler temperature regulation can be achieved with fewer starts of the burner, which means less pollution of the burner and less environmental pollution.

The main problem with low-power oil burners is the small cross-sections of the nozzle channels. The fine nozzle channels lead to poor reproducibility of the oil throughput and often to blockages.

It is known to counter these disadvantages by preheating the heating oil in front of the nozzle. Preheating lowers the viscosity of the oil and perfect atomization can be achieved with lower atomizing pressure. The lower pressure leads to lower oil throughput and lower burner output. The low viscosity also reduces the risk of constipation. On the other hand, due to the lower atomization pressure, the cross section of the nozzle channels can be increased if the oil throughput and thus the burner output are not to be reduced. In this case, there is a substantial reduction in the risk of clogging and thus an increase in the reliability of the burner.

It is known to use an electrical resistance heater to preheat the heating oil. The electrical resistance heater has the disadvantage of a large space requirement. An even more serious disadvantage is that electrical resistance heating can cause the oil to overheat above the optimal temperature of, for example, 70 ° -80 ° C, especially when the burner is at a standstill or the flow rate of the oil is reduced. Overheating can lead to undesirable cracking of the heating oil.

These disadvantages of electrical resistance heating are avoided by the device known from German utility model 7 811 098. In this device, a current-carrying PTC element is used to preheat the heating oil. The PTC thermistor element has the property of regulating its heating power itself in a known manner. This self-regulation prevents the heating oil from overheating without the need for complex additional control measures.

In this known device, the PTC thermistor element is inserted radially into a heat-conducting metallic sleeve which encloses the line carrying the heating oil. The effectiveness of this preheating device is extremely poor because, on the one hand, the electrical insulation required between the PTC thermistor element and the metallic sleeve also represents a thermal resistance, and on the other hand, because of its large surface area, the metallic sleeve leads to high heat losses. Finally, the metallic sleeve has a high thermal capacity, so that the self-regulation of the PTC thermistor element is sluggish and overheating of the heating oil cannot be reliably ruled out. Finally, the device attached to the outside of the feed line takes up a considerable amount of space, so that it cannot be used without structural changes to the entire burner.

The invention has for its object to improve a device for preheating heating oil of the type mentioned in such a way that the preheating takes place with a high degree of efficiency, that the self-regulation of the PTC thermistor works practically without delay and that the device integrates space-saving into the nozzle assembly of the burner and can therefore be used without changing the burner structure.

This object is achieved in that at least one plate-shaped PTC element is inserted into the cross section of the nozzle assembly of the burner, that the line carrying the heating oil in the region of the PTC element is designed as at least one flat channel and that at least one flat side of the PTC element on a wall thereof flat channel with thermal contact.

Advantageous embodiments and developments of the invention are specified in the subclaims.

In the device according to the invention, the plate-shaped PTC thermistor element sits in the cross section of the nozzle assembly and the supply line for the heating oil is designed as a channel which lies flat against the entire flat side of the PTC thermistor element. The device can therefore be fully integrated into the nozzle assembly of the burner, only the electrical connection lines of the PTC thermistor element having to be led out of the nozzle assembly. The device therefore does not require any changes to the burner structure and can be used in existing burner designs without any problems will.

The large-area and direct thermal contact between the PTC thermistor element and the heating oil results in optimal preheating efficiency. Since there are no parts with heat capacity between the PTC thermistor element and the heating oil, the self-regulation of the PTC thermistor element is practically instantaneous. The heating oil is therefore always kept at the optimal preheating temperature and overheating is reliably prevented.

The safety regulations require that the heating oil temperature must under no circumstances exceed 95 ° Celsius. This requirement cannot be met in all cases by the self-regulating property of the PTC thermistor elements with absolute certainty, because the electrical data of the PTC thermistor elements have a production-related spread and the heat capacity and heat dissipation of the entire device is also subject to certain production tolerances. According to the invention, a safety thermostat is therefore used in addition to the self-regulating effect of the PTC thermistor element, which interrupts the power supply to the PTC thermistor element as soon as the heating oil exceeds the permissible maximum temperature.

Advantageously, a control thermostat can also be used, as is done in connection with other types of preheating, e.g. B. by electrical resistance heating, is known per se. Such a control thermostat connected to the burner control circuit closes an electrical contact when a predetermined minimum oil temperature is reached, as a result of which the oil burner can be put into operation.

This prevents the burner from starting if the oil temperature is too low. The control thermostat also opens the electrical contact when the oil falls below the specified minimum oil temperature and shuts down the burner. This prevents the boiler from becoming sooty if the oil temperature is too low.

The safety thermostat and the control thermostat are arranged in direct, large-area, heat-conducting contact with the flat channels carrying the heating oil, in which the preheating takes place through the PTC thermistor elements. In this way, the safety thermostat and the control thermostat can also be integrated into the cross section of the nozzle assembly and do not change its dimensions which are advantageous for installation. The large-area heat-conducting contact leads to an almost inertia-free determination of the actual heating oil temperature by the thermostats directly at the point at which the heating oil is heated by the PTC thermistor elements. The safety thermostat thus responds to the highest temperature actually reached by the preheating in the entire oil supply line without a major delay. Reliable compliance with the prescribed maximum temperature is thus guaranteed for the entire oil supply system.

• Fig. 1: Einen Axialschnitt einer ersten Ausführungsform der Erfindung,
• Fig. 2: eine Stirnansicht der Vorrichtung der Fig. 1 von links,
• Fig. 3: einen Schnitt gemäß-A-A in Fig. 1,
• Fig. 4: einen Axialschnitt einer zweiten Ausführungsform der Erfindung,
• Fig. 5: eine Stirnansicht der Vorrichtung der Fig. 4 von links,
• Fig. 6: einen Schnitt gemäß B-B in Fig. 4,
• Fig. 7: einen Axialschnitt einer dritten Ausführungsfonl1 der Erfindung,
• Fig. 8: eine Stirnansicht der Vorrichtung der Fig. 7 von links,
• Fig. 9: einen Schnitt gemäß C-C in Fig. 7,
• Fig. 10: einen Axialschnitt einer vierten Ausführungsform der Erfindung,
• Fig. 11: eine Stirnansicht der Vorrichtung der Fig. 10 von links,
• Fig. 12: einen Schnitt gemäß D-D in Fig. 10 und
• Fig. 13: eine Abwandlung der Ausführungsform der Fig. 4.

Further advantages and features of the invention emerge from the following description of exemplary embodiments of the invention illustrated in the drawing. It shows

• 1 shows an axial section of a first embodiment of the invention,
• 2: an end view of the device of FIG. 1 from the left,
• 3 shows a section according to AA in FIG. 1,
• 4 shows an axial section of a second embodiment of the invention,
• 5: an end view of the device of FIG. 4 from the left,
• 6: a section according to BB in Fig. 4,
• 7 shows an axial section of a third embodiment of the invention,
• 8: an end view of the device of FIG. 7 from the left,
• 9: a section according to CC in FIG. 7,
• 10 shows an axial section of a fourth embodiment of the invention,
• 11: an end view of the device of FIG. 10 from the left,
• Fig. 12: a section according to DD in Fig. 10 and
• 13: a modification of the embodiment of FIG. 4.

1-3, a first embodiment is shown. The device for preheating heating oil has two metallic connecting pieces 10 and 12, the cross section of which is adapted to the cross section of the nozzle assembly of a burner. The connector 10 has a coaxial receptacle with an internal thread, into which the nozzle rod can be screwed. The connector 12 has a receptacle with an internal thread into which the nozzle of the nozzle assembly can be screwed. Through axial bores of the connecting pieces 10 and 12 serve to supply the heating oil to the nozzle. Two plate-shaped PTC elements 14 are inserted between the connecting pieces 10 and 12. The PTC thermistor elements 14 are arranged with their longitudinal center axis coaxial to the connecting pieces 10 and 12 and thus to the nozzle assembly and axially adjoining one another. On both flat sides of the PTC thermistor elements 14 are channels 16, which are preferably formed from flat-edge tubes made of brass. The flat edge tubes 16 connect the coaxial bores of the connecting pieces 10 and 12 and serve to supply the heating oil. The width of the flat edge tubes 16 corresponds to the width of the PTC thermistor elements 14, so that they lie over a large area on their entire flat side.

Immediately on the opposite flat sides of the PTC thermistor elements 14, conductor layers 18 are applied, which serve as a power supply and are connected to a power source via connecting lines. Between the conductor layers 18 and a thin electrically insulating layer 20 is arranged in the flat edge tubes 16. This insulating layer consists, for example, of thermally sprayed-on aluminum oxide and offers a low thermal resistance.

In another embodiment, the electrically insulating layer 20 is a layer made of a plastic with high dielectric strength and high heat resistance. Because of the simple production, a film is preferably used. A polyimide film (trade name Kapton) has proven to be particularly suitable. Such a film has a dielectric strength of 280 kV / mm, heat resistance up to 180 ° C for a short time even up to 275 ° C and a high tensile strength. Adequate electrical insulation can therefore be obtained with a film thickness of 0.1 mm. This low film thickness means low thermal insulation and thus the desired good heat transfer.

The entire arrangement consisting of PTC thermistor elements 14, their electrical connection lines and the flat edge tubes 16 is cast into an insulating plastic 22 and is held coaxially between the connection pieces 10 and 12 by this. A metallic sleeve 24 pushed over the connecting pieces 10 and 12 encloses the plastic to the outside and serves as an external shape when the plastic is poured.

During operation, a current supplied via the conductor layers 18 flows through the thermistor elements 14 and heats them. The oil supplied through the flat-edge pipes 16 to the nozzle is heated by the PTC thermistor elements 14, the effect of the PTC thermistor elements 14, which limits current as the temperature rises, has the consequence that the oil is preheated to a predetermined optimal temperature in a self-regulating manner.

In the embodiment of FIGS. 1-3, the flat edge tubes 16 themselves can also be used as power supply lines for the PTC thermistor elements 14. The flat edge tubes 16 only have to be soldered in an electrically conductive manner to the flat sides of the PTC thermistor elements 14. The power connection lines can then be soldered to the flat edge tubes 16.

It is, of course, necessary in this embodiment that the flat-edge pipes 16 do not come into electrically conductive contact with the metallic connecting pieces 10 and 12 or the nozzle rod or nozzle inserted into them. For this purpose, the flat edge tubes 16 are also covered at both ends by the insulating plastic 22 and are only connected to the bores of the connecting pieces 10 and 12 via bores in this plastic 22.

Insofar as the following exemplary embodiments of the invention correspond to the exemplary embodiment of FIGS. 1-3, corresponding parts are provided with the same reference symbols and reference is made to the above description thereof.

In the embodiment shown in FIGS. 4-6, the connecting pieces 10 and 12 are not continuous, but are closed on their mutually facing end faces. The flat edge tubes 16 are inserted into corresponding through bores of these closed end faces of the connecting pieces 10 and 12 and are soldered to them at 26.

Since, in this embodiment, the flat edge tubes 16 are in electrically conductive connection with the connecting pieces 10 and 12, current supply to the PTC elements 14 via the flat edge tubes 16 is not possible. Rather, the power supply must always take place via conductor layers 18 which are separated from the flat-edge tubes 16 by insulating layers 20.

In the embodiment of FIGS. 4-6, the connecting pieces 10 and 12 are connected and held together during manufacture by the flat-edge tubes 16 used, so that the pouring of the plastic 22 is simplified. The pushed-on sleeve 24 can be omitted in this embodiment.

In the third embodiment shown in FIGS. 7-9, no flat edge tubes 16 are used. Flat channels 28 are recessed in the plastic 22 on both flat sides of the PTC thermistor element 14. The width of these channels 28 corresponds to the width of the PTC thermistor element 14. The channels 28 are formed when the plastic 22 is poured in. Instead of flat channels 28, closely spaced holes in the plastic can also be provided, which cover the entire flat sides of the PTC thermistor element.

The current supply to the PTC thermistor element 14 takes place via conductor layers 18, which are protected by an insulating layer 20 against the oil flowing directly past.

In this embodiment, a pushed-on sleeve 24 is also provided, which essentially serves to fix the connecting pieces 10 and 12 during the plastic molding process.

In Fig. 7 only a PTC element 14 is shown. As in the previous exemplary embodiments, two or more PTC thermistor elements 14 can of course be arranged axially one after the other. The number of PTC thermistor elements 14 depends essentially on the heating power required, i. H. essentially after oil flow.

In the fourth exemplary embodiment shown in FIGS. 10-12, a single flat tube 16 is provided, which is arranged with its longitudinal central axis coaxial with the connecting pieces 10 and 12. As in the exemplary embodiment in FIGS. 4-6, the flat tube 16 is soldered into corresponding bores in the closed end faces of the connecting pieces 10 and 12.

Two axially adjoining PTC thermistor elements 14 rest against the mutually opposite walls of the flat tube 16. The heating of the by Flat tube 16 flowing oil thus takes place through a total of four PTC elements 14.

The PTC thermistor elements 14 arranged on both sides of the flat tube 16 are preferably connected in series. This can be done by an electrical line embedded in the plastic 22, which connects the conductor layers of the PTC thermistor elements 14 facing the flat edge tube 16.

There is also the possibility of directly connecting the PTC thermistor elements 14 to the flat tube 16 in an electrically conductive manner, so that this forms the conductive connection for the series connection of the PTC thermistor elements 14. In this case, of course, the flat tube 16 must not be soldered into the connectors 10 and 12, but must be electrically insulated from them by the plastic 22, as was explained with reference to the embodiment of FIGS. 1-3.

The embodiment of FIGS. 10-12 is particularly suitable for applications where a high heating power is required without the axial length of the device being allowed to be increased.

Further modifications of the embodiment of FIGS. 10-12 are readily apparent. For example, further flat edge tubes 16 can be arranged on the outer flat sides of the PTC thermistor elements 14 in order to enlarge the oil passage cross section.

The structure of the embodiment of FIG. 13 basically corresponds to the embodiment of FIGS. 4-6. In addition, however, a safety thermostat 29 is placed on the outer (in the drawing upper) flat side of the one flat edge tube 16 facing away from the PTC thermistor elements 14. The safety thermostat 29, the conventional type, for. B. can be a bimetal thermostat, lies on the flat side of the flat edge tube 16, so that a good heat transfer between the flat tube 16 and the safety thermostat 29 is guaranteed.

The safety thermostat 29 is connected in series in the circuit of the PTC thermistor elements 14 and interrupts this circuit as soon as it reaches a predetermined maximum temperature. This specified maximum temperature is somewhat lower than the maximum oil temperature permitted for preheating the heating oil, which is set at 95 ° C according to the safety regulations. This difference between the maximum allowable oil temperature of z. B. 95 ° C and the response temperature of the safety thermostat 29 takes into account the time delay caused by heat capacity and heat conduction, with which the safety thermostat 29 assumes the temperature of the PTC thermistor elements 14.

On the outer (lower in the drawing) flat side of the other flat tube 16, a control thermostat 30 is seated in the same way over a large area. This control thermostat can also be of a conventional type. The control thermostat 30 is connected to the control circuit of the burner and activates it when a predetermined temperature of z. B. 60 ° C so that the burner can be ignited. If the temperature falls below a predetermined value of z R 40 ° C, the control thermostat 30 puts the burner out of operation. This prevents on the one hand an uneconomical ignition of the burner when the oil temperature is too low and on the other hand prevents sooting when the oil temperature is too low while the burner is in operation.

The safety thermostat 29 and the control thermostat 30 also fit into the cross section of the connecting pieces 10 and 12 and thus into the cross section of the nozzle assembly. The thermostats 29 and 30 are also cast in the insulating plastic 22.

All embodiments have in common that it is a device whose cross section and thus the outer circumference corresponds to the cross section and outer circumference of the nozzle block, so that this device can be inserted axially into the nozzle block without the geometry and dimensions of the nozzle block and the burner to change. It is also common to all the embodiments that the oil with a large heat exchange surface is passed directly past the PTC thermistor elements, so that optimum efficiency and low inertia are obtained when preheating the heating oil. Despite the large heat exchange surface, the oil does not come into direct contact with the PTC thermistor elements, so that the oil cannot act chemically on the PTC thermistor material.

Finally, all of the embodiments can be produced from a few simple parts in a manner which is simple in terms of production and assembly technology.

Claims (17)

1. I. Device for preheating fuel oil before the nozzle of a burner with a PTC resistor through which current flows and which is in thermally conducting contact with a fuel oil line to the nozzle, characterised in that,

   - at least one plate-shaped PTC resistor (14) is inserted in the cross section of the burner penstock,

   - the fuel oil line in the region of the PTC resistor (14) is formed as at least one flat shallow channel (16, 28), and

   - at least one flat side of the PTC resistor (14) rests in thermal contact against a wall of this flat channel (16, 28).
2. 2. Device according to Claim 1, characterised in that one PTC resistor (14) is provided on both of whose flat sides rests a flat channel (16, 28).
3. 3. Device according to Claim 1, characterised in that a flat channel (16) is provided on both of whose walls rests a PTC resistor (14), the PTC resistors preferably being connected in series.
4. 4. Device according to Claim 3, characterised in that a further flat channel rests against each of the two outer flat sides of the PTC resistors (14).
5. 5. Device according to Claim 1, characterised in that the PTC resistors (14) and the flat channels (16, 28) are embedded in an insulating plastics material (22).
6. 6. Device according to Claim 5, characterised in that the respective flat channels are flat metal tubes (16) connected in an electrically conducting manner to the respective PTC resistors (14) and forming their current supply, and that the flat tubes (16) are electrically insulated by the plastics material (22) with respect to the metal penstock.
7. 7. Device according to Claim 1, characterised in that the respective flat channels are flat metal tubes (16) which are preferably joined, in particular soldered, to the metal penstock, and that conducting layers (18) are applied to the flat sides of the respective PTC resistors (14) to form their current supply, which are separated with a low thermal resistance from the flat tubes (16) by means of an electrically insulating layer (20).
8. 8. Device according to Claim 5, characterised in that the respective PTC resistors (14) are completely embedded in the plastics material (22) and that the respective flat channels are recessed out from the plastics material or are channels (28) bored therethrough, which are separated by an electrically insulating layer (20) of low thermal resistance from the current supply-forming conducting layers (18) of the PTC resistors (14).
9. 9. Device according to Claim 7 or 8, characterised in that the electrically conducting layer (20) of low thermal resistance consists of thermally sprayed-on aluminium oxide.
10. 10. Device according to Claim 7 or 8, characterised in that the low thermal resistance electrically conducting layer (20) is a plastics layer of high break-down resistance and high thermal stability, in particular a plastics foil and preferably a polyimide foil.
11. 11. Device according to Claim 1, characterised in that the PTC resistor or resistors (14) are in each case replaced by two or more axially connected PTC resistors.
12. 12. Device according to Claim 1, characterised in that the respective PTC resistors (14) and the flat channels (16, 28) are arranged axially between two metal connecting pieces (10, 12), which are preferably adapted by means of a screw thread for axial insertion in the penstock.
13. 13. Device according to Claims 5 and 12, characterised in that the insulating plastics material (22) is cast between the connecting pieces (10, 12), the said connecting pieces (10, 12) preferably being held together by means of a slipped-over metal sleeve (24) for the casting of the plastics material (22).
14. 14. Device according to Claim 1, characterised in that a safety thermostat (29) connected in series with the respective PTC resistors (14) is arranged in thermally conducting contact against a wall of one of the flat channels (16). -
15. 15. Device according to Claim 1, characterised in that a control thermostat (30) incorporated in the control circuit of the burner is arranged in thermally conducting contact against a wall of one of the flat channels (16).
16. 16. Device according to Claims 2, 14 and 15, characterised in that the safety thermostat (29) and the control thermostat (30) rest in each case against the outer surface of one these flat channels (16).
17. 17. Device according to Claims 5 and 16, characterised in that the safety thermostat (29) and control thermostat (20) are embedded together with the PTC resistor (14) and the flat channels (16) in the insulating plastics material (22).

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