WO2004109183A1

WO2004109183A1 - Burner for liquid fuels

Info

Publication number: WO2004109183A1
Application number: PCT/CH2004/000022
Authority: WO
Inventors: Michael Eger; Andreas Schelp; Josef Wüest; Erwin Schlup
Original assignee: Toby Ag
Priority date: 2003-06-11
Filing date: 2004-01-16
Publication date: 2004-12-16
Also published as: CH696153A5; EP1636524A1

Abstract

The invention relates to a burner (1) for liquid fuels, comprising a blower (5) which is driven by a motor (2), an evaporation chamber (6) which can be heated by an electric heating device (7) and wherein a spray device (8) and a mixing wheel (9) are arranged, also comprising a cylindrical flame holder (10). According to the invention, the burner is embodied as a plunging burner wherein the evaporation chamber (6) is arranged below the blower (5). The inner wall of the evaporation chamber has an increased surface due to structural characteristics. The total surface Aeff of the structured surface is at least 50 % greater than the unstructured surface Asmooth. An injection disk (8) is arranged in the inner chamber of the evaporation chamber (6) and the mixing wheel (9) is arranged under said injection disk (8), said mixing wheel being provided with wings, and the cylindrical flame holder (10) is arranged below the evaporation chamber (6). Said type of burner for liquid fuels can be used in the construction of a condensing boiler because the function thereof is not affected by condensation and because condensation can not be contaminated by heating oil.

Description

Liquid fuel burner

The invention relates to a burner of the type mentioned in the preamble of claim 1.

Such burners are advantageously used in heating systems of wobii and non-residential buildings. The heat generated by the burner when burning the fuel heats up water in a boiler, for example. In addition to burners for liquid fuels such as heavy fuel oil, extra light heating oil or kerosene, there are burners for gaseous fuels such as natural gas. The latter are characterized in particular by the fact that their heat generation can be regulated over a large output range, which is referred to in the specialist world as modulability. In addition, gas burners have favorable values with regard to pollutant emissions.

A burner of the type mentioned in the preamble of claim 1 is known from WO-Al-00/12935. It is extremely light for burning heating oil. Such a burner is arranged in the lower region of the boiler.

In order to keep the Nerluste during operation of the boiler as low as possible, so to obtain an optimal energy yield, boilers have been designed as so-called condensing boilers, in which the exhaust gas is condensed so that the heat of condensation of the exhaust gas can be used. The boiler temperature is only as high as is absolutely necessary. If, for example, due to the prevailing weather, a normal temperature of 30 degrees Celsius is sufficient to operate the heating, the boiler has this temperature.

If a burner of the type mentioned in WO-Al-00/12935 is used in such a boiler, the problem arises that the condensate can drip onto the burner, which seriously disturbs burner operation.

To avoid this problem, so-called lintel burners have been developed that are installed in the boiler from above. Such a fall burner is known from DE-Al-40 11 691. From this document, however, only a solution can be seen in the event that the fuel is a combustible gas. Like a burner for liquid Fuels must be designed so that it acts as a fall burner, is also not hinted at.

A nerburning device which can be built into a boiler at the top is known from JP-A-57 101 209. However, this is not a burner in the actual sense, but a catalytic ner combustion device. If such a combustion device is installed in a condensing boiler, it can be assumed that the special design as a catalytic combustion device precludes liquid fuel from getting into the boiler and contaminating the condensate that forms at the bottom of the boiler.

A burner is known from US-A-5, 154,597 and the associated family members such as EP-A2-0 346284, in which the fuel is atomized by means of a nozzle and then gasified by a heating device. Although it is mentioned that the burner can also be arranged in a vertical position instead of the usual horizontal position, this certainly means the installation from below, so that it is not a lintel burner. It is also not recognizable that such a burner could be suitable for a condensing boiler.

The invention has for its object to provide a burner for liquid fuels, which is suitable for installation in a condensing boiler.

According to the invention, the stated object is achieved by the features of claim 1. Advantageous further developments result from the dependent claims.

An exemplary embodiment of the invention is explained in more detail below with reference to the drawing.

1 shows a sectional drawing of a burner according to the invention,

2 details of an evaporator chamber,

3 details of a ventilation of the inner wall of the evaporator chamber,

4 shows a section of an evaporation device,

5 is a view of an atomizer disc, 6 shows a section of the atomizer disc,

7 is a diagram of a structure of the atomizing disc,

Fig. 8 is a diagram with a jacket around a flame holder and

Fig. 9 shows a variant.

1 shows a burner 1. This has an electric motor 2, on the shaft 3 of which two rotors 4 are fastened, which are parts of a blower 5 which is not shown in all details. This fan 5 demands the air required for combustion. Below the blower 5 there is an evaporator chamber 6, in the housing of which an electrical heating device 7 is integrated. An atomizer disk 8 and a mixing wheel 9 are arranged in the interior of the evaporator chamber 6, both of which are fastened on the shaft 3 and are thus driven by the electric motor 2 like the rotors 4. Arranged below the evaporator chamber 6 is a cylindrical flame holder 10, on the outer surface of which the flame is generated. The supply of the heating oil to the atomizing disc 8 is not shown here for reasons of clarity.

The elements described above are known per se from WO-Al-00/12935. However, the burner described there is not suitable for condensing boilers because it is installed at the bottom of the boiler. In a condensing boiler, condensate would drip onto the burner and seriously impair its function. According to the invention, the burner 1 is designed as a fall burner, in which the evaporator chamber 6 is arranged below the blower 5, in the interior of which the atomizing disc 8 and below this the mixing wheel 9 are arranged. The cylindrical flame holder 10 is arranged below the evaporator chamber 6. The fall burner is thus mirrored with respect to the horizontal arrangement of the fan 5, the evaporator chamber 6 and the flame holder 10. This does not exhaust the invention, however, because this does not yet solve the problem. It is essential to the invention that the evaporator chamber 6 has a surface of its inner wall 11 which is enlarged by structural features, which will be described below. In addition, a means for collecting a limited excess amount of heating oil is advantageously provided in the lower part of the inner wall 11. In the shown Ausföhrungsbeispiel this means is a circumferential groove 12 on the lower part of the inner wall 11th

Due to the increased surface area of the inner wall 11 of the evaporator chamber 6, the evaporation of the heating oil is improved because the given amount of heating oil is distributed over a larger area, that is to say forms a thinner film. The evaporation of the heating oil thus takes place completely, so that it is excluded that drops of heating oil fall under the effect of gravity into the flame holder 10 and from there at most to the bottom of the boiler, where the condensate collects. This prevents the condensate from being contaminated by heating oil.

The arrangement of the mixing wheel 9 below the atomizing disc 8 also contributes to preventing such contamination. In principle, the heating oil is thrown onto the inner wall 11 of the evaporator chamber 6 by the rotation of the atomizing disc 8. But should a drop of the heating oil fall down from the edge of the atomizer disc 8, it would fall onto the mixing wheel 9. Since this mixing wheel 9 the same

Speed has like the atomizing disc 8, but the diameter of the mixing wheel 9 is larger than the diameter of the atomizing disc 8, it follows that the centrifugal force acting on the heating oil at the edge of the mixing wheel 9 is even greater, so that the heating oil from the mixing wheel 9 below is thrown onto the inner wall 11 of the evaporator chamber 6 in all circumstances. This will be an extraordinarily large one

Safety achieved that no oil drops can fall into the flame holder 10. The circumferential channel 12 offers a further increase in safety. All these measures completely rule out that the condensate collecting at the bottom of the boiler is contaminated by heating oil. The features of the invention make it possible to create a burner for liquid fuels that can be installed and operated in condensing boilers in compliance with the applicable regulations.

In WO-Al-00/12935 it is explained in more detail that the electric heating device 7 only has to be in operation for some time after the burner has started. There, a deflection collar serves to divert part of the exhaust gas from the flame holder 10 downwards in order to heat the evaporator chamber 6. The burner 1 described here is one Deflection collar is not necessary because the heat generated on the flame holder 10, namely the hot exhaust gas, rises all by itself and thus heats the evaporator chamber 6.

The features essential to the invention include the structuring of the inner wall 11 of the evaporator chamber 6. An exemplary embodiment of the evaporator chamber 6 with such a structuring is shown in FIG. 2. The representation largely corresponds to that of FIG. 1, but FIG. 2 shows details of the structuring which had been omitted from FIG. 1 for reasons of clarity. It can be seen from FIG. 2 that the inner wall 11 of the evaporator chamber 6 heated by the electric heater 7 is not smooth, but has a structure. As a result of this structuring, the total surface area A _{eff of} the structured surface is significantly larger than the unstructured surface A _g ι _a tt in the case of a smooth inner wall 11, as is known from WO-Al-00/12935. The circumferential channel 12 is also shown here.

If the total surface area A _e ff is, for example, 50% larger than the surface area A _g ι _a tt, the result is that the thickness of the aforementioned film of heating oil on the inner wall 11 is only two thirds as large because the amount of Heating oil distributed over the larger surface A _ef τ. If the total surface area A _{eff is} twice as large as the surface area A _g ι _att , the result is that the thickness of the aforementioned film of heating oil on the inner wall 11 is only half as large. This facilitates evaporation and also prevents coking residues. Because of the bigger one

Surface A _eff evaporation is faster because the heat transfer from surface A _eff is better. The heating oil on the inner wall 11 thus evaporates completely.

A very particularly advantageous structuring is shown in FIG. 3. It shows a detail of the inner wall 11 in section, the position of which is shown in FIG. 2 in a circle with the designation III. 11 'here denotes the surface of the inner wall which is smooth before the structuring, with the surface A _g ι _a t _t and is shown as a dashed line. In this original smooth inner wall grooves 21 are pierced, which are asymmetrical V-shaped. This results in teeth 22 with flanks 23 and 24. In the exemplary embodiment shown, the flanks 23 and 24 have different inclinations. The flanks 23, 24 advantageously form an angle of approximately 60 °, and are therefore relatively acute. The teeth 22 are therefore sharp-edged, which brings a remarkable advantage. On Part of the droplets of the heating oil impinging on the inner wall 20 will impinge on these tips of the teeth 22, the droplets being broken up.

The inclination of the flanks 23, 24 also has the advantage that splashes of droplets of the heating oil impinging on these flanks 23, 24 are very likely not to be directed into the interior of the evaporator chamber 6 because the rebound angle with the angle of incidence on the flanks 23, 24 correlated.

At the specified angle of 60 °, the surface A _eff , which is formed by the totality of all flanks 23, 24, is approximately 80% larger than the originally smooth surface A _g ι _att . Compared to the prior art, this means a significant enlargement of the inner wall 11, with the result that the evaporation of the heating oil is improved so that coking residues cannot arise as a result of insufficient evaporation. The distance from tooth tip to tooth tip is advantageously about 1 mm. Depending on the angle, here 60 °, the tooth height Z is approximately 0.65 mm.

With regard to the evaporation of the heating oil on the inner wall 11, it also matters how large the oil drops are that hit the inner wall 11 from the atomizer disc 8. An improvement in the evaporation of the heating oil is achieved if the oil drops are relatively small.

4, the vaporization device of the burner 1 is shown again in detail. Here is the evaporator chamber 6 with the electrical integrated in its housing

Heater 7 shown, in the interior of the atomizing disc 8 and the mixing wheel 9, both attached to the shaft 3, rotate. The oil supply, which is designated by the reference number 28, is now also shown here. Also indicated here are blades 29 on the mixing wheel 9, which bring about intensive mixing of the air with the evaporated heating oil. The heating oil supplied by means of the oil supply 28 drops onto the atomizing disc 8 rotating with the shaft 3 and is thrown by the centrifugal force onto the inner wall 11 of the evaporator chamber 6, where the heating oil evaporates. This heating oil vapor is mixed by means of the mixing wheel 9 with the air entering from above and this mixture of heating oil vapor and air is supplied to the flame holder 10 (FIG. 1). For reasons of clarity, the structuring of the inner wall 11 of the evaporator chamber 6 is not shown here, nor is the channel 12 (FIG. 1). It is of great importance for the function of the burner that the heating oil is completely evaporated in the evaporator chamber 6 and that no coking residues arise on the inner wall of the evaporator chamber 6. The evaporation of the heating oil on the inner wall 11 of the evaporator chamber 6 is significantly influenced by how large the drops of the heating oil are from the rotating one

Atomizer disc 8 are flung away in the direction of the inner wall 11 of the evaporator chamber 6. The drops of heating oil should be as small as possible.

In order to achieve this, the atomizer disc 8 is advantageously designed in an advantageous manner. 5, this advantageous embodiment of the atomizer disc 8 is shown in a view, in FIG. 6 as a section. The atomizer disc 8 advantageously has a plate 30 arranged perpendicular to its axis A, which has a horizontally lying inner surface 31 and an upwardly inclined outer surface 32. The angle of inclination α is approximately 10 to 20 degrees. At least the outer surface 32, but advantageously also the inner surface 31, has a structuring S. The structuring S advantageously consists of embossed grooves 34 which, for example, run radially. For reasons of clarity, this is shown in FIG. 5 only for a partial area of the surface, but the entire surface is provided with such a structuring S.

This advantageous embodiment of the atomizer disc 8 causes on the one hand that the heating oil dripping from the oil supply 28 (FIG. 4) onto the plate 30 reaches the grooves 34 and then due to the rotation of the atomizer disc 8 by the acting centrifugal force in the grooves 34 against the outer edge of the atomizer disc 8 moves, that is on the inner surface 31 outwards to the outer surface 32 and then on this outer surface 32 against the edge. Oil drops are then thrown off the edge. The size of the oil drops is determined by a number of factors, namely firstly by the surface tension of the heating oil, then by the shape of the grooves 34, by the centrifugal force dependent on the speed of the shaft 3 (FIG. 4), and in the region of the upward inclined outer surface 32 of the ratio of centrifugal to gravity. Due to the advantageous design of the atomizer disc 4, the oil drops reach an optimal size, which means that the heating oil on the inner wall 11 (FIG. 2) of the evaporator chamber 6 (FIG. 1) evaporates completely and without residue. At the same time, the oil drops are evenly over the distributed over the entire circumference of the atomizer disc 8 so that they also hit the inner wall 11 of the evaporating chamber 6 in a uniformly distributed manner. This means that there is no local accumulation of large quantities of heating oil. This effect also contributes to the improvement of the evaporation.

In the case of modulating burners, that is to say those with variable output, the speed of the shaft 3 is changed in the same way as the oil supply, which is determined by the speed of an oil pump. When the heating power is high, the speed of shaft 3 is high. It then follows that the centrifugal force acting on the edge of the atomizing disc 8 is greater. Although the amount of heating oil reaching the atomizer disc 8 is then greater, the advantageous embodiment does not result in larger oil drops. Even with a high heating output, this guarantees that the evaporation takes place completely.

7 shows an advantageous embodiment of the structuring S of the surface of the atomizer disc 8. Here, multiple intersecting grooves 34 are embossed on the surfaces 31, 32, so that elevations 35 are formed which have an approximately pyramidal shape, the base surface of which depends on the angle of intersection. In the example shown, the base area has the shape of a rhombus. If the grooves 34 intersect at an angle of 90 degrees, the elevations 35 have the shape of pyramids with a square base. On the inner edge of the inner surface 31 and on the outer edge of the outer surface 32, the elevations 35 consist only of parts of the pyramid-shaped structures. This design of the structuring improves the distribution of the oil drops which are thrown away by the atomizing disc 8.

WO-Al-00/12935 describes that the electric heater 7 is switched on before the burner starts. As soon as the burner is started, the flame is generated on the flame holder 10. It has already been mentioned that the evaporator chamber 6 is then heated by rising exhaust gas. Therefore, the electric heater 7 can then also be switched off in the burner according to the invention described here. It has already been mentioned that the deflecting collar described in WO-Al-00/12935 is not required.

The heating of the evaporator chamber 6 by the rising exhaust gases is relatively indefinite. It can be ruled out that the evaporator chamber 6 through the exhaust gases is insufficiently heated, but it may happen that the evaporator chamber 6 is heated too much. This can be disadvantageous in terms of evaporation. It may therefore be advantageous to take special measures to ensure that the evaporator chamber 6 is heated sufficiently, but not excessively, by the exhaust gases. Such advantageous measures are shown in FIGS. 8 and 9.

8 and 9, schemes with the evaporator chamber 6 and the flame holder 10 are shown. The evaporator chamber 6 is fastened at the bottom to a base plate 39, which can already be seen in FIG. 1, but is not identified there. It lies between the blower 5 (FIG. 1) and the evaporator chamber 6. The flame holder 10 connects to the bottom of the evaporator chamber 6. According to the advantageous embodiment, the flame holder 10 is surrounded by a jacket 40. The flame burns in the space between the flame holder 10 and the jacket 40.

In the embodiment shown in FIG. 8 for the jacket 40, this consists of two oppositely arranged truncated cone jacket surfaces. The jacket 40 thus widens upwards and downwards. The narrowest point between the flame holder 10 and the jacket 15 is determined by the line of contact of the two truncated cone jacket surfaces. The exhaust gas which flows above this narrowest point from the flame holder 10 will predominantly take the path upwards, that is to say in the direction of the evaporator chamber 6, and heat the evaporator chamber 6. The exhaust gas, on the other hand, which flows below this narrowest point from the flame holder 10 will predominantly take the way down. In this way, the dimensioning of the two truncated cone lateral surfaces can determine quite precisely which portion of the exhaust gas flows in the direction of the evaporator chamber 6 and heats it. It is thus advantageously achieved that it is determined how strongly the evaporator chamber 6 is heated, which has a positive effect on the evaporation on the inner wall 11 (FIG. 1) of the evaporator chamber 6.

The jacket 40 still has an extremely significant positive effect. It prevents the direct radiation of heat from the flame holder 10 onto the inner wall of the boiler. The radiation of heat from the flame holder 10 onto the inner wall of the boiler can impair the stability of the flame, which is disadvantageous. It has been shown that it is for the stability of the flame of the burner 1st is disadvantageous if the boiler temperature is subject to strong fluctuations. This can occur in particular in the case of condensing low-temperature boilers. In particular, if the required power is low, ie if little fuel is burned per unit of time, the flame may not burn stably, so that the burner 1 could emit pollutants, can go out and its control switches to malfunction. A non-optimally burning flame also affects the previously described heating of the evaporating chamber 6 by the exhaust gas, so that the evaporation could also be adversely affected.

The heat radiated by the flame holder 10 strikes the inner wall of the jacket 40 which, like the flame holder 10, is made of heat-resistant steel sheet. After this

If the flame arises on the flame holder 10, the jacket 40 is heated up very quickly because its heat capacity is extremely small, compared to the heat capacity of the boiler it is insignificantly small. The temperature of the inner wall of the boiler is therefore irrelevant to the stability of the flame. Due to the effect of the jacket 15, the flame burns completely stable a few seconds after it is formed, regardless of the temperature of the boiler.

The same effect can also be achieved in the embodiment according to FIG. 9. Here, the jacket 40 has a purely cylindrical shape. A separating ring 41 is fastened in the interior of the jacket 40, the outside diameter of which corresponds to the inside diameter of the jacket 40, while the inside diameter is somewhat larger than the outside diameter of the flame holder 10. This dividing ring 41 creates a division in a manner analogous to that of the exemplary embodiment in FIG the partial flows up and down. The position of the separating ring 41 determines how large the partial flow is upwards in relation to the partial flow downwards. In terms of production technology, this solution is considerably cheaper than the solution according to FIG. 8.

A burner designed according to the invention can be used in condensing boilers because its function cannot be impaired by condensate that forms and because it is ensured that the condensate cannot be contaminated by dripping heating oil.

Claims

claims

1. burner (1) for liquid fuels with a fan (5) driven by a motor (2), an evaporator chamber (6) which can be heated by an electric heater (7), in which an atomizing device (8) and a mixing wheel (9) are arranged, and with a cylindrical flame holder (10), characterized in that

- the burner is designed as a fall burner,

- In which the evaporator chamber (6) is arranged below the fan (5),

which has an enlarged surface due to structural features (21, 22, 23, 24), the total surface area A _{ef of} the structured surface being at least 50% larger than the unstructured surface A _g ι _att ,

- That in the interior of the evaporator chamber (6) has an atomizer disc (8) and

- Below the atomizer disc (8) the blades (29) equipped mixing wheel (9) are arranged, and

- That the cylindrical flame holder (10) is arranged below the evaporator chamber (6).

2. Burner according to claim 1, characterized in that in the original smooth inner wall grooves (21) are inserted, so that the inner wall (11) consists of inclined flanks (23, 24).

3. Burner according to claim 2, characterized in that the grooves (21) are asymmetrically V-shaped.

4. Burner according to claim 3, characterized in that the flanks (23, 24) enclose an angle of approximately 60 °.

5. Burner according to claim 4, characterized in that the first flanks (23) are approximately 45 ° downwards and downward and the second flanks (24) are inclined approximately 15 ° outwards.

6. Burner according to one of claims 2 to 5, characterized in that the atomizer disc (8) has a plate (30) arranged perpendicular to its axis A, which has a horizontally lying inner surface (31) and an inclined upward has outer surface (32), at least the outer surface (32) having a structure S.

7. Burner according to claim 6, characterized in that the angle of inclination α is approximately 10 to 20 degrees.

8. Burner according to claim 6 or 7, characterized in that the structuring S is formed by embossed grooves (34).

9. Burner according to claim 8, characterized in that the grooves (34) extend approximately radially.

10. Burner according to claim 8, characterized in that on the surfaces (31, 32) intersecting grooves (34) are stamped.

11. Burner according to one of claims 2 to 10, characterized in that the evaporator chamber (6) has means (12) for collecting a limited excess amount of heating oil.

12. Burner according to one of claims 2 to 10, characterized in that a jacket (40) is placed around the flame holder (10).

13. Burner according to claim 12, characterized in that the jacket (40) has a cylindrical shape and that a separating ring (35) is arranged in the jacket (40).

14. Burner (1) according to claim 12, characterized in that the jacket (40) is formed from two oppositely arranged truncated cone jacket surfaces, so that the clear space between the flame holder (10) and jacket (40) from a narrowest point is expanded up and down.