EP0905447A2 - Vaporising device for liquid fuels - Google Patents

Abstract

The evaporator has an electrically heated capillary tube (10) with a bore diameter (d) of 0.3-2.0 mm, a length (L) of 500-3000 times the bore diameter, and a wall thickness of 2.0-0.5 times the bore diameter, in which the liquid fuel is evaporated. The chrome-nickel steel tube can be helically- or spirally-wound and can be electrically heated with a directly applied voltage no greater than about 50 V, or indirectly by a resistance heater element.

Description

The invention relates to a device for vaporizing liquid fuels according to the preamble of claim 1.

The residue-free evaporation of liquid hydrocarbon fuels, such as. Heating oil and diesel fuel in the Gram range represents a previously unsatisfactorily solved technical problem. The evaporation of such fuels runs in a temperature range of 160 to 380 ° C, what a complete evaporation temperatures of the heat transfer surfaces of more than 200 to 450 ° C is required. Around keeping the wall temperature at the evaporators low, small temperature differences are used and the heat exchangers are formed over a large area and / or with a large volume.

The thermal load on heating and diesel oil leads to longer exposure times to polymerizations and clumping of the macromolecules that are on the heat transfer surfaces drop. At the end of the boiling zone, there is additional storage the non-evaporated residual fractions. These deposits can cause thermal insulation, which further increases the temperature has the consequence. This causes coking and an increased deposition of the clumps, which leads to constipation the flow channels can lead.

Large-volume evaporators can be found as so-called cup burners used in chewing oil stoves. Evaporation takes place here on the free surface of the liquid fuel phase. The resulting deposits settle on the floor and are disposed of periodically.

DE 32 43 395 A1 describes a device at the beginning known genus known. The fuel is in a pipe evaporates, which is directly or indirectly electrically heated becomes. The tube is large in volume with a relatively large inner diameter educated. There are wall temperatures of more than Provided 1000 ° C, accordingly, over the pipe wall transmit very high heat flux densities. Due to the relatively long residence time of the fuel in the pipe and due to the high wall temperatures, deposits appear on the Pipe wall on. The tube serving as the evaporation chamber has strong cross-sectional changes, the unfavorable flow conditions with blind spots cause what the Formation of deposits favors. It is therefore envisaged heating up the pipe periodically during a cleaning phase, to burn the deposits to ashes and then out blow out the pipe into the combustion chamber.

It is also known to use evaporators with a large heat transfer area and small dimensions in that the fuel passed through a network of whisker threads (e.g. H. Schladitz "Fuel Processing and Environmental Protection" in "Oil and gas firing", 1973, Issue 3, page 164 to 168). The whisker mesh forms a structure with a high Porosity and thus a large pore volume and a large one Heat transfer surface. The metallic whisker threads can be used directly as electrical resistance heating become. The flow through the fine-pored structure leads to Connection with the relatively large volume to long dwell times of fuel, which in turn is the deposit of higher-boiling or solid components and cracked macromolecules in the porous whisker skeleton.

The invention has for its object a device for To provide vaporization of liquid fuels the most residue-free evaporation smaller and smallest quantities of liquid fuels in the gram range enables.

According to the invention, this object is achieved by a device with the features of claim 1.

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

The main idea of the invention is the liquid Vaporizing fuel in a heatable capillary tube where the inside diameter of the capillary tube as possible is kept small. To the necessary heat transfer area to get the length of the capillary tube accordingly large size. To despite the great length of the capillary tube produce an evaporator with small dimensions To be able to, the capillary tube is preferably in turns arranged to a large length of the capillary tube in one to accommodate small volumes. The heating of the capillary tube can either be done directly by the capillary tube itself is used as a heating conductor, or indirectly by using the Capillary tube is in contact with a heating cartridge.

The reduction in the inside diameter of the pipe through which the fuel is passed through for evaporation a capillary tube surprisingly does not lead to one rapid clogging and clogging of the capillary tube like this would have been expected according to the prior art. It has rather, it was shown that a largely residue-free Evaporation can be achieved and also over long periods of operation No deposits occur that are the narrow cross section of the capillary tube. It is believed that this is due to the fact that by narrowing the inside diameter throughput times are significantly reduced, whereby in addition, the long capillary tube has no cross-sectional jumps which leads to flow separation and flow shadows could lead. The large length and small cross section of the Capillary tube and periodically small changes in Heating power and the mass flow lead to temporal Fluctuations in the distribution of heat flux density over the Length of the capillary tube, which in turn means that the critical zone in which the liquid phase of the fuel the vapor phase transitions upstream and downstream migrates to the capillary tube. Deposits in a particular This avoids length ranges.

According to the invention, the capillary tube has an inner diameter from about 0.3 to 2.0 mm, preferably from 0.5 to 1.3 mm. The ratio of the length of the capillary tube to its inside diameter is in the range of about 500 to 3000, preferably from 900 to 2300. Given this dimensioning the residence times of the fuel in the capillary tube are in the millisecond range.

In the zone where the liquid phase is in the vapor phase passes over, the low-boiling fractions evaporate first and form an axial steam flow in the capillary. The higher boilers Fractions are thereby against the wall of the Capillary tube pushed so that they are heated more intensely. The entrainment of the high-boiling fractions at speeds up to 160 m / s prevent deposits of residual fractions. With regard to the fluctuation of the evaporation zone and to ensure flow stability is at the outlet end the capillary tube has an overheating length, in which also the required minimum system pressure from about 1 to 2 b is generated.

The capillary tube evaporator according to the invention can in all Use cases are used in which one if possible residue-free evaporation of hydrocarbon mixtures is sought. For example, the device can be used as a heating oil evaporator for aerosol formation with the combustion air in Premix burners are used. There is also a stake as a heating oil evaporator for fuel-air mixture formation in Burner heads with and without injector or in combination with Air nozzles with integrated swirl generation possible. Since the Evaporators in particular in a mass flow range of 0.1 works effectively up to 4.0 kg / h, it is particularly suitable for use in furnaces with a heat output below 10 kW. The capillary tube evaporator can be used for firing larger outputs can be used as pilot and pilot burners. Finally it can also be used as a preheater for heating oil Installation in pressure atomizer nozzle shafts.

Fig. 1

schematisch ein Kapillarrohr, wie es erfindungsgemäß verwendet wird,

Fig. 2

das Kapillarrohr in einer ersten Ausführung,

Fig. 3

die komplette Vorrichtung in der ersten Ausführung,

Fig. 4

die Vorrichtung in der ersten Ausführung in einen Brenner eingebaut,

Fig. 5

die Vorrichtung in der ersten Ausführung in einer modifizierten Einbausituation,

Fig. 6

eine Abwandlung der ersten Ausführung der Vorrichtung,

Fig. 7

eine vergrößerte Detaildarstellung der Fig. 6,

Fig. 8

eine zweite Ausführung des Kapillarrohres,

Fig. 9

eine dritte Ausführung des Kapillarrohres,

Fig. 10

eine vierte Ausführung des Kapillarrohres und

Fig. 11

eine fünfte Ausführung des Kapillarrohres.

The invention is explained in more detail below on the basis of exemplary embodiments illustrated in the drawing. Show it:

Fig. 1

schematically a capillary tube, as used according to the invention,

Fig. 2

the capillary tube in a first embodiment,

Fig. 3

the complete device in the first version,

Fig. 4

the device in the first embodiment installed in a burner,

Fig. 5

the device in the first embodiment in a modified installation situation,

Fig. 6

a modification of the first embodiment of the device,

Fig. 7

6 shows an enlarged detailed illustration of FIG. 6,

Fig. 8

a second embodiment of the capillary tube,

Fig. 9

a third embodiment of the capillary tube,

Fig. 10

a fourth version of the capillary tube and

Fig. 11

a fifth version of the capillary tube.

Fig. 1 shows a capillary tube as it is according to the invention for the Device for vaporizing hydrocarbon fuels, such as heating oil and diesel oil in a mass flow range of 0.1 up to 4.0 kg / h, preferably from 0.2 to 2.4 kg / h becomes.

The capillary tube 10 has an inner diameter d that between 0.3 and 2.0 mm, preferably between 0.5 and 1.3 mm lies. The ratio of the wall thickness of the capillary tube 10 to the inside diameter is 0.2 to 0.5. The length L of the Capillary tube 10 is 500 to 3000 times the inner diameter d, preferably 900 to 2300 times.

The wall of the capillary tube 10 is described in later Way heated. The liquid fuel Mf is in the capillary 10 initiated, flows through the capillary tube 10 and emerges from the capillary tube 10 as vapor MD.

In a first length section L1 on the entry side, the liquid fuel supplied through the heated wall of the Capillary tube 10 heated to its boiling point. In a subsequent length section L 2, the fuel evaporates starting with the low boiling fractions. In one the last outlet-side length section L3 is the liquid one Fuel evaporates completely and is additionally overheated. The heating of the wall of the capillary tube 10 leads to a temporally fluctuating heat generation over the length the capillary tube 10. In addition, the temperature of the supplied liquid fuel. This results in a axial position of the evaporation zone L2 which fluctuates over time. The the superheating zone L3 downstream of the evaporation zone L2 ensures that despite the fluctuations in the evaporation zone L2 the fuel reliably exits the capillary tube 10 is completely evaporated. In addition, the Overheating zone L3 ensures that the fuel vapor with stable flow and the required minimum system pressure from 1 to 2 b emerges from the capillary tube 10.

Figures 2 and 3 show a first embodiment of the device.

Space-saving around the long capillary tube 10 in a burner To be able to accommodate, the capillary tube 10 is helical bent into a spiral. The exit end the capillary tube 10 is bent so that it is in the The central axis of the spiral runs. The entry end of the Capillary tube 10 is also in the central axis of the coil bent. A transition tube piece closes at the inlet end 12, which serves to cross-section the Fuel supply line to the small cross section of the capillary tube 10 to reduce. The transition pipe section 12 goes on the entry side into a threaded sleeve 14, which with a Collar 16 and one on the external thread of the threaded sleeve 14 seated lock nut 18 for screwing the device in the bulkhead of a burner is used.

FIG. 3 shows how the capillary tube 10 shown in FIG. 2 is installed in a complete evaporator. For this, the coiled capillary tube 10 inserted into a protective sleeve 20, whose inner wall is insulated by an insulating sleeve 22. In the outlet end of the protective sleeve 20 is an insulating insert 24 used, the axis of the outlet side End of the capillary tube 10 is penetrated. The transition pipe piece 12 with the subsequent threaded sleeve 14 is centered held in an insulating body 26. Is on the entry side the protective sleeve 20 between the collar 16 and the lock nut 18th fixed on the threaded sleeve 14. In the insulating body 26 radial plug connector contacts 28 and 39 are used. The connector connection contact 28 is with a electrical guided axially parallel in the insulating body 26 Conductor 32 connected. This conductor 32 carries out axially parallel the coil of the capillary tube 10 and is with its front End set in the insulating insert 24. The front end of the Conductor 32 is directly behind the insulating insert 24 a terminal 34 electrically conductive with the outlet end of the capillary tube 10 connected. The second connector connector 30 leads radially through the insulating body 26 and contacts the transition tube piece in an electrically conductive manner 12th

About the connector terminals 28 and 30 that can Capillary tube 10 can be connected to a power supply.

For example, the connector connector 28 the phase and to the connector terminal contact 30 the Ground of a low-voltage network of up to 42 V.

In this embodiment, the capillary tube 10 consists of a Heating conductor metal, e.g. made of a chrome-nickel steel. In this The capillary tube 10 is executed by the capillary tube 10 flowing current directly heated.

Figure 4 shows the installation of the device of Figures 2 and 3 into a burner tube. The device is with its protective sleeve 20 coaxially inserted into the hub of an air nozzle 36, and by means of a clamping ring 38 set in the air nozzle 36. The Air nozzle 36 also has a hub coaxially surrounding the hub Swirl body 40. The air nozzle 36 is centered in one Schott 42 used, which in turn in a burner stem 44 sits and closes this except for the air nozzle 36. The burner main pipe 44 is connected to a burner blower socket 46 scheduled. At the downstream end of the burner stem 44, a flame tube 48 is attached, which for generation an injector effect lateral recirculation openings having. A flame monitoring probe is also in the bulkhead 42 50 and a pair of ignition electrodes 52 are used. From The structure of the burner tube is apart from the evaporator device known per se.

FIG. 5 shows a modification of the installation situation in FIG. 4, in which the evaporator device is axially downstream extends beyond the air nozzle 36, with the air nozzle 36 axially a catch tube 54 is placed.

In the structure of Figure 4, the combustion air is Air nozzle 36 conical and by means of the swirl body 40 with swirl acted upon in the emerging from the capillary tube 10 Fuel steam jet initiated to intensive mixing of combustion air and fuel vapor. In the exemplary embodiment in FIG. 5, the swirl is over combustion air supplied to the air nozzle 36 in the trap 54 steered so that it swirls over the widening downstream Catch pipe 54 emerges and with the fuel vapor mixed forms an expanding flame cone.

Figures 6 and 7 show a modification of the first embodiment the device, the connection and installation of the helically bent capillary tube 10 are modified.

In this version, the helically curved capillary tube sits 10 in an electrically conductive protective sleeve 56. Die Protective sleeve 56 is at its downstream end through a electrically conductive cap 58 completed, the centric Exit end of the capillary tube 10 receives, fixed and contacted electrically conductive. That on the entry side Transition tube piece 12 adjoining the end of the capillary tube 10 is inserted into an insulating bush 60. The insulating bush 60 with the transition pipe piece 12 is with the threaded sleeve 14th screwed. For this purpose, the threaded sleeve 14 has a connecting nipple 62 on which a union nut 64 with a conical clamping ring 66 is screwed on. An electric one Terminal contact 68 insulates the protective sleeve 56 and is conductive with the transition pipe section 12 and thus the Capillary tube 10 in connection. The connection contact 68 serves to connect the phase of the power supply while the Protective sleeve 56 establishes the ground connection.

FIG. 8 shows a second embodiment of the capillary tube 10. In this embodiment, the capillary tube 10 is not in the form of a Spiral but bent in the form of a spiral. The transition pipe piece 12 to supply the liquid fuel is there arranged at the outer end of the spiral, while the outlet end is arranged in the middle.

FIG. 9 shows a third embodiment of the capillary tube 10. In In this embodiment, the capillary tube 10 is in several hairpin bends bent so that going back and forth parallel sections of the capillary tube 10 result. The hairpin bends can be bent so tight that you Radius of curvature R only three times the inner diameter d of the capillary tube is 10.

FIG. 10 shows a fourth embodiment of the capillary tube 10, which differs in the electrical contact. On the capillary tube 10 is coaxially an electrically conductive jacket tube 70 postponed. The casing tube 70 has only one small outer diameter of e.g. 2 to 3 mm and is from the capillary tube 10 separated by insulation 72 which e.g. is designed as a thin film or varnish. At the exit end of the capillary tube 10 is the jacket tube 70 conductively connected to the capillary tube 10. On the entry side An insulating plug 74 is provided at the end, one Connection contact 76 of the jacket tube 70 against the transition tube piece 12 electrically isolated, which is the second electrical Has contact.

In this embodiment, the capillary tube 10 with the jacket tube 70 can be bent and installed in any shape without that additional measures for electrical contacting and Power supply to the exit end of the capillary tube 10 are necessary.

While in the versions described so far the capillary tube 10 is designed as a heating conductor and heated directly 11 shows an embodiment in which the capillary tube 10 is indirectly heated. The material of the capillary tube 10 can therefore regardless of its electrical conductivity to get voted.

In this embodiment, the capillary tube 10 is helical on the outer surface of a cylindrical heat-conducting Sleeve 78 wrapped. In the sleeve 78 is coaxial a heating cartridge 80 with the electrical line connections 82 and 84 used. The heating cartridge 80 is heated via the thermally conductive sleeve 78, the capillary tube 10 indirectly. The heating cartridge 80 can in a manner known per se for high voltage or low voltage.

Reference list

10th

Capillary tube

12th

Transition pipe piece

14

Threaded sleeve

16

Federation

18th

Lock nut

20th

Protective sleeve

22

Insulating sleeve

24th

Insulating insert

26

Insulating body

28

Connector connector contact phase

30th

Connector terminal contact ground

32

ladder

34

Connector

36

Air nozzle

38

Clamping ring

40

Swirl body

42

Schott

44

Burner stem pipe

46

Burner fan connector

48

Flame tube

50

Flame monitoring probe

52

Ignition electrodes

54

Tube

56

Protective sleeve

58

cap

60

Insulating bush

62

Connection nipple

64

Cap nut

66

Clamping ring

68

Connection contact

70

Casing pipe

72

insulation

74

Insulating plug

76

Connection contact

78

Sleeve

80

Heating cartridge

82

Connection

84

Connection

d

Inside diameter

L

length

L1

Heating length

L2

Evaporation length

L3

Superheat length

Claims (20)

Device for vaporizing liquid fuels, with a pipe through which the fuel is passed and the wall is electrically heated is to supply the heat of vaporization to the fuel, characterized in that the tube is a capillary tube (10), whose inside diameter (d) is 0.3 to 2.0 mm and its length (L) is 500 to 3000 times the Inner diameter (d). Device according to claim 1, characterized in that the inner diameter (d) of the capillary tube (10) 0.5 to Is 1.3 mm. Device according to claim 1 or 2, characterized in that that the length (L) of the capillary tube (10) the 900-bis 2300 times the inside diameter (d). Device according to one of the preceding claims, characterized in that the wall thickness of the capillary tube (10) 0.2 to 0.5 times the inside diameter (d) is. Device according to one of the preceding claims, characterized in that the capillary tube (10) as Heating conductor is designed and for direct heating electrical current passed through the capillary tube (10) becomes. Apparatus according to claim 5, characterized in that the capillary tube (10) consists of a CrNi steel. Device according to claim 5 or 6, characterized in that that at the ends of the capillary tube (10) a low voltage of less than about 50 V is applied. Device according to one of claims 5 to 7, characterized characterized in that the outlet end of the capillary tube (10) via a separate conductor (32) to the Voltage is applied. Device according to one of claims 5 to 7, characterized characterized in that the outlet end of the capillary tube (10) via a protective sleeve (56, 58) at ground potential is placed. Device according to one of claims 5 to 7, characterized characterized in that the capillary tube (10) by an electrical conductive jacket tube (70) and enclosed insulation (72) insulated against the casing tube (70) is that the casing tube (70) at the outlet end of the capillary tube (10) with this in an electrically conductive manner Connection is established and that the jacket tube (70) as an electrical Connection of the exit end of the capillary tube (10) serves. Device according to one of claims 1 to 4, characterized characterized in that the wall of the capillary tube (10) indirectly heated by an electrical resistance heater becomes. Device according to claim 11, characterized in that the capillary tube (10) with the outer surface of one Heating cartridge (80) is in contact or with the outer surface a thermally conductive sleeve (78) into which the Cartridge (80) is used. Device according to one of claims 1 to 12, characterized characterized in that the capillary tube (10) as a helical Spiral is bent. Device according to one of claims 1 to 12, characterized characterized in that the capillary tube (10) as a spiral is bent. Device according to one of claims 1 to 12, characterized characterized in that the capillary tube (10) with hairpin bends in parallel sections is bent. Use of a device according to one of claims 1 to 15 as a heating oil evaporator for aerosol formation with the Combustion air in premix burners. Use of a device according to one of claims 1 up to 15 as a heating oil evaporator for fuel-air mixture formation in burner heads for heat outputs below 10 KW. Use of a device according to claim 17 with a Air nozzle (36), the device (40) for acting which has combustion air with swirl. Use of a device according to one of claims 1 up to 15 larger than pilot and pilot burners in furnaces Services or in multi-stage module burners. Use of a device according to one of claims 1 up to 15 as a heating oil preheater for installation in pressure atomizer nozzle shafts.

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