EP0028025B1 - Method and device for the production of microdroplets of liquid - Google Patents

Description

The invention relates to a method for producing micro-liquid droplets, in which a liquid is injected through an opening into a swirl chamber and from there is passed into a transport or reaction space, in which the liquid is acted upon by an external gas flow, the flow path of which is concentric and helical runs to the axis of the opening opening into the reaction space, and a device for carrying out such a method and the use of the method or the device for the combustion of oil.

Such a method and such a device, inter alia for the combustion of oil, are known from US-A-4120 640. In the known solution, the liquid is injected into the reaction space in a very compact spray cone, which opens only insignificantly, the opening opening into the reaction space being surrounded by a concentric ring which leaves an annular space between itself and the inner wall of the reaction space, into which a nozzle for the external gas flow opens. The gas flow accordingly already causes an outer zone with excess pressure in this annular space, which is essentially maintained over the entire length of the reaction space, as a result of which the spray cone is literally held together and deposits of liquid droplets on the inner wall of the reaction space can be reliably avoided. On the other hand, the consequence of this construction is that the reaction space has to be built relatively long in order to obtain a reasonably satisfactory atomization of the injected liquid.

In contrast, the present invention is based on the object of providing a method and a device of the type mentioned at the outset which permit extremely fine atomization of the liquid injected into the reaction space, even in the case of an extremely short reaction space.

This object is achieved procedurally in that a hollow-cone-shaped flow profile is formed in the vortex chamber, which undergoes an additional widening in the subsequent reaction space as a result of a negative pressure immediately behind the inlet opening into the reaction space.

The measures according to the invention achieve a spontaneous fanning out of the liquid injected into the reaction space, which results in a correspondingly fine atomization. The hollow spray cone introduced into the reaction space is literally pulled apart in the radial direction by the negative pressure which forms immediately behind the inlet opening, which leads to an extremely rapid increase in surface area, which leads to the fine atomization mentioned over a very short distance. The external gas flow prevents, in a manner known per se, that liquid droplets are deposited on the inner wall of the reaction space and lead to incrustations.

From US-A-3 758 259 and DE-A-2 356 229 it is known in each case to set the liquid emerging from a nozzle in rotation by an external gas flow, so that the liquid assumes a tubular or hollow-conical flow profile , whereby a relatively uniform fine atomization of the emerging liquid is obtained (see, for example, DE-A-2 356 229, page 2, paragraph 3). Moreover, in the known solutions, however, no provisions are made for an additional spontaneous fanning out of the hollow-cone-shaped flow profile after exiting the nozzle, which leads to an even finer atomization at an extremely short distance.

Surprisingly, the effects according to the invention also occur when the liquid is injected into the swirl chamber with only low pressure and from there into the reaction space.

Preferred developments of the method according to the invention are described in more detail in claims 2 to 5, wherein the measures according to claim 5 result in an even greater refinement of the liquid droplets. In this embodiment, the gas flow is characterized by two superimposed rotational movements.

In terms of the device, the object is achieved by the measures according to claim 6, with advantageous constructive developments of the device according to the invention being described in more detail in claims 7 to 11.

wobei c eine Konstante ist. Die Prozeßzeit t ist die notwendige Aufenthaltsdauer im Reaktionsraum, wobei bei der Erfindung diese Aufenthaltsdauer auch bei einem sehr kurz gebautem Reaktionsraum eingehalten werden kann. Trotz der kurzen Baulänge der erfindungsgemäßen Vorrichtung läßt sich eine praktisch rückstandsfreie Verbrennung erzielen mit extrem niedrigen Anteilen an CO, NO_x und CH_x. Die Verbrennung kann gefahrlos in einen offenen Raum erfolgen.The method according to the invention and the device according to the invention are particularly suitable for the combustion of oil. It is generally known that the smaller the droplets of the combustion liquid (oil), the faster and more complete the combustion. The relationship between the process time t (combustion time) and the droplet diameter d is as follows:

where c is a constant. The process time t is the necessary length of stay in the reaction space, and in the invention, this length of stay can also be maintained in a very short reaction space. Despite the short overall length of the device according to the invention, a practically residue-free combustion can be achieved with extremely low proportions of CO, NO _x and CH _x . The combustion can take place safely in an open space.

The method according to the invention is described below with reference to the preferred exemplary embodiments of the invention according to the invention, which are shown schematically in the accompanying drawings Device explained in more detail ..

• Figur 1 eine Vorrichtung gemäß der Erfindung im Schnitt,
• Figur 2 eine Anordnung der Vorrichtung gemäß Fig. 1 in einem Wärmetauscher und
• Figuren 3 und 4 graphische Darstellungen zur Demonstration der vorteilhaften Wirkung der Vorrichtung gemäß Fig. 1.

Show it :

• 1 shows a device according to the invention in section,
• Figure 2 shows an arrangement of the device of FIG. 1 in a heat exchanger and
• FIGS. 3 and 4 are graphical representations to demonstrate the advantageous effect of the device according to FIG. 1.

1 comprises a swirl chamber 12, into which a nozzle 10 opens, and a reaction chamber 20, which directly adjoins the swirl chamber 12. The liquid 15 emerging from the nozzle 10 is set in rotation in the swirl chamber 12 by an external gas flow 13, so that the liquid in the swirl chamber 12 assumes a hollow-cone-shaped flow profile. This hollow-cone-shaped flow profile passes through an opening 22 located opposite the nozzle 10 from the swirl chamber 12 into the downstream reaction chamber 20, where it experiences a spontaneous additional expansion due to a negative pressure immediately behind the inlet opening 22 into the reaction chamber 20. This fanning out is identified in FIG. 1 by the reference number 19. 1, the reaction space 20 is pot-shaped, the inlet opening 22 being arranged centrally in the end face of the reaction space 20. At a distance from the inlet opening 22, several gas inlet openings 24 are provided approximately uniformly distributed over the circumference and are inclined to the radial in order to impart a predetermined screw movement through the reaction space 20 to the gas flow 21. The inner diameter of the pot-shaped reaction space 20 can be dimensioned such that the outer gas flow 21 practically no longer acts on the inner surface of the side wall 28. This eliminates the risk of deposits of liquid droplets 19 or their reaction products on the inner surface of the side wall 28. Such deposits would lead to a change in the flow conditions and would require cleaning of the reaction space 20 after a certain period of operation.

In order to be absolutely certain that the droplets do not deposit on the inner surface of the side wall 28, gas inlet tubes 30 projecting beyond the inner surface of the side wall 28 are inserted into the openings 24 (FIG. 1).

To adapt to different droplet sizes, reaction times of the droplet material, etc., it can be advantageous if the tubes 30 are slidably inserted within the openings 24 so that the length of the part projecting beyond the inner surface of the side wall 28 can be changed. The easiest way to solve this problem is to screw the tubes 30 into the openings 24.

Finally, it is also conceivable to change the jet directions of the openings 24 or the tubes 30 for the purpose of adapting to different droplet sizes, etc.

It has been found that a negative pressure is formed in the annular space between the closed end face of the pot-shaped reaction space 20 and the inlet 24 or 30 for the external gas flow 21, which spontaneously pulls the hollow-conical flow profile emerging from the opening 22 radially outwards or expands, whereby an extremely fine atomization is obtained. The outer gas flow 21 supports this atomization and at the same time prevents liquid droplets 19 from being deposited on the inner surface of the side wall 28.

In order to additionally increase the fanning out of the liquid droplets introduced into the transport space, a distributor body 32 is arranged at a distance in front of the inlet opening 22, the side of the distributor body facing the opening 22 being flat. Depending on the external parameters, such as gas entry speed, droplet size, etc., the plane of the distributor body 32 facing the opening 22 can also have a convex or conical shape.

The distributor body 32 thus favors rapid mixing of the droplets with the gas flow 21, the degree of mixing being able to be set by the shape of the distributor body 32. The distance between the distributor body 32 and the opening 22 also has an influence on the degree of mixing or fanning out of the liquid droplets introduced into the reaction space. To vary the degree of mixing or fanning out, the distributor body 32 is therefore preferably mounted so that it can be moved back and forth in the direction of the longitudinal axis 9 of the reaction space 20. Good results can be achieved if the distributor body 32 lies in a plane between the inlet opening 22 and the plane defined by the gas inlet tubes 30 close to the same. The distributor body 32 promotes, in particular, the uniform distribution of the introduced droplets 19 over the cross section of the reaction space 20. The distributor body 32 thus prevents local droplet accumulations, so that uniform mixing into the gas stream 21 is achieved. In the embodiment shown in FIG. 1, the distributor body 32 is attached to a rigid wire. However, other fastening options are also conceivable, but care must be taken that the fastening means do not adversely affect the flow, in particular the swirl movement of the gas-droplet flow in the reaction space 20. If the reaction chamber 20 is to serve as a combustion chamber, an ignition device 36 is preferably provided in the area of the droplet inlet opening 22 in order to burn the liquid droplets, e.g. B. oil droplets to start.

In the embodiment according to FIG. 1, the swirl movement of the gas flow 13 in the swirl chamber 12 is obtained by gas guide means 16 arranged on the outer periphery of the nozzle 10 obliquely to the longitudinal axis of the nozzle, whereby as Gas guide means baffles or swirl grooves arranged on the outer circumference of the nozzle 10 can serve. The vortex chamber 12 is frustoconical, the smaller end face being formed through the inlet opening 22 into the reaction space 20.

In FIG. 2, the unit according to FIG. 1 is used as an oil burner and is identified by the reference number 41. The burner 41 is attached to the upper end of an upright heat exchanger 42, the reaction space 20 projecting slightly into an exhaust gas space 43. In the application example shown schematically in FIG. 2, the reaction chamber 20 serves as the combustion chamber, the flame 44 knocking somewhat out of the combustion chamber 20. The hot combustion gases are passed through the exhaust gas space 43 in accordance with the arrows 45, a tubular radiation body 34 being arranged concentrically on the inside of the exhaust gas space 43 away from the burner. The outer diameter of the tubular radiation body 34 is slightly smaller than the inner diameter of the exhaust gas space 43, which is also tubular in the embodiment shown. Both the radiation body 34 and the wall of the exhaust gas space 43 are preferably made of heat-resistant metal (steel) and have a dark, preferably black color, so that they serve as ideal radiation bodies. The additional radiation body 34 and the exhaust pipe delimiting the exhaust gas space 43 promote the heat exchange between the hot combustion gases and the environment, in the present case a heat exchange medium 38 which is guided past the exhaust pipe.

Heat is exchanged by convection between the hot combustion gases and the exhaust pipe and in particular the black radiation body 34. The heat absorbed by the exhaust pipe and / or radiation body 34 is emitted again by radiation to the environment or to the heat exchange medium 38 and transported through this to another location.

In addition to the tubular radiation body 34 or instead, black radiation bodies, which are flushed by the hot combustion gases, can also be arranged behind the outlet of the exhaust pipe or in the gas guide channels 46 extending through the heat exchanger 42. The shape of the radiation body can e.g. B. be egg-shaped. However, tubular radiation bodies can also be used again. Care must, of course, be taken to ensure that the arrangement of the radiation bodies in the gas guide channels does not cause excessive pressure drops.

The black radiation bodies are made of metal, preferably of heat-resistant, stainless steel. But they can just as well be made of ceramic or stone. The material depends on the gas flowing around the radiation body or the chemical and / or physical reactions taking place in the reaction space 20.

If the radiation bodies are arranged relatively far from the combustion flame, the flame temperature and thus the combustion are not influenced by the radiation bodies.

If the radiation bodies are arranged in the immediate vicinity of the flame or the reaction site, the radiation bodies, which are heat to the outside, ie. H. dissipate to the environment, achieved a cooling effect that z. B. results in the reaction speed being reduced or a reaction not taking place at all (e.g. cracking processes).

In some chemical or physical processes, it may also be necessary to add heat from the outside to allow the reactions to take place. Up to now, this has usually only been accomplished by heating the reaction space by means of a heater or the like. It has now been shown that the heat transfer from the outside into the reaction space can be considerably intensified by using the radiation bodies described above in the reaction space. The radiation bodies arranged in the reaction space enable additional heat to be supplied by means of heat radiation.

The radiation bodies are also particularly suitable for the controlled afterburning of exhaust gases in an exhaust duct. For this purpose, the radiation bodies are arranged in the exhaust duct at a suitable distance from the combustion flame and heated from the outside by heat radiation. The heat then emitted from the radiation body by convection to the exhaust gases causes the exhaust gases to re-ignite, so that complete combustion is achieved before the exhaust gases exit to the outside.

As can be clearly seen from the above statements, the described invention is particularly suitable for an oil burner. Therefore, the conditions in an oil burner and the advantages achieved by the solution according to the invention are discussed in detail again below.

wobei

• m = die Massendurchflußrate pro Masseneinheit eines Tröpfchens,
• d = der Tröpfchendurchmesser,
• cy = die Konzentration des « Öldampfes » an der Tröpfchenoberfläche
• c_f = die Dampfkonzentration in der Flamme, = die Dichte des Öls bei Tropfentemperatur, und
• β = der Transferkoeffizient für den Dampf bedeuten.

There are many methods to reduce soot formation in an oil burner. Some of these methods are e.g. B. in a publication by Peterson and Skoog "Stoftbildning vid oljeeldning", Stockholm, 1972, described in more detail. The known methods relate primarily to the use of heavy oils. Among these known methods, the use of an emulsion of oil and water has been found to be the most suitable. However, this process cannot avoid the formation of small soot particles that lead to aggressive SO ₃ concentrations if light oils are used as fuel. The development of these small soot particles, which are dangerous for human lungs, can be improved by improving the ver burning can be reduced. The combustion intensity or mass flow rate that is burned per unit mass of oil can be defined as follows:

in which

• m = the mass flow rate per unit mass of a droplet,
• d = the droplet diameter,
• cy = the concentration of the «oil vapor» on the droplet surface
• c _f = the vapor concentration in the flame, = the density of the oil at drop temperature, and
• β = the transfer coefficient for the steam.

• a) einer Reduzierung des Tröpfchendurchmessers,
• b) einer Zunahme des Wertes von cy, der durch Erhöhung der Öltemperatur, z. B. durch Vorwärmung, erhöht werden kann, und
• c) einer Erhöhung des Wertes von ß, der durch folgende Gleichung bestimmt wird :
  
  wobei
  • D = der Diffusionskoeffizient,
  • p_f = der Partialdruck entsprechend dem Wert von c_Y, und
  • p_tot = der Gesamtdruck'in der Brennzone bedeuten.

It can be seen from equation (1) above that the combustion intensity increases with:

• a) a reduction in the droplet diameter,
• b) an increase in the value of cy caused by increasing the oil temperature, e.g. B. can be increased by preheating, and
• c) an increase in the value of ß, which is determined by the following equation:
  
  in which
  • D = the diffusion coefficient,
  • p _f = the partial pressure corresponding to the value of c _Y , and
  • p _tot = the total pressure in the firing zone.

The application of equation (2) is limited to the case in which there is no influence of a relative movement between the droplet and the environment.

• - kleine Öltröpfchen,
• - höhere Temperaturen des die Tröpfchen umgebenden Mediums, meist Luft.

As can be seen from equation (2), the value β - and consequently the value m - can be increased by increasing the temperature of the environment around the oil droplet, usually the air atmosphere, since the value of D is temperature-dependent and dD / dT> 0 is. The droplet size is therefore of great importance, since smaller droplets lead to a higher value of β. To summarize, it follows that the combustion can be improved by

• - small droplets of oil,
• - higher temperatures of the medium surrounding the droplets, mostly air.

These two first conditions are optimally met by the device described.

The third condition can also be met very simply by preheating the oil to be burned.

As has already been explained in detail above in connection with the reaction chamber 20, the formation of a negative pressure according to the invention immediately behind the liquid inlet opening 22 and screw movement of the liquid droplets through the reaction chamber achieves a sufficient residence time for the droplets in the reaction chamber 20 for complete combustion (0, 01 s), although the reaction space 20 is very short. The short construction of the reaction space 20 has the additional advantage that heat radiation losses in the area of the reaction space are correspondingly low.

Despite the short construction of the reaction space 20, complete combustion in this space is thus ensured in the solution according to the invention.

Experiments have shown that the soot formation when using the method according to the invention or using the device according to the invention according to FIG. 1 is almost zero. It has proven to be advantageous if, when the atomizer chamber and reaction chamber are arranged one behind the other, about 15% of the compressed gas available is introduced into the atomizer chamber and 85% into the transport chamber. The speed of the compressed gas introduced into the transport space, e.g. B. air, is preferably between about 50 to about 150 m / second. These values have proven to be particularly advantageous, in particular excess air is avoided, which leads to undesirable SO ₃ formation. A low SO ₃ formation also results in a decrease in soot formation, as already described by Gaydon et al in the publication «Proc. of Royal Society », London, 1947.

A few words about the formation of nitrogen oxides should be mentioned below. Nitrogen oxides (NO _x ) are particularly dangerous for animals and humans. For this reason, laws in many countries require that the nitrogen oxide concentration in exhaust gases must not exceed a certain value. In Germany, the nitrogen oxide concentration in oil burners (fueled with heavy oil) must not exceed 500 ppm in the exhaust gas.

• - dem Anteil von Stickstoffatomen in den Öl bildenden Substanzen. Etwa 50 % der Stickoxide, die bei der Verbrennung entstehen, stammen unmittelbar von den Öl bildenden Komponenten,
• - der Bildung von Stickoxiden bei der Verbrennung.

The formation of nitrogen oxides is a consequence of

• - The proportion of nitrogen atoms in the oil-forming substances. About 50% of the nitrogen oxides that are generated during combustion come directly from the oil-forming components,
• - The formation of nitrogen oxides during combustion.

• - eine Erhöhung der Flammentemperatur vermindert die Entstehung von NO,
• - geringer Luftüberschuß fördert die Bildung von NO,
• - die Bildung von NO ist sehr stark abhängig von der Zeit, die für die Bildung zur Verfügung steht. Es wird in diesem Zusammenhang auf die Fig. 9 hingewiesen, in der die Entstehung von NO in Abhängigkeit von der Verweilzeit der Verbrennungsgase im Brennraum graphisch dargestellt ist. Aus Fig. 9 geht auch hervor, daß die Entstehung von NO von der Brennlufttemperatur abhängt.

The latter produces NO and N0 ₂ . The formation of NO has been intensively investigated. The following results were obtained:

• an increase in the flame temperature reduces the formation of NO,
• - low excess air promotes the formation of NO,
• - The formation of NO is very dependent on the time available for the formation. In this connection, reference is made to FIG. 9, in which the formation of NO as a function of the residence time of the combustion gases in the combustion chamber is shown graphically. 9 also shows that the formation of NO depends on the combustion air temperature.

When using the unit of FIG. 1 as Due to the small design (extremely short reaction space 20), oil burners have a correspondingly short dwell time for the combustion gases. Furthermore, the burning time is reduced to a minimum even due to the extremely small liquid or oil droplets. The residence time of the droplets and exhaust gases in the unit according to FIG. 1 is approximately 0.07 seconds. According to FIG. 3, approximately 20 ppm NO are formed when the unit according to FIG. 1 is used as an oil burner. With this short dwell time, it hardly matters if the combustion air is preheated. As has been explained above, preheating the combustion air improves the combustion itself or the combustion intensity.

In Fig. 4, the NOx values of an oil burner designed according to the invention are shown again schematically compared to conventional oil burners, depending on the oil flow rate (1 / h) and the oxygen content during combustion.

The use of the device according to FIG. 1 with an atomizer unit and reaction unit as an oil burner thus leads to an optimal, soot-free combustion with extremely low excess air with an efficiency of at least 92%.

Claims (12)

1. Process for production of micro liquid drops in which a liquid is injected through an opening into a swirl chamber (12) and passed from there into a transport or reaction space (20) in which the liquid is charged by an external flow of gas (13), the flow path of which is concentric and helical-shaped relative to the axis of the opening (22) merging into the reaction space (20), charac_- terized by the fact that a hollow cone-shaped flow pattern is formed in the swirl chamber (12), which is subject to an additional enlargement in the subsequent reaction space (20) due to a vacuum directly after the inlet opening (22) into the reaction space (20).

2. Process according to claim 1, characterized by the fact that the direction of the gas flow in the reaction space is selected identical to that in the upstream swirl chamber.

3. Process according to claim 1, characterized by the fact that the direction of the gas flow in the reaction space is selected opposite to that in the upstream swirl chamber.

4. Process according to one of claims 1 to 3, characterized by the fact that the gas is introduced into the swirl chamber and/or transport space at a distance from the inner surface of the wall of the space in such a way as to reliably avoid contact of the liquid drops with the inside of the walls of the space.

5. Process according to one of the claims 1 to 4, characterized by the fact that the gas executes a self-swirling or rotational motion along its flow path.

6. Device for the production of micro liquid drops in accordance with the process according to one of the claims 1 to 6 with a nozzle merging into a swirl chamber (12) and a transport or reaction space (20) adjoining the swirl chamber (12) with a gas inlet for a gas flow, the flow path of which is concentric and helical-shaped relative to the axis of the opening (22) merging into the reaction space (20), characterized by the fact that several holes (24) or similar extending inclined to the radial are provided at the side wall (28) forming the side confines of reaction space (20) at a distance from the inlet opening (22) for the input of gas.

7. Device according to claim 6, characterized by the fact that a tube (30) extending beyond the inner surface of the side wall (28) is inserted into the hole (24) so as to reliably avoid contact of the liquid drops borne by the helical gas flow with the inside of the side wall as they are transported throught the transport space.

8. Device according to claim 7, characterized by the fact that the length of the tube(s) (30) extending into the transport space (20) can be varied.

9. Device according to one of the claims 6 to 8, characterized by the fact that the hole (24) is also angled slightly in the direction of flow.

10. Device according to one of the claims 6 to 9, characterized by the fact that a distributor element (32) is provided in the reaction space (20) at a distance from the inlet opening for the drops (22), which is designed to radially disperse and uniformly distribute the drops introduced into the reaction space (20) over the cross section of the space.

11. Device according to one of the claims 6 to 10, characterized by the fact that dark, preferably black radiation elements (34) are provided after the reaction space (20), which dissipate to the surroundings by means of radiation the heat absorbed by means of convection by the drop/gas mixture or reaction gas, respectively, with the radiation elements being formed preferably by a tube section arranged concentrically in a duct (42) following the reaction space (20). ^-

12. Application of the process according to one of the claims 1 to 5 or of the device according to one of the claims 6 to 11 for the combustion of oil.

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