Abstract:
A novel device is described for combusting a liquid or powdered fuel having an atomizer nozzle ( 2 ), which has a valve configuration ( 41 ) for the control of the supply of the fuel, a compressed air connection ( 4 ), a mixing chamber ( 38 ) for mixing the fuel with compressed air, and a nozzle opening ( 23 ) for atomizing a mist of fuel in compressed air. A supply line ( 28 ) for the fuel and a preheating apparatus ( 5 ) are provided, which are attached in a nozzle assembly surrounding the nozzle ( 2 ). Furthermore, air channels in a sheath ( 3 ) enclosing the preheating apparatus ( 5 ) and a fastening sleeve ( 13 ) having connection channels adjoining the air channels are provided, the sheath ( 3 ) forming a ring gap ( 21 ) for the supply and heating of the compressed air with the nozzle assembly ( 12 ) of the atomizer nozzle ( 2 ). Air supply lines ( 50 ) are provided in the nozzle body ( 20 ) originating from the ring gap ( 21 ) in such a way that the valve configuration ( 41 ) is activatable by the compressed air.

Description:
[0001]    The present invention is concerned with the field of combustion technology and relates to a device for combusting a liquid or powdered fuel having an atomizing nozzle, which has a valve configuration for controlling the supply of the fuel, a compressed air connection, a mixing chamber for mixing the fuel with compressed air, and a nozzle opening for atomizing a mist of fuel in compressed air. Furthermore, an apparatus is provided for preheating the fuel to a predetermined temperature, which is attached in a nozzle assembly surrounding the nozzle. The invention also relates to a method for combusting a fuel using the above-mentioned device. 
       PRIOR ART 
       [0002]    Such devices are generally known in the field of combustion technology and are operated, for example, using a compressed-air oil atomizer nozzle known from EP-A-0 566 855 or EP-A-0 731 315. In oil-operated heating systems, the heating oil to be combusted is sprayed at a pressure of several bar (approximately 5 bar) through a compressed-air atomizer nozzle into the burner chamber and atomized. To prevent the heating oil from dribbling due to the high pressure when the burner is shut down, in the above-mentioned publications, a diaphragm having a closing piston pre-tensioned by a compression spring (EP-A-0 566 855) or a diaphragm clamped between two springs (EP-A-0 731 315) is provided. 
         [0003]    These known devices are especially implemented for heating oil, which must maintain special qualities because of the environmental technology guidelines. In particular, it is not possible to combust other vegetable oils such as canola oil or also fat using such a device. 
       SUMMARY OF THE INVENTION 
       [0004]    It is the object of the present invention to improve such a device for combusting liquid fuels in such a way that it is possible to combust types of oils and fats other than heating oil. 
         [0005]    This object is achieved by a device having the features of claim  1  and by a method having the features of claim  6 . 
         [0006]    The essential finding of the present invention is that, in contrast to the typical compressed-air atomizer nozzles, the compressed air is used as an energy carrier and control medium for the valve configuration. The supply of liquid or powdered fuel may thus be performed at a lower pressure and thus a very precise control of the valve configuration may be achieved. The compressed air used for the control suctions the liquid or powdered fuel because of the partial vacuum, so that outstanding mixing and/or atomization of the fuel with the compressed air already occurs in the mixing chamber. 
         [0007]    Using the device according to the invention, various types of fuel and qualities of fuel may be combusted without any parts having to be replaced. Fuels having an admixture of up to 20% water may also be combusted without problems. If the compressed air is replaced by pure oxygen, a part of the water entrained as mist is decomposed and combusted, which results in a higher flame temperature. 
     
    
     
         [0008]    Further advantages of the invention result from the dependent claims and from the following description, in which the invention is explained in greater detail on the basis of an exemplary embodiment illustrated in the schematic drawings. In the figures: 
           [0009]      FIG. 1  shows a combustion device having an atomizer nozzle, a pre-heater, and a compressed air supply, 
           [0010]      FIG. 2  shows the atomizer nozzle of  FIG. 1  in greater detail, clamped in a nozzle assembly having a sheath, shortly before the valve is opened, 
           [0011]      FIG. 3  shows the same atomizer nozzle of  FIG. 2  having closed valve, 
           [0012]      FIG. 4  shows the same atomizer nozzle of  FIG. 2  with open valve, 
           [0013]      FIG. 5  shows the same atomizer nozzle of  FIG. 2  after the valve is closed, 
           [0014]      FIG. 6  shows a cross-section in the longitudinal direction through a flame pipe, 
           [0015]      FIG. 7  shows a cross-section in the transverse direction through the flame pipe of  FIG. 6 , 
           [0016]      FIG. 8  shows a pneumatic-hydraulic control scheme for the controller of the combustion device, and 
           [0017]      FIG. 9  shows a variant of the atomizer nozzle. 
       
    
    
     DESCRIPTION OF THE INVENTION 
       [0018]    The same reference numerals have been used in each case for the same elements in the figures and initial explanations relate to all figures, if not otherwise expressly noted. 
         [0019]      FIG. 1  shows a combustion device  1  having an atomizer nozzle  2 , a sheath  3  having a compressed air connection  4 , and an oil preheater  5 . The sheath  3  essentially encloses the oil preheater  5 , so that the compressed air which flows through the sheath  3  is simultaneously preheated by the preheater  5  to approximately the same temperature as the oil. The oil preheater  5  comprises a shaft  6  having a resistance heater  7  wound thereon and a plastic housing  8  for the terminals  9  for the heating coil. A fuel supply pipe  10  is mechanically connected to the shaft  6 . A connection sleeve  12  is screwed onto the oil preheater  5 , which carries the atomizer nozzle  2  on the other side using a screwed-on fastening sleeve  13 . The connection sleeve  12  is provided with a so-called volustat throttle  14  having a small flow-through hole  15 , in which the fuel pressure and the flow rate are decreased. Furthermore, a large-mesh filter  16  made of sintered metal is attached in front of the volustat throttle  14 . The pumping pressure of the oil is dissipated with the aid of the throttle  14  and simultaneously the desired oil quantity is metered as a function of the pumping pressure depending on the power demand. The throttle  14  may also be installed in the nozzle assembly directly after the oil pump. 
         [0020]    Further details of the atomizer nozzle  2  are shown and explained on the basis of  FIGS. 2 and 3 . An axially-symmetric receptacle chamber  21  is formed between the fastening sleeve  13  and the screwed-in nozzle body  20  of atomizer nozzle  2 . Viewed from this receptacle chamber  21 , an axial pocket hole  22  is shaped into the nozzle body  20 , which tapers at its base in a truncated cone up to a nozzle opening  23  of the nozzle body  20 . An axially-symmetric insert  24  is screwed into this pocket hole  22  of the nozzle body  20 . The rear end of the insert  24  facing away from the nozzle opening  23  has a front sleeve section  25 , which is inserted into the connection sleeve  12  implemented as the nozzle assembly and guided sealed therein. The seal is produced by an O-ring  26 . This O-ring  26  presses on the other side against the inner wall of an axial sliding chamber  27  of the connection sleeve  12 , in which a supply line  28  for the liquid or powdered fuel opens. 
         [0021]    Compressed air—shown by arrows  30 —is supplied in the receptacle chamber  21  of the fastening sleeve  13 . The receptacle chamber  21  then passes via air supply lines or holes  50 —see below—into an essentially cylindrical ring gap  31 , which is formed between the insert  24  and the nozzle body  20 , and which in turn passes because of the tapering in a truncated cone of the pocket hole  22  toward the nozzle opening  23  into a gap  32  essentially in the form of a truncated cone. The cylindrical ring gap  31  arises in that the diameter of the pocket hole  22  is somewhat greater than the diameter of the forward sleeve section  25  of the insert  24  facing toward the nozzle opening  23 . The gap  32  in the form of a truncated cone arises through a corresponding axial offset between the base in the form of a truncated cone of the pocket hole  22  and a front part of an axially-symmetric clamping element  33 , situated on the insert  24 , which is described below. The base of the pocket hole  22  is covered by guide channels—not shown here—running approximately tangentially to the nozzle opening  23 , as shown in FIGS. 2 and 3 of EP-A-0 566 855. The cylindrical ring gap  31  and the gap  32  in the form of a truncated cone thus together form an axially-symmetric intermediate space between the insert  24  and the nozzle body  20 . 
         [0022]    Viewed from the forward sleeve section  25 , a continuous axial hole  36  is shaped into a metal part  34  and, adjoining thereto, into the rear sleeve section  35  of the insert  24 , which is connected to the rear to the sliding chamber  27  and to the supply line  28  for oil. This axial hole  36  tapers at its other end, the end being enclosed by a ring wall  37 . The upper edge of the ring wall  37  is in the same plane as a ring shoulder  42  of the forward sleeve section  25 , so that a ring groove  38  implemented as a mixing chamber is implemented on the other side of the ring wall  37 , which is connected via radial holes or radial channels  39  to the cylindrical ring gap  31 . 
         [0023]    A disc-shaped diaphragm  41  lies on the upper edge of the ring wall  37 , which overlaps the ring groove  38  and has its edge resting on the ring shoulder  42  of the forward sleeve section  25 . The diaphragm  41  is clamped on its edge on this ring shoulder  42  using a clamping element  33 . This clamping element  33  is pushed into the forward sleeve section  25  using a press fit and thus fastened. This clamping element  33  is shaped in the form of a truncated cone toward the nozzle opening  23  in the area of the base of the pocket hole  22  of the nozzle body  20 , to form the gap  32  in the form of a truncated cone of the above-mentioned axially-symmetric intermediate space. 
         [0024]    A pocket hole  43  is shaped into the clamping element  33 , in which a closing piston  44  is retained so it slides. This closing piston  44  presses against the diaphragm  41  using a compression spring  45 . The compression spring  45  is supported on one side against the funnel-shaped floor of a pocket hole  46  in the closing piston  44  and on the other side against a funnel-shaped floor of the pocket hole  43 . In addition, a relief hole  48  leads out of this hole to the gap  32  in the form of a truncated cone, which is situated axially to the diametrically opposite nozzle opening  23  of the nozzle body  20 . 
         [0025]    Furthermore, holes  50  implemented as air supply lines are provided in the middle part  34  of the insert  24 , which lead from the receptacle chamber  21  to the ring groove  38 . These holes  50  connect the receptacle chamber  21  to the ring groove  38 , so that the compressed air  30  is directed directly onto the diaphragm  41 . 
         [0026]    The atomizer nozzle  2  is shown in  FIGS. 4 and 5  having the valve or the diaphragm  41  in the open state and in the closed state, respectively. 
         [0027]    A special flame pipe  55  is shown in  FIGS. 6 and 7 , which is fastened onto a typical fastening pipe (not shown here) using screws in the threaded holes  56 . The combustion device shown in  FIG. 1  has a typical mixing system—not shown further here—on the front side having ignition electrodes and is mounted having the atomizer nozzle  2  at the intake of the flame pipe  55 . As is obvious from  FIGS. 6 and 7 , the flame pipe  55  is largely tapered in the intake area  57  and is only screwed onto the fastening pipe at the protrusions  58 , which correspond to the internal diameter of the fastening pipe, so that the heat in the flame pipe is only transferred in a limited way to the fastening pipe. The flame pipe  55  is preferably produced from a ceramic material. Hot exhaust gases are supplied once again to the flame by the so-called recirculation gap between the flame pipe  55  and the fastening pipe. These exhaust gases are sucked back from the outside at the flame pipe  55  through the recirculation gap. More optimum exhaust gas values are achieved by the entrained gases. 
         [0028]    The flame pipe  55  may also be produced from metal and be internally lined with a felt made of fireproof ceramic fibers or with a vacuum-compressed and/or drawn internal pipe made of ceramic fibers. The sheath  3  (see  FIG. 1 ) is preferably also covered on the flame side with such a felt. This lining or felt prevents the spray mist from condensing on the relatively cold surface of the flame pipe  55  in the cold state. Furthermore, the felt insulates the flame pipe  55  and the sheath  3  from the hot flame, so that less material aging results. 
         [0029]      FIG. 8  shows a pneumatic-hydraulic control scheme for the combustion device  1  according to the invention. Regulating electronics  60  having a heater  61 , a feeler element  62 , and a thermostat  63  are provided in the retainer of the compressed air atomizer nozzle  1 . The thermostat  63  is connected to a time delay  64 . A double diaphragm compressor  66  on one hand and an oil pump  67  on the other hand are driven using a motor M. A solenoid valve  69  and a compressed air monitor  70  and a compressed air regulator  71  are provided in the compressed air supply line  68 . A solenoid valve  73  is provided in the oil supply line  72 . 
         [0030]      FIG. 9  shows a variant of the atomizer nozzle  2 . Identical elements are identified using identical reference numerals and are not explained further here. An axially-symmetric clamping element  33 ′ is fastened in the pocket hole  22 ′ of the nozzle body  20 ′, which, with the base of the pocket hole  22 ′, forms a gap  32 ′ in the form of a truncated cone having guide channels running tangentially to the nozzle opening  23 ′. The closing piston  44 ′ is now implemented having a peripheral ring groove  82 , in which an O-ring  83  is inserted, which completely seals the gap between closing piston  44 ′ and clamping element  33 ′. Instead of the diaphragm  41  of the embodiment of  FIG. 1 , a sealing disc  84  made of rubber is now inserted in a recess  85  in the form of a circular disc, which forms the valve. Holes  50 ′ implemented as air supply lines and situated parallel to the axial hole  36 ′, which lead to the ring groove  38 ′, are now provided in the middle part  34 ′ of the insert  24 ′. This ring groove  38 ′ passes into a ring groove  86  in the form of a truncated cone toward the center, which is sealed by the sealing disc  84 . This sealing disc  84  simultaneously seals the axial hole  36 ′, which is used for the oil supply. 
         [0031]    The mode of operation of the combustion device  1  may be explained as follows on the basis of the figures: 
         [0032]    When the burner receives a pulse to start the combustion procedure, fuel is firstly heated in the nozzle assembly using oil preheater up to a temperature of at most 80° C., to prevent the oil from coking. After release by the thermostat  63 , the time relay  64  is activated using a settable delay time. For easily ignitable oils such as petroleum, the delay time may be set to zero, so that the burner starts immediately. For less flammable fuels such as vegetable oils, the delay time may be set to several minutes so that the generated heat may propagate over the volustat throttle  14  up to the nozzle  2 . After the set time has passed, the burner is started. 
         [0033]    During the preliminary flushing time of the burner, the compressed air is built up using the double diaphragm compressor  66  and is then available at the solenoid valve  69 . When the control mechanism of the burner gives the start release, the solenoid valve  69  is opened. The compressed air then flows in the direction of nozzle  2 . In order that the compressed air does not cool down the fuel to be atomized, it is guided on the oil preheater  5  in the sheath  3 . The preheated air is available at the valve or at the diaphragm  41  of the nozzle  2 . As soon as the pressure of the compressed air is greater than the counter pressure exerted by the closing piston  44  and the compression spring  45  on the diaphragm  41 , the valve or the diaphragm  41  is opened and the oil flows into the ring groove  38  implemented as a mixing chamber, so that air and oil are mixed and the oil is entrained by the outflowing air. The partial vacuum generated at the nozzle opening  23  also additionally acts on the closing piston  44  and thus on the diaphragm  41 . The fuel flowing out of the valve is entrained by the air flowing past and caused to rotate shortly before the nozzle outlet by tangential channels (as also known from FIGS. 2 and 3 of EP-A-0 566 855). An extremely fine fuel mist, which is similar to a gas, arises through this rotation and the forward flow of the fuel-air mixture as it leaves the nozzle opening  23 . Due to this fine misting or gasification, the poorly flammable mixture has become easier to ignite. The ignited mixture thus burns better, because the flame is not only supplied with air from the outside, but rather the compressed air which is used for atomization now also reacts from the flame middle toward the outside, which significantly accelerates the combustion. The combustion preferably occurs in a flame pipe  55 , which advantageously comprises a ceramic. The exhaust gases exiting from the flame pipe  55  have no unburned residues and thus do not require any post-combustion. 
         [0034]    It is obvious to one skilled in the art that the mode of operation of the atomizer nozzle according to  FIG. 9  is similar. The closing piston  44 ′ is also moved by the partial vacuum toward the nozzle opening  23 ′ and the valve is thus opened. 
         [0035]    The flame pipe  55  may be set using an adjustable recirculation gap on the fastening pipe, by which the combustion may be additionally optimized.