Abstract:
A method for creating flames, wherein combustible powder material is injected into a gas stream ( 120 ) and the dispersed mixture of powder and gas is ignited and discharged through a nozzle ( 124 ). An arrangement suitable for implementing the method is also disclosed.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to a method and arrangement for producing special effects such as low-energy flames. 
       BACKGROUND 
       [0002]    Pyrotechnic effects producing large flames have been traditionally created by quickly burning large amounts of flammable liquid or gas. For example, explosion-like special effects may be achieved by dispersing a container filled with a flammable liquid with a small explosive charge. As a result the liquid is dispersed and ignited in the surrounding air, thereby creating a large fireball. A large special effect may correspondingly require very large amounts, e.g. tens or hundreds of liters of flammable liquid. 
         [0003]    Continuous large flames are typically generated by burning large volumes of some suitable flammable gas, e.g. butane or propane streaming out of a nozzle. By varying the flow rate of the gas and the nozzle properties, flames of various sizes and shapes can be created. 
         [0004]    Burning large volumes of flammable high-energy fuels such as gasoline or propane causes significant safety risks as lots of heat is released in the combustion process. This significantly limits the usability of such methods. For example, creating large flames indoors is very challenging and in many cases impossible because of the safety risks. 
         [0005]    Some solutions have been developed for producing small flame effects indoors, e.g. in theatres. These solutions are typically based on pyrotechnic compounds or burning e.g. black or smokeless gunpowder. These solutions are not completely risk-free as the smoke may be toxic and/or the compounds may explode in an uncontrollable manner. In addition, they require licenses and clearances to be used legally and are hazardous in storage and transport. 
         [0006]    In prior art solutions using flammable liquids or gases, the flame may be colored by e.g. adding color-donating salts into the liquid or gas. The resulting mixtures may develop toxic gases. For example, a green flame may be achieved by adding barium chloride into the fuel, e.g. methanol. Additionally, some source of chlorine, e.g. hydrochloric acid, may be needed to make the color more vivid. Chlorinated materials may generate e.g. phosgene which is toxic even in small amounts. 
         [0007]    Some power plants, e.g. those burning coal, are arranged to blow air into the middle of a fuel cloud comprising of coal dust. As a result, the coal dust burns as quickly and efficiently as possible releasing as much energy as possible. 
         [0008]    Publication JP2001132910 discloses a flame generator for achieving special effects. The generator consists of four nozzles that are arranged around an ignition device. 
         [0009]    Publication JP7052114 discloses a fireworks device that is capable of spreading the desired fireworks effect into a large area in a controllable manner. The publication discloses the use of saw dust in a fireworks device. 
         [0010]    Publication US2270443 discloses a method and device for altering color of a flame using some suitable powdered material. The flame in this disclosure is produced by burning some suitable gas as is generally known in prior art. 
         [0011]    Publication U.S. Pat. No. 6,953,401 discloses a device for simulating a flame effect. The flame simulation is achieved by creating a wall of fog onto which a suitable beam of light is projected. 
         [0012]    U.S. Pat. No. 5,756,920 discloses a flame cannon for producing an explosion-like effect. The cannon includes a tank, a valve, a nozzle and an igniter. The tank is coupled to a carbon dioxide and a propane source. 
         [0013]    Thus, numerous techniques for producing large flames e.g. for special effect purposes are known in the art. 
         [0014]    The objective of the present invention is to provide a method and arrangement for producing large low-energy flames by burning powdered material(s), such as a powder comprising fine particles. Another objective is to improve the safety of special effects with large flames. Yet another objective is to improve the controllability of special effect flames. 
       SUMMARY OF THE INVENTION 
       [0015]    The present invention discloses a method and arrangement for producing a low-energy flame using powdered materials. 
         [0016]    The method of the present invention is characterized in that combustible powder, e.g. some suitable powdered material is injected into a gas stream and the dispersed mixture of powder and gas is discharged through a nozzle and ignited. 
         [0017]    The gas stream may comprise a core and an envelope component. The gas flow in the core component may be faster than the flow speed of the envelope component. The gas flow in the core component may advantageously be at least slightly turbulent. Turbulence depends on the flow velocity. Especially when the flow velocity is low, a guiding structure may be applied to adjust the turbulence so as to maintain the flame stable and/or prevent it from going out. The gas flow in the envelope component may advantageously be laminar. 
         [0018]    The nozzle may comprise at least one static or moving structure that divides the gas flow into the core component and the envelope component surrounding the core component. 
         [0019]    The nozzle may comprise a component in which the diameter of the nozzle may expand by 100%, 200%, 300% or 500% allowing the diameter of the gas stream to expand while flowing through the nozzle. 
         [0020]    The nozzle may further comprise a cylindrical component. 
         [0021]    The nozzle may be arranged to comprise or be attached to some suitable means for igniting the mixture of gas and powder. The means may include e.g. an ignition flame, electric spark or an electric heating element. The amount of energy used by the ignition means may be adjustable. 
         [0022]    Preferably the utilized gas is relatively cold, e.g. below the autoignition temperature of the used fuel, and contains enough oxidant to burn a substantial portion of the powder and maintain the flame. 
         [0023]    The gas advantageously contains oxygen. Suitably, the gas may be air. 
         [0024]    The gas stream may be created using e.g. pressurized gas or a blower. The velocity of the gas stream may be adjusted to be suitable e.g. for the powdered material and/or nozzle used. 
         [0025]    The nozzle may comprise a means for generating turbulence in the gas stream. The turbulence may be advantageously generated such that it occurs in the core component of the gas stream. Further advantageously, creation of turbulence is avoided in the envelope component of the gas stream. 
         [0026]    The flow velocity of the gas stream at the nozzle exit may be e.g. at least about 1, 10 or 20 m/s. At maximum, the flow rate of the gas stream may be e.g. up to about 20, 50 or 100 m/s or more. Preferably, the flow velocity may be between about 5 and 20 m/s. 
         [0027]    The feed rate of powder material into the mixing chamber and/or nozzle may be e.g. at least about 20 g/s/m 3 , 200 g/s/m 3 , 2 kg/s/m 3  or 20 kg/s/m 3  calculated to normal pressure. 
         [0028]    The powder may be any suitable combustible powder, e.g. wood dust, potato flour, or wheat flour. It shall be noted that the heat of combustion of such powders are substantially lower than of conventional fuels. In general, any finely divided, combustible organic or inorganic material may be applicable as a powdered fuel. 
         [0029]    The minimum particle size (diameter) of the powder may be e.g. about 1, 5 or 10 micrometers. The maximum particle size of the powder may be e.g. about 20, 100, 500 or 1000 micrometers. 
         [0030]    In some embodiments, a bimodal powder comprising a finely divided and coarse grained component may be used. 
         [0031]    The powder may comprise additional particles or bodies suitable for producing additional effect in the flame. The additional effect may be e.g. a change of color of the flame or a pyrotechnic effect, e.g. an explosion. Such additional effects may also be achievable by injecting, e.g. via an applicable injector, some suitable liquid into the gas stream. Examples of such materials are granulate or pellets or the like comprising or consisting of a pyrotechnic composition, which ignites later in the flame creating e.g. small explosion-like effects along the length of the flame. The added particles may comprise easily ignitable metal powders creating bright sparks in the flame and enhancing the visual effect. The liquid may be a combustible or noncombustible liquid, which contains dissolved, color-enhancing materials coloring the flame to red, green, blue, lilac, violet, yellow or any other, desired color except black. The particles, bodies or liquid added may also generate smoke in the desired colors and/or they may produce any desired odour not normally obtained from burning fuels. 
         [0032]    The fuel-to-gas ratio (kilograms of fuel/cubic meters of air calculated to normal pressure) in the nozzle may be at maximum about 20 kg/m 3 , 10 kg/m 3  or 5 kg/m 3 . 
         [0033]    and at minimum 2 kg/m 3 , 1 kg/m 3 1/g or 0.5 kg/m 3 , or even less, for example. The suitable ratio depends e.g. on the powdered material used and its moisture content as well as on the carrier gas used. 
         [0034]    The components of the arrangement of the invention may be dimensioned and/or the feed rate of fuel and/or flow rate of gas may be adapted so as to produce a flame having a length of at least about 2, 3 or 4 meters. Basically the flame may range from about 0.1 to over 10 meters. 
         [0035]    The invention also concerns an arrangement that implements the method disclosed herein. 
         [0036]    As to the utility of the present invention, the inventors have surprisingly observed that the method and apparatus disclosed herein allow controlled, relatively slow burning of powdered material that according to prior art would either burn explosively or not ignite at all. Inventors believe that the flow of gas as disclosed in various embodiments of the invention contribute significantly to the phenomenon. The invention solves shortcomings of the prior art for example by creating flames that emit relatively low amount of heat since they burn at an unusually slow rate for the material. The invention may be applied to produce relatively large flames that can be safely used even by inexperienced operators and indoors. As a further benefit, fuel, which is not classified as hazardous material, may be used. 
         [0037]    Some embodiments of the invention are described herein, and further applications and adaptations of the invention will be apparent to those of ordinary skill in the art. 
     
    
     
       BRIEF DESCRIPTION OF RELATED DRAWINGS 
         [0038]    In the following, the invention is described in more detail with reference to the accompanying drawings in which 
           [0039]      FIG. 1   a  depicts an arrangement of an embodiment of the present invention, 
           [0040]      FIG. 1   b  is a combined block and flow diagram of an embodiment of the present invention, 
           [0041]      FIG. 1   c  is a flow diagram of an embodiment of the present invention, 
           [0042]      FIG. 2  depicts an exemplary nozzle of an embodiment of the present invention, 
           [0043]      FIG. 3  depicts an exemplary nozzle according to another embodiment of the present invention, 
           [0044]      FIG. 4   a  depicts a side view of an embodiment of the present invention, and 
           [0045]      FIG. 4   b  depicts a frontal view of the embodiment of  FIG. 4 . 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0046]      FIG. 1   a  illustrates a merely exemplary arrangement according to an embodiment of the present invention. The arrangement comprises a fuel silo/hopper  100  that is connected to an injector  102  through a connector  101 . The connector  101  may comprise a means  105 , such as a feeder, to control the flow rate of the fuel powder (e.g. wood dust) from the fuel silo  100  to the injector  102 . A gas flow is provided by blowing gas (e.g. air) into the injector  102  through an air valve  104 . In some embodiments, e.g. in those where the gas stream is provided by a fan, the air valve  104  may be optional. A dispersion of gas and fuel powder is lead from the injector  102  to the nozzle  103  in which it is ignited by an ignition means (see e.g.  FIG. 2  and related text) while being blown out of the arrangement to form a preferably low-energy flame. Alternatively, an ignition means external to the nozzle  103  may be applied. For example, the ignition means may be attached by a stand to the outer surface of the nozzle or other element of the arrangement and be aligned so as to enable igniting the dispersion exiting the nozzle  103 . 
         [0047]      FIG. 1   b  illustrates a combined block and flow diagram of an embodiment of the present invention. Broken arrows indicate gas flow, a thin arrow indicates the flow of fuel powder, thick arrows indicate the flow of gas/fuel dispersion, and a hollow arrow indicates the emission a flame. Fuel storage  100   b  such as the aforesaid silo is utilized for providing the fuel powder into a feeder/mixer block  102   b  wherein it is mixed with the gas provided thereto e.g. by a compressor or other feasible gas stream creation element  104   b  and optionally an intermediate transport pipe  106 . Subsequently, the dispersion is conveyed to the nozzle/ignition block  103   b , optionally via another transport pipe  108 . Control logic and optional safety circuit(s)  110  may be applied in controlling and monitoring the operation of various elements of the arrangement as indicated in the figure by the connecting lines. The logic  110  may include a microprocessor, a microcontroller, a programmable logic chip, an ASIC, etc. in addition to various data storage means such as a RAM/ROM memory chip. Power systems  112  may supply power to one or more elements by a battery, for instance. 
         [0048]      FIG. 1   c  discloses a flow diagram of a basic embodiment of a method in accordance with the present invention. Such method may be executed by an arrangement according to the present invention, such as the arrangement of  FIG. 1   a  or  1   b . At  120  the fuel powder is mixed with gas as described hereinbefore. Then the obtained dispersion is optionally adjusted as desired. For example, the stream may be divided into core and envelope components, and turbulence may be introduced thereto. At  124  the mixture is ignited and discharged through the nozzle, the actual temporal order of these actions being dependent on e.g. whether the ignition means is integrated in the nozzle (i.e. substantially simultaneous ignition and discharge) or implemented as a separate element (discharged first). A skilled person will appreciate the fact that the presented method may be supplemented with various additional phases and operations in view of the teachings provided herein. 
         [0049]      FIG. 2  illustrates a nozzle  200  (corresponding to e.g. nozzle  103  of  FIG. 1 ) of an embodiment of the present invention in more detail. The nozzle  200  is attached to a connector  201  through which the gas stream is flowing. In one embodiment, the length of the nozzle is about 150 millimeters and the outer diameter is about 50 mm. The connector  201  has a length of about 30 mm and inner diameter of about 15 mm. Inside the nozzle, there may be one or more structures or other arrangements  202 ,  203  to divide the gas stream into core and envelope components and optionally to cause suitable turbulence in the core component of the stream before the dispersed mixture is ignited using an ignition means  204 . 
         [0050]      FIG. 3  illustrates a nozzle  300  of another embodiment of the present invention depicted in two side view projections. The nozzle comprises a conical section  301  and a cylindrical section  302 . A structure assembled from perforated steel band ( 303 - 305 ) is attached to the cylindrical section. The width of the perforated steel band (e.g. “Patent Band”) may be e.g. about 1-2 cm. The structure comprises a connection means  303  that connects the structure to the cylinder section  302 . The guiding structure  304  divides the gas flow into core component and envelope component. The structure  305  causes slight turbulence to the core component of the gas stream consisting of mixture of gas and powder, e.g. wood dust, potato flour or wheat flour in air. 
         [0051]    Various features of the afore-explained embodiments relating to nozzles  200 ,  300  may also be modified and/or combined by a skilled person. 
         [0052]    In the following, few test results of using an embodiment described in  FIGS. 1 and 2  are provided. A butane torch (100 g/h) was used for igniting the mixture of fuel and air. A compressor capable of compressing air to pressure of up to 6 bar and a 20 liter tank were used as the source of air. Surprisingly, positive pressure of less than 1 bar gauge was needed in the tests. The inventors thus became convinced that suitable gas stream may also be achievable with a low-pressure blower, e.g. the one utilized in a common household vacuum cleaner. 
         [0053]    When operating the arrangement described in  FIGS. 1 and 2  using wood dust as fuel and fuel-to-air ratio of about 6 kg/m 3 , the arrangement produced a horizontally oriented flame of about 7 meters length. 
         [0054]    In the tests, the flame was burning for about 7-8 seconds, on average. Some test runs tried to maximize the burning time of the flame on same amount of fuel. In these test runs, the burning times were between about 10-12 seconds. At all times the flame died when the fuel ran out. Hence, it is evident that unlimited fuel and air supply would lead to an unlimited time of controlled burn. 
         [0055]    When operating the arrangement using wood dust (moisture content about 4.3%) and fuel-to-air ratio of about 3 kg/m 3 , the arrangement produced a horizontally oriented flame of about 3.8 meters length. 
         [0056]    When operating the arrangement using wheat flour (moisture content about 10%) and fuel-to-air ratio of about 10 kg/m 3 , the arrangement produced a horizontally oriented flame of about 3 meters length. 
         [0057]      FIG. 4   a  depicts a side view of an embodiment of the present invention. The arrangement comprises a fuel intake  400 , a feeder  405 , such as a rotary feeder, an air intake  404  comprising e.g. a blower, a mixer  402 , a nozzle  403 , a feeder motor  405   b , one or more pressure sensors  410  and a sensor air pipe  412  related thereto for precise control of the operational parameters (DATA refers to a pressure signal). An ignition means may be integrated, optionally removably, with the nozzle  403  (built-in, for example) or be external thereto. 
         [0058]      FIG. 4   b  depicts a frontal view of the same embodiment wherein one possible implementation of a rotary feeder  405   c  is shown in more detail (rotor shaft with vanes) on the left. Advantageously the overall construction of the arrangement is modular in a sense that various elements thereof are separable parts including the feeder  405 , the air intake  404 , the mixer  402 , and/or the nozzle  403 , for instance. Modularity enables changing individual elements to better fit each potential use scenario or upon a failure. 
         [0059]    As shown in the above examples, the embodiments of the present invention facilitate burning a powder comprising fine particles in a controllable manner. As only a relatively low amount of relatively low-energy fuel is needed to generate a large flame, the amount of energy (heat) released by the combustion is quite low. The controllability of the flame has been observed to be quite easy e.g. by controlling the feed rate of gas (air) and/or fuel. For example, changes in the fuel feed rate are practically immediately observable in the flame. Another advantage of the embodiments of the present invention is that, unlike the fuels of prior art solutions, the fuel usable in the various embodiments of the invention is safe to store, transport, handle and use. Typically, no permissions and/or special skills or caution is required when dealing with the fuel. Furthermore, the fuel usable in the embodiments of the invention is typically not classified as a hazardous material. 
         [0060]    The scope of the invention can be found in the following claims. Notwithstanding the various embodiments described hereinbefore in detail, a person skilled in the art will understand that different modifications may be introduced to the explicitly disclosed solutions without diverging from the fulcrum of the present invention as set forth in this text and defined by the independent claims. For example, selected features of different embodiments may be cleverly combined to come up with a new embodiment with desired properties.