JP2009541710A - Fixed fuel stove with improved combustion - Google Patents

Abstract

  The present invention relates to a solid fuel stove including a combustion chamber (12) for containing combustion fuel and a blower assembly (50) configured to provide an air flow entering the combustion chamber in an operating condition. When the guide means (40) establishes an air flow that enters the combustion chamber substantially downward, the stove combustion process is very clean and efficient.

Description

  The present invention relates to a cooking stove with improved fuel. Specifically, the present invention relates to a cooking stove that can burn fixed fuel, such as wood, using forced intake air circulation in a combustion chamber.

  It is estimated that about 250 million people around the world burn wood for cooking. Known stoves and processes are typically inadequate, have incomplete combustion, and contribute to substantial smoke emissions and global warming processes. Many deaths can be attributed to such contaminated smoke emissions. In addition, poorly efficient wood stoves use more natural timber sources and result in deforestation.

  In domestic combustion of wood, air pollution occurs due to incomplete combustion of volatile materials released from the wood. Volatile inorganic compounds are released from the wood at temperatures similar to room temperature, and a substantial rapid release only begins when the exothermic reaction begins (250 ° C.). Volatile materials form a complex mixture of combustible gases. The starting temperature for combustible gas mixing is about 600 ° C. Many of the unburned volatiles released from the wood condense to form fine particles when cooled to near ambient temperatures. This is what we call wood smoke. Incomplete combustion of volatile materials occurs for several reasons. When a wood bundle is added, the heat from the coal and equipment immediately releases the gas from the wood. When lit, the burning paper and ignition bring heat. If volatiles are not exposed to a high temperature source (flame or red hot charcoal), they will not ignite and rise through the flue / chimney and move the contamination. If the gas ignites, it can be extinguished if it is cooled by a cooling surface (eg, a metal wall of a cooling firebox) or cooling combustion air. If the combustible gas is not well mixed with air (oxygen), it will not burn. If the combustion air is reduced to slow down the combustion rate, there may be insufficient air for complete combustion.

  GB2125160 describes a cooking stove with a combustion air chamber in which combustion air is drawn from outside the stove by natural convection or by a manually operated air pump or a combination of both. Air enters the combustion chamber through one or more holes in the bottom of the combustion chamber.

  The aim is to provide a solid fuel stove that enables a clean combustion process.

  In accordance with the present invention, a combustion chamber for containing combustion fuel, including a lower side portion for containing fuel and an upper side portion, and an air flow entering the combustion chamber in an operating state are provided. A blower assembly and guide means for directing the air flow into the combustion chamber, the guide means being provided with a solid fuel wood stove for directing the air flow from the upper side to the lower side.

  The stove according to the invention has proven to result in a very clean combustion process. A cleaner combustion process reduces emissions of both harmful combustion gases such as carbon monoxide (CO) and condensed volatile inorganic compounds. The special air flow as created by the guide means allows the combustion gases in the hot combustion chamber to burn completely before finally leaving the combustion chamber, thus improving the cleanliness of the combustion process. When a lateral or upward air flow is established in the combustion chamber, there is a risk that the combustion gas is caused by such air flow outside the chamber before the combustion gas is completely combusted. This is especially true when such gases reach the higher part of the combustion chamber where the temperature is relatively low. The air flow according to the invention produces a kind of turbulent mixture, which is clearly very advantageous for complete combustion. There is more time for the combustion gases in the combustion chamber to burn completely before finally leaving the combustion chamber. As is generally known, complete combustion means clean combustion. Detailed measurements using a stove according to the present invention show reduced levels of residual smoke and volatile inorganic materials. An additional advantage is that the flame does not touch the cooking container placed on the stove longer, allowing a significant reduction in the level of soot on the cooking container. The guiding means may have a relatively simple structure that does not complicate the stove design. Of course, apart from the blower assembly, other sources of air can enter the combustion chamber, such that air enters by (convective) open upper side or through lower side openings by natural convection. If the air flow in the combustion is directed substantially from the upper side to the lower side, the combustion process is very clean, as shown by some experiments.

  According to a preferred embodiment, the guiding means comprises a plurality of holes provided in the wall of the combustion chamber on the upper side. By providing the hole, a simple but effective guide means can be obtained. It is particularly preferred if the upper edge of the hole is inclined inward with respect to the combustion chamber and the lower edge of the hole is inclined outward with respect to the combustion chamber. This structure is advantageous with respect to manufacturability in the case of relatively thin walls. This is because it is easier to deform the wall around the hole. In another preferred embodiment, the holes comprise perforations having an inclined pitch with respect to the wall. Such holes are easier to manufacture in the case of relatively thick walls.

  Furthermore, it is preferred if the holes are distributed substantially evenly along the contour of the combustion chamber. This improves the combustion process while the opposing air flow impinges somewhere in the center of the combustion chamber, resulting in a turbulent mixture.

  It is also advantageous if each hole is located away from the upper side. This has the advantage that the flame does not directly contact the cooking utensil placed on the stove, thereby preventing the formation of soot on such cooking utensils.

  According to another preferred embodiment, the guiding means establish an air flow on the lower side of the combustion chamber. For this purpose, the guiding means preferably comprises a plurality of holes in the lower side of the combustion chamber. Experiments have demonstrated that applying a stream of air to the lower side of the combustion chamber helps gasify components that are usually difficult to gasify, such as charcoal. This benefits the combustion process.

  When the preheating chamber is positioned around the combustion chamber, the preheating chamber provides air flow communication from the blower assembly to the combustion chamber and is configured to reflect heat radiated from the combustion chamber back to the combustion chamber. It preferably includes an air distributor including a heat reflector. The air distributor guides the air flow and reflects heat back into the combustion chamber. The air entering the combustion chamber is preheated while the outer surface remains sufficiently cooled during operation so that it is safe to touch.

  In a preferred embodiment, a rechargeable power source is provided for driving the blower assembly and the thermoelectric element, the thermoelectric element being configured to provide power to the blower assembly as well as to a rechargeable power source. This gives more freedom with respect to the (electrical) power source for driving the blower assembly, making the wood stove independent of the main power grid or connection to an external battery. Moreover, in view of the fact that a wood stove according to the present invention is typically powered by a rechargeable energy source, such as a start-up battery, it is highly advantageous with respect to total energy consumption. Wood stoves with thermoelectric elements are described in detail in the unpublished application IB 2006/050920, which is hereby incorporated by reference.

  It should be appreciated that the embodiments described above or their features can be combined.

  Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings.

  Referring to FIG. 1, a solid fuel stove 10 includes a substantially cylindrical housing 11 and a generally open upper side 15 formed within the upper portion of the housing and used as a cooking surface. And a combustion chamber 12 having the same. The generally open upper side 15 includes a number of support struts or similar members for supporting a cooking utensil such as a pan at the top. The generally open upper side 15 is provided by a mesh, grid, or other open structure (not shown) to allow heat to exit efficiently in an upward direction while further supporting the cooking vessel. It can be at least partially covered. The stove 10 is preferably arranged on a flat and stable surface 5.

  Opposite the open upper side 15, the lower side 17 (shown in phantom in FIG. 1) of the combustion chamber 12 provides a containment for solid fuel. Fuel is typically thrown into the combustion chamber 12 through the open upper portion 15 by hand whenever a fresh supply of fuel is required. The terms “upper side” and “lower side” are used herein to distinguish between typical portions of a combustion chamber when the combustion chamber is in a normal upright operating position as shown in FIG. It is only used to make it possible.

  The housing 11 includes a series of air inlets 14 at its lower end for entraining air, which is used for forced air convection through the combustion chamber 12 as described below. The stove 10 is preferably a portable stove and thus may include a removable transport handle (also not shown) that may be attached to a bracket (not shown) on the housing 11. A series of upper holes 23 in the combustion chamber 12 are also seen in FIG.

  FIG. 2 shows the internal configuration of the preferred embodiment of the stove 10. An inner cylindrical wall 21 defines the combustion chamber 12. The guide means 40 of the combustion chamber 12 includes a series of lower holes or air outlets 22 and a series of upper holes or air outlets 23. The upper hole is shaped so that the air flowing into the combustion chamber is directed from the open upper side to the lower side or downward with respect to the support surface 5. The holes produce at least an airflow component that is directed from the upper side to the lower side. Next to the downward component, the air flow velocity in the combustion chamber also preferably has a velocity component that is directed from the wall 21 toward the center of the chamber.

  Considering the air entering the combustion chamber through each of the upper and lower holes, it is preferable if the majority of the air enters through the upper hole. The preferred distribution appears to be 75% air entering through the upper hole, while the remaining 25% enters through the lower hole. This can be easily determined by selecting an appropriate ratio between the total pore surfaces on the bottom side and the lower side, respectively.

  The upper holes 23 are arranged in two rows along the outer shape of the combustion chamber 12. Preferably, the holes in the row are distributed substantially evenly along this profile. Furthermore, it is preferred if the holes in both rows provide some kind of alternating perforation as shown in FIG. 1 and clearly shown by FIG. This appears to be advantageous with respect to the air exiting the combustion chamber. Moreover, it is advantageous with respect to having as many holes as possible in a small surface.

  An annular space 18 is formed between the cylindrical wall 21 and the housing 11, and this space acts as a preheating chamber. The annular space is filled with an air distributor 24, which preferably includes a series of cylindrical metal sheets 24a with punched ribs 24b that maintain separation between the sheets to provide an air conduit. The metal sheet 24a guides the air flow, reflects heat back into the combustion chamber 12, preheats the air entering the combustion chamber through the upper air outlet 23, and the outer surface of the housing 11 is safe to touch. Assure that it is cold enough during operation. The cylindrical metal sheet is held at a predetermined position by the support structure 24c.

  On the lower side 27, a support surface 29 for holding solid fuel is arranged.

  The air flow in the combustion chamber appears to generate a regular combustion process of solid particles. These particles can be any kind of solid fuel, but preferably wood is used. The present invention is not related to fluidized bed combustion processes.

  The base of the cylindrical container 21 includes a heat insulating structure 25, which acts as a heat shield that reduces downward radiation of heat toward the intermediate chamber 26 and the lower chamber 27 of the housing 11. The intermediate chamber 26 and the lower chamber 27 are separated by a wall 28 having an opening (not shown). Adjacent to these holes is a blower assembly 50, preferably a central motor 52, and an integrally outwardly radiating blade 53 that forms an impeller that directs air through an opening in the wall 28. Have The central motor 52 is preferably protected by a further heat shield 51, which may be a thin layer of heat reflective material such as aluminum foil disposed on the motor. The lower chamber 27 is bounded by the housing 11 including the air inlet 14.

  In use, the blower assembly 50 draws air from the air inlet 14 and blows air into the intermediate chamber 26 through the opening in the wall 28. The intermediate chamber 26 functions as a distribution chamber that sends air into the annular space 13 and the air distributor 24. The air flows between the sheets 24a of the air distributor 24 to warm the air and direct the air to the air inlets 22, 23 below and above the combustion chamber 12.

  In one embodiment, blower assembly or fan 50 includes a 1W brushless DC fan driven by a 3-7V power supply (not shown) compatible with a 5V motor. In another embodiment, the fan is 12V driven with a 6-14V power supply. The power source is typically an internally mounted battery that is accessible from the base of the stove. Alternatively, an external power source can be used whenever available. The stove 11 can boil 4 liters of water in 4 minutes at combustion temperatures above 1000 ° C. without significant soot and smoke. Food can be boiled in a lower voltage range or boiled in a higher voltage range, thereby providing good cooking control.

  The intermediate chamber 26 preferably comprises a thermoelectric element having a first active surface proximate to the combustion chamber 12 and a second active surface positioned to receive cooling ventilation from the blower assembly 50. In the preferred embodiment shown, the second active surface of the thermoelectric element is in direct thermal relationship with, or forms part of, a heat sink configuration 32 that is cooled by a fan. The first active surface of the thermoelectric element may be in direct contact with the lower wall of the combustion chamber 12 or the insulating structure 25 in close proximity. The thermoelectric element 31 can be embedded in the insulating structure 25 to increase the temperature available at the first active surface. In view of the thermal shielding effect of the thermoelectric element 31 and the heat sink 32, a separate thermal shield for the motor 52 may not be required in this configuration.

  The thermoelectric element 31 is any suitable device that converts thermal energy into electrical energy, such as a thermocouple or Peltier element. Such thermoelectric elements conventionally generate a voltage based on a temperature gradient across the device between its first and second active surfaces. The thermoelectric element provides power to the blower assembly 50. In use, the blower assembly 50 provides an air flow to the heat sink 32 and thermoelectric element 31 and to the air distributor 24. In this way, the second active surface of the thermoelectric element is maintained at a substantially lower temperature than otherwise, which increases the power output available from the element and thus available to the combustion chamber 12. Increase air flow.

  An electronic control unit 33 controls the blower assembly or fan and is also housed in the lower chamber 27, where it is also protected from the heat of the stove. The electronic control unit 33 includes a rechargeable battery and a controller configured to operate the stove. The thermoelectric element provides power to the fan 50 and the rechargeable battery, thereby extending battery life. In a preferred embodiment, the electronic control unit is automatically adapted to the order through each of the available modes of the wood stove, such as a start mode or a stop mode. Preferably, the electronic control unit employs subsequent steps according to sensing operating conditions, eg, heat of fire. A temperature sensor (not shown) can be used to determine the heat of combustion, or this can be inferred from the electrical output of the thermoelectric element 31.

  Usually, rechargeable electrons are only used to supply power during the startup phase. In normal operation, the battery can then be recharged by the thermoelectric element for subsequent activation.

  FIG. 3 shows a cross section according to line II of FIG. 2, showing one of the holes in more detail. It shows a portion of the cylindrical wall in detail, illustrating that the upper edge 61 of the hole is inclined inward relative to the combustion chamber 12. The lower edge 62 is inclined outward with respect to the combustion chamber. Preferably, the cylindrical wall comprises a refractory metal sheet, such as stainless steel. This allows any air flow that enters through the hole to be directed downwards, ie from the upper side of the combustion chamber to its lower side. This is particularly advantageous in the case of relatively thin walls, where it is easier to deform the wall around the hole. When the wall is somewhat thicker, the holes may include perforations that have an inclined pitch with respect to the wall. In this case, the combustion chamber walls remain substantially flat.

  An alternative advantageous embodiment should have guiding means comprising a nozzle with an outlet directed from the upper side to the lower side. The nozzle outlet may extend through the wall of the combustion chamber. Alternatively, such a nozzle can be arranged outside the combustion chamber on its upper side.

  When the air flow A in FIG. 3 collides with the air flow B flowing through the opposing holes, both flows affect each other and produce a turbulent mixture that is considered to be annular. Experiments show that air flow contributes significantly to a cleaner combustion process.

  The simplest way to create the hole shown in FIG. 3 is to pierce a tool, such as a metal rod, through a hole with straight edges. Subsequently, the tool is tilted and the outer portion of the combustion chamber is tilted upward. This plastically deforms the edge of the hole. Preferably, the diameter of the metal rod is slightly smaller than the diameter of the hole. This provides a simple and reliable way to create the appropriate hole.

  A specific size and number of holes are preferred to develop the required airflow. In view of the fact that the stove is intended for cooking, the desired thermal power is in the range of 2-5 kW. It then determines the burn rate for gram wood per minute. It then determines the required air flow. A very significant surplus of air is used to ensure clean combustion. After careful experimentation, the required airflow was found to be in the range of 100 1 / min for low power settings and in the range of 200 1 / min for high power settings. About 75% of the air is used as secondary combustion air.

  A larger number of small holes is preferred over a small number of large holes. The optimum was found to be 64 holes with a diameter of 2.5 mm.

  A small improvement in combustion properties was found by using two rows of 32 holes arranged vertically by a few mm. Each row is located some distance from the upper side. Preferably both rows are arranged in an alternating structure. This configuration appears to provide better mixing of the combustion gases with the available air. A typical outer diameter of a wood stove is 30 centimeters high and 20 centimeters in diameter.

  Wood stoves according to the present invention are typically applied in home cooking and benefit from a clean combustion process. However, wood stoves can also be applied outdoors such as camping. This is because it can operate on a normal (rechargeable) battery. Another possible area of application is disaster areas, when people need fire, it is easy to establish with respect to providing (emergency) cooking and warmth.

  A significant advantage of the stove design described above is that the fan is well protected from a direct source of heat, inexpensive mass production with plastic components even though it is only placed at a short distance from the combustion chamber A motor can be used, resulting in a compact stove. Such motors have also been found to be much more reliable and have a longer design life. The positioning of the motor within the supply air stream is that the motor is automatically cooled and can be conveniently used to cool the cold side of the thermoelectric element.

  While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive. The invention is not limited to the disclosed embodiments. From studying the drawings, disclosure, and appended claims, other variations to the disclosed embodiments can be understood and made by those skilled in the art practicing the claimed invention. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article does not exclude a plurality. A single processor or other unit may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.

  The present invention comprises a combustion chamber (12) for containing combustion fuel and a combustion chamber for including a blower assembly (50) configured to provide an air flow entering the combustion chamber in operating condition. Regarding fuel stoves. When the guide means (40) establishes an air flow that enters the combustion chamber substantially downward, the stove combustion process is very clean and efficient.

It is a perspective view which shows the solid fuel stove suitable for cooking. It is a perspective view which shows roughly the internal detail of the stove of FIG. FIG. 3 is a cross-sectional view schematically showing a cross section taken along line II in FIG. 2.

Claims (12)

A combustion chamber for containing combustion fuel, comprising a lower side for containing fuel and an upper side;
A blower assembly configured to provide an air flow entering the combustion chamber in an operating condition;
Guiding means for directing the air flow into the combustion chamber;
The guide means directs the air flow from the upper side to the lower side;
Solid fuel stove.   The solid fuel stove according to claim 1, wherein the guide means includes a plurality of holes provided in a wall of the combustion chamber on the upper side portion.   The solid fuel stove of claim 2, wherein an upper edge of the hole is inclined inward with respect to the combustion chamber, and a lower edge of the hole is inclined outward with respect to the combustion chamber.   The solid fuel stove of claim 2, wherein the holes include perforations having an inclined pitch with respect to the wall.   The solid fuel stove of claim 2, wherein the holes are distributed substantially evenly along the contour of the combustion chamber.   The solid fuel stove according to claim 2, wherein each hole is disposed away from the upper side portion.   The solid fuel stove as claimed in claim 1, wherein the guide means establishes an air flow at the lower side of the combustion chamber.   The solid fuel stove according to claim 7, wherein the guide means includes a plurality of holes in the lower side portion of the combustion chamber.   A preheating chamber is disposed around the combustion chamber, which provides air flow communication from the blower assembly to the combustion chamber and reflects heat radiated from the combustion chamber toward the combustion chamber. The solid fuel stove of claim 1, comprising a heat reflector configured to move back.   The rechargeable power source and thermoelectric element for driving the blower assembly are provided, the thermoelectric element being configured to provide power to the blower assembly and to the rechargeable power source. The solid fuel stove described.   The solid fuel stove of claim 1, wherein the blower assembly includes a DC brushless motor and an impeller coupled to the DC brushless motor.   The solid fuel stove of claim 1, wherein an electronic control unit is provided and the unit is configured to supply variable drive power to the blower assembly to control a combustion temperature in the stove.

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