MX2008015818A

MX2008015818A - A solid fuel stove with improved combustion.

Info

Publication number: MX2008015818A
Application number: MX2008015818A
Authority: MX
Inventors: Paul Van Der Sluis
Original assignee: Koninkl Philips Electronics Nv
Priority date: 2006-06-26
Filing date: 2007-06-20
Publication date: 2009-01-12
Also published as: AP2535A; EP2035751A2; RU2436015C2; CN101479533A; KR20090026194A; BRPI0713368A2; WO2008001276A2; ZA200900557B; WO2008001276A3; JP2015014453A; EG26627A; BRPI0713368A8; JP5938455B2; JP2009541710A; CA2656187A1; AP2009004748A0; KR101423479B1; CN101479533B; RU2009102232A; US20090165769A1

Abstract

The invention relates to a solid fuel stove comprising a combustion chamber (12) for containing combustion fuel and a blower assembly (50) configured to provide airflow entering the combustion chamber in operating condition. When guiding means (40) establish airflow entering the combustion chamber substantially in a downwardly direction the combustion process of the stove is very clean and efficient.

Description

SOLID FUEL STOVE WITH IMPROVED COMBUSTION Description of the Invention The present invention relates to kitchen stoves with improved combustion. In particular, the present invention relates to cooking stoves with the ability to burn solid fuels, such as wood, using the forced circulation of air in the combustion chamber. It is estimated that approximately 2.5 billion people in the world burn wood for cooking. Normally, known stoves and processes are inefficient and have incomplete combustion, which causes substantial smoke emissions and contributes to the global warming process. Many deaths each year could be attributed to these smoke polluting emissions. In addition, wood stoves with poor efficiency use more natural wood resources with the consequent deforestation. In the domestic combustion of wood, air pollution occurs due to incomplete combustion of volatile compounds released from wood. Volatile organic compounds are released from wood at temperatures as low as room temperature, although substantially, rapid release only begins when the exothermic reactions begin (250 REF. 198158 ° C). The volatile compounds form a complex mixture of combustible gases. The ignition temperature of the fuel gas mixture is approximately 600 ° C. Many of the unburned volatile compounds that are released from wood will condense to form fine particles when cooled to near ambient temperatures. This is what is observed as wood smoke. Incomplete combustion of volatile compounds happens for several reasons. When a batch of wood is added, the heat from the coals and the apparatus quickly causes the gases to be released from the wood. When a fire is lit, the paper and fuel wood provide this heat. If volatile compounds were not exposed to a high temperature source (flame or incandescent charcoal) they could not ignite and would simply pass up the exhaust / chimney causing contamination. If the gas does not ignite, it could be cooled rapidly if cooled by a cold surface (for example, the metal walls of a cold-combustion chamber) or cold air from combustion. If the fuel gas was not well mixed with the air (oxygen) it would not burn. If the combustion air were reduced by a slow combustion rate, there could be an insufficient amount of oxygen for complete combustion. The document GB 2125160 describes a stove of kitchen that has an air combustion chamber inside which is extracted the air for combustion from the outside of the stove either by natural convection or through a hand operated air pump or by means of the combination of both. The air enters the combustion chambers through one or more openings in the lower part of the chamber. An object of the present invention is to provide a solid fuel stove that allows a clean combustion process. According to the present invention, there is provided a solid wood fuel stove comprising: a combustion chamber containing the combustion fuel, the chamber having a lower side portion accommodating the fuel and an open top side portion; a blower or fan assembly that is configured to provide the air flow that enters the combustion chamber in operating condition; guide means directing the flow of air into the combustion chamber; wherein the guide means directs the air flow from the upper lateral portion open to the lower lateral portion, wherein the guide means '40 comprises a plurality of openings 23 provided in a wall 21 of the combustion chamber 12 in the open upper side portion 15, wherein the guide means 40 establish the air flow in the lower lateral portion of the combustion chamber, wherein the guide means 40 comprises a plurality of openings 22 in the lower lateral portion 17 of the combustion chamber 12, and wherein the majority of the air enters through the plurality of openings 22 in the open upper side portion 15. The stove according to the present invention has proven the supply of a very clean combustion process. A cleaner combustion process decreases both the emission of harmful combustion gases such as carbon monoxide (CO) and volatile organic condensates. The specific air flow that is created through the guide means allows the combustible gases in the hot combustion chamber to burn out completely before they eventually exit the combustion chamber, and therefore, the cleanliness of the combustion process is improved. When a transverse or ascending air flow is established in the combustion chamber, there is a risk that the combustion gases will be linked by this air flow out of the chamber before the combustion gases are burned completely. This is especially the case when these gases reach the highest part of the combustion chamber where the temperature is relatively low. The air flow according to the invention generates some kind of turbulent air mixture, which apparently is very advantageous in relation to a complete combustion. There is a longer time for the combustion gases in the combustion chamber to burn completely before leaving, eventually, the combustion chamber. As is generally known, complete combustion means clean combustion. Detailed measurements with the stoves according to the present invention indicate reduced levels of residual smoke and volatile organic matter. An additional advantage is that the flames no longer make contact with the cooking vessel located above the heater allowing a significant reduction of the levels of soot in the cooking vessels. The guide means may have a relatively simple construction, which does not complicate the design of the stove. Obviously, apart from the blower or fan assembly, there are other air sources that can enter the combustion chamber, such as the air that enters through an open upper side portion (partially) or through holes in the side portion lower by the natural convection. If the air flow in combustion was substantially directed from the upper lateral portion to the lower lateral portion, the combustion process would be very clean, as indicated by several experiments. According to a preferred embodiment, the guiding means comprises a plurality of openings which is provided in the wall of the combustion chamber in the upper lateral portion. By providing openings, guiding means that are simple and still effective can be obtained. It would be especially preferred if the upper edge of an opening were inclined inwardly relative to the combustion chamber and the lower edge of the opening sloped outwardly relative to the combustion chamber. This construction is advantageous in relation to the degree of manufacture in the case of a relatively thin wall, because it is easier to form the wall around the openings. In another preferred embodiment, the apertures comprise perforation holes having an inclined slope relative to the wall. These openings are easier to manufacture in the case of a relatively thick wall. Furthermore, it would be preferable if the openings were evenly distributed substantially along the contour of the combustion chamber. This has the advantage that the opposite air flows will coincide somewhere in the center of the combustion chamber, which causes a turbulent mixing of air while improving the combustion process. According to another preferred embodiment, the guide means establish the air flow in the lower side portion of the combustion chamber. The guide means at this end is preferred to be constituted of a plurality of openings in the lower side portion of the combustion chamber. Experiments have proven that the addition of airflow in the lower side portion of the combustion chamber will aid the gasification process of components that are normally difficult to gasify, such as charcoal. This will benefit the combustion process. It is preferred when a preheating chamber is located around the combustion chamber, the preheating chamber provides an airflow communication of the blower assembly within the combustion chamber and comprises an air distributor that includes heat reflectors that are adapted to reflect the heat radiated from the combustion chamber back towards the combustion chamber. The air distributor directs the air flow and reflects the heat back into the combustion chamber. The air that enters the combustion chamber is previously heated, while the outer surface remains cold enough in operation so that it is safe for contact. In a preferred embodiment, a rechargeable electric power source for the drive of the blower assembly and a thermoelectric element are provided, wherein the thermoelectric element is configured in order to provide power to the blower assembly and the rechargeable power source. This provides greater freedom in relation to the (electrical) power supply for the blower assembly drive and makes the wood stove independent of the connection to the main power grid or external battery. Furthermore, it would be very advantageous with respect to the total energy consumption, above all, in view of the fact that wood stoves according to the invention are normally fed through a rechargeable energy source, such as a starting battery. A wood stove provided with the thermoelectric element is described in detail in the unpublished application IB2006 / 050920, which is incorporated herein by reference. It should be recognized that the modalities described above, or the aspects thereof, could be combined. Next, the embodiments of the present invention will be described by way of example and with reference to the accompanying figures, in which: Figure 1 shows a perspective view of a solid fuel stove suitable for cooking; Figure 2 is a cross-sectional view showing, schematically, the internal detail of the stove of Figure 1; Figure 3 shows a schematic cross-sectional side view according to line II in Figure 2. With reference to Figure 1, a solid fuel stove 10 comprises a substantially cylindrical housing 11, a combustion chamber 12 formed within the upper portion of the housing and having a generally open upper side portion 15 for use as a cooking surface. The generally open upper side portion 15 includes a number of support columns or braces 13, or the like, which hold the cooking utensils such as a pot on top. The generally open upper side portion 15 could be covered, at least partially, by a mesh, grid or other open structure (not shown) for additional support of the cooking vessel while still allowing efficient heat output in one direction upward. Preferably, the stove 10 is placed on a flat and stable surface 5. Opposite the open top side portion 15, the lower side portion 17 (shown in dotted line in Figure 1) of combustion chamber 12 provides accommodation for solid fuel. Commonly, the fuel is thrown by hand into the combustion chamber 12 through the open top side portion 15 whenever a new fuel supply is necessary. It should be noted that the terms "upper lateral portion" and "lower lateral portion" are only used to have the ability to distinguish between the common parts of the combustion chamber as it is placed in its normal vertical operating position as shown in the Figure 1. The housing 11 includes a series of air inlets 14 at the lower end thereof for the entry of air, which are used for the forced convection of air through the combustion chamber 12 as will be described below. Preferably, the stove 10 is a portable stove and therefore, could be provided with a removable transport lever (not shown) that could be joined with the clamps in the housing 11 (not shown). A series of upper openings 23 of the combustion chamber 12 is also visible in Figure 1. Figure 2 shows the internal arrangements of a preferred embodiment of the stove 10. A cylindrical wall interior 21 defines the combustion chamber 12. The guide means 40 of the combustion chamber 12 comprises a series of lower air openings or outlets 22 and a series of upper air openings or outlets 23. The upper openings are configured, of The air flowing into the combustion chamber is directed from the upper side portion open to the lower side portion or down relative to the support surface 5. The openings create at least one airflow component directed from the lateral portion superior to the inferior lateral portion. Beside the descending component, the velocity of the air flow in the combustion chamber is preferably also having a velocity component which is directed from the wall 21 towards the center of the chamber. Considering that air enters the combustion chamber through the upper and lower openings, respectively, it is preferred if most of the air enters through the upper openings. A favorable distribution seems to be 75% of the air that enters through the upper openings, while the remaining 25% enters through the lower openings. This can be easily established by choosing an appropriate ratio between the total opening surface, respectively, in the lower lateral portion and in the lower lateral portion.

The upper openings 23 are located in two rows along the contour of the combustion chamber 12. Preferably, the openings in a row are uniformly distributed substantially along this contour. Furthermore, it would be preferred if the openings in both rows provided some type of alternating perforation as shown in Figure 1 and more clearly in Figure 2. This seems to be advantageous in relation to the air leaving the combustion chamber. In addition, it would be favorable in relation to a small surface, to have as many openings as possible. The annular space 18 is formed between the cylindrical wall 21 and the housing 11, this space acts as a preheating chamber. The annular space is filled with an air distributor 24 which is preferred to comprise a series of metal cylindrical sheets 24a with the die-cut edges 24b which maintain the spacing between the sheets in order to provide air passages. The metal sheets 24a direct the flow of air and reflect the heat to the combustion chamber 12, preheating the air entering the combustion chamber through the upper air outlets 23 and ensuring that the outer surface of the housing 11 stay cool enough in the operation so that it is safe to touch or touch. The cylindrical metal sheets are maintained in place through support structure 24c. In the lower lateral portion 27, the support surface 29 retaining the solid fuel is located. The air flow in the combustion chamber is so as to generate the regular combustion process of the solid particles. These particles can be of any type of solid material, although it is preferred that only wood be used. The present invention does not relate to fluidized bed types of combustion processes. The base of the cylindrical container 21 includes a thermal insulation structure 25 which acts as a heat shield that reduces the downward radiation of heat to the intermediate chamber 26 and the lower chamber 27 of the housing 11. The intermediate chamber 26 and the lower chamber 27 they are separated by a wall 28 having holes (not shown). Adjacent to these openings is a blower assembly or fan 50, preferably having a central motor 52 and integral radiation blades 53 outwardly forming an impeller which directs the air through the holes in the wall 28. Preferably , the central motor 52 is protected by an additional heat protection element 51, which could be a thin layer of heat reflective material, such as a thin sheet of aluminum located in the motor. The lower chamber 27 is joined by the housing 11 including the air inlets 14. In use, the blower or fan assembly 50 extracts air through the air inlets 14 and blows it through the holes in the wall 28 into the intermediate chamber 26. The intermediate chamber 26 acts as a distribution chamber for supplying air to the annular space 13 and the air distributor 24. The air moves between the leaves 24a of the air distributor 24 to heat the air and direct it towards the upper inlets and lower airs 22, 23 of the combustion chamber 12. In one embodiment, the blower or fan assembly 50 comprises a 1 W brushless DC fan driven by a power supply of 3 to 7 V (not shown), compatible with a 5 V motor. In another mode, the fan is a 12 V driven fan through a power supply of 6 to 14 V. Commonly, the power supply is a battery mounted in a form internal accessible from the base of the stove. Alternatively, an external supply could be used whenever it is available. Tests have shown that stove 11 is capable of boiling a liter of water in 4 minutes, without significant soot and smoke, with a combustion temperature greater than 1000 ° C. The food could be boiled over a low heat in a lower voltage interval or it could be boiled in a Higher voltage range, which provides good cooking control. Preferably, the intermediate chamber 26 is provided with a thermoelectric element 31 having a first active surface in close proximity to the combustion chamber 12 and a second active surface positioned to receive a cooling air stream from the blower assembly 50. In the preferred arrangement shown, the second active surface of the thermoelectric element is in direct thermal association or is part of the heat sink arrangement 32 which is cooled by the fan. The first active surface of the thermoelectric element could be in close direct contact with the lower wall of the combustion chamber 12 or with the insulating structure 25. The thermoelectric element 31 could be embedded within the insulation structure 25 in order to increase the available temperature in the first active surface. In view of the thermal protection effects of the thermoelectric element 31 and the heat sink 32, separate heat protection for the motor 52 could not be required with this arrangement. The thermoelectric element 31 is any suitable device that converts thermal energy into electrical energy, such as a thermocouple or Peltier element. These thermoelectric elements generate, in a conventional, a voltage based on the thermal gradient through the device between the first and second active surfaces thereof. The thermoelectric element provides electrical energy to the blower assembly 50. In use, the blower assembly 50 provides the air flow to the heat sink 32 and the thermoelectric element 31, as well as, to the air distributor 24. Thus, the second surface The active element of the thermoelectric element is maintained at a substantially lower temperature than would otherwise be the case, which increases the efficiency of the available energy of the element, and therefore increases the air flow available to the combustion chamber. An electronic control unit 33 regulates the blower or fan assembly 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 that is configured to operate the stove. The thermoelectric element provides electrical power to the fan 50 and the rechargeable battery, thereby extending the battery life. In the preferred embodiment, the electronic control unit is adapted to work in sequence, automatically, through each of the available modes of the wood stove, such as in start-up or shut-down mode. Preferably, the electronic control unit it adapts the subsequent stages according to the detected operating conditions, for example, the heat of the fire. A temperature sensor (not shown) could be used to determine the heat of combustion or this could be deduced from the electrical output of the thermoelectric element 31. Normally, the rechargeable battery is only used to supply power in the starting phase. In normal operation, the battery can be recharged sufficiently by the thermoelectric element for the next start. Figure 3 shows a cross section according to the line I-I in Figure 2 showing one of the openings in greater detail. This shows a part of the cylindrical wall in detail and illustrates that the upper edge 61 of the openings is inclined inwardly relative to the combustion chamber. The lower edge 62 is inclined outward relative to the combustion chamber. Preferably, the cylindrical wall comprises a heat resistant metal sheet, such as stainless steel. This allows any air flow passing through the opening to be directed downward, i.e., from the upper side portion of the combustion chamber to its lower lateral portion. This is especially advantageous in the case of a relatively thin wall, where the formation of the wall around the openings is easier. When the If the wall is somewhat thicker, the openings could comprise drilling holes that have an inclined slope relative to the wall. In this case, the wall of the combustion chamber will remain substantially flat. An advantageous alternative embodiment is to have guide means comprising nozzles having a directed outlet from the upper lateral portion toward the lower lateral portion. An outlet of the nozzle could extend through the wall of the combustion chamber. Alternatively, these nozzles could be located outside the combustion chamber in the upper side portion of the combustion chamber. When the air flow A in Figure 3 meets the air flow B that travels through the opposite aperture, both flows will influence each other creating a turbulent mixture of air, which is believed to be in a form of bull. Experiments have indicated that the air flow contributes significantly to a cleaner combustion process. The simplest way to create the opening shown in Figure 3 is the introduction of a tool, such as a metal rod through an opening having straight edges. Subsequently, the tool is tilted, while the outside of the combustion chamber tilts upwards. As a result, the edges of the opening are deformed in a plastic manner. Preferably, The diameter of the metal rod is slightly smaller than the diameter of the opening. This provides a simple and reliable method of creating proper openings. In order to develop the required air flow, certain sizes and numbers of openings are preferred. Considering the fact that the stove is for cooking, the thermal energy that is required is in the range of 2 - 5 kw. In turn, this determines a combustion ratio in terms of gram of wood per minute. This in turn determines the air flow required. A very significant surplus or excess of air is used to ensure clean combustion. After careful experiments, it was found that the required air flow is in the range of 100 liters / minute for the low energy setting and 200 liters / minute for the high energy setting. Approximately 75% of the air is used as secondary combustion air. A larger number of small openings is preferred over the small number of large openings. The optimum was found in 64 openings of a diameter of 2. 5 mm. A small improvement of combustion properties was found by using two rows of 32 openings displaced in vertical direction by a few millimeters. Each row is located at some distance from the upper lateral portion. Preferably, both rows are placed in an alternating configuration. This arrangement seemed to result in an even better mixing of the combustible gases with the available air. The common exterior dimensions of the wood stove are a height of 30 centimeters and a diameter of 20 centimeters. Wood stoves according to the present invention are normally used in domestic kitchens, where benefits of the clean combustion process are obtained. However, the wood stove can also be applied outdoors, such as during camping, because it can usually operate with batteries (rechargeable), another possible field of application is in disaster areas, when people are in need of fire so that they are easy to establish in relation to cooking (emergency) and provide heat. An important advantage of the design of the stove described above is that the fan is sufficiently protected from the direct source of heat so that the engine mass produced with the plastic components can be used, even when it is placed only at a short distance of the combustion chamber, originating a compact stove. These engines also prove that they are much more reliable and have a longer design life. The positioning of the motor in the air stream of Supply means that the motor can cool on its own and can also be conveniently used to cool the cold side of the thermoelectric element. While the invention has been illustrated and described in detail in the figures and the foregoing description, this illustration and description will be considered illustrative or exemplary and not restrictive; The invention is not limited to the described modalities. Other variations to the described modalities can be understood and effected by those skilled in the art in the practice of the claimed invention, from the study of the figures, the description and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. A single processor or other unit could fulfill the functions of several items indicated in the claims. The simple fact that certain measures are indicated in the reciprocally different dependent claims does not indicate that a combination of these measures can not be used as an advantage. Any of the reference signs in the claims should not be construed as limiting the scope. The invention relates to a solid fuel stove comprising a combustion chamber 12 containing a combustion fuel and a blower assembly 50 configured to provide a flow of air entering the combustion chamber in operating condition. When the guide means 40 establish the air flow entering the combustion chamber, substantially in a downward direction, the combustion process of the stove is very clean and efficient. It is noted that in relation to this date the best method known by the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Claims

CLAIMS Having described the invention as above, the content of the following claims is claimed as property: 1. A solid fuel stove, characterized in that it comprises: a combustion chamber containing the combustion fuel, the chamber has a lower side portion for the fuel arrangement and an open upper side portion; a blower assembly that is configured to provide the flow of air entering the combustion chamber in operating condition; the guide means directing the flow of air into the combustion chamber; wherein the guiding means directs the air flow from the upper lateral portion open to the lower lateral portion, wherein the guiding means comprises a plurality of openings provided in a wall of the combustion chamber in the open upper side portion, wherein the guide means establish the air flow in the lower side portion of the combustion chamber, wherein the guide means include a plurality of openings in the lower lateral portion of the combustion chamber, wherein the majority of air enters through the plurality of openings in the open upper lateral portion. The heater according to claim 1, characterized in that the upper edge of an opening is inclined inwardly relative to the combustion chamber and the lower edge of the opening is inclined outwardly relative to the combustion chamber. The heater according to claim 1, characterized in that the openings comprise drilling holes having a slope inclined with respect to the wall. 4. The stove according to claim 1, characterized in that the openings are uniformly distributed substantially along the contour of the combustion chamber. The stove according to claim 1, characterized in that a preheating chamber is located around the combustion chamber, the preheating chamber provides air flow communication from the blower assembly to the combustion chamber and comprises an air distributor which includes heat reflectors that are adapted to reflect the radiated heat of the combustion chamber towards the combustion chamber. The stove according to claim 1, characterized in that a rechargeable electric power source for driving the blower assembly and the thermoelectric element is provided, and wherein the thermoelectric element is configured in order to provide power to the blower assembly and to the Rechargeable power source. The heater according to claim 1, characterized in that the blower assembly comprises a DC brushless motor and an impeller coupled therewith. The stove according to claim 1, characterized in that an electronic control unit is provided, the unit is adapted to supply variable drive power to the blower assembly in order to control the combustion temperature in the stove.