RU2436015C2 - Solid fuel fired furnace with improved combustion process - Google Patents

Abstract

FIELD: power industry.

SUBSTANCE: solid fuel fired furnace includes the following: combustion chamber having lower side part for fuel arrangement in it and open upper side part, blasting station for air flow supply to combustion chamber, guiding devices for guiding air flow to combustion chamber. Guiding device guides air flow from open upper side part to lower side part, includes many holes made in the wall of combustion chamber at open upper side part and many holes in lower side part of combustion chamber. Guiding devices establish air flow in lower side part of combustion chamber. The major part of air is supplied through multiple holes at open upper side part.

EFFECT: reduction of emission of harmful gaseous combustion products and condensed volatile organic compounds.

8 cl, 3 dwg

Description

The invention relates to improved combustion stoves. In particular, the present invention relates to kitchen stoves configured to burn solid fuels, such as wood, using forced air circulation in the combustion chamber.

An estimated 2.5 billion people in the world burn wood for cooking. Known stoves and processes, as a rule, are inefficient and have incomplete combustion, which leads to significant smoke emissions and contributes to the global warming process. At the expense of such polluting smoke emissions, many deaths can be attributed every year. In addition, inefficient wood stoves consume more natural wood resources, resulting in deforestation.

When wood is burned in the home, pollution occurs due to incomplete combustion of volatile substances released from the wood. Volatile organic compounds are released from wood at temperatures as low as room temperature, but significant rapid release begins only when exothermic reactions begin (250 ° C). Volatile substances form a complex mixture of combustible gases. The ignition temperature of this combustible gas mixture is approximately 600 ° C. Many of the unburnt volatile substances released from the wood will condense, forming particles, when cooled to temperatures close to ambient temperature. This is what we observe as wood smoke. Incomplete combustion of volatile substances occurs for several reasons. When a batch of firewood is planted, the heat from the coals and the stove itself soon causes the release of gases from the wood. When lighting a fire, ignition paper and splinter provide this heat. If volatiles are not exposed to a high temperature source (flame or a hot layer of charcoal), they will not ignite, but simply pass up into a fume or chimney, causing pollution. If the gas ignites, it can be extinguished if it is cooled using a cold surface (for example, the metal walls of a cold combustion chamber) or cold combustion air. If the combustible gas is not well mixed with air (oxygen), then it will not burn. If the amount of combustion air is reduced to reduce the burning rate, then oxygen may not be sufficient for complete combustion.

GB 2125160 describes a kitchen stove having an air combustion chamber into which cold combustion air is sucked from the outside of the stove either by natural convection, or by means of a hand-held air pump, or a combination thereof. Air enters the combustion chamber through one or more openings in the bottom of the chamber.

An object of the present invention is to provide a solid fuel stove that provides a clean combustion process.

In accordance with the present invention, there is provided a wood-fired stove operating on solid fuel, comprising:

a combustion chamber designed to contain combustible fuel, which has a lower side for enclosing fuel and an open upper side,

a blast assembly configured to provide an air stream entering the combustion chamber in working condition,

guiding means for directing the air flow into the combustion chamber,

wherein the guiding means direct the air flow from the open upper side to the lower side,

wherein the guiding means comprise a plurality of holes provided in the wall of the combustion chamber in the open upper side part,

while the guiding means set the air flow in the lower side of the combustion chamber,

wherein the guiding means comprise a plurality of holes in the lower side of the combustion chamber, and

however, most of the air enters through many holes in the open upper side.

The stove in accordance with the present invention has proven to provide a very clean combustion process. A cleaner combustion process reduces the emission of both harmful gaseous products of combustion, such as carbon monoxide (CO) and condensed volatile organic compounds. The special air flow created by the guiding means ensures the complete combustion of combustible gases in the combustion chamber before they finally leave the combustion chamber, and thereby increase the purity of the combustion process. When a transverse or upward flow of air is established in the combustion chamber, there is a risk that such an air flow will entrain the combustible gases outward from the combustion chamber before the combustible gases are completely burnt. In particular, this occurs when such gases reach the top of the combustion chamber, where the temperature is relatively low. The air flow in accordance with the invention creates a kind of turbulent air mixture, which is clearly more advantageous in the context of complete combustion. Combustible gases in the combustion chamber have more time for complete combustion before they finally leave the combustion chamber. Generally speaking, as you know, complete combustion means pure combustion. Detailed measurements made with furnaces of the present invention indicate reduced levels of residual smoke and volatile organic substances. An additional advantage is that the flames no longer touch the kitchen container standing on the stove, providing a significant reduction in soot levels in kitchen containers. The guide means may have a relatively simple design that does not complicate the design of the stove. Of course, in addition to the blower unit, there are other sources from which air can enter the combustion chamber, for example, it can be air entering through the (partially) open upper side part by means of natural convection. If the air flow during combustion is directed essentially from the upper side to the lower side, the combustion process will be very clean, as several experiments have shown.

According to a preferred embodiment, the guiding means comprise a plurality of holes provided in the wall of the combustion chamber in the upper side. By providing these holes, you can get simple, and even effective guiding means. Preferably, in particular, the upper edge of the hole is inclined inward relative to the combustion chamber, and the lower edge of the hole is inclined outward relative to the combustion chamber. This design is advantageous due to manufacturability in the case of a relatively thin wall, since the deformation of the wall around the holes is simplified. In another preferred embodiment, the holes are drilled holes having an angle of inclination relative to the wall. Such holes are easier to make in the case of a relatively thick wall.

In addition, it is preferred that the openings are substantially uniformly distributed along the contour of the combustion chamber. This has the advantage that opposing air flows will occur somewhere in the center of the combustion chamber, resulting in turbulent mixing of air while improving the combustion process.

It is also advantageous if each hole is located at a distance from the upper side. This has the advantage that the flames will not directly contact the cooking utensils standing on the stove, which prevents the formation of soot on such utensils.

According to another preferred embodiment, the guiding means sets the air flow in the lower side of the combustion chamber. To this end, the guiding means preferably comprise a plurality of holes in the lower side of the combustion chamber. Experiments have proven that introducing airflow into the lower side of the combustion chamber will help to convert components into gas that are usually difficult to convert to gas, such as charcoal. This will facilitate the combustion process.

It is preferable that a heating chamber is located around the combustion chamber, which provides air flow from the blast assembly to the combustion chamber and includes an air distributor including heat deflectors configured to reflect the heat emitted from the combustion chamber back into the combustion chamber. An air distributor directs the air flow and reflects heat back to the combustion chamber. The air entering the combustion chamber is heated, and enough cold air remains at the outer surface during operation so that it can safely be touched.

In a preferred embodiment, a rechargeable power source for driving the blower assembly and a thermoelectric element are provided, the thermoelectric element being configured to supply power to the blower assembly and to the rechargeable power source. This gives more freedom in relation to the supply of (electric) power for the drive of the blower assembly and makes the wood stove independent of the connection to the power supply or to an external battery. Moreover, this is very advantageous in relation to the total energy consumption, especially since the wood stoves of the invention are typically fed with a rechargeable energy source, such as a starting battery. A wood-burning stove with a thermoelectric element is described in detail in the previously unpublished application IB2006 / 050902, which is mentioned here for reference.

It should be understood that the above described embodiments or aspects thereof may be combined.

Now, by way of example and with reference to the accompanying drawings, a description will be given of embodiments of the present invention. In the drawings:

FIG. 1 is a perspective view of a solid fuel stove suitable for cooking; FIG.

figure 2 is a view in cross section, schematically illustrating the internal structure of the stove according to figure 1; and

figure 3 is a schematic side view in cross section along line I-I of figure 2.

1, a solid fuel-fired stove 10 comprises a substantially cylindrical body 11, a combustion chamber 12 formed within the upper part of the body and having a generally open upper side portion 15 for use as a cooking surface. In general, the open upper side portion 15 includes a number of support posts 13 or similar means for supporting kitchen utensils from above, such as a pan. In general, the open upper side portion 15 may be at least partially covered by a net, grill or other open structure (not shown) to further support the kitchen vessel, while still providing a sufficient upward heat output. The stove 10 is preferably mounted on a flat and stable surface 5.

Located opposite the open upper side part 15, the lower side part 17 (shown by the dashed line in FIG. 1) of the combustion chamber 12 ensures that solid fuel is enclosed therein. Fuel, as a rule, is thrown into the combustion chamber 12 through the open upper side portion 15 manually each time a fresh portion of fuel is needed. It should be noted that the terms “upper side part” and “lower side part” are used here only to distinguish between typical parts of the combustion chamber when it is located in the normal vertical operating position, as shown in FIG.

The housing 11 includes a group of air inlets 14 at its lower end for air intake, which is used for forced air convection through the combustion chamber 12, as will be described below. The stove 10 is preferably a portable stove and therefore can be equipped with a removable carrying handle (not shown), which can be attached to the brackets (they are also not shown) on the housing 11. The group of upper openings 23 of the combustion chamber is also visible in FIG.

Figure 2 shows the internal arrangement according to a preferred embodiment of the stove 10. The combustion chamber 12 is delimited by the inner wall 21. The guide means 40 of the combustion chamber 12 comprise a group of lower openings, which can also be called air outlet openings 22, and a group of upper openings, which can also be called air outlets 23. The upper openings are shaped so that air flowing into the combustion chamber is directed from the open upper side to the lower side, i.e. down to the bearing surface 5. These holes create at least a component of the air flow directed from the upper side to the lower side. Further, with respect to this downward-directed component, the air velocity in the combustion chamber will also preferably have a velocity component that is directed from the wall 21 to the center of the chamber.

Given that air enters the combustion chamber through the upper and lower openings, it is accordingly preferable if most of the air enters through the upper openings. A favorable distribution is that in which 75% of the air enters through the upper openings and the remaining 25% enters through the lower openings. This distribution can be easily established by choosing the appropriate ratio between the total surfaces of the holes in the upper side and lower side, respectively.

The upper holes 23 are arranged in 2 rows along the contour of the combustion chamber 12. In a preferred embodiment, the openings in the row are distributed substantially uniformly along the contour. In addition, it is preferable if the holes in both rows provide some kind of alternating perforation, as shown in figure 1 and more clearly shown in figure 2. This turned out to be beneficial in relation to the air that exits the combustion chamber. Moreover, this also favors the possibility of having as many holes as possible on a small surface.

An annular space 18 is formed between the cylindrical wall 21 and the housing 11, which acts as a heating chamber. This annular space is filled with an air distributor 24, which preferably comprises a group of cylindrical metal sheets 24a with embossed ribs 24b supporting separation between the sheets to provide air ducts. The metal sheets 24a direct the air flow and reflect heat back into the combustion chamber 12, heating the air that enters the combustion chamber through the upper air outlets 23, and ensuring that the outer surface of the housing 11 remains cold enough during operation so that you can safely touch this surface. Cylindrical metal sheets are supported in place by a supporting structure 24c.

At the lower side 27 is a bearing surface 29 for maintaining solid fuel.

The air flow in the combustion chamber is such that a regular process of combustion of solid particles occurs. These particles may belong to any type of solid material, but firewood is preferably used. The present invention is not related to combustion processes such as those involving a fluidized bed.

The base of the cylindrical vessel 21 includes a heat-insulating structure 25, which acts as a heat shield, reducing heat radiation down to 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 openings (not shown). Next to these openings is a blast assembly 50, preferably having a central electric motor 52 and integrated impeller blades 53 forming an impeller, for directing air through the openings in the wall 28. The central electric motor 52 is preferably protected by an additional heat-shielding element 51, which may be a thin layer of heat-reflecting material, such as aluminum foil, located on an electric motor. The lower chamber 27 is bounded by a housing 11, which includes air inlets 14.

During operation, the blower assembly 50 draws in air through the air inlet openings 14 and blows it through the openings of the wall 28 into the intermediate chamber 26. The intermediate chamber 26 acts as a distribution chamber for supplying air to the annular space 18 and the air distributor 24. Air flows between the sheets 24a of the air distributor 24. as a result, the air is heated, and directing it to the lower and upper air intake holes 22, 23 of the combustion chamber 12.

In one embodiment, the blower assembly or fan 50 comprises a 1 W brushless DC fan driven by a 3-7 V power supply (not shown) compatible with an electric motor whose voltage rating is 5 V. In another embodiment, a fan with a voltage rating of 12 V is driven by a 6-14 V power supply. The power source is typically a battery installed inside and accessible from the base of the stove. Alternatively, you can use an external source whenever the opportunity arises. Tests showed that the stove 10 is able to boil a liter of water in 4 minutes without significant formation of soot and smoke at a combustion temperature above 1000 ° C. Food can be cooked over low heat in a lower voltage range or boiled in a higher voltage range, thereby providing good cooking control.

The intermediate chamber 26 is preferably equipped with a thermoelectric element 31, which has a first active surface in close proximity to the combustion chamber 12, and a second active surface arranged to receive cooling from the blower assembly 50. In the preferred arrangement shown, the second active surface of the intermediate thermoelectric element is in direct thermal connection with the radiator device 32, which is cooled by a fan, or forms part of this device Lenia. The first active surface of the thermoelectric element can be in close direct contact with the bottom wall of the combustion chamber 12 or the insulating structure 25. The thermoelectric element 31 can be embedded in the insulating structure 25 to increase the temperature that can be achieved on the first active surface. Due to the effects of thermal shielding of the thermoelectric element 31 and the radiator 32, with this arrangement a separate heat shield for the motor 52 may not be necessary.

The thermoelectric element 31 is any suitable device that converts thermal energy into electrical energy, such as a thermocouple or a Peltier element. Such thermoelectric elements typically generate voltage based on the temperature gradient on the device between its first and second active surfaces. The thermoelectric element provides electric power for the blower assembly 50. During operation, the blower assembly 50 provides air flow to the radiator 32 and the thermoelectric element 31, as well as to the air diffuser 24. Thus, the second active surface of the thermoelectric element is maintained at a significantly lower temperature than that which could otherwise be, which increases the power output that can be obtained from this element, and thereby increases the available air flow in the chamber ru 12 combustion.

The electronic control unit 33 controls the blowing unit or fan and is also enclosed in the lower chamber 27, where it is also protected from the heat of the stove. The electronic control unit 33 includes a battery and a controller configured to drive the stove. The thermoelectric element provides electricity for the fan 50 and the battery, thereby extending the life of this battery. In a preferred embodiment, the electronic control unit is adapted to automatically pass sequentially through each of the available wood stove modes, such as a start or shutdown mode. The electronic control unit preferably adapts the successive steps to the perceived operating conditions, for example, to the heat of the fire. To determine the calorific value, a temperature sensor (not shown) can be used, or this parameter can be removed from the electrical output of the thermoelectric element 31.

Typically, a battery is often used to supply power during the start-up phase. During normal operation, after this - for the next start - it will be enough to recharge the battery with the help of a thermoelectric element.

Figure 3 shows a schematic cross-section along the line I-I of figure 2, illustrating in more detail one of the holes. Here, a part of the cylindrical wall is shown in detail and it is shown that the upper edge 61 of the holes is inclined inward with respect to the combustion chamber. The lower edge 62 is inclined outward relative to the combustion chamber. The cylindrical wall preferably comprises a heat-resistant metal sheet, such as a stainless steel sheet. This provides a situation in which any air flow entering through the hole will be directed downward, i.e. from the upper side of the combustion chamber to its lower side. This is especially advantageous in the case of a relatively thin wall, simplifying the deformation of the wall around the holes. When the wall is slightly thicker, the holes can be drilled holes having an angle of inclination relative to the wall. In this case, the wall of the combustion chamber will remain substantially flat.

An alternative advantageous embodiment provides for guiding means comprising nozzles having 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 nozzles may be located outside the combustion chamber - at its upper side.

When air flow A, shown in FIG. 3, collides with air flow B flowing through the opposite opening, both flows will mutually influence each other, creating a turbulent air mixture, which is assumed to have a torus shape. Experiments have shown that airflow makes a significant contribution to a cleaner combustion process.

The simplest way to create the hole shown in FIG. 3 is to strike with a tool, such as a metal rod, to punch a hole with straight edges. After that, the tool is tilted, and at the same time its part located outside the combustion chamber is tilted up. Along with this, plastic deformation of the edges of the hole occurs. The diameter of the metal rod is slightly smaller than the diameter of the hole. This provides a simple and reliable way to create suitable holes.

To create the required air flow, certain sizes and number of holes are preferred. Given the fact that the stove is designed for cooking, the desired heat output is in the range of 2-5 kW. In turn, this determines the rate of combustion, expressed in grams of wood per minute. And this, in turn, determines the required air flow. A very significant excess of air is used to guarantee clean combustion. After careful experiments, it was found that the required air flow should be in the range of 100 l / min when setting low power and 200 l / min when setting high power. Approximately 75% of this air is used as secondary combustion air.

A larger number of small holes is preferable to a small number of large holes. It was found that the optimum corresponds to 64 holes with a diameter of 2.5 mm.

A slight improvement in combustion properties was found when using two rows of 32 holes located vertically a few millimeters. Each row is located at some distance from the upper side. Both rows are preferably arranged in an alternating configuration. This arrangement has led to even better mixing of combustible gases with the available air. Typical external dimensions of a wood-burning stove are as follows: height - 30 centimeters, and diameter - 20 centimeters.

Wood stoves in accordance with the present invention are typically used for cooking in the home, and the user benefits from a clean combustion process. However, a wood-burning stove can also be used outdoors, for example, in camping, since it can usually work on (rechargeable) batteries. Another possible area of application is disaster zones, when people (in an emergency) need to quickly light a fire in connection with cooking and providing heat.

A significant advantage of the design of the stove described above is that the fan is essentially protected from a direct heat source, so that you can use a cheap, mass-produced electric motor with plastic components, even though it is located at a small distance from the combustion chamber; the result is a compact stove. The location of the electric motor in the air flow means self-cooling of the electric motor, and this flow can also be conveniently used to cool the cold side of the thermoelectric element.

Although the invention is illustrated and described in detail in the drawings and in the foregoing description, such drawings and description should be considered illustrative or possible, and not restrictive, so that the invention is not limited to the described embodiments. Having studied the drawings, description and the attached claims, specialists in the art in the process of practical embodiment of the invention will be able to make other changes to the described embodiments. In the claims, the word “comprising” (“comprising”) does not exclude other elements or steps, and the singular does not exclude plurality. A single processor or other unit can perform the functions of several components specified in the claims. The mere fact that certain measures are indicated in mutually different dependent claims does not mean that it is impossible to take advantage of the combination of these measures. No reference position in the claims should not be considered limiting its scope.

The invention relates to a solid fuel stove containing a combustion chamber (12) for containing combustible fuel, and a blast assembly (50) configured to provide air flow to the combustion chamber in working condition. When the guiding means (40) set the air flow entering the combustion chamber substantially in the downward direction, the combustion process is very clean and efficient.

Claims (8)

1. A solid fuel-fired stove (10), comprising:
a combustion chamber (12) designed to accommodate combustible fuel in it and having a lower side part (17) for placing fuel in it and an open upper side part (15),
a blast assembly (50), configured to bring the air flow entering the combustion chamber into working condition,
guide means (40) for directing the air flow into the combustion chamber, wherein:
guide means (40) direct the air flow from the open upper side to the lower side,
the guiding means (40) contain a plurality of holes (23) made in the wall (21) of the combustion chamber (12) at the open upper side part (15),
guide means (40) set the air flow in the lower side part (17) of the combustion chamber (12),
the guiding means (40) comprise a plurality of holes (22) in the lower side part (17) of the combustion chamber (12), and
most air enters through multiple openings (23) at the open upper side part (15). 2. The stove (10) according to claim 1, in which the upper edge (61) of the hole is tilted inward relative to the combustion chamber (12), and the lower edge (63) of the hole is tilted outward with respect to the combustion chamber. 3. The stove (10) according to claim 1, in which the holes (23) are drilled holes having an angle of inclination relative to the wall (21). 4. The stove (10) according to claim 1, in which the holes (23) are substantially uniformly distributed along the contour of the combustion chamber. 5. The stove (10) according to claim 1, in which a heating chamber (18) is located around the combustion chamber, which ensures the transfer of air flow from the blast assembly to the combustion chamber and comprises an air distributor (24) including heat reflectors (14a) made with the possibility of reflection of the heat radiated from the combustion chamber (12), back to the combustion chamber. 6. The stove (10) according to claim 1, in which a rechargeable power supply for driving the blower assembly and a thermoelectric element (31) are provided, the thermoelectric element being configured to supply power to the blower assembly and to the rechargeable power source. 7. The stove (10) according to claim 1, in which the blast assembly (50) comprises a brushless DC motor (52) and an impeller (53) associated with it. 8. The stove (10) according to claim 1, in which an electronic control unit (33) is provided, configured to supply variable power to the blower unit (50) to control the combustion temperature in the stove.

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