Device for controlling flow rate of air and solid fuel burner

Abstract

An apparatus for controlling the flow of air and a solid fuel burner. The apparatus comprises: a mechanical temperature sensor for sensing a temperature within the solid fuel burner, the sensor comprising a first elongated portion and a second elongated portion, the first elongated portion and the second elongated portion have different linear thermal expansion coefficients and are arranged such that a first end of the first elongated portion linearly moves relative to a first end of the second elongated portion in response to a change in sensed temperature; a movable valve member for controlling the flow of air through the air inlet; and a mechanism for coupling the first end of the first elongate portion to the movable valve member to close or restrict the air inlet when the sensed temperature increases.

Description

[0001] This application is a divisional application of the patent application for the utility model named "Equipment and solid fuel burner for controlling air flow" with application number 202221229965.4 and application date of May 19, 2022, whose applicant is "Aotai Thermostat (Huizhou) Co., Ltd." Technical Field

[0002] The utility model relates to equipment for controlling the flow of air and a solid fuel burner. Background Art

[0003] Many people around the world rely on solid fuels for heating and cooking, particularly biomass such as wood, agricultural waste, charcoal, and animal dung. The use of wood as a fuel is not limited to developing countries. Many people in developed countries view wood burning as an ecological, carbon-neutral option. If the wood is sourced sustainably, burning wood for heating and cooking can be nearly carbon-neutral.

[0004] Unfortunately, the burning of wood has potentially harmful consequences in the form of the emission of harmful pollutants in the form of smaller carbon particles. These harmful pollutants are known as PM2.5 particles, which are less than 2.5 microns in diameter. In Europe, PM2.5 emissions from wood-burning stoves are already capped, and legislation due in 2022 will reduce the limit to 40mg / m 3 .

[0005] PM2.5 particle emissions from solid fuel burners can be reduced by ensuring the flue gases are above a specific temperature, allowing the particles to be fully combusted before leaving the burner. For example, instructions for a wood-burning stove should provide guidance on how to adjust one or more dampers on the stove to ensure the correct temperature is maintained within the stove. Unfortunately, users are often unaware of damper controls or understand the importance of maintaining a high temperature.

[0006] Automatically controlling the temperature of the flue gases can reduce PM2.5 particulate matter emissions, thereby ensuring that pollutant levels are reduced and the furnace meets the requirements of current and future legislation.

[0007] Most existing solutions involve mechanisms that automatically close the air inlet valve when a specified temperature is reached.The method of sensing temperature can take many forms, each of which has some disadvantages.

[0008] The temperature can be effectively sensed using an electrical sensor such as a thermocouple or thermistor. Simple electronic circuitry can sense when the specified temperature has been reached and energize a solenoid or motor to close the valve. One problem is that many stoves do not have an electrical power source and users do not want to be complicated by batteries in what is essentially considered a simple, low-tech device.

[0009] Some devices use the capillary tube thermostat principle. This employs a hollow metal bulb connected to a diaphragm via a small diameter tube. The bulb, tube, and diaphragm are filled with a liquid or gas with a relatively high coefficient of thermal expansion. When the bulb is heated, the fluid expands, causing the diaphragm to move. This movement is used to close the air inlet valve. A problem with this system is that if the furnace reaches too high a temperature, the fluid can expand to the point where the bulb, tube, or diaphragm ruptures.

[0010] The third type of sensor is the bimetallic strip. This works by bonding together two metal strips with different coefficients of thermal expansion. The resulting strip will bend when subjected to a change in temperature. This movement can be used to close an air inlet valve. The problem with thermal bimetallics is that the maximum temperature they can withstand is 550°C. These high-temperature bimetallics are made from two different grades of stainless steel: the coefficient of expansion is typically 17.2×10 -6 / K austenitic stainless steel and the expansion coefficient is usually 10.5×10 -6 / K ferritic stainless steel. At 550°C, the stress at the interface between the two stainless steels is sufficient to cause plastic deformation of the materials. The result is a relationship between temperature and the shape of the strip, and therefore, if the furnace reaches too high a temperature, the relationship between temperature and whether the valve opens or closes will change. One solution to this is to place the bimetal outside the furnace and use a metal with a higher thermal conductivity, such as copper or brass, to conduct heat to the bimetal. This has the effect of increasing the response time of the device, but also adds an unknown variable, as the temperature difference between the inside and outside of the furnace will be affected by the environmental conditions surrounding the furnace device. Utility Model Content

[0011] Aspects of the invention are defined by the accompanying claims.

[0012] In some embodiments, an apparatus for controlling the flow of air through an air inlet in a solid fuel burner comprises: a mechanical temperature sensor for sensing a temperature within the solid fuel burner, the sensor comprising a first elongated portion and a second elongated portion, the first elongated portion and the second elongated portion having different linear thermal expansion coefficients and arranged such that a first end of the first elongated portion moves linearly in an elongated direction relative to a first end of the second elongated portion in response to a change in the sensed temperature; a movable valve member for controlling the flow of air through the air inlet; and a mechanism for connecting the first end of the first elongated portion to the movable valve member to close or restrict the air inlet when the sensed temperature increases.

[0013] At least some embodiments of the present invention include mechanical devices that rely on the different coefficients of thermal expansion of two materials. However, instead of configuring these materials as a bimetallic strip, the difference in the change in length of two components made of the two materials is used to sense the temperature. For example, if a rod made of a lower expansion material is installed within a tube of a relatively higher expansion material, and one end of each of the rod and the tube is securely fixed together, a change in temperature will cause the free end of the rod to move relative to the free end of the tube along the length of the rod. If the temperature increases, the free end of the rod will move toward its fixed end. A decrease in temperature will cause movement away from the fixed end.

[0014] An advantage of this arrangement is that the resulting movement is dependent on the average temperature change along the length of the two components. Another advantage is that, unlike a bimetallic drive system, the force that can be exerted by the relative movement is very large and is limited only by the buckling force of the rod or tube.

[0015] The rod and tube assembly can be made of any suitable material with different coefficients of thermal expansion. The alloy typically used for this type of temperature sensor is an iron / nickel alloy, commonly known as Invar. The most common composition of this alloy is 36% nickel, the remainder iron. This alloy has a nearly zero coefficient of thermal expansion between -100°C and 200°C. At 150°C, the coefficient is 2×10 -6 / K, at 250℃, the coefficient is 4×10- 6 / K, and at 400°C, the coefficient is 8×10 -6 / K.

[0016] The problem of the increased coefficient of expansion of Invar alloys at high temperatures can be overcome by using suitable ceramic materials. One such material is cordierite, which has a coefficient of expansion of less than 2×10 -6 / K. Another suitable material is quartz, which has an expansion coefficient of 5.5×10 -7 / K. Another suitable material is borosilicate glass.

[0017] Brass or copper has a very high coefficient of expansion, so materials with higher coefficients are suitable. Copper has a coefficient of expansion of 17.7×10 -6 / K (average value between 20°C and 300°C), and brass has a coefficient of 21×10 -6 / K (average value between 20°C and 300°C).

[0018] However, the combustion gases present in wood-burning stoves can corrode copper and brass. A protective coating can be applied to overcome these problems. One suitable coating is nickel, which can be applied electrochemically or using a chemical nickel plating process (electroless nickel plating process).

[0019] Another suitable material with a relatively high coefficient of expansion is stainless steel, particularly austenitic or face-centered cubic stainless steel. Suitable stainless steel grades are grade 321 (SS321) or 1.4341, which have titanium added to them to make them corrosion resistant at high temperatures. SS321 has a 17×10 -6 / K (average value between 20°C and 300°C).

[0020] The assembly of the SS321 tube and the quartz rod within it provides for suitable differential expansion. A 300 mm tube and rod assembly results in a relative motion (or amount of motion) of approximately 0.005 mm per degree Kelvin, and for a temperature change of 400 K, a motion (or amount of motion) of approximately 2 mm. This degree of motion is insufficient to open or close the valve, so a suitable mechanical system is required to amplify the motion (or amount of motion). This can be achieved using a simple lever mechanism.

[0021] An alternative arrangement is to replace the tube with one or preferably more rods. The rods can be joined together at their fixed ends. This allows a material with a higher coefficient of expansion to be located in the center of the assembly while still exposing it directly to the hot flue gases. This system can be arranged so that the mechanism is not damaged if the furnace reaches excessive temperatures. If the tube is made of a material with a higher coefficient of expansion, the end of the rod will move away from the lever if excessive temperatures are reached. If the rod is made of a material with a higher coefficient of expansion, a similar system can be employed by forming a head or step on the end of the rod.

[0022] The rod or tubes typically have a length in the range 200mm to 500mm to give sufficient relative movement (or amount of movement) for the temperature range encountered in a solid fuel burner. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] A detailed description of embodiments of the present invention will now be made, by way of example only, with reference to the drawings identified below.

[0024] Figure 1a and Figure 1b A perspective view of a valve assembly in a first embodiment is shown, wherein Figure 1b Shown in detail Figure 1a The outlined area in .

[0025] Figure 1c and Figure 1d Side views of the valve assembly according to the first embodiment are shown in a closed state and an open state, respectively.

[0026] Figure 2a A perspective view of a valve assembly in a second embodiment is shown.

[0027] Figure 2b and Figure 2c Side views of the valve assembly according to the second embodiment are shown in a closed state and an open state, respectively.

[0028] Figure 3a A side view of a valve assembly is shown in a third embodiment.

[0029] Figure 3b and Figure 3c 2 are perspective views of the valve assembly according to the third embodiment in a closed state and an open state, respectively.

[0030] Figures 4a to 4c 1 is a side view of the valve assembly according to the third embodiment in an open state, a closed state, and an overheated state, respectively.

[0031] Figure 5a is a perspective view of a valve assembly in a fourth embodiment.

[0032] Figure 5b 、 Figure 5c and Figure 5d 1 is a side view of the valve assembly according to the fourth embodiment in an open state, a closed state, and an overheated state, respectively.

[0033] Figure 6a is a perspective view of a valve assembly according to the fifth embodiment.

[0034] Figure 6b and Figure 6care cross-sectional side views of the valve assembly according to the fifth embodiment in an open position and a closed position, respectively.

[0035] Figure 7 A cross-sectional view shows an alternative temperature sensor arrangement used in an embodiment according to the present invention.

[0036] Figure 8 A valve assembly according to an embodiment of the present invention is shown installed in a wood burning stove. DETAILED DESCRIPTION

[0037] In the following description, the same reference numerals are used to indicate functionally similar components. References to directions such as clockwise or counterclockwise are relative to the figures as shown. In some figures, multiple components may be omitted, for example, to more clearly illustrate other components.

[0038] Figures 1a to 1d The valve assembly according to the first embodiment is shown, having a temperature sensor comprising a tube 1 having a relatively high coefficient of thermal expansion and an actuating rod 2 having a relatively low coefficient of thermal expansion positioned within the tube 1. The tube 1 is fixed at one end to a bracket 3 supporting a pivot 4 of a lever 5. Figure 1b An enlarged view of the bracket 3 and tube 1 is shown, with the actuating rod 2 extending from the tube 1. The ends of the actuating rod 2 and the tube 1 located distal to the bracket 3 are fixed together by suitable means (such as a bushing). The outer diameter of the actuating rod 2 is smaller than the inner diameter of the tube 1, thereby allowing relative longitudinal movement of the free ends of the actuating rod 2 and the tube 1 due to differential thermal expansion.

[0039] The free end of the actuating rod 2 is supported on the lever 5, which pivots about the pivot 4 on the bracket 3. When the tube 1 and the actuating rod 2 cool, the length of the tube 1 decreases more than the length of the actuating rod 2, so that the length of the actuating rod 2 extending outside the tube 1 increases. When the temperature increases, the length of the tube 1 increases more than the length of the actuating rod 2, so that the length of the actuating rod 2 extending outside the tube 1 decreases. The change in the length of the actuating rod 2 extending outside the tube 1 allows the lever 5 to pivot. The lever 5 biases the end of the actuating rod 2, for example, by a spring (not shown) and / or by gravity. A movable valve member 6 is mounted at the end of the lever 5.

[0040] The bracket 3 may be mounted on the outer surface of a side wall of a solid fuel burning stove (shown in dotted outline), with the tube 1 and actuating rod 2 projecting into the stove through an aperture in the side wall and the lever 5 extending vertically downwardly from the bracket 3. The movable valve member 6 may be a flapper that moves into contact with the air inlet of the side wall of the stove to block or restrict the air inlet when the valve assembly is in the closed state, as shown. Figure 1d As shown in .

[0041] If the temperature increases beyond the temperature at which the valve assembly moves to the closed state, the protrusion of the end of the actuating rod 2 beyond the end of the tube 1 continues to decrease, causing the actuating rod 2 to lose contact with the lever, thereby ensuring that it will not be damaged due to excessive temperature.

[0042] Figure 7 An alternative arrangement is shown in which the actuator rod 2 comprises a plurality of discrete elements or segments, such as beads or spheres, arranged in a sliding manner and in end-to-end contact within the tube 1. This arrangement is particularly suitable where the actuator rod 2 comprises a brittle material, such as quartz or ceramic.

[0043] Figures 2a to 2c A valve assembly according to a second embodiment is shown, which differs from the first embodiment in that the free end of the actuator rod 2, which has a higher coefficient of thermal expansion, is coupled to the lever 5, for example, by a step or portion of reduced diameter that fits within a slot in one end of the lever 5. This portion extends over a sufficient length of the actuator rod 2 to allow the length of the actuator rod 2 to continue to increase at excessive temperatures without applying force to the end of the lever 5. Alternatively, the rod 2 may have a head portion of increased diameter.

[0044] To ensure that the lever 5 moves in the required direction in response to changes in temperature, the pivot 4 is located between the end of the lever 5 and the moving valve member 6, i.e. the lever 5 is a first order lever rather than a third order lever as in the first embodiment.

[0045] Instead of the tube 1 in the first embodiment, the bracket 3 is connected to the first ends of a pair of fixed rods 1 having a lower thermal expansion coefficient, wherein the second ends of the fixed rods 1 are connected to the fixed ends of the actuating rods 2 having a higher thermal expansion coefficient through connectors 10.

[0046] Alternatively, the fixed rod 1 can be omitted, and the fixed end of the actuating rod 2 can be supported by a structure within the interior of the burner (e.g., opposing inner sidewalls). In another alternative, a pair of brackets 3 can be mounted on opposing sidewalls of the burner, with the actuating rods extending through holes in the opposing sidewalls and actuating corresponding levers on the opposing sidewalls. Thus, at least in the case where the actuating rods have a high linear thermal expansion coefficient, the actuating rod 2 only needs to be supported in some manner so as to be able to actuate the mechanism for closing the air inlet when the temperature increases above a threshold.

[0047] Figures 3a to 3c A valve assembly according to a third embodiment is shown, in which the lever 5 is actuated by the free end of the actuating rod 2 having a higher coefficient of thermal expansion, and the bracket 3 is connected to the fixed end of the actuating rod 2 by a plurality (in this case, four) of fixed rods 1 having a lower coefficient of thermal expansion, as in the second embodiment. However, in this embodiment, the lever 5 comprises two coupled levers 5a, 5b, which provide a greater movement of the movable valve member 6 for a given movement of the free end of the actuating rod 2 and / or allow the length of the lever 5 to be reduced.

[0048] The free end of the actuating lever 2 acts on the first lever 5a, which is arranged as a third-stage lever, causing the first lever 5a to rotate counterclockwise about its pivot axis 4a when the temperature of the actuating lever 2 increases. The free end of the first lever 5a acts on the first end of the second lever 5b, which is arranged as a first-stage lever, causing the second lever 5b to rotate clockwise about its pivot axis 4b, thereby moving the movable valve member 6, which is attached to the second end of the second lever 5b, to its closed position. The free end of the first lever 5a and the first end of the second lever 5b are biased toward the bracket 3 by a spring 7.

[0049] The first lever 5a amplifies the movement (or amount of movement) of the free end of the actuating lever 2 according to the ratio of the distance between the free end of the first lever 5a and the first pivot 4a to the distance between the contact point of the free end of the actuating lever 2 and the first pivot 4a. The second lever 5b also amplifies the movement (or amount of movement) according to the ratio of the distance between the second end and the second pivot 4b to the distance between the first end of the second lever 5b and the second pivot 4b, such that the total amplification is a multiple of these two ratios.

[0050] Figures 4a to 4c One way of showing how overtravel may be provided in the third embodiment to prevent damage if the temperature exceeds the temperature at which the valve is fully closed is shown. Figure 4a The valve is shown in the cool open position, and Figure 4b The valve is shown in the hot, closed position. Figure 4c The valve is shown in an overheated state; the levers 5a, 5b have continued to rotate beyond the closed position. The movable valve member 6 is slidably mounted on a shaft 8 and is biased to the end of the shaft 8 by a spring 9, so that when the shaft 8 slides past the movable valve member 6, the second lever 5b is allowed to continue to rotate even if the movable valve member 6 is in the closed position.

[0051] Figures 5a to 5d A fourth embodiment is shown, which uses a movable valve member 6 that slides parallel to the air inlet opening. In this embodiment, the actuating rod 2 acts on one end of a pivoting crank 5 mounted on the bracket 3. A connecting rod 11 is coupled between the other end of the crank 5 and the movable valve member 6, which is configured as a sliding hit-and-miss vent cover comprising a series of slots within the exhaust portion of the bracket 3.

[0052] In the above embodiment, the movable valve member 6 is positioned a distance away from temperature sensitive components such as the fixed rods / tubes 1, 2. This may be suitable where it is desired to sense the temperature in an upper portion of the furnace or burner, for example just below the flue, but where the air inlet needs to be located at a lower portion of the furnace or burner to allow combustion of pellets. One such arrangement is Figure 8 , in which the bracket 3 is mounted to the outer surface of a side wall 12 of a wood-burning stove, with the temperature sensors 1, 2 protruding through holes in the side wall 12 into the interior of the stove and located below the flue 13. The sensors 1, 2 may protrude perpendicularly to the side wall 12 or at an angle to the side wall 12. The air inlet is located in the lower part of the side wall 12, adjacent to the grille 14.

[0053] Alternatively, in some furnaces it may be desirable to place the air inlet portion of the valve near the temperature sensors 1, 2. In this case, a valve may be used such as Figures 6a to 6c FIG. 1 shows a valve arrangement in a fifth embodiment. In this embodiment, the valve is actuated by the free end of an actuator rod 2 having a relatively low coefficient of thermal expansion. The free end of the actuator rod 2 passes through a hole in the bracket 3; the remainder of the actuator rod 2 and the fixed rod or tube 1 connected between the bracket 3 and the fixed end of the actuator rod 2 are not shown.

[0054] The free end of the actuating rod 2 actuates a pivoting lever 5 which serves to open and close a pair of moving valve parts 6 or flappers by means of a cam mechanism formed by a slot in the lever 5 and a pin connected to a moving valve member 6 which is biased to a closed position, for example by a spring.

[0055] In some embodiments of the present invention, one or more of the movable valve members 6 can be manually moved to an open or closed position, thereby overriding the actuation performed by the temperature sensor. In particular, it may be desirable to allow one or more of the valve members 6 to be manually moved to an open position rather than a closed position. This can be achieved, for example, by a manually operable latch that locks the lever 5 and / or the valve member 6 in the open position.

[0056] Alternative embodiments

[0057] Although the above embodiments have been described with respect to stoves, such as wood-burning stoves or coal-burning stoves, embodiments of the invention may also be applied to other types of solid fuel burners, such as ovens and stoves.

[0058] In some embodiments, the individual features as described above may be combined or omitted.On reading the above description, the skilled person may envision alternative embodiments, which however fall within the scope of the appended claims.

Claims

1. A device for controlling the flow of air through an air inlet in a solid fuel burner, characterized in that The device comprises: a. a mechanical temperature sensor for sensing a temperature within the solid fuel burner, the mechanical temperature sensor comprising a first elongated portion and a second elongated portion, the first elongated portion and the second elongated portion having different linear thermal expansion coefficients and arranged such that a first end of the first elongated portion moves linearly in an elongated direction relative to a first end of the second elongated portion in response to a change in the sensed temperature; b. a movable valve member for controlling the flow rate of the air through the air inlet; and c. Means for coupling the first end of the first elongated portion to the movable valve member to close or restrict the air inlet when the sensed temperature increases.

2. A solid fuel burner, characterized in that: The solid fuel burner comprises the apparatus of claim 1 .

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