EP2292975A2 - Draught inducing apparatus for wood firing apparatus - Google Patents

Abstract

The device has a gas supplying unit (11) that is arranged outside of a gas exhausting line. An air guiding line (12,13,14,15) is provided in flow direction of a combustion chamber (2). The gas supplying unit is provided to supply air or other gas by the air guiding line. A cross-section surface of the air guiding line is smaller than the cross-section surface of the gas exhausting line. Independent claims are also included for the following: (1) a wood combustion device, particularly wood stove, chimney or boiler; and (2) a method for operating an in-channel-setting device.

Description

The invention relates to wood firing (wood stoves, cheminees, apartment barbecues, etc.) based on the natural draft principle (or chimney effect). Such wood furnaces are widely used both in residential and commercial as well as in holiday homes and in mountain huts as well as, for example, central heating devices in the form of automatic pellet or woodchip boilers. In particular, the invention relates to a device for improved starting of a firing process of a wood firing.

The chimney effect or natural draft is a physical phenomenon that is based in particular on traditional, conventional wood firing. The fire, warms the air. Due to the lower density compared to cold air, a buoyancy is created for the warm air. The warm air rises and exits through the mouth of the fireplace. This creates a vacuum at the bottom, which draws in oxygen-rich fresh air, which further fuels the fire. As a result, the fire temperature rises, and there is a positive feedback. In the chimney effect, the height of the chimney is an important factor: For example, in the case of chimney construction, the rule of thumb is that the chimney height must be at least four times that of any oven pipe sections that may run across the room.

In contrast to natural train combustion, there are wood gasification boilers, which have a significantly better efficiency and lower emission values than natural draft combustion systems. Such wood gasification boilers are based on a forced draft. In wood gasification boilers, controlled air supply and controlled draft ensure that gasification of the fuel is spatially separated from combustion of the fuel gas produced. Wood gasification boilers are based on the DC gasifier (or gasifier) principle, where the gas produced is at a very high temperature, completely breaking down tar and pyrolysis products, which has a beneficial effect on both efficiency and emissions. The combustion of the wood takes place in a low-oxygen (reducing) atmosphere downwards, contrary to the natural tendency of hot gases to flow upwards. Therefore, the natural chimney effect can not be used or at least not directly. in the Generally, therefore, a suitable blower is required, which promotes the combustion gases down. Depending on the design, there is usually a heat-resistant induced draft fan in the exhaust gas flow or a pressure fan in the fresh air supply.

In wood furnaces based on the natural draft principle, the draft of air through a combustion chamber or combustion chamber always takes place from bottom to top, and also the gas discharge from the combustion chamber or combustion station increases monotonously, with at most horizontal sections. However, a widespread problem associated with the operation of wood-burning stoves and the like inside living quarters is the initial start-up of the fire when the furnace and the pipes for discharging the flue gases (stovepipe, chimney) are still cold. Often, the fire will suffocate relatively soon after firing, and thick smoke will flow out of the furnace into the interior of the house. This is attributable to the fact that the rising flue gases cool in the chimney and therefore do not rise further - the draft is interrupted. Often one tries to counter this by trying to keep the fire going by blowing, possibly by means of bladder, into the combustion chamber, but this does not solve the problem, and moreover it is very tedious. Kaminbauer offer more professional solutions to the problem. A first solution is to raise the chimney height to increase the chimney effect. However, this solution is often not feasible for a variety of reasons, moreover it is expensive and does not always work. Another professional, effective, but also expensive solution to the problem is placing a chimney fan, ie a gas conveyor - generally an axial fan with the diameter of the stovepipe; other geometries are also on the market - in the fireplace. By this a draft is forced through the furnace and the Gasabführleitung, which effectively solves the problem. A disadvantage of this solution is the very high cost and the fact that moving parts in a highly corrosive environment in the interior of the gas discharge line or at the outlet to the atmosphere are present. The solutions according to the prior art have in common that they start causally appropriate for the actual fireplace, ie in the vertical part of the gas discharge, as far away from the burning location and as close to the mouth of the fireplace.

Analogous to the problem described above with the operation of wood-burning stoves, the automatic setting of the fire in pellets and woodchip boilers is also difficult, and often additional equipment or geometric changes to the exhaust ducts are necessary here as well.

From the scriptures US 4,441,436 . US 4,413,571 and FR 2 284 828 approaches are known to obtain the necessary forced train in wood gasification boilers. In US 4,441,436 It is proposed to assist the train generated by a downstream stack by blowing gas at a colder temperature than the draft gas. This method is based on the fact that the temperature difference promotes convection; however, the process only works when the gas flowing in the chimney is already hot, ie after the burning process has started. According to US 4,413,571 a blower is used to blow air into the combustion chamber; with the same blower, in particular during the refilling of fuel, the train in the gas discharge line can be maintained by also blowing air into the fume hood. The FR 2 284 828 teaches to generate the train through a Venturi pump on a downdraft carburetor. These approaches have in common that they concern DC gasifier, in which a train in the combustion chamber is to be generated against the natural flow direction. The approaches concern the continuous operation of this carburetor and not putting it into gear. Due to the higher demands on the boilers and the combustion and the very high combustion temperatures of approx. 1100 ° C, which are necessary for the effect, such DC gasifier approaches are completely unsuitable for the improvement of conventional wood combustion systems.

It is an object of the invention to provide a device for improving the burning behavior in wood furnaces (wood stoves, fireplaces, apartment grills, boilers for pellets or wood chips, etc.) which overcomes the disadvantages of the prior art and which in particular is inexpensive and simple the maintenance is.

A device according to the invention is suitable both for attachment to already existing wood firing systems and as a component of newly produced wood firing systems. Such wood furnaces have a combustion chamber or burning point, at which the wood fire should burn, as well as an air supply into the combustion chamber or to the combustion chamber and a Gasabführleitung, which usually has a fireplace and often also in this opening stovepipe. The direction of flow in the combustion chamber or at the firing point is from bottom to top, as a result of which the wood firing is based on the natural draft principle (and also the gas discharge from the combustion chamber or firing point preferably increases monotonically, with at most horizontal sections). The device according to the invention is characterized essentially by the fact that it has a gas conveyor arranged outside the gas discharge line, which conveys ambient air (or possibly another gas such as nitrogen) via an air supply line into the gas discharge line in such a way that at the mouth of the air supply line in the Gasabführleitung the air flow has a parallel to the flow direction of the combustion gases component. The air supply line has a significantly smaller cross-sectional area than the gas discharge line, at least in the area of the mouth into the gas discharge line.

The ambient air supplied to the gas discharge line (or the other gas) does not have to be heated during this process; for the sake of minimizing energy consumption, the air supplied is advantageously not heated (this of course does not preclude a minimum warm-up by the waste heat of the gas-conveying means, but rather means "unheated" that there are no separate heating means).

When starting a fire in an oven, fireplace or boiler, there may be a problem that the inside of the gas exhaust duct (ie, the chimney and the stovepipe) is colder and therefore heavier than the ambient air, and therefore a flow through the in General upwards and in the environment leading gas discharge line initially does not materialize. A similar problem can also result in otherwise unfavorable weather conditions, unfavorably sized fireplaces, etc. According to the invention it is now proposed to remedy this problem by simply blowing air into the chimney, in the direction of flow.

It has been shown in experiments that the problem of setting in motion of the burning process is reliably solved by this amazingly simple and easy to implement approach. It is also surprising that contrary to the previous view of the professional world sufficient if in the inventive way a train in the vicinity of the combustion chamber / combustion, for example. A maximum of 2 m away, is generated (the distance is, for example, from the grid on which the fire burns ago measured). Although the problem to be solved is the lack of heating of the chimney (ie, the natural draft producing vertical portion of the gas exhaust duct) and the resulting cooling of the gases even before reaching the chimney muzzle, the draft need not be generated near the orifice. This can happen, for example, even in the horizontal section of the gas discharge line, and even if there is no temperature difference between the injected gas and the gas in the gas discharge line. This allows an easy retrofitting of existing wood firing, for example, in the room in which the oven is, by installing an air supply into the easily accessible stovepipe inside.

One mechanism which may contribute to the functioning of the approach according to the invention is that a flow is also generated in the gas discharge line by the incoming air, whereby, according to Bernoulli's theorem, a slight negative pressure is created. As a result, gas is sucked in from the combustion chamber or combustion point, thus initiating the necessary flow.

• Erstens kann anstelle eines sehr teueren und grossen sowie aufwändig zu installierenden (im Innern des Kamins oder als Kaminaufsatz auf dem Hausdach) ein kostengünstiger Lüfter verwendet werden, der bloss Luft durch eine im Querschnitt verhältnismässig kleine Luftförderleitung - die Querschnittsfläche beträgt im Allgemeinen weniger als ein Fünftel, besser weniger als ein Zehntel, vorzugsweise weniger als ein Zwanzigstel oder sogar weniger als ein Dreissigstel der Querschnittsfläche der Gasabführleitung am Ort der Mündung - fördern muss. Es reicht daher im Allgemeinen ein Lüfter mit einer Leistung von weniger als 150 Watt, oft gar weniger als 100 Watt oder weniger als 70 Watt und beispielsweise nur 15-60 Watt. Durch diese geringe Leistungsaufnahme kommt die erfindungsgemässe Einrichtung auch für Berghütten ohne Stromanschluss und nur mit Photovoltaik-Anlage in Frage

Compared to conventional chimney fans, the procedure according to the invention has distinct advantages:

• First, instead of a very expensive and large and expensive to install (inside the fireplace or as a mantel on the house roof), a low-cost fan can be used, the air only through a relatively small in cross-section air conveyor line - the cross-sectional area is generally less than one-fifth , preferably less than one-tenth, preferably less than one-twentieth, or even less than one-thirtieth of the cross-sectional area of the gas exhaust duct at the location of the orifice. Therefore, a fan with a power of less than 150 watts, often less than 100 watts or less than 70 watts, and for example only 15-60 watts, is generally sufficient. Due to this low power consumption, the inventive device is also suitable for mountain huts without electricity and only with photovoltaic system in question

As a fan, a radial fan is preferably used, which can promote even at the mentioned comparatively small power and air through an air supply line, for example, a few decimeters to a few meters with a sufficiently large throughput; but also axial fans or other gas delivery principles are not excluded. With a ratio of the cross-sectional area between Gasabführleitung and air supply line at the location of the mouth, for example, between 30 and 40, the air velocity in the region of the mouth is preferably about 5-25 m / s.

Second, the fan only needs to deliver ambient air and no aggressive fumes. Therefore, it does not have to be particularly resistant to corrosion. There are preferably no moving and therefore potentially repair-prone parts inside the Gasabführleitung and therefore difficult to access and exposed to the flue gas.

As a fan alternative gas conveying a pressure bottle in question, from which the gas (compressed air, nitrogen, etc.) flows directly into the air supply line. Particularly advantageous because virtually maintenance-free, however, as mentioned, the use of a fan, which promotes ambient air into the air supply.

The mouth of the air supply line into the gas discharge line is connected downstream in the direction of flow of the combustion chamber or combustion station, i. It is located in the area where no flames have come in during normal operation of the wood firing. It is located, for example, at least 50 cm from the point at which the fire burns in normal operation. However, it can be arranged as mentioned in the not too great distance, for example. A maximum of 2.5 m or 2 m away from the place of wood firing.

Advantageously, the supply of the air flow in a region in which the gas discharge line is substantially straight. The air supply line then preferably extends into the gas discharge line and has a section parallel to the gas discharge line in front of its mouth. The section extending parallel to the gas discharge line is preferably at least approximately 3 times as long as its diameter.

The device according to the invention will be used, for example, during an initial operation. Depending on the furnace configuration and existing burning power, as well as other factors such as weather, etc., the initial operation, during which an air supply by means of gas conveyors in the gas discharge line, maintained during a limited period of, for example, between 30 and 60 minutes, during this period often only during very short intervals of a few seconds to about 1 minute air must be supplied. Instead of the initial operation with air supply at intervals (for example, each manually set in smoke or in pre-programmed intervals) and an initial operation with continuous air supply is possible.

Following initial operation, the gas flow is generally kept going by itself due to the thermals. The gas conveying means can be switched off; a controller can cause this, for example, automatically.

The device may optionally have, in addition to the described means, a sensor which detects a smoke development and is in communication communication with a controller which sets the gas conveying means in smoke development immediately automatically.

• Figur 1 eine sehr schematische Darstellung eines Holzofens, an welchem mögliche Platzierungen von Luftzuführleitungen eingezeichnet sind; und
• Figur 2 eine Darstellung, teilweise im Schnitt, eines Holzofens.

Hereinafter, embodiments of the invention will be described in more detail with reference to figures. In the figures, like reference characters designate like or analogous elements. Show it:

• FIG. 1 a very schematic representation of a wood stove, on which possible placements of air supply lines are shown; and
• FIG. 2 a representation, partly in section, of a wood stove.

The wood stove 1 according FIG. 1 is of the type wood stove cooker. It has a combustion chamber 2, the bottom of which is formed by a grate 3. Below the grate 3 an ash receptacle is present, in which an air supply 4 opens from outside the furnace. On the upper side, a horizontal smoke extraction area 5 closes to the combustion chamber 5 on, through which the hot flue gases are passed and thereby, for example, a not directly above the combustion chamber lying hearth and / or a baking area warms up. To the horizontal smoke extraction area closes a stove pipe 7, which opens into a chimney 8. The smoke extraction area 5 of the oven, the stovepipe 7 and the chimney 8 together form the Gasabführleitung. The solid arrows 10 illustrate the gas flow in normal operation. In continuous operation, the gas flow is generally kept in motion by the thermals of the furnace itself, and no dedicated drive means are required.

However, at the beginning of the kiln operation, when it is completely cooled, the gas drain often does not come by itself, which is why the fire in the combustion chamber 2 is often stifled and biting smoke flows out of the combustion chamber.

According to the invention, in such a situation or in order to prevent such a situation, air is now blown into the gas discharge line, namely parallel or approximately parallel to the intended direction of flow, that is to say in the forward direction. This happens after the combustion chamber, i. the incoming air does not enter the fire but rather is blown away in the direction of it. Thereby, a gas flow is obtained on the intended path shown by the solid arrows, and the burning process and the gas exhaust behavior are kept going and stabilized.

In the FIG. 1 schematically a gas conveying means 11 - for example, an electrically operated radial fan - and four possible placements of the air supply line or its mouth region are shown, wherein per oven preferably only one of these air supply lines 12, 13, 14, 15 is present. As represented by the corresponding dashed arrows 12, 13, 14, 15, the corresponding air supply line has a mouth section at least approximately parallel to the flow direction in the gas discharge line.

FIG. 2 shows a furnace 1 of a type without a horizontal flue, wherein the air supply line 16 is tapered in the area in front of its mouth in order to obtain the optimum inflow velocity in the mouth region and still to optimize the flow resistance.

Example 1:

To start a firing process in a furnace of the type according to FIG. 1 with a stovepipe 120 mm in diameter, a radial fan with a power of about 20 watts and an air supply line of a length of about 60 cm and a diameter of about 20 mm were used to air at the in FIG. 1 Blow in place designated 14. The calculated flow velocity in the area of the mouth of the air supply line was about 12 m / s. Any incipient smoke development was stopped immediately by switching on the radial fan in this configuration and the firing process was immediately started again.

Example 2:

In an oven of the type according to FIG. 2 with a furnace tube of diameter 200 mm, a radial fan with a power of about 56 watts and an air supply line with a length of about 1.5 m and a diameter of about 60 mm and at the mouth area of 30 mm were used to air the in Fig. 2 Blow in place designated 16. The calculated flow velocity in the area of the mouth of the air supply line was about 15 m / s. Here, too, any incipient smoke development was stopped immediately by switching on the radial fan in this configuration and the firing process was immediately started again.

Claims (11)

Device for improved setting of a firing process in a wood firing (1), wherein the wood firing a combustion chamber (2) or combustion with an air supply (4) and a Gasabführleitung (5, 7, 8), whereby a flow direction of the Air supply is defined by the combustion chamber and the gas discharge line to a mouth of the gas discharge line, wherein the flow direction in the combustion chamber or at the focal point from bottom to top, and wherein the device comprises a gas conveying means (11), characterized in that the gas conveying means (11) is arranged outside the gas discharge line (5, 7, 8), and in that the device further comprises an air supply line (12, 13, 14, 15, 16) which opens downstream into the gas discharge line in the flow direction of the combustion chamber (2) or combustion station. wherein the gas conveying means conveys air or another gas through the air supply line and the air supply line in the region of Mouth in the gas discharge line has a component parallel to the flow direction, and wherein a cross-sectional area of the air supply line is smaller than a cross-sectional area of the gas discharge line. Device according to claim 1, characterized in that it is free of moving parts in the flue gas in the Gasabführleitung (5, 7, 8). Device according to claim 1 or 2, characterized in that the air supply line (12, 13, 14, 15, 16) in the region of its mouth into the Gasabführleitung (5, 7, 8) is parallel to the flow direction. Device according to one of the preceding claims, characterized in that the gas conveying means (11) is an electrically operated fan. Device according to claim 4, characterized in that the fan is a radial fan. Device according to one of the preceding claims, characterized in that in the region of the mouth of the air supply line into the Gasabführleitung the inner cross-sectional area of the air supply line is less than one twentieth of the inner cross-sectional area of the gas discharge line. Device according to one of the preceding claims, characterized in that the mouth of the air supply line is at least 50 cm from the point at which a fire burns during normal operation of the device. Device according to one of the preceding claims, characterized in that the mouth of the air supply line is at most 2 m away from the point at which a fire burns during normal operation of the device. Device according to one of the preceding claims, characterized in that the gas conveying means is so controlled or controlled that it is permanently switched off after reaching a normal operating state. Wood firing, in particular wood-burning oven (1), fireplace or boiler, with a combustion chamber or combustion chamber, with an air supply (4) and with a Gasabführleitung (5, 7, 8), whereby a flow direction of the air supply through the combustion chamber or the burner and Gas discharge line is defined to a mouth of the gas discharge line, wherein the flow direction in the combustion chamber or at the focal point from bottom to top, characterized by a device according to one of the preceding claims. A method of operating a device according to any one of claims 1 to 9 or a wood firing according to claim 10, wherein a fire is lit in the combustion chamber or at the focal point and the gas conveying means are switched on when smoke develops, and wherein the gas conveying means is switched off after reaching a normal operating state.

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