Patent Application
20100229768
The invention relates to a method for regulating the output of a solid-fuel furnace having two combustion chambers arranged one above the other or next to each other and separated from each other by a floor or wall, but nevertheless connected to each other by at least one floor or wall opening, wherein the secondary combustion chamber is connected by a secondary exhaust-gas channel to a flue-gas passage, wherein the primary combustion chamber is connected to the flue-gas passage by a transition opening, wherein the transition opening can be closed at least partially by a flue-gas flap, and wherein both a primary air supply and also a secondary air supply are provided. The invention further relates to furnaces having a regulator of the type described above.
A furnace of the type mentioned above is known from European patent application publication EP 1 340 943 A2. The furnace known from the prior art has an upper chamber and a lower chamber, a so-called primary chamber and a so-called secondary chamber connected to each other by a floor, wherein the floor has a floor opening. In the region of the floor opening there is a grate for holding the combustion material. The furnace also has openings in the region of the grate for feeding the primary air, as well as openings for the secondary air in the region of the floor, and here particularly, in the region of the floor opening. Going out from the lower chamber, an exhaust-gas channel is provided that opens into the flue-gas passage of the smokestack. The upper combustion chamber is also provided with an opening to the flue-gas passage. For blocking either the transition from the upper combustion chamber to the flue-gas passage or the opening from the exhaust-gas channel to the flue-gas passage, a pivoting flap is provided. This flap is activated by hand. In addition, another control flap that can be activated manually by a lever is located laterally on the furnace in the region of the floor between the two combustion chambers. The fresh-air supply, that is, on the primary and secondary sides, is regulated as a function of the position of the control flap.
The function of this known furnace is constructed so that, in the mode where the fire burns upwardly as air streams in from the side or from below and streams upward through the opening (“Durchbrand” in German, herein referred to as “upward burning mode”). That is, when the furnace is firing, the flap assumes a position in the region of the flue-gas passage such that the transition from the upper combustion chamber to the flue-gas passage is completely open. At the same time, the position of the control flap is such that a maximum primary air supply is provided. The consequence of this situation is that during this upward burning mode during the firing stage, the combustion material located on the grate, for example wood, “burns up.” After the combustion process, the furnace must be switched by hand to the mode in which the bottom of the pile of combustion fuel, e.g. heap of wood, moves downwardly as it burns (“Unterbrand” in German, herein referred to as “bottom burning mode”). In this mode the flames are directed downwardly or to the side, depending on whether the second combustion chamber is below or to the side of the pile of combustion fuel. This is performed, in particular, in that the flap is pivoted in the region of the flue-gas passage. Here, the operating personnel estimates how far the flap must close the transition opening of the primary chamber to the flue-gas passage, in order to ensure that combustion actually takes place in the lower chamber, that is, so that the flame is directed downwardly into the lower combustion chamber. If such switching of the flap does not take place, then there is the risk of overheating both of the furnace and also of the flue-gas passage. At this point it should be noted that the operation of the furnace in the bottom burning mode has the additional advantage that this operation reduces both the carbon monoxide and also the fine dust content. This is due to relatively high temperatures prevailing in the lower combustion chamber. That is, the goal is always that the switching into the bottom burning mode takes place as quickly as possible.
As already stated at another point, the switching takes place manually in the furnace according to the prior art. Thus, it could definitely happen that someone forgets to pivot the flap in the flue-gas passage, so that the furnace operates completely in the upward burning mode. In such a case or also if the switching to the bottom burning mode is performed too late, output peaks are generated that can lead, as already stated, to increased temperatures in the primary chamber and also in the flue-gas passage, and can possibly cause damage there. Finally, these output peaks also reduce the efficiency, because a large part of the heat in the upward burning mode escapes directly into the smokestack via the flue-gas passage.
Furthermore, a general problem in the batch combustion of solid fuels that exhibit strong out-gassing, as for example wood, is that the combustion profile has a pronounced output peak in the first third of the combustion cycle. In order to prevent emissions of non-combusted gases, in the unregulated operation, the air supply, especially the secondary air, must be designed for this output peak. If the primary air and secondary air are set together, then a high primary air flow is produced, which amplifies the output peak even more. This output peak, in which the greatest part of the fuel batch is combusted, is followed by a phase of the remaining combustion of the wood charcoal with an unnecessarily high air excess. The problem becomes more evident with the use of more fuel.
From this it is clear that the regulation of the furnace by hand is extremely difficult and consequently requires increased attention. In particular, in most cases it cannot be avoided that output peaks are produced during the combustion, wherein these peaks lead to an early burning up of the combustion material and also result in possible damage to the furnace or in the flue-gas passage with correspondingly high temperatures during the upward burning mode.
The object forming the basis of the present invention consequently resides in performing a regulation by which output peaks can be limited with the goal of a continuous output of the furnace, wherein this goal should be achieved essentially automatically.
This object is achieved in that the secondary exhaust-gas channel has a first temperature sensor that regulates the primary air volume flow as a function of the temperature in the secondary exhaust-gas channel, and wherein the secondary air volume flow is kept substantially constant.
This will become clear from the following. At the beginning of the upward burning mode the transition opening from the primary combustion chamber to the flue-gas passage is completely open. In order to move now into the bottom burning mode, the flue-gas flap is at least partially closed. The consequence of this is that the secondary exhaust-gas channel carries a flow of exhaust gases from the secondary combustion chamber. As a result, the temperature increases in the secondary exhaust-gas channel. Now, as a function of the combustion behavior of the combustion material in the first combustion chamber, the flue-gas flap is closed even further. That is, the transition opening between the primary combustion chamber and the flue-gas passage is reduced in cross section even further, which has the result that the temperature in the secondary exhaust-gas channel rises further. When a specified temperature range between 250° C. and 400° C. is reached, the primary air volume flow is now reduced by the first temperature sensor, while the secondary air volume flow is held substantially constant. The reduction of the primary air volume flow by a regulating device connected to the first temperature sensor can be achieved, for one, in that a pivoting primary air flap is arranged in a primary air channel of the furnace, and the position of the flap can be regulated, as already stated, by the first temperature sensor.
A different variation resides in that the cross section of opening of the floor or the wall between the two combustion chambers is adjustable, indeed as viewed from the side of the primary combustion chamber, so that the secondary air flow is not affected by the reduction of the primary air volume flow. The consequence of this is that the combustion behavior is held essentially constant by temperature control.
As already explained at another point, the transition opening from the primary combustion chamber to the flue-gas passage can be blocked at least partially by a flue-gas flap. The outlet of the secondary exhaust-gas channel to the flue-gas passage likewise can be blocked. That is, during the upward burning phase, the transition opening between the primary chamber and the flue-gas passage is completely open or essentially completely open and, in parallel to this, the outlet of the secondary exhaust-gas channel is blocked. The opening of the secondary exhaust-gas channel is realized in parallel with the blocking of the transition opening between the primary combustion chamber and the flue-gas passage. In this connection it is provided that a single flue-gas flap is provided for blocking the outlet of the secondary exhaust-gas channel and the transition opening. In this way, a reduction of the transition opening between the primary combustion chamber and the flue-gas passage results, virtually automatically, in an increase of the throughput of the secondary exhaust-gas channel to the flue-gas passage.
In this connection, in particular, a second temperature sensor is provided in the flue-gas passage essentially directly after the transition opening from the primary combustion chamber to the flue-gas passage, wherein the position of the flue-gas flap is regulated by this sensor as a function of the temperature at the second temperature sensor. As a whole, not only the output limit of the furnace is now achieved with the goal of a constant combustion behavior, but in this way the possibility is likewise opened up that the operation of the furnace is quasi-automated. Thus, the temperature, which the second temperature sensor measures after the transition opening, is characteristic for the progress of the combustion material in the upward burning mode. If this second temperature sensor indicates a high temperature, then the exhaust-gas flow from the primary combustion chamber is to be reduced, in order to prevent damage both to the primary combustion chamber and also to the flue-gas passage. A corresponding change in the position of the flue-gas flap takes place in the temperature range between 150° C. and 300° C., preferably however at approximately 200° C. That is, when a temperature of approximately 200° C. is reached in the flue-gas passage directly after the transition opening, the flue-gas flap now assumes an angled position from the position in the state of combustion—that is, during upward burning in which the transition opening from the primary combustion chamber was open and the secondary exhaust-gas channel was closed—so that the transition opening is closed to the degree that the secondary exhaust-gas channel is open. Through such temperature-dependent regulation both of the primary air supply and also the position of the flue-gas flap, not only is the combustion made more uniform with the goal of preventing output peaks, but the operation convenience is also increased due to the temperature-controlled regulation.
A furnace with a regulation of the type described above distinguishes itself by a slide for changing the free cross section in the wall or floor opening. This can take place, for one, in that the slide has two discs that can rotate relative to each other, in particular rotatable discs having individual openings, which have the advantage that a visually pleasant flame image is achieved according to the orientation of the openings in the slide.
According to another feature of the invention, a thermal energy accumulator is arranged in the secondary combustion chamber. Such an energy accumulator does not primarily have the task of storing the heat in the furnace and thus allowing a uniform heat discharge, but instead is used, in particular, for reducing the CO content in the exhaust gas. This is realized to the extent that, when the combustion output decreases due to the progress of the combustion of the combustion material, the exhaust-gas temperature is held high by the energy accumulator, constructed, for example, as a grog plate, at least for a certain time period so that residual-gas combustion is guaranteed.
According to another feature of the invention it is provided, in one embodiment, that the floor of the primary combustion chamber is constructed so that, on the one hand, it has an opening to the secondary combustion chamber and, on the other hand, as an ash pan it receives the ash. According to the second embodiment, the ash pan is located on the floor of the primary combustion chamber. Thus, only the fly ash, i.e., particles entrained with the flow, still passes through the opening in the floor or the wall. For a low ash fraction in the secondary combustion chamber, better mixture of the flue gases with the secondary air can be achieved by corresponding installed equipment. Finally, a very thorough mixture of the pyrolysis gases with the secondary air ensures a reduction of the CO content in the exhaust gas. As an additional advantage, the unpleasant appearance of ash in the secondary combustion chamber is eliminated and this secondary combustion chamber can be freely shaped. The support grate in the primary combustion chamber can be mounted on the ash pan and is very easily accessible for cleaning.
It was already noted at another point that for reducing the primary air volume flow, the secondary air volume flow is held substantially constant. This is realized in the simplest case in that the volume flow can be regulated separately both in the secondary air channel and also in the primary air channel.
According to another advantageous feature of the invention, it is provided that the primary air channel opens into the upper region of the primary combustion chamber. That is, the primary air flows through the primary combustion chamber from the top to the bottom. In contrast to the prior art in which both the primary air and also the secondary air are introduced laterally into the furnace housing, by the separation according to the invention it is guaranteed that the volume flows are not interrupted and that the primary air is used simultaneously for flushing the discs, without the direction of flow having to be reversed. The secondary air channel for the supply of the secondary air volume flow is provided in the area of the floor or the wall between the combustion chambers.
The foregoing summary, as well as the following detailed description of the invention, will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there are shown in the drawings embodiments which are presently preferred. It should be understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown.
In the drawings:
The components of both furnace embodiments are identical in function. They are designated differently below only through the addition of the letter “a,” because they have, in part, different positions in the furnace.
The furnace designated overall by 1 has two chambers, namely the primary combustion chamber 10, 10a and the secondary combustion chamber 20, 20a. The furnace slides to be opened are designated by 12, 22; 12a, 22a. The primary combustion chamber 10, 10a and the secondary combustion chamber 20, 20a are separated by a respective partition, namely the floor designated overall by 30 or the wall designated by 30a. The floor 30 or the wall 30a has an opening 31, 31a, wherein a secondary air channel 32, 32a used for supplying the secondary air volume flow is also provided in the floor or in the wall. In addition, the furnace exhibits a primary air channel 40, 40a having a primary air flap 45, 45a by which the volume flow is adjustable. The air flows of both channels are controlled or regulated separately. The ash pan 33, 33a connected to the support grate 34, 34a is arranged on the floor.
In front of the opening 31, 31a there is a slide 35, 35a, connected to the temperature measurement point 28, 28a, and the cross section of the opening is changed by this slide in a controlled way.
The secondary combustion chamber 20, 20a has an opening to the secondary exhaust-gas channel 25, 25a. The secondary exhaust-gas channel 25, 25a opens into the flue-gas passage 60, 60a. Between the primary combustion chamber 10, 10a and the flue-gas passage 60, 60a there is a transition opening designated by 11, 11a, where the secondary exhaust-gas channel 25, 25a opens into the same flue-gas passage 60, 60a. The secondary exhaust-gas channel 25, 25a is closed by the flue-gas flap 65, 65a arranged so that it can pivot on the furnace in a position “A” (upward burning mode—shown in
The subject matter of the invention is now, in particular, the arrangement of a first temperature sensor in the secondary exhaust-gas channel 25, 25a, preferably in the region of the floor 30 or the wall 30a. The temperature sensor 28, 28a arranged there connects to a lever mechanism and ensures that, for example, in the construction as a bimetal, the floor or wall opening 31, 31a is reduced or increased in size by the slide 35, 35a as a function of the measured temperature. The temperature measurement sensor could also be connected selectively to the fresh-air supply flap 45, 45a and could regulate, in this way, the supply of primary air. Thus, in fact, the primary air volume flow is actually regulated both by the change in the free cross section of the floor or wall opening 31, 31a and also by the direct change of the primary air volume flow.
In addition, a second temperature sensor 68, 68a, which controls the position of the flue-gas flap 65, 65a, is located in the flue-gas passage directly behind the transition opening 11, 11a.
The functioning of the furnace is represented as follows. During the firing, that is in the upward burning mode, the flue-gas flap 65, 65a is in position “A” and blocks, in this respect, the secondary exhaust-gas channel 25, 25a to the flue-gas passage 60, 60a. That is, all of the flue gases generated during the upward burning mode escape through the transition opening into the flue-gas passage 60, 60a. The supply of primary air is at a maximum. In this mode, the air from the channel 32, 32a acts as the primary air. Now, when a temperature of approximately 200° C. is detected by the second temperature sensor 68, 68a, then the flue-gas flap 65, 65a is pivoted in the direction of the arrow 69, that is to the transition opening 11, 11a. The consequence of this is that the flame changes quickly due to the suction and the at least partially closed transition opening 11, 11a, and the opening of the secondary exhaust-gas channel into the secondary combustion chamber 20, 20a changes correspondingly thereto. If a temperature that lies at approximately 300° C. to 350° C. is detected by the first temperature sensor 28, 28a, then the primary air volume flow is reduced. This takes place, in particular, either in that the free cross section of the floor or wall opening is reduced between the two combustion chambers, or else in that the flap 45, 45a is pivoted correspondingly in the primary volume flow. That is, the combustion is regulated. In this way, the temperature at the temperature sensor 28, 28a naturally decreases. This has the consequence that the primary air volume flow increases, which is implemented, in particular, in that the free cross section of the floor or wall opening between the combustion chambers increases or correspondingly the position of the flap 45, 45a provides for an increase in the primary air volume flow. In this way, the output of the furnace increases, because, as already stated, the primary air volume flow, that is the supply of fresh air, is increased. Correspondingly, the secondary air volume flow decreases proportionately. In this connection, it was already explained that the secondary air volume flow and the primary air volume flow correlate with each other in terms of quantity. Now, if the temperature at the temperature sensor 68, 68a falls below approximately 200° C., then the flue-gas flap 65, 65a opens corresponding to the arrow 69a. That is, finally, the secondary exhaust-gas channel is progressively closed by the flue-gas flap 65, 65a. The combustion material located in the primary chamber now burns further upward, whereby it is ensured that the exhaust gases can escape directly upward into the flue-gas passage.
The furnace also has available a heat accumulator 70, 70a arranged in the secondary combustion chamber 20. By the combustion in the secondary combustion chamber in the bottom burning mode, this accumulator 70, 70a heats up and ensures that, in the case of reduced combustion output due to increasing combustion of the combustion material, the temperature in the secondary combustion chamber still remains relatively high for a certain time period, which boosts the combustion of the residual gases.
It will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular embodiments disclosed, but it is intended to cover modifications within the spirit and scope of the present invention as defined by the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2009 012 905.7 | Mar 2009 | DE | national |
