EP3008383B1 - Small-scale furnace system with integrated structure - Google Patents

Description

The registration concerns a small combustion system with installation.

State of the art

Small combustion systems are one of the main sources of particulate and numerous gaseous emissions, such as CO, VOC and PAHs, which have a significant impact on human health. These pollutants are formed in the event of incomplete combustion due to non-optimal oxidation conditions (local oxygen, active residence time and temperature). Due to the complicated process involved in the combustion of solid fuels, the fulfillment of the oxidation conditions is only possible through highly developed, well-designed combustion technology with intelligent control.

The small combustion systems most common in residential areas have a thermal output of less than 15 kW. There is a tendency to use more and more small combustion systems with a thermal output of less than 15 kW due to the increasing number of passive and low-energy houses as well as the energetic renovation of existing buildings. The improvement of the combustion in these plants should lead to a significant reduction of the pollutant emissions in residential areas.

The systems available to date for reducing flammable dust and gaseous pollutant components in small combustion systems are based on the catalytic principle or the filtration principle. These systems are either installed within the combustion systems or are installed downstream outside the combustion systems or in exhaust systems
Recently, a large number of different catalytic exhaust gas cleaning systems have been developed for use in small combustion systems for the treatment of flammable gaseous and dusty pollutants (soot, CO, CnHm, PAH, etc.), which, however, are not to be described in detail here. With catalytic exhaust gas cleaning systems, this is sometimes the case Problem that the catalytic converter is damaged over time and its function is impaired
A number of non-catalytic emission control systems have also been developed. The non-catalytic exhaust gas cleaning systems, which are to be installed in the small combustion system or in the connection piece, are mostly based on the principle of the storage filter. A foam structure is used, which can also be catalytically coated. The dusty pollutants should be deposited on and in the foam structure and, when favorable temperatures are reached, be burned freely. The inorganic constituents remain in the foam structure, which has to be cleaned manually from time to time due to the increase in flow resistance.

From the DE 20 2010 007 246 U1 an apparatus for treating exhaust gases in a small combustion plant is known. The apparatus comprises a housing with a base and a cover. A catalytic converter device, which has a catalytic material, is present in the housing. This is a ceramic that can be used to catalyze the oxidation of the exhaust gases. The catalytic converter device has a multiplicity of openings through which the exhaust gases can flow. The bottom of the apparatus has an opening through which exhaust gas from the small combustion system can be passed into the apparatus and the lid has an opening through which the treated exhaust gas can be discharged.

From the DE 10 2008 009 004 A1 a small combustion system for biogenic fuels is known. This has a feed device for solid fuels, a boiler containing a combustion chamber and heat exchanger, an induced draft and a chimney. A fine dust filter with a renewable, profiled filter medium for separating coarse, fine and / or fine dust is provided as a filtering separator between the boiler and the induced draft or the chimney. This reduces fine dust emissions.

The DE 29 27 725 A1 discloses a method and a device for preventing condensation, in particular for heating chimneys. For this purpose, a connection is provided between the warm air atmosphere in the vicinity of the boiler and the fresh air supply. A mixture of dry, warm, externally supplied gas with the gas mixture located in the chimney is to be produced by means of a device for mixing and fed into the chimney area and passed through the chimney to dry. The mixture should be produced essentially over the entire circumference of the exhaust pipe. The warm externally supplied gas can in particular be room air.

From the FR 658 071 A a combustion system is known. Solids are burned in the furnace. The flue gas flows through flame tubes. The flame tubes are kept at a temperature which is intended to ensure complete combustion of the flue gas.

From the DE 94 04 544 U1 a furnace is known which has a flue gas duct which is arranged in the interior of the furnace. The flue gas pass starts from the combustion chamber and tapers in cross-section. A helix for guiding the flue gas is arranged in the flue gas duct.

From the EP 0 798 510 A2 a heating boiler that can be filled with solid fuels, in particular wood, is known. The boiler has a combustion zone that can be flown through from bottom to top. The combustion zone has a chimney-shaped combustion shaft arranged with an upright axis, which at its lower end is connected to the filling shaft via at least one tangentially opening inflow channel. An insert made of refractory material with high heat capacity is arranged in the combustion shaft. EP 0 798 510 A2 discloses the preamble of claim 1.

From the GB 473 417 A a device for consuming the smoke from a kiln is known. For this purpose, a body with a high heat capacity is arranged in the flue gas duct, which body has several baffles. A gas flame protrudes into the flue gas duct to burn the smoke.

From the DE 640 470 C a furnace is known with a furnace closing device for flue gas dedusting and combustion. In this case, incompletely burned gases are passed through a highly heated blade system consisting of heat-storing surfaces and irradiated from the grate. This gives the gases time to take on the temperature required for combustion and to mix well with the addition of second air.

Exchange page

From the EP 2 530 386 A1 a chimney fireplace is known which comprises a combustion chamber with an openable door and a chimney connection in order to supply heating gases from the combustion chamber through the chimney connection to a chimney. There is also a heating gas space which is arranged in the flow direction of the heating gases between a filter element through which heating gases flow and the chimney connection. The filter element is located in the upper, in particular the rear, area of the combustion chamber. Soot and aerosols are filtered in the filter element and burned at high temperatures.

The object of the invention is to provide a small combustion system which enables low-emission operation with as little effort as possible.

Solution

The object is achieved in particular by the features of the independent claim. The dependent claims indicate advantageous further developments. The description and drawings provide further details.

According to the invention, a small combustion system is disclosed with an installation which mixes combustible exhaust gas components with combustion air and has a heat capacity which prevents the temperature of the combustion from falling below a desired minimum temperature due to a temporarily reduced combustion output. The mix should generally be fine. Mixing is usually achieved with the benefit of microturbulence. The heat capacity of the installation is a prerequisite for storing a sufficient amount of energy in the form of heat. It is also necessary that the energy is quickly absorbed and released quickly. The desired minimum temperature is usually the minimum oxidation temperature.

The installation can thus fulfill two functions at the same time, which improve the combustion. On the one hand, the important mixing of combustion air and combustible exhaust gas components is improved. In addition, falling below the minimum temperature is prevented. For example, when adding more wood, the combustion output temporarily drops in a small combustion system. In addition, heat is required to warm the wood. Without countermeasures, this would lead to the temperature falling below a desired minimum temperature. The heat capacity of the installation can counteract this. Of course, this presupposes that the installation has previously been appropriately heated by the combustion, i.e. that sufficient energy has been stored in the form of heat for the oxidation. However, this is exactly what is usually guaranteed. Except at the beginning of the combustion operation, the combustion output is usually sufficient to achieve this. In addition, some of the combustion takes place during the installation anyway. The installation therefore causes an increased constancy of the temperature, i.e. a homogeneous temperature distribution or a homogeneous temperature field. Avoiding falling below the minimum temperature leads to improved combustion. This has two major advantages. On the one hand, this reduces unwanted exhaust emissions. On the other hand, the efficiency of the combustion increases. Because of the improved Combustion, i.e. the improved oxidation, the installation can also be viewed as an oxidation module. Because of the heat storage properties, a designation as high-temperature storage module is also appropriate.

In addition to a sufficiently high heat capacity that allows a sufficient amount of energy to be stored, the heat conduction and heat transfer must also be high enough so that the heat can get into the installation quickly enough and, above all, removed from the installation quickly enough and for the oxidation reactions can be provided.

The materials used and, as a result, especially the installation as a whole, must be sufficiently resistant to temperature changes in order to withstand the temperature changes.

The structure not only improves the mixing of combustible exhaust gas components with the combustion air, but also generally ensures an extension of the active dwell time during the combustion. The stored thermal energy enables oxidation in unfavorable operating phases such as B. when placing wood and leads to a stable operation, i.e. a stable combustion process, during the entire combustion process.

The effects of incorrect operation, in particular the placing of wood in too large a quantity by unskilled users, can be reduced accordingly.

The operation of the installation does not require an active energy supply. A certain energy requirement results from the pressure loss, even if this is low. The energy consumed by the pressure loss is converted into heat that is desired anyway. If the pressure loss does not require the use or higher performance of a fan, the energy consumption due to the pressure loss is irrelevant anyway. This can only be a disadvantage when using, for example, electrical energy for a fan.

The installation generally leads to an increase in performance. The installation is therefore also advantageous for the user himself, in any case it is not a disadvantage. Many measures known in the prior art for reducing emissions are associated with a reduction in the performance of the small combustion system. This leads to the temptation to bypass the installation or to expand it again. The elimination of this temptation is an advantage of the present installation, since it can be assumed that the achievable reduction in emissions will actually be achieved is achieved. The installation can also be made inaccessible, which limits manipulation. Since the cross-section is not significantly reduced when the built-in unit is used, no bypass or heating flap is required. This facilitates the construction and in turn avoids the possibility of manipulation.

The improved thermal oxidation achieved through the installation is not subject to aging and is not damaged by undesirable exhaust gas components such as sulfur dioxide, heavy metals and fine dust, including chloride and potassium salts, as can happen in the catalytic process, as these exhaust gas components often lead to the poisoning of the catalytic converter.

Although doing without a catalytic exhaust gas treatment avoids some problems, it is nevertheless possible to continue to provide catalytic surfaces in order to supplement and / or strengthen the effect of the installation.

By preheating the installation before the start of operation of the small combustion system or heating the installation during operation, the minimum temperature can sometimes be prevented even better, so that the expenditure on equipment and the additional energy consumption can be justified.

In one embodiment of the invention, the incorporation brings about an enlargement of the reaction zone, that is to say the volume in which the oxidation takes place is enlarged. Since this is an active reaction, it is often referred to as an active reaction zone. The increase in volume is due to the above-described effects of better mixing of combustible exhaust gas components with combustion air, i.e. mostly by favoring the microturbulence and the increased temperature constancy.In a larger reaction zone, the combustion can take place better overall.

As a rule, the installation is not only easy and inexpensive to implement, disposal is also usually simple.

According to the invention, the installation is made up of a plurality of elements. This enables problem-free adaptation to various small combustion systems. The installation can usually be easily retrofitted anyway. This applies in particular to an installation made up of a plurality of elements. Uniform or different elements can be combined. The elements can be linked deterministically or non-deterministically, systematically or not systematically, in a structured or non-structured manner.

The elements can be cross-linked for better functionality. This can be advantageous for the thermal conduction described later within the installation, but it can also serve to improve mechanical stability.

Of course, it is also possible to provide larger modules, so that in many cases a single module could be sufficient as an installation.

In one embodiment of the invention, the installation is formed by one or more modules made of cast material. A module made of cast material is comparatively easy to manufacture. The heat can often be transported well within such a module, since there are no thermal resistances at the transition from one element to an adjacent element. As a rule, it should be beneficial to provide a single module. An installation can also consist of several modules.

According to the invention, the elements of the installation are Pall rings. A Pall ring is a hollow cylinder with blades that point inward. There are usually holes on the outside. The blades and holes give the impression that the blades are formed, as it were, from the wall of the hollow cylinder that is bent inward at the points of the holes. Such Pall rings are commercially available and can be assembled for installation with the properties and advantages outlined above.

In one embodiment of the invention, the built-in elements are metallic and / or ceramic and / or stony components or a combination of both. Of course, it is crucial that the elements can withstand the high temperatures. Therefore, the choice will very often fall on ceramic or stony components, since ceramic components, including components of a different type than the components described here, have proven themselves in small combustion systems. For example, the Pall rings described above are available in ceramic. With the Pall rings as elements you can. In general, materials can be used which have already proven themselves in many industrial applications.

In one embodiment of the invention, the installation causes microturbulence in the combustion air. With a low increase in flow resistance, microturbulence improves the mixing of combustible exhaust gas components and combustion air.

In one embodiment of the invention, the installation has thermal conduction properties which are suitable for compensating for temperature differences within the installation. So can Local temperature drops can be avoided, since the installation allows the heat to flow away quickly enough from areas in which the temperature is high enough that the temperature does not fall below the minimum even if there is heat flow. This generally ensures a homogeneous temperature field. The heat conduction properties of the installation depend on the one hand on the heat conduction of the material used. Particularly in the case of an installation made up of elements, it is also necessary to ensure good thermal contact between the elements.

According to the invention, the installation has surfaces with adhesive properties for exhaust gas components such as soot and aerosols. This is achieved by using suitable materials. In addition, the structure of the surface is important, so a rough surface is usually desirable. On the one hand, roughness increases the available surface; on the other hand, soot and aerosols can more easily accumulate on a rough surface. While in the case of the filters mentioned in the prior art, the dust has to be removed by more or more complex processes, in the case of the installation proposed here this is done in the course of the operation of the small combustion system. There can be operational situations in which soot and aerosols accumulate. However, these are regularly followed by operating situations in which soot and aerosols are removed from the surfaces and are burned. Soot and aerosols often contain pollutants or are in themselves pollutants.

In one embodiment of the invention, the installation causes a multiple diversion of combustion air and / or exhaust gas. This can be achieved, for example, by arranging a large number of Pall rings. But other built-in components can also do this. A multiple diversion of the combustion air and / or the exhaust gas leads to an improved mixture of combustible exhaust gas components and combustion air and thus to lower emissions and higher combustion efficiency. Above all, however, the combustion is improved by the increased residence time.

Further details are to be explained below with the aid of figures.

Fig. 1

eine Seitenansicht eines Einbaus aus einer Vielzahl von Pall-Ringen als Elemente

Fig. 2

eine Sicht von oben auf den Einbau nach Fig. 1

Fig. 3

einen Vergleich der CO-Emissionen mit und ohne Einbau

Fig. 4

einen Vergleich der CnHm-Emissionen mit und ohne Einbau

Fig. 5

einen Vergleich der CO₂-Emissionen mit und ohne Einbau

Show it

Fig. 1

a side view of an assembly of a plurality of Pall rings as elements

Fig. 2

a view from above of the installation according to Fig. 1

Fig. 3

a comparison of the CO emissions with and without installation

Fig. 4

a comparison of the CnHm emissions with and without installation

Fig. 5

a comparison of the CO ₂ emissions with and without installation

Figure 1 Figure 12 shows a side perspective view of an installation with a plurality of elements formed by Pall rings. Pall rings of this type are normally used in process engineering equipment to improve flow conditions, phase separation and to generate large mass transfer surfaces. Up to now, such an installation has not been used or investigated in combustion processes.

Figure 2 shows a plan view of the installation according to Fig. 1 . Ceramic Pall rings with a diameter of 50 mm and a thickness of 0.8 mm are used as elements.

Due to the larger exhaust gas paths in the installation shown, the dust particles cannot be separated out by sedimentation or spearing. Flue gas routes with dimensions> 3 mm are available for installation. As a result, blockage of the installation and thus an increase in the flow resistance is not to be expected.

A low flow resistance or pressure loss can be achieved through the structured systematic construction of the installation, which ensures sufficiently large defined exhaust gas paths. With an exhaust gas volume flow of 50 Nm3 / h through an installation with the dimensions 30 x 25 x 20 cm, a pressure loss of 3 to 5 Pascal is to be expected.

Since the installation consists or has to be built up from several elements, if necessary also elements with different sizes, there is the possibility of installing this technology in many combustion systems with different constructions without great effort.

The ceramic used is available and durable. A service life of more than 15 years can be expected. The ceramic has proven to be very robust against unfavorable fuels such as damp wood and waste as well as against rough operating phases and unsteady combustion, such as. B. proven in the start-up phase.

The installation used should have a very rough surface and have mini-turbulators that are distributed horizontally (or transversely to the exhaust gas flow) in the entire installation cross-section at different heights.

Figure 3 shows the mean carbon monoxide, Figure 4 the mean hydrocarbon and Figure 5 the mean carbon dioxide concentration curves when burning beech wood in one old wood stove with and without ceramic installation under standard test conditions. In doing so, four burn-ups were averaged. The dashed line shows the course without installation, the solid line with installation

It can be seen that the carbon monoxide (CO) and the hydrocarbons (CnHm) are significantly lower with the use of the built-in than without the built-in. The two components (CO and CnHm) sink quickly after the wood stove door is closed and remain at a low level for a long time, even in the burnout phase. This behavior is more noticeable with hydrocarbons than with carbon monoxide. The reason for this is that the installation can provide the heat required for the oxidation - even over a long period of combustion and in critical operating phases. It should be noted that the in Figures 3 to 5 The CO and CnHm and CO ₂ curves shown were obtained for all burns (over 260 burns) regardless of the type of fuel charge or the operator of the wood-burning stove.

Out Figure 5 it can be seen that the _{volume fraction of CO 2} in the exhaust gas is higher when built-in is used than without built-in. This is due to the better conversion of the fuel carbon during the combustion process. The efficiency of the combustion can be improved by increasing the _{proportion of CO 2 in the exhaust gas.} In the preliminary test program or in this test series, the efficiency was increased from 71% to 80%.

The polycyclic aromatic hydrocarbons (PAHs) and volatile organic compounds (VOCs) when using internals can be reduced, as they normally correlate with the CO and CnHm over a long period of the combustion process or can be treated thermally accordingly.

It should be mentioned that the results described above can be improved even further from the current point of view, since an optimization should be possible through professional action.

Claims (7)

1. Small-scale furnace having an installation that brings about mixing of combustible exhaust gas constituents with combustion air and has a heat capacity that prevents a drop in the combustion temperature below a desired minimum temperature by a temporary lowering of the combustion output, characterized in that the installation has surfaces having adhesive properties for exhaust gas components such as soot and aerosols and is constructed from a multitude of elements, wherein the elements of the installation are Pall rings.
2. Small-scale furnace according to Claim 1, characterized in that the installation brings about an increase in size of a reaction zone.
3. Small-scale furnace according to either of the preceding claims, characterized in that the installation is formed by one or more modules made of cast material.
4. Small-scale furnace according to any of the preceding claims, characterized in that the elements of the installation are metallic and/or ceramic and/or lithoid components.
5. Small-scale furnace according to any of the preceding claims, characterized in that the installation causes microturbulences in the combustion air.
6. Small-scale furnace according to any of the preceding claims, characterized in that the installation has thermal conduction properties capable of compensating for temperature differences within the installation.
7. Small-scale furnace according to any of the preceding claims, characterized in that the installation brings about repeated deflection of combustion air and/or exhaust gas.

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