EP0472895A1 - Apparatus for controlling the exhaust gas temperature in a furnace - Google Patents

Abstract

An apparatus for controlling the exhaust gas temperature in heating boilers (10) is proposed, in which boilers the exhaust gases are conducted to the outside by at least one exhaust gas flue (11 to 13) which is provided with heat exchange ribs (17) which cool the exhaust gases. A bypass pipe, which bridges at least a part of the at least one exhaust gas flue (13), is designed as a pipe (18) which can be inserted into this exhaust gas flue and the flow outlet end (20) of which bears an element (23, 24) which changes the flow cross-section depending upon the temperature. With decreasing output of the heating boiler, the exhaust gas temperature at the outlet would cool so that there is a danger of formation of condensates. This is prevented in that the element (23) opens in the event of cooling exhaust gas temperature at the outlet, so that the exhaust gases essentially flow through the pipe (18) with decreasing cooling. This pipe (18) for exhaust gas temperature control can be inserted into heating boilers simply and economically, even subsequently. <IMAGE>

Description

The invention relates to a device for regulating the exhaust gas temperature in boilers, in which the exhaust gases are guided to the outside through at least one exhaust gas duct which is provided with heat exchanger fins which cool the exhaust gases, with a bypass line bridging at least part of the at least one exhaust gas duct with a flow cross section increasing temperature reducing element is provided.

In modern boilers, the flue gas temperature, i.e. the temperature of the flue gases when leaving the boiler, must be set very precisely, because on the one hand, when the temperature falls below a minimum temperature of 160 ° C, condensate condenses in the flue gas pipes, from which acids form, which lead to a strong Cause corrosion. On the other hand, an upper limit temperature of 260 ° C should not be exceeded with regard to legal regulations, whereby high exhaust gas temperatures also lead to a reduction in efficiency. For boilers with constant output are driven, the problems described are relatively easy to master, since the exhaust gas temperature can be adjusted in the desired manner by dimensioning the exhaust gas flues and heat exchanger fins. With modern boilers, however, there is an increasing tendency to run with variable output, for example to reduce the burner output to 30% in the transition period. This leads to a drastic reduction in the exhaust gas temperature. If the burner output is highly variable, it is therefore not possible to keep the flue gas temperature within the specified temperature range without additional measures.

From DE-OS 36 04 842 a device for controlling the exhaust gas temperature in boilers according to the type mentioned is known. There, separate exhaust gas channels without heat exchanger fins are provided for setting the exhaust gas temperature, which either lead from the combustion chamber to the outlet of the exhaust system or bridge two exhaust gas ducts. The throughput through these exhaust gas ducts can be varied by means of an adjustable flap, with a large throughput increasing the exhaust gas temperature and a closed flap leading to lowering the exhaust gas temperature.

The disadvantage of this known device is that these additional flue gas channels take up an additional volume and are therefore difficult to implement or can only be implemented with great effort in boilers which are of compact construction anyway. Furthermore, a complete redesign of a boiler would be required, and retrofitting in older systems is not possible.

An object of the present invention is therefore to improve a device for regulating the exhaust gas temperature in boilers according to the type mentioned in such a way that a redesign of existing boilers can be avoided with a space-saving arrangement and that existing boilers can also be retrofitted with exhaust gas temperature control in a simple manner can be provided.

This object is achieved according to the invention in that the bypass line is designed as a tube which can be inserted into the at least one exhaust gas duct, the end of which on the flow outlet side carries the element which changes the flow cross section as a function of temperature.

Since this regulating pipe can be used in existing flue gas flues, practically no additional space is required and such an installation is also possible retrospectively with existing boilers. Since this pipe also carries the element which changes the flow cross-section as a function of temperature, it can be inserted as a complete unit in at least one flue gas duct of a heating boiler without requiring any additional assembly work. Both the manufacture and the assembly are therefore very simple and inexpensive. By dimensioning the pipe cross section and / or The element that changes the flow cross section can be easily adapted to the respective boiler construction or to the desired flue gas temperature.

Advantageous further developments and improvements of the device specified in claim 1 are possible through the measures listed in the subclaims.

The insertable pipe is preferably arranged in the central region of the exhaust gas duct and extends radially outward essentially up to the heat exchanger fins. When the flow cross section is reduced by the element, the exhaust gas is therefore increasingly forced to flow exclusively along the heat exchanger fins, where it is cooled. On the other hand, the pipe has hardly any effect on the flow conditions when the flow cross-section is open, so that conditions then exist as when the pipe is not used. This pipe can therefore be used to lower the flue gas temperature from the originally designed flue gas temperature at the boiler outlet. This insertable tube is expediently carried by the heat exchanger fins, so that additional holding devices can largely or completely be dispensed with.

By arranging the end of the pipe on the flow outlet side in the connection region of the boiler with an exhaust pipe, the exhaust gas temperature at the element that changes the flow cross section can be simultaneously at the same time right place.

The element which changes the flow cross section is advantageously designed as a temperature-dependent deflectable flap, through which an opening on an outlet-side end plate of the tube can be closed. The flap is expediently designed as a swivel flap. These measures also help to simplify and reduce the cost of the construction.

Another measure to simplify the construction is that a deflection device for the flap consists essentially of a temperature-dependent changing element. As a result, the measured value acquisition, that is to say the temperature acquisition, the controller and the actuator, is realized by one element. This temperature-dependent element is expediently designed as a bimetallic element, which is preferably designed as a helically wound bimetallic sheet which carries the flap at its free end.

The device according to the invention is also particularly suitable for boilers with a plurality of flue gas ducts connected in parallel, in which case such pipes designed as a bypass line are used in all or most of these flue gas ducts, as required. If the output of the burner is only slightly varied, it may be sufficient to use such a pipe only in one of several flue gas ducts.

The pipe and the element changing the flow cross-section are expediently dimensioned such that the set temperature of the exhaust gas when it emerges from the boiler is between 160 ° and 260 ° C., preferably 180 ° C.

Embodiments of the invention are shown in the drawing and explained in more detail in the following description.

Fig. 1

einen Heizkessel mit drei Abgaszügen in einer Querschnittsdarstellung, wobei in den oberen Abgaszug ein Rohr mit den Strömungsquerschnitt temperaturabhängig veränderndem Element eingesetzt ist, als erstes Ausführungsbeispiel der Erfindung,

Fig. 2

einen Vertikal schnitt durch den in Fig. 1 dargestellten oberen Abgaszug senkrecht zur Bildebene von Fig. 1,

Fig. 3

eine vergrößerte Darstellung des als schneckenförmig aufgewickeltes Bimetallblech ausgebildeten Elements am austrittsseitigen Ende des Rohres und

Fig. 4

eine Vertikalschnittdarstellung eines Heizkessels mit mehreren parallelgeschalteten Abgaszügen in einer Bildebene gemäß Fig.2 als zweites Ausführungsbeispiel der Erfindung.

Show it:

Fig. 1

a boiler with three flue gas ducts in a cross-sectional view, a pipe with an element which changes the flow cross section depending on the temperature being inserted in the upper flue gas duct, as a first exemplary embodiment of the invention,

Fig. 2

2 shows a vertical section through the upper exhaust duct shown in FIG. 1, perpendicular to the image plane of FIG. 1,

Fig. 3

an enlarged view of the formed as a helical bimetallic element at the outlet end of the tube and

Fig. 4

a vertical sectional view of a boiler with a plurality of flue gas ducts connected in parallel in an image plane according to Figure 2 as a second embodiment of the invention.

In the first exemplary embodiment shown in FIGS. 1 to 3, a boiler 10 has three serpentine exhaust gas flues 11 to 13, the exhaust gas flue 11 being designed as a combustion chamber in the lowest level. At the outward opening of the flue gas duct 11 or the combustion chamber, a combustion chamber door 8 is arranged, which carries a burner 9, which can be designed as a gas, oil or solid fuel burner and generates a burner flame 14 pointing into the interior of the boiler 10 during operation . The cavities 15, which are arranged around the exhaust gas flues 11 to 13 and are separated by walls (not shown), contain the heating medium or heating medium channels (not shown) through which the heating medium flows, the heating medium being represented by small serpentine lines. This can be a liquid, such as water, or a gas, which is pumped in a known manner through radiators (not shown) of a heating system. At the outlet end of the last, upper exhaust duct 13, an exhaust pipe 16 is flanged, which leads the exhaust gases to a chimney, not shown.

The walls of the exhaust gas flues 11 to 13 are provided with heat exchanger ribs 17 which protrude radially inwards into the exhaust gas flues 11 to 13. For simplification, such heat exchanger fins 17 are only shown on the walls of the upper exhaust duct 13. These heat exchanger fins 17 serve for better heat transfer from the burner flame 14 or the exhaust gases formed thereby to the heating medium.

The previous description relates to the part of the boiler 10 which is known per se. Therefore, the simplifications mentioned have been made in the illustration and the description could also be limited to the basic things. The following part relates to the actual device for regulating the exhaust gas temperature of the boiler 10.

In the upper exhaust duct 13, a flat tube 18 with a rectangular cross-section is inserted in such a way that it lies against the radially inward-facing end faces of the heat exchanger fins 17 and is held by them. 2, no heat exchanger fins are shown on the sides of the tube 18, so that it extends there essentially up to the walls 19 of the exhaust gas duct 13. Of course, heat exchanger fins can also be arranged on these sides. The rectangular cross section of the tube 18 is determined by the substantially correspondingly shaped cross section of the exhaust gas duct 13. If this has a different cross-sectional shape, the corresponding shape of the tube 18 naturally also changes.

At the flow outlet end 20 of the tube 18, this is closed by an end plate 21 which has a through opening 22 which is only slightly smaller than the inner cross section of the tube 18. This passage opening 22 can be closed by a pivotable flap 23, which in the region of its pivot axis is attached to a bimetallic sheet wound in a helical shape 24 is attached. Of course, the flap 23 itself can also be designed as a one-piece, flat extension of the bimetallic sheet 24. The inner end of the helically wound bimetallic sheet is rigidly connected to the end plate 21 by a holding device 25 shown in broken lines. This holding device 25 can also be designed, for example, as a housing which accommodates the bimetallic sheet 24 which is wound in a helical shape.

The mode of operation of the first exemplary embodiment shown in FIGS. 1 to 3 consists essentially in that the exhaust gas temperature at the exhaust gas outlet of the boiler 10, that is to say at its connection point to the exhaust pipe 16, is detected by the bimetallic sheet 24. Depending on the temperature prevailing there, the flap 23 opens more or less. A partially open flap is shown in dashed lines in FIG. 3. If the output of the burner 3 is reduced, the exhaust gas temperature at the outlet of the boiler 10 would decrease and possibly drop below 160 ° C., which could lead to the formation of condensate and correspondingly to corrosion. In order to counteract this, the flap 23 opens more and more when the exhaust gas temperature drops, so that the exhaust gases in the upper exhaust gas duct 13 essentially flow through the pipe 18 and no longer past the heat exchanger fins 17, where there is a substantially higher flow resistance. As a result of the flow through the tube 18, there is only a small amount of heat exchange and the exhaust gases are cooled only slightly in the exhaust gas duct 13. Increases on the other hand, the exhaust gas temperature again, the flap 23 closes accordingly, and the exhaust gases are forced to flow past the heat exchanger fins 17 again, where they are cooled more.

By suitable dimensioning of the cross sections of the tube 18, the through opening 22 and the bimetallic sheet 24 it can be achieved that the exhaust gas temperature at the outlet of the boiler 10 is always about 180 ° C. regardless of the output of the burner 13.

In a modification of the exemplary embodiment shown, the tube 18 can also only partially extend into the exhaust gas duct 13 if, for example, only a smaller power reduction of the burner 13 is provided. In such cases, for example, the cross section of the tube 18 can also be smaller than the free space between the heat exchanger fins 17, the tube 18 optionally also having a separate holder and no longer abutting the heat exchanger fins 17.

Depending on the location at which the exhaust gas temperature is to be regulated, the tube 18 can also extend more or less into the exhaust tube 16.

In the second exemplary embodiment shown in FIG. 4, the flue gas duct 12 of a boiler 10 'is divided into two flue gas ducts 12a and 12b connected in parallel, while the third flue gas duct 13 is divided into three parallel flue gas flues 13a, 13b and 13c. A pipe 18 for exhaust gas temperature control is used in each of the exhaust gas flues 13a to 13c. Here, too, it depends on the dimensioning and the power range of the burner whether such pipes 18 are used in all exhaust gas flues 13a to 13c or only in one or two of them.

Other boiler designs can also have a much larger number of flue gas ducts connected in parallel. Here, too, the exhaust gas control can be finely adjusted by inserting a more or less large number of tubes 18 into these exhaust ducts connected in parallel.

Boilers with three trains are shown and described in the exemplary embodiments. Of course, the invention can also be used for boilers with a different number of trains, for example for boilers with two trains.

In particular in the case of a boiler being fitted as standard with such tubes 18 for regulating the exhaust gas temperature, these tubes can also be permanently installed, for example firmly connected to the heat exchanger fins and / or to free walls of the exhaust gas flues.

Claims (12)

Device for regulating the exhaust gas temperature in boilers, in which the exhaust gases are led to the outside through at least one exhaust gas duct which is provided with heat exchanger ribs which cool the exhaust gases, wherein a bypass line bridging at least part of the at least one exhaust gas duct with an element which reduces the flow cross section with increasing temperature is provided, characterized in that the bypass line is designed as a tube (18) which can be inserted into the at least one exhaust gas flue (13; 13a, 13b, 13c) and whose end (20) on the flow outlet side carries the element (23, 24) which changes the flow cross section as a function of temperature . Device according to claim 1, characterized in that the insertable pipe (18) is arranged in the central region of the exhaust gas duct (13; 13a, 13b, 13c) and extends radially outwards essentially up to the heat exchanger fins (17). Device according to claim 2, characterized in that the insertable tube (18) is carried by the heat exchanger fins (17). Device according to one of the preceding claims, characterized in that the end (20) of the pipe (18) on the flow outlet side is arranged in the connection region of the boiler (10) with an exhaust pipe (16). Device according to one of the preceding claims, characterized in that the element which changes the flow cross section is designed as a temperature-dependent deflectable flap (23) through which an opening (22) on an outlet-side end plate (21) of the tube (18) can be closed. Apparatus according to claim 5, characterized in that the flap (23) is designed as a swivel flap. Apparatus according to claim 5 or 6, characterized in that a deflection device for the flap (23) consists essentially of an element (24) which changes as a function of temperature. Device according to claim 7, characterized in that the temperature-dependent element (24) is a bimetal element. Apparatus according to claim 8, characterized in that the bimetallic element (24) is designed as a helically wound bimetallic sheet which carries the flap (23) at its free end. Device according to claim 9, characterized in that the bimetal element (24) is arranged on the outside of the end plate (21). Device for boilers with several flue gas ducts connected in parallel according to one of the preceding claims, characterized in that such pipes (18) designed as a bypass line are inserted in all or in most of these flue gas ducts (13a, 13b, 13c). Device according to one of the preceding claims, characterized in that the temperature of the exhaust gas set by the at least one inserted pipe (18) when it emerges from the boiler is between 160 ° and 260 ° C, preferably 180 ° C.

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