EP0079980B1 - Gas or oil fired water-heating or steam-generating boiler - Google Patents

Abstract

1. Warm water, hot water or steam boiler having gas or oil firing, in particular for heat supply to small and medium consumers, in which the flue surfaces bounding the combustion chamber are formed as a membrane wall consisting of annular tubes (11) receiving the heat-carrying medium which are connected together by thin plates, characterised in that the flue (1) is formed as a body of revolution having a changing cross-section corresponding to the amount of heat flow and is outwardly surrounded by a convective heat transfer surface (2) which is adapted to its shape and is also formed as a membrane wall and forms a flue gas channel (3), the annular tubes (11) of the membrane wall of the flue (1) being arranged offset relative to the annular tubes (12) of the membrane wall of the convective heat transfer surface (2).

Description

The invention relates to a hot water, hot water or steam boiler with gas or oil firing, in particular for supplying heat to small and medium-sized consumers.

The construction of the gas and oil-fired boilers that are currently being produced and used to supply heat to heating centers, communal buildings, houses, etc. was actually developed from conventional designs by redesigning the coal-fired boilers. The conventional boiler designs are designed to meet the requirements of coal firing. With the spread of gas and oil firing, the manufacturers tried to make their existing designs suitable for gas and oil firing with the least possible redesign. As a result, the gas and oil-fired boilers do not yet meet the requirements of modern heating technology in many respects. During the conversion process of the boilers, such constructions were first developed in which the heat transfer took place primarily by convection. The use of thermal radiation only started later, and this development path is not yet complete. From what has been said, it is clear why most types of boilers hardly differ from the designs for coal firing.

A distinction can be made between two basic types of industrial boilers: the cylindrical horizontal boiler and the so-called steep tube boiler with an angular combustion chamber. The former form the basis of the heating systems with lower output, while the latter are used particularly for large consumers.

With the cylindrical lying boilers you can see that the conversion to gas and oil firing consists only of the removal of the fire grate and a slight change in the cross-section of the flues. The extent of this redesign suggests that these measures did not produce good results when the coal-fired boilers were converted to gas and oil. However, the above-mentioned modifications resulted in a number of disadvantages, the most important of which is that the construction of the conventional flame tube can no longer meet the requirements of modern heating and heating technology. In the earlier boiler designs for coal firing, there were completely different heat loads and internal pressure conditions. It was possible to achieve favorable heat transfer by making slight use of the radiation energy, but in particular by convection at a low operating steam pressure (and thus in connection with lower strength loads and a smaller wall thickness).

Today's modern gas and oil burners allow a much more effective use of radiation energy. Approximately 70 to 80% of the energy entered in the combustion chamber is made usable by radiation, through a considerable thermal load on the surfaces delimiting the combustion chamber. The share of convective heat emission drops from 60 to 70% to 10 to 20%. The efficiency has improved and instead of 60 to 70% you can already reach 80 to 95%. The consequence of these decisive changes is that the heat load on the combustion chamber boundary surfaces has become considerably larger and the heat distribution has become more uneven. The radiation energy can increase along the flame axis, from the burner in the direction of combustion, depending on the firing conditions, even by orders of magnitude. At the same time, the convective heat transfer both in the axial direction and on the horizontal or vertical planes means a different heat load.

In general, the first, front part of the flame tube is subjected to a relatively low, the middle part to a larger and the rear part or the turning chamber to a much too high heat load. In addition to this excessive heat load on certain parts of the flame tube, there is also the fact that precisely at such points no sufficiently intensive circulation is guaranteed, which results from the construction of the boiler. As a result, the requirements for the quality of the feed water also increase. Uniform heat dissipation is one of the most important operating conditions, which further increases the operating problems and costs.

Another disadvantage of the conventional, cylindrical, horizontal boiler is that, together with the performance, the dimensions of the structures and their wall thickness must also be increased. The wall thicknesses, which are much too large, limit the possibility of increasing the output. This relationship also determines the performance range of these constructions. For this reason, the operation and manufacture of such boiler designs at higher outputs is no longer economical.

Another disadvantage of these constructions is that the heat transfer factor of the areas exposed to the greatest heat, i. H. of the flame tube end, the turning chamber and the flame tube wall is unfavorable.

In contrast to what is desired, the flue gas pipe is the cheapest in terms of strength, although it is only exposed to convection and a relatively low thermal effect. In addition, its heat transfer factor is also more favorable than that of the structural parts with high thermal loads.

The much too high thermal load on the irradiated surfaces, their unfavorable cooling and high surface temperature as well as their unfavorable heat transfer factor also affect the strength of these construction parts. This significantly reduces the lifespan of these boiler designs. The lifespan of the original designs (for coal firing) was around 50 years, while that of today's designs is only 15 years. This significant reduction in lifespan results from the boiler technology disadvantages of this system, i. H. from the lack of adaptation of the design to the new operating conditions.

As a result of the disadvantages of the horizontal, cylindrical boiler construction mentioned, a device which is much too large is built for a relatively low output, the unnecessarily installed materials being a disadvantage in every respect. Only 50% of the built-in area is used for heat transfer. The manufacture of this type of boiler is expensive, the transportation and the accommodation of such devices is quite cumbersome because they take up a lot of space.

In addition to the disadvantages mentioned, the horizontal cylindrical boiler designs have the advantage that the combustion chamber has a cylindrical cross section, so that they are relatively well adapted to the radial heat radiation. The heat loads of the combustion chamber resulting from the convection can be distributed relatively evenly in the radial direction by the eccentric arrangement of the burner - by changing the amount of heat radiation.

In modern steep tube boilers with an angular combustion chamber, the boundary walls are known as membrane walls, i.e. H. formed from ring tubes connected by thin plates (see e.g. GB-A-2 023 780). These boiler systems were also developed from the coal-fired boilers, but with significant changes. The advantage of the vertical tube boiler systems with membrane wall is that the strength relationships of the construction are not related to the increase in performance. The wall thickness of the surfaces exposed to the greatest heat load - and thus the strength and heat transfer conditions - is quite favorable. The proportion of heat-transferring and heat-emitting surfaces is 1.7 times as large as that of the horizontal cylindrical structures. The strength ratios of the steep tube boilers are 10 times cheaper than the flame tube boilers (i.e. the horizontal cylindrical boilers) with the same output. From the point of view of modern heating and heating requirements, however, there are still numerous problems that can be derived from the "conventional" design. A significant disadvantage of this type of boiler is, for example, that its life decreases by 30 to 40% when switching to gas or oil heating. Another disadvantage is that the intensity of the radially directed radiation is smallest in the corners and greatest in the line of the planes lying in the vertical and horizontal axial directions, the greatest convective heat load also affecting the top surfaces the most.

The two boiler systems also have common disadvantages. The combustion chamber surfaces are unevenly loaded in both cases because the amount of heat emitted by radiation changes along the flame axis. The heat load on the combustion chamber surfaces is lowest due to the radiation in the vicinity of the burner and at the end of the flame, i. H. at the rear of the boiler, the largest.

The flue gases generated during the combustion are formed in the foremost part of the flame in the least and in the middle in the greatest amount. Due to their convective heat transfer, the heat load on the rear combustion chamber surfaces increases even further.

Neither natural circulation nor pressure circulation is adapted to these changing heat loads, and they cannot be adjusted satisfactorily due to technical difficulties. In this way, the surface temperature of the components exposed to the critical thermal loads is considerably higher than desired.

The unfavorable thermal conditions also affect the quality requirements of the feed water, which results in a significant increase in investment costs. In the above-mentioned mode of operation, the boilers can easily become defective, so that their service life is 40% to 50% shorter than that which can be achieved with a uniform thermal load. The built-in areas are only about 60% used for heat generation. The unnecessarily installed materials increase the manufacturing costs.

The aim of the invention is to eliminate the disadvantages of the conventional designs while maintaining or increasing their advantages.

The invention has for its object to provide a boiler with fully utilized heat transfer surfaces and long life, which ensures better operational safety and more economical heat production than the previous constructions and can be produced with modern manufacturing technology with a low material cost.

The invention was developed using the latest test results of modern heating and heating technology, in particular the results of the measurements carried out with the aid of infrared technology in the combustion chamber. It was recognized that the cross section of the flame tube changed in accordance with the distribution and extent of the radiant heat energy and the convective heat transfer should be, whereby a uniform heat load on the combustion chamber surfaces can be guaranteed. According to a further finding, a uniform heat transport and thus a further increase in the service life can be achieved by a water-side circulation which is designed in accordance with the heat transfer.

The object is achieved according to the invention in that the flame tube of the boiler, the surfaces of which are designed as a membrane wall, is designed as a rotating body with a cross section which changes in accordance with the degree of heat radiation, and from the outside by a convective shape which is adapted to its shape and is also designed as a membrane wall Heat transfer surface forming a flue gas channel is surrounded, the ring tubes of the membrane wall of the flame tube being offset relative to the ring tubes of the membrane wall of the convective heat transfer surface, are expediently arranged in each case half the distance between the ring tubes of the other membrane wall.

According to an advantageous embodiment of the invention, the flame tube is designed as a truncated cone which extends from the end wall holding the burner to the rear wall of the combustion chamber.

According to a further advantageous embodiment of the invention, a further flue gas duct is formed between the heat-insulating jacket of the boiler and the convective heat transfer surface.

• Fig. 1 einen vertikalen Längsschnitt durch einen erfindungsgemäßen Kessel mit einem herkömmlichen (offenen) Feuerraum,
• Fig. 2 einen Querschnitt nach der Linie A-A in Fig. 1,
• Fig. 3 einen horizontalen Längsschnitt des in Fig. 1 gezeigten Kessels,
• Fig. 4 einen Querschnitt nach der Linie B-B in Fig. 1,
• Fig. 5 einen horizontalen Längsschnitt durch einen erfindungsgemäßen Kessel mit einem sogenannten sackförmigen (hinten geschlossenen) Feuerraum,
• Fig. 6 einen Querschnitt nach der Linie C-C in Fig. 5.

The invention is explained in more detail with reference to the drawing, in which two exemplary embodiments of the boiler according to the invention are shown. It shows

• 1 is a vertical longitudinal section through a boiler according to the invention with a conventional (open) combustion chamber,
• 2 shows a cross section along the line AA in FIG. 1,
• 3 shows a horizontal longitudinal section of the boiler shown in FIG. 1,
• 4 shows a cross section along the line BB in FIG. 1,
• 5 shows a horizontal longitudinal section through a boiler according to the invention with a so-called sack-shaped (closed at the rear) combustion chamber,
• 6 shows a cross section along the line CC in FIG. 5.

As can be seen from the drawing, the two embodiments are of the same or similar construction in their most important details, and they also have a similar mode of operation. For this reason, the same reference numbers have been used for the same details in both embodiments. From the figures it can be seen that there is a major difference between the two embodiments essentially only with regard to the direction of the flue gas duct.

The essence of the boiler according to the invention is explained with reference to the embodiment shown in FIGS. 1 to 4.

As can be seen from the figures, the combustion chamber of the boiler according to the invention is delimited all around by a truncated cone-shaped flame tube 1, which widens towards the rear, towards the rear combustion chamber boundary wall 6, the shape of which changes along the flame of a gas attached to the end face 8 of the boiler - Or oil burner 10 corresponds to the given radiation energy. However, this shape can also be a sphere or another rotating body with a change in cross section, depending on how the distribution of the heat radiation along the flame axis, which is dependent on the size and temperature of the flame and on the length of the infrared waves. Due to this changing cross-section, it is achieved that the largest heat transfer surfaces are located precisely at the places exposed to the greatest heat load, whereby on the one hand better energy utilization and on the other hand the protection of the device, ie. H. the increase in their lifespan is made possible.

The flame tube 1 is designed as a membrane wall, ie the jacket of the flame tube 1 is formed by ring tubes 11 receiving the heated medium and relatively thin plate sections connecting them. This solution, which is known per se, enables good heat transfer on the one hand and material savings while ensuring the necessary strength on the other. The end wall 8 holding the burner 10 is designed as an annular membrane wall. The rear end of the flame tube 1 is formed by circular water tubes, between which the flue gas passes into the turning chamber 7 delimited by the rear combustion chamber boundary wall 6 and from here into the flue gas duct 3 designed as a second train. The flue gas duct 3 forming the second train is bounded on one side by the outer jacket of the flame tube 1 and on the other side by a convective heat transfer flank 2. Both the combustion chamber boundary wall 6 of the turning chamber 7 and the convective heat transfer surface 2 are designed as a membrane wall. An important feature of the invention is that the ring tubes 12 of the membrane wall of the convective heat transfer surface 2 are offset from the ring tubes 11 of the membrane wall of the flame tube 1, expediently offset by half a distance between the adjacent ring tubes of the other membrane wall. So the flue gases flow between these ring tubes 11 and 12 in the longitudinal direction, in an annular, corrugated spiral line, whereby the convective heat transfer is significantly improved after the flue gas speeds increase along the wall surfaces. At the end of the flue gas duct 3 (ie on the front part of the boiler), the flue gases turn into a further flue gas duct 4, which is designed as a third train and is delimited from the inside by the outer jacket of the convective heat transfer surface 2 and from the outside by a heat-insulating casing 5. In this train, the flue gases also give off their residual heat to the convective heat transfer surface 2, so that the heat utilization of the built-in heat transfer surfaces is now 100 percent compared to the previous 50 to 60%. Since the convective heat transfer surface 2 is similar to the shape of the flame tube 1, the size of the convective heat transfer surface 2 is proportional to the size of the heat energy that can be transferred by convection. This means that the hottest flue gases act on the largest heat transfer surfaces, ie the heat transport is adapted to the extent of the heat load.

Incidentally, the flue gases leave the boiler via the smoke chamber 15 and via a flue gas nozzle 9 formed in the end wall of the boiler.

As far as the water side of the boiler is concerned, the ring tubes of all membrane walls converge at the bottom and top in a lower distribution chamber 13 and an upper collecting chamber 14. In the lower distribution chamber 13, the connecting piece of the return line or the downcomer is formed and in the upper collecting chamber 14, the connecting piece of the forward line or the riser is formed, through which the boiler is connected to the heat absorption system or, in the case of a steam boiler, the drum.

The other embodiment of the boiler according to the invention shown in FIGS. 5 and 6, which has a so-called sack-shaped combustion chamber, differs from the first embodiment only in that the combustion chamber is sealed gas-tight at the rear by a combustion chamber boundary wall 6 designed as an annular membrane wall, so that the flue gases as second train flow back to the front part of the boiler, where they pass through corresponding openings in a third train designed as a third train, which is delimited from the outside by a convective heat transfer surface 2. The flue gases are finally discharged through the smoke chamber 15 and the smoke nozzle 9 at the end of the boiler, the end wall 17 of the boiler also being designed as a membrane wall.

In the boiler according to the invention, the circulation circuits on the water side are designed in such a way that the heat transport is ensured either by natural or forced flow or circulation. The lower distribution chamber 13 and the upper collecting chamber 14 serve this task. In the case of a steam boiler, the uniform heat transport is ensured by the corresponding arrangement and size of the falling and rising lines connecting the boiler to the drum, which are connected to the above-mentioned chambers 13 and 14.

The piping system contains little resistance, as a result the resistance of the circulation system is low. An intensive flow can thus be guaranteed.

• - Die eingebauten Wärmeübertragungsflächen sind hundertprozentig ausgenutzt, während dies bei den herkömmlichen Konstruktionen nur zu 50 bis 60% der Fall ist.
• - Infolge der gleichmäßigen Wärmezustände und Wärmeströme sind die Anforderungen gegenüber der Qualität des Speisewassers nicht mehr so hoch, und die Kesselkonstruktion kann die Wärmeentzugsänderungen günstiger vertragen.
• - Die Festigkeitsverhältnisse des erfindungsgemäßen Kessels sind nicht von der Leistung des Kessels abhängig, d. h. die Leistung kann erhöht werden, ohne daß seine Festigkeitsparameter oder der damit im Zusammenhang stehende Wärmeentzugsfaktor abnehmen. Die Konstruktion des Kessels begrenzt also nicht die Wärmeleistung, sondern sie gewährleistet eine effektive Wärmeübertragung, einen Kreuzstrom der Rauchgase und die hundertprozentige Ausnutzung der Heizflächen.

The most important advantages of the boiler according to the invention are as follows:

• - The built-in heat transfer surfaces are fully utilized, while this is only 50 to 60% the case with conventional designs.
• - As a result of the uniform heat conditions and heat flows, the requirements for the quality of the feed water are no longer so high, and the boiler design can tolerate the changes in heat extraction more favorably.
• - The strength ratios of the boiler according to the invention are not dependent on the output of the boiler, ie the output can be increased without its strength parameters or the associated heat removal factor decreasing. The design of the boiler does not limit the heat output, but rather ensures effective heat transfer, cross-flow of the flue gases and 100% utilization of the heating surfaces.

The fundamental improvement in the strength relationships is the result of the use of membrane walls; as a result, only a fraction of the previous wall thickness is required. The smaller wall thickness enables significantly cheaper heat transfer, significant material savings, lower thermal inertia, more economical production, as well as less space and lower investment costs.

With the boiler according to the invention, the advantages of previous boiler designs are not only combined, but further increased, both in terms of strength as well as heat transfer, circulation and heat utilization.

Claims (4)

1. Warm water, hot water or steam boiler having gas or oil firing, in particular for heat supply to small and medium consumers, in which the flue surfaces bounding the combustion chamber are formed as a membrane wall consisting of annular tubes (11) receiving the heat-carrying medium which are connected together by thin plates, characterised in that the flue (1) is formed as a body of revolution having a changing cross- section corresponding to the amount of heat flow and is outwardly surrounded by a convective heat transfer surface (2) which is adapted to its shape and is also formed as a membrane wall and forms a flue gas channel (3), the annular tubes (11) of the membrane wall of the flue (1) being arranged offset relative to the annular tubes (12) of the membrane wall of the convective heat transfer surface (2).

2. Boiler according to claim 1 characterised in that the flue (1) is formed as a truncated cone widening from the front wall (8) holding the burner (10) to the rear combustion chamber bounding wall (6).

3. Boiler according to claim 1 or 2 characterised in that the annular tubes (11) of the membrane wall of the flue are in each case arranged approximately at half the distance between two annular tubes (12) of the membrane wall of the convective heat transfer surface (2).

4. Boiler according to one of claims 1 to 3 characterised in that between the heat isolating jacket (5) of the boiler and the convective heat transfer surface (2) a further flue gas channel (4) is arranged.

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