GB2103342A - A high-efficiency boiler without a blower - Google Patents

Abstract

A high-efficiency boiler with a burner 2, a heat exchanger 3 and means for supplying air and discharging flue gases. According to the invention the supply and discharge means form a closed system and comprise a hot-gas column directly linking up with the burner, and of which the thermal draught generated with it can overcome at least the resistance across the heat exchanger. By virtue of this construction the boiler can be operated without the need of a blower for aiding the discharge of the flue gases.

Description

SPECIFICATION High-efficiency boiler without a blower This invention relates to a high-efficiency boiler with a capacity of up to approximately 35kW, and comprising a burner, a heat exchanger, and means for supplying air and discharge flue gases.

In the case of gas-fired boilers, a high-efficiency boiler means one whose measured efficiency in use is at least 88%, calculated on the gross calorific value, unlike normal boiers, in which this efficiency is in the order of 70-75%. One result of the high efficiency however, is that the temperature of the flue gases decreases to such an extent that a high-efficiency boiler requires particular measures, as compared with a normal boiler, to ensure that the flue gases are properly discharged. In a normal boiler connected to a flue, the draught generated therein can be used for overcoming the resistance across the heat exchanger, and owing to the relatively high temperature of the flue gases discharged, sufficient draught can be generated in the flue.Boiler draught and chimney draught are often separated from each other by a damper, which in boilers which draw their air from the space where they are installed is a requirement. In prior high-efficiency boilers, however, in which owing to an enlarged heat exchange surface area more heat is withdrawn from the flue gases, which often results in an increased resistance and a decreased flue gas temperature, the draught generated in the chimney is insufficient. For that reason prior high-efficiency boilers, in which the heat exchanger often consists of two heat exchanger portions placed substantially in side-by-side relationship and interconnected by a curved flue section, are fitted with a blower in the air/flue gas system. The incorporation of a blower in the system, however, is accompanied with some disadvantages.

In addition to the circumstance that the use of a blower means that extra - electrical - energy must be supplied, additional regulations and safety devices are needed, which tend to raise the cost, and in addition involve an increased chance of failure.

It is an object of the present invention to provide a high-efficiency boiler in which the discharge of the flue gases can be realized in a reliable manner without the need of using a blower; and hence with elimination of the disadvantages connected with a blower.

In a high-efficiency boiler of the kind defined in the opening paragraph of this specification, this object is achieved according to the present invention, by virtue of the fact that the supply and discharge means form a closed system and comprise a hot-gas column, directly linking up with the burner, and of which the thermal draught generated with it can overcome at least the resistance across the heat exchanger, and there being provided means for limiting heat emission by the hot-gas column. Owing to these features, a relatively large thermal motor in the form of a hot-gas column is created in the high-efficiency boiler, while the use of a closed system for supply and discharge - that is to say, inlet and outlet are disposed in proximity to each other outside the space where the boiler is installed, i.e.

often in the outer air, while no damper is provided between the heat exchanger and the flue - creates such supplementary conditions that flue gas discharge is ensured without external aids with the disadvantages inherent therein. It is surprisingly found, therefore, that the effect referred to can also be realized in a high-efficiency boiler, and this by using purely natural phenomena in an optimum manner. A particularly advantageous effect produced by the closed system, also referred to as a balanced-flue system, is that any variations in pressure difference in the air/flue gas system are eliminated, so that the operation of the hot-gas column cannot be influenced by such vibrations in pressure differential.

Owing to the provisions for limiting the emission of heat by the hot-gas column, the operation of the thermal motor is optimized. This is in contrast to prior boilers, in which means for deliberately withdrawing heat are often provided in the wall portion of the boiler above the burner, albeit, of course, with the object of utilizing such heat in an effective manner, for example, for warming-up the heat transporting medium in modern, so-called "wet-foot" boilers. Accordingly, in order to arrive at the present, inventive system for a high-efficiency boiler, it is necessary to break with this principle, which is often used nowadays, and which by itself is advantageous, it is true, but in the high-efficiency boiler may destroy the natural discharge of the flue gases.

In a preferred embodiment of the invention, the high-efficiency boiler is adapted to be operated using gas as a fuel, and the boiler is characterized by a comparatively mildly decreasing temperature gradient in said hot-gas column over a height depending on its capacity, and ranging from approximately 20 cm or more at a maximum boiler capacity of 8kW to approximately 35 cm or more at a maximum boiler capacity of 35 kW. By virtue of this arrangement, it is possible to produce a high-efficiency boiler which as regards its dimensions in the vertical direction hardly differs from prior boilers. This is in particular the case if, in acco%dance with a further preferred embodiment of the invention, the direction of flow in the supply and discharge of air and flue gases is substantially vertical, as in this way the flow resistance, and hence the hot-gas column can be minimized.According to a further preferred embodiment of the invention, the design of the highefficiency boiler is considerably improved if the hot-gas column has a jacket of such construction that the sum of the heat emission from radiation and from convection is in the minimum range, owing to the fact that heat transferred to the jacket is then already minimized in the design. The transfer of heat by the hot-gas column can be improved still further if the jacket of the hot-gas column comprises an insulator or a poor conductor.

If, as is conventional in prior boilers, at least a portion of the heat exchanger is placed substantially vertically above the burner, the dimensions of the high-efficiency boiler according to the invention can be minimized, with an optimum effect, if the hot-gas column, which is bounded at the bottom end by the burner, is bounded at the top end by said heat exchanger.

Within the framework of the present invention it is also possible for the high-efficiency boiler to be designed so that the heat exchanger consist of a substantially vertically extending, double-walled tube of suitable cross-sectional configuration, with the burner being disposed at the bottom end of said tube.

Two embodiments of the high-efficiency boiler according to the invention will now be described in more detail, by way of example, with reference to the accompanying, highly diagrammatic drawings.

In said drawings: Figure I shows a first embodiment; and Figure 2 shows a second embodiment of a highefficiency boiler according to the present invention.

Figure 1 shows a gas-fired high-efficiency boiler 1, comprising a burner 2, a heat exchanger 3, and a superjacent flue gas collecting space 4 terminating in a flue 5. Provided between burner2 and heat exchanger 3, which comprises a water inlet pipe 6 and a water outlet pipe 7, is a space 8 having a height whose dimension is sufficient to form a thermal motor in the form of a hot-gas column according to the invention, depending on the capacity of boiler 1.

Forthis purpose, such height should be approximately 20 cm or more in a small boiler having a maximum capacity of approximately 8kW, and approximately 35 cm or more in a large boiler having a maximum capacity of approximately 35kW.

In this hot-gas column, the temperature adjacent burner 2 is highest, which temperature decreases exponentially if the hot-gas column is hardly, if at all, disturbed. As the capacity of the thermal motor is determined by the temperature and the height of the hot-gas column, the temperature decrease in the column, and hence the emission of heat by the column should be minimized. This can be achieved by constructing the boiler jacket in the vicinity of the hot-gas column, depending on the burner used, in such a manner that the sum of the heat transfer by radiation and by convection is in the minimum range, taking account of the decrease in heat transfer by convection and the increase of that by radiation when the boiler walls are set apart, which manner of minimization of the added heat transfer need not exclude the use of a water jacket.In addition it is naturally also possible for the boiler jacket to be equipped with an insulator or a poor conductor.

Furthermore, the boiler 1 is provided with a closed supply and discharge system for air and flue gases.

For this purpose an air supply line 9 is provided, which has its inlet in the vicinity of the outlet of the flue 5, which normally terminates in the atmosphere, and both of which ducts extend through an envelope from the space within which boiler 1 is installed.

Owing to this disposition of the air supply line 9, boiler 1 is fully sealed from the space within which it is placed. Such a construction is known by the name of "balanced4lue system", which in cooperation with the thermal motor makes it possible to ensure the proper discharge of the flue gases in a high efficiency boiler, without having to resort to extra aids, such as a blower. As the "balanced-fiue system" eliminates variations in pressure differential between supply and discharge, a damper, which is required in open systems, may be omitted. As a consequence, the hot-gas column operating as a thermal motor is capabie of supplying sufficient draught for an adequate supply and discharge of air and flue gases, and thus ensures proper operation of the present system.

Figure 2 illustrates an alternative embodiment of the boiler according to the invention in the form of a high-efficiency boiler 11 with a burner 12. A heat exchanger 13 is provided in the form of a doublewalled tube forming a narrowing space 14 above burner 12, which is continued in a duct 15 of constant cross-sectional area, comparable to a flue.

A medium such as water flows through the doublewalled tube serving as a heat exchanger 13, which is provided for the purpose with a water supply line 16 and a water discharge line 17. The space 14 and duct 15 may have any shape in order to optimize the transfer of heat between flue gases and water.

Interposed between burner 12 and the narrowing space 14 is a space 18 of constant cross-sectional area and having a heightsufficientto ensure the formation of a thermal motor in the form of a hot-gas column according to the invention, depending on the capacity of boiler 11.

Owing to the particular form of heat exchanger 13, there is, in this embodiment, already such an envelope for the hot-gas column that its heat emission is limited in the desired, favourable manner. Naturally, in this embodiment, too, the boiler jacket may be of such construction that, again, the sum of the heat transfer from radiation and from convection is in the minimum range.

In order that, in this embodiment, too, flue gas discharge is ensured without having to resort two external aids, there is further provided an air supply line 19 having an inlet outside the space where boiler 11 is installed in the vicinity of the outlet of flue 15 to form a closed supply and discharge system. For this purpose air supply line 19 and flue 15, which is concentric relative to it, extend to outside an envelope 20.

Naturally, many modifications and variants are possible without departing from the scope of the invention, and the embodiments shown are not intended to limit the present inventive principle in any way. Thus, a water/air heat exchanger is shown in the drawings and described in the specification.

This may naturally be replaced by an air/air heat exchanger.

Claims (8)

1. A high-efficiency boiler with a capacity of up to approximately 35kW, and comprising a burner, a heat exchanger, and means for supplying air and discharging flue gases, characterized in that the supply and discharge means form a closed system and comprise a hot-gas column directly linking up with the burner, and of which the thermal draught generated with it can overcome at least the resist ance across the heat exchanger, there being provided means for limiting heat emission by the hot-gas column.

2. A high-efficiency boiler according to claim 1, adapted to be operated using gas as a fuel, characterized by a comparatively mildly decreasing temperature gradient in said hot-gas column over a height depending on its capacity, and ranging from approximately 20 cm or more at a maximum boiler capacity of 8kW to approximately 35 cm or more at a maximum boiler capacity of 35kW.

3. A high-efficiency boiler according to claim 1 or 2, characterized in that the direction of flow in the supply and discharge of air and flue gases is substantially vertical.

4. A high-efficiency boiler according to any one of the preceding claims, characterized in that the hot-gas column has a jacket of such construction that the sum of the heat emission from radiation and from convection is in the minimum range.

5. A high-efficiency boiler according to any one of the preceding claims, characterized in the jacket of the hot-gas column comprises an insulator or a poor conductor.

6. A high-efficiency boiler according to any one of the preceding claims, in which at least a portion of the heat exchanger is placed substantially vertically above the burner, characterized in that the hot-gas column, which is bounded at the bottom end by the burner, is bounded at the top end by said heat exchanger.

7. A high-efficiency boiler according to any of claims 1-5, characterized in that the heat exchanger consists of a substantially vertically extending, double-walled tube of suitable cross-sectional configuration, with the burner being disposed at the bottom end of said tube.

8. A high-efficiency boiler substantially as described herein with reference to and as shown in Figure 1 or Figure 2 of the accompanying drawings.