EP0189708B1 - Gas-fired water heater - Google Patents

Abstract

1. A gas-fired water heater including a vertical shaft (2) in which the hot gases circulate in an ascending current, the wall (2) of this shaft defining a peripheral water jacket (7) constituting a portion of a water circulation circuit of a first exchanger surrounding the vertical shaft and at least a second exchanger element (3) constituted by an axial tube (5) and a peripheral jacket (18), mounted vertically inside said shaft (2), characterized in that each second exchanger element (3) forms an overheater for the water already heated in the first exchanger, the inflow of the water to this or these second exchanger elements being effected, from the top of the peripheral water jacket (7) of the first exchanger in contact with the shaft (2), via the descending current axial tube (5) of this second exchanger element and the outflow, from the top of the peripheral jacket (18) of this second exchanger element toward an intermediate point (19) of the inner water circulation circuit of the heater, and in which the water flows while being channelled from the periphery to the center, the water to be heated coming in this peripheral jacket (7) in direct contact with the wall (2) of the jacket at the bottom point (14) in order to be discharged at the top point of said jacket.

Description

The present invention relates to hot water generators heated by gas, according to the preamble of claim 1. A hot water generator of this type is described in GB-A-154,476.

The invention also aims to avoid condensation in such a boiler in the chimney or combustion chamber which directly overcomes the burner.

Yet another object of the present invention is to ensure, in the heat exchange circuit between the hot gases and the water, a circulation accelerated by the phenomenon of the thermo-siphon and to improve the heat exchange by one or several superheaters in which circulation is ensured, independently of the overall circulation of water in the generator, by said phenomenon of thermo-siphon.

FR-A-414 223 describes a solid fuel boiler with, in the hot gas flow, exchangers each consisting of a vertical tube with closed lower end in which is mounted a second axial tube open at its two ends, the upper ends of the two tubes being in communication with the water chamber to have circulation by thermo-siphon with the descent of the relatively cold water by the axial tube and the rise of the water heated by the peripheral jacket.

Neither of these two patents suggests making the boiler so that the part of the exchanger mounted in the central chimney and which is therefore insulated against any loss by heat exchange with the atmosphere and is at the most temperature high, constitutes an effective superheater.

Furthermore, FR-A-1 095 505 describes a high pressure steam or hot water boiler, comprising two exchangers, a double jacket with tubes arranged in the chimney to improve the heat exchange between the combustion gases and the water. cold arriving in this envelope, as well as a superheater constituted by a balloon placed in the chimney to which the hot water arrives from the top of the envelope and leaves it by a tube towards the use. The boiler described in this document, which runs on coal, does not allow the superheater to be connected so as to avoid the water vaporizer.

The problem is solved by the features of the second part of claim 1.

In the case of a domestic hot water generator operating in an open circuit with a water inlet and outlet connected to the boiler, the first exchanger element constitutes a cylindrical boiler which surrounds the central vertical chimney and is subdivided by walls in concentric cylindrical chambers communicating alternately at their high and low points, the arrival of the water to be heated or heated taking place in the peripheral chamber and the departure of hot water at the high point of the most central chamber. With this embodiment, the mass of water filling the boiler constituted by itself the insulation, the largest part of the volume and the coldest being in contact with the outer wall. The walls other than that delimiting the central chimney which is in direct contact with the flame, remain at very low temperatures and they can be made of inexpensive materials such as plastics.

In the case of the hot water generator in open circuit above, the outlet of the second exchanger element (s) is connected to the high point of the second chamber from the chamber formed by the water jacket in contact with the wall from the chimney of the first exchanger to ensure its mixing with water at medium temperature, the mixture remaining thermally insulated from the outside by the peripheral water jackets.

• La figure 1 est une coupe axiale schématique d'un générateur d'eau chaude à circuit ouvert et la figure 2 est une coupe axiale schématique d'un ballon d'eau chaude sanitaire dont le circuit fermé d'eau chaude est réalisé conformément à l'invention.

The invention will be described in more detail below in its application to an open circuit hot water generator and in its application to a closed circuit hot water generator with heat exchange in a domestic water tank, applications described by way of examples with reference to the attached schematic drawings in which:

• Figure 1 is a schematic axial section of an open circuit hot water generator and Figure 2 is a schematic axial section of a domestic hot water tank whose closed hot water circuit is produced in accordance with l 'invention.

In the drawings, the reference 1 designates the burner and the reference 2 the chimney which surmounts the burner and in which the hot gases G circulate in the direction of the double arrows. In the center of the chimney 2 is mounted a superheater designated by the general reference 3 which is constituted by a peripheral cylindrical tube 4 closed at its two ends and by a central tube 5 whose lower end is open. In the two embodiments, the chimney 2 is doubled by a tubular wall 6 so as to form in contact with the chimney 2 a concentric chamber forming a water jacket 7.

In the open circuit hot water generator the boiler is delimited by a peripheral cylindrical casing 8 closed at its two ends and the internal volume is subdivided therefrom, in addition by the tubular wall 6, by other concentric tubular walls 9 and 10 so as to form water jackets in concentric chambers 11, 12 and 13. The tubular wall 6 is interrupted at a certain distance from the bottom of the peripheral cylindrical envelope 8 to provide a lower passage 14 between chambers 11 and 7 , the concentric tubular wall 9 is interrupted at a certain distance from the upper wall of the peripheral cylindrical casing 8 to provide an upper passage 15 between the concentric chambers 11 and 12 and the concentric tubular wall 10 is interrupted at a certain distance from the bottom of the envelope to spare an inferior passage 16 between the concentric chambers 13 and 12.

The central tube 5 of the superheater 3 is connected at its upper part by one or more tubes 17 with the high point of the central water jacket 7 while the high point of the peripheral water jacket 18 of the superheater 3 produced between the tube 4 and the central tube 5 is connected, by one or more tubes 19, with the upper part of the concentric chamber 11.

The water to be heated arrives by the tube 20 connected to the upper part of the concentric chamber 13 and the drawing is carried out by a tube 21. The water circulation is materialized by arrows with simple point E. The water arrives via the tube 20 substantially at ambient temperature and descends into the concentric chamber 13 at low speed given the large section of this chamber. It then passes through the passage 16 and rises in the concentric chamber 12, passes at the top of the latter by the passage 15 and descends in the concentric chamber 11 while heating by heat exchange through the tubular wall 6 and also by injection of '' a current of hot water from the superheater as explained below. At the bottom of the concentric chamber 11 the water passes into the water jacket 7 through the lower passage 14 and circulates in the latter in the upward direction under the effect of the water withdrawal by the drawing tube 21 and the thermo-siphon phenomenon which arises in the water jacket 7 and in the superheater 3.

Indeed, the water column located in the water jacket 7 heats up by direct exchange with the hot gases through the wall of the chimney 2 and the part of the ascending current which is not drawn off by the drawing-off tube. 21 is discharged through the tube or tubes 17 into the central tube 5 of the superheater 3. This stream of water descends into the central tube 5 of the superheater and passes at the lower end of this tube in the peripheral water jacket 18 of the superheater where it is intensively heated by direct exchange through the wall 4, which results in an acceleration of the flow rate resulting from the thermo-siphon phenomenon and this flow rate is returned by the tube or tubes 19 to the top of the concentric chamber 11. It therefore occurs under the effect of the thermo-siphon phenomenon which arises intensely in the water jacket 7 and 18 an internal circulation of hot water which is independent of the flow rate. This circulation is ascending in the jacket 7, passes through the tubes 17, is descending in the central tube 5 of the superheater and ascending in the water jacket 18, passes through the tubes 19 and is descending in the concentric jacket 11 where the circulating volume mixes with a flow coming from the concentric chamber 12 equal to the drawing flow.

Because of this operation, better heat exchange is obtained due to the flow speed, much higher than that corresponding to the simple drawing rate, of water in contact with the walls licked by hot gases and a tendency to l 'temperature equalization at all points of said walls. The part of the boiler where this intense heat exchange takes place is insulated by the mass of incoming water which circulates in the concentric chambers 13 and 12 at a very low speed due to the large section of these chambers and the reduced flow which corresponds to the only drawing flow.

In FIG. 2, the same references have been used to designate the elements equivalent to those of FIG. 1. The essential difference lies in the fact that the generator is in a closed circuit, the hot water circuit of the generator being enclosed in a tank. constituted by a wall 22 surrounded by a thermal insulation layer 23, the sanitary water arriving via a pipe 24 which is preferably extended, as illustrated in phantom in Figure 2 in 24 ', to the bottom of the reserve and being taken off through a pipe 25. The concentric chambers 11, 12 and 13 which are embedded in the volume of water in the balloon each consist of two cylindrical walls 25 crimped welded at their two ends. The tubular wall 6 is also welded at its two ends to the outer surface of the wall defining the chimney 2, the passages 14, 15, 16 at the successively high and low points between the concentric chambers are produced by tubes 27 distributed around the periphery . The circulation in the water circuit constituted by the water jacket 7 and the concentric chambers 11, 12 and 13 is done only under the effect of the phenomenon of thermo-siphon in the water jacket 7 and it is done the inner jacket towards the outer chamber with return from the bottom of the peripheral concentric chamber 13 to the bottom of the water jacket 7 by the tubes 27. The upward flow in the water jacket 7 which results solely from the thermo-siphon phenomenon is distributed between a pumped flow, as illustrated by arrow 28, at the top of the concentric chamber 11 and a flow by the tube 17 towards the central tube 5 of the superheater, flow which is induced by the phenomenon of thermo-siphon in said superheater , this flow being reinjected by the tube 19 with the flow discharged according to arrow 28 to ensure circulation in the concentric chambers 11, 12 and 13. In addition to improving the heat exchange with the hot gases resulting from the speed circulation in contact with the walls heated by the gases described above, the invention ensures natural circulation in the exchange circuit with a speed in said circuit, all the more reduced as the difference in temperatures between the water of the generator and the water to be heated is reduced which promotes heat exchange. It is obvious that the concentric chambers 11, 12 and 13 and their connection tubes could be replaced by a coil connecting the tubes 19 and 27 taking advantage of the circulation induced by the water jacket 7 and the superheater 3 but the speed d flow would be constant throughout the exchange circuit which would remove the above advantage of a flow velocity in contact with the walls the lower the difference in temperature of the liquids participating in the exchange is smaller.

The embodiments described above by way of examples are capable of receiving various modifications without departing from the scope of the claims. Thus several open circuit generators as described with reference to Figure 1 can be connected in parallel to form a battery and increase the power of the installation. It is also possible to operate the installation with an accelerator with variable flow rate or with control operation by probe or aquastat in a known manner. Finally by increasing the diameter of the chimney or combustion chamber 2 it is possible to mount a plurality of superheaters, for example at least three for reasons of symmetry, these superheaters being connected in parallel.

Claims (3)

1. A gas-fired water heater including a vertical shaft (2) in which the hot gases circulate in an ascending current, the wall (2) of this shaft defining a peripheral water jacket (7) constituting a portion of a water circulation circuit of a first exchanger surrounding the vertical shaft and at least a second exchanger element (3) constituted by an axial tube (5) and a peripheral jacket (18), mounted vertically inside said shaft (2), characterized in that each second exchanger element (3) forms an overheater for the water already heated in the first exchanger, the inflow of the water to this or these second exchanger elements being effected, from the top of the peripheral water jacket (7) of the first exchanger in contact with the shaft (2), via the descending current axial tube (5) of this second exchanger element and the outflow, from the top of the peripheral jacket (18) of this second exchanger element toward an intermediate point (19) of the inner water circulation circuit of the heater, and in which the water flows while being channelled from the periphery to the center, the water to be heated coming in this peripheral jacket (7) in direct contact with the wall (2) of the jacket at the bottom point (14) in order to be discharged at the top point of said jacket.

2. A gas-fired water heater according to claim 1, operating as an open circuit with a water inlet (20) and a water outlet (21) connected to the boiler, characterized in that the first exchanger constitutes a cylindrical boiler (8) which surrounds the central vertical shaft (2) and is subdivided by walls (6, 9, 10) into concentrical cylindrical chambers (7, 11, 12, 13) communicating alternately at their top and bottom points (14, 15, 16), the inlet (20) for the water to be heated or reheated being provided in the peripheral chamber (13) and the outlet (21) for the hot water at the top point of the most central chamber (7).

3. A water heater according to claim 2, characterized in that the outlet (19) of the second exchanger element or elements is connected at the top point of the second chamber (11) starting from the chamber constituted by the water jacket in contact with the wall of the shaft of the first exchanger in order to ensure its mixture with water at a medium temperature, the mixture remaining thermally insulated from the outside by the peripheral water jackets (12-13).

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