WO2002050480A1

WO2002050480A1 - Heat exchanger apparatus

Info

Publication number: WO2002050480A1
Application number: PCT/IB2001/002290
Authority: WO
Inventors: Ruggero Marchetti
Original assignee: Merloni Termosanitari SpA
Current assignee: Merloni Termosanitari SpA
Priority date: 2000-12-20
Filing date: 2001-12-03
Publication date: 2002-06-27
Anticipated expiration: 2003-06-20
Also published as: AU2002218433A1; ITTO20001183A1; IT1321118B1; ITTO20001183A0

Abstract

A heat exchanger apparatus, in particular, for heaters, said exchanger apparatus comprising a set of substantially identical modular components, wherein an exchange liquid flows, wherein high temperature flue gas, generated by a source of flue gas, touch the external face of said modular components, which in turn can be connected together so that water can flow indifferently through said components either in series or in parallel or, more in general, in groups connected in parallel and in turn connected in series. According to the invention said modular components (13, 113) have a radial symmetry compared to an axis and the set of modular components (11, 152, 153) is located around said axis, along which the source of flue gas is basically arranged (131).

Description

HEAT EXCHANGER APPARATUS

DESCRIPTION

This invention relates to a heat exchanger apparatus, in particular for boilers, wherein said exchanger apparatus comprises a set of substantially identical modular components, inside which an exchange liquid flows as well as flue gas at a high temperature, generated by a source of flue gas, which touch the external part of said modular components, which can be connected one to the other so that water can flow through these either in series or in parallel, or, more in general, arranged in groups connected in parallel, which in turn are connected in series.

Condensing boilers exploiting the condensation of the water vapor of the combustion flue gas coming from a burner for the recovery of the sensible heat and latent heat are known. Said recovery operation is carried out by means of appropriate heat exchangers exchanging the heat between the flue gas and water by receiving said incoming flue gas at temperatures comprised between 800 and 1000°C and releasing said outgoing flue gas at a temperature of 30-50 °C. Since the condensed flue gas contain large quantities of acid residues, the exchangers must be duly made of a suitable material such as stainless steel or aluminum.

It is known that to improve the efficiency of the system formed by the exchangers, said exchangers are to be positioned around the burner, which is arranged either horizontally or vertically. Said exchangers are made with the shape-finned pipes, so that the burner seems to be surrounded by a bundle of finned pipes. A similar solution is described for instance in French patent applications no.'s FR 2 479 428, FR 2 349 106, and FR 2 506 910, wherein, in particular, the burner is completely surrounded by finned pipes through which water flows; the combustion chamber is pressurized and the heat exchange between the flue gas and water is basically countercurrent;

Said boilers offer a high efficiency because the heat can be yielded externally only through said exchangers, which receive also all the irradiated heat. Furthermore, the countercurrent exchange allows for the utmost cooling of the combustion flue gas.

Patent application FR 2 506 910 introduces also two other important innovations: the finned pipes have staggered fins so that the finned pipes can be best arranged together; furthermore, a separator located below the burner divides the boiler into two areas (the combustion chamber and the flue gas chamber) thus forcing the flue gas to pass through the exchanger and the combustion chamber twice and to return thus making the countercurrent exchange even more efficient. The boilers must have a low thermal inertia, i.e. the minimum possible volume of water with the same thermal horsepower and exchange surface. Said boilers with finned pipes have a number of drawbacks. First of all, not all the flue gas filaments produced by the burner touch a same exchange surface. Therefore, not all of the flue gas filaments manage to yield the same quantity of heat. Furthermore, there are limits to the fin surface/pipe volume ration owing to limits to the maximum fin diameter. In fact, by increasing the diameter of the fins while maintaining unaltered other parameters, the efficiency of the exchange surface thus obtained is reduced. The maximum fin diameter in the aforementioned conditions, i.e. combustion in a pressurized chamber and hence with the flue gas expelled at an adequate pressure, is about three times the diameter of the pipe.

Another drawback is the fact that, despite a number of countermeasures, such as, for instance, the use of deflectors to favor a more even distribution of the flue gas on the fins, the portion of fin, which is not touched directly by the flue gas because it is located on the hidden face of the pipe compared to the burner, does not exchange heat in a very effective manner; in this portion, the speed of the flue gas is much lower and the condensates stagnate thus corroding even materials resistant to the attack of acids in the long run. This invention aims at solving the aforementioned drawbacks and to provide an improved heat exchanger apparatus which is more efficient compared to known solutions. Within this framework, the main purpose of this invention is that of providing a heat exchanger apparatus enabling all the flue gas filaments to touch the exchange surface and hence render more even the quantity of exchanged heat and the speed of the flue gas on the exchange surface.

A further purpose of this invention is that of illustrating a heat exchanger apparatus capable of increasing substantially the ratio existing between the exchange surface and the water volume.

Another purpose of this invention is that of developing a heat exchanger apparatus capable of eliminating the blind zones and hence the stagnation of acid condensates.

Another purpose of this invention is that of developing a heat exchanger apparatus capable of providing for the creation of a wide range of flue gas/water modular exchangers, wherein said modules can be easily connected to one another either in series or in parallel, or, in general, in sets arranged in parallel that, in turn, can then be connected in series.

Another purpose of this invention is that of developing a heat exchanger apparatus that makes it possible to eliminate collectors necessary to collect the water from the single exchange components. Another purpose of this invention is that of developing a heat exchanger apparatus capable of increasing the speed at which water flows on the exchange surface and the speed at which the flue gas run over the exchange surface.

In order to attain these purposes, the subject matter of this invention is a heat exchanger apparatus incorporating the characteristics of the enclosed claims, which are an integral part of this description.

The other purposes, characteristics and advantages of this invention will be illustrated in the detailed description below and in the attached drawings, provided by way of example and without posing any limitation whatsoever, wherein:

Figure 1 provides a perspective sectional view of the components of a heat exchanger apparatus according to the invention;

- Figure 2 provides a lateral sectional view of the heat exchanger apparatus;

- Figure 3 provides a horizontal projection of the component of heat exchanger apparatus illustrated in Figure 1 ;

- Figure 4 provides a partial diagram of a boiler used as a heat exchanger apparatus according to the invention.

Figure 1 shows a perspective view of two flat components 13 of a heat exchanger 11 according to the invention. Said flat components 13 have the shape of an annulus and are illustrated overlapped and sectioned along the diameter passing through the holes 14. Near said holes 14 it can be seen that there is a cavity 17 inside each flat component 13, which is hence hollow on the inside. A series of collars 15 are obtained around the 5 passage holes 14. Some of the passage holes 14 can be closed, i.e. not cut at the moment of the making of the flat component 13, depending on whether flat components 13 are to be connected in series or in parallel. The upper surface of the flat component 13 is also provided with radial ribs 16 used as spacers with the superjacent flat components 13 in order to provide for the passage of the flue gas between the flat component 13 and the

I o other in a channel 21.

Figure 2 shows a sectional view of the heat exchanger 11 composed of a series of flat components 13 stacked one on top of the other near the diameter through the passage holes 14. The flat components 13 are laid on the collars 15 of the passage holes 14 and said collars 15 have seal devices 26 to avoid the leakage out of the flat components 13.

15 A pipe 12 for water is connected below and above the flat components 13 near the passage holes 14 of the flat components 13 respectively on the bottom and on tip of the stack of the flat components 13. Figure 2 clearly shows the cavity 17 in the flat components 13 through which the water from water pipe 12 flows evenly in the while of flat component 13. Figure 3 show the flat component 13 as seen by horizontal projection. As stated above, said 0 flat component 13 is shaped like an annulus with an external diameter 19 and an internal diameter 20. The flat component 13 has the two passage holes 14 arranged symmetrically in order to establish a connection either in series or in parallel depending on the passage hole 14 used for the connection to the flat component 13 above or below. The arrows 18 indicate the radial movement of the flue gas which flow inside the hole 5 associated to the internal diameter 20 towards the external diameter 19 passing through channel 21 which is visible in Figure 1.

Said flat components 13 have preferably an external diameter 19 of 500 mm, an internal diameter 20 of 200 mm and a height of 14 mm for cavity 17. Said Figure 3 shows also the radial ribs 16 pressed on the flat component 13; these ribs are 0 used to keep the necessary distance for the passage of the flue gas between the stacked components and to consolidate the structure of the flat component 13 so that it can bear the pressure of the water in the cavities 17. Furthermore, the radial rib 16 may cause turbulence between the flue gas and the water so as to improve the exchange.

The previous figures clearly show how the flat components 13 of the exchanger 11 have a radial symmetry around an axis passing through the center of the annulus that each flat component 13 forms.

Figure 4 shows a heat exchanger 111 in the form of variant of the heat exchanger 11 of Figure 1 and mounted in a boiler 130.

Said boiler 130 comprises a combustion chamber 140 and a flue gas chamber 141, which are divided by a separator 142. The combustion chamber 140 contains a burner 131, which is supplied by a gas pipe 132. The flue gas generated by the combustion of the gas in the burner 131 are indicated by the thin arrows 118. The heat exchanger 111 is composed of two sets of flat components 13 and 113. A first set

152 of flat components 13, similar to those illustrated in figures 1, 2 and 3, is located in the combustion chamber 140, so that it can house the burner 131 in the hole of the corresponding diameter 20 in a position corresponding basically to its axis of radial symmetry. A second set

153 used flat components 113 provided with an annulus surface much larger compared to the flat components 13. The reason is that said second set 153 is housed in the flue gas chamber 141, wherein the burner 131 is not located, and can hence exploit at best the available space by increasing the exchange surface to effectively exchange with the flue gas cold by then. Furthermore, the internal diameter 20 of the components 113 can be smaller because the flue gas passing through them have a low volume.

A water pipe 112 supplies cold water indicated by the thick arrows 143 to the second set 153 of flat components 113, which are interconnected by means of the collars 15 of the passage holes 14. The first set 152 of the flat components 13 comprises three packs 150, each comprising five flat components 13, which are connected in parallel with one another. The packs 150, instead, are connected in turn with one another in series.

The second set 153 of flat components 113 comprises three packs 151, each comprising five flat components 113, which are connected in parallel with one another. The packs 151, instead, are connected in turn with one another in series.

The second set 153 of flat components 113 is hence connected in series to the first set 152 of the flat components 13. The water pipe 112 discharges the water, now hot, downstream of said first set 152 of flat components 13.

The flue gas 118 flow countercurrent compared to the water 143, as it can be easily seen in Figure 4 and these are collected by means of a flue gas pipe 144, connected to the flue gas chamber 141 ; the latter flue gas pipe 144 has a condensate drainage pipe 145.

The stack of flat components 13 and 113 is held by tie rods not illustrated in Figure 4. In any case, collars 15 and 115 can be welded together to ensure both their connection and hold. The description provided above clearly illustrates the characteristics of this invention as well as the resulting advantages. The heat exchanger apparatus according to the invention enables all the flue gas filaments emitted by the burner to touch evenly the exchange surface of the exchanger component, which is made in such a manner that it is radially symmetric to the burner and, in particular, the component is shaped like an annulus. This makes it possible to surround the burner completely with the exchanger and hence capture effectively also the heat radiated by the burner.

The heat exchanger apparatus according to the invention is advantageously provided with a high exchange ratio between the exchange surface and the volume of water, as the height of the cavity of each component is of just a few millimeters. Said limited height makes it possible to stack a great number of components and hence increase the exchange surface around the burner. Furthermore, said limited height provides for the high speed at which the water flows in the exchangers thus further improving the effectiveness of the thermal exchange. By reducing the height of the cavity by half, the surface/volume ratio and the flow speed are doubled. Furthermore, it is possible to obtain extremely narrow channels for the flue gas by using spacers on the lowermost components. Furthermore, the exchange can be improved by increasing the turbulence by means of an appropriate design of said spacers. The use of said spacers and the low height of the channel for the flue gas also makes it possible to solve effectively the problems attached to the limit layer which can limit the exchange. Furthermore, the heat exchanger apparatus according to the invention does not have blind zones and stagnation areas of acid condensate flue gas owing to the particularly simple and flat shape of its components. Furthermore, the heat exchanger apparatus according to the invention is particularly suitable for modular assemblies, as the flat circular structure with passage holes provides a simple and compact solution to join the desired number of components connected to one another in series just by leaving closed some of the passage holes 14 or in parallel depending on the necessity.

In addition, the heat exchanger apparatus according to the invention is an advantageous solution that makes it possible to avoid the use of a ring collector to collect the water which, on the contrary, was necessary when using finned pipes. Another advantage of the heat exchanger apparatus according to the invention is that it is formed by flat components that can be easily made by way of molding, for instance, with stainless steel plates, and then by welding. In addition, the overall accordion shape of the exchanger makes it possible to absorb thermal expansion. Furthermore, there is no limit in terms of construction with regard to parameters like the high flue gas and water speeds, as the only limits are those regarding the admissible flow resistance for both fluids. Finally, the heat exchanger apparatus according to the invention provides an advantageous solution to obtain components with a larger surface in the water preheating and flue gas condensation area without any complication whatsoever in terms of its construction and to use as best as possible the available volume. It is clear that experts of the sector can make many variants to the heat exchanger apparatus described in the example, without however transcending the novelty inherent to the idea inspiring the invention, as it is just as clear that in its practical implementation the shapes of the illustrated items can vary and that the same can be replaced with technically equivalent components. The heat exchanger apparatus can be built with a modular design and hence comprise 2, 3, 4 packs or more, connected in series, for multiple voltages of 50 - 60 kW.

For instance, for a 500 - 600 kW boiler it is assumed that up to 50 plates in 10 packs for a total height of 1 meter can be used.

The course of the flue gas can either be through a single channel through the exchanger or through a double channel as in the recommended embodiment illustrated in Figure 4, with a flue gas chamber and a combustion chamber.

In this case the components of the stacks of the flue gas chamber can have an internal hole with a much smaller diameter.

The shape of the spacers between the components can be extremely varied depending on the functions these are to perform. The design of the ribs can be modified to create an uneven course for the flue gas and water in order to activate the thermal exchange. Instead of the ribs or together with these, it is possible to make a series of bulges on the surface of the plates in order to render the course of the flue gas between said bulges uneven; moreover, the drawing and the arrangement of the bulges and of the ribs can make it possible to intercept completely the heat radiation hence avoiding that it passes in part through the whole flue gas channel 21. Since the flue gas enter the exchanger at a high speed of approximately 10 m/s and exit at a low speed of approximately 0.4 m/s owing to the drop in their temperature and hence in their volume and owing to the fact that the radial symmetry of the components increases radially the section for the passage of the flue gas in order to favor the discharge of the condensate that forms on the components, it is possible to decrease radially the height of the flue gas channel between one component and another from the internal diameter 20 to the external diameter 19, i.e. to obtain a greater height near the internal diameter and lower height near the external diameter in order to keep the speed of said flue gas high.

Claims

1. Heat exchanger apparatus in particular for boilers, wherein said exchanger apparatus comprises a set of substantially identical modular components, inside of which an exchange liquid flows; wherein high temperature flue gas generated by a source of flue gas touch the external face of said modular components; wherein said components are connected with one another so that water can flow through these either in series or in parallel or, more in general, in groups connected in parallel and in turn connected in series. According to the invention, said modular components (13, 1 13) have a radial symmetry compared to an axis and the set of the modular components (11, 152, 153) is arranged around said axis, in which the source of flue gas is generally found (131).

2. Heat exchanger apparatus according to claim 1, characterized by the fact that said modular components have the shape of an annulus or ring and an external diameter (19) and an internal diameter (20), with a source of flue gas (131) located inside said internal diameter (20).

3. Heat exchanger apparatus according to claim 2, characterized by the fact that said modular components (13, 113) are completely hollow on the inside and provided with holes (14) to provide for the supply of the exchange liquid inside a cavity (17).

4. Heat exchanger apparatus according to claim 3, characterized by the fact that said cavity has a height substantially lower than the dimensions of the external diameter

(19) and of the internal diameter (20).

5. Heat exchanger apparatus according to any of the previous claims, characterized by the fact that said modular components (13, 113) in the sets of components (11, 152, 153) are arranged one top of the other, but are separated by means of a flue gas channel (21 ).

6. Heat exchanger apparatus according to claim 5, characterized by the fact that the height of said flue gas channel (21) can vary radially so that said height diminishes from the internal diameter (20) to the external diameter (19).

7. Heat exchanger apparatus according to claim 5, characterized by the fact that said flue gas channel (21) is obtained by means of spacers (16) located on the surface of the modular components (13, 113).

8. Heat exchanger apparatus according to claim 7, characterized by the fact that said spacers (16) are formed by a series of ribs on the surface of the modular components (13, 113).

9. Heat exchanger apparatus according to claim 7, characterized by the fact that said spacers (16) are formed by bulges on the surface of the modular components (13,

1 13).

10. Heat exchanger apparatus according to claims 7 to 9, characterized by the fact that said spacers (16) are designed and/or arranged to intercept all of the heat radiation penetrating in the flue gas channel (21).

1 1. Heat exchanger apparatus according to one or more of the previous claims, characterized by the fact that the passage holes (14) are provided with collars (15, 1 15).

12. Heat exchanger apparatus according to claim 11, characterized by the fact that adjacent modular components (13, 113) are sealed together my means of seal rings (26) located near the collars (15, 115).

13. Heat exchanger apparatus according to claim 11, characterized by the fact that the adjacent modular components (13, 113) are welded around the collars (15, 1 15).

14. Heat exchanger apparatus according to at least one of the previous claims, characterized by the fact that the adjacent modular components (13, 113) can be connected together in series by simply leaving some of the passage holes (14) closed or in parallel by opening said passage holes (14).

15. Heat exchanger apparatus according to at least one of the previous claims, characterized by the fact that it comprises a first set (152) of modular components (13) and a second set (153) of modular components (1 13) with an internal diameter (20) smaller than that of the components of the first set (152).

16. Heat exchanger apparatus according to claim 15, characterized by the fact that said first set (152) and second set (153) are connected with one another and that the first set (152) is located inside a combustion chamber (140) of a boiler (130), while the second set (153) is located in a flue gas chamber (141) of said boiler (130).

17. Boiler comprising a gas burner (131) and a heat exchanger (11, 1 11) to cool the burner flue gas, characterized by the fact that said heat exchanger (1 1, 1 1 1) is composed of a set (152, 153) of modular components (134), with radial symmetry, stacked and connected together and arranged around said gas burner (131).

18. Boiler according to claim 17, characterized by the fact that it comprises a combustion chamber (140) and a flue gas chamber (141) and that said heat exchanger (11) comprises a first set (152) of modular components (13) in the combustion chamber (140) and a second set (153) of modular components (113) with an internal diameter (20) smaller than that of the components of the first set (152), located in the flue gas chamber (141).

19. Heat exchanger apparatus and/or boiler according to the principles of this description and the attached drawings.