Description

Technical Field

[0001 ] The invention relates to a heat exchanger comprising a combustion

chamber, for boiler and heating applications. More in particular, the present invention relates to a heat exchanger with minimal CO generation when in use in a boiler.

Background Art

[0002] WO09/053247A1 discloses a heat exchanger element comprising a

premix burner with an outward curved or ridged burner surface. The heat exchanger element further comprises a combustion chamber. The combustion chamber is bound on one side by the burner and is further made up of water cooled walls which, starting from the burner and in downstream direction, first widens and thereafter narrows down to the width of a customary heat exchanger element. This creates enough space for a proper combustion, avoiding dead angles and recirculation or too early ending of the combustion reaction, thereby reaching low emissions of NOx and CO. In an embodiment, the combustion chamber comprises fins elongated in the downstream flue gas flow direction.

Disclosure of Invention

[0003] It is an objective of the invention to provide a heat exchanger that provides further reduced CO (carbon monoxide) emissions while not affecting efficiency negatively.

[0004] The first aspect of the invention is a condensing heat exchanger

comprising a combustion chamber. At the top of the combustion chamber, room is provided for the installation of a premix gas burner, preferably for the installation of an outwardly curved or ridged premix gas burner, more preferably for the installation of a surface stabilized premix gas burner having a burner deck that is outwardly curved or ridged. The heat exchanger comprises a flue gas draft; delimited by walls among which two, preferably parallel, water cooled walls between which flue gas can flow. The two water cooled walls each comprise channels for water flow. It is possible however that more than two of the walls are water cooled. The combustion chamber is bound at its top at least partly by the room provided for the burner; at its sides by a set of two first combustion chamber walls opposite to each other; and by a set of two second combustion walls opposite to each other. Preferably the first combustion chamber walls are longer than the second combustion chamber walls. The first combustion chamber walls are provided with channels for water flow. The combustion chamber is bound at its bottom by the flue gas draft. The first combustion chamber walls are provided as extensions of water cooled walls delimiting the flue gas draft. The two first combustion chamber walls each comprise a first segment and a second segment. The second segment is located below the first segment; meaning that the second segment is provided in flue gas flow direction downstream from the first segment. Preferably the second segment immediately follows the first segment downstream in the flue gas flow direction. The first segments are each curved - and preferably continuously curved - so that the section of the combustion chamber bound by the first segments - preferably continuously - widens in the downstream flue gas flow direction. Each of the two first segments is provided with channels for water flow. The second segments are each curved - and preferably continuously curved - so that the section of the combustion chamber bound by the second segments - preferably continuously - narrows in flue gas downstream direction. The second segment of the first combustion chamber walls comprises longitudinal fins elongated in the direction away from the top of the combustion chamber. The fins extend in the combustion chamber. The first segment of the first combustion chamber walls is smooth meaning that it does not comprise heat exchange increasing protrusions extending in the combustion chamber.

The condensing heat exchanger of the invention showed the surprising result that CO production was significantly reduced, while there was no negative effect on the efficiency of the heat exchanger. The result is surprising; because a skilled person would expect that the absence of heat exchange increasing protrusions on the first segments of the first combustion chamber walls would considerably reduce the efficiency of the heat exchanger because of the reduced heat exchanger surface. [0006] In a preferred embodiment, the second combustion chamber walls do not comprise heat exchange increasing protrusions extending in the

combustion chamber.

[0007] In a preferred embodiment, the combustion chamber has a beam shape.

[0008] In a preferred embodiment, one of the or both second combustion

chamber walls opposite to each other is/are provided with channels for water flow.

[0009] Preferably, the height of the fins is constant over at least half of the

second segment; and preferably over at least 75% of the second segment. The height of the fins is the dimension of the fin measured perpendicularly to the wall onto which the fin is provided.

[0010] Preferably, the second segment comprises a part wherein the height of the fins decreases in the direction from the bottom of the second segment to the end of the second segment. More preferably, the fin is - preferably linearly - chamfered at a part where the height of the fins decreases in the direction from the bottom of the second segment in the direction towards the end of the second segment.

[001 1 ] In a preferred embodiment, the height of the fins is constant over at least half of the second segment; and preferably over at least 75% of the second segment. A part where the height of the fins decreases is provided above where the height of the fins is constant over at least half of the second segment; and preferably over at least 75% of the second segment.

[0012] Preferably, water cooled walls delimiting the flue gas draft comprise pins extending into the flue gas draft. More preferably, pins, and preferably all pins, on the water cooled walls delimiting the flue gas draft, are continuous pins extending over the full distance between two water cooled walls delimiting the flue gas channel.

[0013] Preferably, in at least one cross section of the condensing heat

exchanger; each of the two first segments comprise a full channel for water flow. For this preferred embodiment, cross sections are considered aligned with the average flue gas flow direction in the condensing heat exchanger. With full channel for water flow is meant that the complete channel for water flow is comprised in the first segment. [0014] In a preferred embodiment, when measured in the average flue gas flow direction in the condensing heat exchanger, the height of the first segment is more than half of the height of the second segment. More preferred is - when measured in the average flue gas flow direction in the condensing heat exchanger, the height of the first segment is more than 60% of the height of the second segment. Even more preferred is when measured in the average flue gas flow direction in the condensing heat exchanger, the height of the first segment is equal to the height of the second segment.

[0015] Preferably, the water cooled walls delimiting the flue gas draft are not provided with fins extending in the flue gas draft.

[0016] Preferably, the condensing heat exchanger is made out of aluminium or out of an aluminium alloy.

[0017] In an example of the invention, the condensing heat exchanger is a

monobloc casting; preferably out of aluminium or out of an aluminium alloy.

[0018] In an example of the invention, the condensing heat exchanger comprises one or more than one metal casted part, preferably out of aluminium or out of an aluminium alloy.

[0019] A second aspect of the invention is a heat cell comprising a condensing heat exchanger as in any embodiment of the first aspect of the invention. The heat cell comprises an outwardly curved or ridged premix gas burner provided at the top end of the combustion chamber. Preferably, the premix gas burner is a surface stabilized premix gas burner of which the burner deck has an outwardly curved or ridged surface. The premix gas burner is provided for the production of flue gas when the heat cell is in use, flue gas that is used to heat water flowing through the condensing heat exchanger.

Brief Description of Figures in the Drawings

[0020] Figure 1 shows a heat cell according to the invention.

Figure 2 shows a cross section of the heat cell of figure 1 .

Mode(s) for Carrying Out the Invention [0021 ] Figure 1 shows an example of a heat cell 10 according to the invention.

Figure 2 shows a cross section 200 of the heat cell of figure 1 according to the plane ΙΙ-ΙΓ of figure 1 .

[0022] The heat cell 10 comprises a condensing heat exchanger 202 as in the first aspect of the invention. An outwardly curved or ridged premix gas burner 204 (not shown in figure 1 , but shown in figure 2) is provided at the top end of the combustion chamber 210 of the heat exchanger 202. The burner 204 is a fully premixed surface stabilized gas burner of which the burner deck has an outwardly curved or ridged surface. The condensing heat exchanger of the example can be provided as a monobloc casting out of an aluminium alloy. The heat exchanger comprises a flue gas draft 212, delimited by walls wherein the walls comprise two water cooled walls 214 between which flue gas can flow. The two water cooled walls 214 each comprise channels 216 for water flow. The combustion chamber 210 is bound at its top by the room provided for the burner; at its sides by a set of two first combustion chamber walls 220 opposite to each other; and by a set of two second first combustion walls opposite to each other. The first combustion chamber walls 220 are provided with channels 222 for water flow. The combustion chamber is bound at its bottom by the flue gas draft 212. The first combustion chamber walls 220 are provided as extensions of water cooled walls 214 delimiting the flue gas draft. The first combustion chamber walls 220 each comprise a first segment 224 and a second segment 226. The second segment 226 is located below the first segment 224; and immediately follows the first segment 224 in the flue gas downstream flow direction. The first segments 224 are each continuously curved so that the section of the combustion chamber 210 bound by the first segments 224 continuously widens in the downstream flue gas flow direction. In the cross section shown in figure 2, each of the two first segments comprises a full channel 223 for water flow. Measured in the average flue gas flow direction in the condensing heat exchanger, the height (A) of the first segment is equal to the height (B) of the second segment.

The second segments 226 are each continuously curved so that the section of the combustion chamber 210 bound by the second segments 226 continuously narrows in the downstream flue gas flow direction. The second segment 226 of the first combustion chamber walls 220 comprises longitudinal fins 228 elongated in the direction away from the top of the combustion chamber. The fins 228 extend in the combustion chamber. The first segment 224 of the first combustion chamber walls 220 is smooth meaning that it does not comprise heat exchange increasing protrusions extending in the combustion chamber 210.

In the example, the height of the fins 228 is constant over about 70% of the length of the second segment 226. The fin is chamfered at a part where the height of the fins decreases in the direction from the bottom of the second segment 226 in the direction towards the end of the second segment 226.

In the exemplary condensing heat exchanger the water cooled walls 214 delimiting the flue gas draft comprise pins 230 extending into the flue gas draft 212. In the example, all pins 230 are continuous pins extending over the full distance between the water cooled walls 214 delimiting the flue gas channel 212.

[0023] Trials have been performed comparing a prior art heat exchanger with the heat exchanger according to the invention. A heat exchanger was provided according to the embodiment of WO09/053247A1 with elongated fins on the metal walls over the full length of the first combustion chamber walls of the combustion chamber. The results of this prior art heat exchanger have been compared with a heat exchanger according to the invention; of the same dimensions and design, with the only difference that the first segment of the two first combustion chamber walls is smooth meaning that it does not comprise heat exchange increasing pins nor fins. The test results showed that the CO content in the flue gas of the prior art heat exchanger was 120 ppm; while the CO content in the flue gas of the inventive heat exchanger was only 90 ppm. No significant difference in efficiency could be measured between the heat exchanger of the prior art and the inventive heat exchanger.

[0024] Further improved performance was obtained by the specific arrangement of the fins as in the example shown in figure 2.