FR2619205A1 - JET IMPACT HEAT EXCHANGER - Google Patents

Abstract

Jet impact gas-gas heat exchanger, comprising alternating circulating layers of a hot gas and a cold gas, composed of parallel separation plates (14) between which rows of unitary blocks (16) are placed freely side by side serving to direct the gas flows and generate the jets which impinge on the walls of the separation plates (14).

Description

JET IMPACT HEAT EXCHANGER
The invention relates to a jet impact heat exchanger, comprising parallel alternating layers of circulation of a stream of hot gas and a stream of cold gas, respectively.

 There are already exchangers of this type, whose components are made of ceramic to withstand temperatures of the order of 1400 1500 OC, but which, due to the very use of ceramics, are of structure and assembly relatively complex. In particular, we know from French patent No. 2,526,930 of the applicant, a ceramic gas-gas exchanger with jet impact, in which the layers or circulation passages of hot gas and cold gas are delimited by series parallel plates placed obliquely and mounted by interlocking their edges in grooves of two lateral ceramic flanges. The relatively large number of these plates complicates the assembly of the exchanger. In addition, the arrangement does not allow to realize easily an exchanger comprising a number of alternate layers of circulation of hot gas and circulation of cold gas, respectively, which is greater than two.

 The object of the invention is in particular to overcome the drawbacks of this prior art and to propose a gas-gas heat exchanger of the jet impact type, which is extremely simple to assemble and whose ceramic components can be standardized and manufactured. in large series.

 To this end, the invention provides a jet impact heat exchanger, comprising parallel alternating layers for the circulation of a stream of hot gas and a stream of cold gas, which are delimited by parallel separation walls forming exchange surface and one side of which is in contact with hot gas and the other side of which is in contact with cold gas, and elements mounted in each layer to deflect the current of gas which circulates therein and form jets of striking gas a partition wall, characterized in that these elements are unitary blocks freely juxtaposed in each sheet between two partition walls, each of these blocks comprising support and positioning means cooperating with the partition walls and making it possible to collect the current gas from a previous block, means for forming two sets of gas jets oriented in opposite directions and striking the partition walls, and means ensuring continuity é of the gas flow to the next block as well as the positioning in relation to this block.

 Thus, according to the invention, the exchanger can be formed very simply by free juxtaposition of unit blocks between parallel separation walls which delimit the hot gas circulation layers and the cold gas circulation layers. These unit blocks are all identical to each other, and their manufacture can be standardized.

 The juxtaposition of these blocks in two perpendicular directions, one of which is parallel to the general direction of the flow of gas in the sheet under consideration, makes it possible at will to increase the size of the exchanger.

 According to one embodiment of the invention, each unit block has substantially the shape of a rectilinear trough with U section, the side walls of which are substantially parallel to the partition walls, the open face of which faces the preceding block. with respect to the gas flow, and the closed face or transverse wall of which faces the next block with respect to the gas flow.

 The side walls of this block include slots or orifices for the passage of gas, which form the above-mentioned jets striking the partition walls.

 The side walls of the block are advantageously bordered, on the side of the open and closed faces of the block, by external flanges forming the aforementioned support and positioning means.

 To ensure continuity of gas flow to the next block, the flanges located on the side of the closed face of the block are perforated or cut.

The blocks are advantageously sections of profile made of thermally refractory material, in particular ceramic. They can be formed by extrusion or by raw molding, then by baking and machining.

 These manufacturing methods are particularly well suited to mass production.

The invention will be better understood and other characteristics, details and advantages thereof will appear more clearly on reading the description which follows, given by way of example with reference to the appended drawings in which:
- Figure 1 is a schematic perspective view of a module of a
heat exchanger according to the invention,
FIG. 2 is a simplified view of two plies of this module,
It illustrates the operation of the exchanger;
- Figure 3 is a partial schematic perspective view of a
element of the exchanger;
- Figure 4 is a partial perspective view of a section of profile
intended to form an element of a heat exchanger according to the invention
- Figure 5 shows the element obtained from this section of
streamlined.

 The module of FIG. 1 comprises two plies 10 for the circulation of a hot gas in parallel, and three plies 12 for the circulation of a cold gas, the plies 10 and 12 being parallel and alternating so that each ply 10 of circulation of hot gas is between two layers -12 of circulation of cold gas.

 In the example of Figure 1, the general circulation of hot gas and cold gas are crossed. They could be parallel and oriented in the same direction, or in the opposite direction against the current.

 Each sheet 10, 12 is delimited by two parallel flat plates 14, made of ceramic, between which are placed unitary blocks for guiding the gas flow, which are juxtaposed freely in two perpendicular directions, one of which is parallel to the direction general of the gas flow in the sheet considered, as indicated by the arrows in Figure 1, and the other of which is perpendicular to the first in the plane of the sheet.

 The heat exchanger also includes inlet and outlet manifolds for hot gas and cold gas, as well as side plates for supporting the plates 14 delimiting the layers. Preferably, the plates 14 are supported by embedding their edges in grooves of the side plates. These may have a honeycomb structure, which facilitates the embedding of the edges of the plates 14.

 The entire heat exchanger is surrounded by thermal insulation elements and contained in a metal structure equipped with means for compensating for differential expansions.

The unitary ceramic blocks which are juxtaposed between the plates 14 have substantially the structure shown schematically in Figures 2 and 3. Each unitary block 16 comprises two side walls 18, parallel to each other and connected at one end by a transverse wall 20 to give in block 16 substantially the shape of a trough with cross section in
U. Two outwardly oriented flanges 22 are formed on the edges of the plates 18 which are parallel and opposite to the edges connected by the transverse wall 20. The latter comprises, from place to place, tabs 24 oriented towards the exterior . Slots 26 or any gas passage openings are formed in the side walls 18.

 The unit blocks 16 are juxtaposed in rows and columns between the plates 14, so that the edges 22 of a block 16 are applied on the legs 24 of the previous block, and that the legs 24 of the same block 16 s' apply to the edges 22 of the next block with respect to the general direction of the gas flow. The gas which circulates in a sheet 10 or 12 between two plates 14 is guided as follows: when it arrives on a block 16, it is deflected by the flanges 22 between the side walls 18 and leaves the block 16 through the slots or orifices 26 of these side walls, forming gas jets which strike the two partition walls 14. The gas then flows, between each side wall 18 and the corresponding partition wall 14, in the direction of the next block where it is again deflected by the outer edges 22 to come between the side walls 18 of this next block.

 A wall 14 between two plies 10 and 12 is therefore regularly struck on one of its faces by jets of hot gas and, on the other of its faces, by jets of cold gas and therefore constitutes a heat exchange surface by convection between hot gas and cold gas, with good efficiency thanks to the impact of gas jets on the two faces of the wall 14. In addition, the side walls 18 of the blocks 16 form screens making it possible to absorb the thermal radiation from the partition walls 14 which are brought to a relatively high temperature. This reduces the heating of the outer walls of the heat exchanger, and therefore the heat loss to the surrounding environment.

 The separation plates 14 and the blocks 16 are preferably made of silicon carbide, but can be produced3 in other ceramic materials, such as silicon nitride and sialon, having a sufficient thermal conductivity (greater than 15 W / .m).

 As can be seen in FIG. 2, the separation plates 14 forming an exchange surface are in fact formed by several plates connected to each other by assembly bars 28 with I-cross section making it possible to juxtapose two plates 14 edge to edge. consecutive.

 Reference will now be made to FIGS. 4 and 5, which schematically represent an example of practical embodiment of the unit blocks 16.

 FIG. 4 shows a section of ceramic profile 30, which can be produced by extrusion or raw spinning of ceramic, then by firing. The profile 30 of FIG. 4 comprises a rectangular channel 32 associated on its two short sides with two channels 34 of trapezoidal section, the small base of which corresponds to the short side of the rectangular channel 32.

 The profile section 30 of FIG. 4 is then machined to take the form shown in FIG. 5 and constitute a unitary block 16. This machining consists in cutting out one of the lateral channels 34 so as to only keep legs 36 at regular intervals, while rectangular cutouts 38 and 40 are formed in the large base and the small base of the other lateral channel 34 and open into the interior of the rectangular channel 32. Finally, parallel slots 42 are formed in the large walls of the rectangular channel 32. A unitary block is thus obtained, the structure of which corresponds to that of block 16 in FIGS. 2 and 3, the openings 38 and 40 forming the gas inlet passages inside the unitary block, the slots 42 corresponding to the slots. or passages 26 for exiting the gas jets towards the separation plates 14, the lugs 36 corresponding to the lugs 24 for support and positioning.

 The unit blocks could also be produced in another way, for example by raw molding, then cooking and machining and / or assembly.

The shapes of these unit blocks could be different from those shown in the figures, provided that they allow the following functions to be fulfilled:
- supply the unit block with the outgoing gas flow
from the previous unit block,
- ensure the continuity of the gas flow leaving this block by
direction of the next block,
- ensure the support and positioning of the unit block between the two
separation walls 14.

 For example, a block could be constituted by a central box associated with two end elements.

A heat exchange module according to the invention such as that shown diagrammatically in FIG. 1, can have a heat recovery capacity of the order of 30 to 60 kW, for the following dimensions:
- height of all the layers 10 and 12: 200 mm,
- dimensions in the plane of a tablecloth: 660 mm X 220 mm.

Claims (9)

 1) Jet impact heat exchanger, comprising parallel alternating layers 3 (10, 12) for the circulation of a stream of hot gas and a stream of cold gas, which are delimited by parallel walls (14) of separation forming an exchange surface, one side of which is in contact with the hot gas and the other side of which is in contact with the cold gas, and elements mounted in each sheet to divert the current of gas which circulates there and form jets of gas striking a partition wall (14), characterized in that these elements are unit blocks (16) freely juxtaposed in each sheet between two partition walls (14), each of these blocks comprising support means (22) and positioning cooperating with the two partition walls (14) and making it possible to capture the gas current coming from a previous block, means (26) for forming two series of gas jets oriented in opposite directions and striking the walls of separation (14) and means (24 ) ensuring the continuity of gas flow to the next block and positioning relative to this block.  2) Exchanger according to claim 1, characterized in that the unit blocks (16) are, in each sheet (10, 12), juxtaposed in two directions, one of which is parallel to the general direction of gas flow in the tablecloth and the other of which is perpendicular to the first in the plane of this tablecloth.  3) Exchanger according to claim 1 or 2, characterized in that each unit block (16) has substantially the shape of a straight trough with cross section U, the side walls (18) of which are substantially parallel to the partition walls, the open face of which faces the preceding block with respect to the gas flow, and the closed face or transverse wall (20) of which faces the next block in relation to the gas flow.  4) Exchanger according to claim 3, characterized in that the side walls (18) of the block (16) comprise slits3 or orifices (26) for passage of gas, forming the aforesaid jets.  5) Exchanger according to claim 3 or 4, characterized in that the side walls (18) of the block are bordered, on the side of open and closed faces of the block, by external flanges (22, 24) forming the aforementioned support means and positioning.  6) Exchanger according to claim 5, characterized in that the flanges (24) located on the side of the closed face (20) are perforated or cut to ensure continuity of the gas flow to the next block.  7) Exchanger according to one of the preceding claims, characterized in that the unit blocks (16) are profile sections (30) of thermally refractory material such as a ceramic.  8) Exchanger according to one of the preceding claims, characterized in that the blocks (16) are formed by extrusion or by raw molding, then by baking and machining.  9) Exchanger according to one of the preceding claims, characterized in that the partition walls (14) are parallel flat plates joined together in a single plane by assembly bars (28), and mounted by embedding their edges in side plates.