FR2526930A1 - HEAT RECOVERY EXCHANGER WITH CONVECTO-RADIATION EFFECT IN CERAMIC MATERIAL - Google Patents

Abstract

EXCHANGER CONSTITUTES AT LEAST ONE MODULE 1, 2, CONTAINING TWO COMPARTMENTS 3, 4, IN THE SHAPE OF A TRUNCATED PRISM, PROVIDED ON EACH OTHER WITH AN EXCHANGE SURFACE 5. EACH COMPARTMENT IS DIVIDED INTO THREE ZONES: ONE FLUID ARRIVAL ZONE 6, A DISTRIBUTION ZONE 7 AND AN EXCHANGE ZONE 8. THE GAS ARRIVAL ZONE IS FAREST FROM THE EXCHANGE SURFACE 5. THE GAS OUTLET 10 IS PROVIDED IN ZONE EXCHANGE 8, AT THE TRUNCATED TOP OF THE PRISM. ACCORDING TO AN EXAMPLE OF AN IMPLEMENTATION, TWO MODULES 1, 2 FORM AN EXCHANGER. THE MODULES CONSTITUTE SIDE FLASES AND PLATES HELD IN SLOTS OF THE FLASES.

Description

The invention relates to a heat exchanger with convective-radiative effect, a

  exchange gas passing through compartments arranged one behind the other, each compartment being divided according to its height in zones, a zone receiving the exchange gas, comprising a wall, having openings separating it

  another zone with an exchange surface

  placed in front of the wall, the gas passing from one zone

  to each other and from one compartment to another.

  Heat transfer heat exchangers generally have

  This is due to the fact that the gas flows parallel to the hot surface and that a very small portion of the gas stream comes into contact with the exchange surface.

  In order to increase the yield, several solu-

  This is how US Pat. No. 3,450,199 proposes a compartment divided in the direction of height by an oblique partition with orifices. The cold gas is deflected towards the exchange surface. through the openings of the partition. The hot gas circulating against the current and

  the other side of the trading area, also meets

  a partition that deviates it towards this surface, the change of direction of the gas flows, with respect to the exchange surface, eliminates the low layer.

  speed and allows a better heat exchange.

  Another type of exchanger is described in US Patent No. 3,771,589 in US Pat.

  which the exchange fluid is caused to take a

swirling event.

  The exchanger is formed of a tube of rectangular section, a wall constitutes the exchange surface The tube is divided along its length into compartments Each compartment is divided into two areas by an inclined partition facing the exchange surface , and defining in the flow direction of the exchange gas, a first zone of

decreasing height.

  The second zone communicates with the first by a longitudinal slot in the partition, the slot whose edges are extended by blanks, directed towards the exchange surface The exchange gas passes through the slot and is channeled by the blanks to the surface

  of exchange against which it escapes by swirling.

  The formation of fluid jets or swirls makes it possible to improve the convective heat transfer, but in the heat exchangers at high temperature, a significant part of the heat is

transfers by radiation.

  In the case of using a gas as

  heat exchange fluid, the radiation exchange is

  In most conventional heat exchangers, the radiation contributes to the heating of the outer walls of the cooling circuit which exchange with the ambient medium, without allowing recovery. and therefore

a valid cooling.

  The exchanger according to the invention not only makes it possible to improve the convective heat exchanges, thanks to the impact of the jets, but also by radiation. The heat radiation from the exchange surface is stopped by a (or several) radiative exchange wall, parallel to the exchange wall separating the hot gases from the cold gases The two exchange walls determine a channel in which the cold or hot gas circulates, at counter-current 0 This technology is particularly well suited for a realization

made of ceramic material.

  The explanations and figures given below, as examples, will help to understand how

  3, the invention can be realized.

  Figure 1 shows in perspective and partial-

  tore a gas-gas exchanger, according to a form of

  preferred embodiment of the invention.

  FIG. 2 is a sectional view along the vertical longitudinal plane of symmetry of the heat exchanger of FIG.

figure 1.

  FIG. 3 is a partially cut-away top view of the exchanger of FIG. 1. FIG. 4 is a perspective view of the two flanges of a single piece of two modules constituting a

exchanger according to the invention.

  Figure 5 is a front view of an element

  support of the blades forming a perforated screen.

  The heat exchanger heat exchanger convecto-radiative, according to the invention, an example of which

  is shown in Figure 1, in perspective

  torn off, has two modules 1 and 2, arranged one behind the other Each module includes

  two compartments (FIG. 2) 3, 4 arranged one

  above each other and separated by an exchange wall 5.

  The compartments receive one the hot gas and the other the cold gas, which come into contact with the surfaces of the exchange wall o they undergo exchange

  convective a variation of their enthalpy.

  The compartments have a truncated prism shape

  and that are symmetrical with respect to the exchange wall Each compartment is divided into three zones parallel to the surface of the exchange wall: a gas inlet zone 6, a distribution zone 7 and an exchange zone The gas inlet zone is furthest from the exchange surface 5, and the inlet pipe 9 of the gas is arranged near the base of the prism. The gas outlet 10 is provided at the top

  truncated prism at the end of the exchange zone 8.

  According to the embodiment shown, the

  compartment 3 of module 1 is in series with the

  11 of the module 2 The compartment 12, symmetrical compartment II relative to the exchange wall 50 of the module 2, is in series with the compartment 4 of the module 1 The compartment 12 also comprises a

inlet manifold 9 of the gas.

  The arrival zone 6 of the gas is separated from the

  distribution zone 7 by a perforated screen 14,

  The distribution zone 7 is separated from the exchange zone 8 by a radiative exchange plate 15, having circular or elongated openings to form gas jets directed towards the exchange plate 5, according to the invention. 2, the openings of the plate 15 are slots directed in the gas flow direction and are arranged in two rows 16, 17, the slots of a row being offset by half a distance by

  compared to the slots of the other row.

  In the case where the perforated screen 14 is constituted

  spaced blades, the openings are directed

  This arrangement makes it possible to avoid preferential leaks and to make the coefficient more uniform.

  homogeneous exchange The length of the blades being

  are relatively large relative to the width, they are maintained at their median part by a blade support 19, resting at least partly on the radiative exchange plate 15 (Figure 5) The triangular support comprises parallel to one of its c 8 tees, elongated openings 19 in which pass

the blades.

  According to the embodiment shown, a module 1 or 2 consists of two lateral flanges

  (Figure 4): a right flange and a left flange.

  The flanges are in the form of parallelograms and carry in their thickness grooves or housings, intended to hold the plates and screens A middle groove 21, approximately diagonal, is provided to receive the ends of the convective exchange plate 5 symmetrically, relative to at the median groove and each c 8 té, a groove 22 for holding the radiative exchange plate 15 and a groove or housing 23 for the perforated plate 14 or bars constituting Parallel to at least a small c 8 té the parallelogram is provided a groove

  24 in which comes the grooves 22 and 23.

  The groove 24 opens itself into the groove 22

  of the convective exchange plate 5, forming the separa-

  The groove 24 is intended to hold the end partition 25 A groove or recess 26 is provided parallel to the long-side edges of the parallelogram and is intended to receive the upper and lower partitions 27 and 28, the partition 27 possibly carrying the arrival

of gas 9.

  When the exchanger consists of two modules, the grooves provided on the short sides of the parallelogram differ from one side to the other housing or groove receiving the partition 29, separating the compartment 4 of the module 1 of the neighboring compartment of the module 2 , is formed by half on each edge,

  during symmetrical assembly of modules 1 and 2.

  The partitions 25 and 29 have longitudinal grooves

  to maintain the plates 5 and 15 and the screen 14.

  To ensure alignment and positioning of the flanges of the modules 1 and 2, there is provided an assembly pin 31 which is placed in a recess 32 and thus extends the grooves 21 and 22 of the flange

of the first module.

  The assembly of a two-module heat exchanger, as described in the invention, operates in a manner

  simple One intertwines, one behind the other and symmetrical

  two identical flanges for each side of the exchanger and the convective exchange plate 5 is introduced into the groove 21 The partitions and 29 are placed and the plates 5 and 15 are slid in the different grooves. perforated 14 is assembled by introducing the bars into the openings 19 of the support 18, then sliding the ends of the bars in the housing 23 of the flanges The flanges, constituting the other side of the exchanger, are placed on the ends of the plates The exchanger is closed by embolization of the walls 27 and 28 These walls are formed of standardized elements allowing a

  easy modification of gas arrivals.

  The set of two modules forming the exchanger is surrounded by a thermal insulator 33 (FIG. 1), and

all of a metal case 34.

  The elements constituting the modules of

  the exchanger are made of a ceramic material,

  both good thermal conductivity and resistant to thermal shock, such as for example silicon carbide, silicon nitride, mullite, stabilized zirconia, cordierite, etc.

  The operation of the exchanger according to the invention

  Figure 1 is as follows: The hot gases are admitted through the inlet manifold 9 into the zone 6 The gases pass through the perforated screen 14 Because of the prismatic shape of the distribution zone 7, the gases are forced substantially uniformly in the slots of the radiative exchange plate 15, and the jets thus created strike the convective exchange plate 5 The flow of hot air convection yields its colors to the exchange plate 5 of the first module, then passes into the second module where it passes through a perforated screen 140, which distributes it along the radiative exchange plate and from there on the convective exchange plate 50 to

  exit 35, from where it leaves at low temperature.

  The cold gas enters through the inlet manifold 90 into the lower compartment of the module 2 and follows a

  course similar to that of hot gas but against

  current, and it comes out of module 1, warmed up, by the

exit 36.

  The convective exchange plates (5, 50) can be brought to a high temperature, they exchange directly by radiation with the environment. Also, it is the interest of having a network of radiative exchange plates (15). , 150) with strongemissivity which, by radiation, recovers a significant fraction of the energy emitted by the convective exchange plates, energy retransmitted by a sector to the currents of

hot or cold gas.

  The recovery exchanger, according to the embodiment described, is particularly suitable for implantation on metallurgical furnaces or on a gas turbine It has among others the following advantages: High overall exchange coefficient, lower pressure losses than for conventional systems (pipe exchangers) with given heat exchange power, Reduction of the exchange surface for a thermal power and a constant temperature difference, Optimum utilization of the exchanges by radiation.

  Za manufacture of the exchanger in modular form

  and with standardized elements allows a simple extension of the elements by stacking and coupling

  inputs and outputs of the various modules.

  By way of example, the characteristics of a module suitable for recovery on a metallurgical furnace for preheating the combustion air are given below. length: 0.340 m width: 0.250 m

height 0.080 m -

  wall thickness: 0.003 m module efficiency: from 0.2 to 0.3 module transfer unit number: from 0.2 to 0.3 Overall exchange coefficient around 150 W / m 2 o C (air at atmospheric pressure) pressure drop of module c 8 air tee:

at 300 PASCAL.

Claims (8)

  1 Heat exchanger with convective effect   radiative gas exchange through compartments   arranged behind each other, each compartment   being divided according to its height into zones, an area   receiving the exchange gas with a wall   openings separating it from another area   carrying an exchange surface arranged opposite the   wall, the gas passing from one zone to another and a   part to the other, characterized in that it is   killed by at least one module (1), comprising two compartments   truncated prism-shaped elements (3, 4) arranged on either side of an exchange surface (5), each compartment being divided into three zones parallel to the exchange surface: an arrival zone of a fluid (6), a distribution zone (7) and an exchange zone (8), the gas inlet zone being the zone furthest from the exchange surface (5), the gas outlet (10) being provided in the exchange zone (8) and at the truncated top of the prism.   2 exchanger according to claim 1, characterized in that a perforated screen (14) and a   radiative exchange plate (15) are provided respectively   between the arrival zone (6) of the gas and the distribution zone (7) and the latter and the zone exchange (8).   3 exchanger according to claim 3, characterized in that the radiative exchange plate (15) has slits directed in the direction of fluid flow and in that the perforated screen (14) has slots directed perpendicularly   those of the radiative exchange plate (15).   4 exchanger according to one of the claims   previous ones, characterized in that a module is con-   provided with two lateral flanges bearing in their thickness a middle groove (21), approximately diagonal, receiving the ends of the convective exchange plate (5) and symmetrically with respect to said middle groove, two grooves (22, 23) provided for receiving the ends of the radiative exchange plate (15) and the perforated screen (14), at least one groove (24) parallel to a small side of the parallelogram, maintaining the end walls (25), and at least two grooves (26) parallel to the large sides to maintain the upper (27) and lower partitions   (28) of the module, said partitions possibly carrying fluid flows (9).   Exchanger according to Claim 4, characterized in that the perforated screen (14) is formed   by parallel spaced blades.   6. Exchanger according to claim 4 or 5, characterized in that one of the grooves parallel to the small sides of the parallelogram is formed by the symmetrical assembly of the flanges of a second module 7 exchanger according to claim 6, characterized in that at least one of the short sides of the parallelogram comprises at least one connecting pin (31).   8 exchanger according to one of the claims   preceding, characterized in that the module or modules   are surrounded by a thermal insulation casing (54).   9 exchanger according to one of the claims   preceding, characterized in that the material constituting   killing the elements of the module or modules is a refractory ceramic.