FR2752926A1 - Fluid heat exchanger - Google Patents

Abstract

The heat exchanger has an inlet manifold (6) for a fluid and an outlet manifold (7) connected by at least two groups of parallel tubes, forming the first (3A) and second (3B) groups defining an panel of tubes which are connected by couplings shaped like hairpins (5). The tubes are in two vertical parallel planes, the helix formed by the one group being surrounded by those forming the first group. The angle of each helix can be between eight and fifteen degrees. The two helices can have the same pitch. The two groups can have the same number of parallel tubes.

Description

 REDUCED HEAT EXCHANGER.

 The present invention relates to a space-saving heat exchanger.

 It relates more precisely to a heat exchanger comprising a fluid inlet manifold and a fluid outlet manifold connected by at least two groups of parallel tubes called first group and second group and forming a panel of hairpin tubes .

 Such a known exchanger is described in patent FR2 622 963. The tubes are all arranged in the same vertical plane, each group forming a zigzag comprising horizontal rectilinear sections connected by hairpins in a vertical plane.

 Such an exchanger can for example be installed in an external fluidized bed intended to equip a circulating fluidized bed hearth.

 In such high-power installations, an increase in the heat exchange surfaces of such an exchanger is sought. This leads to the need to increase the dimensions of the exchanger or to associate a relatively number of such exchangers. In all cases, the size is increased.

 The object of the invention is to considerably increase the exchange surfaces, while retaining limited dimensions of the exchanger.

 To do this, according to the invention, each group forms a flat helix consisting of rectilinear sections connected by hairpins and arranged in two parallel vertical planes, the helix formed by the second group being nested in that formed by the first group.

 With substantially identical dimensions, it is thus possible to multiply the heat exchange surface by a coefficient of the order of three.

 According to the preferred embodiment, the angle of each propeller is between 8 and 150, in order to allow a natural circulation supply and the use of the exchanger as a vaporizer.

 Preferably, the two propellers have the same pitch and, advantageously, the two groups have the same number of parallel tubes.

 According to an alternative embodiment, the adjacent tubes of the same group are connected by a continuous fin.

 The invention is described below in more detail using figures showing only a preferred embodiment of the invention.

 FIG. 1 represents part of a dense fluidized bed and more precisely in a box 1 consisting of a metal sheet reinforced with stiffeners and a layer of internal concrete, a chamber 2 into which the solids are poured after their passage through- above a low wall downstream of a chamber for receiving these solids.

 Chamber 2 is equipped with a lower fluidization air supply box, not shown, fluidization air injection nozzles, not shown, disposed on the lower wall 2A of chamber 2, and with a heat exchanger consisting a plurality of parallel arrangements of tubes 3 carrying a heat transfer fluid, for example steam, arranged transversely to the chamber 2 and suspended from the upper wall 2B of the chamber 2, each arrangement of tubes being connected at the bottom to an inlet manifold for the heat transfer fluid 6 consisting of a tube arranged longitudinally in the casing 1 and in the upper part to an outlet manifold for this heated fluid 7 consisting of a tube arranged longitudinally in the casing 1.

 In this chamber 2 therefore takes place the dense fluidization of the solids and heat recovery by the exchanger 3.

 Such a bed is generally intended for a combustion installation comprising a circulating fluidized bed hearth comprising a gas outlet opening into a separation cyclone whose recovered solids are treated in this external fluidized bed before being at least partially reinjected into the circulating fluidized bed hearth.

 The inlet manifold 6 is housed under the bottom wall 2A of the chamber 2 and arranged in the central plane of the chamber 2. The exchanger arrangement 3 is connected to this manifold 6 by a slot 9 made in the bottom wall 2A of chamber 2 and coated with concrete 16, which ensures its fixation and protection.

 To this inlet manifold 6 are connected the arrangements of heat exchange tubes 3 which conventionally extend up to the height of said low wall.

 The outlet manifold 7 coated with concrete is placed inside the chamber 2, in the longitudinal central plane of the chamber 2 and more precisely under the upper wall 2B of the chamber 2 and is equipped with at least one manifold of outlet of the heated heat transfer fluid 8 passing through this upper wall 2B and connected to the outlet manifold 7 by a tee fitting also ensuring the suspension of the outlet manifold 6 from the upper wall 2B.

 Several sets of collectors and tube arrangements as previously described can be installed in the chamber 2, aligned in the longitudinal direction thereof.

 The heat exchanger arrangement 3 which will be called heat exchanger 3 comprises two groups of parallel tubes called first group 3A and second group 3B which form a panel of hairpin tubes. In addition to their connecting sections to the collectors 6, 7, each group forms a flat helix consisting of rectilinear sections 4 connected by hairpins 5 and arranged in two parallel vertical planes, the helix formed by the second group 3B being nested in that formed by the first group 3A.

 The straight sections 4 are inclined and the angle of each propeller is between 8 and 150.

 Advantageously, the two propellers have the same pitch, the tubes all being substantially of identical length, which eliminates any differential tension.

 Each group of tubes therefore comprises a first substantially vertical section 10 connected to the inlet manifold 6 and passing through the bottom wall 2A, then a flat helix consisting of inclined rectilinear sections 4 and hairpins and a second substantially vertical section 11 connecting propeller and outlet manifold 7.

 At least one of the tubes of this second section 11 has a hairpin 12 which passes through the upper wall 2B and is coated therewith in order to suspend the exchanger. Vertically, in line with these suspensions, the suspension of the exchanger can be reinforced by short fins 13 welded as shown in FIG. 2 or an arrangement of suspension suspensions as described in patent FR-2 622 963 can be used.

 In order to stiffen the exchanger and improve its mechanical strength, it is also possible to connect the adjacent tubes of the same group 3A, 3B by a continuous fin 14, as shown in Figure 3 (detail III of the figure 1). Each group 3A, 3B then consists of a panel cased in the form of a ribbon and shaped into a helix.

 The exchanger according to the invention is self-supporting and allows the supply in natural circulation.

 Although described in an external fluidized bed installation, it can be used in any heat exchange installation, for example in a recovery boiler at the outlet of the incinerator.

Claims (5)

 1) Heat exchanger comprising an inlet manifold (6) of a fluid and an outlet manifold (7) of the fluid connected by at least two groups of parallel tubes called first group (3A) and second group (3B) and forming a panel of hairpin tubes, characterized in that each group forms a flat helix made up of rectilinear sections (4) connected by hairpins (5) and arranged in two parallel vertical planes, the helix formed by the second group (3B) being nested in that formed by the first group (3A).  2) Exchanger according to claim 1, characterized in that the angle of each propeller is between 8 and 150.  3) Exchanger according to claim 1 or 2, characterized in that the two propellers have the same pitch.  4) Exchanger according to one of the preceding claims, characterized in that the two groups (3A, 3B) have the same number of parallel tubes.  5) Exchanger according to one of the preceding claims, characterized in that the adjacent tubes of the same group are connected by a continuous fin (14).