EP0787946A1 - External fluidized bed for equipping a circulating fluidized bed furnace - Google Patents

Abstract

The fluidised bed is located inside a furnace chamber (2) which receives solids. It has a lower fluidising air feed (3) with injector nozzles (4) situated in the chamber's lower wall (2A). The furnace has a heat exchanger (5) made from a series of parallel tubes connected to an inlet manifold (6) embedded in the lower wall of the chamber. The outlet manifold (7) is situated inside the chamber at the top and has at least one outlet pipe (8) for the heated fluid which passes through the chamber's upper wall (2B). The two manifolds are situated in the chamber's central lengthwise plane, with the inlet manifold situated in a lower wall recess and covered with sand or concrete.

Description

The present invention relates to an external fluidized bed intended to equip a circulating fluidized bed hearth.

More precisely, it relates to a dense fluidized bed comprising in a box a chamber into which solids are poured out and equipped with a lower box for supplying fluidizing air, with nozzles for injecting fluidizing air arranged on its lower wall. and a heat exchanger made up of a plurality of parallel arrangements of tubes conveying a heat-transfer fluid, arranged transversely to the chamber and suspended from the upper wall of the chamber, each arrangement of tubes being connected at the bottom to a collector inlet of the heat transfer fluid consisting of a tube disposed longitudinally in the box and in the upper part to an outlet manifold of this heated fluid consisting of a tube disposed longitudinally in the box.

In such a known external fluidized bed, the inlet and outlet manifolds are arranged outside the box. The inlet manifold is arranged next to the box and the heat exchange tube arrangements have a first part opening out of the box to connect to this manifold. The outlet manifold is arranged above the box and the heat exchange tube arrangements have a second part opening out of the box to connect to this manifold. These parts therefore cross, one the side wall, the other the upper wall of the box, forming upper and lateral protrusions which must be taken into account when considering the size of the bed.

Furthermore, assembly and repair operations require intervention on these walls, in order to dismantle the parts of tubes external to the box.

The present invention solves these problems and consists of a compactly shaped bed, the manufacture and repair of which are particularly easy and rapid.

To do this, in accordance with the invention, the inlet manifold is housed in the lower wall of the chamber and the outlet manifold is disposed inside the chamber and is equipped with at least one outlet manifold for the heated heat transfer fluid passing through a wall of the chamber.

According to the preferred embodiment of the invention, the outlet manifold is disposed under the upper wall of the chamber and said tube passes through this upper wall.

Preferably, the two collectors are arranged in the longitudinal central plane of the chamber.

Advantageously, all the tubes of each tube arrangement are of substantially identical length.

Preferably, the inlet manifold is housed in a slot made in the bottom wall of the chamber and coated with sand.

Advantageously, a pipe for supplying heat transfer fluid passes through the fluidization box and is connected to the inlet manifold.

The invention also relates to a combustion installation comprising a circulating fluidized bed hearth comprising a gas outlet opening into a separation cyclone whose recovered solids are treated in an external fluidized bed as specified above.

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

Figure 1 is a perspective view of a bed according to the invention, its wall being partially broken away.

Figure 2 is a cross-sectional view of this bed.

• une chambre de réception des solides 11 dans laquelle sont introduits des solides par un orifice 12,
• une chambre 2 dans laquelle se déversent les solides après leur passage au-dessus d'un premier muret 13,
• une chambre de sortie 15 des solides partiellement représentée sur la figure 1, recevant les solides après leur passage au-dessus d'un second muret 14 et comportant un orifice d'évacuation des solides non visible sur la figure.

The dense fluidized bed comprises in a box 1 made up of a metal sheet 20 reinforced with stiffeners and an internal concrete layer 21, three chambers:

• a solid receiving chamber 11 into which solids are introduced through an orifice 12,
• a chamber 2 into which the solids are discharged after their passage over a first low wall 13,
• an outlet chamber 15 for the solids partially shown in FIG. 1, receiving the solids after their passage over a second wall 14 and comprising a solids evacuation orifice not visible in the figure.

Chamber 2 is equipped with a lower fluidization air supply box 3, nozzles 4 for injecting fluidization air arranged on the lower wall 2A of chamber 2 and a heat exchanger 5 consisting of '' a plurality of parallel arrangements of tubes conveying 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 a manifold inlet of the heat transfer fluid 6 consisting of a tube disposed longitudinally in the casing 1 and in the upper part to an outlet manifold of this heated fluid 7 consisting of a tube disposed longitudinally in the casing 1.

In this chamber 2 therefore takes place the dense fluidization of the solids and heat recovery by the exchanger 5.

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 in the bottom wall 2A of the chamber 2 and arranged in the central plane of the chamber 2. More precisely, it is housed in a slot 9 made in the lower wall 2A of the chamber 2 and coated with sand or concrete 16, which ensures its fixing and its protection. A heat transfer fluid supply line 10 passes through the fluidization box 3 and is connected to the inlet manifold 6 by a T-connector.

To this inlet manifold 6 are connected the arrangements of heat exchange tubes which are conventionally essentially horizontal and hairpin and extend to the height of the walls 13, 14. The arrangements are suspended by pair to the upper wall 2B of the chamber 2 by two vertical support tubes 17, 18 which are connected to the inlet manifold 5, pass through the upper wall 2B and return by return sections 17A, 18A connect to the outlet manifold 6 to which the tubes of the tube arrangements are connected. Advantageously, these support tubes 17, 18 can be of the type described in patent document FR-2 622 963 and be secured to the horizontal sections by connecting pieces ensuring both the mechanical support and the hydraulic connection, the support tubes constituting an extension of one of the hairpin tubes. The horizontal hairpin tubes are all of identical length, which eliminates any differential tension in the support tubes 17, 18.

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 6 by a T-connector also ensuring the suspension of the outlet manifold 6 from the upper wall 2B.

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

Such a bed allows a particularly improved manufacturing, which reduces manufacturing and assembly times on site.

Indeed, the box 1 without its upper wall can be manufactured in a first assembly, such as an open box. The upper wall with the collectors 5, 6 and the arrangements of suspended tubes can be prefabricated in a second set, in the workshop or on site. It suffices during the final assembly to introduce the second set from above into the first set, the inlet manifold 5 being installed in the slot 9, placed on the metal sheet 20 and then coated with sand or concrete.

The complete dismantling of the device is carried out by destruction of the possible concrete 16 and removal from the top of the second set.

The coating of the inlet manifold 5 with sand facilitates disassembly thereof and any intervention on it.

In the event of a leak and necessary repair, partial disassembly is carried out by cutting off the pair of damaged tube arrangements and the corresponding support tubes 17, 18 just above and just below the pair of tube arrangements and by translating this pair of arrangements in the box up or down in order to carry out the repair on the cleared tube arrangements.

In the upper part, disassembly requires less space than in known beds and it is thus possible to make a bed of less height and size.

Thanks to this new design of the bed, the heat exchange takes place as soon as the fluid leaves the inlet manifold 5 in the arrangements of heat exchange tubes, all of these arrangements being inside the chamber. 2.

Claims (7)

Dense fluidized bed comprising in a box (1) a chamber (2) into which solids are discharged and equipped with a lower box for supplying fluidizing air (3), nozzles for injecting fluidizing air ( 4) arranged on its lower wall (2A) and a heat exchanger (5) consisting of a plurality of parallel arrangements of tubes conveying a heat transfer fluid, arranged transversely to the chamber (2) and suspended from the upper wall (2B) of the chamber (2), each arrangement of tubes being connected in the lower part to an inlet manifold for the heat-transfer fluid (6) consisting of a tube disposed longitudinally in the box (1) and in the upper part to a manifold outlet of this heated fluid (7) consisting of a tube disposed longitudinally to the box (1), characterized in that the inlet manifold (6) is housed in the bottom wall (2A) of the chamber and in that the outlet manifold (7) is arranged inside d e the chamber (2) and is equipped with at least one outlet pipe for the heated heat transfer fluid (8) passing through a wall of the chamber (2). Bed according to claim 1, characterized in that the outlet manifold (7) is arranged under the upper wall (2B) of the chamber (2) and said tube (8) passes through this upper wall (2B). Bed according to one of the preceding claims, characterized in that the two collectors (6, 7) are arranged in the longitudinal central plane of the chamber (2). Bed according to claim 3, characterized in that all the tubes of each tube arrangement are of substantially identical length. Bed according to one of the preceding claims, characterized in that the inlet manifold (6) is housed in a slot (9) made in the lower wall (2A) of the chamber (2) and coated with sand. Bed according to one of the preceding claims, characterized in that a supply pipe for heat transfer fluid (10) passes through the fluidization box (3) and is connected to the inlet manifold (6). Combustion installation comprising a circulating fluidized bed hearth comprising a gas outlet opening into a separation cyclone, the recovered solids of which are treated in an external fluidized bed according to one of the preceding claims.

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