Title of Invention	A FLUIDIZED-BED DEVICE
Abstract	The invention relates to a fluidized-bed device (F1, F2) provided with a hearth (1, 23) equipped with gas mixture feeds called primary feeds, said gas mixture being enriched with oxygen, and said hearth (1, 23) being provided with a network of two types of primary feed nozzle, a first type of nozzle (B1, B'1) injecting a first gas mixture at a first level close to the hearth (1, 23) and a second type of nozzle (B2, B'2) injecting a second oxygen-enriched gas mixture at a second level above the first level. According to the invention, said second type of nozzle (B2, B'2) consists of a device for mixing oxygen with a second gas component and connected by its lower end to an oxygen feed (11A, 11A') and to a feed of second gas component, and of a device for injecting this mixture into the combustion chamber.

Title of Invention

A FLUIDIZED-BED DEVICE

Abstract

The invention relates to a fluidized-bed device (F1, F2) provided with a hearth (1, 23) equipped with gas mixture feeds called primary feeds, said gas mixture being enriched with oxygen, and said hearth (1, 23) being provided with a network of two types of primary feed nozzle, a first type of nozzle (B1, B'1) injecting a first gas mixture at a first level close to the hearth (1, 23) and a second type of nozzle (B2, B'2) injecting a second oxygen-enriched gas mixture at a second level above the first level. According to the invention, said second type of nozzle (B2, B'2) consists of a device for mixing oxygen with a second gas component and connected by its lower end to an oxygen feed (11A, 11A') and to a feed of second gas component, and of a device for injecting this mixture into the combustion chamber.

Full Text	FLUIDIZED-EED DEVICE WITH OXYGEN-ENRICHED OXIDIZER The present invention relates to a fluidized-bed device with oxygen-enriched oxidizer. Fluidized-bed device here means both a circulating fluidized-bed combustion chamber and a dense fluidized-bed combustion chamber. The development of new regulations limiting greenhouse gas emissions, including carbon dioxide in fossil fuel power plants, is leading to the implementation of technologies for capturing the carbon dioxide present in air combustion flue gases. The frequently used carbon dioxide capture technology consists in scrubbing the flue gases diluted with nitrogen from the combustion air using solvents which absorb the carbon dioxide and then restore it as a concentrated carbon dioxide gas stream after regenerating the solvent by heating. This method consumes a considerable amount of energy and substantially reduces the efficiency of fossil fuel power plants, namely reducing the efficiency by more than 15 percentage points. Patents US 4 498 289 and US 5 175 995 teach the use of oxygen as oxidizer instead of air in power generation boilers. The advantage of using oxygen as oxidizer is the reduction, to the point of elimination, of the nitrogen ballast diluting the carbon dioxide present in the flue gases and originating from the nitrogen present in the combustion air, and the substantial reduction of the size of the necessary equipment. The application of this principle to a circulating fluidized-bed boiler is disclosed in patent US 6 505 567. According to this document, a fluidized-bed combustion chamber or steam generator comprises means for introducing substantially pure oxygen into the generator. The advantage of the circulating fluidized-bed technique is that it allows the extraction of the heat on the circulating solids loop and the maintenance of a low combustion temperature, independently of the oxygen content of the oxidizer. Hence this technique is particularly attractive and serves to maximize the fraction of oxygen in the oxidizer and to minimize the size of the boiler which depends directly on the flow rate of flue gases produced. However, in this prior document, no details are provided concerning these injection means. In fact, this oxygen injection into the combustion chamber is particularly difficult and the creation of local hot spots is liable to cause caking of the bed and destruction of the injection nozzles. In fact, the medium of a circulating fluidized bed is not a perfectly stirred medium in practice, despite the high solids concentration which guarantees local turbulence. Furthermore, this injection must ensure an appropriate oxygen distribution over the cross section of the combustion chamber. The contacting and the reaction of the fuel introduced into the bed with the oxidizer is essential for the satisfactory progress of the reactions and, in particular, to minimize the formation of nitrogen oxides and maximize the conversion of desulfurization limestone injected into the combustion chamber. Patent document US 4 62 8 831 describes a fluidized-bed device provided with a hearth equipped with gas mixture feeds called primary feeds, said gas mixture containing oxygen, said hearth being provided with a network of two types of primary feed nozzles, a first type of nozzle injecting the gas mixture at a first level close to the hearth and a second type of nozzle injecting the gas mixture at a second level above the first level. According to that document, the gas mixture must be prepared upstream in large volumes. This implies a large overall size of the boiler. Added to this are safety problems inherent in the presence of large volumes of oxygen-concentrated gases. The invention solves these technical problems and, for this purpose, it proposes a fluidized-bed device provided with a hearth equipped with gas mixture feeds called primary feeds, said gas mixture being enriched with oxygen, and said hearth being provided with a network of two types of primary feed nozzle, a first type of nozzle injecting a first gas mixture at a first level close to the hearth and a second type of nozzle injecting a second oxygen-enriched gas mixture at a second level above the first level, characterized in that said second type of nozzle consists of a device for mixing oxygen with a second gas component and connected by its lower end to an oxygen feed and to a feed of second gas component, and of a device for injecting this mixture into the combustion chamber. The two types of nozzle installed on the hearth of the device inject the gases at different height levels to ensure optimal fluidization conditions. In fact, it is essential for the upper injections of oxygen- enriched mixture by the second type of nozzle to take place in a medium already fluidized by the first type of nozzle injecting the first gas mixture, that is air or carbon dioxide. Thanks to the invention, the oxygen is dissipated in a turbulent mixing medium. This feature serves to inject the oxygen directly into the combustion chamber without the need for previous premixing in large volumes. Greater compactness of the boiler and increased safety are thereby achieved. Furthermore, the mixing function is thereby dissociated from the injection function in the nozzle. The design of the nozzle is thereby facilitated, as regards the pressure drops at the gas orifices and the prevention of the return of solids via these orifices. According to a preferred embodiment, these two gas mixtures are different. According to a preferred embodiment, the device is provided with at least one oxidizer feed called secondary feed, and said secondary feed also injects an oxygen-enriched mixture. In the case of a circulating fluidized-bed combustion chamber, such a secondary feed in the expanded part of the combustion chamber is preferred to a tertiary feed in the cylindrical part of the combustion chamber, this expanded part being generally equipped with a refractory lining. However, this other type of tertiary oxidizer feed is also feasible. Several secondary and, optionally, tertiary feeds may be arranged at different height levels of the combustion chamber, above the primary hearth, to ensure appropriate staging of the oxygen over the height of the combustion chamber. Advantageously, said secondary feed consists of a nozzle comprising a double concentric tube for injecting said oxygen-enriched mixture into the inner tube and for injecting the first gas mixture into the outer tube. Said oxygen-enriched mixture may contain 21 to 100% of oxygen. Said oxygen-rich mixture may comprise a second gas component consisting of carbon dioxide and said first gas mixture may be carbon dioxide. Said oxygen-rich mixture may comprise a second gas component consisting of nitrogen and said first gas mixture may be carbon dioxide. Said oxygen-rich mixture may be oxygen-enriched air and said first gas mixture may be air. Advantageously, said mixing device consists of two substantially vertical concentric tubes of which the outer tube is closed at its upper end and provided with orifices on its side wall. Advantageously, said injection device consists of a cap covering said mixing device and provided with orifices in its upper part. According to a second variant, said second type of nozzle consists of two substantially vertical concentric tubes of which the outer tube is provided with orifices on its side wall. Preferably, said concentric tubes are covered with a cap provided with orifices in its upper part. Advantageously, said cap is provided with an internal wall for forming a baffle. Preferably, said oxygen feed is provided by a manifold to which the inner concentric tube is connected. Said feed of second gas component may be provided by direct connection of the outer concentric tube to said windbox filled with second gas component or by a manifold to which the outer concentric tube is connected. The oxygen-enriched mixture may contain water vapor and/or sulfur dioxide. The risk of formation of hot spots in the combustion chamber close to the injection points is thereby further reduced. This water injection in fact promotes a local gasification of the fuel by decreasing the oxygen partial pressure. The invention further relates to a circulating fluidized-bed combustion chamber as described above. According to a first application, a circulating fluidized-bed boiler comprising such a circulating fluidized-bed combustion camber and a dense fluidized bed with a heat exchanger and receiving solids at the outlet of a clone, said dense fluidized bed is provided with at least one secondary feed injecting an oxygen-enriched mixture into its return line to the circulating fluidized-bed combustion chamber. The invention further relates to a dense fluidized bed with a heat exchanger as described above. The invention finally relates to a second application consisting of a circulating fluidized-bed boiler comprising such a circulating fluidized-bed combustion chamber and an associated dense fluidized bed with a heat exchanger and receiving solids at the outlet of a cyclone. Said derive fluidized bed may be provided with at least one secondary feed injecting an oxygen-enriched mixture above the bed. Said combustion chamber with dense fluidized-bed heat exchanger may be provided with at least one secondary feed injecting an oxygen-enriched mixture into its return line to the circulating fluidized-bed combustion chamber. The invention finally relates to a circulating fluidized-bed boiler comprising a circulating fluidized-bed combustion chamber as described above and a dense fluidized bed receiving solids at the outlet of a cyclone, characterized in that the dense bed is fluidized by air or a component thereof. The invention therefore proposes a device for optimizing the oxygen consumption while preserving the advantages of airless combustion. According to a preferred embodiment, the dense bed is fluidized by nitrogen. Advantageously, this nitrogen is obtained from a cryogenic air separation unit which supplies oxygen to the boiler. This fluidization with nitrogen serves to avoid post-combustion of the carbon present in the dense bed, which could lead to carbon dioxide leakage from the stack and to a lower overall carbon dioxide capture efficiency. Preferably, the fluidization gas of the dense bed is cooled in a heat exchanger before release to the atmosphere. The particles of the dense bed may be separated from the fluidization gas before injection into the combustion chamber. The particles may be separated from the fluidization gas by a siphon. Advantageously, the siphon is fluidized by a gas mixture composed of O2/CO2. The invention is described below in greater detail with the aid of accompanying figures representing only one preferred embodiment of the invention. Figure 1 is a schematic view of a vertical cross section of a circulating fluidized-bed boiler combustion chamber according to the invention. Figure 2 shows a vertical cross section of a second type of nozzle installed in the hearth of a combustion chamber of a circulating fluidized-bed boiler according to a first variant of the invention. Figure 3 shows a vertical cross section of a second type of nozzle installed in the hearth of a combustion chamber of a circulating fluidized-bed boiler according to a second variant of the invention. Figure 4 is a schematic view of a vertical cross section of a circulating fluidized-bed boiler comprising a circulating fluidized-bed combustion chamber and a dense fluidized bed with a heat exchanger receiving solids at the outlet of a cyclone, according to the invention. Figure 5 is a schematic view of a vertical cross section of a circulating fluidized-bed boiler comprising a circulating fluidized-bed combustion chamber and a dense fluidized bed receiving solids at the outlet of a cyclone, according to the invention, in another variant. Figure 6 is a detailed view of the dense bed and its siphon. Figure 7 is a schematic view of an exemplary embodiment. The invention preferably relates to a fluidized- bed device in which combustion takes place by means of a mixture of oxygen and carbon dioxide or nitrogen with fluidization injection of carbon dioxide. It further relates to a fluidized-bed device in which combustion is effected by means of oxygen-enriched air with fluidization injection of air. A circulating fluidized-bed boiler combustion chamber shown schematically in Figure 1 is provided with a hearth 1 consisting of a solid or tubular cooling wall and equipped with oxidizer feeds called primary feeds and surmounted by a first expanded part 2 provided with at least one oxidizer feed called secondary feed and itself surmounted by a cylindrical part 3. A box called a windbox 4 and filled with pressurized gas is arranged under the hearth 1. The hearth 1 is provided with a network of two types of primary feed nozzle, a first nozzle type B1 injecting air or carbon dioxide at a first level close to the hearth and a second nozzle type B2 injecting an oxygen-enriched mixture at a second level above the first level. The nozzles Bl of the first type are of known design and directly supplied by the windbox 4 filled with pressurized air or carbon dioxide. The nozzles B2 of the second type are supplied here, on the one hand, by a common oxygen inlet manifold 7 and, on the other, with a second gas component, either directly by the windbox 4, or by a common manifold which may be located in the windbox 4. These various nozzles are described in greater detail below. The combustion chamber comprises secondary feeds A1, A2 also injecting an oxygen-enriched mixture. These secondary feeds each consist of a nozzle comprising a double concentric tube for injecting said oxygen-enriched mixture, advantageously even pure oxygen, into the inner tube 5 and for injecting air or carbon dioxide into the outer tube 6. The oxygen-enriched mixture may contain 21 to 100% of oxygen, the other fraction consisting of carbon dioxide or nitrogen. Figure 2 shows a first variant of a second type of nozzle B2 for injecting oxygen-enriched mixture. This nozzle B2 consists of a device for mixing oxygen with the second gas component and connected by its lower end to an oxygen feed and to a second gas component feed, and of a device for injecting this mixture into the combustion chamber. More precisely, the mixing device consists of two substantially vertical concentric tubes of which the outer tube 10 passes through the hearth of the combustion chamber 1 and is closed at both its ends. This outer tube 10 is connected at its lower part to an inlet 10A of second gas component from the windbox 4 or from a manifold that may be located in said windbox. In its upper part, this tube 10 is provided with orifices 10B on its side wall for gas escape. Advantageously, the orifices 10B are distributed around the tube 10 and at several levels. The inner tube 11 of these two concentric tubes passes through the lower closure wall of the outer tube 10 and extends along most of the height of this outer tube 10. It is connected at its lower end to an oxygen manifold 11A, located in the windbox 4 and is open at its upper end 11B from where the oxygen escapes. At this escape point, the oxygen is mixed with the second gas component and an oxygen-enriched gas mixture issues through the orifices 10B. The injection device consists of a cap 12 covering the mixing device, fixed in a sealed manner to the hearth 1, for example by screwing or welding, and provided with orifices 12B in its upper part through which the gas mixture is injected into the combustion chamber. Advantageously, the orifices 12B are distributed around the cap 12. By dismantling this cap 12, it is easily possible to reach the interior of the nozzle B2. Figure 3 shows a second variant of a second type of nozzle B2 for injecting oxygen-enriched mixture. This figure also shows a first type of nozzle B1 known per se injecting air or carbon dioxide via the outlet orifices S1. The second type of nozzle B'2 consists of two substantially vertical concentric tubes of which the outer tube 10' passes through the hearth of the combustion chamber 1 and is closed at its upper end by a wall 10'A. This outer tube 10' is fixed by its lower end in a sealed manner to the hearth 1 and is fed with second gas component issuing from the windbox 4. In its upper part, this tube 10' is provided with orifices 10'C on its side wall for gas escape. Advantageously, the orifices 10'C are distributed around the tube 10' and at several levels. The inner tube 11' of these two concentric tubes extends along the entire height of this outer tube 10' and is guided in this outer tube by spacers 10'D at the hearth 1. This system of spacers can advantageously perform a function of blocking the return of solids thanks to an annular type of geometry comprising orifices distributed on the periphery. It is connected at its lower end to an oxygen manifold 11'A located in the windbox 4 and is open at its upper end 11'B where the oxygen escapes. Above this unit is placed a cap type of element 12' which, in its upper part, forms orifices 12'A for the lateral outlet of oxygen toward a lateral space inside this cap where the oxygen and second gas component are mixed before escaping via the side orifices 12'B of the cap where the oxygen-enriched mixture is injected into the combustion chamber. Advantageously, the side orifices 12'A, 12'B are distributed along the periphery of the element bearing them. Advantageously, a vertical cylindrical wall 12'C is placed in this internal lateral space of the cap, thereby providing a baffle and turbulence improving the mixing of the two gases. According to an essential feature, the first type of nozzle B1 injects the first gas mixture at a first level close to the hearth 1, corresponding to the height of the orifices S1, and the second type of nozzle B'2 injects the oxygen-enriched mixture at a second level above the first level and corresponding to the height of the orifices 12'B. The upper injections of oxygen-enriched mixture by the second type of nozzle B'2 thereby take place in a medium already fluidized by the nozzles of the first type Bl injecting the first gas mixture. This is shown schematically in Figure 3, by a representation of a nonfluidized layer C on the hearth 1 outside which the injection orifices 12' B of the second type of nozzle B'2 are arranged. This injection height can be adjusted and determined by- choosing the position of these orifices 12'B in the cap 12 and/or by choosing the height of the nozzle B'2 itself. In the preceding description of nozzles B'2, the dimensions and gas feed pressures are calculated and selected so that the oxygen-rich mixture contains 21 to 100% of oxygen, the other fraction consisting of carbon dioxide or nitrogen, the mixture thereby corresponding to enriched air. Since the pressure at the bottom of the combustion chamber can reach 800 mbar, the dimensions of the gas outlet orifices are also determined to prevent the passage or return of gas and/or solids into the nozzles, the transfer speeds being selected between 10 and 100 m/s. The oxygen-enriched mixture injected into the combustion chamber may contain water vapor, to avoid the formation of hot spots. Figure 4 shows a first embodiment of a fluidized- bed boiler according to the invention. The device F2 is a dense fluidized bed associated here with a circulating fluidized-bed combustion chamber F1. This dense fluidized bed F2 also comprises a hearth 23 provided with a network of two types of primary feed nozzle, a first type of nozzle B'1 injecting air or carbon dioxide at a first level close to the hearth, and a second type of nozzle B'2 injecting an oxygen-enriched mixture at a second level above the first level. The nozzles B'1 of the first type are of known design and are directly fed by the windbox 26 filled with pressurized air or carbon dioxide. The nozzles B'2 of the second type are fed here, on the one hand, by a common oxygen inlet manifold 27 and, on the other, with second gas component, either directly by the windbox 26, or by a common manifold which may be located in the windbox 26. These various nozzles are preferably of the same type as those already described above and shown in Figures 2 and 3. This dense fluidized bed F2 also comprises at least one secondary feed A'1 also injecting an oxygen- enriched mixture. In its specific application shown in Figure 4, this dense fluidized-bed heat exchanger F2 is associated with a circulating fluidized-bed combustion chamber F1 and serves to control the temperatures of the circulating fluidized-bed combustion chamber F1. The solids contained in the flue gases leaving the combustion chamber F1 are separated in a cyclone 21 and returned to the bottom of the combustion chamber Fl by a siphon 20. The base of the siphon 20 is provided with an extraction of solids at a flow rate controlled by a valve. The solids extracted are also transferred to the dense fluidized bed F2 in a heat exchanger immersed in its bed 24. The cooled solids leave the bed and are transferred via a line 25 to the circulating fluidized-bed combustion chamber F1. An additional injection of oxygen-enriched gas mixture can also be made in the overhead 22 above the bed 24 of the dense bed with the heat exchanger F2 and in the overhead of the line 25, by nozzles A'1 and A'2 similar to those already described as secondary nozzles for the circulating fluidized-bed combustion chamber Fl. Figure 5 shows a second embodiment of a fluidized- bed boiler according to the invention. In this application, a dense fluidized bed E with a heat exchanger is associated with a circulating fluidized-bed combustion chamber F1 and serves to control the temperatures of the circulating fluidized- bed combustion chamber F1. The solids contained in the flue gases leaving the combustion chamber F1 are separated in a cyclone 21 and conveyed to the bottom of the combustion chamber Fl by a fluidized siphon 20 providing air- and carbon dioxide atmosphere-tightness between the dense bed and the circulating fluidized-bed combustion chamber F1. The base of the siphon 20 is equipped with a solids extraction at a flow rate controlled by a valve. The solids extracted are transferred to a dense fluidized bed E containing a heat exchanger immersed in its bed 24. The cooled solids leave the bed and are transferred via a line 2 5 to the circulating fluidized-bed combustion chamber F1 via a fluidized siphon 28 which provides a seal between the dense bed and the circulating fluidized-bed combustion chamber. An additional injection of oxygen- enriched gas mixture can also be made in the overhead of the line 25 downstream of the siphon 28, by a nozzle A" 2 similar to the one already described as secondary nozzles for the circulating fluidized-bed combustion chamber Fl in this line 25. In this variant, the dense fluidized bed E is equipped with a specific vent 30 for venting the fluidization gas toward the rear cage 31 of the boiler to avoid diluting the carbon dioxide produced in the combustion chamber with the nitrogen present in this gas. This variant has the advantage of not using recycled carbon dioxide for fluidizing the dense bed exchangers. Contrary to the variant in Figure 4, this carbon dioxide is accordingly preserved for the oxygen- rich gas mixture feed to the combustion chamber and serves to decrease the oxygen concentration of the gas mixture. Figure 6 shows that the dense fluidized bed E is equipped with a specific vent 3 0 for removing the fluidization air or nitrogen, arriving via B1, toward a specific rear cage 31 of the boiler to avoid diluting the carbon dioxide produced in the combustion chamber with this gas. The siphon 2 is fluidized by a gas mixture comprising O2/CO2, this mixture arrives via fluidization nozzles B2. The use of the O2/CO2 gas to fluidize permits a substitution of the air or nitrogen remaining between the solid particles by said gas and thereby to ensure that all the fluidization gas of the dense bed is properly removed without returning to the combustion chamber F1. The solid particles return toward the combustion chamber F1 via a solids return 25. Figure 7 shows an exemplary embodiment according to the invention, in which the combustion chamber Fl has two separators 21 each with a siphon 20. Each siphon 20 is connected to two external beds E each having a siphon 2. Thus the solids circulation loop is duplicated, each loop comprising a separator 21 and a siphon 20. The solids extraction from each siphon 20 can also be duplicated, as in Figure 3. Each siphon 20 thereby comprises two outlets at flow rates each controlled by a valve and feeds two external beds E. Each external bed E is fluidized by air or nitrogen and followed by a siphon 2. WE CLAIMS 1. A fluidized-bed device (F1, F2) comprising a hearth (1, 23) equipped with gas mixture feeds called primary feeds, said gas mixture is containing with oxygen, and said hearth (1, 23) being provided with a network of two types of primary feed nozzle, a first type of nozzle (Bl, B'1) injecting a first gas mixture at a first level close to the hearth (1, 23) and a second type of nozzle (B2, B'2) injecting a second oxygen-enriched gas mixture at a second level above the first level, wherein said second type of nozzle (B2, B' 2) consists of a device for mixing oxygen with a second gas component and connected by its lower end to an oxygen feed (11A, 11A'), a feed of second gas component, and of a device for injecting the mixture into the combustion chamber. 2. The device as claimed in claim 1, wherein these two gas mixtures are different. 3. The device as claimed in one of the preceding claims, comprising at least one oxidizer feed called secondary feed, wherein said secondary feed (A1, A2, A'1, A'2, A"2) injects an oxygen-enriched mixture. 4. The device as claimed in claim 3, wherein said secondary feed consists of a nozzle comprising a double, concentric tube for injecting said oxygen- enriched mixture into an inner tube and for injecting the first gas mixture into the outer tube (6). 5. The device as claimed in one of the preceding claims, wherein said oxygen-enriched mixture contains 21 to 100% of oxygen. 6. The device as claimed in one of the preceding claims, wherein said oxygen-enriched mixture comprises a second gas component consisting of carbon dioxide and said first gas mixture is carbon dioxide. 7. The device as claimed in one of claims 1 to 5, wherein said oxygen- enriched mixture comprises a second gas component consisting of nitrogen and said first gas mixture is carbon dioxide. 8. The device as claimed in one of claims 1 to 5, wherein said oxygen- enriched mixture is oxygen-enriched air and said first gas mixture is air. 9. The device as claimed in one of the preceding claims, wherein said mixing device consists of two substantially vertical concentric tubes of which the outer tube (10) is closed at its upper end and provided with orifices (10B) on its side wall. 10.The device as claimed in one of the preceding claims, wherein said injection device consists of a cap (12) covering said mixing device and provided with orifices (12B) in its upper part. 11.The device as claimed in one of claims 1 to 8, wherein said second type of nozzle (B'2) consists of two substantially vertical concentric tubes of which the outer tube (10') is provided with orifices (10'C) on its side wall. 12.The device as claimed in claim 11, wherein said concentric tubes (10' 11') are covered with a cap (12') provided with orifices (12'B) in its upper part. 13.The device as claimed in claim 12, wherein said cap (12') is provided with an internal wall (12'C) for forming a baffle. 14.The device as claimed in one of the preceding claims, wherein said oxygen feed is provided by a manifold (11A) to which the inner concentric tube (11) is connected. 15.The device as claimed in one of the preceding claims, wherein said feed of second gas component is provided by direct connection of the outer concentric tube (10') to a windbox (4) filled with this gas. 16.The device as claimed in one of claims 1 to 14, wherein said feed of second gas component is provided by a manifold, to which the outer concentric tube (10) is connected. 17.The device as claimed in one of the preceding claims, wherein the oxygen-enriched mixture contains water vapor and/or sulfur dioxide. 18. A circulating fluidized-bed boiler comprising a fluidized-bed combustion chamber (F1) as claimed in claim 17 and a dense fluidized bed with a heat exchanger and receiving solids at the outlet of a cyclone, said dense fluidized bed (E) is provided with at least one secondary feed (A"2) injecting an oxygen-enriched mixture into its return line to the circulating fluidized-bed combustion chamber (F1). 19.The boiler as claimed in claim 18, wherein said dense fluidized bed is provided with at least one secondary feed (A'1) injecting an oxygen- enriched mixture above the bed. 20.The boiler as claimed in one of claim 19, wherein said dense fluidized bed is provided with at least one secondary feed (A'2) injecting an oxygen- enriched mixture into its return line to the circulating fluidized-bed combustion chamber. 21.The boiler as claimed in claim 18, wherein the dense bed (E) is fluidized by air or a component thereof. 22.The boiler as claimed in one of the preceding claims, wherein the dense bed (E) is fluidized by nitrogen from a cryogenic air separation unit. 23.The boiler as claimed in one of claims 20 and 21, wherein the fluidization gas of the dense bed (E) is cooled In a heat exchanger before release to the atmosphere. 24.The boiler as claimed in one of claims 20 to 23, wherein the particles of the dense bed (E) are separated from the fluidization gas before injection into the combustion chamber (F1). 25.The boiler as claimed in the preceding claim, wherein the particles are separated from the fluidization gas by a siphon (2). 26.The device as claimed in the preceding claim, wherein the siphon (2) is fluidized by a gas mixture composed of O2/CO2. The invention relates to a fluidized-bed device (F1, F2) provided with a hearth (1, 23) equipped with gas mixture feeds called primary feeds, said gas mixture being enriched with oxygen, and said hearth (1, 23) being provided with a network of two types of primary feed nozzle, a first type of nozzle (B1, B'1) injecting a first gas mixture at a first level close to the hearth (1, 23) and a second type of nozzle (B2, B'2) injecting a second oxygen-enriched gas mixture at a second level above the first level. According to the invention, said second type of nozzle (B2, B'2) consists of a device for mixing oxygen with a second gas component and connected by its lower end to an oxygen feed (11A, 11A') and to a feed of second gas component, and of a device for injecting this mixture into the combustion chamber.

Full Text

FLUIDIZED-EED DEVICE WITH OXYGEN-ENRICHED OXIDIZER
The present invention relates to a fluidized-bed
device with oxygen-enriched oxidizer. Fluidized-bed
device here means both a circulating fluidized-bed
combustion chamber and a dense fluidized-bed combustion
chamber.
The development of new regulations limiting
greenhouse gas emissions, including carbon dioxide in
fossil fuel power plants, is leading to the
implementation of technologies for capturing the carbon
dioxide present in air combustion flue gases.
The frequently used carbon dioxide capture
technology consists in scrubbing the flue gases diluted
with nitrogen from the combustion air using solvents
which absorb the carbon dioxide and then restore it as
a concentrated carbon dioxide gas stream after
regenerating the solvent by heating.
This method consumes a considerable amount of
energy and substantially reduces the efficiency of
fossil fuel power plants, namely reducing the
efficiency by more than 15 percentage points.
Patents US 4 498 289 and US 5 175 995 teach the
use of oxygen as oxidizer instead of air in power
generation boilers.
The advantage of using oxygen as oxidizer is the
reduction, to the point of elimination, of the nitrogen
ballast diluting the carbon dioxide present in the flue
gases and originating from the nitrogen present in the
combustion air, and the substantial reduction of the
size of the necessary equipment.
The application of this principle to a circulating
fluidized-bed boiler is disclosed in patent US
6 505 567. According to this document, a fluidized-bed
combustion chamber or steam generator comprises means
for introducing substantially pure oxygen into the
generator.
The advantage of the circulating fluidized-bed
technique is that it allows the extraction of the heat

on the circulating solids loop and the maintenance of a
low combustion temperature, independently of the oxygen
content of the oxidizer. Hence this technique is
particularly attractive and serves to maximize the
fraction of oxygen in the oxidizer and to minimize the
size of the boiler which depends directly on the flow
rate of flue gases produced.
However, in this prior document, no details are
provided concerning these injection means.
In fact, this oxygen injection into the combustion
chamber is particularly difficult and the creation of
local hot spots is liable to cause caking of the bed
and destruction of the injection nozzles. In fact, the
medium of a circulating fluidized bed is not a
perfectly stirred medium in practice, despite the high
solids concentration which guarantees local turbulence.
Furthermore, this injection must ensure an
appropriate oxygen distribution over the cross section
of the combustion chamber. The contacting and the
reaction of the fuel introduced into the bed with the
oxidizer is essential for the satisfactory progress of
the reactions and, in particular, to minimize the
formation of nitrogen oxides and maximize the
conversion of desulfurization limestone injected into
the combustion chamber.
Patent document US 4 62 8 831 describes a
fluidized-bed device provided with a hearth equipped
with gas mixture feeds called primary feeds, said gas
mixture containing oxygen, said hearth being provided
with a network of two types of primary feed nozzles, a
first type of nozzle injecting the gas mixture at a
first level close to the hearth and a second type of
nozzle injecting the gas mixture at a second level
above the first level.
According to that document, the gas mixture must
be prepared upstream in large volumes. This implies a
large overall size of the boiler.
Added to this are safety problems inherent in the
presence of large volumes of oxygen-concentrated gases.

The invention solves these technical problems and,
for this purpose, it proposes a fluidized-bed device
provided with a hearth equipped with gas mixture feeds
called primary feeds, said gas mixture being enriched
with oxygen, and said hearth being provided with a
network of two types of primary feed nozzle, a first
type of nozzle injecting a first gas mixture at a first
level close to the hearth and a second type of nozzle
injecting a second oxygen-enriched gas mixture at a
second level above the first level, characterized in
that said second type of nozzle consists of a device
for mixing oxygen with a second gas component and
connected by its lower end to an oxygen feed and to a
feed of second gas component, and of a device for
injecting this mixture into the combustion chamber.
The two types of nozzle installed on the hearth of
the device inject the gases at different height levels
to ensure optimal fluidization conditions. In fact, it
is essential for the upper injections of oxygen-
enriched mixture by the second type of nozzle to take
place in a medium already fluidized by the first type
of nozzle injecting the first gas mixture, that is air
or carbon dioxide. Thanks to the invention, the oxygen
is dissipated in a turbulent mixing medium.
This feature serves to inject the oxygen directly
into the combustion chamber without the need for
previous premixing in large volumes. Greater
compactness of the boiler and increased safety are
thereby achieved.
Furthermore, the mixing function is thereby
dissociated from the injection function in the nozzle.
The design of the nozzle is thereby facilitated, as
regards the pressure drops at the gas orifices and the
prevention of the return of solids via these orifices.
According to a preferred embodiment, these two gas
mixtures are different.
According to a preferred embodiment, the device is
provided with at least one oxidizer feed called

secondary feed, and said secondary feed also injects an
oxygen-enriched mixture.
In the case of a circulating fluidized-bed
combustion chamber, such a secondary feed in the
expanded part of the combustion chamber is preferred to
a tertiary feed in the cylindrical part of the
combustion chamber, this expanded part being generally
equipped with a refractory lining. However, this other
type of tertiary oxidizer feed is also feasible.
Several secondary and, optionally, tertiary feeds
may be arranged at different height levels of the
combustion chamber, above the primary hearth, to ensure
appropriate staging of the oxygen over the height of
the combustion chamber.
Advantageously, said secondary feed consists of a
nozzle comprising a double concentric tube for
injecting said oxygen-enriched mixture into the inner
tube and for injecting the first gas mixture into the
outer tube.
Said oxygen-enriched mixture may contain 21 to
100% of oxygen.
Said oxygen-rich mixture may comprise a second gas
component consisting of carbon dioxide and said first
gas mixture may be carbon dioxide.
Said oxygen-rich mixture may comprise a second gas
component consisting of nitrogen and said first gas
mixture may be carbon dioxide.
Said oxygen-rich mixture may be oxygen-enriched
air and said first gas mixture may be air.
Advantageously, said mixing device consists of two
substantially vertical concentric tubes of which the
outer tube is closed at its upper end and provided with
orifices on its side wall.
Advantageously, said injection device consists of
a cap covering said mixing device and provided with
orifices in its upper part.
According to a second variant, said second type of
nozzle consists of two substantially vertical

concentric tubes of which the outer tube is provided
with orifices on its side wall.
Preferably, said concentric tubes are covered with
a cap provided with orifices in its upper part.
Advantageously, said cap is provided with an
internal wall for forming a baffle.
Preferably, said oxygen feed is provided by a
manifold to which the inner concentric tube is
connected.
Said feed of second gas component may be provided
by direct connection of the outer concentric tube to
said windbox filled with second gas component or by a
manifold to which the outer concentric tube is
connected.
The oxygen-enriched mixture may contain water
vapor and/or sulfur dioxide.
The risk of formation of hot spots in the
combustion chamber close to the injection points is
thereby further reduced. This water injection in fact
promotes a local gasification of the fuel by decreasing
the oxygen partial pressure.
The invention further relates to a circulating
fluidized-bed combustion chamber as described above.
According to a first application, a circulating
fluidized-bed boiler comprising such a circulating
fluidized-bed combustion camber and a dense fluidized
bed with a heat exchanger and receiving solids at the
outlet of a clone, said dense fluidized bed is
provided with at least one secondary feed injecting an
oxygen-enriched mixture into its return line to the
circulating fluidized-bed combustion chamber.
The invention further relates to a dense fluidized
bed with a heat exchanger as described above.
The invention finally relates to a second
application consisting of a circulating fluidized-bed
boiler comprising such a circulating fluidized-bed
combustion chamber and an associated dense fluidized
bed with a heat exchanger and receiving solids at the
outlet of a cyclone.

Said derive fluidized bed may be provided with at
least one secondary feed injecting an oxygen-enriched
mixture above the bed.
Said combustion chamber with dense fluidized-bed
heat exchanger may be provided with at least one
secondary feed injecting an oxygen-enriched mixture
into its return line to the circulating fluidized-bed
combustion chamber.
The invention finally relates to a circulating
fluidized-bed boiler comprising a circulating
fluidized-bed combustion chamber as described above and
a dense fluidized bed receiving solids at the outlet of
a cyclone, characterized in that the dense bed is
fluidized by air or a component thereof.
The invention therefore proposes a device for
optimizing the oxygen consumption while preserving the
advantages of airless combustion.
According to a preferred embodiment, the dense bed
is fluidized by nitrogen.
Advantageously, this nitrogen is obtained from a
cryogenic air separation unit which supplies oxygen to
the boiler. This fluidization with nitrogen serves to
avoid post-combustion of the carbon present in the
dense bed, which could lead to carbon dioxide leakage
from the stack and to a lower overall carbon dioxide
capture efficiency.
Preferably, the fluidization gas of the dense bed
is cooled in a heat exchanger before release to the
atmosphere.
The particles of the dense bed may be separated
from the fluidization gas before injection into the
combustion chamber.
The particles may be separated from the
fluidization gas by a siphon.
Advantageously, the siphon is fluidized by a gas
mixture composed of O2/CO2.
The invention is described below in greater detail
with the aid of accompanying figures representing only one preferred
embodiment of the invention.

Figure 1 is a schematic view of a vertical cross
section of a circulating fluidized-bed boiler
combustion chamber according to the invention.
Figure 2 shows a vertical cross section of a
second type of nozzle installed in the hearth of a
combustion chamber of a circulating fluidized-bed
boiler according to a first variant of the invention.
Figure 3 shows a vertical cross section of a
second type of nozzle installed in the hearth of a
combustion chamber of a circulating fluidized-bed
boiler according to a second variant of the invention.
Figure 4 is a schematic view of a vertical cross
section of a circulating fluidized-bed boiler
comprising a circulating fluidized-bed combustion
chamber and a dense fluidized bed with a heat exchanger
receiving solids at the outlet of a cyclone, according
to the invention.
Figure 5 is a schematic view of a vertical cross
section of a circulating fluidized-bed boiler
comprising a circulating fluidized-bed combustion
chamber and a dense fluidized bed receiving solids at
the outlet of a cyclone, according to the invention, in
another variant.
Figure 6 is a detailed view of the dense bed and
its siphon.
Figure 7 is a schematic view of an exemplary
embodiment.
The invention preferably relates to a fluidized-
bed device in which combustion takes place by means of
a mixture of oxygen and carbon dioxide or nitrogen with
fluidization injection of carbon dioxide. It further
relates to a fluidized-bed device in which combustion
is effected by means of oxygen-enriched air with
fluidization injection of air.
A circulating fluidized-bed boiler combustion
chamber shown schematically in Figure 1 is provided
with a hearth 1 consisting of a solid or tubular
cooling wall and equipped with oxidizer feeds called
primary feeds and surmounted by a first expanded part 2

provided with at least one oxidizer feed called
secondary feed and itself surmounted by a cylindrical
part 3. A box called a windbox 4 and filled with
pressurized gas is arranged under the hearth 1.
The hearth 1 is provided with a network of two
types of primary feed nozzle, a first nozzle type B1
injecting air or carbon dioxide at a first level close
to the hearth and a second nozzle type B2 injecting an
oxygen-enriched mixture at a second level above the
first level. The nozzles Bl of the first type are of
known design and directly supplied by the windbox 4
filled with pressurized air or carbon dioxide. The
nozzles B2 of the second type are supplied here, on the
one hand, by a common oxygen inlet manifold 7 and, on
the other, with a second gas component, either directly
by the windbox 4, or by a common manifold which may be
located in the windbox 4. These various nozzles are
described in greater detail below.
The combustion chamber comprises secondary feeds
A1, A2 also injecting an oxygen-enriched mixture.
These secondary feeds each consist of a nozzle
comprising a double concentric tube for injecting said
oxygen-enriched mixture, advantageously even pure
oxygen, into the inner tube 5 and for injecting air or
carbon dioxide into the outer tube 6.
The oxygen-enriched mixture may contain 21 to 100%
of oxygen, the other fraction consisting of carbon
dioxide or nitrogen.
Figure 2 shows a first variant of a second type of
nozzle B2 for injecting oxygen-enriched mixture.
This nozzle B2 consists of a device for mixing
oxygen with the second gas component and connected by
its lower end to an oxygen feed and to a second gas
component feed, and of a device for injecting this
mixture into the combustion chamber.
More precisely, the mixing device consists of two
substantially vertical concentric tubes of which the
outer tube 10 passes through the hearth of the
combustion chamber 1 and is closed at both its ends.

This outer tube 10 is connected at its lower part to an
inlet 10A of second gas component from the windbox 4 or
from a manifold that may be located in said windbox.
In its upper part, this tube 10 is provided with
orifices 10B on its side wall for gas escape.
Advantageously, the orifices 10B are distributed around
the tube 10 and at several levels.
The inner tube 11 of these two concentric tubes
passes through the lower closure wall of the outer tube
10 and extends along most of the height of this outer
tube 10. It is connected at its lower end to an oxygen
manifold 11A, located in the windbox 4 and is open at
its upper end 11B from where the oxygen escapes. At
this escape point, the oxygen is mixed with the second
gas component and an oxygen-enriched gas mixture issues
through the orifices 10B.
The injection device consists of a cap 12
covering the mixing device, fixed in a sealed manner to
the hearth 1, for example by screwing or welding, and
provided with orifices 12B in its upper part through
which the gas mixture is injected into the combustion
chamber. Advantageously, the orifices 12B are
distributed around the cap 12. By dismantling this cap
12, it is easily possible to reach the interior of the
nozzle B2.
Figure 3 shows a second variant of a second type
of nozzle B2 for injecting oxygen-enriched mixture.
This figure also shows a first type of nozzle B1
known per se injecting air or carbon dioxide via the
outlet orifices S1.
The second type of nozzle B'2 consists of two
substantially vertical concentric tubes of which the
outer tube 10' passes through the hearth of the
combustion chamber 1 and is closed at its upper end by
a wall 10'A. This outer tube 10' is fixed by its lower
end in a sealed manner to the hearth 1 and is fed with
second gas component issuing from the windbox 4.
In its upper part, this tube 10' is provided with
orifices 10'C on its side wall for gas escape.

Advantageously, the orifices 10'C are distributed
around the tube 10' and at several levels.
The inner tube 11' of these two concentric tubes
extends along the entire height of this outer tube 10'
and is guided in this outer tube by spacers 10'D at the
hearth 1. This system of spacers can advantageously
perform a function of blocking the return of solids
thanks to an annular type of geometry comprising
orifices distributed on the periphery. It is connected
at its lower end to an oxygen manifold 11'A located in
the windbox 4 and is open at its upper end 11'B where
the oxygen escapes.
Above this unit is placed a cap type of element
12' which, in its upper part, forms orifices 12'A for
the lateral outlet of oxygen toward a lateral space
inside this cap where the oxygen and second gas
component are mixed before escaping via the side
orifices 12'B of the cap where the oxygen-enriched
mixture is injected into the combustion chamber.
Advantageously, the side orifices 12'A, 12'B are
distributed along the periphery of the element bearing
them. Advantageously, a vertical cylindrical wall 12'C
is placed in this internal lateral space of the cap,
thereby providing a baffle and turbulence improving the
mixing of the two gases.
According to an essential feature, the first type
of nozzle B1 injects the first gas mixture at a first
level close to the hearth 1, corresponding to the
height of the orifices S1, and the second type of
nozzle B'2 injects the oxygen-enriched mixture at a
second level above the first level and corresponding to
the height of the orifices 12'B. The upper injections
of oxygen-enriched mixture by the second type of nozzle
B'2 thereby take place in a medium already fluidized by
the nozzles of the first type Bl injecting the first
gas mixture. This is shown schematically in Figure 3,
by a representation of a nonfluidized layer C on the
hearth 1 outside which the injection orifices 12' B of
the second type of nozzle B'2 are arranged. This

injection height can be adjusted and determined by-
choosing the position of these orifices 12'B in the cap
12 and/or by choosing the height of the nozzle B'2
itself.
In the preceding description of nozzles B'2, the
dimensions and gas feed pressures are calculated and
selected so that the oxygen-rich mixture contains 21 to
100% of oxygen, the other fraction consisting of carbon
dioxide or nitrogen, the mixture thereby corresponding
to enriched air.
Since the pressure at the bottom of the combustion
chamber can reach 800 mbar, the dimensions of the gas
outlet orifices are also determined to prevent the
passage or return of gas and/or solids into the
nozzles, the transfer speeds being selected between 10
and 100 m/s.
The oxygen-enriched mixture injected into the
combustion chamber may contain water vapor, to avoid
the formation of hot spots.
Figure 4 shows a first embodiment of a fluidized-
bed boiler according to the invention.
The device F2 is a dense fluidized bed associated
here with a circulating fluidized-bed combustion
chamber F1.
This dense fluidized bed F2 also comprises a
hearth 23 provided with a network of two types of
primary feed nozzle, a first type of nozzle B'1
injecting air or carbon dioxide at a first level close
to the hearth, and a second type of nozzle B'2
injecting an oxygen-enriched mixture at a second level
above the first level. The nozzles B'1 of the first
type are of known design and are directly fed by the
windbox 26 filled with pressurized air or carbon
dioxide. The nozzles B'2 of the second type are fed
here, on the one hand, by a common oxygen inlet
manifold 27 and, on the other, with second gas
component, either directly by the windbox 26, or by a
common manifold which may be located in the windbox 26.
These various nozzles are preferably of the same type

as those already described above and shown in Figures 2
and 3. This dense fluidized bed F2 also comprises at
least one secondary feed A'1 also injecting an oxygen-
enriched mixture.
In its specific application shown in Figure 4,
this dense fluidized-bed heat exchanger F2 is
associated with a circulating fluidized-bed combustion
chamber F1 and serves to control the temperatures of
the circulating fluidized-bed combustion chamber F1.
The solids contained in the flue gases leaving the
combustion chamber F1 are separated in a cyclone 21 and
returned to the bottom of the combustion chamber Fl by
a siphon 20. The base of the siphon 20 is provided
with an extraction of solids at a flow rate controlled
by a valve. The solids extracted are also transferred
to the dense fluidized bed F2 in a heat exchanger
immersed in its bed 24. The cooled solids leave the
bed and are transferred via a line 25 to the
circulating fluidized-bed combustion chamber F1. An
additional injection of oxygen-enriched gas mixture can
also be made in the overhead 22 above the bed 24 of the
dense bed with the heat exchanger F2 and in the
overhead of the line 25, by nozzles A'1 and A'2 similar
to those already described as secondary nozzles for the
circulating fluidized-bed combustion chamber Fl.
Figure 5 shows a second embodiment of a fluidized-
bed boiler according to the invention.
In this application, a dense fluidized bed E with
a heat exchanger is associated with a circulating
fluidized-bed combustion chamber F1 and serves to
control the temperatures of the circulating fluidized-
bed combustion chamber F1. The solids contained in the
flue gases leaving the combustion chamber F1 are
separated in a cyclone 21 and conveyed to the bottom of
the combustion chamber Fl by a fluidized siphon 20
providing air- and carbon dioxide atmosphere-tightness
between the dense bed and the circulating fluidized-bed
combustion chamber F1. The base of the siphon 20 is
equipped with a solids extraction at a flow rate

controlled by a valve. The solids extracted are
transferred to a dense fluidized bed E containing a
heat exchanger immersed in its bed 24. The cooled
solids leave the bed and are transferred via a line 2 5
to the circulating fluidized-bed combustion chamber F1
via a fluidized siphon 28 which provides a seal between
the dense bed and the circulating fluidized-bed
combustion chamber. An additional injection of oxygen-
enriched gas mixture can also be made in the overhead
of the line 25 downstream of the siphon 28, by a nozzle
A" 2 similar to the one already described as secondary
nozzles for the circulating fluidized-bed combustion
chamber Fl in this line 25.
In this variant, the dense fluidized bed E is
equipped with a specific vent 30 for venting the
fluidization gas toward the rear cage 31 of the boiler
to avoid diluting the carbon dioxide produced in the
combustion chamber with the nitrogen present in this
gas. This variant has the advantage of not using
recycled carbon dioxide for fluidizing the dense bed
exchangers. Contrary to the variant in Figure 4, this
carbon dioxide is accordingly preserved for the oxygen-
rich gas mixture feed to the combustion chamber and
serves to decrease the oxygen concentration of the gas
mixture.
Figure 6 shows that the dense fluidized bed E is
equipped with a specific vent 3 0 for removing the
fluidization air or nitrogen, arriving via B1, toward a
specific rear cage 31 of the boiler to avoid diluting
the carbon dioxide produced in the combustion chamber
with this gas. The siphon 2 is fluidized by a gas
mixture comprising O2/CO2, this mixture arrives via
fluidization nozzles B2. The use of the O2/CO2 gas to
fluidize permits a substitution of the air or nitrogen
remaining between the solid particles by said gas and
thereby to ensure that all the fluidization gas of the
dense bed is properly removed without returning to the
combustion chamber F1. The solid particles return

toward the combustion chamber F1 via a solids return
25.
Figure 7 shows an exemplary embodiment according
to the invention, in which the combustion chamber Fl
has two separators 21 each with a siphon 20. Each
siphon 20 is connected to two external beds E each
having a siphon 2. Thus the solids circulation loop is
duplicated, each loop comprising a separator 21 and a
siphon 20. The solids extraction from each siphon 20
can also be duplicated, as in Figure 3. Each siphon 20
thereby comprises two outlets at flow rates each
controlled by a valve and feeds two external beds E.
Each external bed E is fluidized by air or nitrogen and
followed by a siphon 2.

WE CLAIMS
1. A fluidized-bed device (F1, F2) comprising a hearth (1, 23) equipped with
gas mixture feeds called primary feeds, said gas mixture is containing with
oxygen, and said hearth (1, 23) being provided with a network of two
types of primary feed nozzle, a first type of nozzle (Bl, B'1) injecting a first
gas mixture at a first level close to the hearth (1, 23) and a second type
of nozzle (B2, B'2) injecting a second oxygen-enriched gas mixture at a
second level above the first level, wherein said second type of nozzle (B2,
B' 2) consists of a device for mixing oxygen with a second gas component
and connected by its lower end to an oxygen feed (11A, 11A'), a feed of
second gas component, and of a device for injecting the mixture into the
combustion chamber.
2. The device as claimed in claim 1, wherein these two gas mixtures are
different.
3. The device as claimed in one of the preceding claims, comprising at least
one oxidizer feed called secondary feed, wherein said secondary feed (A1,
A2, A'1, A'2, A"2) injects an oxygen-enriched mixture.
4. The device as claimed in claim 3, wherein said secondary feed consists of
a nozzle comprising a double, concentric tube for injecting said oxygen-
enriched mixture into an inner tube and for injecting the first gas mixture
into the outer tube (6).

5. The device as claimed in one of the preceding claims, wherein said
oxygen-enriched mixture contains 21 to 100% of oxygen.
6. The device as claimed in one of the preceding claims, wherein said
oxygen-enriched mixture comprises a second gas component consisting of
carbon dioxide and said first gas mixture is carbon dioxide.
7. The device as claimed in one of claims 1 to 5, wherein said oxygen-
enriched mixture comprises a second gas component consisting of
nitrogen and said first gas mixture is carbon dioxide.
8. The device as claimed in one of claims 1 to 5, wherein said oxygen-
enriched mixture is oxygen-enriched air and said first gas mixture is air.
9. The device as claimed in one of the preceding claims, wherein said mixing
device consists of two substantially vertical concentric tubes of which the
outer tube (10) is closed at its upper end and provided with orifices (10B)
on its side wall.
10.The device as claimed in one of the preceding claims, wherein said
injection device consists of a cap (12) covering said mixing device and
provided with orifices (12B) in its upper part.
11.The device as claimed in one of claims 1 to 8, wherein said second type of
nozzle (B'2) consists of two substantially vertical concentric tubes of which
the outer tube (10') is provided with orifices (10'C) on its side wall.

12.The device as claimed in claim 11, wherein said concentric tubes (10' 11')
are covered with a cap (12') provided with orifices (12'B) in its upper part.
13.The device as claimed in claim 12, wherein said cap (12') is provided with
an internal wall (12'C) for forming a baffle.
14.The device as claimed in one of the preceding claims, wherein said
oxygen feed is provided by a manifold (11A) to which the inner concentric
tube (11) is connected.
15.The device as claimed in one of the preceding claims, wherein said feed of
second gas component is provided by direct connection of the outer
concentric tube (10') to a windbox (4) filled with this gas.
16.The device as claimed in one of claims 1 to 14, wherein said feed of
second gas component is provided by a manifold, to which the outer
concentric tube (10) is connected.
17.The device as claimed in one of the preceding claims, wherein the
oxygen-enriched mixture contains water vapor and/or sulfur dioxide.
18. A circulating fluidized-bed boiler comprising a fluidized-bed combustion
chamber (F1) as claimed in claim 17 and a dense fluidized bed with a heat
exchanger and receiving solids at the outlet of a cyclone, said dense
fluidized bed (E) is provided with at least one secondary feed (A"2)

injecting an oxygen-enriched mixture into its return line to the circulating
fluidized-bed combustion chamber (F1).
19.The boiler as claimed in claim 18, wherein said dense fluidized bed is
provided with at least one secondary feed (A'1) injecting an oxygen-
enriched mixture above the bed.
20.The boiler as claimed in one of claim 19, wherein said dense fluidized bed
is provided with at least one secondary feed (A'2) injecting an oxygen-
enriched mixture into its return line to the circulating fluidized-bed
combustion chamber.
21.The boiler as claimed in claim 18, wherein the dense bed (E) is fluidized
by air or a component thereof.
22.The boiler as claimed in one of the preceding claims, wherein the dense
bed (E) is fluidized by nitrogen from a cryogenic air separation unit.
23.The boiler as claimed in one of claims 20 and 21, wherein the fluidization
gas of the dense bed (E) is cooled In a heat exchanger before release to
the atmosphere.
24.The boiler as claimed in one of claims 20 to 23, wherein the particles of
the dense bed (E) are separated from the fluidization gas before injection
into the combustion chamber (F1).

25.The boiler as claimed in the preceding claim, wherein the particles are
separated from the fluidization gas by a siphon (2).
26.The device as claimed in the preceding claim, wherein the siphon (2) is
fluidized by a gas mixture composed of O2/CO2.

The invention relates to a fluidized-bed device (F1, F2) provided with a hearth
(1, 23) equipped with gas mixture feeds called primary feeds, said gas mixture
being enriched with oxygen, and said hearth (1, 23) being provided with a
network of two types of primary feed nozzle, a first type of nozzle (B1, B'1)
injecting a first gas mixture at a first level close to the hearth (1, 23) and a
second type of nozzle (B2, B'2) injecting a second oxygen-enriched gas mixture
at a second level above the first level. According to the invention, said second
type of nozzle (B2, B'2) consists of a device for mixing oxygen with a second gas
component and connected by its lower end to an oxygen feed (11A, 11A') and to
a feed of second gas component, and of a device for injecting this mixture into
the combustion chamber.

A FLUIDIZED-BED DEVICE

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