METHOD AND DEVICE IN THE COOLING OF THE CIRCULATING MATERIAL IN A FLUIDIZED-BED BOILER

Abstract: The invention concerns a method and a device in the cooling of the circulating material in a fluidized-bed boiler. In the method the fuel (A) is introduced into the circulating-powder combustion chamber (10) of the fluidized-bed boiler into the lower part of the circulating-powder combustion chamber (10) and an inert circulating material, which contains a proportion of unburned powdered fuel (A), is circulated from the top part of the circulating-powder combustion chamber (10) to the lower part of the circulating-powder combustion chamber (10). The flue gases are passed in the method from the powder separator (13) along the duct (15) into the exhaust-gas boiler (16), through whose heat exchanger (16a) thermal energy of the flue gases is transferred further to other useful use. In the method, part of the cooled flue gases are recirculated along the duct (20) into the circulating material and, by means of the cooled flue gases, the capacity of cooling of the fluidized-bed furnace is regulated by affecting the temperature of the circulating material.

Description: Method and device in the cooling of the circulating material in a fluidized-bed boiler The invention concerns a method and a device in the cooling of the circulating material in a fluidized-bed boiler. In fluidized-bed boilers based on the circulating-powder technique, the mass ratio of circulating powder to flue gases is typically 20...50.1. An abundance of powder equalizes the temperature profile of the furnace in a circulating-powder boiler quite efficiently even though the combustion takes place mainly in the lower part of the furnace and the cooling in the upper parts. The difference between the maximal and m iimal temperatures in the circulation circuit is, at the maximum, 100 K. The capacity of cooling of the furnace of a circulating-powder boiler is typically 30...50% of the total capacity of the boiler. As a rule, the cooling of the furnace has been accomplished by means of membrane heat-exchanger faces placed on the walls of the furnace and protected by a thin protective masonwork. The shield is needed because of erosion caused by the powder and because of corrosion caused by the reducing conditions. Tube packages can be placed in the upper part of the furnace, where they do not have to be protected, because in the upper part the conditions are oxidizing and the risk of corrosion is no longer as high as in the combustion zone. Lowering of the capacity of cooling of the furnace of a circulating-powder boiler is problematic in fluidized-bed combustion. Lowering of the temperature in the furnace can hardly be used for regulation, because then the conditions of combustion would become unfavourable. Prior-art solutions for regulation of the capacity of cooling of the furnace include the following modes of cooling: The regulation of the capacity of cooling of the furnace takes place so that the quantity of circulating powder is affected by means of the distribution of air for the furnace. The quantity of circulating powder affects the heat-transfer coeffi¬ cient. If the furnace is not cooled, the temperature will rise up to 1500°C and the ashes will melt. In such a case, the fluidization of the circulating material in the reactor is disturbed. If the fluidization is disturbed, the combustion in the reactor is also disturbed. For regulation of the capacity of cooling of the furnace, the method has also been used in which the hot circulating material that was separated in the powder separator after the furnace is recirculated directly into the combustion chamber. The circulating material has been cooled by means of separate heat-exchanger faces before returning into the combustion chamber. The heat-exchanger faces are placed in a separate fluidized bed, into which all or part of the hot circulat- ing material is passed and from which the cooled circulating material is returned into the combustion chamber. The fluidization air of the separate fluidized bed is passed to the circulating-powder boiler as secondary air. In the prior-art solutions, the dimensioning of the furnace cooling and the operation of the boiler with the use of fuels of different qualities have proved quite problematic even for the most experienced boiler manufacturers. Along with the power level, the conditions of combustion in circulating-powder boilers have changed so extensively that optimal conditions for the removal of sulphur and nitrogen cannot be maintained within the entire capacity range. The cooling of the circulating material by means of heat-exchanger faces is problematic because of particle erosion, corrosion, and increased costs. Moreover, the scaling up of the power ranges of fluidized-bed boilers has proved difficult, because, owing to the internal circulation of material inside the furnace, the density of the circulating material on the furnace walls cannot be predicted precisely. This is why dimensioning of the heat-exchanger faces has not been successful. The use of combustion air for regulation of the amount of circulating material and for regulation of the heat transfer has deteriorated the conditions of com¬ bustion in the lower part of the reactor and lowered the efficiency of the sulphur removal and of the combustion. In the present application, attempts have been made to find a solution for the problems mentioned above. The basic idea of the invention is separation of the combustion in the furnace of the circulating-powder boiler and of the heat transfer from one another so that the cooling of the furnace is carried out exclusively or partially by means of cold circulating gases taken from the final part of the boiler. In the solution in accordance with the invention, the circulating gases are not mixed into the combustion air, but said gases are used for the cooling of the inert circulating material in the circulating-powder combustion process. Owing to the mixing of the circulating gases, the temperature of the flue gases is lowered little, because, at the mixing point, there is an abundance of circulat¬ ing powder, whose thermal capacity is multiple as compared with the flue gases. The circulating gases may be passed from several points into the space between the fluidized bed in the furnace and the powder separator. By changing the point of introduction of the circulating gases into the boiler, it is possible to regulate the amount of circulating material if desired. The taking of the flue gases to recirculation takes place in a steam boiler favourably from between the economizer and the heat exchanger, but they may also be taken after the heat exchanger or after the filtering of the flue gases. It is essential that the circulating gases have been cooled by means of convection heat-exchanger faces so that the temperature of the flue gases is low enough when part of the flue gases are passed to recirculation. The fluidized-bed reactor may be any prior-art circulating-material reactor with a single-draft or multi-draft reactor part, the essential feature being that the circulating material must have a sufficiently high consistency. The invention can be applied both to new fluidized-bed boilers and to existing fluidized-bed boilers as a novel mode of regulation. When a boiler has been dimensioned for peat fuel and it is also desirable to burn coal in the plant with full capacity, this can be accomplished by means of partial use of circulating gas in accordance with the invention. In one embodiment of the invention, the fluidization part, i.e. the reactor, and the cyclone used for separation of the powder have been combined as one device. The top part of the reactor has been constructed as a cyclone of circular section, into which the powder-containing gases enter from below. The powder- containing gas is brought into a revolving movement by means of secondary gas blown tangentially into the top part of the reactor. Thus, in the top part, a cyclone separator is formed, in which the powder is separated onto the walls of the reactor. The thick powder suspension formed on the faces of the walls flows along the walls of the reactor, in a non-fluidized state, into the lower part of the reactor. The circulating powder that has been returned into the lower part of the reactor is mixed with the rest of the bed material in the furnace. The clean gas is removed from the top part of the reactor through the axial central pipe. In this embodiment of the invention, the secondary gas is preferably the purified exhaust gas, which has been removed from the reactor, which has been cooled by means of the convection heat-exchanger faces of the boiler, and which is passed back into the reactor. By regulating the quantity of the secondary gas, it is possible to regulate the capacity of cooling of the whole furnace continuously. The method in accordance with the invention for cooling of the circulating material in a fluidized-bed boiler is mainly characterized in that in the method part of the cooled flue gases are recirculated into the circulating material and, by means of the cooled flue gases, the capacity of cooling of the fluidized-bed furnace is regulated by affecting the temperature of the circulating material, and that in the method the recirculated gases are passed to the powder separator or to the front side of same, seen in the flow direction of the flue gases, and that the recirculated gases are passed to a point in the cycle of the circulating material from which they are not mixed with the combustion air and, thus, do not participate in the combustion process. The device in accordance with the invention for cooling of the circulating material in a fluidized-bed boiler is mainly characterized in that there is a feedback duct through which the cold flue gases are recirculated into the inert circulating material in the circulating-powder chamber, and that in the solution of equipment the feedback duct is passed to the powder separator or to the front side of same, seen in the direction of circulation of the flue gases, and to a point from which the circulating gases are not mixed with the combustion air, whereby, thus, the circulating gases do not participate in the combustion process. The passing of the circulating gases into the circulating material provides a number of advantages: - the whole of the combustion zone is oxidizing and at the desired temperature, for which reason the combustion, the removal of sulphur, and the removal of nitrogen are intensified because of the optimal conditions; - the cooling of the reactor can be accomplished efficiently, accurately and advantageously; - the costs of the use of circulating gas are favourable because of the low loss of pressure in the powder separator and on the convection faces as compared with the overall pressure losses in the reactor; - the mode of regulation is easy and accurate. Optimal conditions of combustion can be maintained even under extreme conditions, because the regulation of the capacity of cooling of the reactor is based on the amount of circulating gas, and combustion air can be used freely in accordance with the requirements of the combustion; - the range of regulation is wide; - the dimensioning of the boiler is easy, because the reactor produces a gas of invariable temperature, and the capacity obtained from the convection heat- exchanger faces depends on the gas quantity alone; - the amount of circulating material can be increased without limitation, in which case either the reactor becomes smaller than the prior-art solutions or the maximal output obtained from reactor units of the present size is increased; - the masonry work in the reactor can be made of more durable materials, because the heat transfer does not have to be taken into account; - all the heat-exchanger faces can be placed in the secondary draft as convection faces. If the separation of powder is accomplished in two stages, it is possible to use higher gas velocities and advantageous ribbed tubes as heat transfer faces, i.e. the heat-exchanger faces would be of the same type as in the exhaust-gas boilers of gas turbines. - it is possible to manufacture a boiler out of prefabricated modules; - large boilers may comprise one common convection-duct part and one steam circuit and a number of reactors; - scaling from one size category to the other is easier, because the combustion unit can be dimensioned without requirements of heat transfer; - unmanned operation of small heating boilers becomes possible because of the efficient principle of regulation; - when an embodiment of the invention is employed in which the powder separator has been formed as a cyclone in connection with the reactor, for example, the following advantages are obtained: - the sets of equipment of the circulating-powder fluidized-bed technique become simpler, and the cost of manufacture is lowered substantially; - it is easy to regulate the amount of circulating powder in the reactor by means of the amount of secondary gas or by means of the nozzle speed, in which case it is also possible to regulate the magnitude of the charring residue in the fluidized-bed furnace accurately; - when cold secondary gas is passed into the cyclone, it is possible to cool the fluidized-bed furnace efficiently. By varying the amount of flue gas, it is possible to regulate the capacity of cooling of the furnace continuously. The invention will be described in the following with reference to the embodi¬ ments of the invention illustrated in the figures in the accompanying drawings, the invention being, however, not supposed to be confined to said embbdiments alone. Figure 1 is a schematic illustration of a first preferred embodiment of the method and the equipment in accordance with the invention. Figure 2 is a schematic illustration of a second preferred embodiment of the method and the equipment in accordance with the invention. Figure 3 is a schematic illustration of a third preferred embodiment of the method and the equipment in accordance with the invention. Figure 4 illustrates a further embodiment of the device in accordance with the invention, wherein the powder separator consists of a number of powder separ¬ ator units fitted one above the other and placed in the top part of the circulat¬ ing-powder combustion chamber. Figure 5 is a separate illustration on an enlarged scale of one powder separator unit of the powder separator shown in Fig. 4. Figure 6 shows the construction between the separator pipes in the powder separator unit. In the way shown in Fig. 1, the fuel A for the circulating-powder combustion chamber 10 of the fluidized-bed boiler is passed into the lower part of the circulating-powder combustion chamber 10. The air needed for the combustion is also passed into the lower part of the circulating-powder combustion chamber 10 by means of the blower device P_, through the duct 11. The fluidization part of the circulating-powder combustion chamber, i.e. the reactor, is constructed as one device with the powder separator 13. The top part of the reactor is constructed as a cyclone of circular section, into which the powder-containing gases arrive from below. The powder-containing gas is brought into a rotatory movement by means of secondary gas blown tangentially into the top part of the reactor. Thus, in the top part, a cyclone separator is formed, in which the powder is separated onto the walls of the reactor. The thick powder suspension formed on the wall faces flows along the reactor walls in a non-fluidized state into the lower part of the reactor. The circulating powder that has returned into the lower part of the reactor is mixed with the rest of the bed material in the combustion chamber. The pure gas is removed from the top part of the reactor through the axial central pipe. In this embodiment of the invention, the secondary gas that is used is the purified exhaust gas removed out of the reactor, whose pressure is raised by means of a blower to the pressure level required by the nozzles. In this embodi¬ ment of the invention, the secondary gas consists of exhaust gas cooled on convection heat-exchanger faces of the boiler, which gas, thus, cools the reactor. By means of the invention, it has been possible to simplify the equipments of the circulating-powder fluidized-bed technique as compared with the prior-art equip¬ ments. The cost of manufacture of the equipments is favourable as compared with the prior-art equipments. The amount of circulating powder in the reactor can be regulated easily by means of the amount of secondary gas or by means of the nozzle speed. This is an important property, for example, when it is desirable to regulate the magnitude of the charring residue in a fluidized-bed furnace. By means of cold secondary gas, it is possible to cool a fluidized-bed furnace efficiently. When flue gas that has been cooled on convection heat-exchanger faces is used as secondary gas, the capacity of cooling of the furnace can be regulated continuously by varying the amount of gas concerned. From the top part of the circulating-powder combustion chamber 10, from the powder separator 13, the flue gases are passed along the duct 15 into an exhaust- gas boiler 16, in whose heat exchanger 16a a heat transfer liquid, preferably water, is circulated. Thus, by means of the heat exchanger 16a, the thermal energy of the exhaust gases is transferred into the liquid circuit of the heat exchanger 16a and further, through the liquid circulation, out of connection with the boiler to useful use. From the outlet side of the exhaust-gas boiler 16, a duct 17a passes to a filter 18. From the filter 18, a duct 17b passes to a blower Pp. From the blower Pp, from its outlet side, a duct 17c passes to the chimney 19. From the duct 17c, according to the invention, a duct 20 is passed as feedback to the powder separator 13 placed in the top part of the circulating-powder combustion chamber 10. Thus, in the solution in accordance with the invention, the capacity of cooling of the furnace of the circulating-powder combustion chamber is regulated by cooling the circulating material in the circulating-powder combustion chamber by means of cold circulating gases taken from the final part of the boiler and cooled by the heat-exchanger faces of the boiler. Thus, in the solution of the present invention, in contrast with the prior art, the circulating gases are not mixed with the combustion air, but they are used expressly for cooling the inert circulating material in the circulating-powder combustion chamber 10. The circulating material mainly consists of inert material, such as sand, fuel ash, limestone, and compounds produced in the removal of sulphur. Further, the circulating material contains unburned fuel, so-called residual coke, as a quantity of 1...4%. Thus, in the solution of the invention, expressly the above inert circulating material M is cooled, which circulating material M runs between the furnace and the powder separator 13. The cooling capacity is regulated by regulating the amount of recirculated flue gas. The amount of recirculated flue gas is regulated by regulating the operation of the blower device P g . The flow of flue gas can also be regulated, besides by regulating the blower device Pg, by adjusting a regulating damper 21 placed in the flue-gas recirculation duct. In the solution in accordance with the invention, the circulating gases are riot mixed with the combustion air, but they are used for cooling the inert circulating material in the circulating-powder combustion process. Thus, in the solution of the invention, the circulating gases are passed in the process into the space placed after the combustion space B of the circulating-powder combustion chamber 10 (seen in the direction of flow S_* of the flue gases), from where the circulating gases are not combined with the combustion air and, thus, do not affect the combustion process. The circulating gases are preferably brought into the top part of the circulating-powder combustion chamber 10 or directly into the powder separator placed after said top part or into the duct placed between these. It is essential that the circulating gases Just cool the circulating material and that, after the cooling, they are made to flow apart out of contact with the circulating material, further into the exhaust-gas boiler and to the heat exchangers. In the second embodiment of the invention shown in Fig. 2, the fuel A for the circulating-powder combustion chamber 10 of the fluidized-bed boiler is passed into the lower part of the circulating-powder combustion chamber 10. The air needed for the combustion is also passed into the lower part of the circulating- powder combustion chamber 10 by means of the blower device P.. through the duct 11. From the top part of the circulating-powder combustion chamber 10, a duct 12 passes to a separate powder separator 13, preferably likewise a cyclone separ¬ ator. By means of the powder separator 13, the fraction with higher powder contents is separated into the duct 14, along which it is passed back to combus- tion into the lower part of the circulating-powder combustion chamber 10. The flue gas and the fraction with lower contents of powder particles are passed from the powder separator 13 into the duct 15 and further to ' the exhaust-gas boiler 16, in whose heat exchanger 16a a heat-transfer liquid, preferably water, is circulated. Thus, through the heat exchanger, the thermal energy of the exhaust gases is transferred to the liquid circuit of the heat exchanger 16a and further, through the liquid circulation, out of connection with the boiler to useful use. From the outlet side of the exhaust-gas boiler 16, a duct 17a passes to the filter 18. From the filter 18, a duct 17b passes to the blower P . From the blower P p , from its outlet side, a duct 17c passes to the chimney 19. From the duct 17c, according to the invention, a duct 20 is passed as feedback to the circulating material and, in this embodiment, into the duct 12 between the circulating-powder combustion chamber 10 and the powder separator 13. Thus, also in this embodiment of the invention, the capacity of cooling of the furnace of the circulating-powder combustion chamber is regulated by cooling the inert circulating material of the circulating-powder combustion chamber by means of cold circulating gases taken from the final part of the boiler and cooled by the heat-exchanger faces of the boiler. Thus, in the solution in accordance with the invention, in contrast with the prior art, the circulating gases are not mixed with the combustion air, but they are used expressly for cooling the circulating material between the top part of the furnace and the powder separ¬ ator 13. The cooling capacity is regulated by regulating the amount of recirculated flue gas. The amount of recirculated flue gas is regulated by regulat¬ ing the operation of the blower device Pg. Fig. 3 shows an embodiment of the invention in which the flue-gas recircuϊation duct 20 includes a blower P 4 operating at an invariable speed of rotation and a regulating damper 21 or equivalent that regulates the amount of recirculation of flue gas. The duct 20 further includes a powder separator 22, which is placed ahead of the blower device P 4 , seen in the direction of circulation of the flue gas, in which case the faces of the blower device are protected from wear by passing a less contaminated flue gas to the blower P 4 . The circulating gas is taken from the branch point 23 placed ahead of the filter 18 in the flow direc¬ tion. In this way, the fine filter 18 does not have to be dimensioned unduly large. Fig. 4 shows an embodiment of the invention in which the recirculation duct 20 is connected to the duct between the exhaust-gas boiler 16 and the final powder separator 18. The other end of the recirculation duct is connected directly to the powder separator 13. The powder separator 13 comprises a number of powder separator units 13a,13b,13c..., which are fitted in the top part of the circulating- powder combustion chamber 10 so that they are placed in the top part of the circulating-powder combustion chamber 10 vertically one above the other and parallel to one side wall 10' of the circulating-powder chamber 10. Fig. 5 shows one powder separator unit 13a on an enlarged scale. The returned circulating gas from the duct 20 is passed along the ducts D.. and Dp into the pipe 23. The pipe 23 contains a second pipe 24 placed centrally in its interior. The circulating gas flows in the space E between the pipes 23 and 24. The circulating gas flows through the guide wings 25 placed on the face of the pipe 24, which wings produce a spiral-shaped run (S p ) for the air. The flow of circulating gas blown out of the space between the pipes 23 and 24 further produces a vortex of the circulating material M. The clean flue-gas flow S_ι passes centrally through the central pipe 23 further into the exhaust-gas boiler 16 and to the heat exchanger 16a. Having been brought into a spiral-shaped rotatory movement by means of the flow S_,, by the effect of centrifugal force, the particles in the circulating material M by-pass the orifice F of the duct 23 to the sides and, by the effect of the force of gravity, fall along the walls 10' of the duct down into the furnace. Fig. 6 shows the pipe construction shown in Fig. 5. The outermost pipe is the pipe 23, and in its interior the pipe 24 is placed centrally. For the flow S_., a flow passage remains between the pipes 23 and 24, and the flow can be made to proceed as spiral-shaped in the way indicated by the arrows Sp by means of the guide wings 25, which have been mounted diagonally in relation to the joint axis of the pipes 23 and 24.

Claims: Claims 1. Method in the cooling of the circulating material in a fluidized-bed boiler, in which method the fuel (A) is introduced into the circulating-powder combustion chamber (10) of the fluidized-bed boiler into the lower part of the circulating- powder combustion chamber (10) and in which method an inert circulating material, which contains a proportion of unburned powdered fuel (A), is circu¬ lated from the top part of the circulating-powder combustion chamber (10) into the lower part of the circulating-powder combustion chamber (10), the flue gases being passed in the method from the powder separator (13) along the duct (15) into the exhaust-gas boiler (16), through whose heat exchanger (16a) thermal energy of the flue gases is transferred further to other useful use, and that in the method the flue gases are passed from the boiler (16) to the chimney (19), and that in the method part of the cooled flue gases are recirculated along the duct (20) into the reactor, characterized in that in the method part of the cooled flue gases are recirculated into the circulating material and, by means of the cooled flue gases, the capacity of cooling of the fluidized-bed furnace is regulated by affecting the temperature of the circulating material, and that in the method the recirculated gases are passed to the powder separator or to the front side of same, seen in the flow direction of the flue gases, and that the recirculated gases are passed to a point in the cycle of the circulating material from which they are not mixed with the combustion air and, thus, do not participate in the combus¬ tion process. 2. Method as claimed in claim 1, characterized in that in the method the flue gases of the recirculation are passed directly into the circulating-powder cham¬ ber. 3. Method as claimed in claim 2, characterized in that the flue gases are passed into the powder separator (13) of the circulating-powder combustion chamber, which separator has been formed as a cyclone so that the flue gases are passed into the circulating-powder combustion chamber (10) tangentially from the side, whereby the powder-containing gas is brought into a rotatory movement by means of the flue gas blown tangentially into the top part of the reactor, whereby a cyclone separator is formed in the top part of the circulating-powder combus¬ tion chamber (10), in which cyclone separator the powder is separated onto the walls of the reactor, and the thick powder suspension formed on the wall faces flows along the walls of the reactor in a non-fluidized state into the lower part of the reactor and is there mixed with the bed material of the furnace, and in which method the clean gas is removed from the top part of the reactor through the axial central pipe. 4. Method as claimed in claim 1, characterized in that in the method a solution of equipment is used which comprises a duct (12) for the circulating material, passing from the top part of the circulating-powder combustion chamber (10) to the powder separator (13), and that in the solution of equipment in accordance with the method, there is a duct (14) passing from the powder separator (13) to the lower part of the circulating-powder combustion chamber (10), whereby, in the method, the flue gases cooled for recirculation are passed into the duct portion (12) between the powder separator (13) and the circulating-powder combustion chamber (10), and in which method the fraction of lower powder contents, preferably the flue gases, are passed from the powder separator (13) into the duct (15) and along the duct (15) into the exhaust-gas boiler (16), through whose heat exchanger (16a) the thermal energy of the flue gases is transferred further to other useful use, whereby the temperature of the flue gases is lowered. 5. Method as claimed in any of the preceding claims, characterized in that the flue gases that are passed as feedback into the circulating material are taken from the outlet side of the exhaust-gas boiler before the chimney (19) and that the recirculation of the flue gases back into the circulating material is achieved by means of a blower device (Pg), whereby, by regulating the operation by means of the blower, the amount of recirculated flue gases is regulated, and thereby the capacity of cooling of the circulating material is regulated. 6. Method as claimed in any of the preceding claims, characterized in that in the method the amount of circulating gases is regulated by means of a regulating damper (21) or equivalent, in which case the blower device (P 4 ) is a blower operating at an invariable speed of rotation. 7. Method as claimed in any of the preceding claims, characterized in that in the method a powder separator is employed before the blower (Pg;PΛ whereby the wing faces of the blower (P 3 ;P 4 ) are protected from wear by passing a less contaminated flue gas to the blower device. 8. Device in the cooling of the circulating material in a fluidized-bed boiler, which boiler comprises a circulating-powder combustion chamber (10), into which the air needed for the combustion is passed and which fluidized-bed boiler comprises a circulation for an inert circulating material, and that the arrange- ment of equipment comprises a powder separator (13) and a duct (15) passed from the powder separator (13) to the exhaust-gas boiler (16), which comprises a heat exchanger (16a), by whose means thermal energy contained in the exhaust gas is transferred further to other useful use and the temperature of the flue gases is lowered, the solution of equipment comprising a duct (17a) passing out from the exhaust-gas boiler, through which duct the flue gases are passed into the chimney (19), and that the equipment comprises a feedback duct (20) for the flue gas for recirculation of cold flue gases back to the reactor, characterized in that there is a feedback duct (20) through which the cold flue gases are recirculated into the inert circulating material (M) in the circulating-powder chamber (10), and that in the solution of equipment the feedback duct is passed to the powder separator or to the front side of same, seen in the direction of circulation of the flue gases, and to a point from which the circulating gases are not mixed with the combustion air, whereby, thus, the circulating gases do not participate in the combustion process. 9. Device as claimed in claim 8, characterized in that the powder separator (13) is a cyclone separator, which has been formed in the top part of the circulating- powder combustion chamber (10) and that the flue gases that are passed along the recirculation duct (20) into the circulating-powder combustion chamber (10) are passed tangentially into the chamber space of the circulating-powder combus¬ tion chamber (10) so that they produce a rotatory movement in the powder- containing gas, whereby, in the cyclone separator, the powder is separated onto the walls of the reactor, the thick powder suspension formed on the wall faces flowing along the walls of the reactor in a non-fluidized state into the lower part of the reactor and being therein mixed with the rest of the bed material in the furnace, and that the clean gas is removed from the top part of the reactor through the axial central pipe. 10. Device as claimed in claim 8, characterized in that the equipment comprises a duct (12) for the inert circulating material (M) from the top part of the circulating-powder combustion chamber (10) to the powder separator (13), and that there is a duct (14) from the powder separator back into the combustion chamber (10), and that the equipment comprises a duct (15) for the cleaner fraction that contains flue gases, passing from the powder separator (13) to the exhaust-gas boiler (16), which comprises a heat exchanger (16a) and therein a liquid circuit, by whose means thermal energy contained in the flue gases is transferred further to other useful use, whereby the temperature of the flue gases is lowered. 11. Device as claimed in any of the preceding claims 8 to 10, characterized in that the inlet end, seen in the flow direction of the flue gases, of the duct (20) for recirculation of the flue gases into the circulating material is connected to the duct (17c) between the exhaust-gas boiler (16) and the chimney (19), whereby it is possible to pass the flue gases to the cooling of the circulating material while as cold as possible. 12. Device as claimed in any of the preceding claims 8 to 11, characterized in that the duct (20) comprises a blower device (Pg;P Λ the amount of recirculated flue gases and, thus, the cooling capacity of said gases being regulated by regulating the operation of said blower device. 13. Device as claimed in any of the preceding claims 10 to 12, characterized in that the duct (20) is connected to the duct (12) between the circulating-powder chamber (10) and the powder separator (13), the flue gases being mixed with the circulating material before the powder separator (13), seen in the direction of circulation of the circulating material. 14. Device as claimed in any of the preceding claims 8 to 13, characterized in that the recirculation duct (20) of flue gases comprises a blower (P 4 ) operating at an invariable speed of rotation and a regulating damper (21) or equivalent, by whose means the amount of recirculated flue gases is regulated. 15. Device as claimed in any of the preceding claims 7 to 14, characterized in that, in the direction of circulation of the flue gases, before the blower device (P Λ the duct (20) includes a powder separator (22), whereby the flue gases are passed as less contaminated to the blower device (P 4 ) which produces the circulation of the flue gases.

Inventors: RAIKO MARKKU, RAIKO, MARKKU
Applicants: IMATRAN VOIMA OY
Application year: 1992
Main classification: F22B31
IPC codes: F22B31, F23C9, F23C10, F23J15