The present invention relates to a cyclone separator comprising a separation chamber having an upper end and a roof and a vertical upper portion and a downwardly tapering conical lower portion, the lower end of which is provided with a discharge opening and the wall of which chamber comprises tubes having inlets connected to a distribution header for cooling medium and outlets connected to a collection header for cooling medium. The invention also relates to a circulating fluidized bed boiler. A cyclone separator is typically used in conjunction with a circulating fluidized bed boiler for separating solid particles from gases exiting the furnace.

Cyclone separators typically have a vertical, mainly cylindrical swirl chamber that acts as separation chamber and has a lower part that is formed as a downwardly conically tapering hopper. The upper part of the swirl chamber is provided with a gas inlet duct for the gas stream to be treated, which inlet duct is arranged tan- gentially with respect to the wall of the swirl chamber. In a cyclone separator discharge of the purified gas usually takes place via a gas discharge conduit adapted centrally in the upper end of the swirl chamber. In cyclone separators the solids are separated from the gases due to centrifugal force onto the wall of the separation chamber and flow along the wall down into the conical part of the cyclone separator, from where the solids are discharged. Separation in a conventional cyclone separator is based on the mutual effect of centrifugal force and changes in the flow velocity. Gas suspension flow entering the swirl chamber of a conventional cyclone separator is there subjected to a swirling motion and travels spirally downwards along the wall of the swirl chamber. The velocity of the swirling motion is accelerated at the lower part of the swirl chamber as the diameter of the cone decreases. The gases change their direction in the lower part of the cyclone separator and flow along the center of the swirl chamber back into the upper part of the separator, wherein a gas discharge conduit is adapted. The solids concentrated on the walls of the lower part of the swirl chamber cannot follow with the gases, but keep flowing downwards into a particle discharge conduit.

Cyclone separators are to be thermal insulated e.g. with brick lining, refractory lining or ceramic heat insulators for keeping the outer surface of the separator relatively cold. For providing the required heat insulation, a thick layer of insulation material is needed, which increases the price, the weight and space requirement of the separator. Further, for resisting hot conditions the interior of cyclone sepa- rators has to be shielded with abrasion resistant refractory layers. Thus, the lining comprises at least two materials of different types, whereby the durability of the construction thus formed suffers and the production thereof has multiple steps.

In order to avoid the above mentioned disadvantages caused by thermal expan- sion and thick lining structure, e.g. European patent 0298671 suggested constructing cyclone separator with water tubes, but the conical part does not have a tube construction.

In US-patents 5,226,936 and 4,944,250 also the wall of the conical part comprises tubes. In known solutions, as the diameter of the cyclone separator changes in the upper and lower parts of the cyclone separator, either the mutual distances between adjacent water tubes have to decreased or the number of adjacent tubes has to be decreased in the constructions e.g. by combining two tubes or by coupling a part of the tubes to the collection headers as the lower part tapers, whereby they will not extend to the discharge opening. None of these alternatives is satisfactory or easy to accomplish.

A purpose of the present invention is to provide a cyclone separator, the tube walls of which that are cooled with a cooling medium such as water, steam or their mixture have a simpler construction and are more economical to make than prior art separator apparatuses. The cyclone separator according to the invention is characterized in what is presented in the characterizing parts of the independent claims. Other embodiments of the invention are characterized in what is presented in the other claims.

A cyclone separator, which is typically used for separating particles from flue gas from a circulating fluidized bed boiler, comprises a separation chamber having a vertical upper portion and a lower portion that tapers downwardly, at the lower end of which a discharge opening is provided and the wall of which chamber comprises tubes having inlets connected to a distribution header for cooling medium and outlets connected to a collection header for cooling medium. The cyclone separator is characterized in that the wall of the separation chamber is formed of at least one tube panel having tubes that comprise a meandering cooling medium channel.

The invention also relates to a circulating fluidized bed boiler for combustion or gasification of fuels, which boiler comprises a cyclone separator for separating solid particles from gases produced in the boiler by burning or gasifying fuel. The cyclone separator comprises a separation chamber having a vertical upper portion and a downwardly tapering lower portion, the lower end of which is provided with a discharge opening, and the wall of which separation chamber comprises a number of tubes having inlets connected to a distribution header for cooling medium and outlets connected to a collection header for cooling medium. What is essential is that the wall of the separation chamber is formed of at least one tube panel having tubes that comprise a meandering cooling medium channel.

The central idea of the novel wall tube construction of the cyclone separator is that the wall has tubes, each of which tubes comprising a meandering cooling medium channel. Thereby the cooling medium flows first to a first direction - upwards or downwards - and after turning to a second direction, which is opposite to the first direction. The cooling medium is typically water, steam or their mixture. The inlet end and outlet end for the cooling medium of the tubes, and thus the distribution header and the collection header, are typically located near each other. It is typical that the cooling medium travels up or down adequately far from the distribution header and thereafter turns back towards the header. The cooling medium can flow several times to different directions in the wall tube.

A wall tube can be formed of one continuous tube that is bent to a suitable mean- dering form. It can also be formed of several, e.g. at least two, individual tube parts connected to each other. Typically the tube parts are straight, and a connecting part is provided between them, by means of which a turn of approximately 180 degrees is caused. Typically the connecting part is a tube elbow. The tube can comprise, in addition to a straight tube portion, also a bent tube portion. The tube can have two or more tube portions, through which the cooling medium flows in a meandering way. Thermal optimizing, for instance, determines the most suitable tube length for each cooling medium.

The distribution header and the collection header for cooling medium, which headers typically extend around the separation chamber, can in the elevation di- rection be situated at a desired level. They can be situated one below the other near to each other. They can be situated in the region of the upper portion of the separation chamber, but in view of space consumption a more advantageous location may be the tapering lower portion. In known cyclone separators each tube of the walls is straight and connected at its upper and lower ends to the cooling medium headers, which can be located at least above and below the separation chamber. In the present novel solution the location of the cooling medium chambers can be chosen more freely. Further, in the new construction the number of coupling points between the wall tubes and the cooling medium headers is small- er, because the tubes are longer and the required wall surface area is achieved with a smaller number of individual tubes.

The wall of the cyclone separator is made of a tube panel or tube panels comprising a number of meandering tubes in accordance with the invention. A tube panel is typically made by joining adjacent tube portions with a fin, which is a method known per se for forming a gas tight structure. A connecting part, such as a tube elbow, between the tube portions is typically at the same level as the tube panel. The connecting part or a bent portion of the tube can, however, be also bent outwards from the tube panel wall, especially in the regions of the tapering lower portion and of the roof. By means of the connecting part or the bent portion of the tube it is also possible to decrease the non-cooled area in the turning area by bending it in a suitable way on the surface of the structure.

The cross section of the cyclone separator can be a circle, whereby its upper part is cylindrical and the downwardly tapering lower part is conical. This structure can be made of a tube panel by bending it to the desired shape. The cross section of the cyclone separator can also be a polygon, most advantageously an octagon, a decagon or a dodecagon. The wall parts of the polygon are formed of tube panels, which are bent and joined together for forming a polygonal separation chamber.

The lower part of the panel tubes of each wall part of the separation chamber is bent inwards for forming the tapering lower portion. The wall of the upper portion of the separation chamber is substantially vertical. For forming its roof the upper part of the tube panel is bent inwards into a horizontal or inclined plane and possibly further upwards to form a duct for the exiting gas. An opening is provided in the center part of the roof for gas discharge. A channel is typically adapted in the roof, which channel can be cylindrical or polygonal and extends into the interior of the separation chamber and is concentric with it. The wall of this channel can also be made of a tube panel either separately or by bending the tubes of the tube panel of the roof further to form the wall of said channel also inside the cyclone separator. The gas discharge channel can also be uncooled as known per se, whereby it can be made e.g. of fireproof steel.

In the roof and in the tapering lower portion of the separation chamber the outermost tube or outermost tubes is/are typically shorter than the other tubes. To put it more exactly, the straight tube portions of them are shorter. Then the sides of the upper part and lower part of the panel are oblique. In the tapering lower portion the curve, bending or tube elbow of the shorter tubes is located in the elevation direction higher than the curve, bending or tube elbow of the longer tubes. By adjusting the length of the tubes the angle of the cone of the lower portion of the cyclone separator is adapted to a desired degree.

The inlet conduit for the gas to be treated is produced as known per se from a tube panel that is connected to the upper portion of the separation chamber.

The inner surface of the wall of the cyclone separator is provided with corrosion- proof lining as known per se. The invention is described in more detail with reference to the accompanying figures, of which

Fig. 1 a illustrates a side view of a cyclone separator according to a preferred embodiment; Fig.1 b illustrates a detail of the cyclone separator of Fig. 1a;

Fig. 2 illustrates a section along line A-A of Fig. 1 a; Fig. 3 illustrates schematically a cyclone separator according to the invention;

Fig. 4 illustrates a horizontal cross section of the upper portion of the cyclone separator according to Fig. 3;

Fig. 5 illustrates a detail of tube wall tubes of a cyclone separator according to the invention; Fig. 6 illustrates another detail of tube wall tubes of a cyclone separator according to the invention;

Fig. 7 illustrates a detail of a tube wall of a cyclone separator according to the invention.

Fig. 1 illustrates a cyclone separator 10 comprising a separation chamber 11 in- eluding a vertical upper portion 12 and a downwardly tapering lower portion 13. In this embodiment the upper portion is cylindrical and the lower portion is conical. The separator also comprises a gas inlet conduit 14, via which particle-containing hot gas is fed from the furnace (not shown) of a circulating fluidized bed boiler into the separation chamber 11 of the cyclone separator. The upper end 24 of the up- per portion is provided with a roof 18 having an opening 16, in which a gas discharge channel 17 is adapted, via which the cleaned gas exits and which is concentric with the cylinder 12 of the upper portion. Particles separated from the gas exit via a bottom opening 15 in the lower end 25 of the conical lower portion 13.

The wall of the cyclone separator is made of tubes 19 comprising straight parts 19a and 19b (Fig. 1 b), which are combined by means of a tube elbow 19c. The tube 19 can also be a single continuous bent tube. The inlet end 20 of the tube is connected to the distribution header 22 for cooling medium. The outlet end 21 of the tube is connected to the collection header 23. Cooling medium, which typically is water, vapor or their mixture, flows in the tube first to a first direction, upwards or downwards, then after the tube elbow to another direction and then after a second tube elbow returns almost to its feeding point. The tubes can also have more than one curve, whereby the cooling medium can flow several times to and fro in the same tube. The number of back and forth portions of the tube depends, inter alia, on thermal reasons and the cooling medium. The tube construction allows a freer chose of the location of the cooling medium headers and e.g. at a point most suitable for layout-reasons, such as in the zone of the tapering lower portion.

The wall tubes extend in the tapering lower portion 13 to different levels in the elevation direction, whereby the straight tube parts of some of the tubes are long- er than those of the other tubes. This way, a simple solution in view of manufacturing technique is obtained in the tapering portion, without need to decrease the number or size of the tubes.

Fig. 2 illustrates a cross cut along line A-A of Fig. 1 a. The cooling medium distribution header 22 surrounds the separation chamber. Fig. 2 illustrates how the wall of the upper portion 12, the roof 18 and the gas discharge channel of the separation chamber is formed of tubes 19 having curves19c. Downstream of the upper portion 12 the tubes are bent inwardly to form a horizontal roof 18, and then the tubes are bent upwards around the gas discharge channel 17. The gas exits via opening 26. Fig. 3 illustrates a perspective/schematic view of a cyclone separator 30 according to the invention. It comprises a separation chamber having a vertical upper portion 31 and a tapering lower portion 32 and a roof 33. Gas is introduced via conduit 34 into the upper portion 31 of the separation chamber. The treated gas exits via a gas discharge conduit formed by a cylindrical channel 35 concentric with the separation chamber. The particles separated from the gas exit via a bottom opening 38.

The separation chamber of Fig. 3 has a cross section of a dodecagon as shown in Fig. 4. Each wall part of the polygon of the separator is formed of tube panels, which are illustrated more closely in Fig. 7. The central idea of the novel wall tube panel structure 40 of a cyclone separator is that each tube 41 comprises a meandering cooling medium channel. In this embodiment the tube is formed of at least two straight tube parts with a tube elbow, i.e. here a turn of 180 degrees, between the parts. Thereby the cooling medium flows first to a first direction - upwards or downwards - and after turning to a second direction, which is opposite to the first direction. The cooling medium is typically water, steam or their mixture. The tube can have two or more tube portions, through which the cooling medium flows in a meandering way. In the roof part 42 and the tapering lower portion 43 of the panel 40 the outermost tube or outermost tubes 41 a is/are typically shorter than the other tubes. To put it more exactly, the straight tube portions of them are shorter. Then the sides of the upper portion and lower portion of the panel are oblique. In the tapering lower portion the tube elbow of the shorter tubes is located in the elevation direction higher than the tube elbow of the longer tubes. If required, also the length of the inner tubes of the panel can vary, due to e.g. the value of the inclination angle of the tapering lower portion.

The wall of the upper portion 31 of the separation chamber of Fig. 3 is substantially vertical. The lower part of the panel tubes of each wall part 31a of the separation chamber is bent inwards for forming the wall part 32a of the tapering lower portion. For forming the roof part 33a of the separation chamber the upper part of the tubes 39 of the tube panel is bent inwards to form a horizontal plane. An opening 36 is provided in the center part of the roof for gas discharge. A channel 35 is typically adapted in the opening, which channel can be cylindrical or polygonal and extends into the interior of the separation chamber and is concentric with it. The wall of this channel 35 can also be made of tube panel either separately or by bending the tubes of the tube panel of the roof further to form the wall. The inlet conduit 34 for the gas to be treated is produced as known per se from a tube panel that is connected to the upper portion of the separation chamber.

In Fig. 3 the feed end and the discharge end 37a and 36b for the cooling medium, and thus the distribution header and the collection header (not shown in Fig. 3) are typically located close to each other in the very lower part of the upper portion 31 of the separation chamber, where the chamber starts tapering. The distribution header and the collection header for the cooling medium, which typically extend around the separation chamber, can in the elevation direction be situated at desired levels. Fig. 5 illustrates in more detail the feed end 51a and the discharge end 51b for the cooling medium of the wall tubes 51 , which ends are located at the point where the separation chamber starts tapering.

In Fig. 6 the wall tube 51 is bent outwards and its cooling medium feed end 51 a is connected to the distribution header 52 for cooling medium and the discharge end 51 b of the wall tube is connected to the collection header 53.

Advantages of the novel tube structure:

The novel structure allows manufacturing the panel by welding with automated machines and forming the final form by bending the welded panels, which has not been possible with the known solutions. In the last mentioned tapering lower por- tion of the cyclone separator part of the tubes are shorter and do not extend to the lower end, and therefore they have to be connected to the separation chamber higher than the longer tubes. In the present novel solution the meandering tubes decrease the number of coupling points of the tubes to the cooling medium chambers, which considerably simplifies the manufacturing of the tube walls. Additionally, characteristic for the novel manufacturing method is that the tubes are typically at a constant distance from each other, which allows automated welding with a typical panel welding robot. The cyclone separator can be formed of straight prefabricated panels by bending them with commonly available machines so that they can be composed to form a cyclone separator of a desired form. Manual work is only needed for small sealing areas at the bending zones of the beforehand bent tubes.