The present invention relates to a method and an apparatus for separting solid particles from flue gases in a circula¬ ting fluidized bed reactor, in which method the flue gases are led to a cyclon separator in which the separated solid particles are discharged and returned to the reactor.

The object of the invention is to accomplish a device by means of which solid particles can effectively be separated from the flue gases in a circulating fluidized bed reactor.

The circulating fluidized bed technique has long been applied e.g. in calcinators and is nowadays applied to a growing extent in various reactors, such as combustion cham¬ bers and gasifiers. In known applications, the separation of solid particles from flue gases takes place in an ordinary, in its lower part funnel-shaped cyclone separator, in the cylin¬ drical vortex chamber of which is disposed a gas outlet pipe that leads the gases upwards, and from which solid particles are returned to the reactor via a discharge pipe.

A strong underpressure and a high axial flow speed are, as known, formed in the center of a cyclon separator. Due to this an ordinary cyclon tends to suck from the discharge pipe. The resulting suction flow does usually not have a tangential speed and consequently all particles transported with it are led out via the central pipe of the cyclon.

The solid material discharged with gas from the separator is mainly fly ash containing particles smaller than 100 μm, which is later separated by means of electro- or tube filters.

Fly ash contains considerable amounts of unburnt particles and lime that has not had time to react with SO-, in the reactor.

The separation degree of a cyclon separator decreases with the growth of the size of the cyclon.

By means of the method according to the invention a conside¬ rable part of the flue gas particles smaller than 100 y can be returned to the reactor.

The method according to the invention is characterized in that solid particles are discharged from a cyclon separator by menas of suction.

The apparatus according to the invention is characterized in that between the lower part of the funnel-shaped cyclon sepa¬ rator and the return duct for the solid particles there is disposed a suction chamber.

The invention is described in detail in the following with reference to the accompanying drawings, in which

Fig. 1 shows a sche atical vertical section of one embodiment of the method according to the invention and

Fig. 2 shows another embodiment of the invention.

In fig. 1 the reference number 1 refers to a vertical circu¬ lating fluidized bed reactor. Flue gases leaving the upper part of the reactor are led to a vortex chamber 3 disposed vertically in a cyclone separator 2 via an inlet duct 4 connected tangentially to the vortex chamber. The upper part 5 of the vortex chamber is cylindrical and the lower part 6 funnel-shaped. Solid particles concentrated on the periphery of the vortex chamber flow to a return pipe 8

via a discharge opening 7 in the lower part and is led back to the reactor. Between the discharge opening and the return duct is disposed a suction chamber 9 to which a pneumatic ejector 10 and a suction pipe 11 have been connected. Compres¬ sed air is supplied to the ejector via a pipe 12 from a fan 13. The outflow opening of the ejector is connected to a combustion chamber 14 of the reactor.

The ejector accomplishes in the discharge opening 7 of the cyclon separator an underpressure that causes suction which again causes a gas flow from the lower part of the separator to the suction chamber. With the gas is discharged fine particles concentrated in the lower part which are returned to the reactor via the ejector 10. By means of the compressed air that functions as an operating gas for the ejector and as a secondary gas for the reactor 1-30%, preferably ca. 10% of the flue gases from the combustion chamber are removed through the lower part of the separator and returned to the . combustion chamber. The main part of the gases are discharged via a gas discharge pipe 15 in the upper part of the separator.

In the embodiment of the invention shown in fig. 2, the suction chamber 9 between a discharge opening 7 in the lower part 6 of the cyclon separator 2 and a return pipe 8 has been connected to an inlet duct 17 of another cyclon separator 16. A gas discharge pipe 23 in the upper part of the separator 16 is connected to a fuel gas fan 19 via a fuel gas duct 18. An ejector 21 into which compressed air is supplied via a pipe 22 is disposed in a discharge pipe 20 for solid particles that is connected to the lower part of the separator. The lower end of the discharge pipe is connected to a combustion chamber 14 of the reactor 1.

From the lower part of the cyclone separator 2 flue gas is sucked into a cyclon separator 15 by means of the flue gas

fan 19. Fine dust particles transported with the flue gas is separated in the separator 16 and returned to the vortex chamber of the reactor by means of the ejector 21. Flue gas is led to the flue gas duct 18.

By means of the method and the apparatus according to the invention, not only coarse particles concentrated on the walls of the vortex chamber, but also a considerable part of the fine particles can be separated from the flue gases and returned to the reactor. Thus the separation degree of the separator improves and more such material is recuperated that has not had time to react when flowing through the combustion chamber.

The invention is not limited to the above embodiments but it can be modified and applied within the inventive concept defined by the claims.