Multibed fluidized bed boiler

Claim 1

A method of operating a multibed fluid bed boiler having at least two fluidizable beds aranged one after the other, in which conventional fuel is supplied to the first bed and in which the combustion of this fuel takes place in the first bed and in at least the immediately following bed, comprising the steps of supplying an alternative fuel to the second bed in order to be burnt there, thus obtaining a simplified fuel feed to the second bed as well as increased protection against clogging of nozzles supplying gas from the first bed to the second bed, and feeding flue gas from a following bed into the combustion space above the first bed for increasing the temperature and the fall of pressure across the nozzles supplying gas to the second heel in the event of low or no combustion in the first bed.

Claim 2

A method of operating a multibed fluid bed boiler having at least two fluidizable beds aranged one after the other, in which conventional fuel is supplied to the first bed and in which the combustion of this fuel takes place in the first bed and in at least the immediately following bed, comprising the steps of supplying an alternative fuel to the second bed in order to be burnt there, thus obtaining a simplified fuel feed to the second bed as well as increased protection against clogging of nozzles supplying gas from the first bed to the second bed, and feeding flue gas from a following bed into the combustion space above the first bed for increasing the temperature and the fall of pressure across the nozzles supplying gas to the second heel in the event of low or no combustion in the first bed.

Claim 4

A method of operating a multibed fluid bed boiler having at least three fluidizable beds arranged one after the other, in which conventional fuel is supplied to the first bed and in which combustion of this fuel takes place in the first bed and in at least the immediately following bed, comprising the steps of supplying an alternative fuel to the second bed in order to be burnt there, thus obtaining a simplified fuel feed to the second bed as well as increased protection against clogging of nozzles supplying gas from the first bed to the second bed, the firing being adapted to be carried out in these beds, whereby in the first bed only coal firing is carried out, the power output of the boiler being controlled by varying the degree of fluidization and bed height of the first bed relative to a first nest of tubes supported adjacent to the first bed, supporting a second nest of tubes adjacent to the third bed and being either completely exposed or at least partially submerged by the third bed, the first nest of tubes being exposed to a corresponding extent in those cases where the conventional fuel partially contains finely-crushed particles.

Claim 5

A method of operating a multibed fluid bed boiler having at least three fluidizable beds arranged one after the other, in which conventional fuel is supplied to the first bed and in which combustion of this fuel takes place in the first bed and in at least the immediately following bed, comprising the steps of supplying an alternative fuel to the second bed in order to be burnt there, thus obtaining a simplified fuel feed to the second bed as well as increased protection against clogging of nozzles supplying gas from the first bed to the second bed, the firing being adapted to be carried out in these beds, whereby in the first bed only coal firing is carried out, the power output of the boiler being controlled by varying the degree of fluidization and bed height of the first bed relative to a first nest of tubes supported adjacent to the first bed, supporting a second nest of tubes adjacent to the third bed and being either completely exposed or at least partially submerged by the third bed, the first nest of tubes being exposed to a corresponding extent in those cases where the conventional fuel partially contains finely-crushed particles.

Claim 8

A method of operating a multibed fluid bed boiler having at least two fluidized beds arranged one after the other, in which conventional fuel is supplied to the first bed and in which the combustion of this fuel takes place in the first bed in at least the immediately following bed, comprising the steps of supplying an alternative fuel to the second bed in order to be burnt there, thus obtaining a simplified fuel feed to the second bed as well as increased protection against clogging of nozzles supplying gas from the first bed to the second bed, providing a third bed after the second bed, whereby conventional fuel can also be supplied to the second bed with the alternative fuel, thus obtaining an increased possibility of low load operation.

Claim 9

A method of operating a multibed fluid bed boiler having at least two fluidized beds arranged one after the other, in which conventional fuel is supplied to the first bed and in which the combustion of this fuel takes place in the first bed in at least the immediately following bed, comprising the steps of supplying an alternative fuel to the second bed in order to be burnt there, thus obtaining a simplified fuel feed to the second bed as well as increased protection against clogging of nozzles supplying gas from the first bed to the second bed, providing a third bed after the second bed, whereby conventional fuel can also be supplied to the second bed with the alternative fuel, thus obtaining an increased possibility of low load operation.

Claim 10

A method of operating a multibed fluid bed boiler having at least two fluidized beds arranged one after the other, in which conventional fuel is supplied to the first bed and in which the combustion of this fuel takes place in the first bed in at least the immediately following bed, comprising the steps of supplying an alternative fuel to the second bed in order to be burnt there, thus obtaining a simplified fuel feed to the second bed as well as increased protection against clogging of nozzles supplying gas from the first bed to the second bed, operating at least one pilot burner, opening out into the first bed, after start-up in order to control the fall of pressure across the nozzles leading to the second bed to enhance the heating effect in the second bed.

Claim 11

A method of operating a multibed fluid bed boiler having at least two fluidized beds arranged one after the other, in which conventional fuel is supplied to the first bed and in which the combustion of this fuel takes place in the first bed in at least the immediately following bed, comprising the steps of supplying an alternative fuel to the second bed in order to be burnt there, thus obtaining a simplified fuel feed to the second bed as well as increased protection against clogging of nozzles supplying gas from the first bed to the second bed, operating at least one pilot burner, opening out into the first bed, after start-up in order to control the fall of pressure across the nozzles leading to the second bed to enhance the heating effect in the second bed.