Air nozzle arrangement in a fluidized bed boiler, grate for a fluidized bed boiler, and a fluidized bed boiler

A fluidized bed boiler comprising:

• a furnace and an air nozzle arrangement, the air nozzle arrangement comprising:
• several air nozzles spaced from each other in a longitudinal direction of the air nozzle arrangement;
• an air feed pipe that is connected to one of the air nozzles and that, with the air nozzle, limits an air feed duct;
• the air feed duct being configured to supply air to a furnace of the fluidized bed boiler;
• and
• a surface, wherein at least part of said surface is configured to protect at least part of at least one of, the air nozzle, and the air feed pipe,
• and
• wherein at least part of said surface is thermally insulated from at least one of , the air nozzle, and the air feed pipe;
• wherein at least one air nozzle is configured to supply air to a furnace of the fluidized bed boiler in a direction which forms an angle not larger than 80 degrees to a horizontal plane and forms an angle of at least 10 degrees to the longitudinal direction;
• wherein at least 50% of the surface is arranged at an angle of at least 10 degrees to the horizontal plane, whereby
• the surface is configured to guide coarse material along said surface in such a way that liquid metal carried along with solids of the furnace does not solidify when it hits the surface, and the solids are guided along the surface downwards and to one side according to the shape of the surface, wherein the temperature of said surface is configured to be high when the fluidized bed boiler is in operation, whereby the solidification of molten material of the fluidized bed at the air nozzle arrangement is reduced, and
• the air flow produced by the air nozzle is configured to guide coarse material towards an ash removal zone of a grate or a coarse material outlet of the fluidized bed boiler;
• wherein the air nozzle arrangement is configured to supply combustion air to the furnace of the fluidized bed boiler.