A fluidized bed boiler comprising - a furnace, limited on the sides by boiler walls and from below by a boiler grate, the boiler grate comprising: - air channels for supplying primary air to the furnace of the fluidized bed boiler; - a set of air nozzles (201, 202), which are arranged to supply primary air into the furnace; - at least one channel that is open on top and placed between the air nozzles (201,202), whereby the channel is arranged to collect ash and material from the furnace; and - an ash chute, which is arranged to remove ash and material from the furnace, and an ash collection conveyor; characterized in that the fluidized bed boiler further comprises: at least one ash removal means (301,701,751), which is placed in said channel and arranged to move ash and material mechanically along the channel; - an actuator placed outside the furnace and attached to the ash removal means (301, 701, 751) - a through hole, through which a part of the ash removal means (301, 701, 751) or a part of the actuator is brought through one of the boiler walls - a protective structure arranged in between the removal means (301, 701, 751) and the rest of the grate to prevent the grate from wearing, wherein the ash removal means (301, 701, 751) is arranged to move ash and material mechanically along the channel towards the ash chute, and ash is configured to move through the ash chute to the ash collection conveyor. - a furnace, limited on the sides by boiler walls and from below by a boiler grate, the boiler grate comprising: - air channels for supplying primary air to the furnace of the fluidized bed boiler; - a set of air nozzles (201, 202), which are arranged to supply primary air into the furnace; - at least one channel that is open on top and placed between the air nozzles (201,202), whereby the channel is arranged to collect ash and material from the furnace; and - an ash chute, which is arranged to remove ash and material from the furnace, and an ash collection conveyor; characterized in that the fluidized bed boiler further comprises: at least one ash removal means (301,701,751), which is placed in said channel and arranged to move ash and material mechanically along the channel; - an actuator placed outside the furnace and attached to the ash removal means (301, 701, 751) - a through hole, through which a part of the ash removal means (301, 701, 751) or a part of the actuator is brought through one of the boiler walls - a protective structure arranged in between the removal means (301, 701, 751) and the rest of the grate to prevent the grate from wearing, wherein the ash removal means (301, 701, 751) is arranged to move ash and material mechanically along the channel towards the ash chute, and ash is configured to move through the ash chute to the ash collection conveyor. - air channels for supplying primary air to the furnace of the fluidized bed boiler; - a set of air nozzles (201, 202), which are arranged to supply primary air into the furnace; - at least one channel that is open on top and placed between the air nozzles (201,202), whereby the channel is arranged to collect ash and material from the furnace; and - an ash chute, which is arranged to remove ash and material from the furnace, and an ash collection conveyor; characterized in that the fluidized bed boiler further comprises: at least one ash removal means (301,701,751), which is placed in said channel and arranged to move ash and material mechanically along the channel; - an actuator placed outside the furnace and attached to the ash removal means (301, 701, 751) - a through hole, through which a part of the ash removal means (301, 701, 751) or a part of the actuator is brought through one of the boiler walls - a protective structure arranged in between the removal means (301, 701, 751) and the rest of the grate to prevent the grate from wearing, wherein the ash removal means (301, 701, 751) is arranged to move ash and material mechanically along the channel towards the ash chute, and ash is configured to move through the ash chute to the ash collection conveyor.