| 主权项 |
1. A separatorless boiler comprising: a can body which is formed by connecting an upper header and a lower header with many water pipes heated by a burner and in which water levels in the water pipes when combustion of the burner is stopped are lower than upper ends of the water pipes; a water supply means for supplying water for a boiler into the can body; and a control means which has an external water level detecting means, disposed outside the can body and communicating respectively with an internal space of the upper header and an internal space of the lower header through communication pipes to detect an external water level in the can body, and which controls actuation of the water supply means according to the detected water level by the external water level detecting means,
wherein a downcomer pipe connecting a lower portion of the upper header and the lower header is provided, the control means carries out a first control for controlling actuation of the water supply means so that the water level in the can body lowers when the detected water level by the external water level detecting means exceeds a first set water level and a second control for controlling actuation of the water supply means so that the water level in the can body rises when the detected water level becomes lower than or equal to a second set water level lower than the first set water level, the first set water level is set to a dryness limit water level, a height of the upper header is set so that dryness of steam flowing out of the upper header becomes higher than or equal to set dryness as a result of the first control, and the second set water level is set to a water level which is higher than or equal to an overheating limit water level and which causes a circulation ratio of can water by the downcomer pipe to be higher than or equal to a set value. |
