Separatorless boiler

Abstract

The separatorless boiler includes a downcomer pipe ( 84 ) connecting a lower portion of the upper header ( 24 ) and the lower header ( 22 ) and a control means ( 70 ) for carrying out a first control for controlling a water supply means ( 60 ) so that a water level in the can body lowers when a detected water level by an external water level detecting means ( 50 ) exceeds a first set water level, and a second control for controlling the water supply means ( 60 ) 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.

1 . A method for controlling a separatorless boiler which includes:
 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;   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,   the method comprising:   detecting, by the external water level detecting means, the external water level in the can body;   causing water existing inside the upper header to return to the lower header, by a downcomer pipe configured to connect a lower portion of the upper header and the lower header;   performing, by the control means, a first control for controlling actuation of the water supply means so that the water level in the can body lowers when the water level detected in the detecting by the external water level detecting means exceeds a first set water level; and   performing, by the control means, a second control for controlling actuation of the water supply means so that the water level in the can body rises when the water level detected in the detecting becomes lower than or equal to a second set water level lower than the first set water level, wherein   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.   
     
     
         2 . The method according to  claim 1 , wherein the first set water level and/or the second set water level are/is adjusted according to one or a plurality of pressure in the can body, a temperature of supplied water, and a degree of concentration of the can water. 
     
     
         3 . The method according to  claim 1 ,
 wherein detection of the first set water level and the second set water level is carried out by a common electrode,   determination of the first set water level by the control means is carried out based on detection of presence of water by the electrode or a lapse of a first set time since the detection of the presence of the water, and determination of the second set water level is carried out based on detection of absence of water by the electrode or a lapse of a second set time since the detection of the absence of the water.   
     
     
         4 . The method according to  claim 1 ,
 wherein the external water level detecting means includes a first electrode for detecting the first set water level and a second electrode for detecting the second set water level,   determination of the first set water level by the control means is carried out based on detection of presence of water by the first electrode or a lapse of a third set time since the detection of the presence of the water, and the determination of the second set water level is carried out based on detection of absence of water by the second electrode or a lapse of a fourth set time since the detection of the absence of the water.   
     
     
         5 . 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;   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; and   a downcomer pipe connecting a lower portion of the upper header and the lower header, the downcomer pipe being configured to differ from the water pipes and to cause water existing inside the upper header to return to the lower header by gravity,   wherein each of the many water pipes is configured to connect a bottom of the upper header, which is located vertically below the lower portion of the upper header, and the lower header.