Boiler operation method and boiler

Abstract

A boiler according to the present invention is equipped with: a water supply system ( 11 ) in which boiler water flows; ammonia addition equipment ( 12 ) that adds an ammonia solution to the boiler water; a pH measurement device ( 14 ) that measures the pH of the boiler water; and a control device ( 15 ). When the boiler water is heated the control device ( 15 ) controls the ammonia addition equipment ( 12 ) such that the pH of the boiler water is within a preservation pH range, and controls the ammonia addition equipment ( 12 ) such that the pH of the boiler water is within the preservation pH range before the flow of the boiler water in the water supply system ( 11 ) is stopped. At this time, a given pH within the preservation pH range is greater than a given pH within the operating pH range. With such a boiler, corrosion of the water supply system ( 11 ) can more easily be prevented than when the water supply system ( 11 ) is charged with preservation boiler water containing hydrazine.

1 . A boiler operation method implemented using a boiler that includes a water supply system through which boiler water flows, and ammonia addition equipment configured to add ammonia solution to the boiler water, the method comprising the steps of:
 measuring a pH of the boiler water;   passing the boiler water through the water supply system when the pH is within an operational pH range so that the boiler water is heated, upon operating the boiler;   controlling the ammonia addition equipment so that ammonia solution is added to the boiler water until the pH is within a preservation pH range, upon stopping the boiler; and   stopping the flow of the boiler water in the water supply system when the pH is within the preservation pH range,   a discretionary pH within the preservation pH range being equal to or greater than a discretionary pH within the operational pH range.   
     
     
         2 . The boiler operation method according to  claim 1 , further comprising passing the boiler water through the water supply system when the pH is within the operational pH range so that the boiler water is heated, upon restarting operation of the boiler after the flow of the boiler water in the water supply system has been stopped. 
     
     
         3 . The boiler operation method according to  claim 1 , further comprising referring to a table of a plurality of preservation periods mapped to a plurality of preservation pH ranges, and introducing the preservation pH range corresponding to the period of time that a power plant is stopped and boiler water is not flowing through the water supply system, from among the plurality of the preservation pH ranges, wherein
 a lower limit of a first preservation pH range corresponding to a first period from among the plurality of preservation pH ranges is greater than a lower limit of a second preservation pH range corresponding to a second period that is longer than the first period from among the plurality of preservation pH ranges.   
     
     
         4 . The boiler operation method according to  claim 3 , wherein the lower limit of the first preservation pH range and the lower limit of the second preservation pH range have values within a range of 9.5 to 10. 
     
     
         5 . A boiler, comprising:
 a water supply system through which boiler water flows;   ammonia addition equipment configured to add ammonia solution to the boiler water;   a pH measurement device configured to measure a pH of the boiler water; and   a control device,   upon operating the boiler, the control device including   a control circuit for normal operation configured to control the ammonia addition equipment so that the pH is within a operational pH range when the boiler water is flowing through the water supply system so that the boiler water is heated, and   a control circuit for preservation period configured to control the ammonia addition equipment so that the pH is within the preservation pH range before stopping the flow of the boiler water through the water supply system upon stopping the boiler,   a discretionary pH within the preservation pH range being equal to or greater than a discretionary pH within the operational pH range.   
     
     
         6 . A gas cooler, comprising:
 the boiler described in  claim 5 ; and   a flow path through which raw syngas generated by gasification of a carbonaceous solid fuel flows,   the water supply system heating the boiler water using heat of the raw syngas.   
     
     
         7 . A heat recovery steam generator, comprising:
 the boiler described in  claim 5 ; and   a flow path through which exhaust gas discharged from a gas turbine flows,   the water supply system heating the boiler water using heat of the exhaust gas.   
     
     
         8 . An integrated coal gasification combined cycle power plant, comprising:
 the boiler according to  claim 5 ;   a gasifier configured to generate raw syngas by gasification of a carbonaceous solid fuel;   a gas turbine configured to discharge exhaust gas by generating power using the raw syngas; and   a steam turbine configured to generate power using steam,   the steam being generated by the water supply system by heating the boiler water using heat of the raw syngas and using heat of the exhaust gas.   
     
     
         9 . The boiler operation method according to  claim 2 , further comprising referring to a table of a plurality of preservation periods mapped to a plurality of preservation pH ranges, and introducing the preservation pH range corresponding to the period of time that a power plant is stopped and boiler water is not flowing through the water supply system, from among the plurality of the preservation pH ranges, wherein
 a lower limit of a first preservation pH range corresponding to a first period from among the plurality of preservation pH ranges is greater than a lower limit of a second preservation pH range corresponding to a second period that is longer than the first period from among the plurality of preservation pH ranges.