| 摘要 |
It is intended to effectively suppress corrosion of a feed-water supply pipe in a preheater, by means of recirculation of boiler water to feed-water to be supplied to a steam boiler, even if a concentration of an alkaline component of the feed-water is relatively high. An alkali metal hydroxide is added from an agent-adding unit (14) to feed-water after removing therefrom a water hardness component in a water-softener unit (15) using a cation exchange resin and then removing therefrom dissolved gas in a degasifier unit (16). Then, the feed-water is supplied to a steam boiler 20 via a feed-water supply line 13 while being heated by a preheater (41). A part of boiler water having a pH value increased along with an increase in concentration of the alkali metal hydroxide resulting from enrichment thereof in the steam boiler (20) is mixed with the feed-water via a recirculation line (38). An alkaline component of the feed-water in the feed-water supply line (13) reacts with hydrogen ions from the cation exchange resin to form a carbonic acid, so that a concentration of the alkaline component is reduced. Thus, when the boiler water is mixed with the feed-water, a pH of the feed-water is increased without being influenced by a buffering ability of the alkaline component, to suppress corrosion of the feed-water supply line (13). |
