My power plant is combined cycle power plant that use gas and steam to generate a power. which have a HRSG (heat recovery steam generator) 3 Drum HP/IP/LP pressure 115/20/4.8 bar and use AVT-O treatment for feed water and Low PO4 for boiler drum. We open continues blowdown 3%/drum 24 hr. to decrease water concentration and release contaminate and don't open intermittent blowdown.

The question is : what is criteria for open intermittent blowdown because some power plant have a plan open intermittent blowdown once a week even though water quality are normal.

*some powerplant use Fe to monitoring blowdown*

Criteria for my power plant (ref. EPRI)

Silica (ppb)

- HP Boiler drum < 400 ppb

- LP/IP Boiler drum < 4,000 ppb

Fe (ppb)

- Feed water < 5 ppb